HighLine Polycarbonate

Printing with Polycarbonate

2012-02-06T11:38:24-08:00

We recently came across a very interesting Blog post by a company called ProtoParadigm. They can be found at http://protoparadigm.com We encourage you to check them out.

The blog post covers a topic that we have not seen before - 3D Printing with Polycarbonate. This technique can be used to construct proto-types from Polycarbonate. The profiles in the photo and video were made by printing with Polycarbonate. With the permission of ProtoParadigm, we have included a video and picture from their blog as well as the text below. Please watch the video, it is an amazing use of technology. Their article also clearly identifies the importance of drying Polycarbonate. As users of Polycarbonate sheet know, Polycarbonate absorbs a lot of moisture and should be dried before thermoforming otherwise a lot of bubbles can form in the finished part.

Here is their post:

"We tracked down a number of material samples from our supplier and a little gem called Polycarbonate (PC) caught our eye. Having seen the success of Richrap printing with Polycarbonate we were anxious to work with it. Polycarbonate (wiki) is a strong thermoplastic with high optical clarity and (relatively) high melting temperature. Unlike PLA with a fast transition temperature, PC slowly softens when heated allowing successful (if not slow) extrusion at lower than processing temperatures. This is useful when switching from a plastic with a lower extrusion temperature as you can slowly start pushing PC through at the temperature of your previous plastic until you clear the hotend. It is important to purge ALL of the previous plastic before raising the printing temperature as ABS puts off some dreadfully nasty fumes at 260C.

The sample we received was extruded to 1/8″ diameter and we had let it sit out in open air for a good while before getting to it. Initial purging at 260C (Modified Makergear Stepstruder) showed extrudate that was bubbly and white; a big red flag that this plastic needed to be dried. 10 hours at 160F in an old food dehydrator showed filament that was noticeably clearer and extruded a smooth clear thread from the nozzle. Setting extruder to 260C and the Polyimide Tape covered heated bed to 120C we repurposed an ABS printing profile for PC and started printing; once flow-rate was dialed in we tried printing our Plastic T-Slot. It was by far the strongest beam we had printed and clear enough that looking straight through it you could make out objects on the other side.

It’s worth noting that adjusting temperature is similar to PLA, printing at higher flow-rates will require higher extruder temperatures for a consistent melt. An indication the flow-rate is to high or temperature to low is stripping or skipping at the filament driver. Those with Bowden style extruders will need to watch for signs of excessive force where the Bowden tube meets the filament driver and hotend. For the Ultimaker I’m using this thing to keep everything secure. If you print PC near the high end of your firmwares temperature limit, PID fluctuations can send it hot enough to force a shutdown of the hotend; temperatures drop, nozzles clog, filaments strip, things get ugly. Also, for hotends that use PTFE (teflon) insulators there is the concern of dangerous fumes when temperatures approach 300C (see Polymer Fume Fever for example.) Care should be taken to avoid inhalation of dangerous fumes or, better yet, to avoid creating them.

", it’s finally time to share what we’ve learned about printing with Polycarbonate. As we recently announced, pre-orders for Polycarbonate in both 3mm and 1.75mm diameters are available. It took us awhile to get the details sorted out, but we’ set for a ship date of January 30, 2012. There’s a whole world of materials out there for that hungry printer on your desk, and we plan to dish up a feast.

Larger prints were prone to peeling off the print-bed if they contained too many long aligned traces; examining the datasheet revealed that this PC had a mold release additive, great for injection molding, not so great for us (the PC available for pre-order does NOT have this additive and should stick easier to print beds). Small objects printed fine with no warping but we needed to find a way to keep large prints held down; enter ABS Glue. Painting a thin coat of that on the bed before printing completely eliminated peeling and warping, we could even print without the heated bed and maybe see only the smallest of curling on the corners of large prints.

To test the effect that leaving the PC out in open air was having we split up the sample; one went in the dehydrator, another into one lucky fellow’s home for a couple days. Printing with them revealed obvious difference. The dried sample printing clear and smooth without hiccups, the sample that had gone through a few days of home living printed white and would occasionally pop and bubble. Comparing prints side by side shows an obvious reduction in clarity and surface quality for the undried filament. While we haven’t done any numerical testing of compared strength, the moisture laden sample felt more brittle and prints made from it break much easier. Objects printed with the dried PC are clear and strong. Returning to the T-Slot it is clear to see the differences between dry filament and filament left where humidity is not controlled. Click the pictures below for high resolution to really see the differences.

All in all, a very simple material to start printing with. As long as it is kept relatively free of moisture and/or dried, printed objects turn out looking good, are well bonded and very strong. This is a plastic that can take a bit more of a beating and stand a little more heat, not bad if you need something close to you’re hotend such as a cooling duct. Printing parameters we’re using so far are:

Makerbot

Extruder – Makergear Plastruder (modified directing heat closer to nozzle and further away from insulator)
Extrusion Temperature – 260C (success at low and high flow rates)
Bed – Heated Polyimide Tape (aka Kapton) bed at 120C OR unheated bed with ABS Glue brushed down before hand

Ultimaker

Stock Extruder
Extrusion Temperature – 270C (evaluating how to safely go hotter for better inter-layer adhesion)
Bed – Unheated BlueTape or Polyimide Tape (recommended for keeping parts flat) bed with ABS Gluebrushed down before hand
Add-on Ultimate BowdenFeeder Repair Kit to keep Bowden assembly secure

We’ve got it on pre-order, prices include shipping within the USA, world wide shipping is available through ourinternational ordering form with an additional $9.00 to match the increased shipping cost of the flat rate mailers we are able to use. We have a scheduled ship date of January 30, 2012 after which the product can batch with other orders and the shipping cost will be subtracted back out of the product listing if we have any remaining inventory. Go on over and grab some in either 3mm or 1.75mm."

How thick does Transparent Armor need to be?

2012-01-10T07:02:24-08:00

A question that we are frequently asked is how thick is transparent armor made from glass and polycarbonate?

The answer to the question depends on what level of threat the armor needs to stop. As we discussed in a recent post, the Kinetic energy of a bullet can be calculated if the weight of the bullet and the speed of the bullet are known using the following formula:

Kinetic Energy (Joules) = 1/2 x Mass of bullet (grams) x [Velocity of bullet (m/s)]^2

The more Kinetic Energy the bullet has, the thicker and heavier the transparent armor needs to be. Of course there are many manufacturers of bullet resistant glass and transparent armor. Each of these manufacturers have their own knowledge of how to produce the lightest and thinest armor to stop a specific threat. However, if we look at the top military transparent armor producers, there is only limited variation in the performance of the products.

We recently compared data published on the internet from the top laminators to see how thick and how heavy their products are to stop a given threat. We compared products that were designed to stop rounds with between 650 Joules and 3500 Joules of Energy. Many of the manufacturers do not publish the data for rounds with Energy above 3500 Joules as much of the information is classified.

Within the energy range considered there was surprisingly little variation in the thickness and weight of products. We analyzed the data and carried out some linear regression and were able to obtain the following equations:

Thickness (mm) = [0.0085 x Energy (Joules)] + 10

Weight (kg/m^2) = [0.02 x Energy (Joules)] +20

Using these equations we can calculate that to stop a bullet weighing 9.45 g and traveling at 830 m/s the energy would be about 3255 Joules.

This would give a thickness of about 38 mm and a weight of about 85 kg/m2.

Of course, just making some transparent armor of this thickness and weight does not guarantee that it will stop this level of threat. The armor has to be properly designed and tested by a certified testing company. The figures do show what the main manufacturers are able to achieve.

It should also be remembered that the Kinetic Energy is not the only factor that needs to be considered - other factors such as the shape of the bullet need to be taken into account.

The above figures are based upon transparent armor solutions using Glass and Polycarbonate. A more expensive option is to use advanced materials in the construction such as transparent ceramics. The performance of these ceramics, while not available in detail, is discussed on some of the manufacturers websites and claims of 20% weight reduction and 10% thickness reduction are listed.

Birefringence, Photoelasticity, Anisotropic Materials, Iridescence and the Rainbow Effect - Part 3

2011-11-15T10:16:17-08:00

In the final blog post of this trilogy we will discuss Iridescence and how it can cause a rainbow effect on abrasion resistant coated Polycarbonate sheet. We will also discuss how the rainbow effect can be minimized.

Iridescence is the rainbow or oil slick type pattern that often appears on the surface of a Polycarbonate sheet particularly under artificial lighting conditions.

Coated Polycarbonate sheet has a thin film of coating on the surface of the sheet in order to protect the sheet against abrasion damage. It is this thin film of coating material that causes the problem, in much the same way that a thin film of oil on the surface of a pool of water exhibits the rainbow patterns. The effect is due to the process known as interference.

As discussed in previous blog posts, whenever light travels from a material with one refractive index to another material with a different refractive index, some of the light is reflected. In the case of the coated Polycarbonate sheet, when light moves from the air into the coating some of the light is reflected. Then, when the light moves from the coating into the actual Polycarbonate, some more of the light is reflected. When the light that is reflected from the first surface comes into contact with the light that is reflected from the second surface the light waves recombine.

Depending on how thick the coating layer is, the light waves may be in sync when they recombine or may be out of sync when they recombine. If they are in sync the two waves will added together and will have constructive interference. If they are out of sync the two waves will start to cancel each other out and will have destructive interference.

Since visible light has wavelengths of 380nm(violet) to 750nm (red) and a typical hard coat has a thickness of 4 to 7 microns [4000 to 7000 nm], the coating thickness is an order of magnitude thicker than the wavelengths of visible light. A small percentage variation in the coating thickness can therefore change whether the constructive interference or destructive interference occurs. If there is variation of coating thickness over a small area of sheet, even if the variation is only tens or hundreds of nanometers, then there will be areas of constructive interference and areas of destructive interference. This variation in the interference patterns is part of the cause of the iridescence or rainbow effect.

The question then becomes, how do we eliminate the variation in coating thickness? Abrasion resistant coatings are often added to sheet by a process known as flow coating. The sheet is hung vertically and coating solution is allowed to run down the surface of the sheet from top to bottom under gravity. The solvents are then allowed to evaporate. If the sheet is allowed to move before most of the solvents have evaporated, the coating surface can become uneven. However, we need to remember that the coating surface is not the only surface that we need to be concerned about - there is also the sheet surface that is reflecting light. The sheet is extruded between large chrome rolls which are powered by motors. If there is any variation in the motor speed of these motors or the motors pulling the sheet, there can be variation in the thickness of the sheet. While the variation in the thickness will be small, it only requires very small variation to cause iridescence.

The reality is that neither the sheet producers or the abrasion resistant coaters have the ability to control their processes to the level of 10-100nm thickness. If we look at sheet producers, many of them state that their thickness specification is plus or minus 10%. On a 0.118" thick sheet that corresponds to 300,000 nanometers. While this is an overall thickness tolerance and not a measure of local variation of thickness, it does give some idea of the magnitude of the problem. Using this information we can determine that the sheet producers and coaters cannot prevent the problem. In many cases sheet producers often blame the coaters for the problem and coaters often blame the sheet producers. This then leaves us with the question of how do we solve the problem?

To answer the question we will briefly move to another topic - different types of lights. Traditional incandescent light bulbs have a relatively smooth light spectrum across the visible region and are similar to sunlight in this respect. When sunlight is split into its component wavelengths (such as in a rainbow) there is a smooth transition from violet through the various colors to red. There are no wavelengths missing. An incandescent light bulb behaves in the same way (as do some full spectrum LED bulbs).

Fluorescent bulbs, mercury bulbs, sodium bulbs and non full spectrum LEDs are different. When the light is split into its component parts, there are peaks at some wavelengths and gaps at other wavelengths. For example, a low sodium bulb emits an almost monochromatic light source at 589.3nm and a standard fluorescent bulb has 22 peaks with the main four being Mercury at 437nm, Terbium at 543nm, Mercury at 547nm and Europium at 611nm. These wavelengths of a fluorescent bulb combine to yield a light that looks like natural light but has discrete wavelengths rather than the continual spectrum of natural light.

Having a light source composed of discrete wavelengths rather than a continuous spectrum is a major problem for iridescence; when the light is reflected from the two surfaces the discrete wavelengths make the problem much larger as there are no intermediate colors to cancel out the iridescent effect. In short, the light source can make the problem of iridescence much greater.

The best way to reduce the effect of iridescence is to change the lighting source to a full spectrum light source such as incandescent bulbs or full spectrum LEDs. If the only option is to use fluorescent bulbs, it is better to use a bulb with more emission peaks to more closely resemble full spectrum light.

Another option to completely resolve the problem is to use what is known as an index matched abrasion resistant coating. The Polycarbonate sheet has a refractive index of 1.585 and most coatings have a refractive index of 1.49. If an abrasion resistant coating with a refractive index of 1.585 is used, the light will treat the coated Polycarbonate sheet as a single layer material and the effect of iridescence will be completely eliminated. While this process sounds great (and HighLine Polycarbonate can offer index matched abrasion resistant coated products) there is a significant downside - index matched coatings are very expensive. In most applications it is better to install full spectrum bulbs to reduce the problem.

Finally, to illustrate the effect of lighting on the visual appearance of iridescence we will recount a case study about the problem. A rail car manufacturer was experiencing oil slick like patterns on the Polycarbonate windows of their railcars. The manufacturer of the windows was inspecting the windows prior to sending them to the rail car manufacturer to try and identify the problem. They were unable to detect the issue as their factory was lit with incandescent lights. When the windows were installed in the railcars, the oil slick appearance was easily visible because the internal lights on the rail car were fluorescent bulbs.

The most practical solution would have been to change the bulb type on the railcar, but unfortunately the window manufacturer did not understand the problem. They told the rail car manufacturer that the problem was due to birefringence, which, as anyone who has read these three blog posts knows, was not the cause of the problem. By understanding the cause of the problem it is easier to recommend a solution to the customer.

Birefringence, Photoelasticity, Anisotropic Materials, Iridescence and the Rainbow Effect - Part 2

2011-11-10T09:53:04-08:00

In the last post we discussed how stresses in Polycarbonate can cause the material to become Anisotropic and exhibit Birefringent properties. Light waves parallel to the stress direction will travel through the sheet at a different speed than the light waves perpendicular to the stress direction.

It is possible to visualize the stresses in the sheet due to the birefringent properties of the sheet. A technique known as Photoelasticity is often used. In this method light is first passed through a polarizing filter, in order to block all components of the light not vibrating in the direction of the plane. The light coming through the filter is then known as polarized light. The light is then allowed to pass through the Polycarbonate part being examined. The birefringent properties caused by the stresses cause the polarized light to be split into two perpendicular components each moving at different speeds which are governed by the amount of stress in each direction. The components of the light waves recombine on leaving the Polycarbonate. When this light is then viewed through a second polarizing filter it is possible to see the effect of the retardation of the light in the form of "rainbow" like patterns. There is a lot of theory that can be explored on the method of Photoelasticity and this theory can easily be researched by carrying out a web search. In this blog we do not plan to go into advanced theory of how the light waves recombine, but rather discuss how the method of Photoelasticity can be practically used.

In the picture at the top of this blog post is a photograph taken of a piece of Polycarbonate with a hole drilled through it. The photograph was taken with a simple phone camera and two polarizing filters bought from a camera shop for $25 each. One filter was put behind the Polycarbonate part and one filter was put in front of the part. Although this cheap set up does not compare with advanced equipment for visualizing and measuring Photoelasticity, it does provide a simple practical tool for visualizing stresses in Polycarbonate parts.

In the Photo it can be seen that there are high levels of stresses on each side of the hole. We suspect that these stresses were caused by poor drilling technique using the wrong drill bit for Polycarbonate and operated at the wrong speed. It is also possible that the drill was started while in contact with the sheet. The technique of Photoelasticity allows us to visualize these stresses and therefore allows us to adjust fabricating methods to minimize stresses. This information is particularly important as we know that areas of increased stress are prone to cracking and damage, especially when exposed to certain solvents.

We invite readers who are involved in fabricating Polycarbonate parts to try this test method themselves to see the stress areas on the parts. All you need to do is buy two Polarizing filters from a camera shop.

In this section of the trilogy of blog posts on the subject of the rainbow effect, we have seen how stresses in Polycarbonate sheet can lead to birefringence and that these stresses can be visualized through polarizing filters as a rainbow type pattern.

However, it should be understood that rainbow effect seen on some hard coated Polycarbonate sheet without the use of polarizing filters is not due to the birefringence of the material. These rainbow type patterns on hard coated sheet are often very easy to see with just the eye and can cause the visual appearance of the sheet to seem very poor. In the last post on this topic, we will discuss what causes the rainbow effect on coated sheet and how its effect can be minimized.

Birefringence, Photoelasticity, Anisotropic Materials, Iridescence and the Rainbow Effect - Part 1

2011-10-27T06:24:20-07:00

One question that we are often asked about Polycarbonate is what causes the rainbow like patterns on coated sheet and how can they be eliminated.

The answer is not simple and we will need to answer the question over two or three posts. There is also a lot of confusion in the industry about what causes the effect. Often people try to explain the effect using the wrong terms.

Birefringence and anisotropic materials

The first term that we will discuss is Birefringence or the double refraction of light when it passes through an Anisotropic material. At this stage, don't worry too much about these terms, we will explain them as we go. Birefringence is often the term that is incorrectly used to explain the rainbow patterns seen on the surface of some coated Polycarbonate sheet. As we will explain, Birefringence can allow us to see stresses in the sheet using polarizing filters - they allow us to see the stresses which will appear as rainbow like effects. However, birefringence is not the cause of the rainbow like effect which can be seen with the eye on the surface of hard coated Polycarbonate sheet.

To explain birefringence and anisotropic materials we will start with a discussion about the structure of Polycarbonate. Polycarbonate is a long molecule containing Carbon, Hydrogen and Oxygen atoms. A simple web search can give details of the chemical formula. When Polycarbonate is heated and allowed to cool without being subject to any stresses, these molecules will be arranged randomly.

During the production of extruded sheet, the Polycarbonate is melted and then extruded through a wide die into a sheet format. The sheet is then pulled out of the die by some pull rollers through some chrome polishing rolls to create a smooth surface on the sheet. The pull rolls create some stress in the sheet in the direction of extrusion, but not in the direction perpendicular to the extrusion. The sheet is cooled and allowed to "set" while still being pulled by these rolls. This difference in stress in the sheet between the extrusion direction and the direction perpendicular to extrusion is commonly referred to as shrinkage. We have discussed shrinkage in more detail in previous blog posts; shrinkage is able to be controlled below 1%, although often it is possible to find sheet with high levels of shrinkage of 10% or more.

The stresses in the Polycarbonate can be eliminate by annealing the sheet - heating it above its glass transition temperature and then allowing it to cool. Also stresses can often be added to the sheet by some fabrication methods.

The more shrinkage that the Polycarbonate sheet has, the more stress it has in the extrusion direction and the more the Polycarbonate molecules are aligned in the extrusion direction. This alignment of the Polycarbonate molecule chains causes the Refractive Index of the Polycarbonate in the direction of the extrusion to be different than the Refractive Index in the direction perpendicular to the extrusion. As explained in previous blog posts, the refractive index is a measure of how fast light travels in a material. The difference of refractive index in the two directions causes extruded Polycarbonate to become what is known as an Anisotropic Material - where the speed of light traveling through the material is dependent upon the direction of the material.

If a Polycarbonate sheet is produced without any stress or 0% shrinkage, it would not be Anisotropic.

The difference in the Refractive Index between the two directions can be calculated using the Stress Optics Law:

(RI1 - RI2) = C x (Stress1 - Stress2)

Where:

RI1 = Refractive Index in extrusion direction

RI2 = Refractive Index in direction perpendicular to extrusion

C = Stress Optic Constant

Stress1 = Stress in extrusion direction

Stress2 = Stress in direction perpendicular to extrusion.

If the Refractive Index in one direction is different than the Refractive Index in the other direction, the components of the waves of light moving through the Polycarbonate in one direction will travel at a different speed than the light in another direction. The more Polycarbonate that the waves travel through, the more the one wave will lag behind the other. This effect is known as Retardation of the wave.

The retardation of the wave can be calculated using the following formula:

Retardation = C x thickness of Polycarbonate x (Stress1 - Stress2)

The amount of retardation of the wave is therefore proportional to both the thickness of the sheet and the differences in the stresses in the two directions. The retardation will be much lower on thin sheet with low shrinkage.

When the components of the light in the two directions emerge from the sheet they will recombine. However, how they recombine will be a function of the phase difference caused by the retardation of the light. There could be constructive or destructive recombining of the waves at different wavelengths.

In the next post on this subject we will look at how these waves combine. We will also look at how we can use a polarizer to look at the stresses in the sheet using an experimental method known as Photoelasticity.

Bonding Polycarbonate Sheet

2011-07-22T10:57:13-07:00

One question that we are often asked is how can two Polycarbonate sheets be bonded together?

At HighLine Polycarbonate we are mainly involved in producing Polycarbonate sheets with a wide range of high tech properties. We only engage in a limited amount of fabrication which includes routing of the sheets into finished part shapes.

We do not engage in fabrication that requires bonding of two sheets together. Some of our customers do engage in this type of fabrication and we will list some of the methods that we know about for joining two sheets of Polycarbonate together. We would be very interested to hear from our readers about other methods that they know about so that we can update the post with additional information.

We do not plan to cover physical methods of joining sheets together such as rivets, screws and tapes.

- The first method that we know about is using Methylene Chloride or a 60%/40% mixture of Methylene Chloride and Ethylene DiChloride. This solvent bonding technique is known to give a good bond strength and excellent optical clarity along with low capital investment. The mixture of Methylene Chloride and Ethylene DiChloride gives a slightly longer curing time than neat Methylene Chloride allowing more time to get the parts in the correct position; this is particularly important for larger parts. Suppliers of these chemicals can be found on Google. We recommend reading the Material Safety Data Sheet for information on safe handling and disposal before using any chemicals. We also recommend that you test any method on a small part before using on critical parts.

Before starting the solvent bonding process, both surfaces should be cleaned with warm water. If there are greasy areas, IsoPropanol (IPA) should be used to wipe the surfaces clean. Some fabricators recommend dissolving between 2% and 5% Polycarbonate saw dust in the Methylene Chloride or Methylene Chloride/Ethylene DiChloride solvents before use in order to give a stronger bond strength. We have yet to see any evidence that the saw dust improves the bond strength. In any case, if you choose to try this method, make sure that all of the saw dust is fully dissolved before use, because otherwise lumps of saw dust may prevent good surface contact between the two parts. Another recommendation that we have heard from fabricators is that in order to prevent whitening of the joint occurring, 10% Glacial Acetic Acid should be added to the solvents. Whitening does not always occur, so we would only recommend that you try this solution if you are having problems with whitening on your particular parts.

Having made up the solution, the solvent should be applied to one of the clean parts. The two parts should then be clamped together with several hundred psi pressure for about 5 minutes. The parts should then be allowed to cure in a well ventilated area at room temperature for between two and five days.

- The second method is to use an adhesive; this is a cheaper solution than solvent bonding but we believe that the bond strength and the optical clarity are not as good. Many customers have had excellent results with products such as "Weld-on". These products can easily be found using Google.

- Other methods such as vibration welding and ultrasonic welding have had varying degrees of success depending on the part shape and thickness. We would suggest that you contact manufacturers of the equipment to see if these options are suitable for your needs. These methods would require capital investment.

- The final option that we know about is to laminate the two parts together using an interlayer material such as transparent Polyurethane. This method is often used to manufacturer ballistics laminates where Polycarbonate layers are bonded to glass. This method requires a lot of specialist knowledge and equipment, such as an autoclave so it is unlikely to be viable for the majority of applications.

We look forward to hearing about more bonding methods from our readers.

FDA and NSF Standard 51 grades and UV absorbers

2011-05-25T08:10:23-07:00

Polycarbonate sheet is widely understood to block UV wavelengths below 385-390 nm. What is not so well known is it is not the Polycarbonate that blocks these wavelengths, but rather the UV absorbers that are added to the Polycarbonate that block the UV light.

Polycarbonate sheet that has no UV absorbers will only block wavelengths below 290 nm. Unfortunately wavelengths below 385 nm will cause the Polycarbonate to weather and become brittle and yellow. Manufacturers therefore add UV absorbers to the Polycarbonate resin to give it some protection against the UV light. Some outdoor grades of Polycarbonate also have an additional cap layer or coating heavily loaded with additional UV absorbers to further protect the sheet against the affect of UV light.

There are some grades of Polycarbonate, that are often known as FDA or NSF Standard 51 compliant grades that have no UV absorbers. The reason that no UV absorbers are added is that these grades are designed to be used in the Food Processing environment and the UV absorbers are not approved by the FDA to be used in Food Processing areas. The manufacturers therefore produce grades without the UV absorbers. Because these FDA grades of Polycarbonate sheet have no UV absorbers, they should not be used outside as they will yellow very quickly.

One question that we are often asked is are the FDA approved grades safe to be used in food contact applications? The FDA grades of Polycarbonate sheet do not have UV absorbers in them because they are not approved for materials used in Food Processing environments. However, the Polycarbonate itself does still have Bisphenol A or BPA in it and there is currently a great deal of debate about whether BPA is safe in food contact applications such as baby feeding bottles. As a result of this debate, at HighLine Polycarbonate we do not sell any Polycarbonate sheet that will be used in applications where it comes into regular, direct contact with food. However, FDA grades of Polycarbonate sheet can be used as machine guards to protect operators on food packaging lines when the machine guards do not come into contact with food that will be eaten.

One un-intended market for FDA approved grades of Polycarbonate sheet is to customers who bond Polycarbonate sheet to other materials using a UV cured adhesive. The adhesive requires light from a UV lamp to pass through the sheet in order to bond it to another material. The UV absorbers in Standard Polycarbonate sheet block the UV light from the lamp preventing the adhesive from curing. By using an FDA grade of Polycarbonate sheet, the adhesive is able to be cured effectively. After bonding, the sheet can be protected against UV light by adding a coating with UV absorbers.

Kinetic Energy of Ballistics rounds and transparent armor

2011-05-09T15:33:53-07:00

We are often asked about the difference between bullet resistant windows installed in 24hrs stores or banks and the transparent armor used by the military.

The bullet resistant windows in convenience stores and banks are often made of cell cast acrylic sheet or a combination of acrylic and Polycarbonate. They are often about 1.25" to 1.375" thick and are designed to protect against threats that are likely to be encountered in that environment. Typical bullet resistant ratings of UL.752 Level 1 to Level 3 are encountered. But what does a UL.752 Level 1, Level 2 or Level 3 mean and how does it compare to the transparent armor of military applications?

A UL.752 Level 1 material is designed to stop 9mm FMCJ rounds weighing 8.0 grams traveling at a velocity of up to 394 meters/second.

A UL.752 Level 2 material is designed to stop 0.357 Magnum JSP rounds weighing 10.2 grams traveling at a velocity of up to 419 meters/second.

A UL.752 Level 3 material is designed to stop 0.44 Magnum rounds weighing 15.6 grams traveling at a velocity of up to 453 meters/second.

But what does this mean? One of the most important factors in determining whether a bullet resistant structure will stop a ballistics round is how much Kinetic Energy does the ballistics round have.

Using the equation for Kinetic Energy:

Kinetic Energy (Joules) = 1/2 x Mass (Kilograms) x Velocity (meters/second)^2

Calculating the Kinetic Energy for the UL.752 Level 1 ballistics round we find:

Kinetic Energy = 1/2 x 0.008 x 394 x 394 = 620 Joules

For the three UL.752 Levels we get:

Level 1 620 Joules

Level 2 895 Joules

Level 3 1600 Joules

We can see as the weight and the velocity of the round increase the Kinetic Energy of the round increases. The bullet resistant material needs to be able to resist a larger amount of Kinetic Energy.

We can now look at the military grades to compare the amount of Kinetic Energy they are designed to stop. Military grades of transparent armor are composed of multiple layers of glass and polycarbonate. The glass can be of various types. In some cases advanced materials such as Spinel and ALON are also used. Often the structures can be many inches thick.

For US military grades a standard known as ATPD.2352 is used. The different rounds that the materials must stop is listed but the velocities are classified. The fact that the velocities are classified makes it difficult to calculate the required Kinetic Energy that must be absorbed; it would be possible to take an educated guess at the velocities, but for the purposes of this blog post, we do not need to do this is we can use the NATO standard AEP55 STANAG 4549 Volume 1.

STANAG 4549 has 5 protection levels for Light Armored Vehicles. For the purposes of the discussion on transparent armor we will just look at Levels 1 and 4.

Level 1 material is designed to stop a 7.62 mm x 51 NATO ball round weighing 9.65 grams traveling at 833 meters/second.

Level 4 material is designed to stop a 14.5 mm x 114 API/B32 round weighing 64 grams traveling at 911 meters/second.

A Level 1 round has a Kinetic Energy of 3,348 Joules

A Level 4 round has a Kinetic Energy of 26,557 Joules

You can see that the energy that a UL.752 Level 1 material needs to stop is over 40 times less than a STANAG 4549 Level 4 material. The reason for this difference is that the type of ballistics rounds likely to be encountered at a convenience store are likely to be very different from those encountered by the military. Indeed the deterrence factor of bullet resistance glass in commercial applications should not be underestimated.

It should be noted that this discussion is very much a simplification and is only meant to compare the Kinetic Energy of the different rounds used for the different tests. There are a number of parameters that have not been discussed in this blog post such as the multi shot spacing and the shape of the round.

Variable Message Signs (VMS) and Polycarbonate

2011-02-14T09:05:38-08:00

Over recent months we have had a large number of customer contact us regarding Variable Message Signs (VMS), also known as Dynamic Message Signs (DMS), and the use of Polycarbonate for these signs. These signs are often used as traffic signs to warn drivers or give special information.

The signs often consist of a bank of either yellow or red LEDs behind a protective Polycarbonate front shield. The Polycarbonate is used to protect the sign against impact damage and environmental conditions.

Most of the questions that we get asked relate to a technical standard such as the European Standard EN.12966 for VMS. The main concern relates to the test, which simulates reflection of sunlight when the sun is at a low angle in the sky (5 or 10 degrees). In this situation, the sun is reflected off the Polycarbonate shield to the driver and partially obscures the light coming from the LEDs, making the sign difficult to read.

The sign can be made easier to read by either reducing the reflection of the sunlight or increasing the amount of LED light transmitted through the sheet – either by increasing the LED brightness or increasing the light transmission of the Polycarbonate sheet.

The test apparatus used for EN.12966 is shown in the picture accompanying this blog post [Please click on the picture to enlarge]. The principal of reducing reflection and increasing transmission is the same as that discussed in our previous blog posts with the exception that we are not concerned with the entire visible spectrum. We are specifically concerned with how the Polycarbonate interacts with the Yellow LEDS (wavelength 635 nm) and the Red LEDs (wavelength 590-595 nm) for the vast majority of VMS.

The problem that most VMS manufacturers have experienced is that they frequently buy general purpose Polycarbonate sheet, that has not been optimized for VMS, from distributors or manufacturers that are not aware of the options available. Much of this material has been produced with the idea of minimizing the production cost; as a result there is often large amounts of second grade (regrind) material in the product. As discussed in our previous blog posts, this regrind has the effect of lowering the transmission across the visible spectrum and in particular in the yellow region of the spectrum used by the yellow LEDs of VMS.

The first method improving the visibility of VMS signs in low sunlight is therefore to use an optical grade of Polycarbonate that has been design for VMS use, such as grades offered by HighLine Polycarbonate. The next method is to reduce the reflection and increase the transmission by the use of specially designed coatings. The added advantage of these coatings is that they improve the UV and weather resistant performance of the Polycarbonate, preventing the material from yellowing over time, which would also reduce the transmission in the yellow part of the spectrum. The coatings also add scratch resistance to the sheet, which is important in a road traffic environment.

The following table shows the effect of using a high quality VMS Polycarbonate and using an anti-reflective hard coat. The sheet used is 3mm / 0.118” thick.

Yellow LED Transmission

Uncoated GP Polycarbonate (*) 83.8%

Uncoated VMS Polycarbonate 89.0%

VMS Polycarbonate with anti-reflective hard coat 91.0%

VMS Polycarbonate with anti-reflective hard coat outside and optical coating inside 93.6%

Red LED Transmission

Uncoated GP Polycarbonate (*) 86.0%

Uncoated VMS Polycarbonate 89.7%

VMS Polycarbonate with anti-reflective hard coat 92.0%

VMS Polycarbonate with anti-reflective hard coat outside and optical coating inside 95.5%

[* the GP Polycarbonate was purchased from a distributor and was produced by a major manufacturer as their standard product].

For Yellow LEDs it is therefore possible to increase the transmission by 8.6% [91.0/83.8 = 8.6% increase] by using a properly designed Polycarbonate with an anti-reflective hard coat, for Red LEDs the increase is 7.0% [92.0/86.0 = 7.0% increase].

For both color LEDs the anti-reflective hard coat is also able to reduce the reflection by 25%.

The combination of the increase in transmission and the reduction in reflection significantly increases the readability of the signs in sunlight.

A further option to improve the performance is to use an advanced optical anti-reflective on the inside surface. The use of the advanced optical coatings is not recommended for the outside surface, as they are not suited to use in a dusty and dirty roadside environment. By using these materials on the inside surface the transmission for yellow LEDs rises to 93.6% and the transmission for red LEDs rises to 95.5%.

These figures give an increase in transmission of 11.6% for yellow LEDs and 11.0% for Red LEDs. They also reduce the reflection by 56%. One question that has not yet been completely answered is whether the additional cost of an optical grade anti-reflective is justified by the performance advantage over an anti-reflective hard coat.

The other option for VMS is to use an anti-glare hard coat. At the moment we are investigating the performance of these materials in this application. Anti-glare materials are different from anti-reflective materials in that they scatter the light to reduce reflection; so while you can reduce reflection you also significantly lower the transmission and the clarity of the sign. It remains to be determined whether the loss in transmission is acceptable. At the moment we are very reluctant to recommend anti-glare coatings for VMS applications even though we are able to provide anti-glare coatings.

To summarize, for VMS signs it is important to use a Polycarbonate sheet that has been designed for VMS applications rather than use general purpose Polycarbonate sheet. With an anti-reflective hard coat the transmission can be increased 7.0% for red LEDs and 8.5% for yellow LEDs and the reflection can also be reduced 25%.

Sheet - conversion between weight and area

2010-09-23T08:31:20-07:00

A short time ago we wrote a blog post about determining how an increase in resin price would affect the sheet price. The calculation involved converting a $ per pound price into a $ per square foot price.

To assist Polycarbonate (and other Polymer) sheet users with this calculation, we have put a simple spreadsheet on our website. This spreadsheet is available to be downloaded and shared. We just ask users not to remove the logo or the disclaimer.

The spreadsheet includes three simple calculations:

1) Given the dimensions of a sheet it allows the user to calculate the sheet weight.

2) Given the dimensions of a sheet and the price in $/lb, it allows the user to calculate the price in $/sqft.

3) Given the dimensions of a sheet and the price in $/sqft, it allows the user to calculate the price in $/lb.

We hope that the spreadsheet is useful and we intend to keep it updated with any feedback and comments that we receive.

Self-repairing coating video

2010-09-14T09:52:54-07:00

Many people have asked us about our self-repairing coating, but it is only when they have seen it in action that they become really excited. We have therefore put together a short video clip so that you can see how well this coating works.

Please click on the link below to view the video.

watch video

If you need more information about this coating, please contact us at info@highlinepc.com

Polycarbonate and the Power of the Brand name

2010-08-17T13:52:27-07:00

In this blog post we have moved away from our normal technical content to discuss a subject that has some major implications for the Polycarbonate sheet market place. The question that we will address is: Are powerful brand names still as important as they once were in the plastic sheet market?

There is no doubt that in the past brand names such as Lexan for Polycarbonate and Plexiglas for Acrylic dominated the market. These products were often specified in to projects and could command a premium price from customers due to actual or perceived quality. We decided to look and see if customers were still referring to the brand names or were just looking for Polycarbonate.
As the web is one of the primary means that customers use to find out information about a product, we decided to look at the search interest for "Polycarbonate" and "Lexan" in the United States. In the first graph, we can see that the search interest for Polycarbonate has remained relatively constant since 2004 with some minor decrease due to the economy.

In the second graph we can see that the search interest for Lexan has dropped off significantly and steadily since 2004. As there is still a good interest in Polycarbonate it is possible to conclude that customers are using the generic term Polycarbonate in searches while moving away from the brand name Lexan. Now this information does not mean that Lexan sales have decreased, customers searching for Polycarbonate may still buy Lexan products. However, it does suggest that the brand name value maybe decreasing and if this is the case, the price premium may also be decreasing.

There are of course many events that have happened over time that may explain this trend. During the period being examined, GE Plastics sold the Lexan Polycarbonate part of the operations to SABIC. This transfer of Lexan from a traditional American company to a Saudi Arabian company could certainly affect the branding strategy and the search interest of the brand.

To see if the affect of the brand importance was confined to Lexan, we also decided to look at the other powerhouse brand in the US clear sheet market - Plexiglas. In the graph below we can see how the Plexiglas name has also decreased in search importance. Of course it can be argued that the transfer of the brand from the respected US company Rohm and Haas to a less well known French company Arkema is similar to the situation at Lexan, at least in the US market shown in the graph,

The results of search importance for both Lexan and Plexiglas lead us to question whether brand is as important as it once was in the US clear sheet market. Having questioned this point, there is still no doubt that these names are still valuable branding tools both now and for the foreseeable future. Now that customers, using the internet, are able to evaluate the alternative options more efficiently, the brand name may not be the dominant factor in the purchasing decision.
We would be interested to hear your comments on whether you think brand names are still as important in the plastics industry as they once were and if not, what are the implications?

Lexan is a brand name of SABIC Basic Industries Corp. Plexiglas is a brand name of Arkema Inc.

The Quality of Polycarbonate and Light Transmission

2010-08-02T06:48:54-07:00

As we explained in a previous blog post, we would typically expect the light transmission of 0.118" one side hard-coated Polycarbonate to be in the range of 90% [with 5.1% reflectance on the uncoated side, 4% reflectance on the coated side and a little internal loss of light transmission due to the internal structure of the Polycarbonate itself]. As the thickness of the Polycarbonate increases, we would expect the internal loss of light transmission to also increase a little.

We were recently asked by a customer to apply an anti-reflective coating to the uncoated side of 0.236" one side hard-coated Polycarbonate. The Polycarbonate was provided by the customer and had been produced by another manufacturer. By applying the anti-reflective coating we were expecting to reduce the reflection on the uncoated side from 5.1% to around 1.0%. We were therefore expecting to increase the overall light transmission from 89-90% to around 94%.

After we had coated the material with the anti-reflective we discovered, to our surprise, that we were only getting a light transmission of 89%. The application of the anti-reflective coating appeared to have failed. We examined our coating process and found no obvious problems. We then decided to test the light transmission of the material before we applied the anti-reflective coating. To our surprise we found that the light transmission was only 84-85% instead of the 90% that we expected. The problem was with the quality of the competitors Polycarbonate and not the anti-reflective coating.

We then measured the reflection on both surfaces and calculated the internal loss of light transmission across the entire visible spectrum. We then repeated this process with our own 0.236" Polycarbonate. We then plotted our the internal loss of light transmission for both materials over the visible spectrum. This plot can be seen in the diagram at the top of the page (for a better view, click on the picture).

The results were shocking.

Over the range of 450-500 nm, our material had an internal loss of light transmission of 2% and the competitors had a loss of 5%

Over the range of 525-575 nm, our material had an internal loss of light transmission of 4% and the competitors had a loss of 7%

Over the range of 650- 750 nm our material had an internal loss of light transmission of 1% and the competitors had a loss of 7%

The end result was that the customer would have been better off buying our HighLine Polycarbonate without an anti-reflective rather than applying an expensive anti-reflective to the competitors material. In the end the customer decided to use our Polycarbonate with an anti-reflective and achieved a light transmission of over 94%.

The lesson to be learned from this recent experience is that not all Polycarbonate sheet is equal. The Polycarbonate sheet from this competitor, who is a major international supplier of Polycarbonate sheet, clearly had a much lower light transmission across the visible spectrum than the Polycarbonate sheet from HighLine Polycarbonate. This lower transmission is caused by inferior resin, use of regrind and the commodity production methods used by some of the large producers. In the vast majority of applications, particularly commodity applications, this loss of light transmission is not important. However, in some quality and high-tech applications, a 6% light transmission loss in the 650-750nm range can be critical. Any application requiring an anti-reflective coating should seriously consider the quality of the base Polycarbonate and should be extremely cautious about buying an off the shelf product from a distributor. Polycarbonate sheet for high quality applications should always be bought directly from the manufacturer so that you can have the material produced specifically for the required application.

All of HighLine Polycarbonate's material is designed for high quality optical applications. If you are using another supplier's material it would be wise to ask for them to provide the light transmission curve for the actual lot number of the sheet you will be receiving. We were certainly surprised by the poor quality of some of the material that is being sold as high quality product.

Bullet Resistant Laminates and Transparent Armor

2011-03-06T08:34:15-08:00

One statement that we often hear is that Polycarbonate is “bullet-proof”. There are two problems with this statement; the first is that a single Polycarbonate sheet by itself should not be used to stop bullets as it really offers very little protection. The second problem is subtle, materials constructed from Polycarbonate are not bullet-proof but rather bullet-resistant; fire enough shots of high enough caliber and velocity and they will eventually fail.

There has been a need in both the civilian and military sectors to develop glazing materials with bullet-resistance. There are a number of ways of achieving this bullet resistance depending on the required stopping power, cost and weight restrictions. While this article cannot cover all of the options in detail, we will try to give an overview of the options:

1) Perhaps the easiest to make and the cheapest product to buy is specially designed Acrylic sheet that has been specifically tested for bullet resistance. Typically a 1.25” thick Acrylic sheet such as Plexiglas SBAR will stop a 9mm bullet as tested by UL.752 Level 1 test. To get increased stopping power, it is necessary to increase the thickness to 1.375”. At this thickness Plexiglas SBAR product will stop a 0.357” shell as tested by UL.752 Level 2 test. The limitation of this technology is the thickness required to achieve greater stopping power becomes difficult to produce and difficult to install due to the size and the weight.

2) The next option is to use a combination of Acrylic and Polycarbonate. This method is used by Sheffield Plastics, amongst others, in their Hygard BR range. The Acrylic and Polycarbonate are laminated together in various configurations in a vacuum chamber using an interlayer to bond the sheets together. The 9mm UL.752 Level 1 protection is achieved by laminating a ½” acrylic sheet between two layers of 1/8” Polycarbonate. The acrylic sheet absorbs the energy while the more flexible Polycarbonate holds the structure together and prevents shards of Acrylic breaking off and injuring the person behind the window. It can be seen that this type of structure is only 0.75” thick to achieve the Level 1 protection compared to 1.25” for the SBAR product. The 0.357 Level 2 protection is achieved by sandwiching two 3/8” Acrylic sheets between two outer 1/8” Polycarbonate sheets giving a total thickness of 1.0”. A UL.752 Level 3 protection, which uses a Magnum 0.44” has a similar construction that is 1.25” thick. These multiple layer plastic constructions offer greater protection from a thinner material, but at the downside of a greater cost.

3) The next option is to introduce glass. Different companies use different options for the configuration, but nearly all of them use glass bonded to Polycarbonate using inter-layers. Typically one or two sheets of 1/8” Polycarbonate are used. The glass absorbs the energy of the ballistics material and the Polycarbonate holds the material together. Often a sheet of Polycarbonate is put on the inside surface to act as a “spall” layer. This layer prevents shards of glass breaking off and injuring the person behind the glass. This type of option is often used in armoring commercial automobiles for VIPs or diplomats. Using the glass gives additional stopping power, but at the expense of cost and additional weight.

4) The next option moves from the area of commercial ballistics laminates to military transparent armor. These laminates often use multiple layers of glass and multiple layers of Polycarbonate – both as spall shields and internal structures. The completed laminates are often many inches thick and can stop a wide range of military projectiles. Often several different types of glass can be used in a single window to give different properties, the hardness of the glass and the energy absorption of the glass are two such properties. Many of the configurations used by different companies are confidential. The performance of these materials is excellent but they are costly and extremely heavy.

5) The final option is to use advanced materials for the construction of the transparent armor. These materials include ALON, Sapphire and Spinel. Details of these materials can be found on the websites of their manufacturers. While these materials offer exceptional protection they are extremely expensive and often the production process can only produce small parts.

At HighLine Polycarbonate we have a great deal of experience in transparent armor. We have developed a Polycarbonate grade that gives increased performance and stopping power in military laminates compared to other commercial grades of Polycarbonate. We have also developed an advanced thermoplastic sheet, which is more flexible than Polycarbonate and gives a significant improvement in performance when used as a spall shield. The material is lighter than Polycarbonate and is resistant to a wide range of chemicals and solvents, making it ideally suited to use in military transparent armor.

At HighLine Polycarbonate we also are able to include EMI/RFI shielding meshes, transparent conductive heaters, self-repairing coatings, anti-fog coatings, super abrasion resistant coatings, IR shielding and anti-microbial properties – all of which enable our products to be used in the harshest of military environments.

Machine Guards and Chemical Resistance

2010-06-29T08:32:09-07:00

Polycarbonate has traditionally been used to produce machine guards due to its virtually unbreakable properties. Its good optical properties, ability to form to shapes and its reasonable cost make it an almost perfect choice for the application.

One problem with Polycarbonate in some machine guard applications is that some cleaning chemicals, oils, fuels and greases can attack the surface of the sheet over time. While this chemical attack does not occur in all applications, it can be a severe problem in some industries. This attack of the sheet means that the guards need to be replaced frequently or the user will have to live with optically and sometimes structurally damaged machine guards. Coating the Polycarbonate can offer some degree of protection against chemical attack, but this is not the ideal solution as any scratches that occur in the coating provide sites for attack. Also, using a coating can be a problem if the guards need to be formed, as standard hard-coats will crack. Another problem with Polycarbonate is that over time the surface can become scratched.

Even though Polycarbonate is reasonably inexpensive, the cost of replacing a damaged machine guard can be expensive particularly once the cost of machining, forming, installing the guard and machine downtime is taken into account.

At HighLine Polycarbonate we have developed a new monolithic sheet product known as Grade 5500. This product has been developed especially for applications requiring exceptional chemical resistance. The sheet will not be damaged at all by the vast majority of cleaning chemicals, oils, fuels and greases. The sheet is also much more resistant to scratches than uncoated Polycarbonate, is virtually unbreakable and is lighter than Polycarbonate. The material has also been approved for contact with foodstuffs having an alcohol content of less than 8% according to the FDA specification 21CFR 177.1500 (11).

All of these properties make it the ideal replacement for Polycarbonate sheet in machine guard applications, even in the food processing industry, where Polycarbonate is becoming damaged and needs to be replaced.

For more information about Grade 5500 sheet, contact HighLine Polycarbonate LLC.

Polycarbonate and chemical resistance

2010-06-04T08:44:16-07:00

When discussing Polycarbonate, the question of chemical resistance often comes up, particularly in high-tech applications. Polycarbonate can come into contact with chemicals in a number of ways – cleaning solvents are frequently used in medical applications and machine guards on food processing lines, solvents are also used in printing ink packages in advanced sensors and displays, rail car windows and bus shelters often need cleaning to remove not only dirt but graffiti.

While chemical resistance is important, it can be a weakness of Polycarbonate with some chemicals and some applications. The level to which a chemical attacks Polycarbonate depends on a number of factors, the type of chemical (acid, polar solvent, non-polar solvent), the temperature, the contact time and the stress that the Polycarbonate part is under. Because of the number of factors influencing the effect of a chemical on a Polycarbonate part, the information in supplier data sheets is very general in nature and often has little real world relevance. There is also very little standardization on suppliers data sheets regarding the chemicals reported and the test methods used to quantify chemical resistance.

In broad terms there are some chemicals that very aggressively attack Polycarbonate. These chemicals include Toluene, Benzene, Acetone and Ammonia to name a few. One interesting experiment to see the effect of these chemicals is to dip a small piece of Polycarbonate into some Acetone. Nothing visually appears to happen, but the surface does become plasticized. If the Polycarbonate is then washed in water, the water provides nucleating sites causing the surface to “crystallize”. The result is that the entire surface instantly turns white.

Other chemicals such as Isopropyl Alcohol and Ethanol have very little effect on the surface of the Polycarbonate. We even recommend that our anti-reflective coatings be sprayed with a 70% Isopropyl Alcohol solution to remove fingerprints.

One method of protecting Polycarbonate sheet from chemical attack is to apply a standard hard-coat to the sheet. This hard-coat provides a protective barrier. However, the hard-coat will not protect against all chemicals and if there is a minor scratch in the hard-coat, chemicals can still attack at that point. It should also be remembered that any edges or drill holes may provide points for chemical attack, so often it is necessary to coat the part after fabrication rather than coat the sheet before fabrication. There are also some advanced coatings design to protect the sheet against specific chemicals.

It is important to discuss the application with the Polycarbonate manufacturer to see if chemical attack will be a problem and whether a coating can provide a solution. At HighLine Polycarbonate we also have some more advanced solutions involving different resin matrices that can protect against solvents in very demanding applications.

Anti graffiti coated Polycarbonate

2010-05-14T10:44:04-07:00

Polycarbonate is virtually unbreakable and this property makes it especially suited to environments where the risk of damage by vandalism is high. These applications include bus shelters, rail car and bus windows, vending machines, advertising and security glazing. However, vandalism comes in many forms, not just breakage. Often vandalism consists of graffiti from marker pens and spray paint. Normally when Polycarbonate is damaged by graffiti the entire Polycarbonate part needs to be replaced.

A better solution is to apply an anti-graffiti coating, which can be added to either uncoated or a hard-coated sheet. This type of coating creates a hydrophobic layer that repels water and reduces the wettability of organic solvents.

When a marker pen is used to write on Polycarbonate with an anti-graffiti coating the inks bead up and do not stick to the sheet; the residue can then be easily wiped of with a soft cloth.

When spray paint is applied to the anti-graffiti coating, the paint does dry; however, with very little effort the paint can be removed with a very mild abrasive that does not damage the Polycarbonate. When spray paint is applied to standard Polycarbonate it is virtually impossible to remove the paint.

Anti-graffiti coated Polycarbonate sheets are more expensive than standard Polycarbonate sheets. However, they are less expensive than having to buy additional sheet to replace graffiti covered parts. Often the cost of additional sheet, fabrication of the parts and the expense of removing and reinstalling the parts can be many times the cost of the anti-graffiti coating.

Anti-microbial Polycarbonate

2011-04-28T10:05:10-07:00

A number of our products are used in touch screen displays. In these applications customers often require Indium Tin Oxide coatings to conduct electricity and anti-reflective coatings to improve viewing characteristics.

Increasingly we are being asked about two other properties, anti-fingerprint and anti-microbial. We will save the discussion about anti-fingerprint properties for another day. Today I will give an overview of anti-microbial properties for Polycarbonate.

Touch screen displays are an ideal product for anti-microbial Polycarbonate. Touch screen displays are often touched by a large number of people and they therefore provide ideal transfer conditions for microbes. With touch screen displays becoming more common as payment points in fast food restaurants and monitors in hospitals, the market for anti-microbial Polycarbonate is small but growing. In addition to touch screen displays there are many other applications where anti-microbial properties are desirable.

It should be noted that when we talk about anti-microbial properties, we are talking about anti-microbial properties built into the Polycarbonate sheet to solely protect the sheet against micro-organisms. The anti-microbial properties are not designed to extend beyond the surface of the sheet itself. No public health claims that extend beyond the Polycarbonate sheet itself are being claimed implicitly or explicitly.

There are three broad groups of anti-microbial agents that can be used in Polycarbonate applications; these anti-microbial agents include silane, silver and triclosan based additives.

Silane based anti-microbials are nano-engineered structures that physically attract the microbes and then mechanically puncture the cell wall, killing the organism. Because the mechanism relies on mechanical damage to the cell, it does not allow the cell to mutate and become resistant. Also the anti-microbial does not need to detach from the surface of the sheet to enter the microbe and therefore does not leach into the environment.

Silver based anti-microbials release ionic free radicals that react with the cell DNA disrupting critical life processes in the cell. Silver based anti-microbials often rely on moisture to function and so have reduced effectiveness in dry environments. Over time certain microbes can also build up resistance to silver based anti-microbials as the organisms adapt. Silver based anti-microbials are perhaps the most common form of anti-microbial available.

Triclosan based anti-microbials release toxic bis Chlorinated Phenols that are consumed or absorbed by the cells, causing lethal mutations in the cells. In order to work the anti-microbial additives must leach from the Polymer into the environment. As with silver based anti-microbials, there is strong evidence that some organisms adapt and become resistant to this type of anti-microbial.

At HighLine Polycarbonate we typically favor using Silane based anti-microbial products, however, we have worked with customers that prefer to use silver based anti-microbials. Once the anti-microbial additive is chosen, there are two main ways to add the additive to the sheet. For small quantities we typically use proprietary technology to formulate a coating to add to the surface of the sheet. This coating technology can be combined with many of our other coating technologies such as hard-coats and anti-reflective coatings. This solution works well as it is only necessary to have the anti-microbial additives at the surface of the sheet and in many applications a coating needs to be applied anyway.

For larger volumes of products that do not require a coating it is possible to add the anti-microbial additive to the Polycarbonate resin and make either the entire sheet or a cap layer anti-microbial. For a limited number of applications this method can be more cost effective. It can also be a better choice where the sheet is cut into small parts requiring the cut edges to contain anti-microbial additives.

At HighLine Polycarbonate we are happy to assist customers specifying anti-microbial products.

Temperatures for thermoforming Polycarbonate

2010-04-03T13:27:15-07:00

When Polycarbonate is cooled below 150 C / 302 F, it transitions from a flexible structure to a rigid structure that locks into what ever shape it is in; this temperature is known as the glass transition temperature. Conversely, when Polycarbonate it heated above its glass transition temperature it becomes flexible and can be bent into various shapes. This property is used in the process of thermoforming.

Thermoforming can be carried out at any temperature above the glass transition temperature and below the melt temperature of 267 C / 512 F, although in practice the Polycarbonate becomes more flexible the higher the temperature and it is not necessary to approach the melt temperature. The Polycarbonate actually becomes difficult to use much above a temperature of 215 C / 450 F.

There are three broad categories of forming – Cold forming, Low temperature thermoforming and high temperature thermoforming.

Cold forming.

Cold forming uses a frame to hold the Polycarbonate sheet in the desired shape. The sheet is then heated to between 302 F and 340 F for several hours until the entire sheet (interior and not just the surface) rises above the glass transition temperature. The sheet is then cooled below the glass transition temperature to set the shape. Cold forming is a simple process, but can only be used for relatively simple shapes (often two dimensional) without tight radius bends.

Low temperature thermoforming.

Low temperature thermoforming is carried out between 350 F and 370 F. This process is often used for simple shapes where the Polycarbonate sheet drapes over a mold or into a mold. While it is possible to achieve relatively simple 3D shapes with low temperature thermoforming, complex shapes with lots of detail are not possible. One advantage of low temperature thermoforming is that pre-drying of the sheets is not necessary.

High temperature thermoforming.

High temperature thermoforming is carried out between 370 F and 420 F. Complex shapes, sharp details and deep draws are all possible with high temperature thermo-forming. Many thermoforming processes use vacuum to achieve some of the complex shapes. One of the disadvantages of high temperature thermoforming is that all moisture must be removed from the sheet by drying the sheet prior to thermoforming. If this drying is not done, the higher temperatures will cause moisture evaporation bubbles to appear in the sheet during thermoforming.

Drying needs to be carried out above the boiling point of water and it is recommended that the sheet is heated to 120 C / 250 F to dry the material. The drying time is dependent upon the sheet thickness. For 0.118” thick sheet about 10 hours of drying is recommended, for 0.236” sheet, this can increase to closer to 30 hours. After drying the sheet should be used within a reasonably short time frame to prevent the sheet re-absorbing moisture from the air.

Hard coatings.

One thing to remember with thermoforming Polycarbonate sheet is that raising the temperature above the glass transition temperature will make the sheet flexible; any hard coating on the sheet will probably not be flexible and will crack during the thermoforming process. When purchasing Polycarbonate sheet for thermoforming it is important to use only hard coatings designed for thermoforming. These coatings are slightly more expensive than standard hard coats, but are considerably cheaper than the alternative of post coating any thermoformed parts.

EMI/RFI shielding of Polycarbonate

2010-03-16T06:55:55-07:00

Electronics systems can cause problems by emitting electromagnetic radiation or they can fail to perform due to electromagnetic radiation in the environment. This electromagnetic radiation is often a combination of noise and information. Leakage of information can be of great concern in applications requiring secure communication. Emissions of electromagnetic radiation can interfere with other systems and may have health and safety implications.

To protect against problems caused by both emission and receipt of electromagnetic radiation, systems can be shielded; this process is known as Electromagnetic Interference (EMI) or Radio Frequency Interference (RFI) Shielding.

To shield against EMI/RFI it is necessary to install a conductive ground plane, which will ground some of the electromagnetic radiation. In applications requiring shielding for transparent Polycarbonate, such as screens and windows, this conductive ground plane can be either applied as a coating to the surface or laminated between two sheets. In this article we will discuss the merits of these two options.

To apply a ground plane using a coating we would typically use a transparent conductive oxide such as Indium Tin Oxide (ITO) or Index Matched Indium Tin Oxide (IMITO). It is also possible to use a thin metal layer such as Gold. With these products we have the option of varying the resistance by varying the amount of oxide applied to the surface. The lower the resistance achieved, the better the ground plane achieved and therefore the better the shielding of the finished product.

Using a 10 Ohms/square surface resistivity we can typically achieve a 20 dB reduction in EMI/RFI over the frequency range of 30 MHz to 1 GHz. A 20 dB reduction is about 100 times reduction in noise. If using ITO, this reduction in EMI/RFI does have a trade off, the ITO does lower the light transmission of the Polycarbonate from 89% down to 82%. One option to resolve this loss in light transmission is to use the more expensive IMITO, which allows a light transmission of 94% to be achieved.

The other solution for shielding is to laminate a wire mesh between two sheets of Polycarbonate. Obviously the visible appearance of a fine wire mesh may not be suitable in all applications. There are many options for the mesh including material of construction, mesh density and diameter of the wire; all of these properties will influence both the shielding effectiveness, visible appearance and light transmission of the finished product. For full details of the technical options for wire mesh shielding you will need to contact your supplier or HighLine Polycarbonate. For a simple comparison with the ITO option we will give some technical data for a couple of wire mesh structures.

For a stainless steel 50 Mesh using 0.0012” diameter wire, we would expect a light transmission of 82% with a 30-40 dB reduction in EMI/RFI over the range of 30 MHz to 1 GHz. A 30 dB reduction is about 1000 times reduction in noise.

If we are prepared to tolerate a lower light transmission, we can use a blackened copper mesh which would give a 50-60 dB reduction over a range of 30 MHz to 1 GHz, but the light transmission would drop to around 70%.

The following table summarizes the results:

	Shielding 30MHz–1GHz	Light Transmission
ITO	20 dB	82%
IMITO	20 dB	94%
50 Mesh SS Wire	30-40 dB	82%
Blackened Copper Wire	50-60 dB	70%

As with most projects, there are trade offs to be made between different attributes and overall cost. This article is intended to give a basic understanding of what needs to be considered when specifying Polycarbonate in EMI/RFI shielding applications.

Anti-reflective coating options for Polycarbonate

2010-03-05T10:59:09-08:00

There are several options available for improving anti-reflective performance of Polycarbonate sheet. The correct choice depends on a number of factors including the level of anti-reflection required, the size of the part, the number of parts required and the cost sensitivity of the application. In this blog entry we will discuss how to make the correct choice for the application.

Anti-reflective coatings are typically applied to Polycarbonate that has an abrasion resistant coating applied to the surface. The abrasion resistant coating provides a better surface for the anti-reflective coating to adhere to than the uncoated Polycarbonate. The finished product is therefore more durable. The abrasion resistant coating itself also improves the anti-reflective properties of the Polycarbonate sheet, as discussed in a previous blog post.

There are essentially two broad types of anti-reflective coatings, liquid anti-reflective coatings and vapor deposition anti-reflective coatings. Liquid anti-reflective coatings are applied to the sheet in a solution and are then cured using either ultraviolet light or heat. Vapor deposition coatings are applied using a sputtering process.

Level of anti-reflection achieved.

The following table shows the amount of reflection from each surface of the sheet with each of the anti-reflective options. These figures are over the visible light range of 420-680 nm.

Uncoated Polycarbonate sheet 5.1%

Abrasion resistant coated Polycarbonate sheet 3.9%

Liquid anti reflective on Polycarbonate sheet 2.0%

Vapor deposition anti-reflective on Polycarbonate sheet 0.75%

If a very low level of reflection is required a vapor deposition anti-reflective is normally used. However, it is often possible to use a liquid anti-reflective or even just an abrasion resistant coated sheet for applications not needing such a low level of reflection.

Cost of anti-reflective solutions.

A liquid anti-reflective coated sheet typically sells for about five times the price of a standard abrasion resistant coated Polycarbonate sheet.

A vapor deposition coated anti-reflective sheet would sell for about five times the price of a liquid anti-reflective sheet.

These broad pricing guidelines obviously depend on a number of factors including part size and the number of parts required, but they do give some indication of what you can expect to pay for increasing levels of anti-reflective performance. Often only very high technology applications can justify the cost of a vapor deposition anti-reflective coating.

Part size and minimum order quantity.

One of the problems of vapor deposition technology is the limitation on the size of the part. Parts of up to 14” x 18” can be produced on a standard sputtering machine in reasonably small quantities. However, once you get above this size you need to use a very large sputtering machine that requires large set up costs and thus large production runs. Parts up to 24” x 36” are easily possible but may require production of at least 1000 parts at a time; this makes it very difficult to obtain a couple of parts for a prototype development if parts over 14” x 18” are required. Once you require parts of over 24” x 36” you need very specialized equipment and the cost is extremely high.

For liquid anti-reflective coatings it is possible to easily coat sheets of 48” x 96” or larger and the minimum production size is much smaller. The easier production makes liquid anti-reflective materials much easier to obtain for prototype development. For large parts we typically recommend that liquid anti-reflective coatings are evaluated first, before trying the expensive vapor deposition anti-reflective coatings.

Transparent Heaters built from ITO coated Polycarbonate

2010-02-12T11:16:12-08:00

Today we have been working with two customers, both of which are considering using ITO coated Polycarbonate sheet as a transparent heater for windows. One of the customers currently uses wires laminated in the sheet to heat the windows. They have recognized that using ITO coated Polycarbonate could be a cheaper option than laminating the wires into a window and the visual appearance of the product would also be much better.

The question that keeps coming up for this application is: “If I need to heat a window with X Watts/square inch, can I use ITO coated Polycarbonate?” Typically the value for X is between 0.2 and 0.8 depending upon the customer’s requirements.

As you might expect, this question is not a yes-no type question, but it involves some simple calculations. In order to carry out the calculation we need some simple information: the voltage (V) that is available for heating and the size of the window to be heated (both the width (W) between the two bus bars and the length (L) of the window/bus bar.

The first step is to calculate the total power requirement for the window, we will assume for this example that 0.5 Watts/square inch is needed.

Power (Watts) = 0.5 (watts/square inch) x W (inches) x L (inches)

We then need to calculate the Heater Resistance (R) where:

R (ohms) = [V (volts)]² / Power (Watts)

We then need to calculate the Surface Resistance (SR) of the sheet where:

SR (ohms/sq) = L (inches) x R (ohms) / W (inches)

Combining these equations into one simple equation:

SR (ohms/sq) = [V (volts)]² / ( 0.5 (watts/square inch) x [W (inches)]²

The limiting factor for Polycarbonate is that the minimum practical Surface Resistance is 10 Ohms/sq. This limitation means that reasonably high voltages will be required for wide heating elements. Smaller heating elements can be achieved with correspondingly lower voltages.

As an example, we will calculate whether a 9” wide x 12” long window requiring 0.5 watts/square inch heating from a 24 volt circuit can be produced from ITO coated Polycarbonate:

Surface Resistance (ohms/sq) =(24 volts x 24 volts) / (0.5 watts/square inch x 9” x 9”)

= 14 ohms/sq

Also the power requirement would be around 40 watts.

The 14 ohms/sq is easily achievable with ITO coated Polycarbonate in this application.

At HighLine Polycarbonate LLC we have a simple Excel spreadsheet to carry out this calculation. If you would like a free copy, please send us an email at info@highlinepc.com requesting a copy and we will send you one.

Regrind and the cost of quality

2010-02-01T13:45:43-08:00

One subject often comes up in discussions with our customers: regrind material. In this blog post we will explain the different types of regrind and why regrind is important to quality.

A Polycarbonate resin plant typically produces 50,000 MT of resin per year. These lines are a continuous production process, operating 24 hours a day, 7 days a week. Each line may produce a number of different grades and when they transition between the grades they do not stop producing. Instead they produce something known as transition material; transition material is between the specification of the initial grade and the grade being transitioned into. Up to 10% of the production of a line may be classified as a transition material.

As the production line is a continuous process, operational problems can also lead to off-specification production. Off specification production may account for another 10% of the production. Between transition material and off specification production as much as 20% of the line output may not be within specification – representing 10,000 MT per year. Obviously this figure varies between manufacturers and also depends on the types of grades being produced on any particular line.

A manufacturer of resin must then decide what to do with this out of specification resin. One option is to sell the material at a discounted price. However, the preferred option is to melt the resin pellets and feed them back into the production process. The amount of resin that is reprocessed again depends upon the manufacturer; but if we look at the figures as much as 10,000 MT of off specification material could be used to make the 50,000 MT of saleable prime resin.

When the resin is then used to make Polycarbonate sheet we also have a similar situation. Changes between different grades and sizes of Polycarbonate sheet can lead to off-specification production. Also when Polycarbonate sheet is being produced the edges are normally not flat and so are trimmed off – this material is then known as edge trim. Both off-specification production and edge trim can then be broken into small pieces in a grinder and then recycled into the sheet extrusion line; this material is known as regrind. In some cases of commodity sheet production as much as 60-70% of the sheet can be composed of regrind material.

Recycling of material, both in the resin and sheet production, can help keep the cost of sheet down – particularly for commodity sheet. However, recycling of material does come at a cost. Polycarbonate is degraded by heat and the more times heat is applied to the material (especially at temperatures high enough to melt and mix the material), the greater the degradation. This degradation manifests itself in three ways, black specks, yellowing and deterioration of mechanical properties. The greater the level of recycled material in the final product (whether from resin or sheet), the greater the possibility and magnitude of problems such as black specks, yellowing and deterioration of mechanical properties. For many commodity applications the price of the sheet is of great importance and the benefits of recycling during production significantly outweigh the consequences. In some applications it may indeed be acceptable to use low priced sheet made from 100% regrind.

At HighLine Polycarbonate we concentrate on high-tech applications requiring exceptional optical and mechanical properties where black specks and yellowing cannot be tolerated. While we take many steps to ensure the quality of the product, we do pay particular attention to recycling. We use only the very best resin from Teijin. Teijin is a Japanese company and is the world’s third largest Polycarbonate resin producer. The grade of resin that we use has no recycled resin in it. Also, most of Teijin’s resin lines are relatively new having been installed in the last ten years. Having modern resin lines also improves the quality.

When we produce the sheet we also do not recycle any off specification material or use any edge trim material. Many other manufactures claim to not use regrind material, but often recycle edge trim material. By using only the very best resin and not using any regrind we are able to produce the very best material for the most demanding applications. Of course there is a cost to quality, but there is also a benefit in some applications.

Polycarbonate sheet - the cost of custom production

2010-01-22T13:04:13-08:00

Polycarbonate is extruded into sheet by large production lines. The more specialty lines typically extrude 3,000 lbs/hr, while commodity lines extrude 5,000-10,000 lbs/hr. For some of the large lines, if they take ten minutes to change dimensions, they could easily generate over 1,000 lb of off specification material, which will either need to be recycled or scraped.

Non-standard width

The maximum width of the sheet is governed by the width of the die installed on the line; most large lines have a die that can produce 96” wide sheet. The extrusion lines produce most efficiently when they are running at maximum throughput, which means running the maximum width of 96”. One option that sheet extruders have is to cut the sheet in half while the sheet is being produced, this process will give two sheets of 48” wide. The widths of 48” and 96” are some of the most common widths. Because they can be produced cheaply they have become industry standards and are nearly always in stock at the major producers and distributors.

If a customer needs a non standard width, this can be achieved by extruding 96” wide material through the die and then cutting down the edges by in line saws. Any off cut material can then either be recycled or sold as scrap. If a customer needs dimensions such as 95” wide or 47” wide, there will not be much scrap generated, even though the material would still need to be custom produced. If the customer needed a width such as 75”, proportionally more scrap would be generated and the cost to produce would go up. For widths of say 60”, the scrap ratio would be too high and the producer could stop the line and block off part of the die to limit the width of the sheet being produced. The stoppage would obviously lead to lost production and then the machine would be run at a lower, more inefficient rate because the die width would be lower. All of these factors add to the cost.

Non-standard length

The length of the sheet is more easily controlled. During production an in-line cross cut saw is used to cut across the sheet. The length can be set to almost any value (as long as it is not too small). It is therefore possible for a producer to make custom lengths without too much additional cost.

Non-standard thickness

For stocking purposes the major producers have standardized on a number of thicknesses – 0.060”, 0.118”, 0.177”, 0.236” are some examples. These sizes are normally carried in stock in both 48” x 96” and 72” x 96”. Adjusting to another thickness really only involves some minor changes to the die and chrome polishing rolls; these changes are quick and do not generate much off specification production. As a consequence, non-standard thicknesses are not difficult to produce, but manufacturers normally insist on a reasonable minimum order size. Also manufacturers will normally only produce non-standard thicknesses against an order, as they do not have a general need for the material. Because the material is custom produced, manufacturers often quote a long lead-time.

Non-standard color

For custom colors, introducing a new color to the line causes a lot of scrap changeover material between the production of the old color and the production of the new color. The lines are not shut down and cleaned between color changes, as that would be too inefficient. Manufacturers dislike frequently changing colors, and often plan large color runs to improve efficiency. Asking a manufacturer to stop the production of a clear material to produce a few hundred pounds of a red material is not likely to be received well, as the change-over produced from going from clear to red and then back to clear is likely to be many thousands of pounds. A manufacturer can not offer a competitive price if they produce ten or more pounds of scrap for every pound of good product.

Summary

Standard production sizes and colors have been established to improve efficiency and reduce cost. If a customer needs a non-standard product it is likely to be more expensive and require greater lead-time and larger minimum orders. Non-standard colors are the most costly, followed by non-standard width, followed by non-standard thickness, with non-standard lengths being reasonably cheap to produce. Considering these factors during product design can help in minimizing later costs and ensuring availability for the customer.

Anti Fog coatings for Polycarbonate explained

2010-01-13T07:11:04-08:00

Fogging can often occur on the surface of a Polycarbonate window when moisture from the air condenses onto the cold surface of the sheet or window. The condensed moisture forms droplets that then obscure the view through the window. This fogging effect also occurs on glass and is most often seen on the windshield of a car on a cold morning or on a bathroom mirror if the room is filled with steam.

There are a number of ways to prevent fogging on Polycarbonate and most of them involve some type of coating. Most of these coatings have hydrophilic properties. The term hydrophilic comes from the Greek words “hydros” meaning water and “philia” meaning friendship. A hydrophilic surface attracts the water. This attraction means that the water condensation, instead of forming droplets, forms a thin water layer along the surface of the sheet or window. This thin film of water will then not obstruct vision in the way that water droplets obstruct vision. Hence a hydrophilic material has anti-fog properties. The thin film of water is also able to evaporate quickly if there is air movement near the window.

One problem for some high-tech applications such as lenses and optical sights is that the thin film of water can cause focusing problems. These issues can become severe in environments where the thin film of water is allowed to build up such as telescopes where the users eye is placed against an eyecup. The moisture from the users eye can condense on the lens and because there is an enclosed space with no air movement, the water film can build up with a hydrophilic coating.

One potential solution is a super-hydrophobic coating. A super-hydrophobic coating actually works in the opposite way to a hydrophilic coating and it actually repels water. This effect means that when water condenses on the window or sheet, it will actually bead up into an almost perfect sphere and immediately roll off the surface rather than sit on the surface as a drop, which obscures vision. At the moment super-hydrophobic coatings exist for opaque surfaces, but there are no commercially available options for transparent plastics.

HighLine Polycarbonate has a range of hydrophilic coatings available for Polycarbonate sheet and we have applied these to a number of commercial products. During 2010 we will be looking at the opportunity to develop a super-hydrophobic anti-fog coating for high-tech Polycarbonate applications.