Transparent Polyamide sheet compared to Polycarbonate Sheet

Transparent Armor Window

Many people are aware of Polycarbonate sheet, PETG sheet and Acrylic sheet, but there is now a new material that has entered the transparent sheet market - Polyamide.

Polyamide is certainly higher in price than other transparent sheets, but it has an interesting range of properties that make it suitable for some technically demanding applications.

Like Polycarbonate, Polyamide can be used to make very high quality optical grade clear sheet.  In fact the light transmission is 90% compared to 89% for Polycarbonate.  Sheets of the same size as Polycarbonate can be easily manufactured.  Also, Polyamide is almost as unbreakable at Polycarbonate which means it can withstand environments that would damage polymer sheets made out  of Acrylic.

Where Polyamide really excels is in properties such as the heat distortion temperature, tensile modulus, density and solvent resistance.  We will look at each of these in turn and compare them to the other Polymers.

Heat distortion temperature.


Material                            Heat distortion temperature (C)     Glass transition temperature (C)
Acrylic                                         95                                               110
Polycarbonate                            137                                             148
Polyamide                                   180                                             190

These figures show that Polyamide can withstand much higher temperatures than both Acrylic and Polycarbonate before they will start to distort under a load.  In many applications, the heat distortion temperature is not an issue, but occasionally the part must be able to operate in higher temperature environments without distorting.  In these applications, Polyamide is an excellent option.

Tensile modulus

Material                           Tensile modulus (psi)
Polycarbonate                     348,000
Polyamide                            232,000

Polycarbonate is a very flexible material, much more so than Acrylic which is rigid by comparison.  This flexibility makes it very useful in applications such as security glazing and transparent armor.   While Polyamide grades are available with a number of different Tensile modulus characteristics, the one that HighLine Polycarbonate LLC is currently using to make sheet has a lower tensile modulus than even Polycarbonate, making the Polyamide sheet more flexible than Polycarbonate sheet.  This property means that in certain configurations, it can be a better material for bullet resistant applications than Polycarbonate.  Of course there is a price-performance balance that means that Polyamide is not suitable for all applications.
Where flexibility is needed, Polyamide is certainly an option to be considered.

Density

Polycarbonate and Acrylic have similar densities of around 1200 kg/m3.  Polyamide has a density of around 1060 kg/m3.  This means that Polyamide is about 10% lighter.  Where weight is important, Polyamide is an option.

Solvent resistance

Polycarbonate, while very resistant to a number of chemicals, does not perform well when exposed to certain other chemicals such as Ketones.  One of the strengths of Polyamide is that it has exceptional solvent resistance performance.  As well as being resistant to Ketones, Polyamide is not attacked by most fuels, oils and lubricants.   This chemical resistant makes it a good choice in transportation and aerospace applications.

As far as we know, HighLine Polycarbonate is the only manufacturer to currently offer clear Polyamide sheet to the market.  If you would like more information on this unique material, please contact us.

Anti Glare Coatings explained

Anti-glare coatings are different to anti-reflective coatings.  Anti-glare coatings are generally produced using an abrasion resistant hard coat with small particles in the coating to give a matte surface.  This matte surface stops light being reflected from the sheet surface back to the viewer so that the user's view is not obscured by glare from lighting or the sun.

One down side to the matte surface is that the light transmission of the sheet is lowered and the view through the sheet is hazy.  The more of the matte agent that is put into the sheet the more the glare is reduce, but also the sheet becomes more hazy and the view more obstructed.

To illustrate the effect of an anti-glare coating we have taken three pictures of an anti-glare sheet with a 40% gloss level.  The 40% gloss is quite a high level of matte agent - we commonly supply product with gloss levels of 60% and as high as 80%.  The 80% gloss level is much more transparent but does not reduce the glare as much as the 40% gloss level material.

We are often asked how much does the reduction in gloss level obscure the view through the sheet?  The answer depends on what you are trying to view.  If you are trying to view something that is a long way away through the sheet, the object is still able to be seen but the view is very blurred.  To show this effect, we positioned a typed page only 15" behind the anti-glare sheet.  The page is visible but the details are not.

We then moved the page to 5" behind the sheet.  Again the page is visible and you can even start to make out the detail of some of the larger font.  48 Point font is clearly legible, even 28 Point font is just visible, while smaller font can be seen but not read.

We then moved the typed page to immediately behind the sheet and the page was even touching the sheet.  Nearly all of the font, even the smallest can be clearly read.  

When choosing an anti-glare gloss level it is important to test it in your application.  The questions that need to be answered are how much do you need to reduce glare and how much haze can you accept.  The answers to these questions depend on what environment you are you using the sheet in and what do you need to see through the sheet.    

 

 Photo 1 - Typed page 15" behind the anti-glare sheet

 Photo 2 - Typed page 5" behind the anti-glare sheet

Photo 3 - Typed page immediately behind the anti-glare sheet (touching)

Clearfix - Repairing Polycarbonate sheet scratches

The above video shows how scratches in both uncoated and abrasion resistant Polycarbonate sheet can be easily repaired using a product developed by 3M and Clearfix Aerospace.  The product was initially developed to repair military helicopter windows; however, HighLine Polycarbonate has worked with 3M and Clearfix Aerospace to evaluate and test the product on Polycarbonate sheet used on transparent armor laminates as well as other applications.

The product works equally well on repairing scratches and other damage on both coated and uncoated Polycarbonate sheet.  Not only can the product be used to repair scratches on in service vehicles but it can also be used to repair scratches on production damaged laminates.  Laminates that would otherwise need to be scrapped can now be repaired allowing manufacturers and users to significantly reduce costs.

The product can be purchased from HighLine Polycarbonate LLC as we are now a primary distributor of Clearfix.  Potential users should contact us to schedule a demonstration at their facility.

LEDs in Polycarbonate

This video shows a new process we are developing to laminate ultra thin LEDs between sheets of Polycarbonate. The first sheet in the video shows the LEDs between two sheets of 0.118" thick clear Polycarbonate. The second sheet shows the LEDs between a mirrored piece of 0.177" Polycarbonate and a piece of clear 0.118" Polycarbonate - the LEDs are only visible when they are lit as normally they are hidden by the mirror.

The next production trial will use a piece of light diffusing Polycarbonate as the front face in order to diffuse the LED light and prevent "hotspots". We also plan to increase the density of the LEDs. We also plan to use thinner Polycarbonate to make the whole structure 0.118" thick in total.

Conventional lamination methods would damage LEDs, but a new technique that we are working on is making these type of products possible. The technique would allow very bright, low weight signs or lighting powered by only a 9 volt supply.

Is Polycarbonate Bullet Resistant?

We recently came across this video on YouTube. It is certainly one of the more interesting and better produced of the videos about Polycarbonate and bullet resistance.



We will concentrate our discussion to the first two rounds fired, the 0.22LR and the 9mm round.

Most ballistics certifications for bullet resistant glass constructions, such as UL.752, start their testing with a 9mm Full Metal copper Jacket with a lead core. This bullet weighs 8 grams and has a test velocity of 358 m/s. The 0.22LR in the video has a weight of about a third of this at 2.6 grams and a velocity of around 290 ms.
Using our Kinetic Energy formula of Energy = 0.5 x Mass x Velocity x Velocity, the 9mm round has about 4.7 times the energy of the 0.22LR round.
For the UL.752 Level 1 test three shots of a 9mm FMJ must be fired at a 12" x 12" target and the shots must land within a 4" triangle area. To pass the test no bullets must pass through the material and no pieces of the material must come off the back with sufficient velocity to damage a cardboard witness plate located a short distance behind the sample.
The 12" x 12" test piece is fully supported and will not move during the testing.

From the video of the 022LR it is clear that the 0.5" Polycarbonate does not allow the round to pass through. One concern that we would have is that the test piece was not supported, so some of the energy was absorbed by moving the piece when it was hit. That would not be realistic in real life where a window would be supported. Also the test in video did not consider multiple hits in a small area as in the UL.752 Level 1 test. However, it appears likely that Polycarbonate that is supported in a frame could stop 0.22LR rounds at a reasonable thickness - however, without testing in a controlled manner it is not possible to say whether the required thickness is 0.5" or greater.

From the video of the 9mm round, two 0.5" pieces of Polycarbonate were clamped together. This test was designed to see if 1.0" of Lexan could stop a 9mm round. We have some similar concerns as for the first test where the test sample was not supported. More importantly the pieces broke free from the clamp and it is not clear whether the second piece was hit straight on or whether the bullet glanced off the piece. We don't think that the video is claiming that a 1.0" piece of Lexan can stop one or more hits from a 9mm round but we would be concerned if someone inferred this from the video.

One thing that we do know is the a 0.75" construction made from 1/8" Polycarbonate - 1/2" Cell cast Acrylic - 1/8" Polycarbonate can be tested to UL.752 Level 1 with the 9mm threat and will pass. So a single 1,0" supported layer of Polycarbonate may or may not be effective for stopping 9mm rounds but there are potentially cheaper and lighter options available that will.

If you put thick enough piece of Polycarbonate in front of a 9mm round it will eventually stop the round. It just may not be the cheapest or lightest way of doing it, which is why Polycarbonate is not normally tested and approved as a bullet resistant material as a stand alone solution.

The video even states that their test is completely unscientific.
All of this does not make the video any less interesting or enjoyable. It is also very well produced.

Drying Polycarbonate sheet

Polycarbonate sheet readily absorbs moisture from the air. Eventually the water content will reach 0.2% by weight.

In most applications this water content is not a problem, however, in applications where you need to process the sheet above a temperature of 250F, this water can vaporize within the sheet during processing and lead to small bubbles forming. As little as 0.05% water can cause these bubbles.

Two processes that require the sheet to be heated above 250F are lamination of the Polycarbonate and thermoforming of the Polycarbonate. Both of these processes can have problems with bubbles if the sheet is not dried correctly.

To dry the sheet there is a wide range of recommendations that have been published. To dry 0.118" thick sheet it is normally recommended to use an oven set at 250F. The drying time suggestions can range from 6 to 12 hours. We would suggest that the longer time the sheet is dried the better and we would use 12 hours. Other recommendations suggest that a lower oven temperature of 180F can be used but the time must be increased to 24 hours. If your oven is only capable of reaching 180F rather than 250F, you could certainly try this method - however, we are very skeptical of this approach as to drive the water off effectively you really need to be above the boiling point of water.

As the thickness of the sheet increases, the drying time will increase significantly as the water needs to be removed from the center of the sheet. For 0.236" thick sheet we would recommend 30 hours of drying at 250F and for 0.375" thick sheet we would recommend 40 hours.

One question that we are asked is "Do you need to remove the masking before drying?" In general the Polyethylene or paper masking is not a very good moisture barrier, so it should not hinder drying very much. There is generally more risk of damage to the sheet if the masking is removed prior to drying, so unless you have good handling conditions to prevent damage, the marginal improvement in drying time is usually not worth the risk.

Once the sheet has been dried, it should either be used immediately or stored in a dehumidified area with a dew point less than 10F. To illustrate why this is the case, on a hot, humid day a dried sheet can absorb 0.5% water within 3 to 4 hours and at this level, bubbles could occur during processing.

Printing with Polycarbonate

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?

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.