As electronic displays are becoming more commonplace in new automobiles, and as these displays are becoming ever larger, the problem of glare on the displays is an increasingly important issue.
Sunlight reflecting off the display can make it difficult or even impossible to read the information. The solution is to make the clear plastic part on the front of the display (usually polycarbonate or acrylic) have anti-glare properties. Up until recently a clear plastic part was coated with an coating containing small particles giving anti-glare properties. Indeed, this was the solution offered by HighLine Polycarbonate to a number of our customers.
Even though the anti-glare coating did achieve the aim of reducing glare from the surface of the display and had a number of other advantages, it is important to note that it was not a solution without problems. The aim of this post is to identify some of the advantages and disadvantages of anti-glare coatings for this application and discuss an alternative approach.
The main advantage of an anti-glare coating is that by varying the amount of anti-glare additive in the coating, you can vary the level of anti-glare properties or “gloss” of the finished sheet. We offered anti-glare coated sheet with gloss levels of between 20% and 90%. By taking this approach you are able to produce a custom gloss level, which is optimized for the customer. Perversely, most manufacturers of anti-glare sheet choose to standardize gloss levels and only offer two or three gloss levels in their range – this standardization has the result of almost eliminating the main advantage of anti-glare coatings.
The next advantage is that the coating provides a barrier on the surface of the sheet that offers some protection against scratches and solvents damaging the sheet. Even though it is undeniable that there is some increased protection, it is minimal when the claim is examined in detail. The scratch protection offered by the coating offers little extra protection to real world damage when compared to uncoated product. This can be easily seen when car keys are thrown lightly at the coated surface (a not uncommon occurrence when car keys are no longer inserted into an ignition but rather stored near the center display). The coating, like the base polymer is easily scratched.
Also when the claim of protection against solvents is examined, the protection is not as great as implied. The coating looses protection in the area of any scratches and only the face of the sheet is protected. The edges of the sheet are not coated and so any solvents getting to the edge of the sheet would do damage.
The main disadvantage of coatings is that it is very difficult to control the level of anti-glare or “gloss” properties from batch to batch, within a batch and over the surface of an individual sheet. To explain the above statement, we need to examine how the coating is applied.
The coating is usually applied in a flow coating process (other processes such as spray and dip coating can cause even greater variation). Flow coating involves hanging the sheet vertically and then flowing a coating solution down the sheet over the surface. Excess coating flows off the bottom edge of the sheet and is recycled for use on the next sheet. The sheet is then cured in an oven.
The problem is that the coating contains heavy anti-glare additives and these additives tend to flow towards the bottom of the sheet. This process makes the bottom of the sheet have much less gloss than the top of the sheet. This variation in gloss can be minimized by coating a smaller sheet; giving less distance between the top and bottom of the sheet. When we produced by this method we were able to reduce the difference in gloss between the top and bottom of the sheet to less than 7% by reducing the sheet size to 24” wide. Most coaters prefer to coat sheets of 48” and 72” wide to improve the economics; this size of sheet has even more significant variation in gloss. When automobile manufacturers are increasingly trying to reduce variations in gloss to 1-2%, coating becomes very problematic.
Also as the coating process moves from sheet to sheet, the solvent level in the coating can vary. This makes variation between sheets and between batches notoriously difficult to control.
Another problem with anti-glare coatings is the cost. Coating is naturally an expensive process; when coupled with a low yield for trying to get a tight tolerance on the gloss levels, it can become very expensive. Coupled with other problems associated with coating such as delamination and dust particles in the coating (which become critical in this application), it is unsurprising that automobile manufactures are moving away from coatings for anti-glare displays.
HighLine Polycarbonate has moved away from offering anti-glare coated product for automobile displays. We now offer an anti-glare texture on the surface of the sheet that is applied during the extrusion of the sheet. This texture has been specifically developed for display applications. It maintains clarity of the information displayed while significantly reducing glare.
The main advantage is that it eliminates variation in glare between the top and bottom of the sheets, between individual sheets in a batch and from batch to batch. The gloss level specification can be held to within 1%.
The greater control of the gloss level makes for a much more consistent product at a much lower cost than coating can achieve.
The sheet does loose some of the resistance to scratches and solvents, but as discussed earlier, these claims are really little more than marketing ploys and offer little real world protection.
The other issue is that at this time we are only able to offer one level of anti-glare that has been selected for this application. Coatings can offer a wide range of anti-glare levels in theory, but in practice, manufactures have avoided offering their customers this option.
HighLine Polycarbonate is able to offer samples of their anti-glare polycarbonate upon request.
Acrylic has replaced tempered glass at many hockey rinks for player and spectator safety reasons. Acrylic is much more flexible than the rigid tempered glass and therefore reduces the potential for injuries such as player concussion. Acrylic also has good optical properties which allow spectators to get a good view of the action.
For many years other polymers were not considered as they were unable to match the optical properties of the Acrylic. However, with recent advances in the production process, the polycarbonate produced by HighLine has changed the equation.
For the same thickness of material, polycarbonate is between 20-25% more flexible than acrylic. This increase in flexibility significantly reduces the risk of concussions by players – a key focus of player safety advocates. However, due to the unbreakable nature of the polycarbonate, it is possible to reduce the thickness from 0.545″ in the case of acrylic to 0.39″ or even 0.32″ in the case of polycarbonate. This reduction in thickness further increases the flexibility and reduces the possibility of concussions. These flexibility results have been confirmed by simulating the impact on the shields by a hockey player using a weighted bag, moving at speeds representative of NHL player speeds. The test set up is shown in the attached photograph. Full test data can be provided by contacting HighLine.
Also, as polycarbonate is unbreakable, shattering acrylic shields around the rink can be a thing of the past; increasing both player and spectator safety. It also eliminates downtime to replace shattered shields during games or practices.
With the reduction in thickness, comes the reduction in weight. The much lighter weight reduces the change over time for rink operations management and makes the shields easier and safer to install.
The key area of improvement that allows polycarbonate to displace acrylic as the material of choice for ice hockey spectator shields is the improvement in optical quality of material produced by HighLine Polycarbonate LLC for hockey rinks. The optical appearance of polycarbonate is virtually identical to that of acrylic in an equivalent thickness. However, because polycarbonate can offer greater protection at thinner thicknesses than acrylic, the optical properties of the thinner material can actually exceed those of the acrylic.
Due to the improved player and spectator safety of polycarbonate, it is starting to displace acrylic at European rinks. With the current interest in reducing player concussions to amateurs and NHL professionals alike, HighLine is at the forefront of bringing polycarbonate rink guards to the North American market.
HighLine Polycarbonate representatives will be walking the NARCE 2016 show in Columbus. If you would like to meet with us at the show for a coffee and chat, please give us a call or send us an email.
With interest in reducing energy bills, there has been a lot of interest in polycarbonate sheet that blocks infra-red (IR) wavelengths. The visible spectrum is in the range of 390-700nm, with UV light below the 390nm and IR light above the 700nm.
Sunlight can cause the inside of buildings and vehicles to heat up by passing through the windows. Lower wavelength light has more energy than higher energy light and causes faster heating. This means that visible light has more energy than infra red light. To reducing the heating, it is necessary to absorb or reflect the light. In the visible region there is only so much energy that you can absorb as by blocking the light you make the window darker, which is often in conflict with the purpose of the window. In addition to making the window darker, another way of reducing the heat build up is to put IR absorbers into the polycarbonate sheet to block the IR light wavelengths.
HighLine is able to offer three colors of IR blocking polycarbonate sheet, each block different amounts of visible and IR light. We currently have Grey, Light Green and Dark Green products.
Color Visible Transmission Solar Transmitted Radiation
Grey 64% 61%
Light Green 65% 53%
Dark Green 48% 34%
The grey and light green products aim to block as little visible light as possible and only have a slight tint. As a result a reasonable amount of heating still occurs in the visible region.
For greater reduction of heating there is the dark green product.
The graph below shows the transmission at the various wavelengths across the UV, visible and IR wavelengths.
It should be noted that the transmission curves for thicker material, such as 5mm or 6mm, are almost identical. Transmission curves for the thicker material, as well as samples of the material can be obtained by contacting HighLine Polycarbonate LLC.
Outside of buildings the major application for IR Blocking Polycarbonate has been for farm and forestry vehicle cabs. The polycarbonate is used to provide protection and the IR absorbers reduce the heating of the cab by the sun. With modern equipment cabs, there are a lot of electronics which also cause heating and these, combined with the sun can put a large load on the vehicle air conditioning. IR blocking polycarbonate has proved to be an effective way of reducing the air conditioning load in these vehicles.
HighLine Polycarbonate has developed a multilayer structure designed to be used by laminators in conjunction with glass or transparent ceramics to extend the life of transparent armor manufactured to ATPD.2352 standards.
The product will improve operational availability of vehicle platforms such as the MRAP and JLTV.
The HighLine product extends the life of transparent armor in three important ways:
Prevents de-lamination by increased bond strength
Over the life of transparent armor, the bond between the polycarbonate and polyurethane weakens. The transparent armor often can delaminate at the polycarbonate–polyurethene interface. Using proprietory technology, we have modified the bonding between the polycarbonate and polyurethane to significantly increase the strength of the bond. This advanced technology significantly extends the life of transparent armor, increases vehicle operational availability and reduces field maintenance and repair costs.
Prevents de-laination due to reduced thermal stresses
The design of the inner polycarbonate layers of the transparent armor can impact the level of thermal stresses experienced. These stresses are caused by the different thermal expansion rates of glass and polycarbonate. The design of the polycarbonate and polyurethane layers have been optimized by mathematical modelling to reduce the thermal stresses in the finished transparent armor. The optimization of the design, in conjunction with the increased bond strength, significantly extends the life of transparent armor systems.
Prevents scratching of inside surface using advanced coating
One of the inherent weaknesses of polycarbonate compared to glass is the tendency of polycarbonate to scratch. To reduce this issue, hard coats have traditionally been applied to the polycarbonate surface. Even with the hard coats, the polycarbonate inside surface of the transparent armor is still prone to damage from the vehicle occupants, reducing the life of the transparent armor. Our advanced coating increases the scatch and abrasion resistance of the polycarbonate to a level similar to glass. The advanced coating will pass the ATPD.2352 specification for the exterior surface.
Structure of HighLine Laminate
Polycarbonate – Flammability
At HighLine Polycarbonate LLC, we receive a lot of questions relating to material flammability. These questions often occur because of the wide range of tests relating to flammability and the limited information available from manufacturers. In this blog post we will discuss some of the most common test methods and what they mean. It should be recognized that there are many local and national regulations that refer to different test methods and that we cannot cover all of these in a single post. In particular, we have decided not to attempt to cover building regulations due to the multitude of local codes. Instead we have concentrated on the transportation industry.
The most common method of defining polycarbonate sheet flammability properties is UL.94; this test method was developed by Underwriters Laboratories in the USA.
There are multiple levels of flammability:
HB – A piece of the material to be tested is held horizontally, a flame is applied to one end of the material for 30 seconds. When the flame is removed the material must extinguish before the flame travels 75mm along the material.
V2 – A piece of the material to be tested is held vertically, a flame is applied to the material for 10 seconds. When the flame is removed, the material must not burn for more than 30 seconds.
V1 – This test is the same as for V2, with the additional requirement that the specimen must not drip flaming particles that ignite cotton placed under the test specimen.
V0 – This test is the same as for V1, with the additional requirement that the material must not burn for more than 10 seconds.
The easiest of these tests to pass is the HB test and the hardest test to pass is V0. As an indication, polycarbonate, without any flame retardant additives, would pass the tests as shown in the table below. Please note that these figures are only be used for information and test certificates should be obtained from your polycarbonate sheet supplier.
HB 0.060” or thicker
V2 0.125” or thicker
V1 0.1875” or thicker
V0 0.25” or thicker
As can be seen, the thicker the polycarbonate, the more resistance it is to the flammability tests.
If the design specification calls for a V0 rating at 0.125” thickness, standard polycarbonate will not be able to meet the specification. In this case, flame retardant polycarbonate sheets would need to be considered. Alternatively, a thicker piece of polycarbonate could be specified. Using a thicker piece of polycarbonate would probably be cheaper if the design allows; the material would also be much more available.
Within the UL.94 standard there are two additional higher levels of flammability, 5VB and 5VA. As these ratings are not as common we will not go into details here. However, a quick internet-search will reveal details on these tests.
Aircraft specifications – FAR 25.853
The FAA (Federal Aviation Administration) developed a standard for materials to be used in aircraft cabin and cargo compartments. This standard is known as FAR.25.853. For polycarbonate sheet there are two relevant parts FAR 25.853a and FAR 25.853d relating to flammability.
FAR 25.853a measures the resistance of material to flames. The material is held vertically and a Bunsen burner is applied for (i) 60 Seconds and (ii)12 seconds. Three items are measured:
The flame time – the time that the specimen continues to burn after the flame is removed.
The drip flame time – the time that any flaming material continues to flame after falling from the material.
The burn length – the distance from the original specimen’s edge to the farthest evidence of damage to the specimen.
To pass the tests the material must achieve the following:
|Test||Flame time (sec)||Drip flame time (sec)||Burn length|
|(i) 60 second||
|(ii) 12 second||
We are aware of a number of transparent polycarbonate sheets with flame retardant additives that can pass this test.
FAR 25.853d consists of two tests. The first, the OSU (Ohio State University) Rate of Heat release tries to limit the possibility that materials will become rapidly involved in a fire or contribute to an existing fire. The rate of heat release is measured using the principle of oxygen consumption using the OSU calorimeter and the test method is published under ASTM E906. The standard requires that the total heat release within the first 2 minutes is <= 65kW per square meter and that the Peal Heat Release Rate is <= 65KW per square meter. In data sheets for flame retardant polycarbonate sheets, if a material passes this test it is often written a FAR 25.853a OSU 65/65.
At this stage we are not aware of any transparent polycarbonate sheets that can pass OSU 65/65 even with flame retardant additives. We are aware of opaque polycarbonate sheet that can pass this test such as the Lexan XHR.6000 and the halogen free Ultem 1668A.
The second test in FAR 25.853d is the smoke density test, which is similar to ASTM E.662 (which we shall discuss later). This test measures the amount of smoke that is generated, which could prevent passengers escaping in a fire situation. To pass this test the 4.0 minute smoke density Ds (4 min) <= 200. A number of transparent polycarbonate sheets, with flame-retardants, are able to pass this test.
To pass all elements of FAR 25.853 a material must list the following:
FAR 25.853a (i) 60 seconds Pass
FAR 25.853a (ii) 12 seconds Pass
FAR 25.853d Rate of Heat Release OSU 65/65
PAR 25.853d Smoke Density Ds(4min) <= 200
Rail car specifications – 49 CFR Part 238
The FRA (Federal Railroad Administration) developed a standard for materials to be used in rail car applications in the US. The part of this standard that deals with flammability is known as 49 CFR Part 238. For polycarbonate sheet Appendix B of this standard requires two tests, ASTM E.162 and ASTM E.662.
ASTM E162 provides a measure of flame spread and heat evolution. The maximum value to pass this test Is <= 100
ASTM E.662 is similar to the test used for the aircraft industry to measure smoke density.
To pass this test, the smoke density after 1.5 minute Ds(1.5 min) <= 100 and the smoke density after 4 minutes Ds (4 min) <= 400. It can be seen that the 4 minute test for the FRA is not a severe as for the FAA.
In general, some of the thicker polycarbonate transparent sheet can pass these tests without the need for flame-retardants. However, test certificates must always be provided by the manufacturer.
Transparent polycarbonate sheet without flame retardant additives has a reasonable level of flame resistance, particularly as the thickness increases. It is able to pass some of the UL.94 tests and can pass some of the Smoke Density, Fame spread and heat release tests required by various transport administrations.
Where these properties are not sufficient, flame retardant additives can be used to improve the properties, but these add to the price. Some significant improvements can be made while still allowing the material to remain transparent.
With some of the more demanding specifications, higher doses of more complex flame retardant additives are required. Achieving some of the higher specifications are not possible while also retaining the transparency of the material. Also, adding these flame retardant additives can impact other properties of the polycarbonate sheet.