Bullet Resistant Laminates and Transparent Armor

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

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

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

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

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

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

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

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

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

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.