Sheet - conversion between weight and area

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

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

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

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

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.