Friday, April 30, 2010

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.

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