Tuesday, June 29, 2010

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.

Friday, June 4, 2010

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.