Polycarbonate and UV

exterior_badheadlight

Polycarbonate is a very versatile material that is used for all sorts of applications including many applications that require ultraviolet light resistance. Most grades are not suitable for these applications unless they are modified with a UV stabilizer additive. It is also important to ensure that you have the right UV additive for your application.

I am going to focus on automotive applications here because they are such a common use for UV stabilized polycarbonates but this applies to non-automotive applications as well.

There are really 3 groups of UV stabilization for polycarbonate currently on the market.

Interior UV

This is polycarbonate that can be colored or clear that is suitable for indoor applications that are exposed to sunlight. Automotive applications typically require this material to meet SAE specification J1885 with an exposure of 225.6 kJ/m². Click here for more information on exactly what these SAE accelerated weathering test methods mean.

Here are a few common grades of polycarbonate suitable for interior UV applications:

  1. Lexan 123R
  2. Lexan 143R
  3. Makrolon 2607
  4. Makrolon 2807
  5. Trinseo Calibre 302-10
  6. Lotte Infino SC1220UR

Most grades of polycarbonate that indicate that they are UV stabilized will meet these requirements but it is always good to check if you are in doubt.

Exterior UV Colored

This is polycarbonate that is suitable for colored applications that are used outside that are directly exposed to weather. If the part is painted or plated this would not apply as the material is protected from the sunlight. Automotive applications typically require this material to meet SAE J1960 with an exposure of 2500 kJ/m². Notice that this is quite a bit more exposure than the interior UV requirements.

Here are a few grades of polycarbonate that suitable for exterior UV colored applications:

  1. Lexan 123R
  2. Lexan 143R
  3. Makrolon 2607
  4. Makrolon 2807

Exterior UV Clear

Polycarbonate that is suitable for exterior use in clear must meet much more difficult requirements. Ordinary UV stabilized grades will turn yellow in a year or two if used for exterior clear applications. For automotive applications, there are federal Government requirements for these materials. The specification is FMVSS 108 which refers to SAE J576. This test method requires 3 year of outdoor weathering exposure and does not spell out any requirements for accelerated weathering testing.

Only a few materials on the market meet these requirements:

  1. Lexan LS1
  2. Lexan LS2
  3. Makrolon AL2447
  4. Makrolon AL2647

There are probably a few more grades that meet this requirement but I was unable to find any. If you know of any more, let me know in the comments.

The reason that the requirement for weathering for clear material is so much more difficult to meet is because the pigments in the colored materials block the UV rays from penetrating the material making it less susceptible to damage.

As you can see, most UV stabilized polycarbonate on the market can be used for interior applications and also for exterior colored applications but exterior clear applications are much more difficult. The materials that must be used for these applications are also significantly more expensive. It should also be noted that general purpose grades such as Lexan 121R and 141R are not UV stabilized and are not suitable for use in sunlight exposure applications.

There are some commercially available UV coatings that can be used to help protect polycarbonate from damage. There are also some coatings that can be purchased at the auto parts store that are made for coating headlights. I am not sure how well these work though.

SABIC also has a range of polycarbonate copolymers that are branded Lexan SLX grades that have a newer technology that improves UV stabilization. You can read about them here.

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