Fig. 2 illustrates a color control scenario with a numeric limitation in CIE L*a*b* color space of 1.0 unit for L*, a* and b* along with a color representation of each. When setting up a color control program, care should be taken not to establish color acceptability limits beyond what is necessary for the usage situation. Depending on the color difference equation used, it will not be unusual to have different limits set for each variable. It is common to have more color rejects and returns as well as increased production costs when using extremely tight color tolerances.
Color control programs can be very detailed depending on the color requirements of an application. For help with setting up a color control program, ASTM International (http://www.astm.org/index.shtml) has several methods and standard practices for evaluating color and for establishing color tolerances and color differences based on visual evaluations and from instrumental color measurements. Color measuring instrument manufacturers can also help with establishing color controls with the purchase of hardware and software.
Finally, it is important that standards, measuring requirements, and established tolerances are communicated and understood throughout your supply chain for any color control program to be successful. A good color control program will help make the regulatory approval process easier and less time-consuming for all involved.
Sterilization Techniques’ Effect on Color
An issue to be aware of during medical device development is the effect sterilization may have on the color of plastic components. The most commonly used sterilization techniques are autoclave, ethylene oxide gas (EtO), and radiation sterilization by either gamma or E-beam radiation. Each sterilization technique has an effect on plastic materials that may adversely affect the color and physical properties. It is recommended to check color in the finished assembled state before and after sterilization to determine the visual and physical effects.
Autoclave – Typical reactions to autoclave may include hydrolysis, warp, and part distortion/deformation; however, color is usually not affected.
EtO is often used for heat-sensitive polymers and usually does not cause significant color change.
Gamma and E-Beam radiation sterilization can cause cross-linking of polymers, chain scission and yellowing of colors. Although not the subject of this technical brief, there are techniques that knowledgeable color suppliers use to stabilize colors against radiation.
Increased regulatory scrutiny placed on colored plastics from Europe, Japan, the United States, and other countries to pass biologic testing makes material and color selection a critical skill when developing new medical devices. Selecting a color compounder with a long history of success in the medical device market is critical as they will have important services such as ISO 10993 resin and pigment selections, resin and color advice based on experience, formulation control, and change management services.
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