Appliance Design - August 2008 - (Page 16)

PLASTICS and turned into pellet form. The pellets will contain the resins, pigments, dyes, and additives all within the resin pellet. Resin pellets are more expensive, have slightly longer lead times and are not as desirable for short runs because if using different colors, the machine needs to be shut down and completely cleaned prior to introducing a new color. However, they are easier to use, deliver better color consistency, and do not require mixing or metering equipment. Whatever method of dispersion is chosen, a proper mix is essential. Colorants can be made from organic or inorganic pigments, and dyes. Typically, color formulas contain four colorants, says Sabreen. Two of which are white and black to control value (lightness and darkness) and chroma (color intensity). Two pigments and dyes establish hue. The pigments themselves can be made from different particle sizes and orientations, which can change a product’s appearance and functionality. The color mixtures can be “tuned” through the use of particle sizes to produce the needed luster and opacity. In general, smaller particles provide opacity while larger particles provide luster, says Sabreen. Small flakes, about 5 microns in size, can give pearlescent pigments a satiny appearance with good opacity. Larger flakes of around 25 microns can give a more lustrous effect. By blending the particle sizes, the appropriate mix of luster and opacity can be achieved. To add luster to the base color, transparent dyes can be added. Adjusting the size of particles in pigments can also affect light scattering, which in turn The Pensonic blender is made from several different polymers and comes in a range of colors. Clariant Masterbatches supplied the company with a series of “combibatches.” can affect a color’s shading, he says. Finer particles shift red pigments toward blue, while bigger, coarser particles move it toward yellower shades. Colorants can also be used to reduce secondary operations. Metallic pigments, for example, due to their conductive properties, can provide the additional benefit of EMI shielding, eliminating the need for applying conductive materials in a post fabrication operation. Clariant Masterbatches chip cube is part of the company's ColorForward program that helps designers identify coming color trends. Metallic pigments with a larger particle size and a lower loading (concentration) can reduce the visibility of flow and weld lines compared to smaller-sized particles, and resins with a lower viscosity can cause the least particle orientation resulting in fewer flow lines, says John Skabardonis, polycarbonates marketing manager, North America, for Pittsburgh-based Bayer MaterialScience LLC. The thermal conductivity properties of metallic pigments also allows them to help with thermal management issues, which may impact part design. While pigments and additives can add color and functionality to a plastic part, they must be used appropriately for the material. For instance, of the newer special effects pigments to hit the market in recent years, not all of them can be used with all plastics; some fluorescent dyes cannot be used in plastics such as polyethylene and polypropylene, but they will work in transparent plastics such as acrylics, polycarbonate, and polyester. Some grades of titanium dioxide white pigment can promote the breakdown of polymer chains in polycarbonate, reducing its impact strength. Special effects pigments and dyes have been known to lower a plastics’ impact resistance. According to Skabardonis, special effects additives can act like stress concentrators in plas- 16 applianceDESIGN August 2008 www.applianceDESIGN.com http://www.appliancedesign.com

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Appliance Design - August 2008 Contents Editorial Shipments/Forecasts News Watch Plastics Switches Noise & Vibration Control Joining New Products Design Marts Association Report: CEA Advertiser’s Index

Appliance Design - August 2008

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