Significance and Use
Before proceeding with this test method, reference should be made to the specification of the material being tested. Any test specimen preparation, conditioning, dimensions, or testing parameters, or a combination thereof, covered in the materials specification shall take precedence over those mentioned in this test method. If there are no material specifications, then default conditions apply.
Note 2—Some materials, such as polyamide (nylon), can be cooled very differently during the production of the pellets. This variation in the cooling of the pellets can result in different levels of crystallinity in the pellets only. More crystalline nylons will be more opaque than amorphous nylons. This will result in differences in pellet opacity. The pellet shape is independent of the crystallinity of the material. This variation in pellet appearance, due to varying levels of crystallinity, does not affect final properties.
Note 3—This test method should not be used for general material specifications.
This test method describes a technique useful for making color comparisons of resins in pellet form that is fast and convenient as it does not require preparation, such as molding or extruding specimens. The test method shall be used only to compare specimens of similar pellet shape, size, texture, and degree of translucency. For example, translucent disc-shaped pellets should be compared to translucent disc-shaped pellets, not with opaque, rectangular shaped pellets.
Exact measurements of resin pellet color may not be directly related to the color of the final cast, molded or extruded product due to the multitude of variables, such as producing variables, methods, and pellet shape and size. Color measurements can be useful for comparing resins in pellet form when all samples are similar in shape and size.
A three-number tristimulus system is necessary to quantify color completely and precisely. The general method used in this procedure measures color using the CIE Systems described in Practice E308, Test Method D2244, the CIE 1976 (X, Y, Z) system, and, the CIELAB 1976 color space.
Individual components of the tristimulus measurement such as CIE Y (Luminance), Hunter L, a, b, or CIE L*, a*, b* values or other useful metrics like yellowness index can be used to describe color attributes of materials. This test method describes a standard procedure on how these measurements are made.
1.1 This test method is intended primarily for the instrumental measurement of the degree of yellowness (or change of degree of yellowness) under daylight illumination of homogeneous, nonfluorescent, nearly-colorless transparent or nearly-white translucent or opaque plastics. The measurement is made on pellets and based on tristimulus values obtained with a spectrophotometer or colorimeter.
1.2 This test method is applicable to the color analysis of plastic pellets. Each material may have unique characteristics that determine the color values.
1.3 This procedure outlines a method to determine color measurements, such as Yellowness Index, CIE X, Y, Z, and Hunter L, a, b, or CIE L*, a*, b*.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
Note 1—There is no equivalent ISO Standard.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
D883 Terminology Relating to Plastics
D2244 Practice for Calculation of Color Tolerances and Color Differences from Instrumentally Measured Color Coordinates
E179 Guide for Selection of Geometric Conditions for Measurement of Reflection and Transmission Properties of Materials
E284 Terminology of Appearance
E308 Practice for Computing the Colors of Objects by Using the CIE System
E313 Practice for Calculating Yellowness and Whiteness Indices from Instrumentally Measured Color Coordinates
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
E1331 Test Method for Reflectance Factor and Color by Spectrophotometry Using Hemispherical Geometry
E1347 Test Method for Color and Color-Difference Measurement by Tristimulus Colorimetry
E1349 Test Method for Reflectance Factor and Color by Spectrophotometry Using Bidirectional (45:0 or 0:45) Geometry
color; pellets; plastics; yellowness; yellowness index; Color--plastics; Daylight; Instrumental measurement--plastics; Pellets; Yellowness index ;
ICS Number Code 17.180.20 (Colours and measurement of light); 83.080.01 (Plastics in general)
ASTM International is a member of CrossRef.
Citing ASTM Standards
[Back to Top]