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D6290-19 – Standard Test Method Technical Guide
🎯 Scope and Significance of D6290-19
This standard, designated D6290-19, outlines a standardized test method for the instrumental measurement of color attributes in plastic pellets. Specifically, it is intended for the color analysis of homogeneous, nonfluorescent, nearly-colorless transparent or nearly-white translucent or opaque plastics. The method is based on tristimulus values obtained from a spectrophotometer or colorimeter under daylight illumination.
⚠️ Critical Developer Note: Before proceeding with this test method, always refer to the specific material specification being tested. Any test specimen preparation, conditioning, dimensions, or testing parameters covered in the material specification shall take precedence over the default conditions mentioned in this test method.
The scope explicitly covers the determination of several key color measurements, including Yellowness Index (YI), CIE X, Y, Z tristimulus values, and opponent color coordinates such as Hunter L, a, b and CIE L*, a*, b*. Values are stated in SI units.
⚙️ Instrumentation and Measurement Procedure
The measurement relies on instruments capable of providing tristimulus values. The standard references specific ASTM practices for determining the geometric conditions and calculation methods. The type of instrument and geometry selected (e.g., hemispherical per E1331 or bidirectional per E1349) must be consistent with the material being measured.
Notably, the standard provides a warning regarding materials like polyamide (nylon), where the cooling rate during pellet production can vary significantly. This variation can lead to differences in the test results, highlighting the importance of consistent specimen preparation and conditioning.
| 📏 Referenced Standard | ⚡ Role in Color Determination |
|---|---|
| ASTM E313 | Primary standard for calculating Yellowness Index (YI) from instrumentally measured color coordinates. |
| ASTM D2244 | Standard practice for calculating color tolerances and color differences (e.g., ΔE*ab, ΔE*Hunter). |
| ASTM E308 | Standard practice for computing the colors of objects using the CIE system. |
| CIE D 001 | Specifies the colorimetric illuminants and standard observers for calculation. |
📊 Key Measured Properties and Coordinates
The method generates a standard set of colorimetric data used for quality control and specification verification. These coordinates allow manufacturers to quantify the “yellowness” or whiteness of their pelletized material objectively. The specific calculations are governed by the referenced standards (E308, E313, D2244).
| 🎯 Color Attribute | 📐 Description & Application |
|---|---|
| Yellowness Index (YI) | Quantifies the degree of yellowness under daylight illumination. A primary metric for this standard. |
| CIE X, Y, Z | Fundamental tristimulus values representing the color stimulus of the sample. |
| CIE L*, a*, b* | Opponent color space coordinates for describing lightness and color-opponent dimensions. |
| Hunter L, a, b | An earlier uniform color scale still widely used for specific plastic applications. |
💡 Technical Note on Correlation: This standard (D6290-19) and ISO 17223 address the same subject matter—the determination of yellowness—but they differ in technical content. Laboratories operating under both frameworks should perform a thorough cross-validation.
❓ Frequently Asked Questions
🔍 What types of plastic pellets are eligible for testing under D6290-19?
The standard applies to homogeneous, nonfluorescent, nearly-colorless transparent or nearly-white translucent or opaque plastics. Each material will have unique characteristics that determine its specific color values.
💡 How does this standard relate to ISO 17223?
As noted in the standard (Note 1), D6290-19 and ISO 17223 address the same subject matter—yellowness determination. However, they differ in specific technical content and methodology. Users must be aware of these differences when applying results internationally.
⚡ Which instruments are required by this test method?
The measurement requires a spectrophotometer or a colorimeter capable of producing tristimulus values (CIE X, Y, Z). The selection of geometric conditions (e.g., hemispherical or bidirectional) must follow ASTM E179, E1331, or E1347/E1349 as appropriate.
📌 Why is the cooling process of pellets mentioned in the standard?
The standard specifically cites polyamide (nylon) as an example where variation in the cooling rate during pellet production can significantly affect the color measurement results. Specifiers and testers must control this process to ensure reproducible outcomes.