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D5895-20 – Standard Test Method Technical Guide
📐 Test Methods and Apparatus
These test methods describe the determination of several stages and the rate of dry-film formation of organic coatings using straight-line and circular mechanical drying-time recording devices. The mechanical recorders are valuable in comparing the drying behavior of coatings of the same generic type, allowing that one coating may form a gel or resist tearing at a faster rate than another. The values stated in SI are to be regarded as the standard, with values in parentheses for information only.
| 📋 Stage | 🕒 Definition | 🔬 Mechanical Recorder Indication |
|---|---|---|
| Set-to-touch time | The film has solidified sufficiently that it no longer flows nor sticks to a finger that lightly touches it. | Pear-shaped depression appears when the film stops flowing over the stylus path, revealing the glass substrate. |
| Dry-hard time | The film is not displaced nor is any noticeable mark left by pinching between thumb and forefinger with a relatively strong force. | The stylus has risen out of the film and rides on the surface, leaving only a mark without disrupting the body of the film. |
| Dry-through time | The film has solidified so completely that a large, twisting force can be applied without distorting the film. | The stylus no longer leaves any visible mark on the film. |
💡 Technical Note: The dry-hard condition is reached when the stylus has risen out of the film and rides on the surface, leaving only a mark without disrupting the body of the film. This is distinct from dry-through, where no visible mark is left.
⚙️ Procedure and Evaluation
The test methods involve using straight-line or circular mechanical drying-time recorders. The coating is applied to test panels, and the recorder stylus moves across the film as it dries. The resulting trace provides a continuous record of film formation. Drying time measured using mechanical recorders may differ from those found using conventional methods such as Test Method D1640 or ISO 9117-3. It is important to use controlled environments as specified in D3924 to ensure consistent results. The following standards are referenced for complementary procedures:
| 📜 Standard | 📖 Description |
|---|---|
| D823 | Practices for Producing Films of Uniform Thickness of Paint, Coatings and Related Products on Test Panels |
| D1005 | Test Method for Measurement of Dry-Film Thickness of Organic Coatings Using Micrometers |
| D1640 | Test Methods for Drying, Curing, or Film Formation of Organic Coatings |
| D3924 | Specification for Standard Environment for Conditioning and Testing Paint, Varnish, Lacquer, and Related Materials |
| D3925 | Practice for Sampling Liquid Paints and Related Pigmented Coatings |
| ISO 9117-3 | Drying tests—Surface-drying test using ballotini |
⚠️ Caution: The drying times recorded using mechanical methods may not directly correlate with conventional methods due to continuous mechanical action. Always compare results within the same test method.
📊 Key Measured Properties
The primary properties measured are the set-to-touch, dry-hard, and dry-through times. These stages are critical for understanding the film formation process and ensuring proper coating application. The set-to-touch time is indicated by a pear-shaped depression in the film when it stops flowing. Dry-hard time is marked by the stylus riding on the surface without disrupting the film body. Dry-through time is when the stylus leaves no visible mark, indicating complete solidification. The values stated in SI are to be regarded as the standard.
This standard does not purport to address all safety concerns. It is the responsibility of the user to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.