Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D2620-87 – Standard Test Method Technical Guide
📐 Specimen Preparation and Requirements
Test specimens are prepared on panels approximately 3 by 5 in. (75 by 125 mm) using white carrara glass or other specified substrates such as white ceramic tile or a white pigmented, light-stable coating. The clear coating is applied to a dry film thickness of 2 ± 0.2 mil (50 ± 5 µm). A reference specimen with known performance is included for comparison. Panel preparation details, including coating method, baking conditions, and film thickness, are recorded per agreement between purchaser and seller.
| 🟦 Parameter | 📏 Specification | 🎯 Tolerance |
|---|---|---|
| Panel Dimensions | 3 by 5 in. (75 by 125 mm) | Standard size |
| Film Thickness | 2 mil (50 µm) | ± 0.2 mil (5 µm) |
| Conditioning (Baked) | 73.5°F (23°C), 50% RH | ± 3.5°F (2°C), ± 5% RH for 48 h |
| Conditioning (Air Dried) | 73.5°F (23°C), 50% RH | ± 3.5°F (2°C), ± 5% RH for 7 days |
⚙️ Test Procedure and Exposure
Prior to exposure, one-half of each test panel is masked with aluminum foil to exclude sunlight from the coating. The tape used to attach the mask should not extend over the edge of the mask but should extend beyond the ends and stick to the rear of the panel. The panels are then placed in an exposure cabinet as described in Practice G 24 and exposed to natural sunlight filtered through glass for a specified time to evaluate light stability.
💡 Tip: Proper masking is crucial; ensure the tape holds the mask from the back to prevent sunlight from reaching the masked area, which could compromise the reference portion.
📊 Key Measured Properties and Evaluation
The primary property evaluated is discoloration, particularly yellowing, which is assessed by comparing the exposed and unexposed portions of the panel. Visual evaluation is conducted according to Practice D 1729 for color differences, or yellowness index can be measured using Test Method D 1925. This test method permits evaluation of the effect of natural indoor light on the color stability of clear coatings, addressing user concerns about noticeable color change.
| 📐 Property | 🎯 Evaluation Method | ⚡ Reference Standard |
|---|---|---|
| Color Discoloration | Visual Comparison | D 1729 |
| Yellowness Index | Instrumental Measurement | D 1925 |
❓ Frequently Asked Questions
🔍 Why is masking of the panel required?
Masking with aluminum foil creates an unexposed reference area on the same panel, allowing direct comparison of color change caused by sunlight exposure.
💡 What substrates are recommended for testing?
Recommended substrates include white carrara glass, white ceramic tile, or a white pigmented, light-stable coating, as specified in the standard.
⚡ How is discoloration evaluated in this test?
Discoloration is evaluated visually according to Practice D 1729 or by measuring yellowness index per Test Method D 1925, comparing exposed and unexposed areas.
📌 What are the conditioning requirements for test specimens?
Condition at 73.5 ± 3.5°F (23 ± 2°C) and 50 ± 5% relative humidity for 48 h if baked, or 7 days if air dried, unless otherwise specified.