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D2793-99 – Standard Test Method Technical Guide
📐 Scope and Significance
This test method covers the determination of block resistance of organic coatings on wood and wood-based panel substrates. Block resistance is defined as the ability of a coating to resist sticking to another surface and to resist any change in appearance when pressed against that surface for a prolonged period of time. Coated wood panel products must be stackable face to face or face to back during warehousing, packaging, and transportation without the finish sticking or becoming damaged. This test method describes a laboratory means of evaluating blocking using factors of pressure, heat, time, and moisture. It can also evaluate degrees of hardness, cure, volatile loss, and the effectiveness of protective packaging materials. The values are stated in SI units, with parentheses for information.
⚙️ Test Procedure and Conditions
This test method requires coatings to be applied to the specified wood substrate under conditions duplicating production application and curing as nearly as possible. A stack of coated panels is formed and subjected to a specified pressure and temperature for a sufficient time to develop sticking tendencies. The pressure is released, and the surfaces are examined for signs of sticking or pressure mottling. If blocking occurs, the material is unsatisfactory. The method can be tailored using guidelines in paragraphs 7.3 and 7.4, and rating methodology is provided in paragraph 7.5. For print resistance of lacquers on furniture, Test Method D2091 should be used. The test may be accelerated with more severe conditions than production finishing.
| 🟦 Factor | 📏 Role in Test |
|---|---|
| Pressure | Simulate stacking load during storage |
| Temperature | Accelerate sticking tendencies |
| Time | Prolonged contact duration |
| Moisture | Environmental effects on coating |
📊 Evaluation and Rating Methodology
After the test, panels are examined for blocking or damage. If no sticking or damage occurs, the coating is satisfactory. If blocking is present, it is unsatisfactory. Rating methodology is provided in paragraph 7.5 to quantify results. The standard emphasizes that degrees of hardness or cure can be evaluated using this blocking test, and the rate of volatile loss can also be assessed.
| 🎯 Result | ⚡ Interpretation |
|---|---|
| No sticking or damage to film | Satisfactory – coating passes under test conditions |
| Blocking (panels stick together) | Unsatisfactory – coating fails |
| Pressure mottling or surface change | Indicates surface damage or sticking tendency |
Tip: Ensure that film thickness, substrate, and cure conditions closely duplicate production finishing for accurate representation of block resistance.
Warning: Variations in user materials and procedures may require adjustments to the general method; refer to paragraphs 7.3 and 7.4 for guidance on tailoring the test.
❓ Frequently Asked Questions
🔍 What is block resistance? Block resistance is the ability of a coating to resist sticking to another surface and resist appearance changes under prolonged pressure, critical for stacking coated panels.
💡 How is the test performed? Coated panels are stacked and subjected to specified pressure and temperature for a sufficient time, then examined for sticking or damage.
⚡ What factors influence blocking? Key factors include pressure, heat, time, and moisture, which simulate real-life warehousing and transportation conditions.
📌 What is the alternative method for print resistance? Test Method D2091 should be used for print resistance or pressure mottling of lacquers on wood-based case goods like furniture.