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D1146-00 – Standard Test Method Technical Guide
ASTM D1146-00 (Reapproved 2018) is a standard test method for determining the blocking point of thermoplastic or hygroscopic layers or coatings of potentially adhesive material. This method simulates moderate pressures and environmental exposures typical of storage conditions to assess the propensity for unwanted adhesion between surfaces.
📖 Scope and Significance of Blocking Tests
This test method applies to materials that exist in a substantially non-adhesive state and are activated by heat or solvents, as defined in Section 1.1. Because many of these materials are both thermoplastic and hygroscopic, the standard provides a unified framework for evaluating both blocking mechanisms simultaneously.
The standard formally defines blocking as the adhesion between touching layers of similar or dissimilar materials occurring under moderate pressure during storage or use (Section 3.2.2). The testing methodology specifically covers two distinct types of blocking: Cohesive Blocking, which involves two similar potentially adhesive faces, and Adhesive Blocking, which involves a potentially adhesive face and a standard test paper (Sections 3.2.1, 3.2.3).
🧪 Apparatus and Environmental Control
Per Section 5 of the standard, the required apparatus includes a constant-temperature oven and specialized humidity chambers. The oven must maintain precise temperature control, and desiccators of a specific minimum size are required to function as controlled humidity environments.
| 🛠️ Apparatus | 📏 Specification | 🎯 Tolerance / Limit |
|---|---|---|
| Constant-Temperature Oven | Up to 85 °C (185 °F) | ± 1 °C (± 2 °F) |
| Desiccators (Humidity Chambers) | Minimum Diameter | 150 mm (6 in) |
💡 Technical Note: The method defines Critical Temperature (Section 3.2.5) and Critical Humidity (Section 3.2.4) as the lowest values at which a specified degree of blocking occurs. Establishing the correct “degree” of blocking is essential for a valid interpretation of these critical thresholds.
📊 Grading and Classification of Blocking
To accommodate varying performance requirements, the standard defines two specific degrees of blocking severity. These definitions allow manufacturers and purchasers to communicate pass/fail criteria precisely.
| 📐 Block Degree | 📄 Definition | ⚡ Parting Characteristic |
|---|---|---|
| First Degree | Lower specimen clings to upper specimen when lifted. | Parts with no evidence of damage to either surface. |
| Second Degree | Strong adherence requiring forced separation. | One surface or the other is damaged upon parting. |
As noted in Section 4.1, the significance of this test lies in its ability to estimate both thermoplastic and hygroscopic blocking on the same material. The standard also permits the designation of other degrees of blocking as mutually agreed upon between the involved parties (Note 1, Section 3.2.7). Many fundamental terms used here are formally established in Terminology D907 (Section 3.1).
📌 Note on Variability: The results of this test are highly dependent on the precise environmental conditions within the oven and desiccators. Per Section 1.3, the user of this standard is responsible for establishing appropriate safety and health practices.
❓ Frequently Asked Questions
🔍 What is the difference between First and Second Degree blocking?
First Degree Blocking occurs when surfaces cling together upon lifting but can be separated with absolutely no evidence of damage to either surface. Second Degree Blocking occurs when the surfaces are damaged during the separation process (Source: Sections 3.2.6, 3.2.7).
💡 How does Cohesive Blocking differ from Adhesive Blocking?
Cohesive Blocking evaluates the adhesion between two similar potentially adhesive faces. Adhesive Blocking evaluates the adhesion between a potentially adhesive face and a standard test paper (Source: Sections 3.2.3, 3.2.1).
⚡ What are the required temperature tolerances for the test oven?
The constant-temperature oven must be capable of maintaining temperatures up to 85 °C with a tolerance of exactly ± 1 °C (or ± 2 °F) as specified in Section 5.1.
📌 What types of materials are covered by this standard?
This test method covers the determination of the blocking point of a thermoplastic or a hygroscopic layer or coating of potentially adhesive material. These materials exist in a substantially non-adhesive state and may be activated by the application of heat or solvents (Source: Section 1.1).