In the automotive industry, the adhesion (blocking) tendency test checks whether two coated or plastic surfaces will stick together when pressed together, especially under heat, pressure, and time. If the parts stick together and then tear, leave marks, or deform when they separate, this is adhesion and is bad news in terms of quality.
Practically,
If they unintentionally stick together, that's adhesion. Car manufacturers take care to prevent this from happening.
Adhesion testing can lead to the following:
That's why original equipment manufacturers want to test this early on to avoid surprises later. While the details vary according to standards, the general process for these tests is as follows:
Adhesion tests are commonly used, primarily for the following:
Test results may include the following:
Original equipment manufacturer standards (BMW, VW, Daimler, Renault) typically define precise temperatures, loads, and acceptance limits.
In short, the automotive industry, particularly in paint and coating applications, refers to a phenomenon called block resistance (ASTM D4946). This is the tendency of newly painted surfaces, such as car body panels, to not adhere to each other when stacked or pressed together after the painting and drying process. The vast majority of references to adhesion tendency testing in the automotive context, since the increasing biodiesel mandates, point to fuel filter block resistance testing.
In the context of paints, coatings, or adhesives, adhesion testing refers to evaluating how well a dried or semi-cured paint film or coating tends to adhere (or block) to itself or another surface when pressed together under specific conditions such as heat, pressure, time, and humidity.
This is a crucial quality control parameter in automotive coatings. Here, parts (e.g., painted panels, trim, or components) may be stacked, nested, or in contact shortly after painting and curing during manufacturing, transportation, or assembly. Poor adhesion can lead to defects such as scratches, gloss changes, marks (printing), or film damage on the surface when separating parts.
The most common testing method is the “ASTM D4946 Standard Test Method for Blocking Resistance of Architectural Paints” developed by the American Society for Testing and Materials (ASTM). This method is also widely applied to industrial and automotive coatings, including water-based and solvent-based systems.
During testing, paint or coating is applied to the panels and allowed to dry/cure for a specific period (e.g., overnight or accelerated). The coated surfaces are cut into squares and placed face-to-face. They are pressed together under controlled conditions: typically high temperature (e.g., 50 degrees), a specific weight/pressure (e.g., approximately 1-2 psi via weight on a stopper), and a holding time (e.g., 30 minutes to hours). After cooling and equilibration, the panels are separated. Resistance is rated subjectively on a scale: 0 means complete adhesion (severe adhesion and damage), 10 means no adhesion (perfect separation, no trace). Factors affecting the results include coating hardness, glass transition temperature, binders, additives, moisture, pressure, and curing time.
Automotive original equipment manufacturer (OEM) specifications typically adapt the ASTM D4946 standard with stricter conditions (e.g., higher temperature and pressure to simulate stacking painted bumpers or doors).
Adhesion tendency tests are considered important in the automotive industry for the following reasons:
For many years, our organization, with its competent and experienced team, has been understanding the needs of its clients, providing the advanced testing services they require, and assisting in the establishment, implementation, and improvement of management systems. Within this framework, we also provide adhesion tendency testing services to businesses.
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