Coating adhesion test

Fig. 2. Coating adhesion testing by MTS machine coated samples were loaded as shown in the...

Adhesion tests may be divided into the methods by which stress is applied to the lilm/coating. Adhesion test methods include tensile tests, peel tests, shear tests, deformation tests, energy deposition tests, fatigue (thermal, mechanical) tests, and many others. Some of these tests are depicted in Figure 12.3. Adhesion testing of thin films on flexible substrates such as webs is a particularly difficult problem.f ... 

Other important properties that can be measured in the laboratory include sealabiHty, printabiHty, or coating adhesion. Many of these tests have been developed by the film manufacturer in cooperation with customers and are specifically designed to measure product performance in the end use. Some tests, like sealabiHty, can be standardi2ed to time, pressure, and temperature of sealing with instmment-measured peel values, but other tests are subjective, such as evaluations of printing loss to puUoff by adhesive tape. 

Testing of Painted Products. The enhancement of paint adhesion is one of the principal functions of conversion coating (20—22). A group of tests based on product deformation is used to test the painted product. The appHance and cod-coating industries use the mandrel bend, the cross-hatch adhesion test, and the direct and reverse impact tests. Adhesion after a water soak is judged using a cross-hatch test performed on the exposed surface. 

The practical result of epitaxy is a very high degree of adhesion between coating and substrate. The force needed to separate the interface is similar to that needed to break the metals on either side. Where a true metallic bond forms at an epitaxial interface it is only possible to measure adhesion if the bond is the weakest of the three near the interface. An adhesion test based on breaking the joint indicates only which of the three is weakest. For practical purposes any epitaxial joint will have a strength more than adequate for service conditions. 

There is a seemingly infinite variety of tests for specific applications, and some even have alternate adaptations for particular industries or customers. This section contains a few examples of common application tests for urethane foams, coatings, adhesives, and elastomers that may be conducted in addition to those described above. Some of these are just specialized versions of tests discussed in die previous section but are presented here because they have been developed for specific applications. Others are more broadly useful and very common. 

The Institute for Research and Technical Assistance (IRTA) identifies, develops, tests and demonstrates safer alternatives in cleaning applications, dry cleaning, paint stripping, coatings, adhesives and lubricants. 

There are some standard adhesion tests used by the paint and coatings industry, which we have adopted for our work. The most common is the Scotch tape test, which is described by an ASTM D3359, method B. 

Test Procedures. Coatings were tested by the following procedures. For crosshatch adhesion, ASTM-D3359, a special scribe was employed which had 11 sharp points spaced approximately 1 mm apart. The film was scored twice with this tool so that scratches were perpendicular. Special tape was then placed firmly over the scored area and pulled off. The number of squares of film coating remaining were counted, and this provided a numerical basis for measuring surface adhesion. No squares are removed for a satisfactory coating. 

For the balanced beam-scrape adhesion test, ASTM-2197, weights were added to a commercial balanced beam tester. The kind of scratch produced by the stylus with the different loadings was recorded and served as a measure of film hardness. Coatings which are not scratched to bare metal by 500 g are desirable. 

Epoxy acrylate (Ebecryl 3700, 50%) combined with 25% TMPTA, 25% I BOA and with DIBF-OPPI-DIDMA pigment and FC-171 as above was also used to coat panels. These panels showed no removal of coating in the cross hatch adhesion test. With 6.8j there was no loosened coating on the frontal impact surface, and only 30% was loosened on the back surface. Five hundred grams were required to scratch to bare metal with the balanced beam. Performance was... 

An important factor of film quality concerns its adhesion to the substrate, namely to the magnesium chip. Figure 4.12 shows images of different coated chips after a standard adhesion test. The upper images show the magnesium-coated chips after the tape was peeled off, while the lower images show the tapes. 

Figure 4.12 Optical images of coated magnesium chips and their corresponding tapes after an adhesion test (A) PTMOS film (B) ZrTPO film (C) combined film. The images of the tapes are somewhat misleading as the coloured area of the combined film is the largest, which is due to its high content of Rhodamine B. (Reproduced from ref. 13, with permission.)...

Paint(s), 28-54-76. See also Coatings adhesion properties of, 28 73 analysis and testing of, 28 68-73 application and appearance properties of, 2860-63... 

Adhesion test is used to evaluate the adhesion of a paint system to the substrate and between coats (layers). The test can be performed by one or a combination of three methods ... 

On zinc phosphate conversion coatings, the "Mannich" derivatives of poly-4-vinylphenol have demonstrated performance equivalent to chromic chromate systems in salt spray, humidity, and physical testing. In addition. Table III illustrates results observed with automotive body paint systems evaluated by the "scab" or "cycle" test which causes failure more typical of actual end use conditions than do salt spray evaluations. Again, results equivalent to chromic-chromate post-treatments were obtained. In addition, the humidity resistance and adhesion tests were essentially equivalent to the chromium controls. 

Adhesion tests can be broken into two categories qualitative and quantitative. They vary from a simple Scotch tape test to a complicated flyer tape test, which requires precision-machined specimens and a very expensive testing facility. Quantitative (such as peeling) tests have been developed for coatings on plastics (12), but not to the same extent for metal-to-metal systems. The quantitative testing systems in limited use, mainly in the electronics industry, are not commonly present in production plants but have been used to aid in process development. For quality control purposes, qualitative tests for metal-to-metal adhesion (13) are usually adequate. The adhesion of some plated metal parts is improved with baking for 1 to 4 h at relatively low (120 to 320°C) temperatures. 

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