In the paint and coating industry, it is important to determine various properties of paints that attribute to life and its quality. There are many different qualities of paints that are needed for better performance of the product. These properties include adhesion, crack resistance, etc. To determine the exact value of these properties, there are different tests that are carried out on paint samples to ensure best quality of end products.
Scrape Adhesion test
This test is used to measure the adhesive strength of any organic coating when it is applied to a smooth and flat surface. The material which is tested is applied with uniform coating so that the force applied is distributed uniformly all over the surface for accurate measurements. Once the adhesive coating is applied completely, the coating is pressed with a round stylus. The stylus is loaded with weights that are changed continuously unless the coating is removed from the surface. This determines the maximum load under which the coating can stay on a particular substrate surface.
The pull-off test is used for determining the minimum required tensile stress that is required to detach a coating from a substrate surface. In this test, tensile stress is maximized hence the results obtained from this test are not comparable with the results from other tests. In this test, the load is placed in the perpendicular direction from the coating surface and the force is applied and is increased gradually until a visible piece of coating is removed from the surface.
Cross hatch method
The cross hatch method is used for determining the resistive strength of paints to separate from the applied surface. In this test method, a cross hatch tester is used to cut a right angle pattern which penetrates the coating all the way to the surface.
This method is used to perform a quick pass/fail test. There are two different ways of performing the test according to the specifications set by ASTM.
In this method, an X-cut is made on the substrate with the help of a carbide tool. The tape is smoothened and then is removed by pulling it off over itself to an angle of 1800. The adhesion is rated between 0 and 5.
In this method, a cross hatch is made on the coating and then a pressure sensitive tape is placed over the area where the cross hatch is made. The tape is then removed slowly to an angle of 1800. The adhesive strength of this test is also measured on a scale of 0 to five.
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