New Tool for Measuring Adhesion of Coatings to Wood

During the past few years, many tests have been developed for measuring the adhesion of surface coatings to various metallic and non-metallic surfaces. In reviewing these tests, it was found that they were not readily adaptable to measuring the adhesion of paints to modified wood products. The tests were either too subjective or too complicated to run efficiently and effectively. The purpose of this paper is to show how a simple test was mechanized and converted into a very effective tool for measuring and recording the adhesion of paints to modified wood products. The first problem was the selection of the tape possessing the desired adhesion sensitivity and tensile strength. The tape that most nearly met the requirements was 3/4-inch Scotch brand pressure sensitive cellophane tape number 600. After the tape was selected, it was necessary to design a machine that would not only mechanically simulate the lifting hand motion in removing the paint, but also measure and record the energy required to remove the paint. Several machines were investigated and an impact type was selected. The machine operates on the principle of a falling pendulum which possesses 2 foot-pounds of potential energy at its upper-most position. As the pendulum falls to the bottom of its swing, it engages the tape and removes it. The energy absorbed is recorded on the back swing of the pendulum. Accessory jigs and fixtures were selected to make the testing procedure as mechanical as possible. These include 1) a jig to locate an exact length of tape on the sample 2) a hand-operated hydraulic tool to apply pressure to the tape, and 3) a positioning fixture for the sample. Detailed analysis of the performance characteristics in evaluating various undercoats on hardboard shows this device to be accurate and simple to operate.

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