Лако-красочные материалы — производство

The universally accepted method for testing adhesion under shear is a static load test [21], where a known surface area of the adhesive-coated product is applied under controlled

conditions to a standard test surface, usually stainless steel or a standard cardboard, or even the product’s own backing. Then this is secured vertically, plus a 2°tilt-back, to prevent any possible low-angle peel. A fixed load is then applied (Fig. 7a), and the time taken for failure is recorded or any slip that occurs in a given time measured. A trip mechanism can be set up so that the falling weight stops a stopclock to denote the failure time. This test can be carried out at elevated temperature; variations of the basic concept exist, such as mounting the test surface horizontally [22] with a small radius of curvature at the edge of the test panel to redirect the tail of the tape under test to the vertical, in order to hang a suitable load (Fig. 7b). A further variation, used in the electrical industry to measure adhesive thermoset characteristics, is a high temperature shear test [23], where a controlled area overlap bond is formed, usually 0.5in. (12mm) by 0.5in. (12mm), either face to face, or face to backing. The adhesive is then given a thermoset cycle, followed by a high temperature shear test (Fig. 7c).

While a static load test is the commonly accepted procedure, in practice many variations in areas and weights are used, to compensate for the various qualities of adhe­sive evaluated, so that the test results will fall into a similar time frame, so it becomes difficult to compare different adhesive systems from accumulated data. It has the disad­vantage of giving variable results for the same adhesive system, and is essentially a pass/ fail test, as many products remain in place at the end of the test period. Experience has shown that the shear properties of pressure-sensitive adhesives to porous and nonporous substrates can be quite different, and each must be judged on its own merits.