Лако-красочные материалы — производство

Peter Walker

Atomic Weapons Establishment Pic, Aldermaston, Berkshire, England

I. INTRODUCTION

It is axiomatic that the paramount property of an adhesive is adhesion to the substrate, but adhesion is also critical in the performance of surface coatings, which must adhere to protect and in obtaining optimum mechanical properties in particulate — and fiber — filled composites. Many surface preparation techniques have been employed to achieve high initial adhesion; these range from removal of surface contamination (solvent and vapor degreasing) to changes in substrate profile (grit blasting) to chemical modi­fication (phosphating of steel, anodic treatments of aluminum). None of these methods solve the most critical problem in adhesion technology: that of the damaging effect of water on organic/inorganic bonds. Hydrolytic stability is essential in many tech­nologies.

It has been shown by Walker that many types of organic coating lose up to 85% of their initial adhesion under water-soaked conditions [1], that adhesives show a marked loss of bond strength in water [2,3], and that glass-fiber-reinforced composites are readily degraded [4]. To improve the initial bond strength between adhesives and substrate, adhesion promoters may be used. These function by improving substrate wetting or by secondary bonding by van der Waals forces, dipole-dipole interactions, hydrogen bonding or acid-base reactions. Relatively weak forces in the range 5-8kca1/mol are involved. If hydrolytic stability of the bond is to be achieved, use of a coupling agent that is capable of forming primary chemical bonds, 50-250 kcal/mol [5], is required. The important distinction here is that in the nature of the bond formed, only coupling agents form primary bonds and can therefore be expected to produce water-resistant bonding. A coupling agent is therefore defined as a compound capable of chemical reaction with both the polymer and the substrate, although there is some evidence that reaction with the polymer is not necessarily a prerequisite. It should be noted that a coupling agent can function as an adhesion promoter; the reverse is not true. Current views are that only a limited range of organometallic compounds are true coupling agents.