Лако-красочные материалы — производство

J. Schultz and M. Nardin

Centre de Recherches sur la Physico-Chimie des Surfaces Solides, CNRS, Mulhouse, France

There are agents in nature able to make the particles of joints stick together by very strong attraction and it is the business of experimental philosophy to find them out.

—Sir Isaac Newton

I. INTRODUCTION

The adhesion phenomenon is relevant to many scientific and technological areas and has become in recent years a very important field of study. The main application of adhesion is bonding by adhesives, this technique replacing, at least partially, more classical mechan­ical attachment techniques such as bolting or riveting. It is considered to be competitive primarily because it allows us to save weight, to ensure a better stress distribution, and offers better aesthetics since the glue line is practically invisible. Applications of bonding by adhesives can be found in many industries, particularly in such advanced technical domains as the aeronautical and space industry, automobile manufacture, and electronics. Adhesives have also been introduced in such areas as dentistry and surgery.

Adhesive joints are not, however, the only applications of adhesion. Adhesion is involved whenever solids are brought into contact, as in coatings, paints, and varnishes; multilayered sandwiches; polymer blends; filled polymers; and composite materials. Since the final performance of these multicomponent materials depends significantly on the quality of the interface that is formed between the solids, it is understandable that a better knowledge of the adhesion phenomenon is required for practical applications.

Adhesion began to create real interest in scientific circles only about 60 years ago. At that time adhesion became a scientific subject in its own right but is still a subject in which empiricism and technology are slightly in advance of science, although the gap between theory and practice has been shortened considerably. In fact, the term adhesion covers a wide variety of concepts and ideas, depending on whether the subject is broached from a molecular, microscopic, or macroscopic point of view or whether one talks about forma­tion of the interface or failure of the formed system. The term adhesion is therefore ambiguous, meaning both the establishment of interfacial bonds and the mechanical load required to break an assembly. As a matter of fact, one of the main difficulties in the study of adhesion mechanisms lies in the fact that the subject is at the boundary of several scientific fields, including macromolecular science, physical chemistry of surfaces and interfaces, materials science, mechanics and micromechanics of fracture, and rheol­ogy. Consequently, the study of adhesion uses various concepts, depending very much on one’s field of expertise, and therefore treatment of the phenomena observed can be considerably different. This variety of approaches is emphasized by the fact that many theoretical models of adhesion have been proposed, which together are both complemen­tary and contradictory:

1. Mechanical interlocking

2. Electronic theory

3. Theory of boundary layers and interphases

4. Adsorption (thermodynamic) theory

5. Diffusion theory

6. Chemical bonding theory.

Among these models, one usually distinguishes rather arbitrarily between mechan­ical and specific adhesion, the latter being based on the various types of bonds (electro­static, secondary, chemical) that can develop between two solids. Actually, each of these theories is valid to some extent, depending on the nature of the solids in contact and the conditions of formation of the bonded system. Therefore, they do not negate each other and their respective importance depends largely on the system chosen.