Adhesion promoters chemistry

Some fabricators use bakes both before and after lamination. The bake before lamination is designed to ensure moisture removal from cores after the apphcation of the adhesion promotion chemistry follow the recommendations of the laminate manufacturer carefully. The bake is also needed if innerlayers are stored at high humidity prior to lamination, or as a standard process for hygroscopic materials such as some of the LFAC laminates or polyimide. Other fabricators use a bake after lamination to complete the cure, reduce warp, and relieve stress. Although a post bake will achieve these goals, it is usually unnecessary in a controlled lamination process. In the case of high-temperature materials such as polyimide, cyanate ester, and PPO, a post bake is a useful way to achieve a full cure in a process where the maximum press temperature is limited. 

Adhesion promoter chemistries, other than those of silanes, have been extensively evaluated for many years. These materials use the same concepts as silane-coupling agents, but they are based on other metallic elements. They have inorganic reactivity on the metallic atom and contain organofunctional groups, such as methacrylate, carboxylate, and others, with dual- or multi-functionality built into the... 

The performance of a product where adhesion plays a role is determined both by its adhesive and cohesive properties. In the case of silicones, the promotion of adhesion and cohesion follows different mechanisms [37]. In this context, adhesion promotion deals with the bonding of a silicone phase to the substrate and reinforcement of the interphase region formed at the silicone-substrate interphase. The thickness and clear definition of this interphase is not well known, and in fact depends on many parameters including the surface physico-chemistry of... 

The present paper will cover just some aspects of the use of silanes as adhesion promoters in the surface coating, adhesive and composite fields from a practical point of view, and review the results in the light of published work. The chemistry and reactions of silanes have already been covered in some detail and do not require further repetition here [12]. 

A search of the literature reveals some industrial applications of zirconium-based adhesion promoters but, in general, there is iittie scientific investigation of their mode of action. However, it is worthwhile at this point to indicate briefly the usage for zirconium compounds and the type of chemistry believed to be involved. 

Evenness of treatment depends on factors such as the designs of the chamber and of the electrode, the levels of energy and pressure, and the period of time of exposure once established at satisfactory values, these parameters can be controlled fairly easily. The surface chemistry is similar to that with simple flame treatment but the use of a gaseous reactant means that even treatment of quite complex shapes is practicable. Besides even and repeatable results the method offers the additional advantage that adhesion promoters are not necessary—with associated savings in costs and enhanced environmental implications. 

Applications of these layers as supports for sensor devices and biocompatible materials as well as for adhesion promotion have illustrated the ability of polymer surface chemistry. 

Well over 100 patents have been issued for a variety of practical applications of calixarene-based molecules. Many of these, not surprisingly, involve the chemistry that is discussed in this book, especially the use of calixarenes in systems in which selective ion complexation plays the central role. A number, however, deal with quite different sorts of applications including, inter alia, the use of calixarenes as adhesion promoters, electrophotographic photoreceptors, ... 

Bitumens are stored at 120-200°C and at these temperatures amine groups in the adhesion promoters can react with acid groups in the bitumen to form less active amido compounds, or can degrade by oxidation. The rate of degradation depends on the acid value of the bitumen and the chemistry of the adhesion promoter. Where possible, the adhesion promoters should be added to the bitumen just before use. So-called heat-stable products based on less reactive tertiary amines or polyamines have been developed for situations where the treated bitumen must be stored for longer than a few hours. Field studies have shown that treatment of bitumens with adhesion promoters improves the performance of roadways. 

One of the most frequent procedures in the formulation of adhesives is the addition of adhesion promoters. Of these, silanes are by far the most frequently used. The silanes form a multi-membered family of chemicals. Numerous publications have described aspects of silane chemistry and the applications of silanes [15-18]. Although many silanes are readily available, in many industrial formulations of adhesives the most frequently used of these are the primary amine and diamine versions because of their relatively low cost. However, these do not necessarily produce optimum benefits in adhesion for all applications. Guidelines for the selection of silanes best suited for specific applications would therefore be useful. These should be based on a fundamental understanding of the manner in which silane compounds affect the interface and interphase in adhesively bonded systems. The... 

The use of primers or coupling agents based upon alkoxide or silane chemistry has been demonstrated to be potentially useful when used in combination with grit blasting or acid etching, though results are highly variable (see Silane adhesion promoters). 

There are relatively few well-documented examples of interfacial primary bonding in the literature but it is possible to find examples in the areas of organic coatings on steel, metallized plastics and adhesion promoters. As the following examples will show, the exact definition of the chemistry resulting from primary bond formation at the interface has only become possible with the advent of surface analysis techniques. Such investigations rely heavily on XPS and ToF-SIMS for interfacial analysis. 

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