Vinyl-phenolic adhesives

They are generally used to bond metals, rubbers, and plastics to themselves or to each other. A major application of vinyl phenolic adhesive is the bonding of copper sheet to plastic laminate in printed circuit board manufacture. 

Owing to the high cure temperature and pressure, the modern trend is to move away from vinyl-phenolic adhesives. 

Table IX. Acetal Resins Used in Vinyl-Phenolic Adhesives...

Cotter has reported the results of weathering conducted at three sites over a period of six years. All adhesives performed best at the desert site, although the epoxy/polyamide bonds were considered the least durable. At the hot, wet tropical site, the epoxy/polyamide bonds lost most of their strength after two years, in sharp contrast to the excellent strength retention of specimens bonded with novolac-epoxy, nitrile-phenolic, and vinyl-phenolic adhesives. It was also found that the combination of environmental exposure and stress was particularly harmful, the effects being more pronounced with certain adhesives. Thus stressed epoxy/polyamide bonds all failed after two years tropical exposure and stressed vinyl-phenolic bonds under the same conditions lost strength rapidly after two years and all specimens had failed after six years. The novolac-epoxy and nitrile-phenolic were less effected by stress, as were an epoxy-phenolic and a modified epoxy. 

Allen and Dean have confirmed the findings of Lewis et al and have tested the reliability of prediction of the endurance limit by cyclic durability testing. They have shown that joints prepared with a vinyl-phenolic adhesive were damaged when subjected to a loading cycle above the endurance limit but not when the loading cycle was below the endurance limit. 

Figure 6 Strenglhs of lap joints in aluminium alloy bonded with a vinyl phenolic adhesive on exposure to wet air at 50°C. O Aged at 50% r.h. and 100% rJi. A aged at 100% r.h. for 5000 h, then at 50% r.h. for a further 5000 h [30]. Crown Copyright.

Vinyl-phenolic. Vinyl-phenolic adhesives are based on a combination of phenolic resin with polyvinyl formal or polyvinyl butyral resins. They have excellent shear and peel strength. Room-temperature shear strength as high as 5,000 Ib/in is available. Maximum operating temperature, however, is only 200°F, because the thermoplastic constituent softens at elevated temperatures. Chemical resistance and impact strength are excellent. 

Epoxy-phenolic adhesives are exceptional in that they have good adhesive properties at both elevated and low temperatures. Vinyl-phenolic adhesives maintain fair shear and peel strength at -423 °F, but strength decreases with decreasing temperature. Nitrile-phenolic adhesives do not have high strength at low service temperatures, because of rigidity. 

Although the manufacture and sale of adhesives is a worldwide enterprise, the adhesives business can be characterized as a fragmented industry. The 1987 Census of Manufacturers obtained reports from 712 companies in the United States, each of which considers itself to be in the adhesives or sealants business only 275 of these companies had more than 20 employees. Phenolics, poly(vinyl acetate) adhesives, rubber cements, and hot-mclt adhesives arc the leading products in terms of monetary value. These products are used primarily in llie wood, paper, and packaging industries. The annual growth rate of the adhesives market is 2.3%, and individual segments of the market are expected to grow faster than this rate. 

Several important types of adhesives used to obtain high-strength bonds are the epoxies, epoxy -phenolics, nitrile-phenolics vinyl-phenolics... 

Extensive information on durability of adhesive joints is more available on aluminum than on other substrates. Figure 15.17 illustrates typical results showing the effect of adhesive variations on joint durability during marine exposure. Vinyl-phenolics and nitrile-phenolics have... 

FIGURE 15.17 Effect of adhesive on the durability of etched 6061-T6 aluminum alloy joints exposed to a marine environment. (1) Two-part epoxy, (2) one-part epoxy, (3) nitrile-phenolic, (4) vinyl-phenolic, (5) vinyl-phenolic.33... 

Polysulfone A number of adhesives have been found useful for joining polysufone to itself or to other materials. These include 3M Company s EC 880 solvent-base adhesive, EC 2216 room-temperaturecuring epoxy two-part paste, Bloomingdale Division, American Cyana-mid Company BR-92 modified epoxy with DICY curing agent, or curing agent "Z" (both spreadable pastes), vinyl-phenolics, epoxy-nylons, epoxies, polyimide, rubber-based adhesives, styrene polyesters, resorcinol-formaldehyde, polyurethanes, and cyanoacrylates. The EC 880, EC 2216, and the two BR-92 adhesives are recommended by the polysulfone manufacturer. Union Carbide (16) (17). 

This class of adhesives contains some of the most traditional materials, for example animal glues and gums derived from natural sources, which are long-chain molecules, are soluble in water, and are either proteins or polysaccharides. Modern technology has brought other water-soluble materials into use for example, poly( vinyl alcohol) adhesives, and a host of resins based on phenol, mea, and formaldehyde (see Formaldehyde Resins in Chapter 4). 

Phenolic resin adhesive films (Resinous Products Chemical Co.) Poly(vinyl acetate) adhesives (Carbide Carbon Chemicals Co.) Chlorinated rubber adhesives... 

A conventional emulsion polymer based on vinyl acetate has been modified by carboxylation (92). The carboxylated ethylene-vinyl acetate adhesive increases the adhesion to metal and polymer surfaces and the resistance to oil, grease, and water. The films are also acid, alkali, and UV resistant. Furthermore, the polymers are cross-linkable through the carboxylic groups. These adhesives can react with aminoplasts, phenolics, and epoxy resins for increased water and creep resistance. 

A special study on aerospace structural adhesives was conducted in 1976 by the National Materials Advisory Board of the National Research Council. The final report was published as one of the series in Treatise on Adhesion and Adhesives (108). That report discussed primarily phenolic and epoxy-based mate rials, e.g., vinyl-phenolics, n itr ile-phenolics, epoxy-phenolics, nylon-epoxies, and elastomer-epoxies. Polyimide and polybenzamidazole adhesives were barely mentioned. Most of the high-temperature adhesives discussed in one of the preceding sections were either not invented or not developed at that time. 

Of the five alloy-tape adhesives, vinyl-phenolic is also available in solvent-based solution and emulsion, liquid, and co-rea ting powder. Epoxy-phenolic... 

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