Neoprene-phenolic, adhesive formulation

Neoprene-phenolic adhesives are formulated for room temperature cure and they are used for bonding metal, wood, and many plastics. A combination of neoprene rubber and a / ara-substituted phenolic resin was first described by Thomson. ... 

Table 18. A Neoprene/Phenolic Adhesive Test Formulation. ... 

Neoprene-phenolic contact adhesives, known for their high green strength and peel values, contain a resole-type resin prepared from 4-t-butylphenol. The alkyl group increases compatibility and reduces cross-linking. This resin reacts or complexes with the metal oxide, eg, MgO, contained in the formulation, and increases the cohesive strength of the adhesive. In fact, the reactivity with MgO is frequently measured to determine the effectiveness of heat-reactive phenolics in the formulation. 

The main reasons for the use of methyl chloroform in formulations for urethane and neoprene/phenolic contact adhesives, mastics, sealants, and natural mbber tire repair cements are its ability to substantially reduce flammability, its non-photochemical reactivity, and the favorable characteristics of the resulting adhesive formulation. 

Toxicity, flammability, and materials shortages associated with organic solvents have resulted in the development of several new water-borne adhesive systems. Many of the previously effective adhesive formulations are not readily converted to water-borne analogs. Many of the previously understood solution property-performance correlations remain valid in water-borne systems some do not. In this work an effort has been made to improve our understanding of the adhesive mechanisms and property-performance correlations in solvent and water-borne contact adhesives. These adhesive systems include phenolic/neoprene and phenolic/acrylic compositions. Some of the physical properties of the individual components and of the phenolic/elastomer blends have been related to contact adhesive performance. 

Consider the data of Tables 1-3, which briefly illustrate the adhesive performance of a few contact adhesive systems. Table 1 illustrates that the proper phenolic can significantly enhance the contact tack of an acrylic or neoprene latex. Table 2 indicates the extent to which specific adhesion can vary between contact adhesion formulations. Table 3 shows an apparent conflict in elevated temperature performance between two different test procedures. In subsequent sections we examine these performance variations in greater detail with the most in-depth analysis being given to the phenomenon of contact tack. 

Phenolic tackifiers (106) in the form of dispersions can be used to formulate neoprene or acrylic latex into waterborne contact adhesives. For example, a solid ratio of latex and phenolic dispersion (Union Carbide-BKUA-2370 or BKUA-2260)of 3 1 can form a stable adhesive at pH 6.0-6.5. 

Waterborne contact adhesives contain an elastomer in latex form, usually an acrylic or neoprene-based latex, and a heat-reactive, cross-linkable phenolic resin in the form of an aqueous dispersion. The phenolic resin improves metal adhesion, green strength, and peel strength at elevated temperature. A typical formulation contains three parts latex and one part phenolic dispersion (dry weight bases). Although metal oxides may be added, reaction of the oxide with the phenolic resin does not occur readily. 

In general, fillers reduce the specific adhesion and cohesive strength of adhesive films. For these reasons, they are rarely used in low solids contact adhesives. In some formulations, e.g., Neoprene-terpene phenolics, the inclusion of a fine particle size reinforcing silica such as HiSil 233 (PPG Industries) will increase film strength. This effect is lost in formulations using reacted magnesium resinate systems. 

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