Phenolics special laminates

Facing materials for use on the laminate board and sandwich panel, etc. include metal plates (steel, iron, and aluminum), metal foils, non-woven cloth and various kinds of paper (glass-fiber, ceramic-fiber, and flame-retardant), and the complex of these materials. Because the adhesive strength of phenolic foam is weak, special measures must be taken on the side of the facing material. 

Furan This is a condensation product involving furfuryl alcohol which may compete with phenol formaldehyde in industrial processes. The advantage stems from the raw material furfural that originates in plants such as straw, com, sugar cane or wood. It is not however much in use in developed covmtries. The polymer itself shows good chemical resistance and serves in special coatings, adhesives and laminates. It is supplied as a relatively cheap fluid resin, hardened by the use of an acidic catalyst. 

Resins based on para-substituted phenols can be either one-step or two-step, but they cannot cure to a thermoset state. In the manufacture of phenolic resins, smaller quantities of acetaldehyde and furfuraldehyde are used in addition to formaldehyde. Furthermore, resorcinol, bisphenol A, and p-alkylphenols are employed, in addition to phenol, when special properties are desired. Formaldehyde concentrations of 37-50 weight % in aqueous solutions are most commonly employed. The catalysts most frequently used are acids such as oxalic, hydrochloric, sulfuric, p-toluenesul-fonic, and phosphoric and bases such as sodium, calcium, and barium hydroxide. In the weakly acidic range metal carboxylates are employed. Thermoset phenolic resins are employed as structural adhesives for laminating and bonding applications. Para-alkyl-substituted resins are employed as tackifiers in contact adhesives, pressure-sensitive adhesives, and hot-melt adhesives. 

Historically, copper-clad laminates with acrylic or epoxy adhesives have been the major materials for flexible circuits. Each manufacturer has developed a special resin grade or special additives to ensure reliable flexibility and bond strength. Other adhesive materials such as phenol resin or silicon resin have been developed however, they have not become standard adhesive materials in flexible circuits. 

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