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Saturday, November 1, 2008

Vinyl Polymers

Certain vinyl polymers such as the polyvinyl acetals, in particular polyvinyl butyral and polyvinyl formal, also polyvinyl esters, are compatible with bisphenol Aglycidyl ethers, and can be added to improve the impact strength and peel strength of an adhesive. Polyvinyl butyral is probably the best in this respect. A 10-20% addition effects a marked improvement by naturally reduces hot strength.

Ease of solubility in the epoxy resin depends to some extent on the grade of the vinyl polymer used; and on its molecular weight. Polyvinyl esters and acetals can be dissolved in melted (solid) epoxy resin as well as liquids, but heating to a temperature of at least 100oC is usually necessary.

A composition having remarkably good adhesion to metal, combined with toughness, consists of a mixture of a plasticised polyvinyl resin particularly polyvinyl chloride or its copolymers which will crosslink by reacting with both resins. This use of polyvinyl chloride is interesting in view of its poor solubility characteristics. Although the composition in intended primarily as a metal coating, it gives excellent strength as a conventional adhesive. A somewhat related type of adhesive, recommended for bonding both synthetic and minearal fibers, consist of a dispersion of plasticised polyvinyl chloride (a plastisol), an epoxy resin and hardeners.