Adhesives NZIC（粘合剂NZIC）.pdfVIP

ADHESIVES An adhesive is a material used for holding two surfaces together. An adhesive must wet the surfaces, adhere to the surfaces, develop strength after it has been applied, and remain stable. Adhesion is a specific interfacial phenomenum. There are three main theories of adhesion: adsorption, electrical and diffusion. All probably apply to most adhesives. Surface preparation before applying the adhesive is of prime importance. The raw materials for adhesives are mainly polymeric materials, both naturally occurring and synthetic. A useful way to classify adhesives is by the way they react chemically after they have been applied to the surfaces to be joined. There is a huge range of adhesives, and one appropriate for the materials being joined must be chosen. INTRODUCTION For a material to perform as an adhesive it must have four main requirements: • It must wet the surfaces - that is it must flow out over the surfaces that are being bonded, displacing all air and other contaminates that are present. • It must adhere to the surfaces - That is after flowing over the whole surface area it must start to adhere and stay in position and become tacky. • It must develop strength - The material must now change its structure to become strong or non-tacky but still adherent. • It must remain stable - The material must remain unaffected by age, environmental conditions and other factors as long as the bond is required. The basic definition of an adhesive as used by the Adhesive Sealant Council in America is A material used for bonding that exhibits flow at the time of application. There is no simple theory of adhesion, and the truth for any one system is probably a combination of adsorption, electrostatic attraction and diffusion. The three main theories are discussed below. There are many methods o