1. Field of the Invention
The present invention relates to adhesives, and particularly to a pressure sensitive adhesive composed of a copolymer of ethylene and propylene.
2. Description of the Related Art
The copolymers of ethylene with higher olefins are vital commercial products. The structure and copolymer composition are supposed to depend on the catalyst characteristics, such as homogeneity and stereospecificity. Studies have found that the physical properties of ethylene-propylene (EP) copolymers are strongly dependent upon the number of chemically inverted propylene units and the monomer sequence distribution.
Ethylene/propylene copolymerization has been carried out by using different catalysts, such Zeigler-Natta catalysts, postmetallocene and metallocene catalysts, and FI catalysts. Recently, diimine nickel and palladium catalysts were found to be promising systems for the homopolymerization and copolymerization of ethylene, producing highly branched, high molecular weight, amorphous or linear semi-crystalline materials due to a chain-walking mechanism. Decreasing the polymerization temperature or pressure resulted in a decrease in the degree of branching and increasing the crystallinity and melting temperature of the resulting polymer A huge increase in activity was obtained when diethylaluminum chloride (DEAC) and 1,3-dichloro-1,3-diisobutyldialuminoxane (DCDAO) were used for ethylene and propylene polymerizations in the presence of Ni(II)-diimine complexes, compared to polymethylaluminoxane (MAO).
Adhesives are substances (either natural or synthetic, and existing as a liquid or semi-liquid) that can be used to bond or adhere objects together. Several mechanisms of adhesion have been proposed, including mechanical interlocking, electronic theory, a theory of boundary layers and interphases, diffusion theory, and chemical bonding theory. Adhesives are classified into different types based on the method of adhesion, such as drying adhesives, contact adhesives, hot adhesives, and pressure sensitive adhesives. There are many types of polymeric adhesives, including natural rubber, polysulfide, polyurethane, polyvinyl acetate, ethylene-vinyl acetate, unsaturated polyester, and epoxy. Adhesives are used in the wood industry, the electronics industry, drug delivery, dentistry, and the automotive industry.
Pressure sensitive adhesives, or PSAs, are adhesives that are able to form bonds on surfaces by the application of light pressure. No heat, solvent, or water is required to stimulate the adhesive. They are classified into three major products, namely, solvent-based, water-based, and hot melt.
Thus, a pressure sensitive adhesive solving the aforementioned problems is desired.