The use of a hot melt adhesive, which is an adhesive melted by heat, has gradually increased as an eco-friendly adhesive since an emission of a volatile organic solvent is very small. Recently, efforts to prevent global warming while preventing a volatile organic compound harmful to human from being emitted have been institutionalized in terms of protecting the environment. As a part of worldwide efforts, the use of resin that less emits carbon dioxide, i.e., has a low life cycle assessment value has been requested. Polypropylene carbonate, which is prepared using carbon dioxide as a raw material, has an LCA value of 1.3, which is much lower value than other polymer resins such as polyethylene, polypropylene. Therefore, a method of reducing carbon emission during a process of preparing a hot melt adhesive composition by preparing the hot melt adhesive using the polypropylene carbonate resin has been suggested. The polypropylene carbonate, which is resin having high polarity, has surface energy that reaches 48 dyne/cm according to Owens calculation. Due to the polar surface, the polypropylene carbonate has excellent adhesion to the polar surface. An example of the polar surface having high adhesion to the polypropylene carbonate may include cellulose of polarity in wood, which has very large adhesion thereto and thus, does not cause interface peeling when being bonded to a surface such as glass. However, it is difficult to sufficiently show the adhesion to a polyvinyl chloride sheet surface having low polarity, which needs to be improved.
Generally, the hot melt adhesive is composed of tackifier in the same amount of ethylene vinyl acetate and wax to lower viscosity.
The most general hot melt adhesive composition is composed of 40 wt % of ethylene vinyl acetate, 40 wt % of tackifier, and 20 wt % of wax. In the ethylene vinyl acetate, a ratio of vinyl acetate is generally 20 to 40 wt %. As the tackifier, gum rosin, rosin ester, C5 petroleum resin, C9 petroleum resin, coumarone resin, acrylic-modified petroleum resin, or the like, may be used. As the wax, paraffin wax, polyethylene wax, polypropylene wax, or the like, are used. The existing hot melt adhesive composition having the above composition shows the adhesion to various materials; however, does not show adhesion approximating to adhesion of an epoxy or urethane adhesive and has low flexibility and adhesion at low temperature. Therefore, the existing hot melt adhesive composition has a limitation in being used as the adhesive in various fields.
Meanwhile, the adhesion to the polar surface of the polypropylene carbonate has very higher than that of the existing ethylene vinyl acetate, which allows the adhesive composition to sufficiently secure adhesion. However, there is a need to combine the tackifier to increase the adhesion to the non-polar surface or the polar surface having low polarity. The polypropylene carbonate resin has compatibility with several polar resins; however, does not have compatibility with the tackifier having low polarity such as rosin, petroleum resin, or the like, which is present in two phases such as a continuous phase and a disperse phase even when being mixed. As a result, the mechanical strength of the hot melt adhesive composition is lowered. In order to use the polypropylene carbonate as the multi-purpose hot melt adhesive, there is a need to improve the adhesion and increase the mechanical strength such as tensile strength by using the tackifier having excellent compatibility.
USPTO Backgrounds
USPTO Backgrounds