Polyester hot melt adhesives have the characteristics of good melt flow, fast curing speed, high bond strength, impact resistance, bending resistance, etc., and are one of the best hot melt adhesives with the best heat resistance. They have satisfactory adhesion to metals, ceramics, glass, cement, wood, and plastics, and are especially suitable for leather, fiber, clothing, automobile interiors, electrical appliances and footwear industries.
At present, polyester hot melt adhesives are mostly obtained by condensation polymerization of diol esters of terephthalic acid, diol esters of isophthalic acid and diol esters of long carbon chain aliphatic diacids. Since the direct esterification reaction rate of terephthalic acid and diol is slow, diol esters of terephthalic acid are often obtained by transesterification of dimethyl terephthalate and the corresponding diol. However, since the above-mentioned transesterification reaction will by-produce methanol, which has a low boiling point and is easily volatile, causing environmental pollution. Moreover, methanol generally contains a small amount of diols or other impurities, and has low recycling value and is often used as a fuel, resulting in increased product costs.
This project adopts a direct esterification and condensation method. Through direct esterification of terephthalic acid, isophthalic acid and at least one aliphatic dicarboxylic acid with aliphatic diol under the action of a composite catalyst, and then polycondensation, the melt index is obtained., glass transition temperature, crystallization properties and adhesion properties meet the expected indicators, and a series of new polyester hot melt adhesive products are obtained. The main innovations are as follows:
(1) Through the formulation design of specific proportions and types of dibasic acid and diol, copolyester hot melt adhesives with fast crystallization speed, high initial melting point, short opening time, good bonding properties and rapid bonding were developed, including polyester hot melt adhesives for retina, composite polyester hot melt adhesives and polyester hot melt adhesives for shoe making.
(2) A highly efficient composite esterification catalyst was developed. The third component SnCl4 is added to the mixture of titanium and silicon, dissolved in alcohol as a solvent, and then co-hydrolyzed within a specific pH range. The obtained catalyst can not only significantly increase the esterification reaction rate of dibasic acid and dibasic alcohol, but also significantly accelerate the condensation reaction, and the obtained copolyester product has good color.
(3) PNT (Mw =16000~20000) with lower molecular weight was synthesized, and maleic anhydride grafted low density polyethylene was used as a compatibilizer. LDPE and PNT were melt blended to obtain a polyester/polyolefin composite hot melt adhesive with excellent mechanical properties, optical properties and weather resistance. This product is used in solar cell busbar in the form of a hot melt adhesive film, which can avoid yellowing caused by the traditional silver welding process on photovoltaic modules, thereby improving its photoelectric conversion rate.
This project has now formed 13 authorized patents, including 6 China invention patents and 7 PCT internationally authorized patents (1 US patent, 2 Australia patents, 2 Korean patents, and 2 Singapore patents). The new products developed in this project have all formed large-scale production, with an additional annual output value of more than 64 million yuan and an additional annual profit and tax of more than 16 million yuan.
In terms of theory, this project focuses on discussing the kinetics of esterification reaction, the functional relationship between polyester molecular weight and intrinsic viscosity, the isothermal crystallization rule of copolyester, and the method of rapid testing of the bond strength of hot melt adhesives in the laboratory. 5 papers have been published in domestic and foreign academic journals, including 4 in SCI and 4 in EI.