Characteristics and composition of hot-melt adhesives
Characteristics of hot melt adhesive
(1) bonded quickly usually from the glue to cement cooling, only tens of seconds, or even a few seconds"
(2) a wide range of bonding on many materials and even recognized on the hard bonding materials (such as polyolefin wax paper!! carbon paper) can also be bonded "especially the use of hot melt adhesive joint, can withstand 105~106 bending times without cracking"
(3) repeated heating and multiple bonding. "
(4) stable and convenient storage! Transportation "
(5) low cost hot melt adhesive without solvent consumption, avoids the presence of the solvent, and the adherend deformed! Dislocation and shrinkage defects, helps reduce the cost and improve the quality of products! "However, there are also some disadvantages of hot melt adhesive is mainly heat resistance and adhesive strength is low, not suitable as a structure the use of adhesive" because the melt viscosity of hot melt adhesive material is generally higher, the wettability is poor, often need to pressure bonding, in order to improve the bonding strength; in addition, hot melt adhesive need special equipment in use, such as hot melt coating machine gun! "So to a certain extent limits its scope of application"
Composition of hot melt adhesive
(1) the basic polymers with various thermoplastic polymers such as: ethylene vinyl acetate copolymer (EVA), styrene butadiene styrene copolymer (SBS), styrene methacrylic styrene block copolymer (SIS), can be used as the basic polymer of hot melt adhesive, and determine the basic properties of hot melt adhesive"
(2) C5 resin, terpene resin, phenolic resin, terpene phenolic resin, rosin, modified rosin and so on, are used to enhance tacky resin. The action is to increase initial adhesion and permanent bonding strength, reduce melt viscosity of hot melt adhesive, improve wettability of sticky materials and improve operation performance.
(3) common viscosity regulators of melt viscosity regulators are waxes, such as paraffin wax, microcrystalline wax, polyethylene wax and so on. The action is to regulate melt viscosity, improve fluidity, increase wettability, speed up solidification and prevent agglomeration of hot melt adhesive.
(4) plasticizers commonly used plasticizers such as phthalates in two formic acid and two octyl phthalate two! Two formic acid benzyl ester tricresyl phosphate! "Role is to reduce the intermolecular secondary force, improve the toughness of hot melt adhesive! Cold and melt flow rate, lower melting point" but should control the amount of otherwise, will reduce the cohesive strength of the adhesive layer"
(5) anti oxidants such as di tert butyl p-cresol! Three benzene phosphite ester, adding anti oxidant can prevent the hot melt under high temperature oxidation and decomposition, in the use of poor thermal stability of raw materials, must join the anti oxidant"
(6) filling agents such as calcium carbonate, silica and talcum powder "accelerate the curing speed of hot melt adhesive, reduce shrinkage, prevent penetration, increase heat resistance and reduce cost". The amount of filler melt is increased, and the wettability and initial viscosity of rubber melt become worse.