Hot melt adhesive is a non-solvent solid adhesive made of thermoplastic resin or thermoplastic elastomer with plasticizer, viscosifier, antioxidant, flame retardant and filler. Due to its non-toxic, no environmental pollution, convenient preparation and other advantages become the adhesive market development direction, the world annual output has been in the rising trend, its growth rate in all kinds of adhesives for the highest, more and more diverse varieties, applications are more and more widely.
Ethylene and vinyl acetate (EVA) hot melt adhesive preparation method is simple, widely used in mechanized packaging, furniture production, shoes, wireless binding, electronic components and daily supplies bonding, quickly become hot melt adhesive in the most widely used, the largest amount of a kind. In 1960, dupont of the United States first realized industrial production and named the commodity Elvax. Later, UCC, USI, Bayer, ICI, Monsanto and other companies produced such products one after another.
1. Composition of EVA adhesive
The main resin of EVA hot melt adhesive is ethylene-vinyl acetate copolymer (EVA), which is manufactured by high pressure bulk polymerization or solution polymerization of ethylene and vinyl acetate. The molecular structure, relative molecular weight and distribution of EVA have a decisive influence on the bonding performance of hot melt adhesive.
There are many kinds of viscose resin, its main function is to increase the wettability and adhesion of the adhesive to the adhesive, so as to improve its adhesion strength. Increases the adhesion resin for 10-10, 000, the relative molecular mass of the softening point of 70 ~ 150 ℃. Viscose resin is generally divided into four categories: (1) rosin and its derivatives, such as rosin glyceride, rosin phenolic resin, etc.; (2) terpene resin and its modifier; (3) petroleum resin, the most important is C5 and C9 resin and its hydride, mixture and copolymer; (4) oxyindene resin and its hydride. The chemical composition, softening point, color, thermal stability, odor, compatibility and price should be considered in the selection of viscose resin for hot melt adhesive.
Petroleum resin has no fixed melting point, and its softening point has become an important factor determining the performance of the resin. Other physical properties, such as the melt viscosity, its compatibility with EVA, and the amount of resin, have an important impact on the bonding performance of EVA hot melt adhesive [2~5]. The higher the softening point of the resin, the stronger the cohesive strength of the resin, the higher the adhesion strength of the adhesive, the higher the temperature of hot melt adhesive and the wider the application range. Usually, the softening point of petroleum resin is in commonly 90 ~ 110 ℃ is more appropriate.
The melt viscosity of petroleum resin can affect the melt viscosity of EVA hot melt adhesive. The hot melt adhesive with low melt viscosity can spread well on the substrate, increase the contact area between the hot melt adhesive and the substrate, improve the infiltration degree of hot melt adhesive to the adhesive, and contribute to the improvement of the interface strength between the hot melt adhesive and the adhesive.
Wax is the most effective viscosity regulator, the main role is to reduce the melt viscosity, improve liquidity infiltration, improve adhesive strength, prevent hot melt cement block, increase surface hardness, reduce costs. Wax according to the source can be divided into: (1) animal wax (such as beeswax, etc.); (2) vegetable wax (e.g. palm wax); (3) mineral wax (such as lignite wax, etc.); (4) petroleum wax (such as paraffin wax, microcrystalline wax, etc.); (5) synthetic wax (such as polyethylene wax, fito wax, etc.).
The function of antioxidant is to prevent the oxidation and thermal decomposition of hot melt adhesive. Hot melt adhesive is generally considered to be used in a hot environment. When the thermal stability of components, such as paraffin paraffins, is poor, it is necessary to add antioxidants. According to the latest research results, adding antioxidants can help improve the toughness, thermal stability and service life of the adhesive. Commonly used antioxidants are: 2,6, 1, 2, tert-butyl p-toluene phenol.
Common hot melt adhesive
Common hot melt adhesive: sealing side, hot melt adhesive coated hot melt adhesive, hot melt adhesive, hot melt adhesive at low temperature, medium temperature hot melt adhesive, filler coated hot melt adhesive, sealing side hot melt adhesive, hot melt glue gun, hot melt adhesive stick, hot melt glue, hot melt glue, hot melt glue, Eva hot melt adhesive, high temperature electronic high temperature hot melt adhesive, polyamide hot melt adhesive, etc.