Due to the high cost, the use of melamine resin adhesive is limited. However, with the development of chemical industry in recent years, the production and use of this kind of adhesive are increasing, which is mainly used for the production of decorative boards and the modification of urea-formaldehyde resins and other adhesives.
Melamine resin adhesive is a kind of amino resin adhesive, including melamine formaldehyde resin adhesive and melamine urea-formaldehyde resin adhesive. The heat resistance and water resistance of the adhesive are higher than those of phenolic resin and urea-formaldehyde resin. Melamine formaldehyde resin hose is called melamine resin glue.
Melamine formaldehyde resin usually contains a certain amount of free formaldehyde,
Moreover, it will volatilize slowly during use, which will endanger the health of operators. Therefore, when synthesizing and producing melamine-formaldehyde resin, some measures are usually taken to reduce the existence of free formaldehyde. By reducing the synthetic molar ratio of melamine to formaldehyde (1: 3.0— 1: 5.0), the content of free formaldehyde can be controlled.
Generally speaking, the smaller the molar ratio of melamine to formaldehyde, the less the free formaldehyde content. When the polycondensation reaction is completed, excess free formaldehyde can be removed by using a formaldehyde binder. Urea and dicyandiamide have low cost and good formaldehyde absorption effect, but the dosage must be moderate, too much will affect the stability of resin solution. Melamine mostly uses latent acid compounds as catalysts, and uses a variety of compounds to form synergistic catalysts to improve the catalytic ability and complete cross-linking at a lower temperature or in a shorter time. The order of catalyst activity from high to low is: synergistic catalyst >; Ammonium nitrate >: ammonium chloride >: ammonium sulfate > zinc nitrate >: ammonium dihydrogen phosphate > diammonium hydrogen phosphate >: zinc chloride >: magnesium chloride.
Melamine formaldehyde resin is a thermosetting resin commonly used in coating and adhesive industry. Its main highlight is its good compatibility with many additives, colorless, and easy use of dyes and pigments. Water-soluble system can reduce the emission of volatile organic compounds into the atmosphere. The cured melamine formaldehyde resin has good solvent resistance, heat resistance, excellent hardness and wear resistance, and the cross-linking density after curing undoubtedly has a direct impact on the mechanical strength, appearance and function of the resin.
Therefore, understanding the dynamic process of phase transformation and crosslinking curing degree is of great significance for controlling and optimizing application and developing new resins. Although many methods such as nuclear magnetic resonance, infrared spectroscopy and differential thermal analysis can be used to study curing, they cannot be used to study the continuous process of reaction. The experimental process is a dehydrated glass body, from prepolymer solution to thickening and then to thermal curing and hardening.
The above methods have nothing to do with curing morphology, physical mechanics and rheology. Rheological testing method directly obtains the information in practical application through dynamic means.