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The surface tension of adhesive spraying is closely related to surfactants

Latex is coated by a coating machine and dried in an oven before being compounded. There are two methods for this process. One method is direct coating, which means that the latex is directly coated on the substrate paper. The other method is transfer coating, which means that the latex is coated on the anti stick paper and dried before being transferred onto the substrate paper. Direct coating of water emulsion on the substrate paper often reduces the hardness of the paper due to moisture, making it prone to breakage during the coating process and dirtying the substrate when dried in an oven. The transfer coating method is used in production (self-made steam heating ovens with widths of 80cm and 120cm). It is difficult to apply water emulsion to anti stick paper. Because the surface of the anti stick paper is hydrophobic, when applying water emulsion.
Ethyl acrylate and vinyl acetate can be used as monomers with film-forming and adhesive properties. Butyl acrylate and isooctyl acrylate not only have film-forming and adhesive properties, but also serve as internal plasticizers to reduce the glass transition temperature of polymers. Methyl acrylate and vinyl acetate can be used as monomers to improve the strength of polymers. Due to the high glass transition temperature of homopolymers of monomers such as styrene and acrylonitrile, they are not commonly used. However, based on the structural characteristics of the substrate, in order to achieve good affinity between the colloid and the substrate, monomers such as styrene or acrylonitrile are sometimes used.
Due to the poor wettability of the two, the water emulsion is prone to shrinkage on the anti adhesive paper, causing the adhesive film to rupture and causing the phenomenon of "blooming". To solve the phenomenon of "blooming", one can start by reducing the surface tension of latex and increasing the viscosity of the system, as surface tension is closely related to surfactants. The obtained lotion has low viscosity, fine particles and is easy to be coated. The method to increase the viscosity of lotion generally uses ammonia to thicken. The thickening mechanism is that ammonia reacts with the carboxyl group in the latex molecule to generate ammonium salt, so that the water solubility of the molecule is improved, and the molecular straightness is also improved, so the viscosity is improved. The test shows that when the pH of lotion is adjusted to 7~8 with ammonia water and the viscosity is about 0.21 Pa · s, the "blooming" phenomenon can be overcome. If the viscosity is too high, the latex has poor leveling performance and is not conducive to coating. Therefore, during lotion polymerization, a certain amount of unsaturated acid is required in the molecular structure, such as acrylic acid, methacrylic acid, maleic acid monoalkyl ester and other monomers. The higher the content of carboxyl group and the stronger the hydrophilicity of comonomer, the greater the alkali thickening of this kind of carboxyl containing copolymer lotion. The introduction of acrylic acid into copolymers has two functions: one is to cause acrylic acid to react with the internal crosslinking agent in the copolymer within the molecule to produce cross-linking; The second is to make acrylic acid on the surface of the emulsion so as to thicken the lotion when neutralized by ammonia. If the thickening viscosity is too high, the leveling performance of the latex is poor, and the stripes on the blade of the adhesive coating machine are easily retained to form "corduroy like" stripes. The adhesive surface is also not bright, and molecular design is carried out based on the characteristics of the comonomer




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