Coatings are widely used in automobiles, furniture, construction, etc., which can not only improve their aesthetics, but also play a certain protective role and prolong their service life. In the process of social and economic development, the role of coatings is becoming more and more important, and people pay great attention to the performance and quality of coatings. At present, people’s living standards are getting higher and higher, their awareness of environmental protection is gradually enhanced, they are cherishing the use of resources more and more, and they have very strict requirements on the quality of paint products. The world paint industry is developing towards the “4E” principle of economy, ecology, energy and efficiency. The main raw material of acrylate coating is methacrylate or acrylate, and mixed resin is made into acrylic resin binder.
Acrylic resin is a copolymer composed of methacrylate, acrylate and vinyl monomers. Compared with other synthetic polymer resin materials, acrylic resin materials have very obvious advantages, such as light resistance, weather resistance, durability It does not change color at 230 °C, and has good acid and alkali corrosion resistance. It is more and more widely used in automobiles, home appliances, construction, plastic products, etc. Combined with different resin structures and production processes, acrylic numerical coatings can be divided into several different types.
The relationship between the structure and properties of acrylic resins
On the one hand, it is stability, including UV resistance, acid and alkali resistance, chemical corrosion resistance, etc. The acrylic resins have lower oxidation resistance and UV resistance than methacrylic resins because of the presence of a-H. Acrylic resin with C-C bond as the main chain, has very good oxidation resistance, acid and alkali resistance and hydrolysis resistance. On the other hand, there are mechanical properties. The mechanical properties of acrylic resins include elongation, hardness, toughness, etc. These properties are largely affected by the density of the polymer molecular structure. With the growth of the side chain, the tensile strength and hardness of the acrylic resin will decrease significantly, and the elongation and flexibility will increase significantly. Due to the presence of methyl groups at the a-position of polymethacrylates, the rotational motion of the C-C main chain is greatly restricted. There is no a-methyl group in polyacrylate, and each chain can rotate around the main chain, which is why polymethacrylate has good hardness and tensile strength, and is inferior to polyacrylate in softness and elongation.
Synthesis of Acrylic Resin
Acrylic resins use free radical reaction as the basic reaction, which can be divided into three processes: chain initiation, chain growth and chain termination, and the whole process is accompanied by chain transfer. In the process of synthesizing thermoplastic acrylic resin, it is necessary to control the molecular weight and molecular weight distribution. Although the mechanical properties of the paint film will increase significantly with the increase of molecular weight, the solution viscosity of the paint film will also increase significantly. Decreasing the solids content, in addition, tends to decrease its solubility with increasing molecular weight. The molecular weight of thermoplastic acrylic resins currently used commercially is around 80,000 to 90,000.
Molecular weight and molecular weight distribution are also easily affected by factors such as monomer feeding method and initiator type. When benzoyl peroxide is selected as the initiator, the benzoyl free radical will decompose and become a highly active wave type free radical, wax used in paint manufacturing which is prone to branching reaction, depriving the hydrogen atom of the monomer or polymer molecular chain, especially with the When the temperature increases, above 130 °C, a large number of branched chains will appear, increasing the molecular weight distribution. In terms of the monomer feeding method, the batch feeding method is selected to obtain a wider molecular weight distribution, and the semi-continuous dropwise addition method and the continuous dropwise addition method can be selected to obtain a narrower molecular weight distribution. Generally, the solvent is first added to the reaction kettle, raised to the reaction temperature, and then the mixed solution is continuously added at a certain speed to maintain the normal concentration of monomers and initiators in the reaction kettle. If the monomer addition rate can maintain normal polymerization temperature, the monomer concentration in the reactor is basically constant. In the aspect of olefin monomer copolymer reaction, it is also necessary to fully analyze and consider the monomer reactivity ratio. If the reaction rate constants of the monomers are similar, the molecular chain structure can be regarded as a random distribution. If the reaction rate constants of the monomers are very different, choosing the batch feeding method will easily affect the uniformity of the molecular chain composition. Select the semi-continuous dropping method and the continuous dropping method, etc., do a good job of controlling the monomer dropping speed, keep it consistent with the polymerization speed, and obtain the average composition molecular chain.
Main properties and uses of acrylic coatings
Acrylic paint raw materials are produced from petrochemical industry, with low cost and very rich resource reserves. In the development process of acrylic coatings, in order to improve performance and reduce production costs, it is necessary to use olefin monomer tools such as acrylamide and styrene. The characteristics of different copolymers are different, and it is necessary to identify different types of coatings according to the specific requirements of the product type.
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