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According to the fact that silicone polymers themselves have the characteristics of low surface energy and low viscosity, it is only in the preparation process that More suitable for practical applications and modified. The modified silicone resin has a wider and better application range, which has been proved by the development trend.
The above is excerpted from a part of "Chapter 3 Silicone Coatings" in "Coating Technology" (Ju Zishan. Chemical Industry Press. ISBN7-5025-1434-1/TQ.786): If you can borrow This book may be of greater help to you;
To prepare silicone resin, two or more units are generally used for hydrolysis. The raw materials are given in the following article. Various monomers are hydrolyzed. Even if the formula is the same, due to different controlled hydrolysis conditions, the components of the intermediate products after hydrolysis and the amount of ring formation are often very different. The influence of various relevant factors during hydrolysis:
1. The influence of PH value of hydrolysis medium
(1) Acidic medium; (2) Neutral medium; (3) Alkaline medium;
2. The influence of the amount of water in the hydrolysis medium: During hydrolysis, the amount of water used is lower than the amount required for the reaction with chlorosilane, resulting in a gradual hydrolysis and polycondensation reaction, which limits the formation of ring bodies. The opposite is true for excess water hydrolysis.
3. The influence of adding solvent to the hydrolysis medium
4. The influence of the stirring speed of the equipment during hydrolysis
5. The influence of temperature during hydrolysis; When the temperature is higher, the component molecules move violently and the chances of collision with each other increase, which is conducive to the growth of polycondensation polymers. When the temperature is low, the opposite is true.
Factors related to formula formulation: According to different resin types, this factor is different, including:
(1) Average degree of substitution of hydrocarbon groups (D.S.); (2) Average quality ( Including SiOx, phenyl, methyl), after careful research experience by many chemists, there is a data range;
Modified resin: has the advantages of both resins, making up for the shortcomings of silicone resin , making it more suitable for coating application needs. Organic resins generally modified with silicone include: alkyd resin, polyester resin, epoxy resin, acrylic resin, polyurethane resin, phenolic resin, etc.;
Two methods of modification: cold spelling method (Physical method); Chemical method;
Progress in research on silicone coatings
Organic silicone is the first elemental organic polymer compound to be widely used because of its unique chemical structure With excellent performance, it is widely used in various fields of the national economy and also occupies a very important position in the coating industry. Silicone coating is a coating that uses silicone polymer or silicone modified polymer as the main film-forming substance. It has excellent heat and cold resistance, electrical insulation, corona resistance, radiation resistance, moisture and water resistance, weather resistance, Properties such as stain resistance and chemical corrosion resistance have been rapidly developed in product performance improvements and applications in recent years.
1 Silicone resin coatings Coatings made of silicone resins as film-forming substances mainly include heat-resistant and weather-resistant silicone anti-corrosion coatings, scratch-resistant transparent silicone coatings, release and moisture-proof coatings and radiation-resistant coatings Paints and other varieties.
Silicone resins for coatings are generally based on methyltrichlorosilane (CH3 SiCl3), dimethyldichlorosilane [(CH3)2SiCl2], phenyltrichlorosilane (C6H5SiCL3), diphenyldichlorosilane It is produced by hydrolysis and polycondensation of chlorosilane [(C6H5) 2SiCl2] and methylphenyldichlorosilane [CHO (C6H5) SiCl2] as raw materials. The monomer structure, number and proportion of functional groups have a great influence on the coating performance. The type of organic groups connected to the silicon atoms also affects the performance of the resin. Different organic groups can cause the silicone resin to exhibit different properties.
For example, when the organic group is a methyl group, it can impart thermal stability, mold release, hydrophobicity, and arc resistance to the silicone resin; when it is a phenyl group, it can impart oxidation stability to the silicone resin and can be destroyed within a certain range. The crystallinity of the polymer;
When it is vinyl, it can improve the curing characteristics of silicone resin and bring coupling properties; when it is phenylethyl, it can improve the bonding between silicone resin and organic matter. ***Mixed sex. The introduction of radicals into the main chain of siloxane can increase its compatibility with alkyd resins, polyester resins, etc.; the introduction of phenylene, diphenyl ether subunits, biphenyl subunits and other aryl subunits and silicon carbon boron Polymers have strong radiation resistance and temperature resistance up to 300-500°C; silicone polymers with a main chain structure of Si-N bonds have thermal stability above 400°C. In practical applications, different silicone monomers can be selected as needed to introduce different organic groups into the silicone resin.
Chenguang Chemical Research Institute uses hydroxyl silicone oil, (CH3)2SiCl2 and methyltriethoxysilane with a viscosity of 20-40mPa·s as raw materials, and controls nR/nsi to equal 1.3-1.4, (CH3) The mass ratio of 2SiCl2 to hydroxyl silicone oil is 7O:3O, and it is hydrolyzed by adding water dropwise at 50°C for 1 hour to obtain methyl silicone resin with good hardness and elasticity, which can be used to prepare flame retardant coatings for metal film resistors. . The Institute of Chemistry, Chinese Academy of Sciences, used CH3SiCl3 as the main raw material and acetone and xylene as solvents to synthesize a soluble trapezoidal polymethyl silicone resin with a narrow molar mass distribution. The resin was used to prepare a high-temperature anti-corrosion product with a certain amount of aluminum powder and room temperature vulcanized silicone rubber. The coating, after aging at 250°C for 1000 hours, has good flexibility, oil resistance and corrosion resistance. Hefei University of Technology uses four-functional silicate esters and three-functional alkyl siloxanes, and strictly controls the hydrolysis reaction to produce a base material that has the characteristics of both silicate and silicone polymers. This base material is similar to Pigments, fillers and other auxiliary materials can be made into silicone heat-resistant coatings according to a certain proportion.
2 Modified silicone resin coating Although silicone resin has many excellent properties, there are also some problems: it generally requires high temperature (150~200℃) for curing, which takes a long time to cure and is inconvenient for large-area construction; It has poor adhesion to the substrate, poor resistance to organic solvents, poor mechanical strength of the paint film at higher temperatures, and is more expensive. To overcome these shortcomings, organic resins are commonly modified with silicone resins. Modified silicone resin usually combines the advantages of both resins and can make up for some of the shortcomings in performance of the two resins, thereby improving performance and expanding application fields. There are two modification methods: physical mixing and chemical modification. The effect of chemical modification is generally better than physical mixing modification. Chemical modification mainly involves the introduction of active groups at the ends or side chains of the polysiloxane chain, and then reacts with other polymers to form block, graft or interpenetrating network polymers to obtain new properties. . In the coating industry, organic resins modified with silicone mainly include alkyd resins. Acrylic resin, epoxy resin, etc.
2.1 Silicone-modified alkyd resin coating
Silicone-modified alkyd resin coating retains the advantages of room temperature curing of alkyd resin paint and good physical and mechanical properties of the coating film , and has the characteristics of silicone resin with good heat resistance, UV aging resistance and water resistance. It is a coating with excellent comprehensive performance. The earliest modification method is to add the silicone resin directly to the alkyd resin reactor where the reaction has reached the end point; through such a simple mixing, the outdoor weather resistance of the alkyd resin is greatly improved. Another modification method is to prepare reactive silicone oligomers to react with the free hydroxyl groups on the alkyd resin; the silicone oligomers can also be used as polyols for polycondensation with the alkyd resin. . Alkyd resins modified through chemical reactions are more weather resistant.
Hunan University used a polycondensation reaction between a hydroxyl-terminated alkyd prepolymer made by alcoholysis method and a silicone prepolymer made by hydrolysis or heterofunctional group method to synthesize an (A-B) n-type silicone-alkyd structure. block polymer, and use the block polymer as the base material to make varnish; the varnish has excellent comprehensive properties, including room temperature curing, film flexibility, impact strength and adhesion of alkyd resin varnish. Focusing on the good advantages, it also greatly improves the performance of heat resistance, atmospheric aging resistance and water medium corrosion resistance.
2.2 Silicone-modified acrylic resin coating
Silicone-modified acrylic resin coating has excellent weather resistance. It has good gloss and color retention, is not easy to powder, and has good gloss; it is widely used in pre-coating of metal sheets, coating of machinery and equipment, and weather-resistant decoration and decoration of interior and exterior walls of buildings. Silicone-modified acrylic resins are available in two types: solvent-based and emulsion-based. Among them, silicone-acrylic latex paint has excellent weather resistance, stain resistance, and chemical resistance, and is an environmentally friendly green paint. Hubei University used a water-soluble free radical initiator, hydrogenated silicone oil and butyl acrylate as raw materials, and synthesized an excellent silicone/acrylate emulsion through emulsion polymerization; the emulsion has good acid and alkali resistance. It is resistant to high and low temperatures and electrolyte stability, and the coatings made with it have good weather resistance and stain resistance. Jinan Institute of Chemical Industry used acrylate monomers, D4 and vinyl heptamethylcyclotetrasiloxane as raw materials. By adding a certain amount of grafting agent, a stable polyacrylate-polysiloxane was synthesized by a one-time feeding method. Alkane complex emulsion. The Sichuan Provincial Institute of Building Materials Industry uses a pre-emulsification process to use active silicone oil and acrylate monomers for emulsion polymerization to obtain a silicone-modified acrylic emulsion. The paint coating prepared with this emulsion has good contamination resistance. Excellent overall performance.
Fudan University used silicone monomers containing vinyl functional groups and monomers such as methacrylate, acrylate, and hydroxyl acrylate through seed emulsion polymerization to obtain stable and excellent silicone modified silicone. Acrylic lotion. Zhejiang University uses silicone monomers to modify acrylic resin to produce silicone-acrylic latex paint. Chongqing University synthesized a polyorganosiloxane-polyacrylate interpenetrating network coating. The coating has the advantages of colorless transparency, high hardness, strong adhesion, resistance to acid settlement, heat aging resistance and good water permeability. It can be used as a friction material. Rock carved weatherproof material.
hh The silicone acrylic resin developed by the Shanghai Academy of Building Sciences is suitable for formulating high weather-resistant coatings with a weather resistance of more than 15 years. Hefei University of Technology reacted polysiloxane obtained by partial hydrolysis and condensation of ethyl orthosilicate with acrylic resin with hydroxyl group to prepare silicone graft-modified acrylic resin; the resin has excellent acid and alkali resistance, salt resistance, and solvent resistance. Compared with pure polysiloxane, its impact strength and impact strength are significantly improved, and its high temperature resistance is significantly improved compared to acrylic resin. Jiangsu Building Materials Research and Design Institute introduced a certain amount of silicone functional groups into the synthesis of acrylic resin to produce a solvent-based highly weather-resistant silicone-modified acrylic resin coating. The Lanzhou Institute of Chemical Physics of the Chinese Academy of Sciences used hydroxyl-terminated polydimethylsiloxane to perform solution polymerization with methacrylic acid (ester) monomers under the action of azobisisobutyronitrile to obtain modified silicone rubber. Acrylic resin, which has good heat resistance.
2.3 Silicone-modified epoxy resin coating
Using silicone to modify epoxy resin can not only reduce the internal stress of the epoxy resin, but also increase the toughness of the epoxy resin. , improve its heat resistance. The polydimethylsiloxane modified o-cresol novolac epoxy resin used by the Chinese Academy of Chemistry has greatly reduced its internal stress and greatly improved its anti-cracking index. Wuhan Material Protection Research Institute uses epoxy resin and reactive silicone oligomers with good miscibility to condense. The silicone-modified epoxy resin produced has the advantages of both epoxy resin and silicone resin. It not only improves the Heat resistance and good corrosion resistance. 2.4
Silicone-modified styrene-acrylic emulsion coating Modifying styrene-acrylic emulsion with silicone emulsion can significantly improve its weather resistance, gloss retention, elasticity and durability.
The silicone-modified styrene-acrylic emulsion synthesized by Shanghai University of Engineering and Technology through graft polymerization has the excellent properties of both silicone and acrylic resin. The coating film has good elasticity and its elongation at break is significantly higher than that of the styrene-acrylic emulsion coating film. . Shanghai Jiaotong University of Science and Technology added a certain amount of organosiloxane to the styrene-acrylic emulsion polymerization process to obtain an organosilicon-modified styrene-acrylic emulsion architectural coating. The coating has good water resistance and wash resistance. performance and durability.
2.5 Silicone-modified other resin coatings
Silicone-modified polyurethane coatings are widely used for the protection of aircraft skins, large storage tank surfaces, building roofs and cultural relics. The Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, used hydroxyl-terminated polydimethylsiloxane and alcoholylated castor oil-modified polyurethane prepolymer for mixed modification. The curing speed of the mixed mixture was improved. After film formation, The adhesion, hardness and heat resistance are also improved. The institute also uses silicone-modified urushiol resin as the base material to produce a coating that is resistant to boiling water and water vapor permeability, and can be used for long-term anti-corrosion of equipment. The Shanghai Institute of Architectural Research uses epoxy resin, acrylic resin, and silicone resin to introduce special hydrophilic functional groups into the main chain during polymerization to make water-soluble epoxy silicone acrylic resin. This resin has excellent physical and mechanical properties. , and has better aging resistance. Anti-ultraviolet and anti-corrosion properties; coatings made from this resin are basically non-toxic, easy to construct, have good overall performance of the coating film, and have good decorative effects. Chenguang Chemical Research Institute uses styrene, methyl methacrylate, acrylonitrile and silicone to polymerize, and develops an impregnating material for electronic devices.
3 Silicone-hardened wear-resistant coatings
Silicon-hardened coatings generally use silica sol as the Q-link component, and silicon-functional alkanes or carbon-functional silane as the Q-link component. The T chain segment component undergoes hydrolysis and partial polycondensation reaction in the presence of water, alcohol and acid catalyst to obtain a TQ silicone resin prepolymer solution containing silicone hydroxyl groups. By adjusting the variety of raw material RSi(OR')3 and the ratio with silica sol, the variety of additives, solvents, etc., hardened and wear-resistant coatings with various properties can be made. The viscosity of silicone hardened coatings is usually 4 to 25 m Pa·s, and the solid content is 20% to 30%. After it is coated on the surface of the substrate, the remaining silicone hydroxyl groups condense under heating conditions to form a hardened wear-resistant layer with a network structure.
Silicone hardened wear-resistant coatings are superior to UV-cured acrylic resin hardening coatings in terms of wear resistance and weather resistance. Transparent plastics treated with silicone hardened coatings have been widely used as eyeglass lenses, automobile headlight covers, instrument scales, optical disks, and window glass for special buildings.
4 Conclusion
With the in-depth research, development and improvement of new materials, the performance of silicone coatings will become even better to meet the different needs of different industries or fields. With the improvement of people's living standards and the increasing requirements for the beautification of homes and buildings, silicone coatings have broad application prospects in the decoration of buildings due to their excellent weather resistance and stain resistance; and, as people With the increasing awareness of environmental protection, silicone coatings will develop in a pollution-free, green and environmentally friendly direction.