Industrial additives: Acrylic resin fluorination modification and application

Acrylic resin is copolymerized from (meth)acrylates and other vinyl monomers. Acrylic resin has light color and good transparency; it has strong weather resistance, is resistant to ultraviolet light irradiation and is not easy to decompose or turn yellow, and has good gloss and color retention; it does not decompose or discolor at 170 ℃, and does not discolor at around 230 ℃ or higher. Still does not change color. Acrylic resin coatings have good resistance to contamination and corrosion from chemicals such as acids, alkalis, salts, greases, detergents, etc., as well as excellent construction performance. Acrylic resin coatings are the mainstream products in industrial coatings, and the largest market is car coatings.

In addition, acrylic resin coatings are widely used in light industry, home appliances, metal furniture, aluminum products, coil industry, instrumentation, construction, textiles, plastic products, wood products, It is widely used in papermaking and other industries. Acrylic resin has become one of the backbone resins in my country’s coatings industry. Although acrylic resin has many of the above advantages, making it widely used, its performance still does not meet people’s expectations. For example, the critical surface tension of acrylic resin is a medium-to-high value among coating resins, reaching 41 mN/m, which is much higher than that of fluorocarbon resin (such as the critical surface tension of polytetrafluoroethylene is mN/m). It has poor water and oil repellency and is anti-corrosion. The performance is not strong and the weather resistance is far inferior to that of fluorocarbon resin. Modification with fluorine materials, hoping to further improve the quality of acrylic resin and continue to expand its uses, is one of the important topics in the coatings research community. This article introduces some progress in research in this area.

Technical route based on fluoroalkyl alcohol (meth)acrylate

Fluoroalkyl alcohol acrylic resin synthesis

The molecular formula of fluoroalkyl (meth)acrylate: RfOOC—C(R1)=CH2 (1) In the formula, R1 is H, —CH3; Rf It is a fluorinated alkyl group with 1 to 20 carbon atoms.

Fluoroalkyl (meth)acrylates have higher polymerization activity than the corresponding (meth)acrylates. Based on it and other non-fluorinated acrylates or methacrylates, styrene, acrylonitrile, vinyl acetate, vinyl chloride and other monomers to prepare copolymers, initiated by peroxides or azo compounds, using solutions or emulsions The polymerization method performs free radical polymerization under normal pressure, which is easier to achieve than the polymerization or copolymerization of ordinary (meth)acrylate and vinyl monomers.

Performance improvements

Fluorinated (meth)acrylate polymer can be expressed by formula (2): Compared with the corresponding (meth)acrylate homopolymer, its thermal The performance, mechanical properties, surface properties, and optical properties have been significantly improved, especially the critical surface tension has been greatly reduced. Depending on the composition of R1 in the molecule, the critical surface tension of the resin has been reduced to a minimum of 10.2 mN/m (see Table 1), which is The anti-sticking and anti-fouling properties of coatings provide a large room for improvement.

Critical Surface Tension of Fluorinated Acrylic Ester Polymer (γc) Table 1 Critical Surface Tension of Fluorinated Acrylic Ester Polymer (γc) mN·m-1 No. R1 R2 H —CH31CH3———15.5 15.54H(CF2)2CH2—20.4 5n-C3F7CH2——(CF2)8CH2—17.016.6 8 H(CF2)6CH2— The solubility of fluorinated modified acrylic resin is reduced, but it is The solubility of fluorinated (meth)acrylate and non-fluorinated acrylate monomer copolymer resin will be greatly increased, close to the solubility of ordinary acrylate copolymer, and the introduced F—C bond can have an impact on the resin performance. Significant improvement.

Application

Select fluorinated acrylate or fluorinated methacrylate monomer and hydroxyl-containing acrylate and other acrylate or vinyl monomers to make hydroxyl type Fluorinated acrylic copolymer resin can be cross-linked and cured with polyurethane curing agent at room temperature, or thermally cross-linked and cured with amino resin. As mentioned above, the stain resistance, weather resistance and optical properties of acrylic resin have been significantly improved, and the application fields of acrylic resin coatings have been expanded. Due to their good optical properties, fluorinated acrylate polymers can be used to produce special coatings such as radiation-curable coatings, optical fiber coatings, and fighter windshield coatings.

Alkyl alcohol synthesis

The synthesis process of the basic monomer fluoroalkyl alcohol used is relatively complex, using perfluoroalkyl iodide and tetrafluoroethylene (TFE) produced by the telomerization method as raw materials The synthetic route is an example[3]:

CF3CF2I ——→CF3CF2(CF3CF2)nI ——→ CF3CF2(CF2CF2)nCH2CH2I

(3) In formula (3), (A) can be hydrolyzed under the action of fuming sulfuric acid to form perfluoroalkylethyl alcohol CF3CF2(CF2CF2)nCH2CH2OHReducing the critical surface tension of acrylic resin, improving its water and oil repellency, and improving anti-corrosion performance and weather resistance are one of its important research topics.

(2) Fluorinated acrylic copolymer resin based on perfluoroalkyl alcohol (meth)acrylate, which significantly improves the heat resistance and mechanical properties of the coating film Performance, surface properties, optical properties, especially the critical surface tension are greatly reduced. It shows good prospects for improving the grade of acrylic resin and expanding its application fields. Fluorocarbon surfactant is a special surfactant with “three highs” and “two hates” and has an irreplaceable role as ordinary hydrocarbon surfactants. The basic monomers used in the above two new varieties – perfluoroalkyl alcohols and fluorocarbons containing 6 to 10 carbon atoms, both have complex synthesis processes, high costs, and the production of banned perfluorooctyl derivatives. affect its promotion and application.

(3) Use tetrafluoropropionic acid and prefabricated hydroxyl-containing acrylic copolymer to directly esterify to synthesize fluorinated acrylic resin. The fluorine content is above the water resistance of the coating. The improvement is very obvious. In addition, the amino resin curing agent used is more than half less than that of traditional amino acrylic resin paints, so there is more room for adjustment of paint performance. By increasing the amount of polyol in the polyester resin and directly esterifying it with tetrafluoropropionic acid, the fluorine content can be introduced according to the need to improve performance, and the polyurethane curing agent is used for cross-linking and curing at room temperature, which has great potential application prospects. The same direct esterification process of tetrafluoropropionic acid is used to synthesize fluorinated acrylic polymer surfactant. Trials in epoxy, alkyd, powder and other coatings have proven that it has good wettability and leveling properties, and improves coating film properties. The technical route of direct esterification of tetrafluoropropionic acid has a simple process, easy availability of raw materials, and avoids the production of prohibited by-products. It is a technical route worthy of in-depth study.