Preparation and Application of Matting Epoxy Acrylic Resin

Preparation and Application of Matting Epoxy Acrylic Resin

[Introduction]

Epoxy acrylic resin is a kind of acrylic polymer containing epoxy groups [1], which mainly refers to the copolymerization of (methyl) glycidyl acrylate, acrylic ester, methacrylate and other monomers containing olefin. This kind of resin is widely used in powder coatings as the main resin of the system, epoxy acrylic resin and additives [2-3]. Due to the special structure of epoxy acrylic resin, the coating film prepared by this type of resin has the advantages of excellent adhesion, light preservation and yellow degeneration resistance [4-6].

Epoxy acrylic resin in the current market is generally made of acrylic ester, methyl acrylate ester and glycidyl methyl acrylate through copolymerization by free radical polymerization. However, the resin used in powder coating extinction system has some problems such as uneven reactivity, poor extinction stability and poor film surface fineness. In order to overcome the shortcomings of traditional resins, this paper introduced glycidyl acrylate monomer [7] with higher reactivity and better flexibility than glycidyl methacrylate, and copolymerized with methyl methacrylate and other special functional monomers in the isopropyl alcohol system to obtain epoxy acrylic resin with outstanding fading performance.

[Part I :Experience]

1.1 Main raw materials

Butyl acrylate, methyl methacrylate: Industrial grade, Shanghai Huayi Acrylic Acid Co., LTD. Isopropyl alcohol, α-methyl styrene: Chemical pure, Sinopharm Chemical Reagent Co., LTD. Polyester SJ5122: Industrial grade, Anhui Excalibur Co., LTD. Polyester GH2209: Industrial grade, Zhejiang Guanghua Technology Co., LTD. Polyester CC2441: Industrial grade, Zhanxin Resin (China) Co., LTD. Polyester P9336: Industrial grade, Hangzhou Zhongfa Industrial Co., LTD. Polyester SJ4#ET: Industrial grade, Anhui Excalibur Co., LTD. Barium extinction: Industrial grade, Qingdao Hongdie New Material Co., LTD. TiO2: Industrial grade, Sichuan Longpython Group Co., LTD. HA501, HL701, HL988, TGIC, epoxy acrylic resin, glycidyl acrylate: industrial grade, Huangshan Huahui Technology Co., LTD. Azodiisobutyronitrile: Chemical pure, Sinopharm Chemical Reagent Co., LTD.

1.2 Instruments and equipment

Infrared spectrometer: Nicolet 380, Nicolet Instrument Corperation; Twin-screw extruder: ZLJ-33, Taizhou Manxin Machinery Technology Co., LTD. Blast oven: LC-223, Shanghai Aspec Environmental Equipment Co., LTD. Gloss instrument: BYK4561, Germany Wacker Chemical Co., LTD.

1.3 Synthesis of epoxy acrylic resin

1.3.1 Monomer mixing

According to the formula amount, α-methylstyrene, methyl methacrylate, butyl acrylate, glycyl acrylate (GA), initiator and isopropyl alcohol were added into the reaction bottle successively, stirring evenly at room temperature, and then added into the drip funnel for use.

1.3.2 Synthesis reaction

Appropriate amount of solvent was added into the four-orifice flask, and the temperature was raised until the solvent reflow. When the reflow was stable, the mixed monomer in the constant pressure dropper funnel obtained in the previous step was dropped into the reaction kettle, the adding speed was controlled, and the mixed monomer was added evenly within 4h, and then reacted at the reflux temperature for 1h to ensure the complete reaction of the mixed monomer.

Isopropyl alcohol was added to the four-neck flask, and the temperature was raised to the reflux temperature of isopropyl alcohol. Then, the mixed material in the drip funnel was gradually added to the reaction flask for polymerization, and the drip was controlled to finish in about 4h. The reflux reaction was continued for 1h to complete the reaction.

1.3.3 Distillation cooling

After the solvent and other small molecules are fully removed by distillation, the volatile content is controlled within 1%, the discharge is cooled and broken to obtain colorless transparent epoxy acrylic resin particles.

1.4 Film preparation

The base material is tinplate, which is processed by sandpaper grinding, cleaning and drying before electrostatic spraying.

120g epoxy acrylic resin was mixed evenly with 480g polyester, 42g TGIC, 200g TiO2, 140g matting barium, 10g leveling agent and 5g brightening agent. The product powder coating was extrusion-melted and crushed by twin-screw extruder, then powdered and screened by grinder to produce the finished powder coating. Finally, the sample was produced by electrostatic spraying. Put it in the oven for full curing at 200℃/10min.

1.5 Performance testing

The coating sheen (60°) test was carried out according to GB/T9754 -- 2007; Impact performance tests were carried out according to standard GB/T1732 -- 1993. Gumming time (s) was tested according to GB/T16995 -- 1997; Stream leveling is performed according to PCI standards.

[Part II :Results and Discussion]

2.1 Research on the optimal usage of epoxy acrylic resin

For matte or matte powder coatings, epoxy acrylic resin has an optimal usage. According to the extinction effect, surface properties, etc., different amounts of epoxy acrylic resin were optimized and compared. The results are shown in Table 1.

As shown in Table 1, the variation rule of the addition amount of epoxy acrylic resin prepared in this study and the film gloss. When the addition amount of epoxy acrylic resin in the formula is more than 12%, the increase of the matting effect is not obvious, and the phenomenon of poor curing performance appears, which may be the reason for the poor mechanical properties of epoxy acrylic resin itself. When the amount of epoxy acrylic resin is less than 8%, the extinction effect and surface properties become worse. Therefore, according to the different film luster, the recommended range of epoxy acrylic resin use is 8%~12%.

2.2 Analysis of selectivity of epoxy acrylic resin to polyester

As shown in Table 2, the type of polyester has a great influence on the extinction property of epoxy acrylic resin, and the better the resin activity, the worse the extinction effect. Similar conclusions are also reflected from the comparison of the length of gelation time. For the same type of polyester, the greater the change of gelation time, the better the extinction effect. SJ5122 polyester is a special polyester for HAA, and the curing reaction rate with TGIC is slow, but the effect is significantly more, which further indicates that the reactivity of polyester has a great influence on the matting effect of epoxy acrylic resin, which can be referred to when choosing polyester in formula.

2.3 Study on extinction properties of different epoxy acrylic resins

The same type of epoxy acrylic resin products in three markets were selected for comparison, and SJ4ET, which is widely used in the market, was selected for polyester test. Other conditions remained unchanged, and the results were shown in Table 3.

As shown in Table 3, there are obvious differences among different epoxy acrylic resins. Among the four samples, the epoxy acrylic resin prepared in this article one has the best extinction effect and surface; epoxy acrylic resin B has poor extinction performance; epoxy acrylic resin A and epoxy acrylic resin C have little difference, but both are slightly worse than the epoxy acrylic resin prepared in this article. It may be caused by the difference in the formulation composition and preparation process of epoxy acrylic resin products. Therefore, the extinction effect and surface properties of epoxy acrylic resin synthesized in this article are better than those of other three different manufacturers in the market.

2.4 Research on curing temperature sensitivity of epoxy acrylic resin

Curing and extinction properties of epoxy acrylic resin in powder coatings are greatly affected by baking temperature. The extinction sensitivity of epoxy acrylic resin under different curing temperatures of 180℃, 200℃ and 230℃ is studied, and the results are shown in Table 4.

As shown in Table 4, curing temperature has a significant impact on the extinction effect of epoxy acrylic resin, the higher the curing temperature, the better the extinction effect, and the performance of products from different manufacturers is more consistent. However, when curing at 180℃, the curing and mechanical properties tend to decrease significantly, so it is not recommended to use this temperature for curing. At the same time, considering the adverse phenomena such as film yellowing caused by high temperature, the more suitable curing temperature is preferably 200℃.

2.5 Infrared spectrum analysis

Figure 1 is the infrared spectrum of epoxy acrylic resin, from which it can be seen that 1636cm-1, 1487cm-1 and 1703cm-1 are the characteristic absorption peaks of benzene ring. 1730cm-1 is the tensile vibration absorption peak of C=O, and the characteristic absorption peak at 908cm-1 and 843cm-1 also indicates that the epoxy group has been successfully introduced into the epoxy acrylic resin.

[Part III:conclusion]

In order to obtain the excellent performance of the extinction type acrylic resin, using azodiisobutyronitrile as initiator, methyl methacrylate, α-methyl styrene monomer copolymerization in isopropyl alcohol to obtain epoxy acrylic resin. The application test results show that the epoxy acrylic resin has excellent extinction performance, the gloss can reach 3.9%, and other coating properties can meet the application requirements, the comprehensive performance is better than the main products on the market at present. The epoxy acrylic resin prepared in this paper is of great significance to promote the development of powder coating industry extinction products.

References:

[1] Dan Mingwei, Zheng Yaping. Study on acrylic resin for powder coating [J]. Coating Industry, 2002,(12):7-10.

[2] Zhang Huadong. Powder coating additives I- leveling agent, degasser, texturing agent, epoxy acrylic resin [J]. Coating and Electroplating, 2008 (6) :8-13.

[3] Wen Wen. Preparation and Properties of acrylic powder coating [D]. Xiangtan University, 2016.

[4] Qin Chuanxiang, Qin Zhizhong. Preparation and properties of acrylic powder coatings [J]. New Chemical Materials,2006,34(10):70-72.

[5] Xu Nan, Liu Yakang. Impact resistance of acrylic powder finish Varnish [J]. Coating Industry,2005, 35(4):21-25.

[6] LV Qingfa, Fan Xiaodong, Qin Huayu. Research progress of acrylic powder coatings [J]. Coating Industry, 2002, 32(3):34-37.

[7] Liu Yakang. Synthesis of glycidyl acrylate [J]. Journal of Beijing University of Chemical Technology,1999,22(3):21-25.