Recently, the H&C Polymer Research Center in Yong'an City, Fujian Province, has made new progress in the study of UV-curable epoxy acrylic coating resins, particularly in terms of the influence of parameters on performance. Experiments were conducted to determine the effect of catalyst selection, dosage, and mode of addition. Among them, the choice and amount of catalyst: Currently used catalysts are mainly tetrabutylammonium bromide, SA230, modified SA230 (ciba), N,N-dimethylbenzylamine, triethanolamine, P115 and other active amines. . In this experiment, tetrabutylammonium bromide was used as a catalyst. The amount of tetrabutylammonium bromide used was 1% (mass fraction). The reaction time was 5-6 hours. The appearance of the obtained product was satisfactory. The catalyst addition method: catalyst and acrylic acid were first used. Mixing evenly and then dropping it into the epoxy resin (E-44) helps to improve the appearance of the epoxy acrylate. The resulting epoxy acrylate resin is clear, transparent, and pale yellow. In order to determine the optimal reaction temperature, the researchers measured the acid value of the reaction system at different temperatures and plotted the scatter plots of ln(lp) and reaction time t. The effect of temperature on the reaction rate is great. The higher the temperature, the faster the acid value decreases, the higher the conversion rate of acrylic acid per unit time, and the lowering rate of acid value at 110°C is significantly faster than the other two temperatures. Although the higher temperature can increase the reaction rate, due to the presence of a large amount of acrylic active material in the reaction system, higher temperatures (≥120° C.) will cause the self-aggregation of acrylic monomers. The optimal reaction temperature is 110°C. The type and amount of inhibitors also have an effect. The reaction temperature is high during the preparation of the epoxy acrylate, and an appropriate amount of polymerization inhibitor needs to be added. However, the polymerization inhibitor develops color due to oxidation at a higher temperature and affects the appearance of the product. Common inhibitors are p-hydroxyanisole and hydroquinone. The greater the functionality of the reactive diluent, the shorter the curing time, and the lower the adhesion of the coating film. This is due to the increase in the functionality of the reactive diluent resulting in an increase in the curing rate and an increase in the crosslinking density under the same amount of conditions. , The volume shrinkage also increases. In order to improve the overall performance of the coating, shorten the curing time, and reduce the shrinkage of the coating, a mixed system consisting of monofunctional, difunctional, and trifunctional reactive diluents should be used. To determine the effect of photoinitiators, the researchers used benzophenone and benzoin ethyl ether as photoinitiators to determine the effect of different amounts on the curing time. The coated substrate was a slide and the light source was a 1000W medium-pressure mercury lamp. The lamp distance is 15cm, and the coating thickness is 40~60um. The effect of benzophenone and benzoin ethyl ether on the curing time is different. With the increase of the amount of benzophenone, the curing time is shortened and the shortening rate is getting smaller and smaller. When the amount exceeds 5%, the curing time increases again. In large quantities, the curing time is almost unchanged. With the increase in the amount of benzoin ether, the curing time is gradually reduced. However, the extent of shortening is almost unchanged. Experiments with the effect of accelerators have shown that the relationship between the amount of different triethanolamines and the curing time is obvious, triethanolamine has different promoting effects on benzoin ethyl ether and benzophenone; the effect of triethanolamine on benzophenone is approximately linear; The effect on benzoin ether is completely non-linear. The reason is that when benzoin ethyl ether is used, triethanolamine is promoted by consuming oxygen on the surface of the coating to reduce the inhibitory effect of oxygen, thereby indirectly increasing the priming efficiency of benzoin ether; when benzophenone is used, The promotion is mainly achieved through direct participation in the production of active free radicals. Finally, the researchers measured the impact of the substrate. After the surface slides, wood and tinplate were used as substrates, respectively, the coating film curing time was determined. According to experts, the formula is epoxy acrylate: ethylene glycol diacrylate (DA): hydroxyethyl acrylate/hydroxypropyl acrylate mixture (HEP): benzoin ether: benzophenone=100:40:10: 4:2, the coating thickness is 40 ~ 60um. Under the same conditions, the use of glass slides and tinplate as the substrate, the coating curing time is shorter than the wood. This is mainly due to the difference in UV radiation reflectance caused by different substrates, resulting in the difference in absorption of UV radiation energy by the coating film.
Compared with traditional solvent-based coatings, UV-curable coatings have the outstanding feature of not containing organic solvents (low VOC emission) and rapid curing. The inert diluents used in the process have minimized the pollution to the environment during use, and Without heating and curing, it has the characteristics of low energy consumption, high efficiency, low shrinkage, good chemical stability, and wide applicability, making it more and more widely used in the surface coating treatment of high-grade printed matter and plastic products. In recent years, with the deepening of its research, UV-curing coatings have also been applied to the fields of wood, metal decoration, electronic component manufacturing, optical fiber coating and bonding, and leather covering. Ultraviolet curing technology has been increasingly applied. Pay attention.
The researchers used epoxy resin (E-44) to react with acrylic acid, using tetrabutylammonium bromide as a catalyst to prepare an epoxy acrylic prepolymer, and regarding the catalyst, reaction temperature, and polymerization inhibitor to synthetic epoxy acrylate. Effects, as well as the effect of different reactive diluents, photoinitiators, accelerators, and substrates on coating film performance are discussed. They first prepared an epoxy acrylic resin by adding a certain amount of epoxy resin and a polymerization inhibitor to a three-necked flask, raising the temperature to 110° C., and adding dropwise a mixed solution of tetrabutylammonium bromide and acrylic acid to control the drop. Acceleration was completed within 30 minutes and the reaction was maintained until the acid value of the system did not exceed 8 mg KOH/g. Subsequently, the prepared epoxy acrylate and epoxy resin were coated on the KBr sample, and the FTIR analysis was performed using a WQF-310 Fourier infrared spectrometer. The sample to be tested was coated on the KBr sample, and the standard plastic bag was placed thereon ( Nitrogen is filled in PET and irradiated with UV light (lamp distance 15cm) at different time intervals at room temperature. Three to five samples are tested at each time point for averaging. C=C specific absorption peak (1640cm-) Absorption intensity is reduced to determine the degree of curing of the curing system.
Source: Coatings Industry Channel
New developments in UV-cured epoxy acrylic coatings