Research and application of the hottest UV curing

Research and application of UV curing adhesive

Abstract: This paper introduces the chemical principle, raw materials and equipment of UV curing adhesive. The action principle and characteristics of photoinitiator, monomer, prepolymer and main additives were discussed. At the same time, the current situation and development of this field are briefly introduced

key words: UV curing, adhesives

preface

UV (UV) and electron beam (EB) curing belong to the category of radiation curing, which has the characteristics of fast, simple, environmental protection and high efficiency. Among them, UV curing technology has been widely used in the coating and printing industry. In recent years, more and more attention has been paid to the application of UV curing technology in adhesives

uv curing adhesive has the following characteristics: 1. It can be cured quickly at room temperature, and the curing time can be controlled from a few seconds to more than ten minutes; 2. The curing process is easy to operate and control and has higher thermal insulation performance, and can be partially cured; 3. One component is solvent-free, meeting the requirements of environmental protection. Therefore, although the development of UV curing adhesives started later than other adhesives, their applications in electronic industry, communication and information industry, optical instrument manufacturing industry and process product production are gradually increasing. Especially in developed countries, the development and application of this kind of adhesives are driven by the efficient and automatic production process and the practicality of a variety of miniaturized UV curing devices

1 basis of UV curing adhesive

1.1 curing principle

in UV curing adhesive, the photoinitiator reaches the excited state after being irradiated by UV light. The initiator molecule indicates that the cracking or hydrogen transfer of the force measuring piston should be replaced to produce active free radicals. These free radicals initiate the alkene bond in acrylate to produce new free radicals (Fig. 1), making the whole system produce free radical chain polymerization

1.2 raw materials and equipment

uv curing adhesives are generally composed of light curing prepolymers (25-90wt%), monomers (15-60%), photoinitiators (1-3%) and other additives, and sometimes sensitizers are used together with photoinitiators to improve the curing efficiency. This kind of adhesive solidifies quickly and simply under the irradiation of ultraviolet light source

1.2.1 photoinitiators

there are many kinds of UV photoinitiators. Aromatic carbonyl compounds are widely used and have good effects, mainly phenyl ketone compounds, such as benzoyl, benzophenone, benzoin and its ether derivatives. According to the mechanism of free radical generation, these initiators can be divided into cracking type and hydrogen transfer type (Fig. 2). Cracking type is more commonly used

benzoin produces two free radicals after photodegradation, and the two primary free radicals can initiate monomer polymerization, but if the primary free radicals diffuse too slowly, it will lead to their coupling and reduce the initiation efficiency. Benzoin has strong intramolecular hydrogen bonds. The results showed that the rate of photodegradation could be increased by etherifying the hydroxyl group of benzoin and destroying the intramolecular hydrogen bond. For example, methyl ether in benzoin tends to increase the light curing rate by about 2 times than benzoin. It should be pointed out that the storage stability of benzoin methyl ether is poor, so in order to obtain better activity and long service life, it is appropriate to use benzoin isopropyl ether

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