Composition IV of the hottest UV curing adhesive

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Composition of UV curing adhesive (IV)

1.3.2 free radical photoinitiator the function of photoinitiator is to produce free radicals after it absorbs UV light energy, so as to initiate unsaturated bond polymerization in the system, crosslink and cure into a whole. The commonly used free radical photoinitiators include cracking type and hydrogen extraction type

1) pyrolysis photoinitiator

pyrolysis photoinitiator mainly includes benzoin ethers (benzoin ethers), benzophthalein ketals and acetophenones. The splitting photoinitiator splits evenly after absorbing ultraviolet light, producing two free radicals, which initiate the polymerization of unsaturated groups

recently, Ciba and other companies have developed a new photoinitiator: acyl phosphine oxides, such as Bapo, 819 and Tim, also belong to cracking photoinitiators. The molecular formulas are as follows:

acyl phosphine oxide photoinitiator has a bright light in the near ultraviolet region, has high initiating activity, good heat and water stability, and has photobleaching effect, which is conducive to deep curing, and the cured product does not turn yellow. It is suitable for thick colored photosensitive coatings, especially to solve the problem that LT and V white coating system is difficult to cure under ultraviolet light and the coating is easy to turn yellow. Bapo can produce four free radicals after decomposition, which has high initiation efficiency. Its mechanism is as follows:

2) hydrogen extraction initiator

hydrogen extraction initiator mainly includes benzophenones and thioxanthones. Among them, the maximum absorption wavelength of thioxanthone photoinitiators in the near ultraviolet region is nm, and they have strong absorption capacity and hydrogen abstraction ability, so they have high initiation efficiency

hydrogen extraction initiators must have hydrogen donors as synergistic components, otherwise, the initiation efficiency is too low to be applied. Triplet free radicals are more likely to extract hydrogen from the third carbon of the hydrogen donor molecule than from the second carbon or methyl. Hydrogen attached to heteroatoms such as oxygen or nitrogen is easier to extract than hydrogen on carbon atoms. Such amine donors include amine, alcohol amine (triethanolamine, methyldiethanolamine, triisopropanolamine, etc.), mercaptan, michinone, etc. When michinone and benzophenone are used together, a cheap and effective initiator system can be obtained. Taking benzophenone as an example, its chemical reactions are as follows:

1.3.3 ionic photoinitiators

1) aromatic sulfonium salts and iodonium salts

such initiators have excellent high-temperature stability and also have stability after being combined with epoxy resin, so they are widely used in cation immobilization systems. However, their longest absorption wavelength is in the far ultraviolet region, and there is no absorption in the near ultraviolet region. Generally, photo sensitizers such as free radical initiators (irgacure 117, 3184 and itx) or photosensitive dyes should be added for sensitization

2) ferrocene salt

ferrocene salt photoinitiator system is a new cationic photoinitiator developed after diaryl iodonium salt and triaryl sulfonium salt. Under light, ferrocene salt ions first form aromatic ligands, and at the same time produce unsaturated iron complexes coordinated with an epoxy molecule. This complex has the characteristics of Lewis acid, and then forms complexes coordinated with three epoxy molecules, One of the epoxy compounds can open the ring to form cations, which can initiate cationic ring opening polymerization to form polymers. At room temperature, because the ferro epoxy complexes and cationic active species of epoxy compounds in the electric power system of Ermo new energy vehicles are more than those of traditional vehicles, it takes time to form, so it needs external heating to improve the polymerization speed

1.4 other additives

the main functions of additives are:

① improve the production process of adhesives

② improve the storage stability of adhesive

③ improve the workability of adhesive

④ improve the performance of adhesive film, etc

The additives of UV curing adhesive mainly include stabilizer, leveling agent, defoamer, plasticizer and coupling agent

1.4.1 stabilizer

stabilizer is used to reduce polymerization during storage and improve the storage stability of resin. Common stabilizers include hydroquinone, p-methoxyphenol, p-benzoquinone, 2,6-DI-TERT-BUTYL cresol, phenothiazine, anthraquinone, etc

1.4.2 leveling agent

leveling agent is used to improve the leveling performance of resin, prevent the formation of coating defects such as shrinkage and pinhole, make the film smooth and improve the gloss. Mixed solvents, silicone, polyacrylate, acetate butyric acid fiber, nitrocellulose and polyvinyl butyral are all effective leveling agents

1.4.3 defoamer

defoamer is used to prevent and eliminate bubbles in the manufacturing and use process of the coating, and to prevent pinpricks and other defects in the coating. Phosphate ester, fatty acid ester and organosilicon can be used as defoamers

1.4.4 plasticizer

linear macromolecules have interaction force, which comes from van der Waals force and hydrogen bond, and its size is related to the structure of the polymer. This interaction will affect many properties of polymers. The role of plasticizer is to weaken the force between polymer molecules, so as to improve the flexibility of the glue, relax the internal stress, and improve the impact strength of the glue; Reduce the softening temperature and glass transition temperature of the adhesive film and improve the low temperature resistance; Reduce the viscosity of the polymer and increase its fluidity, so as to increase the infiltration of the adhesive on the bonding surface and improve the bonding strength of the joint

1.4.5 coupling agent

coupling agent is a kind of substance with amphoteric structure. Some groups in their molecules can react with chemical groups on the surface of inorganic substances to form strong chemical bonds; The other part of the group has the property of organophile, which can react with organic molecules or physically entangle, so as to firmly combine the two materials with different properties and sizes. At present, the coupling agents used in industry are divided into silane, phthalate, zirconium and organic chromium complexes according to their chemical structures. Silane is widely used in UV curing adhesives, such as γ- Propionacetyl trimethoxysilane methacrylate (KH-570), γ- Aminopropyl triethoxysilane (KH-550), etc

in a word, at present, the research of UV curing technology has received widespread attention, its rapid development has also attracted the attention of all industries, and has made remarkable achievements in development and application. Among them, UV curing adhesives have also made breakthroughs, and now they have been used in various fields, such as medical and health care, aviation, electronic assembly, printing, optical instruments, packaging, information, national defense and military industry, glass products, craft products and daily life. In the 21st century, with the enhancement of people's awareness of environmental protection and energy conservation, UV curing adhesive technology, a green industrial product, will surely achieve greater development

however, at present, the research, development and application of UV curing adhesives in China are still relatively backward

1) among hundreds of adhesive production units in China, only a few companies produce UV curing adhesives. Although there are some research reports in the literature, few companies are truly industrialized. Therefore, its industrialization process needs to be developed and studied, and the production scale needs to be expanded

2) the research of UV curing adhesive in China started late, so there is a big gap between China and foreign countries in the fields of research, development, production, application and so on. Therefore, it is necessary to strengthen the research and development in this charming field

source: fine chemicals in the 21st century

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