Composition of UV curing coating and its industria

2022-06-23
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UV curing is a kind of radiation curing technology and a rapidly developing "green" new technology. UV curable coating (UVCC) is an energy-saving and environment-friendly coating developed in the 1960s. After UV irradiation, it will undergo photochemical reaction, and the liquid oligomer (including monomer) coating will be instantly formed into a solid coating through cross-linking polymerization. UVCC can be widely used and developed because it has the unique advantages of energy saving and environmental protection, excellent coating performance and high production efficiency

cc composition

uvcc is mainly composed of crosslinkable prepolymer (photoactive oligomer), active diluent (photoactive monomer), photoinitiator, auxiliary (leveling agent, defoamer, matting agent, surface smoothing agent). Their performances and research progress are as follows

1.1 oligomer

oligomer is one of the components with the largest proportion in UV curing products. It is the base resin of UV curing formula and determines the basic properties of cured products (including hardness, flexibility, adhesion, optical properties, aging resistance, etc.). It mainly includes unsaturated polyester resin, epoxy acrylate, polyurethane acrylate, polyester, and acrylated polyacrylate. In the late 1930s, unsaturated polyester resin was first developed as a UV curing oligomer. Epoxy acrylate is a kind of light curing oligomer, which is prepared from commercial epoxy resin and acrylic acid or methacrylate. It is the largest consumption in the domestic light curing industry at present. Its chemical corrosion resistance, strong adhesion and good wettability to pigments make it widely used in paper coatings, wood coatings and metal primers

in order to highlight the performance advantages of oligomerization field, there are many studies on its modification at home and abroad, such as amine modified epoxy acrylate, introducing quaternary amine group. Its main characteristics are high curing speed, increased adhesion of cured film, and enhanced toughness. Therefore, it has important application value in screen printing, lithography and flexo printing inks. In addition, there are phosphate ester modification, polybasic anhydride modification, siloxane modification, long-chain fatty acid modification of epoxy acrylate, etc. The application of polyurethane acrylate is second only to epoxy acrylate, especially in the light curing finishing of paper, leather, fabric and other soft substrates. However, due to its slow curing and relatively high price, it is less used as the main oligomer in the UV curing formula, but as an auxiliary functional resin

at the end of 1980s, oligomers, i.e. non acrylate oligomers, which were cured by cationic mechanism such as vinyl ether series and epoxy series, emerged. The curing of these oligomers was not affected by the polymerization inhibition of oxygen in the air, and the curing speed was fast and developed rapidly. Hybrid oligomers with acrylate group and ethylene group have been synthesized. With the continuous development of UVCC and the enhancement of people's awareness of environmental protection, various water-based oligomers continue to appear. This paper reports unsaturated polyester used in UV curable waterborne coatings. Phifips et al reported that polyester acrylates synthesized with different polyols and polybasic acids believed that in order to obtain good water solubility, there must be at least 6% ~ 7% hydrophilic groups with a relative molecular weight of, and the cured products have good solvent resistance and water resistance

1.2 photo active monomer

traditional solvent based coatings usually need to add organic solvents to adjust the viscosity. These organic solvents generally do not participate in the film-forming reaction. Volatilizing into the air during the film-forming process will cause special rock wool spraying insulation coating and environmental pollution. In the UV curing system, the photo active monomer (active diluent) not only plays a role in regulating the viscosity of the system, but also usually participates in the curing film-forming reaction, rarely volatilizes into the air, giving the system environmental protection characteristics. According to the reactive groups contained in the molecules, active diluents can be divided into monofunctional and multifunctional active diluents. Young studied the effect of functionality on the polymerization rate. The results showed that the greater the functionality, the faster the curing rate and the higher the crosslinking degree. This was used to evaluate the pendulum impact properties of the films

currently, the most widely used active diluents are (meth) acrylates, which have developed into the third generation of active diluents with the advantages of high reactivity and low shrinkage

1.3 photoinitiator

photoinitiator is the key component of UVCC, and its function is to produce active groups that initiate curing reaction. It is generally divided into free radical polymerization photoinitiator and cationic polymerization photoinitiator. There are few studies on anionic photoinitiators, and no commercial application report has been found. Free radical photoinitiators can be divided into two types: cracking type and hydrogen capturing type. Cracking free radical photoinitiators are mainly aryl alkyl ketone derivatives, such as benzoin derivatives, benzoyl ketal derivatives, dialkyloxyacetophenone, a-hydroxyalkylbenzone, a-aminoalkylbenzone, etc. benzoin is an early developed photoinitiator, which is rarely used now because of its yellowing defect. At present, a-hydroxyalkylbenzone is the most successful photoinitiator. I~ocuy1173 and irgacure 184 of Ciba company are the most widely used in China. Hydrogen scavenging initiator uses tertiary amine photosensitizers to form an initiator/photosensitizer composite initiator system, which can inhibit the polymerization inhibition of oxygen and improve the curing speed. The cationic initiator represented by barrel salt can quickly initiate oligomer and monomer to solidify into film, and is not affected by the polymerization inhibition of O, in air. Several kinds of Weng salt have been synthesized, the initiation behavior of Weng salt has been deeply studied, and their photoinitiation efficiency has been compared. The results show that not all the extracted salts have the function of cationic initiation. Effective onium salts include thioonium salt, iodonium salt, azoonium salt, ferrocene salt, etc. its negative ions include [b (phf5) 4], PF6 1, sbf6 1, asf6 1, etc. the curing speed depends on the activity of these negative ions. It is found that its activity is sbf6 ≥ asf6 ≥ PF6 ≥ BF4 1 [b (phf5) 4] 1. The results showed that the activity of [b (phf5) 4] one was stronger than that of sbf6 one. Using 0.4% iodonium salt of [b (phf5) 4] one to initiate the functionalized siloxane polymer, the curing linear speed could reach 457m/rain. Because SBF - has certain toxicity, the [b (phf5) 4] salt tends to replace the commonly used sb - salt. In addition, polymer photoinitiators and polymerizable photoinitiators were also studied to overcome the degradation of the cured film caused by the small molecules or fragments left in the cured film after the decomposition of small molecular photoinitiators

1.4 other additives in practical application, various additives are often added to the UV curing system to meet other application requirements. For example, in colored systems (paints, inks, etc.), pigments need to be added; In order to achieve good flow smoothness, it is necessary to add leveling agent; In order to suppress the formation of bubbles in the system, defoamers are often added; The addition of matting agent is to reduce the gloss of the cured film and obtain low gloss or matt coatings. Up

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