UV curing technology is a kind of high-efficiency, environmental protection, energy-saving and high-quality material surface technology. It is known as a new technology for green industry in the 21st century. With the development of science and technology, the application of UV curing technology has developed from the earliest printed boards and photoresists to UV curing coatings, inks and adhesives. The application field has been expanding, forming a new industry.
UV curing products are most commonly divided into UV coatings, UV inks and UV adhesives. Their biggest feature is that they have a fast curing rate, generally between a few seconds and tens of seconds, and the fastest can be cured within 0.05~0.1s. They are the fastest drying and curing among various coatings, inks and adhesives at present.
UV curing means UV curing. UV is the English abbreviation of UV. Curing refers to the process that substances change from low molecules to polymers. UV curing generally refers to the curing conditions or requirements of coatings (paints), inks, adhesives (glues) or other potting sealants requiring UV curing, which are different from heating curing, curing with adhesives (curing agents), natural curing, etc. [1].
The basic components of UV curing products include oligomers, active diluents, photoinitiators, additives and so on. Oligomer is the main body of UV curing products, and its performance basically determines the main performance of cured materials. Therefore, the selection and design of oligomer is undoubtedly an important link in the formulation of UV curing products.
What these oligomers have in common is that they all have Unsaturated double bond resins are ranked by the reaction rate of free radical polymerization: acryloyloxy > methacrylyloxy > vinyl > allyl.Therefore, the oligomers used in free radical UV curing are mainly various acrylic resins, such as epoxy acrylate, polyurethane acrylate, polyester acrylate, polyether acrylate, acrylate resin or vinyl resin, and the most commonly used are epoxy acrylate resin, polyurethane acrylate resin and polyester acrylic resin. These three resins are briefly introduced below.
Epoxy acrylate
Epoxy acrylic acid value is the most widely used and the largest amount of UV curing oligomer at present. It is prepared from epoxy resin and (meth) acrylate. Epoxy acrylates can be divided into bisphenol A epoxy acrylates, phenolic epoxy acrylates, modified epoxy acrylates and epoxidized acrylates according to their structural types, and bisphenol A epoxy acrylates are the most widely used.
Bisphenol A epoxy acrylate is one of the oligomers with the fastest light curing rate. The cured film has high hardness, high gloss, excellent chemical resistance, good heat resistance and electrical properties. In addition, bisphenol A oxygen exchange acrylate has simple raw material formula and low price. Therefore, it is commonly used as the main resin for light curing paper, wood, plastic and metal coatings, and also as the main resin for light curing ink and light curing adhesive.
Polyurethane acrylate
Polyurethane acrylate (PUA) is another important UV curable oligomer. It is synthesized by two-step reaction of polyisocyanate, long-chain diol and hydroxyl acrylate. Due to the multiple structures of polyisocyanates and long-chain diols, oligomers with set properties are synthesized through molecular design. Therefore, they are the oligomers with the most product brands at present, and are widely used in UV curing coatings, inks and adhesives.
Polyester Acrylate
Polyester acrylate (PEA) is also a common oligomer, which is prepared from low molecular weight polyester glycol by acrylate. Polyester acrylate is characterized by low price and low viscosity. Due to its low viscosity, polyester acrylate can be used as both oligomer and active diluent. In addition, most polyester acrylates have low odor, low irritation, good flexibility and pigment wettability, and are suitable for color paints and inks. In order to improve the high curing rate, multifunctional polyester acrylate can be prepared; Amine modified polyester acrylate can not only reduce the influence of oxygen polymerization inhibition, improve the curing rate, but also improve the adhesion, gloss and wear resistance.
Active diluents usually contain reactive groups, which can dissolve and dilute oligomers, and play an important role in the UV curing process and film properties. According to the number of reactive groups, common monofunctional active diluents include isodecyl acrylate, lauryl acrylate, hydroxyethyl methacrylate, glycidyl methacrylate, etc; Bifunctional active diluents include polyethylene glycol diacrylate series, dipropylene glycol diacrylate, neopentyl glycol diacrylate, etc; Multifunctional active diluents such as trimethylolpropane triacrylate, etc. [2].
Initiator has an important influence on the curing rate of UV curing products. In UV curing products, the amount of photoinitiator is generally 3%~5%. In addition, pigments and filler additives also have an important impact on the final performance of UV cured products.
Post time: Jun-15-2022