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Regarding oligomers, an introduction to oligomers in UV-curable coatings
Release time:
2014-08-05 15:56
In light-curable coatings, oligomers serve as the equivalent of resins in conventional coatings—they are both film-forming substances. Their properties play a crucial role in determining the overall performance of the coating. Structurally, oligomers must possess photopolymerizable groups, such as various unsaturated double bonds or epoxy groups, and thus belong to the category of photosensitive resins. Among all the components of a light-curable coating, oligomers constitute the main body of the formulation; their properties essentially dictate the key performance characteristics of the cured material. Therefore, the synthesis and selection of oligomers undoubtedly represent an important step in the formulation design of light-curable coatings.
The oligomers used in free-radical photopolymerization are primarily various acrylic resins, such as epoxy-acrylic resins, polyurethane-acrylic resins, polyester-acrylic resins, polyether-acrylic resins, and acrylate resins. Among these, epoxy-acrylic resins and polyurethane-acrylic resins are the most widely used in practical applications. Oligomers used in cationic photopolymerization coatings feature epoxy groups or vinyl ether groups, such as epoxy resins and vinyl ether resins. When selecting oligomers for photopolymerization coatings, the following factors should be considered comprehensively: low viscosity, fast photopolymerization speed, excellent physical and mechanical properties, glass transition temperature, curing shrinkage rate, and low toxicity and low irritation potential. Unsaturated polyesters are generally used in photopolymerization wood coatings due to their relatively low cost, which is nearly comparable to that of traditional solvent-based coatings. However, as the prices of other types of oligomers continue to decline and their performance significantly surpasses that of unsaturated polyester systems, the market share of unsaturated polyesters has been gradually shrinking. Epoxy-acrylic resins are relatively easy to synthesize and their prices have steadily approached those of unsaturated polyesters. They exhibit outstanding performance in terms of curing speed, hardness of the cured film, resistance to solvents, corrosion resistance, tensile strength, and adhesion to most substrates, offering high cost-effectiveness and thus becoming the preferred material for current photopolymerization coating formulations. A drawback of epoxy acrylates is that their cured products tend to be hard and brittle; therefore, they are typically used in combination with 2-ethylhexyl acrylate, second-generation acrylate reactive diluents, or resins with better flexibility. Polyurethane-acrylic resins, depending on their structural characteristics, can produce either highly rigid cured films or coatings with excellent flexibility. In coatings, polyurethane-acrylic resins with longer soft segments are commonly employed. The main advantage of polyurethane-acrylic resins lies in their cured films, which display exceptional flexibility, outstanding adhesion to most substrates, and superior corrosion resistance. However, their overall synthesis cost is relatively higher, and their photopolymerization rate is slightly slower than that of epoxy-acrylic resins.
Polyurethane acrylates are often used in combination with epoxy acrylates and polyfunctional acrylate reactive diluents. Polyester acrylates have lower viscosity and lower costs, and their photocuring speed is generally moderate. High-functional polyester acrylates exhibit excellent pigment wetting properties and can be used in UV-curable tinted coatings. Polyester acrylates are seldom used alone in UV-curable coatings; they are typically blended with commonly used resins such as epoxy acrylates and polyurethane acrylates.
Acrylic resin oligomers are seldom used alone in the photopolymerizable coating industry. Although they have relatively high molecular weights and viscosities, they exhibit low shrinkage upon curing, which helps improve the adhesion of the cured film. Carboxyl-modified acrylic resin oligomers can effectively stabilize and disperse pigments in pigment-based coloring systems. Therefore, these oligomers can be used as functional auxiliary resins in photopolymerizable coating formulations, as appropriate.
Guangzhou Boxing Chemical Technology Co., Ltd. specializes in the production of UV resins and boasts many years of experience in both manufacturing and R&D. Our technology is well-established, and our products have consistently received high praise from numerous customers. You're welcome to contact us for sample requests.
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