What are the elements in selecting UV oligomers for light-curing coating formulations?
Light curing coatings are also known as UV curing coatings, which use UV light as the energy source for curing the coating. They can be cured quickly on substrates such as paper, plastic, leather and wood without the need for heat. Light-curing coatings are mainly composed of light-curing resins (oligomers), photoinitiators (photosensitisers), thinners and additives. Light-curing resins are generally low molecular weight resins with unsaturated bonds, such as unsaturated polyesters, acrylic oligomers, etc. This article discusses the elements of light-curing resin (oligomer) selection in light-curing paint formulations.
The choice of low viscosity resin, can reduce the amount of active diluent. But low viscosity resin often low relative molecular mass, will affect the physical and mechanical properties of the cured film.
Second, the light curing rate.
Generally speaking, the higher the functional degree of light curing resin, the faster the light curing rate, epoxy acrylate light curing rate is fast, amine modified oligomer light curing rate is also fast. It is a very important condition to choose a resin with fast light curing rate, which can not only reduce the amount of photoinitiator, but also meet the requirements of fast curing of light curing coating line.
Third, physical and mechanical properties.
The physical and mechanical properties of light-curing paint film are mainly determined by the performance of the light-curing resin curing film, and the physical and mechanical properties of different varieties of light-curing paint requirements are different, the choice of light-curing resin is also different. The physical and mechanical properties of the paint film are mainly the following indicators.
Hardness, epoxy acrylate and unsaturated polyester general hardness, oligomer containing benzene ring structure is also conducive to improve the hardness. High functionality, high crosslink density, high Tg and high hardness.
Flexibility, urethane acrylics, polyester acrylics, polyether acrylics and pure acrylics are generally more flexible. Oligomers contain aliphatic long carbon chain structures and are flexible. The higher the relative molecular mass, the better the flexibility. Low crosslink density, good flexibility. low Tg, good flex cut.
Abrasion resistance, urethane acrylic resin has good abrasion resistance. Good abrasion resistance for oligomers with easy formation of hydrogen bonds between molecules. High cross-link density, good abrasion resistance.
Tensile strength, epoxy acrylates and unsaturated polyesters have high tensile strength, generally higher relative molecular mass, greater polarity, less flexibility and higher cross-linked oligomers have higher tensile strength.
Impact resistance, urethane acrylic resins, polyester acrylic resins, polyether acrylic resins and pure acrylics have better impact resistance. Low Tg, flexible oligomers with good impact resistance in general.
Adhesion, oligomers with low shrinkage, good adhesion to substrates; oligomers containing groups such as -OH and -COOH have good adhesion to metals. Oligomers with low surface tension, good wetting and spreading to substrates, good for adhesion.
Yellowing resistance, aliphatic polyurethane acrylic resins, polyether acrylic resins and pure acrylics have good resistance to yellowing. The addition of suitable anti-yellowing agents to the formulation can often effectively improve the yellowing resistance of light-cured coatings.
Chemical resistance, epoxy acrylates, polyurethane acrylics and polyester acrylics all have good chemical resistance, but polyester acrylics are less resistant to alkalis; increasing the crosslinking density during curing increases the chemical resistance of the product.
Gloss, epoxy acrylates and unsaturated polyesters have high gloss, crosslink density increases, gloss increases. high Tg, high refractive index of oligomers good gloss.
Pigment wettability, general fatty acid modified and amine modified oligomers have better wettability of pigments, containing -OH and -COOH oligomers also have better pigment wettability.
Fourth, the light-curing resin (oligomer) curing shrinkage.
Low curing shrinkage is conducive to improving the adhesion of the cured film to the substrate, oligomer functionalities increase, crosslinking density increases, curing shrinkage also increases.
Fifth, the oligomer glass transition temperature Tg.
Oligomer Tg high, generally high hardness, good gloss; oligomer Tg low, good flexibility, impact resistance or.
Sixth, toxicity and irritation.
Oligomer due to the relative molecular mass are larger, most of the viscous resin, not volatile, not flammable and explosive items, its toxicity is also low, skin irritation is also low.
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