September 23, 2022 Longchang Chemical

UV oligomers used in light-curing coatings

Light-curing coatings used oligomer is also known as prepolymer, which has a small molecular weight, has the characteristics of polymerization groups, viscosity, is the main body of light-curing coatings film. Light curing is the polymerization reaction between unsaturated molecules, according to the initiator initiation mechanism, there are free radical polymerization and cationic polymerization, more common is the free radical polymerization, this C-C polymerization cross-linking reaction is a rigid cross-linking. Free radical polymerization reaction is rapid, shrinkage is large; polymerization degree change is small, blocking polymerization influence is large (0.01-0.1% of the blocking agent to prevent the reaction). Light-curing coatings after curing cross-linking shrinkage rate is high, the study found that the double bond is not polymerized when its spacing is long, once polymerized, the generation of covalent bonds, spacing shortened, causing volume reduction, all unsaturated polymerization double bond shrinkage up to 11%.

Light-curing coating formulations have complexity, with the following performance.

First, there are many types of monomers, and many types of base oligomers (resins). At present, according to the synthesis of functional groups to be divided into unsaturated polyester class PE, epoxy EA, polyurethane class PUA, polyester class PEA, amino class, polyether class, organosilicon class, phosphate ester class, mixed class, etc..

Second, according to the function of the light-curing coatings commonly used in the resin has the following categories.

1、Hard resin-High Tg, high hardness, good chemical properties, most curing speed. Such as standard bisphenol A EA; high functional group PUA and small molecular weight 2fPUA; high functional group amino acrylate; methacrylate oligomers, etc.

2, soft resin – Tg small, good flexibility, slow curing speed, low crosslink density. Such as modified epoxy – epoxy soybean oil acrylate, etc.; long-chain polyester acrylate; straight-chain structure with an average molecular weight of more than 1200 PUA; some pure acrylate oligomers, etc.

3, polar resin, is the oligomer containing active hydrogen or easy to form hydrogen bonds, can change the polarity or surface tension. Such as phosphate acrylate; silicone oligomers; carboxyl acrylate oligomers, etc.

4, water-based UV oligomers, common emulsion type, water-dispersion type, water-soluble type.

5, non-crosslinking class resins in the formulation of light-curing coatings have a filling role, improve crosslinking density, increase adhesion, change flexibility, enhance wettability and other roles. Commonly, these resins are long oil alkyd resin; thermoplastic acrylate resin; aldehyde and ketone resin; petroleum resin, etc.

Third, the design of light-curing (UV) coating formula when the choice of resin.

Before designing the coating formula, the coating type should be clear, i.e. primer, topcoat or color paint; and understand the basic properties of the coated material, such as polarity size (surface tension), with or without crystallization, belonging to thermoplastic or thermosetting, etc. The specific description is as follows.

1, the choice of primer resin. First of all, it is the requirement of adhesion, which is the generality of primer resin; wettability, which refers to the wetting of color and filler and the wetting of substrate, which are two different requirements, because the surface tension of substrate and color filler will not be exactly the same; flexibility, which mainly involves sanding and interlayer adhesion.

2、Selecting resin for top coat. The performance of the topcoat and the choice of resin are described below.

Fullness and levelness of the film. To achieve this requirement, it is necessary to choose compatible resins and monomers with good compatibility, improve the wetting and leveling with the primer, increase the cross-linking degree appropriately, and choose a higher refractive index resin.

Toughness, mainly involves hardness and abrasion resistance. These two properties are related, but not necessarily identical, and need to be treated differently.

Interlayer adhesion. The solution of interlayer adhesion needs to meet the wetting and leveling and resin polarity with.

EA, PUA (polyester) has good chemical resistance, PE, polyether is poorer; generally, aliphatic PUA, pure polyether acrylate, pure C, amino class have good yellowing resistance, the formulation of adding the appropriate anti-yellowing agent can also effectively enhance the yellowing resistance of the top coat.

Matte requirement. Some resins with slightly smaller molecular weight or very large will have a certain matte effect; some polyurethane resin matte effect is also good.

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