UV ink and UV varnish need to adapt to the viscosity of the coater when coating. Generally, the viscosity of prepolymer is reduced by adding 20% ~ 80% monomer. At the same time, the monomer polymerizes itself and becomes a part of the cured film.Active diluent, also known as cross-linked monomer, is a functional monomer. Its role in ink is to adjust the viscosity, curing speed and curing film properties of ink. The active diluent also contains "C = C" unsaturated double bonds, which can be acryloyl, methylpropionyl, vinyl and allyl. In view of the fastest light solid speed of acryloyl group, most of the active diluents used at present are acrylate monomers. Due to the different amount of acryloyl group, it can be divided into single functional group and double functional group. The release effect and curing speed of various functional group active diluents are different. Generally speaking, the more functionality, the faster the curing speed, but the worse the dilution effect.
Traditional active diluents, such as styrene and the first generation acrylate monomers, are highly toxic. Some acrylate monomers have a strong stimulating effect on the skin. In order to reduce the skin irritation of active diluents, there are usually two methods: one is to increase the molecular weight of monomers by ring opening polymerization of ethylene oxide, propylene oxide and hexyl ester; The second is to change the ester structure of monomers; Another is to change the previous method of alcohol esterification. When alcohol is added to acryloyl group, the skin irritation of multi-functional monomer is greatly reduced. For example, when neopentyl glycol diacrylate is synthesized by esterification, the pH value (skin irritation index) is 4.96, while when it is synthesized by addition method, the pH value is reduced to 0.3.
Recently, some monomers with good properties have been developed, such as alkoxyacrylate, carbonate monoacrylate, imidazole monoacrylate, cyclic carbonate monoacrylate, epoxy silicone monomer, silicone acrylate and vinyl ether monomer. When selecting monomer, the following principles shall be followed:
a. Low viscosity and good dilution effect;
b. Fast curing;
c. Good adhesion on materials;
d. Little skin irritation and toxicity;
e. Leave no smell in the coating.
