The main components of UV inks are polymerizable prepolymers, photosensitive monomers, photoinitiators, and auxiliary components are coloring pigments, fillers, additives (leveling agents, polymerization inhibitors), etc.

1. Polymeric prepolymer

Polymeric prepolymer is an important component that determines the performance of UV varnish coating. It is the most basic component in UV ink and a film-forming substance. Its performance plays an important role in the curing process and the properties of the cured ink film. Generally classified according to the skeleton structure. Skeleton structure affects coating hardness, abrasion resistance, adhesion, light resistance, chemical resistance and water resistance, etc.

In terms of structure, oligomers are low molecular resins containing "C=C" unsaturated double bonds, such as acryloyl, methacryloyl, vinyl, allyl and the like. There are mainly epoxy acrylate resin, polyurethane acrylate resin, polyester acrylate resin, polyether acrylic resin, polypropyl acrylate, unsaturated polyester resin and other resin types. Under the same conditions, the light-curing speed of acryl group is the fastest, so most of the oligomers are acrylic resins.

2. Photosensitive monomer (active diluent)

UV ink and UV varnish need to adapt to the viscosity of the coating machine when coating. Generally, the viscosity of the prepolymer is reduced by adding 20% to 80% of the monomer. At the same time, the monomer polymerizes itself to become a cured film. a part of.

Reactive diluent, also called cross-linking monomer, is a functional monomer whose function in ink is to adjust ink viscosity, curing speed and cured film performance. The reactive diluent also contains "C=C" unsaturated double bonds in its structure, which can be acryloyl, methacryloyl, vinyl and allyl. In view of the fastest photo-curing speed of acryloyl groups, most of the reactive diluents currently used are acrylate monomers. Due to the difference in the number of acryloyl groups, they can be divided into three types: monofunctional and bifunctional. The release effect and curing speed of various functional group reactive diluents are different. In general, the more functionality, the faster the cure, but the less effective the dilution.

Traditional reactive diluents, such as styrene and first-generation acrylate monomers, are highly toxic, and some acrylate monomers have a strong irritating effect on the skin. In order to reduce the irritation of the active diluent to the skin, there are usually two methods: one is to increase the molecular weight of the monomer by ring-opening polymerization of ethylene oxide, propylene oxide and hexyl ester; the other is to change the structure of the monomer ester group; One is to change the alcohol esterification method previously used. When alcohol is added to the acryloyl group, the skin irritation of multifunctional monomers is greatly reduced. For example, when neopentyl glycol diacrylate is synthesized by esterification, the PH value (skin irritation index) is 4.96, while the skin irritation index of polyfunctional monomer is greatly reduced. During synthesis, the pH value dropped to 0.3.

3. Photoinitiator

Photoinitiators are substances that can absorb radiant energy and produce reactive intermediates with initiator polymerization ability through chemical changes, and are also the main components required for any UV curing system. Photoinitiators can be divided into hydrogen abstraction type and cracking type; hydrogen abstraction type is a bimolecular photoinitiator that needs to cooperate with a compound containing active hydrogen (generally called co-initiator) to form free radicals through hydrogen abstraction reaction. ; The cracking type is that the photoinitiator is decomposed into free radicals in the molecule after being emitted by the laser, and it is a single-molecule photoinitiator.