Application of Radiation Curing Coating Innovation Technology (2)

3 radiation curing formula system

All radiation curable systems contain functionalized oligomers, monofunctional or polyfunctional monomers, and photoinitiators or photosensitizers must be added to the UV curing system.

3.1 Photoinitiator/Photosensitizer System

Photoinitiators or photosensitizers are used in the UV curing system to produce reactive free radicals or reactive ion groups that initiate the reaction. Commonly used radical initiators such as benzoin ether, benzil acetal, acetophenone, and thioxanthone are strongly inhibited by O2 in the air, and photoinitiated cationic polymerization systems are not inhibited by oxygen. Rapid and complete polymerization can be achieved in the air. The cesium salt is a relatively new type of stable, non-absorbent and highly efficient cationic photoinitiator. For example, diphenyl iodonium salt generates free radicals in addition to ionic radicals under light irradiation, and can simultaneously initiate cationic polymerization and radical polymerization. Cationic photopolymerization is now used for UV curing and is promising for polysiloxane epoxy resin photopolymerization applications. However, sulfonium salt cationic photoinitiators also have a number of disadvantages: if they contain highly toxic metal ions such as SbF-6, they have poor solubility in polysiloxanes and low thermal stability. The use of boron instead of hydrazine can reduce its toxicity, improve solubility, and still maintain high activity. The use of photoinitiators in combination can increase the efficiency of the photocuring process; the addition of certain additives can also increase the activity, such as keto-amine-onium salts or keto-amine-bromides (such as CBr4, bromoketones, etc.). Some of the active particles produced in the light often act as a stop.

The newly proposed “three-component system” can overcome this termination reaction, mainly using scavengers to remove active particles that terminate the growth chain, and if possible, generate new initiation radicals through charge transfer, such as Keto-amine-hydrazine salt system.

3.2 Monomers and Oligomers

Generally, the viscosity of the oligomers for radiation curing is relatively large, and diluents, ie, monomers, must be added to adjust the construction viscosity. The first generation of multi-functional acrylate monomers was developed in the 1970s, including TMPTA, HDDA, PETA, and TTEGDA. These monomers have good dilution and cure properties, low volatility, and moderate price, but are irritating to the skin. Although they are still used in large quantities, the general trend is to develop less irritating monomers. In the late 1980s, vinyl ethers were gradually replaced by acrylic monomers. Vinyl ether has good dilution properties, fast cure, and cationic polymerization. Oligomers have also undergone a series of developmental processes. Acrylic ester resins are the second generation of photocurable resins developed after unsaturated resins. They have high reactivity and many varieties, especially acrylic epoxy resins and acrylic polyurethanes. The most extensive.

In addition, the maleate and vinyl ether oligomers are attractive as "non-acrylate" systems. Fast-curing and low-viscosity alignment polymers are often difficult to obtain at the same time. Therefore, it is necessary to balance the viscosity, the curing speed, and the final physical and chemical properties of the cured film. The new amino-modified polyester is a major development in this area. It can be used as a varnish for various materials. Of course, obtaining low viscosity and low irritation at the same time is still a difficult problem. Research in this area is still in its ascendant. In photocuring systems, photoinitiators often produce odors that can be improved by the introduction of photoinitiators on the oligomer backbone, but at the same time this can cause slowing of the cure rate. Water has been studied for many years as a solvent for radiation curing systems. The replacement of organic monomers with water provides both low construction viscosity and the performance of pure oligomers. Water-based acrylic urethane and acrylic polyester resins have been successfully used in the finishing of screen printing inks, wood coatings and porous substrates such as leather and fabrics. In recent years, the development of adhesives for UV/EB-cured composites has attracted attention. For example, EB-cured carbon fiber composites require oligomers with high glass transition temperature and high thermal deformation temperature. The main direction of research is epoxy. Resin materials. Due to the shrinkage of free radicals on the substrate, the adhesive force is affected, but much progress has been made recently. Long-chain acrylate compounds have small curing shrinkage and good weatherability and have been obtained on many substrates. application.

4 Application Status of Radiation Cured Coatings

4.1 Application

Radiation curing has the characteristics of less pollution, faster curing, and lower energy consumption. In recent years, radiation curing has gradually replaced traditional paints in wood coatings, metal decoration and printing industries, and has begun to be widely used in precision industries such as optical lenses, electronic devices, and optical fiber coatings. The following is a list of UV and EB curing applications.

4.1.1 Wood Coating

Wood primers and surface varnish and paints, fillers (filled wood panels and surface voids), water-based furniture coatings.
4.1.2 Plastic Coating

Thin film coatings and hard coatings, metallized plastic substrate coatings for automotive parts, equipment, optical discs, credit cards, window films, and automotive headlights and lighting components.
4.1.3 Paper Coating

Surface coating of decorative paper, labels, cards and writing, metallized paper substrate coating.
4.1.4 Floor Coating

Vinyl Flooring, Vinyl Silicon Parquet.

4.1.5 Metal Coating

Food cans, car and equipment decoration, traffic tunnel wall panels.

4.1.6 Silicone Coating (Paper/Film)

Stripping lining, labels, castings.
4.1.7 Electronic coating

Conformal coating, encapsulating compound, photoresist, soft (hard) disk, optical disk, video tape, tape optical fiber.

4.1.8 Ink

Lithography (cardboard boxes, flexible packaging, magazines, publications), screen printing (plastic labels, plastic bottles, foils, paper and cardboard packaging) and offset printing.

4.1.9 Adhesives

Laminates (paper or film/wood, film/film, paper/foil, etc.), ordinary adhesives (automotive parts, optics) and pressure-sensitive adhesives (labels, contact paper/film, etc.).

4.1.10 Crosslinking

Heat shrinkable film, electrically insulating material.

(to be continued)