UV curing technology is a highly efficient, environmentally friendly, energy-saving, high-quality material surface technology, known as a new technology for green industry in the 21st century. With the development of science and technology, the application of photocurable technology has developed from the earliest printed boards and photoresists to photocurable coatings, inks, and adhesives. The application field has continuously expanded, forming a new industry.

The most common types of UV curable products are UV coatings, UV inks, and UV adhesives. Their biggest characteristic is their fast curing rate, which typically ranges from a few seconds to tens of seconds, and the fastest can be cured within 0.05 to 0.1 seconds. They are currently the fastest drying and curing of various coatings, inks, and adhesives.

UV curing refers to the process of converting a substance from low molecular weight to high molecular weight. UV curing generally refers to the curing conditions or requirements of coatings (paints), inks, adhesives (glue), or other potting sealants that require UV curing, which is different from heating curing, curing with adhesives (curing agents), and natural curing.

The basic components of UV curable products include oligomers, active diluents, photoinitiators, additives, and so on. Oligomers are the main body of UV curable products, and their performance basically determines the main performance of the cured material. Therefore, the selection and design of oligomers is undoubtedly an important link in the formulation of UV curable products.

What these oligomers have in common is that they all have"" Unsaturated double bond resins are ordered by the rate of free radical polymerization reaction: acryloyloxy> methacryloyloxy> vinyl> allyl.

Therefore, the oligomers used for free radical photocuring are mainly various types of acrylic resins, such as epoxy acrylate, polyurethane acrylate, polyester acrylate, polyether acrylate, acrylate resin or vinyl resin. The most commonly used oligomers are epoxyacrylic resin, polyurethane acrylate resin, and polyester acrylic resin. The following is a brief introduction to these three resins.

//Epoxy acrylate

Epoxy acrylic acid value is currently the most widely used and widely used light curable oligomer, which is prepared by esterification of epoxy resin and (meth) acrylate. Epoxy acrylate can be divided into bisphenol A epoxy acrylate, phenolic epoxy acrylate, modified epoxy acrylate, and epoxidized acrylate according to their structural types, with bisphenol A epoxy acrylate being the most widely used.

Bisphenol A epoxy acrylate is one of the fastest light curing polymers. The cured film has high hardness, high gloss, excellent chemical resistance, good heat resistance, and electrical properties. In addition, the raw material formulation of bisphenol A epoxy acrylate is simple, and the price is cheap. Therefore, it is commonly used as the main resin for light curing paper, wood, plastics, and metal coatings, and also as a light curing ink The main resin of a light curing adhesive.

//Polyurethane acrylate

Polyurethane acrylate (PUA) is another important light curable oligomer. It is synthesized by a two-step reaction of polyisocyanates, long chain glycols, and hydroxyl acrylate. Due to the multiple structures of polyisocyanates and long chain glycols, oligomers with set performance are synthesized through molecular design, making them the most widely used oligomers in UV curable coatings, inks, and adhesives.

//Polyester acrylate

Polyester acrylate (PEA) is also a common oligomer, which is prepared by acrylate esterification of low molecular weight polyester glycols. The main characteristics of polyester acrylate are its low price and low viscosity. Due to its low viscosity, polyester acrylate can be used as both an oligomer and an active diluent. In addition, most polyester acrylate esters have low odor, low irritation, good flexibility, and pigment wettability, making them suitable for paints and inks. In order to improve the high curing rate, polyfunctional polyester acrylate can be prepared; Using amine modified polyester acrylate can not only reduce the impact of oxygen polymerization inhibition, increase the curing rate, but also improve adhesion, gloss, and wear resistance.

Active diluents usually contain reactive groups that dissolve and dilute oligomers, and play an important role in the UV curing process and film performance. According to the number of reactive groups contained, common monofunctional active diluents include isodecyl acrylate, lauryl acrylate, hydroxyethyl methacrylate, and glycidyl methacrylate; Bifunctional active diluents include polyethylene glycol diacrylate series, dipropylene glycol diacrylate, neopentyl glycol diacrylate, etc; Multifunctional active diluents such as trimethylolpropane triacrylate, etc. [2].

Initiators have an important impact on the curing rate of UV curable products. In UV curable products, the addition amount of photoinitiators is generally between 3% and 5%. In addition, pigments and filler additives also have an important impact on the final performance of UV curable products.

Application of UV curing technology in different fields

Due to its advantages such as fast curing, energy conservation, and environmental protection, UV curable products are widely used in various fields, and were first mainly used in the field of wood painting. In recent years, with the development of new initiators, active diluents, and photosensitive oligomers, the application of UV curable coatings has gradually expanded to the fields of paper, plastics, metals, fabrics, and automotive components. The following will briefly introduce the applications of several UV curing technologies in different fields.

UV curable 3D printing

Photocurable 3D printing is currently one of the most accurate and commercialized rapid prototyping technologies. It has many advantages, such as low energy consumption, low cost, high accuracy, smooth surface, and good repeatability. It has been widely used in aerospace, automotive, mold manufacturing, jewelry design, and medical fields.

For example, printing a rocket engine prototype with a complex structure and analyzing the flow pattern of gas can help design a rocket engine with a more compact structure and higher combustion efficiency, effectively improving the research and development efficiency of complex components and shortening the vehicle research and development cycle; You can also directly print out molds or inverted molds for rapid mold making, and so on.

Stereolithography (SLA), digital projection (DLP), three-dimensional inkjet molding (3DP), continuous liquid surface growth (CLIP), and other technologies have been developed in the light curing 3D printing technology. As its printing material, photosensitive resins for photocurable 3D printing have also made significant progress, and are developing towards functionalization based on application needs.

UV curable products for electronic packaging

The innovation of packaging technology has promoted the transition of packaging materials from metal packaging and ceramic packaging to plastic packaging. Epoxy resin is also widely used in plastic packaging. Excellent mechanical properties, heat and humidity resistance are prerequisites for high-quality packaging. In addition to the structure of the epoxy resin body, the impact of curing agents is also a very important factor in determining the performance of epoxy resin.

Compared to the thermal curing method used for conventional epoxy resins, cationic UV curing not only has better storage stability of the photoinitiator, but also has a faster curing speed of the system. The curing can be completed within tens of seconds, with extremely high efficiency, and there is no oxygen inhibition, enabling deep curing. These advantages increasingly highlight the importance of cationic UV curing technology in the field of electronic packaging.

With the rapid development of semiconductor technology, electronic components increasingly tend to be highly integrated and miniaturized. Light weight, high strength, good heat resistance, and excellent dielectric properties will be the development trend of new high-performance epoxy packaging materials. Photocuring technology will definitely play a more important role in the development of the electronic packaging industry.

Printing ink

In the field of packaging and printing, the use of flexographic printing technology is becoming more and more important, and it has become the mainstream technology of printing and packaging, and is an inevitable trend for future development.

There are many types of flexographic printing inks, mainly including the following categories: water-based inks, solvent based inks, and ultraviolet curable (UV) inks. The main use of solvent based ink is non absorbent plastic film printing; Water-based inks are mainly used in printing materials such as newspapers, corrugated cardboard, and cardboard; UV ink has a wide range of uses, with good printing effects on materials such as plastic film, paper, and metal foil [4].

UV ink has the characteristics of environmental friendliness, high efficiency, good printing quality, and strong adaptability. It is currently a very popular and highly focused new environmentally friendly ink, with a very promising development prospect.

Flexographic UV ink packaging printing has a wide range of applications. Flexographic UV ink has the following advantages [5]:.

(1) Flexographic UV ink has no solvent discharge, is safe and reliable to use, has a high melting point, and is pollution-free. Therefore, it is suitable for producing food, medicine, beverage, and other packaging materials that require high safety and non-toxic requirements.

(2) During printing, the physical properties of the ink remain unchanged, and there are no volatile solvents. The viscosity remains unchanged, which will not cause damage to the printing plate and cause it to paste or stack. When printing with higher viscosity ink, the printing effect is still good.

(3) Ink drying speed is fast, and product printing efficiency is high. It can be widely used in various printing methods, such as plastic, paper, film, and other substrates.

With the development of new oligomer structures, active diluents, and initiators, the future application range of UV curable products is immeasurable, and the market development space is unlimited.

Microspectrum has rich analytical and research experience in the field of UV curable products. It has built a powerful spectrogram database and has complete large-scale analytical instruments. Through proprietary sample pretreatment methods and instrumental analysis methods, it can determine the synthetic monomers and structures of various oligomers, a variety of active diluents, photoinitiators, and micro additives. At the same time, Microspectrum is closely following the update of new products in the market, conducting project research on new UV curable products in multiple fields, which can conduct comparative analysis of product excellence, assist enterprises in solving difficulties and blind spots encountered in the product development process, shorten the research and development cycle, and improve product performance.