2023 The Complete Guide To UV light curing: The Ultimate Guide
Light curing technology is a highly efficient, environmentally friendly, energy-saving, high-quality material surface technology, known as the new technology for the 21st century green industry. With the development of science and technology, light curing technology applications from the earliest printed plates, photoresist development to light curing coatings, inks, adhesives, applications continue to expand, forming a new industry.
Light curing products are most commonly divided into UV coatings, UV inks and UV adhesives, their biggest feature is the fast curing rate, generally between a few seconds to tens of seconds, the fastest can be cured in 0.05 to 0.1s time, is currently the fastest drying and curing of various coatings, inks and adhesives.
UV curing is ultraviolet curing, UV is the abbreviation for ultraviolet light, curing refers to the process of transformation of substances from low molecules to high molecules. UV curing generally refers to the need for UV curing of coatings (paints), inks, adhesives (glues) or other potting sealants curing conditions or requirements, which are distinguished from heating curing, glue linker (curing agent) curing, natural curing, etc. [1].
The basic components of light-curing products include oligomers, reactive diluents, photoinitiators, additive additives, and so on. Oligomers are the main body of light-cured products, and its performance basically determines the main properties of the cured material, therefore, the selection and design of oligomers is undoubtedly an important part of the formulation of light-cured products.
The common denominator of these oligomers is that they all have ”
” unsaturated double bond resin, according to the free radical polymerization reaction rate in order of speed: acryloyloxy> methacryloyloxy> vinyl> allyl.
Therefore, free radical light curing using oligomers are mainly various types of acrylic resins, such as epoxy acrylate, urethane acrylate, polyester acrylate, polyether acrylate, acrylated acrylate resin or vinyl resin, etc. The most practical applications are epoxy acrylate resin, urethane acrylate resin and polyester acrylate resin. These three resins are briefly introduced below.
Epoxy acrylate
Epoxy acrylic value is currently the most widely used, the largest amount of light-curing oligomer, it is made from epoxy resin and (meth)acrylic esterification. Epoxy acrylate can be divided into bisphenol A epoxy acrylate, phenolic epoxy acrylate, modified epoxy acrylate and epoxy acrylate according to the type of structure, with bisphenol A epoxy acrylate being the most widely used.
Bisphenol A epoxy acrylate in the oligomer is the fastest rate of light curing, curing film with hardness, high gloss, excellent chemical resistance, good heat resistance and electrical properties, plus bisphenol A for oxygen acrylate raw material formula is simple, cheap, so in commonly used in light curing paper, wood, plastic, metal coatings of the main resin, but also for light curing inks, light curing adhesives of the main resin.
Polyurethane acrylate
Polyurethane acrylate (PUA) is another important light-curing oligomer. It is synthesized by two-step reaction with polyisocyanate, long-chain diol and hydroxy acrylate. Since the multiple structures of polyisocyanates and long-chain diols can be selected to synthesize oligomers with set properties by molecular design, it is the oligomer with the largest number of product grades and is widely used in light-curing coatings, inks and adhesives.
Polyester acrylates
Polyester acrylate (PEA) is also a common oligomer, which is produced by esterifying low molecular weight polyester diols with acrylic acid. The low price and low viscosity of polyester acrylate are the most important features. Due to the low viscosity, polyester acrylate can be used both as an oligomer and as a reactive diluent. In addition, polyester acrylates mostly have low odor, low irritation, good flexibility and pigment wetting properties, suitable for color paints and inks. In order to improve the high curing rate, polyester acrylate with multiple functionalities can be prepared; the use of amine-modified polyester acrylate can not only reduce the effect of oxygen blocking, improve the curing rate, but also improve adhesion, gloss and abrasion resistance.
Reactive diluents usually contain reactive groups, which play a solubilizing and diluting role for oligomers and play an important role in the light curing process and coating film properties. According to the number of reactive groups contained, monofunctional reactive diluents commonly include isodecyl acrylate, lauryl acrylate, hydroxyethyl methacrylate, glycidyl methacrylate, etc.; bifunctional reactive diluents include polyethylene glycol diacrylate series, dipropylene glycol class diacrylate, neopentyl glycol diacrylate, etc.; multifunctional reactive diluents such as trimethylolpropane triacrylate [2 ].
The initiator has an important impact on the curing rate of light-cured products, and the amount of photoinitiator added in light-cured products is generally 3% to 5%. In addition, pigments and filler additives also have an important impact on the final performance of light-cured products.
Light curing technology in different fields of application】
Light curing products due to fast curing, energy saving and environmental protection advantages of a wide range of applications, the first mainly used in the field of wood coating. In recent years, with the development of new initiators, active diluents and photosensitive oligomers, the application of light-curing coatings gradually expanded to paper, plastics, metals, fabrics, automotive parts and other fields. The following will briefly introduce several light-curing technologies in different fields of application.
Light-curing 3D printing
Light-cured 3D printing is one of the most accurate and commercially available additive manufacturing technologies. It has many advantages, such as low energy consumption, low cost, high precision, smooth surface and repeatability, and has begun to be widely used in aerospace, automotive, mold making, jewelry design and medical fields.
For example, by printing a prototype rocket engine with a complex structure and analyzing the flow pattern of gases, it helps to design a rocket engine with a more compact structure and higher combustion efficiency, which can effectively improve the efficiency of the development of complex spare parts and shorten the development cycle of automobiles; it can also directly print out molds or inverted molds, so as to quickly make molds and so on.
Light-curing 3D printing technology has developed stereolithography (SLA), digital projection technology (DLP) and three-dimensional inkjet forming (3DP), continuous liquid growth (CLIP) and other technologies [3]. As its printing materials, photosensitive resins for light-curing 3D printing have also made great progress and developed toward functionalization according to the needs of applications.
UV light-curable products for electronic packaging
The innovation of packaging technology has led to the transition of packaging materials from metal and ceramic packaging to plastic packaging. Plastic encapsulation and epoxy resin is the most widely used, excellent mechanical and mechanical properties, heat and moisture resistance is the premise of high-quality packaging, and determine the performance of the epoxy resin, in addition to the structure of the main epoxy resin, the impact of the curing agent is also a very important factor.
Compared with the conventional epoxy resin used in the thermal curing method, cationic UV curing not only photoinitiator chemical stability is better, the curing speed of the system is faster, within tens of seconds to complete the curing, the efficiency is very high, there is no oxygen blocking aggregation, can be deep curing, these advantages highlight the importance of cationic UV curing technology in the field of electronic packaging.
With the rapid development of semiconductor technology, electronic components tend to be more and more highly integrated, miniaturization direction, light weight, high strength, good heat resistance, excellent dielectric properties, etc. will be the development of new high-performance epoxy packaging materials, light curing technology in the development of the electronic packaging industry will play a more important role.
Printing ink
In the field of packaging printing, flexographic printing technology is increasingly used to account for an increasing proportion, it has become the mainstream technology of printing and packaging, and is the inevitable trend of future development.
Flexographic ink has a variety of types, including the following categories: water-based inks, solvent-based inks and ultraviolet curable (UV) ink. Solvent-based inks are mainly used for non-absorbent plastic-type film printing; water-based inks are mainly used in printing materials such as newspapers, corrugated cardboard and cardboard; UV inks are more widely used, and they are more effective in printing on plastic film, paper, and metal foil [4].
UV ink has environmentally friendly, high efficiency, good printing quality, adaptability and other characteristics, is currently very popular and attention to the new environmentally friendly ink, the development prospects are very good.
Flexo UV ink packaging printing in a wide range of applications. Flexographic UV ink has the following advantages [5].
(1) Flexo UV ink solvent-free emissions, the use of safe and reliable, high melting point, non-polluting, so it is suitable for the production of safe and non-toxic packaging materials require high food, drugs, beverages and other packaging.
(2) the physical properties of the ink remain unchanged when printing, and there is no volatile solvent, viscosity remains unchanged, will not cause damage to the printing plate so that it occurs paste plate, pile plate and other phenomena, in the use of higher viscosity ink printing, the printing effect is still better.
(3) ink drying speed, product printing efficiency, can be widely used in a variety of printing methods, in plastic, paper, film and other substrates.
With the new oligomer structure, the development of active diluents and initiators, the future application areas of light-curing products are immeasurable, the market development space is unlimited.