Common knowledge of coatings: Research Progress of UV curable coatings

Abstract: UV curable coating has the advantages of environmental friendliness, economy, high efficiency, energy saving and wide adaptability With the in-depth study of oligomers, active diluents, photoinitiators, additives, pigments and fillers, and the continuous development of new products, liquid UV curable coatings are rapidly expanding in various fields of application of traditional coatings In this paper, the research progress of the main components of solvent UV curable coatings is summarized Key words: UV curable coating; oligomer; active monomer; photoinitiator Chinese Library Classification No.: tq630.7 document identification code Application scope and advantages of roller ceramic coating Recommended introduction: the surface of ceramic rubber plate used for roller ceramic coating is cast into durable rubber plate by hundreds of independent small ceramic pieces Each ceramic piece has raised characteristics Under general conveyor belt pressure, thousands of unique cast bumps can produce positive traction, prevent slipping and extend the service life of conveyor belt roller At the same time, the bottom layer adopts high-quality rubber, which has strong elasticity and can play a good impact resistance role The scope of application of roller ceramic coating is one three six 83857180 (the same as V) 1 Roller coating in extremely harsh working environment 2 The belt joint is not suitable for fixing with iron buckle; 3 It is suitable for leather Abstract: UV curable coatings have the advantages of environmental friendliness, economy, high efficiency, energy saving and wide adaptability With the in-depth study of oligomers, active diluents, photoinitiators, additives, pigments and fillers, and the continuous development of new products, liquid UV curable coatings are rapidly expanding in various fields of application of traditional coatings In this paper, the research progress of the main components of solvent UV curable coatings is summarized Key words: UV curable coatings; oligomers; active monomers; photo initiator Chinese Classification Number: tq630.7 document identification code: a article number: 2095-2562 (2013) 01-0004-04 in 1968 Bayer company of Germany developed UV curable coatings (UVCC), realizing the industrialization of UVCC technology At the International Conference on radiation curing in North America held in May 2004, experts agreed that UVCC technology has the characteristics of "5E": environmental friendly, economic, efficient, energy saving and widely adaptable UVCC has a variety of forms such as liquid type, powder type, water dispersing type, etc it is widely used in the coating of paper, wood, plastic, metal and other base materials It has maintained a rapid development, is an important new force in the coating industry, and has become the research hotspot of the majority of coating workers [1-4] The liquid UV curable coating is mainly composed of oligomer, photoinitiator, reactive diluents, etc., in which the matrix oligomer plays a key role in the film performance, and various additives and fillers are added to meet the industrial requirements [5,6] With the development of oligomers, active diluents, photoinitiators, auxiliaries, pigments and fillers, new materials are emerging Liquid UV curable coatings will expand rapidly to various application fields of traditional coatings The following is a brief introduction of the research on the components 1 Oligomer oligomer of UV curable coating is also called oligomer, also known as prepolymer, which is the matrix resin of UV curable coating As the skeleton, it occupies a considerable proportion in the UV curable coating system, and plays a decisive role in the basic performance of the system (including adhesion, hardness, flexibility, wear resistance, heat resistance, chemical resistance, durability, optical performance and aging resistance) The main types of oligomers used in UV curable coatings are unsaturated polyester, epoxy acrylate and polyurethane acrylate 1.1 unsaturated polyester (UPE) is the first oligomer used in UV curable coatings It refers to the straight chain or branched polyester macromolecule with reactive = C double bond Active vinyl and other monomers copolymerized with UPE initiated by active radicals can crosslink and solidify the network structure However, the polymerization time is long, the temperature is high, and the polymerization process of oxygen polymerization is serious, which increases the yellowing of the film, so the application is limited Using hyperbranched technology to prepare multifunctional unsaturated polyester is one of the directions to solve the problem [7,8] Hyperbranched oligomers have unique three-dimensional molecular structure, which makes them have good solubility, low viscosity and high reactivity The shrinkage rate of the cured film is smaller, and it has good substrate adhesion performance, and it can avoid the use of volatile active diluent, so it is more environmentally friendly 1.2 epoxy acrylate (EA) is obtained by ring opening esterification of epoxy resin with acrylic acid or methacrylic acid under the action of catalyst It can be divided into bisphenol-A epoxy acrylate, phenolic epoxy acrylate, modified epoxy acrylate and epoxy oil acrylate according to its structure type EA is the largest UV curing oligomer in the UV curing industry due to its fast reaction rate, good adhesion, hardness, strength, glossiness and chemical resistance, and low price EA viscosity is high, which affects construction and leveling, and the cured film is brittle, poor flexibility and aging resistant Therefore, the research on improving the performance of epoxy acrylate has been carried out, such as increasing the relative molecular weight of oligomer to reduce the shrinkage rate during curing, introducing silicon containing compounds to synthesize a prepolymer to improve the heat resistance of the film, introducing flexible long chain to overcome the brittleness of epoxy resin, etc [9-10] 1.3 polyurethane acrylate (PUA) is a kind of important UV curable oligomer, which is produced by the reaction of NCO group of polyisocyanate with hydroxyl group of polyol and the introduction of UV active group by acrylate containing hydroxyl group Star hyperbranched polymer with three-dimensional spherical structure of PUA is becoming a research hotspot Different from traditional linear polymer, this kind of polymer has the characteristics of high functionality, no entanglement between and within molecules Therefore, this kind of polymer has high activity, low viscosity, good solubility, easy modification of functional groups, etc., which can obtain appropriate construction performance and excellent coating performance [7,11] Although the price of PUA is relatively high, polyurethane acrylate curing film has the advantages of excellent flexibility and wear resistance, good chemical resistance and impact resistance, good adhesion, etc., so PUA is a oligomer whose dosage is less than EA [7,12] 2 Active diluents, photoinitiators and auxiliaries of UV curing coatings and pigments and fillers, Such as wear resistance, hardness and flexibility [13-15] 1) Single functional group active diluent (meth) acrylate and so on, each molecule contains only one group which can participate in the curing reaction, generally with the characteristics of low viscosity, high conversion, low curing rate, small volume shrinkage, low crosslinking density and so on 2) Bifunctional active diluent It contains two (meth) acrylate functional groups Compared with single functional group active diluent, it is generally characterized by good dilution, faster curing rate and increased crosslinking density 3) Multifunctional active diluent There are three or more (meth) acrylate functional groups, which have the characteristics of high viscosity, fast curing speed and high film hardness 4) Active diluent of cationic UV curing system Such as alicyclic epoxy resin, polyol and vinyl ether In the selection of active diluent, the following problems should be considered: compatibility with oligomer, dilution capacity, curing speed, curing shrinkage and the effect on the performance of curing film 2.2 photoinitiator is one of the key components of UV curing system Its performance determines the curing rate and degree of UV curing coating According to the different reaction mechanism, it is free radical polymerization photoinitiator and cationic polymerization photoinitiator Free radical photoinitiator can be divided into two types: cracking type and hydrogen grabbing type In the field of UV curable coatings, small molecule free radical photopolymerization initiators are widely used, in which unreacted photoinitiators and photodegradation fragments are easy to cause the film to age and turn yellow; polymerization hydrogen abstraction photoinitiators can also be used, in which the incomplete reaction of photoinitiators will also cause the film to age and turn yellow If the photoinitiator is macromoleculized and multifunctional (containing two or more photochemical active groups), the yellowing of the film caused by the photoinitiator can be reduced [16-17] For cationic curing system, only vinyl ether functional group resin, epoxy resin and epoxy functionalized polysiloxane resin are suitable for oligomer, which limits the use of cationic curing agent The free radical photoinitiator has the advantage of low price Most UV curing coatings are cured by free radical, but also by cation and free radical mixed dual UV curing, which can form interpenetrating network structure to improve the performance of the coating The curing rate and degree can be adjusted to meet different needs by reasonably using the type and amount of photoinitiator and the compatibility technology with photosensitizer [18] UV curable coatings are difficult to cure when they are used in the components with complex shapes It is also difficult to cure in thick coatings, opaque media and colored systems These can be overcome by a dual curing system, i.e through a light curing reaction stage and a dark reaction (including a heat curing, moisture curing, oxidation curing or anaerobic curing reaction) stage, wherein the light curing reaction makes the system quickly set or reach the surface dry, while the dark reaction makes the bottom part or the shadow part completely solidified [19-20] 2.3 in the actual application of UV curable coatings, due to the rapid rate of UV curable, in addition to the basic components, various additives (including leveling agent, defoamer, wetting dispersant, coupling agent and extinction agent) should be added to meet the use requirements [21-22] The addition of leveling agent can solve the defects on the surface of UV curable coating caused by leveling; the addition of wetting dispersant and defoamer can increase the product stability and construction performance; the addition of coupling agent can improve the construction performance and adhesion With the development of the application field of UV curable coatings, in order to meet the application requirements of the coated objects, the additives available are matting agent, thermal polymerization inhibitor, sensitizer, stabilizer, etc 2.4 pigments and fillers shall be used to prepare UV curable colored paint, and pigments and fillers shall also be added 1) Pigments Attention should be paid to the influence of pigments on the performance of coatings Many pigments (such as carbon black, iron yellow, etc.) can scatter or absorb UV radiation, which hinders UV curing [23] There is a big difference between the UV absorption of pigment on the surface and the depth of the film, which may cause the film shrinkage and wrinkling due to the asynchronous curing of the surface and the bottom Therefore, it is necessary to choose the pigment matching with the system 2) packing The results show that talcum powder and calcium carbonate can be used as fillers for UV curable coatings The addition of some nano fillers increased the wear resistance, antibacterial property, aging resistance, flexibility and gloss of the coating significantly [24-25] Conclusion: UV curable coating is a kind of high-efficiency energy-saving and environmental protection coating The film has excellent performance It is expanding to various application fields of traditional coating step by step With the deepening of research, it has great development potential in industrial application Compared with developed countries, China's UV curable coating industry still has some gaps in research and development, market scale and other aspects, but the development speed is startling, facing an opportunity to cooperate with the implementation of sustainable development strategy, and I believe that it will be further improved with the efforts of the majority of scientific researchers