UV curing coating composition and performance

China Coatings Online News
With the in-depth research on lymers, active thinners, light triggers, additives and pigments, new materials continue to appear, liquid UV-cured coatings will be rapidly expanded into various applications of traditional coatings, the following is a general overview of the components of the study.1· UV-cured coating oligomeroligopolymer, also known as prepolymer, is the base resin of UV-cured coating, as a skeleton in the UV-cured coating system occupies a considerable proportion of the system's basic properties (including adhesion, hardness, flexibility, wear resistance, heat resistance, chemical resistance, durability, optical properties and aging resistance) play a decisive role. UV curing coating research and application of a wide range of low-polypolymer types are mainly unsaturated polyester, epoxy acrylates and polyurethane acrylates.1.1 Unsaturated PolyesterUnsaturated Polyester (Unsaturated Polyester, UPE) is the first low-polymer used in UV-cured coatings, which refers to a molecule containing a straight chain or branch-chain polyester molecule that reacts to the C double bond. In the active free-form caused by the occurrence of lively vinyl and other monomers and UPE co-ed, can cross-link curing network structure. However, the polymerization reaction time is long, the temperature is high, and the oxygen resistance of the polymerization process is more serious, which increases the yellowing of the coating film and therefore the application is limited. The use of overspending technology to prepare unsaturated polyester with multi-official energy is one of the ways to solve the problem. Overspending lysum has a unique three-dimensional molecular structure, so that it has good solubility, low viscosity and high reactive properties, the shrinkage of curing film is smaller, has a good substrate attachment performance, and can also avoid the use of volatile active thinners, so more environmentally friendly.1.2 epoxy acrylatesEpoxy acrylates (Epoxyacrylate, EA) are obtained by epoxy resins and acrylic or methyl acrylic acid under the action of catalysts, according to the structure type can be divided into bisphenol acrylic acrylates, phenolic acrylic acrylates, modified epoxy acrylates and acrylic acrylic. EA photo-curing reaction rate is fast, curing film adhesion, hardness, strength, gloss and chemical resistance are good, and the price is low, is the largest consumption of photo-curing low-lying property in the photo-curing industry. EA viscosity is high, affecting construction and leveling, curing film brittleness, poor flexibility, not resistant to aging, so the improvement of epoxy acrylic performance research has been ongoing, such as increasing the relative molecular mass of low polymers to reduce shrinkage when curing, the introduction of silicone compound synthesis of a prepolymer to improve coating heat resistance, the introduction of flexible long chain to overcome the brittleness of epoxy resin.1.3 Polyurethane Acrylates (PUA)Polyurethane acrylate (PUA) are NCO groups and polyols made from polycyanate Hydroxyl reaction, and the introduction of photoactive groups using hydroxypropyl acrylics, with the increase of molecular mass and the increase of photoreactive groups contained in the molecule curing speed, is an important type of photo-curing lymer. The star-shaped overspending polymer with three-dimensional spline structure of PUA is becoming the focus of research, which is different from the traditional linear polymer, so that the polymer has the characteristics of high-level energy, inter-molecular and non-tangled molecules, so the polymer has high activity, low viscosity, good solubility, and easy change of the function group, etc., can obtain suitable construction performance and excellent coating properties. Although PUA price is relatively high, but polyurethane acrylic curing film has excellent flexibility and wear resistance, good chemical resistance and impact resistance, better adhesion and other advantages, so PUA is the amount of low-polymer next to EA.2· Active diluents, light triggers and additives for UV-cured coatings and pigments 2.1 active thinnersactive thinners are small organic molecules containing polymeric energy groups that dissolve and dilute low-polymers, regulate the viscosity of the system, improve construction performance, and can participate in polymerization curing into films, regulating the speed of photo-curing and various properties of curing membranes, such as toughness, hardness, flexibility, etc.1) Single-cell active diluent. (meth) acrylic, etc., each molecule contains only one can participate in the curing reaction group, generally has a low viscosity, high conversion rate, low curing rate, small volume shrinkage, low cross-link density and so on.2) Double-ernation group active thinner. Contains two (methyl) acrylic groups, compared with single-function group active thinners, generally has good dilution, curing rate accelerated, cross-link density increased and so on.3) Multi-official group active thinner. Contains 3 and above (methyl) acrylic energy group, generally has a larger viscosity, fast light curing speed, film hardness and high characteristics.4) the active thinner of the cation UV curing system. Such as lipid ring epoxy resin, polyol and vinyl ether. The following issues should be considered when selecting active thinners: compatible with lysate, dilution capacity, curing speed, curing shrinkage and effect on curing coating properties.2.2 light triggerguangensor is one of the key groups of photo-curing system, its performance determines the curing rate and curing degree of UV curing coating, according to the reaction structure of the different free-based polymerizing light trigger and cation polymerizing light trigger, free-based photoretic agent is divided into two types of lysate and hydrogen-grabbing type. In the field of UV-cured coatings, more small molecules free-based photoreagulation agents are used, in which unresponsive light triggers and photolysisfragments tend to make the coating film aging yellow; A polymerized hydrogen-grabbing light trigger can also be used, wherein the incompletely reactive light trigger will also make the coating film aging yellowing. If the light trigger is largely molecularized and multi-ernatic (containing 2 or more photochemically active groups), the yellowing of the coating film caused by the light trigger can be reduced. For cation photo-curing system, the applicable low-polymer only vinyl ether group resin, epoxy resin and epoxy-energy polysilicae resin, so that the use of cation photo-curing agent is limited.free-based light trigger has low-cost advantages, most UV curing coatings use free-based curing, but also the use of cation and free-based hybrid dual UV curing, can form an interoperability network structure to improve film coating performance. The curing rate and curing degree are adjusted to meet different needs by rationally utilizing the type and dosage of light triggers and the technology of matching with photosensitive agents. 。 UV curing coatings can be difficult to cure when used in complex-shaped components, as well as for thick coatings, opaque media and colored systems. These can be overcome by a dual curing system, i.e. through the photo-curing reaction phase and the dark reaction (including thermo cure, moisture curing, oxidation curing or anaerobic curing reaction, etc.), wherein the photo-curing reaction makes the system quickly shaped or reached the table dry, while the dark reaction makes the underlying part or shadow part cured completely. 2.3 additives in the actual UV curing coating applications, due to the fast rate of light curing, in addition to the basic ingredients, but also to add a variety of additives (including leveling agents, deblisters, moisturizing dispersants, coupled agents and detergents, etc.) to meet the requirements of use. The addition of leveling agent can solve the defects of UV curing coating due to the poor leveling and the coating surface, etc. The addition of wetting dispersants and desiccants can increase product stability and construction performance. The addition of the coupled agent can improve construction performance and adhesion, etc. With the continuous expansion of UV curing coating applications, in order to meet the requirements of the use of coated objects, optional additives are also anti-light, thermal inhibitors, sensors, stabilizers and so on. 2.4 pigment fillers to prepare UV-cured colored coatings, but also to add pigment fillers. 1) pigments. The effect of pigments on coating performance should be noted, and many pigments (e.g. carbon black, iron yellow, etc.) scatter or absorb UV radiation to prevent UV curing. Pigments in the coating surface and the depth of the coating film on the UV suction also has a large difference, may cause the surface and bottom curing out of step caused by the coating film contraction wrinkles, so choose to match the system pigment. 2) Filler. Experiments show that talcum powder and calcium carbonate can be used as fillers for UV-cured coatings. The addition of some nanofillers has significantly improved coating wear resistance, antibacteriality, aging resistance, flexibility and gloss. 3 Conclusion UV curing coating is a kind of energy-efficient and environmental protection coating, coating film has excellent performance, is further expanding to the traditional coating application areas, with the depth of research in the industry has great potential for development. China's UV cured coating industry in research and development, market size and other aspects compared with developed countries, there are still some gaps, but the pace of development is alarming, facing an opportunity to cooperate with the implementation of sustainable development strategy, I believe that in the vast number of scientific research workers and other efforts will be further promoted and developed.
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