2023 The Complete Guide To Improvement and future trends of UV technology
Light (UV) curing technology is a highly efficient, environmentally friendly, energy-saving, high-quality new technology for the 21st century, widely used in coatings, adhesives, inks, optoelectronics and other fields. Since 1946, the United States Inmont made the first UV-curable ink patent, in 1968, Germany Bayer developed the first generation of UV-curable wood coatings, light-curing coatings in the world to obtain rapid development. In recent decades, a large number of new, efficient photoinitiators, resins, monomers and advanced UV light sources are used in UV curing, promoting the development of the UV curing coatings industry.
Light curing technology continues to progress
Light curing technology refers to the light as the energy source, through the light to make the decomposition of photoinitiators to produce radicals or ions and other active species, these active species trigger the polymerization of monomers, so that the rapid conversion from liquid to solid polymer technology, due to its low energy consumption (1/5 to 1/10 of the thermal polymerization), fast (seconds to dozens of seconds to complete the polymerization process), no pollution (no solvent volatilization) and other advantages and is known as the green technology.
At present, China has become one of the largest applications of photopolymeric materials, in the field of development of international attention. In today’s increasingly serious environmental pollution, the development of non-polluting and environmentally friendly photopolymerization technology is very important. According to statistics, the global annual release of hydrocarbons into the atmosphere is about 20 million tons, most of which are organic solvents in paints. The organic solvents emitted into the atmosphere during the manufacturing process of coatings are 2% of the production of coatings, and the organic solvents volatilized during the use of coatings are 50% to 80% of the amount of coatings. In order to reduce pollution emissions, UV-curable coatings are gradually replacing traditional heat-curable coatings and solvent-based coatings.
With the continuous progress of light curing technology, its application areas will also be gradually broadened. Early light curing technology was mainly in coatings, because at that time it was not possible to solve the problem of light penetration and absorption in colored systems. However, with the development of photoinitiators and the improvement of light source power, light curing technology can gradually adapt to the needs of different ink systems, light-curing ink has gained rapid development. The continuous progress of light-curing technology in recent years has allowed it to penetrate into other fields. Due to the progress of basic research, a deeper understanding of the basic mechanism of light curing, and changes in the social environment will also put forward new requirements for light curing technology, light curing technology has been able to innovate and develop.
Light-curing coatings are increasingly widely used
UV-curable coatings include.
Light-curing bamboo coatings: as a special product in China, bamboo furniture and bamboo flooring and other products are now mostly used UV-curable coatings. The proportion of various domestic floor UV coating is very high, is one of the important uses of UV coating.
Light-curing paper coating: As one of the first UV coating varieties used, UV paper varnishing coating is used in various printed materials, especially advertising and publication covers, which are still the larger UV coating varieties.
Light-curing plastic coatings: Plastic products need to be painted for aesthetic and resistance requirements. UV plastic coatings have many types and vary greatly in requirements, but are mostly decorative, and the most common UV plastic coatings are the shells of various home appliances, cell phones, etc.
Light-curing vacuum coating coatings: To increase the texture of packaging, the most common method is to metalize the plastic by vacuum vapor deposition, this process requires the use of UV primer, top coat and other products, its main use is cosmetic packaging.
Light-curing metal coatings: UV coatings for metals include UV antirust primers, UV-curing metal temporary protection coatings, metal UV decorative coatings, metal UV surface protection coatings, etc.
Light-curing optical fiber coating: The production of optical fiber needs to be coated 4~5 times from bottom to surface, which is almost all done by light-curing at present. UV optical fiber coating is also the most successful example of light-curing application, and its light-curing speed can be up to 3000m/min.
Light-curing conformal coating: for outdoor products, especially electronic products, need to withstand the test of wind and rain and other natural environmental changes, in order to ensure the long-term normal use of the product, the need to protect the electrical appliances, etc., UV conformal coating is developed for this application, designed to extend the service life of electrical appliances and the use of stability.
Light-curing glass coatings: glass itself is poorly decorative, if you need the glass to produce color effects, you need to paint, UV glass coatings were born, this type of product on aging resistance, acid and alkali resistance requirements are high, is a high-end UV products.
Light-curing ceramic coatings: ceramics in order to increase its beauty, the need for surface coating, UV coatings currently applied to ceramics are mainly ceramic inkjet coatings, ceramic flower paper coatings, etc.
Light-curing stone coatings: natural stone will have a variety of defects, in order to improve its aesthetics, the need for stone finishing, the main purpose of light-curing stone coatings is to repair the defects of natural stone, high requirements for strength, color, wear resistance, aging resistance.
Light-curing leather coatings: UV leather coatings have two categories, one is UV leather release coating, used in the preparation of artificial leather patterned paper, its dosage is very large; the other is the decorative coating of leather, change the appearance of natural or artificial leather, enhance its decorative nature.
Light curing automotive coatings: lights from inside to outside will use light curing technology, light bowls, lamp shades need to be painted through light curing technology; a large number of parts in the interior and exterior of the car use light curing technology such as instrument panels, mirrors, steering wheels, gear handles, wheels, interior trim strips, etc.; the car’s bumper is prepared through light curing technology, and the surface coating is also light polymerization to complete; a large number of electronic parts of the car such as The preparation of car display, central control panel, etc. also need to use light-curing materials; and now the popular car coat, its surface aging-resistant coating is also completed by light-curing technology; and car body coating has been achieved light-curing; car paint film repair, glass breakage repair, etc. will also use light-curing technology.
Light-curing water-based coatings: In order to solve the problem of pollution caused by the need to add solvents for UV coating spraying, an important direction is the water-based UV coatings, water as a solvent to improve the construction performance of UV coatings, water-based coatings at home and abroad are in the initial stage.
Light-curing powder coatings: the combination of ordinary powder coatings and light-curing technology, the development of light-curing powder coatings with low curing temperature, excellent product quality, wide range of applications. The coating is in the research and development stage in China, but has been industrialized abroad.
Light-curing antistatic coating: Light-curing antistatic coating is a special coating that adds antistatic components to UV coatings to increase the antistatic ability of the coating, although the amount of application is not large, but has its own special characteristics.
Light-curing flame retardant coatings: Light-curing coatings sometimes need flame retardant effects, and thus can be solved by adding special flame retardants to the coating’s flame retardant problem. Although some general flame retardants can be applied to UV coatings to give them flame retardant effects, UV flame retardant coatings also have their own special structural requirements due to the special characteristics of UV coatings, such as light transmission requirements.
Light-curing fluorocarbon coatings: Fluorocarbon coatings are widely used because of their good weathering performance, and the application of light-curing fluorocarbon coatings is becoming more and more common. The key is to solve the problem of mutual solubility of different components, which requires the preparation of UV fluorocarbon coating raw materials that meet the requirements of use, starting from the structural design of the material.
Improve light curing technology from raw materials and technology
In terms of light curing technology itself, in order to maintain its inherent advantages and enhance its competitiveness, it is also necessary to constantly update its own technology, from raw materials, new technologies and other aspects to make continuous progress, mainly in the following areas.
Light curing surface modification
Light curing technology due to the limitations of light transmission, can not penetrate into the interior of the material, and therefore its application is mainly the chemical reaction of the surface of the material. In general material surface applications, from ordinary printing varnish to home decoration, building materials, automotive interiors, outdoor protection, light curing technology is also playing its advantage. For some special environments and time-sensitive applications, light-curing technology has an irreplaceable position, such as for the renovation of schools, hospitals, indoor outlets, garages and other sites. Due to time constraints, such as schools needing to use short holidays to complete reworking, hospitals needing to use nighttime recesses to complete the renovation of operating rooms, etc., a technology that is both fast and safe is needed to complete, and light-curing technology is the best choice. On the other hand, because light-curing coatings have no solvent emissions, making them much safer.
Light curing patterning
Light curing can be used for the preparation and transfer of graphics due to its spatial and temporal controllability. Photolithography is achieved by taking advantage of the spatio-temporal controllable nature of photocuring technology. Through photopolymerization technology, different levels of photolithography applications for chip, LCD display, and circuit board manufacturing can be realized, and different sizes of graphics can be transferred to different substrates to achieve precision graphics production. Currently, microelectronic components are getting smaller and higher performance, an important reason is that the photolithography technology is getting higher and the lines obtained are getting smaller, making the miniaturization of microelectronic devices possible, and the energy consumption is also getting lower. In addition, light-curing technology can also be used for microfluidic processing, three-dimensional image preparation, complex structure processing, etc. These precision processing techniques require very high requirements for light-curing materials, and their purity is completely different from ordinary inks and coatings.
Light-curing 3D printing
Light curing is particularly suitable for rapid processing and molding, such as 3D printing, due to its fast curing characteristics, which can realize the rapid molding of complex objects. At present, 3D printing technology, light-curing 3D printing is the most widely used, such as laser as the light source of three-dimensional lithography is the basis of 3D printing, is the first generation of 3D printing technology, the use of laser as a light source for rapid surface sweeping, to achieve three-dimensional graphics fixed. At present, light-curing 3D printing technology has expanded into numerous products, and the light source has gradually developed from the earliest ultraviolet light to visible light.
Light-curing biomaterials
The application of light-curing technology in biomedicine mainly includes oral repair materials, bone repair, rapid tissue wireless suturing, surgical clinical simulation models, cardiac surgery fixation, tissue defect repair, soft tissue hydrogel preparation, etc. The earliest developed light-curing biomaterials is light-curing dental repair materials, the current orthodontic model of light-curing 3D printing has been widely used; light-curing orthopedic materials are mainly used to replace the traditional bone repair stainless steel materials, both to achieve rapid repair, but also to reduce the pain of secondary surgery to remove fixed parts; light-curing cardiac surgery fixation, tissue defect repair and light-curing bone repair is relatively similar, only the site is different For example, the heart needs to beat, so the material needs to be elastic, unlike bone which is rigid, and different human tissues have different functions and structures, so the repair material needs to have the same structure and function, otherwise the repaired tissue cannot work properly. Wireless suture technology is a technique that uses light curing to enable rapid repair of patient wounds without the need for sutures, and these light curing adhesives are also degradable and do not need to be removed, thus reducing the stitch removal process for the patient, which is important for in vivo surgery, but in clinical practice, light curing wireless sutures face numerous challenges.
Light-cured propriety materials
With the advancement of light-curing technology, processes combining photopolymerization with other technologies have begun to be applied, such as photo-thermal and photo-tidal technologies, front-line photopolymerization, and cationic photopolymerization. Light curing has begun to gradually shift from surface modification to propriety materials for the preparation of various propriety materials such as light-cured composites, light-cured block materials, light-cured automotive, aircraft, spacecraft components, etc. For example, light is used as the driving force to first realize the polymerization of the material surface. As the material polymerization emits a large amount of heat, when the heat released from the polymerization is sufficient to trigger the traditional thermal polymerization, light is no longer needed, and the thermal polymerization will also generate heat to further trigger the subsequent polymerization. Similarly, after the material surface polymerization is achieved using photopolymerization, if subsequent tidal polymerization can occur, water in the air can continuously penetrate into the material so that tidal curing can continue to occur until all materials are polymerized and stopped, which can be used to prepare materials of great thickness. For photocation polymerization, the cations, once generated, will survive for a long time, so that light can be used to initiate cation polymerization first, and for parts that light cannot penetrate to, the cations already present can be used to achieve continued curing of the cations by heating. These technologies have been used in the production of automotive bumpers, automotive interior parts, aviation parts, and aircraft parts, especially after the lightweighting of automobiles is on the agenda, and the application of carbon fiber composites in automobiles is gradually achieving mass production, and the application of light curing technology is becoming more and more popular.
Other potential applications of light curing
solar panels in the preparation process will be used in the light curing technology such as EVA diaphragm cross-linking, solar surface stain-resistant coating, organic solar cells roll-to-roll light curing coating.
The preparation of wind power blades can already achieve light curing, and when the wind blade damage repair, light curing is one of the easiest, most effective and most economical methods.
In addition to the aforementioned automotive, aircraft and other applications of light curing, light curing technology in the interior trim parts of high-speed rail, high-speed rail composite materials, ship interior materials also have a large number of applications, such as light-curing fire-resistant interior panels for high-speed rail and cruise ships, high-speed rail overall bathroom coating.
Light-curing technology for repair of damaged roads, its performance is similar to that of concrete, and can achieve a quick completion of 30 minutes, so as not to cause extensive traffic jams.
For highway signs, due to long-term exposure to complex environments, both high temperature, high humidity, and very low temperature, wind and sun, and should not be frequently replaced, so the requirements are very high, foreign countries have used electron beam (EB) curing technology for highway signs surface coating to achieve aging resistance, high temperature and high humidity, rain and snow resistance, etc.
In recent years, with the development of microelectronics preparation technology, the application of light curing technology in the optical film is becoming increasingly mature, from ordinary hardening film to brightening film, from polarized film to diffusion film preparation have light curing figure, and the chip manufacturing photoresist is very critical.
Future trends in light curing technology
The development of light curing and its raw materials, equipment, technological advances are inseparable, the future development of light curing including the following aspects.
Development of functionalized resins
Resins containing low surface energy functional groups will be used for stain-resistant coatings, these include silicon-containing, fluorine-containing structural units, the silicon-fluorine structure can effectively reduce the surface energy of the system, thus playing a role in stain resistance and self-cleaning.
Light-curing water-based resins are mainly resins containing cationic, anionic or non-ionic groups, which can be dissolved or dispersed in water, so that water can be used as a diluent to reduce the application of organic solvents and thus reduce VOCs emissions. The biggest problem with current water-based UV resins is that the final properties of the prepared coatings such as water resistance, acid and alkali resistance, solvent resistance, and scratch resistance do not meet the demand.
Inorganic-organic hybrid resins are used for the preparation of high-performance surface coatings to improve hardness and scratch resistance. These resins are mainly prepared by sol-gel method with inorganic nanoparticles, which are uniformly dispersed in the organic phase, with the organic phase providing polymerization properties and the inorganic particles providing other functionalization.
The development of ultra-low viscosity resins has become imperative in recent years due to the development of light-cured products such as 3D printing, inkjet printing, and solvent-free spraying, where the demand for low-viscosity resins has been increasing year by year. As modern light-curing materials for curing coating performance requirements are increasingly high, in order to improve material performance, the need for high-functional resins to improve polymer properties to improve material performance, a more advantageous program is modified with hyperbranched polyester, etc., the synthesis of polymerizable resins.
The development of resin based on renewable resources is the current development of hot spots, such as natural oils and fats, natural sugar compounds, natural polymers, plant and animal extracts based on the preparation of resin has been a lot of basic research, some products such as soybean oil modified acrylate, furfural resin acrylate, etc. have been industrialized.
The development of light sources
Traditional light curing to high-pressure mercury lamp as the light source, the use of the process will produce ozone and pollution of the environment, a large amount of heat and energy waste, and mercury itself is a toxic substance, making the application of mercury lamps are limited, the development of new light sources is a major task, energy-saving, safe, efficient LED light source is an effective alternative.
The development of different wavelengths, especially wavelengths in the 300nm to 365nm LED light source is a major need for light curing technology, the light source of efficient light is the key to energy saving. For long wavelength LEDs such as 385 to 405nm wavelengths are well established, but the problem is that there are very few photoinitiators matching these wavelengths, making their application limited; on the other hand, long wavelength LED light sources are not yet good enough to solve the problem of material surface curing, and thus the need to develop short wavelength LED light sources. However, the shorter the wavelength, the higher the energy of light, high energy will destroy organic molecules to decompose, thus the short-wavelength LED packaging materials is the biggest difficulty, if the final solution to the short-wavelength LED packaging and its high energy, that will make the application of light curing technology has been greater development, because the LED light source long life, low cost, low energy consumption, these will be very conducive to the promotion of light curing technology.
Light curing new technology
EB curing technology is also essentially light polymerization technology, the difference is that EB technology is shorter wavelength, higher energy. EB curing technology in China is still in its infancy, but with the maturity of domestic EB equipment, the application of the technology will be promoted. In recent years, EB curing in printing applications have taken off, because EB curing printing more energy efficient, higher speed, better product quality. Cigarette filters are a direct contact with the human mouth material, and therefore its requirements are extremely high, neither dissolved in water, and can not have any compounds migrate out, but also can not have an odor. However, the filter is a paper that is not water resistant at all. A coating needs to be applied to this paper to achieve water resistance, biosafety and other properties, and EB cured coating is one of the best options.
EB cured release film is also starting to be applied in China, mainly by using the high energy of EB, which enables the material to be highly cross-linked so that no small molecules are released from the release layer, ensuring the release stability of the release film, especially for high performance film materials like optical films, any contamination in the release layer will reduce the performance of the optical film and make it unusable, thus EB release film is mainly used for high-end products.
The application of EB in the coil steel coating has been achieved in mass production abroad, but in China is still in the initial stage, its biggest advantage is the fast curing speed, which can greatly improve the production efficiency and reduce energy consumption, in addition, its product performance is also very good, especially the outdoor aging resistance is much higher than the light-curing coating and traditional heat-curing coating. Solvent-free spraying technology is mainly developed to solve the problem of solvent pollution caused by the need to add a certain amount of solvent to dilute the spraying.
Cationic photopolymerization technology
The current rapid development of free radical system due to its own shortcomings, can not meet the requirements of some applications, and therefore the development of cationic photopolymerization is an effective complement. For example, for highly flexible coatings, general free radical photopolymerization cannot be achieved due to the material’s own characteristics, while photo-cationic polymerization with epoxy as the main body can be easier to obtain highly flexible coatings. In addition to the coating of metal substrates, free radical photopolymerization system due to its rapid polymerization and volume shrinkage, the coating adhesion is poor, while the use of cationic photopolymerization, epoxy in the polymerization process to open the ring and cause volume expansion, can greatly improve the adhesion of the coating.
The development of photopolymerization technology is related to its own technological progress, but also with the national policy, the requirements of other areas, other industry technological breakthroughs are related to the strict environmental policy in China, solvent emissions are restricted, non-polluting photopolymerization technology will be favored.