UV ink: a blooming sun flower in the ink family

UV ink is a new type of environment-friendly ink. It has fast drying, high production efficiency; no solvent discharge, no environmental pollution; low energy consumption; suitable for a variety of substrates, especially for heat-sensitive substrates (such as Paper, plastics, etc.); excellent performance of printed products; combined with the advantages of low investment in UV curing equipment, small footprint, etc., have always been valued by countries around the world and have achieved rapid development, especially in the printing and packaging industry and the electronics industry. Application (see Table 1).

* North American and European statistics for 2002 and Japan for 2001 statistics.
* Electronic chemicals also include photoresist and dry film.

Table 1 UV ink production statistics for North America, Europe and Japan*(t)

Since UV inks fully comply with the “5E” features: Efficient, Enabling, Economical, Energy Saving, and Environmental Friendly, it is a green industrial product, so not only Developed countries and also in developing countries are also vigorously promote the application.

In the early seventies of the last century, ink printing plants in Shanghai and Tianjin began to develop UV inks for printing. However, due to the lack of raw materials at that time, the light sources and curing equipment could not be matched, and thus they could not be industrialized. After the reform and opening up, due to the development of the printing and packaging industry and the electronics industry, a number of foreign UV curing production lines were introduced and various UV inks were required; domestic companies could not only produce UV light sources and UV curing equipment but also assemble various products through digestion and absorption. In the production line, the market for UV inks has rapidly expanded, which has led to the development and production of domestic UV inks. At the end of the last century, raw materials needed for UV inks: reactive diluents, oligomers, and photoinitiators were rapidly localized, and UV inks were also produced. Provides a material basis, since the end of the last century, China's UV ink production has been unprecedented development. Since 1998, China Photographic Association began statistics, when the domestic UV ink production was only 1030 tons, to 9056.5 tons in 2004, 8.8 times in 1998, the growth rate is far faster than China's sustained rapid development of the national economy (See Table 2). The variety of UV inks has also increased from the original 4-5 kinds to more than 20 kinds at present. High-grade UV offset printing inks, screen printing inks, optical disc inks, and photo-imaging PCB inks have all been mass-produced, and it is even more gratifying to have a small amount of UV screen printing ink, UV ink for PCB and CD ink export. The industry has also emerged a number of key enterprises with a certain scale and R&D strength, such as Hangzhou Hanghua Ink Chemical Company, Shenzhen Miramar Ink Coating Company, Guangzhou Xuwei Fine Chemicals Research Institute, Zhongshan Zhongyi Ink Coating Company, Panyu Guangxin Silk screen materials company, Shenzhen Rongda Electronic Materials Co., Ltd., Fuji Chemical Research (Kunshan) Co., Ltd., Beijing Rio Tinto Technology Co., Ltd., etc., have become the vanguard of the sustainable development of UV inks in the future.

Table II Statistical Summary of UV Ink Production in China 1998-2004

UV inks are produced by dispersing and milling oligomers, reactive diluents, photoinitiators and pigments, fillers and various additives. They use UV light to generate free radicals or cations for photoinitiators. The polymer and the reactive diluent undergo polymerization and cross-linking, allowing the liquid ink to dry quickly. UV inks can be categorized into two categories according to their uses, namely UV printing inks used in the printing and packaging industry and UV inks used in the electronics industry.

The most common UV printing inks are UV and UV screen printing inks, as well as UV coatings.

The use of UV offset printing inks has changed the past due to the shortcomings of inks that cannot be dried immediately due to the inability of inks to print; due to the rapid curing of UV inks, the penetration and diffusion to paper is reduced, and the color of prints is more saturated and clearer. The use of UV inks does not volatilize solvents and is both environmentally friendly and safer. At present, UV inks have been applied in different printing methods such as embossing, flexo printing, gravure printing, silk screen printing, and pad printing. In particular, various UV inks with special effects such as ice printing ink and matte ink have been developed in silk screen printing. , Refraction ink, wrinkle ink, hammer ink, coral ink, crystal ink, foam ink, etc., they have become important printing materials for high-end tobacco and alcohol, tea, health products and food packaging. Most toothpaste and cosmetic hose packaging has been screened with UV ink and then UV-coated. The use of UV inks and paints is also used for the coating and decoration of metal containers for foods such as cans, candies, and snacks. A variety of advertising, signage, billboards, flags, etc. are all applications of UV screen printing inks. In the 21st century, large-format UV inkjet printing equipment and UV inkjet inks were successfully developed. UV inks have entered the new field of digital imaging materials and will become a new force for outdoor large advertising and signage production. In addition, UV offset printing on paper or silk printing and partial glossing have become important decorative methods for books and magazine covers, postcards, advertising posters, carton packaging, and decorative paper bags.

UV inks used in the electronics industry are mainly used in the production of printed circuit boards, optical fibers, optical disks, and magnetic cards.

Printed circuit board (PCB) manufacturing is a very successful area for UV ink applications: UV-resist inks, UV solder mask inks, and UV character inks are required for the fabrication of single-sided and flexible boards; light imaging is required for the fabrication of double-sided and multilayer boards. Anti-corrosion and plating resist inks, photo-imaging solder mask inks, and UV character inks. In optical fiber manufacturing, in addition to using a variety of UV fiber coatings and adhesives, UV optical fiber pigmented inks are also applied. There are 12 different colors to distinguish different fibers and perform bonding. In the manufacture of optical discs, UV coatings and adhesives are also required. Finally, screen printing or offset printing of UV inks is used to print patterns and texts to produce finished products. Cards, smart card text pattern printing, televisions, refrigerators, air conditioners and other home appliances and computers, mobile phone keyboard production, keyboard surface printing, touch switch production, etc. are inseparable from the UV ink. The production of various nameplates and signs also requires UV inks.

Although UV inks have many advantages, they are still relatively expensive; some raw materials still have certain shortcomings: some reactive diluents have a certain irritation to human skin and mucous membranes, and some photoinitiators have odorous photodegradation products. Therefore, it is not suitable for use in pharmaceuticals, foods, and children's toys and other packaging products; UV inks are suitable for flat printing and finishing. For the three-dimensional coating due to uneven light, the parts with poor lighting are not well dried and the original coating is difficult to cure. . In order to overcome the above-mentioned problems, people have conducted exploration and research in the following areas in recent years and have made great progress.

1. Development of water-based UV inks: This is a new type of UV ink that was developed in the 1990s. It has the advantages of high UV ink production efficiency, energy saving, environmental protection, and non-toxic and safe water-based inks. A hot spot of research on UV curing materials at home and abroad. Water-based UV inks are characterized by using water as a diluent to adjust the viscosity of the system, which is safe and economical. It also completely avoids the irritation and odor of skin caused by the use of acrylic functional monomers as diluents in general UV inks, and also equipment and containers. Easy to clean. At present, some large foreign companies such as Cytec, Sartomer, BASF, Bayer, Corning, Ciba, and Ninbo Di have developed oligomers and photoinitiators for waterborne UV systems. US Lida, Beijing Yingli Technology and other companies have introduced water-based UV screen printing inks.

2.UV inkjet inks will gain rapid development: Inkjet printing is a non-contact printing process that requires no printing plate to form an image by ejecting ink droplets onto the substrate. Inkjet printing composes graphics and texts by computer, and controls inkjet printers to jet ink droplets to obtain accurate images. It is a process of digital imaging. It is the most rapidly developing digital imaging method with on-demand printing. Speed, high quality, color saturation and other advantages. UV inkjet is also a new technology developed at the end of the last century. It combines the respective advantages of inkjet printing technology and UV curing technology, both the convenience of use and operation of inkjet printing technology, and UV curing technology. The economic and technical advantages have become a shining new star in the field of digital imaging. UV inkjet printing has long been used in the digital coding and marking industry, such as printing and digital printing of bar codes on various beverages, packaging and labels, marking and data printing on cable wires, optical fibers, automotive hoses, and the like. In recent years, it has been widely used in the production of large-format, small-batch billboards and outdoor signs in the field of platform printers. Although the current market share of UV inkjet printing inks is less than 1% in the global ink-jet ink market, online survey statistics show that the UV ink-jet ink has the highest growth rate among all inkjet printing methods. It is expected that UV inkjet inks will be available by 2010. In the inkjet market, the proportion will exceed 10%, especially in the platform inkjet printers, UV inkjet inks will occupy a dominant position. In addition to ink jet printing, UV ink-jet printing technology has been expanded to include computer-to-plate making of offset printing, flexo printing, and screen printing, digital manufacturing of printed circuit boards, and inkjet printing and imaging of passive components and electronic materials. Inkjet inks will become a new force in the field of digital imaging materials. At present, Cytec and Sartomer all introduce oligomers using UV ink jet inks; foreign companies such as Creo, Selecom, Witt, 3M, and domestic companies such as Shenzhen Runtianzhi, Shanghai Taiwei, and Shenyang flight boats. The company has successively manufactured UV platform inkjet printers; Selenk, DIC, Flint, Orvis, Toyo, 3M and other companies have developed UV inkjet inks, and China's own UV products are also under development.

3. Application of dual-curing system in UV ink: As UV ink contains a large amount of pigment, they will absorb, reflect, and scatter ultraviolet rays, which will seriously affect the UV absorption of the photoinitiator, reduce the photoinitiation efficiency, and result in the ink cannot be completely dried. Especially for thick coating and three-dimensional coating weak light parts, the above problems are more likely to occur. At present, dual curing systems can be used, that is, in addition to free radical curing, cationic curing, thermal curing, redox curing, moisture curing, and anaerobic curing can be used to stop the illumination. After free radical curing, Post-curing can be continued to ensure that the ink is completely dry. Dual curing systems have been used in photoimaging PCB inks.

4.Advancement of EB inks: Electron beam (EB) curing is the use of high-energy electron beams generated by electron accelerators to cause the decomposition of compounds to produce radicals, ions and other highly reactive intermediate products, thereby initiating polymerization, cross-linking, and making liquid inks. Curing. Because it does not require the use of photoinitiators, curing is more complete. Therefore, EB ink can be allowed to be used in packaging materials such as medicine, food and children's toys in developed countries in Europe and America. At present, there are several electron beam accelerators for printing and packaging in the United States, Europe and Japan. China has just started and will build EB production lines in Shenzhen and Shanghai. It is believed that EB ink will be put into use in China soon.

With the advancement of science and technology, the development of UV curing technology, and the development of various new materials, it is expected that more, newer, better, and lower-priced UV inks will be developed, and the application of UV inks Will be more extensive, UV ink - the rising star in the ink family, like the blooming sun flower, will be more open, for the benefit of society.

Author: Chinese Photographic Society of Professional Committee of radiation curing Secretary-General Kim Yang Zhi