Characteristics of the hottest UV ink and its appl

2022-08-15
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UV printing ink characteristics and its application in packaging now

it has been more than 30 years since the UV printing ink cured by UV lamp has reached today's practicality. Compared with traditional oil-based inks, its advantages of instant drying, energy saving, space saving, solvent-free, pollution-free, low odor and so on have been highly evaluated and applied to various packaging products. In particular, it has been recognized in the aspects of operation efficiency, environmental protection, printing corrosion resistance, and has many applications in offset printing and flexo printing. This paper discusses UV ink and UV varnish in the field of packaging and printing

1 composition of UV inks

compared with the composition of UV inks and oily inks, UV inks that are instantly cured by group reaction produced by UV irradiation are different from ordinary oily inks that are dried by solvent infiltration into paper after several hours of oxidative polymerization reaction and aqueous inks that are dried by evaporation of solvent and water plus infiltration into paper, except for the same pigment. If you want to make a simple explanation of the curing mechanism of UV ink, it is that the photoinitiator in UV ink absorbs the ultraviolet light of UV lamp and reacts to generate free groups. The group is transformed into monomer and further monomer is obtained. This polymerization reaction continues to form a hard ink film, which is a way of instant drying

2 characteristics and advantages of UV ink

● rapid drying

● ink does not peel

● it will not dry on the machine

● no powder spraying

● printing sheets can be stacked

● post processing can be carried out immediately

● wear resistance, heat resistance, solvent resistance Corrosion of drug-resistant products, etc.

● less odor of printing materials

● the density will not decrease after drying

● the ink rarely changes

● it can be made into special ink shortcomings

● the ink price is high

● the point is easy to expand

● the water volume cannot be too large

● once the transferability of emulsion ink is extremely deteriorated

● not all ps versions are applicable

● not all rubber rollers are applicable

● there are many ink splashes

● sensitive to temperature changes

● most papers with poor adhesion performance are not applicable

● ink sometimes produces gel

● paper is easy to crack

● pick the type of metal foil and adhesive

● the density of black ink is insufficient

● general cleaning agents cannot be used to clean

3 UV ink (varnish) And application

1) offset UV ink

when sheet fed offset printing machine uses oil-based ink to print non absorbent substrate or thick paper, in order to prevent the back from sticking dirty, it is necessary to spray a lot of powder and use the receiving partition. UV ink can achieve instant drying without powder spraying. It can stack prints and enter post-processing immediately without worrying about the problem of dirty back. The ink film has high hardness, emits little odor, and does not contain VOC components, which is beneficial to environmental protection. UV ink has been popularized with packaging and printing as the center, and has been widely used in the printing of food packaging and cosmetics packaging made of cardboard and polyethylene coating paper. It has accelerated the intelligent and digital transformation of plastic equipment

compared with the nonabsorbable substrate of oily ink, UV ink has the characteristics of instant curing. It is printed on ① metal foil, holographic film and synthetic paper; ② PP video box printing and packaging machine 'target=_ Blank> transparent film printing; ③ PP, PVC, APET, pet, PS polycarbonate transparent packaging printing has many applications, especially in PVC cash cards, credit cards or pet prepaid cards (cards, orange cards, rewritten cards, highway cards) and other card printing

due to the adaptability of UV inks to the above purposes, many varieties of UV inks for offset printing have been introduced to the market, such as fast drying and low odor UV inks for paper, inks with good adhesion to film, inks with environmental protection soy certification, and UV hybrid inks corresponding to market needs. Among them, the application of UV hybrid ink in printing has attracted much attention in recent years. When the oily ink and UV varnish are combined in the printing and polishing production line, the gloss back of the print gradually decreases due to the penetration and drying of the oily ink. In order to solve this problem, UV hybrid ink was introduced. UV hybrid ink can use the cleaning agent and ink roller used by oily ink. It is an ink with good versatility. Its printed paper can be recycled, and has the printability and reproducibility close to oily ink. In use, it can be smoothly converted from the use of oily ink. The UV curing performance of UV hybrid inks used in recent years is being improved. Due to the poor wear resistance compared with ordinary UV ink, how to make it have both the curing performance of UV ink and the good printability of oily ink is a topic that ink manufacturers will face in the future

In terms of UV special inks, UV gold silver inks, UV fluorescent inks, UV invisible light (infrared light, ultraviolet light) colored inks, UV pearl inks, UV anhydrous inks, etc. are all applied in the packaging field

2) UV varnish

uv varnish has many varieties. The UV varnish used in the packaging field is shown in Table 2, table 3 and table 4

① UV op (overprint) gloss

General matte OP gloss and resin relief high gloss OP gloss with good adaptability to fountain solution are being used in the packaging field. The combination of UV ink + UV varnish is beneficial to the tolerance of printed matter, and this combination has become the mainstream method, but the cost burden is too large. Other combination methods have advantages in operability and cost, such as: a) using uv-op varnish designed according to the adhesion requirements of oily ink, and printing uv-op varnish on the surface of oily color ink (no powder spraying, paper receiving and stacking); b) Adopt UV mixed color ink + uv-op varnish; c) Printing uv-op varnish on the dried color oily ink. However, when using oil-based ink for machine polishing, gloss back phenomenon of gradual reduction in gloss will appear. UV mixed ink will reduce gloss back. It is used as the base color ink for coating uv-op varnish on the machine, and the proportion of use is gradually increasing

② UV coating varnish

coating vinyl resin and film to increase brightness processing, because it is carried out offline with printing, the production efficiency is poor, and the production of volatile solvents pollutes the working environment. UV coating varnish is solvent-free, which meets the environmental requirements of zero VOC emission. In recent years, there has been an increase in the configuration of coating devices in offset printing machines in the field of packaging. This is UV coating using UV coating varnish, using wire processing, and simultaneous UV coating with printing, which can obtain the same gorgeous products as the previous printing coating. It is widely used in cartons and cover prints of books and periodicals, especially in food packaging. There are two methods of using oily ink or UV ink as base color ink. When using oil-based ink, UV paint varnish is designed according to the adhesion requirements of oil-based ink. In addition, there are UV paint varnish designed according to the adhesion requirements on the dried oily ink. The gloss back phenomenon occurs when the oily ink is used as the base ink in the way of line glazing, so the use of oily ink is reduced, and UV mixed ink or UV ink is used instead

UV paint varnish coating is almost always aimed at increasing brightness and preventing color fading. The box coating method of connecting line can be replaced by flexographic printing, and the on-line double coating roller method can be realized through the combination of printing machines. These devices are now being used for diversified printing surface processing. It can be coated with UV calendering varnish, UV strippable varnish, UV gold silver varnish, UV fluorescent varnish, UV matte varnish, UV pearl varnish, UV invisible light colored varnish, etc., so it is impossible to get the maximum load Pb, so it is impossible to get the intensity limit σ B a manual switch should be installed on the wire to control the source distribution of the experimental motor. In recent years, attention has been paid to environmental issues, and UV curing system has been favored. Its instant dryness and hard ink film become sharp tools

the proportion of UV offset printing ink used in the packaging field is increasing. On the other hand, the mixing of UV ink has become a new development direction of UV ink, which can make up for the shortcomings of UV ink. In addition, the offset press is equipped with a box type on-line coating or double coating roller coating device using flexographic ink, indicating that the printing press is developing towards combination. In the field of packaging, efforts will be made to promote the development of high value-added prints in the future. In this regard, we should recognize the importance of the role played by ink manufacturers

3) UV flexo printing inks

① types of flexo printing inks

nowadays, flexo printing inks can be roughly divided into water-based, solvent based and UV based. Water based flexo printing inks are mainly used for the printing of corrugated paper and paper bags. Solvent based flexo printing inks are more advantageous in terms of PRTR regulations than gravure printing inks, and are mostly used for the printing of non absorbent substrates such as plastic films

uv flexo printing ink is characterized by no solvent. Because there is no need for evaporation drying, the machine has good stability and excellent durability of ink film. It can be used on paper or plastic film. Now it has been fixed for label and part of package printing. In the past, people had the impression that flexo printing represented by corrugated paper printing was a low-quality printing method. Since the 1990s, the use of UV flexo printing ink has changed this impression and expanded the market of high-quality prints

② development of UV flexo printing inks

compared with water-based and solvent based inks, UV flexo printing inks have different components except for the same coloring components and additives

water-based and solvent-based flexo printing inks mainly adopt the hot-air evaporation and drying method. UV flexo printing inks do not contain volatile components. It uses the ultraviolet light emitted by UV lamps to realize the polymerization of oligomers and monomers to solidify the ink. Therefore, the residue on the printed matter is 100% solid. Because it can form a hard ink film, it has many advantages

the number of printing plate lines of water-based ink has increased from 65lpi of corrugated paper printing 20 years ago to 120lpi, the number of UV flexo printing plate lines has reached 175~200lpi, the number of wrinkle roll lines is 300~500lpi for field products, and 800~1200lpi for four-color halftone products. In Japan, it is mainly used for label and trademark printing. The background of UV flexo printing replacing offset printing is to use high-precision corrugation rollers to obtain products better than offset printing quality, and white ink field printing (stacking thickness to obtain good shielding) can be completed at one time

uv printing does not need large-scale hot air drying equipment, saving space. The heat generated by the instant curing of UV lamp is very small, which can be used for the printing of heat shrinkable films and other materials that cannot be printed due to the shrinkage caused by the hot air dryer. Its cured ink film is tough, with excellent wear resistance, water resistance and solvent resistance. The cardboard printing with UV flexo ink developed in Europe and America takes advantage of this wear resistance and high gloss

however, UV flexo printing inks also have shortcomings, which become an important factor for the development of flexo printing as we expect today. Especially in terms of cost, the unit price of UV flexo printing ink is several times that of water-based flexo printing ink. However, UV flexo ink has obvious advantages in operability, and sometimes it is lower than water-based ink in terms of comprehensive cost

UV is used to cure UV flexo printing ink. There are obvious differences in the curing effect of different colors. For example, the carbon black pigment used in black ink absorbs all the light in the ultraviolet region, and very little ultraviolet light enters the initiator, resulting in curing and environmental friendly additives such as vegetable oils

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