UV ink

UV ink is a kind of rapidly developing green ink. Compared with thermosetting and volatile drying inks, it has low-temperature rapid curing, does not contain volatile organic solvents, has less pollution, occupies a small area, has high efficiency, and has low energy consumption. Features. With the increase in the number of UV-curable raw materials and the sharp drop in price, the growth rate of UV ink usage and variety is surprising. The application field is also expanding, and UV special inks with various functions and varieties are emerging. For example, the use of UV materials without volatile solvents has led to the development of UV embossed inks, Braille inks, crystal inks, and marble inks; it has been developed using cured films with high cross-link density, heat resistance, and abrasion resistance. UV resistance soldering, UV character ink, etc.

The application of UV curing system in printing began in the United States. The main products are UV inks for lithographic printing and UV varnish. They are applied to multicolor offset printing presses. The resins used are acrylic oligomers. The printing system used a drying system with six high-power ultraviolet mercury lamps of 80 W/cm, and the curing time was a few seconds. Since then, the UV curing system has been widely used in offset printing, letterpress printing, and screen printing.

UV ink composition

The main components of the UV ink are a polymerizable prepolymer, a photosensitive monomer, and a photoinitiator, and auxiliary components are coloring pigments, fillers, additives (leveling agents, defoamers, polymerization inhibitors, and the like) and the like.

1 Polymeric Prepolymers Polymeric prepolymers are important components that determine the properties of the UV varnish coating and are generally classified according to the skeleton structure. Skeleton structure affects coating hardness, abrasion resistance, adhesion, light resistance, chemical resistance, and water resistance.

Prepolymers mainly include epoxy acrylate resins, urethane acrylate resins, polyester acrylate resins, polyether acrylate resins, polyacrylic propyl esters, and unsaturated polyester resins.

2 photosensitive monomer (active diluent)
UV inks and UV varnish oils need to have a viscosity suitable for the coating machine during coating. Generally, the viscosity of the prepolymer is reduced by adding 20% ​​to 80% of the monomers, and the monomer itself undergoes polymerization to become a cured film. Part. When selecting monomers, follow these guidelines:

a. Low viscosity, good dilution effect;
b. Fast curing;
c. Good adhesion on the material;
d. Less irritating to skin and less toxic;
e. No odor is left in the coating.
3 Photoinitiator The role of photoinitiator is to absorb ultraviolet light energy, generate free radicals, so that the ink polymerization. The selection of photoinitiators should follow the following principles:
a. High UV absorption efficiency;
b. Relative stability is good;
d. Good compatibility with prepolymer and monomer;
e. Little odor;
f. Low cost.

Use of UV inks

UV inks can be divided into two major categories from use: UV printing inks and UV printed circuit board inks. Currently, UV printing inks for the printing industry are used in various printing fields such as offset printing, letter printing (including flexographic printing), gravure printing, screen printing, and inkjet printing. UV printing circuit board inks are mainly used in circuit boards in the electronics industry. (PCB) printing.

1. Offset UV ink

The use of UV inks for offset printing eliminates dusting, facilitates the cleaning of the printing environment, and avoids the troubles caused by powder spraying to post-press processing, such as the effects on coating and film coating, and can be used for connection. Processing.

UV ink can also prevent ink crusting, which solves the worries of the offset machine when it stops, and at the same time it can increase the drying speed. Especially in the packaging and printing, it is often necessary to print a large area on the ground, requiring a higher density, and therefore have to increase the amount of ink, then the ink drying problem becomes very important, often because the ink is not easy to dry and affect the printing Productivity. With UV inks, this problem is easily solved.

UV inks are brightly colored and have excellent abrasion resistance, making them ideal for packaging and book cover printing.

UV inks do not penetrate when cured and can be printed on non-absorbent substrates, such as card printing. This is an area where ordinary offset inks cannot be covered.

In addition, offset UV inks are also widely used in direct mail, business forms and other ticket printing. In foreign countries, the largest market for UV inks is offset UV inks.

2. Letterpress UV ink

Toppan printing UV ink is mainly used for label printing, but also for packaging printing, such as hose printing.

In flexo printing, especially in narrow flexographic printing, people pay more attention to less downtime, more friction resistance, and better print quality. With UV ink printing product network with high resolution, small dot gain, bright ink, compared with water-based ink printing to improve a grade. UV inks have broad prospects for development.

At present, most flexographic printing presses are equipped with UV curing devices, and there are many types.

3. Gravure printing UV ink

In the field of gravure printing, UV inks have been selectively used, but the technology and cost have been correspondingly increased. With the growing demand for environmental protection and the increasingly stringent requirements for the safety of packaging printed materials, especially food packaging, UV inks will become a trend in the development of gravure printing inks.

UV ink development

Foreign UV Ink Development

The development of foreign UV inks is very fast. In the United States, the largest market for UV inks is offset printing, which accounts for about 40% of the market. Followed by screen printing (30%), the growth in the 1990s was particularly strong, becoming one of the preferred technologies for optical disc manufacturing. European 2000 UV ink products totaled 20,500 tons. The Asian UV ink market started late compared to Europe and the Americas, but the growth rate is not low. Among Asian countries, Japan has the largest market share.

Domestic UV ink development

Although the domestic UV ink market started late, it has been thriving in recent years with the sustained rapid growth of the domestic economy. According to the inaccurate statistics of the China Radiation Society Professional Committee on Radiation Curing, the output of UV inks reached 6,514 tons in 2003, an increase of 64.2% over 2002, with an output value of 441,310,000 yuan, an increase of 55.7% over 2002. Among them, offset printing UV inks, photoimaging resist inks, optical imaging solder mask inks, optical disc inks and other high-grade ink production have greatly increased. Since domestic UV inks have a low starting point and UV inks are favored by the industry, domestic UV inks will have better market prospects and will achieve rapid development in the coming years.

Inverted light

In China, the main substrates for UV printing are non-absorbent materials. In Europe and the United States, printing companies not only use the co-curing process to print the same quality prints as traditional UV inks, but also do not satisfy their high-gloss mirror effects or transparency effects, and further improve this process to achieve more. High printing contrast. To this end, an early version of the so-called "back-lighting process" was developed. At that time, however, some details were not solved, such as adhesion, so they were not really implemented. After several years of improvement, this process has matured. The following section describes the local glazing process using this technique.

Pro-Cure is relative to traditional local glazing. In the past, regardless of the type of glazing (flexographic printing, screen printing, or gravure printing) used for local glazing, the last glazing process must use partial glazing printing in order to achieve high contrast in local graphics. , Polishing and printing accuracy of the key to the glazing process.

The retrograde light process breaks through the above laws and solves the problem of registration. The process flow is as follows.
Before glazing, it is necessary to complete conventional printing and determine that the ink has been completely dried or cured; then, the non-high-light areas on the design draft are printed with transparent reverse ink by offset printing in a wired or offline manner; The printing method applies UV varnish to the printing surface and cures.

At this time, the optical oil forms a small-particle-like ink film by forming a cohesive reaction with the reverse-light-up ink contact region, and forms a mirror surface in the counter-light-up region.

Obviously, with the retro-reflective process, both high-gloss and non-high-gloss effects will be present on the same print. Moreover, because the non-highlighted part is an offset printing, overprinting is accurate, and at the same time, the accuracy of the graphic part of the high light part is also guaranteed.

UV co-curing process

In order to perfect the UV printing process, Grafix, a German UV system manufacturer, cooperated with INX ink company to develop a new UV co-curing process. The process is the use of a new ink technology to break the incompatibility of traditional UV inks and common inks, and then combined with high-power UV curing device to improve the UV ink curing quality, solve some problems in UV printing, and reduce The technical threshold for printers to enter the special printing field.

The characteristics of the UV co-curing process are as follows:

(1) It can be cleaned with general cleaning agents, and the cleaning time is short, avoiding the problem of long downtime in the printing process.
(2) The time required for the conversion between ordinary ink printing and co-curing ink printing is the same as that for normal ink printing, and the operation is simple.
(3) Co-curing inks have the same ink balance in printing as ordinary offset inks. Therefore, problems such as ink emulsification and dirty printing are easily controlled, and the stability of printing quality is improved.
(4) The printing dot is more sharp than the ordinary UV printing, and the surface of the printing ink film is delicate and has the effect of color transparency.
(5) Co-curing ink does not require expensive UV-specific roller.
(6) The overprintability between inks is excellent. Only a set of intermediate seats can be cured to enhance the overprint effect and reduce hardware investment.

Source: China Tobacco Packaging Ink Information Network