UV curing ink industry progress and application details

1. Introduction Green ink gradually replaces traditional, volatile organic solvent inks, which is the direction and trend of the printing industry. The three major factors that determine the environmental protection ink:

Low-VOC (Volatile Organic Compound) Emissions: At present, water-based inks have been partially or totally used in flexible printing and gravure printing at home and abroad. Water penetration and volatilization are used as drying means to reduce the ink to a large extent. The VOC content. The development of UV-curable inks has further improved this situation.

Easily degradable: The ink's raw materials must be easily degraded under the influence of physical, chemical and biological agents. Usually used as a raw material in plants, such as soybean oil, such inks are more easily degraded than inks synthesized from other chemical materials.

Raw materials can be recycled: The ink produced by plants can be regenerated, and the inks made from chemical products such as coal cannot be regenerated.

Ultraviolet (UV) inks refer to inks that cure instantaneously by ultraviolet light. The UV-curing ink is composed of a binder, a pigment, and related auxiliary 3 parts. The UV radical-curable ink is exposed to ultraviolet light, and the initiator initiates radical polymerization of unsaturated bonds in the binder, and the ink is cured and formed into a film. UV-cured inks have long been studied abroad, and many products have been introduced to the market in recent years. Because it can be printed on the surface of non-absorbent substrates, it is currently used in various fields. UV curing ink is a reactive ink that cures in seconds and is suitable for high speed printing. Due to the reactive dry cross-linking process, adhesion to most substrates is good. Traditional solvent inks generally need to be dried after being applied. The drying process needs to consume a large amount of heat sources, the speed is slow, and the solvents are volatilized. After the drying, the adhesion is not ideal, and the subsequent process also has an impact.

In UV inks, liquid monomers and oligomers displace the resin binder so that the pigment molecules can be dispersed. Since there is no volatilization of any solvent, the thickness of the cured ink layer is exactly the same as the thickness before curing, so we generally refer to UV ink as "100% solid" ink.

In the initial stage of the development of UV inks, the chemical raw materials (photoinitiators, resins, monomers, etc.) that make up the inks have limited selectivity due to conditions, and there is also a lack of UV light sources suitable for industrial applications. Ink manufacturers can now choose from thousands of raw materials. UV curing The entire curing system is a solvent-free system, UV ink printing has a stable adaptability, can increase the actual production efficiency and reduce costs, can give investors the economic benefits of high productivity and high yield. Because of this, this technology is favored by many application vendors, which is the main reason why this technology has been rapidly promoted and applied. In recent years, Europe’s demand for energy-curable inks and varnish has grown, especially in the area of ​​packaging and printing. After the 1990s, UV-curing inks began to enter the use stage on a large scale.

2, UV curing ink advantages and common problems

UV light solid ink has many advantages, mainly in:

1 Curing speed, saving time and energy. 2 The equipment has a small footprint and is economical. 3 is a non-solvent ink, there is no natural volatility, the ink viscosity is good stability, there will be no wire drawing phenomenon. 4 high gloss, the ink layer has good resistance to friction and resistance after curing. 5UV light solid ink is small, so it can print fine patterns. 6 There are no organic volatiles, environmental protection, etc.

UV photopolymer inks are widely used in recent years due to their many advantages. However, there are the following problems in use, classified as follows:

1 The substrate and the ink are incompatible and the surface of the substrate is contaminated with no adhesion. 2 The adhesion between layers is weak when overprinted. 3 appears stripes, markings. 4 The ink is streaky after curing. 5 can not be cured or sticky surface and residual odor. 6 Resolution or sharpness is not enough. The 7-point imprint is enlarged. 8 edge curled. 9 fish eyes, white spots. 10 low gloss.

There are many series of UV inks, and the diversity of their composition constitutes the complexity of their influencing factors. The main factors affecting the ink curing adequacy and the best curing speed are the following: External conditions are the curing temperature, curing environment conditions, photoinitiator, radiation intensity of the light source, etc.; internal conditions are pigment properties, ink ink Layer thickness, substrate surface properties, etc.

Co., Ltd. has developed special screen printing that provides prints that do not suffer from jagged, color, pinhole, and transmissive defects, and have a stable printability, and that can produce highly glossy mirror-printed, colorful mirror-glossed prints. Ink.

Hitachi Maxell Co., Ltd. invented an oily pigment ink composition. Compared with the prior art, the oily pigment ink composition does not have the problems of safety and odor existing in the use of the organic solvent ink composition and can be Printed media with low-cost polyvinyl chloride films that do not have a receiving layer can be used in outdoor environments.

3, UV curing ink common varieties and progress

(1) UV screen printing ink

Screen printing is one of the mainstream printing processes and belongs to stencil printing. It is widely used. Screen printing can produce relatively thick ink film, the printing surface can be flat, it can be curved, low cost. However, the printing speed is not high and the UV screen printing ink has a high thickness, which poses a challenge to the curing of the bottom layer. The thicker the ink, the lower the cure rate of the bottom layer. Fortunately, the rate of screen printing itself is not high. UV screen printing is best suited for applications that require thick ink layer printing, such as poster printing.

UV curing is often performed using free radicals and cationic polymerization. In recent years, cationic UV ink (also known as cationic ink) is a new type of special ink developed with the development of UV technology. Cationic UV inks are mostly used for the printing of short-sleeve, sleeve-type heat-shrinkable films. Free-radical inks are used in paper-based substrates because of the small shrinkage of the ink film. The advantage of cationic UV inks is that the reaction type is a gradual ring-opening polymerization of typical epoxy groups, which can significantly increase the active ingredient content of the ink.

The free radical ink has a fast reaction speed, but it will cause the flexibility of the free-radical UV ink to decrease, and the affinity and adhesiveness will deteriorate. In contrast, radical inks can only be thoroughly dried using UV exposure, resulting in increased volatilization. Cation UV ink curing speed is slightly inferior to free radical ink, can be secondary curing, not easily oxidized, no shrinkage, excellent adhesion and so on. Cationic UV inks have low volatility and low odor, but most of the pigments contain strong nucleophilic groups, and the choice of cationic photoinitiators is too small and the price is too high.

UV screen printing metal ink is mainly composed of photosensitive resin, photosensitizer, pigment and additives. In the application process, UV screen printing metal ink has the characteristics of saving energy and space, and improving work efficiency. In the printing process, since the ink on the screen cannot contact the ultraviolet radiation, it will never block the network, which brings great convenience to the printing of the graphic and continuous operation. UV screen printing metal inks have obvious advantages compared with common solvent metal inks in terms of environmental protection, cost, and efficiency. Therefore, its application prospects must be very broad. At the same time, this kind of ink is being gradually understood and adopted by printing manufacturers. At present, the mature UV metal screen printing inks used in the domestic market include Germany's lougre ink and UV-5000 screen printing metal ink produced by Hangzhou Henderson Ink Coating Co., Ltd., with two series of conventional ink and matte colors.

In 2005, at the FESPA 2005 exhibition held in Munich, Germany, the exhibition center of the world screen printing and imaging industry, the new generation of V-Screen screens displayed by Japan NBC Co., Ltd., its silk thread adopts a new synthetic aryl group. The polymer has twice the strength of the wire mesh, and the V-Screen wire has a large opening area, which greatly increases the ink penetration on the wire mesh.

Nor-Cote International Limited, USA, showed off their UV ink series, including PTXUV inks for membrane switch materials, licenses and nameplates, and UV conductive inks for electroluminescent photo printing. This type of ink is not only solvent-based. The ink has good adhesion and abrasion resistance, and it also has instant dry characteristics that are not possessed by the solvent ink.

The new transfer material, TransferRite ULTRA, launched by American Biltrite, Inc., enables the adhesive tape to be completely flat on the silicon-coated backing paper. Swiss company FOTEC AG has attracted many customers with its new emulsion. Emulsion contains 60% solid particles, low viscosity, can be single-sided coated screen, brought a revolution in screen exposure technology, screens made with this emulsion for UV curing ink screen printing.

(2) UV offset printing ink

The drying mechanism of ordinary offset printing inks is to infiltrate and then dry the oxidized conjunctiva. The drying mechanism of offset UV ink is totally different from this. The first step is to irradiate the ink with ultraviolet light so that the photosensitizer molecules are excited to produce highly active free radicals or ions. These highly active free radicals then initiate the interlocking polymerization of the unsaturated double bonds in the photocurable resin and reactive diluent molecules to achieve molecular crosslink polymerization. , so that the ink curing dry.

Offset printing is one of the fastest growing and most widely used types in offset printing. Offset printing technology is based on the different adhesion properties of the ink to the printing plate's lipophilic and hydrophilic areas, requiring the ink to have strong selectivity for these two areas. Traditional solvent-based offset printing inks need to be printed and dried. The drying system makes the printing machine bulky. Photocuring can properly reduce the volume of the drying system. UV offset ink curing basically no film thickness loss, extinction may not be as severe as solvent-based inks. UV offset printing technology is able to obtain colorful and exquisite patterns that can exhibit delicate color changes. Suitable for exquisite product packaging and printing, mainly for paper printing materials. UV offset inks have a high solids content, and the ratio of pigment to binder before curing is similar to that of ordinary offset inks, and therefore were first applied in offset printing.

UV offset inks cure without penetrating problems, not only on paper, but also on non-absorbent substrates. In foreign countries, the largest market for UV inks is offset inks. China's UV offset printing ink started late, but the development momentum in the past two years is very rapid. According to the inaccurate statistics of the China Photographic Society's radiation curing professional committee, the production volume of UV offset printing ink was only 232 tons in 2002, 662 tons in 2003 and 1459 tons in 2004, and its output has become second only to UV printing ink. The second largest UV ink, and the smaller the gap with the UV screen printing ink.

(3) UV flexo ink

Flexo is a letter print that embosses ink onto a printing surface through a prominent part. UV embossing is very suitable for hard plastic printing such as cups, tubes, etc. Traditional flexo inks (solvent type and water based) should not use inks with excessive viscosity. The main difference between UV flexo inks and other types of inks is also the polymer rheology. UV flexo inks may generally have a higher viscosity than solvent-based flexo inks. As the quality of flexographic printing continues to improve and the application area expands, the need for special physical fitness continues to grow. In the UV flexo printing process, the most attractive to people is the increasing chemical resistance of prints. In addition, the advantages of low energy consumption, short standby time, and low organic volatiles will continue to drive the development of the market.

At the most recent 51st session of the German-Spanish flexo professional conference, the Hartmann/Sun Chemical Ink Company reported on the subject of electron beam curing flexo inks. This flexo ink has also become popular in flexible packaging. UV inks are less popular in flexible packaging because UV inks contain photoinitiators and monomers that can cause packaging to produce sensory problems.

(4) UV inkjet ink

Inkjet printing is non-impact printing. It is the process of jetting ink droplets to the substrate to form images. UV-curable inkjet inks combine all the advantages of UV-curable inks and inkjet printing technology. Both UV curing and economical and technical Advantages also have the convenience of use and operation of inkjet printing technology. These advantages include: no volatile organic substances; low energy requirements; fast curing; suitable for a variety of substrates; no drying before curing; no clogging of the nozzle; constant ink composition; good print quality, resistance