UV ink characteristics and its application in packaging

It has been more than 30 years since the UV printing ink cured by irradiation with a UV lamp reached practical use today. Compared with traditional oil-based inks, its advantages of instant drying, energy saving, space saving, solvent-free, pollution-free and low odor have been highly evaluated and applied to various packaging products. Especially in the work efficiency, environmental protection, print corrosion resistance is recognized, and there are many applications in offset and flexo. This article discusses UV inks and UV varnish in the field of packaging and printing.

1 composition of UV ink

Comparing the composition of UV inks and oil inks, UV inks that cure instantly upon UV irradiation produce radically oily inks that rely on solvents that permeate paper for several hours of oxidative polymerization and dry by ordinary oily inks and solvents and water. The water-based ink that is evaporated and added to the paper to dry is different from the water-based ink except that the pigments are the same. If you want to make a brief description of the UV ink curing mechanism, it is that the photoinitiator in the UV ink absorbs the ultraviolet light of the UV lamp to generate a radical group. The group is converted into monomers, and the monomers are further obtained. This polymerization reaction proceeds continuously to form a hard ink film, which is an instant drying method.

2 Features of UV ink

● Fast drying ● The ink does not become crusted ● Does not dry on the machine ● Does not require dusting ● Sheets can be piled up ● Can be post-processed immediately ● Resistant to abrasion, heat, solvents, chemicals, etc. ● Odors of prints Less ● Density does not decrease after drying ● Ink changes rarely ● Can be made into special inks Disadvantages ● High ink price ● Easy to expand outlets ● Water should not be too large ● Extremely deteriorated transferability of emulsified inks ● Not applicable for all PS plates ● Not suitable for all rubber rollers ● Many cases of ink splashes ● Sensitive to temperature changes ● Papers with poor adhesive properties are not suitable for most applications ● Gels are sometimes produced in ink ● Paper is easily cracked ● Metal foils and adhesives are picked Agent type ● Insufficient density of black ink ● Cannot be cleaned with general cleaning agent

3 UV ink (gloss) and application

1) Offset UV ink

When a sheet-fed offset press uses oil-based ink to print non-absorbent substrates or thick paper, it requires a lot of dusting and the use of a delivery separator in order to prevent the backside from sticking. UV ink can achieve instantaneous drying, no need to spray powder, you can pile up printed products, immediately into the post-processing, do not have to worry about the back of the sticky problem, the ink film hardness, emissions of odor is very small, does not contain VOC components, for Environmental protection is beneficial. UV inks are popularized by centering on packaging and printing, and have many applications in the printing of food packaging and cosmetics packaging using cardboard, polyethylene coated paper.

Compared to the oil-absorbing ink headache non-absorbent substrate, due to the UV ink has the characteristics of instant curing, in a metal foil, holographic film, synthetic paper printing; 2PP video box printing, packaging machine 'target = _blank> transparent film printing; 3PP, PVC, APET, PET, PS Polycarbonate Transparent packaging printing has more applications, especially PVC cash cards, credit cards or PET prepaid cards (phone cards, orange cards, rewrite cards, highway cards) cards Card printing has been widely used.

Since UV inks are compatible with the above applications, there are many varieties of UV inks used in offset printing, such as fast-drying, low-odor type UV inks for paper, inks with good film adhesion, and environmentally friendly SOY certified inks and markets. Corresponding UV hybrid inks and the like are required. Among them, the application of UV mixed inks in printing has attracted much attention in recent years. When the oil-based ink and the UV-varnish oil are used in combination on a printing lacquer production line, the gloss of the print gradually decreases due to the penetration and drying of the oil-based ink. To solve this problem, UV hybrid inks were introduced. The UV mixed ink can be used with cleaning agents and ink rollers used in oil inks. It is an ink with good compatibility. The printed paper can be recycled and has printability and reproducibility close to that of oil inks. In use can be more smoothly from the use of oily ink conversion. UV curing inks used in recent years have been improved in their UV curing performance. Due to poor abrasion resistance compared with ordinary UV inks, it is an issue faced by ink manufacturers in the future how to combine the curing performance of UV inks with the good printability of oil inks.

UV special ink, UV gold and silver ink, UV fluorescent ink, UV invisible light (infrared light, ultraviolet light) color ink, UV pearl ink, UV waterless ink, etc. have applications in the packaging field.

2) UV Varnish

There are many varieties of UV Varnish. The UV varnish used in the packaging field is shown in Table 2, Table 3, and Table 4.

1UV-OP (overprint) Varnish

The packaging industry is using general-purpose matte OP Varnish and resin-engraved high-gloss OP Varnish for fountain solution. The combination of UV inks and UV varnish is advantageous for print tolerance, and this combination has become mainstream, but the cost burden is high. Some other combinations have advantages in terms of operability and cost, such as: a) UV-OP varnish designed according to the requirements of oily ink adhesion, and UV-OP varnish printing on the surface of oil color ink (without dust collection) Paper stacking method; b) Using UV mixed color ink + UV-OP Varnish; c) Printing UV-OP Varnish on dried colored oily ink. However, when oil-based inks are used on the machine, there will be Gloss back which gradually decreases the gloss. The UV mixed ink will reduce Gloss back, and it will be used as the background ink for on-machine coating of UV-OP varnish. The use ratio is gradually increasing.

2UV coating varnish

The application of vinyl resin and film increase the brightness processing, and the production efficiency is poor due to off-line printing, and the generation of volatile solvents brings pollution to the working environment. UV-coated lacquer is solvent-free and adapts to the environmental requirements of zero-VOC emissions. In recent years, there has been an increase in the number of coating machines for offset presses in the packaging industry. This is a UV coating process using UV coating varnish, which is applied in tandem with printing, and can be obtained with conventional printing coating. Equally gorgeous products. It is widely used in cartons and book cover prints, especially in food packaging. There are two methods of using oil inks or UV inks as background inks. When using oil-based inks, UV coating varnish is designed according to the adhesion requirements of oily inks. In addition, there is also a UV coating varnish designed to adhere to the dried oily ink. When the oil-based ink is used as a background ink in a line-on-line manner, a Gloss back phenomenon occurs, so that the use of the oil-based ink is reduced, and a UV mixed ink or a UV ink is used instead.

Most of the UV coating varnish coating is for the purpose of increasing brightness and preventing color fading. Wired box coating can be replaced with flexographic printing, as well as on-press dual roll-on-press combinations. These devices are now being used for a variety of printing surface processing. UV varnish, UV varnish, UV varnish, UV varnish, UV varnish, UV varnish, UV invisible varnish, etc. can be applied. In recent years, attention has been paid to environmental issues and UV curing systems have become popular. Its instant dryness and hard ink film become a weapon.

The proportion of UV offset inks used in the packaging field is increasing. On the other hand, the mixing of UV inks has become a new UV ink development direction that can make up for the disadvantages of UV inks. In addition, the offset printing machine was equipped with a box-type in-line coating or a double-coated roll coating device using a flexo ink, indicating that the printing press has developed toward a combination. In the field of packaging, we will use our high value-added printing products to promote their development. In this regard, the importance of the role of the ink manufacturer should be recognized.

3) UV flexo ink

1 type of flexo ink

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

The biggest feature of UV flexo inks is solvent-free. Since it does not require evaporative drying, the machine has good stability and excellent ink film durability, and can be used either on paper or plastic film. It is now fixed for use on labels as well as on some packaging prints. The impression left in the past is that flexo printing, represented by corrugated printing, is a low-quality printing method. Since the 1990s, the use of UV flexo ink has changed the impression and expanded the market for high-quality prints. .

2UV flexo ink development

Compared with water-based and solvent-based inks, UV flexo inks are not the same except that the coloring ingredients and additives are the same.

Water-based and solvent-based flexo inks are mainly produced by the hot-air evaporation method. UV flexo inks do not contain volatile components. UV rays from UV lamps are used to polymerize oligomers and monomers to cure the ink. Therefore, 100% of the residue on the print is a solid material. Due to the formation of a hard ink film, it has many advantages.

The number of waterborne ink plate lines has increased from 65lpi printed on corrugated paper 20 years ago to 120lpi, the number of UV flexo plate lines has been 175~200lpi, and the number of anilox roller lines is 300~500lpi for four colors Halftone products are printed with 800~1200 lpi anilox rollers. Japan is mainly used for label trademark printing. The background for the development of UV flexo instead of offset printing is to use high-accuracy anilox rollers to achieve better quality than offset printing, and white ink printing in situ (stack thickness for good masking) can be done in one go.

UV printing does not require large hot air drying equipment, saving space. The amount of heat generated by the instant curing of the UV lamp is small, and it can be used for the printing of materials such as heat-shrinkable films that cannot be printed due to the shrinkage caused by the hot-air dryer. The cured ink film is tough, excellent in abrasion resistance, water resistance, and solvent resistance. The use of the UV flexo printing inks developed in Europe and the United States for the paperboard printing utilizes this wear resistance and high gloss characteristics.

However, UV flexo printing inks also have shortcomings, and these shortcomings have become an important factor in the development of flexo printing as we are expecting today. Especially with regard to the cost, the unit price of the UV flexo ink is several times that of the aqueous flexo ink. However, UV flexo ink has obvious advantages in terms of operability, and is sometimes lower than water-based ink in terms of comprehensive cost.

The use of UV light to achieve the UV flexo ink curing, different colors have significant differences in the curing effect. For example, the carbon black pigment used in the black ink absorbs all the light in the ultraviolet region, and there is little ultraviolet light entering the initiator, resulting in poor curing failure. For this reason, the concentration of the black ink is lower than that of the aqueous ink, and high-concentration black inks are currently being obtained by using complementary colors and improvements to the initiator.

The odor issue of UV prints is particularly criticized. As for the odor generated during printing, the ammonia odor of the aqueous ink and the odor of organic compounds volatilized from the solvent ink are stronger, and the UV printing is blamed on the residual odor generated on the printed matter after printing. The UV initiator is irradiated with ultraviolet rays to promote the reaction as a catalyst, and in addition, a decomposed substance is generated which remains in the form of an odor in the printed product. Therefore, as a printing ink for food packaging film, which has been well-deserved, despite the fact that there is no clear restriction in the food hygiene law, customers are still far from it. In order to reduce this residual odor, UV ion inks have been developed and electron beams have been developed using a curing system with a small amount of initiator or without initiators that used to produce decomposition products.