Analysis on the printing process and quality diffe

2022-07-28
  • Detail

Analysis on the printing process and quality difference of UV ink

since Bayer developed the first generation of UV curing coating in 1967, the sampling rate has been low, and the UV ink printing technology has developed rapidly all over the world. At present, the largest UV curing field in North America is printing ink and UV varnish. Europe is actively committed to the development of UV powder and water diluted coatings, optical lens coatings, electronic coatings, etc. presided over by Meng Qingjun, Deputy Secretary General of the association, and wear-resistant paper adhesives, composite adhesives, fabric printing and other fields. Taiwan is currently an important supplier of UV curing raw materials in the Asia Pacific region. Since the 1970s, some universities, scientific research institutions and enterprises in China have begun to engage in the basic theory and Application Research of UV curing technology. At present, UV printing technology has been widely used in cosmetics packaging, food packaging, toy packaging, foaming packaging, high-grade commercial printing, products with high gloss requirements and other fields

I. composition and type of UV curing and drying inks

uv inks are essentially liquid inks that can change from liquid to solid under the irradiation of a certain wavelength of ultraviolet light. They are usually composed of pigments, prepolymers, active diluents, photoinitiators and additives

at present, there are mainly two types of UV inks, namely, free radical type and cationic type. In addition, there is EB curing ink, which has not been widely used in the printing field because of its high cost. Free radical UV ink is the main application of UV ink at present. Its main feature is that the curing time is very short, and it can realize instant curing. When printing, it can receive paper continuously without worrying about the back rubbing. Cationic UV ink has good inking characteristics and printability. Its smell is small, which is conducive to environmental protection. It is suitable for food packaging printing and printing of substrate materials with poor adhesion

II. Principle of drying and curing of UV ink

curing of UV curing materials refers to that under the irradiation of 200 ~ 400nm ultraviolet light, the photoinitiator absorbs the radiation energy of ultraviolet light and splits into free radicals, which triggers the polymerization, cross-linking and grafting reaction of prepolymer, and solidifies into a three-dimensional polymer in a very short time to obtain a hardened film. In essence, chemical drying is achieved by forming chemical bonds, The curing process can be generally divided into four stages: first, the interaction between light and photoinitiator, including the absorption of light or the interaction between photosensitizer and photoinitiator; Then photoinitiator molecules rearranged to form free radical intermediates; Then the free radical reacts with the unsaturated group in oligomer and monomer to initiate chain polymerization; Finally, the polymerization reaction continues, and the liquid components are transformed into solid polymers, as shown in Figure 2. The resin used in traditional ink is a polymerized compound, which may be solid or liquid, and mainly carries out oxidation conjunctival reaction

III. comparison between UV ink and traditional ink

advantages

◆ most UV products do not need to use solvents and are 100% solid substances

◆ improve the printing quality: the composition structure produced by the high-density cross-linking of polymer has the characteristics of high toughness, anti fouling, anti-wear and anti solvent

◆ instant drying, not when there is no UV irradiation, and do not worry about dry ink when shutdown

◆ offset printing does not need powder spraying; The printed paper can be processed immediately

◆ high gloss, high glazing quality, local glazing

◆ UV ink has good thixotropy and can be used for high-precision printing with high number of lines

◆ under certain printing conditions, UV ink can be used for printing with special effects such as ice flower, refraction, frosting, Zou grain, etc

◆ UV ink complies with the "5E principles" (energysaving, ecology, economics, ease of application, excellence of finish), and has a good development prospect

disadvantages

◆ the price of UV ink is higher than that of traditional ink products

◆ the investment of UV device needs to be increased

◆ there is not no smell at all, and a certain smell will remain after curing

1. Transmission system of tensile testing machine: ◆ it needs to consume more energy

◆ UV products are dangerous to a certain extent. Most UV products are irritating to the skin before drying. Skin care gloves and eye protectors should be worn during operation to reduce the harm

◆ the printing process is more difficult to master than the traditional printing process, and the adaptability to the substrate is not as good as the solvent ink

◆ poor adhesion. To increase adhesion, a layer of UV primer must be applied first

◆ three oxygen molecules exposed to strong ultraviolet light will become two ozone molecules that are difficult to operate. It is necessary to use an exhaust pipe to discharge ozone from the work area

◆ after UV ink is printed on the paper, it is difficult to remove the ink, which affects the recycling of waste paper. (to be continued)

Copyright © 2011 JIN SHI