Analysis of Printing Process and Quality Difference of UV Ink

Since Bayer developed the first generation of UV-curable coatings in 1967, UV ink printing technology has been rapidly developed worldwide. Currently in North America, the largest areas of UV curing are printing inks and UV coatings. Europe is actively working on the development of UV powder and water dilution coatings, optical lens coatings, electronic coatings, wear-resistant paper adhesives, composite adhesives, and textile printing. Taiwan is currently an important supplier of UV-cured 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 applied research of UV curing technology. At present, UV printing technology in cosmetics packaging, food packaging, toy packaging, foam packaging, high-end commercial printing, high Glossy requirements for products and other fields have been widely used.

First, the composition and type of UV curing ink

The UV ink is essentially a liquid ink that can be converted from a liquid state to a solid state under irradiation with a certain wavelength of ultraviolet rays. It is usually composed of a pigment, a prepolymer, a reactive diluent, a photoinitiator, and an auxiliary agent.

At present, there are mainly two kinds of UV inks, namely free radical type and cationic type. In addition, there are electron beam EB curing inks. Due to the high cost of EB curing inks, they are not widely used in the printing industry. Radical type UV ink is the main body of UV ink application at present, its main characteristic is the curing time is extremely short, can realize the instant solidification, can receive the paper continuously while printing, needn't worry about the back dirty. Cationic UV inks have good ink characteristics and printability. They have a small odor and are conducive to environmental protection. They are suitable for food packaging, printing, and printing substrates with poor adhesion.

Second, UV ink drying curing principle

The curing of UV-curing material means that the photoinitiator absorbs the radiant energy of ultraviolet light and then splits into free radicals under the irradiation of ultraviolet light of 200-400 nm, and initiates polymerization of the prepolymer and cross-linking of the graft in a very short time. The curing of a three-dimensional net-like polymer is achieved by chemically drying a chemical bond. The curing process can generally be divided into four stages. Firstly, the interaction between light and photo-initiator includes light. Absorption of an interaction between a photosensitizer and a photoinitiator; followed by rearrangement of a photoinitiator molecule to form a free radical intermediate; then a free radical interacts with an unsaturated group in the oligomer and monomer to initiate chain polymerization The reaction; the final polymerization reaction continues, and the liquid components are converted into solid polymers, see Figure 2. The resin used in traditional inks is a compound that has been polymerized, and may be a solid or a liquid. The main reaction is an oxidized conjunctiva reaction.

Third, UV ink and traditional ink contrast

advantage

â—† Most UV products do not require the use of solvents, 100% solids;
â—† Improve printing quality: through the composition of high-density cross-linked polymer, the resulting structure has a high degree of toughness, stain resistance, anti-wear and anti-solvent properties;
â—† Instant dry, no dry when no UV irradiation, do not worry about dry ink when shutting down;
â—† Offset does not need to spray powder; printed paper can be processed immediately;
â—† high gloss, high gloss quality, can be partially glazing;
â—† UV ink has a good thixotropy, can be high-precision printing of high-line printing lines;
â—† UV ink can print ice, refraction, matte, Zou and other special effects under certain printing conditions;
â—† UV ink meets the "5E principle" (Energysaving, Ecology, Economics, Ease of application, Excellence of finish), and has good development prospects;

Shortcomings

â—† UV ink prices higher than traditional ink products;
â—† UV devices need to increase investment;
â—† It is not completely odorless. After curing, it will leave a certain taste;
â—† need to consume more energy;
â—† UV products have a certain degree of danger. Most UV products have no irritation to the skin before drying. Skin gloves and eye protection goggles should be worn during operation to reduce hazards.
â—† The printing process is harder to master than the traditional printing process, and the adaptability to the substrate is not as good as that of the solvent-based ink;
â—† poor adhesion, to increase adhesion must be preceded by a layer of UV primer;

â—† Strong ultraviolet radiation will cause 3 oxygen molecules to become 2 ozone molecules, and exhaust pipes will be required to remove ozone from the work area.
â—† After the UV ink is printed on the paper, the ink is not well removed and the recovery of waste paper is affected. (to be continued)