Detailed ink curing and UV drying technology

Improving the printing speed has great potential for the printing press itself, but the drying speed of the ink is the bottleneck of development. Therefore, in recent years, research on ink UV curing, heat drying and quick drying ink is very active. This article mainly discusses the development of ink UV curing and thermal drying light source and device design based on the ink drying principle.

The drying of printing ink mainly includes oxidized conjunctiva drying, penetration drying, volatile drying and radiation drying.

1. Dry oxidized conjunctiva

The ink contains dry oil. The unsaturated fatty acid in the molecular structure of the oil reacts with oxygen in the air, and the small molecule linear structure is polymerized into a macromolecular network structure to form a solid substance. This chemical reaction process is called The oxidized conjunctiva dries.

2. Penetration drying

The ink binder contains more mineral oil, such as gasoline, high boiling point kerosene, etc. When the mineral oil in the ink penetrates into the porous paper fibers, the pigment is fixed on the surface of the paper to form a solid film, called infiltration drying.

3. Volatile drying

The ink contains a large amount of volatile substances, such as aliphatic hydrocarbon rosin esters, aromatic hydrocarbon solvents, alcohols, ketones, ester solvents, etc. After the ink is transferred to the surface of the printing material, the solvent volatilizes and the pigment is fixed to form a solid film, which is called volatile drying.

4. Radiation curing

Radiation curing is a chemical reaction in which chemical monomers cross-link into a polymer network structure to form a solid, and the curing speed is fast, and the formed film layer is hard and bright, but the adhesion is not good. There are currently three types of radiation curing methods commonly used.

(1) Infrared radiation drying. The ink contains a chelating agent, which can be irradiated with medium-wave infrared light with a wavelength of 3 to 30 μm to accelerate the polymerization reaction, and the heat generated at the same time promotes the evaporation of the solvent and accelerates the drying of the ink. Short-wave and long-wave infrared are not conducive to the drying of ink.

(2) Ultraviolet (UV) radiation curing. The ink contains photoinitiators, such as benzophenone (absorption wavelength 240-340nm), 2-chlorinated thioxanthone (absorption wavelength 200-400nm) and other derivatives, and the photoinitiator is in the wavelength range of 250-420nm Under the irradiation of UV light, the unsaturated double bond can be quickly opened in less than 0.1 seconds to initiate the resin, such as polyurethane, epoxy acrylate, etc., cross-linking and curing to a solid and drying. UV-curable inks are essentially free of solvents.

(3) Electron beam (EB) radiation curing. Thermionic cathode tube emits a high-energy radiation electron beam, and the radiation wavelength is selected by adjusting the cathode tube emitter, so there is no visible light and infrared radiation, and it is completely a cold light source. The effective radiation intensity of the electron beam is very high, which can directly induce the polymerization of the resin into a solid. Therefore, the photoinitiator may not be used in the EB ink. The photoinitiator in the UV ink can be removed or added in a small amount to act as an electron beam curing ink.

Generally, the drying of printing ink is not a single drying method, but several kinds of drying occur simultaneously. For example, the drying of offset printing ink is caused by oxidative conjunctiva, penetration, and volatilization. The drying of oxidized conjunctiva is the main method; the drying of newspaper printing ink is the penetration of the main;

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