The trend of ink curing and drying (1)

At last drupa show, the maximum speed of sheetfed offset press has reached 20,000 sheets/hour, and the maximum speed of rotary newspaper press has reached 100,000 copies/hour. The customers who favor these high speed machines are China. Printers, especially cigarette packs and newspaper printing plants. It can be said that increasing the printing speed has great potential for the printing press itself, but the drying speed of the ink is a bottleneck for development. Therefore, research on UV curing, thermal drying, and quick-drying inks of inks has been active in recent years. This article mainly starts from the principle of ink drying, and discusses the latest development of UV curing and thermal drying light source and device design of ink.

Ink drying and curing principle

Drying of printing inks mainly includes oxidative conjunctiva drying, osmotic drying, volatile drying and radiation drying.

1. Oxidative conjunctiva drying

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

2. Infiltration drying

Ink linking materials contain more mineral oils, such as gasoline, high boiling point kerosene, etc. When the mineral oil in the ink penetrates into the porous paper fibers, the pigments are fixed on the surface of the paper to form a solid film layer, which is called osmotic drying.

3. Volatile drying

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

4. Radiation curing

Radiation curing is a chemical reaction in which a chemical monomer is cross-linked into a macromolecular 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. At present, there are three kinds 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 3-30 μm to accelerate the polymerization reaction. At the same time, the generated heat promotes the volatilization of the solvent and accelerates the ink drying. Short wave, long wave infrared is not conducive to ink drying.

(2) Ultraviolet (UV) radiation curing. Ink contains photoinitiators, such as benzophenone (absorption wavelength of 240 ~ 340nm), 2-chlorothianthone (absorption wavelength of 200 ~ 400nm) derivatives, photoinitiator in the wavelength of 250 ~ 420nm range Under the irradiation of UV light, the unsaturated double bond inducing resin can be quickly opened in less than 0.1 second, and cross-linked curing such as polyurethane, epoxy acrylate and the like can be solidified and dried. UV curable inks are essentially solvent-free.

(3) Electron beam (EB) radiation curing. The thermionic cathode tube emits a high-energy radiation electron beam, and the radiation wavelength is selected by adjusting the cathode tube emitter so that there is no visible light and infrared ray accompanying radiation, and it is completely a cold light source. The electron beam has a high effective radiation intensity and can directly initiate the polymerization of the resin into a solid. Therefore, photoinitiators may not be used in the EB ink. The photoinitiator in the UV ink is removed or added in small amounts as electron beam curing ink.

In general, printing ink drying is not a single drying method, but several kinds of drying occur simultaneously. For example, the drying of offset printing ink is oxidative conjunctiva, infiltration, and volatilization at the same time. The drying of oxidized conjunctiva is the main method; the newspaper printing ink is mainly osmotic drying; the gravure printing ink is mainly volatile and dry.