Offset printing inks are classified in different ways.
1. Classification according to substrate
According to the chemical name of the substrate, it can be divided into: polyethylene, polypropylene (non-polar) ink. PVC, polystyrene, ABS polycarbonate (polar) ink. According to the form of the substrate, it can be divided into soft plastic ink and hard plastic ink.
2. According to the classification of printing machinery
According to the classification of printing machinery, it can be divided into sheet-fed offset printing ink and rotary offset printing ink; the selection of offset printing ink for different printing machinery and different substrates .
1. Ink used in web offset printing presses The ink used in web offset printing presses is what is usually called offset web ink. This kind of ink is basically of the following two types:
a. Penetration and bleeding drying type: Because the printing speed of newsprint and offset paper web offset printing machines is high and the ink dries quickly, the commonly used inks are mostly of the bleeding and bleeding type.
b. Thermosetting ink: In modern commercial web offset printing presses, a drying device is added to the second half of the printing device. To adapt to this production condition, thermosetting ink is used. This ink is heated in the drying device, and the content of the ink is The evaporation of the solvent allows the ink film to dry quickly, and the content of drying oil (such as linseed oil) in thermosetting ink is less. While the content of petroleum agent is relatively high, and the other components are similar to those of sheet-fed offset printing ink, the paper used for thermosetting ink is of better quality than the paper used for seepage drying ink. 2. Sheetfed offset printing machine ink 1), offset printing gloss Offset printing gloss ink is made of synthetic resin, dry vegetable oil and high boiling point alkane oil. Colloidal ink composed of high-quality pigments and additives. It is used for single-color, two-color or multi-color offset printing machines to print albums, pictures and other high-end exquisite prints on coated paper. The gloss of the ink is mainly produced by the condensation of the binder after drying. The gloss of the ink and the leveling properties of the ink film should be good. It should be able to form a plane when attached to the surface of the substrate, which can directionally reflect the incident light, that is, it has a mirror effect. This is The connecting material is required to stay on the surface of the substrate as much as possible. 2) Offset resin ink Offset resin ink is made of synthetic resin, dry vegetable oil, mineral oil, high-quality pigments and fillers, and is prepared and ground. Offset resin inks are characterized by less vegetable oil content and a high proportion of solvents, usually high-boiling point alkanes, which play a viscosity-reducing role in the ink. When the ink is transferred to the paper, this part of the solvent quickly penetrates into the paper fibers under the action of capillaries, speeding up the drying of the ink and reducing the problem of smearing on the printed product. 3) UV offset printing ink UV ink is used for printing in offset printing, which is usually called UV offset printing. UV offset printing ink is a type of ink that uses ultraviolet (UV) radiation energy to solidify liquid chemicals into an ink film through rapid cross-linking. It requires a UV curing unit in the printing press. As a kind of offset printing ink, UV offset printing ink must first be able to be printed by offset printing, so UV offset printing ink should also have some characteristics of ordinary offset printing ink to meet the requirements of printability. 4) Offset synthetic paper ink. In the absence of a UV offset printing machine, if you use a normal four-color printing machine to print cardboard, synthetic paper and other special papers where the ink does not dry easily on the surface of the substrate, you need to use offset synthetic paper ink. , this kind of ink is suitable for printing on non-absorbent printing substrates such as various synthetic papers (gold cardboard, silver cardboard, aluminum foil paper, special paper). Its ink has the characteristics of fast drying and good adhesion on printed matter. . Because this ink dries very quickly, when the printing process is stopped, the ink on the rubber roller should be cleaned in time to prevent the ink from forming and drying.
3. Classification according to drying methods
According to different drying methods, it can be divided into three types: penetrating type, oxidative conjunctival type, and volatile type. Let’s learn more about volatile drying inks, UV curing inks, and oxidative drying inks.
1. Volatile drying ink: It is the most commonly used ink in screen printing. The main components of the ink film are polymer substances. After printing, the solvent evaporates, and the polymer substances form the ink film. This evaporation and drying process is reversible, that is, the dried ink film can be redissolved using solvent.
After the ink is transferred to the substrate, there will be an ink film of solvent, and the solvent will evaporate first. The solvent in the ink diffuses in the atmosphere due to vapor pressure, forms a liquid film on the surface of the ink film, and then evaporates through the liquid film. In this drying process, the internal drying is generally slow, and sometimes blowing is needed to speed up the drying process. Volatile ink is easy to use and generally dries quickly, so it is widely used. 2. Ultraviolet light-curable ink (UV ink): UV ink can produce photochemical reactions and can be completely cured within a few seconds. It is increasingly used in plastic printing. The main components of ink are photopolymerizable resin, initiator, colorants and additives. In principle, organic solvents are not used. The main features of UV ink are: no solvent evaporation, no pollution, and environmentally friendly. It is widely used in food packaging printing. It has good printability and is suitable for printing on paper cardboard, plastic products, metal, textiles and other printing materials. It has a short curing time. , less energy consumption and good print quality. 3. Oxidative drying ink: The ink contains polymers with smaller molecular weights, which are oxidized in the air and form a polymer film through chemical reactions of heat, light or reactive substances. After this kind of ink is printed on the surface of the substrate, it generally needs to be heated to promote hardening. With the development of science and technology, people's requirements for environmental protection are increasing day by day, so environmentally friendly inks have emerged. Environmentally friendly ink is also called green ink. In offset printing, it mainly includes soybean ink and ultraviolet curing ink.