Ink is made by mixing coloring material, connecting material, filling material and auxiliary agent. The binder is the liquid component of the ink and the carrier of solid powders such as colorants and fillers. It evenly disperses the colorants and fillers, so that the ink has proper rheological properties and drying properties. At the same time, it is also a film-forming substance, and the pigment must be firmly attached to the surface of the substrate by the dry film-forming property of the binder. Therefore, the binder determines the drying properties and film quality of the ink. This article analyzes the drying method and drying mechanism of inks on the basis of performance comparison and optimization of various types of binders, in order to help you to distinguish the drying methods and drying mechanisms of various inks in essence. Only by knowing what kind of connecting material is used in the ink can we correctly distinguish so many drying methods, and we can choose the ink that meets the printability requirements and print quality requirements.
1 Performance and combination of linking materials
The drying of the ink is a process that changes from liquid to solid, and at the same time forms a film (if the connecting material is dried, if the film cannot be formed, the pigment and filler cannot be wrapped and dried on the surface of the substrate, and powdering will occur), so in the ink The liquid binder plays a decisive role in the drying process of the ink. To analyze the dry form of ink, we must start with the linking material.
If only a single substance is used as a linking material, only one vegetable oil can meet the requirements of curing and conjunctiva at the same time, because only it can dry itself and can also form an ink film. Therefore, only through the combination of various connecting materials can a variety of dry forms of ink be prepared.
Through a series of combinations, we have obtained 7 combinations and 6 different drying forms, namely oxidized conjunctival drying, infiltration drying, infiltration oxidized conjunctival drying, volatile drying, thermosetting drying and UV drying. These drying methods are currently more commonly used drying methods.
2 Ink drying mechanism of various drying methods
1) Infiltration drying
The binder of penetrating and drying ink is composed of mineral oil and resin, which is called non-drying mineral oil binder. The drying mechanism is based on the penetration of mineral oil and the absorption of paper to complete the drying. The drying process is: after the ink is transferred to the paper, the mineral oil in the binder penetrates into the paper, and the pigment and resin left on the paper surface are quickly fixed to complete the drying process.
The advantage of penetration drying is fast drying speed, especially suitable for use on high-speed printing machines. The penetrating and drying ink is mainly offset printing ink, which is used to print paper with loose structure such as newsprint and writing paper.
2) Dry oxidized conjunctiva
It can be seen from Table 2 that the binder of the oxidized conjunctiva drying ink is composed of dry vegetable oil, which is called grease-type binder. The drying mechanism is to use oxidative polymerization to change the ink layer from liquid to solid. The drying process is: after the ink is transferred to the substrate, the binding material in the ink, that is, the dry vegetable oil absorbs the oxygen in the air and undergoes an oxidative polymerization reaction, so that the dry oil molecules distributed in three dimensions become a huge three-dimensional network structure. Molecules, dry on the surface of the substrate.
The drying rate of the oxidized conjunctiva is very slow. It usually takes more than ten hours to completely harden the film, but the ink film formed has good gloss, is firmly combined with paper, has good friction resistance, and has certain elasticity.
In the past, oxidized conjunctive drying inks were mainly sheet-fed offset printing inks and engraved gravure inks, which were called grease-based inks. Due to its slow drying speed, it can not meet the requirements of high-speed printing, so this ink gradually fades out of the application field of sheet-fed offset printing ink.
3) Infiltration and oxidation conjunctiva drying
The binder of the penetrating oxidized conjunctiva drying ink is composed of dry vegetable oil, high boiling point kerosene, and resin. It is called resin binder. The drying mechanism depends on the penetration of high-boiling kerosene and the oxidative conjunctive reaction of dry vegetable oil to complete drying. The drying process is: after the ink is transferred to the paper, the high-boiling kerosene quickly penetrates into the paper, and the resin agglomerates due to the penetration of the high-boiling kerosene into the paper. At the same time, the dry vegetable oil absorbs oxygen in the air and undergoes oxidative polymerization, which is finally completed dry.
Penetrating oxidation conjunctiva drying fast, good gloss, bright colors, strong ink film, is an ideal form of drying. Osmotic oxidative conjunctiva drying combines the advantages of infiltration and oxidative conjunctiva drying methods. It utilizes the rapid penetration of high-boiling kerosene to achieve fast fixation, so that the phenomenon of dirt on the back side does not occur; then it is slowly oxidized with dry vegetable oil Form a firm and smooth ink film. Therefore, the permeation and oxidation conjunctiva drying can not only meet the drying requirements of high-speed printing, but also achieve the quality requirements of bright and high gloss. The penetrating oxidation conjunctiva drying ink is mainly used in modern sheetfed offset printing ink, which can print exquisite graphic information on medium and high grade paper substrates.
4) Volatile drying
The connecting material of volatile drying ink is composed of organic solvent and resin or water and resin. The former is traditional volatile drying ink, which is widely used in gravure printing, and the latter is the representative of new environmentally friendly ink, and the development momentum is rapid.
â‘ Solvent-based volatile drying
The mechanism of solvent-based volatile drying is to rely on the solvent in the ink to evaporate into the space to complete the drying. The drying process is: after the ink is transferred to the substrate, the solvent in the binder volatilizes into the air, and the remaining binder (mainly resin) forms a solid film layer with the pigment and solidifies on the surface of the substrate.
Solvent-based volatile dry inks mainly include photogravure inks and flexographic inks, which are printed on medium and high-grade packaging materials, such as cardboard, tile, cardboard, and plastic.
â‘¡Water-based volatile drying
The mechanism and process of water-based volatile drying are the same as those of the solvent type, except that the protagonist of volatility is changed from solvent to water. The rate of water volatility directly affects the drying speed of this ink. Compared with solvent-based volatile dry ink, water-based volatile dry ink significantly reduces the discharge of organic solvents into the atmosphere, prevents atmospheric pollution, improves the working environment, is beneficial to the health of employees, and also reduces fires caused by static electricity and flammable solvents. Dangers and hidden dangers.
Like solvent-based inks, water-based volatile dry inks mainly include photogravure inks and flexographic inks, especially flexographic inks are currently being changed to water-based inks to improve their environmental protection.
5) Thermosetting and drying
The binder of thermosetting dry ink is composed of a small amount of dry vegetable oil, more mineral oil (mainly a narrow boiling range of high boiling point kerosene) and resin, called thermosetting binder. The drying mechanism is to use a heating and drying device to speed up the evaporation and drying of high boiling point kerosene. The drying process is: after the ink is transferred to the substrate, the high-boiling kerosene in the ink layer is quickly volatilized by the heating device, and the resin in the ink is heated to soften, the solid pigment particles penetrate into the semi-flowing resin, after cooling Together cured on the printing surface. The heating device of ink includes hot air drying, gas flame drying, hot air mixed drying and electronic drying.
Thermosetting drying inks have a fast drying speed, but consume a lot of energy during drying. High temperatures up to 200 ° C also have an impact on the quality of the printed product. Thermosetting drying inks are mainly used in commercial rotary offset presses for printing on coated paper, which meets the requirements for rapid printing on high smoothness paper.
6) Light solid drying (UV drying)
The linking material of photo-curable dry ink is composed of photo-setting resin, crosslinking agent and photosensitizer, and is called photo-curing (UV) type linking material. The drying mechanism is to use ultraviolet radiation to decompose the photosensitizer to form free radicals. These free radicals make the photocurable resin and crosslinking agent crosslink and solidify on the surface of the substrate. The drying process is: after the ink is transferred to the substrate, the photosensitizer is excited by ultraviolet radiation to form free radicals, and the free radicals crosslink and copolymerize the photocurable resin and the crosslinking agent to complete the drying process, as shown in FIG. 1.
UV ink has excellent performance, fast drying speed, and can be dried in 0.1 seconds without sticking. It has no solvent volatilization and will not pollute the environment. It is an environmentally friendly ink. This ink will not dry before irradiated with ultraviolet light, and it is easy to clean the printing plate and blanket. Ink drying is not affected by the pH value of the substrate and fountain solution, and can be applied to a variety of substrates. At the same time, it also has good adhesion performance, suitable for the printing of high-grade offset paper, metal foil paper, synthetic paper, composite gold and silver cardboard, PE, PVC, PET and other non-absorbent materials.
To sum up, comparing the ingredients of various binders to find out which drying method they belong to, whether they can form a film, and then optimize the combination according to their own characteristics can help us distinguish their binders from so many inks Composition, drying method, drying mechanism and application field, choose the right ink for printing for various printing products.
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