Combinations of binders and ink drying

Ink is a mixture of colorants, binders, fillers, and additives. Among them, the linking material is a liquid component in the ink, and is a carrier of a solid powder such as a colorant and a filler, and it evenly disperses the colorant and the filler, so that the ink has an appropriate rheological property and drying performance. At the same time, it is a kind of film-forming substance, and the pigment must adhere firmly to the surface of the substrate by virtue of the dry film-forming property of the binder. Therefore, the binder determines the dryness and film quality of the ink. This paper analyzes the drying methods and drying mechanisms of various inks by comparing and optimizing the performance of various types of binders in order to help everyone distinguish the drying methods and drying mechanisms of various inks. Only knowing which kind of linking material is used in ink can correctly distinguish so many drying methods, and can correctly select inks that meet printability requirements and print quality requirements.
1 Performance and combination of binders

Ink drying is a process that changes from a liquid to a solid and forms a film at the same time (if the film does not form a film, it cannot wrap the pigment and the filler will dry on the surface of the substrate, and the phenomenon of chalking will occur). The liquid binder plays a decisive role in the drying process of the ink. To analyze the dried form of the ink, start with the binder.

If only a single substance is used as the linking material, only one kind of vegetable oil can satisfy both the curing and the conjunctiva requirements because only it can dry itself and it can also form an ink film. Therefore, it is only through the combination of various linking materials that a variety of dry inks can be formulated.

Through a series of combinations, we obtained 7 combinations and 6 different drying forms, namely, oxidative conjunctiva drying, osmotic drying, permeation oxidative conjunctiva drying, volatile drying, thermosetting drying, and UV drying. These kinds of drying methods are currently more commonly used drying methods.

2 Various drying methods of ink drying mechanism

1) Infiltration drying

The linking material of the osmotic drying ink is composed of mineral oil and resin and is called a non-dried 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 as follows: After the ink is transferred to the paper, the mineral oil in the link material 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 osmotic drying is the fast drying speed, which is particularly suitable for use on high-speed printing presses. The osmotic drying ink is mainly offset printing rotary ink and is used to print loose paper such as newsprint, writing paper and the like.

2) Oxidative conjunctiva drying

It can be seen from Table 2 that the binder of the oxidized conjunctiva dry ink is composed of dry vegetable oil and is called a fat 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 dried vegetable oil in the ink absorbs the oxygen in the air and undergoes an oxidative polymerization reaction, so that the three-dimensional spatial distribution of the dry oil molecules becomes a huge three-dimensional network structure. Molecular, dried solid on the surface of the substrate.

The rate of drying of the oxidized conjunctiva is very slow, and generally it takes more than ten hours to fully harden the film, but the formed ink film has good gloss, combines well with the paper, has good friction resistance, and has a certain degree of elasticity.

Oxidation conjunctiva drying inks used to be primarily sheetfed offset inks and engraved gravure inks. They are called grease type inks. Due to its slower drying speed and the inability to adapt to high-speed printing requirements, this type of ink gradually fades out of the field of application of sheet-fed offset printing inks.

3) Drying of osmotic oxidative film

The linking material of the infiltration oxidative conjunctiva dry ink consists of dry vegetable oil, high-boiling point kerosene, and resin, and is called a resin-type linking material. The drying mechanism is based on the penetration of high-boiling kerosene and the drying of the oxidative conjunctiva reaction of the dry vegetable oil. The drying process is: After the ink is transferred to the paper, the high-boiling kerosene quickly penetrates into the paper, and the resin is condensed due to the penetration of the high-boiling kerosene into the paper. At the same time, the dry vegetable oil absorbs the oxygen in the air and undergoes an oxidative polymerization reaction, and is finally completed. dry.

The osmotic oxidative conjunctiva is an ideal dry form because of its quick fixation, good gloss, vivid color, and firm ink film. Permeation oxide conjunctiva drying combines the advantages of both infiltration and oxidative conjunctiva drying. It utilizes the rapid penetration of high-boiling kerosene to achieve fast fixation, so that no back-scratching occurs, followed by the slow oxidation of dry vegetable oils. Form a strong and smooth ink film. Therefore, the osmotic oxidative conjunctiva drying can not only meet the high-speed printing drying requirements, but also can realize the bright and high-gloss quality requirements. Infiltration oxidative conjunctiva drying ink is mainly used in modern sheetfed offset printing inks. It can print exquisite graphic information on medium and high-grade paper substrates.

4) Volatile drying

The linking material of volatile drying ink is composed of organic solvent and resin or water and resin. The former is a traditional volatile drying ink, which is widely used in gravure printing. The latter is a representative of new environmentally friendly ink, and its development momentum is rapid.

1 solvent type volatile drying

The mechanism of solvent-based volatile drying relies on the solvent evaporation of the solvent in the ink to complete the drying. The drying process is: after the ink is transferred to the substrate, the solvent in the binder is volatilized into the air, and the remaining binder (mainly the resin) forms a solid film together with the pigment and solidifies on the surface of the substrate.

Solvent-based volatile drying inks mainly include photogravure inks and flexographic inks, which are printed on medium and high-grade packaging materials such as cardboard, corrugated board, and plastics.

2 aqueous volatile drying

The mechanism and process of waterborne volatile drying is the same as the solvent type, except that the volatilized protagonist is changed from solvent to water. The evaporation rate of water directly affects the drying speed of the ink. Aqueous volatile drying ink is a solvent-based volatile drying ink, which significantly reduces the emission of organic solvents into the atmosphere, prevents air pollution, improves the working environment, and is conducive to the health of employees. It also reduces the fire caused by static electricity and flammable solvents. Danger and hidden dangers.

Like solvent-based inks, water-based volatile drying inks mainly include photogravure inks and flexographic inks. In particular, flexographic inks are currently undergoing a large number of changes in water-based inks to improve their environmental performance.

5) Hot solid drying

The binder of the thermoset drying ink is composed of a small amount of dry vegetable oil, more mineral oil (mainly narrow-range high-boiling point kerosene) and a resin, which is called a thermosetting binder. The drying mechanism is to use a heating and drying device to speed up the evaporation of high boiling point kerosene. The drying process is: after the ink is transferred to the substrate, the high-boiling point kerosene in the ink layer is rapidly volatilized by the heating device, and the resin in the ink is heated and softened, and the solid pigment particles penetrate into the semi-fluid state resin, and after cooling, the Cures together on the printing surface. The ink heating devices include hot air drying, gas flame drying, hot air mixing drying, and electronic drying.

Thermosetting drying inks have fast drying speeds, but they consume a lot of energy when they are dry. High temperatures of up to 200°C also affect the quality of printed products. Thermosetting drying inks are mainly used in commercial offset printing presses for the printing of coated papers, which meet the requirements for rapid printing on high-smoothness papers.

6) Drying (UV drying)

The binder of photocurable drying ink consists of photo-setting resin, cross-linking agent and photosensitizer, which is called photo-curable (UV) type binder. The drying mechanism is the use of ultraviolet radiation to decompose the photosensitizer to form free radicals. These radicals cause the photocurable resin and the crosslinking agent to 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 rays to be excited to form free radicals, and the free radicals crosslink and copolymerize the photo-curable resin and the cross-linking agent to complete the drying process, as shown in FIG. 1 .

The UV ink has excellent performance and fast drying speed. It can be dried in 0.1 seconds without stickiness. It does not volatilize solvents and does not pollute the environment. It is an environmentally friendly ink. This type of ink does not dry before it is irradiated with ultraviolet rays, and it is easy to clean the plate and blanket. Ink drying is not affected by the pH of the substrate and fountain solution, and can be applied to a variety of substrates. At the same time also has a good adhesion performance, suitable for advanced offset paper, metal foil, synthetic paper, composite gold and silver cardboard, PE, PVC, PET and other non-absorbent materials.

In summary, comparing the ingredients of various binders to find out which drying method they belong to, whether they can form a film, and then optimizing and combining according to their own characteristics, can help us to differentiate their binders from such a variety of inks. Ingredients, drying methods, drying mechanism and application fields, for the printing of various printing products using the correct ink.