The solvents we often use in printing inks are alcohols, ketones, esters and aromatic hydrogen solvents.
1, esters. The solubility is good and the smell is easy to accept, but the price is high. Commonly used are ethyl, butyl acetate and so on.
2, alcohols. It is mainly used for alcohol-soluble inks and polyamide-type surface printing inks. Ethylisopropanol and n-butanol are commonly used.
3, ketones. Very strong solubility, low toxicity, but with a certain odor and high price.

First, the role of solvent in the ink
The substance that can dissolve other substances is called a solvent. The substance dissolves in a solvent and forms a solution of the substance. The solvent's ability to disperse and dissolve the dissolved substance is called dissolving power. The stronger the dissolving power, the faster the dissolving speed and the lower the dissolving viscosity. Since the solvent is a low-viscosity liquid, it can be added to the ink with the purpose of lowering the viscosity of the ink. As there are many types of printing inks, common ones are table printing intaglio printing inks (also known as polyamide printing inks), plastic printing inks (also known as chlorinated polypropylene inks), and PET printing inks of polyurethane systems. With the increase of environmental awareness, there are also solvent-free water-based inks on the market. Therefore, in order to obtain high-quality prints, it is necessary to use compatible solvents. The role of solvents includes:

1. The solvent can dissolve the materials such as resin, additives and additives to make it fluid, so that the pigment can be uniformly dispersed, which helps the transfer of the ink on the printing press and makes it adhere to the printed material.

2, the solvent is a very low viscosity liquid, added to the printing ink with higher viscosity, can reduce the viscosity of the ink. The operator can adjust the viscosity of the ink according to the depth of the printing plate roller, the number of lines, the printing speed and other conditions to obtain the best printing effect.

3, the printer can also use the solvent to adjust the ink drying speed according to the gravure printing machine's printing speed, drying device drying capacity, weather conditions, the size of the pattern and other conditions. Under normal printing conditions, the drying speed should be adjusted by using a fast drying solvent or slow drying solvent as the conditions change. Different solvents have different volatilization rates. The use of a mixed solvent is a combination of the characteristics of multiple single solvents to meet the requirements of printing conditions. Gravure printing often uses a mixed solvent to dissolve the ink. The function of adjusting the drying speed by the diluent and the function of dissolving the resin are the most important properties of the solvent.

4. The organic solvent generally has a small surface tension and a small contact with the surface of the printing material plastic film, which can improve the absorption of the printed film. The solvent in the ink will cause some dissolution or swelling of the printed film, thereby increasing the affinity of the ink and the film.

5. The solvent is diluted with the mixed solvent to meet the needs of printed products. The remaining printing ink is easy to save and can be used again next time.

Second, the choice of solvent
1, in the ink printing process, the solvent is based on the temperature of the workshop, humidity and printing speed and other factors using a variety of solvents prepared by a certain ratio, its role is to dilute the viscosity of the ink to achieve the required printing viscosity, and finally passed The drying process dries the solvent, so the solvent is required to have good volatility at a certain wind speed and temperature. Toluene is a petroleum toluene and it is not possible to use coked toluene and mixed toluene. At the same time, toluene can not contain moisture. Due to the incompatibility between toluene and water, it often affects the volatility, solvent residue, poor adhesion of the ink layer in the printing process, and eventually produces quality problems. General solvents must be tested before entering the warehouse, such as appearance and moisture. The solvent ethyl acetate, which is commonly used in printing, often also contains a certain amount of moisture. Since ethyl acetate has some compatibility with water, it must be tested. The flexible packaging industry stipulates that the moisture content cannot be ≥ 2%, and that inks with high water content are susceptible to delamination in the printing process. The phenomenon of watermarking is caused by the graphics, which affects the volatilization of the solvent, increases the residual solvent, and even the ink layer. Adhesion occurred on the back of the printed film.

2, according to the ink resin system to choose. Nowadays, there are many types of inks. In order to meet the performance and printing requirements of different printing films, different types of resins have been produced as substrates for connecting materials. At present, the commonly used resin for domestic gravure inks are: polyamide resins, vinyl acetate resins, chloroprene resins, polyurethanes, and the like. The following is the analysis of the printing ink and the printing ink to illustrate the problem of solvent selectivity.

The gravure printing ink is a polyamide resin (including modified) as the substrate of the connecting material. According to the solubility parameter theory, the solubility parameter range of polyamide in strong hydrogen-bonded solvents is in the range of 9.5 to 11.4. The only solvent that corresponds to this solubility parameter range is isopropyl alcohol and n-butanol. Therefore, we used toluene, xylene, isopropanol, ethanol and other aromatic hydrogen and alcohol mixed solvents to replace, in order to adjust the solvent evaporation rate, reduce costs. The mixed solvent needs to contain a certain amount of true solvent such as isopropyl alcohol and n-butanol. Frequently, a certain amount of spurious solvent, such as ethyl acetate, is also added in order to adjust the volatilization rate and meet the requirements for improving quality. Ethyl acetate is usually added in an amount of no more than 20%. Too much will make the printed text white and the evaporation rate too fast. 100% toluene is often used for dilution during the actual printing process. General table printing ink solvent composition has the following kinds of toluene: Isopropanol: Ethyl blue 50%: 30%:

20% (or 60%: 30%:10%); Toluene: Isopropanol: Ethyl: n-Butanol 2 60%: 20%:

10%: 10%; toluene: ethyl ester 20%: 10% etc. No matter how the ratio must be followed a principle: to ensure product quality and meet customer requirements. The solubility parameters of the mixed solvent can be calculated by the following formula: §: V1 § 1 + V1 § 2+ ...... where V1, V2 are the volume percentages of the added solvent, and 1 § and § 2 are the dissolution parameters of various solvents. It can be seen that the appropriate volume of solvent is also able to achieve the dissolution of a particular polymer resin. At the same time, it is also necessary to take into account the inconsistent ratio of solvent volatilization in the mixed solvent over time, which may damage the system and cause quality problems, such as ink sedimentation, etc. Therefore, certain true solvents must be maintained.

Surface printing inks are often used to print PVC films. This printing ink is mainly based on the binary copolymerization of vinyl chloride as a binder. When printing PVC film, it has a good affinity and can resist the precipitation of a large amount of plasticizer in the PVC film without the phenomenon of ink sticking. Ketones and n-butyl esters can be used as diluent true solvents. The ratio is generally toluene:butanone:butyl ester:

60%: 30%: 10%. Too many ketone solvents can easily melt the PVC film, which is mainly due to the high boiling point. In the actual printing process, such as stopping, it is recommended to release the printing rubber roller to reduce the occurrence of cracking due to the erosion of the solvent.

Ink printing ink is often a chlorinated polypropylene resin system. Ink printing ink is also called compound ink. Since compound inks are often printed on OPP films, chloroprene resins are soluble in esters, ketones, and aromatic hydrogens but not in alcoholic solvents. Actually, in consideration of high cost, general color printing companies use toluene and xylene. A small amount of esters such as ethyl acetate are added. Isopropyl alcohol is generally added in small amounts, but adding isopropyl alcohol can reduce the surface tension of the ink. In fact, the composite ink is generally printed: toluene: butanone: ethyl ester 70%: 20%: 10%; toluene

100%; toluene: xylene: ethyl ester 70%:

20%: 10% and so on. It must be noted that the selection of solvents should pay attention to product quality and specific actual conditions. The solvent is too fast drying, the volatilization rate is too fast, the graphic product is white and dull, and the reproducibility is poor; if it is too slow, the ink sticking traction roller and residual solvent increase. Only the right solvent can print good product quality.

3, solubility and drying properties. Resins and additives and auxiliary aids and other materials should have strong solvency, as far as possible with the appropriate dissolution and swelling of the plastic film, and maintain the proper evaporation rate for the ink. The mixed solvent is preferably slower than the solvent that dilutes the solvent itself.

4. Select other considerations for the solvent. Solvents should be volatilized as cleanly as possible, odor problems should be avoided, and the detachment of the binder resin should be good. The price of various solvents is also not the same, as far as possible to maintain the low price in the premise of ensuring the printing quality.

Source: Ink Information

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