Application of Solvent in Plastic Gravure

Solvents are the most important auxiliary materials in the gravure printing of plastic packaging films. Intaglio printing inks use the lowest viscosity and the fastest drying speed in all kinds of printing, which is mainly determined by the properties of solvents. Solvents use it as a liquid to suit printing needs. The main component of gravure printing ink is solid, which accounts for 50%-70% of the ink composition and cannot be directly used for printing. The solvent not only adjusts the viscosity of the ink, so that it can meet the printable requirements of the printed substrate, and has a great influence on the quality of the plastic packaging printing product. Therefore, it should attract the attention of printing companies.

The role of solvent

The substance that can dissolve other substances is called a solvent. The substance is dissolved in a solvent to form a solution of the substance, and the solvent is dispersed and dissolved by the dissolved substance and is called a solvency. 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 reducing the viscosity of the oil black. As there are many types of printing inks, there are common printing inks (also known as polyamide printing inks), plastic printing inks (also known as chlorinated polypropylene inks), printing inks of polyurethane systems, etc. With the increasing awareness of environmental protection, water-based inks without solvents are also on the market, so to obtain them, high-quality prints must use matching solvents.The role of solvents includes:

1. Solvents can dissolve materials such as additives, additives, and additives to make them fluid and evenly disperse pigments. This helps the transfer of ink on printing presses, and makes them adhere to printing materials.

2. Solvents are very low viscosity liquids and are added to higher viscosity printing inks to 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 according to the conditions such as the printing speed of the gravure printing machine, drying capability of the drying device, weather conditions, and the size of the pattern: {: drying speed. In general printing conditions—F, the drying speed should be adjusted with the use of a fast 'F' solvent or a slow-drying solvent final 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 low surface tension and a small contact with the surface of the printing material plastic film, which can improve the absorbability of the printed film. The solvent in the ink will dissolve or swell the printed film to increase the affinity of the ink and the film.

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

Solvent selection requirements and methods

1. In the ink printing process, the solvent is formulated according to the temperature of the workshop, the humidity, the speed of the printing press and other factors using a variety of solvents according to a certain ratio, the role of which is to dilute the viscosity of the ink to the required printing viscosity, and finally through the drying tunnel The solvent is dried, 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 ultimately causes 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%. The ink with high water content is easily delaminated during the printing process. The phenomenon of watermarking is caused by the graphic and text, which affects the volatilization of the solvent, the residual solvent increases, and even the ink layer Adhesion with the back of the printed film

2. According to the choice of the ink resin system, there are many types of inks. In order to meet the performance and printing requirements of different printing films, different types of resins are produced as the substrate of the connecting material. 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 table printing inks and Weiyin inks 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 theory of solubility parameter, the solubility parameter of polyamide in strong hydrogen-bonding solvent is in the range of 9.5 to 11.4. The only solvent that can be used in this solubility parameter range is isopropyl alcohol and n-butanol. Therefore, we use a mixed solvent of aromatic hydrogen and alcohols such as methyl, benzene, xylene, isopropanol, and ethanol to take the temperature of 10°C to adjust the volatilization rate of the solvent and reduce the cost. The mixed solvents must contain 'quantitative true solvents such as propanol and n-butanol. Frequently, a certain amount of spurious solvents, such as ethyl acetate, is added to the electricity to regulate 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 is too fast. The actual printing process often uses [00% toluene for dilution. General table printing ink solvent composition includes the following types of toluene: isopropyl alcohol: ethyl ester 2 50%: 30%: 20% (or 60%: 30%: 10%); toluene: isopropanol: ethyl ester: N-butanol 20%: 20%: 10%: 10%; toluene: ethyl ester 20%: 10% and so on. No matter how the ratio must be followed a principle: to ensure product quality and meet customer requirements. The dissolution parameters of the mixed solvent can be calculated by the formula: §=VI§1+V1§2+... where VI, 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 that the ratio of solvent volatilization in the mixed solvent over time is not likely to cause damage to the system and cause quality problems, such as deposition of precipitates from the ink layer. Therefore, certain solvents must be maintained.

Table printing ink is often used to print PVC film. 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, so as to resist the precipitation of a large amount of plasticizer in the PVC film. No ink sticking phenomenon occurs. The company uses ketones and n-butyl esters as dilution solvents. The ratio is generally toluene: butanone: butyl ester: 60%: 30%: i0%. 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%. 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: Other considerations for selecting 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.

The basic performance of the solvent

The solvents we often use in printing are alcohols, ketones, esters, and aromatic hydrogen solvents.

1. Ester. 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 a constant odor, high price.

Author / Chen Xirong