The function of the hottest solvent in gravure pri

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The role of solvents in gravure printing inks

release date: Source: China paper

the solvents we often use in packaging printing inks include alcohols, ketones, esters and aromatic hydrogen solvents. Today, China paper will introduce the related functions of gravure printing ink in detail

1. Esters. The solubility is good, and the smell is easy to accept, but the price is high. Commonly used are ethyl ester, butyl acetate, etc

2. Alcohols. It is mainly used for alcohol soluble inks and polyamide surface printing inks, commonly used are isopropyl alcohol and n-butanol

3, ketones. It has strong solubility and low toxicity, but it has a certain smell and high price

I. The role of solvents in inks

substances that can dissolve other substances are referred to as solvents for short. When a substance is dissolved in a solvent, it becomes a solution of the substance. The dispersion and dissolution ability of the solvent to the dissolved substance is called the solubility. The stronger the solubility, the faster the dissolution rate and the lower the dissolution viscosity. Because the solvent is a low viscosity liquid, it can be added to the ink to reduce the viscosity of the ink. Because there are many kinds of printing inks now, common ones are surface Gravure plastic printing ink (also known as polyamide surface printing ink), inner plastic printing ink (also known as chlorinated polypropylene ink), pet printing ink of polyurethane system, etc. With the increasing awareness of environmental protection, water-based inks without solvents also appear on the market. Therefore, in order to obtain high-quality prints, we must choose the matching solvent. The flame retardant grade of the solvent reaches B1 level, and its functions include:

1. The solvent can dissolve resins, additives, additives and other materials, make them flowable, make the pigments disperse evenly, and help the transfer of ink on the printing machine and bond it with the printing materials

2. The solvent is a liquid with very low viscosity. Adding it to the printing ink with high 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 solvents to adjust the drying speed of the ink according to the printing speed of the gravure printing machine, the drying capacity of the drying device, climatic conditions, the size of the pattern and other conditions. Under normal printing conditions, the drying speed should be adjusted by using fast drying solvent or slow drying solvent as the conditions change. Different solvents have different volatilization rates. The use of mixed solvents is to integrate the characteristics of a variety of single solvents to meet the requirements of printing conditions. In gravure printing, mixed solvents are often used to dissolve ink. The function of diluent to adjust drying speed and the function of dissolving resin are the most important properties of solvent

4. Generally, the surface tension of organic solvents is small, and the contact with the surface of the plastic film of the printing material is small, which can improve the absorption of the printed film. The solvent in the ink will dissolve or swell the printed film to a certain extent, so as to improve the affinity between the ink and the film

5. The solvent adopts mixed solvent to dilute the ink to meet the needs of printing products. The remaining printing ink is easy to save and can be reused next time

II. Selection method of solvent

1. In the process of ink printing, the solvent is prepared by using a variety of solvents according to a certain proportion according to the temperature, humidity and printing machine speed of the workshop. Its function is to dilute the viscosity of the ink to the required printing viscosity, and finally dry the solvent through the drying tunnel, so it is required that the solvent has good volatility under a certain wind speed and temperature. Toluene is petroleum toluene, so coking toluene and mixed toluene cannot be used. At the same time, toluene cannot contain water. Due to its incompatibility with water, toluene often affects volatility, solvent residue, and poor adhesion of the ink layer in the printing process, resulting in quality problems. General solvents must be tested before entering the warehouse, such as appearance, moisture, etc. Ethyl acetate, a commonly used solvent in printing, often contains a certain amount of water. Because ethyl acetate is miscible with water, it must be tested. The flexible packaging industry stipulates that the moisture content should not be greater than 2%. The ink with high moisture content is prone to delamination in the printing process, and the phenomenon of water marks in graphics and texts affects the volatilization of solvents, the increase of residual solvents, and even the adhesion between the ink layer and the back of the printing film

2. Choose according to the resin system of the ink. At present, there are many kinds of inks. In order to meet the performance and printing requirements of different printing films, different types of resins have been produced as the substrate of connecting materials. At present, the resins commonly used in gravure printing inks in China include polyamide resin, chloroacetic resin, chloropropyl resin, polyurethane, etc. The following is an analysis of surface printing ink and internal printing ink to illustrate the selectivity of solvents

the surface printing ink of gravure is based on polyamide resin (including modification) as the connecting material. According to the solubility parameter theory, the solubility parameter range of polyamide in strong hydrogen bonded solvents is 9.5-11.4. Within this solubility parameter range, the corresponding single solvent is only a small number of solvents such as isopropanol and n-butanol, which will show a stable and progressive situation in the export growth of extruder products in China. Therefore, we choose toluene, xylene, isopropanol, ethanol and other aromatic hydrogen and alcohol mixed solvents to replace, in order to adjust the volatile speed of the solvent and reduce costs. The mixed solvent needs to contain a certain amount of isopropanol, n-butanol and other real solvents. A certain amount of pseudosolvent, such as ethyl acetate, is often added in order to adjust the volatilization rate and meet the requirements of improving quality. Generally, the amount of ethyl acetate added is not more than 20%. Too much will make the printed text white and the volatilization speed is too fast. In the actual printing process, 100% toluene is often used for dilution. Generally, the mixed composition of surface printing ink solvent is as follows: isopropyl alcohol: ethyl ester blue 50%:30%:

20% (or 60%:30%:10%); Toluene: isopropanol: ethyl ester: n-butanol di 60%:20%:

10%:10%; Toluene: ethyl ester di 90%:10%, etc. No matter how it is proportioned, we must follow a principle: ensure product quality and meet customer requirements. The dissolution parameters of mixed solvents can be calculated by the following formula: §: V1 § 1 + V1 § 2 +... Where V1 and V2 are the volume percentage of added solvents, and 1 §, § 2 are the dissolution parameters of various solvents. It can be seen that proper solvent with corresponding volume can also dissolve a specific polymer resin. At the same time, we should also consider that the volatile ratio of the mixed solvent is inconsistent with the passage of time, which may damage the system and cause quality failures, such as ink delamination precipitation, so we must maintain a certain amount of real solvent

surface printing inks are often used to print PVC films. This printing ink mainly uses the copolymerization of vinyl chloride as the connecting material. It has good affinity when printing PVC film, and can resist the precipitation of a large number of plasticizers in PVC film without the phenomenon of ink anti adhesion. Ketones and n-butyl can be used as diluting true solvents. The proportion is generally toluene: butanone: butyl ester:

60%:30%:10%. Too many ketone solvents are easy to fuse the PVC film, which is mainly caused by too high boiling point. In the process that the price of industrial products falls into a state of runaway in a short time due to actual printing, if the machine is shut down, it is recommended to loosen the printing glue roller to reduce the fracture phenomenon caused by solvent erosion

internal printing ink is often chlorinated polypropylene resin system, and internal printing ink is also called composite ink. Now composite inks are often used for printing OPP films. Chloropropylene resin is soluble in esters, ketones and aromatic hydrogen, but insoluble in alcohol solvents. In fact, considering the high cost, general color printing enterprises use toluene and xylene, with a small amount of esters such as ethyl acetate added. Isopropanol is generally added less, but the addition of isopropanol can reduce the surface tension of the ink. In fact, when printing with composite ink, it is generally: toluene: butanone: ethyl ester, 70% to 20% to 10%; Toluene

100%; Toluene: xylene: ethyl ester di 70%:

20%:10%, etc. It must be noted that when selecting solvents, attention should be paid to product quality and specific actual conditions. The solvent dries too fast, volatilizes too fast, and the graphic products are white, Matt, and poor reproducibility; It dries too slowly, causing ink to adhere to the traction roller and increasing residual solvent. Only the right solvent can print good product quality

3. Solubility and drying performance. Resins, additives, auxiliary additives and other materials should have strong solubility, try to have appropriate solubility and swelling of plastic film, and maintain appropriate evaporation rate of ink. The drying speed of the mixed solvent is better than that of the diluted solvent itself

4. Other precautions for solvent selection. The solvent should be volatilized as far as possible, and the materials used in some industries should be avoided. The resin of the connecting material has good escape property. The prices of various solvents are also different. Try to keep the price low on the premise of ensuring the printing quality

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