Water-based ink properties and application analysis

This article describes the performance of water-based inks and their practical application in the printing field.

With the growing awareness of human environmental protection, green environmental protection has become the theme of development in the 21st century. In recent years, many countries have added many requirements and restrictions on packaging and printing in terms of hygiene and environmental protection, especially for food packaging and printing, due to the use of organic solvent inks and coating oils. Will emit hydrocarbons. Air pollution. And detrimental to health. Therefore, food packaging and printing in developed countries has basically no longer use solvent-based printing materials, but research and development and application of small pollution, low pollution green packaging materials. It can be seen that green packaging printing materials that are conducive to the environment will surely receive more attention and development.

First, the composition of water-based ink
Water-based ink is an ink prepared from a combination of a specific aqueous polymer resin, a pigment, water, and a solubilizer added by a combination of physical and chemical processes, abbreviation: ink. The difference between solvents is the biggest difference between aqueous inks and solvent inks. Water ink is based on water as a solvent. After the ink is transferred to the EI~fJ substrate, moisture evaporates into the environment or into the substrate. The ink dries with the evaporation of moisture. : Sex polymer resin is the most important component of water-based ink, it plays a role in the link of ink Ink I. It allows the pigment to be uniformly dispersed, allowing the ink to: have a certain degree of fluidity and provide adhesion to the substrate material, allowing the oil to form a uniform ink layer after printing. At present, most of the research and development use of alkali soluble resin, this type of resin can be dissolved by water. Made of water-based binder, printed and dried to become insoluble in water.

The hue of aqueous inks depends mainly on the pigment. The pigments are evenly distributed in the binder in the form of particles. The pigment particles can absorb, reflect, refract, and transmit light. Therefore, it can present a certain color. General requirements pigments have a bright color. Suitable coloring power and hiding power. And higher degree of dispersion. In addition, depending on the purpose of use. It is also possible to select specific solvents that are resistant to different resistances. The role of solvent is to dissolve the resin. The ink has a certain degree of fluidity and can be transferred smoothly during the printing process. And adjust the ink viscosity and drying performance. Auxiliaries have a great influence on ink performance. It is an indispensable part of ink painting. Commonly used additives in inks are pH stabilizers, slow drying agents, defoamers, dilutants, and the like.

Second, the environmental safety features of water-based ink
The biggest distinguishing feature of water-based inks from solvent-based inks lies in the dissolving vehicle used. Solvent-based inks are dissolved in organic solvents such as toluene, ethyl acetate, and ethanol. The aqueous ink dissolving carrier is water and a small amount of alcohol (about 3% to 5%). As water is used as a carrier. Water-based ink has significant environmental safety features: safe, non-toxic, non-inflammable, non-explosive and almost no volatile organic gas production, mainly in the following four aspects.

1. No pollution to the atmosphere. Due to water-based ink as a carrier for dissolution. So no matter it is in the production process or when it is used for printing. Almost no volatile organic gas (VOC) is emitted to the atmosphere, and VOC is considered as one of the major sources of pollution in the global atmospheric environment. This is unmatched by solvent inks. In the production process, solvent-based inks emit large amounts of low-concentration VOCs. According to the estimate. General solvent ink manufacturing factory. If the production equipment is not fully enclosed, the volatile loss of the organic solvent accounts for about 0.3% to 1% of the ink production. For the treatment of low-concentration VOC, except for a few ink factories that use high-cost processing methods such as activated carbon adsorption. Most of them are directly discharged into the atmosphere at high altitude. Not only that, in the printing process, organic solvents in solvent-based inks are almost completely dried and quickly evaporate. In addition to the use of high-concentration VOCs above the press, such as catalytic combustion or microbial treatment processes, low-concentration VOCs diffused in the air of the printing plant are often discharged directly into the atmosphere, if the proportion of organic solvents in the solvent-based ink is Calculated from 25% to 35%, the amount of VOC directly discharged into the atmosphere is quite alarming. Water-based ink precisely overcomes this shortcoming. This unique feature of non-polluting the atmosphere is being favored by more and more printing companies.

2. Reducing residual poisons on printed surfaces. Ensure food hygiene and safety. Water-based inks completely solve the toxicity problems of solvent-based inks. Due to the absence of organic solvents, the toxic substances remaining on the print surface are greatly reduced. This feature. In the cigarette, wine, food, beverages, medicines, children's toys and other health requirements of strict packaging and printing products in the more good health and safety. In the present day when human beings pay more and more attention to food safety. Has been concerned about the health and safety of food packaging. The amount of harmful substances in packaging materials and packaging printing is very important. For example, KFC, McDonald's and other fast food companies have strict restrictions on the amount of residual solvents on food packaging. Shanghai Tobacco Group Company also requires strict benzene residue on cigarette packs. The use of solvent-based ink prints is difficult to achieve food hygiene and safety requirements. And this is for prints using water-based inks. It is an easy task.

3. Reduce resource consumption and reduce environmental costs. Due to the inherent characteristics of water-based inks - high isoform content. Can be deposited on thinner ink films. So compared to solvent-based inks. Its coating amount (the amount of ink consumed per unit of printing area) is less. After trials. Compared with solvent-based inks. Reduced the amount of coating by about 10%. That is, print the same number and specification of prints. The consumption of aqueous ink is reduced by about 10% compared to solvent inks. Not only that, because the printing needs to be cleaned often. So use solvent-based ink printing. Need to use a lot of organic solvent cleaning solution, and use water-based ink printing. The cleaning medium is mainly water. From the perspective of resource consumption. Water-based ink is more economical. In line with the theme of a conservation-minded society advocated by the world today.

4. Improve the safety of the operating environment to ensure the health of the contact operators. Solvent-based inks are quite dangerous during their manufacture and during printing. Organic solvents and solvent-based inks are themselves flammable liquids. Organic solvents easily evaporate. In the air will form explosive mixtures. An explosion occurs when Mars meets the explosion limit concentration. therefore. The risk of fire and explosion in production operating environments is quite high. According to China's current regulations, the production of solvent-based inks is dangerous chemical production. Must have a sound production and management conditions for hazardous chemicals in order to obtain a production license. The specific toxicity of organic solvents is extremely detrimental to the health of production workers. The national health supervision administrative department defines such operations as occupational hazards. There are strict regulations on the concentration of VOC in the air at the job site. Operators must regularly perform occupational health examinations to ensure the health of the operators.

Third, the application of water-based ink

From a printing point of view, water-based inks are not yet suitable for offset printing, and its main application areas are flexographic printing and gravure printing.

1. Application in the field of flexographic printing. We know that most flexographic and gravure printing products are packaging products, including food packaging. Tobacco and wine packaging, children's toy packaging, etc., occupy a considerable proportion of packaged prints that require strict hygienic conditions. Therefore, there is an urgent need for "green" printing materials, and aqueous ink is undoubtedly one of the best choices. With the impact of the “green revolution” set off in the world, flexographic printing has developed rapidly. The main reason is that most of the flexographic printing uses water-based inks. Has excellent environmental performance, in line with the development trend of modern packaging and printing. In the United States, 95% of flexographic products use water-based inks. In Japan, 70% of flexographic plates are used for corrugated board printing, and 95% of them use water-based inks. In China, the proportion of flexo printing is increasing day by day. There are nearly 200 narrow flexographic printing production lines in China, and the annual demand for water-based ink is more than 100,000 tons.

2. Application in the field of gravure printing. Water-based gravure ink was widely used in the printing of packaging paper and cardboard carton in the 1970s. Due to the better evaporation drying and absorption drying in paper printing, the drying problem of water-based ink is better solved and popularization is earlier. In the United States, 80% of gravure prints use water-based inks. In addition. Overall. An important reason for the delay in the further popularization of water-based gravure inks is that the contradiction between gravure speed and print quality and the performance of the gravure dryer has not been resolved.

3. Application in the field of screen printing. Countries that have used water-based screen printing inks in large quantities are Sweden, Germany and the United States. Since the 1980s, gloss and matt water-based inks have been developed internationally for the printing of fabrics, paper, PVC PS, aluminum foils and metals. The development of screen printing in our country is very fast, and the progress in the development and popularization of screen printing water ink is slow. It is gratifying that China has attracted people's attention in the research and development of screen printing inks. After several years of hard work, some results have been achieved. According to reports, screen-printed water-based inks have been applied to printing materials such as paper and plastics in China.

Fourth, the impact of water-based ink properties on print quality
1. Viscosity. Viscosity is the most important control indicator in aqueous ink applications. It is a property that prevents fluid flow. Since the viscosity directly affects the transferability and printing quality of the ink, it is very important to control the viscosity of the ink. During the printing process. The viscosity of water-based inks can affect the following factors: spreadability of the ink on the substrate, magnification of dots, reproducibility of image tone levels, color strength of the print, and the like. Too low a viscosity of water-based ink will cause the ink to develop slowly before drying, or due to the ink shop