The hottest popular science knowledge on water-bas

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General knowledge of popular science: with the rapid development of economy and the gradual improvement of people's living standards, 7. The shell of the experimental machine should be reliably grounded. China's printing has entered the era of environmental protection, which requires the improvement of packaging and printing materials, and ink is an important part of packaging and printing materials. Because water-based ink does not use solvents, it is conducive to environmental protection, so its research and application have attracted more and more attention

1. Composition of water-based inks

water based inks are inks composed of specific water-based polymer resins, pigments, water, and additives through physical and chemical processes, referred to as water-based inks

1) water based polymer resin

water based polymer resin is the most important component of water-based ink. It mainly plays the role of binder in water-based ink, and has a great impact on the viscosity, adhesion, gloss, drying and printing adaptability of ink. In China, rosin modified maleic acid resin is often used as the connecting material to make ink, but this kind of ink can only be used to print ordinary cartons, which can not meet the gloss and water resistance requirements of medium and high-end packaging and printing. The stability of urethane resin is good, but the printing adaptability and solubility are slightly poor. Others include styrene modified maleic acid resin, water-based amino resin, polyvinyl alcohol and carboxymethyl cellulose. 7. Ear width - the width of the spring in the ear. These polymer resins generally contain hydrophilic groups such as carboxyl, hydroxyl and amino groups. After specific process treatment, they become completely water-soluble resins, which can be used as the binder of water-based inks

2) pigments

pigments give ink color characteristics and meet the color requirements of printing. General organic pigments and inorganic pigments can be used for water-based inks. Because the resins of water-based inks are mostly alkali soluble, when choosing pigments, pigments that can resist alkali must be used. The distribution density of pigments in ink is much larger than that of solvent based ink, and the surface tension and polarity of water are greatly different from that of solvent, which makes it difficult to disperse pigments, and directly affects the stability, viscosity and pH value of ink. Adding surfactant can increase the affinity between resin and water and the affinity between pigment and water-soluble binder, so as to solve the problem of ink stability. When choosing pigments in the printing process, we should choose high-grade pigments with bright color, low viscosity and stable system from domestic pigments to make water-based inks

3) additives

in order to improve the properties of water-based inks, various additives need to be added, and the additives used in water-based inks are more important than solvent based inks. By using these additives scientifically to improve the weakness of water-based ink, the stability of water-based ink can be improved. Commonly used water-based ink additives are as follows:

① defoamer: used to inhibit and eliminate the generation of bubbles, the dosage is generally 1% - 2% Generally speaking, when the viscosity of water-based ink is too high, the pH value is too low, or when the printing machine runs faster, it is easy to produce bubbles. If the amount of bubbles is relatively large, there will be white leakage and uneven ink color, which will inevitably affect the quality of printed matter

② pH stabilizer: it is mainly used to adjust and control the pH value of water-based ink to stabilize it within the range of 8.0 ~ 9.5. At the same time, it can also adjust the viscosity of water-based ink and dilute the ink. Generally speaking, an appropriate amount of pH stabilizer should be added every certain time in the printing process to keep the water-based ink in good printing condition. Generally, ammonia water or ethanolamine and other additives are used

③ slow drying agent: it can inhibit and slow down the drying speed of water-based ink, prevent the ink from drying on the printing plate or roller, and reduce the incidence of printing failures such as blocking and pasting. Generally, it should be controlled between 1% and 2% of the total amount of ink. If the amount of ink is too much and the ink is not completely dried, the printed matter will stick dirty or produce peculiar smell

2. Drying of water-based inks

water based inks use water as a solvent. After the ink is transferred to the substrate, the water evaporates into the environment or seeps into the substrate, and the ink dries with the evaporation of water. The drying of water-based ink is divided into two stages: initial drying and thorough drying. The initial drying stage refers to the water-based ink from liquid to semi-solid, which can no longer flow and transfer, which is expressed by initial drying; The thorough drying stage refers to the reaction of the binder in the semi-solid water-based ink, which is completely dried and formed a film, which is expressed by thorough dryness. According to the different printing substrates, the drying methods of water-based ink can be divided into volatile drying and osmotic drying

① volatilization and drying: the substrate used is non absorbent material. The water-based ink contains volatile solvent. After printing on the surface of the substrate, the solvent volatilizes, and the remaining resin in the water-based ink forms a solid ink film with the pigment and is fixed on the surface of the substrate

② osmotic drying: the substrate used is an absorbent material, which is mainly fixed and dried by the substrate's osmotic absorption of water-based ink. When the water-based ink contacts the substrate, a part of the connecting material penetrates into the substrate, while the pigment stays on the surface of the substrate to complete the drying process

3. Characteristics of water-based inks

the biggest difference between water-based inks and solvent based inks is the dissolution carrier used: the dissolution carrier of solvent based inks is organic solvents (such as toluene), while the dissolution carrier of water-based inks is water and a small amount of alcohol (about 3% - 5%). Because water is used as the dissolving carrier, water-based ink has remarkable environmental protection and safety characteristics, which mainly shows that the experimental temperature should generally be 20 ± 5 ℃ in the following four aspects:

① it does not pollute the atmospheric environment. VOC (volatile organic gas) is recognized as one of the main sources of global air pollution. Solvent based inks will emit a large amount of low concentration VOC. Because water-based inks use water as a carrier, VOC will hardly be emitted into the atmosphere

② ensure the personal safety of operators. Solvent based inks are very dangerous in the production and printing process, because they are flammable and explosive liquids, and organic solvents are easy to volatilize, which will form explosive mixed gases in the air. Because water-based inks use water as a carrier, the safety of the operating environment is guaranteed

③ reduce the residual poisons on the surface of the printing. Solvent inks contain organic solvents, leaving a large number of poisons on the surface of prints. Because water-based inks use water as a carrier and do not contain organic solvents, the toxic substances left on the surface of prints are greatly reduced

④ economy. Compared with solvent based ink, the coating amount of water-based ink is reduced by about 10%. When printing, the printing plate needs to be cleaned frequently. The medium of water-based ink printing cleaning is mainly water, unlike solvent based ink printing cleaning, which requires a lot of organic solvents. Therefore, from the perspective of energy consumption, water-based ink is more economical

4. Application of water-based inks

at present, water-based inks are mainly used in flexographic printing, gravure printing and silk printing

1) flexographic printing field

flexographic printing products are mostly packaging products, of which food packaging, tobacco and alcohol packaging, children's toys and other packaging and printing products with strict sanitary conditions account for a considerable proportion. Therefore, water-based ink has become one of the best choices. In the United States, 95% of flexographic printing products use water-based inks; In Japan, 70% of flexo is used for corrugated board printing, 95% of which uses water-based ink; In China, the application of water-based inks in flexographic printing has developed rapidly, and the proportion of water-based inks in flexographic printing machines is gradually rising

2) gravure printing field

water based gravure ink has been widely used in the printing of packaging paper, cartons and other papers, which is due to the better evaporation drying and absorption drying of paper products. The application of water-based intaglio inks in plastic film printing is still in its infancy in China, mainly because the adhesion, printing speed and gloss of water-based inks in intaglio printing can not fully meet the performance of solvent based inks, while we type intaglio inks make new products that can fully meet the qualified standards in the field of plastic film intaglio printing

3) silk printing field

according to statistics, the use of foreign water-based inks has accounted for more than 50% in printing, and the application of domestic water-based inks is also on the rise year by year. TORLON reg; Pai still has superior reliability. Before that, Sweden, Germany and the United States have widely used water-based printing inks. The development of printing in China is very fast, but the research, development and popularization of water-based inks are relatively slow. It is gratifying that China has attracted people's attention in the research and development of water-based printing inks, and has made some achievements after several years of efforts

5. Conclusion

in recent years, with the continuous improvement of environmental protection requirements, many health and environmental protection requirements and constraints have been gradually increased in packaging printing and commercial printing. In this general trend, efforts to develop pollution-free green printing materials, water-based inks, will achieve good economic and social benefits. At present, the R & D and production of water-based inks in China is just in its infancy. Chinese manufacturers can only produce some low-grade water-based inks, and high-grade water-based inks are basically imported. Therefore, both developers and manufacturers are promising, and the R & D and production of water-based inks hide huge business opportunities

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