Foreword [1] In the mid-1960s, due to the requirements of environmental protection and the shortage of petroleum raw materials, some developed countries gradually restricted the use of petroleum products for the manufacture of printing inks. People started the research and application of water-based inks. Initially, water-based inks mainly use dextrin, shellac, casein, and sodium natrium as the connecting materials for some low-grade prints, such as general books, magazines, etc., and also in industries where corrugated paper and other printing performance requirements are low. start using. By the end of the 1960s, with the development of materials science, the synthesis technology of rosin modified maleic resin had been successful, replacing shellac, casein and other materials, becoming the main connecting material for water-based inks, and basically meeting the needs of printing at that time. . By the 1970s, air pollution became a worldwide problem. National ink developers have also developed a new generation of water-based inks based on styrene-acrylic copolymer resins. In the carton packaging industry in Japan and Western Europe, the use ratio of water-based inks is higher than 90% [2]. At present, the application fields of water-based inks are being continuously broadened and gradually used in the field of flexographic printing. The most competitive application area is in the packaging of milk and beverage composite paper, and has achieved great success. Although water-based inks have undergone many technical updates, they have been widely used and rapidly developed in some developed countries. However, the application of water-based ink in China is not very popular, and there is still a considerable gap compared with developed countries. In China, water-based inks currently used in the packaging industry account for only about 7% of the total ink consumption [3]. With the continuous development of the domestic packaging industry and social progress. It is predicted that by 2010, China's water-based ink will account for 25% to 30% of total ink consumption [3]. 1 main components Like other liquid inks (such as solvent-based inks), water-based inks are mainly composed of colorants, binders, dissolving carriers, additives, etc. The main components and contents are as follows [4]: Pigment (pigment or dye): 12% ~40%; binder (resin): 20% ~28%; dissolving carrier (water and a small amount of alcohol): 33% ~ 50%; auxiliaries (defoamers, etc.): 3% ~4%; alkali (amine or ammonia): 4% ~ 6%. 1.1 Colors The colorant can impart a certain color to the ink, and it selectively absorbs and then scatters light waves of a certain wavelength to present a specific color. At the same time have resistance, such as light resistance, high temperature resistance and weather resistance. In general, the colorants used in aqueous inks are strongly alkali-resistant pigments or dyes and have good dispersibility in water. Compared with solvent-based inks, water-based inks require higher colorants, require lighter, softer, non-corrosive, high color saturation, bright color and pure, and have good affinity with the binder, wettability and dispersion Sex, no aggregation, precipitation and good fluidity will occur in the finished product, and discoloration and fading will not occur. Commonly used are: fast red, permanent red (red), benzidine yellow, light yellow, permanent orange (yellow), indigo blue (blue), titanium dioxide coating (white), carbon black ( Black) etc. 1.2 Binder The role is to disperse the color material, and produce adhesion with the substrate to form a solid imprint, and form a certain degree of gloss after the ink is dried and filmed. It is usually required that the binder can be dissolved by water when the ink is finished, and becomes insoluble in water after the printing is dried. Usually an alkaline solution of acidic resin, in the solution by adding an appropriate amount of alkali (ammonium hydroxide or ammonia), the two after the formation of soluble resin salts, in the ink printing and drying process, ammonia volatilized after the connection material changed Insoluble in water. At present, acrylic resins or alkyd resins are widely used. 1.3 Dissolving Carrier Water-based ink uses water and a small amount of alcohol (< 5%) as a carrier for dissolving. The main function is to dissolve the binder and colorant, adjust the viscosity, adjust the drying speed and promote the wettability of the surface of the substrate. The role of a small amount of alcohol is to accelerate the drying speed of the ink, reduce the surface tension of the ink, and prevent foaming. Ethanol or isopropanol is usually used. 1.4 Additives Mainly include: defoamers, wetting agents, surfactants, adhesion promoters, fungicides and so on. Defoamers are indispensable components in aqueous inks, otherwise the ink will generate tiny bubbles on the surface of the substrate. The role of the wetting agent is to provide abrasion resistance to the printed matter and reduce the vitrification phenomenon of the ink film layer, and polyethylene wax and polypropylene wax are more commonly used. Surfactants can reduce the surface tension of the ink, improve the ability of the ink to lubricate, and improve the printing adaptability to suit the performance of different substrates and printing presses. Adhesion promoters are used to enhance the ink's ability to adhere to some of the more specific substrates. Because of the presence of water in the water-based ink, it is easy to produce bacteria, and in order to increase the shelf life, it is necessary to add a bactericide. 1.5 Alkali Alkaline substances are used to promote the solubility of the resin binder in water and adjust the pH of the aqueous ink. Organic amines or ammonia are used. 2 Environmental safety features 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, while aqueous inks are dissolved in water and a small amount of alcohol (about 3% to 5%). Due to the use of water as a carrier for dissolving, aqueous inks have significant environmental and safety features: safe, non-toxic, non-hazardous, non-inflammable, non-explosive, and virtually free of volatile organic gases. Mainly in the following four aspects: 2.1 No pollution to the atmosphere Since water-based inks are used as a carrier for water dissolving, no matter how much they are used in the production process or when they are used for printing, they will hardly dissipate volatile organic gases (VOCs) into the atmosphere. VOCs are considered to be the major current global atmospheric environment. One of the sources of pollution. This is unmatched by solvent inks. Solvent-based inks emit a large amount of low-concentration VOCs during the production process. According to estimates, the general solvent-based ink factory, if not fully sealed production equipment, organic solvent evaporation loss accounted for about 0.3% ~ 1% of the ink production. For the treatment of low-concentration VOCs, most of them are directly discharged into the atmosphere at high altitudes, except for a few high-cost treatment methods such as activated carbon adsorption. The photochemical pollution caused by VOCs to the atmosphere is considered one of the most serious. Not only that, during the printing process, organic solvents in solvent-based inks are almost completely dried and quickly evaporate, with the exception of high-concentration VOCs that are used above the press, such as catalytic combustion or microbiological treatment processes, to permeate the air in the printing shop. The low concentration of VOC in the medium is often directly discharged into the atmosphere. If the proportion of the organic solvent in the solvent-based ink is 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. 2.2 Reducing residual poisons on the surface of printed matter to 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 amount of toxic substances remaining on the print surface is greatly reduced. This feature reflects good health and safety in cigarettes, wine, food, beverages, medicines, children's toys and other sanitary packaging products that require strict hygiene conditions. With the increasing emphasis on food safety by human beings, attention has been paid to the hygienic 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 meet the requirements of food hygiene and safety, and this is an easy matter for prints using water-based inks. Because of the inherent characteristics of water-based inks, which are higher in solids content, they can be deposited on thinner ink films. Therefore, its coating amount (the amount of ink consumed per unit area of ​​printing) is lower than that of a solvent type ink. After testing, compared with solvent-based inks, a reduction of approx. 10% in coating weight was achieved [1]. In other words, the same number and size of prints are printed, and the consumption of water-based inks is reduced by about 10% compared with solvent-based inks. Moreover, since the printing plate needs to be frequently cleaned during printing, the use of a solvent-based ink requires the use of a large amount of organic solvent for cleaning, and the use of water-based ink for printing. The medium to be cleaned is mainly water. From the perspective of resource consumption, water-based inks are more economical and are in line with the theme of a conservation-minded society advocated by the world today. 2.4 Improve the safety of the operating environment and ensure the health of contact operators Solvent-based inks are quite dangerous during their manufacture and use. Organic solvents and solvent-based inks are themselves flammable liquids. Organic solvents easily evaporate and form explosive mixtures in the air. Exposure to Mars in an explosion-thick concentration can cause explosions. 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 belongs to the production of dangerous chemicals. It is necessary to have complete production and management conditions for hazardous chemicals in order to obtain production licenses. 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, and has strict regulations on the concentration of VOCs in the air at the operation site. Operators must regularly perform occupational health examinations to ensure the health of the operators. For water-based inks, it is almost safe and non-toxic in terms of both the fire hazard and the environmental health hazard.
2.3 Reduce resource consumption and reduce environmental costs.