Green ink for green printing

There are generally three classification methods for inks. According to the printing plate type classification, there are flexographic printing inks, gravure printing inks, and mesh printing inks and roll printing inks. According to the main components of ink classification, there are web and board printing inks, alcohol-soluble printing inks and water-based printing inks. According to the ink use classification, there are paper printing inks, plastic printing inks and so on. With the development of ink technology today, environmental protection, high-tech and other trends have emerged, and the technological content has become higher and higher, and the damage to the environment has also been reduced. The harm of ink to the environment In the printing industry, the impact of ink on the environment is very large, and, when used in food packaging printing in Beijing, the harmful components of the ink will directly harm the health of consumers. The environmental issues related to printing inks are: (1) Components harmful to the human body in printing inks Printing inks consist of pigments, binding agents, solvents, adjuvants, and the like. Among them, organic solvents and heavy metal elements cause serious damage to the human body. There are two kinds of pigments in inks, namely inorganic pigments and organic pigments. Its nature is insoluble in water and other media, and has a distinctive color and stability. Some inorganic pigments contain heavy metals such as lead, chromium, cadmium, and mercury, all of which are toxic. They cannot be used in printed food packaging and children's toys. Some of organic pigments contain binuryl aniline, which contains carcinogenic components and should not be used. . Organic solvents dissolve many natural resins and synthetic resins and are an important part of various inks. Organic solvents can damage the human body and subcutaneous fat. Long-term exposure to certain solvents can cause chapped and rough skin. If it permeates the skin or penetrates blood vessels, it can endanger blood cells and hematopoietic function of the person with blood circulation. Solvent gas is sucked into the air-intake tube, bronchus, lungs, or through blood vessels and lymphatic vessels. Other organs may even cause chronic poisoning of the body. In the production process of composite packaging materials, a large amount of inks, organic solvents, and adhesives are used. Although these accessories are not in direct contact with foods, some toxic substances will migrate to foods in the process of food packaging and storage, and endanger people. Health must arouse concern. The toxicity of heavy metal ions in inks, and the carcinogenicity of certain components in pigments and dyes require careful study. Ethanol, isopropanol, butanol, propanol, butanone, ethyl acetate, butyl ester, toluene, xylene and other organic solvents are often used in printing inks. Although most of these organic solvents can be removed by drying, migration of residual solvents into the food can cause harm to the human body. Solvents in gravure inks typically include high boiling point, odorous, and toxic solvents such as butanone, xylene, toluene, and butanol. Especially butanone, the residual odor is very strong. Since the pigment particles in the ink are very fine and have a strong adsorption capacity, they have been heated and dried at the time of printing, but due to the short time and high speed, they often do not dry completely, especially the printed matter with large inked area and thick ink layer. There are many residual solvents, and these residual solvents are brought into the compounding process. After the compounding, the residual solvent is difficult to escape for a short time, and it will slowly migrate and infiltrate. Therefore, the solvent residue must be kept to a minimum. (2) Air pollution and odor caused by volatilization of the solvent in the ink. Problems such as air pollution caused by volatilization of the solvent in the ink. The gravure ink is the most serious because the gravure ink uses more volatile organic compounds (VOC). As a solvent. Long-term exposure to high concentrations of VOCs will cause great damage to the human body, especially the nervous system; VOCs will also react photochemically with the nitrogen oxides in the air to produce odors and fumes that cause air pollution. In order to reduce VOCs, there are two solutions for recovery and combustion of discharged solvents, but many gravure machines are not equipped with such devices. In addition, the discharge of waste water to clean water-based ink will cause water pollution, and discharge of offset printing fluid will cause water pollution. The disposal of industrial waste such as printed materials and ink containers is also a very thorny issue. The development of environmentally friendly ink In order to fundamentally improve the impact of ink on the environment, we should start from changing the composition of the ink, that is to use environmentally friendly materials to formulate new environmentally friendly ink, researchers in various countries are stepping up development in this area. At present, there are three major categories of such inks, namely water-based inks, UV inks, and water-based UV inks. (1) Water-based ink The most prominent feature of water-based ink is no pollution to the environment, no effect on human health, non-flammability, good safety, stable ink, bright colors, non-corrosive media, simple operation, and low price It is strong in force, strong in water resistance, fast drying, and printing speeds of up to 150-200m/min. It is especially suitable for the printing and use of food packaging, pharmaceuticals, cosmetics and other packaging and decorating and printing products that require strict hygienic conditions. The biggest difference between aqueous inks and solvent inks is that water-based inks use water instead of organic solvents. Since solvent-based inks mostly use volatile drying as the main method, the lower the boiling point of the solvent, the more volatile it is, and the volatilized toxic gas is emitted, contaminating the surrounding environment and harmful to the human body. After the printing is completed, there are residual harmful substances on the surface. Not suitable for printing food packaging, pharmaceutical packaging, children's toys and other packaging. According to relevant information, at present, 40% of U.S. plastic film printing uses water-based ink, and other economically developed countries, such as Japan, Germany, and France, use water-based ink in plastic film printing more and more. In June 2001, the United Kingdom enacted legislation to prohibit the printing of food films using solvent-based inks. According to information, the United States has a regulation for organic solvents that can cause photochemical smog: Limit the total amount of VOC (organic volatiles) emissions, and the following two standards should be met for water-based inks that comply with the VOC regulations: 1 In use ink composition The proportion of volatile components is 25% or less, and the moisture content is 75% or more. In the case of using 2 inks with a small amount of water, the nonvolatile content is 60%. In recent years, China's packaging of food has also made this provision, and the status of “green” printed materials will be further improved. In the use of water-based inks, the wastewater treatment work should also be emphasized. The waste water from washing rolls, washing tanks and washing tanks should be concentrated in a waste water treatment tank, and acidic substances should be added to precipitate. A Sino-foreign joint venture food production enterprise in Tianjin used OPP/CPP composite film packaging food produced by a certain company in Shantou. After opening the line, it smelled a strong odor. After testing by the National Packaging Products Quality Supervision and Inspection Center, only one xylene residue was reached. At 18.03 mg/m2, the total solvent residue reached 21.4 mg/m2, which was seriously exceeded. Although the food production company later received financial compensation, its reputation loss cannot be completely recovered. This is caused by the fact that food manufacturers did not strictly select the packaging materials before using packaging materials. Each food packaging plant should learn from it. lesson. A thorough solution is to use water-based inks for printing and pre-coating the film with hot melt adhesives. No solvents are present and odors and migration will not occur. Water-based inks are commonly used for the printing of paper products including paper-plastic composite products. Its characteristics are to meet the paper printing ink absorption, making the print color full, more rare is its solvent is water and ethanol, the environment is small, known as green ink. (2) The UV inks used for UV inks are brightly colored and have high image resolution. UV flexo printing is a promising technology from the perspective of environmental protection and technological development. UV inks are photocurable inks that can change from a liquid state to a solid state under irradiation with a certain wavelength of ultraviolet light. The advantages of UV inks are that they do not use solvents, which are beneficial to environmental protection, fast drying, low energy consumption, good gloss, bright color, water resistance, abrasion resistance, oil resistance, and solvent resistance. The main components of UV-curable inks include polymerizable prepolymers, photosensitive monomers, photopolymerization initiators, organic pigments, and additives. Photoinitiators in inks are compounds that are susceptible to light excitation, and they become excited after absorption of photons. Radical energy is transferred to photosensitive photons or photocrosslinkers to cause UV curing of the ink. UV inks will only dry when exposed to UV light. Even when stored in the ink fountain for a long period of time, the performance is stable, the drying speed is fast (up to 500 m/min) and thorough, solvent-free discharge, and there is no need to prevent contamination between the prints. Taking dusting measures, the printers and workshops are clean and dust free, and the printed paper can be recycled and recycled. When UV ink is used, the ozone generated by ultraviolet rays should be removed, and the protection against harmful ultraviolet rays to human eyes should be taken care of. (3) Water-based UV inks Water-based UV inks are a new research direction in the UV ink field. The viscosity of prepolymers in ordinary UV inks is generally very large, and reactive diluents need to be added for dilution. However, the currently used reactive diluent acrylate compounds have different degrees of skin irritation and toxicity. For this reason, in the development of low-viscosity prepolymers and low-toxicity reactive diluents, on the other hand, development of water-based UV inks has been pursued. Ethanol as a solvent will have good compatibility and excellent adhesion to alcohol-soluble inks. Ethyl acetate, on the other hand, has an aggressive effect on certain printing inks, which can cause blooming of the ink. This problem often occurs in surface printing inks. In the process of developing environmentally friendly inks, the improvement of solvent inks should be enhanced at the same time to improve safety. The safety of solvents is mainly reflected by the toxicity and flammability of solvents. Special attention must be paid to: (1) Ether can generate explosive peroxides; (2) Non-flammable solvents or carbon tetrachloride and sodium, potassium, calcium , Magnesium, barium and other metal contacts can cause explosive reactions; (3) trichloroethylene and sodium hydroxide, potassium hydroxide contact to generate dichloroacetylene, dichloroacetylene due to auto-oxidation and easy to explode. Advanced countries have proposed not to use benzene solvents. China has specified in the international GB9685-94 (Use of Sanitary Standards for the Use of Additives for Food Containers and Packaging Materials) that solvents used in paints, adhesives, and inks include ethanol, butanol, and acetone. Ethyl acetate. GB/T10004-1998 "Retort-resistant composite film, bag" provides a total solvent residue of 10mg/m2, and the provisions of which benzene solvent 3.0mg/m2. (Yu Jin Bai Mu Zhou Jie)