There are generally three classification methods for inks. According to the printing 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 cardboard printing inks, alcohol-soluble printing inks and water-based printing inks. According to ink use classification, there are paper printing ink, plastic ink and so on. With the development of ink technology today, trends in environmental protection, high-tech, etc. have emerged, and the technological content has become higher and higher, and the destructiveness to environmental protection is also decreasing.
Green ink - to achieve green printing 1, the harm of the ink to the environment In the printing industry, ink on the environment is very large, and when used in food packaging and printing, the ink harmful to the human body will also directly harm The health of the consumer. The environmental issues related to printing inks are:
(1) Components harmful to the human body in printing inks Printing inks consist of pigments, binders, solvents, and adjuvants. 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. Their properties are insoluble in water and other media, and they have vivid color and stability. Some inorganic pigments contain lead, chromium, copper, mercury and other heavy metal elements, all of which have certain toxicity and cannot be used for printing food packaging and children's toys. Some of organic pigments contain conjugated biphenyl gum, which contains carcinogenic ingredients and should be strictly prohibited. use. 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 penetrates into or penetrates into blood vessels, it can endanger human blood cells and hematopoietic function with blood. 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 do not have direct contact with food, some toxic substances will migrate into foods during food packaging and storage. People's health must attract attention. The toxicity of heavy metal ions in inks, and the carcinogenicity of certain ingredients in pigments and dyes require careful study.
Ethanol, isopropyl alcohol, butanol, propanol, butanone, ethyl acetate, butyl acetate, toluene, xylene and other organic solvents are often used in printing inks. Although most of these organic solvents can be removed by drying, residual solvents migrate into foods and cause harm to human bodies. Solvents used in gravure inks typically have high boiling, odorous, 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 short time and high speed, they often do not dry completely, especially the printed materials with large inked area and thick ink layer. There are many residual solvents. These residual solvents are brought into the compounding process. After compounding, they are more difficult to run off and will slowly migrate and infiltrate. Therefore, the solvent residue must be kept to a minimum.
(2) Air pollution and odor caused by volatilization of solvents in the ink. Problems such as air pollution caused by volatilization of solvents 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 significant damage to the human body, especially the nervous system; VOCs will also react photochemically with nitrogen oxides in the air to produce ozone and fumes, causing air pollution. In order to reduce VOC, there are two solutions for recovery and combustion of the discharged solvent, but many gravure machines are not equipped with such devices.
In addition, the discharge of water that cleans water-based inks can cause water pollution, and the discharge of offset-printing fountain solution can also cause water pollution. The disposal of industrial waste such as printed matter and ink containers is also a very thorny issue.
2, the development of environmentally friendly ink In order to fundamentally improve the impact on the environment, we should start from changing the composition of the ink, that is, as far as possible the use of environmentally friendly materials to formulate a new type of environmentally friendly ink. Researchers in various countries are stepping up research and development in this area. At present, there are three major categories of such inks: water-based inks, UV inks, and water-based UV inks.
(1) Water-based inks Water-based inks are characterized by no pollution to the environment, no impact 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, etc., for packaging and decorating 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, which pollutes the surrounding environment and is harmful to the workers. After printing, the surface is also left with harmful effects. Substances are 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 printing uses water-based ink, and other economically developed countries, such as Japan, Germany, and France, are using more and more water-based inks in plastic film printing. In June this year, the United Kingdom enacted legislation to prohibit the printing of food films using solvent-based inks. According to the relevant information, the United States has a regulation on organic solvents capable of producing photochemical smog: the total amount of VOC (organic volatiles) emissions is limited, and the following two standards are met for water-based inks that comply with the VOC regulations:
(1) In the ink composition in use, the proportion of volatile components is 25% or less, and the moisture content is 75% or more.
(2) In the case of ink with less water, the amount of non-volatile components is more than 60%. In recent years, China has made some provisions for food packaging. The status of “green†printing materials will be further improved. When using water-based inks, wastewater treatment work should be emphasized at the same time. Washing, washing and washing of waste water should be carried out. Focus on a waste water treatment tank and add acid precipitation.
A Chinese-foreign joint venture food production company used a company's OPP/CPP composite film to package foods. After opening the bag, it smelled a strong odor. After testing by the National Packaging Products Quality Supervision and Inspection Center, only one xylene residue amounted to 18.03mg. /m2, the total solvent residue reached 21.4 mg/m2, exceeding the standard. Although the food production company later received financial compensation, its reputation loss cannot be fully recovered. This is caused by the fact that food manufacturers do not strictly require the quality of packaging materials before using packaging materials. Each food packaging plant should learn from them. A thorough approach is to use water-based inks for printing and composite hot-melt adhesives for pre-coating films. No solvents are present and odors and migration do not occur.
Water-based inks are generally 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, even more rare is the solvent is water and ethanol, the environment is small, known as green ink. (To be continued)