Environmental hazards of printing inks and the development of environmentally friendly inks

Ink is currently the largest pollution source in the printing industry, and the world's annual output of ink has reached 3 million tons. The annual global emissions of volatile organic compounds (VOC) caused by inks have reached hundreds of thousands of tons. These organic volatiles can form a more serious greenhouse effect than carbon dioxide, and will form oxides and photochemical smog under sunlight, which seriously pollutes the atmosphere and affects people's health. In addition, heavy metals and other harmful components in common inks for packaging and printing foods, toys, etc. will directly endanger the health of consumers.

(1) Impact on human health

Printing ink is composed of pigments, linking agents, solvents, and auxiliary agents. Among them, organic solvents and heavy metals cause serious damage to the human body. There are two kinds of pigments in inks-inorganic and organic, both of which are insoluble in water and other media, and have bright color and stability. Some inorganic pigments contain heavy metals such as lead, chromium, copper, mercury, etc., which are toxic and cannot be used for printing food packaging and children's toys; some organic pigments contain biphenyl gum, which has carcinogenic ingredients, and should be strictly prohibited. Organic solvents can dissolve many natural resins and synthetic resins, and are important components of various inks. However, some of them can damage the human body and subcutaneous fat. Long-term contact will make the skin dry and rough. If it penetrates into the skin or blood vessels, it will endanger people with the blood. Blood cells and hematopoietic function; being inhaled into the air duct, bronchi, lungs or through blood vessels, lymphatic vessels to other organs, and may even cause chronic body poisoning. Some inks have the toxicity problem of heavy metal ions. Pigments and dyes contain carcinogens, which are very harmful to human health. Composite packaging materials use a lot of inks, organic solvents, and adhesives in printing. Although these auxiliary materials have no direct contact with food, certain toxic substances will migrate into the food during the food packaging and storage process and endanger people's health. Organic solvents such as ethanol, isopropanol, butanol, propanol, butanone, ethyl acetate, butyl acetate, toluene, and xylene are often used in printing inks. Although most of these solvents can be removed by drying, the remaining solvents will migrate into the food and harm the human body. Solvents used in gravure inks generally include methyl ethyl ketone, xylene, toluene, butanol, etc. Especially methyl ethyl ketone, the residual smell is very strong. Because the pigment particles in the ink are very small and have strong adsorption power, although they have been heated and dried during printing, they are often not dried completely due to the short time and fast speed, especially for printed materials with large ink areas and thick ink layers. There are more residual solvents. These residual solvents are brought to the compounding process, and it is more difficult to run off after compounding, and will slowly migrate and penetrate. Therefore, solvent residues must be controlled to a minimum.

(2) Impact on environmental quality

The problem of atmospheric pollution caused by the volatilization of solvents in the ink is most serious with gravure ink, because it uses more VOC as a solvent. Long-term exposure to high-concentration VOCs will cause great damage to the human body, especially the nervous system. VOCs will also react with nitrogen oxides in the air to produce ozone and smog and cause air pollution. To reduce VOC, there are two solutions: recycling and burning and discharging solvents, but there are many gravure presses that are not equipped with such devices. In addition, draining water for cleaning water-based inks and offset printing fountain solution can contaminate water quality. The disposal of industrial wastes such as printed matter and ink containers is also very tricky.