How to reduce the pollution of photosensitive materials and inks in screen printing

Among the printing environment pollutants, there are mainly the following three types: Air pollutants: including aerosols (smoke, dust, fog), harmful gases (sulfur oxides, hydrocarbons, carbon dioxide, hydrogen chloride, etc.). Water pollutants: including inorganic suspended solids (slag, iron scrap), toxic pollutants (chemical wastes such as mercury, lead, chromium, phenol, chlorine, etc.), acid and alkali pollutants (acid and alkali), oil (oil, grease) Classes, etc.) In addition, hot water, high temperature exhaust gas and other heat sources also cause pollution to the water and the atmosphere.

Solid contaminants: Solid contaminants include paper, plastics (information on the development of the plastic packaging industry), solid wastes such as glass, metal, ceramics, sawdust, etc. Noise and vibration are also sources of environmental pollution. For screen printing, the resulting contaminants are mainly caused by photosensitive materials, inks (solvents and pigments), and the like.

1. Contamination caused by plate-making photographic materials Dichromate-based photographic materials commonly used in screen-printing plates, due to the presence of a large amount of hexavalent chromium ions in the effluent discharged during the platemaking process, are toxic, if the human body comes into contact with 6 The solution of chromium ions will produce dermatitis and other diseases, and the waste liquid will cause pollution to the environment, which will seriously affect the normal growth of animals and plants. Therefore, the use of non-toxic diazonium salts and diazo resin emulsion emulsions to eradicate the pollution of chromium ions will be the main direction of future plate making.

2. Pollution caused by solvents in printing ink In the printing industry, the impact of ink on the environment is very large, and ink is currently the largest source of pollution in the printing industry. The annual output of ink in the world has reached 3 million tons. Annual global emissions of organic volatile compounds (VOC) caused by ink have reached hundreds of thousands of tons. These organic volatiles can form a greenhouse effect that is more severe than carbon dioxide. Under the irradiation of sunlight, they form oxides and photochemical smog, which seriously pollute the atmosphere and affect people's health and environmental quality. In addition, when foods, toys, etc. are packaged and printed, the harmful components such as heavy metals in ordinary ink components will directly harm the health of consumers.

(1) Impact on human health.

Printing inks consist of pigments, binders, solvents, and adjuvants. Among them, organic solvents and heavy metal elements cause serious damage to the human body. Certain solvents in screen printing inks, which are volatilized or emitted into the air, can pollute the environment, affect the growth of plants, and especially the volatile inks are very serious for air pollution. In addition, some of the solvents and auxiliaries in the ink have a relatively low ignition point. When they accumulate in the air and reach a certain concentration, they can cause fire in the event of fire. 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 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 dry, rough skin. If it permeates the skin or penetrates blood vessels, it can endanger blood cells and hematopoietic function of humans. The 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.

The toxicity of heavy metal ions in inks, pigments and dyes contain certain carcinogenic ingredients, which are harmful to human health. In the printing of composite packaging materials, a large amount of ink, organic solvents and adhesives are used. Although these accessories do not have direct contact with food, some toxic substances will migrate to the food during the process of food packaging and storage. People's health. 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, odor, 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, the adsorption ability is very strong. Although it has been heated and dried at the time of printing, due to the short time and high speed, the drying is often incomplete, especially the larger inked area and the thicker 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) Impact on environmental quality.

The problem of air pollution caused by volatilization of the solvent in the ink is mainly due to the volatile organic compounds (VOC) contained in the ink. Since gravure ink uses more VOC as a solvent, the pollution is most serious. However, screen printing and other printing also have the same problem. 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 nitrogen oxides in the air. Produce ozone and smoke, causing air pollution.

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