Environmental printing ink in green printing
With the increasing demand for environmental protection, as the main component of green printing, the environmental protection requirements for printing ink are also increasing. It can be said that environmental protection ink is the development of ink in the future must first consider the problem.
1. The harm of ink to the environment
Ink is currently the largest source of pollution in printing industry, and the annual output of world ink has reached 3 million tons. Annual emissions of organic volatile matter (VOC) caused by ink have reached hundreds of thousands of tons. These organic volatiles can form a greenhouse effect that is more serious than carbon dioxide, and will form oxide and photochemical smog under the sunlight, which seriously pollute the atmosphere and affect people's health. In addition, heavy metals such as food, toys, packaging and printing, ordinary ink, and other harmful components will directly harm the health of the consumers.
(1) influence on human health
Printing ink consists of pigment, linking agent, solvent and auxiliary agent. Organic solvents and heavy metal elements are harmful to the human body. There are two kinds of pigment in ink: inorganic and organic, both of which are insoluble in water and other media, and have distinct color and stability. Some inorganic pigments contain lead, chromium, copper, mercury and other heavy metal elements, which are toxic and can not be used in printed food packaging and children's toys; some organic pigments contain biphenyl gum, which have carcinogenic ingredients and should be strictly prohibited. Organic solvents can dissolve many natural and synthetic resins, which are important components of various inks, but part of them can damage the human body and subcutaneous fat. Long term contact makes the skin dry and rough. If it infiltrates into the skin or blood vessels, it will endanger the blood cells and hematopoiesis with the blood; it is sucked into the trachea, bronchus, lungs or classics. Blood vessels and lymphatics pass to other organs, and may even cause chronic poisoning of the body. Some ink has the toxicity of heavy metal ions, and pigments and dyes contain carcinogenic elements, which are very harmful to human health. A large number of printing inks, organic solvents and adhesives are used in the printing of composite packaging materials. Although these materials have no direct contact with food, some toxic substances will be migrated to food in the process of food packaging and storage, which will harm people's health. Printing ink is often used in ethanol, isopropanol, butanol, propanol, butanone, ethyl acetate, butyl acetate, toluene, xylene and other organic solvents. Although these solvents can remove most of them by drying, the residual solvents will migrate to food and harm the human body. The solvents used in gravure ink are butanone, xylene, toluene, butanol and so on. Especially butanone, the residual smell is very strong. Because of the small pigment particles in the ink, strong adsorption force, although the printing has been heated and dry, but because of the short time and fast speed, it is often dry, especially the larger ink area and thick ink layer, with more residual solvent. These residual solvents are brought to the composite process, which are more difficult to escape after being compounded, and will slowly migrate and permeate. Therefore, the residual solvents must be kept to a minimum.
(2) influence on environmental quality
The problem of air pollution caused by solvent evaporation in printing ink is gravure ink, because it uses more VOC as solvent. In the high concentration of VOC, it will cause great damage to the human body, especially the nervous system, and the VOC will also react with the nitrogen oxides in the air to produce the ozone and smoke, causing the air pollution. To reduce VOC, there are two ways to recover and burn emissions. However, there are many gravure printing machines that are not equipped with such devices. In addition, the discharge of water and offset printing solution for washing water-based ink will pollute the water quality. The disposal of industrial waste such as printing and ink containers is also very difficult.
Two. Some of the main environmental inks at present
To meet the requirements of environmental protection, we should first change the ink composition, that is, using environmentally-friendly materials to prepare new ink. At present, environment-friendly ink mainly consists of water-based ink, UV ink, water-borne UV ink and some alcohol soluble ink.
(1) water-based ink
The biggest difference between water-based ink and solvent type ink is that the solvent is water instead of organic solvent, it can obviously reduce VOC emission, prevent air pollution, do not affect human health, burn, ink stability, bright color, no corrosion of plate, easy operation, cheap price, good adhesion and water resistance in the post press. Strong and dry, it is especially suitable for packaging and printing of food, beverage, medicine and so on. It is recognized as the world's environmental protection type printing material, and is the only printing ink approved by the American food and Drug Association in all printing ink. At present, 40% of the American plastic printing uses water-based ink, and the use of water-based ink in plastic film printing is becoming more and more in other developed countries (such as Japan, Germany, France, etc.). In June this year, Britain banned solvent based printing of food films. According to relevant information, in the United States, in the United States, the water-based ink that meets the VOC requirements must reach the use of ink composition, the proportion of volatile components less than 25%, moisture over 75%; less water in the use of ink in the use of non volatile components above 60% of the two standards. Water-based ink is usually used for printing paper products, including paper plastic composite products. The characteristic is that it can satisfy the ink absorption of paper printing, make the printed material plump, and more rare is the solvent is water and ethanol, and the environmental pollution is small, it is known as green ink.