With the increasing voice of environmental protection, as the main part of green printing, the requirements for environmental protection of ink are also increasing. It can be said that environmental protection ink is the first consideration for the development of ink in the future.
Ink is the largest pollution source in the printing industry, and the annual output of ink in the world has reached 3 million tons. Global Organic volatiles caused by ink every year (VOC) pollution emissions 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 the sunlight, which will seriously pollute the atmospheric environment and affect people’s health. In addition, heavy metals and other harmful components in packaging and printing ordinary inks such as food and toys will also directly endanger human consumption Good health.
(1) Impact on human health
Printing ink is composed of pigment, binder, solvent and auxiliary agent. Among them, organic solvents and heavy metals cause serious damage to human body. There are two kinds of pigments in ink – inorganic and organic. Both are insoluble in water and other media, and have bright color and stability.
Some inorganic pigments contain heavy metals such as lead, chromium, copper and mercury, which are toxic and can not be used to print food packaging and children’s toys; Some organic pigments contain biphenyl glue and have carcinogenic components, so they should not be used. Organic solvents can dissolve many natural and synthetic resins.
They are important components of various inks, but some will damage human body and subcutaneous fat. Long term contact will make skin dry and rough. If they penetrate into skin or blood vessels, they will endanger human blood cells and hematopoietic function with blood; It is sucked into the trachea, bronchus, lungs or transmitted to other organs through blood vessels and lymphatic vessels, and may even cause chronic poisoning of the body.
Some inks have the toxicity of heavy metal ions. Pigments and dyes contain carcinogenic components, which is very harmful to human health. A large number of inks, organic solvents and adhesives are used in the printing of composite packaging materials. Although these auxiliary materials have no direct contact with food, some toxic substances will migrate to food and endanger people’s health in the process of food packaging and storage.
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 residual solvents will migrate to food and endanger human body. The solvents used in gravure ink generally include butanone, xylene, toluene, butanol and so on. Especially butanone, the residual smell is very strong.
Because the pigment particles in the ink are very small and have strong adsorption, although they have been heated and dried during printing, they are often not dried completely due to short time and fast speed, especially for printed materials with large inking area and thick ink layer, there are more residual solvents. These residual solvents are brought to the compounding process. After compounding, they are more difficult to run away and will migrate and penetrate slowly. Therefore, the residual solvents must be controlled to a minimum.
(2) Impact on environmental quality
Among the air pollution problems caused by solvent volatilization in ink, gravure ink is the most serious because it uses more VOC as solvent. Long term exposure to high concentrations of VOC will cause great damage to the human body, especially the nervous system.
VOC will also photochemical react with nitrogen oxides in the air, produce ozone and smoke, and cause air pollution. To reduce VOC, there are two solutions: recycling and burning solvent emissions, but there are many gravure presses without such devices. In addition, the discharge of water for cleaning water-based ink and offset fountain solution will pollute the water quality. The disposal of industrial wastes such as printing materials and ink containers is also very difficult.
II. At present, there are several main environmentally friendly inks
To meet the requirements of environmental protection, we should first change the ink composition, that is, use environmental friendly materials to prepare new ink. At present, environmental protection inks mainly include water-based ink, UV ink, water-based UV ink and some alcohol soluble inks.
(1) Water based ink
The biggest difference between water-based ink and solvent based ink is that the solvent used is water rather than organic solvent, which significantly reduces VOC emissions, prevents air pollution, does not affect human health, is not easy to burn, has stable ink properties, bright colors, does not corrode plates, has the advantages of simple operation, low price, good post press adhesion, strong water resistance and rapid drying, so it is especially suitable for food Beverage, medicine and other packaging printing materials are recognized as environmentally friendly printing materials in the world.
They are also the only printing ink recognized by the American food and Drug Association. At present, 40% of plastic printing in the United States uses water-based ink, Other economically developed countries (such as Japan, Germany, France, etc.) more and more water-based inks are used in plastic film printing. In June this year, Britain legislated to prohibit solvent based inks from printing food films.
According to relevant data reports, in the United States, the proportion of volatile components in the ink composition that meets the VOC regulations must reach the use state is less than 25%, and the moisture content is more than 75%; those with little moisture When the ink is in use, the nonvolatile component is more than 60%. Water based ink is usually used for printing paper products, including paper plastic composite products.
The characteristic is that it can meet the ink absorption of paper printing and make the printing color plump. What’s more, its solvent is water and ethanol, which has little environmental pollution. It is known as an environmental friendly green ink.
(2) UV curable ink
UV curing (UV) ink refers to the ink that forms film and dries the ink under UV irradiation by using ultraviolet light of different wavelengths and energy. Different energy can be generated by using different UV spectra to polymerize the monomers in different ink binders into polymers. Therefore, the color film of UV ink has good mechanical and chemical properties. The main advantages of UV ink are:
(1) No solvent;
(2) fast drying speed and less energy consumption;
(3) good luster and bright color; (4) Water resistance, solvent resistance and good wear resistance. Photoinitiator in UV ink is a compound easily excited by light. After absorbing light, it is excited into free radicals, and the energy is transferred to photosensitive molecules or light crosslinking agents to make UV ink photocurable.
At present, UV ink has become a mature ink technology, and its pollutant emission is almost zero. According to statistics, the annual output of UV ink is increasing day by day About 16000 tons in this, 18000 tons in Europe and 19000 tons in North America.
In addition to solvent-free, UV ink has the advantages of not easy to paste, clear dot, bright ink color, excellent chemical resistance, saving dosage and so on. According to statistics, the United States used 3500 tons of UV ink for flexographic printing in 2000.