Environmental friendly ink in the hottest green pr

2022-09-23
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Environmental friendly ink in green printing

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 friendly ink is the first consideration for the development of ink in the future

I The harm of ink to the environment

ink is the largest pollution source in the printing industry at present, and the annual output of ink in the world has reached 3million tons. Every year, the global emission of organic volatile compounds (VOC) pollution caused by ink has 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, seriously polluting the atmospheric environment and affecting people's health. In addition, the harmful ingredients such as heavy metals in ordinary printing inks for packaging and printing of food and toys will also directly endanger the health of consumers

(1) impact on human health

printing ink is composed of pigments, binders, solvents and auxiliary agents. 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 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 and mercury, which are toxic and cannot be used for printing food packaging and children's toys; Some organic pigments contain biphenyl glue, which has carcinogenic ingredients and should not be used. When conducting tensile tests, organic solvents mainly have swing angle and swing speed, and the conditioning range is small. They can dissolve many natural resins and synthetic resins. They are important components of various inks, but some of them will damage human body and subcutaneous fat. Long term contact will make the skin dry and rough. If they penetrate into the skin or blood vessels, they will endanger human blood cells and hematopoietic function with the blood; Being sucked into the trachea, bronchus, lungs or transmitted to other organs through blood vessels and lymphatic vessels may even cause chronic poisoning of the body. Some inks have the toxicity of heavy metal ions. Pigments and dyes contain carcinogenic ingredients, which are 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 into food during the process of food packaging and storage, which will endanger people's health. Ethanol, isopropanol, butanol, propanol, butanone, ethyl acetate, butyl acetate, toluene, xylene and other organic solvents 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. Solvents used in gravure printing inks generally include butanone, xylene, toluene, butanol, etc. 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 completely dried due to short time and fast speed, especially for printing materials with large inking area and thick ink layer, there are more residual solvents. These residual solvents are brought into the compounding process, which is more difficult to run away after compounding, and will slowly migrate and penetrate. Therefore, the residual solvents must be controlled to a minimum

(2) impact on environmental quality

among the problems of atmospheric pollution 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 have photochemical reactions with nitrogen oxides in the air, producing ozone and smoke, causing air pollution. To reduce VOC, there are two solutions: recycling and burning solvents, but there are many gravure printing machines 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, the main environmental protection inks

to meet the environmental protection requirements, we should first change the ink composition, that is, use environmental protection materials to prepare new inks. At present, environmental protection inks mainly include water-based inks, UV inks, water-based UV inks and some alcohol soluble inks

(1) water based inks

the biggest difference between water-based inks and solvent based inks is that the solvent used is water rather than organic solvents, which significantly reduces VOC emissions, prevents air pollution, does not affect human health, is not easy to burn, has stable inkiness, bright colors, does not corrode plates, is simple to operate, cheap, has good adhesion after printing, is strong in water resistance, and dries quickly, so it is especially suitable for food, beverages Drugs and other packages have been modified, and their fire resistance has reached A2 Level. It is a world recognized environmental friendly printing material, and it is also the only ink approved by the American food and drug association among all printing inks at present. At present, 40% of plastic printing in the United States uses water-based ink, and other economically developed countries (such as Japan, Germany, France, etc.) use more and more water-based ink in plastic film printing. In June this year, Britain legislated to prohibit solvent based inks from printing food films. According to relevant information, in the United States, the proportion of volatile components is less than 25% and the moisture content is more than 75% in the ink composition of water-based inks that meet the VOC regulations and must reach the use state; Less water in the use of ink, non-volatile ingredients in more than 60% of these two standards. Water based inks are usually used for printing paper products, including paper plastic composite products. Its characteristic is that it can meet the ink absorption of paper printing and make the printing color plump. What is more difficult is that its solvent is water and ethanol, which has little pollution to the environment and is known as an environmental friendly green ink

(2) UV curable ink

UV curable (UV) ink refers to an ink that uses ultraviolet light of different wavelengths and energies to form a film and dry the ink under UV irradiation. Using different UV spectra, different energies can be generated to polymerize the monomers in different ink binders into polymers, so 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 gloss and bright colors; (4) Water resistance, solvent resistance, good wear resistance. Photoinitiator in UV ink is a compound that is easily excited by light. After absorbing light, it is excited into free radicals, and the energy is transferred to photosensitive molecules or photocrosslinking agents, so that UV ink can undergo light curing reaction. 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 about 16000 tons in Japan, 18000 tons in Europe and 19000 tons in North America due to different test methods. In addition to solvent-free, UV ink also has the advantages of not easy to paste, clear dots, bright and 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

(3) water based UV ink

water based UV ink is a new research direction in the field of UV ink at present. The viscosity of prepolymer in ordinary UV ink is generally very high, which needs to be diluted with active diluent. At present, the diluent acrylate compounds have different degrees of skin irritation and toxicity. Therefore, while developing low viscosity prepolymers and low toxicity active diluents, another development direction is to study water-based UV inks, that is, using water and ethanol as diluents. At present, water-based UV ink has been successfully developed and applied in some printing. In addition, alcohol soluble ink, which mainly plays a role in flexographic printing, is also an ink with little public hazard. It is mainly used in the packaging and printing of food, drugs, beverages, tobacco and alcohol, and daily necessities in contact with human body

(4) biological ink

American scientists have long been committed to the study of a protein molecule called bacteriorhodopsin. Natural materials often exhibit complex functions that cannot be easily obtained by materials such as semiconductors. Bacteriorhodopsin is derived from an intense purple cell membrane that grows on a body called halophilus halophilus in saline marshes. Illuminating its protein can trigger a photochemical reaction circle. The principle is that the photochemical reaction circle transports protons along the channel surrounding the cell membrane. The purple of this cell membrane comes from the bacteriorhodopsin component called "optic membrane". Amino acids in cell membrane channels are firmly bound to the "optic membrane". In the dissolved state, the "optic membrane" does not bind to amino acid and is pale yellow. By alternately irradiating two groups of lasers with different wavelengths on this protein molecule, the protein molecule can be converted back and forth between the purple structure and the Yellow structure. It is this habit that inspires people to study and use it. It can be used as a photosensitive element in analog visual film, a memory element in prion based processing device or a memory element in optical computer. Its film can also change color according to the conversion of external electric field. In conventional bacteriorhodopsin, low contrast color changes from purple to blue will be formed under the action of different electric fields. However, the bacteriorhodopsin structure produced by a certain mutant will change from blue to light yellow under the action of strong electric field. A display plate can be made by clamping the protein film into a transparent plate with a large number of electrodes. Applying appropriate voltage to different parts of the film can "write" a page of manuscript or "insert" an image. Like ink, the image on bacteriorhodopsin display plate can also be seen in ordinary light. Moreover, the color change time can be accelerated to 200 μ m。 At present, the main difficulty faced by the whole research work is the need to use hundreds of volts of electric field to stimulate its color transformation. Researchers are making efforts to carry out research in this area, hoping to make breakthroughs

(5) new environmentally friendly ink "opis100"

Osaka printing ink company in Japan recently launched a new environmentally friendly ink "opis100", which is a sheet fed offset printing ink, which meets the green mark recognition standard revised by the Japan Environmental Association at the end of last year, and has the following characteristics: (1) it meets the newly revised green mark "lithographic ink V-2" standard; (2) Recognized by the American Soybean Association; (3) Comply with the environmental protection standards of Japan Printing Industry Federation; (4) Comply with GPN ordering guidelines; (5) It is 100% vegetable oil ink based on soybean oil; (6) VOC content is less than 1%; (7) Good stability and transferability on board; (8) Good friction resistance, gloss and hair color; (9) Good adaptability of fountain solution; (10) Easily biodegradable and deinking; (11) Excellent fusion with uv-op varnish and better gloss; (12) It also has excellent printability for double-sided 8-color machine

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