Research and development of the hottest environmen

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Research and development of environmental friendly inks (I)

today, with the development of science and technology and the explosion of knowledge, the printing industry has achieved unprecedented development. All kinds of books, newspapers, commercial printing materials and all kinds of exquisite packaging enrich our spiritual and material life. At the same time, the materials used in the production of these printing materials, such as the volatiles of ink, also have an impact on the environment. In order to protect our living environment and achieve sustainable development, it is imperative to vigorously develop and use environmental friendly inks

at present, in the printing industry of all countries in the world, offset printing is mainly used in books, periodicals and commercial printing, gravure printing and flexo printing are increasingly used in packaging printing, silk printing is also developing rapidly, and the emerging inkjet printing technology is also being promoted. Now the petroleum solvents in printing inks contain ingredients harmful to human body, such as benzene, toluene, xylene, etc; Solvent based inks used in gravure printing and silk printing contain 50% - 60% volatile components; Diluents used to adjust ink viscosity may also cause harm to printers and the environment. With the development of the printing industry and the increasing voice of people for environmental protection, higher requirements have been put forward for the printing industry and printing ink industry. We need to transform the original printing process and the printing materials used, and launch printing materials and processes that meet the requirements of environmental protection

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some developed countries in Europe and the United States legislated as early as the 1990s to limit the emission of volatile organic solvents (VOC), such as the concentration of volatile substances in the workshop must be lower than: volatile organic solvents 50mg/m3; Carbon monoxide 100mg/m3; Nitric oxide 100mg/m3. Japan began to implement the "environmental protection purchase law" in April 2001; In August, 2001, the Japan printing industry federation formulated the industrial environmental protection standard, "offset printing service" standard, implemented the environmental protection purchase law in the printing ink industry, and implemented the PRTR (pollutant release and transfer register) system and MSDS (material safety data sheet) system. The former is a system in which the government counts and publishes the emission and transfer of chemical substances in the production process of enterprises; The latter is published by the chemical manufacturing company on the instructions for the safe use of chemical substances in each product. Two systems stipulate the ink standards:

(1) do not use substances harmful to human body, such as benzene, fluorine, aromatic amines, biphenyl chloride, dioxin, etc

(2) do not use chlorine containing resin, because the unreacted free chlorine is harmful to human body after being approved, and dibenzo-p-dioxin like toxic substances will be produced during combustion

(3) reduce the use of chemical substances pointed out in the PRTR law, such as toxic heavy metals lead, cadmium, hexavalent chromium, mercury, etc., because these substances will cause serious damage and pollution to human body and the environment

(4) inhibit the production of VOC, because volatile organic compounds in solvents will produce chemical smoke and become the culprit of air pollution

at present, from the global research trends and development trends of inks, the following categories of inks are the main development directions of environmental friendly inks

theme - water based ink

1 Component

water based inks use water as the main solvent. The proportion of volatile components in its components is less than 25%, and for inks with less water, the volatile components are less than 40%. Water based ink components usually include water-soluble or water dispersible resins, insoluble pigments, organic pigment surfactants, additives, water and some solvents. Among them, pigments mainly play the role of coloring and light blocking. Resin is the binder of ink, which can firmly adhere the ink film to the substrate. The varieties of resins have experienced several development stages in the 20th century, including rosin amine salts in the 1970s, acrylic acid solutions in the 1980s and acrylic lotion or colloidal dispersions in the 1990s. Different from solvent based inks, they are either emulsions, solvents, or both, and can interact with water to form lotion or colloidal suspension, suspending pigments and other components in inks, After printing, water and some solvents volatilize, and the formed resin particle colloid attaches the pigment particles to the substrate to form an ink film. Of course, a small amount of solvent in water-based ink is also essential, because the polarity of water is large and the surface tension is high, so when the resin is attached to the substrate, water is not conducive to the formation and attachment of the ink film on the substrate, and the solvent is conducive to the resin adsorption on the substrate

the use of additives in water-based inks is very important. Dispersants can make pigments disperse well and do not fade in the sun, such as dep; The mixed solvent can dissolve the components in the ink, eliminate the surface suspended solids, and increase the leveling of ink, such as pi-35; Crosslinking agent can speed up the drying of ink film and improve the hardness, wear resistance, water resistance and heat resistance of ink film

2. Features

water based inks are "green" printing inks, which have no impact on human health, no pollution to the environment, and are not flammable. In fact, there is no great distinction in terms of technology. They are safe to use, stable in nature, bright in color, high purity, strong color reduction, fine and greasy ink layer, clear dots, good post press adhesion, strong water resistance, anti-static, non-corrosive plates, suitable for cosmetics, medicine, food, tobacco, alcohol Children's toys and packaging and printing with strict requirements for sanitary conditions

one of the major shortcomings of water-based ink is its slow drying speed, but this can be solved by increasing the flow of cold air, lengthening the drying channel, reducing the thickness of the film, and then strengthening the research on ink drying speed and drying system

the use of water-based ink is convenient for equipment cleaning. At present, it is mainly used for flexographic printing and gravure printing. It is understood that 95% of flexographic printing and 80% of gravure printing in the United States now use water-based ink, and the development and research trend has become the trend of the world. If water-based inks are widely used, wastewater treatment must be carried out. The wastewater used for barrel washing, tank washing, roller washing, etc. should be centrally precipitated and recycled, so as to achieve real cleaner production and environmental protection

3. Product gap

at present, domestic water-based inks are inferior to imported inks in chromaticity, gloss and stability, and the gap is more obvious in high-speed overprint. The main reason is the gap between pigments and binders. The oil absorption value of domestic pigments is generally high, which is not suitable for aqueous systems. If water is used as solvent, there will be insufficient color saturation, which will affect the quality of prints. The binder in water-based ink is usually polymer lotion or water dispersible resin. Water soluble acrylic copolymer resin is generally used abroad, which performs well in gloss, water resistance, chemical resistance, etc. in China, rosin was previously used to modify it. 2. The current main problem is maleic acid resin, whose gloss, water resistance and chemical resistance are inferior. Later, domestic acrylic resin lotion was used, which affected the quality of water-based ink due to its poor stability. Therefore, to improve the quality of water-based inks in China, the key is to change from raw materials

uv ink is maturing

uv ink is mainly composed of photopolymerization prepolymer, photoinitiator, diluent monomer (active monomer), organic pigment, filler, etc. Photopolymerization prepolymer is the main component of UV ink. Generally, acrylic resin, acrylic polyurethane, epoxy acrylic resin, acrylic polyester, modified acrylic polyester, etc. are used. Photopolymerization prepolymer is the binder of UV ink, which determines the adhesion, wear resistance, chemical resistance, solvent resistance, hardness, viscosity and curing speed of UV ink. Photoinitiator is an active organic group crosslinked by light-emitting polymer prepolymer. The curing process of UV ink is a polymer crosslinking process. Photoinitiator is excited into free radicals or ions under the irradiation of external light source (usually ultraviolet light of a certain wavelength), and then through the energy transfer between molecules, the prepolymer and photosensitive monomer in the ink form charge transfer complexes, which are continuously crosslinked, Thus, UV ink can produce light curing reaction, and change from liquid to solid. There is basically no solvent volatilization in this reaction process, which is conducive to environmental protection

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