Overview of "Green Ink"
The most important meaning of green ink is the environmentally-friendly and safe ink variety that does not pose a threat or harm to human health and the ecological environment.
It is well known that inks are usually composed of five major components: pigments, binders, solvents, auxiliaries and fillers. These components, if not controlled, tend to "carry" toxic or hazardous substances more or less: in benzenes, alcohols or ketones such as benzene, toluene, xylene, which are widely used in gravure inks. It has been listed in the list of carcinogens by the World Health Organization; some pigments may contain excessive heavy metals such as lead, chromium and mercury; aromatic hydrocarbons in petroleum solvents contain volatile organic compounds (VOC), which will constitute human health and the natural environment. A certain degree of threat.
In contrast, if an ink is environmentally improved in some respects and in many aspects, the author believes that it can also be regarded as a green ink. Green ink is actually a relative concept. It is an environmentally-friendly improvement of the conventional ink. There is no strict judgment standard at present.
In reality, there are various inks for label printing , such as solvent inks, water-based inks, common inks for aromatic hydrocarbons, and UV inks without VOC. In order to meet the printing requirements, but also reduce the harm to the environment and users, ink manufacturers have carried out "green" improvement of these inks from different angles, and formed their own characteristics and specific uses.
(1) Compared with solvent-based and flexographic inks, the "aqueousization" of the diluent in the ink is a major direction of environmental protection. Among them, water-based ink is the only environmentally-friendly ink recognized by the US FDA, and is widely used in the field of milk or beverage laminating paper or other food packaging.
(2) Compared with the common offset printing inks for aromatic hydrocarbons, vegetable oil-modified offset printing inks represented by soybean oil and tung oil are more in line with the requirements of green environmental protection. At present, environmentally-friendly soy-based inks have been vigorously promoted in the publishing and printing industry, and are an important part of printing companies to achieve green certification.
(3) Compared with the traditional inks containing organic solvents, the new UV inks have the characteristics of fast curing speed, no VOC, energy saving and high efficiency. They are a kind of green and environmentally friendly ink, and are now widely used in commercial label printing.
Types of green UV inks and their applications
1. Low odor UV ink
In reality, although the UV ink itself does not contain VOC and is 100% involved in the curing reaction, it does not guarantee that it is absolutely odorless. The source of odor of UV ink is its own raw materials (such as monomer diluent, low molecular weight initiator, resin binder and other raw materials), which emits unpleasant odor slowly under certain conditions. Second, UV ink curing After that, an unpleasant gas such as an aldehyde or a sulfur generated by cracking of a raw material such as an initiator or a resin is used. At the current stage, most of the odors printed by UV inks are mainly derived from substances released before and after curing of the UV ink itself.
To achieve the environmental goal of low odor after UV ink curing, it is recommended to select suitable raw materials, mainly referring to resins, acrylic monomers, initiators, fillers or pigments.
First, considering the polyester, polyurethane, epoxy acrylic resin and monomers used in UV inks, some are produced by the "solvent method", that is, the reaction medium in organic solvents such as benzenes, alkanes or ethers. In the middle, low temperature conditions, it may cause solvent odor residue in this process. Therefore, materials that have been extracted several times should be selected to reduce the presence of odor.
Secondly, in a UV ink, a plurality of initiators are often added to obtain energy photons by absorption of different ultraviolet spectra, thereby initiating functional group polymerization in the system to complete curing. There are hundreds of initiators available on the market, but the efficiency, price, color depth and range of use vary widely. For example, at present, most of the domestic UV inks use 907 initiator, the chemical name is 2-methyl-1-(4-methylthiophenyl)-2-morpholine-1-propanone, which will be cleaved during curing. An unpleasant "methylthio" problem. In addition, initiators such as EDAB and BP benzophenone also produce odor during curing. Therefore, in order to alleviate the odor problem, it is recommended not to use such an initiator, and try to choose high-grade low-odor type 369, EHA, TPO and other initiators.
The low-odor UV inks manufactured as described above can be applied to some areas sensitive to odors, such as food packaging labels, mineral water bottle labels, and outer packaging of paper towels. Such UV inks have received a lot of attention from specific markets due to their low odor after curing and no destructive effect on the odor of the packaged product.
2. Plant-based modified UV ink
Most of the raw materials of traditional UV inks, such as urethanes such as polyurethane, polyester, epoxy or polyether, acrylic monomer diluents, etc., occupy 50% to 70% of the formulation, and all come from petroleum cracking, but The sustainable development of UV inks has also been challenged by the increasing depletion of petrochemical sources.
Plant-based UV inks have greatly increased the proportion of renewable raw materials. It uses plant resources such as rosin, soybean oil and tung oil to reduce costs and improve the utilization of biological resources. On the other hand, it helps to improve ink and print. Biodegradability reduces the dependence on petroleum products. At present, soybean oil-modified UV ink (UVSOYA system) has appeared on the market, which is favored by some customers in the European and American regions with advanced environmental protection concepts. It has been applied to some children's toys.
3.LEDUV ink
The light sources used in conventional UV curing devices are generally high pressure mercury lamps and metal halide lamps. They have large power consumption, the surface temperature of the lamp can reach 800 ° C, and the heat is large, which is easy to cause aging damage to the printing machine itself and the substrate. In order to solve this series of problems in traditional UV curing devices, foreign researchers have developed LED UV printing systems by applying ultraviolet light emitting diode (LED) technology to the curing of UV inks.
Compared with the traditional UV printing system, the newly developed LEDUV printing system has the following advantages: (1) LED curing device requires less power, can save energy costs, and greatly reduce CO2 emissions; (2) LED The heat generated by curing is less, suitable for printing on “heat sensitive†materials; (3) the life of LED light source components is about 12 times that of UV lamps, the frequency of light source replacement is greatly reduced, and the consumption of equipment is reduced; (4) LED It can be turned on or off instantly, without the need for preheating and cooling like UV lamps, and the work efficiency is improved.
Based on this, it can be said that the LEDUV printing system further enhances the friendly coordination of the environment compared to the conventional UV printing system.
Label printing is the first in the field of using LEDUV curing equipment and ink products at home and abroad. At present, there is no problem in the development of LEDUV inks, and well-known ink manufacturers at home and abroad have launched related products. However, the problem now is that the cost performance of the LEDUV ink is not high, and the production efficiency of changing the LEDUV device for printing has not been significantly increased compared with the conventional method. Although the future development of LED curing technology is promising, there is still a long way to go before it can be applied to actual printing on a large scale.
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