Introduction of printing ink for food bags

At present, the most widely used printing ink for plastic food packaging is benzene-soluble chlorinated polypropylene ink series. This series of inks have good gel-forming properties and gloss, and the drying speed is relatively fast. Usually, gravure printing and BOPP (biaxially oriented polypropylene) matte film are used for inner printing, and the production process and technical application are relatively mature. The shortcomings are: 1. The thermal stability of chlorinated polypropylene is relatively poor, and it is easy to react with air to generate hydrochloric acid (hydrogen chloride) when heated. The pH value of the ink is acidic, which is highly corrosive to the printing plate. 2. The printing ink contains toluene. Although the printing layer does not directly contact the food, the residual solvent is relatively high, which is easy to cause pollution to the food in the food bag and is harmful to the human body. 3. Due to the poor thermal stability of benzene-soluble chlorinated polypropylene ink, it is easy to react with air to produce hydrogen chloride and other substances, which has a damaging effect on the ozone layer in the atmosphere, thereby destroying the ecological environment. Therefore, many developed countries such as Europe and the United States have expressly prohibit or control the laws and regulations of the use of benzene-soluble chlorinated polypropylene inks. In order to solve a series of problems such as benzene-soluble chlorinated polypropylene inks, environmentally friendly inks have been developed and have been vigorously supported and used by governments around the world. Environmentally friendly ink will not pollute the environment during production and use, nor will it cause harm to the user’s body, and will not contaminate the food in the food packaging bag. At present, there are three kinds of environmentally friendly inks that are most used in China: 1. Water-based ink Water-based ink, also known as Yanhuang ink, flexographic ink or liquid ink, is mainly composed of water-soluble resins, organic pigments, solvents and related co-solvents through compound grinding. Hence it is. Water-based ink is the ink used in most flexographic packaging printing at home and abroad. Water-soluble resin is the binder of water-based ink. Water-soluble acrylic modified resin is often used as binder in China. It has significant advantages in heat resistance, weather resistance, chemical resistance, pollution resistance and gloss. Dissolved and still synthesized polymer emulsion, all show excellent performance. Water-based ink does not contain volatile organic solvents, which can not only reduce the toxicity of printed product residues, but also prevent fire due to static electricity and flammable solvents. Water-based ink is not only a new type of “green” printing ink, so it is the best product to replace benzene-soluble ink. Water-based inks are especially suitable for packaging and printing products with strict hygiene requirements such as tobacco, wine, food, beverages, medicines, and children’s toys. 2. Ultraviolet (UV) curing ink The curing process of ultraviolet curing ink is a photochemical reaction process, that is, under the action of ultraviolet light, it is cured with the polymer in a very short time to form a film. In addition to curing the surface of the ink, ultraviolet rays , can penetrate deeper into the liquid UV-curable ink, and stimulate the further curing of the deep ink and film. In traditional inks, oil-based inks are solidified under the action of oxidation, while solvent- or water-based inks are mainly cured by evaporation of water or solvents, and some inks can penetrate into paper. Therefore, compared with traditional inks, the polymerization and drying of UV-curable inks are more thorough, without any evaporation or solvent-based contamination, and the ink and film are 100% cured. UV-curable inks are mainly used for flexographic printing on soft substrates and consist of polymers, reactive diluents, pigments, additives, photoinitiators/composites. Among them, the choice of reactive diluent has an impact on the migration reaction in the ink formulation; the performance of the additive on the ink (printability, ink migration, wetting of the substrate, friction coefficient, abrasion resistance, pigment dispersion and stability) properties) and the smell of the printed matter; it is required that the spectral range of the pigment to absorb ultraviolet light is as small as possible. The characteristic of the reaction is no hindrance. When printing with UV-curable ink, attention should be paid to the inhibition of polymerization, surface tension and wetting, the correlation between ink viscosity and humidity, and the expansion of the printing plate; due to the poor adhesion of ink to plastic, it is necessary to The plastic is flame-treated or corona-discharged to improve the adhesion of the plastic surface. 3. Electron beam curable ink (EB ink) Electron beam curable ink refers to the ink that can quickly change from liquid to solid under the irradiation of high-energy electron beam, also known as EB ink. Electron beam curing ink is mainly composed of pigments, binders, auxiliary agents, colorants, etc. The energy of the electron beam is high, and it has strong penetrating power to solid components such as pigments and fillers, and the ink will not be blocked by the pigments or fillers, and the drying inside the ink film will not be affected. The drying of the ink film layer after ordinary ink printing is generally because the binder in the ink is absorbed and volatilized by the substrate, and the solid substances remain on the surface of the substrate to form a thin layer of ink. Electron beam curing is a process of rapid drying and curing at room temperature by means of electron beam as irradiation energy, radiation chemical reaction with active liquid chemical formula. Since electron beam is a type of radiation, electron beam radiation can also be classified as radiation curing. Radiation curing is a new technology developed on the basis of existing science and technology. It mainly uses a scanning electron accelerator. In radiation curing, the electron beam of the electron accelerator scans the surface of the substrate to realize curing processing. The basic meaning is to use ultraviolet light or electron beam as an energy source to initiate a chemically active liquid formulation to achieve a rapid reaction curing process on the surface of the substrate. The biggest advantage of UV curing and electron beam curing technology different from traditional technologies (such as thermal curing) is that radiation curing uses high-efficiency UV light or electron beam as an initiation means to quickly achieve coating curing. Among them, electron beam radiation is composed of a batch of accelerated electron currents. Under the action of high-energy electron beams, free radicals or ionic groups are generated, and the free radicals or ionic groups are then cross-linked with other substances to form a network polymer. Compared with ultraviolet light, the particle energy is much higher than that of ultraviolet light, which can ionize the air, and electron beam curing generally does not require a photoinitiator, which can directly trigger chemical reactions, and its penetrating power to substances is also greater than that of ultraviolet light. With the improvement of the country’s requirements and standards for the printing industry, the emphasis on environmental protection awareness and the continuous development of environmental protection printing technology, consumers have higher and higher requirements for food bag packaging, which also puts forward more requirements for the use of ink materials in printing. high demands. Therefore, environmentally friendly ink will surely become one of the mainstream printing material products in the food packaging industry in the future. Vacuum packaging bags, tea packaging bags