With the improvement of living standards, people have put forward higher requirements for food packaging. Ink as a printing material, when it is used in food packaging, must comply with the principle of non-transfer. Food packaging must not use conventional inks. The printing manufacturer must ensure that all the solvent in the ink is volatile after printing. The ink must be completely cured and meet the corresponding standards of the application industry.
In the current food plastic packaging printing, benzene-soluble chlorinated polypropylene ink is the most widely used. The manufacturing and use technology of this type of ink is mature, and it is mainly used in the inner printing of BOPP (bidirectionally stretched polypropylene) material, and the gravure printing method is adopted. Although this ink has excellent printability, good post-printing processing performance, and fast drying, due to (1) the relative toxicity of toluene, the residual solvent value of the printed matter is high; (2) the thermal stability of chlorinated polypropylene is poor In the production and storage process, chlorine is easily released to form hydrogen chloride, which makes the ink more acidic, which causes heavy corrosion to the printing plate roller; (3) benzene-soluble ink can destroy the ozone layer, and it will also Harm to the health and safety of workers, and the residue left in the packaging products, under certain conditions, will cause a certain degree of pollution to the food in the package. This ink is tending to be eliminated, and regulations for banning or controlling the use of this ink have been formulated in Europe and some developed countries.
It is precisely because of the various problems of benzene soluble ink, environmentally friendly ink came into being. The use of environmentally friendly inks not only causes no pollution to the environment, but also does not cause physical harm to the operators, and it will not cause damage to the food inside. Environmentally friendly inks that are already on the market are:
1. Water-based ink: Water-based ink is the ink used in most flexographic packaging and printing at home and abroad. It is mainly made of water-soluble resin, organic pigments, solvents and related additives through compound grinding. Water-soluble resin is the linking material of water-based ink. Water-soluble acrylic modified resin is often used as the linking material in China. Its heat resistance, weather resistance, chemical resistance, pollution resistance and glossiness have significant advantages, regardless of direct dispersion. Dissolved or synthetic polymer emulsions all exhibit excellent performance. Water-based inks do not contain volatile organic solvents, which not only reduces the residual toxicity of printed products, but also prevents fire due to static electricity and flammable solvents. Water-based ink is not only a new type of "green" printing ink, but also the best product to replace benzene-soluble ink.
2. Ultraviolet (UV) curing ink Ultraviolet curing ink refers to the crosslinking reaction of the binder in the ink under the irradiation of ultraviolet light of a certain wavelength, which changes from liquid to solid to complete the curing of the ink. Before the binder dissolves, The macromolecular prepolymer firmly forms the ink film. UV-curable ink is mainly used for flexible printing of soft substrates. It consists of prepolymer, reactive diluent, pigment, additives, photoinitiator / composite. Among them, the choice of reactive diluent has an effect on the migration reaction in the ink formulation; the performance of the additive on the ink (printability, ink migration, substrate wetting, friction coefficient, wear resistance, pigment dispersion and stability Properties) and the odor of the printed matter; the spectral range of the ultraviolet absorption of the pigment is required to be as small as possible. The ideal pigment should have good dispersibility, good leveling, strong coloring power, small ultraviolet absorption under light irradiation, and polymerization The characteristics of the reaction without hindrance. When printing with UV-curable inks, attention should be paid to the inhibition of polymerization, surface tension and wetting, the correlation between the viscosity of the ink and humidity, and the expansion of the printing plate; due to the poor adhesion of the ink to plastic, the Plastic is treated with flame or corona discharge to improve the adhesion of the plastic surface.
3. Electron beam curing ink (EB ink) Electron beam curing 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. The electron beam energy is high, and it has strong penetrating power to solid components such as pigments and fillers. There will be no situation where the ink is hindered by the pigments or fillers. The drying inside the ink film will not be affected. The composition of EB ink mainly includes pigments, binders, auxiliary agents, etc. Because the curing of the ink is achieved by electron beam, the choice of binders has specific requirements. The main components are acrylic resins and participation in the reaction Active monomer. Most of the food and beverage packaging industry uses electron beam curing printing, and the printing method is offset printing. EB ink adapts to the development direction of high-speed, multi-color printing in the printing industry. Because the electron beam curing ink saves energy, contains no solvent in the components, has no pollution to the environment and packaging, has short curing time, fast processing speed, high output, small dot expansion rate, good imprint brightness, wear resistance and chemical resistance This technology has been rapidly promoted and applied, especially in the field of food packaging, with broad application prospects. The main difference between EB ink and LIV curing ink is whether there is a photoinitiator in the binder. When a certain amount of photoinitiator is added to the EB ink, UV curing can also be performed.
4. Digital printing ink: Digital printing technology has penetrated into the food packaging and printing industry as people's increasing demand for personalized packaging. Using digital printing technology can achieve high enough image resolution, can ideally reproduce the details of the image. In addition, digital printing technology can provide faster and smaller batch services. Dye ink for digital inkjet printing, solid toner for electrostatic printing, and e-liquid ink for digital offset printing. The toner is melted by heating the ceramic crystal and fixed on the printing material. Most of the printing materials are foil, aluminum, PET (polyester), paper, etc., and are suitable for printing web paper. It is very important to choose the proper fixing temperature for toner, because the best fixing temperature can control the toner fixing process well. The toner should have a certain flexibility to facilitate the folding of the printing material. Solvent resistance is also extremely important for electrostatic digital printing. Prints with poor solvent resistance will not be able to complete the subsequent processes, such as glazing and laminating.
Today, environmental protection has become the theme of the printing field, and high-quality, multi-color printing is increasingly required for food packaging. Therefore, printing ink must adapt to the call of the development of the times and develop towards benzene-free and environmental protection.
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