With the improvement of people’s living standards, higher requirements have been put on food packaging. In particular, ink has attracted attention in packaging. As a printing material, inks should satisfy various functional requirements such as non-toxicity, heat resistance, cold resistance, solvent resistance, oil resistance, friction resistance, and radiation resistance. The inks used in internationally recognized food printing must abide by the principle of non-transfer; the inner surface of food packaging materials must not use conventional inks; the printing manufacturers must ensure that the solvents in the inks are completely volatilized after printing, and the inks are required to be completely cured and reach the corresponding requirements of the application industry. standard. This shows that the role of ink in food packaging printing is extraordinary. The following describes the characteristics of the inks used in food packaging, the printing methods used, and the printing materials used.
Benzene-soluble chlorinated polypropylene ink is the most widely used ink for food plastic packaging and printing. This type of ink has matured both in terms of manufacturing and use technology, and is mainly used for BOPP (Biaxially Extruded Polypropylene) materials for printing and gravure printing. Although this ink has excellent printability, good after-printing performance and fast drying, due to the relatively high relative toxicity of toluene, the residual solvent value of the printed matter is high, and the thermal stability of chlorinated polypropylene is poor. During storage, chlorine is easily released to form hydrogen chloride, which makes the ink more acidic, causing serious corrosion to the printing plate roller, which makes this ink tend to be eliminated. Because people have realized that benzene-soluble ink can damage the ozone layer, it will also cause harm to the health and safety of workers during the use process, and residues left in the packaging products will, under certain conditions, cause a certain degree of Pollution. Therefore, inks that prohibit or control the use of aromatic solvents have been successively developed in Europe and some developed countries. Therefore, the development of inks that meet the requirements of environmental protection and food hygiene is an urgent problem to be solved.
Environmentally friendly inks should not cause any pollution to the environment, nor cause any harm to the operators' bodies, and they will not damage the interior foods.
1. Water-based ink
Water-based ink is the ink used in most flexographic packaging and printing at home and abroad. It is mainly composed of water-soluble resin, organic pigments, solvents and related additives through compound grinding. Water-soluble resin is the link material of water-based ink, and water-soluble acrylic modified resin is often used as the linking material in China, and its heat resistance, weather resistance, chemical resistance, pollution resistance and glossiness have significant advantages, regardless of direct dispersion. Dissolving or synthesizing polymer emulsions, all exhibit excellent performance. Water-based inks do not contain volatile organic solvents, which not only reduces the toxicity of printed products, but also prevents the occurrence of fire due to contact with static electricity and flammable solvents. Green" printing ink. Water-based inks are also the best alternative to benzene-soluble inks.
2. Ultraviolet (LIV) curing ink
UV-curing ink is a kind of ink that undergoes cross-linking reaction in the ink under irradiation of a certain wavelength of ultraviolet light, and changes from liquid to solid-state curing ink. Before the linking material is dissolved, the macromolecule prepolymer is firmly fixed. Form ink film.
UV-curing inks are mainly used for flexible printing of flexible substrates. They consist of prepolymers, reactive diluents, pigments, additives, photoinitiators/composites. 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, migration of the ink, wetting of the substrate, coefficient of friction, abrasion resistance, dispersion and stabilization of the pigment) The odor of the prints and prints is adjusted; the spectrum of light absorbed by the pigment is required to be as small as possible. The ideal pigment should have good dispersibility, good leveling property, strong coloring power, small UV absorption under light irradiation, and no harm to the polymerization reaction.
When printing with UV-curing inks, attention should be paid to the inhibition of polymerization, surface tension and wetting, the correlation between the viscosity and humidity of the ink, and the expansion of the printing plate. Because the adhesion of the ink to the plastic is not good, the printed plastic must be flame treated or corona discharge treated to improve the adhesion of the plastic surface.
3. Electron beam curing ink (EB ink) Electron beam curing ink is an ink that can rapidly change from a liquid to a solid state under the irradiation of high-energy electron beams, also known as EB ink. The electron beam energy is high, and it has strong penetrability for solid components such as pigments and fillers, and the ink will not be hindered from being absorbed by the pigment or filler, and the internal drying of the ink film will not be affected. The composition of EB ink is mainly pigments, binders, auxiliary agents, etc. Since the curing of ink is realized by electron beam, the choice of binder material has specific requirements. The main components of acrylic ink are acrylic resin and participate in the reaction. The active monomer.
Most of the food and beverage packaging industry adopts electron beam curing printing, and the printing method is offset printing. EB ink adapts to the printing industry's development direction of high-speed, multi-color one-time printing. It has been developed and applied in foreign countries in the 1980s, and it has only recently been applied in China. Because the electron beam assimilation ink saves energy, components do not contain solvent, no pollution to the environment, packaging, curing time is short, the processing speed is fast, the output is high, the dot enlargement rate is small, the imprinting brightness is good, and it has abrasion resistance and chemical resistance. Such advantages, so this technology is quickly promoted and applied, especially in the food packaging field has broad application prospects. The main difference between EB inks and LIV inks is the presence or absence of photoinitiators in the binders. When a certain amount of photoinitiator is added to the EB inks, UV curing can also be performed. EB can cure thicker ink layers,
Since no photoinitiator is required in the ink, the cost is relatively lower than the LIV ink, but the electron beam curing equipment investment is higher than the LIV curing.
4. Digital printing ink
Digital printing technology has penetrated into the food packaging and printing industry as people's demand for increasingly personalized packaging has penetrated. With digital printing technology, a sufficiently high image resolution can be achieved and the details of the image can be ideally reproduced.
In addition, digital printing technology can provide faster and smaller batches of services. Digital printing inks can be divided into ink dyed inks, electrostatic printing solid toners, and digital offset electronic liquid inks according to the different printing methods used. The toner is melted and fixed on the printing material after being heated by ceramic crystals. Most printing materials are foil, metal aluminum, PET (polyester), paper, etc., and are suitable for printing webs. It is important that the toner is selected with a suitable fixing temperature, because the optimum fixing temperature can control the fixing process of the toner well. The toner should have a certain degree of flexibility to facilitate folding processing of the printing material. Solvent resistance is also very important for electrostatic digital printing. Prints with poor solvent resistance will not be able to complete the next process, such as light and film.
In today's green environment and the demand for food packaging safety, high quality, multi-color printing, printing inks should also adapt to the development of the times, toward the direction of benzene-free, environmental protection.
Zhanbo Industrial Co., Ltd. , http://www.lyceramic.com