When ink is applied to food packaging as a printing material, it must be non-transferable. Prints in food packaging should not use conventional inks. The printing company must ensure that all the solvents in the ink are completely volatilized after printing. The ink needs thorough curing and meet the corresponding industry standards.
::Phasing out of Hazardous Benzene-solvent Inks::
In current printing for plastic food packaging, benzene-soluble chlorinated polypropylene inks are the most widely used, both the manufacture and use of which are in good practice. Such inks are mainly used in the printing of BOPP (biaxially oriented polypropylene) materials, and through gravure. Despite the benefits of good printing suitability & post-press processing performance and fast drying, they also have as big disadvantages. Firstly, the solvent residual in prints from such inks is high and toluene is toxic. Secondly, as the thermal stability of the chlorinated polypropylene is poor, the solvents tend to release chlorine to form hydrogen chloride during the production and storage, which makes the ink more acidic, causing severe corrosion to the printing plate roller. Also, the benzene-soluble ink can destroy the ozone layer and cause harm to workers' health and safety during use. And the residue remaining in the packaged product will cause a certain degree of contamination of the food in the package. This type of inks are phasing out, and regulations for prohibiting or controlling the use of this ink have already been developed in Europe and some other countries.
Because of the problems of benzene-soluble inks, environmentally friendly inks came into being. The use of environmentally-friendly inks does not pollute the environment, nor cause physical harm to the operator, nor incur contamination to the contents.
::Environmentally friendly inks in the Supply::
(1) Water-based Ink
Water-based ink is the ink used in most of the flexographic packaging printing at home and abroad. It is mainly processed by composite grinding of water-soluble resin, organic pigment, solvent and related additives. Water-soluble resin is a joint of water-based ink. Water-soluble acrylic resin is often used as a binder in China. It has significant advantages in heat resistance, weather resistance, chemical resistance, pollution resistance and gloss, 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 reduce the toxicity of printed residues, but also prevent fires caused by contact with static electricity and flammable solvents. Water-based inks are not only a new type of "green" printing ink, but also the best alternative to benzene-soluble inks.
(2) UV-curable Inks
UV-curable ink refers to a type of ink that dries or cures under a certain wavelength of ultraviolet light. It involves a cross-linking photochemical reaction, where a solid-state ink is converted from liquid. UV-curable inks are primarily used for flexo printing over flexible substrates. They consist of prepolymers, reactive diluents, pigments, additives, photoinitiators/compositions. The choice of reactive diluent has an bearing on the migration reaction in the ink formulation; the additives would regulate the ink performances (printability, ink migration, substrate wetting, friction coefficient, abrasion resistance, pigment dispersion and stability) and the odor of the prints. the spectral range of the pigments’ absorption of ultraviolet light should be kept minimum The ideal pigment should have good dispersibility, good leveling property, strong coloring power, and low UV absorption under light irradiation, and not harmful to the polymerization reaction. When printing with UV-curable inks, attention should be paid to the inhibition of polymerization, surface tension and wetting, the correlation between viscosity and humidity of the ink, and the expansion of the printing plate. Because of the poor adhesion of ink to plastic, it’s necessary to perform flame treatment or corona discharge treatment on the printed plastic.
(3) Electron-Beam Curable Inks
EB-curable ink refers to a type of ink that can be quickly converted from liquid to solid under the irradiation of a high-energy electron beam. Since electron beam has high energy, and has strong penetrating power for solid components such as pigments and fillers, thus pigment or filler won’t block the drying.