With the improvement of living standards, people have put forward higher requirements for food packaging. As a printing material, ink must comply with the principle of no transfer when it is used in food packaging. Conventional inks must not be used for food packaging. Printing manufacturers must ensure that all solvents in the inks evaporate after printing. The inks are required to be completely cured and meet the corresponding standards of the application industry.

In the current food plastic packaging printing, benzene-soluble chlorinated polypropylene inks are the most widely used. The manufacturing and use technologies of this type of ink are mature, and it is mainly used for the inner printing of BOPP (biaxially oriented polypropylene) materials, and it adopts gravure printing. Although this type of ink has excellent printability, good post-printing processing performance, and fast drying, benzene-soluble chlorinated polypropylene ink is tending to be eliminatedit due to (1) the relative toxicity of toluene; relatively high residual solvent value in printed products (2) the poor thermal stability of chlorinated polypropylene, which easily releases chlorine to form hydrogen chloride during production and storage, making the ink highly acidic and causing severe corrosion to the printing plate roller; (3) benzene-soluble ink can destroy the ozone layer and cause harm to the health and safety of workers during use. In addition, the residues left in the packaging products will cause a certain degree of pollution to the food in the packaging under certain conditions. Regulations have been successively formulated in Europe and some developed countries to prohibit or control the use of this type of ink.

It is precisely because of the various problems of benzene-soluble ink that environmentally friendly inks have come into being. The use of environmentally friendly inks will not pollute the environment, cause no harm to the operator, and will not damage the food inside.

Environmentally friendly inks that have been launched on the market include:

1. Water-based ink
Water-based ink is the ink used for most flexographic packaging printing at home and abroad. It is mainly made of water-soluble resin, organic pigment, solvent and related additives through composite grinding. Water-soluble resin is the binder of water-based ink. It has significant advantages in heat resistance, weather resistance, chemical resistance, pollution resistance and gloss. Whether it is directly dispersed and dissolved or synthesized polymer emulsion, it shows excellent performance. Water-based ink does not contain volatile organic solvents, which can not only reduce the residual toxicity of printed product, but also prevent fire caused by contact between 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 ink that is cured from liquid to solid when the binder in the ink undergoes cross-linking reaction under the irradiation of ultraviolet light of a certain wavelength. Before the binder dissolves, the macromolecular prepolymer forms a solid ink film. UV curing ink is mainly used for flexible printing on soft substrates. It is composed of prepolymers, reactive diluents, pigments, additives, and photoinitiators/synthetics. Among them, the selection of reactive diluents affects the migration reaction in the ink formula; additives adjust the performance of the ink (printability, migration of the ink, wetting of the substrate, friction coefficient, wear resistance, dispersion and stability of the pigment) and the odor of the printed product; the spectral range of the pigment's absorption of ultraviolet light is required to be as small as possible. The ideal pigment should have the characteristics of good dispersibility, good leveling, strong tinting strength, small ultraviolet absorption under light irradiation, and no interference with the polymerization reaction. When printing with UV-curing ink, attention should be paid to the inhibition of polymerization reaction, surface tension and wetting, the correlation between ink viscosity and humidity, and the expansion of the printing plate. Since the ink has poor adhesion to plastic, the to-be-printed plastic needs to be flame treated or corona discharged to improve the adhesion of the plastic surface.

3. Electron Beam Curing Ink (EB ink)
Electron beam curing ink refers to ink that can quickly transform from liquid to solid under the irradiation of high-energy electron beams, also known as EB ink. The EB ink has high energy and has strong penetration into solid components such as pigments and fillers. The ink will not be blocked by pigments or fillers for absorption, and the drying inside the ink film will not be affected.

EB ink is mainly composed of pigments, binders, auxiliary agents, etc. Since the curing of ink is achieved by electron beams, the selection of binders has specific requirements. Main components of binders are acrylic resins and active monomers participating in the reaction. 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 one-time printing in the printing industry. Electron beam curing ink saves energy, does not contain solvents in the components, does not pollute the environment and packaging, has a short curing time, fast processing speed, high output, good print brightness, wear resistance and chemical corrosion resistance, so this technology has been rapidly promoted and applied, especially in the field of food packaging, where it has 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 EB ink, it can also be cured by ultraviolet light.

4. Digital Printing Ink
Digital printing technology has penetrated into the food packaging printing industry as people's demand for personalized packaging has increased. Digital printing technology can achieve sufficiently high image resolution and can ideally reproduce the details of the image. In addition, digital printing technology can provide faster small-batch printing services. Digital inkjet printing inks include dye ink and pigment ink.

Nano Pigment Ink: High-quality raw materials, bright colors: innovative resin encapsulation technology is used in producing the pigment ink, so that the diffuse reflection of pigment ink on the paper base becomes specular reflection, which increases the transparency of printing works printed with pigment ink. Light resistant, UV resistant: the ink is developed with extremely high physical and chemical stability, so finished product of the ink is waterproof, light resistance and anti-ultraviolet, and longer storage time. Waterproof and moisture-proof: the outer layer of the ink colorant is attached to a high-quality water-based resin layer, so the ink has good stability and good water resistance.

Dye Ink: high saturation, wide color gamut, high safety for printheads. In particular, the bright colors, smooth printing, and low cost have made dye inks widely used in the digital printing industry.

Today, green environmental protection has become the theme of the printing field, food packaging is increasingly required to be high-quality and multi-color printing. Therefore, printing inks must adapt to the call of the times and develop in the direction of benzene-free and environmentally friendly.