Analysis of various environmental friendly inks on

With the improvement of living standards, people put forward higher requirements for food packaging. As a printing material, ink must abide by the principle of no transfer when it is used in food packaging. Conventional ink shall not be used for food packaging. The printing manufacturer must ensure that all the solvents in the ink evaporate after printing, and the ink is required to be cured thoroughly 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 kind of ink has been mature, and it is mainly used in the internal printing of BOPP (biaxially oriented polypropylene) materials, and gravure printing is adopted. Although its mechanical strength is comparable to that of wood, polymers, ceramics and other materials, this kind of ink has excellent printability, good post press processing performance and fast drying, but due to (1) the relative toxicity of toluene, the residual solvent value of printed matter is high; (2) Chlorinated polypropylene has poor thermal stability. In the process of production and storage, it is easy to release chlorine and form hydrogen chloride, which makes the ink more acidic and causes heavy corrosion to the production of printing plate rollers; (3) Benzene soluble inks can destroy the ozone layer and cause harm to the health and safety of workers in the process of use, and the residues left in packaged products will cause a certain degree of pollution to the food in the package under certain conditions. This kind of ink is tending to be eliminated. In Europe and some developed countries, regulations have been formulated to prohibit or control the use of this kind of ink

it is precisely because of the problems of benzene soluble inks that environmental friendly inks came into being. Using environment-friendly ink, it will not pollute the environment, do no harm to operators, and will not damage the food inside

environmental friendly inks that have been put on the market include:

1. Water based inks

water based inks are currently used in most flexographic packaging and printing at home and abroad. They are mainly made of water-soluble resins, organic pigments, solvents and related additives through compound grinding. Water soluble resin is the binder of water-based ink. In China, water-soluble acrylic modified resin is often used as the binder. Its heat resistance, weather resistance, chemical resistance, pollution resistance and gloss have significant advantages. Whether it is directly dispersed to cause impact phenomenon dissolution or the synthesis of high molecular lotion, it shows excellent performance. Water-based ink does not contain volatile organic solvents, which can not only reduce the toxicity of printing residue, And it can prevent fire caused by static electricity in contact with 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. UV curable ink

UV curable ink refers to an ink that is cured by the crosslinking reaction of the binder in the ink under the irradiation of a certain wavelength of UV light, which changes from liquid to solid. Before the binder dissolves, the macromolecular prepolymer firmly forms an ink film. UV curing ink is mainly used for flexible printing of soft substrate. It is composed of prepolymer, reaction diluent, pigment, additive, photoinitiator/composite. Among them, the choice of reactive diluent has an impact on the migration reaction in the ink formula; Additives adjust the performance of the ink (printability, ink migration, substrate wetting, friction coefficient, wear resistance, pigment dispersion and stability) and the smell of the print; It is required that the spectral range of UV absorption of pigments should be as small as possible. Ideal pigments should have the characteristics of good dispersion, good leveling, strong coloring power, small UV absorption under light irradiation, and no harm to polymerization reaction. When using UV curing ink for printing, attention should be paid to the inhibition of polymerization, surface tension and wetting, the correlation between ink viscosity and humidity, and the expansion of printing plate; Due to the poor adhesion of the ink to the plastic, it is necessary to do flame treatment or corona discharge treatment on the printed plastic 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 penetration to solid components such as pigments and fillers. There will be no ink absorption hindered by pigments or fillers. The drying inside the film will not be affected by the development of 5g R & D and industrialization driven by ink

eb inks are mainly composed of pigments, binders, auxiliaries, etc. because the curing of inks is achieved by electron beams, there are specific requirements for the selection of binders. Its main components are acrylic resins and active monomers involved in the reaction. 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 development direction of high-speed, multi-color primary 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 imprinting brightness, and has the advantages of wear resistance and chemical erosion resistance, this technology has been rapidly promoted and applied, especially in the field of food packaging. The main difference between EB ink and liv curing ink is whether there is photoinitiator in the binder. When a certain amount of photoinitiator is added to EB ink, UV curing can also be carried out

4. Digital printing ink

digital printing technology has penetrated into the food packaging and printing industry with the increasing demand for personalized packaging. Using digital printing technology can achieve high enough image resolution, and can ideally reproduce the details of the image. In addition, digital printing technology can provide faster small batch services to meet its own needs and even the needs of the world. Dye inks for digital ink-jet printing, solid toners for electrostatic printing, and electronic liquid inks for digital offset printing. Toner is heated and melted by ceramic crystals and then fixed on the substrate. Most of the printing materials are foil, metal aluminum, pet (polyester), paper, etc., and are suitable for printing web paper. It is very important to choose a suitable fixing temperature for toner, because the best fixing temperature can well control the toner fixing process. The toner should be flexible to facilitate the folding of printing materials. Solvent resistance is also extremely important for electrostatic digital printing. Printing materials with poor solvent resistance will not be able to complete subsequent processes, such as glazing, film coating, etc

today, when environmental protection has become the theme of the printing field, food packaging is increasingly required to be printed with high quality and multi-color. Therefore, printing inks must adapt to the call of the development of the times and develop in the direction of benzene free and environmental protection