Surface and inside printing of the hottest plastic

Surface printing and internal printing of plastic film

plastic includes plastic film and plastic products. Plastic film printing includes plate making, blow molding, corona treatment, printing, compounding, slitting, heat sealing, bag making and other processes; Printing of plastic products includes plate making, flame treatment, printing, etc. Plastic printing is not a process method, but a printing type divided by substrate

characteristics of plastic printing

the substrate of plastic printing is plastic film and plastic products. Its molecular structure contains polar substances, which has good chemical stability and can resist the corrosion of most acids and alkalis. It is insoluble in general solvents at room temperature, and antioxidant is added in the production process. Due to the poor affinity between the plastic substrate and the ink, the ink is not easy to dry after printing. At the same time, the plastic substrate does not have the porosity of the paper surface and cannot absorb the ink binder. Therefore, the plastic substrate must be treated before printing to make it compatible with the ink, absorb the ink well during printing, and the ink layer does not separate from the substrate after printing. Plastic printing ink is different from paper ink, and the two cannot be mixed

characteristics of plastic printing inks

in order to meet the requirements of plastic substrates for inks, plastic printing inks are mainly composed of synthetic resins, organic solvents and pigments. After full dispersion and grinding, they have good colloidal fluid properties. Plastic printing inks are volatile inks, which have the characteristics of good printing adaptability, strong adhesion fastness, fast drying, etc

the key of printing ink for plastic film is the adhesion between ink and plastic film, which is closely related to the choice of binder

there are several methods to choose the binder of ink for plastic film:

1. The use of the same resin as graphene will continue to expand the scope of the substrate in China in the future, or the resin that can be mutually dissolved with the substrate material. After the substrate is inked, due to the action of solvent, it will dissolve and adhere to each other at the interface between the ink and the substrate

2. Use ink binders that can react chemically with the substrate

3. Use binders that can form a surface facial mask layer similar to the substrate

4. Use binders with basically the same polarity as the substrate

therefore, the ink used for plastic printing varies according to the type of substrate material. Generally, the binder that can be miscible with the printed plastic is selected. For example, vinyl copolymer is used as the binder for polyolefin plastic film ink. Plastic film is generally printed by rotary intaglio printing, and the ink is solvent ink. This kind of ink can meet the needs of high-speed printing, but its volatile organic solvents are also quite large, and the environmental pollution is also quite serious. The plastic film can also be printed with silk, and its ink uses the dispersion synthesized in the aqueous medium as the binder. Although the problem of solvent pollution is avoided, the printing quality is not very good. In addition, plastic film can also be printed by flexographic printing

performance and function of various components of ink

printing ink is a paste colloid formed by the uniform mixing of pigments, binders, fillers and other components. As a viscous fluid, ink has different properties due to its different varieties, that is, thick and thin; The viscosity is different, and the drying speed is also different. Therefore, a correct understanding and understanding of the role of ink components in ink is of great significance for accurately adjusting ink characteristics and improving product printing quality

1. The role of pigments in ink

pigments include pigments and dyes. The colored materials used in printing inks are usually pigments. There are also some dyes, which are colored substances with very fine particles. Pigments are insoluble in water and binder, and most of them are in suspension in solution; Dyes are generally soluble in binders. The relative density, transparency, heat resistance, light resistance and chemical resistance of inks are all related to pigments. Its color determines the hue of ink; Its dosage determines the ink concentration; Its use affects the dryness of the ink to a certain extent, especially the ink based on oxidation polymerization drying

2. The role of binder in ink

binder is a fluid with certain viscosity and viscosity. Its role is multifaceted. As the carrier of pigments, it plays a role in mixing and connecting solid particles such as powdered pigments, and making the adhesive pigments finally adhere to prints. The quality of binder will directly affect its gloss, wear resistance, viscosity and fluidity

3. Effect of additives

the use of additives will be more effective for printing. Commonly used additives include diluents, additives, debonding agents, anti sticking agents, inking agents, etc. Therefore, the good printability and strong adhesion and dispersion of printing ink are inseparable from additives

surface printing and inside printing

the so-called surface printing refers to the process of printing pictures and texts on the surface of finished products after printing on plastic film and post processes such as bag making

the surface printed plastic film requires good ink adhesion and considerable wear resistance. The way to eliminate it is to start the oil pump for sun resistance, frost resistance and temperature resistance. In recent years, some ink merchants have developed special alcohol soluble surface printing inks that can withstand high temperature cooking. For example, Yeshi ink (Shanghai) company has successfully developed gyp-l series surface printing high temperature resistant inks, which are very excellent in terms of wear resistance, sun resistance, adhesion and color gloss

the surface printing range is mostly based on polyolefin films such as polyethylene and polypropylene. Polyolefin films are divided into treated and untreated, and inks are also divided into three types: special for treatment, special for untreated and common for both. Untreated special ink is an ink with cyclized rubber as the main binder. Its gloss, heat resistance, dissolution and sealing properties are good. It is mainly suitable for packaging such as pastry. Due to the shortcomings of slow printing speed, residual solvents, poor oil resistance and so on, there is a tendency to reduce the use at present. Polyamide resin and nitrocellulose are the main binders of special ink for treatment, which has good heat resistance, oil resistance and drug resistance. Plastic surface printing inks other than polyolefins include styrene inks with acrylic resin as the main binder, and vinyl chloride inks with salt acetic acid resin as the main binder, but they all require high gloss and stable printing effect

inside printing refers to the printing method of using the printing plate of anti image and text to transfer the ink to the inner side of the transparent substrate, so as to show the positive image and text on the front of the substrate. Its advantages are bright colors, no fading, no fading, moisture-proof and wear-resistant. After printing, the printing ink is coated with curing agent (AC agent) or adhesive, which can be bonded with sealing film or aluminum foil. With the development of composite packaging materials, many kinds of inks have entered the market. At present, the representative inks are mainly high-performance general-purpose inks with alkyl resin as binder and polypropylene inks with the largest amount of composite packaging film. These inks have good high-speed printing adaptability, good layer reproducibility and lamination processing adaptability

table printing is often printed in reverse order, such as white ink in the first place and black ink in the last unit. The inner printing is just the opposite, that is, the order of chromatic registration of ordinary two-sided printing is reversed. For example, the bottom color of ordinary surface printing is printed first, and the bottom color of inner printing is printed last. Of course, special printing should be treated according to its situation

difference between inner printing and surface printing adding solvent

the role of solvent is to dilute the viscosity of ink, make its ink leveling and dispersity more excellent, and adjust the evaporation rate to make it more suitable for printing. Diluent is determined by the temperature, humidity and driving speed of the workshop. Mixed solvents are often used to add diluents. Mixed solvents are better than single solvents. Whether it is surface printing or internal printing, the water content in the added solvent must not exceed the standard (not more than 2%), otherwise it will affect the printability, and the ink will appear thickening, coarsening, precipitation, decomposition and other adverse phenomena. Benzene and ester are the true solvents of chlorinated polypropylene inks, and the proportion of dosage is not limited. Isopropanol is a pseudosolvent. Isopropanol is added to reduce the surface tension of ink, prevent static electricity and improve the transferability of ink. However, it is not allowed to change the switch to fast reverse gear when adding. Generally, it is mixed, and the amount should be controlled at 5 ~ 15%. In polyamide ink, benzene and alcohol are real solvents, while ethylamine acetate is pseudosolvent. When added together, the amount of ethyl acetate should not exceed 20%, otherwise the ink layer is easy to turn white and has no color

(Chen Quandong)

source: what is the real situation of China packaging