Printability of common food flexible packaging materials
PE film ink adhesion is poor, need to use electrical treatment to improve. The wetting tension is often used to evaluate the quality of corona treatment. Three kinds of LDPE, LLDPE film in 38 ~ 420mn / m, HDPE film in 40 ~ 44mn / m, commonly used in polyamide ink printing. LDPE film has low expansion strength, high elongation and difficult color registration. Therefore, when printing, the tension control should be small, and the tension should be constant. If it is multicolor overprint, in order to ensure the accuracy of overprint, it is best to use large roller printing machine. LDPE films soften when heated a little. It is easy to stretch and deform, so the film surface temperature should not exceed 55 ℃ when printing and drying. In order to prevent ink adhesion, the film temperature should be cooled to below 35 ℃ when rewinding.
Similar to PE, PP film has poor adhesion to ink, and corona treatment should be carried out before printing. The wetting tension of PP film is 10 ~ 14mn / m. Commonly used polyamide ink, chlorinated polypropylene ink (composite) printing. When using polyamide ink to print PP film, the ink adhesion is low, after about one day aging, it shows good adhesion, and if polyurethane adhesive composite film is used at the same time, the failure of low peeling force will appear.
PET film is not easy to stretch, and its tension control requirement is lower than that of PE film. It is often printed by inner printing process and combined with CPP to make cooking bag. PET film has good insulation and is easy to generate static electricity in the printing process, and it is not easy to disappear. In serious cases, the film will be absorbed on the roller and cannot be printed. Therefore, in high-speed printing, the need to use electrostatic eliminator. The drying temperature of PET film can be controlled higher, but the film surface temperature should not exceed 85 ℃. During winding, the film should be cooled to room temperature or slightly higher than room temperature.
Printing methods of food packaging materials
Gravure and flexographic printing are mainly used in food flexible packaging printing, but there are many differences compared with general gravure printing and flexible printing used in publishing and commodity printing. For example: flexible packaging printing is to print on the surface of the roller like substrate. If it is a transparent film, you can see the pattern from the back. Sometimes you need to print a layer of white paint or use the inner printing process.
Inner printing is a special printing method that uses the reverse image printing plate to transfer the ink to the inner side of the transparent printing material, so as to display the positive image text on the front of the printed object. Compared with the surface printed matter, the inner printed matter is bright, beautiful, bright colored, non fading, moisture-proof and wear-resistant; and because the ink layer is sandwiched between the two films after the inner printing, it will not pollute the packaging materials.
The printing color sequence of inner printing process is opposite to that of ordinary surface printing. For example, ordinary printing first prints the background color, while the inner printing is the last. Inner printing is a unique process of plastic composite packaging printing, which has been diversified, multifunctional and serialized in printing equipment. Such as the introduction of various models of plastic packaging gravure printing production line, blow molding, printing, compounding, cutting, bag making and other processes linked together.
The second is to use flexographic printing machine to print plastic film. Flexographic printing machine and dry laminating machine constitute the production line.
Composite methods of food packaging materials
Soft packaging materials generally do not use a single material, but composite film. The main composite methods are as follows:

① Wet compound method. A layer of water-soluble adhesive was coated on the surface of the substrate (plastic film, aluminum foil), and then it was compounded with other materials (paper and cellophane) by pressing roller, and then dried by hot drying channel to form composite film. This method is suitable for packaging dry food.

② Dry compound method. Firstly, the solvent based adhesive is evenly coated on the substrate, and then sent to the hot drying channel to fully volatilize the solvent, and then it is immediately compounded with another layer of film. For example, polypropylene film (OPP) is usually compounded with other materials by dry composite process after printing. The typical structures are: Biaxially oriented polypropylene film (BOPP, 12 μ m), aluminum foil (AIU, 9 μ m) and unidirectional polypropylene film (CPP, 70 μ m). The process is that the solvent type "dry adhesive powder" is evenly coated on the base material by roller coating device, and then sent to the hot drying channel to fully volatilize the solvent, and then the composite roller is used to composite with another layer of film.
③ Extrusion compound method. The curtain like melt polyethylene extruded from the slit of T casting mould is pressed by clamping roller and salivated on paper or film for polyethylene coating, or other films are supplied from the second feeding part, and polyethylene is used as bonding layer.
④ Hot melt composite method. Polyethylene acrylate copolymer, vinyl acid ethylene copolymer and paraffin wax are heated and melted together, then coated on the substrate, and then compounded with other composite materials and then cooled.
⑤ Multi layer extrusion compound method. A variety of different properties of plastic resin through a number of extruders, extruded into the mold composite film. This process is suitable for food packaging with longer shelf life without adhesive and organic solvent, and without odor and harmful solvent penetration. If the general structure of LLDPE / PP / LLDPE has good transparency, the thickness is generally 50 ~ 60 μ m, if the shelf life is longer. More than five layers of high barrier coextrusion films are needed, and the intermediate layers are high barrier materials PA, pet and EVOH.
Dongguan Beite packaging materials Co., Ltd. - located in Dongguan City, the world's manufacturing city, is a subsidiary of Beite packaging (China) Co., Ltd., with a plant area of 6000 square meters. It is a flexible packaging enterprise integrating R & D, production and sales. It has a complete set of domestic advanced production equipment, a scientific and humanized management system and a group of experienced technical personnel For backing, to provide customers with quality products and first-class service.
The company produces composite bags, roll film, fruit bags, aluminum foil bags, suction mouth bags, self-supporting bags, zipper bags, anti-static bags, special-shaped bags, etc., which are suitable for the internal and external packaging of food, daily chemicals, electronics, toys, medicine, cosmetics, industrial products and other industries.
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