Printing suitability of common food packaging bag materialsPEThe film ink adhesion is poor and needs to be treated with electricity to improve. The index of wetting tension is often used to identify the quality of corona treatment. threeLDPE,LLDPEfilm in38~420mN/m,HDPEfilm in40~44mN/mPreferably, polyamide inks are commonly used for printing.LDPEThe expansion strength of the film is low, the tensile elongation is large, and the registration of color registration is difficult. Therefore, the tension control should be small during printing, and the tension should be constant everywhere. If it is multi-color overprinting, in order to ensure the overprinting accuracy, it is best to use a large roller type printing machine.LDPEThe film softens with a small amount of heat. It is very easy to stretch and deform, so when printing and drying, the surface temperature of the film should not exceed55°C. To prevent ink sticking, the film temperature should be cooled to35℃ or lower.andPEsame,PPThe adhesion of the film to the ink is poor, and corona treatment should be performed before printing, and its wetting tension is in the10~14mN/mbetter. Commonly used polyamide ink, chlorinated polypropylene ink(composite)print. Printed with polyamide inksPPWhen the film is used as a film, the ink adhesion is low, and good adhesion occurs after about one day of aging. However, if a polyurethane-based adhesive composite film is used at the same time, there will be a failure of small peeling force. PETThe film is not easy to stretch, and the tension control requires morePEThe film is low, often printed by the inner printing process, and theCPPCompound for cooking bags.PETThe film has good insulation, and during the printing process, static electricity is easily generated, and it is not easy to disappear. In severe cases, the film will also be sucked on the roller and cannot be printed. Therefore, in high-speed printing, a static elimination device is required.PETThe drying temperature of the film can be controlled higher, but its film surface temperature should not exceed85°C. When reeling, the film should cool to room temperature or slightly above.Printing method of food packaging materialsFood flexible packaging printing is mainly gravure and flexographic printing, but there are many differences compared with general gravure and flexographic printing used in publishing and commodity printing. For example, flexible packaging printing is to print on the surface of a roll-shaped substrate. If it is a transparent film, the pattern can be seen from the back. Sometimes a layer of white paint needs to be added, or an inner printing process is used.Inner printing refers to a special printing method that uses a printing plate with reverse image text to transfer the ink to the inner side of the transparent printing material, so as to express the positive image text on the front of the printed object. The inner printed matter is brighter and more beautiful than the surface printed matter, with bright colors, no fading, and moisture-proof and wear-resistant.;And because of the composite processing after the lining, the ink layer is sandwiched between the two layers of films, so it will not contaminate the packaged items.The printing color sequence of the inner printing process is opposite to that of ordinary surface printing. For example, ordinary printing prints the base color first, and the inner printing is the last base color. Inner printing is a unique process for plastic composite packaging printing, and it has become diversified, multi-functional and serialized in printing equipment. For example, the introduced gravure printing production lines for plastic packaging of various modes have linked multiple processes such as blow molding, printing, compounding, slitting, and bag making.The second is to use a flexographic printing machine to print plastic films. Most of the flexographic printing machines and dry laminating machines form a production line.Composite way of food packaging bag materialsFood packaging bag materials generally do not use a single material, but mainly composite films. The main composite methods are as follows:①Wet compound method. on the substrate(Plastic film, aluminum foil)The surface is coated with a layer of water-soluble adhesive, which is passed through the pressure roller and other materials(paper, cellophane)composite, and then dried in a hot drying tunnel to form a composite film. This method is suitable for packaging dry food.②Dry compound method. First, the solvent-based adhesive is evenly coated on the substrate, and then sent to the hot drying tunnel to fully volatilize the solvent, and then immediately compound with another layer of film. such as stretched polypropylene film(OPP), After printing, the dry lamination process is generally used to compound with other materials. The typical structure is: biaxially oriented polypropylene film(BOPP,12μm), aluminum foil(AIU,9μm)and uniaxially oriented polypropylene film(CPP,70μm). The process is to use a roller coating device to coat the solvent-based”dry binder powder”It is evenly coated on the base material, and then sent to the hot drying tunnel to fully volatilize the solvent, and then composite with another layer of film with a composite roller.③ extrusion compound method. WillTCurtains of molten polyethylene extruded from a die slot, pressurized by pinch rolls, drooled onto paper or film, polyethylene coated, or2The other film is supplied to the paper feed part, and polyethylene is used as an adhesive layer for bonding.④ hot melt composite method. the polyethylene——Acrylate copolymer, vinyl acid——The ethylene copolymer and paraffin are heated and melted together, then coated on the substrate, immediately compounded with other composite materials and then cooled to make.⑤ Multi-layer extrusion compound method. A variety of plastic resins with different properties are passed through multiple extruders and extruded into a mold to form a composite film. This process does not require adhesives and organic solvents between layers, the film has no peculiar smell, and no penetration of harmful solvents, which is suitable for food packaging with a longer shelf life. as general structureLLDPE/PP/LLDPEGood transparency, average thickness50~60μm, if the shelf life is longer. More than five layers of high-barrier co-extruded films are required, and the middle layer is a high-barrier materialPA,PETandEVOH.
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