一、 Printing of food flexible packaging materials
① Printing method
Food flexible packaging printing is mainly gravure printing and flexographic printing, followed by the use of flexographic printing machine to print plastic film (flexographic printing machine and dry composite machine mostly form a production line), but there are many differences compared with general gravure printing and flexographic printing used in publishing and commodity printing. For example, flexible packaging printing is carried out on the surface of the roll-shaped substrate. If it is a transparent film, the pattern can be seen from the back, and sometimes a layer of white paint needs to be printed, or the inner printing process is used.
② Definition of internal printing process
Inner printing refers to a special printing method that uses the printing plate of the reverse image image to transfer the ink to the inner side of the transparent printing material, so as to display the positive image image on the front of the printed object.
③ Advantages of India
Compared with the surface printed products, the interior printed products have the advantages of bright and beautiful, bright color/fastness, moisture and wear resistance; After internal printing, the ink layer is sandwiched between two layers of film, which will not pollute the packaging.
二、 Composite of food flexible packaging materials
① Wet composite method
A layer of water-soluble adhesive is coated on the surface of the base material (plastic film, aluminum foil), which is compounded with other materials (paper, cellophane) through the pressure roller, and then dried into a composite film through the hot drying channel. This method is applicable to packaging dry food.
② Dry compound method
First, evenly coat the solvent-based adhesive on the substrate, and then send it into the hot drying channel to make the solvent fully volatilize, and then immediately compound with another layer of film. For example, the stretched polypropylene film (OPP) is generally compounded with other materials by dry composite process after internal printing. The typical structure is: biaxially oriented polypropylene film (BOPP, 12 μ m) Aluminum foil (AIU, 9 μ m) And unidirectionally stretched polypropylene film (CPP, 70 μ m)。 The process is to evenly coat the solvent-type "dry adhesive powder" on the base material with a roller coating device, and then send it into the hot drying channel to fully volatilize the solvent, and then compound it with another layer of film with a composite roller.
③ Extrusion compound method
The curtain-like molten polyethylene extruded from the slit of the T mold is pressurized by the clamping roller and salivated onto the paper or film for polyethylene coating, or other films are supplied from the second paper feeding part, and the polyethylene is bonded as a bonding layer.
④ Hot-melt composite method
Polyethylene-acrylate copolymer, vinyl acid-ethylene copolymer and paraffin are heated and melted together, then coated on the base material, immediately compounded with other composite materials and then cooled.
⑤ Multi-layer extrusion composite method
A variety of plastic resins with different properties are squeezed into the mold through multiple extruders to form a composite film. This process does not use adhesives and organic solvents between layers. The film has no peculiar smell and no harmful solvent penetration. It is suitable for food packaging with a longer shelf life. For example, the general structure LLDPE/PP/LLDPE has good transparency, and the thickness is generally 50-60 μ m. If the shelf life is longer, it is necessary to use more than five layers of high barrier co-extruded film, and the middle layer is high barrier material PA, PET and EVOH.
Post time: Mar-07-2023
