Printing suitability, printing method and compounding method of Food Boxes For Sushi materials

Printing suitability, printing method and compounding method of Food Boxes For Sushi materials

The printing suitability, printing method and compounding method of Food Boxes For Sushi materials are the necessary knowledge for the employees of the flexible packaging factory. This article is detailed for reference.

1. Printing suitability of common Food Boxes For Sushi materials

The adhesion of PE film ink is poor and needs to be improved by electric treatment. The index of wetting tension is often used to identify the quality of corona treatment. Generally, LDPE and LLDPE films are 38~420mN/m, and HDPE films are preferably 40~44mN/m. Polyamide inks are commonly used for printing.

The expansion strength of LDPE film is low, the tensile elongation is large, and the 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. LDPE film will soften after a small amount of heat. It is easy to be stretched and deformed. When printing and drying, the surface temperature of the film should not exceed 55 °C. In order to prevent the ink from sticking, the film temperature should be cooled to below 35℃ during winding.

Like PE, PP film has poor adhesion to ink, and corona treatment should be done before printing. Its wetting tension is preferably 10~14mN/m. Commonly used polyamide ink, chlorinated polypropylene ink (composite) printing. When polyamide ink is used to print PP film, the ink adhesion is low, and good adhesion is exhibited after about one day of aging, while if a polyurethane-based adhesive composite film is used at the same time, there will be a failure of small peeling force.

PET film is not easy to stretch, and its tension control requirements are lower than that of PE film. It is often printed by lining process and combined with CPP for cooking bags. PET film has good insulation, and static electricity is easily generated during the printing process, 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. The drying temperature of PET film can be controlled higher, but its film surface temperature should not exceed 85 ℃. When reeling, the film should cool to room temperature or slightly above.

2. Printing method of food packaging materials

The printing of Food Boxes For Sushi 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.

Inside 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. Compared with the surface printed matter, the inner printed matter is brighter and more beautiful, brighter in color, not fading, and moisture-proof and wear-resistant; and after the inner printing is compounded, the ink layer is sandwiched between the two layers of film, so it will not pollute 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.

3. Composite way of food packaging materials

Flexible packaging materials generally do not use a single material, but mainly composite films. The main composite methods are as follows:

①Wet composite method

Coat a layer of water-soluble adhesive on the surface of the substrate (plastic film, aluminum foil), compound it with other materials (paper, cellophane) through a pressing roller, and then dry it through a hot drying tunnel to become 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. For example, oriented polypropylene film (OPP) is generally composited with other materials by dry lamination process after printing. The typical structure is: biaxially oriented polypropylene film (BOPP, 12μm), aluminum foil (AIU, 9μm) and unidirectional Stretch polypropylene film (CPP, 70 μm). The process is to use a roller coating device to evenly coat the solvent-based "dry adhesive powder" on the base material, and then send it into a hot drying tunnel to fully volatilize the solvent, and then use a composite roller to composite with another layer of film.

③Extrusion compound method

The curtain-shaped molten polyethylene extruded from the slit of the T casting mold is pressed by the pinch roll, and drooled onto the paper or film, and polyethylene coating is carried out, or other films are supplied from the second paper feeding part, and the polyethylene is used as the adhesive. Bonding layers.

④Hot-melt composite method

It is made by heating and melting polyethylene-acrylate copolymer, ethylene acid-ethylene copolymer and paraffin, and then coating it on the substrate, immediately compounding with other composite materials and then cooling.

⑤Multilayer extrusion compounding method

A variety of plastic resins with different properties are passed through multiple extruders and extruded into the 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. For example, the general structure of LLDPE/PP/LLDPE has good transparency, and the thickness is generally 50~60μm, if the shelf life is longer. More than five layers of high-barrier co-extruded film are required, and the middle layer is high-barrier material PA, PET and EVOH.

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