Dry composite method
The dry composite method uses various sheets or films as a substrate, and a layer of adhesive is applied on the surface of the substrate by a gravure roll, dried and tackified by a drying tunnel, and then laminated on the composite roll. . This is currently the most commonly used method for producing composite membranes in China. The dry composite is characterized by wide adaptability and selection of suitable adhesives. Any sheet or film can be compounded, such as PE film, PP film, PET film, PA film, etc. The dry composite method has high composite strength and fast composite speed, but the dry compounding cost is high, and since the amount of the binder is generally 2.5 to 5 (g·m-2) (dry solid amount), there is solvent residue and environment. Pollution problems exist.
The process of the coating compounding method is relatively simple, and a barrier resin which is difficult to be separately processed into a film, such as PVA, PVDC, or the like, can be applied by coating. The melting temperature of PVC is 220 to 240 ° C, and the decomposition temperature is 200 ° C. To form a film, it is necessary to add a plasticizer and a stabilizer to increase the thermal decomposition temperature and lower the melting temperature. PVA is water-soluble. In practical use, a mixture of water and ethanol is used as a solvent, and a PVA having a thickness of 4 to 6 μm is coated on a PE or PP film. Since PVA has poor water resistance, it can be added in a PVA solution. The combination agent improves the water resistance, and also improves the adhesion of PVA to PE and PP, and the primer can be omitted, which is convenient for bag making.
The PVA-coated PE or PP film can be dry-composited with other films to form a composite film coated with PVA/PE (or PP)/LDPE structure. The film has good barrier properties and the vacuuming effect is better than PA/LDPE. Better, the cost is lower. The PVDC used for coating is a copolymer of emulsion polymerization of vinylidene chloride and acrylate monomer. After adding suitable solvents and additives, it is coated on cellophane, BOPP, nylon and polyester to make it have good resistance. Wet gas barrier performance and heat sealing performance, the biggest problem with PVDC is its safety and hygiene. It is generally considered that the monomer content should be less than 1×10-6.