Soft Plastic Packaging Q&A (2)

What are the performance characteristics of flow film, blown film, and oriented film? How to apply in composite film?
A: The cast film is produced by the solvent drooling method or the extrusion drool method. Since it is not stretched in the production process, it has the following characteristics: (1) The balance of longitudinal and transverse properties of the film, excellent heat sealability (2) The roving film has good transparency. After extruding from the open mouth film, it directly flows on the chill roll and cools rapidly, which improves the transparency of the rogue film. (3) The roving film has no internal stress and is used as cooking. When the bag heat-sealing the inner layer material, the shrinkage rate is the minimum; (4) The flow film is the smallest among the three types of film in terms of mechanical physical properties; (5) The film produced by the rogue method is faster than the inflation method, and can produce extremely thin type Film.
The inflation film is a tubular film that is extruded from a circular die of an extruder and is blown with compressed air. The performance of the film is between the flow film and the orientation film, and the film is blown. The performance is not only related to the type of resin, the relative molecular mass size and distribution, and the degree of crystallinity, but also has a lot to do with the process parameters of the blown film production, especially the temperature, the blow-up ratio, the traction ratio, the dew point line height, etc. Its performance characteristics are: (1) the inflation method is limited by the cooling effect, the production line speed is low, generally 30 ~ 60m/min, and pp in the blowing, only the use of blowing water cooling can have good transparency Sex, otherwise pp blown film transparency is poor; (2) blown film due to the film by the compressed air lateral inflation and pulling the longitudinal pull of the roller, so there are some molecules in both vertical and horizontal orientation, crystalline polymer oriented by stretching After that, the strength is increased, so the mechanical and physical properties of the blown film are larger than that of the cast film, and because of the small degree of orientation, it is lower than the oriented film; (3) The blown film can be heat-sealed, but the heat sealability is poorer than that of the cast film; 4) Blown film Internal stress, therefore, there are various problems caused by internal stress, such as: heat shrinkage rate, especially when cooking bag heat sealing inner material, the size of the bag after cooking, the greater the contraction; (5) blowing The imbalance between the longitudinal and transverse properties of the swelled film is relatively large. Due to unbalanced blow-up ratio and traction ratio, longitudinal or transverse tearing tends to occur, and the film strength is greatly reduced.
The orientation film is used to extrude a thick sheet from an open die using an extruder or quench it into an amorphous molecule by extruding a cylindrical thick film from a circular die, and then heated to a high elasticity state. Vertical and horizontal stretch orientation, heat-set film. This stretching technology was developed in the 1970s. Due to the stretching orientation, the mechanical physical strength of the film is greatly improved, the crystallinity of the polymer is improved, and the crystals are finely divided. Therefore, the transparency and the barrier property are improved. Both have greater improvements. Its performance characteristics are: (1) has the greatest mechanical strength, a high degree of crystallinity, the molecular orientation of the extrusion promoted the increase in the degree of crystallinity in the highly elastic state and subtle, mechanical strength is the highest of the three membranes; (2 ) Transparency and barrier properties (gas barrier, moisture barrier) are the best among the three films; (3) The heat sealability is lost due to the highly crystalline and oriented molecules, and the biaxially stretched film does not have heat sealability. Extrusion of the composite method produces heat sealability, but this is not a single layer, but a double film; the secondary tear strength of the oriented film is poor, as long as there is a slight gap, you can tear easily. It is the two major drawbacks of the oriented film. Oriented film is a commonly used surface layer material in composite films because of its high strength and good transparency and gloss. After printing, the prints are beautiful and vivid. Therefore, it is very suitable as a surface layer material. The commonly used surface orientation films are BOPP, BOPET, BOPA6.
It should be pointed out that both rogue and blown films have heat-sealing properties. Some people reject the use of the blown film because its heat-sealing property is not as good as that of the rogue film. The comparison we make refers to the same kind of plastic film of the same type, with different The comparison between the films produced by the method is relatively speaking. Due to the fact that the film blowing unit is commonly used in China, there are few rogue machines and basically all of them are imported equipment. For this reason, blown films are mostly used as the inner seal layer. Of course, some problems that may arise during use should be given sufficient attention.
Second, the use of BOPP12/LDPE30 dry composite film packaging mature lard, hot day 1 month mature lard on the mold deterioration, and the two-layer film delamination, why? What kind of structure should be used better?
Answer: Cooked lard is a kind of cooking oil containing fatty acids. LDPE has poor oil resistance. It penetrates LDPE into dry compound adhesives, making polyurethane adhesives lose their adhesive force and peel off. Therefore, it is not suitable. Used to pack more oily foods. Both BOPP and LDPE are plastic films with high oxygen permeability. Using this structural material to package cooked lard, the oxygen content in the bag is large, and it easily deteriorates due to oxidation of fat on hot days. Should use a good barrier and can be filled with nitrogen packaging, have a longer shelf life, such as KOPET14/CPP70 after nitrogen filling is more appropriate. Because KOPET has good strength, rigidity and barrier properties, CPP has good resistance to grease, N2 gas can prevent nitriding and prevent bacteria from multiplying. (Zhou Xiangxing)