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Further Improvement Of The Heat Seal Strength
May 28, 2018

The heat-sealing strength of the heat-sealing biaxially oriented polypropylene pearl film in food bag production should not be less than 15 mm. Tests have shown that the heat seal strength has a significant dependence on the thickness of the surface layer. It is advantageous to obtain a heat seal strength of 15 mm and a thickness of the surface layer in the range of 1 to 1.1 μm, due to the following points: Further increase in the thickness of the surface layer leads to a further increase in the heat seal strength. As the thickness of the surface layer increases, the cost of the co-polypropylene is higher than that of the homopolypropylene. As the thickness of the surface layer increases, the film strength decreases even if the total thickness does not change. Preheating and longitudinal stretching, setting conditions are: After four groups of preheating rollers with a temperature gradient of 115 to 130 degrees Celsius, the temperature of the blank film is raised to a high elasticity state of the entire film, and then the two drawing rolls at a temperature of 110 degrees Celsius A longitudinal stretch of 4.5 to 5 times was performed, the blank film was voided during stretching, and the density was reduced to 0.7 grams per cubic centimeter.

The two-layer co-extruded heat-shrinkable film that is produced by stretching at high temperature in the food bag production has poor low-temperature heat shrinkability and its shrinkage performance is quite low even at high temperatures, so it should be emphasized that the density of LLDPE should be 0.91 g per Less than cubic centimeters, order food packaging bags, Vicat temperature below 80 degrees Celsius. If the melting point of the polypropylene in the intermediate layer exceeds 150 degrees Celsius, not only the three-layer co-extruded heat-shrinkable film obtained has poor low-temperature shrinkability, but also high temperature shrinkage, and the narrow range of the heat shrinkage temperature is when the melting point is lower than 135 degrees Celsius. The resulting co-extruded heat-shrinkable film does not have a further increase in low-temperature shrinkage properties, but the heat resistance decreases, and the shrinkage temperature range narrows. In addition, when the Vicat temperature of the polypropylene of the intermediate layer exceeds 110 degrees Celsius, the low-temperature stretching of the raw film is difficult, and drawing at a high temperature is required, and the resulting three-layer co-extruded heat-shrinkable film is deteriorated in low-temperature shrinkability.

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