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In the same product of the printed ziplock bag, the shrinkage rate of the portion with a larger wall thickness is always greater than the portion with a small wall thickness. The shrinkage of the hem-sealed ziplock bag is always smaller than the unobstructed direction, and the shrinkage near the insert portion is smaller than the shrinkage away from the insert portion. There is also a significant difference between the flow direction of the printed ziplock bag and the contraction perpendicular to the flow direction, generally the shrinkage rate in the flow direction is greater than the shrinkage rate perpendicular to the flow direction.
Increasing the pressure can result in an increase in the density of the hem pockets and a reduction in shrinkage. Increasing the temperature of the material will cause the volume of the product to expand and the material pressed into the cavity to decrease, so that the shrinkage rate will increase; but the increase in the temperature of the material will reduce the viscosity, but it will facilitate the transfer of pressure into the cavity and shrinkage. The rate is reduced and the final shrinkage depends on the combined effect of the above two effects. Plastics whose viscosity is sensitive to temperature changes have a large effect on the latter effect, resulting in a decrease in shrinkage: plastics whose viscosity is not sensitive to temperature changes have a large influence on the former effect, resulting in an increase in shrinkage.
Increasing the temperature of the embossed bag from the hem, generally increases the shrinkage, especially for crystalline plastics. Extending the dwell time can reduce the shrinkage. However, once the gate has been closed, extending the dwell time will no longer affect the shrinkage.
The self-sealing bag has good processing performance and can adapt to the forming, filling and sealing process of high-speed automatic packaging machinery. It has good transparency, which makes the product have display effect or opacity, which can prevent the goods from being damaged by light.
At the same time, the printed ziplock bag also has good physical and mechanical properties, anti-penetration, tear resistance, anti-extrusion and folding resistance. The printed ziplock bag also has good product flatness and easy to package. Good packaging performance and printing performance, easy to decorate and The printing of the text description. The film should be soft in texture, easy to form and can be wound up for easy sealing and bonding.
