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make plastic filmHow to solve the unavoidable crystal point problem?

As we all know, crystal point is a common problem for film manufacturers. For the transparent plastic bag, the crystal point obviously affects the appearance of the transparent plastic bag. For plastic bags that require high printing quality, especially for large-area plastic bag printing, the”White dot”Waste and defective products are a large proportion of the loss in the industrial production process of plastic bags. Therefore, controlling the generation of crystal points and eliminating the causes of crystal points is an important process link to improve the technical level of the plastic bag industry.1, what is crystal pointThe crystal point is actually”overpolymer”,which is:”crystal point”The molecular weight of the site polymer is higher than that of the surrounding same polymer. Due to the high molecular weight, the crystal site polymer has a higher melting point#FormatStrongID_2#When melted, the melt has a relatively high viscosity. The polymer at the crystal point cannot be uniformly dispersed and mixed with the surrounding polymer of the same kind during film blowing or casting, and solidifies before the surrounding polymer of the same kind after the melt is blown or cast into a film. Therefore, forming”arrow-shaped”or”spherical”A coagulation of excess polymer, customarily called”crystal point”.2.The reason for the formation of crystal pointsmaterial reason(1)Residual catalyst in polymer ;(2)Polymer melt sticks to production equipment(Including polymerization equipment and blown film equipment)metal surfaces, at high temperatures, residual ;(3)The catalyst continues to catalyze the polymerization of the polymer, thus forming an overpolymer ;The oxygen contained in the polymer will also cause the polymer melt to produce crystal points(Adding a certain amount of antioxidants can prevent the generation of oxygen on the crystal point).Process reasons(1)Crystal points created by the polymerization process. Different polymerization equipment and processes have different effects on the formation of crystal points. For example: some famous factory raw materials, due to the high production technology, the residual catalyst content in the polymer is low, and the equipment structure is good, so the raw materials themselves contain few crystal points. However, some raw materials with poor quality have many crystal points in the raw materials due to production technology and equipment problems.(2)The crystal point caused by the process. For example: the film prepared by good molding equipment has few crystal points. The film made by poor equipment has many crystal points.3.Methods for reducing or substantially eliminating crystalline pointsIn summary, there are two main ways to eliminate crystal points in the film blowing process:(1)Improve the filter fineness of processing equipment(For example: change the filter to120eyes, or even150target-for ultrathin films).(2)In the production process, surface lubricants are added to prevent the polymer melt being processed from sticking to the surface of the blown film equipment.In terms of production process, although the use of a finer filter screen can filter out most of the primary crystal points in the polymer, it can also filter out the crystals caused by the polymer sticking to the surface of the screw in the screw and barrel of the equipment. point, but the problem is that the back pressure of the equipment is therefore increased, and for some old molding equipment


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