Problems that should be paid attention to in the precipitation of PVC protective film

In the process of producing stretched films, precipitation sometimes occurs, that is, a layer of hoarfrost is produced on the surface of the film or on the calender roll (or traction roll), which in severe cases will affect the use of the film, and even make the film scrapped (such as light boxes). The film will affect the ink absorption of the light box cloth due to surface precipitation). From the production situation, the precipitated materials are mainly lubricants, powder stabilizers and calcium carbonate.

In the process of producing PVC calendered film, a certain amount of lubricant is added to the plastic in order to make the surface of the product smooth and beautiful, and also to improve the flow properties of the plastic melt and reduce and avoid the adhesion and friction to the equipment. However, when the lubricant is used improperly and exceeds its compatibility limit, it is easy to precipitate on the surface of the product, which is commonly referred to as blooming, which affects the appearance of the product and also affects the ink absorption of the inkjet advertising cloth; the amount of lubricant is too small and No lubrication effect, the amount of lubricant is generally less than 1%. Commonly used lubricants are stearic acid, polyethylene wax, etc.

The processing temperature of PVC is very similar to its decomposition temperature. When processed at 160~200 °C, severe thermal degradation will occur, the product will be discolored, and its performance will deteriorate. Therefore, in the processing of PVC, heat stabilizers must be added. Many heat stabilizers not only have a stabilizing effect, but also have a certain lubricating effect, such as (powder) barium stearate and cadmium stearate. If the compatibility of these materials is poor, frost, migration and other phenomena will occur. In order to improve the mechanical properties of the product and reduce the cost and the unit consumption of the resin, an appropriate amount of filler material is added. Adding an appropriate amount of additives will reduce the linear expansion coefficient of the plastic and the molding shrinkage rate of the product, and can improve the heat resistance, flame retardancy and strength of the plastic. The amount of additives should be appropriate, too much will precipitate from the surface of the film. Increasing the fineness of the additive can increase the dosage of the additive, for example, the amount of superfine calcium carbonate is more than that of ordinary calcium carbonate. Calcium carbonate can also be treated with a coupling agent to increase the tightness of the combination of calcium carbonate and PVC materials.