Common problems and treatment analysis in the production process of PVC board

Compared with other plastic extruded products, the production of skinned low-foaming PVC plastic products requires not only good plasticization and molding under a certain melting pressure, but also the size, number and uniformity of the foaming holes, as well as the thickness and hardness of the skin. , brightness, smoothness, etc. have corresponding technical requirements. The quality of the foam is not only related to the formula and raw materials, but also directly affected by the shear performance of the extruder screw, melt pressure, temperature, extrusion (traction) speed, die lip clearance, shaping template clearance, cooling water temperature, etc. factors and constraints. Therefore, compared with other extruded plastic products, skinned foamed plastic products have certain technical difficulties, and there are many unsolved problems in practice and theory that are worthy of research and solution by industry technicians.


1. Production technology and characteristics of skinned foamed PVC plastic sheet

The technical difficulty in the production of skinned foamed PVC plastic products is foaming. Foaming is the result of the rise and expansion of the melt viscosity, the gas pressure generated by the blowing agent and the atmospheric pressure.

The foaming process generally goes through 3 stages:

(1) The foaming gas dissolves into the plasticized and uniform mixture melt at a certain temperature and pressure in the extruder and reaches a saturated state to form a bubble nucleus;

(2) The melt is extruded from the die, and with the release of pressure, the supersaturated dissolved gas nucleates, expands, and precipitates, forming uniform and dense cells in the gap between the shaping templates;

(3) Under the cooling effect of the shaping device, the foamed product is solidified and shaped. High-quality skinned foamed PVC plastic products have many and dense cells, small and uniform, density and thickness meet the requirements, smooth appearance, high hardness and brightness.
2. Factors affecting the quality of skinned foamed PVC plastic sheets

The main raw materials that directly affect the quality of plastic cell structure are foaming agent and foaming coordinator. Stabilizers, lubricants, calcium carbonate and other raw materials and extrusion process control have a certain role in promoting and coordinating the foaming quality. Since the plasticizing temperature of the melt in the extrusion production process of the foamed product must be slightly lower than the decomposition temperature of the blowing agent, the lower the average degree of polymerization of the PVC resin, the lower the processing temperature required for melt plasticizing. In order to obtain fully foamed foamed plastic products, the viscosity of the resin used should not be too high. At the same time, compared with other foamed products, the skinned foamed plastic sheet has a wider cross-section, and it must be distributed to a width of about 1.3 m from the extruder head into the die. In order to facilitate the dispersion and expansion of air bubbles, The pressure of the entire cross-section of the plate should be coordinated, and the fluidity of the melt is required to be high, and the resin used for it is generally small in molecular weight, such as SC-7 or SC-8 type loose resin with suspension method is more suitable.