09
2021
-
11
Common Problems and Their Solutions in the PVC Sheet Production Process
Compared with other extruded plastic products, the production of skin‑formed, low‑foam PVC articles not only requires excellent plasticization and molding under a specified melt pressure, but also imposes specific technical requirements on the size, number, and uniformity of the foam cells, as well as on the skin layer’s thickness, hardness, gloss, and surface finish. The quality of the foamed structure depends not only on the formulation and raw materials, but is also directly influenced and constrained by factors such as the extruder screw’s shear performance, melt pressure, temperature, extrusion (traction) speed, die lip clearance, sizing‑die gap, and cooling‑water temperature. Consequently, skin‑formed foamed plastic products present greater technical challenges than conventional extruded plastics, leaving numerous unresolved issues—both practical and theoretical—that warrant further investigation and resolution by industry professionals.
Compared with other extruded plastic products, the production of skin‑formed, low‑foam PVC articles not only requires excellent plasticization and molding under a specified melt pressure, but also imposes specific technical requirements on the size, number, and uniformity of the foam cells, as well as on the skin layer’s thickness, hardness, gloss, and surface finish. The quality of the foamed structure depends not only on the formulation and raw materials, but is also directly influenced and constrained by factors such as the extruder screw’s shear performance, melt pressure, temperature, extrusion (traction) speed, die lip clearance, sizing‑die gap, and cooling‑water temperature. Consequently, skin‑formed foamed plastic products present greater technical challenges than conventional extruded plastics, leaving numerous unresolved issues—both practical and theoretical—that warrant further investigation and resolution by industry professionals.
1. Production Technology and Characteristics of Skin-Formed Foamed PVC Plastic Sheets
The primary technical challenge in producing skin‑foamed PVC plastic products is the foaming process itself. Foaming arises from the combined effects of increasing melt viscosity and expansion, as well as the pressure generated by the blowing agent and atmospheric pressure.
The foaming process typically proceeds through three stages:
(1) Under specific temperature and pressure conditions within the extruder, the foaming gas dissolves into the uniformly plasticized polymer melt until saturation is reached, thereby forming bubble nuclei.
(2) The melt is extruded through the die; as the pressure is relieved, supersaturated dissolved gases nucleate, expand, and precipitate, forming a uniform, densely packed cellular structure within the gap of the shaping template.
(3) Under the cooling action of the shaping device, the foamed product is cured and set into its final shape. High‑quality skin‑foamed PVC products are characterized by a dense, fine, and uniformly distributed cellular structure; dimensions that meet specified density and thickness requirements; a smooth surface; and high hardness and gloss.
2. Factors Affecting the Quality of Skin-Formed Foamed PVC Plastic Sheets
The primary raw materials that directly influence the quality of the cellular structure in plastics are the blowing agent and the foaming‑control agent. Stabilizers, lubricants, calcium carbonate, and other additives, along with careful control of the extrusion process, also play a role in enhancing and optimizing foam quality. Since, during extrusion, the melt must be plasticized at a temperature slightly below 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 plasticization. To produce well‑foamed plastic products, the resin viscosity should not be excessively high. Furthermore, compared with other foamed articles, skin‑forming foam sheets have a wider cross‑section; as the melt exits the die and spreads across a width of approximately 1.3 meters, uniform pressure distribution throughout the entire cross‑section is essential to facilitate bubble dispersion and expansion. This places higher demands on melt flow, so resins with relatively low molecular weights are typically preferred—suspension‑type, loose‑structured resins such as SC‑7 or SC‑8 are particularly suitable.
Related Information
What are the applications and maintenance procedures for sheet extruders?
As the pace of life continues to accelerate, people’s daily habits have also evolved, including the upgrading and replacement of everyday consumer goods. The advent of plastic products has, in many ways, transformed certain aspects of our lifestyles. Sheet extruders are the key equipment used to manufacture these plastic products.
Company email:info@gwell.cn
Nantong Company Address: No. 69, Hongrong Road, Chongchuan District, Nantong City
Suzhou Company Address: No. 16, Donglin Lianfa Industrial Park, Guojia Road, Chengxiang Town, Taicang, Suzhou
Yancheng Company Address: No. 90, Shenfeng Road, Dafeng District, Yancheng City
Shanghai Company Address: Room 2205A, 22nd Floor, No. 28 Maji Road, China (Shanghai) Pilot Free Trade Zone
Nanjing Company Address: No. 8, Huyue East Road, Longchi Subdistrict, Liuhe District, Nanjing City, Jiangsu Province
Browse on mobile