Double machine co-extruded core layer foamed PVC pipe
DATE：2021/9/3 8:28:48 / READ： / SOURCE：This station
Double machine co-extruded core layer foamed PVC pipe
The PVC-U core layer foamed pipe is a new type of plastic pipe. It is formed by the extruder using a multi-layer co-extrusion production process by adding an appropriate amount of additives to the PC resin. This process has been widely used in the world. Using two extruders to co-extrude to a batching die at the same time, one of the extruded PVC material is divided into two molten streams in the batching die, and the two molten streams form the inner and outer skin layers of the pipe; and Another extruder inputs the foamed PNC into the same batching die, which is located between the inner and outer layers, which is the core layer. Because the PVC-U core layer foamed pipe is harder than it is. PVC solid-wall pipes have more advantages, and the application areas are constantly expanding.
my country's co-extruded PNC-U core layer foamed pipes began to be produced and applied in the 1990s. In recent years, it has introduced more than ten production lines for co-extrusion of PVC core foamed pipes in France, Austria, South Korea, Taiwan, etc., and more than 20 production lines in Dalian, Qingdao, Fang, Wuhan, Nantong, etc. , Which effectively promoted the production and application of core foam pipes in my country.
1. Material selection and formula design
(1) PVC pipe foaming principle During the processing of PC-U, an appropriate amount of foaming agent is added to the material. At a certain temperature, the foaming agent decomposes and the released gas forms voids in the melt to polymerize PVC The volume of the product increases, which correspondingly reduces the density of the product. In the extrusion foaming process, the expansion of the blowing agent occurs in an environment close to the melting temperature of the polymer (extruder brief), and the expansion must occur after the polymer is melted, so the expansion must occur at the same temperature The two processes of melting and melting are separated from each other, so that they will not interfere with each other and affect the quality of products.
By testing different foaming agents and addition amounts, the best formula must ensure the following points
①The internal foaming ratio and cell size of the melt are uniform, and there is no continuous cavity, so as to ensure that the product has good mechanical properties: ②No strength drop caused by microscopic changes ③No bubbles on the surface, and the surface layer is as dense as possible. When the C melt containing the blowing agent passes through the groove and the die head at high temperature, the pressure exerted by the line on the melt should be uniformly released in the die. In order to prevent the melt, the internal pressure of the foam die should be higher than the pressure of the blowing agent gas, and it should be used as far as possible. The melt containing the foaming agent must expand at the beginning. If the body is filmed in the die, it will generate shear force and destroy the formed cells, resulting in the PC-U co-foaming system on the surface of the product being composed of C grease, Modifier, fixative, agent, foaming agent, nucleating agent, etc. Compared with the ordinary C formula, this system needs to consider the influence of its components on the AC foaming effect and the relationship between the body strength and the cell structure in the formula.
Author：admin