Foamed cable insulator
DATE：2022/4/28 8:44:28 / READ： / SOURCE：This station
Foamed cable insulator
The development of this application field is the telephone carrying line of micro coaxial TV cable (CATV). For telephone lines, both chemical foaming and physical foaming can be used. However, CATV can only be formed by chemical foaming method.1. Chemical foaming method, which is widely used in the production of foamed cable insulator. The raw materials used in different regions are different. The cable insulation layer in Western Europe is made of LDPE. Both HDPP and HDPE are used in North America. Both materials need the expandable melt of LDPE masterbatch. It is usually required to maintain a low die pressure to make the production speed reach the required index. 2. Physical foaming method the physical foaming of this product takes the gas injection method as the basic method, in which chemical foaming is used as nucleating agent. The application of gas foaming obtains special electrical performance advantages because it has no polar residues.
3. Coextrusion method; The low-density foamed insulating layer is produced by CO extrusion, so that a uniform non foamed outer layer is added to the outer surface of the product, so that the product will not lose the original wear resistance and will not be easy to break in the weaving process. Coextrusion technology can also solve the problem of maintaining bubble quality under the condition of low bulk elasticity in hdpepp process, that is, controlling the rate of pressure attenuation. The die used for foaming cable insulation layer is not very different from the ordinary cable die except that it should follow the design elements proposed above. Other devices can also use ordinary cable equipment. Coating compound equipment www.handern.com com
Special extrusion foaming process. In some special extrusion foaming process, the extruder is only used to mix and shape the billet. The foaming process exists as an operation unit separated from the extrusion host. Now there are three kinds of widely used. 1. Crosslinking foaming of polyolefin in this field, LDPE crosslinking foaming products formed by chemical foaming method are dominant. Crosslinking occurs before foaming, which can strengthen the surface tension of cell wall and obtain uniform and dense micro cell structure. There are two crosslinking methods for LDPE, one is chemical crosslinking, and the other is molecular chain breaking caused by ionizing radiation. At present, the development of ldve crosslinked hair products can be reflected from three aspects. ① Compress for 22h, the deformation is 50%, and the recovery time is 24h (2) the production process and formula are used to prepare foamed plastics with a foaming ratio of 40. If Azodicarbonamide is used as the foaming agent, 20 parts are usually added to 100 parts of LDPE. In order to disperse the foaming agent evenly, the surface of the resin can be coated with white oil, turpentine, cyclopropane or ethylene oxide, and the foaming agent can be stuck to the LDPE resin, mixed with a small amount of powdered resin with high softening temperature. When chemical crosslinking agent is used for atmospheric pressure crosslinking, it is also necessary to prevent the decomposition of crosslinking agent in the process of mixing and forming billet. Therefore, the processing temperature needs to be strictly controlled. Generally, when diisopropyl peroxide is used as crosslinking agent, it is appropriate to extrude at 135 ~ 143 ℃. Use 2,5 When dimethyl-2,52 tert butyl hexane peroxide is used, 157 ~ 160 ℃ is appropriate. In addition, the resin can be swelled with organic solvent to reduce the extrusion temperature to prevent the early decomposition of crosslinking agent. There are two methods for heating the primary billet after mixing and forming. One is to heat at a fixed temperature for a period of time to decompose the crosslinking agent (but the foaming agent cannot decompose), and the tree shop is crosslinked; Then raise the temperature to decompose the foaming agent. This method is called two-stage heating method. There is also a one-stage heating method, that is, directly heating the initial damage to the temperature of the foamed heat separation clothes. In the one-stage heating method, part of the crosslinking agent decomposes before the foaming agent. The method is the same as the previous one. However, the amount of cross-linking agent used in the one-stage heating method is greater than that used in the antipyretic method, which improves the degree of cross-linking and thus the pre incubation heat of foamed plastic products. Coating compound equipment www.handern.com com
No matter which heating method is used, the resin needs to be heated to the surface for crosslinking purposes. Therefore, the decomposition of crosslinking agent should be prevented when mixing and forming the initial blank. When the crosslinking agent is heated at the beginning of molding to crosslink it, the crosslinking agent is best to dissolve quickly. Add these two requirements of the project. In addition, if the crosslinking agent is selected and the decomposition temperature is high, the resin will be in a state of low external melting viscosity for a long time, resulting in the deformation of the billet due to flow and the problem of landing on the carrier belt. The following methods can be used to solve the problem of adhesive carrier tape: ① B. no material is carrier tape; ② Anti sticking materials such as silicone oil, polytetrafluoroethylene lotion and mica powder ③ salt bath floating or air floating; ④ Shape. When crosslinking with ray radiation, only LDPE and foaming agent need to be mixed at a temperature lower than the foaming agent division temperature and formed into primary billet. Then, it was crosslinked by radiation with a dose of 1 ~ 200kgy (0.120mrad). Then it is heated above the decomposition temperature of the foaming agent, so that the foaming agent can be decomposed and vented to make foamed plastic products. For example, radiation crosslinking under heating can further improve the crosslinking efficiency. In addition, radiation crosslinking can be carried out in oxygen-containing gas, and then heated and foamed under reduced pressure.
In addition to being carried out under high and low temperature conditions, the crosslinking by radiation does not need to be carried, and the crosslinking time is short when the dose is appropriate. Coating compound equipment www.handern.com com
Another method of combining chemical crosslinking agent and radiation crosslinking is to radiate the expandable billet containing chemical foaming agent and chemical crosslinking agent with electron ray to make it crosslinked, and then heat it to decompose both crosslinking agent and foaming agent. This method can not only solve the problem of adhesion to the carrier tape when using the chemical crosslinking method, but also make up for the deficiency of the ray crosslinking method. It is suitable for making thick foamed plastic products. Coating compound equipment www.handern.com com
Author：admin