Silane crosslinked polyethylene pipe (PE-X pipe)
DATE：2022/8/22 9:06:54 / READ： / SOURCE：This station
Silane crosslinked polyethylene pipe (PE-X pipe)
Silane crosslinking method is used to form crosslinked polyethylene pipes. The forming process mainly includes polyethylene silane melt grafting reaction and hydrolysis condensation reaction of silane grafted polyethylene. Polyethylene silane grafting reaction is obtained in the process of extruding raw materials in the extruder in a molten state; The hydrolysis condensation reaction of silane grafted polyethylene is completed in the crosslinking tank. Silane grafting and tube forming process can be divided into one-step and two-step. The one-step molding process requires a special reactive extruder, and the process conditions and operation control requirements in the extrusion reaction are relatively strict. This method of producing cross-linked polyethylene pipe is suitable for large-scale enterprises. The two-step forming of silane crosslinked polyethylene pipe is to extrude and granulate the raw materials after the combination and reaction grafting in a professional factory, and then extrude the pipes with a general-purpose extruder for extruding polyolefin materials in a common plastic product factory. The cost of forming silane crosslinked polyethylene pipe by this method is higher. (1) Extrusion process sequence the production process sequence of silane crosslinked polyethylene pipe is divided into two-step and one-step processes. ① Two step polyethylene silane peroxide mixing, extrusion granulation crosslinkable graft copolymer (a) material mixing a: B = small polyethylene catalyst antioxidant mixing, extrusion granulation catalytic masterbatch (b) material extrusion melt forming tube blank shaping cooling traction winding or fixed length cutting high-temperature water tank 60 ~ 95 ℃ cross-linked finished silane crosslinked polyethylene pipe molding adopts two steps, First, two extruders are used to produce polyethylene silane graft material (a) and catalytic masterbatch (b) respectively. After that, 9 parts and 5 parts of B powder shall be mixed evenly (note that the two materials must be dry and should not be stored for a long time). The mixing temperature of the materials is about 80 ℃. The uniformly mixed material is directly put into the extruder for melting and molding. ② One step method: silane peroxide catalyst is mixed with polyethylene, extruded and melted to form tube blank, shaped polyethylene antioxidant is cooled, pulled, wound or cut in fixed length, and the finished silane crosslinked polyethylene tube is cross-linked in high-temperature water at 60 ~ 95 ℃. The one-step method is used to form the silane crosslinked polyethylene tube. Polyethylene, silane crosslinking agent, peroxides, catalysts and antioxidants are mixed together and added to the same extruder, and the graft polymerization, molding The production of each cross-linking process is completed at one time. The crosslinking degree of crosslinked polyethylene pipe products produced by one-step method is higher than that of two-step method. (2) There are many formulation schemes for raw material selection and silane crosslinked polyethylene pipe forming. The following is an example of one - step and two - step formula for producing silane crosslinked polyethylene pipe Supply time reference. ① The main material for the material formulation of silane crosslinked polyethylene pipe is 100 parts of high-density polyethylene (HDPE) (density: about 0.95g/cm3, melt flow rate: mfp-7g / 10min), 18 parts of grafted monomer vinyl triethoxysilane (VTEs), 1.5 parts of initiator diisopropylbenzene peroxide (DCP), 0.1 parts of catalyst dibutyltin dilaurate, 0.2 parts of antioxidant (1010), and 0.2 parts of antioxidant lauryl THIODIPROPIONATE modifier. (DLTP) 0.3 parts. In order to improve the fluidity of the molten material, properly add some flow modifier ② to form the material formula for silane crosslinked polyethylene pipe. A. graft material (a) the main material of the formula is 100 parts of low-density polyethylene (LDPE) (density: 0.919g/cm3, melt flow rate: MFR = 0.3g/10min), 2 parts of graft monomer vinyl triethoxysilane (VTEs), and 0.15 parts of initiator diisopropyl peroxide (DCP). b. 100 parts of low-density polyethylene (LDPE) (density: 0.919g/cm3, melt flow rate: MFR = 0.3g/10min), 0.25 parts of diisopropyl peroxide (DCP) as initiator and 2.5 parts of dibutyltin dilaurate as catalyst are used for the formulation of catalytic masterbatch (b). (3) The extruding machine for granulation in the piece forming silicone polyethylene pipe can be a co rotating twin-screw extruder (specification: screw diameter p57mm, center distance 48mm, working speed 30 ~ 40R / min). The extrusion and melting of raw materials and the forming of pipe blank can be performed by the general single screw extruder for extruding polyolefin materials, which is more difficult than the process control for extruding low density polyethylene pipes. A special reactive extruder is needed to form silane crosslinked polyethylene pipe in one step. The reactive extruder extrudes silane crosslinked polyethylene pipe. When working, it not only plasticizes and melts raw materials, but also grafts polyethylene with silane. The structural requirements of the screw in the reactive extruder are: the length diameter ratio of the screw is large, generally about 30; The feeding section shall be appropriately lengthened, the thread of the homogenization section shall not be too deep, and the working surface of the thread shall be as smooth as possible, so that the molten material can run smoothly and with small resistance, and the operation of raw materials cannot be blocked; The requirement that the homogenization section should not be too deep is to prevent excessive shear of the butt branch and improve the crosslinking. It has been proved in production practice that the screw thread of the special reactive extruder should be divided into four functional sections, namely, feeding section, plasticizing section, homogenizing section and reaction section (also called grafting section). The characteristics of these four sections of screw are: the feeding section is longer than the feeding section of the ordinary screw, the compression ratio is slightly larger than that of the ordinary screw, the thread groove of the homogenization section is deeper than that of the ordinary screw, and the thread groove of the final reaction section is deeper. Such a screw structure is used for slightly decompressing the melting reaction. The plasticizing section of the screw shall be provided with separate threads and mixing elements to accelerate the melting of raw materials in the barrel. The inner wall of the feeding section of the barrel shall be provided with longitudinal grooves to increase the running friction of raw materials and facilitate the transportation and forward movement of solid raw materials in this section. The reaction section is behind the homogenization section. The screw groove should be deepened and there should be enough k degree. The deepening of the thread groove can not only depressurize the molten material, but also make the reaction more uniform; The decompressed material reduces the shear rate, and the melt is not easy to rise due to the reduction of the shear rate, thus avoiding the thermal decomposition of the melt; The lengthening of the reaction section is to complete the reaction and increase the residence time of the library materials in the reaction section.
Author：admin