Three Cross-linking Technology for LSZH flame retardant XLPO cable compound

Three Cross-linking Technology for LSZH flame retardant XLPO cable compound

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Cross-linking can help improve the mechanical properties, heat resistance, ESCR, etc performances of the cable compound, and also expand their applications, improve the reliability and life of materials. Currently in China, there mainly three cross-linking technology are applied in LSZH FR XLPO compound: Irradiation cross-linking, ultraviolet cross-linking, and silane cross-linking.

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Irradiation Cross-linking

Irradiated cross-linking technology is the earliest and most used method for cross-linking low smoke halogen-free flame retardant polyolefin cable material in China, and the cable forming process is simple. Due to the high cost of irradiating equipment and its affiliated cost, most domestic cable factories do not have irradiating equipment. For manufacturers who do not have irradiating equipment, irradiated cross-linking materials must be processed by outsourcing. In addition to inconvenient cross-linking, irradiated cross-linking materials also have drawbacks such as unstable cross-linking, material color change, deterioration of aging performance, fuzzy inkjet marking, etc.

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Ultraviolet cross-linking

Taking polyolefin as the main raw material, adding an appropriate amount of photoinitiator, irradiating with ultraviolet light, and absorbing ultraviolet light of specific wavelength through the photoinitiator, polyolefin free radicals are generated, and then a series of rapid polymerization reactions take place to generate cross-linked polyolefin with three-dimensional network structure. The cross-linked polyolefin material has excellent high-temperature resistance, solvent resistance, excellent electrical properties, and significantly enhanced mechanical properties.

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Although UV cross-linking technology overcomes the disadvantages of irradiation cross-linking mentioned above, it can be cross-linked online at one time, and it is also a new kind of cross-linking material emerging in recent years. But because of its use of ultraviolet online cross-linking methods, so the production efficiency is low, if the extrusion speed is too fast, it is easy to appear no cross-linking phenomenon, if the extrusion speed is too slow, there shall be over curing. And the ultraviolet lamp often needs to change, if it is not changed in time, the product also can appear not cross-linked phenomenon, and it is not easy to make sure when to replace tubes.

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Once the UV crosslinked wire is not cross-linked well, it cannot be cross-linked again. In addition, the color of the diplomatic coupling material will also affect the degree of cross-linking. In a word, UV cross-linking material is a new material developed and researched after irradiation cross-linking material. Due to the influence of its material performance and equipment, further development and research should be carried out to adopt this material and its supporting equipment. Therefore, its material application has certain limitations.

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Silane cross-linking

Silane cross-linking low smoke halogen-free flame retardant polyolefin cable material is a new cable material formed by organically combining silane cross-linking technology with halogen-free flame retardant technology. It not only has high production efficiency but also is convenient for cross-linking. It can choose warm water or steam cross-linking. At the same time, its cross-linking quality is stable, and the degree of cross-linking is not affected by color.

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The actual use of silane crosslinking mainly has two methods, one is the British Dow Corning company invented a two-step method, known as Sioplas method; The other, a one-step process developed by BICC and Maillefer, is called the Monosil process. In recent years, the silane copolymer method appeared because of the attention of petrochemical resin manufacturers to polyethylene products.

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Sioplas method is a two-step method, that is, two extruders are used to produce polyethylsilane grafting material and catalytic masterbatch in advance, and then the two materials are mixed in a certain proportion, and the cross-linked polyethylene material is produced in the third extruder.

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Monosil method is a one-step method, which is characterized by the direct addition of silane, peroxide and catalyst into the same extruder. The cross-linking degree of products produced by one-step method is higher than that by two-step method.

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