Cross-linked polyethylene is widely used in the wire and cable industry mainly for the following three reasons: good performance, low price, and simple manufacturing process.

There are currently four popular cross-linking methods in the cable industry:

1. Peroxide thermochemical cross-linking (mostly used for the insulation of high-voltage and ultra-high-voltage power cables of 10kV and above);

2. Silane warm water cross-linking (mostly used for the insulation of medium and low voltage cables below 10kV);

3. Electronic irradiation cross-linking (mostly used for the insulation of medium and low voltage cables below 10kV);

4. In addition, there is a very small amount of UV cross-linking.

Of these four cross-linking methods, peroxide cross-linking is the most commonly used in terms of usage, followed by silane cross-linking. Electronic irradiation cross-linking is mostly used for special cables (such as high temperature resistant, halogen-free flame retardant cables). cable), UV cross-linking is only suitable for transparent and translucent materials; among these cross-linking methods, the most prominent advantages of silane cross-linking are simple processing methods and low material prices. Wire and cable factory users only need to buy the materials, put them into a conventional plastic extruder, extrude them using the general plastic cable production method, and then put them into warm water or a steam room (sauna) to complete the process in about 6 hours. Cross-linking. Several other cross-linking methods require special equipment (such as dry cross-linking lines, electron accelerators, and ultraviolet rays) to complete cross-linking after cable extrusion. This adds a lot of manufacturing costs.

The patent for silane cross-linked polyethylene expired in the early 1970s; this coincided with my country's reform and opening up and the great development of the electric power industry and wires and cables. As a result, this cross-linking method was quickly popularized and promoted in my country's cable industry.

There are two types of silanes currently available for cross-linking:

A-171: Vinyltrimethoxysilane

A-151: Vinyltriethoxysilane

Through decades of practice and comparison, since the grafting reaction of A-171 is faster than that of A-151, most countries around the world use A-171 as the grafting monomer. The main catalyst for cross-linking is mostly dibutyltin dilaurate (DBTD), and the initiator is dicumyl peroxide (DCP).

1. Varieties and classifications of silane cross-linking

The production sequence of silane cross-linked wires and cables is: first graft the silane monomer onto polyethylene macromolecules, and then shrink and cross-link under the action of a catalyst. Therefore, the varieties of silane cross-linked materials can be classified in the following three ways:

1. According to production method:

Copolymerization method: that is, ethylene monomer and silane monomer are polymerized in a reactor in a certain proportion; from the perspective of molecular structure, silane can still be regarded as a group grafted on the polyethylene main chain.

Two-step method: polyethylene and silane are melt-grafted in co-rotating twin-screws to complete the first step; the second step is to mix with the catalyst for extrusion molding and then condense with water to cross-link.

One-step method: Polyethylene, silane, and catalyst are mixed and absorbed into dry particles. The chemical reaction of grafting is completed during screw extrusion molding.

The advantage of the copolymerization method is that the product quality is excellent and stable; the content of grafted silane is high and it is not easy to