JPH0137809B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an insulated wire comprising a flame-retardant protective coating provided around the outer periphery of a flammable insulator. Polyethylene is widely used as an insulator for conventional insulated wires, such as shielded wires and coaxial cords. However, polyethylene is easily flammable, and attempts have been made to add other mixtures to make it flame retardant, but these often impair the excellent electrical properties inherent to polyethylene. Therefore, as a method of imparting flame retardancy to an insulated wire having a flammable insulator, a method has been adopted in which a sheath material provided around the outer periphery of the insulator is made flame retardant. A typical sheath material is plasticized polyvinyl chloride, taking into account the practically required properties, workability, flexibility, etc. Although the polyvinyl chloride itself in this sheath material is self-extinguishing, it is easily flammable because it is mixed with 20 to 40% by weight of plasticizer to give it flexibility. In order to improve the flame retardancy of plasticized polyvinyl chloride, good flame retardancy can be obtained by mixing chlorinated paraffin and a phosphorus organic compound with antimony trioxide. However, even with such a polyvinyl chloride composition, it cannot be used for insulated wires that use polyethylene as the insulator.
The sheath material will not provide sufficient flame retardancy to pass the flammability test specified in UL Standard VW-1. In other words, in a combustion test, a specified flame of a gas burner is applied to an insulated wire held vertically for 15 seconds, and the burning time and falling objects are observed after the flame is removed.This is repeated five times. Either it burns and disappears, or it cracks and ignites the internal polyethylene insulation, causing the fire to spread. The present invention has been made in view of the above, and its purpose is to protect the internal combustible insulator from combustion by forming a foamed carbonized layer on the sheath when exposed to flame, thereby providing excellent resistance to fire. The object of the present invention is to provide an insulated wire having flammability. In the insulated wire of the present invention, a flame-retardant sheath provided around the outer periphery of the flammable insulator is made of ethylene-vinyl acetate copolymer having a vinyl acetate content of 15% by weight or more based on 100 parts by weight of polyvinyl chloride. It is characterized in that it is formed from a foaming carbonizable polyvinyl chloride composition obtained by mixing at least part by weight and further adding a zinc compound. That is, in the present invention, the ethylene-vinyl acetate copolymer has the property of melting and softening as the temperature rises during contact with the flame, and the gas generated during combustion acts as a foaming agent to form a foam. be done. Furthermore, polyvinyl chloride has the property of being easily carbonized during combustion, but when a zinc compound is added to it, zinc chloride is produced, which promotes the action of dehydrochlorination and further improves carbonization. In this way, a strong foamed carbonized layer is obtained, whose thermal insulation action protects the internal combustible insulation from combustion. As an ethylene-vinyl acetate copolymer, there are
It is necessary to use a material with a vinyl acetate content of 15% by weight or more. Furthermore, a copolymer of ethylene-vinyl acetate with another monomer, such as an ethylene-vinyl acetate-acrylic acid copolymer, can also be used. The amount of the ethylene-vinyl acetate copolymer added must be at least 30 parts by weight per 100 parts by weight of polyvinyl chloride; if it is less than this, the foaming properties will be poor. The ethylene-vinyl acetate copolymer imparts plasticity to polyvinyl chloride, but in the present invention, in addition to these, commonly known plasticizers for polyvinyl chloride, such as trioctyl trimeryl, are used. There is no problem in using Tate (TOTM) etc. However, since these plasticizers reduce flame retardancy, the amount used must be kept to a small amount. Particularly preferred zinc compounds are zinc carbonate, zinc borate, and zinc pyromellitate, which act as excellent carbonization catalysts. Incidentally, the same effect can be obtained by using one type of zinc compound alone or by using two or more types in combination. The amount of the zinc compound added is not particularly limited, but 1 to 50 phr is appropriate. In the present invention, other stabilizers, fillers, antioxidants, colorants, etc. may be added in addition to the above components. Further, a free radical generating agent may be added and heated after sheath formation, or crosslinking may be performed by irradiating an energy-rich beam. Crosslinking makes it possible to improve heat deformation resistance and chemical resistance. Examples of the present invention will be described below in comparison with comparative examples. A conductor with an outer diameter of 1.2 mm was extruded and coated with polyethylene as an insulator to a thickness of 1.4 mm to form a core with an outer diameter of 4 mm. The outer periphery of this core was extruded and coated with a polyvinyl chloride composition having the formulation shown in each example in Table 1 to a thickness of 0.5 mm to form a sheath. The flame retardancy of this insulated wire was evaluated in accordance with the UL standard VW-1 combustion test, and the results were evaluated as
It is shown in the bottom column of the table. Furthermore, Table 1 also shows the evaluation results regarding the foaming carbonization property during combustion.

【table】

[Table] As is clear from Table 1, the examples of the present invention have good foaming carbonization properties during combustion, so they meet the UL standards.
It has passed the VW-1 combustion test. As explained above, the present invention uses a polyvinyl chloride composition that foams when exposed to flame to form a strong carbonized layer as a sheath material. Since the body can be protected from combustion, insulated wires such as shielded wires and coaxial cords with excellent electrical properties can be realized.

Claims (1)

[Claims] 1. In an insulated wire in which a flammable insulator is provided on the outer periphery of a conductor and a flame-retardant sheath is provided on this outer periphery, the flame-retardant sheath has a vinyl acetate content of 15% by weight based on 100 parts by weight of polyvinyl chloride. A flame-retardant insulated wire comprising a foamed carbonized polyvinyl chloride composition prepared by mixing 30 parts by weight or more of the above ethylene-vinyl acetate copolymer and further adding a zinc compound.