JPH0133004B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an insulated wire having high watertightness. When the conductor of an insulated wire comes into contact with water containing dissolved corrosive components under tensile stress or the like, the conductor undergoes so-called stress corrosion and is rapidly eroded, causing wire breakage and the like. In order to prevent this stress corrosion, a watertight resin composition is filled in the gaps between the conductor strands as a filling layer.
Furthermore, watertight insulated wires are known in which the conductor strands and the filling layer are covered with an insulator such as cross-linked polyethylene. The resin composition used for this filled layer is mainly composed of ethylene propylene rubber, ethylene vinyl acetate copolymer, ethylene ethyl acrylate copolymer, or the like. By the way, in order to improve the watertightness of such an insulated wire, it is necessary that the resin composition adhere well to the strands and the insulator constituting the stranded wire, and that moisture does not enter the interface between these wires. However, if the adhesion of the resin composition is good, on the contrary, the peeling property (peeling property) during the terminal connection work of the insulated wire becomes poor, resulting in a disadvantage that the work is laborious. For this reason, the reality is that a resin composition having appropriate adhesion is selected based on the balance between watertightness and peelability. This invention was made in view of the above circumstances,
The object of the present invention is to provide a watertight insulated electric wire that has the contradictory characteristics of high watertightness and good peelability. Hereinafter, the present invention will be explained in detail with reference to the drawings. The drawing shows an example of the watertight insulated wire of the present invention, and reference numeral 1 in the drawing indicates a wire made of hard copper wire or the like. Nineteen of these wires 1 are twisted together to form a twisted wire 2. An insulator 3 made of crosslinked polyethylene is provided on the outside of the stranded wire 2 to cover it. Further, the void formed between the stranded wires 2 and the insulator 3 is filled with a resin composition made of a crosslinked ethylene vinyl acetate copolymer or a crosslinked ethylene ethyl acrylate copolymer to form a filling layer 4 . The crosslinked ethylene vinyl acetate copolymer used herein preferably has a vinyl acetate content of 10 to 40% by weight, and the crosslinked ethylene ethyl acrylate copolymer preferably has an ethyl acrylate content of 10 to 30% by weight. Furthermore, among the filling layers 4, the outer filling layer 4a (the part outside the circle indicated by the dashed line in the figure) located between the outermost layer of the stranded wires 2 and the insulator 3 is
The gel fraction of the resin composition is said to be 70% or more, and the inner filling layer 4 is located between the strands 1 of the stranded wire 2.
In b, the resin composition has a gel fraction of 10 to 70%. If the gel fraction of the resin composition of the outer filling layer 4a is less than 70%, the composition will not be sufficiently hard, and the interfacial fusion property with the crosslinked polyethylene of the insulator 3 will decrease, and the adhesion will decrease. It is susceptible to mechanical deformation, and when it is peeled off, a portion of the resin composition adheres to the surface of the strand 1, resulting in poor workability. In addition, the gel fraction of the resin composition of the inner filling layer 4b is less than 10% or
If it exceeds 70%, watertightness becomes poor. This is because when the gel fraction is 10 to 70%, the adhesion between the resin composition and the strand 1 is good, and the strand 1 and the resin composition are tightly adhered to each other, preventing moisture from penetrating. it is conceivable that. The specification of the gel fraction is almost unrelated to the types of ethylene vinyl acetate copolymer and ethylene ethyl acrylate copolymer (vinyl acetate content, ethyl acrylate content, etc.). In the filling layer 4 made of a resin composition having such a composition, the inner filling layer 4b in the inner part is soft and highly watertight, and the outer filling layer 4a in the outer part is hard and has good adhesion to the insulator 3 and is skin-friendly. The hookability is also good. Next, a method for manufacturing a watertight insulated wire according to the present invention will be explained. After forming strands 2 using a stranding machine, a resin composition made of uncrosslinked ethylene vinyl acetate copolymer or ethylene ethyl acrylate copolymer is press-fitted from the outside of strands 2 into the voids of strands 2 under high pressure. Then, an insulator 3 made of uncrosslinked polyethylene is formed using an extruder equipped with a crosshead die. This material is introduced into a continuous crosslinking device and crosslinked. At this time, the crosslinking conditions are adjusted so that the gel fraction of the resin composition of the outer filling layer 4a of the filling layer 4 is 70% or more, and the gel fraction of the resin composition of the inner filling layer 4b is set to 10% or more.
~70%. In fact, if the heating conditions are appropriate, the heat becomes weaker toward the inside, so it is relatively easy to keep the gel fraction within the above range. In addition, by changing the blending amount of the crosslinking agent, etc. in the resin composition corresponding to the outer filling layer 4a and the resin composition corresponding to the inner filling layer 4b, the outer filling layer 4a is made to have a composition that allows crosslinking to proceed more easily. There is also a method in which the insulator 3 is filled separately at different times, and then the insulator 3 is formed and crosslinked. Hereinafter, a specific explanation will be given by showing examples. Example: A cross-linked polyethylene insulated wire was manufactured using a 60 mm ² hard copper stranded wire 2 as a conductor, provided with an inner filling layer 4b and an outer filling layer 4a having different gel fractions, and the skin tightness and watertightness of each wire were examined. . For peeling property, peeling was performed using a special peeling tool, and the presence or absence of adhesion of the filler layer to the stranded wires was checked. In addition, watertightness is determined by the length
A water pressure of 0.5 kg/cm ² was applied to one cut surface of a 10 cm insulated wire and left for 24 hours, and evaluation was made based on whether water oozed out from the other cut surface. Filled layer 4
The composition and gel fraction are shown in the table.

【table】

[Table] As is clear from the table, when the gel fraction of the outer filling layer 4a is 70% or more, the peeling property is good, and when the gel fraction of the inner filling layer 4b is 10 to 70%, the watertightness is good. In the end, the gel fraction of the outer packed layer 4a was set to 70% or more, and the gel fraction of the inner packed layer 4 was
It can be seen that by setting the gel fraction of b to 10 to 70%, it is possible to obtain a material that satisfies both the properties of skin tightness and watertightness. As explained above, in the watertight insulated wire of the present invention, the filling layer is formed of a resin composition made of ethylene vinyl acetate copolymer or ethylene ethyl acrylate copolymer, and the outermost stranded wire layer of the filling layer is insulated. The gel fraction in the area between the body and the body is 70.
% or more, and the gel fraction of other parts is 10 to 70.
%, it combines the conflicting properties required of a packed bed: good peeling properties and sufficient watertightness. Therefore, this watertight insulated electric wire has advantages such as being free from damage due to stress corrosion of the conductor and making it easy to connect the terminals.

[Brief explanation of drawings]

The drawing is a schematic cross-sectional view showing an example of the watertight insulated wire of the present invention. 2...Twisted wire, 3...Insulator, 4...Filled layer, 4
a... Outer packed layer, 4b... Inner packed layer.

Claims (1)

[Claims] 1. An insulated wire having a stranded conductor, an insulator made of cross-linked polyethylene that covers the stranded conductor, and a filling layer in which a gap formed by the stranded conductor and the insulator is filled with a watertight material. The filling layer is formed of a resin composition consisting of a crosslinked ethylene vinyl acetate copolymer or a crosslinked ethylene ethyl acrylate copolymer, and the gel content of the resin composition of the filling layer located between the outermost layer of the stranded wire conductor and the insulator is rate 70%
A watertight insulated electric wire as described above, characterized in that the resin composition of the filled layer located between the stranded wire conductors has a gel fraction of 10 to 70%.