JPS6143808B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an insulated wire, particularly a method for manufacturing an insulated wire with excellent tree deterioration resistance.

FIG. 1 shows an example of a conventional insulated wire.

That is, a single insulating material (for example polypropylene) having a single melt viscosity is placed on the circumference of the conductor 11.
This structure has an insulating layer 13 formed by extrusion molding. (12 is a copper damage resistance layer provided as necessary.) In this conventional structure, as shown in the figure, the tree T
They extend radially from the conductor, have a short lifespan before dielectric breakdown, and are particularly noticeable when the insulation layer is thin.

Furthermore, even when such an insulating layer is mechanically squeezed, it cannot absorb the stress and the microcracks C extend radially, resulting in a short lifespan leading to dielectric breakdown. This point also occurs when the insulating layer is thin. It was noticeable.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing an insulated wire that eliminates the drawbacks of the conventional products described above and has excellent tree deterioration resistance.

That is, the gist of the present invention is to form insulating materials of the same kind or different kinds having different melt viscosities on the circumference of a conductor into a spherical or pellet shape and physically mix them so that the respective components do not dissolve. This method of manufacturing an insulated wire is characterized in that a spiral pattern is formed in the intermediate layer portion in the thickness direction of the insulating layer by extrusion molding the insulating layer at a temperature at which each component melts.

Electrical insulating materials are not only used alone;
Often, two or more different types of compatible materials are mixed and used in order to utilize and complement each other's properties.

However, in that case, it is common knowledge that kneading or other methods are used until homogenization.

However, in the present invention, in order to prevent dielectric breakdown due to the generation and growth of electrical trees, contrary to the common sense of homogenization, insulating materials of the same type or different types having different melt viscosities are mixed and extruded unevenly to form an insulating layer. It is composed of

In other words, different types of insulating materials with different melt viscosities (which can also be referred to as different molecular weights) or the same type of insulating materials are physically mixed in appropriate proportions in the form of spherical or pellet-like agglomerates of desired size. However, when this is put into a screw type extruder and extrusion molding is performed at a temperature where each component melts, the flow characteristics in the screw groove are vortex mixing, so for example, some components with low viscosity The components with high viscosity are not completely uniformly kneaded and exist as a spiral semi-mixture as shown in FIG. 2, forming a swirl pattern.

When such a semi-mixed material is coated concentrically around the conductor, the high viscosity component behaves as if it were non-fluid compared to the mobility of the low viscosity component, resulting in what is called a plug flow shape in terms of rheology. For example, the cross section of the insulating layer has a shape in which swirl-like particles of high viscosity components are present in the center, so the cross section takes on a form separated into three irregular layers.

Insulating materials used in the present invention include polyolefin materials such as polyethylene and polypropylene, ethylene-vinyl acetate copolymers, and ethylene-vinyl acetate copolymers.
Ethylene copolymers such as ethyl acrylate copolymer, ethylene-ethyl acrylate copolymer,
Synthetic rubbers such as ethylene-propylene copolymer rubber, ethylene-propylene-diene copolymer rubber, chlorosulfonated polyethylene, chlorinated polyethylene, polychloroprene, butyl rubber, silicone rubber, vinyl materials such as polyvinyl chloride,
It can be used from a wide range of insulating materials for electric wires, including fluororesin and polyamide resin.

An embodiment of the present invention will be described with reference to FIG. 1 is an annealed copper wire conductor having a cross-sectional area of 1.4 mm, and a copper damage resistance layer 2 coated with epoxy resin is provided directly above the annealed copper wire conductor.

On the circumference of this conductor, 75% by weight of polypropylene with a melt viscosity index of 3 and ethylene with a melt viscosity index of 0.2 are coated.
25% by weight of propylene copolymer, each component is physically mixed in a spherical shape, put into a screw type extruder, and extruded to form an insulating layer 3 with a coating thickness of 0.3.
is configured.

In this case, melting index measurement conditions: 230℃, 2.16Kg, 10 minutes Conductor temperature: Approximately 10℃ Cooling conditions: Rapid cooling with water (water temperature approximately 0℃).

It is.

Now, as shown in FIG. 2, the insulating layer 3 consists of an inner layer part 31 and an outer layer part 32 which are low viscosity components, and an intermediate layer part 30 which is a high viscosity component and has a swirl pattern formed therein. It has a layered structure.

This example is an example of a magnet wire for an underwater motor.

If the structure of the above embodiment is used, as shown in the figure,
The extension of the tree T is inhibited by the presence of vortices or it is curved into a spiral shape, which is the same as increasing the apparent thickness of the insulating layer, and lengthening the lifespan until dielectric breakdown occurs.

In addition, when mechanically squeezed, the number of microcracks is reduced due to stress absorption by vortices, and the extending direction of microcracks C is also curved along the spiral shape, which also extends the lifespan until dielectric breakdown occurs. .

Here, the conventional insulated wire (having a single insulating layer of polypropylene) shown in FIG.
Regarding the insulated wire manufactured by the method of the present invention shown in the figure, both of which are the same size,
The breakdown voltage-accelerated deterioration time characteristics are shown in Figure 3 A and B.

A is a conventional insulated wire, and B is an insulated wire manufactured by the method of the present invention.

Accelerated deterioration conditions are 60℃ sewage immersion, 9KHz, 1KVp
It is chargeable.

As is clear from the results shown in FIG. 3, the insulated wire manufactured by the method of the present invention is clearly effective in terms of tree deterioration resistance.

Incidentally, the insulated wire manufactured by the method of the present invention is
Compared to conventional insulated wires, the initial AC breakdown voltage characteristics are inferior, but this is because insulating materials with different melt viscosities exist as a semi-mixture.
Microvoids and the like occur, resulting in poor characteristics, whereas conventional insulated wires made of pure insulating materials initially have superior characteristics.

However, as is clear from FIG. 3, the subsequent deterioration of the characteristics shows that the insulated wire manufactured by the method of the present invention has better tree deterioration resistance.

The manufacturing method of the present invention is particularly effective as the insulated wire has a thinner insulation layer, but even when the insulation layer is thick, it can be expected to be effective in terms of tree deterioration resistance.

Therefore, effects can also be expected when applied to insulated wires used at a rating of 600V or higher (for example, cross-linked polyethylene cables, etc.).

The insulated wire manufactured by the manufacturing method of the present invention as described above has less decrease in dielectric breakdown value and has a significantly improved lifespan than conventional wires of this type.

In other words, the trees generated near the conductor are prevented from elongating radially due to the presence of the intermediate layer portion or the intermediate layer portion and the inner layer portion in which the vortex-like pattern is formed, so that the trees are highly effective in preventing tree deterioration. , the lifespan has been improved.

In addition, even when mechanical bending (straining) is applied, the occurrence of microcracks is reduced due to stress absorption by vortices, and even if microcracks occur, their elongation direction is curved along the spiral shape, so that they can be easily seen from this plane. The lifespan until dielectric breakdown occurs is extended.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing an example of a conventional insulated wire;
FIG. 2 is a sectional view showing an example of an insulated wire manufactured by the manufacturing method of the present invention, and FIG. 3 A and B are
3 is a diagram showing the breakdown voltage-accelerated deterioration time characteristics of the electric wires of FIGS. 1 and 2, respectively. FIG. DESCRIPTION OF SYMBOLS 1... Conductor, 3... Insulating layer, 31, 32... Inner layer part and outer layer part which are a low viscosity component, 30... An intermediate layer part which is a high viscosity component and has a swirl pattern formed therein.

Claims (1)

[Claims] 1. Insulating materials of the same type or different types with different melt viscosities are formed into a spherical or pellet shape on the circumference of a conductor, and physically mixed so that each component does not melt, and the temperature at which each component melts using a screw type extruder is determined. 1. A method of manufacturing an insulated wire, characterized in that a spiral pattern is formed in an intermediate layer portion in the thickness direction of the insulating layer by extrusion molding the insulating layer.