JPH03843Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Industrial Application Field] The present invention relates to a heat-shrinkable multilayer insulating tube used for cable connections. [Conventional technology and its problems] For power distribution connections, in order to reduce the need for on-site work and reduce work time, recently heat-shrinkable tubes with various characteristics have been combined and laminated to form insulators. This is being implemented. Since these structures are assembled by heat-shrinking the various tubes one by one, it is necessary to secure insertion space, and the connecting portion becomes unnecessarily long. In addition, an increase in the number of tubes used increases the shrinking operation time, and the increase in the number of tube interfaces increases the risk of interface defects. On the other hand, various tubes are made of polyolefin, EP rubber, silicone rubber, etc. as base materials. Polyethylene is suitable for obtaining high insulation performance, but since polyethylene is a hard material when subjected to electrical heat cycles, it does not follow thermal expansion and contraction, and defects are likely to occur at the interface. Rubber-based materials, on the other hand, follow electrical heat cycles due to their elasticity, but their own poor insulation performance requires thicker insulation structures. [Means for Solving the Problems] Therefore, in the present invention, an insulating tube is constructed from a composite material of an EP rubber-based material and a polyolefin-based material. [Example] FIG. 1 shows an example of a heat-shrinkable multilayer insulation tube according to the present invention. The heat-shrinkable multilayer insulation tube 1 includes an inner layer 1a made of a material based on EP rubber, and a material laminated integrally on the inner layer 1a and made of a material based on polyolefin, for example cross-linked polyethylene. The ratio of the inner layer 1a to the whole is 20~20.
Consisting of 40%. To be more specific, the inner layer 1a consists of an EP rubber-based high-resistance layer 2 and an EP rubber-based insulating layer 3 thereon, and the outer layer 1b consists of the inner layer 1a.
It consists of an upper polyolefin insulating layer 3' and an overlying polyolefin semiconducting layer. The high-resistance layer 2 is preferably one in which a filler and carbon are mixed to have a volume resistivity of 10 ⁸ to 10 ¹⁴ Ω·cm.
The semiconducting layer 4 contains carbon to increase the volume resistivity.
It is preferable that the resistance be 10 ⁶ Ω·cm or less. The heat-shrinkable multilayer insulation tube 1 is produced by, for example, molding a material containing a crosslinking agent by simultaneous extrusion of four layers or tandem extrusion of two layers, pressurizing and heating them at the same time to crosslink them, and then cooling them. It is manufactured by In this case, it is preferable to use a core material to prevent deformation during crosslinking and promote integration between the layers. Next, the multilayer insulating tube from which the core material has been removed is uniformly heated, expanded by a vacuum method, gas pressurization method, mechanical expansion method, etc., and rapidly cooled to impart heat shrinkability. When the heat-shrinkable multilayer insulating tube 1 manufactured in this manner is applied to a connection part, the result will be as shown in FIG. 2. In FIG. 2, the conductors of the stripped cable 11 are connected by a conductor connecting tube 12, and a shield layer 13 is provided around the outer periphery of the conductor. This shield layer 13 is formed of a putty-like material, a tape wrap, a shrinkable tube, etc. having a volume resistivity of 10 ⁷ Ω·cm or less. Next, cable 1
The heat-shrinkable multilayer insulation tube 1 inserted onto the cable 11 is moved to the outer periphery of the shield layer 13, heat-shrinked, and the cable 11 is
Connect to. The heating method is gas burner,
Although hot air, electric heaters, etc. can be used, radiant heating using far infrared rays is preferable because the insulating layer becomes thicker. By the way, the multilayer insulation tube is made of a composite material of EP rubber and polyolefin, and the ratio of the EP rubber inner layer to the whole is 20 to 40%, which is based on the corona characteristics shown in the table below. A heat-shrinkable multilayer insulation tube (Fig. 1) with a thickness of approximately 7 mm was manufactured using a 15 kV CV cable, and a
Assembled as shown. The conductor insulated tube was then subjected to a 90°C current heat cycle test, and the corona levels before and after the test were measured, and the results shown in the table below were obtained.

【table】

[Table] As is clear from the table above, when the proportion of polyolefin materials, such as crosslinked PE, exceeds 80%,
In other words, when the proportion of EP rubber is less than 20%, the corona level before heat cycle improves, but
The expansion and contraction after the heat cycle reduces the adhesion of the interface and significantly lowers the corona level. On the other hand, when the proportion of EP rubber exceeds 40%, the initial corona level is low, but the decrease due to heat cycling is also small. This is because the adhesion does not deteriorate even during heat cycles due to the cushioning effect of the rubber, but since the tensile strength of the rubber itself is lower than that of PE and the tightening force during contraction is weak, the initial corona level does not improve. Therefore, an EP rubber layer is placed on the inside.
A composite tube with a cross-linked polyethylene (XLPE) layer on the outside, with the EP rubber layer accounting for 20 to 40% of the total, provides extremely excellent corona properties. [Effects of the invention] According to the heat-shrinkable multilayer insulation tube of the invention,
Since the inner layer is made of an EP rubber base material and the outer layer is made of a polyolefin base material, and the ratio of the inner layer to the total is specified to be 20 to 40%, it is possible to use an EP rubber base material or a polyolefin base material. It has significantly better corona properties than a single insulating tube, and has good interface adhesion.
Not only does it have excellent insulation performance, it also allows heating and shrinking work to be performed in a short time, greatly reducing the work space and making it extremely easy to assemble multi-core cables.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing an embodiment of the heat-shrinkable multilayer insulating tube according to the present invention, and Fig. 2 is a cross-sectional view of the heat-shrinkable multilayer insulating tube shown in Fig. 1 when applied to a cable connection part. It is a front view. 1: heat-shrinkable multilayer insulation tube, 1a: inner layer, 1b: outer layer, 2: EP rubber-based high resistance layer,
3: EP rubber-based insulating layer, 3': Hoperiolefin-based insulating layer, 4: Polyolefin-based semiconducting layer, 11:
Stripped cable, 12: Conductor insulated tube, 13:
Shield layer, 14: Shield layer.

Claims (1)

[Scope of utility model registration request] An outer layer consisting of a polyolefin semiconductive layer integrally formed on the outer surface of a polyolefin insulating layer is laminated on the outer periphery of an inner layer consisting of an EP rubber high resistance layer integrally formed on the inner surface of an EP rubber insulating layer. The ratio of the inner layer to the whole is 20 to 40%.
A heat-shrinkable multilayer insulating tube characterized by being constructed in the following range.