JPH031143B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a heat-shrinkable polyethylene sleeve made of crosslinked polyethylene, and particularly to a method for manufacturing the sleeve using injection molding.

Polyethylene is a material with excellent insulation and water resistance, and crosslinking improves its heat resistance. Polyethylene sleeves with heat shrink properties are widely used for insulated connections or anti-corrosion connections. .

The production method is extrusion molding for small-diameter products, but for large-diameter products, cross-linked polyethylene that has been made heat-shrinkable by electron beam irradiation stretching etc. is used for large-diameter products. It is manufactured by laminating films or tapes in a sushi-wound or horizontal-wound manner and fusing each layer together in a heating bath at a constant temperature. Recently, as shown in Fig. 7, in order to give the inner layer of the sleeve adhesive properties, polyethylene films or tapes containing no crosslinking agent are laminated in a sushi-wound or cross-wound manner, and this is the inner layer a, and the outer layer is made of cross-linked polyethylene. A cylindrical double sleeve is manufactured and used, in which the outer layer b is formed by laminating in a sushi roll or a horizontal roll, and these are heat-fused to form a double layer.

In addition, as shown in Figure 8, the sleeve is partially cut in the longitudinal direction for reconnection of the cable sheath, etc., to form a curved plate as a whole, and linear ribs are attached to both side edges of the curved plate. Ribbed sleeves, which are marked with c and whose portions can be opened and closed via fasteners, have also appeared and have continued to this day.

Conventional methods for manufacturing such relatively large-diameter heat-shrinkable sleeves involve biaxially stretching the film or tape that serves as the raw material for the heat-shrinkable sleeve. Although it contracts in the radial direction, it also has the disadvantage that it remains contractible in the longitudinal direction.

The object of the present invention is to obtain a polyethylene heat-shrinkable sleeve that is shrinkable only in the radial direction and not in the longitudinal direction, and furthermore, by providing a method that allows mass production, it can be made into any size and shape. Polyethylene heat-shrinkable sleeves are also intended to be extremely easy to manufacture.

The present invention was made in order to solve the above-mentioned object, and the present invention has a core made of polyethylene containing a crosslinking agent so that most of the center part has a constant small diameter part and it becomes a constant large diameter part towards both ends. A polyethylene layer containing a crosslinking agent of a constant thickness is formed on the outside of the core by injection molding using a two-split mold, and then the polyethylene layer containing a crosslinking agent is placed in another two split molds each having a large cavity. After inserting the core provided with the polyethylene and heating it while applying fluid pressure from the cavity side to cross-link the polyethylene, air pressure is applied from inside the core while keeping the cross-linked polyethylene layer heated, and the wall of the mold cavity is heated. After expanding the small diameter part of the cross-linked polyethylene layer, the cross-linked polyethylene is removed from the mold and core, and both ends are cut off to produce a heat-shrinkable sleeve. This is a manufacturing method that uses injection molding.

Next, the present invention will be explained in detail with reference to embodiments shown in the drawings.

However, the figure describes the manufacture of a double sleeve in which the inner layer is a polyethylene layer that does not contain a crosslinking agent and the outer layer is crosslinked polyethylene.

Regarding FIG. 1, the mold 10a is divided into two parts,
A core 12 having a bobbin-like shape with a cylindrical small diameter part 12a at the center and large diameter parts 12b at both ends is installed inside the mold 10 consisting of the molds 10a and 10b. Polyethylene not containing a crosslinking agent is filled in the cavity between the core 12 by injection, and the polyethylene coating 1 is applied to the core 12.
form 4. This is the first step. Note 16
is a polyethylene melting passage provided at the seam of the two-split mold 10a.

To explain FIG. 2, the core 12 provided with the above-mentioned polyethylene coating 14 is mounted as it is inside the mold 18 consisting of another two-part mold 18a and 18b, and the mold 18 is A new polyethylene containing a crosslinking agent is filled in the cavity between the core 12 and the core 12 provided with the polyethylene coating 14 by injection, thereby forming a polyethylene coating 14 that does not contain a crosslinking agent and a polyethylene containing a crosslinking agent. Covering layer 20
Provide a double layer with. This is the second step.

In addition, 22 is a melting channel of polyethylene containing a crosslinking agent provided at the seam of the halved molds 18a and 18b.

To explain FIG. 3, the core 12 provided with a double layer of the above-mentioned polyethylene coating 14 not containing a crosslinking agent and the polyethylene coating 20 containing a crosslinking agent is further divided into two molds. That is, it is inserted into a mold 24 consisting of two halves 24a and 24b having a cylindrical part equal to the large diameter part, and a fluid is introduced into the large cavity 26, and the mold is pressed while being pressurized with, for example, air, steam, or silicone oil. 24 and polyethylene 20 containing a crosslinking agent at 180° C., 6 kg/cm ²
It is crosslinked by heating and pressurizing. This is the third step.

Note that 28 represents a passage for pressurized fluid, and 30 represents a heater coil.

In the figure, the mold itself has a built-in heater, but the heating may be done by other means, or the pressurized fluid itself may be heated to a temperature higher than the decomposition temperature of the crosslinking agent.

In the present invention, a double coating layer of polyethylene and crosslinked polyethylene is formed on the core 12 in the mold in this way, but then the pressure with the fluid is stopped and the temperature is reduced to about 50°C due to the crosslinking temperature. After cooling the mold 24 to a temperature of about 180° C. and preheating the mold 24 again to about 180° C., as shown in FIG. , the double coat of cross-linked polyethylene expands radially into a headed tube of uniform outer diameter along the cylindrical wall within the mold. Reference numeral 32 denotes an air flow path provided in the core, which is not clearly shown in FIGS. 1 to 3, but is provided in the core 12 in advance.

This diameter expansion imparts a strain that causes contraction in the radial direction.

The above is the third step, and when the product is taken out, it consists of an inner polyethylene layer 14 and an outer crosslinked polyethylene layer 20, as shown in FIG. 5, and a cylindrical body with a head at only one end is obtained.

FIG. 6 shows a polyethylene sleeve, which is the object of the present invention, by cutting off both ends of the sleeve shown in FIG. 5 and leaving only the initially small diameter portion.

In each of the upper and lower figures, one side of the two-split mold is connected to the opening/closing means of the mold, and the other side is connected to the fixing means.

In the example illustrated above, a shrinkable sleeve having an inner layer of non-crosslinked polyethylene was described, but for a shrinkable sleeve without this layer, the process shown in FIG. It will be readily understood that the step of applying a polyethylene coating containing the agent is as follows.

Furthermore, if the flow characteristics of the inner and outer resins are different during production of the double sleeve, it is also possible to cover the core with a single injection molding.

Further, although the split molds are not shown in the drawings, it goes without saying that one side is provided with a fixing means and the other side is provided with a movable means so that they can be opened and closed automatically.

As described above, since the present invention exclusively applies injection molding technology, it is possible to mass-produce even sleeves with large diameters.Moreover, the present invention provides shrinkability only in the radial direction, and has no shrinkability at all in the length direction. No cross-linked polyethylene sleeves can be provided.

In carrying out the present invention, for example, when producing a shrinkable sleeve with ribs that are linear in the longitudinal direction, the present invention can be carried out in the same manner by using a core and a mold having a corresponding shape.

[Brief explanation of the drawing]

The figures show one embodiment of the present invention, in which Figure 1 is a partial longitudinal cross-sectional view of a mold in which a polyethylene layer containing no crosslinking agent is formed, and Figure 2 is a partial vertical cross-sectional view of a mold in which a polyethylene layer containing no crosslinking agent and a crosslinking agent are formed. FIG. 3 is a partial vertical cross-sectional view of another metal mold in which a double layer of polyethylene has been formed; FIG. A longitudinal cross-sectional view showing the state in which the diameter is expanded by applying pressure from inside the multilayer, Fig. 5 is a longitudinal cross-sectional view showing the structure of the sleeve taken out from the mold, and Fig. 6 shows both ends of the sleeve shown in Fig. 5. FIG. 7 is a perspective view showing the structure of the cylindrical double sleeve, and FIG. 8 is a perspective view showing the structure of the ribbed sleeve. 10... First mold, 10a, 10b... Half mold, 12... Core, 12a... Small diameter part, 12
b...Large diameter part, 14...Polyethylene not containing a crosslinking agent, 16...Resin flow hole, 18...Second mold, 18a, 18b...Half-split mold, 20...
Polyethylene containing crosslinking agent, 22...resin flow hole,
24...Third mold, 24a, 24b...Half mold, 26...Cavity, 28...Fluid passage,
30...Heater, 32...Air flow path in the core.

Claims (1)

[Claims] 1 Polyethylene containing a crosslinking agent is injected to a constant thickness into a cavity formed by a split mold and a core so that most of the center part has a constant small diameter and the ends have a constant large diameter part. a step of molding and a polyethylene layer containing a crosslinking agent on the core,
In another two-split mold having a cavity equal to the large diameter part, a step of heating the polyethylene while applying fluid pressure from the cavity side to crosslink the polyethylene to form a crosslinked polyethylene layer; and a step of forming a crosslinked polyethylene layer. While heating, blowing gas from inside the core to expand the small diameter part at the center within the cavity of the mold, and removing the expanded crosslinked polyethylene from the mold and core and cutting off both ends. A method for producing a heat-shrinkable polyethylene sleeve, comprising the steps of: