JPH08296785A - Electric fusion joint and manufacture of the same - Google Patents

Abstract

PURPOSE: To improve a weather resisting property and chlorine water resisting property by providing an inner tube layer having a heating member, intermediate layer and outer tube layer and forming the inner tube layer, intermediate tube layer and outer tube layer of at least two kinds of thermoplastic resin. CONSTITUTION: The electric fusion welding joint 1 consists of an inner tube layer 10 and intermediate layer containing no carbon black and an outer tube layer 40 combining about 2-3% of medium density polyethylene. The inner tube layer 10 is formed integrally with a spiral recessed groove and provided on both ends with a base seat erect a connector pin 3. An electric heating wire 2 as a resistance heating wire is wound along the recessed groove and both ends thereof are connected to the connector pin 3. Thus, the resin combining the carbon black is used for the outer tube layer 40, so that the weather resisting property is obtained, and the resin containing no carbon black is used for the inner tube layer 10 and intermediate layer 20, so that the sufficient durability of a chlorine water resisting property is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric fusion joint having a plurality of structures, which is used for water supply and hot water supply piping and has an inner layer containing no carbon black and an outer layer containing carbon black, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, there is a polyethylene pipe containing carbon black in consideration of weather resistance so that it can be used outdoors as a pipe used for hot water supply and hot water supply piping. However, it has been found that carbon black has a catalytic action against the deterioration of chlorine water, and when it is contacted with water containing chlorine for a long time, water bubbles,
So-called blisters may occur and rarely cause deterioration such as peeling. Therefore, in order to improve the chlorine water resistance as well, a polyethylene pipe having a two-layer structure consisting of an inner layer of polyethylene not containing carbon black (called natural) and an outer layer of polyethylene containing carbon black, a so-called two-layer pipe (see JISK6762). ) Is becoming more popular.

On the other hand, the electric fusion splicing joint (hereinafter sometimes simply referred to as joint) is well known, and recently, it has come to be used also for water supply and hot water supply. An example is shown in FIG. In this joint, the heating wire 2 is spirally wound and embedded in the inner peripheral portion of the both end receiving portion 61 of the joint main body 60 made of a thermoplastic resin such as polyethylene or polybutene, and both ends are connected to the connector pin 3 rising to the outside. Connected.
The fusion control is performed by passing a current through the heating wire from an external controller, but is not as strict as a normal gas joint, and is often energized for a predetermined time for each product size.
The left side of the figure shows the state in which the double-layered pipe 5 is inserted, and the right side shows the state after fusion.

By the way, in the joint for supplying hot water and hot water, for the purpose of improving the weather resistance and the chlorine resistance like the above-mentioned pipe, for example, in JP-A-4-370493, a medium to high density polyethylene is provided with a certain amount of It has been proposed to incorporate carbon black.

Further, Japanese Unexamined Patent Publication No. 2-186193 discloses a joint having a two-layer structure in which a non-crosslinked polyethylene body having a heating wire embedded therein is arranged and the outside thereof is covered with a crosslinked polyethylene having excellent heat resistance. Has been done. In addition, since the cross-linked polyethylene itself is not flowable and cannot be injection-molded in this joint manufacturing method, the cross-linked polyethylene in an uncross-linked state is injection-molded into the inner layer formed in advance with non-cross-linked polyethylene, and then integrally molded. The cross-linking treatment is performed so that only the outer layer is cross-linked.

[0006]

However, as can be seen from FIG. 6, the inner surface of the joint and the outer surface of the pipe are fused with a gap e left between them, so that the circulating water also melts in the gap e. It will also penetrate the landing part f and will be attacked by chlorine. In such a case, the former one of the above-mentioned conventional techniques is basically weak in chlorine water resistance and is anxious about long-term quality because most of it contains carbon black. On the other hand, in the latter case, since the outer layer does not contain carbon black, it is significantly deteriorated by ultraviolet rays and cannot be used outdoors. Even if carbon black is blended in the outer layer, the natural inner layer is thin and most of it is a layer containing carbon black. Therefore, similarly to the above, there is a problem that deterioration due to attack of chlorine water occurs.

The present invention solves such a problem, and provides an electric fusion joint having weather resistance and sufficiently improved chlorine water resistance, and a manufacturing method capable of efficiently manufacturing this joint without defects. The purpose is to do.

[0008]

The present invention has achieved the above object by forming a joint having a multilayer structure by a manufacturing method in which each layer is molded, and by constructing each layer with a resin material suitable for the required characteristics. It is a thing. That is, the present invention comprises an inner cylinder layer having a heating member in the inner peripheral portion, an intermediate layer formed outside the inner cylinder layer, and an outer cylinder layer formed outside the intermediate layer. And the intermediate layer and the outer cylinder layer are electrofusion joints made of two or more kinds of thermoplastic resin materials. Here, each of the intermediate layer and / or the outer cylinder layer is 2
As a multi-layered structure including more than one layer, each may be molded with resins having different characteristics. Further, in the case of water supply and hot water used outdoors, it is desirable that carbon black be blended in the resin of the outer cylinder layer and carbon black be not blended in the resin of the intermediate layer and the inner cylinder layer. At this time, the inner cylinder layer and the intermediate layer can be made of the same natural polyethylene, or the inner cylinder layer can be made of medium density polyethylene and the intermediate layer can be made of high density polyethylene by combining resins having different characteristics.

Further, according to the present invention, an inner cylinder member made of a thermoplastic resin a is molded, a heating wire is wound around the inner cylinder member, and connector pins are connected to both ends of the inner cylinder member. It is mounted in the cavity, the thermoplastic resin b is injection-molded to form an intermediate member having an intermediate layer formed on the outside of the inner cylindrical member, and the intermediate member is mounted in the cavity of the joint body molding die. Then, the thermoplastic resin c is injection-molded to form an outer cylinder layer on the outer side of the intermediate member, and the joint body is molded. Here, it is desirable to use different resins having different characteristics as the thermoplastic resins a, b and c. For example, the resins a and b are natural ones containing no carbon black, and the resin c is blended with carbon black. However, it is assumed here that they are included in different kinds of resins.

[0010]

As described above, a joint having different characteristics can be obtained by selectively forming the inner cylinder layer, the intermediate layer and the outer cylinder layer with different resin materials. For example, since the outer cylinder layer uses a resin containing carbon black, it has sufficient weather resistance. If both the inner cylinder layer and the intermediate layer are made of a resin that does not contain carbon black, the natural layer becomes thicker due to the presence of the intermediate layer, so that it has sufficient durability against chlorine water resistance. Furthermore, the inner cylinder layer is medium density polyethylene,
If the middle layer is made of high density polyethylene, etc., it will be excellent in strength, and if the inner cylinder layer is made of a resin that has a good compatibility with the pipe to be connected, the strength and performance of the fused part will be excellent. . In this way, it is possible to obtain joints having different characteristics for each layer.

In the above-mentioned manufacturing method, the step of manufacturing the inner cylinder member, the step of manufacturing the intermediate member, and the step of manufacturing the final joint body are separately performed, and the resin is laminated on the outside of each member. In other words, since it is a multi-layer molding means, it is possible to selectively change the resin material for each layer. This multi-layer molding is more efficient if the manufacturing of each member is performed synchronously, such as simultaneously molding the intermediate member and the joint body while molding the inner tubular member. Further, particularly in a thick-walled joint having a large diameter, the molding time of each member can be shortened, so that the overall molding tact is shortened, and at the same time, the possibility of defects such as sink marks is reduced.

[0012]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of an electric fusion joint showing a first embodiment of the present invention. FIG. 2 is a schematic diagram for explaining the molding process. FIG. 3 is a sectional view of an electric fusion splicing joint showing a second embodiment of the present invention, and shows a state in which a two-layer tube is inserted on the right side.
FIG. 4 is a top view of an injection molding die for explaining the manufacturing method of the present invention. In these figures, the same reference numerals indicate the same parts.

First, the joint 1 shown in FIG. 1 has an inner cylinder layer 10 of natural medium-density polyethylene containing no carbon black, an intermediate layer 20 of natural medium-density polyethylene containing no carbon black, and a few layers of carbon black.
% Of a medium density polyethylene outer cylinder layer 40.
The inner cylinder layer 10 corresponds to an inner cylinder member described later and is integrally formed with a spiral groove 13, and the connector pins 3 are provided at both ends.
A pedestal for standing is provided (see FIG. 2). The heating wire 2 is a resistance heating wire wound around the groove 13, and both ends thereof are connected to the connector pin 3. However, the heating element does not necessarily have to be a heating wire, and may be a heating element such as a sheet heating element, a conductive resin, or a coated heating wire. A middle layer 20 is provided outside the inner cylinder layer 10.
Is provided and the inner cylinder layer 10 and the intermediate layer 20 are combined to form an intermediate member 30 (see FIG. 2). The outer cylinder layer 40 is provided outside the intermediate layer.
To form the joint body 1 (see the lower part of FIG. 2).

Now, in the electric fusion joint, the distance from the heating wire 2 to the inner surface of the joint is an important dimension for determining the quality of the fusion, and is usually on the order of 0.1 mm. Therefore, the inner cylinder layer 10 is inevitably a thin layer, and in this respect, it is weak against the attack of chlorine water. However, as shown in the figure, by providing the thick intermediate layer 20 separately, the natural layer becomes thicker, and it becomes an excellent joint that sufficiently withstands chlorine water resistance. The middle layer 20 occupies most of the natural layer, but the total thickness is 60%.
It is recommended to make up to 80% natural layer (inner cylinder layer + middle layer). On the other hand, even though the outer cylinder layer 40 is thin, since it contains an appropriate amount of carbon black, it is sufficiently excellent in weather resistance. Although the intermediate layer 20 and the outer cylinder layer 40 are in a uniform single-layer state, in some cases, the intermediate layer and / or the outer cylinder layer may be two layers.
It can also be formed in layers and three layers.

Next, the joint 15 of FIG. 3 is composed of an inner cylinder layer 11, an intermediate layer 21 and an outer cylinder layer 41, as in the above example. However, the inner cylindrical layer 10 is integrally provided with a cylindrical extending portion 12 that is sealingly fitted to the inner surface of the pipe 5 to be connected. The outer surface of the extending portion 12 is formed into a tapered surface whose diameter is reduced toward the inner side, or an O-ring or a sealant is interposed so as to prevent the circulating water from entering the fused portion. As a result, the adverse effect of chlorine water can be further reduced.
Further, the presence of the extending portion 12 is convenient because it has an effect of centering the pipe, an effect of preventing the pipe from coming off, and an effect of receiving the resin expansion pressure at the time of fusion. Further, in this example, the weather resistance is further improved by covering the outer cylinder layer 41 up to the end face side of the joint.

Although the above-mentioned embodiment is for water supply and hot water supply as an example, it can be applied for drainage and gas. At this time, a resin having good compatibility with the pipe to which the inner tubular layer is to be connected is used, or in consideration of strength, the inner tubular layer is made of medium density polyethylene and the intermediate layer is made of high density polyethylene. Resin density, for example, low density is 0.910 to 0.930 g / cm
³ , medium density is 0.930 to 0.942 g / cm ³ , high density is 0.942 to g
/ Cm ^3, and it is possible to combine these appropriately.
There are also modifications such as forming them from polybutene.

Next, the manufacturing method of the present invention will be described.
FIG. 4 shows an example of a mold, and in this example, three cavity parts A for molding molten resin in a set of molds 4,
B and C are provided. The outer diameters of the respective cavity portions are sequentially increased, and a common mandrel 6 is attached to each of the cavity portions so that they can be molded. The molten resin injected from the die inlet 7 passes through the runner 8 and the gate 9 and the respective cavities A, B, C.
Filled inside. In this example, the same resin is injected from the inlet 7 into the cavities A and B, and the resin having different characteristics from the inlet 7'is injected into the cavity C. Naturally, the cavities A, B and C are injected into the cavities A, B and C, respectively. Alternatively, another resin may be injected. Further, each may be molded by a different mold.

First, when the mandrel 10 is mounted in the cavity A and the molten resin is injected, the thin inner cylindrical member 10 of the electric fusion joint shown in FIGS. 1 and 2 is molded. After the resin injection-molded in the cavity A is solidified, the inner cylinder member 10 with the mandrel 6 is taken out from the mold, and the heating wire 2 is inserted into the outer peripheral groove 13 of the inner cylinder member 10 with the mandrel 6 attached. Wind up. The connector pins 3 and 3 are inserted into and fixed to the ends of the inner cylinder member 10, and both ends of the heating wire 2 are connected to the connector pins 3.

Inner cylinder member with heating wire 2 molded in this way
10 is attached to the cavity of B with the mandrel 6 attached, and the molten resin of the intermediate layer 20 is injection-molded in the cavity of B to obtain the intermediate member 30 including the inner cylinder member 10 and the intermediate layer 20. Even while the intermediate member 30 is being injection-molded, the inner tubular member 10 is molded in the cavity portion A. After the intermediate member 30 is injection-molded in the cavity B, the intermediate member is molded with the mandrel 6 inside the mold as described above.
The intermediate member 30 is taken out, then this intermediate member 30 is mounted in the cavity portion of C, and a resin different from the cavities A and B, for example, a resin containing carbon black is injection-molded to form the intermediate member.
An outer cylinder layer 40 is injection-molded on the outer surface of 30. Even while the outer cylinder layer 40 is injection-molded in the cavity portion C, the inner cylinder member 10 in the different cavity portion A and the intermediate member 30 in the cavity portion B are synchronously molded. . After molding the outer cylinder layer 40 on the outer surface of the intermediate member 30 in this manner, the joint molded product is taken out from the mold with the mandrel 6 attached, and the mandrel 6 is removed from the molded product. The joint 1 is completed.

The resin layers of the inner cylinder layer 10, the intermediate layer 20, and the outer cylinder layer 40 thus formed into three layers are melted at their contact surfaces by the heat of the molten resin injected to the outer surface of each layer. The electro-fusion joint 1 is attached and integrally bonded. At this time, it may be difficult to distinguish between the layers of the joint, but different characteristics are obtained for each layer. As a result of the above, the cavity portion A,
The longest molding time of either B or C becomes the overall tact time, and the injection molding time of each layer is shortened, so that the overall molding tact is greatly shortened.

FIG. 5 is a top view of a mold showing another embodiment. In this example, the inner cylinder member 10 and the intermediate member 30 are the same mold 70.
This is an example in which the mold, that is, the molding machine, is divided so that the finished product of the joint body 1 is separately molded by the mold 80. Therefore, similarly to the above, it is suitable that the inner cylinder layer and the intermediate layer are synchronously molded with the same resin, and the outer cylinder layer 40 is injection molded with another resin. When the amount and type of injection resin increase, a larger injection molding machine and number are required, which causes problems in capital investment and installation location. Therefore, it may be more efficient to manufacture the mold by dividing it into a plurality of sets according to the amount of molding resin and the capacity of the molding machine.

[0022]

As described above, according to the present invention, it is possible to efficiently manufacture a multi-layered joint without defects.
Therefore, since it is possible to mold each layer with a different resin, it is possible to obtain an electric fusion joint having different characteristics with each layer having a characteristic. As an example, the electrical fusion-bonded joint has weather resistance and sufficient chlorine water resistance.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an electric fusion joint showing an embodiment of the present invention.

2 is a schematic view showing a process of forming the joint of FIG. 1. FIG.

FIG. 3 is a sectional view of an electric fusion joint showing another embodiment of the present invention.

FIG. 4 is a top view of a mold for explaining the manufacturing method of the present invention.

FIG. 5 is a top view showing a mold of another embodiment used in the manufacturing method of the present invention.

FIG. 6 is a sectional view showing an example of a conventional electric fusion joint.

[Explanation of symbols] 1,15 ... Electrical fusion joint 2 ... Heating wire
3 ... Connector pin 4, 70, 80 ... Mold for molding 5 ... Double layer tube
6 ... Mandrel 7, 7 '... Ejection port 8, 8' ... Runner
9, 9 '... Gate 10, 11 ... Inner tube layer, Inner tube member 20, 21 ... Intermediate layer
30, 31 ... Intermediate member 40, 41 ... Outer cylinder layer

Claims (6)

[Claims] 1. An inner cylinder layer having a heating member on an inner periphery thereof, an intermediate layer formed outside the inner cylinder layer, and an outer cylinder layer formed outside the intermediate layer, the inner cylinder layer comprising: An electric fusion-bonding joint, wherein the intermediate layer and the outer cylinder layer are made of two or more kinds of thermoplastic resins. 2. The electric fusion joint according to claim 1, wherein each of the intermediate layer and / or the outer cylinder layer has a multilayer structure of two or more layers. 3. The electric fusion bonding according to claim 1, wherein carbon black is blended in the resin of the outer cylinder layer, and carbon black is not blended in the resin of the intermediate layer and the inner cylinder layer. Fittings. 4. An inner cylinder member made of a thermoplastic resin a is molded, a heating member is provided on the inner cylinder member, and the inner cylinder member is mounted in a cavity of a mold for molding an intermediate member. b is injection-molded to form an intermediate member having an intermediate layer formed on the outer side of the inner cylindrical member, the intermediate member is mounted in the cavity of the joint body molding die, and the thermoplastic resin c is injection-molded. A method of manufacturing an electric fusion-bonded joint, wherein an outer cylinder layer is formed outside the intermediate member to obtain a joint body. 5. The method for manufacturing an electric fusion joint according to claim 4, wherein the step of molding the intermediate layer and / or the step of molding the outer cylinder layer is performed in multiple stages. 6. One or a plurality of molding dies each having an inner cylinder member molding die portion, an intermediate member molding die portion, and a joint body molding die portion are provided. A step of molding the inner cylindrical member in each cavity of the mold,
The method for producing an electric fusion joint according to claim 4 or 5, wherein the step of forming the intermediate member and the step of forming the joint body are performed in synchronization with each other.