JP7602334B2 - Electrical fusion resin tube and its manufacturing method - Google Patents

Description

The present invention relates to an electrical fusion resin tube and its manufacturing method.

Electric fusion joints used to connect plastic pipes are made of thermoplastic resin and have sockets at both ends. A heating element is embedded in the inner circumference of each socket, and when electricity is passed through the heating element with the end of the plastic pipe inserted into the socket, the inner surface of the socket and the outer surface of the end of the plastic pipe melt, fusing both sides together and joining the electric fusion joint and the plastic pipe.

The outer surface of the plastic pipe may have a skin layer that contains impurities, oxidized deterioration substances, bleed-out additives, etc. This skin layer cannot be removed by cleaning with acetone and prevents good fusion. Therefore, it is necessary to scrape the outer surface of the end of the plastic pipe before electric fusion.

Known methods for preventing forgetting to scrape include marking the outer surface of the end of the plastic pipe in advance and laminating an identification layer of a different color from the plastic pipe (see, for example, Patent Document 1). When the outer surface is scraped, the marking and identification layer are removed, so that it is possible to visually confirm that the scraping operation has been completed.
However, with the visual confirmation method alone, there remains a slight possibility that the scraping operation will be forgotten and even confirmation that scraping is complete will be neglected, resulting in the electric fusion of a plastic pipe with a skin layer and an electric fusion joint.

Usually, after electric fusion is completed, water pressure is applied to the water-passing space of the plastic pipe and the electric fusion joint to check for leaks at the joint between the two (water pressure test). If the end of the plastic pipe has not been scraped, a joint defect can be discovered by the occurrence of water leakage during the water pressure test. However, depending on the condition of the outer surface of the plastic pipe, the joint defect may be so minute that the leak cannot be detected during the water pressure test and the pipe may be judged as passing. In this case, water may start to leak from the joint after service begins, and the leakage situation may worsen over time.

Therefore, Patent Document 2 proposes a method in which a fusion-preventing layer made of a material that will not fuse to the electric fusion joint during electric fusion is attached to the outer surface of the end of the resin pipe.
In this method, if the fusion-inhibiting layer is removed by scraping, the plastic pipe and the electrofusion joint can be electrofused. However, if scraping is forgotten and electrofusion is performed, the plastic pipe and the electrofusion joint will not be fused in the area where the fusion-inhibiting layer exists, so water leakage will inevitably occur during water pressure testing, and a joint defect can be detected.

Japanese Patent Application Publication No. 6-2794 JP 2019-158147 A

However, the method described in Patent Document 2 has the disadvantage that in order to attach a fusion-inhibiting layer to the outer surface of the resin pipe, an adhesive layer must be provided between them, resulting in a large thickness of the layer to be removed by scraping.
The present invention provides a novel resin tube for electrical fusion that can detect poor fusion caused by forgetting to scrape, and a method for manufacturing the same.

The present invention has the following aspects.
[1] A resin pipe for electrical fusion comprising a resin pipe body and a hard-to-fuse layer present on an outer surface of the resin pipe body, a part of the outer surface of the resin pipe body in the pipe axial direction being a planned fusion region to be used for fusion with the inner surface of an electric fusion joint, the hard-to-fuse layer being made of a resin composition having an MFR of less than 2.3 g/10 min, having a thickness of 550 μm or less, and being present continuously in the pipe axial direction at least in the planned fusion region.
[2] The resin tube for electrical fusion according to [1], wherein the resin contained in the fusion-resistant layer has a solubility parameter of 15.3 (J/cm ³ ) ^1/2 or more.
[3] The electrical fusion resin tube according to [1] or [2], wherein the resin contained in the hard-to-melt layer is polypropylene.
[4] The resin tube for electrical fusion according to any one of [1] to [3], wherein the resin contained in the resin composition constituting the outer surface of the resin tube body is polyethylene.
[5] The resin tube for electrical fusion according to any one of [1] to [4], wherein the resin tube body and the hard-to-melt layer are formed by a co-extrusion method.
[6] A method for producing an electric fusion resin tube according to any one of [1] to [4], comprising molding the resin tube body and the hard-to-melt layer by a co-extrusion method.

The present invention provides an electrical fusion resin tube that can detect poor connections caused by forgetting to scrape, and a method for manufacturing the same.

1 is a plan view showing an embodiment of an electrical fusion resin tube according to the present invention. FIG. 2 is an enlarged cross-sectional view of a main portion taken along line AA in FIG. 1.

The MFR (melt mass flow rate) of a thermoplastic resin is a value indicating the fluidity of the resin in a molten state, and the test method is specified by JIS and ISO.
For example, the MFR of polyethylene is specified in JIS K 6922-1:2018 and is measured under conditions of a temperature of 190° C. and a load of 5.0 kg. The MFR of polypropylene is specified in JIS K 6921-2 (ISO 19069-2:2016) and is measured under conditions of a temperature of 230° C. and a load of 2.16 kg.

<Resin tube for electrical fusion>
FIG. 1 is a plan view of an electric fusion resin tube according to this embodiment, and FIG. 2 is an enlarged cross-sectional view of a main portion taken along line AA in FIG.
The resin tube 1 for electrical fusion (hereinafter also simply referred to as a resin tube) of this embodiment has a resin tube body 10 and a non-fusible layer 11 present on the outer surface of the resin tube body 10. The resin tube body 10 is cylindrical and has openings 10a, 10b at both ends.

In the electrical fusion of the electrical fusion resin tube 1 and the electrical fusion joint (hereinafter also simply referred to as the joint), as described below, a part of the outer peripheral surface of the resin tube body 10 (heated area 10c) is fused to the inner peripheral surface of the joint.
In the pipe axis direction of the plastic pipe body 10, the area from the opening 10a of the plastic pipe body 10 to the end 10e of the nearby heating area 10c is the planned fusion area 12 used for fusion with the inner surface of the joint. The distance in the pipe axis direction from the opening 10a of the plastic pipe body 10 to the start end 10d of the heating area 10c and the distance from the start end 10d of the heating area 10c to the end end 10e are determined by the structure of the joint used for electric fusion.

The resin pipe body 10 is made of, for example, a resin composition mainly composed of polyolefin. In this specification, "a resin composition mainly composed of polyolefin" means a resin composition containing 50 mass% or more of polyolefin. Specifically, examples of the resin composition include a resin composition composed of one or more types of polyolefin, or a resin composition containing one or more types of polyolefin and additives as required. A resin composition containing fibers may also be used.
The polyolefin is preferably polyethylene, and more preferably high density polyethylene (HDPE).
In this embodiment, the resin pipe body 10 is made of a uniform resin composition. It may have a structure in which two or more layers having different compositions are laminated in the radial direction.
The radial size of the plastic pipe body 10 is, for example, a nominal diameter of 20 to 300 (outer diameter of 27 to 355 mm, thickness of 3.4 to 32.2 mm).

The resin contained in the resin composition (hereinafter also referred to as "resin composition B") constituting the outer surface of the resin pipe body 10 is preferably polyethylene. The MFR of resin composition B is preferably 0.1 to 2.3 g/10 min, more preferably 0.2 to 2.0 g/10 min. When the MFR of resin composition B is equal to or higher than the lower limit of the above range, it is excellent in moldability, and when it is equal to or lower than the upper limit, it is difficult to fuse to the hard-to-fuse layer.
In this specification, the MFR of the polyethylene-containing resin composition B is a value measured in accordance with JIS K 6922-1:2018 under conditions of a temperature of 190 ° C. and a load of 5.0 kg.

In this embodiment, the melt-resistant layer 11 is in the form of a continuous strip in the axial direction of the plastic pipe body 10 and exists over the entire length of the plastic pipe body 10 .
The hard-to-fuse layer 11 is a layer made of a resin composition having an MFR of less than 2.3 g/10 min (hereinafter also referred to as "resin composition A"). If the MFR is less than 2.3 g/10 min, the hard-to-fuse layer 11 and the inner peripheral surface of the joint are difficult to fuse together, and water leakage is likely to occur during a water pressure test. The MFR is preferably 2.0 g/10 min or less.

The resin composition A is, for example, a resin composition containing one or more resins and, if necessary, additives. The additives may contain coloring components such as pigments.
The solubility parameter of the resin contained in the resin composition A is preferably 15.3 (J/ ^cm3 ) ^1/2 or more, more preferably 17.0 (J/ ^cm3 ) ^1/2 or more, and even more preferably 19.0 (J/ ^cm3 ) ^1/2 or more. If the solubility parameter is equal to or more than the lower limit, the adhesive strength between the hard-to-melt layer 11 and the resin pipe body 10 is likely to be weakened, and peeling is likely to occur at the interface between the two.
It is preferable that the resin contained in the resin composition A is different from the resin contained in the resin composition B constituting the outer surface of the resin pipe body 10. The absolute value of the difference in the solubility parameters of the two is preferably 1.0 (J/ ^cm3 ) ^1/2 or more, more preferably 1.5 (J/ ^cm3 ) ^1/2 or more, even more preferably 2.0 (J/ ^cm3 ) ^1/2 or more, particularly preferably 3.0 (J/ ^cm3 ) ^1/2 or more, and most preferably 4.0 (J/ ^cm3 ) ^1/2 or more. If the absolute value of the difference in the solubility parameters is equal to or more than the lower limit, the adhesive strength between the hard-to-melt layer 11 and the resin pipe body 10 is likely to be weakened, and peeling is likely to occur at the interface between the two.
For example, the solubility parameter of HDPE used in manufacturing the resin pipe body 10 is 14.8 to 18.1 (J/cm ³ ) ^1/2 according to the polymer database.

The resin contained in the resin composition A is preferably polypropylene. The polypropylene may be a homopolymer (homopolypropylene) or a copolymer (random polypropylene, block polypropylene). The polypropylene may be one type or two or more types may be used in combination. It is more preferable that the resin composition A contains homopolypropylene.
The solubility parameter of homopolypropylene is 15.3 to 19.0 (J/cm ³ ) ^1/2 (literature value, polymer database).

The MFR of the polypropylene-containing resin composition A is preferably 0.3 g/10 min or more and less than 2.3 g/10 min, more preferably 0.45 to 2.0 g/10 min. When the MFR is equal to or more than the lower limit of the above range, the resin composition has excellent moldability, and when the MFR is equal to or less than the upper limit, the resin composition is prone to leak during a water pressure test.
In this specification, the MFR of the resin composition A containing polypropylene is a value measured in accordance with JIS K 6921-2 (ISO 19069-2:2016) under conditions of a temperature of 230 ° C. and a load of 2.16 kg.

The thickness of the hard-to-melt layer 11 is 550 μm or less, and preferably 300 μm or less. If the thickness of the hard-to-melt layer 11 is less than the upper limit, water leakage is likely to occur during water pressure testing. In addition, the hard-to-melt layer 11 can be easily removed by scraping.
The lower limit of the thickness of the hard-to-melt layer 11 is not particularly limited, and is greater than 0. From the viewpoint of ease of molding, the thickness is preferably 5 μm or more, and more preferably 10 μm or more.
The thickness of the non-melting layer 11 is obtained by measuring the thickness of the non-melting layer 11 in the radial direction of the resin pipe 1 in a cross section perpendicular to the axial direction of the resin pipe 1. If the thickness of the non-melting layer 11 is not uniform in the circumferential direction of the resin pipe 1, the maximum value is taken as the thickness of the non-melting layer 11.

<Production Method>
The plastic pipe 1 of this embodiment can be manufactured by molding the plastic pipe body 10 and the melt-resistant layer 11 by a co-extrusion method.
In the co-extrusion method, the resin composition constituting the resin pipe main body 10 and the resin composition A constituting the hard-to-melt layer 11 are extruded simultaneously using two extruders, passed through one die, and laminated and molded into the desired shape.
If the resin pipe is molded by the co-extrusion method, it is not necessary to provide an adhesive layer between the resin pipe body 10 and the hard-to-melt layer 11, so the thickness of the layer to be removed by scraping can be reduced. This makes the scraping operation more stable and easier.
In addition, by using the co-extrusion method, the costs of equipment and raw materials during molding can be easily reduced, and the molding temperature is not high compared to the method described in Patent Document 2, making stable production easier.

<How to use>
The plastic pipes 1 can be connected to each other or to other plastic pipes via electric fusion joints. The shape of the joint is not limited. For example, a joint that is cylindrical and has sockets at both ends, with the inner diameter of the sockets corresponding to the outer diameter of the plastic pipe body 10, can be used.

The joint is made of, for example, a resin composition mainly composed of polyolefin. Specifically, examples of the resin composition include a resin composition composed of one or more types of polyolefin, and a resin composition containing one or more types of polyolefin and additives as required.
The polyolefin is preferably polyethylene, and more preferably high density polyethylene (HDPE).

The resin contained in the resin composition (hereinafter also referred to as "resin composition C") constituting the inner surface of the joint is preferably polyethylene. The MFR of resin composition C is preferably 0.2 g/10 min or more, more preferably 0.4 g/10 min or more, in terms of fusion performance, and the upper limit is preferably 1.5 g/10 min or less, more preferably 2.0 g/10 min or less.
In this specification, the MFR of the resin composition C containing polyethylene is a value measured in accordance with JIS K 6922-1:2018 under conditions of a temperature of 190 ° C. and a load of 5.0 kg.

It is preferable that the resin contained in the resin composition A constituting the hard-to-fuse layer 11 is different from the resin contained in the resin composition C constituting the inner peripheral surface of the joint. The absolute value of the difference in the solubility parameters of the two is preferably 1.0 (J/cm ³ ) ^1/2 or more, more preferably 1.5 (J/cm ³ ) ^1/2 or more, even more preferably 2.0 (J/cm ³ ) ^1/2 or more, particularly preferably 3.0 (J/cm ³ ) ^1/2 or more, and most preferably 4.0 (J/cm ³ ) ^1/2 or more. If the absolute value of the difference in the solubility parameters is equal to or more than the lower limit, the bonding strength between the hard-to-fuse layer 11 and the inner peripheral surface of the joint after electric fusion is likely to be weak, and peeling is likely to occur at the interface between the two.
For example, the solubility parameter of HDPE used in the manufacture of electrofusion joints is 14.8 to 18.1 (J/cm ³ ) ^1/2 (literature values, polymer database).

The electric fusion step can be carried out in the following manner.
The end of the resin pipe body 10 including the region 12 to be fused is scraped in advance to scrape off the refractory layer 11 and the skin layer (a layer containing impurities, oxidized deterioration substances, bleed-out of additives, etc.). The scraping operation can be performed using a cutting tool such as a plane or an abrasive tool such as a sander. After scraping, the end of the resin pipe body 10 is cleaned with acetone to remove adhering shavings, etc., to prepare it in a state suitable for electric fusion.

After the scraping process, the end of the plastic pipe body 10 is inserted into the socket of the joint to a predetermined position. For example, the end of the plastic pipe body 10 is inserted until it abuts against a positioning protrusion protruding from the inner peripheral surface of the socket.
Next, electricity is passed through the heating element embedded in the inner circumferential surface of the receiving port. When electricity is passed through, the heating element generates heat, and the resin composition in the vicinity of the heating element is heated and melted. That is, a part of the inner circumferential surface of the receiving port and a part of the outer circumferential surface of the resin pipe body 10 adjacent thereto (heated area 10c) melt. These molten materials expand thermally and are pressurized inside the receiving port. After passing electricity for a predetermined time, the molten material is cooled and solidified, and the inner circumferential surface of the fitting and the outer circumferential surface of the resin pipe body 10 are integrally joined. In this way, the electrical fusion between the fitting and the resin pipe 1 is completed.
After completion of the electric fusion, a water pressure test is carried out. The water pressure test is preferably carried out under the conditions of a test water pressure of 1.75 MPa and a holding time of 1 minute.

In the present embodiment, if scraping is forgotten and electrical fusion is performed without confirming that scraping is complete (i.e., if electrical fusion is performed in a state where a non-fusible layer 11 is present on the outer surface of the intended fusion area 12), a water leak will occur during water pressure testing, and a poor joint will be detected, as shown in the examples described below.
The reason is considered as follows. The resin composition A constituting the hard-to-fuse layer 11 has a low MFR, so it is difficult to flow during electric fusion, and the fusion state is likely to be weak. If the MFR of the resin composition A is less than 2.3 g/10 min, the molten material of the hard-to-fuse layer 11 and the molten material of the inner circumferential surface of the joint and the outer circumferential surface of the resin pipe body 10 are difficult to mix, and the bonding strength after they are cooled and solidified is considered to be very weak. In addition, if the thickness of the hard-to-fuse layer 11 is 550 μm or less, it is considered that stress concentration on the hard-to-fuse layer 11 is likely to occur during water pressure testing. As a result, if a water pressure test is performed in a state where the resin pipe 1 and the joint are electrically fused without scraping, peeling of the fusion interface or destruction of the hard-to-fuse layer 11 easily occurs due to water pressure, and water leakage is considered to occur reliably.

Furthermore, when the solubility parameter of the resin constituting the hard-to-melt layer 11 is 15.3 (J/ ^cm3 ) ^1/2 or more, the difference between the solubility parameter of the resin constituting the resin pipe body 10 tends to become large. As a result, during electrical fusion, the molten material of the hard-to-melt layer 11 hardly mixes with the molten material on the outer circumferential surface of the resin pipe body 10, and peeling tends to occur at the interface between them after cooling and solidification.
Furthermore, if the solubility parameter of the resin constituting the hard-to-fuse layer 11 is 15.3 (J/ ^cm3 ) ^1/2 or more, the difference from the solubility parameter of the resin constituting the joint is likely to become large. As a result, the molten material of the hard-to-fuse layer 11 hardly mixes with the molten material on the inner peripheral surface of the joint during electrical fusion, and peeling is likely to occur at the interface between them after cooling and solidification.

Furthermore, if the color of the non-fusible layer 11 is different from the color of the outer surface of the plastic pipe body 10, it is possible to visually confirm that the non-fusible layer 11 has been removed, which is preferable in that it makes it easy to confirm that the scraping operation is complete.

The resin pipe 1 of this embodiment can also be used for connection using mechanical joints (watertight packing, cap nut tightening, etc.) without removing the non-melting layer 11. Because the non-melting layer is thin, the watertight function of the packing, etc. is not impaired.

In this embodiment, the hard-to-melt layer 11 is provided over the entire length of the resin pipe body 10, but it is sufficient that the hard-to-melt layer 11 exists continuously in the axial direction of the pipe at least in the intended fusion region 12.
For example, when the plastic pipe 1 is to be cut to an arbitrary length for use, any position of the plastic pipe body 10 can become the planned fusion region 12, so it is preferable that the non-fusible layer 11 is present continuously over the entire length of the plastic pipe body 10. On the other hand, when the plastic pipe 1 is to be used without being cut, the non-fusible layer 11 may be provided only on the end portion including the planned fusion region 12.
In order to facilitate simultaneous molding of the resin pipe body 10 and the non-melting layer 11 by co-extrusion, it is preferable that the non-melting layer 11 be present continuously over the entire length of the resin pipe body 10 .

In this embodiment, the band-shaped non-melting layer 11 is present on a portion of the circumference of the resin pipe body 10, but the non-melting layer may be present on the entire circumference.
For example, the entire outer surface of the plastic pipe body 10 may be covered with the hard-to-melt layer 11. Alternatively, when the hard-to-melt layer is provided only on the end portion of the plastic pipe body 10, the hard-to-melt layer may be present over the entire circumference of the end portion.
When the hard-to-melt layer 11 is in a band shape, the width of the hard-to-melt layer 11 in the circumferential direction is, for example, preferably 5 mm or more, and more preferably 10 mm to 170 mm.

The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.
(Examples 1 to 10)
Examples 1 to 6 are working examples, and Examples 7 to 10 are comparative examples.

A resin composition A constituting the melt-resistant layer 11 and a resin composition B (MFR: 0.4 g/10 min) constituting the resin pipe body 10 were prepared.
The resin contained in resin composition A was homopolypropylene (solubility parameter: 17.0 (J/cm ³ ) ^1/2 ), and the resin contained in resin composition B was HDPE (solubility parameter: 16.4 (J/cm ³ ) ^1/2 ). Resin composition A was colored black, and resin composition B was colored blue.
As the resin composition A, three types (the following resin compositions A1 to A3) having different MFR were prepared.
Resin composition A1: MFR is 0.45 g/10 min.
Resin composition A2: MFR is 2.0 g/10 min.
Resin composition A3: MFR is 2.3 g/10 min.

Resin composition A and resin composition B were molded by co-extrusion to produce a resin pipe 1 having the structure shown in Figs.
The resin pipe body 10 made of resin composition B had a nominal diameter of 50, an outer diameter of 60 mm, a thickness of 5.5 mm and a length of 5 m.
The hard-to-melt layer 11 made of the resin composition A was provided continuously over the entire length of the resin pipe body 10 so as to cover the entire outer surface of the resin pipe body 10 .
The type of resin composition A and the thickness of the melt-resistant layer 11 were changed as shown in Table 1 to produce 10 types of resin pipes 1 (Examples 1 to 10).

In each example, two of the obtained resin pipes (5 m) were joined via an electric fusion joint without scraping, and then a water pressure test was performed by the following method.
The resin contained in resin composition C constituting the inner peripheral surface of the electric fusion joint was HDPE (solubility parameter: 16.4 (J/cm ³ ) ^1/2 ), and the MFR of resin composition C was 0.4 g/10 min.
[Water pressure test]
A water pressure of 1.75 MPa was applied to the pipe consisting of the two resin pipes and the electric fusion joint, and the pressure was maintained for 1 minute, and then the pressure was temporarily reduced to 1.0 MPa. After 3 minutes had elapsed while maintaining this water pressure, the presence or absence of water leakage was visually confirmed.
The results are shown in Table 1. The cases where leakage occurred are marked with an ◯, and the cases where leakage did not occur are marked with an X.

As shown in Table 1, in Examples 1 to 6 in which the MFR of the resin composition A constituting the hard-to-fuse layer was less than 2.3 g/10 min and the thickness of the hard-to-fuse layer was 550 μm or less, a large amount of water leakage occurred. Therefore, the connection failure caused by forgetting to scrape was detected.
In contrast, in Example 7 in which the MFR of the resin composition A was less than 2.3 g/10 min and the thickness of the hard-to-melt layer was 700 μm, no water leakage was observed.
Furthermore, in Examples 8 to 10 in which the thickness of the hard-to-melt layer was 550 μm or less but the MFR of the resin composition A was 2.3 g/10 min, no water leakage was observed.

Reference Signs List 1: Resin tube for electric fusion 10: Resin tube body 11: Hard-to-fuse layer 12: Region to be fused

Claims (5)

A resin pipe body and a melt-resistant layer on an outer surface of the resin pipe body,
a part of an outer surface of the resin pipe body in the pipe axial direction is a fusion region to be used for fusion with an inner surface of an electric fusion joint,
the melt-resistant layer is made of a resin composition having an MFR of less than 2.3 g/10 min, the resin composition containing polypropylene,
The resin tube for electrical fusion, wherein the hard-to-fuse layer has a thickness of 550 μm or less and is present continuously in the axial direction of the tube at least in the region to be fused. The resin tube for electrical fusion according to claim 1, wherein the polypropylene has a solubility parameter of 15.3 (J/cm ³ ) ^1/2 or more. 3. The resin tube for electrical fusion according to claim 1 , wherein the resin contained in the resin composition constituting the outer surface of the resin tube body is polyethylene. The resin tube for electrical fusion according to any one of claims 1 to 3 , wherein the resin tube body and the hard-to-melt layer are formed by co-extrusion. A method for producing the resin tube for electrical fusion according to any one of claims 1 to 3 , comprising forming the resin tube body and the hard-to-melt layer by a co-extrusion method.

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