JP7497495B2 - Piping structure and manufacturing method thereof - Google Patents

Description

The present invention relates to a piping structure and its manufacturing method.

2. Description of the Related Art Conventionally, when connecting synthetic resin gas pipes or water and sewerage pipes, a technique is known in which an electric fusion joint having an electric heating wire embedded therein is energized to fuse and connect the pipes.
When connecting synthetic resin pipes by fusion, the optimum conditions for fusion, such as voltage and time, vary depending on the properties of the resin and the diameter and thickness of the pipes.
Fusion conditions vary depending on the type of pipe or joint, and a fusion management tag on which information about the fusion conditions is recorded is attached to an electric fusion joint (see, for example, Patent Document 1).

JP 2009-92111 A

The bodies of the pipes and fittings are color-coded according to their type.
However, fittings are not necessarily colored the same as pipes having the same application, and it is desirable to be able to easily identify the application of a fitting regardless of the color of the fitting body (main body portion).

The present invention aims to develop an electric fusion joint, a piping structure, and a method for manufacturing an electric fusion joint that allows the use of the joint to be easily identified.

In order to solve the above problems, the present invention has the following aspects.
[1] An electric fusion joint comprising a main body and an identification portion formed integrally with the main body, the identification portion having a color difference (ΔE) of 1 or more with respect to the main body, and the use of the joint can be identified based on the color of the identification portion.
[2] The electric fusion joint described in [1], wherein the main body portion is formed in a tubular shape, and the identification portion is formed in a layer that covers the inner surface of the main body portion from the inside in the radial direction.
[3] The electric fusion joint described in [1], wherein an electric heating wire is embedded in the inner circumferential surface of the main body, and the identification portion covers the electric heating wire.
[4] A piping structure comprising an electric fusion joint according to any one of [1] to [3], a cylindrical main body, and a resin pipe having one or more identification layers formed integrally with the outer surface of the main body and extending in the axial direction of the main body, wherein a color difference (ΔE) between the identification portion and the identification layer is 10 or less.
[5] A method for manufacturing an electric fusion joint as described in [2], comprising the steps of: placing the identification part in a resin molding die; and injecting a first resin onto the outer peripheral surface of the identification part to mold the main body.
[6] A method for manufacturing an electric fusion joint as described in [3], comprising the steps of winding the heating wire covered by the identification part around a core die, opening a gap from the outside around the core die around which the heating wire is wound, and fitting a resin molding die into the resin molding die; and injecting a first resin into the resin molding die to mold the main body.

The present invention also has the following aspects.
<1>
An electric fusion joint; and a resin tube inserted into an opening of the electric fusion joint,
The electric fusion joint includes a main body and a first identification portion integrally formed with the main body,
The resin tube includes a cylindrical main body and a second identification portion integrally formed on an outer surface of the main body,
A piping structure, wherein the first distinguishable portion and the second distinguishable portion are of the same color scheme.
＜2＞
the first identification portion has a color difference (ΔE) of 1 or more with respect to the main body portion in the L*a*b* color system defined in JIS Z8781-4:2013;
The piping structure according to <1>, wherein the color difference (ΔE) between the second distinguishable portion and the main body is 1 or more.
＜3＞
The piping structure according to <1> or <2>, wherein the color difference (ΔE) between the first distinguishing portion and the second distinguishing portion in the L*a*b* color system defined in JIS Z8781-4:2013 is 10 or less.
＜4＞
The piping structure according to any one of <1> to <3>, wherein the second identification portion is a band extending in a pipe axis direction of the main body.
＜5＞
Confirm that the first identification portion of the electric fusion joint and the second identification portion of the plastic pipe are the same color.
Next, the plastic pipe is inserted into an opening of the electric fusion joint, and electricity is passed through an electric heating wire of the electric fusion joint to join the plastic pipe and the electric fusion joint.

The electric fusion joint of the present invention makes it easy to identify the purpose of the joint.

1 is a cross-sectional view showing an electric fusion joint according to one embodiment of the present invention. FIG. 11 is a cross-sectional view showing an electric fusion joint according to another embodiment of the present invention. 1 is a partial cross-sectional view showing a piping structure according to an embodiment of the present invention. 4 is a side view of the piping structure of FIG. 3 as viewed from a direction A.

[Electric fusion joint]
The electric fusion joint of the present invention comprises a joint body and an identification member attached to the outer surface of the joint body.
Hereinafter, an electric fusion joint according to one embodiment of the present invention will be described with reference to the drawings.

1, the electric fusion joint 1 of this embodiment includes a main body 10 formed in a tubular shape, and an identification part 30 formed integrally with the main body 10. The electric fusion joint 1 is a so-called socket formed in a straight tube shape.
The identification portion 30 is formed in a layer that covers the inner peripheral surface 10a of the main body portion 10 from the radially inside. A ring-shaped stopper 14 is formed on the inner peripheral surface near the center in the tube axial direction of the identification portion 30. The stopper 14 has the function of stopping the connected resin tube.
The electric fusion joint 1 comprises terminal cover parts 11, 11 protruding from the outer surface of a main body part 10, and terminals 12, 12 provided in the vicinity of the terminal cover parts 11, 11.
Openings 21 and 22 are formed on both ends of the main body 10 in the tube axis direction.

The electric fusion joint 1 is equipped with a heating wire 13 such as a nichrome wire. The heating wire 13 is embedded in the inner peripheral surface 10a of the main body 10 of the electric fusion joint 1. When electricity is applied, the heating wire 13 generates heat and melts the surrounding synthetic resin.

The terminal cover parts 11, 11 are formed in a cylindrical shape integral with the main body part 10 in order to protect the metal terminals 12, 12 therein.
The outer diameter of the terminal cover parts 11, 11 is determined to match the connector (not shown) of the fusion device, and is therefore of a constant size regardless of the resin properties, diameter, thickness, etc. of the resin tube to be connected.

The terminals 12, 12 protected by the terminal cover parts 11, 11 are connected to a heating wire 13 embedded in the inner surface 10a of the main body part 10, and are configured so that electricity can be passed through the heating wire 13 by connecting the connector of the fusion device to the terminals 12, 12.

The identification portion 30 is colored in a color that corresponds to the application of the electric fusion joint 1 .
Examples of applications of the electric fusion joint 1 include water supply, sewage, gas, plants, and rentals.
The electric fusion joint 1 has different sizes, shapes, withstand pressures, etc. depending on the application, and is preferably connected to a resin pipe used for the same application.
By matching the use of the electric fusion joint 1 with the use of the plastic pipe, the electric fusion joint 1 and the plastic pipe can be joined more reliably, making it easier to prevent leakage of fluid flowing through the path of the plastic pipe.

The color difference (ΔE) between the identification portion 30 and the main body portion 10 is 1 or more, preferably 5 or more, and more preferably 10 or more. If the color difference is equal to or more than the above-mentioned lower limit, the worker can easily recognize the identification portion 30 during the fusion work. The upper limit of the color difference is not particularly limited, but is, for example, 100 or less, and preferably 80 or less in practical use.
The color difference may be the color difference in the L*a*b* color system defined in JIS Z8781-4:2013.
The color difference can be measured using a spectrophotometer (handy spectrophotometer "NF333" manufactured by Nippon Denshoku Industries Co., Ltd.), and it is preferable to measure in a darkened environment such as a darkroom.
Here, the color difference (ΔE) is calculated by the following formula.
ΔE=√((L ₁ −L ₂ ) ² +(a ₁ −a ₂ ) ² +(b ₁ −b ₂ ) ² ) (1)
In formula (1), _L1 , _a1 , and _b1 respectively represent the lightness L, chromaticity a in the red direction, and chromaticity b in the yellow direction of the identification unit 30, and _L2 , _a2 , and _b2 respectively represent the lightness L, chromaticity a in the red direction, and chromaticity b in the yellow direction of the main body unit 10.

Examples of the synthetic resin (first resin) constituting the main body 10 include polyolefin resins such as high density polyethylene, medium density polyethylene, cross-linked polyethylene, polypropylene, and polybutene, polyphenylene sulfide, polyethylene terephthalate, and vinyl chloride.
From the viewpoints of moldability and cost, the first resin is preferably high-density polyethylene, medium-density polyethylene, or crosslinked polyethylene, and more preferably high-density polyethylene or medium-density polyethylene.
These first resins may be used alone or in combination of two or more.

The mass average molecular weight of the first resin is preferably 1.0 × 10 ² or more and 1.0 × 10 ⁶ or less, and more preferably 1.5 × 10 ² or more and 3.0 × 10 ⁵ or less. When the mass average molecular weight is within the above numerical range, the main body 10 is likely to have desired physical properties as a joint.
The mass average molecular weight of the first resin is measured in accordance with JIS K 7252-1.

The content of the first resin is preferably 90% by mass or more and 100% by mass or less with respect to the total mass of the main body 10. When the content of the first resin is within the above numerical range, the main body 10 is likely to have the desired physical properties as a joint.

In addition to the first resin, the main body 10 may contain various additives such as antioxidants, ultraviolet absorbers (UVA), light stabilizers, and pigments.

The synthetic resin (second resin) constituting the identification unit 30 may be the same as the first resin. The second resin may be the same as the first resin or may be different.

In addition to the second resin, the identification portion 30 preferably contains a colorant from the viewpoint of improving the distinguishability between the main body portion 10 and the identification portion 30. Examples of the colorant include pigments and dyes, and commercially available products can be used.
Examples of pigments include organic pigments such as azo-based, phthalocyanine-based, threne-based, and dye lake-based pigments; and inorganic pigments such as oxide-based, molybdenum chromate-based, sulfide-selenide-based, and ferrocyanide-based pigments.
The type and content of the colorant can be appropriately determined depending on the color of the identification portion 30. The color of the identification portion 30 can be appropriately determined depending on the application of the electric fusion joint 1.
For example, if the electrofusion joint 1 is used for drinking water, the identification portion 30 is preferably yellow or red, and if the electrofusion joint 1 is used for gas, the identification portion 30 is preferably blue or black.
By including a coloring agent in the identification portion 30, the identification portion 30 can be colored in a color that corresponds to the application of the electrofusion joint 1. In addition, the application of the electrofusion joint 1 can be identified by the color of the identification portion 30, regardless of the color of the main body portion 10.

Next, a method for manufacturing the electric fusion joint 1 will be described.
The manufacturing method of the electric fusion joint 1 includes the steps of placing the identification portion 30 in a resin molding die (not shown) and injecting a first resin onto the outer peripheral surface of the identification portion 30 to mold the main body portion 10.
First, the identification portion 30 is formed as a preform in accordance with the shape of the electric fusion joint 1 (preformation step). In this embodiment, the identification portion 30 is preferably in the shape of a straight tube.
Next, the identification part 30, which is a preform, is placed in a resin molding die (placement step).The heating wire 13 is wound spirally around the outer circumferential surface of the identification part 30 (winding step).
Next, a first resin is injected onto the outer peripheral surface of the identification part 30 around which the heating wire 13 is wound in a spiral shape, to form the main body 10 (main body molding process).
Through the above steps, an electric fusion joint 1 is obtained that includes an identification portion 30 that is integrally formed in a layer that covers the inner circumferential surface 10a of the main body portion 10 from the radially inside.
The winding step may be performed before the disposing step.

The electric fusion joint 1 has an identification portion 30 that has a color difference of 1 or more from the main body portion 10. The identification portion 30 is given a color that indicates the use of the electric fusion joint 1, so that the use of the joint can be easily identified regardless of the color of the main body portion 10.
In addition, since the color difference between the identification portion 30 and the main body portion 10 is 1 or more, the identification portion 30 can be easily visually recognized, and the use of the fitting can be more easily identified.
Furthermore, when the electric fusion joint 1 is viewed from the opening 21 or the opening 22, the identification portion 30 is exposed at the open end, so that the color of the identification portion 30 can be easily seen even after the electric fusion joint 1 and the plastic tube are connected.
Furthermore, since the identification portion 30 of the electric fusion joint 1 is formed integrally with the main body portion 10, there is no risk of the identification portion 30 becoming detached from the main body portion 10, compared to the fusion management tag of Patent Document 1.

Next, an electric fusion joint according to another embodiment of the present invention will be described.
In addition, among the components of the electrofusion joint 2 shown in FIG. 2, the same components as those of the electrofusion joint 1 are denoted by the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 2, the electric fusion joint 2 includes a main body 10 formed in a tubular shape and a heating wire 13 embedded in the inner circumferential surface 10a of the main body 10. The heating wire 13 is covered with an identification portion 32. A part of the identification portion 32 is exposed on the inner circumferential surface 10a of the main body 10. The identification portion 32 does not have to be exposed from the main body 10, and in this case, the identification portion 32 may be visible through the inner circumferential surface of the main body 10. In this case, the transmission is not limited to complete transmission. In other words, the color of the identification portion 32 may be visible through the main body 10 while the color of the identification portion 32 and the color of the main body 10 are mixed (so-called semi-transmission).

The color of the indicator 32 is the same as the color of the indicator 30 described above.
In other words, the color difference (ΔE) between the identification portion 32 and the main body portion 10 is 1 or more.
The identification portion 32 may be made of the above-mentioned second resin or other materials, such as resin paint.

Next, a method for manufacturing the electric fusion joint 2 will be described.
The manufacturing method of the electric fusion joint 2 includes a step of winding a heating wire 13 covered by an identification portion 32 around a core mold (not shown), opening a gap from the outside around the core mold around which the heating wire 13 is wound, and fitting a resin molding mold (not shown) into the core mold; and a step of injecting a first resin into the resin molding mold to form the main body portion 10.
First, the heating wire 13 is covered with the identification portion 32 (covering step). The covering step may be performed by spraying the material constituting the identification portion 32 onto the heating wire 13, or by immersing the heating wire 13 in the material constituting the identification portion 32.
Next, the heating wire 13 covered with the identification portion 32 is wound spirally around the core die (winding step).
Next, a resin molding die having a gate for injecting the first resin is fitted from the outside into the core die around which the heating wire 13 is wound, with a gap therebetween (fitting step).
Next, a first resin is injected into the inside of the resin molding die to mold the main body 10 (main body molding step).
Next, after the injection molding is completed, the resin molding die is removed.
Next, the core dies are separated from each other along the axial direction to remove the core dies from the injection molded body (core die removal step).
Finally, the first resin injected into the gate is cut out from the injection molded body to obtain the electric fusion joint 2.
Through the above steps, the heating wire 13 covered with the identification portion 32 is embedded into the inner surface 10a of the main body 10, thereby obtaining an electric fusion joint 2 in which the main body 10 and the identification portion 32 are integrally formed.

The electric fusion joint 2 has an identification portion 32 that has a color difference of 1 or more from the main body portion 10. The identification portion 32 is given a color that indicates the use of the electric fusion joint 2, so that the use of the joint can be easily identified regardless of the color of the main body portion 10.
In addition, since the color difference between the identification portion 32 and the main body portion 10 is 1 or more, the identification portion 32 can be easily visually recognized, and the use of the fitting can be more easily identified.
Furthermore, the identification portion 32 can be formed using a smaller amount of material than the identification portion 30 described above, which allows costs to be reduced.

[Piping structure]
As shown in FIG. 3 , the piping structure S of this embodiment includes an electric fusion joint 1 and a resin tube 40 that is inserted into the opening 22 of the electric fusion joint 1 .
In FIG. 3, the resin tube to be inserted into the opening 21 is omitted.

The resin pipe 40 comprises a cylindrical main body 41 and one or more discrimination layers 42 that are integrally formed on the outer surface of the main body 41 and extend in the axial direction of the main body 41 .
The discrimination layer 42 is in a band shape. As shown in FIG. 4 , four discrimination layers 42 are positioned annularly at 90° intervals around the tube axis of the main body 41.
The outer diameter of the resin tube 40 is formed to be approximately the same as the inner diameter of the opening 22 of the electric fusion joint 1. The resin tube 40 is connected by fitting an end of the resin tube 40 into the stopper 14 of the electric fusion joint 1 so that the end of the resin tube 40 comes into contact with the stopper 14, and fusing the end to the stopper 14.

The resin pipe 40 is made of synthetic resin and has a cylindrical shape. Examples of the synthetic resin (third resin) constituting the resin pipe 40 include the same resin as the synthetic resin (first resin) constituting the main body 10 described above.
From the viewpoints of moldability and cost, the third resin is preferably high-density polyethylene, medium-density polyethylene, or crosslinked polyethylene, and more preferably high-density polyethylene or medium-density polyethylene.
These third resins may be used alone or in combination of two or more.

The mass average molecular weight of the third resin is preferably 1.0 × 10 ² or more and 1.0 × 10 ⁶ or less, and more preferably 1.5 × 10 ² or more and 3.0 × 10 ⁵ or less. When the mass average molecular weight is within the above numerical range, the main body 41 is likely to have desired physical properties as a pipe.
The mass average molecular weight of the third resin is measured by the same method as for the mass average molecular weight of the first resin.

The content of the third resin is preferably 90% by mass or more and 100% by mass or less with respect to the total mass of the main body 41. When the content of the third resin is within the above numerical range, the main body 41 is likely to obtain the desired physical properties as a resin pipe.

In addition to the third resin, the main body 41 may contain various additives such as antioxidants, ultraviolet absorbers (UVA), light stabilizers, pigments, etc.

The color difference (ΔE) between the main body 41 and the discrimination layer 42 in the L*a*b* color system defined in JIS Z8781-4:2013 is preferably 1 or more, more preferably 5 or more, and even more preferably 10 or more. When the color difference is equal to or more than the above-mentioned lower limit, it is easy to distinguish between the main body 41 and the discrimination layer 42. The upper limit of the color difference is not particularly limited, but is, for example, 100 or less, and preferably 80 or less in practical use.
The color difference in the resin tube 40 can be measured in the same manner as the color difference (ΔE) between the identification portion 30 and the main body portion 10 described above.
The color difference in the resin tube 40 is calculated by the above-mentioned formula (1).
In the resin tube 40, in formula (1), L ₁ , a ₁ , and b ₁ respectively represent the lightness L, chromaticity a in the red direction, and chromaticity b in the yellow direction of the main body 41, and L ₂ , a ₂ , and b ₂ respectively represent the lightness L, chromaticity a in the red direction, and chromaticity b in the yellow direction of the discrimination layer 42.

The lightness (L*) of the main body 41 or the discrimination layer 42 in the L*a*b* color system defined in JIS Z8781-4:2013 is preferably 20 or more. If the lightness (L*) of the main body 41 or the discrimination layer 42 is 20 or more, the main body 41 or the discrimination layer 42 is easily visible even in a dark place such as a pipe space in which the resin pipe 40 is installed.

The resin (fourth resin) constituting the identification layer 42 may be the same type of resin as the first resin or a different type of resin. The fourth resin may be the same type of resin as the second resin or a different type of resin. The fourth resin may be the same type of resin as the third resin or a different type of resin. From the viewpoint of the resistance to peeling of the identification layer 42 from the outer surface of the main body 41, the fourth resin is preferably the same type of resin as the third resin.
The fourth resin may be the same as the third resin, and is preferably high-density polyethylene, medium-density polyethylene, or crosslinked polyethylene, more preferably high-density polyethylene or medium-density polyethylene.
The fourth resin may be used alone or in combination of two or more kinds.

The weight average molecular weight of the fourth resin is the same as the weight average molecular weight of the third resin.

The content of the fourth resin is preferably 1.0 × 10 ⁻⁵ mass % or more and 10 mass % or less with respect to the total mass of the discrimination layer 42. When the content of the fourth resin is within the above numerical range, the discrimination layer 42 is likely to have desired physical properties as a resin pipe.

From the viewpoint of improving weather resistance, it is preferable that the discrimination layer 42 contains an antioxidant. Examples of the antioxidant include phenol-based antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants, amine-based antioxidants, and lactone-based antioxidants.

The content of the antioxidant is preferably 10 ppm (ppm is based on mass; the same applies below) to 5000 ppm, more preferably 100 ppm to 2000 ppm, and even more preferably 300 ppm to 1500 ppm, relative to the total mass of the discrimination layer 42. When the content of the antioxidant is equal to or greater than the above lower limit, the weather resistance of the discrimination layer 42 is easily improved. When the content of the antioxidant is equal to or less than the above upper limit, the balance with the contents of other additives is excellent, and the physical properties of the discrimination layer 42 are easily improved.
The antioxidants may be used alone or in combination of two or more.

From the viewpoint of improving weather resistance, the discrimination layer 42 preferably contains an ultraviolet absorbing agent (UVA). Examples of the ultraviolet absorbing agent include a benzophenone-based ultraviolet absorbing agent, a salumarate-based ultraviolet absorbing agent, a benzocoat-based ultraviolet absorbing agent, a benzotriazole-based ultraviolet absorbing agent, a cyanoacrylate-based ultraviolet absorbing agent, and a quencher.
As the ultraviolet absorbing agent, a benzophenone-based ultraviolet absorbing agent or a benzotriazole-based ultraviolet absorbing agent is particularly preferred for polyethylene or polypropylene.
Benzophenone-based ultraviolet absorbents include 2-hydroxy-4-methoxy-benzophenone.
Examples of the benzotriazole-based ultraviolet absorbers include 2-(2-hydroxy-5-methylphenyl)benzotriazole (Sumisorb 200, manufactured by Sumika Chemtex Co., Ltd.), 2-(2-hydroxy-5-t-butyl-5-methylphenyl)-5-chlorobenzotriazole (Tinuvin 326, manufactured by BASF Corporation), 2-(2-hydroxy-3,5-di-t-butylphenyl)-5-chlorobenzotriazole (Tinuvin 327, manufactured by BASF Corporation), and 2-(2-hydroxy-3,5-di-t-amylphenyl)benzotriazole (Tinuvin 328, manufactured by BASF Corporation).

The content of the ultraviolet absorber is preferably 10 ppm to 1000 ppm, more preferably 50 ppm to 800 ppm, and even more preferably 80 ppm to 400 ppm, relative to the total mass of the discrimination layer 42. When the content of the ultraviolet absorber is equal to or more than the above lower limit, it is easy to improve the weather resistance of the discrimination layer 42. When the content of the ultraviolet absorber is equal to or less than the above upper limit, it is easy to improve the physical properties of the discrimination layer 42 by achieving an excellent balance with the contents of other additives.
The ultraviolet absorbents may be used alone or in combination of two or more.

From the viewpoint of improving weather resistance, the discrimination layer 42 preferably contains a light stabilizer. Examples of the light stabilizer include a salicylic acid ester-based light stabilizer, a benzophenone-based light stabilizer, a benzotriazole-based light stabilizer, a cyanoacrylate-based light stabilizer, and a hindered amine-based light stabilizer (HALS).
As the light stabilizer, a hindered amine light stabilizer is preferred.
Examples of the hindered amine light stabilizer include tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)butane-1,2,3,4-tetracarboxylate (manufactured by ADEKA CORPORATION, trade name "ADK STAB LA-52"), 2,2,6,6-tetramethyl-4-piperidyl methacrylate (manufactured by ADEKA CORPORATION, trade name "ADK STAB LA-87"), and bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate (manufactured by ADEKA CORPORATION, trade names "ADK STAB LA-77Y" and "ADK STAB LA-77G").

The content of the light stabilizer is preferably 10 ppm to 1000 ppm, more preferably 50 ppm to 800 ppm, and even more preferably 80 ppm to 400 ppm, relative to the total mass of the discrimination layer 42. When the content of the light stabilizer is equal to or greater than the above lower limit, it is easy to improve the weather resistance of the discrimination layer 42. When the content of the light stabilizer is equal to or less than the above upper limit, it is easy to improve the physical properties of the discrimination layer 42, with an excellent balance with the contents of other additives.
The light stabilizer may be used alone or in combination of two or more kinds.

The discrimination layer 42 may contain carbon black from the viewpoint of improving weather resistance and visibility of the resin pipe 40. Examples of carbon black include furnace black, acetylene black, channel black, and thermal black.
The carbon black content is preferably from 1000 ppm to 5.0×10 ⁵ ppm, more preferably from 2000 ppm to 3.0×10 ⁵ ppm, and even more preferably from 20000 ppm to 1.0×10 ⁵ ppm, relative to the total mass of the discrimination layer 42. When the carbon black content is equal to or greater than the above lower limit, the weather resistance of the discrimination layer 42 is improved, and the discrimination between the main body 41 and the discrimination layer 42 is easily improved. When the carbon black content is equal to or less than the above upper limit, the balance with the contents of other additives is excellent, and the physical properties of the discrimination layer 42 are easily improved.
The carbon black may be used alone or in combination of two or more kinds.

The discrimination layer 42 preferably contains a colorant from the viewpoint of improving discrimination between the main body 41 and the discrimination layer 42. Examples of the colorant include the same colorants as those used in the discrimination part 30 described above.
The type and content of the colorant can be appropriately determined depending on the color of the identification layer 42. The color of the identification layer 42 can be appropriately determined depending on the application of the electric fusion joint 1.
For example, when the electrofusion joint 1 is used for drinking water, the discrimination layer 42 is preferably yellow or red, and when the electrofusion joint 1 is used for gas, the discrimination layer 42 is preferably blue or black.
By including a coloring agent in the identification layer 42, the identification layer 42 can be given a color according to the application of the electrofusion joint 1. In addition, the application of the electrofusion joint 1 can be identified by the color of the identification layer 42, regardless of the color of the main body 10.

The content of the colorant is preferably 1 ppm or more and 25,000 ppm or less with respect to the total mass of the discrimination layer 42. When the content of the colorant is equal to or more than the above-mentioned lower limit, it is easy to improve the discrimination between the main body 41 and the discrimination layer 42. When the content of the colorant is equal to or less than the above-mentioned upper limit, it is easy to improve the physical properties of the discrimination layer 42 by being well balanced with the contents of other additives.
The colorant may be used alone or in combination of two or more kinds.

In the piping structure S, the color difference between the identification part 30 formed integrally with the main body 10 and the identification layer 42 formed on the plastic tube 40 is preferably 10 or less, more preferably 5 or less, and even more preferably 1 or less. When the color difference is less than the upper limit, it is easy to recognize that the electric fusion joint 1 and the plastic tube 40 have the same application. As a result, it is easy to prevent erroneous connection between the electric fusion joint 1 and the plastic tube 40, and it is easy to reduce poor connection between the electric fusion joint 1 and the plastic tube 40.
Moreover, it is preferable that the identification portion 30 and the identification layer 42 are colored in the same color scheme according to the application of the piping structure S. By coloring the identification portion 30 and the identification layer 42 in the same color scheme, it is easy to recognize that the application of the electric fusion joint 1 and the application of the plastic pipe 40 are the same, and the above-mentioned effects are easily obtained.

The piping structure S is obtained by inserting a resin tube 40 into the opening 22 of the electric fusion joint 1, passing electricity through the heating wire 13 of the electric fusion joint 1 to generate heat, and melting the synthetic resin around the heating wire 13, thereby joining the identification portion 30 and the resin tube 40.
The fusion conditions for the electric fusion joint 1 can be appropriately determined depending on the size, type, application, etc. of the electric fusion joint 1 .

The manufacturing method of the resin pipe 40 includes a step of forming the main body 41 and the discrimination layer 42 by co-extrusion molding.
An example of a manufacturing device for the resin pipe 40 is a manufacturing device including an extrusion molding machine, a sizing die, a cooling tank, and a cutting machine. The extrusion molding machine is a molding machine capable of co-extrusion. The extrusion molding machine has at least two supply ports. The sizing die is a cylindrical member whose diameter decreases toward the downstream. The cooling tank is a device that cools the resin pipe whose diameter has been reduced and hardens the resin. An example of the cooling tank is a water-cooled cooling tank.

An example of a method for manufacturing the resin pipe 40 using the above-mentioned manufacturing apparatus will be described below.
A third resin and, if necessary, an additive (the third resin and the additive may be collectively referred to as a third resin composition) are fed from one feed port of the extruder. A fourth resin and an additive (the fourth resin and the additive may be collectively referred to as a fourth resin composition) are fed from another feed port of the extruder. The third resin composition is heated to a melting point of the third resin or higher and kneaded. The fourth resin composition is heated to a melting point of the fourth resin or higher and kneaded. Next, the third resin composition and the fourth resin composition are extruded into a cylindrical shape by the extruder. The third resin composition and the fourth resin composition flow through separate flow paths and then merge, and the fourth resin composition forms the discrimination layer 42.
This results in a cylindrical molded body having the identification layer 42 integrally formed on the outer surface of the main body 41.

Next, the cylindrical molding is inserted into a sizing die. As the cylindrical molding passes through the sizing die, it becomes the desired thickness. The cylindrical molding adjusted to the desired thickness is inserted into a cooling tank. The cooling tank cools the cylindrical molding and hardens the resin. The hardened cylindrical molding is cut to the desired length to form a resin pipe 40.

The heating temperature for the third resin composition in the extrusion molding machine is, for example, preferably 170° C. or more and 250° C. or less, and more preferably 180° C. or more and 220° C. or less. When the heating temperature is within the above numerical range, good fluidity can be obtained while suppressing thermal decomposition of the third resin.
The heating temperature for the fourth resin composition in the extruder is the same as the heating temperature for the third resin composition.

The temperature of the cooling water in the cooling tank is preferably, for example, 20°C or higher and 30°C or lower. If the temperature of the cooling water is within the above range, the cylindrical molded body can be sufficiently hardened.

The inner diameter of the body 41 of the resin tube 40, the thickness of the body 41, the thickness of the identification layer 42, the width of the identification layer 42, and the number of identification layers 42 can be adjusted depending on the size and shape of the mold and sizing die of the extrusion molding machine.

As described above, in the piping structure S of this embodiment, the identification portion 30 and the identification layer 42 are colored in the same color scheme, which makes it easy to recognize that the electric fusion joint 1 and the plastic tube 40 have the same use, makes it easy to prevent incorrect connection between the electric fusion joint 1 and the plastic tube 40, and makes it easy to reduce poor connection between the electric fusion joint 1 and the plastic tube 40.
In the piping structure S, color combinations of the identification layer 42, the main body portion 10, and the identification portion 30 include, for example, the following combinations: the identification layer 42 is red, the main body portion 10 is black, and the identification portion 30 is red; the identification layer 42 is green, the main body portion 10 is white, and the identification portion 30 is green; the identification layer 42 is gray, the main body portion 10 is black, and the identification portion 30 is gray.

The piping structure S of this embodiment is a structure in which an electric fusion joint 1 is connected to a resin tube 40. However, the piping structure is not limited to this embodiment, and an electric fusion joint 2 may be used instead of the electric fusion joint 1.

The present invention is not limited to the above-described embodiments.
In the above-described embodiment, the electrofusion joints 1 and 2 have a socket shape. However, the present invention is not limited to this, and the electrofusion joints may have an elbow shape or a Tee shape.
In the above embodiment, the plastic pipe 40 is formed with the discrimination layer 42. However, the present invention is not limited to this, and the plastic pipe may not have a discrimination layer. In this case, it is preferable that the discrimination portion and the main body of the plastic pipe are colored in the same color scheme.
In the above-described embodiment, the identification portion 30 is formed over the entire inner circumferential surface 10a of the main body portion 10. The present invention is not limited to this, and the identification portion may be formed on a part of the inner circumferential surface of the main body portion.

Reference Signs List 1, 2 Electric fusion joint 10 Main body 10a Inner surface of main body 11 Terminal cover 12 Terminal 13 Heating wire 14 Stopper 21, 22 Opening 30, 32 Identification part 40 Resin tube 41 Main body 42 Identification layer S Piping structure

Claims (5)

An electric fusion joint; and a resin tube inserted into an opening of the electric fusion joint,
The electric fusion joint includes a main body and a first identification portion integrally formed with the main body,
The resin tube includes a cylindrical main body and a second identification portion integrally formed on an outer surface of the main body,
The first resin constituting the main body of the electric fusion joint is a polyolefin resin,
the third resin constituting the body of the resin pipe is a polyolefin-based resin;
the third resin and the fourth resin constituting the second identification portion are the same type of resin,
A piping structure, wherein the first distinguishable portion and the second distinguishable portion are of the same color scheme. the first identification portion has a color difference (ΔE) of 1 or more with respect to the main body portion in the L*a*b* color system defined in JIS Z8781-4:2013;
The piping structure according to claim 1 , wherein the color difference (ΔE) of the second distinguishable portion from the main body is 1 or more. The piping structure according to claim 1 or 2, wherein the color difference (ΔE) between the first distinguishing portion and the second distinguishing portion in the L*a*b* color system defined in JIS Z8781-4:2013 is 10 or less. The piping structure according to any one of claims 1 to 3, wherein the second identification portion is a band extending in the axial direction of the main body. A method for manufacturing the piping structure according to any one of claims 1 to 4,
confirming that the first distinguishing portion and the second distinguishing portion are of the same color;
Next, the plastic pipe is inserted into an opening of the electric fusion joint, and electricity is passed through an electric heating wire of the electric fusion joint to join the plastic pipe and the electric fusion joint.

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