JP7207871B2 - Polyethylene resin pipe and its manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyethylene resin pipe and a manufacturing method thereof.

Conventionally, resin pipes such as polyethylene pipes (polyethylene resin pipes) have been widely used for various purposes such as water pipes and gas pipes. For this reason, resin pipes are color-coded for each application. As the number of uses for resin pipes increases, even if you try to distinguish them only by their color tone, their color tones will become similar. When the color tone for each application becomes similar, there is a problem that it becomes difficult to distinguish the application of the resin pipe by appearance. Especially in a dark place, it is difficult to identify the application of the resin pipe by color tone.

To address these problems, for example, Patent Document 1 discloses a resin pipe provided with a linear marking layer formed integrally with the main body on the outer surface of the main body. This marking layer includes a luminescent material and a metallic material. In the invention of Patent Document 1, by providing an identification layer such as a marking layer, the visibility of the resin pipe in a dark place is facilitated, and detection by a metal detector is enabled.

JP 2014-188757 A

However, if an identification layer such as a linear marking layer is simply formed on the outer surface of the main body, the identification layer is distorted and the appearance deteriorates. In addition, the identification layer is easily peeled off from the main body. If the identification layer peels off from the main body, the appearance of the resin pipe is spoiled.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a polyethylene resin pipe excellent in identifiability and appearance.

In order to form an identification layer on the outer surface of the main body, there is a method of manufacturing a resin pipe by co-extrusion molding.
The present inventors have obtained the following findings as a result of earnest studies.
If the resin of the main body and the resin of the identification layer flow differently in the mold of the co-extrusion molding machine, the thickness and width of the identification layer become uneven, and the surface of the identification layer is difficult to smooth. In addition, it becomes difficult for the resin of the main body and the resin of the identification layer to be compatible with each other, and the identification layer is easily peeled off from the main body.
The present invention has been completed based on the above findings, and has the following aspects.

[1] A cylindrical main body, and one or more identification layers integrally formed on the outer surface of the main body and extending in the tube axis direction of the main body,
A polyethylene resin pipe in which the first resin constituting the main body and the second resin constituting the identification layer satisfy any one of the following (1), (2) and (3).
(1) The first resin and the second resin are low density polyethylene.
(2) The first resin and the second resin are medium density polyethylene.
(3) The first resin and the second resin are high density polyethylene.
[2] The polyethylene resin according to [1], wherein the first resin and the second resin are the same or different in the type shown in Annex Table 2 of JIS K 6922-1: 1997. tube.
[3] The method for manufacturing a polyethylene resin pipe according to [1] or [2], wherein the main body and the identification layer are formed by co-extrusion molding.

The polyethylene resin pipe of the present invention is excellent in identifiability and appearance.

1 is a perspective view of a polyethylene resin pipe according to one embodiment of the present invention; FIG. FIG. 2 is a cross-sectional view taken along the line II-II of FIG. 1;

[Polyethylene resin pipe]
A polyethylene resin pipe (hereinafter sometimes simply referred to as a resin pipe) of the present invention includes a cylindrical main body and an identification layer formed on the outer surface of the main body.
Hereinafter, a polyethylene resin pipe according to one embodiment will be described with reference to the drawings.

The resin pipe 1 of FIG. 1 includes a tubular main body 10 and four identification layers 20 .
The identification layer 20 is located on the outer surface of the body 10 . The identification layer 20 is strip-shaped. The identification layer 20 extends in the tube axis O1 direction of the main body 10 . The identification layer 20 is formed integrally with the main body 10 .
As shown in FIG. 2, the four identification layers 20 are annularly positioned at intervals of 90° around the tube axis O1 of the main body 10. As shown in FIG.

The length of the main body 10 is determined according to the use of the resin pipe 1, and is preferably 2 m or more and 10 m or less, for example. The length of body 10 is the distance from one open end to the other open end.
The inner diameter R1 of the main body 10 is determined according to the application of the resin pipe 1, and is preferably 10 mm or more and 600 mm or less, for example.
The thickness d1 of the main body 10 (that is, the length in the radial direction of the resin pipe 1) is determined according to the application of the resin pipe 1, and is preferably 1 mm or more and 50 mm or less, for example.

The color tone of the main body 10 is not particularly limited, and is appropriately determined according to the application and purpose.

The first resin forming the main body 10 is polyethylene. The content of polyethylene with respect to 100 parts by mass of the resin in the main body 10 is 100 parts by mass.
Polyethylene is homopolymer of ethylene (homopolyethylene), copolymer of ethylene and 5 mol% or less of 1-olefin monomer, ethylene and 1 mol% or less having only carbon, hydrogen and hydrogen atoms in functional groups. is a copolymer with a non-olefinic monomer.

The type of first resin may be either low density polyethylene, medium density polyethylene or high density polyethylene. Among them, high-density polyethylene is preferable as the first resin. Types of polyethylene are shown in Annex Tables 1 and 2 of JIS K 6922-1:1997.
Low-density polyethylene meets the conditions of any of Class 1, Class 1 to Class 6 in Annex Table 2. The density of low-density polyethylene is 910 kg/m ³ or more and less than 930 kg/m ³ .
Medium-density polyethylene meets the conditions of any of two types 1 to 5 in Annex Table 2. The density of medium density polyethylene is 930 kg/m ³ or more and less than 942 kg/m ³ .
High-density polyethylene meets the conditions of any of the 3 types 1 to 5 in Annex Table 2. The density of high density polyethylene is 942 kg/m ³ or higher.
As shown in Annex Tables 1 and 2, the types of polyethylene are classified according to the combination of "species" and "class", such as "● type ●".

The melt flow rate (MFR) of the first resin is, for example, preferably 0.01 g/10 min or more and 200 g/10 min or less, more preferably 0.1 g/10 min or more and 100 g/10 min or less, and 0.2 g/ 10 minutes or more and 50 g/10 minutes or less is more preferable, and 0.3 g/10 minutes or more and 10 g/10 minutes or less is particularly preferable.
The melt flow rate (MFR) of the first resin is a value measured at a test temperature of 190 ° C. and a test load of 21.18 N according to JIS K 6922-2: 2010 Annex 4.1 (melt flow rate). be.

The tensile strength of the first resin is preferably 5.9 MPa or higher, more preferably 19.6 MPa or higher, and even more preferably 25 MPa or higher. The upper limit of tensile strength of the first resin is usually 100 MPa.
The tensile strength of the first resin is a value measured according to JIS K 6922-2:2010 Annex 4.3 (tensile test).

The tensile elongation at break of the first resin is preferably 100% or more, more preferably 350% or more, and even more preferably 500% or more. The upper limit of the tensile elongation at break of the first resin is usually 1200%.
The tensile elongation at break of the first resin is a value measured according to JIS K 6922-2:2010 Annex 4.3 (tensile test).

The durometer hardness of the first resin is preferably 30H _DD or more, more preferably 60H _DD or more, and even more preferably 65H _DD or more. The upper limit of the durometer hardness of the first resin is usually 200H _DD .
The durometer hardness of the first resin is a value measured according to JIS K 6922-2:2010 Annex 4.4 (durometer D hardness test).

The Vicat softening point of the first resin is preferably 65° C. or higher, more preferably 90° C. or higher, and even more preferably 100° C. or higher. The upper limit of the Vicat softening point of the first resin is usually 150°C.
The Vicat softening point of the first resin is a value measured according to JIS K 6922-2:2010 Annex 4.5 (Vicat softening point test).

The mass average molecular weight of the first resin is preferably 0.5×10 ⁵ or more and 10.0×10 ⁵ or less, more preferably 1.5×10 ⁵ or more and 3.0×10 ⁵ or less. If the mass average molecular weight is within the above range, the fluidity of the resin will be moderate and the productivity will be enhanced.
The mass average molecular weight of the first resin is measured according to JIS K 7252-1:2008.

The number average molecular weight of the first resin is preferably 0.1×10 ⁴ or more and 2.0×10 ⁴ or less, more preferably 0.5×10 ⁴ or more and 1.0×10 ⁴ or less. If the number-average molecular weight is within the above range, the fluidity of the resin will be moderate and the productivity will be enhanced.
The number average molecular weight of the first resin is measured according to JIS K 7252-1:2008.

The glass transition point of the first resin is preferably -140°C or higher and -90°C or lower, more preferably -120°C or higher and -100°C or lower. If the glass transition point is within the above range, the fluidity of the resin will be moderate and the productivity will be enhanced.
The glass transition point of the first resin is a value measured with a differential scanning calorimeter (DSC).

The melting point of the first resin is preferably 110° C. or higher and 130° C. or lower, more preferably 120° C. or higher and 125° C. or lower. If the melting point is within the above range, the fluidity of the resin will be moderate and the productivity will be enhanced.
The melting point of the first resin is a value measured by a differential scanning calorimeter (DSC).

The crystallinity of the first resin is preferably 60% or more and 80% or less, more preferably 65% or more and 70% or less. If the degree of crystallinity is within the above range, the fluidity of the resin will be moderate and the productivity will be enhanced.
The crystallinity of the first resin is a value measured by DSC.

The pencil hardness of the first resin is preferably HB or more and 7B or less, more preferably HB or more and 6B or less. If the pencil hardness is within the above range, it becomes difficult to be scratched and the appearance can be further improved.
The pencil hardness of the first resin is a value measured according to JIS K 5600-5-4:1999.

The content of the first resin is preferably 90% by mass or more and 99.99999% by mass or less with respect to the total mass of the main body 10 .

The body 10 may contain additives such as colorants, antioxidants, ultraviolet absorbers (UVA), hindered amine light stabilizers (HALS), and the like.
The content of the additive in main body 10 is determined in consideration of the type of additive. The content of the additive with respect to 100 parts by mass of the first resin is preferably 1.0 × 10 ^-5 parts by weight or more and 10 parts by weight or less, and more preferably 1.0 × 10 ^-3 parts by weight or more and 1.0 parts by weight or less. preferable.

The length of the identification layer 20 is similar to the length of the body 10 . The length of identification layer 20 may be the same as or different from the length of body 10 . The length of the identification layer 20 is preferably equal to the length of the main body 10 .

The width w2 of the identification layer 20 (that is, the length in the circumferential direction of the resin pipe 1) is appropriately determined according to the purpose of the identification layer 20, and is, for example, 2 mm or more and 50 mm or less, preferably 4 mm or more and 40 mm or less. Also, the ratio of the width w2 to the outer circumference (peripheral length around the tube axis O1) of the resin pipe 1 (w2 ratio) is, for example, 5% or more and 30% or less, preferably 7% or more and 25% or less. If the width w2 is equal to or greater than the above lower limit, the identification layer 20 is easy to see. If the width w2 is equal to or less than the upper limit, the color tone of the main body 10 can be easily recognized in a side view.
The w2 ratio is obtained by [width w2 of identification layer 20]÷[peripheral length of resin pipe 1]×100.

The thickness d2 of the identification layer 20 (that is, the length in the radial direction of the resin pipe 1) is appropriately determined according to the thickness d1 of the main body 10, and is preferably 0.02 mm or more and 2.0 mm or less. It is more preferably 1 mm or more and 0.5 mm or less. If the thickness d2 is equal to or greater than the above lower limit, the strength of the identification layer 20 can be increased. If the thickness d2 is equal to or greater than the above lower limit, the color tone of the identification layer 20 can be easily identified regardless of the color depth of the identification layer 20 . If the thickness d2 is equal to or less than the above upper limit, the thickness of the main body 10 does not become too thin at the position of the identification layer 20, and the strength of the main body 10 can be increased. If the thickness d2 is equal to or less than the above upper limit, the discrimination layer 20 disappears due to cutting work on the surface of the resin pipe 1 when connecting to the electric fusion joint, and it is easy to confirm that the cutting work has been performed. can.
The thickness ratio represented by d2/d1 is preferably 3.0×10 ⁻⁶ or more and 3.0×10 ⁻² or less, more preferably 3.0×10 ⁻⁵ or more and 3.0×10 ⁻³ or less. .

Although the color tone of the identification layer 20 is not particularly limited, it is preferably different from the color tone of the main body 10 . Since the color tone of the identification layer 20 is different from the color tone of the main body 10, a striped pattern appears on the outer periphery of the resin pipe 1. - 特許庁By combining the color tones of the identification layer 20 and the main body 10, the color-coded variations of the resin pipe 1 are increased.

The second resin constituting the identification layer 20 is polyethylene resin. The content of the polyethylene resin is 100 parts by mass with respect to 100 parts by mass of the resin in the identification layer 20 .
The second resin seed is the same as the first resin seed.
That is, the first resin and the second resin satisfy any of the following (1), (2) and (3).
(1) The first resin and the second resin are low density polyethylene.
(2) The first resin and the second resin are medium density polyethylene.
(3) The first resin and the second resin are high density polyethylene.
That is, the first resin and the second resin have the same "species" of polyethylene in Appendix Table 2 of JIS K 6922-1:1997.
Since the species of the first resin and the second resin are the same, the first resin and the second resin are easily compatible with each other. Therefore, the identification layer 20 is in close contact with the main body 10 .
In addition, if the species of the first resin and the second resin are the same, the fluidity of both will be the same. Therefore, the identification layer 20 is less likely to be distorted. Furthermore, since the first resin and the second resin have the same fluidity, the surface of the identification layer 20 becomes as smooth as the surface of the main body 10 . Therefore, the appearance of the resin pipe 1 is improved.

The first resin and the second resin preferably have the same “class” in Appendix Table 2 of JIS K 6922-1:1997 or one class different. For example, if the first resin is 3 types and 1 type, the second resin is preferably 3 types and 1 type or 1 type and 2 types. Further, for example, if the first resin is 3 types and 3 types, the second resin is preferably 3 types and 2 types, 3 types and 3 types, and 3 types and 4 types. Above all, the first resin and the second resin preferably have the same “species” and “kinds”.

The MFR of the second resin is similar to the MFR of the first resin. The difference between the MFR of the second resin and the MFR of the first resin is preferably 0 g/10 min or more and 1 g/10 min or less, more preferably 0 g/10 min or more and 0.3 g/10 min or less.
If the difference in MFR between the first resin and the second resin is within the above range, the appearance of the identification layer 20 can be improved.

The tensile strength of the second resin is similar to the tensile strength of the first resin. The difference between the tensile strength of the second resin and the tensile strength of the first resin is preferably 0 MPa or more and 10 MPa or less, more preferably 0 MPa or more and 5 MPa or less.
If the difference in tensile strength between the first resin and the second resin is within the above range, the appearance of the identification layer 20 can be improved.

The tensile elongation at break of the second resin is similar to the tensile elongation at break of the first resin. The difference between the tensile elongation at break of the second resin and the tensile elongation at break of the first resin is preferably 0% or more and 100% or less, more preferably 0% or more and 50% or less.
If the difference in tensile elongation at break between the first resin and the second resin is within the above range, the appearance of the identification layer 20 can be improved.

The durometer hardness of the second resin is similar to the durometer hardness of the first resin. The difference between the durometer hardness of the second resin and the durometer hardness of the first resin is preferably 0 H _D D or more and 30 H _D or less, more preferably 0 H _D D or more and 15 H _D or less.
If the difference in durometer hardness between the first resin and the second resin is within the above range, the appearance of the identification layer 20 can be improved.

The Vicat softening point of the second resin is similar to the Vicat softening point of the first resin. The difference between the Vicat softening point of the second resin and the Vicat softening point of the first resin is preferably 0° to 10°C, more preferably 0° to 5°C.
If the difference in Vicat softening point between the first resin and the second resin is within the above range, the appearance of the identification layer 20 can be improved.

The weight average molecular weight of the second resin is similar to the weight average molecular weight of the first resin. The difference between the mass average molecular weight of the second resin and the mass average molecular weight of the first resin is preferably 0 or more and 1.0×10 ³ or less, more preferably 0 or more and 0.5×10 ³ or less.
If the difference in mass average molecular weight between the first resin and the second resin is within the above range, the appearance of the identification layer 20 can be improved.

The number average molecular weight of the second resin is similar to the number average molecular weight of the first resin. The difference between the number average molecular weight of the second resin and the number average molecular weight of the first resin is preferably 0 or more and 1.0×10 ³ or less, more preferably 0 or more and 0.5×10 ³ or less.
If the difference in number average molecular weight between the first resin and the second resin is within the above range, the appearance of the identification layer 20 can be improved.

The glass transition point of the second resin is similar to that of the first resin. The difference between the glass transition point of the second resin and the glass transition point of the first resin is preferably 0° C. or higher and 10° C. or lower, more preferably 0° C. or higher and 5° C. or lower.
If the difference in glass transition point between the first resin and the second resin is within the above range, the appearance of the identification layer 20 can be improved.

The melting point of the second resin is similar to that of the first resin. The difference between the melting point of the second resin and the melting point of the first resin is preferably 0° C. or higher and 10° C. or lower, more preferably 0° C. or higher and 5° C. or lower.
If the difference in melting point between the first resin and the second resin is within the above range, the appearance of the identification layer 20 can be improved.

The crystallinity of the second resin is similar to the crystallinity of the first resin. The difference between the crystallinity of the second resin and the crystallinity of the first resin is preferably 0% or more and 10% or less, more preferably 0% or more and 5% or less.
If the difference in crystallinity between the first resin and the second resin is within the above range, the appearance of the identification layer 20 can be improved.

The pencil hardness of the second resin is similar to that of the first resin. The difference between the pencil hardness of the second resin and the pencil hardness of the first resin is preferably 0 or more and 2B or less, more preferably 0 or more and 1B or less.
If the difference in hardness between the first resin and the second resin is within the above range, the appearance of the identification layer 20 can be improved.

The content of the second resin is preferably 90% by mass or more and 99.99999% by mass or less with respect to the total mass of the identification layer 20 .

The identification layer 20 may contain additives. The additive contained in the identification layer 20 is the same as the additive contained in the main body 10 . The additive of the main body 10 and the additive of the identification layer 20 may be the same or different.
The content of the additive in the identification layer 20 is determined in consideration of the type of additive. The content of the additive with respect to 100 parts by mass of the second resin is preferably 1.0 × 10 ^-5 parts by weight or more and 10 parts by weight or less, and more preferably 1.0 × 10 ^-3 parts by weight or more and 1.0 parts by weight or less. preferable.

[Manufacturing method of resin pipe]
A method of manufacturing the resin pipe 1 includes a step of forming the main body 10 and the identification layer 20 by co-extrusion molding.
As a manufacturing apparatus for the resin pipe 1, for example, a manufacturing apparatus including an extruder, a sizing die, a cooling tank, and a cutting machine can be exemplified.
An extruder is a coextrusion capable former. The extruder has at least two feed ports.
A sizing die is a cylindrical member whose diameter decreases as it goes downstream.
The cooling bath is a device that cools the diameter-reduced resin pipe and hardens the resin. As the cooling bath, for example, a water-cooled cooling bath can be used.

An example of a method for manufacturing a resin pipe using the above manufacturing apparatus will be shown.
A first resin and, if necessary, an additive (the first resin and the additive may be collectively referred to as a first resin composition) are introduced from one supply port of the extruder. A second resin and, if necessary, an additive (the second resin and the additive may be collectively referred to as a second resin composition) are introduced from another supply port of the extruder. The first resin composition is heated above the melting point of the first resin and kneaded. The second resin composition is heated above the melting point of the second resin and kneaded. Next, the first resin composition and the second resin composition are extruded into a cylinder by an extruder. The first resin composition and the second resin composition flow through separate channels and then join together, and the second resin composition forms the identification layer 20 . At this time, since the first resin and the second resin are the same "seed", the first resin composition and the second resin composition have the same fluidity. Since the second resin composition flows in the same manner as the first resin composition, distortion of the identification layer 20 is suppressed and the surface of the identification layer 20 becomes smooth. In addition, the first resin and the second resin are easily compatible with each other, making it difficult for the identification layer 20 to separate from the main body 10 .
As a result, a cylindrical molded body in which the identification layer 20 is integrally formed on the outer surface of the main body 10 is obtained.

Next, the cylindrical compact is inserted into a sizing die. The cylindrical molded body has a desired thickness as it passes through the sizing die. A cylindrical molded body adjusted to a desired thickness is inserted into a cooling bath. The cooling bath cools the cylindrical molded body and hardens the resin. The cured cylindrical molded body is cut to a desired length to form the resin pipe 1 .

The heating temperature of the first resin composition in the extruder is, for example, preferably 170° C. or higher and 250° C. or lower, more preferably 180° C. or higher and 220° C. or lower. If the heating temperature is within the above range, good fluidity can be obtained while suppressing thermal decomposition of the first resin.
The heating temperature for the second resin composition in the extruder is the same as the heating temperature for the first resin composition.

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

After passing through the cooling bath, the cylindrical molded body is cut to a desired length by a cutting machine to form the resin pipe 1 .

According to the resin pipe of this embodiment, the identification layer is provided on the outer surface of the main body. Additionally, the first resin and the second resin are of the same species. Therefore, the resin pipe is excellent in identifiability and appearance.

The invention is not limited to the embodiments described above.
The embodiment described above comprises four identification layers. The present invention is not limited to this, and the number of identification layers may be three or less, or may be five or more. Above all, the number of identification layers is preferably 4 or more, more preferably 4 or more and 8 or less, and more preferably 4 or more and 6 or less so that the identification layers can be visually recognized at any angle.

In the embodiment described above, the four identification layers are positioned at 90° intervals around the tube axis. That is, the four identification layers are equally spaced. However, the present invention is not limited to this, and the distance between each identification layer may be different.
However, the identification layer is preferably positioned so as to be visible when the resin pipe is rotated about the pipe axis.

In the above-described embodiments, the straight strip-shaped identification layer extends over the entire length of the main body (from one open end to the other open end). However, the invention is not limited to this, and individual identification layers may be dashed lines. Also, the identification layer may be wave-shaped, zigzag-shaped, or otherwise non-linear. However, from the viewpoint of increasing the fluidity of the second resin in the extruder and obtaining a more beautiful identification layer, a linear strip-shaped identification layer is preferable.

(Raw materials used)
- Resin A: High density polyethylene of 3 types and 1 type. Density = 942 kg/m ³ , MFR = 0.39 g/10 min, Durometer = 65 H _D D, Vicat softening point = 120°C.
- Resin B: High density polyethylene of 3 types and 2 types. Density = 943 kg/m ³ , MFR = 0.59 g/10 min, Durometer = 80 H _D D, Vicat softening point = 125°C.
- Resin C: Medium density polyethylene of 2 types and 1 type. Density = 935 kg/m ³ , MFR = 1.6 g/10 min, Durometer = 50 H _D D, Vicat softening point = 100°C.
- Resin D: High density polyethylene of 3 types and 1 type. Density = 950 kg/m ³ , MFR = 0.11 g/10 min, Durometer = 67 H _D D, Vicat softening point = 125°C.
・Resin E: High density polyethylene of 3 types and 2 types. Density = 951 kg/m ³ , MFR = 0.80 g/10 min, Durometer = 62 H _D D, Vicat softening point = 122°C.

(Examples 1 to 4)
According to the description in Table 1, 100 parts by mass of the first resin, 7.0 × 10 ^-4 parts by weight of the coloring agent, 3.0 × 10 ^-4 parts by weight of the antioxidant, and 1 part by weight of the ultraviolet absorber (UVA). 5×10 ⁻⁴ parts by weight were fed to the extruder.
According to the description in Table 1, 100 parts by mass of the second resin, 7.0 × 10 ^-4 parts by weight of the coloring agent, 3.0 × 10 ^-4 parts by weight of the antioxidant, and 1.5 parts by weight of the ultraviolet absorber (UVA). 5×10 ⁻⁴ parts by weight were fed to the extruder.
The supplied resin was melted at 190° C. and extruded while being kneaded to obtain a cylindrical molded body. The cylindrical compact was cooled with cooling water at 23°C for 60 minutes. The cooled cylindrical molded body was cut to obtain a resin pipe having an inner diameter R1=87 mm, length=5 m, thickness d1=13.3 mm, thickness d2=0.1 mm, and width w2=20 mm. The resulting resin tube had four linear discriminating layers.
The appearance, creep performance and tensile strength of the obtained resin pipe were measured, and the results are shown in Table 1.

(Comparative example 1)
A resin tube was obtained in the same manner as in Example 1, except that resin C was used as the resin constituting the identification layer.
The appearance, creep performance and tensile strength of the obtained resin pipe were measured, and the results are shown in Table 1.

(Evaluation method)
<Appearance>
The resin pipe of each example was visually confirmed and evaluated according to the following evaluation criteria.
≪Evaluation Criteria≫
Good: No cracks, voids, or irregularities were observed on the surface of the resin pipe.
x: Cracks, voids, or irregularities are observed on the surface of the resin pipe.

<Creep performance>
A creep performance test was conducted in accordance with JWWA K 144, a standard of the Japan Water Works Association. From the resin pipe of each example, a tubular test piece having a length of at least three times the outer diameter of the resin pipe was cut and used as a sample. Both ends of the sample were fixed with a hydraulic test jig or the like. Water was used as the test medium both inside and outside the specimen. The test was performed using the test pressure calculated by the formula (1).

P=2σ/(SDR−1) (1)
P: test pressure (MPa).
σ: Circumferential stress of the tube (MPa).

The test temperature was 20° C. (+3° C. to −1° C.) for normal temperature internal pressure creep, and 80° C. (±1° C.) for hot internal pressure creep and long-term hot internal pressure creep.
The test time was 100 hours for normal temperature internal pressure creep, 165 hours for hot internal pressure creep, and 1000 hours for long-term hot internal pressure creep.
Perform the creep test at the above test temperature and test time, and if no cracks or fractures occur in any of the normal temperature internal pressure creep, hot internal pressure creep, and long-term hot internal pressure creep If not, it was evaluated as "○", and if cracks or breakage occurred in any of the tests, it was evaluated as "X".

<Tensile strength>
The tensile elongation at break of the resin pipe of each example was determined according to JIS K 6922-2. The obtained values were evaluated by applying the following evaluation criteria.
≪Evaluation Criteria≫
Good: Tensile elongation at break is 500% or more.
Δ: Tensile elongation at break is 100% or more and less than 500%.
x: Tensile elongation at break is less than 100%.

As shown in Table 1, in Example 1 to which the present invention was applied, the evaluations of appearance, creep performance and tensile strength performance were "good" or "fair".
On the other hand, in Comparative Example 1, in which the first resin was 3 types and 1 type, and the second resin was 2 types and 1 type, the appearance and creep performance were evaluated as "x".

1 polyethylene resin pipe 10 main body 20 identification layer O1 pipe shaft

Claims (5)

comprising a cylindrical main body and one or more identification layers integrally formed on the outer surface of the main body and extending in the tube axis direction of the main body,
[Width of identification layer of 1 ] ÷ [Peripheral length of resin pipe] × 100 The ratio obtained is 5% or more and 30% or less,
A polyethylene resin pipe in which the first resin constituting the main body and the second resin constituting the identification layer satisfy any one of the following (1), (2) and (3).
(1) The first resin and the second resin are low density polyethylene.
(2) The first resin and the second resin are medium density polyethylene.
(3) The first resin and the second resin are high density polyethylene. 2. The polyethylene resin pipe according to claim 1, wherein said first resin and said second resin are of the same type or different by one type as shown in Appendix Table 2 of JIS K 6922-1:1997. 3. The polyethylene resin pipe according to claim 1, wherein the width of one of the identification layers is 2 mm or more and 50 mm or less. The polyethylene resin pipe according to any one of claims 1 to 3, wherein the identification layer has a thickness of 0.02 mm or more and 2.0 mm or less. The method for manufacturing a polyethylene resin pipe according to any one of claims 1 to 4, wherein the main body and the identification layer are formed by co-extrusion molding.

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