Coated pipes and composite pipes

Abstract

To enhance contraction workability of a cladding pipe formed of a corrugated pipe in a multiple pipe.SOLUTION: A multiple pipe 1 includes a flexible inner pipe 2 and a cladding pipe 10 covering the flexible inner pipe. The cladding pipe 10 comprises a single layer of a foamed resin containing polyethylene as a main component, which has a foaming ratio of 1.2 to 4 times, and is composed of a flexible corrugated pipe in which peaks 11 and valleys 12 are alternately formed in a pipe axial direction. An index value α=(H-tav) / φ obtained by dividing the difference, which is obtained by subtracting an average thickness tav of the peaks 11 and the valleys 12 from a height H along a pipe radial direction from a valley bottom 12c of the valley 12 to a crest 11c of the peak 11, by an outer diameter φ of the peak 11, is 4.2% or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a cladding pipe that is placed over a flexible inner pipe suitable for transporting fluids, and a composite pipe that includes this inner pipe and cladding pipe. In particular, the present invention relates to a cladding pipe made of a corrugated pipe in which peaks and valleys are formed alternately in the axial direction of the pipe, and a composite pipe that includes this cladding pipe. [Background technology]

[0002] Composite pipes, which are flexible pipes (inner pipes) covered with a covering pipe to protect them for hot and cold water supply, are widely used. Examples of covering pipes include 5 mm thick insulation pipes and corrugated pipes with alternating peaks and valleys in the axial direction (see Patent Document 1, etc.). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-044780 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, corrugated pipes for this type of composite pipe have a certain degree of hardness to ensure scratch resistance. Therefore, when exposing the end of the inner pipe and connecting a joint, it is difficult to shrink the corrugated pipe (cladding pipe) in the pipe axial direction. Even if it can be shrunk, it shrinks distortedly, resulting in a poor appearance. In view of the above circumstances, the present invention aims to improve the shrinkability (ease of shrinking and good appearance when shrunk) of a cladding pipe made of a corrugated pipe in a composite pipe. [Means for solving the problem]

[0005] In order to solve the above problems, the present invention provides a covering tube that is placed over a flexible inner tube, comprising: The pipe is made of a flexible corrugated pipe consisting of a single layer of foamed resin whose main component is polyethylene and whose expansion ratio is 1.2 to 4 times, and in which peaks and valleys are alternately formed in the axial direction of the pipe. The pipe has an index value of 4.2% or more, preferably 5% or more, obtained by subtracting the average thickness of the peaks and valleys from the height from the bottom of the valleys to the top of the peaks along the pipe diameter direction, by the outer diameter of the peaks. With a cladding pipe made of a corrugated pipe having these characteristics, by setting the index value at 4.2% or more, preferably 5% or more, it is possible to ensure ease of shrinkage workability, including ease of shrinkage along the pipe axis (ease of shrinkage) and good appearance when shrunken (shrunken appearance).By using a foamed resin whose main component is polyethylene with an expansion ratio of 1.2 to 4 times as the material for the cladding pipe, it is possible to ensure heat retention.

[0006] The index value is preferably 20% or less, more preferably 15% or less. This makes it possible to prevent the height along the pipe diameter direction from the bottom of the valley portion to the top of the peak portion (difference in radius between the peak portion and the valley portion) from becoming excessively large, and to prevent the thickness difference between the peak portion and the valley portion from becoming too large during molding, which would make the pipe prone to tearing or create extremely thin-walled portions.

[0007] It is preferable that a plurality of retaining projections projecting further inward than the valley portions are formed in a dispersed manner, and that the retaining projections position the inner pipe substantially concentrically with the cladding pipe. It is preferable that the retaining projections are distributed in the axial and circumferential directions of the cladding pipe. This not only forms an air layer between the inner circumferential surface of the crest of the cladding pipe and the outer circumferential surface of the inner pipe, but also forms an air layer between the valley of the cladding pipe and the inner pipe, at least as high as the height of the retaining protrusions protruding from the valley, which further improves the thermal insulation of the composite pipe.

[0008] The composite pipe according to the present invention comprises a cladding pipe and an inner pipe, and the cladding pipe is provided with a plurality of retaining protrusions dispersedly formed on the cladding pipe, protruding further inward than the valley portion, and the retaining protrusions form an air layer between the inner surface of the cladding pipe and the outer surface of the inner pipe. The air layer serves as an insulating layer. It is preferable to arrange the retaining protrusions on the cladding pipe so that an air insulating layer is effectively formed. The cladding pipe can be made of a foamed resin to improve thermal insulation. Another advantage of using a foamed resin cladding pipe is that it requires less contraction force when connecting joints, improving workability. Furthermore, the provision of retaining protrusions eliminates the need for an intermediate layer between the cladding pipe and the inner pipe, thereby reducing manufacturing costs.

[0009] It is preferable that at least two of the holding projections are in contact with the outer peripheral surface of the inner tube. It is preferable that the inner tube be positioned approximately at the center of the cross section of the cladding tube by point contact with these retaining protrusions. This improves heat retention. Furthermore, by constructing the cladding tube, including the point contact parts, from a foamed resin, heat dissipation from the contact parts can be suppressed. In addition, by having the retaining protrusions contact the inner tube, it is possible to effectively prevent the generation of sheath rattle noise due to water hammer.

[0010] The resin constituting the cladding tube has a tensile yield strength before foaming That is, the tensile yield stress just before foaming (same below) is preferably greater than 10 MPa and the tensile yield strength before foaming is preferably (n×10) MPa or less (n: foaming ratio). This ensures the workability of shrinking the cladding pipe (ease of shrinking and appearance after shrinking).

[0011] The covering pipe may contain 10 wt% to 30 wt% of polypropylene (PP) based on the entire foamed resin. By making the PP content 10 wt% or more, the thermal insulation properties of the covering pipe are improved. By making the PP content 30 wt% or less, it is possible to prevent any problems with shrinkage workability.

[0012] The inner pipe is preferably a cross-linked polyethylene (PEX) pipe, a polybutene (PB) pipe, a polyethylene (PE) pipe, a heat-resistant polyethylene (PE-RT) pipe, a composite resin pipe containing two or more resins selected from PEX, PB, PE, and PE-RT, or a metal-reinforced composite pipe containing at least one of PEX, PB, PE, and PE-RT and a metal. Preferably, the polyethylene that is the main component of the cladding pipe contains low density polyethylene (LDPE), and the expansion ratio n is 1.2 to 4 times, and preferably the tensile yield strength before expansion is 1.2 to 4 times. stress is (n×10) MPa or less, and more preferably the tensile yield strength before foaming is stress As long as the compressive strength is greater than 10 MPa, medium density polyethylene (MDPE) or high density polyethylene (HDPE) may be included. This ensures shrinkage workability of the cladding pipe. 。 [Effects of the Invention]

[0013] According to the present invention, it is possible to ensure the shrinkability (ease of shrinking and appearance after shrinking) of a cladding pipe made of a corrugated pipe in a composite pipe. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a side view, partially in cross section, of a compound pipe according to a first embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged cross-sectional side view of a portion of the cladding pipe of the composite pipe. [Figure 3] FIG. 3 is a schematic diagram showing an example of an apparatus for manufacturing the composite pipe. [Figure 4] FIG. 4 is a cross-sectional side view of the composite pipe in a state where the cladding pipe is contracted in the pipe axial direction. [Figure 5] FIG. 5 shows a second embodiment of the present invention and is a side cross-sectional view of a portion of a compound pipe. [Figure 6] FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. <First embodiment (FIGS. 1 to 4)> As shown in FIG. 1, a composite pipe 1 includes an inner pipe 2 and a cladding pipe 10 . A fluid such as water at a temperature of 95°C or less is transported through the internal flow path of the inner pipe 2. The inner pipe 2 is a flexible resin pipe. Examples of the inner pipe 2 include a cross-linked polyethylene (PEX) pipe, a polybutene (PB) pipe, a polyethylene (PE) pipe, a heat-resistant polyethylene (PE-RT) pipe, a composite resin pipe containing two or more of PEX, PB, PE, and PE-RT, and a metal-reinforced composite pipe containing at least one of PEX, PB, PE, and PE-RT and a metal.

[0016] The outer periphery of the inner pipe 2 is covered with a resin cladding pipe 10. The cladding pipe 10 is flexible. The cladding pipe 10 is made of a single layer of foamed resin whose main component is polyethylene and whose foaming ratio n is n=1.2 to 4 times. Preferably, the polyethylene-based resin constituting the cladding pipe 10 has a tensile yield strength before foaming at the stage of raw resin 19 (Fig. 3). stress is greater than 10 MPa and the tensile yield point before foaming is stress is (n × 10) MPa or less (n is the expansion ratio).

[0017] The main component refers to a component that accounts for at least 50 wt % of the entire cladding tube 10, and preferably 70 wt % or more. The polyethylene that is the main component of the cladding tube 10 is preferably low density polyethylene (LDPE), but the tensile yield strength before foaming is stress is greater than 10 MPa and the tensile yield point before foaming is stress As long as the compressive strength is (n × 10) MPa or less, the polyethylene may be medium-density polyethylene (MDPE) or high-density polyethylene (HDPE), or may be a mixed polyethylene made by mixing two or more of LDPE, MDPE, and HDPE.

[0018] The cladding pipe 10 may contain 10 wt% to 30 wt% of polypropylene (PP). Since PP has a lower thermal conductivity than PE, the thermal insulation of the cladding pipe is improved by making the PP content 10 wt% or more. If the PP content is 30 wt% or less, the tensile yield strength before foaming is 10 wt% or less. stress is greater than 10 MPa and the tensile yield point before foaming is stress is likely to fall within the range of (n × 10) MPa or less, and the required softness can be maintained. In addition, 100% PP resin has a tensile yield strength before foaming. stress is about 33 MPa, making it hard and difficult to stretch.

[0019] By setting the expansion ratio of the foamed resin that makes up the cladding tube 10 to 1.2 times or more, it is possible to reduce the rigidity of the cladding tube 10 and ensure its shrinkability. By setting the expansion ratio to 4 times or less, it is possible to make the cladding tube 10 self-supporting and able to maintain its shape. The foamed resin preferably has closed cells in order to ensure heat retention. However, in cases where a skin layer can be formed on the inner and outer surfaces of the cladding tube 10, the foamed resin does not need to have completely closed cells. The foaming agent for the cladding tube 10 is preferably foamable microcapsules, but is not limited to this and may be an inorganic chemical foaming agent or a physical foaming agent such as chlorofluorocarbon.

[0020] The cladding tube 10 is composed of a corrugated pipe having peaks 11 that protrude radially outward and valleys 12 that recess radially inward. The peaks 11 and valleys 12 are both annular and extend around the entire circumference of the cladding tube 10. The peaks 11 and valleys 12 are alternately and continuously formed in the axial direction of the cladding tube 10.

[0021] 2, the axial cross section of the ridge portion 11 is curved so as to be convex toward the outside (hereinafter referred to as "outside the tube") of the cladding tube 10. The central portion of the ridge portion 11 in the width direction (left-right direction in FIG. 2) along the tube axis is the apex 11c that protrudes most toward the outside of the tube (upper side in FIG. 2).

[0022] As shown in Fig. 2, the axial cross section of the valley portion 12 is curved so as to be convex toward the inside of the cladding tube 10 (hereinafter referred to as the "tube inside"). More specifically, the axial cross section of the valley portion 12 is approximately semicircular. The center of the valley portion 12 in the width direction (left-right direction in Fig. 2) along the tube axis forms a valley bottom 12c that is recessed most toward the tube inside (the lower side in Fig. 2).

[0023] The curvature of the valley portions 12 in the axial cross section is steeper than the curvature of the peak portions 11. The width of the valley portions 12 is smaller than the width of the peak portions 11. Specifically, the width of the valley portions 12 is about half the width of the peak portions 11. The cross-sectional shapes of the peaks 11 and valleys 12 are not limited to those shown in Fig. 2. The curvatures of the valleys 12 and peaks 11 may be approximately equal, or the curvature of the valleys 12 may be gentler than the curvature of the peaks 11. The widths of the valleys 12 and peaks 11 may be approximately equal, or the width of the valleys 12 may be greater than the width of the peaks 11.

[0024] As shown in Fig. 2, a side wall 13 is provided between the peaks 11 and the valleys 12. The side wall 13 has a straight cross section connecting the peaks 11 and the valleys 12, and is annular over the entire circumference of the cladding tube 10. The outer peripheral end of the side wall 13 (upper side in Fig. 2) smoothly connects with the end of the peaks 11. The inner peripheral end of the side wall 13 (lower side in Fig. 2) smoothly connects with the end of the valleys 12.

[0025] In the cladding tube 10, the following formula 1 holds true. (Ht av ) / φ≧4.2%=0.042 (Equation 1) 2, H is the height from the valley bottom 12c to the peak 11c in the radial direction of the cladding tube 10. In other words, the height H corresponds to the difference in radius between the peak 11 and the valley 12. t av is the thickness t of the ridge portion 11 11 and the thickness t of the valley portion 12 12 It is the average of t av =(t 11 +t 12 ) / 2. As shown in FIG. 1, φ is the outer diameter (outer diameter) of the ridge portion 11, that is, the tube diameter (outer diameter) of the cladding tube . Below, the value of the left side of Equation 1 (Ht av ) / φ is referred to as the "index value α." α=(Ht av ) / φ (Equation 2) In short, Equation 1 is expressed as the average thickness t of the peaks 11 and valleys 12 from the height H along the pipe diameter direction from the bottom 12c of the valleys 12 to the peaks 11c of the peaks 11. av This indicates that the index value α obtained by dividing the difference obtained by subtracting α by the outer diameter φ of the ridge portion 11 is 4.2% or more.

[0026] Preferably, the index value α is 5% or more. α≧5%=0.05 (Formula 3) More preferably, the index value α is 20% or less. α≦20%=0.20 (Formula 4) More preferably, the index value α is 15% or less. α≦15%=0.15 (Formula 5)

[0027] 1, the inner diameter of the valley portion 12 of the cladding tube 10 is larger than the outer diameter of the inner tube 2. Therefore, an air layer 3 is formed over the entire area between the cladding tube 10 and the inner tube 2. The valley portion 12 directly faces the outer peripheral surface of the inner pipe 2. No shock-absorbing material such as sound-deadening tape or foamed resin sheet is wrapped around the inner pipe 2. No solid intermediate layer such as a shock-absorbing material is formed between the cladding pipe 10 and the inner pipe 2.

[0028] The composite pipe 1 is manufactured as follows. The inner pipe 2 is produced by extrusion molding. As shown in Fig. 3, the inner pipe 2 is introduced into a corrugating device 20. The inner pipe 2 is fed out from the central hole of a resin extruding section 21 of the corrugating device 20. At the same time, the raw resin 19 of the cladding tube 10 is mixed with a foaming agent in the resin supply section 22 and extruded from the annular outlet surrounding the central hole of the resin extrusion section 21. The extruded raw resin 19 is formed into a tubular shape, and the inner tube 2 is passed through the inside of the tubular shape. At the same time, foaming of the raw resin 19 occurs. Preferably, chemical foaming occurs. The amount of foaming agent added is adjusted so that the expansion ratio n becomes 1.2 to 4 times.

[0029] A corrugating unit 23 is disposed downstream in the extrusion direction of the resin extrusion unit 21 of the corrugating device 20. The corrugating unit 23 has a plurality of half dies 25 arranged on a pair of annular tracks 24. Each half die 25 has a corrugated die surface 25a. These half dies 25 circulate along each annular track 24, and corresponding half dies 25 of the pair of annular tracks 24 come together on an extension of the extrusion direction to form a closed cylindrical die 26. The tubular raw resin 19 is passed through the die 25, and a vacuum mechanism 27 expands the diameter of the tubular raw resin 19 and sucks it against the die surface 25a, thereby forming the corrugated pipe 10. Compressed air may be introduced into the tubular raw resin material by a blow mechanism to press the raw resin material against the mold surface 25a, thereby forming it into a wave shape. In this way, a composite pipe 1 is produced in which the inner pipe 2 is covered with the cladding pipe 10 having a corrugated cross section. According to the composite pipe 1, there is no need to insert a shock absorbing material such as a sound absorbing tape between the cladding pipe 10 and the inner pipe 2, and the manufacturing cost can be reduced.

[0030] As shown in Figure 4, in such a composite pipe 1, the covering pipe 10 is made of a foamed resin whose main component is polyethylene, so when the end of the inner pipe 2 is exposed and a joint (not shown) is connected, the covering pipe 10 is easily shrunk. stress is greater than 10 MPa and the tensile yield point before foaming is stressBy selecting a foaming ratio of (n×10) MPa or less, the cladding tube 10 can be reliably softened and the ease of shrinking can be ensured. By setting the foaming ratio to 1.2 times or more, the flexibility of the cladding tube 10 can be increased and the ease of shrinking can be reliably ensured.

[0031] Furthermore, by having the cladding tube 10 satisfy formula 1 (α≧4.2%), and preferably formula 3 (α≧5%), when the cladding tube 10 is shrunk, each peak 11 is deformed into a uniform semicircular cross section, and each valley 12 is deformed so as to be neatly folded. This allows the cladding tube 10 to be shrunk neatly. In other words, it is possible to prevent the corrugated shape of the cladding tube 10 from being distorted, and it is possible to prevent the cladding tube 10 from being shrunk into an irregular shape. As a result, it is possible to ensure ease of shrinking the cladding tube 10 along its axial direction (ease of shrinking) and ease of shrinking workability, including a good appearance when shrunk (shrinkage appearance).

[0032] It is more preferable that the cladding tube 10 satisfies formula 4 (α≦20%), and even more preferable that it satisfies formula 5 (α≦15%), thereby preventing the height H (difference in radius between the peaks and valleys) from becoming excessively large, and preventing the thickness difference between the peaks 11 and valleys 12 from becoming too large during molding, which would make the tube more susceptible to tearing, or prevent the creation of extremely thin-walled portions.

[0033] A fluid such as water at 95°C or less is passed through the inner pipe 2 of the compound pipe 1. By making the covering pipe 10 from a foamed resin, the heat retention of the composite pipe 1 can be improved, and the temperature of the fluid can be maintained constant. The foaming ratio is preferably 1.1 times or more, and more preferably 1.2 times or more. This makes it possible to lower the thermal conductivity than non-foamed polyethylene, and to reliably ensure heat retention. Furthermore, by adding polypropylene (PP) as a foaming resin component, the heat retention can be further improved.

[0034] By setting the foaming ratio to 4 times or less, the cladding tube 10 can be prevented from becoming too soft, thereby ensuring the shape retention of the cladding tube 10. Therefore, even if the inner diameter of the valley portions 12 of the cladding tube 10 is made larger than the outer diameter of the inner tube 2, the cladding tube 10 can be prevented from losing its shape. By making the inner diameter of the valley portions 12 larger than the outer diameter of the inner tube 2, the air layer 3 can be formed continuously throughout the entire area between the cladding tube 10 and the inner tube 2, further improving the heat retention. Furthermore, by making the cladding tube 10 from a foamed resin, it is possible to suppress to some extent the occurrence of rattle noise (contact noise between the cladding tube 10 and the inner tube 2).

[0035] Next, another embodiment of the present invention will be described. In the following embodiments, the same components as those already described will be denoted by the same reference numerals in the drawings and the description thereof will be omitted. <Second embodiment (FIGS. 5 and 6)> 5 and 6, a cladding pipe 10B in the compound pipe 1B of the second embodiment is formed with a plurality of holding protrusions 14. Each holding protrusion 14 has a height ΔH 14 and are in contact with the outer peripheral surface of the inner pipe 2. At least two of the holding protrusions 14 are in contact with the outer peripheral surface of the inner pipe 2. The multiple holding protrusions 14 are distributed and arranged in the axial and circumferential directions of the cladding pipe 10B. In the cladding tube 10B of the second embodiment, the width of the valley portions 12 along the tube axis direction is approximately equal to the width of the ridge portions 11. The holding protrusions 14 are provided in the valley portions 12, but are not limited thereto and may be provided in the ridge portions 11. The holding protrusions 14 are in the form of spots, but may also be in the form of stripes extending in the tube axis direction.

[0036] In the cladding tube 10B, not only is an air layer 3 formed between the inner peripheral surface of the crest portion 11 and the outer peripheral surface of the inner tube 2, but also a height ΔH is formed between the valley portion 12 and the inner tube 2. 14The covering pipe 10B has an air layer 3 formed therein. The air layer 3 can further enhance the heat retention of the composite pipe 1. In addition, with the covering pipe 10B, the holding protrusions 14 come into contact with the inner pipe 2 and hold the inner pipe 2, thereby preventing the generation of sheath rattle noise caused by water hammer. With the covering pipe 10B, there is no need to form a buffering intermediate layer, such as a sound-deadening tape or a foamed resin sheet, on the inner pipe 2 to prevent sheath rattle noise, which can reduce costs.

[0037] The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the invention. For example, the cross-sectional shape of the cladding tube can be appropriately modified within a range satisfying formula 1, and preferably formulas 3 to 5. The cross section of the peaks 11 is not limited to a circular arc convex outward in the radial direction, but may be flat. Similarly, the cross section of the valleys 12 is not limited to a circular arc convex inward in the radial direction, but may be flat. The inner pipe 2 is not limited to being used for transporting liquids such as water or hot water, but may also be used for transporting gases or other fluids. [Example]

[0038] EXAMPLES The present invention is not limited to the following examples. <Evaluation of shrinkage workability (shrinkage appearance)> As shown in Table 1, in Example 1, molds (no. 1, 3, 4) for molding cladding tubes having cross-sectional shapes similar to those shown in Figures 1 and 2 were prepared, and multiple types of cladding tube samples (A) to (I) with different post-molding dimensions were molded using each mold. The materials of each cladding sample were low-density polyethylene (LPDE) and polypropylene (PP), with a weight ratio of these resin components of LPDE:PP = 8:2. 8.5 parts by weight of a foaming agent was added to 100 parts by weight of these resin components (LPDE + PP).

[0039] The height H and average thickness t of each cladding sample after molding av , and the outer diameter φ was measured. The height from the valley bottom 12c to the peak 11c was measured at four to eight points in the circumferential direction of each cladding tube sample using a depth bar of a vernier caliper, and the average value was taken as the height H. The thickness of each cladding sample was measured at four or eight points around the circumferential direction of the peaks and valleys using a micrometer, and the average thickness t av In some cladding samples, the valley 12 was narrow and the micrometer spindle could not be inserted, so the cladding sample was cut in the axial direction at four or eight points around the circumference of the tip of the cladding sample, and the thickness of the cross section was measured with a vernier caliper. av asked for. The outer diameter φ of each cladding tube sample was measured using a vernier caliper.

[0040] The tip of each cladding pipe sample was shrunk in the axial direction of the pipe, and the shrinkage workability was evaluated. [Table 1]

[0041] In Table 1, "○" in the evaluation column for shrinkability indicates that the product could be shrunk easily and neatly. "×" indicates that the product could be shrunk, but the external shape was distorted, which was judged to have impaired the product's appeal. "XX" indicates that the product could not be shrunk. As a result, the height H and average thickness t av It was found that shrinkage workability can be improved by setting the outer diameter φ so as to satisfy formula 1 (α≧4.2%). Furthermore, it was found that shrinkage workability can be reliably improved by setting it so as to satisfy formula 3 (α≧5%). The results for sample (F) indicate that good shrink workability can be achieved even if formula 1 is not satisfied. Therefore, formula 1 can be used as a slightly stricter index for shrink workability. [Example]

[0042] In Example 2, cladding tube samples were produced using the following seven raw material compositions (1) to (7). (1) 100 parts by weight of HDPE and 8.5 parts by weight of foaming agent (2) 100 parts by weight of HDPE and 8.5 parts by weight of foaming agent (3) 100 parts by weight of LDPE and 8.5 parts by weight of a blowing agent (4) 80 parts by weight of LDPE, 20 parts by weight of PP, and 8.5 parts by weight of a foaming agent (5) 70 parts by weight of LDPE, 30 parts by weight of PP, and 8.5 parts by weight of a foaming agent (6) 60 parts by weight of LDPE, 40 parts by weight of PP, and 8.5 parts by weight of a foaming agent (7) 100 parts by weight of PP and 8.5 parts by weight of foaming agent As the HDPE in (1), Suntec (registered trademark) HD ​​B470 manufactured by Asahi Kasei Corporation was used. (2) As the HDPE, Novatec (registered trademark) HD ​​HE121 manufactured by Japan Polyethylene Co., Ltd. was used. As the LDPE of (3) to (6), Suntec (registered trademark) LD M1820 manufactured by Asahi Kasei Corporation was used. As the PP of (4) to (7), Waymax (registered trademark) EX6000 manufactured by Japan Polypropylene Corporation was used. As the blowing agent for (1) to (7), microcapsule MB5885 manufactured by Sankyo Kasei Co., Ltd. was used.

[0043] The cross-sectional shape of each sample was set to be approximately the same as that shown in FIGS. 1 and 2, so as to satisfy Equation 1. Specifically, the height H from the valley bottom 12c to the peak 11c was H=1.9 mm. The average thickness t of the peaks 11 and valleys 12 av is t av =0.5mm. The tube diameter φ was φ=28.5 mm. Index value α(=(Ht av ) / φ) was α=4.9%.

[0044] Tensile yield strength of resin components in each sample before foaming stress The calculated values, expansion ratio (n), n × 10 MPa, and thermal conductivity (calculated values) were as shown in Table 2. Each sample was evaluated for heat retention and shrinkage workability, and further evaluated overall. As for shrinkage workability, the ease of shrinkage (ease of shrinkage) was mainly evaluated for cladding tube samples of the same shape made in the same mold.

[0045] [Table 2]

[0046] In Table 2, "◎" in the evaluation column indicates particularly good, "◯" indicates good, "△" indicates slightly bad, and "×" indicates bad. From Table 2, the tensile yield before foaming stress It was found that those with a tensile yield strength of more than (n × 10) MPa had a large resistance when contracted. stress is greater than 10 MPa and the tensile yield point before foaming is stress It was found that ease of shrinking could be ensured by setting the compressive strength to (n×10) MPa or less. Those with an overall rating of "Excellent" are promising in terms of both heat retention and shrink workability. That is, in the above examples, (4) LDPE:PP=8:2, etc. was considered to be the best. [Industrial Applicability]

[0047] The present invention can be applied to, for example, cold and hot water supply pipes. [Explanation of symbols]

[0048] 1,1B composite pipe 2 Inner tube 3 Air layer 10,10B cladding tube 11 Yamabe 11c summit 12 Valley 12c valley bottom 13 Side wall 14 Retaining protrusion

Claims

1. A covering tube that covers a flexible inner tube, a flexible corrugated pipe comprising a single layer of foamed resin containing polyethylene as a main component and having an expansion ratio of 1.2 to 4 times, wherein the polyethylene accounts for 50 wt % or more of the entire foamed resin, the polyethylene accounting for 50 wt % or more of the foamed resin, the width of the valleys along the pipe axis direction is smaller than the width of the peaks along the pipe axis direction, and the index value obtained by subtracting the average thickness of the peaks and valleys from the height along the pipe diameter direction from the bottom of the valleys to the top of the peaks, by the outer diameter of the peaks, is 4.2% or more and 5.13% or less.

2. 2. The cladding tube according to claim 1, wherein the index value is 5% or more.

3. 3. The cladding tube according to claim 1, wherein the index value is 15% or less.

4. The cladding tube according to any one of claims 1 to 3, characterized in that a plurality of retaining protrusions are formed in a dispersed manner and protrude further toward the inside of the tube than the valley portion, and these retaining protrusions position the inner tube substantially concentrically with the cladding tube.

5. 5. A composite pipe comprising the cladding pipe according to claim 1 and an inner pipe, wherein a plurality of retaining projections are formed dispersedly on the cladding pipe, the retaining projections projecting further inward than the valley portions, and an air layer is formed between the inner surface of the cladding pipe and the outer surface of the inner pipe by the retaining projections.

6. 6. The compound pipe according to claim 5, wherein at least two of the retaining projections are in contact with the outer circumferential surface of the inner pipe.

7. 7. The composite pipe according to claim 5, wherein the resin constituting the covering pipe has a tensile yield stress immediately before foaming that is greater than 10 MPa and not greater than (n×10) MPa (n is the foaming ratio).

8. 8. The composite pipe according to claim 5, wherein the covering pipe contains polypropylene in an amount of 10 wt % to 30 wt % of the entire foamed resin.

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