Coated pipes and composite pipes

Abstract

To enhance contractibility and heat insulation property of a cladding pipe formed of a corrugated pipe in a multiple pipe.SOLUTION: A flexible inner pipe 2 is covered with a cladding pipe 10. The cladding pipe 10 comprises a single layer of a foamed resin containing polyethylene as a main component, which has a foaming ratio n of 1.2 to 4 times and a tensile yield strength before foaming of (n×10) MPa or less, and is composed of a flexible corrugated pipe in which peaks 11 and valleys 12 are formed alternately in a pipe axial direction.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. Additionally, the covering pipe of a composite pipe is often required to have thermal insulation properties to maintain the temperature of the liquid flowing inside the inner pipe, but corrugated pipes have inferior thermal insulation properties compared to 5mm thick insulation material. In view of the above circumstances, the present invention aims to improve the shrinkability (ease of shrinking and good appearance when shrunk) and heat retention 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 pipe to be fitted over a flexible inner pipe, the covering pipe having a foaming ratio n of 1.1 to 4 times and a tensile yield strength before foaming. stress The coating pipe is characterized by being made of a flexible corrugated pipe consisting of a single layer of foamed resin whose main component is polyethylene, with a foam strength of (n × 10) MPa or less, and in which peaks and valleys are alternately formed in the axial direction of the pipe. The foaming ratio is preferably 1.1 times or more, and more preferably 1.2 times or more. According to the cladding pipe made of the corrugated pipe having such characteristics, the foaming ratio n is 1.2 to 4 times and the tensile yield point before foaming is 1.2 to 4 times. stress is (n × 10) MPa or less, in other words, the tensile yield point before foaming stress By using a resin with a value of 10 MPa or less when the tensile yield strength (MPa) divided by the expansion ratio is obtained, the ease of shrinking along the pipe axis (ease of shrinking) and the appearance when shrunk (shrinkage appearance) can be secured. By setting the expansion ratio at 1.2 to 4 times, heat retention can be secured. In other words, the tensile yield strength before expansion is 10 MPa or less. stress In the case of a resin with a high tensile yield strength and a hardness, the resin can be applied to the cladding pipe of the present invention by increasing the expansion ratio. stress In the case of a resin with a foaming ratio of 13 MPa, it is applicable if the foaming ratio is 1.3 times or more. stress Resins of 13 MPa or less are applicable, and for example, resins of 9 MPa are also applicable.

[0006] The present invention aims to achieve both shrinkability and heat retention for a cladding pipe. Shrinkability includes ease of shrinking and appearance after shrinking. From the perspective of ensuring appearance after shrinking, it is preferable that the distance along the pipe diameter from the outer surface of the valley portion to the center of the wall thickness of the crest portion be equal to or greater than the half-width value along the pipe axis of the crest portion, or that the distance along the pipe diameter from the inner surface of the crest portion to the center of the wall thickness of the valley portion be equal to or greater than the half-width value along the pipe axis of the valley portion. This ensures appearance after shrinking, and prevents the corrugated shape from being distorted, which would result in a poor appearance, when the cladding pipe is shrinked in the axial direction. The half width value refers to half (one half) of the width of the peak or valley along the tube axis. When the half width of the peaks is greater than the half width of the valleys, it is more preferable that the distance from the outer surface of the valleys to the center of the peaks along the diameter of the tube be equal to or greater than the half width of the peaks.When the half width of the valleys is greater than the half width of the peaks, it is more preferable that the distance from the inner surface of the peaks to the center of the valleys along the diameter of the tube be equal to or greater than the half width of the valleys.

[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 rattle noise due to water hammer.

[0010] The cladding tube is tensile yielded before foaming. stress is greater than 10 MPa and the tensile yield point before foaming is stress is preferably (n×10) MPa or less. 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 heat retention of the covering pipe is improved. If the PP content is 30 wt% or less, shrinkage workability can be prevented from being hindered.

[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), but the foaming ratio n is 1.2 to 4 times, and the tensile yield point before foaming is 0.01 to 0.02. stress is (n×10) MPa or less, and more preferably the tensile yield strength before foaming is stress It may also comprise medium density polyethylene (MDPE) or high density polyethylene (HDPE) as long as the modulus of elasticity is greater than 10 MPa. 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) and heat retention of the 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 part of a cladding tube. [Figure 6] FIG. 6 shows a third embodiment of the present invention and is a side cross-sectional view of a part of a cladding tube. [Figure 7] FIG. 7 shows a fourth embodiment of the present invention and is a side cross-sectional view of a portion of a compound pipe. [Figure 8] FIG. 8 is a cross-sectional view taken along line VIII-VIII 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 has a foaming ratio n of 1.2 to 4 times and a tensile yield strength before foaming of 1.2 to 4 times. stress The foamed resin is composed of a polyethylene foam having a compressive strength of (n×10) MPa or less as a main component, and is flexible. 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.

[0017] 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 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 likely to be less than (n × 10) MPa, 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] The cladding tube 10 is composed of a single layer of foamed resin whose main component is polyethylene. The foaming ratio of the foamed resin is 1.2 to 4 times. By setting the foaming ratio to 1.2 times or more, the rigidity of the cladding tube 10 can be reduced and shrinkability can be ensured. By setting the foaming ratio to 4 times or less, the cladding tube 10 can stand on its own and maintain its shape. The foamed resin preferably has closed cells from the viewpoint of ensuring 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] As shown in Fig. 2, the cross section of the ridges 11 cut along a plane including the tube axis of the cladding tube 10 is curved so as to be convex toward the outside of the cladding tube 10 (hereinafter referred to as "outside the tube"). More specifically, each ridge 11 has a central ridge portion 11a in the tube axis direction and ridge end portions 11c at both ends in the tube axis direction. The ridge portion 11a has a relatively gentle curvature and is formed into an arc-shaped cross section that is convex toward the outside of the tube (particularly, the radially outward direction). The ridge end portions 11c have a steeper curvature than the ridge portions 11a and are formed into an arc-shaped cross section that is convex toward the outside of the tube.

[0022] The cross section of the valley portion 12 cut along a plane including the tube axis of the cladding tube 10 is curved so as to convex toward the inside of the cladding tube 10 (hereinafter referred to as the "tube inside"). More specifically, each valley portion 12 has a central valley portion 12a in the tube axis direction and valley end portions 12c at both ends in the tube axis direction. The valley portion 12a has a relatively gentle curvature and is formed into an arc-shaped cross section that convex toward the tube inside (particularly the radially inner side). The valley end portions 11c have a curvature that is steeper than that of the valley portion 12a and are formed into an arc-shaped cross section that convex toward the tube inside.

[0023] 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 11c and the valleys 12c, and is annular over the entire circumference of the cladding tube 10. The outer peripheral end (upper side in Fig. 2) of the side wall 13 smoothly connects with the peak end 11c. The inner peripheral end (lower side in Fig. 2) of the side wall 13 smoothly connects with the valley end 12c.

[0024] In FIG. 2, the width W of the ridge portion 11 along the tube axis direction 11 is the width W of the valley portion 12 along the pipe axis direction. 12 Greater than (W 11 >W 12 ) where the width W of the ridge 11 11 The width W of the valley portion 12 is the width of the crest portion 11 as seen from the outside of the cladding tube 10, and is the total width including not only the crest portion 11a but also the crest end portions 11c on both sides of the crest portion 11a. 12 refers to the width of the valley portion 12 as seen from the inside of the cladding tube 10, and refers to the total width including not only the valley portion 12a but also the valley end portions 12c on both sides thereof.

[0025] As shown in Figure 2, 11 >W 12 In the cladding tube 10, preferably, the distance L along the tube diameter from the outer surface of the valley portion 12 to the center of the wall thickness of the peak portion 11 is 13 The half width W of the peak 11 11half The above is set. In other words, Equation 1 holds true. W 11half <L 13 (Formula 1)

[0026] Since the cladding tube 10 is made of a foamed resin and is flexible, the distance L 13 If this is too large, only the tip of the cladding pipe 10 will extend, and the tip of the inner pipe 2 will likely be relatively retracted into the cladding pipe 10. For example, when working to pass the composite pipe 1 through a through-hole in the floor from under the floor of a building, if you try to grab and pull up the cladding pipe 10 at the tip of the composite pipe 1 that is slightly protruding from the through-hole, the middle part of the cladding pipe 10 will get caught on the edge of the through-hole, and from there only the tip side of the cladding pipe 10 will extend, and the inner pipe 2 inside will likely be left behind and not be able to be pulled up. Pulling out the inner pipe 2 that has once retracted in this way is quite cumbersome, and if such a situation occurs at a construction site, there will be a lot of work loss. Therefore, to prevent this situation, the distance L 13 It is preferable not to make the distance L 13 The upper limit of L 13 ≦2×W 11half =W 11 In short, it is preferable that the formula 2 is satisfied. W 11half <L 13 ≦W 11 (Formula 2)

[0027] 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, 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. The amount of foaming agent added is adjusted so that the expansion ratio is 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 The tensile yield strength before foaming is preferably selected to be (n × 10) MPa or less. stressBy selecting a foaming ratio of 1.2 or more, the flexibility of the cladding tube 10 can be increased and the ease of shrinking can be reliably ensured. By ensuring that the dimensional relationship between the ridges 11 and the side wall 13 satisfies Equation 1, when the cladding tube 10 is shrunk, the ridges 11 are deformed into a semicircular cross section that is convex radially and outward, and the side wall 13 is deformed into a concave cross section that is a quarter circle, as shown in Figure 4. This prevents the corrugated shape of the cladding tube 10 from being distorted.

[0031] A fluid such as water at 95°C or less is passed through the inner pipe 2 of the compound pipe 1. By using a foamed resin for the covering pipe 10, the heat retention of the composite pipe 1 can be improved, and the temperature of the fluid can be maintained constant. By setting the expansion ratio to 1.2 or more, the thermal conductivity can be made lower than that of non-foamed polyethylene, ensuring heat retention. Furthermore, by adding polypropylene (PP) as a foaming resin component, the heat retention can be further improved.

[0032] 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).

[0033] 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. The cross-sectional shape of the cladding tube can be appropriately modified within a range that preferably satisfies formula 1 or an equivalent formula. <Second embodiment (Fig. 5)> As shown in Fig. 5, in the cladding tube 10B of the second embodiment, the cross section of the valley portion 12 is generally semicircular. That is, the valley portion 12a and the valley end portion 12c have approximately the same curvature. The width W of the valley portion 12 12 is the width W of the peak 11 11 It is about half of that. Preferably, the cladding tube 10B also satisfies formula 1. This makes it possible to prevent the corrugated shape from being destroyed when the cladding tube 10B is shrunk.

[0034] <Third embodiment (Fig. 6)> As shown in FIG. 6, in the cladding tube 10C of the third embodiment, the width W 12 The width W of the peak 11 11 Greater than (W 11 <W 12 In the cladding tube 10C, it is preferable that the distance L along the tube diameter from the inner surface of the crest portion 11 to the center of the wall thickness of the valley portion 12 is 13 ' is the half width W of the valley 12 12half The above is set. In other words, Equation 1' holds true. W 12half <L 13 ' (Formula 1') This prevents the corrugated shape from being destroyed when the cladding tube 10C is contracted, as in the first and second embodiments. Furthermore, in order to prevent only the tip of the cladding tube 10C from expanding and the tip of the inner tube 2 from being relatively retracted into the cladding tube 10, the distance L 13 The upper limit of ' is L 13 '≦2×W 12half =W 12 In short, it is preferable that the formula 2' is satisfied. W 12half <L 13 '≦W 12 (Formula 2')

[0035] <Fourth embodiment (FIGS. 7 and 8)> 7 and 8, a cladding pipe 10D in the compound pipe 1 of the fourth embodiment is formed with a plurality of holding projections 14. Each holding projection 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 10D. The holding protrusions 14 are provided on the valley portions 12, but are not limited thereto and may be provided on the peak portions 11. The holding protrusions 14 are in the form of spots, but may also be in the form of stripes extending in the axial direction of the tube.

[0036] In the cladding tube 10D, not only is an air layer 3 formed between the inner peripheral surface of the ridge portion 11 and the outer peripheral surface of the inner tube 2, but also a height ΔH 14 The covering pipe 10D has an air layer 3 formed therein. The air layer 3 can further enhance the heat retention of the composite pipe 1. In addition, according to the covering pipe 10D, 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. The covering pipe 10D does not require the formation of a buffer intermediate layer, such as a sound-deadening tape or a foamed resin sheet, on the inner pipe 2 to prevent sheath rattle noise, thereby reducing 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 section of the peak portion 11a is not limited to a circular arc convex outward in the radial direction, but may be flat. Similarly, the cross section of the valley portion 12a 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. Cladding tube samples were produced using the following seven different 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. The cross-sectional shape of each sample was set to be approximately the same as that shown in FIG. 5, so that Equation 1 was satisfied. The thickness of each sample was 0.5 mm, especially at the peaks. Tensile yield strength of resin components in each sample before foaming stress The expansion ratio (n), n × 10 MPa, and thermal conductivity (calculated value) were as shown in Table 1.

[0039] 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.

[0040] [Table 1]

[0041] In Table 1, "◎" in the evaluation column indicates particularly good, "◯" indicates good, "△" indicates slightly bad, and "×" indicates bad. From Table 1, 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 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.

[0042] <Evaluation of heat retention> Sample (4) was selected and its thermal conductivity was measured, which was 0.12 W / (m·K). After hot water was made to flow through the inner pipe 2 of the composite pipe using the sample (4) as the covering pipe, the temperature drop of the hot water was measured. As the inner pipe 2, a cross-linked polyethylene pipe having an inner diameter of 12.8 mm and a thickness of 2.1 mm was used. The length of the composite pipe was 1500 mm. The initial temperature of the hot water was 42°C. At the same time as the start of the measurement, the flow of hot water in the inner pipe 2 was stopped (flow velocity 0 m / s). The ambient temperature was 5°C. The measured temperature of the hot water in the inner pipe 2 was 19.1°C 30 minutes after the start of the measurement. A heat retention performance equivalent to or better than the measurement result (19.0°C) obtained under the same conditions for a 5 mm insulated cross-linked polyethylene pipe (a comparative example pipe) was achieved.

[0043] From the heat retention evaluation results and thermal conductivity (Table 1) of the sample (4) and the comparative example pipe, the heat retention of the other samples (1) to (3) and (5) to (7) was evaluated as shown in Table 1. In the "Heat Retention" column of Table 1, "○" indicates good heat retention (equivalent to or better than 5mm insulated PEX pipe), and "△" indicates that heat retention is slightly inferior to 5mm insulated PEX pipe.

[0044] Based on the above results, a comprehensive evaluation was made on a four-point scale of "◎", "○", "△", and "×" in order of best performance from the viewpoint of ensuring both heat retention and shrinkage workability, as shown in Table 1. stress It was confirmed that the insulation and shrinkage workability could be secured by using a covering pipe made of a single-layer foamed resin whose main component is polyethylene with a compressive strength of (n×10) MPa or less. [Example]

[0045] <Evaluation of shrinkage workability (shrinkage appearance)> As shown in Table 2, in Example 2, cladding tube molding dies (nos. 1, 3, and 4) corresponding to the configuration in Fig. 5 and a cladding tube molding die (no. 2) corresponding to the configuration in Fig. 6 were prepared. Using each die, multiple types of cladding tube samples (nos. 1 to 24) with different material compositions, wall thicknesses, etc. were molded. The tip end of each cladding tube sample was shrunk in the axial direction of the tube, and the appearance of the shrunk tube was evaluated.

[0046] In Table 2, the parts by weight of the foaming agent are values based on 100 parts by weight of the resin components (LPDE+PP). [Table 2]

[0047] In Table 2, "○" in the evaluation column for shrinking appearance indicates that the product was able to be shrunk easily and neatly. "×" indicates that the product was able to be shrunk, but the appearance 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, it was confirmed that the cladding tube can have a good shrink appearance by having a shape that satisfies formula 1 or formula 1'. The results of Samples No. 9 and 22 show that good shrinkage appearance can be achieved even if Formula 1 or Formula 1' is not satisfied. Therefore, Formula 1 or Formula 1' can be used as a slightly stricter index for shrinkage appearance. [Industrial Applicability]

[0048] The present invention can be applied to, for example, cold and hot water supply pipes. [Explanation of symbols]

[0049] 1,1D composite pipe 2 Inner tube 3 Air layer 10 Cladding tube 10B~10D Cladding tube 11 Yamabe 12 Valley 11a Mountain part 11c Mountain end part 12a Valley part 12c Valley edge part 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 the main component, with an expansion ratio n of 1.2 to 4 times and a tensile yield stress before foaming of (n x 10) MPa or less and more than 10 MPa, wherein the polyethylene accounts for 50 wt % or more of the entire foamed resin, and wherein peaks and valleys are alternately formed in the axial direction of the pipe.

2. 2. The cladding tube according to claim 1, wherein a distance along the tube diameter from an outer surface of the valley portion to a center of wall thickness of the crest portion is equal to or greater than a half-width value of the crest portion along the tube axis, or a distance along the tube diameter from an inner surface of the crest portion to a center of wall thickness of the valley portion along the tube axis is equal to or greater than a half-width value of the valley portion along the tube axis.

3. The cladding tube according to any one of claims 1 to 2, 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.

4. 4. 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.

5. 5. The compound pipe according to claim 4, wherein at least two of the retaining projections are in contact with the outer circumferential surface of the inner pipe.

6. 6. The composite pipe according to claim 4, wherein the covering pipe contains polypropylene in an amount of 10 wt % to 30 wt % of the total foamed resin.

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