Multilayer pipe and method for manufacturing the same

Abstract

To provide a multilayer pipe including a plurality of foam layers, and a method for manufacturing the same.SOLUTION: A multilayer pipe 10 includes a first layer 12 composed of a foam layer made of a vinyl chloride-based resin, and a second layer 14 which is formed on the outer peripheral side of the first layer and is composed of a foam layer made of a vinyl chloride-based resin, wherein an average expansion ratio of the first layer is lower than an average expansion ratio of the second layer. The average expansion ratio of the first layer can be set to exceed 1.00 time and 1.05 times or less. The first layer can include a first skin layer having the expansion ratio lower than the average expansion ratio of the first layer on the inner peripheral side thereof.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present invention relates to a multi-layer pipe including multiple foamed layers and a method for making the same. [Background technology]

[0002] Multi-layer pipes made of polyvinyl chloride resin are used as piping for passing fluids, such as drain pipes and air conditioning drain pipes (see, for example, Patent Document 1). A multi-layer pipe is constructed by forming a second layer around the outer periphery of a first layer located on the inside, and then forming a third layer around the outer periphery of that. The first and third layers are non-foamed layers that do not contain a foaming agent, and the second layer between them is a foamed layer. The inclusion of a foamed layer can reduce the weight of the multi-layer pipe, and the foamed layer exerts soundproofing and heat insulation effects, thereby reducing the flow noise, heat radiation, and condensation of the fluid passing through the pipe. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2001-173846 A Summary of the Invention [Problem to be solved by the invention]

[0004] When a multi-layer pipe 10 in which the first layer 12 and the third layer 16 are non-foamed layers and the second layer 14 is a foamed layer is cut with a cutting machine, cracks 90 may occur in the first layer 12 or the third layer 16, as shown in the photograph in Figure 14. In the figure, a crack 90 has occurred in the third layer 16, which is the outer layer.

[0005] As a result of extensive research, the inventors have found that the cracks 90 are caused by poor adhesion between the foamed layer and the non-foamed layer.

[0006] It is an object of the present invention to provide a multi-layer pipe containing multiple foamed layers and a method for making the same. [Means for solving the problem]

[0007] The multilayer tube of the present invention is A first layer made of a polyvinyl chloride resin foam layer; a second layer formed on the outer periphery of the first layer and made of a foamed layer made of a vinyl chloride resin; A multi-layer pipe comprising: The average expansion ratio of the first layer is lower than the average expansion ratio of the second layer.

[0008] The average expansion ratio of the first layer may be more than 1.00 and not more than 1.05.

[0009] The first layer may include, on the inner periphery side, a first skin layer having an expansion ratio smaller than the average expansion ratio of the first layer.

[0010] It is desirable for the breaking water pressure performance to be 8MPa or more.

[0011] The second layer may include, on the outer periphery thereof, a second skin layer having an expansion ratio smaller than the average expansion ratio of the second layer.

[0012] A third layer is provided on the outer periphery of the second layer, the third layer being a foam layer made of a vinyl chloride resin. The average expansion ratio of the third layer is lower than the average expansion ratio of the second layer.

[0013] The average expansion ratio of the third layer may be more than 1.00 and not more than 1.05.

[0014] The average expansion ratio of the first layer may be the same as the average expansion ratio of the third layer.

[0015] The average expansion ratio of the first layer can be lower than the average expansion ratio of the third layer.

[0016] The average expansion ratio of the first layer can be higher than the average expansion ratio of the third layer.

[0017] The third layer may include, on the outer periphery thereof, a third skin layer having an expansion ratio smaller than the average expansion ratio of the third layer.

[0018] The method for producing a multilayer pipe of the present invention comprises the steps of: A method for manufacturing a multi-layer pipe including a first layer made of a polyvinyl chloride-based resin foamed layer, and a second layer formed on an outer circumferential side of the first layer and also made of a polyvinyl chloride-based resin foamed layer, comprising: A first raw material is prepared by adding a foaming agent to a vinyl chloride resin that forms the first layer, and a second raw material is prepared by adding a foaming agent to a vinyl chloride resin that forms the second layer in an amount that makes the average foaming ratio higher than that of the first raw material, The first raw material and the second raw material are heated and melted under pressure, and extruded into a tubular shape so that the first raw material is on the inner periphery side and the second raw material is on the outer periphery side to form a laminated body; The laminate is expanded in diameter while releasing the pressure to form a tubular shape, thereby foaming the foaming agent; The laminate in which the foaming agent has been foamed is sized on the outer and inner periphery and then cooled, thereby forming the first layer on the inner periphery side and the second layer having an average foaming ratio higher than that of the first layer on the outer periphery side.

[0019] The method for producing a multilayer pipe of the present invention further comprises the steps of: A method for manufacturing a multi-layer pipe including a first layer made of a polyvinyl chloride resin foamed layer, a second layer formed on the outer periphery of the first layer and made of a polyvinyl chloride resin foamed layer, and a third layer formed on the outer periphery of the second layer and made of a polyvinyl chloride resin foamed layer, comprising: A first raw material is prepared by adding a foaming agent to a vinyl chloride resin forming the first layer, a second raw material is prepared by adding a foaming agent to a vinyl chloride resin forming the second layer in an amount such that the average foaming ratio is higher than that of the first raw material, and a third raw material is prepared by adding a foaming agent to a vinyl chloride resin forming the third layer in an amount such that the average foaming ratio is lower than that of the second raw material, The first raw material, the second raw material, and the third raw material are heated and melted under pressure, and extruded into a tubular shape such that the first raw material is on the inner periphery side, the second raw material is in the middle, and the third raw material is on the outer periphery side of the second raw material to form a laminated body; The laminate is expanded in diameter while releasing the pressure to form a tubular shape, thereby foaming the foaming agent; The laminate in which the foaming agent has been foamed is sized on the outer and inner periphery and then cooled to form the first layer on the inner periphery side, the second layer having a higher average foaming ratio than the first layer in the middle, and the third layer having a lower average foaming ratio than the second layer on the outer periphery side.

[0020] The first ingredient and the third ingredient may be the same. Effect of the Invention

[0021] In the multi-layer pipe of the present invention, in the case of a two-layer pipe, both the first and second layers are foamed, and in the case of a three-layer pipe, the first, second and third layers are foamed, so that each layer is made of a material containing a vinyl chloride resin and a foaming agent, and the materials of the two layers can be made similar to each other. This makes it possible to improve the bonding between the layers during extrusion molding. Since the multi-layer pipe of the present invention has high bonding between the layers, it is possible to prevent cracks from occurring in any of the layers when the multi-layer pipe is cut. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is a cross-sectional view of a multi-layer pipe according to a first embodiment. [Diagram 2] FIG. 2 is an enlarged photograph of a cross section of the multi-layer pipe of the first embodiment. [Diagram 3] FIG. 3 is an explanatory diagram showing a cross section of the open cell rate measuring device. [Figure 4] FIG. 4 is a cross-sectional view of a multi-layer pipe of a first embodiment including a skin layer. [Diagram 5] FIG. 5 is a close-up photograph of the first skin layer. [Figure 6] FIG. 6 is a close-up photograph of the third skin layer. [Figure 7] FIG. 7 is an explanatory diagram showing a manufacturing apparatus for a multi-layer pipe. [Figure 8] FIG. 8 is a cross-sectional view of a die for extruding a three-layer tube. [Figure 9]FIG. 9 is an explanatory diagram of a vacuum sizing device. [Figure 10] FIG. 10 is a cross-sectional view of a multi-layer pipe according to the second embodiment. [Figure 11] FIG. 11 is a cross-sectional view of a die for extruding a two-layer tube. [Figure 12] FIG. 12 is a cross-sectional view of a multi-layer pipe of a second embodiment including a skin layer. [Figure 13] FIG. 13 is a photograph of a cross section of the multi-layer pipe of the first embodiment (Example 3). [Figure 14] FIG. 14 is a photograph of a cross section of a multi-layer pipe of a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The multi-layer pipe 10 according to one embodiment of the present invention can be used for various purposes such as a drain pipe for passing a fluid or an air conditioning drain pipe.

[0024] First Embodiment Fig. 1 is a cross-sectional view showing one embodiment of a multi-layer pipe 10 of the present invention. Fig. 2 shows photographs of a cut surface, where (a) is an enlarged photograph of the cut surface, (b) is an enlarged photograph of a first layer 12 and a second layer 14, and (c) is an enlarged photograph of the second layer 14 and a third layer 16. In the first embodiment, a multi-layer pipe 10 having a three-layer structure (a three-layer pipe) will be described. Note that in each figure, the thickness of each layer is exaggerated, and may not match the numerical values ​​given below.

[0025] 1 and 2, the multi-layer pipe 10 of the first embodiment includes a cylindrical first layer 12 provided on the innermost circumference, a cylindrical second layer 14 formed on the outer circumference of the first layer 12, and a cylindrical third layer 16 formed on the outer circumference of the first layer 12. In this embodiment, the multi-layer pipe 10 includes an inner layer through which a fluid passes inside the first layer 12, an outer layer in which the third layer 16 serves as an outer shell, and an intermediate layer in which the second layer 14 is an intermediate layer. Although the first layer 12, the second layer 14, and the third layer 16 are each shown as a single layer in the drawings, each may be a multiple layer structure.

[0026] [Material] The multi-layer pipe 10 of the present invention is characterized in that the first layer 12, the second layer 14, and the third layer 16 are all composed of foamed layers of a vinyl chloride resin, and the average expansion ratios of the first layer 12 and the third layer 16 are lower than the average expansion ratio of the second layer 14. The average expansion ratio can be calculated by cutting out each layer and measuring the density according to JIS K 7112:1999.

[0027] Specifically, the average expansion ratio of the first layer 12 and the third layer 16 is more than 1.00 and is not more than 1.05, more preferably not more than 1.03, and desirably not more than 1.025, and is finely expanded. The average expansion ratios of the first layer 12 and the third layer 16 may be the same or different. The average expansion ratios of the first layer 12 and the third layer 16 being different means that the average expansion ratio of the first layer 12 is lower than the average expansion ratio of the third layer 16, or that the average expansion ratio of the first layer 12 is higher than the average expansion ratio of the third layer 16.

[0028] Since the fluid flows through the inner surface of the first layer 12, by making the average expansion ratio of the first layer 12 lower than that of the third layer 16, the unevenness of the inner surface of the multi-layer pipe 10 can be reduced and the water flow performance can be improved.

[0029] By making the average expansion ratio of the third layer 16 higher than that of the first layer 12, it is possible to provide high soundproofing and heat insulating effects. Conversely, by making the average expansion ratio of the third layer 16 lower than that of the first layer 12, it is possible to increase the strength of the multi-layer pipe 10.

[0030] On the other hand, the average expansion ratio of the second layer 14 is set to be higher than the average expansion ratios of the first layer 12 and the third layer 16. Specifically, the average expansion ratio of the second layer 14 is preferably 1.50 times or more, more preferably 3.00 times or more, and particularly preferably 4.00 times or more. The average expansion ratio of the second layer 14 is preferably 10.0 times or less, more preferably 8.00 times or less, and particularly preferably 6.00 times or less.

[0031] The vinyl chloride resin used above may be, but is not limited to, polyvinyl chloride, a copolymer of vinyl chloride monomer and ethylene, etc. The vinyl chloride resins of each layer may be the same or different materials, including the average polymerization degree described below. For example, the first layer 12 and the third layer 16, which are micro-foamed layers, may be made of the same material, and only the second layer 14, which is a foamed layer with a higher average expansion ratio than the micro-foamed layer, may be made of a different material.

[0032] The average degree of polymerization of the vinyl chloride resin is preferably 400 or more, and desirably 2000 or less. If the average degree of polymerization of the vinyl chloride resin is less than 400, the thermal stability and fatigue properties are likely to decrease, and if the average degree of polymerization exceeds 2000, molding at a general molding temperature becomes difficult, and the vinyl chloride resin decomposes. More desirably, the average degree of polymerization of the vinyl chloride resin is 600 or more at the lower limit and 1500 or less at the upper limit.

[0033] The vinyl chloride resin is preferably made to have an average degree of polymerization of the first layer 12 and the third layer 16 larger than that of the second layer 14, which is the intermediate layer. The first layer 12, which is the inner layer, is in direct contact with the fluid, and therefore has strength to prevent breakage and to enhance the water pressure breaking performance. The third layer 16 is an outer shell that provides external strength. On the other hand, the second layer 14 is preferably made of a vinyl chloride resin with a low degree of polymerization in order to promote foaming. The average degree of polymerization of the vinyl chloride resin of the first layer 12 and the third layer 16 is preferably 800 to 1500, and the average degree of polymerization of the vinyl chloride resin of the second layer 14 is preferably 400 to 800. The average degree of polymerization of the first layer 12 and the third layer 16 is more preferably 100 or more larger than that of the second layer 14.

[0034] A foaming agent is added to the vinyl chloride resin of each layer to foam. The foaming agent may be a volatile one, a decomposition type one, or a thermally expandable microcapsule. Examples of volatile foaming agents include, but are not limited to, aliphatic hydrocarbons, alicyclic hydrocarbons, halogenated hydrocarbons, ethers, ketones, etc. Examples of decomposition type foaming agents include, but are not limited to, sodium bicarbonate, sodium carbonate, ammonium bicarbonate, ammonium nitrite, etc. Note that the foaming agent may be used alone or in combination of multiple types. The foaming agent may also be a gas such as carbon dioxide gas, air, or nitrogen gas.

[0035] In the present invention, in order to make the average expansion ratio of the second layer 14 higher than those of the first layer 12 and the third layer 16, the amount of foaming agent added to the vinyl chloride resin of the second layer 14 is made greater than those added to the first layer 12 and the third layer 16. Alternatively, a foaming agent with a higher average expansion ratio is used.

[0036] Specifically, the amount of the foaming agent added to the first layer 12 and the third layer 16 is more than 0 parts by mass and 0.5 parts by mass or less, more preferably 0.3 parts by mass or less, and desirably 0.2 parts by mass or less, relative to 100 parts by mass of the vinyl chloride resin. The amount of the foaming agent added to the first layer 12 and the third layer 16 may be the same or different. For example, by making the amount of the foaming agent added to the first layer 12 and the amount of the foaming agent added to the third layer 16 the same, the average expansion ratio of the first layer 12 and the average expansion ratio of the third layer 16 can be made the same. By making the amount of the foaming agent added to the first layer 12 less than the amount of the foaming agent added to the third layer 16, the average expansion ratio of the first layer 12 can be made lower than the average expansion ratio of the third layer 16. Also, by making the amount of the foaming agent added to the first layer 12 more than the amount of the foaming agent added to the third layer 16, the average expansion ratio of the first layer 12 can be made higher than the average expansion ratio of the third layer 16.

[0037] On the other hand, the amount of foaming agent added to the second layer 14 is greater than the amounts of foaming agent added to the first layer 12 and the third layer 16. Specifically, the amount of foaming agent added to the second layer 14 is preferably 1.0 part by mass or more, more preferably 4.0 parts by mass or more, and particularly preferably 6.0 parts by mass or more, per 100 parts by mass of the vinyl chloride resin. The amount of foaming agent added to the second layer 14 is preferably 18.0 parts by mass or less, more preferably 14.0 parts by mass or less, and particularly preferably 10.0 parts by mass or less.

[0038] It is preferable that the vinyl chloride resin contains a stabilizer to improve moldability and product characteristics. Examples of stabilizers include Ca-Zn, Ba-Zn, Sn, and Pb stabilizers. The third layer 16, which is the outer layer, may contain a pigment. By containing a pigment, the appearance of the multi-layer pipe 10 can be improved, or coloring can be provided according to the needs of the user.

[0039] [shape] The multi-layer pipe 10 may be in the form of a circular ring as shown in Fig. 1. The inner diameter, outer diameter, and thickness of the multi-layer pipe 10, which is the combination of the first layer 12, the second layer 14, and the third layer 16, may be appropriately selected. For example, the inner diameter of the multi-layer pipe 10 is preferably 20 mm or more and preferably 65 mm or less. The outer diameter of the multi-layer pipe 10 is preferably 32 mm or more (nominal diameter 20) and preferably 89 mm or less (nominal diameter 65). In addition, the thickness of the multi-layer pipe is preferably 6.0 mm or more and preferably 11.0 mm or less.

[0040] With regard to the thickness of each layer (average: the same applies below), the first layer 12 is preferably at least 35% thicker than the second layer 14, more preferably at least 40%, and even more preferably at least 45% thicker. Since the finely foamed first layer 12 with a low average expansion ratio has higher rigidity than the second layer 14 with a high average expansion ratio, by defining the thickness of the first layer 12 as above, it is possible to provide high rigidity to the inner circumference of the multi-layer pipe 10 and prevent deformation and damage due to contact with the fluid flowing inside.

[0041] On the other hand, the first layer 12, which is a micro-foamed layer, has a higher specific gravity than the second layer 14, which has a higher average expansion ratio, so that an increase in the thickness of the first layer 12 leads to an increase in the weight of the multi-layer pipe 10. Furthermore, the second layer 14 has a high soundproofing effect and heat insulation effect because it is porous and has a high average expansion ratio, but these effects decrease when the second layer 14 becomes thinner. Therefore, the first layer 12 is preferably 85% or less of the thickness of the second layer 14, desirably 80% or less, and more desirably 75% or less.

[0042] The third layer 16 is preferably more than 30% thick, more preferably 35% or more thick, and even more preferably 40% or more thick, of the second layer 14. Since the third layer 16, which is a micro-foamed layer, has higher rigidity than the second layer 14, which is a foamed layer, by defining the thickness of the third layer 16 as described above, the outer periphery of the multi-layer pipe 10 can be provided with high rigidity, and deformation and damage can be prevented.

[0043] On the other hand, the third layer 16, which is a micro-foamed layer, has a higher specific gravity than the second layer 14, which has a higher average expansion ratio, so that an increase in the thickness of the third layer 16 leads to an increase in the weight of the multi-layer pipe 10. Also, the second layer 14 has a high soundproofing effect and heat insulation effect because it is porous and has a high average expansion ratio, but these effects decrease when the second layer 14 becomes thinner. Therefore, the third layer 16 is preferably 55% or less of the thickness of the second layer 14, desirably 50% or less, and more desirably 45% or less.

[0044] When comparing the thickness of the first layer 12 and the third layer 16, making the third layer 16 thicker allows the first layer 12 in contact with the fluid to absorb the effects of the temperature of the fluid while maintaining the strength of the entire pipe. Specifically, the third layer 16 is preferably more than 1.0 times that of the first layer 12, desirably 1.2 times or more, and more desirably 1.4 times or more.

[0045] Conversely, by making the first layer 12 thicker, it is possible to suppress deformation of the first layer 12 (fluid path) that comes into contact with the fluid while allowing some degree of deflection of the entire pipe. Specifically, the first layer 12 is preferably more than 1.0 times the thickness of the third layer 16, desirably 1.2 times or more, and more desirably 1.4 times or more.

[0046] The second layer 14 preferably has an open cell ratio, in which the cells contained in the layer are connected to each other, of 50% or more, and preferably 70% or more. The upper limit of the open cell ratio is preferably 90% or less, and preferably 85% or less. The open cell ratio can be measured in accordance with JIS K 7138:2006. Conversely, the closed cell ratio is preferably 15% or less, and preferably 10% or less.

[0047] It is desirable to set the lower limit of the open cell ratio and the upper limit of the closed cell ratio as above, because the higher the open cell ratio and the lower the closed cell ratio, the higher the average expansion ratio, the lighter the second layer 14 becomes, and the better the heat insulating performance becomes. On the other hand, if the open cell ratio becomes too high, the strength and water impermeability of the second layer 14 decrease, so it is desirable to set the upper limit as above.

[0048] The open cell ratio can be measured, for example, by using an open cell ratio measuring device 80 shown in FIG. 3. The open cell ratio measuring device 80 includes a pair of upper and lower caps 81, 82 and a pump 83 connected to the lower cap 82. The multi-layer pipe 10 is cut to a length of 400 mm, and the flow path 19 inside the first layer 12 is airtightly blocked by an air packer 84. A seal ring 85 is attached between the third layer 16 and the inner surface of the caps 81, 82 at both ends of the multi-layer pipe 10, and the caps 81, 82 are attached leaving a gap of 1 mm from the end face of the third layer 16. Water is then pumped in from the pump 83 at a pressure of 10 kPa and allowed to stand for 15 minutes. After 15 minutes, the multi-layer pipe 10 is cut vertically, and the cross section of the second layer 14 with the highest average expansion ratio is observed. The open cell ratio can be quantified based on the height of the second layer 14 to which the water has penetrated.

[0049] As shown in FIG. 4, the inner peripheral side of the first layer 12 may include a first skin layer 13 having an average expansion ratio smaller than that of the first layer 12 on the inner peripheral surface. The first skin layer 13 is a layer having almost no bubbles (expansion ratio 1.00 times) or smaller than the average expansion ratio of the first layer 12. The first skin layer 13 is a part of the first layer 12, and is a layer formed by, for example, contacting the inner peripheral side of the first layer 12 with the space in the vacuum sizing device 24 and cooling it when manufacturing the multi-layer pipe 10 by the manufacturing method (FIGS. 7 to 9) shown below, without sufficient or no foaming of the foaming agent, and the raw material of the first layer 12 and the first skin layer 13 is the same. FIG. 5 is an enlarged photograph of the inner surface of the first skin layer 13, and is an embodiment in which microcapsules are used as the foaming agent 18. Referring to the figure, it can be seen that the foaming agent 18 does not foam in the first skin layer 13 and remains as microcapsules. The first skin layer 13, in which the foaming agent is not foamed, is formed on the inner side of the first layer 12, thereby preventing the fluid flowing inside the multi-layer pipe 10 from penetrating into the first layer 12. In addition, since the foaming ratio is low, this serves to increase the strength of the inner side of the first layer 12 and, ultimately, the strength of the multi-layer pipe 10.

[0050] The lower limit of the thickness of first skin layer 13 is 5%, preferably 7%, of first layer 12. The upper limit of the thickness of first skin layer 13 is 55%, preferably 50%, and particularly preferably 45% of first layer 12. If first skin layer 13 is thinner than the above, the effect of first skin layer 13 cannot be fully exhibited, whereas if first skin layer 13 is thicker than the above, first layer 12, which is a foamed layer, becomes heavy.

[0051] As shown in FIG. 4, the third skin layer 17, whose average expansion ratio is smaller than that of the third layer 16, may be included on the outer peripheral surface of the third layer 16. The third skin layer 17 is a layer with almost no bubbles (expansion ratio 1.00 times) or smaller than the average expansion ratio of the third layer 16. The third skin layer 17 is a part of the third layer 16, and is a layer formed without sufficient or complete expansion of the foaming agent by contacting the outer periphery of the third layer 16 with the sizing sleeve 64 when manufacturing the multi-layer pipe 10 by the manufacturing method (FIGS. 7 to 9) shown below, and the raw material of the third layer 16 and the third skin layer 17 is the same. FIG. 6 is an enlarged photograph of the outer surface of the third skin layer 17, which is an embodiment in which microcapsules are used as the foaming agent 18. Referring to the figure, it can be seen that the foaming agent 18 is not foamed and remains as microcapsules in the third skin layer 17. The third skin layer 17, in which the foaming agent is not foamed, is formed on the outer periphery of the third layer 16, thereby increasing the strength of the outer periphery of the third layer 16 and, ultimately, the strength of the multi-layer pipe 10, and protecting the second layer 14 from external impacts.

[0052] The lower limit of the thickness of third skin layer 17 is 2%, and preferably 11%, of third layer 16. The upper limit of the thickness of third skin layer 17 is 75%, and preferably 70% of third layer 16. If third skin layer 17 is thinner than the above, the effect of third skin layer 17 cannot be fully exhibited, whereas if third skin layer 17 is thicker than the above, third layer 16, which is a foamed layer, becomes heavy.

[0053] [Method of manufacturing multi-layer pipe 10] The multi-layer pipe 10 can be manufactured, for example, by using a manufacturing apparatus 20 as shown in Fig. 7. The manufacturing apparatus 20 includes a first extruder 21 for extruding the first layer 12 and the third layer 16, a second extruder 22 for extruding the second layer 14, a vacuum sizing device 24, a take-off machine 26, and a cutter 28. The manufacturing apparatus 20 of this embodiment uses one extruder 21 to mold the first layer 12 and the third layer 16 from the same raw material (first raw material), but the extruder may be divided into two and the first layer 12 and the third layer 16 may be molded from different raw materials (first raw material and third raw material).

[0054] The first extruder 21 and the second extruder 22 include a first extruder 34 and a second extruder 36 that heat, melt and extrude the raw materials supplied from hoppers 30, 32, and dies 38 are attached to the outlets of the first extruder 34 and the second extruder 36. The hopper 30 of the first extruder 21 is supplied with the first raw materials that constitute the first layer 12 and the third layer 16 of the multi-layer pipe 10, and the hopper 32 of the second extruder 22 is supplied with the second raw materials that constitute the second layer 14.

[0055] The first raw material contains a vinyl chloride resin and a predetermined amount of a foaming agent. The second raw material also contains a vinyl chloride resin and a predetermined amount of a foaming agent. The content of the foaming agent in the first raw material is an amount that results in a lower average expansion ratio than the second raw material. The content of the foaming agent in the second raw material is an amount that results in a higher average expansion ratio than the first raw material. When a third raw material different from the first raw material is used for the third layer 16, the third raw material only needs to contain an amount of foaming agent that results in a lower average expansion ratio than the second raw material.

[0056] The first raw material is melted under pressure in the first extruder 34 to become a molten resin 44. The second raw material is also melted under pressure in the second extruder 36 to become a molten resin 46. Even if a foaming agent is mixed in, the molten resins 44, 46 do not foam in the first extruder 34 and the second extruder 36 under high pressure.

[0057] As shown in FIG. 8, the mold 38 is a mold for multi-layer (three-layer) extrusion, and includes a confluence section 40 and a molding section 42. In the confluence section 40, the molten resins 44 and 46 introduced from the first extruder 34 and the second extruder 36 are merged and laminated near the outlet to form a laminate. The laminate including the laminated molten resins 44 and 46 is molded into a tubular shape while being laminated in the molding section 42. That is, the molten resin 44 later becomes the first layer 12 and the third layer 16, and the molten resin 46 becomes the second layer 14. At this time, the pressure of the molten resins 44 and 46 is released, and the foaming agent foams. The thicknesses of the first layer 12, the second layer 14, and the third layer 16 can be appropriately adjusted by adjusting the supply pressure of the molten resins 44 and 46 or the flow path area thereof.

[0058] The molten resins 44 and 46 in the laminate are regulated to a certain degree of appropriate size on the outer and inner circumferences by the die ring 48 and mandrel 50 provided at the tip of the molding section 42, and are extruded as a continuous tube 52 consisting of multiple layers, with the first layer 12 on the inner circumference side, the second layer 14 in the middle, and the third layer 16 on the outer circumference side. Reference numerals 49 and 51 denote heaters disposed on the outer circumference of the die ring 48 and the inner circumference of the mandrel 50. The first layer 12 and the second layer 14, and the second layer 14 and the third layer 16 are made of similar materials and contain a foaming agent (in different amounts) in the vinyl chloride resin, so the pressure of the resin increases due to the pressure of the foaming agent trying to expand. As a result, the adhesion of the resin layers that meet in the mold increases, and the bonding strength increases.

[0059] In addition, when the first layer 12 is extruded while in contact with the die ring 48, a first skin layer 13 having an expansion ratio lower than the average expansion ratio of the first layer 12 or substantially zero can be formed on the inner peripheral surface layer of the first layer 12.

[0060] In addition, when the third layer 16 is extruded while in contact with the mandrel 50, a third skin layer 17 having an expansion ratio lower than the average expansion ratio of the third layer 16 or substantially zero is formed on the outer peripheral surface layer of the third layer 16.

[0061] The continuous tube 52 that has passed between the die ring 48 and the mandrel 50 is sent to the vacuum sizing device 24. The vacuum sizing device 24 is disposed downstream of the die 38, and serves to size and cool the outer surface of the continuous tube 52 extruded from the die 38. As shown in FIG. 9, the vacuum sizing device 24 includes a body 54 extending in the extrusion direction of the continuous tube 52. One end and the other end of the body 54 in the longitudinal direction are formed with an inlet 56 and an outlet 58 for the tube. A vacuum chamber 62 to which a vacuum pump 60 is connected is provided on the inlet 56 side of the body 54, and a sizing sleeve 64 is disposed within the vacuum chamber 62, with one end of the sizing sleeve 64 connected to the inlet 56. A cooling chamber 66 is provided between the vacuum chamber 62 and the outlet 58, and a water sprinkling pipe 68 is disposed in the vacuum chamber 62 and the cooling chamber 66.

[0062] When the continuous pipe 52 is fed to the vacuum sizing device 24, the continuous pipe 52 is expanded by the negative pressure of the vacuum pump 60, and the outer surface of the continuous pipe 52 is brought into close contact with the inner surface of the sizing sleeve 64, thereby being sized. The sized continuous pipe 52 is then cooled and hardened by the cooling water sprayed from the water spray pipe 68.

[0063] The take-up machine 26 is for taking up the continuous tube 52 at a constant speed, and includes take-up rollers 70 pressed against the lower and upper parts of the continuous tube 52. At least one of the take-up rollers 70 is connected to a motor (not shown), and the take-up speed of the continuous tube 52 is adjusted by controlling the number of rotations of the motor.

[0064] The cutter 28 is used to cut the continuous tube 52 to a predetermined length, and includes a sensor 71 that detects the position of the tip of the continuous tube 52, and saw blades 72 that are driven in conjunction with the sensor 71. When the tip of the continuous tube 52 presses the sensor 71, the saw blades 72 are driven to cut the continuous tube 52, and a multi-layer tube 10 including a first layer 12, a second layer 14, and a third layer 16 as shown in Figures 1, 2, and 4 is obtained.

[0065] The above manufacturing method is an example, and it is of course possible to manufacture the multi-layer pipe 10 by other methods. For example, when the average expansion ratio is to be changed between the first layer 12 and the third layer 16, the temperature of the heater 51 contributing to the first layer 12 and the heater 49 contributing to the third layer 16 may be differentiated, and the temperature of the heater on the side where the expansion ratio is to be increased may be set higher, and the temperature of the heater on the side where the expansion ratio is to be decreased may be set lower. Also, the multi-layer pipe 10 may be obtained by dividing the supply route of the hopper 30 of the first extruder 21 and the molten resin 44 between the first layer 12 and the third layer 16, using different raw materials (first raw material and third raw material) for the first layer 12 and the third layer 16, extruding the first layer 12, and then molding the second layer 14 and the third layer 16 on the first layer 12 in separate steps.

[0066] Fig. 1 is a cross-sectional view of a multi-layer pipe 10 having three layers, a first layer 12, a second layer 14, and a third layer 16, and Fig. 2 is an enlarged photograph of the cut surface. In the illustrated multi-layer pipe 10, the first skin layer 13 is not present on the inner periphery of the first layer 12, or the first skin layer 13 is formed very thinly, and the third layer 16 is also not present on the outer periphery of the third skin layer 17, or the third skin layer 17 is formed very thinly. Referring to Fig. 2, it can be seen that the second layer 14, which is an intermediate layer, has a mottled pattern and is foamed to a degree that can be confirmed by the naked eye. In addition, the first layer 12 and the third layer 16 have a fine spotted pattern, and these spotted parts are foamed parts.

[0067] 2(b) and (c), it can be seen that the first layer 12 and the second layer 14 of the multi-layer pipe 10 are firmly bonded to each other, and that the second layer 14 and the third layer 16 are also firmly bonded to each other. This is because the layers are all made of similar materials, such as polyvinyl chloride resin containing a foaming agent, and therefore can be bonded well. As a result, as shown in the examples, when the multi-layer pipe 10 is cut with a cutting machine, it is possible to prevent cracks from occurring in the first layer 12 and / or the third layer 16.

[0068] 4 is a cross-sectional view of a multi-layer pipe 10 including a first skin layer 13 on the inner periphery of the first layer 12 and a third skin layer 17 on the outer periphery of the third layer 16. Since the molded multi-layer pipe 10 includes the first skin layer 13 on the inner periphery, it is possible to prevent the fluid flowing inside the multi-layer pipe 10 from seeping out, and the first skin layer 13 and the third skin layer 17 can increase the strength of the multi-layer pipe 10.

[0069] <Second embodiment> Fig. 10 is a cross-sectional view showing one embodiment of a multi-layer pipe 10 of the present invention. As shown in the figure, the multi-layer pipe 10 includes a cylindrical first layer 12 provided on the innermost circumference and a cylindrical second layer 14 formed on the outer circumference thereof, and is a two-layer pipe that omits the third layer 16 of the first embodiment. Descriptions of configurations, effects, etc. common to the first embodiment will be omitted as appropriate.

[0070] The multi-layer pipe 10 of the present invention is characterized in that the first layer 12 and the second layer 14 are composed of foamed layers of a vinyl chloride resin, and the average expansion ratio of the first layer 12 is lower than that of the second layer 14. Specifically, the average expansion ratio of the first layer 12 is more than 1.00 times and is 1.05 times or less, more preferably 1.03 times or less, and desirably 1.025 times or less. The average expansion ratio of the second layer 14 is higher than the average expansion ratio of the first layer 12, and is preferably 1.50 times or more, desirably 3.00 times or more, and particularly desirably 4.00 times or more. The average expansion ratio of the second layer 14 is preferably 10.0 times or less, desirably 8.00 times or less, and particularly desirably 6.00 times or less. The average expansion ratio can be calculated by cutting out each layer and measuring the density according to JIS K 7112:1999.

[0071] The type of vinyl chloride resin, the average degree of polymerization, and the type and amount of the foaming agent added are the same as those in the first embodiment. The stabilizers, pigments, etc. added are also the same as those in the first embodiment.

[0072] [shape] The multi-layer pipe 10 may be in the form of a circular ring as shown in Fig. 10. The inner diameter, outer diameter, and thickness of the multi-layer pipe 10, which is the combination of the first layer 12 and the second layer 14, may be appropriately selected. For example, the inner diameter of the multi-layer pipe 10 is preferably 20 mm or more and preferably 65 mm or less. The outer diameter of the multi-layer pipe 10 is preferably 32 mm or more (nominal diameter 20) and preferably 89 mm or less (nominal diameter 65). The thickness of the multi-layer pipe is preferably 6.0 mm or more and preferably 11.0 mm or less.

[0073] Regarding the thickness of the first layer 12 and the second layer 14, the first layer 12 is preferably at least 40% of the thickness of the second layer 14, more preferably at least 45%, and even more preferably at least 50%. Since the first layer 12, which has a lower average expansion ratio, is more rigid than the second layer 14, by defining the thickness of the first layer 12 as above, it is possible to provide the multi-layer pipe 10 with high rigidity, thereby preventing deformation and damage due to contact with the fluid flowing inside.

[0074] On the other hand, by making the second layer 14, which has a high average expansion ratio, thicker, it is possible to reduce the weight of the multi-layer pipe 10. In addition, since the second layer 14 has a high average expansion ratio, it can have high soundproofing and heat insulating effects.

[0075] The second layer 14 having a high average expansion ratio has an open cell ratio, in which the cells are connected to each other, of preferably 50% or more, and more preferably 70% or more. The upper limit of the open cell ratio is preferably 90% or less, and more preferably 85% or less. The open cell ratio can be measured in accordance with JIS K 7138:2006. Conversely, the closed cell ratio is preferably 15% or less, and more preferably 10% or less.

[0076] The average expansion ratio and open cell ratio of the first layer 12 and the second layer 14 are the same as those in the first embodiment.

[0077] Furthermore, the first layer 12 may include, on its inner periphery side, the first skin layer 13 described in the first embodiment.

[0078] The second skin layer 15, whose average expansion ratio is smaller than that of the second layer 14, may be included on the inner peripheral side of the outer peripheral side of the second layer 14. The second skin layer 15 is a layer that has almost no bubbles (expansion ratio 1.00 times) or has an average expansion ratio smaller than that of the second layer 14. The second skin layer 15 is a part of the second layer 14, and is a layer that is formed without sufficient or no foaming agent when the outer periphery of the second layer 14 comes into contact with the sizing sleeve 64 during the manufacture of the multi-layer pipe 10. That is, the raw material of the second layer 14 and the second skin layer 15 are the same. The second skin layer 15 is formed on the outer periphery side of the second layer 14, thereby playing a role in increasing the strength of the outer periphery of the second layer 14 and, in turn, the strength of the multi-layer pipe 10.

[0079] The lower limit of the thickness of second skin layer 15 is 4.0%, and preferably 4.5%, of second layer 14. The upper limit of the thickness of second skin layer 15 is 35%, and preferably 30%, of second layer 14. If second skin layer 15 is thinner than the above, the effect of second skin layer 15 cannot be fully exhibited, whereas if second skin layer 15 is thicker than the above, second layer 14, which is a foamed layer, becomes heavy.

[0080] [Method of manufacturing multi-layer pipe 10] A multi-layer pipe 10 (two-layer pipe) consisting of a first layer 12 and a second layer 14 can be manufactured in the manufacturing apparatus 20 of the first embodiment by using a two-layer pipe extrusion die 38a in which the route of the molten resin 44 branching to the third layer 16 is eliminated in a die 38 as shown in FIG. 11. The difference between the two-layer pipe extrusion die 38a and the three-layer pipe extrusion die 38 of FIG. 8 is that the molten resin 44 is extruded only to the inner layer side of the molten resin 46 of the second layer 14. The other configurations and manufacturing methods are the same as those of the first embodiment, and therefore will not be described. Note that the multi-layer pipe 10 can also be obtained by extruding the first layer 12 and then molding the second layer 14 on the first layer 12 in a separate process.

[0081] Fig. 11 is a cross-sectional view of a multi-layer pipe 10. As shown in the figure, the molded multi-layer pipe 10 has a first layer 12 formed on the inner circumference side and a second layer 14 formed on the outer circumference side. In the multi-layer pipe 10, the first layer 12 and the second layer 14 are firmly bonded. This is because both layers are made of similar materials, that is, polyvinyl chloride resin containing a foaming agent, and therefore can be bonded well. As a result, as shown in the examples, when the multi-layer pipe 10 is cut with a cutting machine, it is possible to prevent cracks from occurring in the first layer 12.

[0082] 12 is a cross-sectional view of a multi-layer pipe 10 including a first skin layer 13 on the inner periphery of the first layer 12 and a second skin layer 15 on the outer periphery of the second layer 14. Since the molded multi-layer pipe 10 includes the first skin layer 13 on the inner periphery, it is possible to prevent the fluid flowing inside the multi-layer pipe 10 from seeping out, and the first skin layer 13 and second skin layer 15 can increase the strength of the multi-layer pipe 10. EXAMPLES

[0083] A multi-layer pipe 10 was produced as described below, and various tests were performed. The multi-layer pipes 10 produced were invention examples 1 to 9 and a comparative example, with invention examples 1 to 8 and the comparative example being three-layer pipes, and invention example 9 being a two-layer pipe. More specifically, invention examples 1 to 6 are invention examples in which the first layer 12 and the third layer 16 have the same average expansion ratio, invention example 7 is an invention example in which the average expansion ratio of the first layer 12 is lower than the average expansion ratio of the third layer 16, and invention example 8 is an invention example in which the average expansion ratio of the first layer is higher than the average expansion ratio of the third layer 16.

[0084] The raw materials of the first layer 12, the second layer 14, and the third layer 16 are as follows. Note that since Example 9 has a two-layer structure of the first layer 12 and the second layer 14, the raw materials of the first layer 12 and the second layer 14 were used.

[0085] First layer 12: Polyvinyl chloride (degree of polymerization 1000, manufactured by Taiyo Vinyl Co., Ltd., product name: TH-1000), foaming agent thermal expansion microcapsule (manufactured by Matsumoto Yushi Seiyaku Co., Ltd., product name: Matsumoto Microsphere F Series, acrylic shell type) Second layer 14: polyvinyl chloride (degree of polymerization 700, manufactured by Taiyo Vinyl Co., Ltd., product name: TH-700), foaming agent: thermally expandable microcapsule (manufactured by Matsumoto Yushi Seiyaku Co., Ltd., product name: Matsumoto Microsphere F Series, acrylic shell type) 3rd layer 16: Same as 2nd layer 14

[0086] The raw material was prepared by mixing 100 parts by weight of polyvinyl chloride for the first layer 12 (the same for the third layer 16), 2.0 parts by weight in total of Pb-based stabilizer (tribasic lead sulfate and lead stearate, manufactured by Mizusawa Industrial Chemicals Co., Ltd.), and the foaming agent in the parts by weight (phr) shown in Table 1. Similarly, the raw material was prepared by mixing 100 parts by weight of polyvinyl chloride for the second layer 14, 1.6 parts by weight of Pb-based stabilizer (same as above), and 8.0 parts by weight of foaming agent.

[0087] [Table 1]

[0088] On the other hand, in the comparative example, the foaming agent was removed from the raw materials to form the first layer 12 and the third layer 16. The second layer 14 of the comparative example contains a foaming agent like the inventive example. For the sake of explanation, the multi-layer pipe and the first to third layers of the comparative example are given the same reference numerals as the inventive examples, but the first layer 12 and the third layer 16 of the comparative example are non-foamed layers.

[0089] These raw materials were supplied to the hoppers 30, 32 of the manufacturing apparatus 20 shown in Figs. 7 to 9 for Examples 1 to 6 and Comparative Example, and extrusion molding was performed to obtain a multi-layer pipe 10 of a nominal diameter 30, which was a test example. The heating and melting temperature of the resin raw materials in the first extruder 34 and the second extruder 36 was 180°C, and the pressure in the die 38 was 10 to 20 MPa. For Examples 7 and 8, the temperatures of the heaters 51 and 49 were set differently to adjust the average expansion ratios of the first layer 12 and the third layer 16. For Example 9, a two-layer pipe extrusion die 38a shown in Fig. 11 was used instead of the three-layer pipe extrusion die 38 in Fig. 8.

[0090] The average expansion ratio of each layer of the test examples is shown in Table 1. Referring to Table 1, due to the difference in the amount of foaming agent added, in invention examples 1 to 8, the average expansion ratio of the first layer 12 and the third layer 16 is lower than the average expansion ratio of the second layer 14. In invention examples 1 to 6, the average expansion ratio of the first layer 12 and the third layer 16 is the same, but in invention example 7, the average expansion ratio of the first layer 12 is lower than the average expansion ratio of the third layer 16, and in invention example 8, the average expansion ratio of the first layer 12 is higher than the average expansion ratio of the third layer 16. In addition, it can be seen that in invention example 9, the average expansion ratio of the first layer 12 is lower than the average expansion ratio of the second layer 14. On the other hand, it can be seen that in the comparative example, both the first layer 12 and the third layer 16 are not foamed.

[0091] In addition, the overall thickness and thickness of each layer (all averages) of the multi-layer pipe 10 of the test example, the ratio of the thickness of the first layer 12 to the second layer 14 (first layer ratio), the ratio of the thickness of the third layer 16 to the second layer 14 (third layer ratio), and the ratio of the total thickness of the first layer 12 and the third layer 16 to the second layer 14 (first layer + third layer ratio) were measured and are shown in Table 1. The first layer ratio was 56% to 85%, the third layer ratio was 35 to 54%, and the first layer + third layer ratio was 90% to 138%.

[0092] Among these test examples, for invention examples 1 to 3, 6, and 9 and the comparative example, the tensile yield strength of the first layer 12, the pressure resistance of the multi-layer pipe 10, and the surface roughness Ra of the first layer 12 were measured. In addition, when each multi-layer pipe 10 of the test examples was cut, the presence or absence of cracks occurring on the cut surface was visually confirmed.

[0093] The tensile yield strength (MPa) of the first layer 12 was measured in accordance with the HIVP of the tensile test method of JIS K 6741:2016. The JIS standard value for the tensile yield strength of the first layer 12 is 40 MPa or more. Therefore, less than 40 MPa was rated "C", 40 MPa or more but less than 42 MPa was rated "B", and 42 MPa or more was rated "A". The results are shown in "First layer tensile yield strength (MPa)" in Table 2.

[0094] [Table 2]

[0095] Referring to Table 2, all of the invention examples and comparative examples were rated "B" or higher, and satisfied the above JIS standard values. In particular, the invention examples and comparative examples, except for invention example 6, were rated "A". The tensile yield strength of the first layer 12 is greatly affected by the average expansion ratio of the first layer 12. That is, as the expansion ratio increases, the soundproofing performance, heat insulation performance, and moisture prevention performance improve, but the strength (tensile yield strength) decreases. Since invention example 6 had an average expansion ratio of more than 1.05 times, the tensile yield strength was inferior to the other invention examples, etc. It is therefore understood that it is preferable for the average expansion ratio of the first layer 12 to be 1.05 times or less.

[0096] Next, the pressure resistance of each test example was measured. The pressure resistance was measured in accordance with JIS K 6739:2016. It is preferable that the long-term pressure resistance is 0.35 MPa or more so that the fluid (condensed water) does not leak from the multilayer pipe 10. All test examples met this standard value for long-term pressure resistance. On the other hand, when it is desired to extend the distance of the fluid to be transported using a pump or the like, it is desirable that the short-term pressure resistance (breaking water pressure performance) of the multilayer pipe 10 is 8 MPa or more, taking into consideration that the thickness of the first layer 12 varies due to manufacturing. Therefore, less than 8 MPa was rated "C", 8 MPa or more and less than 8.5 MPa was rated "B", and 8.5 MPa or more was rated "A". The results are shown in "Short-term pressure resistance (MPa)" in Table 2.

[0097] With reference to Table 2, both the invention examples and the comparative examples were rated "B" or higher, meeting the criteria for short-term pressure resistance. Comparing the invention examples with the comparative examples, all the invention examples were rated "A", which was better than the comparative examples, which were rated "B".

[0098] It is the first layer 12 located on the innermost side that affects the short-term pressure resistance (burst water pressure performance). For this reason, it is expected that the comparative example of the non-foamed layer will have better short-term pressure resistance (burst water pressure performance) than the invention example in which the first layer 12 is a micro-foamed layer. However, as described above, the invention example has better short-term pressure resistance (burst water pressure performance). This is thought to be because the first layer 12 is a micro-foamed layer and the material of the second layer 14, which is a foamed layer, is made similar, thereby improving the bonding between the first layer 12 and the second layer 14, that is, promoting their integration. Therefore, when a foamed layer is used for the second layer 14, it is desirable that the first layer 12, which is on the inner side, is also a foamed layer. This also applies to the second layer 14 and the third layer 16.

[0099] The surface roughness Ra (arithmetic mean roughness of the inner surface) of the first layer 12 was measured in accordance with JIS B 0601:2013. Since the first layer 12 comes into direct contact with the fluid, it is desirable to reduce the surface roughness so as not to impede the flow of the fluid. However, increasing the water flow performance reduces productivity (cost, etc.). Therefore, with reference to the evaluation of the amount of mud adhesion, a surface roughness Ra of more than 2 μm was rated "C", more than 1.8 μm and 2 μm or less was rated "B", and 1.8 μm or less was rated "A". The results are shown in Table 2 under "First layer surface roughness Ra (μm)".

[0100] Referring to Table 2, invention examples 1, 2, 9 and the comparative example were all rated "A", invention example 3 was rated "B", and invention example 6 was rated "C". The reason for the low ratings of invention examples 3 and 6 is believed to be that the amount of foaming agent contained in the first layer 12 was large, and the foaming agent was exposed to the inner surface in the form of particles. Therefore, it can be seen that the average expansion ratio of the first layer 12 is preferably 1.05 times or less, and more preferably 1.025 times or less.

[0101] When each multi-layer pipe 10 of the test example was cut, the presence or absence of cracks on the cut surface was visually confirmed. If no cracks occurred in the first layer 12 or the third layer 16, it was marked as "no cracks", and if cracks occurred, it was marked as "present". The results are shown in Table 2 for cracks.

[0102] Referring to Table 2, none of the invention examples had cracks, while the comparative examples had cracks. A photograph of the cut surface of the invention example 3 is shown in FIG. 13. A photograph of the cut surface of the comparative example is shown in FIG. 14. The invention example 3 had no cracks, but the comparative example had a crack 90 in the third layer 16. The reason that no cracks were generated on the cut surface of the invention examples is that the first layer 12 and the second layer 14, and the second layer 14 and the third layer 16 were made of similar materials by including a foaming agent in each layer, and thus the layers were suitably bonded to each other. On the other hand, in the comparative example, the second layer 14 included a foaming agent, but the first layer 12 and the third layer 16 were made of materials that did not include a foaming agent, which reduced the bonding strength between the layers, and the strength of the tube to absorb impacts throughout the entire thickness of the tube was weaker than that of the second layer 14. It is considered that stress was concentrated in the hard layer (the third layer 16 in FIG. 14) to cause the crack 90.

[0103] The above description of the embodiment is for the purpose of explaining the present invention, and should not be interpreted as limiting the invention described in the claims or narrowing its scope. Furthermore, the configuration of each part of the present invention is not limited to the above embodiment, and various modifications are possible within the technical scope described in the claims.

[0104] For example, when comparing polyvinyl chloride resin containing a foaming agent with polyvinyl chloride resin not containing a foaming agent, the color difference can be made closer by forming each layer using polyvinyl chloride resin containing a foaming agent, thereby reducing the sense of incongruity that would be felt if the layers were clearly visible on the cut surface. [Explanation of symbols]

[0105] 10 Multilayer pipe 12 1st layer 13 First Skin Layer 14 2nd layer 15 Second Skin Layer 16 3rd layer 17 Third Skin Layer 18 Foaming Agent

Claims

1. A first layer made of a polyvinyl chloride resin foam layer; a second layer formed on the outer periphery of the first layer and made of a foamed layer made of a vinyl chloride resin; A multi-layer pipe comprising: The average expansion ratio of the first layer is lower than the average expansion ratio of the second layer. Multilayer tube.

2. The average expansion ratio of the first layer is more than 1.00 times and not more than 1.05 times. The multi-layer pipe according to claim 1.

3. The first layer includes a first skin layer on an inner circumferential side, the first skin layer having an expansion ratio smaller than an average expansion ratio of the first layer. The multi-layer pipe according to claim 2.

4. The breaking water pressure performance is 8 MPa or more. The multi-layer pipe according to claim 3.

5. The second layer includes a second skin layer on an outer circumferential side, the second skin layer having an expansion ratio smaller than the average expansion ratio of the second layer. A multi-layer pipe according to any one of claims 1 to 4.

6. a third layer formed of a polyvinyl chloride resin foam layer on the outer periphery of the second layer; The average expansion ratio of the third layer is lower than the average expansion ratio of the second layer. A multi-layer pipe according to any one of claims 1 to 4.

7. The average expansion ratio of the third layer is more than 1.00 times and not more than 1.05 times. The multi-layer pipe according to claim 6.

8. The average expansion ratio of the first layer is the same as the average expansion ratio of the third layer. The multi-layer pipe according to claim 7.

9. The average expansion ratio of the first layer is lower than the average expansion ratio of the third layer. The multi-layer pipe according to claim 7.

10. The average expansion ratio of the first layer is higher than the average expansion ratio of the third layer. The multi-layer pipe according to claim 7.

11. The third layer includes a third skin layer on an outer circumferential side, the third skin layer having an expansion ratio smaller than the average expansion ratio of the third layer. The multi-layer pipe according to claim 7.

12. A method for manufacturing a multi-layer pipe including a first layer made of a polyvinyl chloride-based resin foamed layer, and a second layer formed on an outer circumferential side of the first layer and also made of a polyvinyl chloride-based resin foamed layer, comprising: preparing a first raw material in which a foaming agent is added to a vinyl chloride resin forming the first layer, and a second raw material in which a foaming agent is added to a vinyl chloride resin forming the second layer in an amount such that the average foaming ratio is higher than that of the first raw material; The first raw material and the second raw material are heated and melted under pressure, and extruded into a tubular shape so that the first raw material is on the inner periphery side and the second raw material is on the outer periphery side to form a laminated body; The laminate is expanded in diameter while releasing the pressure to form a tubular shape, thereby foaming the foaming agent; the laminate in which the foaming agent has been foamed is sized on the outer periphery and the inner periphery and cooled to form the first layer on the inner periphery side and the second layer having an average foaming ratio higher than that of the first layer on the outer periphery side; A method for manufacturing a multi-layer pipe.

13. A method for manufacturing a multi-layer pipe including a first layer made of a polyvinyl chloride resin foamed layer, a second layer formed on the outer periphery of the first layer and made of a polyvinyl chloride resin foamed layer, and a third layer formed on the outer periphery of the second layer and made of a polyvinyl chloride resin foamed layer, a first raw material in which a foaming agent is added to a vinyl chloride resin forming the first layer; a second raw material in which a foaming agent is added to a vinyl chloride resin forming the second layer in an amount such that the average foaming ratio is higher than that of the first raw material; and a third raw material in which a foaming agent is added to a vinyl chloride resin forming the third layer in an amount such that the average foaming ratio is lower than that of the second raw material, The first raw material, the second raw material, and the third raw material are heated and melted under pressure, and extruded into a tubular shape such that the first raw material is on the inner periphery side, the second raw material is in the middle, and the third raw material is on the outer periphery side of the second raw material to form a laminated body; The laminate is expanded in diameter while releasing the pressure to form a tubular shape, thereby foaming the foaming agent; the laminate in which the foaming agent has been foamed is sized on the outer and inner peripheries and cooled to form the first layer on the inner periphery side, the second layer in the middle having an average foaming ratio higher than that of the first layer, and the third layer on the outer periphery having an average foaming ratio lower than that of the second layer; A method for manufacturing a multi-layer pipe.

14. The first raw material and the third raw material are the same; A method for producing a multi-layer tube according to claim 13.

Images