Multilayer tube

Abstract

To provide a multilayered pipe capable of enhancing heat insulating properties and fire resistance.SOLUTION: The multilayer pipe according to the present invention includes an inner layer, a foamed layer disposed outside the inner layer, and an outer layer disposed outside the foamed layer, wherein at least one layer of the three layers of the inner layer, the foamed layer, and the outer layer is a layer A containing a thermoplastic resin and an inosilicate mineral.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a multi-layer pipe comprising a foam layer. [Background technology]

[0002] Drain pipes for air conditioning equipment are installed throughout buildings. Multi-layer pipes made of resin are used for drain pipes for air conditioning equipment. As construction technology becomes more advanced, high insulation properties are required for drain pipes for air conditioning equipment. To improve insulation properties, multi-layer pipes with a foam layer are sometimes used.

[0003] Furthermore, in order to use drain piping for air conditioning equipment in a fire compartment, it is necessary to satisfy the fire resistance standards stipulated by the ISO (International Organization for Standardization).

[0004] However, conventional drain piping for air conditioning equipment requires special treatment when used in a compartment penetration, which is a significant burden in terms of cost and construction.If the air conditioning equipment drain piping itself has the fire resistance properties specified by ISO, the piping can be used in a fire compartment without special treatment.

[0005] A specific fire resistance performance of drain piping for air conditioning equipment is that the piping expands when heated by a heat source, causing the piping to close and prevent the spread of fire through the piping. To achieve this performance, the use of expandable graphite is being considered.

[0006] Patent Document 1 below discloses a multi-layer pipe including an inner skin layer, an outer skin layer, and a foam layer between the inner and outer skin layers. In Patent Document 1, the foam structure of the foam layer is controlled to improve thermal insulation.

[0007] Patent Document 2 below discloses a multi-layer pipe including a foamed layer and a coating layer on at least one of the outer and inner sides of the foamed layer. In this multi-layer pipe, the foamed layer contains a thermoplastic resin and expanded graphite. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-283733 [Patent Document 2] Japanese Patent Publication No. 2020-159476 Summary of the Invention [Problem to be solved by the invention]

[0009] The multi-layer pipe described in Patent Document 1 is provided with the foam layer, and therefore can improve heat insulation to a certain extent.

[0010] However, there is a limit to how much heat insulation can be improved simply by controlling the foam structure in the foam layer. Furthermore, the multi-layer pipe described in Patent Document 1 may have low fire resistance. In order to satisfy the fire resistance specified by ISO, the multi-layer pipe described in Patent Document 1 may require special treatment when installing the multi-layer pipe, which imposes a large burden in terms of cost and work.

[0011] Furthermore, in order to improve the fire resistance of a multi-layer pipe as described in Patent Document 1, it is conceivable to add a new layer with excellent fire resistance. However, when a new layer with excellent fire resistance is added, the thickness of the layer with excellent heat insulation must be reduced in order to maintain the thickness of the multi-layer pipe. As a result, even if the fire resistance can be improved, there is the drawback that the heat insulation will be reduced.

[0012] The multi-layer pipe described in Patent Document 2 is provided with the foam layer, which allows for a certain degree of improvement in heat insulation. Furthermore, the multi-layer pipe described in Patent Document 2 has the foam layer containing expanded graphite, which allows for a certain degree of improvement in fire resistance. The use of the expanded graphite causes the multi-layer pipe to expand and close during combustion, preventing the spread of fire through the multi-layer pipe.

[0013] However, even if the multi-layer pipe described in Patent Document 2 can improve the heat insulating property to some extent, it may be difficult to improve the heat insulating property sufficiently because the thermal conductivity of the expanded graphite is high.

[0014] Conventional multi-layer pipes have a problem in that it is quite difficult to achieve both high thermal insulation and high fire resistance.

[0015] An object of the present invention is to provide a multi-layer pipe that can improve heat insulation and fire resistance. [Means for solving the problem]

[0016] The following multi-layer pipes are disclosed herein:

[0017] Item 1. A multilayer pipe comprising an inner layer, a foamed layer disposed on the outside of the inner layer, and an outer layer disposed on the outside of the foamed layer, wherein at least one of the three layers, the inner layer, the foamed layer, and the outer layer, is a layer A containing a thermoplastic resin and an inosilicate mineral.

[0018] Item 2. The multi-layer pipe according to Item 1, wherein the thermoplastic resin is a vinyl chloride resin.

[0019] Item 3. The multilayer pipe according to Item 1 or 2, wherein the inosilicate mineral is wollastonite.

[0020] Item 4. The multi-layer pipe according to any one of Items 1 to 3, wherein the inosilicate mineral has an aspect ratio of 10.0 or more and 24.0 or less.

[0021] Item 5. The multi-layer pipe according to any one of Items 1 to 4, wherein the content of the inosilicate mineral in Layer A is 1 part by weight or more and 20 parts by weight or less relative to 100 parts by weight of the thermoplastic resin in Layer A.

[0022] Item 6. The multi-layer pipe according to Item 5, wherein the content of the inosilicate mineral in Layer A is 5 parts by weight or more and 15 parts by weight or less per 100 parts by weight of the thermoplastic resin in Layer A.

[0023] Item 7. The multi-layer pipe according to any one of Items 1 to 6, wherein the content of the inosilicate mineral is 0.2% by weight or more and 15% by weight or less, based on 100% by weight of the multi-layer pipe.

[0024] Item 8. The multi-layer pipe according to any one of Items 1 to 7, wherein at least the inner layer of the three layers of the inner layer, the foamed layer, and the outer layer is Layer A, or at least the outer layer of the three layers of the inner layer, the foamed layer, and the outer layer is Layer A.

[0025] Item 9. The multi-layer pipe according to Item 8, wherein at least the inner layer and the outer layer out of the three layers of the inner layer, the foam layer, and the outer layer are layer A.

[0026] Item 10. The multi-layer pipe according to any one of Items 1 to 9, wherein at least the foamed layer of the three layers of the inner layer, the foamed layer, and the outer layer is Layer A.

[0027] Item 11. The multi-layer pipe according to any one of Items 1 to 10, wherein the multi-layer pipe does not contain expanded graphite or contains expanded graphite in an amount of less than 5% by weight based on 100% by weight of the multi-layer pipe.

[0028] Item 12. The multi-layer pipe according to any one of Items 1 to 11, wherein the multi-layer pipe is a drain pipe for an air conditioning system. [Effects of the Invention]

[0029] The multi-layer pipe of the present invention comprises an inner layer, a foamed layer disposed outside the inner layer, and an outer layer disposed outside the foamed layer. In the multi-layer pipe of the present invention, at least one of the three layers, the inner layer, the foamed layer, and the outer layer, is Layer A, which contains a thermoplastic resin and an inosilicate mineral. The multi-layer pipe of the present invention has the above-described configuration, and therefore can improve both thermal insulation and fire resistance. [Brief explanation of the drawings]

[0030] [Figure 1] FIG. 1 is a cross-sectional view schematically showing a multi-layer pipe according to one embodiment of the present invention. [Figure 2] FIG. 2 is a plan view schematically showing a manufacturing apparatus used to manufacture a multi-layer pipe according to one embodiment of the present invention. [Figure 3] FIG. 3 is a front view schematically showing a manufacturing apparatus used to manufacture a multi-layer pipe according to one embodiment of the present invention. [Figure 4] FIG. 4 is an enlarged cross-sectional view showing a mold portion and a tube portion for forming the outer surface of a pipe in the manufacturing apparatus. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention will be described in detail below.

[0032] The multi-layer pipe according to the present invention comprises an inner layer, a foamed layer disposed outside the inner layer, and an outer layer disposed outside the foamed layer.

[0033] In this specification, the "layer containing a thermoplastic resin and an inosilicate mineral" is referred to as "layer A." In the multi-layer pipe according to the present invention, at least one of the three layers, i.e., the inner layer, the foam layer, and the outer layer, is layer A containing a thermoplastic resin and an inosilicate mineral. Therefore, the multi-layer pipe according to the present invention includes layer A.

[0034] The multi-layer pipe according to the present invention satisfies at least one of the following first, second and third configurations. Therefore, the multi-layer pipe according to the present invention comprises the layer A described above.

[0035] First configuration: the inner layer is a layer A containing a thermoplastic resin and an inosilicate mineral. Second configuration: The foam layer is a layer A containing a thermoplastic resin and an inosilicate mineral. Third configuration: The outer layer is a layer A containing a thermoplastic resin and an inosilicate mineral.

[0036] The multi-layer pipe of the present invention has the above-mentioned configuration, and therefore can improve both thermal insulation and fire resistance. The multi-layer pipe of the present invention has the foam layer, and therefore can improve thermal insulation. Furthermore, the multi-layer pipe of the present invention has layer A containing a thermoplastic resin and an inosilicate mineral, and therefore can improve fire resistance while maintaining high thermal insulation. The present invention can achieve both high thermal insulation and high fire resistance. Furthermore, the present invention can stably exhibit the fire resistance of the multi-layer pipe.

[0037] Furthermore, in terms of the fire resistance effect, the multi-layer pipe of the present invention maintains high strength (high residual strength) when exposed to high temperatures, and therefore can function as a multi-layer pipe for a long time even when heated by a heat source.

[0038] Furthermore, since the multi-layer pipe according to the present invention is provided with the foam layer, the weight of the multi-layer pipe can be increased, and the manufacturing cost can be reduced.

[0039] The multi-layer pipe comprises, from the inner surface side to the outer surface side of the multi-layer pipe, an inner layer, a foam layer, and an outer layer in this order. In the multi-layer pipe, the foam layer is an intermediate layer. The inner layer is a layer located inside the foam layer. The outer layer is a layer located outside the foam layer.

[0040] The inner layer may or may not be layer A. The multi-layer pipe may have layer A as the inner layer. The foamed layer may or may not be layer A. The multi-layer pipe may have layer A as the foamed layer. The outer layer may or may not be layer A. The multi-layer pipe may have layer A as the outer layer.

[0041] At least the inner layer of the three layers, the inner layer, the foam layer, and the outer layer, may be layer A. At least the outer layer of the three layers, the inner layer, the foam layer, and the outer layer, may be layer A. At least the foam layer of the three layers, the inner layer, the foam layer, and the outer layer, may be layer A. At least two layers of the three layers, the inner layer, the foam layer, and the outer layer, may be layer A. At least the inner layer and the foam layer of the three layers, the inner layer, the foam layer, and the outer layer, may be layer A. At least the inner layer and the outer layer of the three layers, the inner layer, the foam layer, and the outer layer, may be layer A. At least the foam layer and the outer layer of the three layers, the inner layer, the foam layer, and the outer layer, may be layer A. The three layers, the inner layer, the foam layer, and the outer layer, may be layer A.

[0042] From the viewpoint of further improving the heat insulation and fire resistance, it is preferable that the inner layer is layer A. From the viewpoint of further improving the heat insulation and fire resistance, it is preferable that the outer layer is layer A. From the viewpoint of further improving the heat insulation and fire resistance, it is preferable that at least the inner layer of the three layers of the inner layer, the foam layer, and the outer layer is layer A, or at least the outer layer of the three layers of the inner layer, the foam layer, and the outer layer is layer A. From the viewpoint of further improving the heat insulation and fire resistance, it is preferable that at least the inner layer of the three layers of the inner layer, the foam layer, and the outer layer is layer A. From the viewpoint of further improving the heat insulation and fire resistance, it is preferable that at least the outer layer of the three layers of the inner layer, the foam layer, and the outer layer is layer A. From the viewpoint of further improving the heat insulation and fire resistance, it is preferable that at least the inner layer and the outer layer of the three layers of the inner layer, the foam layer, and the outer layer are layer A. When the inner layer is layer A, the foam layer does not have to be layer A, and the outer layer does not have to be layer A. When the outer layer is layer A, the inner layer does not have to be layer A, and the foam layer does not have to be layer A.

[0043] From the viewpoint of further improving the heat insulating properties and fire resistance, it is preferable that at least two of the three layers, i.e., the inner layer, the foam layer, and the outer layer, are layer A. From the viewpoint of further improving the heat insulating properties and fire resistance, it is preferable that the three layers, i.e., the inner layer, the foam layer, and the outer layer, are layer A.

[0044] From the viewpoint of reducing costs and further increasing productivity, it is preferable that two or fewer of the three layers, i.e., the inner layer, the foam layer, and the outer layer, are the layer A. From the viewpoint of reducing costs and further increasing productivity, it is preferable that only one of the three layers, i.e., the inner layer, the foam layer, and the outer layer, is the layer A.

[0045] Specific embodiments of the present invention will be described below with reference to the drawings. Note that in the drawings, the size, thickness, shape, etc. may differ from the actual size, thickness, shape, etc. for the sake of convenience of illustration.

[0046] Fig. 1 is a cross-sectional view schematically showing a multi-layer pipe according to one embodiment of the present invention, showing a cross-section along the radial direction of the multi-layer pipe.

[0047] The multi-layer pipe 10 shown in Figure 1 comprises an inner layer 1, a foam layer 2, and an outer layer 3. In the multi-layer pipe 10, the inner layer 1, the foam layer 2, and the outer layer 3 are arranged in this order from the inner surface side to the outer surface side of the multi-layer pipe 10. The multi-layer pipe 10 has a three-layer structure. The foam layer 2 is arranged on the outside of the inner layer 1. The outer layer 3 is arranged on the outside of the foam layer 2. The foam layer 2 is arranged on the outer surface of the inner layer 1 and is laminated thereon. The outer layer 3 is arranged on the outer surface of the foam layer 2 and is laminated thereon. The inner layer 1 is the innermost layer and is a surface layer. The foam layer 2 is an intermediate layer. The outer layer 3 is the outermost layer and is a surface layer. The inner layer 1, the foam layer 2, and the outer layer 3 are each tubular.

[0048] In the multi-layer pipe 10, at least one of the inner layer 1, the foamed layer 2, and the outer layer 3 is the layer A containing a thermoplastic resin and an inosilicate mineral.

[0049] Other details of the foam layer, the inner layer, and the outer layer will be described below.

[0050] (Foam layer) The foam layer is a foam foamed with a foaming agent. The foam layer is a foam. The foam layer is preferably a resin foam, and more preferably a resin foam molded article.

[0051] The specific gravity of the foam layer (foam) is preferably 0.05 or more, more preferably 0.07 or more, even more preferably 0.08 or more, particularly preferably 0.10 or more, and is preferably 0.30 or less, more preferably 0.20 or less, even more preferably 0.19 or less, particularly preferably 0.18 or less, and most preferably 0.15 or less. When the specific gravity of the foam layer is above the lower limit, the impact resistance can be further improved. When the specific gravity of the foam layer is below the upper limit, the heat insulating properties can be further improved.

[0052] The closed cell ratio of the foam layer is preferably 20% or more, more preferably 30% or more, even more preferably 40% or more, even more preferably 50% or more, even more preferably 60% or more, particularly preferably 70% or more, and most preferably 80% or more. When the closed cell ratio of the foam layer is equal to or greater than the lower limit, the risk of water permeating the entire foam layer through the bubbles when water penetrates into the foam layer from the end of the multilayer tube due to capillary action or the like can be reduced. This can prevent a decrease in heat insulating properties. The upper limit of the closed cell ratio of the foam layer is not particularly limited. The closed cell ratio of the foam layer may be 90% or less, 80% or less, or 70% or less.

[0053] The expansion ratio of the foam layer is preferably 3.0 times or more, more preferably 3.5 times or more, even more preferably 4.0 times or more, particularly preferably 4.5 times or more, and most preferably 5.0 times or more, and is preferably 30.0 times or less, more preferably 25.0 times or less, and even more preferably 20.0 times or less. When the expansion ratio of the foam layer is above the lower limit, the heat insulating properties can be further improved. When the expansion ratio of the foam layer is below the upper limit, the cell diameter can be made uniform and the closed cell ratio of the foam layer can be increased. When the closed cell ratio of the foam layer is high, for example, when water penetrates into the foam layer from the end of the multilayer pipe due to capillary action or the like, the risk of water permeating the entire foam layer through the bubbles can be reduced. Therefore, a decrease in heat insulating properties can be suppressed.

[0054] The thickness of the foamed layer is preferably 3.0 mm or more, more preferably 4.0 mm or more, even more preferably 5.0 mm or more, and is preferably 20.0 mm or less, more preferably 18.0 mm or less, even more preferably 16.0 mm or less. When the thickness of the foamed layer is equal to or greater than the above-mentioned lower limit, the heat insulating properties can be further improved. When the thickness of the foamed layer is equal to or less than the above-mentioned upper limit, the inner diameter can be uniformly formed during the production of the multi-layer pipe.

[0055] The ratio of the thickness of the foam layer to the thickness of the outer layer is referred to as the ratio (thickness of foam layer / thickness of outer layer). The ratio (thickness of foam layer / thickness of outer layer) is preferably 1.5 or more, more preferably 2.0 or more, even more preferably 2.5 or more, particularly preferably 3.0 or more, and is preferably 10.0 or less, more preferably 9.5 or less, even more preferably 9.0 or less, particularly preferably 8.5 or less. When the ratio (thickness of foam layer / thickness of outer layer) is equal to or greater than the lower limit, the heat insulating properties can be further improved. When the ratio (thickness of foam layer / thickness of outer layer) is equal to or less than the upper limit, the impact resistance can be further improved.

[0056] The ratio of the thickness of the foamed layer to the sum of the thickness of the inner layer and the thickness of the outer layer is referred to as the ratio (thickness of foamed layer / total thickness of inner layer and outer layer). The ratio (thickness of foamed layer / total thickness of inner layer and outer layer) is preferably 1.0 or more, more preferably 1.3 or more, even more preferably 1.5 or more, particularly preferably 2.0 or more, and is preferably 6.5 or less, more preferably 6.0 or less, even more preferably 5.5 or less, particularly preferably 5.0 or less. When the ratio (thickness of foamed layer / total thickness of inner layer and outer layer) is equal to or greater than the lower limit, the heat insulating properties can be further improved. When the ratio (thickness of foamed layer / total thickness of inner layer and outer layer) is equal to or less than the upper limit, the inner diameter can be uniformly formed during the production of the multi-layer pipe.

[0057] (inner layer) The inner layer does not have to be a foamed layer, and may be a non-foamed layer.

[0058] The thickness of the inner layer is preferably 0.5 mm or more, more preferably 0.7 mm or more, even more preferably 1.0 mm or more, and is preferably 4.0 mm or less, more preferably 3.8 mm or less, even more preferably 3.5 mm or less. When the thickness of the inner layer is equal to or greater than the lower limit, a sufficient amount of water can flow through the multi-layer pipe. When the thickness of the inner layer is equal to or less than the upper limit, the heat insulation can be further improved.

[0059] (outer layer) The outer layer does not have to be a foamed layer. The outer layer may be a non-foamed layer.

[0060] The thickness of the outer layer is preferably 0.5 mm or more, more preferably 1.0 mm or more, even more preferably 1.3 mm or more, particularly preferably 1.5 mm or more, and is preferably 7.0 mm or less, more preferably 6.5 mm or less, and even more preferably 6.0 mm or less. When the thickness of the outer layer is equal to or greater than the lower limit, the heat insulating properties can be further improved. When the thickness of the outer layer is equal to or less than the upper limit, the impact resistance can be further improved.

[0061] The materials used in the foam layer, the inner layer, and the outer layer will be described below.

[0062] <Resin> The foam layer (foam layer material) preferably contains a resin. The inner layer (inner layer material) preferably contains a resin. The outer layer (outer layer material) preferably contains a resin. Layer A (layer A material) contains a thermoplastic resin. The multi-layer pipe contains a thermoplastic resin.

[0063] The resin is not particularly limited, and examples thereof include vinyl chloride resins, polyethylene (PE), polypropylene (PP), polymethyl methacrylate (PMMA), polycarbonate (PC), and polyvinylidene fluoride (PVDF). Only one of the resins may be used, or two or more of them may be used in combination. When the resin is a thermoplastic resin, only one of the thermoplastic resins may be used, or two or more of them may be used in combination.

[0064] From the viewpoint of improving fire resistance, the resin is preferably a thermoplastic resin, more preferably a vinyl chloride resin. From the viewpoint of improving fire resistance, the foam layer preferably contains a thermoplastic resin, more preferably a vinyl chloride resin. From the viewpoint of improving fire resistance, the inner layer preferably contains a thermoplastic resin, more preferably a vinyl chloride resin. From the viewpoint of improving fire resistance, the outer layer preferably contains a thermoplastic resin, more preferably a vinyl chloride resin. From the viewpoint of improving fire resistance, the layer A preferably contains a vinyl chloride resin. From the viewpoint of improving fire resistance, the thermoplastic resin in the layer A is preferably a vinyl chloride resin.

[0065] As the vinyl chloride resin, conventionally known vinyl chloride resins can be used. Examples of the vinyl chloride resin include (1) a homopolymer of a vinyl chloride monomer, (2) a copolymer of a vinyl chloride monomer and a polymerizable compound other than a vinyl chloride monomer, and (3) a graft polymer in which a vinyl chloride monomer or a vinyl chloride resin is graft-polymerized onto a polymer other than a vinyl chloride resin. The vinyl chloride resin may be used alone or in combination of two or more.

[0066] Examples of polymerizable compounds other than the vinyl chloride monomer include α-olefins having 16 or less carbon atoms (e.g., ethylene, propylene, and butylene); vinyl esters of aliphatic carboxylic acids having from 2 to 16 carbon atoms (e.g., vinyl acetate and vinyl propionate); alkyl vinyl ethers having 16 or less carbon atoms (e.g., butyl vinyl ether and cetyl vinyl ether); alkyl (meth)acrylates having 16 or less carbon atoms (e.g., methyl (meth)acrylate, ethyl (meth)acrylate, and butyl (meth)acrylate); aryl (meth)acrylates (e.g., phenyl (meth)acrylate); aromatic vinyls (e.g., styrene and α-substituted styrenes (e.g., α-methylstyrene)); vinyl halides (e.g., vinylidene chloride and vinylidene fluoride); and N-substituted maleimides (N-phenylmaleimide and N-cyclohexylmaleimide). The polymerizable compounds other than the vinyl chloride monomer may be used alone or in combination of two or more.

[0067] When the vinyl chloride resin is a copolymer, the copolymer may be a random copolymer, a block copolymer, or a graft copolymer.

[0068] Examples of polymers other than vinyl chloride resins that are graft-polymerized with vinyl chloride monomers or vinyl chloride resins include copolymers of α-olefins and vinyl esters (e.g., ethylene-vinyl acetate copolymers); copolymers of α-olefins, vinyl esters, and carbon monoxide (e.g., ethylene-vinyl acetate-carbon monoxide copolymers); copolymers of α-olefins and alkyl (meth)acrylates (e.g., ethylene-methyl (meth)acrylate copolymers and ethylene-ethyl (meth)acrylate copolymers); copolymers of α-olefins, alkyl (meth)acrylates, and carbon monoxide (e.g., ethylene-butyl (meth)acrylate-carbon monoxide copolymers); copolymers of two or more different α-olefins (e.g., ethylene-propylene copolymers); copolymers of unsaturated nitriles and dienes (e.g., acrylonitrile-butadiene copolymers); polyurethanes; and chlorinated polyolefins (e.g., chlorinated polyethylene and chlorinated polypropylene). The polymers other than vinyl chloride resins may be used alone or in combination of two or more.

[0069] The vinyl chloride-derived structural units are preferably 70% by weight or more, more preferably 75% by weight or more, even more preferably 80% by weight or more, and particularly preferably 90% by weight or more, and are preferably 100% by weight or less, more preferably 98% by weight or less, and even more preferably 95% by weight or less, based on 100% by weight of the vinyl chloride-based resin. When the vinyl chloride-derived structural units are at or above the lower limit, flame retardancy can be further improved. When the vinyl chloride-derived structural units are at or below the upper limit, moldability can be improved and thermal decomposition of the vinyl chloride-based resin during molding can be suppressed. The vinyl chloride-derived structural units may be 100% by weight (total amount) based on 100% by weight of the vinyl chloride-based resin.

[0070] The degree of polymerization of the vinyl chloride resin is preferably 400 or more, more preferably 500 or more, even more preferably 600 or more, particularly preferably 800 or more, and most preferably 1000 or more, and is preferably 1600 or less, more preferably 1400 or less. When the degree of polymerization of the vinyl chloride resin is equal to or greater than the lower limit, the mechanical strength of the multilayer pipe can be increased. When the degree of polymerization of the vinyl chloride resin is equal to or less than the upper limit, high temperatures are not required during molding, and processability is further improved.

[0071] The degree of polymerization (average degree of polymerization) of the vinyl chloride resin can be measured as follows: A chlorinated vinyl chloride resin is dissolved in tetrahydrofuran (THF), and unnecessary components are removed by filtration. The THF in the filtrate is then dried to remove the resulting resin. The average degree of polymerization of the vinyl chloride resin is measured according to JIS K6721 "Testing methods for vinyl chloride resins."

[0072] The chlorine content of the vinyl chloride resin is preferably 58% by weight or more, more preferably 60% by weight or more, even more preferably 62% by weight or more, and particularly preferably 64% by weight or more, and is preferably 75% by weight or less, more preferably 72% by weight or less, and even more preferably 70% by weight or less. When the chlorine content is above the above lower limit and below the above upper limit, the heat resistance of the multi-layer pipe can be improved. Furthermore, when the chlorine content is above the above lower limit and below the above upper limit, the closed cell ratio of the foamed layer using the vinyl chloride resin can be increased, and the effects of the present invention can be more effectively exhibited.

[0073] The vinyl chloride resin may be a chlorinated vinyl chloride resin, or may not be a chlorinated vinyl chloride resin. The chlorinated vinyl chloride resin is a resin obtained by chlorinating a vinyl chloride resin. In this specification, chlorinated vinyl chloride resins are included in vinyl chloride resins. In this specification, "chlorinated vinyl chloride resins" may also be referred to as "vinyl chloride resins."

[0074] The chlorinated vinyl chloride resin may be a commercially available product, such as H829, H716S, H727, H527, H516A, H547, H536, and H305 (all manufactured by Kaneka Corporation); HA-15E, HA-05E, HA-15F, HA-24F, HA-22H, HA-36F, HA-05K, HA-24K, HA-24L, HA-31K, HA-54K, and HA-58K (all manufactured by Tokuyama Sekisui Kogyo Co., Ltd.).

[0075] The content of the resin in 100% by weight of the foam layer is preferably 10% by weight or more, more preferably 20% by weight or more, even more preferably 30% by weight or more, particularly preferably 40% by weight or more, and most preferably 50% by weight or more, and is preferably 100% by weight or less, more preferably 99% by weight or less, even more preferably 98% by weight or less, even more preferably 95% by weight or less, even more preferably 90% by weight or less, particularly preferably 85% by weight or less, and most preferably 80% by weight or less. When the content of the resin is above the lower limit and below the upper limit, the heat insulating properties and fire resistance can be further improved. When the resin is the thermoplastic resin, the content of the resin is the content of the thermoplastic resin. When the resin is the vinyl chloride resin, the content of the resin is the content of the vinyl chloride resin.

[0076] The content of the resin in 100% by weight of the inner layer is preferably 10% by weight or more, more preferably 20% by weight or more, even more preferably 30% by weight or more, particularly preferably 40% by weight or more, and most preferably 50% by weight or more, and is preferably 100% by weight or less, more preferably 99% by weight or less, even more preferably 98% by weight or less, even more preferably 95% by weight or less, even more preferably 90% by weight or less, particularly preferably 85% by weight or less, and most preferably 80% by weight or less. When the content of the resin is equal to or greater than the lower limit and equal to or less than the upper limit, the heat insulating properties and fire resistance can be further improved. When the resin is a thermoplastic resin, the content of the resin is the content of the thermoplastic resin. When the resin is a vinyl chloride resin, the content of the resin is the content of the vinyl chloride resin.

[0077] The content of the resin in 100% by weight of the outer layer is preferably 10% by weight or more, more preferably 20% by weight or more, even more preferably 30% by weight or more, particularly preferably 40% by weight or more, and most preferably 50% by weight or more, and is preferably 100% by weight or less, more preferably 99% by weight or less, even more preferably 98% by weight or less, even more preferably 95% by weight or less, even more preferably 90% by weight or less, particularly preferably 85% by weight or less, and most preferably 80% by weight or less. When the content of the resin is equal to or greater than the lower limit and equal to or less than the upper limit, the heat insulating properties and fire resistance can be further improved. When the resin is a thermoplastic resin, the content of the resin is the content of the thermoplastic resin. When the resin is a vinyl chloride resin, the content of the resin is the content of the vinyl chloride resin.

[0078] The content of the thermoplastic resin in 100% by weight of Layer A is preferably 10% by weight or more, more preferably 20% by weight or more, even more preferably 30% by weight or more, particularly preferably 40% by weight or more, and most preferably 50% by weight or more, and is preferably 99% by weight or less, more preferably 98% by weight or less, even more preferably 95% by weight or less, even more preferably 90% by weight or less, particularly preferably 85% by weight or less, and most preferably 80% by weight or less. When the content of the thermoplastic resin is equal to or greater than the above-mentioned lower limit and equal to or less than the above-mentioned upper limit, the heat insulating properties and fire resistance can be further improved. When 100% by weight of Layer A is preferably equal to or greater than the above-mentioned lower limit and equal to or less than the above-mentioned upper limit. When the thermoplastic resin is the vinyl chloride resin, the content of the thermoplastic resin refers to the content of the vinyl chloride resin.

[0079] <Inosilicate minerals> The foam layer (foam layer material) may or may not contain an inosilicate mineral. From the viewpoint of further improving thermal insulation and fire resistance, it is preferable that the foam layer (foam layer material) contains an inosilicate mineral. The inner layer (inner layer material) may or may not contain an inosilicate mineral. From the viewpoint of further improving thermal insulation and fire resistance, it is preferable that the inner layer (inner layer material) contains an inosilicate mineral. The outer layer (outer layer material) may or may not contain an inosilicate mineral. From the viewpoint of further improving thermal insulation and fire resistance, it is preferable that the outer layer (outer layer material) contains an inosilicate mineral. Layer A (layer A material) contains an inosilicate mineral. The multilayer pipe (multilayer pipe material) contains an inosilicate mineral.

[0080] The inosilicate mineral is a mineral containing inosilicate. The inosilicate mineral contains SiO4 or SiO2 in its molecule. The inosilicate mineral has a crystalline structure. The inosilicate mineral preferably has a fibrous crystalline structure.

[0081] The inosilicate mineral preferably contains a metal oxide. The inosilicate mineral preferably contains an inosilicate and a metal oxide. Examples of the metal oxide include K2O, Na2O, Li2O, BaO, CaO, ZnO, MnO, FeO, MgO, Fe2O3, ZrO2, and Al2O3. The inosilicate mineral may contain only one type of metal oxide, or may contain two or more types of metal oxides.

[0082] Examples of the inosilicate mineral containing the above-mentioned metal oxide include the following inosilicate minerals. The above-mentioned inosilicate minerals may be used alone or in combination of two or more. The notation in parentheses following the chemical formula is the name of the mineral containing the inosilicate mineral as the main component. The mineral in parentheses may be used as the inosilicate mineral.

[0083] Specific examples of silicate minerals (inosilicate minerals and silicate minerals other than inosilicate minerals) include the following compounds.

[0084] Silicate minerals containing K2O include K2O·SiO2, K2O·4SiO2·H2O, K2O·Al2O3·2SiO2 (kalsilite), K2O·Al2O3·4SiO2 (leucite), and K2O·Al2O3·6SiO2 (orthoclase).

[0085] Silicate minerals containing Na2O include Na2O·SiO2 and its hydrates, Na2O·2SiO2, 2Na2O·SiO2, Na2O·4SiO2, Na2O·3SiO2·3H2O, Na2O·Al2O3·2SiO2, Na2O·Al2O3·4SiO2 (jadeite), 2Na2O·3CaO·5SiO2, 3Na2O·2CaO·5SiO2, and Na2O·Al2O3·6SiO2 (albite).

[0086] Silicate minerals containing Li2O include Li2O·SiO2, 2Li2O·SiO2, Li2O·SiO2·H2O, 3Li2O·2SiO2, Li2O·Al2O3·4SiO2 (petalite), Li2O·Al2O3·2SiO2 (eucryptite), and Li2O·Al2O3·4SiO2 (spodumene).

[0087] Silicate minerals containing BaO include BaO·SiO2, 2BaO·SiO2, BaO·Al2O3·2SiO2 (celsian), and BaO·TiO2·3SiO2 (bentite).

[0088] Silicate minerals containing CaO include 3CaO·SiO2 (alite, a cement clinker mineral), 2CaO·SiO2 (belite, a cement clinker mineral), 2CaO·MgO·2SiO2 (akermanite), 2CaO·Al2O3·SiO2 (gehlenite), a solid solution of akermanite and gehlenite (melilite), CaO·SiO2 (wollastonite (α- and β-types)), CaO·MgO·2SiO2 (diopside), CaO·MgO·SiO2 (magnesium olivine), 3CaO·MgO·2SiO2 (merwinite), CaO·Al2O3·2SiO2 (anorthite), 5CaO·6SiO2·5H2O (tobermorite, and others such as 5CaO·6SiO2·9H2O), and other tobermorite group hydrates such as 2CaO·MgO·2SiO2 (wollastonite (α- and β-types)). Examples include wollastonite group hydrates such as CaO·SiO2·H2O (hillebrandite), xonotlite group hydrates such as 6CaO·6SiO2·H2O (xonotlite), gyrolite group hydrates such as 2CaO·SiO2·2H2O (gyrolite), CaO·Al2O3·2SiO2·H2O (lawsonite), CaO·FeO·2SiO2 (hedengite), 3CaO·2SiO2 (chilcoanite), 3CaO·Al2O3·3SiO2 (grossula), 3CaO·Fe2O3·3SiO2 (andradite), 6CaO·4Al2O3·FeO·SiO2 (pleochroite), clinozoisite, piedonite, allanite, vesuvianite, agnite, scotite, augite, and metamorphite (actinolite).

[0089] The silicate mineral containing CaO may be Portland cement. The type of Portland cement is not particularly limited. The Portland cement may be ordinary Portland cement, high-early-strength Portland cement, ultra-high-early-strength Portland cement, medium-heat Portland cement, sulfate-resistant Portland cement, or white Portland cement. The Portland cement may be a blended cement such as blast-furnace cement, silica cement, and fly ash cement. The silicate mineral containing CaO may be blast-furnace slag or ferrite.

[0090] Silicate minerals containing ZnO include ZnO·SiO2, 2ZnO·SiO2 (troostite), and 4ZnO·2SiO2·H2O (hemimorphite).

[0091] Examples of silicate minerals containing MnO include MnO·SiO2, 2MnO·SiO2, CaO·2MnO·3SiO2 (bastemite), FeO·6MnO·7SiO2 (pyroxmangite), CaO·4MnO·5SiO2 (rhodonite), and cosrite.

[0092] Silicate minerals containing FeO include FeO·SiO2 (ferrosilite), 2FeO·SiO2 (ferroolivine), 3FeO·Al2O3·3SiO2 (almandine), and 2CaO·5FeO·8SiO2·H2O (actinocene), and grunerite.

[0093] Examples of silicate minerals containing CoO include CoO·SiO2 and 2CoO·SiO2.

[0094] Silicate minerals containing MgO include MgO·SiO2 (steatite, enstatite), 2MgO·SiO2 (forsterite), 3MgO·Al2O3·3SiO2 (byrope), 2MgO·2Al2O3·5SiO2 (cordierite), 2MgO·3SiO2·5H2O, 3MgO·4SiO2·H2O (talc), 5MgO·8SiO2·9H2O (attapulgite), and 4MgO·6SiO2·7H2O (sepiolite). Examples include 3MgO·2SiO2·2H2O (chrysolite), 5MgO·2CaO·8SiO2·H2O (tremolite), 5MgO·Al2O3·3SiO2·4H2O (chlorite), K2O·6MgO·Al2O3·6SiO2·2H2O (phlogovite), Na2O·3MgO·3Al2O3·8SiO2·H2O (lanthusite), magnesium tourmaline, anthosphite, cummingtonite, vermiculite, and smectite.

[0095] Examples of silicate minerals containing Fe2O3 include Fe2O3·SiO2.

[0096] Examples of silicate minerals containing ZrO2 include ZrO2·SiO2 (zircon) and AZS refractories.

[0097] Silicate minerals containing Al2O3 include Al2O3·SiO2 (sillimanite, andalusite, kyanite), 2Al2O3·SiO2, Al2O3·3SiO2, 3Al2O3·2SiO2 (mullite), Al2O3·2SiO2·2H2O (kaolinite), Al2O3·4SiO2·H2O (pyrophyllite), Al2O3·4SiO2·H2O (bentonite), K2O·3Na2O·4Al2O3·8SiO2 (nepheline), K2O·3Al2O3·6SiO2·2H2O (muscovite, sericite), K2O·6MgO·Al2O3·6SiO2·2H2O (phlogovite), various zeolites, fluorphlogopite, and biotite.

[0098] Among the silicate minerals mentioned above, inosilicate minerals are selected and used in the present invention.

[0099] From the viewpoint of further improving the thermal insulation and fire resistance, the inosilicate mineral is preferably CaO SiO2 (wollastonite), CaO 2MnO 3SiO2 (bastemite), CaO 4MnO 5SiO2 (rhodonite), or FeO 6MnO 7SiO2 (pyroxmangite). From the viewpoint of further improving the thermal insulation and fire resistance, the inosilicate mineral is more preferably CaO SiO2 (wollastonite).

[0100] The wollastonite contains CaSiO3 as an inosilicate mineral. In the wollastonite, calcium oxide (CaO) and silicon dioxide (SiO2) are bonded in a 1:1 ratio. The wollastonite has a triclinic or monoclinic crystal structure.

[0101] The inosilicate mineral may be a natural product or an artificially synthesized product. The method for synthesizing the artificially synthesized product is not particularly limited. The artificially synthesized product may be synthesized by a solid-state reaction, a hydrothermal reaction, an ultra-high pressure reaction, or the like.

[0102] The aspect ratio of the inosilicate mineral is preferably 10.0 or more, more preferably 12.0 or more, even more preferably 15.0 or more, and preferably 24.0 or less, more preferably 22.0 or less, even more preferably 20.0 or less. When the aspect ratio of the inosilicate mineral is equal to or greater than the lower limit, the residual strength of the multi-layer tube when exposed to high temperatures can be increased, further improving fire resistance. When the aspect ratio of the inosilicate mineral is equal to or less than the upper limit, the mechanical strength of the multi-layer tube can be increased.

[0103] The content of the inosilicate mineral in Layer A relative to 100 parts by weight of the thermoplastic resin in Layer A is preferably 0.1 parts by weight or more, more preferably 0.5 parts by weight or more, even more preferably 1 part by weight or more, particularly preferably 2 parts by weight or more, and most preferably 5 parts by weight or more, and is preferably 25 parts by weight or less, more preferably 20 parts by weight or less, even more preferably 15 parts by weight or less, particularly preferably 12 parts by weight or less, and most preferably 10 parts by weight or less. When the content of the inosilicate mineral in Layer A is equal to or greater than the above-mentioned lower limit, the residual strength of the multi-layer pipe when exposed to high temperatures can be increased, further improving fire resistance. When the content of the inosilicate mineral in Layer A is equal to or less than the above-mentioned upper limit, the shape retention of the multi-layer pipe when exposed to high temperatures can be increased, further improving fire resistance. When the content of the inosilicate mineral in Layer A is equal to or greater than the above-mentioned lower limit, the shape retention of the multi-layer pipe when exposed to high temperatures can be increased, further improving fire resistance. Preferably, the content of the inosilicate mineral in Layer A relative to 100 parts by weight of the thermoplastic resin in Layer A is equal to or greater than the above-mentioned lower limit but equal to or less than the above-mentioned upper limit. When the inosilicate mineral is the wollastonite, the content of the inosilicate mineral is the content of the wollastonite.

[0104] The content of the inosilicate mineral in 100% by weight of the layer A is preferably 0.09% by weight or more, more preferably 0.2% by weight or more, even more preferably 0.8% by weight or more, particularly preferably 1.5% by weight or more, and preferably 20% by weight or less, more preferably 15% by weight or less, even more preferably 12% by weight or less, particularly preferably 10% by weight or less. When the content of the inosilicate mineral is equal to or greater than the lower limit, the residual strength of the multi-layer tube when exposed to high temperatures can be increased, further improving fire resistance. When the content of the inosilicate mineral is equal to or less than the upper limit, the shape retention rate of the multi-layer tube when exposed to high temperatures can be increased, further improving fire resistance. When the content of the inosilicate mineral is equal to or less than the lower limit, the content of the inosilicate mineral in 100% by weight of the layer A is preferably equal to or greater than the lower limit and equal to or less than the upper limit. When the inosilicate mineral is wollastonite, the content of the inosilicate mineral is the content of the wollastonite.

[0105] The content of the inosilicate mineral in 100% by weight of the multi-layer pipe is preferably 0.09% by weight or more, more preferably 0.15% by weight or more, even more preferably 0.18% by weight or more, particularly preferably 0.2% by weight or more, and is preferably 25% by weight or less, more preferably 20% by weight or less, even more preferably 18% by weight or less, particularly preferably 15% by weight or less. When the content of the inosilicate mineral is above the lower limit, the residual strength of the multi-layer pipe when exposed to high temperatures can be increased, further improving fire resistance. When the content of the inosilicate mineral is below the upper limit, the shape retention rate of the multi-layer pipe when exposed to high temperatures can be increased, further improving fire resistance. The content of the inosilicate mineral in 100% by weight of the multi-layer pipe is preferably above the lower limit and below the upper limit. When the inosilicate mineral is wollastonite, the content of the inosilicate mineral is the content of the wollastonite.

[0106] <Expanded graphite> The foam layer (foam layer material) may or may not contain expanded graphite. The inner layer (inner layer material) may or may not contain expanded graphite. The outer layer (outer layer material) may or may not contain expanded graphite. The layer A (layer A material) may or may not contain expanded graphite. The multilayer pipe may or may not contain expanded graphite.

[0107] The expanded graphite can be obtained by reacting graphite powder, such as natural flake graphite, pyrolytic graphite, or kish graphite, with an inorganic acid and a strong oxidizing agent to generate a compound between the graphite layers. The expanded graphite is a crystalline compound that maintains the layer structure of graphite. Examples of the inorganic acid include concentrated sulfuric acid, nitric acid, and selenic acid. Examples of the strong oxidizing agent include concentrated nitric acid, perchloric acid, perchlorates, permanganates, dichromates, and hydrogen peroxide.

[0108] In order to improve fire resistance, it is considered to increase the content of expanded graphite, while in order to improve heat insulation, it is preferable to decrease the content of expanded graphite. The preferable content of expanded graphite varies depending on these purposes.

[0109] From the viewpoint of further improving fire resistance, the content of the expanded graphite in 100% by weight of the foamed layer may be more than 0% by weight, 0.1% by weight or more, 1% by weight or more, or 3% by weight or more. From the viewpoint of further improving heat insulation, the content of the expanded graphite in 100% by weight of the foamed layer is preferably 5% by weight or less, more preferably less than 5% by weight, even more preferably 3% by weight or less, particularly preferably 1% by weight or less, and most preferably 0.1% by weight or less. From the viewpoint of further improving heat insulation, it is preferable that the foamed layer does not contain expanded graphite or contains expanded graphite in an amount in 100% by weight of the foamed layer that is less than or equal to the upper limit mentioned above, and it is more preferable that the foamed layer does not contain expanded graphite.

[0110] From the viewpoint of further improving fire resistance, the content of the expanded graphite in 100% by weight of the inner layer may be more than 0% by weight, may be 0.1% by weight or more, may be 1% by weight or more, or may be 3% by weight or more. From the viewpoint of further improving heat insulating properties, the content of the expanded graphite in 100% by weight of the inner layer is preferably 5% by weight or less, more preferably less than 5% by weight, even more preferably 3% by weight or less, particularly preferably 1% by weight or less, and most preferably 0.1% by weight or less. From the viewpoint of further improving heat insulating properties, it is preferable that the inner layer does not contain expanded graphite or contains expanded graphite in an amount in 100% by weight of the inner layer that is less than or equal to the above upper limit, and it is more preferable that the inner layer does not contain expanded graphite.

[0111] From the viewpoint of further improving fire resistance, the content of the expanded graphite in 100% by weight of the outer layer may be more than 0% by weight, 0.1% by weight or more, 1% by weight or more, or 3% by weight or more. From the viewpoint of further improving heat insulating properties, the content of the expanded graphite in 100% by weight of the outer layer is preferably 5% by weight or less, more preferably less than 5% by weight, even more preferably 3% by weight or less, particularly preferably 1% by weight or less, and most preferably 0.1% by weight or less. From the viewpoint of further improving heat insulating properties, it is preferable that the outer layer does not contain expanded graphite, or contains expanded graphite in an amount in 100% by weight of the outer layer that is less than or equal to the above upper limit, and it is more preferable that the outer layer does not contain expanded graphite.

[0112] From the viewpoint of further improving fire resistance, the content of the expanded graphite may be more than 0% by weight, 0.1% by weight or more, 1% by weight or more, or 3% by weight or more, based on 100% by weight of the multi-layer pipe. From the viewpoint of further improving thermal insulation, the content of the expanded graphite is preferably 5% by weight or less, more preferably less than 5% by weight, even more preferably 3% by weight or less, particularly preferably 1% by weight or less, and most preferably 0.1% by weight or less, based on 100% by weight of the multi-layer pipe. From the viewpoint of further improving thermal insulation, it is preferable that the multi-layer pipe does not contain expanded graphite, or contains expanded graphite in an amount below or equal to the above-mentioned upper limit, based on 100% by weight of the multi-layer pipe, and more preferably does not contain expanded graphite.

[0113] <Foaming agent> The foam layer can be obtained using a foaming agent. Examples of the foaming agent include chemical foaming agents and physical foaming agents. The foaming agents may be used alone or in combination of two or more.

[0114] The chemical foaming agent may be an inorganic foaming agent or an organic foaming agent. The chemical foaming agent may be an inorganic foaming agent or an organic foaming agent. The chemical foaming agent may be used alone or in combination of two or more types.

[0115] Examples of the inorganic foaming agent include sodium bicarbonate (sodium hydrogen carbonate), sodium carbonate, ammonium bicarbonate, ammonium nitrite, azide compounds, sodium borohydride, etc. The inorganic foaming agents may be used alone or in combination of two or more.

[0116] Examples of the organic foaming agent include azo foaming agents and amine foaming agents, etc. The organic foaming agents may be used alone or in combination of two or more.

[0117] Examples of the azo-based foaming agent include azodicarbonamide and barium azodicarboxylate.

[0118] The amine-based foaming agent includes dinitrosopentamethylenetetramine.

[0119] As the chemical foaming agent, a thermally expandable capsule in which the chemical foaming agent is encapsulated in a thermoplastic resin as an encapsulating component may be used.

[0120] <Other ingredients> The inner layer, the foam layer, the outer layer, and Layer A may each contain additives as necessary. Examples of the additives include other fillers, heat stabilizers, stabilizing aids, lubricants, flame retardants, nucleating agents, pigments, processing aids, impact modifiers, antioxidants, UV absorbers, antistatic agents, light stabilizers, and plasticizers. The additives may be used alone or in combination of two or more.

[0121] Examples of the other fillers include inorganic fillers and organic fillers. Examples of the inorganic fillers include carbonates such as talc, heavy calcium carbonate, precipitated calcium carbonate, and colloidal calcium carbonate, aluminum hydroxide, magnesium hydroxide, titanium oxide, zinc oxide, magnesium oxide, carbon black, graphite, glass beads, glass fiber, carbon fiber, and metal fiber. Examples of the organic fillers include polyamide. One type of the other fillers may be used alone, or two or more types may be used in combination.

[0122] Examples of the heat stabilizer include organic tin stabilizers such as dimethyltin mercapto, dibutyltin mercapto, dioctyltin mercapto, dibutyltin maleate, dibutyltin maleate polymer, dioctyltin maleate, dioctyltin maleate polymer, dibutyltin laurate, and dibutyltin laurate polymer; lead-based stabilizers such as lead stearate, dibasic lead phosphite, and tribasic lead sulfate; calcium-zinc-based stabilizers; barium-zinc-based stabilizers; and barium-cadmium-based stabilizers. The heat stabilizers may be used alone or in combination of two or more.

[0123] Examples of the stabilizing aid include epoxidized soybean oil, epoxidized linseed oil, epoxidized tetrahydrophthalate, epoxidized polybutadiene, phosphate ester, polyol, zeolite, etc. The stabilizing aid may be used alone or in combination of two or more.

[0124] The lubricant may be an internal lubricant or an external lubricant. One type of lubricant may be used alone, or two or more types may be used in combination.

[0125] The internal lubricant is used to reduce the flow viscosity of the molten resin during molding and to prevent frictional heat generation. Examples of the internal lubricant include butyl stearate, lauryl alcohol, stearyl alcohol, epoxy soybean oil, glycerin monostearate, stearic acid, and bisamide. One type of the internal lubricant may be used alone, or two or more types may be used in combination.

[0126] The external lubricant is used to improve the sliding effect between the molten resin and the metal surface during molding. Examples of the external lubricant include paraffin wax, polyolefin wax, ester wax, and Montan acid wax. The external lubricant may be used alone or in combination of two or more.

[0127] Examples of the flame retardant include bromine-based flame retardants, phosphorus-based flame retardants, intumescent flame retardants such as ammonium polyphosphate and melamine cyanurate, hydroxide compounds such as aluminum hydroxide and magnesium hydroxide, antimony oxide, zinc oxide, etc. The flame retardants may be used alone or in combination of two or more.

[0128] Examples of the nucleating agent include inorganic compounds such as silica, calcium silicate, kaolin, clay, mica, zinc oxide, calcium carbonate, zeolite, and talc.

[0129] Examples of the pigment include organic pigments such as azo pigments, phthalocyanine pigments, threne pigments, and dye lake pigments, and inorganic pigments such as oxide pigments, molybdenum chromate pigments, sulfide / selenide pigments, and ferrocyanide pigments. The pigments may be used alone or in combination of two or more.

[0130] (Other details of multi-layer pipes) The material of the inner layer and the material of the outer layer may be the same or different. From the viewpoint of improving production efficiency, reducing the number of extruders, and simplifying the structure of the extruders, it is preferable that the material of the inner layer and the material of the outer layer are the same. In the multi-layer pipe, the inner layer and the outer layer may be formed from the same composition, or may be formed from different compositions. From the viewpoint of improving production efficiency, reducing the number of extruders, and simplifying the structure of the extruders, it is preferable that the inner layer and the outer layer are formed from the same composition.

[0131] The multi-layer pipe may include layers other than the three layers of the inner layer, the foam layer, and the outer layer. The multi-layer pipe may have a structure of three or more layers. The multi-layer pipe may have a structure of three layers, a structure of four or more layers, a structure of five or more layers, or a structure of ten or less layers.

[0132] The ratio of the thickness of layer A to the thickness of the multilayer pipe is referred to as the ratio (thickness of layer A / thickness of multilayer pipe). The ratio (thickness of layer A / thickness of multilayer pipe) is preferably 0.03 or more, more preferably 0.05 or more, even more preferably 0.07 or more, particularly preferably 0.08 or more, and most preferably 0.10 or more. The ratio (thickness of layer A / thickness of multilayer pipe) is preferably 1.0 or less, more preferably 0.90 or less, even more preferably 0.80 or less, even more preferably 0.75 or less, even more preferably 0.74 or less, particularly preferably 0.70 or less, particularly preferably 0.65 or less, and most preferably 0.63 or less. When the ratio (thickness of layer A / thickness of multilayer pipe) is above the above lower limit and below the above upper limit, the thermal insulation and fire resistance can be further improved. The ratio (thickness of layer A / thickness of multilayer pipe) is preferably above the above lower limit and below the above upper limit. When the multilayer pipe has only one layer A, the thickness of the layer A is the thickness of one layer A. When the multilayer pipe has two or more layers A, the thickness of the layer A is the sum of the thicknesses of the two or more layers A.

[0133] The inner diameter of the multi-layer pipe is preferably 10 mm or more, more preferably 15 mm or more, even more preferably 20 mm or more, and is preferably 100 mm or less, more preferably 90 mm or less, even more preferably 80 mm or less. When the inner diameter of the multi-layer pipe is above the lower limit, a sufficient amount of water can be passed through the multi-layer pipe. When the inner diameter of the multi-layer pipe is below the upper limit, the heat insulation can be further improved.

[0134] The outer diameter of the multi-layer pipe is preferably 20 mm or more, more preferably 30 mm or more, even more preferably 40 mm or more, and is preferably 120 mm or less, more preferably 110 mm or less, even more preferably 100 mm or less. When the outer diameter of the multi-layer pipe is equal to or greater than the lower limit, the strength of the multi-layer pipe can be increased. When the outer diameter of the multi-layer pipe is equal to or less than the upper limit, workability can be improved.

[0135] The ratio of the outer diameter of the multilayer pipe to the inner diameter of the multilayer pipe is referred to as the ratio (outer diameter of multilayer pipe / inner diameter of multilayer pipe). The ratio (outer diameter of multilayer pipe / inner diameter of multilayer pipe) is preferably 1.2 or more, more preferably 1.3 or more, even more preferably 1.4 or more, particularly preferably 1.6 or more, and most preferably 1.8 or more, and is preferably 2.5 or less, more preferably 2.4 or less, and even more preferably 2.3 or less. When the ratio (outer diameter of multilayer pipe / inner diameter of multilayer pipe) is equal to or greater than the lower limit, the impact resistance of the multilayer pipe can be improved. When the ratio (outer diameter of multilayer pipe / inner diameter of multilayer pipe) is equal to or less than the upper limit, workability can be improved.

[0136] The multilayer pipe may be a drain pipe for an air conditioning system. As described above, the drain pipe for an air conditioning system is required to have high thermal insulation and high fire resistance. Since the multilayer pipe is excellent in both thermal insulation and fire resistance, it is preferable that the multilayer pipe be a drain pipe for an air conditioning system.

[0137] (Manufacturing method of multilayer pipe) Fig. 2 is a plan view schematically showing a manufacturing apparatus used to manufacture a multi-layer pipe according to one embodiment of the present invention. Fig. 3 is a front view schematically showing a manufacturing apparatus used to manufacture a multi-layer pipe according to one embodiment of the present invention. Figs. 2 and 3 are diagrams schematically showing a manufacturing apparatus for manufacturing a multi-layer pipe 10.

[0138] The manufacturing apparatus 20 includes an inner and outer layer extruder 11, a foam layer extruder 12, a mold 13, a cooling water tank 15, a take-up machine 16, and a cutter 17. The mold 13 is connected to the inner and outer layer extruder 11 and the foam layer extruder 12. The cooling water tank 15 is connected to the mold 13. The take-up machine 16 is connected to the cooling water tank 15. The cutter 17 is connected to the take-up machine 16. A gas cylinder 18 and a metering pump 19 are connected to the foam layer extruder 12.

[0139] The inner layer material and outer layer material are fed from a hopper, and the inner layer material and outer layer material (compositions for obtaining the inner layer and outer layer) are melt-kneaded in the inner and outer layer extruder 11 and extruded into a mold 13 .

[0140] The material for the foam layer is fed from a hopper, and the material for the foam layer (composition for obtaining the foam layer) is melt-kneaded in the foam layer extruder 12 and extruded into the mold 13 .

[0141] From the outlet of the die 13, an uncured multi-layer tube having a three-layer structure is extruded.

[0142] A tube 14 for forming the outer surface of the uncured multi-layer pipe to a predetermined size is attached to the cooling water tank 15, and the outer surface of the uncured multi-layer pipe is cooled while in contact with the tube 14. A take-up machine 16 receives the multi-layer pipe 10 cooled in the cooling water tank 15. A cutter 17 cuts the multi-layer pipe 10 sent from the take-up machine 16 to a predetermined length.

[0143] FIG. 4 is an enlarged cross-sectional view showing a mold portion and a tube portion for forming the outer surface of a pipe in the manufacturing apparatus.

[0144] The inner layer material 21 and the outer layer material 23 melt-mixed by the inner and outer layer extruder 11 and the foam layer material 22 melt-mixed by the foam layer extruder 12 are injected into a mold 13 to form an uncured multi-layer pipe 10X. The uncured multi-layer pipe 10X comprises an uncured inner layer 31, an uncured outer layer 33, and an uncured foam layer 32.

[0145] The uncured multi-layer pipe 10X is inserted into a tube 14 for forming the outer surface of the pipe, and is cooled in a cooling water tank 15 while being molded to a predetermined size.

[0146] 2 and 3, a take-up machine 16 is used to take up the multi-layer pipe 10 cooled in the cooling water tank 15, and a cutter 17 is used to cut the multi-layer pipe 10 sent from the take-up machine 16 to a predetermined length. In this way, a multi-layer pipe 10 having a predetermined length is obtained.

[0147] The heating temperature in the mold 13 is preferably 140° C. or higher, more preferably 160° C. or higher, and preferably 200° C. or lower, more preferably 190° C. or lower. The heating time in the mold 13 is preferably 10 minutes or longer, preferably 30 minutes or shorter, more preferably 20 minutes or shorter.

[0148] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0149] The outer layer was prepared using the following materials. Components (1) to (2) listed in the "(Outer layer materials)" column below were blended in the amounts (parts by weight) shown in the table. Components (3) to (8) listed in the "(Outer layer materials)" column below were blended in the amounts (parts by weight) shown in the "(Outer layer materials)" column below, and the amounts listed in the table have been omitted.

[0150] (Outer layer material) (1) Thermoplastic resin (vinyl chloride resin, "TS-1000R" manufactured by Tokuyama Sekisui Kogyo Co., Ltd.) (2) Inosilicate mineral (wollastonite, Nippon Talc Co., Ltd. "WFB15", aspect ratio 17) (3) Organic tin stabilizer ("TVS-8832" manufactured by Nitto Kasei Co., Ltd.): Blend amount: 1 part by weight (4) MBS resin (Kaneka Corporation "B-564"): 1 part by weight (5) High molecular weight acrylic resin with a molecular weight of 3 million or more (Kaneka Corporation's "PA-20"): 1 part by weight (6) Lubricant (Mitsui Chemicals "Hiwax 220MP"): 1 part by weight (7) Lubricant ("Roxiol 259" manufactured by Emery Oleochemicals Japan Co., Ltd.): Blend amount: 1 part by weight (8) Calcium carbonate (Shiraishi Kogyo Co., Ltd. "CCR"): 1 part by weight

[0151] The foam layer was prepared using the following materials. Components (1) to (3) listed in the "(Foam Layer Materials)" column below were blended in the amounts (parts by weight) shown in the table. Components (4) to (8) listed in the "(Foam Layer Materials)" column below were blended in the amounts (parts by weight) shown in the "(Foam Layer Materials)" column below, and the amounts listed in the table are omitted.

[0152] (Foam layer material) (1) Thermoplastic resin (vinyl chloride resin, "TS-1000R" manufactured by Tokuyama Sekisui Kogyo Co., Ltd.) (2) Inosilicate mineral (wollastonite, Nippon Talc Co., Ltd. "WFB15", aspect ratio 17) (3) Expanded graphite (Suzuhiro Chemical Co., Ltd. "GREP-EG") (4) High molecular weight acrylic resin with a molecular weight of 3 million or more (Kaneka Corporation's "PA-40"): 20 parts by weight (5) Baking soda (Eiwa Chemical Industry Co., Ltd. "Celbon SC-855"): 3 parts by weight (6) Organic tin stabilizer ("TVS-8832" manufactured by Nitto Kasei Co., Ltd.): Blend amount: 1 part by weight (7) Lubricant ("Roxiol 259" manufactured by Emery Oleochemicals Japan Co., Ltd.): Blend amount: 1 part by weight (8) Colorant (Hexa Chemical Company's "D-13486"): 1 part by weight

[0153] The inner layer was prepared using the following materials. Components (1) to (2) listed in the "(Inner layer materials)" column below were blended in the amounts (parts by weight) shown in the table. Components (3) to (8) listed in the "(Inner layer materials)" column below were blended in the amounts (parts by weight) shown in the "(Inner layer materials)" column below, and the amounts listed in the table have been omitted.

[0154] (Inner layer material) (1) Thermoplastic resin (vinyl chloride resin, "TS-1000R" manufactured by Tokuyama Sekisui Kogyo Co., Ltd.) (2) Inosilicate mineral (wollastonite, Nippon Talc Co., Ltd. "WFB15", aspect ratio 17) (3) Organic tin stabilizer ("TVS-8832" manufactured by Nitto Kasei Co., Ltd.): Blend amount: 1 part by weight (4) MBS resin (Kaneka Corporation "B-564"): 1 part by weight (5) High molecular weight acrylic resin with a molecular weight of 3 million or more (Kaneka Corporation's "PA-20"): 1 part by weight (6) Lubricant (Mitsui Chemicals "Hiwax 220MP"): 1 part by weight (7) Lubricant ("Roxiol 259" manufactured by Emery Oleochemicals Japan Co., Ltd.): Blend amount: 1 part by weight (8) Calcium carbonate (Shiraishi Kogyo Co., Ltd. "CCR"): 1 part by weight

[0155] (Examples 1 to 14 and Comparative Examples 1 and 2) A three-layered multilayer pipe (drain pipe for air conditioning equipment) was fabricated, which had an inner layer, a foamed layer, and an outer layer in that order from the inner surface to the outer surface of the multilayer pipe. The thickness of the multilayer pipe, the thickness of the inner layer, the thickness of the foamed layer, the thickness of the outer layer, and the inner diameter of the multilayer pipe were set within the following ranges.

[0156] Multilayer pipe thickness: 9.5±1.0mm Inner layer thickness: 2.5±0.5mm Foam layer thickness: 5.9±1.0mm Outer layer thickness: 1.2±0.5mm Inner diameter of multilayer pipe: 57.0±0.5mm

[0157] (evaluation) (1) Fire resistance (1-1)Residue remaining rate Test pieces measuring 30±1 mm in length, 30±1 mm in width, and the thickness of the multi-layer tube were cut out from the resulting multi-layer tube. After measuring the weight of a heat-resistant dish (made of quartz glass), the resulting test pieces were placed on the heat-resistant dish, and the combined weight of the heat-resistant dish and test pieces was measured. The weight of the test pieces before combustion was calculated by subtracting the weight of the heat-resistant dish from the combined weight of the heat-resistant dish and test pieces. Next, the test pieces, while still on the heat-resistant dish, were placed in an electric furnace heated to 850°C for 3 minutes, then removed, and the combined weight of the heat-resistant dish and the test pieces after combustion was measured. The weight of the test pieces (residue) after combustion was similarly calculated. The residue remaining rate of the test pieces was calculated using the following formula. Fire resistance (residue remaining rate) was evaluated according to the following criteria. Note that the higher the residue remaining rate, the better the fire resistance. A residue remaining rate of more than 10% is considered to be sufficient for practical use.

[0158] Residue remaining rate (%) = weight of test piece after combustion × 100 / weight of test piece before combustion

[0159] [Fire resistance (residue remaining rate) evaluation criteria] ○○: Residue remaining rate is 20% or more ○: Residue remaining rate is more than 10% but less than 20% ×: Residue remaining rate is 10% or less

[0160] (1-2) Shape retention rate Test pieces measuring 30±1 mm in length, 30±1 mm in width, and the thickness of the multi-layer pipe were cut out from the resulting multi-layer pipe. The length of the resulting test piece was measured and used as the length of the test piece before combustion. The test piece was then placed in an electric furnace heated to 350°C for 5 minutes, then removed and the length of the test piece after combustion was measured. The shape retention rate of the test piece was calculated using the following formula. The fire resistance (shape retention rate) was evaluated according to the following criteria. The higher the shape retention rate, the better the fire resistance. A shape retention rate of 70% or more can be considered to have sufficient fire resistance for practical use.

[0161] Shape retention rate (%) = length of test piece after combustion × 100 / length of test piece before combustion

[0162] [Fire resistance (shape retention) criteria] ○○: Shape retention rate is 75% or more ○: Shape retention rate is 70% or more but less than 75% ×: Shape retention rate is less than 70%

[0163] (1-3)Residue strength Test pieces measuring 30±1 mm in length, 30±1 mm in width, and the thickness of the multilayer tube were cut out from the resulting multilayer tube. A hole of approximately 1 mm was drilled at the end of the test piece, a wire was passed through the hole, and the test piece was hung on a metal stand. The test piece hanging from the metal stand was placed in an electric furnace heated to 500°C for 3 minutes to create combustion residue, and then removed (residue creation process). This residue creation process was performed on five test pieces, and the number of test pieces that fell was counted.

[0164] If the residual strength is low, the test piece will fall from the metal stand. The fewer the number of test pieces that fall, the better the fire resistance. If the number of test pieces that fall is four or less, it can be determined that the residual strength is sufficient for practical use. Fire resistance (residue strength) was evaluated according to the following criteria.

[0165] [Fire resistance (residue strength) criteria] ○○: Of the five test pieces, 0 or 1 fell. ○: Two out of five test pieces fell △: Three or four of the five test pieces fell. ×: 5 out of 5 test pieces fell

[0166] (2) Thermal insulation The resulting multi-layer pipe (4 m long) was placed in a temperature and humidity chamber at a temperature of 20°C and a relative humidity of 80% at a gradient of 1 / 50. After running tap water at 7°C through the multi-layer pipe at a flow rate of 6 L / h for 1 hour, the presence or absence of condensation was confirmed by touching the bottom of the multi-layer pipe with a hand. The thermal insulation was evaluated according to the following criteria.

[0167] [Insulation criteria] ○: No condensation ×: Condensation has occurred

[0168] [Table 1]

[0169] [Table 2]

[0170] [Table 3]

[0171] [Table 4] [Explanation of symbols]

[0172] 1...Inner layer 2...Foam layer 3…Outer layer 10…Multilayer pipe 10X: Uncured multi-layer pipe 11...Inner and outer layer extruder 12...Foam layer extruder 13...Mold 14...Tube for forming outer surface of pipe 15...Cooling water tank 16...Removal machine 17…cutting machine 18...Gas cylinder 19...Metering pump 20…Manufacturing equipment 21...Inner layer material 22...Foam layer material 23...Outer layer material 31...Unhardened inner layer 32...Uncured foam layer 33...Uncured outer layer

Claims

1. an inner layer, a foam layer disposed outside the inner layer, and an outer layer disposed outside the foam layer; A multi-layer pipe, wherein at least one of the three layers, i.e., the inner layer, the foam layer, and the outer layer, is a layer A containing a thermoplastic resin and an inosilicate mineral.

2. 2. The multi-layer pipe according to claim 1, wherein the thermoplastic resin is a vinyl chloride resin.

3. 3. The multi-layer pipe according to claim 1, wherein the inosilicate mineral is wollastonite.

4. 3. The multi-layer pipe according to claim 1, wherein the inosilicate mineral has an aspect ratio of 10.0 or more and 24.0 or less.

5. 3. The multi-layer pipe according to claim 1, wherein the content of the inosilicate mineral in the layer A is 1 part by weight or more and 20 parts by weight or less relative to 100 parts by weight of the thermoplastic resin in the layer A.

6. 6. The multi-layer pipe according to claim 5, wherein the content of the inosilicate mineral in the layer A is 5 parts by weight or more and 15 parts by weight or less relative to 100 parts by weight of the thermoplastic resin in the layer A.

7. 3. The multi-layer pipe according to claim 1, wherein the content of the inosilicate mineral is 0.2% by weight or more and 15% by weight or less, based on 100% by weight of the multi-layer pipe.

8. 3. The multi-layer pipe according to claim 1, wherein at least the inner layer of the three layers of the inner layer, the foam layer, and the outer layer is layer A, or at least the outer layer of the three layers of the inner layer, the foam layer, and the outer layer is layer A.

9. 9. The multi-layer pipe according to claim 8, wherein at least the inner layer and the outer layer out of the three layers of the inner layer, the foamed layer and the outer layer are layer A.

10. 3. The multi-layer pipe according to claim 1, wherein at least the foamed layer of the three layers of the inner layer, the foamed layer and the outer layer is layer A.

11. 3. The multi-layer pipe according to claim 1, wherein the multi-layer pipe does not contain expanded graphite or contains less than 5% by weight of expanded graphite per 100% by weight of the multi-layer pipe.

12. The multi-layer pipe according to claim 1 or 2, wherein the multi-layer pipe is a drain pipe for an air conditioning system.

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