Multilayer pipe

Abstract

To provide a multi-layer pipe that can improve both thermal insulation and fire resistance. [Solution] The multilayer tube according to the present invention is a multilayer tube comprising a foamed layer and at least one of an inner layer disposed inside the foamed layer and an outer layer disposed outside the foamed layer, wherein at least one layer in the multilayer tube is layer A containing a thermoplastic resin and glass frit, and the softening point of the glass frit in layer A is 420°C or higher and 800°C or lower.

Description

Technical Field

[0001] The present invention relates to a multilayer pipe provided with a foam layer.

Background Art

[0002] Drain pipes for air conditioning equipment are laid throughout buildings. Resin-made multilayer pipes are used as drain pipes for air conditioning equipment. With the advancement of construction technology, high heat insulating properties are required for drain pipes for air conditioning equipment. In order to improve heat insulating properties, multilayer pipes provided with a foam layer are sometimes used.

[0003] In addition, in order to use drain pipes for air conditioning equipment in fire compartments, it is necessary to satisfy the fire resistance specified by ISO (International Organization for Standardization).

[0004] However, in conventional drain pipes for air conditioning equipment, when the pipe is used at a section penetration part, special treatment is required, which imposes a large burden in terms of cost and construction. If the drain pipe for air conditioning equipment itself has the property of satisfying the above-mentioned fire resistance specified by ISO, the pipe can be used in a fire compartment without performing special treatment.

[0005] Specific examples of fire resistance performance in drain pipes for air conditioning equipment include the performance of preventing fire spread through the pipe by expanding the pipe heated by a heat source and blocking the pipe itself. In order to exhibit such performance, the use of expanded graphite has been studied.

[0006] The following Patent Document 1 discloses a multilayer pipe including an inner skin layer, an outer skin layer, and a foam layer between the inner skin layer and the outer skin layer. In Patent Document 1, the foam structure in the foam layer is controlled in order to improve heat insulating properties.

[0007] Patent Document 2 below discloses a multilayer tube comprising a foamed layer and a coating layer on at least one of the outer and inner surfaces of the foamed layer. In this multilayer tube, the foamed layer comprises a thermoplastic resin and expanded graphite. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2007-283733 [Patent Document 2] Japanese Patent Publication No. 2020-159476 [Overview of the project] [Problems that the invention aims to solve]

[0009] In the multilayer pipe described in Patent Document 1, the above-mentioned foamed layer is provided, so the heat insulation can be improved to a certain extent.

[0010] However, simply controlling the foam structure in the foam layer has limitations in improving thermal insulation. Furthermore, the multilayer pipe described in Patent Document 1 may have low fire resistance. In order to meet the fire resistance requirements specified by ISO, the multilayer pipe described in Patent Document 1 may require special treatment when installing it, which is costly and labor-intensive.

[0011] Furthermore, in multilayer pipes like the one described in Patent Document 1, it is conceivable to add a new layer with superior fire resistance in order to improve fire resistance. However, if a new layer with superior fire resistance is added, the thickness of the layer with superior heat insulation must be reduced in order to maintain the thickness of the multilayer pipe. As a result, even if fire resistance can be improved, there is the drawback of reduced heat insulation.

[0012] In the multilayer tube described in Patent Document 2, the foamed layer is provided, which allows for a certain degree of improved heat insulation. Furthermore, in the multilayer tube described in Patent Document 2, the foamed layer contains expanded graphite, which allows for a certain degree of improved fire resistance. The use of expanded graphite causes the multilayer tube to expand and close during combustion, thus preventing the spread of fire through the multilayer tube.

[0013] However, even if the thermal insulation of the multilayer tube described in Patent Document 2 can be improved to some extent, it can be difficult to sufficiently improve the thermal insulation because the thermal conductivity of expanded graphite is high.

[0014] Conventional multi-layer pipes have the problem of being quite difficult to achieve both high thermal insulation and high fire resistance at the same time.

[0015] The objective of the present invention is to provide a multilayer pipe that can enhance both thermal insulation and fire resistance. [Means for solving the problem]

[0016] This specification discloses the following multilayer tubes.

[0017] Item 1. A multilayer tube comprising a foamed layer and at least one of an inner layer disposed inside the foamed layer and an outer layer disposed outside the foamed layer, wherein at least one layer in the multilayer tube is layer A comprising a thermoplastic resin and glass frit, and the softening point of the glass frit in layer A is 420°C or higher and 800°C or lower.

[0018] Item 2. The multilayer tube according to Item 1, wherein the thermoplastic resin in layer A is a vinyl chloride resin.

[0019] Item 3. The multilayer tube according to Item 1 or 2, wherein the content of the glass frit in layer A is 0.05 parts by weight or more and 35 parts by weight or less, relative to 100 parts by weight of the thermoplastic resin in layer A.

[0020] Item 4. The multilayer pipe according to Item 3, wherein the content of the glass frit in the layer A is 1 part by weight or more and 20 parts by weight or less based on 100 parts by weight of the thermoplastic resin in the layer A.

[0021] Item 5. The multilayer pipe according to any one of Items 1 to 4, wherein the glass frit in the layer A contains boron or aluminum.

[0022] Item 6. The multilayer pipe according to any one of Items 1 to 5, wherein the multilayer pipe comprises the inner layer, the foamed layer, and the outer layer, and at least the foamed layer among the three layers of the inner layer, the foamed layer, and the outer layer is the layer A.

[0023] Item 7. The multilayer pipe according to any one of Items 1 to 6, wherein the multilayer 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 multilayer pipe.

[0024] Item 8. The multilayer pipe according to any one of Items 1 to 7, wherein the multilayer pipe is a drain pipe for air conditioning equipment. Effects of the Invention

[0025] The multilayer pipe according to the present invention is a multilayer pipe comprising a foamed layer and at least one of an inner layer arranged inside the foamed layer and an outer layer arranged outside the foamed layer. In the multilayer pipe according to the present invention, at least one layer in the multilayer pipe is layer A containing a thermoplastic resin and glass frit. In the multilayer pipe according to the present invention, the softening point of the glass frit in the layer A is 420°C or higher and 800°C or lower. Since the multilayer pipe according to the present invention has the above configuration, it can improve both heat insulation and fire resistance. Brief Description of the Drawings

[0026] [Figure 1] Figure 1 is a cross-sectional view schematically showing a multilayer pipe according to one embodiment of the present invention. [Figure 2] Figure 2 is a plan view schematically showing a manufacturing apparatus used for manufacturing a multilayer pipe according to one embodiment of the present invention. [Figure 3] Figure 3 is a schematic front view showing a manufacturing apparatus used to manufacture a multilayer tube according to one embodiment of the present invention. [Figure 4] Figure 4 is a magnified cross-sectional view showing the mold portion and the tube portion for forming the outer surface of the pipe in the manufacturing apparatus. [Modes for carrying out the invention]

[0027] The present invention will be described in detail below.

[0028] The multilayer tube according to the present invention comprises a foamed layer and at least one of an inner layer disposed inside the foamed layer and an outer layer disposed outside the foamed layer.

[0029] In this specification, the "layer containing thermoplastic resin and glass frit" is referred to as "layer A". In the multilayer tube according to the present invention, at least one layer in the multilayer tube is layer A, which contains thermoplastic resin and glass frit. In the multilayer tube according to 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 thermoplastic resin and glass frit. Therefore, the multilayer tube according to the present invention comprises layer A. In the multilayer tube according to the present invention, the softening point of the glass frit in layer A is 420°C or higher and 800°C or lower.

[0030] Conventional multi-layer pipes have the problem of being quite difficult to achieve both high thermal insulation and high fire resistance at the same time.

[0031] The inventors have found that the above problems can be solved by using glass frit having a specific softening point in a multilayer tube. The multilayer tube according to the present invention has the above configuration, so it can improve both heat insulation and fire resistance. The multilayer tube according to the present invention has the above foamed layer, so it can improve heat insulation. The multilayer tube according to the present invention has the above layer A containing thermoplastic resin and glass frit, so it can maintain high heat insulation while also improving fire resistance. The present invention makes it possible to achieve both high heat insulation and high fire resistance. Specifically regarding fire resistance, when the multilayer tube is exposed to high temperatures, the glass frit melts and coats the surface of the combustion residue, thereby (1) blocking the supply of oxygen necessary for combustion, (2) preventing further thermal decomposition of the thermoplastic resin due to the conduction of combustion heat, and (3) inhibiting the diffusion of flammable gases generated during the thermal decomposition of the thermoplastic resin. As a result, combustion of the multilayer tube can be suppressed, and the fire resistance of the multilayer tube can be improved. Furthermore, when multilayer tubes are exposed to high temperatures, the glass frit melts and forms a glass coating on the surface of the combustion residue, allowing the multilayer tubes to maintain high strength (high residue strength) and preventing the combustion residue from falling. As a result, even when multilayer tubes are exposed to high temperatures, they can maintain their function as multilayer tubes for a long time, thereby improving the fire resistance of the multilayer tubes.

[0032] Furthermore, since the multilayer tube according to the present invention is equipped with the above-mentioned foamed layer, the lightness of the multilayer tube can be increased, and the manufacturing cost can be reduced.

[0033] The multilayer tube comprises a foamed layer and at least one of an inner layer disposed inside the foamed layer and an outer layer disposed outside the foamed layer. That is, the multilayer tube has a structure of two or more layers. The multilayer tube may comprise the foamed layer and an inner layer disposed inside the foamed layer. The multilayer tube may comprise the foamed layer and an outer layer disposed outside the foamed layer. The multilayer tube may comprise the foamed layer, an inner layer disposed inside the foamed layer and an outer layer disposed outside the foamed layer. From the viewpoint of further improving thermal insulation, it is preferable that the multilayer tube comprises the foamed layer, an inner layer disposed inside the foamed layer and an outer layer disposed outside the foamed layer. When the multilayer tube comprises the foamed layer, the inner layer and the outer layer, the foamed layer is an intermediate layer.

[0034] The inner layer is a layer located inside the foam layer. The outer layer is a layer located outside the foam layer. The foam layer may be a single layer or a multi-layer layer. The foam layer may be one layer, two layers, two or more layers, three or more layers, ten or fewer layers, or five or fewer layers. The inner layer may be a single layer or a multi-layer layer. The inner layer may be one layer, two layers, two or more layers, three or more layers, ten or fewer layers, or five or fewer layers. The outer layer may be a single layer or a multi-layer layer. The outer layer may be one layer, two layers, two or more layers, three or more layers, ten or fewer layers, or five or fewer layers.

[0035] The inner layer described above does not have to be a foamed layer. Preferably, the inner layer is formed from a composition for obtaining the inner layer (a composition other than the material for the foamed layer). The outer layer described above does not have to be a foamed layer. Preferably, the outer layer is formed from a composition for obtaining the outer layer (a composition other than the material for the foamed layer).

[0036] If the multilayer tube has the inner layer, the inner layer may be layer A or not. The multilayer tube may have layer A as the inner layer. The foamed layer may be layer A or not. The multilayer tube may have layer A as the foamed layer. If the multilayer tube has the outer layer, the outer layer may be layer A or not. The multilayer tube may have layer A as the outer layer.

[0037] At least the inner layer among the three layers described above (inner layer, foam layer, and outer layer) may be layer A. At least the foam layer among the three layers described above (inner layer, foam layer, and outer layer) may be layer A. At least the foam layer in the multilayer tube may be layer A. At least the outer layer among the three layers described above (inner layer, foam layer, and outer layer) may be layer A. At least two of the three layers described above (inner layer, foam layer, and outer layer) may be layer A. At least the inner layer and foam layer among the three layers described above (inner layer, foam layer, and outer layer) may be layer A. At least the inner layer and outer layer among the three layers described above (inner layer, foam layer, and outer layer) may be layer A. When the multilayer tube comprises the inner layer, the foamed layer, and the outer layer, the three layers of the inner layer, the foamed layer, and the outer layer may be layer A.

[0038] From the viewpoint of further improving heat insulation and fire resistance, it is preferable that the multilayer pipe comprises the inner layer, the foamed layer, and the outer layer, and that at least the foamed layer among the three layers is layer A. When the foamed layer is layer A, the inner layer does not have to be layer A, and the outer layer does not have to be layer A.

[0039] From the viewpoint of further enhancing heat insulation and fire resistance, it is preferable that the multilayer pipe comprises the inner layer, the foamed layer, and the outer layer, and that at least two of the three layers—the inner layer, the foamed layer, and the outer layer—are layer A. From the viewpoint of further enhancing heat insulation and fire resistance, it is preferable that the multilayer pipe comprises the inner layer, the foamed layer, and the outer layer, and that the three layers—the inner layer, the foamed layer, and the outer layer—are layer A.

[0040] From the viewpoint of reducing manufacturing costs and further increasing productivity, it is preferable that two or fewer of the three layers—the inner layer, the foamed layer, and the outer layer—are layer A. From the viewpoint of reducing manufacturing costs and further increasing productivity, it is preferable that only one of the three layers—the inner layer, the foamed layer, and the outer layer—is layer A.

[0041] Specific embodiments of the present invention will be described below with reference to the drawings. Note that the size, thickness, and shape shown in the following drawings may differ from the actual size, thickness, and shape for illustrative purposes.

[0042] Figure 1 is a schematic cross-sectional view of a multilayer tube according to one embodiment of the present invention. Figure 1 shows a cross-sectional view along the radial direction of the multilayer tube.

[0043] The multilayer tube 10 shown in Figure 1 comprises an inner layer 1, a foamed layer 2, and an outer layer 3. In the multilayer tube 10, the inner layer 1, the foamed layer 2, and the outer layer 3 are arranged in this order from the inner surface side to the outer surface side of the multilayer tube 10. The multilayer tube 10 has a three-layer structure. The foamed layer 2 is located outside the inner layer 1. The outer layer 3 is located outside the foamed layer 2. The foamed layer 2 is located on the outer surface of the inner layer 1 and is stacked. The outer layer 3 is located on the outer surface of the foamed layer 2 and is stacked. The inner layer 1 is the innermost layer and is the surface layer. The foamed layer 2 is the intermediate layer. The outer layer 3 is the outermost layer and is the surface layer. The inner layer 1, the foamed layer 2, and the outer layer 3 are each tubular in shape.

[0044] In the multilayer tube 10, at least one of the inner layer 1, foamed layer 2, and outer layer 3 is layer A, which contains a thermoplastic resin and glass frit.

[0045] Further details of the foam layer, inner layer, and outer layer described above will be explained below.

[0046] (Foam layer) The foamed layer described above is a foamed material produced by foaming with a foaming agent. The foamed layer described above is a foam. The foamed layer described above is preferably a resin foam, and more preferably a resin foam molded article.

[0047] The specific gravity of the foam layer (foam) is preferably 0.05 or higher, more preferably 0.07 or higher, even more preferably 0.08 or higher, particularly preferably 0.10 or higher, preferably 0.30 or lower, more preferably 0.20 or lower, even more preferably 0.19 or lower, particularly preferably 0.18 or lower, and most preferably 0.15 or lower. If the specific gravity of the foam layer is above the lower limit, the impact resistance can be further enhanced. If the specific gravity of the foam layer is below the upper limit, the heat insulation can be further enhanced.

[0048] The closed-cell ratio of the foamed layer is preferably 20% or more, more preferably 30% or more, even more preferably 40% or more, still more preferably 50% or more, still more preferably 60% or more, particularly preferably 70% or more, and most preferably 80% or more. If the closed-cell ratio of the foamed layer is above the lower limit, the risk of water seeping into the foamed layer through the bubbles when water penetrates into the foamed layer from the end of the multilayer tube by capillary action, etc., can be reduced. Therefore, a decrease in thermal insulation performance can be suppressed. There is no particular upper limit to the closed-cell ratio of the foamed layer. The closed-cell ratio of the foamed layer may be 100% or less, 90% or less, 80% or less, or 70% or less. The range of the closed-cell ratio of the foamed layer can be set by appropriately selecting the lower limit and upper limit values.

[0049] The foaming ratio of the foamed 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, most preferably 5.0 times or more, preferably 30.0 times or less, more preferably 25.0 times or less, and even more preferably 20.0 times or less. If the foaming ratio of the foamed layer is above the lower limit, the heat insulation performance can be further improved. If the foaming ratio of the foamed layer is below the upper limit, the bubble diameter can be made uniform, and the closed-cell ratio of the foamed layer can be increased.

[0050] 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, preferably 20.0 mm or less, more preferably 18.0 mm or less, and even more preferably 16.0 mm or less. If the thickness of the foamed layer is above the lower limit, the heat insulation performance can be further improved. If the thickness of the foamed layer is below the upper limit, the inner diameter can be formed uniformly during the manufacture of the multilayer tube.

[0051] The ratio of the thickness of the foam layer to the thickness of the outer layer is denoted 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, preferably 10.0 or less, more preferably 9.5 or less, even more preferably 9.0 or less, and particularly preferably 8.5 or less. If the ratio (thickness of foam layer / thickness of outer layer) is above the lower limit, the thermal insulation performance can be further enhanced. If the ratio (thickness of foam layer / thickness of outer layer) is below the upper limit, the impact resistance can be further enhanced.

[0052] The ratio of the thickness of the foam layer to the thickness of the inner layer is denoted as the ratio (thickness of foam layer / thickness of inner layer). The ratio (thickness of foam layer / thickness of inner 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, preferably 10.0 or less, more preferably 9.5 or less, even more preferably 9.0 or less, and particularly preferably 8.5 or less. If the ratio (thickness of foam layer / thickness of inner layer) is above the lower limit, the thermal insulation performance can be further enhanced. If the ratio (thickness of foam layer / thickness of inner layer) is below the upper limit, the impact resistance can be further enhanced.

[0053] The ratio of the thickness of the foamed layer to the sum of the thicknesses of the inner and outer layers is denoted as the ratio (thickness of foamed layer / sum of inner and outer layer thicknesses). The ratio (thickness of foamed layer / sum of inner and outer layer thicknesses) 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, preferably 6.5 or less, more preferably 6.0 or less, even more preferably 5.5 or less, and particularly preferably 5.0 or less. If the ratio (thickness of foamed layer / sum of inner and outer layer thicknesses) is above the lower limit, the thermal insulation performance can be further improved. If the ratio (thickness of foamed layer / sum of inner and outer layer thicknesses) is below the upper limit, the inner diameter can be uniformly formed during the manufacturing of the multilayer tube.

[0054] (Inner layer) The above inner layer does not have to be a foamed layer. The above inner layer may also be a non-foamed layer.

[0055] 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, preferably 4.0 mm or less, more preferably 3.8 mm or less, and even more preferably 3.5 mm or less. If the thickness of the inner layer is above the lower limit, a sufficient amount of water can flow through the multilayer pipe. If the thickness of the inner layer is below the upper limit, the heat insulation performance can be further improved.

[0056] (outer layer) The outer layer described above does not have to be a foamed layer. The outer layer described above may also be a non-foamed layer.

[0057] 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, preferably 7.0 mm or less, more preferably 6.5 mm or less, and even more preferably 6.0 mm or less. If the thickness of the outer layer is above the lower limit, the heat insulation performance can be further enhanced. If the thickness of the outer layer is below the upper limit, the impact resistance can be further enhanced.

[0058] The following describes the materials used in the foamed layer, the inner layer, and the outer layer.

[0059] <Resin> The foamed layer (material of the foamed layer) preferably contains resin. The inner layer (material of the inner layer) preferably contains resin. The outer layer (material of the outer layer) preferably contains resin. Layer A (material of layer A) contains thermoplastic resin. The multilayer tube contains thermoplastic resin.

[0060] Examples of the above resins include vinyl chloride resins, polyethylene (PE), polypropylene (PP), polymethyl methacrylate (PMMA), polycarbonate (PC), and polyvinylidene fluoride (PVDF). Only one of these resins may be used, or two or more may be used in combination. If the above resin is a thermoplastic resin, only one of these thermoplastic resins may be used, or two or more may be used in combination.

[0061] From the viewpoint of further enhancing fire resistance, the above resin is preferably a thermoplastic resin, and more preferably a vinyl chloride resin. From the viewpoint of further enhancing fire resistance, the above foam layer is preferably a thermoplastic resin, and more preferably a vinyl chloride resin. From the viewpoint of further enhancing fire resistance, the above inner layer is preferably a thermoplastic resin, and more preferably a vinyl chloride resin. From the viewpoint of further enhancing fire resistance, the above outer layer is preferably a thermoplastic resin, and more preferably a vinyl chloride resin. From the viewpoint of further enhancing fire resistance, layer A is preferably a vinyl chloride resin. From the viewpoint of further enhancing fire resistance, the above thermoplastic resin in layer A is preferably a vinyl chloride resin.

[0062] Conventionally known vinyl chloride resins can be used as the vinyl chloride resin mentioned above. Examples of vinyl chloride resins include (1) homopolymers of vinyl chloride monomer, (2) copolymers of vinyl chloride monomer and polymerizable compounds other than vinyl chloride monomer, and (3) graft polymers in which vinyl chloride monomer or vinyl chloride resin is graft polymerized onto a polymer other than a vinyl chloride resin. Only one type of vinyl chloride resin may be used, or two or more types may be used in combination.

[0063] Examples of polymerizable compounds other than the vinyl chloride monomers mentioned above include α-olefins having 16 or fewer carbon atoms (e.g., ethylene, propylene, and butylene); vinyl esters of aliphatic carboxylic acids having 2 to 16 carbon atoms (e.g., vinyl acetate and vinyl propionate); alkyl vinyl ethers having 16 or fewer carbon atoms (e.g., butyl vinyl ether and cetyl vinyl ether); alkyl (meth)acrylates having 16 or fewer 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 styrene (e.g., α-methylstyrene)); vinyl halides (e.g., vinylidene chloride and vinylidene fluoride); and N-substituted maleimides (N-phenylmaleimide and N-cyclohexylmaleimide). Only one of the polymerizable compounds other than the vinyl chloride monomers may be used, or two or more may be used in combination.

[0064] When the vinyl chloride resin is a copolymer, the copolymer may be a random copolymer, a block copolymer, or a graft copolymer.

[0065] Polymers other than vinyl chloride resins in which vinyl chloride monomer or vinyl chloride resin is graft polymerized include copolymers of α-olefins and vinyl esters (e.g., ethylene-vinyl acetate copolymer); copolymers of α-olefins, vinyl esters, and carbon monoxide (e.g., ethylene-vinyl acetate-carbon monoxide copolymer); copolymers of α-olefins and alkyl (meth)acrylates (e.g., ethylene-methyl (meth)acrylate copolymer and ethylene-ethyl (meth)acrylate copolymer); copolymers of α-olefins, alkyl (meth)acrylate, and carbon monoxide (e.g., ethylene-butyl (meth)acrylate-carbon monoxide copolymer); copolymers of two or more different α-olefins (e.g., ethylene-propylene copolymer); copolymers of unsaturated nitriles and dienes (e.g., acrylonitrile-butadiene copolymer); polyurethane; chlorinated polyolefins (e.g., chlorinated polyethylene and chlorinated polypropylene), etc. Only one of the polymers other than vinyl chloride resins may be used, or two or more may be used in combination.

[0066] In 100% by weight of the above vinyl chloride resin, the structural units derived from vinyl chloride are preferably 70% by weight or more, more preferably 75% by weight or more, even more preferably 80% by weight or more, particularly preferably 90% by weight or more, preferably 100% by weight or less, more preferably 98% by weight or less, and even more preferably 95% by weight or less. If the amount of structural units derived from vinyl chloride is above the lower limit, the fire resistance can be further enhanced. If the amount of structural units derived from vinyl chloride is below the upper limit, the moldability of the multilayer pipe can be enhanced, and the thermal decomposition of the vinyl chloride resin during molding can be suppressed. In addition, the amount of structural units derived from vinyl chloride in 100% by weight of the above vinyl chloride resin may be 100% by weight (total amount).

[0067] The degree of polymerization of the vinyl chloride resin is preferably 400 or higher, more preferably 500 or higher, even more preferably 600 or higher, particularly preferably 800 or higher, most preferably 1000 or higher, preferably 1600 or lower, and more preferably 1400 or lower. If the degree of polymerization of the vinyl chloride resin is above the lower limit, the mechanical strength of the multilayer tube can be increased. If the degree of polymerization of the vinyl chloride resin is below the upper limit, it is not necessary to raise the temperature during molding, and the processability becomes even better.

[0068] The degree of polymerization (average degree of polymerization) of the above-mentioned vinyl chloride resin can be measured as follows: The chlorinated vinyl chloride resin is dissolved in tetrahydrofuran (THF), unwanted components are removed by filtration, and the THF in the filtrate is dried off to obtain the resin, which is used as a sample. The average degree of polymerization of the above-mentioned vinyl chloride resin is measured in accordance with JIS K6721 "Test Method for Vinyl Chloride Resins".

[0069] The chlorine content in 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, particularly preferably 64% by weight or more, 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 lower limit and below the upper limit, the heat resistance of the multilayer tube can be improved. Furthermore, when the chlorine content is above the lower limit and below the 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 exhibited even more effectively.

[0070] The vinyl chloride resin described above may be a chlorinated vinyl chloride resin, or it may not be a chlorinated vinyl chloride resin. The chlorinated vinyl chloride resin described above is a vinyl chloride resin that has been chlorinated. In this specification, chlorinated vinyl chloride resin is included in vinyl chloride resin. In this specification, "chlorinated vinyl chloride resin" may also be referred to as "vinyl chloride resin".

[0071] Commercially available chlorinated vinyl chloride resins may be used as described above. Examples of commercially available chlorinated vinyl chloride resins include 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.).

[0072] In 100% by weight of the foamed layer, the content of the resin 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, most preferably 50% by weight or more, 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. If the content of the resin is above the lower limit and below the upper limit, the heat insulation and fire resistance can be further enhanced. In 100% by weight of the foamed layer, the content of the resin is preferably above the lower limit and below the upper limit. 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.

[0073] In 100% by weight of the inner layer, the content of the resin 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, most preferably 50% by weight or more, 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. If the content of the resin is above the lower limit and below the upper limit, the heat insulation and fire resistance can be further enhanced. In 100% by weight of the inner layer, the content of the resin is preferably above the lower limit and below the upper limit. 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.

[0074] In 100% by weight of the outer layer, the content of the resin 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, most preferably 50% by weight or more, 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. If the content of the resin is above the lower limit and below the upper limit, the heat insulation and fire resistance can be further enhanced. In 100% by weight of the outer layer, the content of the resin is preferably above the lower limit and below the upper limit. 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.

[0075] In 100% by weight of layer A, the content of the thermoplastic resin 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, most preferably 50% by weight or more, preferably 99.97% by weight or less, more preferably 99.9% by weight or less, even more preferably 99.2% by weight or less, even more preferably 99% by weight or less, even more preferably 98.5% by weight or less, even more preferably 98% by weight or less, even more preferably 97% 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. If the content of the thermoplastic resin is above the lower limit and below the upper limit, the heat insulation and fire resistance can be further improved. In 100% by weight of layer A, the content of the thermoplastic resin is preferably above the lower limit and below the upper limit. When the thermoplastic resin is the vinyl chloride resin, the content of the thermoplastic resin is the content of the vinyl chloride resin.

[0076] <Glass frit> The foamed layer (material of the foamed layer) may or may not contain glass frit. From the viewpoint of further improving fire resistance, it is preferable that the foamed layer (material of the foamed layer) contains glass frit. The inner layer (material of the inner layer) may or may not contain glass frit. From the viewpoint of further improving fire resistance, it is preferable that the inner layer (material of the inner layer) contains glass frit. The outer layer (material of the outer layer) may or may not contain glass frit. From the viewpoint of further improving fire resistance, it is preferable that the outer layer (material of the outer layer) contains glass frit. Layer A (material of layer A) contains glass frit. The multilayer tube (material of the multilayer tube) contains glass frit.

[0077] Examples of the above-mentioned glass frits include phosphate-based glass frits, boric acid-based glass frits, and silicate-based glass frits. Only one type of glass frit may be used, or two or more types may be used in combination.

[0078] The above glass frit preferably contains a metal oxide. Examples of the above metal oxides include B2O3, P2O5, ZnO, SiO2, Bi2O3, Al2O3, BaO, CaO, MgO, MnO2, ZrO2, TiO2, CeO2, SrO, V2O5, SnO2, Li2O, Na2O, K2O, CuO, and Fe2O3. The above glass frit may contain only one of the above metal oxides, or it may contain two or more.

[0079] From the viewpoint of further increasing the residue strength due to the surface coating of the residue, it is preferable that the glass frit contains phosphorus, zinc, boron, or aluminum, and more preferably boron or aluminum. From the viewpoint of further increasing the residue strength due to the surface coating of the residue, it is preferable that the glass frit in layer A contains phosphorus, zinc, boron, or aluminum, and more preferably boron or aluminum.

[0080] From the viewpoint of further increasing the residue strength due to the surface coating of the residue, it is preferable that the glass frit contains P2O5, ZnO, B2O3, or Al2O3, and more preferably B2O3 or Al2O3. From the viewpoint of further increasing the residue strength due to the surface coating of the residue, it is preferable that the glass frit in layer A contains P2O5, ZnO, B2O3, or Al2O3, and more preferably B2O3 or Al2O3.

[0081] The softening point of the glass frit in layer A is 420°C or higher and 800°C or lower. Preferably, the softening point of the glass frit in layer A is 430°C or higher, more preferably 450°C or higher, even more preferably 500°C or higher, preferably 780°C or lower, more preferably 750°C or lower, and even more preferably 700°C or lower. If the softening point of the glass frit in layer A is above the lower limit, the glass agent melts during combustion and can glass-coat the resin surface. If the softening point of the glass frit in layer A is below the upper limit, the resin surface can glass-coat before the residue falls off.

[0082] The softening point of the above glass frit can be measured using a thermogravimetric analyzer (for example, BRUKER AXS's "TG-DTA2000SA").

[0083] The average particle size of the glass frit is preferably 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.5 μm or more, preferably 20 μm or less, more preferably 10 μm or less, and even more preferably 5 μm or less. If the average particle size of the glass frit is above the lower limit, the glass agent and resin can be uniformly mixed during molding. If the average particle size of the glass frit is below the upper limit, the mechanical strength of the multilayer tube can be increased.

[0084] The average particle diameter of the glass frit described above is preferably the volume-average particle diameter. The volume-average particle diameter is the average particle diameter measured on a volume basis and is the value of the median diameter (D50) at which 50% is reached. The volume-average particle diameter can be measured by laser diffraction / scattering methods, etc.

[0085] The content of the glass frit in layer A relative to 100 parts by weight of the thermoplastic resin in layer A is preferably 0.05 parts by weight or more, more preferably 0.1 parts by weight or more, even more preferably 1 part by weight or more, particularly preferably 2 parts by weight or more, most preferably 5 parts by weight or more, preferably 35 parts by weight or less, more preferably 30 parts by weight or less, even more preferably 20 parts by weight or less, particularly preferably 15 parts by weight or less, and most preferably 10 parts by weight or less. If the content of the glass frit in layer A is above the lower limit, the residual strength of the multilayer tube when the multilayer tube is exposed to high temperatures can be increased, and the fire resistance can be further enhanced. If the content of the glass frit in layer A is below the upper limit, the shape retention rate of the multilayer tube when the multilayer tube is exposed to high temperatures can be increased, and the fire resistance can be further enhanced.

[0086] When the foamed layer is layer A, the content of the glass frit in the foamed layer relative to 100 parts by weight of the thermoplastic resin in the foamed layer is preferably 0.05 parts by weight or more, more preferably 0.1 parts by weight or more, even more preferably 1 part by weight or more, particularly preferably 2 parts by weight or more, most preferably 5 parts by weight or more, preferably 35 parts by weight or less, more preferably 30 parts by weight or less, even more preferably 20 parts by weight or less, particularly preferably 15 parts by weight or less, and most preferably 10 parts by weight or less. If the content of the glass frit in the foamed layer is above the lower limit, the residual strength of the multilayer tube when the multilayer tube is exposed to high temperatures can be increased, and the fire resistance can be further enhanced. If the content of the glass frit in the foamed layer is below the upper limit, the shape retention rate of the multilayer tube when the multilayer tube is exposed to high temperatures can be increased, and the fire resistance can be further enhanced.

[0087] When the inner layer is layer A, the content of the glass frit in the inner layer relative to 100 parts by weight of the thermoplastic resin in the inner layer is preferably 0.05 parts by weight or more, more preferably 0.1 parts by weight or more, even more preferably 1 part by weight or more, particularly preferably 2 parts by weight or more, most preferably 5 parts by weight or more, preferably 35 parts by weight or less, more preferably 30 parts by weight or less, even more preferably 20 parts by weight or less, particularly preferably 15 parts by weight or less, and most preferably 10 parts by weight or less. If the content of the glass frit in the inner layer is above the lower limit, the residual strength of the multilayer tube when the multilayer tube is exposed to high temperatures can be increased, and the fire resistance can be further enhanced. If the content of the glass frit in the inner layer is below the upper limit, the shape retention rate of the multilayer tube when the multilayer tube is exposed to high temperatures can be increased, and the fire resistance can be further enhanced.

[0088] When the outer layer is layer A, the content of the glass frit in the outer layer relative to 100 parts by weight of the thermoplastic resin in the outer layer is preferably 0.05 parts by weight or more, more preferably 0.1 parts by weight or more, even more preferably 1 part by weight or more, particularly preferably 2 parts by weight or more, most preferably 5 parts by weight or more, preferably 35 parts by weight or less, more preferably 30 parts by weight or less, even more preferably 20 parts by weight or less, particularly preferably 15 parts by weight or less, and most preferably 10 parts by weight or less. If the content of the glass frit in the outer layer is above the lower limit, the residual strength of the multilayer tube when the multilayer tube is exposed to high temperatures can be increased, and the fire resistance can be further enhanced. If the content of the glass frit in the outer layer is below the upper limit, the shape retention rate of the multilayer tube when the multilayer tube is exposed to high temperatures can be increased, and the fire resistance can be further enhanced.

[0089] In 100% by weight of layer A, the content of the glass frit is preferably 0.03% by weight or more, more preferably 0.1% by weight or more, even more preferably 0.8% by weight or more, particularly preferably 1.5% by weight or more, most preferably 3% by weight or more, preferably 35% by weight or less, more preferably 30% by weight or less, even more preferably 20% by weight or less, and particularly preferably 15% by weight or less. If the content of the glass frit is above the lower limit, the residual strength of the multilayer tube when the multilayer tube is exposed to high temperatures can be increased, and the fire resistance can be further enhanced. If the content of the glass frit is below the upper limit, the shape retention rate of the multilayer tube when the multilayer tube is exposed to high temperatures can be increased, and the fire resistance can be further enhanced.

[0090] In 100% by weight of the above multilayer tube, the content of the above glass frit is preferably 0.03% by weight or more, more preferably 0.1% by weight or more, even more preferably 0.8% by weight or more, particularly preferably 1.5% by weight or more, most preferably 3% by weight or more, preferably 35% by weight or less, more preferably 30% by weight or less, even more preferably 20% by weight or less, and particularly preferably 15% by weight or less. If the content of the above glass frit is above the lower limit, the residual strength of the multilayer tube when exposed to high temperatures can be increased, and the fire resistance can be further enhanced. If the content of the above glass frit is below the upper limit, the shape retention rate of the multilayer tube when exposed to high temperatures can be increased, and the fire resistance can be further enhanced.

[0091] <Expanded Graphite> The foamed layer (material of the foamed layer) may or may not contain expanded graphite. The inner layer (material of the inner layer) may or may not contain expanded graphite. The outer layer (material of the outer layer) may or may not contain expanded graphite. Layer A (material of layer A) may or may not contain expanded graphite. The multilayer tube may or may not contain expanded graphite.

[0092] The expanded graphite described above can be obtained by reacting graphite powder, such as natural scaly graphite, pyrolysis graphite, and quiche graphite, with an inorganic acid and a strong oxidizing agent to form compounds between the graphite layers. The expanded graphite is a crystalline compound in which the layered structure of graphite is maintained. 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, perchlorate, permanganate, dichromate, and hydrogen peroxide.

[0093] From the perspective of improving fire resistance, it is advisable to increase the content of expanded graphite, while from the perspective of improving thermal insulation, it is preferable to decrease the content of expanded graphite. The preferred content of expanded graphite differs depending on these objectives.

[0094] From the viewpoint of further enhancing fire resistance, the content of expanded graphite in 100% by weight of layer A may be greater 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 enhancing heat insulation, the content of expanded graphite in 100% by weight of layer A 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 enhancing heat insulation, it is preferable that layer A does not contain expanded graphite, or contains expanded graphite in 100% by weight of layer A in an amount less than or equal to the above upper limit, and more preferably does not contain expanded graphite.

[0095] From the viewpoint of further enhancing fire resistance, the content of expanded graphite in 100% by weight of the foamed layer may be greater 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 enhancing heat insulation, the content of 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 enhancing heat insulation, it is preferable that the foamed layer does not contain expanded graphite, or contains expanded graphite in 100% by weight of the foamed layer in an amount less than or equal to the above upper limit, and more preferably does not contain expanded graphite.

[0096] From the viewpoint of further enhancing fire resistance, the content of expanded graphite in 100% by weight of the inner layer may be greater 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 enhancing heat insulation, the content of 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 enhancing heat insulation, it is preferable that the inner layer does not contain expanded graphite, or contains expanded graphite in 100% by weight of the inner layer in an amount less than or equal to the above upper limit, and it is more preferable that it does not contain expanded graphite.

[0097] From the viewpoint of further enhancing fire resistance, the content of expanded graphite in 100% by weight of the outer layer may be greater 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 enhancing heat insulation, the content of 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 enhancing heat insulation, it is preferable that the outer layer does not contain expanded graphite, or contains expanded graphite in 100% by weight of the outer layer in an amount less than or equal to the above upper limit, and it is more preferable that it does not contain expanded graphite.

[0098] From the viewpoint of further improving fire resistance, the content of expanded graphite in 100% by weight of the multilayer tube may be greater 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 thermal insulation, the content of expanded graphite in 100% by weight of the multilayer tube 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 thermal insulation, it is preferable that the multilayer tube does not contain expanded graphite, or contains expanded graphite in 100% by weight of the multilayer tube in an amount less than or equal to the above upper limit, and more preferably does not contain expanded graphite.

[0099] <Foaming agent> The foamed layer described above can be obtained using a foaming agent. Examples of foaming agents include chemical foaming agents and physical foaming agents. Only one type of foaming agent may be used, or two or more types may be used in combination.

[0100] Examples of the above-mentioned chemical blowing agents include inorganic blowing agents and organic blowing agents. The above-mentioned chemical blowing agent may be an inorganic blowing agent or an organic blowing agent. The above-mentioned chemical blowing agent may be used alone or two or more types may be used in combination.

[0101] Examples of the inorganic blowing agents mentioned above include sodium bicarbonate (sodium hydrogen carbonate), sodium carbonate, ammonium bicarbonate, ammonium nitrite, azide compounds, and sodium boride. The inorganic blowing agents may be used individually or in combination of two or more.

[0102] Examples of the above-mentioned organic blowing agents include azo-based blowing agents and amine-based blowing agents. The above-mentioned organic blowing agents may be used individually or in combination of two or more types.

[0103] Examples of the above-mentioned azo-based blowing agents include azodicarbonamide and barium azodicarboxylate.

[0104] Examples of the amine-based foaming agents mentioned above include dinitrosopentamethylenetetramine.

[0105] As the above-mentioned chemical blowing agent, a heat-expandable capsule in which the chemical blowing agent is encapsulated as an internal component within a thermoplastic resin may be used.

[0106] <Other ingredients> The inner layer, foam layer, outer layer, and layer A may each contain additives as needed. Examples of such additives include fillers, heat stabilizers, stabilizing aids, lubricants, flame retardants, nucleating agents, pigments, processing aids, impact modifiers, antioxidants, ultraviolet absorbers, antistatic agents, light stabilizers, and plasticizers. Only one of these additives may be used, or two or more may be used in combination.

[0107] Examples of the above-mentioned fillers include inorganic fillers and organic fillers. Examples of the above-mentioned inorganic fillers include talc, heavy calcium carbonate, precipitated calcium carbonate, colloidal calcium carbonate and other carbonates, aluminum hydroxide, magnesium hydroxide, titanium dioxide, zinc oxide, magnesium oxide, carbon black, graphite, glass fibers, carbon fibers, and metal fibers. Examples of the above-mentioned organic fillers include polyamides. The above-mentioned fillers may be used individually or in combination of two or more types.

[0108] Examples of the above-mentioned heat stabilizers include organotin 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 stabilizers; barium-zinc stabilizers; and barium-cadmium stabilizers. The above-mentioned heat stabilizers may be used individually or in combination of two or more.

[0109] Examples of the above-mentioned stabilizing agents include epoxidized soybean oil, epoxidized linseed oil, epoxidized tetrahydrophthalate, epoxidized polybutadiene, phosphate esters, polyols, and zeolites. These stabilizing agents may be used individually or in combination of two or more.

[0110] Examples of the above-mentioned lubricants include internal lubricants and external lubricants. One type of lubricant may be used, or two or more types may be used in combination.

[0111] The above-mentioned internal lubricant is used to reduce the flow viscosity of the molten resin during molding and to prevent frictional heat generation. Examples of the above-mentioned internal lubricant include butyl stearate, lauryl alcohol, stearyl alcohol, epoxy soybean oil, glycerin monostearate, stearic acid, and bisamide. The above-mentioned internal lubricant may be used alone or in combination of two or more types.

[0112] The above-mentioned external lubricants are used to improve the sliding effect between the molten resin and the metal surface during molding. Examples of the above-mentioned external lubricants include paraffin wax, polyolefin wax, ester wax, and montanic acid wax. Only one type of the above-mentioned external lubricant may be used, or two or more types may be used in combination.

[0113] Examples of the above-mentioned flame retardants include brominated flame retardants, phosphorus-based flame retardants, intomescent flame retardants such as ammonium polyphosphate and melamine cyanurate, hydroxide compounds such as aluminum hydroxide and magnesium hydroxide, antimony oxide, and zinc oxide. Only one of these flame retardants may be used, or two or more may be used in combination.

[0114] Examples of the nucleating agents mentioned above include inorganic compounds such as silica, calcium silicate, kaolin, clay, mica, zinc oxide, calcium carbonate, zeolite, and talc.

[0115] Examples of the above-mentioned pigments include organic pigments such as azo, phthalocyanine, slene, and dye lake pigments; and inorganic pigments such as oxide, molybdenum chromate, sulfide / selenium, and ferrocyanide pigments. Only one of these pigments may be used, or two or more may be used in combination.

[0116] (Other details about multilayer tubes) The inner layer material and the outer layer material may be the same or different. From the viewpoint of improving manufacturing efficiency and reducing the number of extrusion molding machines or simplifying the structure of the extrusion molding machines, it is preferable that the inner layer material and the outer layer material are the same. In the multilayer tube, the inner layer and the outer layer may be formed from the same composition or from different compositions. From the viewpoint of improving manufacturing efficiency and reducing the number of extrusion molding machines or simplifying the structure of the extrusion molding machines, it is preferable that the inner layer and the outer layer of the multilayer tube are formed from the same composition.

[0117] The multilayer tube described above may have layers other than the three layers described above: the inner layer, the foamed layer, and the outer layer. The multilayer tube described above has a structure of two or more layers. The multilayer tube described above may have a structure of two layers, a structure of three or more layers, a structure of four or more layers, a structure of five or more layers, or a structure of ten or fewer layers.

[0118] The ratio of the thickness of layer A to the thickness of the multilayer tube is denoted as the ratio (thickness of layer A / thickness of multilayer tube). The ratio (thickness of layer A / thickness of multilayer tube) 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 tube) 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 more preferably 0.65 or less, and most preferably 0.63 or less. If the ratio (thickness of layer A / thickness of multilayer tube) is above the lower limit and below the upper limit, the fire resistance can be further improved. It is preferable that the ratio (thickness of layer A / thickness of multilayer tube) is above the lower limit and below the upper limit. If the multilayer tube has only one layer A, the thickness of layer A is the thickness of that single layer A. If the multilayer tube has two or more layers A, the thickness of layer A is the sum of the thicknesses of the two or more layers A.

[0119] The inner diameter of the above multilayer pipe is preferably 10 mm or more, more preferably 15 mm or more, even more preferably 20 mm or more, preferably 100 mm or less, more preferably 90 mm or less, and even more preferably 80 mm or less. If the inner diameter of the above multilayer pipe is above the lower limit, a sufficient amount of water can flow through the multilayer pipe. If the inner diameter of the above multilayer pipe is below the upper limit, the heat insulation performance can be further improved.

[0120] The outer diameter of the above-mentioned multilayer pipe is preferably 20 mm or more, more preferably 30 mm or more, even more preferably 40 mm or more, preferably 120 mm or less, more preferably 110 mm or less, and even more preferably 100 mm or less. If the outer diameter of the above-mentioned multilayer pipe is above the lower limit, the strength of the multilayer pipe can be increased. If the outer diameter of the above-mentioned multilayer pipe is below the upper limit, the workability can be improved.

[0121] The ratio of the outer diameter of the multilayer pipe to the inner diameter of the multilayer pipe is denoted as the ratio (outer diameter of the multilayer pipe / inner diameter of the multilayer pipe). The ratio (outer diameter of the multilayer pipe / inner diameter of the 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, most preferably 1.8 or more, preferably 2.5 or less, more preferably 2.4 or less, and even more preferably 2.3 or less. If the ratio (outer diameter of the multilayer pipe / inner diameter of the multilayer pipe) is above the lower limit, the impact resistance of the multilayer pipe can be improved. If the ratio (outer diameter of the multilayer pipe / inner diameter of the multilayer pipe) is below the upper limit, the workability can be improved.

[0122] Examples of the multilayer pipes mentioned above include drain pipes for air conditioning systems. As stated above, drain pipes for air conditioning systems require high thermal insulation and high fire resistance. Since the multilayer pipes mentioned above are excellent in both thermal insulation and fire resistance, they are preferable for use as drain pipes for air conditioning systems.

[0123] (Manufacturing method for multilayer tubes) Figure 2 is a schematic plan view showing a manufacturing apparatus used to manufacture a multilayer tube according to one embodiment of the present invention. Figure 3 is a schematic front view showing a manufacturing apparatus used to manufacture a multilayer tube according to one embodiment of the present invention. Figures 2 and 3 are schematic diagrams showing a manufacturing apparatus for manufacturing a multilayer tube 10.

[0124] The manufacturing apparatus 20 comprises 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 cutting machine 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 cutting machine 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.

[0125] The inner layer material and the outer layer material are placed in the hopper, and the inner layer material and the outer layer material (composition for obtaining the inner and outer layers) are melted and kneaded in the inner and outer layer extruder 11 and extruded into the mold 13.

[0126] The foaming material is placed in the hopper, the foaming material (composition for obtaining the foaming layer) is melted and kneaded in the foaming extruder 12, and then extruded into the mold 13.

[0127] An uncured multilayer tube having a three-layer structure is extruded from the exit of the mold 13.

[0128] The cooling water tank 15 is fitted with a tube 14 for forming the outer surface of the tube to shape the uncured multilayer tube to a predetermined size, and the outer surface of the uncured multilayer tube is cooled in contact with the tube 14. The take-up machine 16 receives the multilayer tube 10 that has been cooled in the cooling water tank 15. The cutting machine 17 cuts the multilayer tube 10 sent from the take-up machine 16 to a predetermined length.

[0129] Figure 4 is a magnified cross-sectional view showing the mold portion and the tube portion for forming the outer surface of the pipe in the manufacturing apparatus.

[0130] The inner layer material 21 and outer layer material 23, which have been melt-kneaded by the inner and outer layer extruder 11 (see Figures 2 and 3), and the foam layer material 22, which has been melt-kneaded by the foam layer extruder 12, are injected into the mold 13 to form an uncured multilayer tube 10X. The uncured multilayer tube 10X comprises an uncured inner layer 31 and an uncured outer layer 33, and an uncured foam layer 32.

[0131] An uncured multilayer tube 10X is inserted into a tube 14 for forming the outer surface of the tube, and the uncured multilayer tube 10X is cooled in a cooling water tank while being formed to a predetermined size.

[0132] Next, as shown in Figures 2 and 3, a retrieval machine 16 is used to retrieve the multilayer pipes 10 cooled in the cooling water tank 15, and a cutting machine 17 is used to cut the multilayer pipes 10 sent from the retrieval machine 16 to a predetermined length. In this way, multilayer pipes 10 of a predetermined length are obtained.

[0133] The heating temperature in the mold 13 is preferably 140°C or higher, more preferably 160°C or higher, preferably 200°C or lower, and more preferably 190°C or lower. The heating time in the mold 13 is preferably 10 minutes or more, preferably 30 minutes or less, and more preferably 20 minutes or less.

[0134] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples.

[0135] The outer layer was prepared using the following materials. Components (1) to (2) listed in the "(Materials for the outer layer)" column below were blended in the amounts (parts by weight) shown in the table. Components (3) to (8) listed in the "(Materials for the outer layer)" column below were blended in the amounts (parts by weight) shown in the "(Materials for the outer layer)" column below, and the amounts were not listed in the table.

[0136] (Material for the outer layer) (1) Thermoplastic resin (vinyl chloride resin, "TS-1000R" manufactured by Tokuyama Sekisui Kogyo Co., Ltd.) (2A) Glass frit (Takara Standard "VY0144", softening point 400℃) (2B) Glass frit (Takara Standard Co., Ltd. "EY0069", softening point 450℃) (2C) Glass frit (Takara Standard Co., Ltd. "JY0005", softening point 660℃) (2D) Glass frit (Takara Standard Co., Ltd. "CK5407", softening point 750℃) (2E) Glass frit (Takara Standard Co., Ltd. "CK0133", softening point 820℃) (3) Organotin stabilizer (Nitto Chemical Co., Ltd. "TVS-8832"): Amount added: 1 part by weight (4) MBS resin (Kaneka Corporation "B-564"): Amount of 1 part by weight (5) High molecular weight acrylic resin with a molecular weight of 3 million or more (Kaneka Corporation's "PA-20"): Amount added: 1 part by weight (6) Lubricant (Mitsui Chemicals, Inc. "High Wax 220MP"): Amount: 1 part by weight (7) Lubricant (Roxyol 259, manufactured by Emery Oleochemicals Japan): Amount: 1 part by weight (8) Calcium carbonate (Shiraishi Kogyo Co., Ltd. "CCR"): Amount added: 1 part by weight

[0137] The foamed layer was prepared using the following materials. Components (1) to (3) listed in the "(Materials for the Foamed Layer)" column below were blended in the amounts (parts by weight) shown in the table. Components (4) to (8) listed in the "(Materials for the Foamed Layer)" column below were blended in the amounts (parts by weight) shown in the "(Materials for the Foamed Layer)" column below, and the amounts were not listed in the table.

[0138] (Material for foam layer) (1) Thermoplastic resin (vinyl chloride resin, "TS-1000R" manufactured by Tokuyama Sekisui Kogyo Co., Ltd.) (2A) Glass frit (Takara Standard "VY0144", softening point 400℃) (2B) Glass frit (Takara Standard Co., Ltd. "EY0069", softening point 450℃) (2C) Glass frit (Takara Standard Co., Ltd. "JY0005", softening point 660℃) (2D) Glass frit (Takara Standard Co., Ltd. "CK5407", softening point 750℃) (2E) Glass frit (Takara Standard Co., Ltd. "CK0133", softening point 820℃) (3) Expanded graphite (GREP-EG, manufactured by Suzuhiro Chemical Co., Ltd.) (4) High molecular weight acrylic resin with a molecular weight of 3 million or more (Kaneka Corporation's "PA-40"): Amount added: 20 parts by weight (5) Baking soda (Cellbon SC-855, manufactured by Eiwa Kasei Kogyo Co., Ltd.): Amount to be added: 3 parts by weight (6) Organotin stabilizer (Nitto Chemical Co., Ltd. "TVS-8832"): Amount added: 1 part by weight (7) Lubricant (Roxyol 259, manufactured by Emery Oleochemicals Japan): Amount: 1 part by weight (8) Coloring agent (Hexa Chemical Co., Ltd. "D-13486"): Amount added: 1 part by weight

[0139] The inner layer was prepared using the following materials. Components (1) to (2) listed in the "(Materials for the inner layer)" column below were blended in the amounts (parts by weight) shown in the table. Components (3) to (8) listed in the "(Materials for the inner layer)" column below were blended in the amounts (parts by weight) shown in the "(Materials for the inner layer)" column below, and the amounts were not listed in the table.

[0140] (Material for the inner layer) (1) Thermoplastic resin (vinyl chloride resin, "TS-1000R" manufactured by Tokuyama Sekisui Kogyo Co., Ltd.) (2A) Glass frit (Takara Standard "VY0144", softening point 400℃) (2B) Glass frit (Takara Standard Co., Ltd. "EY0069", softening point 450℃) (2C) Glass frit (Takara Standard Co., Ltd. "JY0005", softening point 660℃) (2D) Glass frit (Takara Standard Co., Ltd. "CK5407", softening point 750℃) (2E) Glass frit (Takara Standard Co., Ltd. "CK0133", softening point 820℃) (3) Organotin stabilizer (Nitto Chemical Co., Ltd. "TVS-8832"): Amount added: 1 part by weight (4) MBS resin (Kaneka Corporation "B-564"): Amount of 1 part by weight (5) High molecular weight acrylic resin with a molecular weight of 3 million or more (Kaneka Corporation's "PA-20"): Amount added: 1 part by weight (6) Lubricant (Mitsui Chemicals, Inc. "High Wax 220MP"): Amount: 1 part by weight (7) Lubricant (Roxyol 259, manufactured by Emery Oleochemicals Japan): Amount: 1 part by weight (8) Calcium carbonate (Shiraishi Kogyo Co., Ltd. "CCR"): Amount added: 1 part by weight

[0141] (Examples 1-13 and Comparative Examples 1-4) A three-layer multilayer pipe (drain pipe for air conditioning equipment) was fabricated, with the inner layer, foam layer, and outer layer arranged in that order from the inner surface to the outer surface. The thickness of the multilayer pipe, the thickness of the inner layer, the thickness of the foam layer, the thickness of the outer layer, and the inner diameter of the multilayer pipe were set to the following numerical ranges.

[0142] Thickness of multilayer tube: 9.5±1.0mm Inner layer thickness: 2.5±0.5mm Foam layer thickness: 5.9 ± 1.0 mm Outer layer thickness: 1.2 ± 0.5 mm Inner diameter of multilayer tube: 57.0 ± 0.5 mm

[0143] (evaluation) (1) Fire resistance (1-1)Residue remaining rate From the obtained multilayer tubes, test specimens measuring 30±1 mm in length, 30±1 mm in width, and the thickness of the multilayer tube were cut out. After measuring the weight of a heat-resistant dish (made of quartz glass), the obtained test specimens were placed on the heat-resistant dish, and the total weight of the heat-resistant dish and test specimens was measured. The weight of the test specimen before combustion was calculated by subtracting the weight of the heat-resistant dish from the total weight of the heat-resistant dish and test specimens. Next, with the test specimens placed on the heat-resistant dish, the dish was placed in an electric furnace heated to 850°C for 3 minutes. After removal, the total weight of the heat-resistant dish and the post-combustion test specimen was measured, and the weight of the post-combustion test specimen (residue) was calculated in the same manner. The residue retention rate of the test specimens was calculated using the following formula. Fire resistance (residue retention rate) was judged according to the following criteria. Note that the higher the residue retention rate, the better the fire resistance. If the residue retention rate exceeds 10%, it can be judged that it has sufficient fire resistance for practical use.

[0144] Residue retention rate (%) = Weight of test specimen after combustion × 100 / Weight of test specimen before combustion

[0145] [Criteria for determining fire resistance (residue retention rate)] ○○: Residue retention rate is 20% or more ○: Residue retention rate is greater than 10% but less than 20% ×: Residue retention rate is 10% or less

[0146] (1-2) Shape retention rate From the obtained multilayer tubes, test specimens measuring 30±1 mm in length, 30±1 mm in width, and the thickness of the multilayer tube were cut out. The length of the obtained test specimens was measured and recorded as the length of the specimen before combustion. Next, the test specimens were placed in an electric furnace heated to 350°C for 5 minutes, then removed and the length of the specimens after combustion was measured. The shape retention rate of the test specimens was calculated using the following formula. The fire resistance (shape retention rate) was judged according to the following criteria. Note that the higher the shape retention rate, the better the fire resistance. A shape retention rate of 70% or more is considered to have sufficient fire resistance for practical use.

[0147] Shape retention rate (%) = Length of test specimen after combustion × 100 / Length of test specimen before combustion

[0148] [Criteria for determining fire resistance (shape retention rate)] ○○: Shape retention rate of 75% or more ○: Shape retention rate is 70% or more but less than 75% ×: Shape retention rate is less than 70%

[0149] (1-3) Residue strength (number of dropped test specimens) From the obtained multilayer tubes, test specimens measuring 30±1 mm in length, 30±1 mm in width, and the thickness of the multilayer tube were cut out. A hole of about 1 mm was drilled in the end of each test specimen, a wire was passed through the hole, and the test specimen was suspended from a metal stand. The test specimens suspended from the metal stand were 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 specimens, and the number of specimens that fell was measured.

[0150] If the residue strength is low, the test specimen will fall from the metal stand. The fewer the number of fallen specimens, the better the fire resistance. If the number of fallen specimens is two or less, it can be judged that the residue strength is practically sufficient. Fire resistance (residue strength) was judged according to the following criteria.

[0151] [Criteria for determining fire resistance (residue strength)] ○○: Out of 5 test pieces, the number of dropped pieces was 0 or 1. ○: Out of 5 test pieces, 2 fell. ×: Three or more out of five test specimens fell.

[0152] (2) Thermal insulation (anti-condensation properties) The resulting multilayer pipe (4m in length) was installed in a constant temperature and humidity chamber at 20°C and 80% relative humidity, with a slope of 1 / 50. After flowing 10°C tap water at a flow rate of 6 L / h through the inside of the multilayer pipe for 1 hour, the presence or absence of condensation was checked by touching the bottom of the multilayer pipe. The thermal insulation performance was judged according to the following criteria.

[0153] [Criteria for determining thermal insulation performance] ○: No condensation has occurred. ×: Condensation is occurring.

[0154] The configuration and results of the multilayer tube are shown in Tables 1-4 below.

[0155] [Table 1]

[0156] [Table 2]

[0157] [Table 3]

[0158] [Table 4] [Explanation of Symbols]

[0159] 1…Inner layer 2…Foam layer 3…Outer layer 10…Multilayer pipe 10X…Uncured multilayer tube 11…Inner and outer layer extruder 12… Foaming extruder 13…Mold 14…Tube for external molding 15…Cooling water tank 16... Pickup machine 17…cutting machine 18... Gas cylinder 19… Metering pump 20…Manufacturing equipment 21…Inner layer material 22…Materials for the foam layer 23…Outer layer material 31…Uncured inner layer 32…Uncured foam layer 33…Uncured outer layer

Claims

1. A multilayer tube comprising a foamed layer, and at least one of an inner layer disposed inside the foamed layer and an outer layer disposed outside the foamed layer, In a multilayer tube, at least one layer is layer A, which comprises a thermoplastic resin and glass frit. A multilayer tube in which the softening point of the glass frit in layer A is 420°C or higher and 800°C or lower.

2. The multilayer tube according to claim 1, wherein the thermoplastic resin in layer A is a vinyl chloride resin.

3. The multilayer tube according to claim 1 or 2, wherein the content of the glass frit in layer A is 0.05 parts by weight or more and 35 parts by weight or less with respect to 100 parts by weight of the thermoplastic resin in layer A.

4. The multilayer tube according to claim 3, wherein the content of the glass frit in layer A is 1 part by weight or more and 20 parts by weight or less with respect to 100 parts by weight of the thermoplastic resin in layer A.

5. The multilayer tube according to claim 1 or 2, wherein the glass frit in layer A contains boron or aluminum.

6. The multilayer tube comprises the inner layer, the foamed layer, and the outer layer, The multilayer tube according to claim 1 or 2, wherein at least the foamed layer among the three layers, the inner layer, the foamed layer, and the outer layer, is layer A.

7. The multilayer tube according to claim 1 or 2, wherein the multilayer tube does not contain expanded graphite, or contains expanded graphite in an amount of less than 5% by weight of 100% by weight of the multilayer tube.

8. The multilayer pipe according to claim 1 or 2, wherein the multilayer pipe is a drain pipe for an air conditioning system.

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