Multilayer pipe

Abstract

To provide a multilayer pipe that is capable of enhancing both fire resistance and heat insulation performance.SOLUTION: A multilayer pipe according to the present invention includes an inner layer, a foam layer disposed on the outer side of the inner layer, and an outer layer disposed on the outer side of the foam layer, wherein at least one of the inner layer, the foam layer, and the outer layer is a layer comprising a thermoplastic resin and a metal phosphate or a metal phosphite.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Multi-layer pipes made of resin are used as air conditioning drain pipes. Air conditioning drain pipes are required to have high thermal insulation. To improve the thermal insulation, multi-layer pipes with a foam layer are sometimes used.

[0003] The following Patent Document 1 discloses a polyvinyl chloride resin foamed pipe comprising an inner skin layer, an outer skin layer, and a foamed layer between the inner skin layer and the outer skin layer. The polyvinyl chloride resin foamed pipe is obtained by extrusion molding. The inner skin layer has a thickness of 0.05 mm to 0.6 mm and has a substantially non-foamed structure. The outer skin layer has a thickness of 0.2 mm to 1.5 mm and has a substantially non-foamed structure. In the polyvinyl chloride resin foamed pipe, the bubbles in the foamed layer are substantially not connected in a direction parallel to the extrusion direction. Patent Document 1 describes that the average cell diameter of the bubbles in a cross section perpendicular to the extrusion direction is 30 μm to 150 μm, and the foaming ratio of the foamed layer is 2 to 5 times. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-283733 A Summary of the Invention [Problem to be solved by the invention]

[0005] In a multi-layer pipe as described in Patent Document 1, the heat insulation can be improved to a certain degree.

[0006] However, in conventional multi-layer pipes, special treatment is required when installing the multi-layer pipes in order to meet the fire resistance standards stipulated by ISO (International Organization for Standardization), which poses the problem of significant cost and labor burden.

[0007] In order to improve the fire resistance of multi-layer pipes, a method has been considered in which a fire-resistant layer is provided on the multi-layer pipe so that the multi-layer pipe expands during combustion to block the inside of the multi-layer pipe, thereby preventing the spread of fire through the inside of the multi-layer pipe. However, when a fire-resistant layer is provided on a multi-layer pipe, the thickness of the insulating layer (foam layer) must be made thin, and as a result, even if the fire resistance can be improved, sufficient insulation may not be obtained.

[0008] In addition, in order to improve the fire resistance of the multi-layer pipe, expanded graphite is sometimes blended into the multi-layer pipe (particularly the foam layer). However, since the thermal conductivity of the expanded graphite itself is high, there is a problem that the heat insulating property of the entire multi-layer pipe is reduced when the expanded graphite is blended.

[0009] In conventional multi-layer pipes, it is difficult to improve both fire resistance and thermal insulation.

[0010] An object of the present invention is to provide a multi-layer pipe that can improve fire resistance and thermal insulation. [Means for solving the problem]

[0011] The following multi-layer pipes are disclosed herein:

[0012] Item 1. A multi-layer 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 inner layer, the foamed layer, and the outer layer is a layer containing a thermoplastic resin and a metal phosphate or a metal phosphite.

[0013] Item 2. The multi-layer pipe according to item 1, wherein the thermoplastic resin comprises a polyvinyl chloride resin or a chlorinated polyvinyl chloride resin.

[0014] Item 3. A multi-layer pipe according to item 1 or 2, wherein in the layer containing the thermoplastic resin and the metal phosphate or the metal phosphite, the total content of the metal phosphate and the metal phosphite is 0.1 parts by weight or more and 10 parts by weight or less per 100 parts by weight of the thermoplastic resin.

[0015] Item 4. The multi-layer pipe according to any one of Items 1 to 3, wherein the inner layer contains the thermoplastic resin and the metal phosphate or the metal phosphite.

[0016] Item 5. The multi-layer pipe according to any one of Items 1 to 4, wherein the outer layer contains the thermoplastic resin and the metal phosphate or the metal phosphite.

[0017] Item 6. The multi-layer pipe according to any one of Items 1 to 5, wherein the layer containing the thermoplastic resin and the metal phosphate or the metal phosphite is a layer containing the thermoplastic resin and aluminum phosphite. Effect of the Invention

[0018] 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, and at least one of the inner layer, the foamed layer, and the outer layer is a layer containing a thermoplastic resin and a metal phosphate or a metal phosphite. Since the multi-layer pipe according to the present invention has the above configuration, it is possible to improve fire resistance and heat insulation. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a cross-sectional view that illustrates a multi-layer tube according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a plan view that illustrates a manufacturing apparatus used for manufacturing a multi-layer pipe according to one embodiment of the present invention. [Diagram 3]FIG. 3 is a front view showing a schematic diagram of a manufacturing apparatus used for manufacturing 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 an outer surface of a pipe in a manufacturing apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The present invention will be described in detail below.

[0021] 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. In the multi-layer pipe according to the present invention, at least one of the inner layer, the foamed layer, and the outer layer is a layer (hereinafter sometimes referred to as layer (X)) containing a thermoplastic resin and a metal phosphate or a metal phosphite.

[0022] Since the multi-layer pipe according to the present invention has the above-mentioned configuration, it is possible to improve the fire resistance and the heat insulation.

[0023] The multi-layer pipe includes, from the center to the outside, an inner layer, a foamed layer, and an outer layer in this order. In the multi-layer pipe, the foamed layer is an intermediate layer. The inner layer is a layer located inside the foamed layer. The outer layer is a layer located outside the foamed layer. The inner layer may be a single layer or may be a multi-layer. The inner layer may be a single layer, two layers, two or more layers, three or more layers, or ten or less layers. The foamed layer may be a single layer or may be a multi-layer. The foamed layer may be a single layer, two layers, two or more layers, three or more layers, or ten or less layers. The outer layer may be a single layer or may be a multi-layer. The outer layer may be a single layer, two layers, two or more layers, three or more layers, or ten or less layers.

[0024] The inner layer does not have to be a foam layer. The inner layer is preferably formed of a composition for obtaining the inner layer (a composition other than the material for the foam layer). The outer layer does not have to be a foam layer. The outer layer is preferably formed of a composition for obtaining the outer layer (a composition other than the material for the foam layer).

[0025] Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. Note that in the following drawings, the size, thickness, shape, etc. may differ from the actual size, thickness, shape, etc. for convenience of illustration.

[0026] Fig. 1 is a cross-sectional view showing a multi-layer pipe according to one embodiment of the present invention, taken along a radial direction of the multi-layer pipe.

[0027] The multi-layer pipe 10 shown in FIG. 1 includes an inner layer 1, a foamed layer 2, and an outer layer 3. The multi-layer pipe 10 has a three-layer structure. The foamed layer 2 is disposed on the outside of the inner layer 1. The outer layer 3 is disposed on the outside of the foamed layer 2. The foamed layer 2 is disposed on the outer surface of the inner layer 1 and laminated therewith. The outer layer 3 is disposed on the outer surface of the foamed layer 2 and laminated therewith. The inner layer 1 is a single layer. The inner layer 1 is the innermost layer and is a surface layer. The foamed layer 2 is a single layer. The foamed layer 2 is an intermediate layer. The outer layer 3 is a single layer. The outer layer 3 is the outermost layer and is a surface layer. The inner layer 1, the foamed layer 2, and the outer layer 3 are each tubular.

[0028] The thickness of the multi-layer pipe is preferably 3.0 mm or more, more preferably 4.0 mm or more, and even more preferably 5.0 mm or more, and is preferably 30.0 mm or less, more preferably 25.0 mm or less, and even more preferably 20.0 mm or less. When the thickness of the multi-layer pipe is equal to or greater than the lower limit, the heat insulating property can be further improved. When the thickness of the multi-layer pipe is equal to or less than the upper limit, the fire resistance can be further improved.

[0029] The thickness of the inner layer is preferably 1.0 mm or more, more preferably 1.2 mm or more, and even more preferably 1.5 mm or more, and is preferably 5.0 mm or less, more preferably 4.5 mm or less, and even more preferably 4.0 mm or less. When the thickness of the inner layer is equal to or greater than the lower limit, a sufficient amount of fluid can be passed 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.

[0030] The thickness of the foamed layer is preferably 1.5 mm or more, more preferably 3.0 mm or more, and even more preferably 4.0 mm or more, and is preferably 20.0 mm or less, more preferably 18.0 mm or less, and even more preferably 16.0 mm or less. When the thickness of the foamed layer is equal to or greater than the lower limit, the heat insulating properties can be further improved. When the thickness of the foamed 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.

[0031] The thickness of the outer layer is preferably 1.0 mm or more, more preferably 1.3 mm or more, and even more 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 property can be further improved. When the thickness of the outer layer is equal to or less than the upper limit, the fire resistance can be further improved.

[0032] The ratio of the thickness of the foam layer to the thickness of the outer layer (thickness of foam layer / thickness of outer layer) is preferably 0.5 or more, more preferably 1.0 or more, even more preferably 1.5 or more, and is preferably 9.0 or less, more preferably 8.0 or less, even more preferably 7.5 or less, particularly preferably 7.0 or less, and most preferably 5.0 or less. When the ratio (thickness of foam layer / thickness of outer layer) is equal to or more than the lower limit, the heat insulating property 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 fire resistance can be further improved.

[0033] 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 (thickness of foamed layer / total thickness of inner layer and outer layer) is preferably 1.3 or more, more preferably 1.5 or more, even more preferably 2.0 or more, and is preferably 6.0 or less, more preferably 5.5 or less, even more preferably 5.0 or less. When the ratio (thickness of foamed layer / total thickness of inner layer and outer layer) is equal to or more than the lower limit, the heat insulation 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.

[0034] The inner diameter of the multi-layer pipe is preferably 10 mm or more, more preferably 15 mm or more, and even more preferably 20 mm or more, and is preferably 100 mm or less, more preferably 90 mm or less, and even more preferably 80 mm or less. When the inner diameter of the multi-layer pipe is equal to or more than the lower limit, a sufficient amount of fluid can be passed through the multi-layer pipe. When the inner diameter of the multi-layer pipe is equal to or less than the upper limit, the heat insulation can be further improved.

[0035] The outer diameter of the multi-layer pipe is preferably 20 mm or more, more preferably 30 mm or more, and even more preferably 40 mm or more, and is preferably 120 mm or less, more preferably 110 mm or less, and even more preferably 100 mm or less. When the outer diameter of the multi-layer pipe is equal to or more 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, the workability can be increased.

[0036] The ratio of the thickness of the multi-layer pipe to the thickness of the outer layer (thickness of the multi-layer pipe / thickness of the outer layer) is preferably 1.5 or more, more preferably 2.0 or more, even more preferably 2.5 or more, and is preferably 11.0 or less, more preferably 10.0 or less, even more preferably 7.0 or less. When the ratio (thickness of the multi-layer pipe / thickness of the outer layer) is equal to or more than the lower limit, the strength of the multi-layer pipe can be increased. When the ratio (thickness of the multi-layer pipe / thickness of the outer layer) is equal to or less than the upper limit, the fire resistance can be further increased.

[0037] The ratio of the thickness of the multilayer pipe to the thickness of the foamed layer (thickness of the multilayer pipe / thickness of the foamed layer) is preferably 1.5 or more, more preferably 2.0 or more, and even more preferably 2.5 or more, and is preferably 10.0 or less, more preferably 8.0 or less, and even more preferably 7.0 or less. When the ratio (thickness of the multilayer pipe / thickness of the foamed layer) is equal to or more than the lower limit, the fire resistance can be further improved. When the ratio (thickness of the multilayer pipe / thickness of the foamed layer) is equal to or less than the upper limit, the heat insulation can be further improved.

[0038] The materials used in the inner layer, the foam layer, and the outer layer are described below. In this specification, "(meth)acrylic" means one or both of "acrylic" and "methacrylic", and "(meth)acrylate" means one or both of "acrylate" and "methacrylate".

[0039] In the multi-layer pipe, at least one of the inner layer, the foam layer, and the outer layer is a layer (X) containing a thermoplastic resin and a metal phosphate or metal phosphite. In the multi-layer pipe, two or more of the inner layer, the foam layer, and the outer layer may contain a thermoplastic resin and a metal phosphate or metal phosphite. In the multi-layer pipe, the inner layer, the foam layer, or the outer layer may contain a thermoplastic resin and a metal phosphate or metal phosphite. In the multi-layer pipe, the inner layer may contain a thermoplastic resin and a metal phosphate or metal phosphite, the foam layer may contain a thermoplastic resin and a metal phosphate or metal phosphite, and the outer layer may contain a thermoplastic resin and a metal phosphate or metal phosphite. In the multi-layer pipe, the inner layer and the foamed layer may contain a thermoplastic resin and a metal phosphate or metal phosphite, the inner layer and the outer layer may contain a thermoplastic resin and a metal phosphate or metal phosphite, and the outer layer and the foamed layer may contain a thermoplastic resin and a metal phosphate or metal phosphite. In the multi-layer pipe, the inner layer, the outer layer and the foamed layer may contain a thermoplastic resin and a metal phosphate or metal phosphite.

[0040] From the viewpoint of further improving fire resistance, it is preferable that the inner layer contains a thermoplastic resin and a metal phosphate or metal phosphite. From the viewpoint of further improving fire resistance, it is preferable that the outer layer contains a thermoplastic resin and a metal phosphate or metal phosphite. From the viewpoint of further improving fire resistance, it is preferable that the inner layer and the outer layer each contain a thermoplastic resin and a metal phosphate or metal phosphite. From the viewpoint of further improving fire resistance, it is preferable that the inner layer contains a thermoplastic resin and a metal phosphite, and it is preferable that the outer layer contains a thermoplastic resin and a metal phosphite, and it is preferable that the inner layer and the outer layer each contain a thermoplastic resin and a metal phosphite.

[0041] <Thermoplastic resin> Examples of the thermoplastic resin include vinyl chloride resin, chlorinated vinyl chloride resin, polyolefin resin, halogenated polyolefin resin, ethylene-vinyl acetate copolymer resin, etc. The thermoplastic resin may be used alone or in combination of two or more kinds.

[0042] From the viewpoint of further improving fire resistance, the thermoplastic resin preferably contains a vinyl chloride resin or a chlorinated vinyl chloride resin. The thermoplastic resin may contain a vinyl chloride resin, a chlorinated vinyl chloride resin, or both a vinyl chloride resin and a chlorinated vinyl chloride resin.

[0043] From the viewpoint of further improving fire resistance, it is preferable that the inner layer contains the thermoplastic resin. From the viewpoint of further improving fire resistance, it is preferable that the foamed layer contains the thermoplastic resin. From the viewpoint of further improving fire resistance, it is preferable that the outer layer contains the thermoplastic resin. From the viewpoint of further improving fire resistance, it is preferable that the inner layer, the foamed layer, and the outer layer each contain the thermoplastic resin.

[0044] In 100% by weight of the layer containing the thermoplastic resin, the content of the thermoplastic resin is preferably 50% by weight or more, more preferably 55% by weight or more, and preferably 90% by weight or less, more preferably 85% by weight or less. When the content of the thermoplastic resin is equal to or more than the lower limit and equal to or less than the upper limit, the effects of the present invention can be more effectively exhibited.

[0045] In 100% by weight of the layer containing the thermoplastic resin, the total content of the vinyl chloride resin and the chlorinated vinyl chloride resin is preferably 50% by weight or more, more preferably 55% by weight or more, and preferably 90% by weight or less, more preferably 85% by weight or less. When the total content of the vinyl chloride resin and the chlorinated vinyl chloride resin is equal to or more than the lower limit and equal to or less than the upper limit, the effect of the present invention can be more effectively exhibited. In addition, when the layer containing the thermoplastic resin contains both the vinyl chloride resin and the chlorinated vinyl chloride resin, the "total content of the vinyl chloride resin and the chlorinated vinyl chloride resin" refers to the sum of the content of the vinyl chloride resin and the content of the chlorinated vinyl chloride resin. In the case where the layer containing the thermoplastic resin contains the vinyl chloride resin and does not contain the chlorinated vinyl chloride resin, the "total content of the vinyl chloride resin and the chlorinated vinyl chloride resin" refers to the content of the vinyl chloride resin. In the case where the layer containing the thermoplastic resin does not contain the vinyl chloride resin but contains the chlorinated vinyl chloride resin, the "total content of the vinyl chloride resin and the chlorinated vinyl chloride resin" refers to the content of the chlorinated vinyl chloride resin.

[0046] (Vinyl chloride resin) Examples of the vinyl chloride resin include a homopolymer of vinyl chloride, a copolymer of vinyl chloride and a monomer other than vinyl chloride, and a graft copolymer in which vinyl chloride or a vinyl chloride resin is grafted onto a polymer other than a vinyl chloride resin, etc. The vinyl chloride resin may be used alone or in combination of two or more kinds.

[0047] Examples of the monomer other than vinyl chloride include α-olefins having 2 to 16 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 2 to 16 carbon atoms (e.g., butyl vinyl ether and cetyl vinyl ether); alkyl (meth)acrylates having 1 to 16 carbon atoms (e.g., methyl (meth)acrylate, ethyl (meth)acrylate, and butyl acrylate); aryl (meth)acrylates (e.g., phenyl methacrylate); 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).

[0048] Examples of polymers other than the 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 methacrylate copolymers and ethylene-ethyl acrylate copolymers); copolymers of α-olefins, alkyl (meth)acrylates and carbon monoxide (e.g., ethylene-butyl 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).

[0049] The average degree of polymerization of the vinyl chloride resin is preferably 400 or more, more preferably 600 or more, and preferably 1600 or less, more preferably 1400 or less. When the average degree of polymerization of the vinyl chloride resin is equal to or more than the lower limit, the impact resistance of the multi-layer pipe can be improved. When the average degree of polymerization of the vinyl chloride resin is equal to or less than the upper limit, an increase in melt viscosity during the preparation of the multi-layer pipe can be prevented, and the moldability of the multi-layer pipe can be improved.

[0050] The average degree of polymerization of the vinyl chloride resin can be measured as follows: The vinyl chloride resin is dissolved in tetrahydrofuran (THF), unnecessary components are removed by filtration, and the THF in the filtrate is dried to remove the obtained resin. The average degree of polymerization of the vinyl chloride resin is measured according to JIS K6721 "Testing method for vinyl chloride resins".

[0051] When the inner layer contains the vinyl chloride resin, the content of the vinyl chloride resin in 100% by weight of the inner layer is preferably 50% by weight or more, more preferably 55% by weight or more, and preferably 100% by weight or less, more preferably 99% by weight or less. When the content of the vinyl chloride resin is equal to or more than the lower limit and equal to or less than the upper limit, the effects of the present invention can be more effectively exhibited.

[0052] When the foam layer contains the vinyl chloride resin, the content of the vinyl chloride resin in 100% by weight of the foam layer is preferably 50% by weight or more, more preferably 55% by weight or more, and preferably 100% by weight or less, more preferably 99% by weight or less. When the content of the vinyl chloride resin is equal to or more than the lower limit and equal to or less than the upper limit, the effects of the present invention can be more effectively exhibited.

[0053] When the outer layer contains the vinyl chloride resin, the content of the vinyl chloride resin in 100% by weight of the outer layer is preferably 50% by weight or more, more preferably 55% by weight or more, and preferably 100% by weight or less, more preferably 99% by weight or less. When the content of the vinyl chloride resin is equal to or more than the lower limit and equal to or less than the upper limit, the effects of the present invention can be more effectively exhibited.

[0054] (Chlorinated polyvinyl chloride resin) The chlorinated vinyl chloride resin is a resin obtained by chlorinating a vinyl chloride resin. Specifically, the chlorinated vinyl chloride resin may be a resin obtained by chlorinating a homopolymer of vinyl chloride, or a resin obtained by chlorinating a copolymer of 80% by weight or more of vinyl chloride and another monomer copolymerizable with vinyl chloride. Examples of the other monomer copolymerizable with vinyl chloride include vinyl acetate, vinylidene chloride, ethylene, propylene, (meth)acrylonitrile, (meth)acrylic acid, and (meth)acrylic acid ester. The chlorinated vinyl chloride resin may be used alone or in combination of two or more kinds. The other monomer copolymerizable with vinyl chloride may be used alone or in combination of two or more kinds.

[0055] The chlorine content of the chlorinated vinyl chloride resin is preferably 60% by weight or more, more preferably 62% by weight or more, and even more 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 equal to or more than the lower limit, the impact resistance and heat resistance of the multi-layer pipe can be improved. When the chlorine content is equal to or less than the upper limit, the impact resistance of the multi-layer pipe can be improved.

[0056] The average degree of polymerization of the chlorinated vinyl chloride resin is preferably 400 or more, more preferably 500 or more, and preferably 1500 or less, more preferably 1000 or less, and even more preferably 800 or less. When the average degree of polymerization of the chlorinated vinyl chloride resin is equal to or more than the lower limit, the impact resistance of the multi-layer pipe can be improved. When the average degree of polymerization of the chlorinated vinyl chloride resin is equal to or less than the upper limit, an increase in melt viscosity during the preparation of the multi-layer pipe can be prevented, and the moldability of the multi-layer pipe can be improved.

[0057] The average degree of polymerization of the chlorinated vinyl chloride resin can be measured as follows: The chlorinated vinyl chloride resin is dissolved in tetrahydrofuran (THF), unnecessary components are removed by filtration, and the THF in the filtrate is dried to obtain a resin sample, which is used to measure the average degree of polymerization of the chlorinated vinyl chloride resin in accordance with JIS K6721 "Testing method for vinyl chloride resins."

[0058] The chlorinated vinyl chloride resin may be a commercially available product. Examples of the commercially available chlorinated vinyl chloride resin 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.).

[0059] When the inner layer contains the chlorinated vinyl chloride resin, the content of the chlorinated vinyl chloride resin in 100% by weight of the inner layer is preferably 50% by weight or more, more preferably 55% by weight or more, and is preferably 100% by weight or less, more preferably 99% by weight or less. When the content of the chlorinated vinyl chloride resin is equal to or more than the lower limit and equal to or less than the upper limit, the effects of the present invention can be more effectively exhibited.

[0060] When the foam layer contains the chlorinated vinyl chloride resin, the content of the chlorinated vinyl chloride 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, even more preferably 40% by weight or more, particularly preferably 50% by weight or more, and most preferably 55% by weight or more. When the foam layer contains the chlorinated vinyl chloride resin, the content of the chlorinated vinyl chloride resin in 100% by weight of the foam layer is preferably 100% by weight or less, more preferably 99% by weight or less. When the content of the chlorinated vinyl chloride resin is the above lower limit or more and the above upper limit or less, the effects of the present invention can be more effectively exhibited.

[0061] When the outer layer contains the chlorinated vinyl chloride resin, the content of the chlorinated vinyl chloride resin in 100% by weight of the outer layer is preferably 50% by weight or more, more preferably 55% by weight or more, and preferably 100% by weight or less, more preferably 99% by weight or less. When the content of the chlorinated vinyl chloride resin is equal to or more than the lower limit and equal to or less than the upper limit, the effects of the present invention can be more effectively exhibited.

[0062] <Acrylic resin> The inner layer, the foam layer, or the outer layer may contain an acrylic resin. From the viewpoint of exerting the effects of the present invention more effectively, it is preferable that the inner layer further contains an acrylic resin. From the viewpoint of increasing the closed cell ratio of the obtained foam layer and exerting the effects of the present invention more effectively, it is preferable that the foam layer further contains an acrylic resin. From the viewpoint of exerting the effects of the present invention more effectively, it is preferable that the outer layer further contains an acrylic resin.

[0063] The acrylic resin is not particularly limited. Examples of the acrylic resin include a polymer of alkyl (meth)acrylate. The polymer of alkyl (meth)acrylate may be a copolymer. The acrylic resin may be a polymer of methyl (meth)acrylate. The polymer of methyl (meth)acrylate is a polymer in which at least methyl (meth)acrylate is used as a polymerizable component. The polymer of methyl (meth)acrylate may be a copolymer of methyl (meth)acrylate and a monomer copolymerizable with the methyl (meth)acrylate. Only one type of the acrylic resin may be used, or two or more types may be used in combination.

[0064] Examples of the monomer copolymerizable with methyl (meth)acrylate include (meth)acrylic acid alkyl esters having an alkyl group with a carbon number of 2 to 8, butylene, substituted styrene, (meth)acrylonitrile, etc. The monomer copolymerizable with methyl (meth)acrylate may be used alone or in combination of two or more kinds.

[0065] The acrylic resin may be a commercially available product, such as Metablen P-530A (manufactured by Mitsubishi Chemical Corporation).

[0066] From the viewpoint of exerting the effects of the present invention more effectively, the weight average molecular weight of the acrylic resin is preferably 2.5 million or more, more preferably 3 million or more, and preferably 8 million or less, more preferably 6 million or less.

[0067] In order to more effectively exert the effects of the present invention, the weight average molecular weight of the acrylic resin is preferably larger than the weight average molecular weights of the vinyl chloride resin and the chlorinated vinyl chloride resin.

[0068] The ratio of the weight average molecular weight of the acrylic resin to the weight average molecular weight of the vinyl chloride resin and the chlorinated vinyl chloride resin is the ratio (weight average molecular weight of the acrylic resin / weight average molecular weight of the vinyl chloride resin and the chlorinated vinyl chloride resin). From the viewpoint of increasing the closed cell ratio of the obtained foamed layer and more effectively exerting the effects of the present invention, the ratio (weight average molecular weight of the acrylic resin / weight average molecular weight of the vinyl chloride resin and the chlorinated vinyl chloride resin) is preferably more than 1.0, more preferably 1.1 or more. The ratio (weight average molecular weight of the acrylic resin / weight average molecular weight of the vinyl chloride resin and the chlorinated vinyl chloride resin) may be 5000 or less, or may be 3000 or less.

[0069] The weight average molecular weight of the acrylic resin, the vinyl chloride resin and the chlorinated vinyl chloride resin indicates a weight average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC).

[0070] When the inner layer contains the acrylic resin, the content of the acrylic resin in 100% by weight of the inner layer is preferably 5% by weight or more, more preferably 10% by weight or more, and preferably 50% by weight or less, more preferably 45% by weight or less. When the content of the acrylic resin is equal to or more than the lower limit and equal to or less than the upper limit, the effects of the present invention can be more effectively exhibited.

[0071] When the foam layer contains the acrylic resin, the content of the acrylic resin in 100% by weight of the foam layer is preferably 5% by weight or more, more preferably 10% by weight or more, and preferably 50% by weight or less, more preferably 45% by weight or less. When the content of the acrylic resin is equal to or more than the lower limit and equal to or less than the upper limit, the bubble retention is increased, and the expansion ratio can be effectively increased.

[0072] When the outer layer contains the acrylic resin, the content of the acrylic resin in 100% by weight of the outer layer is preferably 5% by weight or more, more preferably 10% by weight or more, and preferably 50% by weight or less, more preferably 45% by weight or less. When the content of the acrylic resin is equal to or more than the lower limit and equal to or less than the upper limit, the effects of the present invention can be more effectively exhibited.

[0073] In the inner layer, the content of the acrylic resin is preferably 5 parts by weight or more, more preferably 8 parts by weight or more, and even more preferably 10 parts by weight or more, based on 100 parts by weight of the total of the vinyl chloride resin and the chlorinated vinyl chloride resin. In the inner layer, the content of the acrylic resin is preferably 40 parts by weight or less, more preferably 35 parts by weight or less, even more preferably 30 parts by weight or less, and particularly preferably 25 parts by weight or less, based on 100 parts by weight of the total of the vinyl chloride resin and the chlorinated vinyl chloride resin. When the content of the acrylic resin is the above lower limit or more and the above upper limit or less, the effects of the present invention can be more effectively exhibited.

[0074] In the foam layer, the content of the acrylic resin is preferably 5 parts by weight or more, more preferably 8 parts by weight or more, and even more preferably 10 parts by weight or more, based on 100 parts by weight of the total of the vinyl chloride resin and the chlorinated vinyl chloride resin. In the foam layer, the content of the acrylic resin is preferably 40 parts by weight or less, more preferably 35 parts by weight or less, even more preferably 30 parts by weight or less, and particularly preferably 25 parts by weight or less, based on 100 parts by weight of the total of the vinyl chloride resin and the chlorinated vinyl chloride resin. When the content of the acrylic resin is the above lower limit or more and the above upper limit or less, the bubble retention is increased, and the expansion ratio can be effectively increased.

[0075] In the outer layer, the content of the acrylic resin is preferably 5 parts by weight or more, more preferably 8 parts by weight or more, and even more preferably 10 parts by weight or more, based on 100 parts by weight of the total of the vinyl chloride resin and the chlorinated vinyl chloride resin. In the outer layer, the content of the acrylic resin is preferably 40 parts by weight or less, more preferably 35 parts by weight or less, even more preferably 30 parts by weight or less, and particularly preferably 25 parts by weight or less, based on 100 parts by weight of the total of the vinyl chloride resin and the chlorinated vinyl chloride resin. When the content of the acrylic resin is the above lower limit or more and the above upper limit or less, the effects of the present invention can be more effectively exhibited.

[0076] <Metal phosphates or metal phosphites> The layer (X) contains a metal phosphate or a metal phosphite. The layer (X) may contain a metal phosphate, may contain a metal phosphite, or may contain both a metal phosphate and a metal phosphite.

[0077] Examples of the metal phosphate or metal phosphite include ammonium salts such as ammonium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate; sodium salts such as monosodium phosphate, disodium phosphate, trisodium phosphate, monosodium phosphite, disodium phosphite, and sodium hypophosphite; potassium salts such as monopotassium phosphate, dipotassium phosphate, tripotassium phosphate, monopotassium phosphite, dipotassium phosphite, and potassium hypophosphite; lithium salts such as monolithium phosphate, dilithium phosphate, trilithium phosphate, monolithium phosphite, dilithium phosphite, and lithium hypophosphite; barium salts such as barium dihydrogen phosphate, barium hydrogen phosphate, tribarium phosphate, and barium hypophosphite; magnesium salts such as monohydrogen magnesium phosphate, magnesium hydrogen phosphate, trimagnesium phosphate, and magnesium hypophosphite; calcium salts such as calcium dihydrogen phosphate, calcium hydrogen phosphate, tricalcium phosphate, and calcium hypophosphite; zinc salts such as zinc phosphate, zinc phosphite, and zinc hypophosphite; and aluminum salts such as monoaluminum phosphate, dialuminum phosphate, trialuminum phosphate, aluminum phosphite, and aluminum hypophosphite. The metal phosphates or metal phosphites may be used alone or in combination of two or more kinds.

[0078] From the viewpoint of further improving fire resistance, the layer (X) is preferably a layer containing the thermoplastic resin and a metal phosphite, and more preferably a layer containing the thermoplastic resin and aluminum phosphite. From the viewpoint of further improving fire resistance, at least one layer among the inner layer, the foamed layer, and the outer layer is preferably a layer containing the thermoplastic resin and a metal phosphite, and more preferably a layer containing the thermoplastic resin and aluminum phosphite.

[0079] In the layer (X) containing the thermoplastic resin and the metal phosphate or metal phosphite, the total content of the metal phosphate and the metal phosphite is preferably 0.1 parts by weight or more, more preferably 1 part by weight or more, even more preferably 2 parts by weight or more, and particularly preferably 3 parts by weight or more, relative to 100 parts by weight of the thermoplastic resin. In the layer (X), the total content of the metal phosphate and the metal phosphite is preferably 10 parts by weight or less, more preferably 9 parts by weight or less, and even more preferably 8 parts by weight or less, relative to 100 parts by weight of the thermoplastic resin. When the total content of the metal phosphate and the metal phosphite is the lower limit or more and the upper limit or less, the fire resistance can be further improved. In addition, when the layer (X) contains both the metal phosphate and the metal phosphite, the "total content of the metal phosphate and the metal phosphite" refers to the sum of the content of the metal phosphate and the content of the metal phosphite. When the layer (X) contains the metal phosphate but not the metal phosphite, the "total content of the metal phosphate and the metal phosphite" refers to the content of the metal phosphate. When the layer (X) does not contain the metal phosphate but does contain the metal phosphite, the "total content of the metal phosphate and the metal phosphite" refers to the content of the metal phosphite (hereinafter the same).

[0080] When the inner layer contains the thermoplastic resin and the metal phosphate or metal phosphite, the total content of the metal phosphate and the metal phosphite in the inner layer is preferably 0.1 parts by weight or more, more preferably 1 part by weight or more, relative to 100 parts by weight of the thermoplastic resin in the inner layer. In this case, the total content of the metal phosphate and the metal phosphite in the inner layer is more preferably 2 parts by weight or more, particularly preferably 3 parts by weight or more, relative to 100 parts by weight of the thermoplastic resin in the inner layer. When the inner layer contains the thermoplastic resin and the metal phosphate or metal phosphite, the total content of the metal phosphate and the metal phosphite in the inner layer is preferably 10 parts by weight or less, more preferably 9 parts by weight or less, and even more preferably 8 parts by weight or less, relative to 100 parts by weight of the thermoplastic resin in the inner layer. When the total content of the metal phosphate and the metal phosphite is the lower limit or more and the upper limit or less, the fire resistance can be further improved.

[0081] When the foam layer contains the thermoplastic resin and the metal phosphate or metal phosphite, the total content of the metal phosphate and the metal phosphite in the foam layer is preferably 1 part by weight or more, more preferably 2 parts by weight or more, and even more preferably 4 parts by weight or more, per 100 parts by weight of the thermoplastic resin in the foam layer. When the foam layer contains the thermoplastic resin and the metal phosphate or metal phosphite, the total content of the metal phosphate and the metal phosphite in the foam layer is preferably 10 parts by weight or less, more preferably 9 parts by weight or less, and even more preferably 7 parts by weight or less, per 100 parts by weight of the thermoplastic resin in the foam layer. When the total content of the metal phosphate and the metal phosphite is the above lower limit or more and the above upper limit or less, the foam layer can be molded to a constant thickness when producing a multi-layer pipe.

[0082] When the outer layer contains the thermoplastic resin and the metal phosphate or metal phosphite, the total content of the metal phosphate and the metal phosphite in the outer layer is preferably 0.1 parts by weight or more, more preferably 1 part by weight or more, relative to 100 parts by weight of the thermoplastic resin in the outer layer. In this case, the total content of the metal phosphate and the metal phosphite in the outer layer is more preferably 2 parts by weight or more, particularly preferably 3 parts by weight or more, relative to 100 parts by weight of the thermoplastic resin in the outer layer. When the outer layer contains the thermoplastic resin and the metal phosphate or metal phosphite, the total content of the metal phosphate and the metal phosphite in the outer layer is preferably 10 parts by weight or less, more preferably 9 parts by weight or less, and even more preferably 8 parts by weight or less, relative to 100 parts by weight of the thermoplastic resin in the outer layer. When the total content of the metal phosphate and the metal phosphite is the lower limit or more and the upper limit or less, the impact resistance can be further improved.

[0083] <Chemical foaming agent> The material of the foam layer preferably contains a chemical foaming agent.The foam layer preferably contains a foam foamed by a chemical foaming agent.

[0084] The above-mentioned chemical foaming agent includes inorganic foaming agents and organic foaming agents. The above-mentioned chemical foaming agent may be an inorganic foaming agent or an organic foaming agent. The above-mentioned chemical foaming agent may be used alone or in combination of two or more kinds.

[0085] 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 agent may be used alone or in combination of two or more kinds.

[0086] 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 kinds.

[0087] Examples of the azo-based foaming agent include azodicarbonamide and barium azodicarboxylate.

[0088] The amine-based foaming agent includes dinitrosopentamethylenetetramine.

[0089] From the viewpoint of effectively exerting the effects of the present invention, the chemical foaming agent is preferably an inorganic foaming agent. From the viewpoint of more effectively exerting the effects of the present invention, the chemical foaming agent is preferably a carbonic acid foaming agent. In particular, when the chemical foaming agent is a carbonic acid foaming agent, a foam having a high closed cell ratio, excellent moldability, and good appearance can be obtained.

[0090] Examples of the carbonate foaming agent include sodium bicarbonate (sodium hydrogen carbonate), sodium carbonate, and ammonium bicarbonate. From the viewpoint of more effectively exerting the effects of the present invention, the carbonate foaming agent preferably contains sodium bicarbonate (sodium hydrogen carbonate), sodium carbonate, or ammonium bicarbonate, and more preferably contains sodium bicarbonate (sodium hydrogen carbonate). The carbonate foaming agent may be used alone or in combination of two or more kinds.

[0091] 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.

[0092] The chemical foaming agent is preferably a thermal decomposition type foaming agent. The thermal decomposition type foaming agent is a foaming agent that self-decomposes when heated to generate gas. The chemical foaming agent is preferably a thermal decomposition type foaming agent having a decomposition temperature higher than the softening point of vinyl chloride resin. The chemical foaming agent is preferably a thermal decomposition type foaming agent having a decomposition temperature higher than the softening point of chlorinated vinyl chloride resin. The chemical foaming agent is preferably a thermal decomposition type foaming agent having a decomposition temperature higher than the softening point of acrylic resin.

[0093] The decomposition temperature of the chemical foaming agent is preferably 130° C. or higher, more preferably 140° C. or higher, and even more preferably 150° C. or higher, and is preferably 220° C. or lower, more preferably 210° C. or lower, and even more preferably 200° C. or lower. When the decomposition temperature of the chemical foaming agent is equal to or higher than the above lower limit and equal to or lower than the above upper limit, the closed cell ratio of the foamed layer can be increased, and the effects of the present invention can be more effectively exhibited.

[0094] The decomposition temperature of the chemical foaming agent can be measured, for example, as follows: The chemical foaming agent is heated in air at a temperature increase rate of 5°C / min from 100°C using a melting point measuring device (e.g., "B540" manufactured by Buchi), and the temperature at which a change in color tone of the chemical foaming agent is visually confirmed is taken as the decomposition temperature of the chemical foaming agent.

[0095] The amount of gas generated when the chemical foaming agent is foamed is preferably 130 ml / g or more, more preferably 140 ml / g or more, even more preferably 150 ml / g or more, and is preferably 220 ml / g or less, more preferably 200 ml / g or less, and even more preferably 180 ml / g or less. When the amount of gas generated when the chemical foaming agent is foamed is equal to or more than the lower limit and equal to or less than the upper limit, the closed cell ratio and the foaming ratio can be increased, so that the effect of the present invention can be more effectively exhibited.

[0096] The amount of gas generated when the chemical foaming agent foams can be measured, for example, as follows. 1.0 g of the chemical foaming agent is placed in a test tube, 10 mL of a heat transfer medium (liquid paraffin) is added to the test tube, and the test tube is connected to a gas burette with a rubber tube. The test tube is immersed in an oil bath at 100°C and heated to 200°C at a temperature increase rate of 5°C / min. All gas generated during heating is collected with a gas burette, and the amount of gas generated (mL) per 1.0 g of the chemical foaming agent is measured. The total amount of gas generated at each temperature is graphed, and the total amount of gas generated at the temperature at which the amount of gas generated becomes constant is regarded as the amount of gas generated when the chemical foaming agent foams.

[0097] The content of the chemical foaming agent in 100% by weight of the material of the foam layer (foam) is preferably 2.0% by weight or more, more preferably 3.0% by weight or more, even more preferably 4.0% by weight or more, and is preferably 15% by weight or less, more preferably 13% by weight or less, and even more preferably 10% by weight or less. When the content of the chemical foaming agent is equal to or more than the lower limit and equal to or less than the upper limit, the closed cell ratio and the expansion ratio can be increased, so that the effects of the present invention can be more effectively exhibited.

[0098] <Other ingredients> The materials of the inner layer, the foam layer, and the outer layer may contain additives as necessary. Examples of the additives include fillers, heat stabilizers, stabilizing aids, lubricants, flame retardants, nucleating agents, and pigments. The additives may be used alone or in combination of two or more.

[0099] Examples of the filler include inorganic fillers and organic fillers. From the viewpoint of more effectively exerting the effects of the present invention, the filler is preferably an inorganic filler. Examples of the inorganic filler include carbonates such as talc, heavy calcium carbonate, precipitated calcium carbonate, and colloidal calcium carbonate, aluminum hydroxide, magnesium hydroxide, titanium oxide, clay, mica, wollastonite, zeolite, silica, zinc oxide, magnesium oxide, carbon black, graphite, glass beads, glass fibers, carbon fibers, and metal fibers. Examples of the organic filler include polyamide. Only one type of the filler may be used, or two or more types may be used in combination.

[0100] 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; barium-cadmium-based stabilizers, etc. The heat stabilizers may be used alone or in combination of two or more.

[0101] Examples of the stabilizing aid include epoxidized soybean oil, epoxidized linseed oil, epoxidized tetrahydrophthalate, epoxidized polybutadiene, phosphate ester, polyol, hydrotalcite, zeolite, etc. The stabilizing aid may be used alone or in combination of two or more kinds.

[0102] The lubricant may be an internal lubricant or an external lubricant. The lubricant may be used alone or in combination of two or more kinds.

[0103] 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. The internal lubricant may be used alone or in combination of two or more.

[0104] The external lubricant is used for the purpose of increasing 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 montanic acid wax. The external lubricant may be used alone or in combination of two or more.

[0105] 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.

[0106] The nucleating agent includes inorganic compounds such as silica, calcium silicate, wollastonite, kaolin, clay, mica, zinc oxide, calcium carbonate, zeolite, and talc.

[0107] <Foam layer> The foam layer preferably contains a foam foamed with a chemical foaming agent, and is preferably a foam foamed with a chemical foaming agent.

[0108] The specific gravity of the foam layer (foam) is preferably 0.05 or more, more preferably 0.08 or more, and even more preferably 0.10 or more, and is preferably 0.20 or less, more preferably 0.18 or less, and even more preferably 0.15 or less. When the specific gravity of the foam layer is equal to or more than the lower limit, the impact resistance can be further improved. When the specific gravity of the foam layer is equal to or less than the upper limit, the heat insulating property can be further improved.

[0109] The specific gravity of the foamed layer (foam) can be measured as follows. The multilayer pipe is cut to an arbitrary length. The inner and outer layers are cut and removed from the cut multilayer pipe to obtain a test piece consisting of only the foamed layer. The specific gravity of the obtained test piece is measured with an electronic specific gravity meter and is regarded as the specific gravity of the foamed layer.

[0110] The closed cell ratio of the foam layer is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, and particularly preferably 80% or more. When the closed cell ratio of the foam layer is equal to or more than the lower limit, when water infiltrates into the foam layer from the end of the multilayer tube due to capillary action or the like, the risk of water permeating the entire foam layer through the bubbles can be reduced. Therefore, the deterioration of the heat insulating property can be suppressed. 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.

[0111] The closed cell ratio of the foamed layer can be measured as follows. The multilayer pipe is cut to an arbitrary length. The inner and outer layers are cut and removed from the cut multilayer pipe to obtain a test piece consisting only of the foamed layer. The thickness of the test piece is measured and the apparent volume V1 of the test piece is calculated. Furthermore, the weight W1 of the test piece is measured. Next, the volume V2 occupied by the bubbles in the test piece is calculated based on the following formula. The density of the test piece is ρ.

[0112] V2=V1-W1 / ρ V1: Apparent volume of the test piece (cm 3 ) V2: Volume occupied by the air bubble in the test piece (cm 3 ) W1: weight of the test piece (g) ρ: Density of test piece (g / cm 3 )

[0113] Next, the test piece is submerged in water at 23°C to a depth of 100 mm from the water surface, and a specified pressure is applied to the test piece for a specified period of time. After that, the test piece is taken out of the water, the water adhering to the surface of the test piece is removed, and the weight W2 of the test piece is measured.

[0114] The closed cell ratio F1 of the test piece is calculated using the following formula.

[0115] F1 = 100-100 × (W2-W1) / V2 F1: Closed cell rate of the test piece (%) W1: Weight of the test piece before submerging in water (g) W2: Weight of the test piece after submerging in water (g) V2: Volume occupied by the air bubble in the test piece (cm 3 )

[0116] The size of the test piece used to measure the closed cell ratio may be 50 mm long x 50 mm wide x 5 mm thick.

[0117] The expansion ratio of the foam layer is preferably 4 times or more, more preferably 6 times or more, and preferably 30 times or less, more preferably 25 times or less, and even more preferably 20 times or less. When the expansion ratio is equal to or more than the lower limit, the heat insulating property can be further improved. When the expansion ratio is equal to or less than the upper limit, the bubble diameter can be made uniform, and the closed cell ratio can be increased. When the closed cell ratio is high, for example, when water penetrates into the foam layer from the end of the multilayer tube due to capillary phenomenon or the like, the risk of water permeating the entire foam layer through the bubbles can be reduced. Therefore, the decrease in heat insulating property can be suppressed.

[0118] The expansion ratio of the foamed layer can be measured as follows. The multi-layer pipe is cut to a length of 50 mm in the axial direction. The cut multi-layer pipe is then cut along the axial direction so as to divide it into four equal parts in the circumferential direction, and the inner and outer layers are then cut and removed to prepare four 50 mm long plate-shaped test pieces composed only of the foamed layer. Using a water displacement specific gravity measuring device, the apparent density of each of the four test pieces at 23°C ± 2°C is determined to three decimal places in accordance with JIS K7112:1999. The expansion ratio for one test piece is calculated according to the following formula (1), and the average value of the expansion ratios of the four test pieces is taken as the expansion ratio of the foamed layer.

[0119] m = γo / γ (1) m: Foaming ratio γ: Apparent density of the test piece (g / cm 3 ) γo: Density of the foam layer material (g / cm 3 )

[0120] The density (γo) of the foam layer material is the density of the foam layer material before the foam layer is formed, that is, the density when unfoamed.

[0121] The density (γo) of the material of the foam layer is, when the material of the foam layer contains components (additives) other than the resin in the foam layer, 0.1 g / cm 3 from the density of the resin in the foam layer. 3 As the density (γo) of the material of the foam layer, for example, the density of the resin described in the Chemical Handbook (Applied Chemistry Volume II, Materials Volume) may be used.

[0122] (Inner and outer layers) The inner layer and the outer layer are preferably not foamed layers (foams), and are preferably non-foamed layers.

[0123] From the viewpoint of improving the adhesion between the inner layer and the outer layer and the foam layer, the inner layer and the outer layer preferably contain the vinyl chloride resin or the chlorinated vinyl chloride resin.

[0124] The materials for the inner layer and the outer layer (the compositions for obtaining the inner layer and the outer layer) preferably do not contain a foaming agent.

[0125] The materials for the inner layer and the outer layer (compositions for obtaining the inner layer and the outer layer) may contain the additives described above.

[0126] (Manufacturing method of multi-layer pipes) Fig. 2 is a plan view showing a schematic diagram of a manufacturing apparatus used for manufacturing a multi-layer pipe according to one embodiment of the present invention. Fig. 3 is a front view showing a schematic diagram of a manufacturing apparatus used for manufacturing a multi-layer pipe according to one embodiment of the present invention. Figs. 2 and 3 are schematic diagrams showing a manufacturing apparatus for manufacturing a multi-layer pipe 10.

[0127] The manufacturing apparatus 20 includes an inner / 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 / 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 take-up machine 16 is connected to the cutter 17. A gas cylinder 18 and a metering pump 19 are connected to the foam layer extruder 12.

[0128] The materials for the inner layer and the outer layer are fed from a hopper, and in the inner and outer layer extruder 11 the materials for the inner layer and the outer layer (compositions for obtaining the inner layer and the outer layer) are melt-kneaded and extruded into a die 13 .

[0129] 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 a die 13 .

[0130] From the outlet of the die 13, an uncured multi-layer tube having a three-layer structure is extruded.

[0131] A tube 14 for forming the outer surface of the uncured multi-layer pipe to a predetermined dimension 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.

[0132] FIG. 4 is an enlarged cross-sectional view showing a mold portion and a tube portion for forming an outer surface of a pipe in a manufacturing apparatus.

[0133] 4, the inner layer material 21 and the outer layer material 23 melt-kneaded by the inner and outer layer extruders, and the foam layer material 22 melt-kneaded by the foam layer extruder are injected into a mold 13 to form an uncured multi-layer pipe 10X. The uncured multi-layer pipe 10X includes an uncured inner layer 31, an uncured outer layer 33, and an uncured foam layer 32.

[0134] The uncured multi-layer pipe 10X is inserted into a tube 14 for forming the outer surface of the pipe, and the uncured multi-layer pipe 10X is cooled in a cooling water tank while being molded to a predetermined size.

[0135] 2 and 3, a take-off machine 16 takes up the multi-layer pipe 10 cooled in the cooling water tank 15, and a cutter 17 cuts the multi-layer pipe 10 sent from the take-off machine 16 to a predetermined length. In this way, a multi-layer pipe 10 having a predetermined length is obtained.

[0136] The heating temperature in the mold 13 is preferably 140° C. or more, more preferably 160° C. or more, and preferably 200° C. or less, more preferably 190° C. or less. The heating time in the mold 13 is preferably 10 minutes or more, preferably 30 minutes or less, more preferably 20 minutes or less.

[0137] 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.

[0138] The following materials were prepared:

[0139] (Inner and outer layer materials) Thermoplastic: Polyvinyl chloride resin (Tokuyama Sekisui Kogyo Co., Ltd. "TS-1000R") Chlorinated polyvinyl chloride resin (Tokuyama Sekisui Kogyo Co., Ltd. "HA-05K", chlorine content 67.5% by weight, average degree of polymerization 500) Metal phosphates or phosphites: Aluminum phosphite (metal phosphite, "APA100" manufactured by Taihei Chemical Industry Co., Ltd.) Sodium phosphate monobasic (metallic phosphate, "Sodium phosphate monobasic (anhydrous)" manufactured by Taihei Chemical Industry Co., Ltd.) Other ingredients: Trixylenyl phosphate ("TXP" manufactured by Daihachi Chemical Industry Co., Ltd.) Acrylic resin (Kaneka Corporation "Kane Ace PA-20") Methyl methacrylate-butadiene-styrene copolymer (MBS resin) (Kaneka Corporation "B-564") Organotin stabilizer ("TVS-8832" manufactured by Nitto Kasei Co., Ltd.) Lubricant (Mitsui Chemicals "Hiwax 220MP") Lubricant (Emery Oleochemicals Japan "Roxiol 259") Calcium carbonate (Shiraishi Kogyo Co., Ltd. "CCR") Coloring agent (manufactured by Resinocolor)

[0140] (Foam layer material) Thermoplastic: Polyvinyl chloride resin (Tokuyama Sekisui Kogyo Co., Ltd. "TS-1000R") Chlorinated polyvinyl chloride resin (Tokuyama Sekisui Kogyo Co., Ltd. "HA-05K", chlorine content 67.5% by weight, average degree of polymerization 500) Metal phosphates or phosphites: Aluminum phosphite ("APA100" manufactured by Taihei Chemical Industry Co., Ltd.) Sodium phosphate monobasic (metallic phosphate, "Sodium phosphate monobasic (anhydrous)" manufactured by Taihei Chemical Industry Co., Ltd.) Other ingredients: Trixylenyl phosphate ("TXP" manufactured by Daihachi Chemical Industry Co., Ltd.) Acrylic resin (Kaneka Corporation "Kane Ace PA-20") Foaming agent (sodium bicarbonate, "Celbon SC-855" manufactured by Eiwa Chemical Industry Co., Ltd.) Organotin stabilizer ("TVS-8832" manufactured by Nitto Kasei Co., Ltd.) Lubricant (Emery Oleochemicals Japan "Roxiol 259") Colorant (Hexa Chemical's "D-13486")

[0141] Example 1 Preparation of inner and outer layer materials: The following components were mixed and stirred in a 200-liter Henschel mixer (Kawata) to obtain materials for the inner and outer layers (compositions for obtaining the inner and outer layers): 100 parts by weight of vinyl chloride resin (Tokuyama Sekisui Kogyo Co., Ltd., "TS-1000R"); 0.1 parts by weight of aluminum phosphite (Taihei Chemical Industry Co., Ltd., "APA100"); 1 part by weight of acrylic resin (Kaneka Corporation, "Kane Ace PA-20"); 1 part by weight of MBS resin (Kaneka Corporation, "B-564"); 1 part by weight of organotin stabilizer (Nitto Kasei Co., Ltd., "TVS-8832"); 1 part by weight of lubricant (Mitsui Chemicals, Inc., "Hiwax 220MP"); 1 part by weight of lubricant (Emery Oleochemicals Japan, Inc., "Roxiol 259"); 1 part by weight of calcium carbonate (Shiraishi Kogyo Co., Ltd., "CCR"). Colorant (manufactured by Resinocolor), 1 part by weight.

[0142] Preparation of foam layer material: The following components were mixed and stirred in a 200-liter Henschel mixer (Kawata Corporation) to obtain a foam layer material (composition for obtaining a foam layer): 100 parts by weight of vinyl chloride resin (Tokuyama Sekisui Kogyo Co., Ltd., "TS-1000R"); 1 part by weight of acrylic resin (Kaneka Corporation, "Kane Ace PA-20"); 3 parts by weight of foaming agent (Eiwa Kasei Kogyo Co., Ltd., "Celbon SC-855"); 1 part by weight of organotin stabilizer (Nitto Kasei Co., Ltd., "TVS-8832"); 1 part by weight of lubricant (Emery Oleochemicals Japan, "Roxiol 259"); 1 part by weight of colorant (Hexa Chemical Co., Ltd., "D-13486").

[0143] Fabrication of multi-layer tubes: The obtained foam layer, inner layer and outer layer materials were extruded by the method described above while adjusting the extrusion speed, extrusion amount, extrusion temperature, etc. so that each layer had the thickness shown in Table 1, to produce a multi-layer pipe.

[0144] (Examples 2 to 11 and Comparative Examples 1 to 4) Materials for the inner layer, foam layer, and outer layer were obtained in the same manner as in Example 1, except that the blending amounts of the vinyl chloride resin, chlorinated vinyl chloride resin, aluminum phosphite, monosodium phosphate, and trixylenyl phosphate were changed as shown in Tables 1 to 4. A multi-layer pipe was produced in the same manner as in Example 1, except that the obtained materials for the inner layer, foam layer, and outer layer were used.

[0145] (evaluation) (1) Thermal insulation The obtained multi-layer pipe, 4 m long, was placed in a constant temperature and humidity environment of 20°C and 80% RH with a gradient of 1 / 50. After 7°C tap water was run 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.

[0146] [Insulation criteria] ○: No condensation ×: Condensation is occurring

[0147] (2) Fire resistance (2-1) Weight change rate A test piece having a length of 50 mm was cut out from the obtained multi-layer tube. The test piece was placed in a heat-resistant glass container and heated in an electric furnace at 950°C for 5 minutes, and then removed from the electric furnace and allowed to cool at room temperature. The weight of the test piece before and after heating was measured, and the weight change rate represented by the following formula was calculated. The fire resistance (weight change rate) was evaluated according to the following criteria.

[0148] Weight change rate (%) = (weight of test specimen before heating - weight of test specimen after heating) x 100 / weight of test specimen before heating

[0149] [Criteria for fire resistance (weight change rate)] ○: Weight change rate is less than 87.0% ×: Weight change rate is 87.0% or more

[0150] (2-2)Residue strength Five test pieces measuring 30 mm ± 1 mm in length, 30 mm ± 1 mm in width, and 3 mm ± 0.1 mm in thickness were cut from the outer surface of the multi-layer pipe. A through hole with a diameter of about 1 mm was drilled at each end of the five test pieces, and the pieces were hung on a metal stand through a wire and heated in an electric furnace at 500°C for 3 minutes, after which the combustion residue was removed. The number of test pieces that had fallen from the metal stand after heating was counted. Fire resistance (residue strength) was judged according to the following criteria.

[0151] [Criteria for determining fire resistance (residue strength)] ○: 0 or 1 test piece fell ×: Two or more test pieces dropped

[0152] The structure and results of the multi-layer pipe are shown in Tables 1 to 4.

[0153] [Table 1]

[0154] [Table 2]

[0155] [Table 3]

[0156] [Table 4] [Explanation of symbols]

[0157] 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 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…Uncured inner layer 32…Uncured foam layer 33…Uncured outer layer

Claims

1. An inner layer, a foam layer disposed on the outer side of the inner layer, and an outer layer disposed on the outer side of the foam layer, At least one of the inner layer, the foam layer, and the outer layer is a layer containing a thermoplastic resin and a metal phosphate or a metal phosphite.

2. 2. The multi-layer pipe according to claim 1, wherein the thermoplastic resin comprises a polyvinyl chloride resin or a chlorinated polyvinyl chloride resin.

3. 3. A multi-layer pipe according to claim 1 or 2, wherein in the layer containing the thermoplastic resin and the metal phosphate or the metal phosphite, the total content of the metal phosphate and the metal phosphite is 0.1 parts by weight or more and 10 parts by weight or less per 100 parts by weight of the thermoplastic resin.

4. 3. The multi-layer pipe according to claim 1, wherein the inner layer comprises the thermoplastic resin and the metal phosphate or metal phosphite.

5. 3. The multi-layer pipe according to claim 1, wherein the outer layer comprises the thermoplastic resin and the metal phosphate or metal phosphite.

6. 3. The multi-layer pipe according to claim 1, wherein the layer containing the thermoplastic resin and the metal phosphate or the metal phosphite is a layer containing the thermoplastic resin and aluminum phosphite.

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