Multilayer pipe

Abstract

To provide a multilayer pipe that barely shows a deterioration of physical properties and has high fireproofing performance.SOLUTION: A multilayer pipe 10 has an inner layer 1, an intermediate layer 2 and an outer layer 3. The intermediate layer 2 contains a polyvinyl chloride resin and thermally-expandable graphite. The outer layer 3 has an uneven part 4 including a plurality of rib grooves 4A provided along the circumferential direction on the outer peripheral surface. The rib grooves 4A have an average depth (d) of 15%-30% relative to the total thickness (T) of the multilayer pipe 10.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] In buildings, as construction technology becomes more sophisticated, piping materials are required to have a variety of properties, and multi-layer pipes are used. Multi-layer pipes as piping materials are required to have high fire resistance, for example, for use in fire compartments.

[0003] A specific function of fire resistance required for piping materials is that the piping material expands due to the heat of fire, blocking the piping itself and preventing the spread of fire through the piping material. As such a piping material, a piping material containing thermally expandable graphite has been proposed (for example, see Patent Document 1).

[0004] In recent years, the demand for standpipes has increased, and therefore piping materials with larger diameters are required, and it is becoming important to have a wide selection of diameters. In general, when the diameter of a piping material is large, the area that is blocked when heat from a fire is applied becomes large, making it difficult to achieve fire resistance. Therefore, in order to improve the fire resistance of piping materials, it has been considered to increase the amount of thermally expandable graphite added to at least one layer of a multi-layer pipe. However, when the amount of thermally expandable graphite added is increased, there is a problem that the physical properties of the multi-layer pipe are deteriorated, such as the thermally expandable graphite becoming a crack starting point and causing cracks, resulting in a decrease in tensile strength, and the increase in the flatness of the thermally expandable graphite causing a decrease in mechanical strength. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2009-74689 A Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above circumstances, an object of the present invention is to provide a multi-layer pipe that suppresses deterioration of physical properties and has high fire resistance. [Means for solving the problem]

[0007] As a result of intensive research to achieve the above object, the inventors have found that by blending a predetermined amount of thermally expandable graphite in the intermediate layer and providing a predetermined uneven portion in the outer layer, it is possible to suppress the deterioration of physical properties and obtain a multi-layer pipe with high fire resistance. Based on this finding, the inventors have further researched and completed the present invention.

[0008] The present invention has been made to solve the above problems, and the gist of the present invention is as follows. [1] A multi-layer pipe comprising an inner layer, an intermediate layer disposed outside the inner layer, and an outer layer disposed outside the intermediate layer, wherein the intermediate layer contains polyvinyl chloride resin and thermally expandable graphite, and the outer layer has an uneven portion consisting of a plurality of rib grooves provided along the circumferential direction on the outer peripheral surface, and the average depth (d) of the rib grooves is 15% to 30% of the total wall thickness (T) of the multi-layer pipe. [2] The multi-layer pipe according to [1], wherein the average depth (d) of the rib groove is 0.5 mm to 2.5 mm. [3] The multi-layer pipe according to [1] or [2], wherein the average width (w) of the rib groove is 1.0 mm to 2.0 mm. [4] The multi-layer pipe according to any one of [1] to [3], wherein the average pitch distance (p) between adjacent rib grooves in a direction perpendicular to the circumferential direction of the outer layer is 1.0 mm to 2.0 mm. [5] The multi-layer pipe according to any one of [1] to [4], wherein the blending amount of the thermally expandable graphite is 4 parts by mass to 18 parts by mass per 100 parts by mass of the polyvinyl chloride resin. Effect of the Invention

[0009] According to the present invention, it is possible to provide a multi-layer pipe which is suppressed from deteriorating in physical properties and has high fire resistance. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1(a) is a schematic cross-sectional view of a multi-layer tube according to an embodiment of the present invention, and FIG. 1(b) is a front view of the multi-layer tube according to the embodiment of the present invention. [Diagram 2] FIG. 2 is a front view of a multi-layer pipe according to an embodiment of the present invention. [Diagram 3] 1 is a plan view showing an example of a multi-layer pipe manufacturing apparatus according to an embodiment of the present invention. [Figure 4] 1 is a front view showing an example of a multi-layer pipe manufacturing apparatus according to an embodiment of the present invention. [Diagram 5] 1 is a cross-sectional view showing an example of a mold and a tube for forming the outer surface of a multi-layer pipe used in a manufacturing apparatus for a multi-layer pipe according to an embodiment of the present invention. [Figure 6] FIG. 1 is a schematic diagram of a fire resistance test furnace used in a fire resistance performance evaluation test in an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] [Multilayer pipe] As shown in Fig. 1, a multi-layer pipe 10 according to an embodiment of the present invention includes an inner layer 1, an intermediate layer 2, and an outer layer 3. The inner layer 1 constitutes the innermost layer of the multi-layer pipe 10, and the outer layer 3 constitutes the outermost layer of the multi-layer pipe 10. The multi-layer pipe 10 shown in Fig. 1 has a multi-layer structure in which the inner layer 1, intermediate layer 2, and outer layer 3 are laminated in this order from the inside of the multi-layer pipe. Note that the structure of the multi-layer pipe 10 is not limited to three layers, and for example, the intermediate layer 2 may be multiple layers.

[0012] The outer layer 3 constituting the multi-layer pipe 10 has an uneven portion 4 consisting of a plurality of rib grooves 4A provided along the circumferential direction on the outer peripheral surface, and the average depth (d) of the rib grooves 4A is 15% to 30% of the total wall thickness (T) of the multi-layer pipe 10. The uneven portion 4 provided on the outer layer 3 increases the contact area with the backfill material of the multi-layer pipe 10, such as mortar, and provides a sufficient anchor effect to keep the combustion residues trapped, resulting in a multi-layer pipe 10 with high fire resistance. The rib grooves 4A may be arranged continuously so as to be in contact with adjacent rib grooves 4A as shown in FIG. 1(a), or may be arranged so as to have a gap between adjacent rib grooves 4A as shown in FIG. 2. The average depth (d) of the rib grooves 4A relative to the total wall thickness (T) of the multi-layer pipe 10 is preferably 16% or more, and more preferably 17% or more. When the average depth (d) of the rib grooves 4A relative to the total wall thickness (T) of the multi-layer pipe 10 is equal to or more than the above lower limit, a sufficient contact area between the uneven portion 4 and the backfill material is ensured, and an anchor effect is exerted to prevent the combustion residue from collapsing, improving fire resistance. Furthermore, the average depth (d) of the rib grooves 4A relative to the total wall thickness (T) of the multi-layer pipe 10 is preferably 29% or less, and more preferably 28% or less. By keeping the average depth (d) of the rib grooves 4A relative to the total wall thickness (T) of the multi-layer pipe 10 below the above upper limit, the amount of material of the outer layer 3 removed by machining the rib grooves 4A can be limited, a sufficient contact area between the uneven portion 4 and the backfill material is ensured, and an anchor effect is exerted to prevent the combustion residue from collapsing, improving fire resistance.

[0013] The overall wall thickness (T) of the multi-layer pipe 10 is preferably 3.6 mm to 10.3 mm, more preferably 3.7 mm to 10.2 mm, and even more preferably 3.8 mm to 10.1 mm. When the overall wall thickness (T) of the multi-layer pipe 10 is within the above range, the overall wall thickness is equivalent to a general VP nominal diameter of 40 to 150, and the multi-layer pipe 10 can be joined to a general joint.

[0014] The thickness of the inner layer 1 is preferably from 0.3 mm to 2.5 mm, more preferably from 0.4 mm to 2.4 mm, and further preferably from 0.5 mm to 2.3 mm. The thickness of the intermediate layer 2 is preferably from 2.1 mm to 9.6 mm, more preferably from 2.2 mm to 9.4 mm, and further preferably from 2.3 mm to 9.2 mm. The thickness of the outer layer 3 is preferably 0.3 mm to 2.5 mm, more preferably 0.4 mm to 2.4 mm, and further preferably 0.5 mm to 2.3 mm.

[0015] The average depth (d) of the rib grooves 4A is preferably 0.5 mm to 2.5 mm, more preferably 0.8 mm to 2.3 mm, and more preferably 1.0 mm to 2.1 mm. By having the average depth (d) of the rib grooves 4A within the above range, the contact area with the backfill material of the multi-layer pipe 10, such as mortar, is increased, and the anchor effect is sufficiently exhibited to keep the combustion residues therein, resulting in a multi-layer pipe 10 with high fire resistance. The average depth (d) of the rib grooves 4A is the average value of all the rib grooves 4A provided in the outer layer 3.

[0016] The average width (w) of the rib groove 4A is preferably 1.0 mm to 2.0 mm, more preferably 1.1 mm to 1.9 mm, and more preferably 1.2 mm to 1.8 mm. By having the average width (w) of the rib groove 4A within the above range, the contact area with the backfill material of the multi-layer pipe 10, such as mortar, is increased, and the anchor effect is sufficiently exhibited so that the combustion residue continues to remain, resulting in a multi-layer pipe 10 with high fire resistance. The average width (w) of the rib grooves 4A is the average value of all the rib grooves 4A provided in the outer layer 3.

[0017] The average pitch distance (p) between adjacent rib grooves 4A in the direction perpendicular to the circumferential direction of the outer layer 3 is preferably 1.0 mm to 2.0 mm, more preferably 1.1 mm to 1.9 mm, and more preferably 1.2 mm to 1.8 mm. By having the average pitch distance (p) between adjacent rib grooves 4A within the above range, the contact area with the backfill material of the multi-layer pipe 10, such as mortar, is increased, and the anchor effect is sufficiently exhibited to allow combustion residue to remain, resulting in a multi-layer pipe 10 with high fire resistance. The average pitch distance (p) between adjacent rib grooves 4A is the average value of all the rib grooves 4A provided in the outer layer 3.

[0018] The inner layer 1, intermediate layer 2, and outer layer 3 constituting the multi-layer pipe 10 contain polyvinyl chloride resin. In particular, the intermediate layer 2 contains polyvinyl chloride resin and thermally expandable graphite. By containing polyvinyl chloride resin and thermally expandable graphite in the intermediate layer 2, the multi-layer pipe 10 can have high fire resistance. Furthermore, by containing polyvinyl chloride resin and thermally expandable graphite in the intermediate layer 2, it is possible to suppress a decrease in tensile strength caused by cracks originating from the thermally expandable graphite, and it is possible to suppress a decrease in mechanical strength caused by increased flatness of the thermally expandable graphite.

[0019] (Polyvinyl chloride resin) As materials for forming the inner layer 1, the intermediate layer 2 and the outer layer 3, polyvinyl chloride resins are preferably used. Examples of polyvinyl chloride resins include (1) polyvinyl chloride homopolymers, (2) copolymers of vinyl chloride monomers and monomers having unsaturated bonds copolymerizable with the vinyl chloride monomers, and (3) graft copolymers in which vinyl chloride is graft-copolymerized with a (co)polymer other than vinyl chloride, and these may be used alone or in combination of two or more. If necessary, the polyvinyl chloride resins may be chlorinated.

[0020] The above (2) monomer having an unsaturated bond copolymerizable with the vinyl chloride monomer is not particularly limited, and examples thereof include α-olefins such as ethylene, propylene, butylene, etc.; vinyl esters such as vinyl acetate, vinyl propionate, etc.; vinyl ethers such as butyl vinyl ether, cetyl vinyl ether, etc.; (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl acrylate, etc.; aromatic vinyls such as styrene, α-methylstyrene, etc.; N-substituted maleimides such as N-phenylmaleimide, N-cyclohexylmaleimide, etc.; and the like. These may be used alone or in combination of two or more kinds.

[0021] The above (3) copolymer to be graft-copolymerized with vinyl chloride is not particularly limited as long as it is a copolymer to be graft-copolymerized with vinyl chloride, and examples thereof include ethylene-vinyl acetate copolymer, ethylene-vinyl acetate-carbon monoxide copolymer, ethylene-ethyl acrylate copolymer, ethylene-butyl acrylate-carbon monoxide copolymer, ethylene-methyl methacrylate copolymer, ethylene-propylene copolymer, acrylonitrile-butadiene copolymer, polyurethane, chlorinated polyethylene, chlorinated polypropylene, and the like. These may be used alone or in combination of two or more kinds.

[0022] The average polymerization degree of the polyvinyl chloride resin is not particularly limited, but a smaller average polymerization degree leads to a decrease in the physical properties of the molded product, while a larger average polymerization degree leads to an increase in melt viscosity making molding difficult, so that the average polymerization degree is preferably 400 to 1,600, more preferably 500 to 1,500, and even more preferably 600 to 1,400. The above-mentioned average degree of polymerization means an average degree of polymerization measured in accordance with JIS K 6720-2:1999 "Plastics-Vinyl chloride homopolymer and copolymer (PVC)-Part 2: Preparation of test pieces and determination of properties" using a resin obtained by dissolving a vinyl chloride resin in tetrahydrofuran (THF), removing insoluble components by filtration, and then drying and removing the THF in the filtrate.

[0023] The polymerization method for the polyvinyl chloride resin is not particularly limited, and any conventionally known polymerization method can be used, such as bulk polymerization, solution polymerization, emulsion polymerization, and suspension polymerization.

[0024] The method for chlorinating the polyvinyl chloride resin is not particularly limited, and any conventionally known chlorination method can be used, such as a thermal chlorination method and a photochlorination method.

[0025] Any of the above polyvinyl chloride resins may be crosslinked or modified to the extent that the fire resistance of the resin composition is not impaired. In this case, a resin that has been crosslinked or modified in advance may be used, or may be crosslinked or modified at the same time as the additives are blended, or may be crosslinked or modified after the above components are blended into the resin. There is no particular limitation on the method for crosslinking the above resin, and examples of the method include ordinary crosslinking methods for polyvinyl chloride resins, such as crosslinking using various crosslinking agents or peroxides, crosslinking by electron beam irradiation, and methods using water-crosslinkable materials.

[0026] (Thermal Expandable Graphite) The thermally expandable graphite contained in the vinyl chloride resin composition constituting the intermediate layer 2 is flaky, spherical, or other thermally expandable graphite. Thermally expandable graphite expands when heated, and is produced by treating powders of natural scaly graphite, pyrolytic graphite, kish graphite, or the like with an inorganic acid and a strong oxidizing agent to generate a graphite intercalation compound, which is a type of crystalline compound that maintains the layered structure of carbon. Examples of inorganic acids include concentrated sulfuric acid, nitric acid, and selenic acid. Examples of strong oxidizing agents include concentrated nitric acid, perchloric acid, perchlorates, permanganates, dichromates, and hydrogen peroxide. The thermally expandable graphite obtained by the acid treatment as described above may be further neutralized with a neutralizing agent such as ammonia, an aliphatic lower amine, an alkali metal compound, or an alkaline earth metal compound. Examples of the aliphatic lower amine include monomethylamine, dimethylamine, trimethylamine, ethylamine, propylamine, and butylamine. Examples of the alkali metal compounds and alkaline earth metal compounds include hydroxides, oxides, carbonates, sulfates, and organic acid salts of potassium, sodium, calcium, barium, magnesium, and the like. These may be used alone or in combination of two or more.

[0027] The expansion starting temperature of the thermally expandable graphite used in the present invention is preferably 150° C. or higher, more preferably 155° C. or higher, and even more preferably 160° C. or higher, from the viewpoint of preventing expansion except when a fire occurs. Moreover, from the viewpoint of increasing the volume increase rate of the thermally expandable graphite when a fire occurs and effectively exerting fire resistance, the temperature is preferably 250° C. or lower, more preferably 240° C. or lower, and even more preferably 230° C. or lower.

[0028] The content of thermally expandable graphite in the vinyl chloride resin composition constituting the intermediate layer 2 is preferably 2 parts by mass or more, more preferably 3 parts by mass or more, and even more preferably 4 parts by mass or more, relative to 100 parts by mass of polyvinyl chloride resin. When the content of thermally expandable graphite is equal to or more than the above lower limit, the thermal expandability of the intermediate layer 2 is sufficient. Furthermore, the content of thermally expandable graphite in the vinyl chloride resin composition constituting the intermediate layer 2 is preferably 20 parts by mass or less, more preferably 19 parts by mass or less, and even more preferably 18 parts by mass or less, relative to 100 parts by mass of polyvinyl chloride resin. When the content of thermally expandable graphite is equal to or less than the above upper limit, the mechanical strength of the multilayer pipe 10 is sufficient.

[0029] (Additives) The materials constituting the inner layer 1, intermediate layer 2, and outer layer 3 of the multi-layer pipe 10 of the present invention may contain additives such as inorganic fillers, lubricants, processing aids, impact modifiers, heat resistance improvers, antioxidants, light stabilizers, UV absorbers, pigments, plasticizers, thermoplastic elastomers, etc., within limits that do not impair the physical properties of the materials.

[0030] As the inorganic filler, a wide variety of known fillers can be used, and there is no particular limitation. Specific examples of the inorganic filler include silica, diatomaceous earth, alumina, zinc oxide, titanium oxide, calcium oxide, magnesium oxide, iron oxide, tin oxide, antimony oxide, ferrites, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, basic magnesium carbonate, calcium carbonate, magnesium carbonate, zinc carbonate, barium carbonate, dawnnite, hydrotalcite, calcium sulfate, barium sulfate, gypsum fiber, calcium silicate, talc, clay, mica, montmorillonite, bentonite, activated clay, sepiolite, imogolite, sericite, glass fiber, glass beads, silica-based balloon, aluminum nitride, boron nitride, silicon nitride, carbon black, graphite, carbon fiber, carbon balloon, charcoal powder, various metal powders, potassium titanate, magnesium sulfate "MOS", lead titanate zirconate, aluminum borate, molybdenum sulfide, silicon carbide, stainless steel fiber, zinc borate, various magnetic powders, slag fiber, fly ash, and dewatered sludge.

[0031] As the lubricant, a wide variety of known lubricants can be used, and there is no particular limitation. Examples of lubricants include internal lubricants and external lubricants. The internal lubricant is used for the purpose of reducing the flow viscosity of the molten resin during molding and preventing frictional heat generation. The internal lubricant is not particularly limited, and for example, one or more selected from the group consisting of butyl stearate, lauryl alcohol, stearyl alcohol, epoxy soybean oil, glycerin monostearate, stearic acid, and bisamide can be used. The external lubricant is used for the purpose of increasing the sliding effect between the molten resin and the metal surface during molding. The external lubricant is not particularly limited, and for example, one or more selected from the group consisting of paraffin wax, polyolefin wax, ester wax, and montanic acid wax can be used.

[0032] The processing aid can be a wide variety of known ones and is not particularly limited. For example, acrylic processing aids such as alkyl acrylate-alkyl methacrylate copolymers having a weight average molecular weight of 100,000 to 2,000,000 can be mentioned. The acrylic processing aid is not particularly limited, and examples thereof include n-butyl acrylate-methyl methacrylate copolymers, 2-ethylhexyl acrylate-methyl methacrylate-butyl methacrylate copolymers, etc. These may be used alone or in combination of two or more kinds.

[0033] The impact modifier may be any of a wide variety of known ones, and is not particularly limited. For example, one or more selected from the group consisting of methyl methacrylate-butadiene-styrene copolymer (MBS), chlorinated polyethylene, acrylic rubber, etc. may be used.

[0034] The heat resistance improver may be any of a wide variety of known ones, and is not particularly limited. For example, α-methylstyrene-based and N-phenylmaleimide-based resins may be used.

[0035] The antioxidant is not particularly limited, and a wide variety of known antioxidants can be used, such as phenol-based antioxidants.

[0036] The light stabilizer is not particularly limited, and a wide variety of known light stabilizers can be used, such as hindered amine light stabilizers.

[0037] The ultraviolet absorbing agent is not particularly limited, and a wide variety of known ultraviolet absorbing agents can be used. For example, ultraviolet absorbing agents such as salicylic acid esters, benzophenones, benzotriazoles, and cyanoacrylates can be used. These agents may be used alone or in combination of two or more.

[0038] The pigment is not particularly limited, and a wide variety of known pigments can be used. For example, organic pigments such as azo, phthalocyanine, threne, and dye lake pigments; inorganic pigments such as oxide, molybdenum chromate, sulfide, selenide, and ferrocyanide pigments can be used. These pigments can be used alone or in combination of two or more.

[0039] A plasticizer may be added to the polyvinyl chloride resin. The plasticizer is not particularly limited, and a wide variety of known plasticizers can be used. For example, one or more selected from the group consisting of dibutyl phthalate, di-2-ethylhexyl phthalate, and di-2-ethylhexyl adipate can be used.

[0040] The thermoplastic elastomer is not particularly limited, and a wide variety of known elastomers can be used. For example, one or more selected from the group consisting of vinyl chloride thermoplastic elastomers such as acrylonitrile-butadiene copolymer (NBR), ethylene-vinyl acetate copolymer (EVA), ethylene-vinyl acetate-carbon monoxide copolymer (EVACO), vinyl chloride-vinyl acetate copolymer, and vinyl chloride-vinylidene chloride copolymer, styrene thermoplastic elastomers, olefin thermoplastic elastomers, urethane thermoplastic elastomers, polyester thermoplastic elastomers, and polyamide thermoplastic elastomers can be used.

[0041] The method for mixing the thermally expandable graphite and additives with the polyvinyl chloride resin can be widely used by known methods, specifically, a method by hot blending, a method by cold blending, etc.

[0042] <Applications of multi-layer pipes> The multi-layer pipe 10 of the present invention obtained as described above is inhibited from deteriorating in physical properties and has high fire resistance, and therefore can be suitably used as piping for buildings such as drainage pipes, ducts, and electric conduits. The multi-layer pipe of the present invention can be suitably used not only as a constituent material for the main body of a pipe, but also as a constituent material for pipe joints.

[0043] <Manufacturing method of multi-layer pipe> Fig. 3 is a plan view showing a manufacturing apparatus 20 used for manufacturing the multi-layer pipe 10 according to one embodiment of the present invention. Fig. 4 is a front view showing a manufacturing apparatus 20 used for manufacturing the multi-layer pipe 10 according to one embodiment of the present invention. As shown in Figures 3 and 4, a manufacturing apparatus 20 for manufacturing a multi-layer pipe 10 includes an inner and outer layer extruder 11, an intermediate layer extruder 12, a die 13, a cooling water tank 15, a take-up machine 16, and a cutter 17. The die 13 is connected to the inner and outer layer extruder 11 and the intermediate layer extruder 12. The die 13 is connected to the cooling water tank 15. The take-up machine 16 is connected to the cooling water tank 15. The take-up machine 16 is connected to the cutter 17.

[0044] In the method for producing a multi-layer pipe of the present invention, first, the materials for the inner layer and the outer layer are fed into an inner / outer layer extruder 11 using a hopper, where the materials for the inner layer and the outer layer are melt-kneaded and extruded into a die 13. In addition, the material for the intermediate layer is fed into an intermediate layer extruder 12 using a hopper, where the material for the intermediate layer is melt-kneaded and extruded into a die 13.

[0045] Next, in the mold 13, the melt-kneaded mixture of the inner layer material, the outer layer material, and the melt-kneaded mixture of the intermediate layer material are heated to form an uncured multi-layer pipe having a three-layer structure. From the viewpoint of improving the fluidity of the materials for the inner layer, intermediate layer and outer layer, the heating temperature in the mold 13 is preferably 160°C or higher and 200°C or lower, more preferably 170°C or higher and 195°C or lower, and even more preferably 180°C or higher and 190°C or lower. The heating time in mold 13 is the time that the materials for the inner layer, intermediate layer, and outer layer are present in mold 13, and from the viewpoint of improving the fluidity of the materials for the inner layer, intermediate layer, and outer layer, is preferably from 3 minutes to 10 minutes, more preferably from 4 minutes to 9 minutes, and even more preferably from 5 minutes to 8 minutes.

[0046] Next, an uncured multi-layer pipe having a three-layer structure is extruded from the outlet of the mold 13 and sent to a cooling water tank 15. A tube 14 for forming the outer surface of the pipe is attached to the cooling water tank 15 to form the uncured multi-layer pipe into a predetermined size, and the outer surface of the uncured multi-layer pipe is cooled in contact with the tube 14 for forming the outer surface of the pipe. FIG. 5 is an enlarged cross-sectional view of the mold 13 and the tube 14 for forming the outer surface of the pipe in the manufacturing apparatus. As shown in FIG. 5, the inner layer material 21 and the outer layer material 23 melt-kneaded by the inner and outer layer extruder 11, and the intermediate layer material 22 melt-kneaded by the intermediate layer extruder 12 are injected into the mold 13 designed so that the outer peripheral edge of the cross-sectional shape of the intermediate layer becomes a perfect circle, and an uncured multi-layer pipe 10' is molded. The uncured multi-layer pipe 10' includes an uncured inner layer 31, an uncured outer layer 33, and an uncured intermediate layer 32 formed by the intermediate layer material 22. When the uncured multi-layer pipe 10' is discharged from the mold 13, the intermediate layer material 22 foams to form the uncured intermediate layer 32. The uncured multi-layer pipe 10' is inserted into a tube 14 for forming the outer surface of the pipe, and is cooled in a cooling water tank 15 while being molded to a predetermined size. In order to sufficiently harden the uncured multi-layer pipe 10', the cooling temperature in the cooling water tank 15 is preferably 14°C or higher and 26°C or lower, more preferably 16°C or higher and 24°C or lower, and even more preferably 18°C ​​or higher and 22°C or lower. The cooling time in the cooling water tank 15 is the time that the uncured multilayer pipe 10' remains in the cooling water tank 15, and from the viewpoint of sufficiently curing the inner layer material and the outer layer material, it is preferably from 4 minutes to 16 minutes, more preferably from 6 minutes to 14 minutes, and even more preferably from 8 minutes to 12 minutes.

[0047] Next, the multi-layer pipe 10 cooled in the cooling water tank 15 is taken up by a take-off machine 16, and the multi-layer pipe 10 sent from the take-off machine 16 is cut to a predetermined length by a cutter 17. In this manner, a multi-layer pipe 10 having a predetermined length is obtained.

[0048] Next, the multi-layer pipe 10 is heated until it is in a state where it can be shaped, and then a mold having a desired rib groove shape is fitted into the pipe so that the average depth (d) of the rib grooves 4A is 15% to 30% of the total wall thickness (T) of the multi-layer pipe 10. In this manner, a multi-layer pipe 10 having a concave-convex portion 4 consisting of the rib grooves 4A of the desired shape is obtained.

[0049] Although the embodiment of the present invention has been described above, the present invention is not limited to these examples, and it is needless to say that the present invention can be embodied in various forms without departing from the gist of the present invention. EXAMPLES

[0050] Hereinafter, the embodiments of the present invention will be described more specifically based on examples, but the present invention is not limited to these.

[0051] Examples and Comparative Examples A multi-layer pipe having a three-layer structure of an inner layer, an intermediate layer, and an outer layer was produced by the above-mentioned multi-layer pipe manufacturing method based on the composition shown in Table 1 below. The produced multi-layer pipe had an average outer diameter of 114.00±0.25 mm, an overall wall thickness (T) of 7.1±0.5 mm (inner layer 1.2 mm±0.5 mm, intermediate layer 4.6 mm±0.5 mm, outer layer 1.3 mm±0.5 mm), and a total length of 4 m. A rib groove was formed in the outer layer of the multi-layer pipe in the circumferential direction, and a test specimen was produced in which an uneven portion with an uneven shape was provided along the circumferential direction of the outer layer.

[0052] <Raw materials used> The materials used in the examples and comparative examples are as follows. <Polyvinyl chloride resin> ·Tokuyama Sekisui Co., Ltd. "TS-1000R" (average degree of polymerization: 1,000) <Ca / Zn stabilizer> Nitto Kasei Co., Ltd. "TVS-8832" <Lubricant> Mitsui Chemicals, Inc. "HIWAX 220RKT" <Coloring Agent> · Reginocolor Co., Ltd. "R1875J" <Thermal Expandable Graphite> ·Suzuhiro Chemical Co., Ltd. "GREP-EG"

[0053] (Fire resistance test) Based on the provisions of ISO834-11:2014, a fire resistance test of a floor section penetration was conducted using a test specimen X in a fire resistance test furnace T shown in Figure 6. A 100 mm thick ALC (Autoclaved Light-weight Concrete) was used as the floor material Z. The test specimen X was exposed 800 mm outside the floor material Z. Mortar was used as the backfill material Y for the test specimen X and the floor material Z. A burner V was installed in the heating chamber U. A thermocouple W for measuring temperature was installed near the tip of the test specimen X, and the temperature of the fire resistance test furnace T was measured using the thermocouple W. The final temperature of the fire resistance test furnace T was set to 950°C, and the time when smoke was generated between the test specimen X and the backfill material Y was measured, and the evaluation was made according to the following criteria. <Judgment criteria> A: 80 minutes or more B: 60 minutes or more but less than 80 minutes C: Less than 60 minutes

[0054] (Tensile strength evaluation test) In accordance with JIS K 7161-1:2014 "Plastics - Determination of tensile properties - Part 1", test pieces for each Example and Comparative Example were prepared from the test specimen, and the tensile yield strength was measured at 5 mm / min. The measurement atmosphere was 23°C. The maximum load until the test piece broke was P (N), and the cross-sectional area of ​​the test piece was S (mm 2 ) and the tensile yield strength F (MPa) was calculated by the following formula: The calculated tensile yield strength F was then judged according to the following criteria. Tensile yield strength: F=P / S <Judgment criteria> A: Tensile yield strength F is 42 (MPa) or more B: Tensile yield strength F is 35 (MPa) or more and less than 42 (MPa) C: Tensile yield strength F is less than 35 (MPa)

[0055] [Table 1] [Explanation of symbols]

[0056] 1…Inner layer 2. Middle class 3…Outer layer 10…Multilayer pipe 4A…Rib groove 4…Uneven part 10´…Unhardened fireproof pipe 11…Inner and outer layer extruder 12...Intermediate layer extruder 13...Mold 14...Tube for forming outer surface 15…Cooling water tank 16...Removal machine 17...Cutting machine 20…Manufacturing equipment 21…Inner layer material 23…Outer layer material 22...Intermediate layer material 31…Uncured inner layer 32…Uncured middle layer 33…Uncured outer layer T……Fireproof test furnace U...Heating chamber V... Burner W...Thermocouple X... Test specimen Y... Mortar Z...Flooring

Claims

1. The inner layer, an intermediate layer disposed on an outer side of the inner layer; an outer layer disposed outside the intermediate layer, the intermediate layer contains a polyvinyl chloride resin and thermally expandable graphite; The outer layer has an uneven portion consisting of a plurality of rib grooves provided along the circumferential direction on the outer peripheral surface, and the average depth (d) of the rib grooves is 15% to 30% of the total wall thickness (T) of the multi-layer pipe.

2. 2. The multi-layer pipe according to claim 1, wherein the average depth (d) of the rib groove is 0.5 mm to 2.5 mm.

3. 3. The multi-layer pipe according to claim 1, wherein the average width (w) of the rib groove is 1.0 mm to 2.0 mm.

4. 4. The multi-layer pipe according to claim 1, wherein an average pitch distance (p) between adjacent rib grooves in a direction perpendicular to the circumferential direction of the outer layer is 1.0 mm to 2.0 mm.

5. 5. The multi-layer pipe according to claim 1, wherein the blending amount of the thermally expandable graphite is 4 to 18 parts by mass based on 100 parts by mass of the polyvinyl chloride resin.

6. A multi-layer pipe described in any one of claims 1 to 5, wherein the overall wall thickness (T) of the multi-layer pipe is 3.6 mm to 10.3 mm.

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