JP2023027505A - multilayer pipe - Google Patents

Abstract

To provide a multilayer pipe capable of suppressing deterioration of physical properties and having high fire resistance.SOLUTION: A multilayer pipe comprises an inner layer 1, an intermediate layer 2 arranged outside the inner layer 1, and an outer layer 3 arranged outside the intermediate layer 2. The intermediate layer 2 contains polyvinyl chloride resin, thermally expandable graphite and zeolite. The content of the thermally expandable graphite is 5 pts.mass to 20 pts.mass with respect to 100 pts.mass of the polyvinyl chloride resin, and the content of the zeolite is 0.5 pt.mass to 3.0 pts.mass with respect to 100 pts.mass of the polyvinyl chloride resin.SELECTED DRAWING: Figure 1

Description

The present invention relates to multilayer pipes.

BACKGROUND ART In buildings, multi-layered pipes are being used because various properties are required for piping materials used in buildings along with the sophistication of construction technology. A multi-layer pipe as a piping material is required to have high fire resistance performance, for example, in order to be used in a fireproof compartment.

As a specific function of fire resistance required for piping materials, the piping materials are required to expand due to the heat of fire to block the piping itself and prevent the spread of fire through the piping materials. As such a piping material, a piping material containing thermally expandable graphite has been proposed (see, for example, Patent Document 1).

In recent years, the use of PVC pipes, which are lightweight and have good workability, has become mainstream for piping materials. Furthermore, due to market conditions, the demand for vertical pipes that require large diameters is increasing, so it is necessary to have a large-diameter product line-up.
PVC pipes exhibit fire resistance when they are burned and clogged with residues. It becomes difficult to develop fire resistance.
If the number of parts of thermally expandable graphite added to improve fire resistance is increased, the thermally expandable graphite will become the starting point of cracks, resulting in a decrease in tensile strength and the increase in flatness of the thermally expandable graphite. There is a problem that physical properties of the multi-layer pipe are deteriorated, such as reduction in physical strength.

JP 2009-74689 A

In view of the circumstances as described above, it is an object of the present invention to provide a multi-layer pipe that suppresses deterioration in physical properties and has high fire resistance.

The present inventors have made intensive studies to achieve the above object, and as a result, by blending a predetermined amount of thermally expandable graphite in the intermediate layer and providing a predetermined uneven portion in the outer layer, the deterioration of physical properties is suppressed and high We have found that it is possible to make a multi-layer pipe having fire resistance. The inventors of the present invention conducted further studies based on such knowledge, and completed the present invention.

The present invention was made to solve the above problems, and the gist of the present invention is as follows.
[1] An inner layer, an intermediate layer arranged outside the inner layer, and an outer layer arranged outside the intermediate layer, the intermediate layer containing polyvinyl chloride resin, thermally expandable graphite and zeolite The content of the thermally expandable graphite is 5 parts by mass to 20 parts by mass with respect to 100 parts by mass of the polyvinyl chloride resin, and the content of the zeolite is 100 parts by mass of the polyvinyl chloride resin. 0.5 parts by mass to 3.0 parts by mass per part of the multi-layer tube.
[2] A thermally expandable material is adsorbed on the cavity wall surface of the zeolite,
The multi-layer tube according to [1], wherein the thermally expandable material generates a total amount of gas of 0.6 mmol/g or more when heated to 220°C to 500°C.

ADVANTAGE OF THE INVENTION According to this invention, the multilayer pipe which suppresses the physical-property deterioration and has high fire resistance performance can be provided.

1 is a schematic cross-sectional view of a multi-layer pipe according to an embodiment of the invention; FIG. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a plan view showing an example of a multi-layer pipe manufacturing apparatus according to an embodiment of the present invention; BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a front view showing an example of a multi-layer pipe manufacturing apparatus according to an embodiment of the present invention; 1 is a configuration diagram showing an example of a mold and a tube for forming the outer surface of a multilayer pipe used in the multilayer pipe manufacturing apparatus according to the embodiment of the present invention; FIG.

[Multilayer pipe]
A multilayer pipe 10 according to an embodiment of the present invention comprises an inner layer 1, an intermediate layer 2 and an outer layer 3, as shown in FIG. The inner layer 1 constitutes the innermost layer of the multilayer pipe 10 , and the outer layer 3 constitutes the outermost layer of the multilayer pipe 10 . A multilayer pipe 10 shown in FIG. 1 has a multilayer structure in which an inner layer 1, an intermediate layer 2 and an outer layer 3 are laminated in this order from the inside of the multilayer pipe. In addition, the structure of the multi-layer pipe 10 is not limited to three layers, and for example, the intermediate layer 2 may have multiple layers.

The overall thickness of the multi-layer tube 10 is preferably 3.5 mm to 9.0 mm, more preferably 3.7 mm to 8.8 mm, even more preferably 4.0 mm to 8.5 mm. When the total thickness of the multilayer pipe 10 is within the above range, it has a thickness corresponding to a general VP nominal diameter of 40 to 150, and can be joined to a general joint.

The thickness of the inner layer 1 is preferably 0.5 mm to 3.2 mm, more preferably 0.7 mm to 3.0 mm, even more preferably 0.9 mm to 2.5 mm.
The thickness of the intermediate layer 2 is preferably 0.5 mm to 4.0 mm, more preferably 0.7 mm to 3.5 mm, even more preferably 0.9 mm to 3.2 mm.
The thickness of the outer layer 3 is preferably 0.5 mm to 3.2 mm, more preferably 0.7 mm to 3.0 mm, even more preferably 0.9 mm to 2.5 mm.

The inner layer 1, the intermediate layer 2 and the outer layer 3 that constitute the multilayer pipe 10 contain a polyvinyl chloride resin. Among them, the intermediate layer 2 contains polyvinyl chloride resin, thermally expandable graphite and zeolite. By including polyvinyl chloride resin, thermally expandable graphite, and zeolite in the intermediate layer 2, the multilayer pipe 10 having high fire resistance can be obtained. By including the thermally expandable graphite in the intermediate layer 2, it is possible to suppress the decrease in tensile strength due to the thermally expandable graphite becoming a crack starting point and cracking, etc., and the flattening of the thermally expandable graphite. The decrease in mechanical strength due to the increase can be suppressed. In addition, by including zeolite to which a thermally expandable material is adsorbed in the intermediate layer 2, the strength of the combustion residue is increased, and the thermally expandable material is adsorbed on the cavity walls constituting the zeolite cavity. Fire resistance can be improved by expanding the residue when ammonia or the like evaporates due to heat.

(polyvinyl chloride resin)
As materials for forming the inner layer 1, the intermediate layer 2 and the outer layer 3, a polyvinyl chloride resin is 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; 3) Graft copolymers obtained by graft-copolymerizing vinyl chloride to (co)polymers other than vinyl chloride may be mentioned, and these may be used alone or in combination of two or more. Moreover, the polyvinyl chloride-based resin may be chlorinated as necessary.

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

The copolymer (3) graft-copolymerized with vinyl chloride is not particularly limited as long as it is graft-copolymerized with vinyl chloride. carbon oxide 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, etc. may be mentioned, and these may be used alone or in combination of two or more.

The average degree of polymerization of the polyvinyl chloride-based resin is not particularly limited, but if it is too small, the physical properties of the molded product will deteriorate. 600 is preferred, 500 to 1,500 is more preferred, and 600 to 1,400 is even more preferred.
The average degree of polymerization refers to a resin obtained by dissolving vinyl chloride resin in tetrahydrofuran (THF), removing insoluble components by filtration, and removing THF in the filtrate by drying. -2: Means the average degree of polymerization measured according to 1999 "Plastics--Vinyl chloride homopolymers and copolymers (PVC)--Part 2: How to make test pieces and how to determine various properties".

The method of polymerizing the polyvinyl chloride resin is not particularly limited, and any conventionally known polymerization method can be employed. For example, bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, etc. mentioned.

The method for chlorinating the polyvinyl chloride-based resin is not particularly limited, and conventionally known chlorinating methods can be employed. Examples thereof include heat chlorinating methods and photochlorinating methods.

Any of the above polyvinyl chloride-based 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 the resin may be crosslinked or modified at the same time as the additive is added, or the resin may be crosslinked or modified after the above components have been added. . The method for crosslinking the resin is not particularly limited, and the usual crosslinking methods for polyvinyl chloride resins, such as crosslinking using various crosslinking agents, peroxides, electron beam irradiation, and water-crosslinkable materials are used. and the like.

(Thermal expandable graphite)
The thermally expandable graphite contained in the vinyl chloride-based resin composition forming the intermediate layer 2 is thermally expandable graphite in the shape of flakes, spheres, or the like. Thermally expandable graphite expands when heated, and is produced by treating powders of natural flake graphite, pyrolytic graphite, Kish graphite, etc. with an inorganic acid and a strong oxidizing agent to form a graphite intercalation compound. It 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, bichromates, and hydrogen peroxide.
The thermally expandable graphite obtained by acid treatment as described above may be further neutralized with a neutralizing agent such as ammonia, lower aliphatic amines, alkali metal compounds, alkaline earth metal compounds and the like. Examples of aliphatic lower amines include monomethylamine, dimethylamine, trimethylamine, ethylamine, propylamine, butylamine and the like. Examples of the alkali metal compounds and alkaline earth metal compounds include hydroxides, oxides, carbonates, sulfates, organic acid salts of potassium, sodium, calcium, barium, magnesium and the like. These may be used alone or in combination of two or more.

The expansion start 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. Also, in the event of fire, the temperature is preferably 250° C. or lower, more preferably 240° C. or lower, and even more preferably 230° C. or lower from the viewpoint of increasing the volume increase rate of the thermally expandable graphite and effectively exhibiting fire resistance.

The content of thermally expandable graphite in the vinyl chloride resin composition forming the intermediate layer 2 is 5 parts by mass to 20 parts by mass with respect to 100 parts by mass of the polyvinyl chloride resin. When the content of the thermally expandable graphite in the vinyl chloride resin composition constituting the intermediate layer 2 is less than 5 parts by mass with respect to 100 parts by mass of the polyvinyl chloride resin, the thermal expansion of the intermediate layer 2 is reduced. insufficient, and sufficient fire resistance cannot be obtained. Moreover, when the content of the thermally expandable graphite in the vinyl chloride resin composition constituting the intermediate layer 2 is more than 20 parts by mass with respect to 100 parts by mass of the polyvinyl chloride resin, the thermally expandable graphite cracks. Tensile strength decreases due to cracks that form starting points, and mechanical strength decreases due to increased flatness of the thermally expandable graphite. The content of the thermally expandable graphite in the vinyl chloride resin composition forming the intermediate layer 2 is preferably 6 parts by mass or more, more preferably 7 parts by mass or more, with respect to 100 parts by mass of the polyvinyl chloride resin. more preferably 8 parts by mass or more. When the content of the thermally expandable graphite is equal to or higher than the above lower limit, the intermediate layer 2 has sufficient thermal expandability. In addition, the content of thermally expandable graphite in the vinyl chloride resin composition constituting the intermediate layer 2 is preferably 18 parts by mass or less, and 16 parts by mass with respect to 100 parts by mass of the polyvinyl chloride resin. It is more preferably 15 parts by mass or less, more preferably 15 parts by mass or less. When the content of the thermally expandable graphite is equal to or less than the above upper limit value, the multilayer pipe 10 has sufficient mechanical strength.

(zeolite)
The skeleton structure of the zeolite contained in the vinyl chloride resin composition forming the intermediate layer 2 is not particularly limited. Specific examples of the framework structure of the zeolite used in the present invention include A-type, ferrierite, MXM-22, ZSM-5, mordenite, L-type, Y-type, X-type, and beta-type. It is one or more types selected from.
Further, a thermally expandable material such as gas or liquid may be adsorbed in advance on the surface of the cavity walls forming the cavity of the porous structure of the zeolite. Any number of types of adsorbed thermally expandable materials may be used as long as they are one or more. When a thermally expansible material is adsorbed on the surface of the cavity walls that make up the zeolite cavity, the thermally expandable material adsorbed on the zeolite is vaporized by heat in the vinyl chloride resin, increasing the expansion ratio. becomes possible.

The content of zeolite contained in the vinyl chloride-based resin composition forming the intermediate layer 2 is 0.5 to 3.0 parts by mass with respect to 100 parts by mass of the polyvinyl chloride-based resin. When the content of zeolite contained in the vinyl chloride resin composition constituting the intermediate layer 2 is less than 0.5 parts by mass with respect to 100 parts by mass of the polyvinyl chloride resin, the expansibility and expansion of the multilayer tube The post-residue strength becomes insufficient, and sufficient fire resistance cannot be obtained. Further, when the content of zeolite in the vinyl chloride resin composition constituting the intermediate layer 2 is more than 3.0 parts by mass with respect to 100 parts by mass of the polyvinyl chloride resin, the amount of the inorganic substance added becomes large. It leads to a decrease in mechanical strength. The content of zeolite contained in the vinyl chloride resin composition that constitutes the intermediate layer 2 is preferably 0.5 parts by mass or more, and 0.7 parts by mass or more with respect to 100 parts by mass of the polyvinyl chloride resin. is more preferably 1.0 parts by mass or more. When the zeolite content is equal to or higher than the above lower limit, the expansibility of the multilayer pipe and the residual strength after expansion are sufficient. In addition, the content of zeolite contained in the vinyl chloride resin composition constituting the intermediate layer 2 is preferably 3.0 parts by mass or less, and 2.7 parts by mass with respect to 100 parts by mass of the polyvinyl chloride resin. It is more preferably 2.5 parts by mass or less, more preferably 2.5 parts by mass or less. When the zeolite content is equal to or less than the above upper limit value, the amount of inorganic substances added is suppressed, and a decrease in mechanical strength can be suppressed.

<Thermal expansion material>
As the thermally expandable material in the present invention, a material that is vaporized by heat and expands the residue of the material forming the intermediate layer to improve the fire resistance is adopted. As the thermally expandable material, it is preferable to adopt a material that does not gasify during molding (for example, 220°C) but can be gasified during combustion (for example, 500°C). ₃ ) and at least one nitrogen-containing compound of nitrogen (N ₂ ).

The amount of the thermally expandable material adsorbed on the cavity wall surface of the zeolite is preferably 0.6 mmol/g or more, more preferably 0.9 mmol/g or more, and 1.2 mmol/g or more. is more preferable. When the amount of the thermally expandable material adsorbed on the cavity wall surface of the zeolite is equal to or greater than the above lower limit, the expansibility of the multi-layer pipe becomes sufficient, and the fire resistance can be improved. In addition, the amount of the thermally expandable material adsorbed on the cavity wall surface of the zeolite is preferably 0.9 mmol/g or less, more preferably 1.2 mmol/g or less, and 1.5 mmol/g or less. g or less is more preferable. When the amount of the thermally expandable material adsorbed on the surface of the cavity wall of the zeolite is equal to or less than the above upper limit, excessive expandability of the multilayer pipe can be suppressed, and the residual strength after expansion becomes sufficient. .
The amount of the thermally expandable material adsorbed on the cavity wall surface of the zeolite can be regarded as the total amount of gas generated when the thermally expandable material is heated to 220°C to 500°C. It can be measured by the method described in .

(Additive)
Materials constituting the inner layer 1, the intermediate layer 2 and the outer layer 3 of the multi-layer tube 10 of the present invention include inorganic fillers, lubricants, processing aids, impact modifiers, and heat resistance improvers within limits that do not impair their physical properties. , antioxidants, light stabilizers, ultraviolet absorbers, pigments, plasticizers, thermoplastic elastomers, and other additives may be added.

A wide range of known inorganic fillers can be used, and there is no particular limitation. Specifically, 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 carbonate Magnesium, 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 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 zirconate titanate, aluminum borate, molybdenum molybdenum sulfide, silicon carbide, stainless steel fiber, zinc borate, various magnetic powders, slag fiber, fly ag, dewatered sludge, etc. can be done.

As the lubricant, a wide range of known lubricants can be used, and there is no particular limitation. Lubricants include internal lubricants and external lubricants. The internal lubricant is used for the purpose of reducing the flow viscosity of 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. can. Further, 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.

A wide range of known processing aids can be used, and there is no particular limitation. Examples thereof include acrylic processing aids such as alkyl acrylate-alkyl methacrylate copolymers having a weight average molecular weight of 100,000 to 2,000,000. The acrylic processing aid is not particularly limited, and examples thereof include n-butyl acrylate-methyl methacrylate copolymer and 2-ethylhexyl acrylate-methyl methacrylate-butyl methacrylate copolymer. These may be used alone or in combination of two or more.

As the impact modifier, a wide range of known ones can be used, and there is no particular limitation. For example, one or more selected from the group consisting of methyl methacrylate-butadiene-styrene copolymer (MBS), chlorinated polyethylene, acrylic rubber and the like can be used.

As the heat resistance improver, it is possible to use a wide range of known ones, and there is no particular limitation. For example, α-methylstyrene-based and N-phenylmaleimide-based resins can be used.

The antioxidant is not particularly limited, and a wide range of known antioxidants can be used. For example, phenol-based antioxidants and the like are included.

The light stabilizer is not particularly limited, and a wide range of known ones can be used. Examples thereof include hindered amine-based light stabilizers.

The ultraviolet absorber is not particularly limited, and a wide range of known ones can be used. Examples thereof include salicylic acid ester-based, benzophenone-based, benzotriazole-based, and cyanoacrylate-based UV absorbers. These may be used alone or in combination of two or more.

The pigment is not particularly limited, and a wide range of known pigments can be used. Examples include organic pigments such as azo, phthalocyanine, threne, and dye lake; inorganic pigments such as oxide, molybdenum chromate, sulfide/selenide, and ferrocyanine. These may be used alone or in combination of two or more.

Further, a plasticizer may be added to the polyvinyl chloride resin. The plasticizer is not particularly limited, and a wide range 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.

The thermoplastic elastomer is not particularly limited, and widely known ones can be used. For example, acrylonitrile-butadiene copolymer (NBR), ethylene-vinyl acetate copolymer (EVA), ethylene-vinyl acetate-carbon monoxide copolymer (EVACO), vinyl chloride-vinyl acetate copolymer and vinyl chloride - selected from the group consisting of vinyl chloride thermoplastic elastomers such as vinylidene chloride copolymers, styrene thermoplastic elastomers, olefin thermoplastic elastomers, urethane thermoplastic elastomers, polyester thermoplastic elastomers, and polyamide thermoplastic elastomers can be used.

As a method for mixing the above-described thermally expandable graphite, zeolite and additive with the polyvinyl chloride resin, it is possible to employ a wide range of known methods. Specific examples include a hot blending method and a cold blending method.

<Usage of multi-layer pipe>
The multi-layer pipe 10 of the present invention as described above suppresses deterioration of physical properties and has high fire resistance performance, so that it can be suitably used as piping such as drain pipes, ducts, and electric conduits in buildings. In addition, the multi-layer pipe 10 of the present invention can be suitably used not only as a constituent material of a pipe main body, but also as a constituent material of pipe joints.

<Manufacturing method of multilayer pipe>
FIG. 2 is a plan view schematically showing a manufacturing apparatus 20 used for manufacturing the multilayer pipe 10 according to one embodiment of the present invention. FIG. 3 is a front view schematically showing a manufacturing apparatus 20 used for manufacturing the multilayer pipe 10 according to one embodiment of the present invention.
2 and 3, a manufacturing apparatus 20 for manufacturing the multilayer pipe 10 includes an inner/outer layer extruder 11, an intermediate layer extruder 12, a mold 13, a cooling water tank 15, and a take-up machine 16. , and a cutting machine 17 . A mold 13 is connected to the inner/outer layer extruder 11 and the intermediate layer extruder 12 . A cooling water tank 15 is connected to the mold 13 . A take-up machine 16 is connected to the cooling water tank 15 . A cutting machine 17 is connected to the take-up machine 16 .

In the method for producing a multilayer pipe of the present invention, first, the inner layer material and the outer layer material are charged into the inner and outer layer extruder 11 using a hopper, and the inner layer material and the outer layer material are extruded in the inner and outer layer extruder 11. It is melt-kneaded and extruded into the mold 13 . Also, the intermediate layer material is fed into the intermediate layer extruder 12 using a hopper, melt-kneaded in the intermediate layer extruder 12 , and extruded into the mold 13 .

Next, in the mold 13, the melt-kneaded material of the inner layer and the outer layer and the melt-kneaded material of the intermediate layer are heated to form an uncured multi-layer pipe having a three-layer structure.
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, from the viewpoint of improving the fluidity of the inner layer material and the outer layer material. More preferably, the temperature is 180°C or higher and 190°C or lower.
The heating time in the mold 13 is the time during which the inner layer material and the outer layer material are present in the mold 13, and from the viewpoint of improving the fluidity of the inner layer material and the outer layer material, it is 3 minutes or more and 10 minutes or less. 4 minutes or more and 9 minutes or less is more preferable, and 5 minutes or more and 8 minutes or less is even more preferable.

Next, an uncured multi-layer tube having a three-layer structure is extruded from the outlet of the mold 13 and sent to the cooling water tank 15 .
A pipe outer surface forming tube 14 for forming the uncured multilayer pipe into a predetermined size is attached to the cooling water tank 15, and the outer surface of the uncured multilayer pipe is in contact with the outer surface forming tube 14. Cool with FIG. 4 is an enlarged cross-sectional view showing the mold 13 and the outer surface forming tube 14 in the manufacturing apparatus. As shown in FIG. 4, an inner layer material 21 and an outer layer material 23 melt-kneaded by an inner/outer layer extruder 11 and an intermediate layer material 22 melt-kneaded by an intermediate layer extruder 12 are shown in cross section of the intermediate layer. It is injected into a mold 13 designed so that the outer peripheral edge of the shape is a perfect circle, and an uncured multi-layer pipe 10' is formed. The uncured multi-layer tube 10 ′ comprises an uncured inner layer 31 and an uncured outer layer 33 and an uncured middle layer 32 formed by the middle layer material 22 . The intermediate layer material 22 foams when the uncured multilayer pipe 10 ′ is discharged from the mold 13 to form an uncured intermediate layer 32 . The uncured multilayer pipe 10' is inserted into the tube 14 for forming the outer surface of the pipe, and the uncured multilayer pipe 10' is cooled in the cooling water tank 15 while being formed into a predetermined size.
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, from the viewpoint of sufficiently hardening the uncured multilayer pipe 10 ′. °C or higher and 22 °C or lower.
The cooling time in the cooling water tank 15 is the time during which the uncured multilayer pipe 10' remains in the cooling water tank 15, and is 4 minutes or more and 16 minutes or less from the viewpoint of sufficiently curing the inner layer material and the outer layer material. more preferably 6 minutes or more and 14 minutes or less, and even more preferably 8 minutes or more and 12 minutes or less.

Next, a take-up machine 16 is used to take up the multilayer pipe 10 cooled in the cooling water tank 15, and a cutting machine 17 is used to cut the multilayer pipe 10 sent from the take-up machine 16 to a predetermined length. . Thus, a multi-layer tube 10 having a predetermined length is obtained.

Although the embodiments of the present invention have been described above, the present invention is by no means limited to such examples, and can of course be embodied in various forms without departing from the gist of the present invention.

EXAMPLES Hereinafter, embodiments of the present invention will be described more specifically based on Examples, but the present invention is not limited to these.

(Examples and Comparative Examples)
Based on the formulation shown in Table 1 below, roll kneading was performed for 3 minutes with an 8-inch mixing roll (manufactured by Yasuda Seiki Seisakusho) at 190°C, and press molding was performed for 3 minutes with a press machine (manufactured by Toho Machinery Co., Ltd.) at 200°C. After that, it was cooled for 3 minutes with a cooling press machine (manufactured by Toho Machinery Co., Ltd.) at 20° C. to prepare a test piece of each example and comparative example with a thickness of 3.1 mm.

<Raw materials used>
Materials used in Examples and Comparative Examples are as follows.
<Polyvinyl chloride resin>
・Tokuyama Sekisui Co., Ltd. “TS1000R” (average degree of polymerization: 1,000)
<Light stabilizer>
・Nitto Kasei Co., Ltd. “TVS-8832”
<Lubricant>
・Mitsui Chemicals Co., Ltd. “Hi-Wax 220RKT”
<Thermal expandable graphite>
・Suzuhiro Chemical Co., Ltd. “GREP-EG”
<Zeolite>
・Mizusawa Chemical Co., Ltd. “Mizukalizer DS”
・Tosoh Corporation “HSZ-300 341NHA”, thermally expandable material “NH ₃ ” (220° C. to 500° C. total gas generation: 1.4 mmol/g)
・Tosoh Corporation “HSZ-700 720NHA”, thermally expandable material “NH ₃ ” (220° C. to 500° C. total gas generation: 1.7 mmol/g)

<Gas Generation Amount of Thermally Expandable Material>
A test tube containing 1.0 g of zeolite containing a thermally expandable material is inserted into an oil bath set to the measurement temperature and heated for 5 minutes, and the gas generated by thermal decomposition is collected with a glass instrument and heated to 20 ° C. , the amount of generated gas was calculated from the volume of the generated gas in the state of 1 atm.

(Expansion ratio evaluation test)
A test piece made into a plate shape by roll pressing was cut into a rectangular parallelepiped shape, and the thickness, length, and width were measured at three points with vernier calipers. After that, the test pieces of each example and comparative example were placed in an electric furnace heated to 500° C. for 3 minutes to expand. After that, it was taken out from the electric furnace and allowed to cool at room temperature. The thickness, length, and width of the expanded test piece were measured with vernier calipers, and the expansion ratio R was calculated by the following formula. If the expansion ratio R was 10 or more, it was determined that the material had a practically sufficient coefficient of thermal expansion.
Thermal expansion coefficient R=( _a1 * _b1 * _c1 )/( _a0 * _b0 * _c0 )
a ₀ : Specimen thickness before expansion (mm)
b ₀ : vertical length of test piece before expansion (mm)
c ₀ : Horizontal length of test piece before expansion (mm)
a ₁ : test piece thickness after expansion (mm)
b ₁ : vertical thickness of test piece after expansion (mm)
c ₁ : lateral length of test piece after expansion (mm)
<Judgment Criteria>
A: Expansion ratio R is 10 or more B: Expansion ratio R is 5 or more and less than 10 C: Expansion ratio R is less than 5

(Residue strength test)
A rectangular parallelepiped having a length of 30±1 mm, a width of 30±1 mm, and a thickness of 3±0.1 mm is cut from a plate-shaped test piece by roll pressing. A hole of about 1 mm was made at the end of the sample, a wire was passed through it, and the sample was suspended from a metal stand and placed in an electric furnace heated to 500° C. for 3 minutes to prepare a combustion residue and taken out. Each test was repeated 5 times, and if the residue strength was low, it would fall off the pedestal.
<Judgment Criteria>
A: Number of drops 0 times B: Number of drops 1-2 times C: Number of drops 3-5 times

(Tensile strength evaluation test)
According to JIS K 7161-1:2014 "Plastics - Determination of tensile properties - Part 1", test pieces of each example and comparative example were prepared from the test body, and the tensile yield strength was measured at 5 mm / min. . The measurement atmosphere at this time was 23°C. The tensile yield strength F (MPa) was calculated by the following formula, where P (N) is the maximum load until the test piece breaks, and S (mm ² ) is the cross-sectional area of the test piece.
Tensile yield strength: F=P/S
<Judgment Criteria>
A: Tensile yield strength F is 40 (MPa) or more B: Tensile yield strength F is 35 (MPa) or more and less than 40 (MPa) C: Tensile yield strength F is less than 35 (MPa)

(Ammonia temperature programmed desorption measurement (NH ₃ -TPD measurement))
1 g of the obtained test piece was cut out. The cut test piece was dissolved in tetrahydrofuran (THF), centrifuged, and then the supernatant was removed. After drying the unnecessary material, it was used as a test piece. When zeolite and other inorganic components were mixed, they were separated by a known separation method (precipitation, filtration, etc.) to obtain an extraction test piece in which only zeolite was extracted.
0.1 g of the extracted test piece was allowed to stand under helium flow at 500° C. for 1 hour for pretreatment. A mixed gas containing 5% by volume of ammonia and 95% by volume of helium was allowed to flow through the sample after pretreatment for 1 hour at room temperature, and ammonia was saturated and adsorbed on the extraction test piece. After circulating the mixed gas for 1 hour, the sample was heated to 100° C. while circulating helium gas instead of the mixed gas. After the temperature was raised, helium gas was allowed to flow at 100° C. for 0.5 hours to remove ammonia remaining in the atmosphere.
After removing the residual ammonia, the temperature was raised to 500 ° C. at a temperature increase rate of 10 ° C./min under helium flow at a flow rate of 30 mL / min. The total amount of gas generated (mmol/g) when heated to °C was taken as the amount of ammonia adsorbed on the sample.

DESCRIPTION OF SYMBOLS 1... Inner layer 2... Intermediate layer 3... Outer layer 10... Multi-layer tube 10'... Uncured fireproof tube 11... Inner/outer layer extruder 12... Intermediate layer extruder 13... Mold 14... Tube for outer surface molding of tube 15... Cooling water tank 16 Take-up machine 17 Cutting machine 20 Manufacturing device 21 Inner layer material 23 Outer layer material 22 Intermediate layer material 31 Uncured inner layer 32 Uncured intermediate layer 33 Uncured outer layer

Claims (2)

inner layer and
an intermediate layer disposed outside the inner layer;
and an outer layer arranged outside the intermediate layer,
The intermediate layer contains polyvinyl chloride resin, thermally expandable graphite and zeolite,
The content of the thermally expandable graphite is 5 parts by mass to 20 parts by mass with respect to 100 parts by mass of the polyvinyl chloride resin,
The multi-layer pipe, wherein the content of the zeolite is 0.5 to 3.0 parts by mass with respect to 100 parts by mass of the polyvinyl chloride resin. A thermally expandable material is adsorbed on the cavity wall surface of the zeolite,
2. The multi-layer tube according to claim 1, wherein the thermally expandable material generates a total amount of gas of 0.6 mmol/g or more when heated to 220.degree. C. to 500.degree.

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