JP2023130588A - multilayer pipe - Google Patents

Abstract

To provide a multilayer pipe that suppresses mold corrosion during molding processing and has high fire resistance.SOLUTION: A multilayer pipe 10 comprises an inner layer 1, an intermediate layer 2 disposed outside the inner layer 1, and an outer layer 3 disposed outside the intermediate layer 2. The intermediate layer 2 includes a vinyl chloride-based resin, thermally expandable graphite and zeolite. A content of the thermally expandable graphite is 5.0-20.0 pts.mass based on 100 pts.mass of polyvinyl chloride, and a content of the zeolite is 0.6-5.0 pts.mass based on 100 pts.mass of the polyvinyl chloride.SELECTED DRAWING: Figure 1

Description

The present invention relates to multilayer pipes.

In buildings, as construction technology becomes more sophisticated, piping materials used in buildings are required to have diverse properties, and multilayer pipes are used. Multilayer pipes as piping materials are required to have high fire resistance performance, for example, in order to be used in fireproof compartments.

A specific fire-resistance function required of piping materials is the ability to prevent fire from spreading through the piping materials by expanding the piping materials due to the heat of the fire and closing the piping itself. As such a piping material, a piping material containing thermally expandable graphite has been proposed (for example, see Patent Document 1).

Furthermore, in recent years, the use of vinyl chloride pipes, which are lightweight and have good workability, has become mainstream as piping materials. Furthermore, due to market conditions, there is an increasing demand for standpipes that require large diameters, making it necessary to have a large-diameter product lineup.
PVC pipes develop fire resistance by burning and turning into residue that blocks the pipe, but generally speaking, as the diameter increases, the area that is blocked by the burnt PVC residue increases when the heat of a fire is applied. Therefore, the residue may fall under its own weight and cannot be blocked before it becomes blocked, making it difficult to develop fire resistance.

In order to improve fire resistance, it is necessary to increase the amount of heat-expandable graphite added, but since heat-expandable graphite contains sulfuric acid, sulfuric acid may seep out from the heat-expandable graphite during molding. This causes the extrusion mold to corrode, causing the problem that the mold needs to be updated more frequently. An increase in the frequency of mold updates leads to an increase in manufacturing costs. Furthermore, as the mold corrodes, foreign matter adheres to the mold, and when the foreign matter peels off, it gets mixed into the molded piping material and becomes defective, so there is a need to develop piping materials that can suppress corrosion. was.
Therefore, a chlorine-containing resin composition containing hydrotalcite has been proposed in order to prevent mold corrosion caused by sulfuric acid (see, for example, Patent Document 2). However, when hydrotalcite is included, the hardness of the molded piping material decreases, resulting in insufficient strength of the vinyl chloride residue upon combustion, resulting in insufficient clogging of the pipe.

Japanese Patent Application Publication No. 2009-74689 JP2020-26445A

In view of the above circumstances, an object of the present invention is to provide a multilayer pipe that suppresses mold corrosion during molding and has high fire resistance.

As a result of extensive research to achieve the above object, the present inventors found that by blending a predetermined amount of thermally expandable graphite and zeolite into the intermediate layer, corrosion of the mold during molding can be suppressed, resulting in high fire resistance. It has been found that it is possible to make a multilayer tube with Based on this knowledge, the present inventors conducted further research and completed the present invention.

The present invention has been made to solve the above problems, and the gist of the present invention is as follows.
[1] An inner layer, an intermediate layer disposed outside the inner layer, and an outer layer disposed outside the intermediate layer, the intermediate layer comprising a polyvinyl chloride resin, thermally expandable graphite, and zeolite. The content of the thermally expandable graphite is 5.0 parts by mass to 20.0 parts by mass based on 100 parts by mass of the polyvinyl chloride, and the content of the zeolite is 100 parts by mass of the polyvinyl chloride. 0.6 parts by mass to 5.0 parts by mass.
[2] The zeolite contains ammonia on its cavity wall surface, and the amount of acid when heated to 500°C is 1.0 mmol/g to 3.0 mmol/g according to ammonia temperature-programmed desorption measurement (NH ₃ -TPD measurement). The multilayer tube according to [1], which has a concentration of 0 mmol/g.
[3] The multilayer pipe according to [1] or [2], wherein the zeolite has a specific surface area of 250 m ² /g or more and 700 m ² /g or less as measured by the BET method.

According to the present invention, it is possible to suppress corrosion of a mold during molding and provide a multilayer pipe having high fire resistance.

FIG. 1 is a schematic cross-sectional view of a multilayer pipe according to an embodiment of the present invention. 1 is a plan view showing an example of a multilayer pipe manufacturing apparatus according to an embodiment of the present invention. 1 is a front view showing an example of a multilayer 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.

[Multilayer pipe]
A multilayer pipe 10 according to an embodiment of the present invention includes an inner layer 1, an intermediate layer 2, and an outer layer 3, as shown in FIG. Inner layer 1 constitutes the innermost layer of multilayer tube 10, and outer layer 3 constitutes the outermost layer of multilayer tube 10. The 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. Note that the structure of the multilayer tube 10 is not limited to three layers, and for example, the intermediate layer 2 may have multiple layers.

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

The thickness of the inner layer 1 is preferably 0.5 mm to 3.0 mm, more preferably 0.7 mm to 2.7 mm, and 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, and even more preferably 0.9 mm to 3.2 mm.
The thickness of the outer layer 3 is preferably 0.5 mm to 3.0 mm, more preferably 0.7 mm to 2.7 mm, and even more preferably 0.9 mm to 2.5 mm.

The inner layer 1, intermediate layer 2, and outer layer 3 that constitute the multilayer pipe 10 contain 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 can have high fire resistance. By including a predetermined amount of thermally expandable graphite in the intermediate layer 2, it is possible to suppress a decrease in tensile strength due to thermally expandable graphite becoming a starting point for cracks, etc. It is possible to suppress a decrease in mechanical strength due to an increase in flatness. 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 to the cavity walls constituting the cavities of the zeolite. Fire resistance can be improved by expanding the residue by vaporizing ammonia or the like with heat.

(Polyvinyl chloride resin)
As the material constituting the inner layer 1, intermediate layer 2, and outer layer 3, polyvinyl chloride resin is suitably used.
Examples of the polyvinyl chloride resin include (1) a polyvinyl chloride homopolymer; (2) a copolymer of a vinyl chloride monomer and a monomer having an unsaturated bond copolymerizable with the vinyl chloride monomer; 3) Examples include graft copolymers obtained by graft copolymerizing vinyl chloride onto (co)polymers other than vinyl chloride, and these may be used alone or in combination of two or more. Further, the polyvinyl chloride resin may be chlorinated if necessary.

The above (2) monomers having an unsaturated bond copolymerizable with the vinyl chloride monomer are not particularly limited, and include, for example, α-olefins such as ethylene, propylene, 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; N Examples include N-substituted maleimides such as -phenylmaleimide and N-cyclohexylmaleimide, which may be used alone or in combination of two or more.

The above (3) copolymer for graft copolymerizing vinyl chloride is not particularly limited as long as it graft copolymerizes vinyl chloride, for example, ethylene-vinyl acetate copolymer, ethylene-vinyl acetate- Carbon oxide copolymer, ethylene-ethyl acrylate copolymer, ethylene-butyl acrylate-carbon monoxide copolymer, ethylene-methyl methacrylate copolymer, ethylene-propylene copolymer, acrylonitrile-butadiene copolymer, polyurethane, Examples include chlorinated polyethylene and chlorinated polypropylene, and these may be used alone or in combination of two or more.

The average degree of polymerization of the above-mentioned polyvinyl chloride resin is not particularly limited, but if it becomes small, the physical properties of the molded product will deteriorate, and if it becomes large, the melt viscosity will increase and molding will become difficult, so it is 400 to 1, 600 is preferable, 500 to 1,500 is more preferable, and even more preferably 600 to 1,400.
The above average degree of polymerization refers to the resin obtained by dissolving vinyl chloride resin in tetrahydrofuran (THF), removing insoluble components by filtration, and then drying and removing THF in the filtrate. -2: 1999 "Plastics - Vinyl chloride homopolymers and copolymers (PVC) - Part 2: How to make test pieces and how to determine various properties" means the average degree of polymerization measured in accordance with "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 above-mentioned polyvinyl chloride resin is not particularly limited, and any conventionally known polymerization method can be adopted, such as bulk polymerization method, solution polymerization method, emulsion polymerization method, suspension polymerization method, etc. Can be mentioned.

The method for chlorinating the polyvinyl chloride resin is not particularly limited, and conventionally known chlorination methods can be employed, such as thermal chlorination methods, photo chlorination methods, and the like.

Any of the above-mentioned polyvinyl chloride resins may be used after being crosslinked or modified as long as the fire resistance performance as a resin composition is not impaired. In this case, a resin that has been crosslinked or modified in advance may be used, or it may be crosslinked or modified at the same time as additives are added, or the resin may be crosslinked or modified after the above components are blended with the resin. . There are no particular limitations on the crosslinking method for the above resin, and conventional crosslinking methods for polyvinyl chloride resins are used, such as crosslinking using various crosslinking agents and peroxides, crosslinking by electron beam irradiation, and water crosslinkable materials. For example, methods such as

(thermal expandable graphite)
The thermally expandable graphite contained in the vinyl chloride resin composition constituting the intermediate layer 2 is thermally expandable graphite in the form of scales, spheres, and the like. Thermally expandable graphite expands when heated, and is produced by treating powder such as natural scale graphite, pyrolytic graphite, or quiche graphite with an inorganic acid and a strong oxidizing agent to generate a graphite intercalation compound. It is a type of crystalline compound that maintains a carbon layered structure. 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.
Further, the thermally expandable graphite obtained by the acid treatment as described above may be further neutralized with a neutralizing agent such as ammonia, 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.

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 other than when a fire occurs. Furthermore, in the event of a 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 thermally expandable graphite and effectively exhibiting fire resistance.

The content of thermally expandable graphite in the vinyl chloride resin composition constituting the intermediate layer 2 is 5 parts by mass to 20 parts by mass based on 100 parts by mass of the polyvinyl chloride resin. If the content of 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 expandability of the intermediate layer 2 will decrease. It becomes insufficient and sufficient fire resistance cannot be obtained. Furthermore, if the content of 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 may crack. Tensile strength decreases due to cracks forming at the starting point. The content of thermally expandable graphite in the vinyl chloride resin composition constituting the intermediate layer 2 is preferably 5.5 parts by mass or more, and 6.0 parts by mass, based on 100 parts by mass of the polyvinyl chloride resin. It is more preferably at least 6.5 parts by mass, and even more preferably at least 6.5 parts by mass. When the content of thermally expandable graphite is at least the above lower limit, the intermediate layer 2 has sufficient thermal expandability. Further, 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, based on 100 parts by mass of the polyvinyl chloride resin. It is more preferably at most 15 parts by mass, and even more preferably at most 15 parts by mass. The tensile strength of the multilayer pipe 10 becomes sufficient because the content of thermally expandable graphite is below the above upper limit.

(zeolite)
The skeleton structure of the zeolite contained in the vinyl chloride resin composition constituting the intermediate layer 2 is not particularly limited. Specific examples of the skeleton structure of the zeolite used in the present invention include A type, ferrierite, MXM-22, ZSM-5, mordenite, L type, Y type, X type, beta type, etc. One or more types selected from the following.
Further, a thermally expandable material such as gas or liquid may be adsorbed in advance on the surface of the cavity wall constituting the cavity of the porous structure of the zeolite. The adsorbed thermally expandable material may be of any number of types as long as it is one or more. When a gaseous or liquid thermally expandable material is adsorbed on the surface of the cavity wall constituting the zeolite cavity, the thermally expandable material adsorbed on the zeolite is vaporized by heat within the vinyl chloride resin. It becomes possible to increase the expansion magnification.

The zeolite content contained in the vinyl chloride resin composition constituting the intermediate layer 2 is 0.6 parts by mass to 5.0 parts by mass based on 100 parts by mass of the polyvinyl chloride resin. If the zeolite content contained in the vinyl chloride resin composition constituting the intermediate layer 2 is less than 0.6 parts by mass based on 100 parts by mass of the polyvinyl chloride resin, the expandability and expansion of the multilayer pipe will deteriorate. The strength of the remaining residue becomes insufficient and sufficient fire resistance cannot be obtained. Furthermore, if the content of zeolite in the vinyl chloride resin composition constituting the intermediate layer 2 is more than 5.0 parts by mass with respect to 100 parts by mass of the polyvinyl chloride resin, the amount of inorganic substances added will increase. This leads to a decrease in mechanical strength. It is preferable that the zeolite content contained in the vinyl chloride resin composition constituting the intermediate layer 2 is 0.7 parts by mass or more, and 0.8 parts by mass or more, based on 100 parts by mass of the polyvinyl chloride resin. It is more preferable that it is, and it is even more preferable that it is 1.0 parts by mass or more. When the content of zeolite is at least the above lower limit, the expandability of the multilayer pipe and the strength of the residue after expansion become sufficient. Further, it is preferable that the zeolite content contained in the vinyl chloride resin composition constituting the intermediate layer 2 is 4.5 parts by mass or less, and 4.0 parts by mass or less, based on 100 parts by mass of the polyvinyl chloride resin. It is more preferably at most 3.5 parts by mass, and even more preferably at most 3.5 parts by mass. When the content of zeolite is below the above upper limit value, the amount of inorganic substances added can be suppressed, and a decrease in mechanical strength can be suppressed.

The ammonia contained on the surface of the cavity wall of the zeolite preferably has an acid amount of 1.0 mmol/g or more when heated to 500° C. as measured by ammonia temperature-programmed desorption measurement (NH ₃ -TPD measurement). It is more preferably 2 mmol/g or more, and even more preferably 1.5 mmol/g or more. When the amount of acid when heated to 500° C. is at least the above lower limit, a sufficient metal corrosion inhibiting effect is exhibited. Furthermore, the amount of acid when heated to 500°C by ammonia temperature-programmed desorption measurement (NH ₃ -TPD measurement) is preferably 3.0 mmol/g or less, more preferably 2.8 mmol/g or less. It is preferably 2.6 mmol/g or more, and more preferably 2.6 mmol/g or more. When the amount of acid when heated to 500°C is below the above upper limit, it is possible to suppress deterioration of the vinyl chloride resin due to generated ammonia and prevent a decrease in mechanical strength.
The method for determining the amount of acid will be explained in detail in the description of Examples, but the outline is as follows. To determine the amount of acid, first, a sample is prepared by cutting out a part of a multilayer tube made of vinyl chloride, and the sample is dissolved in an organic solvent to separate the zeolite contained in the sample. Take it out. After the obtained zeolite is pretreated under a rare gas, ammonia is adsorbed using a mixed gas. Next, after a predetermined period of time, change to a mixed gas and circulate the rare gas at a predetermined temperature for a predetermined period of time to remove ammonia, and use a thermal conductivity detector (TCD detector) to determine the amount of residual ammonia as the amount of ammonia adsorbed. Can be done.

The specific surface area of zeolite measured by the BET method is preferably 200 m ² /g or more, more preferably 250 m ² /g or more, and even more preferably 300 m ² /g or more. When the specific surface area of zeolite measured by the BET method is equal to or larger than the above lower limit, the amount of ammonia generated on the low temperature side increases, and the corrosion inhibiting effect is likely to be exhibited. Further, the specific surface area of the zeolite measured by the BET method is preferably 700 m ² /g or less, more preferably 680 m ² /g or less, and even more preferably 650 m ² /g or less. When the specific surface area of the zeolite measured by the BET method is less than or equal to the above upper limit, it is possible to suppress the amount of ammonia generated during molding from becoming excessive, and to prevent deterioration in the strength of the resin base material itself.

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

As the inorganic filler, a wide variety of known inorganic fillers can be used, and there are no particular limitations. 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, dawnite, hydrotalcite, calcium sulfate, barium sulfate, gypsum fiber, calcium silicate, talc, clay, mica, montmorillonite, bentonite, activated clay, sepiolite, imogolite , sericite, glass fiber, glass beads, silica balloons, aluminum nitride, boron nitride, silicon nitride, carbon black, graphite, carbon fiber, carbon balloons, charcoal powder, various metal powders, potassium titanate, magnesium sulfate "MOS" , lead zirconate titanate, aluminum borate, molybdenum sulfide, silicon carbide, stainless fiber, zinc borate, various magnetic powders, slag fibers, fly ash, dehydrated sludge, etc. I can do it.

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 lowering 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. 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 types selected from the group consisting of paraffin wax, polyolefin wax, ester wax, and montan acid wax can be used.

A wide range of known processing aids can be used, and there are no particular limitations. Examples 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, 2-ethylhexyl acrylate-methyl methacrylate-butyl methacrylate copolymer, and the like. These may be used alone or in combination of two or more.

As the impact modifier, a wide variety of known impact modifiers 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, etc. can be used.

As the heat resistance improver, a wide variety of known ones can be used, and there is no particular limitation. For example, α-methylstyrene resin, N-phenylmaleimide resin, etc. can be used.

The antioxidant is not particularly limited, and a wide variety of known antioxidants can be used. Examples include phenolic antioxidants.

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

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

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

Furthermore, 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.

The thermoplastic elastomer is not particularly limited, and a wide variety of known thermoplastic elastomers 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 elastomer such as vinylidene chloride copolymer, styrene thermoplastic elastomer, olefin thermoplastic elastomer, urethane thermoplastic elastomer, polyester thermoplastic elastomer, and polyamide thermoplastic elastomer One or more types can be used.

As a method for mixing the above-mentioned thermally expandable graphite, zeolite, and additives into the polyvinyl chloride resin, a wide variety of known methods can be employed. Specifically, hot blending methods, cold blending methods, etc. may be mentioned.

<Applications for multilayer pipes>
The multilayer pipe 10 of the present invention as described above has high thermal expansivity and suppresses thermal deformation of the multilayer pipe, so it can be suitably used as plumbing such as drainage pipes, ducts, and electrical conduits in buildings. It is. Moreover, the multilayer pipe 10 of the present invention can be suitably used not only as a constituent material of a piping body but also as a constituent material of a joint of a pipe.

<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 an 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 an embodiment of the present invention.
As shown in FIGS. 2 and 3, the manufacturing apparatus 20 for manufacturing the multilayer pipe 10 includes an inner and outer layer extruder 11, an intermediate layer extruder 12, a mold 13, a cooling water tank 15, and a take-off machine 16. , and a cutting machine 17. A mold 13 is connected to the inner and 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 taking machine 16.

In the method for manufacturing a multilayer pipe of the present invention, first, the material for the inner layer and the material for the outer layer are charged into the inner and outer layer extruder 11 using a hopper. The mixture is melted and kneaded and extruded into a mold 13. Further, the material for the intermediate layer is charged into the intermediate layer extruder 12 using a hopper, the material for the intermediate layer is melted and kneaded in the intermediate layer extruder 12, and extruded into the mold 13.

Next, in the mold 13, the inner layer material, the outer layer material, and the intermediate layer material are heated to form an uncured multilayer tube having a three-layer structure.
The heating temperature in the mold 13 is preferably 160° C. or more and 200° C. or less, more preferably 170° C. or more and 195° C. or less, 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 more and 190°C or less.
The heating time in the mold 13 is the time during which the inner layer material and the outer layer material exist in the mold 13, and from the viewpoint of improving the fluidity of the inner layer material and the outer layer material, the heating time is 3 minutes or more and 10 minutes or less. It is preferably 4 minutes or more and 9 minutes or less, and even more preferably 5 minutes or more and 8 minutes or less.

Next, an uncured multilayer tube having a three-layer structure is extruded from the outlet of the mold 13 and sent to the cooling water tank 15.
A tube outer surface forming tube 14 for forming the uncured multilayer tube into a predetermined size is attached to the cooling water tank 15, and the outer surface of the uncured multilayer tube is in contact with the tube outer surface forming tube 14. Cool it down. FIG. 4 is an enlarged sectional view showing the mold 13 and tube outer surface forming tube 14 in the manufacturing apparatus. As shown in FIG. 4, the inner layer material 21 and outer layer material 23 melt-kneaded by the inner and outer layer extruder 11 and the middle layer material 22 melt-kneaded by the middle layer extruder 12 are combined into a cross section of the middle layer. The mixture is injected into a mold 13 designed so that the outer periphery thereof is a perfect circle to form an uncured multilayer pipe 10'. The unhardened multilayer tube 10' includes an unhardened inner layer 31, an unhardened outer layer 33, and an unhardened intermediate layer 32 formed of the intermediate layer material 22. The intermediate layer material 22 is foamed when the uncured multilayer tube 10' is discharged from the mold 13, and an uncured intermediate layer 32 is formed. The unhardened multilayer pipe 10' is inserted into the tube outer surface forming tube 14, and the unhardened multilayer pipe 10' is cooled in the cooling water tank 15 while being molded 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′. It is more preferable that the temperature is not less than 0.degree. C. and not more than 22.degree.
The cooling time in the cooling water tank 15 is the time during which the uncured multilayer pipe 10' exists in the cooling water tank 15, and from the viewpoint of sufficiently curing the inner layer material and the outer layer material, it is 4 minutes or more and 16 minutes or less. The time is preferably 6 minutes or more and 14 minutes or less, and even more preferably 8 minutes or more and 12 minutes or less.

Next, the multilayer pipe 10 cooled in the cooling water tank 15 is taken over using the take-off machine 16, and the multi-layer pipe 10 sent from the take-off machine 16 is cut into a predetermined length using the cutting machine 17. . In this way, a multilayer tube 10 having a predetermined length is obtained.

Although the embodiments of the present invention have been described above, the present invention is not limited to these examples at all, and it goes without saying that the present invention can be implemented in various forms without departing from the gist of the present invention.

Hereinafter, embodiments of the present invention will be described in more detail based on Examples, but the present invention is not limited thereto.

(Example and comparative example)
A resin composition was prepared using a 20 L Henschel mixer (manufactured by Kawata Co., Ltd.) based on the formulation shown in Table 1 below. After that, a part of the prepared resin composition was roll-kneaded with an 8-inch mixing roll (manufactured by Yasuda Seiki Seisakusho) at 190°C, and then press-molded with a press machine (manufactured by Toho Machinery Co., Ltd.) at 200°C to obtain a thickness. 3 mm test pieces for each example and comparative example were prepared.

<Raw materials used>
The materials used in the examples and comparative examples are as follows.
<Polyvinyl chloride resin (PVC)>
・Tokuyama Sekisui Kogyo Co., Ltd. "TS-1000R" (average degree of polymerization: 1,000)
<Thermally expandable graphite>
・Suzuhiro Chemical Co., Ltd. “GREP-EG”
<Zeolite>
・Tosoh Corporation “HSZ”

(Residue strength test)
A test piece made into a plate by roll pressing is cut into a rectangular parallelepiped having a length of 30±1 mm, a width of 30±1 mm, and a thickness of 3±0.1 mm. A hole of about 1 mm was made in 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 create a combustion residue, which was then taken out. Each test was repeated 5 times, and if the strength of the residue was low, it would fall from the mount.
<Judgment criteria>
A: Number of falls: 0 times B: Number of falls: 1 to 2 times C: Number of falls: 3 to 5 times

(Expansion magnification 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 using a caliper. Thereafter, the test pieces of each example and comparative example were placed in an electric furnace heated to 500° C. for 3 minutes to expand. Thereafter, it was taken out of the electric furnace and allowed to cool at room temperature. The thickness, length, and width of the expanded test piece that had been left to cool was measured using calipers, and the expansion ratio R was calculated using 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=(a ₁ ×b ₁ ×c ₁ )/(a ₀ ×b ₀ ×c ₀ )
_a0 : Thickness of test piece before expansion (mm)
b ₀ : Vertical length of test piece before expansion (mm)
c ₀ : Lateral length of test piece before expansion (mm)
_a1 : Thickness of test piece 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 magnification R is 7.5 or more B: Expansion magnification R is less than 7.5

(Tensile strength evaluation test)
In accordance with JIS K 7161-1:2014 "Plastics - How to determine tensile properties - Part 1", test pieces for each example and comparative example were prepared from the test specimens, and the tensile yield strength was measured at 5 mm/min. . The measurement atmosphere at this time was 23°C. Note that the tensile yield strength F (MPa) was calculated using the following formula, where the maximum load until the test piece breaks is P (N), and the cross-sectional area of the test piece is S (mm ² ).
Tensile yield strength: F=P/S
<Judgment criteria>
A: Tensile yield strength F is 45 (MPa) or more B: Tensile yield strength F is 40 (MPa) or more and less than 45 (MPa) C: Tensile yield strength F is 35 (MPa) or more and less than 40 (MPa) D : Tensile yield strength F is less than 35 (MPa)

(Metal corrosion test)
0.5 g of the resin composition prepared using a 20 L Henschel mixer (manufactured by Kawata Co., Ltd.) was sandwiched between two iron plates measuring 5 cm x 5 cm x 1 mm thick, and pressed for 10 minutes with a press machine (manufactured by Toho Machinery Co., Ltd.) at 190°C. The iron plate was cool-pressed for 1 minute to remove the resin composition on the surface, and the iron plate was checked for discoloration.
<Judgment criteria>
A: No discoloration B: Discoloration

(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 the supernatant liquid was removed. After drying the insoluble matter, a test piece was prepared. If zeolite and other inorganic components were mixed, they were separated by known separation methods (precipitation, filtration, etc.), and an extraction test piece was obtained in which only zeolite was extracted.
0.1 g of the extraction test piece was left standing under helium flow at 500° C. for 1 hour, and this was used as pretreatment. After 1 hour of pretreatment, a mixed gas containing 5% by volume of ammonia and 95% by volume of helium was passed through the sample at room temperature to saturately adsorb ammonia onto the extraction test piece. After flowing the mixed gas for 1 hour, the sample was heated to 100° C. while flowing helium gas instead of the mixed gas. After the temperature was raised, ammonia remaining in the atmosphere was removed by flowing helium gas at 100° C. for 0.5 hours.
After removing residual ammonia, the temperature was raised to 500 °C at a temperature increase rate of 10 °C/min under a helium flow rate of 30 mL/min, and the temperature was measured using a TCD detector (manufactured by Micro Track Bell) during the heating process. The measured amount of ammonia was taken as the amount of ammonia adsorbed on the sample. The amount of adsorbed ammonia per unit mass of the sample was defined as the amount of solid acid (mmol/g).

(Specific surface area measurement)
1 g of the obtained test piece was cut out. The cut test piece was dissolved in tetrahydrofuran (THF), centrifuged, and the supernatant liquid was removed. After drying the insoluble matter, a test piece was prepared. If zeolite and other inorganic components were mixed, they were separated by known separation methods (precipitation, filtration, etc.), and an extraction test piece was obtained in which only zeolite was extracted.
0.1 g of the extracted test piece is discarded under vacuum while being heated at 200°C, and the weight of the test piece after degassing is measured. Thereafter, the amount of nitrogen gas adsorbed on the solid surface was measured at the temperature of liquid nitrogen in a relative pressure range of 0.05 to 0.995, and the specific surface area was calculated from the obtained adsorption isotherm.

1... Inner layer 2... Intermediate layer 3... Outer layer 10... Multilayer pipe 10'... Uncured fireproof pipe 11... Inner and outer layer extruder 12... Intermediate layer extruder 13... Mold 14... Tube for forming the tube outer surface 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 (3)

inner layer and
an intermediate layer disposed outside the inner layer;
an outer layer disposed outside the intermediate layer,
The intermediate layer includes a polyvinyl chloride resin, thermally expandable graphite, and zeolite,
The content of the thermally expandable graphite is 5.0 parts by mass to 20.0 parts by mass based on 100 parts by mass of the polyvinyl chloride,
In the multilayer pipe, the content of the zeolite is 0.6 parts by mass to 5.0 parts by mass based on 100 parts by mass of the polyvinyl chloride. The zeolite contains ammonia on the cavity wall surface,
The multilayer tube according to claim 1, having an acid amount of 1.0 mmol/g to 3.0 mmol/g when heated to 500° C. as measured by ammonia temperature-programmed desorption measurement (NH ₃ -TPD measurement). The multilayer pipe according to claim 1 or 2, wherein the zeolite has a specific surface area of 250 m ² /g or more and 700 m ² /g or less as measured by the BET method.