JP2022052466A - Multilayer pipe and resin composition for the same - Google Patents

Abstract

To provide a multilayer pipe and a resin composition for the same having fire resistance and thermal deformation suppressing performance.SOLUTION: A multilayer pipe includes 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. At least one of the inner layer 1, the intermediate layer 2, and the outer layer 3 includes polyvinyl chloride-based resin, thermal expansible graphite, and borosilicate glass.SELECTED DRAWING: Figure 1

Description

The present invention relates to a multilayer tube and a resin composition for a multilayer tube.

In buildings, various properties are required for pipe materials used with the advancement of building technology. For example, in order to use the pipe material in the fire protection section, high fire resistance is required.

As a specific performance of fire resistance, there is a demand for a function of expanding a pipe material due to the heat of fire to block the pipe itself and preventing the transfer of fire through the pipe. As a resin composition for piping used for such piping, a resin composition for piping containing thermally expandable graphite has been proposed (see, for example, Patent Document 1).

On the other hand, the temperature has risen due to abnormal weather in recent years, and the room temperature inside the room where the pipe material is stored for a long time before construction may rise. In such an environment, the pipe material stores heat, but when it contains heat-expandable graphite, the heat-expandable graphite becomes a heat storage material, so that there is a further tendency to store heat. When the pipe materials are stacked and stored, the pipe material having a perfect circular cross section may be thermally deformed and the cross section may become elliptical. If thermal deformation occurs, it will come off when it is bonded to the joint, and even if it can be bonded, a gap will be created, which will cause water leakage.

In order to suppress such thermal deformation, a tube material having a multilayer structure having an intermediate layer in which a tube having a fire resistance and a borosilicate glass having a low coefficient of linear expansion is blended has been studied (see, for example, Patent Document 2). However, with borosilicate glass alone, although thermal deformation resistance can be obtained, it is difficult to maintain fire resistance, and there is a tendency for gaps to be easily created between the backfill material at the section penetration and the outer layer, and smoke leaks from the gaps. It tends to be difficult to develop fire resistance.

Japanese Unexamined Patent Publication No. 2009-74689 International Publication 2011/136245

In view of the above circumstances, it is an object of the present invention to provide a resin composition for a multilayer tube and a multilayer tube having fire resistance and thermal deformation suppressing performance.

As a result of diligent research to achieve the above object, the present inventors have made a multilayer structure having a polyvinyl chloride resin, a heat-expandable graphite and borosilicate glass in the same layer, so that not only the fire resistance but also the fire resistance can be achieved. It has been found that it is possible to make a multi-layer tube that is also excellent in suppressing thermal deformation. The present inventors have further studied based on such findings, and have 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 arranged outside the inner layer, and an outer layer arranged outside the intermediate layer are provided, and at least one of the inner layer, the intermediate layer, and the outer layer is polyvinyl chloride. Multilayer tube containing based resin, thermally expandable graphite and borosilicate glass.
[2] The multilayer tube according to [1], wherein the fiber length of the borosilicate glass is 0.5 mm or more and 6.0 mm or less.
[3] The multilayer tube according to [1] or [2], wherein the content of the thermally expandable graphite is 3 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the polyvinyl chloride resin.
[4] The multilayer according to any one of [1] to [3], wherein the content of the borosilicate glass is 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by weight of the polyvinyl chloride resin. tube.
[5] The multilayer tube according to any one of [1] to [4], wherein the polyvinyl chloride resin, the heat-expandable graphite, and the borosilicate glass are contained in the intermediate layer.
[6] A resin composition for a multilayer tube, which comprises a polyvinyl chloride resin, a heat-expandable graphite, and borosilicate glass.

According to the present invention, it is possible to provide a resin composition for a multi-layer pipe and a multi-layer pipe having fire resistance and thermal deformation suppressing performance.

It is a schematic cross-sectional view of the multilayer tube which concerns on embodiment of this invention. It is a top view which shows an example of the manufacturing apparatus of the multilayer tube which concerns on embodiment of this invention. It is a front view which shows an example of the manufacturing apparatus of the multilayer tube which concerns on embodiment of this invention. It is a block diagram which shows an example of the mold used for the manufacturing apparatus of the multilayer tube which concerns on embodiment of this invention, and the tube for forming the outer surface of a multilayer tube.

[Multi-layer tube]
As shown in FIG. 1, the multilayer tube 10 according to the 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 multilayer tube 10, and the outer layer 3 constitutes the outermost layer of the multilayer tube 10. The multilayer tube 10 shown in FIG. 1 has a multilayer structure in which the inner layer 1, the intermediate layer 2, and the outer layer 3 are laminated from the inside of the multilayer tube in this order. The configuration of the multilayer tube 10 is not limited to three layers, and for example, the intermediate layer 2 may be a plurality of layers.
At least one of the inner layer 1, the intermediate layer 2 and the outer layer 3 contains a polyvinyl chloride resin, a heat-expandable graphite, and borosilicate glass. By containing polyvinyl chloride resin, thermally expandable graphite and borosilicate glass in at least one of the inner layer 1, the intermediate layer 2 and the outer layer 3 constituting the multilayer tube 10, not only the fire resistance but also the suppression of thermal deformation is achieved. Can also be an excellent multilayer tube 10. From the above viewpoint, it is preferable that it is contained in all of the inner layer 1, the intermediate layer 2 and the outer layer 3, and it is more preferable that it is contained in the intermediate layer 2.

The thickness of the inner layer 1 is preferably 0.2 mm or more and 3.0 mm or less, more preferably 0.4 mm or more and 2.5 mm or less, and further preferably 0.6 mm or more and 2.0 mm or less. ..
The thickness of the intermediate layer 2 is preferably 0.2 mm or more and 3.0 mm or less, more preferably 0.4 mm or more and 2.5 mm or less, and further preferably 0.6 mm or more and 2.0 mm or less. preferable.
The thickness of the outer layer 3 is preferably 0.2 mm or more and 3.0 mm or less, more preferably 0.4 mm or more and 2.5 mm or less, and further preferably 0.6 mm or more and 2.0 mm or less. ..
The thickness of the multilayer tube 10 is preferably 0.6 mm or more and 9.0 mm or less, more preferably 1.2 mm or more and 7.5 mm or less, and further preferably 1.8 mm or more and 6.0 mm or less. preferable.

(Polyvinyl chloride resin)
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 commutable with the vinyl chloride monomer; 3) Examples thereof include a graft copolymer obtained by graft-copolymerizing vinyl chloride to a (co) polymer 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 monomer having an unsaturated bond copolymerizable with the above (2) vinyl chloride monomer is not particularly limited, and for example, α-olefins such as ethylene, propylene and butylene; vinyl esters such as vinyl acetate and vinyl propionate. Classes; 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 thereof include N-substituted maleimides such as phenylmaleimide and N-cyclohexylmaleimide, which may be used alone or in combination of two or more.

The copolymer for graft-copolymerizing vinyl chloride (3) is not particularly limited as long as it is for graft-copolymerizing vinyl chloride, and is, for example, an ethylene-vinyl acetate copolymer or an ethylene-vinyl acetate-1. 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 thereof 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 polyvinyl chloride resin is not particularly limited, but if it is small, the physical properties of the molded product are deteriorated, and if it is large, the melt viscosity becomes high and molding becomes difficult. 600 is preferable, 500 to 1,500 is more preferable, and 600 to 1,400 is further preferable.
The average degree of polymerization is the JIS K 6720, which is a resin obtained by dissolving a vinyl chloride resin in tetrahydrofuran (THF), removing insoluble components by filtration, and then drying and removing THF in the filtrate as a sample. -2: 1999 Means the average degree of polymerization measured in accordance with "Plastic-Vinyl Chloride Homopolymers and Copolymers (PVC) -Part 2: How to Make Specimens and Obtain Various Properties".

The polymerization method of the polyvinyl chloride-based resin is not particularly limited, and any conventionally known polymerization method can be adopted. For example, a bulk polymerization method, a solution polymerization method, an emulsion polymerization method, a suspension polymerization method and the like can be used. Can be mentioned.

The chlorination method for the polyvinyl chloride resin is not particularly limited, and conventionally known chlorination methods can be adopted, and examples thereof include a thermal chlorination method and a photochlorination method.

Any of the above polyvinyl chloride resins may be crosslinked or modified before use as long as 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, may be crosslinked or modified at the same time when the additive or the like is added, or may be crosslinked or modified after the above components are added to the resin. .. The cross-linking method of the above resin is also not particularly limited, and a usual cross-linking method of a polyvinyl chloride resin, for example, various cross-linking agents, cross-linking using a peroxide, cross-linking by electron beam irradiation, and a water cross-linking material are used. The method used is mentioned.

(Thermal expandable graphite)
As the heat-expandable graphite, known ones can be widely used, and there is no particular limitation. Specific examples of the heat-expandable graphite include monomethylamine, dimethylamine, trimethylamine, ethylamine, propylamine, and butylamine. Examples of the alkali metal compound and the alkaline earth metal compound include hydroxides such as potassium, sodium, calcium, barium and magnesium, oxides, carbonates, sulfates and organic acid salts. These may be used alone or in combination of two or more.
The shape of the heat-expandable graphite contained in the multilayer tube of the present invention is not particularly limited, but is preferably a scaly heat-expandable graphite.

The content of the heat-expandable graphite contained in the multilayer tube of the present invention is preferably 1 part by mass or more, more preferably 2 parts by mass or more, based on 100 parts by mass of the polyvinyl chloride resin. It is more preferably 3 parts by mass or more. When the content of the heat-expandable graphite is at least the above lower limit value, the heat-expandability of the multilayer tube becomes sufficient. Further, the content of the heat-expandable graphite contained in the multilayer tube of the present invention is preferably 20 parts by mass or less, and more preferably 18 parts by mass or less with respect to 100 parts by mass of the polyvinyl chloride resin. It is preferably 16 parts by mass or less, and more preferably 16 parts by mass or less. When the content of the heat-expandable graphite is not more than the above upper limit value, the strength of the multilayer tube becomes sufficient.

(Borosilicate glass)
The fiber length of the borosilicate glass contained in the multilayer tube of the present invention is preferably 0.5 mm or more, more preferably 0.7 mm or more, and further preferably 0.9 mm or more. When the fiber length of the borosilicate glass is equal to or greater than the above lower limit, the borosilicate glass having a small linear expansion coefficient does not stretch even when the multilayer tube is heat-stored and the polyvinyl chloride is thermally deformed, so that the multilayer tube does not stretch. It is possible to suppress the shape deformation of. Further, the fiber length of the borosilicate glass contained in the multilayer tube of the present invention is preferably 6.0 mm or less, more preferably 5.5 mm or less, and further preferably 5.0 mm or less. When the fiber length of the borosilicate glass is not more than the above upper limit value, the fire resistance is easily exhibited without suppressing the effect of the heat-expandable graphite.
As the borosilicate glass, for example, "FC" manufactured by Nissin Material Co., Ltd. can be commercially obtained.

The content of the borosilicate glass contained in the multilayer tube of the present invention is preferably 0.5 parts by mass or more, and preferably 1.0 part by mass or more with respect to 100 parts by mass of the polyvinyl chloride resin. More preferably, it is more preferably 1.5 parts by mass or more. When the content of the borosilicate glass contained in the multilayer tube is at least the above lower limit value, the shape deformation of the multilayer tube due to heat can be suppressed. The content of the borosilicate glass contained in the multilayer tube of the present invention is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, based on 100 parts by mass of the polyvinyl chloride resin. , 6 parts by mass or less is more preferable. When the content of the borosilicate glass contained in the multilayer tube is not more than the above upper limit value, the fire resistance is easily exhibited without suppressing the effect of the heat-expandable graphite.

(Additive)
The multilayer tube of the present invention includes inorganic fillers, lubricants, processing aids, impact modifiers, heat-resistant improvers, antioxidants, light stabilizers, ultraviolet absorbers, pigments, as long as the physical properties are not impaired. Additives such as plasticizers and thermoplastic elastomers may be added.

As the inorganic filler, known ones can be widely used, and there is no particular limitation. Specific examples of the inorganic filler include silica, diatomaceous soil, alumina, zinc oxide, titanium oxide, calcium oxide, magnesium oxide, iron oxide, tin oxide, antimony oxide, ferrites, calcium hydroxide, magnesium hydroxide, and water. Aluminum oxide, basic magnesium carbonate, calcium carbonate, magnesium carbonate, zinc carbonate, barium carbonate, dawn night, hydrotalcite, calcium sulfate, barium sulfate, gypsum fiber, calcium silicate, talc, clay, mica, montmorillonite, bentonite, Active white clay, sepiolite, imogolite, sericite, glass fiber, glass beads, silica-based balun, aluminum nitride, boron nitride, silicon nitride, carbon black, graphite, carbon fiber, carbon balun, charcoal powder, various metal powders, potassium titanate , Magnesium sulfate, lead zirconate titanate, aluminum volate, molybdenum sulfide, silicon carbide, stainless fiber, zinc borate, various magnetic powders, slag fibers, fly ash, dehydrated sludge, etc. Can be mentioned.

As the lubricant, known ones can be widely used, and there is no particular limitation. Examples of the lubricant include an internal lubricant and an external lubricant. 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 may be used. can. Further, the external lubricant is used for the purpose of enhancing the sliding effect between the molten resin and the metal surface during the molding process. 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.

As the processing aid, known ones can be widely used, and there is no particular limitation. Examples of the processing aid include acrylic processing aids such as alkylacrylate-alkylmethacrylate 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 an n-butyl acrylate-methyl methacrylate copolymer and a 2-ethylhexyl acrylate-methyl methacrylate-butyl methacrylate copolymer. These may be used alone or in combination of two or more.

As the impact modifier, known ones can be widely used, and there is no particular limitation. As the impact modifier, 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, known ones can be widely used, and there is no particular limitation. As the heat resistance improver, for example, α-methylstyrene-based resin, N-phenylmaleimide-based resin and the like can be used.

The antioxidant is not particularly limited, and known ones can be widely used. Examples of the antioxidant include phenolic antioxidants and the like.

The light stabilizer is not particularly limited, and known ones can be widely used. Examples of the light stabilizer include a hindered amine-based light stabilizer and the like.

The ultraviolet absorber is not particularly limited, and known ones can be widely used. Examples of the ultraviolet absorber 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 known pigments can be widely used. Examples of the pigment include organic pigments such as azo-based, phthalocyanine-based, slene-based, and dye lake-based; inorganic pigments such as oxide-based, molybdenum chromate-based, sulfide / selenium-based, and ferrocyanine-based pigments. Be done. These may be used alone or in combination of two or more.

The plasticizer is not particularly limited, and known ones can be widely used. As the plasticizer, 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 known ones can be widely used. Examples of the thermoplastic elastomer include acrylic nitrile-butadiene copolymer (NBR), ethylene-vinyl acetate copolymer (EVA), ethylene-vinyl acetate-carbon monoxide copolymer (EVACO), and vinyl chloride-vinyl acetate. Vinyl chloride-based thermoplastic elastomers such as copolymers and vinyl chloride-vinylidene chloride copolymers, styrene-based thermoplastic elastomers, olefin-based thermoplastic elastomers, urethane-based thermoplastic elastomers, polyester-based thermoplastic elastomers, and polyamide-based thermoplastics. One or more selected from the group consisting of elastomers can be used.

As a method of mixing the above-mentioned thermally expandable graphite, borosilicate glass, and an additive with a polyvinyl chloride resin, a known method can be widely adopted. Specific examples thereof include a method using hot blending and a method using cold blending.

<Resin composition for multi-layer pipe>
The resin composition for a multilayer tube of the present invention contains the above-mentioned polyvinyl chloride-based resin, thermally expandable graphite, and borosilicate glass. As long as the resin composition for a multilayer tube does not impair its physical properties, the above-mentioned inorganic filler, lubricant, processing aid, impact modifier, heat resistance improver, antioxidant, light stabilizer, ultraviolet absorber, etc. Additives such as pigments, plasticizers and thermoplastic elastomers may be added.
The resin composition for a multilayer tube of the present invention can be used by changing the content ratio of each material according to the purpose or application such as which of the inner layer 1, the intermediate layer 2 and the outer layer 3 is formed.

<Usage of multi-layer pipe>
The multi-layer pipe of the present invention as described above has high thermal expansion, suppresses thermal deformation during storage, and can be suitably used as pipes for drainage pipes, ducts, conduits, etc. of buildings. .. Further, the multilayer pipe 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 a pipe joint.

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

In the method for manufacturing a multilayer tube of the present invention, first, the inner layer material and the outer layer material are charged into the inner / outer layer extruder 11 by using a hopper, and the inner layer material and the outer layer material are charged in the inner / outer layer extruder 11. It is melt-kneaded and extruded into a mold 13. Further, the material of the intermediate layer is put into the intermediate layer extruder 12 by using a hopper, and the material of the intermediate layer is melt-kneaded in the intermediate layer extruder 12 and extruded into the mold 13.

Next, in the mold 13, the material of the inner layer and the material of the outer layer are melt-kneaded and the material of the intermediate layer is melt-kneaded and kneaded 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 higher and 200 ° C. or lower, more preferably 170 ° C. or higher and 195 ° C. or lower, and further preferably 180 ° C. or higher and 190 ° C. or lower.
The heating time in the mold 13 is preferably 3 minutes or more and 10 minutes or less, more preferably 4 minutes or more and 9 minutes or less, and further preferably 5 minutes or more and 8 minutes or less.

Next, an uncured multilayer pipe 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 an uncured multilayer tube to 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 with. FIG. 4 is an enlarged cross-sectional view showing the mold 13 and the tube outer surface forming tube 14 in the manufacturing apparatus. As shown in FIG. 4, the cross section of the intermediate layer is obtained by combining the inner layer material 21 and the outer layer material 23 melt-kneaded by the inner-outer layer extruder 11 and the intermediate layer material 22 melt-kneaded by the intermediate layer extruder 12. It is injected into a mold 13 designed so that the shape of the outer peripheral edge of the shape is a perfect circle, and an uncured multilayer tube 10'is formed. The uncured multilayer tube 10'includes an uncured inner layer 31 and an uncured outer layer 33, and an uncured intermediate layer 32 formed of the material 22 of the intermediate layer. The material 22 of the intermediate layer foams when the uncured multilayer tube 10'is discharged from the mold 13, and the uncured intermediate layer 32 is formed. The uncured multilayer tube 10'is inserted into the tube outer surface forming tube 14, and the uncured multilayer tube 10'is cooled in the cooling water tank 15 while being molded to 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, and further preferably 18 ° C. or higher and 22 ° C. or lower.
The cooling time in the cooling water tank 15 is preferably 4 minutes or more and 16 minutes or less, more preferably 6 minutes or more and 14 minutes or less, and further preferably 8 minutes or more and 12 minutes or less.

Next, the take-up machine 16 is used to take up the multi-layer pipe 10 cooled in the cooling water tank 15, and the cutting machine 17 is used to cut the multi-layer pipe 10 sent from the take-up machine 16 to a predetermined length. .. 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, and it is needless to say 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.

(Examples and comparative examples)
Based on the formulation shown in Table 1 below, roll knead with an 8-inch mixing roll (manufactured by Yasuda Seiki Seisakusho) at 190 ° C for 3 minutes, and press-molded with a press machine at 200 ° C (manufactured by Toho Machinery Co., Ltd.) for 2 minutes. An inner and outer layers having a thickness of 1 mm were prepared.
Based on the formulation shown in Table 1 below, roll knead with an 8-inch mixing roll (manufactured by Yasuda Seiki Seisakusho) at 190 ° C for 3 minutes, and press-molded with a press machine at 200 ° C (manufactured by Toho Machinery Co., Ltd.) for 2 minutes. An intermediate layer having a thickness of 1 mm was prepared.
Next, with the intermediate layer sandwiched between the prepared inner and outer layers, a test piece having a thickness of 3 mm (Examples 1 to 12, Comparative Example) was press-molded for 1 minute with a press machine at 200 ° C. (manufactured by Toho Machinery Co., Ltd.). 1 to 2) were produced.
Table 1 shows the configurations and results of the prepared test pieces.

(Expansion magnification evaluation test)
A plate-shaped test piece (length and width: 30 mm × 30 mm × 3 mm) was cut out into a rectangular parallelepiped shape by a roll press, and the thickness, length, and width of the test piece before being put into the electric furnace were measured with a caliper. Then, the test pieces of each Example and Comparative Example were placed in an electric furnace heated to 950 ° C. for 4 minutes and expanded. After that, it was taken out from an electric furnace and allowed to cool at room temperature. The thickness, length, and width of the cooled expanded test piece were measured with a caliper, and the expansion ratio R was calculated by the following formula and determined according to the following criteria.
Expansion ratio: R = (a1 × b1 × c1) / (a0 × b0 × c0)
a0: Specimen thickness (mm) before expansion
b0: Vertical length of test piece before expansion (mm)
c0: Specimen lateral length (mm) before expansion
a1: Specimen thickness (mm) after expansion
b1: Vertical length of the test piece after expansion (mm)
c1: Horizontal length of test piece after expansion (mm)
<Judgment criteria>
A: Expansion ratio R is 5 or more B: Expansion ratio R is less than 5 4 or more C: Expansion ratio R is less than 4

(Linear expansion test)
A plate-shaped test piece (length and width: 100 mm × 100 mm × 3 mm) is cut out by a roll press and annealed at 100 ° C. for 1 hour. Then, in a constant temperature room maintained at 23 ° C. (T ₀ ), a total of 5 point marks are marked on the surface of the test piece at 1 cm intervals from the center (L ₀ ). The test piece is placed in an oven at a constant temperature of 80 ° C. (T ₁ ) for 3 hours, then taken out, the length between marked lines (L ₁ ) is measured, and the coefficient of linear expansion L is calculated by the following formula.
Linear expansion rate: L = (L ₁ -L ₀ ) / (L ₀ x (T ₁ -T ₀ )) (mm / mm · ° C)
<Judgment criteria>
A: Linear expansion rate L is 6.0 × 10 ^-5 or less B: Linear expansion rate L is larger than 6.0 × 10 ^-5 and 6.3 × 10 ^-5 or less C: Linear expansion rate L is 6.3 × Greater than ^10-5

(Tensile strength evaluation test)
In accordance with JIS K 7161-1: 2014 "Plastic-How to determine tensile properties-Part 1", the tensile yield strength was measured at 5 mm / min for the test pieces of each Example and Comparative Example. The measurement atmosphere at this time was 23 ° C. The tensile yield strength F (MPa) was calculated by the following formula, where the maximum load until the test piece broke was P (N) and the cross-sectional area of the test piece was S (mm ² ).
Tensile yield strength: F = P / S
<Judgment criteria>
A: Tension yield strength F is 42 (MPa) or more B: Tension yield strength F is 35 (MPa) or more and less than 42 (MPa) C: Tension yield strength F is less than 35 (MPa)

1 ... Inner layer 2 ... Intermediate layer 3 ... Outer layer 10 ... Multilayer pipe 10'... Uncured multilayer pipe 11 ... Inner / outer layer extruder 12 ... Intermediate layer extruder 13 ... Mold 14 ... Pipe outer surface forming tube 15 ... Cooling water tank 16 ... Pick-up machine 17 ... Cutting machine 20 ... Manufacturing equipment 21 ... Inner layer material 22 ... Intermediate layer material 23 ... Outer layer material 31 ... Uncured inner layer 32 ... Uncured intermediate layer 33 ... Uncured outer layer

Claims (6)

Inner layer and
An intermediate layer arranged outside the inner layer and
With an outer layer arranged on the outside of the intermediate layer,
At least one of the inner layer, the intermediate layer, and the outer layer is a multilayer tube containing a polyvinyl chloride resin, a heat-expandable graphite, and borosilicate glass. The multilayer tube according to claim 1, wherein the fiber length of the borosilicate glass is 0.5 mm or more and 6.0 mm or less. The multilayer tube according to claim 1 or 2, wherein the content of the heat-expandable graphite is 3 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the polyvinyl chloride resin. The multilayer tube according to any one of claims 1 to 3, wherein the content of the borosilicate glass is 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by weight of the polyvinyl chloride resin. The multilayer tube according to any one of claims 1 to 4, wherein the polyvinyl chloride resin, the heat-expandable graphite, and the borosilicate glass are contained in the intermediate layer. A resin composition for a multilayer tube, which comprises a polyvinyl chloride resin, a heat-expandable graphite, and borosilicate glass.

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