Two-layer tube and production method therefor

Abstract

Provided is a two-layer tube comprising an inner layer (A) and an outer layer (B) directly formed on the inner layer (A), wherein the inner layer (A) includes a copolymer (a) comprising a tetrafluoroethylene unit and a perfluoro(propyl vinyl ether) unit and the outer layer (B) includes a polymer (b) containing at least a chlorotrifluoroethylene unit. The copolymer (a) has a weight loss through one-hour heating at 380°C of 0.05 mass% or less. The ratio of the thickness of the inner layer (A) to the thickness of the outer layer (B), (A) / (B), is 30.0 / 70.0 to 67.0 / 33.0.

Description

Double-layer tube and its manufacturing method

[0001] The present disclosure relates to a double-walled tube and a method for manufacturing the same.

[0002] Patent Document 1 describes a chlorotrifluoroethylene copolymer-containing laminate having a layer (A) made of a tetrafluoroethylene / perfluorovinyl ether copolymer and / or a tetrafluoroethylene / hexafluoropropylene copolymer and a layer (B) made of a chlorotrifluoroethylene copolymer, characterized in that the layer (A) and the layer (B) are laminated by co-extrusion molding under conditions in which the flow path temperature before contact between the material (a) of the layer (A) and the material (b) of the layer (B) in a multi-layer die is 300 to 400°C for the flow path (pa) through which the material (a) flows and 250 to 350°C for the flow path (pb) through which the material (b) flows.

[0003] WO 2006 / 095857

[0004] An object of the present disclosure is to provide a double-walled tube that maintains low hydrochloric acid permeability even when left in warm water for a long period of time with an aqueous hydrochloric acid solution sealed therein.

[0005] According to the present disclosure, there is provided a two-layer tube comprising an inner layer (A) and an outer layer (B) provided directly on the inner layer (A), wherein the inner layer (A) contains a copolymer (a) containing tetrafluoroethylene units and perfluoro(propyl vinyl ether) units, and the outer layer (B) contains a polymer (b) containing at least chlorotrifluoroethylene units, wherein the weight loss rate of the copolymer (a) after heat treatment at 380°C for 1 hour is 0.05 mass% or less, and the ratio of the thickness of the inner layer (A) to the thickness of the outer layer (B) ((A) / (B)) is 30.0 / 70.0 to 67.0 / 33.0.

[0006] According to the present disclosure, it is possible to provide a double-walled tube that maintains low hydrochloric acid permeability even when left in warm water for a long period of time with an aqueous hydrochloric acid solution sealed therein.

[0007] Fig. 1 is a cross-sectional image of the tube produced in Comparative Example 1. Fig. 2 is a cross-sectional image of the tube produced in Comparative Example 2. Fig. 3 is a cross-sectional image of the tube produced in Example 1. Fig. 4 is a schematic diagram of an experimental apparatus used to measure the 35 mass % hydrochloric acid permeability coefficient of the double-layer tube.

[0008] Specific embodiments of the present disclosure will be described in detail below, but the present disclosure is not limited to the following embodiments.

[0009] The present disclosure relates to a double-layer tube comprising an inner layer (A) and an outer layer (B).

[0010] Patent Document 1 describes that conventionally, when transporting chemical solutions such as hydrochloric acid, hydrofluoric acid, nitric acid, etc., which are used in semiconductor factories and liquid crystal factories, fluororesin tubes such as PFA resin tubes have been widely used, but the permeation of chemical solutions from the tubes causes the tubes themselves to whiten and deteriorate, increasing the acid concentration in the factory and causing problems such as corrosion of equipment and environmental pollution, and that in order to improve this, it is desirable to have tubes with a small chemical solution permeation coefficient.

[0011] Therefore, Patent Document 1 describes that when a laminate is produced by forming layer (A) using a tetrafluoroethylene / perfluorovinyl ether copolymer and / or a tetrafluoroethylene / hexafluoropropylene copolymer, forming layer (B) using a chlorotrifluoroethylene copolymer, and laminating layer (A) and layer (B) by co-extrusion molding under conditions where the flow path temperature is in a specific range described below, the resulting laminate has a small 35% by mass hydrochloric acid permeability coefficient at 25°C.

[0012] However, it has now been discovered that while conventional tubes are difficult for hydrochloric acid to pass through in low-temperature water, cracks occur in the inner layer when left in warm water for a long period of time, and that they are unable to sufficiently inhibit the permeation of hydrochloric acid when left in water at room temperature for a long period of time.

[0013] As a result of intensive research into a solution to this problem, it was found that by forming the inner layer of a double-walled tube from a copolymer containing tetrafluoroethylene units and perfluoro(propyl vinyl ether) units, with an appropriately adjusted weight loss rate after heat treatment at 380°C for 1 hour, and further adjusting the thicknesses of the inner layer and outer layer within an extremely limited range, it is possible to obtain a double-walled tube that is less likely to crack in the inner layer even when left in hot water with a hydrochloric acid solution sealed therein for a long period of time, and that can maintain low hydrochloric acid permeability even when left in water at room temperature for a long period of time.The double-walled tube of the present disclosure has been completed based on this finding.

[0014] Next, the configuration of the double-layer tube of the present disclosure will be described in more detail.

[0015] The two-layer tube of the present disclosure comprises an inner layer (A) and an outer layer (B), wherein the inner layer (A) contains a copolymer (a) containing tetrafluoroethylene (TFE) units and perfluoro(propyl vinyl ether) (PPVE) units, and the outer layer (B) contains a polymer (b) containing at least chlorotrifluoroethylene (CTFE) units.

[0016] <Inner Layer (A)> The inner layer (A) contains a copolymer (a) containing TFE units and PPVE units, and the copolymer (a) has a specific weight loss rate.

[0017] The weight loss rate of the copolymer (a) is 0.05% by mass or less, and preferably 0.01% by mass or more.

[0018] The weight loss rate of the copolymer (a) can be reduced to 0.05% by mass or less by subjecting the copolymer (a) to an appropriate heat treatment, as will be described later.

[0019] The weight loss rate of the copolymer (a) can be calculated from the weight of the copolymer (a) before and after heat treatment at 380°C for 1 hour according to the following formula: Weight loss rate (mass%) = [(weight before heating) - (weight after heating)] / (weight before heating) x 100

[0020] It is presumed that copolymers with a low weight loss rate after heat treatment at 380°C for 1 hour contain almost no high-temperature volatile matter with a molecular weight of 3,000 or less. High-temperature volatile matter with a molecular weight of 3,000 or less may exist in an amorphous state in a molded product of crystalline copolymer (a), forming an amorphous, low-density fine phase. Hydrochloric acid flowing through the interior of the two-wall tube may remain in this phase, and the heat of association between acid molecules and water molecules may cause thermal expansion stress, which may result in cracking or, even if cracking does not occur, may result in insufficient suppression of hydrochloric acid permeation. It is presumed that forming the inner layer (A) from copolymer (a) with a weight loss rate of 0.05% by mass or less suppresses the formation of an amorphous, low-density phase, thereby suppressing the occurrence of microcracks that may occur in the inner layer (A), thereby maintaining the excellent low hydrochloric acid permeability of the two-wall tube.

[0021] The zero shear viscosity of the copolymer (a) is preferably 2.00 × 10 because it can further suppress the occurrence of cracks in the inner layer and further suppress the permeation of hydrochloric acid while maintaining good moldability of the copolymer (a). ４ Pa·S or more, more preferably 2.50×10 ４ Pa·S or more, and more preferably 3.00×10 ４ Pa·S or more, preferably 10.00×10 ４ Pa·S or less, more preferably 8.00×10 ４ Pa·S or less, and more preferably 5.00×10 ４ It is below Pa·S.

[0022] The zero shear viscosity of the copolymer (a) can be adjusted by adjusting the melt flow rate and the content of PPVE units of the copolymer (a), as well as by adjusting the amount of polymerization initiator, the amount of chain transfer agent, polymerization pressure, polymerization time, etc. when producing the copolymer (a).

[0023] The zero shear viscosity of the copolymer (a) is the viscosity at a frequency of 0.1 rad / sec at 340° C. in the melt viscoelasticity measurement of the copolymer (a). The zero shear viscosity can be measured using a melt viscoelasticity measuring device.

[0024] The MIT value of the copolymer (a) is preferably 2.6 million or more, more preferably 10 million or less, and even more preferably 5 million or less, because it can further suppress the occurrence of cracks in the inner layer and further suppress the permeation of hydrochloric acid.

[0025] The MIT value of the copolymer (a) can be adjusted by adjusting the melt flow rate and the content of PPVE units of the copolymer (a).

[0026] The MIT value of the copolymer (a) can be determined by compression-molding the copolymer (a) to prepare a test piece having a width of 12.7 mm, a length of 90 mm, and a thickness of 0.20 to 0.25 mm, bending the test piece under the conditions of a load of 1.25 kg, a left and right bending angle of 135 degrees each, and a number of bending times of 175 times / min, and measuring the number of bending times (MIT value) until the test piece breaks.

[0027] The copolymer (a) contains TFE units and PPVE units.

[0028] The content of the PPVE units in the copolymer (a) is preferably 4.0 to 6.5% by mass, more preferably 4.5% by mass or more, even more preferably 5.0% by mass or more, and particularly preferably 5.5% by mass or more, based on the total monomer units, because this can further suppress the occurrence of cracks in the inner layer and further suppress the permeation of hydrochloric acid.

[0029] The content of TFE units in copolymer (a) is preferably 93.5 to 96.0% by mass, more preferably 95.5% by mass or less, even more preferably 95.0% by mass or less, and particularly preferably 94.5% by mass or less, based on the total monomer units.

[0030] The copolymer (a) may contain monomer units derived from a monomer copolymerizable with TFE and PPVE.

[0031] Monomers copolymerizable with TFE and PPVE include hexafluoropropylene (HFP), CZ ３ Z ４ =CZ ５ (CF ２) ｎ Z ６ (In the formula, Z ３ , Z ４ and Z ５ are the same or different and represent H or F; Z ６ represents H, F or Cl, and n represents an integer of 2 to 10.) and a vinyl monomer represented by CF ２ =CF-OCH ２ -Rf ７ (wherein, Rf ７ represents a perfluoroalkyl group having 1 to 5 carbon atoms. Among these, HFP is preferred.

[0032] The content of monomer units derived from monomers copolymerizable with TFE and PPVE is preferably 0 to 1.5% by mass, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less.

[0033] As the copolymer (a), at least one selected from the group consisting of a copolymer consisting of only TFE units and PPVE units and a TFE / HFP / PPVE copolymer is preferred, as it can further suppress the occurrence of cracks in the inner layer and further suppress the permeation of hydrochloric acid, and a copolymer consisting of only TFE units and PPVE units is more preferred.

[0034] In the present disclosure, the content of each monomer unit in the copolymer is: １９ It is measured by F-NMR.

[0035] The melting point of the copolymer (a) is preferably 295 to 308° C., since this can further suppress the occurrence of cracks in the inner layer and further suppress the permeation of hydrochloric acid.

[0036] In the present disclosure, the melting point of the copolymer (a) is the temperature corresponding to the maximum value in the heat of fusion curve when the temperature is increased at a rate of 10°C / min (second run) using a differential scanning calorimeter (DSC).

[0037] The copolymer (a) is preferably a melt-processable fluororesin. In the present disclosure, melt-processable means that the polymer can be melted and processed using conventional processing equipment such as an extruder or an injection molding machine. Therefore, melt-processable fluororesins usually have a melt flow rate of 0.01 to 500 g / 10 min, as measured by the measurement method described below.

[0038] The melt flow rate (MFR) of the copolymer (a) is preferably 10.0 g / 10 min or less, more preferably 5.0 g / 10 min or less, and even more preferably 3.0 g / 10 min or less, and is preferably 0.01 g / 10 min or more, more preferably 0.1 g / 10 min or more, and even more preferably 1.0 g / 10 min or more, because this can further suppress the occurrence of cracks in the inner layer and further suppress the permeation of hydrochloric acid.

[0039] The MFR of the copolymer (a) is measured in accordance with ASTM D1238 using a die having a diameter of 2.1 mm and a length of 8 mm, under a load of 5 kg and at 372°C.

[0040] The number of functional groups in the copolymer (a) is 10 carbon atoms. ６ The number of molecules per molecule may be 500 or less, preferably 300 or less, more preferably 200 or less, even more preferably 100 or less, still more preferably 50 or less, and particularly preferably 10 or less.

[0041] The functional groups are those present at the ends of the main chain or side chains of the copolymer, and those present in the main chain or side chains. ２ , -CF ２ H, -COF, -COOH, -COOCH ３ , -CONH ２ and -CH ２ At least one selected from the group consisting of OH is preferred.

[0042] Infrared spectroscopy can be used to identify the type of functional group and measure the number of functional groups.

[0043] The number of functional groups is specifically measured by the following method. First, the copolymer is melted at 340 to 350°C for 30 minutes and compression molded to produce a film with a thickness of 0.05 to 0.25 mm. This film is analyzed by Fourier transform infrared spectroscopy to obtain an infrared absorption spectrum of the copolymer, and a difference spectrum is obtained from a base spectrum that is completely fluorinated and has no functional groups. From the absorption peaks of specific functional groups that appear in this difference spectrum, the number of carbon atoms in the copolymer is calculated according to the following formula (A): ６ The number of functional groups per particle, N, is calculated as follows: N = I x K / t (A), where I is absorbance, K is correction coefficient, and t is film thickness (mm).

[0044] For reference, the absorption frequencies, molar absorption coefficients, and correction coefficients for the functional groups in this disclosure are shown in Table 1. The molar absorption coefficients were determined from FT-IR measurement data of low molecular weight model compounds.

[0045]

[0046] -CH ２ CF ２ H, —CH ２ COF, -CH ２ COOH, -CH ２ COOCH ３ , -CH ２ CONH ２ The absorption frequencies of -CF are shown in the table. ２ H, -COF, -COOH free and -COOH bonded, -COOCH ３ , -CONH ２ absorption frequency from tens of Kaiser (cm －１ ) is lower. For example, the number of functional groups of -COF is -CF ２ Absorption frequency due to COF: 1883 cm －１ The number of functional groups determined from the absorption peak of -CH ２ Absorption frequency due to COF: 1840 cm －１ The number of functional groups is the sum of the number of functional groups determined from the absorption peaks of the compounds.

[0047] The number of functional groups is -CF=CF ２ , -CF２ H, -COF, -COOH, -COOCH ３ , -CONH ２ and -CH ２ It may be the total number of OH.

[0048] A functional group is introduced into the copolymer by, for example, a chain transfer agent or a polymerization initiator used in producing the copolymer. For example, an alcohol is used as a chain transfer agent, and a —CH ２ When a peroxide having an OH structure is used, the main chain end of the copolymer is formed with -CH ２ Furthermore, by polymerizing a monomer having a functional group, a functional group is introduced into the side chain terminal of the copolymer.

[0049] By subjecting a copolymer having such functional groups to a fluorination treatment, a copolymer having the number of functional groups within the above range can be obtained. That is, the copolymer (a) may be fluorination-treated. The copolymer (a) may also contain -CF ３ It may have a terminal group.

[0050] The inner layer (A) may contain various additives, such as a conductive filler, a stabilizer such as a heat stabilizer, a reinforcing agent, a bulking agent, an ultraviolet absorber, and a pigment, as long as the object of the present disclosure is not impaired.

[0051] <Outer Layer (B)> The outer layer (B) contains a polymer (b) containing at least a CTFE unit.

[0052] As the polymer (b), at least one selected from the group consisting of polychlorotrifluoroethylene [PCTFE] and CTFE copolymer is preferred, since it can further suppress the occurrence of cracks in the inner layer and further suppress the permeation of hydrochloric acid, more preferably at least one selected from the group consisting of PCTFE, CTFE / TFE copolymer, and ethylene / CTFE copolymer, and even more preferably CTFE / TFE copolymer.

[0053] The polymer (b) is preferably a CTFE copolymer. The CTFE copolymer is preferably a copolymer containing a CTFE unit and a copolymer of TFE, HFP, PAVE, vinylidene fluoride (VdF), vinyl fluoride, hexafluoroisobutene, or a copolymer of the formula: CH ２ =CX １ (CF ２ ) ｎ X ２ (In the formula, X １ is H or F, X ２ is H, F or Cl, and n is an integer of 1 to 10), and units derived from at least one monomer selected from the group consisting of ethylene, propylene, 1-butene, 2-butene, vinyl chloride, and vinylidene chloride.

[0054] The CTFE copolymer is more preferably at least one selected from the group consisting of ethylene / CTFE copolymers and copolymers containing CTFE units and units derived from at least one monomer selected from the group consisting of TFE, HFP, and PAVE.

[0055] The ethylene / CTFE copolymer (ECTFE) is a copolymer containing ethylene units and CTFE units, and preferably contains 46 to 52 mol% of ethylene units and 54 to 48 mol% of CTFE units relative to the total of the ethylene units and CTFE units. The ECTFE may be a binary copolymer consisting of only ethylene units and CTFE units, or may further contain polymerized units based on a monomer copolymerizable with ethylene and CTFE (for example, a perfluoro(alkyl vinyl ether) (PAVE) derivative).

[0056] The content of polymerized units based on a monomer copolymerizable with ethylene and CTFE is preferably 0.01 to 5 mol % based on the total of ethylene units, CTFE units, and polymerized units based on the above copolymerizable monomers.

[0057] The MFR of ECTFE is preferably 0.01 to 100 g / 10 min. The MFR of ECTFE is measured at a temperature of 230° C. under a load of 2.16 kg.

[0058] As the polymer (b), one containing a CTFE unit, a TFE unit, and a monomer (α) unit derived from a monomer (α) copolymerizable therewith is particularly preferred, since it can further suppress the occurrence of cracks in the inner layer and further suppress the permeation of hydrochloric acid.

[0059] The monomer (α) is not particularly limited as long as it is a monomer copolymerizable with CTFE and TFE, and examples thereof include ethylene, VdF, CF ２ =CF-ORf １ (wherein, Rf １ is a perfluoro(alkyl vinyl ether) [PAVE] represented by a perfluoroalkyl group having 1 to 8 carbon atoms, CX ３ X ４ =CX ５ (CF ２ ) ｎ X ６ (In the formula, X ３ , X ４ and X ５ are the same or different and are a hydrogen atom or a fluorine atom; X ６ is a hydrogen atom, a fluorine atom, or a chlorine atom; and n is an integer of 1 to 10), ２ =CF-OCH ２ -Rf ２ (wherein, Rf ２ and alkyl perfluorovinyl ether derivatives represented by the formula (I) (wherein R represents a perfluoroalkyl group having 1 to 5 carbon atoms), and among these, at least one selected from the group consisting of PAVE, the vinyl monomers, and alkyl perfluorovinyl ether derivatives is preferred, at least one selected from the group consisting of PAVE and HFP is more preferred, and PAVE is even more preferred.

[0060] As for PAVE, CF ２ =CF-ORf ３ (wherein, Rf ３represents a perfluoroalkyl group having 1 to 5 carbon atoms.) are preferred, and examples thereof include perfluoro(methyl vinyl ether) [PMVE], perfluoro(ethyl vinyl ether) [PEVE], perfluoro(propyl vinyl ether) [PPVE], and perfluoro(butyl vinyl ether). Among these, at least one selected from the group consisting of PMVE, PEVE, and PPVE is more preferred, and PPVE is even more preferred.

[0061] Examples of alkyl perfluorovinyl ether derivatives include Rf ２ is preferably a perfluoroalkyl group having 1 to 3 carbon atoms, and CF ２ =CF-OCH ２ -CF ２ CF ３ is more preferred.

[0062] The ratio of CTFE units to TFE units in polymer (b) is preferably 15 to 90 mol % of CTFE units and 85 to 10 mol % of TFE units, more preferably 20 to 90 mol % of CTFE units and 80 to 10 mol % of TFE units. Also preferred is a copolymer composed of 15 to 25 mol % of CTFE units and 85 to 75 mol % of TFE units.

[0063] The polymer (b) preferably contains 90 to 99.9 mol% of CTFE units and TFE units in total, and 0.1 to 10 mol% of monomer (α) units. If the monomer (α) unit content is less than 0.1 mol%, the polymer tends to be inferior in moldability, environmental stress cracking resistance, and fuel cracking resistance, while if it exceeds 10 mol%, the polymer tends to be inferior in fuel barrier properties, heat resistance, and mechanical properties.

[0064] As the polymer (b), a CTFE / TFE / PAVE copolymer is particularly preferred, since it can further suppress the occurrence of cracks in the inner layer and further suppress the permeation of hydrochloric acid.

[0065] In the CTFE / TFE / PAVE copolymer, examples of the PAVE include perfluoro(methyl vinyl ether) [PMVE], perfluoro(ethyl vinyl ether) [PEVE], perfluoro(propyl vinyl ether) [PPVE], and perfluoro(butyl vinyl ether). Of these, at least one selected from the group consisting of PMVE, PEVE, and PPVE is preferred, with PPVE being more preferred.

[0066] In the CTFE / TFE / PAVE copolymer, the PAVE units preferably account for 0.5 mol % or more and 5 mol % or less of the total monomer units. The content ratio (mol %) of each monomer in the CTFE / TFE / PAVE copolymer is preferably (15.0 to 24.9) / (75.0 to 84.9) / (0.1 to 10.0), more preferably (15.0 to 24.9) / (75.0 to 84.9) / (0.1 to 3.0).

[0067] The melting point of the polymer (b) is not particularly limited, but is preferably 160 to 270°C.

[0068] The melting point of the polymer (b) is the temperature corresponding to the maximum value on the heat of fusion curve when the temperature is increased at a rate of 10° C. / min using a differential scanning calorimeter (DSC).

[0069] The polymer (b) is preferably a melt-processable fluororesin. The MFR of the polymer (b) is preferably 0.5 to 100 g / 10 min, more preferably 1 g / 10 min or more, even more preferably 2 g / 10 min or more, more preferably 50 g / 10 min or less, and even more preferably 40 g / 10 min or less.

[0070] The MFR of polymer (b) is measured in accordance with ASTM D1238 using a die having a diameter of 2.1 mm and a length of 8 mm, under a load of 5 kg, at any temperature (e.g., 297°C) within the molding temperature range of approximately 230 to 350°C, which is the general molding temperature range for fluoropolymers. The measurement temperature for the MFR of a CTFE / TFE / PAVE copolymer is 297°C.

[0071] The outer layer (B) may contain various additives, such as a conductive filler, a stabilizer such as a heat stabilizer, a reinforcing agent, a bulking agent, an ultraviolet absorber, and a pigment, as long as the object of the present disclosure is not impaired.

[0072] <Layer Structure of Tube> The two-layer tube of the present disclosure comprises an inner layer (A) and an outer layer (B), with the outer layer (B) directly bonded to the inner layer (A). In the two-layer tube of the present disclosure, the boundary between the adjacent layers does not necessarily need to be clear, and the molecular chains of the polymers constituting the layers may interpenetrate each other from the contacting surfaces, resulting in a layer structure with a concentration gradient.

[0073] In the two-layer tube of the present disclosure, the ratio ((A) / (B)) of the thickness of the inner layer (A) to the thickness of the outer layer (B) is 30.0 / 70.0 to 67.0 / 33.0. If the ratio ((A) / (B)) is too small, when the tube is left in hot water for a long period of time with an aqueous hydrochloric acid solution sealed therein, cracks are likely to occur in the inner layer, and low hydrochloric acid permeability cannot be maintained. If the ratio ((A) / (B)) is too large, permeation of hydrochloric acid cannot be sufficiently suppressed.

[0074] The ratio ((A) / (B)) of the thickness of the inner layer (A) to the thickness of the outer layer (B) is preferably 50.0 / 50.0 or more, more preferably 60.0 / 40.0 or more, because this further suppresses cracking in the inner layer and further suppresses permeation of hydrochloric acid. A larger ratio ((A) / (B)) is also advantageous in that it facilitates welding of the two-layer tube of the present disclosure to other members, such as fittings, and also increases the mechanical strength of the welded portion.

[0075] The thickness of the dual-layer tube of the present disclosure, i.e., the total thickness of the inner layer (A) and the outer layer (B), is preferably 1.3 mm or more, more preferably 1.5 mm or more, and preferably 10.0 mm or less, more preferably 5.0 mm or less, and even more preferably 2.0 mm or less. The thickness of the dual-layer tube of the present disclosure may be about 1.6 mm (e.g., 1.56 to 1.64 mm). The dual-layer tube of the present disclosure may be a 3 / 4-inch tube or a 1 / 2-inch tube.

[0076] A two-wall tube according to one embodiment of the present disclosure is characterized in that, after an acid aqueous solution containing at least one acid selected from the group consisting of hydrochloric acid, hydrofluoric acid, nitric acid, and sulfuric acid is sealed in the two-wall tube and allowed to stand at room temperature for 150 days or more, no cracks of 10 μm or more in length are present in the inner layer (A). The presence or absence of cracks can be confirmed by observing the cross section of the two-wall tube using a microscope.

[0077] A two-wall tube according to one embodiment of the present disclosure is characterized in that the inner layer (A) does not have cracks with a length of 10 μm or more after 35% by mass hydrochloric acid is sealed therein and the tube is left in warm water at 80° C. for 90 hours. The presence or absence of cracks can be confirmed by observing the cross section of the two-wall tube using a microscope.

[0078] The two-layer tube of the present disclosure can be produced, for example, by a production method in which copolymer (a) is subjected to a heat treatment by blowing hot air at 200 to 280°C for 6 hours or more, and then the resulting copolymer (a) and polymer (b) are laminated to obtain a two-layer tube.

[0079] The temperature of the hot air is preferably 230° C. or higher, more preferably 250° C. or higher, and preferably 270° C. or lower, more preferably 260° C. or lower. If the hot air temperature is too low, high-temperature volatile matter cannot be sufficiently removed from the copolymer (a). If the hot air temperature is too high, the copolymer (a) may fuse to form lumps, or, when pellets of the copolymer (a) are used for the heat treatment, the pellets may be deformed.

[0080] The time for blowing hot air is 6 hours or more, preferably 8 hours or more, preferably 30 hours or less, more preferably 20 hours or less, and even more preferably 15 hours or less. Continuously blowing hot air can promote the removal of high-temperature volatile matter from the copolymer (a). When molding the copolymer (a), the copolymer (a) is heated and melted, but short-term heating during molding cannot sufficiently remove high-temperature volatile matter from the copolymer (a).

[0081] The hot air that has come into contact with the copolymer (a) may contain high-temperature volatile matter. In order to promote the removal of high-temperature volatile matter from the copolymer (a), it is preferable to blow the hot air onto the copolymer (a) while discharging part or all of the hot air that has come into contact with the copolymer (a). If the hot air blown onto the copolymer (a) is circulated and then blown onto the copolymer (a) again, or if the copolymer (a) is brought into contact with high-temperature gas in a closed system, the removal of high-temperature volatile matter may not proceed, and the weight loss rate of the copolymer (a) may not be adjusted to the above-mentioned range.

[0082] As a method for treating copolymer (a), a fluorination treatment for reducing the number of functional groups of copolymer (a) is known. Since the fluorination treatment is carried out by contacting a highly reactive fluorinating agent with copolymer (a) in a sealed container, even if the fluorination treatment is carried out at a high temperature for a long period of time, the weight loss rate of copolymer (a) cannot be adjusted to fall within the above-mentioned range.

[0083] The hot air may be heated air, heated inert gas, etc. The stronger the hot air is blown, the more the removal of high-temperature volatile matter from the copolymer (a) can be promoted, but the amount of air must be such that the copolymer (a) does not fly up.

[0084] The form of the copolymer (a) to which the hot air is blown is not particularly limited, and may be a powder, pellets, etc. If the copolymer (a) is in the form of a powder, there is a high possibility that it will be blown up by the hot air, so the copolymer (a) is preferably in the form of pellets.

[0085] Examples of methods for laminating copolymer (a) and polymer (b) include: a method of co-extrusion molding copolymer (a) and polymer (b) to thermally fuse (melt-bond) the layers together; a method of separately preparing a layer containing copolymer (a) and a layer containing polymer (b) using an extruder, superimposing the layers, and bonding the layers together by thermal fusion; a method of preparing a monolayer tube containing copolymer (a) and extruding polymer (b) onto the surface of the monolayer tube using an extruder; and a method of preparing a monolayer tube containing copolymer (a), electrostatically coating the surface of the monolayer tube with polymer (b), and then heating the resulting coated product either overall or from the coated side to heat-melt polymer (b).

[0086] Examples of the coextrusion molding include conventionally known multilayer coextrusion manufacturing methods such as a multi-manifold method and a feed block method.

[0087] The two-layer tube of the present disclosure can be suitably used as a chemical piping tube for circulating chemicals, and is particularly suitably used as a chemical piping tube used for transporting high-purity chemicals for semiconductor device manufacturing. The two-layer tube of the present disclosure is less susceptible to cracking in the inner layer and can maintain low chemical permeability for a long period of time, so it can be replaced less frequently than conventional two-layer tubes.

[0088] The double-walled tube of the present disclosure is preferably a tube for piping a chemical solution for circulating the chemical solution. Examples of the chemical solution include chemical solutions used in semiconductor manufacturing, such as ammonia water, ozone water, hydrogen peroxide solution, hydrochloric acid, sulfuric acid, resist solution, thinner solution, and developer. The chemical solution is preferably an acid aqueous solution containing at least one acid selected from the group consisting of hydrochloric acid, hydrofluoric acid, nitric acid, and sulfuric acid. The double-walled tube of the present disclosure can suppress permeation of the acid in such an acid aqueous solution for a long period of time.

[0089] The double-walled tube of the present disclosure can be used, for example, as a tube for use in semiconductor manufacturing facilities or semiconductor manufacturing equipment such as a chemical liquid supply line for semiconductor manufacturing, a chemical liquid supply facility for semiconductor manufacturing, a semiconductor cleaning device, or a coater developer.

[0090] It is also preferable to use the two-layer tube of the present disclosure in a low-humidity environment. By using the two-layer tube in a low-humidity environment, the occurrence of cracks in the inner layer can be further suppressed, and the permeation of hydrochloric acid can be further suppressed. The humidity of the usage environment is preferably 60% or less, and more preferably 30% or less.

[0091] Although the embodiments have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the claims.

[0092] <1> According to a first aspect of the present disclosure, there is provided a bilayer tube comprising an inner layer (A) and an outer layer (B) provided directly on the inner layer (A), wherein the inner layer (A) contains a copolymer (a) containing tetrafluoroethylene units and perfluoro(propyl vinyl ether) units, and the outer layer (B) contains a polymer (b) containing at least chlorotrifluoroethylene units, wherein the weight loss rate of the copolymer (a) after heat treatment at 380°C for 1 hour is 0.05 mass% or less, and the ratio of the thickness of the inner layer (A) to the thickness of the outer layer (B) ((A) / (B)) is 30.0 / 70.0 to 67.0 / 33.0. <2> According to a second aspect of the present disclosure, there is provided a bilayer tube according to the first aspect, wherein the combined thickness of the inner layer (A) and the outer layer (B) is 1.3 mm or more. <3> According to a third aspect of the present disclosure, there is provided a two-layer tube according to the first or second aspect, wherein the total thickness of the inner layer (A) and the outer layer (B) is 1.6 mm. <4> According to a fourth aspect of the present disclosure, there is provided a two-layer tube according to any one of the first to third aspects, wherein the content of perfluoro(propyl vinyl ether) units in copolymer (a) is 4.0 to 6.5 mass% based on the total monomer units constituting copolymer (a). <5> According to a fifth aspect of the present disclosure, there is provided a two-layer tube according to any one of the first to fourth aspects, wherein copolymer (a) has a melting point of 295 to 308°C. <6> According to a sixth aspect of the present disclosure, there is provided a two-layer tube according to any one of the first to fifth aspects, wherein polymer (b) is a copolymer containing chlorotrifluoroethylene units, tetrafluoroethylene units, and monomer (α) units derived from a monomer (α) copolymerizable therewith. <7> According to a seventh aspect of the present disclosure, there is provided the double-layer tube according to any one of the first to sixth aspects, wherein the polymer (b) is a copolymer containing chlorotrifluoroethylene units, tetrafluoroethylene units, and perfluoro(alkyl vinyl ether) units. <8> According to an eighth aspect of the present disclosure, there is provided the double-layer tube according to any one of the first to sixth aspects, wherein the copolymer (a) has a zero shear viscosity of 2.00 × 10 ４A two-layer tube according to any one of the first to seventh aspects is provided, in which the copolymer (a) has an MIT value of 2.6 million cycles or more. <9> According to a ninth aspect of the present disclosure, there is provided a two-layer tube according to any one of the first to eighth aspects, in which the copolymer (a) has an MIT value of 2.6 million cycles or more. <10> According to a tenth aspect of the present disclosure, there is provided a two-layer tube according to any one of the first to ninth aspects, in which an acid aqueous solution containing at least one acid selected from the group consisting of hydrochloric acid, hydrofluoric acid, nitric acid, and sulfuric acid is sealed inside the two-layer tube, and after standing at room temperature for 150 days or more, no cracks having a length of 10 μm or more are present in the inner layer (A). <11> According to an eleventh aspect of the present disclosure, there is provided a two-layer tube according to any one of the first to tenth aspects, in which an acid aqueous solution containing at least one acid selected from the group consisting of hydrochloric acid, hydrofluoric acid, nitric acid, and sulfuric acid is sealed inside the two-layer tube, and after standing at room temperature for 90 days or more, no cracks having a length of 10 μm or more are present in the inner layer (A).<12> According to a twelfth aspect of the present disclosure, copolymer (a) contains tetrafluoroethylene units, perfluoro(propyl vinyl ether) units, and other monomer units derived from monomers copolymerizable with tetrafluoroethylene and perfluoro(propyl vinyl ether), the content of perfluoro(propyl vinyl ether) units in copolymer (a) is 4.0 to 6.5 mass% based on all monomer units constituting copolymer (a), the content of tetrafluoroethylene units in copolymer (a) is 93.5 to 96.0 mass% based on all monomer units constituting copolymer (a), and the content of other monomer units in copolymer (a) is 0 to 1.5 mass% based on all monomer units constituting copolymer (a); The two-layer tube according to any one of the first to eleventh aspects is provided, wherein the polymer (b) is a copolymer containing chlorotrifluoroethylene units, tetrafluoroethylene units, and perfluoro(alkyl vinyl ether) units, and the content ratio of each monomer (chlorotrifluoroethylene units / tetrafluoroethylene units / perfluoro(alkyl vinyl ether) units (mol %)) is (15.0 to 24.9) / (75.0 to 84.9) / (0.1 to 10.0), the total thickness of the inner layer (A) and the outer layer (B) is 1.56 to 1.64 mm, and the ratio of the thickness of the inner layer (A) to the thickness of the outer layer (B) ((A) / (B)) is 60.0 / 40.0 to 67.0 / 33.0. <13> A thirteenth aspect of the present disclosure provides a method for producing a bilayer tube according to any one of the first to twelfth aspects, comprising: subjecting copolymer (a) to a heat treatment in which hot air at 200 to 280°C is blown onto the copolymer (a) for six hours or more; and then laminating the resulting copolymer (a) and polymer (b) to obtain a bilayer tube.

[0093] Next, embodiments of the present disclosure will be described with reference to examples, but the present disclosure is not limited to these examples.

[0094] The values ​​in the examples were measured by the following methods.

[0095] (Polymer Composition) １９ Measurement was carried out by F-NMR.

[0096] (Melt Flow Rate (MFR)) In accordance with ASTM D1238, the mass (g / 10 min) of the copolymer flowing out of a nozzle having an inner diameter of 2.1 mm and a length of 8 mm at 372°C or 297°C under a load of 5 kg per 10 min was determined using a melt indexer (manufactured by Yasuda Seiki Seisakusho Co., Ltd.).

[0097] (Weight Loss Rate) The aluminum cup was heated at 380°C for 30 minutes to remove volatile matter from the aluminum cup. Approximately 10 g of copolymer pellets were placed in the aluminum cup, and the aluminum cup containing the pellets was precisely weighed. The aluminum cup containing the pellets was heated at 380°C for 60 minutes. After heating, the aluminum cup containing the pellets was precisely weighed. The weight loss rate of the copolymer was calculated using the following formula: Weight loss rate (mass%) = [(weight before heating) - (weight after heating)] / (weight before heating) x 100

[0098] (Zero Shear Viscosity) The zero shear viscosity of the copolymer was measured using a melt viscoelasticity measuring device MCR-302 manufactured by Anton Paar, with a parallel plate attached as a measuring jig. The measurement temperature was 340°C, and the sample thickness was 1 mm. The frequency was swept from high to low, and the viscosity at a frequency of 0.1 rad / sec was taken as the zero shear viscosity.

[0099] (MIT Value) The MIT value of the copolymer was measured in accordance with ASTM D 2176. Specifically, the copolymer was compression molded to prepare a test piece having a width of 12.7 mm, a length of 90 mm, and a thickness of 0.20 to 0.25 mm, and the test piece was mounted in an MIT testing machine (model number 12176, manufactured by Yasuda Seiki Seisakusho Co., Ltd.), and the test piece was bent under the conditions of a load of 1.25 kg, a left and right bending angle of 135 degrees each, and a number of bending times of 175 times / min, and the number of bending times (MIT value) until the test piece broke was measured.

[0100] (Melting Point) The melting points (2nd run) of copolymers (a1) and (a2) were determined as the temperatures corresponding to the maximum value in the heat of fusion curve when heated at a rate of 10°C / min (second run) using a differential scanning calorimeter (DSC). The melting point of polymer (b1) was determined as the temperature corresponding to the maximum value in the heat of fusion curve when heated at a rate of 10°C / min using a differential scanning calorimeter (DSC).

[0101] In the examples and comparative examples, the following materials were used.

[0102] Copolymer (a1) TFE / PPVE copolymer TFE / PPVE (mass ratio): 96.5 / 3.5 MFR (372°C, 5 kg): 2.0 g / 10 min Weight loss rate after heat treatment at 380°C for 1 hour: 0.25 mass% Zero shear viscosity (340°C): 2.85 x 10 ４ Pa・S MIT value: 800,000 times Melting point: 308℃

[0103] Copolymer (a2) TFE / PPVE copolymer TFE / PPVE (mass ratio): 94.0 / 6.0 MFR (372°C, 5 kg): 1.6 g / 10 min Weight loss rate after heat treatment at 380°C for 1 hour: 0.05 mass% Zero shear viscosity (340°C): 3.32 x 10 ４ Pa・S MIT value: 2.6 million times Melting point: 300℃

[0104] The weight loss rate of copolymer (a2) was adjusted by the following method. 1 to 3 kg of pellets of the TFE / PPVE copolymer having the above-mentioned composition and MFR were spread on a tray, and the tray was placed in a hot air circulation type electric furnace. While heating the hot air circulation type electric furnace so that the temperature inside the heating furnace reached 250°C, hot air was passed through the heating furnace, and the pellets on the tray were heat-treated for 10 hours. In order to smoothly remove high-temperature volatile matter from the pellets, the heat treatment was carried out while a portion of the hot air that had passed through the heating furnace was exhausted to the outside of the heating furnace.

[0105] Polymer (b1) TFE / CTFE / PPVE copolymer TFE / CTFE / PPVE (molar ratio): 76.3 / 21.3 / 2.4 Melting point: 245°C MFR: 3g / 10min (297°C, 5kg)

[0106] Comparative Example 1 Pellets of copolymer (a1) and a tube manufacturing apparatus were used to manufacture a 1 / 2 inch tube having an outer diameter of 12.70 mm and a thickness of 1.58 mm.

[0107] Comparative Example 2 A 1 / 2 inch tube was produced in the same manner as in Comparative Example 1, except that copolymer (a2) was used instead of copolymer (a1).

[0108] Comparative Example 3 Using a two-kind, two-layer tube extrusion apparatus equipped with a multi-manifold, the inner layer (A) was copolymer (a1) and the outer layer (B) was polymer (b1), and each was supplied to two extruders to produce a ½-inch tube having an outer diameter of 12.70 mm and a thickness of 1.58 mm. The thickness of the inner layer (A) was 1.05 mm, and the thickness of the outer layer (B) was 0.53 mm.

[0109] Example 1 A 1 / 2 inch tube was produced in the same manner as in Comparative Example 3, except that copolymer (a2) was used instead of copolymer (a1).

[0110] (Tube Evaluation) 35% by mass hydrochloric acid was sealed in the tubes produced in Comparative Examples 1 and 2 and Example 1, and the tubes were left in hot water at 80°C for 90 hours. The tubes were removed from the hot water, and the cross sections of the tubes were observed using a digital microscope. Images of the cross sections of the tubes are shown in Figures 1 to 3.

[0111] The cross-sectional image of the tube shown in Figure 3 reveals that the tube having an inner layer formed from copolymer (a) with an appropriately adjusted weight loss rate has no cracks in the inner layer, whereas the cross-sectional images of the tube shown in Figures 1 and 2 reveal that the single-layer tube has numerous cracks with lengths of 10 μm or more.

[0112] (Measurement of 35% Hydrochloric Acid Permeability Coefficient) As shown in FIG. 4 , one end of the tubes prepared in Comparative Example 3 and Example 1 was heat-sealed, 52 ml of 35% by mass hydrochloric acid was placed in tube 21, and the other end of the tube was also heat-sealed. Tube 21 containing hydrochloric acid was inserted into glass tube 22 and fixed with fluororubber gasket 23. Next, 110 ml of pure water was charged through sampling port 24, and the tube was placed in a thermostatic chamber at 25°C. At this time, the tube between gaskets 23 was in contact with the pure water, and the length of the wetted portion was 18.5 cm. After leaving the tube in this state, about 1 ml was sampled through sampling port 24, and the chloride ion concentration Y (ppm) contained in the pure water was quantified using an ion chromatograph (trade name: IC7000-E, manufactured by Yokogawa Electric Corporation). The hydrochloric acid permeability coefficient (X) (ng cm / cm) was calculated using the following formula: ２ / days) was calculated using the formula: X = [(β × film thickness) / cross-sectional area] / (8.64 × 10 ７ ) β (unit: μg / sec): The slope of the tangent to the permeation curve for 150 to 250 days (T = 150 to 250) among the permeation curves drawn by plotting α against T. α: Total amount permeated (unit: μg) = Y × W Y: Chloride ion concentration (unit: ppm) W: Amount of pure water (unit: ml) T: Elapsed time from the start of permeation (the point at which hydrochloric acid was poured into the double-walled tube) to sampling (unit: seconds) Membrane thickness: The thickness of the tube (unit: cm, 1.58 mm (0.158 cm)) Cross-sectional area: The area of ​​the contact part between the double-walled tube and pure water in the experimental apparatus shown in Figure 4 (unit: cm ２ )

[0113] The 35% hydrochloric acid permeability coefficients (150 to 250 days) of the tubes prepared in Comparative Example 3 and Example 1 were as follows: Comparative Example 3: 20 ng cm / cm ２ / days Example 1: 7 ng cm / cm ２ / days

Claims

1. A two-layer tube comprising an inner layer (A) and an outer layer (B) provided directly on the inner layer (A), wherein the inner layer (A) contains a copolymer (a) containing tetrafluoroethylene units and perfluoro(propyl vinyl ether) units, and the outer layer (B) contains a polymer (b) containing at least chlorotrifluoroethylene units, wherein the weight loss rate of the copolymer (a) after heat treatment at 380°C for 1 hour is 0.05 mass% or less, and the ratio of the thickness of the inner layer (A) to the thickness of the outer layer (B) ((A) / (B)) is 30.0 / 70.0 to 67.0 / 33.

0.

2. The double-layer tube according to claim 1, wherein the total thickness of the inner layer (A) and the outer layer (B) is 1.3 mm or more.

3. The double-layer tube according to claim 1 or 2, wherein the total thickness of the inner layer (A) and the outer layer (B) is 1.56 to 1.64 mm.

4. A double-layer tube according to any one of claims 1 to 3, wherein the content of perfluoro(propyl vinyl ether) units in copolymer (a) is 4.0 to 6.5 mass% based on the total monomer units constituting copolymer (a).

5. The double-layer tube according to any one of claims 1 to 4, wherein the melting point of the copolymer (a) is 295 to 308°C.

6. A double-layer tube according to any one of claims 1 to 5, wherein the polymer (b) is a copolymer containing chlorotrifluoroethylene units, tetrafluoroethylene units and monomer (α) units derived from a monomer (α) copolymerizable therewith.

7. The double-layer tube according to any one of claims 1 to 6, wherein the polymer (b) is a copolymer containing chlorotrifluoroethylene units, tetrafluoroethylene units and perfluoro(alkyl vinyl ether) units.

8. The zero shear viscosity of copolymer (a) is 2.00 x 10 ４ The double-layer tube according to any one of claims 1 to 7, having a viscosity of Pa·S or more.

9. The double-layer tube according to any one of claims 1 to 8, wherein the MIT value of the copolymer (a) is 2.6 million or more.

10. The two-layer tube according to any one of claims 1 to 9, wherein no cracks having a length of 10 µm or more are present in the inner layer (A) after sealing an acid aqueous solution containing at least one acid selected from the group consisting of hydrochloric acid, hydrofluoric acid, nitric acid, and sulfuric acid and leaving it at room temperature for 150 days or more.

11. A two-layer tube according to any one of claims 1 to 10, in which no cracks having a length of 10 µm or more are present in the inner layer (A) after 35% by mass hydrochloric acid is sealed therein and the inner layer (A) is left in warm water at 80°C for 90 hours.

12. The copolymer (a) may contain other monomer units derived from monomers copolymerizable with tetrafluoroethylene and perfluoro(propyl vinyl ether), the content of perfluoro(propyl vinyl ether) units in the copolymer (a) being 4.0 to 6.5 mass% based on the total monomer units constituting the copolymer (a), the content of tetrafluoroethylene units in the copolymer (a) being 93.5 to 96.0 mass% based on the total monomer units constituting the copolymer (a), and the content of other monomer units in the copolymer (a) being 0 to 1.5 mass% based on the total monomer units constituting the copolymer (a); The two-layer tube according to any one of claims 1 to 11, wherein the polymer (b) is a copolymer containing chlorotrifluoroethylene units, tetrafluoroethylene units and perfluoro(alkyl vinyl ether) units, and the content ratio of each monomer (chlorotrifluoroethylene units / tetrafluoroethylene units / perfluoro(alkyl vinyl ether) units (mol %)) is (15.0 to 24.9) / (75.0 to 84.9) / (0.1 to 10.0), the total thickness of the inner layer (A) and the outer layer (B) is 1.56 to 1.64 mm, and the ratio of the thickness of the inner layer (A) to the thickness of the outer layer (B) ((A) / (B)) is 60.0 / 40.0 to 67.0 / 33.

0.

13. A method for producing a bilayer tube according to any one of claims 1 to 12, comprising the steps of: subjecting copolymer (a) to a heat treatment in which hot air at 200 to 280°C is blown onto it for at least 6 hours; and then laminating the resulting copolymer (a) and polymer (b) to obtain a bilayer tube.

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