Fluoropolymer composition

Abstract

The objective is to provide a fluororesin composition that has properties suitable for melt extrusion molding, and that can produce molded articles with high mechanical strength and a low oxygen permeability coefficient. [Solution] A fluororesin composition comprising (A) PFA, (B) a first low molecular weight PTFE, and (C) a second low molecular weight PTFE, wherein the melt flow rate at 372°C is in the range of 1.0 to 5.0 g / 10 min, and in a DSC chart obtained when calorimetry is performed by a predetermined process using a differential scanning calorimeter (DSC), there is an endothermic peak 1 with a peak top in the temperature range of 310°C to 330°C, and an endothermic peak 2 with a peak top in a temperature range lower than that of endothermic peak 1, and the ratio of the heights of endothermic peak 1 and endothermic peak 2 (height of endothermic peak 1 (W / g) ÷ height of endothermic peak 2 (W / g)) is 1 or more and 50 or less.

Description

Technical Field

[0001] The present invention relates to a fluororesin composition, and more particularly to a fluororesin composition having properties suitable for melt extrusion molding, capable of obtaining a molded article with high mechanical strength and low oxygen permeability coefficient.

Background Art

[0002] A copolymer (PFA) of tetrafluoroethylene (TFE) and perfluoro(alkyl vinyl ether) (PAVE) has excellent properties such as heat resistance and chemical resistance possessed by TFE and also has heat meltability. Therefore, it is used in melt molding such as melt extrusion molding, injection molding, blow molding, and melt compression molding. The obtained molded products are used as pipes, joints, or storage containers for chemical liquid transportation in semiconductor manufacturing processes, chemical plants, etc. In such applications, it is desired to have low gas permeability as well as durability. However, while the gas permeability of PFA improves by improving crystallinity, there is a problem that durability decreases when crystallinity is increased. Therefore, for the purpose of improving the gas barrier property of PFA, etc., it has been proposed to make a mixture with low molecular weight polytetrafluoroethylene (PTFE) (Patent Document 1).

[0003] In Patent Document 1 mentioned above, by containing PTFE in a PFA and PTFE mixture in an amount of 5 to 30% by mass, the permeability of nitrogen gas can be reduced and excellent durability can be exhibited. However, there is a problem that it is difficult to efficiently use low molecular weight PTFE obtained by low-cost polymerization. In order to solve such problems, Patent Document 2 below proposes a fluororesin composition for melt molding obtained by combining low molecular weight PTFE by polymerization and low molecular weight PTFE by radiation decomposition in PFA.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] In the fluororesin composition for melt molding described in Patent Document 2 above, nitrogen gas permeability and durability are obtained even when a large amount of polymerized low molecular weight PTFE is used, by blending low molecular weight PTFE produced by polymerization and PTFE produced by radiolysis with PFA in predetermined proportions, which have a predetermined melt flow rate (MFR). However, since adding PTFE to PFA tends to worsen moldability and mechanical strength, it is difficult to find a specific composition that satisfies moldability and mechanical strength while maintaining the aforementioned gas permeability resistance and durability.

[0006] Therefore, an object of the present invention is to provide a fluororesin composition of specific PFA and specific PTFE that has properties suitable for melt extrusion molding, and that can produce a molded article with high mechanical strength and a low oxygen permeability coefficient. [Means for solving the problem]

[0007] According to the present invention, a composition containing (A) a copolymer of tetrafluoroethylene and perfluoro(alkyl vinyl ether), (B) a first low molecular weight polytetrafluoroethylene in an amount of 10 to 40% by mass, and (C) a second low molecular weight polytetrafluoroethylene in an amount of 3% by mass or less, wherein the first low molecular weight polytetrafluoroethylene (B) has a melt flow rate of 10 to 55 g / 10 min at 372°C. to Yes, the exothermic peak (ΔHc) in step (4) below is in the range of 65 to 77 J / g, and the second low molecular weight polytetrafluoroethylene (C) has a melt flow rate of 0.03 to 0.4 g / 10 min at 372°C. toYes, the exothermic peak (ΔHc) in step (4) below is in the range of 60 to 67 J / g, the melt flow rate of the composition at 372°C is in the range of 1.0 to 2.5 g / 10 min, and when calorimetry is performed by sequentially carrying out the following steps (1) to (6) using a differential scanning calorimeter (DSC), Step (1): A first holding step in which the sample to be measured is held at a temperature of 140°C for at least one minute; Step (2): After step (1), a first heating step is performed in which the sample to be measured is heated from a temperature of 140°C to 360°C at a heating rate of 10°C / min; Step (3): A second holding step following step (2), in which the sample to be measured is held at a temperature of 360°C for 3 minutes or more; Step (4): After step (3), a first cooling step is performed in which the sample to be measured is cooled from a temperature of 360°C to 140°C at a cooling rate of 10°C / min; Step (5): A third holding step in which the sample to be measured is held at a temperature of 140°C for 3 minutes or more after step (4); Step (6): A second heating step is performed after step (5), in which the sample to be measured is heated from a temperature of 140°C to 360°C at a heating rate of 10°C / min; In the DSC chart obtained in step (6) above, there is an endothermic peak 1 having its peak top in a temperature range of 310°C to 330°C, and an endothermic peak 2 having its peak top in a temperature range lower than that of endothermic peak 1. A fluororesin composition for melt extrusion molding is provided, characterized in that the ratio of the heights of the endothermic peak 1 to the height of the endothermic peak 2 (height of endothermic peak 1 (W / g) ÷ height of endothermic peak 2 (W / g)) is 1 or more and 50 or less, the unit based on tetrafluoroethylene is 95 to 99% by mass of the composition, and the unit based on perfluoro(alkyl vinyl ether) is 1 to 5% by mass of the composition.

[0008] In the fluororesin composition of the present invention teeth, [ 1 The amount of tetrafluoroethylene-based units in the composition is 95-97% by mass, and the amount of perfluoro(alkyl vinyl ether)-based units in the composition is 3-5% by mass. and, [ 2] The composition has 1 × 10 carbon atoms. 6 The number of unstable terminal groups per unit must be 50 or less. This is preferable.

[0009] The present invention also provides a molded article containing the above-mentioned fluororesin composition. The molded article of the present invention is preferably one of the following: a tube, a bottle, a fitting, a valve, a pipe, or a seat. [Effects of the Invention]

[0010] The fluororesin composition of the present invention consists of a mixture of specific PFA and specific PTFE, has a limited melt flow rate, and the ratio of endothermic peak heights measured by differential scanning calorimeter (DSC) is within a predetermined range. As a result, it is possible to obtain a molded article that not only has excellent moldability but also very high high-temperature modulus and flex life, and furthermore, a very low oxygen permeability coefficient. This is also evident from the results of the examples described later. In other words, even with fluororesin compositions consisting of (A) to (C) above, if the ratio of the MFR and / or endothermic peak height of the fluororesin composition falls outside the above range (Comparative Examples 1 and 2), they do not possess a good balance of melt extrusion moldability, elongation at room temperature, high-temperature tensile modulus, flex life, and oxygen permeability resistance. In contrast, the fluororesin compositions of the present invention possess a good balance of all these properties (Examples 1 to 7). [Modes for carrying out the invention]

[0011] The first important feature of the present invention is a fluororesin composition comprising (A) a copolymer of tetrafluoroethylene and perfluoro(alkyl vinyl ether), (B) a first low molecular weight polytetrafluoroethylene, and (C) a second low molecular weight polytetrafluoroethylene, wherein the MFR (according to ASTM D1238), measured at a load of 5 kg and a measurement temperature of 372°C, is in the range of 1.0 to 5.0 g / 10 min, particularly 1.2 to 4.0 g / 10 min, and especially preferably 1.5 to 3.0 g / 10 min. When the MFR of the fluororesin composition is within the above range, it has excellent melt moldability in extrusion molding, injection molding, etc., has excellent mechanical strength, and can obtain a molded body that is also excellent in oxygen barrier properties (oxygen permeation resistance). When the MFR is smaller than the above range, the moldability is poor, and the oxygen permeation coefficient of the obtained molded body tends to deteriorate. On the other hand, when the MFR is larger than the above range, the obtained molded body has a significantly reduced elongation rate and flex life value at room temperature, and the mechanical strength becomes inferior.

[0012] Also, when the fluororesin composition of the present invention performs calorimetry by sequentially performing the above-described steps (1) to (6) using a differential scanning calorimeter (DSC), in the DSC chart obtained in step (6), there is an endothermic peak 1 having a peak top in the temperature range of 310 °C or higher and 330 °C or lower, and an endothermic peak 2 having a peak top in a temperature range lower than the endothermic peak 1. The ratio of the height of the endothermic peak 1 to the height of the endothermic peak 2 (endothermic peak 1 height (W / g) ÷ endothermic peak 2 height (W / g)) being 1 or more and 50 or less is the second important feature. Here, the endothermic peak 1 is derived from (B) the first low molecular weight polytetrafluoroethylene and (C) the second low molecular weight polytetrafluoroethylene in the fluororesin composition of the present invention. Similarly, the endothermic peak 2 is a peak derived from the copolymer containing (A) tetrafluoroethylene and perfluoro(alkyl vinyl ether).

[0013] That is, in the fluororesin composition of the present invention, although the peak derived from the low molecular weight PTFE is shown to be larger than the peak derived from the PFA, a molded body excellent in mechanical strength shown by the tensile properties and flex life, which are the advantages of the PFA, can be obtained. Also, when the ratio of the height of the endothermic peak 1 to the height of the endothermic peak 2 is within the range of 1 or more and 50 or less, a molded body excellent in both mechanical strength and oxygen permeation resistance can be obtained as compared with the case outside the above range. The temperature range where the endothermic peak 2 derived from PFA is located varies depending on the MFR of PFA, the type and content of the alkyl group in PAVE, etc., but it preferably has an endothermic peak 2 in the temperature range of 260 to 300°C.

[0014] The fluororesin composition of the present invention preferably contains units based on TFE in the range of 90 to 99% by mass, preferably in the range of 95 to 99% by mass, more preferably in the range of 95 to 97% by mass, and units based on PAVE in the range of 1 to 10% by mass, preferably in the range of 1 to 5% by mass, more preferably in the range of 3 to 5% by mass. As the alkyl group of PAVE, those having 1 to 3 carbon atoms are preferred, and those having 2 carbon atoms (that is, perfluoro(ethyl vinyl ether)) are particularly preferred.

[0015] In the fluororesin composition of the present invention, it is preferable to contain 40% by mass or more of a copolymer (PFA) of TFE and PAVE, more preferably 50% by mass or more, and particularly preferably 55% by mass or more. Also, it is preferable to contain 10 to 40% by mass of the first low molecular weight PTFE, and more preferably 15 to 40% by mass. Further, it is preferable to contain the second low molecular weight PTFE in an amount of 3% by mass or less (excluding 0), and more preferably 0.5 to 2% by mass. When the content of PFA is less than the above range, the moldability becomes inferior compared to the case within the above range, and the mechanical strength of the obtained molded body may be inferior. On the other hand, when the content of PFA is more than the above range and the amount of low molecular weight PTFE is less, the oxygen permeability resistance may be inferior compared to the case within the above range.

[0016] The fluororesin composition of the present invention preferably has 50 or less, particularly 10 or less, unstable end groups per carbon atom in the composition. 6 In other words, unstable end groups such as -CH2OH, -CONH2, and -COF end groups present in copolymers are chemically reactive and thermally unstable, which can lead to the generation of corrosive HF gas. Reducing such unstable end groups can reduce corrosion of molding machines. Furthermore, by performing the fluorination treatment described later to reduce unstable end groups, the ends of the PFA become -CF3 groups, which can further improve heat resistance, solvent resistance, etc.

[0017] The fluororesin composition of the present invention contains the above-mentioned components (A), (B), and (C), and the MFR is adjusted to the above-mentioned range. Furthermore, the ratio of endothermic peak heights in a predetermined temperature range determined by DSC is within the above-mentioned range. As can be seen from the results of the examples described later, the following characteristics can be satisfied. In other words, the tensile test (compliant with ASTM D3307), which will be described later, shows that the elongation at room temperature is 200% or more, and the tensile modulus at 200°C is 50 MPa or more, indicating excellent mechanical strength at both room temperature and high temperatures.

[0018] Furthermore, the fluororesin composition of the present invention has an MIT flex life value (FL value) of 200,000 cycles or more, as measured by the method described later, making it suitable for use in applications where flexibility is required, such as in tubes. The FL value indicates the resistance to repeated bending, and can generally be improved by increasing the melt viscosity or the content of copolymer components (PAVE). However, in the fluororesin composition of the present invention, the FL value is adjusted to be above the above value while maintaining a balance with other properties such as moldability and mechanical strength.

[0019] Furthermore, the fluororesin composition of the present invention has an oxygen permeability coefficient of 3 × 10, as measured by the method described later. -10 (cm 3 ·cm / (cm 2Its oxygen permeability is very low, with a value of less than 0.5g (s·cmHg). This makes it suitable for use in medical, aerospace, and electronic component fields where high oxygen barrier properties are required.

[0020] (A) Copolymer of tetrafluoroethylene and perfluoro(alkyl vinyl ether) In the present invention, (A)PFA is a copolymer of TFE as the main component and PAVE as a comonomer, and can be produced by conventionally known methods such as solution polymerization, emulsion polymerization, and suspension polymerization. In these polymerizations, conventionally known conditions such as temperature, pressure, and stirring speed, as well as polymerization initiators, surfactants, chain transfer agents, and solvents, can be used according to known formulations. Examples of surfactants (emulsifiers) used in emulsion polymerization include fluoroether acids described in Japanese Patent Publication No. 5588679 and hydrocarbon surfactants described in Japanese Patent Publication No. 6109073. In each polymerization method, the desired MFR can be achieved by adjusting the type and amount of polymerization initiators, chain transfer agents, etc.

[0021] PAVE, also known as perfluoroalkoxytrifluoroethylene, can be represented by the following formulas (1) or (2).

[0022] [ka] (In the formula, X represents H or F, n is an integer between 0 and 4, and m is an integer between 0 and 7.)

[0023] [ka] (In the formula, q is an integer between 0 and 3.)

[0024] The PAVE used in (A)PFA, which constitutes the fluororesin composition of the present invention, is preferably perfluoro(methyl vinyl ether) (PMVE), perfluoro(ethyl vinyl ether) (PEVE), or perfluoro(propyl vinyl ether) (PPVE), with perfluoro(ethyl vinyl ether) (PEVE) being the most preferred.

[0025] In the present invention, (A) it is desirable that the PAVE content in PFA be 3% by mass or more. If the content is less than 3% by mass, the durability will be unsatisfactory. The preferred lower limit of the content is 5% by mass. Generally, the higher the content, the better the durability of the composition obtained by mixing with PTFE as described below, but a content exceeding 20% ​​by mass is undesirable because it reduces the high-temperature mechanical properties of the molded article. The preferred upper limit of the content is 15% by mass, more preferably 12% by mass, and even more preferably 10% by mass.

[0026] (A) PFA may contain additional copolymerizable comonomers. In this case, the additional comonomer content is preferably less than the PAVE content and less than 1% by mass. Examples of comonomers copolymerizable with TFE include fluorine-containing comonomers such as perfluoroalkenes with 3 to 6 carbon atoms, PAVEs with 1 to 6 carbon atoms, chlorotrifluoroethylene, vinylidene fluoride, and vinyl fluoride, as well as fluorine-free comonomers such as ethylene and propylene.

[0027] The (A)PFA obtained by polymerization is preferably subjected to fluorination treatment, which makes it possible to reduce the amount of unstable end groups mentioned above. The fluorination treatment can be carried out by the method described in Japanese Patent Publication No. 62-104822, etc. Specifically, although not limited to this, the TFE / PEVE copolymer is brought into contact with a fluorine gas at atmospheric pressure or in the range of 0 to 1 MPa (gauge pressure) at a temperature of 50°C to 250°C, preferably 200°C, for 1 to 20 hours. Pure fluorine gas may be used, but for safety reasons, it is preferable to use fluorine gas diluted to 2 to 50% by volume with an inert gas such as nitrogen gas, helium gas, or argon gas. The shape of the (A)PFA to be brought into contact is not particularly limited and may be in powder, pellet, flake, or any other form.

[0028] (A) The PFA is preferably in the range of 0.1 to 5.0 g / 10 min, particularly 0.2 to 3.0 g / 10 min, and especially preferably 0.5 to 2.0 g / 10 min, when measured with a load of 5 kg and a measurement temperature of 372 °C, according to ASTM D1238. You may also mix two or more PFAs with different MFRs and adjust them to the above range.

[0029] (B) First low molecular weight polytetrafluoroethylene In the present invention, (B) the first low molecular weight PTFE is a PTFE that exhibits melt fluidity, obtained by polymerization of TFE. Specifically, the PTFE has an MFR in the range of 1 to 100 g / 10 min, preferably 10 to 80 g / 10 min, and particularly preferably 10 to 55 g / 10 min. (B) For the first low molecular weight PTFE, when steps (1) to (6) described above are performed using a differential scanning calorimeter (DSC), the exothermic peak (ΔHc) observed in step (4) is preferably in the range of 60 to 80 J / g, and more preferably in the range of 65 to 77 J / g. This ΔHc is an indicator of crystallinity and is known to correlate with molecular weight (Macromol. Mater. Eng. 2004, 289, 420-425). Such low molecular weight PTFE can be produced by conventionally known methods such as solvent polymerization, emulsion polymerization, and suspension polymerization of TFE. (B) The shape of the first low molecular weight PTFE is not particularly limited, and fine particles with an average particle size of 0.01 to 100 μm that are commonly available can be used. To improve uniformity in the composition, a preferred average particle size is 0.05 to 50 μm, and a more preferred average particle size is 0.05 to 25 μm.

[0030] (C) Second low molecular weight polytetrafluoroethylene In the present invention, (C) the second low molecular weight PTFE is PTFE obtained by radiolysis of high molecular weight non-meltable fluid PTFE. Specifically, the PTFE has an MFR in the range of 0.01 to 0.5 g / 10 min, preferably 0.03 to 0.4 g / 10 min. (C) As for the second low molecular weight PTFE, when steps (1) to (6) described above are performed using a differential scanning calorimeter (DSC), the exothermic peak (ΔHc) observed in step (4) is preferably in the range of 55 to 70 J / g, and more preferably in the range of 60 to 67 J / g. Such low molecular weight PTFE can be prepared by irradiating high molecular weight PTFE, called "molding powder" or "fine powder," with ionizing radiation such as gamma rays or electron beams at a temperature below its melting point, typically until it receives an irradiation dose of 10 kGy to 1 MGy, in a vacuum, air, or inert atmosphere. (C) The shape of the second low molecular weight PTFE is not particularly limited, and the same shape and average particle size as the first low molecular weight PTFE described above (B) can be used.

[0031] In the production of the fluororesin composition of the present invention, it is preferable to introduce the above-mentioned components (A) to (C) into a known batch-type or continuous-type kneader or twin-screw extruder and uniformly melt and knead them. The PFA and PTFE powders can be pre-mixed using conventional dry blending or wet blending methods before melting and kneading. Alternatively, particles (B) and (C) can be present in the polymerization medium in the polymerization tank beforehand, and the polymerization of PFA can be started to obtain a mixed powder with a core / shell structure. Another method is to present particles (A) in the polymerization medium, start the polymerization of PTFE, and then further mix (C) into the resulting mixed powder with a core / shell structure.

[0032] In the present invention, it is preferable to fluorinate components (A) to (C) before or after melt-kneading. The method of fluorination treatment is as described above.

[0033] The fluororesin composition of the present invention can be used in melt molding such as extrusion molding, injection molding, and compression molding, and is particularly suitable for melt extrusion molding. It is preferably used for molding molded articles such as tubes, pipes, hoses, films, sheets, round bars, and square bars. [Examples]

[0034] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. The method for measuring physical properties and the raw materials used in this invention are as follows.

[0035] A. Measurement of physical properties (1) MFR A melt indexer (manufactured by Toyo Seiki Seisakusho Co., Ltd.) equipped with a corrosion-resistant cylinder, orifice, and piston compliant with ASTM D1238 was used. 5g of the sample was filled into a cylinder maintained at 372±1℃ and held for 5 minutes. Then, under a load of 5kg (piston and weight), the sample was extruded through the orifice, and the amount of molten material extruded per 10 minutes (g / 10 min) was determined as the MFR (Metal Flow Rate).

[0036] (2) Content of PAVE units Using a sample with a known PAVE content of approximately 50 μm and a Fourier transform infrared spectrometer (Thermo Fisher Scientific FT-IR iS50), the 4.25 μm absorption band was used as the internal thickness standard. The presence of PAVE was confirmed in the 9.17 μm infrared band, and the ratio of the absorbance at 9.17 μm to the absorbance at 4.25 μm was used to determine a calibration curve for PAVE content using the calibration curve method. After melt-compressing the sample at 350°C and then water-cooling, a film with a thickness of approximately 50 μm was obtained. The PAVE content was then determined from the calibration curve and the obtained infrared absorption spectrum according to the method described in U.S. Patent No. 5760151.

[0037] (3) Number of unstable terminal groups Using a Fourier transform infrared spectrometer (FT-IR iS50, Thermo Fisher Scientific Co., Ltd.) and a sample with a known end group content of approximately 250 μm, the absorbances of -COF 5.31 μm, -COOH groups (-C=O(M) 5.52 μm, -C=O(D) 5.63 μm, and -CONH2 groups (-NH2 2.91 μm) were confirmed, and a calibration curve was created using the calibration curve method. After melt-compressing the sample at 350°C and then water-cooling, films with a thickness of 0.25 to 0.3 mm were obtained, and the carbon atoms were analyzed from the calibration curve and the obtained infrared absorption spectra according to the method described in U.S. Patent No. 4675380. 6 The number of unstable terminal cardinals per unit was calculated. When the number of unstable terminal bands is less than the detection limit, it is expressed as "less than 6" or "<6".

[0038] (4) Ratio of endothermic peak heights A differential scanning calorimeter (PerkinElmer DSC8500) was used. A 10 mg sample was weighed, placed in a dedicated aluminum pan, crimped using a dedicated crimper, and then placed in the DSC unit. Calorimetry was then performed by sequentially following the steps (1) to (6) below. Step (1): A first holding step in which the sample to be measured is held at a temperature of 140°C for at least one minute; Step (2): After step (1), a first heating step is performed in which the sample to be measured is heated from a temperature of 140°C to 360°C at a heating rate of 10°C / min; Step (3): A second holding step following step (2), in which the sample to be measured is held at a temperature of 360°C for 3 minutes or more; Step (4): After step (3), a first cooling step is performed in which the sample to be measured is cooled from a temperature of 360°C to 140°C at a cooling rate of 10°C / min; Step (5): A third holding step in which the sample to be measured is held at a temperature of 140°C for 3 minutes or more after step (4); Step (6): A second heating step is performed after step (5), in which the sample to be measured is heated from a temperature of 140°C to 360°C at a heating rate of 10°C / min; In the DSC chart obtained in step (6) above, the endothermic peak having its peak top in the temperature range of 310°C to 330°C was defined as endothermic peak 1. Furthermore, an endothermic peak with a peak top in a temperature range lower than endothermic peak 1 was designated as endothermic peak 2. The ratio of the heights of endothermic peak 1 and endothermic peak 2 (height of endothermic peak 1 (W / g) ÷ height of endothermic peak 2 (W / g)) was calculated.

[0039] (5) Melt extrusion moldability A fluororesin composition was melt-kneaded at a temperature of 360°C using a melt extrusion molding machine, and a tubular molded body was obtained by melt extrusion at an extrusion speed of 1 m / min. We marked those molded parts without any problems with ○, and those molded parts with surface roughness with ×.

[0040] (6) Elongation at room temperature, tensile modulus at high temperature Measurements were performed in accordance with ASTM D3307. A dumbbell-shaped test specimen (5 mm wide and 22 mm long in the parallel section) was prepared from a film approximately 1.5 mm thick obtained by melt-compression molding the sample at 350°C, using a mold in accordance with ASTM D3307. Measurements were performed using a Tensilon tensile strength analyzer manufactured by Orientec Co., Ltd., while maintaining the specimen temperature at 23°C, with an initial chuck distance of 22 mm and a tensile speed of 50 mm / min. The elongation rate was calculated by dividing the deformation of the specimen at the fracture point by the original length of the specimen. The high-temperature tensile modulus was determined by performing the same measurement while maintaining the sample temperature at 200°C, and calculating the slope of the resulting stress-strain curve.

[0041] (7) MIT Flex Life Value Measurements were performed in accordance with JIS P8115. A test specimen approximately 110 mm long and 15 mm wide was prepared from a film approximately 0.2 mm thick obtained by melt-compression molding the sample at 350°C. Using a triple-bike MIT folding resistance tester manufactured by MIZ Test Machine Co., Ltd., the specimen was bent at a speed of 175 times / minute at an angle of 135 degrees to the left and right under a load of 1 kg, and the number of bends until the test specimen broke was determined.

[0042] (8) Oxygen permeability coefficient Using a film approximately 0.3 mm thick obtained by melt-compressing the sample at 350°C, the oxygen gas permeability coefficient (cm) was measured at 23°C using an OTR-C6 gas / water vapor permeability measuring device manufactured by Toyo Seiki Seisakusho Co., Ltd. 3 ·cm / (cm 2 The following measurements were taken: (·s·cmHg).

[0043] B. Raw materials (A) PFA PFA1: Copolymer of TFE and PPVE (PPVE content 3.0 wt%, MFR 1.3, manufactured by Mitsui Chemours Fluoroproducts Co., Ltd.) PFA2: Copolymer of TFE and PPVE (PPVE content 3.1 wt%, MFR 0.5, manufactured by Mitsui Chemours Fluoroproducts Co., Ltd.) PFA3: Copolymer of TFE and PPVE (PPVE content 3.0 wt%, MFR 0.8, manufactured by Mitsui Chemours Fluoroproducts Co., Ltd.) PFA4: Copolymer of TFE and PPVE (PPVE content 3.0 wt%, MFR 1.1, manufactured by Mitsui Chemours Fluoroproducts Co., Ltd.) PFA5: Copolymer of TFE and PPVE (PPVE content 5.9 wt%, MFR 1.3, manufactured by Mitsui Chemours Fluoroproducts Co., Ltd.) PFA6: Copolymer of TFE and PEVE (PEVE content 5.3 wt%, MFR 0.6, manufactured by Mitsui Chemours Fluoroproducts Co., Ltd.) PFA7: Copolymer of TFE and PEVE (PEVE content 5.0 wt%, MFR 1.2, manufactured by Mitsui Chemours Fluoroproducts Co., Ltd.) PFA8: Copolymer of TFE and PEVE (PEVE content 6.6 wt%, MFR 2.0, manufactured by Mitsui Chemours Fluoroproducts Co., Ltd.)

[0044] (B) First low molecular weight PTFE PTFE1:PTFE obtained by emulsion polymerization of TFE (MFR21, ΔHc73J / g, manufactured by Mitsui Chemours Fluoroproducts Co., Ltd.) PTFE obtained by emulsion polymerization of PTFE2:TFE (MFR53, ΔHc72J / g, manufactured by Mitsui Chemours Fluoroproducts Co., Ltd.) PTFE3:PTFE obtained by emulsion polymerization of TFE (MFR15, ΔHc73J / g, manufactured by Mitsui Chemours Fluoroproducts Co., Ltd.)

[0045] (C) Second low molecular weight PTFE PTFE4: PTFE obtained by radiolysis of high molecular weight PTFE (MFR 0.05, ΔHc 65 J / g, manufactured by Mitsui Chemours Fluoroproducts Co., Ltd.) PTFE5: PTFE obtained by radiolysis of high molecular weight PTFE (MFR 0.3, ΔHc 63 J / g, manufactured by Mitsui Chemours Fluoroproducts Co., Ltd.)

[0046] (Examples 1-7, Comparative Examples 1-2) Components (A) to (C) were added to a Toyo Seiki Plastmill (KF70V type) in the proportions shown in Table 1, and melt-mixed at 380°C and 10 rpm for 5 minutes. Subsequently, the terminal groups were stabilized (fluorinated) by treatment with fluorine gas using the method described in Japanese Patent Publication No. 62-104822.

[0047] [Table 1]

[0048] Table 2 shows the physical properties of the compositions obtained in the examples and comparative examples. Additionally, Table 2 shows the physical properties of PFA8 alone as Reference Example 1.

[0049] [Table 2]

Claims

1. (A) Copolymer of tetrafluoroethylene and perfluoro(alkyl vinyl ether) (B) 10 to 40% by mass of a first low molecular weight polytetrafluoroethylene, and (C) A composition containing a second low molecular weight polytetrafluoroethylene in an amount of 3% by mass or less, The first low molecular weight polytetrafluoroethylene (B) has a melt flow rate in the range of 10 to 55 g / 10 min at 372°C, and the exothermic peak (ΔHc) in step (4) below is in the range of 65 to 77 J / g. The aforementioned (C) second low molecular weight polytetrafluoroethylene has a melt flow rate in the range of 0.03 to 0.4 g / 10 min at 372°C, and the exothermic peak (ΔHc) in step (4) below is in the range of 60 to 67 J / g. The composition has a melt flow rate at 372°C in the range of 1.0 to 2.5 g / 10 min. When performing a calorimetry measurement using a differential scanning calorimeter (DSC) by sequentially performing the following steps (1) to (6), Step (1): A first holding step in which the sample to be measured is held at a temperature of 140°C for at least one minute; Step (2): After step (1), a first heating step is performed in which the sample to be measured is heated from a temperature of 140°C to a temperature of 360°C at a heating rate of 10°C / min; Step (3): A second holding step in which the sample to be measured is held at a temperature of 360°C for 3 minutes or more after step (2); Step (4): After step (3), a first cooling step is performed in which the sample to be measured is cooled from a temperature of 360°C to a temperature of 140°C at a cooling rate of 10°C / min; Step (5): A third holding step following step (4), in which the sample to be measured is held at a temperature of 140°C for 3 minutes or more; Step (6): A second heating step is performed after step (5), in which the sample to be measured is heated from a temperature of 140°C to 360°C at a heating rate of 10°C / min; In the DSC chart obtained in step (6) above, there is an endothermic peak 1 having its peak top in a temperature range of 310°C to 330°C, and an endothermic peak 2 having its peak top in a temperature range lower than that of endothermic peak 1. A fluororesin composition for melt extrusion molding, characterized in that the ratio of the heights of the endothermic peak 1 to the height of the endothermic peak 2 (height of endothermic peak 1 (W / g) ÷ height of endothermic peak 2 (W / g)) is 1 or more and 50 or less, the unit based on tetrafluoroethylene is 95 to 99% by mass of the composition, and the unit based on perfluoro(alkyl vinyl ether) is 1 to 5% by mass of the composition.

2. The fluororesin composition according to claim 1, characterized in that units based on tetrafluoroethylene constitute 95 to 97% by mass of the composition, and units based on perfluoro(alkyl vinyl ether) constitute 3 to 5% by mass of the composition.

3. The composition has 1 × 10 carbon atoms. ６ The fluororesin composition according to claim 1 or 2, wherein the number of unstable end groups per unit is 50 or less.

4. A molded article comprising the fluororesin composition according to claim 1.

5. A molded article according to claim 4, which is any of a tube, bottle, fitting, valve, pipe, or seat.

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