Heat-meltable fluororesin for injection molding

Abstract

To provide a heat-meltable fluororesin for injection molding which contains a copolymer containing TFE and PEVE and which has excellent properties such as heat resistance, injection moldability (mold fillability), mechanical strength, flex resistance, solvent resistance, and the like, and to provide an injection molded article containing this heat-meltable fluororesin. A heat-meltable fluororesin for injection molding, comprising: a copolymer containing more than 90.6 mass% and less than 93.5 mass% of tetrafluoroethylene and more than 6.5 mass% and less than 9.4 mass% of perfluoro(ethyl vinyl ether); wherein the melt flow rate at 372°C is in a range of 22 to 50 g / 10 min; and the number of unstable terminal groups per 1 × 106 carbon atoms in the copolymer is 50 or less.

Description

AP0443-W001TITLE OF INVENTION HEAT-MELTABLE FLUORORESIN FOR INJECTION MOLDING CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of Japanese Patent Application No. 2025-016966 filed February 4, 2025 and claims the benefit of priority of Japanese Patent Application No. 2025-204029 filed November 26, 2025, the disclosures of which are incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] The present invention relates to a heat-meltable fluororesin, and more specifically to a heat-meltable fluororesin having properties suitable for injection molding and a well-balanced combination of properties such as heat resistance, mechanical strength, bending resistance, and the like, and to an injection molded article made of the heat-meltable fluororesin.BACKGROUND ART

[0003] A copolymer (PFA) of tetrafluoroethylene (TFE) and perfluoro(alkyl vinyl ether) (PAVE) has excellent properties similar to TFE, such as heat resistance, chemical resistance, and the like, as well as thermal melting properties, and therefore is used in melt molding such as melt extrusion molding, injection molding, blow molding, melt compression molding, and the like. The obtained molded products are used as pipes and joints for transporting chemical solutions, storage containers, and the like in semiconductor manufacturing processes, chemical plants, and the like.

[0004] Of the aforementioned molding methods, injection molding is capable of molding products having complex shapes such as joints and the like, and generally uses PFA having a high melt flow rate (MFR). For example, the following Patent Document 1 describes a molding material made of PFA having an MFR of 14.8 to 50 g / 10 min, containing 4 mass% or more of PAVE units, having a melting point of 295°C or higher, and having 50 or less unstable terminal groups per 1 xio6carbon atoms in the copolymer, and describes that,AP0443-W001perfluoro(propyl vinyl ether) (PPVE) is preferably used as a copolymerization component in the aforementioned molding material, from the viewpoint of heat resistance, and the like, but although the aforementioned Patent Document 1 lists perfluoro(ethyl vinyl ether) (PEVE) as one of the PAVE units that is a copolymerization component, Patent Document 1 does not specifically mention PFA containing PEVE as a copolymerization component.

[0005] On the other hand, Patent Document 2 listed below describes a copolymer that contains at least 3 mass% PEVE and has a melt viscosity of 25 x io3Pa s or less at 372°C, and when the amount of PEVE exceeds 10 mass%, the melt viscosity exceeds 25 103Pa s at 372°C. Patent Document 2 also describes that this TFE / PEVE copolymer has excellent melt processability, and that molded articles obtained therefrom have high toughness and long flexural life.

[0006] Furthermore, Patent Document 3 listed below describes a copolymer containing 4.4 to 6.2 mass% of PEVE, having an MFR of 0.8 to 4.0 g / 10 min, and having 20 or fewer unstable terminal groups per 106main chain carbon atoms of the copolymer.Patent Literature

[0007] Patent Document 1 : Patent No. 4228917Patent Document 2: Patent No. 3519411Patent Document 3: Patent No. 7364989SUMMARY OF INVENTION TECHNICAL PROBLEM

[0008] The TFE / PEVE copolymer described in Patent Document 2 is melt-processable, but a wide range of melt viscosities are described, and the range of PFA that exhibit suitable injection moldability and provide an injection molded article having excellent heat resistance (usability at high temperatures), mechanical strength, flex resistance, solvent resistance, and processability is unclear.AP0443-W001

[0009] Furthermore, the aforementioned Patent Document 3 describes that the PFA is a copolymer that can be molded by melt extrusion molding or the like into sheets or films, such as release films or processing sheets used in hot press molding. However, the PFA disclosed in Patent Document 3 has a low MFR, inhibiting use for injection molding, and thus a suitable injection molded article cannot be obtained.

[0010] In general, when PEVE is used as a copolymerization component, as compared to when PPVE is used as a copolymerization component, there are advantages in that the copolymerization component is incorporated more uniformly and in larger amounts into the molecular chain, the reaction rate with TFE is faster, the polymerization reaction is easier to control, and the like. However, PFAs containing PEVE as a copolymerization component tend to have reduced heat resistance as the amount of PEVE increases. Therefore, it is desirable to obtain injection molded articles having excellent heat resistance that can be used under high-temperature conditions, even with injection molded articles made from PFA containing a prescribed range of PEVE as a copolymerization component.

[0011] Furthermore, the properties required of a heat-meltable fluororesin for injection molding, such as injection moldability, heat resistance of the obtained injection molded article (usability at high temperatures), mechanical strength, bending resistance, solvent resistance, processability, and the like are affected by the amount of PEVE units, which is a copolymerization component, the MFR value, and the like. For example, increasing the amount of PEVE units improves the injection moldability and bending resistance, but tends to decrease the heat resistance and mechanical strength, and thus there is difficulty in preparing a heat-meltable fluororesin for injection molding having all the properties in a good balance.

[0012] Accordingly, an object of the present invention is to provide a heat-meltable fluororesin for injection molding which contains a copolymer containing TFE and PEVE and which has a good balance of excellent properties such as heat resistance, injection moldability, mechanical strength,AP0443-W001flex resistance, solvent resistance, and the like, and to provide an injection molded article containing this heat-meltable fluororesin.

[0013] The present invention provides a heat-meltable fluororesin for injection molding, comprising:a copolymer containing more than 90.6 mass% and less than 93.5 mass% of tetrafluoroethylene and more than 6.5 mass% and less than 9.4 mass% of perfluoro(ethyl vinyl ether);wherein the melt flow rate at 372°C is in a range of 22 to 50 g / 10 min; andthe number of unstable terminal groups per 1 x 106carbon atoms in the co-polymer is 50 or less.

[0014] The heat-meltable fluororesin for injection molding of the present invention preferably has:(1 ) a glass transition temperature of 75°C or higher; and (2) a melting point of 268°C or higher and a crystallization temperature of 260°C or higher, as measured by a differential scanning calorimeter.

[0015] The present invention also provides an injection molded article containing the aforementioned heat-meltable fluororesin for injection molding.

[0016] The injection molded article is preferably any one of a tube, a bottle, a joint, a valve, or a pipe.ADVANTAGEOUS EFFECT

[0017] The heat-meltable fluororesin for injection molding of the present invention can provide a well-balanced combination of all the properties required for a heat-meltable fluororesin for injection molding, such as heat resistance (usability at high temperatures), injection moldability, as well as mechanical strength bending resistance, solvent resistance, and processability of the obtained injection molded article, by adjusting the amountAP0443-W001of TFE units and PEVE units in the TFE / PEVE copolymer, the MFR, and the number of unstable terminal groups.

[0018] In other words, as is clear from the results of the examples described later, the heat-meltable fluororesin of the present invention satisfies all of the characteristics of heat resistance (usability at high temperature) indicated by the glass transition temperature, melting point, crystallization temperature, and the like, as well as mold filling property indicated by the zero shear viscosity (injection moldability in which molten resin reliably spreads to every corner of the molding die during injection molding, such that an injection molded article can be stably molded by the mold), mechanical strength indicated by the yield stress, maximum stress, and the like, measured by the tensile test, bending resistance indicated by the flex life test, processability indicated by the strain hardening coefficient similarly measured by a tensile test, and solvent resistance indicated by the weight change rate obtained by an isopropanol immersion test, in a well-balanced manner (Examples 1 to 5).

[0019] In contrast, at least one of the aforementioned properties cannot be satisfied by a heat-meltable fluororesin containing a copolymer that does not satisfy any one of the amount of TFE units and PEVE units, and the MFR value (Comparative Examples 1 to 7).DESCRIPTION OF EMBODIMENTS

[0020] A first important feature of the present invention is that the heat-meltable fluororesin contains a TFE / PEVE copolymer containing more than 90.6 mass% and less than 93.5 mass%, particularly a range of 90.7 to 93.0 mass%, particularly preferably a range of 90.8 to 92.5 mass%, of TFE units and more than 6.5 mass% and less than 9.4 mass%, particularly a range of 7.0 to 9.3 mass%, particularly preferably a range of 7.5 to 9.2 mass%, of PEVE units.

[0021] In other words, when the amount of TFE units is more than the aforementioned range and the amount of PEVE units is less than the aforementioned range, the flex resistance of the injection molded article isAP0443-W001lowered as compared to a case where the amount of TFE units is within the aforementioned range. On the other hand, when the amount of TFE units is lower and the amount of the PEVE unit is larger than the aforementioned ranges, the glass transition temperature, the melting point and the crystallization temperature will tend to be lower than the case where the amount of TFE units is within the aforementioned ranges, and the heat resistance will be inferior. An injection molded article having a favorable balance of properties that are affected by the amount of PEVE units, such as heat resistance, mechanical strength, and flex resistance, can be molded by adjusting the amount of PEVE units in the heat-meltable fluororesin of the present invention to a specific range.

[0022] Furthermore, a second important feature of the heat-meltable fluororesin of the present invention is that the MFR (according toASTM D1238) measured at a load of 5 kg and a measuring temperature of 372°C is in a range of 22 to 50 g / 10 minutes, particularly 23 to 45 g / 10 minutes, and particularly preferably 25 to 42 g / 10 minutes.

[0023] In other words, when the MFR is smaller than the aforementioned range, the mold filling property during injection molding will be inferior, so molding an injection molded article having excellent dimensional stability to match the mold will be difficult, as compared with the case where the MFR is within the aforementioned range. On the other hand, when the MFR is larger than the aforementioned range, the maximum stress in the tensile test is lowered as compared with the case where the MFR is within the aforementioned range, and thus satisfactory mechanical strength cannot be obtained and the solvent resistance is inferior.

[0024] With the heat-meltable fluororesin of the present invention, even those resins having a high MFR suitable for injection molding can be made to satisfy all the performance properties affected by the MFR, such as the mold filling property expressed by the zero shear viscosity described later, the flex resistance expressed by the MIT flex life value, and the mechanical strength, in a well-balanced manner, by adjusting the MFR to the aforementioned range.AP0443-W001

[0025] A third important feature of the heat-meltable fluororesin of the present invention is that the number of unstable terminal groups per 1 x 106carbon atoms in the copolymer is not more than 50, especially not more than 10.

[0026] In other words, unstable terminal groups such as -CH2OH terminal groups, -CONH2 terminal groups, and -COF terminal groups present in the copolymer are chemically reactive and thermally unstable, and thus there is a possibility that corrosive HF gas can be generated. The heat-meltable fluororesin of the present invention has a reduced number of such unstable terminal groups, and thus the occurrence of corrosion of an injection molding die is remarkably reduced. In addition, the fluorination treatment described below for reducing the number of unstable terminal groups makes the terminal of the TFE / PEVE copolymer a -CF3 group, and thus the heat resistance, solvent resistance, and the like can be further improved.

[0027] The heat-meltable fluororesin of the present invention can satisfy the following properties by adjusting the amount of comonomer and MFR of the TFE / PEVE copolymer to the aforementioned ranges.

[0028] In other words, the glass transition temperature (Tg) of the TFE / PEVE copolymer is preferably adjusted to 75°C or higher, particularly 77°C or higher. As a result, the injection molded article made of the heat-meltable fluororesin can have high heat resistance so as to be usable under high temperature conditions.

[0029] The melting point (Tm) of the heat-meltable fluororesin of the present invention as measured by a differential scanning calorimeter (DSC) is preferably 268°C or higher, particularly preferably 280°C or higher. Furthermore, the crystallization temperature (Tc) measured by a DSC is preferably 260°C or higher. When coupled with a high glass transition temperature, this provides excellent heat resistance (usability at high temperature).AP0443-W001

[0030] Furthermore, with the heat-meltable fluororesin of the present invention, the lower limit of the zero shear viscosity is 1000 Pa s or more, preferably 1200 Pa s or more, and the upper limit of the zero shear viscosity is 2400 Pa s or less, preferably 2200 Pa s or less, more preferably 2000 Pa s or less.

[0031] In other words, when the zero shear viscosity is lower than the aforementioned range, the mechanical strength and solvent resistance of the obtained injection molded article may be inferior, as compared with the case where the zero shear viscosity is within the aforementioned range, and when the zero shear viscosity is higher than the aforementioned range, the mold filling property may be inferior as compared with the case where the zero shear viscosity is within the aforementioned range, but with the heat-meltable fluororesin of the present invention, the mold filling property of the molten resin at the time of injection molding is excellent, so the injection molded article can be stably molded to match the mold, and the mechanical strength and solvent resistance of the obtained injection molded article will also be favorable.

[0032] The heat-meltable fluororesin of the present invention has properties that exceed a certain value, namely a yield strength of more than 14.5 MPa, a maximum strength of 28 MPa or more, and a strain hardening coefficient of 6.5 MPa or more, as determined by a tensile test (in accordance with ASTM D3307) described later, and thus has excellent mechanical strength, and also has an effect of having excellent processability because a molded article having a predetermined hardness can be obtained.

[0033] Furthermore, the heat-meltable fluororesin of the present invention has an MIT flex life value (FL value) of 20000 times or more, more preferably 50000 times or more, as measured by the method described later, and thus can also be suitably used in applications requiring flex resistance, such as tubes.

[0034] The FL value indicates the resistance to repeated bending, and can be generally improved by increasing the melt viscosity or increasing theAP0443-W001amount of the copolymer component, but in the heat-meltable fluororesin of the present invention, the FL value is adjusted to the aforementioned value or more while balancing with other performance properties such as moldability and heat resistance.

[0035] Furthermore, the heat-meltable fluororesin of the present invention has a small isopropanol (IPA) weight change rate (%) of less than 0.1% as measured by the method described later, and thus can be molded into an injection molded article having excellent solvent resistance and which is not affected by chemical solutions and the like.

[0036] The heat-meltable fluororesin of the present invention contains a copolymer containing TFE units and PEVE units in the aforementioned amounts, and is preferably a TFE / PEVE binary copolymer, but may contain other additional non-functional or functional fluorinated comonomers, on condition that the TFE units and the PEVE units are contained in the aforementioned ranges.

[0037] Other additional non-functional fluorinated comonomers that may be included can include, for example, fluoroolefins (other than TFE) having 2 to 8 carbon atoms and fluorinated alkyl vinyl ethers where the alkyl group contains 1 or 3 to 5 carbon atoms. Preferred examples of fluoroolefins include hexafluoropropylene (HFP) and chlorotrifluoroethylene (CTFE).

[0038] The heat-meltable fluororesin of the present invention (TFE / PEVE copolymer) can be prepared by a conventionally known polymerization method such as suspension polymerization, solution polymerization, emulsion polymerization, bulk polymerization, and the like.

[0039] Furthermore, during polymerization, the conditions such as temperature, pressure, stirring speed, and the like, as well as the polymerization initiator, surfactant, chain transfer agent, solvent, and the like, may be as conventionally known and used in accordance with known formulations. The surfactant (emulsifier) used during emulsion polymerization can be, for example, the fluoroether acids described in Japanese Patent No.AP0443-W0015588679, hydrocarbon surfactants described in Japanese Patent No.6109073, and the like. In each polymerization method, the MFR can be adjusted to a desired value by adjusting the type and amount of the polymerization initiator, chain transfer agent, and the like.

[0040] The TFE / PEVE copolymer obtained by polymerization is preferably subjected to a fluorination treatment, whereby the number of unstable terminal groups described above can be reduced. The fluorination treatment can be carried out by the method described in Japanese Unexamined Patent Application No. S62-104822.

[0041] In particular, although not a limitation, the TFE / PEVE copolymers are brought into contact with a fluoride gas at a temperature of 50°C to 250°C, preferably up to 200°C, at atmospheric pressure or 0 to 1 MPa (gauge) pressure for 1 to 20 hours. The fluorine gas to be used can be pure fluorine gas, but from the viewpoint of safety, fluorine gas diluted to 2 to 50% by volume with an inert gas such as nitrogen gas, helium gas, argon gas, or the like is preferably used. The shape of the TFE / PEVE copolymer to be contacted is not particularly limited, and may be any shape such as powder shape, pellet shape, flake shape, or the like.

[0042] The heat-meltable fluororesin for injection molding of the present invention may be blended with other thermoplastic resins such as polyolefins, polyesters, polyamides, and the like, styrene-based thermoplastic elastomers, or thermosetting resins such as phenol resins, epoxy resins, and the like, as long as the properties of the heat-meltable fluororesin of the present invention are in good balance and are not impaired during injection molding.

[0043] Furthermore, PFA and / or PTFE other than the TFE / PEVE copolymer of the present invention may be included. Examples of PFA include TFE and PAVE having 4 or fewer carbon atoms, or in other words, perfluoro(methyl vinyl ether) (PMVE), perfluoro(propyl vinyl ether) (PPVE), and perfluoro(butyl vinyl ether) (PBVE).AP0443-W001

[0044] Furthermore, various additives such as antioxidants, ultraviolet stabilizers, crosslinking agents, lubricants, plasticizers, thickeners, fillers, pigments, dyes, flame retardants, antistatic agents, and the like may be added as needed within a range that does not impair the properties of the heat-meltable fluororesin of the present invention.

[0045] As described above, the heat-meltable fluororesin of the present invention has excellent mold filling properties and has a reduced number of unstable terminal groups that affect the molding die, and thus is suitably used for injection molding.

[0046] The resulting injection molded article can be suitably molded into a hollow shape such as a tube, bottle, joint, valve, pipe, and the like, but is not limited thereto.

[0047] The injection molded article containing the heat-meltable fluororesin of the present invention has excellent properties such as heat resistance, mechanical strength, processability, flex resistance, solvent resistance, and the like, in a well-balanced manner, and thus is suitably used particularly in semiconductor production processes, chemical plants, and the like.EXAMPLES

[0048] The present invention is described below in further detail by presenting examples and comparative examples, but the present invention is not limited to these examples.

[0049] The measurement methods of the physical properties and the raw materials that are used in the present invention are as shown below.A. Measurement of physical properties(1) MFR

[0050] Using a corrosive-resistant melt indexer (manufactured by Toyo Seiki Seisaku-sho, Ltd.) equipped with a cylinder, orifice, and piston in accordance with ASTM D 1238, 5 g of the sample was filled into the cylinder maintained at 372 ± 1°C for five minutes, then extruded through an orificeAP0443-W001under a 5 kg load (piston and weight), after which the amount of the melt extruded at this time per 10 minutes (g / 10 min) was determined as the MFR. (2) Amount of TFE units and PEVE units

[0051] A calibration curve for the amount of PEVE was obtained by a calibration curve method using a sample with a known amount of PEVE of about 50 pm and a ratio of absorbance at 9.17 pm to absorbance at 4.25 pm, the presence of PEVE being confirmed in an infrared band at 9.17 pm using an absorption band at 4.25 pm as an internal thickness standard by means of a Fourier transformation infrared spectrophotometer (FT-IR iS50 manufactured by Thermo Scientific). A film having a thickness of about 50 p m obtained by melt compression molding at 350°C and then watercooling was measured for the PEVE amount in the TFE / PEVE copolymer from the calibration curve and the obtained infrared absorption spectrum according to the method described in U.S. Pat. No. 5760151.(3) Number of unstable terminal groups

[0052] Using a sample having a known number of terminal groups of about 250 pm and a Fourier transformation infrared spectroscopic analyzer (FT-IR iS50 manufactured by Thermo Fisher Scientific Inc.), the absorbance of -COF 5.31 pm, -C=O(M) 5.52 pm and -C=O(D) 5.63 pm among -COOH groups, and -NH22.91 pm among -CONH2 groups was confirmed, and a calibration curve was prepared using a calibration curve method. The sample was meltcompression molded at 350°C, and then water-cooled to obtain a film having a thickness of 0.25 to 0.3 mm, where the number of unstable terminal groups per 106carbon atoms contained in the TFE / PEVE was determined from the calibration curve and the obtained infrared spectrum according to the method described in US Patent No. 4675380.(4) Zero shear viscosity

[0053] A sample was melt-compression molded at 350°C, and then water-cooled to obtain a film having a thickness of 1.5 mm, which was cut into a circular shape having a 25 mm diameter, and the thickness was measured using a dynamic viscoelasticity measurement device (ARES manufactured byAP0443-W001Rheometric Scientific F. E.) in a parallel plate mode at a temperature of 340°C in a frequency range of 100 to 0.1 rad / sec. The Cox-Merz rule was applied to the obtained data of the complex viscosity, and curve fitting was performed using the Cross model. The zero shear viscosity was calculated by curve fitting using the following formula.Formula y = (C1 - C2) / (1 + (C3 * x)AC4) + C2 C1 = zero shear viscosityC2 = infinite shear viscosityC3 = consistency factorC4 = shear rate indexx = frequency (rad / sec)y = shear viscosity (Pa ■ s)The shear viscosity at x = 0 in the fitted curve was defined as the zero shear viscosity.(5) Glass transition temperature (Tg)

[0054] Afilm having a thickness of 1.5 mm obtained by melt-compression molding a sample at 350°C and then water-cooling the sample was cut into a rectangle of 45 mm x 12.7 mm (length x width), and the temperature was raised from -40°C to 200°C at a rate of 5°C / min at a measuring frequency of 6.28 rad / sec in a parallel plate mode using a dynamic viscoelasticity measuring apparatus (ARES manufactured by Rheometric Scientific F. E.), and then the storage modulus G' and the loss modulus G" were calculated. The loss tangent tan5 can be calculated by the following formula using G' and G".Loss tangent tan5 = loss elastic modulus G'Vstorage elastic modulus G' The temperature at the peak of the loss factor (tanb) was defined as the glass transition temperature.(6) Melting point (Tm) and crystallization temperature (Tc)

[0055] A differential scanning calorimeter (DSC 8500 manufactured by PerkinElmer Inc.) was used. 10 mg of test sample was weighed and placed in a dedicated aluminum pan, crimped by a dedicated crimper, and stored in the DSC main unit, and then temperature increase was started. The temperatureAP0443-W001was raised from 150°C to 360°C at a rate of 10°C / min, held at 360°C for 3 minutes, and then lowered to 150°C at a rate of 10°C / min. The crystallization peak temperature of the crystallization curve obtained at this time was calculated as the crystallization temperature (Tc). Furthermore, the temperature of the sample was again increased from 150°C to 360°C, and the melting peak temperature was determined from the melting curve obtained at this time as the melting point (Tm).(7) Tensile properties (yield stress, maximum stress, and strain hardening coefficient)

[0056] The measurement was carried out in accordance with ASTM D3307. A dumbbell test piece (parallel portion is 5 mm wide and 22 mm long) was prepared from a film having a thickness of about 1.5 mm obtained by meltcompression molding a sample at 350°C in a molding die in accordance with ASTM D3307, measurement was performed at a chuck-to-chuck distance of 22 mm and a rate of 50 mm / min while maintaining the sample temperature at 23°C using a Tensilon manufactured by Orientec Co., Ltd., and the yield stress and the maximum stress were determined from the stress-strain curve that was obtained.

[0057] The strain hardening coefficient Gp was determined from the values of the draw ratio A and the nominal stress o in the linear portion in the plastic deformation region of the stress-strain curve using the following relational expression.Equation 1(where C is an arbitrary constant)Each measurement value was measured for five test pieces, and the average value thereof was determined.AP0443-W001(8) MIT flex life value

[0058] The measurement was performed in accordance with JIS P8115. A test piece having a length of about 110 mm and a width of 15 mm was prepared from a film having a thickness of about 0.2 mm obtained by melt-compression molding a sample at 350°C, and the test piece was bent at an angle of 135 degrees in the right and left directions at a rate of 175 times / min under a load of 1 kg using a triple MIT folding endurance tester manufactured by Myss Shikenki Co., Ltd., and the number of times of bending until the test piece broke was determined.(9) Weight change ratio in isopropanol (I PA)

[0059] The test piece used in the aforementioned tensile property measurement was kept at 70°C for 2 weeks in a thermostat safety oven manufactured by ESPEC Corp, while maintaining a state of being completely immersed in I PA. The sample was removed from the container and dried overnight, and then the weight was measured, and the weight change rate was calculated from the weight of the sample before and after immersion in I PA. B. Raw materialsExample 1

[0060] A dispersion of tetrafluoroethylene-perfluoroethyl vinyl ether (TFE / PEVE) copolymer was prepared by a method according to Examples 1 to 3 described in Japanese Patent No. 5,588,679, except that perfluoroethyl vinyl ether (PEVE) was used instead of perfluoropropyl vinyl ether (PPVE).

[0061] Specifically, the surfactant for aqueous emulsion polymerization was a solution (II) obtained by mixing a fluoromonoether acid (I) expressed by CF3CF2CF2OCF(CF3)COOH and a perfluoropolyether acid (PFPEA) expressed by C3F7O(CFCF3CF2O)nCFCF3COOH having a number average molecular weight of about 1500, with t-BuOH at a ratio of 1:1.5, neutralizing the mixture with aqueous ammonia, and then diluting the neutralized mixture with degassed water.AP0443-W001

[0062] 1850 mL of deionized water was degassed by evacuation and purging with nitrogen gas in a 1 gallon (3. 8L) reaction vessel equipped with a horizontal stirring blade. 250 g of the fluoromonoether acid of the aforementioned solution (II) and 7.5 g of the fluoromonoether acid of the aforementioned formula (I) were added to a reaction vessel at atmospheric pressure to net 0.29 g of perfluoropolyether acid (PFPEA). After the stirrer was operated at 110 rpm, the temperature was raised to 85°C and ethane was fed to the reaction vessel until the pressure in the reaction vessel rose to 0.03 MPa. Furthermore, 83 g of perfluoroethyl vinyl ether (PEVE) was fed into the reaction vessel. Furthermore, the reactor was pressurized with tetrafluoroethylene (TFE) to 2.1 MPa. Then, 3.0 g / L of ammonium persulfate (APS) in 100 g of aqueous solution was fed into the reaction vessel as an initiator. After initiation of the reaction as determined by a 0.03 MPa pressure drop, 1.90 g / L of an APS aqueous solution wasted ata rate of 1.0 g / min, PEVE was fed at a rate to provide a 72 g feed rate during the polymerization, and TFE was fed to maintain the pressure at 2.10 MPa. When 948 g of TFE had been fed after the start of the reaction, all feeding and stirring was stopped. Thereafter, the reactor was degassed to obtain a dispersion of TFE / PEVE copolymer.

[0063] The obtained dispersion was stirred and aggregated to obtain an aggregate, and then dried at 240°C for 15 hours to obtain a powdery TFE / PEVE copolymer. The obtained powder was extruded at 340°C using a <t>20mm single screw extruder manufactured by Tanabe Plastics Co., Ltd., and pelletized using a strand cutter. The pellets thus obtained were treated with fluorine gas by the method described in Japanese Unexamined Patent Application S62 -104822 to stabilize (fluorinate) the terminal groups.Example 2

[0064] Polymerization, coagulation, extrusion and fluorination were carried out in the same manner as in Example 1 , except that the stirring speed of the stirrer was changed to 115 rpm, 102 g of PEVE was added before TFE was fed to the reaction vessel, the concentration of the APS aqueous solutionAP0443-W001before the start of polymerization was 2.0 g / L, the concentration of the aqueous APS solution fed during polymerization was 1.28g / L, and the amount of PEVE fed was 86 g.Example 3

[0065] Polymerization, coagulation, extrusion and fluorination were carried out in the same manner as in Example 1 , except that the stirring speed of the stirrer was changed to 120 rpm, 94 g of PEVE was added before TFE was supplied to the reaction vessel, and the amount of PEVE supplied during polymerization was changed to 80 g.Example 4

[0066] Polymerization, aggregation, extrusion and fluorination were carried out in the same manner as in Example 1 , except that the stirring speed of the stirrer was changed to 115 rpm, 94 g of PEVE was added before TFE was supplied to the reaction vessel, and the amount of PEVE supplied during polymerization was changed to 80 g.Example 5

[0067] Polymerization, coagulation, extrusion and fluorination were carried out in the same manner as in Example 1, except that 111 g of PEVE was added before TFE was fed to the reaction vessel, the concentration of the APS aqueous solution before the start of polymerization was 2.75 g / L, the concentration of the aqueous APS solution fed during polymerization was 1.8g / L, and the amount of PEVE fed was 94 g.Comparative Example 1

[0068] Polymerization, coagulation, extrusion and fluorination were carried out in the same manner as in Example 1 , except that the stirring speed of the stirrer was changed to 120 rpm, 102 g of PEVE was added before TFE was supplied to the reaction vessel, the concentration of the APS aqueous solution before the start of polymerization was 2.0 g / L, the concentration of the aqueous APS solution fed during polymerization was 1.28g / L, and the amount of PEVE supplied during polymerization was changed to 86 g.AP0443-W001Comparative Example 2

[0069] Polymerization, aggregation, extrusion and fluorination were carried out in the same manner as in Example 1 , except that the stirring speed of the stirrer was changed to 120 rpm, 76 g of PEVE was added before TFE was supplied to the reaction vessel, and the amount of PEVE supplied during polymerization was changed to 65 g.Comparative Example 3

[0070] Polymerization, coagulation, extrusion and fluorination were carried out in the same manner as in Example 1 , except that the stirring speed of the stirrer was changed to 120 rpm, 102 g of PEVE was added before TFE was supplied to the reaction vessel, and the amount of PEVE supplied during polymerization was changed to 86 g.Comparative Example 4

[0071] Polymerization, coagulation, extrusion and fluorination were carried out in the same manner as in Example 1 , except that the stirring speed of the stirrer was changed to 120 rpm, 110 g of PEVE was added before TFE was supplied to the reaction vessel, and the amount of PEVE supplied during polymerization was changed to 94 g.Comparative Example 5

[0072] Polymerization, coagulation, extrusion and fluorination were carried out in the same manner as in Example 1, except that the stirring rate of the stirrer was changed to 120 rpm.Comparative Example 6

[0073] Polymerization, coagulation, extrusion and fluorination were carried out in the same manner as in Example 1 , except that the stirring speed of the stirrer was changed to 105 rpm, 94 g of PEVE was added before TFE was supplied to the reaction vessel, and the amount of PEVE supplied during polymerization was changed to 80 g.AP0443-W001Comparative Example 7

[0074] Polymerization, coagulation, extrusion and fluorination were carried out in the same manner as in Example 1, except that 110 g of PEVE was added before TFE was supplied to the reaction vessel, the concentration of the APS aqueous solution before the start of polymerization was 2.75 g / L, the concentration of the aqueous APS solution fed during polymerization was 1.8g / L, and the amount of PEVE supplied during polymerization was changed to 94 g.Table 1< < < < <<<<<<<<AP0443-W001Table 1 (continued)

Claims

AP0443-W001Claims1. A heat-meltable fluororesin for injection molding, comprising: a copolymer containing more than 90.6 mass% and less than 93.5 mass% of tetrafluoroethylene and more than 6.5 mass% and less than 9.4 mass% of perfluoro(ethyl vinyl ether);wherein the melt flow rate at 372°C is in a range of 22 to 50 g / 10 min; andthe number of unstable terminal groups per 1 x 106carbon atoms in the copolymer is 50 or less.

2. The heat-meltable fluororesin for injection molding according to claim 1 , wherein the glass transition temperature is 75°C or higher.

3. The heat-meltable fluororesin for injection molding according to claim 1 or claim 2, wherein the melting point is 268°C or higher and the crystallization temperature is 260°C or higher, as measured by a differential scanning calorimeter.

4. An injection molded article, comprising the heat-meltable fluororesin for injection molding according to claim 1 or 2.

5. The injection molded article according to claim 4, which is any one of a tube, a bottle, a joint, a valve, or a pipe.

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