Method for producing polytetrafluoroethylene molded body and polytetrafluoroethylene molded body

Abstract

The present disclosure provides: a method for producing a polytetrafluoroethylene molded body without using a special infrared radiation device or a rubber mold, where it is possible to improve the tensile strength of the polytetrafluoroethylene molded body regardless of whether the polytetrafluoroethylene is a recycled product or a virgin product; and a polytetrafluoroethylene molded body. The present disclosure is a method for producing a polytetrafluoroethylene molded body, the method including a rolling step for rolling polytetrafluoroethylene at 50 MPa or more to obtain a molded body.

Description

Method for manufacturing a polytetrafluoroethylene molded body and a polytetrafluoroethylene molded body

[0001] The present disclosure relates to a method for manufacturing a polytetrafluoroethylene molded body and a polytetrafluoroethylene molded body.

[0002] Generally, when regenerated powder (regenerated product) of polytetrafluoroethylene is molded by a normal method, its strength and the like tend to be inferior to those of a molded product using unfired powder (virgin product). As a method for solving this problem, in Patent Document 1, molding using infrared irradiation has been studied.

[0003] Japanese Unexamined Patent Application Publication No. 2024-027916

[0004] However, the method of Patent Document 1 has room for improvement in that a special infrared irradiation device and a rubber mold are required, and there are cases where the rubber mold cannot withstand the molding temperature of polytetrafluoroethylene depending on the type of the rubber mold.

[0005] Further, improvement of the strength of polytetrafluoroethylene is required not only for regenerated products but also for virgin products.

[0006] An object of the present disclosure is to provide a method for manufacturing a polytetrafluoroethylene molded body capable of improving the tensile strength of a polytetrafluoroethylene molded body without using a special infrared irradiation device or a rubber mold, regardless of whether the polytetrafluoroethylene is a regenerated product or a virgin product, and a polytetrafluoroethylene molded body.

[0007] The present disclosure (1) is a method for manufacturing a polytetrafluoroethylene molded body including a rolling step of rolling polytetrafluoroethylene at 50 MPa or more to obtain a molded body.

[0008] The present disclosure (2) is the method for manufacturing a polytetrafluoroethylene molded body according to the present disclosure (1), wherein the rolling step is carried out at 200°C or higher.

[0009] The present disclosure (3) is the method for manufacturing a polytetrafluoroethylene molded body according to the present disclosure (1) or (2), wherein the pressure in the rolling step is 100 to 2000 MPa and the temperature is 200 to 600°C.

[0010] The present disclosure (4) is a method for producing a polytetrafluoroethylene molded article according to any one of the present disclosures (1) to (3), further comprising: a first pre-forming step of compressing the polytetrafluoroethylene at a temperature of less than 200°C to obtain a pre-molded article before the rolling step; and a firing step of heating the pre-molded article to a temperature above the melting point of the polytetrafluoroethylene to obtain a fired article, wherein the rolling step involves rolling the fired article.

[0011] The present disclosure (5) is a method for producing a polytetrafluoroethylene molded article according to the present disclosure (4), wherein the pressure in the first pre-molding step is 5 to 45 MPa, the temperature is 30°C or higher and less than 200°C, and the heating temperature in the firing step is 340 to 500°C and the heating time is 5 minutes to 200 hours.

[0012] Disclosure (6) is a method for producing a polytetrafluoroethylene molded article according to any one of Disclosures (1) to (5), wherein the polytetrafluoroethylene does not exhibit molten fluidity after being heated to a temperature above its melting point.

[0013] The present disclosure (7) is a polytetrafluoroethylene molded article obtained by a method for producing a polytetrafluoroethylene molded article described in any of the present disclosures (1) to (6), having a tensile strength of 25 MPa or more and a tensile elongation of 100% or more.

[0014] The present disclosure (8) is a polytetrafluoroethylene molded article according to the present disclosure (7), having a tensile strength of 25 to 60 MPa and a tensile elongation of 100 to 400%.

[0015] The present disclosure (9) is a polytetrafluoroethylene molded article having a tensile strength of 25 MPa or more, a tensile elongation of 100% or more, and an endothermic peak temperature of 330°C or more during the first heating step as measured by a differential scanning calorimeter.

[0016] The present disclosure (10) is a polytetrafluoroethylene molded article according to the present disclosure (9), having a tensile strength of 25 to 60 MPa, a tensile elongation of 100 to 400%, and an endothermic peak temperature of 330°C to 450°C during the first heating cycle as measured by differential scanning calorimeter.

[0017] The present disclosure (11) is a polytetrafluoroethylene molded article in which the endothermic peak temperature during the first heating cycle, as measured by differential scanning calorimeter, is 2°C or higher than the endothermic peak temperature during the second heating cycle.

[0018] The present disclosure (12) is a polytetrafluoroethylene molded article according to the present disclosure (11), wherein the endothermic peak temperature during the first heating phase minus the endothermic peak temperature during the second heating phase, as measured by differential scanning calorimeter, is 2 to 30°C.

[0019] According to this disclosure, a method for manufacturing a polytetrafluoroethylene molded article and a polytetrafluoroethylene molded article can be provided that improve the tensile strength of the polytetrafluoroethylene molded article, regardless of whether the polytetrafluoroethylene is recycled or virgin, without using a special infrared irradiation device or rubber mold.

[0020] <Method for manufacturing a polytetrafluoroethylene molded article> The manufacturing method of the present disclosure includes a rolling step of rolling polytetrafluoroethylene (PTFE) at 50 MPa or more to obtain a molded article.

[0021] Generally, PTFE molded articles are manufactured by compressing (pre-molding) PTFE powder and then sintering it. In the case of virgin PTFE, it is believed that high strength is obtained when molecular chains are drawn out from the powder particles by compression, and then the molecular chains become entangled during sintering, causing the particles to fuse together in that state. On the other hand, in the case of recycled PTFE, since the molecular chains are already entangled, it is believed that high strength cannot be obtained even when compressed because the molecular chains are not drawn out. In contrast, in the manufacturing method disclosed herein, it is believed that high strength can be obtained even in recycled PTFE where the molecular chains are entangled, by performing a rolling process at a higher pressure than the compression in conventional methods.

[0022] Furthermore, while the manufacturing method disclosed herein is particularly effective for recycled PTFE, which is difficult to obtain high strength from, it is not limited to recycled PTFE; the strength-improving effect can also be observed with virgin PTFE. This is thought to be because the rolling process extracts more molecular chains than conventional methods.

[0023] From the standpoint of easily achieving the effect of improving strength, it is preferable that the PTFE rolled in the rolling process be a sintered body.

[0024] The pressure during the rolling process should be 50 MPa or higher, preferably 100 MPa or higher, more preferably 150 MPa or higher, and even more preferably 200 MPa or higher. There is no upper limit, but it can be 2000 MPa or lower.

[0025] The temperature of the rolling process is preferably 200°C or higher, more preferably 230°C or higher, even more preferably 250°C or higher, and also preferably 600°C or lower, more preferably 500°C or lower, and even more preferably 400°C or lower. From the viewpoint of obtaining good tensile strength as well as tensile elongation, the temperature of the rolling process is preferably 310°C or higher, more preferably 330°C or higher. From the viewpoint of being able to increase the degree of crystallinity, the temperature of the rolling process is preferably 320°C or lower, more preferably 300°C or lower, and even more preferably 280°C or lower.

[0026] The rolling process is preferably carried out under a pressure of 100 to 2000 MPa and a temperature of 200 to 600°C, more preferably under a pressure of 150 to 2000 MPa and a temperature of 230 to 500°C, and even more preferably under a pressure of 200 to 2000 MPa and a temperature of 250 to 400°C.

[0027] The PTFE may be one that has been heated to a temperature above its melting point and does not exhibit molten fluidity. PTFE having this property is usually recycled PTFE, and the manufacturing method of this disclosure is particularly effective.

[0028] PTFE preferably has a melting point in the temperature range below 333°C. More preferably, this temperature range is below 332°C, even more preferably below 331°C, preferably 250°C or higher, and more preferably 300°C or higher. A melting point within this range indicates that the material has a history of being heated to a temperature above its melting point. PTFE may also have a melting point in the temperature range above 333°C.

[0029] In this specification, the melting point of PTFE is the temperature corresponding to the minimum point in the heat of fusion curve obtained when the temperature is increased at a rate of 10°C / min using a differential scanning calorimeter (DSC). If there are two or more minimum points in a single melting peak, the higher one is taken as the melting point, regardless of the size of the peak area.

[0030] In this specification, "not exhibiting melt flowability" means that the melt flow rate (MFR) is less than 0.25 g / 10 min, preferably less than 0.10 g / 10 min, and more preferably 0.05 g / 10 min or less. In this specification, MFR is a value obtained according to ASTM D1238 using a melt indexer, at a measurement temperature of 372°C and a load of 5 kg, as the mass of polymer flowing out of a nozzle with an inner diameter of 2.095 mm and a length of 8 mm per 10 minutes (g / 10 min). If no polymer flows out under these conditions, the MFR is set to 0 g / 10 min.

[0031] Furthermore, if a pre-molded body (unfired molded body) made by compression molding PTFE is heated at a temperature above the melting point of the PTFE for one hour or more, and the reduction in thickness after heating compared to the thickness before heating is less than 20%, or if the thickness after heating is greater than the thickness before heating, it also means that the PTFE does not exhibit melt-fluidity.

[0032] PTFE may be a TFE homopolymer consisting only of tetrafluoroethylene (TFE) units, or it may be a modified PTFE containing TFE units and modified monomer units based on modified monomers copolymerizable with TFE.

[0033] The modified monomer is not particularly limited as long as it can copolymerize with TFE, and examples include perfluoroolefins such as hexafluoropropylene [HFP]; chlorofluoroolefins such as chlorotrifluoroethylene [CTFE]; hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride [VdF]; perfluorovinyl ether; perfluoroalkyl allyl ether; (perfluoroalkyl)ethylene; ethylene, etc. Furthermore, one or more modified monomers may be used.

[0034] The perfluorovinyl ether is not particularly limited; for example, the following general formula (1) CF ２ Examples of perfluorounsaturated compounds represented by the formula =CF-ORf (1) (wherein Rf represents a perfluoroorganic group) include perfluorounsaturated compounds. In this specification, the term "perfluoroorganic group" means an organic group in which all hydrogen atoms bonded to a carbon atom are replaced with fluorine atoms. The perfluoroorganic group may have an ether oxygen.

[0035] Examples of perfluorovinyl ethers include perfluoro(alkyl vinyl ether) [PAVE], in which Rf in general formula (1) represents a perfluoroalkyl group having 1 to 10 carbon atoms. The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5.

[0036] Examples of perfluoroalkyl groups in PAVE include perfluoromethyl, perfluoroethyl, perfluoropropyl, perfluorobutyl, perfluoropentyl, and perfluorohexyl groups, but perfluoro(propyl vinyl ether) [PPVE] in which the perfluoroalkyl group is a perfluoropropyl group is preferred.

[0037] As perfluorovinyl ethers, in general formula (1), Rf is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, and Rf is given by the following formula:

[0038]

[0039] (In the formula, m represents an integer from 0 to 4.) The base Rf is represented by the following formula:

[0040]

[0041] Examples include the base represented by (wherein n represents an integer from 1 to 4).

[0042] (Perfluoroalkyl)ethylene is not particularly limited and examples include (perfluorobutyl)ethylene [PFBE], (perfluorohexyl)ethylene [PFHE], and (perfluorooctyl)ethylene.

[0043] As the modified monomer in the modified PTFE, it is preferably at least one selected from the group consisting of HFP, CTFE, VdF, PPVE, PFBE, and ethylene. More preferably, it is at least one selected from the group consisting of HFP and CTFE.

[0044] In the modified PTFE, the content of the modified monomer unit is preferably in the range of 0.00001 to 1.0% by mass. As the lower limit of the content of the modified monomer unit, 0.0001% by mass is more preferable, 0.001% by mass is further more preferable, 0.005% by mass is even more preferable, 0.010% by mass is particularly more preferable, and 0.030% by mass is particularly preferable. As the upper limit of the content of the modified monomer unit, 0.90% by mass is preferable, 0.50% by mass is more preferable, 0.40% by mass is further more preferable, and 0.30% by mass is even more preferable. In this specification, the modified monomer unit means a part of the molecular structure of the modified PTFE that is derived from the modified monomer.

[0045] The PTFE preferably has a standard specific gravity (SSG) of 2.130 to 2.280. The SSG is more preferably 2.220 or less, and even more preferably 2.200 or less. Also, it is preferably 2.140 or more, and even more preferably 2.150 or more. The SSG is measured by the water displacement method in accordance with ASTM D-792 using a sample molded in accordance with ASTM D 4895-89.

[0046] Examples of the PTFE include PTFE having non-melting secondary processability and PTFE having melting secondary processability. However, the PTFE in the present disclosure preferably has non-melting secondary processability. In this specification, non-melting secondary processability means the property that the melt flow rate cannot be measured at a temperature higher than the crystallization melting point in accordance with ASTM D-1238 and D-2116.

[0047] PTFE with non-melt secondary processing properties can be obtained by suspension polymerization or emulsion polymerization. PTFE powder obtained by suspension polymerization is called molding powder, and PTFE powder obtained by emulsion polymerization is called fine powder. In suspension polymerization, coarsely ground particles are obtained by coarsely grinding the suspension polymerization particles obtained by polymerization, and finely ground particles are obtained by further finely grinding the coarsely ground fine particles. In this disclosure, molding powder refers to finely ground particles. In emulsion polymerization, an aqueous dispersion is obtained in which primary PTFE particles are stably dispersed in an aqueous medium, and fine powder can be obtained by coagulating and drying the primary particles in the aqueous dispersion.

[0048] Examples of PTFE with melt-processability include low molecular weight PTFE, which can be obtained by suspension polymerization or emulsion polymerization, or by subjecting powder or molded articles of non-melt-processable PTFE to electron beam irradiation and pulverization treatment.

[0049] The PTFE powder is preferably at least one selected from the group consisting of finely ground particles, coarsely ground particles, and granulated particles. Finely ground particles are preferred because the resulting PTFE molded article has excellent physical properties such as electrical insulation and tensile elongation, and is also low-cost. Granulated particles are preferred because they offer excellent productivity during molding. Coarsely ground particles are obtained by coarsely grinding suspension polymerized particles obtained by suspension polymerization. Finely ground particles are obtained by further finely grinding the coarsely ground particles. Granulated particles are obtained by granulating the finely ground particles using an aqueous medium containing a surfactant or an organic solvent, for purposes such as improving the fluidity of the powder.

[0050] The particles obtained by suspension polymerization consist of particles of various sizes and, upon pulverization, include particles with whisker-like protrusions. The particles obtained by emulsion polymerization have an average primary particle diameter of 100 nm to 400 nm and are secondary particles consisting of a uniform aggregate of primary particles exhibiting an ellipsoidal particle shape. The recycled powder (recycled particles) obtained by pulverizing PTFE molded products exhibits a flaky particle shape. Such particle morphology can be confirmed by microscopic observation.

[0051] The average primary particle diameter of the finely ground particles is preferably 10 μm or more and less than 100 μm. The average primary particle diameter of the coarsely ground particles is preferably 50 μm or more and less than 500 μm. The average primary particle diameter of the granulated particles is preferably 400 μm or more and less than 1200 μm. Furthermore, the apparent density of the finely ground particles is preferably 100 g / L or more and less than 600 g / L. The apparent density of the coarsely ground particles is preferably 400 g / L or more and less than 700 g / L. The apparent density of the granulated particles is preferably 600 g / L or more and less than 1200 g / L. The average primary particle diameter and apparent density can be measured by ASTM D4894.

[0052] The manufacturing method of the present disclosure further includes a first pre-forming step of compressing PTFE at a temperature below 200°C to obtain a pre-molded body, and a firing step of heating the pre-molded body to a temperature above the melting point of PTFE to obtain a fired body, wherein in the rolling step, it is preferable to roll the fired body. This makes it possible to easily manufacture a molded body even when the PTFE is in powder form.

[0053] The pressure in the first pre-forming step is preferably 5 MPa or more, more preferably 10 MPa or more, even more preferably 15 MPa or more, and also preferably 45 MPa or less, more preferably 35 MPa or less, and even more preferably 25 MPa or less.

[0054] The temperature of the first pre-molding step may be less than 200°C, but is preferably less than 150°C, and more preferably less than 100°C. The lower limit is not particularly limited, but can be 30°C or higher.

[0055] In the case of recycled PTFE, since it tends to solidify less easily than virgin PTFE, a second pre-molding step may be performed after the first pre-molding step and before the firing step, in which the pre-molded body is compressed at 200°C or higher. In this case, the firing step only requires heating the pre-molded body after the second pre-molding step. Note that even with recycled PTFE, the second pre-molding step is not mandatory and may be performed as needed.

[0056] The temperature of the second pre-molding step may be 200°C or higher, but more preferably 250°C or higher, even more preferably 280°C or higher, and also preferably 430°C or lower, more preferably 400°C or lower, and even more preferably 370°C or lower.

[0057] The pressure in the second pre-forming step is preferably 5 MPa or more, more preferably 10 MPa or more, and also preferably 45 MPa or less, more preferably 35 MPa or less, and even more preferably 25 MPa or less.

[0058] The heating temperature in the firing process should be above the melting point of PTFE, but preferably 340°C or higher, more preferably 350°C or higher, even more preferably 360°C or higher, even more preferably 370°C or higher, and also preferably 500°C or lower, more preferably 480°C or lower, even more preferably 460°C or lower, and even more preferably 440°C or lower. The above heating temperature is the maximum temperature in the firing process.

[0059] The heating time in the firing process can be adjusted as appropriate according to the size of the object, but is preferably 5 minutes or more, more preferably 30 minutes or more, even more preferably 60 minutes or more, and also preferably 200 hours or less, more preferably 150 hours or less, and even more preferably 100 hours or less. The above heating time is the holding time at the highest temperature in the firing process.

[0060] The heating rate during the firing process is preferably 0.05°C / min or more, more preferably 0.1°C / min or more, even more preferably 0.2°C / min or more, and also preferably 3°C / min or less, more preferably 2.5°C / min or less, and even more preferably 2°C / min or less. Since heating causes expansion and makes cracks more likely, a lower heating rate is better for larger objects.

[0061] In the firing process, it is preferable to cool the object gradually after reaching the maximum temperature. In this case, the cooling rate is preferably 0.01°C / min or more, more preferably 0.05°C / min or more, even more preferably 0.1°C / min or more, and also preferably 2°C / min or less, more preferably 1.5°C / min or less, and even more preferably 1°C / min or less. Furthermore, it is particularly preferable to slow down the cooling rate around 310 to 340°C. In this temperature range, the cooling rate may be 0.01°C / hour or more, 0.05°C / hour or more, 0.1°C / hour or more, and may also be 2°C / min or less, 1.5°C / min or less, or 1°C / min or less. The larger the object, the better the cooling rate should be.

[0062] The method for carrying out the rolling process, the first pre-forming process, and the second pre-forming process is not particularly limited, and general molding machines such as heated presses can be used. Similarly, the method for carrying out the firing process is not particularly limited, and general heating machines such as electric muffle furnaces can be used.

[0063] The manufacturing method of this disclosure yields PTFE molded articles with excellent tensile strength and other properties, as described below. Furthermore, these physical properties can be adjusted by adjusting the manufacturing conditions (pressure, temperature, etc.). For example, the degree of crystallinity can be improved by setting the temperature of the rolling process below the melting point of PTFE. Although the exact mechanism is unclear, it is thought that because PTFE has a transition point near room temperature and high molecular chain mobility, microcrystals tend to form in the amorphous region, which was in a supercooled state, even below the melting point, when stress is applied.

[0064] The tensile strength of the PTFE molded article is preferably 25 MPa or higher, more preferably 30 MPa or higher, and even more preferably 32 MPa or higher. There is no particular upper limit, and a higher value is preferable, but it is usually 60 MPa or lower. The tensile strength is measured by the method described in the examples below.

[0065] The tensile elongation of the PTFE molded article is preferably 100% or more, more preferably 130% or more, even more preferably 160% or more, and particularly preferably 190% or more. There is no particular upper limit, and a higher value is preferable, but it is usually 400% or less. The tensile elongation is measured by the method described in the examples below.

[0066] The transmittance of the PTFE molded article is preferably 30% or more, more preferably 40% or more, even more preferably 45% or more, and also preferably 80% or less, more preferably 70% or less, and preferably 65% ​​or less. The transmittance is the value obtained when a sample with a thickness of 0.3 mm is irradiated with light of a wavelength of 550 nm, and is measured by the method of the examples described later.

[0067] The PTFE molded article preferably has an endothermic peak temperature at the first heating stage, measured by differential scanning calorimeter (DSC), that is 2°C or higher, more preferably 3°C or higher, and even more preferably 4°C or higher, than the endothermic peak temperature at the second heating stage. There is no particular upper limit to the difference in endothermic peak temperatures (endothermic peak temperature at the first heating stage - endothermic peak temperature at the second heating stage), but it is usually 30°C or lower. The DSC measurement is performed using the method described in the examples below. Furthermore, if there are multiple endothermic peaks (minimal points) in the heat of fusion curve obtained by the DSC measurement, the one with the highest temperature is taken as the endothermic peak temperature, regardless of the size of the peak area.

[0068] When the PTFE molded body is measured by DSC, the endothermic peak temperature during the first heating cycle is preferably 280°C or higher, more preferably 300°C or higher, even more preferably 330°C or higher, and also preferably 450°C or lower, more preferably 420°C or lower, and even more preferably 400°C or lower.

[0069] When the PTFE molded body is measured by DSC, the endothermic peak temperature during the second heating is preferably 260°C or higher, more preferably 280°C or higher, even more preferably 300°C or higher, and also preferably 430°C or lower, more preferably 400°C or lower, and even more preferably 380°C or lower.

[0070] The crystallinity of the PTFE molded article is preferably 10% or more, more preferably 20% or more, even more preferably 25% or more, and also preferably 95% or less, more preferably 85% or less, and even more preferably 75% or less. The crystallinity is measured by the method described in the examples below.

[0071] <First Polytetrafluoroethylene Molded Article> The first polytetrafluoroethylene (PTFE) molded article of this disclosure has a tensile strength of 25 MPa or more, a tensile elongation of 100% or more, and an endothermic peak temperature of 330°C or more during the first heating cycle as measured by differential scanning calorimeter. This provides a PTFE molded article with excellent tensile strength.

[0072] In the first PTFE molded article of this disclosure, the PTFE can be the same as that described in the manufacturing method of this disclosure.

[0073] The first PTFE molded article of this disclosure can be manufactured, for example, by the manufacturing method of this disclosure. Furthermore, various physical properties can be adjusted by adjusting the manufacturing conditions (pressure, temperature, etc.).

[0074] The tensile strength of the first PTFE molded article of this disclosure may be 25 MPa or more, but is preferably 30 MPa or more, and more preferably 32 MPa or more. There is no particular upper limit, and a higher is preferable, but it is usually 60 MPa or less.

[0075] The tensile elongation of the first PTFE molded article of this disclosure may be 100% or more, but is preferably 130% or more, more preferably 160% or more, and even more preferably 190% or more. There is no particular upper limit, and a higher value is preferable, but it is usually 400% or less.

[0076] The endothermic peak temperature during the first heating step when the first PTFE molded body of the present disclosure is measured by DSC may be 330°C or higher, but is preferably 450°C or lower, more preferably 420°C or lower, and even more preferably 400°C or lower.

[0077] The endothermic peak temperature during the second heating step when the first PTFE molded body of the present disclosure is measured by DSC is preferably 260°C or higher, more preferably 280°C or higher, even more preferably 300°C or higher, and also preferably 430°C or lower, more preferably 400°C or lower, and even more preferably 380°C or lower.

[0078] The first PTFE molded article of this disclosure preferably has an endothermic peak temperature during the first heating cycle, as measured by differential scanning calorimeter (DSC), that is 2°C or higher, more preferably 3°C or higher, and even more preferably 4°C or higher, than the endothermic peak temperature during the second heating cycle. The upper limit of the difference in endothermic peak temperatures (endothermic peak temperature during the first heating cycle - endothermic peak temperature during the second heating cycle) is not particularly limited, but is usually 30°C or lower.

[0079] The crystallinity of the first PTFE molded article of this disclosure is preferably 10% or more, more preferably 20% or more, even more preferably 25% or more, and also preferably 95% or less, more preferably 85% or less, and even more preferably 75% or less.

[0080] <Second Polytetrafluoroethylene Molded Article> The second polytetrafluoroethylene (PTFE) molded article of this disclosure has an endothermic peak temperature during the first heating stage, as measured by differential scanning calorimeter, that is 2°C or higher than the endothermic peak temperature during the second heating stage, preferably 3°C or higher, and more preferably 4°C or higher. This provides a PTFE molded article with excellent tensile strength. The upper limit of the difference in endothermic peak temperatures (endothermic peak temperature during the first heating stage - endothermic peak temperature during the second heating stage) is not particularly limited, but is usually 30°C or lower.

[0081] In the second PTFE molded article of this disclosure, the PTFE can be the same as that described in the manufacturing method of this disclosure.

[0082] The second PTFE molded article of this disclosure can be manufactured, for example, by the manufacturing method of this disclosure. Furthermore, various physical properties can be adjusted by adjusting the manufacturing conditions (pressure, temperature, etc.).

[0083] The endothermic peak temperature during the first heating step when the second PTFE molded body of the present disclosure is measured by DSC is preferably 280°C or higher, more preferably 300°C or higher, even more preferably 330°C or higher, and also preferably 450°C or lower, more preferably 420°C or lower, and even more preferably 400°C or lower.

[0084] The endothermic peak temperature during the second heating step when the second PTFE molded body of the present disclosure is measured by DSC is preferably 260°C or higher, more preferably 280°C or higher, even more preferably 300°C or higher, and also preferably 430°C or lower, more preferably 400°C or lower, and even more preferably 380°C or lower.

[0085] The tensile strength of the second PTFE molded article of this disclosure is preferably 25 MPa or more, more preferably 30 MPa or more, and even more preferably 32 MPa or more. The upper limit is not particularly limited, and a higher value is preferable, but it is usually 60 MPa or less.

[0086] The tensile elongation of the second PTFE molded article of this disclosure is preferably 100% or more, more preferably 130% or more, even more preferably 160% or more, and particularly preferably 190% or more. The upper limit is not particularly limited, and a higher value is preferred, but it is usually 400% or less.

[0087] The crystallinity of the second PTFE molded article of this disclosure is preferably 10% or more, more preferably 20% or more, even more preferably 25% or more, and also preferably 95% or less, more preferably 85% or less, and even more preferably 75% or less.

[0088] The PTFE molded article obtained by the manufacturing method of the present disclosure, the first PTFE molded article of the present disclosure, and the second PTFE molded article of the present disclosure may contain components other than PTFE (such as fillers).

[0089] The PTFE molded articles obtained by the manufacturing method of the present disclosure, the first PTFE molded article of the present disclosure, and the second PTFE molded article of the present disclosure can be suitably used in fields such as sheets, lining sheets, packings, gaskets, diaphragm valves, release sheets, sealing materials, casings, sleeves, bellows, hoses, piston rings, butterfly valves, rectangular tanks, and wafer carriers.

[0090] The PTFE molded articles obtained by the manufacturing method of this disclosure, the first PTFE molded article of this disclosure, and the second PTFE molded article of this disclosure have excellent tensile strength and elongation. Therefore, by machining the PTFE molded articles, PTFE sheets with excellent tensile strength and elongation can be obtained. The obtained PTFE sheets can be suitably used as lining sheets, packings, gaskets, and diaphragm valves. The obtained PTFE sheets can also be suitably used as heat-resistant insulating tapes and release sheets for vehicle motors and generators. Furthermore, if the PTFE molded articles obtained by the manufacturing method of this disclosure, the first PTFE molded article of this disclosure, and the second PTFE molded article of this disclosure contain fillers, they can be suitably used as conductive sheets and heat dissipation sheets. The PTFE molded articles obtained by the manufacturing method of this disclosure, the first PTFE molded article of this disclosure, and the second PTFE molded article of this disclosure can also be suitably used as components for semiconductor manufacturing-related equipment. Examples of the above-mentioned components include containers, piping, nozzles, tubes, tanks, fittings, valves, pumps, housings, spin chucks, O-rings, packings, gaskets, washers, sealing materials, nuts, bolts, films, bottles, hoses, pipes, seats, rollers, cocks, connectors, filter housings, filter cages, flow meters, wafer carriers, wafer boxes, and the like. The PTFE molded articles obtained by the manufacturing method of the present disclosure, the first PTFE molded article of the present disclosure, and the second PTFE molded article of the present disclosure can be suitably used as automotive-related components. Examples of the above-mentioned components include fuel tubes, fuel hoses, gaskets, sealing materials, cable sheathing materials, O-rings, packings, valve core materials, diaphragms, hoses, tanks, bellows, spacers, rollers, bumpers, door trims, instrument panels, and the like. The PTFE molded articles obtained by the manufacturing method of this disclosure, the first PTFE molded article of this disclosure, and the second PTFE molded article of this disclosure can be suitably used as electronic component materials such as flexible printed circuit boards, capacitor films, battery package films, and fuel cell stack materials. They can also be suitably used for flexible device applications, insulation applications in cryogenic environments such as superconductivity, and chemical protection applications in semiconductor manufacturing processes.

[0091] Although embodiments have been described above, it should be understood that various modifications to the form and details are possible without departing from the spirit and scope of the claims.

[0092] The present disclosure will now be further described with reference to examples, but the present disclosure is not limited to these examples.

[0093] <Molded articles using recycled PTFE> Examples 1-6 Recycled PTFE (melting point: 327°C, MFR: 0 g / 10 min, SSG: 2.17) was compressed at 30°C and 15 MPa for 5 minutes using a manual vacuum hydraulic heating press to obtain a pre-molded article. (First pre-molding step) Next, the obtained pre-molded article was compressed at 360°C and 15 MPa for 1 minute using a manual vacuum hydraulic heating press. (Second pre-molding step) Next, the pre-molded article after the second pre-molding step was heated in an electric muffle furnace (Daiwa Keisoku: FUW232PA) from room temperature to 300°C in 180 minutes, and from 300°C to 370°C in 240 minutes, and then held at 370°C for 180 minutes. After that, it was cooled to 300°C over 300 minutes to obtain a fired article. (Firing Process) Next, the fired body was rolled using a 100t lab machine (Sato Iron Works: SVP10) at the rolling temperatures and pressures shown in Tables 1 and 2 to obtain a molded body. (Rolling Process)

[0094] Comparative Example 1 A molded article was obtained by the same method as in Examples 1 to 6, except that a rolling process was not performed.

[0095] <Molded articles using virgin PTFE> Example 7 A molded article was obtained in the same manner as in Examples 1 to 6, except that virgin PTFE (melting point: 337.7°C, MFR: 0 g / 10 min, SSG: 2.15) was used instead of recycled PTFE.

[0096] Comparative Example 2 A molded body was obtained in the same manner as in Example 7, except that the second pre-forming step and rolling step described above were not performed.

[0097] The above molded products were evaluated using the following method. The results are shown in Tables 1 to 3.

[0098] <Tensile Strength and Tensile Elongation> Dumbbell-shaped test specimens were prepared from the above molded body, and the tensile strength (MPa) and tensile elongation (%) were measured in accordance with ASTM D638 at 25°C, with a chuck distance of 24.5 mm and a tensile speed of 50 mm / min.

[0099] <DSC Measurement> An X-DSC7000 differential scanning calorimeter (DSC) (manufactured by Hitachi High-Tech Science Corporation) was used to raise the temperature to 380°C at a rate of 10°C / min, and the first heat of fusion curve was obtained. After that, the temperature was cooled to 200°C, and then raised to 380°C under the same conditions as the first time, and the second heat of fusion curve was obtained. The endothermic peak temperature was calculated from the obtained heat of fusion curves. If multiple endothermic peaks were observed, the one with the highest temperature was taken as the endothermic peak temperature (melting point).

[0100] <Crystallization> Calculated from the specific heat of a differential scanning calorimeter (DSC). The total heat of fusion of PTFE was defined as 82.05 J / g, and the degree of crystallinity was calculated using the following formula: Crystallinity (%) = 100 × (Peak area derived from PTFE crystals / Total heat of fusion of PTFE) The peak area derived from PTFE crystals is the sum of the areas of peaks derived from PTFE crystals.

[0101] <Transmittance> A sample with a thickness of 0.3 mm was prepared from the above molded body, and the transmittance (%) was measured when irradiated with light of a wavelength of 550 nm using an ultraviolet spectrophotometer.

[0102]

[0103]

[0104] As shown in Tables 1 and 2, Examples 1 to 6, in which the rolling process was performed, showed improved tensile strength and acceptable tensile elongation compared to Comparative Example 1, in which the rolling process was not performed. In other words, Examples 1 to 6 were able to achieve both good tensile strength and tensile elongation. Furthermore, Examples 3 to 6, in which the rolling temperature was set to 340°C, showed improved tensile strength and tensile elongation compared to Comparative Example 1.

[0105]

[0106] As shown in Table 3, even virgin PTFE showed improved tensile strength through the rolling process.

Claims

1. A method for producing a polytetrafluoroethylene molded article, comprising a rolling step of rolling polytetrafluoroethylene at 50 MPa or more to obtain a molded article.

2. The method for producing a polytetrafluoroethylene molded article according to claim 1, wherein the rolling step is carried out at a temperature of 200°C or higher.

3. A method for producing a polytetrafluoroethylene molded article according to claim 1 or 2, wherein the pressure of the rolling step is 100 to 2000 MPa and the temperature is 200 to 600°C.

4. A method for producing a polytetrafluoroethylene molded article according to any one of claims 1 to 3, further comprising: a first pre-molding step of compressing the polytetrafluoroethylene at a temperature of less than 200°C to obtain a pre-molded article before the rolling step; and a firing step of heating the pre-molded article to a temperature above the melting point of the polytetrafluoroethylene to obtain a fired article, wherein the rolling step involves rolling the fired article.

5. The method for producing a polytetrafluoroethylene molded article according to claim 4, wherein the pressure in the first pre-molding step is 5 to 45 MPa, the temperature is 30°C or higher and less than 200°C, and the heating temperature in the firing step is 340 to 500°C, and the heating time is 5 minutes to 200 hours.

6. A method for producing a polytetrafluoroethylene molded article according to any one of claims 1 to 5, wherein the polytetrafluoroethylene does not exhibit molten fluidity after being heated to a temperature above its melting point.

7. A polytetrafluoroethylene molded article obtained by a method for producing a polytetrafluoroethylene molded article according to any one of claims 1 to 6, wherein the tensile strength is 25 MPa or more and the tensile elongation is 100% or more.

8. The polytetrafluoroethylene molded article according to claim 7, having a tensile strength of 25 to 60 MPa and a tensile elongation of 100 to 400%.

9. A polytetrafluoroethylene molded article having a tensile strength of 25 MPa or more, a tensile elongation of 100% or more, and an endothermic peak temperature of 330°C or higher during the first heating cycle as measured by differential scanning calorimeter.

10. The polytetrafluoroethylene molded article according to claim 9, wherein the tensile strength is 25 to 60 MPa, the tensile elongation is 100 to 400%, and the endothermic peak temperature during the first heating cycle, as measured by differential scanning calorimeter, is 330°C to 450°C.

11. A polytetrafluoroethylene molded article in which the endothermic peak temperature during the first heating cycle, as measured by differential scanning calorimeter, is 2°C or higher than the endothermic peak temperature during the second heating cycle.

12. The polytetrafluoroethylene molded article according to claim 11, wherein the difference between the endothermic peak temperature during the first heating phase and the endothermic peak temperature during the second heating phase, as measured by differential scanning calorimeter, is 2 to 30°C.

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