Method for producing a polytetrafluoroethylene molded article, and polytetrafluoroethylene molded article

Abstract

The present invention provides a method for manufacturing a polytetrafluoroethylene molded article and a polytetrafluoroethylene molded article that can improve the tensile strength of the polytetrafluoroethylene molded article, regardless of whether the polytetrafluoroethylene is recycled or virgin, without using special infrared irradiation equipment or rubber molds. [Solution] 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.

Description

Technical Field

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

Background Art

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

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[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 depending on the type of rubber mold, it may not be able to withstand the molding temperature of polytetrafluoroethylene.

[0005] In addition, an improvement in the strength of polytetrafluoroethylene is required not only for recycled 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 the polytetrafluoroethylene molded body without using a special infrared irradiation device or a rubber mold, regardless of whether the polytetrafluoroethylene is a recycled product or a virgin product, and a polytetrafluoroethylene molded body.

Means for Solving the Problems

[0007] (1) This disclosure relates to a method for producing a polytetrafluoroethylene molded article, which includes a rolling step of rolling polytetrafluoroethylene at 50 MPa or more to obtain a molded article.

[0008] Disclosure (2) is a method for producing a polytetrafluoroethylene molded article according to Disclosure (1), wherein the rolling step is carried out at 200°C or higher.

[0009] Disclosure (3) is a method for producing a polytetrafluoroethylene molded article according to Disclosure (1) or (2), wherein the pressure of the rolling step is 100 to 2000 MPa and the temperature is 200 to 600°C.

[0010] This disclosure (4) relates to the rolling process prior to the rolling process. A first pre-molding step involves compressing the aforementioned polytetrafluoroethylene at a temperature below 200°C to obtain a pre-molded body, The process further includes a firing step of heating the pre-molded body to a temperature above the melting point of the polytetrafluoroethylene to obtain a fired body, The rolling step is a method for producing a polytetrafluoroethylene molded article according to any one of (1) to (3) of this disclosure, in which the calcined body is rolled.

[0011] This disclosure (5) describes a first pre-forming process in which the pressure is 5 to 45 MPa and the temperature is 30°C or higher and less than 200°C. The method for producing a polytetrafluoroethylene molded article according to disclosure (4) is characterized in that 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] Disclosure (7) is obtained by a method for producing a polytetrafluoroethylene molded article as described in any of Disclosures (1) to (6), The tensile strength is 25 MPa or more. This is a polytetrafluoroethylene molded article with a tensile elongation of 100% or more.

[0014] This disclosure (8) has a tensile strength of 25 to 60 MPa, The polytetrafluoroethylene molded article according to this disclosure (7) has a tensile elongation of 100 to 400%.

[0015] This disclosure (9) has a tensile strength of 25 MPa or more, The tensile elongation is 100% or more, This is a polytetrafluoroethylene molded article in which the endothermic peak temperature during the first heating cycle, as measured by differential scanning calorimeter, is 330°C or higher.

[0016] This disclosure (10) has a tensile strength of 25 to 60 MPa, The tensile elongation is 100-400%, The polytetrafluoroethylene molded article according to disclosure (9) is characterized in that the endothermic peak temperature during the first heating step, as measured by differential scanning calorimeter, is 330°C to 450°C.

[0017] The present disclosure (11) relates to a polytetrafluoroethylene molded article in which the endothermic peak temperature during the first heating cycle, as measured by a 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. [Effects of the Invention]

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

Embodiments for Carrying Out the Invention

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

[0021] Generally, a molded body of PTFE is manufactured by compressing (preforming) PTFE powder and then sintering it. In the case of virgin PTFE, it is considered that after the molecular chains are drawn out from the powder particles by compression, the molecular chains are intertwined by sintering, and high strength is obtained by fusing the particles in that state. On the other hand, in the case of recycled PTFE, since the molecular chains are already intertwined, it is considered that the molecular chains cannot be drawn out even by compression, and high strength cannot be obtained. In contrast, in the manufacturing method of the present disclosure, it is considered that even in the case of recycled PTFE with intertwined molecular chains, the molecular chains are drawn out and high strength is obtained by a rolling step carried out at a pressure higher than compression in the conventional method.

[0022] In addition, the manufacturing method of the present disclosure is particularly effective for recycled PTFE for which it is difficult to obtain high strength, but is not limited to recycled PTFE, and the effect of improving strength is also exhibited for virgin PTFE. This is considered to be because more molecular chains are drawn out by the rolling step than in the conventional method.

[0023] From the viewpoint of easily obtaining the effect of improving strength, the PTFE to be rolled in the rolling step is preferably a fired 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 specific upper limit, but it can be 2000 MPa or lower.

[0025] The temperature during 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. In order to achieve not only good tensile strength but also good tensile elongation, the temperature of the rolling process is preferably 310°C or higher, and more preferably 330°C or higher. In order 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] PTFE may be material 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 disclosed herein is particularly effective for it.

[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 the above range indicates that the material has been heated to a temperature above its melting point. PTFE may have a melting point in the temperature range of 333°C or higher.

[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 considered the melting point, regardless of the size of the peak area.

[0030] In this specification, "not exhibiting melt fluidity" 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 defined as the mass of polymer (g / 10 min) flowing out of a nozzle with an inner diameter of 2.095 mm and a length of 8 mm per 10 minutes, using a melt indexer according to ASTM D1238, at a measurement temperature of 372°C and a load of 5 kg. If no polymer flows out under these conditions, the MFR is defined as 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 decrease 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 ethers; perfluoroalkyl allyl ethers; (perfluoroalkyl)ethylene; and ethylene. Furthermore, one or more modified monomers may be used.

[0034] The perfluorovinyl ether is not particularly limited; for example, the following general formula (1) CF2 = CF - ORf (1) Examples include perfluorounsaturated compounds represented by the formula (wherein Rf represents a perfluoroorganic group). 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] Perfluorovinyl ethers are further defined as those in general formula (1) where Rf is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, and where Rf is in the following formula:

[0038] [ka]

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

[0040] [ka]

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

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

[0046] Examples of PTFE include PTFE with non-melt secondary processing properties and PTFE with melt secondary processing properties, but the PTFE in this disclosure preferably has non-melt secondary processing properties. In this specification, non-melt 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 PTFE powder or molded articles with non-melt-processability to electron beam irradiation and pulverization.

[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 they offer excellent properties such as electrical insulation and tensile elongation in the resulting PTFE molded article, and because they are 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 grinding the coarsely ground particles. Granulated particles are obtained by granulating finely ground particles using an aqueous medium containing a surfactant or an organic solvent, for purposes such as improving the flowability of the powder.

[0050] The particles obtained by suspension polymerization consist of particles of various sizes and, upon pulverization, contain particles with whisker-like protrusions. The particles obtained by emulsion polymerization are secondary particles consisting of a uniform aggregate of primary particles with an average primary particle diameter of 100 nm to 400 nm and exhibiting an ellipsoidal particle shape. The recycled powder (recycled particles) obtained by crushing PTFE molded products exhibits a flaky particle shape. This 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 size and apparent density can be measured according to 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. Even with recycled PTFE, the second pre-molding process is not mandatory and should be performed only if necessary.

[0056] The temperature of the second pre-molding step should be 200°C or higher, 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 higher, more preferably 10 MPa or higher, and also preferably 45 MPa or lower, more preferably 35 MPa or lower, and even more preferably 25 MPa or lower.

[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 heating temperature mentioned above is the maximum temperature during 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. Note that the above heating time is the holding time at the highest temperature during the baking process.

[0060] The heating rate during the firing process is preferably 0.05°C / min or higher, more preferably 0.1°C / min or higher, even more preferably 0.2°C / min or higher, and also preferably 3°C / min or lower, more preferably 2.5°C / min or lower, and even more preferably 2°C / min or lower. 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 gradually cool the product 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 310-340°C. The cooling rate in this temperature range may be 0.01°C / hour or more, 0.05°C / hour or more, 0.1°C / hour or more, 2°C / minute or less, 1.5°C / minute or less, or 1°C / minute 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 a PTFE molded article with excellent tensile strength and other properties, as described below. Furthermore, these physical properties can be adjusted by controlling 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 0.3 mm thick sample is irradiated with light of a wavelength of 550 nm, and is measured by the method described in the examples below.

[0067] The PTFE molded article preferably has an endothermic peak temperature during the first heating cycle 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, as measured by differential scanning calorimeter (DSC). There is no particular upper limit to the difference in endothermic peak temperatures (endothermic peak temperature during the first heating cycle - endothermic peak temperature during the second heating cycle), but it is usually 30°C or lower. The DSC measurement will be performed using the method described in the examples below. Furthermore, if multiple endothermic peaks (minimal points) exist in the heat of fusion curve obtained by DSC measurement, the highest temperature peak is considered the endothermic peak temperature, regardless of the size of the peak area.

[0068] When measuring the PTFE molded body with DSC, the endothermic peak temperature during the first heating stage 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 stage 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 degree of 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 degree of crystallinity is measured by the method described in the examples below.

[0071] <First polytetrafluoroethylene molded product> 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 product> The second polytetrafluoroethylene (PTFE) molded article of this disclosure has an endothermic peak temperature during the first heating cycle, as measured by differential scanning calorimeter, that is 2°C or higher than the endothermic peak temperature during the second heating cycle, preferably 3°C or higher, and more preferably 4°C or higher. This results in a PTFE molded article with excellent tensile strength. There is no particular upper limit to the difference in endothermic peak temperatures (endothermic peak temperature during the first heating cycle - endothermic peak temperature during the second heating cycle), but it is usually 30°C or less.

[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. There is no upper limit, and a higher value is preferable, 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 resulting PTFE sheets can be suitably used as lining sheets, packings, gaskets, and diaphragm valves. Furthermore, the resulting PTFE sheets can be suitably used as heat-resistant insulating tapes for vehicle motors and generators, release sheets, and the like. Furthermore, if the PTFE molded article 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 a filler, they can be suitably used as conductive sheets, heat dissipation sheets, 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 also be suitably used as components for semiconductor manufacturing-related equipment. Examples of such components include containers, pipes, nozzles, tubes, tanks, fittings, valves, pumps, housings, spin chucks, O-rings, packings, gaskets, washers, sealing materials, nuts, bolts, films, bottles, hoses, pipes, sheets, 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 in automotive-related components. Examples of such 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. [Examples]

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

[0094] Comparative Example 1 A formed body was obtained in the same manner as in Examples 1 to 6, except that the rolling step was not performed.

[0095] <Formed body using virgin PTFE> Example 7 A formed body 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 formed body was obtained in the same manner as in Example 7, except that the above-described second preforming step and rolling step were not performed.

[0097] The above formed bodies were evaluated by the following method. The results are shown in Tables 1 to 3.

[0098] <Tensile strength and elongation> Dog-bone shaped test pieces were prepared from the above formed bodies, and the tensile strength (MPa) and elongation (%) were measured at 25 °C, a chuck distance of 24.5 mm, and a tensile rate of 50 mm / min in accordance with ASTM D638.

[0099] <DSC measurement> Using an X-DSC7000 (manufactured by Hitachi High-Tech Science Corporation) as a differential scanning calorimeter (DSC), the temperature was raised to 380 °C at a rate of 10 °C / min to obtain the first melting heat curve. Thereafter, it was cooled to 200 °C and then raised to 380 °C under the same conditions as the first time to obtain the second melting heat curve. The endothermic peak temperature was calculated from the obtained heat of fusion curve. When multiple endothermic peaks were observed, the one with the highest temperature was considered the endothermic peak temperature (melting point).

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

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

[0102] [Table 1]

[0103] [Table 2]

[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 high tensile strength and tensile elongation. Furthermore, in Examples 3-6, where the rolling temperature was set to 340°C, both tensile strength and tensile elongation were improved compared to Comparative Example 1.

[0105] [Table 3]

[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. A method for producing a polytetrafluoroethylene molded article according to claim 1, wherein the rolling step is carried out at 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. Before the aforementioned rolling process, A first pre-molding step involves compressing the aforementioned polytetrafluoroethylene at a temperature below 200°C to obtain a pre-molded body, The process further includes a firing step of heating the pre-molded body to a temperature above the melting point of the polytetrafluoroethylene to obtain a fired body, The method for producing a polytetrafluoroethylene molded article according to claim 1 or 2, wherein the rolling step involves rolling the calcined body.

5. The pressure in the first pre-forming step is 5 to 45 MPa, and the temperature is 30°C or higher and less than 200°C. The method for producing a polytetrafluoroethylene molded article according to claim 4, wherein 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 claim 1 or 2, wherein the polytetrafluoroethylene does not exhibit molten fluidity after being heated to a temperature above its melting point.

7. Obtained by the method for producing a polytetrafluoroethylene molded article according to claim 1 or 2, The tensile strength is 25 MPa or more. A polytetrafluoroethylene molded article having a tensile elongation of 100% or more.

8. The tensile strength is 25 to 60 MPa. The polytetrafluoroethylene molded article according to claim 7, wherein the tensile elongation is 100 to 400%.

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

10. The tensile strength is 25 to 60 MPa. The tensile elongation is 100-400%, The polytetrafluoroethylene molded article according to claim 9, wherein the endothermic peak temperature during the first heating cycle, as measured by a 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 a differential scanning calorimeter, is 2 to 30°C.

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