Fluororesin material, molded article thereof, and method for producing same

Abstract

This fluororesin material has a melting point of not more than 333. 5°C, a number-average molecular weight of not less than 1.0×105, and a lamellar thickness of not more than 450 nm.

Description

Fluororesin material, molded article thereof, and method for manufacturing the same

[0001] The present invention relates to a fluororesin material, a molded article thereof, and a method for producing the same. More specifically, it relates to a material and a molded article using a fluororesin (recycled fluororesin) that has been heated to a temperature above its melting point.

[0002] Fluororesins are synthetic resins with excellent heat resistance, electrical insulation, and weather resistance, and are widely used in industrial fields such as chemical materials, electrical and electronic components, semiconductors, and automobiles. However, there is a problem in that when fluororesins such as polytetrafluoroethylene (PTFE) that have been heat-treated (fired) are used again as raw material powder, the mechanical strength of the resulting molded product decreases significantly. Various studies have been conducted on methods for utilizing heat-treated (fired) fluororesins, such as those described in Patent Documents 1 to 10.

[0003] Japanese Patent Publication No. 4714310, Japanese Unexamined Patent Publication No. 2015-108126, Japanese Patent Publication No. 6612001, Japanese Unexamined Patent Publication No. 2003-245983, Japanese Unexamined Patent Publication No. 4-23658, Japanese Unexamined Patent Publication No. 2022-159201, Japanese Unexamined Patent Publication No. 2022-159202, Japanese Unexamined Patent Publication No. 2022-159203, Japanese Unexamined Patent Publication No. 2022-159204, Japanese Unexamined Patent Publication No. 2022-159205

[0004] Currently, the technologies being considered primarily involve mixing recycled fluororesin with fluororesin that has not been heated (virgin) fluororesin, which has not necessarily yielded sufficient results in reducing environmental impact or raw material costs. In particular, molded articles made from recycled fluororesin have the problem of significant deterioration in mechanical properties such as tensile strength and tensile elongation.

[0005] The object of the present invention is to provide a fluororesin material that can improve the mechanical properties of a molded article made from recycled fluororesin without using a fluororesin that has not undergone heating. Furthermore, the object is to provide a molded article made from the fluororesin material and a method for manufacturing the fluororesin material.

[0006] Since the molecular weight of recycled fluororesin is usually smaller than that of fluororesin without heating history, increasing the molecular weight of recycled fluororesin to be larger than a predetermined value is important for improving the mechanical properties of the molded article. As a result of intensive research by the present inventors, it has been found that when the molecular weight and the lamellar thickness of the recycled fluororesin satisfy predetermined conditions, the mechanical properties of the molded article can be improved, and the present invention has been completed.

[0007] According to the present invention, the following fluororesin materials and the like are provided. 1. A fluororesin material having a melting point of 333.5 ° C or lower, a number average molecular weight of 1.0 × 10 ５ or more, and a lamellar thickness of 450 nm or less. 2. The fluororesin material according to 1, comprising recycled polytetrafluoroethylene resin (A) or a mixture of the recycled polytetrafluoroethylene resin (A) and recycled modified polytetrafluoroethylene resin (B), wherein the mixing mass ratio of the recycled polytetrafluoroethylene resin (A) to the recycled modified polytetrafluoroethylene resin (B) (resin (A): resin (B)) is 100: 0 to 1:99. 3. The fluororesin material according to 2, wherein the median diameter D ５０ of the recycled polytetrafluoroethylene resin (A) is 10 μm to 10,000 μm. 4. The fluororesin material according to 2 or 3, wherein the median diameter D ５０ of the recycled modified polytetrafluoroethylene resin (B) is 10 μm to 10,000 μm. 5. A molded article obtained by molding the fluororesin material according to any one of ~4. 6. The molded article according to 5, having a tensile strength of 12 MPa or more. 7. The molded article according to 5 or 6, having a tensile elongation rate of 100% or more. 8. The molded article according to any one of 5 to 7, having a specific gravity of 1.81 or more. 9. A method for producing a fluororesin material, comprising a step of adjusting the number average molecular weight of a fluororesin material having a melting point of 333.5 ° C or lower to 1.0 × 10 ５ or more and the lamellar thickness to 450 nm or less.

[0008] According to the present invention, the mechanical properties of a molded article using only recycled fluororesin can be improved without using fluororesin without heating history.

[0009] It is a diagram for explaining a method for producing a molded article of the present invention.

[0010] Hereinafter, the fluororesin material and the molded body according to the present invention will be described. In this specification, "x to y" represents a numerical range of "x or more and y or less". Regarding one technical matter, when there are a plurality of lower limit values such as "x or more", or when there are a plurality of upper limit values such as "y or less", the upper limit value and the lower limit value can be arbitrarily selected and combined.

[0011] [Fluororesin Material] The fluororesin material according to one aspect of the present invention has a melting point of 333.5 ° C or lower, a number average molecular weight of 1.0 × 10 ５ or more, and a lamellar thickness of 450 nm or less. Examples of the fluororesin material in this aspect include polytetrafluoroethylene resin, modified polytetrafluoroethylene resin, perfluoroalkoxyalkane (PFA), and ethylene-tetrafluoroethylene copolymer (ETFE). A mixture of two or more of these may be used. Preferably, it is a polytetrafluoroethylene resin, a modified polytetrafluoroethylene resin, or a mixture of a polytetrafluoroethylene resin and a modified polytetrafluoroethylene resin.

[0012] Further, the fluororesin material according to one aspect of the present invention contains recycled polytetrafluoroethylene resin (A), or the recycled polytetrafluoroethylene resin (A) and recycled modified polytetrafluoroethylene resin (B). And the mixing ratio of the recycled polytetrafluoroethylene resin (A) and the recycled modified polytetrafluoroethylene resin (B) (resin (A): resin (B)) is 100:0 to 1:99, and the number average molecular weight is 1.0 × 10 ５ or more, and the lamellar thickness is 450 nm or less.

[0013] In the present invention, the number average molecular weight of the fluororesin material is 1.0 × 10 ５As described above, and with a lamellar thickness of 450 nm or less, the mechanical properties of molded fluororesin materials can be improved even when using only recycled fluororesin. This is presumed to be because a larger number-average molecular weight leads to longer molecular chains that form the network between crystals, thus improving tensile elongation. Furthermore, the small lamellar thickness and fine crystal structure increase crystal mobility, allowing for repositioning and stress distribution under load, resulting in a tougher molded body.

[0014] Hereinafter, polytetrafluoroethylene resin and modified polytetrafluoroethylene resin may be collectively referred to as fluororesin. Furthermore, polytetrafluoroethylene resin may be referred to as homo-PTFE, and modified polytetrafluoroethylene resin as modified PTFE. In this specification, recycled fluororesin is a fluororesin that has been heated to a temperature above its melting point. When processing fluororesin material into a molded body, the powder is usually molded into the desired shape, and then heated to a temperature above its melting point (for example, 350°C or higher) and fired. Recycled fluororesin refers to fluororesin that has been recovered by processing the molded body into powder or the like for reuse.

[0015] The fact that a fluororesin is a recycled fluororesin can be confirmed, for example, by its melting point. A melting point of fluororesin of 333.5°C or lower means that the fluororesin has been heated to a temperature above its melting point in the past. This fact is also disclosed in Patent Documents 6 to 10. The melting point of recycled fluororesin may be less than 333.0°C. The lower limit of the melting point of recycled fluororesin is not particularly limited, but for example, it may be 100.0°C or higher or 300.0°C or higher. In this embodiment, both homo-PTFE and modified PTFE are resins that have a history of being heated to a temperature above their melting point in the past, like recycled products. The melting points of homo-PTFE and modified PTFE without a heating history are usually 340.0°C or higher.

[0016] Homogeneous PTFE is a homopolymer of tetrafluoroethylene (TFE). Modified PTFE is a copolymer of TFE and a modified monomer. Examples of the modified monomer include perfluoroolefins such as hexafluoropropylene (HFP); hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride (VDF); perhaloolefins such as chlorotrifluoroethylene; perfluorovinyl ether: perfluoroallyl ether; (perfluoroalkyl)ethylene, and ethylene. The modified monomer may be one kind, or a plurality of kinds.

[0017] In one embodiment, the modified PTFE (B) is PTFE modified with a perfluoroalkyl vinyl ether represented by the following formula (1). CF ２ =CF−OR ｆ (1) (In formula (1), R ｆ is a perfluoroalkyl group having 1 to 10 carbon atoms, or a perfluoroorganic group represented by the following formula (2).) (In formula (2), n is an integer of 1 to 4.)

[0018] Examples of the perfluoroalkyl group having 1 to 10 carbon atoms in formula (1) include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, a perfluorohexyl group, etc. A perfluoropropyl group is preferred.

[0019] The proportion of the perfluoroalkyl vinyl ether polymerization unit represented by the above formula (1) is preferably 1% by weight or less, and preferably in the range of 0.001% to 1% by mass. Thereby, fusion between powders is likely to occur during firing, and the molded body obtained after heating has excellent strength.

[0020] The number average molecular weight of the fluororesin material is 1.0×10 ５ or more, preferably 5.0×10 ５ or more, particularly preferably 1.0×10 ６ or more. The upper limit of the number average molecular weight is not particularly limited, but for example, 1.0×10 ７The following applies: The number-average molecular weight of the fluororesin material in this embodiment is preferably 1.0 × 10⁻⁶. ５ The above 1.0 x 10 ７ The following, and more preferably 5.0 × 10 ５ The above 5.0 x 10 ６ The following, and particularly preferably 1.0 × 10 ６ The above 4.0 x 10 ６ The following applies: The number-average molecular weight of the fluoropolymer material can be controlled by adjusting the number-average molecular weight of the raw materials, regenerated homo-PTFE (A) and regenerated modified PTFE (B), and their blending ratio.

[0021] The number-average molecular weight of the fluororesin material is the average value calculated by measuring the number-average molecular weight of recycled homo-PTFE (A) and recycled modified PTFE (B), and multiplying them by the mixing ratio (mass ratio) of resin (A) and resin (B). Details of the measurement methods for recycled homo-PTFE (A), recycled modified PTFE (B), and the number-average molecular weight of the fluororesin material are described in the examples.

[0022] In one embodiment, the number-average molecular weight of regenerated homo-PTFE (A) is 1.0 × 10⁻⁶. ４ The above is 1.0 x 10 ５ The above is 2.0 x 10 ５ The above, or 1.0 × 10 ６ That's all. Also, 1.0 × 10 ７ Below, 5.0 x 10 ６ The following, or 2.0 x 10 ６ The following is preferred: 1.0 × 10 ４ The above 1.0 x 10 ７ The following, and more preferably 1.0 × 10 ５ The above 5.0 x 10 ６ The following, and particularly preferably 2.0 × 10 ５ The above 2.0 x 10 ６ The following applies. Furthermore, if the fluororesin material consists solely of recycled homo-PTFE(A), the number-average molecular weight of recycled homo-PTFE(A) is 1.0 × 10⁻⁶. ５ The above, preferably 5.0 × 10 ５ The above is the most preferred, and is particularly preferably 1.0 × 10 ６ That's all.

[0023] In one embodiment, the number average molecular weight of regenerated modified PTFE(B) is 1.0 × 10⁻⁶. ５ The above is 1.0 x 10 ６ The above is 1.5 x 10 ６ The above, or 2.0 x 10 ６ That's all. Also, 1.0 × 10 ８ Below, 1.0 × 10 ７ The following, or 6.0 x 10 ６ The following is preferred: 1.0 × 10 ５ The above 1.0 x 10 ８ The following, and more preferably 1.0 × 10 ６ The above 1.0 x 10 ７ The following, and particularly preferably 1.5 × 10 ６ The above 6.0 x 10 ６ The following applies. Furthermore, if the fluororesin material consists solely of regenerated modified PTFE(B), the number-average molecular weight of regenerated modified PTFE(B) is 1.0 × 10⁻⁶. ５ The above, preferably 5.0 × 10 ５ The above is the most preferred, and is particularly preferably 1.0 × 10 ６ That's all.

[0024] The lamellar thickness of the fluororesin material in this embodiment is 450 nm or less, preferably 400 nm or less, and more preferably 350 nm or less. The lower limit of the lamellar thickness is not limited, but for example, it is 10 nm. The lamellar thickness of the fluororesin material is preferably 10 nm or more and 450 nm or less, more preferably 50 nm or more and 400 nm or less, and more preferably 100 nm or more and 350 nm or less. The lamellar thickness of the fluororesin material can be controlled by adjusting the lamellar thickness of the raw materials, regenerated homo-PTFE (A) and regenerated modified PTFE (B), and their blending ratio.

[0025] The lamellar thickness of the fluororesin material is the average value calculated by measuring the lamellar thickness of recycled homo-PTFE (A) and recycled modified PTFE (B), and multiplying them by the mixing ratio (mass ratio) of resin (A) and resin (B). Details of the measurement methods for the lamellar thickness of recycled homo-PTFE (A), recycled modified PTFE (B), and the fluororesin material are described in the examples.

[0026] In one embodiment, the lamellar thickness of the recycled homo-PTFE (A) is 1000 nm or less, preferably 700 nm or less, and more preferably 500 nm or less. The lower limit of the lamellar thickness is not limited, but for example, it is 10 nm or more. The lamellar thickness of the recycled homo-PTFE (A) is preferably 10 nm or more and 1000 nm or less, more preferably 50 nm or more and 700 nm or less, and more preferably 100 nm or more and 500 nm or less. When the fluororesin material consists only of recycled homo-PTFE (A), the lamellar thickness of the recycled homo-PTFE (A) is preferably 10 nm or more and 450 nm or less, more preferably 50 nm or more and 400 nm or less, and more preferably 100 nm or more and 350 nm or less.

[0027] In one embodiment, the lamellar thickness of the regenerated modified PTFE (B) is 500 nm or less, preferably 300 nm or less, and more preferably 150 nm or less. The lower limit of the lamellar thickness is not limited, but for example, it is 10 nm or more. The lamellar thickness of the regenerated modified PTFE (B) is preferably 10 nm or more and 500 nm or less, more preferably 50 nm or more and 300 nm or less, and more preferably 100 nm or more and 150 nm or less. When the fluororesin material consists only of regenerated modified PTFE (B), the lamellar thickness of the regenerated modified PTFE (B) is preferably 10 nm or more and 450 nm or less, more preferably 50 nm or more and 400 nm or less, and more preferably 100 nm or more and 350 nm or less.

[0028] In the fluororesin material of this embodiment, the mixed mass ratio (resin (A):resin (B)) of recycled homo-PTFE (A) and recycled modified PTFE (B) is 100:0 to 1:99, preferably 90:10 to 10:90, more preferably 60:40 to 40:60, and particularly preferably 55:45 to 45:55.

[0029] In one embodiment, the fluororesin material is in powder form. Recycled homo PTFE (A) has a median diameter D ５０ The powder is 10 μm to 10,000 μm in size. This makes it easier to obtain dense molded products. Median diameter D of recycled homo PTFE (A) ５０The median diameter D of the recycled homo PTFE (A) resin is 50 μm or more, 100 μm or more, 150 μm or more, or 180 μm or more. ５０ The particle size is 8000 μm or less, 6000 μm or less, or 4500 μm or less.

[0030] In one embodiment, the regenerated modified PTFE (B) has a median diameter D ５０ The powder is 10 μm to 10,000 μm in size. This makes it easier to obtain dense molded articles. Median diameter D of regenerated modified PTFE (B) resin ５０ The median diameter D of regenerated modified PTFE (B) is 30 μm or larger, 50 μm or larger, 100 μm or larger, or 150 μm or larger. ５０ The median diameter D of the powder is 8000 μm or less, 6000 μm or less, or 5500 μm or less. ５０ This is measured by the method described in the examples.

[0031] The fluororesin material of the resin according to this embodiment is a fluororesin material with a melting point of 333.5°C or lower and a number average molecular weight of 1.0 × 10 ５ The above is achieved by a manufacturing method that also includes a step of adjusting the lamellar thickness to 450 nm or less.

[0032] For example, the fluororesin material of the resin according to this embodiment is a pulverized polytetrafluoroethylene resin molded product, or a mixture containing a pulverized polytetrafluoroethylene resin molded product and a pulverized modified polytetrafluoroethylene resin molded product, with a number average molecular weight of 1.0 × 10 ５ The above is achieved by adjusting the lamellar thickness to 450 nm or less. The pulverized homo-PTFE molded body and the pulverized modified PTFE molded body are the regenerated homo-PTFE (A) and regenerated modified PTFE (B) described above, and can be obtained, for example, by pulverizing the homo-PTFE molded body and the modified PTFE molded body.

[0033] The grinding process is not particularly limited as long as it is a method that can grind the molded body to a desired particle size. For example, a mixer, hammer mill, jet mill, stone mill grinder, or freeze grinder can be used. Grinding may be performed in one go using one type of equipment, or it may be performed in stages using multiple types of equipment. For example, homo-PTFE and modified PTFE, which are in the form of individual molded bodies, may be ground to a desired particle size using a mixer, or the individual homo-PTFE and modified PTFE may be ground to a predetermined particle size using a mixer, and then ground to a desired particle size using a hammer mill. In some cases, the number-average molecular weight of the obtained powder can be adjusted by the grinding conditions of the hammer mill. For example, increasing the grinding time or the number of grinding cycles may further break the intramolecular bonds of PTFE, which may decrease the number-average molecular weight of the powder. The change in number-average molecular weight due to the grinding conditions of the hammer mill is smaller for modified PTFE than for homo-PTFE.

[0034] Cryogenic pulverization may be employed, in which molded articles of homo-PTFE and modified PTFE are cooled to a frozen state and then pulverized. In cryogenic pulverization, it is preferable to cool to a temperature below the glass transition temperature of the resin. For example, it is preferable to cool to -190°C or below, -196°C or below, and even to -250°C or below.

[0035] The powder of regenerated homo-PTFE (A) obtained in the above grinding process and the powder of regenerated modified PTFE (B) are mixed to obtain a number average molecular weight of 1.0 × 10⁻⁶. ５ In addition to the above, the lamellar thickness is adjusted to 450 nm or less. The mixing ratio can be appropriately determined considering the number-average molecular weight and lamellar thickness of the recycled fluororesin. The mixing method is not particularly limited, and known equipment such as a stirrer can be used.

[0036] [Molded Article] A molded article according to one embodiment of the present invention is obtained by molding the fluororesin material of the present invention described above. The molded article of this embodiment may contain optional components in addition to the fluororesin material of the present invention, as long as the effects of the present invention are not lost. Examples of optional components include flame retardants, flame retardant aids, pigments, antioxidants, reflective agents, opacities, lubricants, processing stabilizers, plasticizers, foaming agents, and fillers. The total content of optional components in the molded article is usually 50% by mass or less. In one embodiment, the molded article does not contain any fluororesins other than the fluororesin material of the present invention described above.

[0037] In one embodiment, the tensile strength of the molded article may be 12 MPa or more, 15 MPa or more, or 18 MPa or more. There is no particular upper limit to the tensile strength of the molded article, but it is usually 50 MPa or less. The tensile strength of the molded article is measured by the method described in the example.

[0038] In one embodiment, the tensile elongation of the molded article may be 100% or more, 150% or more, or 200% or more. The upper limit of the tensile strength of the molded article is not particularly limited, but is usually 500% or less. The tensile elongation of the molded article is measured by the method described in the examples.

[0039] In one embodiment, the specific gravity of the molded article is 1.81 or higher. Because the molded article of this embodiment has high density, it possesses excellent mechanical properties. The specific gravity may be 2.00 or higher, 2.10 or higher, or 2.15 or higher. Typically, it is 2.30 or lower. The specific gravity of the molded article is measured by the method described in the examples.

[0040] A molded article according to this embodiment can be obtained, for example, by a manufacturing method including the following steps (1) and (2): (1) A step of filling a mold with the fluororesin material of the present invention described above and applying pressure; (2) A step of heating the mold filled with powder to sinter the powder filled in the mold.

[0041] (Step (1) Pressurization of Powder) Figure 1 is a diagram illustrating the method for manufacturing a molded article of the present invention. The fluororesin material 10 of the present invention described above is filled into a mold and pressurized. The pressurized powder is compressed and molded within the mold (see Figure 1(a)).

[0042] In one embodiment, the median diameter D of the regenerated modified PTFE (B) powder to be filled into the mold is ５０ The particle size is preferably 20 μm to 500 μm. This facilitates fusion when the molded body of the powder is heated and fired in step (2) described later, resulting in a denser molded body with excellent strength after heating. The smaller the particle size of the powder, the higher the strength of the molded body obtained after reheating tends to be.

[0043] The pressurized pressure may be 5 MPa to 100 MPa, 20 MPa to 60 MPa, or 30 MPa to 50 MPa. By pressurizing within the above range, when the molded body obtained in this process is heated and fired in step (2) described later, weldability between the PTFE powder particles is easily achieved, and excellent strength can be obtained in the molded body obtained after heating.

[0044] (Step (2) Firing of the molded body) The mold filled with powder is heated to sinter the powder filled in the mold (see Figures 1(b) and (c)). The sintering temperature may be 300°C to 400°C, 330°C to 370°C, or 360°C to 370°C. By sintering within the above temperature range, the fluidity of the PTFE constituting the molded body 11 is moderately increased, the fusion of the PTFE powder particles 10 to each other proceeds easily, and excellent strength is obtained in the molded body obtained after this step.

[0045] The firing of the molded body can be performed, for example, by placing a mold filled with powder into a heating furnace, raising the temperature inside the furnace at a predetermined rate, and holding it at the firing temperature for a predetermined time. When raising the temperature inside the furnace after placing a mold filled with powder into the heating furnace, the rate of heating may be 0.01 to 20°C / min, 0.05 to 10°C / min, or 0.1 to 3.0°C / min.

[0046] During firing, the heating rate may be kept constant until the firing temperature is reached, or the heating rate may be changed in stages until the firing temperature is reached. When the heating rate is changed in stages, it is preferable to heat the material at a predetermined rate until a temperature range close to the firing temperature is reached, for example, a temperature range about 1°C to 20°C lower than the firing temperature, and then to further heat it until the firing temperature is reached, using a lower heating rate than the previous heating rates.

[0047] After firing, the mold filled with powder may be cooled by lowering the temperature inside the furnace at a predetermined rate. The rate of cooling in this case is not particularly limited, but may be 0.01 to 20°C / min, 0.05 to 10°C / min, or 0.1 to 3.0°C / min.

[0048] Furthermore, the firing of the molded body is not limited to a method in which a mold filled with powder is placed in a heating furnace and the temperature inside the heating furnace is raised at a predetermined rate. For example, it may also be performed by placing a mold filled with powder into a heating furnace set to the firing temperature and holding it there for a predetermined time.

[0049] The molded articles of this embodiment described above can be used, for example, by forming them into block or pipe shapes, or by forming them into sheets by skiving. The molded articles of this embodiment are suitably used as valve seats, gaskets, packings, heat-resistant materials such as heat-resistant insulating tapes, substrates for printed circuit boards, printed circuit boards, and release sheets.

[0050] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way by these examples.

[0051] [Preparation of Recycled Homo-PTFE] As recycled homo-PTFE, cutting chips from molded bodies obtained by calcining homo-PTFE recovered from the production facility were used. There are 11 types of cutting chip samples, (A-1) to (A-11). For example, sample (A-7) has a number average molecular weight of 1.1 × 10⁻⁶. ７ This is cutting chips generated when a molded body (100 mm x 100 mm x 100 mm) of homo PTFE, which has a melting point of 342.5°C, is shaped using a lathe.

[0052] Samples (A-1) to (A-11) were subjected to pulverization. Specifically, the cutting shavings were cut with scissors to obtain pieces with a major diameter of 3 mm to 5 mm, and then coarsely pulverized into a powder with a particle size of 1 mm or less using a juice mixer. Next, the obtained coarse powder was cooled to -196°C with liquid nitrogen and then freeze-pulverized using a hammer mill cooled with liquid nitrogen, or pulverized using a wet stone mill type pulverizer. For samples (A-9) and (A-10), the pulverized material was fired at 365°C for 2 hours or 4 hours to obtain molded bodies, which were then subjected to pulverization again. For sample (A-11), the following steps a to c were repeated three times. a. Pre-molding the pulverized material (35 MPa). b. Firing at 365°C for 2 hours to obtain molded bodies. c. Pulverizing the molded bodies to obtain pulverized material. The obtained powder was classified using a sieve to obtain recycled homo-PTFE powder. Table 1 shows the physical properties of recycled homo-PTFE powders (A-1) to (A-11).

[0053]

[0054] [Preparation of Regenerated Modified PTFE] As the regenerated modified PTFE, cutting chips from molded bodies obtained by calcining modified PTFE recovered from the production facility were used. There are eight types of cutting chip samples, (B-1) to (B-8). For example, sample (B-6) has a number average molecular weight of 5.9 × 10⁻⁶. ６ This is cutting chips generated when a molded body (100 mm × 100 mm × 100 mm) of modified PTFE (which has a melting point of 341.3 °C) obtained by firing it at 355 °C for 1 hour was shaped using a lathe. The cutting chips were crushed in the same manner as in the preparation of recycled homo-PTFE to obtain recycled modified PTFE powder. The physical properties of the recycled modified PTFE powders (B-1) to (B-8) are shown in Table 2.

[0055]

[0056] The physical properties of the recycled fluororesin material samples, the number-average molecular weight of homo-PTFE in sample (A-7), and the number-average molecular weight of modified PTFE in sample (B-6) were measured as follows.

[0057] <Median diameter D ５０> Using a particle size analyzer, the particle size was measured under the following equipment and conditions, and the value was set to be equal to the particle size corresponding to 50% of the integrated particle size distribution (volume basis). Measurement equipment: Laser diffraction particle size analyzer "Mastersizer 3000" (Malvern Panalogical) Measurement method: Dry vacuum pressure: 4 bar

[0058] <Melting Point and Heat of Crystallization> (1) Annealing Treatment Each sample (powder) was heated at 365°C for 30 minutes and then cooled to 300°C at a cooling rate of 0.33°C / min. (2) DSC Measurement The samples after annealing treatment were measured using DSC under the following equipment and conditions. The melting point is the melting peak temperature in the obtained heat of fusion curve. The heat of crystallization is the crystallization peak area in the obtained heat of crystallization curve. Measurement equipment: DSC8500 (PerkinElmer) Measurement conditions: Heating rate 10°C / min

[0059] <Lamellar thickness> The lamellar thickness was determined from the melting point in (2) above using the following formula. (In the formula, l is the lamellar thickness (nm) and Tm is the melting point (°C))

[0060] <Number-average molecular weight> The number-average molecular weight was determined from the heat of crystallization in (2) above using the following formula. (In the formula, Mn is the number-average molecular weight, and ΔHc is the heat of crystallization (J / g).)

[0061] Example 1 A recycled homo-PTFE powder sample (A-1) and a recycled modified PTFE powder sample (B-1) were mixed in a mass ratio of 50:50 to obtain a fluororesin material (mixed powder). The mixed powder was filled into a cylindrical mold with an inner diameter of 20 mm and compressed from the top at a press pressure of 35 MPa for 1 minute (molding process (see Figure 1(a))). Next, the top and bottom surfaces of the cylindrical mold were sandwiched between metal flanges and fixed with bolts and nuts. Then, the bolts on the top surface were loosened and a 1 mm spacer was inserted, and the bolts were tightened to remove the spacer. Next, the cylindrical mold was placed in an electric furnace, and the furnace temperature of the electric furnace was changed in the following order to sinter the mixed powder (see Figure 1(b)) (sintering process), to obtain a cylindrical molded body with a diameter of 20 mm and a height of 50 mm (see Figure 1(c)). (Temperature control) First stage: Increase temperature from 30°C to 300°C at a rate of 1°C / min. Second stage: Increase temperature from 300°C to 365°C at a rate of 0.33°C / min. Third stage: Maintain temperature at 365°C for 4.5 hours. Fourth stage: Depress temperature from 365°C to 300°C at a rate of 0.33°C / min. Fifth stage: Depress temperature from 300°C to 30°C at a rate of 1°C / min.

[0062] Examples 2-8 Comparative Examples 1-3 Fluororesin materials were prepared in the same manner as in Example 1, except that the types and mass ratios of recycled homo-PTFE powder (A) and recycled modified PTFE powder (B) in the mixed powder were changed as shown in Table 3, and molded articles were obtained.

[0063] Table 3 shows the tensile strength, tensile elongation, and specific gravity of the molded articles obtained in Examples 1-8 and Comparative Examples 1-3.

[0064]

[0065] The physical properties of the fluororesin material (mixed powder) and molded articles were measured as follows.

[0066] <Lamellar Thickness> The lamellar thickness of the mixed powder was determined from the lamellar thickness of the regenerated homo-PTFE powder sample and the lamellar thickness of the regenerated modified PTFE powder sample using the following formula. (In the formula, l' is the lamellar thickness (nm) of the mixed powder, l Ｈ is the lamellar thickness (nm) of the recycled homo-PTFE powder sample, and l Ｍ(where is the lamellar thickness (nm) of the regenerated modified PTFE powder sample, and α is the mixing ratio (mass%) of the regenerated modified PTFE powder sample.)

[0067] <Number-average molecular weight> The number-average molecular weight of the mixed powder was determined from the number-average molecular weight of the regenerated homo-PTFE powder sample and the number-average molecular weight of the regenerated modified PTFE powder sample using the following formula. (In the formula, Mn' is the number-average molecular weight of the mixed powder, and Mn Ｈ This is the number-average molecular weight of the recycled homo-PTFE powder sample, and Mn Ｍ (where α is the number-average molecular weight of the regenerated modified PTFE powder sample, and α is the mixing ratio (mass%) of the regenerated modified PTFE powder sample.)

[0068] <Tensile Test> The molded bodies obtained in the examples and comparative examples were cut with a band saw to obtain strip-shaped test pieces (length 50 mm, width 15 mm, thickness 1.35 mm to 2.2 mm). The obtained test pieces were punched out into No. 7 dumbbell shapes using a clicker press to obtain samples for tensile testing. After measuring the thickness and specific gravity of the obtained tensile test samples, a tensile test was performed using a benchtop universal testing machine (manufactured by Shimadzu Corporation) under the conditions of a tensile speed of 200 mm / min and a chuck distance of 20 mm. The strength at which the sample broke (the value obtained by dividing the tensile load value by the cross-sectional area of ​​the test piece) and the length of the sample were measured, and the tensile strength (MPa) and tensile elongation (%) were calculated. The tensile elongation was calculated using the following formula (A). The results are shown in Table 3. Tensile elongation (%) = (L - L) ｏ ) / L ｏ ×100...(A) L ｏ : Sample length before testing L: Sample length at fracture

[0069] <Specific Gravity> Using the water displacement method, the specific gravity was determined from the mass measured in air and the mass measured in water of the same sample using the following formula. (In the formula, d is the specific gravity of the test specimen, and m Ｓ，Ａ m is the mass (g) of the test specimen measured in air. Ｓ，Ｌ (This is the mass (g) of the test specimen measured in water.)

[0070] Table 3 shows that the number-average molecular weight of the fluororesin material is 1.0 × 10⁻⁶. ５When the above conditions are met and the lamellar thickness is 450 nm or less, it can be confirmed that the resulting molded article has high tensile strength and tensile elongation. On the other hand, in Comparative Examples 1 and 2, although the number-average molecular weight of the fluororesin material is larger than that of Examples 4 and 6, it can be confirmed that the resulting molded article has lower tensile strength and tensile elongation than the examples.

[0071] Molded articles formed using the fluororesin material of the present invention are suitably used as heat-resistant materials such as valve seats, gaskets, packings, and heat-resistant insulating tapes, as well as substrates for printed circuit boards, printed circuit boards, and release sheets.

[0072] Although several embodiments and / or examples of the present invention have been described in detail above, those skilled in the art will find it easy to make many modifications to these exemplary embodiments and / or examples without substantially departing from the novel teachings and effects of the present invention. Accordingly, many of these modifications fall within the scope of the present invention. All references to the documents described in this specification and the contents of the application on which the priority claim under the Paris Convention of this application is based are incorporated herein by reference.

Claims

1. The melting point is 333.5°C or lower, and the number-average molecular weight is 1.0 × 10⁻⁶. ５ The above describes a fluoropolymer material having a lamellar thickness of 450 nm or less.

2. The fluororesin material according to claim 1, comprising recycled polytetrafluoroethylene resin (A), or the recycled polytetrafluoroethylene resin (A) and a regenerated modified polytetrafluoroethylene resin (B), wherein the mixed mass ratio (resin (A):resin (B)) of the recycled polytetrafluoroethylene resin (A) and the regenerated modified polytetrafluoroethylene resin (B) is 100:0 to 1:

99.

3. Median diameter D of the recycled polytetrafluoroethylene resin (A) ５０ The fluororesin material according to claim 2, wherein the particle size is 10 μm to 10,000 μm.

4. Median diameter D of the regenerated modified polytetrafluoroethylene resin (B) ５０ The fluororesin material according to claim 2, wherein the particle size is 10 μm to 10,000 μm.

5. A molded article obtained by molding a fluororesin material according to any one of claims 1 to 4.

6. The molded article according to claim 5, wherein the tensile strength is 12 MPa or more.

7. The molded article according to claim 5, wherein the tensile elongation is 100% or more.

8. The molded article according to claim 5, wherein the specific gravity is 1.81 or higher.

9. The number average molecular weight of a fluoropolymer material with a melting point of 333.5°C or lower is 1.0 × 10⁻⁶. ５ A method for producing a fluororesin material, comprising the above steps, and further including a step of adjusting the lamellar thickness to 450 nm or less.

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