Polytetrafluoroethylene granulated powder

Abstract

Provided is a polytetrafluoroethylene granulated powder with which it is possible to obtain a molded article having little discoloration and excellent crack resistance. A polytetrafluoroethylene granulated powder having a moisture content of 0.020 mass% or less and a Z value of 90 or more.

Description

Technical Field

[0001] This disclosure relates to granulated polytetrafluoroethylene powder. Background Technology

[0002] Previously, methods for manufacturing (granulated) polytetrafluoroethylene granules included stirring in water containing an organic solvent, stirring in warm water, and applying mechanical force (rolling) while the mixture was moistened with a small amount of organic solvent.

[0003] Patent documents 1 and 2 describe a method of wetting polytetrafluoroethylene powder with a specified aqueous solution of surfactant and applying mechanical force.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 10-298300

[0007] Patent Document 2: Japanese Patent Application Publication No. 8-208929 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] The purpose of this disclosure is to provide a granulated polytetrafluoroethylene powder that can produce molded bodies with less coloring and excellent crack resistance.

[0010] Methods for solving problems

[0011] This disclosure (1) relates to a polytetrafluoroethylene granulated powder having a moisture content of less than 0.020% by mass and a Z value of more than 90.

[0012] This disclosure (2) relates to the polytetrafluoroethylene granulated powder described in this disclosure (1), wherein the granulation binder used in granulation is an aqueous solution of a nonionic surfactant.

[0013] This disclosure (3) relates to the polytetrafluoroethylene granulated powder described in this disclosure (2), wherein the nonionic surfactant aqueous solution is selected from at least one of the groups consisting of polyoxyethylene alkyl ethers, segmented polyalkylene glycols, and alkylamine oxides.

[0014] This disclosure (4) relates to polytetrafluoroethylene granulated powder in any combination with any of the present disclosures (1) to (3), having an average particle size of 200 to 700 μm.

[0015] This disclosure (5) relates to the polytetrafluoroethylene granulated powder described in this disclosure (4), which has an average particle size of 200 to 600 μm.

[0016] This disclosure (6) relates to polytetrafluoroethylene granulated powder in any combination with any of the present disclosures (1) to (5), having an apparent density of 0.60 to 0.90 g / ml.

[0017] This disclosure (7) relates to polytetrafluoroethylene granulated powder in any combination with any of the present disclosures (1) to (6), having an average aspect ratio of 1.25 or less.

[0018] This disclosure (8) relates to polytetrafluoroethylene granulated powder in any combination with any of the disclosures (1) to (7), wherein the high-temperature volatile content is less than 0.050% by mass.

[0019] This disclosure (9) relates to polytetrafluoroethylene granulated powder in any combination with any of the present disclosures (1) to (8), wherein the moisture content is less than 0.001% by mass.

[0020] Invention Effects

[0021] According to this disclosure, a polytetrafluoroethylene granulated powder can be provided, which can produce molded bodies with less coloring and excellent crack resistance. Attached Figure Description

[0022] Figure 1 This is a schematic diagram illustrating the apparatus used in determining the flowability of granulated powder. Detailed Implementation

[0023] The following details this disclosure.

[0024] This disclosure relates to granulated polytetrafluoroethylene (PTFE) powder with a moisture content of less than 0.020% by mass and a Z value of more than 90.

[0025] The moisture content and Z-value of the PTFE granulated powder disclosed herein are within a specific range, thus enabling the production of molded articles with less coloring and excellent crack resistance.

[0026] The moisture content of the PTFE granulated powder disclosed herein is 0.020% by mass or less. From the perspective of obtaining molded articles with superior crack resistance, it is preferably 0.015% by mass or less, more preferably 0.010% by mass or less, even more preferably 0.005% by mass or less, even more preferably 0.003% by mass or less, even more preferably 0.002% by mass or less, and particularly preferably 0.001% by mass or less. The lower limit is not limited and can be 0% by mass.

[0027] The moisture content was determined using the following method.

[0028] The mass of approximately 20g of PTFE granulated powder before and after heating at 150℃ for 2 hours was determined and calculated using the following formula. Three samples were taken, and the mass was calculated for each sample. The average value was then used.

[0029]

[0030] The Z-value of the PTFE granulated powder disclosed herein is 90 or higher, preferably 91 or higher, more preferably 95 or higher, even more preferably 100 or higher, and can be 110 or lower from the viewpoint of obtaining molded articles with less coloring.

[0031] The Z-values ​​mentioned above were determined using the following method.

[0032] 200g of PTFE granulated powder was filled into a mold with a diameter of 50mm, and the molding pressure was 300kg / cm². 2 Hold for 5 minutes, heat treat the resulting preform (approximately 50 mm in diameter and 50 mm in thickness) at 370°C for 2 hours, and then transversely divide the resulting molded part at approximately 25 mm from the end (center portion) using a lathe. Measure the Z-value of the center portion of the cut part based on the Z-value determination method of the XYZ system specified by the International Commission on Illumination.

[0033] From the perspective of excellent operability, the average particle size of the PTFE granulated powder disclosed herein is preferably 200 μm or more, more preferably 250 μm or more, further preferably 300 μm or more, even more preferably 350 μm or more, and preferably 700 μm or less, more preferably 650 μm or less, even more preferably 600 μm or less, and even more preferably 550 μm or less.

[0034] The average particle size mentioned above was determined by the following method.

[0035] Standard sieves of 10, 20, 32, 48, 60, and 80 mesh (inch mesh) are stacked sequentially from top to bottom. PTFE granulated powder is placed on a 10-mesh sieve, and the sieve is vibrated to cause the fine PTFE granulated powder particles to fall downwards sequentially. The proportion of PTFE granulated powder remaining on each sieve is calculated as a percentage by mass. The cumulative percentage of the remaining proportion is then marked on logarithmic probability paper relative to the mesh size of each sieve (horizontal axis) (vertical axis). These points are connected by a straight line, and the particle size at 50% mass on this line is calculated. This value is taken as the average particle size.

[0036] From the perspective of excellent operability, the apparent density of the PTFE granulated powder disclosed herein is preferably 0.60 g / ml or more, more preferably 0.65 g / ml or more, even more preferably 0.70 g / ml or more, and even more preferably 0.75 g / ml or more. In addition, it can be 0.90 g / ml or less.

[0037] The apparent density was determined according to JIS K 6891.

[0038] From the perspective of excellent operability, the average aspect ratio of the PTFE granulated powder disclosed herein is preferably 1.25 or less, more preferably 1.20 or less, further preferably 1.15 or less, even more preferably 1.10 or less, particularly preferably 1.05 or less, and may also be 1.00 or more.

[0039] For the above average aspect ratio, the PTFE granulated powder was observed using a video microscope. More than 50 randomly selected particles were image-processed, and the average aspect ratio was calculated from the average of their major and minor diameter ratios.

[0040] From the perspective of obtaining a molded body with less coloring and better crack resistance, the high-temperature volatile content of the PTFE granulated powder disclosed herein is preferably 0.050% by mass or less, more preferably 0.040% by mass or less, even more preferably 0.030% by mass or less, even more preferably 0.020% by mass or less, particularly preferably 0.010% by mass or less, and may be 0.0001% by mass or more, 0.001% by mass or more, 0.002% by mass or more, or 0.003% by mass or more.

[0041] The content of the above-mentioned high-temperature volatile components was determined according to JIS K 6891, based on the mass of PTFE granulated powder heated at 370°C for 2 hours, and calculated using the following formula.

[0042]

[0043] The tensile strength of the PTFE granulated powder disclosed herein is preferably 25 MPa or more, more preferably 30 MPa or more, even more preferably 35 MPa or more, even more preferably 38 MPa or more, particularly preferably 40 MPa or more, and may be 60 MPa or less.

[0044] The elongation of the PTFE granulated powder disclosed herein is preferably 150% or more, more preferably 200% or more, even more preferably 250% or more, even more preferably 290% or more, particularly preferably 300% or more, and may be 500% or less.

[0045] The tensile strength and elongation mentioned above were determined by the following methods.

[0046] Fill a 97mm×18mm mold with 5g of PTFE granulated powder and slowly apply pressure until it reaches approximately 300kg / cm². 2Maintain this pressure for another 2 minutes to create a preform. Remove the preform from the mold and place it in an electric furnace maintained at 370°C. Firing for 5.5 hours, then cooling at 50°C / hr, yields the sintered body. Using a JIS dumbbell No. 3 die, cut test pieces from the sintered body. Following JIS K 6891-58, use an automatic plotter with a total load of 500 kg and a tensile speed of 200 mm / min to measure the stress and elongation at fracture (elongation at break).

[0047] From the perspective of excellent operability, the flowability of the PTFE granulated powder disclosed herein is preferably 0.5 times or more, more preferably 1.0 times or more, even more preferably 1.5 times or more, and can be 5 times or less.

[0048] The above-mentioned flowability was measured using the method described in the examples described later.

[0049] The PTFE in the PTFE granulated powder disclosed herein may be a homopolymer of tetrafluoroethylene (TFE) or a modified PTFE comprising TFE-based polymerization units (TFE units) and polymerization units based on modified monomers capable of copolymerizing with TFE (hereinafter also referred to as "modified monomer units").

[0050] The homopolymer of TFE mentioned above refers to a substance in which the content of modified monomer units relative to all polymer units is less than 0.0001% by mass.

[0051] The modified PTFE described above may contain more than 99.0% by mass of TFE units and less than 1.0% by mass of modified monomer units. Alternatively, the modified PTFE described above may consist only of TFE units and modified monomer units.

[0052] The modified PTFE preferably contains modified monomer units in the range of 0.0001% to 1.0% by mass relative to all polymer units. The lower limit of the modified monomer unit content is more preferably 0.001% by mass, further preferably 0.010% by mass, even more preferably 0.015% by mass, even more preferably 0.020% by mass, and particularly preferably 0.050% by mass. The upper limit of the modified monomer unit content is preferably 0.80% by mass, more preferably 0.60% by mass, further preferably 0.50% by mass, even more preferably 0.40% by mass, even more preferably 0.30% by mass, and particularly preferably 0.20% by mass.

[0053] In this specification, the modified monomer unit refers to a portion of the molecular structure of PTFE derived from the modified monomer.

[0054] The content of each of the above-mentioned polymerization units can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and fluorescence X-ray analysis according to the type of monomer.

[0055] As for the aforementioned modified monomers, there are no particular limitations as long as they can copolymerize with TFE. Examples include perfluoroolefins such as hexafluoropropylene [HFP]; hydrofluoroolefins such as trifluoroethylene and vinylidene fluoride [VDF]; perhaloolefins such as chlorotrifluoroethylene [CTFE]; perfluorovinyl ethers; perfluoroallyl ethers; (perfluoroalkyl)ethylene; and ethylene. Furthermore, one or more modified monomers can be used.

[0056] The perfluorovinyl ethers mentioned above are not particularly limited; for example, perfluorounsaturated compounds represented by the following general formula (A) can be cited.

[0057] (where Rf) 1 (This refers to a perfluorinated organic group). In this specification, "perfluorinated organic group" refers to an organic group in which all hydrogen atoms bonded to carbon atoms are replaced by fluorine atoms. The aforementioned perfluorinated organic group may contain ether oxygen.

[0058] Examples of perfluorovinyl ethers include, for instance, Rf in general formula (A). 1 The perfluoroalkyl group is a perfluoro(alkyl vinyl ether) [PAVE] with 1 to 10 carbon atoms. The preferred number of carbon atoms in the perfluoroalkyl group is 1 to 5.

[0059] Examples of perfluoroalkyl groups in the aforementioned PAVE include perfluoromethyl, perfluoroethyl, perfluoropropyl, perfluorobutyl, perfluoropentyl, and perfluorohexyl.

[0060] As a further example of the aforementioned perfluorovinyl ether, Rf in the above general formula (A) can be cited. 1 Substances with a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms; Rf 1 Substances with groups represented by the following formula;

Chemistry 1

[0061] (In the formula, m represents 0 or an integer from 1 to 4); Rf 1 Substances containing groups represented by the following formulas,

Chemistry 2

[0062] (In the formula, n represents an integer from 1 to 4).

[0063] There is no particular limitation as to (perfluoroalkyl)ethylene [PFAE], for example, (perfluorobutyl)ethylene [PFBE], (perfluorohexyl)ethylene, etc.

[0064] Examples of perfluoroallyl ethers include, for example, fluorinated monomers represented by general formula (B).

[0065] (where Rf) 2 (Indicates a perfluorinated organic group).

[0066] Rf 2 Preferred are perfluoroalkyl groups having 1 to 10 carbon atoms or perfluoroalkoxyalkyl groups having 1 to 10 carbon atoms. As the above-mentioned perfluoroallyl ether, it is preferably selected from at least one of the group consisting of CF2=CF-CF2-O-CF3, CF2=CF-CF2-O-C2F5, CF2=CF-CF2-O-C3F7, and CF2=CF-CF2-O-C4F9, more preferably from at least one of the group consisting of CF2=CF-CF2-O-C2F5, CF2=CF-CF2-O-C3F7, and CF2=CF-CF2-O-C4F9, and even more preferably from CF2=CF-CF2-O-CF2CF2CF3.

[0067] As the modified monomers mentioned above, it is preferred to select at least one from the group consisting of CTFE, HFP, perfluoro(methyl vinyl ether) [PMVE], perfluoro(propyl vinyl ether) [PPVE], PFBE and VDF, more preferably at least one from the group consisting of CTFE, HFP, PMVE and PPVE, even more preferably at least one from the group consisting of CTFE, HFP and PPVE, and particularly preferably at least one from the group consisting of PPVE and HFP.

[0068] The aforementioned PTFE can have a core-shell structure. Examples of PTFEs with a core-shell structure include modified PTFE, which contains a core of high molecular weight PTFE and a shell of lower molecular weight PTFE or modified PTFE within the particles. Examples of such modified PTFEs include the PTFE described in Japanese Patent Application Publication No. 2005-527652.

[0069] The PTFE described above preferably has non-melting secondary processability. This non-melting secondary processability refers to the property, according to ASTM D-1238 and D-2116, that the melt flow rate cannot be determined at temperatures above the melting point; in other words, it does not flow easily even in the melting temperature range.

[0070] The PTFE mentioned above can be obtained through suspension polymerization.

[0071] The PTFE granulated powder disclosed herein may contain fillers, provided that the effect is not impaired. As fillers, white or transparent fillers are preferred from the perspective of preventing the molded article from becoming discolored; examples include glass fiber, titanium dioxide powder, and boron nitride powder. Aromatic heat-resistant resin powders such as polyoxybenzoyl polyester can also be used as fillers.

[0072] The content of the filler relative to PTFE is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less.

[0073] From the perspective of reducing the coloring of the molded body, it is preferable to have a small amount of filler, and more preferably, the PTFE granulated powder of this disclosure is filler-free.

[0074] The PTFE granulated powder disclosed herein can be manufactured by granulating PTFE powder obtained by suspension polymerization. In the case of manufacturing PTFE granulated powder containing fillers, a mixture of PTFE powder and filler powder can be used instead of the original PTFE powder.

[0075] Suspension polymerization can be carried out as follows: monomers such as TFE, an aqueous medium, and other additives as needed are added to a reactor; the contents of the reactor are stirred; the reactor is then maintained at a specified polymerization temperature; a specified amount of polymerization initiator is added to initiate the polymerization reaction. After the polymerization reaction begins, monomers such as TFE, polymerization initiators, chain transfer agents, etc., may be added as needed, depending on the desired outcome.

[0076] The obtained suspended polymer particles are then crushed, dried, and classified as needed to obtain PTFE powder for granulation.

[0077] From the perspective of obtaining molded bodies with less coloring, the granulation of PTFE powder is preferably dry granulation using an aqueous solution of a nonionic surfactant as a granulation binder. Using an aqueous solution of a nonionic surfactant as a granulation binder is one of the preferred methods of this disclosure. It is also preferable not to use organic solvents in the granulation process.

[0078] Granulation can be achieved, for example, by wetting PTFE powder with an aqueous solution of a nonionic surfactant, applying mechanical force, and then drying it.

[0079] In this disclosure, wetting includes, for example, a state in which the PTFE powder is wetted and does not separate from the surfactant aqueous solution when an aqueous surfactant solution is added to the PTFE powder.

[0080] The aforementioned nonionic surfactants can be hydrocarbon-based surfactants or non-fluorinated surfactants.

[0081] Examples of nonionic surfactants include polyoxyethylene amine oxides, alkylamine oxides, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, glycerol esters, polyoxyethylene alkylamines, segmented polyalkylene glycols having hydrophobic segments composed of poly(oxyalkylene) units with 3 to 4 carbon atoms and hydrophilic segments composed of poly(oxyethylene) units, and their derivatives.

[0082] More specifically, examples of polyoxyethylamine oxides include dimethyloxyethylamine oxide.

[0083] Examples of alkylamine oxides include dimethylmyristamine oxide, dimethyllauroamine oxide, dimethyldecylamine oxide, and dimethyloleylamine oxide.

[0084] Examples of polyoxyethylene alkyl ethers include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oil-based ether, and polyoxyethylene behenyl ether.

[0085] Examples of polyoxyethylene alkylphenyl ethers include polyoxyethylene nonylphenyl ether and polyoxyethylene octylphenyl ether.

[0086] Examples of polyoxyethylene fatty acid esters include polyoxyethylene monolaurate, polyoxyethylene monooleate, and polyoxyethylene monostearate.

[0087] Examples of sorbitan fatty acid esters include sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, and sorbitan monooleate.

[0088] Examples of polyoxyethylene sorbitan fatty acid esters include polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, and polyoxyethylene sorbitan monostearate.

[0089] Examples of glycerides include glyceryl monomyristate, glyceryl monostearate, and glyceryl monooleate.

[0090] In addition, as derivatives of them, examples include polyoxyethylene alkylphenyl-formaldehyde condensates and polyoxyethylene alkyl ether phosphates.

[0091] As segmented polyalkylene glycols having both hydrophobic and hydrophilic segments, substances with the following formulas are preferred, for example.

[0092] (In the formula, A is -CH(CH3)CH2O- or -CH(CH3)CH2CH2O-, p is an integer from 5 to 200, and q is an integer from 2 to 400). From the perspective of easy adsorption to PTFE resin, p is preferably 15 to 40, and q is preferably 7 to 100.

[0093] Among them, polyoxyethylene alkyl ethers, segmented polyalkylene glycols, and alkylamine oxides are preferred, and polyoxyethylene alkyl ethers and segmented polyalkylene glycols are even more preferred.

[0094] The concentration of the nonionic surfactant in the above aqueous solution is preferably 0.50% by mass or more, more preferably 0.75% by mass or more, even more preferably 1.00% by mass or more, and preferably 4.00% by mass or less, more preferably 3.50% by mass or less, and even more preferably 3.00% by mass or less.

[0095] The amount of the above-mentioned aqueous solution added relative to the PTFE powder is preferably 15% by mass or more, more preferably 20% by mass or more, even more preferably 25% by mass or more, and preferably 45% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less.

[0096] Wetting can be carried out in any suitable device such as a plow mixer, a Warin mixer, a paddle mixer, or a belt mixer. These devices may or may not have high-speed components.

[0097] Alternatively, wetting can be carried out in the device (granulator) used to apply mechanical force, which will be described later.

[0098] Moist PTFE powder can be pulverized to the target particle size using known methods.

[0099] Methods of applying mechanical force include rolling and stirring. In this specification, rolling refers to the back-and-forth movement of PTFE particles while they rub against each other or are in contact with the wall of the granulator. Examples of granulators used for rolling PTFE powder include rotary disc granulators, V-type agitators, C-type agitators, tilting disc granulators, and side-rotating granulators.

[0100] In addition, as a mixing method, one can cite the use of a high-speed mixer, etc.

[0101] The speed, time, temperature, and other conditions for rolling and stirring can be set according to the target material properties (apparent density, flowability, etc.).

[0102] Drying of moistened powder subjected to mechanical force can be carried out using methods such as vacuum, high frequency, or hot air. The drying temperature is preferably 200°C or higher, more preferably 210°C or higher, even more preferably 220°C or higher, and even more preferably 230°C or higher. In addition, it is preferably 270°C or lower, more preferably 260°C or lower, and even more preferably 250°C or lower.

[0103] If the drying temperature is too low, moisture and surfactants cannot be completely removed; if the drying temperature is too high, some of the PTFE particles will melt, which may reduce tensile strength or elongation.

[0104] Before drying within the aforementioned temperature range, drying at a low temperature can be performed. This allows for more efficient removal of moisture and surfactants. The low-temperature drying temperature is preferably 100°C or higher, more preferably 110°C or higher, and further preferably 180°C or lower, more preferably 150°C or lower.

[0105] From the perspective of being able to remove moisture and surfactants more efficiently, the total drying time is preferably 5 hours or more, more preferably 8 hours or more, more preferably 10 hours or more, even more preferably 15 hours or more, and preferably 100 hours or less, more preferably 50 hours or less, and even more preferably 30 hours or less.

[0106] From the perspective of more efficient removal of moisture and surfactants, the air velocity during drying is preferably 0.01 m / s or more, more preferably 0.03 m / s or more, further preferably 0.05 m / s or more, and even more preferably 0.1 m / s or more. Furthermore, from the perspective of suppressing powder scattering, it is preferably 50 m / s or less, more preferably 30 m / s or less, and even more preferably 10 m / s or less.

[0107] Drying can be carried out using an electric furnace or a steam furnace. For example, a parallel-flow box furnace, a pneumatic box furnace, a pneumatic conveyor furnace, a belt furnace, a radiant conveyor furnace, a fluidized bed furnace, a vacuum furnace, a stirred furnace, an airflow furnace, a hot air circulation furnace, or a corresponding steam furnace can be used. From the perspective of more efficient removal of moisture and fluorine-containing compounds, parallel-flow box furnaces, pneumatic box furnaces, pneumatic conveyor furnaces, belt furnaces, fluidized bed furnaces, hot air circulation furnaces, and corresponding steam furnaces are preferred.

[0108] From the perspective of more efficient removal of moisture and surfactants, drying is preferably carried out by placing the moistened PTFE powder in a container with a breathable bottom and / or sides. The container with a breathable bottom and / or sides need only be able to withstand the aforementioned heat treatment temperature, and is preferably made of metal such as stainless steel.

[0109] As a container with a breathable bottom and / or sides, a tray (basin) with a breathable bottom and / or sides is preferred, and a tray (mesh tray) with a breathable bottom and / or sides made of mesh is more preferred.

[0110] The aforementioned mesh is preferably either woven mesh or perforated mesh.

[0111] The mesh size of the aforementioned mesh is preferably 2000 μm or less (10 mesh or more according to ASTM standards), more preferably 595 μm or less (30 mesh or more), even more preferably 297 μm or less (50 mesh or more), further more preferably 177 μm or less (80 mesh or more), particularly preferably 149 μm or less (100 mesh or more), and especially preferably 74 μm or less (200 mesh or more). Additionally, it is preferably 25 μm or more (500 mesh or less).

[0112] For example, when the aforementioned mesh is used as a woven net, weaving methods include plain weave, twill weave, flat overlay weave, and twill overlay weave.

[0113] When the aforementioned mesh is a perforated mesh, the open area ratio is preferably 10% or more, more preferably 20% or more, and even more preferably 30% or more. Furthermore, it is preferably 95% or less.

[0114] From the perspective of more efficient removal of moisture and surfactants, the preferred amount of dried moist powder is 10 g / cm³. 2 The preferred value is 8g / cm³. 2 The following is a further preferred value: 5g / cm 2 The following is particularly preferred: 3g / cm 2 Furthermore, 0.01 g / cm³ is preferred. 2 The above, more preferably 0.05 g / cm³ 2 The above is further preferred to be 0.1 g / cm³. 2 above.

[0115] The obtained granulated powder can also be classified using known methods such as air classification. Classification can remove very small particles and very large coarse particles, resulting in granulated powder with the desired average particle size or particle size distribution.

[0116] The PTFE granulated powder of the present disclosure can be suitably used as a molding material for molding methods such as compression molding, plunger extrusion molding, and isostatic compression molding.

[0117] As described above, the embodiments have been described. However, it should be understood that various changes can be made to the embodiments and specific situations without departing from the spirit and scope of the claims.

[0118] Examples

[0119] Next, examples are given to explain the present disclosure in more detail. However, the present disclosure is not limited to these examples.

[0120] Various physical properties were measured by the following methods.

[0121] <Moisture content>

[0122] The mass of about 20 g of PTFE granulated powder before and after heating at 150 °C for 2 hours was measured and calculated according to the following formula. Three samples were taken, calculated separately, and the average value was obtained, and this average value was adopted.

[0123]

[0124] <Z value>

[0125] 200 g of PTFE granulated powder was filled into a mold with a diameter of 50 mm, and the molding pressure was maintained at 300 kg / cm 2 for 5 minutes. The obtained preformed product (diameter about 50 mm, thickness 50 mm) was heat-treated at 370 °C for 2 hours. The obtained molded product was transversely divided at a position about 25 mm (center part) from the end by a lathe, and the Z value of the center part of the cut-out part was measured based on the Z value measurement method of the XYZ system defined by the International Commission on Illumination.

[0126] <Average particle size>

[0127] Standard sieves of 10, 20, 32, 48, 60, and 80 mesh (inch mesh) were sequentially overlapped from the top. The PTFE granulated powder was placed on the 10-mesh sieve, and the sieve was vibrated to sequentially let the fine PTFE granulated powder particles fall downward. After obtaining the proportion of the PTFE granulated powder remaining on each sieve in mass%, the cumulative percentage of the remaining proportion was plotted on a logarithmic probability paper against the mesh size (horizontal axis) of each sieve (vertical axis). These points were connected by a straight line, and the particle size at which the proportion was 50 mass% on this straight line was obtained and taken as the average particle size.

[0128] <Apparent density>

[0129] Measurement was carried out in accordance with JIS K 6891.

[0130] <Average aspect ratio>

[0131] The PTFE granulated powder was observed using a video microscope. More than 50 randomly selected particles were image-processed, and the average ratio of their major axis to minor axis was calculated.

[0132] <Tensile strength and elongation>

[0133] Fill a 97mm×18mm mold with 5g of PTFE granulated powder and slowly apply pressure until it reaches approximately 300kg / cm². 2 Maintain this pressure for another 2 minutes to create a preform. Remove the preform from the mold and place it in an electric furnace maintained at 370°C. Firing for 5.5 hours, then cooling at 50°C / hr, yields the sintered body. Using a JIS dumbbell No. 3 die, cut test pieces from the sintered body. Following JIS K 6891-58, use an automatic plotter with a total load of 500 kg and a tensile speed of 200 mm / min to measure the stress and elongation at fracture.

[0134] <High-Temperature Volatile Components>

[0135] According to JIS K 6891, the mass of PTFE granulated powder after heating at 370℃ for 2 hours was determined and calculated using the following formula.

[0136]

[0137] <Flowability>

[0138] The determination was performed according to the method described in Japanese Patent Application Publication No. 3-259925.

[0139] That is, as a measuring device, such as Figure 1 (As shown in Figure 3 of Japanese Patent Application Publication No. 3-259925), hoppers 31 and 32 are used, supported vertically on a support platform 42 with their center lines aligned. The upper hopper 31 has an inlet 33 with a diameter of 74 mm, an outlet 34 with a diameter of 12 mm, and a height of 123 mm from inlet 33 to outlet 34. A partition plate 35 is provided at outlet 34 to properly hold or allow powder to fall. The lower hopper 32 has an inlet 36 with a diameter of 76 mm, an outlet 37 with a diameter of 11 mm, and a height of 120 mm from inlet 36 to outlet 37. Similar to the upper hopper, a partition plate 38 is provided at outlet 37. The distance between the upper and lower hoppers is adjusted so that the distance between each partition plate is 15 cm. It should be noted that... Figure 1 In the middle, 39 and 40 are the outlet covers of each hopper, and 41 is the receiver for the falling powder.

[0140] For the determination of flowability, approximately 200g of the powder to be tested is placed in a room at a temperature of 23.5–24.5°C for more than 4 hours, sieved through a 10-mesh sieve (1680 micrometers (μm)), and then the test is performed at the same temperature.

[0141] (I) First, using a 30cc cup, place exactly one cup of the powder to be tested into the upper hopper 31, and immediately remove the partition plate 35 to allow the powder to fall into the lower hopper. If it does not fall, use a wire to push it down. After the powder has completely fallen into the lower hopper 32, wait 15±2 seconds, then remove the partition plate 38 of the lower hopper and observe whether the powder flows down from the outlet 37. If more than 99% by mass of the powder flows down within 8 seconds, it is considered to have fallen.

[0142] (II) Repeat the same test three times and observe whether it flows out. If it flows out more than twice in three tests, the flowability is judged as "good". If it does not flow out at all, the flowability is judged as "poor". If it flows out only once in three tests, perform two more tests. If it flows out in both tests, the flowability of the powder is judged as "good". Otherwise, the flowability is judged as "poor".

[0143] (III) For powders that were determined to have "good" flowability in the above tests, place the next two 30cc cups of powder into the upper hopper and perform the tests in the same manner as above. If the result is "good" flowability, increase the number of cups of powder sequentially until "poor," up to a maximum of 8 cups. In each test, the powder that flowed out of the lower hopper in the previous test can also be used again.

[0144] (IV) In the above tests, the more PTFE powder used, the more difficult it was to flow down.

[0145] Therefore, the number obtained by subtracting 1 from the number of cups when the powder becomes "poor" flowability is defined as the "flowability" of the powder.

[0146] Coloring of Molded Products

[0147] Based on the Z-values ​​measured above, the following criteria are used for evaluation.

[0148] ◎: Z-value above 95

[0149] ○: Z value is 90 or higher and less than 95

[0150] ×: Z value is less than 90

[0151] Crack resistance

[0152] 200g of PTFE granulated powder was filled into a mold with an outer diameter of 50mm and an inner diameter of 20mm, and molded at a pressure of 300kg / cm². 2 Hold for 5 minutes, then heat the resulting preform (approximately 50 mm outer diameter, 20 mm inner diameter, and 50 mm thickness) to 370°C. Hold at 370°C for 5.5 hours, then cool to 40°C at 50°C / hr. Use a lathe to fabricate a 0.1 mm thick film from the resulting preform. Visually confirm the number of cracks and then evaluate it by converting the number of cracks per 100 g.

[0153]

[0154] Example 1

[0155] 2.0 kg of PTFE molding powder with an average particle size of 50 μm obtained by suspension polymerization was added to a belt stirrer, and surfactant A (H-(OCH2CH2CH2)) was added after being diluted to 1% with deionized water. n -(OCH2CH2) m 0.8 kg of an aqueous solution of -OH was mixed for 3 minutes to obtain a moist powder. The moist powder was then fed into a crusher with a discharge mesh opening of 0.8 mm for crushing, thereby adjusting the particle size. Next, the powder was granulated using a rotary disc granulator for 3 minutes. Then, the moist powder was placed in a stainless steel mesh tray and dried using a hot air dryer at 120°C for 7 hours, followed by drying at 250°C for 8 hours. After drying, coarse particles were removed using a 10-mesh sieve, and various measurements and evaluations were performed.

[0156] Examples 2-4 and Comparative Example 1

[0157] As shown in Table 1, the type of surfactant was changed, and otherwise, PTFE granulated powder was obtained in the same manner as in Example 1.

[0158] Comparative Example 2

[0159] As shown in Table 1, the drying conditions were changed, but otherwise, PTFE granulated powder was obtained in the same manner as in Example 3.

[0160] Comparative Example 3

[0161] As shown in Table 1, the drying conditions were changed, but otherwise, PTFE granulated powder was obtained in the same manner as in Example 4.

[0162] The PTFE granulated powders obtained above were evaluated using the methods described above. The results are shown in Table 1.

[0163] [Table 1]

[0164] The abbreviations in the table are as follows.

[0165] A: H-(OCH2CH2CH2) n -(OCH2CH2) m -OH

[0166] B: C 12 H 25 -O-(CH2CH2O)9-H

[0167] C:C 12 H 25 -O-(CH2CH2O)9-H (The structure of the alkyl group is different from that of surfactant B)

[0168] D:C 12 H 25 -N + (CH3)2-O -

[0169] E:C 12 H 25 -SO3Na

[0170] Symbol Explanation

[0171] 31: Upper hopper

[0172] 32: Lower hopper

[0173] 33, 36: Entrance

[0174] 34, 37: Exports

[0175] 35, 38: Divider

[0176] 39, 40: Exit cover

[0177] 41: Receiver

[0178] 42: Support platform

Claims

1. A polytetrafluoroethylene granulated powder having a moisture content of less than 0.020% by mass and a Z-value of more than 90.

2. The polytetrafluoroethylene granulated powder according to claim 1, wherein, The granulation binder used in granulation is an aqueous solution of a nonionic surfactant.

3. The polytetrafluoroethylene granulated powder according to claim 2, wherein, The nonionic surfactant aqueous solution is selected from at least one of the following groups: polyoxyethylene alkyl ethers, segmented polyalkylene glycols, and alkylamine oxides.

4. The polytetrafluoroethylene granulated powder according to any one of claims 1 to 3, wherein the average particle size is 200 μm to 700 μm.

5. The polytetrafluoroethylene granulated powder according to claim 4 has an average particle size of 200 μm to 600 μm.

6. The polytetrafluoroethylene granulated powder according to any one of claims 1 to 5, wherein the apparent density is 0.60 g / ml to 0.90 g / ml.

7. The polytetrafluoroethylene granulated powder according to any one of claims 1 to 6, wherein the average aspect ratio is 1.25 or less.

8. The polytetrafluoroethylene granulated powder according to any one of claims 1 to 7, wherein the high-temperature volatile content is less than 0.050% by mass.

9. The polytetrafluoroethylene granulated powder according to any one of claims 1 to 8, wherein, The moisture content is less than 0.001% by mass.

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