Polytetrafluoroethylene granulated powder

Abstract

Provided is a polytetrafluoroethylene granulated powder by which a molded body having little coloration and excellent cracking resistance can be obtained. The polytetrafluoroethylene granulated powder has a moisture content of 0.020 mass% or less and a Z value of 90 or greater.

Description

Polytetrafluoroethylene granulated powder

[0001] The present disclosure relates to polytetrafluoroethylene granulated powder.

[0002] Conventionally, methods for producing (granulating) granular powder of polytetrafluoroethylene include a method of stirring in water containing an organic solvent, a method of stirring in warm water, and a method of applying mechanical force (rolling) in a state where the material is wetted with a small amount of organic solvent.

[0003] Patent Documents 1 and 2 describe a method in which polytetrafluoroethylene powder is wetted with a predetermined aqueous surfactant solution and mechanical force is applied to the powder.

[0004] JP-A-10-298300 JP-A-8-208929

[0005] An object of the present disclosure is to provide a polytetrafluoroethylene granulated powder that can give a molded product that is less colored and has excellent crack resistance.

[0006] The present disclosure (1) is a polytetrafluoroethylene granulated powder having a moisture content of 0.020 mass% or less and a Z value of 90 or more.

[0007] The present disclosure (2) is the polytetrafluoroethylene granulated powder according to the present disclosure (1), in which the granulation binder used for granulation is an aqueous solution of a nonionic surfactant.

[0008] The present disclosure (3) is the polytetrafluoroethylene granulated powder according to the present disclosure (2), wherein the nonionic surfactant aqueous solution is at least one selected from the group consisting of polyoxyethylene alkyl ethers, segmented polyalkylene glycols, and alkylamine oxides.

[0009] The present disclosure (4) is the polytetrafluoroethylene granulated powder according to any combination with any of the present disclosures (1) to (3), which has an average particle size of 200 to 700 μm.

[0010] The present disclosure (5) is the polytetrafluoroethylene granulated powder according to the present disclosure (4), having an average particle size of 200 to 600 μm.

[0011] The present disclosure (6) is a 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.

[0012] The present disclosure (7) is a 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.

[0013] The present disclosure (8) is a polytetrafluoroethylene granulated powder in any combination with any of the present disclosures (1) to (7), having a high-temperature volatile content of 0.050 mass% or less.

[0014] The present disclosure (9) is a polytetrafluoroethylene granulated powder in any combination with any of the present disclosures (1) to (8), in which the moisture content is 0.001% by mass or less.

[0015] According to the present disclosure, it is possible to provide polytetrafluoroethylene granulated powder that can be used to obtain a molded product that is less colored and has excellent crack resistance.

[0016] FIG. 1 is a schematic explanatory diagram of an apparatus used to measure the flowability of a granulated powder.

[0017] The present disclosure will be specifically described below.

[0018] The present disclosure relates to polytetrafluoroethylene (PTFE) granulated powder having a moisture content of 0.020 mass% or less and a Z value of 90 or more.

[0019] The PTFE granulated powder of the present disclosure has a moisture content and a Z value within specific ranges, and therefore, a molded product with little coloring and excellent crack resistance can be obtained.

[0020] The moisture content of the PTFE granulated powder of the present disclosure is 0.020% by mass or less. However, in order to obtain a molded product with even better 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, but it may be 0% by mass. The moisture content is measured by the following method. Approximately 20 g of PTFE granulated powder is heated at 150°C for 2 hours, and the mass is measured before and after heating, and calculated according to the following formula. A sample is taken three times, and the values ​​are calculated for each time, and the average is calculated and adopted. Moisture content (mass%)=[(mass (g) of PTFE granulated powder before heating)−(mass (g) of PTFE granulated powder after heating)] / (mass (g) of PTFE granulated powder before heating)×100

[0021] The Z value of the PTFE granulated powder of the present disclosure is 90 or more, but in order to obtain a molded product with even less coloring, it is preferably 91 or more, more preferably 95 or more, even more preferably 100 or more, and may be 110 or less. The Z value is measured by the following method. 200 g of the PTFE granulated powder is filled into a mold with a diameter of 50 mm, and molding is performed under a molding pressure of 300 kg / cm. ２ The resulting preform (approximately 50 mm in diameter and 50 mm in thickness) is then heat-treated at 370°C for 2 hours to obtain a molded product, which is then cut crosswise on a lathe at a point approximately 25 mm from the edge (the center part), and the Z value of the center part of the cut-out part is measured in accordance with the XYZ system Z value measurement method established by the International Commission on Illumination.

[0022] In terms of excellent handleability, the PTFE granulated powder of the present disclosure preferably has an average particle size of 200 μm or more, more preferably 250 μm or more, even more preferably 300 μm or more, and 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. The average particle size is measured by the following method. Standard sieves of 10, 20, 32, 48, 60, and 80 mesh (inch mesh) are stacked in order from top to bottom, and the PTFE granulated powder is placed on the 10-mesh sieve. The sieves are vibrated to allow successively finer PTFE granulated powder particles to fall downward. The proportion of the PTFE granulated powder remaining on each sieve is determined in mass%, and then the cumulative percentage of the remaining proportion (vertical axis) is scaled against the mesh opening of each sieve (horizontal axis) on a logarithmic probability paper. These points are connected by a straight line, and the particle size on this line at which the proportion becomes 50 mass% is determined; this value is the average particle size.

[0023] In view of excellent handleability, the PTFE granulated powder of the present disclosure preferably has an apparent density of 0.60 g / ml or more, more preferably 0.65 g / ml or more, even more preferably 0.70 g / ml or more, even more preferably 0.75 g / ml or more, and may be 0.90 g / ml or less. The apparent density is measured in accordance with JIS K 6891.

[0024] In terms of excellent handleability, the PTFE granulated powder of the present disclosure preferably has an average aspect ratio of 1.25 or less, more preferably 1.20 or less, even more preferably 1.15 or less, even more preferably 1.10 or less, particularly preferably 1.05 or less, and may be 1.00 or more. The average aspect ratio is determined by observing the PTFE granulated powder with a video microscope, processing the images of 50 or more randomly selected particles, and averaging the ratios of their major axis to their minor axis.

[0025] The PTFE granulated powder of the present disclosure preferably has a high-temperature volatile content of 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, and particularly preferably 0.010% by mass or less, in order to obtain a molded product with less coloration and more excellent crack resistance. Alternatively, the high-temperature volatile content 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. The high-temperature volatile content is calculated according to JIS K 6891 by measuring the mass of the PTFE granulated powder after heating it at 370°C for 2 hours and then using the following formula: High-temperature volatile content (mass%)=[(mass (g) of PTFE granulated powder before heating)−(mass (g) of PTFE granulated powder after heating)] / (mass (g) of PTFE granulated powder before heating)×100

[0026] The PTFE granulated powder of the present disclosure preferably has a tensile strength of 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.

[0027] The PTFE granulated powder of the present disclosure preferably has an elongation of 150% or more, more preferably 200% or more, even more preferably 250% or more, still more preferably 290% or more, particularly preferably 300% or more, and may have an elongation of 500% or less.

[0028] The tensile strength and elongation are measured by the following method: 5 g of PTFE granulated powder is filled into a 97 mm x 18 mm mold and subjected to a pressure of about 300 kg / cm ２Pressure is gradually applied until the temperature reaches a constant value, and this pressure is maintained for an additional 2 minutes to produce a preform. The preform is removed from the mold and placed in an electric furnace maintained at 370°C. After sintering for 5.5 hours, the preform is cooled at 50°C / hr to obtain a sintered body. Test specimens are punched out of the sintered body using a JIS dumbbell No. 3, and in accordance with JIS K 6891-58, they are stretched using an autograph with a total load of 500 kg at a tension rate of 200 mm / min to measure the stress at break and elongation (breaking elongation).

[0029] In terms of excellent handleability, the PTFE granulated powder of the present disclosure preferably has a fluidity of 0.5 times or more, more preferably 1.0 times or more, even more preferably 1.5 times or more, and may have a fluidity of 5 times or less. The fluidity is measured by the method described in the Examples below.

[0030] The PTFE in the PTFE granulated powder of the present disclosure may be a homopolymer of tetrafluoroethylene (TFE), or may be a modified PTFE containing polymerized units based on TFE (TFE units) and polymerized units based on a modified monomer copolymerizable with TFE (hereinafter also referred to as "modified monomer units"). The TFE homopolymer refers to one in which the content of modified monomer units relative to the total polymerized units is less than 0.0001% by mass. The modified PTFE may contain 99.0% by mass or more of TFE units and 1.0% by mass or less of modified monomer units. The modified PTFE may also consist solely of TFE units and modified monomer units.

[0031] The content of the modified monomer unit in the modified PTFE is preferably in the range of 0.0001 to 1.0% by mass relative to the total polymerized units. The lower limit of the content of the modified monomer unit is more preferably 0.001% by mass, even more 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 content of the modified monomer unit is preferably 0.80% by mass, more preferably 0.60% by mass, even more 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. In this specification, the modified monomer unit refers to a part of the molecular structure of PTFE that is derived from the modified monomer.

[0032] The content of each of the above-mentioned polymerized units can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and X-ray fluorescence analysis depending on the type of monomer.

[0033] The above-mentioned modified monomer is not particularly limited as long as it can be copolymerized with TFE, and for example, can be listed perfluoroolefin such as hexafluoropropylene (HFP); hydrogen-containing fluoroolefin such as trifluoroethylene, vinylidene fluoride (VDF); perhaloolefin such as chlorotrifluoroethylene (CTFE); perfluorovinyl ether; perfluoroallyl ether; (perfluoroalkyl) ethylene, ethylene etc. In addition, the modified monomer used can be one kind or multiple kinds.

[0034] The perfluorovinyl ether is not particularly limited, and examples thereof include perfluorovinyl ethers represented by the following general formula (A): CF ２ =CF-ORf １ (A) (wherein, Rf １ represents a perfluoroorganic group. ) and perfluorounsaturated compounds represented by the following formula: In this specification, the "perfluoroorganic group" refers to an organic group in which all hydrogen atoms bonded to carbon atoms are substituted with fluorine atoms. The perfluoroorganic group may have an ether oxygen.

[0035] The perfluorovinyl ether may be, for example, a compound represented by the general formula (A) in which Rf １ is 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 the perfluoroalkyl group in the PAVE include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group.

[0037] The perfluorovinyl ether further includes a compound represented by the general formula (A) below, wherein Rf １ is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, Rf １ is of the following formula:

[0038]

[0039] (wherein m represents 0 or an integer of 1 to 4), Rf １ is of the following formula:

[0040]

[0041] (wherein n represents an integer of 1 to 4).

[0042] The (perfluoroalkyl)ethylene [PFAE] is not particularly limited, and examples thereof include (perfluorobutyl)ethylene [PFBE] and (perfluorohexyl)ethylene.

[0043] Examples of perfluoroallyl ethers include those represented by the general formula (B): CF ２ =CF-CF ２ -ORf ２ (B) (wherein, Rf ２ represents a perfluoroorganic group.

[0044] Rf ２is preferably a perfluoroalkyl group having 1 to 10 carbon atoms or a perfluoroalkoxyalkyl group having 1 to 10 carbon atoms. ２ =CF-CF ２ -O-CF ３ , C.F. ２ =CF-CF ２ -O-C ２ F ５ , C.F. ２ =CF-CF ２ -O-C ３ F ７ , and CF ２ =CF-CF ２ -O-C ４ F ９ At least one selected from the group consisting of CF ２ =CF-CF ２ -O-C ２ F ５ , C.F. ２ =CF-CF ２ -O-C ３ F ７ , and CF ２ =CF-CF ２ -O-C ４ F ９ More preferably, at least one selected from the group consisting of CF ２ =CF-CF ２ -O-CF ２ CF ２ CF ３ is more preferred.

[0045] The modified monomer is preferably at least one selected 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 selected from the group consisting of CTFE, HFP, PMVE, and PPVE, even more preferably at least one selected from the group consisting of CTFE, HFP, and PPVE, and particularly preferably at least one selected from the group consisting of PPVE and HFP.

[0046] The PTFE may have a core-shell structure. Examples of PTFE having a core-shell structure include modified PTFE particles containing a core of high molecular weight PTFE and a shell of lower molecular weight PTFE or modified PTFE. Examples of such modified PTFE include the PTFE described in JP-A-2005-527652.

[0047] The PTFE preferably has non-melt secondary processability, which means that the melt flow rate cannot be measured at a temperature higher than the melting point in accordance with ASTM D-1238 and D-2116, in other words, that the PTFE does not easily flow even in the melting temperature range.

[0048] The PTFE may be obtained by suspension polymerization.

[0049] The PTFE granulated powder of the present disclosure may contain a filler within a range that does not impair the effects. The filler is preferably a white or transparent filler, which is less likely to discolor the molded product, and examples of the filler include glass fiber, titanium oxide powder, and boron nitride powder. Other examples of the filler include aromatic heat-resistant resin powders such as polyoxybenzoyl polyester.

[0050] The content of the filler is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less, based on the PTFE. In terms of reducing coloration of the molded product, a smaller amount of filler is preferable, and the PTFE granulated powder of the present disclosure more preferably does not contain a filler.

[0051] The PTFE granulated powder of the present disclosure can be produced by granulating PTFE powder obtained by suspension polymerization. When producing PTFE granulated powder containing a filler, a mixed powder of PTFE powder and a filler may be used instead of the PTFE powder.

[0052] Suspension polymerization can be carried out, for example, by charging a reactor with a monomer such as TFE, an aqueous medium, and other additives as necessary, stirring the contents of the reactor, maintaining the reactor at a predetermined polymerization temperature, and then adding a predetermined amount of polymerization initiator to initiate the polymerization reaction. After the start of the polymerization reaction, additional monomers such as TFE, polymerization initiators, chain transfer agents, etc. may be added depending on the purpose.

[0053] The resulting suspension polymerized particles are subjected to pulverization, drying, classification, etc. as required to obtain PTFE powder that is the target of granulation.

[0054] The granulation of PTFE powder is preferably dry granulation using a nonionic surfactant aqueous solution as the granulation binder, since this allows for the production of molded products with less coloration. One of the preferred embodiments of the present disclosure is that the granulation binder used in granulation is a nonionic surfactant aqueous solution. It is also preferable not to use an organic solvent in granulation.

[0055] Granulation can be carried out, for example, by wetting the PTFE powder with a nonionic surfactant aqueous solution, applying mechanical force, and then drying. In the present disclosure, wetting includes a state in which, for example, when the surfactant aqueous solution is added to the PTFE powder, the PTFE powder is wetted and does not separate from the surfactant aqueous solution.

[0056] The nonionic surfactant may be a hydrocarbon surfactant or a non-fluorine-containing surfactant.

[0057] Examples of the nonionic surfactant include polyoxyethylamine oxides, alkylamine oxides, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, glycerin esters, polyoxyethylene alkylamines, segmented polyalkylene glycols having a hydrophobic segment composed of a poly(oxyalkylene) unit having 3 to 4 carbon atoms and a hydrophilic segment composed of a poly(oxyethylene) unit, and derivatives thereof.

[0058] More specifically, examples of polyoxyethylamine oxides include dimethyloxyethylamine oxide.

[0059] Examples of alkylamine oxides include dimethylmyristylamine oxide, dimethyllaurylamine oxide, dimethyldecylamine oxide, and dimethyloleylamine oxide.

[0060] Examples of polyoxyethylene alkyl ethers include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, and polyoxyethylene behenyl ether.

[0061] Examples of polyoxyethylene alkylphenyl ethers include polyoxyethylene nonylphenyl ether and polyoxyethylene octylphenyl ether.

[0062] Examples of polyoxyethylene fatty acid esters include polyoxyethylene monolaurate, polyoxyethylene monooleate, and polyoxyethylene monostearate.

[0063] Examples of sorbitan fatty acid esters include sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, and sorbitan monooleate.

[0064] Examples of polyoxyethylene sorbitan fatty acid esters include polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, and polyoxyethylene sorbitan monostearate.

[0065] Examples of glycerin esters include glyceryl monomyristate, glyceryl monostearate, and glyceryl monooleate.

[0066] Examples of derivatives thereof include polyoxyethylene alkylphenyl-formaldehyde condensates, polyoxyethylene alkyl ether phosphates, and the like.

[0067] Examples of the segmented polyalkylene glycols having a hydrophobic segment and a hydrophilic segment include those represented by the following formula: ２ CH ２ ) ｑ -(A) ｐ - (CH ２ CH ２ O) ｑ -H (wherein A is -CH(CH ３ ) CH ２ O- or -CH(CH ３ ) CH ２ CH ２ O-, p is an integer of 5 to 200, and q is an integer of 2 to 400. In view of ease of adsorption to PTFE resin, it is preferable that p is 15 to 40 and q is 7 to 100.

[0068] Among these, polyoxyethylene alkyl ethers, segmented polyalkylene glycols, and alkylamine oxides are preferred, and polyoxyethylene alkyl ethers and segmented polyalkylene glycols are more preferred.

[0069] The concentration of the nonionic surfactant in the aqueous solution is preferably 0.50% by mass or more, more preferably 0.75% by mass or more, and even more preferably 1.00% by mass or more, and is 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.

[0070] The amount of the aqueous solution added is preferably 15% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more, relative to the PTFE powder, and is preferably 45% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less.

[0071] Wetting can be carried out in any suitable equipment such as a plow blender, Waring blender, paddle blender, ribbon blender, with or without high speed elements, or in a mechanical force application device (granulator) as described below.

[0072] The wet PTFE powder may be crushed to a desired particle size by known methods.

[0073] Methods of applying mechanical force include, for example, rolling and stirring. In this specification, rolling refers to the rotation and movement of PTFE particles while they rub against each other or while they are in contact with the wall surface inside the granulator. Examples of granulators used to roll and granulate PTFE powder include disk rotary granulators, V-type blenders, C-type blenders, inclined disk and side rotary granulators, etc. Furthermore, examples of stirring methods include methods using high-speed stirrers. Conditions such as the speed, time, and temperature of rolling and stirring may be set according to the desired physical properties (apparent density, flowability, etc.).

[0074] The drying of the wet powder subjected to mechanical force can be carried out using means 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, and is preferably 270°C or lower, more preferably 260°C or lower, and even more preferably 250°C or lower. If the drying temperature is too low, moisture and surfactants cannot be sufficiently removed, and if it is too high, some of the PTFE particles will melt, which may result in a decrease in tensile strength and elongation.

[0075] Before drying at the above temperature range, drying at a low temperature may 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 is preferably 180°C or lower, more preferably 150°C or lower.

[0076] The drying time is preferably 5 hours or more in total, more preferably 8 hours or more, more preferably 10 hours or more, and even more preferably 15 hours or more, in terms of being able to remove moisture and surfactant more efficiently, and is preferably 100 hours or less, more preferably 50 hours or less, and even more preferably 30 hours or less.

[0077] The air speed during drying is preferably 0.01 m / s or more, more preferably 0.03 m / s or more, even more preferably 0.05 m / s or more, and even more preferably 0.1 m / s or more, from the viewpoint of more efficiently removing moisture and surfactant, and is preferably 50 m / s or less, more preferably 30 m / s or less, and even more preferably 10 m / s or less, from the viewpoint of suppressing scattering of powder.

[0078] Drying can be carried out using an electric furnace or a steam furnace. For example, it can be carried out using an electric furnace such as a parallel-flow box-type electric furnace, a ventilated box-type electric furnace, a ventilated conveyor-type electric furnace, a band furnace, a radiant conveyor-type electric furnace, a fluidized-bed electric furnace, a vacuum electric furnace, an agitator-type electric furnace, an airflow-type electric furnace, or a hot-air circulation electric furnace, or a steam furnace corresponding to the above (an apparatus obtained by replacing the electric furnace in the apparatus name of each of the above electric furnaces with a steam furnace). In terms of being able to remove moisture and fluorine-containing compounds more efficiently, a parallel-flow box-type electric furnace, a ventilated box-type electric furnace, a ventilated conveyor-type electric furnace, a band furnace, a fluidized-bed electric furnace, a hot-air circulation electric furnace, or a steam furnace corresponding to the above (an apparatus obtained by replacing the electric furnace in the apparatus name of each of the above electric furnaces with a steam furnace) is preferred.

[0079] The drying is preferably performed by placing the wet PTFE powder in a container with breathable bottom and / or sides, as this allows for more efficient removal of moisture and surfactants. The container with breathable bottom and / or sides may be any container that can withstand the drying temperature, but is preferably made of metal such as stainless steel. The container with breathable bottom and / or sides is preferably a tray (bath) with breathable bottom and / or sides, and more preferably a tray with a mesh bottom and / or sides (mesh tray). The mesh is preferably either a woven mesh or a punched metal. The mesh opening is preferably 2000 μm or less (ASTM standard 10 mesh or more), more preferably 595 μm or less (30 mesh or more), even more preferably 297 μm or less (50 mesh or more), even more preferably 177 μm or less (80 mesh or more), particularly preferably 149 μm or less (100 mesh or more), and particularly preferably 74 μm or less (200 mesh or more). Furthermore, it is preferably 25 μm or more (500 mesh or less). When the mesh is a woven net, the weaving method may be, for example, plain weave, twill weave, plain dutch weave, or twill dutch weave. When the mesh is a punched metal, the opening rate is preferably 10% or more, more preferably 20% or more, and even more preferably 30% or more. Furthermore, it is preferably 95% or less.

[0080] The amount of the wet powder to be dried is set to 10 g / cm in order to more efficiently remove moisture and surfactant. ２ Preferably, it is 8 g / cm or less. ２ More preferably, it is 5 g / cm or less. ２ More preferably, it is 3 g / cm or less. ２ It is particularly preferable that the density is 0.01 g / cm or less. ２ It is preferable that the density is 0.05 g / cm or more. ２ More preferably, it is 0.1 g / cm or more. ２ More preferably, it is equal to or greater than this.

[0081] The obtained granulated powder may be classified by a known method such as air classification, etc. By classifying, fine particles with very small particle diameters and coarse particles with very large particle diameters can be removed, thereby obtaining a granulated powder having a desired average particle diameter or a desired particle size distribution.

[0082] The PTFE granulated powder of the present disclosure can be suitably used, for example, as a molding material in molding methods such as compression molding, ram extrusion molding, and isopressure compression molding.

[0083] Although the embodiments have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the claims.

[0084] The present disclosure will now be described in more detail with reference to examples, but the present disclosure is not limited to these examples.

[0085] Various physical properties were measured by the following methods.

[0086] <Moisture content> Approximately 20 g of PTFE granulated powder was heated at 150°C for 2 hours, and the mass was measured before and after, and calculated according to the following formula. Three samples were taken, and the mass was calculated for each sample, and the average value was calculated and used. Moisture content (mass %) = [(mass (g) of PTFE granulated powder before heating) - (mass (g) of PTFE granulated powder after heating)] / (mass (g) of PTFE granulated powder before heating) x 100

[0087] <Z value> 200 g of PTFE granulated powder was filled into a mold having a diameter of 50 mm, and the molding pressure was 300 kg / cm ２ The obtained preform (diameter: approximately 50 mm, thickness: 50 mm) was heat-treated at 370°C for 2 hours to obtain a molded article, which was then cut crosswise on a lathe at a position approximately 25 mm from the edge (center portion), and the Z value of the center of the cut-out portion was measured in accordance with the XYZ system Z value measurement method specified by the International Commission on Illumination.

[0088] <Average particle size> Standard sieves of 10, 20, 32, 48, 60, and 80 mesh (inch mesh) were stacked in order from top to bottom, and the PTFE granulated powder was placed on the 10-mesh sieve. The sieves were vibrated to allow successively finer PTFE granulated powder particles to fall downward, and the proportion of the PTFE granulated powder remaining on each sieve was determined in mass %, and then the cumulative percentage of the remaining proportion (vertical axis) was scaled against the mesh opening of each sieve (horizontal axis) on a logarithmic probability paper. These points were connected with a straight line, and the particle size on this line at which the proportion was 50 mass % was determined, and this value was defined as the average particle size.

[0089] <Apparent Density> Measured in accordance with JIS K 6891.

[0090] <Average Aspect Ratio> The PTFE granulated powder was observed under a video microscope, and images of 50 or more randomly selected particles were processed, and the average aspect ratio was determined from the ratio of the major axis to the minor axis.

[0091] <Tensile strength and elongation> 5 g of PTFE granulated powder was filled into a 97 mm x 18 mm mold, and the tensile strength and elongation were measured at a pressure of about 300 kg / cm ２ Pressure was gradually applied until the temperature reached 370°C, and the pressure was maintained for another 2 minutes to produce a preform. The preform was removed from the mold and placed in an electric furnace maintained at 370°C. After sintering for 5.5 hours, the preform was cooled at 50°C / hr to obtain a sintered body. Test specimens were punched out from the sintered body using a JIS dumbbell No. 3, and the specimens were subjected to tension at a tensile speed of 200 mm / min using an autograph with a total load of 500 kg in accordance with JIS K 6891-58, and the stress and elongation at break were measured.

[0092] <High-temperature volatile content> According to JIS K 6891, the mass of the PTFE granulated powder was measured after heating at 370°C for 2 hours, and the mass was calculated using the following formula: High-temperature volatile content (mass%) = [(mass (g) of PTFE granulated powder before heating) - (mass (g) of PTFE granulated powder after heating)] / (mass (g) of PTFE granulated powder before heating) x 100

[0093] <Flowability> Measurement was performed according to the method described in JP-A-3-259925. Specifically, the measurement device used consisted of upper and lower hoppers 31 and 32 supported on a support base 42 with their centerlines aligned, as shown in FIG. 1 (corresponding to FIG. 3 of JP-A-3-259925). The upper hopper 31 had 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 the inlet 33 to the outlet 34. The outlet 34 was provided with a partition plate 35, which allowed the powder inside to be appropriately retained or dropped. The lower hopper 32 had 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 the inlet 36 to the outlet 37. Similar to the upper hopper, a partition plate 38 was provided at the outlet 37. The distance between the upper and lower hoppers was adjusted so that the distance between the partition plates was 15 cm. In FIG. 1, reference numerals 39 and 40 denote outlet covers for the hoppers, respectively, and reference numeral 41 denotes a receiver for the dropped powder.

[0094] The flow rate is measured by leaving about 200 g of the powder to be measured in a room adjusted to 23.5 to 24.5°C for 4 hours or more, sieving it through a 10 mesh (openings 1680 microns (μm)), and then measuring it at the same temperature.

[0095] (I) First, put exactly one 30 cc cup of powder to be measured into the upper hopper 31, then immediately pull out the partition plate 35 and allow the powder to fall into the lower hopper. If the powder does not fall, poke it with a wire to make it fall. After the powder has completely fallen into the lower hopper 32, leave it for 15±2 seconds, then pull out the partition plate 38 of the lower hopper and observe whether the powder flows out of the outlet 37. If 99% by mass or more of the powder has flowed out within 8 seconds, it is judged to have fallen.

[0096] (II) Repeat the same measurement as above three times to see if it flows or not, and if it flows or not twice out of three times, judge the fluidity as "good", and if it does not flow even once, judge the fluidity as "poor". If it flows or not once out of three times, make the same measurement twice more, and if it flows or not both times, judge the fluidity of the powder as "good", otherwise judge the fluidity as "poor".

[0097] (III) For powders judged to have "good" fluidity in the above measurements, place two cups of powder of the same volume (30 cc) into the upper hopper and measure in the same manner as above. If the result is "good" fluidity, increase the number of cups of powder in succession until the result is "poor," up to a maximum of eight cups. For each measurement, powder that has flowed out of the lower hopper in the previous measurement may be reused.

[0098] (IV) In the above measurements, the more PTFE powder used, the less likely it is to flow off.

[0099] Therefore, the "fluidity" of the powder is determined by subtracting 1 from the number of cups when the fluidity is "poor."

[0100] <Coloration of molded article> Based on the Z value measured above, the coloration was evaluated according to the following criteria: ⊚: Z value was 95 or more; ◯: Z value was 90 or more but less than 95; ×: Z value was less than 90

[0101] <Crack Resistance> 200 g of PTFE granulated powder was filled into a mold having an outer diameter of 50 mm and an inner diameter of 20 mm, and the molding pressure was 300 kg / cm ２ The resulting preform (outer diameter: approximately 50 mm, inner diameter: 20 mm, thickness: 50 mm) was heated to 370°C, held at 370°C for 5.5 hours, and then cooled to 40°C at 50°C / hr. A 0.1 mm thick film was cut from the molded product on a lathe, and the number of cracks was visually confirmed and converted into the number of cracks per 100 g for evaluation. Crack resistance (cracks / 100 g) = (number of cracks in film (cracks)) / (film weight (g)) x 100

[0102] Example 1 2.0 kg of PTFE molding powder with an average particle size of 50 μm obtained by suspension polymerization was charged into a ribbon blender, and surfactant A (H-(OCH ２ CH ２ CH ２ ) ｎ -(OCH ２ CH ２ ) ｍ0.8 kg of an aqueous solution of 1,2-dimethyl-2,4-trimethylsilyl-1,2 ...

[0103] Examples 2 to 4 and Comparative Example 1 PTFE granulated powder was obtained in the same manner as in Example 1, except that the type of surfactant was changed as shown in Table 1.

[0104] Comparative Example 2 A PTFE granulated powder was obtained in the same manner as in Example 3, except that the drying conditions were changed as shown in Table 1.

[0105] Comparative Example 3 A PTFE granulated powder was obtained in the same manner as in Example 4, except that the drying conditions were changed as shown in Table 1.

[0106] Each of the PTFE granulated powders obtained above was evaluated by the above-mentioned method. The results are shown in Table 1.

[0107]

[0108] The abbreviations in the table are as follows: A: H-(OCH ２ CH ２ CH ２ ) ｎ -(OCH ２ CH ２ ) ｍ -OH B:C １２ H ２５ -O-(CH ２ CH ２ O) ９ -HC:C １２ H ２５ -O-(CH ２ CH ２ O) ９ -H (the alkyl group structure is different from that of surfactant B) D:C １２ H ２５ -N ＋ (CH ３ ) ２ -O － E:C１２ H ２５ -SO ３ Na

[0109] 31: Upper hopper 32: Lower hopper 33, 36: Inlet 34, 37: Outlet 35, 38: Partition plate 39, 40: Outlet cover 41: Receiver 42: Support stand

Claims

1. Polytetrafluoroethylene granulated powder having a moisture content of 0.020% by mass or less and a Z value of 90 or more.

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

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

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

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

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

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

8. A polytetrafluoroethylene granulated powder according to any one of claims 1 to 7, having a high-temperature volatile content of 0.050 mass% or less.

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

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