Fluororesin molded body and production method therefor

Abstract

Provided is a fluororesin molded body comprising a fluororesin composition that contains an inorganic filler, wherein: the fluororesin composition has, as a matrix, a fluororesin having a melt viscosity of not less than 1010 Pa·sec; the inorganic filler includes pitch-based carbon fibers and a particulate inorganic filler having a D50 particle size or an average particle size of 0.01-1 μm; and the pitch-based carbon fibers have a side-surface roughness of not more than 1.0×10-2 μm. Thus, it is possible to provide, for example, a fluororesin molded body in which a linear expansion coefficient with respect to a desired metal does not become excessively small but can remain within a prescribed range, which has toughness that makes cracking less likely to occur under a wide range of temperature conditions, and which has suitable strength against deformation during use.

Description

Fluororesin molded body and its manufacturing method

[0001] The present invention relates to a fluororesin molded article and a method for producing the same.

[0002] Labyrinth seals have traditionally been used as shaft seals for metal rotating shafts in various rotating equipment. A labyrinth seal is a type of sealing structure for fluids flowing axially through a gap between the outer circumferential surface of a rotating shaft and a stationary portion of a housing facing the outer circumferential surface. For example, by providing fins on the stationary portion, multiple uneven gaps are formed between the rotating shaft and the stationary portion, gradually reducing the leakage pressure and the amount of leakage at each stage. When the rotating shaft and the stationary portion constituting a labyrinth seal are both made of metal, contact between the two can cause seizure between the metals, damaging the rotating equipment. To avoid this, the stationary portion can be made of resin. Examples of such resins include fluororesins. Fluororesins have excellent properties, such as heat resistance, chemical resistance, non-stickiness, and sliding properties, and are widely used in various sealing and sliding materials. However, when fluororesin is used as a sealing material for the metal rotating shaft of a rotating device, the thermal expansion coefficient of fluororesin is higher than that of common metals such as aluminum and steel, which are commonly used for rotating shafts. As a result, the gap between the rotating shaft and the sealing material becomes larger as the temperature rises, and fluids may become more likely to leak through this gap.

[0003] Therefore, the applicant has decided to use a polymer having a melt viscosity of 10 １０ The fluororesin composition has a matrix of fluororesin having a viscosity of Pa sec or more, and contains 40% by volume or more and 70% by volume or less of a particulate inorganic filler that is not coated with a silane coating and has a D50 particle size of 0.01 to 1 μm. This composition has a linear expansion coefficient of 30 ppm (3.0 × 10) at 25°C to 200°C. －５ ) / K or less, and have a practically acceptable strength. It has also been proposed that the fluororesin composition may contain a predetermined amount of an adhesive fluorine-containing copolymer other than the pitch-based carbon fiber and the fluororesin that serves as the matrix.

[0004] Japanese Patent Application Laid-Open No. 2022-175901

[0005] However, the fluororesin molded article described in Patent Document 1 is prone to cracking when used as, for example, a shaft seal, and may have an excessively small linear expansion coefficient relative to the metal used in the shaft seal.

[0006] Therefore, an object of the present invention is to provide a fluororesin molded article that can be adjusted to a predetermined range of linear expansion coefficient relative to a desired metal without being too small, has toughness that makes it less likely to crack under a wide range of temperature conditions, and has appropriate strength against deformation during use.Another object of the present invention is to provide a method for easily producing such a fluororesin molded article.

[0007] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, they have found that by using a predetermined fluororesin as a matrix resin, employing a particulate inorganic filler with a predetermined particle size and a predetermined pitch-based carbon fiber, and employing a predetermined manufacturing method, it is possible to easily obtain a fluororesin molded article that, for example, has a linear expansion coefficient relative to a desired metal that is not too small but within a predetermined range, has toughness that makes it less likely to crack under a wide range of temperature conditions, and is strong enough to withstand deformation during use. The gist of the present invention is as follows.

[0008] A first aspect of the present invention is a fluororesin molded article made of a fluororesin composition containing an inorganic filler, wherein the fluororesin composition has a melt viscosity of 10 １０ The matrix is ​​a fluororesin having a viscosity of Pa sec or more, the inorganic filler includes pitch-based carbon fiber and a particulate inorganic filler having a D50 particle size or an average particle size of 0.01 to 1 μm, and the pitch-based carbon fiber has a surface roughness of 1.0 × 10 －２ The present invention relates to a fluororesin molded article having a particle size of 1 μm or less.

[0009] In an embodiment of the present invention, the fluororesin may be polytetrafluoroethylene.

[0010] In an embodiment of the present invention, the pitch-based carbon fiber may have a crystallinity of 40% or more.

[0011] In an embodiment of the present invention, the pitch-based carbon fiber may be contained in an amount of 10% by volume or more and 30% by volume or less based on the entire fluororesin composition.

[0012] In an embodiment of the present invention, the particulate inorganic filler may not be coated with a silane coating, and may be contained in an amount of 40% by volume or more and 70% by volume or less based on the entire fluororesin composition.

[0013] In an embodiment of the present invention, the particulate inorganic filler may comprise fused silica.

[0014] In an embodiment of the present invention, the linear expansion coefficient of the fluororesin molded body at 25°C to 90°C is 1.3 × 10 －５ ~4.5 x 10 －５ / K may also be used.

[0015] A second aspect of the present invention relates to a method for producing a fluororesin molded article according to the first aspect of the present invention, which comprises hot-press molding in which the fluororesin composition is pressurized in a molten state and cooled and solidified under pressure.

[0016] In the first aspect of the present invention, the configurations of the above-described embodiments can be combined in any manner, and the same applies to the second aspect of the present invention.

[0017] According to the present invention, it is possible to provide a fluororesin molded article that, for example, can have a linear expansion coefficient relative to a desired metal that is not too small and that is within a predetermined range, has toughness that makes it less likely to crack under a wide range of temperature conditions, and has appropriate strength against deformation during use. It is also possible to provide a manufacturing method that can easily produce such a fluororesin molded article. It is also possible to provide a manufacturing method that can easily produce such a fluororesin molded article.

[0018] 1(a) and 1(b) are scanning electron microscope images of pitch-based carbon fiber A used in Example 1, where (a) is an example of a scanning electron microscope image, and (b) is an example of a schematic illustration of the arrangement of the baseline set when measuring and calculating the surface roughness of pitch-based carbon fiber A in FIG. 1(a). 1(a) is a scanning electron microscope image of pitch-based carbon fiber B used in Example 2, where (a) is an example of a scanning electron microscope image, and (b) is an example of a schematic illustration of the arrangement of the baseline set when measuring and calculating the surface roughness of pitch-based carbon fiber B in FIG. 2(a). 1(b) is a scanning electron microscope image of pitch-based carbon fiber C used in Comparative Examples 1 and 2, where (a) is an example of a scanning electron microscope image, and (b) is an example of a schematic illustration of the arrangement of the baseline set when measuring and calculating the surface roughness of pitch-based carbon fiber C in FIG. 3(a).

[0019] The fluororesin molded article according to the embodiment of the present invention is made of a fluororesin composition containing an inorganic filler. １０ The matrix is ​​a fluororesin having a viscosity of Pa·sec or more, and the inorganic filler includes pitch-based carbon fiber and a particulate inorganic filler having a D50 particle size or an average particle size of 0.01 to 1 μm. The pitch-based carbon fiber has a surface roughness of 1.0×10 －２ The thickness is less than μm.

[0020] By using a particulate inorganic filler having a predetermined fine particle diameter, １０ Even when a fluororesin with a high melt viscosity of Pa·sec or more is used, the contact area between the fluororesin and the particulate inorganic filler in the fluororesin molded product increases, and the physical constraint of the fluororesin during thermal expansion increases, making it possible to reduce the coefficient of linear expansion. Furthermore, by using pitch-based carbon fibers with a surface roughness of a predetermined value or less in combination with the carbon fibers that have a low constraint force at the interface with the fluororesin, it is thought that it is possible to mitigate the effect of the particulate inorganic filler in reducing the coefficient of linear expansion and to impart to the fluororesin molded product toughness that makes it less likely to crack under a wide range of temperature conditions and appropriate strength against deformation during use.

[0021] The fluororesin that constitutes the matrix has a melt viscosity of 10 １０A fluororesin having a viscosity of Pa·sec or higher is used. Examples of such fluororesins include polytetrafluoroethylene (PTFE), and PTFE is particularly preferred because it generally has excellent sliding properties, chemical resistance, and the like, and does not seize even when in contact at high speed. Because PTFE has these properties, it is suitable, for example, as a constituent material for sealing members of metal rotating shafts of rotating equipment. It is particularly suitable as a matrix resin material for labyrinth seals of metal rotating shafts. PTFE obtained by known manufacturing methods can be used, and examples include fine powder (emulsion polymerization product) produced by emulsion polymerization and molding powder (suspension polymerization product) produced by suspension polymerization.

[0022] Commercially available PTFE can be used, such as Teflon (registered trademark) 6-J, 6C-J, 62-J, 640-J, and 641-J manufactured by Mitsui-Chemours Fluoroproducts Co., Ltd., and Polyflon PTFE F series (F-104, F-204, F205, F-208, F-308, and the like) manufactured by Daikin Industries, Ltd.

[0023] Melt viscosity is 10 １０ The content of the fluororesin having a viscosity of Pa·sec or more in the entire fluororesin composition can be, for example, 10 to 50% by volume, taking into account other components. By setting the content of the fluororesin within this range, a fluororesin composition molded article having better strength and a lower linear expansion coefficient can be obtained. The lower limit is preferably 15% by volume or more, more preferably 20% by volume or more, and even more preferably 25% by volume or more. The upper limit is preferably 45% by volume or less, more preferably 40% by volume or less. Here, the volume percentage used as the content of the components contained in the fluororesin composition can be calculated, for example, from the density of the components used and the amounts added.

[0024] The melt viscosity of the fluororesin constituting the matrix can be measured, for example, in accordance with ASTM D 1238 using a flow tester (manufactured by Shimadzu Corporation).

[0025] The inorganic filler includes a particulate inorganic filler having a D50 particle size or average particle size of 0.01 to 1 μm. The particulate inorganic filler refers to a non-fibrous inorganic filler. Examples of particulate inorganic fillers include silica, graphite, mica, talc, glass spheres, metal particles, and ceramic spheres. Among these, silica and mica are preferred, and silica is preferred from the viewpoints of reducing the linear expansion coefficient of the molded body, uniform dispersibility in the fluororesin, and abrasion resistance. Silica may be crystalline or amorphous. However, amorphous silica is preferred, and fused silica is more preferred, because it is easy to obtain spherical particles, as described below, which makes it easier to suppress the anisotropy of thermal expansion of the molded body. The shape of the particulate inorganic filler is not particularly limited, but a spherical shape is preferred from the viewpoints of uniform dispersibility in the fluororesin matrix, high packing ability, and isotropy of thermal expansion of the molded body. A spherical shape close to a perfect sphere is preferred. As a standard for sphericity, for example, the sphericity described in International Publication No. 2020 / 145133 can be used. Specifically, a photograph is taken with a scanning electron microscope (SEM), and from the area and perimeter of the observed particle, (sphericity) = {4π × (area) ÷ (perimeter)} ２}. The closer the sphericity is to 1, the closer it is to a perfect sphere. The values ​​of area and perimeter used to calculate the sphericity can be average values ​​measured for 100 particles using, for example, an image processing device. The sphericity calculated in this manner is preferably 0.80 or more, more preferably 0.85 or more, even more preferably 0.90 or more, and most preferably 0.95 or more. As described above, spherical fused silica is particularly suitable as a particulate inorganic filler with a specified particle size. Such spherical fused silica can be commercially available.

[0026] Preferably, the particulate inorganic filler is not coated with a silane coating, as described in, for example, JP-A-63-259907. This can suppress the generation of voids due to gas originating from the silane coating during melt molding using a fluororesin composition. This allows the particulate inorganic filler to effectively exhibit its effect of lowering the linear expansion coefficient. As described above, the significance of not being coated with a silane coating is to prevent the generation of gas originating from the coating during melt molding. Therefore, it is preferable to use a filler that is not coated with a coating other than a silane coating, but that does not contain a component that causes such gas generation. Conversely, a coating may be formed as long as it does not contain a substance that causes gas generation. Note that there are cases in which particulate inorganic fillers that are coated with a silane coating are acceptable.

[0027] The particle diameter of the particulate inorganic filler may be any particle diameter as long as the D50 particle diameter (median diameter) or average particle diameter is within the aforementioned range, preferably 0.3 to 0.9 μm. The content of such particulate inorganic filler may be any particle diameter as long as it is within the range described below relative to the entire fluororesin composition. The D50 particle diameter of the particulate inorganic filler can be measured, for example, by a laser diffraction / scattering method. Specifically, the particle diameter at which the cumulative volume is 50% as measured using a laser diffraction / scattering particle size distribution analyzer (Horiba, Ltd., Partial LA-960V2) can be used. The average particle diameter of the particulate inorganic filler can be measured using a laser diffraction / scattering particle size distribution analyzer or a dynamic light scattering particle size distribution analyzer. Specifically, it can be determined by the cumulant method using a dynamic light scattering particle size distribution analyzer (Otsuka Electronics Co., Ltd., Particle Size Analyzer FPAR-1000).

[0028] When silica is used as the particulate inorganic filler, commercially available silica can be used, for example, AEROSIL R972, AEROSIL R104, AEROSIL R202, AEROSIL 805, AEROSIL R812, AEROSIL RX200, AEROSIL R9200, AEROSIL 200, and AEROSIL R7200 (all trade names, manufactured by Nippon Aerosil Co., Ltd.), and the Reolosil (registered trademark) series. Examples of suitable silicas include MT-10, MT-10C, DM-10, DM-10C, DM-20S, DM-30, DM-30S, KS-20SC, HG-09, HM-20L, HM-30S, ZD-30ST, PM-09, PM-20, PM-20L, X-20, and X-30 (amorphous fumed silica, manufactured by Tokuyama Corporation), CMC-12, VX-S, and VX-SR (all of which are trade names of crystalline silica, manufactured by Tatsumori Co., Ltd.), SFP-30M, SFP-20M, SFP-30MHE, and SFP-130MC (manufactured by Denka Company Limited), and the EXCELICA (registered trademark) series (trade names of fused silica, manufactured by Tokuyama Corporation).

[0029] The inorganic filler includes pitch-based carbon fiber. The surface roughness of the side surface of the pitch-based carbon fiber is 1.0 × 10 －２

[0013] The average particle size of the pitch-based carbon fiber is 1 μm or less. Thus, pitch-based carbon fibers having a smooth surface with a surface roughness of a predetermined value or less have fewer irregularities on the fiber surface, and the height of the protrusions is low. Therefore, the physical restraint at the interface with the predetermined fluororesin matrix of the molded article is lower than that of pitch-based carbon fibers having a surface roughness greater than the predetermined value. Therefore, it is believed that the effect of lowering the linear expansion coefficient of the molded article is smaller than that of the particulate inorganic filler described above. Furthermore, because pitch-based carbon fibers are fibrous, they have the function of improving the toughness of the molded article. Since pitch-based carbon fibers having such a smooth surface have low restraint on the fluororesin matrix and can improve the toughness of the molded article, it is believed that by using them in combination with the particulate inorganic filler described above, the effect of lowering the linear expansion coefficient of the molded article due to the particulate inorganic filler can be appropriately suppressed, making it possible to adjust the linear expansion coefficient of the molded article to a predetermined range and improving the toughness of the molded article.

[0030] Here, the surface roughness of the side surface of pitch-based carbon fiber can be measured and calculated by the method described in the Examples section below. The outline is as follows: Using a scanning electron microscope image (SEM image) taken so that the longitudinal surface of the pitch-based carbon fiber, i.e., the side surface, is viewed from the front, a straight baseline is set along the ridgeline of the fiber in the SEM image (the boundary between the fiber and its outer surface) (see, for example, Figure 1(b)), and the total area of ​​the portion (protrusion) existing outside the fiber relative to the baseline is calculated. The total area divided by the measured length is used as the "surface roughness." The total area and measured length of the protrusions can be calculated using image analysis software.

[0031] The crystallinity of the pitch-based carbon fiber is preferably 40% or more, from the viewpoint of more appropriately suppressing the decrease in the linear expansion coefficient of the molded body. The crystallinity can be measured and calculated using an X-ray diffractometer as described in the Examples section below.

[0032] The size of the predetermined pitch-based carbon fiber is not particularly limited, but from the viewpoint of uniform dispersion, short fibers having an average fiber length of 0.01 to 0.3 mm and an average fiber diameter of 5 to 20 μm are preferred.

[0033] The specific gravity (g / cm) of a given pitch-based carbon fiber ３ ) is usually 1.6 to 2.2, but from the viewpoint of dispersibility in a predetermined fluororesin, it is more preferably 1.8 or more, and even more preferably 2.0 or more.

[0034] Examples of the predetermined pitch-based carbon fiber include those obtained by spinning petroleum or coal pitch and then treating it in a calcination furnace, and those obtained by spinning optically anisotropic pitch and then treating it in a calcination furnace.

[0035] The predetermined pitch-based carbon fiber may be commercially available, for example, KUREKA CHOP M-101S, M-101F, M-101T, M-104T, M-107T, M-201S, and M-201F (manufactured by Kureha Corporation) under the trade name "KUREKA," ​​DIALEAD under the trade name manufactured by Mitsubishi Chemical Corporation, and GRANOC series, ZY-300, and XN-100 manufactured by Nippon Graphite Fiber Co., Ltd.

[0036] From the viewpoint of improving the strength of the molded body and the sliding properties, the inorganic filler may contain a fibrous inorganic filler other than the aforementioned specified pitch-based carbon fiber. Examples of the fibrous inorganic filler include the aforementioned specified pitch-based carbon fiber, glass fiber, metal fiber, whisker, etc.

[0037] From the viewpoint of uniform dispersion in the fluororesin matrix, the inorganic filler preferably has a specific gravity close to that of the fluororesin matrix. That is, the specific gravities of the particulate inorganic filler and fibrous inorganic filler (A) are preferably close to that of the fluororesin (B), and the ratio of specific gravities (A / B) is preferably 0.7 to 1.5.

[0038] The content of the particulate inorganic filler is preferably 40% by volume or more and 70% by volume or less relative to the entire fluororesin composition. From the viewpoints of the linear expansion coefficient, toughness, and strength of the molded body, the content of the specified pitch-based carbon fiber is preferably 10% by volume or more and 30% by volume or less relative to the entire fluororesin composition. Furthermore, the content of the inorganic filler is preferably 80% by volume or less relative to the entire fluororesin composition. In other words, the total of the particulate inorganic filler, the specified pitch-based carbon fiber, and the optional fibrous inorganic filler other than the specified pitch-based carbon fiber is preferably 80% by volume or less. From the viewpoints of the linear expansion coefficient, toughness, and strength of the molded body, the content of the inorganic filler is preferably 50% by volume or more.

[0039] In addition to the above-described components, the fluororesin composition may contain other additives, such as colorants. The content of such additives may be 5% by volume or less.

[0040] The fluororesin composition can be obtained by mixing the aforementioned components to a desired volumetric content and stirring the mixture with a stirrer such as a Henschel mixer. The properties of the fluororesin composition are determined appropriately depending on the properties of the components and the mixing conditions. However, a powder form is preferred from the viewpoint of ensuring a good mixing state of the components and uniform dispersion of the components during melt molding. When obtaining such a powdered fluororesin composition, it is preferred to use each component in powder form, and it is preferred to adjust the temperature during stirring so that the components remain in powder form. It is also preferred to use powders with similar specific gravities for the components. The content of each component can be calculated from the mass of each component added and the density of each component, as described above. The volumetric content of each component in the fluororesin composition is maintained in the molded product.

[0041] The fluororesin molded article according to the embodiment is, for example, a molded article obtained by molding using the above-described fluororesin composition. For example, by manufacturing the molded article by the method described below, it is possible to obtain a molded article having a linear expansion coefficient within a predetermined range. Furthermore, this molded article has toughness that makes it difficult to crack under a wide range of temperature conditions when used as a sealing material, sliding material, etc., and has adequate strength against deformation during use. Here, the linear expansion coefficient can be measured by a method conforming to JIS K7197. For example, when used as a shaft seal, from the viewpoint of preventing the linear expansion coefficient from being too small relative to the desired metal, the linear expansion coefficient at 25°C to 90°C should be 1.3 x 10. －５ ~4.5 x 10 －５ / K is preferred, and 1.3 × 10 －５ ~3.3 x 10 －５ / K is more preferable. Furthermore, as a criterion for toughness that is less likely to crack under a wide range of temperature conditions, for example, a nominal compressive fracture strain of 30% or more measured in accordance with JIS K7181 can be used. As a criterion for appropriate strength against deformation during use, it is preferable to use the strength in a range of deformation without fracture or yield as an index, and for example, a 5% compressive deformation strength of 15 to 30 MPa measured in accordance with JIS K7181 can be used.

[0042] A fluororesin molded article can be produced, for example, by hot-press molding, which is characterized by pressurizing the aforementioned fluororesin composition in a molten state and then cooling and solidifying it under pressure, as follows. First, the desired fluororesin composition is filled into, for example, a compression molding mold, and compressed at room temperature using a compression press at a predetermined pressure for a predetermined time, followed by depressurization (preforming step). In the free-sintering method, the preform is then released from the mold and placed in a heating furnace, but when the aforementioned fluororesin composition is used, it is difficult or impossible to maintain the shape. Therefore, by carrying out the following steps, it is possible to maintain the final shape and impart the desired linear expansion coefficient, toughness, and strength.

[0043] After the preforming step, the depressurized compression molding mold filled with the fluororesin composition is placed in a heating furnace heated to a temperature equal to or higher than the melting point of the fluororesin, and heated for a predetermined period of time to melt the fluororesin in the compression mold (in-mold heating and melting step). Any heating furnace can be used as long as it can heat the mold uniformly, and a hot air circulation furnace, for example, can be used.

[0044] Next, the compression molding mold is removed from the heating furnace while the fluororesin is still in a molten state, and immediately placed in a compression press. At room temperature, pressure is applied at a pressure equal to or greater than that used in the preforming process. After the mold temperature reaches 150 ° C or less, the pressure is released and the mold is released (pressure molding process). After cooling to room temperature, it can be machined into a desired shape as needed. In this way, the molten fluororesin is cooled and solidified under pressure, and the fluororesin sufficiently wets the inorganic filler, increasing the interfacial adhesion between the fluororesin particles and the inorganic filler. The synergistic effect of the properties of the particulate inorganic filler and the specified pitch-based carbon fiber is thought to produce a molded product that is tough enough to withstand a wide range of temperature conditions, has adequate strength against deformation during use, and can maintain its shape. When the fluororesin is PTFE, the desired molded product is thought to be obtained by the PTFE particles fusing together well.

[0045] The above-described fluororesin molded article has a low linear expansion coefficient within a predetermined range, thereby suppressing dimensional changes due to temperature changes such as heating. Therefore, it is applicable to various applications in which it is used in combination with components with a low linear expansion coefficient. In particular, since it contains a predetermined fluororesin as a matrix, it is suitable as a sealing member or sliding member for various rotating devices. It is particularly suitable as a sealing member for the metal rotating shaft of a rotating device, particularly as a sealing member constituting a labyrinth seal or an abradable seal. An abradable seal is a seal having a machinable sealing member in the stationary portion, and the rotation of fins formed on the rotating shaft abrades the machinable sealing member, thereby ensuring an optimal distance. A labyrinth seal does not use a machinable sealing member like an abradable seal. As described above, for example, fins are provided on the stationary portion, and multiple uneven gaps are formed between the rotating shaft and the stationary portion. The above-described labyrinth seal for a rotating device is particularly suitable as a sealing member for a turbo compressor.

[0046] Hereinafter, the embodiments of the present invention will be described in more detail based on examples.

[0047] Example 1 Preparation of Fluororesin Composition PTFE (fine) (manufactured by Mitsui Chemours Fluoroproducts Co., Ltd., Teflon (registered trademark) PTFE fine powder 641-J, emulsion polymerization product, average particle size: 400 μm, specific gravity: 2.17, melting point: 327° C., melt viscosity: 10 １２ A fluororesin composition was obtained by mixing 30% by volume of a fluororesin having a viscosity of 100 Pa·sec, 50% by volume of a particulate inorganic filler (UFP-35HH, fused silica, manufactured by Denka Company Limited, D50 particle size: 0.7 μm, average particle size: 0.06 to 0.5 μm, specific gravity: 2.2, shape: spherical (spherical)), and 20% by volume of pitch-based carbon fiber A (Kureka Chop, manufactured by Kureha Corporation, average fiber length: 0.15 mm, average fiber diameter: 14.5 μm, specific gravity: 1.60; for surface roughness and crystallinity, see Table 1). The mixture was stirred for 2 minutes in a small laboratory blender.

[0048] <Production of fluororesin molded article> Using the obtained fluororesin composition, a fluororesin molded article was obtained by hot press molding as follows. First, the obtained fluororesin composition was placed in a compression mold capable of forming a cylindrical cavity of φ40 mm, and preformed in a compression press at a molding pressure of 10 MPa and a mold temperature of 25 ° C. After that, the mold with the composition inside was heated in a heating furnace at 360 ° C. to melt the PTFE. Next, the mold was removed from the heating furnace and placed in a compression press so that the PTFE remained in a molten state. After natural cooling while pressurized at 30 MPa, the mold was demolded to obtain a fluororesin molded article of φ40 mm × 70 mm height. The obtained fluororesin molded article was used for the evaluation described below.

[0049] Example 2 A fluororesin composition was prepared and a fluororesin molded article was produced in the same manner as in Example 1, except that pitch-based carbon fiber A was changed to pitch-based carbon fiber B (GRANOC, manufactured by Nippon Graphite Fiber Co., Ltd., average fiber length 25 μm, average fiber diameter 10 μm, specific gravity: 2.2, surface roughness and crystallinity see Table 1). The obtained fluororesin molded article was used for the evaluations described below.

[0050] Examples 3 to 12, Comparative Examples 1 to 4 Fluororesin compositions were prepared and fluororesin molded articles were produced in the same manner as in Example 1, except that the component compositions were as shown in Table 2. The obtained fluororesin molded articles were used for the evaluations described below. In Examples 6 to 12, silica (0.5 μm) (manufactured by Denka Company Limited, SFP-20M, fused silica, D50: 0.4 μm, average particle size: 0.3 to 0.5 μm, specific gravity: 2.2, shape: spherical (spherical)) was used as the predetermined particulate inorganic filler. In Comparative Examples 1 and 2, pitch-based carbon fiber C (manufactured by Kureha Corporation, KUREKA CHOP, average fiber length 0.10 mm, average fiber diameter 14.5 μm, specific gravity: 1.60; see Table 1 for surface roughness and crystallinity) was used as the pitch-based carbon fiber. In Comparative Example 2, Fluon+ EA-2000 (powder, specific gravity: 2.13, melting point: 310°C, melt viscosity: 104 Pa sec, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (adhesive PFA) into which adhesive functional groups have been introduced) manufactured by AGC Inc. was used as the adhesive fluorine-containing copolymer.

[0051] (Evaluation 1) <Measurement of surface roughness of pitch-based carbon fibers> For pitch-based carbon fibers A to C, SEM images were taken using a scanning electron microscope (Hitachi High-Technologies Corporation, S-3400N, acceleration voltage: 15 kV) so that the longitudinal surfaces, i.e., side surfaces, of pitch-based carbon fibers A to C were viewed from the front, to obtain secondary electron images (see, for example, Figures 1(a), 2(a), and 3(a)). Using the obtained images, surface roughness was calculated using an image processing device (Nireco Corporation, Luzex AP). First, in the obtained images, a straight baseline was set along the ridgeline of the fiber at the ridgeline portion (the boundary between the fiber and its outer surface) (see the dashed line in each of Figures 1 to 3(b)). The setting position of this baseline was determined by visually determining the convex portions of the carbon fiber surface by image analysis, and then visually determining a straight line that passed through the lowest part of the convex portion and was approximately parallel to the ridgeline of the carbon fiber. Next, the measurement range (inside the rectangular frame in each of (b) of Figures 1 to 3) was determined, and the total area of ​​each convex portion (see each of (b) of Figures 2 and 3), which is the portion that exists on the outer side of the fiber with respect to the base line, was calculated. Next, the total area was divided by the measured length in the longitudinal direction of the fiber along the ridge line (base line) to obtain a value.

[0052] <Measurement of Crystallinity of Pitch-Based Carbon Fiber> For pitch-based carbon fibers A to C, an X-ray diffraction test was performed using a high-speed X-ray diffractometer (XRD) (D8 DISCOVER, manufactured by Bruker), and the crystallinity was determined from the diffraction peak. The instrument conditions were as follows: Tube: Cu, Irradiation angle: 0.2°, Measurement range 2θ: 10° to 40°

[0053] (Evaluation 2) <Measurement of Linear Expansion Coefficient> The linear expansion coefficient was measured in accordance with JIS K 7197. First, test specimens measuring φ5×10 mm were prepared by machining from the fluororesin molded articles obtained in Examples 1 to 12 and Comparative Examples 1 to 4. Next, the average linear expansion coefficient of each test specimen was measured by increasing the temperature at a rate of 5°C / min in the temperature range of 25°C to 90°C using a thermomechanical measuring device (TMA / SS6100, manufactured by Hitachi High-Tech Science Corporation).

[0054] <Compression Strength Measurement> Compression properties were measured in accordance with JIS K 7181. First, test pieces measuring φ8 × 20 mm were prepared by machining from the fluororesin molded articles obtained in Examples 1 to 12 and Comparative Examples 1 to 4. Next, the compression strength of each of the obtained test pieces was measured at a test speed of 5 mm / min using an Autograph AG-X Plus manufactured by Shimadzu Corporation, and the 5% compression deformation strength was determined.

[0055] <Measurement of Nominal Strain at Compression Failure> Compression characteristics were measured in accordance with JIS K7181 to determine the nominal strain at compression failure.

[0056] Table 1 shows the results of Evaluation 1 for pitch-based carbon fibers A to C, and Table 2 shows the component compositions and the results of Evaluation 2 for Examples 1 to 12 and Comparative Examples 1 to 4.

[0057]

[0058]

[0059] As shown in Table 2, in the case of fluororesin compositions (Examples 1 to 12) containing a specific inorganic filler and a fluororesin matrix having a predetermined melt viscosity, the fluororesin molded articles obtained by hot-press molding thereof have a linear expansion coefficient within a predetermined range, are tough enough to resist cracking under a wide range of temperature conditions, and have appropriate strength against deformation during use.

Claims

1. A fluororesin molded article made of a fluororesin composition containing an inorganic filler, wherein the fluororesin composition has a melt viscosity of 10 １０ The matrix is ​​a fluororesin having a viscosity of Pa sec or more, the inorganic filler includes pitch-based carbon fiber and a particulate inorganic filler having a D50 particle size or an average particle size of 0.01 to 1 μm, and the pitch-based carbon fiber has a surface roughness of 1.0 × 10 －２ Fluororesin molded article having a particle size of 1 μm or less.

2. The fluororesin molded article according to claim 1, wherein said fluororesin is polytetrafluoroethylene.

3. The fluororesin molded article according to claim 1 or 2, wherein the pitch-based carbon fiber has a crystallinity of 40% or more.

4. The fluororesin molded article according to claim 1 or 2, wherein the pitch-based carbon fiber is contained in an amount of 10% by volume to 30% by volume based on the total volume of the fluororesin composition.

5. A fluororesin molded article according to claim 1 or 2, wherein the particulate inorganic filler is not coated with a silane coating and is contained in an amount of 40% by volume or more and 70% by volume or less of the total fluororesin composition.

6. The fluororesin molded article according to claim 1 or 2, wherein the particulate inorganic filler contains fused silica.

7. The linear expansion coefficient of the fluororesin molded article at 25°C to 90°C is 1.3 x 10 －５ ~4.5 x 10 －５ 3. The fluororesin molded article according to claim 1, wherein the fluororesin moulded article has a viscosity of 1000 MPa or less.

8. The method for producing a fluororesin molded article according to claim 1 or 2, wherein the fluororesin composition is pressurized in a molten state and then cooled and solidified under pressure by hot press molding.

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