WO2013084760A1 - フッ素樹脂繊維を含んでなるフッ素樹脂系シートおよびその製造方法 - Google Patents
フッ素樹脂繊維を含んでなるフッ素樹脂系シートおよびその製造方法 Download PDFInfo
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- WO2013084760A1 WO2013084760A1 PCT/JP2012/080674 JP2012080674W WO2013084760A1 WO 2013084760 A1 WO2013084760 A1 WO 2013084760A1 JP 2012080674 W JP2012080674 W JP 2012080674W WO 2013084760 A1 WO2013084760 A1 WO 2013084760A1
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- D—TEXTILES; PAPER
- D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
- D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
- D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
- D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
- D04H1/42—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties characterised by the use of certain kinds of fibres insofar as this use has no preponderant influence on the consolidation of the fleece
- D04H1/4326—Condensation or reaction polymers
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- D—TEXTILES; PAPER
- D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
- D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
- D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
- D04H1/70—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres
- D04H1/72—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres the fibres being randomly arranged
- D04H1/728—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres the fibres being randomly arranged by electro-spinning
Definitions
- the present invention uses a fiber made of only polytetrafluoroethylene [PTFE] or a fiber containing PTFE and a fluororesin other than PTFE (both are collectively referred to as “fluororesin fiber”).
- PTFE polytetrafluoroethylene
- fluororesin fiber a fiber made of only polytetrafluoroethylene [PTFE] or a fiber containing PTFE and a fluororesin other than PTFE (both are collectively referred to as “fluororesin fiber”).
- PTFE has excellent chemical resistance, heat resistance, electrical insulation, and has characteristics such as self-lubrication and non-adhesiveness, so it is widely used not only in the industrial field but also in the field of daily life. Has been.
- these characteristics indicate the difficulty in processing PTFE. That is, PTFE is classified as a thermoplastic resin, but unlike general plastics such as polyethylene, vinyl chloride resin, etc., it does not exhibit fluidity even when heated to 327 ° C. or higher, which becomes an amorphous state. Screw extrusion, injection molding, rolling molding, etc. in a heated state cannot be applied.
- the processing method of PTFE developed so far is similar to the method of powder metallurgy, for example, a method in which PTFE is press-molded near room temperature and heated to 327 ° C or higher; this (sintered body) ) Is further formed by mechanical cutting, heat coining, etc .; a liquid lubricant is mixed with PTFE powder, this is extruded with a ram type extruder, dried and sintered to produce pipes and tubes;
- Examples of the method of covering the wire include a method of coating the base material by coating, dipping, etc. using an aqueous suspension of PTFE resin, followed by sintering.
- Patent Document 1 discloses a method for producing nanofibers as shown in FIG. 1 by spinning from a PTFE-dispersed aqueous solution containing polyethylene oxide [PEO] by electrospinning and then removing PEO simultaneously with firing.
- the fiber diameter, basis weight, and the like can be adjusted according to the solution conditions and spinning conditions, and the fibers can be oriented by using a special device.
- the composite of the materials is easy, and nanofibers having a uniform fiber diameter with a high aspect ratio can be manufactured.
- the minimum fiber diameter is about 500 nm.
- Patent Document 2 discloses a nonwoven fabric in which ultrafine fibers having a fiber diameter of 0.001 to 1 ⁇ m formed by an electrospinning method and ultrafine fibers having a fiber diameter of 2 to 25 ⁇ m formed by a melt blow method are mixed, Polyvinylidene fluoride [PVDF] is cited as a fluorine-based resin constituting the ultrafine fiber formed by the electrostatic spinning method (paragraph [0019]).
- PVDF Polyvinylidene fluoride
- Patent Document 3 discloses an apparatus capable of preventing interference between adjacent nozzles and simultaneously depositing different polymer solutions in a multi-nozzle type electrodeposition method (electrospinning method). Has been. The polymer web produced by such an apparatus is not connected even if the fibers are entangled with each other.
- Patent Document 4 a polymer substance is dissolved in a solvent in one rotating container in which a plurality of types of small holes having different diameters are formed on the outer peripheral portion or in a plurality of rotating containers that are concentrically integrated. Supplying the polymer solution, rotating the rotating container and charging the polymer solution flowing out of the small hole with electric charge, and stretching the polymer solution flowing out of the small hole by electrostatic explosion caused by centrifugal force and evaporation of the solvent And a process for producing nanofibers made of a polymer substance.
- a polymer web formed by mixing or laminating a plurality of types of nanofibers having different physical properties can be produced, but there is no aspect in which fibers having different physical properties are connected.
- an unsintered tetrafluoroethylene resin that is, PTFE
- a liquid lubricant is formed by extrusion and / or rolling, and then stretched in at least one direction in an unsintered state.
- a method for producing a porous structure (FIG. 2) that is heated to about 327 ° C. or higher in a state is disclosed.
- Unsintered tetrafluoroethylene resin becomes a fine fibrous structure when subjected to a shearing force, such as when it is extruded from a die in the extrusion process, when it is rolled with a roll, or when it is vigorously stirred. Tend.
- Resins containing liquid lubricants are more easily fiberized (page 2, right column, lines 9-13).
- nodes of thick blocks also referred to as “nodules”
- fibrils of thin fibers are mixed, the fiber diameter of the nodes is several ⁇ m to 1 ⁇ m, and the fiber diameter of the fibrils is about 100 nm. is there.
- fiber orientation is possible by a stretching treatment and a heat treatment.
- Patent Document 6 discloses a polytetrafluoroethylene porous body having a fine fibrous structure composed of fibers and nodules connected to each other by the fibers, and this PTFE porous body has a three-dimensional network shape. There are short portions of continuous fibers.
- a liquid lubricant is mixed into a PTFE green powder, extruded, rolled, and formed into a desired shape.
- the liquid lubricant may or may not be removed from the obtained molded body, and when it is stretched at least in a uniaxial direction, a PTFE porous material having a fine fibrous structure composed of fibers and knots connected to each other by the fibers The body is formed.
- a fiber assembly is formed by an electrospinning method from a spinning solution containing polyvinylidene fluoride [PVDF], a polyvinylidene fluoride-hexafluoropropylene copolymer (paragraph [0016]), and the like.
- PVDF polyvinylidene fluoride
- paragraph [0016] polyvinylidene fluoride-hexafluoropropylene copolymer
- Patent Document 8 discloses a method for producing a continuous filament composed of nanofibers preferably having a fiber diameter of 500 nm or less using an electrospinning method in a continuous process.
- Specific polymers constituting such nanofibers are exemplified by poly ( ⁇ -caprolacton) polymer (Example 1), polyurethane resin (Example 2), and nylon 6-resin (Example 3). Has been.
- a continuous filament composed of nanofibers having a fiber diameter of 500 nm or less is preferably produced by a continuous process from a polymer spinning solution containing nylon resin (Example 1) using an electrospinning method. A method is disclosed.
- Patent Document 10 discloses that a wholly aromatic polyamide fiber is formed at the intersection of fibers by irradiating a wet fiber web composed of a fibril-containing wholly aromatic polyamide fiber and a polyester resin fiber with no infrared pressure.
- a wet nonwoven fabric is disclosed which is fixed by a polyester resin solidified in a non-fiber state. Further, it is described that PTFE can be used in place of the wholly aromatic polyamide fiber (paragraph [0032]), but is not specifically shown in Examples or the like.
- the sheet-like filter that combines the excellent properties of PTFE (water repellency, heat resistance, chemical resistance, sound permeability, etc.) with a high specific surface area. There is room for further improvement.
- An object of the present invention is to provide a fluororesin-based sheet comprising PTFE fibers, in which filter performance and the like are remarkably improved as compared with conventional ones.
- the inventors of the present invention after pressing the fluororesin fiber sheet made of PTFE fiber obtained by the method described in Patent Document 1 in a 360 ° C. electric furnace while generating stress in the press vertical direction The surface was observed with a scanning electron microscope [SEM] at room temperature and normal pressure after being taken out from the electric furnace.
- SEM scanning electron microscope
- the fluororesin fiber sheet (a0) subjected to heating / pressurizing treatment was used.
- the thick fibers (main fibers) that were the original PTFE fibers that existed in the inside
- thin fibers (subfibers) that were not found in the original fluororesin fiber sheet (a0) were heated and pressurized.
- the fluororesin-based sheet of the present invention comprises a main fiber and a sub fiber having a fiber diameter smaller than the fiber diameter of the main fiber, and the sub fiber crosslinks within the same main fiber and / or between different main fibers.
- a nodule is not formed at the cross-linking point, and the main fiber and the sub fiber are made of a fluororesin fiber containing polytetrafluoroethylene [PTFE].
- the fiber diameter of the main fiber is 100 nm or more and 50 ⁇ m or less, and the fiber diameter of the sub fiber is preferably 10 nm or more and less than 1 ⁇ m from the viewpoint of strength, air permeability, filter performance, and the like.
- the fluororesin fiber is composed only of PTFE in terms of characteristics (water repellency, heat resistance, chemical resistance, sound permeability, etc.) and performance (filter performance) of the obtained fluororesin sheet.
- the fluororesin fiber is not only PTFE but also tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer [PFA], tetrafluoroethylene-hexafluoropropylene copolymer [FEP], tetrafluoroethylene-hexa.
- the method for producing a fluororesin-based sheet of the present invention is characterized in that the subfibers are generated by generating stress in at least two directions in a heated state with respect to a fluororesin fiber sheet made of fluororesin fibers. To do.
- the temperature under the above heating is usually 50 ° C. or more and 400 ° C. or less, preferably 180 ° C. or more and 400 ° C.
- the above-mentioned stress is a compression stress and a shear stress of 0.05 kg / cm 2 or more and 10 kg / cm 2 or less, and the secondary fibers having a desired thickness are uniformly spread between the main fibers, and the main fibers Nodule is not generated at the cross-linking (joining) site between the selenium and the secondary fiber, and the above properties and performance are excellent.
- the temperature under the above heating eg, in an electric furnace
- the temperature under the above heating is completely melted to change the fiber shape.
- conditions are preferred so as not lost, for example, usually 50 ° C. or higher 360 ° C. or less, preferably not more than 360 ° C. 0.99 ° C. or higher
- the stress is at 0.01 kg / cm 2 or more 20 kg / cm 2 or less of compressive stress and shear stress It is preferable from the viewpoint of fiber shape stability.
- the fluororesin-based sheet of the present invention contains PTFE alone (PTFE: 100% by weight) or at least PTFE as a fiber (PTFE content: usually 50% by weight or more and less than 100% by weight, preferably 80% by weight) (Below 100% by weight) Therefore, the PTFE exhibits various properties (water repellency, heat resistance, chemical resistance, sound permeability, etc.) that are potentially possessed, and at the same time, the secondary fiber is a nanofiber. The characteristic which it has can be exhibited. In particular, when the fiber diameter of the secondary fiber is around 100 nm, the filter performance is remarkably high.
- the main fiber and the sub-fiber are integrated, so that mainly the strength derived from the main fiber and the nanofiber characteristics derived from the sub-fiber can be achieved, and the fibers are separated from each other. Since it is difficult to occur, the composite stability is high.
- the fluororesin-based sheet of the present invention exhibits isotropic physical properties because subfibers are randomly generated between randomly arranged main fibers.
- seat which shows an anisotropic physical property value can also be manufactured by using the sheet
- the fiber diameter of the secondary fiber to be generated and the density of the secondary fiber are determined depending on the molten state of the resin constituting the fiber and the stress in two directions (that is, the sheet pressing direction and its perpendicular Direction). For example, the fiber diameter increases as the resin melt ratio increases, and the fiber density tends to increase as the stress increases.
- FIG. 1 shows an image obtained by enlarging the surface of the PTFE mat disclosed in Patent Document 1 to 1,000 times by SEM. According to FIG. 1, it can be seen that only fibers having a fiber diameter of 500 nm or more are observed.
- FIG. 2 shows an image obtained by enlarging the surface of the porous structure made of PTFE disclosed in Patent Document 5 to 1,000 times by SEM. According to FIG. 2, it can be seen that there are many nodules (nodes of thick chunks) and the direction of the nodules is constant.
- FIG. 3 shows an image magnified 5,000 times by SEM of the surface of the fluororesin-based sheet produced in Example 2. According to FIG. 3, it can be seen that a fluororesin-based sheet (a composite of a main fiber and a sub fiber having a fiber diameter smaller than that of the main fiber) in which the sub fiber is generated is obtained.
- the fluororesin-based sheet of the present invention is obtained through a specific process using fibers made only of PTFE (PTFE single fibers) or fibers containing PTFE and a fluororesin other than PTFE (fluororesin fibers).
- a sheet preferably a sheet obtained by the production method of the present invention, for example, as shown in an image magnified 5,000 times that in Example 2 in FIG.
- the sub-fibers have a fiber diameter smaller than the diameter, and the sub-fibers can also be expressed as “cross-link” (or “connect”) within the same main fiber and / or between different main fibers. This is a mode different from “entanglement”, and it can be said that a side chain is bridged over the main chain of the polymer.) However, a nodule is not formed at the cross-linking point.
- fluororesin fibers fibers made only of PTFE, or fibers comprising PTFE and a fluororesin other than PTFE are collectively referred to as “fluororesin fibers”, and a sheet using this fluororesin fiber by a conventionally known method is used. What is molded into a shape is called a “fluororesin fiber sheet”, and what is obtained through a specific process using this fluororesin fiber sheet is called a “fluororesin-based sheet” (that is, the fluororesin-based sheet of the present invention). .
- the fluororesin fiber sheet is also referred to as “fluororesin fiber sheet (a0)”, and is obtained through a specific process using this fluororesin fiber sheet (a0). This is also referred to as “fluororesin-based sheet (a1)”.
- the fluororesin fiber sheet is a fiber composed of PTFE and a fluororesin other than PTFE
- the fluororesin fiber sheet is also referred to as “fluororesin fiber sheet (b0)” and specified using this fluororesin fiber sheet (b0). What is obtained through this step is also referred to as “fluororesin-based sheet (b1)”.
- the fiber diameter of each of the main fiber and the secondary fiber is usually the main fiber, considering the strength, particle trapping performance, stability, etc. It is preferably 100 nm or more and 50 ⁇ m or less, and the secondary fiber is preferably 10 nm or more and less than 1 ⁇ m, more preferably the main fiber is 500 nm or more and 1 ⁇ m or less, the secondary fiber is 30 nm or more and 300 nm or less, and further preferably the secondary fiber is 30 nm. It is 100 nm or less.
- “fiber diameter” is all measured by a method of measuring using an image by SEM, and means an average value.
- this average value is obtained by randomly selecting a region for SEM observation with respect to the fluororesin-based sheet to be measured, and subjecting this region to SEM observation (magnification: 10,000 times). It is a value calculated based on the measurement results of these fluororesin fibers selected from fluororesin fibers.
- the fiber diameter of the secondary fiber is 300 nm or less, the air resistance is extremely reduced, the “slip flow effect” is exhibited, the specific surface area is extremely increased, and the supramolecular alignment effect is obtained. It is suitable when the fluororesin-based sheet of the present invention is used for applications such as filters.
- an SEM observation region is selected for the fluororesin-based sheet to be measured, and this region is subjected to SEM observation (magnification 5,000 times). It is calculated by calculating
- the above fibers include tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer [PFA] (for example, “Dyneon® PFA” (trade name) manufactured by Sumitomo 3M Limited) and “Fluon” manufactured by Asahi Glass Co., Ltd.
- PFA tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer
- PTFE When the fiber is composed of PTFE and the “other fluororesin” other than PTFE, PTFE is preferably contained in an amount of 50% by weight or more (however, the total of PTFE and the other fluororesin is 100% by weight). %). When the PTFE is less than 50% by weight, in the production method described later, the other fluororesin may be eluted in a heated state and cannot be molded as a sheet.
- the method for producing a fluororesin-based sheet of the present invention preferably includes the following steps (i) to (iv), and particularly includes the following step (iii).
- a fluororesin fiber (that is, the main fiber) is produced by an electrospinning method; As step (ii), this fluororesin fiber is formed into a sheet (that is, fluororesin fiber sheets (a0) and (b0) are produced); As step (iii), in a heated state (eg in an electric furnace), the sheet is subjected to stress in at least two directions (preferably compressive stress and shear stress perpendicular to the compressive stress); and step (iv) ), The fluororesin-based sheets (a1) and (b1) in which the auxiliary fibers are generated are produced by releasing the pressure after cooling under this pressure.
- a raw sheet made of main fibers and having no sub fibers is pressurized in a heating furnace (eg, an electric furnace), and stress is applied in at least two directions, so that the outer surface of each main fiber is applied.
- the resulting partial resin eg, resin constituting the main fiber such as PTFE
- the elastic restoring force of the main fiber contained in the sheet or the sheet As a result, the distance between the main fibers is widened, so that the natto yarns extend between the adjacent main fiber surfaces, so that the secondary fibers that connect the main fibers are generated and extended.
- the produced subfibers are also solidified, and as a result, subfibers thinner than the main fibers are formed so as to bridge the main fibers.
- auxiliary fibers thinner than the main fibers are further crosslinked so as to bridge between the main fibers and the auxiliary fibers and / or between the auxiliary fibers and the auxiliary fibers. Also good.
- an external force (external force) that acts on the fluororesin sheet is referred to as a “load”, and when a load acts on the fluororesin sheet, an internal force that resists the load and keeps balance inside the sheet. “Stress”. The stress is equal to the load and the direction is opposite.
- step (i) for example, the method described in Patent Document 1 (US Patent Publication No. 2010/0193999 A1) can be used.
- the temperature in the electric furnace for ensuring the heating conditions is usually 50 ° C. or more and 400 ° C., preferably 180 ° C. or more and 400 ° C. or less in the fluororesin fiber sheet (a0) made of PTFE single fiber. More preferably, it is 270 ° C. or higher and 380 ° C. or lower, and further preferably 320 ° C. or higher and 380 ° C. or lower.
- Compressive stress is usually 0.01 kg / cm 2 or more 10 kg / cm 2 or less, preferably 0.05 kg / cm 2 or more 1 kg / cm 2 or less, more preferably 0.05 kg / cm 2 or more 0.40 kg / cm 2 or less More preferably, it is 0.10 kg / cm 2 or more and 0.40 kg / cm 2 or less.
- the secondary fibers of the desired thickness are uniformly spread between the main fibers, and no nodules are generated at the cross-linking (joining) sites between the main fibers and the secondary fibers. It is preferable because of its excellent characteristics and performance.
- the temperature under the above heating is such that the thick fibers (main fibers) are on the surface. It is preferable that the fiber is melted only and completely melted to the inside thereof, and the fiber shape is not lost, for example, usually 50 ° C. or higher and 360 ° C. or lower, preferably 150 ° C. or higher and 360 ° C. or lower, and the compressive stress is 0.01 kg / cm 2 or more and 20 kg / cm 2 or less. It is preferable in terms of fiber shape stability that the temperature and stress are within the above ranges.
- step (iii) in order to generate stress in at least two directions, for example, the fluororesin fiber sheet is sandwiched between a pair of stainless steel plates and weighted, and at least one of the stainless steel plates is shifted horizontally and the rotational speed is different.
- seat between the rolls of a book, the aspect (iron system) to which a flat plate is moved horizontally while applying a weight, etc. are mentioned, this invention is not limited to these aspects.
- the mechanism by which the secondary fiber is generated by the production method of the present invention can be estimated as follows.
- Part 1 After the main fibers contact with each other in step (iii), when the main fibers are released from the load and separated from each other in step (iv), a resin (for example, PTFE) on the surface of some main fibers is natto yarn.
- the sub-fibers are generated by pulling and pulling the yarn so that the fiber stretches.
- the main fibers are preferably made into fine fibers by shearing force.
- PTFE is known to form fibrils by shearing force (for example, paragraph [0016] of Japanese Patent Application Laid-Open No. 2004-154652, etc.), and a weak shearing force acts in the release process of pressurization. Although it is not such a molded article, it is considered that fibrils (subfibers) were formed.
- the fluororesin-based sheet of the present invention is suitable for filter applications.
- Specific examples of the filter include an air filter and a vent filter.
- Example 1 A fluororesin fiber sheet made of PTFE fibers made by an existing electrospinning method and made of PTFE fibers with a length of 10 cm, a width of 10 cm, a thickness of 65.7 ⁇ m, a weight of 18.6 mg, and an average fiber diameter of 1 ⁇ m is sandwiched between a pair of stainless plates, and 6 kg by a mold.
- the mold lower part and the lower stainless plate are held in a fixed state so that shear stress is generated in the direction perpendicular to the compressive stress with respect to the fluororesin fiber sheet.
- Example 5 a fluororesin-based sheet was produced in the same manner as in Example 4 except that the temperature of the electric furnace was changed to 100 ° C., and the presence or absence of secondary fibers was confirmed. The results are shown in Table 1.
- Example 6 In Example 4, a fluororesin-based sheet was produced in the same manner as in Example 4 except that the temperature of the electric furnace was changed to 150 ° C., and the presence or absence of secondary fibers was confirmed. The results are shown in Table 1.
- Example 1 a fluororesin-based sheet was produced in the same manner as in Example 1 except that no load and shear stress were generated, and the presence or absence of secondary fibers was confirmed. The results are shown in Table 1.
- Example 3 a fluororesin-based sheet was produced in the same manner as in Example 3 except that no shear stress was generated, and the presence or absence of secondary fibers was confirmed. The results are shown in Table 1.
- Example 4 a fluororesin-based sheet was produced in the same manner as in Example 4 except that the temperature of the electric furnace was changed to 25 ° C., and the presence or absence of secondary fibers was confirmed. The results are shown in Table 1.
- the thickness of the fluororesin-based sheet was measured with a LIMETASIC VL-50 (manufactured by Mitutoyo Corporation) which is a micrometer.
- a dumbbell-shaped test piece having a center width of 5 mm was punched out using a micro dumbbell, and the width (using calipers) and thickness (using “LITEMATIC VL-50A” manufactured by Mitutoyo Corporation) were precisely weighed.
- the test piece was attached to a tensile tester so that the length between the grips was 25 mm, and was pulled at a crosshead speed of 20 mm / min, and the maximum stress was obtained from the maximum load when the test piece was broken.
- the bubble point pore diameter indicates the maximum pore diameter of the fluororesin-based sheet, and was calculated by a bubble point method (ASTM F316-86).
- Galwick (15.9 dyn / cm) was used as the immersion liquid.
- a fluororesin-based sheet that is well immersed in a liquid exhibits the same characteristics as a capillary filled with liquid, overcomes the surface tension of the liquid in the capillary, and measures the pressure that pushes the liquid out of the pore. It can be calculated.
- the bubble point pore diameter d [m] is calculated from the following bubble point formula.
- ⁇ 4 ⁇ cos ⁇ / ⁇ P
- ⁇ represents the contact angle between the fluororesin-based sheet and the liquid
- ⁇ [N / m] represents the surface tension of the liquid
- ⁇ P represents the bubble point pressure.
- Average flow diameter / average flow diameter pressure The average flow diameter was determined by the half dry method of ASTM E1294-89. For measurement, Galwick (15.9 dyn / cm) was used as the immersion liquid.
- the half-dry method is a half-slope curve (Half Dry Curve) of the fluororesin-based sheet (Wet Curve) in a well-immersed liquid and a dry sample (Dry Curve). ) At the intersection (mean flow diameter pressure), and substitute this into the bubble point formula to find the average flow diameter.
- the particle collection rate was measured in accordance with JIS B 9908 as the particle capture rate of the fluororesin-based sheet.
- the fluororesin-based sheet having a size of 100 mm ⁇ 100 mm obtained in Example 3 and Comparative Examples 1 and 2 was used, and atmospheric dust (with a particle diameter of 0.15 ⁇ m to 10 ⁇ m was used as measurement dust).
- the air flow rate was 14.8 cm / s.
- Example 1 to 3 the temperature in the electric furnace was set to 360 ° C., but it was confirmed that secondary fibers were generated even at 300 ° C. In Examples 1 to 3, the temperature at which stress was applied in two directions was set at 360 ° C., but it was confirmed that secondary fibers were also generated when stress was applied after cooling to 180 ° C.
- the fluororesin-based sheet of the present invention retains excellent water repellency, heat resistance, chemical resistance, sound permeability, etc. derived from PTFE, and has a remarkably large fiber specific surface area. Therefore, it is used for filters such as air filters. Is preferred.
Abstract
Description
本発明のフッ素樹脂系シートは、PTFEのみからなる繊維(PTFE単独繊維)、または、PTFEとPTFE以外のフッ素樹脂とを含んでなる繊維(フッ素樹脂繊維)を用いて、特定の工程を経て得られるシート(好ましくは本発明の製造方法により得られるシート)であって、例えば図3中、実施例2の5,000倍に拡大した画像に示すように、該繊維が、主繊維と主繊維の繊維径より小さい繊維径を有する副繊維とからなり、同じ主繊維内および/または異なる主繊維間を該副繊維が「架橋する」(あるいは「繋げる」とも表現でき、単純に「接触させる」や「絡める」とは異なる態様であって、高分子主鎖に側鎖が架渡したような状態とも言える。)が、その架橋点に結節が形成されていないことを特徴とする。
本発明のフッ素樹脂系シートの製造方法は、下記工程(i)~(iv)を含むことが好ましく、なかでも下記工程(iii)を含むことを特徴とする。
工程(ii)として、このフッ素樹脂繊維をシート状に成形(すなわちフッ素樹脂繊維シート(a0),(b0)を製造)し;
工程(iii)として、加熱された状態(例えば電気炉の中)で、このシートに少なくとも二方向の応力(好ましくは圧縮応力と、圧縮応力に垂直なせん断応力)を発生させ;および
工程(iv)として、この加圧下で冷却した後に加圧を開放することによって、上記副繊維が生成されたフッ素樹脂系シート(a1),(b1)が製造される。
本発明のフッ素樹脂系シートは、フィルタ用途に好適である。具体的なフィルタとしては、例えば、エアフィルタやベントフィルタなどが挙げられる。
既存の電界紡糸法により作製した、縦10cm、横10cm、厚さ65.7μm、重量18.6mg、平均繊維径1μmのPTFE繊維からなるフッ素樹脂繊維シートを、一対のステンレス板の間に挟み、金型により6kgを加重することによって、該フッ素樹脂繊維シートに0.06kg/cm2の圧縮応力を発生させながら360℃の電気炉の中で1時間保持した。
実施例1において、加重を20kg(=0.20kg/cm2の圧縮応力)に変更した以外は実施例1と同様にしてフッ素樹脂系シートを製造し、副繊維の発生有無を確認した。この結果を表1に示す。
実施例1において、加重を35kg(=0.35kg/cm2の圧縮応力)に変更した以外は実施例1と同様にしてフッ素樹脂系シートを製造し、副繊維の発生有無を確認した。この結果を表1に示す。
実施例1において、加重を50kg(=0.5kg/cm2の圧縮応力)、電気炉の温度を50℃に変更した以外は実施例1と同様にしてフッ素樹脂系シートを製造し、副繊維の発生有無を確認した。この結果を表1に示す。
実施例4において、電気炉の温度を100℃に変更した以外は実施例4と同様にしてフッ素樹脂系シートを製造し、副繊維の発生有無を確認した。この結果を表1に示す。
実施例4において、電気炉の温度を150℃に変更した以外は実施例4と同様にしてフッ素樹脂系シートを製造し、副繊維の発生有無を確認した。この結果を表1に示す。
実施例1において、加重およびせん断応力を発生させなかった以外は実施例1と同様にしてフッ素樹脂系シートを製造し、副繊維の発生有無を確認した。この結果を表1に示す。
実施例3において、せん断応力を発生させなかった以外は実施例3と同様にしてフッ素樹脂系シートを製造し、副繊維の発生有無を確認した。この結果を表1に示す。
実施例4において、電気炉の温度を25℃に変更した以外は実施例4と同様にしてフッ素樹脂系シートを製造し、副繊維の発生有無を確認した。この結果を表1に示す。
フッ素樹脂系シートの厚さを、マイクロメータであるLITEMATIC VL-50((株)ミツトヨ製)により測定した。
フッ素樹脂系シートの強度に関して、(株)島津製作所製の「EZ-test」を用い引張試験を行った。測定方法は次の通りである。
バブルポイント細孔径とは、フッ素樹脂系シートの最大細孔径を示し、バブルポイント法(ASTM F316-86)により算出した。なお、測定にはGalwick(15.9dyn/cm)を浸漬液として使用した。
(式中、θはフッ素樹脂系シートと液体との接触角を、γ[N/m]は液体の表面張力を、ΔPがバブルポイント圧力を表す。)
(平均流量径/平均流量径圧力)
平均流量径は、ASTM E1294-89のハーフドライ法により求めた。なお、測定にはGalwick(15.9dyn/cm)を浸漬液として使用した。
フッ素樹脂系シートの粒子捕捉率として、JIS B 9908に準じて、粒子捕集率を測定した。この際、フィルタユニットの替わりに、実施例3および比較例1,2で得られた100mm×100mmの大きさのフッ素樹脂系シートを用い、測定用粉じんとして大気塵(0.15μm~10μm粒径の塵を含む)を用い、空気の流量を面速度14.8cm/sとした。
Claims (6)
- 主繊維と主繊維の繊維径より小さい繊維径を有する副繊維とからなり、
同じ主繊維内および/または異なる主繊維間を該副繊維が架橋しており、
その架橋点に結節が形成されておらず、
該主繊維および該副繊維が、ポリテトラフルオロエチレン〔PTFE〕を含むフッ素樹脂繊維からなることを特徴とするフッ素樹脂系シート。 - 上記主繊維の繊維径が100nm以上50μm以下であり、
上記副繊維の繊維径が10nm以上1μm未満である請求項1に記載のフッ素樹脂系シート。 - 上記フッ素樹脂繊維が、PTFE以外に、テトラフルオロエチレン-パーフルオロアルキルビニルエーテル共重合体〔PFA〕,テトラフルオロエチレン-ヘキサフルオロプロピレン共重合体〔FEP〕,テトラフルオロエチレン-ヘキサフルオロプロピレン-パーフルオロアルキルビニルエーテル共重合体〔EPE〕,ポリ(クロロトリフルオロエチレン)〔PCTFE〕,テトラフルオロエチレン-エチレン共重合体〔ETFE〕,低融点エチレン-テトラフルオロエチレン共重合体,エチレン-クロロトリフルオエチレン共重合体〔ECTFE〕,ポリフッ化ビニリデン〔PVDF〕,フルオロエチレン-ビニルエーテル共重合体〔FEVE〕,およびテトラフルオロエチレン-パーフルオロジオキソール共重合体〔TFEPD〕からなる群から選択される少なくとも一種のフッ素樹脂を含んでなり、
PTFEと該フッ素樹脂との合計を100重量%とするとき、該フッ素樹脂が0重量%を超えて50重量%未満で含有される請求項1または2に記載のフッ素樹脂系シート。 - 上記フッ素樹脂繊維が、PTFEのみを含んでなる請求項1または2に記載のフッ素樹脂系シート。
- 請求項1に記載のフッ素樹脂系シートを製造する方法であって、
ポリテトラフルオロエチレン〔PTFE〕を含むフッ素樹脂繊維からなるフッ素樹脂繊維シートに対し、加熱された状態で、少なくとも二方向の応力を発生させることによって上記副繊維を生成させることを特徴とする、フッ素樹脂系シートの製造方法。 - 上記フッ素樹脂繊維シートが、電界紡糸法により作製したフッ素樹脂繊維をシート状に成形したフッ素樹脂繊維シートであり、
上記加熱の温度が、50℃以上400℃以下であり、
上記応力が、0.01kg/cm2以上10kg/cm2以下の圧縮応力およびせん断応力である、請求項5に記載のフッ素樹脂系シートの製造方法。
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