JP2006241606A - Mixed polytetrafluoroethylene fiber with different fineness fiber, method for producing the same and cloth by using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conventionally unavailable cloth excellent in finer dust-catching property and improved with ventilating property. <P>SOLUTION: This mixed polytetrafluoroethylene fiber with different fineness fibers having the mixed presence of a thin fineness polytetrafluoroethylene fiber having ≤2.5 dtex fineness and thick fineness polytetrafluoroethylene fiber having ≥3.3 dtex is provided. Preferably, the fineness of the thick fineness polytetrafluoroethylene fiber is ≥3.3 dtex and ≤18.0 dtex and the unevenness of the fineness is ≤10% of the fineness. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a different fineness mixed polytetrafluoroethylene fiber in which a fineness polytetrafluoroethylene fiber having a fineness of 2.5 dtex or less and a thick polytetrafluoroethylene fiber having a fineness of 3.3 dtex or more are mixed. The present invention also relates to the fiber, a fabric using the fiber, a filter material or a fine particle sealing material using the fabric.

  Fluororesin fibers represented by polytetrafluoroethylene (hereinafter abbreviated as PTFE) fibers are widely used in industrial materials because of their excellent heat resistance, chemical resistance, electrical properties, and low friction coefficient. Yes.

  PTFE is insoluble and has a very high melt viscosity when heated and melted. The production method is produced by a conventionally known matrix method (also called an emulsion method), split peeling method, paste extrusion method or the like. On the other hand, a copolymer-based fluororesin copolymerized with PTFE (4-fluoroethylene-6-fluoropropylene copolymer (FEP), 4-fluoroethylene-perfluoroalkoxy copolymer (PFA)) Alternatively, 4-fluoroethylene-olefin copolymer (ETFE) and the like can be produced by a melt spinning method.

  A modified cross-section PTFE fiber and a felt-shaped filter material using the modified cross-section fiber are known (Patent Document 1). However, the irregular cross-section fiber obtained by the split peeling method has a flat cross-sectional shape due to its manufacturing method, and its shape and fineness are random and non-uniform, so that it is difficult to produce nep during felt processing and difficult to produce was there.

  Also, a modified cross-section fiber by melt spinning using a copolymer type fluororesin and a bag filter using the same are known (Patent Documents 2 and 3). However, since the copolymer-type fluororesin that performs melt spinning is copolymerized for the purpose of providing fluidity at the time of melting, the chemical resistance and heat resistance are inevitably inferior to those of PTFE.

  The production method of PTFE fiber by the emulsion method is known from Patent Documents 4 and 5. Patent Document 4 describes a fine fineness PTFE fiber having an average fineness of 3d or less. However, according to this method, there is a problem that yarn breakage occurs during yarn production and stable production is difficult. Even with the method of Patent Document 5, it has been difficult to stably produce fineness PTFE fibers.

  That is, until now, no industrially practical method for producing PTFE fiber that has a uniform fineness and can be stably produced with a fineness has not been found. Further, there was no PTFE fiber in which fineness PTFE fiber and irregular cross-section PTFE were mixed.

  On the other hand, PTFE fiber is particularly widely used in bag filters for garbage incinerators among its uses, and composite products of fluorine fibers and glass fibers are widely used. Alternatively, bag filters using heat-resistant fibers other than glass fibers, such as aramid, polyphenylene sulfide, polyimide or polyparaphenylene benzoxazole, are also widely used.

  In contrast to the bag filter using the above heat-resistant fiber, a bag filter having higher dust collection efficiency is currently required. This is a bag filter used in, for example, a gasification melting furnace and the like, and is a high collection efficiency filter capable of collecting dust having a small particle diameter.

  Alternatively, a fine particle sealing material using a fluororesin fiber is also widely used. For example, it is a toner sealing material for a printer and seals a minute amount of toner at a temperature of 150 ° C. or higher. As the colorization of toner progresses, a material capable of encapsulating a finer amount of toner is required.

  Therefore, a method has been proposed in which a fluororesin microporous film is bonded to the felt surface of the heat resistant fiber, and dust is collected with high efficiency by the microporous film (Patent Document 6). Certainly, this method has a high dust collection efficiency of 0.5 μm or less, but has a problem of peeling because the adhesion between the fluororesin microporous film and other materials is poor. Further, when used for a bag filter, there is a problem that separation occurs due to this frictional force because friction occurs with the retainer when a backwash pulse is applied.

  Alternatively, as disclosed in Patent Document 7, the ultrafine fiber layer and the felt base material layer are integrated by needle punching, and the distribution of the ultrafine fiber is gradually reduced from the front surface to the back surface, and then by a high-pressure water punch. A filter with high collection efficiency is known in which a fiber that can be made ultrafine is divided into ultrafine fibers. However, in this filter, it is necessary to laminate two or more kinds of different fibers, and there is a problem that there are many processing steps. Furthermore, the ultrathinnable fiber of Patent Document 7 is only exemplified as a polyamide / polyester split fiber.

In addition, Patent Document 8 describes a filter medium using a fluororesin fiber having branches and / or loops, and the fiber is branched by needle punching after being carded to form a web. And / or fibers that produce loops. The fabric having branches and / or loops obtained by this method has a problem that the strength of the web is lowered because the fluororesin fibers are divided on the entire surface and inside.
JP 2001-276528 A (Claims, page 2) Japanese Patent Publication No. 3-10723 (Claims) JP 2002-282627 A (3rd, 5th and 6th columns) Registration No. 2571379 (Claims, page 4) Registration No. 3327027 (Claims, pages 3 and 4) Japanese Unexamined Patent Publication No. 2000-140588, etc. (Claims) JP-A-4-32649 (Claims) JP 2000-61224 A (Claims)

An object of the present invention is to intensively study a fabric excellent in improving dust collection and air permeability without impairing the properties of PTFE fiber, and fineness PTFE fiber having a fineness of 2.5 dtex or less. It was found that this problem can be solved all at once by arranging different fineness mixed PTFE fibers mixed with PTFE fibers having a high fineness of 3.3 dtex or more. Furthermore, it is providing the method of manufacturing such a fiber stably by a matrix spinning method.

  In order to solve the above problems, the following means are adopted.

  That is, the present invention is a mixed fine polytetrafluoroethylene having different fineness characterized by comprising a fineness polytetrafluoroethylene fiber having a fineness of 2.5 dtex or less and a thick polytetrafluoroethylene fiber having a fineness of 3.3 dtex or more. Also, a mixture of viscose as a matrix and an aqueous dispersion of polytetrafluoroethylene is discharged from a plurality of die holes into a coagulation bath containing sulfuric acid concentration of 7 to 13% and sodium sulfate concentration of 7 to 15%. Then, after spinning and scouring, after half-baking at a temperature of 80 to less than 320 ° C. while giving a relaxation of 1 to 5% between the baking rollers, firing at a temperature of 320 to 380 ° C. Polytetrafluoro, which is characterized by splitting a fiber stretched as it is as a fiber or a fabric and then splitting by physical impact It is a method for producing a styrene fiber.

  Furthermore, the present invention is a fabric using at least a part of the above-mentioned different fineness mixed polytetrafluoroethylene, a filter material and a fine particle sealing material using such a fabric.

  ADVANTAGE OF THE INVENTION According to this invention, the fiber which can manufacture the cloth which is more breathable than before and excellent in the collection property of minute dust can be obtained. In addition, when the fiber obtained by the method of the present invention is used, a fabric having better air permeability and better dust collection than ever can be obtained. This fabric and a fabric obtained by fibrillating the fabric can be suitably used as a filter material or a fine particle sealing material. Furthermore, such a fiber can be stably produced by a matrix spinning method.

  Hereinafter, the present invention will be described in detail together with preferred embodiments.

  In addition to PTFE, the fluoropolymer may be 4-fluoroethylene-6 fluoropropylene copolymer (FEP), 4-fluoroethylene-perfluoroalkoxy copolymer (PFA) copolymerized with PTFE, or 4 -Fluorinated ethylene-olefin copolymer (ETFE) and the like are produced by melt spinning. However, PTFE is the most excellent in terms of heat resistance. The present invention relates to a different fineness mixed PTFE fiber, which has not been disclosed so far, in which a fineness PTFE fiber having a fineness of 2.5 dtex or less and a thick PTFE fiber having a fineness of 3.3 dtex or more are mixed.

  Conventionally, a matrix spinning method (also called an emulsion method), a split peeling method, a paste extrusion method, and the like are known as methods for producing PTFE fibers.

  The split peeling method is a manufacturing method in which PTFE powder is compressed by cylinder, sintered, split peeled and then stretched.

  The paste extrusion method is a method in which PTFE powder is kneaded with a wax-like lubricant without using a matrix polymer, molded into a rod-like or film-like form, then removed, stretched and fired (may not be fired). It is a manufacturing method to do. However, in these two production methods, the final fibrous material obtained by slicing the production method has a flat cross section, and it is random and inferior in uniformity. Etc. were easily generated.

  The PTFE fiber according to the present invention is a different fineness mixed PTFE fiber in which a fineness PTFE fiber having a fineness of 2.5 dtex or less and a thick PTFE fiber having a fineness of 3.3 dtex or more are mixed. In order to improve dust collection efficiency, it is effective to reduce the fineness in order to increase the surface area. The fineness PTFE is 2.5 dtex or less. Within this range, a felt that far exceeds the conventional dust collection performance is obtained. On the other hand, increasing the fineness is also required for the purpose of improving air permeability. The fineness PTFE needs to be 3.3 dtex or more. The PTFE fiber provided by the present invention provides a felt having a high dust collection performance while maintaining a high level of air permeability because the fine and large fine yarns are in a specific fineness range.

At this time, the mixing ratio of the thick fineness PTFE referred to in the present invention is not particularly limited, but is preferably 10 to 90%, more preferably 30 to 70% from the viewpoints of card passing property, air permeability, and dust collecting performance.
Furthermore, in the present invention, it is preferable that at least a portion of fine PTFE fiber having a fineness of 3.3 dtex or more and 18.0 dtex or less and having a fineness variation of 10% or less of the fineness is mixed. As described above, the cross section of the fiber obtained by the split peeling method or paste extrusion method is random, the variation in fineness exceeds 10% of the fineness of the fiber, and the fineness is not uniform. That the fineness variation exceeds 10% of the fineness means that the cross-sectional shape and the fineness are not uniform. Therefore, the dust collection performance is good, but on the other hand, there is a drawback that the nep and the like are easily generated during the felt processing, and the processing is difficult. Since the present invention invented a fine PTFE fiber that defines fineness and fineness variation as well as fineness, and by mixing it, it has become possible to achieve both dust collection performance and felt workability such as card passability. is there.
When the fineness of the thick fineness PTFE fiber is less than 3.3 dtex, the dust collection performance is excellent, but the air permeability is poor. Moreover, when it exceeds 18 dtex, although it is excellent in air permeability, since it is inferior to dust collection performance, it is preferable that a fineness is 3.3 dtex or more and 18.0 dtex or less.
In addition, it is preferable that a high-density polytetrafluoroethylene fiber having a fiber cross section including a plurality of convex portions at least partially or a flat fiber cross section is mixed. It is possible to improve the dust collecting property while maintaining good air permeability by mixing the fiber cross section including a plurality of convex portions or the thick fine PTFE fiber having a flat fiber cross section. Furthermore, it is preferable that the number of the convex portions is 3 to 8 leaves from the viewpoint of the effect of improving the air permeability by the modification. In the case of 8 or more leaves, the effect of improving the air permeability due to the modification is reduced, which is not preferable.
The fiber as used in the present invention refers to a drawn yarn wound around a bobbin, a twisted yarn obtained by processing the drawn yarn, a short fiber that has been crimped and cut, and is not particularly limited.

The fabric referred to in the present invention refers to a woven or knitted fabric made of drawn yarn, a non-woven fabric obtained by passing short fibers through a roller card, felt, and the like, but is not particularly limited.
Also, the production method may be produced by mixing a thick fine yarn and a fine fine yarn at the spinning stage, and spinning and drawing. Alternatively, a thick fine yarn and a fine fine yarn are produced separately and mixed afterwards. You may manufacture as a thread | yarn. Furthermore, a thick fine yarn having a plurality of convex portions is manufactured, and the convex portions are split by physical impact at the spinning / drawing stage, and may be made into a fine fineness PTFE fiber. Splitting and fineness PTFE fibers can also be used. In this case as well, an advantage that uniform fineness PTFE fibers after splitting can be obtained is obtained by suppressing variation in fineness of the deformed PTFE fibers before splitting.

  Furthermore, when the PTFE fiber of the present invention is cut and used as a short fiber, the fiber length may be about 30 to 100 mm, but is not particularly limited.

The single yarn strength of the PTFE fiber of the present invention is preferably 0.7 cN / dtex or more, and the single yarn elongation is preferably 50% or less. When a fiber having a single yarn strength of less than 0.7 cN / dtex and a single yarn elongation of more than 50% is post-processed, the single fiber is stretched, resulting in poor processability.
Moreover, it is preferable that the dry heat shrinkage rate in 300 degreeC * 30 minutes of the short fiber of this invention is 30% or less. When a felt is actually produced and used, because of the heat resistance of the material, the felt that is used in a high temperature and has a shrinkage that is too high shrinks and is likely to be clogged. The dry heat shrinkage is more preferably 20% or less.

  The fine fineness PTFE fiber of the present invention is obtained by mixing the different fineness PTFE fiber and the thick fineness PTFE fiber, and the fine fineness PTFE fiber having a fineness variation within the range and having a plurality of convex portions or flat fiber cross sections. It is necessary to carry out the matrix spinning method. In the matrix spinning method, viscose or the like is used as a matrix and a mixed solution of PTFE with an aqueous dispersion of PTFE is discharged into a coagulation bath to be fiberized, and then refined and then fired. By firing at a temperature equal to or higher than the melting point of the polymer, PTFE is melted and the particles are fused while the majority of the matrix polymer is fired and scattered. After firing, the undrawn yarn is drawn directly in one or two stages to develop strength.

  The fine fineness PTFE fiber in which the fine fineness PTFE fiber and the thick fineness PTFE fiber referred to in the present invention are mixed, and further, the fine fineness PTFE fiber having a fineness variation within a range and having a plurality of convex portions or flat fiber cross sections. In order to obtain, it is obtained for the first time by using the matrix spinning method and by producing yarn under specific conditions, and cannot be obtained by the split peeling method or paste extrusion method.

  The fine fineness PTFE fiber in which the fine fineness PTFE fiber and the thick fineness PTFE fiber of the present invention are mixed, and the fine fineness PTFE fiber having a fineness variation within a range and having a plurality of convex portions or flat fiber cross sections, Viscose was used as a matrix, and a mixed solution of PTFE in water was discharged from a plurality of nozzle holes into a coagulation bath controlled to a sulfuric acid concentration of 7 to 13% and a sodium sulfate concentration of 7 to 15%, and was spun and scoured. After that, it is necessary to perform baking at a temperature of 320 to 380 ° C. after passing through a semi-baking step at a temperature of 80 to less than 320 ° C. while giving a relaxation of 1 to 5% between the baking rollers. .

  The viscose used in the present invention is preferably those usually used for rayon production, that is, a cellulose concentration of 5 to 10% by weight, an alkali concentration of 4 to 10% by weight, and carbon disulfide of 27 to 32% by weight (based on cellulose).

  The aqueous dispersion of PTFE used in the present invention preferably has a concentration of 50 to 70% by weight and contains a nonionic or anionic surfactant as a stabilizer in an amount of 3 to 10% by weight based on the PTFE polymer. The size of the dispersed particles of the PTFE aqueous dispersion is 0.5 μm or less, preferably 0.3 μm or less.

  These viscose and PTFE aqueous dispersions are mixed to prepare a mixed solution. At this time, the PTFE concentration in the mixed solution is 20 to 40%, preferably 25 to 35%, while the cellulose concentration is about 2 to 6%, preferably about 3 to 5%.

  At this time, if the PTFE concentration exceeds 40% and is too high, the yarn is difficult to coagulate in the coagulation bath. In addition, PTFE particles fall off from the yarn in a scouring bath / alkaline bath, and stable spinning cannot be performed. Further, it is not preferable because the fusion between the PTFE particles becomes strong at the time of firing and the fusion between the single yarns becomes intense, and the fibrillation of the single yarns itself is hardly exhibited. If the PTFE concentration is less than 20%, it is easy to coagulate in the coagulation bath, but it becomes difficult to maintain a uniform cross-sectional shape during firing, and a large amount of carbonized components remain in the fiber after firing. The fiber strength is undesirably lowered.

  The mixed liquid is defoamed, but if the temperature is high at this time, there is a concern that the viscose will solidify, and there is a concern that the moisture evaporates and PTFE aggregates. Therefore, it is preferable to control to a low temperature of 15 ° C. or lower during defoaming. The degree of vacuum is preferably about 10 Torr. Regarding the timing of mixing the viscose and PTFE, a method of mixing the viscose and the PTFE aqueous dispersion before defoaming or mixing them immediately before defoaming and introducing them to a die using a static mixer or the like can be employed.

  Next, the spinning mixture is discharged from a molding die composed of a large number of discharge holes immersed in a coagulation bath and solidified.

  As the coagulation bath, an aqueous solution of an inorganic mineral acid and / or an inorganic salt is used. In the present invention, a mixed aqueous solution of sulfuric acid and sodium sulfate is used.

  At this time, the sulfuric acid concentration needs to be 7 to 13%. If the sulfuric acid concentration is less than 7%, the rate at which the yarn solidifies in the coagulation bath becomes very slow, which makes it difficult to obtain the desired round shape or flat cross section. On the other hand, if the sulfuric acid concentration exceeds 13%, the sulfuric acid attached to the fiber surface is not easily deoxidized, and yarn breakage occurs frequently in the firing process, and the rate at which the yarn solidifies in the coagulation bath becomes very fast. This is not preferable because it is difficult to control the cross-sectional shape.

  It is necessary to adjust the sodium sulfate concentration to 7 to 15%. Sodium sulfate suppresses rapid coagulation of cellulose. When the sodium sulfate concentration is less than 7%, the rate at which the yarn solidifies in the coagulation bath becomes very fast, and it becomes difficult to control the cross-sectional shape, which is not preferable. On the other hand, when the concentration of sodium sulfate exceeds 15%, the rate at which the yarn solidifies in the coagulation bath becomes very slow, which makes it difficult to obtain a desired cross-sectional shape, which is not preferable. That is, in the present invention, uniform PTFE fibers could be produced by adjusting both the sulfuric acid concentration and the sodium sulfate concentration within a specific range using the matrix method.

  For the half firing, a contact type firing roller or a non-contact type firing heater can be used, but a contact type firing roller is preferably used. After squeezing the unfired yarn derived from the scouring bath or the alkali bath as it is or with a nip roller, a semi-baking step at a temperature of 80 to less than 320 ° C. is performed while relaxing 1 to 5% between the firing rollers. is necessary. The unfired yarn guided to the roller in the contact-type semi-baking process maintained at a temperature of 80 to 320 ° C. rapidly shrinks on the roller and increases the tension. If the relaxation rate is less than 1%, the tension becomes too high, making it difficult to maintain a round or desired irregular cross-sectional shape uniformly, and particularly when producing fine yarns of 3.3 dtex or less. Many yarn breaks due to shrinkage occur. If it exceeds 5%, the relaxation rate is too high, and the yarn loosens, causing a problem in the processability. However, the relaxation of 1 to 5% can be performed not only once between the firing rollers immediately after entering the semi-baking, but also between the rollers in the semi-baking process or between the rollers in the baking process. The semi-baking process is a process that must be performed before entering the subsequent baking process. When the roller temperature in the semi-baking process is lower than 80 ° C., the fiber is heated at a stretch in the subsequent baking process, so that the fiber cross section is deformed or fusion between single yarns occurs. On the other hand, when the temperature is higher than 320 ° C., the fiber is heated at a stretch in the semi-firing stage, so that the fiber cross section is easily deformed or fusion between single yarns easily occurs. Therefore, it is necessary to keep the roller in the semi-baking step in a temperature range of 80 to 320 ° C.

At this time, each roller temperature can be changed independently, and can be set without any limitation as long as it is within the above range.
The roller temperature in the semi-baking process varies depending on the number of baking rollers. The roller temperature in the semi-baking step is preferably 150 or more and less than 320 ° C, more preferably 250 or more and less than 320 ° C.

  The semi-fired yarn is then fired at a temperature of 320-380 ° C. At this stage, most of the cellulose is burned and scattered, and the PTFE particles in the cellulose are thermally fused in a fibrous form to obtain an unstretched PTFE yarn. When the firing temperature is lower than 320 ° C., the PTFE particles in the fiber are not sufficiently fused, and yarn breakage frequently occurs during stretching after firing, and the fiber strength is also lowered. On the other hand, if the firing temperature is higher than 380 ° C., the fiber cross-sectional shape is deformed by heat, and it becomes difficult to obtain a desired uniform cross-sectional shape. Further, it is not preferable because fusion between single yarns also occurs, resulting in an adverse effect on the openability of the product. Moreover, at the time of baking, each roller temperature can be changed independently, and if it exists in the said range, it can set without limitation.

  Next, the PTFE undrawn yarn is heat-drawn at a temperature of 300 to 400 ° C. by a commonly used drawing method to obtain a PTFE drawn yarn.

  Further, it can be produced in the same manner as described above using a non-contact type firing heater during firing.

  After the refining, it is preferable to perform a washing step with an alkali at an alkali concentration of 0.08 to 0.16% before performing the semi-baking and baking steps. In such an alkali cleaning bath, an aqueous solution of a compound selected from alkali metal or alkaline earth metal hydroxides, carbonates and bicarbonates is used, but generally an aqueous alkali metal solution, particularly an aqueous caustic soda solution is preferably used. It is done. The concentration of the compound is preferably 0.08 to 0.16 wt%. Generally, although depending on the firing temperature range of the next step, when PTFE fiber enters the firing step, yarn breakage frequently occurs in the firing step if an acid component remains on the fiber surface. If the PTFE fiber has a fineness exceeding 3.3 dtex, the cleaning is sufficient even if only the refining process takes into account the refining time. However, when producing a PTFE fiber having a fineness of 3.3 dtex or less as referred to in the present invention, the surface acid component is preferably neutralized and washed with an alkali because of the large surface area of the fineness yarn surface. Washing with alkali affects not only the yarn breakage due to deoxidation, but also the degree of firing, that is, the color and fibrillation. If it is in the range of the semi-baking and baking temperature of this invention, the density | concentration of an alkaline bath is preferable 0.08 to 0.16%. When the concentration of the alkaline bath is less than 0.08 wt%, the cellulose content is difficult to decompose during firing, and as a result, a large amount of cellulose remains that cannot be decomposed in the fiber after firing, making subsequent stretching difficult and stretching. Yarn breakage tends to occur frequently in the process. On the other hand, when the concentration of the alkaline bath exceeds 0.16 wt%, the cellulose starts to dissolve during alkali cleaning, and the residue tends to accumulate in the alkaline bath or in the guide. Further, the strength of the unfired yarn at the time of entering the semi-firing / firing process becomes weak, and troubles in passing through the process are likely to occur, which is not preferable. Further, the fusion of the PTFE particles inside the fibers during firing becomes strong and is difficult to fibrillate. A more preferable alkali concentration is 0.10 to 0.14 wt%.

  Furthermore, the temperature of the alkaline bath is preferably 20 ° C. or less. When the temperature of the alkaline bath exceeds 20 ° C., the cellulose begins to dissolve during alkali washing, as in the case where the alkali concentration is too high, and the residue tends to accumulate in the alkaline bath and the guide. This is not preferable because the unfired yarn strength becomes weak and troubles in passing through the process easily occur. The temperature of the alkaline bath is preferably 15 ° C. or lower.

  The form using the PTFE fiber of the present invention as at least a part of the present invention is not particularly limited in its form such as woven / knitted fabric, non-woven fabric and felt. The fabric can be prepared by mixing glass fiber, aramid, polyphenylene sulfide, polyimide, polyparaphenylenebenzoxazole and the like together with the PTFE fiber of the present invention. However, although aramid has an excellent decomposition temperature of 500 ° C. or higher, it has a weak point of low acid resistance. Polyphenylene sulfide has excellent chemical resistance, but its melting point is 285 ° C., which is slightly low in heat resistance. In the case of polyimide, there is a slight problem in alkali resistance, and polyphenylenebenzoxazole has high strength, but the market price is very expensive. Glass fiber has a decomposition point of 700 ° C. or higher and no heat resistance, but has a slight problem with alkali resistance. In contrast, fluororesin fibers, especially PTFE, exhibit excellent chemical resistance except that they melt into a specific perfluorinated organic liquid at 299 ° C or higher and are slightly attacked by molten alkali metal. As for heat resistance, since the melting point is as high as 327 ° C., the fluororesin fiber exhibits the most balanced and excellent performance as a whole. Therefore, it is most suitable for filter applications. As the mixing ratio, it is preferable to mix the PTFE fiber of the present invention at a ratio of 20 to 100%, preferably 40 to 100%. Although the PTFE fiber of the present invention can be used as a fabric as it is, it is more effective when used as a fibrillated fabric as described below.

  The fabric having fibrillation referred to in the present invention preferably has fibrillated PTFE fibers occupying 50% or more of the total area of the fabric surface. This is because when less than 50% of the total area is occupied, only a fabric having a low dust collection efficiency of 0.5 μm or less can be obtained.

  Next, the manufacturing method of this fabric is demonstrated. That is, the fabric made of such fibrillated PTFE fibers uses a means for generating fibrillated PTFE fibers on the surface of the fabric made of non-fibrillated PTFE fibers by applying a physical impact. Are manufactured.

  In the fabric of the present invention, there is a fibrillated PTFE fiber having a minimum fineness of 1.1 dtex or less, and further 0.1 dtex or less on the surface, and the proportion of PTFE fibers having a high fineness gradually increases from the surface toward the inside. Is preferred. This is because a cloth made of PTFE fibers fibrillated in the thickness direction of the cloth is not preferable because all the constituent fibers are finely divided, and the strength of the cloth is lowered. Moreover, the PTFE fiber which maintained the irregular cross section which exists in the inside of a fabric without fibrillation with the PTFE fiber fibrillated on the fabric surface improves dust collection efficiency. The fabric made of non-fibrillated PTFE fibers can be used without any problem as long as it is a felt in which a web made of PTFE short fibers is integrated with a needle punch. The felt herein may be a laminate of a web made of short PTFE fibers and a base fabric made of a woven fabric made of heat-resistant multifilaments or monofilaments, or may be made of fluororesin fibers (4 fibers). Woven fabrics and knitted fabrics made of fluorinated ethylene-6 fluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkoxy group copolymer (PFA) or tetrafluoroethylene-olefin copolymer (ETFE), etc. But it can be used without problems. Further, the fabric made of non-fibrillated PTFE fiber may be a single web made of PTFE fiber, or may be used without any problem even with a fabric calendered with this web or a resin bonded nonwoven fabric cured by attaching a resin. it can.

  The physical impact of the present invention is preferably high pressure jet water flow treatment. This is because high-pressure jet water flow treatment can provide a physical impact while minimizing the occurrence of needle holes or fiber breaks caused by, for example, needle punching.

  The high-pressure jet water flow treatment here is 3 MPa. The above processing pressure is preferable. Compared with the fluorine fiber having a round cross section, the processing pressure is 3 MPa. Splitting is possible even if set to a low value, and damage to the fiber can be suppressed as much as possible. On the other hand, the treatment pressure is 3 MPa. If it is less than the range, it is not preferred because the fiber is difficult to split and only a fabric having a low dust collection efficiency of 0.5 μm or less can be obtained.

  The fabric obtained by the present invention can be suitably used for filter materials or fine particle sealing materials. According to the fabric of the present invention, not only a filter that collects fly ash and dust, but also a filtration filter for liquid can be used without any problem. Further, as a fine particle sealing material, for example, a toner seal of a printer. Although it can be used as a stopping material, it is not limited to these uses.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these. In addition, the measuring method of each physical property of a fabric is as follows.

[Fineness variation]
A sample is randomly extracted from the PTFE drawn yarn before fibrillation, and a cross-sectional photograph is taken by the embedding method as described below. Then, each cross-sectional photograph was cut out and the weight was measured to determine the cross-sectional area, and the fineness of the PTFE fiber of the present invention was calculated using a specific gravity of 2.30 g / cm ³ . Thirty samples are randomly measured and the average value is calculated. The average value, the minimum fineness, and the degree of variation of the larger maximum fineness were measured.
At this time, the cross section of the fiber obtained by the split peeling method or paste extrusion method has a random flat shape and is inferior in uniformity. In addition, the fiber is sharply cut because of its production method, and the fiber corners are sharp, which can be excluded and clearly measured unlike the PTFE fiber obtained by the matrix spinning method.

<Embedding method>
Apply some tension to the forming frame and fix it with cellophane tape. Heat at 200 ° C. to melt the mixture of paraffin and stearic acid. When the temperature reaches 130 ° C., ethyl cellulose is added little by little, and the mixture is kept warm for 1 hour with stirring to remove bubbles. After dropping to 100 ° C., it is poured into a forming frame. After cooling and solidifying, cut into blocks of appropriate size. Using a microtome, cut a section (thickness of about 7 μm) from the block and place it on a slide glass. At this time, thinly spread arbumen on a slide glass (albumen is an egg white and glycerin equivalent amount, and 1 wt% sodium salicylate is added as a preservative). It is left to stand in a dryer maintained at 70 ° C. for 20 minutes, heat-treated and dried, then immersed in an isoamyl acetate bath for about 1 hour, decapsulated, and then air-dried. Put a drop of liquid paraffin on the slide glass, place the cover glass gently so that air does not enter, and take a picture using a microscope.

[Card passability]
The room temperature was set to 30 ° C. and the relative humidity was set to 60%. While putting 2 g / m to 10 g / m of raw cotton into the card machine, the winding of the cylinder roller when passing through the roller and the occurrence of nep were observed and evaluated as follows. .
○ Good △ Somewhat bad × Very bad.

[Proportion of fibril yarn in the total area of the fabric surface (hereinafter referred to as fibril proportion)]
A photograph of the surface of the fabric was taken and the area occupied by the fibril yarn was read. The photographing magnification was 50 times, and a video high scope was used.

[Minimum fiber diameter]
A cross-sectional photograph of the fabric is taken with an electron microscope, the fiber with the smallest fiber diameter is selected, and the fiber diameter of the fiber is read. The shooting magnification is 1000 times.

[Dust collection efficiency]
The collection efficiency was carried out by the atmospheric dust counting method. The dust particle size is 0.5 μm or less, the filtration wind speed is 1.0 m / min, and the data is obtained by measuring the dust collection efficiency in the atmosphere using a particle counter.

[Air flow rate]
The measurement was performed based on the fragile method defined in JIS L 1096. Five measurement samples were randomly selected and measured.

(Examples 1-6)
Viscose maturity (salt point) 8.0, cellulose concentration 9.0%, alkali concentration 6.2% viscose 50% by weight and 60% concentration PTFE aqueous dispersion 50% mixed, then reduced pressure of 10 Torr Defoaming was performed below to obtain a forming stock solution having a polymer concentration of 30%. The PTFE resin content relative to the polymer in the stock solution was 87.0%, and the stock solution viscosity at 30 ° C. was 132 poise. This stock solution was introduced into a molding die having a plurality of ejection holes, and the spinning die was changed as follows so as to have the cross-sectional shape and fineness shown in Table 1, and was discharged into the coagulation bath. In addition, the fine fine yarn and the thick fine yarn were discharged from the same nozzle and mixed from the spinning stage to perform spinning.

<Fine yarn>
Round cross-section shaped fiber: 0.08 mmφ × 200 holes <thickness yarn>
Trefoil cross-section fiber: 0.12 mm (W) -0.08 mm (L) x 400 holes Five-leaf cross-section fiber: 0.10 mm (W) -0.08 mm (L) x 400 holes Flat cross-section fiber: 0 .14 mm (W) -0.08 mm (L) × 400 hole Round cross-section fiber: 0.12 mmφ × 400 hole.

  The coagulation bath was a mixed aqueous solution having a sulfuric acid concentration of 10.0% and a sodium sulfate concentration of 11.0%, and the temperature was 10 ° C. Next, the solidified unfired yarn was washed with warm water having a temperature of 80 ° C., and then introduced into an alkaline bath containing an aqueous caustic soda solution having a concentration of 0.12%, followed by scouring to completely remove the acid component. Thereafter, the unfired yarn led from the alkaline bath is squeezed with a nip roller, then subjected to half-baking at a temperature of 280 ° C. while giving a relaxation of 4%, and then baked using a baking roller kept at 350 ° C. An undrawn yarn was obtained by taking up at a speed of / min. Next, the undrawn yarn was heat-drawn at a temperature of 350 ° C. to obtain a PTFE drawn yarn having a cross-sectional shape shown in Table 1. In this spinning and drawing process, the process passability was good, and the number of yarn breaks per spindle was about once every 15 hours.

The obtained PTFE drawn yarns were combined, crimped and cut to obtain PTFE staples. The staple was carded to obtain a web. Thereafter, the above web was laminated on both the front and back sides of a woven fabric made of PTFE multifilament (TOYOFLON # 4300 manufactured by Toray Fine Chemical Co., Ltd.) and integrated by needle punching treatment at 350 pieces / cm ² to obtain a felt (Example) 5, 6). The treatment water pressure is 15 MPa. 3 times from the front and back surfaces of the felt. Then, water jet punching was performed at a feed rate of 5 m / min to obtain a fibrillated fabric (Examples 1 to 4). Table 1 shows the results of measurement of the fiber shape, fineness, fineness variation, card passing property, fibril ratio of the fabric, minimum fiber diameter, air flow rate, and collection efficiency.

(Comparative Example 1)
A non-fibrillated felt fabric was obtained in the same manner as in Example 1 using PTFE staple fiber (“TOYOFLON” 7.4 dtex × 70 mm; round cross section manufactured by Toray Fine Chemical Co., Ltd.). The fibril ratio, minimum fiber diameter, air flow rate, and collection efficiency of the fabric were measured. The results are shown in Table 1. When Examples 5 and 6 which are non-fibrillated fabrics were compared with Comparative Example 1, Examples 5 and 6 using the PTFE fiber of the present invention were far superior in dust collection efficiency.

(Comparative Examples 2 and 3)
The thick fine PTFE fiber and the fine fine PTFE fiber obtained in Example 1 were divided to obtain respective fine fine PTFE fibers (Mitsuha, 7.7 dtex) and fine fine PTFE fibers (circle, 1.5 dtex). Using each fiber, a non-fibrillated felt fabric was obtained in the same manner as in Example 1. The fibril ratio, minimum fiber diameter, air flow rate, and collection efficiency of the fabric were measured. The results are shown in Table 1. When Examples 5 and 6 which are non-fibrillated fabrics are compared with Comparative Example 2, the amount of airflow is similar, but Examples 5 and 6 using the PTFE fiber of the present invention have a higher dust collection efficiency. It was excellent. Moreover, although the comparative example 3 was excellent in the dust collection efficiency, it resulted in a small air flow rate and inferior air permeability.

(Comparative Example 4)
Using the PTFE aqueous dispersion stock solution obtained in Example 4, this stock solution was introduced into a molding die having a plurality of round holes in the same manner as in Example 4, and the fineness of the drawn yarn was 7.4 and 1.5 dtex. Was discharged into the coagulation bath. The coagulation bath was a mixed aqueous solution having a sulfuric acid concentration of 7% and a sodium sulfate concentration of 20.0%, and the temperature was 23 ° C. Next, the coagulated unfired yarn is washed with warm water at a temperature of 80 ° C. and then introduced into an alkaline bath containing a caustic soda aqueous solution having a concentration of 0.05 mol / l (0.2%) and scoured to completely remove the acid component. did. Thereafter, the unfired yarn led from the alkaline bath is squeezed with a nip roller, and then fired by contacting it with a roller heated to 380 ° C. as it is without carrying out the relaxation semi-firing referred to in the present invention, at a speed of 30 m / min. The undrawn yarn was obtained by taking up. Next, the undrawn yarn was heat-drawn at a temperature of 350 ° C. to obtain PTFE drawn yarn having a circular cross-sectional shape of 7.4 and 1.5 dtex.
Under these conditions, the concentration of sodium sulfate exceeded 15%, the rate at which the yarn solidified in the coagulation bath became very slow, and it was brought into contact with a roller heated to 380 ° C. without relaxing and semi-firing. Due to the rapid thermal shrinkage during firing, the process passability was poor, and the yarn breakage was severe in the spinning and drawing process, and the number of yarn breakage per spindle was about once every 10 minutes. In addition, since the thermal firing was carried out rapidly without relaxing semi-firing, the stretched yarn after drawing was severely fused between the single yarns, and therefore the fiber variation was a very large value of ± 20% for the large fineness PTFE fiber. .

  As is clear from these results, the present invention is characterized in that fine fineness polytetrafluoroethylene fibers having a fineness of 2.5 dtex or less obtained in the present invention and thick fineness polytetrafluoroethylene fibers having a fineness of 3.3 dtex or more are mixed. When the different fineness mixed polytetrafluoroethylene fiber is used, a fabric having a better collection of fine dust can be obtained. In addition, the fine-fine PTFE fiber produced by the matrix spinning method and the thick-fine PTFE fiber mixed with the fine-fine PTFE fiber, and the fineness variation is within a range, and a plurality of convex or flat fiber cross sections are present. In order to stably produce a PTFE fiber having a large fineness, a mixed solution of PTFE in the present invention with an aqueous dispersion of PTFE is discharged from a plurality of nozzle holes into a coagulation bath adjusted to a specific component and concentration. In particular, when firing is performed, it is necessary to perform firing at a specific temperature after a semi-baking step at a specific temperature while giving relaxation at a specific relaxation rate.

Claims (12)

A different fineness mixed polytetrafluoroethylene fiber comprising a fineness polytetrafluoroethylene fiber having a fineness of 2.5 dtex or less and a thick polytetrafluoroethylene fiber having a fineness of 3.3 dtex or more.   2. The different fineness mixed poly according to claim 1, wherein the fineness of the polytetrafluoroethylene fiber is 3.3 dtex or more and 18.0 dtex or less, and the variation in fineness is 10% or less of the fineness. Tetrafluoroethylene fiber. The different-fineness mixed polytetrafluoroethylene fiber according to claim 1 or 2, wherein the high-fineness polytetrafluoroethylene fiber contains a fiber having a fiber cross section including a plurality of convex portions or a flat fiber cross section.   A mixture of viscose as a matrix and an aqueous dispersion of polytetrafluoroethylene is discharged from a plurality of nozzle holes into a coagulation bath containing a sulfuric acid concentration of 7 to 13% and a sodium sulfate concentration of 7 to 15%, and spinning. After scouring, half-baking at a temperature of 80 to less than 320 ° C. while giving a relaxation of 1 to 5% between the baking rollers, firing at a temperature of 320 to 380 ° C., and then winding or stretching as it is A method for producing a polytetrafluoroethylene fiber, characterized in that the fiber is made into a fabric or a fabric and then split by physical impact. The method for producing polytetrafluoroethylene fiber according to claim 4, wherein semi-firing is performed using a contact-type calcining roller.   The method for producing polytetrafluoroethylene fibers according to claim 4 or 5, wherein washing with an alkaline aqueous solution having a concentration of 0.08 to 0.16% is performed before half-firing and firing.   A fabric using at least a part of the thick and fine yarn mixed polytetrafluoroethylene fiber according to claim 1.   The fabric according to claim 7, comprising fibrils.   The fabric according to claim 8, wherein the fibril is formed by physical impact.   10. The fabric according to claim 9, wherein the physical impact is high pressure jet water flow treatment.   A filter material using the fabric according to claim 7 or 8.   A fine particle sealing material using the fabric according to claim 7 or 8.