JPWO1994023098A1 - Polytetrafluoroethylene fiber, cotton-like material containing same, and method for producing same - Google Patents

Abstract

(57) [Abstract] This publication contains application data prior to electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] Polytetrafluoroethylene Fiber, Cotton-Like Material Containing the Same, and Method for Producing the Same Technical Field The present invention relates to novel polytetrafluoroethylene (PTFE) fibers with excellent entanglement properties, cotton-like materials containing the same, and methods for producing the same.

BACKGROUND ART In recent years, synthetic nonwoven fabrics have been used in a wide variety of fields, including clothing, medical supplies, civil engineering and construction materials, and industrial product materials, taking advantage of the unique properties of the fibers that make them up.

Among these, nonwoven fabrics containing PTFE fibers are particularly well-suited for heat resistance, chemical resistance, and abrasion resistance, and are expected to become highly functional nonwoven fabrics in the future.

The PTFE cotton material that is the raw material for such PTFE nonwoven fabric is an aggregate of PTFE fibers and is conventionally manufactured as a patch.

(1) A method in which continuous filaments are produced and then cut to desired lengths.

Methods for producing PTFE filaments are roughly divided into two methods.

(One example is the emulsion spinning method disclosed in U.S. Pat. No. 2,772,444. This method involves extrusion-spinning an emulsion containing PTFE particles and a binder such as viscose, followed by sintering to spin long fibers having a circular cross section.

The biggest problem with this method is that when the spun PTFE fibers are baked, the binder remains as a carbonaceous residue, causing the fibers to turn brown. Even if the carbonaceous residue is oxidized to whiten the fibers, the original purity cannot be maintained.

(1b) The method disclosed in Japanese Patent Publication No. 36-22915 or Japanese Patent Publication No. 48-8769 involves slitting a PTFE film to a desired width and then stretching the resulting fibers. The problem with this method is that the narrower the slit width, the more likely the fibers are to break during stretching.

Furthermore, the PTFE fibers obtained by methods (11) and (1b) both have the low coefficient of friction and high specific gravity inherent to PTFE, so even if they are crimped, the fibers do not entangle with each other (see Japanese Patent Publication No. 50-22621).

(2) A method in which bulb-shaped PTFE fiber powder is prepared and then made into a sheet by papermaking (U.S. Patent No. 3,003,912, Japanese Patent Publication No. 1969-15906).

The method of the U.S. patent involves cutting PTFE filaments obtained by paste extrusion into short lengths and applying frictional force to form fibers.

On the other hand, the method disclosed in Japanese Patent Publication No. 44-15906 is a method in which a shear force is applied to PTFE powder to form fibers.

The fibrous powders obtained by these methods are short and bulb-shaped, and although they can be made into sheets by papermaking, they cannot be made into nonwoven fabrics using carding or needle punching machines.

An object of the present invention is to provide PTFE fibers having excellent entanglement properties and a cotton-like material containing the same.

Another object of the present invention is to provide a method for directly obtaining staple fiber (relatively short fiber) PTFE cotton-like material without producing multifilaments (multiple continuous fibers) from a long film obtained by uniaxially stretching PTFE.

DISCLOSURE OF THE INVENTION The present invention relates to PTFE fibers obtained by mechanically defibrating uniaxially stretched PTFE molded articles, and to a cotton-like material containing the same.

The PTFE fibers of the present invention preferably have a fiber length of 5 to 150 ITI m.

Furthermore, the PTFE fiber of the present invention preferably has a branched structure, a fineness of 2 to 200 denier, a number of crimps of 1 to 15 per 20 mm, and an irregular fiber cross section.

As used herein, "irregular cross-sectional shape" means that the fiber cross-section has no regularity and varies from fiber to fiber. More specifically, the cross-section of the fiber of the present invention is less prone to complex irregularities and generally has angular features, resembling a shape more similar to crushed stone. While this may vary depending on manufacturing conditions, as can be seen in Figure 13 (50x magnification), the fiber often contains a large proportion of flat fibers. The proportion of such flat fibers increases as the thickness of the stretched film of the material decreases.

Furthermore, the raw material PTFE molded product is preferably semi-sintered or sintered.

The present invention also relates to a PTFE cotton-like material containing 30% or more of the PTFE fibers of the present invention.

The present invention further relates to a method for producing a PTFE flocculant by uniaxially stretching a PTFE molded article and then defibrating the uniaxially stretched article by mechanical force.

The PTFE molded product used is preferably semi-sintered or sintered. In the case of semi-sintered products, the uniaxial stretching ratio is preferably at least 6 times, and in the case of sintered products, it is preferably at least 3 times.

Preferred mechanical fiberization methods include contacting a uniaxially stretched semi-sintered PTFE film stretched at least six times with the projections of a rapidly rotating cylinder with sharp projections on the periphery, or passing a uniaxially stretched sintered PTFE film stretched at least three times between at least one pair of rapidly rotating needle blade rolls. In the latter case, the needle density of the needle blade rolls is preferably 20 to 100 needles/cm².

Furthermore, it is preferable to heat-treat uniaxially stretched films of semi-sintered or sintered PTFE at a temperature equal to or higher than the temperature during stretching.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram showing the branching state of the PTFE fibers contained in the PTFE cotton material of the present invention.

FIG. 2 is a schematic cross-sectional view of one embodiment of a fiberizer that can be used in the manufacturing method of the present invention.

FIG. 3 is a schematic cross-sectional view of another embodiment of a fiberizer that can be used in the manufacturing method of the present invention.

FIG. 4 is an explanatory diagram showing an example of the arrangement of needle blades on the rolls of the opener shown in FIG. 3 .

FIG. 5 is a schematic cross-sectional view illustrating the needle angle (θ) of the needle blade of the fiberizer shown in FIG. 3.

FIG. 6 is a schematic cross-sectional view of a conventional carding machine that can be used to produce nonwoven fabrics using the cotton-like material of the present invention.

FIG. 7 is a scanning electron microscope photograph (x 500) showing the cross-sectional shape of the fiber of the present invention obtained in Example 2.

8 to 12 are photographs (X1, 5) showing the shape of the fibers of the present invention obtained in Example 5.

Figure 13 is a scanning electron microscope photograph (50x magnification) showing the cross-sectional shape of the fiber of the present invention obtained in Example 5.

Figure 14 shows an example of a differential scanning calorimeter (hereinafter referred to as rDS CJ) crystalline melting curve for the heating step (1) of an unsintered PTFE body used to measure the crystalline conversion rate of semi-sintered PTFE.

Figure 15 shows an example of a DSC crystalline melting curve for the heating step (3) of the sintered PTFE body used to measure the crystalline conversion rate of the semi-sintered PTFE body.

FIG. 16 shows an example of a DSC crystalline melting curve in a heating step of a semi-sintered PTFE body used to measure the crystalline conversion rate of the semi-sintered PTFE body.

BEST MODE FOR CARRYING OUT THE INVENTION The PTFE molded articles used in this invention include, for example, those obtained by paste extrusion molding of PTFE fine powder (PTFE fine powder obtained by emulsion polymerization) or those obtained by compression molding of PTFE molding powder (PTFE powder obtained by suspension polymerization). The molded articles are preferably in the form of films, tapes, sheets, ribbons, etc., with thicknesses of 5 to 300 μm, preferably 5 to 150 μm, to ensure stable stretching.

PTFE films can be made by calendering fine powder paste extrusions, or by skiving from moldings/compression molded wood products.

The PTFE molded article to be monoaxially stretched is preferably a semi-sintered or sintered body. Semi-sintered PTFE is obtained by heat-treating unsintered PTFE at a temperature between the melting point of sintered PTFE (approximately 327°C) and the melting point of unsintered PTFE (approximately 337 to 347°C). The crystalline conversion ratio of the semi-sintered PTFE is 0.10 to 0.85, preferably 0.15 to 0.70.

The crystalline conversion rate of the semi-sintered PTFE product is determined as follows.

First, 10.0±0.1 mg of the semi-sintered body was weighed and cut out to serve as a sample. Because thermal modification of PTFE progresses from the surface to the interior, the degree of semi-sintering is not necessarily uniform throughout the sample. This tendency is naturally more pronounced in thicker films.

When collecting the above samples, care must be taken to ensure that each degree of modification is evenly distributed across the thickness of the sample. Using the above samples, first obtain a crystalline melting curve using the following method.

The crystalline melting curve was recorded using a DSC (Perkin Elmer DSC-2). First, a sample of unsintered PTFE was placed in an aluminum pan of the DSC, and the heat of fusion of the unsintered and sintered PTFE samples was measured using the following procedure.

(1) The sample is heated to 277°C at a heating rate of 1606°C/min, and then heated from 277°C to 360°C at a heating rate of 10°C/min.

An example of a crystalline melting curve recorded during this heating process is shown in Figure 14. The position of the endothermic curve that appears during this process is defined as the "melting point" of the PTFE unsintered body or PTFE fine powder.

(2) Immediately after heating to 360°C, the sample is cooled to 277°C at a rate of 80°C/min.

(3) The sample is again heated to 360°C at a heating rate of 10°C/min.

An example of a crystalline melting curve recorded in the heating step (3) is shown in Figure 15. The position of the endothermic curve that appears in the heating step (3) is defined as the "melting point" of the sintered rPTFE body.

The heat of fusion of unsintered or sintered PTFE is proportional to the area between the endothermic curve and the baseline. The baseline (C) is the straight line drawn from 307°C (580°K) on the DSC (C) to the base of the right end of the endothermic curve.

Next, the crystalline melting curve of the semi-sintered PTFE body is recorded according to step 1.

An example of the curve in this case is shown in FIG.

The crystalline conversion rate is calculated using the following formula: crystalline conversion rate - (S -3)/(S -32), where S is the area of the endothermic curve for unsintered PTFE (see Figure 14), S is the area of the endothermic curve for sintered PTFE (see Figure 15), and S is the area of the endothermic curve for semi-sintered PTFE (see Figure 16).

The crystalline conversion rate of the semi-sintered PTFE used in the present invention is 0.10 to 0.85, preferably 0.15 to 0.70.

Sintered PTFE can be obtained by heat treating unsintered PTFE or semi-sintered PTFE at a temperature equal to or higher than the melting point of unsintered PTFE.

The uniaxial stretching in the present invention can be carried out by a conventional method, such as stretching between two rolls heated to about 250 to 320°C and rotating at different speeds. The stretching ratio preferably varies depending on the degree of sintering; for semi-sintered PTFE, it is at least 6 times, preferably 10 times or more, and for sintered PTFE, it is at least 3 times, preferably 3.5 times or more. This is because semi-sintered PTFE has poorer longitudinal cleavage properties and therefore requires increased orientation by stretching. Furthermore, to obtain fine fibers, it is desirable to stretch to as high a ratio as possible, but the maximum possible stretching ratio is usually about 10 times for sintered PTFE and about 30 times for semi-sintered PTFE.

If the stretch ratio is too low, even if mechanical force is applied to open the fibers, wide ribbon-like objects that cannot be called fibers will be produced, and since the fibers remain stretched, they will become tangled on the protrusions and needle blades of the opener, causing problems.

In the case of semi-sintered and sintered PTFE bodies, additional heat treatment after uniaxial stretching can prevent thermal shrinkage of the fibers obtained after defibration, maintain the bulkiness of the cotton-like material, and prevent a decrease in breathability. The heat treatment temperature is usually 300°C or higher.

The monoaxially stretched semi-sintered PTFE or sintered PTFE thus obtained is defibrated by mechanical force.

The mechanical force applied for defibration should be sufficient to abrade and defibrate the uniaxially stretched PTFE molded product. Examples of methods for doing so include:

(1) A cylindrical object having sharp projections on its outer periphery is rotated at high speed, and a uniaxially stretched PTFE molded product is brought into contact with the projections, causing abrasion and defibration (see, for example, Japanese Patent Publication No. 1-35093).

(2) A uniaxially stretched PTFE molded article is passed between at least one pair of needle blade rolls rotating at high speed to be abraded and defibrated (see, for example, Japanese Patent Application Laid-Open No. 58-180621).

The reason for (1) is unclear, but when sintered PTFE is used, it is easy to produce a wide tape-like product, so it is suitable when semi-sintered PTFE is used.

A preferred example thereof will be described with reference to FIG.

In Figure 2, 20 denotes a uniaxially stretched PTFE film, which is fed by pinch roll 21 toward roll 22. Protrusions 23 are formed on the outer periphery of roll 22. These protrusions are obtained, for example, by winding garnet wire around the roll. A hood 24 is located behind roll 22, and a conveyor belt 25 is installed below hood 24.

A uniaxially stretched PTFE film 20 is fed at a constant speed toward roll 22 by pinch roll 21. Roll 22 rotates at high speed, and the fed film 20 comes into contact with the garnet wire on its surface, is abraded and defibrated, and is discharged behind roll 22. The pressure inside hood 24 is reduced toward conveyor belt 25, so that defibrated fibers 26 emerging from roll 22 fall and accumulate on belt 25. Typically, the film feed speed is about 0.1 to 10 m/min, preferably about 0.1 to 5 m/min, and the peripheral speed of roll 22 is about 200 to 2000 m/min, preferably 400 to 1500 m/min.

When semi-sintered PTFE film is used, the PTFE fibers tend to become entangled in the needle blades of the needle blade roll. Therefore, method (2) is suitable for uniaxially stretched PTFE sintered film (including films obtained by sintering a uniaxially stretched semi-sintered film at a temperature above the melting point of the semi-sintered PTFE), which does not experience this phenomenon. A preferred example is illustrated in Figure 3.

In Figure 3, 30 denotes a uniaxially stretched film of sintered PTFE, which is fed to a pair of needle blade rolls 31 and 32 by a feeding means (not shown). A pipe 33 is disposed behind the needle blade rolls 31 and 32, and the inside of the pipe is under reduced pressure. As the fed film 30 passes between the needle blade rolls 31 and 32, it is abraded and defibrated by needle blades 34 and 35 embedded in the outer surfaces of the needle blade rolls 31 and 32. The defibrated fibers 36 are collected in the pipe 33, which is also under reduced pressure, and become a flocculent material (not shown).

The relationship between the feed speed of the uniaxially stretched film (V3) and the rotation speed (circumferential speed (v4)) of the needle blade roll is v4 > v3.

The arrangement, number, length, diameter, and needle angle of the needle blades 34 and 35 on the needle blade rolls 31 and 32 may be determined as appropriate, taking into consideration factors such as the thickness of the fibers to be grown. Typically, the arrangement is preferably a single row along the longitudinal direction of the roll, with 20 to 100 needles/cm² and an angle of 50 to 70°, but is not limited to these. Furthermore, the needles on the needle blade roll 31 and the needle blade roll 32 may be either identical or different. The distance between the needle blade rolls 31 and 32 may also be adjusted as appropriate, but a distance that allows the needle tips to overlap by approximately 1 to 5 mm is generally preferred.

The PTFE cotton-like material of the present invention thus obtained has an appearance similar to natural cotton, but is actually an aggregate of PTFE fibers, each of which varies in length and shape, with branched fibers accounting for the majority (30% or more, preferably 50% or more, and more preferably 70% or more).

The PTFE cotton material of the present invention can be called an aggregate of so-called PTFE stable fibers, which have a relatively short fiber length.

The fiber length of this PTFE cotton varies depending on the manufacturing conditions, but ranges from about 1 mm to 250 mm.

Short fibers have poor intertwining properties, while too long fibers make it difficult to separate the sliver. For these reasons, the fiber length is preferably 5 to 150 mm, and more preferably 25 to 150 mm.

The preferred fiber length content in the cotton-like material is 30% or more, preferably 50% or more, and more preferably 70% or more, from the viewpoint of entanglement. Furthermore, when the content is within this range, problems such as clogging of the carding machine's carding cloth can be reduced.

It is particularly preferred that the fibers of the present invention have a branched structure, a fineness of 2 to 200 denier, preferably 2 to 50 denier, a crimp count of 1 to 15 crimps per 20 mm, and an irregular cross section. From the viewpoint of processability into nonwoven fabrics, it is preferred that such fibers account for at least about 30%, and particularly at least about 50%, of the entire cotton-like material.

Examples of branched structures include those shown in Figure 1. The branched structure shown in (a) has multiple branches 2 extending from fiber 1, (b) has a branch 3 extending from branch 2, and (c) is simply split into two. The structures shown here are merely models, and no fibers actually have the same shape (see Figures 8-12). While the number and length of the branches are not particularly limited, the presence of these branches is an important factor in improving the entanglement of fibers.

There is preferably at least one branch per 5 cm of fiber, and more preferably at least two.

The fineness is 2 to 200 denier, preferably 2 to 50 denier. As will be seen from Figures 8 to 12 described later, this fineness range does not mean that the fineness is uniform throughout the fiber, and fibers that fall within this range, including branches, will produce a desirable cotton-like material.

Therefore, some of the fibers may fall outside the above-mentioned fineness range. In the cotton-like material of the present invention, it is preferable to limit the proportion of fibers less than 2 denier or more than 200 denier to less than 10%, and particularly less than 5%, in order to avoid deterioration of entanglement properties.

As shown in Figure 1, the fibers 1 constituting the cotton-like material of the present invention preferably have crimps 4 in some areas. These crimps also contribute to improved entanglement. The preferred number of crimps 5 is 1 to 15 per 20 mm. According to the manufacturing method of the present invention, crimps are generated without a special crimping step.

The cross-sectional shape of the fibers is irregular due to the abrasion caused by mechanical force, which contributes to entanglement of the fibers.

The PTFE cotton of the present invention has excellent entanglement properties and is therefore suitable as a raw material for spun yarns and nonwoven fabrics.

Nonwoven fabrics are manufactured using a carding machine, needle punch machine, water jet needle machine, etc. However, conventional PTFE fibers have a low coefficient of friction and a high specific gravity, making them difficult to process in the same way as other polyolefins, and their mechanical strength is relatively low.

For example, when manufacturing nonwoven fabric using the carding machine shown in Figure 6, a cotton-like material (not shown) conveyed on a cotton wad conveyor 60 passes through carding machine 61 to form a web, which is then wound from dowel 62 onto drum 63. The carding machine used in the present invention (Figure 6) is designed for polyolefin fibers such as polypropylene, and the distance between dowel 62 and drum 63 (referred to as the "carding distance") is set to approximately 28 cm. When using conventional PTFE fibers, sagging occurs between the dowel and drum at this distance, so the fibers must be moved closer to approximately 5 cm before they can be wound onto the drum.

When the PTFE cotton of the present invention is used, the web can be wound onto a drum without any difficulty at the same card crossing distance (about 28 cm) as with polyolefin cotton.

The present invention will now be described with reference to examples, but the present invention is not limited to these examples.

Example I: PTFE fine powder (Polyflon F-104, manufactured by Daikin Industries, Ltd., melting point 345°C) was paste extruded and calendered to obtain an unsintered tape (width 200 mm, thickness 100 μm). This was then heat-treated in a 340°C atmosphere for 30 seconds to produce a semi-sintered PTFE tape with a crystal conversion rate of 0.45.

Next, this semi-sintered tape was stretched 12.5 times in the longitudinal direction between a first roll (roll diameter 300 mmφ, temperature 300°C, peripheral speed 0.5 m/min) and a second roll (roll diameter 220 mmφ, temperature 300°C, peripheral speed 6.25 m/min), to obtain a uniaxially stretched film of semi-sintered PTFE.

Next, one side of the semi-sintered PTFE uniaxially stretched film was fixed, and a jig with 0.4 mm diameter, 5 mm long straight needles (25 needles per cm²) was placed over the entire surface of a 20 cm x 5 cm rectangle. The needles were then vigorously rubbed with the needle tips to loosen the fibers and obtain a flocculent material.

The obtained cotton-like material had fibers with the following physical properties:

Fiber length = 5 to 243 mm, of which 88% are 5 to 150 mm.

Number of branches: 20-3/5cm, with 32% being 1/5cm or larger.

Fineness: 2 to 462 denier, of which 93% are 2 to 200 denier.

Number of crimps: 0-3 per 20 mm, of which 28% have 1-15 per 20 mm (excluding those in branches).

Cross-sectional shape: irregular The above physical properties were measured as follows:

(Fiber length and number of branches) The length and number of branches were measured for 100 randomly sampled fibers.

(Cross-sectional shape) Randomly sampled fiber bundles were measured using a scanning electron microscope.

(Fiber V) 100 randomly sampled fibers were measured using an electronic fineness meter (manufactured by Search), which utilizes fiber resonance for measurement.

The fibers to be measured were selected from those 3 cm or longer that could be measured with this measuring device, separated into trunk and branch sections. However, fibers with large branches or numerous branches within a 3 cm section were excluded because they would affect the measurement results. Since the fineness that can be measured with this measuring device ranges from 2 to 70 denier, the fineness of fibers exceeding 70 denier was determined by weight measurement.

(Number of crimps) In accordance with the method of JIS L 1015, 100 randomly sampled fibers were measured using an automatic crimp performance measuring instrument manufactured by Koa Shokai Co., Ltd. (crimps present in the branches were not measured, however).

Approximately 2% by weight of an antistatic agent (Elimina, manufactured by Maruzen Chemical Co., Ltd.) was sprayed onto the cotton-like material, and a web was then formed using a carding machine (SC=360DR1, manufactured by Yamato Kiko Co., Ltd.). A web with a uniform basis weight of 300 g/m was easily produced (carding distance: 28 cm).

Next, this web was placed on a woven fabric (Neenex C01200, manufactured by Teijin Limited) and needled with a needle punching machine (manufactured by Yamato Kiko Co., Ltd., 2,400 needles per 100 cm2) to obtain a felt in which fibers were implanted on the woven fabric.

Example 2 (1) PTFE fine powder (Polyflon F104U1, manufactured by Daikin Industries, Ltd., melting point 345°C) was mixed with an auxiliary agent (IP-2028, manufactured by Idemitsu Petrochemical Co., Ltd.), and the mixture was aged at room temperature for two days to form a preform. The preform was then paste extruded and calendered to produce an unsintered film.

(2) This unsintered film was heat-treated for 53 seconds in a salt bath heated to 337°C to obtain a semi-sintered film having a width of 155 mm, a thickness of 125 µm, and a crystalline conversion rate of 0.38.

(3) This semi-baked film was stretched 15 times in the longitudinal direction using two rolls heated to 300°C and rotating at different speeds to obtain a uniaxially stretched film with a width of 104 mm and a thickness of 32 μm.

(4) The obtained uniaxially stretched film was defibrated by rubbing it with a roll wound with garnet wire rotating at high speed as shown in Figure 2, to obtain a cotton-like material. The garnet wire used had five ridges per inch and a wire thickness of 1 mm. The film feed speed (vl) was 1.5 rn/min, and the roll peripheral speed (V2) was 1,200 m/min.

The resulting flocculent contained fibers having the following physical properties:

Fiber length: 1 to 103 mm, of which 68% are 5 to 150 mm.

Number of branches: 20-10 per 5 cm, with 51% being 1 per 5 cm or larger.

Fineness: 2 to 103 denier, 100% of which is 2 to 200 denier.

Number of crimps: 20-4 per 20 mm, of which 89% are 1-15 per 20 mm.

Cross-sectional shape: irregular (Figure 7 shows the cross-sectional shape of the fiber (×500).) Examples 3.4 A PTFE cotton-like material was obtained by the same process as in Example 2, except that steps (2) to (4) in Example 2 were changed as shown in Table 1. The physical properties of the fibers contained in this material were investigated in the same manner as in Example 2. The results are shown in Table 2.

[Blank space follows] Example 5 (1) PTFE fine powder (Polyflon F104U, Daikin Industries, Ltd.) was mixed with an auxiliary agent (IP-2028, Idemitsu Chemical Co., Ltd.), and the mixture was aged at room temperature for two days to form a preform. The preform was then subjected to pre-extrusion and calendering to produce an unsintered film.

(2) The unsintered film was heat-treated for 60 seconds in a salt bath heated to 360°C to obtain a sintered film having a width of 155 mm and a thickness of 60 μm.

(3) The fired film was stretched four times in the longitudinal direction using two rolls heated to 320°C and rotating at different speeds to obtain a uniaxially stretched film with a width of 85 mm and a thickness of 24 μm.

(4) The monoaxially stretched film was rubbed and defibrated between a pair of upper and lower needle blade rolls as shown in Figure 3, with the film feed speed (v3) being 1.6 m/min and the needle blade roll peripheral speed (v4) being 48 m/min, for a v4/v3 speed ratio of 30. The pressure was reduced on the side opposite the film inlet (the outlet for the treated material) to produce a flocculent material.

The shape of the needle blade roll and the arrangement and meshing of the needle blades of the upper and lower needle blade rolls are as follows: When film 30 was passed at the same speed as the pair of upper and lower needle blade rolls 31 and 32 shown in Figure 3, the film was perforated as shown in Figure 4. A in Figure 4 shows the pinholes of the upper needle blade roll 31, and the circumferential pitch was P1, which was 2.5 mm.

B denotes the needle holes of the lower needle blade roll 32, and their pitch P2 was 2.5 mm, the same as P1. The number of needles implanted in the longitudinal direction of the roll, a, was 13 per cm. As shown in Figure 5, the implantation angle (θ) was set to form an acute angle (60°) with respect to the film 30 being drawn into the roll 31 or 32. As shown in Figure 4, the upper and lower needle blade rolls were interlocked such that the needles of the upper needle blade roll 31 and the lower needle blade roll 32 alternated in the circumferential direction. The longitudinal length of the needle blade roll was 250 mm.

The diameter at the tip of the needle blade roll was 5Q mm.

(5) The physical properties of the obtained fibers were measured in the same manner as in Example 1. The results are shown in Table 4.

(6) Photographs (X1, 5) showing the shape of the obtained fibers are shown in Figures 8 to 12, and the cross-sectional shape of the fibers (X50) is shown in Figure 13.

Examples 6 and 7 A PTFE cotton-like material was obtained in the same manner as in Example 5, except that steps (2) to (4) in Example 5 were changed as shown in Table 3. The physical properties of the fibers contained in this material were investigated in the same manner as in Example 5. The results are shown in Table 4.

[Blank space follows] Example 8 (1) The cotton-like material obtained in Example 2 was sprayed with approximately 2% by weight of the antistatic agent Elimina (Maruzen Yuka Co., Ltd.), and then passed through the carding machine (SC-360DR, Yamato Kiko Co., Ltd.) shown in Figure 6. This produced a web with a basis weight of 450 g/m².

At this time, the cylinder rotation speed was 183 rpm, the dowel rotation speed was 5 rpm, the drum rotation speed was 5 rpm, and the card transfer distance was 28 cm.

(2) The obtained web was placed on a woven fabric (base fabric) of Neenex C01200 (manufactured by Ondai Co., Ltd.) and needled using a needle punch machine (manufactured by Yamato Kiko Co., Ltd.) at a needle punch density of 25 needles/cm² to produce a needle-punched nonwoven fabric.

The air permeability of the obtained needle-punched nonwoven fabric was measured and found to be 27 cm 70 m²/sec.

(Air permeability) Measured using a Frazier-type air permeability tester.

Example 9 (1) In Example 2, a web with a basis weight of 350 g/m2 was produced on the conveying sheet shown in Figure 2 using Neenex C01200 (manufactured by Ondai Co., Ltd.).

(2) The obtained web was water-jet needled using a water-jet needling device (Perfojet) to produce a nonwoven fabric with a base fabric of Neenex C01200.

The water jet needle had 800 nozzles with a diameter of 100 μm, spaced 1 mm apart across the width, arranged in three rows along the length. The pressures were 40 kg/cm² for the first row, 100 kg/cm² for the second row, and 130 kg/cm² for the third row.

(3) The air permeability of the water-jet needled nonwoven fabric was measured in the same manner as in Example 8 and was found to be 18 cm3/cm2/Sec.

Example 10 (1) The cotton-like material obtained in Example 3 was passed through a carding machine in the same manner as in Example 8 (1) to produce a web with a basis weight of 350 g/m2 (carding distance: 28 cm).

(2) The obtained web was placed on a woven fabric (base fabric) of Neenex C01200 (manufactured by Ondai Co., Ltd.) and needled using a needle punch machine (manufactured by Yamato Kiko Co., Ltd.) at a needle punch density of 25 needles/cm to produce a needle-punched nonwoven fabric.

(3) The breathability of this nonwoven fabric was 30 cm/cm²/sec.

Example 11 (1) In Example 3, a web with a basis weight of 350 g/m2 was produced on the transfer sheet shown in Figure 2 using Neenex C01200 (manufactured by Ondai Co., Ltd.).

(2) The obtained web was water jet needled using a water jet needle device (manufactured by Perforjet) to produce a nonwoven fabric with a base fabric of Neenex C01200.

The water jet needle had 800 nozzles with a diameter of 100 μm, spaced 1 mm apart across the width, arranged in three rows along the length. The pressures were 40 kg/cm² for the first row, 100 kg/cm² for the second row, and 130 kg/cm² for the third row.

(3) The breathability of this nonwoven fabric was 18 cm²/cm²/sec eC.

Example 12 (1) The cotton-like material obtained in Example 4 was passed through a carding machine in the same manner as in Example 8 (1) to produce a web with a basis weight of 350 g/m2 (carding distance: 28 cm).

(2) The obtained web was placed on a woven fabric (base fabric) of Neenex C01200 (manufactured by Ondai Co., Ltd.) and needled at a needle punch density of 25 needles/cm using a needle punching machine (manufactured by Yamato Kiko Co., Ltd.) to produce a needle-punched nonwoven fabric.

(3) The breathability of this nonwoven fabric was 33 cm/cm²/sec.

Example 13 (1) In Example 4, a web with a basis weight of 350 g/m2 was produced on the transfer sheet shown in Figure 2 using Neenex C01200 (manufactured by Ondai Co., Ltd.).

(2) The obtained web was water-jet needled using a water-jet needling device (Perforjet Co., Ltd.) to produce a nonwoven fabric with Neenex C01200 as the base fabric.

The water jet needle had 800 nozzles with a diameter of 100 μm, spaced 1 mm apart across the width, arranged in three rows along the length. The pressure was 40 kg/cm for the first row, 100 g/am for the second row, and 1301 g/cm for the third row.

(3) The breathability of this nonwoven fabric was 20 cm³/cm²/sec.

Example 14 (1) The cotton-like material obtained in Example 5 was passed through a carding machine in the same manner as in Example 8 (1) to produce a web with a basis weight of 350 g/m2 (carding distance 28 cm).

(2) The obtained web was placed on a woven fabric (base fabric) of Neenex C01200 (manufactured by Ondai Co., Ltd.) and needled using a needle punch machine (manufactured by Yamato Kiko Co., Ltd.) at a needle punch density of 25 needles/cm to produce a needle-punched nonwoven fabric.

(3) The breathability of this nonwoven fabric was 38 cm3/cm2/sec.

Example 15 (1) The cotton-like material obtained in Example 6 was passed through a carding machine in the same manner as in Example 8 (1) to produce a web with a basis weight of 350 g/m2 (carding distance: 28 cm).

(2) The obtained web was placed on a woven fabric (base fabric) of Neenex C01200 (manufactured by Ondai Co., Ltd.) and needled at a needle punch density of 25 needles/cm² using a needle punch machine (manufactured by Yamato Kiko Co., Ltd.) to produce a needle-punched nonwoven fabric.

(3) The breathability of this nonwoven fabric was 36 crr+3/cm2/sec.

Example 16 (1) The cotton-like material obtained in Example 7 was passed through a carding machine in the same manner as in Example 8 (1) to produce a web with a basis weight of 350 g/m2 (carding distance: 28 cm).

(2) The obtained web was placed on a woven fabric (base fabric) of Neenex C01200 (manufactured by Ondai Co., Ltd.) and needled at a needle punch density of 25 needles/cm² using a needle punch machine (manufactured by Yamato Kiko Co., Ltd.) to produce a needle-punched nonwoven fabric.

(3) The air permeability of this nonwoven fabric was 39 Cm3/Cm2/SeC.

Comparative Example 1 Toyoflon [F] Type 201 staple fiber manufactured by Toshiba Fine Chemical Co., Ltd. using the emulsion spinning method, had a fiber length of 70 mm, a fineness of 6.7 denier (measured as in the Examples, the number of crimps was 7 per 20 mm per minute, and the number of crimps was zero; the cross section was circular). When passed through a carding machine in the same manner as in Example 8 (1), the web sagged at a carding distance of 28 cm and could not be wound onto the drum.

INDUSTRIAL APPLICABILITY The PTFE fibers with excellent entanglement properties and the PTFE cotton-like material containing them of the present invention can provide PTFE nonwoven fabrics that take advantage of the excellent properties of PTFH.

Claims (16)

[Claims] 1. Polytetrafluoroethylene flocculent obtained by mechanically defibrating a uniaxially stretched polytetrafluoroethylene molded product. 2. Polytetrafluoroethylene fibers having a fiber length of 5 to 150 mm obtained by mechanically defibrating a uniaxially stretched polytetrafluoroethylene molded article. 3. The fiber according to claim 2, which has a branched structure. 4. The fiber according to claim 2 or 3, having a fineness of 2 to 200 denier. 5. The fiber according to claim 2, 3, or 4, wherein the number of crimps is 1 to 15 per 20 mm. 6. The fiber according to claim 2, 3, 4, or 5, having an irregular cross-sectional shape. 7. The fiber according to claim 2, 3, 4, 5 or 6, wherein the polytetrafluoroethylene molded article is a semi-sintered polytetrafluoroethylene body. 8. The fiber according to claim 2, 3, 4, 5, or 6, wherein the polytetrafluoroethylene molded article is a sintered polytetrafluoroethylene body. 9. The cotton-like material according to claim 1, containing 30% or more of the fibers according to any one of claims 2 to 8. 10. A method for producing a polytetrafluoroethylene flocculant by mechanically defibrating a uniaxially stretched polytetrafluoroethylene molded product. 11. The manufacturing method according to claim 10, wherein the polytetrafluoroethylene cotton-like material is the cotton-like material according to claim 9. 12. The method of claim 10 or 11, wherein the polytetrafluoroethylene molded article is a semi-sintered body and is uniaxially stretched at a stretching ratio of at least 6 times. 13. The method of claim 10 or 11, wherein the polytetrafluoroethylene molded article is a sintered product and is uniaxially stretched at a stretch ratio of at least 3 times. 14. The manufacturing method according to claim 10 or 11, wherein the uniaxially stretched polytetrafluoroethylene film is defibrated by bringing it into contact with a rotating cylinder having sharp projections formed on the outer periphery thereof and rotating at high speed. 15. The manufacturing method according to claim 10 or 11, in which the uniaxially stretched polytetrafluoroethylene film is defibrated by passing it between at least one pair of needle blade rolls rotating at high speed. 16. A manufacturing method according to claim 10, 11, 12 or 13, in which a uniaxially stretched polytetrafluoroethylene molded article is heat-treated at a temperature equal to or higher than the temperature at which it was uniaxially stretched, and then defibrated.