JP2571379B2 - Method for producing polytetrafluoroellen fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an ultrafine polytetrafluoroethylene-based fiber of 3.0 d or less.

[Prior Art] Polytetrafluoroethylene (hereinafter referred to simply as PTFE) fibers are widely used in a wide range of fields including industrial materials because of their properties such as releasability.

Conventionally, PTFE-based polymers have the disadvantage that the polymer solution viscosity is high and nozzle clogging is likely to occur, and the spinnability is also poor and thread-making is easy to break.At present, at most 5d exists as the finest fineness. However, fibers smaller than this are considered difficult to produce and produce, and the fact is that they have not been commercialized industrially.

[Problems to be Solved by the Invention] As a result of examining the ultrafineness of the PTFE-based fiber, the present invention has found that although it is an ultrafine fiber, it has excellent strength, has no single yarn breakage or fluff, has a very small friction coefficient, and has a small size. The present invention has provided a method for producing a PTFE-based fiber having good stability.

The present invention fundamentally breaks down the conventional concept of PTFE-based fibers, which have a strong image of heavy and difficult-to-handle fibers, and is sufficiently applicable to fields that could not be used in the past, and is extremely fine. It is possible to exhibit the characteristic that it can be easily mixed and dispersed with various kinds of fibers and other kinds of resins.

Taking advantage of such characteristics, the characteristics can be sufficiently utilized in an extremely small amount as compared with the related art, and the degree of freedom in designing the application of the PTFE-based fiber can be remarkably expanded.

[Means for Solving the Problems] The present invention has the following configuration. That is, the method for producing a polytetrafluoroethylene-based fiber of the present invention comprises dispersing a polytetrafluoroethylene-based polymer in water under a surfactant until the particle size of the polymer becomes 1 μm or less. After forming the dispersion, the dispersion was mixed with viscose to form a spinning dope. The spinning dope was spun into a coagulation bath, scoured, washed with alkali,
Firing at 焼 結 450 ° C. and sintering, the average fineness of the polytetrafluoroethylene polymer is 3d or less, and the small angle X-ray scattering intensity of 2θ = 1 ° by the small angle X-ray scattering method is 80 cps or less. It is characterized by producing a consolidated fiber.

In the present invention, the PTFE-based polymer means a tetrafluoroethylene homopolymer or a copolymer in which 90 mol% or more, preferably 95 mol% or more of the whole is tetrafluoroethylene.

Monomers copolymerizable with tetrafluoroethylene include trifluoroethylene, trifluorochloroethylene,
Tetrafluoropropylene, vinyl fluoride compounds such as hexafluoropropylene and further propylene, ethylene,
Examples include, but are not limited to, vinyl compounds such as isobutylene, styrene, and acrylonitrile.

Among these monomers, vinyl fluoride compounds, which are also compounds having a high fluorine content, are preferred from the viewpoint of fiber properties.

The PTFE-based fiber obtained by the production method of the present invention is a fine sintered fiber having an average fineness of 3d or less, preferably 2d or less, but as the sintered fiber becomes thinner,
As a result, it is excellent in the above-described application development effect, and therefore, according to the method of the present invention, even an extremely thin product of 1d or less can be produced.

The PTFE fiber obtained by the production method of the present invention has a value of 80 cps or less, preferably 50 cps or less, particularly preferably 40 cps or less when the small-angle X-ray scattering intensity at 2θ = 1 ° is measured by the small-angle X-ray scattering method. There is a feature that there is.

That is, if it exceeds 80 cps, the fibers become brittle, and there is no degree of freedom in application development from the viewpoint of fiber characteristics, which is not preferable. That is, the PTFE-based fiber of the present invention has a small concentration of microvoids in the crystal of the constituting polymer and is dense.

The fiber obtained by the production method of the present invention is characterized in that the small-angle X-ray scattering intensity is low and the crystal size of the (110) plane by wide-angle X-ray diffraction (counter method) is 95 ° or more, preferably 100 ° or more. Some have a thickness of. In other words, a large crystal size means that the crystal is growing thicker.

That is, in the PTFE-based fiber obtained by the production method of the present invention, despite the thin fiber as a synergistic effect of the small-angle X-ray scattering intensity and the crystal size of the (110) plane, the crystal is sufficiently grown. It can provide fibers excellent in strength and dimensional stability.

 The small-angle X-ray scattering intensity is measured as follows.

Sample fibers are arranged in the fiber axis direction and cut to a length of 4 cm.
A weight of 60 mg is weighed, loaded into a mold having a depth of 1 mm and a width of 2 mm, and solidified using a collodion solution to form a prism, which is used as a sample.

Attach the sample vertically to the X-ray beam,
The scattering intensity at 2θ = 1 ° when a small angle having a directional angle of 0 to 3 ° is scanned is measured under the following conditions.

Measurement method: Small-angle X-ray scattering method (Small-angle X-ray diffraction method) X-ray generator; RU-200B manufactured by Rigaku Corporation (rotating anti-cathode type) X-ray source: CuKα (using flat graphite single crystal incident monochromator) Output: 40kV 200mA Optical system; Rigaku Denki's cracky camera U slit: width 70μm, height 10mm Light receiving side: light receiving slit 0.14mm, vertical restriction slit 15mm, scattering prevention slit 0.3mm, vertical scattering prevention slit 6mm, detector: scintillation counter The data obtained from this counter is applied to a counting and recording device to draw a chart.

The crystal size of the (110) plane in the present invention is measured as follows.

Sample fibers are arranged in the fiber axis direction and cut to a length of 4 cm.
Weigh 20 mg, load it into a 1 mm deep, 1 mm wide mold, and solidify using a collodion solution to make a prism,
Use as a sample.

The obtained sample was mounted so as to be perpendicular to the X-ray beam, and when the azimuth angle 2θ was scanned from 0 to 90 ° by the transmission method, the peak band of the (110) plane (about 18.3 °) was observed. Full width (half width) at half the maximum value of the intensity distribution
It is calculated from B and the azimuth angle 2θ by the following Scherrer equation.

L = Kλ / [(B−b) · Cos θ] where K = 1.0, b = 0.0105 rad, and λ = 1.5418 °.

 The peak band of the (110) plane is measured by the following method.

Measurement method: Wide-angle X-ray diffraction method (counter method) X-ray generator; RU-200B manufactured by Rigaku Corporation (rotating anti-cathode type) X-ray source: CuKα (using Ni filter) Output: 35kV 15mA Goniometer; Goniometer made by company Slit system: 2mmφ 1 ゜ -1 ゜ Detector; scintillation counter The data obtained from this counter is sent to a counting and recording device to draw a chart.

The PTFE fiber obtained by the production method of the present invention has the following fiber characteristics.

That is, strength 1.0 g / d or more, preferably 1.5 g / d or more,
Elongation 30% or less, preferably 20% or less, dry heat shrinkage (230
(° C x 30 ') 20% or less, preferably 15% or less. In particular, the elongation is significantly different from that of the conventional PTFE-based fiber which is around 40%.

Although the PTFE-based fiber obtained by the production method of the present invention has well-balanced fiber properties excellent in dimensional stability as described above, despite being as thin as 3.0 d or less, various types of fibers and various types of resins are used. It has good familiarity with the above, exhibits characteristics that mixing and dispersion can be uniformly and easily achieved, and is thin, so that it is possible to modify the surface characteristics with a smaller amount.

Next, the method for producing the PTFE-based fiber of the present invention will be described in detail. That is, the point of the manufacturing method of the present invention is
A polytetrafluoroethylene-based polymer is dispersed in water under a surfactant until the particle size of the polymer becomes 1 μm or less to form a dispersion. That is, the smaller the particle size of the dispersion polymer, the more excellent the fiber having excellent spinnability and fiber properties can be formed. Next, this dispersion is mixed with viscose to form a spinning dope, and this spinning dope is spun into a coagulation bath, scoured, washed with alkali, and then fired and sintered at 300 to 450 ° C. to obtain a sintered body. Manufacture fiber. In the following, “%” in the present invention means “% by weight”.

As a feature of the production method of the present invention, washing from the spinning stock solution,
Water and chemicals used in each step such as alkali treatment are all high-purity systems with few impurities (foreign matter). By adopting such a system,
For the first time, it has been possible to provide a fiber with good crystal growth and few voids by controlling single yarn breakage and fluffing.
In addition, the particles generated during the process are controlled as much as possible,
Care should be taken to eliminate large foreign objects.

As a spinning solution of the present invention, a mixed solution of viscose and PTFE dispersion is used, and this is discharged into a coagulation bath,
After coagulation, it is washed and scoured. After scouring, it is immersed in alkaline water and squeezed, and then dried or directly led to a firing step, where firing and stretching are performed. Firing and stretching may be separate. Next, the fired fiber is oxidized and aged in a high-temperature atmosphere.

Water used in the present invention, in any step,
Ion exchange water or distilled water is used.

The above PTFE dispersion uses PTFE in ion-exchanged water.
It is 20 to 75%, preferably around 60% compounded and dispersed. As the dispersant, a nonionic surfactant or an anionic surfactant is used, and in particular, a nonionic surfactant is selected. The compounding amount is 3 to 10% based on the PTFE amount. Such dispersants include, for example, polyoxyalkylene glycol-based nonionic surfactants and alkyl allyl polyether alcohols ("Triton X-100").

The size of the dispersion particles of the PTFE-based polymer of the dispersion thus obtained is 1 μm or less, preferably 0.005 to
Preferably, the particle size is 0.6 μm.
The smaller the smaller, the more excellent the fiber properties such as spinnability, strength and elongation can be provided.

Viscose is cellulose 3-15%, preferably 5-
10%, caustic soda 2-12%, preferably 6-9%, carbon disulfide 27-32%, preferably 28-30%, and its degree of polymerization is 200-600, preferably 300-400. is there. The more mature (older) the composition, the better.

Such a PTFE dispersion and viscose are mixed to form a spinning dope. At this time, the PTFE in the mixed polymer of the spinning dope is 60 to 98%, preferably 70 to 96%, particularly preferably 87 to 93%. The composition is adjusted within the range, but the higher the PTFE concentration, the better the fiber properties. That is, the cellulose concentration in the spinning solution is 5 to 20%, preferably about 10 to 15%.

The viscosity of this stock solution is about 30-190 pois at 20 ° C,
Preferably it is adjusted to 50 to 140 pois. In order to stabilize the dispersion dispersibility of the mixed stock solution, a nonionic surfactant or a dispersant such as glycerin or hexametaphosphate can be further added. The amount of this dispersant added
It is about 3 to 10% based on the amount of PTFE.

In this stock solution, 0.5 to 30%, preferably 3 to 20%, of molybdenum disulfide having a particle size of 100 μ or less, preferably 50 μ or less.
When mixed in%, the fiber separation property, strong rigidity, and abrasion resistance are improved.

Such undiluted solution is defoamed, but at this time water evaporates,
There is a problem that PTFE particles aggregate. The aggregated particles are usually 20
In the present invention, it is important to control not to form or grow such agglomerated particles, and in the present invention, a low-temperature vacuum mixing method of 10 ° C. or less is particularly preferable because the evaporation of water is small since water evaporation is small. Adopted. The degree of vacuum is about 10 Torr. Further, it is also preferable to pass the undiluted solution after defoaming.

The spinning dope is then spun into an aqueous coagulation bath composed of inorganic mineral acids and / or inorganic mineral salts. As such an inorganic mineral acid, sulfuric acid is preferable, but nitric acid, hydrochloric acid, phosphoric acid and the like can also be applied. The content of inorganic mineral acid is 0.1-50
%, Preferably 0.5 to 35%, more preferably 0.5 to 15%.

If necessary, the inorganic mineral salt used in combination may be a sulfate such as ammonium sulfate, zinc sulfate or sodium sulfate. Preferably, sodium sulfate is selected. Such an inorganic mineral salt is added and blended in an amount of about 30% or less.

The spinning solution is extruded into the coagulation bath, and is spun and coagulated as a multifilament. The spinning speed at this time is, for example, about 20 to 50 m / min or less, and the spinning is slowly performed.

This coagulated multifilament is sufficiently scoured as it is in warm water at 40 to 90 ° C, preferably around 80 ° C. Since the refining temperature is related to the formation of cavities, it is necessary to control the temperature appropriately. However, in the case of producing a modified cross-section yarn, it is preferable to maintain the temperature of the scouring bath at a low temperature of 60 ° C. or less from the viewpoint of shape maintenance. It is preferable from the viewpoint of fiber properties that the metal salt is sufficiently removed in this scouring step, and this has a good effect.

The scoured filament is then alkali washed and then squeezed.

As such an alkaline treatment bath, an aqueous solution of a compound selected from hydroxides, carbonates, and bicarbonates of alkali metals or alkaline earth metals is used. The concentration of the compound is about 0.001 to 2% based on the weight of the fiber (0.0005 to 0.05 mol / ι).
It is. Since such a metal has a function of smoothly progressing the baking, it is attached to the fiber (about 0.003 to 0.32%).

The alkali-treated multifilament bundle is 30
Baking at 0 to 450 ° C, preferably 320 to 400 ° C. In this case, firing and stretching may be performed separately. You may stretch simultaneously. Stretching is performed at least 5 to 10 times. At this time, it is preferable to select conditions for carbonizing until the cellulose carbide becomes 3.0% by weight or less. The resulting fiber has a brown or black color because it contains cellulose carbide.

The PTFE yarn fiber obtained in this way is 300 ° C or more,
Preferably, it is whitened by air oxidation and aging at 310-340 ° C for at least 50 hours, preferably 60 hours or more.

 Next, the present invention will be described in more detail with reference to examples.

[Example] Example 1 A dispersion containing 60% of a PTFE-based resin dispersed in ion-exchanged water to have a mean particle size of 0.1 µm using an alkylallyl polyether alcohol as a dispersant was prepared.
114 parts and viscose (cellulose 8.9% and caustic soda 5.
4%, 29% of carbon disulfide / cellulose amount, 100 parts of remaining ion-exchanged water) were charged into a vacuum mixer at 8 ° C.
The mixture was mixed and defoamed at Torr for 21 hours to prepare a spinning stock solution.

This spinning dope was introduced into a die having 240 holes of 0.12 mmφ at 43 g / min and discharged into a coagulation bath controlled at 23 ° C. at a speed of 23 m / min. Coagulation bath is 7% sulfuric acid, 20% sodium sulfate
% Was dissolved in ion-exchanged water.

This coagulated fiber is led to an ion exchange water tank at 80 ° C,
m / min, slowly and thoroughly washed, squeezed with a mangle, immersed in an ion exchange aqueous solution having a caustic soda concentration of 0.05 mol / ι,
%.

The alkali-containing fiber was then fired by contacting a roll heated to 380 ° C.

The fired fiber was stretched 7 times while being in contact with a heating roll at 350 ° C.

The fiber was left in a relaxed state in an air atmosphere heated to 320 ° C. for 72 hours.

The obtained PTFE fiber is white, strength 1.3 g / d, elongation 1
It had well-balanced properties of 6.1% and dry heat shrinkage (230 ° C x 30 minutes) 12.3%.

Small angle X of 2θ = 1 ° by small angle X-ray scattering method of this fiber
The X-ray scattering intensity was 38 cps, which was determined by wide-angle X-ray diffraction (11
The crystal size of the 0) plane was 107 °.

The commercially available 6.7d white PTFE fiber has an unusually high elongation of 1.3g / d, an elongation of 40%, and a dry heat shrinkage (230 ° C x 30 minutes) of 5.3%. Met.

Small angle X of 2θ = 1 ° by small angle X-ray scattering method of this fiber
The X-ray scattering intensity was 86 cps, which was determined by the wide-angle X-ray diffraction method (11
The crystal size of the 0) plane was 94 °.

(Effects of the Invention) The present invention is an ultrafine fiber, and can be easily mixed and dispersed with various kinds of fibers and various kinds of resins. Therefore, the present invention can be sufficiently applied to fields where conventional applications could not be developed.

Continuation of front page (72) Inventor Haruo Sasamori 1515 Tsutsui, Matsumae-cho, Iyo-gun, Ehime Prefecture Toray Ehime Plant (56) References JP-A-59-216915 (JP, A) JP-A-59-187615 (JP) , A) Japanese Patent Publication 47-50662 (JP, B1) Japanese Patent Publication 50-22621 (JP, B2)

Claims (6)

(57) [Claims] A dispersion is formed by dispersing a polytetrafluoroethylene-based polymer in water under a surfactant until the particle size of the polymer becomes 1 μm or less to form a dispersion. Mix with viscose to form a spinning dope, spinning this spinning dope into a coagulation bath, scouring, washing with alkali, firing at 300-450 ° C and sintering, from polytetrafluoroethylene-based polymer Producing a sintered fiber having an average fineness of 3d or less and a small-angle X-ray scattering intensity at 2θ = 1 ° by a small-angle X-ray scattering method of 80 cps or less. . 2. The polymer according to claim 1, wherein the average particle diameter is 0.6 μm.
The method for producing a polytetrafluoroethylene-based fiber according to claim 1, which is adjusted as follows. 3. The method for producing a polytetrafluoroethylene fiber according to claim 1, wherein said surfactant is one of a nonionic surfactant and an anionic surfactant. 4. The method for producing a polytetrafluoroethylene-based fiber according to claim 1, wherein the water and the chemical used in each step of said production method are of high purity. 5. The method for producing a polytetrafluoroethylene fiber according to claim 4, wherein said water is ion-exchanged water or distilled water. 6. The method for producing a polytetrafluoroethylene-based fiber according to claim 1, wherein said calcination is carried out under conditions for carbonizing the cellulose carbide to 3% by weight or less.