JPH03161523A - Pitch-based carbon fiber - Google Patents

Abstract

PURPOSE:To obtain the subject fiber, composed of continuous liquid crystal pitch-based single filament having a specific diameter or above and useful as electrically conductive materials (heating elements or electrode materials), electromagnetic wave shielding, antistatic, heat- and chemical-resistant materials (filter cloth and working clothes), etc. CONSTITUTION:The objective fiber composed of continuous liquid crystal pitch- based single filament having >=20mum average fiber diameter, preferably >=80000 kgf/mm<2> elastic modulus and preferably >=200kgf/mm<2> tensile strength.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to carbon fibers in which the constituent single fibers have a large diameter.
Furthermore, the present invention is directed to a continuous monofilament of a liquid crystal pitch system or a structure similar to the monofilament. @Concerning continuous carbon fiber with a small number of fibers. In addition, the liquid crystal pitch L of the present invention
L is a general term for pitches containing optically anisotropic components or pitches that are easily converted into optical anisotropy by heat or stress.

Constituent single fiber carbon fiber with large diameter is used as a conductive material (heating element,
Electrode materials), electromagnetic shielding materials, antistatic materials, heat-resistant and chemical-resistant materials (filtering cloth, work clothes, protective clothing, protective gear, heat insulation materials)
Used for etc. Conventional carbon fibers have drawbacks such as easy fluffing due to their thin single fibers and large number of single fibers, making them inconvenient to handle as raw materials for such industrial materials. Carbon wA fibers, which have large diameter constituent single fibers, have the advantage of being strong and difficult to deform due to the flow of matrix components, as a reinforcing material for fiber composite materials. In particular, when the matrix component is a t,t material with extremely high surface tension, such as a metal,
Even in the case of materials with extremely high viscosity such as certain thermoplastic resins, the carbon fibers of the present invention have a small tendency to move and spread out due to the flow of matrix components, so they are suitable for use in textile and navy blue composites. Shows excellent performance as a reinforcing material.

Structure i Carbon fibers with a small number of fibers, especially monofilaments, exhibit excellent performance as core materials for ceramic fibers and the like produced by coating boron, silicon carbide, silicon nitride, etc. by CVD method or the like.

[Conventional {Summary ■] It is well known that when a brittle material such as glass is formed into a very thin material, its strength increases.

This is because there is a certain probability that scratches will occur due to distortion during molding, etc.
It is explained that the thinner the test piece is, the smaller the probability that it will contain scratches, so the thinner the test piece, the more quickly the strength will increase.

It has been reported that such a phenomenon also exists in the case of monocarbon fibers. In the case of PAN-based carbon fibers, the strength increases as the fiber diameter decreases, so as time passes, thinner fibers are gradually being made.

In the case of isotropic pitch-based carbon fibers, Otani investigated the relationship between fiber diameter and strength and reported that the strength decreases rapidly when the diameter becomes larger than 10 μm [, +: arbo
n3,:N~38 (1965)]. In the case of mesophase pitch carbon fiber, D. M. Riggs and J.
f;. Vellner has a carbonization temperature of 4 soo C and 20
00℃ has a strength of 450 KSI or more when the fiber diameter is 8 μm or less, and the strength decreases rapidly as the diameter increases, and it is 250 KSI at a diameter of 13.5 μm.
It is reported that the following will occur. (16tlBienn
ial Conference on Carb
Under these circumstances, it has not been possible to obtain liquid crystal pitch-based carbon fiber monofilaments, particularly continuous monofilaments, having a diameter of 20 μm or more.

Conventionally, synthetic fiber monofilament is produced by extruding the spinning solution from a spinneret and solidifying it, then continuously drawing and heat-treating it, and then separating the fibers one or several fibers at a time and winding them up. Manufactured.

Although this method of gamma removal is simple and does not require advanced technology, the quality of the product is high and it is used by cutting into many synthetic resins such as polyamide, polyester, and polyolefin.

In addition, for fibers with high strength and stiffness such as bolyamide, a method is also used in which a relatively single filament yarn with a large denier is untwisted and divided one or two filaments at a time and then wound.

In the case of bitch fibers, it is difficult to use these methods because the strength of the spun single fibers is extremely low. The spun pitch fibers are either wound up immediately after being bundled, or placed in a can or on a porous belt. The pitch fibers are infusible and carbonized while being wound around a bobbin, stored in a can, or on a belt without forming any knots. It goes without saying that rough processing such as fiber splitting cannot be carried out unless the carbonization is advanced, but even after one charcoal burn, many thin single fibers are bundled and carbonized. Separating carbon fibers and extracting continuous monofilaments is extremely difficult from both strength and technical standpoints.

[What the invention attempts to solve] [11 The main use of conventional carbon fibers is to strengthen composite materials with fibers, so there was extremely little demand for yarns with a small number of I'A single fibers, such as fibers for clothing. .

However, in recent years, the quality of carbon fiber has improved, and its unique physical properties are attracting attention as a fiber for industrial materials. Therefore, there is a tendency for demand for yarns with a thickness similar to that of general synthetic fibers to increase rapidly.

In order to meet these demanding demands for carbon fiber, monofilaments with high elastic modulus and tensile strength are required. However, it is known that conventional carbon fibers have a problem in that their strength rapidly decreases when the diameter of a single fiber increases from about 10 μm.

In order to solve this problem, we were investigating the manufacturing conditions for monofilament, and found that it has a high elastic modulus and
We have discovered a liquid crystal pitch-based carbon fiber whose strength does not change significantly even when the fiber diameter changes, leading to the present invention. [Means for Solving the Problems] The present invention is a carbon fiber composed of continuous bay pitch-based single fibers having an average fiber &It11I diameter of 20 μm or more.

Wood's carbon fiber is 80,000k) (f/ms 2
It is possible to have an elastic modulus of 200 kg f/ms 2 or more and a tensile strength of 200 kg f/ms 2 or more.

Furthermore, the carbon fiber of the present invention can be used as a multifilament consisting of a large number of m fibers like conventional charcoal fiber, but it can also be used as a monofilament consisting of one single fiber. Particularly preferred.

The carbon fiber of the present invention is produced from a 1α pitch with a relatively high softening point and a molecular weight distribution, preferably a petroleum pitch with a softening point of 270 to 360°C and an optically anisotropic component content of $85 to 100%. It is something. When using pitch with a softening point of 270°C or lower, the viscosity of the melt is low, making it difficult to spin fibers with a large diameter, and as the amount of low molecular weight components increases, defects in the carbon fiber increase. However, there is a problem that the strength decreases. Therefore, it is preferable to remove low molecular weight components from the liquid crystal pitch by performing a vacuum treatment or the like.

If a pitch with a softening point of 360° C. or higher is used, there is a problem that 1-low resonance tends to occur during spinning, making it difficult to produce 1-fibers with a uniform diameter. When preparing liquid crystal pitch, one effective method is to heat-treat the pitch by separating and removing the mesophase produced during the initial heat treatment to remove components that tend to have high molecular weight and foreign substances, etc. as a raw material. . As the optically anisotropic component content decreases, the decrease in fiber strength increases as the fiber diameter increases;
Further, an increase in the optically isotropic component is not preferable because the spinnability decreases. The optical anisotropic fraction content is preferably 85% or more, particularly preferably substantially 100%.

In addition to optically anisotropic pitch with a normal flow pattern, liquid crystal pitch includes a collection of components that can be easily converted to optically anisotropic by solvent extraction from heavy oils and pitches, or optically anisotropic pitch. can be reduced to isotropic pitch, which is easily converted into optical anisotropy. Petroleum-based heavy oils and pitches are particularly preferred. In the production of the carbon fiber of the Wood Invention, it is preferable to spin the molten pitch through a spinning hole whose cross-sectional area increases in the downstream direction. One of the advantages of using such spinning holes is that the pressure drop across the spinning holes is increased and the amount of pitch discharged from each spinning hole is made uniform. Another advantage is the ability to change the orientation of pitch molecules from a radial type that is easy to break, to a random type that is easy to break, or a radial type that is sliding. In the case of Wilt with a large diameter like the one of the present invention, as shown in Fig. 1, the surface layer and center part are radial, and the middle part is random.
It was found that they often have a layered structure.

There was a tendency that the lower the spinning speed, the higher the elastic modulus of the carbon fiber produced.

One of the problems is that if the cooling becomes uneven, draw resonance will occur and the single fiber diameter will likely become uneven. i! of the carbon fiber of the present invention! In the process of making the pitch fibers infusible, it is necessary to slow down the temperature increase rate, and it is preferable to perform the process at a temperature increase rate of 1.0° C./min or less in heating air a. If the temperature increase rate is too high, the infusibility of the center of the foam will be insufficient, resulting in foaming and forming weak points, which is not preferable. On the other hand, if the temperature increase rate is too low, the cost will increase, which is not preferable.

Increase=speed is preferably 0. OI~0.5°C/min.

In the case of infusibility of the pitch fibers of the present invention, the infusibility reaction can be promoted by a commonly practiced method such as treatment in IJ [Iv4 air with increased oxygen concentration.

The carbon fibers of the present invention are preferably treated at a lower heating rate than conventional carbon fibers during the initial stage of the carbonization process. In particular, the temperature increase rate in a temperature range of 600°C or higher is preferably 100°C/min or less, particularly preferably 30°C/min or less.

The carbon fibers of the present invention can be processed by winding the melt-spun pitch fibers immediately, storing them in a can, or placing them on a perforated belt, performing infusibility and carbonization treatment, and then winding them. It is preferable to provide Pitch fibers immediately after melt spinning are extremely weak and brittle even though they have a large diameter, so the utmost care must be taken when handling them as one or several single fibers. However, if it is made infusible and carbonized, its strength increases and its brittleness decreases, making it suitable for use as a single or several strands of ordinary yarn. ! ! It becomes possible to treat it as 0.

At this stage, it becomes possible to divide the thick wA ITO into multiple fiber bundles with approximately the same number of single fibers.
Thin multifilament yarns and monofilaments can also be produced using this method.

In this case, it is preferable to process the pitch fibers by increasing the number of single fibers from the time when the pitch fibers are produced until the carbonization progresses a little and the brittleness decreases, and then process a plurality of fiber bundles having approximately the same number of single wA fibers. It is possible to produce a carbon fiber monofilament with a small number of constituent single fibers or a carbon fiber monofilament with one single single fiber.

It is said that in conventional carbon fibers, the strength tends to decrease as the single fiber diameter increases, but in the case of the carbon fibers of the present invention, this tendency is not remarkable, and the tensile strength is 200%.
kg f/w 2 or more and elastic modulus of 80,000 kg
f/! IIlm2 or higher is possible. on the other hand,
As the single fiber diameter increases, the wear resistance improves.
When the fiber aggregate is used as it is without being coated with another matrix material, it is preferable that the single fiber diameter is large.

However, as the single fiber diameter increases, it becomes difficult to make it infusible.
This requires low-temperature, long-term oxidation treatment. Furthermore, pitch fibers tend to become non-uniform during spinning. For these reasons, the carbon fiber single TaiIIIt of the present invention
The diameter is preferably 200 lm or less, most preferably 150 m or less. The strength of PAN or rayon-based carbon fibers decreases rapidly as the diameter of the single fiber increases. The reason for this is said to be that the strength of the fiber depends on the probability that scratches will be present on the surface, and as the diameter increases, the 11 ratio that scratches will be present increases.

However, the liquid crystal pitch-based charcoal i-fiber C of the present invention exhibits less decrease in strength when the diameter of the single fiber increases, and has excellent properties in rigidity and shape retention. In addition, since the specific surface area is small, it has a f-point that makes it easy to process as a substitute. By coating the surface with titanium carbide, silicon carbide, etc., it can ensure abrasion resistance against substances that strongly corrode carbon, such as molten metal, and is excellent as a reinforcing material for composite T-materials with Hama Yukin P as a matrix. It has excellent performance.

In addition, it is possible to thicken the layer of these materials and make the fibers mainly made of titanium carbide, silicon carbide, etc., and it is possible to make the fibers mainly made of titanium carbide, silicon carbide, etc. It is possible to Iff.

The carbon fiber monofilament of the present invention has strength, corrosion resistance,
Excellent till straightness, shape retention, etc. In addition, when used as a fiber reinforcement material for composite materials, it has a f-point that causes disturbances in the arrangement and arrangement of fibers due to the flow of the matrix component during molding, which causes defects in the molded product. According to the present invention, it is possible to produce crystalline pitch-based carbon fibers with a thickness of 20 μm or more, but liquid crystal pitch-based carbon fibers with a thickness of 30 μm or more are particularly preferred from the viewpoint of operability in subsequent processing. In producing the carbon fiber of the present invention, when splitting the fibers, it is preferable to form the pitch fiber into a thin plate shape and wind it up.
Subsequently, infusibility and carbonization are performed while maintaining the plate-like shape. During molding (I), glue or Ci oil with good focusing properties is applied, and the thin plate-like shape is rolled up to prevent it from turning over or splitting.

During this winding, it is preferable to use a traversing guide for the winding machine that has a narrow gap to the extent that the position of the single fiber does not shift. This gap may be formed in the shape of a guide, or may be formed by a combination of a fiber bundle flattening device and a wide guide. This gap in Ayaya Rigite
W1 is preferably smaller than two times the fiber diameter.

This thin plate-shaped fiber bundle is unwound without being turned over or split, and is made infusible and carbonized. In this case, it is also possible to perform continuous processing from pitch spinning to carbonization without winding. However, since there are differences in the suitable processing speed for each process, it is preferable to wind the yarn after pitch spinning. [Function] The present invention is a carbon fiber composed of continuous liquid crystal pitch-based single fibers having a large fiber diameter and excellent strength and elastic modulus.

It is not clear why such carbon fiber fibers can be obtained, but it is due to the synergistic effects of the use of liquid crystal pitch with a high softening point and narrow molecular weight distribution, and the use of spinning holes whose cross-sectional area increases in the downstream direction. It is surmised that a unique fine 11i fiber was produced which has high strength and elastic modulus even if the fiber diameter is large and does not produce defects such as cracks even after carbonization. In addition, petroleum-based pitch has an extremely low amount of non-flowing impurities such as carbon particles contained in the pitch compared to coal-based pitch, so it has excellent strength even if the single fiber diameter is large. It is thought that charcoal fibers can be obtained. [Practical Examples] Next, the present invention will be explained in more detail with reference to Examples. Example 1 Petroleum pitch with a softening point of 318°C and an optically anisotropic component content of 100% is used as a raw material, and the diameter of the narrowest part of the spinning hole is 0.1+w
Using a spinneret having a spinning hole with a diameter of 0.25 mm at the exit of the spinning hole, while blowing nitrogen at a spinning temperature of 329.2°C,
IfJ melt spinning was performed. Pitch discharge amount 0.070g/
The hole was ◆min, and the winding speed was 30m/min.

After oiling, the spun fibers were wound up while being traversed at a speed that would allow the fibers to be wound in a parallel, almost close contact manner. The spun fiber was heated to 300°C at a heating rate of 0.1°C/min, kept at 300°C for 30 minutes for infusibility treatment, and then roughly raised to 700°C at a heating rate of 5°C/min. Light carbonization was performed using Subsequently, the material was continuously supplied to a furnace with a maximum temperature of 2500°C, and the temperature was increased at a rate of 12°C/min for carbonization. The obtained fibers had a diameter of approximately 32 μm.
Tensile strength is 275kgf/2, elastic modulus is 85,000
kgf/am2. When the cross section of the fiber was observed, as shown in FIG. 1, the cross-sectional structure was found to be radial in the surface layer and center and random in the middle, and no cracks or voids were observed.

Furthermore, when carbonizing at 2500°C, the strength decreased to 198 kg f/+w2 when the heating rate was increased to 36°C/min, and 85 kg f/m2 when the temperature was increased to 120°C/min.
It dropped to .

Example 2 Instead of the spinneret of Example 1, the diameter of the narrowest part of the spinning hole was 0. 1 mvm, exit diameter of spinning hole 0.25Il
Bitch A fibers were spun at a spinning temperature of 330°C using a spinneret with 100 lI spinning holes and using the same pitch. The pitch discharge was jl LOgl, and the winding speed was 30 m/min.● The spun fibers were bundled using a polyacrylamide sizing agent and wound up as a tape-shaped molded product of Il1!4lI1m. The wound tape was treated to be infusible in the same manner as in Example 1, and then carbonized at a maximum temperature of 2700°C. During the treatment, the fiber bundles were prevented from turning over or being scraped.

After the carbonization treatment, the obtained fibers were separated and wound up as a 10-wood multifilament. The resulting fiber has a diameter of approximately 3
It is a multi-filament made of approximately 10 single fibers from 2μ country and has excellent processability, and has a tensile strength of 295kg f.
lys 2, elastic modulus is 92. OOOkg f/IIIm
2. Example 3 Using a spinneret similar to the spinneret of Example 1, petroleum pitches having various softening points and optical anisotropic component contents were used, and the spinning metallurgy was adjusted to softening point +18. Melt spinning was performed at ℃ with different fiber diameters. The obtained pitch fibers were made infusible and carbonized in the same manner as in Example 1. Table 1 shows the softening point of the pitch used, the optically anisotropic component content, and the fiber performance obtained. Table 1 Pitch characteristics and fiber performance Bitch Na 2 3 4 5 Softening point ("C) 272 28+ 290 340 358 Optical anomaly 11 property f a11' ratio (1) 8G 1 no 3 100 !00 +00 Monochrome Skewer 1 Straight t1f (4m) 22285598147 Tensile strength (kκf/s+m2) 234 256 264
270 259 Side deviation rate (IO3kgf/ms'> 81 82
84 91 87 Inuzets f'jl+ 4 Coal tar pitch is treated to reduce the content of mesophase spherules to approximately 2%, and the average pore diameter is 1.27lmσ]Josei? Purified pitch was obtained by passing through a gold filter.

σ) Refining pitch +1! Heat treated to soften {hi point 316
°C, ) I (containing anisotropic components I 90%, quinoline insoluble content 45% and 1 tap), melt spinning was carried out in the same manner as in Example 1, -f melting and charcoal went.

The diameter of the obtained carbon fiber was approximately 34 am. Tensile strength 220
kgf/m south 2, elastic modulus 81 na 00 kgf/m2. Although this straightness is superior to conventional carbon fibers with a large diameter, the elastic modulus and strength are slightly inferior when compared with Example 1. [Effects of the Invention] The present invention The present invention relates to a carbon fiber having a large fiber diameter.The present invention is a continuous monofilament of a liquid crystal pitch type, or a carbon fiber with a small number of monofilaments (nearly horizontal monofilament).

Carbon fiber composition Single & large diameter carbon fiber is conductive material (heating element, electrode material) electromagnetic wave shield 4.4t4, anti-static material, mlvN material, 1 mulberry steel material (tank cloth, work 8,
It is used in protective clothing, protective equipment, protective materials), etc. Conventional carbon fiber has shortcomings such as easy fluffing due to its thin horizontal ridged fibers and large number of monofilament dark blue fibers. be.

Simple composition! Fiusa's large diameter carbon fiber is fiber &It'
As a reinforcing material for the Ii composite material, the tiles are strong and have the advantage of being difficult to deform due to the flow of matrix components. This is a special material whose matrix component has an extremely high surface tension like that of a metal.
t4 as the thermoplastic tree n}i of 0·, 1h in the field 4
14. ! /) Even in the case of a phase material with a large viscosity, the carbon fiber navy blue of the present invention has a small tendency to become unevenly distributed due to the flow of matrix components.
1 shows performance superior to that of v4.

{Carbon fiber with a small number of h-formed single fibers, carbon fiber with a small number of monofilaments→
Men 1 f. tCVD/Okasa uses boron, silicon carbide, Qi ff: 'r-yield, etc. How to make the core of ceramics, ribbons, etc.! -11'T. We did not accept the f1 performance that had been disrupted.

4, M side C7) vI tun Q AQ Ming figure 1 is fiber & I
1. Represents 1,000 microscopic photographs of t-crossings.

Sennin Co., Ltd. Be !・ mosquito

Claims (1)

[Scope of Claims] 1. A carbon fiber composed of continuous liquid crystal pitch single fibers having an average fiber diameter of 20 μm or more. 2. The carbon fiber according to claim 1, characterized in that the number of constituent single fibers is one. 3. The carbon fiber according to claim 1 or 2, having an elastic modulus of 80,000 kgf/mm^2 or more and a tensile strength of 200 kgf/mm^2 or more.