JP3055295B2 - Pitch-based carbon fiber and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a carbon fiber and a method for producing the same, and more particularly, to a pitch-based carbon fiber having particularly excellent compressive strength and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, carbon fibers and graphitized fibers have been lightweight,
Due to its excellent properties such as high elasticity and high rigidity, it has been used as a reinforcing material for various composite materials. For example, they are widely used from sports equipment such as golf clubs, rackets for tennis and the like, fishing rods and other medical equipment such as artificial hands and artificial legs, to structural materials for vehicles and aerospace machines. Polyacrylonitrile (PAN) is a type of high-performance carbon fiber.
System and pitch system. Among these, pitch-based carbon fiber and graphite fiber are made from pitch obtained from coal, petroleum, etc., and this is used to generate an optically anisotropic phase portion of liquid crystal, which is a precursor structure of graphite structure, by using means such as heating. Then, it is spun, infusibilized in an oxidizing atmosphere, then carbonized, and if necessary, graphitized to obtain high-performance carbon fibers. Here, the reason for generating the optically anisotropic phase portion is that, since the optically anisotropic phase portion which is a liquid crystal has an orientation, the obtained carbon fiber also has an excellent orientation and a high strength. This is because it is easy to develop. For example, JP-A-49-361
No. 70 describes that a high performance carbon fiber can be obtained by using a pitch in which the optically anisotropic phase portion accounts for 40 to 90%.

[0003] Particularly, in producing a spinning pitch containing a large amount of an optically anisotropic phase, a carbonaceous raw material is used as disclosed in JP-A-57-42924 and JP-A-58-168687. Manufacturing a spinning pitch by heat treatment while expanding sales or further blowing an inert gas or the like, or JP-B-63-5433, JP-B-1-5
It is already known to produce a spinning pitch by heat-treating a carbonaceous raw material as disclosed in Japanese Patent Publication No. 3317, each publication, and then reacting with an aromatic solvent to recover solvent-insoluble components by solvent separation. .

In recent years, for example, Japanese Patent Application Laid-Open No. 61-83319
JP-A-63-315 describes an optically anisotropic synthetic pitch obtained from a raw material such as naphthalene as described in
It is also known to obtain a carbon fiber from an optically anisotropic synthetic pitch obtained from a material in which alkylbenzene is crosslinked and heaviened with formaldehyde as described in JP-A-614-614.

[0005]

However, such pitch-based fibers are comparable to PAN-based fibers in tensile strength, elastic modulus, etc., but are inferior in compressive strength. Further improvement has been desired.

[0006]

The inventors of the present invention have conducted intensive studies and have found that such problems can be solved by using a specific pitch as a raw material pitch, and have reached the present invention. That is, the object of the present invention is high elastic modulus,
An object of the present invention is to provide a pitch-based carbon fiber having both high tensile strength and high compressive strength and a method for producing the same, and an object of the present invention is to provide a spinning pitch for carbon fiber having a shear viscosity of 200 poise and a temperature of 220 to 370 ° C. That the optically anisotropic phase accounts for 5 to 40% by volume of the whole and that the optically anisotropic phase is substantially all dispersed as optically anisotropic small spheres of 0.1 to 100 μm. A pitch-based carbon fiber having a characteristic pitch as a spinning material pitch, a carbon fiber spinning pitch having a shear viscosity of 200 poise and a temperature of 220 to 370 ° C, a glass transition temperature width of 40 ° C or less, and Pitch-based carbon fiber having a pitch of less than 5% by weight of a quinoline-insoluble content as a spinning material pitch, and toluene / hexane = 80% by volume from coal tar pitch
/ 20 vol% to 10 vol% / 90 vol% by obtaining a mixed solvent-soluble matter to obtain a spinning pitch for carbon fiber having a shear viscosity of 200 poise and a temperature of 220 to 370 ° C. The sexual phase is 5 to 40% by volume of the whole,
And the optically anisotropic phase is substantially all 0.1-100 μm.
a pitch having a glass transition temperature width of 40 ° C. or less and a quinoline-insoluble content of less than 5% by weight dispersed as optically anisotropic small spheres having a pitch of m. It is easily achieved by a method for producing carbon fibers.

The carbon fiber according to the first aspect of the present invention has a shear viscosity of 200 poise at a temperature of 220 to 370 as a spinning raw material.
A pitch that is in ° C. is used, which is a requirement for spinning at the right temperature. Also, the pitch differs from many conventional spinning pitches in that the optically anisotropic phase does not consist of large domains having a flow structure, but has a diameter of 0.1 mm.
It consists of small spheres of 1 to 100 μm, more preferably 0.1 to 30 μm.
It has a unique structure that occupies 0% by volume. The remaining portion only needs to have a characteristic that it looks optically isotropic under a polarizing microscope magnified from 100 times to 600 times, and is particularly limited by the type of the starting carbonaceous material and the processing method thereof. Not something. To examine the portion of the pitch sample that shows optical anisotropy with a polarizing microscope, crush the pitch sample into a few mm square, embed it in the usual way on the front surface of a 2 cm diameter resin surface, and polish the surface. Afterwards, a polarizing microscope (100 to 600 times) over the entire surface
Observe below.

[0008] The volume ratio of the optically anisotropic portion or the optically anisotropic small sphere portion is determined by measuring the ratio of the area of the optically anisotropic small sphere portion to the total surface area of the sample. The carbon fiber of the present invention using such a pitch as a spinning raw material has sufficient spinnability, a high elastic modulus, and a high 0 ° compression strength. Although the mechanism of the development of such physical properties is not clear, it is governed by the size and orientation of the graphite crystallites constituting the carbon fiber, and the graphite crystal must be neatly oriented in the carbon fiber axial direction to exhibit a high elastic modulus. There is.

[0009] On the other hand, the compressive strength of carbon fiber is generally lower as the graphite crystal has a higher elastic modulus, but this is due to the compressive stress in the case of highly crystallized carbon fiber due to the "complexity of graphite crystal hexagon". It is considered that a "slip between mesh planes" occurs and breakage occurs. In order to obtain carbon fibers having a high 0 ° compressive strength, it is necessary to restrict the development of graphite crystals. In particular, it is considered that 0 ° compression fracture caused by “slip between hexagonal mesh planes of graphite crystal” starts at a point where stress such as minute voids or large crystal boundaries in the carbon fiber tends to concentrate, etc. Can be

In the case where the optically anisotropic phase has a "flow structure" as in the prior art, or in the case where the optically anisotropic portion has a spherical shape or the like and has a size of 100 μm or more, a spinning nozzle is used. When stretched, the liquid crystal of optical anisotropy, which is a precursor of the graphite crystal, is stretched in the carbon fiber axis direction and the graphite crystal is oriented in the fiber axis direction, and although the elastic modulus is easily developed, the graphite crystal becomes large. However, the 0 ° compressive strength of the carbon fiber is low.

On the other hand, 0.1 to 100 μm, preferably 0.1
３０30 μm spherulite-shaped optically anisotropic spheres,
The spinning pitch occupying 0% by volume is such that when the liquid crystal is drawn from the spinning nozzle, the liquid crystal is stretched in the fiber axis direction and the graphite crystal is orderly aligned in the fiber axis direction, but the size of the optically anisotropic liquid crystal is small. Further, since the crystal is covered with the optically isotropic portion, it is restricted that the crystal becomes larger than necessary. For such a reason, it is considered that physical properties such as high elastic modulus and high 0 ° compression strength are exhibited.

Therefore, the volume ratio of the optically anisotropic portion is 40%.
When the diameter exceeds 100 μm, or when the diameter of the optically anisotropic small sphere is larger than 100 μm, the graphite crystal size of the carbon fiber becomes large, and a high 0 ° compression strength cannot be obtained. Furthermore, a spinning nozzle is usually drawn from a nozzle having a diameter of 0.05 to 0.5 mm to produce a carbon fiber having a diameter of 5 to 30 μm. In this case, unevenness in viscosity occurs during the process of stretching the high-viscosity optically anisotropic portion and the low-viscosity optically isotropic portion from the nozzle tip, and it becomes difficult to spin. On the other hand, if the volume ratio of the optically anisotropic portion is less than 5%, the desired high elasticity carbon fiber cannot be obtained because the orientation in the fiber axis direction is impaired during spinning.

Next, the features of the spinning material pitch used in the second aspect of the present invention will be described. The conditions relating to the shear viscosity are the same as those in the first invention of the present specification, and therefore will not be described. To explain the conditions relating to the glass transition temperature range, the present inventors have found that, as described above, where stresses such as minute voids existing in carbon fibers and defects such as large crystal boundaries are likely to concentrate, It is thought to be generated due to the non-uniform structure of the pitch for use, and in order to prevent such a starting point of fracture from being generated, the problem is solved by providing a pitch with a non-uniform molecular weight and a uniform molecular weight distribution for spinning I found something to be done. The molecular weight distribution or homogeneity of the pitch can be easily known from the glass transition temperature width (ΔT _g ) which can be determined by measuring with a differential scanning calorimeter.

That is, when the glass transition temperature width (ΔT _g ) is 4
The spinning pitch of 0 ° C. or less has sufficient homogeneity,
The carbon fiber produced therefrom has a high 0 ° compression strength. Essentially, the glass transition point is the temperature inherent in a substance,
The temperature at which physical properties such as specific heat of a substance change discontinuously. However, in the case of a substance such as a pitch for spinning, which has various molecular structures and a broad molecular weight distribution from a low softening point component to a high softening point component, the temperature at which the glass transition occurs is limited because the mixture is a mixture. Will exist. In other words, many molecular species from low softening point component to high softening point component,
In the case of a spinning pitch having a molecular weight distribution, the glass transition temperature width increases.

The glass transition temperature width (ΔT _g )
Is measured with a differential scanning calorimeter. The measurement is based on “JIS K
7121-1987 Method for measuring transition temperature of plastic ". From the DCS curve obtained by this method, the glass transition temperature width (ΔT _g ) is determined according to“ JIS K712.
1-11987 9.3 Determination of glass transition temperature ”, and the difference between T _ig and T _eg shown in FIG. 3. Specifically, a straight line obtained by extending each baseline before and after the glass transition, The temperature at the intersection with the tangent drawn at the point where the slope of the curve of the step change portion of the glass transition becomes the maximum is T _ig and T _eg (corresponding to the low-temperature baseline and the high-temperature baseline, respectively). I do.

The width of the glass transition region, that is, the glass transition temperature width ΔT _g is obtained as the difference between T _ig and T _eg . Further, in this case, it is essential that the quinoline-insoluble content, which is a requirement of the second invention, is 5% by weight or less. This is because heavy components such as quinoline-insoluble content exceed 5% by weight. If it is contained, the homogeneity in the carbon fiber spinning pitch is impaired, and it becomes impossible to produce pitch-based carbon fibers having excellent compressive strength. A pitch for spinning carbon fiber containing a quinoline-insoluble content exceeding 5% by weight and having a narrow molecular weight distribution such that the glass transition temperature width (ΔT _g ) is 40 ° C. or less is used as the softening point of the pitch. This is because the temperature required for melt spinning is 370 ° C. or higher, and spinning becomes extremely difficult due to the generation of bubbles and the like accompanying the thermal decomposition reaction. The quinoline-insoluble content in the present invention can be measured by a method according to Japanese Industrial Standards "JIS K2421".

By using a pitch having such characteristics, a pitch-based carbon fiber having excellent properties in all of tensile strength, elastic modulus and compressive strength can be obtained. It is clear that a pitch that satisfies the conditions of both the first invention and the second invention is more preferable. Further, the method for producing such a pitch is not particularly limited as long as the pitch having the above-mentioned characteristics can be obtained. For example, if the raw material pitch is subjected to solvent separation, such a pitch can be obtained.

Examples of the carbonaceous raw material pitch used in the present invention include coal-based coal tar, coal-tar pitch, coal liquefaction, petroleum heavy oil, pitch, a thermal polycondensation reaction product of petroleum resin, Examples include polymerization reaction products obtained by a catalytic reaction of naphthalene or anthracene. These carbonaceous raw materials contain impurities such as free carbon, undissolved lime, ash, and catalysts. These impurities are well-known in the art, such as filtration, centrifugation, or stationary sedimentation using a solvent. It is desirable to remove them in advance by a method.

The carbonaceous raw material is subjected to a pretreatment by, for example, a heat treatment followed by extraction of a soluble component with a specific solvent, or a hydrogenation treatment in the presence of a hydrogen donor solvent and hydrogen gas. You may keep it. In particular, it is preferable to use coal tar pitch as a starting material of the raw material pitch used in the present invention. As the coal tar pitch, a toluene insoluble content of 60% by weight or less, preferably 50% by weight or less, more preferably The addition treatment changed the toluene-insoluble content to 30% by weight or less.

The hydrogenation treatment is performed to adjust the molecular weight and the degree of aromatization of the coal tar pitch. For example, a hydrogen-donating solvent such as tetralin, dihydro-phenanthrene, tetrahydroquinoline, or hydrogenated aromatic oil is used. Add a solvent such as quinoline, naphthalene oil, anthracene oil that can be treated or easily converted to a hydrogen-donating solvent, and a co-catalyst such as an iron-based, molybdenum-based, nickel-based, chromium-based, zinc-based, or sulfur compound. And then 10-500kg / cm
^The hydrogenation treatment is performed at a temperature of 360 to 500 ° C. for 1 to 24 hours under a hydrogen gas pressure of ² G, preferably 20 to 300 kg / cm ² G. Further, it is more preferable to perform a pretreatment by a method of removing a solid substance by filtration or the like as necessary, and removing a solvent by distillation to obtain a residue, if necessary.

Specifically, the method includes removing the soluble components of coal tar pitch or its hydrogenated product with a mixed solvent of toluene and hexane. The mixing ratio of toluene and hexane is toluene / hexane = 90% by volume / 10% by volume to 50% by volume / 50% by volume. Solvent treatment conditions for removing solubles include, besides the mixing ratio of toluene and hexane, the solvent amount ratio to pitch, temperature, time, etc.
It is necessary to remove soluble components by a general method such as filtration or centrifugation, and to produce a desired pitch by a method such as heat treatment under reduced pressure. More specifically, in order to obtain a pitch having the characteristics of the present invention from the above-mentioned coal tar pitch or its hydrogenated one, when the toluene / hexane ratio is small, increase the solvent amount ratio or increase the processing temperature. If the toluene / hexane ratio is high, the objective can be achieved by appropriately reducing the solvent ratio, the processing temperature, and the time. Can be achieved.

The spinning pitch thus obtained is used for carbon fiber production according to a conventional method. In the production of carbon fibers, such a spinning pitch is melt-spun at a temperature of, for example, 220 ° to 400 ° C., then infused under an oxidizing atmosphere, and the resulting fiber bundle is carbonized at about 1500 to 2000 ° C. Depending on the temperature, a graphitization treatment can be performed at a temperature of about 2200 to 3000 ° C. to produce a target carbon fiber or graphite fiber. In particular, the spinning pitch of the present invention can exhibit a high elastic modulus by firing at a relatively low temperature. In other words, carbon fibers having a remarkably high elastic modulus can be obtained when compared at the same firing temperature.

[0023]

The present invention will be described below in more detail with reference to examples, but the present invention is not limited to the examples unless it exceeds the gist.

Comparative Example 1 A quinoline-insoluble solid was removed from an autoclave equipped with a stirrer.
100 parts coal-based coal tar pitch, creosote oil 1
00 part, a mixture of 5 parts of iron oxide and 2.4 parts of sulfur are continuously supplied, and the hydrogen pressure is 150 kg / cm ² · G, the temperature is 420
The mixture was hydrogenated at a temperature of 1 ° C. and an average residence time of 1 hour. After filtering the treated product to remove the iron catalyst and the like, the solvent was distilled off under reduced pressure to obtain a hydrogenated isotropic pitch.

The hydrogenated pitch is passed under normal pressure while flowing nitrogen.
Heat treatment was performed at 24 ° C. for 260 minutes. The obtained pitch for spinning is embedded in a resin by a conventional method, polished, and photographed with a polarizing microscope (“OPTIPHOT-POL” manufactured by Nikon Corporation) using an objective lens: × 20 and a photographing exclusive photographing lens: × 5. As a result of observation with a polarizing microscope photograph at a magnification of 425 times, a large flow structure was obtained, and the ratio of the flow structure portion exhibiting anisotropy was 95% by volume. The quinoline insoluble content of this pitch was 28.4% by weight.
When this spinning pitch was melt spun, pitch fibers having a diameter of 10 μm could be spun for 2 hours without breaking. The obtained pitch fiber was made infusible at 310 ° C. in the air, and then fired in argon gas to obtain a carbon fiber. As a result of measuring the physical properties of the carbon fiber according to the single fiber tensile test method specified in JIS-R-7601, the fiber diameter was 7.
7 μm, tensile strength 290 kg / mm ² , tensile modulus 52 ton
/ Mm ² . As a result of measuring according to the 0 ° compression strength test method specified in ASTM-D3410, the 0 ° compression strength of CFRP having a fiber volume% of Vf60% was 39 kg.
/ Mm ² .

The spinning pitch used for the spinning is measured using a SSC580 series DSC-20 type device manufactured by Seiko Denshi Co., Ltd. according to the method of "JIS K7121-1987".
The SC curve was measured. Specifically, an aluminum dish was used as the sample dish, an empty aluminum dish was also used as the reference material, and a spinning pitch of 15 mg was previously set to 35 mg under a nitrogen gas flow of 50 ml / min.
Heat treatment was performed at 0 ° C., quenched to room temperature, and then heat treated at a constant rate of 15 ° C./min for measurement. The glass transition temperature width (ΔT _g ) thus determined was 62 ° C.

Example 1 Hydrogenated isotropic pitch 5 prepared exactly as in Comparative Example 1.
To 150 g, a mixed solvent of toluene / hexane = 65% by volume / 35% by volume was added at a rate of 150 ml, extracted at about 80 ° C., and filtered with a 0.5 μm membrane filter to remove soluble components. The solvent was removed from the insoluble matter under reduced pressure to obtain a spinning pitch. The obtained spinning pitch was observed with a polarizing microscope photograph in the same manner as in Comparative Example 1, and as shown in FIG. 1, optically anisotropic small spheres having a diameter of 0.2 to 20 μm were dispersed in the isotropic phase. The optical anisotropic small spheres accounted for 20% by volume of the whole. Also,
The quinoline-insoluble content of this pitch is about 0% by weight.
The temperature showing 00 poise was 345 ° C., and the glass transition temperature width (ΔT _g ) determined by DSC was 34 ° C. From this spinning pitch, a carbon fiber was prepared in the same manner as in Comparative Example 1. The obtained carbon fiber had a fiber diameter of 9.4 μm and a tensile strength of 3
40 kg / mm ² , a tensile modulus of elasticity of 58 ton / mm ² , and a carbon fiber reinforced resin (CF
RP) had a compressive strength at 0 ° of 64 kg / mm ² .

Comparative Example 2 A hydrogenated isotropic pitch obtained by hydrogenating a coal tar pitch was heat-treated at 430 ° C. for 20 minutes under a normal pressure while flowing nitrogen. The obtained spinning pitch was observed with a polarizing microscope photograph in the same manner as in Comparative Example 1, and as a result, as shown in FIG.
It had a structure in which optically anisotropic small spheres having a diameter exceeding 300 μm were dispersed in the isotropic phase, and the optically anisotropic small spheres accounted for 30% by volume of the whole. The quinoline insoluble content of this pitch was 1% by weight, the temperature at which 200 pitches were exhibited was 280 ° C., and the glass transition temperature width determined by DSC was 65 ° C. Spinning was attempted with the same spinning pitch as in Comparative Example 1, but spinning was not possible due to uneven viscosity.

[0029]

Industrial Applicability The carbon fiber of the present invention provides a carbon fiber having sufficient spinnability, high elastic modulus, and high 0 ° compression strength.

[Brief description of the drawings]

FIG. 1 is a 425-fold polarizing microscope photograph (crystal structure) of a spinning pitch used in Example 1.

FIG. 2 is a 425-fold polarization micrograph (crystal structure) of a spinning pitch used in Comparative Example 2.

FIG. 3 is an explanatory diagram of how to determine a glass transition temperature width (ΔT _g ).

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) D01F 9/145 D01F 9/14 511

Claims (4)

(57) [Claims] The temperature at which the shear viscosity is 200 poise is 22
A spinning pitch for carbon fiber at 0 to 370 ° C., wherein the optically anisotropic phase is 5 to 40% by volume of the whole and the optically anisotropic phase is substantially 0.1 to 100 μm. A pitch-based carbon fiber having a pitch dispersed as anisotropic small spheres, wherein the pitch is a raw material pitch. 2. A temperature at which a shear viscosity of 200 poise is 22
A pitch as a spinning raw material pitch, wherein the pitch is a carbon fiber spinning pitch of 0 to 370 ° C., wherein the glass transition temperature width is 40 ° C. or less and a quinoline insoluble content is less than 5% by weight. Based carbon fiber. 3. The temperature at which the shear viscosity is 200 poise is 22.
The pitch-based carbon fiber according to claim 1, which is a spinning pitch for carbon fiber having a glass transition temperature width of 40 ° C or less and a quinoline-insoluble content of less than 5% by weight. 4. By obtaining a soluble content of a mixed solvent of toluene / hexane = 80% by volume / 20% by volume to 10% by volume / 90% by volume from coal tar pitch, a shear viscosity of 2% is obtained.
A spinning pitch for carbon fiber having a temperature of 220 poise at 220 to 370 ° C., wherein the optically anisotropic phase is 5 to 4
0% by volume, and the optically anisotropic phase is substantially all dispersed as optically anisotropic small spheres of 0.1 to 100 μm, the glass transition temperature width is 40 ° C. or less, and quinoline A method for producing pitch-based carbon fiber, wherein the pitch is a spinning raw material pitch, wherein an insoluble content is less than 5% by weight.