JP3031197B2 - Pitch-based carbon fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pitch-based carbon fiber, a pitch-based carbon fiber woven fabric and a method for producing the same. The pitch-based carbon fiber and the woven fabric produced according to the present invention exhibit high strength, high elasticity and high thermal conductivity, and are required to have high dimensional stability and thermal shock resistance, It is suitably used as a heat radiation material for high energy density electronic devices.

[0002]

2. Description of the Related Art High-performance carbon fibers are roughly classified into PAN-based carbon fibers made from polyacrylonitrile (PAN) and pitch-based carbon fibers made from pitches, and have high specific strength and high specific elastic modulus, respectively. It is widely used as a material for aircraft, a material for sporting goods, a material for building, etc. by taking advantage of this feature.

However, in applications such as space materials that require dimensional stability under a large temperature distribution and thermal shock resistance, and heat radiation materials for electronic devices in which high energy densities continue to increase, the above-described machines are used. High thermal conductivity is required in addition to the mechanical properties, and many studies have been made to improve the thermal conductivity of carbon fibers. However, the thermal conductivity of a commercially available PAN-based carbon fiber is 200 W / m
-It is smaller than k.

On the other hand, pitch-based carbon fibers are generally
Although it has been confirmed that a high thermal conductivity can be easily achieved as compared with the system carbon fiber, the thermal conductivity of a commercially available pitch system carbon fiber is usually smaller than 700 W / m · k. Recently, there has been proposed a method of producing a carbon fiber having higher heat conductivity by defining a softening point of a pitch, a spinning temperature, and a firing temperature (JP-A-2-242919, JP-A-4-1633).
No. 18, JP-A-4-163319).

However, thermal conductivity of 500 to 1500
High W / m · K and compressive strength of 35 kg
/ Mm ² or more carbon fibers high compression strength or tensile strength carbon fiber and a production method thereof high tensile strength is 400 kg / mm ² or more has not been reported. A woven fabric woven from carbon fibers having the above-mentioned properties has not been reported.

[0006]

As described above, carbon fibers having high thermal conductivity are being developed, but the properties in terms of strength and elasticity are insufficient. Due to the shortage, it was difficult to use and improved.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies in order to solve the above problems, and as a result, have found that the lamination thickness L of graphite crystals
c and the ratio La of the spread of the graphite crystal in the layer plane direction (La / L
c) In addition, the present invention was found to be achieved by graphitizing a raw carbon fiber whose domain size was adjusted to an appropriate size under special conditions, and reached the present invention.

That is, an object of the present invention is to provide a carbon fiber having high thermal conductivity and simultaneously excellent compressive strength and tensile modulus, and various materials using the same.
The purpose is that the thermal conductivity in the fiber axis direction is 500 to 150.
0 W / m · K , tensile modulus of 85 ton / mm ² or more,
The compressive strength is 35 kg / mm ² or more, the lamination thickness Lc of the graphite crystal is 30 to 50 nm, and the ratio (La / Lc) to the spread La of the graphite crystal in the layer surface direction is 1.5 or more .
One domain size when observed with polarizing microscope fiber axis direction of the cross section at 1000 times magnification is readily achieved by the pitch-based carbon fiber characterized in that less than substantially 500 nm.

Hereinafter, the present invention will be described in more detail. As the spinning pitch for obtaining the carbon fiber used in the present invention,
There is no particular limitation as long as a molecular species that is easily oriented is formed and gives an optically anisotropic carbon fiber.

Examples of the carbonaceous raw material for obtaining the spinning pitch include coal-based coal tar, coal-tar pitch, coal liquefaction, petroleum heavy oil, tar, pitch, and catalytic reaction of naphthalene and anthracene. And the like. These carbonaceous materials include
It contains impurities such as free carbon, undissolved coal, ash, and catalysts. These impurities are filtered, centrifuged,
Alternatively, it is desirable to remove in advance by a known method such as stationary sedimentation using a solvent.

[0011] Further, for example, a method of subjecting the carbonaceous raw material to heat treatment and then extracting a soluble component with a specific solvent,
Alternatively, preliminary treatment may be performed by a method such as hydrogenation treatment in the presence of a hydrogen-donating solvent and hydrogen gas.
In the present invention, a carbonaceous raw material containing an optically anisotropic structure of 40% or more, preferably 70% or more, more preferably 90% or more is suitable. Is usually heated at 350 to 500 ° C., preferably 380 to 450 ° C., for 2 minutes to 50 hours, preferably 5 minutes to 5 hours, under an atmosphere of an inert gas such as nitrogen, argon, or steam, or under blowing. Sometimes.

The optically anisotropic structure ratio of pitch in the present invention is a value obtained as an area ratio of a portion showing optical anisotropy in a pitch sample with a polarizing microscope at room temperature. Specifically, for example, a pitch sample crushed into a few mm square is embedded with a sample piece over substantially the entire surface of a resin having a diameter of 2 cm according to a conventional method, and after polishing the surface, a polarizing microscope is applied to the entire surface. It is determined by observing under (100 magnification) and measuring the ratio of the area of the optically anisotropic portion to the total surface area of the sample.

As a result of various studies conducted prior to preparing a carbon fiber having a high thermal conductivity, the thermal conductivity of the carbon fiber was found to be:
It was found that the size was controlled only by the size of the graphite crystallites constituting the carbon fiber. That is, regardless of the raw material and manufacturing method of the carbon fiber, the larger the graphite crystallite, the smaller the scattering of electric and heat carriers due to lattice defects and the higher the thermal conductivity.

On the other hand, the tensile strength and compressive strength of the pitch-based carbon fiber have a structure in which the above-mentioned graphite crystallites are aggregated, that is, 0.1 mm.
It is governed by the “texture structure” evaluated at a size of about 1 μm to 100 μm (Sugio Otani, Yuzo Sanada, Basic Ohmsha Co., Ltd. (1980) 130). In other words, a large void existing at a place such as a boundary of a structure larger than the crystallite size controls the strength. As in the case of the carbon fiber of the present invention, high compressive strength of 35 kg / mm ² or more,
In order to obtain a high tensile modulus of elasticity of 85 ton / mm ² or more, it is necessary to minimize and reduce this void.

This "tissue structure" is obtained by a scanning electron microscope.
It can be observed at a magnification of 000 to 10000 times,
It can also be observed as a "domain" with a polarizing microscope at a magnification of 400 to 1500 times. The carbon fiber of the present invention substantially consists of a domain of 500 nm or less when observed at a magnification of 1000 times.

The better the orientation of the carbon fiber in the pitch fiber axis direction at the stage of the pitch fiber, the larger the graphite crystallite of the carbon fiber is in the subsequent carbonization or graphitization step. Considering that if the "domain" or "domain" is too large, the properties in terms of strength are degraded, the inventors of the present invention intend to increase the thermal conductivity of carbon fibers and to produce carbon fibers having high compressive strength and tensile strength. First, in the spinning process, it is important to use a pitch having good orientation and to prevent pitch fibers having an unnecessarily large "domain" from being formed. Specifically, the domain size is set to 500 nm or less. For this purpose, for example, when spinning pitch fibers from the pitch described above, the orientation of pitch molecules is increased, and the disorder of orientation due to stretching is reduced. To, the viscosity of the spinning pitch at the discharge hole to prepare a highly oriented good pitch fiber subjected to spinning at a temperature equal to or less than 150 poise. At this time, the temperature is usually 32 ° C. or more from the Mettler softening point of the pitch.
The temperature is desirably 5 ° C or lower, preferably 360 ° C or higher and 42 ° C or lower.

In order to further reduce the domain size, it is preferable to provide a filler for dividing the liquid crystal pitch flow path inside the nozzle hole. The filling is 40
A filter of up to 2000 mesh, preferably 100 to 1000 mesh can be used. Any material can be used as the filler as long as it has a function of dividing the flow path in the nozzle hole. For example, metal or ceramic glass beads, metal powder used as a shear filter, and the like can be used.

The pitch fiber thus obtained is infusibilized in a conventional manner, and carbonized and / or graphitized at a desired temperature to obtain the carbon fiber "raw material" of the carbon fiber of the present invention. obtain.

More specifically, the infusible fiber tow is obtained by subjecting pitch fibers to heat treatment at 300 to 380 ° C. in an oxidizing gas atmosphere. Furthermore, this infusible fiber tow is nitrogen,
800 to 300 in an inert gas atmosphere such as argon
Carbonized and graphitized at 0 ° C. The carbonization or graphitization treatment at this time is performed at a temperature at which the carbon content of the obtained carbonized or graphitized fiber becomes 97% or more, preferably at a temperature at which the carbon content becomes 99% or more. By treating at such a temperature, the dimensional change due to carbonization shrinkage of the carbon fiber in the graphitization treatment in the next step can be suppressed as small as possible, and a decrease in carbon fiber strength due to yarn damage can be prevented beforehand. I can do it.

Next, after a surface treatment is carried out by a usual method, a sizing agent is impregnated in the fiber in an amount of 0.2 to 10% by weight, preferably 0.5 to 7% by weight, to obtain a carbon fiber. Any commonly used sizing agent can be used, and specific examples include an epoxy compound, a water-soluble polyamide compound, a saturated or unsaturated polyester, vinyl acetate, water or alcohol, glycol alone or a mixture thereof.
The carbon fiber thus obtained can easily have a tensile modulus of 85 due to the low viscosity during spinning and the presence of a filter or the like.
ton / mm ² or more, compressive strength 35 kg / mm ² or more,
The carbon fiber has a thermal conductivity of 500 to 1500 W / m · K in the fiber axis direction. Further, the lamination thickness Lc of the graphite fiber in the carbon fiber is 30 to 50 nm, and the spread L of the graphite crystal in the layer surface direction is L.
The ratio (La / Lc) to a is 1.5 times or more. The domain size of the cross section in the fiber axis direction is 5 by the method described later.
00 nm or less.

Further, in order to obtain the carbon fiber fabric of the present invention, plain weave or satin weave is preliminarily woven using the above-mentioned "raw material carbon fiber" tow using, for example, a shuttle loom or a rapier loom. FAW (Fiber Real
Weight: weight per unit area of the fabric) 50 to
250 g / m ² of “raw carbon fiber fabric” is manufactured.

Next, in the present invention, the above-described "raw carbon fiber" or "raw carbon fiber fabric" is placed in a graphite crucible together with packing coke which has been previously graphitized, and is graphitized. The size and shape of the graphite crucible are not particularly limited as long as the desired amount of the above-mentioned carbon fiber or carbon fiber fabric can be put therein. In order to prevent damage to the carbon fiber or the carbon fiber fabric due to the reaction with the gas or the carbon vapor, a highly airtight material with a lid is preferred.

The carbon fiber or the carbon fiber fabric is wound around a graphite bobbin or a core material, and the graphite crucible filled in the graphite crucible is filled together with the packing coke which has been graphitized in advance. The graphitization temperature is required to be higher than the temperature at which the devolatilized component of the packing coke is achieved. If necessary, the coke is graphitized at a temperature of 1400 ° C to 3500 ° C, preferably 2500 ° C to 3500 ° C.

The average particle size is 0.1 mm or more and 100 m or more.
m, preferably 5 mm or more and 30 mm or less. The graphitization treatment is performed at a temperature of 2500 ° C to 3500 ° C, preferably 2800 ° C to 3300 ° C, more preferably 2900 ° C to 3100 ° C.

As equipment for graphitization, it is particularly preferable to use an Acheson resistance heating furnace from the viewpoint of production efficiency, but it is possible to perform the treatment at a temperature of 2500 ° C. or more. There is no particular restriction as long as it can be installed in The graphitization time is at a temperature of 2500 ° C. or more for 1 hour to 300 days, preferably 4 hours to 30 days. Thus, the carbon fiber or carbon fiber fabric of the present invention can be obtained.

The carbon fiber or the carbon fiber fabric is impregnated with a thermosetting resin according to a conventional method so that the carbon fiber is excellent in heat resistance (excellent in heat dissipation) and high in strength and light in weight. A fiber reinforced resin can be obtained. Such carbon fiber reinforced resin has high thermal conductivity,
The present invention can be particularly suitably used as an IC substrate or a solar cell substrate in which a rise in temperature is directly linked to destruction of an element or reduction in efficiency. In particular, it exerts an excellent effect as a solar cell substrate for a spacecraft that requires all of the strength, lightness and high thermal conductivity of carbon fiber reinforced resin.

[0027]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the examples unless it exceeds the gist. In the examples, the lamination thickness Lc of graphite crystallites and the spread La of graphite crystals in the layer plane direction were determined by the 117th Committee of the Japan Society for the Promotion of Science, “Method of measuring lattice constant and crystallite size of artificial graphite” (Otani Sugiro et al. Carbon Fiber Modern Editing (1986) P733-740)
02) Diffraction line and (110) diffraction line.

The domain size is determined by embedding a carbon fiber in a resin, molding a sample such that a cross section parallel to the carbon fiber axis direction becomes a surface, polishing the sample, and measuring the size under a polarizing microscope with a magnification of 1000 times. The domain size is determined as an average value of the width of each of a bright portion and a dark portion that are observed in a band shape in the carbon fiber axis direction at each angle while rotating the sample on the sample table at least 10 ° or more under a polarizing microscope.

The thermal conductivity was measured by using a carbon fiber as a disc-shaped unidirectional carbon fiber reinforced plastic (CFRP) having a diameter of 10 mm and a thickness of 3 to 6 mm. The CFR
The specific heat and thermal diffusivity of P were measured and calculated by the following equation.

K = Cp · α · ρ / Vf where K is the thermal conductivity of carbon fiber, Cp is the specific heat of CFRP, α is the thermal diffusivity of CFRP, ρ is the density of CFRP, V
f represents the volume fraction of carbon fibers contained in CFRP.

The thickness of the CFRP was changed according to the thermal conductivity of the carbon fiber. The sample having a large thermal conductivity was made thick, and the sample having a small thermal conductivity was made thin. Specifically, after laser irradiation, the temperature on the back surface of the sample increases, and it takes several tens of msec to reach the maximum temperature.
However, the thickness of the CFRP was adjusted so that the time t1 / 2 until the temperature rises by 1/2 of the temperature rise width ΔTm at that time was 10 msec or more (maximum 15 msec) (see FIG. 1).

The specific heat was determined by attaching glassy carbon as a light receiving plate to the front surface of the sample and measuring the temperature rise after laser irradiation with an R thermocouple bonded to the center of the back surface of the sample. The measured values were calibrated using sapphire as a standard sample. The thermal diffusivity was determined by applying a film to both surfaces of the sample by carbon spray until the surface was no longer visible and measuring the temperature change on the back surface of the sample after laser irradiation with an infrared detector. The thermal conductivity of the carbon fiber can be estimated from the electrical conductivity using a very good correlation between the thermal conductivity and the electrical conductivity of the carbon fiber.

Example 1 A mesophase pitch having an optical anisotropy ratio of 100% observed from a coal tar pitch under a polarizing microscope and having a softening point of 302 ° C. determined by the Metra method was prepared. This mesophase pitch is set at a nozzle diameter of 0.1 mm at the discharge hole of the nozzle and 400 mm at the narrowest portion of the nozzle hole.
Spinning was performed with a spinneret having a number of holes of 2000 requiring a mesh filter so that the spinning temperature at the discharge hole of the spinning nozzle was 340 ° C. and the melt viscosity was 120 poise to obtain a pitch fiber tow having a yarn diameter of 12 μm. .

This pitch fiber is heated to 360 ° C. in air for about 1 hour.
The temperature was slowly increased at a rate of ° C./min, followed by heat treatment to obtain infusible fibers. Further, the infusibilized fiber was calcined in an inert gas up to a maximum temperature of 2700 ° C. to be pregraphitized.
Its carbon content was 99% or more. Next, after surface treatment, 2% of an epoxy sizing agent was impregnated to obtain a carbon fiber tow. This carbon fiber had a yarn diameter of 9 μm, a strand tensile elasticity of 87 t / mm ² , a strand tensile strength of 290 kg / mm ² and a thermal conductivity of 290 W / m · K.

The carbon fiber was further wound around a graphite bobbin, embedded in a pre-graphitized packing coke, placed in a graphite crucible, and graphitized at 3000 ° C. in an Acheson resistance heating furnace. . Result thread diameter 9
μm, thermal conductivity 640 W / mk, strand tensile elasticity 96 t / mm ² , strand tensile strength 440 kg / m
m ² , the compressive strength of FRP having a Vf of 60% measured by ASTM D3410 method was 40 kg / mm ² . Further, the X-ray parameter Lc of the graphite crystal of the carbon fiber is 350
Å, La / Lc = 1.75 and domain size is 33
It was 0 nm.

Example 2 In the same manner as in Example 1, a pitch fiber tow having a thread diameter of 9.5 μm was obtained. After infusibilizing this pitch fiber, the maximum temperature is 2 in an inert gas atmosphere.
It was baked to 700 ° C and pregraphitized. Its carbon content was 99% or more. Then after surface treatment,
2% of an epoxy sizing agent was impregnated to obtain a carbon fiber tow. This carbon fiber has a yarn type of 7 μm, a strand tensile elasticity of 79 t / mm ² , and a strand tensile strength of 380 kg / m.
At m ² , the thermal conductivity was 240 W / mk.

The carbon fiber tow was woven using a rapier loom to obtain a carbon fiber woven fabric having a FAW of 80 g / m ² . Subsequently, the carbon fiber fabric was further wound on a graphite bobbin, which was then buried in a packing coke which had been previously graphitized, placed in a graphite crucible, and graphitized at 3000 ° C. in an Acheson resistance heating furnace. . The FAW of the obtained carbon fiber fabric was 82 g / m ² .

The carbon fiber of this woven fabric has a yarn diameter of 7 μm, a thermal conductivity of 600 W / m · K, a tensile modulus of 89 t / mm ² , a tensile strength of 390 kg / mm ² , an X-ray parameter Lc of graphite crystal of 33 nm, and La / Lc. = 1.7 and the domain size was 330 nm. The carbon fiber woven fabric was impregnated with a thermosetting resin, molded and cured, and the composite material having Vf = 50% had a flexural modulus of 19 t / mm ² .

In order to use the composite material as a solar cell plate for an artificial satellite, two solar cell plates having a size of 10 × 2 m were prepared. Each plate uses composite material on both sides,
In addition, one composite material was formed by laminating two carbon fiber cloths. Therefore, the size of the carbon fiber cloth used was 10 ×
2 (one area) × 2 (number of cloths per composite) × 2 (front and back) × 2 (normal satellites have two solar cells) = 160 m ² . The weight of the two solar cell plates was about 20 kg.

[0040]

According to the present invention, it is possible to provide carbon fibers having high thermal conductivity, high tensile modulus, and high compressive strength, and various materials using the same.

[Brief description of the drawings]

FIG. 1 shows the time elapsed after laser irradiation and the temperature of the back surface of a sample when the thermal conductivity is determined using a thermal constant measuring device TC-3000 manufactured by Vacuum Riko Co., Ltd. in Examples of the present invention. 5 is a graph showing the relationship of.

Continuation of the front page (72) Inventor Kazuo Shirasaki 1000 Kamoshita-cho, Midori-ku, Yokohama-shi, Kanagawa Prefecture, Mitsubishi Research Institute, Ltd. (56) References JP-A-4-163319 (JP, A) JP-A 1-272827 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) D01F 9/12-9/155

Claims (11)

(57) [Claims] 1. A thermal conductivity in a fiber axis direction of 500 to 150.
0 W / m · K , tensile modulus of 85 ton / mm ² or more,
The compressive strength is 35 kg / mm ² or more, the lamination thickness Lc of the graphite crystal is 30 to 50 nm, and the ratio (La / Lc) to the spread La of the graphite crystal in the layer surface direction is 1.5 or more .
Pitch-based carbon fiber characterized by One domain size when observed with polarizing microscope fiber axis direction of the cross section at 1000 times magnification is less than substantially 500 nm. 2. The pitch-based carbon fiber according to claim 1, wherein the tensile strength is 400 kg / mm ² or more. 3. A FAW having a structure woven with a tow comprising the pitch-based carbon fiber according to claim 1.
(Weight per unit area of woven fabric) 50 to 250 g / m
^2. A carbon fiber woven fabric, which is ² . 4. A pipe containing at least 70% of an optically anisotropic structure.
With a filling inside that separates the pitch channel
Using a nozzle, the viscosity of the pitch at the discharge hole is 150
Spun into a pitch fiber at a temperature below the poise
Heat treatment of pitch fiber in oxidizing gas atmosphere to make it infusible
Fiber and heat the infusible fiber in an inert gas atmosphere
It is processed to a carbon fiber with a carbon content of 97% or more.
Put the carbon fiber in a graphite crucible and heat it to 2500 ° C or higher.
2. The material is graphitized by heating.
Or the method for producing a pitch-based carbon fiber according to 2. 5. A pipe containing an optically anisotropic structure of 70% or more.
With a filling inside that separates the pitch channel
Using a nozzle, the viscosity of the pitch at the discharge hole is 150
Spun into a pitch fiber at a temperature below the poise
Heat treatment of pitch fiber in oxidizing gas atmosphere to make it infusible
Fiber and heat the infusible fiber in an inert gas atmosphere
It is processed to a carbon fiber with a carbon content of 97% or more.
After forming a woven fabric with carbon fiber, it is turned into a graphite crucible.
Graphitize by putting and heating to 2500 ° C or more
4. The method for producing a carbon fiber woven fabric according to claim 3, wherein
Law. 6. The spinning of a pitch is performed at a pitch at a discharge port.
Is between (Mettler softening point + 32 ° C)
And carrying out a range of Butler softening point + 45 ° C.)
The pitch-based carbon fiber according to claim 4, or the charcoal according to claim 5.
Manufacturing method of raw fiber material. 7. Graphite can be graphitized in advance in a graphite crucible.
Of coking coke coke.
A pitch system according to any one of claims 4 to 6, characterized in that:
A method for producing carbon fiber or carbon fiber fabric. 8. The method for producing a pitch-based carbon fiber or carbon fiber woven fabric according to claim 4, wherein the graphitization is carried out in an Acheson resistance heating furnace. 9. A pitch according to claim 1 or claim 2.
A prepreg obtained by impregnating a thermosetting resin into the base carbon fiber or the carbon fiber fabric according to claim 3. 10. A solar cell substrate comprising a carbon fiber reinforced plastic obtained by molding and curing the prepreg according to claim 9 as a main material. 11. An IC substrate comprising a carbon fiber reinforced plastic obtained by molding and curing the prepreg according to claim 9 as a main material.