JPH09217236A - Carbon fiber bundle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a pitch-based continuous carbon fiber bundle excellent in processability into prepregs or woven fabrics despite being of low modulus, also capable of giving FRP products with excellent properties. SOLUTION: This pitch-based continuous carbon fiber bundle has the following characteristics: made up of 1000 or more filaments of carbon fiber; elastic modulus: 5-8tonf/mm<2> ; carbon content: >=97wt.%; tensile strength: >=100kgf/mm<2> ; fiber diameter: >=4μm but <10μm; and water absorption: <=4wt.%. Thereby, this carbon fiber bundle is light in weight, low in rigidity, excellent in processability into FRP products, and yields stable and excellent composite performances with no effect such as moisture absorption.

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 bundle, which has a tensile modulus lower than that of a conventionally known carbon fiber bundle and is excellent in processability for FRP products and the like. The present invention relates to a pitch-based continuous carbon fiber bundle. The carbon fiber bundle obtained in the present invention is lightweight and has a low elastic modulus, and is suitable as a reinforcing fiber of a composite material used in various industrial fields including the sports, leisure industry and aerospace fields.

[0002]

2. Description of the Related Art Generally, carbon fiber bundles are known as a material having a high specific strength and a high specific elastic modulus.
It is attracting attention as a strong and light material in the automobile industry and other industrial fields. On the other hand, in recent years, FRP products having low rigidity are also demanded mainly in fields such as sports and leisure.

Particularly in the field of fishing rods and the like, the PA is light and durable.
N-based carbon fiber bundles are widely used because they have good workability, but carbon fiber bundles generally have an elastic modulus of 2
It is difficult to make one having a tonf / mm ² or less, and a heavy glass fiber bundle is generally used as a reinforcing material in a portion where low elasticity is required.

Japanese Patent Publication No. 3-16086 discloses a low-elasticity PAN-based carbon fiber bundle having an elastic modulus of 12 to 19 tonf / mm ² , but it is equivalent to a glass fiber bundle of 5 to 8 t.
Onf / mm ² is not known.

On the other hand, carbon fibers made of rayon, pitch, etc., which are called general-purpose carbon fibers, have an elastic modulus of 4 to
Although a carbon fiber bundle of about nf / mm ² was obtained, the handling property of the fiber was poor and a continuous fiber form could not be obtained, or only a relatively thick fiber having a fiber diameter of 10 μm or more could be produced. Further, the hygroscopicity of the fiber bundle including the low elastic PAN-based carbon fiber bundle is high, and therefore FR
There is also a problem in that the performance of the P product becomes a problem and the application is limited.

[0006]

As described above, the elastic modulus of the conventionally known continuous carbon fiber bundle having good workability is high, and the relatively low elastic modulus which is conventionally used for the glass fiber bundle or the like is required. It was not possible to adapt to the parts that were covered. An object of the present invention is to provide a pitch-based continuous carbon fiber bundle which has a low elastic modulus and is excellent in processability into a prepreg or a woven fabric, and which is excellent in properties when used as an FRP product.

[0007]

[Means for Solving the Problems] That is, the present invention comprises carbon fibers of 1,000 filaments or more, an elastic modulus of 5 to 8 tonf / mm ² , a carbon content of 97% or more, a tensile strength of 100 kgf / mm ² or more, Fiber diameter 4 μm or more 10
The pitch-based continuous carbon fiber bundle is less than μm and has a water absorption rate of 4% or less.

The contents of the present invention will be described in detail below. The pitch, which is the starting material for the carbon fiber of the present invention, is an isotropic pitch exhibiting a non-graphitizable property, and it is necessary to use a pitch having an extremely good spinnability. Generally, pitches obtained by thermally polymerizing conventionally known coal tar, ethylene tar and the like have insufficient spinnability. Specifically, for example, after the coal tar is deQI-treated (quinoline-insoluble matter), the sulfur content contained in the raw material tar is reduced to 25 by a hydrogenation catalyst.
~ 70%, more preferably 40-60% or more,
Then, after heat treatment under reduced pressure at 10 to 300 mmHg, further heat treatment at a high temperature of 400 ° C. or higher under a high vacuum of 5 mmHg or less, preferably 3 mmHg or less, the softening point is 220 to 270 ° C., and substantially QI Does not include
Further, a pitch that does not completely include an optically anisotropic structure is preferable.

The pitch used in the present invention has a lower strength in the pitch fiber than the general meso-face pitch, and is extremely difficult to spin. For example, caliber 0.05 to 0.12
Using a nozzle having 1,000 mm or more of capillaries with a diameter of 100 mm, a pipe having a viscosity of 200 to 900 poise and a pressure of 5 to 40 kg / cm ² is extruded at a take-up speed of 100 to 500 m / min while extruding the pitch. , Fiber diameter 5 ~ 11μm, filament number 1,0
A pitch fiber bundle of 00 or more is obtained.

Subsequently, the obtained pitch fiber bundle is infusibilized. At the time of infusibilization, the nitrogen dioxide concentration is preferably 1 to 10% by volume and the oxygen concentration is 5 to 5%.
0% by volume, and the remaining gas is an inert gas such as nitrogen or water vapor under a mixed gas atmosphere at a temperature of 100 to 25.
The first step of infusibilization is carried out at 0 ° C., then the nitrogen dioxide concentration is 0.1-5% by volume, preferably 0.2-2% by volume, and the oxygen concentration is 5-40% by volume, preferably 10%. ~ 30
It is preferable to carry out the second stage infusibilization at a temperature of 200 to 350 ° C. in an atmosphere of an inert gas such as nitrogen or a mixed gas atmosphere in which the remaining gas is volume% and an inert gas and water vapor. Next, this infusible fiber bundle is carbonized in an inert gas atmosphere at a temperature of 350 to 800 ° C. without tension to obtain a primary carbonized fiber bundle. This primary carbonized fiber bundle is 0.1-5 gf / tex
Carry out carbonization and graphitization while applying the tension. The final firing temperature of the fiber is 1,300 to 2,400 ° C, preferably 1,500 to 2,200 ° C.

By such treatment, the carbon fibers 1,0
It is composed of more than 00 filaments and has an elastic modulus of 5 to 8 tons.
f / mm ² , carbon content 97% or more, tensile strength 100k
A pitch-based continuous carbon fiber bundle having characteristics of gf / mm ² or more, fiber diameter of 4 μm or more and less than 10 μm, and water absorption of 4% or less is obtained.

The amount of moisture absorption (water absorption) was measured by the following method. After washing 10 g of fiber with acetone, 110 ° C
It is dried at a temperature of 2 hours, returned to room temperature in a desiccator to be in an absolutely dry state, and this is weighed and designated as A. Next, this sample is left to stand in a humidity control apparatus at 30 ° C. and 100% humidity for 24 hours, and then weighed and designated as B. The water absorption rate C (%) is calculated by the following equation. C (%) = [(B−A) / A] × 100

Conventionally known low-elasticity carbon fibers have a carbon content of 90% or less, and since the fibers themselves have active groups, they have a high water absorption rate and also have poor chemical resistance and the like. It was common. On the other hand, the fiber bundle of the present invention has a high carbon content, a low water absorption rate, and is also excellent in chemical resistance. Therefore, when it is made into a composite, it is excellent in chemical stability. Further, since the fiber bundle of the present invention is a continuous fiber having a small fiber diameter of 4 to 10 μm and having a sufficient number of filaments, it is excellent in processability into a prepreg and the like. If the fiber diameter is less than 4 μm, spinning at the pitch fiber stage becomes extremely difficult,
The productivity is remarkably lowered, and when the fiber diameter is 10 μm or more, voids and the like are likely to be contained when processed into a composite, and sufficient composite physical properties are not expressed.

The number of filaments is 1,000 filaments or more, preferably 2,000, in relation to the fiber processing step.
More than filaments, preferably 100,000
It should be less than or equal to the filament. If it is less than 1,000 filaments, the productivity in the fiber processing step will be reduced, and the strength of the carbon fiber bundle itself will be low and the handling will be reduced.
On the other hand, if it exceeds 100,000 filaments, it will be very difficult to industrially produce continuous carbon fibers. Further, the tensile strength is 100 kgf / mm ² or more, and the elongation is 1.
If it is 3% or more, preferably 1.6% or more, more preferably 2.0% or more, handling as a fiber becomes difficult.

[0015]

The present invention will now be described more specifically based on examples and comparative examples.

Example 1 Coal tar pitch having a softening point of 80 ° C. from which quinoline insoluble matter was removed was used as a raw material, and the temperature was 360 ° C. and the pressure was 120 kg / in the presence of a hydrogenation catalyst (Ketjenfine-840, manufactured by Nippon Ketjen). Hydrogenation was carried out under the condition of cm ² to remove 40% of the sulfur content in the raw material. The hydrogenated coal tar pitch obtained was heated at a temperature of 400 ° C. and a pressure of 40.
Heat treatment under reduced pressure for 5 hours under conditions of mmHg, softening point 16
A pitch of 0 ° C. was obtained. This heat treatment pitch is heated at a temperature of 450 ° C.
And a pressure of 0.5 mmHg was applied for a further 5 minutes to obtain a spinning pitch.

The resulting spinning pitch has a softening point of 250 ° C.
The toluene insoluble content was 50% by weight, the quinoline insoluble content was 0% by weight (not detected), and the mesophase-free optical isotropic pitch was obtained.

Using this spinning pitch, an inner diameter of 0.1 m
m spinneret having 3,000 holes of capillary, spinning viscosity of 400 poise and spinning speed of 400 m /
The fiber diameter is 9.5 μm and the number of filaments is 3 under the condition of min.
000, and a continuous pitch fiber bundle having a length of 9,000 m was obtained.

The continuous pitch fiber bundle obtained was subjected to 1 in a mixed gas atmosphere containing a nitrogen dioxide concentration of 4% and an oxygen concentration of 30%.
It was treated at a temperature of 20 to 240 ° C. for 2 hours and then treated at a temperature of 240 to 330 ° C. for 2 hours in a mixed gas atmosphere containing a nitrogen dioxide concentration of 0.4% and an oxygen concentration of 10% to obtain an infusibilized yarn. . The obtained infusible yarn is heated to 390 ° C under a nitrogen atmosphere.
And primary carbonization under the condition of no tension, and then, applying a tension of 0.1 gf / tex to the primary carbonized fiber bundle,
Carbonization was performed at 00 ° C., and then graphitization was performed at a temperature of 1,800 ° C. while applying a tension of 0.6 gf / tex to obtain a carbon fiber bundle having a length of 7,500 m and a filament number of 3,000.

This carbon fiber bundle has a tensile strength of 130 kgf.
/ Mm ² , the elastic modulus was 6.0 tonf / mm ² , and the fiber diameter was 7.7 μm. When the elemental analysis of this carbon fiber was carried out, the carbon content was 99.8% or more. Further, the water absorption was measured and found to be 0.3%.

Using this carbon fiber bundle, a basis weight of 35 g /
As a result of trial production of a unidirectional prepreg of m ² , it was possible to make a beautiful prepreg with no openings. A unidirectional composite having a volume content (Vf) of 60% was prepared from this prepreg, and its physical properties were measured.
kgf / mm ^2, compression strength 110 kgf / mm ^2, and to have excellent composite properties that 0 ° flexural strength 102kgf / mm ² was confirmed.

Comparative Example 1 A coal tar pitch having a softening point of 80 ° C. from which quinoline insoluble matter was removed was used as a raw material, and unlike Example 1, without hydrogenation, the temperature was 400 ° C. and the pressure was 40%.
Decompression heat treatment is performed for 4 hours under the condition of mmHg, and the softening point is 15
A pitch of 5 ° C was obtained. This heat treatment pitch is set to a temperature of 435 ° C.
And further heat-treated for 7 minutes under the conditions of a pressure of 0.5 mmHg to obtain a pitch for spinning.

This spinning pitch has a softening point of 250 ° C., a toluene insoluble content of 60% by weight, a quinoline insoluble content of 0% by weight (not detected), and optical properties such as mesophase-free. It was an anisotropic pitch.

Using this spinning pitch and the same spinneret as in Example 1, spinning was performed with a spinning diameter of 9.5 μm and a spinning viscosity of 400 poise and a spinning speed of 400 m / min. It was not possible to obtain a continuous fiber bundle. Therefore, the spinning speed is 200 m / mi
n, fiber diameter 13.4 μm, filament number 3,
000, and a continuous pitch fiber bundle having a length of 3,000 m was obtained. The pitch fiber bundle was subjected to infusibilization treatment, carbonization treatment, and graphitization treatment in the same manner as in Example 1 to obtain lengths of 2 and 5
A carbon fiber bundle having a length of 00 m and a filament number of 3,000 was obtained.

The characteristics of this carbon fiber bundle were measured in the same manner as in Example 1. The tensile strength was 90 kgf / mm.
² , elastic modulus 5.0 tonf / mm ² , fiber diameter 11.2μ
m, carbon content 99.9%, and water absorption 0.3%. Further, using this carbon fiber bundle, a unidirectional prepreg having a basis weight of 50 g / m ² was experimentally produced in the same manner as in Example 1, and it was found that the prepreg had many openings and was poor in quality.

Comparative Example 2 For a coal-based mesophase pitch having a softening point of 302 ° C. and an optical anisotropy of 92%, using the same spinning apparatus as in Example 1, a spinning viscosity of 500 poise and a spinning speed of 300 m were used.
A pitch fiber bundle having a fiber diameter of 10 μm and a filament number of 3,000 was obtained under the condition of / min. This pitch fiber was made infusible and carbonized at 800 ° C. to obtain a continuous carbon fiber bundle. The carbon fiber bundle obtained has a tensile strength of 70 kgf / m.
m ² , elastic modulus 5.5 tonf / mm ² , fiber diameter 8.2μ
m, carbon content 89%, and water absorption 8.5%.

[0027]

INDUSTRIAL APPLICABILITY The carbon fiber bundle of the present invention is suitable for the production of a prepreg for FRP products which is lightweight and has low rigidity. Since it has a high carbon content and a low water absorption rate, it exhibits stable composite performance. Therefore, it can be used without problems even in applications such as fishing rods where the effect of moisture absorption is a concern. Moreover, according to the carbon fiber bundle of the present invention, since the fiber diameter is small and the moldability is excellent, FR having excellent voids and excellent composite physical properties and excellent appearance is obtained.
P products can be manufactured.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ken Kobayashi 1st Fujimachi, Hirohata-ku, Himeji City, Hyogo Prefecture, Nippon Steel Works Hirohata Works

Claims (1)

[Claims] 1. A carbon fiber composed of 1,000 filaments or more, an elastic modulus of 5 to 8 tonf / mm ² , a carbon content of 97% or more, a tensile strength of 100 kgf / mm ² or more, a fiber diameter of 4 μm or more and less than 10 μm, and a water absorption rate. A pitch-based continuous carbon fiber bundle characterized by being 4% or less.