JPH0742614B2 - Method for manufacturing pitch-based carbon fiber - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing pitch-based carbon fibers, and more particularly to a method for efficiently and stably producing pitch-based carbon fibers exhibiting improved strength. It is about.

Conventional technology Carbon fiber was originally manufactured from rayon,
In terms of its characteristics and economy, it is currently occupied by PAN-based carbon fibers made from polyacrylonitrile (PAN) fiber and pitch-based carbon fibers made from coal or petroleum pitch. Among them, the technology for producing high-performance grade carbon fiber using pitch as a raw material is attracting attention because of its excellent economic efficiency.For example, pitch fiber obtained by melt spinning of optically anisotropic pitch is It is known that the melted and fired carbon fiber has higher strength and higher elastic modulus than the conventional pitch-based carbon fibers (Japanese Patent Publication No. 54).
-1810).

Such a pitch-based carbon fiber manufacturing process generally includes a pitch preparing step, a pitch melt-spinning step, a pitch fiber infusibilizing step, and the infusibilized fiber in an atmosphere of an inert gas such as nitrogen or argon. It consists of a firing process of heating at high temperature to carbonize or graphitize to form carbon fibers.

Among these, the infusibilizing step is an indispensable step for carbonizing the pitch fiber without melting it, and a method of heating for a long time in high temperature air is generally adopted.
This infusibilization by air or oxygen basically utilizes the oxidation reaction of pitch fibers, but if this is insufficient, fusion between fibers occurs in the firing step, and if it is excessive, firing ( The strength / Young's modulus of the fiber after carbonization decreases. Therefore, this infusibilizing step is an important step that affects the physical properties of fibers in the industrial production of pitch-based carbon fibers. However, the optimum conditions for infusibilization by air have not yet been fully clarified, and the reproducibility of the physical properties of fibers still remains a problem.

As the infusibilizing treatment system replacing air, for example, one using ozone (Carbon. Vol 3,31 (1965)), one using air containing NO ₂ (JP-A-55-98914), a mixed gas of chlorine and air is used. What is used (JP-A-49-75828), one that is soaked in saturated chlorine water and then air-oxidized (JP-A-49-72828), treated with fine powder of activated carbon impregnated with sulfuric acid and bromine gas, and then air-oxidized Things (13th Conference on Carbon, p94 (197
7)) has been proposed, but either method is intended to substantially shorten the infusible treatment time,
It does not have the effect of improving the physical properties of the fiber after carbonization.

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention The present invention is to provide an infusibilizing method for producing pitch-based carbon fibers, which stably and efficiently improves the physical properties of carbon fibers after firing.

Means for Solving the Problems According to the present invention, the above-mentioned problem is that when the pitch fiber is fired to produce the carbon fiber, the pitch fiber is treated with ozone gas and then infusibilized in the presence of at least iodine. Then, carbonization or graphitization is achieved by heating and baking treatment in an inert atmosphere.

As the spinning pitch, which is the raw material of the pitch fiber used in the method of the present invention, petroleum-based or coal-based pitch is used.
The method of the present invention has the effect of shortening the infusibilizing treatment time regardless of the composition of the pitch and improving the physical properties of the carbon fiber after the firing treatment. It is preferable to use a pitch having 50% or more, preferably 80% or more, of a directional region.

The melting point of the spinning pitch according to the Mettler method is preferably 280 to 340 ° C, more preferably 290 to 330 ° C. Further, the proportion of the quinoline-soluble portion of the spinning pitch is preferably 30% by weight or more, and particularly preferably 50% by weight or more. The larger the ratio of the optically anisotropic region of the spinning pitch that is preferably used in the present invention (hereinafter referred to as the amount of optical anisotropy), the better. Such a pitch has a homogeneous system and is excellent in spinnability.

As raw materials for such spinning pitch, for example, coal-based heavy oil such as coal tar pitch and coal liquefaction, atmospheric residual oil of petroleum, vacuum distillation residual oil, and by-products of heat treatment of these residual oils are produced. It is obtained by using refined petroleum heavy oil such as tar, pitch, oil sand, and bitumen, which is combined with heat treatment, solvent extraction, hydrogenation treatment and the like.

When melt-spinning the pitch, the form and structure of the spinneret are not particularly limited, but in order to produce high-performance carbon fiber, the method (a) and / or (b) described below is used. It is preferable to use any of the above.

(A) As the hole shape of the spinning nozzle, US Pat. No. 4,628,
When the centerline distance of the wetting edge in the spinning hole of the spinning nozzle as described in No. 001 is Ln and the wetting edge width is Wn, at least one of the Ln satisfies the following two equations Ln <10mm 1.0 <Ln / Wn ≦ 20 at the same time. A non-circular shape, preferably a slit shape, is used.

(B) In a spinning nozzle composed of an introduction hole portion and a fine hole portion, a stationary fractionation element and / or a stationary kneading element is arranged upstream of the introduction hole portion, and a stationary fractionation element and And / or a distance l measured from the position of the most downstream part of the static kneading element as the origin and in the direction of the outlet of the spinning nozzle
The cross-sectional area of the nozzle hole in (mm) is S (l) (mm ² ),
The distance L ₀ (mm) from the most downstream part of the stationary fractionating element and / or the stationary kneading element to the outlet of the spinning nozzle, the viscosity η (poise) of the spinning pitch in the spinning nozzle Which satisfy the following conditions, and the introduction angle θ (degree) from the introduction part to the pore part, the pore part length lc (mm), and the discharge rate per hole Q (g / min) of the spinning pitch The following two formulas, 150 ° ≦ θ ≦ 180 ° lc · η / Q> 20, are used respectively, and the spinning pitch is passed through the stationary fractionating element and / or the stationary kneading element, and the above conditions are continued. Satisfying spinning nozzles are introduced in the order of the introduction hole part and the fine hole part in this order and spun. Here, the static kneading element refers to an element in which the flow is subdivided and kneaded by the molten spinning pitch passing through the element.

By spinning using either of the above (a) or (b), or a method in which both are combined, the generation of cracks in the cross section of the carbon fiber can be effectively suppressed.

In the melt spinning of pitch, the spinning temperature is preferably higher than the melting point of pitch and lower than 360 ° C.
The spinning draft ratio is preferably 30 or more, particularly 50 or more, and the spinning speed is preferably 100 to 1500 m / min.

In the method of the present invention, with respect to the pitch fiber thus obtained,
Ozone treatment is carried out, followed by treatment in the presence of iodine, preferably by heating in the presence of iodine and oxygen, thereby infusibilizing treatment, and then heating in an inert atmosphere for baking treatment. A high performance pitch-based carbon fiber is obtained.

As a method of such ozone treatment, a method of treating the spun pitch fiber in a mixed gas of ozone and oxygen or ozone and air can be used. The concentration of ozone used in this method is not particularly limited, but the concentration of ozone in the mixed gas is preferably 0.01 mol% or more. The treatment temperature is preferably 40 ° C to 300 ° C. In this case, if the temperature is 40 ° C. or lower, the time required for the treatment only becomes long, and if the temperature is 300 ° C. or higher, the treatment becomes excessive in a very short time, and strict control of the treatment conditions is only required. However, even if it is out of this range, the effect of producing a pitch-based carbon fiber having improved physical properties is not impaired.

In the present invention, the ozone-treated fiber thus obtained is infusibilized by treating it in the presence of iodine. This infusibilizing treatment is carried out in the state where iodine and oxygen are present in the fiber or in the atmosphere. preferable. As a concrete method,
There are two methods: a method of containing iodine in the ozone-treated fiber and then heat-treating it in air, and a method of heat-treating the ozone-treated fiber in a mixed gas of oxygen and iodine.

Next, each method will be described in detail.

In the above method, the method of incorporating iodine into the ozone-treated fiber is not particularly limited, but the following method can be adopted, for example.

(A) Contacting the ozone-treated fiber with iodine vapor.

(B) A solution in which iodine is dissolved or dispersed in a solvent such as aliphatic hydrocarbon or polyhydric alcohol is applied to the ozone-treated fiber.

At this time, the amount of iodine contained in the ozone-treated fiber must be 1% or more based on the weight of the fiber to be treated,
It is preferably at least 3%, more preferably at least 5%.
When the amount of iodine is 1% or less, the effect of improving the physical properties of the fiber after carbonization is poor in reproducibility. The upper limit of the iodine content is not particularly limited, and the effect of the present invention is exhibited at any concentration up to the saturation concentration of iodine with respect to the ozone-treated fiber. Also, when applying a solution in which iodine is dissolved or dispersed in pitch fibers,
The presence of iodine at a saturation concentration or higher relative to the ozone-treated fiber in the fiber surface or in the fiber gaps in the fiber bundle does not cause any obstacle in carrying out the method of the present invention, and in this case also, the effect of the method of the present invention is Can be expressed.

Thus, the ozone-treated fiber containing iodine is 350 ° C.
The following treatment is performed in air at preferably 300 ° C or lower, more preferably 250 ° C or lower to infusibilize. When treated at a temperature higher than 350 ° C, the physical properties of carbon fiber after firing (carbonization) are not necessarily impaired, but infusibilization progresses in an extremely short time, and the infusibilization oxidation reaction tends to become excessive, and the physical properties are reproduced. Poor sex. The lower limit of the air treatment temperature is not particularly limited, but when a low temperature is used, the time required for the treatment becomes too long. Therefore, it is preferable to carry out the treatment at 100 ° C. or higher, more preferably 200 ° C. or higher. is there.

The method of the present invention can be more effectively carried out when iodine vapor is contained in the air used for infusibilizing the air. Further, the air may contain components other than air and iodine, for example, carbon monoxide, carbon dioxide, nitrogen oxides, hydrocarbons and the like.

The pressure during the air treatment is not particularly limited, and the higher the pressure, the shorter the treatment time.

In this method, when air is treated, iodine is contained in the ozone-treated fiber in advance, and then the fiber is subjected to air treatment, but the amount of iodine contained in the ozone-treated fiber during or after the air treatment is decreased. Alternatively, even if it disappears substantially, the effect of the method of the present invention is not hindered. The treatment time depends on the treatment temperature, but usually 3 hours or less is sufficient, and if the conditions are selected, the treatment can be completed within several minutes.

Thus, after containing iodine, the air-treated ozone-treated fiber is infusibilized, and the fiber is subsequently fired at a temperature of 1000 ° C. or higher in an inert atmosphere to be carbonized,
Pitch-based carbon fibers having excellent physical properties can be produced by further performing graphitization treatment if necessary.

On the other hand, in the latter method, ozone-treated fibers are treated in a mixed gas containing iodine vapor and oxygen, and then heated in an inert atmosphere and fired to obtain pitch-based carbon fibers.
That is, this method substantially eliminates the infusibilizing step with air, which has been an essential step in the conventional pitch-based carbon fiber manufacturing method.

The concentrations of iodine and oxygen in the mixed gas used in this method are not particularly limited. However, in order to effectively carry out the present invention, the iodine concentration in the mixed gas should be 0.01 mol%.
It is preferable that the oxygen concentration is not less than the above and the oxygen concentration is not less than 1 mol%. However, when the iodine concentration is 0.01 mol% or less, or the oxygen concentration is 1 mol% or less, the time required for the treatment is only prolonged and the effect of producing pitch-based carbon fibers having improved physical properties is impaired. It's not a thing. Further, it is economically advantageous to use air instead of oxygen gas.

The mixed gas used in the present invention includes components other than iodine, oxygen or air, such as carbon monoxide, carbon dioxide, nitrogen,
It can also contain nitrogen oxides, hydrocarbon gas, and the like.

The treatment temperature for treating the ozone-treated fiber with a mixed gas containing iodine and oxygen is not limited, but is preferably 100 to 400 ° C, particularly 200 to 300 ° C. In this case, if the temperature is 100 ° C. or lower, the time required for the treatment is prolonged, and the effect of producing the pitch-based carbon fiber having the improved physical properties is not impaired. Further, the atmospheric pressure during the treatment is not limited, but the higher the pressure, the more efficiently the effect can be exhibited.

The treatment time with the mixed gas containing iodine and oxygen depends on the treatment temperature, but usually 3 hours or less is sufficient, and in some cases, it can be completed within several minutes. The ozone-treated fibers treated with the mixed gas in this manner are continuously fired at a temperature of 1000 ° C. or higher in an inert atmosphere to be carbonized, and if necessary, further graphitized to obtain a pitch-based carbon having excellent physical properties. Fibers can be manufactured.

Further, in the present invention, after the pitch fiber is treated with ozone, it is treated with an iodine gas atmosphere substantially free of oxygen or with a solution containing iodine, and then fired under an inert atmosphere under the same conditions as described above. It can also be processed.

Actions / Effects The carbon fibers obtained by the above-mentioned methods have extremely high elongation and high strength compared to those obtained by infusibilizing pitch fibers spun in the conventional manner with air, and reproduce the physical properties. It has excellent properties. Further, when compared at the same temperature and the same pressure, the time required for the infusibilizing treatment is drastically shortened as compared with the case of the above conventional method.

Although the mechanism by which the above-mentioned effects are exhibited by the method of the present invention has not been completely elucidated, it can be explained as follows. That is, iodine alone reacts with the pitch,
The molecules in the pitch are made to have a high molecular weight, the aromaticity of each molecule is improved, and the viscosity of the pitch is rapidly increased.

Further, iodine rapidly diffuses into the pitch fiber and a homogeneous infusibilization reaction occurs up to the center of the fiber. On the other hand, although ozone has extremely high reactivity with the pitch fiber, it is slow to diffuse into the pitch fiber, and an excessive oxidation reaction tends to occur in the fiber surface layer portion. The method of the present invention combines the above-mentioned reaction characteristics of iodine and ozone with respect to the pitch fiber,
The infusible state of the fiber surface layer and the inner layer is controlled. That is, when the infusibilization reaction is excessively large, the pitch fiber is hardly graphitized, and the fiber after firing has a high elongation but a low Young's modulus, and in order to maintain the original graphitization characteristics of the pitch, the infusibilization reaction is It is preferable to suppress it to the minimum necessary level. However, if the infusibilization reaction is not sufficient, deterioration of the physical properties of the fiber is observed due to the occurrence of defects such as fusion between fibers accompanying the softening during firing or the formation of spontaneous wedges, and in the case where no defects occur during firing. Even after firing, the surface layer of the fiber has a high defect susceptibility to microcracks and the like, the generated cracks are easily propagated and become brittle.

In the method of the present invention, it is possible to selectively excessively infusibilize only the surface layer portion of the pitch fiber by ozone treatment, and to control the inside of the fiber to a homogeneous and minimum infusibilized state by iodine. Therefore, the occurrence of defects during firing is avoided, and the propagation of cracks and the like is suppressed due to the formation of a difficult graphite layer in the surface layer portion of the fired fiber, and the inner layer portion exhibits excellent graphitization. Therefore, it is possible to produce pitch-based carbon fibers exhibiting the original fiber characteristics of graphite and thus having extremely high elongation and high Young's modulus.

Thus, in the method of the present invention, after the pitch fiber is treated with ozone, it is treated with air after containing iodine, or with a mixed gas of iodine and oxygen, whereby the physical properties of the carbon fiber after firing are remarkably improved. The strength, elongation, and modulus of the PAN-based carbon fiber are comparable or superior to those of the PAN-based carbon fiber as shown in Examples described later.
At the same time, the time required for the infusibilizing treatment can be greatly reduced.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples.
The strength and elongation physical properties of the carbon fibers in the examples are values measured according to JIS R-7601.

Example 1 Using commercially available coal tar as a raw material, according to the method described in JP-A-59-53717, the amount of optical anisotropy was 92%, the quinoline-soluble portion was 95.4%, and the melting point by the Mettler method was 305 ° C. A spinning pitch was prepared.

The spinning pitch was charged into a fixed-quantity feeder equipped with a heater, and after melting and defoaming, slit width was 60 microns, center line distance was 54
Melt spinning was performed on a spinneret with a 0 micron single slit spin hole.

In this case, the feeder discharge rate was set to 0.032 ml / min / hole, the die temperature was 335 ° C, and the winding speed was 600 m / min.

This pitch fiber was kept in air containing 150 mol of ozone at 1.5 mol% for 30 minutes to react with the ozone. The ozone-treated fiber was kept in iodine vapor at 100 ° C. for 5 minutes to absorb iodine. At this time, the iodine content in the ozone-treated fiber is
It was 50 parts by weight with respect to 100 parts by weight. This iodine-containing ozone-treated fiber was heated in air from room temperature to 225 ° C. at a temperature rising rate of 2.5 ° C./min and held at 225 ° C. for 1 hour.

Next, at a temperature rise rate of 500 ° C / min in a nitrogen atmosphere, 1800 ° C
It was heated up to and heated (carbonized). As a result of measuring the physical properties, the carbon fiber obtained showed excellent values of strength 650 kg / mm ² , elongation 1.9%, Young's modulus 35 T / mm ² .

Example 2 Pitch fibers were prepared by spinning in the same manner as in Example 1 and treated with ozone in the same manner. Iodine was absorbed in this ozone-treated fiber. The ozone-treated fiber was heated from room temperature to 225 ° C. at a heating rate of 2.5 ° C./min in air containing 0.5 mol% of iodine vapor and kept at 225 ° C. for 0.5 hours.

Next, at a temperature rise rate of 500 ° C / min in a nitrogen atmosphere, 1800 ° C
It was heated up to and heated (carbonized). As a result of measuring physical properties, the obtained carbon fiber had excellent values of strength 654 kg / mm ² , elongation 1.9%, and Young's modulus 34 T / mm ² .

Comparative Example 1 Pitch fibers were prepared by spinning in exactly the same manner as in Example 1. This pitch fiber was heated in the air from room temperature to 300 ° C. at a temperature rising rate of 2.5 ° C./min without absorbing iodine, and kept at 300 ° C. for 0.5 hours.

Next, at a temperature rise rate of 500 ° C / min in a nitrogen atmosphere, 1800 ° C
It was heated up to and heated (carbonized). As a result of measuring the physical properties of the obtained carbon fiber, the strength was 523 kg / mm ² , the elongation was 1.7%, and the Young's modulus was 30 T / mm ² .

Example 3 Using commercially available coal tar pitch as a raw material, JP-A-59-53717.
According to the method described in the publication, having an optical anisotropy amount of 92%,
Quinoline soluble part 95.4%, melting point 305 ° C by the METTLER method
The spinning pitch of was prepared.

The spinning pitch was charged into a fixed-quantity feeder equipped with a heater, and after melting and defoaming, slit width was 60 microns, center line distance was 54
Spinning was performed with a spinneret having a 0 micron single slit spin hole.

In this case, the feeder discharge rate was 0.032 ml / min / hole, the die temperature was 335 ° C, and the take-up speed was 600 m / min.

1% of this pitch fiber in oxygen containing 1.5% ozone at 150 ℃
It was kept for a time and treated with ozone. This ozone-treated fiber was heated from room temperature to 225 ° C. at a heating rate of 2.5 ° C./min in air containing 0.5 mol% iodine, and kept at 225 ° C. for 1 hour.

Next, at a temperature rise rate of 500 ° C / min in a nitrogen atmosphere, 1800 ° C
It was heated up to and heated (carbonized). As a result of measuring physical properties, the obtained carbon fiber exhibited excellent values of a strength of 641 kg / mm ² , an elongation of 1.8% and a Young's modulus of 36 T / mm ² .

Example 4 Pitch fibers were prepared by spinning in exactly the same manner as in Example 3 and subjected to ozone treatment, and then in air containing 0.5% iodine vapor at a temperature rising rate of 5 ° C./min from room temperature to 250 ° C. The temperature was raised to 250 ° C. and held at 250 ° C. for 0.1 hour.

Next, at a temperature rise rate of 500 ° C / min in a nitrogen atmosphere, 1800 ° C
It was heated up to and heated (carbonized). As a result of measuring physical properties, the obtained carbon fiber showed excellent values of a strength of 585 kg / mm ² , an elongation of 1.7% and a Young's modulus of 33 T / mm ² .

Comparative Example 2 Pitch fibers were prepared by spinning in exactly the same manner as in Example 3, and without ozone treatment, in air containing 0.5% iodine vapor at room temperature to 250 ° C. at a temperature rising rate of 5 ° C./min. The temperature was raised to 250 ° C. and held at 250 ° C. for 0.1 hour.

Next, at a temperature rise rate of 500 ° C / min in a nitrogen atmosphere, 1800 ° C
When heated up to the temperature, the fibers were softened and fused.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-246420 (JP, A) JP-A 61-28019 (JP, A) European patent application 169023 (EP, A-169023)

Claims (5)

[Claims] 1. A process for producing pitch-based carbon fibers, characterized in that melt-spun pitch fibers are treated with ozone, then infusibilized in the presence of at least iodine, and then calcined in an inert atmosphere. Method. 2. Melt-spun pitch fibers are treated with ozone, and then the fibers are made to contain 1.0% by weight or more of iodine, and 350
The method for producing a pitch-based carbon fiber according to claim 1, wherein the pitch-based carbon fiber is treated in air at a temperature of not higher than 0 ° C. to make it infusible, and then heated in an inert atmosphere to be fired. 3. After the pitch fiber is treated with ozone, iodine is added.
The pitch-based carbon fiber according to claim (2), containing 3.0% by weight or more, heated in air to a temperature of 100 to 300 ° C. to infusibilize, and then heated in an inert atmosphere for firing treatment. Production method. 4. The melt-spun pitch fiber is treated with ozone, heated in a mixed gas containing iodine and oxygen to be infusibilized, and then heated in an inert atmosphere for firing treatment. The manufacturing method of the pitch type | system | group carbon fiber of statement. 5. A heat treatment in a mixed gas of iodine and oxygen
The method for producing a pitch-based carbon fiber according to claim 4, which is performed at 100 to 400 ° C.