JP2946779B2 - Manufacturing method of graphitized fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing graphitized fibers,
In particular, the present invention relates to a method for producing a graphitized fiber having high graphite crystallinity and excellent elastic modulus and strength.

[0002]

2. Description of the Related Art Carbon fibers are widely used as reinforcing materials for various reinforcing materials such as aerospace, leisure goods and industrial materials because of their excellent mechanical properties, particularly high specific strength and specific elastic modulus. . In particular, in the case of graphitized fibers having a high elastic modulus, a thin structural material can be obtained by utilizing the rigidity thereof, and a further weight saving effect is realized. However, its performance is not yet sufficient, and the development of a high-performance graphitized fiber having a higher elastic modulus and strength has been desired.

[0003] In order to produce such a high-performance graphitized fiber, it is particularly important to increase the graphite crystallinity of the fiber so as to approach a more complete crystal structure.

[0004] As a technique for this purpose, for example, Japanese Patent Publication No. Sho 47
Japanese Patent No. 50331 discloses a catalyst graphitization technique in which an aqueous solution of a boron compound is immersed in an acrylic oxide fiber and then calcined. A graphitization technique for stretching in the temperature range is shown.

[0005]

However, in the graphitization of the catalyst for adhering the boron compound, the problem of uneven adhesion of the boron compound to the fiber or the time required for adhering to the fiber is extremely long. There is a problem that production is difficult. On the other hand, carbon fiber
Graphitization, which is performed at a temperature of 00 ° C. or higher, is intended to increase the orientation of a substantially amorphous, isotropic carbonaceous fiber obtained from pitch and natural asphalt, and the obtained graphitized fiber is at most elastic. Rate is 400GPa, strength is 2.0GPa,
Only products far from high rigidity and high strength products required in the field of graphitized fibers today are obtained.

The present invention focuses on significantly improving the crystallinity in the graphitization process as compared with the conventional product, and as a result of intensive studies, the present invention has shown that graphitization of carbon fibers has been added. The present inventors have found that it is particularly effective to carry out stretching under twisting in a pressure inert atmosphere, and have reached the present invention. That is, an object of the present invention is to provide a method for producing graphitized fibers having high graphite crystallinity and excellent elastic modulus and strength.

[0007]

The above object of the present invention is to provide:
The carbon fiber obtained by firing at less than 000 ° C. is twisted at a temperature of 2,000 ° C. or more in a pressurized inert atmosphere at a temperature of not less than 5% under twisting.
The problem can be solved by firing while applying the above stretching.

Hereinafter, the configuration of the present invention will be sequentially described.

In the present invention, the carbon fiber obtained by firing at less than 2000 ° C.
At a temperature of 0 ° C. or more, the graphite is graphitized while being stretched by 5% or more.
Moreover, the carbon fibers to be graphitized are twisted in advance.

That is, in order to further grow the graphite crystal formed by carbonization up to 2000 ° C., it is necessary to perform stretching under a pressurized inert atmosphere. Thereby, the growth of the graphite crystal can be further promoted.

In this case, the higher the graphitization pressure, the greater the effect of crystal growth, preferably 0.1 kg / cm ² · G or less.
Above, more preferably 0.5 kg / cm ² · G or more, even more preferably 1.0 kg / cm ² · G or more, particularly preferably 1.
It is 5 kg / cm ² · G or more. On the other hand, with respect to the upper limit of the pressure, if the pressure exceeds 50 kg / cm ² · G, the temperature is high and special equipment is required for a firing apparatus such as an autoclave. In some cases, it is economically disadvantageous. Therefore,
As the graphitization pressure, a pressure state exceeding normal pressure, preferably
Is 0.1 to 50 kg / cm ² · G, more preferably 0.5 to
50 kg / cm ² · G, more preferably 1.0 to 30 kg /
cm ² · G, particularly preferably about 1.5 to 10 kg / cm ² · G is practical. The pressure medium is preferably an inert gas such as nitrogen or argon. As a method for supplying these pressure media (pressurized atmosphere), the gas may be supplied by a cylinder or may be supplied continuously by using a compressor.

The graphitization temperature is at least 2,000 ° C., preferably at least 2500 ° C., more preferably at least 280 ° C.
The temperature is 0 ° C. or higher. That is, in order to cause the rearrangement of the crystal inside the carbonized yarn, a temperature of 2000 ° C. or higher is required. At a temperature lower than 2000 ° C., the rearrangement of the crystal is unlikely to occur, and the effect is insufficient even when the pressure is applied. It is. The upper limit temperature is not particularly limited, but it is preferable to stop the temperature at a temperature at which carbon does not sublime, from the viewpoint of the physical properties of the graphitized fiber or the extension of the life of the graphitization furnace. In addition, the heating rate at the time of heating, in the temperature range of 2000 ° C. or more,
Preferably 300 ° C./min or less, more preferably 100 ° C.
/ Min or less is effective for improving the denseness of the graphitized fiber and for promoting the crystal orientation.

The stretching conditions for graphitization are 5% or more,
The stretching ratio is preferably 10% or more, more preferably 15% or more. Such stretching conditions are for maximizing the reorientation of the crystals in the graphitization. At a stretching ratio of less than 5%, the degree of orientation is reduced, and the physical properties are reduced. The upper limit of the draw ratio is not particularly limited, but the pressure and the pressure are set so that the graphitized fibers do not fluff or break.
It is preferable to appropriately optimize the temperature.

On the other hand, in the present invention, carbon fibers are twisted prior to graphitization. The number of twists is preferably at least 2 turns / m, more preferably at least 5 turns / m, even more preferably at least 10 turns / m. If the upper limit of twisting exceeds 30 turns / m, the yarn is twisted, making it difficult to obtain the effect of drawing, and further causing yarn damage, which may lower the tensile strength of the graphitized fiber. Twisting of the carbon fiber may be performed at any stage of the precursor, the oxidized fiber and the carbon fiber. By this twisting, the fiber to be treated is stretched and graphitized under a pressurized atmosphere, the single yarn breaks, It is possible to prevent the generation of fluff due to the friction with the seal stopper portion of the firing device, and the damage of the fibers due to the gas blown out from the seal stopper. In other words, by twisting the carbon fiber prior to the graphitization, it is possible to pressurize and stretch the carbon fiber for the first time.

As the firing method for graphitization, continuous firing is preferable. In addition, the yarn inlet and outlet seals of the graphitizing furnace are smoothed, and the opening diameter of the seal stopper is optimized with respect to the yarn bundle diameter. This is also desirable from the viewpoint of controlling the amount of yarn damage and the amount of inert gas blown out. The obtained graphitized fiber can be subjected to a surface treatment, a sizing agent application, and the like, if necessary, by a conventionally known technique.

The carbon fiber in the present invention has a temperature of 2000 ° C.
Acrylic carbon fiber, pitch-based carbon fiber, rayon-based carbon fiber, and the like obtained by calcination of less than 10% can be applied, and examples of the production of acrylic carbon fiber will be described below as typical examples thereof.

That is, first, as the acrylic polymer, a copolymerizable vinyl monomer of 90 mol% or more and acrylonitrile of 10 mol% or less, for example, acrylic acid, methacrylic acid, itaconic acid and their alkali metal salts, ammonium Copolymers such as salts and lower alkyl esters, acrylamide and derivatives thereof, allylsulfonic acid, methallylsulfonic acid, and salts or alkyl esters thereof can be given.
If the copolymerization exceeds 10 mol%, adhesion between single yarns is likely to occur in a flame-proofing step described below, which is not preferable.

As for the polymerization method, conventionally known solution polymerization,
Suspension polymerization, emulsion polymerization and the like can be applied, but the degree of polymerization is preferably at least 1.2, more preferably 1. 1 in intrinsic viscosity ([η]), in order to prevent spinnability and prevent adhesion between single yarns. It is good to be 7 or more.

As the spinning method, a wet spinning method, a dry-wet spinning method or a dry spinning method can be employed. The obtained coagulated yarn is subjected to conventionally known bath drawing, steam drawing, application of a process oil agent, drying and densification, etc., to obtain a precursor fiber (precursor) having a predetermined denier and orientation degree.

In order to improve graphite crystallinity, it is effective to improve the denseness of the precursor. The denseness of the precursor is preferably 50 or less, more preferably 30 or less, and still more preferably 10 or less, as a value of ΔL measured by an iodine adsorption method. Δ by iodine adsorption method
Effective means for obtaining a dense precursor having a value of L of 50 or less include lowering the temperature of the spinning solution and the coagulation bath solution, lowering the tension during coagulation, and optimizing the draw ratio and drawing temperature.

The oxidizing conditions of such a precursor are as follows: the density is preferably 1.30 g / cm ³ or more, more preferably 1.35 g / cm ³ , in an oxidizing atmosphere at 200 to 300 ° C. under tension or stretching conditions. It is better to heat until the above. That is, if the flame resistance is insufficient,
The density of the flame-resistant yarn is preferably 1.30 g / cm ³ or more in order to easily cause adhesion between single yarns during carbonization and to obtain graphitized fibers having high elasticity and high strength. For the atmosphere,
A known oxidizing atmosphere such as air, oxygen, nitrogen dioxide, and hydrogen chloride can be employed, but air is preferred from the viewpoint of economy.

The carbonization treatment is performed at a maximum temperature of less than 2000.degree. C. and in a temperature range of 300 to 500.degree. C. and 1000 to 1200.degree.
It is effective to carbonize at a heating rate of 0 ° C./min or less, more preferably 100 ° C./min or less, in order to improve the compactness. At this time, it is effective to add a stretching of preferably 5% or more, more preferably 10% or more, in order to prevent the orientation of the crystal from being relaxed by heat.

The carbon fiber thus obtained is subjected to drawing graphitization in a pressurized atmosphere in the present invention in a twisted state, and the carbon fiber is twisted by a precursor, an oxidized fiber and a carbon fiber. It can be at any stage of
As described above.

[0024]

The present invention will be described more specifically with reference to the following examples. In this embodiment, ΔL and crystal size L
c, the degree of orientation π002, and the resin-impregnated strand characteristics are values obtained by the following methods, respectively.

About 0.5 g of a dry sample having a ΔL fiber length of 5 to 7 cm by the iodine adsorption method was precisely weighed,
Then, the solution was taken into a 1 ml Erlenmeyer flask with a stopper and an iodine solution (I ₂ : 51 g, 2,4-dichlorophenol 10 g, acetic acid 90 g, and potassium iodide 100 g) were weighed, transferred to a 1-liter volumetric flask and dissolved with water. Constant volume) 100
Add ml, and perform adsorption treatment while shaking at 60 ° C for 50 minutes. The sample adsorbed with iodine is washed with running water for 30 minutes, then centrifugally dehydrated (2000 rpm × 1 minute) and quickly air-dried. After opening the sample, the lightness (L value) is measured (L ₁ ) with a Hunter-type color difference meter [CM-25, manufactured by Color Machine Co., Ltd.].

On the other hand, the corresponding sample not subjected to the iodine adsorption treatment was opened, the lightness (L ₀ ) was measured by the hunter type color difference meter, and the lightness difference ΔL was obtained from L ₀ -L ₁ . .

The crystal size Lc fiber bundle is cut into a length of 40 mm, 20 mg is precisely weighed and sampled, and the sample fiber axes are aligned so as to be exactly parallel. The sample fiber bundle was prepared into a uniform sample fiber bundle. After being impregnated with a thin collodion solution and fixed so as not to lose its shape, it was fixed to a sample table for wide-angle X-ray diffraction measurement. As the X-ray source, an X-ray generator manufactured by Rigaku Denki KK was used, and a CuKα ray (using a Ni filter) having an output of 35 kV-15 mA was used. Using a goniometer manufactured by Rigaku Denki Co., the surface index of graphite (00
A diffraction peak near 2θ = 26 ° corresponding to 2) was detected by a scintillation counter.

The crystal size Lc was determined from the half width at the diffraction peak using the following equation. Lc = λ / (β ₀ COS θ) where λ is the wavelength of the used X-ray (here, 1.5K angstroms using CuKα ray), and θ is the diffraction angle of Bragg. Β ₀ is the true half-value width, which was determined by the following equation.

Β ₀ ² = β _E ² −β _L ² (β _E : apparent half width, β _L : apparatus constant (in this case, 1.
05 × 10 ^-2 rad)) Crystal orientation degree π002 The sample was adjusted in the same manner as in the case of the crystal size Lc, and a half of the spread of the profile in the meridian direction including the highest intensity of the (002) diffraction obtained by the same analysis method. The degree of crystal orientation π ₀₀₂ (%) was determined from the valence width (H ゜) using the following equation.

The _{π 002 = [(180-H} ) / 180] × 100 resin-impregnated strands characteristic carbon fiber bundle to "Bakelite" ERL-4221 / boron trifluoride monoethyl amine (BF ₃ MEA) / acetone = 100/3 / 4 parts, and the obtained resin-impregnated strands were cured by heating at 130 ° C. for 30 minutes.
-Measured according to the resin impregnated strand test method specified in R-7601.

Example 1, Example 2, Comparative Example 1 Using a copolymer consisting of 99.5 mol% of acrylonitrile (AN) and 0.5 mol% of methacrylic acid, the concentration was 2
A 0% by weight dimethyl sulfoxide (DMSO) solution was prepared. The solution was adjusted to 35 ° C., and the pore size was 0.12 mm,
Once it is discharged into the air through a spinneret with 3,000 holes and runs through a space of about 3 mm, the temperature is 5 ° C and the concentration is 30%.
In DMSO solution. After washing the coagulated yarn with water,
After stretching by 3.5 times by bath stretching in a step, applying a silicone-based oil agent, it is brought into contact with a roller surface heated to 130 to 160 ° C. to be dried and densified, and further to 3.6 kg / cm ^2.
Stretched 3 times in pressurized steam of G, and single yarn fineness 0.75
d, A fiber bundle of total denier 2250D was obtained. ΔL of the fiber bundle was 30.

The obtained fiber bundle is heated in air at 240 to 280 ° C. at a draw ratio of 5% to convert the fiber bundle into oxidized fiber having a density of 1.36 g / cm ³ , and in an inert atmosphere at 900 ° C. 5%
Pre-carbonization was performed at a stretching ratio of 5%, and heating was performed at 1600 ° C. at a stretching ratio of 5% to obtain carbon fibers. 300 ° C to 500 ° C
And the rate of temperature rise at 1000 ° C to 1200 ° C were 200 ° C / min and 500 ° C / min, respectively.

Next, the obtained carbon fiber was subjected to 15 turns / m
Twist to 0.1 kg / cm ² · G and 3 kg / cm with argon
It was continuously supplied to a pressurized graphitizing furnace held under pressure under two conditions of ² · G , and was continuously graphitized at 3000 ° C. and 30% elongation. In addition, as a comparative sample, the same method under normal pressure (0 kg / cm ² · G), 3000 ° C., 30%
Graphitization was performed by stretching. After the surface treatment, a sizing agent was applied to each of the graphitized yarns.

As a result of measuring the characteristics of the resin-impregnated strand,
As shown in Table 1, the graphitized fiber obtained under pressure had significantly improved elastic modulus and strength compared to the graphitized fiber obtained under normal pressure.

The results of X-ray diffraction, compared with the graphite fibers obtained in atmospheric pressure, the graphitized fiber obtained under pressure, crystallinity (degree of orientation, crystal size) by the pressure is high Graphitized fibers were obtained.

Comparative Example 2 The carbon fiber used in Example 1 was twisted up to 25 turns / m, and was pressed under a pressure of 3 kg / cm ² · G using a pressurized graphitization furnace.
Graphitization was continuously performed at 3000 ° C. by stretching at 3%.

As a result of X-ray diffraction of the obtained graphitized fiber, the degree of orientation π 002 was 93.0% and the crystal size Lc was 62 Å. Also, the resin impregnated strand characteristics were measured, and as a result, the elastic modulus was 510 GPa and the strength was 3.2 GPa.
The strength was low.

Comparative Example 3 The non-twisted carbon fiber in Example 1 was graphitized at 3000 ° C. and 30% under a pressure of 3 kg / cm ² · G.
Fluff was generated at the seal stopper of the pressurized graphitizing furnace, and the yarn was broken.

Examples 3 to 8 and Comparative Examples 4 to 5 As shown in Table 2, the graphitization was continuously performed using the carbon fiber of Example 1 by changing the number of twists, the pressure, the temperature and the stretching ratio. went.

As can be seen from Table 2, under the twisted state, the higher the pressure, the higher the temperature, and the higher the draw ratio, the higher the crystallinity of the graphitized fiber and the higher the elasticity and strength. An excellent graphitized fiber can be obtained.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

According to the graphitization method of the present invention, it is possible to easily produce graphite having improved graphite crystallinity and excellent elastic modulus and strength.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) D01F 9/12-9/32

Claims (2)

(57) [Claims] 1. A carbon fiber obtained by firing at a temperature of less than 2000 ° C. is fired in a pressurized inert atmosphere at a temperature of 2000 ° C. or more, while being twisted and stretched by 5% or more. Of producing graphitized fibers. 2. The method according to claim 1, wherein the number of twists of the carbon fiber is 2 to 2.
A method for producing a graphitized fiber, wherein the production speed is 30 turns / m.