JPH04272231A - Production of graphitized fiber - Google Patents

Abstract

PURPOSE:To obtain a graphitized fiber having high crystallinity of graphite and excellent elastic modulus and strength by producing a carbon fiber by baking at a temperature below a specific level and baking the obtained fiber in a pressurized inert atmosphere at a temperature above a specific level under drawing and twisting. CONSTITUTION:A carbon fiber such as an acrylic carbon fiber produced by baking at <2000 deg.C is baked in a pressurized inert atmosphere at >=2000 deg.C under twisting while applying elongation of >=5%. The crystallinity of graphite can easily be improved by this process to obtain the objective fiber having excellent elastic modulus, etc. The twist number of the carbon fiber is preferably 2-30turn/m.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for producing graphitized fibers,
In particular, the present invention relates to a method for producing graphitized fibers that have high graphite crystallinity, excellent elastic modulus, and strength.

0002

[Prior Art] Due to its excellent mechanical properties, especially its high specific strength and specific modulus, carbon fiber is widely used as a reinforcing material for various reinforcement materials for aerospace, leisure goods, industrial materials, etc. . In particular, graphitized fibers with a high modulus of elasticity can be used to make thin structural materials by utilizing their rigidity, resulting in further weight reduction. However, its performance is still insufficient, and there is a desire to develop high-performance graphitized fibers with even higher elastic modulus and strength.

[0003] In order to produce such high-performance graphitized fibers, it is particularly important to increase the graphite crystallinity of the fibers and bring them closer to a perfect crystal structure.

[0004] As a technique for this purpose, for example,
Publication No. 50331 discloses a catalytic graphitization technology in which acrylic oxidized fibers are immersed in an aqueous solution of a boron compound and then fired, and Japanese Patent Application Laid-Open No. 1983-3908 discloses carbon fibers heated to a temperature of 2000°C or more. A graphitization technique that stretches in a temperature range is shown.

[0005]

[Problems to be Solved by the Invention] However, in the above-mentioned catalytic graphitization method in which boron compounds are attached, there is a problem that the boron compounds adhere unevenly to the fibers, or the time required to attach the boron compounds to the fibers is extremely long and continuous. There are problems such as production difficulties. On the other hand, 20 carbon fiber
Graphitization by drawing at temperatures above 00°C aims to highly orient the substantially amorphous and isotropic carbonaceous fibers obtained from pitch and natural asphalt, and the graphitized fibers obtained are at most elastic. rate is 400GPa, strength is 2.0GPa
and the high rigidity and stiffness required in today's graphitized fiber field.
The results obtained are far from high-strength products.

The present invention focuses on improving the crystallinity during the graphitization process compared to conventional products, and as a result of intensive studies, the present invention has developed a method for graphitizing carbon fibers. It has been found that it is particularly effective to carry out stretching while twisting in a pressurized inert atmosphere, leading to the present invention. That is, an object of the present invention is to provide a method for producing graphitized fibers with high graphite crystallinity and excellent elastic modulus and strength.

[0007]

[Means for Solving the Problems] The above problems of the present invention are as follows:
Carbon fiber obtained by firing at a temperature of less than 000°C is twisted at a temperature of 2000°C or more in a pressurized inert atmosphere to give a 5%
This problem can be solved by firing while applying the above stretching.

[0008] The configuration of the present invention will be sequentially explained below.

In the present invention, carbon fibers obtained by firing at temperatures below 2000°C are heated at 200°C in an inert atmosphere.
Graphitization is carried out at a temperature of 0° C. or higher while applying a stretching of 5% or more. At this time, the inert atmosphere is particularly pressurized,
Moreover, the carbon fibers to be subjected to graphitization are twisted in advance.

[0010] That is, in order to further grow graphite crystals produced by carbonization up to 2000°C, it is necessary to draw the graphite crystals under pressure in an inert atmosphere. This can further promote the growth of graphite crystals.

[0011] The higher the graphitization pressure in this case, the greater the crystal growth effect, and is preferably 0.5 Kg/cm2.
G or more, more preferably 1.0 Kg/cm2.G or more, still more preferably 1.5 Kg/cm2.G or more. On the other hand, the upper limit of pressure is 50Kg/cm2
・If the pressure exceeds G, the temperature will be high and special firing equipment such as an autoclave will be required, making it expensive, or it will be economically disadvantageous because continuous firing will be difficult. There is. Therefore, the graphitization pressure is preferably about 0.5 to 50 Kg/cm2 ・G, more preferably 1.0 to 30 Kg/cm2 ・G, and still more preferably about 1.5 to 10 Kg/cm2 ・G. be. Further, the pressure medium is preferably an inert gas such as nitrogen or argon. The gas serving as the pressure medium (pressurized atmosphere) may be supplied using a cylinder or continuously using a compressor.

[0012] The graphitization temperature is 2000°C or higher, preferably 2500°C or higher, more preferably 280°C or higher.
The temperature shall be 0°C or higher. In other words, a temperature of 2000°C or higher is required to cause crystal rearrangement inside the carbonized thread, and at temperatures below 2000°C, crystal rearrangement is difficult to occur, and even if pressure is applied, the effect is insufficient. It is. The upper limit temperature is not particularly limited, but it is preferable to limit the temperature to a temperature at which carbon does not sublimate, from the viewpoint of physical properties of the graphitized fibers and extension of the life of the graphitization furnace. In addition, the temperature increase rate when heating is in the temperature range of 2000℃ or higher,
Preferably 300°C/min or less, more preferably 100°C
/min or less is effective in improving the density of graphitized fibers and advancing crystal orientation.

[0013] Further, the stretching conditions during 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 crystals during graphitization, and a stretching ratio of less than 5% lowers the degree of orientation and causes deterioration of physical properties. Although the upper limit of the stretching ratio is not particularly limited, it is preferable to appropriately optimize the stretching ratio by adjusting the pressure and temperature so as not to cause fuzz or thread breakage of the graphitized fibers.

On the other hand, in the present invention, the carbon fibers are twisted prior to graphitization. The number of twists is preferably 2 turns/m or more, more preferably 5 turns/m or more, even more preferably 10 turns/m or more. As for the upper limit of twisting, if it exceeds 30 turns/m, the yarn will be twisted, making it difficult to produce a stretching effect, and may also cause damage to the yarn, resulting in a decrease in the tensile strength of the graphitized fiber. Twisting carbon fiber is
This twisting may be applied at any stage of the precursor, flame-retardant fiber, or carbon fiber, and this twisting allows the fiber to be treated to be stretched and graphitized in a pressurized atmosphere, to break single filaments, and to prevent connection with the sealing plug part of the firing equipment. It is possible to prevent the generation of fuzz due to friction and damage to the fibers due to the gas blown from the seal plug. In other words, by twisting the carbon fibers prior to graphitization, it becomes possible to pressurize and draw the carbon fibers into graphitization for the first time.

[0015] Continuous firing is preferable as the above graphitization firing method, and the yarn inlet and yarn outlet seals of the graphitization furnace are made smooth, and the opening diameter of the seal plug is optimized with respect to the yarn bundle diameter. This is desirable from the viewpoint of controlling yarn damage and the amount of inert gas blown out. The obtained graphitized fibers can be subjected to surface treatment, addition of a sizing agent, etc. by conventionally known techniques, if necessary.

[0016] The carbon fiber in the present invention has a temperature of 2000°C.
Acrylic carbon fibers, pitch carbon fibers, rayon carbon fibers, etc. obtained by firing under the following conditions can be applied, and as a representative example of these, an example of manufacturing acrylic carbon fibers will be described below.

That is, first, as an acrylic polymer, 90 mol% or more of acrylonitrile and 10 mol% or less of a copolymerizable vinyl monomer, such as acrylic acid,
Examples include copolymers of methacrylic acid, itaconic acid and their alkali metal salts, ammonium salts and lower alkyl esters, acrylamide and its derivatives, allylsulfonic acid, methallylsulfonic acid and their salts or alkyl esters. can. If the amount of copolymerization exceeds 10 mol%, adhesion between single yarns tends to occur in the flameproofing process described later, which is not preferable.

Regarding the polymerization method, conventionally known solution polymerization,
Suspension polymerization, emulsion polymerization, etc. can be applied, but the degree of polymerization is preferably 1.2 or more in terms of intrinsic viscosity ([η]), more preferably 1.2 in terms of intrinsic viscosity ([η]), in order to improve spinnability and prevent adhesion between single filaments. It is best to set it to 7 or higher.

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

[0020] In order to improve graphite crystallinity, it is effective to improve the density of the precursor. The denseness of the precursor is preferably 50 or less, more preferably 30 or less, still more preferably 10 or less as a value of ΔL determined by the iodine adsorption method. Δ by iodine adsorption method
Effective means for obtaining a dense precursor with an L value of 50 or less include lowering the temperature of the spinning dope and coagulation bath, lowering the tension during coagulation, and optimizing the stretching ratio and stretching temperature.

[0021] The conditions for making the precursor flame resistant are as follows: in an oxidizing atmosphere at 200 to 300°C, under tension or stretching conditions, and with a density of preferably 1.30 g/cm3.
It is preferable to heat up to 1.35 g/cm3 or more, more preferably 1.35 g/cm3 or more. In other words, if flame resistance is insufficient, adhesion between single yarns is likely to occur during carbonization, and in order to obtain graphitized fibers with high elasticity and high strength, the density of flame-resistant yarn is 1.30 g / cm3. The above is preferable. Regarding the atmosphere, any known oxidizing atmosphere such as air, oxygen, nitrogen dioxide, or hydrogen chloride can be used, but air is preferable from the economic point of view.

[0022] The carbonization treatment is carried out at a maximum temperature of less than 2000°C, in the temperature range of 300-500°C and 1000-1200°C, at a rate of 500°C/min or less, preferably 30°C.
Carbonization at a heating rate of 0° C./min or less, more preferably 100° C./min or less, is effective in improving the compactness. At this time, in order to prevent relaxation of crystal orientation due to heat, it is effective to apply stretching preferably by 5% or more, more preferably by 10% or more.

[0023] The carbon fibers thus obtained are subjected to stretching graphitization in a pressurized atmosphere in the present invention in a twisted state. What can be done at any stage is
As mentioned above.

[0024]

[Examples] The present invention will be explained in more detail with reference to Examples below. In this example, ΔL, crystal size L
c, degree of orientation π002, and resin-impregnated strand characteristics are values determined by the following methods, respectively.

ΔL by iodine adsorption method Approximately 0.5 g of a dry sample with a fiber length of 5 to 7 cm was accurately weighed, and 20
Pour into a 0 ml Erlenmeyer flask with a stopper, add iodine solution (I2: 51 g, 2,4-dichlorophenol 10
Weigh out 90 g of acetic acid, 100 g of potassium iodide, transfer to a 1 liter volumetric flask, dissolve with water to make a constant volume), add 100 ml of the mixture, and conduct adsorption treatment at 60° C. for 50 minutes while shaking. A sample with iodine adsorbed was placed in running water for 30 minutes.
After washing with water for a minute, centrifugal dehydration (2000 rpm x 1 minute)
and quickly air dry. After opening this sample, the lightness (L value) is measured using a Hunter type color difference meter [CM-25 model, manufactured by Color Machine Co., Ltd.] (L1).

On the other hand, a corresponding sample without iodine adsorption treatment was opened, and the lightness (
L0) was measured, and the brightness difference ΔL was determined from L0-L1.

Crystal size Lc Cut the fiber bundle into a length of 40 mm, accurately weigh and collect 20 mg, align the sample fiber axes so that they are exactly parallel, and then use a sample preparation jig to cut the fiber bundle into a 1 mm wide and thick sample. The sample fibers were arranged into bundles with uniform texture. After being impregnated with a thin collodion solution and fixed so as not to lose its shape, it was fixed on a sample stage for wide-angle X-ray diffraction measurement. As an X-ray source, an X-ray generator manufactured by Rigaku Denki Co., Ltd. was used, and CuKα rays (N
i filter) was used. Using a goniometer manufactured by Rigaku Denki Co., Ltd., the surface index of graphite (0
A diffraction peak near 2θ=26° corresponding to 02) was detected using a scintillation counter.

The crystal size Lc was determined from the half width of the diffraction peak using the following formula. Lc=λ/(β0 COS θ) However, λ is the wavelength of the X-ray used (CuKα ray is used here, 1.5418 angstrom), and θ is B
ragg is the diffraction angle. Further, β0 is the true half-width, and was determined by the following formula.

β0 2 =βE 2 -βL2 (βE
: apparent half-value width, βL : device constant (in this case 1.
05×10-2 rad)) Degree of crystal orientation π002 Half value of the spread of the profile in the meridian direction including the maximum intensity of (002) diffraction obtained by preparing the sample in the same way as in the case of crystal size Lc and using the same analytical method. The degree of crystal orientation π002 (%) was determined from the width (H°) using the following formula.

π002 = [(180-H)/180] × 100 Resin-impregnated strand characteristics Carbon fiber bundle with “Bakelite” ERL-4221/Boron trifluoride monoethylamine (BF3 MEA)/Acetone = 100/3/4 The resulting resin-impregnated strand was cured by heating at 130°C for 30 minutes, and JI
It was measured according to the resin-impregnated strand test method specified in SR-7601.

Example 1, 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. This solution was adjusted to 35°C and the pore size was 0.12mm.
, Once discharged into the air through a spinneret with 3000 holes and run through a space of about 3 mm, the temperature was 5°C and the concentration was 3.
Coagulated in 0% DMSO solution. After washing the coagulated yarn with water, it was stretched to 3.5 times in three stages of bath stretching, and after applying a silicone oil agent, it was brought into contact with the surface of a roller heated to 130 to 160°C to be dried and densified, and 3. 6Kg/
The fiber bundle was drawn three times in a pressurized steam of cm2.G to obtain a fiber bundle with a single yarn fineness of 0.75 d and a total denier of 2250 D. The fiber bundle had a ΔL of 30.

The obtained fiber bundle was heated in air at 240 to 280°C at a stretching rate of 5%, and the density was 1.36 g/cm.
3, pre-carbonized in an inert atmosphere at 900°C at a stretching rate of 5%, and further carbonized at 1600°C for 5%.
% to obtain a carbon fiber. 300℃～5
The temperature increase rate at 00°C and 1000°C to 1200°C is
They were 200°C/min and 500°C/min, respectively.

Next, the obtained carbon fiber was turned at 15 turns/m.
The graphitization furnace was continuously fed to a pressurized graphitization furnace maintained at a pressure of 3 kg/cm2・G with argon.
Graphitization was performed continuously at 30% stretching at ℃. In addition, as a comparative sample, a sample was prepared under normal pressure (0 kg/cm) using the same method.
2.G), graphitization was performed at 3000°C and 30% stretching. A sizing agent was applied to each graphitized yarn after surface treatment.

[0034] As a result of measuring the resin-impregnated strand characteristics,
As shown in Table 1, the graphitized fiber obtained under pressure has an elastic modulus of 725 GPa and the strength of 4.6 GPa, and the graphitized fiber obtained under normal pressure has an elastic modulus of 700 GPa and a strength of 4.
．． Both the elastic modulus and strength were significantly improved compared to 5GPa).

As a result of X-ray diffraction, the graphitized fiber obtained under normal pressure had an orientation degree π002 of 95.5% and a crystal size Lc of 71 angstroms, whereas the graphitized fiber obtained under pressure The fibers had a degree of orientation of 96.5% and a crystal size Lc of 73 angstroms, and graphitized fibers with high crystallinity (degree of orientation, crystal size) were obtained by applying pressure.

Comparative Example 2 The carbon fibers used in Example 1 were twisted to 25 turns/m and stretched by 3% at 3000° C. under a pressure of 3 Kg/cm 2 ·G using a pressure graphitization furnace. Graphitization was performed continuously.

As a result of X-ray diffraction of the obtained graphitized fiber, the degree of orientation π002 was 93.0% and the crystal size Lc was 62 angstroms. In addition, as a result of measuring the characteristics of the resin-impregnated strand, the elastic modulus was 510 GPa, and the strength was 3.2.
GPa, and both the elastic modulus and strength were lower than that of the 30% drawn graphitized yarn of Example 1.

Comparative Example 3 The untwisted carbon fiber in Example 1 was
・Graphitization was performed at 3000℃ and 30% stretching under pressure of G, but fuzz was generated at the seal plug part of the pressure graphitization furnace.
The thread broke.

Examples 2 to 6, Comparative Examples 4 to 5 The carbon fiber of Example 1 was continuously graphitized by changing the number of twists, pressure, temperature, and stretching ratio as shown in Table 2. went.

As can be seen from Table 2, under twisted conditions, the higher the pressure, the higher the temperature, and the higher the stretching ratio, the crystallinity of graphitized fibers improves, and the elastic modulus and strength improve. Excellent graphitized fibers can be obtained.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

[Effects of the Invention] According to the graphitization method of the present invention, graphite crystallinity can be easily improved, and carbon fibers having excellent elastic modulus and strength can be easily produced.

Claims (2)

[Claims] Claim 1: Carbon fiber obtained by firing at a temperature of less than 2000°C is fired at a temperature of 2000°C or higher in a pressurized inert atmosphere while being twisted and stretched by 5% or more. A method for producing graphitized fiber. [Claim 2] In Claim 1, the number of twists of the carbon fibers is 2 to 2.
A method for producing graphitized fiber, characterized in that the turning rate is 30 turns/m.