JPH086211B2 - Low-density high-modulus graphitized fiber and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a high-performance graphitized fiber, particularly to a graphitized fiber having a low density, a high elastic modulus and a high specific elastic modulus, and a method for producing the same.

[Prior Art] With the expansion of applications of graphitized fibers in recent years, there is an increasing demand for improvement in specific elastic modulus. That is, a graphitized fiber having a high elastic modulus and a low density is required. Especially in aerospace or fishing rod applications where the weight reduction effect is great, lighter graphitized fibers are required to reduce the weight as much as possible.

Conventional graphitized fibers have higher elastic modulus and higher density than high-strength carbon fibers, so even if the elastic modulus is improved, it will not be sufficiently reflected in the specific elastic modulus that is actually a problem. There was a problem. In particular, pitch-based graphitized fiber has a very high density of 2.0 g / cm ³ or more, and acrylic-based graphitized fiber also has a high density of 1.8 g / cm ³ or more.
The specific elastic modulus was not sufficiently improved.

Therefore, the present inventors previously found that the density is as low as 1.75 g / cm ³ or less, and the strength and elastic modulus are respectively high as 650 kg / mm ² or more and 35 t / mm ² or more, that is, the specific strength and the specific elastic modulus are 3.7 respectively. We have proposed a carbon fiber with a high density of 10 ⁷ cm or more and 2.0 10 ⁹ cm or more (Japanese Patent Application No. 63-134032), but it has a lower density and a high elastic modulus of 45 t / mm ² or more, and therefore a specific elastic modulus. The present invention has been made through intensive studies on graphitized fibers having a very high value.

[Problems to be Solved by the Invention] An object of the present invention is to provide a graphitized fiber having a low density and a very high elastic modulus of 45 t / mm ² or more, which cannot be achieved by the above-mentioned conventional techniques. Especially.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the low-density high-modulus graphitized fiber of the present invention has the following constitution. That is, the acrylonitrile-based polymer, a polymer other than polyacrylonitrile, blended with one or more selected from surfactants and silicone compounds, single fiber denier is 1.0d or less,
Oriented by wide-angle X-ray diffraction (π ₄₀₀ ) is 85% or more and is made by baking acrylic fiber, and its density is 1.70 g / cm ³
A low-density high-modulus graphitized fiber having the following tensile modulus of elasticity of 45 t / mm ² or more.

Here, the acrylic fiber used for the firing is
Furthermore, it is preferable to satisfy the condition that the value of ΔL by the iodine adsorption method is 30 or less.

Further, the method for producing a low-density high-modulus graphitized fiber of the present invention has the following constitution. That is, acrylonitrile-based polymer, a polymer other than polyacrylonitrile,
One or more selected from surfactants and silicone compounds are mixed in an amount of 0.5 to 30% by weight, after spinning, heated in an oxidizing atmosphere at 240 to 300 ° C, and then heated in an inert atmosphere at 350 to 5%.
Stretching by 3% or more in the temperature range of 00 ° C, then once passing through the driving roller outside the furnace, further stretching by 5% or more in the temperature range of 2000 ° C to the maximum temperature, and finally exceeding 2300 ° C. A method for producing a low-density high-modulus graphitized fiber, which is characterized by performing heat treatment in an inert atmosphere.

The manufacturing method of the present invention further includes the following aspects.

-The above heating in an oxidizing atmosphere at 240 to 300 ° C is performed until the density reaches 1.30 g / cm ³ or more.

-Take a drive roller outside the furnace once in the temperature range of 1500-2000 ° C.

-The rate of temperature rise in the temperature range of 350 to 500 ° C should be 500 ° C / min or less.

That graphitized fibers of the present invention is 1.70 g / cm ³ or less, preferably 1.65 g / cm ³ or less and a tensile modulus of 45t / mm ² or more,
A low-density high-modulus graphitized fiber having a high specific elasticity of 2.6 × 10 ⁹ cm at the same time, which has a physical property level of 50 t / mm ² or more, which is extremely difficult to achieve by any one of the conventional techniques, is high. With regard to the elastic modulus of graphitized fiber, a high elastic modulus of 50 t / mm ² or more has recently been achieved for acrylic-based graphitized fiber, and a high elastic modulus of 70 t / mm ² or higher for pitch-based graphitized fiber. Has been achieved. However, in all cases, the higher the elastic modulus, the higher the density, and thus the fiber having a high elastic modulus and a high equol density. Therefore, the lowest density graphitized fiber, ie 1.70 g /
It was a dream for material developers and structural designers to develop graphitized fibers with a density even lower than that of conventional high-strength type carbon fiber low density yarns of cm ³ or less. Especially for space applications, 1g is said to be worth over 10,000 yen, and density is a very important point.

The density in the present invention is a value measured according to the density measuring method specified in JIS-R-7601, and the tensile elastic modulus is a value determined by the resin-impregnated strand test method specified in JIS-R-7601. That is, "Bakelite" E
RL-4221 Boron trifluoride monoethylamine / acetone = 100/3/4 parts is impregnated in carbon fiber, and the obtained resin-impregnated strand is heated at 130 ° C. for 30 minutes to be cured, and then JIS-R-
It was determined by the resin-impregnated strand test method specified in 7601.

Regarding the above-mentioned low-density high-modulus graphitized fiber, an example of a method for producing the same will be described by taking acrylic-based graphitized fiber as an example. That is, as the acrylic polymer constituting the acrylic fiber (precursor) which is a raw material fiber of the acrylic graphitized fiber, at least 90 mol% or more of acrylonitrile and 10
Not more than mol% of copolymerizable vinyl monomers such as acrylic acid, methacrylic acid, itaconic acid and their alkali metal salts, ammonium salts and lower alkyl esters, acrylamide and its derivatives, allylsulfonic acid, methallylsulfonic acid and Examples thereof include copolymers with salts or alkyl esters thereof, but are not particularly limited.

Regarding the polymerization method, conventionally known solution polymerization, suspension polymerization,
Emulsion polymerization or the like can be applied, but the degree of polymerization is 1.3 or more, preferably 1.7 or more in terms of intrinsic viscosity ([η]). That is, when the intrinsic viscosity ([η]) is less than 1.3, the elastic modulus is difficult to develop, which is not preferable.

It is essential to add and mix one or more substances selected from polymers other than polyacrylonitrile, surfactants, and silicon compounds to the acrylic polymer. The amount added is preferably 0.5% to 30% by weight, more preferably 2% to 10% by weight. If the amount added is less than 0.5% by weight, the effect of decreasing the density is small, and if it exceeds 30% by weight, the elastic modulus tends to be difficult to develop.

Additives that are compatible with the acrylic polymer so that they can be uniformly mixed, or components that do not produce metal elements such as iron and sulfur, which produce defects such as extremely large voids when added. Is preferred.

Polymers include polyvinyl alcohol, polyacrylic acid, polyamide, polyethylene oxide, polyimide,
Polymers such as polypropylene, polyacrylamide, and polyethylene terephthalate are mentioned. As the surfactant, higher alcohol ethylene oxide adduct, alkylphenol ethylene oxide adduct, fatty acid ethylene oxide adduct, higher alkylamine ethylene oxide adduct, glycerol fatty acid Examples thereof include nonionic surfactants such as esters and fatty acid esters of pentaerythritol, and ionic surfactants such as sodium lauryl alcohol sulfate and trialkylammonium chloride. Further, examples of the silicon compound include alkyl or aryl silicone such as dimethyl silicone, and modified polysiloxane such as epoxy modified and amino modified.

As a method of addition, a method of mechanically mixing using a stirring blade, a method of adding after dissolving in a solvent, or the like can be applied, but in any case, uniform mixing is important.

As the spinning method, a wet spinning method, a dry spinning method, a dry-wet spinning method, or the like can be adopted, but a dry-wet spinning method is preferable because a precursor having high compactness can be obtained.

In order to obtain a carbon fiber having a high elastic modulus, a precursor having a high density is effective. As the denseness, a dense precursor having a ΔL value of 30 or less, preferably 20 or less, and more preferably 10 or less by an iodine adsorption method is preferable.

Further, in order to obtain a graphitized fiber having a high elastic modulus, a precursor having a high degree of orientation is preferred, and an acrylic fiber having an orientation degree (π ₄₀₀ ) by wide-angle X-ray diffraction of 85% or more, preferably 91% or more is particularly preferable. Orientation degree by wide-angle X-ray diffraction (π
₄₀₀ ) is 85% or more, as a means for obtaining acrylic fibers, coagulated yarn obtained by a wet spinning method or a dry-wet spinning method is drawn by hot water drawing, steam drawing or drawing in a solvent such as glycerin. As the single fiber denier of the precursor to which the means can be applied, a fine denier of 1.0 d or less, particularly 0.8 d or less is preferable for improving the elastic modulus.

As a flameproofing condition when firing such a precursor, heating to a density of 1.30 g / cm ³ or more, preferably 1.35 g / cm ³ or more in an oxidizing atmosphere of 240 to 300 ° C. improves strength and elastic modulus. It is effective in making it happen. At this time, the total stretching ratio is preferably 1.00 or more. In particular, increasing the flameproof stretch ratio as the amount added is effective in improving the elastic modulus. As the atmosphere, known oxidizing atmospheres such as air, oxygen, nitrogen dioxide, and hydrogen chloride can be adopted, but air is preferable from the economical point of view.

It is important for obtaining a high elastic modulus that the maximum temperature at which the obtained flame-resistant fiber is fired in an inert atmosphere exceeds 2300 ° C, preferably 2500 ° C. Although the upper limit of the maximum temperature is not limited, it is preferable to set the maximum temperature in the range of 2300 to 2900 ° C in consideration of the life of the furnace material.

Furthermore, in the range of 2000 ℃ ~ maximum temperature, 5-40%,
It is important to perform stretching of preferably 5 to 35%, more preferably 10 to 30% in order to obtain a high elastic modulus.

In carrying out such stretching treatment, 1500-2000
In the region of ℃, it is possible to once pass through the drive roller outside the furnace 2000
It is effective for increasing the firing tension in the range of ° C to the maximum temperature, and is therefore effective for improving the elastic modulus. In other words, it is possible to control the firing tension by separating the carbonization process into the first half and the second half. If the carbonization step is not separated into the first half and the second half in this way, it becomes difficult to increase the firing tension in the 2000 ° C. to maximum temperature region and stretch by 5% or more, and therefore, it is not possible to expect an improvement in the elastic modulus.

Stretching by 3% or more, preferably 5% or more in the range of 350 to 500 ° C. is a preferable condition for obtaining a high elastic modulus.

As the temperature rising rate conditions, the temperature rising rate in the temperature range of 350 to 500 ° C is 500 ° C / minute or less, preferably 200 ° C / minute or less, and the temperature rising rate from 2000 to the maximum temperature is 1000 ° C / minute. Below, it is effective to set the temperature to preferably 500 ° C./min or less in order to improve the stretchability and prevent the generation of fluff. Further, setting the rate of temperature rise in the temperature range of 500 to 2000 ° C. to 500 ° C./min or more, preferably 700 ° C./min or more is effective in reducing the density of the graphitized yarn.

As described above, as an example of the method for producing the fiber of the present invention, the polymer, the precursor, the yarn making, the flame resistance, the carbonization and the graphitization conditions can be specified. These techniques can also be applied to other graphitized fibers such as pitch-based.

Hereinafter, the present invention will be described in more detail with reference to Examples.

In the present invention, ΔL of the precursor by the iodine adsorption method and the degree of orientation by the wide angle X-ray diffraction (π ₄₀₀ )
Are values obtained by the following methods.

△ L fiber length by iodine adsorption method is about 0.5g accurately weighed dry samples of 5-7 cm, placed in a stoppered Erlenmeyer flask 200 ml, which in an iodine solution (I _2: 5
1 g, 2,4-dichlorophenol 10 g, acetic acid 90 g and potassium iodide 100 g are weighed and transferred to a measuring flask 1 and dissolved in water to a constant volume) 100 ml is added, and the mixture is shaken at 60 ° C for 50 minutes while shaking. Perform adsorption processing. After washing the sample with adsorbed iodine in running water for 30 minutes, centrifugal dehydration (2000 rpm x 1
Minutes) and air-dry quickly. After the sample is opened, the lightness (L value) is measured with a Hunter-type color difference meter (CM-25, manufactured by Color Machine Co., Ltd.) (L ₁ ).

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

Orientation degree by wide-angle X-ray diffraction (π ₄₀₀ ) Using Kα rays of Cu monochromated with a Ni filter as an X-ray source, the surface index (40) observed near 2θ = 17.0 °
The peak of (0) was scanned in the circumferential direction, and the full width at half maximum H (°) of the peak was used to obtain π ₄₀₀ = {(180−H) / 180} × 100 (%).

Examples 1 to 5, Comparative Example 1 Acrylonitrile (AN) 99.4 mol% and methacrylic acid 0.
Using a copolymer consisting of 6 mol%, a dimethyl sulfoxide (DMSO) solution having a concentration of 20% by weight was prepared. Add the additives shown in Table 1 to this solution, mix thoroughly using a stirring blade, and adjust to a temperature of 35 ° C, pore diameter 0.12 mm, hole number 300.
It was once discharged into the air through a spinneret of 0 to run in a space of about 6 mm, and then solidified in a DMSO aqueous solution having a temperature of 5 ° C. and a concentration of 30%. After washing the coagulated yarn with water, use a 3-stage warm water drawing bath for 3.5
After stretching twice and applying silicone oil, 130-160 ℃
Contact with the roller surface heated to dry and densify,
Further, it was drawn three times in a pressure steam of 3.7 kg / cm ² to obtain a fiber bundle having a single yarn fineness of 0.8 d and a total denier of 2400 D. The ΔL of the obtained acrylic fiber was 18. The degree of orientation (π ₄₀₀ ) by wide-angle X-ray diffraction was in the range of 86 to 92%.

The obtained fiber bundle was heated in the air at 240 to 280 ° C. under the condition that the total draw ratio is as shown in Table 1, and the density was 1.36 g / cm ³
It was converted to flame resistant fiber. Then, the temperature rising rate in the temperature range of 350 to 450 ° C was set to 200 ° C / min and 8% stretching was performed, and then at 900 ° C, once again, through a driving roller outside the furnace, 1
It was baked up to 800 ° C. The temperature rise rate in the 900-1800 ℃ range is 60
The rate was 0 ° C./minute, and the shrinkage was 1%. 20 in a nitrogen atmosphere with a maximum temperature of 2600 ° C via a drive roller outside the furnace.
The temperature rising rate in the region of 00 to 2600 ° C. was 500 ° C./minute, and 10% drawing was performed in this region to obtain a graphitized fiber. The characteristics of the obtained graphitized fiber are shown in Table 1.

Examples 6 to 7, Comparative Examples 2 to 3 Example 1 except that the graphitization maximum temperature and the draw ratio from 2000 ° C. to the maximum temperature in Example 1 are changed as shown in Table 2.
Graphitized fiber was obtained under the same conditions as above. The characteristics of the obtained graphitized fiber are shown in Table 2.

EFFECTS OF THE INVENTION The graphitized fiber of the present invention has a density of 1.70 g / cm ³ or less, a high tensile elastic modulus of 45 t / mm ² or more, and a specific elastic modulus of 2.6 × 10 6.
It is a fiber with a low density and high elastic modulus of ⁹ cm, which makes it possible to make aerospace materials and sports materials such as fishing rods lighter and thinner, and to further expand the range of utilization of graphitized fibers.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 59-71417 (JP, A) JP 57-121621 (JP, A) JP 59-137512 (JP, A) JP 61- 152826 (JP, A)

Claims (6)

[Claims] 1. An acrylonitrile-based polymer is blended with one or more selected from polymers other than polyacrylonitrile, a surfactant and a silicone compound, and has a single fiber denier of 1.0 d or less and a degree of orientation by wide angle X-ray diffraction ( π ₄₀₀ ) is 8
A low-density, high-modulus graphitized fiber characterized by being obtained by firing acrylic fiber of 5% or more, having a density of 1.70 g / cm ³ or less and a tensile modulus of 45 t / mm ² or more. . 2. The low-density high-modulus graphitized fiber according to claim 1, wherein the acrylic fiber used for the firing has a ΔL value of 30 or less by an iodine adsorption method. 3. An acrylonitrile-based polymer is mixed with 0.5 to 30% by weight of one or more selected from polymers other than polyacrylonitrile, a surfactant and a silicone compound, and after spinning, in an oxidizing atmosphere at 240 to 300 ° C. After being heated in an inert atmosphere, it is stretched by 3% or more in a temperature range of 350 to 500 ° C, then once passed through a driving roller outside the furnace, and further heated in a temperature range of 2000 ° C to a maximum temperature of 5 ° C. % Or more, and finally heat-treated in an inert atmosphere exceeding 2300 ° C. to obtain a low-density high-modulus graphitized fiber. 4. The low-density and high-modulus graphite according to claim 3, wherein the heating in the oxidizing atmosphere at 240 to 300 ° C. is performed until the density becomes 1.30 g / cm ³ or more. Method for producing synthetic fiber. 5. The method for producing a low-density high-modulus graphitized fiber according to claim 3, wherein a driving roller outside the furnace is once interposed in a temperature range of 1500 to 2000 ° C. 6. A heating rate of 500 in a temperature range of 350 to 500.degree.
6. The method for producing a low-density high-modulus graphitized fiber according to claim 3, 4 or 5, characterized in that the temperature is not higher than ° C / min.