JP2002145957A - Acrylonitrile polymer and carbon material produced by using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acrylonitrile polymer having stabilized thermal oxidation reactivity and suitable as a raw material for a carbonaceous material such as carbon fiber. SOLUTION: The acrylonitrile polymer satisfies the formula: x=0.03 to 0.6 and formula (1) wherein (x) is defined by Da/(Da+Db) (Da is the infrared absorbance caused by the C-O double bond of carboxy group and measured by KBr tablet method and Db is the infrared absorbance caused by C-N triple bond of cyano group) and (y) is the reciprocal of tp (min) (1/tp) defined by the time to develop the exothermic peak on the isothermal heat-generation curve measured in an air stream of 100 mL/min at 230 deg.C by a heat-flux differential scanning calorimeter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a raw material for a carbon material, which has a large thermal oxidation reactivity as a whole and is excellent, and in which the thermal oxidation reactivity can be finely controlled according to the purpose by adjusting the composition. The present invention relates to a suitable acrylonitrile-based polymer and a carbon material using the same.

[0002]

2. Description of the Related Art Acrylonitrile-based polymers have hitherto been mainly produced as raw materials for acrylic fibers, but carbon fibers produced from acrylonitrile-based polymers, so-called PAN-based carbon fibers, have particularly excellent strength properties. And its use as a carbon fiber raw material is increasing. Recently, more than 90% of all carbon fibers are PAN-based carbon fibers. In addition, the development of carbon electrode materials and carbon films for secondary batteries using acrylonitrile-based polymers as raw materials is also progressing, and future growth of technologies using acrylonitrile-based polymers is expected. When carbon fibers are produced from an acrylonitrile-based polymer, an acrylic fiber obtained by spinning the acrylonitrile-based polymer, that is, a precursor for carbon fiber, is subjected to a flame-resistant treatment at 200 to 400 ° C. in an oxidizing atmosphere. Fiber. Next, the oxidized fiber is carbonized at 800 to 2000 ° C. in an inert gas atmosphere to produce a carbon fiber. Further, the carbon fiber thus obtained may be further treated in a high-temperature inert gas to obtain a graphite fiber.

[0003] In such a manufacturing process, the oxidization and cyclization of the acrylonitrile-based polymer is accompanied by heat generation in the oxidization and cyclization of the acrylonitrile-based polymer in the oxidizing and oxidizing process. If the reaction runs away in this step, the physical properties of the finally obtained carbon fiber deteriorate. In addition, when the time for the oxidization treatment is shortened, although the oxidization of the surface layer proceeds, the inside of the surface layer is burnt, and the physical properties of the finally obtained carbon fiber also decrease. For this reason, it is necessary to take a long time in the flame-proofing step and to stably perform these reactions while sufficiently controlling these reactions. As described above, the oxidization step is an important step because it affects the physical properties of the carbon fiber, but it is not efficient because it requires a long time. Therefore, an acrylonitrile-based polymer containing an acid comonomer other than an acrylonitrile monomer such as itaconic acid or acrylic acid is used as a precursor to increase the thermal oxidation reactivity and shorten the flame resistance process.

[0004]

However, when an acrylonitrile-based polymer containing an acid comonomer is used as a precursor as described above, the time required for the flame-proofing step can be reduced, but the type of acid comonomer in the acrylonitrile-based polymer can be reduced. In some cases, only slight differences in the amount of the acid comonomer used or the amount of the acid comonomer significantly change the thermal oxidation reactivity. For this reason, even if the composition of the acrylonitrile-based polymer obtained by the polymerization reaction slightly differs depending on the reaction batch, the thermal oxidation reactivity may fluctuate greatly, and the stabilization step may not be performed stably. When the proportion of the acid comonomer is increased, the strength of the finally obtained carbon fiber or the like may be insufficient.

The present invention has been made in view of the above circumstances, and has a high thermal oxidation reactivity and is excellent. Further, the thermal oxidation reactivity can be controlled more finely and stably by adjusting the composition. It is an object of the present invention to provide an acrylonitrile-based polymer capable of producing a carbon material suitable for a purpose, such as production of a carbon fiber or production of an extremely low-cost carbon fiber.

[0006]

The acrylonitrile polymer of the present invention is characterized in that, in the infrared absorption spectrum measured by the KBr tablet method, the absorbance of the absorption due to the carbon-oxygen double bond of the carboxyl group is defined as Da, Carbon of cyano group
The absorbance ratio Da / (Da + Db) calculated from the absorbance of the absorption caused by the nitrogen triple bond as Db is 0.03 to 0.
6, and 100 m with a heat flux type differential scanning calorimeter.
The reciprocal 1 / t of the heat generation peak appearance time tp (min) in the isothermal heat generation curve measured at 230 ° C. in an air flow of 1 / min.
p and the absorbance ratio Da / (Da + Db) satisfy the relationship of the following equation (1).

(Equation 2) (Where x = Da / (Da + Db), y = 1 / tp). The acrylonitrile-based polymer contains acrylonitrile as a monomer unit and further itaconic acid, and all of the monomer units Among them, it is preferable that the ratio of acrylonitrile is the highest, and then that of itaconic acid is highest. Also, acrylonitrile is 96 to 99.95 mol%.
Preferably, the amount of itaconic acid is 0.05 to 4 mol%. Further, the acrylonitrile-based polymer is preferably polymerized by a polymerization method using an organic azo-based initiator in a mixed system of water and an organic solvent. The carbon fiber precursor of the present invention is characterized by comprising the acrylonitrile-based polymer. Further, the carbon fiber of the present invention is characterized by being manufactured from the above-mentioned precursor for carbon fiber. Furthermore, the carbon material of the present invention is characterized by being manufactured from the acrylonitrile-based polymer.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The acrylonitrile-based polymer of the present invention has, in an infrared absorption spectrum measured by a KBr tablet method, an absorbance Da of an absorption around 1735 cm ^-1 due to a carbon-oxygen double bond of a carboxyl group and a carbon- The absorbance ratio Da / (Da + Db) calculated from the absorbance Db of the absorption around 2240 cm ⁻¹ due to the nitrogen triple bond is 0.03 to
0.6. The KBr tablet method is a method in which a solid measurement sample is ground together with potassium bromide in a mortar or the like, and then molded into a tablet using a compression molding machine or the like and measured.

The absorbance ratio Da / (Da + Db) is 0.03
If less than, the thermal oxidation reactivity of the acrylonitrile-based polymer is too low, for example, when producing carbon fibers from this polymer, the time required for the flame-resistant treatment of a fibrous precursor made of this polymer becomes longer, The productivity of carbon fiber may decrease. On the other hand, if it exceeds 0.6, the thermal oxidation reactivity of the acrylonitrile-based polymer may be too high, and the oxidation reaction and the cyclization reaction may run away during the oxidation treatment of the precursor. In some cases, the physical properties of the carbon fiber obtained in a desired manner may be reduced.

Further, the acrylonitrile copolymer of the present invention can be prepared by using a heat flux type differential scanning calorimeter in an amount of 100 ml / ml.
In an isothermal heat generation curve measured when the temperature is maintained at 230 ° C. in an airflow for one minute, the heat generation peak is at tp (minute). That is, the heat generation peak appearance time is tp (minutes). In a heat flux type differential scanning calorimeter, when the measurement sample and the standard sample are held at a constant temperature and a temperature difference occurs between them, the heat flow around either the measurement sample or the standard sample increases to cancel this. Or be suppressed. Here, the isothermal heat generation curve is obtained by plotting the heat flow velocity difference Δq between the two against the retention time. Then, the time when the measurement sample generates heat and a peak due to the heat generation is observed is referred to as a heat generation peak appearance time. Here, 4 mg of acrylonitrile-based polymer powder was placed in an aluminum open container, and then covered with a stainless steel mesh cover.
This was placed in a dry air stream at a flow rate of 100 ml / min.
And measure the isothermal heating curve. The acrylonitrile-based polymer powder that has passed through a 380 mesh sieve is used.

In the acrylonitrile copolymer of the present invention, the reciprocal 1 / tp of the exothermic peak appearance time tp (min) in the isothermal exothermic curve and the absorbance ratio Da /
(Da + Db) and the following equation (1).

(Equation 3) (Where x = Da / (Da + Db) and y = 1 / tp.) An acrylonitrile-based polymer having such a relationship between Da / (Da + Db) and 1 / tp has a thermal oxidation reactivity. In addition to being large, the thermal oxidation reactivity can be more finely controlled according to the purpose by further adjusting the composition. If 1 / tp is less than such a range, the thermal oxidation reactivity may not increase even if the composition is adjusted, and if it exceeds such a range, the thermal oxidation reactivity may not increase even if the composition is adjusted. Sometimes too large to control.

The acrylonitrile polymer of the present invention may contain, as a comonomer, an acid comonomer copolymerizable with acrylonitrile in addition to acrylonitrile. When an acid comonomer is contained, the thermal oxidation reactivity of the acrylonitrile-based polymer is increased, and the time required for the flame-proofing step in producing carbon fibers and the thermal oxidation reaction in producing other carbon materials can be shortened. The acid comonomer is not particularly limited, and includes itaconic acid, acrylic acid, methacrylic acid, maleic acid, fumaric acid, crotonic acid, etc., with itaconic acid being preferred. Further, it is preferable that the ratio of acrylonitrile is the highest among all the monomer units constituting the acrylonitrile-based polymer, and the ratio of itaconic acid is the second highest. More preferably, acrylonitrile is 96
９９99.95 mol%, and itaconic acid is 0.05-4 mol%. If the amount of itaconic acid is less than 0.05 mol%, the thermal oxidation reactivity may be low, and the solution of the acrylonitrile-based polymer may not be sufficient when the polymer is spun to produce a precursor for carbon fiber. May be stable. on the other hand,
If it exceeds 4 mol%, the fibers may be fused together in the flame-proofing step, or the physical properties of the finally obtained carbon material such as carbon fiber may be reduced.

Such an acrylonitrile-based polymer can be produced by various methods such as a suspension polymerization method, a solution polymerization method, and an emulsion polymerization method. However, in a mixed system of water and an organic solvent, an organic azo initiator is used. It is preferable to produce by a suspension polymerization method. As the organic solvent, it is more preferable to use at least one selected from dimethylsulfoxide, dimethylformamide, and dimethylacetamide. Organic azo initiators include 2,2′-azobis (4-methoxy-
2,4-dimethylvaleronitrile), AIBN and the like can be used.

The acrylonitrile polymer thus produced is calculated from the absorbance Da of the absorption caused by the carbon-oxygen double bond of the carboxyl group and the absorbance Db of the absorption caused by the carbon-nitrogen triple bond of the cyano group. The absorbance ratio Da / (Da + Db) is 0.03-0.6, and the reciprocal 1 / tp of the exothermic peak appearance time tp (min) in the isothermal heat curve and the absorbance ratio Da / (Da + Db) are represented by the above formula. Since it satisfies (1), it has high thermal oxidation reactivity,
By adjusting the type and ratio of the acid comonomer, the degree thereof can be variously controlled according to the purpose, and various acrylonitrile-based polymers can be obtained according to the application.

For example, Da / (Da + Db) and 1 / tp
Within the above range, increasing the proportion of acrylonitrile in the acrylonitrile-based polymer and decreasing the proportion of the acid comonomer, while maintaining the magnitude of thermal oxidation reactivity, the strength failure due to the acid comonomer was suppressed High performance carbon fiber can be manufactured. On the other hand, when the proportion of acrylonitrile in the acrylonitrile-based polymer is reduced, the thermal oxidation reactivity is very large, and for example, an acrylonitrile-based polymer that can efficiently perform a flame-proofing step in the case of producing carbon fibers is obtained. Fibers can be produced at very low cost. Therefore, Da / (Da + Db) and 1 / tp
By adjusting the composition of the acrylonitrile-based polymer within the above range, it is possible to produce a very high-performance carbon fiber or an extremely low-cost carbon fiber according to the purpose.

The obtained acrylonitrile-based polymer is dissolved in an organic solvent such as dimethylformamide, dimethylacetamide, dimethylsulfoxide and the like, and spun by a conventional method such as a dry-wet spinning method and a wet spinning method to obtain a carbon fiber. Precursors for fibers can be manufactured. Next, the carbon fiber precursor is subjected to an oxidizing atmosphere at 200 to 300 ° C. in an oxidizing atmosphere to obtain an oxidized fiber. Thereafter, a carbonization step of treating the oxidized fiber in an inert gas at 800 to 2000 ° C. is performed to produce a carbon fiber.
Furthermore, this carbon fiber is 2,500-280 in an inert gas.
By treating at a high temperature of about 0 ° C., graphite fibers can be produced.

Further, such an acrylonitrile-based polymer is suitable for use in carbon materials other than carbon fibers. For example, a carbon material for an electrode can be produced by a method in which a powder or a film of an acrylonitrile-based polymer is subjected to a flame-proof treatment and then a carbonization step is performed. In addition, by dissolving the acrylonitrile-based polymer in a solvent such as dimethyl sulfoxide to form a film, and if necessary, processing such as uniaxial stretching, biaxial stretching, and then, by performing a flame-resistant treatment, carbonization treatment, Can produce carbon film.

Such an acrylonitrile-based polymer is
The thermal oxidation reactivity is generally large and excellent, and further fine-tuning of the thermal oxidation reactivity can be controlled according to the purpose by adjusting the composition. Therefore, by adjusting the composition, it is possible to produce very high-performance carbon fibers and to produce carbon fibers with extremely low production costs.
Such an acrylonitrile-based polymer is suitable for producing carbon materials such as carbon fibers, carbon materials for electrodes, and carbon films, but is particularly suitable for producing carbon fibers.

[0018]

The present invention will be described in more detail with reference to the following examples and comparative examples. [Examples 1 to 4] The weight ratio of water / dimethylacetamide / monomer was kept at 5/1/1, and 2,2 ′ was used as an initiator.
-Azobis (4-methoxy-2,4-dimethylvaleronitrile) was added at 0.6% by weight to the monomer,
An acrylonitrile-itaconic acid copolymer as shown in Table 1 was produced at a polymerization time of 3 ° C. for 120 minutes. Each of these intrinsic viscosities was about 1.8. These polymers were kept at 230 ° C. in an air flow of 100 ml / min with a heat flux type differential scanning calorimeter, and the reciprocal 1 / tp of the exothermic peak appearance time tp (min) in the obtained isothermal exothermic curve is shown in Table 1. . Table 1 also shows the absorbance ratio Da / (Da + Db) calculated from the infrared absorption spectra of these polymers.

Further, after dissolving the polymer obtained in Example 2 in dimethyl sulfoxide to prepare a solution having a concentration of 20% by weight, the solution was spun by a dry-wet spinning method, and then stretched in hot water. After applying the oil agent, the mixture was further dried and densified with a heating roller, and then subjected to steam stretching to produce a precursor. This precursor is heat-treated in air in a hot-air circulation type flame stabilization furnace of 220-260 ° C. in a stepwise manner at a temperature of 220-260 ° C. for 60 minutes while giving 6% elongation (flame stabilization step). A low-temperature heat treatment was performed at 600 ° C. for 2 minutes at an elongation rate of 6%, and further a heat treatment furnace at a maximum temperature of 1400 ° C. under 0% elongation for about 1.5 minutes under the same atmosphere. The obtained carbon fiber has a strand strength of 580 kg /
mm ² , the strand elastic modulus was 27 ton / mm ² , and it was a high-strength carbon fiber.

Of these, the polymer obtained in Example 4 was dissolved in dimethyl sulfoxide to prepare a 20% by weight solution, which was spun by a wet spinning method and then stretched in hot water. After applying the oil agent, the mixture was further dried and densified with a heating roller, and then subjected to steam stretching to produce a precursor. This precursor was subjected to a heat treatment (flame-proofing step) in air at 230 to 270 ° C. in a hot-air circulation-type flame-proofing furnace at a temperature as low as 25 minutes while increasing the temperature stepwise while giving 5% elongation. Thereafter, a low-temperature heat treatment is performed for 1.5 minutes at a maximum temperature of 600 ° C. and an elongation of 5% in a nitrogen atmosphere for 1.5 minutes, and a -5% elongation is performed in a high-temperature heat treatment furnace having a maximum temperature of 1400 ° C. in the same atmosphere. For about 1.5 minutes. The obtained carbon fiber has a strand strength of 420 kg /
mm ² , and the strand elastic modulus was 25 ton / mm ² .

Various measurements were made as follows. (1) Composition of copolymer: ¹ H-NMR method (JEOL GS
X-400 type superconducting FT-NMR). (2) Intrinsic viscosity η of polymer: measured with a dimethylformamide solution at 25 ° C. (3) Isothermal DSC exothermic curve: 4 mg of the polymer powder passed through a 380 mesh sieve was accurately weighed, placed in an aluminum open sample container, and held down with a stainless steel mesh cover at a flow rate of 100 ml / min. Measured at 230 ° C. in a stream of dry air. As a heat flux type differential scanning calorimeter, DSC220C manufactured by Seiko Denshi Kogyo was used. (4) Infrared absorption spectrum: After 1 mg of a sample was uniformly mixed with 100 mg of potassium bromide powder, this was shaped into a tablet, and measured by FT-IR7300 manufactured by JASCO Corporation.

[Comparative Examples 1 to 3] 1867 g of water and 133 g of monomer were added, and the weight ratio of water / monomer was 14/1.
And 1.5 g of ammonium persulfate, 4.6 g of a 50 wt% aqueous solution of ammonium bisulfite, 18 g of a 1.0% aqueous solution of sulfuric acid, and 1.3 g of an aqueous solution of 30 ppm iron sulfate were added. An acrylonitrile-methacrylic acid copolymer as shown was prepared. All of these intrinsic viscosities were 1.8. Table 1 also shows the results obtained for 1 / tp and the absorbance ratio Da / (Da + Db) of these polymers in the same manner as in Example 1. When these obtained polymers were treated in the same manner as in Example 1,
In most cases, a double cross-sectional structure was formed in the flame-proofing step, and the strength development properties as a carbon fiber were not exhibited.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

As described above, the acrylonitrile-based polymer of the present invention has a large thermal oxidation reactivity as a whole and is excellent. Further, by adjusting the composition, it can be used for a high-performance carbon fiber or a flame-proofing process. It is possible to produce a low-cost carbon fiber that requires a very short time. Therefore, it is possible to efficiently provide an acrylonitrile-based polymer that meets the performance required by carbon fibers. Such an acrylonitrile-based polymer is suitable for producing carbon materials such as carbon fibers, carbon materials for electrodes, and carbon films, but is particularly suitable for producing carbon fibers.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // (C08F 220/44 (C08F 220/44 222: 02) 222: 02) F-term (Reference) 4G046 CA04 CB01 4J015 AA01 4J100 AJ08Q AM02P CA04 DA22 FA03 JA11 4L035 BB03 BB04 BB06 BB59 BB69 BB72 BB80 BB85 FF01 GG02 GG04 HH10 MB04 4L037 CS03 CT10 FA06 PA55 PA61 PA65 PC10 PC11 PC13 PF19 PS20 PS27

Claims (7)

[Claims] 1. In an infrared absorption spectrum measured by a KBr tablet method, the absorbance of absorption due to a carbon-oxygen double bond of a carboxyl group is defined as Da, and the carbon-
The absorbance ratio Da / (Da + Db) calculated from the absorbance of the absorption caused by the nitrogen triple bond as Db is 0.03 to 0.
6. Further, the reciprocal 1 / tp of an exothermic peak appearance time tp (min) in an isothermal exothermic curve measured at 230 ° C. in an air flow of 100 ml / min with a heat flux type differential scanning calorimeter, and the absorbance ratio An acrylonitrile-based polymer, wherein Da / (Da + Db) satisfies the relationship of the following formula (1). (Equation 1) (Where x = Da / (Da + Db) and y = 1 / tp) 2. An acrylonitrile as a monomer unit,
The acrylonitrile-based polymer according to claim 1, further comprising itaconic acid, wherein the ratio of acrylonitrile is the highest among all the monomer units, and then the ratio of itaconic acid is large. 3. The acrylonitrile-based polymer according to claim 2, wherein the acrylonitrile is 96 to 99.95 mol% and the itaconic acid is 0.05 to 4 mol%. 4. The acrylonitrile-based polymer according to claim 1, wherein the acrylonitrile-based polymer is polymerized by a polymerization method using an organic azo-based initiator in a mixed system of water and an organic solvent. 5. A precursor for carbon fiber, comprising the acrylonitrile-based polymer according to any one of claims 1 to 4. 6. A carbon fiber produced from the carbon fiber precursor according to claim 5. Description: 7. A carbon material produced from the acrylonitrile polymer according to any one of claims 1 to 4.