JP2020117630A - Carbon material precursor and method for producing carbon material using the same - Google Patents

Abstract

To provide a carbon material precursor capable of obtaining a carbon material having good appearance quality which hardly generates foaming during heating such as flame resistance treatment or carbonization treatment.SOLUTION: There is provided a carbon material precursor comprising an acrylamide/vinyl cyanide-based copolymer which contains 50 to 99.9 mol% of acrylamide-based monomer unit and 0.1 to 50 mol% of vinyl cyanide-based monomer unit and has a number average molecular weight Mn of 35000 to 70000, a weight average molecular weight Mw of 40000 to 470000 and a molecular weight distribution Mw/Mn of 1.1 or more.SELECTED DRAWING: None

Description

The present invention relates to a carbon material precursor and a method for producing a carbon material using the same, and more particularly to a carbon material precursor made of an acrylamide copolymer and a method for producing a carbon material using the same.

As a method for producing a carbon fiber, which is one kind of carbon material, a method of subjecting a carbon fiber precursor obtained by spinning polyacrylonitrile to a flameproofing treatment and then a carbonization treatment has been mainly adopted. (For example, JP-B-37-4405 (Patent Document 1), JP-A-2015-74844 (Patent Document 2), JP-A-2016-40419 (Patent Document 3), and JP-A-2016-113726 ( Patent Document 4)). Since polyacrylonitrile used in this method is difficult to dissolve in an inexpensive general-purpose solvent, it is necessary to use an expensive solvent such as dimethylsulfoxide or N,N-dimethylacetamide during polymerization or spinning, which results in the production of carbon fiber. There was a problem of high cost.

Further, in JP 2013-103992 A (Patent Document 5), 96 to 97.5 parts by mass of an acrylonitrile unit, 2.5 to 4 parts by mass of an acrylamide unit, and 0.01 to 0. A carbon material precursor fiber composed of a polyacrylonitrile-based copolymer composed of 5 parts by mass is described. This polyacrylonitrile-based copolymer contains an acrylamide unit or a carboxylic acid-containing vinyl monomer unit that contributes to the water solubility of the polymer, but since their content is low, they are insoluble in water, and are not suitable for polymerization or molding. At this time, it is necessary to use an expensive solvent such as N,N-dimethylacetamide, which causes a problem that the production cost of the carbon fiber is increased.

Furthermore, when heat treatment is performed on polyacrylonitrile or its copolymer, a rapid heat generation occurs and the thermal decomposition of polyacrylonitrile or its copolymer is accelerated, resulting in a low yield of carbon material (carbon fiber). There was a problem. For this reason, when producing a carbon material (carbon fiber) using polyacrylonitrile or its copolymer, it takes a long time to prevent rapid heat generation during the temperature rising process of flameproofing treatment or carbonization treatment. It was necessary to gradually raise the temperature over time.

On the other hand, acrylamide-based polymers containing a large amount of acrylamide units are water-soluble polymers, and inexpensive and environmentally friendly water should be used as a solvent during polymerization or molding (film formation, sheet formation, spinning, etc.). Therefore, it is expected to reduce the manufacturing cost of carbon materials. JP-A-2018-90791 (Patent Document 6) describes a carbon material precursor containing an acrylamide polymer and at least one additive component selected from the group consisting of acids and salts thereof. ..

Japanese Examined Patent Publication No. 37-4405 JP, 2005-74844, A JP, 2016-40419, A JP, 2016-113726, A JP, 2013-103992, A JP, 2008-90791, A

However, a carbon material precursor composed of an acrylamide polymer may cause foaming due to a desorbed component during heating such as flameproofing treatment or carbonization treatment, and the appearance quality of the carbon material may deteriorate.

The present invention has been made in view of the problems of the above-mentioned conventional techniques, and foaming is less likely to occur during heating such as flameproofing treatment and carbonization treatment, and a carbon material capable of obtaining a carbon material having good appearance quality can be obtained. It is an object to provide a precursor and a method for producing a carbon material using the precursor.

As a result of intensive studies to achieve the above object, the present inventors have found that the acrylamide-based monomer unit and the vinyl cyanide-based monomer unit are contained in a specific ratio, and the specific number average molecular weight, weight average molecular weight and molecular weight are By using an acrylamide/vinyl cyanide-based copolymer having a distribution, it was found that a carbon material precursor in which foaming does not easily occur during heating such as flameproofing treatment or carbonization treatment can be obtained, and the present invention has been completed. ..

That is, the carbon material precursor of the present invention contains 50 to 99.9 mol% of an acrylamide monomer unit and 0.1 to 50 mol% of a vinyl cyanide monomer unit, and has a number average molecular weight Mn of 35,000. To 70,000, the weight average molecular weight Mw is 40,000 to 470,000, and the molecular weight distribution Mw/Mn is 1.1 or more, and is composed of an acrylamide/vinyl cyanide-based copolymer. .. In such a carbon material precursor, the weight average molecular weight Mw is preferably 50,000 to 400,000.

Further, the method for producing a carbon material of the present invention is a method characterized by subjecting the carbon material precursor of the present invention to carbonization treatment. In such a carbon material manufacturing method, it is preferable that the carbon material precursor is subjected to flameproofing treatment before the carbonization treatment.

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to obtain the carbon material precursor from which foaming does not easily occur at the time of heating such as flameproofing treatment or carbonization treatment and which makes it possible to obtain a carbon material having good appearance quality. Further, by using such a carbon material precursor of the present invention, it becomes possible to efficiently manufacture a carbon material having good appearance quality.

Hereinafter, the present invention will be described in detail with reference to its preferred embodiments.

[Carbon material precursor]
First, the carbon material precursor of the present invention will be described. The carbon material precursor of the present invention contains 50 to 99.9 mol% of acrylamide-based monomer units and 0.1 to 50 mol% of vinyl cyanide-based monomer units, and has a number average molecular weight Mn of 35,000 to 7%. Precursor having a weight average molecular weight Mw of 40,000 to 470,000 and a molecular weight distribution Mw/Mn of 1.1 or more and used for producing a carbon material. It is a material.

(Acrylamide/vinyl cyanide copolymer)
The acrylamide/vinyl cyanide copolymer used in the present invention contains the acrylamide monomer unit in a proportion of 50 to 99.9 mol% based on 100 mol% of all the monomer units. When the content of the acrylamide-based monomer unit is less than the lower limit, the acrylamide/vinyl cyanide-based copolymer becomes difficult to dissolve in an aqueous solvent or an aqueous mixed solvent described later. On the other hand, if the content of the acrylamide monomer unit exceeds the upper limit, a carbon material precursor having a high flameproofing yield, a high carbonization yield, and a high total flameproofing/carbonization yield cannot be obtained. Further, from the viewpoint of solubility of the copolymer in an aqueous solvent or an aqueous mixed solvent, the lower limit of the content of the acrylamide monomer unit is preferably 60 mol% or more, more preferably 70 mol% or more. Further, from the viewpoint that the flame resistance yield and carbonization yield of the carbon material precursor and the total yield of flame resistance/carbonization are improved, the upper limit of the content of the acrylamide monomer unit is preferably 99 mol% or less, 97 mol% or less is more preferable, 95 mol% or less is still more preferable, and 90 mol% or less is particularly preferable.

Further, the acrylamide/vinyl cyanide-based copolymer contains the vinyl cyanide-based monomer unit in a proportion of 0.1 to 50 mol% based on 100 mol% of all the monomer units. When the content of the vinyl cyanide-based monomer unit is less than the above lower limit, the moldability (film workability, sheet workability, spinnability, etc.) of the carbon material precursor deteriorates. On the other hand, when the content of the vinyl cyanide-based monomer unit exceeds the above upper limit, the acrylamide/vinyl cyanide-based copolymer becomes difficult to dissolve in an aqueous solvent or an aqueous mixed solvent described later. Further, from the viewpoint of improving the molding processability (film processability, sheet processability, spinnability, etc.) of the carbon material precursor, the lower limit of the content of the vinyl cyanide-based monomer unit is preferably 1 mol% or more. 3 mol% or more is more preferable, 5 mol% or more is further preferable, and 10 mol% or more is particularly preferable. Further, from the viewpoint of the solubility of the copolymer in an aqueous solvent or an aqueous mixed solvent, the upper limit of the content of vinyl cyanide-based monomer units is preferably 40 mol% or less, more preferably 30 mol% or less.

Further, the acrylamide/vinyl cyanide-based copolymer has a number average molecular weight Mn of 35,000 to 70,000. When the number average molecular weight of the acrylamide/vinyl cyanide-based copolymer is less than the lower limit, foaming is likely to occur during heating when the carbon material precursor is subjected to molding processing (film formation, sheet formation, spinning, etc.), and the resulting carbon is obtained. The appearance quality of the material is degraded. On the other hand, when the number average molecular weight of the acrylamide/vinyl cyanide copolymer exceeds the above upper limit, the moldability (film workability, sheet workability, spinnability, etc.) of the carbon material precursor is deteriorated. In addition, the upper limit of the number average molecular weight of the acrylamide/vinyl cyanide copolymer is 6.5 from the viewpoint that the carbon material precursor can be molded (filmed, sheeted, spun, etc.) with good appearance quality. It is preferably 10,000 or less, more preferably 60,000 or less, still more preferably 50,000 or less. Further, as the lower limit of the number average molecular weight of the acrylamide/vinyl cyanide copolymer, foaming at the time of heating when the carbon material precursor is molded (formed into a film, formed into a sheet, spun, etc.) is suppressed, which is favorable. From the viewpoint of obtaining a carbon material having an appearance quality, it is preferably 36,000 or more, more preferably 37,000 or more, still more preferably 38,000 or more.

The weight average molecular weight Mw of the acrylamide/vinyl cyanide copolymer is 40,000 to 470,000. When the weight average molecular weight of the acrylamide/vinyl cyanide-based copolymer is less than the lower limit, the strength of the carbon material precursor is lowered. On the other hand, when the weight average molecular weight of the acrylamide/vinyl cyanide-based copolymer exceeds the above upper limit, the moldability (film processability, sheet processability, spinnability, etc.) of the carbon material precursor deteriorates. Further, the upper limit of the weight average molecular weight of the acrylamide/vinyl cyanide-based copolymer is 400,000 from the viewpoint of improving the moldability (film processability, sheet processability, spinnability, etc.) of the carbon material precursor. The following is preferable, 350,000 or less is more preferable, 300,000 or less is further preferable, and 250,000 or less is particularly preferable. Further, the lower limit of the weight average molecular weight of the acrylamide/vinyl cyanide-based copolymer is preferably 50,000 or more, more preferably 70,000 or more, and more preferably 80,000 or more from the viewpoint of improving the strength of the carbon material precursor. More preferably, 90,000 or more is particularly preferable.

Furthermore, the acrylamide/vinyl cyanide-based copolymer has a molecular weight distribution Mw/Mn of 1.1 or more. If the molecular weight distribution of the acrylamide/vinyl cyanide-based copolymer is less than the lower limit, the moldability (film workability, sheet workability, spinnability, etc.) of the carbon material precursor will deteriorate. Further, the lower limit of the molecular weight distribution of the acrylamide/vinyl cyanide-based copolymer is 1.5 from the viewpoint that the moldability (film processability, sheet processability, spinnability, etc.) of the carbon material precursor is improved. The above is preferable, 1.8 or more is more preferable, and 2.0 or more is further preferable. Further, the upper limit of the molecular weight distribution of the acrylamide/vinyl cyanide-based copolymer is preferably 15.0 or less, more preferably 13.0 or less, from the viewpoint of improving the flame resistance yield and the carbonization yield. 0.0 or less is more preferable.

The number average molecular weight Mn, the weight average molecular weight Mw, and the molecular weight distribution Mw/Mn of the acrylamide/vinyl cyanide-based copolymer are those measured by gel permeation chromatography.

The acrylamide/vinyl cyanide copolymer used in the present invention is an aqueous solvent (water, alcohol, etc., or a mixed solvent thereof) and an aqueous mixed solvent (a mixture of the aqueous solvent and an organic solvent (tetrahydrofuran, etc.)). It is preferably soluble in at least one of (solvent). Accordingly, when the carbon material precursor is molded, dry molding (dry spinning), dry-wet molding (dry-wet spinning), wet molding (wet spinning), or electroforming using the aqueous solvent or the aqueous mixed solvent is performed. Spinning becomes possible, and the carbon material can be manufactured safely at low cost. Further, when the carbon material precursor composition described later is produced, wet mixing using the aqueous solvent or the aqueous mixed solvent becomes possible, and the acrylamide/vinyl cyanide copolymer and the additional component described below are uniformly mixed. In addition, it is possible to mix safely at low cost. Furthermore, when the obtained carbon material precursor composition is molded, dry molding (dry spinning), dry-wet molding (dry-wet spinning), wet molding (wet spinning) using the aqueous solvent or the aqueous mixed solvent is performed. ) Or electrospinning becomes possible, and it becomes possible to manufacture a carbon material safely at low cost. The content of the organic solvent in the water-based mixed solvent is not particularly limited as long as it is an amount of an acrylamide/vinyl cyanide-based copolymer that is insoluble or hardly soluble in the aqueous solvent and is dissolved by mixing the organic solvent. There is no. Further, among such acrylamide/vinyl cyanide-based copolymers, it becomes possible to mold a carbon material precursor and manufacture a carbon material precursor composition or a carbon material at a lower cost and safely. From this viewpoint, the acrylamide/vinyl cyanide-based copolymer soluble in the aqueous solvent is preferable, and the water-soluble (water-soluble) acrylamide/vinyl cyanide-based copolymer is more preferable.

Examples of the acrylamide monomer include acrylamide; N-methylacrylamide, N-ethylacrylamide, Nn-propylacrylamide, N-isopropylacrylamide, Nn-butylacrylamide, N-tert-butylacrylamide and the like N-. Alkyl acrylamide; N-cycloalkyl acrylamide such as N-cyclohexyl acrylamide; Dialkyl acrylamide such as N,N-dimethyl acrylamide; Dialkyl aminoalkyl acrylamide such as dimethylaminoethyl acrylamide, dimethylaminopropyl acrylamide; N-(hydroxymethyl) acrylamide Hydroxyalkyl acrylamides such as N-(hydroxyethyl) acrylamide; N-aryl acrylamides such as N-phenyl acrylamide; diacetone acrylamide; N,N'-alkylene bis acrylamides such as N,N'-methylene bis acrylamide; methacrylamide. N-alkyl methacrylamides, such as N-methyl methacrylamide, N-ethyl methacrylamide, Nn-propyl methacrylamide, N-isopropyl methacrylamide, Nn-butyl methacrylamide, N-tert-butyl methacrylamide; N N-cycloalkyl methacrylamide such as cyclohexyl methacrylamide; Dialkyl methacrylamide such as N,N-dimethyl methacrylamide; Dialkyl aminoalkyl methacrylamide such as dimethylaminoethyl methacrylamide, dimethylaminopropyl methacrylamide; N-(hydroxymethyl ) Hydroxyalkylmethacrylamides such as methacrylamide, N-(hydroxyethyl)methacrylamide; N-arylmethacrylamides such as N-phenylmethacrylamide; diacetonemethacrylamide; N, such as N,N'-methylenebismethacrylamide. N'-alkylene bis methacrylamide is mentioned. These acrylamide monomers may be used alone or in combination of two or more. Among these acrylamide monomers, acrylamide, N-alkyl acrylamide, dialkyl acrylamide, methacrylamide, N-alkyl methacrylamide, and dialkyl methacrylamide are preferable from the viewpoint of high solubility in an aqueous solvent or an aqueous mixed solvent. , Acrylamide is particularly preferred.

Examples of the vinyl cyanide-based monomer include acrylonitrile, methacrylonitrile, 2-hydroxyethyl acrylonitrile, chloroacrylonitrile, chloromethacrylonitrile, methoxyacrylonitrile, and methoxymethacrylonitrile. These vinyl cyanide-based monomers may be used alone or in combination of two or more. Among these vinyl cyanide-based monomers, acrylonitrile is preferable from the viewpoint of improving the flameproofing yield, carbonization yield, and total flameproofing/carbonization yield of the carbon material precursor.

In addition, the acrylamide/vinyl cyanide-based copolymer used in the present invention contains a polymerizable monomer unit other than the acrylamide-based monomer unit and the vinyl cyanide-based monomer unit as long as the effect of the present invention is not impaired. It may be. The content of such other polymerizable monomer units is preferably 49.9 mol% or less, and more preferably 40 mol% or less with respect to 100 mol% of all the monomer units of the acrylamide/vinyl cyanide copolymer. It is preferably 30 mol% or less, and particularly preferably 30 mol% or less. Examples of the other polymerizable monomer include unsaturated carboxylic acids such as acrylic acid, methacrylic acid and itaconic acid and salts thereof; unsaturated carboxylic acid anhydrides such as maleic anhydride and itaconic anhydride; methyl acrylate. Unsaturated carboxylic acid esters such as methyl methacrylate, 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate; aromatic vinyl monomers such as styrene and α-methylstyrene; vinyl cyanide such as vinyl chloride and vinyl alcohol. Vinyl-based monomers other than the system-based monomers; olefin-based monomers such as ethylene and propylene.

As a method for producing the carbon material precursor of the present invention comprising such an acrylamide/vinyl cyanide copolymer, known polymerization reactions such as radical polymerization, cationic polymerization, anionic polymerization and living radical polymerization are carried out by solution polymerization. , Suspension polymerization, precipitation polymerization, dispersion polymerization, emulsion polymerization (for example, reverse phase emulsion polymerization) and the like may be used. Among the above-mentioned polymerization reactions, the weight average molecular weight Mw of the acrylamide/vinyl cyanide-based copolymer can be reduced, the processability of the carbon material precursor (film processability, sheet processability, spinnability, etc.) can be improved, and From the viewpoint that the carbon material precursor can be produced at low cost, radical polymerization is preferable. Further, when adopting the solution polymerization, it is preferable to use, as the solvent, a solvent in which the raw material monomer and the resulting acrylamide/vinyl cyanide copolymer are dissolved, and from the viewpoint of safe production at low cost, It is more preferable to use the aqueous solvent (water, alcohol, etc., and a mixed solvent thereof) or the aqueous mixed solvent (mixed solvent of the aqueous solvent and an organic solvent (tetrahydrofuran, etc.)), and the aqueous solvent is used. Is particularly preferable, and it is most preferable to use water.

In the radical polymerization, as a polymerization initiator, conventionally known radical polymerization initiation of azobisisobutyronitrile, benzoyl peroxide, 4,4′-azobis(4-cyanovaleric acid), ammonium persulfate, potassium persulfate, etc. Although an agent can be used, when the aqueous solvent or the aqueous mixed solvent is used as the solvent, 4,4′-azobis(4-cyanovaleric acid), ammonium persulfate, potassium persulfate and the like aqueous A radical polymerization initiator soluble in a solvent or the aqueous mixed solvent (preferably the aqueous solvent, more preferably water) is preferable. Further, from the viewpoint that the weight average molecular weight Mw of the acrylamide/vinyl cyanide-based copolymer can be reduced and the molding processability (film processability, sheet processability, spinnability, etc.) of the carbon material precursor is improved, the above-mentioned polymerization Instead of or in addition to the initiator, it is preferable to use a conventionally known polymerization accelerator such as tetramethylethylenediamine or a molecular weight regulator such as alkyl mercaptan such as n-dodecyl mercaptan, and the polymerization initiator and the polymerization accelerator. Is preferably used together, and particularly preferably, ammonium persulfate and tetramethylethylenediamine are used together.

Further, the addition amount of the polymerization initiator can be appropriately set according to the temperature when the polymerization initiator is added, but the number average molecular weight Mn of the acrylamide/vinyl cyanide copolymer can be increased and foaming From the viewpoint of obtaining a carbon material that is suppressed and has good appearance quality, it is preferably 1 mol% or less, and more preferably 0.9 mol% or less, based on the number of moles of the monomer at the start of polymerization. It is more preferably 0.8 mol% or less.

The temperature at which the polymerization initiator is added is not particularly limited, but the weight average molecular weight Mw of the acrylamide/vinyl cyanide-based copolymer can be reduced, and the moldability (film processability, sheet processability) of the carbon material precursor can be reduced. From the viewpoint of improving the properties, spinnability, etc.), 30° C. or higher is preferable, 40° C. or higher is more preferable, 50° C. or higher is further preferable, and 60° C. or higher is particularly preferable. The temperature of the polymerization reaction is not particularly limited, but the weight average molecular weight Mw of the acrylamide/vinyl cyanide-based copolymer can be reduced, and the processability of the carbon material precursor (film processability, sheet processability, From the viewpoint of improving spinnability, etc., 50° C. or higher is preferable, 60° C. or higher is more preferable, 70° C. or higher is particularly preferable, and 75° C. or higher is most preferable.

Further, as the monomer concentration [=mass of monomer/(mass of monomer+mass of solvent)] at the initiation of polymerization, the number average molecular weight Mn of the acrylamide/vinyl cyanide-based copolymer can be increased and the carbon material precursor From the viewpoint that foaming at the time of heating during molding processing (film formation, sheet formation, spinning, etc.) is suppressed and a carbon material having good appearance quality is obtained, 4% by mass or more is preferable, and 6% by mass or more is preferable. More preferably, it is more preferably 9% by mass or more, particularly preferably 12% by mass or more, and most preferably 15% by mass or more.

[Carbon material precursor composition]
The carbon material precursor of the present invention can be used as it is for the production of a carbon material without adding an additive component such as an acid, but the flame resistance yield, the carbonization yield, the flame resistance/carbonization total From the viewpoint of improving the yield, a carbon material precursor composition is prepared by blending the carbon material precursor of the present invention with at least one additive component selected from the group consisting of acids and salts thereof. It is preferable to use the carbon material precursor composition in the production of the carbon material.

In such a carbon material precursor composition, as the content of the additive component, from the viewpoint of improving the flameproofing yield, the carbonization yield, and the total flameproofing/carbonization yield, the carbon material precursor 100 is used. 0.1 to 100 parts by mass is preferable, 0.2 to 50 parts by mass is more preferable, 0.5 to 30 parts by mass is further preferable, and 1 to 20 parts by mass is particularly preferable.

Examples of the acid include inorganic acids such as phosphoric acid, polyphosphoric acid, boric acid, polyboric acid, sulfuric acid, nitric acid, carbonic acid and hydrochloric acid, and organic acids such as oxalic acid, citric acid, sulfonic acid and acetic acid. Examples of the salt of such an acid include metal salts (for example, sodium salt, potassium salt), ammonium salt, amine salt and the like, preferably ammonium salt and amine salt, and more preferably ammonium salt. In particular, among these additive components, from the viewpoint of further improving the flameproofing yield and carbonization yield of the obtained carbon material precursor, the total yield of flameproofing and carbonization, phosphoric acid, polyphosphoric acid, boric acid, Polyboric acid, sulfuric acid, and ammonium salts thereof are preferable, and phosphoric acid, polyphosphoric acid, and ammonium salts thereof are particularly preferable.

The additive component is preferably soluble in at least one of the aqueous solvent and the aqueous mixed solvent (more preferably the aqueous solvent, particularly preferably water). Thereby, when the carbon material precursor composition is produced, wet mixing using the aqueous solvent or the aqueous mixed solvent becomes possible, and the acrylamide/vinyl cyanide-based copolymer and the additional component are uniformly mixed. It is possible to mix safely at low cost. When the obtained carbon material precursor composition is molded, dry molding (dry spinning), dry-wet molding (dry-wet spinning), wet molding (wet spinning) using the aqueous solvent or the aqueous mixed solvent is performed. ) Or electrospinning becomes possible, and it becomes possible to manufacture a carbon material safely at low cost.

As a method for producing such a carbon material precursor composition, a method of directly mixing the additive component with the carbon material precursor in a molten state (melt mixing), a method of dry the carbon material precursor and the additive component A method of blending (dry mixing), an aqueous solution or an aqueous mixed solution containing the additive component, or a solution in which the carbon material precursor is not completely dissolved but the additive component is dissolved in a desired shape (for example, It is also possible to adopt a method of dipping or passing the carbon material precursor molded into a film shape, a sheet shape, a fibrous shape, etc., but the carbon material precursor and the additive component to be used are When soluble in the aqueous solvent or the water-based mixed solvent, the carbon material precursor and the additional component are the same as those described above, from the viewpoint that the carbon material precursor and the additional component can be uniformly mixed. A method of mixing in an aqueous solvent or the aqueous mixed solvent (wet mixing) is preferable. Further, as the wet mixing, in the production of the carbon material precursor, when the above-mentioned polymerization is carried out in the aqueous solvent or the aqueous mixed solvent, a method of mixing the additive components after the polymerization is also adopted. be able to. Furthermore, the carbon material precursor composition can be recovered by removing the solvent from the resulting solution, and can be used for the production of the carbon material described later, and the obtained solution can be obtained without removing the solvent. It can also be used as it is for the production of a carbon material described later. In the wet mixing, it is preferable to use the aqueous solvent as a solvent, and more preferable to use water, from the viewpoint that the carbon material precursor composition can be produced safely at lower cost. Further, the method for removing the solvent is not particularly limited, and at least one of known methods such as distillation under reduced pressure, reprecipitation, hot air drying, vacuum drying, and freeze drying can be adopted.

[Method for producing carbon material]
Next, a method for manufacturing the carbon material of the present invention will be described. In the method for producing a carbon material according to the present invention, the carbon material precursor or the carbon material precursor composition is subjected to a heat treatment (carbonization treatment) under an inert atmosphere (in an inert gas such as nitrogen, argon or helium). Is the way. Thereby, the carbon material precursor is carbonized to obtain a desired carbon material. Further, since the carbon material precursor of the present invention is composed of an acrylamide/vinyl cyanide-based copolymer having a relatively large number average molecular weight, the carbon material precursor or the carbon material precursor composition is heated. Foaming does not easily occur even if the treatment is performed, and a carbon material having good appearance quality can be obtained. The “carbonization treatment” according to the present invention may generally include “graphitization” performed by heating at 2000 to 3000° C. in an inert gas atmosphere.

The carbonization temperature is preferably 500°C or higher, more preferably 1000°C or higher. The upper limit of the carbonization temperature is preferably 3000°C or lower, more preferably 2500°C or lower. Further, in the carbonization treatment, for example, the heat treatment may be performed at a temperature lower than 1000° C. first, and then the heat treatment may be performed at a temperature of 1000° C. or higher, for example, a plurality of heat treatments may be performed. Furthermore, the heating time (carbonization time) in the carbonization treatment is not particularly limited, but is preferably 1 to 60 minutes, more preferably 1 to 30 minutes.

In the method for producing a carbon material of the present invention, before the carbonization treatment, the carbon material precursor or the carbon material precursor composition may be added to the carbon material precursor under an oxidizing atmosphere (for example, in air), if necessary. Heat treatment (flame resistance treatment) may be performed. As a result, the structure of the acrylamide polymer that constitutes the carbon material precursor is converted into a structure having high heat resistance, and thus a high flame resistance yield is exhibited. Further, since the carbon material precursor (flame resistant material) that has been subjected to the flameproofing treatment has a structure with high heat resistance, it shows a high carbonization yield, and the final yield of the carbon material is improved. In particular, in the carbon material precursor composition, the deammonification reaction or dehydration reaction of the acrylamide polymer is promoted by the catalytic action of the acid or salt thereof as an additive component, so that a cyclic structure (imide ring structure) is formed in the molecule. ) Is easily formed, and the structure of the acrylamide polymer is easily converted into a structure having high heat resistance, so that the flame resistance yield of the carbon material precursor and the carbonization yield of the flame resistant compound are further increased, and the final carbon material The yield is further improved. Further, since the carbon material precursor of the present invention is composed of an acrylamide/vinyl cyanide-based copolymer having a relatively large number average molecular weight, the carbon material precursor or the carbon material precursor composition is flame resistant. It is possible to obtain a carbon material having a good appearance quality since foaming hardly occurs even if the carbonization treatment is performed.

The flameproofing treatment temperature is preferably 150 to 500°C, more preferably 200 to 450°C, further preferably 240 to 420°C, further preferably 280 to 410°C, particularly preferably 310 to 400°C, and 320 to Most preferred is 390°C. The heating time in the flameproofing treatment (flameproofing treatment time) is not particularly limited, and heating for a long time (for example, more than 1 hour) is possible, but from the viewpoint of cost reduction, it is preferably 1 to 60 minutes.

In the method for producing a carbon material of the present invention, the carbon material precursor or the carbon material precursor composition used before the flameproofing treatment (or before the carbonization treatment when the flameproofing treatment is not applied) to be used. It is preferable to preform into a desired shape (for example, a film shape, a sheet shape, a fiber shape) in advance. At this time, the carbon material precursor of the present invention is composed of an acrylamide/vinyl cyanide-based copolymer having a relatively small weight average molecular weight, and has molding processability (film processability, sheet processability, spinnability, etc.). ) Is excellent, and the carbon material precursor or the carbon material precursor composition is directly pressure-molded, or melt-molded using a carbon material precursor or a carbon material precursor composition in a molten state (for example, Melt cast molding, melt extrusion molding, injection molding, melt spinning, spun bond, melt blown, centrifugal spinning), but the carbon material precursor or the carbon material precursor composition is the aqueous solvent or the aqueous mixed solvent. In the case of being soluble in, the moldability (film processability, sheet processability, spinnability, etc.) is further increased, and the carbon material precursor or the carbon material precursor composition is added to the aqueous solvent or Dissolving in an aqueous mixed solvent and molding using the obtained aqueous solution or aqueous mixed solution, or a solution of the carbon material precursor after the above polymerization or a carbon material precursor composition obtained by the above wet mixing It is preferable to mold the solution as it is or after adjusting it to a desired concentration. As such a molding method, solution casting, wet molding, dry spinning, wet spinning, dry wet spinning, gel spinning, flash spinning, or electrospinning is preferably performed. Thereby, the carbon material precursor or the carbon material precursor composition having a desired shape can be produced safely at low cost. Further, from the viewpoint that the carbon material can be produced safely at a lower cost, it is more preferable to use the aqueous solvent as the solvent, and it is particularly preferable to use water. By using the carbon material precursor or the carbon material precursor composition which has been previously shaped into a desired shape, a carbon material having a desired shape (for example, a carbon film, a carbon sheet, a carbon fiber) can be produced. it can.

The concentration of the carbon material precursor or the carbon material precursor composition in the aqueous solution or the aqueous mixed solution is not particularly limited, but when the carbon material precursor of the present invention uses a high concentration solution It has excellent moldability (film processability, sheet processability, spinnability, etc.), and a high concentration of 20 mass% or more is preferable from the viewpoint of productivity improvement and cost reduction. When the concentration of the carbon material precursor or the carbon material precursor composition is too high, the viscosity of the aqueous solution or the aqueous mixed solution becomes high, and the molding processability (film processability, sheet processability, spinning process) is increased. Properties, etc.), the concentration of the aqueous solution or the aqueous mixed solution is preferably adjusted to a concentration at which molding processing (film formation, sheet formation, spinning, etc.) can be performed using viscosity as an index.

Hereinafter, the present invention will be described more specifically based on Examples and Comparative Examples, but the present invention is not limited to the following Examples.

(Example 1)
96.0 g (1.35 mol) of acrylamide (AAm) and 23.9 g (0.45 mol) of acrylonitrile (AN) were dissolved in 480 ml of ion-exchanged water, and the resulting aqueous solution (monomer concentration: 20.0 mass%) was added with tetra. 3.75 ml (0.025 mol) of methylethylenediamine was added, and the temperature was raised from room temperature (23°C) to 35°C with stirring under a nitrogen atmosphere. Next, 1.03 g (0.0045 mol) of ammonium persulfate was added to start the polymerization reaction, and the polymerization reaction was carried out at 60° C. for 3 hours. The obtained aqueous solution is put into methanol to precipitate a copolymer, and the copolymer is recovered and vacuum dried to obtain a carbon material composed of a water-soluble acrylamide/acrylonitrile copolymer (AAm/AN copolymer). A precursor was obtained.

(Example 2)
96.0 g (1.35 mol) of acrylamide (AAm) and 23.9 g (0.45 mol) of acrylonitrile (AN) were dissolved in 480 ml of ion-exchanged water, and the resulting aqueous solution (monomer concentration: 20.0 mass%) was added with tetra. 6.75 ml (0.045 mol) of methylethylenediamine was added, and the temperature was raised from room temperature (23°C) to 50°C with stirring under a nitrogen atmosphere. Next, 1.52 g (0.0067 mol) of ammonium persulfate was added to start the polymerization reaction, and the polymerization reaction was carried out at 50° C. for 3 hours. The obtained aqueous solution is put into methanol to precipitate a copolymer, and the copolymer is recovered and vacuum dried to obtain a carbon material composed of a water-soluble acrylamide/acrylonitrile copolymer (AAm/AN copolymer). A precursor was obtained.

(Example 3)
A carbon material precursor composed of a water-soluble acrylamide/acrylonitrile copolymer (AAm/AN copolymer) was obtained in the same manner as in Example 2 except that the amount of ammonium persulfate was changed to 2.52 g (0.011 mol). It was

(Comparative Example 1)
A carbon material precursor composed of a water-soluble acrylamide/acrylonitrile copolymer (AAm/AN copolymer) was obtained in the same manner as in Example 2 except that the amount of ammonium persulfate was changed to 4.11 g (0.018 mol). It was

(Comparative example 2)
96.0 g (1.35 mol) of acrylamide (AAm) and 23.9 g (0.45 mol) of acrylonitrile (AN) were dissolved in 480 ml of ion-exchanged water, and the resulting aqueous solution (monomer concentration: 20.0 mass%) was added with tetra. 6.75 ml (0.045 mol) of methylethylenediamine and 4.11 g (0.018 mol) of ammonium persulfate were added to start the polymerization reaction, and the temperature was raised from room temperature (23°C) to 60°C with stirring under a nitrogen atmosphere. Then, the temperature was maintained at 60° C. to carry out a polymerization reaction for 3 hours. The obtained aqueous solution is put into methanol to precipitate a copolymer, and the copolymer is recovered and vacuum dried to obtain a carbon material composed of a water-soluble acrylamide/acrylonitrile copolymer (AAm/AN copolymer). A precursor was obtained.

(Comparative example 3)
96.0 g (1.35 mol) of acrylamide (AAm) and 23.9 g (0.45 mol) of acrylonitrile (AN) were dissolved in 480 ml of ion-exchanged water, and the resulting aqueous solution (monomer concentration: 20.0 mass%) was added with tetra. 6.75 ml (0.045 mol) of methylethylenediamine was added, and the temperature was raised from room temperature (23°C) to 50°C with stirring under a nitrogen atmosphere. Then, 6.17 g (0.027 mol) of ammonium persulfate was added to start the polymerization reaction, and the polymerization reaction was performed at 60° C. for 3 hours. The obtained aqueous solution is put into methanol to precipitate a copolymer, and the copolymer is recovered and vacuum dried to obtain a carbon material composed of a water-soluble acrylamide/acrylonitrile copolymer (AAm/AN copolymer). A precursor was obtained.

(Comparative Example 4)
Water is removed from the aqueous solution by vacuum-drying a 10% aqueous solution of polyacrylamide (manufactured by Tokyo Chemical Industry Co., Ltd., product number: A0140) to obtain a carbon material precursor composed of water-soluble polyacrylamide (PAAm). It was

(Comparative example 5)
Acrylamide (AAm) 8.52 g (120 mmol) was dissolved in ion-exchanged water 190 ml, and 4,4′-azobis(4-cyanovaleric acid) was added as a polymerization initiator to the obtained aqueous solution (monomer concentration: 4.29% by mass). ) 336 mg (1.20 mmol) was added, and radical polymerization was performed at 70° C. for 3 hours. The obtained aqueous solution was put into methanol to precipitate a polymer, which was collected and vacuum dried to obtain a carbon material precursor composed of water-soluble polyacrylamide (PAAm).

(Comparative example 6)
Acrylamide (AAm) (12.8 g, 0.18 mol) was dissolved in 180 ml of ion-exchanged water, and the resulting aqueous solution (monomer concentration: 6.64 mass%) contained 1.35 ml (0.009 mol) of tetramethylethylenediamine and ammonium persulfate. 0.252 g (0.0011 mol) was added to start the polymerization reaction, and the temperature was raised from room temperature (23° C.) to 60° C. with stirring under a nitrogen atmosphere, and then the polymerization reaction was performed at 60° C. for 3 hours. It was The obtained aqueous solution was put into methanol to precipitate a copolymer, which was collected and vacuum dried to obtain a carbon material precursor composed of water-soluble polyacrylamide (PAAm).

<Measurement of composition ratio of copolymer>
The AAm/AN copolymers constituting the carbon material precursors obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were each dissolved in heavy water (dissolved in deuterated dimethyl sulfoxide when insoluble in heavy water). For each of the obtained solutions, ¹³ C-NMR measurement was performed under the conditions of room temperature and a frequency of 100 MHz. In the obtained ¹³ C-NMR spectrum, a peak derived from carbon of the cyano group of acrylonitrile, which appears at about 121 ppm to about 122 ppm, and a peak derived from carbon of the carbonyl group of acrylamide, which appears on about 177 ppm to 182 ppm, The molar ratio (AAm/AN) of the acrylamide (AAm) unit and the acrylonitrile (AN) unit in the AAm/AN copolymer was calculated based on the integrated intensity ratio. The results are shown in Table 1.

<Measurement of weight average molecular weight Mw and number average molecular weight Mn>
The weight average molecular weight Mw and the number average molecular weight Mn of the AAm/AN copolymers (Examples 1 to 3 and Comparative Examples 1 to 3) and PAAm (Comparative Examples 4 to 6) constituting the obtained carbon material precursor are The molecular weight distribution Mw/Mn was calculated using gel permeation chromatography ("HLC-8220GPC" manufactured by Tosoh Corporation) under the following conditions. The results are shown in Table 1.
〔Measurement condition〕
Column: TSKgel GMPW _XL x 2 + TSKgel G2500PW _XL x 1
Eluent: 100 mM aqueous sodium nitrate/acetonitrile=80/20.
Eluent flow rate: 1.0 ml/min.
Column temperature: 40°C.
Molecular weight standard: standard polyethylene oxide/standard polyethylene glycol.
Detector: Differential refractive index detector.

<Measurement of carbonization yield>
Each of the carbon material precursors obtained in Examples and Comparative Examples was weighed in an amount of 1 to 2 mg, and using a differential thermal balance (“TG8120” manufactured by Rigaku Co., Ltd.), under a nitrogen atmosphere with a nitrogen flow rate of 500 ml/min, a heating rate. A carbon material was obtained by heating (carbonization treatment) from room temperature to 1000° C. at 20° C./min. The mass retention of the carbon material precursor before and after the carbonization treatment (carbonization yield of the carbon material precursor at 1000° C.) is considered in consideration of the effect of water adsorbed on the carbon material precursor after vacuum drying, and the carbon material at 150° C. Based on the mass of the precursor, the following formula:
Carbonization yield of carbon material precursor [%]=M ₁₀₀₀ /M ₁₅₀ ×100
[M ₁₀₀₀ : mass of carbon material precursor (carbon material) after heating to 1000° C. under nitrogen atmosphere, M ₁₅₀ : mass of carbon material precursor at 150° C.]
Sought by. The results are shown in Table 1.

<Measurement of 5% mass reduction temperature and mass reduction rate>
Each of the carbon material precursors obtained in Examples and Comparative Examples was weighed in an amount of 1 to 2 mg, and using a differential thermal balance (“TG8120” manufactured by Rigaku Co., Ltd.), in an air atmosphere with an air flow rate of 500 ml/min, a heating rate. Thermogravimetric analysis was performed by heating from room temperature to 350° C. at 10° C./min. Based on the obtained thermogravimetric analysis results, the temperature at which a mass reduction of 5 mass% was observed with respect to the mass of the carbon material precursor at 150° C. (5% mass reduction temperature) was determined. Further, the ratio of the mass of the carbon material precursor at 250° C. to the mass of the carbon material precursor at 200° C. (mass reduction rate at 200 to 250° C.) is expressed by the following formula:
Mass reduction rate at 200 to 250° C. [%]={(M ₂₀₀ −M ₂₅₀ )/M ₂₀₀ }×100
[M ₂₅₀ : Mass of Carbon Material Precursor at 250° C., M ₂₀₀ : Mass of Carbon Material Precursor at 200° C.]
Sought by. The results are shown in Table 1.

<Evaluation of film formability (dilute solution)>
The carbon material precursors obtained in Examples and Comparative Examples were each dissolved in ion-exchanged water so that the carbon material precursor concentration was 5% by mass. 0.05 ml of the obtained aqueous solution was cast on a slide glass (18 mm×18 mm) and then dried at 60° C. for 2 hours to obtain a carbon material precursor film. The obtained carbon material precursor film was visually observed and evaluated according to the following criteria. The results are shown in Table 1.

〔Evaluation criteria〕
A: No bubbles were confirmed in the film.
B: Bubbles were not confirmed in the film, but fine irregularities were confirmed on a part of the surface.
C: Bubbles were confirmed in the film.

<Evaluation of film formability (concentrated solution)>
The carbon material precursors obtained in Examples and Comparative Examples were each dissolved in ion-exchanged water so that the carbon material precursor concentration was 10% by mass. The obtained aqueous solution was cast on a Teflon (registered trademark) sheet and then left standing at room temperature for 18 hours. Then, vacuum drying was performed to obtain a carbon material precursor film (about 20 mm×about 20 mm, thickness: about 150 μm). The obtained carbon material precursor film was visually observed and evaluated according to the following criteria. The results are shown in Table 1.

〔Evaluation criteria〕
A: No bubbles were confirmed in the film.
B: Bubbles were not confirmed in the film, but fine irregularities were confirmed on a part of the surface.
C: Bubbles were confirmed in the film.

<Presence or absence of foam>
The carbon material precursors obtained in Examples and Comparative Examples were each dissolved in ion-exchanged water so that the carbon material precursor concentration was 5% by mass. After casting 0.05 ml of the obtained aqueous solution on a slide glass (18 mm×18 mm), it was heated to 150° C. in an air atmosphere. Then, the temperature was raised from 150° C. to 350° C. over 10 minutes to obtain a film. The appearance of the obtained film was visually observed and evaluated according to the following criteria. The results are shown in Table 1.

〔Evaluation criteria〕
A: No evidence of foaming was observed on the film surface, and transparency was maintained.
B: A slight trace of foaming was confirmed on the film surface, but transparency was retained.
C: The film was opaque with evidence of foaming on the film surface.

As is clear from the results shown in Table 1, the carbon material precursors obtained in Examples and Comparative Examples all have a carbonization yield of 19% or more, and particularly, Examples 1 to 3 and Comparative Examples 1 to 1 The carbon material precursor composed of the acrylamide/vinyl cyanide copolymer obtained in 3 had a carbonization yield of 21% or more.

Further, the carbon material precursors obtained in the examples and the comparative examples all had good film forming properties when a dilute solution was used. Furthermore, the carbon material precursors (Examples 1 to 3 and Comparative Examples 1 to 3 and 6) made of an acrylamide polymer having a weight average molecular weight of 450,000 or less have good film forming properties when a concentrated solution is used, In particular, the carbon material precursors (Examples 2 to 3 and Comparative Examples 1 to 3 and 6) made of an acrylamide polymer having a weight average molecular weight of 130,000 or less were excellent in film forming property when a concentrated solution was used. On the other hand, the carbon material precursor (Comparative Examples 4 to 5) composed of an acrylamide polymer having a weight average molecular weight of 490,000 or more was inferior in film forming property when a concentrated solution was used.

Further, a carbon material precursor (Examples 1 to 3) composed of an acrylamide/acrylonitrile copolymer having a number average molecular weight of 38,000 or more, or a carbon composed of a homopolymer of acrylamide having a number average molecular weight of 78,000 or more. When the material precursor (Comparative Examples 4 to 5) is used, a film having good transparency can be obtained, and particularly, an acrylamide/acrylonitrile copolymer having a number average molecular weight of 38,000 or more and 410,000 or less can be obtained. When a carbon material precursor composed of a polymer (Examples 1 and 3) or a carbon material precursor composed of a homopolymer of acrylamide having a number average molecular weight of 84,000 (Comparative Example 4) was used, transparency was improved. An excellent film could be obtained. On the other hand, a carbon material precursor (Comparative Examples 1 to 3) composed of an acrylamide/acrylonitrile copolymer having a number average molecular weight of 28,000 or less, or a carbon material composed of an acrylamide homopolymer having a number average molecular weight of 430,000. When the precursor (Comparative Example 6) was used, foaming occurred due to heating during film formation, and a transparent film could not be obtained.

As described above, according to the present invention, it is possible to obtain a carbon material precursor capable of obtaining a carbon material having good appearance quality, which is less likely to cause foaming during heating such as flameproofing treatment or carbonization treatment. Becomes

Therefore, in the method for producing a carbon material of the present invention, the carbon material precursor to be used is excellent in moldability (film processability, sheet processability, spinnability, etc.), and foaming hardly occurs when heated. Therefore, it is useful as a method for efficiently producing a carbon material having good appearance quality.

Claims (4)

It contains 50 to 99.9 mol% of an acrylamide monomer unit and 0.1 to 50 mol% of a vinyl cyanide monomer unit, has a number average molecular weight Mn of 35,000 to 70,000 and a weight average molecular weight Mw. A carbon material precursor characterized by comprising an acrylamide/vinyl cyanide-based copolymer having a molecular weight distribution Mw/Mn of 40,000 to 470,000 and 1.1 or more. The carbon material precursor according to claim 1, wherein the weight average molecular weight Mw is 50,000 to 400,000. A method for producing a carbon material, comprising carbonizing the carbon material precursor according to claim 1 or 2. The method for producing a carbon material according to claim 3, wherein the carbon material precursor is subjected to a flameproofing treatment before the carbonization treatment.