Carbon material

Abstract

To provide a carbon material using biomass as a raw material.SOLUTION: A carbon material contains a carbide of a resin composition containing a lignin-modified novolac type phenol resin.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a carbon material, and more particularly to a carbon material used for refractories, glassy carbon, graphite molded bodies, carbon fiber reinforced carbon composite materials, carbon brushes, battery materials, activated carbon, etc. [Background technology]

[0002] Carbon materials are used in a wide range of applications, including refractories, glassy carbon, graphite compacts, carbon fiber-reinforced carbon composites, carbon brushes, battery materials, and activated carbon, and this is an area where further development is expected in the future. These carbon materials are made from raw materials such as coconut shells, coal coke, coal or petroleum pitch, furan resins, and phenolic resins. For example, Patent Document 1 describes a method for obtaining a carbon material by carbonizing a cured mixture containing a resol-type phenolic resin and an oleophilic material. Furthermore, given the recent emergence of environmental problems on a global scale, it is considered desirable to effectively utilize renewable, non-edible biomass as a raw material for these applications as well. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 05-43345 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a carbon material using biomass as a raw material. [Means for solving the problem]

[0005] According to the present invention, the following carbon material is provided. [1] A carbon material comprising a carbonized resin composition containing a lignin-modified novolac-type phenolic resin. [2] The carbon material according to [1], further comprising a carbon substance. [3] The carbon material according to [2], wherein the carbon substance includes at least one selected from graphitizable carbon, non-graphitizable carbon, natural graphite, artificial graphite, carbon black, carbon fiber, and carbon nanofiber. [4] The carbon material according to any one of [1] to [3], wherein the resin composition further contains a hydrophobic hydrocarbon. [5] The carbon material according to [4], wherein the hydrophobic hydrocarbon contains an aromatic ring. [6] The carbon material according to [4], wherein the hydrophobic hydrocarbon comprises a residue or extract of crude oil or coal. [7] The carbon material according to [4], wherein the hydrophobic hydrocarbon includes asphalt, coal tar, and coal tar pitch. [8] The carbon material according to [7], wherein the asphalt is at least one selected from the group consisting of natural asphalt, petroleum asphalt, petroleum pitch, recycled asphalt, and modified asphalt. [9] The carbon material according to any one of [1] to [8], wherein the resin composition further contains a curing agent.

[10] The carbon material according to [9], wherein the curing agent contains hexamethylenetetramine. [Effects of the Invention]

[0006] According to the present invention, there is provided a carbon material that can be suitably used as a carbon material for refractories, glassy carbon, graphite molded bodies, carbon fiber reinforced carbon composite materials, carbon brushes, battery materials, activated carbon, and the like. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, an embodiment of the present invention will be described. In this specification, the expression "a to b" in the description of a range of numerical values ​​means "a or more and b or less" unless otherwise specified. For example, "5 to 90%" means "5% or more and 90% or less."

[0008] [Carbon materials] The carbon material according to this embodiment is a carbon material used for negative electrodes for lithium ion secondary batteries, carbon fiber reinforced carbon composite materials, carbon brushes, and the like. The carbon material of the present embodiment includes a carbonized product of a resin composition containing a lignin-modified novolac phenolic resin. In other words, the carbon material of the present invention is a carbonized material obtained by carbonizing a resin composition containing a lignin-modified novolac phenolic resin, and includes a carbonized product of the lignin-modified novolac phenolic resin. Hereinafter, each component used in the resin composition that is subjected to carbonization treatment to produce the carbon material of this embodiment will be described.

[0009] (lignin-modified novolac phenolic resin) The lignin-modified novolac phenolic resin used in the resin composition for producing the carbon material of this embodiment is a phenolic resin obtained by reacting lignins, phenols, and aldehydes, and having a lignin-derived structure as a structural unit. The lignin-modified novolac phenolic resin preferably has a weight-average molecular weight of 3,000 or more.

[0010] In one embodiment, the lignin-modified novolac phenolic resin has a lignin modification rate of 5% to 60%. Since the lignin-modified novolac phenolic resin has a lignin modification rate within the above range, it is a biomass-derived material, which reduces the environmental impact, and its carbonized product can be suitably used as a carbon material for electrodes and the like.

[0011] (Method of producing lignin-modified novolac phenolic resin) The lignin-modified novolac phenolic resin is a phenolic resin obtained by reacting lignins, phenols, and aldehydes in the presence of an acid catalyst. More specifically, the lignin-modified novolac phenolic resin can be produced by reacting lignins, phenols, and aldehydes in the presence of an acid catalyst under conditions where the molar ratio of aldehydes to phenols (F / P) is 0.2 or higher, preferably 0.3 to 1.2. The upper limit of the molar ratio (F / P) is preferably 1.1 or lower, more preferably 1.0 or lower. The lower limit of the molar ratio (F / P) is preferably 0.4 or higher, more preferably 0.5 or higher. By carrying out the reaction under conditions where the molar ratio of aldehydes to phenols (F / P) is within the above range, a lignin-modified novolac phenolic resin having a desired weight-average molecular weight and lignin modification rate can be produced.

[0012] The materials and production conditions used in producing the lignin-modified novolac phenolic resin of this embodiment will be described in detail below.

[0013] (phenols) Phenols used to produce the lignin-modified novolac phenolic resin include phenol, phenol derivatives, and combinations thereof. Phenol derivatives can be used in which any substituent has been introduced into the benzene ring. Examples of the substituent include a hydroxyl group, a lower alkyl group such as a methyl group or an ethyl group, a halogen atom such as fluorine, chlorine, bromine, or iodine, an amino group, a nitro group, and a carboxyl group. Specific examples of usable phenols include phenol, catechol, resorcinol, hydroquinone, o-cresol, m-cresol, p-cresol, o-fluorophenol, m-fluorophenol, p-fluorophenol, o-chlorophenol, m-chlorophenol, p-chlorophenol, o-bromophenol, m-bromophenol, p-bromophenol, o-iodophenol, m-iodophenol, p-iodophenol, o-aminophenol, m-aminophenol, p-aminophenol, o-nitrophenol, m-nitrophenol, p-nitrophenol, 2,4-dinitrophenol, 2,4,6-trinitrophenol, salicylic acid, p-hydroxybenzoic acid, and combinations thereof. One type of phenol may be used alone, or two or more types may be used in combination.

[0014] As the phenol, alkylphenols having 2 to 18 carbon atoms can be used. The alkylphenols may have a branched chain or an unsaturated bond in the alkyl chain. The substitution position of the alkyl chain on the benzene ring may be ortho-, meta-, or para-substituted. Examples of alkylphenols include ethylphenol, propylphenol, isopropylphenol, butylphenol, secondary butylphenol, tertiary butylphenol, amylphenol, tertiary aminophenol, hexylphenol, heptylphenol, octylphenol, tertiary octylphenol, nonylphenol, tertiary nonylphenol, decylphenol, undecylphenol, dodecylphenol, tridecylphenol, tetradecylphenol, pentadecylphenol, cardanol, cardol, urushiol, hexadecylphenol, methyl cardol, heptadecylphenol, laccol, thiol, and octadecylphenol. Vegetable oils such as cashew nut shell liquid (cashew oil) and urushi extract can also be used as alkylphenols.

[0015] Among these, it is preferable to use one or more phenols selected from the group consisting of phenol, cresol, xylenol, alkylphenols, and bisphenols, and from the viewpoint of production costs, it is preferable to use phenol, cresol, butylphenol, bisphenol A, or cashew nut shell liquid (cashew oil).

[0016] (lignins) The lignins used in the production of the lignin-modified novolac phenolic resin include at least one selected from lignin and lignin derivatives. Lignin, along with cellulose and hemicellulose, is a major component of plant structure and one of the most abundant aromatic compounds in nature. Because lignin exists in plants as lignocellulose, a portion of the lignin is bound together, often referring to compounds obtained from plants through decomposition or other processes. Examples include pulp lignins such as kraft lignin, lignosulfonic acid, soda lignin, and soda-anthraquinone lignin; organosolv lignin; lignophenols, which are compounds in which phenol is added to high-temperature, high-pressure water-treated lignin or explosive lignin during extraction with concentrated sulfuric acid; and phenolized lignin. The origin of lignin is not particularly limited, and examples include wood and herbaceous plants that contain lignin and form woody parts, such as conifers such as cedar, pine, cypress, and spruce; broad-leaved trees such as beech, birch, oak, zelkova, and eucalyptus; and grasses (herbaceous plants) such as rice, wheat, corn, and bamboo.

[0017] In this embodiment, the term "lignin derivative" refers to a compound having a unit structure constituting lignin or a structure similar to the unit structure constituting lignin. The lignin derivative has a unit structure of a phenol derivative. This unit structure has a chemically and biologically stable carbon-carbon bond or carbon-oxygen-carbon bond, and therefore is resistant to chemical deterioration and biological decomposition.

[0018] Examples of lignin derivatives include guaiacylpropane (ferulic acid) represented by formula (A) in the following formula (1), syringylpropane (sinapic acid) represented by formula (B) below, and 4-hydroxyphenylpropane (coumaric acid) represented by formula (C) below. The composition of the lignin derivative varies depending on the biomass used as the raw material. Lignin derivatives containing a guaiacylpropane structure are mainly extracted from coniferous trees. Lignin derivatives containing a guaiacylpropane structure and a syringylpropane structure are mainly extracted from broad-leaved trees. Lignin derivatives containing a guaiacylpropane structure, a syringylpropane structure, and a 4-hydroxyphenylpropane structure are mainly extracted from herbaceous plants.

[0019] [ka]

[0020] The lignin derivative is preferably one obtained by decomposing biomass. Since biomass is formed by capturing and immobilizing carbon dioxide from the atmosphere during the photosynthesis process, biomass contributes to suppressing the increase in carbon dioxide in the atmosphere, and industrial use of biomass can contribute to suppressing global warming. Examples of biomass include lignocellulosic biomass. Examples of lignocellulosic biomass include leaves, bark, branches, and wood of lignin-containing plants, as well as processed products thereof. Examples of lignin-containing plants include the above-mentioned broad-leaved trees, conifers, and herbaceous plants.

[0021] Biomass decomposition methods include chemical treatment, hydrolysis, steam explosion, supercritical water treatment, subcritical water treatment, mechanical treatment, cresol sulfate, and pulp production. From the viewpoint of environmental impact, steam explosion, subcritical water treatment, and mechanical treatment are preferred. From the viewpoint of cost, pulp production is preferred. Furthermore, from the viewpoint of cost, it is preferable to use by-products of biomass utilization. Lignin derivatives can be prepared, for example, by decomposing biomass in the presence of various cooking liquors or solvents at 150 to 400°C, 1 to 40 MPa, and 8 hours or less. Lignin derivatives can also be prepared by methods disclosed in JP 2009-084320 A and JP 2012-201828 A.

[0022] Examples of lignin derivatives include those obtained by decomposing lignocellulose, which is a combination of lignin, cellulose, and hemicellulose. Lignin derivatives may include lignin decomposition products, cellulose decomposition products, hemicellulose decomposition products, and the like, each of which is composed primarily of a compound having a lignin skeleton. Lignin derivatives may also contain inorganic substances derived from biomass or processes. When used in the applications of this embodiment, the content of inorganic substances is preferably 10% by mass or less of the total lignin derivative used.

[0023] The lignin derivative preferably has many reactive sites where the curing agent acts through an electrophilic substitution reaction with the aromatic ring. Since less steric hindrance near the reactive site improves reactivity, it is preferable that at least one of the ortho- and para-positions of the aromatic ring containing a phenolic hydroxyl group is unsubstituted. Preferred lignin derivatives are those derived from conifers or herbs that contain many guaiacyl nucleus or 4-hydroxyphenyl nucleus structures as aromatic units of the lignin. Examples of lignin derivatives that can be used include those disclosed in JP 2009-084320 A and JP 2012-201828 A.

[0024] In addition to the above basic structure, the lignin derivative may be a lignin derivative having a functional group (a secondary lignin derivative).

[0025] The functional groups possessed by the secondary lignin derivatives are not particularly limited, but are preferably those in which two or more of the same functional groups can react with each other or with other functional groups. Specific examples include epoxy groups, methylol groups, and vinyl groups with carbon-carbon unsaturated bonds, ethynyl groups, maleimide groups, cyanate groups, and isocyanate groups. Among these, lignin derivatives into which methylol groups have been introduced (methylolated) are preferred. Such secondary lignin derivatives undergo self-crosslinking through a self-condensation reaction between methylol groups and also crosslink with alkoxymethyl groups and hydroxyl groups in the crosslinking agent described below. As a result, lignin-modified novolac-type phenolic resins with a particularly homogeneous and rigid skeleton and excellent solvent resistance can be obtained.

[0026] Furthermore, the lignin derivative may have a carboxyl group. Lignin obtained by a pulp process or high-temperature, high-pressure water treatment may have a carboxyl group. A lignin-modified novolac phenolic resin obtained from a lignin derivative having a carboxyl group has many crosslinking points for the curing agent described below, and therefore the crosslinking density of the obtained crosslinked product can be improved, resulting in a crosslinked product with excellent solvent resistance.

[0027] In addition, when the above-mentioned lignin derivative has a carboxyl group, the carboxyl group belongs to the carboxyl group. 13 When subjected to C-NMR analysis, this can be confirmed by the presence or absence of absorption peaks at 172 to 174 ppm.

[0028] The lignins used in producing the lignin-modified novolac phenolic resin have a weight-average molecular weight of, for example, 2,000 to 100,000. The lower limit of the weight-average molecular weight is preferably 2,500 or more, more preferably 3,000 or more, and even more preferably 4,000 or more. The upper limit of the weight-average molecular weight is preferably 90,000 or less, more preferably 80,000 or less, and even more preferably 75,000 or less. By using lignins having a weight-average molecular weight within the above range, the resulting lignin-modified novolac phenolic resin has excellent curability. The weight-average molecular weight is a polystyrene-equivalent number-average molecular weight measured by gel permeation chromatography and can be determined by the method in the Examples.

[0029] The number-average molecular weight of the lignins used in producing the lignin-modified novolac phenolic resin is, for example, 200 to 5,000. The lower limit of the number-average molecular weight is preferably 300 or more, more preferably 350 or more, and even more preferably 400 or more. The upper limit of the number-average molecular weight is preferably 4,000 or less, more preferably 3,000 or less, and even more preferably 2,000 or less. Lignins having a number-average molecular weight within the above range are preferred because they have excellent reactivity and therefore excellent workability in the production process of the lignin-modified novolac phenolic resin. Furthermore, by using lignins having a number-average molecular weight within the above range, the resulting lignin-modified novolac phenolic resin has excellent curability and the cured product thereof can have high mechanical strength. The number-average molecular weight is the polystyrene-equivalent number-average molecular weight measured by gel permeation chromatography and can be determined by the method described in the Examples.

[0030] Here, an example of a method for measuring the molecular weight by gel permeation chromatography will be described. In a method for measuring molecular weight by gel permeation chromatography, a lignin derivative is first dissolved in a solvent to prepare a measurement sample. The solvent used is not particularly limited as long as it can dissolve the lignin derivative; however, from the viewpoint of measurement accuracy by gel permeation chromatography, for example, tetrahydrofuran or N-methyl-2-pyrrolidone is preferred. Since the lignins of this embodiment may contain insoluble matter due to biomass, process-derived inorganic matter, and high-molecular-weight organic matter derived from plants, the molecular weight of the lignins is determined by selecting an appropriate solvent and filtering the insoluble matter. Furthermore, to increase the lignin modification rate of the resulting lignin-modified novolac phenolic resin, the insoluble matter of the lignins used is preferably 30% by mass or less in an appropriate solvent. Similarly, the molecular weight of the lignin-modified novolac phenolic resin is determined by filtering the insoluble matter. The insoluble matter content of the lignin-modified novolac phenolic resin is preferably 15% by mass or less, more preferably 10% by mass or less. When the content is within the above range, the lignin-modified novolac phenolic resin has good curability, and in particular, can be cured uniformly.

[0031] Next, a GPC system "HLC-8320GPC (Tosoh)" was connected in series with a general-purpose organic column "TSKgel GMHXL (Tosoh)" packed with a styrene-based polymer filler, and a "G2000HXL (Tosoh)." 200 μL of the sample was injected into this GPC system, and the eluent, tetrahydrofuran, was developed at 1.0 mL / min at 40 °C. Retention times were measured using refractive index (RI) and ultraviolet absorbance (UV). The number-average molecular weight and weight-average molecular weight of the target lignins could be calculated from a calibration curve showing the relationship between retention time and molecular weight for a separately prepared standard polystyrene. Refractive index was the preferred detection mode.

[0032] The molecular weight of the standard polystyrene used to prepare the calibration curve is not particularly limited, but for example, standard polystyrenes (manufactured by Tosoh) with weight average molecular weights of 1,090,000, 427,000, 190,000, 96,400, 37,900, 18,100, 10,200, 5,970, 2,630, 1,050, and 500 can be used.

[0033] The lignins used in producing the lignin-modified novolac phenolic resin preferably have a softening point of 90°C or higher, more preferably 110°C or higher, and even more preferably 130°C or higher. On the other hand, lignins whose softening points are too high to be measured can also be used. When such lignins are used to produce a lignin-modified novolac phenolic resin with a high degree of modification, the resulting modified novolac phenolic resin has a high molecular weight, low fluidity, and poor processability. However, the lignin-modified novolac phenolic resin of this embodiment unexpectedly exhibits good processability, despite the high lignin modification rate and high molecular weight of the lignin-modified phenolic resin obtained from such lignins.

[0034] The volatile content of the lignins used is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less. By keeping the volatile content of the lignins within the above range, the reactivity of the lignins can be improved, thereby increasing the reaction rate of the resulting lignin-modified novolac phenolic resin. The main volatile content is often water, which can be calculated by, for example, spreading 4 g of the lignin in an aluminum cup and drying it at 80°C for 20 hours.

[0035] The softening point of lignins can be measured using a ring and ball softening point tester (for example, ASP-MG2 model manufactured by Meltec Co., Ltd.) in accordance with JIS K2207. Note that if the lignin contains a large amount of water, it is measured after being completely dried at 70°C or less. In this embodiment, if a good sample cannot be prepared due to the thermal melting properties of the lignin, for example, using a hot plate at 150 to 200°C, it is determined that the softening point is too high to be measured.

[0036] When using lignins obtained by decomposing biomass, they may contain large amounts of low-molecular-weight components, which can cause volatile content, odor, and a lower softening point when heated. These components can be used as is, or can be removed by heating, drying, or other methods to adjust the softening point and odor.

[0037] (aldehydes) Examples of aldehydes used in producing the lignin-modified novolac phenolic resin include formaldehyde, paraformaldehyde, trioxane, acetaldehyde, propionaldehyde, polyoxymethylene, chloral, hexamethylenetetramine, furfural, glyoxal, n-butylaldehyde, caproaldehyde, allylaldehyde, benzaldehyde, crotonaldehyde, acrolein, tetraoxymethylene, phenylacetaldehyde, o-tolualdehyde, salicylaldehyde, and paraxylene dimethyl ether. Preferred examples include formaldehyde, paraformaldehyde, trioxane, polyoxymethylene, acetaldehyde, and paraxylene dimethyl ether, as well as combinations thereof. The aldehydes may be used alone or in combinations of two or more. Among these, formaldehyde or acetaldehyde is preferably used from the viewpoints of productivity and cost.

[0038] (acid catalyst) The acid catalyst used in producing the lignin-modified novolac phenolic resin may be any acid that can be used as a reaction catalyst, and organic acids, inorganic acids, and combinations thereof may be used. Examples of organic acids include acetic acid, formic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, benzoic acid, salicylic acid, sulfonic acid, phenolsulfonic acid, paratoluenesulfonic acid, and zinc acetate. Examples of inorganic acids include hydrochloric acid, sulfuric acid, sulfates, phosphoric acid, and phosphates.

[0039] In the production of the lignin-modified novolac phenolic resin, the molar ratio of aldehydes to phenols (F / P) is, for example, 0.2 or more, preferably 0.3 or more, and more preferably 0.4 or more. The upper limit of the molar ratio of aldehydes to phenols (F / P) is, for example, 1.2 or less, preferably 1.1 or less, and more preferably 1.0 or less. By carrying out the reaction under conditions where the molar ratio of aldehydes to phenols (F / P) is within the above range, it is possible to obtain a lignin-modified novolac phenolic resin having a weight-average molecular weight of 3,000 or more and improved processability and strength.

[0040] In the production of the lignin-modified novolac phenolic resin, the step of reacting lignins, phenols, and aldehydes in the presence of an acid catalyst may include the following steps: mixing lignins and phenols under heating at a temperature of 70°C to 120°C to disperse the lignins and obtain a mixture (step 1); mixing an acid catalyst simultaneously with or after step 1 (step 2); and mixing aldehydes after step 2 (step 3). The step of reacting lignins, phenols, and aldehydes in the presence of an acid catalyst is preferably carried out at a temperature of, for example, 60°C to 120°C, preferably 80°C to 100°C, for a reaction time of, for example, 10 to 100 minutes. This allows the reaction to proceed efficiently and sufficiently. Furthermore, by carrying out the reaction under heating, the starting materials are uniformly mixed, and the resulting lignin-modified novolac phenolic resin can be uniformly cured due to intermolecular entanglement and interactions, thereby achieving molding with excellent dimensional accuracy. The reaction time is not particularly limited and can be determined appropriately depending on the type of starting materials, the molar ratio, the amount and type of catalyst used, and the reaction conditions. Furthermore, the reaction mixture after the reaction may be post-treated. For post-treatment, for example, distillation under heating (e.g., 150°C or higher), distillation under normal pressure, or distillation under reduced pressure, or a combination of these, can be used.

[0041] The above steps 1, 2, and 3 are preferably carried out without a solvent, but an organic solvent or water may be used as the solvent. Instead of adding water, hydrous lignin may be used. Examples of organic solvents include alcohols, ketones, esters, ethers, and hydrocarbons. Examples of alcohols include methanol, ethanol, propanol, isopropanol, butanol, pentanol, hexanol, octanol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, and glycerin. Examples of ketones include acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, and cyclohexanone. Examples of esters include methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methoxybutyl acetate, amyl acetate, methyl lactate, ethyl lactate, and butyl lactate. Examples of ethers include propyl ether, dioxane, methyl cellosolve, ethyl cellosolve, propyl cellosolve, butyl cellosolve, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, methyl carbitol, ethyl carbitol, butyl carbitol, methyl cellosolve acetate, ethyl cellosolve acetate, propyl cellosolve acetate, butyl cellosolve acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monopropyl ether acetate, and propylene glycol monobutyl ether acetate. Examples of hydrocarbons include toluene, xylene, pentane, hexane, cyclohexane, heptane, octane, decane, solvent naphtha, industrial gasoline, petroleum ether, petroleum benzine, and ligroin. These may be used alone or in combination of two or more.

[0042] In the conventional method of increasing the molecular weight of a lignin-modified novolac phenolic resin by adjusting the reaction ratio of phenols, lignins, and aldehydes, the viscosity of the reaction product increases, making dehydration difficult, which can result in a long process time and can also result in a large amount of unreacted phenols remaining. In contrast, the method of the present embodiment can shorten the process time and increase the resin yield compared to conventional methods of increasing the molecular weight by varying the reaction ratio of phenols, lignins, and aldehydes. Furthermore, by setting the molar ratio of aldehydes to phenols (F / P) within the above range and adjusting the molecular weight, molecular weight distribution, and amount of lignins used, the properties of the resulting lignin-modified novolac phenolic resin and the physical properties of the resin material can be adjusted within desired ranges.

[0043] The lignin-modified novolac phenolic resin obtained by the above method has a weight-average molecular weight of 3,000 or more. The weight-average molecular weight of the lignin-modified novolac phenolic resin of this embodiment is, for example, 3,000 to 55,000, preferably 5,500 to 50,000, and more preferably 6,000 to 45,000. Lignin-modified novolac phenolic resins having a weight-average molecular weight within the above range have excellent curing properties, and their cured products have high mechanical strength. Furthermore, the lignin-modified novolac phenolic resin of this embodiment has a lignin modification rate of 5 to 60%, preferably 10 to 55%, and more preferably 20 to 55%. By having a lignin modification rate within the above range, the lignin-modified novolac phenolic resin has excellent compatibility with petroleum heavy oil, and its cured products have excellent strength and heat resistance.

[0044] The amount of the lignin-modified novolac phenolic resin in the resin composition for producing a carbon material is, for example, 5 to 100 mass %, preferably 10 to 95 mass %, and more preferably 20 to 90 mass %, based on the total solid content of the resin composition.

[0045] The lignin-modified novolac phenolic resin can be provided in the form of, for example, fine powder, granules, pellets, or varnish, and the form of the lignin-modified novolac phenolic resin can be appropriately selected depending on the application.

[0046] (hydrophobic hydrocarbons) The resin composition for producing a carbon material according to this embodiment may contain a hydrophobic hydrocarbon. The hydrophobic hydrocarbon is preferably a heavy oil derived from coal or petroleum, in other words, an aromatic mineral oil that is a residue or extract of crude oil or coal. Specific examples of the hydrophobic hydrocarbon include asphalt, coal tar, and coal tar pitch. Examples of asphalt include natural asphalt, petroleum asphalt, petroleum pitch, recycled asphalt, and modified asphalt.

[0047] The amount of hydrophobic hydrocarbons blended in the resin composition for producing a carbon material is, for example, 5 to 95 mass %, preferably 20 to 90 mass %, and more preferably 30 to 80 mass %, based on the total solid content of the resin composition.

[0048] (carbon substances) The resin composition for producing the carbon material of the present embodiment may contain a carbon substance, such as graphitizable carbon, non-graphitizable carbon, natural graphite, artificial graphite, carbon black, carbon fiber, and carbon nanofiber, but is not limited to these.

[0049] (hardening agent) The resin composition for producing the carbon material of this embodiment may contain a curing agent. As the curing agent, an amine-based curing agent is preferably used, and specifically, hexamethylenetetramine or hexamethoxymethylmelamine is preferably used.

[0050] The content of the curing agent is, for example, 5 to 30 parts by weight, preferably 7 to 25 parts by weight, relative to 100 parts by weight of the lignin-modified novolac phenolic resin. By setting the content within the above numerical range, a resin composition having good curability can be obtained, and a carbonized product obtained by carbonizing such a resin composition can be suitably used as a carbon material.

[0051] (Method of producing resin composition) The resin composition of the present embodiment is provided as a solid or liquid resin composition by melt-kneading the above-mentioned lignin-modified novolac-type phenolic resin, a hydrophobic hydrocarbon, and, as optional components as required, a carbon substance and a curing agent under heating.

[0052] (Method of manufacturing carbon materials) The carbon material of this embodiment can be obtained by carbonizing the resin composition. The carbonization is performed by a method commonly used in the art. Specifically, the carbon material can be produced by heating the resin composition to obtain a cured product, followed by carbonization and calcination, and pulverization.

[0053] (Application) The carbon material of this embodiment is used as a material for, for example, carbon fiber reinforced carbon composite materials, carbon brushes, negative electrodes for lithium ion secondary batteries, electrodes for capacitors, electrodes for electrolysis, activated carbon, and the like. The carbon material of this embodiment is useful as a battery electrode, and is particularly useful as a negative electrode material for non-aqueous secondary batteries such as lithium secondary batteries.

[0054] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations can also be adopted. [Example]

[0055] EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these.

[0056] [Preparation of lignin derivatives or lignin-modified phenolic resins] (Preparation Example 1) (Preparation of Lignin Derivative A1) A lignin derivative was prepared according to the following procedure. 1500 parts by weight of cedar wood flour with a moisture content of 50% was charged into a 10 L stainless steel autoclave with 5000 parts by weight of pure water as cooking liquor, 150 parts by weight of sodium hydroxide, 80 parts by weight of sodium sulfide, 70 parts by weight of sodium carbonate, and 7.5 parts by weight of 9,10-anthraquinone as cooking aid. The cooking reaction was carried out at 170 °C for 3 hours with stirring. After the reaction, the cooking liquor was cooled to room temperature, the pulp components were removed through a screen, and the black liquor containing lignin was separated. The separated black liquor was adjusted to pH 8 with dilute sulfuric acid, and the resulting precipitate was centrifuged. After washing twice with 500 parts by weight of water, the precipitate was suspended in five times the volume of water and readjusted to pH 2 with dilute sulfuric acid. The precipitated lignin was centrifuged again, washed with water, filtered under suction, spread on a tray, air-dried, and then dried in a vacuum oven at 80°C or below, yielding 140 to 150 parts by weight (solid content equivalent) of brown powdered alkaline lignin (lignin derivative A1) with a solid content of 70% or more. The solid content of the lignin was calculated from the residual fraction after placing a 4g sample in an aluminum cup and drying it by heating at 135°C for 1 hour.

[0057] (Preparation Example 2) (Preparation of lignin derivative A2) Beech wood flour with a moisture content of 50% was cooked at 195°C for 1 hour using 3,000 parts by weight of ethanol and 2,250 parts by weight of water as the cooking liquor, and the aqueous solution obtained by fractionating the ethanol from the cooking liquor was centrifuged and freeze-dried to obtain lignin derivative A2 with a solid content of 90% or more, in the same manner as in Preparation Example 1.

[0058] (Preparation Example 3) (Preparation of lignin derivative A3) Lignin derivative A3 was obtained in the same manner as in Preparation Example 1, except that 5,000 parts by weight of pure water, 150 parts by weight of sodium hydroxide, 80 parts by weight of sodium sulfide, and 70 parts by weight of sodium carbonate were used as the cooking liquor, and 7.5 parts by weight of 9,10-anthraquinone was used as the cooking aid. (Preparation of Lignin-Modified Phenolic Resin B3) Subsequently, lignin-modified phenolic resin B3 was synthesized according to the following procedure. 100 parts by weight of phenol was added to a four-neck flask equipped with a stirrer, a condenser, and a thermometer, and 37.4 parts by weight of the solid content of lignin derivative A3 was gradually added and mixed and dispersed at 60°C or higher. 1.5 parts by weight of oxalic acid was added, and 51.2 parts by weight of a 37% aqueous formaldehyde solution was gradually added over 60 minutes and reacted at 100°C. After the addition, the mixture was reacted at 100°C for 60 minutes, and the temperature was raised to 150°C or higher by dehydration at normal pressure and reduced pressure. When the phenol concentration reached 0.7%, the mixture was removed and 124.2 parts by weight of lignin-modified phenolic resin B3 (lignin modification rate 31%) was obtained.

[0059] (Preparation Example 4) (Preparation of Lignin Derivative A3) Lignin derivative A3 was obtained in the same manner as in Preparation Example 3. (Preparation of Lignin-Modified Phenolic Resin B4) Subsequently, lignin-modified phenolic resin B4 was synthesized according to the following procedure. 100 parts by weight of phenol was added to a four-neck flask equipped with a stirrer, a condenser, and a thermometer, and 32.8 parts by weight of the solid content of lignin derivative A3 was gradually added and mixed and dispersed at 60°C or higher. 1.5 parts by weight of oxalic acid was added, and 49.2 parts by weight of a 37% aqueous formaldehyde solution was gradually added over 60 minutes and reacted at 100°C. After the addition, the mixture was reacted at 100°C for 60 minutes, and the temperature was raised to 150°C or higher by dehydration at normal pressure and reduced pressure. When the phenol concentration reached 4%, the mixture was removed and 122.3 parts by weight of lignin-modified phenolic resin B4 (lignin modification rate 28%) was obtained.

[0060] (Preparation Example 5) (Preparation of Lignin Derivative A3) Lignin derivative A3 was obtained in the same manner as in Preparation Example 3. (Preparation of Lignin-Modified Phenolic Resin B5) Subsequently, lignin-modified phenolic resin B5 was synthesized according to the following procedure. A four-neck flask equipped with a stirrer, a condenser, and a thermometer was charged with 100 parts by weight of phenol, and 35.8 parts by weight of the solid content of lignin derivative A3 was gradually added and mixed and dispersed at 60°C or higher. 53.0 parts by weight of cashew shell oil was added and mixed, and then 1.5 parts by weight of 98% sulfuric acid was added. 53.9 parts by weight of a 37% aqueous formaldehyde solution was gradually added over 60 minutes and reacted at 100°C. After the addition, the mixture was reacted at 100°C for 60 minutes. After the addition, the mixture was heated to 140°C or higher by atmospheric dehydration, 46 parts by weight of 25% sodium hydroxide was gradually added to neutralize it, and the mixture was heated to 150°C or higher by reduced pressure dehydration until the phenol concentration reached less than 1%. The mixture was then discharged, yielding 172.3 parts by weight of lignin-modified phenolic resin B5 (lignin modification rate: 21%, cashew modification rate: 30%).

[0061] (Preparation Example 6) (Preparation of lignin derivative A6) Beech wood flour with a moisture content of 50% was cooked at 195°C for 1 hour using 3,000 parts by weight of ethanol and 2,250 parts by weight of water as the cooking liquor, and the aqueous solution obtained by fractionating the ethanol from the cooking liquor was centrifuged and freeze-dried to obtain lignin derivative A6 with a solid content of 90% or more, in the same manner as in Preparation Example 1. (Preparation of lignin-modified phenolic resin B6) 100 parts by weight of phenol was added to a four-neck flask equipped with a stirrer, a condenser, and a thermometer, and 37.4 parts by weight of the solid content of lignin derivative A6 was gradually added and mixed and dispersed at 60°C or higher. 1.5 parts by weight of oxalic acid was added, and 51.2 parts by weight of a 37% aqueous formaldehyde solution was gradually added over 60 minutes to react at 100°C. After the addition, the mixture was reacted at 100°C for 60 minutes, and the temperature was raised to 150°C or higher by dehydration at normal pressure and reduced pressure. When the phenol concentration reached 0.5%, the mixture was removed, yielding 122.8 parts by weight of lignin-modified phenolic resin B6 (lignin modification rate 31%).

[0062] (Preparation Example 7: Preparation of Unmodified Novolac Phenolic Resin B7) To a mixture of 1,000 parts by weight of phenol and 10 parts by weight of oxalic acid, 720 parts by weight of 37% formalin was gradually added over 2 hours, and the mixture was allowed to react at 100°C for 2 hours. After that, the reaction mixture was dehydrated by atmospheric distillation until the temperature reached 140°C, and then the pressure was gradually reduced to 0.9 kPa while the reaction mixture was distilled under reduced pressure until the temperature reached 220°C, yielding unmodified novolac phenolic resin B7. The unmodified novolac phenolic resin B7 had a weight average molecular weight of 8,900 and a number average molecular weight of 1,270.

[0063] [Examples 1 to 4, Reference Example 1, Comparative Examples 1 and 2] (Carbide manufacturing) The fixed carbon contents of the lignin derivatives A1 and A2, the novolac-modified phenolic resins B3 to B6, and the unmodified novolac-type phenolic resin B7 obtained above were measured in accordance with JIS K 6910. The results are shown in Table 1.

[0064] [Table 1]

[0065] As shown in Table 1, the lignin derivative has a lower fixed carbon content than the unmodified novolac phenolic resin, but it was confirmed that the lignin-modified phenolic resin has a fixed carbon content equal to or close to that of the unmodified novolac phenolic resin, demonstrating its usefulness as a carbon material.

[0066] (Properties of lignin derivatives / lignin-modified phenolic resins) The softening points of the lignin derivatives A1 and A2 and the lignin-modified phenolic resins B3 to B6 obtained in the above Preparation Examples were measured by the following method. The results are shown in Table 2. (Method for measuring softening point) The softening points of the target lignin derivatives or lignin-modified phenolic resins were measured using a ring and ball softening point tester (Model ASP-MG2 manufactured by Meltec Co., Ltd.) in accordance with JIS K2207.

[0067] (Production of Resin Composition) Resin compositions were produced using the lignin derivatives A1 and A2 or the novolac-modified phenolic resins B3 to B6 obtained above. The components and amounts used in each example are shown in Table 2. (Performance evaluation of resin composition) The resin compositions obtained in each example were evaluated for the following items. (compatibility, uniform appearance) In each example, the lignin derivative or lignin-modified phenolic resin was mixed with solid pitch at 165°C using a spatula. The state of the mixture was visually inspected and evaluated according to the following criteria. The results are shown in Table 2. A: The lignin-modified phenolic resin / lignin derivative and solid pitch are compatible with each other, resulting in a liquid mixture. B: The lignin-modified phenolic resin / lignin derivative and the solid pitch do not mix together, and a mixture with remaining solids is obtained.

[0068] [Table 2]

[0069] As shown in Table 2, it was confirmed that lignin derivatives do not dissolve in solid pitch, whereas lignin-modified phenolic resins are compatible. The lignin derivatives were also incompatible, resulting in heterogeneous carbonized products, whereas lignin-modified phenolic resins produced homogeneous carbonized products. It was also confirmed that lignin-modified phenolic resins are useful as carbon materials when mixed with hydrophobic hydrocarbons such as solid pitch.

[0070] (Preparation of carbon materials) In each example, a resin composition was obtained by mixing the lignin derivative, unmodified phenolic resin, or lignin-modified phenolic resin with solid pitch in the amounts shown in Table 3 using a spatula while heating at 165°C. The fixed carbon content of the resulting resin composition was measured in accordance with JIS K 6910. The results are shown in Table 3.

[0071] [Table 3]

[0072] As shown in Table 3, the resin composition containing lignin-modified phenolic resin and hexamethylenetetramine had a significantly increased fixed carbon content compared to the lignin-modified phenolic resin alone. This indicates that lignin-modified phenolic resin has high reactivity with hexamethylenetetramine, and therefore, it was confirmed that useful carbon materials can be obtained by blending lignin-modified phenolic resin with a curing agent such as hexamethylenetetramine hexamine.

Claims

1. A carbon material comprising a carbonized resin composition containing a lignin-modified novolac-type phenolic resin.

2. The carbon material of claim 1 further comprising a carbon substance.

3. 3. The carbon material according to claim 2, wherein the carbon substance comprises at least one selected from graphitizable carbon, non-graphitizable carbon, natural graphite, artificial graphite, carbon black, carbon fiber, and carbon nanofiber.

4. The carbon material according to claim 1 , wherein the resin composition further comprises a hydrophobic hydrocarbon.

5. The carbon material according to claim 4 , wherein the hydrophobic hydrocarbon contains an aromatic ring.

6. The carbon material of claim 4 , wherein the hydrophobic hydrocarbon comprises a residue or extract of crude oil or coal.

7. The carbon material according to claim 4 , wherein the hydrophobic hydrocarbon comprises asphalt, coal tar, or coal tar pitch.

8. The carbon material according to claim 7, wherein the asphalt is at least one selected from the group consisting of natural asphalt, petroleum asphalt, petroleum pitch, recycled asphalt, and modified asphalt.

9. The carbon material according to claim 1 , wherein the resin composition further comprises a curing agent.

10. The carbon material according to claim 9 , wherein the curing agent comprises at least one selected from hexamethylenetetramine and hexamethoxymethylmelamine.

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