Sintering aid for ceramic, ceramic material, and method for producing ceramic sintered body

Abstract

To provide a sintering aid capable of obtaining a ceramic sintered body having a uniform microstructure, thereby having high strength.SOLUTION: A sintering aid for ceramics comprises: a carboxyl group-containing novolac-type phenol resin having a structural unit represented by formula (1) (where X is a 1-6C alkylene group, and R1 is independently a hydrogen atom, a 1-20C alkyl group, or a hydroxyl group) and a structural unit in which phenol nuclei are bonded with a methylene group; an amine; and water.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a sintering aid for ceramics, a ceramic material containing the sintering aid, and a method for producing a ceramic sintered body using the ceramic material. [Background technology]

[0002] Ceramic sintered bodies containing silicon carbide as a main component have excellent heat resistance, impact resistance, corrosion resistance, wear resistance, etc., and are therefore used as materials for gas turbine parts, engine parts, pump parts, mechanical seals, bearings, and other engineering materials, furnace materials for metal melting, structural materials for ceramic firing, furnace material parts, etc.

[0003] Sintered ceramics are generally produced by compressing silicon carbide grains with a small amount of additives and water, followed by firing in a reducing atmosphere to densify and sinter them. Various additives are used as sintering aids to obtain high-density, high-strength sintered ceramics. For example, Patent Document 1 proposes a technique for producing silicon carbide ceramics that uses at least one sintering aid selected from B, BC, BO, HBO, BN, BP, Al, AlO, AIN, Be, and BeO, and at least one other sintering aid selected from carbon black, phenolic resin, and tannin. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 01-290560 Summary of the Invention [Problem to be solved by the invention]

[0005] However, silicon carbide ceramics produced using conventional sintering aids often lack the strength required for applications such as gas turbine parts and engine parts.

Means for Solving the Problem

[0006] The present invention has been made in view of the above problems, and an object thereof is to provide a sintering aid capable of obtaining a ceramic sintered body having a uniform and dense fine structure and thus high strength.

[0007] According to the present invention, there are provided a sintering aid for ceramics, a ceramic material, and a method for producing a ceramic sintered body, which are shown below. [1] A carboxy group-containing novolak-type phenol resin having a structural unit represented by formula (1) and a structural unit represented by formula (2); an amine; and water, a sintering aid for ceramics, [Chemical formula] In formula (1), X is an alkylene group having 1 to 6 carbon atoms, R 1 is independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a hydroxyl group, [Chemical formula] In formula (2), R 2 is independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a hydroxyl group, a sintering aid. [2] The sintering aid according to item [1], wherein R 1 and R 2 in the formula (1) are independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a hydroxyl group. [3] The sintering aid according to item [1] or [2], wherein the proportion of the structural unit represented by the formula (1) in the carboxy group-containing phenol resin is 5 mol% or more and 90 mol% or less with respect to the entire carboxy group-containing phenol resin. [4] The sintering aid according to any one of items [1] to [3], wherein the amine contains a tertiary amine. [5] The sintering aid according to any one of items [1] to [4], which is in the form of an aqueous solution. [6] The sintering aid according to any one of items [1] to [4], which is in the form of an aqueous dispersion. [7] The sintering aid according to any one of items [1] to [6], wherein the ceramics contains at least one selected from silicon carbide, boron carbide, tungsten carbide, titanium carbide, silicon nitride, and aluminum nitride. [8] A ceramic material comprising ceramic powder and the sintering aid according to any one of items [1] to [7]. [9] The ceramic material according to item [8], wherein the ceramic powder contains at least one selected from silicon carbide, boron carbide, tungsten carbide, titanium carbide, silicon nitride, and aluminum nitride.

[10] The ceramic material according to item [8] or [9], wherein the sintering aid is in an amount of 0.1% by mass or more and 10% by mass or less based on the total solid content of the ceramic material.

[11] A method for manufacturing a ceramic sintered body, the method comprising a step of mixing ceramic powder and the sintering aid according to any one of items [1] to [7] to prepare a casting liquid that becomes a ceramic material; a step of casting the casting liquid into a mold; and a step of obtaining a ceramic sintered body by pressure-sintering the mold. Method.

Advantages of the Invention

[0008] According to the present invention, there is provided a sintering aid capable of obtaining a ceramic sintered body having a uniform and dense fine structure and thus high strength.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described. In this specification, the notation "a~b" in the description of a numerical range means "a or more and b or less" unless otherwise specified. For example, "5~90 mass%" means "5 mass% or more and 90 mass% or less".

[0010] [Sintering aid] The sintering aid for ceramics of this embodiment is a carboxyl group-containing phenolic resin having a structural unit represented by formula (1) and a structural unit represented by formula (2); amine; and water.

[0011] [Chemical formula]

[0012] In formula (1), X is an alkylene group having 1 to 6 carbon atoms, R 1 is independently a hydrogen atom (H), an alkyl group having 1 to 20 carbon atoms, or a hydroxyl group (-OH).

[0013] [Chemical formula]

[0014] In formula (2), R 2 is independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a hydroxyl group.

[0015] In the sintering aid of this embodiment, the carboxyl group-containing phenolic resin has a structural unit represented by formula (1) and a structural unit represented by formula (2). The carboxyl group-containing phenolic resin having such a structural unit functions to uniformly disperse the ceramic raw material powder in a slurry containing the ceramic raw material powder. When such a slurry is dried and then sintered, a ceramic sintered body having a uniform and dense fine structure and good characteristics or small variation in characteristics can be obtained.

[0016] In the sintering aid of the present embodiment, the carboxy group-containing phenol resin exists as a water-soluble oil by the neutralization of the carboxy group of the structural unit represented by the formula (1) by the interaction with the amine contained in the sintering aid. Therefore, the sintering aid of the present embodiment is an aqueous solution or slurry using water as a solvent or dispersion medium, and thus has excellent dispersibility with respect to the slurry containing the ceramic raw material powder. Further, since the sintering aid of the present embodiment is an aqueous solution or slurry using water as a solvent or dispersion medium, aggregation or sedimentation of the resin does not occur, and the storage stability is excellent. Furthermore, since the sintering aid of the present embodiment substantially does not use an organic solvent, the environmental load is reduced. In addition, since the sintering aid of the present embodiment does not contain a metal hydroxide, the obtained ceramic sintered body does not contain a metal derived from the metal hydroxide. Therefore, the ceramic sintered body obtained by using the sintering aid of the present embodiment can be applied to fields such as electronic components where the presence of a metal is disadvantageous. Hereinafter, each component constituting the sintering aid of the present embodiment will be described.

[0017] (Phenol resin) The carboxy group-containing novolak type phenol resin used in the sintering aid of the present embodiment has a structural unit represented by the formula (1) and a structural unit represented by the above formula (2). As shown in the formula (1), this phenol resin is characterized by having a structure in which a carboxy group is introduced into the side chain. In the present specification, the carboxy group-containing novolak type phenol resin having the above structure may be simply referred to as "phenol resin".

[0018] [Chemical formula]

[0019] In formula (1), X is an alkylene group having 1 to 6 carbon atoms, R 1 is independently a hydrogen atom (H), an alkyl group having 1 to 20 carbon atoms, or a hydroxyl group (-OH).

[0020]

Chem.

[0021] In formula (2), R 2 is independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a hydroxyl group.

[0022] The alkylene group having 1 to 6 carbon atoms that can form X in formula (1) may be linear, branched, or cyclic. For example, linear or branched alkylene having 1 to 6 carbon atoms such as a methylene group, an ethylene group, a propylene group, and a butylene group can be mentioned. From the viewpoint of ease of production, it is preferably a methylene group or an ethylene group. The structure of X in formula (1) can be adjusted by selecting the type of carboxylic acid compound used in the production of the carboxy group-containing phenol resin described in detail below.

[0023] R in formulas (1) and (2) 1 and R 2 The alkyl group having 1 to 20 carbon atoms that can form may be linear, branched, or cyclic. Examples of the linear or branched alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a neopentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, and a decyl group. Examples of the cyclic alkyl group include an adamantyl group, a cyclopentyl group, a cyclohexyl group, and a cyclooctyl group.

[0024] The structures of the structural unit represented by formula (1) and the structural unit represented by formula (2) can be controlled by selecting the type of raw material monomer used in the production of the carboxy group-containing novolak-type phenol resin described in detail below, or by selecting the production conditions.

[0025] The phenol resin is R in the structural unit represented by formula (1)1 is a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a hydroxyl group, and R in the structural unit represented by the formula (2) 2 is a novolak-type phenolic resin in which R is a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a hydroxyl group.

[0026] In one embodiment, the sintering aid is in the form of an aqueous solution in which a carboxy group-containing novolak-type phenolic resin is present in a state dissolved in water. In one embodiment, the sintering aid is in the form of an aqueous dispersion in which a carboxy group-containing novolak-type phenolic resin is present in a state dispersed in water.

[0027] In one embodiment, the carboxy group-containing novolak-type phenolic resin has a structure in which the proportion of the structural unit containing a carboxy group represented by the above formula (1) is 5 to 90 mol% with respect to the whole carboxy group-containing novolak-type phenolic resin. The proportion of the structural unit represented by the formula (1) in the carboxy group-containing novolak-type phenolic resin is preferably 5 to 70 mol%, more preferably 5 to 50 mol%, and even more preferably 5 to 30 mol%. The carboxy group-containing novolak-type phenolic resin in which the proportion of the structural unit represented by the formula (1) is within the above range is excellent in water solubility or water dispersibility, and thus the resulting sintering aid is excellent in handleability. The proportion of the structural unit represented by the formula (1) in the carboxy group-containing novolak-type phenolic resin can be changed by adjusting the blending ratio of the raw materials used or by adjusting the production conditions in the production of the phenolic resin described below.

[0028] The carboxy group-containing novolak-type phenolic resin can typically be produced by reacting a carboxylic acid compound with a reaction product obtained by reacting phenols and aldehydes (Step 1). Specifically, in the production of the carboxy group-containing novolak-type phenol resin, Step 1 includes Step 1-1a of subjecting phenols and aldehydes to condensation polymerization in the presence of an acid catalyst to obtain a novolak-type phenol resin, and Step 1-2a of reacting the novolak-type phenol resin obtained in Step 1-1a with a carboxylic acid compound in the presence of a basic catalyst to obtain a carboxy group-containing novolak-type phenol resin.

[0029] Examples of phenols that can be used in the production of the carboxy group-containing novolak-type phenol resin include phenol; cresols such as o-cresol, m-cresol, and p-cresol; ethylphenols such as o-ethylphenol, m-ethylphenol, and p-ethylphenol; butylphenols such as isopropylphenol, butylphenol, and p-tert-butylphenol; alkylphenols such as p-tert-amylphenol, p-octylphenol, p-nonylphenol, and p-cumylphenol; halogenated phenols such as fluorophenol, chlorophenol, bromophenol, and iodophenol; monovalent phenol substituents such as p-phenylphenol, aminophenol, nitrophenol, dinitrophenol, and trinitrophenol; monohydric phenols such as 1-naphthol and 2-naphthol; and polyhydric phenols such as resorcin, alkylresorcin, pyrogallol, catechol, alkylcatechol, hydroquinone, alkylhydroquinone, phloroglucin, bisphenol A, bisphenol F, bisphenol S, and dihydroxynaphthalene. These can be used alone or in admixture of two or more. Among them, from the viewpoint of production cost, it is preferable to use phenol.

[0030] Examples of aldehydes that can be used in the production of carboxy group-containing novolak-type phenolic resins include formaldehyde, paraformaldehyde, trioxane, acetaldehyde, propionaldehyde, polyoxymethylene, chloral, hexamethylenetetramine, furfural, glyoxal, n-butylaldehyde, caproaldehyde, allyl aldehyde, benzaldehyde, crotonaldehyde, acrolein, tetraoxymethylene, phenylacetaldehyde, o-tolualdehyde, salicylaldehyde, and the like. These may be used alone or in combination of two or more. Further, precursors of these aldehydes or solutions of these aldehydes can also be used. Among them, from the viewpoint of production cost, it is preferable to use an aqueous formaldehyde solution.

[0031] The carboxylic acid compound used in the production of the carboxy group-containing novolak-type phenolic resin is used to derive a structural unit represented by the above formula (1) in which an -X-COOH group is bonded to the oxygen atom of the phenolic hydroxyl group. Here, "X" in the -X-COOH group has the same meaning as "X" in the formula (1) and represents an alkylene group having 1 to 6 carbon atoms. Examples of such a carboxylic acid compound include a compound represented by the formula (CA). L-X-COOH (CA) In the formula (CA), L represents a halogen, and X represents an alkylene group having 1 to 6 carbon atoms. Specific examples of the carboxylic acid compound represented by the formula (CA) include 1-chloroacetic acid, 1-bromoacetic acid, 1-iodoacetic acid, 2-chloropropionic acid, 3-chlorobutyric acid, or alkali metal salts thereof (for example, sodium 1-chloroacetate), but are not limited thereto.

[0032] Examples of the acid catalyst that can be used for producing the carboxy group-containing novolak type phenol resin include organic acids such as acetic acid, formic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, benzoic acid, salicylic acid, sulfonic acid, phenolsulfonic acid, and p-toluenesulfonic acid; or inorganic acids such as hydrochloric acid, sulfuric acid, sulfuric acid ester, phosphoric acid, and phosphoric acid ester.

[0033] In the reaction of phenols and aldehydes in the above step 1-1a, the molar ratio (F / P) of aldehydes to phenols is, for example, 0.5 or more, preferably 0.55 or more, and more preferably 0.6 or more. The upper limit value of the molar ratio (F / P) of aldehydes to phenols 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 the condition that the molar ratio (F / P) of aldehydes to phenols is within the above range, a carboxy group-containing novolak type phenol resin having a desired weight average molecular weight can be obtained.

[0034] The step of reacting phenols and aldehydes in the presence of an acid catalyst in step 1-1a is preferably carried out, for example, at a temperature of 60°C to 120°C, preferably at a temperature of 80°C to 100°C, and for a reaction time of, for example, 10 minutes to 100 minutes. Thereby, the reaction can proceed efficiently and sufficiently. The step of reacting the novolak type phenol resin and the carboxylic acid compound in the presence of a basic catalyst in step 1-2a is carried out by adding the basic catalyst to the reaction mixture obtained in step 1-1a, then adding the carboxylic acid compound, and preferably at a temperature of 60°C to 120°C, preferably at a temperature of 80°C to 100°C, and for a reaction time of, for example, 10 minutes to 180 minutes. By carrying out the above steps under heating, the starting materials are uniformly mixed, and the molecular weight of the obtained carboxy group-containing novolak type phenol resin can be made uniform by intermolecular entanglement and intermolecular action. The reaction time is not particularly limited and may be appropriately determined according to the types of starting materials, the compounding molar ratio, the amount and type of catalyst, and the reaction conditions.

[0035] Water is generally used as the reaction solvent for producing the carboxyl group-containing novolak-type phenolic resin in Step 1-1a and Step 1-2a, but an organic solvent may also be used. Specific examples of such organic solvents include alcohols, ketones, aromatics, etc. Specific examples of alcohols include methanol, ethanol, propyl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, glycerin, etc. Specific examples of ketones include acetone, methyl ethyl ketone, etc. Specific examples of aromatics include toluene, xylene, etc.

[0036] The weight average molecular weight of the carboxyl group-containing phenolic resin obtained through Step 1-1a and Step 1-2a is, for example, 100 or more and 8,000 or less, preferably 400 or more and 7,000 or less, and more preferably 500 or more and 6,000 or less. The carboxyl group-containing novolak-type phenolic resin having a weight average molecular weight within the above range is preferable because it can be dispersed and present in water.

[0037] The carboxyl group-containing novolak-type phenolic resin produced by the above method may be subjected to post-treatment for removing unreacted free phenol contained therein, if necessary. As the post-treatment, a method of performing atmospheric distillation up to 150°C and then performing vacuum distillation at 500 Pa up to 250°C can be used. The content of unreacted free phenols in the carboxyl group-containing novolak-type phenolic resin obtained by the above method is reduced to 1.0 mass% or less, preferably 0.8 mass% or less, and more preferably 0.6 mass% or less. Also, the content of unreacted free aldehydes in the carboxyl group-containing novolak-type phenolic resin obtained by the above method is reduced to 1.0 mass% or less, preferably 0.8 mass% or less, and more preferably 0.6 mass% or less.

[0038] (amine) The sintering aid of this embodiment contains an amine. In the sintering aid, the amine interacts with the carboxyl group of the above-mentioned carboxyl group-containing phenolic resin (the carboxyl group of the structural unit represented by formula (1)), whereby the carboxyl group is neutralized, and the carboxyl group-containing novolak-type phenolic resin exists as a water-soluble or water-dispersible oil.

[0039] As the amine used in the sintering aid of this embodiment, a tertiary amine having an appropriate basicity for neutralizing the carboxyl group-containing novolak phenolic resin and being water-soluble is preferable. Examples of such tertiary amines include trimethylamine, triethylamine, tripropylamine, tributylamine, trioctylamine, diisopropylethylamine, quinuclidine, 1,4-diazabicyclo[2.2.2]octane (DABCO), triethanolamine, triisopropanolamine, N-dimethylaminoethanol, N-diethylaminoethanol, pyridine, 2,6-lutidine, 4-dimethylaminopyridine, quinoline, isoquinoline, and the like. Among them, N-dimethylaminoethanol is preferably used because it has an appropriate basicity, is water-soluble, and is easily available.

[0040] (Method for producing sintering aid) The sintering aid of this embodiment can be produced by mixing the above-mentioned carboxyl group-containing novolak-type phenolic resin and the above-mentioned amine in water. The carboxyl group-containing novolak-type phenolic resin can be blended in an amount such that the solid content of the resulting sintering aid is 10 to 90% by mass. The solid content can be changed by adjusting the amount of water used, and can be adjusted to a desired range according to the type of ceramic raw material. The blending amount of the amine is, for example, 0.3 to 2.0 mol, preferably 0.5 to 1.5 mol, per 1 mol of the carboxyl group of the carboxyl group-containing novolak-type phenolic resin. The sintering aid containing the carboxyl group-containing novolak-type phenolic resin and the amine in such a blending amount has excellent handleability.

[0041] (Use) The sintering aid of this embodiment is suitably used as a sintering aid for manufacturing a ceramic sintered body. Examples of the ceramic raw material constituting the ceramic sintered body include silicon carbide, boron carbide, tungsten carbide, titanium carbide, silicon nitride, and aluminum nitride.

[0042] [Ceramic Material] The ceramic material of this embodiment includes a ceramic powder and the above sintering aid. The ceramic material of this embodiment is preferably provided as an aqueous dispersion (slurry) in which the ceramic powder and the sintering aid are dispersed in water.

[0043] Examples of the ceramic powder include silicon carbide, boron carbide, tungsten carbide, titanium carbide, silicon nitride, and aluminum nitride. The ceramic powder may be used alone or in combination of two or more.

[0044] The content of the sintering aid in the ceramic material is preferably in the range of 0.1 mass% or more and 10 mass% or less based on the total solid content of the ceramic material. The content of the sintering aid in the ceramic material is preferably such that the amount of the phenolic resin contained in the sintering aid relative to the ceramic powder is 0.1 to 10% by weight. When the amount of the phenolic resin relative to the ceramic powder is less than 0.1% by weight, the effect of uniform dispersion of the ceramic powder may not be obtained. When the above amount exceeds 10 mass%, the desired sinterability and uniform fine structure may not be obtained.

[0045] [Ceramic Sintered Body] The above-mentioned ceramic material can be sintered to produce a ceramic sintered body. More specifically, the ceramic sintered body can be produced by a process including mixing a ceramic powder and a sintering aid of the present embodiment to prepare a casting liquid as the ceramic material, casting the obtained casting liquid into a mold, and obtaining a ceramic sintered body by subjecting this mold to pressure sintering. In a preferred embodiment, the casting liquid is an aqueous dispersion (slurry) in which a ceramic powder and a sintering aid are dispersed in water. Sintering is to sinter the ceramic material to obtain a ceramic sintered body, and a known firing method can be used.

[0046] The ceramic sintered body obtained by the method of the present embodiment has a uniform and dense fine structure, has small variations in properties, and has high strength.

[0047] As described above, embodiments of the present invention have been described, but these are examples of the present invention, and various configurations other than the above can also be adopted.

Examples

[0048] Hereinafter, the present invention will be described with reference to examples and comparative examples, but the present invention is not limited thereto.

[0049] [Preparation of Phenolic Resin and Preparation of Sintering Aid] (Synthesis Example 1: Synthesis of Unmodified Novolak-Type Phenolic Resin A) A mixture of 1000 parts of phenol (P), 570 parts of 37% formalin (F), and 10 parts of oxalic acid was reacted at 100°C for 3 hours, then dehydrated by atmospheric distillation until the temperature of the reaction mixture reached 140°C, and further dehydrated and monomer-removed by vacuum distillation while gradually reducing the pressure to 0.9 kPa until the temperature of the reaction mixture reached 220°C, to obtain an unmodified novolak-type phenolic resin A with a hydroxyl equivalent of 106. The molar ratio of formalin to phenol (F / P) was 0.77.

[0050] (Synthesis Example 2: Synthesis of Butylphenol-Modified Novolak-Type Phenolic Resin B) 1,000 parts of butylphenol was reacted with a mixture of 625 parts of phenol, 553 parts of 37% formalin, and 10 parts of oxalic acid at 100°C for 3 hours, and then the reaction mixture was dehydrated by atmospheric distillation until the temperature reached 140°C.The pressure was then gradually reduced to 0.9 kPa, and the reaction mixture was further dehydrated and demonomerized by vacuum distillation until the temperature reached 220°C, yielding a butylphenol-modified novolac phenolic resin B with a hydroxyl group equivalent of 140. F / P=0.77.

[0051] (Example A1: Preparation of sintering aid 1 containing carboxy group-containing novolac type phenolic resin) 250 parts of novolac phenolic resin A was melted and dissolved in 125 parts of butanol, and 84 parts of a 50% sodium hydroxide solution and 100 parts of pure water were added. 28 parts of sodium chloroacetate was added to the resulting mixture, and the mixture was reacted at 80°C for 2 hours. After that, 195 parts of a 25% aqueous sulfuric acid solution was added to neutralize the mixture, and the mixture was washed four times with 500 parts of pure water each to remove the neutralized salt. Thereafter, 75 parts of N-dimethylaminoethanol and 300 parts of pure water were added to obtain an aqueous dispersion of a carboxyl group-containing novolac type phenolic resin (sintering aid 1).

[0052] (Comparative Example A1: Preparation of Sintering Aid 2 Containing Unmodified Novolac Phenolic Resin) 1000 parts of the unmodified novolac phenolic resin A obtained in Synthesis Example 1 was dissolved in 1000 parts of ethanol to prepare an unmodified novolac phenolic resin A (sintering aid 2) in an ethanol solvent.

[0053] (Comparative Example A2: Preparation of Sintering Aid 3 Containing Carboxy Group-Containing Resol-Type Phenol Resin) 250 parts of novolac phenolic resin B was melted and dissolved in 125 parts of butanol, and 84 parts of a 50% sodium hydroxide solution and 100 parts of pure water were added. 60 parts of sodium chloroacetate was added to the resulting mixture, and the mixture was reacted at 80°C for 2 hours. After that, 195 parts of a 25% aqueous sulfuric acid solution was added to neutralize the mixture, and the mixture was washed four times with 500 parts of pure water each to remove the neutralized salt. Subsequently, 75 parts of N-dimethylaminoethanol and 80 parts of 37% aqueous formalin solution were added, and the mixture was reacted at 60 °C for 1 hour to effect methylolation. Then, 300 parts of pure water was added to obtain an aqueous dispersion of a resol-type carboxyl group-containing phenolic resin (sintering aid 3).

[0054] [Performance Evaluation of Sintering Aid] The sintering aid obtained above was evaluated for the following items. (Content of Unreacted Formaldehyde) The content of free formaldehyde in the sintering aid obtained above was measured using the hydroxylammonium chloride method of JIS K 6910. The results are shown in Table 1.

[0055] (Storage Stability) The storage stability of the sintering aid obtained above was evaluated using the increase rate of viscosity after storage for 1 month relative to the viscosity immediately after production (viscosity before storage) as an index. Specifically, first, the viscosity immediately after the preparation of the above resin composition was measured and recorded as the viscosity before storage. Next, this resin composition was placed in a constant temperature bath at 30 °C and allowed to stand for 1 month. The viscosity of the resin composition after standing was measured. The viscosity measurement was carried out in accordance with Method B of Viscosity in 5.3.2 of JIS-K-6910 "Test Methods for Phenolic Resins". From the values of the viscosity before storage and the viscosity after storage, the viscosity increase rate (%) was calculated according to the following formula. (Formula) Viscosity increase rate (%) = [(Viscosity after storage) / (Viscosity before storage)] × 100 The measurement results of the viscosity increase rate (%) are shown in Table 1. A smaller value of the viscosity increase rate indicates better stability over time.

[0056] [Manufacture of Ceramic Sintered Body] (Example B1) 100 g of α-SiC powder with an average particle size of 0.5 μm, 1 (3.5 g of the solid content of the phenolic resin contained therein) of the sintering aid prepared in Example A1, and 1.4 g of methyl borate were mixed with 300 ml of water, and dispersed, dissolved, and mixed in a plastic ball mill for 24 hours to prepare a mixed slurry. The obtained mixed slurry was heat-treated to distill off and remove water to obtain SiC powder particles. The obtained powder particles were sieved through a 60-mesh sieve to adjust the particle size, and using the sieved powder particles, they were uniaxially pressed at 500 kgf / cm 2 and further subjected to CIP (isostatic pressing) treatment at 1.5 tons / cm 3 to obtain a plate-shaped compact of 50 × 50 × 6 (mm). The obtained compact was heat-treated at 600 °C for 1 hour in a nitrogen atmosphere for debinding, and then sintered at 2100 °C for 2 hours in an argon atmosphere to obtain a SiC sintered body.

[0057] (Comparative Example B1) A SiC sintered body was obtained in the same manner as in Example B1, except that sintering aid 1 was replaced with sintering aid 2. (Comparative Example B2) A SiC sintered body was obtained in the same manner as in Example B1, except that sintering aid 1 was replaced with sintering aid 3.

[0058] [Performance Evaluation of Ceramic Sintered Bodies] Each of the sintered bodies obtained above was evaluated for the following physical properties. (Uniformity) Samples were cut out from each of the obtained SiC sintered bodies, and their density and flexural strength were measured using the Archimedes method and the three-point flexural strength at room temperature (JIS R1601), respectively. The results are shown in Table 1. The higher the value of the flexural strength, the higher the uniformity of the carbon source (phenolic resin) of the sintering aid is considered to be. Also, the higher the density, the more uniform and dense the structure of the sintered body is shown to be.

[0059]

Table 1

Claims

1. A carboxy group-containing novolak type phenol resin having a structural unit represented by formula (1) and a structural unit represented by formula (2); An amine; and Water, a sintering aid for ceramics, 【Chemical 1】 In formula (1), X is an alkylene group having 1 to 6 carbon atoms, R １ is, independently, a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a hydroxyl group, 【Chemical 2】 In formula (2), R ２ is, independently, a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a hydroxyl group, and is a sintering aid.

2. R in the formula (1) above １ and R ２ are each independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a hydroxyl group, and the sintering aid according to claim 1.

3. The proportion of the structural unit represented by the formula (1) in the carboxy group-containing phenol resin is 5 mol% or more and 90 mol% or less based on the entire carboxy group-containing phenol resin. The sintering aid according to claim 1.

4. The amine contains a tertiary amine. The sintering aid according to claim 1.

5. The sintering aid according to claim 1 is in the form of an aqueous solution.

6. The sintering aid according to claim 1 is in the form of an aqueous dispersion.

7. The ceramics contain at least one selected from silicon carbide, boron carbide, tungsten carbide, titanium carbide, silicon nitride, and aluminum nitride. The sintering aid according to claim 1.

8. A ceramic powder and The sintering aid according to any one of claims 1 to 7, a ceramic material.

9. The ceramic powder contains at least one selected from silicon carbide, boron carbide, tungsten carbide, titanium carbide, silicon nitride, and aluminum nitride. The ceramic material according to claim 8.

10. The sintering aid is in an amount of 0.1% by mass or more and 10% by mass or less based on the total solid content of the ceramic material. The ceramic material according to claim 8.

11. A method for manufacturing a ceramic sintered body, The method includes Mixing a ceramic powder and the sintering aid according to any one of claims 1 to 7 to prepare a casting liquid that becomes a ceramic material, Casting the casting liquid into a mold, Obtaining a ceramic sintered body by pressure-sintering the mold. Method.

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