Composition containing a sizing agent for inorganic fibers and a method for producing inorganic fibers

Abstract

The present invention provides a composition containing an inorganic fiber sizing agent, which can improve the heat resistance of a film obtained using the inorganic fiber sizing agent and the long-term stability of a composition containing the inorganic fiber sizing agent with water. The composition containing the inorganic fiber sizing agent of the present invention contains an inorganic fiber sizing agent and water, the inorganic fiber sizing agent containing a polyamide compound composed of structural unit A and structural unit B, and a nitrogen-containing compound, the molar ratio of structural unit A to structural unit B being structural unit A / structural unit B = 49.0 / 51.0 to 43.0 / 57.0. Structural unit A is a structure containing a structural unit formed from a tetracarboxylic acid or a derivative thereof. Structural unit B is a structure containing a structural unit formed from a diamine or a derivative thereof. The nitrogen-containing compound is at least one selected from the group consisting of ammonia, a tertiary amine compound, and an aprotic nitrogen-containing heterocyclic compound.

Description

Technical Field

[0001] This invention relates to compositions containing sizing agents for inorganic fibers and methods for manufacturing inorganic fibers using the compositions. The compositions can simultaneously improve the heat resistance of films obtained using inorganic fiber sizing agents and improve the long-term stability of water-containing compositions containing inorganic fiber sizing agents. Background Technology

[0002] For example, inorganic fibers such as carbon fiber are used as composite materials impregnated with matrix resins such as epoxy resin, or as reinforcing fibers for concrete. For example, carbon fiber is pre-treated by attaching a sizing agent to the surface to impart bundle properties to the carbon fiber strand.

[0003] Sizing agents for inorganic fibers are known in the past, as disclosed in Patent Documents 1 and 2. Regarding the sizing agent for carbon fibers in Patent Document 1, it discloses carbon fibers reinforced with polyimide resins and sizing agent compositions comprising polymaleimide and epoxy resin with a defined structure. Patent Document 2 discloses heat-stable fibers coated with a sizing composition comprising a copolymer of a defined polyamide-amic acid A unit and a polyamide-imide B unit.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Publication No. 1-38911

[0007] Patent Document 2: Japanese Patent Application Publication No. 61-75880 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] However, these existing inorganic fiber sizing agents have the problem of simultaneously improving the heat resistance of the film obtained by using inorganic fiber sizing agents and improving the long-term stability of water-containing compositions containing inorganic fiber sizing agents.

[0010] Methods for solving problems

[0011] In order to solve the above-mentioned problems, the inventors conducted research and found that it is just right to contain the following polyamide compounds and nitrogen-containing compounds in the composition containing the sizing agent for inorganic fibers.

[0012] To address the aforementioned issues, a key aspect of the composition containing an inorganic fiber sizing agent according to one aspect of the present invention is that it contains an inorganic fiber sizing agent and water, wherein the inorganic fiber sizing agent contains a polyamide compound composed of structural unit A and structural unit B, and a nitrogen-containing compound, wherein the molar ratio of structural unit A to structural unit B is structural unit A / structural unit B = 49.0 / 51.0 to 43.0 / 57.0.

[0013] Structural unit A: A structure containing structural units formed from tetracarboxylic acids or their derivatives.

[0014] Structural unit B: A structure containing structural units formed from diamines or their derivatives.

[0015] Nitrogen-containing compounds: selected from at least one of ammonia, tertiary amine compounds, and aprotic nitrogen-containing heterocyclic compounds.

[0016] In the above-mentioned composition containing an inorganic fiber sizing agent, the above-mentioned structural unit A may comprise a structural unit formed of a tetracarboxylic acid or a derivative thereof having an aromatic group.

[0017] In the above-mentioned composition containing an inorganic fiber sizing agent, the above-mentioned structural unit B may comprise a structural unit formed of a diamine or a derivative thereof having an aromatic group.

[0018] In the above-mentioned composition containing an inorganic fiber sizing agent, the nitrogen-containing compound may include at least one selected from 1,2-dimethylimidazole and 1-piperidineethanol.

[0019] The mass ratio of the content of the polyamide compound to the content of the nitrogen-containing compound in the above-mentioned composition containing an inorganic fiber sizing agent can be polyamide compound / nitrogen-containing compound = 54 / 46 to 31 / 69.

[0020] In the above-mentioned composition containing an inorganic fiber sizing agent, the mass ratio of the inorganic fiber sizing agent to the water can be inorganic fiber sizing agent / water = 10 / 90 to 80 / 20.

[0021] The above-mentioned composition containing an inorganic fiber sizing agent can be applied to carbon fibers.

[0022] To address the aforementioned issues, another aspect of the present invention provides a method for manufacturing inorganic fibers that includes a step of attaching the composition containing the sizing agent for inorganic fibers to the inorganic fibers.

[0023] In the above-mentioned method for manufacturing inorganic fibers, the inorganic fibers can be carbon fiber filaments.

[0024] Invention Effects

[0025] According to the present invention, it is possible to simultaneously improve the heat resistance of films obtained using inorganic fiber sizing agents and improve the long-term stability of water-containing compositions containing inorganic fiber sizing agents. Detailed Implementation

[0026] <First Implementation>

[0027] First, a first embodiment embodying the composition of the present invention containing an inorganic fiber sizing agent (hereinafter referred to as the sizing agent-containing composition) will be described. The sizing agent-containing composition contains an inorganic fiber sizing agent (hereinafter referred to as the sizing agent) and water as a solvent. The sizing agent contains a polyamide compound composed of structural units A and B as shown below, and a nitrogen-containing compound as shown below.

[0028] (Polyamide compounds)

[0029] The polyamide compound provided in this embodiment represents a polyamic acid (polyimide precursor) formed by the polymerization of structural unit A and structural unit B via amide bonds, as described later. This polyamide compound is applied to inorganic fibers in the form of a water-containing dilution, and then subjected to heat dehydration and ring-closure (imidization) under specified heating conditions to form a heat-resistant polyimide coating.

[0030] Structural unit A comprises a structural unit formed from a tetracarboxylic acid or a derivative thereof. Structural unit A is not particularly limited as long as it is a compound capable of forming a polyamic acid (polyimide precursor) by amide bond polymerization with structural unit B in the presence of a nitrogen-containing compound in a diluted solution.

[0031] As a tetracarboxylic acid, it can be a tetracarboxylic acid with an aromatic group or an aliphatic tetracarboxylic acid. As derivatives of tetracarboxylic acids, examples include dianhydrides of tetracarboxylic acids, alkyl esters such as methyl esters of tetracarboxylic acids, etc.

[0032] Specific examples of dianhydrides of tetracarboxylic acids having aromatic groups include pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, hydroquinone-bis(triphenylene trioxide), methylhydroquinone-bis(triphenylene trioxide), 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-biphenyl sulfone tetracarboxylic dianhydride, 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropionic acid dianhydride, 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropionic acid dianhydride, etc. 4-Dicarboxyphenyl)propionic dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 4,4'-bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-ylcarbonyloxy)biphenyl, 4,4'-bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-ylcarbonyloxy)-3,3'-dimethylbiphenyl, 4,4”-bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-ylcarbonyloxy)-3-methyl-p-terphenyl, 4,4”'-bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-ylcarbonyloxy)-3,3”'-dimethyl-p-tetraphenyl, etc.

[0033] Specific examples of dianhydrides that are aliphatic tetracarboxylic acids include, for example, bicyclo[2.2.2]oct-7-en-2,3,5,6-tetracarboxylic anhydride, 5-(dioxotetrahydrofuranyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, 4-(2,5-dioxotetrahydrofuran-3-yl)-tetrahydronaphthalene-1,2-dicarboxylic anhydride, tetrahydrofuran-2,3,4,5-tetracarboxylic anhydride, bicyclo-3,3',4,4'-tetracarboxylic anhydride, 1,2,4,5-cyclohexanetetracarboxylic anhydride, 1,2,3,4-cyclobutanetetracarboxylic anhydride, and 1,2,3,4-cyclopentanetetracarboxylic anhydride.

[0034] Structural unit A can be used alone or in combination of two or more types. Among these, it is preferred to use a structural unit formed of a tetracarboxylic acid or its derivative having an aromatic group that can form a polyimide coating with excellent heat resistance.

[0035] Structural unit B comprises a structural unit formed from a diamine or a derivative thereof. Structural unit B is not particularly limited to any compound capable of forming a polyamic acid (polyimide precursor) via amide bond polymerization with structural unit A in the presence of a nitrogen-containing compound in a composition containing a sizing agent. The diamine or its derivative may be an aromatic diamine or an aliphatic diamine; either is acceptable.

[0036] Specific examples of diamines having aromatic groups include p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 2,4-diaminotoluene, 2,5-diaminotoluene, 2,4-diaminoxylene, 2,4-diaminotrimethylbenzene, 4,4'-diaminodiphenylmethane, 4,4'-methylenebis(2-methylaniline), 4,4'-methylenebis(2-ethylaniline), 4,4'-methylenebis(2,6-dimethylaniline), 4,4'-methylenebis(2,6-diethylaniline), 4,4'-oxodiphenylamine, 3,4'-oxodiphenylamine, 3,3'-oxodiphenylamine, 2,4'-oxodiphenylamine, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, and 4,4'-diaminodiphenylmethane. Ketones, 3,3'-diaminobenzophenone, 4,4'-diaminobenzoylaniline, 4-aminophenyl-4'-aminobenzoate, benzidine, 3,3'-dihydroxybenzidine, 3,3'-dimethoxybenzidine, o-toluidine, meta-toluidine, 2,2'-bis(trifluoromethyl)benzidine, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,3- Bis(3-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)biphenyl, bis(4-(3-aminophenoxy)phenyl)sulfone, bis(4-(4-aminophenoxy)phenyl)sulfone, 2,2-bis(4-(4-aminophenoxy)phenyl)propane, 2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane, 2,2-bis(4-aminophenyl)hexafluoropropane, p-terphenyldiamine, etc.

[0037] Specific examples of aliphatic diamines include 4,4'-methylenebis(cyclohexylamine), isophorone diamine, trans-1,4-cyclohexanediamine, cis-1,4-cyclohexanediamine, 1,4-cyclohexanebis(methylamine), 2,5-bis(aminomethyl)bicyclo[2.2.1]heptane, 2,6-bis(aminomethyl)bicyclo[2.2.1]heptane, 3,8-bis(aminomethyl)tricyclo[5.2.1.0]decane, 1,3-diaminoadamantane, 2,2-bis(4-aminocyclohexyl)propane, 2,2-bis(4-aminocyclohexyl)hexafluoropropane, 1,3-propanediamine, 1,4-tetramethylenediamine, 1,5-pentamethylenediamine, 1,6-hexanediamine, 1,7-heptamethylenediamine, 1,8-octamethylenediamine, and 1,9-nonamethylenediamine.

[0038] Structural unit B can be used alone or in combination of two or more. Among these, it is preferred to include structural units formed of diamines or their derivatives having aromatic groups (the diamines or their derivatives are capable of forming a polyimide coating with excellent heat resistance).

[0039] The molar ratio of structural unit A to structural unit B in the mixed raw materials is structural unit A / structural unit B = 49.0 / 51.0 to 43.0 / 57.0. Compositions containing sizing agents and including polyamide compounds synthesized within this range are particularly effective in improving long-term stability.

[0040] (Nitrogen-containing compounds)

[0041] Examples of nitrogen-containing compounds supplied in this embodiment include ammonia, tertiary amine compounds, and aprotic nitrogen-containing heterocyclic compounds.

[0042] Specific examples of tertiary amine compounds include 1-piperidineethanol, N-methylpyrrolidone, N,N-dimethylacetamide, N,N-diethylacetamide, dimethylformamide, hexamethylphosphoramide, 1,3-dimethyl-2-imidazolinone, dimethylaminoethanol, diethylaminoethanol, diisopropylaminoethanol, triethanolamine, dimethylethanolamine, diethylethanolamine, dibutylethanolamine, tetramethylethylenediamine, triethylenediamine, N-methylmorpholine, N-ethylmorpholine, dimethylbenzylamine, N,N,N',N'-tetramethyl-1,6-diaminohexane, N,N,N',N”N”-pentamethyldiethylenetriamine, bis-(2-dimethylaminoethyl) ether, 1,8-diazabicyclo[5.4.0]undecene-7, etc.

[0043] Specific examples of aprotic nitrogen-containing heterocyclic compounds include methylpyridine, pyridine, N,N-dimethyl-4-aminopyridine, 1,2-dimethylimidazole, and N-methylimidazole. It should be noted that aprotic nitrogen-containing compounds also include substances that are simultaneously tertiary amine compounds.

[0044] These nitrogen-containing compounds can be used alone or in combination of two or more.

[0045] Among nitrogen-containing compounds, 1,2-dimethylimidazole and 1-piperidineethanol are preferred. Using these compounds can further improve the long-term stability of compositions containing sizing agents.

[0046] The mass ratio of polyamide compound to nitrogen-containing compound in the composition containing the sizing agent can be suitably set, preferably polyamide compound / nitrogen-containing compound = 54 / 46 to 30 / 70, more preferably polyamide compound / nitrogen-containing compound = 54 / 46 to 31 / 69. A range formed by any combination of the above upper and lower limits can also be set. By limiting it to this range, long-term stability can be further improved.

[0047] (water)

[0048] The mass ratio of sizing agent to water in the composition containing the sizing agent can be suitably set, preferably sizing agent / water = 5 / 95 to 85 / 15, more preferably sizing agent / water = 10 / 90 to 80 / 20. A range formed by any combination of the above upper and lower limits can also be set. By limiting it to this range, long-term stability can be further improved.

[0049] Polyamic acid (a polyimide precursor) as a polyamide compound is synthesized as follows: Structural units A and B are dissolved or suspended in water in the presence of a nitrogen-containing compound. Then, under heating conditions of, for example, 50°C to 80°C, preferably 60°C to 70°C, a polymerization reaction based on amide bonds is promoted for, for example, 1 hour to 10 hours, preferably 5 hours to 7 hours. The composition containing the polyamide compound obtained through polymerization, the nitrogen-containing compound added during the reaction, and water, along with a sizing agent, can have its water content adjusted as needed.

[0050] <Second Implementation Method>

[0051] Next, a second embodiment embodying the method for manufacturing the inorganic fiber of the present invention will be described. The method for manufacturing the inorganic fiber in this embodiment includes a step of attaching the composition containing a sizing agent from the first embodiment to carbon fibers. There is no particular limitation on the amount attached (excluding solvent), but it is preferable to attach the inorganic fiber with an amount of 0.01% by mass or more and 10% by mass or less as the sizing agent. By limiting this range, the bundle properties and other effects of the inorganic fiber can be further improved. There is no particular limitation on the type of inorganic fiber used in this embodiment; examples include glass fiber, carbon fiber, ceramic fiber, metal fiber, mineral fiber, rock fiber, and slag fiber. Among these, carbon fiber is preferred, and carbon fiber yarn is more preferred, from the perspective of more effectively demonstrating the effects of the present invention. Examples of types of carbon fiber include PAN-based carbon fiber obtained from acrylic fiber, pitch-based carbon fiber obtained from pitch, recycled carbon fiber, and carbon fiber obtained from polyester fiber.

[0052] To obtain inorganic fibers by attaching the sizing agent-containing composition of the first embodiment to inorganic fibers, industrially common methods can be used. Examples include roller impregnation, roller contact, spraying, and papermaking. The inorganic fibers with the sizing agent-containing composition of the first embodiment attached are then subjected to a drying process to remove water, nitrogen-containing compounds, and other substances contained in the sizing agent-containing composition, thereby obtaining inorganic fibers. This drying process can be performed using methods such as hot air, hot plates, rollers, or various infrared heaters as the heat medium. The drying temperature is preferably 130°C or higher and 220°C or lower. Within this temperature range, the polyamic acid undergoes thermal dehydration and ring-closure (imidization), forming a heat-resistant polyimide coating.

[0053] (effect)

[0054] Next, the effects of the composition containing the sizing agent as described above and the method for manufacturing carbon fiber will be explained.

[0055] In the above embodiments, a sizing agent containing a polyamide compound composed of the above-mentioned structural unit A and structural unit B, and the above-mentioned nitrogen-containing compound is used.

[0056] For example, when 3,3',4,4'-biphenyltetracarboxylic anhydride is used as structural unit A, p-phenylenediamine as structural unit B, and 1,2-dimethylimidazole as a nitrogen-containing compound, polyamic acid (polyimide precursor) as a polyamide compound is synthesized using the following method. Specifically, p-phenylenediamine and 1,2-dimethylimidazole are first dissolved in water. Then, 3,3',4,4'-biphenyltetracarboxylic anhydride is suspended, and a polymerization reaction based on amide bonds is promoted under conditions of 50°C to 80°C and for 1 hour to 10 hours. Thus, polyamic acid (polyimide precursor) as a polyamide compound is synthesized by the reaction shown in Chemical 1 below.

[0057] [Chemistry 1]

[0058]

[0059] A composition containing a polyamide compound and a sizing agent is attached to an inorganic fiber and then dried at a specified temperature, for example, above 130°C and below 220°C. At this time, a heat-resistant polyimide coating can be formed by heating and dehydrating the ring (imidization) as shown in Chemical 2 below.

[0060] [Chemistry 2]

[0061]

[0062] The molar ratio of structural unit A to structural unit B in the mixed raw materials is limited to a range of structural unit A / structural unit B = 49.0 / 51.0 to 43.0 / 57.0. Therefore, structural unit B is located at the end of the predominantly generated polymer. Furthermore, a polymer with a molecular weight preferred for exhibiting heat resistance and long-term stability can be obtained. Therefore, polymer reactivity during storage can be suppressed, and long-term storage stability can be improved. Additionally, a polymer with excellent heat resistance can be obtained.

[0063] The following effects can be obtained by using the composition containing sizing agent and the method for manufacturing carbon fiber according to the above embodiments.

[0064] In the above embodiments, a composition containing a sizing agent is used. This composition contains a sizing agent and water. The sizing agent contains a polyamide compound in which the molar ratio of the mixed raw materials of structural unit A and structural unit B is limited to structural unit A / structural unit B = 49.0 / 51.0 to 43.0 / 57.0, and the aforementioned nitrogen-containing compound. Therefore, it is possible to simultaneously improve the heat resistance of the film obtained using the inorganic fiber sizing agent and improve the long-term stability of the composition containing the water-based inorganic fiber sizing agent.

[0065] It should be noted that the above implementation method can be modified as follows.

[0066] In the sizing agent-containing compositions of the above embodiments, from the perspective of maintaining the performance of the sizing agent-containing compositions, it is permissible to mix in surfactants, trace amounts of organic solvents, smoothing agents, antioxidants, preservatives, etc., which are other components, within a range that does not impair the effects of the present invention.

[0067] The application areas of the inorganic fibers described in the above embodiments are not particularly limited. For example, they can be applied to carbon fiber reinforced polymer (CFRP) composites impregnated with matrix resins such as polyimide resin, and as reinforcing fibers for concrete.

[0068] Example

[0069] To illustrate the structure and effects of the present invention more specifically, embodiments are given below, but the present invention is not limited to these embodiments. It should be noted that in the following descriptions of embodiments and comparative examples, parts refer to parts by mass, and % refers to percentages by mass.

[0070] Experimental Group 1 (Preparation of Compositions Containing Sizing Agents)

[0071] • Preparation of the composition containing a sizing agent in Example 1

[0072] 360 g of water as a solvent was added to a 500 mL glass reaction vessel. 8.29 g of 4,4'-diaminodiphenyl ether (structural unit B) and 20.00 g of 1,2-dimethylimidazole (a nitrogen-containing compound) were then added. The mixture was stirred at 25°C for 1 hour to dissolve the solution. 11.71 g of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (structural unit A) was then added to the solution. The mixture was stirred at 70°C for 6 hours to synthesize a polyamide compound (polyamic acid as a polyimide precursor) (P-1), simultaneously obtaining the composition containing a sizing agent as described in Example 1.

[0073] Preparation of the compositions containing sizing agents in Examples 2-49

[0074] Similar to the composition containing sizing agent in Example 1, polyamide compounds (P-1) to (P-22) were synthesized by combining structural units A and B of the polyamide compounds (P-2) to (P-22) as shown in Table 1, and nitrogen-containing compounds as shown in Table 2. Compositions containing sizing agents in Examples 2 to 49 were prepared concurrently.

[0075] Preparation of the compositions containing sizing agents in Comparative Examples 1-6

[0076] Using the structural units A and B of the polyamide compounds (P-3), (rp-1) to (rp-3) shown in Table 1, and the combinations of nitrogen-containing compounds shown in Table 2, the sizing agent-containing compositions of Comparative Examples 1 to 6 were prepared by reacting them using the same method as the composition containing the sizing agent in Example 1.

[0077] It should be noted that for the above polyamide compounds (P-1) to (P-22) and (rp-1) to (rp-3), the proportions (molar ratios) of structural unit A, structural unit B, and the raw materials used are shown in the "Structural Unit A" column, "Structural Unit B" column, and "Structural Unit A / Structural Unit B (molar ratio)" column of Table 1 below.

[0078] The types and contents of polyamide compounds, nitrogen compounds, and water content in the sizing agent compositions of each example are shown in the "Polyamide Compounds," "Nitrogen Compounds," and "Water" columns of Table 2, respectively. Furthermore, the mass ratio of the polyamide compound content to the nitrogen compound content is shown in the "Polyamide Compound / Nitrogen Compound (Mass Ratio)" column.

[0079] [Table 1]

[0080]

[0081] [Table 2]

[0082]

[0083] The detailed information of the nitrogen-containing compounds listed in Table 2 is shown below.

[0084] C-1: 1,2-Dimethylimidazole

[0085] C-2: 1-Piperidinol

[0086] C-3: Dimethylaminoethanol

[0087] C-4: Diethylaminoethanol

[0088] C-5: 1-Methylpyrrolidone

[0089] C-6: Ammonia

[0090] rc-1: NaOH

[0091] Experimental Group 2 (Evaluation of Long-Term Stability)

[0092] Long-term stability of compositions containing sizing agents

[0093] Each composition containing a sizing agent was allowed to stand at 25°C for 6 months. After standing, the appearance of the compositions containing the sizing agent was visually observed and evaluated according to the following criteria. The results are shown in the "Long-term stability" column of Table 2.

[0094] ◎◎◎ (Excellent): No precipitation, separation, or gelation occurred even after 6 months.

[0095] ◎◎ (Excellent): No precipitation, separation, or gelation occurred even after 3 months, but precipitation, separation, or gelation occurred after 6 months.

[0096] ◎(Good): No precipitation, separation, or gelation occurred even after 1 month, but precipitation, separation, or gelation occurred after 3 months.

[0097] ○ (Pass): No precipitation, separation, or gelation occurred even after 2 weeks, but precipitation, separation, or gelation occurred after 1 month.

[0098] × (Defective): Precipitation, separation, or gelation occurs after 2 weeks.

[0099] ×× (Very Undesirable): Precipitation or separation occurs immediately after preparation.

[0100] • Heat resistance evaluation

[0101] Each example composition containing a sizing agent was dried at 200°C for 1 hour to obtain a solid component. 1 g of the solid component was sampled in an aluminum cup with a diameter of 50 mm and treated in an electric furnace at 400°C for 30 minutes. The residual rate (%) was calculated using the following formula.

[0102] Residual rate (%) = (mass after treatment) / (mass before treatment) × 100

[0103] The heat resistance was evaluated using the following criteria. The results are shown in the "Heat Resistance" column of Table 2.

[0104] ◎◎(Excellent): Residue rate of 90% or higher

[0105] ◎(Good): The residue rate is 85% or higher but less than 90%.

[0106] ○ (Qualified): The residue rate is 75% or higher but less than 85%.

[0107] × (Defective): Cases where the residual rate is less than 75%.

[0108] As can be seen from the results in Table 2 above, according to the present invention, a composition containing a sizing agent that yields a polyimide coating with excellent heat resistance can be provided. Furthermore, the composition containing the sizing agent maintains high stability even after long-term storage. It should be noted that the compositions containing the sizing agent in Comparative Examples 5 and 6 exhibited very poor stability and were difficult to sample uniformly, thus making it impossible to determine and evaluate their heat resistance. In the compositions containing the sizing agent in Comparative Examples 5 and 6, it can be considered that structural unit A and structural unit B did not undergo the formation of polyamic acid through amide bond polymerization.

Claims

1. A composition containing an inorganic fiber sizing agent, characterized in that, It contains an inorganic fiber sizing agent and water. The inorganic fiber sizing agent contains a polyamide compound composed of structural unit A and structural unit B, and a nitrogen-containing compound, wherein the molar ratio of structural unit A to structural unit B is structural unit A / structural unit B = 49.0 / 51.0 to 43.0 / 57.

0. The mass ratio of the polyamide compound content to the nitrogen-containing compound content in the composition containing the inorganic fiber sizing agent is polyamide compound / nitrogen-containing compound = 54 / 46 to 31 / 69. Structural unit A: A structure containing structural units formed from tetracarboxylic acids or their derivatives; Structural unit B: A structure containing structural units formed from diamines or their derivatives; Nitrogen-containing compounds: selected from at least one of ammonia, tertiary amine compounds, and aprotic nitrogen-containing heterocyclic compounds.

2. The composition containing an inorganic fiber sizing agent according to claim 1, wherein, The structural unit A comprises a structural unit formed from a tetracarboxylic acid or a derivative thereof having an aromatic group.

3. The composition containing an inorganic fiber sizing agent according to claim 1, wherein, The structural unit B comprises a structural unit formed from a diamine or a derivative thereof having an aromatic group.

4. The composition containing an inorganic fiber sizing agent according to claim 1, wherein, The nitrogen-containing compound comprises at least one selected from 1,2-dimethylimidazole and 1-piperidineethanol.

5. The composition containing an inorganic fiber sizing agent according to claim 1, wherein, The mass ratio of the inorganic fiber sizing agent to the water in the composition containing the inorganic fiber sizing agent is 10 / 90 to 80 / 20.

6. The composition containing an inorganic fiber sizing agent according to claim 1, wherein, The composition containing an inorganic fiber sizing agent is applied to carbon fibers.

7. A method for manufacturing inorganic fibers, characterized in that, It includes the step of attaching the composition containing the sizing agent for inorganic fibers as described in any one of claims 1 to 5 to inorganic fibers.

8. The method for manufacturing inorganic fibers according to claim 7, wherein, The inorganic fiber is carbon fiber yarn.

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