Polycarbosilane, method for producing polycarbosilane, and method for producing silicon carbide fiber

Abstract

The polycarbosilane according to the present embodiment has a bonding index represented by formula (1) as an index of the degree of branching of 2.63 or more and an oxygen content of 1.15 wt% or less. # imgabs0 #

Description

Technical Field

[0001] The invention relates to polycarbosilane and a method for producing the same, as well as a method for producing silicon carbide fiber. Background Art

[0002] Silicon carbide fiber is a fiber that has excellent heat resistance and oxidation resistance even in high-temperature atmospheres of several thousand degrees. Therefore, utilizing this characteristic, it is expected to be used in the fields of nuclear energy and aerospace.

[0003] It is known that silicon carbide fibers are obtained by adjusting the molecular weight of an organic silicon polymer compound such as polycarbosilane as a precursor, spinning, and calcining.

[0004] For example, Patent Document 1 discloses a method of synthesizing polycarbosilane from polysilane by a liquid-gas phase pyrolysis condensation method and producing silicon carbide fibers from the synthesized polycarbosilane.

[0005] Patent Document 2 discloses a method for producing an organosilicon polymer compound having silicon and carbon as main skeleton components, and describes an example in which a cyclic silane compound is used as a raw material.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2019-137935

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 51-126300 Summary of the invention

[0010] Problem that the invention aims to solve

[0011] Silicon carbide fibers are also expected to be used in the fields of nuclear energy and aerospace, and therefore silicon carbide fibers having higher strength than conventional fibers are required.

[0012] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a polycarbosilane capable of producing high-strength silicon carbide fibers.

[0013] Technical Solution

[0014] The present inventors have conducted intensive studies and have found that highly branched polycarbosilane can be obtained by using a cyclic silane compound as a raw material and producing it by a predetermined method, thereby enabling production of high-strength silicon carbide fibers, thereby completing the present invention.

[0015] The polycarbosilane according to one embodiment of the present invention has a bonding index represented by the following formula (1), which is an index of the degree of branching, of 2.63 or more, and an oxygen content of 1.15 wt % or less.

[0016] [Formula 1]

[0017]

[0018] [In formula (1), X CH3 , X CH2 , X CH and X C is the value obtained by dividing the weight percentage of primary carbon atoms, secondary carbon atoms, tertiary carbon atoms and quaternary carbon atoms by 12. SiH3 , Y SiH2 , Y SiH and Y Si It is the value obtained by dividing the weight percentage of primary silicon atoms, secondary silicon atoms, tertiary silicon atoms and quaternary silicon atoms by 28.086.]

[0019] A method for producing polycarbosilane according to one embodiment of the present invention is a method for producing polycarbosilane according to one embodiment of the present invention, which includes a polycarbosilane synthesis step, and the polycarbosilane synthesis step includes repeatedly performing the following treatments: heating a raw material containing a cyclic silane compound at a first temperature to generate a gas phase; heating the gas phase at a second temperature higher than the first temperature to generate polycarbosilane; and cooling the polycarbosilane and returning it to the raw material, and heating it at the first temperature to thereby perform a treatment to increase the molecular weight of the polycarbosilane.

[0020] A method for producing silicon carbide fibers according to one embodiment of the present invention includes a spinning step of forming polycarbosilane according to one embodiment of the present invention into fibers; and a calcining step of calcining the polycarbosilane fibers produced by the spinning step.

[0021] Beneficial Effects

[0022] According to one embodiment of the present invention, a highly branched polycarbosilane is provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 FIG. 1 is a diagram showing a liquid-gas phase pyrolysis apparatus 10 that can be used for synthesizing polycarbosilane.

[0024] Figure 2 This is a graph showing the relationship between the bonding index of polycarbosilane and the tensile strength of silicon carbide fibers. DETAILED DESCRIPTION

[0025] 〔1. Polycarbosilane〕

[0026] The polycarbosilane of one embodiment of the present invention has a bond index represented by the following formula (1) as an index of the degree of branching of 2.58 or more, and an oxygen content of 1.15 wt % or less. With such a structure, a highly branched polycarbosilane can be obtained.

[0027] [Formula 2]

[0028]

[0029] [In formula (1), X CH3 , X CH2 , X CH and X C is the value obtained by dividing the weight percentage of primary carbon atoms, secondary carbon atoms, tertiary carbon atoms and quaternary carbon atoms by 12; SiH3 , Y SiH2 , Y SiH and Y Si It is the value obtained by dividing the weight percentage of primary silicon atoms, secondary silicon atoms, tertiary silicon atoms and quaternary silicon atoms by 28.086.]

[0030] (Bond Index)

[0031] The "bonding index" in this specification is an indicator of the degree of branching of polycarbosilane, and is a value obtained by the above formula (1). In this specification, "branching" refers to the portion where carbon atoms or silicon atoms are bonded to atoms other than hydrogen atoms. For example, the branching of CH3-CH3 refers to the portion where the carbon atoms recorded on the left are bonded to atoms other than hydrogen atoms and the portion where the carbon atoms recorded on the right are bonded to atoms other than hydrogen atoms. Similarly, the branching of silicon atoms refers to the portion where all silicon atoms are bonded to atoms other than hydrogen atoms. Therefore, the larger the bonding index, the more highly branched the polycarbosilane is.

[0032] In formula (1), X CH3 , X CH2 , X CH and X C is the value obtained by dividing the weight percentage of primary carbon atoms, secondary carbon atoms, tertiary carbon atoms and quaternary carbon atoms by 12. In this specification, "primary carbon" refers to carbon with three hydrogen atoms bonded to it. "Secondary carbon" refers to carbon with two hydrogen atoms bonded to it. "Tertiary carbon" refers to carbon with one hydrogen atoms bonded to it. "Quaternary carbon" refers to carbon with no hydrogen atoms bonded to it. In addition, in formula (1), 12 is the atomic weight of carbon. Therefore, X CH3 , X CH2 , X CH and X C The details are as shown in the following formulas (2) to (5).

[0033] [Formula 3]

[0034]

[0035] [Formula 4]

[0036]

[0037] [Formula 5]

[0038]

[0039] [Formula 6]

[0040]

[0041] Wherein, the weight % of primary carbon atoms, secondary carbon atoms and tertiary carbon atoms is the value obtained by dividing the weight % of hydrogen atoms of each carbon by the product of the number of hydrogen atoms bonded to each carbon and the atomic weight of hydrogen, multiplied by the atomic weight of carbon. It should be noted that in this specification, the atomic weight of hydrogen is used as 1 for calculation. In addition, the weight % of quaternary carbon atoms is the value obtained by deducting the weight % of primary carbon atoms, secondary carbon atoms and tertiary carbon atoms from the elemental analysis value of carbon atoms. Therefore, the weight % of primary carbon atoms, secondary carbon atoms, tertiary carbon atoms and quaternary carbon atoms are shown in detail in the following formulas (6) to (9). The elemental analysis value of carbon atoms can be obtained by a known method.

[0042] [Formula 7]

[0043]

[0044] [Formula 8]

[0045]

[0046] [Formula 9]

[0047]

[0048] [Formula 10]

[0049] Weight% of quaternary carbon atoms

[0050] = Elemental analysis value of carbon atoms (weight %) - (weight % of primary carbon atoms + weight % of secondary carbon atoms + weight % of tertiary carbon atoms)

[0051] …(9)

[0052] The weight percent of hydrogen atoms in primary carbon, secondary carbon, and tertiary carbon is calculated by multiplying the elemental analysis value of hydrogen atoms by the weight percent of hydrogen atoms in primary carbon, secondary carbon, and tertiary carbon. 1 The area ratio of primary, secondary and tertiary carbon is obtained by H-NMR. 1 The area ratio of H-NMR is the ratio of each area ratio of hydrogen atoms of primary carbon, secondary carbon and tertiary carbon to the total area ratio obtained as follows: 1The area values ​​of Si-H and hydrogen atoms of primary, secondary and tertiary carbons measured by H-NMR are normalized. Therefore, the weight % of hydrogen atoms of primary, secondary and tertiary carbons are specifically represented by the following formulas (10) to (12).

[0053] [Formula 11]

[0054] Weight % of hydrogen atoms of primary carbon =

[0055] Primary Carbon 1 H-NMR area ratio × elemental analysis value of hydrogen atoms (weight %) (10)

[0056] [Formula 12]

[0057] Weight % of hydrogen atoms of secondary carbon =

[0058] Area ratio of secondary carbon in 1H-NMR × elemental analysis value of hydrogen atom (weight %) (11)

[0059] [Formula 13]

[0060] Weight % of hydrogen atoms of tertiary carbon =

[0061] Tertiary 1 H-NMR area ratio × elemental analysis value of hydrogen atoms (weight %)··(12)

[0062] 1 The area values ​​of hydrogen atoms of primary carbon, secondary carbon and tertiary carbon in polycarbosilane in H-NMR can be obtained as follows: the signal of 5.5 to 3.5 ppm is taken as the signal from hydrogen (-SiH<) on tertiary silicon, the signal of 1.0 to 0 ppm is taken as the signal from hydrogen (CH3-) on primary carbon, the signal of 0 to -0.4 ppm is taken as the signal from hydrogen (-CH2-) on secondary carbon, and the signal of -0.4 to -1.0 ppm is taken as the signal from hydrogen (-CH<) on tertiary carbon, and the integral value is calculated. In addition, the elemental analysis value of hydrogen atoms can be obtained by a known method.

[0063] In addition, in formula (1), Y SiH3 , Y SiH2 , Y SiH and Y Si is the value obtained by dividing the weight percentage of primary silicon atoms, secondary silicon atoms, tertiary silicon atoms and quaternary silicon atoms by 28.086. In this specification, "primary silicon" refers to silicon with three hydrogen atoms bonded to it. "Secondary silicon" refers to silicon with two hydrogen atoms bonded to it. "Tertiary silicon" refers to silicon with one hydrogen atoms bonded to it. "Quaternary silicon" refers to silicon with no hydrogen atoms bonded to it. In addition, in formula (1), 28.086 is the atomic weight of silicon. Therefore, Y SiH3 , Y SiH2 , Y SiHand Y Si The details are as shown in the following formulas (13) to (16).

[0064] [Formula 14]

[0065]

[0066] [Formula 15]

[0067]

[0068] [Formula 16]

[0069]

[0070] [Formula 17]

[0071]

[0072] The weight percentage of primary silicon atoms, secondary silicon atoms, and tertiary silicon atoms is calculated by multiplying the elemental analysis value of hydrogen atoms by the weight percentage of primary silicon atoms, secondary silicon atoms, and tertiary silicon atoms. 29 The area ratio of primary silicon atoms, secondary silicon atoms, tertiary silicon atoms and quaternary silicon atoms is obtained by Si-NMR. 29 The area ratio of Si-NMR is the ratio of each area ratio of primary silicon atoms, secondary silicon atoms, tertiary silicon atoms and quaternary silicon atoms to the total area ratio obtained by standardizing the area ratios of primary silicon atoms, secondary silicon atoms, tertiary silicon atoms and quaternary silicon atoms with quaternary silicon atoms. Therefore, the weight % of primary silicon atoms, secondary silicon atoms, tertiary silicon atoms and quaternary silicon atoms are shown in detail in the following formulas (17) to (20).

[0073] [Formula 18]

[0074] Weight % of primary silicon atoms =

[0075] Primary silicon atom 29 Area ratio of Si-NMR × elemental analysis value of silicon atoms (weight %)…(17)

[0076] [Formula 19]

[0077] Weight % of secondary silicon atoms =

[0078] Secondary silicon atoms 29 Area ratio of Si-NMR × elemental analysis value of silicon atoms (weight %)…(18)

[0079] [Formula 20]

[0080] Weight % of tertiary silicon atoms =

[0081] Tertiary silicon atom 29Area ratio of Si-NMR × elemental analysis value of silicon atoms (weight %)…(19)

[0082] [Formula 21]

[0083] Weight % of quaternary silicon atoms =

[0084] Quaternary silicon atom 29 Area ratio of Si-NMR × elemental analysis value of silicon atoms (weight %)…(20)

[0085] 29 The area ratio of primary silicon atoms, secondary silicon atoms, tertiary silicon atoms and quaternary silicon atoms in polycarbosilane in Si-NMR can be obtained as follows: the signal of 10 to -8 ppm is taken as the signal from quaternary silicon (>Si<), the signal of -8 to -24 ppm is taken as the signal from tertiary silicon (-SiH<), the signal of -30 to -50 ppm is taken as the signal from secondary silicon (-SiH2-), and the signal of -40 to -70 ppm is taken as primary silicon (-SiH3), and the integral value is calculated. In addition, the elemental analysis value of silicon atoms can be obtained by a known method.

[0086] By the above calculation method, the bonding index can be calculated.

[0087] The bonding index of the polycarbosilane of this embodiment is 2.58 or more, preferably 2.61 or more, and more preferably 2.63 or more. By making the bonding index within such a range, a highly branched polycarbosilane is obtained. In addition, when silicon carbide fiber (hereinafter also referred to as "SiC fiber") is manufactured from polycarbosilane having such a bonding index, SiC fiber with high tensile strength can be obtained. The tensile strength will be described later.

[0088] 〔Oxygen content〕

[0089] The oxygen content of polycarbosilane is 1.15 wt% or less, preferably 1.0 wt% or less, more preferably 0.9 wt% or less, and further preferably 0.8 wt% or less. When SiC fiber is produced from polycarbosilane having an oxygen content within such a range, SiC fiber with high heat resistance can be obtained.

[0090] The oxygen content can be measured by a known method for measuring the oxygen content of polycarbosilane, for example, it can be calculated by elemental analysis.

[0091] (Number average molecular weight)

[0092] The number average molecular weight of the polycarbosilane in this embodiment can be less than 6000, preferably less than 5500, and more preferably less than 5000. Even if the number average molecular weight is less than 6000, it is allowed, so the low molecular weight polycarbosilane to be removed by molecular weight adjustment can be reduced, and as a result, the yield of polycarbosilane is improved. In addition, in the case of manufacturing raw silk from polycarbosilane, polycarbosilane with a number average molecular weight of less than 6000 can be preferably used for dry spinning. Specifically, polycarbosilane with a number average molecular weight of less than 6000 can increase the concentration of the spinning solution, thereby suppressing the amount of solvent evaporation and making spinning easier. In addition, polycarbosilane with a number average molecular weight of less than 6000 is not easy to become gel-like because it contains a large amount of low molecular weight polycarbosilane, and the spinning solution can be easily adjusted.

[0093] In addition, the softening point, which indicates the temperature at which polycarbosilane begins to melt, is proportional to both the molecular weight and the branching. The bonding index of the polycarbosilane in the present embodiment, which is an indicator of the degree of branching, is 2.58 or more, so even if the polycarbosilane has a number average molecular weight of less than 6000, the softening point will not become too low. Therefore, when the fiber made of polycarbosilane is fired, the fiber is not easy to fuse. From the viewpoint of making the softening point reach a degree that the fiber does not fuse during firing, the number average molecular weight is preferably 1500 or more, more preferably 2500 or more, and further preferably 4000 or more.

[0094] The number average molecular weight can be determined by a known method for measuring the number average molecular weight, for example, by GPC (gel permeation chromatography).

[0095] [2. Method for producing polycarbosilane]

[0096] A method for producing polycarbosilane according to one embodiment of the present invention is a method for producing polycarbosilane according to one embodiment of the present invention, comprising a polycarbosilane synthesis step, the polycarbosilane synthesis step comprising: heating a raw material containing a cyclic silane compound at a first temperature to generate a gas phase (hereinafter referred to as "first heating treatment"); heating the gas phase at a second temperature higher than the first temperature to generate polycarbosilane (hereinafter referred to as "second heating treatment"); and cooling the polycarbosilane and returning it to the raw material, and heating it at the first temperature to increase the molecular weight of the polycarbosilane (hereinafter referred to as "high molecular weight treatment"). With such a structure, highly branched polycarbosilane can be produced.

[0097] (Polycarbosilane synthesis process)

[0098] The polycarbosilane synthesis step includes a first heat treatment, a second heat treatment, and a molecular weight increasing treatment, and is a step of synthesizing polycarbosilane from a cyclic silane compound by repeating the reactions of this series of steps.

[0099] The first heat treatment is a treatment in which a raw material containing a cyclic silane compound is heated at a first temperature to generate a gas phase. The raw material containing the cyclic silane compound may be a solid, a liquid, or a mixture of a liquid and a solid. In this specification, the first temperature represents the measurement result of the internal temperature of the reaction container after the raw material is added. That is, the first temperature is the temperature of the contents of the reaction container itself. The first temperature is not particularly limited as long as it is a temperature at which at least a portion of the cyclic silane compound can be vaporized to generate a gas phase. Typically, it can be in the range of 100°C to 500°C, and can be in the range of 400°C to 500°C. By heating at the temperature, the cyclic silane compound is pyrolyzed to generate a gas phase, and a gas phase is also generated by the sublimation or liquefaction of the cyclic silane compound.

[0100] In the method for producing polycarbosilane of one embodiment of the present invention, the cyclic silane compound is a compound having a skeleton consisting only of Si-Si bonds as the main chain and the main chain forming a ring. The number of atoms of the cyclic silane compound used in the method for producing polycarbosilane is preferably 15 or less, more preferably 10 or less, and further preferably 7 or less. In addition, the cyclic silane compound may be a single ring or may have multiple rings. In addition, the side chain of the cyclic silane compound may have an arbitrary structure. Examples of the cyclic silane compound include octamethylcyclotetrasilane, decamethylcyclopentasilane, dodecamethylcyclohexasilane, and tetradecamethylcycloheptasilane. From the viewpoint of raw material supply, the cyclic silane compound is preferably dodecamethylcyclohexasilane.

[0101] The amount of the cyclic silane compound used in the polycarbosilane synthesis step can be appropriately adjusted according to the apparatus for synthesizing polycarbosilane and the desired amount of polycarbosilane to be synthesized.

[0102] The second heat treatment is a treatment for heating the gas phase generated in the first heat treatment at a second temperature higher than the first temperature to generate polycarbosilane. The second heat treatment causes free radical cleavage and rearrangement of Si-Si bonds of the cyclic silane compound, thereby generating polycarbosilane. In this specification, the second temperature refers to the measurement result of the internal temperature of the reaction tube after the gas phase is added when the gas phase generated by the raw material containing the cyclic silane compound is heated. That is, the second temperature is the temperature of the gas phase itself heated in the second heat treatment. The generated polycarbosilane is cooled and returned to the raw material undergoing the first heat treatment.

[0103] From the perspective of the oxygen content of the synthesized polycarbosilane, the oxygen content of the polycarbosilane is not easy to increase, so the second temperature is preferably less than 660°C, more preferably below 650°C, and further preferably below 600°C. The results of the study confirmed that in the method of the present embodiment using a cyclic silane compound as a raw material, if the second temperature becomes higher, the viscosity of the generated polycarbosilane increases significantly, which may cause clogging of the piping depending on the device. Therefore, from the perspective of the operability of the device for synthesizing polycarbosilane, in order to prevent the piping of the device from being clogged by the synthesized polycarbosilane, the second temperature is preferably below 650°C. In addition, from the perspective of rearranging the cyclic silane compound, the second temperature is preferably above 500°C, and from the perspective of increasing the branching of the polycarbosilane, it is preferably above 600°C.

[0104] The high molecular weight treatment is to cool the polycarbosilane generated in the second heat treatment and return it to the raw material, and then heat it at the first temperature to perform a high molecular weight treatment of the polycarbosilane. The high molecular weight treatment can condense the polycarbosilane generated by the second heat treatment to achieve high molecular weight. The cooling temperature is not particularly limited as long as it can cool the polycarbosilane in a gaseous state to a temperature that becomes a liquid. The first temperature is the same as the description of the first temperature in the first heat treatment.

[0105] By repeating this series of reactions, the molecular weight of the polycarbosilane gradually increases, thereby obtaining a polycarbosilane having a large molecular weight.

[0106] The synthesis time of the polycarbosilane synthesis step can be appropriately adjusted according to the desired molecular weight and branching of the polycarbosilane. For example, the synthesis time can be set to 4 hours to 10 hours, preferably 4 hours to 8 hours, and more preferably 6 hours to 7 hours.

[0107] Reference Figure 1 , an embodiment of the polycarbosilane synthesis process is described. Figure 1 This is a diagram showing a liquid-gas phase pyrolysis device 10 used for synthesizing polycarbosilane.

[0108] The liquid-gas phase pyrolysis device 10 includes a liquid phase reaction container 1 , a liquid phase heater 2 , a liquid phase thermocouple 3 , a gas phase reaction tube 4 , a gas phase heater 5 , a gas phase thermocouple 6 , a first cooling tube 7 , a flow meter 8 , and a valve 9 .

[0109] First, cyclic polysilane is added to a liquid phase reaction vessel 1, and heated at a first temperature using a liquid phase heater 2 under an inert gas, thereby generating a gas phase. As the inert gas, for example, nitrogen and argon can be used. The first temperature is measured using a liquid phase thermocouple 3. In addition, the amount of the inert gas is adjusted using a flow meter 8.

[0110] Next, the generated gas phase moves to the gas phase reaction tube 4 and is heated at a second temperature using the gas phase heater 5 to generate polycarbosilane. The second temperature is measured using the gas phase thermocouple 6.

[0111] Next, the generated polycarbosilane is cooled by the first cooling pipe 7, and the liquid phase is returned to the liquid phase reaction vessel 1, and heated at the first temperature by the liquid phase heater 2, thereby increasing the molecular weight of the polycarbosilane.

[0112] This series of reactions is repeated, and after a predetermined synthesis time has passed, the liquid phase and the gas phase are cooled, and the synthesized polycarbosilane is collected from the liquid phase reaction vessel 1. In this way, polycarbosilane before molecular weight adjustment is obtained.

[0113] (Molecular weight adjustment step)

[0114] The method for producing polycarbosilane according to one embodiment of the present invention preferably further includes: a molecular weight adjustment step of removing low molecular weight polycarbosilane from the polycarbosilane synthesized by the polycarbosilane synthesis step. The molecular weight adjustment step can increase the average molecular weight of the polycarbosilane. As low molecular weight polycarbosilane, for example, polycarbosilane with a molecular weight of less than 5500 can be listed. In addition, by the molecular weight adjustment step, the bonding index of the polycarbosilane can be increased, and finally a polycarbosilane with a bonding index of more than 2.58 can be obtained. Therefore, according to the method for producing polycarbosilane according to one embodiment of the present invention, highly branched polycarbosilane can be produced. In addition, when the polycarbosilane is used to produce SiC fibers, the fibers are not easily welded during firing, and the generation of decomposition gas is suppressed. Furthermore, by including the molecular weight adjustment step, the SiC fibers become SiC fibers with high tensile strength.

[0115] The molecular weight adjustment step is not particularly limited as long as it can remove low molecular weight polycarbosilane and does not impair the effects of the present application. For example, low molecular weight polycarbosilane can be removed by adding a solvent to the polycarbosilane synthesized in the polycarbosilane synthesis step to remove the dissolved components.

[0116] The solvent added to the polycarbosilane is not particularly limited as long as it is a solvent that can extract low molecular weight polycarbosilane, and can be appropriately selected according to the molecular weight range to be removed. In addition, the solvent can be a single solvent or a mixed solvent. As a single solvent, for example, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, sec-butyl acetate, acetone, methyl ethyl ketone, dichloromethane, hexane and tetrahydrofuran can be listed. In addition, the amount of solvent added can be appropriately set by a person skilled in the art in consideration of the molecular weight range to be removed, for example, it can be 1 to 8 times by weight relative to the polycarbosilane, preferably 5 times by weight.

[0117] The extraction temperature of the dissolved component can be appropriately set by a person skilled in the art, and can be, for example, 20° C. or higher and below the boiling point of the solvent.

[0118] The molecular weight adjustment process can be performed only once or multiple times. From the viewpoint of yield and operability, it is preferably 5 times or less, and more preferably 4 times or less. In the case of multiple molecular weight adjustment processes, the following treatment can be repeated: polycarbosilane synthesized by the polycarbosilane synthesis process is added to the solvent, the dissolved components are removed, and then the solvent is added to the insoluble components to remove the dissolved components. In addition, in the case of multiple molecular weight adjustment processes, the solvent added to the polycarbosilane can be the same solvent each time, or it can be a different solvent. Considering the ease of waste liquid treatment or the ease of solvent treatment, the solvent added to the polycarbosilane in the molecular weight adjustment process is preferably ethyl acetate or hexane. Considering that the polycarbosilane of the desired molecular weight range can be easily obtained by changing the amount of solvent, extraction temperature or number of operations, ethyl acetate is more preferred. As described above, ethyl acetate can be used for only one treatment or multiple treatments. In addition, ethyl acetate can be used for one or more treatments and then treated with hexane.

[0119] (Other processes)

[0120] The production method of one embodiment of the present invention may include other steps in addition to the polycarbosilane synthesis step and the molecular weight adjustment step. The other steps are not particularly limited as long as the effects of the present invention are not impaired.

[0121] The manufacturing method of one embodiment of the present invention may include, after the molecular weight adjustment step, a removal step of adding a solvent to the polycarbosilane after the molecular weight adjustment to remove insoluble components. The removal step can remove impurities contained in the polycarbosilane after the molecular weight adjustment. The insoluble components can be removed, for example, by filtration. The solvent is not particularly limited as long as it is a solvent that can extract polycarbosilane. As solvents, for example: aromatic hydrocarbons such as benzene, toluene, ethylbenzene, xylene and mesitylene; aliphatic hydrocarbons such as hexane, heptane, octane and nonane; and halogenated hydrocarbons such as chloroform and dichloromethane. The amount of solvent added can be an amount in which polycarbosilane will dissolve, and can be appropriately set by a person skilled in the art. The extraction temperature can be appropriately set by a person skilled in the art, for example, it can be room temperature (22°C).

[0122] [3. Method for producing silicon carbide fiber]

[0123] A method for producing silicon carbide fibers according to one embodiment of the present invention comprises: a spinning step of spinning the polycarbosilane according to one embodiment of the present invention into fibers; and a calcining step of calcining the polycarbosilane fibers produced by the spinning step. With such a structure, SiC fibers with high tensile strength can be produced.

[0124] (Spinning process)

[0125] The spinning step is a step of forming the polycarbosilane of one embodiment of the present invention into a fiber. The polycarbosilane of one embodiment of the present invention is the same as described in [1. Polycarbosilane].

[0126] As the spinning method, melt spinning, dry spinning and wet spinning can be listed. From the viewpoint that spinning can be performed even without high temperature conditions and that there is no sharp temperature drop after spinning, thus reducing the deviation of the fiber diameter, dry spinning is preferred. In addition, the polycarbosilane of one embodiment of the present invention has a given number average molecular weight, so dry spinning can be performed well. In the case of dry spinning, spinning can be performed, for example, by the following method. That is, the polycarbosilane of one embodiment of the present invention is dissolved in a solvent to adjust a dry spinning solution. Next, the dry spinning solution is supplied to a spinning device to generate polycarbosilane fibers.

[0127] The solvent for dissolving polycarbosilane may be any solvent that can dissolve polycarbosilane, and examples thereof include aromatic hydrocarbons such as benzene, toluene, ethylbenzene, xylene, and mesitylene; aliphatic hydrocarbons such as hexane, heptane, octane, and nonane; and halogenated hydrocarbons such as chloroform and dichloromethane. Polycarbosilane has excellent solubility and volatility, so toluene or xylene is preferably used.

[0128] The concentration of the dry spinning solution can be appropriately adjusted by those skilled in the art, and can be, for example, 50 to 70%.

[0129] The viscosity of the dry spinning solution can be appropriately adjusted by a person skilled in the art according to the nozzle diameter of the spinning device, for example, when the nozzle diameter is 65 μm, it can be 10 to 30 Pa·s at 25° C. The viscosity can be determined by a known method for measuring the viscosity of a solution, for example, it can be measured using an E-type viscometer.

[0130] The spinning device used for spinning can be any device commonly used in the art. For example, raw silk can be obtained by supplying a dry spinning solution to a spinning device and spinning under the conditions of a spinning nozzle diameter of 65 μm, a discharge pressure of 2 to 3.5 MPa, and a spinning speed of 10 to 30 mg / min. The raw silk produced under such conditions can be, for example, polycarbosilane fibers having a raw silk diameter of 17.0 to 19.0.

[0131] (Firing process)

[0132] The calcining step is a step of calcining the polycarbosilane fibers produced in the spinning step. The polycarbosilane fibers are calcined to form ceramics, thereby producing silicon carbide fibers.

[0133] The firing conditions can be appropriately set by a person skilled in the art. For example, the firing can be performed under the conditions described in Table 1 described below. Alternatively, the firing can be performed under the conditions where the maximum temperature in Table 1 is changed to 1400°C.

[0134] The tensile strength can be measured by a known method. For example, the breaking stress can be measured by performing a tensile test on a single fiber, and the tensile strength can be obtained by dividing the cross-sectional area of ​​the SiC fiber by the breaking stress.

[0135] The tensile modulus is a value calculated by dividing the elongation relative to the gauge length in a tensile test by the obtained tensile strength.

[0136] The tensile strength of the silicon carbide fiber produced by the method for producing silicon carbide fibers according to one embodiment of the present invention is preferably 2.18 GPa or more, and more preferably 2.71 GPa or more.

[0137] 〔Summarize〕

[0138] The polycarbosilane of the first aspect of the present invention has a bonding index represented by the following formula (1), which is an index of the degree of branching, of 2.63 or more, and an oxygen content of 1.15% by weight or less.

[0139] [Formula 22]

[0140]

[0141] [In formula (1), X CH3 , X CH2 , X CH and X C is the value obtained by dividing the weight percentage of primary carbon atoms, secondary carbon atoms, tertiary carbon atoms and quaternary carbon atoms by 12; SiH3 , Y SiH2 , Y SiH and Y Si It is the value obtained by dividing the weight percentage of primary silicon atoms, secondary silicon atoms, tertiary silicon atoms and quaternary silicon atoms by 28.086.]

[0142] The polycarbosilane of the second aspect of the present invention, in the first aspect, preferably has a number average molecular weight of less than 6,000.

[0143] The method for producing polycarbosilane of scheme 3 of the present invention is a method for producing polycarbosilane as described in scheme 1 or scheme 2, which includes a polycarbosilane synthesis step, and the polycarbosilane synthesis step includes repeatedly performing the following treatments: heating a raw material containing a cyclic silane compound at a first temperature to generate a gas phase; heating the gas phase at a second temperature higher than the first temperature to generate polycarbosilane; and cooling the polycarbosilane and returning it to the raw material, and heating it at the first temperature to increase the molecular weight of the polycarbosilane.

[0144] The method for producing polycarbosilane according to aspect 4 of the present invention is preferably in aspect 3, further comprising a molecular weight adjustment step of removing low molecular weight polycarbosilane from the polycarbosilane synthesized in the polycarbosilane synthesis step.

[0145] In the method for producing polycarbosilane according to aspect 5 of the present invention, in aspect 3 or 4, it is preferred that the second temperature is 650° C. or lower.

[0146] In the method for producing polycarbosilane according to aspect 6 of the present invention, in any one of aspects 3 to 5, it is preferred that the cyclic silane compound is dodecamethylcyclohexasilane.

[0147] A method for producing silicon carbide fibers according to a seventh aspect of the present invention comprises: a spinning step of forming the polycarbosilane according to the first or second aspect into fibers; and a calcining step of calcining the polycarbosilane fibers produced by the spinning step.

[0148] The method for producing silicon carbide fibers according to aspect 8 of the present invention is preferably such that in aspect 7, in the spinning step, the polycarbosilane is formed into fibers by dry spinning.

[0149] Example

[0150] The following examples are shown to further illustrate embodiments of the present invention. Of course, the present invention is not limited to the following examples, and it is beyond doubt that various schemes can be adopted for details. It should be noted that the reagents and devices of the manufacturers not recorded in the examples use the reagents and devices commonly used in the art.

[0151] 〔1. Synthesis of polycarbosilane (PCS)〕

[0152] [Synthesis example 1]

[0153] Dodecamethylcyclohexasilane (DMCHS) was added to Figure 1The liquid phase in the liquid phase reaction vessel of the liquid phase-gas phase pyrolysis device shown in FIG. Next, the liquid phase in the liquid phase reaction vessel is heated to 400-500° C., and the gas phase in the gas phase reaction tube is heated to 650° C., and the reaction is carried out for 4 hours and 25 minutes to synthesize PCS. DMCHS uses DMCHS manufactured according to a known manufacturing method.

[0154] [Synthesis example 2]

[0155] PCS was synthesized in the same manner as in Synthesis Example 1 except that the gas phase in the gas phase reaction tube was heated to 600° C. and the reaction time was set to 6 hours.

[0156] [Synthesis example 3]

[0157] PCS was synthesized in the same manner as in Synthesis Example 2 except that the reaction time was changed to 6 hours and 30 minutes.

[0158] [Synthesis Example 4]

[0159] Polydimethylsilane (PDMS) was added to the liquid phase reaction vessel instead of DMCHS. Then, the liquid phase in the liquid phase reaction vessel was heated to 400-500°C, and the gas phase in the gas phase reaction tube was heated to 600°C. The reaction was carried out for 5 hours to synthesize PCS.

[0160] [Synthesis example 5]

[0161] PCS was synthesized in the same manner as in Synthesis Example 4 except that the reaction time was changed to 8 hours.

[0162] [Synthesis Example 6]

[0163] An attempt was made to synthesize PCS in the same manner as in Synthesis Example 4 except that the gas phase in the gas phase reaction tube was heated to 670° C. However, the synthesis was interrupted because the gas phase reaction product clogged the various pipes during the reaction.

[0164] [Synthesis Example 7]

[0165] An attempt was made to synthesize PCS in the same manner as in Synthesis Example 1 except that the gas phase in the gas phase reaction tube was heated to 670° C. However, the synthesis was interrupted because the gas phase reaction product clogged the various pipes during the reaction.

[0166] [Synthesis example 8]

[0167] PCS was synthesized in the same manner as in Synthesis Example 1 except that the gas phase in the gas phase reaction tube was heated at 660° C. and the reaction time was 1.5 hours.

[0168] 〔2. Molecular weight adjustment and impurity removal〕

[0169] [Example 1]

[0170] The molecular weight was adjusted by washing 4 times at 50°C with ethyl acetate in an amount 5 times the weight of the PCS synthesized in Synthesis Example 1, separating the soluble component and the insoluble component. Then, the molecular weight was adjusted by washing the insoluble component with hexane at room temperature, separating the soluble component and the insoluble component. Next, the obtained insoluble component was dissolved in toluene at room temperature. The PCS obtained by removing the solvent after removing the insoluble component by filtration was used as Example 1.

[0171] [Examples 2 to 5]

[0172] The molecular weight was adjusted by washing 1 to 4 times at 50°C with ethyl acetate in an amount 5 times the weight of the PCS synthesized in Synthesis Example 2 to separate the soluble component and the insoluble component. Then, the insoluble component was dissolved in toluene at room temperature. The PCS obtained by removing the solvent after removing the insoluble component by filtration was designated as Examples 2 to 5.

[0173] [Example 6 and Comparative Examples 1 to 3]

[0174] PCS was obtained in the same manner as in Example 5 except that ethyl acetate was used in an amount 5 times the weight of the PCS synthesized in Synthesis Examples 3 to 5 and 8. Synthesis Example 3 was used in Example 6, Synthesis Examples 4 to 5 were used in Comparative Examples 1 and 2, respectively, and Synthesis Example 8 was used in Comparative Example 3.

[0175] [Example 7]

[0176] The PCS synthesized in Synthesis Example 3 was dissolved in toluene at room temperature without molecular weight adjustment, and then filtered to remove insoluble components. The PCS obtained by removing the solvent was used as Example 7.

[0177] 〔3. Spinning〕

[0178] The PCS from which the insoluble components were removed was dissolved in xylene so that the viscosity of the spinning solution at 25°C was 14 to 25 Pa·s, thereby preparing a dry spinning solution. The prepared solution was then extruded from a spinneret (nozzle) having a nozzle diameter of 65 μm and wound to obtain polycarbosilane fibers (raw silk) having a yarn diameter of 17 to 19 μm.

[0179] 〔4. Firing〕

[0180] The PCS raw yarns of Examples 1 to 7 and Comparative Examples 1 and 2 were sintered at a maximum temperature of 1000° C. under the conditions shown in Table 1 to obtain silicon carbide fibers.

[0181] [Table 1]

[0182]

[0183] Silicon carbide fibers were obtained by firing the PCS raw yarns of Examples 4, 6 to 7 and Comparative Example 1 under conditions where the maximum temperature was changed to 1400°C.

[0184] 〔5. Evaluation〕

[0185] (Elemental Analysis)

[0186] The oxygen content of the PCS synthesized in Synthesis Examples 1 to 5 and 8, and the PCS after the insoluble component removal process of Examples 1 to 7 and Comparative Examples 1 to 3 was measured using EMGA-930 manufactured by Horiba, Ltd. The elemental analysis value of the number of carbon atoms of the PCS synthesized in Synthesis Examples 1 to 5 and 8, and the PCS after the insoluble component removal process of Examples 1 to 7 and Comparative Examples 1 to 3 was measured using a carbon-sulfur analyzer CS844 manufactured by LECO, and the elemental analysis value of hydrogen atoms was measured using a Series II CHNS / O ANLYZER 2400 manufactured by PerkinElmer. The elemental analysis value of silicon atoms is the remaining amount after removing the elemental analysis values ​​of carbon and hydrogen and the oxygen content from the total ratio (100%).

[0187] (Determination of Molecular Weight)

[0188] The molecular weights of the PCS synthesized in Synthesis Examples 1 to 5 and 8 and the PCS after the insoluble component removal step in Examples 1 to 7 and Comparative Examples 1 to 3 were determined by GPC measurement under the following conditions.

[0189] Apparatus name: HPLC manufactured by Shimadzu Corporation.

[0190] Chromatographic columns: One each of KF-604, KF-602, and KF-601 (all manufactured by Showa Denko K.K.) were connected and used so as to flow liquid in sequence from the pump side.

[0191] Measurement solvent: toluene.

[0192] Flow rate: analytical part and reference: 0.40 mL / min.

[0193] Oven: 40℃.

[0194] Detector: Differential refractometer (RID-20A manufactured by Shimadzu Corporation).

[0195] Sample solution: 0.5 wt%.

[0196] ( 1 H-NMR analysis)

[0197] The PCS synthesized in Synthesis Examples 1 to 5 and 8, and the PCS of Examples 1 to 7 and Comparative Examples 1 to 3 were dissolved in deuterated chloroform and subjected to the following conditions: 1 H-NMR analysis. The signal of 5.5 to 3.5 ppm is taken as the signal from hydrogen on tertiary silicon (-SiH<), the signal of 1.0 to 0 ppm is taken as the signal from hydrogen on primary carbon (CH3-), the signal of 0 to -0.4 ppm is taken as the signal from hydrogen on secondary carbon (-CH2-), and the signal of -0.4 to -1.0 ppm is taken as the signal from hydrogen on tertiary carbon (-CH<), and the integral value is calculated. It should be noted that the signal from hydrogen on primary and secondary silicon cannot be confirmed.

[0198] Measuring equipment: JNM-ECZ600R / S1 (manufactured by JEOL Ltd.).

[0199] Cumulative number of times: 8 times.

[0200] ( 29 Si-NMR analysis)

[0201] The PCS synthesized in Synthesis Examples 1 to 5 and 8, and the PCS of Examples 1 to 7 and Comparative Examples 1 to 3 were dissolved in deuterated chloroform and subjected to the following conditions: 29 Si-NMR analysis: The signal from 10 to -8 ppm was regarded as the signal from quaternary silicon (>Si<), and the signal from -8 to -24 ppm was regarded as the signal from tertiary silicon (-SiH<), and the integral value was calculated. It should be noted that the signals from primary silicon and secondary silicon could not be confirmed.

[0202] Measuring equipment: JNM-ECZ600R / S1 (manufactured by JEOL Ltd.).

[0203] Details of the measurement method: The measurement was carried out under a pulse sequence with no rotation; 45 degree pulse irradiation; acquisition time 0.659 seconds; and delay interval 16 seconds.

[0204] Cumulative number of times: 512 times.

[0205] (Determination of Spinning Solution Viscosity)

[0206] An E-type viscometer (ARES-G2 manufactured by TA Instruments) was used at a temperature of 25°C and a shear rate of 200 sec. -1 The viscosity of the dry spinning solution was measured under the conditions of .

[0207] (Calculation of bonding index)

[0208] Calculations were performed according to the formulas (1) to (20) described in the above embodiment. However, primary silicon and secondary silicon were not confirmed.

[0209] (Operability)

[0210] The operability of the liquid-gas phase pyrolysis device in the synthesis of polycarbosilane was evaluated for each test area. If the evaluation was qualified or good, it can be said that there was no obstacle to the synthesis of polycarbosilane. It should be noted that metal pipes with a nominal diameter of 15A were used as the device piping.

[0211] Good: The viscosity of the polycarbosilane flowing in the pipe is low, and the possibility of causing pipe clogging during operation is low.

[0212] Acceptable: The viscosity of the polycarbosilane flowing in the pipe is high, and the pipe needs to be heated appropriately to prevent clogging during operation. In addition, solid matter adheres to the outlet of the gas phase reaction tube, and a part of the pipe is narrow.

[0213] Unqualified: The viscosity of the polycarbosilane flowing in the pipe was very high, and a large amount of solid matter adhered to the outlet of the gas phase reaction tube. As a result, the pipe was clogged, making it difficult to complete the operation.

[0214] (yield)

[0215] The yield in the polycarbosilane synthesis step was calculated as a weight yield expressed as a percentage by dividing the weight of PCS obtained from the liquid phase reaction vessel by the weight of the raw materials charged into the reaction vessel.

[0216] The PCS yield after molecular weight adjustment was calculated as a weight yield in percentage by dividing the dry weight of PCS obtained after the step of removing insoluble components following molecular weight adjustment by the weight of PCS before molecular weight adjustment.

[0217] (Wire diameter)

[0218] The diameter of the SiC fiber was measured at a magnification of 2000 times using an optical microscope VHX-5000 manufactured by KEYENCE CORPORATION.

[0219] (Tensile Strength)

[0220] The tensile test of the single filament was carried out using STA-1150 manufactured by ORIENTEC Co., Ltd. with a gauge length of 25 mm and a crosshead speed of 5 mm / min to measure the breaking stress. The breaking stress measured was divided by the cross-sectional area of ​​the SiC fiber to obtain the tensile strength. The tensile strength of this embodiment was the average value of 10 tensile tests.

[0221] (tensile modulus)

[0222] The tensile modulus is calculated by dividing the tensile strength obtained by the elongation relative to the gauge length during the tensile test.

[0223] 〔6. Results〕

[0224] The above evaluation results are shown in Tables 2 to 5. Specifically, the evaluation results of PCS after synthesis are shown in Table 2, the evaluation results of PCS after the molecular weight adjustment and insoluble component removal steps are shown in Table 3, the evaluation results of PCS fibers after spinning are shown in Table 4, and the evaluation results of SiC fibers after calcination are shown in Table 5. It should be noted that in Tables 2 to 5, the items for which data were not measured are recorded as "rods and lines", and the items for which data could not be measured are recorded as "unable to be measured".

[0225] [Table 2]

[0226]

[0227] [Table 3]

[0228]

[0229] [Table 4]

[0230]

[0231] [Table 5]

[0232]

[0233] In addition, a graph showing the relationship between the bonding index of polycarbosilane and the tensile strength of SiC fiber is shown in FIG. Figure 2 . Figure 2 In the figure, the horizontal axis represents the bonding index of the polycarbosilane of Examples 1 to 7 and Comparative Examples 1 to 2, and the vertical axis represents the tensile strength of the SiC fibers produced by Examples 1 to 7 and Comparative Examples 1 to 2. The range surrounded by the dotted line represents a range where the bonding index is greater than 2.58 and the tensile strength is greater than 1.50 GPa. The range surrounded by the light gray line represents a range where the bonding index is greater than 2.58 and the tensile strength is greater than 2.18 GPa. The range surrounded by the dark gray line represents a range where the bonding index is greater than 2.63 and the tensile strength is greater than 2.71 GPa.

[0234] The above results show that the polycarbosilane produced from the cyclic silane compound has a higher bonding index than the polycarbosilane produced from the acyclic polysilane. Therefore, it is shown that the polycarbosilane of one embodiment of the present invention is a highly branched polycarbosilane. Figure 2 It was shown that highly branched polycarbosilane improves the tensile strength of SiC fibers. Therefore, it was shown that the tensile strength of SiC fibers produced using the polycarbosilane of one embodiment of the present invention becomes higher.

[0235] Industrial Applicability

[0236] The polycarbosilane according to one embodiment of the present invention can be preferably used as a raw material for silicon carbide fibers.

[0237] Description of Reference Numerals

[0238] 1: Liquid phase reaction vessel;

[0239] 2: Liquid phase heater;

[0240] 3: Liquid phase thermocouple;

[0241] 4: Gas phase reaction tube;

[0242] 5: Gas phase heater;

[0243] 6: Gas phase thermocouple;

[0244] 7: first cooling pipe;

[0245] 8: Flow meter;

[0246] 9: Valve;

[0247] 10: Liquid-gas phase pyrolysis device.

Claims

1. A polycarbosilane having a bonding index represented by the following formula (1) as an index of the degree of branching of 2.63 or more, [Formula 1] The oxygen content is 1.15% by weight or less, In formula (1), X CH3 , X CH2 , X CH and X C is the value obtained by dividing the weight percentage of primary carbon atoms, secondary carbon atoms, tertiary carbon atoms and quaternary carbon atoms by 12. SiH3 , Y SiH2 , Y SiH and Y Si These are values ​​obtained by dividing the weight % of each of primary silicon atoms, secondary silicon atoms, tertiary silicon atoms, and quaternary silicon atoms by 28.

086.

2. The polycarbosilane according to claim 1, wherein The number average molecular weight is less than 6000.

3. A method for producing polycarbosilane, the method for producing polycarbosilane is a method for producing the polycarbosilane as described in claim 1 or 2, comprising a polycarbosilane synthesis step, the polycarbosilane synthesis step comprising repeatedly performing the following treatments: heating a raw material containing a cyclic silane compound at a first temperature to thereby generate a gas phase; heating the gas phase at a second temperature higher than the first temperature to generate polycarbosilane; and cooling the polycarbosilane and returning it to the raw material, and heating it at the first temperature to thereby perform a treatment to increase the molecular weight of the polycarbosilane.

4. The method for producing polycarbosilane according to claim 3, wherein: The method for producing polycarbosilane further includes a molecular weight adjustment step of removing low molecular weight polycarbosilane from the polycarbosilane synthesized in the polycarbosilane synthesis step.

5. The method for producing polycarbosilane according to claim 3, wherein: The second temperature is 650° C. or lower.

6. The method for producing polycarbosilane according to claim 3, wherein: The cyclic silane compound is dodecamethylcyclohexasilane.

7. A method for producing silicon carbide fiber, the method comprising: A spinning step of forming the polycarbosilane as claimed in claim 1 or 2 into a fiber; and a calcining step of calcining the polycarbosilane fibers produced by the spinning step.

8. The method for producing silicon carbide fiber according to claim 7, wherein: In the spinning step, the polycarbosilane is formed into fibers by dry spinning.

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