WO2019065018A1 - 黒鉛材料 - Google Patents

黒鉛材料 Download PDF

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WO2019065018A1
WO2019065018A1 PCT/JP2018/031214 JP2018031214W WO2019065018A1 WO 2019065018 A1 WO2019065018 A1 WO 2019065018A1 JP 2018031214 W JP2018031214 W JP 2018031214W WO 2019065018 A1 WO2019065018 A1 WO 2019065018A1
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specific resistance
graphite material
less
graphite
ratio
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PCT/JP2018/031214
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English (en)
French (fr)
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薄葉　秀彦
俊哉 鈴木
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新日本テクノカーボン株式会社
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Priority to ES18860329T priority Critical patent/ES2937687T3/es
Priority to EP18860329.4A priority patent/EP3549925B1/en
Priority to CN201880009042.8A priority patent/CN110248911B/zh
Priority to KR1020197021877A priority patent/KR102119563B1/ko
Priority to US16/476,966 priority patent/US10550001B2/en
Priority to JP2019525930A priority patent/JP6595150B2/ja
Publication of WO2019065018A1 publication Critical patent/WO2019065018A1/ja

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    • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
    • C04B35/52—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbon, e.g. graphite
    • C04B35/522—Graphite
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    • C04B35/52—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbon, e.g. graphite
    • C04B35/528—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbon, e.g. graphite obtained from carbonaceous particles with or without other non-organic components
    • C04B35/532—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbon, e.g. graphite obtained from carbonaceous particles with or without other non-organic components containing a carbonisable binder
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B3/00—Ohmic-resistance heating
    • H05B3/10—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor
    • H05B3/12—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material
    • H05B3/14—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material the material being non-metallic
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B3/00—Ohmic-resistance heating
    • H05B3/10—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor
    • H05B3/12—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material
    • H05B3/14—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material the material being non-metallic
    • H05B3/145—Carbon only, e.g. carbon black, graphite
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Definitions

  • the present invention relates to a graphite material suitable for a graphite heater.
  • Graphite materials have high heat resistance in a non-oxidizing atmosphere, and are widely used as materials for various applications requiring high temperatures, such as graphite heaters, jigs and devices. However, its properties are known to change depending on the temperature to which it is exposed, and in particular, the resistivity is different from metal materials etc., and the resistivity decreases as the temperature rises, and it reverses after a certain temperature. Resistivity is known to rise.
  • the method of using this graphite material as a heat source may use arc discharge at the tip or joule heating of the main body, but in either case, the specific resistance at high temperature becomes important . In the case of arc discharge, a low resistivity is desirable in order to efficiently supply power when the body resistance is low.
  • Patent Document 1 discloses a method of producing isotropic graphite having high specific resistance by adding graphite powder to coke powder as a raw material filler, but the high temperature specific resistance Is not mentioned and is not considered enough.
  • Patent Document 2 proposes a graphite material and manufacturing method in which the resistance change rate at high temperature is suppressed to within 15% by adding titanium element, aluminum element and boron element in addition to coke powder and graphite powder as raw material filler.
  • the metal-based element contained in the described graphite material is not preferable because it becomes an impurity in a semiconductor manufacturing apparatus or the like.
  • An object of the present invention is to provide a graphite material suitable as a heating element utilizing Joule heat generation, which has a small difference between the resistance at room temperature and the resistance at high temperature without adding a metal compound as an impurity.
  • a graphite material is an aggregate of minute graphite crystals, and the specific resistance changes depending on the size of the crystal particles, and the behavior to temperature change also changes.
  • the specific resistance at room temperature is low, and when the temperature is high, the specific resistance tends to increase.
  • the specific resistance at room temperature becomes large, and when the temperature is raised, the specific resistance tends to decrease in the low temperature range, and the specific resistance tends to increase when it exceeds a certain temperature range.
  • the size of the crystal is influenced by the raw material and manufacturing method of the graphite material.
  • coke powder, graphite powder, natural graphite powder, carbon black and the like are used as the aggregate, and tar, pitch and the like are used as the binder, and these are crushed, heat-kneaded (bonded), crushed, shaped, fired, Although it is made into a graphite material through each process of graphitization, it changes with kinds, combination of these materials, and manufacturing conditions.
  • the present inventors examined the morphology of many aggregates, the average particle size, the compounding amount, and the compounding amount of the binder, and as a result of earnestly examining the properties of the graphite material, Joule heat is generated stably even in a high temperature range.
  • a graphite material having optimum resistance characteristics that can be made to achieve the present invention.
  • the resistivity ( 25 25 ) at 25 ° C. is 10.0 ⁇ ⁇ m or more and 12.0 ⁇ ⁇ m or less
  • the resistivity ( ⁇ 1600 ) at 1600 ° C. is 9.5 ⁇ ⁇ m or more .0 ⁇ ⁇ m or less
  • the ratio ( ⁇ 1600 / ⁇ 25 ) of specific resistance at 25 ° C. and 1600 ° C. is 0.85 or more and 1.00 or less
  • the temperature showing the minimum specific resistance ( ⁇ min ) is 500 ° C. or higher , 800 ° C.
  • the minimum specific resistance and the specific resistivity at 25 °C ( ⁇ min / ⁇ 25 ) is 0.70 or more and 0.80 or less, and a bulk density of 1.69 g / cm 3 or more, 1 It is a graphite material characterized by having .80 g / cm 3 or less.
  • the interplanar distance of the hexagonal carbon layers (d 002) is more than 0.3360 nm, 0.3365 nm or less, the c-axis direction of crystallites showing the thickness of the carbon net plane layer are laminated size (Lc) is 55 nm or more and 85 nm or less, and the size (La) in the a-axis direction of the crystallite showing the spread of the carbon network plane is 60 nm or more and 105 nm or less, and the degree of graphitization (P1) is 0 Preferably, it is not less than .53 and not more than 0.60.
  • the graphite material of the present invention can be suitably used as a graphite heater used utilizing Joule heat generation.
  • the degree of graphitization P1 corresponds to the probability that adjacent mesh planes will form a graphitic arrangement. It is obtained from Fourier analysis of the intensity distribution of two-dimensional (hk) diffraction in the X-ray diffraction pattern. Also, the product of the value of Lc indicating the thickness at which the carbon network layer is stacked, the value of La indicating the spread of the carbon network plane, and the P1 value indicating the degree of graphitization is the free electron in the unit volume of the graphite material. If this value is 1900 nm 2 or more, it can be said that there are enough free electrons. On the other hand, if this value exceeds 5000 nm 2 , although there are sufficient free electrons, the influence of the thermal movement of the carbon network surface in a high temperature state becomes large, and the specific resistance tends to be greatly increased.
  • the joule heating element using the graphite material according to the present invention has a good balance of the specific resistance at 25 ° C. and the specific resistance at 1600 ° C., and can efficiently perform heating up to a region of 1600 ° C. or more. In addition, it is possible to provide a heating device that has high heating efficiency and is easy to control.
  • the graphite material of the present invention has a specific resistance ( ⁇ 25 ) at 25 ° C. of 10.0 to 12.0 ⁇ ⁇ m, and a specific resistance ( ⁇ 1600 ) at 1600 ° C. of 9.5 to 11.0 ⁇ ⁇ m
  • the ratio ( ⁇ 1600 / ⁇ 25 ) of specific resistance at 25 ° C. and 1600 ° C. is 0.85 to 1.00.
  • the ratio of specific resistances ( 1600 1600 / ⁇ 25 ) is also referred to as the specific resistance change rate.
  • the specific resistance change rate can also be expressed as a specific resistance decrease rate (100-100 1600 1600 / ⁇ 25 ), and is 15% or less.
  • the temperature showing the minimum specific resistance min min is 500 to 800 ° C.
  • the minimum specific resistance ( ⁇ min ) is 7.0 to 9.0 ⁇ ⁇ m
  • the ratio of the minimum specific resistance to the specific resistance at 25 ° C. ( ⁇ min / ⁇ 25 ) is 0.70 to 0.80.
  • the ratio of specific resistance ( ⁇ min / / 25 ) is also referred to as the minimum specific resistance change rate.
  • the graphite material of the present invention has a bulk density of 1.69 to 1.80 g / cm 3 , preferably 1.69 to 1.75 g / cm 3 .
  • the product (Lc ⁇ La ⁇ P1) may be 1900 to 5000 nm 2 , preferably 3000 to 5000 nm 2 .
  • the above (P1), (d 002 ), (Lc) and (La) are related to the graphitization degree, but (Lc) and (La) are related to the crystallite size, and these have simple correlations
  • (d 002 ) tends to decrease as the degree of graphitization increases and others increase as the degree of graphitization increases, these values may be adjusted by adjusting the graphitization temperature, It can control by selecting the graphitizable raw material, changing the amount of use, etc.
  • the product (Lc ⁇ La ⁇ P1) is a product of numerical values indicating the crystallinity and graphitization degree of the graphite material. By setting this range to the above range, the specific resistance at each temperature is maintained high. It has been found that the rate of change in specific resistance can be suppressed.
  • the graphite material of the present invention can be suitably used as a graphite heater used utilizing Joule heat generation, and is particularly useful as a graphite heater for heating a graphite crucible containing a quartz crucible as a component for a semiconductor pull-up device.
  • the method to manufacture the graphite material of this invention is not specifically limited, For example, it can obtain by the manufacturing method which has the following processes.
  • a step of grinding aggregate to be a raw material to a predetermined particle diameter (pulverizing step), a step of mixing the crushed aggregate and binder in a predetermined ratio, and heating and kneading (composition step), and this intermediate material (composition) Product) is crushed to a predetermined particle size, filled into a rubber mold and the like (molding process), the obtained molded product is heated and fired in a non-oxidative atmosphere (baking process), and the fired product is
  • a graphitic material can be obtained by passing through the step of graphitizing by heating from 2800 ° C. to 3000 ° C. in a non-oxidative atmosphere (graphitization step).
  • pitch coke obtained by heating and coke-izing raw material pitches, such as petroleum-based pitch and coal-based pitch.
  • Pitch coke can control its morphology by adjusting the characteristics of the raw material pitch.
  • pitch coke is a mixture of a flow texture portion in which graphite crystals easily develop and an amorphous texture portion in which graphite crystals hardly develop, and the proportion of these textures is controlled by adjusting the characteristics of the raw material pitch.
  • graphite materials such as natural graphite and artificial graphite other than pitch coke, can also be used as an aggregate.
  • the pitch coke and the graphite material are mixed and used.
  • Two or more types of pitch coke and a graphite material can be used, respectively.
  • a mixed material of 40 to 60 parts by weight of pitch coke (needle coke) in which crystal structures are aligned in one direction and 40 to 60 parts by weight of amorphous pitch coke (amorphous coke) having random crystal directions is preferable.
  • a mixed material of 40 to 60 parts by weight of pitch coke and 40 to 60 parts by weight of graphite is also suitable.
  • the binder a material having a high carbonization yield is preferable, and a resin-based or pitch-based binder can be used, but it is desirable to use a binder pitch using coal-based pitch as a raw material.
  • the blending ratio of the aggregate and the binder is preferably 50 to 30 parts by weight of the binder with respect to 50 to 70 parts by weight of the aggregate.
  • the aggregate is ground beforehand to a predetermined particle size of median particle size 5 to 70 ⁇ m, preferably 5 to 20 ⁇ m, blended with a binder having a particle size of 5 mm or less, and then heat-kneaded at 200 ° C. to 300 ° C. Get the goods.
  • a common kneader can be used for the mixing, but a kneader capable of heating is suitable.
  • the obtained composite is once cooled and then crushed to a predetermined particle size, for example, 5 to 70 ⁇ m, preferably 20 to 60 ⁇ m by a grinder.
  • the pulverized product is filled in a mold such as a rubber mold or a rubber case and sealed, and then a pressure of, for example, 0.5 to 2.0 t / cm 2 is applied to obtain a molded article.
  • a pressure of, for example, 0.5 to 2.0 t / cm 2 is applied to obtain a molded article.
  • the resulting molded product is fired at about 800 ° C. to 1000 ° C. in a non-oxidizing atmosphere to obtain a fired product, which is further heated at 2800 ° C. to 3000 ° C. in a non-oxidizing atmosphere to graphitize to obtain a graphite material .
  • the measurement method will be described below.
  • the X-ray diffraction test was carried out by using a CuK ⁇ ray by an Ultima 3 system manufactured by Rigaku Corporation, and the applied voltage to the X-ray tube was 40 kV and the current was 20 mA.
  • the scanning speed of the counter was 2 ° / min, the scanning range was 10 ° to 90 °, and was measured at 0.02 ° intervals.
  • the value of (d 002 ) is the position (angle) of the peak of the (002) plane at a diffraction angle 2 ⁇ of around 26 ° and the (111) plane of metallic silicon at a diffraction angle 2 ⁇ of around 28 ° previously added as an internal standard.
  • the peak position (angle) of The value of (Lc) is the half width of the peak of the (002) plane at a diffraction angle 2 ⁇ of around 26 ° and the peak of the (111) plane of metallic silicon at a diffraction angle 2 ⁇ of around 28 ° previously added as an internal standard. Determined from the half price range.
  • the value of (La) the half value width of the peak of the (110) plane at a diffraction angle 2 ⁇ of around 77.6 ° and the diffraction angle 2 ⁇ previously added as an internal standard of the metallic silicon of around 76.4 ° (331) From the half width of the peak of the surface, it was calculated and obtained based on the Gakushin method.
  • the P1 value representing the degree of graphitization was determined by the method described in the literature (Iwashita, Carbon, No. 188, p 147 to 151 (1999) “Crystal analysis structure of carbon material by X-ray powder analysis method”). In other words, integration of (hk2) diffraction angles (10 diffraction lines 2 ⁇ : 42.39 to 50.73 °, 11 diffraction lines 2 ⁇ : 77.54 to 83.67 °) from (hk0) diffraction angles is performed at each angle. The Fourier coefficient An (hk) was calculated from the integral value of the product of the intensity and the periodic function to obtain the P1 value.
  • the bulk density was determined by measuring the volume and mass of a sample cut into 10 mm ⁇ 10 mm ⁇ 60 mm, and in accordance with JIS-R 7222-2017 “Method of measuring physical characteristics of graphite material”.
  • the specific resistance value ( ⁇ 25 ) is a 10 mm ⁇ 10 mm ⁇ 60 mm sample cut out and a current of 1 A applied in the longitudinal direction to measure the voltage drop in the 50 mm section, JIS-R7222-2017 “Physical characteristics measurement method of graphite material Calculated according to the method based on The specific resistance value () 1600 ) is a sample of ⁇ 10 mm ⁇ 100 mm cut out, high temperature specific resistance measuring device (Adachi et al., Carbon, No. 146, p33-36 (1991) “temperature of electric specific resistance of polycrystalline graphite at 900 K-2800 K Voltage drop was measured while changing the temperature from 25 ° C. to 1600 ° C.).
  • Example 1 Aggregate coke 1 obtained by grinding pitch coke (needle coke) whose flow structure is observed in polarized light microscope observation to a particle diameter of 15 ⁇ m (the particle diameter is median, the same applies hereinafter), and pitch coke Agglomerate coke 2 is crushed to a particle size of 15 ⁇ m, and a binder B obtained by crushing a coal-based binder pitch having a softening point of 105 ° C. to a particle size of 5 mm or less is blended at a ratio of 30:30:40 by weight. The mixture was heated and kneaded at 200 to 300.degree. C. in a kneader and then mixed.
  • the composite was reground to about 50 ⁇ m, filled into a rubber case, and molded by a hydrostatic press at a pressure of 1 t / cm 2 .
  • the obtained molded product was fired to 1000 ° C. in a non-oxidizing atmosphere to obtain a fired product, and this was further heated to 3000 ° C. in a non-oxidizing atmosphere to graphitize to obtain a graphite material 1.
  • Example 2 In the same manner as in Example 1, except that the aggregate 1, the aggregate 2 and the binder B were compounded in a ratio of 33:33:34 by weight, respectively, they were bonded, crushed, molded, calcined and graphitized. , Graphite material 2 was obtained.
  • Example 3 In the same manner as in Example 1, except that the aggregate 1 and the aggregate 3 obtained by grinding an artificial graphite powder to a particle size of 70 ⁇ m and the binder B were blended in a ratio of 40:20:40 by weight, respectively, The resultant was ground, molded, fired, and graphitized to obtain a graphite material 3.
  • Comparative Example 1 In the same manner as in Example 1, except that the aggregate 2, the aggregate 3 and the binder B were blended in a ratio of 45:15:40 by weight, respectively, they were bonded, crushed, molded, calcined, graphitized, , And a graphite material C1.
  • Comparative example 2 In the same manner as in Example 1 except that the aggregate 2 and the binder B were blended in a ratio of 65: 35 by weight, respectively, they were bonded, crushed, molded, fired and graphitized to obtain a graphite material C 2 .
  • Comparative example 3 Same as Example 1, except that the aggregate 2 and the aggregate 4 consisting of carbon black and the binder B were blended in a ratio of 55:10:35 by weight, respectively, and they were bonded, crushed, molded, and fired. And graphitized to obtain a graphite material C3.
  • Comparative example 4 In the same manner as in Example 1, except that the aggregate 2 and the binder B were blended in a ratio of 65: 35 by weight, respectively, they were bonded, crushed, molded, fired, and graphitized to obtain a graphite material C4. .
  • Comparative example 5 The aggregate 5 in which needle coke was crushed to a particle diameter of 2 mm and the binder B were blended at a weight ratio of 65:35, respectively, and were heat-kneaded at 150 to 250 ° C. in a kneader to be bonded. After cooling, the composite was reground to 50 ⁇ m, filled into a mold, and molded with a 2000 t press. The resulting molded product was fired to 1000 ° C. in a non-oxidative atmosphere to obtain a fired product. This baked product was impregnated with pitch, baked again at 1000 ° C., and further heated to 3000 ° C. in a non-oxidative atmosphere to graphitize, thereby obtaining a graphite material C5.
  • the specific resistance change rate ( ⁇ 1600 / ⁇ 25 ) is desirably closer to 1.0, but Examples 1 to 3 are closer to 1.0 than Comparative Examples 1 to 3 and 5.
  • Comparative Example 4 has a problem that the specific resistance change rate is close to 1.0, but the specific resistance values at 25 ° C. and 1600 ° C. are small, and the cross-sectional area becomes small in the heater design. And about a product (LcxLaxP1), it turns out that specific resistance change rate is far from 1.0 whether the value is smaller or larger than a predetermined range. In all of Examples 1 to 3, the specific resistance is stably maintained in the temperature range of 25 to 1600 ° C., and the specific resistance change rate (specific resistance decrease rate) is also small.
  • a graphite material having well-balanced resistivity at 25 ° C. and 1600 ° C. can be provided, which can contribute to efficient design of a device dependent on the resistivity such as Joule heating.

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Abstract

ジュール発熱を利用する黒鉛材料において、金属系不純物を添加することなく、かつ、室温での抵抗と高温での抵抗のバランスの良いものを提供すること。　２５℃での固有抵抗（ρ25）が１０．０μΩ・ｍ以上、１２．０μΩ・ｍ以下、１６００℃での固有抵抗（ρ1600）が９．５μΩ・ｍ以上、１１．０μΩ・ｍ以下、２５℃と１６００℃の固有抵抗の比（ρ1600／ρ25）が０．８５以上、１．００以下であり、最小固有抵抗値（ρmin）を示す温度が５００℃以上、８００℃以下であり、最小固有抵抗と２５℃での固有抵抗の比（ρmin／ρ25）が０．７０以上、０．８０以下であり、且つかさ密度が１．６９ｇ／ｃｍ３以上１．８０ｇ／ｃｍ３以下である黒鉛材料。

Description

黒鉛材料
　本発明は、黒鉛ヒーター用として好適な黒鉛材料に関するものである。
　黒鉛材料は非酸化性の雰囲気下では高い耐熱性を有し、高温を必要とする各種用途、例えば黒鉛ヒーター、治具や装置の部品材料として広く使用されている。
　しかしながら、その特性は晒されている温度によって変化することが知られており、特に固有抵抗については金属材料等とは異なり、温度が上昇するにつれ固有抵抗が低下し、ある温度を過ぎると反転して固有抵抗が上昇することが知られている。
　この黒鉛材料を発熱源として使用する方法には、先端部でのアーク放電を利用する場合と、本体のジュール発熱を利用する場合があるが、どちらの場合も高温での固有抵抗が重要となる。アーク放電の場合は本体抵抗が低い方が電力の供給を効率よくするために低固有抵抗品が望まれる。一方、ジュール発熱を利用する場合は効率よく発熱させるために、高固有抵抗品が望まれる傾向にあるが、室温での抵抗が高いと高温時の抵抗の低下が大きくなる傾向にあり、電源装置の最高電圧もしくは最高電流の制約から室温の抵抗と高温の抵抗のバランスが重要となる。また、高温での固有抵抗の低下率が小さいものは室温での抵抗が低くなる傾向にあり、必要な発熱量を得るためにはヒーターの設計断面を小さくする必要があり、耐久性が劣る傾向にある。
　このような課題に対して、特許文献１では原料フィラーとしてコークス粉末に黒鉛粉末を添加することで高固有抵抗を有する等方性黒鉛を製造する方法が開示されているが、その高温の固有抵抗の挙動について言及されておらず、十分に検討されてはいない。
　一方、特許文献２では原料フィラーとしてコークス粉末と黒鉛粉末以外にチタン元素やアルミニウム元素及びホウ素元素を添加することにより、高温での抵抗変化率を１５％以内に抑制した黒鉛材及び製造方法が提案されているが、記載された黒鉛材料に含まれる金属系元素は、半導体製造装置等では、不純物となり好ましいものではない。
　また、特許文献３では、１６００℃での固有抵抗を高く維持した黒鉛材が提案されているが、室温の値と比較すると約３０％前後の低下があり、電源装置の出力領域を広く設計する必要があり、やはり好ましいものではない。
特開平２－５９４６８号公報 特開平９－４８６６５号公報 特開２００１－３１４７３号公報
　本発明は、不純物となる金属化合物を添加することなく、室温での抵抗と高温での抵抗の差が小さく、ジュール発熱を利用する発熱体として適した黒鉛材料を提供することを目的とする。
　一般に黒鉛材料は微小な黒鉛結晶の集合体であり、その結晶粒子の大きさによって固有抵抗が変化し、温度変化に対する挙動も変化する。結晶粒子が大きいと室温の固有抵抗は低くなり、高温になると固有抵抗が上昇する傾向となる。一方、結晶粒子が小さいと、室温での固有抵抗が大きくなり、温度上昇させると、低温域では固有抵抗が低下していき、ある温度域を超えると固有抵抗が増大する傾向にある。
　そして、結晶の大きさは黒鉛材料の原料及び製造方法に影響される。具体的には骨材としてはコークス粉、黒鉛粉、天然黒鉛粉、カーボンブラック等を、結合材としてはタール、ピッチ等を用い、これらを粉砕、加熱混練（捏合）、粉砕、成形、焼成、黒鉛化の各工程を経て黒鉛材料とされるが、これらの原料の種類や配合、製造条件によって変化する。
　本発明者らは、多くの骨材の組織形態、平均粒度、配合量、並びに結合材の配合量を検討し、その黒鉛材料の性状を鋭意検討した結果、ジュール発熱を高温域でも安定に生じさせることができる最適な抵抗特性を有する黒鉛材料を見出し、本発明を成すに至った。
　すなわち、本発明は、２５℃での固有抵抗（ρ25）が１０．０μΩ・ｍ以上、１２．０μΩ・ｍ以下、１６００℃での固有抵抗（ρ1600）が９．５μΩ・ｍ以上、１１．０μΩ・ｍ以下、２５℃と１６００℃の固有抵抗の比（ρ1600／ρ25）が０．８５以上、１．００以下であり、最小固有抵抗（ρmin）を示す温度が５００℃以上、８００℃以下、最小固有抵抗と２５℃での固有抵抗の比（ρmin／ρ25）が０．７０以上、０．８０以下であり、且つかさ密度が１．６９ｇ／ｃｍ３以上、１．８０ｇ／ｃｍ３以下であることを特徴とする黒鉛材料である。
　本発明の黒鉛材料は、炭素網面層の面間距離（ｄ００２）が、０．３３６０ｎｍ以上、０．３３６５ｎｍ以下、炭素網面層が積層した厚さを示す結晶子のｃ軸方向の大きさ（Ｌｃ）が５５ｎｍ以上、８５ｎｍ以下、及び炭素網面の広がりを示す結晶子のａ軸方向の大きさ（Ｌａ）が６０ｎｍ以上、１０５ｎｍ以下であり、黒鉛化度を表す（Ｐ１）が０．５３以上、０．６０以下であることが好ましい。Ｌｃ値と、Ｌａ値と、Ｐ１値との積（Ｌｃ×Ｌａ×Ｐ１）が、１９００ｎｍ2以上、５０００ｎｍ2以下であることが好ましい。本発明の黒鉛材料は、ジュール発熱を利用して用いる黒鉛ヒーターとして好適に使用できる。
　黒鉛化度Ｐ１は、隣接網面が黒鉛的配列をとる確率に相当する。Ｘ線回折図中の二次元（ｈｋ）回折の強度分布のフーリエ解析から求められる。また炭素網面層が積層した厚さを示すＬｃの値と、炭素網面の広がりを示すＬａの値と、黒鉛化度を表すＰ１値との積は、黒鉛材単位体積中のフリーの電子の量を代表する値であり、この値が１９００ｎｍ2以上であればフリーの電子が十分にある状態といえる。一方、この値が５０００ｎｍ2を超えるとフリーの電子は十分にあるものの、高温状態での炭素網面の熱運動の影響が大きくなり固有抵抗を大きく上昇させる傾向となる。
　本発明による黒鉛材料を用いたジュール発熱体は、２５℃の固有抵抗と１６００℃の固有抵抗のバランスが良好であり、１６００℃以上域までの加熱を効率よく行うことができる。また、加熱効率がよく、制御が容易な加熱装置を提供可能とする。
　以下、本発明の実施形態について説明する。
　本発明の黒鉛材料は、２５℃での固有抵抗（ρ25）が１０．０～１２．０μΩ・ｍであり、１６００℃での固有抵抗（ρ1600）が９．５～１１．０μΩ・ｍであり、２５℃と１６００℃の固有抵抗の比（ρ1600／ρ25）が０．８５～１．００である。固有抵抗の比（ρ1600／ρ25）を固有抵抗変化率ともいう。固有抵抗変化率は、固有抵抗低下率（100－100ρ1600／ρ25）として表すこともでき、１５％以下である。
　また、最小固有抵抗ρminを示す温度が５００～８００℃であり、最小固有抵抗（ρmin）が７．０～９．０μΩ・ｍであり、最小固有抵抗と２５℃での固有抵抗の比（ρmin／ρ25）が０．７０～０．８０である。固有抵抗の比（ρmin／ρ25）を最小固有抵抗変化率ともいう。
　本発明の黒鉛材料は、かさ密度が１．６９～１．８０ｇ／ｃｍ３ 、好ましくは１．６９～１．７５ｇ／ｃｍ３である。
　本発明の黒鉛材料の結晶構造については、炭素網面層の面間距離（ｄ００２）が、０．３３６０～０．３３６５ｎｍ、炭素網面層が積層した厚さを示す（Ｌｃ）が５５～８５ｎｍ、炭素網面の広がりを示す（Ｌａ）が６０～１０５ｎｍ、黒鉛化度（Ｐ１）が０．５５～０．６０であることが好ましい。
　そして、上記積（Ｌｃ×Ｌａ×Ｐ１）が、１９００～５０００ｎｍ2、好ましくは３０００～５０００ｎｍ2であることがよい。
　上記（Ｐ１）、（ｄ００２）、（Ｌｃ）及び（Ｌａ）は黒鉛化度と関係するが、（Ｌｃ）及び（Ｌａ）は結晶子サイズと関係し、これらが単純な相関関係を有するものではないが、（ｄ００２）は黒鉛化度が高くなると数字が小さくなり、その他は黒鉛化度が高くなると数字が大きくなる傾向があるので、これらの値は黒鉛化温度を調整することや、易黒鉛化性原料を選択したり、その使用量を変えるなどにより制御することができる。
　上記積（Ｌｃ×Ｌａ×Ｐ１）は、黒鉛材料の結晶性及び黒鉛化度を示す数値の積であるが、この範囲を上記範囲にすることにより、各温度における固有抵抗を高く維持しつつ、固有抵抗変化率を抑制できることが見出された。
　本発明の黒鉛材料は、ジュール発熱を利用して用いる黒鉛ヒーターとして好適に使用でき、特に半導体引上装置用部品として石英ルツボを収納する黒鉛ルツボを加熱する黒鉛ヒーター等として有用である。
　本発明の黒鉛材料を製造する方法は特に限定されないが、例えば以下の工程を有する製造方法により得ることができる。
　原料となる骨材を所定の粒径に粉砕する工程（粉砕工程）と、粉砕された骨材と結合材を所定の割合で配合し加熱混練する工程（捏合工程）と、この中間材料（捏合品）を所定の粒径に粉砕し、ゴム型などに充填し成形する工程（成形工程）、得られた成形品を非酸化性雰囲気で加熱し焼成する工程（焼成工程）、焼成した製品を非酸化性雰囲気で２８００℃から３０００℃まで加熱昇温し黒鉛化する工程（黒鉛化工程）を経ることにより黒鉛材料を得ることができる。
　原料となる骨材の一つは石油系ピッチ、石炭系のピッチ等の原料ピッチを加熱、コークス化して得られるピッチコークスである。ピッチコークスは原料ピッチの特性を調整することによりその組織形態をコントロールすることができる。具体的には、ピッチコークスは黒鉛結晶が発達しやすい流れ組織部分と黒鉛結晶の発達しにくいアモルファス組織部分の混合物であり、原料ピッチの特性を調整することにより、これら組織の割合をコントロールすることが可能である。
　また、骨材としてピッチコークスの他に天然黒鉛、人造黒鉛などの黒鉛材を使用することもできる。好ましくは、ピッチコークスと黒鉛材を混合して使用することがよい。ピッチコークスと黒鉛材はそれぞれ２種以上使用することができる。
　特に、結晶組織が一方向に揃ったピッチコークス（ニードルコークス）４０～６０重量部と結晶方向がランダムなアモルファス状のピッチコークス（アモルファスコークス）４０～６０重量部との混合原料が好適である。また、ピッチコークス４０～６０重量部と黒鉛４０～６０重量部との混合原料も好適である。
　結合材としては炭化歩留まりの高い材料が好ましく、樹脂系並びにピッチ系の結合材を使用することができるが、石炭系ピッチを原料としたバインダーピッチを使用することが望ましい。骨材と結合材との配合割合は、骨材５０～７０重量部に対して、結合材５０～３０重量部であることが好ましい。
　骨材は予めメジアン粒径５～７０μｍ、好ましくは５～２０μｍの所定の粒径まで粉砕して、粒径５ｍｍ以下の結合材と配合し、そののち２００℃以上３００℃以下で加熱混練し捏合品を得る。捏合には一般的な混練機を使用することができるが、加熱ができるニーダーが適する。得られた捏合品は一旦冷却したあと、粉砕機により所定の粒径、例えば５～７０μｍ、好ましくは２０～６０μｍまで粉砕する。この粉砕品をゴム型もしくはラバーケースなどの型に充填し密封したのち、例えば０．５～２．０ｔ/ｃｍ2の圧力をかけ成形品を得る。圧力かける方法としては、種々の方法があるが、ラバーケースを用いた場合は静水圧プレス機により加圧することが望ましい。
　得られた成形品を非酸化性雰囲気下で８００℃～１０００℃程度で焼成して焼成品とし、さらにこれを非酸化性雰囲気下で２８００℃～３０００℃で加熱し黒鉛化して黒鉛材料を得る。
　以下、測定方法について説明する。
Ｘ線回折試験は、株式会社リガク製Ｕｌｔｉｍａ３システムにより、ＣｕＫα線を用い、Ｘ線管球への印加電圧は４０ｋＶ、電流は２０ｍＡとした。計数管の走査速度は２°／分、走査範囲は１０°～９０°で、０．０２°間隔で測定した。
　（ｄ００２）の値は、回折角2θが２６°付近の（００２）面のピークの位置（角度）と、内部標準として予め加えた回折角2θが２８°付近の金属ケイ素の（１１１）面のピーク位置（角度）とから求めた。
　（Ｌｃ）の値は、回折角2θが２６°付近の（００２）面のピークの半値幅と、内部標準として予め加えた回折角2θが２８°付近の金属ケイ素の（１１１）面のピークの半値幅とから求めた。（Ｌａ）の値は、回折角2θが７７．６°付近の（１１０）面のピークの半値幅と、内部標準として予め加えた回折角2θは７６．４°付近の金属ケイ素の（３３１）面のピークの半値幅とから、それぞれ学振法に基づいて計算して求めた。
　黒鉛化度を表すＰ１値は、文献記載の方法（岩下，炭素，Ｎｏ１８８，ｐ１４７～１５１（１９９９）「Ｘ線粉末解析法による炭素材料の結晶解析構造」）により求めた。即ち、（ｈｋ０）回折角度から（ｈｋ２）回折角度（１０回折線２θ：４２．３９～５０．７３°、１１回折線２θ：７７．５４～８３．６７°）の積分を行い、各角度における強度と周期関数の積の積分値からフーリエ係数Ａn(ｈｋ)を算出し、Ｐ１値を求めた。
　かさ密度は、１０ｍｍ×１０ｍｍ×６０ｍｍに切り出したサンプルの体積と質量を計測し、ＪＩＳ－Ｒ７２２２－２０１７「黒鉛素材の物理特性測定方法」に準拠した方法により求めた。
　固有抵抗値（ρ25）は、１０ｍｍ×１０ｍｍ×６０ｍｍのサンプルを切り出し長手方向に１Ａの電流を流し、５０ｍｍの区間の電圧降下を測定し、ＪＩＳ－Ｒ７２２２－２０１７「黒鉛素材の物理特性測定方法」に準拠した方法より算出した。
　固有抵抗値（ρ１６００）は、φ１０ｍｍ×１００ｍｍのサンプルを切り出し、高温固有抵抗測定装置（足立ら，炭素，No１４６，ｐ３３～３６（１９９１）「９００Ｋ－２８００Ｋにおける多結晶黒鉛の電気比抵抗の温度依存性」参照）により２５℃から１６００℃まで温度を変化させつつ電圧降下を測定して求めた。
　本発明を実施例と比較例により具体的に説明する。
実施例１
　偏光顕微鏡観察において流れ組織が観察されるピッチコークス（ニードルコークス）を粒径１５μｍ（粒径はメジアンである。以下、同じ。）に粉砕した骨材１と、アモルファス組織が観察されるピッチコークス（アモルファスコークス）を粒径１５μｍに粉砕した骨材２と、軟化点１０５℃の石炭系バインダーピッチを粒径５ｍｍ以下に粉砕した結合材Ｂを、それぞれ重量部で３０：３０：４０の割合で配合し、ニーダーにて２００～３００℃で加熱混練し捏合した。この捏合品を冷却後約５０μｍに再粉砕し、これをラバーケースに充填し、静水圧プレス機により１ｔ/ｃｍ2の圧力で成形した。得られた成形品を非酸化性雰囲気下で１０００℃まで焼成して焼成品とし、さらにこれを非酸化性雰囲気下で３０００℃まで加熱して黒鉛化することで黒鉛材料１を得た。
実施例２
　骨材１と、骨材２と、結合材Ｂを、それぞれ重量部で３３：３３：３４の割合で配合した他は、実施例１と同様にして捏合、粉砕、成形、焼成、黒鉛化して、黒鉛材料２を得た。
実施例３
　骨材１と、人造黒鉛粉を粒径７０μｍに粉砕した骨材３と、結合材Ｂを、それぞれ重量部で４０：２０：４０の割合で配合した他は、実施例１と同様にして捏合、粉砕、成形、焼成、黒鉛化して、黒鉛材料３を得た。
比較例１
　骨材２と、骨材３と、結合材Ｂを、それぞれ重量部で４５：１５：４０の割合で配合した他は、実施例１と同様にして捏合、粉砕、成形、焼成、黒鉛化して、黒鉛材料Ｃ１を得た。
比較例２
　骨材２と、結合材Ｂを、それぞれ重量部で６５：３５の割合で配合した他は、実施例１と同様にして捏合、粉砕、成形、焼成、黒鉛化して、黒鉛材料Ｃ２を得た。
比較例３
　骨材２と、カーボンブラックからなる骨材４、及び結合材Ｂを、それぞれ重量部で５５：１０：３５の割合で配合した他は、実施例１と同様にして捏合、粉砕、成形、焼成、黒鉛化して、黒鉛材料Ｃ３を得た。
比較例４
　骨材２と、結合材Ｂを、それぞれ重量部で６５：３５の割合で配合した他は、実施例１と同様にして捏合、粉砕、成形、焼成、黒鉛化して、黒鉛材料Ｃ４を得た。
比較例５
　ニードルコークスを粒径２ｍｍに粉砕した骨材５と、結合材Ｂを、それぞれ重量部で６５：３５の割合で配合し、ニーダーにて１５０～２５０℃で加熱混練し捏合した。この捏合品を冷却後５０μｍに再粉砕し、これを金型に充填し、２０００ｔのプレス機で成形した。得られた成形品を非酸化性雰囲気下で１０００℃まで焼成して焼成品とした。この焼成品にピッチを含浸し、再度１０００℃で焼成し、さらにこれを非酸化性雰囲気下で３０００℃まで加熱し黒鉛化することで黒鉛材料Ｃ５を得た。
　得られた黒鉛材料の物性測定結果を表１、表２に示した。 
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
　上記のように固有抵抗変化率（ρ1600/ρ25）は、１．０に近いほど望ましいが、実施例１～３は、比較例１～３、及び５より１．０に近い。比較例４は、固有抵抗変化率は１．０に近いが、２５℃及び１６００℃での固有抵抗値が小さく、ヒーター設計ではその断面積が小さくなるという問題がある。
　そして、積（Ｌｃ×Ｌａ×Ｐ１）については、その値が所定範囲より小さくても、大きくても、固有抵抗変化率が１．０から離れていることが分かる。
　実施例１～３はいずれも、温度域２５～１６００℃において固有抵抗を安定に維持し、固有抵抗変化率（固有抵抗低下率）も小さい。
　本発明によれば、２５℃と１６００℃での固有抵抗のバランスの良い黒鉛材料を提供することができ、ジュール発熱など固有抵抗に依存する装置の効率的な設計に寄与することができる。 

Claims (4)

  1. 　２５℃での固有抵抗（ρ25）が１０．０μΩ・ｍ以上、１２．０μΩ・ｍ以下、１６００℃での固有抵抗（ρ1600）が９．５μΩ・ｍ以上、１１．０μΩ・ｍ以下、２５℃と１６００℃の固有抵抗の比（ρ1600／ρ25）が０．８５以上、１．００以下であり、最小固有抵抗（ρmin）を示す温度が５００℃以上、８００℃以下、最小固有抵抗と２５℃での固有抵抗の比（ρmin／ρ25）が０．７０以上、０．８０以下であり、且つかさ密度が１．６９ｇ／ｃｍ３以上、１．８０ｇ／ｃｍ３以下であることを特徴とする黒鉛材料。
  2. 　炭素網面層の面間距離（ｄ００２）が、０．３３６０ｎｍ以上、０．３３６５ｎｍ以下、炭素網面層が積層した厚さを示す結晶子のｃ軸方向の大きさ（Ｌｃ）が５５ｎｍ以上、８５ｎｍ以下、及び炭素網面の広がりを示す結晶子のａ軸方向の大きさ（Ｌａ）が６０ｎｍ以上、１０５ｎｍ以下であり、黒鉛化度を表す（Ｐ１）が０．５３以上、０．６０以下である請求項１に記載の黒鉛材料。
  3. 　Ｌｃ値と、Ｌａ値と、Ｐ１値との積（Ｌｃ×Ｌａ×Ｐ１）が、１９００ｎｍ2以上、５０００ｎｍ2以下である請求項２に記載の黒鉛材料。
  4. 　ジュール発熱を利用する黒鉛ヒーター用である請求項１～３のいずれか一項に記載の黒鉛材料。 
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