JP2008308543A - Carbon fiber composite sheet and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbon fiber composite sheet that exhibits high thermoconductivity and is remarkably highly loaded with a pitch-based carbon short fiber, and its manufacturing method. <P>SOLUTION: A sheet exhibiting high thermoconductivity having incorporated therewith a very large amount of a pitch-based carbon fiber filler is manufactured by a wet method by using an aromatic polyamide as a resin matrix. A thermoconductive sheet, an electroconductive sheet and an electrical wave-shielding item obtained by using the same are also provided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a carbon fiber composite sheet and a method for producing the same. More specifically, the present invention relates to a carbon fiber composite material sheet having high thermal conductivity in which pitch-based carbon short fibers are highly filled using aromatic polyamide and a method for producing the same.

  High-performance carbon fibers can be classified into PAN-based carbon fibers made from polyacrylonitrile (PAN) and pitch-based carbon fibers made from a series of pitches. Carbon fibers are widely used in aerospace applications, construction / civil engineering applications, sports / leisure applications, etc., taking advantage of their extremely high strength and elastic modulus compared to ordinary synthetic polymers.

  In recent years, while an efficient use method of energy typified by energy saving has been attracting attention, heat generation due to Joule heat in high-speed CPUs and electronic circuits has become a problem. In order to solve these problems, it is necessary to achieve so-called thermal management in which heat is efficiently processed.

  Carbon fibers have a higher thermal conductivity than ordinary synthetic polymers, but further improvements in thermal conductivity are being studied. However, the thermal conductivity of commercially available PAN-based carbon fibers is usually less than 200 W / (m · K) and is not necessarily suitable from the viewpoint of thermal management. On the other hand, it is recognized that pitch-based carbon fibers have a high graphitization property and thus can easily achieve high thermal conductivity compared to PAN-based carbon fibers.

  In general, as a thermally conductive filler, metal oxides such as aluminum oxide, boron nitride, aluminum nitride, magnesium oxide, zinc oxide, silicon carbide, quartz, aluminum hydroxide, metal nitride, metal carbide, metal hydroxide, etc. Is known and is an isotropic material. In addition, the metal-based filler has a high specific gravity and becomes heavy when used as a composite material. On the other hand, when a spherical material such as carbon black, which is a carbon-based material, is added in a high amount, so-called dusting occurs, and particularly in an electronic device, its conductivity adversely affects the device. Further, these materials are so-called processed products of soot, and it is difficult to say that their thermal conductivity is high. On the other hand, carbon fiber not only has the advantage of reducing the weight of the composite material when added in the same volume as the metallic material-based filler, but also has an anisotropic shape. Therefore, there is also an advantage that powder falling is difficult to occur.

  Next, the characteristics of the composite material used for thermal management are discussed. In order to effectively use the high thermal conductivity of the carbon fiber, it is preferable that the carbon fiber forms a network in a state where some matrix is interposed. When the network is formed three-dimensionally, high heat conduction of the carbon fiber is achieved not only in the in-plane direction of the molded body but also in the thickness direction, which is very effective for applications such as a heat sink. It is thought that. In order to produce such an ideal molded body, it is necessary to successfully form a heat conduction path that exhibits thermal conductivity.

  Further, when focusing on heat conduction, in order to achieve high heat conductivity, it is necessary to disperse the heat conducting material at a high concentration in the resin. However, in the conventional addition of the heat conductive material to the matrix, there is a limit to the amount that can be reached.

  As a prior example focusing on enhancing the heat conduction of a composite material, Patent Document 1 discloses a heat conductive molding having a high mechanical strength in which carbon fibers aligned in one direction are impregnated with graphite powder and a thermosetting resin. The product is disclosed. However, in molding with carbon fibers aligned in one direction, it is difficult to follow complicated shapes that can be considered as applied products. Also, a continuous molding method becomes a special method. In order to easily demonstrate the thermal conductivity of a small amount of carbon fiber, it is considered desirable to devise the shape of the carbon fiber.

  Further, Patent Document 2 discloses improving physical properties such as thermal conductivity by improving the physical properties of carbon fibers, but it is unclear regarding ease of use of the molded body and clear performance improvement of thermal physical properties. .

  Furthermore, in Patent Document 3, a carbon fiber precursor fiber having a fiber length of 2 to 12 mm and a papermaking binder are mixed to obtain a precursor fiber coarse sheet, and then a resin treatment is performed to add a resin, followed by firing and carbonization. A method for producing a carbon fiber sheet is disclosed.

Japanese Patent Laid-Open No. 5-17593 JP-A-2-242919 JP 2004-27435 A

  As described above, development is progressing from the viewpoint of increasing the thermal conductivity of carbon fibers. However, from the viewpoint of thermal management, it has been required that the thermal conductivity as a composite material is high. Therefore, studies have been made on carbon fibers that can be added to the matrix in large quantities. However, there is still a problem that the amount of addition is limited by the matrix.

  Accordingly, there has been a strong demand for the selection of a matrix capable of maximizing the thermal conductivity of the composite material and the emergence of a manufacturing method using the matrix. Further, it has been desired to improve the thermal conductivity of the composite material by a highly versatile method rather than a special technique.

  In view of the fact that a large amount of pitch-based carbon short fibers need to be added in order to improve the thermal conductivity of the carbon fiber composite material, the inventors of the present invention are particularly interested in matrix resins to which fillers are added. It was found that it was strongly influenced by the type. As a result, when an aromatic polyamide-based resin is used as a matrix, pitch-based carbon short fibers can be added at an extremely high concentration, a heat conduction path is efficiently formed, high heat conductivity is expressed, and surprisingly, The present inventors have found that a carbon fiber composite sheet in which powdering of filler is suppressed is obtained.

  That is, the present invention is a carbon fiber composite sheet having a thickness of 0.03 to 1 mm, comprising 50 to 94 parts by weight of pitch-based carbon short fibers having an average fiber length of 10 to 700 μm and 6 to 50 parts by weight of aromatic polyamide. is there. Preferably, the average fiber diameter is 5 to 15 μm, the percentage of the value obtained by dividing the dispersion of the fiber diameter by the average fiber diameter is 5 to 20%, and the thermal conductivity in the fiber axis direction is 200 W / (m · K) or more. A carbon fiber having an ash content of 0.2% by weight or less, a crystallite size derived from the growth direction of the hexagonal network surface of 30 nm or more, and a crystallite size derived from the overlapping direction of the hexagonal network surface of 20 nm or more. It is a composite sheet. More preferably, the aromatic polyamide is a carbon fiber composite sheet having a meta-type aromatic diamine and / or a para-type aromatic diamine as a main skeleton. More preferably, the carbon fiber composite sheet is a carbon fiber composite sheet having a thermal conductivity of 2 W / (m · K) or more.

  In addition, the carbon fiber composite sheet of the present invention is manufactured by forming a mixed solution composed of aromatic polyamide dissolved in an organic solvent and pitch-based carbon short fibers into a film by a casting method, removing the organic solvent, and pressing the mixture. can do. In that case, it is preferable that the solid content density | concentration which consists of the pitch-type carbon short fiber and aromatic polyamide in the said liquid mixture is 5 to 30 weight%. The casting method is preferably at least one method selected from the group consisting of a gravure coating method, a doctor knife method, and an extrusion method. The organic solvent is preferably at least one selected from the group consisting of NMP, DMAc, toluene, xylene, 1M2P, and MIBK. Moreover, it is preferable that the method of removing an organic solvent is drying, and the temperature of a drying process is 200 degreeC or more. It is preferable that the pressing step comprises at least one method selected from the group consisting of a calender method using heating and / or room temperature rolls, a vacuum pressing method, an atmospheric pressing method, and a belt pressing method. Moreover, in the carbon fiber composite sheet produced by this carbon fiber composite sheet manufacturing method, the residual solvent is preferably 0.1% by weight or less. The carbon fiber composite sheet of the present invention can be used as a heat conductive sheet, an electrically conductive sheet, and a radio wave shielding sheet.

  The carbon fiber composite sheet of the present invention uses an aromatic polyamide as a resin matrix to which pitch-based carbon short fibers are added, and pitch-based carbon short fibers having an average fiber length of 10 to 700 μm. Short fibers can be added at a high concentration with good dispersibility and excellent in thermal conductivity, and can be manufactured by a processing method as a planar body, and can be applied to various heat countermeasure fields.

  Next, embodiments of the present invention will be described sequentially.

  Examples of the raw material for pitch-based carbon short fibers used in the present invention include condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene, and condensed heterocyclic compounds such as petroleum-based pitch and coal-based pitch. Among them, condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene are preferable, and optically anisotropic pitch, that is, mesophase pitch is particularly preferable. These may be used singly or in appropriate combination of two or more. However, using mesophase pitch alone improves the thermal conductivity by controlling the crystal orientation of pitch-based carbon short fibers. Is particularly desirable.

  The softening point of the raw material pitch can be determined by the Mettler method, and is preferably 260 ° C or higher and 355 ° C or lower. When the softening point is lower than 260 ° C., fusion between fibers or large heat shrinkage occurs during infusibility. On the other hand, when the temperature is higher than 355 ° C., thermal decomposition of the pitch occurs and it becomes difficult to form a yarn.

  The raw material pitch can be spun by a known method. A continuous fiber or a short fiber by a melt blow method is generally used. In the present invention, from the viewpoint of high productivity, the main object is to perform spinning by the melt blow method. The pitch spun by the melt blow method is made into a three-dimensional random mat shape, and then becomes a three-dimensional random mat-like carbon fiber by infusibilization and firing. This is pulverized and graphitized to produce pitch-based carbon short fibers. Each step will be described below.

  In the present invention, there is no particular restriction on the shape of the spinning nozzle of the pitch fiber used as the raw material for the pitch-based carbon short fiber, but it is preferable that the ratio of the nozzle hole length to the hole diameter is larger than 2, Those larger than 5 are preferably used. The temperature of the nozzle at the time of spinning is not particularly limited, and the temperature at which a stable spinning state can be maintained, that is, the viscosity of the spinning pitch is 2 to 25 Pa · S (20 to 250 Poise), preferably 5 to 17 Pa · S (50 to The temperature may be 170 poise).

  The pitch fibers drawn out from the nozzle holes are shortened by blowing a gas having a linear velocity of 100 to 10000 m per minute heated to 100 to 360 ° C. in the vicinity of the thinning point to become pitch fibers. As the gas to be blown, air, nitrogen, or argon can be used, but air is preferable from the viewpoint of cost performance.

  The pitch fibers are collected on a wire mesh belt to form a continuous mat shape, and further cross-wrapped to form a three-dimensional random mat shape.

  The three-dimensional random mat refers to a mat-like form in which pitch fibers are entangled three-dimensionally in addition to being cross-wrapped. This entanglement is achieved in a cylinder called chimney while reaching the wire mesh belt from the nozzle. Since the linear fibers are entangled three-dimensionally, the characteristics of the fibers that normally exhibit only one-dimensional behavior are reflected three-dimensionally.

  The three-dimensional random mat made of pitch fibers thus obtained is infusible by a known method and finally graphitized at 2000 to 3500 ° C.

  Infusibilization is achieved at 200 to 350 ° C. using air or a gas obtained by adding ozone, nitrogen dioxide, nitrogen, oxygen, iodine, bromine to air. Considering safety and convenience, it is desirable to carry out in air.

  The infusible pitch fiber is fired at a low temperature to such an extent that the shape can be maintained in a vacuum or in an inert gas such as nitrogen, argon or krypton. The low-temperature firing is performed at normal pressure and in low-cost nitrogen. The temperature for the low-temperature firing is about 500 to 1200 ° C. This is because the subsequent pulverization step can be easily performed by low-temperature firing at a minimum temperature capable of maintaining the shape.

  The fired three-dimensional random mat is pulverized by a known method. A pulverizer such as a rotary rotor type, a collision pulverization type, a jet mill, a ball mill, or a turbo mill can be used for the pulverization. Moreover, in order to control the average fiber length, a mesh of an appropriate size may be placed and classified. Furthermore, a plurality of methods of pulverization can be combined as appropriate. Further, the average fiber length can be controlled by pulverization.

  The carbon short fibers thus pulverized are then graphitized. The graphitization temperature is preferably 2300 to 3500 ° C. in order to increase the thermal conductivity of the carbon fiber. More preferably, it is 2500-3500 degreeC. It is preferable to put it in a graphite crucible at the time of graphitization because the physical and chemical action from the outside can be blocked. The crucible made of graphite is not limited in size and shape as long as the desired amount of short carbon fibers used as the raw material can be added, but the oxidizing property in the furnace during graphitization or cooling is not limited. In order to prevent the short carbon fibers from being damaged by the reaction with the above gas or carbon vapor, a highly airtight one with a lid can be suitably used. Graphitization is performed in a non-oxidizing atmosphere in an Atchison furnace or the like.

  The pitch-based carbon fiber used in the present invention is a carbon short fiber that is preferably obtained through the above-described steps. Here, carbon fibers having an average fiber length of 1 mm or less are referred to as carbon short fibers. Such carbon fibers are sometimes called cut fibers or milled fibers. And the average fiber length of the pitch-type carbon short fiber used for this invention is 10-700 micrometers, It is characterized by the above-mentioned. When the average fiber length is less than 10 μm, it is difficult to construct a heat conduction path. When the average fiber length is 700 μm or more, it is difficult to fill the resin side in any way. More desirably, it is in the range of 20 to 500 μm.

  The pitch-based carbon short fibers used in the present invention preferably have a crystallite size derived from the overlapping direction of the hexagonal network surfaces of 20 nm or more. The crystallite size derived from the overlapping direction of the hexagonal mesh planes can be determined by a known method, and can be determined by diffraction lines from the (002) plane of the carbon crystal obtained by the X-ray diffraction method. More desirably, the thickness is 30 nm or more, and further desirably 40 nm or more. Similarly, the crystallite size derived from the growth direction of the hexagonal network surface is 30 nm or more. More desirably, the thickness is 50 nm or more, and further desirably 70 nm or more. The crystallite size in the growth direction of the hexagonal network surface is required to be large in order to reduce phonon loss.

  The true density of the pitch-based carbon short fibers used in the present invention has a density of 1.5 to 2.2 g / cc. A more desirable range is 1.9 to 2.2 g / cc, and it is considered that the higher the density, the higher the dispersibility in the resin.

  The average fiber diameter of the pitch-based carbon short fibers is preferably 5 to 20 μm. If it is less than 5 μm, the shape of the pitch fiber may not be maintained, and productivity is poor. When the average fiber diameter exceeds 20 μm, unevenness in the infusibilization process becomes large, and a portion where fusion occurs partially occurs. More preferably, it is 6-15 micrometers, More preferably, it is 7-12 micrometers. The CV value obtained as a percentage of the dispersion value of the average fiber diameter with respect to the average value of the average fiber diameter is desirably 5 to 20%. More desirably, it is 7 to 17% of range. If the CV value exceeds 20%, fibers having a fiber diameter exceeding 20 μm causing trouble due to infusibilization increase, which is not desirable from the viewpoint of productivity. Moreover, it is difficult to produce pitch fibers with fluctuations of 5% or less.

  Here, the CV value is a percentage with respect to the average of the dispersion represented by the following formula (I).

  The addition amount of the pitch-based carbon short fibers is in the range of 50 to 94 parts by weight with respect to 6 to 50 parts by weight of the aromatic polyamide. If the amount is less than 50 parts by weight, the thermal conductivity of the molded carbon fiber composite material is small. On the other hand, if it exceeds 94 parts by weight, the filler may fall, although a part of the molding is possible.

  The pitch-based carbon short fibers used in the present invention have an ash content of 0.2% by weight or less. More desirably, it is 0.1% by weight or less. Ash refers to residual impurities, and less is a pitch-based carbon short fiber with high purity and high thermal conductivity.

  The thermal conductivity of the pitch-based carbon short fibers used in the present invention can be determined from the electrical resistivity, and the thermal conductivity in the fiber axis direction is 200 W / (m · K) or more, more preferably 400 W / ( m · K) or more, more preferably 600 W / (m · K) or more.

  After the surface treatment of the pitch-based carbon short fibers, 0.01 to 10 parts by weight, preferably 0.1 to 2.5 parts by weight, may be added to the sizing agent with respect to 100 parts by weight of the pitch-based carbon short fibers. As the sizing agent, any commonly used sizing agent can be used. Specifically, an epoxy compound, a water-soluble polyamide compound, a saturated polyester, an unsaturated polyester, vinyl acetate, water, alcohol, glycol are used alone or in a mixture thereof. Can do. Such surface treatment is effective in view of increasing the bulk density. However, since the excessive sizing agent is added to the heat resistance, this can be carried out according to the required physical properties.

  Further, the pitch-based carbon short fibers can be used in which the surface is modified by an oxidation treatment such as electrolytic oxidation, or a treatment with a coupling agent or a sizing agent. Also, by electroless plating method, electrolytic plating method, physical vapor deposition method such as vacuum deposition, sputtering, ion plating, chemical vapor deposition method, painting, dipping, mechanochemical method for mechanically fixing fine particles, etc. Metal or ceramics can be coated on the surface.

The carbon fiber composite sheet of the present invention is characterized by using aromatic polyamide as a resin matrix. An aromatic polyamide is a polymer in which one or more divalent aromatic groups are directly linked by an amide bond. It is preferable that the aromatic polyamide has a main skeleton of a meta-type aromatic diamine and / or a para-type aromatic diamine. The aromatic polyamide is substantially represented by the following formulas (A) and (B):
-NH-Ar ¹ -NH- (A)
—OC—Ar ² —CO— (B)
(Ar ¹ and Ar ² each independently represents a divalent aromatic group having 6 to 20 carbon atoms)
These two structural units are alternately repeated.

Said ^Ar 1, Ar ² is each independently a divalent aromatic group having 6 to 20 carbon atoms, and specific examples thereof include metaphenylene group, a paraphenylene group, ortho-phenylene group, 2,6-naphthylene Group, 2,7-naphthylene group, 4,4′-isopropylidene diphenylene group, 4,4′-biphenylene group, 4,4′-diphenylene sulfide group, 4,4′-diphenylene sulfone group, 4, Examples thereof include 4′-diphenylene ketone group, 4,4′-diphenylene ether group, 3,4′-diphenylene ether group, metaxylylene group, paraxylylene group, and orthoxylylene group.

  1 or more of hydrogen atoms of these aromatic groups are each independently halogen groups such as fluorine, chlorine, bromine; alkyl groups having 1 to 6 carbon atoms such as methyl group, ethyl group, propyl group, hexyl group; A cycloalkyl group having 5 to 10 carbon atoms such as a cyclopentyl group and a cyclohexyl group; an aromatic group having 6 to 10 carbon atoms such as a phenyl group may be substituted. In addition, the structural unit of the above formula (A) and / or (B) may be a copolymer composed of two or more aromatic groups.

Of these, Ar ¹ is preferably a metaphenylene group, a paraphenylene group, or a 3,4′-diphenylene ether group, and a paraphenylene group or a combination of a paraphenylene group and a 3,4′-diphenylene ether group. Is more preferable, and when a paraphenylene group and a 3,4′-diphenylene ether group are used in combination, the molar ratio is more preferably in the range of 1: 0.8 to 1: 1.2.

Ar ² is preferably a metaphenylene group or a paraphenylene group, and more preferably a paraphenylene group.

  Organic solvents that dissolve aromatic polyamides include NMP (N-methylpyrrolidone), DMAc (N, N-dimethylacetamide), toluene, xylene, 1M2P (propylene glycol α-monomethyl ether), and MIBK (methyl isobutyl ketone). At least one selected from the group consisting of can be used.

  The solid content concentration of the aromatic polyamide dissolved in the organic solvent is preferably about 6% by weight from the viewpoint of handling. Furthermore, it is desirable that the mixed liquid has good handling during casting when the solid content concentration of pitch-based carbon short fibers and aromatic polyamide is 5 to 30% by weight. If it exceeds 30% by weight, the sheet will crack when the solvent is dried. If it is less than 5% by weight, the finished sheet becomes too thin and it becomes difficult to uniformly disperse the pitch-based carbon short fibers. The solid content concentration is more desirably 10 to 25% by weight, and particularly preferably 12 to 23% by weight.

  Thus, it is preferable that the viscosity of the liquid mixture of the aromatic polyamide and the pitch-based carbon short fiber whose solid content concentration is adjusted is about 10,000 to 500,000 cPoise (10 to 500 Pa · s). However, this is not the case depending on the type of aromatic polyamide.

  The carbon fiber composite sheet of the present invention is produced by mixing pitch-based short carbon fibers and aromatic polyamide in a solvent. When mixing, a mixing device such as a mixer or a revolving stirrer or kneading is used. A device is preferably used. The carbon fiber composite sheet is produced by a casting method, and the casting method can be achieved by at least one method selected from the group consisting of a gravure coating method, a doctor knife method, and an extrusion method.

  The carbon fiber composite sheet of the present invention is a process in which a mixed liquid composed of an aromatic polyamide and pitch-based carbon carbon fibers dissolved in an organic solvent is formed into a film shape by the above-described method, and then the organic solvent is removed and then pressed. Can be manufactured.

  Examples of the method for removing the organic solvent include a drying method and a method by centrifugation, but a drying method is preferable. In particular, after sparse drying, it is preferably subjected to a final drying step after a water washing treatment.

  Although the drying time of the organic solvent in a drying process can be determined suitably, if it becomes a level which the film | membrane becomes self-supporting, it can progress to a final drying process. When drying of the organic solvent can be performed rapidly, the final drying can be performed by continuously raising the drying temperature after the expression of self-sustainability. However, it is not preferable to evaporate a large amount of the organic solvent preferably used in the method of the present invention. If these can be recovered as equipment, it is desirable from the viewpoint of productivity to continuously heat and finally dry.

  In cases other than the case where the organic solvent is rapidly dried, it is desirable to carry out a final drying step subsequent to the water washing treatment after the film is self-supporting due to sparse drying. Washing with water has the effect of promoting solvent removal. After the amount of organic solvent contained in the carbon fiber composite sheet is reduced by washing with water, it is preferably subjected to final drying.

  In the final drying step, the drying temperature is desirably 200 ° C. or higher, more preferably 300 ° C., and further preferably 350 ° C. or higher. Although the final drying time depends on how much solvent is removed by the water washing treatment, it can be appropriately carried out between 10 minutes and 120 minutes.

  The carbon fiber composite sheet of the present invention can enhance planarity by a pressing process. As the pressing step, at least one method selected from the group consisting of a calendering method using a roll at normal temperature and / or room temperature, a vacuum pressing method, an atmospheric pressing method, and a belt pressing method can be applied. In order to produce the carbon fiber composite sheet with a small diameter, a vacuum pressing method and an atmospheric pressure pressing method can be suitably used. In order to continuously produce the carbon fiber composite sheet, a calendar method or a belt press method is preferably used.

After the pressing step is performed, the thickness of the carbon fiber composite sheet is preferably 0.03 to 1 mm. If the thickness is less than 0.03 mm, the pitch-based carbon short fibers become uneven during drying, which becomes manifest as uneven heat conduction performance. If the thickness is greater than 1 mm, the flatness is deteriorated, causing thermal resistance. More preferably, it is 0.05-0.2 mm.
The carbon fiber composite sheet thus produced has a thermal conductivity of 2 W / (m · K) or more. More preferably, it is 5 W / (m · K) or more. Moreover, a residual solvent is 0.1 weight% or less. More preferably, it is 0.05 weight% or less. The thermal conductivity of 2 W / (m · K) is about one digit higher than that of the resin matrix.

  The thermal conductivity of the carbon fiber composite sheet of the present invention can be measured by a known method. Among them, the probe method, hot disk method, and laser flash method are preferable, and the probe method is particularly simple and preferable. In general, the thermal conductivity of carbon fiber itself is several hundred W / (m · K), but when it is molded, the thermal conductivity is drastically reduced due to defects, air contamination, and unexpected voids. To do. Therefore, it has been considered that it is difficult for the thermal conductivity of the thermally conductive molded body to substantially exceed 1 W / (m · K). However, in the present invention, by using an aromatic polyamide as the matrix resin, it is possible to fill the pitch-based carbon short fibers at an extremely high concentration and achieve high heat conduction.

  In the present invention, pitch-based carbon short fibers are mainly used as a heat conductive material, but in order to give a new function, a metal oxide selected from the group consisting of aluminum, silicon, boron, and zinc, and Fine particles of nitride and / or oxynitride and / or carbide may be co-added. The size of the fine particles is preferably 1 to 100 μm, more preferably 1 to 50 μm. The addition amount depends on the required function, but may be added in a range of 10 to 90% with respect to the addition weight of the pitch-based carbon short fibers.

  And the carbon fiber composite sheet of this invention can be used as a heat conductive sheet, an electrically conductive sheet, or a radio wave blocking sheet.

Examples are shown below, but the present invention is not limited thereto.
In addition, each value in a present Example was calculated | required according to the following method.
(1) The average fiber diameter of pitch-based carbon short fibers was determined from the average value of 20 carbon short fibers that were graphitized using a scale under an optical microscope.
(2) The average fiber length of the pitch-based carbon short fibers was determined from the average value of 2,000 carbon short fibers subjected to graphitization using a scale under an optical microscope.
(3) The thermal conductivity of the thermally conductive molded body was determined by a probe method using QTM-500 manufactured by Kyoto Electronics.
(4) The crystallite size of the pitch-based carbon short fibers appears in X-ray diffraction with the (110) plane appearing in X-ray diffraction as the growth direction of the hexagonal mesh plane and the overlapping direction of the hexagonal mesh plane as (002). The reflection from the surface was obtained by a method based on the Gakushin Law.
(5) The density of the pitch-based carbon short fibers was determined by a gas replacement method.
(6) The ash content of the pitch-based carbon short fibers was determined by measuring the weight of the residual ash by sufficiently burning the specimen charged in a platinum crucible at a constant weight in air.
(7) The thermal conductivity of the pitch-based carbon short fibers was graphitized from a three-dimensional random mat that did not pass through the pulverization process, a single yarn was extracted from the graphitized three-dimensional random mat, and the specific resistance of the pitch-based carbon fibers was measured. It was determined from the following formula (2) representing the relationship between the thermal conductivity and the electrical resistivity disclosed in JP-A-11-117143.
K = 1272.4 / ER-49.4 (2)
Here, K represents the thermal conductivity W / (m · K) of the pitch-based short carbon fiber after graphitization, and ER represents the electrical specific resistance μΩm of the same pitch-based short carbon fiber.
(8) The thermal conductivity of the carbon fiber composite sheet was measured with a QTM-500 made by Kyoto Electronics from a carbon fiber composite sheet made from the same production method of 0.3 mm.
(9) The residual solvent amount of the carbon fiber composite sheet was determined from the weight change before and after the heat treatment at 250 ° C. for 10 minutes.
(10) The powder fall of the carbon fiber composite sheet was judged by the color of the cloth surface after lightly rubbing the surface three times with a white cotton cloth. It was judged that there was no powder falling when the color was not transferred, and there was powder falling when the color was transferred.

[Example 1]
A pitch made of a condensed polycyclic hydrocarbon compound was used as a main raw material. The optical anisotropy ratio was 100%, and the softening point was 270 ° C. Using a cap with a hole with a diameter of 0.2 mmφ, heated air was ejected from the slit at a linear velocity of 5600 m / min, and the melt pitch was pulled to produce pitch fibers with an average fiber diameter of 11.2 μm. The spun fibers were collected on a belt to form a mat, and then a three-dimensional random mat composed of pitch fibers having a basis weight of 350 g / m ^{2 by} cross wrapping.
This three-dimensional random mat was heated from 190 ° C. to 320 ° C. at an average temperature rising rate of 6 ° C./min for infusibilization. The infusible three-dimensional random mat was fired at 800 ° C. The fired three-dimensional random mat was pulverized by a rotary rotor mill to obtain a pitch-based carbon short fiber intermediate and graphitized at 3000 ° C. The average fiber diameter of the pitch-based short carbon fibers after graphitization was 8.2 μm, and the ratio of the fiber diameter dispersion to the average fiber diameter was 13%. The average fiber length was 200 μm. The crystallite size derived from the growth direction of the hexagonal network surface was 90 nm. The crystallite size derived from the overlapping direction of the hexagonal mesh plane was 27 nm. The density was 2.20 g / cc. The ash content was 0.1% by weight or less. The electrical resistivity was 1.7 μΩm, and the thermal conductivity was 700 W / (m · K). This was designated as pitch-based carbon short fiber A.
As the aromatic polyamide, a 3% NMP solution of copolyparaphenylene 3,4′-oxydiphenylene terephthalamide (Technola (registered trademark) manufactured by Teijin Techno Products) was used as the resin matrix dope A. 180 g of the heated resin matrix dope A and 20 g of pitch-based carbon short fibers A were stirred so as to be uniform, and a mixed solution A having a solid content concentration of 13% was prepared. The weight of the solid content of the aromatic polyamide component in the mixed solution A was 5 g, and the pitch-based carbon short fiber A was 80 parts by weight with respect to 20 parts by weight of the aromatic polyamide.
The mixed solution A was applied to a glass plate of A4 size with a thickness of 0.3 mm by a doctor knife method, and lyophilized at 110 ° C. for 20 minutes. Then, NMP which is a solvent was poured in running water, the coating film was peeled from the glass plate, and the sheet | seat which consists of aromatic polyamide and a pitch-type carbon short fiber was obtained. The sheet was immersed in running water for 1 hour under constant length, dried at room temperature, and heat-treated for 10 minutes in a hot air dryer heated to 200 ° C. The sheet thus produced was pressed at 2 MPa for 1 minute in a normal pressure press to obtain a carbon fiber composite sheet A. The thickness was 0.1 mm. The amount of residual solvent was 0.1% by weight or less. There was no powder falling. The thermal conductivity was 5 W / (m · K).

[Example 2]
Pitch-based carbon short fibers having an average fiber length of 50 μm were produced in the same manner as in Example 1 except that the pulverization of the three-dimensional random mat was changed from the rotary rotor mill to the turbo mill. This is referred to as pitch-based carbon short fiber B.
In the same manner as in Example 1, 180 g of heated resin matrix dope A and 20 g of pitch-based carbon short fibers B were stirred visually so as to prepare a mixed solution B having a solid content concentration of 13%. The solid content weight of the aromatic polyamide component of the mixed solution B was 5 g, and the pitch-based carbon short fiber A was 80 parts by weight with respect to 20 parts by weight of the aromatic polyamide.
The mixed solution B was applied to a glass plate of A4 size with a thickness of 0.3 mm by a doctor knife method, and lyophilized at 110 ° C. for 20 minutes. Then, NMP which is a solvent was poured in running water, the coating film was peeled from the glass plate, and the sheet | seat which consists of aromatic polyamide and a pitch-type carbon short fiber was obtained. The sheet was immersed in running water for 1 hour under constant length, dried at room temperature, and heat-treated for 10 minutes in a hot air dryer heated to 200 ° C. The sheet thus prepared was pressed at 2 MPa for 1 minute in an atmospheric press to obtain a carbon fiber composite sheet B. The thickness was 0.1 mm. The amount of residual solvent was 0.1% by weight or less. There was no powder falling. The thermal conductivity was 2.7 W / (m · K).

[Example 3]
Using the same pitch-based carbon short fibers as in Example 1, the heated resin matrix dope A180 g and the pitch-based carbon short fibers A50 g were stirred so as to be uniform visually, and a mixed solution C having a solid content concentration of 24% Was made. The solid weight of the aromatic polyamide component in the mixed liquid C was 5 g, and the pitch-based carbon short fiber A was 90 parts by weight with respect to 10 parts by weight of the aromatic polyamide.

  The mixed liquid C was applied to a glass plate of A4 size with a thickness of 0.2 mm by a doctor knife method, and lyophilized at 110 ° C. for 10 minutes. Then, NMP which is a solvent was poured in running water, the coating film was peeled from the glass plate, and the sheet | seat which consists of aromatic polyamide and a pitch-type carbon short fiber was obtained. The sheet was immersed in running water for 1 hour under constant length, dried at room temperature, and heat-treated for 10 minutes in a hot air dryer heated to 200 ° C. The sheet thus produced was pressed at 2 MPa for 1 minute in a normal pressure press to obtain a carbon fiber composite sheet C. The thickness was 0.1 mm. The amount of residual solvent was 0.1% by weight or less. There was no powder falling. The thermal conductivity was 6.0 W / (m · K).

[Example 4]
Using the same pitch-based carbon short fibers as in Example 2, 180 g of the heated resin matrix dope A and 50 g of the pitch-based carbon short fibers B are stirred so as to be uniform, and a mixed solution D having a solid content concentration of 24%. Was made. The solid content weight of the aromatic polyamide component of the mixed solution D was 5 g, and the pitch-based carbon short fiber B was 90 parts by weight with respect to 10 parts by weight of the aromatic polyamide.
The mixed solution D was applied to a glass plate of A4 size with a thickness of 0.2 mm by a doctor knife method, and lyophilized at 110 ° C. for 10 minutes. Then, NMP which is a solvent was poured in running water, the coating film was peeled from the glass plate, and the sheet | seat which consists of aromatic polyamide and a pitch-type carbon short fiber was obtained. The sheet was immersed in running water for 1 hour under constant length, dried at room temperature, and heat-treated for 10 minutes in a hot air dryer heated to 200 ° C. The sheet thus prepared was pressed at 2 MPa for 1 minute in an atmospheric press to obtain a carbon fiber composite sheet D. The thickness was 0.1 mm. The amount of residual solvent was 0.1% by weight or less. There was no powder falling. The thermal conductivity was 3.2 W / (m · K).

[Example 5]
The heated resin matrix dope A 180 g, the pitch-based carbon short fibers A 20 g used in Example 1 and the pitch-based carbon short fibers B 30 g used in Example 2 were stirred so as to be uniform, and the solid content concentration was 24. % Mixed solution E was prepared. The solid content weight of the aromatic polyamide component in the mixed solution E was 5 g, and the total of the pitch-based carbon short fibers A and B was 90 parts by weight with respect to 10 parts by weight of the aromatic polyamide.
The mixed solution E was applied to a glass plate of A4 size with a thickness of 0.2 mm by a doctor knife method, and lyophilized at 110 ° C. for 10 minutes. Then, NMP which is a solvent was poured in running water, the coating film was peeled from the glass plate, and the sheet | seat which consists of aromatic polyamide and a pitch-type carbon short fiber was obtained. The sheet was immersed in running water for 1 hour under constant length, dried at room temperature, and heat-treated for 10 minutes in a hot air dryer heated to 200 ° C. The sheet thus prepared was pressed at 2 MPa for 1 minute in an atmospheric press to obtain a carbon fiber composite sheet D. The thickness was 0.1 mm. The amount of residual solvent was 0.1% by weight or less. There was no powder falling. The thermal conductivity was 6 W / (m · K).

[Comparative Example 1]
Using the same pitch-based carbon short fibers as in Example 1, 180 g of the heated resin matrix dope A and the pitch-based carbon short fibers A4 g were stirred so as to be uniform visually, and a mixed solution F having a solid content concentration of 5% Was made. The solid weight of the aromatic polyamide component in the mixed solution F was 5 g, and the pitch-based carbon short fiber A was 42 parts by weight with respect to 58 parts by weight of the aromatic polyamide.
The mixture F was applied to a glass plate of A4 size by a doctor knife method with a clearance of 1 mm, but the dispersion of pitch-based carbon short fibers was uneven when drying at 110 ° C. In the powder-off test, there was no powder-off, but the sheet was torn. The thermal conductivity was 1.2 W / (m · K).

[Comparative Example 2]
Using the same pitch-based carbon short fibers as in Example 1, 180 g of the heated resin matrix dope A and the pitch-based carbon short fibers A110 g were stirred so as to be uniform visually, and a mixed solution G having a solid content concentration of 39% Was made. The weight of the solid content of the aromatic polyamide component in the mixed solution G was 5 g, and the pitch-based carbon short fiber A was 95 parts by weight with respect to 5 parts by weight of the aromatic polyamide.
The mixed solution G was applied to an A4 size glass plate with a thickness of 0.15 mm by a doctor knife method, and lyophilized at 110 ° C. for 10 minutes. Then, NMP which is a solvent was poured in running water, the coating film was peeled from the glass plate, and the sheet | seat which consists of aromatic polyamide and a pitch-type carbon short fiber was obtained. This sheet was immersed in running water for 1 hour under constant length, dried at room temperature, and heat-treated for 10 minutes in a hot air dryer heated to 200 ° C. The sheet thus prepared was pressed at 2 MPa for 1 minute in an atmospheric pressure press to obtain a carbon fiber composite sheet G. The thickness was 0.1 mm. The amount of residual solvent was 0.1% by weight or less. There is powder fall and is not suitable for electronic parts.

[Example 6]
A 20 g weight heated to 70 ° C. was placed on a 0.1 mm-thick carbon fiber composite sheet using the mixed solution A prepared in Example 3, and heated for 150 seconds to bring the temperature of the carbon fiber composite sheet to about 70 ° C. . Thereafter, when the weight was removed and the heat was released, the temperature was 30 ° C. after 60 seconds. It was found that the heat dissipation effect was high.

[Comparative Example 3]
A 20 g weight heated to 70 ° C. was placed on a 0.1 mmt-thick carbon fiber composite sheet using the mixed solution G prepared in Comparative Example 1 and heated for 150 seconds to bring the temperature of the carbon fiber composite sheet to about 70 ° C. . Thereafter, when the weight was removed and the heat was released, the temperature was 55 ° C. after 60 seconds. It was found that the heat dissipation effect was not so high.

[Example 7]
The carbon fiber composite sheet used in Example 6 had a surface resistance of 1.4Ω / □ and was a conductive sheet.

[Example 8]
When the cutoff performance of the near field of the 1 to 3 GHz radio wave of the carbon fiber composite sheet produced in Example 6 was measured, the average was 16 dB.

[Comparative Example 4]
When the carbon fiber composite sheet produced in Comparative Example 3 was measured for the near-field blocking performance of 1 to 3 GHz radio waves, the average was 8 dB. Compared to Example 8, the shielding performance was small.

Claims (15)

  A carbon fiber composite sheet having a thickness of 0.03 to 1 mm, comprising 50 to 94 parts by weight of pitch-based carbon short fibers having an average fiber length in the range of 10 to 700 μm and 6 to 50 parts by weight of aromatic polyamide.   The average fiber diameter of the pitch-based carbon short fibers is 5 to 20 μm, the percentage of the value obtained by dividing the dispersion of the fiber diameter by the average fiber diameter is 5 to 20%, and the thermal conductivity in the fiber axis direction is 200 W / (m K) or more, ash content of 0.2% by weight or less, crystallite size derived from the growth direction of the hexagonal network surface is 30 nm or more, and crystallite size derived from the overlapping direction of the hexagonal network surface is 20 nm or more The carbon fiber composite sheet according to claim 1.   The carbon fiber composite sheet according to claim 1 or 2, wherein the aromatic polyamide has a meta-type aromatic diamine and / or a para-type aromatic diamine as a main skeleton.   The carbon fiber composite sheet according to any one of claims 1 to 3, wherein the carbon fiber composite sheet has a thermal conductivity of 2 W / (m · K) or more.   The mixed liquid consisting of aromatic polyamide and pitch-based carbon short fibers dissolved in an organic solvent is formed into a film by a casting method, and after removing the organic solvent, pressing is performed according to any one of claims 1 to 4. A method for producing a carbon fiber composite sheet.   The method for producing a carbon fiber composite sheet according to claim 5, wherein a solid content concentration of the pitch-based carbon short fibers and the aromatic polyamide in the mixed solution is 5 to 30% by weight.   The method for producing a carbon fiber composite sheet according to claim 5 or 6, wherein the casting method is at least one method selected from the group consisting of a gravure coating method, a doctor knife method, and an extrusion method.   The method for producing a carbon fiber composite sheet according to any one of claims 5 to 7, wherein the organic solvent is at least one selected from the group consisting of NMP, DMAc, toluene, xylene, 1M2P, and MIBK.   The method for producing a carbon fiber composite sheet according to any one of claims 5 to 8, wherein the method of removing the organic solvent is a method of subjecting to a final drying step subsequent to a water washing treatment after lyophobic drying.   The method for producing a carbon fiber composite sheet according to any one of claims 5 to 9, wherein the method for removing the organic solvent is a drying method, and the final drying temperature is 200 ° C or higher.   11. The method according to claim 5, wherein the pressing step comprises at least one method selected from the group consisting of a calendering method using heating and / or room temperature rolls, a vacuum pressing method, an atmospheric pressing method, and a belt pressing method. A method for producing a carbon fiber composite sheet according to claim 1.   The carbon fiber composite sheet produced with the manufacturing method of the carbon fiber composite sheet in any one of Claims 5-11 WHEREIN: A carbon fiber composite sheet whose residual solvent is 0.1 weight% or less.   The heat conductive sheet using the carbon fiber composite sheet in any one of Claims 1-4 and 12.   An electrically conductive sheet using the carbon fiber composite sheet according to claim 1.   A radio wave shielding sheet using the carbon fiber composite sheet according to claim 1.