JP2008280432A - Thermally conductive carbon fiber composite sheet and production method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermally conductive carbon fiber composite sheet which is flexible, is anisotropic in terms of heat radiation and can be produced with high productivity. <P>SOLUTION: A pitch carbon fiber filler and a thermosetting resin component are continuously made into a composite to produce the thermosetting carbon fiber composite sheet which is highly flexible and is anisotropic in terms of heat conductivity. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a thermally conductive carbon fiber composite sheet having anisotropy in thermal conductivity and a continuous production method thereof in a composite sheet using pitch-based carbon fiber filler as a raw material.

  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. 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.

  However, in order to completely control the heat from the heat source, it is considered necessary to develop anisotropy as a concept of a three-dimensional isotropic pair. This is because there is an increasing demand for releasing heat in one direction among recent miniaturized elements.

  By the way, the composite material may be used as a connection between a heating element and a heat sink. At this time, if a highly rigid resin composition is used, a gap may be formed between the heating element and the heat sink, and efficient heat conduction cannot be achieved. Therefore, it has been desired for the composite material to be more flexible and have high followability on the surfaces of the heating element and the heat sink. The flexibility of the material can be measured with a hardness meter, but it is desired to measure with Asker C rather than Type A durometer, especially for flexible materials. Therefore, the evaluation with the Asker C than the type A durometer accurately measures a softer material, and can better reflect the actually required softness characteristics.

  Now, a composite material obtained by forming a fiber from a conventional fiber into a composite material with a matrix has improved in-plane thermal conductivity, and furthermore, by using a so-called UD material, anisotropy of thermal conductivity is achieved. Can also be expressed. For example, Patent Document 1 discloses a thermally conductive molded article having high mechanical strength in which carbon fiber aligned in one direction is impregnated with graphite powder and a thermosetting resin. However, high mechanical strength is an idea that is contrary to flexibility. Also, the continuous molding method has become a special method. Therefore, it is considered that flexibility and thermal conductivity anisotropy could not be achieved in the prior art.

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. .
As described above, a product having anisotropy in thermal conductivity while maintaining flexibility has been demanded particularly in a miniaturized electronic device, but a sufficient product has not been obtained yet.

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

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 molded body is high. Moreover, in order to improve the adhesiveness of the said molded object and a heat generating body, the softness | flexibility was calculated | required. Furthermore, anisotropy of heat conduction has been demanded.
Therefore, there has been a strong demand for the appearance of a carbon fiber composite sheet having anisotropy in the thermal conductivity of the molded body and having high flexibility. It was also strongly desired that continuous production was possible.

  The present inventors have found that, as a technique for imparting anisotropy to the thermal conductivity of a composite material, particularly focusing on the dispersion state of carbon fibers, the dispersion state can be controlled when using a specific molding method. . As a result, it has been found that anisotropy appears in the thermal conductivity. Furthermore, making the resin composition into a thermosetting resin component having high formability and pre-mixing the pitch-based carbon fiber filler and the thermosetting resin component, then molding and processing, the thermal conductivity anisotropy and The present inventors have found that it is very effective in continuously producing a sheet-like material imparted with flexibility, and reached the present invention.

That is, the object of the present invention is to
A pitch-based carbon fiber filler and a thermosetting resin component are mixed in a shafted horizontal kneading device and / or a paddle type vertical kneading device, and the resulting mixture is formed into a sheet form by either extrusion molding or cast molding. The volume fraction of the pitch-based carbon fiber filler is 15 to 50% (25 to 70 by weight fraction) based on the thermally conductive carbon fiber composite sheet molded into %), The maximum thermal conductivity is greater than 1 W / (m · K), and the ratio of the maximum thermal conductivity direction divided by the thermal conductivity with the perpendicular direction is 1.1 to 3.0. The heat conductive carbon fiber composite sheet having an Asker C hardness of 85 or less can be achieved.

Still another object of the present invention is to
In producing the heat conductive carbon fiber composite sheet described above, an extrusion step of extruding a mixture of a pitch-based carbon fiber filler and a thermosetting resin component onto a continuous carrier film, and then further onto the extruded mixture, Heat conduction, sequentially passing a film sticking step for sticking a continuous film, a compression step for passing a mixture sandwiched between films through at least a pair of rollers having a certain clearance, and a step for heat-treating the compressed mixture This can be achieved by a method for producing a functional carbon fiber composite sheet.

  The heat conductive carbon fiber composite sheet of this invention mixes a pitch-type carbon fiber filler and a thermosetting resin component previously, and makes it into a sheet form by an appropriate method after that. In particular, it can be continuously produced by an extrusion method, which is effective in reducing production costs. Thermal conductivity can be improved by adding pitch-based carbon fiber filler compared to resin alone, and by controlling the dispersion state of pitch-based carbon fiber filler, the thermal conductivity can be made anisotropic. Can do. Furthermore, since it is rich in flexibility, heat conduction efficiency to a heat radiation sheet for electronic parts, a heat exchanger, and the like is increased in a specific direction, and flexibility can be used to adapt to a complicated shape. Furthermore, continuous production becomes possible.

Next, embodiments of the present invention will be described sequentially.
Examples of the raw material for the pitch-based carbon fiber filler 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 combination of two or more, but it is particularly desirable to use mesophase pitch alone to improve the thermal conductivity of the pitch-based carbon fiber filler.

  The softening point of the raw material pitch can be obtained by the Mettler method, and is preferably 250 ° C. or higher and 340 ° C. or lower. When the softening point is lower than 250 ° C., fusion between fibers and large heat shrinkage occur during infusibilization. On the other hand, when the temperature is higher than 340 ° C., thermal decomposition of the pitch occurs and it becomes difficult to form a string.

  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, spinning was performed by a melt blow method from the viewpoint of high productivity. The pitch fibers spun by the melt blow method are made into a mat shape in which the pitch fibers are entangled three-dimensionally (hereinafter sometimes referred to as a three-dimensional random mat), and then infusible and fired to form a mat-shaped carbon fiber precursor. Become a body. This is pulverized and graphitized to form a pitch-based carbon fiber filler. 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 a raw material for the pitch-based carbon fiber filler, but a nozzle hole length / hole diameter ratio smaller than 3 is preferably used, and more preferably Is smaller than 1.5. The temperature of the nozzle at the time of spinning is also 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 30 Pa · s (20 to 300 Poise), preferably 8 to 20 Pa · s (80 to 200 poise) is sufficient.

  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 340 ° 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 in which pitch fibers are entangled three-dimensionally in addition to being cross-wrapped. This entanglement is formed in a cylinder called chimney while reaching the wire mesh belt from the nozzle. When the linear fibers are entangled three-dimensionally, the characteristics of the fibers that normally show only one-dimensional behavior are reflected in the three-dimensional.

  The three-dimensional random mat-like pitch fiber thus obtained is infusible by a known method and fired at 2000 to 3500 ° C. Infusibilization is achieved at 200 to 340 ° 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 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 firing temperature is about 500 to 1200 ° C. This is because the subsequent pulverization step can be easily performed by firing at a minimum temperature capable of maintaining the shape.

  The calcined three-dimensional random mat-like carbon fiber precursor 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.

  The carbon fiber precursor thus pulverized is 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 place it in a graphite crucible at the time of firing because it can block physical and chemical effects from the outside. The crucible made of graphite is not limited in size and shape as long as a desired amount of the pitch-based carbon fiber filler used as the raw material can be added, but is not limited in the furnace during graphitization or cooling. In order to prevent damage to the pitch-based carbon fiber filler due to reaction with oxidizing gas or carbon vapor, a highly airtight one with a lid can be suitably used.

  The pitch-based carbon fiber filler used in the present invention desirably has a crystallite size derived from the growth direction of the hexagonal network surface of 5 nm or more. The crystallite size derived from the growth direction of the hexagonal network surface can be determined by a known method, and can be determined by diffraction lines from the (110) plane of the carbon crystal obtained by the X-ray diffraction method. The reason why the crystallite size is important is that heat conduction is mainly performed by phonons, and it is the crystals that generate phonons. More preferably, it is 20 nm or more, and more preferably 30 nm or more.

  The average fiber diameter of the pitch-based carbon fiber filler 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%, the number of fibers having a fiber diameter exceeding 20 μm causing trouble due to infusibilization increases, 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 dispersion represented by the following mathematical formula.

  The average fiber length of the pitch-based carbon fiber filler is preferably 10 to 1000 μm. When the average fiber length is less than 10 μm, the thermal conductivity anisotropy is reduced, and it becomes difficult to achieve the thermal conductivity anisotropy of the composite sheet. On the other hand, when it exceeds 1000 μm, the increase in the viscosity becomes remarkably remarkable when mixing with the resin, which hinders the formation of the sheet. More preferably, it is 20-800 micrometers, More preferably, it is 30-600 micrometers.

  The hardness of the heat conductive carbon fiber composite sheet of the present invention is measured with an Asker C hardness meter. The hardness is preferably 20 to 85. If it is less than 20, it becomes extremely weak against tearing, which is a practical problem. On the other hand, when it exceeds 85, a flexible state is impaired and it comes to feel hardness. More preferably, it is 20 to 70.

  The thermal conductivity of the thermally conductive carbon fiber composite sheet of the present invention can be measured by a known method. Among them, the probe method, the hot disk method, and the 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 the thermal conductivity of the thermally conductive carbon fiber composite sheet is substantially difficult to exceed 1 W / (m · K). However, the present invention has solved this problem by using a pitch-based carbon fiber filler having an aspect.

  The thermosetting resin component used in the thermally conductive carbon fiber composite sheet of the present invention is desirably 0.001 to 10 Pa · s (0.01 to 100 Poise) in viscosity measurement at 30 ° C. before curing. More desirably, it is 0.01 to 2 Pa · s (0.01 to 20 poise). The thermosetting resin composition is preferably a two-component type composed of a main agent and a curing agent. This is because when a mixture of a pitch-based carbon fiber filler and a thermosetting resin component is produced, heat is generated by shearing, and curing starts during mixing. Curing is completed by a treatment corresponding to 180 ° C. for 15 minutes. The thermosetting resin component has an addition reaction type and a condensation reaction type, but an addition reaction type in which the third component is hardly involved can be preferably used.

As the thermosetting resin component, at least one selected from the group consisting of a silicone resin, an epoxy resin, a urethane resin, and a melamine resin can be used. From the viewpoint of flexibility and heat resistance, silicone resins and epoxy resins are preferably used.
As such a thermosetting resin component, SE series SE1886 and SE1821, which are thermosetting silicone elastomers manufactured by Toray Dow Corning, have low viscosity and excellent workability.

  The hardness of the cured thermosetting resin component alone in the Asker C after curing is preferably 80 or less from the viewpoint of ensuring the flexibility of the thermally conductive carbon fiber composite sheet after adding the pitch-based carbon fiber filler. A material having an Asker C hardness greater than 80 alone does not exhibit a hardness less than 80 when formed into a composite material. Therefore, in order to achieve the present invention, it is necessary to select a thermosetting resin having an Asker C hardness of 80 or less as the resin component.

  Moreover, the thermosetting resin component which can be used for this invention can use resin which can also heat-process at 200 degreeC for 4 hours. Heat treatment at such a temperature has the effect of volatilizing the low molecular weight component contained in the thermosetting resin component, and in particular, a smaller amount of impurities can be suitably used for such semiconductor applications.

  The heat conductive carbon fiber composite sheet of the present invention can include an extrusion molding method, a casting molding method and the like as a specific molding method. Of these, the extrusion molding method is preferred in view of the point of molding into a sheet.

  In the present invention, a mixture in which a pitch-based carbon fiber filler and a thermosetting resin component are mixed in advance is handled before molding. These mixing methods are carried out using a shaft-type horizontal kneading device and / or a paddle type vertical kneading device or the like by appropriately introducing a pitch-based carbon fiber filler into a container to which the main component of the thermosetting resin component has been added in advance. In the axial horizontal kneader, it is preferable to use a uniaxial or biaxial one, but a multiaxial structure having three or more axes may be used. It is preferable to carry out vacuum degassing at the same time during the stirring because the productivity is improved. The pitch-based carbon fiber filler added to the main component of the thermosetting resin component is preferably 15 to 50% in volume fraction (25 to 70% in weight fraction). If the volume fraction exceeds 50%, the viscosity will increase too much and kneading will not be possible. Further, if the volume fraction is 15% or less, the thermal conductivity cannot be sufficiently increased.

  The viscosity of the mixture of the pitch-based carbon fiber filler and the thermosetting resin component has a point of 1000 Pa · s (10000 poise) or less at 30 ° C. and a shear rate of 1 to 10 per second before curing. If the viscosity is higher than 1000 Pa · s (10000 Poise), the fluidity is poor and extrusion molding becomes difficult. Further, in other casting molding and injection molding, poor fluidity is affected, and it becomes difficult to obtain a uniform sheet. More preferably, it is 500 Pa.s (5000 poise) or less, More preferably, it is 50 Pa.s (500 poise) or less. All viscosities affect the handling of the molding process. Moreover, since it becomes higher than the viscosity of the thermosetting resin component which is a raw material, the viscosity of a thermosetting resin component single-piece | unit becomes a minimum automatically.

  The pitch-based carbon fiber filler can be used with a surface modified by an oxidation treatment such as electrolytic oxidation or a coupling agent or a sizing agent before mixing with the thermosetting resin component. 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 thickness of the thermally conductive carbon fiber composite sheet can be freely set depending on the application, but 0.2 to 10 mm is desirable for improving the molding yield. If the thickness is 0.2 mm or less, uniform molding is difficult, and if it is 10 mm or more, it is difficult to control thickness unevenness.

  The method for producing the heat conductive carbon fiber composite sheet of the present invention will be mentioned. The thermally conductive carbon fiber composite sheet of the present invention is a mixture with controlled viscosity comprising a pitch-based carbon fiber filler and a thermosetting resin component. The process of making this carry | support on a carrier film using an extruder is made into an extrusion process. In the extrusion process, a certain amount of the mixture can be discharged from a certain clearance called a die or lip. Or the method of extruding by natural fall may be used. The mixture discharged from the appropriate outlet is received by a carrier film and conveyed. Since the mixture continuously flows out from the discharge port, the carrier film that receives the mixture needs to be continuous. This film can be continuously fed from an unwinder. Next, a cover film is bonded also to the air layer side of the extruded mixture. This is the film attachment process. And it is molded to a certain thickness by passing over a plurality of rolls with a determined clearance. This process is a compression process. Next, it is cured with an infrared heater or the like (thermal curing step). In this case, the thermosetting resin component can be cured by applying energy corresponding to 180 ° C. for 15 minutes. Further, only the curing may be a separate process. In that case, a hot-air dryer or the like can be used. The sheet that has undergone the curing process proceeds to the winding process and is continuously wound.

The heat conductive carbon fiber composite sheet produced in this way achieves uniform dispersion of the pitch-based carbon fiber filler. It is well known that the pitch-based carbon fiber filler has unidirectionality during injection molding, but in the present invention, the pitch-based carbon fiber filler has pseudo unidirectionality due to the share during extrusion. Therefore, anisotropy occurs in the thermal conductivity.
The thermal conductivity ratio obtained by dividing the thermal conductivity in the direction of maximum thermal conductivity by the thermal conductivity in the direction perpendicular thereto is in the range of 1.1 to 3.0. It is desirable that this value be high.

  As the film used for the continuous process, a polymer film having a melting point of 180 ° C. or higher is preferably used, and a polyethylene terephthalate film (PET film), a polyethylene naphthalate film (PEN film), and the like are preferably used. If a thermosetting resin component having a low curing temperature is used, the types of films that can be used increase. For example, an inexpensive film such as polycarbonate or polypropylene having a softening point temperature of around 150 ° C. can be used. There is no restriction on the thickness, and any thickness may be used as long as handling properties are not impaired. The film used for the carrier cover can be used as a release film.

  The heat conductive carbon fiber composite sheet thus obtained may be subjected to processing such as adhesion processing on the surface. And it can affix on an adhesive material or a heat generating body directly, and can be used as a heat conductive molded object. More specifically, the use of the molded body will be described. The molded body can be used as a heat radiating member, a heat transfer member, or a constituent material thereof for effectively radiating heat generated by electronic components such as a semiconductor element, a power source, and a light source in an electronic device or the like. . In recent years, these parts have a complicated shape, so that they can follow them with flexibility. Moreover, the heat conductive carbon fiber composite sheet of the present invention can be easily cut with a scissors. More specifically, it is processed into an arbitrary shape capable of forming a shaping mold and used between a heat-generating member such as a semiconductor element and a heat-dissipating member such as a radiator, or a heat sink or a component for a semiconductor package. , Heat sinks, heat spreaders, die pads, printed wiring boards, components for cooling fans, heat pipes, casings, and the like can be used. It can be used in three dimensions as well as in plane. In the case of a heat pipe, it becomes possible to make it a flexible form.

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 the pitch-based carbon fiber filler was measured using a scale under the optical microscope with the diameter of 60 pitch-based carbon fiber fillers subjected to graphitization.
(2) The average fiber length of the pitch-based carbon fiber filler was measured using a scale under the optical microscope for the length of 60 graphitized pitch-based carbon fiber fillers.
(3) The thermal conductivity of the thermally conductive carbon fiber composite sheet was determined by a probe method using QTM-500 manufactured by Kyoto Electronics. The maximum thermal conductivity direction was determined from the point where the electrical resistance of the sheet cut into a strip shape in 30 ° increments was the smallest.
(4) The crystallite size of the pitch-based carbon fiber filler was determined by the Gakushin method by measuring reflection from the (110) plane appearing in X-ray diffraction.
(5) The hardness of the heat conductive carbon fiber composite sheet and the thermosetting resin component was determined by an Asker C hardness meter.

[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 280 ° C. Using a hole cap having a diameter of 0.2 mmφ, heated air was ejected from the slit at a linear velocity of 5500 m / min, and the melt pitch was pulled to produce pitch fibers having an average fiber diameter of 11.5 μm. The spun fibers were collected on a belt to form a mat, and further, a three-dimensional random mat-like pitch fiber having a basis weight of 290 g / m ² was obtained by cross wrapping.

  This three-dimensional random mat-like pitch fiber was heated from 190 ° C. to 310 ° C. at an average temperature rising rate of 6 ° C./min for infusibilization. The infusible three-dimensional random mat was fired at 650 ° C. The fired three-dimensional random mat was pulverized into a pitch-based carbon fiber precursor and graphitized at 3000 ° C. The average fiber diameter of the finally obtained pitch-based carbon fiber filler was 8.3 μm, and the ratio of the fiber diameter dispersion to the average fiber diameter was 13%. The average fiber length was 50 μm. The crystallite size derived from the growth direction of the hexagonal network surface was 35 nm.

A silicone resin was selected as the thermosetting resin component. SE1740 manufactured by Toray Dow Corning Co., which consists of a main agent and a curing agent was used. The viscosity of the thermosetting resin component was 1.1 Pa · s (11 Poise). The hardness of the silicone resin component alone after curing at 180 ° C. for 15 minutes was 13 for Asker C.
Stir the pitch-based carbon fiber filler and the main component of the silicone resin component with a paddle-type vertical kneader, add a curing agent and contain a pitch-based carbon fiber filler with a volume fraction of 30% (weight fraction 50%) To make a mixture. The viscosity of the mixture was 60 Pa · s (600 poise) at 30 ° C. and a shear rate of 1.7 per second.

A 75 μm PET film was used as the carrier film, and the mixture was extruded from the 1.5 mm extrusion slit onto the carrier film with a coater. Next, a 75 μm PET film was bonded as a cover film. Next, a roller having a clearance of 1 mm was passed, and a roller having a clearance of 0.5 mm was further passed to form a compression process. Thereafter, heat treatment was performed at 180 ° C. for 15 minutes using a hot-air dryer as a curing zone, and a thermosetting process was performed.
The Asker C hardness of the heat conductive carbon fiber composite sheet thus produced was 30. The maximum thermal conductivity was 1.5 W / (m · K). The thermal conductivity in the perpendicular direction was 1.2 W / (m · K), and the thermal conductivity ratio was 1.3.

[Example 2]
Other steps except the pulverization step were the same as those in Example 1, and a pitch-based carbon fiber filler was produced using a mesh that increased the average fiber length in the pulverization step. The average fiber length was 100 μm.
A silicone resin was selected as the thermosetting resin component. SE1740 manufactured by Toray Dow Corning Co., which consists of a main agent and a curing agent was used. The viscosity of the thermosetting resin component was 1.1 Pa · s (11 Poise). The hardness of the silicone resin component alone after curing at 180 ° C. for 15 minutes was 16 for Asker C.

The pitch-based carbon fiber filler and the main component of the silicone resin component were mixed with a paddle type vertical kneader, and further a curing agent was mixed to obtain a mixture. The viscosity of the mixture was 74 Pa · s (740 Poise) at 30 ° C. and a shear rate of 1.7 per second. And the heat conductive carbon fiber composite sheet was produced with the manufacturing method similar to Example 1. FIG.
The Asker C hardness of the heat conductive carbon fiber composite sheet thus produced was 46. The maximum thermal conductivity was 2.2 W / (m · K). The thermal conductivity in the perpendicular direction was 1.6 W / (m · K), and the thermal conductivity ratio was 1.4.

[Example 3]
Other steps except the pulverization step were the same as those in Example 1, and a pitch-based carbon fiber filler was produced using a mesh that increased the average fiber length in the pulverization step. The average fiber length was 500 μm.
A silicone resin was selected as the thermosetting resin component. SE1740 manufactured by Toray Dow Corning Co., which consists of a main agent and a curing agent was used. The viscosity of the thermosetting resin component was 1.1 Pa · s (11 Poise). The hardness of the silicone resin component alone after curing at 180 ° C. for 15 minutes was 16 for Asker C.

The pitch-based carbon fiber filler and the main component of the silicone resin component were mixed with a paddle type vertical kneader, and further a curing agent was mixed to obtain a mixture. The viscosity of the mixture was 91 Pa · s (910 Poise) at 30 ° C. and a shear rate of 1.7 per second. And the heat conductive carbon fiber composite sheet was produced with the manufacturing method similar to Example 1. FIG.
The Asker C hardness of the heat conductive carbon fiber composite sheet thus produced was 51. The maximum thermal conductivity was 6.2 W / (m · K). The thermal conductivity in the perpendicular direction was 5.0 W / (m · K), and the thermal conductivity ratio was 1.2.

[Example 4]
A pitch-based carbon fiber filler was produced in the same manner as in Example 2.
A silicone resin was selected as the thermosetting resin component. SE1740 manufactured by Toray Dow Corning Co., which consists of a main agent and a curing agent was used. The viscosity of the thermosetting resin component was 1.1 Pa · s (11 Poise). The hardness of the silicone resin component alone after curing at 180 ° C. for 15 minutes was 16 for Asker C.
The pitch-based carbon fiber filler and the main component of the silicone resin component were mixed with a paddle type vertical kneader, and further a curing agent was mixed to obtain a mixture. The viscosity of the mixture was 74 Pa · s (740 Poise) at 30 ° C. and a shear rate of 1.7 per second.

A 75 μm PET film was used as the carrier film, and the mixture was extruded from the 2.5 mm extrusion slit onto the carrier film with a coater. Next, a 75 μm PET film was bonded as a cover film. Next, the roller was passed through a roller having a clearance of 1.5 mm, and further passed between rollers having a clearance of 1.0 mm and between rollers having a clearance of 0.5 mm. Then, it heat-processed at 180 degreeC for 15 minutes with the hot air type dryer as a hardening zone, and was set as the thermosetting process.
The Asker C hardness of the heat conductive carbon fiber composite sheet thus produced was 46. The maximum thermal conductivity was 2.8 W / (m · K). The thermal conductivity in the perpendicular direction was 1.4 W / (m · K), and the thermal conductivity ratio was 2.0.

[Example 5]
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 283 ° C. Using a hole cap having a diameter of 0.2 mmφ, heated air was ejected from the slit at a linear velocity of 5500 m / min, and the melt pitch was pulled to produce pitch fibers having an average fiber diameter of 14.5 μm. The spun pitch fibers were collected on a belt to form a mat, and further formed into a three-dimensional random mat-like pitch fiber having a basis weight of 330 g / m ^{2 by} cross wrapping.
Thereafter, a pitch-based carbon fiber filler was produced in the same manner as in Example 2 using three-dimensional random mat-like pitch fibers. The average fiber diameter of the pitch-based carbon fiber filler was 9.6 μm, and the ratio of the fiber diameter dispersion to the average fiber diameter was 11%. The average fiber length was 100 μm. The crystallite size derived from the growth direction of the hexagonal mesh surface was 40 nm.

A silicone resin was selected as the thermosetting resin component. SE1740 manufactured by Toray Dow Corning Co., which consists of a main agent and a curing agent was used. The viscosity of the resin component was 1.1 Pa · s (11 Poise). The hardness of the silicone resin component alone was 16 for Asker C after curing at 180 ° C. for 15 minutes.
Stir the pitch-based carbon fiber filler and the main component of the silicone resin component with a paddle-type vertical kneader, add a curing agent, and add 30% volume fraction (50% by weight) 3D random matte carbon A mixture containing the fibers was made. The viscosity of the mixture was 35 Pa · s (350 poise) at 30 ° C. and a shear rate of 1.7 per second.

A 75 μm PET film was used as the carrier film, and the mixture was extruded from the 1.5 mm extrusion slit onto the carrier film with a coater. Next, a 75 μm PET film was bonded as a cover film. Next, a roller having a clearance of 1 mm was passed, and a roller having a clearance of 0.5 mm was further passed to form a compression process. Thereafter, heat treatment was performed at 180 ° C. for 15 minutes using a hot-air dryer as a curing zone, and a thermosetting process was performed.
The Asker C hardness of the heat conductive carbon fiber composite sheet thus produced was 56. The maximum thermal conductivity was 2.5 W / (m · K). The thermal conductivity in the perpendicular direction was 2.1 W / (m · K), and the thermal conductivity ratio was 1.2.

[Comparative Example 1]
A carbon fiber composite sheet was produced in the same manner as in Example 1 except that graphitized three-dimensional random mat-like carbon fibers that were not pulverized were used.
It was 39 when hardness was measured with the Asker C hardness meter about the produced heat conductive carbon fiber composite sheet. The maximum thermal conductivity was 6.8 W / (m · K). The thermal conductivity in the perpendicular direction was 6.8 W / (m · K), and the thermal conductivity ratio was 1.0. It is considered that the in-plane anisotropy disappeared due to the influence of the three-dimensional random mat.

[Comparative Example 2]
In Example 1, a multi-axis mixer comprising a pitch-based carbon fiber filler with a volume fraction of 10% (weight fraction of 20%) and a silicone resin component with a volume fraction of 90% (weight fraction of 80%). To prepare a mixture. The viscosity of the mixture was 24 Pa · s (240 poise) at a 30 ° C. shear rate of 1.7 per second. The carbon fiber composite sheet produced by the same production method as in Example 1 had an Asker C hardness of 27. The maximum thermal conductivity was 0.9 W / mK. The thermal conductivity was not sufficient.

[Comparative Example 3]
In Example 1, 45% of the pitch-based carbon fiber filler and 55% of the thermosetting silicone resin component by volume were stirred with a paddle type vertical kneader to prepare a mixture. The viscosity of the mixture was 2500 Pa · s (25000 Poise) at a 30 ° C. shear rate of 1.7 per second, and a flat heat conductive carbon fiber composite sheet could not be produced due to poor extrudability.

[Comparative Example 4]
In Example 1, the carbon fiber composite sheet was prepared in the same manner except that SE6746A / B manufactured by Toray Dow Corning Co., Ltd., which is a silicone resin having a viscosity of 200 Pa · s (2000 Poise) composed of a main component and a curing agent, was used as the thermosetting resin component. I tried to make it. However, even if the volume fraction of the pitch-based carbon fiber filler was 15% (30% by weight fraction), a mixture could not be produced with a paddle type vertical kneader.

[Comparative Example 5]
A carbon fiber composite sheet was produced in the same manner as in Example 1 except that the curing time was 100 ° C. for 15 minutes. Curing was insufficient and it was not realized as a sheet.

Claims (9)

  A pitch-based carbon fiber filler and a thermosetting resin component are mixed in a shafted horizontal kneading device and / or a paddle type vertical kneading device, and the resulting mixture is formed into a sheet form by either extrusion molding or cast molding. The volume fraction of the pitch-based carbon fiber filler is 15 to 50% (25 to 70 by weight fraction) based on the thermally conductive carbon fiber composite sheet molded into %), The maximum thermal conductivity is greater than 1 W / (m · K), and the ratio of the maximum thermal conductivity direction divided by the thermal conductivity with the perpendicular direction is 1.1 to 3.0. A heat conductive carbon fiber composite sheet having an Asker C hardness of 85 or less.   The pitch-based carbon fiber filler is made from mesophase pitch, the average fiber diameter is 5 to 20 μm, the percentage of the ratio of fiber diameter dispersion to the average fiber diameter is 5 to 20%, and the average fiber length is 10 to 1000 μm. The thermally conductive carbon fiber composite sheet described.   The thermally conductive carbon fiber composite sheet according to claim 1 or 2, wherein the size of the crystallites of the pitch-based carbon fiber filler in the hexagonal network surface direction is 5 nm or more.   The thermally conductive carbon fiber composite sheet according to any one of claims 1 to 3, wherein the thermosetting resin component has a pre-curing viscosity of 0.01 to 10 Pa · s (0.01 to 100 poise) at a temperature of 30 ° C. .   The thermosetting resin component is a component in which the thermosetting silicone resin component is cured by holding at 180 ° C for 15 minutes, and the cured Asker C hardness is 80 or less. The thermally conductive carbon fiber composite sheet described.   The thermal conductivity according to any one of claims 1 to 5, wherein the thermosetting resin component comprises at least a main agent and a curing agent, and comprises at least one component selected from the group consisting of a silicone resin, an epoxy resin, a urethane resin, and a melamine resin. Carbon fiber composite sheet.   The heat according to any one of claims 1 to 6, wherein the viscosity of the mixture of the pitch-based carbon fiber filler and the thermosetting resin component has a point of 1000 Pa · s (10000 poise) or less in a range of 1 to 10 at 30 ° C share rate per second. Conductive carbon fiber composite sheet.   The heat conductive carbon fiber composite sheet according to any one of claims 1 to 7, wherein the axial horizontal kneading device is a uniaxial horizontal kneading device or a biaxial horizontal kneading device.   When producing the thermally conductive carbon fiber composite sheet according to any one of claims 1 to 8, an extrusion step of extruding a mixture of a pitch-based carbon fiber filler and a thermosetting resin component onto a continuous carrier film, followed by extrusion Further, a film sticking step of sticking a continuous film on the mixture, a compression step of passing the mixture sandwiched between the films through at least a pair of rollers having a certain clearance, and a step of heat-treating the mixture after compression are sequentially performed. The manufacturing method of the heat conductive carbon fiber composite sheet which is allowed to pass through.