JP2010056299A - Method of producing thermally-conductive rubber sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production method for achieving a thermally-conductive rubber sheet having high thermal conductivity in a thickness direction by using simple and highly productive processes. <P>SOLUTION: A rubber precursor composition includes a total amount 100 pts.wt. consisting of 35-85 pts.wt. of a rubber component prior to crosslinking and 15-65 pts.wt. of a graphitized short carbon fiber that is made from a mesophase pitch and has a crystallite size, derived from the thickness direction of a hexagonal net plane, of 30 nm or more. The method of producing the thermally-conductive rubber sheet includes: a step (1) of preparing a rubber precursor sheet, in which carbon fibers are substantially uniaxially oriented within the sheet, by kneading or kneading/extruding the rubber precursor composition under such a condition that relatively strong shear force and/or elongation force are/is generated in one direction in the sheet; a step (2) of slicing the sheet to a width of 0.05-100 mm along a plane perpendicular to the orientation direction of the carbon fibers; and a step (3) of preparing a rubber sheet, in which the orientation of the carbon fibers is fixed, by hot-pressing each sheet in its thickness direction for rubber crosslinking. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The manufacturing method of the heat conductive rubber sheet of this invention is related with the manufacturing technique of the heat conductive rubber sheet in which heat diffusion and heat transport which are highly efficient especially in the thickness direction are possible.

  Thermal diffusive sheets are CPU, MPU, power transistor, LED, laser diode, various batteries (various secondary batteries such as lithium ion batteries, various fuel cells, capacitors, Around various electrical devices such as amorphous silicon, crystalline silicon, compound semiconductors, wet solar cells, etc., around the heat source of heating equipment that requires effective use of heat, heat from heat exchangers and floor heating devices It is preferably used around piping.

  In particular, it is used between various heat sources (various devices such as CPUs, transistors, LEDs, etc.) and metal heat sinks with heat dissipation fins, etc., to improve the heat flow between them and to efficiently dissipate heat. As a target low thermal resistance type thermal conductive sheet, a sheet having high thermal conductivity and appropriate flexibility in the thickness direction is required.

In particular, sheets with a thermal conductivity of 5 W / m · K or more measured in the thickness direction measured by the laser flash method are in increasing demand, especially for applications that require high heat dissipation. Manufacturing simple and highly productive is now a major challenge.
As a method for obtaining a thermal conductive sheet having a thermal conductivity in the thickness direction of 5 W / m · K or more, for example, the following has been disclosed (Patent Document 1).

However, in the method disclosed in Patent Document 1, a large-scale device is necessary because of the use of a strong magnetic field for the orientation of carbon fibers, and in principle, it can be manufactured only in a portion to which a magnetic field is applied. There was a problem that the productivity of the sheet was low.
JP 2002-88171 A

  An object of the present invention is to produce a heat conductive rubber sheet having a highly efficient heat diffusion and a sufficient heat conduction performance particularly in the thickness direction of the sheet by a simple and efficient method.

The present invention includes: 1) Graphitized carbon short fibers 15 to 65 having 35 to 85 parts by weight of an uncrosslinked rubber component and mesophase pitch as raw materials and having a crystallite size of 30 nm or more derived from the thickness direction of the hexagonal mesh surface. Carbon fiber by kneading or kneading and extruding a rubber precursor composition containing 100 parts by weight of a total of parts by weight under conditions such that a relatively strong shearing force and / or elongation force is generated in one direction inside the sheet. A step of creating a rubber precursor sheet substantially uniaxially oriented in the sheet surface,
2) A step of slicing the sheet with a width of 0.05 to 100 mm by a plane perpendicular to the orientation direction of the carbon fibers,
3) A step of creating a rubber sheet in which the orientation of carbon fibers is fixed by cross-linking rubber by heat-pressing in the thickness direction of the sheet,
A carbon fiber is approximately uniaxially oriented in the thickness direction with a thickness of 0.05 to 100 mm, and a sheet having a thermal conductivity of 5 W / m · K or more in the thickness direction is manufactured.

  According to the method of the present invention, it is possible to obtain a rubber sheet having high thermal conductivity in the thickness direction, which is highly needed for various applications, by a simple method.

Next, embodiments of the present invention will be described in more detail.
The heat conductive rubber sheet targeted by the production method of the present invention is a sheet having a thickness of 0.05 to 100 mm, in which carbon fibers are substantially uniaxially oriented in the thickness direction, and having a heat conductivity of 5 W / m · K or more in the thickness direction. is there.

  The thermal conductivity in the thickness direction of the sheet is preferably at least 5 W / m · K or more, more preferably 7 W / m · K or more, still more preferably 10 W / m · K or more, as measured by the laser flash method. Most preferably, it is 15 W / m · K or more.

In addition, in the low thermal resistance type heat radiation sheet assumed as an application, the thermal conductivity in the in-plane direction of the sheet may be a low value of less than 2 W / m · K, for example.
Thus, as a method for obtaining a rubber sheet having a particularly high thermal conductivity in the thickness direction, it is preferable to perform at least the following three steps in the production method of the present invention.

That is,
[Step 1] 35 to 85 parts by weight of a rubber component in an uncrosslinked stage and 15 to 65 parts by weight of graphitized carbon short fibers having a crystallite size of 30 nm or more derived from the thickness direction of the hexagonal mesh surface using mesophase pitch as a raw material The carbon fiber is made into a sheet by kneading or kneading and extruding a rubber precursor composition containing a total of 100 parts by weight under conditions such that a relatively strong shearing force and / or elongation force is generated in one direction inside the sheet. A step of creating a rubber precursor sheet substantially uniaxially oriented in the plane;
[Step 2] A step of slicing a sheet with a width of 0.05 to 100 mm by a plane perpendicular to the orientation direction of the carbon fibers,
[Step 3] A step of cross-linking rubber by heat-pressing in the thickness direction of the sheet to create a rubber sheet in which the orientation of carbon fibers is fixed,
It is three.

  In Step 1, the kneading or kneading extrusion method of the rubber precursor composition is a major point, and it is important to adopt a kneading method in which a particularly strong shearing force is applied in one direction, thereby improving the uniaxial orientation of graphitized carbon short fibers. Can be raised. As such a kneading method, for example, an inter-roll kneading method using two or more rolls is preferably exemplified. As a specific example of the kneading method, the rubber precursor composition is first passed through a gap of a roll kneader to obtain a sheet of the rubber precursor composition, and the sheet is further passed through a roll a plurality of times so that the carbon fiber is removed from the sheet surface by shearing force. A method for almost uniaxially aligning is preferably used. A schematic diagram in this case is shown in FIG. In the figure, graphitized carbon short fibers are schematically enlarged. In FIG. 1, when a sheet of the rubber precursor composition sandwiched between two rolls passes through this gap, the sheet is subjected to a strong shearing force by the rotating roll, and in a direction parallel to the rotation direction of the roll. Get stretched. As the matrix is elongated, more graphitized carbon short fibers mixed in the sheet are arranged in the same direction. As a result, a state occurs in which the carbon fibers are oriented in one direction within the sheet surface. In order to enhance the orientation, the sheet is preferably passed through a roll a plurality of times. However, it is preferable that the sheet attached to the roll is once peeled off and turned over, and further passed through a roll.

  When kneading the rubber precursor composition, after preliminarily kneading in a closed kneader such as a Banbury mixer, kneading or kneading so that the carbon fibers are almost uniaxially oriented in the sheet surface by shearing in a roll kneader. The method of extruding is also mentioned.

  Here, the graphitized carbon short fiber is an anisotropic material having a fiber shape with an average aspect ratio of about 2 to 10000. Therefore, by increasing the uniaxial orientation of the carbon fiber, extremely high heat is generated in the orientation direction. Conductivity can be obtained.

  In the rubber precursor sheet prepared in step 1, the carbon fibers are oriented in one direction in the plane, and the direction having the maximum thermal conductivity is in one direction in the sheet plane. That is, the orientation direction of the carbon fiber can be defined as a direction in which the thermal conductivity is maximized when the thermal conductivity is measured by a laser flash method in various directions in the sheet. For example, in the roll kneading method exemplified above, carbon fibers are generally oriented in a direction parallel to the rotation direction of the roll, that is, in a direction perpendicular to the axis of the roller, and the thermal conductivity is maximized in this direction.

  Step 2 is a step of slicing the sheet in which the carbon fibers are oriented in one direction in the plane in a plane perpendicular to the orientation direction, thereby creating a sheet in which the carbon fibers are oriented in the thickness direction. I can do things. That is, by preparing a sheet sliced in a direction perpendicular to the orientation direction of the carbon fiber and rotating it 90 degrees, a heat conductive rubber sheet in which the orientation direction of the carbon fiber coincides with the thickness direction can be obtained.

  The rubber sheet cutting method includes, for example, a punching method using a blade, a water jet method, a laser knife method, etc., but the smoothness of the cut surface is extremely important in realizing the low thermal resistance performance required for the rubber sheet. Yes, it is necessary to optimize cutting conditions simultaneously with the cutting method.

Step 3 is a step of vulcanization molding of the rubber precursor sheet. Various methods such as hot press, hot press between rolls, and calendering can be used, but sufficient heat energy can be supplied for sufficient rubber cross-linking, uniformity of sheet thickness and surface smoothness (or moldability). ) Is more preferable.
From this point of view, a compression molding method is preferably used in which after the rubber precursor sheet is set in a predetermined mold, a hot press is performed in a mold under vacuum as necessary.

Regarding these three steps, step 1 needs to be performed before step 2 and step 3, but there is no particular restriction on the order of execution of step 2 and step 3.
For example, the order of step 2 → step 3 has the advantage that the surface smoothness of the rubber sheet is increased, and the order of step 3 → step 2 has the advantage that the orientation of the carbon fibers can be easily controlled and the handling property is good. Because there is, it can be selected according to the purpose.

[Rubber matrix material]
As the rubber component serving as a matrix, natural rubber (NR), acrylic rubber, acrylonitrile butadiene rubber (NBR rubber), isoprene rubber (IR), urethane rubber, ethylene propylene rubber (EPM), epichlorohydrin rubber, chloroprene rubber (CR), Silicone rubber, styrene butadiene rubber (SBR), butadiene rubber (BR), butyl rubber and the like are suitably disclosed.

[Graphitized carbon short fiber]
Graphitized carbon short fibers are made from mesophase pitch, and have an average fiber diameter of 5 to 20 μm, a fiber diameter dispersion percentage with respect to the average fiber diameter (CV value) of 5 to 20%, and an average aspect ratio of 2 to 10000 on average. A graphitized carbon short fiber having a substantially smooth observation surface with a scanning electron microscope and having a graphene sheet closed in end face observation with a transmission electron microscope is preferably used.

  Examples of materials used as raw materials for graphitized carbon short fibers include condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene, condensed heterocyclic compounds such as petroleum pitch and coal pitch. Among these, condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene are preferable, and mesophase pitch is particularly preferable. The mesophase ratio of the mesophase pitch is at least 90% or more, more preferably 95% or more, and further preferably 99% or more. The mesophase rate of the mesophase pitch can be confirmed by observing the pitch in the molten state with a deflection microscope. Furthermore, the softening point of the raw material pitch is preferably 230 ° C. or higher and 340 ° C. or lower. The infusibilization treatment needs to be performed at a temperature lower than the softening point. For this reason, when the softening point is lower than 230 ° C., it is necessary to perform the infusibilization treatment at a temperature at least lower than the softening point. On the other hand, if the softening point exceeds 340 ° C., a high temperature exceeding 340 ° C. is required for spinning, which causes thermal decomposition of the pitch and causes problems such as generation of bubbles in the yarn due to the generated gas. A more preferable range of the softening point is 250 ° C. or higher and 320 ° C. or lower, and more preferably 260 ° C. or higher and 310 ° C. or lower. The softening point of the raw material pitch can be obtained by the Mettler method. Two or more raw material pitches may be used in appropriate combination. The mesophase ratio of the raw material pitch to be combined is preferably at least 90% or more, and the softening point is preferably 230 ° C. or higher and 340 ° C. or lower.

  The graphitized carbon short fibers used in the present invention preferably have an average fiber diameter (D1) of 5 to 20 μm observed with an optical microscope. When D1 is less than 5 μm, handling becomes difficult. Conversely, when D1 exceeds 20 μm, a gap is formed when the film is formed by heating, and the adhesion strength of the film becomes insufficient. A more preferable range of D1 is 5 to 15 μm, and further preferably 7 to 13 μm.

  The graphitized carbon short fiber preferably has a fiber diameter dispersion (S1) percentage (CV value) to D1 of 5 to 20 in the pitch-based carbon short fiber filler observed with an optical microscope. The smaller the CV value, the higher the process stability and the smaller the product variation. When the CV value is smaller than 5, the fiber diameters are extremely uniform, so there is less room for other fillers to enter the gaps between the fillers, and it becomes difficult to add a large amount of filler when compounding with the resin material. It is not preferable for increasing the thermal conductivity of the thermal diffusion layer. On the other hand, when the CV value is larger than 20, the dispersibility upon compounding with the resin deteriorates, and the performance uniformity of the heat diffusion layer tends to decrease. The CV value is more preferably 5-15.

  The average fiber length (L1) of the graphitized carbon short fibers in the present invention is preferably at least 20 μm or more. Here, the average fiber length is a number average fiber length, and a predetermined number is measured in a plurality of fields of view using a length measuring device under an optical microscope, and can be obtained from the average value. When L1 is smaller than 20 μm, it becomes difficult for the fillers to come into contact with each other, and it is difficult to expect the formation of an effective heat conduction path.

On the other hand, the upper limit of the average fiber length is not particularly limited. However, in practice, it depends on the method of compounding with the resin, but is determined within a range where stable production is possible. Generally, when the average fiber length exceeds 100 mm (100,000 μm), stable production tends to be considerably difficult.
The average aspect ratio of the graphitized carbon short fibers is 2 to 10000, preferably 3 to 1000, more preferably 4 to 100, and still more preferably 5 to 50.

  The graphitized carbon short fiber filler preferably has a crystallite size derived from the thickness direction of the hexagonal network surface of 30 nm or more, and further a crystallite size derived from the growth direction of the hexagonal network surface of 50 nm or more. The crystallite size corresponds to graphitization in both the thickness direction of the hexagonal network surface and the growth direction of the hexagonal network surface, and a certain size or more is necessary to exhibit thermophysical properties. The crystallite size derived from the thickness direction of the hexagonal mesh surface and the crystallite size in the growth direction of the hexagonal mesh surface can be obtained by an X-ray diffraction method. The measurement method was the concentration method, and the Gakushin method was used as the analysis method. The crystallite size in the thickness direction of the hexagonal mesh plane is obtained using diffraction lines from the (002) plane, and the crystallite size in the growth direction of the hexagonal mesh plane is obtained using diffraction lines from the (110) plane. be able to.

The true density of the graphitized carbon short fibers is preferably at least 1.9 or more, preferably 2.1 or more, more preferably 2.15 or more, and most preferably 2.2 or more.
Further, the thermal conductivity in the fiber axis direction of the graphitized carbon short fibers is preferably at least 300 W / (m · K) or more, more preferably 400 W / (m · K) or more, and further preferably 500 W / (m · K). K) or higher, most preferably 600 W / (m · K) or higher.

  The graphitized carbon short fiber preferably has a substantially flat observation surface with a scanning electron microscope. Here, “substantially flat” means that the surface of the pitch-based carbon short fiber filler does not have severe unevenness like a fibril structure. When defects such as severe irregularities are present on the surface of the short carbon fibers, the viscosity increases with the increase in the surface area when kneading with the matrix resin, and the moldability is deteriorated. Therefore, it is desirable that defects such as surface irregularities be as small as possible. More specifically, it is assumed that there are 10 or less defects such as irregularities in the observation visual field in an image observed at 1000 times with a scanning electron microscope.

  The graphitized carbon short fiber preferably has a structure in which the graphene sheet is closed at the end face by observation with a transmission electron microscope. When the end face is closed as a graphene sheet, generation of extra functional groups and localization of electrons due to the shape do not occur, so that it becomes difficult to have an active point. As a result, inhibition of curing due to a decrease in the catalytic activity of the thermosetting resin can be suppressed. Furthermore, adsorption of water or the like can be reduced, and wet heat durability performance can be improved.

  In particular, in a short fiber-like carbon fiber, a structure in which the graphene sheet is closed is particularly preferable because the ratio of the end face to the surface area of the carbon fiber is high. Note that the graphene sheet is closed means that the end of the graphene sheet itself constituting the filler is not exposed at the end of the filler, the graphite layer is curved substantially U-shaped, and the curved portion is exposed at the end of the filler. It is in a state of being. These effects become particularly apparent when such a state occupies 80% or more of the entire end face.

[Method for producing graphitized carbon short fiber]
Next, a preferred method for producing graphitized carbon short fibers is shown below.
The pitch used as a raw material is spun by a melting method, and then becomes a graphitized carbon short fiber by infusibilization, firing, milling, and graphitization. In some cases, a classification step may be added after milling. As mentioned above, it is preferable that the graphene sheet is closed in the filler end face observation of the graphitized carbon short fiber with a transmission electron microscope, but such graphitized carbon short fiber is subjected to graphitization after milling. By doing, it can obtain preferably. This is because, when milling after graphitization, the graphene sheet generated with graphitization remains open at the cut end face, whereas the carbonized pitch fiber web is milled to form pitch-based carbonized short fibers. When graphitization is performed, a graphene growth process in which a graphene sheet on the end face of a short fiber closes in a loop shape is used. Hereinafter, preferred embodiments of each step will be described.

  The spinning method is not particularly limited, but a so-called melt spinning method can be preferably exemplified. Specific examples include a normal spinning drawing method in which the raw material pitch discharged from the die is drawn by a winder, a melt blow method using hot air as an atomizing source, and a drawing spinning method in which the raw material pitch is drawn using centrifugal force. Among them, it is desirable to use the melt blow method for reasons such as control of the form of pitch fibers and high productivity. Therefore, hereinafter, the melt blow method will be described with respect to the method for producing graphitized carbon short fibers.

  There is no restriction | limiting in particular about the shape of the spinning nozzle for forming the pitch fiber used as the raw material of a graphitized carbon short fiber. Usually, a round shape is used, but there is no problem even if an irregular shape such as an ellipse is used in a timely manner. The ratio of the nozzle hole length (LN) to the hole diameter (DN) (LN / DN) is preferably in the range of 2-20. When LN / DN exceeds 20, a strong shearing force is imparted to the raw material pitch passing through the nozzle, and a radial structure appears in the fiber cross section. The expression of the radial structure is not preferable because the cross section of the fiber may be cracked during the graphitization process and the mechanical characteristics may be deteriorated. On the other hand, when LN / DN is less than 2, shearing cannot be imparted to the raw material pitch, and as a result, the fibers have low orientation of graphite. For this reason, even if graphitization is performed, the degree of graphitization is not sufficiently increased, making it difficult to improve thermal conductivity, which is not preferable. In order to achieve both mechanical strength and thermal conductivity, it is necessary to impart appropriate shear to the raw material pitch. For this reason, the ratio (LN / DN) of the nozzle hole length (LN) to the hole diameter (DN) is preferably in the range of 2 to 20, and more preferably in the range of 3 to 12.

  The temperature of the nozzle at the time of spinning is not particularly limited, and a temperature at which a stable spinning state can be maintained, that is, a temperature at which the viscosity of the raw material pitch is in the range of 1 to 100 Pa · s is preferable. When the viscosity of the raw material pitch is less than 1 Pa · s, it is not preferable because the viscosity is too low to maintain the yarn shape. On the other hand, when the viscosity of the raw material pitch exceeds 100 Pa · s, a strong shearing force is imparted when passing through the nozzle, and a radial structure appears in the generated pitch fiber cross section, which is not preferable. In order to bring the shearing force into an appropriate range and maintain the fiber shape, it is necessary to appropriately control the viscosity of the raw material pitch. For this reason, the viscosity of the raw material pitch is preferably in the range of 1 to 100 Pa · s, more preferably 3 to 30 Pa · s, and even more preferably 5 to 25 Pa · s.

  Graphitized carbon short fibers are characterized by having an average fiber diameter (D1) of 5 to 20 μm, and this fiber diameter control method changes the nozzle hole diameter or discharges the raw material pitch from the nozzle. This can be done by changing the draft ratio. The change of the draft ratio can be achieved by blowing a gas having a linear velocity of 100 to 10,000 m / minute heated to 100 to 400 ° C. in the vicinity of the thinning point. There is no particular restriction on the gas to be blown, but air is desirable from the viewpoint of cost performance and safety.

The spun pitch fibers are collected on a belt such as a wire mesh to form a pitch fiber web. At that time, the weight per unit area can be adjusted according to the belt conveyance speed, but if necessary, it may be laminated by a method such as cross wrapping. The basis weight of the pitch fiber web is preferably 150 to 1000 g / m ^{2 in} consideration of productivity and process stability.

  The pitch fiber web thus obtained is infusibilized by a known method to obtain an infusible pitch fiber web. Infusibilization can be performed in air or in an oxidizing atmosphere using a gas in which ozone, nitrogen dioxide, nitrogen, oxygen, iodine, or bromine is added to air, but in consideration of safety and convenience, it is performed in air. It is desirable. Further, both batch processing and continuous processing can be performed, but continuous processing is desirable in consideration of productivity. The infusibilization treatment is achieved by applying a heat treatment for a predetermined time at a temperature of 150 to 350 ° C. A more preferable temperature range is 160 to 340 ° C, and a more preferable range is 170 to 330 ° C. A heating rate of 1 to 10 ° C./min is preferably used. In the case of continuous treatment, the above heating rate can be achieved by sequentially passing through a plurality of reaction chambers set at arbitrary temperatures. A more preferable range of the temperature raising rate is 3 to 8 ° C./min, and more preferably 4 to 6 ° C./min in consideration of productivity and process stability.

  The infusibilized pitch fiber web is fired at a temperature of 500 to 1500 ° C. in a vacuum or in a non-oxidizing atmosphere using an inert gas such as nitrogen, argon, krypton, etc., to become a carbonized pitch fiber web. In view of cost, the firing treatment is preferably performed at normal pressure and in a nitrogen atmosphere. Further, both batch processing and continuous processing can be performed, but continuous processing is desirable in consideration of productivity.

  The fired carbonized pitch fiber web is subjected to processing such as cutting, crushing and pulverization in order to obtain a desired fiber length. In some cases, classification processing is performed. The treatment method is selected according to the desired fiber length. For cutting, guillotine type, rotary type cutters, 1-axis, 2-axis and multi-axis rotary blade types are preferably used for crushing and crushing. Crushers such as hammer type, pin type, ball type, bead type and rod type using impact action, high-speed rotation type using collision between particles, roll type using compression / tearing action, cone type and screw type -A crusher etc. are used suitably. In order to obtain a desired fiber length, cutting, crushing and pulverization may be configured by a plurality of machines. The treatment atmosphere may be either wet or dry. For the classification treatment, a classification device such as a vibration sieve type, a centrifugal separation type, an inertial force type, and a filtration type is preferably used. The desired fiber length can be obtained not only by selecting a model, but also by controlling the number of revolutions of the rotor / rotating blade, supply amount, clearance between blades, residence time in the system, and the like. Moreover, when using a classification process, desired fiber length can be obtained also by adjusting a sieve mesh hole diameter.

  The pitch-based carbonized short fibers prepared by using the above-described cutting, crushing / pulverizing treatment, and, in some cases, classification treatment, are heated to 2500-3500 ° C. and graphitized to obtain a final pitch-based carbon short fiber filler. Graphitization is performed in an Atchison furnace, an electric furnace, or the like, and is performed in a vacuum or in a non-oxidizing atmosphere using an inert gas such as nitrogen, argon, or krypton.

The filler produced in this manner has a very high carbon purity inside and on the surface of the fiber. That is, the content of impurities such as reactive organic functional groups and metals and metal compounds is extremely low.
Further, as described above, the graphene sheet is closed in the cut cross section of the carbon fiber, and the crystal edge surface having high reaction activity is hardly exposed.

  In general, these are very preferable characteristics with respect to the suppression of the degradation degradation reaction of the resin matrix material generated based on organic functional groups, crystal edge surfaces and other reactive active sites, metallic impurities, and the like. Further, when a resin material (including rubber or the like) having crosslinkability and curability is used as a matrix, a preferable result is obtained that no inhibition of the crosslinking reaction and the curing reaction is caused, which is also a preferable feature.

  Of course, if necessary, various surface treatments and sizing treatments may be performed for the purpose of enhancing the affinity with the resin, dispersibility, and adhesion. Further, sizing treatment may be performed after surface treatment as necessary. The surface treatment method is not particularly limited, and specific examples include ozone treatment, plasma treatment, and acid treatment. There is no particular limitation on the sizing agent used for the sizing treatment, but specifically, an epoxy compound, a water-soluble polyamide compound, a saturated polyester, an unsaturated polyester, vinyl acetate, water, alcohol, glycol may be used alone or in a mixture thereof. it can. You may make a sizing agent adhere 0.01-10 weight part with respect to 100 weight part of carbon short fiber fillers. However, since the sizing agent-attached graphitized carbon short fiber filler may have active sites, it is preferable that the sizing treatment is as little as possible. A preferable adhesion amount is 0.1 to 2.5% by weight.

[Other ingredients]
In addition, the components mixed and added to the rubber precursor composition include, for example, the following, but these are hardly different from the conventional rubber technology, and the conventional technology can be sufficiently referred to. .
1) Rubber cross-linking agent: An appropriate amount of a known sulfur-based cross-linking agent (vulcanizing agent) is preferably added. When silicone rubber is used for the matrix, it is preferable to add a known curing agent for curing silicone (for example, a tertiary amine compound).
2) Curing accelerator: It is preferable to add an appropriate amount of a vulcanization accelerating auxiliary such as zinc oxide having a particle size of about 0.1 to 0.9 μm and / or active zinc oxide, and other curing accelerators.
3) Carbon black: In order to ensure the mechanical strength of the rubber, it is preferable to mix an appropriate amount of carbon black (Ketjen black, acetylene black, etc.) having a particle size of about 30 to 90 nm if necessary.
4) Plasticizer: An appropriate amount of plasticizer can be added as needed from the viewpoint of adjusting the hardness of the rubber.
5) Others: An antioxidant, oil, lubricant, inorganic particles (silica, alumina, etc.), etc. can be added as necessary.

[Mixing ratio of each component]
Regarding the weight ratio of the rubber matrix component and the graphitized carbon short fiber, when the total of both components is 100 parts by weight, the graphitized carbon short fiber is 15 to 65 parts by weight with respect to 35 to 85 parts by weight of the rubber component. It is preferable to be in the range.
If the rubber component is less than 35 parts by weight, it becomes difficult to ensure flexibility and mechanical strength. Further, when the graphitized carbon fiber is less than 15 parts by weight, it is difficult to ensure high thermal conductivity.

[Hardness of rubber sheet]
The hardness of the rubber sheet is deeply related to the low heat resistance performance (heat transfer performance), and the rubber hardness value by Shore A is preferably in the range of at least 10 to 100, preferably 15 to 85, more preferably 20 to 70, most preferably 25-60. When the number is 100 or more, flexibility and deformability are low, and thus there is a problem that the surface irregularities of the device and the heat sink cannot be followed. On the other hand, if it is less than 10, the deformability is too large, which often causes a problem in mechanical strength.

[Measurement of thermal conductivity]
The measurement of thermal conductivity is generally performed by a method such as a probe method, a hot disk method, a laser flash method, etc., but the laser flash method is adopted in the present invention. The thermal conductivity may vary greatly depending on the measurement method. Therefore, in the comparison between the present invention and the prior art, a comparative study should be made with the same measured thermal conductivity value.

Examples are shown below, but the present invention is not limited thereto.
(1) Average fiber diameter and fiber diameter dispersion of graphitized carbon short fibers:
According to JIS R7607, 60 graphitic carbon short fiber fillers were measured using a scale under an optical microscope, and the average value was obtained.

(2) Average fiber length of graphitized carbon short fibers:
The average fiber length is a number average fiber length, and 2000 or more carbon short fiber fillers that have undergone graphitization were measured with a length measuring device under an optical microscope, and obtained from the average value. The magnification was appropriately adjusted according to the fiber length.

(3) Crystal size:
Obtained by X-ray diffraction method, the crystallite size derived from the thickness direction of the hexagonal mesh surface is obtained using diffraction lines from the (002) plane, and the crystallite size derived from the growth direction of the hexagonal mesh surface is (110). It was determined using diffraction lines from the surface. In addition, the request was made in accordance with the Gakushin Law.

(4) Thermal conductivity of graphitized carbon short fiber:
The yarn was extracted from the graphitized pitch-based carbon fiber web produced under the same conditions except for the pulverization step, the resistivity was measured, and the thermal conductivity and electrical resistivity disclosed in JP-A-11-117143 were measured. It calculated | required from following formula (1) showing a relationship.
K = 1272.4 / ER-49.4 (1)
Here, K represents thermal conductivity W / (m · K), and ER represents electrical specific resistance μΩm.

(5) Fine structure of end face of graphene sheet of graphitized carbon short fiber:
The number of closed graphene sheets in the field of view of an image obtained by observing the carbon short fiber filler with a transmission electron microscope at 50,000 times was measured.

(6) Confirmation of a substantially flat surface:
The number of defects such as irregularities was counted in an image obtained by observing the graphitized carbon short fiber filler at 1000 times with a scanning electron microscope. In the case of 10 places or less, it was smooth.

(7) Thermal conductivity:
Using a sample cut into a diameter of 10 mm and a thickness of 2 mm, the measurement was performed at an ambient temperature of 25 ° C. using a known laser flash method. As a laser flash measuring device, a thermal constant measuring device TC-7000 type manufactured by Vacuum Riko was used.

(8) Rubber hardness:
Measured as Shore A hardness.

[Reference Example 1] (Preparation of graphitized carbon short fiber)
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 285 ° C. Using a spinneret having a diameter of 0.2 mm, heated air was ejected from the slit at a linear velocity of 4000 m / min, and the pitch pitch carbon fiber having an average fiber diameter of 14 μm was drawn by pulling the melt pitch. The spun fibers were collected on a belt to form a mat, and a web made of pitch-based carbon fibers having a basis weight of 320 g / m ² by cross-wrapping.

  The web was infusibilized by increasing the temperature from 175 ° C. to 280 ° C. in air at an average temperature increase rate of 7 ° C./min. The infusible web was fired at 800 ° C. in a nitrogen atmosphere, and then cut and milled to obtain carbon fibers having an average fiber length of about 180 μm. Then, it graphitized by heat-processing at 3000 degreeC with the electric furnace made into air atmosphere. The average fiber diameter of the graphitized carbon fiber was 9.7 μm, and the percentage of the fiber diameter dispersion to the average fiber diameter was about 13%. The true density was 2.20 g / cc.

  Using a transmission electron microscope, this pitch-based graphitized carbon fiber was observed at a magnification of 1,000,000, and only a structure in which the graphene sheet was closed was observed in an image magnified on a photograph at 4,000,000 times. Further, the pitch-type graphitized carbon fiber had one unevenness on the surface observed with a scanning electron microscope at a magnification of 4000 times and was substantially smooth.

  The crystal size (crystallite size in the c-axis direction) derived from the thickness direction of the hexagonal network surface of the graphite crystal obtained by the X-ray diffraction method of the pitch-based graphitized carbon fiber was 42 nm. The crystal size derived from the growth direction of the hexagonal network surface of the graphite crystal (crystallite size in the ab axis direction) was 76 nm.

Moreover, the single yarn was extracted from the graphitized web heat-treated at 3000 ° C. in an electric furnace in a non-oxidizing atmosphere, and the electrical specific resistance was measured. However, it was 1.6 μΩ · m. The thermal conductivity obtained using the following formula (1) was 750 W / m · K.
C = 1272.4 / ER-49.4 (1)
(ER indicates the electrical resistivity, and the unit here is μΩ · m)

[Example 1]
As a matrix material for the rubber sheet, 55 parts by weight of a nitrile-butadiene rubber precursor (N-230SL manufactured by JSR), 45 parts by weight of graphitized carbon short fibers prepared in Reference Example 1, carbon black having an average particle size of 78 μm (Asahi Carbon Co., Ltd.) Company) 25 parts by weight, plasticizer (Morton "TP-95") 10 parts by weight, diene rubber vulcanizing agent (Tsurumi Chemical "Salfux PMC") 0.7 parts by weight, vulcanization accelerator After mixing 2.5 parts by weight of zinc oxide fine particles having a particle size of 0.3 μm, a small amount of curing accelerator, and an anti-aging agent as an agent, it is turned over several times using a roll kneader (16-inch mixing roll manufactured by Otake Machinery Co., Ltd.). Roll kneading was performed to obtain a rubber precursor sheet having a thickness of 20 mm, a length of 900 mm, and a width of 500 mm. Here, the vertical direction corresponds to the rotation direction of the kneading roll, and the horizontal direction corresponds to the axial direction of the roll.

Next, the rubber precursor sheet is cut to a predetermined size, set in a mold, and heated and pressed in the sheet thickness direction under vacuum to obtain a vulcanized rubber sheet having a thickness of 17 mm, a length of 600 mm, and a width of 300 mm. It was. The rubber hardness of this sheet was 55.
Subsequently, this rubber sheet was punched out with a blade arranged at an equal interval of 10 mm in a direction perpendicular to the longitudinal direction of the sheet to obtain a sliced rubber sheet having a thickness of 10 mm, a length of 17 mm, and a width of 300 mm.
The rubber sheet thus obtained has a thermal conductivity of 6.5 W / m · K in the thickness direction, 0.8 W / m · K in the vertical direction, and 1.3 W / m · K in the horizontal direction. A rubber sheet having a high thermal conductivity in the direction of 5 W / m · K or more was obtained.

[Example 2]
A rubber precursor sheet having a thickness of 20 mm, a length of 900 mm, and a width of 500 mm created in Example 1 was punched out with blades arranged at equal intervals of 25 mm in a direction perpendicular to the longitudinal direction of the sheet, and the thickness was 25 mm, length 20 mm, width 500 mm. A sliced rubber precursor sheet was obtained.
Next, this sheet was cut to a predetermined size, set in a mold, and heated and pressed in the sheet thickness direction under vacuum to obtain a crosslinked rubber sheet having a thickness of 20 mm, a length of 25 mm, and a width of 50 mm. The rubber hardness of this sheet was 59.
The rubber sheet thus obtained has a thermal conductivity of 5.7 W / m · K in the thickness direction, 1.0 W / m · K in the vertical direction, and 1.5 W / m · K in the horizontal direction. A rubber sheet having a high thermal conductivity of 5 W / m · K or more was obtained.
Further, the surface smoothness of the rubber sheet was very good.

[Example 3]
Except that the mixing amount of the nitrile-butadiene rubber precursor was 50 parts by weight, the mixing amount of graphitized carbon short fibers was 50 parts by weight, and the mixing amount of carbon black was 20 parts by weight as the matrix material of the rubber sheet. A rubber sheet was prepared exactly as in 1.
The rubber sheet thus obtained has a rubber hardness of 67, a thermal conductivity of 7.8 W / m · K in the thickness direction, 0.9 W / m · K in the vertical direction, and 1.5 W / m · in the horizontal direction. A rubber sheet having a very high thermal conductivity of 7 W / m · K or more in the thickness direction was obtained.

[Example 4]
43 parts by weight of nitrile-butadiene rubber precursor, 57 parts by weight of graphitized carbon short fiber, 15 parts by weight of carbon black, and 13 parts by weight of plasticizer as a matrix material for the rubber sheet A rubber sheet was prepared in exactly the same manner as in Example 1 except that the part was used.
The rubber sheet thus obtained has a rubber hardness of 79, a thermal conductivity of 10.1 W / m · K in the thickness direction, 1.0 W / m · K in the vertical direction, and 1.7 W / m · in the horizontal direction. A rubber sheet having a very high thermal conductivity of 10 W / m · K or more in the thickness direction was obtained.

[Example 5]
A rubber precursor sheet having a thickness of 20 mm, a length of 900 mm, and a width of 500 mm created in Example 3 was punched with a blade arranged at regular intervals of 4 mm in a direction perpendicular to the longitudinal direction of the sheet, and the thickness was 4 mm, length 20 mm, width 500 mm. A sliced rubber precursor sheet was obtained.
Next, the sheet was cut to a predetermined size, set in a mold, and heated and pressed in the sheet thickness direction under vacuum to obtain a crosslinked rubber sheet having a thickness of 2 mm, a length of 30 mm, and a width of 60 mm. The rubber hardness of this sheet was 58.
The rubber sheet thus obtained has a thermal conductivity of 5.2 W / m · K in the thickness direction, 1.2 W / m · K in the vertical direction, and 1.7 W / m · K in the horizontal direction. A rubber sheet having a high thermal conductivity of 5 W / m · K or more was obtained.
Further, the surface smoothness of the rubber sheet was very good.

[Example 6]
Five rubber precursor sheets prepared in Example 1 were stacked and set in a mold, and heated and pressed in the sheet thickness direction under vacuum to obtain a vulcanized rubber sheet having a thickness of 87 mm, a length of 600 mm, and a width of 300 mm. The rubber hardness of this sheet was 54.
Subsequently, this rubber sheet was punched out with a blade arranged at an equal interval of 30 mm in a direction perpendicular to the longitudinal direction of the sheet to obtain a sliced rubber sheet having a thickness of 30 mm, a length of 87 mm, and a width of 300 mm.
The rubber sheet thus obtained has a thermal conductivity of 6.4 W / m · K in the thickness direction, 0.8 W / m · K in the vertical direction, and 1.4 W / m · K in the horizontal direction. A rubber sheet having a high thermal conductivity in the direction of 5 W / m · K or more was obtained.

The schematic diagram of the specific example of the kneading | mixing method between rolls. In an Example, it is a schematic diagram explaining the method of stamping out a rubber sheet to a predetermined direction and obtaining the rubber sheet of high heat conductivity in the thickness direction.

Explanation of symbols

1. 1. Roll for kneading 2. Roll for kneading 3. Sheet of rubber precursor composition Rubber sheet (rubber precursor sheet or rubber vulcanized sheet)
5). 5. Rubber sheet sliced by punching Punching tool

Claims (1)

1) 35 to 85 parts by weight of an uncrosslinked rubber component and 15 to 65 parts by weight of graphitized carbon short fibers having a crystallite size derived from the thickness direction of the hexagonal mesh surface of 30 nm or more, using mesophase pitch as a raw material. By kneading or kneading and extruding a rubber precursor composition containing 100 parts by weight under conditions such that a relatively strong shearing force and / or elongation force is generated in one direction inside the sheet, A step of creating a rubber precursor sheet substantially uniaxially oriented,
2) A step of slicing the sheet with a width of 0.05 to 100 mm by a plane perpendicular to the orientation direction of the carbon fibers,
3) A step of creating a rubber sheet in which the orientation of carbon fibers is fixed by cross-linking rubber by heat-pressing in the thickness direction of the sheet,
The manufacturing method of the heat conductive rubber sheet which manufactures the sheet | seat which has a thermal conductivity of 5 W / m * K or more in the thickness direction in which carbon fiber is substantially uniaxially oriented in the thickness direction with a thickness of 0.05 to 100 mm.

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