JP2010003981A - Heat-conducting sheet with graphite oriented in thickness direction - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-performance heat radiation sheet having flexibility in the thickness direction although it is made of a material exhibiting ultrahigh thermal conductivity exceeding 100 W/mK in the thickness direction of the sheet, and capable of reducing contact thermal resistance by being interposed between a heating element and a radiator. <P>SOLUTION: In this heat-conducting sheet with graphite oriented in the thickness direction which has a thickness ≤5 mm, graphite films 1 each having a thickness ≤1 mm are laminated through organic layers 2 so as to orient the crystal plane of the graphite in the thickness direction; and the ratio of graphite area/organic layer area observed from the surface direction of the sheet is 75/25 to 10/90. This application also provides a manufacturing method of the heat-conducting sheet with graphite oriented in the thickness direction which has high thermal conductivity in the thickness direction, and is formed by cutting, in a thickness ≤5 mm at a plane forming an angle ≥45° with respect to the crystal plane of the graphite, a graphite laminated body composed by laminating the graphite films 1 each having a thickness ≤1 mm through the organic layers 2 by a superposing or winding means. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a heat conductive sheet used for heat dissipation of devices such as a personal computer, a mobile phone, and a PDA.

  In recent years, the performance of electronic devices such as personal computers, mobile phones, and PDAs has improved significantly, and this is due to the significant improvement in CPU (MPU) performance. Along with such an improvement in CPU performance, the amount of heat generated by the CPU also increases remarkably, and how to dissipate heat in electronic devices is an important issue.

  As heat countermeasures, there are methods such as air cooling with fans, heat pipes, water cooling with water, etc., but these all require new heat dissipation devices, which not only increase the weight of the equipment, but also noise and Since there is a problem of causing an increase in the amount of electricity used, a method of releasing heat using a heat radiator such as a heat sink is often employed.

  Flexible heat conductive sheets such as silicone rubber are used for the purpose of efficiently transferring heat generated by heat generating elements such as semiconductor elements and electronic components to heat radiating elements such as a heat sink. These thermal conductive sheets have high thermal conductivity metals and alloys such as silver, copper, gold, aluminum and nickel, aluminum oxide, magnesium oxide, silicon oxide, boron nitride and nitridation to increase thermal conductivity. A thermally conductive filler obtained by processing ceramics such as aluminum, silicon nitride, and silicon carbide, carbon such as carbon black and diamond, and the like into a granular shape or a fiber shape is blended. The flexible heat-dissipating sheet is a material that fills a small gap between the heat-generating element and the heat-dissipating element and removes the thermal resistance, and therefore has high thermal conductivity especially in the thickness direction of the sheet. Is preferred. In addition, the lower the surface hardness of the sheet, the higher the thermal hardness of the sheet. The lower the surface hardness of the sheet, the closer the heating element and heat dissipation unit are to the heat transfer effect. There is.

  As an attempt to impart high thermal conductivity in the thickness direction of the sheet, Patent Document 1 discloses that anisotropic thermal conductivity having high thermal conductivity in the thickness direction of the sheet is obtained by orienting carbon fibers in the thickness direction of the silicone rubber. It has been shown that sheets with can be produced. When a sheet is produced by such a method, a sheet having higher thermal conductivity in the thickness direction than a sheet obtained by a normal production method can be obtained. However, if the carbon fiber is densely filled in the thickness direction, the surface hardness of the sheet becomes hard, so that the adhesion with the heat generating member and the heat radiating member is lowered, and the thermal resistance is increased. For this reason, the upper limit of the thermal conductivity in the sheet thickness direction obtained by the sheet in which the carbon fibers are oriented in the thickness direction is 50 W / mK at most.

Moreover, in patent document 2, after laminating a graphite film obtained by processing a polymer film at a high temperature of 2400 ° C. or higher to form a graphite block, the block is thinly cut in a direction perpendicular to the graphite surface. It has been shown that a graphite plate having ultra-high thermal conductivity in the thickness direction can be obtained. However, the material obtained in this way is a high-hardness material that should be called a plate rather than a sheet, and an effect that reduces the thermal resistance between the heat generator and the heat radiator cannot be expected.
JP 2000-195998 A Japanese Patent No. 3345986

  An object of the present invention is to provide a flexible thermal conductive sheet made of graphite having ultra-high thermal conductivity in the thickness direction and having low surface hardness and flexible characteristics.

  In order to solve the above problems, we tried to combine graphite film with various organic layers. As a result, after selecting an appropriate organic layer as described in this specification, the graphite block created by laminating the graphite film to the organic layer in a certain range is thinly cut in a specific direction. Or, by slicing, unlike graphite block cutting products that have been used in the past, it is possible to realize a graphite heat dissipation sheet that combines ultra-high thermal conductivity in the thickness direction with low surface hardness and flexible properties. Discovered and led to the present invention.

  That is, the present invention relates to the following 1) to 14).

  1) A graphite film having a thickness of 1 mm or less is laminated so that the crystal plane of graphite is oriented in the thickness direction through the organic layer, and the ratio of [graphite area / organic layer area] observed from the plane direction of the sheet is A thickness-oriented graphite oriented heat conductive sheet having a thickness of 5 mm or less, which is a ratio of 75/25 to 10/90.

  2) The thickness direction according to 1), wherein the thermal conductivity in the film surface direction of the graphite film is 100 W / mK or more, and the thermal conductivity in the direction perpendicular to the film surface is 50 W / mK or less. Graphite oriented thermal conductive sheet.

  3) The thickness-oriented graphite oriented heat conductive sheet according to any one of 1) to 2), wherein the raw graphite film is a film having a thickness of 400 μm or less.

  4) The thickness direction graphite oriented thermal conductive sheet according to any one of 1) to 3), wherein the thermal conductivity of the graphite film in a plane direction is 600 W / m · K or more.

  5) The thickness direction graphite orientation heat conduction according to any one of 1) to 4), wherein the graphite film is produced using at least expanded graphite produced by an expanding method. Sheet.

  6) The graphite film is obtained by heat treatment of at least one resin selected from the group consisting of polyimide resin, polyparaphenylene vinylene resin, and polyoxadiazole resin. 5) The thickness direction graphite orientation heat conductive sheet of any one of 5).

  7) The thickness direction graphite oriented heat conductive sheet according to any one of 1) to 6), wherein the graphite film has a thickness of 100 μm or less.

  8) The thickness-oriented graphite oriented heat conductive sheet according to any one of 1) to 7), wherein the thickness of the organic layer is ½ or more of the thickness of the graphite film.

  9) The thickness direction graphite oriented thermal conductive sheet according to any one of 1) to 8), wherein the organic layer is a material containing an acrylic pressure-sensitive adhesive and / or a silicone pressure-sensitive adhesive.

  10) The said organic layer contains the composite material of an adhesive and a base material formed by apply | coating an adhesive to both surfaces of a base material, The any one of 1) -9) characterized by the above-mentioned. Thickness direction oriented graphite thermal conductive sheet.

  11) The thickness direction graphite oriented heat conductive sheet according to any one of 1) to 8), wherein the organic layer contains a thermosetting resin.

12) The manufacturing method of the thickness direction graphite orientation heat conductive sheet which consists of following process (i)-(ii).
(I) Step of forming a graphite block by laminating a graphite film having a thickness of 1 mm or less via an organic layer (ii) 5 mm at a surface forming an angle of 45 ° or more with respect to the crystal plane of the graphite The step of cutting to the following thickness 13) In the step (i), a graphite film having a thickness of 1 mm or less is laminated by means of superposition or winding through an adhesive layer to create a graphite block, 12) The manufacturing method as described.

  14) In the step (i), an uncured curable polymer is applied to one or both surfaces of a graphite film having a thickness of 1 mm or less, and then laminated by means of superposition or winding, and this laminate is cured with the curable polymer. The production method according to 12), wherein the graphite block is prepared by curing under the curing conditions of

  15) In the step (i), after superposing a thermoplastic resin film on one side or both sides of a graphite film having a thickness of 1 mm or less, the laminate is laminated by means of superposition or winding, and the laminate is not lower than the softening temperature of the thermoplastic resin. To produce a graphite block.

  16) The method for producing a thickness-oriented graphite-oriented heat conductive sheet according to any one of 12) to 15), wherein a pressure of 0.1 MPa or more is applied to the laminate when producing the graphite block. .

  By using the present invention, the surface has excellent thermal conductivity that exceeds that of high thermal conductivity metals such as copper in the thickness direction, while the surface is soft with low hardness and excellent adhesion between the heating element and the heat dissipation element, and metal, etc. Since it has a low density compared to the above, an extremely lightweight heat conductive sheet can be obtained. Therefore, it is suitable for a heat dissipation material in which adhesion is particularly important.

<Graphite film>
The graphite film used in the present invention is a film-like graphite having a thickness of 1 mm or less in which graphite crystals are arranged along the direction of the film surface. The thermal conductivity in the film surface direction is preferably 100 W / mK or more, and the thermal conductivity in the direction perpendicular to the film surface is preferably 50 W / mK or less. The thermal conductivity in the film surface direction is more preferably 600 W / mK or more. The thermal conductivity of graphite has anisotropy of thermal conductivity derived from the original structure of graphite. The higher the thermal conductivity in the plane direction, the smaller the thermal conductivity in the thickness direction. Since the object of the present invention is to utilize the thermal diffusion anisotropy of graphite, it is extremely important for the graphite of the present invention that the thermal conductivity in the surface direction is large. There are two typical methods for producing a graphite film having such anisotropy.

  The first method for producing a graphite film preferably used in the present invention is a graphite film obtained by pressing graphite powder into a sheet. In order for the graphite powder to be formed into a film, the powder needs to be in the form of flakes or scales. The most common method for producing such graphite powder is a method called an expanded (expanded graphite) method. In this method, graphite is immersed in an acid such as sulfuric acid to produce a graphite intercalation compound, which is then heat-treated and foamed to separate the graphite layers. After peeling, the graphite powder is washed to remove the acid to obtain a thin film graphite powder. The graphite powder obtained by such a method is further subjected to rolling roll molding to obtain film-like graphite. A graphite film produced by using such a method and produced using expanded graphite is flexible and has a high thermal conductivity in the film surface direction, so that it is preferably used for the purpose of the present invention.

  The second method for producing a graphite film preferably used in the present invention is produced by heat treatment of at least one resin selected from the group consisting of polyimide resin, polyparaphenylene vinylene resin, and polyoxadiazole resin. It is a thing. The resin most commonly used in this method is a polyimide resin.

Moreover, it is excellent that it is a graphite film produced by heat-treating a film having an average coefficient of linear expansion in the range of 100 to 200 ° C. of 2.5 × 10 ⁻⁵ cm / cm / ° C. or less at a temperature of 2400 ° C. or more. It is preferable for realizing high thermal conductivity.

  In addition, it is preferable to produce a graphite film by heat-treating a polyimide film having a birefringence of 0.13 or more at a temperature of 2400 ° C. or more in order to realize excellent thermal conductivity.

Of course, a polyimide film having an average linear expansion coefficient in the range of 100 to 200 ° C. of 2.5 × 10 ⁻⁵ cm / cm / ° C. or less and a birefringence of 0.13 or more is obtained at a temperature of 2400 ° C. or more. It is preferable to produce a graphite film by heat treatment in order to realize excellent thermal conductivity.

As a polyimide preferably used for such graphitization, a polyimide composed of a repeating unit represented by the following chemical formula (1), a polyimide composed of a repeating unit represented by the chemical formula (2), and a chemical formula (3) Examples thereof include polyimide composed of repeating units.
Formula (1)

Formula (2)

Formula (3)

(R ¹ represents the formula (4)

A divalent organic group selected from the group consisting of Each R ² is independently —CH ₃ , —Cl, —Br, —F, or —CH ₃ O. R is the formula (5)

It is a bivalent organic group represented by these. Here, n is an integer of 1 to 3, X and Y are each independently hydrogen, halogen, carboxyl group, lower alkyl group having 6 or less carbon atoms, or alkoxy group having 6 or less carbon atoms, and A is —O -, - S -, - CO -, - SO 2 -, or -CH ₂ -, a. )
Among the repeating units represented by the formula (3), the repeating units represented by the following formulas (6) and (7) are particularly preferable.
Formula (6)

Formula (7)

  The polyimide resin used for obtaining the graphite film may be a polyimide composed of only one type of repeating unit, or may be a copolymer of two or more types of repeating units. Moreover, the film which consists of 1 type of polyimide may be used independently, and the mixed film of 2 or more types of polyimides may be used.

  Examples of combinations using two or more types include, for example, at least two or more types of repeating units selected from the group consisting of the repeating units represented by the above formulas (1), (2), and (3). Polyimide copolymer film, or a mixture of at least two polyimide copolymers selected from the group consisting of polyimide copolymers represented by formula (1), formula (2), and formula (3) A film and a polyimide co-polymer having at least three types of repeating units selected from the group consisting of repeating units represented by the above formula (1), formula (2), and the above formula (6) and formula (7). A polymer or a mixture of at least three or more selected from the group consisting of polyimide copolymers represented by formula (1), formula (2), general formula (6), and general formula (7) is included. Polyimide co-weight Body, and the like.

  Furthermore, when using combining 2 or more types of repeating units, the usage ratio can be selected suitably. For example, a polyimide copolymer polyimide film having a repeating unit represented by the formulas (1) and (2), wherein 4,4′-oxydianiline and paraphenylenediamine are used in a molar ratio of 9/1 to 4 /. A polyimide film obtained using a diamine containing 6 is also preferably used to obtain the graphite used in the present invention. Above all, the polyimide is a polyimide copolymer having repeating units represented by the formulas (1), (2), (6) and (7), and the number of each repeating unit is represented by a, b, c. When a is a polyimide film satisfying (a + b) / s, (a + c) / s, (b + d) / s, and (c + d) / s, where a + b + c + d is s, Preferably used.

  The graphite sheet used in the present invention can be obtained by heat-treating these polyimides at a temperature of 2400 ° C. or higher.

By using the polyimide described above, the average linear expansion coefficient in the range of 100 to 200 ° C. is 2.5 × 10 ⁻⁵ cm / cm / ° C. or less, preferably 2.0 × 10 ⁻⁵ cm / cm / ° C. or less. More preferably, a polyimide film that is 1.5 × 10 ⁻⁵ cm / cm / ° C. or less can be obtained. The linear expansion coefficient of the film was measured using a TMA (thermomechanical analyzer), first the sample was heated to 350 ° C. at a temperature increase rate of 10 ° C./min, then air-cooled to room temperature, and then increased again to 10 ° C./min. The temperature was increased to 350 ° C. at a temperature rate, and the average linear expansion coefficient was 100 ° C. to 200 ° C. from the second temperature increase. Further, the elastic modulus of the film is 200 kg / mm ² or more, further 250 kg / mm ² or more, more preferably 350 kg / mm ² or more.

The polyimide film used in the present invention has a birefringence Δn indicating in-plane orientation of 0.13 or more, preferably 0.15 or more, and most preferably 0.16 or more in any direction in the film plane. It is preferable. The birefringence here is the difference between the refractive index in the in-plane direction of the film and the refractive index in the thickness direction. In this specification, the birefringence Δnx in the in-plane direction of the film is given by the following equation.
Birefringence Δnx = (refractive index Nx in in-plane X direction) − (refractive index Nz in thickness direction)
A specific measuring method will be described. When a film sample is cut into a wedge shape, sodium light is applied from a direction perpendicular to the X direction in the film plane, and observed with a polarizing microscope, interference fringes are observed. When the number of interference fringes is n, the birefringence Δnx in the X direction in the film plane is
Δn = n × λ / d
It is represented by Here, λ is the wavelength of sodium light 589 nm, and d is the width of the sample (nm). Details are described in “New Experimental Chemistry Course” Vol. 19 (Maruzen Co., Ltd.).

  The above-mentioned “birefringence Δn is in any direction in the film plane” means, for example, 0 ° direction, 45 ° direction, 90 ° direction, 135 ° in the plane with reference to the flow direction during film formation. It means in any direction.

<Preparation method of polyimide film>
The polyimide film used in the present invention is prepared by mixing an organic solution of polyamic acid, which is a polyimide precursor, with an imidization accelerator, and then casting it on a support such as an endless belt or a stainless drum, followed by drying and baking. Can be produced by imidization.

  As a method for producing the polyamic acid used in the present invention, a known method can be used. Usually, at least one kind of aromatic dianhydride and at least one kind of diamine are substantially equimolar amounts in an organic solvent. Dissolved in. The obtained organic solution is stirred under controlled temperature conditions until the polymerization of the acid dianhydride and the diamine is completed, whereby a polyamic acid can be produced. Such a polyamic acid solution is usually obtained at a concentration of 5 to 35 wt%, preferably 10 to 30 wt%. When the concentration is in this range, an appropriate molecular weight and solution viscosity can be obtained.

  Any known method can be used as the polymerization method. For example, the following polymerization methods <1> to <5> are preferable.

  <1> A method in which an aromatic diamine is dissolved in an organic polar solvent, and this is reacted with a substantially equimolar amount of an aromatic tetracarboxylic dianhydride for polymerization.

<2> An aromatic tetracarboxylic dianhydride and a small molar amount of the aromatic diamine compound are reacted with each other in an organic polar solvent to obtain a prepolymer having acid anhydride groups at both ends. Then, the method of superposing | polymerizing using an aromatic diamine compound so that it may become substantially equimolar with respect to aromatic tetracarboxylic dianhydride.
This is the same as the method of synthesizing a prepolymer having the acid dianhydride at both ends using a diamine and an acid dianhydride, and reacting the prepolymer with a diamine different from the above to synthesize a polyamic acid.

  <3> An aromatic tetracarboxylic dianhydride is reacted with an excess molar amount of an aromatic diamine compound in an organic polar solvent to obtain a prepolymer having amino groups at both ends. Subsequently, after adding an aromatic diamine compound to the prepolymer, polymerization was performed using the aromatic tetracarboxylic dianhydride so that the aromatic tetracarboxylic dianhydride and the aromatic diamine compound are substantially equimolar. how to.

  <4> After the aromatic tetracarboxylic dianhydride is dissolved and / or dispersed in an organic polar solvent, an aromatic diamine compound is used so as to be substantially equimolar with respect to the acid dianhydride. Polymerization method.

  <5> A method in which a substantially equimolar mixture of aromatic tetracarboxylic dianhydride and aromatic diamine is reacted in an organic polar solvent for polymerization.

  Acid dianhydrides that can be used for the synthesis of polyimide in the present invention are pyromellitic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyl. Tetracarboxylic dianhydride, 1,2,5,6-naphthalene tetracarboxylic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4 ′ -Benzophenonetetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, bis (3,4- Dicarboxyphenyl) propane dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride, bis (2 , 3-Zical Xylphenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) ethane dianhydride, oxydiphthalic dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, p-phenylenebis (trimerit Acid monoester acid anhydride), ethylene bis (trimellitic acid monoester acid anhydride), bisphenol A bis (trimellitic acid monoester acid anhydride), and the like, which may be used alone or in any It can be used in a mixture of proportions.

  Examples of diamines that can be used for the synthesis of polyimide in the present invention include 4,4′-oxydianiline, p-phenylenediamine, 4,4′-diaminodiphenylpropane, 4,4′-diaminodiphenylmethane, benzidine, and 3,3. '-Dichlorobenzidine, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl ether (4,4'-oxydianiline), 3,3'-diaminodiphenyl ether (3,3'-oxydianiline), 3,4'-diaminodiphenyl ether (3,4'-oxydianiline), 1,5-diaminonaphthalene, 4,4'-diaminodiphenyl Diethylsilane, 4,4'-diaminodiphenylsilane, 4,4 ' Diaminodiphenylethylphosphine oxide, 4,4′-diaminodiphenyl N-methylamine, 4,4′-diaminodiphenyl N-phenylamine, 1,4-diaminobenzene (p-phenylenediamine), 1,3-diaminobenzene, Including 1,2-diaminobenzene and the like, which can be used alone or in any proportion of the mixture.

  In particular, from the viewpoint of increasing the elastic modulus and increasing the birefringence by reducing the linear expansion coefficient, in the production of the polyimide film in the present invention, an acid that forms the repeating unit represented by the chemical formula (3). It is preferable to use a dianhydride as a raw material.

  By using the acid dianhydride that forms the repeating unit represented by the chemical formula (3) described above, a polyimide film having a relatively low water absorption is obtained, and this causes foaming due to moisture during the graphitization process. It is also preferable from the viewpoint that it can be prevented.

In particular, when an organic group containing a benzene nucleus as shown in Formula (4) is used as R ¹ in Chemical Formula (3) in the acid dianhydride forming the repeating unit, molecular orientation of the resulting polyimide film It is preferable from the viewpoints of high properties, low coefficient of linear expansion, high elastic modulus, high birefringence, and low water absorption.

  In order to further reduce the linear expansion coefficient, increase the elastic modulus, increase the birefringence, and decrease the water absorption, the synthesis of the polyimide in the present invention is represented by the chemical formula (6) or the chemical formula (7). An acid dianhydride capable of forming a repeating unit may be used as a raw material.

In particular, a polyimide film obtained by using an acid dianhydride having a structure in which a benzene ring is linearly bonded by two or more ester bonds as a raw material has a very linear conformation as a whole although it contains a bent chain. It has a relatively rigid property. As a result, the linear expansion coefficient of the polyimide film can be reduced by using this raw material, for example, 1.5 × 10 ⁻⁵ / cm / cm / ° C. or less.

  In order to further reduce the linear expansion coefficient, increase the elastic modulus, and increase the birefringence, the polyimide in the present invention is preferably synthesized using p-phenylenediamine as a raw material.

  Among them, preferred diamines are 4,4′-oxydianiline and p-phenylenediamine, and the total moles of these alone or the two are 40 mol% or more, further 50 mol% or more, further 70 It is preferably at least mol%, and more preferably at least 80 mol%. Furthermore, it is preferable that p-phenylenediamine contains 10 mol% or more, further 20 mol% or more, further 30 mol% or more, and further 40 mol% or more. If the content of these diamines is less than the lower limit of these mol% ranges, the resulting polyimide film tends to have a high linear expansion coefficient, a low elastic modulus, and a low birefringence. However, if the total amount of diamine is p-phenylenediamine, it is difficult to obtain a thick polyimide film with less foaming, so 4,4'-oxydianiline is preferably used. In addition, the carbon ratio can be reduced, the amount of cracked gas generated can be reduced, the need for rearrangement of aromatic rings is reduced, and graphite having excellent appearance and thermal conductivity can be obtained.

  The most suitable acid dianhydride used for the synthesis of the polyimide film in the present invention is pyromellitic dianhydride and / or p-phenylenebis (trimellitic acid monoester which forms a repeating unit represented by the formula (7) Acid dianhydride), and the total mole of these alone or both is 40 mol% or more, further 50 mol% or more, further 70 mol% or more, or even 80 mol based on the total acid dianhydride. % Or more is preferable. If the amount of these acid dianhydrides used is less than 40 mol%, the resulting polyimide film tends to have a large linear expansion coefficient, a small elastic modulus, and a small birefringence.

Moreover, you may add additives, such as carbon black and a graphite, with respect to a polyimide film, a polyamic acid, and a polyimide resin.
Preferred solvents for synthesizing the polyamic acid are amide solvents N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, and the like. N, N-dimethylformamide, N, N-dimethylacetamide can be used particularly preferably.

  Next, a polyimide production method includes a heat curing method in which polyamic acid as a precursor is converted to imide by heating, or a polyhydric acid such as acetic anhydride and other dehydrating agents, picoline, quinoline, isoquinoline, Any of the chemical curing methods in which imide conversion is performed using a tertiary amine such as pyridine as an imidization accelerator may be used. Among them, a higher boiling point such as isoquinoline is preferable. This is preferable because it does not evaporate in the initial stage of film production, and the catalytic effect is easily exhibited until the last step of drying. In particular, the resulting film has a low coefficient of linear expansion, high modulus of elasticity, high birefringence, and can be rapidly graphitized at a relatively low temperature to obtain high-quality graphite. Cure is preferred. In particular, the combined use of a dehydrating agent and an imidization accelerator is preferable because the resulting film has a small linear expansion coefficient, a large elastic modulus, and a large birefringence. In addition, the chemical cure method is an industrially advantageous method that is excellent in productivity because the imidization reaction proceeds faster and the imidization reaction can be completed in a short time in the heat treatment.

  In the production of a film by a specific chemical cure, first, an imidization accelerator comprising a dehydrating agent and a catalyst of a stoichiometric amount or more is added to a polyamic acid solution, an organic film such as a support plate, PET, a drum, or an endless belt A film having self-supporting properties is obtained by casting or coating on a support such as a film to evaporate the organic solvent. Next, the self-supporting film is further heated and dried to be imidized to obtain a polyimide film. The temperature during the heating is preferably in the range of 150 ° C to 550 ° C. There is no particular limitation on the rate of temperature increase at the time of heating, but it is preferable to gradually heat in a continuous or stepwise manner so that the maximum temperature falls within the predetermined temperature range. Although the heating time varies depending on the film thickness and the maximum temperature, it is generally preferably in the range of 10 seconds to 10 minutes after reaching the maximum temperature. Furthermore, if the process of making the polyimide film includes a step of bringing the film into contact with the container, fixing, holding or stretching in order to prevent shrinkage, the resulting film has a low coefficient of linear expansion and an elastic modulus. It is preferable because it tends to be high and the birefringence tends to increase.

<Graphization of polyimide>
Next, the process of graphitization of the polyimide film will be described.
In the present invention, the starting polyimide film is preheated in nitrogen gas to perform carbonization. The preheating is usually performed at a temperature of about 1000 ° C., and for example, when pretreatment is performed at a rate of temperature increase of 10 ° C./min, it is desirable to hold for about 30 minutes in a temperature range of 1000 ° C. In the pretreatment stage, it is effective to apply a pressure in the plane direction that does not cause the film to break so that the orientation of the starting polymer film is not lost.

  Next, the film carbonized by the above method is set in an ultra-high temperature furnace so that it can be freely expanded and contracted, and graphite is applied. Graphitization is carried out in an inert gas, but argon is most suitable as the inert gas, and it is more preferable to add a small amount of helium to the argon. The treatment temperature is required to be at least 2400 ° C., and the treatment is finally performed at a temperature of 2700 ° C. or more, more preferably 2800 ° C. or more.

  The higher the treatment temperature is, the higher the quality of graphite can be converted, but from the viewpoint of economy, it is preferable that it can be converted to high quality graphite at the lowest possible temperature. In order to create an ultra-high temperature of 2500 ° C. or higher, an electric current is usually passed directly to a graphite heater, and heating is performed using the juule heat. Graphitization occurs by converting the carbonized film prepared in the pretreatment to a graphite structure, and in that case, the carbon-carbon bond must be cleaved and recombined. In order for the graphitization to occur smoothly, the cleavage and recombination must occur with minimal energy, and the molecular orientation of the starting polyimide film affects the carbon alignment of the carbonized film, which is graphitization. This has the effect of reducing the energy of carbon-carbon bond cleavage and recombination. Therefore, by designing the molecules so that the molecules are oriented and realizing a high degree of orientation, graphitization at a low temperature and conversion to a high-quality graphite film becomes possible.

<Thickness of graphite film>
The thickness of the graphite film produced by the production method of the present invention needs to be 1 mm or less. Preferably it is 400 micrometers or less, More preferably, it is 100 micrometers or less, More preferably, it is 75 micrometers or less, Most preferably, it is 50 micrometers or less. The thinner the graphite film is, the more preferable it is because the surface hardness of the sheet after cutting or slicing can be kept low. Further, the thinner the original thickness of the graphite film, the higher the crystal orientation of the film and the better the surface direction thermal conductivity of the film.

<Organic layer>
The thickness direction graphite oriented heat conductive sheet of the present invention is characterized in that a graphite film is laminated through an organic layer so that the crystal plane of graphite is oriented in the thickness direction. By using the organic layer at a certain ratio, the surface hardness of the sheet can be lowered, and a heat conductive sheet having flexibility and high adhesion can be obtained.

  As the organic layer, any polymer, oligomer, or reactive low molecular weight compound can be used without particular limitation as long as it is a material that can be held so that the graphite sheets are not separated from each other. Preferable materials for the organic layer include pressure-sensitive adhesives, adhesives, curable polymers, thermoplastic polymers, and the like. The organic layer is preferably an adhesive layer from the viewpoint that a heat conductive sheet excellent in flexibility and adhesion can be obtained. In addition, it is preferable to use a curable polymer or a thermoplastic polymer in the organic layer from the viewpoint that the graphite block can be manufactured inexpensively and easily.

<Adhesive layer>
Examples of the material for the pressure-sensitive adhesive layer include acrylic pressure-sensitive adhesives and silicone-based pressure-sensitive adhesives, and these materials have excellent heat resistance, and have sufficient long-term reliability even when combined with heat-generating parts and heat-dissipating parts. Sex is obtained. Moreover, the surface hardness of the thickness direction graphite orientation heat conductive sheet finally obtained can be kept low by using these adhesives.

  Moreover, it is preferable that an adhesive layer is a material containing a base material with an adhesive. More preferably, it is a composite material obtained by applying a pressure-sensitive adhesive to both surfaces of a substrate. By including the base material, the bonding operation becomes easy. In particular, when using a graphite film having excellent crystallinity and thermal diffusivity, the film may be easily peeled in layers, but the presence of the base material can improve the peelability. . In addition, the presence of the base material increases the strength of the thickness direction graphite oriented thermal conductive sheet, and can prevent the thickness direction graphite oriented thermal conductive sheet from being damaged at the time of mounting, mechanically crimped and fixed, or during rework. It becomes.

  The base material of the pressure-sensitive adhesive layer is preferably a material containing polyimide and polyethylene terephthalate. Polyimide and polyethylene terephthalate have excellent heat resistance, strength, and dimensional stability. When combined, they do not lose thermal conductivity, and also have excellent anti-peeling properties and scratch resistance when cutting or slicing blocks. . The thickness of the substrate is preferably 6 μm or less. When the thickness of the substrate is thin, it is possible to laminate without deteriorating the excellent thermal diffusibility of the graphite film.

  These pressure-sensitive adhesive layers may be directly formed on a graphite film by coating, printing, dipping, vapor deposition, or the like, or may be formed by transferring using a laminate. The adhesive layer can be formed by dip or roll coating, film adhesive applied to the graphite film, adhesive film applied to both sides of the polymer thin film as the base material, and then the graphite film like a tape. There are methods such as affixing to the substrate, and any of them can be preferably used.

<Curable polymer or thermoplastic polymer>
When a curable polymer is used as the material for the organic layer, the curing means is not particularly limited, and any material such as a thermosetting polymer, an ultraviolet curable polymer, and a humidity curable polymer can be used. It is. As the curable polymer, a wide variety of polymers such as epoxy resin, unsaturated polyester resin, unsaturated vinyl resin, polyimide resin, phenol resin, and silicone resin can be used. Among them, a curable resin marketed as an adhesive can be preferably used.

  When a thermoplastic polymer is used as the material for the organic layer, it becomes difficult to use the thermoplastic polymer at a temperature exceeding the softening temperature of the thermoplastic polymer. Therefore, it is necessary to select a material that meets the use conditions. Since the thickness direction graphite oriented heat conductive sheet is often used in close contact with a portion that generates heat, it is preferable to use a polymer material having excellent heat resistance.

  Examples of thermoplastic polymers that can be used for such purposes include polyamide resins, polyester resins, polyarylene sulfide resins, polycarbonate resins, crystalline polyolefin resins such as polyethylene, and cyclic olefin resins. A wide range of polymers such as polyolefin resins, aromatic vinyl resins, acrylic resins and the like can be used. In particular, a resin excellent in adhesiveness is preferably used.

  As a method for imparting adhesiveness to the thermoplastic polymer, it is preferable to use a modified thermoplastic polymer having a reactive functional group such as an epoxy group. As such an adhesive polymer film, various materials that are commercially available as hot melt films can be used.

  These curable polymers and thermoplastic polymers may be directly formed by coating, printing, dipping, vapor deposition, etc. on a graphite film, or the laminate of the polymer as it is or its precursor dissolved in a solvent. It may be formed by transferring using Formation of the polymer layer includes a coating method by dip or roll, a method of laminating a film-like polymer with a graphite film, a method of attaching a film-like polymer to the graphite film, etc., all of which are preferably used. I can do it.

<Ratio of [graphite area / organic layer area]>
In order to make the thickness-oriented graphite oriented heat conductive sheet as soft as possible, the ratio of [graphite area / organic layer area] when observing the obtained thickness-oriented graphite oriented heat conductive sheet from the surface direction of the sheet is It is important to keep it within a certain range. Since the graphite film is a hard material as compared with the organic layer, the flexibility of the obtained oriented sheet can be improved by setting the ratio of the graphite layer to a certain value or less. On the other hand, if the proportion of the graphite layer is too small, the thermal conductivity is lowered, which is not preferable. For the above reasons, the ratio of [graphite area / organic layer area] needs to be in the range of 75/25 to 10/90. The ratio of the two is preferably in the range of 72/28 to 13/87, more preferably 70/30 to 15/85, still more preferably 67/33 to 17/83, and most preferably 65/35 to 20/80. is there. Moreover, it is preferable that the thickness of the said organic layer is 1/2 or more of the thickness of the said graphite film.

<Lamination of graphite film with organic layer>
The thickness direction graphite oriented heat conductive sheet of the present invention comprises the following steps (i) to (ii):
(I) Step of forming a graphite block by laminating a graphite film having a thickness of 1 mm or less via an organic layer (ii) 5 mm at a surface forming an angle of 45 ° or more with respect to the crystal plane of the graphite It can manufacture with the manufacturing method which consists of the process cut to the following thickness.

  When an adhesive is used as the organic layer, in the step (i), it is preferable that a graphite film having a thickness of 1 mm or less is laminated by an overlapping or winding means via an adhesive to create a graphite block.

  When a curable polymer is used as the organic layer, in the step (i), an uncured curable resin is applied to one or both sides of a graphite film having a thickness of 1 mm or less, and then laminated by means of superposition or winding. The laminate is preferably cured under the curing conditions of the curable resin to produce a graphite block.

  When a thermoplastic polymer is used as the organic layer, in the step (i), a thermoplastic resin film is laminated on one side or both sides of a graphite film having a thickness of 1 mm or less, and then laminated by means of superposition or winding. It is preferable to produce the graphite block by heating the laminate above the softening temperature of the thermoplastic resin.

  After providing an organic layer on the graphite film as described above, a laminated block in which the graphite film is oriented in an arbitrary direction can be obtained by laminating the film thickly by means such as overlapping and winding the film. . At this time, if a graphite film is laminated by a method such as superposition, a block in which graphite crystals are oriented in biaxial directions can be obtained (FIG. 1). When a graphite film is laminated by a method such as winding, a block in which graphite crystals are oriented in a uniaxial direction can be obtained (FIG. 2).

  When a sheet is obtained by processing from the obtained block by a method such as cutting or slicing, the thickness is obtained by cutting or slicing on a plane that forms an angle of 45 ° or more with respect to an arbitrary orientation plane of graphite. It is possible to obtain a thickness-oriented graphite-oriented heat conductive sheet in which heat is more easily transmitted in the direction. The angle formed between an arbitrary orientation plane of graphite and the plane to be cut or sliced is preferably 50 ° or more, more preferably 60 ° or more, still more preferably 70 ° or more, and most preferably 80 ° or more.

  When the graphite block is biaxially oriented, a sheet that easily conducts heat in two directions is obtained. When the graphite block is uniaxially oriented, a sheet that easily conducts heat only in one direction is obtained. These can be used according to the required characteristics. In general, it is preferable to use a biaxially oriented block for an application where the flexibility of the sheet is more required, and it is preferable to use a uniaxially oriented block for an application where the strength of the sheet is required.

  When producing a graphite block, it is preferable to apply a pressure of 0.1 MPa or more to the graphite block. By making it under pressure, the adhesion between the layers of each graphite film is improved, and peeling when the graphite block is cut or sliced can be prevented. The pressure applied to the graphite block is more preferably 0.2 MPa or more, and most preferably 0.5 MPa or more.

<Cutting or slicing of graphite blocks>
There is no particular limitation on the processing method for obtaining a thickness-oriented graphite oriented heat conductive sheet from biaxially or uniaxially oriented graphite blocks, and various cutting methods and slicing methods can be used. For example, a method of cutting a block using a cutter, cutting out a sheet by laser processing, or slicing a sheet by slicing processing can be exemplified.

  In these processes, since peeling may occur in the original graphite film layer, it is preferable to appropriately control the processing conditions so that peeling does not occur.

  Also, in order to prevent exfoliation in the original graphite film layer due to the stress applied to the sheet during cutting, the entire graphite block is preliminarily cured with a curable resin composition such as a thermosetting resin, a photocurable resin, or a humidity curable resin. A method of embedding with an object is also useful.

<Characteristics of Thickness Orientation Graphite Oriented Thermal Conductive Sheet>
The thus obtained thickness direction graphite oriented heat conductive sheet generally has a thermal conductivity in the thickness direction of 50 W / mK or more, preferably 100 W / mK or more, more preferably 200 W / mK or more, most preferably. It has a thermal conductivity of 300 W / mK or more.

  In order to reduce the thermal resistance between the heat generating body and the heat radiating body, the thickness of the thickness direction graphite oriented sheet needs to be 5 mm or less. The thickness of the sheet is preferably 4 mm or less, more preferably 3 mm or less, still more preferably 2 mm or less, and most preferably 1 mm or less.

  Moreover, in order to reduce the thermal resistance between a heat generating body and a heat radiating body, the surface hardness of the thickness direction graphite orientation sheet is so preferable that it is soft. The surface hardness measured by DuroE is preferably 85 or less, more preferably 80 or less, further preferably 75 or less, and most preferably 70 or less.

EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited to these Examples.
The measurement was performed as follows.

(Measurement of surface direction thermal conductivity of polyimide film)
The thermal diffusivity in the surface direction was measured with a laser pit manufactured by ULVAC. Further, the heat capacity of the graphite film was calculated from comparison with a reference standard substance Mo having a known heat capacity. From these measured values, the surface direction thermal conductivity was calculated by the following equation.
[Thermal conductivity] = [thermal diffusivity] x [density] x [specific heat]

(Measurement of thermal conductivity in the thickness direction of polyimide film)
In the thickness direction thermal conductivity measurement of the graphite film, Xe flash analyzer LFA447 Nanoflash manufactured by NETZSCH was used in accordance with ASTM E1461. A graphite film is cut to a diameter of 10 mm, and Xe light absorbing spray (Black Guard Spray FC-153 manufactured by Fine Chemical Japan Co., Ltd.) is applied to both surfaces of the film and dried. The thermal diffusivity of was measured. Further, the heat capacity of the graphite film was calculated from comparison with a reference standard substance Mo having a known heat capacity. From these measured values, the surface direction thermal conductivity was calculated by the following equation.
[Thermal conductivity] = [thermal diffusivity] x [density] x [specific heat]

(Preparation method of polyimide film A)
One equivalent of pyromellitic dianhydride was dissolved in a DMF (dimethylformamide) solution in which one equivalent of 4,4′-oxydianiline was dissolved to obtain a polyamic acid solution (18.5 wt%).

  While this solution was cooled, an imidation catalyst containing 1 equivalent of acetic anhydride, 1 equivalent of isoquinoline, and DMF was added to the carboxylic acid group contained in the polyamic acid to degas. Next, this mixed solution was applied onto an aluminum foil so as to have a predetermined thickness after drying. The mixed solution layer on the aluminum foil was dried using a hot air oven and a far infrared heater.

  The drying conditions for film production when the finished thickness is 75 μm are shown. The mixed solution layer on the aluminum foil was dried in a hot air oven at 120 ° C. for 240 seconds to form a self-supporting gel film. The gel film was peeled off from the aluminum foil and fixed to the frame. Furthermore, the gel film is heated stepwise in a hot air oven at 120 ° C. for 30 seconds, 275 ° C. for 40 seconds, 400 ° C. for 43 seconds, 450 ° C. for 50 seconds, and a far infrared heater at 460 ° C. for 23 seconds. And dried.

  As described above, a polyimide film having a thickness of 75 μm (polyimide film A: elastic modulus 3.1 GPa, water absorption 2.5%, birefringence 0.10, linear expansion coefficient 3.0 × 10 −5 / ° C.) manufactured. In addition, when producing films with other thicknesses, the firing time was adjusted in proportion to the thickness. For example, in the case of a film having a thickness of 225 μm, the firing time was set to three times that in the case of 75 μm. Further, when the thickness is large, it is necessary to take a sufficient baking time at a low temperature in order to prevent foaming due to evaporation of the solvent or imidization catalyst of the polyimide film.

(Method for producing carbonized film A)
A 75 μm thick polyimide film A is sandwiched between graphite plates, heated to 1000 ° C. in a nitrogen atmosphere using an electric furnace, and then heat-treated at 1000 ° C. for 1 hour for carbonization (carbonization treatment). It was. This carbonized film is designated as carbonized film A.

(Method for producing carbonized film B)
A polyimide film A having a thickness of 175 μm is sandwiched between graphite plates, heated to 1000 ° C. in a nitrogen atmosphere using an electric furnace, and then heat-treated at 1000 ° C. for 1 hour for carbonization (carbonization treatment). It was. This carbonized film is designated as carbonized film B.

(Method for producing graphite film A)
Carbonized film A (400 cm ² (length 200 mm × width 200 mm)) obtained by carbonization treatment is sandwiched from above and below by plate-like smooth graphite of length 270 mm × width 270 mm × thickness 3 mm, length 300 mm × width 300 mm × The graphite film A was obtained by compressing the graphite after the heat treatment obtained by holding in a graphite container having a thickness of 60 mm and heating to 3000 ° C. by a single plate press method. The surface direction thermal conductivity was 1300 W / mK, the thickness direction thermal conductivity was 6.8 W / mK, and the density was 2.0 g / cm ³ .

(Method for producing graphite film B)
A graphite film B was obtained in the same manner as the graphite film A except that a 10 wt% methanol solution of iron nitrate was applied to the carbonized film B obtained by the carbonization treatment, and then sandwiched between graphite plates and set in a graphite container. As a result of the measurement, the thickness 85 .mu.m, the surface direction thermal conductivity 850W / mK, thickness direction thermal conductivity of 5.3 W / mK, and a density of 2.0 g / cm ^3.

(Graphite film C)
It is a PGS graphite sheet “EYGS182310” manufactured by Matsushita Electric Industrial Co., Ltd. manufactured by high-temperature treatment of a polyimide film. As a result of the measurement, the thickness was 80 μm, the thermal conductivity in the plane direction was 740 W / mK, the thermal conductivity in the thickness direction was 5.3 W / mK, and the density was 2.0 g / cm ³ .

(Graphite film D)
This is an expanded graphite gasket M / # 8100ClaasB manufactured by Japan Matex Co., Ltd., manufactured by the expanding method. As a result of the measurement, the thickness was 250 μm, the plane direction thermal conductivity 190 W / mK, the thickness direction thermal conductivity 7.4 W / mK, and the density 1.0 g / cm ³ .

Example 1
Acrylic double-sided tape 1 (Teraoka Seisakusho 707: Acrylic 13 μm / PET 4 μm / Acrylic 13 μm) was bonded to one side of a 200 mm × 300 mm graphite film-A with a laminator. 3000 sheets of the obtained graphite film with pressure-sensitive adhesive were laminated, and a pressure of 0.5 MPa was applied for 1 minute by a press machine to create a graphite block in which graphite crystals were oriented in a biaxial direction of 200 mm × 300 mm × 210 mm. (FIG. 1).
The obtained block was cut to a thickness of 1 mm using a tip saw at an angle of 90 ° with respect to the crystal plane of the graphite to obtain a thickness-oriented graphite-oriented heat conductive sheet 1 of 200 mm × 210 mm × thickness 1 mm. .

(Example 2)
Except for using graphite film-B instead of graphite film-A and using acrylic double-sided tape 2 (Teraoka Seisakusho 7642: acrylic 35 μm / PET 25 μm / acrylic 35 μm) instead of acrylic double-sided tape 1 In the same manner as in Example 1, a thickness-oriented graphite-oriented heat conductive sheet 2 was obtained.

(Example 3)
Except for using graphite film-C instead of graphite film-A and using acrylic double-sided tape 2 (Teraoka Seisakusho 7642: acrylic 35 μm / PET 25 μm / acrylic 35 μm) instead of acrylic double-sided tape 1 In the same manner as in Example 1, a thickness-oriented graphite-oriented heat conductive sheet 3 was obtained.

Example 4
The thickness direction graphite oriented heat conductive sheet 4 was formed in the same manner as in Example 1 except that the obtained block was cut at an angle of 60 ° with respect to the crystal plane of the graphite so as to have a thickness of 1 mm using a tip saw. Obtained.

(Example 5)
Acrylic double-sided tape 1 (Teraoka Seisakusho 707: Acrylic 13 μm / PET 4 μm / Acrylic 13 μm) was bonded to one side of a 200 mm × 300 mm graphite film-A with a laminator. The obtained graphite film with pressure-sensitive adhesive was laminated by winding and laminating in a roll shape, thereby producing a graphite cylinder block in which graphite crystals were oriented in a uniaxial direction of 300 mm × 100 mmφ (FIG. 2). To this, a pressure of 0.5 MPa was applied for 1 minute by a press machine to obtain a prismatic graphite block.

  The obtained block was cut to a thickness of 1 mm using a tip saw at an angle of 90 ° with respect to the crystal plane of graphite to obtain a thickness-oriented graphite oriented heat conductive sheet 5.

(Example 6)
Acrylic double-sided tape 1 (Teraoka Seisakusho 707: Acrylic 13 μm / PET 4 μm / Acrylic 13 μm) was bonded to one side of a 200 mm × 300 mm graphite film-A with a laminator. The obtained graphite film with pressure-sensitive adhesive is laminated in such a manner that it is pressed into a box shape while being bent in an arbitrary shape in the same direction, and a pressure of 0.5 MPa is applied for 1 minute by a press machine, thereby 300 mm × 100 mm A graphite cuboid block having graphite crystals oriented in a uniaxial direction of × 100 mm was produced (FIG. 3).

  The obtained block was cut to a thickness of 1 mm using a tip saw at an angle of 90 ° with respect to the crystal plane of graphite, and a thickness direction graphite oriented heat conductive sheet 6 was obtained.

(Example 7)
Example: Except that a graphite block was prepared by applying an epoxy adhesive on one side of graphite film-A to a thickness of 50 μm and applying a pressure of 0.5 MPa for 1 minute by a press machine heated to 180 ° C. In the same manner as in No. 1, a thickness direction graphite oriented heat conductive sheet 7 was obtained.

(Example 8)
Except that a graphite block was prepared by laminating a graphite film-D and a thermoplastic polyethylene hot melt film having a thickness of 250 μm and applying a pressure of 0.5 MPa for 1 minute by a press machine heated to 180 ° C. In the same manner as in No. 1, a thickness-oriented graphite oriented heat conductive sheet 8 was obtained.

(Comparative Example 1)
Acrylic double-sided tape 1 (Teraoka Seisakusho 707: Acrylic 13 μm / PET 4 μm / Acrylic 13 μm) was bonded to one side of a 200 mm × 300 mm graphite film-A with a laminator. By laminating 14 sheets of the obtained graphite film with pressure-sensitive adhesive, and finally laminating another 200 mm × 300 mm size graphite film-A, a pressure of 0.5 MPa was applied for 1 minute with a press machine. A surface-oriented graphite-oriented heat conductive sheet 11 having a size of 200 mm × 300 mm × thickness 1 mm was obtained.

(Comparative Example 2)
A commercially available expanded graphite powder, BSP-80 (manufactured by Chuetsu Graphite Industries Co., Ltd.) was filled into a box mold and pressed to prepare a 50 mm square graphite block in which the graphite powder was oriented almost randomly. This graphite block was cut to a thickness of 1 mm using a tip saw to obtain a graphite sheet 12 of 50 mm × 50 mm × thickness 1 mm.

(Comparative Example 3)
On one side of a 200 mm × 300 mm size graphite film-B, a solution-like polyimide precursor (Torney manufactured by Toray Industries, Inc.) was applied to a thickness of 10 μm. 3000 sheets of the obtained graphite film with a polyimide precursor were laminated, heated to 300 ° C. with a press machine, applied with a pressure of 0.5 MPa for 10 minutes, and then cooled to obtain a 200 mm × 300 mm × 210 mm two-layer film. A graphite block having graphite crystals oriented in the axial direction was prepared.
The obtained block was cut to a thickness of 1 mm using a tip saw at an angle of 90 ° with respect to the crystal plane of the graphite to obtain a thickness-oriented graphite-oriented heat conductive sheet 13 of 200 mm × 210 mm × thickness 1 mm. .

(Comparative Example 4)
Carbonized film A (400 cm ² (length 200 mm × width 200 mm)) obtained by the carbonization treatment is stacked on 5000 sheets, held in a graphite container of length 300 mm × width 300 mm × thickness 60 mm, and a pressure of 20 MPa is applied. While heating to 3000 ° C., a graphite block in which the graphite films were adhered to each other was produced.

  The central portion of the obtained block is cut at an angle of 90 ° with respect to the crystal plane of the graphite so as to have a thickness of 1 mm using a tip saw, and a 120 mm × 120 mm × thickness 1 mm thickness direction graphite oriented heat conductive sheet 14 Got.

[Thermal conductivity of sheet]
After cutting out a 12.7 mmφ disk-shaped sample from the obtained graphite-oriented heat conductive sheet, applying a spray for absorbing laser light (Black Guard Spray FC-153 manufactured by Fine Chemical Japan Co., Ltd.) to the sample surface and drying, Based on ASTM E1461, the thermal diffusivity in the thickness direction was measured using a Xe flash analyzer LFA447 Nanoflash manufactured by NETZSCH. Further, the heat capacity of the graphite film was calculated from comparison with a reference standard substance Mo having a known heat capacity. From these measured values, the thickness direction thermal conductivity was calculated by the following equation.
[Thermal conductivity] = [thermal diffusivity] x [density] x [specific heat]

[surface hardness]
According to JIS K-6253, durometer hardness type E was measured at 23 ° C. × 50% RH using an Asker rubber hardness meter E type.

Ratio of [graphite area / organic layer area] The obtained graphite oriented heat conductive sheet was observed with an operation electron microscope from the surface direction of the sheet, thereby calculating a ratio of [graphite area / organic layer area].
Table 1 shows various physical properties of the sheets of Examples and Comparative Examples.

  As shown in the table, the thickness direction graphite oriented heat conductive sheet obtained in the examples has ultrahigh thermal conductivity in the thickness direction, and the surface hardness is kept low. It turns out to be optimal for transmission applications.

  The thickness direction graphite oriented heat conductive sheet of the present invention has a high thermal conductivity that exceeds the metal in the thickness direction, but has a lower surface hardness and a lower density than metals. Therefore, the present invention is optimal for heat dissipation of electronic devices such as electronic devices, especially portable electronic devices that require weight reduction such as mobile phones, and is industrially useful.

It is a schematic diagram of the block which the crystal | crystallization of the graphite film orientated in the biaxial direction. It is a schematic diagram of the block which the crystal | crystallization of the graphite film orientated in the uniaxial direction. It is a schematic diagram of the block which the crystal | crystallization of the graphite film orientated in the uniaxial direction.

Explanation of symbols

1 Graphite film layer 2 Organic layer 3 Adhesive coated graphite film 4 Box type

Claims (16)

  A graphite film having a thickness of 1 mm or less is laminated so that the crystal plane of graphite is oriented in the thickness direction through the organic layer, and the ratio of [graphite area / organic layer area] observed from the plane direction of the sheet is 75 / A thickness-oriented graphite-oriented heat conductive sheet having a thickness of 5 mm or less and a ratio of 25 to 10/90.   2. The thickness direction graphite according to claim 1, wherein the graphite film has a thermal conductivity in a film surface direction of 100 W / mK or more and a thermal conductivity in a direction perpendicular to the film surface of 50 W / mK or less. Oriented heat conductive sheet.   3. The thickness-oriented graphite oriented heat conductive sheet according to claim 1, wherein the graphite film as a raw material is a film having a thickness of 400 μm or less.   The thickness direction graphite oriented heat conductive sheet according to any one of claims 1 to 3, wherein the graphite film has a thermal conductivity in a plane direction of 600 W / m · K or more.   The thickness-oriented graphite oriented heat conductive sheet according to any one of claims 1 to 4, wherein the graphite film is produced using at least expanded graphite produced by an expanding method.   The graphite film is obtained by heat treatment of at least one resin selected from the group consisting of polyimide resin, polyparaphenylene vinylene resin, and polyoxadiazole resin. The thickness direction graphite orientation heat conductive sheet of any one of these.   The thickness direction graphite oriented heat conductive sheet according to any one of claims 1 to 6, wherein the graphite film has a thickness of 100 µm or less.   The thickness direction graphite oriented heat conductive sheet according to any one of claims 1 to 7, wherein the thickness of the organic layer is 1/2 or more of the thickness of the graphite film.   The thickness direction graphite oriented heat conductive sheet according to any one of claims 1 to 8, wherein the organic layer is a material containing an acrylic adhesive and / or a silicone adhesive.   The thickness direction according to any one of claims 1 to 9, wherein the organic layer includes a composite material of an adhesive and a substrate formed by applying an adhesive to both surfaces of the substrate. Graphite oriented thermal conductive sheet.   The thickness direction graphite oriented thermal conductive sheet according to any one of claims 1 to 8, wherein the organic layer contains a curable polymer. The manufacturing method of the thickness direction graphite orientation heat conductive sheet which consists of following process (i)-(ii).
(I) Step of forming a graphite block by laminating a graphite film having a thickness of 1 mm or less via an organic layer (ii) 5 mm at a surface forming an angle of 45 ° or more with respect to the crystal plane of the graphite Cutting to the following thickness   The manufacturing method according to claim 12, wherein, in the step (i), a graphite film having a thickness of 1 mm or less is laminated by means of superposition or winding through an adhesive layer to produce a graphite block.   In the step (i), an uncured curable polymer is applied to one or both surfaces of a graphite film having a thickness of 1 mm or less, and then laminated by means of superposition or winding, and this laminate is cured with the curable polymer. The manufacturing method of Claim 12 which hardens on conditions and produces a graphite block.   In the step (i), after superposing a thermoplastic resin film on one or both sides of a graphite film having a thickness of 1 mm or less, it is laminated by means of superposition or winding, and this laminate is heated to a temperature higher than the softening temperature of the thermoplastic resin. The method according to claim 12, wherein a graphite block is produced.   The method for producing a thickness-oriented graphite oriented heat conductive sheet according to any one of claims 12 to 15, wherein a pressure of 0.1 MPa or more is applied to the laminate when the graphite block is produced.

Images