JP6423633B2 - Polyimide film for graphite sheet and method for producing the same - Google Patents

Description

  The present invention relates to a polyimide film used for the production of a graphite sheet having flexibility and bending resistance, which is used as a heat radiating material, a soaking material as an electric conductor or a heat conductor, and a method for producing the same.

  Polyimide film is known to have excellent properties in heat resistance, cold resistance, chemical resistance, electrical insulation, mechanical strength, and the like. Electrical insulation material for wire, heat insulating material, flexible printed circuit board (FPC) It is widely used as a base film, a carrier tape film for IC automated tape bonding (TAB), an IC lead frame fixing tape, and the like.

  When a polyimide film is used in these applications, an important practical property is the slipperiness (slidability) of the film. In various film processing steps, the film support (for example, roll) and the slipperiness of the film and the slipperiness between the films are ensured, thereby improving the operability and handleability in each step. Generation of defects such as wrinkles on the film can be avoided.

  In the conventional smoothing technology for polyimide films, an inert inorganic compound (for example, alkaline earth metal orthophosphate, dibasic calcium phosphate anhydride, calcium pyrophosphate, silica, talc) is added to polyamic acid (patent document) 1) is known.

  In addition, a graphite sheet obtained by heat-treating a polyimide film in an inert gas at a temperature of 2400 ° C. or higher and rolling it as necessary creates a uniform foamed state by heat-treating at a high temperature. It is known that a flexible graphite sheet having flexibility and elasticity can be obtained (see Patent Documents 2 and 3). In recent years, graphite sheets have attracted attention as heat dissipation members for electronic devices because they have higher thermal conductivity than metal sheets such as copper and aluminum.

  It is known that it is preferable to add an inorganic or organic filler to graphitize a polymer compound such as polyimide (see Patent Document 3 and Patent Document 4). The role of the filler is to make the film after heat treatment into a uniform foamed state. That is, the added filler generates a gas during heating, and the cavity after the generation of the gas becomes a passage to help the gentle passage of the decomposition gas from the inside of the film. The filler thus serves to create a uniform foamed state.

As a method of controlling the degree of foaming, a method of controlling the temperature rising rate during graphitization is known (see Patent Document 5).
However, the degree of foaming of the film may not be sufficient only by controlling the heating rate during graphitization, and the thermal conductivity, flexibility, and bending resistance of the obtained graphite sheet are sufficient as a heat radiating member for electronic devices. There was no case.

JP-A-62-68852 JP-A-3-75211 JP-A-4-21508 JP-A-8-267647 JP 2008-024571 A

  In view of the above situation, the present invention has good foaming of the film at the time of graphitization by heat treatment, and the graphitized sheet has excellent thermal conductivity, flexibility and bending resistance, amount of inorganic particles, dispersion An object of the present invention is to provide a polyimide film that is appropriately controlled.

  As a result of intensive studies to solve the above problems, the present inventors have a linear expansion coefficient of 20 ppm / ° C. or less, paraphenylenediamine or paraphenylenediamine, 4,4′-diaminodiphenyl ether, and pyromellitic acid. A polyimide produced by containing, as a raw material, one or more acid anhydrides selected from the group consisting of dianhydrides and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydrides, and inorganic particles dispersed therein The film has good foaming when it is graphitized by heat treatment at a temperature of 2000 ° C. or higher, and it is found that the graphite sheet obtained by the heat treatment is excellent in thermal conductivity, flexibility and bending resistance. Based on this, the present invention has been completed.

The present invention relates to the following inventions.
[1] selected from the group consisting of paraphenylenediamine or paraphenylenediamine, 4,4′-diaminodiphenyl ether, pyromellitic dianhydride and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride A polyimide film produced by containing one or more acid anhydrides as raw materials and having inorganic particles dispersed therein, wherein the polyimide film is heat-treated at a temperature of 2000 ° C. or more to produce a graphite sheet. A polyimide film having a linear expansion coefficient of 20 ppm / ° C. or less.
[2] The polyimide film as described in [1] above, wherein the inorganic particles are contained in a ratio of 0.03 to 1.00% by weight per 1 weight of the film resin.
[3] The polyimide film as described in [1] or [2], wherein the average particle diameter of the inorganic particles is 0.1 to 2.0 μm.
[4] In any one of the above [1] to [3], the inorganic particles having a particle size of 0.5 to 2.5 μm occupy a ratio of 80% by volume or more based on the total inorganic particles. The polyimide film as described.
[5] The polyimide film according to any one of [1] to [4], wherein the inorganic particles contain calcium hydrogen phosphate as a main component.
[6] The polyimide film as described in any one of [1] to [5], wherein the molar ratio of paraphenylenediamine to 4,4′-diaminodiphenyl ether is 40/60 to 10/90. .
[7] The above-mentioned [1], wherein the molar ratio of pyromellitic dianhydride and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride is 80/20 to 60/40. The polyimide film according to any one of [5].
[8] Selected from the group consisting of paraphenylenediamine or paraphenylenediamine and 4,4′-diaminodiphenyl ether, pyromellitic dianhydride and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride When the polyamic acid is produced by reacting with one or more acid anhydrides in a polar organic solvent, and the polyamic acid is heated to form a film, the average particle size is 0.1 to 2.0 μm. And a slurry in which inorganic particles having a particle size distribution in which inorganic particles having a particle diameter of 0.5 to 2.5 μm account for 80% by volume or more in all particles are dispersed in the same polar organic solvent as the polar organic solvent. The polyamic acid solution is characterized in that the inorganic particles are added to the polyamic acid in a ratio of 0.03 to 1.00% by weight per 1 weight of the resin. ] The manufacturing method of the polyimide film of any one of [7].
[9] A graphite sheet obtained by firing the polyimide film according to any one of [1] to [7].
[10] A method for producing a graphite sheet, comprising firing the polyimide film according to any one of [1] to [7].

  The polyimide film of the present invention has good foaming during graphitization by heat treatment, and the graphite sheet produced by heat-treating the polyimide film of the present invention has excellent thermal conductivity, flexibility and bending resistance.

Hereinafter, the present invention will be described in more detail.
The polyimide film of the present invention has a linear expansion coefficient of 20 ppm / ° C. or less, paraphenylenediamine or paraphenylenediamine and 4,4′-diaminodiphenyl ether, pyromellitic dianhydride and 3,3 ′, 4,4. A polyimide film produced by using one or more acid anhydrides selected from the group consisting of '-biphenyltetracarboxylic dianhydride as a raw material and having inorganic particles dispersed therein, the polyimide film being at least 2000 ° C A graphite sheet is produced by heat treatment at a temperature of

[Polyamic acid]
In obtaining the polyimide film of the present invention, first, an aromatic diamine component and an aromatic acid anhydride component are polymerized in an organic solvent to obtain a polyamic acid solution (hereinafter also referred to as a polyamic acid solution). Hereinafter, the polyamic acid solution will be described.

In the present invention, the polyamic acid solution can be obtained by polymerizing a raw material aromatic diamine component and aromatic dianhydride component, or a chemical substance mainly composed of both in an organic solvent.
As an aromatic diamine component, it is preferable that paraphenylene diamine is included as an essential component, and 4,4'- diaminodiphenyl ether is included as another aromatic diamine component.
As the aromatic anhydride component, pyromellitic dianhydride and / or 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride is preferable.

  In the present invention, the molar ratio of paraphenylenediamine and 4-4′-diaminodiphenyl ether used as a film raw material is preferably 40/60 to 10/90, and preferably 30/70 to 15/85. Is more preferable.

  In the present invention, the molar ratio of pyromellitic dianhydride used as a film raw material to 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride is 80/20 to 60/40. Is more preferable, and 75/25 to 65/35 is more preferable.

  In the present invention, in addition to paraphenylenediamine and 4,4'-diaminodiphenyl ether, a small amount of one or more other diamines may be added as long as the effects of the present invention are not impaired. Further, in addition to pyromellitic dianhydride and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, a small amount of other acid dianhydrides 1 or 2 as long as the effects of the present invention are not hindered. More than seeds may be added. Specific examples of other diamines and acid dianhydrides include, but are not limited to:

  Examples of the other diamine include 3,3′-diaminodiphenyl ether, metaphenylenediamine, 4,4′-diaminodiphenylpropane, 3,4′-diaminodiphenylpropane, 3,3′-diaminodiphenylpropane, and 4,4 ′. -Diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, benzidine, 4,4'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 4 , 4'-diaminodiphenylsulfone, 3,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 2,6-diaminopyridine, bis- (4-aminophenyl) diethylsilane, 3,3'-dichloro Benzidine, bis- (4-aminophen E) ethylphosphinoxide, bis- (4-aminophenyl) phenylphosphinoxide, bis- (4-aminophenyl) -N-phenylamine, bis- (4-aminophenyl) -N-methylamine, 1,5-diaminonaphthalene, 3,3′-dimethyl-4,4′-diaminobiphenyl, 3,4′-dimethyl-3 ′, 4-diaminobiphenyl-3,3′-dimethoxybenzidine, 2,4- Bis (p-β-amino-t-butylphenyl) ether, bis (p-β-amino-t-butylphenyl) ether, p-bis (2-methyl-4-aminopentyl) benzene, p-bis- ( 1,1-dimethyl-5-aminopentyl) benzene, m-xylylenediamine, p-xylylenediamine, 1,3-diaminoadamantane, 3,3′-diamino-1,1′- Aminoadamantane, 3,3′-diaminomethyl-1,1′-diadamantane, bis (p-aminocyclohexyl) methane, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, 3- Methylheptamethylenediamine, 4,4′-dimethylheptamethylenediamine, 2,11-diaminododecane, 1,2-bis (3-aminopropoxy) ethane, 2,2-dimethylpropylenediamine, 3-methoxyhexaethylenediamine, 2 , 5-dimethylhexamethylenediamine, 2,5-dimethylheptamethylenediamine, 5-methylnonamethylenediamine, 1,4-diaminocyclohexane, 1,12-diaminooctadecane, 2,5-diamino-1,3,4- Oxadiazo , 2,2-bis (4-aminophenyl) hexafluoropropane, N-(3- aminophenyl) -4-aminobenzamide, 4-aminophenyl-3-aminobenzoate, and the like.

  Examples of the other acid dianhydrides include 2,3 ′, 3,4′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride, 2,3, 6,7-naphthalenedicarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) ether, pyridine-2,3,5,6-tetracarboxylic dianhydride, 1,2,4 5-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,4,5,8-decahydronaphthalenetetracarboxylic dianhydride, 4,8-dimethyl- 1,2,5,6-hexahydronaphthalenetetracarboxylic dianhydride, 2,6-dichloro-1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,7-dichloro-1,4, 5,8-Naphthalenetetracarbo Acid dianhydride, 2,3,6,7-tetrachloro-1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,8,9,10-phenanthrenetetracarboxylic dianhydride, 2 , 2-bis (2,3-dicarboxyphenyl) propane dianhydride, 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ) Ethane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride Benzene-1,2,3,4-tetracarboxylic dianhydride, 3,4,3 ′, 4′-benzophenone tetracarboxylic dianhydride, and the like.

  In the present invention, specific examples of the organic solvent used for forming the polyamic acid solution include sulfoxide solvents such as dimethyl sulfoxide and diethyl sulfoxide, N, N-dimethylformamide, N, N-diethylformamide and the like. Formamide solvents, N, N-dimethylacetamide, acetamide solvents such as N, N-diethylacetamide, pyrrolidone solvents such as N-methyl-2-pyrrolidone and N-vinyl-2-pyrrolidone, phenol, o-, Examples of phenolic solvents such as m- or p-cresol, xylenol, halogenated phenol, and catechol include aprotic polar solvents such as hexamethylphosphoramide and γ-butyrolactone. These can be used singly or in combination of two or more, and further can be used in combination with aromatic hydrocarbons such as xylene and toluene.

The polymerization method of the polyamic acid solution may be performed by any known method, for example,
(1) A method in which the total amount of the aromatic diamine component is first put in a solvent, and then the aromatic acid anhydride component is added so as to be equivalent to the total amount of the aromatic diamine component for polymerization.
(2) A method in which the total amount of the aromatic acid anhydride component is first put in a solvent, and then the aromatic diamine component is added so as to be equivalent to the aromatic acid anhydride component for polymerization.
(3) After putting one aromatic diamine compound in a solvent, after mixing for the time required for reaction in the ratio from which an aromatic acid anhydride compound becomes 95-105 mol% with respect to the reaction component, the other A method in which an aromatic diamine compound is added and then the other aromatic acid anhydride compound is added and polymerized so that the total aromatic diamine component and the total aromatic acid anhydride component are approximately equivalent.
(4) After putting the aromatic acid anhydride compound in the solvent, after mixing for the time required for the reaction at a ratio of 95 to 105 mol% of one aromatic diamine compound with respect to the reaction component, A method of polymerizing by adding an aromatic acid anhydride compound and then adding the other aromatic diamine compound so that the total aromatic diamine component and the total aromatic acid anhydride component are approximately equivalent.
(5) A polyamic acid solution (A) is prepared by reacting one aromatic diamine component and an aromatic acid anhydride component in a solvent so that either one becomes excessive, and the other aromatic diamine component in another solvent. The polyamic acid solution (B) is prepared by reacting either the diamine component or the aromatic acid anhydride component so as to be excessive. A method in which the polyamic acid solutions (A) and (B) thus obtained are mixed to complete the polymerization. At this time, when adjusting the polyamic acid solution (A), if the aromatic diamine component is excessive, the polyamic acid solution (B) has excessive aromatic acid anhydride component, and the polyamic acid solution (A) has aromatic acid anhydride. When the component is excessive, in the polyamic acid solution (B), the aromatic diamine component is excessive, and the polyamic acid solutions (A) and (B) are mixed and the wholly aromatic diamine component and wholly aromatic used in these reactions. The method of adjusting so that an acid anhydride component may become substantially equivalent, etc. are mentioned.
The polymerization method is not limited to these, and other known methods may be used.

  In the present invention, the aromatic acid anhydride component and the aromatic diamine component constituting the polyamic acid are polymerized at a ratio in which the respective mole numbers are approximately equal, one of which is 10 mol%, preferably 5 mol%. You may mix | blend excessively with respect to the other within the range.

  The polymerization reaction is preferably performed with stirring and mixing in an organic solvent. The polymerization temperature is not particularly limited, but is usually carried out at an internal temperature of the reaction solution of 0 to 80 ° C. The polymerization time is not particularly limited, but it is preferably performed continuously for 10 minutes to 30 hours. In the polymerization reaction, the polymerization reaction may be divided or the temperature may be increased or decreased as necessary. Although there is no restriction | limiting in particular in the addition order of both reactants, It is preferable to add an aromatic acid anhydride in the solution of an aromatic diamine component. Vacuum defoaming during the polymerization reaction is an effective method for producing a high-quality polyamic acid organic solvent solution. Further, the polymerization reaction may be controlled by adding a small amount of an end-capping agent to the aromatic diamine before the polymerization reaction. The end-capping agent is not particularly limited, and a known one can be used.

  The polyamic acid solution thus obtained contains a solid content of usually 5 to 40% by weight, preferably 10 to 30% by weight. The viscosity is a value measured with a Brookfield viscometer and is not particularly limited, but is usually 10 to 2000 Pa · s, and preferably 100 to 1000 Pa · s for stable liquid feeding. In addition, the polyamic acid in the organic solvent solution may be partially imidized.

[Inorganic particles]
The inorganic particles dispersed in the polyimide film of the present invention are preferably insoluble in all chemical substances that are contacted in the polyimide film manufacturing process of the present invention.

As inorganic particles that can be used in the present invention, SiO ₂ (silica), TiO ₂ (titania), CaHPO ₄ (calcium hydrogen phosphate), Ca ₂ P ₂ O ₇ (calcium pyrophosphate) and the like can be preferably exemplified. . Among them CaHPO ₄ is caused good swelling by gas generated when the sublimed from within a polyimide film, for good graphite sheet having excellent thermal conductivity is obtained, it is particularly preferable that the main component CaHPO _4.

  The content of the inorganic particles in the polyimide film is preferably 0.03 to 1.0% by weight, more preferably 0.1 to 0.8% by weight per 1 weight of the film resin. If it is 0.03% by weight or less, the mechanical strength and thermal conductivity of the graphite sheet obtained by firing the polyimide film are undesirably low. On the other hand, if it is 1.0% by weight or more, the uniformity of foaming during graphitization is lowered, which is not preferable.

  The average particle diameter of the inorganic particles is preferably from 0.1 to 2.0 μm, more preferably from 0.5 to 1.5 μm, and even more preferably from the viewpoint that foaming during graphitization becomes more uniform. .8 to 1.2 μm.

  As for the particle size distribution of the inorganic particles, it is better that the particle size distribution is narrow, that is, the proportion of particles having similar sizes in all particles is high. Specifically, inorganic particles having a particle size of 0.5 to 2.5 μm are used. It is preferable to occupy a ratio of 80% by volume or more with respect to all inorganic particles. If the proportion of particles smaller than this range and 0.5 μm or less is increased, the mechanical strength of the graphite sheet is weak and the thermal conductivity is lowered, which is not preferable. In addition, it is possible to remove coarse particles with a 5 μm cut filter or a 20 μm cut filter when feeding inorganic particles, but if the proportion of inorganic particles with a size exceeding 6.0 μm increases, the filter eyes This is not preferable because clogging frequently occurs and process stability is deteriorated and coarse aggregation of inorganic particles is likely to occur. Therefore, the inorganic particles preferably have a total particle size in the range of 6.0 μm or less. The average particle size, particle size, and particle size distribution are values measured using a laser diffraction / scattering particle size distribution measuring apparatus LA-910 manufactured by Horiba, Ltd. as in the examples described later.

  The inorganic particles can be used as a slurry uniformly dispersed in a polar solvent such as N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone, etc., thereby preventing aggregation of the particles. Therefore, it is preferable. Since this slurry has a very small particle size, the sedimentation rate is low and stable. Even if it settles, it can be easily redispersed by re-stirring. The inorganic particle slurry can be obtained using a conventional method.

  In the present invention, the method for dispersing the inorganic particles in the polyimide film is not particularly limited. However, in order to prevent sedimentation / aggregation of the inorganic particle slurry, it is added to a prepolymerized polyamic acid solution, followed by decyclization and desolvation. It is preferable to obtain a polyimide film. Moreover, after adding an inorganic particle slurry in the organic solvent before polyamic acid polymerization, you may obtain a polyimide film through polyamic acid polymerization and decyclization desolvation. The inorganic particle slurry can be added in any step of polyimide film production as long as it is a step before decyclization and solvent removal. Moreover, it is preferable that the polar solvent used for an inorganic particle slurry is the same polar solvent as the organic solvent used for manufacture of a polyamic acid.

  The dispersion is preferably performed using a homogenizer or a grinding mill in order to disperse the filler uniformly. The homogenizer and the grinding mill are not particularly limited, and conventionally known ones can be used.

  The polyamic acid solution used in the present invention may contain one or more compounds other than the inorganic particles. Examples of compounds other than the inorganic particles include carbon, metal oxides such as alumina and titania, and boron compounds such as boron nitride.

[Polyimide film]
Next, the manufacturing method of the polyimide film of this invention is demonstrated.

The polyimide film is produced by heating a polyamic acid solution, which will be described in detail below.
As a method for producing a polyimide film, a polyamic acid solution is cast into a film and thermally decyclized and desolvated to obtain a polyimide film, and a polyamic acid solution is mixed with a cyclization catalyst and a dehydrating agent to form a chemical film. The method of obtaining a polyimide film by preparing a gel film by decyclizing to a film and heating it to remove the solvent is mentioned, but the latter can reduce the thermal expansion coefficient of the polyimide film obtained, and the film Since the height distribution in the surface direction is increased, it is preferable because good thermal conductivity and thickness of graphite can be obtained.

  In the method of chemically decyclizing, first, the polyamic acid solution is prepared. The polyamic acid solution can contain a cyclization catalyst (imidization catalyst), a dehydrating agent, a gelation retarder, and the like.

  Specific examples of the cyclization catalyst used in the present invention include aliphatic tertiary amines such as trimethylamine and triethylenediamine, aromatic tertiary amines such as dimethylaniline, and complex such as isoquinoline, pyridine, and β-picoline. Examples thereof include cyclic tertiary amines, and these can be used alone or in combination of two or more. Among these, an embodiment in which at least one heterocyclic tertiary amine is used is preferable.

  Specific examples of the dehydrating agent used in the present invention include aliphatic carboxylic acid anhydrides such as acetic anhydride, propionic anhydride and butyric anhydride, and aromatic carboxylic acid anhydrides such as benzoic anhydride. Of these, acetic anhydride and / or benzoic anhydride are preferred.

  As a method for producing a polyimide film from a polyamic acid solution, a polyamic acid solution containing a cyclization catalyst and a dehydrating agent is cast on a support from a base with a slit and formed into a film, and an imide is formed on the support. The gel film is partially advanced to form a gel film having self-supporting properties, and then peeled off from the support, heat-dried / imidized, and subjected to heat treatment.

  The polyamic acid solution is formed into a film shape through a slit-shaped base, cast on a heated support, undergoes a thermal ring-closing reaction on the support, and becomes a gel film having self-supporting properties. It is peeled from the body.

  The support is a metal rotating drum or an endless belt, and its temperature is controlled by radiant heat from a liquid or gaseous heat medium and / or an electric heater.

  The gel film is usually heated to 30 to 200 ° C., preferably 40 to 150 ° C. by receiving heat from the support and / or receiving heat from a heat source such as hot air or an electric heater. It becomes self-supporting by drying the volatile matter of and is peeled from the support.

  The gel film peeled off from the support is usually stretched in the running direction while regulating the running speed with a rotating roll. Stretching is usually carried out at a temperature of 140 ° C. or lower at a magnification of 1.01-1.90 times, preferably 1.05-1.60 times, more preferably 1.10-1.50 times. The gel film stretched in the running direction is introduced into the tenter device, and both ends in the width direction are held by the tenter clip, and stretched in the width method while running with the tenter clip.

  The film dried in the above drying zone is usually heated for 15 seconds to 30 minutes with a wind, an infrared heater or the like. Next, heat treatment is usually performed at a temperature of 250 to 500 for 15 seconds to 30 minutes with hot air and / or an electric heater. The thickness of the polyimide film is adjusted while adjusting the draw ratio in the running direction and the draw ratio in the width direction.

  Although the thickness of the polyimide film used by this invention is not specifically limited, It is preferable that it is the range of 5 micrometers or more and 200 micrometers or less, and it is more preferable that it is the range of 10 micrometers or more and 150 micrometers or less.

  The linear expansion coefficient of the polyimide film of the present invention produced as described above is usually about 20 ppm / ° C. or less, preferably about 18 ppm / ° C. or less. In addition, a linear expansion coefficient is the value measured by the method as described in the Example mentioned later, and is an average value of the value of the width direction (TD) of a polyimide film, and a machine conveyance direction (MD) normally.

[Graphite sheet]
The graphite sheet of the present invention can be obtained by baking and graphitizing the polyimide film of the present invention.
The manufacturing method of the graphite sheet of this invention is demonstrated below.

  In obtaining the graphite sheet of the present invention, first, the polyimide film is cut into a predetermined size, and the film surface of the polyimide film is horizontal or the film surface is set up in a graphite holding container.

  The temperature of the graphitization firing (hereinafter also referred to as the main heat treatment) is usually 2000 ° C. or higher, preferably 2400 ° C. or higher, and more preferably 2600 ° C. or higher. The final firing temperature is preferably 2700 ° C. or higher, more preferably 2800 ° C. or higher, and still more preferably around 3000 ° C. When the firing temperature is higher than 3500 ° C., the heat-resistant deterioration of the firing furnace is large and long-time production is difficult. When the maximum firing temperature is less than 2000 ° C., the obtained graphite sheet tends to be hard and brittle. Although the temperature increase rate at the time of baking is not specifically limited, For example, it is performed at about 1-10 degreeC / min. A known heating means can be used for firing. Further, the firing time is not particularly limited.

  Firing is usually performed in an inert gas. The inert gas is not particularly limited, and examples thereof include helium, argon, nitrogen, etc., but it is preferable to use argon. Moreover, the pressure at the time of baking may be a normal pressure.

  Prior to the firing (main heat treatment), a pre-heat treatment may be performed as necessary. The temperature of the preliminary heat treatment is preferably lower than the temperature of the main heat treatment. Specifically, about 900 ° C. or higher and 1500 ° C. or lower is preferable. The temperature increase rate of the preheating treatment is not particularly limited, but is, for example, about 1 to 15 ° C./min. The preheating treatment is also usually performed in an inert gas. As the inert gas, the same ones as described above can be used. The time for the preheating treatment is not particularly limited.

  The fired graphite sheet is preferably rolled by being sandwiched between rolling rollers. Thickness unevenness caused by swelling of the graphite sheet after firing can be reduced by rolling treatment. Moreover, the density of the graphite sheet after baking can be enlarged and thermal conductivity can be improved by a rolling process.

Since the graphite sheet of the present invention produced as described above has a large thermal diffusion coefficient, it has excellent thermal conductivity. The thermal diffusion coefficient is a value measured by the method described in Examples described later.
The thermal diffusion coefficient of the graphite sheet of the present invention is not particularly limited, but is preferably 7.0 (cm ² / s) or more.

  Moreover, the breaking strength of the graphite sheet of this invention is 10 MPa or more normally, Preferably it is 15 MPa or more, More preferably, it is 20 MPa or more. The breaking strength is a value measured by the method described in Examples described later.

  EXAMPLES Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples at all, and many variations are within the technical idea of the present invention. This is possible by those with ordinary knowledge.

  The measurement method in the present invention will be described below.

[Evaluation of inorganic particles]
Using a laser diffraction / scattering type particle size distribution measuring apparatus LA-910 manufactured by HORIBA, a sample dispersed in a polar solvent was measured and analyzed. As a result, a particle size range, an average particle size, and a particle size of 0.5 to all particles were measured. The occupancy of 2.5 μm particles was read.

[Linear expansion coefficient]
Samples having a size of 5 mm wide × 10 mm long were collected, and each sample was heated under the following conditions using TMA-50 manufactured by Shimadzu Corporation.
First temperature increase: room temperature → 300 ° C. (temperature increase rate 10 ° C./min)
Temperature drop: 300 ° C → 35 ° C (temperature drop rate 5 ° C / min)
Second temperature increase: 35 ° C. → 220 ° C. (temperature increase rate 10 ° C./min)
The analysis of the linear expansion coefficient was performed under the temperature range of 50 ° C. to 200 ° C. at the second temperature increase.
In addition, the linear expansion coefficient calculated | required the average value of the value of the width direction (TD) of a polyimide film and a machine conveyance direction (MD) as an average linear expansion coefficient.

[density]
Measuring method: Archimedes method Measuring device: Electronic analysis balance AUX-120 manufactured by Shimadzu Corporation
Measurement temperature: 25 ° C
Dipping liquid: water

[Thermal diffusion coefficient]
Measuring method: Xenon flash method Measuring device: Heat conduction measuring device LFA447 manufactured by NETZSCH
Measurement temperature: 25 ° C
Light source: Xenon flash lamp IR detector: InSb detector (liquid nitrogen cooling)

[Breaking strength]
Measuring device: Autograph AGS-X manufactured by Shimadzu Corporation
Measurement temperature: 25 ° C
Distance between chucks: 50mm
Tensile speed: 25 mm / min Test piece: width 10 mm

[Thickness of polyimide film and graphite sheet]
Measurements were made using Mitutoyo lightmatic (Series 318).

[Foaming]
A 100 mm square graphite sheet was visually evaluated according to the following evaluation criteria.
Good (O): Foaming is not uniform throughout (x): No foaming or spots

[Flexibility]
A graphite sheet of 100 mm (vertical) × 100 mm (width) was folded so that the ends in the vertical direction or the ends in the width direction were exactly overlapped, and then a load of 100 g was applied to the center of the fold of the sheet for 3 seconds. The sheet after pressing and unloading was returned to its original state and visually evaluated according to the following evaluation criteria. In the present invention, flexibility means that the sheet returns almost to its original state in this evaluation method.
Good (O): The sheet returns almost to its original state (X): The sheet is partially deformed

[Examples of polyamic acid synthesis]
Pyromellitic dianhydride (molecular weight 218.12) / 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (molecular weight 294.22) / 4,4′-diaminodiphenyl ether (molecular weight 200.24) / Paraphenylenediamine (molecular weight 108.14) is prepared in a molar ratio of 65/35/80/20, polymerized in a 20% by weight solution in DMAc (N, N-dimethylacetamide), and a 3500 poise polyamide An acid solution was obtained.

[Example 1]
The total particle size of the inorganic particles is 0.01 μm or more and 6.0 μm or less, and the average particle size is 0.87 μm, and the particle size is 0.5 to 2.5 μm. 0.15 wt% of N, N-dimethylacetamide slurry of calcium hydrogen oxyhydrate per weight of the solution resin was added to the polyamic acid solution obtained in the synthesis example and sufficiently stirred and dispersed. The polyamic acid solution was mixed and stirred with a conversion agent composed of acetic anhydride (molecular weight 102.09) and β-picoline at a ratio of 2.0 molar equivalents with respect to the polyamic acid. The obtained mixture was cast on a stainless steel drum at 65 ° C. rotating from a die to obtain a gel film having self-supporting properties. This gel film was peeled off from the drum, and both ends thereof were gripped and treated in a heating furnace at 250 ° C. for 30 seconds, 400 ° C. for 30 seconds, and 550 ° C. for 30 seconds to obtain a polyimide film having a thickness of 50 μm.

  The polyimide film obtained as described above was cut into a size of 250 mm × 600 mm in width, and the film surface was placed upright in a cylindrical cylindrical low and high holding container. Subsequently, the temperature was raised to 1000 ° C. at 3 ° C./min in argon gas and held for 1 hour, further heated to 2800 ° C. at 3 ° C./min and held for 1 hour to baked the polyimide film, and graphitized. went. The obtained graphite sheet was sandwiched between two rolling rolls, rolled by rolling, and a graphite sheet having a thickness of 25 μm was produced.

[Examples 2 and 3]
Example 1 except that the rotation speed of the drum and the conveyance speed (film formation speed) of the gel film in the heating furnace, that is, the heating time at each heating temperature, were adjusted so that the thickness of the resulting polyimide film was 25 μm and 75 μm. In the same manner, a polyimide film was obtained. The obtained polyimide film was baked in the same manner as in Example 1 to obtain a graphite sheet. A rolling process was performed in the same manner as in Example 1 to prepare graphite sheets having respective thicknesses.

[Comparative Example 1]
A polyimide film was obtained in the same manner as in Example 1 except that the amount of calcium hydrogen phosphate added per 1 weight of the solution resin added to the polyamic acid solution was 0.02% by weight. The obtained polyimide film was baked in the same manner as in Example 1 to obtain a graphite sheet. A rolling process was performed in the same manner as in Example 1 to produce a graphite sheet having a thickness of 25 μm.

  The characteristics of the polyimide films obtained in Examples 1 to 3 and Comparative Example 1 are shown in Table 1. The polyimide film is fired, the thickness, density, thermal diffusion coefficient, breaking strength and flexibility of the graphite sheet after rolling, the polyimide film Table 2 shows the foamability during graphitization. The thermal diffusion coefficient is a thermal diffusion coefficient in the sheet surface direction.

  As is clear from the results of Comparative Example 1, a polyimide film containing no inorganic particles in an amount of 0.03% by weight or more per 1 weight of the film resin was obtained from the polyimide film because the foamability of the film during graphitization was poor. The graphite sheet was found to have a low breaking strength and a low thermal diffusion coefficient. On the other hand, as is clear from the results of Examples 1 to 3, the polyimide film containing inorganic particles in an amount of 0.03% by weight or more per 1 weight of the film resin has good foamability of the film during graphitization. The graphite sheet obtained from the polyimide film had a high breaking strength and had excellent thermal conductivity, flexibility, and bending resistance.

  The polyimide film of the present invention has good foamability when graphitized by heat treatment, and the graphite sheet produced by heat-treating the polyimide film has excellent thermal conductivity, flexibility and bending resistance. It is suitable as a heat dissipation member for electronic equipment.

Claims (7)

One or more selected from the group consisting of paraphenylenediamine or paraphenylenediamine and 4,4′-diaminodiphenyl ether, pyromellitic dianhydride and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride A polyimide film produced by containing an acid anhydride as a raw material and having inorganic particles dispersed therein, wherein the inorganic particles have an average particle diameter of 0.1 to 2.0 μm, and the inorganic particles per weight of the film resin. 0.03 to 1.00% by weight of inorganic particles having a particle size of 0.5 to 2.5 μm account for 80% by volume or more of the total inorganic particles, and the polyimide film is 2,000 ° C. or more. A polyimide film having a linear expansion coefficient of 20 ppm / ° C. or less, wherein a graphite sheet is produced by heat treatment at a temperature of 5 ° C. The polyimide film according to claim 1, wherein the inorganic particles contain calcium hydrogen phosphate as a main component. Polyimide film according to claim 1 or 2 molar ratio of paraphenylene diamine and 4,4'-diaminodiphenyl ether is characterized by a 40/60 to 10/90. Pyromellitic dianhydride and 3,3 ', claim 1-3, wherein the molar ratio of 4,4'-biphenyltetracarboxylic dianhydride is 80 / 20-60 / 40 Item 1. The polyimide film according to item 1. One or more selected from the group consisting of paraphenylenediamine or paraphenylenediamine and 4,4′-diaminodiphenyl ether, pyromellitic dianhydride and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride When an acid anhydride is reacted in a polar organic solvent to produce a polyamic acid, and the polyamic acid is heated to form a film, the average particle size is 0.1 to 2.0 μm, and the particles A slurry in which inorganic particles having a particle size distribution in which inorganic particles having a diameter of 0.5 to 2.5 μm account for 80% by volume or more in all particles is dispersed in the same polar organic solvent as the polar organic solvent is used. claim, wherein the inorganic particles in an acid solution is added to the polyamic acid so that the proportion of 0.03 to 1.00 wt% per resin 1 weight 1-4 The process for producing a polyimide film as described in any one. A graphite sheet obtained by firing the polyimide film according to any one of claims 1 to 4 . A method for producing a graphite sheet, comprising firing the polyimide film according to any one of claims 1 to 4 .