KR20160007442A - Polyimid film for graphite sheet and method for manufacturing thereof - Google Patents

Abstract

Provided is a polyimide film of which foaming of a film is favorable in graphitization via heat treatment, and the graphitized sheet has excellent thermal conductivity, flexibility, and bending resistance. The polyimide film of the present invention is produced by containing at least one acid anhydride in a raw material, wherein the acid anhydride is selected from the group composed of paraphenylenediamine or paraphenylendiamine and 4,4′-diaminodiphenyl ether; pyromellitic dianhydride (PMDA), and 3 3′ 4 4′-biphenyltetracarbonic acid anhydride. In addition, inorganic particles are dispersed in the polyimide film, and graphite sheet can be produced by heat-treating the polyimide film at a temperature higher than or equal to 2000°C, wherein the coefficient of linear expansion of the polyimide film is less than or equal to 20 ppm/°C.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyimide film for a graphite sheet,

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

The polyimide film is known to have excellent properties in terms of heat resistance, cold resistance, chemical resistance, electrical insulation, mechanical strength, and the like. The polyimide film is excellent in electrical insulation materials for electric wires, A carrier tape film for TAB bonding, and a lead frame fixing tape for IC.

When a polyimide film is used in these applications, an important practical property is the lubrication (passivity) of the film. In the various film processing steps, the compatibility of the film support with the film (for example, roll) and the film, and the compatibility between the films are secured, thereby improving operability and handling in each step, Occurrence of defective parts such as wrinkles can be avoided.

As a conventional technique for deactivating polyimide films, a method of adding an inert inorganic compound (for example, orthophosphate of an alkaline earth metal, calcium anhydride, calcium pyrophosphate, silica, talc) to a polyamic acid (See Patent Document 1).

In the graphite sheet obtained by heat-treating the polyimide film in an inert gas at a temperature of 2400 占 폚 or higher and rolling if necessary, a homogeneous foaming state is produced by high-temperature heat treatment and subjected to a rolling treatment, It is known that a flexible graphite sheet can be obtained (see Patent Documents 2 and 3). Since the graphite sheet has a higher thermal conductivity than metal sheets such as copper and aluminum, it has recently attracted attention as a heat dissipating member of electronic equipment.

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

As a method of controlling the degree of foaming, a method of controlling the rate of temperature rise during graphitization is known (see Patent Document 5).

However, the degree of foaming of the film may not be sufficient by controlling the heating rate at the time of graphitization, and the thermal conductivity, flexibility, and flex resistance of the resulting graphite sheet may not be sufficient as heat dissipating members of electronic apparatuses.

Japanese Patent Publication No. 62-68852 Japanese Patent Application Laid-Open No. 3-75211 Publication No. 4-21508 Japanese Patent Application Laid-Open No. 8-267647 Japanese Patent Application Laid-Open No. 2008-24571

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In view of the above phenomenon, it is an object of the present invention to provide a process for producing a graphite sheet which is excellent in foaming of the film during graphitization by heat treatment, in which the graphitized sheet has excellent thermal conductivity, flexibility and bending resistance, And a polyimide film.

DISCLOSURE OF THE INVENTION As a result of intensive studies to solve the above problems, the inventors of the present invention have found that a polyphenylenediamine or para-phenylenediamine, a 4,4'-diaminodiphenyl ether, and a pyromellitic acid having a coefficient of linear expansion of 20 ppm / A polyimide film prepared by incorporating at least one acid anhydride selected from the group consisting of acid dianhydride and 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride into a raw material and having inorganic particles dispersed therein, The graphite sheet obtained by heat treatment at a temperature of 2000 占 폚 or higher and being graphitized is excellent and the graphite sheet obtained by the heat treatment is excellent in heat conductivity, flexibility and bending resistance, and further research is conducted based on this finding. It came to the following.

The present invention relates to the following invention.

[1] A process for producing a polyimide film, which comprises the steps of [1] preparing a film comprising para-phenylenediamine or a mixture of paraphenylenediamine and 4,4'-diaminodiphenyl ether, pyromellitic dianhydride and 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride , Wherein the polyimide film is heat treated at a temperature of 2000 占 폚 or higher to produce a graphite sheet, characterized in that the polyimide film is produced by incorporating at least one acid anhydride selected from the group consisting of Is not more than 20 ppm / 占 폚.

[2] The polyimide film according to [1], wherein the inorganic particles are contained in an amount of 0.03 to 1.00% by weight per 1 weight of the film resin.

[3] The polyimide film according to [1] or [2], wherein the inorganic particles have an average particle diameter of 0.1 to 2.0 μm.

[4] The polyimide film according to any one of [1] to [3], wherein the inorganic particles having a particle diameter of 0.5 to 2.5 μm occupy 80% by volume or more of the total inorganic particles.

[5] The polyimide film according to any one of [1] to [4], wherein the inorganic particles comprise calcium hydrogen phosphate as a main component.

[6] The polyimide film according to any one of [1] to [5], wherein the molar ratio of paraphenylenediamine to 4,4'-diaminodiphenyl ether is 40/60 to 10/90.

1] to [5], wherein the molar ratio of the pyromellitic acid dianhydride to the 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride is 80/20 to 60/40. A polyimide film according to claim 1.

[8] A photoresist composition comprising para-phenylenediamine or para-phenylenediamine, 4,4'-diaminodiphenyl ether, pyromellitic dianhydride and 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride Is reacted in a polar organic solvent to prepare a polyamic acid, and the polyamic acid is heated to form a film, wherein an average particle diameter is 0.1 to 2.0 占 퐉 and a particle diameter is 0.5 to 2.5 of inorganic particles having a particle size distribution occupying 80% by volume or more of the total particles in a polar organic solvent same as that of the polar organic solvent is dispersed in the polyamic acid solution to 1 weight of the resin The method for producing a polyimide film according to any one of the above [1] to [7], wherein the polyamic acid is added to the polyamic acid so as to have a ratio of 0.03 to 1.00% by weight.

[9] A graphite sheet obtained by firing the polyimide film according to any one of [1] to [7].

[10] A process for producing a graphite sheet characterized by firing the polyimide film according to any one of [1] to [7].

The polyimide film of the present invention is excellent in foaming at the time of 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 coefficient of linear expansion of 20 ppm / ° C or lower, and is selected from the group consisting of paraphenylenediamine or paraphenylenediamine, 4,4'-diaminodiphenyl ether, pyromellitic acid dianhydride and 3,3 ' 4, 4'-biphenyltetracarboxylic dianhydride, and the inorganic particles are dispersed in the raw material. The polyimide film is a polyimide film prepared by incorporating at least one acid anhydride selected from the group consisting of 4,4'- To thereby produce a graphite sheet.

[Polyamic acid]

 To obtain the polyimide film of the present invention, a polyamic acid solution (hereinafter also referred to as a polyamic acid solution) is obtained by first polymerizing an aromatic diamine component and an aromatic acid anhydride component in an organic solvent. Hereinafter, the polyamic acid solution will be described.

In the present invention, the polyamic acid solution can be obtained by polymerizing an aromatic diamine component of a raw material and an aromatic acid dianhydride component, or a chemical material containing both of them as an essential component in an organic solvent.

As the aromatic diamine component, it is preferable that para-phenylenediamine is contained as an essential component and 4,4'-diaminodiphenyl ether is contained as other aromatic diamine component.

As the aromatic anhydride component, pyromellitic dianhydride and / or 3, 3 ', 4, 4'-biphenyltetracarboxylic dianhydride are preferable.

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

In the present invention, the molar ratio of the pyromellitic acid dianhydride and the 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride used as the raw material of the film is preferably 80/20 to 60/40, / 25 to 65/35.

With respect to the present invention, in addition to paraphenylenediamine and 4,4'-diaminodiphenyl ether, a small amount of one or more other diamines may be added within the range not to impair the effect of the present invention. In addition to the pyromellitic acid dianhydride and the 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride, a small amount of one or more other dianhydrides may be added in a range not hindering the effect of the present invention May be added. Specific examples of other diamines and acid dianhydrides include, but are not limited to, the following.

Examples of the other diamine include 3,3'-diaminodiphenyl ether, metaphenylenediamine, 4,4'-diaminodiphenylpropane, 3,4'-diaminodiphenylpropane, 3,3'-diamine Diaminodiphenylmethane, 3, 3'-diaminodiphenylmethane, benzidine, 4,4'-diaminodiphenylsulfide, 4,4'-diaminodiphenylmethane, , 3'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 3,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 3,4'- (4-aminophenyl) ethylphosphine oxide, bis- (4-aminophenyl) diethylsilane, 3,3'-dichlorobenzidine, bis Aminophenyl) -N-methylamine, 1,5-diaminonaphthalene, 3,3 ', 4,4'-diaminodiphenylsulfone, -Dimethyl-4,4'-diaminobiphenyl, 3,4'-dimethyl-3 ', 4-diaminobiphenyl-3,3'-dimethoxybenzidine Bis (p-beta-amino-t-butylphenyl) ether, bis p-xylylenediamine, 1,3-diaminoamantane, 3,3'-diamino-1, 1, 3-diaminodiphenylmethane, Diaminocyclohexylmethane, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, p-aminocyclohexylmethane, p-aminocyclohexylmethane, , Decamethylenediamine, 3-methylheptamethylenediamine, 4,4'-dimethylheptamethylenediamine, 2,11-diaminododecane, 1,2-bis (3-aminopropoxy) Propylene diamine, 1, 4-diaminocyclohexane, 1, 2, 5-dimethylhexamethylenediamine, 2,5-dimethylhexamethylenediamine, 2, 5-diamino-1, 3, 4-oxadiazole, 2, 2- Bis (4-aminophenyl) hexafluoropropane, N- (3-aminophenyl) -4-aminobenzamide and 4-aminophenyl-3-aminobenzoate.

Examples of the other acid dianhydride include di-, tri-, tri-, tetra-biphenyltetracarboxylic dianhydrides, 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride, Naphthalene dicarboxylic dianhydride, 1,2-bis (3,4-dicarboxyphenyl) ether, pyridine-2,3,5,6-tetracarboxylic dianhydride, 1,2,4,5- Tetradecarboxylic dianhydride, 1,4,8-naphthalenetetracarboxylic dianhydride, 1,4,5,8-decahydronaphthalenetetracarboxylic dianhydride, 4,8-dimethyl-1,2,5- 6-hexahydronaphthalene tetracarboxylic dianhydride, 2,6-dichloro-1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,7-dichloro-1,4,5,8-naphthalenetetracarboxylic dianhydride, 2, 3, 6, 7-tetrachloro-1, 4,5, 8-naphthalenetetracarboxylic dianhydride, 1,8,9,10-phenanthrenetetracarboxylic dianhydride, 2,2- (2,3-dicarboxyphenyl) propane dianhydride, 1,1-bis (3,4-dicarboxype ) Dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis , Bis (3,4-dicarboxyphenyl) sulfone dianhydride, benzene-1,2,3,4-tetracarboxylic dianhydride, 3,4,4'-benzophenonetetracarboxylic dianhydride, .

Further, in the present invention, specific examples of the organic solvent used for forming the polyamic acid solution include sulfoxide-based solvents such as dimethylsulfoxide and diethylsulfoxide, N, N-dimethylformamide, N , And N-diethylformamide, acetamide-based solvents such as N, N-dimethylacetamide and N, N-diethylacetamide, N-methyl-2-pyrrolidone, N-vinyl Phenol, o-, m-, or phenol-based solvents such as p-cresol, xylenol, halogenated phenol, catechol and the like, such as hexamethylphosphoramide, gamma -butyrolactone, -Butylolactone, and the like. These may be used alone or in combination of two or more, and may be used in combination with aromatic hydrocarbons such as xylene, toluene and the like.

The polymerization of the polyamic acid solution may be carried out by any known method. For example,

(1) First, all the aromatic diamine component is added to the solvent, and then the aromatic acid anhydride component is added so as to be equivalent to the total amount of the aromatic diamine component.

(2) First, all of the aromatic acid anhydride components are added to a solvent, and then the aromatic diamine component is added so as to be equivalent to the aromatic acid anhydride component.

(3) After adding one aromatic diamine compound into the solvent, the other aromatic diamine compound is added to the reaction mixture in such a ratio that the aromatic acid anhydride compound becomes 95 to 105 mol% with respect to the reaction component, And then adding the other aromatic acid anhydride compound so that the wholly aromatic diamine component and the wholly aromatic acid anhydride component are substantially equivalent.

(4) After adding the aromatic acid anhydride compound into the solvent, the other aromatic acid anhydride compound is added to the reaction component in such a ratio that the amount of one of the aromatic diamine compounds becomes 95 to 105 mol% , And then adding the other aromatic diamine compound so that the wholly aromatic diamine component and the wholly aromatic acid anhydride component are substantially equivalent.

(5) The polyamic acid solution (A) is prepared by reacting one of the aromatic diamine component and the aromatic acid anhydride component in the solvent so as to be excessive, and the other one of the aromatic diamine component and the aromatic acid anhydride component And the polyamic acid solution (B) is adjusted. A method in which each of the polyamic acid solutions (A) and (B) thus obtained is mixed and the polymerization is completed. At this time, when the aromatic diamine component is excessive in the preparation of the polyamic acid solution (A), the aromatic acid anhydride component is excessively used in the polyamic acid solution (B) and the aromatic acid anhydride component is excessive in the polyamic acid solution (A) , And the polyamic acid solution (B) is excessively aromatic and the polyamic acid solution (A) and the polyamic acid solution (B) are mixed to adjust the wholly aromatic diamine component and the wholly aromatic acid anhydride component , And the like.

Incidentally, 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 in such a ratio that their molar numbers become approximately equal, but one of them is contained in an amount of 10 mol%, preferably 5 mol% Or may be blended excessively to the other side.

The polymerization reaction is preferably carried out while stirring and mixing in an organic solvent. The polymerization temperature is not particularly limited, but is usually conducted at a temperature of 0 to 80 캜 in the reaction solution. The polymerization time is not particularly limited, but it is preferably carried out continuously for 10 minutes to 30 hours. The polymerization reaction may be carried out by dividing the polymerization reaction or raising or lowering the temperature, if necessary. The order of adding the two reactants is not particularly limited, but it is preferable to add an aromatic acid anhydride to the solution of the aromatic diamine component. Vacuum defoaming during the polymerization reaction is an effective method for producing an organic solvent solution of high quality polyamic acid. The polymerization reaction may be controlled by adding a small amount of end-capping agent to the aromatic diamines before the polymerization reaction. The terminal sealing agent is not particularly limited and a known one can be used.

The polyamic acid solution thus obtained contains 5 to 40% by weight, preferably 10 to 30% by weight, of the solid content. The viscosity is a value measured by a Brookfield clay system and is not particularly limited, but is usually from 10 to 2000 Pa · s, and preferably from 100 to 1000 Pa · s for stable pumping. 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 the chemical substances in contact with the polyimide film in the production process of the polyimide film of the present invention.

As the inorganic particles usable in the present invention, SiO ₂ (silica), TiO ₂ (titania), CaHPO ₄ (calcium hydrogen phosphate), Ca ₂ P ₂ O ₇ (calcium pyrophosphate) . Among them, CaHPO _4, the polyimide film is good looking and expanded by the gas generated in the case of sublimation from the inside, since the thermal conductivity can be obtained in good to excellent graphite sheet, it is particularly preferred that the main component of CaHPO _4.

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

The average particle diameter of the inorganic particles is preferably from 0.1 to 2.0 占 퐉, more preferably from 0.5 to 1.5 占 퐉, and still more preferably from 0.8 to 1.2 占 퐉 in view of more uniform foaming at the time of graphitization.

It is preferable that the particle size distribution of the inorganic particles is narrow, that is, the ratio of particles of similar size to all the particles is preferably high. Specifically, the inorganic particles having a particle diameter of 0.5 to 2.5 占 퐉 should be 80 volume % Or more. If the ratio is less than 0.5 μm and the proportion of the particles is less than 0.5 μm, the mechanical strength of the graphite sheet is low and the thermal conductivity is low. When inorganic particles are poured, it is possible to remove the assembly by using a 5-μm cut filter or a 20-μm cut filter. However, if the proportion of the inorganic particles having a size exceeding 6.0 μm is increased, clogging of the filter becomes frequent, It is not preferable since coarse aggregation of the inorganic particles tends to occur. Therefore, as the inorganic particles, it is preferable that the total particle diameter is within the range of 6.0 μm or less. The average particle diameter, particle diameter and particle size distribution are values measured using a laser diffraction / scattering type particle size distribution analyzer LA-910 manufactured by Horiba, Inc., as described in the following embodiments.

The inorganic particles are preferably used as a slurry uniformly dispersed in a polar solvent such as N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide or N-methylpyrrolidone, It is preferable because it is possible to prevent it. Since the slurry has a very small particle diameter, the sedimentation rate is slow and stable. Further, even if sedimentation occurs, re-dispersion can be easily performed by re-crosslinking. The inorganic particle slurry can be obtained by a conventional method.

In the present invention, the method of dispersing the inorganic particles in the polyimide film is not particularly limited. However, in order to prevent sedimentation and agglomeration of the inorganic particle slurry, it is added to a pre-polymerized polyamic acid solution, To obtain a polyimide film. Also, after the inorganic particle slurry is added to the organic solvent before the polyamic acid polymerization, the polyimide film may be obtained through the polyamic acid polymerization and the recrystallization desolvation solvent. It is possible to add the inorganic particle slurry to any step of the production of the polyimide film in the process before the solvent removal before the recrystallization. The polar solvent used for the inorganic particle slurry is preferably the same polar solvent as the organic solvent used for producing the polyamic acid.

The dispersion is preferably carried out using a homogenizer or a milling mill to uniformly disperse the filler. The homogenizer and the milling mill are not particularly limited and conventionally known mills 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 the compound other than the inorganic particles include metal oxides such as carbon, alumina and titanium dioxide, and boron compounds such as boron nitride.

[Polyimide film]

Next, a method for producing the polyimide film of the present invention will be described.

The polyimide film is produced by heating a polyamic acid solution, but will be described in detail below.

Examples of the method for producing the polyimide film include a method of casting a polyamic acid solution into a film form and thermally depolarizing and removing the solvent to obtain a polyimide film and a method in which a polyamic acid solution is mixed with a cyclization catalyst and a dehydrating agent, And a method of obtaining a polyimide film by heating and removing the solvent therefrom. However, since the coefficient of thermal expansion of the latter polyimide film can be suppressed to a low level and the backing property in the film surface direction becomes high, The thermal conductivity and the thickness of the substrate can be obtained.

In the method of chemically de-catalyzing, the polyamic acid solution is first prepared. The polyamic acid solution may contain a cyclization catalyst (imidization catalyst), a dehydrating agent and a gelling retarder.

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 complexes such as isoquinoline, pyridine, Cyclic tertiary amines, and the like, which may be used alone or in combination of two or more. Among them, a mode of using at least one heterocyclic tertiary amine is preferable.

Specific examples of the dehydrating agent used in the present invention include aliphatic carboxylic anhydrides such as acetic anhydride, propionic anhydride, and butyric anhydride, and aromatic carboxylic acid anhydrides such as benzoic anhydride. Of these, acetic anhydride and / Anhydrous benzoic acid is 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 poured on a support from a slit attachment type to form a film, and imidation is partially progressed on the support To form a gel film having self-supporting property, then peeled 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 apex, is softened on a heated support, thermally cycled on the support, and becomes a gel film having self-supporting properties and peeled from the support.

The support is a metal rotary drum or endless belt, and its temperature is controlled by the heat of the liquid or gas and / or the radiant heat of the electric heater or the like.

The gel film is heated to a temperature of usually 30 to 200 ° C, preferably 40 to 150 ° C due to heat reception from the support and / or heat reception from a heat source such as hot air or an electric heater, , And volatile components such as an advantageous organic solvent are dried to have self-supporting property and peeled from the support.

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

The film dried in the above-mentioned drying zone is usually heated in a wind, an infrared heater or the like for 15 seconds to 30 minutes. Heat treatment is then carried out at a temperature of usually 250 to 500 ° C. for 15 seconds to 30 minutes by 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.

The thickness of the polyimide film used in the present invention is not particularly limited, but is preferably in the range of 5 m to 200 m, more preferably 10 m to 150 m.

The coefficient of linear expansion 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. The coefficient of linear expansion is a value measured by the method described in Examples described later and is usually an average value of the values in the width direction TD of the polyimide film and the machine direction MD.

[Graphite sheet]

The graphite sheet of the present invention can be obtained by baking and graphitizing the polyimide film of the present invention.

A method of producing the graphite sheet of the present invention will be described below.

In obtaining the graphite sheet of the present invention, first, the polyimide film is cut to a predetermined size, and the film surface of the polyimide film is placed horizontally or on the film surface into the graphite container.

The temperature of the graphitization calcination (hereinafter also referred to as the present 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 占 폚 or higher, more preferably 2800 占 폚 or higher, and still more preferably around 3000 占 폚. If the firing temperature is higher than 3500 DEG C, the deterioration of heat resistance of the firing furnace is large, and production for a long time is difficult. When the maximum firing temperature is less than 2000 占 폚, the obtained graphite sheet tends to become hard and brittle. The heating rate at the time of firing is not particularly limited, but is, for example, about 1 to 10 ° C / minute. For baking, a known heating means can be used. The baking time is not particularly limited.

The firing is usually performed in an inert gas. The inert gas is not particularly limited, and examples thereof include helium, argon, nitrogen and the like, but argon is preferably used. The pressure at the time of firing is preferably atmospheric pressure.

Prior to the firing (main heating process), a preliminary heating process may be carried out if necessary. The temperature of the preheating treatment is preferably lower than the temperature of the present heat treatment. Concretely, it is preferably about 900 DEG C or more and 1500 DEG C or less. The heating rate of the preheating treatment is not particularly limited, but is, for example, about 1 to 15 ° C / minute. The preheating treatment is also usually conducted in an inert gas. As the inert gas, the same gas as described above may be used. The time for the preheating treatment is not particularly limited.

The sintered graphite sheet is preferably rolled by sandwiching it with a rolling roller. It is possible to reduce the unevenness in thickness caused by the expansion of the graphite sheet after firing by the rolling treatment. In addition, the density of the graphite sheet after firing can be increased by the rolling treatment to increase the thermal conductivity.

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 the following embodiments.

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.

The breaking strength of the graphite sheet of the present invention is usually 10 MPa or more, preferably 15 MPa or more, and more preferably 20 MPa or more. The breaking strength is a value measured by the method described in the following embodiments.

[ Example ]

The present invention will now be described more specifically with reference to the following examples. However, it should be understood that the present invention is not limited by these examples, and many variations are possible within the technical scope of the present invention. It is possible by the person having it.

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

[Evaluation of inorganic particles]

From the results of measurement and analysis of a sample dispersed in a polar solvent using a laser diffraction / scattering type particle size distribution analyzer LA-910 manufactured by Horiba, the particle diameter range, average particle diameter, particle diameter from 0.5 to 2.5 μm Of the particles.

[Linear Expansion Coefficient]

Samples of 5 mm in width and 10 mm in length were sampled and each sample was heated under the following conditions using TMA-50 manufactured by Shimadzu Corporation.

First rising temperature: room temperature? 300 占 (heating rate: 10 占 폚 / min)

Lowering temperature: 300 占 폚? 35 占 폚 (rate of temperature decrease: 5 占 폚 / min)

Second temperature elevation: 35 占 폚? 220 占 (heating rate 10 占 폚 / min)

The analysis of the coefficient of linear expansion was carried out under the conditions of a temperature range of 50 占 폚 to 200 占 폚 at the second elevated temperature.

The coefficient of linear expansion was obtained as an average coefficient of linear expansion of the polyimide film in the width direction (TD) and the machine direction (MD).

[density]

Measuring method: Archimedes method

Measurement apparatus: Electronic analysis balance AUX-120 (manufactured by Shimadzu Corporation)

Measuring temperature: 25 ° C

Water solution: water

[Thermal Diffusion Coefficient]

Measuring method: Kisenon flash method

Measuring device: LFA447 thermal conductivity measuring device manufactured by NETZSCH

Measuring temperature: 25 ° C

Light source: Kisenon flash lamp

IR detector: InSb detector (liquid nitrogen cooling)

[Breaking Strength]

Measurement apparatus: Autograph AGS-X manufactured by Shimadzu Corporation

Measuring temperature: 25 ° C

Chuck distance: 50 mm

Tensile speed: 25 mm / min

Specimen: Width 10 mm

 [Thickness of polyimide film and graphite sheet]

Measured using a Mitutoyo Lightmatic (Series318).

 [firing]

A graphite sheet of 100 mm square was evaluated by the following evaluation criteria.

Good (O): When the foaming is uniform as a whole

Bad (X): Does not fire or has stains

[flexibility]

The graphite sheets of 100 mm (length) x 100 mm (width) were folded and bent so that the end portions in the longitudinal direction or the end portions in the width direction were perfectly overlapped with each other. Then, a load of 100 g was pressed for 3 seconds The sheets after the load were restored to their original state and evaluated by the following criteria. The flexibility in the present invention means that the sheet returns to its original state in this evaluation method.

Good (O): The sheet returns to a substantially circular state

Bad (X): The sheet is partially deformed

 [Polyamicamic acid synthesis example]

Biphenyltetracarboxylic dianhydride (molecular weight 294.22) / 4,4'-diaminodiphenyl ether (molecular weight 200.24) / paraphenylene dianhydride (molecular weight 218.12) / 3,3 ', 4,4'- Diamine (molecular weight: 108.14) was prepared at a molar ratio of 65/35/80/20 and polymerized as a 20 wt% solution in DMAc (N, N-dimethylacetamide) to obtain a polyamic acid solution of 3500 poise .

 [Example 1]

N, N-dimethylacetamide having an average particle diameter of 0.87 mu m and a particle diameter of 0.5 to 2.5 mu m in the total particle size of 81.5 vol% The slurry was added to the polyamic acid solution obtained in Synthesis Example in an amount of 0.15% by weight per 1 weight of the solution resin, and sufficiently stirred and dispersed. To the polyamic acid solution, 2.0 molar equivalents of acetic anhydride (molecular weight: 102.09) and a dialking agent composed of? -Picoline were added to the polyamic acid, and the mixture was stirred. The obtained mixture was cast on a stainless steel drum rotating at 65 DEG C rather than the mouthpiece to obtain a gel film having self-supporting properties. The gel film was peeled off from the drum and both ends thereof were held and treated in a heating furnace at 250 캜 for 30 seconds, 400 캜 for 30 seconds, and 550 캜 for 30 seconds to obtain a polyimide film having a thickness of 50 탆.

The polyimide film thus obtained was cut into a size of 250 mm x 600 mm in width and the film surface was placed in a holding container having a bottom made of graphite and having a bottom. Then, the temperature was raised to 1000 占 폚 at 3 占 폚 / min in an argon gas, held for 1 hour, heated to 28 占 폚 at 3 占 폚 / min and held for 1 hour to fuse the polyimide film to perform graphitization. The obtained graphite sheet was sandwiched between two rolling rolls, rolled and rolled to produce a graphite sheet having a thickness of 25 mu m.

[Examples 2 and 3]

Except that the rotational speed of the drum and the conveying speed (film forming 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 obtained polyimide film was 25 占 퐉 and 75 占 퐉 A polyimide film was obtained in the same manner as in Example 1. The polyimide film thus obtained was fired in the same manner as in Example 1 to obtain a graphite sheet. A rolling treatment was carried out in the same manner as in Example 1 to produce graphite sheets of respective thicknesses.

 [Comparative Example 1]

A polyimide film was obtained in the same manner as in Example 1 except that the amount of calcium hydrogenphosphate added per 1 weight of the solution resin added to the polyamic acid solution was 0.02 wt%. The obtained polyimide film was baked as in Example 1 to obtain a graphite sheet. A rolling process was performed as in Example 1 to produce a graphite sheet having a thickness of 25 占 퐉.

The properties of the polyimide films obtained in Examples 1 to 3 and Comparative Example 1 are shown in Table 1. The thickness, density, thermal diffusion coefficient, fracture strength and flexibility of the graphite sheet after firing and rolling the polyimide film, Table 2 shows the foaming properties at the time of firing. The thermal diffusivity coefficient is the thermal diffusion coefficient in the sheet surface direction.

Characteristics of polyimide film
Thickness of polyimide film (μm) Amount of inorganic particles added per 1 weight of film resin
(weight%) Average linear expansion coefficient
(ppm / DEG C) Example 1 50 0.15 16 Example 2 25 0.15 16 Example 3 75 0.15 16 Comparative Example 1 50 0.02 16

Characteristics of graphite sheet Thickness of graphite sheet (μm) Density (g / cm ³⁾ Thermal diffusivity coefficient
(cm ² / s) Breaking strength
(MPa) firing flexibility After firing After rolling Example 1 40 25 1.8 10.5 30 ○ ○ Example 2 18 10 2.0 11.8 45 ○ ○ Example 3 90 45 1.5 7.5 25 ○ ○ Comparative Example 1 30 25 2.1 6.3 <10 × ×

As is clear from the results of Comparative Example 1, the polyimide film containing 0.03 wt% or more of inorganic particles per 1 wt. Of the film resin had poor foamability of the film at the time of graphitization and the graphite sheet obtained from the polyimide film had a fracture The strength was weak, and the thermal diffusion coefficient was low. On the other hand, as is clear from the results of Examples 1 to 3, the polyimide film containing 0.03% by weight or more of inorganic particles per 1 weight of the film resin has good foamability of the film upon graphitization, The graphite sheet had strong breaking strength, and also had excellent thermal conductivity, flexibility, and bending resistance.

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

Claims (10)

Selected from the group consisting of paraphenylenediamine or para-phenylenediamine, 4,4'-diaminodiphenyl ether, pyromellitic dianhydride and 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride. Wherein the polyimide film is heat-treated at a temperature of 2000 占 폚 or higher to produce a graphite sheet. The polyimide film has a linear expansion coefficient of 20 ppm / Lt; 0 &gt; C or less.
The polyimide film according to claim 1, wherein the inorganic particles are contained in an amount of 0.03 to 1.00% by weight per one weight of the film resin.
The polyimide film according to claim 1 or 2, wherein the inorganic particles have an average particle diameter of 0.1 to 2.0 μm.
The polyimide film according to any one of claims 1 to 3, wherein the inorganic particles having a particle diameter of 0.5 to 2.5 μm occupy 80% by volume or more of the total inorganic particles.
The polyimide film according to any one of claims 1 to 4, wherein the inorganic particles comprise calcium hydrogen phosphate as a main component.
The polyimide film according to any one of claims 1 to 5, wherein the molar ratio of paraphenylenediamine to 4,4'-diaminodiphenyl ether is 40/60 to 10/90.
The polyimide film according to any one of claims 1 to 5, wherein the molar ratio of pyromellitic acid dianhydride to 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride is 80/20 to 60/40. Mid-film.
Selected from the group consisting of paraphenylenediamine or para-phenylenediamine, 4,4'-diaminodiphenyl ether, pyromellitic dianhydride and 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride. In the polar organic solvent to produce a polyamic acid and heating the polyamic acid to form a film, wherein the polyamic acid has a mean particle diameter of 0.1 to 2.0 占 퐉 and a particle diameter of 0.5 to 2.5 占 퐉 Wherein the inorganic particles having a particle size distribution in which the particles occupy 80% by volume or more of the total particles are dispersed in the same polar organic solvent as that of the polar organic solvent to the polyamic acid solution, Wherein the polyamic acid is added to the polyamic acid so that the ratio of the polyamic acid to the polyamic acid is 1.00 wt%.
A graphite sheet obtained by firing the polyimide film according to any one of claims 1 to 7.
A process for producing a graphite sheet characterized by firing the polyimide film according to any one of claims 1 to 7.