JP2014136721A - Polyimide film and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyimide film applicable to a graphite sheet which has excellent slipperiness of a film and is obtained by performing a heat treatment and to provide a method for producing the same.SOLUTION: There is provided a polyimide film which is produced mainly by imidization of a 4,4'-diaminodiphenyl ether as a diamine component and a pyromellitic acid dianhydride as an acid dianhydride component, wherein inorganic particles, which have a particle diameter of 0.01 to 6.0 μm and an average particle diameter of 0.5 to 1.5 μm and in which inorganic particles with a particle diameter of 0.5 to 2.5 μm have a particle size distribution occupying a ratio of 80 volume% or more in all particles, are dispersed in the film in an amount of 0.05 to 0.5 wt.% per film resin weight.

Description

  The present invention relates to a polyimide film and a method for producing the same. More specifically, the added inorganic particles are not exposed, and surface protrusions can be generated in a state of being uniformly dispersed in the film, so that the surface state can be controlled well, and the film has excellent running properties and is obtained by heat treatment. The present invention relates to a polyimide film applicable to a graphite sheet 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 has been widely used as a base film. In recent years, a graphite sheet obtained by heat-treating a polyimide film has attracted attention as a heat radiating member for electronic devices because of its very high thermal conductivity.

  An important practical characteristic when a polyimide film is used in these applications is the slipperiness (slidability) of the film. In various film processing steps, the slidability between the film support (for example, roll) and the film and the slidability between the films are ensured, thereby improving the operability and handling in each step. This is because the occurrence of defects such as wrinkles on the film can be avoided (Patent Document 1).

  On the other hand, in a graphite application obtained by firing a polyimide film, swelling occurs due to gas generated when inorganic particles sublime from the inside of the film. This swelling phenomenon affects the thickness of the graphite after firing. For example, in the graphite obtained by the method of Patent Document 2, when the particle size of inorganic particles added to the polyimide film is large, partial abnormal swelling is likely to occur. In addition, when the ratio of the inorganic particles to the film resin weight is small, swelling does not occur and the thickness after firing becomes thin, and it is impossible to exhibit sufficient heat dissipation capability for graphite applications.

  In particular, the greater the thickness of the polyimide film before firing, the greater the influence of gas permeability when the inorganic particles sublimate from the inside of the film, and the partial swelling of graphite and the thickness after firing are more likely to occur. The partial blistering caused a foaming phenomenon on the graphite surface, which deteriorated the appearance. Furthermore, since the density was lowered, the thermal conductivity was also deteriorated, the strength was weakened and it was easy to break. On the other hand, a thicker graphite sheet was needed. Therefore, the thickness of the polyimide film before firing is also required, improving the runnability at the time of film processing obtained by adding inorganic particles and high heat dissipation and high quality obtained by thickening the polyimide film before firing. The polyimide film which can obtain both graphite sheets was a conflicting problem.

JP 2008-106141 A Special table 2010-215441 gazette

  The present invention has been achieved as a result of studying the solution of the problems in the prior art described above as an issue. Therefore, the object of the present invention is to improve the runnability at the time of film processing obtained by adding inorganic particles and the polyimide film applicable to a high-heat-dissipating graphite sheet obtained by baking the polyimide film and its It is to provide a manufacturing method.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention mainly comprise 4,4′-diaminodiphenyl ether as a diamine component and pyromellitic dianhydride as an acid dianhydride component in a polyimide film. It was found that the above-mentioned problems could be solved by selecting the particle size and content to be dispersed in the film while selecting it as a component, and further research based on this knowledge led to the completion of the present invention. .

That is, the present invention relates to the following inventions.
[1] 4,4′-diaminodiphenyl ether as a diamine component, and pyromellitic dianhydride as a main component as an acid dianhydride component, and a polyimide film manufactured by imidization, the film being included in the polyimide film Inorganic particles are dispersed at a rate of 0.05 to 0.50% by weight per resin weight, the average particle size of the inorganic particles is 0.5 to 1.5 μm, and the particle size is 0.5 to 2 A polyimide film characterized in that inorganic particles of .5 μm occupy a proportion of 80% by volume or more in all particles.
[2] The polyimide film according to [1], wherein the film thickness is 25 to 80 μm.
[3] The polyimide film as described in [1] or [2], wherein the inorganic particles are contained at a ratio of 0.05 to 0.30% by weight with respect to the weight of the film resin.
[4] The polyimide film according to any one of [1] to [3], wherein the inorganic particles have an average particle size of 0.5 to 1.0 μm.
[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 total particle diameter of the inorganic particles is in a range of 6.0 μm or less.
[7] A polyamic acid is produced by reacting a diamine component composed of 4,4′-diaminodiphenyl ether and a tetracarboxylic dianhydride component composed of pyromellitic dianhydride in a polar organic solvent. The particle size in which the average particle diameter is 0.5 to 1.5 μm and the inorganic particles having a particle diameter of 0.5 to 2.5 μm account for 80% by volume or more of all the particles when formed into a film using A slurry obtained by dispersing inorganic particles having a distribution in the same polar organic solvent as the polar organic solvent so that the inorganic particles in the polyamic acid solution have a ratio of 0.05 to 0.50% by weight per resin weight. The method for producing a polyimide film according to any one of [1] to [6], wherein the polyimide film is added to.
[8] A graphite sheet obtained by firing the polyimide film according to any one of [1] to [6].
[9] A method for producing a graphite sheet, comprising firing the polyimide film according to any one of [1] to [6].

  According to the present invention, as described below, the added inorganic particles are not exposed, and surface protrusions can be generated in a state of being uniformly dispersed in the film, so that the surface state can be well controlled, and the running property of the film In addition, it is possible to obtain a polyimide film that can be applied to a high-quality heat-dissipating graphite sheet obtained by baking a polyimide film.

  Hereinafter, the present invention will be described in detail. The polyimide film of the present invention is a polyimide film produced by imidization, mainly comprising 4,4′-diaminodiphenyl ether as a diamine component and pyromellitic dianhydride as an acid dianhydride component. Inorganic particles are dispersed in the film at a rate of 0.05 to 0.50% by weight per film resin weight, the average particle size of the inorganic particles is 0.5 to 1.5 μm, and the particle size is 0 The inorganic particles of 0.5 to 2.5 μm occupy 80% by volume or more of the total particles.

  The polyimide film of this invention is manufactured by imidation using the polyamic acid which is a precursor. First, a polyamic acid solution is obtained by polymerizing a diamine component and an acid anhydride component in an organic solvent.

  In the present invention, an aromatic tetracarboxylic dianhydride component and an aromatic diamine component or a chemical substance mainly composed of these components is subjected to addition polymerization in an organic solvent to obtain a varnish-like polyamic acid. 4,4'-diaminodiphenyl ether is used as the aromatic diamine component, and pyromellitic dianhydride is used as the main component for the aromatic tetracarboxylic dianhydride component. That is, it can be obtained by using two types of 4,4'-diaminodiphenyl ether and pyromellitic dianhydride as essential constituents, and adding only these two types or a small amount of other components in addition to these two types.

  In the present invention, as described above, in addition to 4,4'-diaminodiphenyl ether, a small amount of other diamines may be added within a range not impeding the effects of the present invention. In addition to pyromellitic dianhydride, a small amount of other acid dianhydrides may be added within a range not impeding the effects of the present invention. Specific examples of other diamines and acid dianhydrides include, but are not limited to:

(1) Diamine Paraphenylenediamine, 3,3′-diaminodiphenyl ether, metaphenylenediamine, 4,4′-diaminodiphenylpropane, 3,4′-diaminodiphenylpropane, 3,3′-diaminodiphenylpropane, 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′- Dichlorobenzidine, bis- (4 Aminophenyl) 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'-diaminoadamantane, 3,3'-diaminomethyl 1,1'-diadamantane, bis (p-aminocyclohexyl) methane, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylene Diamine, 3-methylheptamethylenediamine, 4,4'-dimethylheptamethylenediamine, 2,11-diaminododecane, 1,2-bis (3-aminopropoxy) ethane, 2,2-dimethylpropylenediamine, 3-methoxy Hexaethylenediamine, 2,5-dimethylhexamethylenediamine, 2,5-dimethylheptamethylenediamine, 5-methylnonamethylenediamine, 1,4-diaminocyclohexane, 1,12-diaminooctadecane, 2,5-diamino-1, 3,4-oxa Azole, 2,2-bis (4-aminophenyl) hexafluoropropane, N-(3- aminophenyl) -4-aminobenzamide, 4-aminophenyl-3-aminobenzoate and the like.

(2) Acid dianhydride 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,3 ′, 3,4′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4 4′-benzophenone tetracarboxylic 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-naphthalene tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride, 1,4,5,8-deca Hydronaphthalenetetracarboxylic dianhydride, 4,8-dimethyl-1,2,5,6-hexahydronaphthalenetetracarboxylic dianhydride, 2,6-dichloro-1,4,5,8-naphthalenetetracarboxylic Acid dianhydride, 2,7-dichloro B-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-bis (2,3-dicarboxyphenyl) propane dianhydride, 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride, , 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 can also include aprotic polar solvents such as hexamethylphosphoramide and γ-butyrolactone, which may be used alone or as a mixture. It is desirable to use as Ren, the use of aromatic hydrocarbons such as toluene are also possible.

The polymerization method may be carried out by any known method. For example, (1) the aromatic diamine component is first added to the solvent, and then the aromatic tetracarboxylic acid component is added in an amount equivalent to the total amount of the aromatic diamine component. To polymerize.
(2) A method in which the total amount of the aromatic tetracarboxylic acid component is first put in a solvent, and then the aromatic diamine component is added in an amount equivalent to the aromatic tetracarboxylic acid component for polymerization.
(3) After one aromatic diamine compound is put in a solvent, the aromatic tetracarboxylic acid compound is mixed at a ratio of 95 to 105 mol% with respect to the reaction components, and then mixed for the other time. A method in which an aromatic diamine compound is added, and then an aromatic tetracarboxylic acid compound is added and polymerized so that the total aromatic diamine component and the total aromatic tetracarboxylic acid component are approximately equivalent.
(4) After putting the aromatic tetracarboxylic acid compound in the solvent, the aromatic tetracarboxylic acid compound is mixed for a time required for the reaction at a ratio of 95 to 105 mol% of one aromatic diamine compound with respect to the reaction component, and then the aromatic tetracarboxylic acid compound is mixed. A method of polymerizing by adding a carboxylic acid compound and then adding the other aromatic diamine compound so that the total aromatic diamine component and the total aromatic tetracarboxylic acid component are approximately equivalent.
(5) A polyamic acid solution (A) is prepared by reacting one aromatic diamine component with an aromatic tetracarboxylic acid in a solvent so that either one becomes excessive, and the other aromatic diamine in another solvent. The polyamic acid solution (B) is prepared by reacting the component and the aromatic tetracarboxylic acid so that either one becomes 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 tetracarboxylic acid component, and the polyamic acid solution (A) has aromatic tetracarboxylic acid. When the acid component is excessive, the polyamic acid solution (B) makes the aromatic diamine component excessive, and the polyamic acid solutions (A) and (B) are mixed and the wholly aromatic diamine component and wholly aromatic used in these reactions. Adjustment is made so that the tetracarboxylic acid component is approximately equivalent. The polymerization method is not limited to these, and other known methods may 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, and the viscosity is a value measured by a Brookfield viscometer and is not particularly limited. However, it is normally 10 to 2000 Pa · s, and preferably 100 to 1000 Pa · s for stable liquid feeding. Moreover, the polyamic acid in the organic solvent solution may be partially imidized.

  The inorganic particles added to the resin in order to form protrusions on the film surface of the present invention must be insoluble in all chemical substances that are contacted in the polyimide film manufacturing process.

Preferred examples of the inorganic particles that can be used in the present invention include SiO ₂ (silica), TiO ₂ , CaHPO ₄ , and Ca ₂ P ₂ O ₇ . Among them CaHPO ₄ containing phosphoric acid, good swelling caused by gas generated when the sublimed from within the film, for good graphite having excellent thermal conductivity is obtained, in particular, that the main component CaHPO ₄ preferable.

  Inorganic particles are preferred because they can be prevented from agglomerating by using them as a slurry uniformly dispersed in a polar solvent such as N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone. 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.

  In the present invention, the inorganic particles added to form protrusions on the surface of the polyimide film have an average particle diameter in the range of 0.5 μm to 1.5 μm, preferably in the range of 0.5 to 1.0 μm. In addition to being able to adapt to a graphite sheet without causing abnormal swelling due to sublimation gas of partial inorganic particles, it is easy to slip between a film support (for example, a roll etc.) and a film, and between films As a result, it is possible to improve the operability and handleability in each process, and to use the film without generating a defective portion such as a wrinkle on the film.

  On the other hand, if the average particle diameter is lower than these ranges, sufficient slipperiness to the film cannot be obtained, and if it exceeds the average, abnormal swelling due to the sublimation gas of the inorganic particles is not preferable. Moreover, the thickness of the polyimide film before firing used in the present invention is preferably 25 μm to 80 μm, and within this thickness range, the inorganic particles in the particle diameter range are completely exposed on the surface of the polyimide film. Never do. If the thickness of the polyimide film before firing is too thin, the graphite sheet after firing may be rounded, or if the graphite sheet is made flat, it may be shattered and a rolled graphite sheet may not be formed. When the thickness of the polyimide film before firing is too thick, abnormal swelling occurs on the surface of the graphite sheet, which is not preferable in appearance.

  The amount of inorganic particles added is preferably 0.05 to 0.50% by weight, more preferably 0.05 to 0.30% by weight, based on the weight of the film resin. If it is 0.05% by weight or less, sufficient slipperiness to the film cannot be obtained due to insufficient number of protrusions on the film surface, the transportability is deteriorated, and the film winding shape when wound on a roll is also deteriorated. Therefore, it is not preferable. On the other hand, if it is 0.50% by weight or more, the slipperiness of the film is improved, but coarse protrusions due to abnormal aggregation of the inorganic particles increase, resulting in partial inorganic particles during firing. This is not preferable because it causes abnormal swelling due to the sublimation gas, impairs the thermal conductivity of the graphite after firing, or causes variations in thickness.

  Regarding the particle size distribution of the inorganic particles, it is better that the particle size distribution is narrow, that is, the proportion of particles of similar size to the whole particle is high, specifically, particles having a particle size of 0.5 to 2.5 μm are all included. It is preferable to occupy a ratio of 80% by volume or more in the particles. If the proportion of particles less than this range and 0.5 μm or less increases, the slipperiness of the film decreases, 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 particles with a size exceeding 6.0 μm increases, the filter will become clogged. This is not preferable because the process stability is deteriorated and the stability of the process is deteriorated and coarse aggregation of 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 particle size distribution, average particle size, and particle size are values measured using a laser diffraction / scattering particle size distribution analyzer LA-910 manufactured by Horiba.

  In the film surface protrusion caused by the inorganic particles, the number of protrusions having a height of 2.0 μm or more is 10 pieces / 40 cm square or less, more preferably 5 pieces / 40 cm square or less, and even more preferably 1 piece / 40 cm square. The following is desirable. If it is more than this, it will cause abnormal swelling due to the sublimation gas of the partial inorganic particles at the time of firing, which is not preferable because the thermal conductivity of the graphite after firing will be hindered or the thickness will vary. .

  In this invention, after adding the slurry which disperse | distributed such an inorganic particle to the same polar solvent as the organic solvent used for the polyamic acid used for manufacture of a polyimide film to the polyamic acid solution in a polyimide manufacturing process It is preferable to obtain a polyimide film by decyclization and desolvation, but after adding an inorganic particle slurry to an organic solvent before polyamic acid polymerization, a polyimide film is obtained through polyamic acid polymerization and decyclization desolvation. For example, the inorganic particle slurry can be added in any step as long as it is a step before decyclization and desolvation.

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

  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. A ring tertiary amine etc. are mentioned, These can be used individually or in combination of 2 or more types. 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 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, etc. By drying the volatile matter, it becomes self-supporting and is peeled off 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 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 drying zone is heated for 15 seconds to 30 minutes with hot air, an infrared heater or the like. Next, heat treatment is 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.

  Next, the manufacturing method of the graphite sheet of this invention is demonstrated.

  The polyimide film is cut into a predetermined dimension, and the film surface of the polyimide film is placed horizontally or with the film surface upright, and placed in a graphite holding container.

  When the polyimide film is put into the holding container, the polyimide film does not come into contact with the support such as the holding container or the like so that the polyimide film is naturally deformed at the time of firing, or when the polyimide film is in contact with the support, Adjust so that it touches with its own weight. Similarly, when a plurality of polyimide films are put in a container, they are similarly stacked so as to be naturally deformed during firing.

  Firing consists of a carbonization step and a graphitization step. In the carbonization step, the polyimide film is heated from room temperature to 1 ° C./min to 10 ° C./min at a constant rate in a non-oxidizing atmosphere such as vacuum or inert gas. The temperature is raised to a firing temperature provided in the range of 1200 ° C. to 1500 ° C., and this temperature is maintained for 30 minutes to 2 hours to carbonize the polyimide film and form a carbonized sheet.

  In the carbonization process, elements other than carbon are released by thermal decomposition of the polyimide film, carbon-carbon recombination is performed, and the polyimide film is fired and contracted.

  In the graphitization step, the carbonized sheet is provided in a non-oxidizing atmosphere such as a vacuum or an inert gas at a maximum temperature of 2400 ° C. to 3500 ° C. at a constant heating rate of 1 ° C./min to 10 ° C./min; The temperature is raised to a firing temperature, and the firing temperature is maintained for 30 minutes to 2 hours for firing.

  In this graphitization step, graphitization occurs in which carbon-carbon bonds are converted into graphite crystals, and a graphite sheet is formed. In addition, inorganic particles uniformly dispersed in the polyimide film are sublimated from the inside of the film during the baking process in which the carbonized sheet becomes a graphite sheet, and the generated gas causes a bulge that increases the thickness of the sheet.

  If the calcination temperature in the graphitization step is less than 2400 ° C., the graphitization of the polyimide film is insufficient, so that high-quality graphite crystals cannot be formed and the thermal conductivity is low. On the other hand, if the firing temperature is higher than 3500 ° C., the heat-resistant deterioration of the firing furnace is great and long-time production is difficult.

  The graphitization step is performed after the polyimide film is taken out into the air at room temperature after the carbonization step. Further, after the carbonization step, the graphitization step may be continuously performed without lowering the temperature.

  Nitrogen or argon is preferably used as the inert gas in the carbonization step and the graphitization step.

  The fired graphite sheet is preferably sandwiched between rolling rollers and subjected to a rolling process, and this rolling process can reduce thickness unevenness caused by swelling of the fired graphite sheet. Further, the density of the fired graphite sheet can be increased by rolling treatment to increase the thermal conductivity. The density and thermal conductivity can be measured, for example, by the method described in JP2010-6890A.

  A method for measuring various physical properties in the present invention will be described below.

[Friction coefficient (Static friction coefficient)]
The processed surfaces of the films were overlapped and measured according to JIS K-7125 (1999). That is, using a slip coefficient measuring apparatus Slip Tester (manufactured by Technonez Co., Ltd.), the film processing surfaces are overlapped with each other, a 200 g weight is placed thereon, one side of the film is fixed, and the other side is fixed at 100 mm / min. Tensile and friction coefficients were measured.

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

[Film thickness]
Measurements were made using Mitutoyo lightmatic (Series 318).

  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.

[Examples of polyamic acid synthesis]
Pyromellitic dianhydride (molecular weight 218.12) / 4,4′-diaminodiphenyl ether (molecular weight 200.24) was prepared at a molar ratio of 1: 1, and 23 in DMAc (N, N-dimethylacetamide). The solution was polymerized to a 7 wt% solution to obtain a 4000 poise polyamic acid solution.

[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. The N, N-dimethylacetamide slurry of calcium oxyhydrogen was added to the polyamic acid solution obtained in the synthesis example in an amount of 0.15% by weight per resin weight 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, both ends thereof were gripped, and treated in a heating furnace at 250 ° C. × 30 seconds, 400 ° C. × 30 seconds, 550 ° C. × 30 seconds to obtain a polyimide film having a thickness of 80 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 1500 ° C. at 5 ° C./min in argon gas and held for 2 hours, and further raised to 3000 ° C. and held for 2 hours for graphitization. Further, the graphite sheet was sandwiched between two rolling rolls and rolled at a pressure of 0.3 MPa to produce a rolled graphite sheet.

[Examples 2 to 4]
The rotation speed of the drum and the gel film were the same as in Example 1 except that the average particle diameter of calcium hydrogen phosphate and the addition amount of calcium hydrogen phosphate per resin weight were set as shown in Table 1 in the polyamic acid solution. A polyimide film of 25 μm and 37.5 μm was obtained by adjusting the conveyance speed (film forming speed).

[Comparative Example 1]
A polyimide film was obtained in the same manner as in Example 1 except that the addition amount of calcium hydrogen phosphate per resin weight added to the polyamic acid solution was 0.03% by weight.

[Comparative Example 2]
A polyimide film was obtained in the same manner as in Example 1 except that the addition amount of calcium hydrogen phosphate per resin weight added to the polyamic acid solution was 0.55% by weight, and a graphite sheet was produced by firing.

[Comparative Example 3]
Except that the average particle size of calcium hydrogen phosphate added to the polyamic acid solution is 2.0 μm, a polyimide film was obtained and fired in the same manner as in Example 1 to prepare a graphite sheet.

[Comparative Example 4]
Except that the average particle diameter of calcium hydrogen phosphate added to the polyamic acid solution is 0.4 μm, a polyimide film was obtained and fired in the same manner as in Example 1 to produce a graphite sheet.

[Comparative Examples 5 and 6]
The average particle size of calcium hydrogen phosphate and the amount of calcium hydrogen phosphate added to the polyamic acid solution per resin weight are adjusted in the same manner as in Example 1 to adjust the drum rotation speed and the gel film conveyance speed (film formation speed). Except having obtained the polyimide film of 20 micrometers and 100 micrometers by this, it obtained the polyimide film like Example 1, and produced the graphite sheet by baking.

  Table 1 shows the characteristics of the polyimide films obtained in Examples 1 to 4 and Comparative Examples 1 to 6, and the thickness, density, and thermal conductivity of the graphite sheet after firing and rolling. The thermal conductivity is the thermal conductivity in the sheet surface direction.

As shown in Table 1, all the graphite films obtained in Examples 1 to 4 had a thermal conductivity of 7.0 × 10 ² (W / mK) or more. As the thickness of the polyimide film before firing becomes thicker, the influence of gas permeability when the inorganic particles sublimate from the inside of the film becomes larger and swelling occurs, so that the density after rolling decreases. As a result, the thermal conductivity tends to decrease.

  In Comparative Examples 1 and 3, the static friction coefficient was high, the slipperiness was poor, wrinkles occurred during film processing, and a graphite sheet could not be produced. In Comparative Examples 2, 4, and 6, abnormal swelling occurred on the surface of the graphite sheet, and the appearance was not excellent. As for Comparative Example 5, when the thickness of the polyimide film was less than 25 μm, the fired graphite sheet was rounded, and when the fired graphite sheet was made flat, it was shattered and a rolled graphite sheet could not be formed.

  As is apparent from the results in Table 1, it is a polyimide film produced mainly by imidization from 4,4′-diaminodiphenyl ether as the diamine component and pyromellitic dianhydride as the acid dianhydride component, and the particle size is 0. A ratio of 0.05 to 0.5% by weight of a powder mainly composed of inorganic particles having an average particle diameter of 0.5 to 2.5 μm within a range of 0.01 to 6.0 μm per film resin weight The polyimide film of the present invention uniformly dispersed in the film exhibits excellent slipperiness and can be applied to a graphite sheet obtained by heat treatment, and has extremely high thermal conductivity, so that heat dissipation of electronic equipment is achieved. It is suitable as a member.

  The polyimide film of the present invention is suitable as a heat radiating member for electronic equipment because it exhibits excellent slipperiness and can be applied to a graphite sheet obtained by heat treatment, and has very high thermal conductivity.

Claims (9)

  4,4'-diaminodiphenyl ether as a diamine component, pyromellitic dianhydride as a main component as an acid dianhydride component, and a polyimide film manufactured by imidization, in the polyimide film Inorganic particles are dispersed at a ratio of 0.05 to 0.50% by weight, the average particle size of the inorganic particles is 0.5 to 1.5 μm, and the particle size is 0.5 to 2.5 μm. A polyimide film characterized in that inorganic particles occupy a proportion of 80% by volume or more in all particles.   The polyimide film according to claim 1, wherein the film thickness is 25 to 80 μm.   The polyimide film according to claim 1 or 2, wherein the inorganic particles are contained in a ratio of 0.05 to 0.30% by weight per film resin weight.   4. The polyimide film according to claim 1, wherein an average particle diameter of the inorganic particles is 0.5 to 1.0 μm.   The polyimide film according to claim 1, wherein the inorganic particles contain calcium hydrogen phosphate as a main component.   6. The polyimide film according to claim 1, wherein the total particle diameter of the inorganic particles is in a range of 6.0 [mu] m or less.   A diamine component composed of 4,4′-diaminodiphenyl ether and a tetracarboxylic dianhydride component composed of pyromellitic dianhydride are reacted in a polar organic solvent to produce a polyamic acid, and the polyamic acid is used. When formed into a film, the average particle size is 0.5 to 1.5 μm, and the inorganic particles having a particle size of 0.5 to 2.5 μm have a particle size distribution occupying a ratio of 80% by volume or more in all particles. A slurry in which inorganic particles are dispersed in the same polar organic solvent as the polar organic solvent is added to the polyamic acid solution so that the inorganic particles have a ratio of 0.05 to 0.50% by weight per resin weight. The manufacturing method of the polyimide film of any one of Claims 1-6 characterized by the above-mentioned.   A graphite sheet obtained by firing the polyimide film according to any one of claims 1 to 6.   A method for producing a graphite sheet, comprising firing the polyimide film according to any one of claims 1 to 6.