TWI675885B - Polyimine film for graphite sheet and manufacturing method thereof - Google Patents

Abstract

The invention provides a polyimide film, which foams well when graphitized by heat treatment, and the graphitized sheet has excellent thermal conductivity, softness, and bending resistance.

The present invention is a polyfluorene imide film with a linear expansion coefficient of 20 ppm / ° C. or less, and is characterized in that it uses p-phenylenediamine or p-phenylenediamine with 4,4'-diaminodiphenyl ether, And one or more types of acid anhydrides selected from the group consisting of pyromellitic dianhydride and 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride are contained in raw materials and are dispersed with inorganic particles And heat treating the polyfluoreneimide film at a temperature of 2000 ° C. or higher to produce a graphite sheet.

Description

Polyimide film for graphite sheet and manufacturing method thereof

The present invention relates to a polyimide film for manufacturing graphite sheets having flexibility and bending resistance, which are used as heat dissipating materials and soaking materials in the form of electrical or thermal conductors, and a method for manufacturing the same.

Polyimide film is known to have excellent characteristics in terms of heat resistance, cold resistance, chemical resistance, electrical insulation, and mechanical strength. It is widely used in electrical insulation materials, heat insulation materials, and flexible printed wiring boards for electric wires. (FPC) base film, IC (Integrated Circuit) tape carrier tape (TAB) carrier film, and IC lead frame fixing tape.

When a polyimide film is used in such applications, an important practical characteristic is the sliding property (easy sliding property) of the film. By ensuring the slippage of the film support (for example, a roller) and the film and the slippage of the film with each other in various film processing steps, the operability and handling of each step can be improved, thereby avoiding the occurrence of wrinkles on the film Bad spots such as folds.

Prior slip technology for polyimide films has been known to add inert inorganic compounds (e.g., orthophosphate of alkaline earth metals, anhydrous calcium hydrogen phosphate, calcium pyrophosphate, silicon dioxide, talc) to polyamic acid (See Patent Document 1).

In addition, as for a graphite sheet obtained by subjecting a polyimide film to an inert gas and heat-treating it at a temperature of 2400 ° C or higher and rolling as necessary, it is known that a uniformly foamed state is produced by performing high-temperature heat treatment, and This is calendered to obtain a flexible graphite sheet having flexibility and elasticity (see Patent Documents 2 and 3). Graphite sheet due to It has higher thermal conductivity than metal sheets such as copper or aluminum, so it has attracted attention as a heat dissipation member of electronic equipment in recent years.

It is known that in order to graphitize a polymer compound such as polyimide, it is preferable to add an inorganic or organic filler (see Patent Document 3 and Patent Document 4). The function of the filler is to make the film after heat treatment uniformly foamed. That is, the added filler generates a gas during heating, and the cavity after the generation of the gas becomes a path, helping the decomposition gas to pass smoothly from the inside of the membrane. The filler works in this way to produce a uniform foamed state.

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

However, only by controlling the rate of temperature increase during graphitization, the degree of foaming of the film may be insufficient, so that the thermal conductivity, flexibility, and bending resistance of the obtained graphite sheet may be insufficient as a heat dissipation member of an electronic device. .

[Prior technical literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 62-68852

[Patent Document 2] Japanese Patent Laid-Open No. 3-75211

[Patent Document 3] Japanese Patent Laid-Open No. 4-21508

[Patent Document 4] Japanese Patent Laid-Open No. 8-267647

[Patent Document 5] Japanese Patent Laid-Open No. 2008-024571

In view of the above-mentioned current situation, an object of the present invention is to provide a polyimide film in which the amount and dispersion of inorganic particles are appropriately controlled, the film foams well when graphitized by heat treatment, and the graphitized sheet has Excellent thermal conductivity, flexibility and bending resistance.

The present inventors and others made diligent efforts to solve the above problems, and the results were At present, the linear expansion coefficient is 20 ppm / ° C or lower, p-phenylenediamine or p-phenylenediamine and 4,4'-diaminodiphenyl ether, and selected from pyromellitic dianhydride and 3,3 ', One or more types of acid anhydrides in a group consisting of 4,4'-biphenyltetracarboxylic dianhydride are contained in raw materials, and the polyimide film in which inorganic particles are dispersed is heat-treated at a temperature of 2000 ° C or higher The graphitization has good foaming, and the graphite sheet obtained by the heat treatment has excellent thermal conductivity, softness, and bending resistance. Based on this knowledge, research is further advanced to complete the present invention.

The present invention relates to the following inventions.

[1] A polyimide film having a linear expansion coefficient of 20 ppm / ° C. or less, characterized in that it comprises p-phenylenediamine or p-phenylenediamine and 4,4'-diaminodiphenyl ether, And one or more types of acid anhydrides selected from the group consisting of pyromellitic dianhydride and 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride are contained in raw materials and are dispersed with inorganic particles And heat treating the polyfluoreneimide film at a temperature of 2000 ° C. or higher to produce a graphite sheet.

[2] The polyfluorene imide film according to the above [1], characterized in that it contains inorganic particles in a ratio of 0.03 to 1.00% by weight based on 1 weight of the film resin.

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

[4] The polyimide film according to any one of the above [1] to [3], characterized in that the ratio of the inorganic particles having a particle diameter of 0.5 to 2.5 μm to 80% by volume of the entire inorganic particles .

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

[6] The polyfluoreneimide film according to any one of the above [1] to [5], characterized in that the molar ratio of p-phenylenediamine to 4,4'-diaminodiphenyl ether is 40/60 ~ 10/90.

[7] The polyimide film according to any one of the above [1] to [5], characterized in that pyromellitic dianhydride and 3,3 ', 4,4'-biphenyltetracarboxylic acid The molar ratio of dianhydride is 80/20 ~ 60/40.

[8] A method for producing a polyimide film according to any one of the above [1] to [7], It is characterized in that p-phenylenediamine or p-phenylenediamine and 4,4'-diaminodiphenyl ether are selected from the group consisting of pyromellitic dianhydride and 3,3 ', 4,4'-diamine. When one or more types of acid anhydrides in a group consisting of pyromellitic dianhydride are reacted in a polar organic solvent to produce a polyamic acid, and the polyamino acid is heated to form a film, the average particle diameter is Inorganic particles having a particle size distribution of 0.1 to 2.0 μm and having a particle size distribution of inorganic particles having a particle size of 0.5 to 2.5 μm occupying 80% by volume or more of all particles are dispersed in the same polar organic solvent as the above-mentioned polar organic solvent. The slurry is added to the polyamine so that the inorganic particles in the polyamino acid solution become a ratio of 0.03 to 1.00% by weight based on 1 weight of the resin.

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

[10] A method for producing a graphite sheet, which is characterized in that the polyimide film described in any one of [1] to [7] above is calcined.

The polyimide film of the present invention foams well when graphitized by heat treatment, and the graphite sheet produced by heat treatment of the polyimide film of the present invention has excellent thermal conductivity, softness, and bending resistance.

Hereinafter, the present invention will be described in more detail.

The polyimide film system of the present invention has a linear expansion coefficient of 20 ppm / ° C or lower, selected from p-phenylenediamine or p-phenylenediamine and 4,4'-diaminodiphenyl ether, and is selected from the group consisting of An acid anhydride and 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride, in which one or more types of acid anhydrides are contained in raw materials and are dispersed with inorganic particles, are characterized in that: The polyimide film is heat-treated at a temperature of 2000 ° C. or higher to produce a graphite sheet.

[Polyamic acid]

When the polyimide film of the present invention is obtained, first, an aromatic diamine component and an aromatic acid anhydride component are polymerized in an organic solvent to obtain a polyamidic acid solution (hereinafter, also referred to as polyamidoamine). Acid solution). The polyamine solution is described below.

In the present invention, the polyamic acid solution can be obtained by polymerizing a chemical substance having an aromatic diamine component and an aromatic acid dianhydride component or both as a main component in an organic solvent.

As the aromatic diamine component, it is preferable to include p-phenylenediamine as an essential component, and to include 4,4'-diaminodiphenyl ether as another aromatic diamine component.

The aromatic anhydride component is preferably pyromellitic dianhydride and / or 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride.

In the present invention, the moles of p-phenylenediamine and 4,4'-diaminodiphenyl ether used as raw materials of the film are preferably 40/60 ~ 10/90, and more preferably 30/70 ~ 15 / 85.

In the present invention, the molar ratio of pyromellitic dianhydride and 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride used as the raw materials of the film is preferably 80/20 ~ 60/40, more It is preferably 75/25 ~ 65/35.

In the present invention, in addition to p-phenylenediamine and 4,4'-diaminodiphenyl ether, a small amount of one or two or more other diamines may be added within a range that does not prevent the effect of the present invention. Furthermore, in addition to pyromellitic dianhydride and 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride, a small amount of one or two or more kinds may be added within a range not hindering the effect of the present invention. Other acid dianhydrides. Specific examples of other diamines and acid dianhydrides include the following, but they are not limited thereto.

二唑、2,2-雙(4-胺基苯基)六氟丙烷、N-(3-胺基苯基)-4-胺基苯甲醯胺、4-胺基苯基-3-胺基苯甲酸酯等。 Examples of the other diamines include 3,3'-diaminodiphenyl ether, m-phenylenediamine, 4,4'-diaminodiphenylpropane, and 3,4'-diaminodiphenyl. Propane, 3,3'-diaminodiphenylpropane, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 3,3'-diamine Diphenylmethane, benzidine, 4,4'-diaminodiphenylsulfide, 3,4'-diaminodiphenylsulfide, 3,3'-diaminodiphenylsulfide, 4,4'-diaminodiphenylphosphonium, 3,4'-diaminodiphenylphosphonium, 3,3'-diaminodiphenylphosphonium, 2,6-diaminopyridine, bis- (4-aminophenyl) diethylsilane, 3,3'-dichlorobenzidine, bis- (4-aminophenyl) ethylphosphine oxide, bis- (4-aminophenyl) phenyl Phosphine oxide, 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-third butylphenyl) ether, bis (p-β-amino-third butylphenyl) ether, p-bis (2-methyl-4-aminopentyl) Phenyl) benzene, p-bis- (1,1-dimethyl-5-aminopentyl) benzene, m-benzene Methylamine, p-xylylenediamine, 1,3-diamine fund adamantane, 3,3'-diamino-1,1'-diamine fund adamantane, 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-amine Propylpropoxy) ethane, 2,2-dimethylpropanediamine, 3-methoxyhexamethylenediamine, 2,5-dimethylhexamethylenediamine, 2,5 -Dimethylheptamethylene diamine, 5-methyl nonamethylene diamine, 1,4-diaminocyclohexane, 1,12-diaminooctadecane, 2,5-diamine Base-1,3,4-

Diazole, 2,2-bis (4-aminophenyl) hexafluoropropane, N- (3-aminophenyl) -4-aminobenzamide, 4-aminophenyl-3-amine Benzoate.

Examples of the other acid dianhydride 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-naphthalenetetracarboxylic dianhydride, 2,3,6,7-tetrachloro-1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,8,9,10-phenanthrenetetracarboxylic acid 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-dicarboxyl Phenyl) fluorene dianhydride, benzene-1,2,3,4-tetracarboxylic dianhydride, 3,4,3 ', 4'-benzophenone tetracarboxylic dianhydride, and the like.

In the present invention, as the organic solvent used to form the polyamino acid solution, Specific examples include, for example, fluorene-based solvents such as dimethyl fluorene and diethyl fluorene; and methylformamides such as N, N-dimethylformamide and N, N-diethylformamide. Solvents; acetamide solvents such as N, N-dimethylacetamide, N, N-diethylacetamide; N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidine Pyrrolidone solvents such as ketones; phenol solvents such as phenol, o-cresol, m-cresol or p-cresol, xylenol, halogenated phenol, and catechol; or hexamethylphosphamide, γ-butane Aprotic polar solvents such as lactones. These can be used individually or in combination of 2 or more types, and can also be used in combination with aromatic hydrocarbons, such as xylene and toluene.

The polymerization method of the polyamic acid solution can be performed by any known method, and examples thereof include the following methods:

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

(2) First, the entire amount of the aromatic acid anhydride component is added to the solvent, and then the aromatic diamine component is added so as to be equivalent to the aromatic acid anhydride component, and polymerization is performed.

(3) One aromatic diamine compound is added to the solvent, and then the time required for the reaction is mixed at a ratio of 95 to 105 mol% of the aromatic anhydride compound with respect to the reaction component, and then another aromatic diamine is added. The compound is further polymerized by adding another aromatic acid anhydride compound so that all the aromatic diamine components and all the aromatic acid anhydride components become approximately equivalent.

(4) Add the aromatic acid anhydride compound to the solvent, and then add another aromatic acid anhydride compound after the time required for the reaction is mixed at a ratio of 95 to 105 mol% of one aromatic diamine compound relative to the reaction component. Then, another aromatic diamine compound is added and polymerized so that all the aromatic diamine components and all the aromatic acid anhydride components become approximately equivalent.

(5) A polyamic acid solution (A) is adjusted by reacting an aromatic diamine component and an aromatic anhydride component in an excess amount in a solvent, and another aromatic solvent is made in another solvent Diamine component and aromatic anhydride component are performed so that either may become excess The reaction adjusts the polyamic acid solution (B). Each of the polyamic acid solutions (A) and (B) obtained in this manner was mixed to complete the polymerization. At this time, when the aromatic diamine component is excessive when the polyamic acid solution (A) is adjusted, the aromatic acid anhydride component is made excessive in the polyamino acid solution (B). When the aromatic acid anhydride component in the solution (A) is excessive, the aromatic diamine component is made excessive in the polyamine solution (B), and the polyamino acid solution (A) and (B) are mixed, and It adjusted so that all the aromatic diamine components and all the aromatic acid anhydride components used for these reactions might become equivalent.

The polymerization method is not limited to these, and a method known in the art may be used.

In the present invention, the aromatic acid anhydride component and the aromatic diamine component constituting the polyamino acid are polymerized at a ratio of approximately equal to the mole number of each, but one of them may be polymerized at 10 mole% or less. It is more preferable that it is blended in an excessive amount in the range of 5 mol% relative to the other.

The polymerization reaction is preferably carried out while stirring and mixing in an organic solvent. The polymerization temperature is not particularly limited, and it 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. Regarding the polymerization reaction, the polymerization reaction may be divided as necessary, or the temperature may be increased or decreased. The order of adding the two reactants is not particularly limited, and it is preferable to add an aromatic acid anhydride to the solution of the aromatic diamine component. Vacuum defoaming during polymerization is an effective method for producing high quality organic solvent solutions of polyamic acid. In addition, the polymerization reaction can be controlled by adding a small amount of a terminal blocking agent to the aromatic diamines before the polymerization reaction. The said terminal blocking agent is not specifically limited, A well-known thing can be used.

The polyamic acid solution obtained in this way contains a solid content of usually 5 to 40% by weight, preferably 10 to 30% by weight. In addition, the viscosity is a measurement value obtained by a Brookfield viscometer, and is not particularly limited. Usually, it is 10 to 2000 Pa · s. For stable liquid delivery, it is preferably 100 to 1000 Pa · s. Furthermore, the polyamidic acid in the organic solvent solution can be partially imidized.

[Inorganic particles]

The inorganic particles dispersed in the polyimide film of the present invention are preferably insoluble to all chemical substances to be contacted in the polyimide film manufacturing step of the present invention.

Examples of the inorganic particles that can be used in the present invention include SiO ₂ (silicon dioxide), TiO ₂ (titanium oxide), CaHPO ₄ (calcium hydrogen phosphate), and Ca ₂ P ₂ O ₇ (calcium pyrophosphate). )Wait. Among them, CaHPO ₄ has good expansion due to gas generated during sublimation from the inside of the polyimide film, and obtains a graphite sheet with excellent thermal conductivity. Therefore, CaHPO _{4 is} particularly preferred as the main component.

The content of the inorganic particles in the polyimide film is preferably a ratio of 0.03 to 1.0% by weight, and more preferably a ratio of 0.1 to 0.8% by weight, based on 1 weight of the film resin. If it is 0.03% by weight or less, the graphite sheet obtained by calcining the polyfluorene imide film has low mechanical strength or thermal conductivity, which is not preferable. On the other hand, if it is 1.0% by weight or more, the uniformity of foaming during graphitization decreases, which is not preferable.

The average particle diameter of the inorganic particles is preferably 0.1 to 2.0 μm, more preferably 0.5 to 1.5 μm, and still more preferably 0.8 to 1.2 μm in terms of more uniform foaming during graphitization.

Regarding the particle size distribution of the inorganic particles, a narrow distribution is preferable, that is, a ratio of particles of a similar size to all particles is high, and specifically, it is preferable that the inorganic particles having a particle diameter of 0.5 to 2.5 μm are relative to all the inorganic particles. A ratio of 80% by volume or more. If the ratio of particles smaller than this range and below 0.5 μm becomes higher, the mechanical strength of the graphite sheet becomes weaker and the thermal conductivity becomes lower, which is not good. In addition, when feeding inorganic particles, coarse particles can be removed by a 5 μm cut-off filter or a 20 μm cut-off filter. If the ratio of inorganic particles larger than 6.0 μm becomes higher, the pores of the filter will be blocked frequently. It is not good because the stability of the step is impaired, and coarse aggregation of inorganic particles becomes easy to occur. Therefore, as the inorganic particles, it is preferable that the total particle diameter is in a range of 6.0 μm or less. The average particle diameter, the particle diameter, and the particle size distribution are values measured using a laser diffraction / scattering particle size distribution measuring device LA-910 of Horiba, in the manner described in the examples described later.

Inorganic particles are in the form of a slurry uniformly dispersed in a polar solvent such as N, N-dimethylformamide, N, N-dimethylacetamide, dimethylarsine, N-methylpyrrolidone, etc. It is preferred to prevent aggregation of the particles during use. Since the slurry has a very small particle size, the precipitation rate is slow and stable. Moreover, even if it precipitates, it can be easily redispersed by re-stirring. The inorganic particle slurry can be obtained by a conventional method.

In the present invention, the method for dispersing the inorganic particles in the polyimide film is not particularly limited. In order to prevent precipitation and aggregation of the inorganic particle slurry, it is preferably added to a polyamic acid solution polymerized in advance. Then, it was decyclized and desolvated, and the polyfluorene imide film was obtained. Alternatively, the inorganic particle slurry may be added to an organic solvent before the polyamic acid polymerization, and then the polyfluorine acid is polymerized, decyclized and desolvated to obtain a polyimide film. As long as it is a step before decyclization and desolvation, it is convenient to add an inorganic particle slurry in any step of manufacturing a polyimide film. The polar solvent used in the inorganic particle slurry is preferably the same polar solvent as the organic solvent used in the production of polyamic acid.

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

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

[Polyimide film]

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

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

As a method for manufacturing a polyimide film, the following methods can be mentioned: a polyimide solution is casted into a film shape and thermally decyclized and desolvated to obtain a polyimide film; and polyimide film; and The cyclization catalyst and dehydrating agent are mixed in the acid solution to chemically decyclize and Making a gel film and heating and desolvating it to obtain a polyimide film; the latter can suppress the thermal expansion coefficient of the obtained polyimide film to be low and the orientation of the film surface direction It is better because it can improve the thermal conductivity or thickness of graphite.

In the method of chemically performing decyclization, the above-mentioned polyamidic acid solution is first prepared. The polyfluorinated acid solution may contain a cyclization catalyst (fluorinated imidization catalyst), a dehydrating agent, a gelling 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 isoquinoline. Heterocyclic tertiary amines such as pyridine, β-methylpyridine, and the like can be used alone or in combination of two or more kinds. Among these, it is preferable to use at least one heterocyclic tertiary amine.

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 anhydrides such as benzoic anhydride. Among them, acetic anhydride and / or Benzoic anhydride.

As a method for producing a polyimide film from a polyacrylic acid solution, a polyamidic acid solution containing a cyclization catalyst and a dehydrating agent is cast on a support by a slit die attached to a support, and formed into a film shape, and After being partially imidized on the support to form a self-supporting gel film, the support is peeled off, dried and heat-treated by imidization.

The polyamic acid solution is formed into a film shape through a slit die, and is cast on a heated support. A thermal ring-closing reaction is performed on the support to form a self-supporting gel film. Peel off the support.

The temperature of the above-mentioned support system metal rotating drum or endless belt can be controlled by the radiant heat of a liquid or gas heat medium and / or an electric heater.

The gel film is heated by a self-supporting body and / or by a heat source such as hot air or an electric heater, and is usually heated to 30 to 200 ° C, preferably to 40 to 150 ° C for closed-loop reaction and freed. Volatile components such as organic solvents are dried, thereby being self-supporting and peeling from the support.

The gel film peeled from the above-mentioned support is usually extended toward the walking direction by rotating the roller while restricting the walking speed. Stretching is usually performed at a temperature below 140 ° C at a magnification of 1.01 to 1.90 times, preferably 1.05 to 1.60 times, and further preferably 1.10 to 1.50 times. The gel film extending in the walking direction is introduced into the tenter device, and the two ends in the width direction are grasped by the tenter clip, while one side travels with the tenter clip and extends in the width direction.

The film dried in the drying area is usually heated by wind, infrared heater, or the like for 15 seconds to 30 minutes. Then, by hot air and / or an electric heater, the heat treatment is usually performed at a temperature of 250 to 500 for 15 seconds to 30 minutes. While adjusting the stretch magnification in the walking direction and the stretch magnification in the width direction, adjust the thickness of the polyimide film.

The thickness of the polyimide film used in the present invention is not particularly limited, but is preferably in a range of 5 μm or more and 200 μm or less, and more preferably in a range of 10 μm or more and 150 μm or less.

The linear expansion coefficient of the polyfluorene imide film of the present invention manufactured in the manner as described above is usually about 20 ppm / ° C or lower, preferably about 18 ppm / ° C or lower. In addition, the coefficient of linear expansion is a value measured by a method described in the examples described later, and is generally an average value of the width direction (TD) and the machine transport direction (MD) of the polyimide film.

[Graphite sheet]

The graphite sheet of the present invention can be obtained by calcining and calcining the polyfluorene imide film of the present invention.

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

When obtaining the graphite sheet of the present invention, first, the polyimide film is cut to a specific size, and the film surface of the polyimide film is placed horizontally or the film surface is placed upright into a graphite holding container.

The temperature of the calcination of graphitization (hereinafter, also referred to as formal heating treatment) is usually 2000 ° C or higher, preferably 2400 ° C or higher, and more preferably 2600 ° C or higher. The final calcination temperature is preferably 2700 ° C or higher, more preferably 2800 ° C or higher, and even more preferably around 3000 ° C. If calcined If the temperature is greater than 3500 ° C, the heat resistance of the calcining furnace is large, and it is difficult to carry out long-term production. When the maximum calcination temperature does not reach 2000 ° C, the obtained graphite sheet tends to become hard and brittle. The rate of temperature increase during firing is not particularly limited, and it is carried out at, for example, about 1 to 10 ° C./minute. For the calcination, a known heating device can be used. The firing time is not particularly limited.

Calcination is usually carried out in an inert gas. The inert gas is not particularly limited, and examples thereof include helium, argon, and nitrogen, and argon is preferably used. The pressure during the calcination may be normal pressure.

Before the above calcination (formal heat treatment), a preheating treatment may be performed as necessary. The temperature of the preheating treatment is preferably lower than the temperature of the formal heat treatment. Specifically, it is preferably about 900 ° C to 1500 ° C. The heating rate of the preheating treatment is not particularly limited, and it is performed at, for example, about 1 to 15 ° C./minute. The preheating treatment is also usually performed in an inert gas. As the inert gas, the same as described above can be used. The time for the preheating treatment is not particularly limited.

The calcined graphite sheet is preferably calendered by being sandwiched between calender rolls. Through the calendering process, it is possible to reduce the thickness unevenness caused by the expansion of the calcined graphite sheet. In addition, the calendering process can increase the density of the calcined graphite sheet and improve the thermal conductivity.

The graphite sheet of the present invention manufactured in the above manner has excellent thermal conductivity due to a large thermal diffusion coefficient. The thermal diffusion coefficient is a value measured by a 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.

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 a method described in Examples described later.

[Example]

Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to this. Such as any limitation of the embodiment, those having ordinary knowledge in the art can make various changes in the technical idea of the present invention.

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

[Evaluation of Inorganic Particles]

Laser-diffraction / scattering particle size distribution measuring device LA-910 from HORIBA, Ltd. was used to measure samples dispersed in a polar solvent. Based on the analysis results, read the particle size range, average particle size, and particle size from 0.5 to Occupancy ratio of 2.5 μm particles to all particles.

[Linear expansion coefficient]

A sample having a width of 5 mm and a length of 10 mm was taken, 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)

Cooling: 300 ℃ → 35 ℃ (cooling speed 5 ℃ / 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 conditions of a temperature range of 50 ° C to 200 ° C during the second temperature increase.

In addition, a linear expansion coefficient is calculated | required as the average linear expansion coefficient by the average value of the width direction (TD) and the machine conveyance direction (MD) of a polyimide film.

[density]

Measurement method: Archimedes method

Measuring device: made by Shimadzu Corporation AUX-120 electronic analytical balance

Measurement temperature: 25 ° C

Dipping solution: water

[Thermal diffusion coefficient]

Measurement method: Xenon flash method

Measuring device: Thermal conductivity measuring device LFA447 made by NETZSCH

Measurement temperature: 25 ° C

Light source: Xenon flash

IR detector: InSb detector (liquid nitrogen cooling)

[Breaking strength]

Measuring device: Autograph AGS-X manufactured by Shimadzu Corporation

Measurement temperature: 25 ° C

Chuck spacing: 50mm

Stretching speed: 25mm / min

Test piece: width 10mm

[Thickness of polyimide film and graphite sheet]

The measurement was performed using LITEMATIC (318 series) manufactured by Mitutoyo.

[Foaming]

A 100-mm square graphite sheet was evaluated visually and using the following evaluation criteria.

Good (○): uniform foaming overall

Bad (×): No foaming or unevenness

[Softness]

After bending a graphite sheet of 100 mm (longitudinal) × 100 mm (wide) such that the longitudinal end portions thereof or the widthwise end portions coincide with each other, press the load of 100 g on the central portion of the crease of the sheet for 3 seconds. The sheet was restored to its original state after unloading, and was evaluated visually using the following evaluation criteria. In the present invention, the term "flexibility" means that, in the evaluation method, the sheet is substantially restored to its original state.

Good (○): The sheet is almost restored to its original state

Bad (×): local deformation of the sheet

[Polyamic acid synthesis example]

Prepare a pyromellitic dianhydride (molecular weight 218.12) / 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride (molecular weight 294.22) / based on a molar ratio of 65/35/80/20 / 4,4'-diaminodiphenyl Ether (molecular weight: 200.24) / p-phenylenediamine (molecular weight: 108.14) was polymerized into a 20% by weight solution in DMAc (N, N-dimethylacetamide) to obtain a polyamic acid solution of 3,500 poise.

[Example 1]

The particle size of all inorganic particles is 0.01 μm or more and 6.0 μm or less, the average particle size is 0.87 μm, and the particle size of 0.5 to 2.5 μm is 81.5% by volume of N, N of calcium hydrogen phosphate in all particles. -Dimethylacetamide slurry is added to the polyamic acid solution obtained in the synthesis example at 0.15% by weight based on 1 weight of the resin in the solution, and is sufficiently stirred to disperse. In this polyamic acid solution, a conversion agent containing acetic anhydride (molecular weight 102.09) and β-methylpyridine was mixed and stirred at a ratio of 2.0 mol equivalents to the polyamino acid. The obtained mixture was casted from a die onto a rotating stainless steel drum at 65 ° C to obtain a self-supporting gel film. The gel film was peeled from the drum, and both ends were grasped, and treated at 250 ° C. × 30 seconds, 400 ° C. × 30 seconds, and 550 ° C. × 30 seconds in a heating furnace to obtain a polyimide film having a thickness of 50 μm.

The polyimide film obtained in the above manner was cut into a size of 250 mm × 600 mm in width, and the film surface was erected into a graphite cylindrical bottomed holding container. Then, the temperature was raised to 1000 ° C. at 3 ° C./min for 1 hour in argon, and further heated to 2800 ° C. for 3 hours at 3 ° C./minute, and the polyimide film was calcined and graphitized. The obtained graphite sheet was sandwiched between two calender rolls and subjected to a calendering treatment to be calendered to produce a graphite sheet having a thickness of 25 μm.

[Examples 2 and 3]

Adjust the rotation speed of the drum and the transfer speed (film-forming speed) of the gel film in the heating furnace, that is, the heating time of each heating temperature, so that the thickness of the obtained polyimide film becomes 25 μm and 75 μm. Otherwise, a polyfluorene film was obtained in the same manner as in Example 1. The obtained polyfluoreneimide film was calcined in the same manner as in Example 1 to obtain a graphite sheet. The calendering was performed in the same manner as in Example 1 to produce various thicknesses. Graphite sheet.

[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 to the polyamic acid solution per 1 weight of the solution resin was 0.02% by weight. The obtained polyfluoreneimide film was calcined in the same manner as in Example 1 to obtain a graphite sheet. The rolling process was performed in the same manner as in Example 1 to produce a graphite sheet having a thickness of 25 μm.

The properties of the polyimide film obtained in Examples 1 to 3 and Comparative Example 1 are shown in Table 1. The thickness, density, thermal diffusion coefficient, and fracture of the graphite sheet after the polyimide film was calcined and rolled. Table 2 shows the strength and flexibility, and the foamability when the polyfluorene film is graphitized. The thermal diffusivity is the thermal diffusivity in the direction of the sheet surface.

From the results of Comparative Example 1, it can be seen that the polyimide film that does not contain inorganic particles equivalent to 0.03% by weight or more of the weight of the film resin at the time of graphitization has poor foaming properties. From this polyimide film, The fracture strength of the obtained graphite sheet is weak, and the thermal diffusion coefficient is also low. On the other hand, according to the results of Examples 1 to 3, it can be seen that the polyimide film containing inorganic particles in an amount of 0.03% by weight or more relative to 1 weight of the film resin has good foamability during graphitization. The graphite sheet obtained from the polyfluorene film has a strong breaking strength, and has excellent thermal conductivity, softness, and bending resistance.

[Industrial availability]

The polyimide film of the present invention has good foaming properties when graphitized by heat treatment. The graphite sheet produced by heat-treating the polyimide film has excellent thermal conductivity, softness, and bending resistance. Suitable as heat dissipation component of electronic equipment.

Claims (7)

A polyimide film having a linear expansion coefficient of 20 ppm / ° C or less is characterized in that it comprises p-phenylenediamine or p-phenylenediamine and 4,4'-diaminodiphenyl ether, and is selected from the group consisting of Pyromellitic dianhydride and 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride. One or more types of acid anhydrides are produced by including raw materials and dispersed with inorganic particles, among which The average particle diameter of the inorganic particles is 0.1 to 2.0 μm, and the inorganic particles are contained in a ratio of 0.03 to 1.00% by weight relative to 1 weight of the polyimide film resin, and the inorganic particles having a particle diameter of 0.5 to 2.5 μm are relative to all The inorganic particles occupy a ratio of 80% by volume or more, and the polyimide film is heat-treated at a temperature of 2000 ° C. to 3500 ° C. to produce a graphite sheet. For example, the polyimide film of claim 1, wherein the inorganic particles mainly include calcium hydrogen phosphate. For example, the polyimide film of claim 1 or 2, wherein the molar ratio of p-phenylenediamine to 4,4'-diaminodiphenyl ether is 40/60 ~ 10/90. For example, the polyimide film of claim 1 or 2, wherein the molar ratio of pyromellitic dianhydride to 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride is 80/20 ~ 60/40 . A method for manufacturing a polyimide film, the polyimide film is the polyimide film according to any one of claims 1 to 4, and is characterized in that p-phenylenediamine or p-phenylenediamine and 4,4'-diaminodiphenyl ether and one or more acid anhydrides selected from the group consisting of pyromellitic dianhydride and 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride When a polyamine is produced by reacting in a polar organic solvent, and the polyamine is heated to form a film, the average particle diameter is 0.1 to 2.0 μm and the inorganic particles have a particle diameter of 0.5 to 2.5 μm. The inorganic particles having a particle size distribution with a ratio of 80% by volume or more of all the particles are dispersed in the same polar organic solvent as the above-mentioned polar organic solvent, and the slurry thus obtained is used to make the above-mentioned inorganic particles relatively in the polyamic acid solution. The resin is added to the polyamic acid in a ratio of 0.03 to 1.00% by weight per 1 weight of the resin. A graphite sheet, characterized in that it is obtained by calcining a polyfluorene imine film according to any one of claims 1 to 4. A method for manufacturing a graphite sheet, which is characterized in that it is a method of calcining a polyfluorene film according to any one of claims 1 to 4.