Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/20—Graphite
  • C01B32/205—Preparation
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G73/00—Macromolecular compounds obtained by reactions forming a linkage containing nitrogen with or without oxygen or carbon in the main chain of the macromolecule, not provided for in groups C08G12/00 - C08G71/00
  • C08G73/06—Polycondensates having nitrogen-containing heterocyclic rings in the main chain of the macromolecule
  • C08G73/10—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/49—Phosphorus-containing compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L79/00—Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing nitrogen with or without oxygen or carbon only, not provided for in groups C08L61/00 - C08L77/00
  • C08L79/04—Polycondensates having nitrogen-containing heterocyclic rings in the main chain; Polyhydrazides; Polyamide acids or similar polyimide precursors
  • C08L79/08—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors

Definitions

• the present invention relates to polyimide films for graphite sheets, graphite sheets, and methods for producing them.
• Graphite sheets have excellent thermal conductivity, so they are used as heat dissipation materials in various electronic devices such as computers, semiconductor elements mounted in electrical devices, and other heat-generating parts.
• Patent Documents 1 to 3 describe a technique for producing a graphite sheet by heat-treating (graphitizing) a polyimide film.
• An object of one embodiment of the present invention is to provide a polyimide film that can produce a high-density graphite sheet with good productivity.
• the present inventors have completed the present invention as a result of intensive research aimed at solving the above problems.
• one embodiment of the present invention includes the following.
• a polyimide film made from an acid dianhydride component and a diamine component contains 50 to 100 mol% of pyromellitic dianhydride (PMDA) and 3,3′,4,4′-benzophenonetetracarboxylic acid in 100 mol% of the total amount of the dianhydride component.
• PMDA pyromellitic dianhydride
• ODPA 4,4'-oxydiphthalic dianhydride
• a method for producing a polyimide film wherein the acid dianhydride component is 50 to 100 mol% of pyromellitic dianhydride (PMDA) in a total amount of 100 mol% of the acid dianhydride component, 3, 0 to 50 mol% of at least one of 3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and 4,4'-oxydiphthalic dianhydride (ODPA), and the diamine component is 50 to 100 mol% of 4,4'-diaminodiphenyl ether (ODA) and 0 to 100 mol% of 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) in the total amount of 100
• a method for producing a graphite sheet comprising a step of heat-treating a polyimide film for a graphite sheet at 2400° C. or higher, wherein the polyimide film for the graphite sheet is made from an acid dianhydride component and a diamine component.
• a polyimide film wherein the acid dianhydride component contains 50 to 100 mol% of pyromellitic dianhydride (PMDA) in 100 mol% of the total amount of the acid dianhydride component, 3,3',4, At least one of 4'-benzophenonetetracarboxylic dianhydride (BTDA) and 4,4'-oxydiphthalic dianhydride (ODPA) is contained in an amount of 0 to 50 mol%, and the diamine component is the total amount of the diamine component.
• PMDA pyromellitic dianhydride
• BTDA 4'-benzophenonetetracarboxylic dianhydride
• ODPA 4,4'-oxydiphthalic dianhydride
• 4,4'-diaminodiphenyl ether is 50 to 100 mol%
• 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) is 0 to 50 mol%
• the total content of anhydride (ODPA) and the 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) is 1 to 50 mol%
• the total amount of the polyimide film is 100% by weight.
• a thick graphite sheet can be produced by heat-treating (graphitizing) a polyimide film having a large thickness (for example, 80 ⁇ m or more).
• a polyimide film having a large thickness (for example, 80 ⁇ m or more).
• the thickness of a conventional polyimide film is simply increased, the surface of the graphite sheet containing the polyimide film as a raw material (made by heat treatment) is greatly foamed and the thermal conductivity is lowered.
• the present inventors have found that problems such as poor appearance occur.
• the inventors of the present invention focused on the outgassing generated in the graphite sheet during the heat treatment of the polyimide film as the cause of the problem that occurs in such a thick graphite sheet.
• the orientation of the graphite (graphite layer) in the resulting graphite sheet has the effect of increasing the orientation of the polyimide film for the purpose of improving interlaminar strength, etc.
• Acid anhydrides (PMDA, BPDA, etc.) and/or diamines (ODA, PDA, etc.) with enhancing properties have been employed as raw materials for polyimide films.
• PMDA, BPDA, etc. acid anhydrides
• ODA, PDA, etc. diamines
• acid anhydride and/or diamine which have the effect of increasing the orientation of the polyimide film, are used as raw materials for the polyimide film.
• a high-density graphite sheet can be made into a polyimide film that can be provided with good productivity, in particular, a thick polyimide film that can provide a thick graphite sheet.
• the present inventors have made intensive studies to provide a polyimide film that can produce a high-density graphite sheet with good productivity.
• the following findings were newly discovered, leading to the completion of the present invention: (1) Acid anhydrides (BTDA, ODPA, etc.) and/or diamines (BAPP, etc.), which have the effect of disturbing (lowering) the orientation of the polyimide film, are used as raw materials for the polyimide film in an appropriate amount.
• the orientation of the resulting polyimide film can be moderately disturbed.
• the orientation of the graphite layer can be moderately disturbed in the resulting graphite sheet.
• the outgassing generated in the graphite sheet can be removed appropriately.
• the graphite sheet can be provided with good productivity because problems such as foaming on the surface of the graphite sheet caused by (2)
• a graphite sheet having a high density can be provided by heat-treating a polyimide film containing an appropriate proportion of an organic phosphorus compound.
• the polyimide film according to one embodiment of the present invention contains an appropriate amount of an acid anhydride and / or diamine that has the effect of disturbing the orientation of the polyimide film, and contains an appropriate proportion of an organic phosphorus compound, so that it has a high density. can be provided with high productivity. Therefore, it can be suitably used for manufacturing graphite sheets, particularly thick graphite sheets.
• Such a polyimide film has not been known in the past and can be said to be a surprising discovery.
• polyimide film A polyimide film according to one embodiment of the present invention (hereinafter sometimes referred to as the present polyimide film) will be described in detail below.
• This polyimide film is a polyimide film made from an acid dianhydride component and a diamine component as raw materials, and the acid dianhydride component contains 50 PMDA in the total amount of 100 mol% of the acid dianhydride component. ⁇ 100 mol%, and at least one of BTDA and ODPA in an amount of 0 to 50 mol%, and the diamine component contains 50 to 100 mol% of ODA and 0 to 50 mol% of BAPP in the total amount of 100 mol% of the diamine component.
• the total content of the BTDA, the ODPA and the BAPP with respect to the total amount of 200 mol% of the acid dianhydride component and the diamine component is 1 to 50 mol% or less, and an organic phosphorus compound 0.1% by weight to 5.0% by weight.
• the present polyimide film has the above structure, by using the present polyimide film as a raw material, a graphite sheet having a high density can be provided with good productivity. That is, the present polyimide film can be suitably used for producing graphite sheets. Therefore, the present polyimide film can also be called a polyimide film for graphite sheets.
• the acid dianhydride component which is the raw material of the present polyimide film, contains 50 to 100 mol% of pyromellitic dianhydride (PMDA) and 3,3',4,4'-benzophenonetetracarboxylic dianhydride. (BTDA) and at least one of 4,4'-oxydiphthalic dianhydride (ODPA) from 0 to 50 mol%.
• the acid dianhydride component may contain only one of BTDA and ODPA, or both of them.
• the acid dianhydride component may contain BTDA and / or ODPA, and does not contain either BTDA or ODPA. It's good.
• the amount of PMDA contained in the acid dianhydride component is 50 mol% or more, preferably 60 mol% or more, relative to 100 mol% of the total amount of the acid dianhydride component, More preferably, it is 70 mol % or more.
• the present polyimide film contains 50 mol % or more of PMDA, it is possible to provide a polyimide film (and a carbonaceous film) having moderate orientation.
• the amount of PMDA contained in the acid dianhydride component may be 80 mol% or more, 90 mol% or more, 95 mol% or more, or 100 mol%. .
• the obtained graphite sheet has good thermal diffusivity and flexibility.
• the content of BTDA and ODPA (the total amount of BTDA and ODPA) is 100% of the total amount of the acid dianhydride component. Based on mol %, it is 1 mol % or more, preferably 5 mol % or more, more preferably 10 mol % or more, and still more preferably 20 mol % or more.
• the upper limit of the content of BTDA and ODPA is 50 mol% or less, preferably 40 mol% or less, more preferably 30 mol% or less.
• the acid dianhydride component contains at least one of BTDA and ODPA in an amount of 1 mol % or more, the orientation of the resulting polyimide film (and carbonaceous film) can be moderately disturbed. Thereby, a graphite sheet can be provided with good productivity. Further, when the content (total amount) of at least one of BTDA and ODPA in the acid dianhydride component is 50 mol% or less, there is no fear that the orientation of the resulting graphite sheet will be excessively disturbed. Good thermal diffusivity and flexibility of the sheet.
• the present polyimide film may contain other acid dianhydrides in addition to the PMDA, the BTDA and the ODPA as acid dianhydride components.
• Other acid dianhydrides include, for example, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,2′,3, 3'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride , 3,4,9,10-perylenetetracarboxylic dianhydride, 1,1-(3,4-dicarboxyphenyl)ethane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)
• the content of the other acid dianhydride in the acid dianhydride component which is the raw material of the present polyimide film is 50 mol% or less, preferably 40 mol, in 100 mol% of the total amount of the acid dianhydride component. %, more preferably 30 mol % or less, still more preferably 20 mol % or less, even more preferably 10 mol % or less, and particularly preferably 0 mol %. That is, it is particularly preferable that the acid dianhydride component, which is the raw material of the present polyimide film, does not contain other acid dianhydrides.
• the diamine component which is the raw material of the present polyimide film, contains 4,4'-diaminodiphenyl ether (ODA) in an amount of 50 to 100 mol%, and 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP ) in an amount of 0 to 50 mol %.
• ODA 4,4'-diaminodiphenyl ether
• BAPP 2,2-bis[4-(4-aminophenoxy)phenyl]propane
• the diamine component may or may not contain BAPP.
• the amount of ODA contained in the diamine component is 50 mol% or more, preferably 60 mol% or more, more preferably 70 mol%, based on 100 mol% of the total amount of the diamine component. % or more.
• the amount of ODA contained in the diamine component may be 80 mol % or more, 90 mol % or more, 95 mol % or more, or 100 mol %.
• the diamine component contains 100 mol % of ODA.
• the dianhydride component contains 50 to 99 mol % of PMDA and 1 to 50 mol of at least one of BTDA and ODPA. % is preferred. With such a configuration, the obtained graphite sheet has good thermal diffusivity and flexibility.
• the content of BAPP is 1 mol% or more, preferably 5 mol% or more, relative to 100 mol% of the total amount of the diamine component. It is preferably 10 mol % or more, more preferably 20 mol % or more.
• the upper limit of the BAPP content is 50 mol % or less, preferably 40 mol % or less, and more preferably 30 mol % or less.
• the content of BAPP in the diamine component is 50 mol% or less, there is no possibility that the orientation of the graphite layers in the graphite sheet is excessively disturbed, and the resulting graphite sheet has good thermal diffusivity and flexibility. .
• the present polyimide film may contain other diamines in addition to the ODA and BAPP as diamine components.
• Other diamines include, for example, p-phenylenediamine (PDA), 4,4'-diaminodiphenylmethane, benzidine, 3,3'-dichlorobenzidine, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl Sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 1,5-diaminonaphthalene, 4,4'-diaminodiphenyldiethylsilane, 4,4'-diamino Diphenylsilane, 4,4'-diminodiphenylethylphosphine oxide, 4,4'-diaminodiphenyl
• the content of the other diamine in the diamine component, which is the raw material of the present polyimide film is 50 mol% or less, preferably 40 mol% or less, more preferably 30%, based on the total amount of 100 mol% of the diamine component. It is mol % or less, more preferably 20 mol % or less, even more preferably 10 mol % or less, and particularly preferably 0 mol %. That is, it is particularly preferable that the diamine component, which is the raw material of the present polyimide film, does not contain other diamines.
• the present polyimide film contains 1 to 50 mol % of the BTDA, the ODPA and the BAPP in total with respect to 200 mol % of the total amount of the acid dianhydride component and the diamine component.
• the orientation of the present polyimide film (and the carbonaceous film) can be moderately disturbed by setting the amounts of the BTDA, the ODPA and the BAPP used within the above ranges. Therefore, a graphite sheet containing the present polyimide film as a raw material can be produced at a high rate of temperature rise and is highly productive.
• the lower limit of the total content of the BTDA, the ODPA and the BAPP with respect to the total amount of 200 mol% of the acid dianhydride component and the diamine component is 1 mol% or more, preferably It is 5 mol % or more, more preferably 10 mol % or more, and still more preferably 20 mol % or more.
• the upper limit of the total content of BTDA, ODPA and BAPP is 50 mol % or less, preferably 40 mol % or less, and more preferably 30 mol % or less.
• This polyimide film is a polyimide film made from substantially equimolar amounts of the acid dianhydride component and the diamine component as raw materials.
• substantially equimolar amounts means that the ratio of molar amounts of two or more different substances (for example, an acid dianhydride component and a diamine component) is from 100:98 to 100:102. It is intended to be within the range, preferably 100:100.
• containing 0 to 50 mol% of at least one of BTDA and ODPA in the total amount of 100 mol% of the acid dianhydride component means "the acid dianhydride component and the diamine component It can also be said that at least one of BTDA and ODPA is contained in an amount of 0 to 50 mol% relative to the total amount of 200 mol%. It can also be said that "0 to 50 mol % of BAPP is contained with respect to 200 mol % of the total amount of the acid dianhydride component and the diamine component".
• the total content of the BTDA, the ODPA and the BAPP with respect to 200 mol% of the total amount of the acid dianhydride component and the diamine component is the content of BTDA and ODPA in the acid dianhydride component and the content of BAPP in the diamine component.
• This polyimide film contains 0.1 to 5.0% by weight of an organophosphorus compound in 100% by weight of the total amount of this polyimide film.
• the content of the organic phosphorus compound in the polyimide film is 0.1 to 5.0% by weight, preferably 0.2 to 3.0% by weight, based on 100% by weight of the total amount of the polyimide film. More preferably 0.3 to 1.5% by weight.
• the content of the organic phosphorus compound in the present polyimide film is 0.1% by weight or more, a graphite sheet with high density can be provided, and when it is 5.0% by weight or less, the foaming rate during graphitization is reduced. , has the advantage of being able to provide graphite sheets with higher productivity.
• the present polyimide film contains an organic phosphorus compound within the above range, so that (1) it can provide a graphite sheet with excellent peelability from a slightly adhesive film, and (2) the carbonaceous film in the graphitization process. Since fusion can be prevented, it also has the advantage of being able to provide graphite sheets with higher productivity.
• organic phosphorous compounds examples include phosphates, phosphine oxides, phosphites, phosphines, phosphonates, phosphinates, and the like. Only one type of these organophosphorus compounds may be contained, or two or more types may be contained. Among the exemplified organophosphorus compounds, phosphate esters are preferred, and triphenyl phosphate is particularly preferred, since they have the advantage of being stable in air.
• the organic phosphorus compound contained in the present polyimide film is preferably an organic phosphorus compound in which the valence of phosphorus is pentavalent. That is, the present polyimide film preferably contains, as the organic phosphorus compound, an organic phosphorus compound in which the valence of phosphorus is pentavalent, and may contain only an organic phosphorus compound in which the valence of phosphorus is pentavalent. more preferred.
• organic phosphorus compounds in which the valence of phosphorus is pentavalent include triphenyl phosphate and trimethyl phosphate.
• the temperature at which the weight loss rate is 5% in TG-DTA measurement is preferably 200 ° C. or higher, more preferably 250 ° C. or higher. It is more preferably 300° C. or higher. If the temperature at which the weight reduction rate of the organic phosphorus compound contained in the present polyimide film is 5% in TG-DTA measurement is 200° C. or higher, contamination of the furnace for forming the polyimide film can be reduced.
• organophosphorus compounds whose temperature at which the weight loss rate reaches 5% in TG-DTA measurement is 200°C or higher include triphenyl phosphate and triphenylphosphine oxide.
• the present polyimide film may contain inorganic particles (filler).
• the present polyimide film contains inorganic particles, the present polyimide film becomes a polyimide film having excellent slipperiness.
• Such a polyimide film having excellent lubricity can suppress the occurrence of scratches during transport of the polyimide film, and can prevent fusion of the carbonaceous film in the graphitization process.
• Inorganic particles that the present polyimide film may contain include calcium carbonate (CaCO 3 ), silica, calcium hydrogen phosphate (CaHPO 4 ), calcium phosphate (Ca 2 P 2 O 7 ), and the like.
• phosphorus-containing inorganic particles such as calcium hydrogen phosphate and calcium phosphate are preferred.
• the upper limit of the average particle size of the inorganic particles that can be contained in the present polyimide film is not particularly limited, but is preferably 2.5 ⁇ m or less, preferably 2.0 ⁇ m or less, and preferably 1.5 ⁇ m or less. , is preferably 1.0 ⁇ m or less.
• the average particle size of the inorganic particles is 2.5 ⁇ m or less, voids generated inside the film after graphitization can be reduced, so that a graphite sheet having an excellent density after compression can be obtained. Thus, a graphite sheet with even better density can be provided.
• the lower limit of the average particle size of the inorganic particles is not particularly limited, but is preferably 0.1 ⁇ m or more, more preferably 0.3 ⁇ m or more, further preferably 0.5 ⁇ m or more, and 0 0.7 ⁇ m or more is even more preferable.
• the average particle size of inorganic particles is intended to be the volume average particle size, and the inorganic particles dispersed in dimethylformamide are measured using a microtrac particle size distribution analyzer MT3000II. is.
• the lower limit of the content of the inorganic particles in the polyimide film is not particularly limited, but is preferably 0.01% by weight or more, more preferably 0.02% by weight. It is preferably 0.03% by weight or more, and more preferably 0.03% by weight or more.
• the upper limit of the content of the inorganic particles is not particularly limited, but is preferably 0.30% by weight or less, more preferably 0.20% by weight or less, and further preferably 0.15% by weight or less. It is preferably 0.10% by weight or less, and more preferably 0.10% by weight or less.
• the thickness of the present polyimide film is preferably 80 ⁇ m to 200 ⁇ m, more preferably more than 80 ⁇ m and 200 ⁇ m or less, even more preferably 90 ⁇ m to 180 ⁇ m, even more preferably 100 ⁇ m to 170 ⁇ m, and 110 ⁇ m. ⁇ 150 ⁇ m is particularly preferred, and 115 ⁇ m to 140 ⁇ m is most preferred. If the thickness of the polyimide film is within the above range, it is possible to provide a graphite sheet having a more excellent thermal diffusivity.
• the lower limit of the thickness of the polyimide film according to one embodiment of the present invention is preferably 80 ⁇ m or more, more preferably more than 80 ⁇ m, even more preferably 90 ⁇ m or more, and even more preferably 100 ⁇ m or more. It is preferably 110 ⁇ m or more, particularly preferably 115 ⁇ m or more, and most preferably 115 ⁇ m or more.
• the upper limit of the thickness of the polyimide film is preferably 200 ⁇ m or less, more preferably 180 ⁇ m or less, even more preferably 160 ⁇ m or less, even more preferably 140 ⁇ m or less, and 150 ⁇ m or less. It is particularly preferred to have A polyimide film having a thickness of 80 ⁇ m or more can be said to be a polyimide film having a large thickness, and can be said to be a polyimide film capable of providing a thick graphite sheet.
• the polyimide film of the present invention can provide a thick graphite sheet with good productivity even when the polyimide film is thick, and the resulting graphite sheet has a high density. That is, the present polyimide film can be suitably used as a thick polyimide film.
• the method for producing a polyimide film according to one embodiment of the present invention (hereinafter sometimes referred to as the method for producing the present polyimide film) is not particularly limited, but for example, a method having the following steps i) to iv) is preferable.
• the acid dianhydride component and the diamine component are monomer units that constitute polyamic acid, which is a copolymer.
• the acid dianhydride component and the diamine component may be collectively referred to as the monomer component.
• polyimide film In the method for producing the present polyimide film, as the step i), the above ⁇ 2.
• Polyimide film> The acid dianhydride component and the diamine component detailed in the section are polymerized (as raw materials), and are not particularly limited as long as polyamic acid can be obtained, for example, the following polymerization methods (1) to (5) Either can be preferably used.
• a method of dissolving a diamine component in an organic solvent (organic polar solvent) and reacting the diamine component with a substantially equimolar amount of an acid dianhydride component for polymerization is a method of dissolving a diamine component in an organic solvent (organic polar solvent) and reacting the diamine component with a substantially equimolar amount of an acid dianhydride component for polymerization.
• a specific example of the method (2) is to synthesize a prepolymer having the acid dianhydride at both ends using a diamine component and an acid dianhydride component, and add the diamine component used in the synthesis of the prepolymer to the prepolymer.
• a method of synthesizing a polyamic acid by reacting a diamine component having the same composition as or a diamine component having a different composition.
• the diamine component to be reacted with the prepolymer may have the same composition as the diamine component used to synthesize the prepolymer, or may have a different composition.
• a diamine component is added in an amount substantially equimolar to the acid dianhydride component to obtain an acid dianhydride.
• a method of polymerizing by reacting a mixture of an acid dianhydride component and a diamine component in substantially equimolar amounts in an organic solvent.
• the i) step preferably includes an addition step of adding (mixing) an organophosphorus compound to the polyamic acid solution obtained by polymerizing the acid dianhydride component and the diamine component.
• the amount of the organophosphorus compound added to the solid content (polyamic acid) of the polyamic acid solution in the addition step is the content of the organophosphorus compound in the resulting polyimide film.
• the addition amount of the organic phosphorus compound in the adding step the content of the organic phosphorus compound in the resulting polyimide film can be adjusted.
• the acid dianhydride component and the diamine component to be reacted (subjected to polymerization) in the i) step become the acid dianhydride component and the diamine component which are raw materials of the resulting polyimide film, and the polyamide in the i) step (addition step)
• the amount of the organophosphorus compound added to the acid can be the content of the organophosphorus compound in the resulting polyimide film.
• step i) in the present method for producing a polyimide film can be expressed as follows: a step of mixing an acid dianhydride component and a diamine component to obtain a polyamic acid, and 100 weight of the polyamic acid %, and the acid dianhydride component is pyromellitic acid in the total amount of 100 mol% of the acid dianhydride component.
• dianhydride dianhydride
• BTDA 3,3′,4,4′-benzophenonetetracarboxylic dianhydride
• ODPA 4,4′-oxydiphthalic dianhydride
• the diamine component includes 50 to 100 mol% of 4,4'-diaminodiphenyl ether (ODA), 2,2-bis[4- (4-Aminophenoxy)phenyl]propane (BAPP) is contained in an amount of 0 to 50 mol%, and the 3,3′,4,4′- total of benzophenonetetracarboxylic dianhydride (BTDA), the 4,4′-oxydiphthalic dianhydride (ODPA) and the 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP)
• the content is 1 to 50 mol %.
• a preferred method for producing the present polyimide film can be expressed as follows: a step of mixing an acid dianhydride component and a diamine component to obtain a polyamic acid; and adding 0.1 to 5.0% by weight of an organic phosphorus compound, wherein the acid dianhydride component is pyromellitic dianhydride in the total amount of 100 mol% of the acid dianhydride component 50 to 100 mol% of (PMDA), at least one of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) and 4,4′-oxydiphthalic dianhydride (ODPA)
• the diamine component contains 50 to 100 mol% of 4,4′-diaminodiphenyl ether (ODA), 2,2-bis[4-(4- containing 0 to 50 mol% of aminophenoxy)phenyl]propane (BAPP), and the 3,3',4,4'-benzophenonetetracarboxylic acid relative to the total amount of 200
• step i) in the method for producing the present polyimide film and the organic phosphorus compound to be added to the polyamic acid are described in ⁇ 2.
• Polyimide film> section can be incorporated as appropriate.
• the steps ii) to iv) in the present method for producing a polyimide film are steps of imidizing the polyamic acid solution to obtain a polyimide film.
• the method for imidizing the polyamic acid includes, for example, (I) a thermal imidization method in which a polyamic acid solution is heated to imidize without using an imidization accelerator, or , (II) polyamic acid, a dehydrating agent (dehydration ring-closing agent) typified by acid dianhydrides such as acetic anhydride, and/or tertiary amines typified by picoline, quinoline, isoquinoline, pyridine, etc.
• a chemical imidization method of imidizing polyamic acid by adding an imidization accelerator such as a catalyst and heating a polyamic acid solution containing the imidization accelerator can be used.
• the resulting polyimide film has a small coefficient of linear expansion, a high elastic modulus, a tendency to increase birefringence, and can be rapidly graphitized at a relatively low temperature, so that a high-quality graphite sheet can be obtained. Therefore, the chemical imidization method is preferred. In particular, it is preferable to use a dehydrating agent and an imidization accelerator in combination, because the resulting polyimide film can have a smaller linear expansion coefficient, a larger elastic modulus, and a larger birefringence. In addition, since the imidization reaction proceeds more rapidly in the chemical imidization method, the imidization reaction can be completed in a short time in the heat treatment, and is an industrially advantageous method with excellent productivity.
• the support used in step ii) is not dissolved by the solution containing the polyimide, and is particularly a support that can withstand the heating required for drying the laminate.
• a glass plate, an aluminum foil, an endless stainless steel belt, a stainless steel drum, etc. can be suitably used.
• the thickness of the finally obtained polyimide film and the heating conditions are set according to the production rate, and the mixed solution layer (polyamic acid solution) coated on the support is subjected to After performing at least one of partial imidization and drying, this is a step of obtaining (peeling) a gel film from the support.
• step iv) more specifically, the gel film (the gel film obtained in step iii) is fixed at its ends and heat-treated while avoiding shrinkage during curing.
• This is a step of removing water, residual solvent, imidization accelerator, etc., and completely imidizing the remaining amic acid (non-imidized amic acid) to obtain a polyimide-containing film (polyimide film).
• the heating conditions in the iv) step may be appropriately set according to the thickness of the film to be finally obtained and the production rate.
• the method for drying the mixed solution layer and the gel film in the iii) step and the iv) step is not particularly limited.
• a method of heating by treatment can be mentioned.
• the drying temperature (heating temperature) in the drying step is not particularly limited as long as a gel film or polyimide film can be obtained. It may be 400°C to 500°C.
• Graphite sheet> In one embodiment of the invention, there is provided a graphite sheet comprising the polyimide film as a raw material. It can also be said that the graphite sheet according to one embodiment of the present invention (hereinafter referred to as the present graphite sheet) is a graphite sheet obtained by heat-treating the present polyimide film. Since the present graphite sheet contains the present polyimide film as a raw material, it has a high density and can be provided with good productivity.
• the graphite sheet refers to both a graphite sheet before being subjected to the rolling process described later (graphite sheet before rolling) and a graphite sheet after being subjected to the rolling process (graphite sheet after rolling). is intended, unless otherwise specified, graphite sheets after rolling are intended.
• the density of the present graphite sheet is preferably more than 2.00 g/cm 3 , more preferably 2.02 g/cm 3 or more, and more preferably 2.04 g/cm 3 or more. more preferably 2.06 g/cm 3 or more.
• the upper limit of the density is not particularly limited, the density of the graphite sheet is usually 2.26 g/cm 3 or less.
• a graphite sheet with a density of 2.00 g/cm 3 or more can be said to be a graphite sheet with a high density, and can achieve efficient heat dissipation, and is used in fields such as electronic devices that require excellent heat dissipation. , can be suitably used as a heat radiating member.
• the method for measuring the density of the graphite sheet is as described in Examples below.
• the thermal conductivity of the graphite sheet can be evaluated by the thermal diffusivity of the graphite sheet (graphite sheet after rolling).
• the thermal diffusivity of the present graphite sheet is preferably 7.0 cm 2 /s or more, more preferably 8.0 cm 2 /s or more, further preferably 9.0 m 2 /s or more, More preferably, it is 9.5 cm 2 /s or more.
• a graphite sheet having a thermal diffusivity of 7.0 cm 2 /s or more has excellent thermal conductivity. In other words, it is excellent in heat dissipation, and can be suitably used as a heat dissipation member in fields such as electronic equipment that require excellent heat dissipation.
• the method for measuring the thermal diffusivity of the graphite sheet is as described in Examples below.
• the productivity of the graphite sheet is defined as the ratio of the thickness of the raw material polyimide film to the thickness of the resulting graphite sheet (graphite sheet before rolling) (thickness of graphite sheet before rolling/thickness of polyimide film). It can be evaluated based on the thickness (hereinafter referred to as "GS thickness/PI thickness"). If the GS thickness/PI thickness is greater than a certain value (for example, greater than 3.0), it means that the graphite sheet surface is foamed due to outgassing during heat treatment, and the heat treatment is performed at a substantially high temperature increase rate. It can also be said that the graphite sheet is a graphite sheet with poor productivity.
• the GS thickness/PI thickness is 3.0 or less, it can be evaluated that the graphite sheet has excellent productivity.
• the GS thickness/PI thickness is preferably 2.5 or less, more preferably 2.0 or less, even more preferably 1.5 or less, and even more preferably 1.0 or less.
• the lower limit of the thickness of the present graphite sheet is preferably 45 ⁇ m or more, more preferably 50 ⁇ m or more, and even more preferably 55 ⁇ m or more.
• the upper limit of the thickness of the graphite sheet after rolling is preferably 110 ⁇ m or less, more preferably 105 ⁇ m or less. If the thickness of the graphite sheet after rolling is 45 ⁇ m or more, it can be said that the graphite sheet has a sufficient thickness, and efficient heat dissipation is possible. Moreover, if the thickness is 110 ⁇ m or less, there is an advantage that it can be mounted in a thin electronic device with little space.
• the method for producing a graphite sheet according to an embodiment of the present invention (hereinafter sometimes referred to as the present graphite sheet producing method) is particularly Although not limited, it includes a step of heat-treating a polyimide film for a graphite sheet to 2400 ° C. or higher, and the polyimide film for the graphite sheet is a polyimide film made from an acid dianhydride component and a diamine component.
• the acid dianhydride component includes 50 to 100 mol% of pyromellitic dianhydride (PMDA), 3,3′,4,4′-benzophenone tetra At least one of carboxylic dianhydride (BTDA) and 4,4'-oxydiphthalic dianhydride (ODPA) is contained in 0 to 50 mol%, and the diamine component contains 100 mol% of the total amount of the diamine component, 50 to 100 mol% of 4,4'-diaminodiphenyl ether (ODA) and 0 to 50 mol% of 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), the acid dianhydride
• the 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) and the 4,4′-oxydiphthalic dianhydride (ODPA) based on 200 mol % of the total amount of the component and the diamine component and the total content of the 2,2-bis
• a high-density graphite sheet can be provided with good productivity.
• the method for producing the present graphite sheet will be described in detail below, taking as an example a method including a step of heat-treating a specific polyimide film at 2400°C or higher.
• a specific polyimide film at 2400°C or higher.
• specific aspects of the polyimide film are described in ⁇ 2. Polyimide Film> section is incorporated as appropriate.
• the method for producing the present graphite sheet is not particularly limited as long as it includes a step of heat-treating a specific polyimide film (the present polyimide film) at 2400 ° C. or higher, but the polyimide film is heat-treated in an inert gas atmosphere or under reduced pressure. It is preferably a so-called polymer thermal decomposition method.
• the present graphite sheet manufacturing method includes a carbonization step of preheating a polyimide film at a temperature of about 1000° C. to obtain a carbonized polyimide film, and a carbonized polyimide film produced in the carbonization step. is heat-treated (heated) at a temperature of 2400° C. or higher to graphitize, and a rolling step of rolling this.
• the carbonization step and the graphitization step may be performed continuously, or after the carbonization step is completed, the graphitization step alone may be performed separately.
• the carbonization step is a step of heat-treating the polyimide film to a temperature of about 1000° C. to carbonize (carbonize) the polyimide film.
• the carbonization method of the polyimide film in the carbonization step is not particularly limited.
• a rectangular polyimide film may be carbonized while being laminated with a graphite sheet, or a roll-shaped polyimide film may be carbonized as it is in a roll.
• the film may be unwound from a roll-shaped polyimide film and carbonized continuously.
• the carbonization step is preferably performed under a vacuum atmosphere, under reduced pressure, or in an inert gas, and nitrogen is preferably used as the inert gas.
• the carbonized polyimide film obtained by the carbonization process may be called a carbonaceous film.
• the graphitization step is a step of heat-treating the carbonaceous film obtained in the carbonization step at a temperature of 2400° C. or higher to graphitize the carbonaceous film.
• the graphitization step can also be said to be a step of heat-treating a carbonaceous film to obtain a graphite sheet (graphite sheet before rolling).
• the temperature (maximum temperature) at which the carbonaceous film obtained in the carbonization step is heat-treated is preferably, for example, 2400° C. or higher, 2600° C. or higher, 2800° C. or higher, 2900° C. or higher, or 3000° C. or higher. .
• the upper limit of the maximum temperature is not particularly limited, it is preferably 3300° C. or lower, more preferably 3200° C. or lower.
• the temperature (maximum temperature) when heat-treating the carbonaceous film obtained in the carbonization step is 2400°C or higher, there is an advantage that the obtained graphite sheet has a good thermal diffusivity. If it is below, there is an advantage that the sublimation of the graphite member in the graphitization furnace can be suppressed.
• the graphitization step is performed under reduced pressure or in an inert gas, and argon or helium can be suitably used as the inert gas.
• a rectangular carbonaceous film may be graphitized in a state of being laminated with a graphite sheet, or a roll-shaped carbonaceous film may be graphitized as it is in a roll. may be drawn out and graphitized continuously.
• the temperature rise rate when heating the carbonaceous film to the maximum temperature is not particularly limited, but from the viewpoint of providing a graphite sheet with good productivity, it is preferably 0.2 ° C./min or more, and 0.3 ° C. /min or more, more preferably 0.4°C/min or more, and even more preferably 0.5°C/min or more.
• a carbonaceous film in which excessive foaming does not occur in the resulting graphite sheet when heat-treated (graphitized) at a rate of temperature increase of 0.2° C./min or more can be said to be a carbonaceous film with excellent productivity.
• a polyimide film that can provide such a carbonaceous film can be said to be a polyimide film with excellent productivity.
• a carbonaceous film obtained by carbonizing the present polyimide film has a somewhat disturbed orientation, similar to the present polyimide film.
• Such a carbonaceous film having a somewhat disturbed orientation is outgassed even when the carbonaceous film is heat-treated (graphitized) at a high temperature increase rate of 0.2 ° C./min or more in the graphitization process. It is easy to come off, and it is possible to suppress the foaming of the obtained graphite sheet, so that the graphite sheet can be provided with good productivity.
• the rolling step is a step of rolling the graphite sheet obtained by the graphitization step (graphite sheet before rolling).
• the rolling process can be said to be a process of obtaining a graphite sheet after rolling, and can also be said to be a compression process.
• the graphite sheet before rolling is in a foamed state due to the influence of outgassing generated in the graphitization process, and may have an excessive thickness unsuitable for practical use. The thickness can be adjusted and flexibility can be imparted.
• the method of rolling the graphite sheet is not particularly limited, and examples thereof include a method of rolling using metal rolls or the like.
• the rolling step may be performed while the manufactured graphite sheet is cooled to room temperature, or may be performed continuously with the graphitization step.
• An embodiment of the present invention may include the following configuration.
• the diamine component contains 50 to 100 mol% of 4,4′-diaminodiphenyl ether (ODA), 2,2-bis[4-(4 -Aminophenoxy)phenyl]propane (BAPP) in an amount of 0 to 50 mol%, and the 3,3′,4,4′-benzophenone tetra Total content of carboxylic dianhydride (BTDA), 4,4'-oxydiphthalic dianhydride (ODPA) and 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP
• BTDA 3',4,4'-benzophenonetetracarboxylic dianhydride
• ODPA 4,4'-oxydiphthalic dianhydride
• a method for producing a polyimide film comprising the step of adding 0.1 to 5.0% by weight of an organic phosphorus compound with respect to 100% by weight of the polyamic acid, wherein the acid dianhydride component is the acid 50 to 100 mol% of pyromellitic dianhydride (PMDA), 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) and 4, At least one of 4'-oxydiphthalic dianhydride (ODPA) is contained in 0 to 50 mol%, and the diamine component contains 4,4'-diaminodiphenyl ether (ODA) in the total amount of 100 mol% of the diamine component.
• PMDA pyromellitic dianhydride
• BTDA 3,3′,4,4′-benzophenonetetracarboxylic dianhydride
• ODA 4,4'-oxydiphthalic dianhydride
• BAPP 2,2-bis[4-(4-aminophenoxy)phenyl]propane
• BAPP 2,2-bis[4-(4-aminophenoxy)phenyl]propane
• the total amount of the acid dianhydride component and the diamine component being 200 mol % of the 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), the 4,4′-oxydiphthalic dianhydride (ODPA) and the 2,2-bis[4-( the total content of 4-aminophenoxy)phenyl]propane (BAPP) is 1-50 mol%
• a method for producing a polyimide film is 1-50 mol%;
• a method for producing a graphite sheet comprising a step of heat-treating a polyimide film for a graphite sheet at 2400° C. or higher, wherein the polyimide film for a graphite sheet comprises an acid dianhydride component and a diamine component.
• a polyimide film as a raw material wherein the acid dianhydride component is 50 to 100 mol% of pyromellitic dianhydride (PMDA) in the total amount of 100 mol% of the acid dianhydride component, 3,3' , 4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and 4,4'-oxydiphthalic dianhydride (ODPA) containing 0 to 50 mol% of at least one, and the diamine component is the diamine 50 to 100 mol% of 4,4'-diaminodiphenyl ether (ODA) and 0 to 50 mol of 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) in 100 mol% of the total amount of components %, the 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), the 4,4′- The total content of oxydiphthalic dianhydride (ODPA) and
• the polyimide film for the graphite sheet contains 100 mol% of pyromellitic dianhydride (PMDA) as the acid dianhydride component, and 4,4'-diaminodiphenyl ether (ODA) as the diamine component. and 1 to 50 mol% of 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP).
• PMDA pyromellitic dianhydride
• ODA 4,4'-diaminodiphenyl ether
• BAPP 2,2-bis[4-(4-aminophenoxy)phenyl]propane
• the polyimide film for the graphite sheet contains 100 mol% of 4,4'-diaminodiphenyl ether (ODA) as the diamine component, and pyromellitic dianhydride (PMDA) as the acid dianhydride component. 50 to 99 mol%, at least one of 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and 4,4'-oxydiphthalic dianhydride (ODPA) from 1 to 50 mol %, the method for producing a graphite sheet according to [9].
• ODA 4,4'-diaminodiphenyl ether
• PMDA pyromellitic dianhydride
• BTDA 3,3',4,4'-benzophenonetetracarboxylic dianhydride
• ODPA 4,4'-oxydiphthalic dianhydride
• the temperature at which the weight loss rate of the organic phosphorus compound contained in the polyimide film for the graphite sheet is 5% in TG-DTA measurement is 200 ° C. or higher, [9] to [13] A method for producing a graphite sheet according to any one of the above.
• the thickness of the graphite sheet before rolling was measured by the following method.
• the thickness of the graphite sheet was measured at four corners and one central point using a Mitutoyo micrometer.
• the "central point” refers to the position of the intersection of diagonal lines drawn from the four measurement points at each corner of the obtained graphite sheet to the diagonal measurement points.
• the average value of the thickness measurement values obtained at a total of five locations was taken as the thickness of the graphite sheet before rolling. Note that the four corners mean the vertices of a rectangular graphite sheet before rolling, which is the object of measurement.
• the thickness of the graphite sheet after rolling was measured by the following method.
• the thickness of the graphite sheet was measured at four corners and one central point using a Mitutoyo micrometer.
• the "central point” refers to the position of the intersection of diagonal lines drawn from the four measurement points at each corner of the obtained graphite sheet to the diagonal measurement points.
• the average value of the thickness measurement values obtained at a total of five locations was taken as the thickness of the graphite sheet after rolling. It should be noted that the four corners are intended to be the vertices when the rolled graphite sheet to be measured is rectangular.
• the thermal diffusivity of the graphite sheet after rolling was measured by the following method.
• a sample of a graphite sheet after rolling cut into a square of 30 mm ⁇ 30 mm was measured using a "Thermo Wave Analyzer TA3" manufactured by Bethel Co., Ltd. under the conditions of an atmosphere of 25 ° C. and a frequency of 75 Hz to determine the thermal diffusivity. was obtained by measuring
• the sample was prepared by punching out the center portion of the graphite sheet after rolling, which is the object of measurement, with a Thomson blade.
• the “central portion” means the central portion of the rolled graphite sheet in the width direction and also in the longitudinal direction.
• Example 1 ⁇ Production of polyimide film> 90 mol% of pyromellitic dianhydride (PMDA) and 3,3′,4,4′-benzophenonetetracarboxylic acid di 10 mol % of anhydride (BTDA) was dissolved to obtain a polyamic acid solution containing 18.5% by weight of polyamic acid. To the obtained polyamic acid solution, triphenyl phosphate (TPP, pentavalence of phosphorus, temperature 220 ° C. at which the weight loss rate becomes 5% in the measurement of TG-DTA), which is an organic phosphorus compound, was added.
• TPP triphenyl phosphate
• Triphenyl phosphate was added so that the concentration of triphenyl phosphate was 0.3% by weight with respect to 100% by weight of the solid content (polyamic acid) of the polyamic acid solution, and calcium hydrogen phosphate having an average particle size of 2.2 ⁇ m ( Inorganic particles) were added so that the concentration of the calcium hydrogen phosphate was 0.08% by weight with respect to 100% by weight of the solid content (polyamic acid) in the polyamic acid solution.
• an imidization catalyst containing 1 equivalent of acetic anhydride, 1 equivalent of isoquinoline and 1 equivalent of dimethylformamide is added to the carboxylic acid groups contained in the polyamic acid, and defoaming.
• a polyamic acid solution (mixed solution) containing an imidization catalyst was obtained.
• the mixed solution was applied onto an aluminum foil so that the thickness after drying was 135 ⁇ m to obtain a mixed solution layer.
• the mixed solution layer on the aluminum foil was dried using a hot air oven and a far infrared heater.
• the drying conditions are as follows. First, the mixed solution layer on the aluminum foil was dried in a hot air oven at 120° C. for 440 seconds to form a self-supporting gel film. The gel film was peeled off from the aluminum foil and fixed to the frame. Further, the gel film was heated stepwise in a hot air oven at 120°C for 60 seconds, 275°C for 72 seconds, 400°C for 77 seconds, 450°C for 93 seconds, and a far infrared heater at 460°C for 40 seconds. and dried to produce a polyimide film (A) having a thickness of 135 ⁇ m.
• the laminate was placed in a carbonization device (a carbonization device manufactured by Kurata Giken Co., Ltd.) (inside a heating space).
• the heating space in the carbonization apparatus in which the laminate was installed was heated to 600° C. at a heating rate of 0.4° C./min, and then held at 600° C. for 1 hour.
• the heating space in the carbonization device is heated to 1000° C. at a heating rate of 0.4° C./min, and then the laminate (polyimide film in the laminate) is heat-treated (carbonized) at 1000° C. for 30 minutes. to obtain a carbonaceous film.
• the obtained carbonaceous film was cooled to room temperature (23°C) and formed into a roll having an inner diameter of 100 mm to obtain a roll of carbonaceous film.
• the carbonaceous film roll is placed on the hearth of a graphitization furnace (graphitization furnace manufactured by Kurata Giken Co., Ltd.) so that the width direction is vertical.
• a graphitization furnace graphitization furnace manufactured by Kurata Giken Co., Ltd.
• the temperature was raised to 2900 ° C. (maximum graphitization temperature) at a heating rate of 0.5 ° C./min, and then held at 2900 ° C. for 30 minutes to obtain a graphitized film (graphite before rolling). sheet) was prepared.
• Table 1 shows the measurement results of the thickness of the obtained graphite sheet before rolling.
• the resulting graphitized film was cooled to room temperature and rolled by a 2-ton precision roll press (clearance type) manufactured by Thank Metal Co., Ltd. to obtain a graphite sheet (graphite sheet after rolling).
• the thickness, thermal diffusivity and density of the obtained graphite sheet after rolling were measured and evaluated. Table 1 shows the results.
• Examples 2-3 Comparative Example 1
• a polyimide film was prepared and heat-treated in the same manner as in Example 1, except that the amount of the organic phosphorus compound added and/or the average particle size of the inorganic particles was changed as shown in Table 1. to obtain a graphite sheet. Each physical property of the obtained graphite sheet was measured and evaluated. Table 1 shows the results.
• Example 4 In the production of polyimide film, 4,4'-diaminodiphenyl ether (ODA) 85 mol% and 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) 15 mol% dissolved in dimethyl 100 mol % of pyromellitic dianhydride (PMDA) was dissolved in a formamide solution to obtain a polyamic acid solution containing 18.5% by weight of polyamic acid.
• ODA 4,4'-diaminodiphenyl ether
• BAPP 2,2-bis[4-(4-aminophenoxy)phenyl]propane
• PMDA pyromellitic dianhydride
• Triphenyl phosphate which is an organic phosphorous compound, was added to the obtained polyamic acid solution so that the concentration of the triphenyl phosphate was 0.00% relative to 100% by weight of the solid content (polyamic acid) in the polyamic acid solution.
• TPP Triphenyl phosphate
• Examples 5-6 Comparative Example 2
• a polyimide film was prepared and heat-treated in the same manner as in Example 4, except that the amount of the organic phosphorus compound added and/or the average particle size of the inorganic particles was changed as shown in Table 2. to obtain a graphite sheet. Each physical property of the obtained graphite sheet was measured and evaluated. Table 1 shows the results.
• the polyimide film contains 90 mol% (within the range of 50 to 100 mol%) of PMDA and 10 mol% (within the range of 0 to 50 mol%) of BTDA as the acid dianhydride component. and 100 mol% (within the range of 50 to 100 mol%) of ODA as a diamine component, and 0.3 to 1.1% by weight (0.1 to 5.0).
• the graphite sheet obtained by heat-treating a polyimide film containing 135 ⁇ m in thickness before heat treatment has a thickness of 135 ⁇ m before heat treatment. It can be seen that the graphite sheet is excellent in Also, from a comparison between Examples 1 to 3 and Comparative Example 1, it can be seen that a graphite sheet having a higher density can be provided by including an organophosphorus compound in the polyimide film.
• the polyimide film contains 100 mol% PMDA (within the range of 50 to 100 mol%) as the acid dianhydride component and 85 mol% ODA as the diamine component (50 to 100 mol% ), 15 mol% (within the range of 0 to 50 mol%) of BAPP, and 0.3 to 1.1% by weight (0.1 to 5.0).
• the graphite sheet obtained by heat-treating the polyimide film containing 135 ⁇ m in thickness before the heat treatment was heat-treated at a relatively high heating rate of 0.5° C./min.
• the thickness of the graphite sheet obtained by rolling is sufficiently thin.
• the graphite sheet is excellent in productivity, in which excessive foaming does not occur even when heat-treated at a relatively high rate of temperature rise. Further, from a comparison between Examples 4 to 6 and Comparative Example 2, it can be seen that a graphite sheet having a higher density can be provided by including an organophosphorus compound in the polyimide film.
• the polyimide film according to one embodiment of the present invention can provide a high-density graphite sheet, particularly a high-density thick graphite sheet, with good productivity.
• a graphite sheet with high density can be provided with good productivity.
• a graphite sheet with such a high density can be suitably used as a heat dissipation member for electronic devices, particularly thin electronic devices.

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