JP2009214424A - Multilayer aromatic polyimide film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer aromatic polyimide film realizing running properties at film making and machining, machining properties such as perforation by laser or the like and cost reduction by reducing the additional amount of filler. <P>SOLUTION: This multilayer aromatic polyimide film is a laminate consisting of at least three layers of aromatic polyimide film, and the outermost layer includes the filler or a polyimide film. The manufacturing method of the multilayer aromatic polyimide film comprises the steps of making polyamide acid by reacting tetracarbonic acid dianhydride and diamine in a polar organic solvent, imidizing the product obtained, then adding, to a polyamide acid solution, a slurry obtained by dispersing inorganic particles with a particle diameter within a range of 0.07-2.0 μm and an average particle diameter of ≤1.0 μm in the polar organic solvent same as the above polar organic solvent for forming a film, and laminating a polyimide film thus obtained as the outermost layer of a laminated film having three or more layers. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a multilayer aromatic polyimide film having excellent runnability and excellent processability, and more specifically, runnability during film formation and processing, workability such as drilling by laser, and low cost due to a decrease in the amount of filler added. The present invention relates to a multilayer aromatic polyimide film that has been realized.

  Polyimide films are known to have excellent properties in heat resistance, cold resistance, chemical resistance, electrical insulation, mechanical strength, etc., and electrical insulation materials for wires, heat insulating materials, flexible printed wiring boards (FPC) It is widely used as a base film of IC, a carrier tape film for IC tape automated bonding (TAB), a tape for fixing IC lead frames, and the like. Of these, polyimide films and copper foils are usually bonded to each other through various adhesives, particularly in applications such as FPC, TAB carrier tape and lead fixing tape. In addition, workability when creating a through hole with a laser is also important.

  An important practical property when polyimide is used in these applications is the slipperiness (slidability) of the film. In various film processing steps, the slidability between the film support (for example, roll) and the film and the slidability between the films are ensured, thereby improving the operability and handling in each step, Generation of defects such as wrinkles on the film can be avoided. On the other hand, in the flexible printed wiring board application, which is the main use of polyimide, it is usually bonded to copper foil via various adhesives, but polyimide has a chemical structure and chemical resistance (solvent) stability. In many cases, the adhesiveness to the copper foil is insufficient, and at present, the polyimide is subjected to surface treatment (alkali treatment, corona treatment, plasma treatment, sandblast treatment, etc.) and bonded. Also, in recent finer pitches of electronic parts, especially in the inspection of FPC, the inspection of visual line width, foreign matter, etc. has been the mainstream, but since the introduction of the automatic optical inspection system (AOI), A heat-resistant film manufactured with a conventional formulation in which inorganic powder is mixed has been sufficiently satisfactory in terms of running performance. However, in AOI, inorganic powder is too large to reduce the pitch of recent FPCs. As a result, the particles are judged to be a foreign substance, which is a major obstacle to the automatic inspection system.

In the conventional smoothing technology for polyimide films, an inert inorganic compound (for example, alkaline earth metal orthophosphate, dibasic calcium phosphate anhydride, calcium pyrophosphate, silica, talc) is added to polyamic acid (Patent Document 1). Further, a method of performing plasma treatment after forming fine protrusions on the film surface with fine particles (see Patent Document 2) is known. However, there is a problem that the particles shown in these figures have a large particle size and cannot be applied to an automatic optical inspection system. In addition, inorganic particles having an average particle size of 0.01 to 100 μm are held on the polyimide surface layer by embedding a part of each particle, and a plurality of protrusions made of the exposed inorganic particles are formed on the surface of the film. A method (see Patent Document 3) in which 1 × 10 to 5 × 10 ⁸ pieces / mm ² exists in a layer is known. This method is an object that effectively obtains a slipperiness effect by actively exposing inorganic particles on the surface and reducing the coefficient of friction on the film surface. However, since some of the inorganic particles are exposed, this method is effective. There is a problem that scratches are generated on the other film surface facing and the appearance is deteriorated.

Further, when creating a through-hole by a laser, there is a problem of poor drilling due to the filler, and furthermore, an expensive filler has a problem that it is not practical because it is expensive.
JP-A-62-68852 JP 2000-191810 A Japanese Patent Laid-Open No. 5-25295

  As a result of diligent research on these market requirements, the present invention simultaneously satisfies the industrial requirements for running performance (slidability), adhesion, workability when creating a through hole, and automatic optical inspection system (AOI). In addition, an expensive filler is added only to the outermost layer to reduce the amount of filler used, and at the same time to reduce the cost.

In order to achieve the above goal, the multilayer aromatic polyimide film of the present invention is:
(1) A multilayer aromatic polyimide film in which three or more aromatic polyimide films are laminated, and the outermost layer contains a filler, and is a multilayer aromatic polyimide film characterized in that it is contained in the outermost layer. The filler is inorganic particles, the particle diameter is 0.07 to 2.0 μm and the average particle diameter is 1.0 μm or less, and fine protrusions are formed on the surface of the outermost layer by the inorganic particles. It is characterized by
(2) The amount of filler contained in the outermost layer is 0.1 to 0.9% by weight,
(3) It is preferable that the outermost layer thickness is 1 to 50 μm and the thickness of the entire multilayer film is 5 to 175 μm.

The method for producing a multilayer aromatic polyimide film of the present invention is as follows. (1) A polycarboxylic acid is produced by reacting tetracarboxylic dianhydride and diamine in a polar organic solvent. In this case, a slurry in which inorganic particles having a particle diameter in the range of 0.07 to 2.0 μm and an average particle diameter of 1.0 μm or less are dispersed in the same polar organic solvent as the polar organic solvent is used as a polyamic acid solution. And the obtained polyimide film is laminated as the outermost layer of a laminated film of three or more layers.

  When the polyimide film of the present invention uses fillers only in the outermost layer, the filler content is reduced throughout the film, and the processability of through holes and expensive inorganic particles are used without sacrificing running performance. Therefore, it is suitable for uses such as a flexible printed wiring board (FPC) and a chip on film (COF) for forming fine wiring.

  The present invention will be described in detail below.

  The polyamic acid that is a precursor for obtaining the polyimide film of the present invention will be described.

  In the present invention, for example, an aromatic tetracarboxylic dianhydride component and an aromatic diamine component, or chemical substances mainly composed of these components are addition-polymerized in an organic solvent to obtain a varnish-like polyamic acid.

  Specific examples of the aromatic diamine component include paraphenylenediamine, metaphenylenediamine, benzidine, paraxylylenediamine, 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylsulfone, 3,3′-dimethyl-4,4′-diaminodiphenylmethane, 1,5-diaminonaphthalene, 3,3′-dimethoxybenzidine, 1,4-bis (3-methyl- 5-aminophenyl) benzene and their amide-forming derivatives. Among them, the amount of diamine such as paraphenylenediamine, benzidine, 3,4'-diaminodiphenyl ether, which has an effect of increasing the tensile modulus of the film, is adjusted, and the finally obtained polyimide film has a tensile modulus of 4. It is preferable for the fine pitch substrate to be 0 GPa or more.

  Specific examples of the aromatic tetracarboxylic dianhydride component include pyromellitic acid, 3,3 ′, 4,4′-biphenyltetracarboxylic acid, 2,3 ′, 3,4′-biphenyltetracarboxylic acid, 3,3 ′, 4,4′-benzophenonetetracarboxylic acid, 2,3,6,7-naphthalenedicarboxylic acid, 2,2-bis (3,4-dicarboxyphenyl) ether, pyridine-2,3,5 , 6-tetracarboxylic acid and acid anhydrides such as amide-forming derivatives thereof.

  Specific examples of the organic solvent used include, for example, sulfoxide solvents such as dimethyl sulfoxide and diethyl sulfoxide, formamide solvents such as N, N-dimethylformamide and N, N-diethylformamide, N, N-dimethylacetamide, Acetamide solvents such as N, N-diethylacetamide, pyrrolidone solvents such as N-methyl-2-pyrrolidone and N-vinyl-2-pyrrolidone, phenol, o-, m-, or p-cresol, xylenol, halogenated Examples thereof include phenolic solvents such as phenol and catechol, or aprotic polar solvents such as hexamethylphosphoramide and γ-butyrolactone, and these are preferably used alone or as a mixture. Aromatic charcoal like The use of hydrogen is also possible.

The polymerization method may be carried out by any known method. For example, (1) the aromatic diamine component is first added to the solvent, and then the aromatic tetracarboxylic acid component is added in an amount equivalent to the total amount of the aromatic diamine component. To polymerize.
(2) A method in which the total amount of the aromatic tetracarboxylic acid component is first put in a solvent, and then the aromatic diamine component is added in an amount equivalent to that of the aromatic tetracarboxylic acid component for polymerization.
(3) After one aromatic diamine compound is put in a solvent, the aromatic tetracarboxylic acid compound is mixed at a ratio of 95 to 105 mol% with respect to the reaction components, and then mixed for the other time. A method in which an aromatic diamine compound is added, and then an aromatic tetracarboxylic acid compound is added and polymerized so that the total aromatic diamine component and the total aromatic tetracarboxylic acid component are approximately equal.
(4) After putting the aromatic tetracarboxylic acid compound in the solvent, the aromatic tetracarboxylic acid compound is mixed for a time required for the reaction at a ratio of 95 to 105 mol% of one aromatic diamine compound with respect to the reaction component, and then the aromatic tetracarboxylic acid compound is mixed. A method in which a carboxylic acid compound is added, and then the other aromatic diamine compound is added and polymerized so that the total aromatic diamine component and the total aromatic tetracarboxylic acid component are approximately equal.
(5) A polyamic acid solution (A) is prepared by reacting one aromatic diamine component and an aromatic tetracarboxylic acid in a solvent so that either one becomes excessive, and the other aromatic diamine in another solvent. The polyamic acid solution (B) is prepared by reacting the component and the aromatic tetracarboxylic acid so that either one becomes excessive. A method of mixing the polyamic acid solutions (A) and (B) thus obtained to complete the polymerization. At this time, when adjusting the polyamic acid solution (A), if the aromatic diamine component is excessive, the polyamic acid solution (B) contains excessive aromatic tetracarboxylic acid component, and the polyamic acid solution (A) contains aromatic tetracarboxylic acid. When the acid component is excessive, the polyamic acid solution (B) makes the aromatic diamine component excessive, and the polyamic acid solutions (A) and (B) are combined to form the wholly aromatic diamine component and wholly aromatic compound used in these reactions. Adjustment is made so that the amount of the tetracarboxylic acid component is approximately equal.

  The polymerization method is not limited to these, and other known methods may be used.

  The polyamic acid solution thus obtained contains a solid content of 5 to 40% by weight, preferably 10 to 30% by weight, and its viscosity is 10 to 2000 Pa · s as measured by a Brookfield viscometer, preferably 100-1000 Pa · s is preferably used for stable liquid feeding. Moreover, the polyamic acid in the organic solvent solution may be partially imidized.

The particles added to form protrusions on the film surface of the present invention must be insoluble in all chemical substances that come into contact in the polyimide film manufacturing process. Examples of the filler that can be used in the present invention include inorganic particles and organic particles, among which inorganic particles are preferable. As inorganic particles, SiO ₂ (silica), TiO ₂ , CaHPO ₄ , Ca ₂ P ₂ O _{7, and the} like can be suitably exemplified. Among these, silica produced by a wet pulverization method using a sol-gel method is preferable because it is stable in a varnish-like polyamic acid solution, physically stable, and does not affect various physical properties of the polyimide.

  Furthermore, the fine silica powder is agglomerated by using it as a silica slurry uniformly dispersed in a polar solvent such as N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide, and n-methylpyrrolidone. It is preferable to prevent this. Since this slurry has a very small particle size, the sedimentation rate is slow and stable. Even if it settles, it can be easily redispersed by re-stirring.

  In the present invention, the particle size of the inorganic particles is in the range of 0.07 to 2.0 μm, and the average particle size is 1.0 μm or less, so that in the automatic optical inspection system of polyimide film Inspection can be applied without problems. Further, it can be used without causing deterioration of the mechanical properties of the film. On the other hand, if the average particle size is below these ranges, sufficient slipperiness to the film cannot be obtained, and if it exceeds, the particles are judged to be foreign matter by an automatic inspection system, which is not preferable. Moreover, since the thickness of the outermost layer in this invention is 5-50 micrometers in the normal film thickness, the particle | grains in this particle diameter range are not exposed to the surface. In addition, since inorganic particles are added only to the outermost layer, the workability for creating through holes does not deteriorate.

  The inorganic particles are preferably 0.1 to 0.9% by weight per film resin weight, and more preferably 0.3 to 0.7% by weight. If the amount is 0.1% by weight or less, the film surface is insufficient in number of protrusions, so that sufficient slipperiness to the film cannot be obtained, the transportability is deteriorated, and the film winding shape when wound on a roll is also deteriorated. Therefore, it is not preferable. Further, if it is 0.9% by weight or more, the slipperiness of the film is improved, but coarse protrusions due to abnormal aggregation of particles increase, and this is judged to be a foreign matter by an automatic inspection system, which causes failure. Absent.

  The surface protrusions of the inorganic particles also increase the film surface area, and the surface is sufficiently roughened so that the anchor effect is observed and the adhesiveness is not impaired.

  It is better that the inorganic particles have a narrow particle size distribution, that is, the proportion of particles having similar sizes in all the particles is high.

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

  As a method for forming a polyimide film, a polyamic acid solution is cast into a film and thermally decyclized and desolvated to obtain a polyimide film, and a polyamic acid solution is mixed with a cyclization catalyst and a dehydrating agent. The method of obtaining a polyimide film by preparing a gel film by decyclizing it and heating it to remove the solvent is preferable, but the latter is preferable because the thermal expansion coefficient of the obtained polyimide film can be kept low. .

  In the method of chemically decyclizing, first, the polyamic acid solution is prepared.

  The polyamic acid solution can contain a cyclization catalyst (imidization catalyst), a dehydrating agent, a gelation retarder, and the like.

  Specific examples of the cyclization catalyst used in the present invention include aliphatic tertiary amines such as trimethylamine and triethylenediamine, aromatic tertiary amines such as dimethylaniline, and complex such as isoquinoline, pyridine and β-picoline. Although a ring tertiary amine etc. are mentioned, it is preferable to use at least 1 sort (s) of amine chosen from a heterocyclic tertiary amine.

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

  As a method for producing a polyimide film from a polyamic acid solution, a polyamic acid solution containing a cyclization catalyst and a dehydrating agent is cast on a support from a multilayer die with a slit and formed into a film shape. After a part of imidization proceeds to obtain a gel film having a self-supporting property, the gel film is peeled off from the support, heat-dried / imidized, and subjected to heat treatment.

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

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

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

  The gel film peeled off from the support is usually stretched in the running direction while regulating the running speed with a rotating roll. Stretching is performed at a temperature of 140 ° C. or less at a magnification of 1.05 to 1.9 times, preferably 1.1 to 1.6 times, and more preferably 1.1 to 1.5 times. The gel film stretched in the running direction is introduced into the tenter device, and both ends in the width direction are held by the tenter clip, and stretched in the width method while running with the tenter clip. The film dried in the drying zone is heated for 15 seconds to 10 minutes with hot air, an infrared heater or the like. Next, heat treatment is performed for 15 seconds to 20 minutes at a temperature of 250 to 500 using hot air and / or an electric heater. It is preferable to adjust the film thickness of the polyimide film obtained to 5 to 175 μm while adjusting the draw ratio in the running direction and the draw ratio in the width direction. Even if it is thicker or thinner than this range, the film forming property is remarkably lowered, which is not preferable.

  As a method of containing a filler, preferably inorganic particles, a slurry in which a filler is dispersed in the same polar solvent as the organic solvent used in the production of polyimide is added to the polyamic acid solution in the polyimide production process, followed by decyclization. A polyimide film containing inorganic particles can be obtained by removing the solvent.

  As a method for producing a multilayer aromatic polyimide film by laminating an aromatic polyimide film containing inorganic particles on the outermost layer, a method of casting on a support using a multilayer die, a method of further applying a polyamic acid on the film Etc. are known.

  In the present invention, the “outermost layer” refers to a layer present on the outermost side of the laminated film. In the present invention, since there are three or more layers, when the layers are stacked in three steps, the first step and the third step are both outermost layers. Accordingly, there are two outermost layers of a laminated film of three or more layers.

(1) Film thickness It measured using the lightmatic (Series318) made from Mitutoyo.

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

(3) Automatic optical inspection (AOI)
The base film was inspected using SK-75 manufactured by Nippon Orbotech Co., Ltd. A case where a foreign substance and a fine particle could be distinguished was evaluated as “◯”, while a case where the foreign substance and the fine particle were similar in size and could not be distinguished from each other was designated as “X”.

(4) Evaluation of inorganic particles Using a laser diffraction / scattering particle size distribution measuring apparatus LA-910 manufactured by Horiba, Ltd., a sample dispersed in a polar solvent was measured and analyzed, and the particle size range, average particle size, and particle size were determined. A range of 0.15 to 0.60 μm was read.

[Example 1]
N, N-dimethylacetamide was used as a solvent, and pyromellitic dianhydride and 4,4′-diaminodiphenyl ether were almost completely reacted in this solvent to obtain a varnish-like polyamic acid solution.

  Next, an N, N-dimethylacetamide slurry of silica having a particle size distribution of 0.07 to 2.0 μm and an average diameter of 0.50 μm is added to the varnish-like polyamic acid solution, and 0.15 wt. %, And a silica-containing varnish-like polyamic acid solution that was sufficiently stirred and dispersed was obtained.

  Using this varnish-like polyamic acid containing silica as the outermost layer, using a varnish-like polyamic acid containing no silica in the center layer, and using a continuous film-forming apparatus having a three-layer die, converting these polyamic acids to polyimide At the same time, it was dried and solidified to obtain a polyimide film comprising three layers. The thickness of the obtained film was 75 μm. Further, the thickness of the central layer was 25 μm, and the thicknesses of the outermost layers (two layers) were 25 μm, respectively, for a total of 50 μm.

[Example 2]
A 75 μm polyimide film was obtained in the same manner as in Example 1 except that the thickness of the center layer was 50 μm and the thickness of all outermost layers was 25 μm.

[Example 3]
In the same manner as in Example 1, the amount of silica added to the outermost layer was changed to 0.3 wt%, and after sufficient stirring and dispersion, a 75 μm polyimide film was obtained in the same manner as in Example 1.

[Example 4]
Pyromellitic dianhydride and 4,4′-diaminodiphenyl ether were almost completely reacted in N, N-dimethylacetamide to obtain a varnish-like polyamic acid solution.

  Next, an N, N-dimethylacetamide slurry of silica having a particle size distribution of 0.07 to 2.0 μm and an average diameter of 0.50 μm is added to the varnish-like polyamic acid solution, and 0.3 wt% of silica particles per resin weight. %, And a silica-containing varnish-like polyamic acid solution that was sufficiently stirred and dispersed was obtained.

  Using this varnish-like polyamic acid containing silica as the outermost layer, using a varnish-like polyamic acid containing no silica in the center layer, and using a continuous film-forming apparatus having a three-layer die, converting these polyamic acids to polyimide At the same time, it was dried and solidified to obtain a polyimide film comprising three layers. The thickness of the obtained film was 37.5 μm. The center layer had a thickness of 12.5 μm, and the outermost layer had a thickness of 12.5 μm.

[Example 5]
In the same manner as in Example 4, the silica addition amount of the outermost layer was changed to 0.6% by weight, and after sufficiently stirring and dispersing, a 37.5 μm polyimide film was obtained by the same method as in Example 4. It was.

[Example 6]
In the same manner as in Example 4, the silica addition amount of the outermost layer was changed to 0.9% by weight, and after sufficiently stirring and dispersing, a 37.5 μm polyimide film was obtained by the same method as in Example 4. It was.

[Comparative Example 1]
Pyromellitic dianhydride and 4,4′-diaminodiphenyl ether were almost completely reacted in N, N-dimethylacetamide to obtain a varnish-like polyamic acid solution.

  Next, an N, N-dimethylacetamide slurry of silica having a particle size distribution of 0.07 to 2.0 μm and an average diameter of 0.50 μm is added to the varnish-like polyamic acid solution, and 0.15 wt. %, And a silica-containing varnish-like polyamic acid solution that was sufficiently stirred and dispersed was obtained.

  This silica-containing varnish-like polyamic acid was converted into polyimide using a continuous film forming apparatus, and simultaneously dried and solidified to obtain a polyimide film. The thickness of the obtained film was 75 μm.

[Comparative Example 2]
In the same manner as in Comparative Example 1, the amount of silica added was changed to 0.3% by weight, and after sufficient stirring and dispersion, a 75 μm polyimide film was obtained in the same manner as in Comparative Example 1.

[Comparative Example 3]
In the same manner as in Comparative Example 1, the silica addition amount was changed to 0.6% by weight, and after sufficient stirring and dispersion, a 75 μm polyimide film was obtained in the same manner as in Comparative Example 1.

[Comparative Example 4]
Pyromellitic dianhydride and 4,4′-diaminodiphenyl ether were almost completely reacted in N 2, N-dimethylacetamide to obtain a varnish-like polyamic acid solution.

  Next, an N, N-dimethylacetamide slurry of silica having a particle size distribution of 0.07 to 2.0 μm and an average diameter of 1.50 μm is added to the varnish-like polyamic acid solution, and 0.3 wt% of silica particles per resin weight. %, And a silica-containing varnish-like polyamic acid solution that was sufficiently stirred and dispersed was obtained.

Using this varnish-like polyamic acid containing silica as the outermost layer, using a varnish-like polyamic acid containing no silica in the center layer, and using a continuous film-forming apparatus having a three-layer die, these polyamic acids are converted to polyimide. At the same time, it was dried and solidified to obtain a polyimide film comprising three layers. The thickness of the obtained film was 75 μm. The thickness of the central layer was 25 μm, and the thickness of the two outermost layers was 50 μm in total.
[Comparative Example 5]

  In the same manner as in Comparative Example 4, the silica particle size distribution was changed to 0.07 to 2.5 μm and the average diameter was changed to 2.0 μm, and after sufficiently stirring and dispersing, the same method as in Comparative Example 1, A 75 μm polyimide film was obtained.

  When the polyimide film of the present invention uses fillers only in the outermost layer, the filler content is reduced throughout the film, and the processability of through holes and expensive inorganic particles are used without sacrificing running performance. Therefore, it is suitable for uses such as a flexible printed wiring board (FPC) and a chip on film (COF) for forming fine wiring.

Claims (4)

A multilayer aromatic polyimide film in which three or more aromatic polyimide films are laminated, wherein the outermost layer contains a filler, and the filler contained in the outermost layer is inorganic. A particle having a particle diameter of 0.07 to 2.0 μm and an average particle diameter of 1.0 μm or less, and fine protrusions of the inorganic particles are formed on the surface of the outermost layer. Multilayer aromatic polyimide film. The multilayer aromatic polyimide film according to claim 1, wherein the amount of filler contained in the outermost layer is 0.1 to 0.9% by weight.
Polyimide film. The outermost layer thickness is 1-50 micrometers, and the thickness of the whole multilayer film is 5-175 micrometers, The multilayer aromatic polyimide film in any one of Claims 1-2 characterized by the above-mentioned. A tetracarboxylic dianhydride and a diamine are reacted in a polar organic solvent to produce a polyamic acid. After imidizing this, when forming into a film, the particle diameter is within a range of 0.07 to 2.0 μm. A slurry in which inorganic particles having an average particle diameter of 1.0 μm or less are dispersed in the same polar organic solvent as the above polar organic solvent is added to the polyamic acid solution, and the resulting polyimide film is a laminated film having three or more layers. A method for producing a multilayer aromatic polyimide film, comprising laminating as an outermost layer.