Multilayer polyimide film and polyimide metal laminate

Abstract

A multilayer polyimide film with excellent heat resistance, low dielectric loss tangent, and dimensional stability is provided. The multilayer polyimide film has a heat-resistant polyimide layer and a heat-sealable polyimide layer laminated on one or both sides. The heat-resistant polyimide is obtained from a tetracarboxylic acid component containing 75 mol% or more of 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) and 25 mol% or less of pyromellitic dianhydride (PMDA), and a diamine component containing 70 mol% to 95 mol% of p-phenylenediamine and 5 mol% to 30 mol% of 2,2'-dimethylbenzidine. The heat-sealable polyimide is obtained from a tetracarboxylic acid component containing 10 mol% to 60 mol% of s-BPDA and 40 mol% to 90 mol% of PMDA, and a diamine component containing 50 mol% or more of 2,2-bis[4-(4-aminophenoxy)phenyl]propane.

Description

[Technical field]

[0001] The present invention relates to a polyimide film and a polyimide-metal laminate. [Background technology]

[0002] Polyimide film has excellent heat resistance and mechanical properties and is widely used as a material for electronic substrates such as flexible printed circuit boards (hereinafter also referred to as FPC) and tape automated bonding (hereinafter also referred to as TAB).

[0003] In the manufacture of FPCs and TABs, polyimide metal laminates (e.g., copper-clad laminates) are used, in which a metal foil such as copper foil and a polyimide film are bonded together. While adhesives such as epoxy resins and acrylic resins are known to be used to bond metal foil and polyimide film, polyimide metal laminates using adhesives have poor heat resistance. Therefore, multilayer polyimide films, in which a heat-resistant polyimide layer and a heat-fusible polyimide layer are laminated together, have been proposed as polyimide films that can be bonded to metal foil such as copper foil without using adhesives (e.g., Patent Document 1).

[0004] On the other hand, with the recent trend toward the use of high-frequency bands in electronic devices, there is an increasing demand for low transmission loss in polyimides, which are used as electronic circuit board materials. Transmission loss is correlated with the dielectric constant and dielectric loss tangent, and reducing the dielectric loss tangent is particularly effective for reducing transmission loss.

[0005] As a polyimide with a small dielectric dissipation factor, Patent Document 2 proposes "a polymer film (claim 1) that contains one or more dianhydrides selected from the group consisting of crankshaft monomers, flexible monomers, rigid rotational monomers, rigid non-rotational monomers, and rotation-reducing monomers, and one or more diamines selected from the group consisting of crankshaft monomers, flexible monomers, rigid rotational monomers, rigid non-rotational monomers, and rotation-reducing monomers, and that has an extinction coefficient Df (synonymous with dielectric dissipation factor) of 0.005 or less and a specific water absorption coefficient, etc."

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the case of an FPC for high - frequency applications, in addition to a low dielectric tangent, a polyimide that satisfies basic physical properties such as high heat resistance and high dimensional stability required for a normal FPC is necessary. High dimensional stability not only suppresses problems such as circuit misalignment, improves the reliability of the circuit board, but also improves the product yield. Generally, it is solved by making the linear thermal expansion coefficient of the polyimide film close to that of the metal foil (such as copper foil).

[0008] However, a multilayer polyimide film that is excellent in heat resistance and achieves both a low dielectric tangent and high dimensional stability even in a high - temperature heating environment has not been known. Patent Document 2 describes using a polyimide film showing a low dielectric tangent as the core layer (heat - resistant polyimide layer) of a multilayer film, but there is no detailed description about the heat - fusion layer (thermoplastic layer), and the performance as a multilayer film or a metal laminate is unknown.

[0009] An object of the present invention is to provide a multilayer polyimide film that is excellent in heat resistance and achieves both a low dielectric tangent and high dimensional stability. A further aspect of the present invention aims to provide a polyimide - metal laminate in which a multilayer polyimide film and a metal foil such as copper foil are laminated.

Means for Solving the Problems

[0010] [[ID=

[0011] 1. A multilayer polyimide film having a heat-resistant polyimide layer composed of a heat-resistant polyimide (PIc), and a heat-fusible polyimide layer composed of a heat-fusible polyimide (PIb) laminated on one or both sides of the heat-resistant polyimide layer wherein; the heat-resistant polyimide (PIc) is obtained by reacting a tetracarboxylic acid component (Ac) containing 3,3’,4,4’-biphenyltetracarboxylic dianhydride in an amount of 75 mol% or more and 100 mol% or less, and pyromellitic dianhydride in an amount of 0 mol% or more and 25 mol% or less, and a diamine component (Bc) containing p-phenylenediamine in an amount of 70 mol% or more and 95 mol% or less, and 2,2’-dimethylbenzidine in an amount of 5 mol% or more and 30 mol% or less ; the heat-fusible polyimide (PIb) is obtained by reacting a tetracarboxylic acid component (Ab) containing 3,3’,4,4’-biphenyltetracarboxylic dianhydride in an amount of 10 mol% or more and 60 mol% or less, and pyromellitic dianhydride in an amount of 40 mol% or more and 90 mol% or less, and a diamine component (Bb) containing 2,2-bis[4-(4-aminophenoxy)phenyl]propane in an amount of 50 mol% or more ; Multilayer polyimide film.

[0012] 2. The heat-resistant polyimide (PIc) is obtained by reacting a tetracarboxylic acid component (Ac) containing 3,3’,4,4’-biphenyltetracarboxylic dianhydride in an amount of 80 mol% or more and less than 100 mol%, and pyromellitic dianhydride in an amount of more than 0 mol% and 20 mol% or less, and a diamine (Bc) containing p-phenylenediamine in an amount of 75 mol% or more and 2,2’-dimethylbenzidine in an amount of 25 mol% or less, and is the multilayer polyimide film according to item 1 above.

[0013] 3. The thermally fusible polyimide (PIb) is a tetracarboxylic acid component (Ab) containing 3,3’,4,4’-biphenyltetracarboxylic dianhydride in an amount of 15 mol% or more and pyromellitic dianhydride in an amount of 85 mol% or less, and a diamine component (Bb) containing 2,2-bis[4-(4-aminophenoxy)phenyl]propane in an amount of 60 mol% or more, and is obtained by reacting them, The multilayer polyimide film according to item 1 or 2 above.

[0014] 4. The dielectric tangent of the multilayer polyimide film is 0.0060 or less, and the dimensional change rate (absolute value) in the machine direction (MD) and the transverse direction (TD) of the polyimide metal laminate is 0.10% or less. The multilayer polyimide film according to any one of items 1 to 3 above (however, the dimensional change rate is measured by measuring the initial dimension (X) of the polyimide metal laminate manufactured using the multilayer polyimide film and the dimension (Y) after heat treatment at 250 °C for 30 minutes after etching the metal foil, and is calculated according to the following formula. Dimensional change rate (%) = (Y - X) / X × 100 ).

[0015] 5. A polyimide metal laminate in which a metal foil is laminated on the side of the thermally fusible polyimide layer of the multilayer polyimide film according to any one of items 1 to 4 above.

[0016] 6. The polyimide metal laminate according to item 5 above, wherein the multilayer polyimide film has thermally fusible polyimide layers on both sides of the heat-resistant polyimide layer, and metal foils are laminated on both sides of the multilayer polyimide film.

[0017] 7. A flexible wiring board manufactured using the polyimide metal laminate according to item 5 above.

Advantages of the Invention

[0018] According to the present invention, it is possible to provide a multilayer polyimide film having a small dielectric tangent in the high-frequency region, excellent heat resistance, and excellent dimensional stability at the same time. Further, according to different aspects of the present invention, it is possible to provide a polyimide metal laminate in which a multilayer polyimide film and a metal foil such as a copper foil are laminated. This polyimide metal laminate is suitable for the production of high-frequency compatible FPCs.

Mode for Carrying Out the Invention

[0019] The multilayer polyimide film of the present invention has a structure in which a heat-fusible polyimide layer (also referred to as a heat-fusion layer) is laminated on one or both sides of a heat-resistant polyimide layer (hereinafter also referred to as a core layer). Hereinafter, the material of the core layer may be represented by attaching a suffix of "c" ( c ore), and the material of the heat-fusion layer may be represented by attaching a suffix of "b" ( b ondable).

[0020] <Heat-resistant polyimide layer> The heat-resistant polyimide layer (core layer) contains a heat-resistant polyimide (PIc) obtained by reacting a tetracarboxylic acid component (Ac) and a diamine component (Bc). The tetracarboxylic acid component (Ac) for producing the heat-resistant polyimide is 75 mol% or more and 100 mol% or less, preferably 80 mol% or more, more preferably 85 mol% or more, preferably less than 100 mol%, more preferably 95 mol% or less of 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) with respect to 100 mol% of the total tetracarboxylic acid component, and 0 mol% or more and 25 mol% or less, preferably more than 0 mol%, more preferably 5 mol% or more, preferably 20 mol% or less, more preferably 15 mol% or less of pyromellitic dianhydride (PMDA) in an amount.

[0021] As the tetracarboxylic acid component (Ac), a tetracarboxylic dianhydride other than s-BPDA and PMDA may be used, but the amount is preferably 10 mol% or less, preferably 5 mol% or less, more preferably 2 mol% or less, and it is very preferable not to contain it at all.

[0022] Examples of the tetracarboxylic acid components that can be used in combination include aromatic tetracarboxylic dianhydrides and aliphatic (especially alicyclic) tetracarboxylic dianhydrides. Specifically, 2,3,3’,4’-biphenyltetracarboxylic dianhydride, 3,3’,4,4’-benzophenonetetracarboxylic dianhydride, 4,4’-oxydiphthalic dianhydride, 3,3’,4,4’-diphenylsulfonetetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid) 1,4-phenylene, para-ta-phenyl-3,3’,4,4’-tetracarboxylic dianhydride, naphthalene-1,4,5,8-tetracarboxylic dianhydride, and 1,2,4,5-cyclohexanetetracarboxylic dianhydride, etc.

[0023] The diamine component (Bc) for producing the heat-resistant polyimide is, based on 100 mol% of the total diamine component, p-phenylenediamine (PPD) in an amount of 70 mol% or more and 95 mol% or less, preferably 75 mol% or more, preferably 93 mol% or less, and 2,2’-dimethylbenzidine (m-TB) in an amount of 5 mol% or more and 30 mol% or less, preferably 7 mol% or more, preferably 25 mol% or less.

[0024] Although diamine compounds other than PPD and m-TB may be used as the diamine component (Bc), the amount thereof is preferably 10 mol% or less, preferably 5 mol% or less, more preferably 2 mol% or less, and it is highly preferable that they are not contained at all.

[0025] Examples of diamine components that can be used in combination include aromatic diamine compounds and aliphatic (especially alicyclic) diamine compounds. Specifically, m-phenylenediamine, 4,4''-diamino-p-terphenyl, 2,4-toluenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,4'-diaminobenzophenone, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 2,2-bis(3-aminophenyl)propane, 2,2-bis(4-aminophenyl)propane, 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene, α,α'-bis(4-aminophenyl)-1,4-diisopropylbenzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene and other bis(aminophenoxy)benzenes, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 4,4'-bis(4-aminophenoxy)biphenyl, and 1,4-cyclohexanediamine, etc.

[0026] The heat-resistant polyimide layer mainly consists of the aforementioned heat-resistant polyimide. The resin component excluding additives preferably consists substantially of the aforementioned heat-resistant polyimide (95% by weight or more, preferably 98% by mass or more), and it is also highly preferable that it consists only of the heat-resistant polyimide (100% by mass).

[0027] The heat-resistant polyimide layer can contain additives as necessary in addition to the heat-resistant polyimide. Typically, fine inorganic or organic fillers can be mentioned. As the inorganic filler, inorganic fillers such as particulate or flat-shaped ones can be mentioned. Specifically, for example, inorganic oxide powders such as particulate titanium dioxide powder, silicon dioxide (silica) powder, magnesium oxide powder, aluminum oxide (alumina) powder, zinc oxide powder, inorganic nitride powders such as particulate silicon nitride powder, titanium nitride powder, inorganic carbide powders such as silicon carbide powder, and inorganic salt powders such as particulate calcium carbonate powder, calcium sulfate powder, barium sulfate powder can be mentioned. As the organic filler, for example, polyimide powder, liquid crystal polymer powder, fluororesin powder, powder of thermosetting resin, etc. can be mentioned. These additives may be used in combination of two or more kinds. Regarding the usage amount and shape (size, aspect ratio) of the filler, it is preferable to select according to the purpose of use. Also, in order to disperse these fillers uniformly, means known per se can be applied.

[0028] These inorganic or organic fillers, particularly preferably silica powder, can be contained in the heat-resistant polyimide layer in an amount preferably of 30% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less (it may be 0% by mass).

[0029] <Heat-fusible polyimide layer> The heat-fusible polyimide layer (heat-fusion layer) contains a heat-fusible polyimide (PIb) obtained by reacting a tetracarboxylic acid component (Ab) and a diamine component (Bb). The tetracarboxylic acid component (Ab) for producing a heat-fusible polyimide contains, relative to 100 mol% of the total tetracarboxylic acid component, 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) in an amount of 10 mol% to 60 mol%, preferably 15 mol% or more, more preferably 20 mol% or more, and also preferably 55 mol% or less, and more preferably 50 mol% or less, and pyromellitic dianhydride (PMDA) in an amount of 40 mol% to 90 mol%, preferably 45 mol% or more, more preferably 50 mol% or more, and also preferably 85 mol% or less, and more preferably 80 mol% or less.

[0030] As the tetracarboxylic acid component (Ab), a tetracarboxylic acid dianhydride other than s-BPDA and PMDA may be used, but the amount thereof is preferably 10 mol % or less, preferably 5 mol % or less, more preferably 2 mol % or less, and it is also highly preferred that no tetracarboxylic acid dianhydride is used at all.

[0031] Examples of tetracarboxylic acid components that can be used in combination include aromatic tetracarboxylic acid dianhydrides and aliphatic (especially alicyclic) tetracarboxylic acid dianhydrides. Specific examples include 2,3,3',4'-biphenyltetracarboxylic acid dianhydride, 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride, 4,4'-oxydiphthalic acid dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic acid dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, and 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride.

[0032] The diamine component (Bb) for producing the heat-fusible polyimide contains 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) in an amount of 50 mol % or more (preferably more than 50 mol %), preferably 60 mol % or more, more preferably 70 mol % or more, even more preferably 80 mol % or more, and even more preferably 90 mol % or more, based on 100 mol % of the total diamine components, and is also preferably 100 mol %.

[0033] As the diamine component (Bb), diamine compounds other than BAPP may be used. Examples of other diamine components used in combination include m-phenylenediamine, 2,2'-dimethylbenzidine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 3,3'-diaminobenzophenone, 4,4'-bis(3-aminophenoxy)biphenyl, 4,4'-bis(4-aminophenoxy)biphenyl, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene, α,α'-bis(4-aminophenyl)-1,4-diisopropylbenzene, bis[4-[4-(4-aminophenoxy)phenoxy]phenyl]ether, and 1,4-cyclohexanediamine.

[0034] The glass transition temperature (Tg) of the heat-fusible polyimide is preferably 250°C to 310°C, more preferably 260°C to 300°C, from the viewpoints of improving the peel strength between the heat-fusible layer and the core layer and between the heat-fusible layer and the metal foil, and the solder heat resistance during FPC manufacturing.

[0035] The heat-fusible polyimide layer mainly consists of the aforementioned heat-fusible polyimide. The resin composition excluding additives preferably consists essentially of the aforementioned heat-fusible polyimide (95% by weight or more, preferably 98% by weight or more), and it is very preferable that it consists only of the heat-fusible polyimide (100% by weight).

[0036] The heat-fusible polyimide layer may contain additives in addition to the heat-fusible polyimide, if necessary. Specific additives and amounts thereof may be those described for the heat-resistant polyimide layer.

[0037] <Multi-layer polyimide film> The thickness of the multilayer polyimide film of the present invention is not particularly limited, but the thickness of the heat-resistant polyimide layer is preferably 3 to 70 μm, more preferably 5 to 65 μm. The thickness of the heat-fusible polyimide layer is preferably 0.5 to 15 μm, more preferably 1 to 12.5 μm. The thickness of the entire multilayer polyimide film is preferably 4 to 100 μm, more preferably 7 to 90 μm.

[0038] The dielectric loss tangent (10 GHz) of the multilayer polyimide film is preferably 0.0060 or less, more preferably less than 0.0060, and even more preferably 0.0055 or less.

[0039] The dimensional change rate (absolute value) of the multilayer polyimide film is preferably 0.10% or less, preferably less than 0.10%, more preferably 0.09% or less. The dimensional change rate was calculated using the following formula by measuring the initial dimension (X) of a polyimide metal laminate produced using a multilayer polyimide film and the dimension (Y) after etching the metal foil, heat treating at 250°C for 30 minutes, and conditioning the humidity. Dimensional change rate (%) = (YX) / X x 100

[0040] <Method of manufacturing multilayer polyimide film> The method for producing the multilayer polyimide film of the present invention is not particularly limited, and any known method can be used. Representative methods include a coating method and a co-extrusion-casting film-forming method, which will be described below.

[0041] (Manufacturing method using coating method) The multilayer polyimide film of the present invention can be obtained by coating one or both sides of a self-supporting film obtained from a polyimide precursor solution (a) that provides a heat-resistant polyimide with a polyimide precursor solution (b) that provides a heat-fusible polyimide, and then heating and drying the resulting multilayer self-supporting film to carry out imidization.

[0042] The polyimide precursor solution (a) that produces a heat-resistant polyimide is obtained by reacting a tetracarboxylic acid component and a diamine component in substantially equimolar amounts or in a slight excess of one component relative to the other in an organic solvent. The structure of the polyimide precursor solution (a) containing multiple tetracarboxylic acid components and diamine components may be a random structure or a block structure, with a random structure being more preferred. A self-supporting film can be obtained by casting the polyimide precursor solution (a) onto a support and drying the cast product by heating.

[0043] On the other hand, the polyimide precursor solution (b) that gives the heat-fusible polyimide can also be obtained by reacting a tetracarboxylic acid component and a diamine component in substantially equimolar amounts or in a slight excess of one component relative to the other in an organic solvent. The structure of the polyimide precursor solution (b) containing multiple tetracarboxylic acid components and diamine components may be a random structure or a block structure, with a random structure being more preferred.

[0044] The monomer compositions for preparing the polyimide precursor solution (a) that gives a heat-resistant polyimide and the polyimide precursor solution (b) that gives a heat-fusible polyimide are the compositions described in <Heat-resistant polyimide layer> and <Heat-fusible polyimide layer>, respectively.

[0045] To the polyimide precursor solution (b) and / or the polyimide precursor solution (a), a phosphorus-based stabilizer, such as triphenyl phosphite or triphenyl phosphate, may be added in an amount of 0.01 to 1 mass % relative to the solid content (polymer) concentration during polymerization of the polyimide precursor solution, in order to suppress gelation. From the viewpoint of the surface condition of the film and productivity, it is preferable to add a phosphate ester or a salt of a tertiary amine and a phosphate ester to the polyimide precursor solution. The amount of these added is preferably 0.01 to 5 parts by mass per 100 parts by mass of the polyimide or polymer. Specific examples of phosphate ester include distearyl phosphate ester and monostearyl phosphate ester. Furthermore, examples of salts of tertiary amines and phosphate esters include monostearyl phosphate triethanolamine salt. Regarding imidization in the present invention, either thermal imidization (thermal imidization) or chemical imidization (chemical imidization) can be applied. Of these, thermal imidization is preferably applied.

[0046] A basic organic compound can be added to the polyimide precursor solution (b) and / or the polyimide precursor solution (a) to promote imidization. For example, a lower alkyl- or aromatic-substituted imidazole such as 1,2-dimethylimidazole, N-methylimidazole, N-benzyl-2-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, or 2-phenylimidazole; a benzimidazole such as 5-methylbenzimidazole; or a substituted pyridine such as isoquinoline, 3,5-dimethylpyridine, 3,4-dimethylpyridine, 2,5-dimethylpyridine, 2,4-dimethylpyridine, or 4-n-propylpyridine can be added in a proportion of 0.05 to 10 mass %, more preferably 0.05 to 7 mass %, and even more preferably 0.1 to 5 mass % based on the solid content (polymer) concentration. When these basic organic compounds are used, the imidization of the polyimide precursor is promoted at a relatively low temperature to form a polyimide film, and therefore these basic organic compounds can be used to avoid insufficient imidization.

[0047] Examples of organic solvents for producing the polyimide precursor solution include amides such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylformamide, N,N-diethylformamide, and hexamethylsulfonamide, sulfoxides such as dimethyl sulfoxide and diethyl sulfoxide, and sulfones such as dimethyl sulfone and diethyl sulfone. These solvents may be used alone or in combination.

[0048] The concentration of all monomers in the organic solvent when carrying out the polymerization reaction of the tetracarboxylic acid component and the diamine component can be appropriately selected depending on the purpose of use. For example, the solid content (polymer) concentration of the polyimide precursor solutions (a) and (b) is preferably 5 to 40 mass %, more preferably 6 to 35 mass %, and particularly preferably 10 to 30 mass %.

[0049] The production temperature for the polyimide precursor solution (a) and the polyimide precursor solution (b) is not particularly limited, but is preferably 25°C to 100°C, more preferably 25°C to 80°C, and even more preferably 30°C to 70°C so as not to excessively proceed with the imidization reaction, and the production time is about 1 to 72 hours, more preferably about 2 to 60 hours. The reaction can be carried out in an air atmosphere, but is usually suitably carried out in an inert gas atmosphere, preferably a nitrogen gas atmosphere.

[0050] The solution viscosities of the polyimide precursor solution (a) and the polyimide precursor solution (b) can be appropriately selected depending on the intended use (e.g., coating, casting, etc.). For example, when the polyimide precursor solution (a) and the polyimide precursor solution (b) are used for casting, from the viewpoint of ease of handling the polyimide precursor solution, the rotational viscosity measured at 30°C is preferably about 100 to 5,000 poise, more preferably 500 to 4,000 poise, and particularly preferably about 1,000 to 3,000 poise. Furthermore, when the polyimide precursor solution (a) and the polyimide precursor solution (b) are used for coating, from the viewpoint of ease of handling the polyimide precursor solution, the rotational viscosity measured at 30°C is preferably 1 to 100 centipoise, more preferably 3 to 50 centipoise, and particularly preferably 5 to 20 centipoise. Therefore, it is desirable to carry out the polymerization reaction to such an extent that the resulting polyimide precursor solution exhibits the above-mentioned viscosity. The viscosity of the solution can also be adjusted by adding the organic solvent described above to the produced polyimide precursor solution.

[0051] A self-supporting film obtained from the polyimide precursor solution (a) that provides a heat-resistant polyimide can be obtained, for example, by casting the polyimide precursor solution (a) onto the surface of a suitable support (e.g., a metal, ceramic, or plastic roll, or a metal belt, etc.) to form a film of uniform thickness, and then heating the film to preferably 50 to 210°C, more preferably 60 to 200°C, using a heat source such as hot air or infrared rays to gradually remove the solvent and drying until the film becomes self-supporting (e.g., to the extent that it can be peeled off from the support).

[0052] The self-supporting film that provides heat-resistant polyimide preferably has a weight loss on heating in the range of 20 to 40% by mass and an imidization rate in the range of 8 to 40%. If the weight loss on heating and the imidization rate are within the above ranges, the mechanical properties of the self-supporting film will be sufficient, it will be easy to evenly coat the polyimide precursor solution (b) on the upper surface of the self-supporting film, and it will be difficult for foaming, cracking, crazing, cracking, and splitting to occur in the polyimide film obtained after imidization. Also, the adhesive strength between the heat-resistant polyimide layer and the heat-fusible polyimide layer will be sufficient. The weight loss on heating of the self-supporting film is calculated according to the following formula from the weight (W1) before drying and the weight (W2) after drying by drying the film to be measured at 400 °C for 30 minutes. Weight loss on heating (% by mass) = {(W1 - W2) / W1} × 100 The imidization rate of the self-supporting film can be calculated using the ratio of the vibration band peak areas by measuring the IR spectra of the self-supporting film and its fully cured product (polyimide film) by the ATR method, respectively. As the vibration band peak, the asymmetric stretching vibration band of the imide carbonyl group, the benzene ring skeleton stretching vibration band, etc. can be used. Also, regarding the measurement of the imidization rate, there is a method using the Karl Fischer moisture meter described in JP-A-9-316199.

[0053] Next, the polyimide precursor solution (b) that provides heat-fusible polyimide is coated on one or both sides of the self-supporting film. The polyimide precursor solution (b) may be coated on the self-supporting film peeled from the support, or may be coated on the self-supporting film on the support before peeling from the support. It is preferable to uniformly coat the polyimide precursor solution (b) on one or both sides of the self-supporting film. Therefore, the self-supporting film of the polyimide precursor solution (a) preferably has a surface on which the polyimide precursor solution (b) can be uniformly coated.

[0054] The method for applying the polyimide precursor solution (b) to the self-supporting film obtained from the polyimide precursor solution (a) is not particularly limited, and examples thereof include known application methods such as gravure coating, spin coating, silk screening, dip coating, spray coating, bar coating, knife coating, roll coating, blade coating, and die coating.

[0055] Next, the self-supporting film of polyimide precursor solution (a) coated with polyimide precursor solution (b) is heated and imidized to obtain a multilayer polyimide film. The maximum heating temperature for the heat treatment for imidization is preferably 330°C to 600°C, more preferably 350°C to 550°C, and even more preferably 370°C to 500°C.

[0056] The heat treatment for imidization is preferably carried out in stages, with a primary heat treatment being carried out at a temperature of 200°C or higher but lower than 300°C for 1 minute to 60 minutes, followed by a secondary heat treatment at a temperature of 300°C or higher but lower than 330°C for 1 minute to 60 minutes, and then a tertiary heat treatment being carried out at a maximum heating temperature of preferably 330°C to 600°C, more preferably 370 to 550°C, and even more preferably 370 to 500°C for 1 minute to 30 minutes. This heat treatment can be carried out using known equipment such as a hot air oven or an infrared heating oven. Furthermore, this heat treatment is preferably carried out by fixing the self-supporting film of polyimide precursor solution (a) coated with polyimide precursor solution (b) using a pin tenter, clips, or the like.

[0057] (Manufacturing method using co-extrusion and casting film production method) The multilayer polyimide film of the present invention can also be produced by a coextrusion-casting film-forming method (hereinafter simply referred to as the "coextrusion method"), in which a polyimide precursor solution (hereinafter also referred to as a dope solution) that provides a heat-resistant polyimide layer and a dope solution that provides a heat-fusible polyimide layer are laminated, dried, and imidized. For this coextrusion method, for example, the method described in JP-A-3-180343 (JP-B-7-102661) can be used.

[0058] More specifically, in this coextrusion method, first, an extruder having a die for extrusion molding with two or more layers is used. A dope solution for providing a heat-resistant polyimide layer and a dope solution for providing a heat-fusible polyimide layer are cast onto a support from the discharge ports of the die, thereby forming a laminated thin film. Then, the thin film on the support is dried to form a multi-layer self-supporting film. Next, the multi-layer self-supporting film is peeled off from the support, and finally, the multi-layer self-supporting film is heat-treated. In this process, the dope solution in contact with the support may be either the dope solution for providing the heat-resistant polyimide layer or the dope solution for providing the heat-fusible polyimide layer.

[0059] Both the dope solution for providing the heat-resistant polyimide layer and the dope solution for providing the heat-fusible polyimide layer are prepared by reacting a tetracarboxylic acid component and a diamine component as described in the (manufacturing method by coating method) to produce polyimide precursor solutions (a) and (b). As the dope solution, the solid content (polymer) concentration is 5 to 40% by weight, particularly about 10 to 30% by weight, and the "solution viscosity (rotational viscosity)" at the discharge temperature from the multi-layer extrusion die for multi-layer extrusion such as the above-mentioned two-layer and three-layer at the time of multi-layer extrusion molding is preferably about 50 to 10,000 poises, particularly about 100 to 6,000 poises.

[0060] Examples of the die for two-layer extrusion molding include those having a dope solution supply port, the dope solution passages being formed from each supply port toward each manifold, the flow paths at the bottom of the manifold merging at a confluence point, and the passage (lip portion) of the dope solution after the merger communicating with a slit-shaped discharge port, and the dope solution being discharged in a thin film shape onto the support from this discharge port (multi-manifold type two-layer die). The interval of the lip portion can be adjusted by a lip adjustment bolt. The gaps in the flow paths at the bottom of each manifold (near the confluence) are adjusted by choke bars. Each manifold preferably has a hanger-coat type shape. The two-layer extrusion die has dope supply ports on the left and right sides of the upper part of the die, and the dope paths immediately converge at a confluence point equipped with a partition plate. The dope paths connect to the manifold from the confluence point, and the dope path (lip) at the bottom of the manifold connects to a slit-shaped discharge port. The die may have a structure in which the dope is discharged from the discharge port in the form of a grooved film onto a support (a feedblock-type two-layer die or a single-manifold-type two-layer die).

[0061] In addition to the two-layer extrusion described above, a die for extrusion molding three or more layers can be used to produce a multi-layer extruded polyimide film using the same molding method as for two-layer extrusion molding. That is, a three-layer polyimide film can be obtained by using a composition of a first dope liquid for forming a heat-sealable polyimide layer, a dope liquid for forming a heat-resistant polyimide layer, and a second dope liquid for forming a heat-sealable polyimide layer. The first and second dope liquids for forming the heat-sealable polyimide layer may be the same or different.

[0062] In the co-extrusion-casting film-forming method, the drying conditions and heating conditions after the operation of continuously extruding onto the support can be applied as is to the above-mentioned "Production method by coating method."

[0063] In either the coating method or the co-extrusion method, when the self-supporting film is heated to produce the polyimide film, a stretching operation may be carried out, if necessary. By the above-mentioned operations, it is possible to continuously produce a long polyimide film. When a thick multilayer polyimide film is required, it can be produced by laminating together the multilayer polyimide films produced by the above-mentioned production method. The lamination operation can also be carried out continuously.

[0064] <Polyimide Metal Laminate> The polyimide metal laminate can be manufactured by laminating a multilayer polyimide film (or layer) and a metal foil (or layer) using the polyimide precursor solution or multilayer polyimide film of the present invention. The polyimide metal laminate has a structure in which a metal foil (or layer) is laminated on one or both sides of a multilayer polyimide film. Examples of the manufacturing method of the polyimide metal laminate include the following methods. (i) A method in which a multilayer polyimide film and a metal foil are directly adhered without an adhesive and laminated by pressure or heat and pressure (ii) A method in which a polyimide precursor solution is applied on a metal foil, dried, and imidized (iii) A method of directly forming a metal layer on a multilayer polyimide film by a dry method (metallizing such as vacuum evaporation and sputtering) and / or a wet method (electroplating).

[0065] As the metal foil in the above (i) and (ii), various metal foils such as foils of copper, aluminum, gold, or alloys thereof can be used. Among these, a copper foil is preferably used. The one using a copper foil as the metal foil is also called a "copper-clad laminate". When metal layers are laminated on both sides of a multilayer polyimide film, the same or different metals can be used. Specific examples of the copper foil include a rolled copper foil and an electrolytic copper foil. Although there is no particular limitation, the thickness of the copper foil is preferably 2 to 35 μm, particularly preferably 5 to 18 μm, and for Ra and Rz indicating the surface roughness, Ra is preferably 0.01 μm to 0.4 μm and Rz is preferably 0.2 μm to 2.0 μm.

[0066] The multi-layer polyimide film and the copper foil are preferably continuously thermocompression bonded under heating by at least a pair of pressing members. The temperature of the pressing part is preferably 50°C or more higher than the glass transition temperature of the heat-fusible polyimide, more preferably 60°C or more higher, and even more preferably 70°C or more higher. By adopting such a heating temperature, an advantageous effect that the multi-layer polyimide film and the copper foil are firmly laminated is achieved. Also, the heating temperature is preferably 420°C or lower from the viewpoint of preventing thermal deterioration of the multi-layer polyimide film and the copper foil. As described above, since the glass transition temperature of the heat-fusible polyimide is preferably 250°C or more, specifically, it is preferably thermocompression bonded in the temperature range of 300°C or more and 420°C or lower, more preferably in the temperature range of 310°C or more and 410°C or lower, and even more preferably in the temperature range of 320°C or more and 400°C or lower.

[0067] Known devices such as a double-belt press or roll lamination using a pressure-bonding metal roll can be used as the thermocompression bonding device. For example, a roll-wound multi-layer polyimide film and a copper foil can be continuously supplied to the thermocompression bonding device respectively, and a copper-clad laminate (polyimide-metal laminate) can be manufactured in a roll-wound state.

[0068] As the dry method (metallizing method) used in the above (iii), known methods such as vacuum evaporation, sputtering, ion plating, and electron beam can be used. As the metal used in the metallizing method, metals such as copper, nickel, chromium, manganese, aluminum, iron, molybdenum, cobalt, tungsten, vanadium, titanium, tantalum, or alloys thereof, or oxides of these metals, carbides of these metals, etc. can be used, but it is not particularly limited to these materials. The thickness of the formed metal layer is, for example, 1 nm to 500 nm, and a metal plating layer such as copper or tin can be provided on this surface to a thickness of, for example, 1 μm to 40 μm by electrolytic plating or electroless plating.

[0069] As the wet method (plating method) used in the above (iii), known plating methods can be used, including electrolytic plating and electroless plating, and these can be combined. There is no limitation on the metal used in the wet plating method as long as it can be wet plated.

[0070] The thickness of the metal layer formed by the wet plating method can be appropriately selected according to the purpose of use, preferably in the range of 0.1 μm to 50 μm, more preferably 1 μm to 30 μm, which is preferable for practical use. The number of layers of the metal layer formed by the wet plating method can be appropriately selected according to the purpose of use, and it may be one layer, two layers, or multiple layers of three or more layers.

[0071] Examples of the wet plating method include conventionally known methods such as the Elfseed process manufactured by Ebara Yusilite Co., Ltd. and the method of performing electroless copper plating after applying the Catalyst Bond process, which is a surface treatment process of Nippon Mining & Metals Co., Ltd.

[0072] The polyimide metal laminate of the present invention has good formability and can be directly subjected to drilling, bending, drawing, metal wiring formation, etc. Further, the multilayer polyimide film of the present invention can be used for thermocompression bonding of electronic circuits onto wiring.

[0073] The multilayer polyimide film and polyimide metal laminate of the present invention can be suitably used as electronic substrate materials such as FPC and TAB, coverlays, and adhesive sheets that require reliability at high temperatures.

Examples

[0074] Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited by the examples.

[0075] Hereinafter, the following abbreviations will be used. <Tetracarboxylic acids> s-BPDA: 3,3’,4,4’-Biphenyltetracarboxylic dianhydride PMDA: Pyromellitic dianhydride <Diamines> PPD: p-Phenylenediamine m-TB: 2,2'-Dimethylbenzidine BAPP: 2,2-Bis[4-(4-aminophenoxy)phenyl]propane TPE-R: 1,3-Bis(4-aminophenoxy)benzene Bis-aniline P: α,α'-Bis(4-aminophenyl)-1,4-diisopropylbenzene <Others> DMAc: N,N-Dimethylacetamide

[0076] <Evaluation of (Multi-layer) Polyimide Film> [Coefficient of Thermal Expansion (CTE)] Using EXSTAR6100 manufactured by SII, a polyimide film sampled to a length of 15 mm / width of 3 mm was measured in tensile mode, with a load of 4 gf and a heating rate of 20 °C / min. Primary heating was performed up to 300 °C to take the thermal shrinkage during film formation. After that, it was allowed to cool to room temperature, and then secondary heating was carried out up to 300 °C at 20 °C / min. The coefficient of linear expansion was calculated from the TMA curve from 50 °C to 200 °C.

[0077] <Measurement of Dielectric Loss Tangent> As a measuring device, a split cylinder resonator 10 GHz CR-710 (manufactured by EM Lab) was used, and the dielectric loss tangent of the polyimide film was measured under the following conditions. Measurement frequency: 10 GHz Measurement conditions: Temperature 25 ± 2 °C, humidity 50 ± 3% RH Measurement sample: A sample left standing for 24 hours under the above measurement conditions was used.

[0078] [MIT Flexing Test] Test pieces for the MIT flexing test with a width of 15 mm across the entire width were cut out. According to ASTM D2176, the number of times until the polyimide film broke was measured at a radius of curvature of 0.38 mm, a load of 9.8 N, a bending speed of 175 times / min, and a left and right bending angle of 135 degrees.

[0079] [Evaluation of Polyimide Metal Laminate (Copper Clad Laminate)] (Manufacture of Copper Clad Laminate) Using a roll laminating device, while overlapping copper foils on both sides of a multilayer polyimide film, and by thermocompression bonding, a copper clad laminate with copper foils laminated on both sides of the multilayer polyimide film was manufactured.

[0080] [Dimensional Change Rate] Using a press hole drilling machine, holes were drilled in the copper clad laminate, and the initial dimensions (X) were measured. Subsequently, after removing the copper foil by double-sided etching, heat treatment was performed at 250 °C for 30 minutes. After heating, conditioning was carried out at 25 °C and 60% RH for 24 hours, and then the dimensions (Y) were measured. The dimensional change rate (%) was calculated according to the following formula. Dimensional change rate (%) = (Y - X) / X × 100

[0081] [Appearance Evaluation] After double-sided etching the copper clad laminate to remove the copper foil, the film surface was observed using an optical microscope and evaluated as follows. ○: Those without defects (foaming) on the surface ×: Those with defects (foaming) on the surface

[0082] [Example 1] [Preparation of Polyimide Precursor Solution] (Polyimide Precursor Solution for Core Layer) DMAc was added to a reaction vessel equipped with a stirrer and a nitrogen inlet tube, and further, PPD and m-TB were added as diamine components. Subsequently, s-BPDA and PMDA were added as tetracarboxylic dianhydride components in an equimolar amount to the diamine components and reacted to obtain a polyimide precursor solution A with a monomer concentration of 18 mass% and a solution viscosity of 2000 poises at 30 °C. The molar ratio of PPD to m-TB was 80:20, and the molar ratio of s-BPDA to PMDA was 90:10.

[0083] (Polyimide Precursor Solution for Thermal Fusion Layer) DMAc was added to a reaction vessel equipped with a stirrer and a nitrogen inlet tube, followed by the addition of BAPP as the diamine component. Subsequently, s-BPDA and PMDA as the tetracarboxylic dianhydride components were added in equimolar amounts to the diamine component and reacted to obtain polyimide precursor solution B with a monomer concentration of 18% by mass and a solution viscosity of 800 poise at 30°C. The molar ratio of s-BPDA to PMDA was 30:70.

[0084] [Production of core single-layer polyimide film] Polyimide precursor solution A was cast onto a glass plate in the form of a thin film, heated in an oven at 120°C for 12 minutes, and peeled off from the glass plate to obtain a self-supporting film. The four sides of this self-supporting film were fixed with pin tenters and gradually heated in a heating furnace from 150°C to 400°C to remove the solvent and imidize the film, obtaining a single-layer polyimide film with a thickness of 25 μm.

[0085] [Manufacturing multilayer polyimide film] Polyimide precursor solution A and polyimide precursor solution B were continuously extruded and cast onto the upper surface of a smooth metal support from a three-layer extrusion die so as to form a thin film in the following order: polyimide precursor solution B (thermal adhesive layer), polyimide precursor solution A (core layer), and polyimide precursor solution B (thermal adhesive layer). The thin-film cast was continuously dried with hot air at 140°C to form a self-supporting film. After peeling the self-supporting film from the support, it was conveyed while holding both ends of the self-supporting film in the width direction using a tenter device and gradually heated from 200°C to 490°C in a heating furnace to remove the solvent and imidize the film, resulting in a long multilayer film with a thickness of 50 μm. The thicknesses of the two thermal adhesive layers were each 5 μm, and the thickness of the core layer was 40 μm. Note that with regard to the resulting multilayer polyimide film, MD (machine direction) refers to the longitudinal direction (conveying direction), and TD (transverse direction) refers to the width direction.

[0086] The obtained polyimide film was subjected to measurement of the coefficient of linear thermal expansion (CTE), measurement of the dielectric loss tangent, and MIT folding endurance test. The results are shown in Table 1.

[0087] [Polyimide Metal Laminated Body (Copper-Clad Laminate)] Using a roll lamination apparatus, while laminating copper foils (manufactured by JX Metals Co., Ltd., BHM-C102F-HA-V2, thickness 12 μm) on both sides of a multilayer polyimide film, thermocompression bonding was performed at a lamination temperature of 360 °C, a lamination pressure of 1.5 MPa, and a lamination speed of 0.5 m / min to produce a copper-clad laminate with copper foils laminated on both sides of the multilayer polyimide film.

[0088] The obtained copper-clad laminate was etched, and the dimensional change rate and appearance were evaluated.

[0089] [Examples 2 to 7, Comparative Examples 1 to 10] In the same manner as in Example 1, a polyimide precursor solution for the core layer and a polyimide precursor solution for the thermal fusion layer were prepared. The compositions are as shown in Tables 1 to 3. Also, in the same manner as in Example 1, a core single-layer polyimide film, a multilayer polyimide film, and a copper-clad laminate were manufactured and evaluated. The results are shown in Table 1 (Examples), Table 2 (Comparative Examples, multilayer film thickness 50 μm), and Table 3 (Comparative Examples, multilayer film thickness 75 μm). In the case of the multilayer polyimide film with a thickness of 75 μm (Examples 6, 7, Comparative Examples 7 to 10), the thicknesses of the two thermal fusion layers were each 7 μm, and the thickness of the core layer was 61 μm.

[0090] [Table 1]

[0091] [Table 2]

[0092] [Table 3]

[0093] As shown in Tables 1 to 3, the multilayer polyimide films of all examples showed a low dielectric tangent of 0.0060 or less. The multilayer polyimide films of Comparative Examples 3, 5, and 9 showed a low dielectric tangent, but had a large dimensional change rate and had practical problems. In all other comparative examples, the dielectric tangent was large. Regarding the dimensional change rate, all examples showed small values, while all comparative examples showed large values. In Comparative Examples 7 and 10, an attempt was made to produce a copper-clad laminate using a 75-μm multilayer film, but foaming occurred and evaluation was not possible. Also, this experiment revealed that the dimensional change rate strongly depends not only on the CTE of the multilayer film but also on the combination of the core layer and the heat-sealing layer. Considering this for a 50-μm thick multilayer polyimide film, the multilayer polyimide film of Comparative Example 6 has a CTE (MD and TD) that matches the CTE of copper foil of 18 ppm / K, and the multilayer polyimide films of Examples 1 to 5 and Comparative Example 1 also have a CTE that is generally close to that of copper foil. However, when comparing the dimensional change rates, the multilayer polyimide films of the examples had an extremely small dimensional change rate, while Comparative Examples 6 and 1 had a large dimensional change rate. Similarly, considering a 75-μm thick multilayer film, the multilayer polyimide film of Example 6 and the multilayer polyimide film of Comparative Example 9 have the same CTE, but for the dimensional change rate, Comparative Example 9 showed a large value. The reason for this is considered to be that the heat-resistant polyimide layer (core layer), which has a large influence on the dielectric tangent, was optimized, and the heat-sealing polyimide layer (heat-sealing layer) was optimized according to the core layer, which is a result that cannot be predicted from the conventional approach based on CTE.

Industrial Applicability

[0094] The polyimide film produced from the polyimide precursor solution of the present invention can be suitably used for high-frequency compatible FPC applications.

Claims

1. A heat-resistant polyimide film having a heat-resistant polyimide layer composed of a heat-resistant polyimide (PIc), and a heat-sealable polyimide layer laminated on one or both sides of the heat-resistant polyimide layer and composed of a heat-sealable polyimide (PIb), wherein: The heat-resistant polyimide (PIc) is a tetracarboxylic acid component (Ac) containing 3,3',4,4'-biphenyltetracarboxylic dianhydride in an amount of 75 mol% or more and 100 mol% or less, and pyromellitic dianhydride in an amount of 0 mol% or more and 25 mol% or less, and a diamine component (Bc) containing p-phenylenediamine in an amount of 70 mol% or more and 95 mol% or less, and 2,2'-dimethylbenzidine in an amount of 5 mol% or more and 30 mol% or less, reacted to obtain; The heat-sealable polyimide (PIb) is a tetracarboxylic acid component (Ab) containing 3,3',4,4'-biphenyltetracarboxylic dianhydride in an amount of 10 mol% or more and 60 mol% or less, and pyromellitic dianhydride in an amount of 40 mol% or more and 90 mol% or less, and a diamine component (Bb) containing 2,2-bis[4-(4-aminophenoxy)phenyl]propane in an amount of 50 mol% or more, reacted to obtain, a multilayer polyimide film.

2. The heat-resistant polyimide (PIc) is a tetracarboxylic acid component (Ac) containing 3,3',4,4'-biphenyltetracarboxylic dianhydride in an amount of 80 mol% or more and less than 100 mol%, and pyromellitic dianhydride in an amount of more than 0 mol% and 20 mol% or less, and a diamine (Bc) containing p-phenylenediamine in an amount of 75 mol% or more and 2,2'-dimethylbenzidine in an amount of 25 mol% or less, reacted to obtain, the multilayer polyimide film according to Claim 1.

3. The heat-sealable polyimide (PIb) is a tetracarboxylic acid component (Ab) containing 3,3',4,4'-biphenyltetracarboxylic dianhydride in an amount of 15 mol% or more and pyromellitic dianhydride in an amount of 85 mol% or less, and a diamine component (Bb) containing 2,2-bis[4-(4-aminophenoxy)phenyl]propane in an amount of 60 mol% or more, reacted to obtain, the multilayer polyimide film according to Claim 1.

4. The dielectric tangent of the multilayer polyimide film is 0.0060 or less, and the dimensional change rate (absolute value) in the longitudinal direction (MD) and the width direction (TD) of the polyimide metal laminate is 0.10% or less. The multilayer polyimide film according to claim 1 (however, the dimensional change rate is measured by measuring the initial dimension (X) of the polyimide metal laminate manufactured using the multilayer polyimide film and the dimension (Y) after heat treatment at 250°C for 30 minutes after etching the metal foil, and is calculated according to the following formula. Dimensional change rate (%) = (Y - X) / X × 100 ）。

5. A polyimide metal laminate in which a metal foil is laminated on the heat-sealable polyimide layer side of the multilayer polyimide film according to claim 1.

6. The polyimide metal laminate according to claim 5, wherein the multilayer polyimide film has heat-sealable polyimide layers on both sides of the heat-resistant polyimide layer, and metal foils are laminated on both sides of the multilayer polyimide film.

7. A flexible wiring board manufactured using the polyimide metal laminate according to claim 5.

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