Thermoplastic polyimide film, multilayer polyimide film, and flexible metal-clad laminate

Abstract

To provide a multilayer polyimide film that can reduce dielectric loss tangent while securing adhesive properties with a metal layer and is excellent in productivity, a method for producing the same, and a metal-clad laminate using the multilayer polyimide film.SOLUTION: A multilayer polyimide film (10) comprises a non-thermoplastic polyimide layer (11) and an adhesive layer (12) comprising polyimide, disposed on at least one surface of the non-thermoplastic polyimide layer (11). The adhesive layer (12) has a 5% thermal decomposition temperature of 570°C or higher and a storage elastic modulus at 360°C of 100 MPa or lower. The polyimide comprised in the adhesive layer (12) comprises one or more tetracarboxylic dianhydride residues selected from the group consisting of pyromellitic dianhydride residue and 3,3',4,4'-biphenyltetracarboxylic dianhydride residue, and one or more diamine residues selected from the group consisting of 1,3-bis(4-aminophenoxy)benzene residue and p-phenylenediamine residue.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a thermoplastic polyimide film, a multilayer polyimide film, and a flexible metal-clad laminate. [Background technology]

[0002] In recent years, demand for flexible printed circuit boards (hereinafter sometimes referred to as "FPCs") has been growing in line with the expansion of demand for electronic products, particularly smartphones, tablet PCs, and laptops. In particular, demand for FPCs made from multilayer polyimide film containing a thermoplastic polyimide layer as an adhesive layer is expected to grow further due to its excellent heat resistance and flexibility.

[0003] FPCs using multilayer polyimide films with improved heat resistance are expected to be used in automobiles, which require heat resistance that exceeds that of electronic products and also require long-term reliability.

[0004] Generally, when the heat resistance of polyimide is improved, the plasticity of the thermoplastic polyimide used in the adhesive layer is lost, and the function as an adhesive layer is not exhibited. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2023-24470 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-187893 [Patent Document 3] WO2022 / 080314 publication

[0006] In Patent Document 1, thermoplasticity is imparted by using an aliphatic diamine, but aliphatic diamines are prone to decomposition and are difficult to use in locations where reliability is required. In Patent Document 2, an improvement is made by using a monomer containing siloxane, but the generation of cyclic siloxane makes it difficult to use in components that require reliability. In Patent Document 3, a diamine with a methyl group in the side chain is used, making it difficult to use in applications where long-term heat resistance is required. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in view of these problems, and an object of the present invention is to provide a multilayer polyimide film that can reduce the dielectric tangent while maintaining adhesion properties with a metal layer and has excellent productivity, a method for producing the same, and a metal-clad laminate using the multilayer polyimide film. [Means for solving the problem]

[0008] As a result of extensive investigations, the present inventors have found that the above problems can be solved by the following means.

[0009] The multilayer polyimide film according to the present invention comprises a non-thermoplastic polyimide layer and an adhesive layer containing a polyimide disposed on at least one surface of the non-thermoplastic polyimide layer, wherein the adhesive layer has a 5% thermogravimetric decomposition temperature of 570°C or higher and a storage modulus at 360°C of 100 MPa or lower, and the polyimide contained in the adhesive layer contains one or more tetracarboxylic dianhydride residues selected from the group consisting of pyromellitic dianhydride residues and 3,3',4,4'-biphenyltetracarboxylic dianhydride residues, and one or more diamine residues selected from the group consisting of 1,3-bis(4-aminophenoxy)benzene residues and p-phenylenediamine residues.

[0010] In the multilayer polyimide film according to one embodiment of the present invention, the adhesive layer is disposed on both sides of the non-thermoplastic polyimide layer.

[0011] In the multilayer polyimide film according to one embodiment of the present invention, the adhesive layer contains a tertiary amine at a content of 1 ppm by mass or more.

[0012] In the multilayer polyimide film according to one embodiment of the present invention, the non-thermoplastic polyimide layer contains a tertiary amine in a content of 1 ppm by mass or more.

[0013] In the multilayer polyimide film according to one embodiment of the present invention, the adhesive layer does not have a melting peak in the temperature range of 100°C or higher and 420°C or lower.

[0014] In the multilayer polyimide film according to one embodiment of the present invention, the polyimide structure contained in the adhesive layer has an oxygen concentration per polymer structural unit of 18 mol % or more.

[0015] The metal-clad laminate according to the present invention comprises the multilayer polyimide film according to the present invention and a metal layer disposed on a main surface of at least one of the adhesive layers of the multilayer polyimide film.

[0016] The method for producing a multilayer polyimide film according to the present invention is a method for producing a multilayer polyimide film having a non-thermoplastic polyimide layer and an adhesive layer containing polyimide disposed on at least one surface of the non-thermoplastic polyimide layer, the method comprising the steps of: a coating step of coating an adhesive layer-forming solution containing polyamic acid onto a support by a co-extrusion-casting coating method; a gel film-forming step of drying the coating film obtained in the coating step to form a gel film having self-supporting properties; and a heating step of heating the gel film obtained in the gel film-forming step under conditions of a maximum temperature of 360°C or higher. and an imidization step of imidizing the polyamic acid in the non-thermoplastic polyimide layer-forming solution and the polyamic acid in the adhesive layer-forming solution, wherein in the coating step, the polyamic acid contained in the adhesive layer-forming solution has pyromellitic dianhydride residues, 3,3',4,4'-biphenyltetracarboxylic dianhydride residues, 1,3-bis(4-aminophenoxy)benzene residues, and p-phenylenediamine residues, and the adhesive layer has a 5% thermogravimetric decomposition temperature of 570°C or higher and a storage modulus at 360°C of 100 MPa or lower.

[0017] In the method for producing a multilayer polyimide film according to one embodiment of the present invention, the adhesive layer does not have a melting peak in the temperature range of 100°C or higher and 420°C or lower.

[0018] In the method for producing a multilayer polyimide film according to one embodiment of the present invention, the adhesive layer has a structure in which the oxygen concentration per polymer structural unit is 18 mol % or more. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a multilayer polyimide film that has improved heat resistance while maintaining adhesion properties to a metal layer and is highly productive, a method for producing the same, and a metal-clad laminate using the multilayer polyimide film. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a cross-sectional view showing an example of a multilayer polyimide film according to the present invention. [Figure 2] 1 is a cross-sectional view showing an example of a metal-clad laminate according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] Preferred embodiments of the present invention will be described in detail below, but the present invention is not limited thereto. In addition, all academic and patent documents described in this specification are incorporated herein by reference.

[0022] First, the terms used in this specification will be explained. A "structural unit" refers to a repeating unit that constitutes a polymer. A "polyimide" is a polymer containing a structural unit represented by the following general formula (1) (hereinafter, sometimes referred to as "structural unit (1)").

[0023] [ka]

[0024] In general formula (1), X1 represents a tetracarboxylic dianhydride residue (a tetravalent organic group derived from a tetracarboxylic dianhydride), and X2 represents a diamine residue (a divalent organic group derived from a diamine).

[0025] The content of the structural unit (1) relative to all structural units constituting the polyimide is, for example, 50 mol% or more and 100 mol% or less, preferably 60 mol% or more and 100 mol% or less, more preferably 70 mol% or more and 100 mol% or less, even more preferably 80 mol% or more and 100 mol% or less, still more preferably 90 mol% or more and 100 mol% or less, and may be 100 mol%.

[0026] A "polyamic acid" is a polymer containing a structural unit represented by the following general formula (2) (hereinafter, sometimes referred to as "structural unit (2)").

[0027] [ka]

[0028] In general formula (2), A1 represents a tetracarboxylic dianhydride residue (a tetravalent organic group derived from a tetracarboxylic dianhydride), and A2 represents a diamine residue (a divalent organic group derived from a diamine).

[0029] The content of the structural unit (2) relative to all structural units constituting the polyamic acid is, for example, 50 mol% or more and 100 mol% or less, preferably 60 mol% or more and 100 mol% or less, more preferably 70 mol% or more and 100 mol% or less, even more preferably 80 mol% or more and 100 mol% or less, still more preferably 90 mol% or more and 100 mol% or less, and may be 100 mol%.

[0030] Polyimide is an imidized product of polyamic acid. Therefore, when the content of structural unit (2) relative to all structural units constituting polyamic acid is 100 mol %, the polyimide, which is an imidized product of polyamic acid, has a residue represented by A1 in general formula (2) as X1 in general formula (1) and a residue represented by A2 in general formula (2) as X2 in general formula (1).

[0031] "Non-thermoplastic polyimide" refers to polyimide that retains its film shape (flat membrane shape) when fixed in film form on a metal frame and heated at 380°C for 2 minutes.

[0032] The "principal surface" of a layered product (more specifically, a non-thermoplastic polyimide layer, an adhesive layer, a multilayer polyimide film, a metal layer, etc.) refers to a surface perpendicular to the thickness direction of the layered product.

[0033] Hereinafter, the compound name may be followed by "system" to refer to the compound and its derivatives collectively. Tetracarboxylic acid dianhydrides may be referred to as "acid dianhydrides." Adhesion properties with metal layers may be simply referred to as "adhesion properties."

[0034] The drawings referred to in the following description mainly show each component in a schematic manner for ease of understanding, and the size, number, shape, etc. of each component shown may differ from the actual size, number, shape, etc. of each component due to the convenience of creating the drawings. Furthermore, for convenience of explanation, in drawings described later, the same components as those in previously described drawings may be assigned the same reference numerals, and their explanation may be omitted.

[0035] Hereinafter, preferred embodiments of the present invention will be described in the order of a method for producing a multilayer polyimide film, a multilayer polyimide film, and a metal-clad laminate.

[0036] <First embodiment: Method for producing a multilayer polyimide film> The method for producing a multilayer polyimide film according to a first embodiment of the present invention is a method for producing a multilayer polyimide film having a non-thermoplastic polyimide layer and a polyimide-containing adhesive layer disposed on at least one side of the non-thermoplastic polyimide layer, and includes a coating step, a gel film-forming step, and an imidization step. In the coating step, a non-thermoplastic polyimide layer-forming solution containing polyamic acid, acetic anhydride, and a tertiary amine and an adhesive layer-forming solution containing polyamic acid are applied onto a support by a co-extrusion-casting coating method. In the gel film-forming step, the coating film obtained in the coating step is dried to form a self-supporting gel film. In the imidization step, the gel film obtained in the gel film-forming step is heated at a maximum temperature of 360°C or higher to imidize the polyamic acid in the non-thermoplastic polyimide layer-forming solution and the polyamic acid in the adhesive layer-forming solution. In the coating process, the polyamic acid contained in the adhesive layer-forming solution has pyromellitic dianhydride residues, 3,3',4,4'-biphenyltetracarboxylic dianhydride residues, 1,3-bis(4-aminophenoxy)benzene residues, and p-phenylenediamine residues.

[0037] The "co-extrusion-casting coating method" is a method for forming a coating film using an extruder having an extrusion die for two or more layers. Specifically, the co-extrusion-casting coating method is a method for forming a coating film having a layer structure of two or more layers on a support by extruding a non-thermoplastic polyimide layer-forming solution and an adhesive layer-forming solution in the form of a thin film having two or more layers from the lip opening of the extrusion die.

[0038] Hereinafter, the self-supporting gel film may be referred to simply as "gel film." Pyromellitic dianhydride may be referred to as "PMDA." 3,3',4,4'-biphenyltetracarboxylic dianhydride may be referred to as "BPDA." 1,3-bis(4-aminophenoxy)benzene may be referred to as "TPE-R." p-Phenylenediamine may be referred to as "PDA." 4,4'-Oxydiphthalic anhydride may be referred to as "ODPA." The non-thermoplastic polyimide contained in the non-thermoplastic polyimide layer may be referred to simply as "non-thermoplastic polyimide."

[0039] The method for producing a multilayer polyimide film according to the first embodiment not only increases productivity but also produces a multilayer polyimide film with improved heat resistance while maintaining adhesion to a metal layer. The reasons for this are presumed to be as follows.

[0040] The production method according to the first embodiment employs a co-extrusion-casting coating method and a method of promoting imidization using acetic anhydride and a tertiary amine (chemical imidization method), thereby simplifying the film formation process and shortening the imidization time, thereby enabling the multilayer polyimide film production method according to the first embodiment to increase productivity.

[0041] In the first embodiment, the polyamic acid contained in the non-thermoplastic polyimide layer-forming solution is imidized by chemical imidization at a maximum temperature of 360°C or higher. When chemical imidization is used, the imidization reaction proceeds more rapidly than in thermal imidization. Therefore, in the first embodiment, the polyamic acid is imidized in a relatively large amount of solvent. In the first embodiment, the polyamic acid having the specific residue is imidized by chemical imidization at a maximum temperature of 360°C or higher, resulting in a high packing property of the resulting non-thermoplastic polyimide. As a result, the non-thermoplastic polyimide layer obtained by the production method according to the first embodiment tends to have a low dielectric loss tangent. Therefore, the multilayer polyimide film production method according to the first embodiment can reduce the dielectric loss tangent of the multilayer polyimide film.

[0042] Furthermore, in the first embodiment, the polyamic acid contained in the adhesive layer-forming solution contains PMDA residues, BPDA residues, TPE-R residues, and PDA residues, so that when imidization is performed under conditions of a maximum temperature of 360° C. or higher, the adhesive properties of the resulting adhesive layer are not reduced and the shape of the film containing the polyamic acid in the adhesive layer-forming solution can be maintained in good condition. Therefore, the method for producing a multilayer polyimide film according to the first embodiment can ensure adhesive properties with a metal layer.

[0043] In the first embodiment, in order to obtain a multilayer polyimide film that can improve the heat resistance while enhancing the adhesive properties with the metal layer, it is preferable that the polyamic acid contained in the adhesive layer-forming solution has a PDA residue.

[0044] Each step of the manufacturing method according to the first embodiment will be described in detail below.

[0045] [Coating process] (Solution for forming thermoplastic polyimide layer) The thermoplastic polyimide layer-forming solution is a solution for forming a thermoplastic polyimide layer, which is an adhesive layer of a multilayer polyimide film, and contains polyamic acid, acetic anhydride, and a tertiary amine.

[0046] The polyamic acid contained in the thermoplastic polyimide layer-forming solution (hereinafter sometimes referred to as "thermoplastic polyamic acid") has one or more acid dianhydride residues selected from the group consisting of PMDA residues and BPDA residues, and one or more diamine residues selected from the group consisting of PDA residues and TPE-R residues. The thermoplastic polyamic acid may contain one or more polyamic acids, but preferably consists of one type of polyamic acid.

[0047] The thermoplastic polyamic acid may have other acid dianhydride residues in addition to one or more acid dianhydride residues selected from the group consisting of PMDA residues and BPDA residues. Examples of acid dianhydrides (monomers) for forming other acid dianhydride residues (acid dianhydride residues other than PMDA residues and BPDA residues) include ODPA, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, and 3,4'-oxydiphthalic acid dianhydride. Examples of the dianhydride include 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, p-phenylene bis(trimellitic acid monoester acid anhydride), ethylene bis(trimellitic acid monoester acid anhydride), bisphenol A bis(trimellitic acid monoester acid anhydride), and derivatives thereof.

[0048] In order to obtain a multilayer polyimide film having improved thermoplasticity while increasing heat resistance, the other acid dianhydride residue is preferably an ODPA residue.

[0049] To obtain a multilayer polyimide film capable of improving heat resistance, the total content of PMDA residues and BPDA residues relative to all acid dianhydride residues constituting the thermoplastic polyamic acid is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, and may even be 100 mol%.

[0050] When an ODPA residue is used as the other acid dianhydride residue, in order to obtain a multilayer polyimide film that can be endowed with increased thermoplasticity while improving heat resistance, the total content of PMDA residues, BPDA residues, and ODPA residues relative to all acid dianhydride residues constituting the thermoplastic polyamic acid is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may even be 100 mol%.

[0051] To obtain a multilayer polyimide film with improved heat resistance, the thermoplastic polyamic acid preferably contains two types of acid dianhydride residues, namely, PMDA residue and BPDA residue.To obtain a multilayer polyimide film with improved heat resistance and reduced dielectric tangent, the non-thermoplastic polyamic acid preferably contains three types of acid dianhydride residues, namely, PMDA residue, BPDA residue, and ODPA residue.

[0052] In order to obtain a multilayer polyimide film with improved heat resistance, the content of PMDA residues relative to all acid dianhydride residues constituting the thermoplastic polyamic acid is preferably 0 mol % or more and 40 mol % or less, and more preferably 10 mol % or more and 30 mol % or less.

[0053] In order to obtain a multilayer polyimide film that can improve heat resistance, the content of BPDA residues relative to all acid dianhydride residues constituting the thermoplastic polyamic acid is preferably 30 mol % or more and 80 mol % or less, and more preferably 40 mol % or more and 70 mol % or less.

[0054] In order to obtain a multilayer polyimide film that can be endowed with thermoplasticity while improving heat resistance, the content of ODPA residues relative to all acid dianhydride residues constituting the thermoplastic polyamic acid is preferably 0 mol % or more and 50 mol % or less, and more preferably 1 mol % or more and 40 mol % or less.

[0055] The thermoplastic polyamic acid has, in addition to the above-mentioned acid dianhydride residues, one or more diamine residues selected from the group consisting of PDA residues and TPE-R residues.

[0056] The non-thermoplastic polyamic acid may have other diamine residues in addition to one or more diamine residues selected from the group consisting of PDA residues and TPE-R residues. Examples of diamines (monomers) for forming other diamine residues (diamine residues other than PDA residues and TPE-R residues) include 1,4-bis(4-aminophenoxy)benzene, 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenylmethane, 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'-diaminodiphenylsilane, 4,4'-diaminodiphenylethylphosphine oxide, 4,4'-diaminodiphenyl N-methylamine, 4,4'-diaminodiphenyl N-phenylamine, 1,3-diaminobenzene, 1,2-diaminobenzene, and derivatives thereof.

[0057] In order to obtain a multilayer polyimide film that can improve heat resistance, the total content of PDA residues and TPE-R residues relative to all diamine residues constituting the thermoplastic polyamic acid is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may be 100 mol%.

[0058] In order to obtain a multilayer polyimide film that can improve heat resistance, the thermoplastic polyamic acid preferably has two types of diamine residues, a PDA residue and a TPE-R residue.

[0059] In order to obtain a multilayer polyimide film that can improve heat resistance, the content of PDA residues relative to all diamine residues constituting the thermoplastic polyamic acid is preferably 0 mol % or more and 60 mol % or less, and more preferably 1 mol % or more and 50 mol % or less.

[0060] In order to obtain a multilayer polyimide film that can improve heat resistance, the content of TPE-R residues relative to all diamine residues constituting the thermoplastic polyamic acid is preferably 40 mol% or more and 100 mol% or less, and more preferably 50 mol% or more and 99 mol% or less.

[0061] Any known method or a combination thereof can be used as a method for producing (synthesizing) thermoplastic polyamic acid. A specific example of a method for producing (synthesizing) thermoplastic polyamic acid is a method of reacting a diamine with a tetracarboxylic dianhydride in an organic solvent. The amount of diamine and the amount of tetracarboxylic dianhydride used during the reaction are preferably substantially equal. When synthesizing a thermoplastic polyamic acid using a diamine and a tetracarboxylic dianhydride, the desired polyamic acid (a polymer of a diamine and a tetracarboxylic dianhydride) can be obtained by adjusting the amount of diamine (or, if multiple diamines are used, the amount of each diamine) and the amount of tetracarboxylic dianhydride (or, if multiple tetracarboxylic dianhydrides are used, the amount of each tetracarboxylic dianhydride). The molar fraction of each residue in the thermoplastic polyamic acid corresponds to, for example, the molar fraction of each monomer (diamine and tetracarboxylic dianhydride) used in the synthesis of the thermoplastic polyamic acid. The temperature conditions for the reaction between the diamine and the tetracarboxylic dianhydride, i.e., the synthesis reaction of the thermoplastic polyamic acid, are not particularly limited, but are, for example, in the range of 10°C to 150°C. The reaction time for the synthesis reaction of the thermoplastic polyamic acid is, for example, in the range of 10 minutes to 30 hours. Any method of adding monomers may be used for synthesizing the thermoplastic polyamic acid.

[0062] The thermoplastic polyimide layer-forming solution contains a tertiary amine as a catalyst in addition to a thermoplastic polyamic acid. The inclusion of a tertiary amine in the thermoplastic polyimide layer-forming solution promotes imidization. Examples of tertiary amines include aliphatic tertiary amines, aromatic tertiary amines, and heterocyclic tertiary amines. To facilitate the promotion of imidization, the tertiary amine is preferably a heterocyclic tertiary amine, and more preferably one or more selected from the group consisting of pyridine compounds (more specifically, β-picoline, γ-picoline, 3,5-dimethylpyridine, etc.) having alkyl groups introduced at the β- and / or γ-positions, pyridine, and isoquinoline.

[0063] The amount of tertiary amine added is preferably 0.5 to 5.0 molar equivalents relative to the amide groups of the thermoplastic polyamic acid, more preferably 0.7 to 2.5 molar equivalents, and even more preferably 0.8 to 2.0 molar equivalents. In this specification, "amide groups of the thermoplastic polyamic acid" refers to amide groups formed by the polymerization reaction of a diamine with a tetracarboxylic dianhydride. When adding the tertiary amine to the polyamic acid solution described below, it may be added directly without dissolving it in an organic solvent, or it may be added dissolved in an organic solvent. If the tertiary amine is added directly without dissolving it in an organic solvent, the reaction may proceed too rapidly before the tertiary amine can diffuse, resulting in the formation of a gel. Therefore, it is preferable to add a solution (imidization accelerator) obtained by dissolving a tertiary amine and acetic anhydride in an organic solvent to the polyamic acid solution.

[0064] The thermoplastic polyimide layer-forming solution can be obtained, for example, by adding a tertiary amine to a polyamic acid solution containing a thermoplastic polyamic acid and an organic solvent. Examples of organic solvents that can be used in polyamic acid solutions include urea-based solvents such as tetramethylurea and N,N-dimethylethylurea; sulfoxide-based solvents such as dimethyl sulfoxide; sulfone-based solvents such as diphenyl sulfone and tetramethyl sulfone; amide-based solvents such as N,N-dimethylacetamide, N,N-dimethylformamide (hereinafter sometimes referred to as "DMF"), N,N-diethylacetamide, N-methyl-2-pyrrolidone, and hexamethylphosphoric acid triamide; ester-based solvents such as γ-butyrolactone; alkyl halide solvents such as chloroform and methylene chloride; aromatic hydrocarbon solvents such as benzene and toluene; phenol-based solvents such as phenol and cresol; ketone-based solvents such as cyclopentanone; and ether-based solvents such as tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dimethyl ether, diethyl ether, diethylene glycol diethyl ether, diethylene glycol dimethyl ether, and p-cresol methyl ether. These solvents are typically used alone, but two or more may be used in combination as needed. When a non-thermoplastic polyamic acid is obtained by the above-mentioned polymerization method, the reaction solution (the solution after the reaction) itself may be used as a polyamic acid solution. In this case, the organic solvent in the polyamic acid solution is the organic solvent used in the reaction in the above-mentioned polymerization method. Alternatively, the solid thermoplastic polyamic acid obtained by removing the solvent from the reaction solution may be dissolved in an organic solvent to prepare a polyamic acid solution.

[0065] The polyamic acid solution may contain additives such as dyes, surfactants, leveling agents, plasticizers, silicones, and sensitizers. Furthermore, a filler may be added to the polyamic acid solution to improve various film properties such as sliding properties, thermal conductivity, electrical conductivity, corona resistance, and loop stiffness. Any filler may be used, but preferred examples include fillers made of silica, titanium oxide, alumina, silicon nitride, boron nitride, calcium hydrogen phosphate, calcium phosphate, mica, and the like.

[0066] The concentration of the non-thermoplastic polyamic acid in the polyamic acid solution is not particularly limited and is, for example, 5% by weight to 35% by weight, preferably 8% by weight to 30% by weight, based on the total amount of the polyamic acid solution.

[0067] (Core layer forming solution) The core layer-forming solution is a non-thermoplastic polyimide solution for forming an adhesive layer to be bonded to the core layer. The non-thermoplastic polyimide solution contains polyamic acid. The non-thermoplastic polyimide solution may contain, in addition to polyamic acid, the above-mentioned acetic anhydride and tertiary amine. Note that, if the thermoplastic polyimide layer-forming solution contains acetic anhydride and a tertiary amine, even if the adhesive layer-forming solution does not contain acetic anhydride and a tertiary amine, the acetic anhydride and the tertiary amine diffuse from the thermoplastic polyimide layer-forming solution to the adhesive layer-forming solution in the imidization step, and the polyamic acid in the non-thermoplastic polyimide solution can be imidized by a chemical imidization method.

[0068] (Application method) The coating method in the coating step is not particularly limited as long as the non-thermoplastic polyimide layer-forming solution and the adhesive layer-forming solution are coated on the support by a co-extrusion-casting coating method. For example, a coating film having a layer structure of two or more layers can be formed on the support by extruding the non-thermoplastic polyimide layer-forming solution and the adhesive layer-forming solution in the form of a thin film of two or more layers from the lip opening of an extrusion die using a known extruder.

[0069] Suitable supports for use in the co-extrusion-casting coating method include glass plates, aluminum foils, stainless steel endless belts, stainless steel drums, and the like.

[0070] [Gel film formation process] In the gel film formation process, the coating film obtained in the coating process is dried to form a self-supporting gel film. The coating film can be dried, for example, on a support. The drying temperature when drying the coating film is, for example, 50°C or higher and 200°C or lower. The drying time when drying the coating film is, for example, 1 minute or higher and 100 minutes or lower. Note that a multi-stage drying process may be performed, such as heating the coating film at a temperature of 50°C for 10 minutes and then at a temperature of 100°C for 10 minutes.

[0071] [Imidization process] In the imidization step, the gel film obtained in the gel film formation step is heated at a maximum temperature of 360°C or higher to imidize the polyamic acid in the non-thermoplastic polyimide layer-forming solution and the polyamic acid in the adhesive layer-forming solution. This step results in a multilayer polyimide film, which is a laminate of a non-thermoplastic polyimide layer and an adhesive layer. In order to further reduce the dielectric loss tangent, the maximum temperature in the imidization step is preferably 380°C or higher. The upper limit of the maximum temperature in the imidization step is, for example, 500°C, preferably 450°C. In order to obtain a multilayer polyimide film with excellent adhesive properties while further reducing the dielectric loss tangent, the heating time of the gel film at the maximum temperature is preferably 10 seconds to 300 seconds, more preferably 20 seconds to 200 seconds, even more preferably 30 seconds to 150 seconds, and even 60 seconds to 100 seconds. Furthermore, the gel film may be held at any temperature for any time until the maximum temperature is reached.

[0072] The imidization process can be carried out in air, under reduced pressure, or in an inert gas such as nitrogen. To prevent shrinkage during film curing, the imidization process is preferably carried out by peeling the gel film from the support and heating the gel film while fixing its edges. The imidization process may also be carried out while stretching the gel film in the conveying direction or a direction perpendicular to the conveying direction.

[0073] [Multilayer polyimide film obtained by the production method according to the first embodiment] Next, the multilayer polyimide film obtained by the production method according to the first embodiment will be described with reference to the drawings.

[0074] Fig. 1 is a cross-sectional view showing an example of a multilayer polyimide film obtained by the production method according to Embodiment 1. As shown in Fig. 1, a multilayer polyimide film 10 has a non-thermoplastic polyimide layer 11 and an adhesive layer 12 disposed on at least one surface (one main surface) of the non-thermoplastic polyimide layer 11.

[0075] In the multilayer polyimide film 10 shown in FIG. 1 , the adhesive layer 12 is provided on only one side of the non-thermoplastic polyimide layer 11. However, as in the multilayer polyimide films produced in the Examples described below, the adhesive layer 12 may be provided on both sides (both main surfaces) of the non-thermoplastic polyimide layer 11. When the adhesive layer 12 is provided on both sides of the non-thermoplastic polyimide layer 11, the two adhesive layers 12 may contain the same type of polyimide or different types of polyimide. The thicknesses of the two adhesive layers 12 may be the same or different. In the present invention, two or more non-thermoplastic polyimide layers 11 and adhesive layers 12 may be provided. In the following description, the term "multilayer polyimide film 10" includes a film in which the adhesive layer 12 is provided on only one side of the non-thermoplastic polyimide layer 11, a film in which the adhesive layer 12 is provided on both sides of the non-thermoplastic polyimide layer 11, and a film in which two or more non-thermoplastic polyimide layers 11 and adhesive layers 12 are provided.

[0076] The thickness of the multilayer polyimide film 10 (total thickness of each layer) is, for example, 6 μm or more and 60 μm or less. The thinner the multilayer polyimide film 10, the easier it is to reduce the weight of the resulting FPC and improve the foldability of the resulting FPC. To facilitate weight reduction of the FPC while maintaining mechanical strength and improve the foldability of the FPC, the thickness of the multilayer polyimide film 10 is preferably 7 μm or more and 60 μm or less, and more preferably 10 μm or more and 60 μm or less. The thickness of the multilayer polyimide film 10 can be measured using a laser hologram.

[0077] To easily achieve a thinner FPC while ensuring adhesion to the metal foil, the thickness of the adhesive layer 12 (when two or more adhesive layers 12 are provided, the thickness of each adhesive layer 12) is preferably 1 μm or more and 15 μm or less. Furthermore, to easily adjust the linear expansion coefficient of the multilayer polyimide film 10, the thickness ratio of the non-thermoplastic polyimide layer 11 to the adhesive layer 12 (thickness of the non-thermoplastic polyimide layer 11 / thickness of the adhesive layer 12) is preferably 55 / 45 or more and 95 / 5 or less. When multiple non-thermoplastic polyimide layers 11 and adhesive layers 12 are provided, the thickness ratio is the ratio of their total thicknesses. Even if the number of adhesive layers 12 is increased, it is preferable that the total thickness of the adhesive layers 12 does not exceed the total thickness of the non-thermoplastic polyimide layers 11.

[0078] In order to suppress warping of the multilayer polyimide film 10, it is preferable that adhesive layers 12 be provided on both sides of the non-thermoplastic polyimide layer 11, and it is more preferable that adhesive layers 12 containing the same type of polyimide be provided on both sides of the non-thermoplastic polyimide layer 11. When adhesive layers 12 are provided on both sides of the non-thermoplastic polyimide layer 11, it is preferable that the thicknesses of the two adhesive layers 12 be the same in order to suppress warping of the multilayer polyimide film 10. Even if the thicknesses of the two adhesive layers 12 are different from each other, warping of the multilayer polyimide film 10 can be suppressed as long as the thickness of the thicker adhesive layer 12 is within a range of 40% or more and less than 100% of the thickness of the other adhesive layer 12.

[0079] To obtain a multilayer polyimide film 10 that can maintain adhesive properties while improving heat resistance, the adhesive layer 12 preferably does not have a melting peak in the temperature range of 100°C to 420°C. Hereinafter, a melting peak in the temperature range of 100°C to 420°C may be simply referred to as the "melting peak." The method for measuring the heat of fusion of the melting peak is the same as or equivalent to the method described in the Examples below. When the adhesive layer 12 does not have a melting peak, the shape of the film containing the polyamic acid in the adhesive layer-forming solution can be maintained well during the imidization process. Therefore, heating to a maximum temperature of 360°C or higher during the imidization process reduces the dielectric loss tangent of the multilayer polyimide film 10 while maintaining the shape of the adhesive layer 12 suitable for bonding to a metal layer. The heat of fusion of the melting peak of the adhesive layer 12 tends to be lower when imidized by chemical imidization. The heat of fusion of the melting peak of the adhesive layer 12 can be adjusted by, for example, changing at least one of the content of each residue constituting the adhesive polyamic acid and the maximum temperature in the imidization step.

[0080] An index of the adhesion between the adhesive layer 12 and the metal layer is the adhesion strength described in the Examples below. To obtain a multilayer polyimide film 10 with excellent adhesive properties, the adhesion strength described in the Examples below is preferably 10 N / cm or more.

[0081] The non-thermoplastic polyimide layer 11 may contain components (additives) other than the non-thermoplastic polyimide. Examples of additives that can be used include dyes, surfactants, leveling agents, plasticizers, silicones, fillers, and sensitizers. The content of the non-thermoplastic polyimide in the non-thermoplastic polyimide layer 11 is, for example, 70% by weight or more, preferably 80% by weight or more, more preferably 90% by weight or more, and may be 100% by weight, based on the total weight of the non-thermoplastic polyimide layer 11.

[0082] The adhesive layer 12 may contain components (additives) other than polyimide. Examples of additives that can be used include dyes, surfactants, leveling agents, plasticizers, silicones, fillers, and sensitizers. The content of polyimide in the adhesive layer 12 is, for example, 70% by weight or more, preferably 80% by weight or more, more preferably 90% by weight or more, and may be 100% by weight, based on the total weight of the adhesive layer 12.

[0083] The non-thermoplastic polyimide layer 11 and the adhesive layer 12 each contain a tertiary amine used as a catalyst at a content of, for example, 1 ppm by mass or more and 1000 ppm by mass or less.

[0084] <Second embodiment: Method for producing multilayer polyimide film> Next, a multilayer polyimide film according to a second embodiment of the present invention will be described. The multilayer polyimide film according to the second embodiment has a non-thermoplastic polyimide layer and a polyimide-containing adhesive layer disposed on at least one side of the non-thermoplastic polyimide layer. The adhesive layer has a 5% weight loss temperature of 570°C or higher and a storage modulus at 360°C of 100 MPa or lower. The polyimide contained in the adhesive layer has one or more tetracarboxylic dianhydride residues selected from the group consisting of PMDA residues and BPDA residues, and one or more diamine residues selected from the group consisting of TPE-R residues and PDA residues. By having the above-mentioned configuration, the multilayer polyimide film according to the second embodiment can improve heat resistance while maintaining adhesion properties to a metal layer, and also has excellent productivity.

[0085] The multilayer polyimide film according to the second embodiment can be produced by the method for producing a multilayer polyimide film according to the first embodiment described above. Therefore, in the following description, the same content as in the first embodiment may be omitted. The following description will focus on the differences from the first embodiment.

[0086] In the multilayer polyimide film according to the second embodiment, the thermoplastic polyimide layer preferably contains one or more tetracarboxylic dianhydride residues selected from the group consisting of PMDA residues and BPDA residues, and one or more diamine residues selected from the group consisting of PDA residues and PDA residues.

[0087] In the multilayer polyimide film according to the second embodiment, the adhesive layer is not particularly limited as long as it satisfies the following conditions A and B. Condition A: The 5% weight loss temperature is 570°C or higher and the storage modulus at 360°C is 100 MPa or lower. Condition B: The polyimide contained in the adhesive layer has one or more tetracarboxylic dianhydride residues selected from the group consisting of PMDA residues and BPDA residues, and one or more diamine residues selected from the group consisting of TPE-R residues and PDA residues.

[0088] However, in the second embodiment, in order to easily obtain an adhesive layer that satisfies the above condition A, the adhesive layer preferably contains a PMDA residue, a BPDA residue, a TPE-R residue, and a PDA residue.

[0089] In the second embodiment, the preferred content of each of the residues listed above and the type of any residue other than the residues listed above are the same as the preferred content of each of the residues of polyamic acid and the type of any residue of polyamic acid in the first embodiment.

[0090] Other aspects of the second embodiment are the same as those described above in the section <Multilayer polyimide film obtained by the production method according to the first embodiment>.

[0091] <Third embodiment: metal-clad laminate> Next, a metal-clad laminate according to a third embodiment of the present invention will be described with reference to the drawings. The metal-clad laminate according to the third embodiment has the multilayer polyimide film according to the second embodiment and a metal layer disposed on the main surface of at least one adhesive layer of the multilayer polyimide film. The metal-clad laminate according to the third embodiment can be manufactured using the multilayer polyimide film according to the second embodiment as a material. Therefore, in the following description, the description of the same content as in the first and second embodiments may be omitted.

[0092] Fig. 2 is a cross-sectional view showing an example of a metal-clad laminate according to embodiment 3. As shown in Fig. 2, a metal-clad laminate 20 includes a multilayer polyimide film 10 and a metal layer 13 (metal foil) disposed on a main surface 12a of an adhesive layer 12 of the multilayer polyimide film 10.

[0093] [Method for manufacturing a metal-clad laminate according to the third embodiment] When manufacturing a metal-clad laminate 20 using a multilayer polyimide film 10, a metal foil that will become the metal layer 13 is laminated to at least one surface of the multilayer polyimide film 10 (for example, in the case of FIG. 2, the main surface 12a of the adhesive layer 12 opposite the non-thermoplastic polyimide layer 11). This results in the metal-clad laminate 20 shown in FIG. 2. The method for laminating the metal foil to the main surface 12a of the adhesive layer 12 is not particularly limited, and various known methods can be used. For example, a continuous processing method using a hot roll laminator having one or more pairs of metal rolls or a double belt press (DBP) can be used. The specific configuration of the means for performing hot roll lamination is not particularly limited, but it is preferable to place a protective material between the pressure surface and the metal foil to improve the appearance of the resulting metal-clad laminate 20.

[0094] When adhesive layers 12 are provided on both sides of the non-thermoplastic polyimide layer 11, a double-sided metal-clad laminate (not shown) can be obtained by laminating metal foil to both sides (both main surfaces) of the multilayer polyimide film 10.

[0095] The metal foil to be used for the metal layer 13 is not particularly limited, and any metal foil can be used. For example, metal foils made of copper, stainless steel, nickel, aluminum, alloys of these metals, etc. are preferably used. Furthermore, copper foils such as rolled copper foils and electrolytic copper foils are often used in general metal-clad laminates, and copper foils are also preferably used in the third embodiment.

[0096] Furthermore, the metal foil may be subjected to a surface treatment or the like to adjust the surface roughness, etc., depending on the purpose. Furthermore, an anti-rust layer, a heat-resistant layer, an adhesive layer, etc. may be formed on the surface of the metal foil. The thickness of the metal foil is not particularly limited, and may be any thickness that can fully demonstrate its functionality depending on the application. To easily achieve a thinner FPC while suppressing the occurrence of wrinkles when bonding to the multilayer polyimide film 10, the thickness of the metal foil is preferably 5 μm or more and 50 μm or less. [Example]

[0097] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0098] <Methods for measuring and evaluating physical properties> [Film forming property] An imidization accelerator consisting of acetic anhydride / isoquinoline / DMF (weight ratio: acetic anhydride / isoquinoline / DMF = 3.0 / 1.2 / 4.4) was added to a polyamic acid solution (more specifically, polyamic acid solution P17 described below) to obtain a solution for forming an adhesive layer. The amount of imidization accelerator added was 50 parts by weight per 100 parts by weight of the polyamic acid solution. The resulting solution for forming an adhesive layer was extruded through a T-die of a film-forming device while stirring with a mixer and cast onto a stainless steel endless belt to form a coating film. The resulting coating film was dried at a temperature of 130°C for 100 seconds, and then the resulting gel film was peeled off from the endless belt and fixed to a tenter clip. The gel film was then heated at a temperature of 250°C for 17 seconds, followed by heating at a temperature of 300°C for 137 seconds to imidize the polyamic acid in the gel film. In this imidization process, if a single layer film consisting of an adhesive layer with a thickness of 17 μm was obtained, it was judged as "film-forming possible," and if problems such as wrinkles or cracks occurred and film formation was not possible, it was judged as "film-forming impossible."

[0099] [Thermal decomposition temperature of adhesive layer] Using a measurement sample (mass: 10 mg) sampled from the adhesive layer of the multilayer polyimide film obtained in the Examples and Comparative Examples described below, the thermal decomposition temperature was measured in air using a differential thermal analysis / thermogravimetric simultaneous analyzer (Seiko Instruments Inc., "TG / DTA220"). Specifically, the measurement sample was placed in a platinum dish (a platinum container), and the platinum dish was set in the measurement section of the differential thermal analysis / thermogravimetric simultaneous analyzer. An empty platinum dish was used as a reference. The ambient temperature was then increased from 0°C to 120°C at a rate of 20°C / min, held for 10 minutes, and dried. The temperature was then increased to 1000°C at a rate of 20°C / min. The maximum value after drying was defined as 100%, and the temperature at which a 5% weight loss was reached was defined as the 5% weight loss temperature.

[0100] [Storage modulus of adhesive layer (E')] A monolayer film obtained by the same procedure as the monolayer film obtained in the evaluation of [Film Formability] above was used as a measurement sample, and E' was measured using a dynamic viscoelasticity measuring device (Hitachi High-Tech Science Corporation, "DM6100"). Specifically, the dynamic viscoelasticity of the sample was measured in an air atmosphere using the dynamic viscoelasticity measuring device, and a graph was created in which E' was plotted against the measurement temperature, and E' at a temperature of 360°C was read from the graph. The measurement conditions are shown below. Sample width: 9 mm Sample holder (gripper) spacing: 20 mm Measurement temperature range: 0℃~440℃ Heating rate: 3°C / min Strain amplitude: 10 μm Measurement frequency: 5Hz Minimum tension / compression force: 100mN Tension / Compression Gain: 1.5 Initial force amplitude: 100 mN

[0101] [Tertiary amine content] Using measurement samples (mass: 0.5 mg) taken from each layer (specifically, adhesive layer and non-thermoplastic polyimide layer) of the multilayer polyimide films obtained in the examples and comparative examples described below, the tertiary amine content of each layer was measured at a heating temperature of 350°C using a pyrolysis gas chromatograph / mass spectrometer (Agilent Technologies, Inc., "Py-GC / MS").

[0102] [Melting temperature and heat of fusion of adhesive layer] Using a measurement sample (mass: 8 mg) sampled from the adhesive layer of the multilayer polyimide film obtained in the Examples and Comparative Examples described below, the melting temperature and heat of fusion were measured using a differential scanning calorimeter (Seiko Instruments Inc., "DSC220"). Specifically, the measurement sample was placed in an aluminum dish (aluminum container), and the aluminum dish was set in the measurement section of the differential scanning calorimeter. An empty aluminum dish was used as a reference. The ambient temperature was then increased from 0°C to 450°C at a heating rate of 10°C / min, and then decreased from 450°C to 0°C at a heating rate of 40°C / min. The sample was then again increased from 0°C to 450°C at a heating rate of 10°C / min. The peak temperature of the endothermic chart during the second heating was taken as the melting temperature. The heat of fusion (unit: J / g) was calculated from the area of ​​the peak in the endothermic chart. In addition, if there is no melting peak in the temperature range of 100°C or higher and 420°C or lower in the endothermic chart, that is, if the adhesive layer being measured does not have a melting peak in the temperature range of 100°C or higher and 420°C or lower, the heat of fusion was taken to be 0 J / g.

[0103] A 12 μm-thick rolled copper foil (BHY-82F-HA-V2 manufactured by JX Nippon Mining & Metals) was placed on both sides of a multilayer polyimide film (one of the multilayer polyimide films obtained in the Examples and Comparative Examples described below). Each rolled copper foil was then covered with a protective film (Apical® 125NPI manufactured by Kaneka Corporation, 125 μm thick). The laminate was then laminated using a hot roll laminator at a lamination temperature of 360°C, a lamination pressure of 314 N / cm (32 kgf / cm), and a lamination speed of 1.0 m / min to obtain a flexible copper-clad laminate. The resulting flexible copper-clad laminate was analyzed according to JIS C 6471-1995, Section 6.5, Peel Strength. Specifically, one electrodeposited copper foil of each flexible copper-clad laminate was peeled off at a peel angle of 90°, a pulling speed of 100 mm / min, and a measurement width of 3 mm, and the load (unit: N / cm) was taken as the adhesion strength. When the adhesion strength was 10 N / cm or more, it was evaluated as "excellent adhesion." On the other hand, when the adhesion strength was less than 10 N / cm, it was evaluated as "poor adhesion."

[0104] [Embeddability] The copper foil of a flexible copper-clad laminate obtained using the same procedure as the flexible copper-clad laminate obtained in the above-mentioned [Adhesion] evaluation was completely removed by etching. The exposed surface of the multilayer polyimide film was then observed using an optical microscope at 20x magnification. If the matte side of the copper foil was uniformly transferred to the surface of the multilayer polyimide film, it was evaluated as "Good (excellent embeddability)." On the other hand, if the matte side of the copper foil was not uniformly transferred to the surface of the multilayer polyimide film, it was evaluated as "Poor (poor embeddability)."

[0105] When the adhesion strength was 10 N / cm or more and the embeddability was evaluated as ◯, the adhesive layer was evaluated as "securing adhesion properties with the metal layer." On the other hand, when the adhesion strength was less than 10 N / cm or the embeddability was evaluated as ×, the adhesive layer was evaluated as "not securing adhesion properties with the metal layer."

[0106] <Preparation of polyamic acid solution> The methods for preparing the polyamic acid solutions P1 to P17 are described below. The preparation of the polyamic acid solutions P1 to P17 was carried out at a temperature of 20° C. in a nitrogen atmosphere.

[0107] [Preparation of polyamic acid solution P1] A reactor was charged with 1509.66 kg of DMF, 126.18 kg of TPE-R, and 2.46 kg of PDA, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, 93.61 kg of BPDA and 26.77 kg of PMDA were charged, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, a pre-prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 2.97 kg, PMDA concentration: 7.2 wt%) was added to the reactor for a predetermined time at a rate that did not cause a sudden increase in the viscosity of the reactor contents. When the viscosity of the reactor contents at 23°C reached 1000 poise, the addition of the PMDA solution and the stirring of the reactor contents were stopped, yielding polyamic acid solution P1.

[0108] [Preparation of polyamic acid solution P2] A reactor was charged with 1504.62 kg of DMF, 90.17 kg of TPE-R, and 22.25 kg of PDA, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, 105.92 kg of BPDA and 30.29 kg of PMDA were charged, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, a pre-prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 3.37 kg, PMDA concentration: 7.2 wt%) was added to the reactor for a predetermined time at a rate that did not cause a sudden increase in the viscosity of the reactor contents. When the viscosity of the reactor contents at 23°C reached 1000 poise, the addition of the PMDA solution and stirring of the reactor contents were stopped, yielding polyamic acid solution P2.

[0109] [Preparation of polyamic acid solution P3] A reactor was charged with 1506.19 kg of DMF, 101.39 kg of TPE-R, and 16.08 kg of PDA, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, 102.09 kg of BPDA and 29.19 kg of PMDA were charged, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, a pre-prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 3.24 kg, PMDA concentration: 7.2 wt%) was added to the reactor for a predetermined time at a rate that did not cause a sudden increase in the viscosity of the reactor contents. When the viscosity of the reactor contents at 23°C reached 1000 poise, the addition of the PMDA solution and the stirring of the reactor contents were stopped, yielding polyamic acid solution P3.

[0110] [Preparation of polyamic acid solution P4] A reactor was charged with 1507.65 kg of DMF, 111.83 kg of TPE-R, and 10.35 kg of PDA, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, 98.52 kg of BPDA and 28.17 kg of PMDA were charged, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, a pre-prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 3.13 kg, PMDA concentration: 7.2 wt%) was added to the reactor for a predetermined time at a rate that did not cause a sudden increase in the viscosity of the reactor contents. When the viscosity of the reactor contents at 23°C reached 1000 poise, the addition of the PMDA solution and stirring of the reactor contents were stopped, yielding polyamic acid solution P4.

[0111] [Preparation of polyamic acid solution P5] A reactor was charged with 1509.02 kg of DMF, 121.56 kg of TPE-R, and 5.00 kg of PDA, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, 95.19 kg of BPDA and 27.22 kg of PMDA were charged, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, a pre-prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 3.02 kg, PMDA concentration: 7.2 wt%) was added to the reactor for a predetermined time at a rate that did not cause a sudden increase in the viscosity of the reactor contents. When the viscosity of the reactor contents at 23°C reached 1000 poise, the addition of the PMDA solution and stirring of the reactor contents were stopped, yielding polyamic acid solution P5.

[0112] [Preparation of polyamic acid solution P6] 1510.29 kg of DMF and 130.66 kg of TPE-R were added to the reactor, and the contents were stirred for 30 minutes. Next, while stirring the contents, 92.09 kg of BPDA and 26.33 kg of PMDA were added to the reactor, and the contents were stirred for 30 minutes. Next, while stirring the contents, a pre-prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 2.93 kg, PMDA concentration: 7.2 wt%) was added to the reactor for a predetermined time at an addition rate that did not cause a sudden increase in the viscosity of the reactor contents. When the viscosity of the reactor contents at 23°C reached 1000 poise, the addition of the PMDA solution and the stirring of the reactor contents were stopped, yielding polyamic acid solution P6.

[0113] [Preparation of polyamic acid solution P7] A reactor was charged with 1505.57 kg of DMF, 88.26 kg of TPE-R, and 21.76 kg of PDA, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, 31.22 kg of ODPA, 88.82 kg of BPDA, and 18.66 kg of PMDA were charged, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, a pre-prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 3.29 kg, PMDA concentration: 7.2 wt%) was added to the reactor for a predetermined time at an addition rate that did not cause a sudden increase in the viscosity of the reactor contents. When the viscosity of the reactor contents at 23°C reached 1000 poise, the addition of the PMDA solution and the stirring of the reactor contents were stopped, yielding polyamic acid solution P7.

[0114] [Preparation of polyamic acid solution P8] A reactor was charged with 1505.10 kg of DMF, 89.22 kg of TPE-R, and 22.00 kg of PDA, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, 15.78 kg of ODPA, 97.27 kg of BPDA, and 24.41 kg of PMDA were charged to the reactor, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, a pre-prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 3.33 kg, PMDA concentration: 7.2 wt%) was added to the reactor for a predetermined time at an addition rate that did not cause a sudden increase in the viscosity of the reactor contents. When the viscosity of the reactor contents at 23°C reached 1000 poise, the addition of the PMDA solution and the stirring of the reactor contents were stopped, yielding polyamic acid solution P8.

[0115] [Preparation of polyamic acid solution P9] A reactor was charged with 1503.95 kg of DMF, 76.35 kg of TPE-R, and 28.24 kg of PDA, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, 32.41 kg of ODPA, 92.21 kg of BPDA, and 19.37 kg of PMDA were charged, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, a pre-prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 3.42 kg, PMDA concentration: 7.2 wt%) was added to the reactor for a predetermined time at a rate that did not cause a sudden increase in the viscosity of the reactor contents. When the viscosity of the reactor contents at 23°C reached 1000 poise, the addition of the PMDA solution and stirring of the reactor contents were stopped, yielding polyamic acid solution P9.

[0116] [Preparation of polyamic acid solution P10] A reactor was charged with 1507.32 kg of DMF, 98.70 kg of TPE-R, and 15.65 kg of PDA, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, 59.85 kg of ODPA, 56.76 kg of BPDA, and 17.88 kg of PMDA were charged, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, a pre-prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 3.16 kg, PMDA concentration: 7.2 wt%) was added to the reactor for a predetermined time at a rate that did not cause a sudden increase in the viscosity of the reactor contents. When the viscosity of the reactor contents at 23°C reached 1000 poise, the addition of the PMDA solution and stirring of the reactor contents were stopped, yielding polyamic acid solution P10.

[0117] [Preparation of polyamic acid solution P11] A reactor was charged with 1502.94 kg of DMF, 78.10 kg of TPE-R, and 28.89 kg of PDA, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, 110.04 kg of BPDA and 31.47 kg of PMDA were charged, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, a pre-prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 3.50 kg, PMDA concentration: 7.2 wt%) was added to the reactor for a predetermined time at an addition rate that did not cause a sudden increase in the viscosity of the reactor contents. When the viscosity of the reactor contents at 23°C reached 1000 poise, the addition of the PMDA solution and stirring of the reactor contents were stopped, yielding polyamic acid solution P11.

[0118] [Preparation of polyamic acid solution P12] A reactor was charged with 1506.29 kg of DMF, 92.53 kg of TPE-R, and 19.25 kg of PDA, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, 58.30 kg of ODPA, 58.20 kg of BPDA, and 20.49 kg of PMDA were charged, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, a pre-prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 3.24 kg, PMDA concentration: 7.2 wt%) was added to the reactor for a predetermined time at a rate that did not cause a sudden increase in the viscosity of the reactor contents. When the viscosity of the reactor contents at 23°C reached 1000 poise, the addition of the PMDA solution and the stirring of the reactor contents were stopped, yielding polyamic acid solution P12.

[0119] [Preparation of polyamic acid solution P13] A reactor was charged with 1514.79 kg of DMF and 161.63 kg of 2,2-bis[4-(4-aminophenoxy)phenyl]propane (hereinafter sometimes referred to as "BAPP"), and the contents of the reactor were stirred for 30 minutes. Next, while stirring the contents of the reactor, 17.38 kg of BPDA and 70.42 kg of PMDA were charged, and the contents of the reactor were stirred for 30 minutes. Next, while stirring the contents of the reactor, a previously prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 2.58 kg, PMDA concentration: 7.2 wt%) was added to the reactor for a predetermined time at an addition rate that did not cause a sudden increase in the viscosity of the reactor contents. When the viscosity of the reactor contents at 23°C reached 1000 poise, the addition of the PMDA solution and the stirring of the reactor contents were stopped, yielding polyamic acid solution P13.

[0120] [Preparation of polyamic acid solution P14] 1499.13 kg of DMF and 125.60 kg of TPE-R were added to the reactor, and the contents were stirred for 30 minutes. Next, 122.61 kg of BPDA was added to the reactor while stirring the contents, and the contents were stirred for 30 minutes. Next, while stirring the contents, a previously prepared BPDA solution (solvent: DMF, dissolved amount of BPDA: 3.79 kg, BPDA concentration: 3.0 wt%) was added to the reactor for a predetermined time at an addition rate that did not cause a sudden increase in the viscosity of the reactor contents. When the viscosity of the reactor contents at 23°C reached 1000 poise, the addition of the BPDA solution and the stirring of the reactor contents were stopped, yielding polyamic acid solution P14.

[0121] [Preparation of polyamic acid solution P15] 1497.84 kg of DMF and 122.26 kg of TPE-R were added to the reactor, and the contents were stirred for 30 minutes. Next, 125.84 kg of ODPA was added to the reactor while stirring the contents, and the contents were stirred for 30 minutes. Next, while stirring the contents, a previously prepared ODPA solution (solvent: DMF, dissolved amount of ODPA: 3.89 kg, ODPA concentration: 7.2 wt%) was added to the reactor for a predetermined time at an addition rate that did not cause a sudden increase in the viscosity of the reactor contents. When the viscosity of the reactor contents at 23°C reached 1000 poise, the addition of the ODPA solution and the stirring of the reactor contents were stopped, yielding polyamic acid solution P15.

[0122] [Preparation of polyamic acid solution P16] A reaction vessel was charged with 1,498.06 kg of DMF, 43.28 kg of TPE-R, and 48.02 kg of PDA, and the contents were stirred for 30 minutes. Next, while stirring the contents, 121.95 kg of BPDA and 34.87 kg of PMDA were charged, and the contents were stirred for 30 minutes. Next, while stirring the contents, a pre-prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 3.87 kg, PMDA concentration: 7.2 wt%) was added to the reaction vessel for a predetermined period of time at a rate that prevented a sudden increase in the viscosity of the reaction vessel contents. When the viscosity of the reaction vessel contents at 23°C reached 1,000 poise, the addition of the PMDA solution and the stirring of the reaction vessel contents were stopped, yielding polyamic acid solution P16.

[0123] [Preparation of polyamic acid solution P17] A reactor was charged with 1477.67 kg of DMF, 37.27 kg of 4,4'-diaminodiphenyl ether (hereinafter referred to as "ODA"), and 50.94 kg of BAPP, and the contents of the reactor were then stirred. After visually confirming that the monomers had dissolved, 39.98 kg of 3,3',4,4'-benzophenonetetracarboxylic dianhydride (hereinafter referred to as "BTDA") and 33.83 kg of PMDA were added to the reactor while stirring the contents of the reactor, and the reactor contents were stirred for 30 minutes. Next, 33.55 kg of PDA was added to the reactor while stirring the contents of the reactor, followed by 70.37 kg of PMDA, and the reactor contents were stirred for 30 minutes. Next, while stirring the contents of the reaction vessel, a previously prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 4.06 kg, PMDA concentration: 7.2 wt%) was added to the reaction vessel for a predetermined time at an addition rate that did not cause a sudden increase in the viscosity of the reaction vessel content. When the viscosity of the reaction vessel content at a temperature of 23°C reached 2000 poise, the addition of the PMDA solution and stirring of the reaction vessel content were stopped, yielding polyamic acid solution P17.

[0124] The polyimide obtained from the polyamic acid in the resulting polyamic acid solution P17 was confirmed to be non-thermoplastic by the following method. First, 40 parts by weight of an imidization accelerator consisting of acetic anhydride / isoquinoline / DMF (weight ratio: acetic anhydride / isoquinoline / DMF = 101 / 51 / 48) was added to 100 parts by weight of the polyamic acid solution P17 to prepare a solution for forming a non-thermoplastic polyimide layer. Next, while stirring with a mixer, the resulting solution for forming a non-thermoplastic polyimide layer was extruded through a T-die of a film-forming device and cast onto a stainless steel endless belt to form a coating film. The resulting coating film was dried at a temperature of 120°C for 400 seconds to obtain a gel film. This gel film was peeled from the stainless steel endless belt, and then both longitudinal ends were pinned and heated at 170°C for 21 seconds, 350°C for 19 seconds, and 380°C for 16 seconds, followed by heating at a maximum temperature of 400°C for 49 seconds to imidize the polyamic acid in the gel film, yielding a 17 μm-thick polyimide film. The resulting polyimide film was fixed to a metal frame and heated at 420°C for 2 minutes, whereupon the shape of the polyimide film was maintained. Therefore, the polyimide obtained from the polyamic acid in polyamic acid solution P17 was a non-thermoplastic polyimide.

[0125] Table 1 shows the materials used in each of the polyamic acid solutions P1 to P17 and their proportions. The molar fraction of each residue in the polyamic acid contained in each of the polyamic acid solutions P1 to P13 was consistent with the molar fraction of each monomer (diamine and tetracarboxylic dianhydride) used. Table 2 shows the results of measurement and evaluation of the monolayer films obtained using each of the polyamic acid solutions P1 to P17 using the above-mentioned method. In Table 1, "-" indicates that the corresponding component was not used. In Table 1, the values ​​in the "Acid Dianhydride" column are the content (unit: mol%) of each acid dianhydride relative to the total amount of acid dianhydrides used. In Table 1, the values ​​in the "Diamine" column are the content (unit: mol%) of each diamine relative to the total amount of diamines used. In Table 2, "-" indicates that measurement was not performed.

[0126] [Table 1]

[0127] [Table 2]

[0128] <Preparation of multilayer polyimide film> The methods for producing the multilayer polyimide films of Examples 1 to 11 and Comparative Examples 1 to 5 will be described below.

[0129] [Example 1]

[0130] A mixture of 142 kg of DMF, 155 kg of isoquinoline, and 303 kg of acetic anhydride was prepared as an imidization accelerator. This imidization accelerator was added to polyamic acid solution P17, and the mixture was stirred with a mixer to obtain a solution for forming a non-thermoplastic polyimide layer. The amount of imidization accelerator added was 40 parts by weight per 100 parts by weight of polyamic acid solution P17. Polyamic acid solution P1 was also prepared as a solution for forming an adhesive layer.

[0131] Next, using an extruder with a three-layer extrusion die, the non-thermoplastic polyimide layer-forming solution and the adhesive layer-forming solution were applied onto a stainless steel endless belt support by a co-extrusion-casting coating method. Specifically, the non-thermoplastic polyimide layer-forming solution was first supplied to the central layer of the extrusion die, and the adhesive layer-forming solution was supplied to the two layers adjacent (on both sides) to the central layer of the extrusion die. The non-thermoplastic polyimide layer-forming solution and the adhesive layer-forming solution were then extruded from the lip opening of the extrusion die by a co-extrusion-casting coating method to form a coating film (a coating film consisting of three layers: adhesive layer-forming solution / non-thermoplastic polyimide layer-forming solution / adhesive layer-forming solution) on the stainless steel endless belt. The resulting coating film was dried on the stainless steel endless belt at 120°C for 400 seconds to obtain a gel film. This gel film was peeled off from the stainless steel endless belt, and then both longitudinal ends were fixed with pins and heated at 170°C for 21 seconds, 350°C for 19 seconds, and 380°C for 16 seconds, and then heated at a temperature (maximum temperature) of 400°C for 49 seconds to imidize the polyamic acid in the non-thermoplastic polyimide layer-forming solution and the polyamic acid in the adhesive layer-forming solution, thereby obtaining the multilayer polyimide film of Example 1. The multilayer polyimide film of Example 1 had a three-layer structure of adhesive layer / non-thermoplastic polyimide layer / adhesive layer, with the thicknesses of the adhesive layer / non-thermoplastic polyimide layer / adhesive layer being 4 μm / 17 μm / 4 μm.

[0132] Furthermore, for the multilayer polyimide film of Example 1, measurement samples (mass: 0.5 mg) taken from each of the adhesive layer and the non-thermoplastic polyimide layer were used to measure the tertiary amine (isoquinoline) content of each layer by the method described above. Isoquinoline was detected at a content of 1 ppm by mass or more in both the adhesive layer and the non-thermoplastic polyimide layer. For Examples 2 to 11 and Comparative Examples 1 to 5 described below, the tertiary amine (isoquinoline) content of each layer was measured by the same method as in Example 1, and isoquinoline was detected at a content of 1 ppm by mass or more in both the adhesive layer and the non-thermoplastic polyimide layer.

[0133] [Examples 2 to 11 and Comparative Examples 1 to 5] The multilayer polyimide films of Examples 2 to 5 and Comparative Examples 1 to 5 were obtained in the same manner as in Example 1 above, except that the types of polyamic acid solutions used to prepare the non-thermoplastic polyimide layer-forming solution and the polyamic acid solutions used as the adhesive layer-forming solution were as shown in Table 3 below.

[0134] <Evaluation results> Table 3 shows the type of polyamic acid solution used to prepare the non-thermoplastic polyimide layer-forming solution, the type of polyamic acid solution used as the adhesive layer-forming solution, and the heat of fusion of the adhesive layer for Examples 1 to 11 and Comparative Examples 1 to 5. Table 4 also shows the peel strength and embeddability for Examples 1 to 11 and Comparative Examples 1 to 5. In Table 3, "non-thermoplastic solution" refers to the polyamic acid solution used to prepare the non-thermoplastic polyimide layer-forming solution. In Table 3, "adhesive solution" refers to the polyamic acid solution used as the adhesive layer-forming solution. In Table 3, "no peak" means that there was no melting peak in the temperature range of 100°C or higher and 420°C or lower.

[0135] [Table 3]

[0136] [Table 4]

[0137] The polyamic acid contained in the adhesive layer-forming solution used to prepare the multilayer polyimide films of Examples 1 to 11 contained PMDA residues, BPDA residues, TPE-R residues, and PDA residues. The adhesive layers of the multilayer polyimide films of Examples 1 to 11 did not have a melting peak in the temperature range of 100°C or higher and 420°C or lower.

[0138] The multilayer polyimide films of Examples 1 to 11 had a peel strength of 10 N / cm or more. Therefore, the multilayer polyimide films of Examples 1 to 11 had excellent adhesion. The multilayer polyimide films of Examples 1 to 11 were evaluated as having good embeddability. Therefore, the multilayer polyimide films of Examples 1 to 11 had excellent embeddability.

[0139] The polyamic acid contained in the adhesive layer-forming solution used to prepare the multilayer polyimide film of Comparative Example 1 contained a PDA residue, but the storage modulus at 360°C was unobservable due to melting. The polyamic acid contained in the adhesive layer-forming solution used to prepare the multilayer polyimide films of Comparative Examples 2 to 4 did not contain a PDA residue. The adhesive layers of the multilayer polyimide films of Comparative Examples 2 to 4 had observed heats of fusion at their melting peaks.

[0140] The multilayer polyimide film of Comparative Example 5 had a peel strength of less than 10 N / cm. Therefore, the multilayer polyimide film of Comparative Example 5 did not have excellent adhesion. The multilayer polyimide film of Comparative Example 5 was evaluated as poor in embeddability. Therefore, it was found that an excessive increase in the amount of PDA results in a polyimide with impaired plasticity.

[0141] The above results demonstrate that the present invention can provide a multilayer polyimide film and a method for producing the same that can reduce the dielectric tangent while maintaining adhesion properties to a metal layer. [Explanation of symbols]

[0142] 10: Multilayer polyimide film 11: Non-thermoplastic polyimide layer 12: Adhesive layer 13: Metal layer 20:Metal clad laminate

Claims

1. A multilayer polyimide film having a non-thermoplastic polyimide layer and an adhesive layer containing a polyimide disposed on at least one surface of the non-thermoplastic polyimide layer, wherein the adhesive layer has a 5% thermogravimetric decomposition temperature of 570°C or higher and a storage modulus at 360°C of 100 MPa or lower, and the polyimide contained in the adhesive layer has one or more tetracarboxylic dianhydride residues selected from the group consisting of pyromellitic dianhydride residues and 3,3',4,4'-biphenyltetracarboxylic dianhydride residues, and one or more diamine residues selected from the group consisting of 1,3-bis(4-aminophenoxy)benzene residues and p-phenylenediamine residues.

2. 2. The multilayer polyimide film according to claim 1, wherein the adhesive layer is disposed on both sides of the non-thermoplastic polyimide layer.

3. The multilayer polyimide film according to claim 1 , wherein the adhesive layer contains a tertiary amine in an amount of 1 ppm by mass or more.

4. 2. The multilayer polyimide film according to claim 1, wherein the non-thermoplastic polyimide layer contains a tertiary amine in an amount of 1 ppm by mass or more.

5. 2. The multilayer polyimide film according to claim 1, wherein the adhesive layer does not have a melting peak in the temperature range of 100°C or higher and 420°C or lower.

6. 2. The multilayer polyimide film according to claim 1, wherein the polyimide structure contained in the adhesive layer has an oxygen concentration per polymer structural unit of 18 mol % or more.

7. A metal-clad laminate comprising the multilayer polyimide film according to any one of claims 1 to 6 and a metal layer disposed on at least one main surface of the adhesive layer of the multilayer polyimide film.

8. A method for producing a multilayer polyimide film having a non-thermoplastic polyimide layer and an adhesive layer containing polyimide disposed on at least one surface of the non-thermoplastic polyimide layer, the method comprising the steps of: applying an adhesive layer-forming solution containing polyamic acid onto a support by a co-extrusion-casting coating method; drying the coated film obtained in the coating step to form a gel film having self-supporting properties; and heating the gel film obtained in the gel film-forming step under conditions of a maximum temperature of 360°C or higher to form the non-thermoplastic polyimide layer-forming solution. and an imidization step of imidizing the polyamic acid in the liquid and the polyamic acid in the adhesive layer-forming solution, wherein in the coating step, the polyamic acid contained in the adhesive layer-forming solution has pyromellitic dianhydride residues, 3,3',4,4'-biphenyltetracarboxylic dianhydride residues, 1,3-bis(4-aminophenoxy)benzene residues, and p-phenylenediamine residues, and the adhesive layer has a 5% thermogravimetric decomposition temperature of 570°C or higher and a storage modulus at 360°C of 100 MPa or lower.

9. The method for producing a multilayer polyimide film according to claim 8, wherein the adhesive layer does not have a melting peak in a temperature range of 100°C or higher and 420°C or lower.

10. 10. The method for producing a multilayer polyimide film according to claim 8, wherein the adhesive layer has a structure in which the oxygen concentration per polymer structural unit is 18 mol% or more.

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