Non-thermoplastic polyimide film, multilayer polyimide film, and metal-clad laminate

Abstract

To provide a non-thermoplastic polyimide film capable of reducing the dielectric loss tangent, and a multi-layer polyimide film and a metal-clad laminate using the non-thermoplastic polyimide film.SOLUTION: There is provided a non-thermoplastic polyimide film comprising a non-thermoplastic polyimide, wherein the non-thermoplastic polyimide has a 3,3',4,4'-biphenyltetracarboxylic anhydride residue and a 4,4'-oxydiphthalic anhydride residue as a tetracarboxylic dianhydride residue and has a p-phenylenediamine residue as a diamine residue and at least one diamine component selected from a 1,3-bis(3-aminophenoxy)benzene residue, a 1,4-bis(4-aminophenoxy)benzene residue and 4,4'-diamino-2,2'-dimethylbiphenyl.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a non-thermoplastic polyimide film, a multilayer polyimide film, and a metal-clad laminate.

Background Art

[0002] In recent years, with the expansion of demand for electronic products centered around smartphones, tablet computers, notebook computers, etc., the demand for flexible printed wiring boards (hereinafter sometimes referred to as "FPC") has been growing. Among them, an FPC using a multilayer polyimide film having a non-thermoplastic polyimide layer (core layer) and a thermoplastic polyimide layer (adhesive layer) as a material is expected to further grow in demand because of its excellent heat resistance and flexibility. In addition, polyimide has sufficient heat resistance to withstand high-temperature processes and a relatively small coefficient of linear expansion, so internal stress is unlikely to occur, making it suitable as a material for FPC.

[0003] In addition, with the high-speed signal transmission of recent electronic devices, there has been an increasing demand for reducing the dielectric constant and dielectric tangent of electronic substrate materials in order to achieve high-frequency electrical signals propagating through circuits. To suppress the transmission loss of electrical signals, it is effective to lower the dielectric constant and dielectric tangent of the electronic substrate material. In recent years, which is the dawn of the IoT society, the trend of high-frequencyization has been advancing, and there is a demand for a substrate material that can suppress transmission loss even in a region of 10 GHz or higher.

[0004] By the way, transmission loss is expressed by the following formula using a proportionality constant (k), frequency (f), dielectric tangent (Df), and relative dielectric constant (Dk), and the contribution to transmission loss is greater for the dielectric tangent than for the relative dielectric constant. Therefore, in order to reduce transmission loss, it is particularly important to lower the dielectric tangent.

[0005] Transmission loss = k × f × Df × (Dk)1 / 2 As a material used for a circuit board adaptable to high-frequencyization, a polyimide film (polyimide layer) that exhibits a low dielectric tangent is known (see, for example, Patent Documents 1 to 4). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Special Publication No. 2014-526399 [Patent Document 2] Japanese Patent Publication No. 2009-246201 [Patent Document 3] International Publication No. 2018 / 079710 [Patent Document 4] International Publication No. 2016 / 159060 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the technologies described in Patent Documents 1 to 4 still have room for improvement in reducing the dielectric loss tangent. The present invention has been made in view of the above issue, and its object is to provide a non-thermoplastic polyimide film that can reduce the dielectric loss tangent, as well as a multilayer polyimide film and a metal-clad laminate using the non-thermoplastic polyimide film. [Means for solving the problem]

[0008] In light of the above situation, the inventors conducted diligent research and found that the above problem can be addressed by the following configuration.

[0009] 1) A non-thermoplastic polyimide film comprising a non-thermoplastic polyimide, wherein the non-thermoplastic polyimide has a 3,3',4,4'-biphenyltetracarboxylic acid dianhydride residue and a 4,4'-oxydiphthalic acid anhydride residue as tetracarboxylic acid dianhydride residues, and has a p-phenylenediamine residue and at least one diamine component selected from a 1,3-bis(3-aminophenoxy)benzene residue, a 1,4-bis(4-aminophenoxy)benzene residue, and a 4,4'-diamino-2,2'-dimethylbiphenyl residue as a diamine residue.

[0010] 2) The non-thermoplastic polyimide film according to 1), wherein the total content of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride residues and 4,4'-oxydiphthalic acid anhydride residues relative to all tetracarboxylic acid dianhydride residues constituting the non-thermoplastic polyimide is 80 mol% or more, and the total content of p-phenylenediamine residues and at least one diamine component selected from 1,3-bis(3-aminophenoxy)benzene residues, 1,4-bis(4-aminophenoxy)benzene residues, and 4,4'-diamino-2,2'-dimethylbiphenyl relative to all diamine residues constituting the non-thermoplastic polyimide is 85 mol% or more.

[0011] 3) The non-thermoplastic polyimide film according to 1) or 2), further comprising a pyromellitic dianhydride residue as a tetracarboxylic dianhydride residue.

[0012] 4) The non-thermoplastic polyimide film according to 3), wherein the content of pyromellitic dianhydride residues relative to the total tetracarboxylic dianhydride residues constituting the non-thermoplastic polyimide is 20 mol% or less.

[0013] 5) A non-thermoplastic polyimide film according to any one of items 1) to 4), wherein the molar ratio obtained by dividing the total amount of tetracarboxylic dianhydride residues constituting the non-thermoplastic polyimide by the total amount of diamine residues constituting the non-thermoplastic polyimide is 0.95 or more and 1.05 or less.

[0014] 6). A multilayer polyimide film having a non-thermoplastic polyimide film according to any one of items 1) to 5), and an adhesive layer containing thermoplastic polyimide disposed on at least one side of the non-thermoplastic polyimide film.

[0015] 7) The multilayer polyimide film according to 6), wherein the adhesive layer is disposed on both sides of the non-thermoplastic polyimide film.

[0016] 8). A metal-clad laminate having the non-thermoplastic polyimide film according to any one of 1) to 7) and a metal layer disposed on at least one side of the non-thermoplastic polyimide film.

[0017] 9). A metal-clad laminate having the multilayer polyimide film according to 6) or 7) and a metal layer disposed on the main surface of at least one of the adhesive layers of the multilayer polyimide film.

Advantages of the Invention

[0018] According to the present invention, it is possible to provide a non-thermoplastic polyimide film capable of reducing the dielectric loss tangent, a multilayer polyimide film using the non-thermoplastic polyimide film, and a metal-clad laminate.

Modes for Carrying Out the Invention

[0019] Hereinafter, preferred embodiments of the present invention will be described in detail, but the present invention is not limited thereto. Also, all of the academic documents and patent documents described in this specification are incorporated herein by reference.

[0020] First, the terms used in this specification will be explained. "Structural unit" refers to a repeating unit that constitutes a polymer. "Polyimide" is a polymer containing a structural unit represented by the following general formula (1) (hereinafter, may be referred to as "structural unit (1)").

Chemical formula

[0021] In general formula (1), X 1 represents a tetracarboxylic dianhydride residue (a tetravalent organic group derived from a tetracarboxylic dianhydride), and X 2 represents a diamine residue (a divalent organic group derived from a diamine). Polyimide can be expressed in the form of a condensation reaction product of an acid dianhydride and a diamine compound.

[0022] The content of structural unit (1) relative to the total structural units constituting 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, even more preferably 90 mol% or more and 100 mol% or less, and may be 100 mol%.

[0023] Unless otherwise specified, the "coefficient of linear expansion" is the coefficient of linear expansion during heating from 50°C to 250°C. The method for measuring the coefficient of linear expansion is the same as or similar to that used in the examples described later.

[0024] The "relative permittivity" is the relative permittivity at a frequency of 10 GHz, a temperature of 23°C, and a relative humidity of 50%. The "dielectric loss tangent" is the dielectric loss tangent at a frequency of 10 GHz, a temperature of 23°C, and a relative humidity of 50%. The method for measuring the relative permittivity and dielectric loss tangent is the same as or similar to the method used in the examples described later.

[0025] "Non-thermoplastic polyimide" refers to polyimide that retains its film shape (flat film shape) when fixed in a metal frame in film form and heated at a temperature of 380°C for 1 minute. "Thermoplastic polyimide" refers to polyimide that does not retain its film shape when fixed in a metal frame in film form and heated at a temperature of 380°C for 1 minute.

[0026] The "main surface" of a layered material (more specifically, a non-thermoplastic polyimide film, adhesive layer, multilayer polyimide film, metal layer, etc.) refers to the surface perpendicular to the thickness direction of the layered material.

[0027] In the following, 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." Non-thermoplastic polyimides contained in non-thermoplastic polyimide films may be simply referred to as "non-thermoplastic polyimides." Thermoplastic polyimides contained in adhesive layers may be simply referred to as "thermoplastic polyimides."

[0028] <Non-thermoplastic polyimide film> The non-thermoplastic polyimide film of the present invention comprises a non-thermoplastic polyimide. The non-thermoplastic polyimide has a 3,3',4,4'-biphenyltetracarboxylic acid dianhydride residue and a 4,4'-oxydiphthalic acid anhydride residue as tetracarboxylic acid dianhydride residues, and has a p-phenylenediamine residue and at least one diamine component selected from a 1,3-bis(3-aminophenoxy)benzene residue, a 1,4-bis(4-aminophenoxy)benzene residue, and a 4,4'-diamino-2,2'-dimethylbiphenyl residue as diamine residues.

[0029] Hereafter, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride may be referred to as "BPDA," 4,4'-oxydiphthalic acid anhydride as "ODPA," pyromellitic acid dianhydride as "PMDA," p-phenylenediamine as "PDA," 1,3-bis(3-aminophenoxy)benzene as "TPE-Q," 1,4-bis(4-aminophenoxy)benzene as "TPE-M," and 4,4'-diamino-2,2'-dimethylbiphenyl as "m-TB." The details of non-thermoplastic polyimide films will be explained below.

[0030] [Non-thermoplastic polyimide] The non-thermoplastic polyimide contained in the non-thermoplastic polyimide film may have other acid dianhydride residues in addition to BPDA and ODPA residues. Examples of acid dianhydrides (monomers) for forming other acid dianhydride residues (acid dianhydride residues other than BPDA and ODPA residues) include PMDA, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, and 3,4'-oxydiphthalic acid dianhydride. Examples include aqueous solutions, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 3,4,9,10-perylenetetracarboxylic acid dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, p-phenylenebis(trimellitic acid monoester anhydride), ethylenebis(trimellitic acid monoester anhydride), bisphenol A bis(trimellitic acid monoester anhydride), and derivatives thereof.

[0031] To obtain a non-thermoplastic polyimide film that can further reduce the dielectric loss tangent, it is preferable to select one or more other acid dianhydride residues from the group consisting of PMDA residues, 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride residues, and p-phenylenebis(trimellitic acid monoester acid anhydride) residues. Furthermore, to obtain a non-thermoplastic polyimide film that can further reduce the dielectric loss tangent while improving heat resistance, it is preferable to select a PMDA residue as the other acid dianhydride residue.

[0032] To obtain a non-thermoplastic polyimide film that can further reduce the dielectric loss tangent, the total content of BPDA residues and ODPA residues relative to the total acid dianhydride residues constituting the non-thermoplastic polyimide is preferably 80 mol% or more, more preferably 85 mol% or more, more preferably 90 mol% or more, and may even be 100 mol%.

[0033] When using PMDA residues as other acid dianhydride residues, in order to obtain a non-thermoplastic polyimide film that can further reduce the dielectric loss tangent while increasing heat resistance, the total content of BPDA residues, ODPA residues, and PMDA residues relative to all acid dianhydride residues constituting the non-thermoplastic polyimide is preferably 85 mol% or more, more preferably 90 mol% or more, and may even be 100 mol%.

[0034] To obtain a non-thermoplastic polyimide film that can further reduce the dielectric loss tangent, the content of BPDA residues relative to the total acid dianhydride residues constituting the non-thermoplastic polyimide is preferably 20 mol% to 70 mol%, and more preferably 25 mol% to 65 mol%.

[0035] To obtain a non-thermoplastic polyimide film that can further reduce the dielectric loss tangent, the content of ODPA residues relative to the total acid dianhydride residues constituting the non-thermoplastic polyimide is preferably 20 mol% to 70 mol%, and more preferably 30 mol% to 60 mol%.

[0036] To obtain a non-thermoplastic polyimide film that can further reduce the dielectric loss tangent while improving heat resistance, the content of PMDA residues relative to the total acid dianhydride residues constituting the non-thermoplastic polyimide is preferably 20 mol% or less, more preferably 1 mol% to 20 mol%, and even more preferably 3 mol% to 12 mol%.

[0037] The non-thermoplastic polyimide contained in the non-thermoplastic polyimide film may have a PDA residue and at least one diamine component selected from TPE-Q residues, TPE-M residues, and m-TB residues, as well as other diamine residues. Examples of diamines (monomers) for forming other diamine residues include 1,3-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.

[0038] In order to obtain a non-thermoplastic polyimide film that can further reduce the dielectric loss tangent, the total content of PDA residues and at least one diamine component selected from TPE-Q residues, TPE-M residues, and m-TB residues relative to all diamine residues constituting the non-thermoplastic polyimide is preferably 85 mol% or more, more preferably 90 mol% or more, even more preferably 95 mol% or more, and may be 100 mol%.

[0039] To obtain a non-thermoplastic polyimide film that can further reduce the dielectric loss tangent, the content of PDA residues relative to the total diamine residues constituting the non-thermoplastic polyimide is preferably 60 mol% to 98 mol%, more preferably 70 mol% to 95 mol%, and even more preferably 80 mol% to 95 mol%.

[0040] To obtain a non-thermoplastic polyimide film that can further reduce the dielectric loss tangent, the content of at least one diamine component selected from TPE-Q residues, TPE-M residues, and m-TB residues relative to all diamine residues constituting the non-thermoplastic polyimide is preferably 2 mol% to 40 mol%, more preferably 2 mol% to 30 mol%, and even more preferably 5 mol% to 20 mol%.

[0041] To obtain a non-thermoplastic polyimide film that can further reduce the dielectric loss tangent, the molar ratio obtained by dividing the total amount of acid dianhydride residues constituting the non-thermoplastic polyimide by the total amount of diamine residues constituting the non-thermoplastic polyimide is preferably 0.95 or more and 1.05 or less, more preferably 0.97 or more and 1.03 or less, and even more preferably 0.99 or more and 1.01 or less.

[0042] The non-thermoplastic polyimide film may contain components (additives) other than non-thermoplastic polyimide. Examples of additives include dyes, surfactants, leveling agents, plasticizers, silicones, fillers, and sensitizers. The non-thermoplastic polyimide content in the non-thermoplastic polyimide film 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 amount of the non-thermoplastic polyimide film.

[0043] [Method for manufacturing non-thermoplastic polyimide film] The non-thermoplastic polyimide contained in the non-thermoplastic polyimide film is obtained by imidizing its precursor, polyamic acid.

[0044] Any known method or a combination thereof can be used to produce polyamic acid (synthesis method). When producing polyamic acid, a diamine and a tetracarboxylic dianhydride are usually reacted in an organic solvent. Preferably, the amount of diamine and the amount of tetracarboxylic dianhydride used in the reaction are substantially equal. When synthesizing polyamic acid using a diamine and a tetracarboxylic dianhydride, the desired polyamic acid (polymer of diamine and tetracarboxylic dianhydride) can be obtained by adjusting the amount of each diamine and the amount of each tetracarboxylic dianhydride. The mole fraction of each residue in the polyimide formed from the polyamic acid is, for example, the same as the mole fraction of each monomer (diamine and tetracarboxylic dianhydride) used in the synthesis of the polyamic acid. The temperature conditions for the reaction between diamine and tetracarboxylic dianhydride, i.e., the synthesis reaction of 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 polyamic acid is, for example, in the range of 10 minutes to 30 hours. In this embodiment, any monomer addition method may be used for the production of polyamic acid.

[0045] When obtaining non-thermoplastic polyimides, a method may be employed in which non-thermoplastic polyimides are obtained from a polyamic acid solution containing polyamic acid and an organic solvent. Organic solvents that can be used in polyamic acid solutions include, for example, 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 hexamethylphosphate triamide; ester-based solvents such as γ-butyrolactone; alkyl halide-based solvents such as chloroform and methylene chloride; aromatic hydrocarbon-based 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 usually used individually, but two or more may be used in appropriate combinations as needed. When polyamic acid is obtained by the polymerization method described above, the reaction solution (the solution after the reaction) itself may be used as a polyamic acid solution to obtain non-thermoplastic polyimide. In this case, the organic solvent in the polyamic acid solution is the organic solvent used in the reaction in the polymerization method described above. Alternatively, the solid polyamic acid obtained by removing the solvent from the reaction solution may be dissolved in an organic solvent to prepare a polyamic acid solution.

[0046] The polyamic acid solution may contain additives such as dyes, surfactants, leveling agents, plasticizers, silicones, fillers, and sensitizers. The concentration of polyamic acid in the polyamic acid solution is not particularly limited, but is, for example, 5% to 35% by weight, preferably 8% to 30% by weight, based on the total amount of the polyamic acid solution. When the concentration of polyamic acid is 5% to 35% by weight, an appropriate molecular weight and solution viscosity can be obtained.

[0047] The method for obtaining a non-thermoplastic polyimide film using a polyamic acid solution is not particularly limited, and various known methods can be applied. For example, a method for obtaining a non-thermoplastic polyimide film can be obtained by following the steps i) to iii) below. Step i): A step of applying a doping solution containing a polyamic acid solution onto a support to form a coating film. Step ii): The above coating film is dried on a support to form a self-supporting polyamic acid film (hereinafter sometimes referred to as "gel film"), and then the gel film is peeled off the support. Step iii) A step of heating the gel film to imidize the polyamic acid in the gel film and obtain a non-thermoplastic polyimide film containing a non-thermoplastic polyimide.

[0048] The methods for obtaining non-thermoplastic polyimide films through steps i) to iii) are broadly classified into thermal imidation and chemical imidation. Thermal imidation involves applying a polyamic acid solution as a doping solution to a support without using dehydrating ring-closing agents, etc., and then heating to promote imidation. Chemical imidation, on the other hand, uses a polyamic acid solution to which at least one of a dehydrating ring-closing agent and a catalyst is added as a doping solution to promote imidation. Either method can be used, but chemical imidation offers superior productivity.

[0049] Acid anhydrides, such as acetic anhydride, are preferably used as dehydrating cyclization agents. Tertiary amines such as aliphatic tertiary amines, aromatic tertiary amines, and heterocyclic tertiary amines (more specifically, isoquinoline, etc.) are preferably used as catalysts. When adding at least one of the dehydrating cyclization agent and catalyst to the polyamic acid solution, they may be added directly without dissolving in an organic solvent, or they may be added after being dissolved in an organic solvent. In the method of adding directly without dissolving in an organic solvent, the reaction may proceed rapidly before at least one of the dehydrating cyclization agent and catalyst diffuses, and a gel may be formed. Therefore, it is preferable to add a solution obtained by dissolving at least one of the dehydrating cyclization agent and catalyst in an organic solvent (imidization accelerator) to the polyamic acid solution.

[0050] In step i), the method for applying the doping solution onto the support is not particularly limited, and conventionally known coating devices such as die coaters, comma coaters (registered trademark), reverse coaters, and knife coaters can be used.

[0051] In step i), suitable support materials for applying the doping solution include glass plates, aluminum foil, endless stainless steel belts, and stainless steel drums. In step ii), the drying conditions (heating conditions) for the coated film are set according to the final film thickness and production speed, and the dried polyamic acid film (gel film) is peeled off from the support. The drying temperature of the coated film is, for example, 50°C to 200°C. The drying time for drying the coated film is, for example, 1 minute to 100 minutes.

[0052] Next, in step iii), for example, by fixing the edges of the gel film to avoid shrinkage during curing and then heat-treating it, water, residual solvent, imidization accelerator, etc. are removed from the gel film, and the remaining polyamic acid is completely imidized to obtain a non-thermoplastic polyimide film containing non-thermoplastic polyimide. The heating conditions are set appropriately according to the final thickness of the film obtained and the production rate. For example, the heating conditions in step iii) are such that the maximum temperature is 350°C or higher and 420°C or lower, and the heating time at the maximum temperature is 10 seconds or higher and 180 seconds or lower. Alternatively, the temperature may be held at any temperature for any time before reaching the maximum temperature. Step iii) can be carried out in air, under reduced pressure, or in an inert gas such as nitrogen. The heating equipment that can be used in step iii) is not particularly limited, and examples include a hot air circulation oven and a far-infrared oven.

[0053] The non-thermoplastic polyimide film obtained in this way can reduce the dielectric loss tangent, making it suitable for use as a material for high-frequency circuit boards (more specifically, the core layer of a multilayer polyimide film, the insulating layer of a metal-clad laminate, etc.).

[0054] [Physical properties of non-thermoplastic polyimide films] To reduce transmission loss, it is preferable that the dielectric constant of the non-thermoplastic polyimide film be 3.60 or less. Furthermore, to reduce transmission loss, it is preferable that the dielectric loss tangent of the non-thermoplastic polyimide film be 0.0050 or less, more preferably 0.0040 or less, and even more preferably less than 0.0033.

[0055] In order to suppress the generation of internal stress when used in FPC, the coefficient of linear expansion of the non-thermoplastic polyimide film is preferably 30 ppm / K or less, more preferably 25 ppm / K or less, and even more preferably 20 ppm / K or less.

[0056] The thickness of the non-thermoplastic polyimide film is not particularly limited, but is, for example, between 5 μm and 50 μm. The thickness of the non-thermoplastic polyimide film can be measured using a laser hologaze.

[0057] <Multilayer polyimide film> Next, a multilayer polyimide film will be described. The multilayer polyimide film comprises a non-thermoplastic polyimide film and an adhesive layer containing thermoplastic polyimide.

[0058] The multilayer polyimide film comprises a non-thermoplastic polyimide film and an adhesive layer containing thermoplastic polyimide disposed on at least one side (one main surface) of the thermoplastic polyimide film.

[0059] Adhesive layers may be provided on both sides (both main surfaces) of the non-thermoplastic polyimide film. When adhesive layers are provided on both sides of the non-thermoplastic polyimide film, the two adhesive layers may contain the same type of polyimide or may contain different types of polyimide. The thicknesses of the two adhesive layers may be the same or different.

[0060] The thickness of the multilayer polyimide film (total thickness of each layer) is, for example, 6 μm to 60 μm. The thinner the multilayer polyimide film, the easier it is to reduce the weight of the resulting FPC, and the more flexible the resulting FPC becomes. To ensure mechanical strength while facilitating weight reduction of the FPC and improving its flexibility, the thickness of the multilayer polyimide film is preferably 7 μm to 60 μm, and more preferably 10 μm to 60 μm. The thickness of the multilayer polyimide film can be measured using a laser hologaze.

[0061] To easily achieve thinning of the FPC while ensuring adhesion to the metal foil, the thickness of the adhesive layer (or the thickness of each adhesive layer if two adhesive layers are provided) is preferably 1 μm or more and 15 μm or less. Furthermore, to easily adjust the coefficient of thermal expansion of the multilayer polyimide film, the thickness ratio of the non-thermoplastic polyimide film to the adhesive layer (thickness of the non-thermoplastic polyimide film / thickness of the adhesive layer) is preferably 55 / 45 or more and 95 / 5 or less. If multiple adhesive layers are provided, the above thickness of the adhesive layer is the total thickness of the adhesive layer.

[0062] To suppress warping of a multilayer polyimide film, it is preferable that adhesive layers be provided on both sides of the non-thermoplastic polyimide film, and more preferably that adhesive layers containing the same type of polyimide are provided on both sides of the non-thermoplastic polyimide film. When adhesive layers are provided on both sides of the non-thermoplastic polyimide film, it is preferable that the thicknesses of the two adhesive layers be the same in order to suppress warping of the multilayer polyimide film. Even if the thicknesses of the two adhesive layers are different, warping of the multilayer polyimide film can be suppressed as long as the thickness of the other adhesive layer is in the range of 40% or more and less than 100% when the thickness of the thicker adhesive layer is used as the reference.

[0063] [Adhesive layer] The thermoplastic polyimide contained in the adhesive layer has acid dianhydride residues and diamine residues. The acid dianhydride (monomer) for forming the acid dianhydride residues in the thermoplastic polyimide is the same compound as the acid dianhydride (monomer) for forming the acid dianhydride residues in the non-thermoplastic polyimide described above. The acid dianhydride residues in the thermoplastic polyimide and the acid dianhydride residues in the non-thermoplastic polyimide may be of the same type or different types.

[0064] To ensure thermoplasticity, the diamine residues in the thermoplastic polyimide are preferably those having a bent structure. To more easily ensure thermoplasticity, the content of diamine residues having a bent structure is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, and may even be 100 mol% based on the total diamine residues constituting the thermoplastic polyimide. Examples of diamines (monomers) for forming diamine residues having a bent structure include 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-bis(3-aminophenoxy)biphenyl, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, and 2,2-bis[4-(4-aminophenoxy)phenyl]propane.

[0065] The adhesive layer may contain components (additives) other than thermoplastic polyimide. Examples of additives include dyes, surfactants, leveling agents, plasticizers, silicones, fillers, sensitizers, etc. The content of thermoplastic polyimide in the adhesive layer 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 amount of the adhesive layer.

[0066] (Method for forming an adhesive layer) The adhesive layer is formed, for example, by applying a polyamic acid solution containing polyamic acid, a precursor of thermoplastic polyimide (hereinafter sometimes referred to as "thermoplastic polyamic acid solution") to at least one side of a non-thermoplastic polyimide film, and then heating (drying and imidization of the polyamic acid). This method yields a multilayer polyimide film having a non-thermoplastic polyimide film and an adhesive layer disposed on at least one side of the non-thermoplastic polyimide film. Alternatively, instead of a thermoplastic polyamic acid solution, a solution containing thermoplastic polyimide (thermoplastic polyimide solution) may be used to form a coating film made of the thermoplastic polyimide solution on at least one side of the non-thermoplastic polyimide film, and this coating film may be dried to form the adhesive layer.

[0067] Alternatively, for example, a co-extrusion die may be used to form a laminate comprising a layer containing polyamic acid, a precursor of non-thermoplastic polyimide, and a layer containing polyamic acid, a precursor of thermoplastic polyimide, and then the resulting laminate may be heated to simultaneously form the non-thermoplastic polyimide film and the adhesive layer. In this method, by using metal foil as a support, a metal-clad laminate (a laminate of multilayer polyimide film and metal foil) is obtained at the same time as the imidization is completed.

[0068] When manufacturing a multilayer polyimide film containing three polyimide layers, it is preferable to repeat the above-described coating and heating steps multiple times, or to form multiple coating films by co-extrusion or continuous coating (continuous casting) and heat them all at once. It is also possible to perform various surface treatments, such as corona treatment or plasma treatment, on the outermost surface of the multilayer polyimide film.

[0069] <Metal-clad laminate (where the metal layer is directly formed on a non-thermoplastic polyimide film)> Next, a metal-clad laminate consisting of a non-thermoplastic polyimide film and a metal layer will be described. The metal-clad laminate has a non-thermoplastic polyimide film and a metal layer directly disposed on at least one side (one main surface) of the non-thermoplastic polyimide film. In the following description, explanations of content that overlaps with that of non-thermoplastic polyimide films and multi-layer polyimide films may be omitted.

[0070] Metal-clad laminates are obtained, for example, by forming a first plating layer on one or both sides of a non-thermoplastic polyimide film using a dry plating method, and then forming a second plating layer on the first plating layer using a wet plating method (such as electroless plating or electrolytic plating). (Hereinafter, this may be referred to as "plating method.") Examples of dry plating methods include vacuum deposition, sputtering, ion plating, and CVD. The thickness of the metal layer consisting of the first and second plating layers (total thickness) is, for example, 1 μm to 50 μm.

[0071] In addition to the above method, another method for obtaining a metal-clad laminate is to bond a metal foil, which will form the metal layer, to at least one side of a non-thermoplastic polyimide film (hereinafter sometimes referred to as the "lamination method").

[0072] The lamination method is not particularly limited, and various known methods can be employed. For example, a continuous processing method using a hot roll laminating apparatus having one or more pairs of metal rolls or a double belt press (DBP) can be employed. The specific configuration of the means for carrying out hot roll lamination is not particularly limited, but in order to obtain a good appearance of the resulting metal-clad laminate, it is preferable to place a protective material between the pressurized surface and the metal foil.

[0073] In addition to the above method, another method for obtaining a metal-clad laminate is to apply a solution containing polyamic acid, which is a precursor of non-thermoplastic polyimide (more specifically, the non-thermoplastic polyimide present in the non-thermoplastic polyimide film), onto a metal foil that will form the metal layer, and then heat the coating film formed on the metal foil (hereinafter sometimes referred to as the "coating method"). By heating the coating film, the solvent is removed and imidization occurs on the metal foil, resulting in a metal-clad laminate, which is a laminate of a non-thermoplastic polyimide film and a metal layer made of metal foil.

[0074] In the coating method, the coating apparatus for coating a solution containing polyamic acid onto a metal foil is not particularly limited, and examples include die coaters, comma coaters (registered trademark), reverse coaters, knife coaters, etc. The heating apparatus for heating the coated film is also not particularly limited, and examples include hot air circulation ovens, far-infrared ovens, etc.

[0075] The metal foil that forms the metal layer of the metal-clad laminate is not particularly limited. Suitable metal foils include, for example, those made from copper, stainless steel, nickel, aluminum, and alloys of these metals. In general metal-clad laminates, copper foil such as rolled copper foil and electrolytic copper foil is frequently used, and in the fourth embodiment, copper foil is also preferably used. Furthermore, the metal foil can be used after surface treatment or other adjustments have been made to adjust the surface roughness, etc., depending on the purpose. In addition, a rust-preventive 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 should be a thickness that allows sufficient functionality to be achieved according to the application. In order to easily achieve thinning of the FPC while ensuring ease of handling, the thickness of the metal foil is preferably 5 μm to 50 μm.

[0076] <Metal-clad laminate (where the metal layer is directly formed on a multilayer polyimide film)> Next, a metal-clad laminate consisting of a multilayer polyimide film and a metal layer will be described. The metal-clad laminate has a multilayer polyimide film disposed on at least one side of an adhesive layer containing thermoplastic polyimide, and a metal layer directly disposed on at least one side (one main surface) of the multilayer polyimide film via the adhesive layer. The method for obtaining the metal-clad laminate is the same as the method for obtaining the metal-clad laminate consisting of the non-thermoplastic polyimide film and metal layer described above, and is not particularly limited. [Examples]

[0077] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0078] <Method for measuring physical properties> First, we will explain the methods for measuring the relative permittivity, dielectric loss tangent, and coefficient of linear expansion of polyimide films.

[0079] [Relative permittivity and dielectric loss tangent] The relative permittivity and dielectric loss tangent of polyimide film were measured using a network analyzer (Hewlett-Packard "8719C") and a cavity resonator perturbation dielectric constant measuring device (EM Lab "CP531"). Specifically, first, polyimide film was cut into 2mm x 100mm pieces to prepare samples for measurement of relative permittivity and dielectric loss tangent. Next, the measurement samples were left for 24 hours in an atmosphere of 23°C and 50% relative humidity. Then, the relative permittivity and dielectric loss tangent were measured using the network analyzer and cavity resonator perturbation dielectric constant measuring device under the conditions of 23°C, 50% relative humidity, and a measurement frequency of 10GHz. If the dielectric loss tangent was less than 0.0033, it was evaluated as "the dielectric loss tangent has been reduced." On the other hand, if the dielectric loss tangent was 0.0033 or greater, it was evaluated as "the dielectric loss tangent has not been reduced."

[0080] [Coefficient of linear expansion (CTE)] Using a thermal analyzer (Hitachi High-Tech Science Corporation's "TMA / SS6100"), a polyimide film (sample) was heated from -10°C to 300°C at a heating rate of 10°C / min, and then cooled down to -10°C at a cooling rate of 40°C / min. Next, the sample was heated again to 300°C at a heating rate of 10°C / min, and the coefficient of linear expansion was determined from the amount of strain between 50°C and 250°C during the second heating cycle. The measurement conditions are shown below. Sample (polyimide film) size: 3mm wide, 10mm long Load: 1g Measurement atmosphere: Air atmosphere

[0081] <Preparation of polyimide film> The following describes the methods for preparing polyimide films in the examples and comparative examples. Compounds and reagents are referred to by the following abbreviations. The polyamic acid solutions used to prepare the polyimide films were all prepared under a nitrogen atmosphere at a temperature of 20°C. DMF: N,N-dimethylformamide PDA: p-phenylenediamine TPE-Q: 1,4-bis(4-aminophenoxy)benzene TPE-M: 1,3-bis(3-aminophenoxy)benzene m-TB: 4,4'-diamino-2,2'-dimethylbiphenyl ODA: 4,4'-oxydianiline BPDA: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride PMDA: Pyromelit acid dianhydride ODPA: 4,4'-Oxydiphthalic anhydride BAPP: 2,2-Bis[4-(4-aminophenoxy)phenyl]propane AA: Acetic anhydride IQ: Isoquinoline

[0082] (Example 1) In a 500 mL glass flask, add 164.18 g of DMF, 2.83 g (0.0097 mol) of TPE-Q, and 6.42 g ( 0.0594After adding 0.0297 mol of PDA, 8.73 g (0.0297 mol) of BPDA and 11.57 g (0.0373 mol) of ODPA were added to the flask while stirring the contents. The contents of the flask were then stirred for 30 minutes. Next, while stirring the contents of the flask, a pre-prepared PMDA solution (solvent: DMF, amount of PMDA dissolved: 0.45 g (0.0021 mol), PMDA concentration: 7.9 wt%) was added to the flask at a rate that did not cause a rapid increase in the viscosity of the contents for a predetermined time. When the viscosity of the contents of the flask reached 1500 poise at a temperature of 23°C, the addition of the PMDA solution was stopped, and the contents of the flask were stirred for another hour to obtain polyamic acid solution P1. The obtained polyamic acid solution P1 had a solid content concentration of 15 wt%. The obtained polyamic acid solution P1 had a viscosity of 1500-2000 poise at a temperature of 23°C.

[0083] Next, 27.5 g of an imidization accelerator consisting of a mixture of AA, IQ, and DMF (weight ratio: AA / IQ / DMF = 42 / 21 / 37) was added to 55 g of polyamic acid solution P1 (polyamic acid solution P1 obtained by the above preparation method) to prepare a dope solution. Then, after degassing the dope solution while stirring in an atmosphere below 0°C, the dope solution was applied to aluminum foil using a comma coater to form a coating film. Next, the coating film was heated at a heating temperature of 110°C for 180 seconds to obtain a self-supporting gel film. The obtained gel film was peeled off the aluminum foil, fixed to a metal fixing frame, and placed in a hot air circulating oven preheated to 300°C, where it was heated at 300°C for 56 seconds. Next, the heated film was placed in a far-infrared (IR) oven preheated to 380°C and heated at 380°C for 49 seconds to imidize the polyamic acid in the gel film. After that, it was separated from the metal fixing frame to obtain the polyimide film of Example 1 (thickness: 17 μm).

[0084] Furthermore, when the polyimide film obtained using the same procedure as described above was fixed to a metal frame and heated in an IR oven at a heating temperature of 380°C for 1 minute, the shape (film shape) of the polyimide film was maintained. Therefore, the polyimide contained in the polyimide film of Example 1 was a non-thermoplastic polyimide. In other words, the polyimide film of Example 1 was a non-thermoplastic polyimide film.

[0085] (Examples 2-9, Comparative Examples 1-5) Polyimide acid solution and polyimide film were obtained by the same method as in Example 1, except that the types and molar ratios of the diamine and acid dianhydride components were changed as shown in Table 1.

[0086] Furthermore, in Examples 2-9 and Comparative Examples 1-5, the obtained polyimide films were fixed to metal frames and heated in an IR oven at a heating temperature of 380°C for 1 minute, and the shape (film shape) of the polyimide films was maintained. Therefore, the polyimide contained in the polyimide films of Examples 2-9 and Comparative Examples 1-5 was non-thermoplastic polyimide. In other words, the polyimide films of Examples 2-9 and Comparative Examples 1-5 were non-thermoplastic polyimide films.

[0087] <Result> Table 1 shows the types and ratios (feeding ratios) of monomers, the relative permittivity, dielectric loss tangent, and CTE of the obtained films for Examples 1-9 and Comparative Examples 1-5. Furthermore, in Table 1, the values ​​in the "Diamine" column represent the content of each diamine relative to the total amount of diamine used (unit: mol%). In Table 1, the values ​​in the "Acid Dianhydride" column represent the content of each acid dianhydride relative to the total amount of acid dianhydrides used (unit: mol%). In the "Diamine" and "Acid Dianhydride" columns of Table 1, "-" means that the component in question (PDA, TPE-Q, TPE-M, m-TB, ODA, BAPP, BPDA, PMDA, and ODPA) was not used. In all of Examples 1-9 and Comparative Examples 1-5, the mole fraction of each residue in the polyimide contained in the obtained polyimide film was consistent with the mole fraction of each monomer used (diamine and tetracarboxylic dianhydride). Furthermore, in all of Examples 1-9 and Comparative Examples 1-5, the molar ratio obtained by dividing the total amount of tetracarboxylic dianhydride residues constituting the polyimide contained in the obtained polyimide film by the total amount of diamine residues constituting the polyimide was between 0.99 and 1.01.

[0088] In Table 1, "-" indicates that measurement was not performed. In Examples 1-9, the dielectric loss tangent was less than 0.0032. Therefore, the polyimide films of Examples 1-9 were able to reduce the dielectric loss tangent. On the other hand, in Comparative Examples 1-5, the dielectric loss tangent was 0.0033 or higher. Therefore, the polyimide films of Comparative Examples 1-8 were not able to reduce the dielectric loss tangent. The above results demonstrate that the present invention can provide a non-thermoplastic polyimide film that can reduce dielectric loss tangent. [Table 1]

[0089] (Example 10) Multilayer polyimide film and metal laminate In a 500 mL glass flask, 167.78 g of DMF, 13.89 g (0.0475 mol) of 1,3-bis(4-aminophenoxy)benzene, and 0.53 g (0.0025 mol) of m-TB were added. Then, while stirring the contents of the flask, 10.30 g (0.0350 mol) of BPDA and 2.95 g (0.0135 mol) of PMDA were added to the flask. Next, the contents of the flask were stirred for 30 minutes. Then, while stirring the contents of the flask, a pre-prepared PMDA solution (solvent: DMF, amount of PMDA dissolved: 0.33 g (0.0015 mol), PMDA concentration: 7.9 wt%) was continuously added to the flask for a predetermined time at an addition rate that did not cause a rapid increase in the viscosity of the contents of the flask. Then, when the viscosity of the flask contents reached 700 poise at a temperature of 23°C, the addition of the PMDA solution was stopped, and the flask contents were stirred for another hour to obtain polyamic acid solution P2. The obtained polyamic acid solution P2 had a solid content concentration of 15% by weight. The obtained polyamic acid solution P1 had a viscosity of 700 to 1000 poise at a temperature of 23°C.

[0090] Next, the polyamic acid solution P2 was applied to both sides of the 17 μm polyimide film of Example 1 so that each side had a thickness of 4 μm. The film was then heated and dried at 110°C for 180 seconds and 300°C for 56 seconds to produce a multilayer polyimide film with a total thickness of 25 μm. A 12 μm thick electrolytic copper foil (CF-T49A-HD2; manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.) was placed on both sides of the multilayer polyimide film obtained above, and a protective material (Apical 125NPI; manufactured by Kaneka Corporation) was placed on both sides of the foil. A metal-clad laminate was then fabricated by continuously heat laminating using a hot roll laminating machine under the following conditions: lamination temperature of 360°C, lamination pressure of 0.8 tons (0.03 tons / cm), and lamination speed of 1.0 m / min. The resulting metal-clad laminate showed strong adhesion between the multilayer polyimide film and the metal layer, and was free from appearance problems such as wrinkles and warping.

Claims

1. A non-thermoplastic polyimide film containing a non-thermoplastic polyimide, The non-thermoplastic polyimide has a 3,3',4,4'-biphenyltetracarboxylic acid dianhydride residue and a 4,4'-oxydiphthalic acid anhydride residue as tetracarboxylic acid dianhydride residues, and has a p-phenylenediamine residue and at least one diamine component selected from a 1,3-bis(3-aminophenoxy)benzene residue, a 1,4-bis(4-aminophenoxy)benzene residue, and a 4,4'-diamino-2,2'-dimethylbiphenyl residue as diamine residues. The non-thermoplastic polyimide further comprises pyromellitic dianhydride residues as tetracarboxylic dianhydride residues, A non-thermoplastic polyimide film in which the content of pyromellitic dianhydride residues relative to the total tetracarboxylic dianhydride residues constituting the non-thermoplastic polyimide is 1 mol% or more and 20 mol% or less.

2. The non-thermoplastic polyimide film according to claim 1, wherein the total content of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride residues and 4,4'-oxydiphthalic acid anhydride residues relative to all tetracarboxylic acid dianhydride residues constituting the non-thermoplastic polyimide is 80 mol% or more, and the total content of p-phenylenediamine residues and at least one diamine component selected from 1,3-bis(3-aminophenoxy)benzene residues, 1,4-bis(4-aminophenoxy)benzene residues, and 4,4'-diamino-2,2'-dimethylbiphenyl relative to all diamine residues constituting the non-thermoplastic polyimide is 85 mol% or more.

3. The non-thermoplastic polyimide film according to claim 1 or 2, wherein the amount of substance ratio obtained by dividing the total amount of tetracarboxylic dianhydride residues constituting the non-thermoplastic polyimide by the total amount of diamine residues constituting the non-thermoplastic polyimide is 0.95 or more and 1.05 or less.

4. The non-thermoplastic polyimide film according to any one of claims 1 to 3, wherein the content of the pyromellitic dianhydride residue relative to the total tetracarboxylic dianhydride residues constituting the non-thermoplastic polyimide is 3 mol% or more and 20 mol% or less.

5. A multilayer polyimide film having a non-thermoplastic polyimide film according to any one of claims 1 to 4, and an adhesive layer containing thermoplastic polyimide disposed on at least one side of the non-thermoplastic polyimide film.

6. The multilayer polyimide film according to claim 5, wherein the adhesive layer is disposed on both sides of the non-thermoplastic polyimide film.

7. A metal-clad laminate comprising a non-thermoplastic polyimide film according to any one of claims 1 to 4, and a metal layer disposed on at least one side of the non-thermoplastic polyimide film.

8. A metal-clad laminate comprising a multilayer polyimide film according to claim 5 or 6, and a metal layer disposed on the main surface of at least one of the adhesive layers of the multilayer polyimide film.

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