Polyimide precursors and polyimides

Abstract

To provide a polyimide and a polyimide precursor capable of reducing dielectric tangent.SOLUTION: There is provided a polyimide precursor which is an addition reaction product of a tetracarboxylic dianhydride component and a diamine component, wherein the diamine component contains p-phenylenediamine and 1,3-bis(4-aminophenoxy)benzene; the tetracarboxylic dianhydride component contains 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 4,4'-oxydiphthalic anhydride (ODPA) and an ester-containing tetracarboxylic dianhydride; and based on all tetracarboxylic dianhydride components, the content of BPDA is 10 to 65 mol%, the content of ODPA is 20 to 70 mol%, the content of the ester-containing tetracarboxylic dianhydride is 10 to 30 mol% and the total content of BPDA and the ester-containing tetracarboxylic dianhydride is 75 mol% or less. There is also provided a polyimide obtained from the polyimide precursor.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a polyimide precursor and a polyimide.

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, FPCs using a polyimide film having a polyimide layer as a material are expected to further grow in demand because of their 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 FPCs.

[0003] Moreover, with the high-speed signal transmission of recent electronic devices, the requirements for reducing the dielectric constant and dielectric tangent of electronic substrate materials are increasing 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 is advancing, and there is a demand for substrate materials that can suppress transmission loss even in the 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) exhibiting a low dielectric tangent is known (see, for example, Patent Documents 1 to 5).

Prior Art Documents

[0006] [Patent Document 1] Special Publication No. 2014-526399 [Patent Document 2] Japanese Patent Publication No. 2009-246201 [Patent Document 3] Japanese Patent Publication No. 2018-150544 [Patent Document 4] International Publication No. 2018 / 079710 [Patent Document 5] 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 5 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 polyimide precursor and a polyimide that can reduce the dielectric loss tangent. [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 polyimide precursor which is an addition reaction product of a tetracarboxylic dianhydride component and a diamine component, wherein the diamine component comprises p-phenylenediamine and 1,3-bis(4-aminophenoxy)benzene, and the tetracarboxylic dianhydride component comprises 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride and ester group-containing tetracarboxylic dianhydride, wherein the content of 3,3',4,4'-biphenyltetracarboxylic dianhydride is 10 to 65 mol%, the content of 4,4'-oxydiphthalic anhydride is 20 to 70 mol%, the content of ester group-containing tetracarboxylic dianhydride is 10 to 30 mol%, and the total content of 3,3',4,4'-biphenyltetracarboxylic dianhydride and ester group-containing tetracarboxylic dianhydride is 75 mol% or less.

[0010] 2) The polyimide precursor according to 1), characterized in that the p-phenylenediamine content is 70 to 95 mol% and the 1,3-bis(4-aminophenoxy)benzene content is 5 to 30 mol% relative to the total diamine components.

[0011] 3) The polyimide precursor according to 1) or 2), characterized in that it further contains pyromellitic dianhydride in an amount of 15 mol% or less relative to the total tetracarboxylic dianhydride component.

[0012] 4) The polyimide precursor according to any one of 1) to 3), characterized in that the ester group-containing tetracarboxylic dianhydride is at least one selected from p-phenylenebis(trimellitic acid monoester anhydride) and p-biphenylenebis(trimellitic acid monoester anhydride).

[0013] 5) A polyimide that is a polycondensate of a tetracarboxylic dianhydride component and a diamine component, wherein the diamine component comprises p-phenylenediamine and 1,3-bis(4-aminophenoxy)benzene, and the tetracarboxylic dianhydride component comprises 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride and ester group-containing tetracarboxylic dianhydride, wherein the content of 3,3',4,4'-biphenyltetracarboxylic dianhydride is 10 to 65 mol%, the content of 4,4'-oxydiphthalic anhydride is 20 to 70 mol%, the content of ester group-containing tetracarboxylic dianhydride is 10 to 30 mol%, and the total content of 3,3',4,4'-biphenyltetracarboxylic dianhydride and ester group-containing tetracarboxylic dianhydride is 75 mol% or less.

[0014] 6) The polyimide according to 5), characterized in that the p-phenylenediamine content is 70 to 95 mol% and the 1,3-bis(4-aminophenoxy)benzene content is 5 to 30 mol% relative to the total diamine components.

[0015] 7) The polyimide according to 5) or 6), characterized in that it further contains pyromellitic dianhydride in an amount of 15 mol% or less relative to the total tetracarboxylic dianhydride components as a tetracarboxylic dianhydride component.

[0016] 8) The polyimide according to any one of 5) to 7), characterized in that the ester group-containing tetracarboxylic dianhydride is at least one selected from p-phenylenebis(trimellitic acid monoester anhydride) and p-biphenylenebis(trimellitic acid monoester anhydride). [Effects of the Invention]

[0017] According to the present invention, a polyimide precursor and polyimide capable of reducing dielectric loss tangent can be provided. [Modes for carrying out the invention]

[0018] <Polyimide precursors and polyimides> A polyimide precursor is obtained by a polyaddition reaction between a tetracarboxylic dianhydride component and a diamine component, and polyimide is obtained by a dehydration and ring-closing reaction of the polyimide precursor. In other words, polyimide is a polycondensation product of a tetracarboxylic dianhydride component and a diamine component. The polyimide precursor is also generally called polyamic acid or polyamic acid.

[0019] The polyimide precursor of the present invention is a polyimide precursor which is an addition reaction product of a tetracarboxylic dianhydride component and a diamine component, wherein the diamine component comprises p-phenylenediamine and 1,3-bis(4-aminophenoxy)benzene, the tetracarboxylic dianhydride component comprises 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride and ester group-containing tetracarboxylic dianhydride, and the polyimide precursor is characterized in that, relative to the total tetracarboxylic dianhydride component, the content of 3,3',4,4'-biphenyltetracarboxylic dianhydride is 10 to 65 mol%, the content of 4,4'-oxydiphthalic anhydride is 20 to 70 mol%, the content of ester group-containing tetracarboxylic dianhydride is 10 to 30 mol%, and the total content of 3,3',4,4'-biphenyltetracarboxylic dianhydride and ester group-containing tetracarboxylic dianhydride is 75 mol% or less.

[0020] The polyimide of the present invention is a polyimide which is a polycondensate of a tetracarboxylic dianhydride component and a diamine component. The diamine component includes p-phenylenediamine (hereinafter sometimes referred to as "PDA") and 1,3-bis(4-aminophenoxy)benzene (hereinafter sometimes referred to as "TPE-R"). The tetracarboxylic dianhydride component includes 3,3',4,4'-biphenyltetracarboxylic dianhydride (hereinafter sometimes referred to as "BPDA"), 4,4'-oxydiphthalic anhydride (hereinafter sometimes referred to as "ODPA") and an ester group-containing tetracarboxylic dianhydride. With respect to all the tetracarboxylic dianhydride components, the content of 3,3',4,4'-biphenyltetracarboxylic dianhydride is 10 to 65 mol%, the content of 4,4'-oxydiphthalic anhydride is 20 to 70 mol%, the content of the ester group-containing tetracarboxylic dianhydride is 10 to 30 mol%, and the total content of 3,3',4,4'-biphenyltetracarboxylic dianhydride and the ester group-containing tetracarboxylic dianhydride is 75 mol% or less. The polyimide is characterized by this.

[0021] (Diamine component) The polyimide precursor and the polyimide of the present invention include PDA and TPE-R as the diamine component.

[0022] In order to obtain a polyimide capable of reducing the dielectric loss tangent, with respect to all the diamine components constituting the polyimide precursor and the polyimide, the content of PDA is preferably 70 to 95 mol%, more preferably 75 to 90 mol%.

[0023] In order to obtain a polyimide capable of reducing the dielectric loss tangent, with respect to all the diamine components constituting the polyimide precursor and the polyimide, the content of TPE-R is preferably 5 to 30 mol%, more preferably 10 to 25 mol%.<​​The polyimide precursor and polyimide of the present invention may have other diamine components in addition to PDA and TPE-R. Other diamine components include, for example, 1,3-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 4,4'-diamino-2,2'-dimethylbiphenyl, 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.

[0025] (Tetradicarboxylic acid dianhydride component) The polyimide precursor and polyimide of the present invention include BPDA, ODPA, and an ester group-containing tetracarboxylic dianhydride as tetracarboxylic dianhydride components.

[0026] To obtain a polyimide that can reduce dielectric loss tangent, the BPDA content is preferably 10 to 65 mol%, and more preferably 15 to 60 mol%, relative to the total tetracarboxylic dianhydride components constituting the polyimide precursor and the polyimide.

[0027] To obtain a polyimide that can reduce dielectric loss tangent, the ODPA content is preferably 20 to 70 mol%, and more preferably 25 to 65 mol%, relative to the total tetracarboxylic dianhydride components constituting the polyimide precursor and the polyimide.

[0028] The polyimide precursor and polyimide of the present invention include an ester-containing tetracarboxylic dianhydride as the tetracarboxylic dianhydride. The ester-containing tetracarboxylic dianhydride is not particularly limited as long as it contains an ester group in its structure. Examples include p-phenylenebis(trimellitic acid monoester anhydride) (hereinafter sometimes referred to as "TMHQ"), ethylenebis(trimellitic acid monoester anhydride), bisphenol A bis(trimellitic acid monoester anhydride), p-biphenylenebis(trimellitic acid monoester anhydride) (hereinafter sometimes referred to as "BP-TME"), 4-[4-(1,3-dioxoisobenzofuran-5-ylcarbonyloxy)-2,3,5-trimethylphenyl]-2,3,6-trimethylphenyl 1,3-dioxoisobenzofuran-5-carboxylate, 4-{[4-(1,3-dioxoisobenzofuran-5-ylcarbonyloxy)phenyl]cyclohexyl}phenyl 1,3-dioxoisobenzofuran-5-carboxylate, and derivatives thereof. Among these ester group-containing tetracarboxylic dianhydrides, TMHQ and BP-TME tend to exhibit low dielectric loss tangents and are particularly preferred.

[0029] To obtain a polyimide that can reduce dielectric loss tangent, the content of ester group-containing tetracarboxylic dianhydride is preferably 10 to 30 mol%, and more preferably 15 to 25 mol%, relative to the total tetracarboxylic dianhydride components constituting the polyimide and the polyimide.

[0030] To obtain a polyimide that can reduce dielectric loss tangent, the total content of BPDA and ester group-containing tetracarboxylic dianhydride relative to the polyimide precursor and the total tetracarboxylic dianhydride components constituting the polyimide is preferably 75 mol% or less, and more preferably 70 mol% or less.

[0031] The polyimide precursor and polyimide of the present invention may contain other tetracarboxylic dianhydride components in addition to BPDA, ODPA, and ester group-containing tetracarboxylic dianhydride. Other tetracarboxylic dianhydride components include, for example, pyromellitic anhydride (hereinafter sometimes referred to as "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, 3,4'-oxydiphthalic anhydride, 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, and derivatives thereof.

[0032] To obtain a polyimide that can further reduce the dielectric loss tangent, it is preferable to select one or more other tetracarboxylic dianhydride components from PMDA and 3,3',4,4'-benzophenonetetracarboxylic dianhydride. Furthermore, to obtain a polyimide that can further reduce the dielectric loss tangent while improving heat resistance, it is preferable to select PMDA as the other tetracarboxylic dianhydride component.

[0033] When PMDA is used as another tetracarboxylic dianhydride component, in order to obtain a polyimide that can further reduce the dielectric loss tangent while improving heat resistance, the content of PMDA relative to the polyimide precursor and the total tetracarboxylic dianhydride components constituting the polyimide is preferably 15 mol% or less, more preferably 12 mol% or less, and even more preferably 10 mol% or less.

[0034] To obtain a polyimide that can further reduce the dielectric loss tangent, the molar ratio obtained by dividing the total amount of substance of the polyimide precursor and all tetradicarboxylic acid dianhydrides constituting the polyimide by the total amount of substance of the polyimide precursor and all diamines constituting the 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.

[0035] The polyimide of the present invention may contain components other than the polyimide precursor and the components constituting the polyimide (additives). Examples of additives include dyes, surfactants, leveling agents, plasticizers, silicones, fillers, sensitizers, etc. The content of additives in the polyimide is, for example, 30% by weight or less, preferably 20% by weight or less, more preferably 10% by weight or less, and may even be 0% by weight, based on the total amount of polyimide.

[0036] <Method for producing polyimide precursors> Any known method or a combination thereof can be used to produce (synthesize) a polyimide precursor. When producing a polyimide precursor, a diamine component and a tetracarboxylic dianhydride component are usually reacted in an organic solvent. Preferably, the amount of substance of the diamine component and the amount of substance of the tetracarboxylic dianhydride component during the reaction are substantially equal. When synthesizing a polyimide precursor using a diamine component and a tetracarboxylic dianhydride component, a desired polyimide precursor (polymer of diamine and tetracarboxylic dianhydride) can be obtained by adjusting the amount of substance of each diamine component and the amount of substance of each tetracarboxylic dianhydride component. The mole fraction of each residue in the polyimide formed from the polyimide precursor is, for example, the same as the mole fraction of each monomer (diamine component and tetracarboxylic dianhydride component) used in the synthesis of the polyimide precursor. The temperature conditions for the reaction between the diamine component and the tetracarboxylic dianhydride component, i.e., the synthesis reaction of the polyimide precursor, are not particularly limited, but are, for example, in the range of 10°C to 150°C. The reaction time for the synthesis of the polyimide precursor is, for example, in the range of 10 minutes to 30 hours. In this embodiment, any method of adding monomers may be used to produce the polyimide precursor.

[0037] When obtaining polyimide, it is preferable to use a method that yields polyimide from a polyimide precursor solution containing a polyimide precursor and an organic solvent. Organic solvents that can be used in polyimide precursor 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 a polyimide precursor is obtained by the polymerization method described above, the reaction solution (the solution after the reaction) itself may be used as the polyimide precursor solution to obtain the polyimide. In this case, the organic solvent in the polyimide precursor solution is the organic solvent used in the reaction in the polymerization method described above. Alternatively, the solid polyimide precursor obtained by removing the solvent from the reaction solution may be dissolved in an organic solvent to prepare a polyimide precursor solution.

[0038] The polyimide precursor solution may contain additives such as dyes, surfactants, leveling agents, plasticizers, silicones, fillers, and sensitizers. The concentration of the polyimide precursor in the polyimide precursor 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 polyimide precursor solution. When the concentration of the polyimide precursor is 5% to 35% by weight, an appropriate molecular weight and solution viscosity can be obtained.

[0039] <Method for producing polyimide and polyimide film> The polyimide precursor and polyimide precursor solution of the present invention may be used as is as materials for manufacturing products and components, or they may be blended with binder resins, additives, etc., to prepare resin compositions. Because of their excellent heat resistance and mechanical properties, it is preferable to imide the polyimide precursor by dehydration and ring closure and use it as a polyimide for practical purposes.

[0040] The method for obtaining a polyimide film using a polyimide precursor solution is not particularly limited, and various known methods can be applied. For example, a method for obtaining a polyimide film through the following steps i) to iii) can be cited. Step i): A step of applying a doping solution containing a polyimide precursor solution onto a support to form a coated film. Step ii): The above coated film is dried on a support to form a self-supporting polyimide precursor film (hereinafter sometimes referred to as "gel film"), and then the gel film is peeled off from the support. Step iii) A step of heating the gel film to imidize the polyimide precursor in the gel film and obtain a polyimide film containing polyimide.

[0041] The methods for obtaining polyimide films through steps i) to iii) are broadly classified into thermal imidation and chemical imidation. Thermal imidation involves coating a support with a polyimide precursor as a doping solution and heating it to promote imidation, without using dehydrating ring-closing agents or the like. Chemical imidation, on the other hand, uses a polyimide precursor 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.

[0042] 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 polyimide precursor solution.

[0043] 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.

[0044] 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 polyimide precursor 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.

[0045] 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 polyimide precursor is completely imidized to obtain a polyimide film containing 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.

[0046] The 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, for example.

[0047] <Physical properties of polyimide films> When used in high-frequency circuit boards, the dielectric constant of the polyimide film is preferably 3.60 or less in order to reduce transmission loss. Furthermore, to reduce transmission loss, the dielectric loss tangent of the polyimide film is preferably 0.0040 or less, more preferably 0.0030 or less, and even more preferably less than 0.0025.

[0048] When used in high-frequency circuit boards, in order to suppress the generation of internal stress, the coefficient of linear expansion of the 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.

[0049] The polyimide film containing the polyimide of the present invention (hereinafter sometimes referred to as "polyimide film") can be made into an FPC by laminating it with a metal layer to form a metal-clad laminate. Furthermore, in order to improve the adhesion between the polyimide film and the metal layer, an adhesive layer containing thermoplastic polyimide can be placed on one or both sides of the polyimide film to form a multilayer polyimide film, which can then be used.

[0050] <Multilayer polyimide film> A multilayer polyimide film is a polyimide film with adhesive layers containing thermoplastic polyimide on one or both sides. When adhesive layers are placed on both sides of the polyimide film, the two adhesive layers may contain the same type of thermoplastic polyimide or different types of thermoplastic polyimide. The thicknesses of the two adhesive layers may be the same or different.

[0051] 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.

[0052] To easily achieve thinning of the FPC while ensuring adhesion to the metal layer, 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 polyimide film to the adhesive layer (thickness of the 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.

[0053] To suppress warping of a multilayer polyimide film, it is preferable that adhesive layers be provided on both sides of the polyimide film, and more preferably that adhesive layers containing the same type of polyimide are provided on both sides of the polyimide film. When adhesive layers are provided on both sides of the 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.

[0054] <Adhesive layer> The thermoplastic polyimide contained in the adhesive layer has a tetradicarboxylic acid dianhydride component and a diamine component. Examples of tetradicarboxylic acid dianhydride (monomers) for forming the tetradicarboxylic acid dianhydride component in the thermoplastic polyimide include the same compounds as those used to form the tetradicarboxylic acid dianhydride component in the polyimide of the present invention. The tetradicarboxylic acid dianhydride in the thermoplastic polyimide and the tetradicarboxylic acid dianhydride in the polyimide of the present invention may be the same type or different types.

[0055] To ensure thermoplasticity, the diamine component of the thermoplastic polyimide is preferably a diamine (monomer) having a bent structure. To more easily ensure thermoplasticity, the content of the diamine component 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 components constituting the thermoplastic polyimide. Examples of diamines (monomers) for forming the diamine component 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.

[0056] The adhesive layer may contain components (additives) other than thermoplastic polyimide. As additives, for example, dyes, surfactants, leveling agents, plasticizers, silicones, fillers, sensitizers, etc., can be used. 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.

[0057] <Method for forming an adhesive layer> The adhesive layer is formed, for example, by applying a polyimide precursor solution (hereinafter sometimes referred to as "thermoplastic polyimide precursor solution") containing a polyimide precursor, which is a precursor of thermoplastic polyimide, to at least one side of a polyimide film, and then heating (drying and imidization of the polyimide precursor). This method yields a multilayer polyimide film having a polyimide film and an adhesive layer disposed on at least one side of the polyimide film. Alternatively, instead of the thermoplastic polyimide precursor 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 polyimide film, and this coating film may be dried to form the adhesive layer.

[0058] Alternatively, for example, a co-extrusion die may be used to form a laminate comprising a layer containing a polyimide precursor, which is a precursor of the polyimide contained in the polyimide film, and a layer containing a polyimide precursor, which is a precursor of thermoplastic polyimide. The resulting laminate may then be heated to simultaneously form the polyimide film and the adhesive layer. In this method, by using a metal layer as a support, a metal-clad laminate (a laminate of a multilayer polyimide film and a metal layer) is obtained at the same time as the imidation is completed.

[0059] When manufacturing a multilayer polyimide film containing three polyimide layers, it is preferable to repeat the above 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.

[0060] <Metal-clad laminate> A metal-clad laminate comprises a polyimide film and a metal layer directly disposed on one or both sides of the polyimide film. Alternatively, a metal-clad laminate may also comprise the above-mentioned multilayer polyimide film and a metal layer disposed on one or both sides of the multilayer polyimide film.

[0061] The method for obtaining a metal-clad laminate is not particularly limited, and various known methods can be employed. Examples include plating, lamination, and coating methods.

[0062] The "plating method" for obtaining metal-clad laminates involves forming a first plating layer on one or both sides of a polyimide film or multilayer 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). Examples of dry plating methods include vacuum deposition, sputtering, ion plating, and CVD. The thickness of the metal layer (total thickness) consisting of the first and second plating layers is, for example, 1 μm to 50 μm.

[0063] The "lamination method," which is a method for obtaining metal-clad laminates, involves bonding a metal foil, which will form the metal layer, to one or both sides of a polyimide film or a multilayer polyimide film.

[0064] 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.

[0065] The "coating method" for obtaining a metal-clad laminate involves coating a solution containing the polyimide precursor of the present invention onto a metal foil that will form the metal layer, and then heating the coating film formed on the metal foil. 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 polyimide film and a metal layer made of metal foil. Alternatively, by alternately coating and heating a solution containing the polyimide precursor of the present invention and a solution containing a thermoplastic polyimide precursor, a metal-clad laminate can be obtained, which is a laminate of a multilayer polyimide film layer and a metal layer made of metal foil.

[0066] 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.

[0067] The metal foil forming 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 copper foil is preferred. Furthermore, the metal foil can be used with its surface roughness adjusted by surface treatment or other means 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 such that it can perform its function adequately according to its 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. [Examples]

[0068] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0069] <Method for measuring physical properties> This document describes methods for measuring the relative permittivity (Dk), dielectric loss tangent (Df), and coefficient of thermal expansion (CTE) of polyimide films.

[0070] [Relative permittivity (Dk) and dielectric loss tangent (Df)] 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 0.0025, it was evaluated as "the dielectric loss tangent has been reduced." On the other hand, if the dielectric loss tangent was 0.0025 or greater, it was evaluated as "the dielectric loss tangent has not been reduced."

[0071] [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

[0072] <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-R: 1,3-bis(4-aminophenoxy)benzene BPDA: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride PMDA: Pyromellitic dianhydride ODPA: 4,4'-Oxydiphthalic anhydride TMHQ: p-phenylenebis(trimellitic acid monoester anhydride) BP-TME: p-biphenylenebis(trimellitic acid monoester anhydride) AA: Acetic anhydride IQ: Isoquinoline

[0073] (Example 1) In a 500 mL glass flask, 164.39 g of DMF, 2.72 g (0.0093 mol) of TPE-R, and 6.19 g (0.00572 mol) of PDA were added. Then, while stirring the contents of the flask, 6.46 g (0.0220 mol) of BPDA, 11.15 g (0.0359 mol) of ODPA, and 3.05 g (0.0067 mol) of TMHQ were added to the flask. 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: 0.44 g (0.0020 mol), PMDA concentration: 7.2 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 flask contents. Then, when the viscosity of the flask contents reached 1500 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 polyimide precursor solution P1. The obtained polyimide precursor solution P1 had a solid content concentration of 15% by weight. Furthermore, the obtained polyimide precursor solution P1 had a viscosity of 1500-2000 poise at a temperature of 23°C.

[0074] Next, 30 g of an imidation accelerator (weight ratio: AA / IQ / DMF = 19 / 22 / 59), consisting of a mixture of AA, IQ, and DMF, was added to 60 g of polyimide precursor solution P1 to prepare a dope solution. Then, under an atmosphere of 0°C or lower, the dope solution was degassed while stirring, and 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 120°C for 160 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).

[0075] (Examples 2-12, Comparative Examples 1-12) A polyimide precursor solution and a polyimide film were obtained by the same method as in Example 1, except that the types and molar ratios of the diamine component and the tetracarboxylic dianhydride component were changed as shown in Table 1.

[0076] <Result> Table 1 shows the types and ratios (charging ratios) of monomers, the relative permittivity, dielectric loss tangent, and CTE of the obtained films for Examples 1-12 and Comparative Examples 1-12. 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 dianhydride used (unit: mol%). In the "Diamine" and "Acid Dianhydride" columns of Table 1, "0" means that the component in question (PDA, TPE-R, BPDA, ODPA, TMHQ, BP-TME, and PMDA) was not used. In all of Examples 1-12 and Comparative Examples 1-12, the mole fraction of each component 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 to 12 and Comparative Examples 1 to 12, 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.

[0077] In Examples 1 to 12, the dielectric loss tangent was less than 0.0025. Therefore, the polyimide films of Examples 1 to 9 were able to reduce the dielectric loss tangent. On the other hand, in Comparative Examples 1 to 12, the dielectric loss tangent was 0.0025 or greater. Therefore, the polyimide films of Comparative Examples 1 to 12 were not able to reduce the dielectric loss tangent. From these results, it is shown that the present invention can provide a polyimide that can reduce the dielectric loss tangent. [Table 1]

Claims

1. A polyimide precursor is obtained as an addition reaction product of a tetracarboxylic dianhydride component and a diamine component, wherein the diamine component comprises p-phenylenediamine and 1,3-bis(4-aminophenoxy)benzene, the tetracarboxylic dianhydride component comprises 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, and ester-containing tetracarboxylic dianhydride, wherein the content of 3,3',4,4'-biphenyltetracarboxylic dianhydride is 10 to 65 mol%, the content of 4,4'-oxydiphthalic anhydride is 20 to 70 mol%, the content of ester-containing tetracarboxylic dianhydride is 10 to 30 mol%, and the total content of 3,3',4,4'-biphenyltetracarboxylic dianhydride and ester-containing tetracarboxylic dianhydride is 75 mol% or less. A polyimide precursor characterized by having a p-phenylenediamine content of 70 to 95 mol% and a 1,3-bis(4-aminophenoxy)benzene content of 5 to 30 mol% relative to the total diamine components.

2. The polyimide precursor according to claim 1, further containing 15 mol% or less of pyromellitic dianhydride as a tetracarboxylic dianhydride component relative to the total tetracarboxylic dianhydride component.

3. The polyimide precursor according to claim 1 or 2, characterized in that the ester group-containing tetracarboxylic dianhydride is at least one selected from p-phenylenebis(trimellitic acid monoester anhydride) and p-biphenylenebis(trimellitic acid monoester anhydride).

4. A polyimide that is a polycondensate of a tetracarboxylic dianhydride component and a diamine component, wherein the diamine component includes p-phenylenediamine and 1,3-bis(4-aminophenoxy)benzene, and the tetracarboxylic dianhydride component includes 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, and ester-containing tetracarboxylic dianhydride, wherein the content of 3,3',4,4'-biphenyltetracarboxylic dianhydride is 10 to 65 mol%, the content of 4,4'-oxydiphthalic anhydride is 20 to 70 mol%, the content of ester-containing tetracarboxylic dianhydride is 10 to 30 mol%, and the total content of 3,3',4,4'-biphenyltetracarboxylic dianhydride and ester-containing tetracarboxylic dianhydride is 75 mol% or less. A polyimide characterized by having a p-phenylenediamine content of 70 to 95 mol% and a 1,3-bis(4-aminophenoxy)benzene content of 5 to 30 mol% relative to the total diamine components.

5. The polyimide according to claim 4, further containing 15 mol% or less of pyromellitic dianhydride as a tetracarboxylic dianhydride component relative to the total tetracarboxylic dianhydride component.

6. The polyimide according to claim 4 or 5, characterized in that the ester group-containing tetracarboxylic dianhydride is at least one selected from p-phenylenebis(trimellitic acid monoester anhydride) and p-biphenylenebis(trimellitic acid monoester anhydride).

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