Multilayer polyimide film, metal-clad laminate, and method for producing multilayer polyimide film

Abstract

This multilayer polyimide film (10) comprises: a non-thermoplastic polyimide layer (11); and an adhesive layer (12) which is disposed on at least one surface of the non-thermoplastic polyimide layer (11) and includes polyimide. The non-thermoplastic polyimide has a dielectric loss tangent of 0.0030 or less at a frequency of 10 GHz, a temperature of 23 °C, and a relative humidity of 50%. The adhesive layer (12) does not have a melting peak or has a melting heat of 1.0 J / g or less at a melting peak in a temperature range of 100-420 °C. The polyimide included in the adhesive layer (12) has: at least one tetracarboxylic dianhydride residue selected from the group consisting of a pyromellitic acid dianhydride residue and a 3,3',4,4'-biphenyltetracarboxylic acid dianhydride residue; and at least one diamine residue selected from the group consisting of a 1,3-bis(4-aminophenoxy)benzene residue and a 4,4'-diamino-2,2'-dimethylbiphenyl residue.

Description

[Technical Field]

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

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

[0003] Furthermore, with the recent trend toward high-speed signal transmission in electronic devices, there is an increasing demand for electronic circuit board materials with low dielectric constants and low dielectric loss tangents to enable higher frequencies of electrical signals propagating through circuits. Reducing the dielectric constant and dielectric loss tangent of electronic circuit board materials is effective in suppressing electrical signal transmission loss. In recent years, as we enter the dawn of the IoT society, the trend toward higher frequencies is accelerating, and there is a demand for circuit board materials that can suppress transmission loss, even in the 10 GHz and higher frequency range.

[0004] Polyimide films that exhibit a low dielectric loss tangent are known as films used in circuit boards that are adaptable to higher frequencies. For example, Patent Document 1 discloses a multilayer polyimide film having a non-thermoplastic polyimide layer that exhibits a low dielectric loss tangent. Patent Document 2 also discloses a multilayer polyimide film that has a thermoplastic polyimide layer on at least one side of the non-thermoplastic polyimide layer and has a dielectric loss tangent of 0.004 or less at 10 GHz. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-145303 [Patent Document 2] International Publication No. 2018 / 061727 Summary of the Invention [Problem to be solved by the invention]

[0006] However, it is difficult to obtain a multilayer polyimide film that can reduce the dielectric tangent while maintaining the adhesive properties with the metal layer (more specifically, the adhesion with the metal layer, the embeddability in the metal layer, etc.) and that is also highly productive using only the techniques described in Patent Documents 1 and 2.

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

[0008] The multilayer polyimide film according to the present invention comprises a non-thermoplastic polyimide layer and a polyimide-containing adhesive layer disposed on at least one side of the non-thermoplastic polyimide layer. The non-thermoplastic polyimide layer has a dielectric loss tangent of 0.0030 or less at a frequency of 10 GHz, a temperature of 23°C, and a relative humidity of 50%. The adhesive layer has no melting peak or a melting peak with a heat of fusion of 1.0 J / g or less within a temperature range of 100°C to 420°C. The polyimide contained in the adhesive layer has one or more tetracarboxylic dianhydride residues selected from the group consisting of pyromellitic dianhydride residues and 3,3',4,4'-biphenyltetracarboxylic dianhydride residues, and one or more diamine residues selected from the group consisting of 1,3-bis(4-aminophenoxy)benzene residues and 4,4'-diamino-2,2'-dimethylbiphenyl residues.

[0009] In the multilayer polyimide film according to one embodiment of the present invention, the adhesive layer is disposed on both sides of the non-thermoplastic polyimide layer.

[0010] In the multilayer polyimide film according to one embodiment of the present invention, the adhesive layer contains a tertiary amine at a content of 1 ppm by mass or more.

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

[0012] In a multilayer polyimide film according to one embodiment of the present invention, the non-thermoplastic polyimide contained in the non-thermoplastic polyimide layer has one or more tetracarboxylic dianhydride residues selected from the group consisting of 3,3',4,4'-biphenyltetracarboxylic dianhydride residues and 4,4'-oxydiphthalic anhydride residues, and one or more diamine residues selected from the group consisting of p-phenylenediamine residues and 1,3-bis(4-aminophenoxy)benzene residues.

[0013] In a multilayer polyimide film according to one embodiment of the present invention, the non-thermoplastic polyimide contained in the non-thermoplastic polyimide layer has a p-phenylenediamine residue, and the polyimide contained in the adhesive layer does not have a p-phenylenediamine residue.

[0014] In the multilayer polyimide film according to one embodiment of the present invention, the adhesive layer does not have a melting peak in the temperature range of 100°C or higher and 420°C or lower.

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

[0016] The method for producing a multilayer polyimide film according to the present invention is a method for producing a multilayer polyimide film having a non-thermoplastic polyimide layer and a polyimide-containing adhesive layer disposed on at least one side of the non-thermoplastic polyimide layer, and comprises a coating step, a gel film-forming step, and an imidization step. In the coating step, a non-thermoplastic polyimide layer-forming solution containing polyamic acid, acetic anhydride, and a tertiary amine and an adhesive layer-forming solution containing polyamic acid are applied to a support by a co-extrusion-casting coating method. In the gel film-forming step, the coating film obtained in the coating step is dried to form a self-supporting gel film. In the imidization step, the gel film obtained in the gel film-forming step is heated at a maximum temperature of 360°C or higher to imidize the polyamic acid in the non-thermoplastic polyimide layer-forming solution and the polyamic acid in the adhesive layer-forming solution. In the coating step, the polyamic acid contained in the adhesive layer-forming solution has pyromellitic dianhydride residues, 3,3',4,4'-biphenyltetracarboxylic dianhydride residues, 1,3-bis(4-aminophenoxy)benzene residues, and 4,4'-diamino-2,2'-dimethylbiphenyl residues. In the coating step, the polyamic acid contained in the non-thermoplastic polyimide layer-forming solution has one or more tetracarboxylic dianhydride residues selected from the group consisting of 3,3',4,4'-biphenyltetracarboxylic dianhydride residues and 4,4'-oxydiphthalic anhydride residues, and one or more diamine residues selected from the group consisting of p-phenylenediamine residues and 1,3-bis(4-aminophenoxy)benzene residues.

[0017] In one embodiment of the method for producing a multilayer polyimide film according to the present invention, in the coating step, the polyamic acid contained in the non-thermoplastic polyimide layer forming solution has a p-phenylenediamine residue, and the polyamic acid contained in the adhesive layer forming solution does not have a p-phenylenediamine residue.

[0018] In the method for producing a multilayer polyimide film according to one embodiment of the present invention, in the imidization step, the gel film is heated at the maximum temperature for 10 seconds or more and 300 seconds or less.

[0019] In one embodiment of the method for producing a multilayer polyimide film according to the present invention, the adhesive layer has no melting peak or the heat of fusion of the melting peak is 1.0 J / g or less in the temperature range of 100°C or more and 420°C or less.

[0020] In the method for producing a multilayer polyimide film according to one embodiment of the present invention, the adhesive layer does not have a melting peak in the temperature range of 100°C or higher and 420°C or lower.

[0021] In the method for producing a multilayer polyimide film according to one embodiment of the present invention, the non-thermoplastic polyimide layer has a dielectric loss tangent of 0.0030 or less at a frequency of 10 GHz, a temperature of 23° C., and a relative humidity of 50%. [Effects of the Invention]

[0022] According to the present invention, it is possible to provide a multilayer polyimide film that can reduce the dielectric tangent while maintaining adhesion properties with a metal layer and has excellent productivity, a method for producing the same, and a metal-clad laminate using the multilayer polyimide film. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a cross-sectional view showing an example of a multilayer polyimide film according to the present invention. [Figure 2] 1 is a cross-sectional view showing an example of a metal-clad laminate according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] Preferred embodiments of the present invention will be described in detail below, but the present invention is not limited thereto. In addition, all academic and patent documents described in this specification are incorporated herein by reference.

[0025] First, the terms used in this specification will be explained. A "structural unit" refers to a repeating unit that constitutes a polymer. A "polyimide" is a polymer containing a structural unit represented by the following general formula (1) (hereinafter, sometimes referred to as "structural unit (1)").

[0026] [ka]

[0027] In general formula (1), X 1 represents a tetracarboxylic dianhydride residue (a tetravalent organic group derived from tetracarboxylic dianhydride), and X 2 represents a diamine residue (a divalent organic group derived from a diamine).

[0028] The content of the structural unit (1) relative to all structural units constituting the polyimide is, for example, 50 mol% or more and 100 mol% or less, preferably 60 mol% or more and 100 mol% or less, more preferably 70 mol% or more and 100 mol% or less, even more preferably 80 mol% or more and 100 mol% or less, still more preferably 90 mol% or more and 100 mol% or less, and may be 100 mol%.

[0029] A "polyamic acid" is a polymer containing a structural unit represented by the following general formula (2) (hereinafter, sometimes referred to as "structural unit (2)").

[0030] [ka]

[0031] In general formula (2), A 1 represents a tetracarboxylic dianhydride residue (a tetravalent organic group derived from a tetracarboxylic dianhydride), and A 2 represents a diamine residue (a divalent organic group derived from a diamine).

[0032] The content of the structural unit (2) relative to all structural units constituting the polyamic acid is, for example, 50 mol% or more and 100 mol% or less, preferably 60 mol% or more and 100 mol% or less, more preferably 70 mol% or more and 100 mol% or less, even more preferably 80 mol% or more and 100 mol% or less, still more preferably 90 mol% or more and 100 mol% or less, and may be 100 mol%.

[0033] Polyimide is an imide of polyamic acid. Therefore, when the content of the structural unit (2) relative to all structural units constituting the polyamic acid is 100 mol %, the polyimide, which is an imide of the polyamic acid, is represented by X in the general formula (1). 1 As A in general formula (2) 1 and X in general formula (1) 2 As A in general formula (2) 2 The residue is represented by:

[0034] 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 dielectric loss tangent is measured by the same method as in the examples described below or a method equivalent thereto.

[0035] "Non-thermoplastic polyimide" refers to polyimide that retains its film shape (flat membrane shape) when fixed in film form on a metal frame and heated at 380°C for 2 minutes.

[0036] The "principal surface" of a layered material (more specifically, a non-thermoplastic polyimide layer, an adhesive layer, a multilayer polyimide film, a metal layer, etc.) refers to a surface perpendicular to the thickness direction of the layered material.

[0037] Hereinafter, the compound name may be followed by "system" to refer to the compound and its derivatives collectively. Tetracarboxylic acid dianhydrides may be referred to as "acid dianhydrides." Adhesion properties with metal layers may be simply referred to as "adhesion properties."

[0038] The drawings referred to in the following description mainly show each component in a schematic manner for ease of understanding, and the size, number, shape, etc. of each component shown may differ from the actual size, number, shape, etc. of each component due to the convenience of creating the drawings. Furthermore, for convenience of explanation, in drawings described later, the same components as those in previously described drawings may be assigned the same reference numerals, and their explanation may be omitted.

[0039] Hereinafter, preferred embodiments of the present invention will be described in the order of a method for producing a multilayer polyimide film, a multilayer polyimide film, and a metal-clad laminate.

[0040] <First embodiment: Method for producing multilayer polyimide film> The method for producing a multilayer polyimide film according to a first embodiment of the present invention is a method for producing a multilayer polyimide film having a non-thermoplastic polyimide layer and a polyimide-containing adhesive layer disposed on at least one side of the non-thermoplastic polyimide layer, and includes a coating step, a gel film-forming step, and an imidization step. In the coating step, a non-thermoplastic polyimide layer-forming solution containing polyamic acid, acetic anhydride, and a tertiary amine and an adhesive layer-forming solution containing polyamic acid are applied to a support by a co-extrusion-casting coating method. In the gel film-forming step, the coating film obtained in the coating step is dried to form a self-supporting gel film. In the imidization step, the gel film obtained in the gel film-forming step is heated at a maximum temperature of 360°C or higher to imidize the polyamic acid in the non-thermoplastic polyimide layer-forming solution and the polyamic acid in the adhesive layer-forming solution. In the coating step, the polyamic acid contained in the adhesive layer-forming solution has pyromellitic dianhydride residues, 3,3',4,4'-biphenyltetracarboxylic dianhydride residues, 1,3-bis(4-aminophenoxy)benzene residues, and 4,4'-diamino-2,2'-dimethylbiphenyl residues. In the coating step, the polyamic acid contained in the non-thermoplastic polyimide layer-forming solution has one or more tetracarboxylic dianhydride residues selected from the group consisting of 3,3',4,4'-biphenyltetracarboxylic dianhydride residues and 4,4'-oxydiphthalic anhydride residues, and one or more diamine residues selected from the group consisting of p-phenylenediamine residues and 1,3-bis(4-aminophenoxy)benzene residues.

[0041] The "co-extrusion-casting coating method" is a method for forming a coating film using an extruder having an extrusion die for two or more layers. Specifically, the co-extrusion-casting coating method is a method for forming a coating film having a layer structure of two or more layers on a support by extruding a non-thermoplastic polyimide layer-forming solution and an adhesive layer-forming solution in the form of a thin film having two or more layers from the lip opening of the extrusion die.

[0042] Hereinafter, the self-supporting gel film may be referred to simply as "gel film." Pyromellitic dianhydride may be referred to as "PMDA." 3,3',4,4'-biphenyltetracarboxylic dianhydride may be referred to as "BPDA." 1,3-bis(4-aminophenoxy)benzene may be referred to as "TPE-R." 4,4'-diamino-2,2'-dimethylbiphenyl may be referred to as "m-TB." p-Phenylenediamine may be referred to as "PDA." 4,4'-oxydiphthalic anhydride may be referred to as "ODPA." The non-thermoplastic polyimide contained in the non-thermoplastic polyimide layer may be referred to simply as "non-thermoplastic polyimide."

[0043] The method for producing a multilayer polyimide film according to the first embodiment not only increases productivity but also enables the production of a multilayer polyimide film that can reduce the dielectric loss tangent while maintaining adhesion properties with a metal layer. The reasons for this are presumed to be as follows.

[0044] The production method according to the first embodiment employs a co-extrusion-casting coating method and a method of promoting imidization using acetic anhydride and a tertiary amine (chemical imidization method), which simplifies the film formation process and shortens the imidization time, thereby enabling the multilayer polyimide film production method according to the first embodiment to increase productivity.

[0045] In the first embodiment, the polyamic acid contained in the non-thermoplastic polyimide layer-forming solution contains one or more acid dianhydride residues selected from the group consisting of BPDA residues and ODPA residues and one or more diamine residues selected from the group consisting of PDA residues and TPE-R residues, and the polyamic acid is imidized by chemical imidization at a maximum temperature of 360°C or higher. Because the imidization reaction occurs more rapidly in chemical imidization than in thermal imidization, in the first embodiment, the polyamic acid is imidized in a relatively large amount of solvent. In the first embodiment, the polyamic acid containing the specific residues is imidized by chemical imidization at a maximum temperature of 360°C or higher, resulting in a non-thermoplastic polyimide with improved packing. As a result, the non-thermoplastic polyimide layer obtained by the production method according to the first embodiment tends to have a low dielectric loss tangent. Therefore, the multilayer polyimide film production method according to the first embodiment can reduce the dielectric loss tangent of the multilayer polyimide film.

[0046] Furthermore, in the first embodiment, the polyamic acid contained in the adhesive layer-forming solution contains PMDA residues, BPDA residues, TPE-R residues, and m-TB residues, so that when imidization is performed at a maximum temperature of 360° C. or higher, the adhesive properties of the resulting adhesive layer are not reduced and the shape of the film containing the polyamic acid in the adhesive layer-forming solution can be maintained in good condition. Therefore, the method for producing a multilayer polyimide film according to the first embodiment ensures adhesive properties with a metal layer.

[0047] In the first embodiment, in order to obtain a multilayer polyimide film that can further reduce the dielectric tangent while improving the adhesive properties with the metal layer, it is preferable that the polyamic acid contained in the non-thermoplastic polyimide layer forming solution has a PDA residue and the polyamic acid contained in the adhesive layer forming solution does not have a PDA residue.

[0048] Each step of the manufacturing method according to the first embodiment will be described in detail below.

[0049] [Coating process] (Solution for forming non-thermoplastic polyimide layer) The non-thermoplastic polyimide layer-forming solution is a solution for forming a non-thermoplastic polyimide layer that is a core layer of a multilayer polyimide film, and contains polyamic acid, acetic anhydride, and a tertiary amine.

[0050] The polyamic acid contained in the non-thermoplastic polyimide layer-forming solution (hereinafter sometimes referred to as "non-thermoplastic polyamic acid") has one or more acid dianhydride residues selected from the group consisting of BPDA residues and ODPA residues, and one or more diamine residues selected from the group consisting of PDA residues and TPE-R residues. The non-thermoplastic polyamic acid may contain one or more polyamic acids, but preferably consists of one type of polyamic acid.

[0051] The non-thermoplastic polyamic acid may have other acid dianhydride residues in addition to one or more acid dianhydride residues selected from the group consisting of BPDA residues and ODPA residues. Examples of acid dianhydrides (monomers) for forming other acid dianhydride residues (acid dianhydride residues other than BPDA residues and ODPA residues) include PMDA, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, and 3,4'-oxydiphthalic acid dianhydride. Examples of the dianhydride include 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, p-phenylene bis(trimellitic acid monoester acid anhydride), ethylene bis(trimellitic acid monoester acid anhydride), bisphenol A bis(trimellitic acid monoester acid anhydride), and derivatives thereof.

[0052] In order to obtain a multilayer polyimide film that can further reduce the dielectric loss tangent while improving the heat resistance, the other acid dianhydride residue is preferably a PMDA residue.

[0053] In order to obtain a multilayer polyimide film that can further reduce the dielectric loss tangent, the total content of BPDA residues and ODPA residues relative to all acid dianhydride residues constituting the non-thermoplastic polyamic acid is preferably 50 mol % or more, more preferably 70 mol % or more, even more preferably 80 mol % or more, even more preferably 90 mol % or more, and may be 100 mol %.

[0054] When a PMDA residue is used as the other acid dianhydride residue, in order to obtain a multilayer polyimide film that can further reduce the dielectric tangent while improving heat resistance, the total content of BPDA residues, ODPA residues, and PMDA residues relative to all acid dianhydride residues constituting the non-thermoplastic polyamic acid is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may even be 100 mol%.

[0055] To obtain a multilayer polyimide film that can further reduce the dielectric loss tangent, the non-thermoplastic polyamic acid preferably contains two types of acid dianhydride residues, i.e., BPDA residue and ODPA residue.To obtain a multilayer polyimide film that can further reduce the dielectric loss tangent while improving heat resistance, the non-thermoplastic polyamic acid preferably contains three types of acid dianhydride residues, i.e., BPDA residue, ODPA residue, and PMDA residue.

[0056] In order to obtain a multilayer polyimide film that can further reduce the dielectric loss tangent, the content of BPDA residues relative to all acid dianhydride residues constituting the non-thermoplastic polyamic acid is preferably 40 mol % or more and 80 mol % or less, and more preferably 50 mol % or more and 70 mol % or less.

[0057] In order to obtain a multilayer polyimide film that can further reduce the dielectric loss tangent, the content of ODPA residues relative to all acid dianhydride residues constituting the non-thermoplastic polyamic acid is preferably 10 mol % or more and 50 mol % or less, and more preferably 20 mol % or more and 40 mol % or less.

[0058] In order to obtain a multilayer polyimide film that can further reduce the dielectric tangent while improving the heat resistance, the content of PMDA residues relative to all acid dianhydride residues constituting the non-thermoplastic polyamic acid is preferably 1 mol % or more and 10 mol % or less, and more preferably 2 mol % or more and 8 mol % or less.

[0059] The non-thermoplastic polyamic acid has, in addition to the above-mentioned acid dianhydride residues, one or more diamine residues selected from the group consisting of PDA residues and TPE-R residues.

[0060] The non-thermoplastic polyamic acid may have other diamine residues in addition to one or more diamine residues selected from the group consisting of PDA residues and TPE-R residues. Examples of diamines (monomers) for forming other diamine residues (diamine residues other than PDA residues and TPE-R residues) include 1,4-bis(4-aminophenoxy)benzene, 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 1,5-diaminonaphthalene, 4,4'-diaminodiphenyldiethylsilane, 4,4'-diaminodiphenylsilane, 4,4'-diaminodiphenylethylphosphine oxide, 4,4'-diaminodiphenyl N-methylamine, 4,4'-diaminodiphenyl N-phenylamine, 1,3-diaminobenzene, 1,2-diaminobenzene, and derivatives thereof.

[0061] In order to obtain a multilayer polyimide film that can further reduce the dielectric loss tangent, the total content of PDA residues and TPE-R residues relative to all diamine residues constituting the non-thermoplastic polyamic acid is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may even be 100 mol%.

[0062] In order to obtain a multilayer polyimide film that can further reduce the dielectric loss tangent, the non-thermoplastic polyamic acid preferably has two types of diamine residues, namely, a PDA residue and a TPE-R residue.

[0063] In order to obtain a multilayer polyimide film that can further reduce the dielectric loss tangent, the content of PDA residues relative to all diamine residues constituting the non-thermoplastic polyamic acid is preferably 60 mol % or more and 95 mol % or less, and more preferably 70 mol % or more and 90 mol % or less.

[0064] In order to obtain a multilayer polyimide film that can further reduce the dielectric loss tangent, the content of TPE-R residues relative to all diamine residues constituting the non-thermoplastic polyamic acid is preferably 5 mol % or more and 40 mol % or less, and more preferably 10 mol % or more and 30 mol % or less.

[0065] Any known method or a combination thereof can be used to produce (synthesize) non-thermoplastic polyamic acid. A specific example of a method for producing (synthesizes) non-thermoplastic polyamic acid is a method of reacting a diamine with a tetracarboxylic dianhydride in an organic solvent. The amount of diamine and the amount of tetracarboxylic dianhydride used during the reaction are preferably substantially equal. When synthesizing non-thermoplastic polyamic acid using a diamine and a tetracarboxylic dianhydride, the desired polyamic acid (a polymer of a diamine and a tetracarboxylic dianhydride) can be obtained by adjusting the amount of diamine (or, if multiple diamines are used, the amount of each diamine) and the amount of tetracarboxylic dianhydride (or, if multiple tetracarboxylic dianhydrides are used, the amount of each tetracarboxylic dianhydride). The molar fraction of each residue in the non-thermoplastic polyamic acid corresponds to, for example, the molar fraction of each monomer (diamine and tetracarboxylic dianhydride) used to synthesize the non-thermoplastic polyamic acid. The temperature conditions for the reaction between the diamine and the tetracarboxylic dianhydride, i.e., the synthesis reaction of the non-thermoplastic polyamic acid, are not particularly limited, but are, for example, in the range of 10°C to 150°C. The reaction time for the synthesis reaction of the non-thermoplastic polyamic acid is, for example, in the range of 10 minutes to 30 hours. Any method of adding monomers may be used for synthesizing the non-thermoplastic polyamic acid.

[0066] The non-thermoplastic polyimide layer-forming solution contains, in addition to a non-thermoplastic polyamic acid, acetic anhydride as a dehydration ring-closing agent and a tertiary amine as a catalyst. The inclusion of acetic anhydride and a tertiary amine in the non-thermoplastic polyimide layer-forming solution promotes imidization. Examples of tertiary amines include aliphatic tertiary amines, aromatic tertiary amines, and heterocyclic tertiary amines. To facilitate the promotion of imidization, the tertiary amine is preferably a heterocyclic tertiary amine, and more preferably one or more selected from the group consisting of pyridine compounds (more specifically, β-picoline, γ-picoline, 3,5-dimethylpyridine, etc.) having alkyl groups introduced at the β- and / or γ-positions, pyridine, and isoquinoline.

[0067] The amount of tertiary amine added is preferably 0.5 to 5.0 molar equivalents, more preferably 0.7 to 2.5 molar equivalents, and even more preferably 0.8 to 2.0 molar equivalents, relative to the amide groups of the non-thermoplastic polyamic acid. The amount of acetic anhydride added is preferably 0.5 to 10.0 molar equivalents, more preferably 0.7 to 5.0 molar equivalents, and even more preferably 0.8 to 3.0 molar equivalents, relative to the amide groups of the non-thermoplastic polyamic acid. In this specification, "amide groups of the non-thermoplastic polyamic acid" refers to amide groups formed by the polymerization reaction of a diamine with a tetracarboxylic dianhydride. When adding the tertiary amine and acetic anhydride to the polyamic acid solution described below, they may be added directly without dissolving them in an organic solvent, or they may be added dissolved in an organic solvent. If the tertiary amine and acetic anhydride are added directly without dissolving them in an organic solvent, the reaction may proceed too quickly before the tertiary amine and acetic anhydride can diffuse, resulting in the formation of a gel. Therefore, it is preferable to add a solution (imidization accelerator) obtained by dissolving the tertiary amine and acetic anhydride in an organic solvent to the polyamic acid solution.

[0068] The non-thermoplastic polyimide layer-forming solution can be obtained, for example, by adding a tertiary amine and acetic anhydride to a polyamic acid solution containing a non-thermoplastic polyamic acid and an organic solvent. Examples of organic solvents that can be used in polyamic acid solutions include urea-based solvents such as tetramethylurea and N,N-dimethylethylurea; sulfoxide-based solvents such as dimethyl sulfoxide; sulfone-based solvents such as diphenyl sulfone and tetramethyl sulfone; amide-based solvents such as N,N-dimethylacetamide, N,N-dimethylformamide (hereinafter sometimes referred to as "DMF"), N,N-diethylacetamide, N-methyl-2-pyrrolidone, and hexamethylphosphoric acid triamide; ester-based solvents such as γ-butyrolactone; alkyl halide solvents such as chloroform and methylene chloride; aromatic hydrocarbon solvents such as benzene and toluene; phenol-based solvents such as phenol and cresol; ketone-based solvents such as cyclopentanone; and ether-based solvents such as tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dimethyl ether, diethyl ether, diethylene glycol diethyl ether, diethylene glycol dimethyl ether, and p-cresol methyl ether. These solvents are typically used alone, but two or more may be used in combination as needed. When a non-thermoplastic polyamic acid is obtained by the above-mentioned polymerization method, the reaction solution (the solution after the reaction) itself may be used as a polyamic acid solution. In this case, the organic solvent in the polyamic acid solution is the organic solvent used in the reaction in the above-mentioned polymerization method. Alternatively, the solid non-thermoplastic polyamic acid obtained by removing the solvent from the reaction solution may be dissolved in an organic solvent to prepare a polyamic acid solution.

[0069] The polyamic acid solution may contain additives such as dyes, surfactants, leveling agents, plasticizers, silicones, and sensitizers. Furthermore, a filler may be added to the polyamic acid solution to improve various film properties such as sliding properties, thermal conductivity, electrical conductivity, corona resistance, and loop stiffness. Any filler may be used, but preferred examples include fillers made of silica, titanium oxide, alumina, silicon nitride, boron nitride, calcium hydrogen phosphate, calcium phosphate, mica, and the like.

[0070] The concentration of the non-thermoplastic polyamic acid in the polyamic acid solution is not particularly limited and is, for example, 5% by weight to 35% by weight, preferably 8% by weight to 30% by weight, based on the total amount of the polyamic acid solution.

[0071] (Adhesive layer forming solution) The adhesive layer-forming solution is a solution for forming an adhesive layer to be bonded to a metal layer. The adhesive layer-forming solution contains a polyamic acid. In addition to the polyamic acid, the adhesive layer-forming solution may also contain the above-mentioned acetic anhydride and tertiary amine. When the adhesive layer-forming solution contains acetic anhydride and a tertiary amine, the preferred ranges of the added amounts of acetic anhydride and tertiary amine are the same as the preferred ranges of the added amounts in the non-thermoplastic polyimide layer-forming solution. Note that, if the non-thermoplastic polyimide layer-forming solution contains acetic anhydride and a tertiary amine, even if the adhesive layer-forming solution does not contain acetic anhydride and a tertiary amine, the acetic anhydride and tertiary amine diffuse from the non-thermoplastic polyimide layer-forming solution into the adhesive layer-forming solution during the imidization step, and the polyamic acid in the adhesive layer-forming solution can be imidized by a chemical imidization method.

[0072] The polyamic acid contained in the adhesive layer-forming solution (hereinafter sometimes referred to as "adhesive polyamic acid") has a PMDA residue, a BPDA residue, a TPE-R residue, and an m-TB residue. The adhesive polyamic acid may contain one or more polyamic acids, but preferably consists of one type of polyamic acid.

[0073] The adhesive polyamic acid may have other acid dianhydride residues in addition to the PMDA residue and the BPDA residue. Examples of the acid dianhydride (monomer) for forming the other acid dianhydride residue (acid dianhydride residue other than the PMDA residue and the BPDA residue) include the same acid dianhydrides as those exemplified as the acid dianhydrides for forming the non-thermoplastic polyamic acid described above.

[0074] In order to obtain a multilayer polyimide film having excellent adhesive properties while further reducing the dielectric tangent, the total content of PMDA residues and BPDA residues relative to all acid dianhydride residues constituting the adhesive polyamic acid is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may even be 100 mol%.

[0075] In order to obtain a multilayer polyimide film having excellent adhesive properties while further reducing the dielectric tangent, the content of PMDA residues relative to all acid dianhydride residues constituting the adhesive polyamic acid is preferably 20 mol % or more and 80 mol % or less, and more preferably 30 mol % or more and 70 mol % or less.

[0076] In order to obtain a multilayer polyimide film having excellent adhesive properties while further reducing the dielectric tangent, the content of BPDA residues relative to all acid dianhydride residues constituting the adhesive polyamic acid is preferably 20 mol % or more and 80 mol % or less, and more preferably 30 mol % or more and 70 mol % or less.

[0077] The adhesive polyamic acid has, in addition to the above-mentioned acid dianhydride residue, a TPE-R residue and an m-TB residue as diamine residues.

[0078] The adhesive polyamic acid may have other diamine residues in addition to the TPE-R residue and the m-TB residue. Examples of diamines (monomers) for forming the other diamine residues (diamine residues other than the TPE-R residue and the m-TB residue) include the same diamines as those exemplified above as diamines for forming the non-thermoplastic polyamic acid.

[0079] In order to obtain a multilayer polyimide film having excellent adhesive properties while further reducing the dielectric loss tangent, the total content of TPE-R residues and m-TB residues relative to all diamine residues constituting the adhesive polyamic acid is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may even be 100 mol%.

[0080] In order to obtain a multilayer polyimide film having excellent adhesive properties while further reducing the dielectric tangent, the content of TPE-R residues relative to all diamine residues constituting the adhesive polyamic acid is preferably 50 mol % or more and 95 mol % or less, and more preferably 60 mol % or more and 95 mol % or less.

[0081] In order to obtain a multilayer polyimide film having excellent adhesive properties while further reducing the dielectric tangent, the content of m-TB residues relative to all diamine residues constituting the adhesive polyamic acid is preferably 5 mol % or more and 50 mol % or less, and more preferably 5 mol % or more and 40 mol % or less.

[0082] The adhesive layer-forming solution may contain additives such as dyes, surfactants, leveling agents, plasticizers, silicones, and sensitizers. Furthermore, a filler may be added to the adhesive layer-forming solution for the purpose of improving various film properties such as sliding properties, thermal conductivity, electrical conductivity, corona resistance, and loop stiffness. Any filler may be used, but preferred examples include fillers made of silica, titanium oxide, alumina, silicon nitride, boron nitride, calcium hydrogen phosphate, calcium phosphate, mica, and the like.

[0083] The method for obtaining the solution for forming an adhesive layer (polyamic acid solution) is the same as the method for obtaining the solution for forming a non-thermoplastic polyimide layer described above, except that an adhesive polyamic acid is synthesized instead of a non-thermoplastic polyamic acid (a monomer for synthesizing an adhesive polyamic acid is used).

[0084] The concentration of the adhesive polyamic acid in the adhesive layer forming solution (polyamic acid solution) is not particularly limited, and is, for example, 5% by weight or more and 35% by weight or less, and preferably 8% by weight or more and 30% by weight or less, relative to the total amount of the adhesive layer forming solution.

[0085] In order to obtain a multilayer polyimide film having an even lower dielectric tangent and even better adhesive properties, the method for producing a multilayer polyimide film according to the first embodiment preferably satisfies the following condition 1, more preferably satisfies the following conditions 1 and 2, and even more preferably satisfies the following conditions 1, 2, and 3. Condition 1: The adhesive polyamic acid has only PMDA residues and BPDA residues as acid dianhydride residues, and only TPE-R residues and m-TB residues as diamine residues. Condition 2: The non-thermoplastic polyamic acid has only BPDA residues, ODPA residues, and PMDA residues as acid dianhydride residues, and only TPE-R residues and PDA residues as diamine residues. Condition 3: In the adhesive polyamic acid, the value obtained by dividing the amount of substance of PMDA residues by the amount of substance of BPDA residues is 0.8 or more and 1.2 or less, and the value obtained by dividing the amount of substance of TPE-R residues by the amount of substance of m-TB residues is 2.0 or more and 2.5 or less.

[0086] When the above conditions 1 and 2 are satisfied, both the polyimide contained in the non-thermoplastic polyimide layer and the polyimide contained in the adhesive layer contain TPE-R residues, PMDA residues, and BPDA residues, and therefore a multilayer polyimide film having excellent adhesion between the non-thermoplastic polyimide layer and the adhesive layer can be obtained.

[0087] (Application method) The coating method in the coating step is not particularly limited as long as the non-thermoplastic polyimide layer-forming solution and the adhesive layer-forming solution are coated on the support by a co-extrusion-casting coating method. For example, a coating film having a layer structure of two or more layers can be formed on the support by extruding the non-thermoplastic polyimide layer-forming solution and the adhesive layer-forming solution in the form of a thin film of two or more layers from the lip opening of an extrusion die using a known extruder.

[0088] Suitable supports for use in the co-extrusion-casting coating method include glass plates, aluminum foils, stainless steel endless belts, stainless steel drums, and the like.

[0089] [Gel film formation process] In the gel film formation process, the coating film obtained in the coating process is dried to form a self-supporting gel film. The coating film can be dried, for example, on a support. The drying temperature when drying the coating film is, for example, 50°C or higher and 200°C or lower. The drying time when drying the coating film is, for example, 1 minute or higher and 100 minutes or lower. Note that a multi-stage drying process may be performed, such as heating the coating film at a temperature of 50°C for 10 minutes and then at a temperature of 100°C for 10 minutes.

[0090] [Imidization process] In the imidization step, the gel film obtained in the gel film formation step is heated at a maximum temperature of 360°C or higher to imidize the polyamic acid in the non-thermoplastic polyimide layer-forming solution and the polyamic acid in the adhesive layer-forming solution. This step results in a multilayer polyimide film, which is a laminate of a non-thermoplastic polyimide layer and an adhesive layer. In order to further reduce the dielectric loss tangent, the maximum temperature in the imidization step is preferably 380°C or higher. The upper limit of the maximum temperature in the imidization step is, for example, 500°C, preferably 450°C. In order to obtain a multilayer polyimide film with excellent adhesive properties while further reducing the dielectric loss tangent, the heating time of the gel film at the maximum temperature is preferably 10 seconds to 300 seconds, more preferably 20 seconds to 200 seconds, even more preferably 30 seconds to 150 seconds, and even 60 seconds to 100 seconds. Furthermore, the gel film may be held at any temperature for any time until the maximum temperature is reached.

[0091] The imidization process can be carried out in air, under reduced pressure, or in an inert gas such as nitrogen. To prevent shrinkage during film curing, the imidization process is preferably carried out by peeling the gel film from the support and heating the gel film while fixing its edges. The imidization process may also be carried out while stretching the gel film in the conveying direction or a direction perpendicular to the conveying direction.

[0092] [Multilayer polyimide film obtained by the production method according to the first embodiment] Next, the multilayer polyimide film obtained by the production method according to the first embodiment will be described with reference to the drawings.

[0093] Fig. 1 is a cross-sectional view showing an example of a multilayer polyimide film obtained by the production method according to Embodiment 1. As shown in Fig. 1, a multilayer polyimide film 10 has a non-thermoplastic polyimide layer 11 and an adhesive layer 12 disposed on at least one surface (one main surface) of the non-thermoplastic polyimide layer 11.

[0094] In the multilayer polyimide film 10 shown in FIG. 1 , the adhesive layer 12 is provided on only one side of the non-thermoplastic polyimide layer 11. However, as in the multilayer polyimide films prepared in the Examples described below, the adhesive layer 12 may be provided on both sides (both main surfaces) of the non-thermoplastic polyimide layer 11. When the adhesive layer 12 is provided on both sides of the non-thermoplastic polyimide layer 11, the two adhesive layers 12 may contain the same type of polyimide or different types of polyimide. The thicknesses of the two adhesive layers 12 may be the same or different. In the present invention, two or more non-thermoplastic polyimide layers 11 and adhesive layers 12 may be provided. In the following description, the term "multilayer polyimide film 10" includes a film in which the adhesive layer 12 is provided on only one side of the non-thermoplastic polyimide layer 11, a film in which the adhesive layer 12 is provided on both sides of the non-thermoplastic polyimide layer 11, and a film in which two or more non-thermoplastic polyimide layers 11 and adhesive layers 12 are provided.

[0095] The thickness of the multilayer polyimide film 10 (total thickness of each layer) is, for example, 6 μm or more and 60 μm or less. The thinner the multilayer polyimide film 10, the easier it is to reduce the weight of the resulting FPC and improve the foldability of the resulting FPC. In order to facilitate weight reduction of the FPC while ensuring mechanical strength and improve the foldability of the FPC, the thickness of the multilayer polyimide film 10 is preferably 7 μm or more and 60 μm or less, and more preferably 10 μm or more and 60 μm or less. The thickness of the multilayer polyimide film 10 can be measured using a laser hologram.

[0096] To easily achieve a thinner FPC while ensuring adhesion to the metal foil, the thickness of the adhesive layer 12 (when two or more adhesive layers 12 are provided, the thickness of each adhesive layer 12) is preferably 1 μm or more and 15 μm or less. Furthermore, to easily adjust the linear expansion coefficient of the multilayer polyimide film 10, the thickness ratio of the non-thermoplastic polyimide layer 11 to the adhesive layer 12 (thickness of the non-thermoplastic polyimide layer 11 / thickness of the adhesive layer 12) is preferably 55 / 45 or more and 95 / 5 or less. When multiple non-thermoplastic polyimide layers 11 and adhesive layers 12 are provided, the thickness ratio is the ratio of their total thicknesses. Even if the number of adhesive layers 12 is increased, it is preferable that the total thickness of the adhesive layers 12 does not exceed the total thickness of the non-thermoplastic polyimide layers 11.

[0097] In order to suppress warping of the multilayer polyimide film 10, it is preferable that adhesive layers 12 be provided on both sides of the non-thermoplastic polyimide layer 11, and it is more preferable that adhesive layers 12 containing the same type of polyimide be provided on both sides of the non-thermoplastic polyimide layer 11. When adhesive layers 12 are provided on both sides of the non-thermoplastic polyimide layer 11, it is preferable that the thicknesses of the two adhesive layers 12 be the same in order to suppress warping of the multilayer polyimide film 10. Even if the thicknesses of the two adhesive layers 12 are different from each other, warping of the multilayer polyimide film 10 can be suppressed as long as the thickness of the thicker adhesive layer 12 is within a range of 40% or more and less than 100%.

[0098] To obtain a multilayer polyimide film 10 with a reduced dielectric dissipation factor, the dielectric dissipation factor of the non-thermoplastic polyimide layer 11 is preferably 0.0030 or less. The dielectric dissipation factor of the non-thermoplastic polyimide layer 11 can be adjusted, for example, by changing at least one of the content of each residue constituting the non-thermoplastic polyamic acid and the maximum temperature in the imidization step. By adjusting the dielectric dissipation factor of the non-thermoplastic polyimide layer 11 to 0.0030 or less, it is possible to reduce the dielectric dissipation factor of the multilayer polyimide film 10 to 0.0040 or less. The lower limit of the dielectric dissipation factor of the non-thermoplastic polyimide layer 11 is not particularly limited, but is, for example, 0.0001.

[0099] To obtain a multilayer polyimide film 10 that can further reduce the dielectric loss tangent while maintaining adhesive properties, the adhesive layer 12 preferably has no melting peak or a melting peak with a heat of fusion of 1.0 J / g or less at temperatures ranging from 100°C to 420°C. Hereinafter, a melting peak in the temperature range of 100°C to 420°C may be simply referred to as the "melting peak." The method for measuring the heat of fusion of the melting peak is the same as or equivalent to the method described in the Examples below. When the adhesive layer 12 has no melting peak or a melting peak with a heat of fusion of 1.0 J / g or less, the shape of the film containing the polyamic acid in the adhesive layer-forming solution can be maintained well during the imidization process. Therefore, heating to a maximum temperature of 360°C or higher during the imidization process reduces the dielectric loss tangent of the multilayer polyimide film 10 while maintaining the shape of the adhesive layer 12 suitable for bonding to a metal layer. The heat of fusion of the melting peak of the adhesive layer 12 tends to be lower when imidized by chemical imidization. The heat of fusion of the melting peak of the adhesive layer 12 can be adjusted by, for example, changing at least one of the content of each residue constituting the adhesive polyamic acid and the maximum temperature in the imidization step.

[0100] In order to obtain a multilayer polyimide film 10 that can further reduce the dielectric loss tangent while maintaining adhesive properties, it is preferable that the adhesive layer 12 does not have a melting peak.

[0101] The adhesive layer 12 preferably has a storage modulus of 20.0 MPa or more at a temperature of 400° C. and a loss modulus of 4.0 MPa or more at a temperature of 400° C. When the storage modulus and loss modulus are within the above ranges, the adhesive layer 12 can withstand heating at high temperatures. Preferably, the storage modulus is 30.0 MPa or more, and the loss modulus is 5.0 MPa or more.

[0102] To obtain a multilayer polyimide film 10 with excellent adhesive properties, the storage modulus of the adhesive layer 12 at a temperature of 360° C. is preferably 1.0 GPa or less, and more preferably 0.1 GPa or less. When a metal-clad laminate is produced using the multilayer polyimide film 10, if the storage modulus of the adhesive layer 12 at a temperature of 360° C. is 1.0 GPa or less, the adhesive layer 12 can have excellent adhesion at the preferred lamination temperature (360° C. or higher) when bonding the adhesive layer 12 to a metal foil.

[0103] The storage modulus and loss modulus of the adhesive layer 12 are measured by the same method as in the examples described below or a method equivalent thereto.

[0104] An index of the adhesion between the adhesive layer 12 and the metal layer is the adhesion strength described in the Examples below. To obtain a multilayer polyimide film 10 with excellent adhesive properties, the adhesion strength described in the Examples below is preferably 10 N / cm or more.

[0105] The non-thermoplastic polyimide layer 11 may contain components (additives) other than the non-thermoplastic polyimide. Examples of additives that can be used include dyes, surfactants, leveling agents, plasticizers, silicones, fillers, and sensitizers. The content of the non-thermoplastic polyimide in the non-thermoplastic polyimide layer 11 is, for example, 70% by weight or more, preferably 80% by weight or more, more preferably 90% by weight or more, and may be 100% by weight, based on the total weight of the non-thermoplastic polyimide layer 11.

[0106] The adhesive layer 12 may contain components (additives) other than polyimide. Examples of additives that can be used include dyes, surfactants, leveling agents, plasticizers, silicones, fillers, and sensitizers. The content of polyimide in the adhesive layer 12 is, for example, 70% by weight or more, preferably 80% by weight or more, more preferably 90% by weight or more, and may be 100% by weight, based on the total weight of the adhesive layer 12.

[0107] The non-thermoplastic polyimide layer 11 and the adhesive layer 12 each contain a tertiary amine used as a catalyst at a content of, for example, 1 ppm by mass or more and 1000 ppm by mass or less.

[0108] <Second embodiment: multilayer polyimide film> Next, a multilayer polyimide film according to a second embodiment of the present invention will be described. The multilayer polyimide film according to the second embodiment comprises a non-thermoplastic polyimide layer and a polyimide-containing adhesive layer disposed on at least one side of the non-thermoplastic polyimide layer. The non-thermoplastic polyimide layer has a dielectric loss tangent of 0.0030 or less at a frequency of 10 GHz, a temperature of 23°C, and a relative humidity of 50%. The adhesive layer has no melting peak or a heat of fusion of the melting peak of 1.0 J / g or less at a temperature range of 100°C to 420°C. The polyimide contained in the adhesive layer contains one or more tetracarboxylic dianhydride residues selected from the group consisting of PMDA residues and BPDA residues, and one or more diamine residues selected from the group consisting of TPE-R residues and m-TB residues. By virtue of the above-described configuration, the multilayer polyimide film according to the second embodiment can reduce the dielectric loss tangent while maintaining adhesion properties to a metal layer, and also has excellent productivity.

[0109] The multilayer polyimide film according to the second embodiment can be manufactured by the method for manufacturing a multilayer polyimide film according to the first embodiment described above. Therefore, in the following description, the description of the same content as in the first embodiment may be omitted. The following description will focus on the differences from the first embodiment.

[0110] In the multilayer polyimide film according to the second embodiment, the non-thermoplastic polyimide layer is not particularly limited as long as the dielectric loss tangent is 0.0030 or less. However, in the second embodiment, in order to easily adjust the dielectric loss tangent to 0.0030 or less, it is preferable that the non-thermoplastic polyimide contained in the non-thermoplastic polyimide layer has one or more tetracarboxylic dianhydride residues selected from the group consisting of BPDA residues and ODPA residues, and one or more diamine residues selected from the group consisting of PDA residues and TPE-R residues.

[0111] In the multilayer polyimide film according to the second embodiment, the adhesive layer is not particularly limited as long as it satisfies the following conditions A and B. Condition A: In the temperature range of 100°C or higher and 420°C or lower, there is no melting peak, or the heat of fusion of the melting peak is 1.0 J / g or lower. Condition B: The polyimide contained in the adhesive layer has one or more tetracarboxylic dianhydride residues selected from the group consisting of PMDA residues and BPDA residues, and one or more diamine residues selected from the group consisting of TPE-R residues and m-TB residues.

[0112] However, in the second embodiment, in order to easily obtain an adhesive layer that satisfies the above condition A, the adhesive layer preferably contains a PMDA residue, a BPDA residue, a TPE-R residue, and an m-TB residue.

[0113] In addition, in the second embodiment, in order to easily adjust the dielectric tangent of the non-thermoplastic polyimide layer to 0.0030 or less while easily obtaining an adhesive layer that satisfies the above condition A, it is preferable that the non-thermoplastic polyimide contained in the non-thermoplastic polyimide layer has a PDA residue and the polyimide contained in the adhesive layer does not have a PDA residue.

[0114] In the second embodiment, the preferred content of each of the residues listed above and the type of any residue other than the residues listed above are the same as the preferred content of each residue of the polyamic acid and the type of any residue of the polyamic acid in the first embodiment.

[0115] Other aspects of the second embodiment are the same as those described above in the section [Multilayer polyimide film obtained by the production method according to the first embodiment].

[0116] <Third embodiment: metal-clad laminate> Next, a metal-clad laminate according to a third embodiment of the present invention will be described with reference to the drawings. The metal-clad laminate according to the third embodiment has the multilayer polyimide film according to the second embodiment and a metal layer disposed on the main surface of at least one adhesive layer of the multilayer polyimide film. The metal-clad laminate according to the third embodiment can be manufactured using the multilayer polyimide film according to the second embodiment as a material. Therefore, in the following description, the description of the same content as in the first and second embodiments may be omitted.

[0117] Fig. 2 is a cross-sectional view showing an example of a metal-clad laminate according to embodiment 3. As shown in Fig. 2, a metal-clad laminate 20 includes a multilayer polyimide film 10 and a metal layer 13 (metal foil) disposed on a main surface 12a of an adhesive layer 12 of the multilayer polyimide film 10.

[0118] [Method for manufacturing a metal-clad laminate according to the third embodiment] When manufacturing a metal-clad laminate 20 using a multilayer polyimide film 10, a metal foil that will become the metal layer 13 is laminated to at least one surface of the multilayer polyimide film 10 (for example, in the case of FIG. 2, the main surface 12a of the adhesive layer 12 opposite the non-thermoplastic polyimide layer 11 side). This results in the metal-clad laminate 20 shown in FIG. 2. The method for laminating the metal foil to the main surface 12a of the adhesive layer 12 is not particularly limited, and various known methods can be used. For example, a continuous processing method using a hot roll laminating device having one or more pairs of metal rolls or a double belt press (DBP) can be used. The specific configuration of the means for performing hot roll lamination is not particularly limited, but it is preferable to place a protective material between the pressing surface and the metal foil to improve the appearance of the resulting metal-clad laminate 20.

[0119] When adhesive layers 12 are provided on both sides of the non-thermoplastic polyimide layer 11, a double-sided metal-clad laminate (not shown) can be obtained by laminating metal foil to both sides (both main surfaces) of the multilayer polyimide film 10.

[0120] The metal foil to be used for the metal layer 13 is not particularly limited, and any metal foil can be used. For example, metal foils made of copper, stainless steel, nickel, aluminum, alloys of these metals, etc. are preferably used. Furthermore, copper foils such as rolled copper foils and electrolytic copper foils are often used in general metal-clad laminates, and copper foils are also preferably used in the third embodiment.

[0121] Furthermore, the metal foil can be used after adjusting the surface roughness, etc., by performing a surface treatment, etc., depending on the purpose. Furthermore, an anti-rust layer, a heat-resistant layer, an adhesive layer, etc., may be formed on the surface of the metal foil. The thickness of the metal foil is not particularly limited, and it is sufficient to have a thickness that can fully function depending on the application. To easily achieve a thinner FPC while suppressing the occurrence of wrinkles when bonding with the multilayer polyimide film 10, the thickness of the metal foil is preferably 5 μm or more and 50 μm or less. [Example]

[0122] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0123] <Methods for measuring and evaluating physical properties> [Film forming property] An imidization accelerator consisting of acetic anhydride / isoquinoline / DMF (weight ratio: acetic anhydride / isoquinoline / DMF = 3.0 / 1.2 / 4.4) was added to a polyamic acid solution (specifically, any of the polyamic acid solutions P4 to P13 described below) to obtain a solution for forming an adhesive layer. The amount of the imidization accelerator added was 50 parts by weight per 100 parts by weight of the polyamic acid solution. The resulting solution for forming an adhesive layer was extruded through a T-die of a film-forming device while stirring with a mixer, and cast onto a stainless steel endless belt to form a coating film. The resulting coating film was dried at a temperature of 130°C for 100 seconds, and then the resulting gel film was peeled off from the endless belt and fixed to tenter clips. The gel film was then heated at a temperature of 250°C for 17 seconds, followed by heating at a temperature of 300°C for 137 seconds to imidize the polyamic acid in the gel film. In this imidization process, if a single layer film consisting of an adhesive layer with a thickness of 17 μm was obtained, it was judged as "film-forming possible," and if problems such as wrinkles or cracks occurred and film formation was not possible, it was judged as "film-forming impossible."

[0124] [Melting temperature and heat of fusion of adhesive layer] Using a measurement sample (mass: 8 mg) sampled from the adhesive layer of the multilayer polyimide film obtained in the Examples and Comparative Examples described below, the melting temperature and heat of fusion were measured using a differential scanning calorimeter (Seiko Instruments Inc., "DSC220"). Specifically, the measurement sample was placed in an aluminum dish (aluminum container), and the aluminum dish was set in the measurement section of the differential scanning calorimeter. An empty aluminum dish was used as a reference. The ambient temperature was then increased from 0°C to 450°C at a heating rate of 10°C / min, and then decreased from 450°C to 0°C at a heating rate of 40°C / min. The sample was then again increased from 0°C to 450°C at a heating rate of 10°C / min. The peak temperature of the endothermic chart during the second heating was taken as the melting temperature. The heat of fusion (unit: J / g) was calculated from the area of ​​the peak in the endothermic chart. In addition, if there is no melting peak in the temperature range of 100°C or higher and 420°C or lower in the endothermic chart, that is, if the adhesive layer being measured does not have a melting peak in the temperature range of 100°C or higher and 420°C or lower, the heat of fusion was taken to be 0 J / g.

[0125] [Storage modulus (E') and loss modulus (E'') of adhesive layer] A monolayer film obtained by the same procedure as the monolayer film obtained in the evaluation of [Film Formability] above was used as a measurement sample, and E' and E'' were measured using a dynamic viscoelasticity measuring device (Hitachi High-Tech Science Corporation, "DM6100"). Specifically, the dynamic viscoelasticity of the sample was measured in an air atmosphere using the dynamic viscoelasticity measuring device, and a graph was created in which E' and E'' were plotted against the measurement temperature. E' at temperatures of 360°C and 400°C, and E'' at a temperature of 400°C were read from the graph. The measurement conditions are shown below. Sample width: 9 mm Sample holder (gripper) spacing: 20 mm Measurement temperature range: 0℃~440℃ Heating rate: 3°C / min Strain amplitude: 10 μm Measurement frequency: 5Hz Minimum tension / compression force: 100mN Tension / Compression Gain: 1.5 Initial force amplitude: 100 mN

[0126] [Tertiary amine content] Using measurement samples (mass: 0.5 mg) taken from each layer (specifically, the adhesive layer and the non-thermoplastic polyimide layer) of the multilayer polyimide films obtained in the Examples and Comparative Examples described below, the tertiary amine content of each layer was measured at a heating temperature of 350°C using a pyrolysis gas chromatograph / mass spectrometer (Agilent Technologies, Inc., "Py-GC / MS").

[0127] [Dissipation Factor] The monolayer films (adhesive layers), non-thermoplastic polyimide layers, and multilayer polyimide films (all layers) obtained in the following examples and comparative examples were used as measurement samples. The dielectric loss tangents were measured using a network analyzer (Keysight Technologies, Inc., "N5224B") and a cavity resonator perturbation dielectric constant measurement device (EM Lab, Inc., "CP531"). Specifically, the samples were left in an atmosphere of 23°C and 50% relative humidity for 24 hours, and then measured using the network analyzer and the cavity resonator perturbation dielectric constant measurement device at 23°C, 50% relative humidity, and a measurement frequency of 10 GHz. Multilayer polyimide films (all layers) with a dielectric loss tangent of 0.0040 or less were evaluated as having a reduced dielectric loss tangent. Multilayer polyimide films (all layers) with a dielectric loss tangent of more than 0.0040 were evaluated as not having a reduced dielectric loss tangent. Regarding the non-thermoplastic polyimide layer, a single-layer film consisting of a non-thermoplastic polyimide layer obtained by scraping each of the adhesive layers on both sides of the multilayer polyimide film obtained in the examples and comparative examples described below with sandpaper (#600) was used as the measurement sample.

[0128] [Adhesion] A 12 μm thick electrolytic copper foil (Fukuda Metal Foil & Powder Co., Ltd., "CF-T49A-HD2") was placed on both sides of a multilayer polyimide film (one of the multilayer polyimide films obtained in the Examples and Comparative Examples described below). Each electrolytic copper foil was then covered with a protective film (Kaneka Corporation, "Apical® 125NPI", 125 μm thick). The laminate was then laminated using a hot roll laminator at a lamination temperature of 360°C, a lamination pressure of 314 N / cm (32 kgf / cm), and a lamination speed of 1.0 m / min to obtain a flexible copper-clad laminate. The resulting flexible copper-clad laminate was analyzed according to "6.5 Peel Strength" of JIS C6471-1995. Specifically, one electrodeposited copper foil of each flexible copper-clad laminate was peeled off at a peel angle of 90°, a pulling speed of 100 mm / min, and a measurement width of 1 mm, and the load (unit: N / cm) was taken as the adhesion strength. When the adhesion strength was 10 N / cm or more, it was evaluated as "excellent adhesion." On the other hand, when the adhesion strength was less than 10 N / cm, it was evaluated as "poor adhesion."

[0129] [Embeddability] The copper foil of a flexible copper-clad laminate obtained using the same procedure as the flexible copper-clad laminate obtained in the above evaluation of [Adhesion] was completely removed by etching. Next, the exposed surface of the multilayer polyimide film was observed using an optical microscope at 20x magnification. If the matte side of the copper foil was uniformly transferred to the surface of the multilayer polyimide film, it was evaluated as "A (excellent embeddability)." On the other hand, if the matte side of the copper foil was not uniformly transferred to the surface of the multilayer polyimide film, it was evaluated as "B (poor embeddability)."

[0130] When the adhesion strength was 10 N / cm or more and the embeddability was rated A, it was evaluated as "the adhesive properties with the metal layer were ensured." On the other hand, when the adhesion strength was less than 10 N / cm or the embeddability was rated B, it was evaluated as "the adhesive properties with the metal layer were not ensured."

[0131] <Preparation of polyamic acid solution> The methods for preparing the polyamic acid solutions P1 to P13 are described below. The preparation of the polyamic acid solutions P1 to P13 was carried out at a temperature of 20° C. in a nitrogen atmosphere.

[0132] [Preparation of polyamic acid solution P1] A reaction vessel was charged with 1,477.48 kg of DMF, 27.28 kg of TPE-R, and 57.24 kg of PDA, followed by the addition of 109.93 kg of BPDA, and the contents of the reaction vessel were stirred. After visually confirming that the BPDA had dissolved, 71.48 kg of ODPA was added to the reaction vessel while stirring the contents of the reaction vessel, and the reaction vessel contents were stirred for 30 minutes. Next, while stirring the reaction vessel contents, a previously prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 4.08 kg, PMDA concentration: 7.2 wt%) was added to the reaction vessel for a predetermined period of time at an addition rate that did not cause a sudden increase in the viscosity of the reaction vessel contents. When the viscosity of the reaction vessel contents at 23°C reached 2,000 poise, the addition of the PMDA solution and the stirring of the reaction vessel contents were stopped, yielding polyamic acid solution P1.

[0133] The polyimide obtained from the polyamic acid in the obtained polyamic acid solution P1 was confirmed to be non-thermoplastic by the following method. First, 40 parts by weight of an imidization accelerator consisting of acetic anhydride / isoquinoline / DMF (weight ratio: acetic anhydride / isoquinoline / DMF = 101 / 51 / 48) was added to 100 parts by weight of the polyamic acid solution P1 to prepare a non-thermoplastic polyimide layer-forming solution. Next, the obtained non-thermoplastic polyimide layer-forming solution was extruded through a T-die of a film-forming apparatus while stirring with a mixer and cast onto a stainless steel endless belt to form a coating film. The resulting coating film was dried at a temperature of 100 °C for 380 seconds, and then the resulting gel film was peeled off from the endless belt and fixed to tenter clips. Next, the gel film was heated at a temperature of 300 °C for 110 seconds, followed by heating at a temperature of 380 °C for 97 seconds to imidize the polyamic acid in the gel film, resulting in a polyimide film with a thickness of 34 μm. The obtained polyimide film was fixed to a metal frame and heated at 380°C for 2 minutes, whereupon the shape of the polyimide film (film shape) was maintained. Therefore, the polyimide obtained from the polyamic acid in polyamic acid solution P1 was a non-thermoplastic polyimide. Regarding polyamic acid solutions P2 and P3, whose preparation methods are shown below, polyimide films obtained by the same method as the film formation method using polyamic acid solution P1 were fixed to a metal frame and heated at 380°C for 2 minutes, whereupon the shape of the polyimide film (film shape) was maintained. Therefore, the polyimides obtained from the polyamic acid in polyamic acid solutions P2 and P3 were both non-thermoplastic polyimides.

[0134] [Preparation of polyamic acid solution P2] A reaction vessel was charged with 1,404.80 kg of DMF, 27.87 kg of TPE-R, and 58.48 kg of PDA, followed by the addition of 112.31 kg of BPDA, and the contents of the reaction vessel were stirred. After visually confirming that the BPDA had dissolved, 65.13 kg of ODPA was added to the reaction vessel while stirring the contents of the reaction vessel, and the reaction vessel contents were stirred for 30 minutes. Next, while stirring the reaction vessel contents, a previously prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 9.71 kg, PMDA concentration: 7.2 wt%) was added to the reaction vessel for a predetermined period of time at an addition rate that did not cause a sudden increase in the viscosity of the reaction vessel contents. When the viscosity of the reaction vessel contents at 23°C reached 2,000 poise, the addition of the PMDA solution and the stirring of the reaction vessel contents were stopped, yielding polyamic acid solution P2.

[0135] [Preparation of polyamic acid solution P3] A reactor was charged with 1,480.09 kg of DMF, 23.70 kg of 4,4'-diaminodiphenyl ether (hereinafter referred to as "ODA"), and 72.89 kg of 2,2-bis[4-(4-aminophenoxy)phenyl]propane (hereinafter referred to as "BAPP"), and the contents of the reactor were then stirred. After visually confirming that the monomers had dissolved, 38.14 kg of 3,3',4,4'-benzophenonetetracarboxylic dianhydride (hereinafter referred to as "BTDA") and 32.27 kg of PMDA were added to the reactor while stirring the contents of the reactor, and the reactor contents were stirred for 30 minutes. Next, 32.00 kg of PDA was added to the reactor while stirring the contents of the reactor, followed by 67.13 kg of PMDA, and the reactor contents were stirred for 30 minutes. Next, while stirring the contents of the reaction vessel, a previously prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 3.87 kg, PMDA concentration: 7.2 wt%) was added to the reaction vessel for a predetermined time at an addition rate that did not cause a sudden increase in the viscosity of the reaction vessel content. When the viscosity of the reaction vessel content at a temperature of 23°C reached 2000 poise, the addition of the PMDA solution and stirring of the reaction vessel content were stopped, yielding polyamic acid solution P3.

[0136] [Preparation of polyamic acid solution P4] 1507.46 kg of DMF, 98.25 kg of TPE-R, and 70.71 kg of BPDA were added to the reactor, and the contents were stirred for 30 minutes. Next, 15.73 kg of PMDA was added to the reactor while stirring the contents, and the contents were stirred for 30 minutes. Next, 30.61 kg of m-TB and 33.55 kg of PMDA were added to the reactor while stirring the contents, and the contents were stirred for 30 minutes. Next, while stirring the contents, a previously prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 3.15 kg, PMDA concentration: 7.2 wt%) was added to the reactor for a predetermined time at an addition rate that did not cause a sudden increase in the viscosity of the reactor contents. When the viscosity of the content of the reaction vessel reached 1000 poise at a temperature of 23° C., the addition of the PMDA solution and the stirring of the content of the reaction vessel were stopped, to obtain a polyamic acid solution P4.

[0137] [Preparation of polyamic acid solution P5] A reaction vessel was charged with 1508.32 kg of DMF, 96.16 kg of TPE-R, and 89.97 kg of BPDA, and the contents were stirred for 30 minutes. Next, while stirring the contents, 29.96 kg of m-TB and 32.84 kg of PMDA were added to the reaction vessel, and the contents were stirred for 30 minutes. Next, while stirring the contents, a pre-prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 3.08 kg, PMDA concentration: 7.2 wt%) was added to the reaction vessel for a predetermined time at an addition rate that did not cause a sudden increase in the viscosity of the reaction vessel contents. When the viscosity of the reaction vessel contents at 23°C reached 1000 poise, the addition of the PMDA solution and the stirring of the reaction vessel contents were stopped, yielding polyamic acid solution P5.

[0138] [Preparation of polyamic acid solution P6] A reactor was charged with 1506.86 kg of DMF, 99.70 kg of TPE-R, and 57.40 kg of BPDA, and the contents were stirred for 30 minutes. Next, 26.60 kg of PMDA was added to the reactor while stirring, and the contents were stirred for 30 minutes. Next, 31.06 kg of m-TB and 34.04 kg of PMDA were added to the reactor while stirring, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, a pre-prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 3.19 kg, PMDA concentration: 7.2 wt%) was added to the reactor for a predetermined time at an addition rate that did not cause a sudden increase in the viscosity of the reactor contents. When the viscosity of the content of the reaction vessel reached 1000 poise at a temperature of 23° C., the addition of the PMDA solution and the stirring of the content of the reaction vessel were stopped, to obtain a polyamic acid solution P6.

[0139] [Preparation of polyamic acid solution P7] A reaction vessel was charged with 1541.34 kg of DMF, 91.60 kg of TPE-R, and 131.86 kg of BPDA, and the contents were stirred for 30 minutes. Next, 25.69 kg of m-TB was added to the reaction vessel while stirring, and the contents were stirred for 30 minutes. Next, while stirring the reaction vessel contents, a previously prepared m-TB solution (solvent: DMF, m-TB dissolved amount: 2.85 kg, m-TB concentration: 30 wt%) was added to the reaction vessel for a predetermined time at an addition rate that did not cause a sudden increase in the viscosity of the reaction vessel contents. When the viscosity of the reaction vessel contents at 23°C reached 1000 poise, the addition of the m-TB solution and the stirring of the reaction vessel contents were stopped, yielding polyamic acid solution P7.

[0140] [Preparation of polyamic acid solution P8] 1541.39 kg of DMF, 97.45 kg of TPE-R, and 130.93 kg of BPDA were added to the reactor, and the contents were stirred for 30 minutes. Next, 20.78 kg of m-TB was added to the reactor while stirring the contents, and the contents were stirred for 30 minutes. Next, while stirring the contents, a previously prepared m-TB solution (solvent: DMF, dissolved amount of m-TB: 2.83 kg, m-TB concentration: 30 wt%) was added to the reactor for a predetermined time at an addition rate that did not cause a sudden increase in the viscosity of the reactor contents. When the viscosity of the reactor contents at 23°C reached 1000 poise, the addition of the m-TB solution and the stirring of the reactor contents were stopped, yielding polyamic acid solution P8.

[0141] [Preparation of polyamic acid solution P9] A reactor was charged with 1541.84 kg of DMF, 96.99 kg of TPE-R, and 139.61 kg of BPDA, and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, 13.85 kg of PDA was charged and the contents were stirred for 30 minutes. Next, while stirring the reactor contents, a previously prepared PDA solution (solvent: DMF, dissolved amount of PDA: 1.54 kg, PDA concentration: 20 wt%) was added to the reactor for a predetermined time at an addition rate that did not cause a sudden increase in the viscosity of the reactor contents. When the viscosity of the reactor contents at 23°C reached 1000 poise, the addition of the PDA solution and the stirring of the reactor contents were stopped, yielding polyamic acid solution P9.

[0142] [Preparation of polyamic acid solution P10] 1540.30 kg of DMF, 105.94 kg of TPE-R, and 113.05 kg of PMDA were added to the reactor, and the contents were stirred for 30 minutes. Next, 29.71 kg of m-TB was added to the reactor while stirring the contents, and the contents were stirred for 30 minutes. Next, while stirring the contents, a previously prepared m-TB solution (solvent: DMF, m-TB dissolved amount: 3.30 kg, m-TB concentration: 30 wt%) was added to the reactor for a predetermined time at an addition rate that did not cause a sudden increase in the viscosity of the reactor contents. When the viscosity of the reactor contents at 23°C reached 1000 poise, the addition of the m-TB solution and the stirring of the reactor contents were stopped, yielding polyamic acid solution P10.

[0143] [Preparation of polyamic acid solution P11] A reaction vessel was charged with 1509.23 kg of DMF, 134.24 kg of TPE-R, and 67.63 kg of BPDA, and the contents were stirred for 30 minutes. Next, while stirring the contents of the reaction vessel, 47.13 kg of PMDA was added to the reaction vessel, and the contents were stirred for 30 minutes. Next, while stirring the contents of the reaction vessel, a pre-prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 3.01 kg, PMDA concentration: 7.2 wt%) was added to the reaction vessel for a predetermined time at an addition rate that did not cause a sudden increase in the viscosity of the reaction vessel contents. When the viscosity of the reaction vessel contents at 23°C reached 1000 poise, the addition of the PMDA solution and the stirring of the reaction vessel contents were stopped, yielding polyamic acid solution P11.

[0144] [Preparation of polyamic acid solution P12] A reactor was charged with 1514.99 kg of DMF, 160.67 kg of BAPP, and 23.03 kg of BPDA, and the contents were stirred for 30 minutes. Next, while stirring the contents, 65.73 kg of PMDA was added to the reactor, and the contents were stirred for 30 minutes. Next, while stirring the contents, a pre-prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 2.56 kg, PMDA concentration: 7.2 wt%) was added to the reactor for a predetermined time at a rate that did not cause a sudden increase in the viscosity of the reactor contents. When the viscosity of the reactor contents at 23°C reached 1000 poise, the addition of the PMDA solution and stirring of the reactor contents were stopped, yielding polyamic acid solution P12.

[0145] [Preparation of polyamic acid solution P13] A reaction vessel was charged with 1510.01 kg of DMF, 124.96 kg of TPE-R, and 92.78 kg of BPDA, and the contents were stirred for 30 minutes. Next, while stirring the contents, 4.78 kg of m-TB and 26.53 kg of PMDA were added to the reaction vessel, and the contents were stirred for 30 minutes. Next, while stirring the contents, a pre-prepared PMDA solution (solvent: DMF, dissolved amount of PMDA: 2.95 kg, PMDA concentration: 7.2 wt%) was added to the reaction vessel for a predetermined period of time at a rate that did not cause a sudden increase in the viscosity of the reaction vessel contents. When the viscosity of the reaction vessel contents at 23°C reached 1000 poise, the addition of the PMDA solution and the stirring of the reaction vessel contents were stopped, yielding polyamic acid solution P13.

[0146] Table 1 shows the materials used in each of the polyamic acid solutions P1 to P13 and their proportions. The molar fraction of each residue in the polyamic acid contained in each of the polyamic acid solutions P1 to P13 was consistent with the molar fraction of each monomer (diamine and tetracarboxylic dianhydride) used. Table 2 shows the results of measurement and evaluation of the monolayer films obtained using each of the polyamic acid solutions P4 to P13 using the above-mentioned method. In Table 1, "-" indicates that the corresponding component was not used. In Table 1, the values ​​in the "Acid Dianhydride" column are the content (unit: mol%) of each acid dianhydride relative to the total amount of acid dianhydride used. In Table 1, the values ​​in the "Diamine" column are the content (unit: mol%) of each diamine relative to the total amount of diamine used. In Table 2, "-" indicates that measurement was not performed.

[0147] [Table 1]

[0148] [Table 2]

[0149] <Preparation of multi-layer polyimide film> The methods for producing the multilayer polyimide films of Examples 1 to 5 and Comparative Examples 1 to 5 will be described below.

[0150] [Example 1] A mixture of 144 kg of DMF, 153 kg of isoquinoline, and 303 kg of acetic anhydride was prepared as an imidization accelerator. This imidization accelerator was added to polyamic acid solution P1, and the mixture was stirred with a mixer to obtain a solution for forming a non-thermoplastic polyimide layer. The amount of imidization accelerator added was 40 parts by weight per 100 parts by weight of polyamic acid solution P1. Furthermore, polyamic acid solution P4 was prepared as a solution for forming an adhesive layer.

[0151] Next, using an extruder with a three-layer extrusion die, the non-thermoplastic polyimide layer-forming solution and the adhesive layer-forming solution were applied onto a stainless steel endless belt support by a co-extrusion-casting coating method. Specifically, the non-thermoplastic polyimide layer-forming solution was first supplied to the central layer of the extrusion die, and the adhesive layer-forming solution was supplied to the two layers adjacent (on both sides) to the central layer of the extrusion die. The opening width of the lip opening of the extrusion die (the length in the short direction of the lip opening) was adjusted to 1.3 mm. Next, the non-thermoplastic polyimide layer-forming solution and the adhesive layer-forming solution were extruded from the lip opening of the extrusion die by a co-extrusion-casting coating method to form a coating film (a coating film consisting of three layers: adhesive layer-forming solution / non-thermoplastic polyimide layer-forming solution / adhesive layer-forming solution) on the stainless steel endless belt. The resulting coating film was dried on the stainless steel endless belt at 100°C for 380 seconds to obtain a gel film. This gel film was peeled off from the stainless steel endless belt, and then both longitudinal ends were fixed with pins and heated at a temperature of 300°C for 110 seconds, followed by heating at a temperature (maximum temperature) of 380°C for 97 seconds to imidize the polyamic acid in the non-thermoplastic polyimide layer-forming solution and the polyamic acid in the adhesive layer-forming solution, thereby obtaining the multilayer polyimide film of Example 1. The multilayer polyimide film of Example 1 had a three-layer structure of adhesive layer / non-thermoplastic polyimide layer / adhesive layer, with the thicknesses of the adhesive layer / non-thermoplastic polyimide layer / adhesive layer being 8 μm / 34 μm / 8 μm.

[0152] Furthermore, for the multilayer polyimide film of Example 1, when the content of tertiary amine (isoquinoline) in each layer was measured by the method described above using measurement samples (mass: 0.5 mg) sampled from each of the adhesive layer and the non-thermoplastic polyimide layer, isoquinoline was detected at a content of 1 ppm by mass or more in both the adhesive layer and the non-thermoplastic polyimide layer. Note that, for Examples 2 to 5 and Comparative Examples 1 to 5 described below, the content of tertiary amine (isoquinoline) in each layer was measured by the same method as in Example 1 above, and isoquinoline was detected at a content of 1 ppm by mass or more in both the adhesive layer and the non-thermoplastic polyimide layer.

[0153] [Examples 2 to 5 and Comparative Examples 1 to 5] The multilayer polyimide films of Examples 2 to 5 and Comparative Examples 1 to 5 were obtained in the same manner as in Example 1 above, except that the types of polyamic acid solutions used to prepare the non-thermoplastic polyimide layer-forming solution and the polyamic acid solutions used as the adhesive layer-forming solution were as shown in Table 3 below.

[0154] <Attempt to fabricate multi-layer polyimide film> Comparative Example 6 An attempt was made to obtain a multilayer polyimide film using the same method as in Example 1 above, except that polyamic acid solution P10 was used instead of polyamic acid solution P4 as the adhesive layer-forming solution. However, cracks occurred in the film, and a good film could not be obtained.

[0155] Comparative Example 7 An attempt was made to obtain a multilayer polyimide film using the same method as in Example 1 above, except that polyamic acid solution P11 was used instead of polyamic acid solution P4 as the adhesive layer-forming solution. However, cracks occurred in the film, and a good film could not be obtained.

[0156] [Comparative Example 8] An attempt was made to obtain a multilayer polyimide film using the same method as in Example 1 above, except that no imidization accelerator was added to the polyamic acid solution P1 and the polyamic acid solution P1 was used as the non-thermoplastic polyimide layer-forming solution. However, the film wrinkled, and a good film could not be obtained. When the tertiary amine content was measured using the above-mentioned method using a measurement sample (mass: 0.5 mg) sampled from a wrinkle-free portion of the film surface (adhesive layer), no tertiary amine was detected. That is, in Comparative Example 8, the tertiary amine content in the adhesive layer was below the lower detection limit (1 ppm by mass). Furthermore, when the melting temperature and heat of fusion were measured using the above-mentioned method using a measurement sample (mass: 8 mg) sampled from a wrinkle-free portion of the film surface (adhesive layer), the melting temperature and heat of fusion were 333 °C and 2.3 J / g, respectively.

[0157] <Preparation of Polyimide Film for Reference Example> As a reference example, a single-layer polyimide film was prepared. In preparing the polyimide film of the reference example, the polyamic acid solution P4 was used as a dope solution without adding an imidization accelerator to the polyamic acid solution P4. First, the polyamic acid solution P4 was applied to one side of a 12 μm-thick electrolytic copper foil ("CF-T49A-HD2" manufactured by Fukuda Metal Foil & Powder Co., Ltd.) using a Comma Coater (registered trademark) to form a coating film. The coating film was then dried at 130°C for 120 seconds to obtain a gel film. The resulting gel film was heated at 120°C for 5 minutes, then heated to 350°C at a heating rate of 5°C / min, and further heated at 350°C for 30 minutes to imidize the polyamic acid in the coating film, thereby obtaining a polyimide film with a thickness of 12 μm. The tertiary amine content was measured using a measurement sample (mass: 0.5 mg) sampled from the polyimide film of the reference example using the method described above, and no tertiary amine was detected. In other words, in the Reference Example, the content of tertiary amine in the polyimide film was below the lower detection limit (1 ppm by mass). Furthermore, when the melting temperature and heat of fusion were measured by the above-mentioned method using a measurement sample (mass: 8 mg) sampled from the polyimide film of the Reference Example, the melting temperature and heat of fusion were 333°C and 2.3 J / g, respectively.

[0158] <Evaluation results> Table 3 shows the type of polyamic acid solution used to prepare the non-thermoplastic polyimide layer-forming solution, the type of polyamic acid solution used as the adhesive layer-forming solution, the melting temperature of the adhesive layer, and the heat of fusion of the adhesive layer for Examples 1 to 5 and Comparative Examples 1 to 5. Table 4 also shows the adhesion strength, embeddability, and dielectric tangent for Examples 1 to 5 and Comparative Examples 1 to 5. In Table 3, "non-thermoplastic solution" refers to the polyamic acid solution used to prepare the non-thermoplastic polyimide layer-forming solution. In Table 3, "adhesive solution" refers to the polyamic acid solution used as the adhesive layer-forming solution. In Table 3, "no peak" means that there was no melting peak in the temperature range of 100°C or higher and 420°C or lower.

[0159] [Table 3]

[0160] [Table 4]

[0161] The polyamic acid contained in the adhesive layer-forming solution used to prepare the multilayer polyimide films of Examples 1 to 5 contained PMDA residues, BPDA residues, TPE-R residues, and m-TB residues. The polyamic acid contained in the non-thermoplastic polyimide layer-forming solution used to prepare the multilayer polyimide films of Examples 1 to 5 contained one or more tetracarboxylic dianhydride residues selected from the group consisting of BPDA residues and ODPA residues, and one or more diamine residues selected from the group consisting of PDA residues and TPE-R residues. The dielectric loss tangent of the non-thermoplastic polyimide layer contained in the multilayer polyimide films of Examples 1 to 5 was 0.0030 or less. The adhesive layer contained in the multilayer polyimide films of Examples 1 to 5 did not have a melting peak in the temperature range of 100°C or higher and 420°C or lower.

[0162] The multilayer polyimide films of Examples 1 to 5 had an adhesion strength of 10 N / cm or more. Therefore, the multilayer polyimide films of Examples 1 to 5 had excellent adhesion. The multilayer polyimide films of Examples 1 to 5 were evaluated as A in embeddability. Therefore, the multilayer polyimide films of Examples 1 to 5 had excellent embeddability. The multilayer polyimide films of Examples 1 to 5 had a dielectric loss tangent of 0.0040 or less for all layers. Therefore, the multilayer polyimide films of Examples 1 to 5 had a reduced dielectric loss tangent.

[0163] The polyamic acid contained in the adhesive layer-forming solution used to prepare the multilayer polyimide films of Comparative Examples 1 to 3 did not contain a PMDA residue. The polyamic acid contained in the adhesive layer-forming solution used to prepare the multilayer polyimide film of Comparative Example 3 did not contain an m-TB residue. The polyamic acid contained in the adhesive layer-forming solution used to prepare the multilayer polyimide film of Comparative Example 4 did not contain a TPE-R residue or an m-TB residue. The polyamic acid contained in the non-thermoplastic polyimide layer-forming solution used to prepare the multilayer polyimide film of Comparative Example 5 did not contain one or more tetracarboxylic dianhydride residues selected from the group consisting of BPDA residues and ODPA residues. The dielectric dissipation factor of the non-thermoplastic polyimide layer in the multilayer polyimide film of Comparative Example 5 exceeded 0.0030. The adhesive layers in the multilayer polyimide films of Comparative Examples 1 to 4 had heats of fusion of their melting peaks exceeding 1.0 J / g.

[0164] The multilayer polyimide films of Comparative Examples 1 to 4 had an adhesion strength of less than 10 N / cm. Therefore, the multilayer polyimide films of Comparative Examples 1 to 4 did not have excellent adhesion. The multilayer polyimide films of Comparative Examples 1 to 3 were evaluated as B in embeddability. Therefore, the multilayer polyimide films of Comparative Examples 1 to 3 did not have excellent embeddability. The multilayer polyimide film of Comparative Example 5 had a dielectric loss tangent of all layers exceeding 0.0040. Therefore, the multilayer polyimide film of Comparative Example 5 was unable to reduce the dielectric loss tangent.

[0165] The above results demonstrate that the present invention can provide a multilayer polyimide film that can reduce the dielectric loss tangent while maintaining adhesion properties with a metal layer, and a method for producing the same. [Explanation of symbols]

[0166] 10: Multi-layer polyimide film 11: Non-thermoplastic polyimide layer 12: Adhesive layer 13: Metal layer 20:Metal clad laminate

Claims

1. A multilayer polyimide film having a non-thermoplastic polyimide layer and an adhesive layer containing polyimide disposed on at least one surface of the non-thermoplastic polyimide layer, the non-thermoplastic polyimide layer has a dielectric loss tangent of 0.0030 or less at a frequency of 10 GHz, a temperature of 23°C and a relative humidity of 50%, the adhesive layer has no melting peak or the heat of fusion of the melting peak is 1.0 J / g or less in a temperature range of 100°C or more and 420°C or less; the polyimide contained in the adhesive layer has a pyromellitic dianhydride residue, a 3,3',4,4'-biphenyltetracarboxylic dianhydride residue, a 1,3-bis(4-aminophenoxy)benzene residue, and a 4,4'-diamino-2,2'-dimethylbiphenyl residue; the non-thermoplastic polyimide contained in the non-thermoplastic polyimide layer has, as diamine residues, a p-phenylenediamine residue and a 1,3-bis(4-aminophenoxy)benzene residue; the content of the p-phenylenediamine residue is 60 mol % or more and 95 mol % or less based on all diamine residues constituting the non-thermoplastic polyimide, The multilayer polyimide film has a content of the 1,3-bis(4-aminophenoxy)benzene residue of 5 mol % or more and 40 mol % or less of all diamine residues constituting the non-thermoplastic polyimide.

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

3. The multilayer polyimide film according to claim 1 or 2, wherein the adhesive layer contains a tertiary amine in a content of 1 ppm by mass or more.

4. The multilayer polyimide film according to any one of claims 1 to 3, wherein the non-thermoplastic polyimide layer contains a tertiary amine in a content of 1 ppm by mass or more.

5. The multilayer polyimide film according to any one of claims 1 to 4, wherein the non-thermoplastic polyimide contained in the non-thermoplastic polyimide layer has one or more tetracarboxylic dianhydride residues selected from the group consisting of 3,3',4,4'-biphenyltetracarboxylic dianhydride residues and 4,4'-oxydiphthalic anhydride residues.

6. 6. The multilayer polyimide film according to claim 5, wherein the polyimide contained in the adhesive layer does not contain a p-phenylenediamine residue.

7. The multilayer polyimide film according to any one of claims 1 to 6, wherein the adhesive layer does not have a melting peak in a temperature range of 100°C or higher and 420°C or lower.

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

9. A method for producing a multilayer polyimide film having a non-thermoplastic polyimide layer and an adhesive layer containing polyimide disposed on at least one surface of the non-thermoplastic polyimide layer, comprising: a coating step of coating a non-thermoplastic polyimide layer-forming solution containing a polyamic acid, acetic anhydride, and a tertiary amine, and an adhesive layer-forming solution containing a polyamic acid, on a support by a co-extrusion-casting coating method; a gel film forming step of drying the coating film obtained in the coating step to form a self-supporting gel film; an imidization step in which the gel film obtained in the gel film formation step is heated under conditions of a maximum temperature of 360°C or more to imidize the polyamic acid in the non-thermoplastic polyimide layer formation solution and the polyamic acid in the adhesive layer formation solution; Equipped with In the coating step, the polyamic acid contained in the adhesive layer-forming solution has a pyromellitic dianhydride residue, a 3,3',4,4'-biphenyltetracarboxylic dianhydride residue, a 1,3-bis(4-aminophenoxy)benzene residue, and a 4,4'-diamino-2,2'-dimethylbiphenyl residue, In the coating step, the polyamic acid contained in the non-thermoplastic polyimide layer-forming solution has, as a tetracarboxylic dianhydride residue, one or more selected from the group consisting of a 3,3',4,4'-biphenyltetracarboxylic dianhydride residue and a 4,4'-oxydiphthalic anhydride residue, and, as a diamine residue, a p-phenylenediamine residue and a 1,3-bis(4-aminophenoxy)benzene residue; the content of the p-phenylenediamine residue is 60 mol % or more and 95 mol % or less with respect to all diamine residues constituting the polyamic acid contained in the non-thermoplastic polyimide layer forming solution, a content of the 1,3-bis(4-aminophenoxy)benzene residue in the non-thermoplastic polyimide layer-forming solution is 5 mol % or more and 40 mol % or less of all diamine residues constituting the polyamic acid contained in the non-thermoplastic polyimide layer-forming solution.

10. 10. The method for producing a multilayer polyimide film according to claim 9, wherein in the coating step, the polyamic acid contained in the adhesive layer-forming solution does not contain a p-phenylenediamine residue.

11. The method for producing a multilayer polyimide film according to claim 9 or 10, wherein in the imidization step, the gel film is heated at the highest temperature for a period of 10 seconds or more and 300 seconds or less.

12. The method for producing a multilayer polyimide film according to any one of claims 9 to 11, wherein the adhesive layer has no melting peak or a melting peak with a heat of fusion of 1.0 J / g or less in a temperature range of 100°C or more and 420°C or less.

13. The method for producing a multilayer polyimide film according to claim 12, wherein the adhesive layer does not have a melting peak in a temperature range of 100°C or higher and 420°C or lower.

14. The method for producing a multilayer polyimide film according to any one of claims 9 to 13, wherein the non-thermoplastic polyimide layer has a dielectric loss tangent of 0.0030 or less at a frequency of 10 GHz, a temperature of 23 ° C., and a relative humidity of 50%.

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