WO2024142635A1 - Polyimide film and method for producing same - Google Patents

Abstract

This method for producing a polyimide film involves a step for irradiating, with far infrared rays, a polyimide film precursor (10) including a polyamide acid to imidize the polyamide acid. The polyamide acid has a 3,3',4,4'-biphenyltetracarboxylic dianhydride residue and a p-phenylenediamine residue or has a pyromellitic dianhydride residue and a 4,4'-diamino-2,2'-dimethylbiphenyl residue. The polyimide film precursor (10) is irradiated with far infrared rays using three or more far infrared heaters (20) disposed along the width direction of the polyimide film precursor (10), wherein the temperatures of the far infrared heaters (20) can be individually controlled.

Description

Polyimide film and its manufacturing method

The present invention relates to a polyimide film and a method for producing the same.

Inverters used in electric vehicles and the like use power semiconductors such as SiC and GaN, which have excellent switching characteristics. However, according to Patent Documents 1 and 2, power semiconductors generate a large amount of heat, so inverters are exposed to high temperatures.

JP 2005-142228 A Patent No. 7175359

As mentioned above, the power semiconductors used in inverters generate a lot of heat and are subjected to high voltages, so the power semiconductors are usually connected to other circuits with thick metal wires, and the surrounding area is insulated and sealed with a resin material. For this reason, inverters made from conventional materials are difficult to miniaturize.

On the other hand, if the connection area between the power semiconductor and other circuits is provided on a flexible printed circuit board, it may be possible to miniaturize the inverter. Flexible printed circuit boards generally use polyimide film, which has a high dielectric breakdown voltage, but even polyimide film may not be able to ensure good insulation when exposed to high temperature and humidity environments. Also, when making a polyimide film with a width of, for example, 1000 mm or more, it is difficult to ensure good insulation across the entire width.

The present invention was made in consideration of these problems, and its purpose is to provide a polyimide film and a method for producing the same that can ensure good insulation across the entire width even when exposed to a high-temperature, high-humidity environment.

<Aspects of the present invention>
The present invention includes the following aspects.

[1] A method for producing a polyimide film, comprising irradiating a polyimide film precursor containing a polyamic acid with far infrared rays to imidize the polyamic acid,
the polyamic acid has 3,3',4,4'-biphenyltetracarboxylic dianhydride residues and p-phenylenediamine residues, or has pyromellitic dianhydride residues and 4,4'-diamino-2,2'-dimethylbiphenyl residues;
the content of the 3,3',4,4'-biphenyltetracarboxylic dianhydride residue or the pyromellitic dianhydride residue is 60 mol % or more based on the total tetracarboxylic dianhydride residues constituting the polyamic acid,
the content of the p-phenylenediamine residue or the 4,4'-diamino-2,2'-dimethylbiphenyl residue is 60 mol % or more based on the total diamine residues constituting the polyamic acid,
In the method for producing a polyimide film, when the far-infrared rays are irradiated, the polyimide film precursor is irradiated with the far-infrared rays using three or more far-infrared heaters which are arranged along the width direction of the polyimide film precursor and whose temperatures can be controlled individually.

[2] The method for producing a polyimide film described in [1] above, in which the difference between the maximum temperature and the minimum temperature in the width direction of the surface of the polyimide film precursor during irradiation with the far infrared rays is 60°C or less.

[3] The method for producing a polyimide film according to [1] or [2], wherein the width of the polyimide film precursor is 1000 mm or more.

[4] A polyimide film having a width of 1000 mm or more,
A polyimide film, wherein C ₁₀₀₀ and C ₂₅₀ derived from the electrical quantities of a laminate in which copper foils are laminated on both sides of the polyimide film satisfy the following formula (A) over the entire width direction of the polyimide film:
_C1000 / _C250 <7.5...(A)
(The above C ₁₀₀₀ represents the ratio of the quantity of electricity, Q ₁₀₀₀ (600)/Q 1000 (0), when the quantity of electricity immediately after application of a DC voltage of 1000 V is Q _{1000 (0) and the quantity of electricity after application of a DC voltage of 1000 V for 600 seconds is Q 1000 ( 600} );
The _C250 represents the ratio of the quantity of electricity, _Q250 (600)/Q250(0), where _Q250 (0) is the quantity of electricity immediately after a DC voltage of 250V is applied and _Q250 (600) is the quantity of electricity after a DC voltage of 250V is applied for ₆₀₀ seconds.

[5] The polyimide film described in [4] above, having a tensile modulus of elasticity of 6.0 GPa or more.

[6] The polyimide film described in [4] or [5] above, having a thickness of 50 μm or less.

[7] The polyimide contained in the polyimide film has a 3,3',4,4'-biphenyltetracarboxylic dianhydride residue and a p-phenylenediamine residue, or has a pyromellitic dianhydride residue and a 4,4'-diamino-2,2'-dimethylbiphenyl residue,
the content of the 3,3',4,4'-biphenyltetracarboxylic dianhydride residue or the pyromellitic dianhydride residue is 60 mol % or more based on the total tetracarboxylic dianhydride residues constituting the polyimide,
The polyimide film according to any one of [4] to [6] above, wherein the content of the p-phenylenediamine residue or the 4,4'-diamino-2,2'-dimethylbiphenyl residue is 60 mol % or more based on all diamine residues constituting the polyimide.

The present invention provides a polyimide film and a method for producing the same that can ensure good insulation across the entire width even when exposed to a high-temperature, high-humidity environment.

FIG. 2 is a plan view of the inside of the far-infrared furnace as viewed from the far-infrared heater side. FIG. 4 is a plan view for explaining measurement points of the quantity of electricity of the polyimide film.

The following provides a detailed description of preferred embodiments of the present invention, but the present invention is not limited to these. In addition, all academic and patent literature described in this specification is incorporated herein by reference.

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

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

The content of 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, even more preferably 90 mol% or more and 100 mol% or less, and may be 100 mol%.

"Polyamic acid" is a polymer containing a structural unit represented by the following general formula (2) (hereinafter sometimes referred to as "structural unit (2)").

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

The content of 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, even more preferably 90 mol% or more and 100 mol% or less, and may be 100 mol%.

Polyimide is an imide of polyamic acid. When the content of structural unit (2) relative to all structural units constituting polyamic acid is 100 mol %, the polyimide, which is an imide of the polyamic acid, has a residue represented by A ¹ in general formula (2) as X ¹ in general formula (1) and has a residue represented by A ² in general formula (2) as X ² in general formula (1).

"Far infrared rays" refers to electromagnetic waves with wavelengths between 4μm and 1000μm.

"Non-thermoplastic polyimide" refers to polyimide that retains a film shape (flat membrane shape) when fixed in film form (thickness: 17 μm) on a metal frame and heated at 450°C for 2 minutes. "Thermoplastic polyimide" refers to polyimide that does not retain a film shape when fixed in film form (thickness: 17 μm) on a metal frame and heated at 450°C for 2 minutes.

Hereinafter, the compound name may be followed by "system" to collectively refer to the compound and its derivatives. Also, when the compound name is followed by "system" to represent the name of a polymer, unless otherwise specified, it means that the repeating unit of the polymer is derived from the compound or its derivative. Also, tetracarboxylic acid dianhydrides may be written as "acid dianhydrides".

Unless otherwise specified, the components and functional groups exemplified in this specification may be used alone or in combination of two or more types.

The drawings referred to in the following explanation 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 due to the convenience of creating the drawings. Also, for the convenience of explanation, in drawings explained later, the same components as those in previously explained drawings may be given the same reference numerals and their explanation may be omitted.

<First embodiment: Method for producing polyimide film>
The method for producing a polyimide film according to the first embodiment of the present invention includes a step of imidizing a polyamic acid by irradiating a polyimide film precursor containing a polyamic acid with far-infrared rays (hereinafter, this step may be referred to as a "far-infrared irradiation step"). The polyamic acid has a 3,3',4,4'-biphenyltetracarboxylic dianhydride residue and a p-phenylenediamine residue, or a pyromellitic dianhydride residue and a 4,4'-diamino-2,2'-dimethylbiphenyl residue. The content of the 3,3',4,4'-biphenyltetracarboxylic dianhydride residue or the pyromellitic dianhydride residue is 60 mol% or more with respect to the total tetracarboxylic dianhydride residues constituting the polyamic acid. The content of the p-phenylenediamine residue or the 4,4'-diamino-2,2'-dimethylbiphenyl residue is 60 mol% or more with respect to the total diamine residues constituting the polyamic acid. In the far-infrared irradiation step, the polyimide film precursor is irradiated with far-infrared rays using three or more far-infrared heaters that are arranged along the width direction of the polyimide film precursor and can be individually temperature-controlled. In this specification, "irradiating the polyimide film precursor with far-infrared rays using far-infrared heaters that can be individually temperature-controlled" means "irradiating the polyimide film precursor with far-infrared rays using far-infrared heaters that are individually temperature-controlled."

Hereinafter, 3,3',4,4'-biphenyltetracarboxylic dianhydride may be written as "BPDA". Also, p-phenylenediamine may be written as "PDA". Also, pyromellitic dianhydride may be written as "PMDA". Also, 4,4'-diamino-2,2'-dimethylbiphenyl may be written as "m-TB".

Hereinafter, the polyamic acid having BPDA residues and PDA residues may be referred to as the "first polyamic acid." The polyamic acid having PMDA residues and m-TB residues may be referred to as the "second polyamic acid." One or more polyamic acids selected from the group consisting of the first polyamic acid and the second polyamic acid may be referred to as the "specific polyamic acid." An imidized product of a specific polyamic acid may be referred to as a "specific polyimide."

In the first polyamic acid, the content of BPDA residues is 60 mol % or more relative to all tetracarboxylic dianhydride residues constituting the first polyamic acid, and the content of PDA residues is 60 mol % or more relative to all diamine residues constituting the first polyamic acid. In the second polyamic acid, the content of PMDA residues is 60 mol % or more relative to all tetracarboxylic dianhydride residues constituting the second polyamic acid, and the content of m-TB residues is 60 mol % or more relative to all diamine residues constituting the second polyamic acid.

The method for producing a polyimide film according to the first embodiment makes it possible to produce a polyimide film that can maintain good insulation across the entire width even when exposed to a high-temperature, high-humidity environment. The reason for this is presumed to be as follows.

In the manufacturing method according to the first embodiment, a polyimide film precursor containing a specific polyamic acid having a specific ratio of specific monomer residues is used as a material. The specific polyimide, which is an imidized product of the specific polyamic acid, has a dense crystal structure and tends to have high resistance to high voltage environments. Therefore, the specific polyimide can ensure good insulation even when exposed to a high-temperature, high-humidity environment. In addition, in the far-infrared irradiation step of the manufacturing method according to the first embodiment, the polyimide film precursor is irradiated with far-infrared rays using three or more far-infrared heaters that are arranged along the width direction of the polyimide film precursor and can be individually temperature-controlled. Therefore, according to the manufacturing method according to the first embodiment, the crystal structure of the specific polyimide can be uniformly controlled over the entire width of the film. For these reasons, according to the manufacturing method according to the first embodiment, a polyimide film can be manufactured that can ensure good insulation over the entire width even when exposed to a high-temperature, high-humidity environment.

Hereinafter, the property of ensuring good insulation even when exposed to high temperature and high humidity environments may be referred to as "high temperature and high humidity insulation."

In order to obtain a polyimide film having superior high-temperature and high-humidity insulation properties using the first polyamic acid, the content of BPDA residues in the first polyamic acid is preferably 60 mol% to 100 mol%, more preferably 60 mol% to 90 mol%, and even more preferably 60 mol% to 80 mol%, based on the total dianhydride residues constituting the first polyamic acid. In order to obtain a polyimide film having superior high-temperature and high-humidity insulation properties using the first polyamic acid, the content of PDA residues in the first polyamic acid is preferably 60 mol% to 100 mol%, more preferably 60 mol% to 95 mol%, and even more preferably 60 mol% to 90 mol%, based on the total diamine residues constituting the first polyamic acid.

The first polyamic acid may have PMDA residues. When the first polyamic acid has PMDA residues, in order to obtain a polyimide film having superior high-temperature, high-humidity insulation properties, it is preferable that the content of PMDA residues is 5 mol% or more and 15 mol% or less with respect to all dianhydride residues constituting the first polyamic acid. The first polyamic acid may also have m-TB residues. When the first polyamic acid has m-TB residues, in order to obtain a polyimide film having superior high-temperature, high-humidity insulation properties, it is preferable that the content of m-TB residues is 5 mol% or more and 15 mol% or less with respect to all diamine residues constituting the first polyamic acid.

In order to obtain a polyimide film having superior high-temperature and high-humidity insulation properties using the second polyamic acid, the content of PMDA residues in the second polyamic acid is preferably 60 mol% or more and 100 mol% or less, and more preferably 60 mol% or more and 90 mol% or less, based on the total dianhydride residues constituting the second polyamic acid. In order to obtain a polyimide film having superior high-temperature and high-humidity insulation properties using the second polyamic acid, the content of m-TB residues in the second polyamic acid is preferably 60 mol% or more and 100 mol% or less, and more preferably 60 mol% or more and 90 mol% or less, based on the total diamine residues constituting the second polyamic acid.

The second polyamic acid may have a BPDA residue. When the second polyamic acid has a BPDA residue, in order to obtain a polyimide film having superior high-temperature and high-humidity insulation properties, the content of the BPDA residue is preferably 5 mol% to 35 mol%, and more preferably 10 mol% to 30 mol%, based on the total dianhydride residues constituting the second polyamic acid. The second polyamic acid may also have a PDA residue. When the second polyamic acid has a PDA residue, in order to obtain a polyimide film having superior high-temperature and high-humidity insulation properties, the content of the PDA residue is preferably 5 mol% to 15 mol%, based on the total diamine residues constituting the second polyamic acid.

As described above, the specific polyamic acid has one or more dianhydride residues selected from the group consisting of BPDA residues and PMDA residues, and one or more diamine residues selected from the group consisting of PDA residues and m-TB residues.

The specific 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 PMDA residues. Examples of acid dianhydrides (monomers) for forming other acid dianhydride residues (acid dianhydride residues other than BPDA residues and PMDA residues) include 3,3',4,4'-benzophenonetetracarboxylic dianhydride (hereinafter sometimes referred to as "BTDA"), 4,4'-oxydiphthalic anhydride (hereinafter sometimes referred to as "ODPA"), 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-benzophenone Examples include tetracarboxylic dianhydride, 3,4'-oxydiphthalic anhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, p-phenylene bis(trimellitic acid monoester anhydride), ethylene bis(trimellitic acid monoester anhydride), bisphenol A bis(trimellitic acid monoester anhydride), and derivatives thereof.

In order to obtain a polyimide film with superior high-temperature and high-humidity insulation properties, the other dianhydride residues are preferably one or more dianhydride residues selected from the group consisting of BTDA residues and ODPA residues.

In order to obtain a polyimide film with superior high-temperature and high-humidity insulation properties, the content of one or more types of dianhydride residues selected from the group consisting of BTDA residues and ODPA residues is preferably 10 mol% or more and 40 mol% or less, more preferably 20 mol% or more and 40 mol% or less, and even more preferably 30 mol% or more and 40 mol% or less, based on the total dianhydride residues constituting the specific polyamic acid.

The specific polyamic acid may have other diamine residues in addition to one or more diamine residues selected from the group consisting of PDA residues and m-TB residues. Examples of diamines (monomers) for forming other diamine residues (diamine residues other than PDA residues and m-TB residues) include 1,3-bis(4-aminophenoxy)benzene (hereinafter sometimes referred to as "TPE-R"), 4,4'-diaminodiphenyl ether (hereinafter sometimes referred to as "ODA"), 1,4-bis(4-aminophenoxy)benzene, 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl ether, 4,4 ... Nilsulfone, 4,4'-diaminodiphenylsulfone, 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.

In order to obtain a polyimide film with superior high-temperature and high-humidity insulation properties, the other diamine residues are preferably one or more diamine residues selected from the group consisting of TPE-R residues and ODA residues.

In order to obtain a polyimide film with superior high-temperature and high-humidity insulation properties, the content of one or more diamine residues selected from the group consisting of TPE-R residues and ODA residues is preferably 5 mol% or more and 40 mol% or less, and more preferably 10 mol% or more and 30 mol% or less, relative to the total diamine residues constituting the specific polyamic acid.

In order to obtain a polyimide film having better high-temperature, high-humidity insulation properties, it is preferable to use a first polyamic acid as the specific polyamic acid, and it is more preferable to use a first polyamic acid having an ODPA residue as the specific polyamic acid. When a first polyamic acid having an ODPA residue is used as the specific polyamic acid, in order to obtain a polyimide film having even better high-temperature, high-humidity insulation properties, it is preferable that the content of ODPA residues is 20 mol% or more and 40 mol% or less with respect to the total acid dianhydride residues constituting the first polyamic acid. Furthermore, when a first polyamic acid having an ODPA residue is used as the specific polyamic acid, in order to obtain a polyimide film having even better high-temperature, high-humidity insulation properties, it is preferable that the first polyamic acid has a TPE-R residue, and it is more preferable that the content of TPE-R residues is 5 mol% or more and 15 mol% or less with respect to the total diamine residues constituting the first polyamic acid.

The method for producing a polyimide film according to the first embodiment may include steps (other steps) other than the far-infrared irradiation step. Examples of the other steps include the "synthesis step of a specific polyamic acid," the "polyimide film precursor formation step," and the "hot air heating step" described below. Each step included in an example of the production method according to the first embodiment will be described in detail below.

[Specific polyamic acid synthesis process]
As a synthesis method (production method) of the specific polyamic acid, any known method or a combination thereof can be used. A specific example of the synthesis method (production method) of the specific 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 during the reaction are preferably substantially the same. When synthesizing the specific polyamic acid using a diamine and a tetracarboxylic dianhydride, the amount of diamine (the amount of each diamine when multiple diamines are used) and the amount of tetracarboxylic dianhydride (the amount of each tetracarboxylic dianhydride when multiple tetracarboxylic dianhydrides are used) can be adjusted to obtain a desired specific polyamic acid (a polymer of diamine and tetracarboxylic dianhydride). The molar fraction of each residue in the specific polyamic acid is, for example, the same as the molar fraction of each monomer (diamine and tetracarboxylic dianhydride) used in the synthesis of the specific polyamic acid. The temperature condition of the reaction between the diamine and the tetracarboxylic dianhydride, i.e., the synthesis reaction of the specific polyamic acid, is not particularly limited, but is, for example, in the range of 10° C. to 150° C. The reaction time of the synthesis reaction of the specific polyamic acid is, for example, in the range of 10 minutes to 30 hours. Any method of adding a monomer may be used for synthesizing the specific polyamic acid. The following method can be used as a method for producing the specific polyamic acid.

An example of a method for producing the specific polyamic acid is a polymerization method (hereinafter sometimes referred to as "polymerization method A") that includes the following steps (Aa) and (Ab).
(A-a): A process for reacting an aromatic diamine with an aromatic acid dianhydride in an organic solvent with an excess of the aromatic diamine to obtain a prepolymer having amino groups at both ends. (A-b): A process for polymerizing by adding an aromatic diamine having a different structure from that used in the process (A-a) and further adding an aromatic acid dianhydride having a different structure from that used in the process (A-a) so that the aromatic diamine and aromatic acid dianhydride are substantially equimolar in all processes.

As a method for producing the specific polyamic acid, there may be mentioned a polymerization method (hereinafter sometimes referred to as "polymerization method B") comprising the following steps (Ba) and (Bb).
(B-a): A process for reacting an aromatic diamine with an aromatic acid dianhydride in an organic solvent with an excess of the aromatic acid dianhydride to obtain a prepolymer having acid anhydride groups at both ends. (B-b): A process for polymerizing by adding an aromatic acid dianhydride having a structure different from that used in the process (B-a) and further adding an aromatic diamine having a structure different from that used in the process (B-a) so that the aromatic diamine and aromatic acid dianhydride are substantially equimolar in all processes.

In this specification, a polymerization method in which the order of addition is set so that a specific diamine or specific acid dianhydride selectively reacts with any or a specific diamine, or any or a specific acid dianhydride (for example, the above-mentioned polymerization method A and polymerization method B) is referred to as sequence polymerization. Among the polymers obtained by sequence polymerization, a polymer having two types of segments is called a diblock copolymer, and a polymer having three types of segments is called a triblock copolymer. In contrast, a polymerization method in which the order of addition of diamines and acid dianhydrides is not set (a polymerization method in which monomers react with each other randomly) is referred to as random polymerization. A polymer obtained by random polymerization is called a random copolymer.

When obtaining a polyimide film precursor, a method may be adopted in which the polyimide film precursor is obtained from a polyamic acid solution containing a specific 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; halogenated alkyl solvents such as chloroform and methylene chloride; aromatic hydrocarbon-based solvents such as benzene and toluene; phenol-based solvents such as phenol and cresol; ketone-based solvents such as cyclopentanone; and ether-based solvents such as tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dimethyl ether, diethyl ether, diethylene glycol diethyl ether, diethylene glycol dimethyl ether, and p-cresol methyl ether. Usually, these solvents are used alone, but two or more of them may be used in appropriate combination as necessary. When a specific 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 for obtaining a polyimide film precursor. 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. In addition, the solid specific polyamic acid obtained by removing the solvent from the reaction solution may be dissolved in an organic solvent to prepare a polyamic acid solution.

Additives such as dyes, surfactants, leveling agents, plasticizers, silicones, and sensitizers may be added to the polyamic acid solution. Fillers may also be added to the polyamic acid solution to improve the film's 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.

The concentration of the specific polyamic acid in the polyamic acid solution is not particularly limited, and is, for example, 5% by weight to 35% by weight, and preferably 8% by weight to 30% by weight, based on the total amount of the polyamic acid solution. When the concentration of the specific polyamic acid is 5% by weight to 35% by weight, an appropriate molecular weight and solution viscosity can be obtained.

[Polyimide film precursor formation process]
The method for forming the polyimide film precursor is not particularly limited, and various known methods can be used. For example, the polyimide film precursor can be formed according to the procedures shown in the following steps (i) and (ii).
Step (i): A step of applying a dope solution containing a polyamic acid solution onto a support to form a coating film. Step (ii): A step of heating the coating film on the support to form a polyimide film precursor having self-supporting properties (hereinafter, sometimes referred to as a "gel film"), and then peeling the gel film off the support.

The methods for manufacturing polyimide films can be broadly divided into thermal imidization and chemical imidization. Thermal imidization does not use a dehydrating ring-closing agent, but instead involves applying a polyamic acid solution as a dope onto a support and heating it to promote imidization. On the other hand, chemical imidization is a method in which a polyamic acid solution to which at least one of a dehydrating ring-closing agent and a catalyst has been added as an imidization accelerator is used as a dope to promote imidization. Either method can be used, but chemical imidization is more productive.

As the dehydration ring-closing agent, an acid anhydride such as acetic anhydride is preferably used. As the catalyst, a tertiary amine such as an aliphatic tertiary amine, an aromatic tertiary amine, or a heterocyclic tertiary amine is preferred, and isoquinoline is more preferred.

The amount of the dehydrating ring-closing agent added is preferably 0.5 to 10.0 molar equivalents relative to the amide group of the specific polyamic acid, more preferably 0.7 to 5.0 molar equivalents, and even more preferably 0.8 to 3.0 molar equivalents. The amount of the catalyst added is preferably 0.5 to 5.0 molar equivalents relative to the amide group of the specific polyamic acid, more preferably 0.7 to 2.5 molar equivalents, and even more preferably 0.8 to 2.0 molar equivalents. In this specification, the term "amide group of the specific polyamic acid" refers to the amide group generated by the polymerization reaction of a diamine and a tetracarboxylic dianhydride.

In step (i), the method for applying the dope liquid onto the support is not particularly limited, and a method using a conventionally known application device such as a die coater, a comma coater (registered trademark), a reverse coater, or a knife coater can be used. As the support onto which the dope liquid is applied in step (i), a glass plate, an aluminum foil, an endless stainless steel belt, a stainless steel drum, or the like is preferably used.

In step (ii), the heating conditions are set according to the thickness of the final film to be obtained and the production speed, and after at least one of partial imidization and drying is performed, the gel film is peeled off from the support to obtain the gel film. The heating conditions in step (ii) are, for example, a heating temperature in the range of 50°C to 200°C and a heating time in the range of 1 minute to 100 minutes.

In the first embodiment, the polyimide film precursor may be formed from a single layer coating film containing one type of polyamic acid, or from a coating film in which two or more layers containing different types of polyamic acid are laminated. A method for forming a coating film in which two or more layers containing different types of polyamic acid are laminated is the co-extrusion-casting coating method. The "co-extrusion-casting coating method" is a method for forming a coating film using an extrusion molding machine having an extrusion molding die with two or more layers. For example, 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 dope liquid containing a specific polyamic acid and a dope liquid containing a polyamic acid different from the specific polyamic acid from the lip opening of the extrusion molding die in the form of a thin film of two or more layers.

Even when forming a polyimide film precursor from a coating film in which two or more layers containing different types of polyamic acid are laminated, the preferred conditions for forming a polyimide film precursor from the coating film are as described above.

In the first embodiment, when a polyimide film precursor is formed from a coating film in which two or more layers containing different types of polyamic acid are laminated, at least one of the two or more layers may contain a specific polyamic acid. For example, when forming a multilayer polyimide film having a three-layer structure of an adhesive layer containing a thermoplastic polyimide/a non-thermoplastic polyimide layer/an adhesive layer containing a thermoplastic polyimide, a specific polyamic acid can be used as the polyamic acid (non-thermoplastic polyamic acid) for forming the non-thermoplastic polyimide layer, and a polyamic acid (thermoplastic polyamic acid) different from the specific polyamic acid can be used as the polyamic acid for forming the adhesive layer (thermoplastic polyimide layer). When using these polyamic acids to form a three-layer coating film by the coextrusion-casting coating method, a method can be adopted in which a solution (dope solution) for forming a non-thermoplastic polyimide layer containing a specific polyamic acid and a solution (dope solution) for forming an adhesive layer containing a thermoplastic polyamic acid are prepared, the solution for forming the non-thermoplastic polyimide layer is supplied to the center layer of the extrusion die, and the solution for forming the adhesive layer is supplied to the two layers adjacent (on both sides) to the center layer of the extrusion die, and these solutions are extruded onto a support.

The acid dianhydride (monomer) for obtaining the thermoplastic polyamic acid may be the same compound as the acid dianhydride (monomer) for forming the acid dianhydride residue in the specific polyamic acid described above. The acid dianhydride residue in the thermoplastic polyamic acid and the acid dianhydride residue in the specific polyamic acid may be the same or different.

In order to ensure thermoplasticity, the diamine residues in the thermoplastic polyamic acid are preferably diamine residues having a bent structure. In order to more easily ensure thermoplasticity, the content of the diamine residues having a bent structure is preferably 50 mol% or more, more preferably 70 mol% or more, and even more preferably 80 mol% or more, and may be 100 mol% based on the total diamine residues constituting the thermoplastic polyamic acid. Examples of diamines (monomers) for forming diamine residues having a bent structure include 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-bis(3-aminophenoxy)biphenyl, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, and 2,2-bis[4-(4-aminophenoxy)phenyl]propane (hereinafter sometimes referred to as "BAPP"). In order to more easily ensure thermoplasticity, the diamine residues in the thermoplastic polyamic acid are preferably BAPP residues.

[Hot air heating process]
In the hot air heating step, in order to apply an appropriate tension to the gel film peeled off from the support, the gel film is heated while being conveyed in a hot air oven, for example, with both ends of the gel film held by pin sheets or clips laid on a tenter rail. In the hot air heating step, multiple hot air ovens may be used to heat the gel film in stages. In order to volatilize the remaining solvent in the gel film and efficiently complete the imidization reaction in the next step, the far-infrared irradiation step, the heating temperature in the hot air heating step is preferably in the range of 200°C or more and 350°C or less. In addition, in order to volatilize the remaining solvent in the gel film and efficiently complete the imidization reaction in the next step, the far-infrared irradiation step, the heating time in the hot air heating step (total time when multiple hot air ovens are used) is preferably in the range of 30 seconds or more and 300 seconds or less.

Below, we will explain in detail the preferred heating conditions for the method using three hot air ovens, which is the preferred heating method in the hot air heating process.

The hot air heating zone, which consists of three hot air stoves, is provided with a first hot air stove, a second hot air stove adjacent to the first hot air stove, and a third hot air stove adjacent to the second hot air stove.

The preferred set temperature of the first hot air stove is 230°C or higher and 280°C or lower, the preferred set temperature of the second hot air stove is 280°C or higher and 300°C or lower, and the preferred set temperature of the third hot air stove is 290°C or higher and 310°C or lower. In this example, it is also preferable that the difference in the set temperatures of the first and second hot air stoves is 50°C or lower, and that the difference in the set temperatures of the second and third hot air stoves is 30°C or lower.

[Far-infrared irradiation process]
Next, the far-infrared irradiation step will be described with reference to Fig. 1. Fig. 1 is a plan view of the inside of an example of a far-infrared furnace that can be used in the first embodiment, as viewed from the far-infrared heater side.

As shown in FIG. 1, in the far-infrared irradiation process, a polyimide film precursor 10 (gel film) containing a specific polyamic acid is irradiated with far-infrared rays to imidize the specific polyamic acid. In the example shown in FIG. 1, when irradiating with far-infrared rays, the polyimide film precursor 10 is irradiated with far-infrared rays using nine far-infrared heaters 20, each of which can be individually temperature-controlled and arranged along the width direction X of the polyimide film precursor 10. The polyimide film precursor 10 is transported along the transport direction Y.

The controller 30 shown in FIG. 1 is configured as a microprocessor centered on a CPU (Central Processing Unit). This controller 30 transmits control signals to each far-infrared heater 20 based on temperature data (specifically, the surface temperature of the polyimide film precursor 10) obtained from a temperature sensor (not shown) corresponding to each far-infrared heater 20, and individually controls the output of each far-infrared heater 20. As a control method using the controller 30, for example, a method of individually PID controlling (Proportional-Integral-Differential Controller) the output of each far-infrared heater 20 based on temperature data obtained from a temperature sensor corresponding to each far-infrared heater 20 so that the temperature difference in the width direction X of the surface of the polyimide film precursor 10 is reduced.

When the far-infrared heater 20 is a far-infrared radiation panel as shown in FIG. 1, the width (length in a direction parallel to the width direction X) of the far-infrared heater 20 is, for example, 1 cm or more and 1 m or less. When the far-infrared heater 20 is a far-infrared radiation panel as shown in FIG. 1, the length (length in a direction parallel to the transport direction Y) of the far-infrared heater 20 is, for example, 1 cm or more and 3 m or less. Note that FIG. 1 shows an example in which a panel-shaped far-infrared heater 20 is used, but the shape of the far-infrared heater that can be used in the first embodiment is not limited to a panel shape and may be another shape, such as a pipe shape. Also, in the first embodiment, multiple far-infrared heaters may be provided along the transport direction of the polyimide film precursor.

In order to further improve the high-temperature, high-humidity insulation properties over the entire width of the polyimide film, in the far-infrared irradiation process, the difference between the maximum and minimum temperatures in the width direction X of the surface of the polyimide film precursor 10 is preferably 60°C or less, more preferably 50°C or less, even more preferably 40°C or less, and even more preferably 30°C or less. In the far-infrared irradiation process, the lower limit of the difference between the maximum and minimum temperatures in the width direction X of the surface of the polyimide film precursor 10 is not particularly limited and may be 0°C. Here, the "difference between the maximum and minimum temperatures in the width direction X of the surface of the polyimide film precursor 10" refers to the difference between the temperature of the temperature sensor that shows the maximum temperature among the temperature sensors corresponding to each far-infrared heater 20 and the temperature of the temperature sensor that shows the minimum temperature among the temperature sensors corresponding to each far-infrared heater 20. In this specification, the "surface temperature of the polyimide film precursor" refers to the ambient temperature up to a height of 10 cm from the surface of the polyimide film precursor, and can be measured by a temperature sensor such as a thermocouple.

In order to increase the productivity of the polyimide film, it is preferable that the width of the polyimide film precursor 10 is 1000 mm or more. In general, when manufacturing a polyimide film from a polyimide film precursor having a width of 1000 mm or more, it is difficult to ensure good high-temperature, high-humidity insulation over the entire width. However, according to the first embodiment, three or more far-infrared heaters that are individually temperature controllable and arranged along the width of the polyimide film precursor are used, so that even if a polyimide film precursor having a width of 1000 mm or more is used, good high-temperature, high-humidity insulation can be ensured over the entire width of the polyimide film. In the first embodiment, in order to easily ensure good high-temperature, high-humidity insulation over the entire width of the polyimide film, it is preferable that the width of the polyimide film precursor is 3000 mm or less.

In FIG. 1, an example is shown in which nine far-infrared heaters 20 are arranged along the width direction X of the polyimide film precursor 10. However, in the first embodiment, the number of far-infrared heaters is not limited as long as three or more far-infrared heaters are arranged along the width direction of the polyimide film precursor. In the first embodiment, in order to further improve the high-temperature and high-humidity insulation across the entire width direction of the polyimide film, the number of far-infrared heaters arranged along the width direction of the polyimide film precursor is preferably four or more, more preferably five or more, even more preferably six or more, even more preferably seven or more, and may be eight or more or nine or more. In the first embodiment, in order to reduce the manufacturing cost, the number of far-infrared heaters arranged along the width direction of the polyimide film precursor is preferably 30 or less.

In addition, in the first embodiment, the size and spacing of the far-infrared heaters may be adjusted, for example, so that the difference between the maximum and minimum temperatures in the width direction of the surface of the polyimide film precursor is 60°C or less. In the first embodiment, in order to further improve the high-temperature, high-humidity insulation across the entire width direction of the polyimide film, it is preferable to evenly arrange the far-infrared heaters to be used across the entire width direction of the polyimide film precursor. In the following, "evenly arranged across the entire area" will simply be referred to as "evenly arranged."

In the far-infrared irradiation process, multiple far-infrared furnaces may be used. When multiple far-infrared furnaces are used, at least one of the multiple far-infrared furnaces may be provided with three or more far-infrared heaters that are arranged along the width direction of the polyimide film precursor and can be individually temperature controlled. When multiple far-infrared furnaces are used in the far-infrared irradiation process, in order to further improve the high-temperature, high-humidity insulation properties over the entire width direction of the polyimide film, it is preferable that each of the multiple far-infrared furnaces is provided with three or more far-infrared heaters that are arranged along the width direction of the polyimide film precursor and can be individually temperature controlled.

In order to efficiently complete the imidization reaction, the heating temperature in the far-infrared irradiation process is preferably in the range of 350°C to 450°C. In addition, in order to efficiently complete the imidization reaction, the heating time in the far-infrared irradiation process (total time when multiple far-infrared furnaces are used) is preferably in the range of 30 seconds to 300 seconds.

Below, we will explain in detail the preferred heating conditions for the method using two far-infrared furnaces, which is the preferred heating method in the far-infrared irradiation process.

The far-infrared heating zone, which consists of two far-infrared furnaces, is provided with a first far-infrared furnace and a second far-infrared furnace adjacent to the first far-infrared furnace.

The preferred set temperature of the first far-infrared furnace is 390°C or higher and 430°C or lower, and the preferred set temperature of the second far-infrared furnace is 330°C or higher and 390°C or lower. In this example, the difference in the set temperatures of the first far-infrared furnace and the second far-infrared furnace is preferably 70°C or lower, and more preferably 60°C or lower.

[Preferred aspect of the first embodiment]
In order to easily ensure good insulation across the entire width even when exposed to a high-temperature, high-humidity environment, the manufacturing method according to the first embodiment preferably satisfies the following condition 1, more preferably satisfies the following condition 2, even more preferably satisfies the following condition 3, even more preferably satisfies the following condition 4, and particularly preferably satisfies the following condition 5.
Condition 1: A first polyamic acid is used as the specific polyamic acid, and in the far-infrared irradiation step, the difference between the maximum temperature and the minimum temperature in the width direction of the surface of the polyimide film precursor is 60° C. or less.
Condition 2: The above condition 1 is satisfied, and the first polyamic acid has an ODPA residue.
Requirement 3: The above requirement 2 is satisfied, and the content of ODPA residues is 20 mol % or more and 40 mol % or less based on the total acid dianhydride residues constituting the first polyamic acid.
Requirement 4: The above requirement 3 is satisfied, and the first polyamic acid has a TPE-R residue.
Requirement 5: The above requirement 4 is satisfied, and the content of TPE-R residues is 5 mol % or more and 15 mol % or less based on the total diamine residues constituting the first polyamic acid.

[Polyimide film obtained by the production method according to the first embodiment]
Next, the polyimide film obtained by the production method according to the first embodiment (hereinafter, may be referred to as "polyimide film A") will be described.

Polyimide film A may be a single-layer polyimide film containing a specific polyimide, or a multilayer polyimide film in which a layer containing the specific polyimide is laminated with a layer containing a polyimide different from the specific polyimide (for example, an adhesive layer containing the thermoplastic polyimide described above). In the case of a multilayer polyimide film containing an adhesive layer, a metal-clad laminate can be formed by laminating a metal foil to the adhesive layer.

The thickness of the polyimide film A (in the case of a multi-layer polyimide film, the total thickness of each layer) is, for example, 6 μm or more and 60 μm or less. The thinner the polyimide film A, the easier it is to reduce the weight of the resulting flexible printed circuit board. In order to make it easier to reduce the weight of the resulting flexible printed circuit board, the thickness of the polyimide film A is preferably 50 μm or less, and more preferably 25 μm or less. In order to ensure the mechanical strength of the resulting flexible printed circuit board, the thickness of the polyimide film A is preferably 7 μm or more, and more preferably 10 μm or more. Since the polyimide film A is manufactured by the manufacturing method according to the first embodiment, good insulation properties can be ensured even if it is thin. The thickness of the polyimide film A can be measured using a laser hologram.

When polyimide film A is a multilayer polyimide film including an adhesive layer, in order to easily realize a thin flexible printed circuit board while ensuring adhesion to the metal foil, the thickness of the adhesive layer (if two adhesive layers are provided, the thickness of each adhesive layer) is preferably 1 μm or more and 15 μm or less. In addition, when polyimide film A is a multilayer polyimide film including an adhesive layer, in order to easily adjust the linear expansion coefficient of polyimide film A, the thickness ratio of the layer containing a specific polyimide to the adhesive layer (thickness of the layer containing a specific polyimide/thickness of the adhesive layer) is preferably 55/45 or more and 95/5 or less. When two adhesive layers are provided, the thickness of the adhesive layer when calculating the above thickness ratio is the total thickness of the two adhesive layers.

In order to obtain a polyimide film A with superior high-temperature and high-humidity insulation properties, the tensile modulus of the polyimide film A is preferably 6.0 GPa or more, more preferably 6.0 GPa to 10.0 GPa, even more preferably 7.0 GPa to 10.0 GPa, and even more preferably 7.5 GPa to 10.0 GPa. The tensile modulus of the polyimide film A can be adjusted by changing the type of monomers used to form the polyimide film A and the ratio of monomers used. The method for measuring the tensile modulus is the same as or similar to the method described in the examples below.

In order to obtain a polyimide film A with superior high-temperature and high-humidity insulation properties, the dielectric breakdown voltage of the polyimide film A is preferably 7.0 kV or more, and more preferably 7.5 kV or more. There is no particular upper limit to the dielectric breakdown voltage of the polyimide film A, but in order to reduce manufacturing costs, the dielectric breakdown voltage of the polyimide film A is preferably 10.0 kV or less. The dielectric breakdown voltage is measured by the same method as in the examples described below or a method equivalent thereto.

In order to obtain a polyimide film A having superior high-temperature and high-humidity insulation properties, it is preferable that C ₁₀₀₀ and C ₂₅₀ derived from the electrical quantities of a laminate in which copper foils are laminated on both sides of the polyimide film A satisfy the following formula (A) over the entire width direction of the polyimide film A.
_C1000 / _C250 <7.5...(A)

In formula (A), C ₁₀₀₀ represents the ratio of the quantity of electricity Q ₁₀₀₀ (600)/Q ₁₀₀₀ (0) when the quantity of electricity immediately after application of a DC voltage of 1000V is Q 1000 (0) and the quantity of electricity after application of a DC voltage of 1000V for 600 seconds is Q ₁₀₀₀ (600). In formula (A), C ₂₅₀ represents the ratio of the quantity of electricity Q ₂₅₀ ( ₆₀₀ )/Q ₂₅₀ (0) when the quantity of electricity immediately after application of a DC voltage of 250V is Q ₂₅₀ (0) and the quantity of electricity after application of a DC voltage of 250V for 600 seconds is Q ₂₅₀ (600).

_Q1000 (0), _Q1000 (600), _Q250 (0) and _Q250 (600) all represent the quantity of electricity (unit: C) measured by the current integration charge method. That is, in this specification, the quantity of electricity measured by the current integration charge method is represented by _Qa (t), where a is the applied DC voltage (unit: V) and t is the application time of the DC voltage (unit: seconds).

The reason why the inventors focused on Q ₁₀₀₀ (600) when a DC voltage of 1000V was applied for 600 seconds is because it is considered important to consider the influence of time in addition to a high voltage such as 1000V in order to measure the quantity of electricity of polyimide film A in a high voltage environment. In other words, it is considered that the measured quantity of electricity reaches a nearly constant increase per unit time after 600 seconds has elapsed, and the quantity of electricity of polyimide film A in a predetermined voltage environment can be accurately detected. The reason why the applied voltage is set to 1000V is that in recent years, in applications where flexible printed circuit boards are used, polyimide films may be exposed to a high voltage environment of about 400 to 800V, and it is considered effective to apply a voltage of 1000V that is sufficiently higher than that. In addition, the reason why the inventors focused on Q ₁₀₀₀ (0) immediately after application of a DC voltage of 1000V is because it is the inherent capacitance of the polyimide film A to be measured. In addition, the reason for determining the ratio _Q1000 (600)/ _Q1000 (0) is that, depending on how large this value is, it is possible to grasp how much of an amount of electricity that exceeds the capacitance of polyimide film A has accumulated in or penetrated polyimide film A when a direct current voltage of 1000 V is applied.

On the other hand, the reason why the inventors focused on Q ₂₅₀ (600) when a DC voltage of 250V was applied for 600 seconds is that it is considered that grasping the characteristics at a DC voltage of 250V is practically important when assuming the use environment of small terminals (smartphones, personal computers, etc.) in which conventional flexible printed circuit boards are mainly used. And, like Q ₁₀₀₀ (600), it is considered that the amount of electricity of the polyimide film A can be accurately detected after 600 seconds. Also, the reason why the inventors focused on Q ₂₅₀ (0) immediately after the application of a DC voltage of 250V is that it is the inherent capacitance of the polyimide film A to be measured. The reason for determining the ratio Q ₂₅₀ (600)/Q ₂₅₀ (0) is that it is possible to grasp how much electricity exceeding the capacitance of the polyimide film A has been accumulated in or penetrated the polyimide film A when a DC voltage of 250V is applied, depending on how large this value is.

The reason for calculating the ratio of _C1000 to _C250 is that it is believed that it is possible to measure the degree of degradation when the environment in which the film is placed is changed from the conventionally assumed low voltage environment of 250 V to a high voltage environment of 1000 V, such as that used in power semiconductors. In other words, the value of _C1000 / _C250 can be said to be an index of voltage dependency.

In this specification, "satisfying formula (A) over the entire width of the polyimide film" means that _C1000 and _C250 derived from the electrical quantities measured at the five measurement points (measurement points 102a, 103a, 104, 103b, and 102b) shown in FIG. 2 all satisfy formula (A). In detail, as shown in FIG. 2, measurement points 102a and 102b are located 200 mm inward from the ends 101a and 101b in the width direction X of the polyimide film 100. Here, the straight line connecting the measurement points 102a and 102b is parallel to the width direction X of the polyimide film 100. The midpoint between the measurement points 102a and 102b is the measurement point 104. The midpoint between measurement points 102a and 104 and the midpoint between measurement points 102b and 104 are designated as measurement points 103a and 103b, respectively. Then, 100 mm x 100 mm pieces of film are cut out centered on each of measurement points 102a, 103a, 104, 103b, and 102b, and the five obtained film pieces are used as film pieces for preparing samples for measuring the quantity of electricity. The method for measuring the quantity of electricity is the same as or similar to the method described in the examples below.

The film piece for measuring the electrical quantity is sampled at any point along the length of the polyimide film. When measuring the tensile modulus and dielectric breakdown voltage, the measurement sample is also sampled at any point along the length of the polyimide film.

Second embodiment: polyimide film
Next, a polyimide film according to a second embodiment of the present invention will be described. The polyimide film according to the second embodiment is a polyimide film having a width of 1000 mm or more, and satisfying the above-mentioned formula (A) over the entire width. Since the polyimide film according to the second embodiment has the above-mentioned configuration, it can ensure good insulation over the entire width even when exposed to a high-temperature and high-humidity environment.

The polyimide film according to the second embodiment can be manufactured by the method for manufacturing a polyimide film according to the first embodiment described above. Therefore, in the following explanation, the contents that overlap with the first embodiment may be omitted. The following explanation will focus on the points that are different from the first embodiment.

In the second embodiment, in order to easily ensure good insulation across the entire width even when exposed to a high-temperature, high-humidity environment, it is preferable that the polyimide contained in the polyimide film is a specific polyimide (an imidized product of the specific polyamic acid described above). That is, it is preferable that the polyimide contained in the polyimide film has BPDA residues and PDA residues, or PMDA residues and m-TB residues, and that the content of BPDA residues or PMDA residues is 60 mol % or more relative to the total acid dianhydride residues constituting the polyimide, and that the content of PDA residues or m-TB residues is 60 mol % or more relative to the total diamine residues constituting the polyimide.

In addition, when the polyimide film according to the second embodiment is a multilayer polyimide film, "the polyimide contained in the polyimide film is a specific polyimide" means that the polyimide contained in at least one of the multiple layers constituting the multilayer polyimide film is a specific polyimide.

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

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In the following, compounds and reagents are described by the following abbreviations.
DMF: N,N-dimethylformamide BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride PMDA: pyromellitic dianhydride BTDA: 3,3',4,4'-benzophenonetetracarboxylic dianhydride ODPA: 4,4'-oxydiphthalic anhydride TPE-R: 1,3-bis(4-aminophenoxy)benzene PDA: p-phenylenediamine ODA: 4,4'-diaminodiphenyl ether m-TB: 4,4'-diamino-2,2'-dimethylbiphenyl BAPP: 2,2-bis[4-(4-aminophenoxy)phenyl]propane

<Preparation of polyamic acid solution>
First, the methods for preparing the polyamic acid solutions P1 to P5 and P7, which are non-thermoplastic polyamic acid solutions, and the method for preparing the polyamic acid solution P6, which is a thermoplastic polyamic acid solution, will be described. Note that the preparation of the polyamic acid solutions P1 to P7 was all carried out in a nitrogen atmosphere at a temperature of 23°C.

[Preparation of polyamic acid solution P1]
Into the reaction vessel, 1170 kg of DMF, 48.7 kg of PDA, and 14.6 kg of TPE-R were added, and the contents of the reaction vessel were stirred for 5 minutes. Next, while stirring the contents of the reaction vessel, 88.3 kg of BPDA was added, and the contents of the reaction vessel were stirred for 10 minutes. Next, while stirring the contents of the reaction vessel, 46.5 kg of ODPA was added, and the contents of the reaction vessel were stirred for 10 minutes. Next, while stirring the contents of the reaction vessel, 9.9 kg of PMDA was added, and the contents of the reaction vessel were stirred for 30 minutes. Next, while stirring the contents of the reaction vessel, a PMDA solution (solvent: DMF, amount of PMDA dissolved: 1 kg, concentration of PMDA: 7.2 wt%) prepared in advance was added to the reaction vessel for a predetermined time at an addition rate such that the viscosity of the contents of the reaction vessel did not increase rapidly. When the viscosity of the content of the reaction vessel reached 2000 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 P1 having a solids concentration of 15% by weight.

[Preparation of polyamic acid solution P2]
1294 kg of DMF and 84.9 kg of m-TB were added to the reaction vessel, and the contents of the reaction vessel were stirred for 5 minutes. Next, 86.2 kg of PMDA was added to the reaction vessel while stirring the contents of the reaction vessel, and the contents of the reaction vessel were stirred for 10 minutes. Next, 29.2 kg of TPE-R was added to the reaction vessel while stirring the contents of the reaction vessel, and the contents of the reaction vessel were stirred for 10 minutes. Next, 29.4 kg of BPDA was added to the reaction vessel while stirring the contents of the reaction vessel, and the contents of the reaction vessel were stirred for 30 minutes. Next, while stirring the contents of the reaction vessel, a PMDA solution (solvent: DMF, amount of PMDA dissolved: 1 kg, concentration of PMDA: 7.2 wt%) prepared in advance was added to the reaction vessel for a predetermined time at an addition rate such that the viscosity of the contents of the reaction vessel did not increase suddenly. When the viscosity of the content of the reaction vessel reached 2000 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 P2 having a solids concentration of 15% by weight.

[Preparation of polyamic acid solution P3]
Into the reaction vessel, 1284 kg of DMF and 30 kg of ODA were added, and the contents of the reaction vessel were stirred for 5 minutes. Next, while stirring the contents of the reaction vessel, 64.4 kg of PMDA was added to the reaction vessel, and the contents of the reaction vessel were stirred for 10 minutes. Next, while stirring the contents of the reaction vessel, 5.4 kg of PDA was added to the reaction vessel, and the contents of the reaction vessel were stirred for 10 minutes. Next, while stirring the contents of the reaction vessel, 63.7 kg of m-TB was added to the reaction vessel, and the contents of the reaction vessel were stirred for 10 minutes. Next, while stirring the contents of the reaction vessel, 64.4 kg of BTDA was added to the reaction vessel, and the contents of the reaction vessel were stirred for 30 minutes. Next, while stirring the contents of the reaction vessel, a PMDA solution (solvent: DMF, amount of PMDA dissolved: 1 kg, concentration of PMDA: 7.2 wt%) prepared in advance was added to the reaction vessel for a predetermined time at an addition rate such that the viscosity of the contents of the reaction vessel did not increase rapidly. When the viscosity of the content of the reaction vessel reached 2000 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 P3 having a solids concentration of 15% by weight.

[Preparation of polyamic acid solution P4]
1292 kg of DMF and 20 kg of ODA were added to the reaction vessel, and the contents of the reaction vessel were stirred for 5 minutes. Then, while stirring the contents of the reaction vessel, 29.4 kg of BTDA were added to the reaction vessel, and the contents of the reaction vessel were stirred for 10 minutes. Then, while stirring the contents of the reaction vessel, 61.6 kg of BAPP were added to the reaction vessel, and the contents of the reaction vessel were stirred for 10 minutes. Then, while stirring the contents of the reaction vessel, 86.2 kg of PMDA were added to the reaction vessel, and the contents of the reaction vessel were stirred for 10 minutes. Then, while stirring the contents of the reaction vessel, 27 kg of PDA were added to the reaction vessel, and the contents of the reaction vessel were stirred for 30 minutes. Then, while stirring the contents of the reaction vessel, a PMDA solution (solvent: DMF, amount of PMDA dissolved: 1 kg, concentration of PMDA: 7.2 wt%) prepared in advance was added to the reaction vessel for a predetermined time at an addition rate such that the viscosity of the contents of the reaction vessel did not increase suddenly. When the viscosity of the content of the reaction vessel reached 2000 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 having a solids concentration of 15% by weight.

[Preparation of polyamic acid solution P5]
The reactor was charged with 1339 kg of DMF, 31.8 kg of m-TB, and 41.1 kg of BAPP, and the reactor contents were stirred for 5 minutes. Then, while stirring the reactor contents, 44.1 kg of BPDA was charged to the reactor, and the reactor contents were stirred for 10 minutes. Then, while stirring the reactor contents, 29.2 kg of TPE-R was charged to the reactor, and the reactor contents were stirred for 10 minutes. Then, while stirring the reactor contents, 16.2 kg of PDA was charged to the reactor, and the reactor contents were stirred for 10 minutes. Then, while stirring the reactor contents, 75.3 kg of PMDA was charged to the reactor, and the reactor contents were stirred for 30 minutes. Next, while stirring the contents of the reaction vessel, a PMDA solution (solvent: DMF, amount of PMDA dissolved: 1 kg, concentration of PMDA: 7.2% by weight) previously prepared 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 contents of the reaction vessel. Then, when the viscosity of the contents of the reaction vessel at a temperature of 23° C. reached 2000 poise, the addition of the PMDA solution and the stirring of the contents of the reaction vessel were stopped, and a polyamic acid solution P5 with a solid content concentration of 15% by weight was obtained.

[Preparation of polyamic acid solution P6]
222 kg of DMF and 20.1 kg of BAPP were added to the reaction vessel, and the reaction vessel contents were stirred for 5 minutes. Next, 7.7 kg of PMDA was added to the reaction vessel while stirring the reaction vessel contents, and the reaction vessel contents were stirred for 10 minutes. Next, 2.9 kg of BPDA was added to the reaction vessel while stirring the reaction vessel contents, and the reaction vessel contents were stirred for 30 minutes. Next, while stirring the reaction vessel contents, a PMDA solution (solvent: DMF, PMDA dissolved amount: 1 kg, PMDA concentration: 7.2 wt%) prepared in advance was added to the reaction vessel for a predetermined time at an addition rate that did not cause the viscosity of the reaction vessel contents to increase suddenly. Then, when the viscosity of the reaction vessel contents at a temperature of 23°C reached 800 poise, the addition of the PMDA solution and the stirring of the reaction vessel contents were stopped, and a polyamic acid solution P6 with a solid content concentration of 12 wt% was obtained.

[Preparation of polyamic acid solution P7]
Into the reaction vessel, 1170 kg of DMF and 100.1 kg of ODA were added, and the contents of the reaction vessel were stirred for 5 minutes. Then, while stirring the contents of the reaction vessel, 108.1 kg of PMDA was added to the reaction vessel, and the contents of the reaction vessel were stirred for 30 minutes. Then, while stirring the contents of the reaction vessel, a PMDA solution (solvent: DMF, amount of PMDA dissolved: 1 kg, concentration of PMDA: 7.2% by weight) prepared in advance was added to the reaction vessel for a predetermined time at an addition rate that did not cause the viscosity of the contents of the reaction vessel to increase suddenly. Then, when the viscosity of the contents of the reaction vessel reached 2000 poise at a temperature of 23°C, the addition of the PMDA solution and the stirring of the contents of the reaction vessel were stopped, and a polyamic acid solution P7 with a solid content concentration of 15% by weight was obtained.

Table 1 shows the materials used and their proportions for each of the polyamic acid solutions P1 to P7. The molar fraction of each residue in the polyamic acid contained in each of the polyamic acid solutions P1 to P7 was consistent with the molar fraction of each monomer (diamine and tetracarboxylic dianhydride) used. In Table 1, "-" means that the corresponding component was not used. In Table 1, the values in the "Dianhydride" column are the content (unit: mol%) of each dianhydride relative to the total amount of dianhydrides used. In Table 1, the values in the "Diamine" column are the content (unit: mol%) of each diamine relative to the total amount of diamines used.

<Preparation of polyimide film>
The methods for producing the polyimide films of Examples 1 to 4 and Comparative Examples 1 to 4 will be described below.

[Example 1]
First, a mixture of acetic anhydride, isoquinoline and DMF (weight ratio: acetic anhydride/isoquinoline/DMF=303/153/144) 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 the imidization accelerator added was 40 parts by weight per 100 parts by weight of polyamic acid in polyamic acid solution P1. In addition, polyamic acid solution P6 was prepared as a solution for forming an adhesive layer.

　Then, using an extruder having 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, which was a support, by a co-extrusion-casting coating method. More specifically, the non-thermoplastic polyimide layer forming solution was supplied to the center layer of the extrusion die, and the adhesive layer forming solution was supplied to the two layers adjacent (on both sides) to the center layer of the extrusion die. 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 obtained coating film was dried on the stainless steel endless belt at a temperature of 120°C for 360 seconds to obtain a gel film (width: 1600 mm).

Then, the gel film obtained was peeled off from the stainless steel endless belt, and both ends in the width direction were fixed by a tenter, and heated for 46 seconds in a first hot air oven set at a temperature of 250°C, followed by heating for 44 seconds in a second hot air oven set at a temperature of 290°C, and then heating for 36 seconds in a third hot air oven set at a temperature of 300°C. Next, the gel film after heating in the third hot air oven was heated for 46 seconds in a first far-infrared oven set at a temperature of 410°C, followed by heating for 44 seconds in a second far-infrared oven set at a temperature of 360°C. Through the above procedure, a roll-shaped polyimide film (polyimide film of Example 1) having a width of 1500 mm was obtained, in which a 4 μm thick adhesive layer was provided on both sides of a 17 μm thick non-thermoplastic polyimide layer. Both the heating (imidization) in the first far-infrared oven and the heating (imidization) in the second far-infrared oven were performed by irradiating the gel film with far-infrared rays from nine individually temperature-controllable far-infrared radiation panels that were evenly arranged along the width of the gel film. The size of each far-infrared radiation panel was 800 mm (transport direction) x 180 mm (width direction). In the heating process in the first far-infrared oven, the difference between the maximum and minimum temperatures in the width direction of the gel film surface was 40°C. In the heating process in the second far-infrared oven, the difference between the maximum and minimum temperatures in the width direction of the gel film surface was 60°C.

[Example 2]
A rolled polyimide film (polyimide film of Example 2) having a width of 1500 mm and a 4 μm thick adhesive layer on both sides of a 17 μm thick non-thermoplastic polyimide layer was obtained by the same method as in Example 1, except that the polyamic acid solution P2 was used instead of the polyamic acid solution P1 to obtain a non-thermoplastic polyimide layer forming solution. In addition, in the heating process in the first far-infrared oven, the difference between the maximum temperature and the minimum temperature in the width direction of the surface of the gel film was 40° C. In addition, in the heating process in the second far-infrared oven, the difference between the maximum temperature and the minimum temperature in the width direction of the surface of the gel film was 60° C.

[Example 3]
A rolled polyimide film (polyimide film of Example 3) having a width of 1500 mm and a 4 μm thick adhesive layer on both sides of a 17 μm thick non-thermoplastic polyimide layer was obtained by the same method as in Example 1, except that the polyamic acid solution P3 was used instead of the polyamic acid solution P1 to obtain a non-thermoplastic polyimide layer forming solution. In addition, in the heating process in the first far-infrared oven, the difference between the maximum temperature and the minimum temperature in the width direction of the surface of the gel film was 40° C. In addition, in the heating process in the second far-infrared oven, the difference between the maximum temperature and the minimum temperature in the width direction of the surface of the gel film was 60° C.

[Example 4]
A non-thermoplastic polyimide layer forming solution was obtained by the same method as the preparation method of the non-thermoplastic polyimide layer forming solution used in Example 1. Next, using an extrusion molding machine having a single extrusion molding die, the non-thermoplastic polyimide layer forming solution was cast onto a stainless steel endless belt to form a coating film made of the non-thermoplastic polyimide layer forming solution. The obtained coating film was dried on the stainless steel endless belt at a temperature of 120°C for 360 seconds to obtain a gel film (width: 1600 mm). Next, the obtained gel film was peeled off from the stainless steel endless belt, and both ends in the width direction were fixed by a tenter, heated for 46 seconds in a first hot air oven set at a temperature of 250°C, heated for 44 seconds in a second hot air oven set at a temperature of 290°C, and further heated for 36 seconds in a third hot air oven set at a temperature of 300°C. Next, the gel film after heating in the third hot air oven was heated for 46 seconds in the first far-infrared oven set at a temperature of 410° C., and then heated for 44 seconds in the second far-infrared oven set at a temperature of 360° C. By the above procedure, a roll-shaped polyimide film (polyimide film of Example 4) having a width of 1500 mm and a thickness of 17 μm was obtained. In addition, both the heating (imidization) in the first far-infrared oven and the heating (imidization) in the second far-infrared oven were performed by irradiating the gel film with far-infrared rays from nine far-infrared radiation panels that were evenly arranged along the width direction of the gel film and were individually temperature-controllable. The size of each far-infrared radiation panel was 800 mm (transport direction) x 180 mm (width direction). In addition, in the heating process in the first far-infrared oven, the difference between the maximum temperature and the minimum temperature in the width direction of the surface of the gel film was 40° C. In addition, in the heating process in the second far-infrared oven, the difference between the maximum temperature and the minimum temperature in the width direction of the surface of the gel film was 60° C.

[Comparative Example 1]
In both the heating (imidization) in the first far-infrared oven and the heating (imidization) in the second far-infrared oven, far-infrared rays were irradiated onto the gel film from one far-infrared radiation panel arranged on the center of the gel film in the width direction, and the set temperature of the first far-infrared oven was changed to 370°C. In the same manner as in Example 1, except that a 17 μm-thick non-thermoplastic polyimide layer was provided on both sides with a 4 μm-thick adhesive layer, a roll-shaped polyimide film (polyimide film of Comparative Example 1) having a width of 1500 mm was obtained. The size of the far-infrared radiation panel used in Comparative Example 1 was 8000 mm (transport direction) x 1800 mm (width direction). In Comparative Example 1, in order to confirm the temperature difference in the width direction of the surface of the gel film, eight thermocouples were used in addition to the thermocouple corresponding to the one far-infrared radiation panel, and a total of nine thermocouples were evenly arranged along the width direction of the gel film. In the heating process in the first far-infrared oven of Comparative Example 1, the difference between the maximum temperature and the minimum temperature in the width direction of the surface of the gel film was 80° C. In addition, in the heating process in the second far-infrared oven of Comparative Example 1, the difference between the maximum temperature and the minimum temperature in the width direction of the surface of the gel film was 80° C.

[Comparative Example 2]
A rolled polyimide film (polyimide film of Comparative Example 2) having a width of 1500 mm and a 4 μm thick adhesive layer on both sides of a 17 μm thick non-thermoplastic polyimide layer was obtained by the same method as in Comparative Example 1, except that the polyamic acid solution P4 was used instead of the polyamic acid solution P1 to obtain a non-thermoplastic polyimide layer forming solution. In addition, in the heating process in the first far-infrared oven, the difference between the maximum temperature and the minimum temperature in the width direction of the surface of the gel film was 80° C. In addition, in the heating process in the second far-infrared oven, the difference between the maximum temperature and the minimum temperature in the width direction of the surface of the gel film was 80° C.

[Comparative Example 3]
A roll-shaped polyimide film having a width of 1,500 mm (polyimide film of Comparative Example 3) was obtained in the same manner as in Example 1, except that the polyamic acid solution P5 was used instead of the polyamic acid solution P1 to obtain a non-thermoplastic polyimide layer forming solution, and the heating step using a far-infrared furnace was changed as follows. The roll-shaped polyimide film had a width of 1,500 mm and had a non-thermoplastic polyimide layer having a thickness of 17 μm and adhesive layers each having a thickness of 4 μm on both sides of the non-thermoplastic polyimide layer (polyimide film of Comparative Example 3).

(Heat process using far-infrared furnace in Comparative Example 3)
In the heating process using the far-infrared oven in Comparative Example 3, the gel film (specifically, the gel film after heating in the third hot air oven) was heated for 46 seconds in the first far-infrared oven set at a temperature of 360° C., and then heated for 44 seconds in the second far-infrared oven set at a temperature of 345° C. In Comparative Example 3, both the heating (imidization) in the first far-infrared oven and the heating (imidization) in the second far-infrared oven were performed by irradiating the gel film with far-infrared rays from nine far-infrared radiation panels that were evenly arranged along the width direction of the gel film and could be temperature-controlled collectively with the same output. The size of each far-infrared radiation panel was 800 mm (transport direction) x 180 mm (width direction). In addition, in the heating process in the first far-infrared oven, the difference between the maximum temperature and the minimum temperature in the width direction of the surface of the gel film was 60° C. In addition, in the heating process in the second far-infrared oven, the difference between the maximum temperature and the minimum temperature in the width direction of the surface of the gel film was 90° C.

[Comparative Example 4]
A rolled polyimide film (polyimide film of Comparative Example 4) having a width of 1500 mm and a thickness of 17 μm was obtained by the same method as in Example 4, except that the polyamic acid solution P7 was used instead of the polyamic acid solution P1 to obtain a non-thermoplastic polyimide layer forming solution. In the heating process in the first far-infrared oven, the difference between the maximum temperature and the minimum temperature in the width direction of the surface of the gel film was 40° C. In the heating process in the second far-infrared oven, the difference between the maximum temperature and the minimum temperature in the width direction of the surface of the gel film was 60° C.

<Measurement and evaluation methods>
The methods for measuring and evaluating the physical properties of the polyimide films of Examples 1 to 4 and Comparative Examples 1 to 4 will be described below.

[Measurement of Electrical Quantity]
(Preparation of copper-clad laminate of Example 1)
For the polyimide film of Example 1, film pieces (a total of five pieces) measuring 100 mm x 100 mm were cut out, each centered on the five measurement points (measurement points 102a, 103a, 104, 103b, and 102b) shown in Fig. 2. Then, copper foil ("BHY-82F-HA" manufactured by JX Metals Corporation, thickness: 12 µm) was placed on both sides of each film piece, and the obtained laminate was pressed in the thickness direction at 10 MPa for 5 minutes while being heated in a nitrogen atmosphere at a temperature of 300°C, to obtain a copper-clad laminate.

(Preparation of copper-clad laminate of Example 4)
For the polyimide film of Example 4, film pieces (a total of five pieces) having a size of 100 mm x 100 mm were cut out around the five measurement points (measurement points 102a, 103a, 104, 103b and 102b) shown in FIG. 2 described above. Next, a semi-cured adhesive layer ("SASF" manufactured by Nikkan Industries Co., Ltd.) was placed on both sides of each film piece, and copper foil ("BHY-82F-HA" manufactured by JX Metals Corporation, thickness: 12 μm) was placed on both outer sides of the adhesive layer. The obtained laminate was heated in a vacuum atmosphere at a temperature of 100 ° C. and pressed in the thickness direction at a condition of 10 MPa, and the adhesive layer was held for 10 minutes in a state where the thickness of both sides became 4 μm. Next, the laminate was heated in a vacuum atmosphere at a temperature of 150 ° C. and pressed in the thickness direction at a condition of 10 MPa for 5 minutes to obtain a copper-clad laminate.

(Preparation of copper-clad laminates of Example 2, Example 3, and Comparative Examples 1 to 4)
For Example 2, Example 3, and Comparative Examples 1 to 3, a copper-clad laminate was obtained by the same method as the copper-clad laminate of Example 1. For Comparative Example 4, a copper-clad laminate was obtained by the same method as the copper-clad laminate of Example 4.

(Calculation of _C1000 / _C250 )
Next, for each copper-clad laminate, the copper foil around the central portion (40 mm × 40 mm) on both sides was etched to obtain a measurement sample. Next, in an environment of 23°C and 60% RH, both sides of the measurement sample were connected to a high-voltage power supply ("PRK-1000-15" manufactured by Matsusada Precision Co., Ltd.) and a DC voltage of 250 V was applied for 600 seconds. The amount of electricity was measured using a current integrator ("AD-9831" manufactured by A&D Co., Ltd.) to obtain data on _Q250 (0) and _Q250 (600).

Next, the applied DC voltage was changed to 1000 V, and the quantity of electricity when a DC voltage of 1000 V was applied to the measurement sample for 600 seconds was measured using a current integrator ("AD-9831" manufactured by A&D Co., Ltd.) to obtain data on Q ₁₀₀₀ (0) and Q ₁₀₀₀ (600).

Then, C ₁₀₀₀ calculated from the data of Q ₁₀₀₀ (0) and Q ₁₀₀₀ (600) was divided by C ₂₅₀ calculated from the data of Q ₂₅₀ (0) and Q ₂₅₀ (600) to obtain the value of C ₁₀₀₀ /C ₂₅₀ .

[Measurement of tensile modulus]
For the polyimide film to be measured, film pieces measuring 200 mm x 200 mm (a total of five pieces for each polyimide film) were cut out centered on the five measurement points (measurement points 102a, 103a, 104, 103b, and 102b) shown in Figure 2. The tensile modulus of elasticity was measured based on IPC-TM-650 using the obtained film pieces.

[High temperature and high humidity bias test]
First, for the polyimide film to be measured, a measurement sample was prepared by the same method as the measurement sample used in the above-mentioned [Measurement of Electrical Quantity]. The obtained measurement samples (a total of 5 for each polyimide film) were subjected to a high temperature and high humidity bias test (DC voltage: 1000V, temperature: 85°C, humidity: 85% RH) for 500 hours based on the JESD22-A110 standard. Then, the case where no dielectric breakdown occurred during the high temperature and high humidity bias test was judged as A, and the case where dielectric breakdown occurred during the high temperature and high humidity bias test was judged as B. When the judgment result for all of the five measurement samples was A, it was evaluated as "good insulation can be secured over the entire width direction even when exposed to a high temperature and high humidity environment". On the other hand, when the judgment result for at least one of the five measurement samples was B, it was evaluated as "good insulation cannot be secured over the entire width direction when exposed to a high temperature and high humidity environment".

[Measurement of dielectric breakdown voltage]
For the polyimide films to be measured, film pieces measuring 200 mm x 200 mm (a total of five pieces for each polyimide film) were cut out centered on the five measurement points (measurement points 102a, 103a, 104, 103b, and 102b) shown in Fig. 2. Using the obtained film pieces, the dielectric breakdown voltage was measured when an AC voltage was applied based on ASTM D149.

<Evaluation Results>
For Examples 1 to 4 and Comparative Examples 1 to 4, the C ₁₀₀₀ /C ₂₅₀ values, the tensile modulus, the results of the high-temperature and high-humidity bias test, and the dielectric breakdown voltage are shown in Table 2.

The polyamic acid used in forming the non-thermoplastic polyimide layer of the polyimide film of Example 1 and the polyamic acid used in forming the polyimide film of Example 4 had BPDA residues and PDA residues. In the polyamic acid used in forming the non-thermoplastic polyimide layer of the polyimide film of Example 1 and the polyamic acid used in forming the polyimide film of Example 4, the content of BPDA residues was 60 mol% or more relative to the total dianhydride residues constituting the polyamic acid. In the polyamic acid used in forming the non-thermoplastic polyimide layer of the polyimide film of Example 1 and the polyamic acid used in forming the polyimide film of Example 4, the content of PDA residues was 60 mol% or more relative to the total diamine residues constituting the polyamic acid.

The polyamic acid used in forming the non-thermoplastic polyimide layer of the polyimide film of Examples 2 and 3 had PMDA residues and m-TB residues. In the polyamic acid used in forming the non-thermoplastic polyimide layer of the polyimide film of Examples 2 and 3, the content of PMDA residues was 60 mol% or more relative to the total dianhydride residues constituting the polyamic acid. In the polyamic acid used in forming the non-thermoplastic polyimide layer of the polyimide film of Examples 2 and 3, the content of m-TB residues was 60 mol% or more relative to the total diamine residues constituting the polyamic acid.

In Examples 1 to 4, far-infrared rays were irradiated onto the polyimide film precursor (gel film) using three or more far-infrared heaters (far-infrared radiation panels) that were arranged along the width direction of the polyimide film precursor (gel film) and were capable of individually controlling the temperature.

As shown in Table 2, in Examples 1 to 4, the result of the high temperature and high humidity bias test was A for all five measurement samples (measurement points 102a, 103a, 104, 103b, and 102b). Therefore, the polyimide films produced in Examples 1 to 4 were able to maintain good insulation across the entire width even when exposed to a high temperature and high humidity environment.

In Comparative Examples 1 and 2, the gel film was irradiated with far-infrared rays from one far-infrared radiation panel arranged on the center of the gel film in the width direction. In the polyamic acid used to form the non-thermoplastic polyimide layer of the polyimide film in Comparative Example 2, the content of PDA residue, which is the diamine residue with the highest content, was less than 60 mol% relative to the total diamine residues constituting the polyamic acid. In Comparative Example 3, the gel film was irradiated with far-infrared rays from nine far-infrared radiation panels that were evenly arranged along the width direction of the gel film and could be temperature-controlled collectively with the same output. In the polyamic acid used to form the non-thermoplastic polyimide layer of the polyimide film in Comparative Example 3, the content of PDA residue and m-TB residue, which are the diamine residues with the highest content, was less than 60 mol% relative to the total diamine residues constituting the polyamic acid. The polyamic acid used to form the polyimide film in Comparative Example 4 had neither PDA residue nor m-TB residue.

As shown in Table 2, in Comparative Examples 1 to 4, the result of the high temperature and high humidity bias test for at least one of the five measurement samples (measurement points 102a, 103a, 104, 103b, and 102b) was B. Therefore, the polyimide films produced in Comparative Examples 1 to 4 did not have good insulation properties across the entire width when exposed to a high temperature and high humidity environment.

These results demonstrate that the present invention makes it possible to produce a polyimide film that maintains good insulation across the entire width even when exposed to a high-temperature, high-humidity environment.

10: Polyimide film precursor 20: Far infrared heater 100: Polyimide film

Claims (7)

A method for producing a polyimide film, comprising irradiating a polyimide film precursor containing a polyamic acid with far infrared rays to imidize the polyamic acid, the method comprising the steps of:
the polyamic acid has 3,3',4,4'-biphenyltetracarboxylic dianhydride residues and p-phenylenediamine residues, or has pyromellitic dianhydride residues and 4,4'-diamino-2,2'-dimethylbiphenyl residues;
the content of the 3,3',4,4'-biphenyltetracarboxylic dianhydride residue or the pyromellitic dianhydride residue is 60 mol % or more based on the total tetracarboxylic dianhydride residues constituting the polyamic acid,
the content of the p-phenylenediamine residue or the 4,4'-diamino-2,2'-dimethylbiphenyl residue is 60 mol % or more based on the total diamine residues constituting the polyamic acid,
In the method for producing a polyimide film, when the far-infrared rays are irradiated, the polyimide film precursor is irradiated with the far-infrared rays using three or more far-infrared heaters, each of which is arranged along a width direction of the polyimide film precursor and is capable of individually controlling its temperature. The method for producing a polyimide film according to claim 1, wherein the difference between the maximum and minimum temperatures in the width direction of the surface of the polyimide film precursor during irradiation with the far infrared rays is 60°C or less. The method for producing a polyimide film according to claim 1, wherein the width of the polyimide film precursor is 1000 mm or more. A polyimide film having a width of 1000 mm or more,
A polyimide film, wherein C ₁₀₀₀ and C ₂₅₀ derived from the electrical quantities of a laminate in which copper foils are laminated on both sides of the polyimide film satisfy the following formula (A) over the entire width direction of the polyimide film:
_C1000 / _C250 <7.5...(A)
(The above C ₁₀₀₀ represents the ratio of the quantity of electricity, Q ₁₀₀₀ (600)/Q 1000 (0), when the quantity of electricity immediately after application of a DC voltage of 1000 V is Q _{1000 (0) and the quantity of electricity after application of a DC voltage of 1000 V for 600 seconds is Q 1000 ( 600} );
The _C250 represents the ratio of the quantity of electricity, _Q250 (600)/Q250(0), where _Q250 (0) is the quantity of electricity immediately after a DC voltage of 250V is applied and _Q250 (600) is the quantity of electricity after a DC voltage of 250V is applied for ₆₀₀ seconds. The polyimide film according to claim 4, having a tensile modulus of elasticity of 6.0 GPa or more. The polyimide film according to claim 4, having a thickness of 50 μm or less. the polyimide contained in the polyimide film has a 3,3',4,4'-biphenyltetracarboxylic dianhydride residue and a p-phenylenediamine residue, or has a pyromellitic dianhydride residue and a 4,4'-diamino-2,2'-dimethylbiphenyl residue;
the content of the 3,3',4,4'-biphenyltetracarboxylic dianhydride residue or the pyromellitic dianhydride residue is 60 mol % or more based on the total tetracarboxylic dianhydride residues constituting the polyimide,
5. The polyimide film according to claim 4, wherein the content of the p-phenylenediamine residue or the 4,4'-diamino-2,2'-dimethylbiphenyl residue is 60 mol % or more based on all diamine residues constituting the polyimide.

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