Polyimide film, and material for reducing yellowness, material for reducing linear expansion coefficient, and material for improving adhesion to metal of polyimide film

Abstract

The problem addressed by the present invention is to further reduce the yellowness and linear expansion coefficient of a polyimide film. A polyimide film according to one aspect of the present invention contains alpha-alumina. The alpha-alumina is preferably dispersed in the polyimide film. In this polyimide film, the alpha-alumina has a plate shape and preferably has an aspect ratio of 2 or more. The alpha-alumina also preferably has a particle size in the range of from more than 0.2 μm to 8 μm.

Description

Polyimide film, and materials for reducing the yellowness of polyimide film, reducing the linear expansion coefficient, and improving adhesion to metal

[0001] The present invention relates to a polyimide film. The present invention also relates to an agent for reducing yellowness of a polyimide film, an agent for reducing the linear expansion coefficient of the polyimide film, and an agent for improving adhesion to metals.

[0002] Polyimide films generally have excellent thermal stability, electrical properties, and mechanical properties, and are used in a variety of products used in relatively harsh environments. However, many polyimide films are colored yellow or brown due to the severe thermal history they undergo before they are formed. When used as a film substrate for a liquid crystal display device, such yellow or brown polyimide films not only obscure the field of view but also impair the inherent functionality of the liquid crystal display device. To address these issues, colorless and transparent polyimide films have been developed. These colorless and transparent polyimide films are now widely used as films for liquid crystal display devices, optical fiber cable coatings, protective coatings for waveguides and solar cells, flexible substrates, and optical solar reflectors (OSRs) (see, for example, JP 62-7733 A, JP 2000-313804 A, JP 2012-040836 A, and Korean Patent Publication No. 10-2015-0046463).

[0003] Japanese Patent Publication No. 62-7733 Japanese Patent Publication No. 2000-313804 Japanese Patent Publication No. 2012-040836 Korean Patent Publication No. 10-2015-0046463

[0004] However, in recent years, there has been a demand for polyimide films that not only have a lower yellowness index than previously proposed colorless and transparent polyimide films, but also have a lower coefficient of linear expansion.

[0005] An object of the present invention is to further reduce the yellowness index and the linear expansion coefficient of a polyimide film.

[0006] A polyimide film according to one aspect of the present invention contains α-alumina, and the α-alumina is preferably dispersed in the polyimide film.

[0007] Incidentally, the above-mentioned polyimide film preferably contains, as its main component, a polyimide resin comprising (A) at least one acid-derived moiety selected from the group consisting of biphenyltetracarboxylic acid compound (BPDA)-derived moieties and 2,2-bis[3,4-(dicarboxyphenoxy)phenyl]propane compound (BPADA)-derived moieties, and (B) at least one diamine-derived moiety selected from the group consisting of 2,2′-bis(trifluoromethyl)benzidine (TFMB)-derived moieties and 3,3′-diaminodiphenylsulfone (3,3′-DDS)-derived moieties. In such a case, the diamine-derived moieties preferably include both 2,2'-bis(trifluoromethyl)benzidine (TFMB)-derived moieties and 3,3'-diaminodiphenyl sulfone (3,3'-DDS)-derived moieties, and the molar ratio of 2,2'-bis(trifluoromethyl)benzidine (TFMB)-derived moieties to 3,3'-diaminodiphenyl sulfone (3,3'-DDS)-derived moieties is within the range of 1 or more and 4 or less.

[0008] Furthermore, the polyimide film preferably contains, as its main component, a polyimide resin comprising (A) at least one acid-derived moiety selected from the group consisting of biphenyltetracarboxylic acid compound (BPDA)-derived moieties and 4,4'-(hexafluoroisopropylidene)diphthalic acid compound (6FDA)-derived moieties, and (B) at least one diamine-derived moiety selected from the group consisting of 2,2'-bis(trifluoromethyl)benzidine (TFMB)-derived moieties and 3,3'-diaminodiphenylsulfone (3,3'-DDS)-derived moieties. In such a case, the diamine-derived moieties preferably include both 2,2'-bis(trifluoromethyl)benzidine (TFMB)-derived moieties and 3,3'-diaminodiphenyl sulfone (3,3'-DDS)-derived moieties, and the molar ratio of 2,2'-bis(trifluoromethyl)benzidine (TFMB)-derived moieties to 3,3'-diaminodiphenyl sulfone (3,3'-DDS)-derived moieties is within the range of 1 or more and 4 or less.

[0009] Furthermore, the polyimide film preferably contains, as its main component, a polyimide resin comprising (A) at least one acid-derived moiety selected from the group consisting of biphenyltetracarboxylic acid compound (BPDA)-derived moieties and 2,2-bis[3,4-(dicarboxyphenoxy)phenyl]propane compound (BPADA)-derived moieties, and (B) at least one diamine-derived moiety selected from the group consisting of 2,2'-bis(trifluoromethyl)benzidine (TFMB)-derived moieties and 4,4'-diaminodiphenylsulfone (4,4'-DDS)-derived moieties. In such a case, the diamine-derived moieties include both 2,2'-bis(trifluoromethyl)benzidine (TFMB)-derived moieties and 4,4'-diaminodiphenyl sulfone (4,4'-DDS)-derived moieties, and it is preferred that the molar ratio of 2,2'-bis(trifluoromethyl)benzidine (TFMB)-derived moieties to 4,4'-diaminodiphenyl sulfone (4,4'-DDS)-derived moieties be within the range of 1 or more and 4 or less.

[0010] In the polyimide film, the α-alumina preferably has a plate shape and an aspect ratio of 2 or more.

[0011] In the polyimide film, the α-alumina preferably has a particle size in the range of more than 0.2 μm and not more than 8 μm.

[0012] The polyimide film preferably has a yellowness index of less than 5.

[0013] The haze of the polyimide film is preferably less than 15%.

[0014] The linear expansion coefficient of the polyimide film is preferably less than 47 ppm / K.

[0015] Furthermore, the polyimide film preferably has a peel strength of 300 N / m or more and 500 N / m or less when peeled from a nickel-20% by mass chromium alloy under conditions of normal pressure, 25°C, a peel angle of 90°, and a peel rate of 50 mm / min.

[0016] Furthermore, the polyimide film preferably has a peel strength of 90 N / m or more and 110 N / m or less when peeled from aluminum at normal pressure, 25°C, a peel angle of 90°, and a peel rate of 50 mm / min.

[0017] Furthermore, the polyimide film preferably has a peel strength of 115 N / m or more and 150 N / m or less when peeled from silver at normal pressure, 25°C, a peel angle of 90°, and a peel rate of 50 mm / min.

[0018] A laminate according to another aspect of the present invention includes the above-described polyimide film and a metal layer of any one of a nickel-chromium alloy, aluminum, and silver laminated on the polyimide film.

[0019] Preferably, the laminate further comprises a copper layer laminated on the metal layer.

[0020] The polyimide film yellowness reducing agent according to another aspect of the present invention contains α-alumina as an active ingredient. The present invention can also be expressed as follows.

[0021] (1) A polyimide film yellowness reducing agent containing α-alumina (note that this polyimide film yellowness reducing agent may contain only α-alumina). (2) A method of heating a polyamic acid solution having α-alumina dispersed therein to reduce the yellowness of the resulting polyimide resin. (3) Use of α-alumina for producing a polyimide film yellowness reducing agent (note that here, only α-alumina may be used). (4) Use of a polyamic acid solution containing α-alumina for producing a polyimide film yellowness reducing agent. (5) Use of α-alumina for reducing the yellowness of a polyimide film. (6) α-alumina used as a polyimide film yellowness reducing agent.

[0022] According to yet another aspect of the present invention, there is provided a polyimide film linear expansion coefficient reducing agent containing α-alumina as an active ingredient.

[0023] (1) A material for reducing the linear expansion coefficient of a polyimide film containing α-alumina (note that this material for reducing the linear expansion coefficient of a polyimide film may contain only α-alumina). (2) A method for reducing the linear expansion coefficient of a polyimide resin by heating a polyamic acid solution having α-alumina dispersed therein. (3) Use of α-alumina for producing a material for reducing the linear expansion coefficient of a polyimide film (note that here only α-alumina may be used). (4) Use of a polyamic acid solution containing α-alumina for producing a material for reducing the linear expansion coefficient of a polyimide film. (5) Use of α-alumina for reducing the linear expansion coefficient of a polyimide film. (6) α-alumina used as a material for reducing the linear expansion coefficient of a polyimide film.

[0024] A polyimide film metal adhesion improver according to still another aspect of the present invention contains α-alumina as an active ingredient. The present invention can also be expressed as follows.

[0025] (1) A material for improving adhesion to metals of a polyimide film containing α-alumina (note that this material for improving adhesion to metals may contain only α-alumina). (2) Use of α-alumina for producing a material for improving adhesion to metals of a polyimide film (note that here only α-alumina may be used). (3) Use of a polyamic acid solution containing α-alumina for producing a material for improving adhesion to metals of a polyimide film. (4) Use of α-alumina for improving adhesion between a polyimide film and a metal. (5) α-alumina used as a material for improving adhesion to metals of a polyimide film.

[0026] The metal in the metal adhesion improver is preferably a nickel-chromium alloy, aluminum or silver.

[0027] The polyimide film according to the present invention contains α-alumina and exhibits not only a lower yellowness index than a polyimide film made solely of the polyimide resin that constitutes the polyimide film, but also a lower linear expansion coefficient than the polyimide film. Specifically, when the polyimide film has a thickness of 25 μm, the polyimide film exhibits a yellowness index of less than 3 and a linear expansion coefficient of less than 47 ppm / K. Furthermore, the polyimide film according to the present invention contains α-alumina and exhibits higher adhesion to metals than a polyimide film made solely of the polyimide resin.

[0028] 1 is a graph showing the effect of the aspect ratio of α-alumina on the yellowness index (YI) of the α-alumina-containing polyimide films according to Examples 1-5. 2 is a graph showing the effect of the aspect ratio of α-alumina on the linear expansion coefficient of the α-alumina-containing polyimide films according to Examples 1-5. 3 is a graph showing the effect of the α-alumina content (vol %) on the yellowness index (YI) of the α-alumina-containing polyimide films according to Examples 1 and 6-10, and the polyimide film according to Comparative Example 1. 4 is a graph showing the effect of the α-alumina content (vol %) on the linear expansion coefficient of the α-alumina-containing polyimide films according to Examples 1 and 6-10, and the polyimide film according to Comparative Example 1. 5 is a graph showing the effect of the molar ratio of TFMB on the yellowness index (YI) of the α-alumina-containing polyimide films according to Examples 11-14, and the polyimide films according to Comparative Examples 4-7. 1 is a graph showing the effect of the molar ratio of TFMB on the linear expansion coefficient of the α-alumina-containing polyimide films according to Examples 11 to 14 and the polyimide films according to Comparative Examples 4 to 7. It is a diagram showing the test method of the peel test in Examples 20 to 23 and Comparative Examples 9 to 12.

[0029] The film according to the embodiment of the present invention is mainly made of polyimide resin and α-alumina (α-Al ２ O ３). α-alumina is trigonal aluminum oxide. α-alumina is obtained by calcining aluminum hydroxide at 1000°C or higher. During the calcination process, aluminum hydroxide transforms into boehmite and gamma alumina, and then into α-alumina. It is obtained by heating boehmite. In the production of the film according to the embodiment of the present invention, powdered α-alumina is preferably used. Here, polyimide resin is preferably the main component of the film. α-alumina is preferably dispersed in the polyimide resin matrix. Polyimide resin is obtained by thermally imidizing a polyamic acid solution composed of an acid dianhydride and a diamine. In other words, the film according to the embodiment of the present invention contains aluminum. Aluminum can be detected by, for example, X-ray diffraction, X-ray photoelectron spectroscopy, X-ray fluorescence analysis, ICP atomic emission spectroscopy, atomic absorption spectroscopy, infrared spectroscopy, and the like.

[0030] The α-alumina added to the film according to the embodiment of the present invention may be spherical or plate-shaped, but plate-shaped α-alumina is preferred due to its effectiveness. The aspect ratio of the plate-shaped α-alumina is preferably 2 or more, more preferably 5 or more, even more preferably 10 or more, even more preferably 20 or more, even more preferably 30 or more, even more preferably 40 or more, even more preferably 50 or more, even more preferably 60 or more, and particularly preferably 70 or more. The larger the aspect ratio, the better, and there is no particular upper limit, although if an upper limit were to be set, it would be 100.

[0031] The particle size of the α-alumina added to the film according to the embodiment of the present invention is preferably in the range of more than 0.2 μm and not more than 8 μm, more preferably in the range of more than 0.2 μm and not more than 6 μm, and even more preferably in the range of more than 0.2 μm and not more than 5 μm.

[0032] Furthermore, in the film according to the embodiment of the present invention, the volume ratio of α-alumina to the total volume of the film is preferably in the range of 0.1% by volume to 5% by volume, more preferably in the range of 0.1% by volume to 3% by volume, even more preferably in the range of 0.1% by mass to 2.5% by mass, even more preferably in the range of 0.1% by mass to 2% by mass, even more preferably in the range of 0.1% by mass to 1.5% by mass, even more preferably in the range of 0.1% by mass to 1% by mass, and particularly preferably in the range of 0.1% by mass to 0.5% by mass.

[0033] α-alumina also functions as an antiblocking agent. When α-alumina is used as an antiblocking agent, the volume ratio of α-alumina to the total volume of the film is preferably 0.3% by volume or more, and more preferably 0.4% by volume or more.

[0034] The film according to the embodiment of the present invention may contain components other than the polyimide resin and α-alumina, provided that the components do not impair the scope of the present invention. Examples of such components include known additives such as release agents, dispersants, solid lubricants, anti-settling agents, leveling agents, surface conditioners, moisture absorbers, anti-gelling agents, antioxidants, UV absorbers, light stabilizers, plasticizers, anti-skinning agents, surfactants, antistatic agents, antifoaming agents, antibacterial agents, anti-fungal agents, preservatives, and thickeners.

[0035] Examples of methods for mixing α-alumina into a polyamic acid solution include (a) directly mixing α-alumina into a polyamic acid solution, and (b) adding α-alumina to an organic solvent to prepare a dispersion of α-alumina, and then adding the dispersion to the polyamic acid solution. The polyamic acid solution may contain the above-mentioned known additives, as well as a dehydrating agent and an imidization catalyst in amounts greater than or equal to the stoichiometric amount.

[0036] The film according to the embodiment of the present invention can be produced by heat-molding the above-mentioned polyamic acid solution to which α-alumina has been added (hereinafter, sometimes referred to as an additive-containing polyamic acid solution) using a known method. For example, the film according to the embodiment of the present invention can be produced by applying the additive-containing polyamic acid solution to a support, drying the coating, and heating the dried coating.

[0037] Examples of acid dianhydrides that can be used to prepare the polyamic acid solution according to the embodiment of the present invention include pyromellitic dianhydride (PMDA), 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,2',3,3'-benzophenone Nontetracarboxylic dianhydride, 2,3,3',4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), bis(3,4-dicarboxyphenyl)sulfone dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, 2,2-bis[3,4-(dicarboxyphenoxy)phenyl] Propane dianhydride (BPADA), 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), oxydiphthalic anhydride (ODPA), bis(3,4-dicarboxyphenyl)sulfone dianhydride, bis(3,4-dicarboxyphenyl)sulfoxide dianhydride, thiodiphthalic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 1,2,7,8-phenanthrenetetracarboxylic dianhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride aromatic tetracarboxylic dianhydrides such as 9,9-bis[4-(3,4'-dicarboxyphenoxy)phenyl]fluorene dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 2,3,4,5-tetrahydrofurantetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 3,4-dicarboxy-1-cyclohexylsuccinic dianhydride, 3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic dianhydride, 4,5'-oxybis(isobenzofuran-1,3-dione), 5,5-[1,4-phenylenebis(oxy)]bis(isobenzofuran-1,3-dione), 4,4'-[2,1-phenylenebis(oxy)]bis(isobenzofuran-1,3-dione), 3,3'-(p-phenylenedioxy)diphthalic anhydride, 5,5'-[1,2-phenylenebis(oxy)bis(isobenzofuran-1,3-dione), 5,5'-[1,3-phenylenebis(oxy)bis(isobenzofuran-1,3-dione), 4,4'-[m-phenylenebis(oxy)bis(isobenzofuran-1,3-dione), 4,5'-[1,4-phenylenebis(oxy)bis(isobenzofuran-1,3-dione), 1,4-bis(dicarboxyphenoxy)benzene dianhydride. Two or more of these acid dianhydrides can also be used in combination.

[0038] Examples of diamines that can be used to prepare the polyamic acid solution according to the embodiment of the present invention include paraphenylenediamine (PPD), metaphenylenediamine (MPDA), 2,5-diaminotoluene, 2,6-diaminotoluene, 4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 2,2-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 3,3'-diaminobiphenyl, 2,2-bis(trifluoromethyl)-4,4 ... Aminodiphenylmethane, 4,4'-diaminodiphenylmethane (MDA), 2,2-bis-(4-aminophenyl)propane, 3,3'-diaminodiphenyl sulfone (3,3'-DDS), 4,4'-diaminodiphenyl sulfone (4,4'-DDS), diaminobenzotrifluoride, bis(trifluoromethyl)phenylenediamine, diaminotetra(trifluoromethyl)benzene, diamino(pentafluoroethyl)benzene, 2,2'-bis(trifluoromethyl )benzidine (TFMB), 3,3'-bis(trifluoromethyl)benzidine, 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether, 3,3'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether, 3,3',5,5'-tetrakis(trifluoromethyl)-4,4'-diaminodiphenyl ether, 3,3'-bis(trifluoromethyl)-4,4'-diaminobenzophenone, bis(aminophenoxy)di(trifluoromethyl) bis(aminophenoxy)tetrakis(trifluoromethyl)benzene, bis[(trifluoromethyl)aminophenoxy]benzene, bis[(trifluoromethyl)aminophenoxy]biphenyl, bis{[(trifluoromethyl)aminophenoxy]phenyl}hexafluoropropane, 2,2-bis{4-(p-aminophenoxy)phenyl}hexafluoropropane, 2,2-bis{4-(m-aminophenoxy)phenyl}hexafluoropropane, 2,2-bis{4-(o-aminophenoxy)phenyl}hexafluoropropane, 2-{4-(p-aminophenoxy)phenyl}-2-{4-(m-aminophenoxy)phenyl}hexafluoropropane, 2-{4-(m-aminophenoxy)phenyl}-2-{4-(o-aminophenoxy)phenyl}hexafluoropropane, 2-{4-(o-aminophenoxy)phenyl}-2-{4-(p-aminophenoxy)phenyl}hexafluoropropane, 3,3'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether (34ODA), 4,4'-diaminodiphenyl ether (ODA), 1,5-diaminonaphthalene, 4,4'-diaminodiphenyldiethylsilane, 4,4 Examples of aromatic diamines include 4,4'-diaminodiphenylsilane, 4,4'-diaminodiphenylethylphosphine oxide, 1,3-bis(3-aminophenoxy)benzene (133APB), 1,3-bis(4-aminophenoxy)benzene (134APB), 1,4-bis(4-aminophenoxy)benzene, bis[4-(3-aminophenoxy)phenyl]sulfone (BAPSM), bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), 2,2-bis(3-aminophenyl)1,1,1,3,3,3-hexafluoropropane, 2,2-bis(4-aminophenyl)1,1,1,3,3,3-hexafluoropropane, and 9,9-bis(4-aminophenyl)fluorene. These diamines may also be used in combination of two or more. ,

[0039] From the viewpoint of imparting transparency to the film according to the embodiment of the present invention, for example, as a display component, it is preferable to use 3,3',4,4'-biphenyltetracarboxylic dianhydride and 2,2-bis[3,4-(dicarboxyphenoxy)phenyl]propane dianhydride (BPADA) as the acid dianhydride and 2,2'-bis(trifluoromethyl)benzidine (TFMB) and 3,3'-diaminodiphenyl sulfone (3,3'-DDS) as the diamine. Note that other acid dianhydrides and other diamines may be added to the above-mentioned acid dianhydrides and diamines within the scope of the present invention.

[0040] The yellowness index (YI) of the film according to the embodiment of the present invention is preferably less than 5, more preferably less than 3, even more preferably less than 2.5, and particularly preferably less than 2. The smaller the yellowness index, the better. There is no particular lower limit, but if a lower limit were to be set, it would be 1. When the thickness of the film according to the embodiment of the present invention is 25 μm, the yellowness index (YI) of the film is preferably less than 3, more preferably less than 2.5, and even more preferably less than 2. In such cases, even if the film thickness is other than 25 μm, it is sufficient that the yellowness index when converted to a film thickness of 25 μm falls within the above-mentioned yellowness index range. Furthermore, when the thickness of the film according to the embodiment of the present invention is 50 μm, the yellowness index (YI) of the film is preferably less than 5, more preferably less than 3, even more preferably less than 2.5, and particularly preferably less than 2. In such cases, even if the film thickness is other than 50 μm, it is sufficient that the yellowness index when converted to a film thickness of 25 μm falls within the above-mentioned yellowness index range.

[0041] The linear expansion coefficient of the film according to the embodiment of the present invention is preferably less than 47 ppm / °C, more preferably less than 40 ppm / °C, even more preferably 35 ppm / °C or less, and particularly preferably less than 30 ppm / °C. The smaller the linear expansion coefficient, the better, and there is no particular lower limit. However, if a lower limit were to be set, it would be 25 ppm / °C. When the film according to the embodiment of the present invention has a thickness of 25 μm, the linear expansion coefficient of the film is preferably less than 47 ppm / °C, more preferably less than 40 ppm / °C, even more preferably 35 ppm / °C or less, and particularly preferably less than 30 ppm / °C. In such cases, even if the film has a thickness other than 25 μm, it is sufficient that the linear expansion coefficient when converted to a film thickness of 25 μm falls within the above-mentioned range of linear expansion coefficients. Furthermore, when the thickness of the film according to the embodiment of the present invention is 50 μm, the linear expansion coefficient of the film is preferably less than 47 ppm / ° C., more preferably less than 40 ppm / ° C., even more preferably 35 ppm / ° C. or less, and particularly preferably less than 30 ppm / ° C. In such cases, even if the film thickness is other than 50 μm, it is sufficient that the linear expansion coefficient when converted into a film thickness of 50 μm is within the above-mentioned range of linear expansion coefficients.

[0042] Furthermore, the total light transmittance of the film according to the embodiment of the present invention is preferably 74% or more, more preferably 75% or more, even more preferably 76% or more, even more preferably 77% or more, even more preferably 78% or more, and particularly preferably 79% or more. The upper limit is 100%. When the thickness of the film according to the embodiment of the present invention is 25 μm, the total light transmittance of the film is preferably 74% or more, more preferably 75% or more, even more preferably 76% or more, even more preferably 77% or more, even more preferably 78% or more, and particularly preferably 79% or more. In such cases, even if the film has a thickness other than 25 μm, it is sufficient that the total light transmittance when converted to a film thickness of 25 μm is within the above range. Furthermore, when the thickness of the film according to the embodiment of the present invention is 50 μm, the total light transmittance of the film is preferably 74% or more, more preferably 75% or more, even more preferably 76% or more, still more preferably 77% or more, still more preferably 78% or more, and particularly preferably 79% or more. In such cases, even if the thickness of the film is other than 50 μm, it is sufficient that the total light transmittance when converted to a film thickness of 50 μm is within the above range of total light transmittance.

[0043] The tensile strength of the film according to the embodiment of the present invention is preferably in the range of 50 MPa or more and 250 MPa or less, and more preferably in the range of 100 MPa or more and 200 MPa or less.

[0044] Furthermore, the tensile modulus of the film according to the embodiment of the present invention is preferably in the range of 3.0 GPa or more and 5.0 GPa or less, and more preferably in the range of 3.5 GPa or more and 4.5 GPa or less.

[0045] The tensile elongation of the film according to the embodiment of the present invention is preferably in the range of 10% to 40%, and more preferably in the range of 13% to 35%.

[0046] The polyimide film according to the present invention can be used as a laminate comprising a metal layer of nickel-chromium alloy, aluminum, or silver laminated thereon. That is, in this laminate, a metal layer of nickel-chromium alloy, aluminum, or silver is laminated on the polyimide film. This laminate can be used as a substrate material in various electronic devices and lighting devices, such as flexible printed circuit boards (FPCs), reflectors, or optical substrate reflectors (OSRs). Furthermore, by further laminating a copper layer on the metal layer in this laminate, the conductivity and durability of the entire laminate can be improved.

[0047] The polyimide film according to the embodiment of the present invention preferably has a peel strength of 200 N / m or more, more preferably 300 N / m or more, even more preferably 350 N / m or more, still more preferably 400 N / m or more, and particularly preferably 450 N / m or more, when peeled from a nickel-20 mass % chromium alloy under conditions of normal pressure, 25°C, a peel angle of 90°, and a peel rate of 50 mm / min.

[0048] The polyimide film according to the embodiment of the present invention preferably has a peel strength of 90 N / m or more, more preferably 95 N / m or more, even more preferably 100 N / m or more, still more preferably 105 N / m or more, and particularly preferably 110 N / m or more, when peeled from aluminum at normal pressure, 25°C, a peel angle of 90°, and a peel rate of 50 mm / min.

[0049] The polyimide film according to the embodiment of the present invention preferably has a peel strength of 115 N / m or more, more preferably 125 N / m or more, even more preferably 135 N / m or more, still more preferably 145 N / m or more, still more preferably 150 N / m or more, and particularly preferably 155 N / m or more, when peeled from silver under conditions of normal pressure, 25°C, a peel angle of 90°, and a peel rate of 50 mm / min.

[0050] <Examples and Comparative Examples> The present invention will be explained in more detail below by introducing examples and comparative examples, but the present invention is not limited to these examples.

[0051] 1. Preparation of Additive-Containing Polyamic Acid Solution: 11.01 g of biphenyltetracarboxylic dianhydride (BPDA), 2.17 g of 2,2-bis[3,4-(dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), 6.66 g of 2,2'-bis(trifluoromethyl)benzidine (TFMB), and 5.16 g of 3,3'-diaminodiphenylsulfone (3,3'-DDS) were reacted in 75 g of N,N-dimethylacetamide (DMAc) to prepare a polyamic acid solution with a solids content of 25% by mass. The molar ratio of the monomers in this polyamic acid (BPDA / BPADA / TFMB / 3,3'-DDS) was 90 / 10 / 50 / 50.

[0052] Next, 1.85 g of α-alumina (manufacturer: Kinseimatec Co., Ltd., product name: Seraph, product number: YFA00610, shape: plate-like, average particle size: 0.6 μm, aspect ratio: 10) was dispersed in 3.69 g of N,N-dimethylacetamide (DMAc) to prepare an α-alumina dispersion. Then, this α-alumina dispersion was added to the above-mentioned polyamic acid solution to prepare an additive-containing polyamic acid solution.

[0053] 2. Film Formation The additive-containing polyamic acid solution was applied to a glass substrate to form a coating film, which was then placed in an oven at 80°C and dried for 15 minutes to obtain a precursor film. The precursor film was then peeled from the glass substrate, and, with its edges fixed with a frame, placed in an oven at 180°C and maintained there for 10 minutes. The oven temperature was then raised to 280°C. The oven temperature was raised from 180°C to 280°C over 22 minutes, and maintained at 280°C for 5 minutes after reaching that temperature. As a result, an α-alumina-containing polyimide film was formed on the glass substrate. The fixtures holding the edges of the α-alumina-containing polyimide film were then removed to obtain a 25 μm-thick α-alumina-containing polyimide film.

[0054] α-alumina does not volatilize even at 280°C. Based on this fact, the amount of α-alumina added and the density (3.97 g / cm3) mentioned above were ３ ) and the solids concentration of the polyamic acid and the density of the polyimide (1.35 g / cm ３ The volume ratio of α-alumina to the total volume of the α-alumina-containing polyimide film finally obtained from the above was calculated to be 2.6% by volume.

[0055] 3. Measurement of Physical Properties of α-Alumina-Containing Polyimide Film The linear expansion coefficient, total light transmittance, yellowness index (YI), and haze of the resulting α-alumina-containing polyimide film having a thickness of 25 μm were determined as follows.

[0056] (1) Linear expansion coefficient of α-alumina-containing polyimide film: A 3.5 mm × 13.0 mm piece of film was fixed to a thermal analyzer (TMA-60) manufactured by Shimadzu Corporation, and the temperature was increased to 300°C at a rate of 5.0°C / min to record the dimensional change of the film piece with respect to temperature, i.e., the TMA curve. The average linear expansion coefficient from 100°C to 200°C was calculated from the obtained TMA curve, and the linear expansion coefficient of the film piece was found to be 42.7 ppm / K.

[0057] (2) Total Light Transmittance of α-alumina-Containing Polyimide Film A piece of film cut to 25.0 mm × 50.0 mm was fixed on a spectrophotometer V-750 manufactured by JASCO Corporation, and then the film piece was irradiated with light having a wavelength of 380 to 780 nm from a deuterium lamp and a halogen lamp. As a result, the total light transmittance of the film piece was 86.0%.

[0058] (3) Yellowness Index (YI) of α-Alumina-Containing Polyimide Film A film piece cut to a size of 25.0 mm x 50.0 mm was fixed to a spectrophotometer V-750 manufactured by JASCO Corporation, and the yellowness index (YI) of the film piece was measured. The yellowness index (YI) of the film piece was found to be 2.3.

[0059] (4) Haze A piece of film cut to 25.0 mm x 50.0 mm was fixed to a spectrophotometer V-750 manufactured by JASCO Corporation, and the haze of the film piece was measured. As a result, the haze of the film piece was 25.04%.

[0060] The target α-alumina-containing polyimide film was obtained in the same manner as in Example 1, except that an α-alumina dispersion was prepared by dispersing 1.85 g of α-alumina (manufacturer: Kinseimatec Co., Ltd., product name: Seraph, product number: YFA02050, shape: plate-like, particle size: 2 μm, aspect ratio: 50) in 3.69 g of N,N-dimethylacetamide (DMAc). The volume ratio of α-alumina to the total volume of this α-alumina-containing polyimide film was calculated to be 2.6% by volume.

[0061] Furthermore, the physical properties of the obtained α-alumina-containing polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 33.7 ppm / K, the total light transmittance was 86.6%, the yellowness index (YI) was 2.1, and the haze was 12.15%.

[0062] The target α-alumina-containing polyimide film was obtained in the same manner as in Example 1, except that an α-alumina dispersion was prepared by dispersing 1.85 g of α-alumina (manufacturer: Kinseimatec Co., Ltd., product name: Seraph, product number: YFA05070, shape: plate-like, particle size: 5 μm, aspect ratio: 70) in 3.69 g of N,N-dimethylacetamide (DMAc). The volume ratio of α-alumina to the total volume of this α-alumina-containing polyimide film was calculated to be 2.6% by volume.

[0063] Furthermore, the physical properties of the obtained α-alumina-containing polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 32.9 ppm / K, the total light transmittance was 86.9%, the yellowness index (YI) was 2.1, and the haze was 13.78%.

[0064] The target α-alumina-containing polyimide film was obtained in the same manner as in Example 1, except that an α-alumina dispersion was prepared by dispersing 1.85 g of α-alumina (manufacturer: DIC Corporation, product name: Ceranex, product number: AP10, shape: plate-like, particle size: 8 μm, aspect ratio: 15) in 3.69 g of N,N-dimethylacetamide (DMAc). The volume ratio of α-alumina to the total volume of this α-alumina-containing polyimide film was determined to be 2.6% by volume.

[0065] Furthermore, the physical properties of the obtained α-alumina-containing polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 38.2 ppm / K, the total light transmittance was 86.7%, the yellowness index (YI) was 2.4, and the haze was 24.11%.

[0066] The target α-alumina-containing polyimide film was obtained in the same manner as in Example 1, except that an α-alumina dispersion was prepared by dispersing 1.85 g of α-alumina (manufacturer: Admatec Co., Ltd., product name: Adfine, product number: AO-502, shape: spherical, particle size: 0.2 μm, aspect ratio: 2) in 3.69 g of N,N-dimethylacetamide (DMAc). The volume ratio of α-alumina to the total volume of this α-alumina-containing polyimide film was determined to be 2.6% by volume.

[0067] Furthermore, the physical properties of the obtained α-alumina-containing polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 41.1 ppm / K, the total light transmittance was 87.1%, the yellowness index (YI) was 2.4, and the haze was 13.15%.

[0068] The target α-alumina-containing polyimide film was obtained in the same manner as in Example 1, except that an α-alumina dispersion was prepared by dispersing 0.14 g of α-alumina (manufacturer: Kinseimatec Co., Ltd., product name: Seraph, product number: YFA02050, shape: plate-like, particle size: 2 μm, aspect ratio: 50) in 0.07 g of N,N-dimethylacetamide (DMAc). The α-alumina content relative to the total volume of this α-alumina-containing polyimide film was determined to be 0.1% by volume.

[0069] The physical properties of the resulting α-alumina-containing polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 41.6 ppm / K, the total light transmittance was 87.7%, the yellowness index (YI) was 2.9, and the haze was 0.58%. The anti-blocking performance of this α-alumina-containing polyimide film was also examined, but no sufficient anti-blocking performance was observed.

[0070] The target α-alumina-containing polyimide film was obtained in the same manner as in Example 1, except that an α-alumina dispersion was prepared by dispersing 0.14 g of α-alumina (manufacturer: Kinseimatec Co., Ltd., product name: Seraph, product number: YFA02050, shape: plate-like, particle size: 2 μm, aspect ratio: 50) in 0.28 g of N,N-dimethylacetamide (DMAc). The volume ratio of α-alumina to the total volume of this α-alumina-containing polyimide film was determined to be 0.2% by volume.

[0071] Furthermore, the physical properties of the obtained α-alumina-containing polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 40.8 ppm / K, the total light transmittance was 88.1%, the yellowness index (YI) was 2.9, and the haze was 1.19%.

[0072] The target α-alumina-containing polyimide film was obtained in the same manner as in Example 1, except that an α-alumina dispersion was prepared by dispersing 0.35 g of α-alumina (manufacturer: Kinseimatec Co., Ltd., product name: Seraph, product number: YFA02050, shape: plate-like, particle size: 2 μm, aspect ratio: 50) in 0.69 g of N,N-dimethylacetamide (DMAc). The volume ratio of α-alumina to the total volume of this α-alumina-containing polyimide film was determined to be 0.5% by volume.

[0073] Furthermore, the physical properties of the obtained α-alumina-containing polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 39.7 ppm / K, the total light transmittance was 87.6%, the yellowness index (YI) was 2.8, and the haze was 3.19%.

[0074] The target α-alumina-containing polyimide film was obtained in the same manner as in Example 1, except that an α-alumina dispersion was prepared by dispersing 0.91 g of α-alumina (manufacturer: Kinseimatec Co., Ltd., product name: Seraph, product number: YFA02050, shape: plate-like, particle size: 2 μm, aspect ratio: 50) in 1.82 g of N,N-dimethylacetamide (DMAc). The volume ratio of α-alumina to the total volume of this α-alumina-containing polyimide film was calculated to be 1.3 vol %.

[0075] Furthermore, the physical properties of the obtained α-alumina-containing polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 37.2 ppm / K, the total light transmittance was 87.1%, the yellowness index (YI) was 2.5, and the haze was 6.12%.

[0076] The target α-alumina-containing polyimide film was obtained in the same manner as in Example 1, except that an α-alumina dispersion was prepared by dispersing 3.64 g of α-alumina (manufacturer: Kinseimatec Co., Ltd., product name: Seraph, product number: YFA02050, shape: plate-like, particle size: 2 μm, aspect ratio: 50) in 7.27 g of N,N-dimethylacetamide (DMAc). The volume ratio of α-alumina to the total volume of this α-alumina-containing polyimide film was determined to be 5% by volume.

[0077] Furthermore, the physical properties of the obtained α-alumina-containing polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 29.1 ppm / K, the total light transmittance was 85.5%, the yellowness index (YI) was 1.4, and the haze was 23.85%.

[0078] The target α-alumina-containing polyimide film was obtained in the same manner as in Example 6, except that 12.72 g of biphenyltetracarboxylic dianhydride (BPDA), 6.92 g of 2,2'-bis(trifluoromethyl)benzidine (TFMB), and 5.37 g of 3,3'-diaminodiphenyl sulfone (3,3'-DDS) were reacted in 75 g of N,N-dimethylacetamide (DMAc) to prepare a polyamic acid solution with a solids content of 25% by mass. The molar ratio of the monomers in this polyamic acid (BPDA / TFMB / 3,3'-DDS) was 100 / 50 / 50. The volume fraction of α-alumina relative to the total volume of this α-alumina-containing polyimide film was determined to be 0.1% by volume.

[0079] Furthermore, the physical properties of the obtained α-alumina-containing polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 37.5 ppm / K, the total light transmittance was 87.3%, the yellowness index (YI) was 4.0, and the haze was 0.6%.

[0080] The target α-alumina-containing polyimide film was obtained in the same manner as in Example 6, except that 12.56 g of biphenyltetracarboxylic dianhydride (BPDA), 8.20 g of 2,2'-bis(trifluoromethyl)benzidine (TFMB), and 4.24 g of 3,3'-diaminodiphenyl sulfone (3,3'-DDS) were reacted in 75 g of N,N-dimethylacetamide (DMAc) to prepare a polyamic acid solution with a solids content of 25% by mass. The molar ratio of the monomers in this polyamic acid (BPDA / TFMB / 3,3'-DDS) was 100 / / 60 / 40. The volume fraction of α-alumina relative to the total volume of this α-alumina-containing polyimide film was determined to be 0.1% by volume.

[0081] Furthermore, the physical properties of the obtained α-alumina-containing polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 35.7 ppm / K, the total light transmittance was 86.9%, the yellowness index (YI) was 4.2, and the haze was 0.8%.

[0082] The target α-alumina-containing polyimide film was obtained in the same manner as in Example 6, except that 12.41 g of biphenyltetracarboxylic dianhydride (BPDA), 9.45 g of 2,2'-bis(trifluoromethyl)benzidine (TFMB), and 3.14 g of 3,3'-diaminodiphenyl sulfone (3,3'-DDS) were reacted in 75 g of N,N-dimethylacetamide (DMAc) to prepare a polyamic acid solution with a solids content of 25% by mass. The molar ratio of the monomers in this polyamic acid (BPDA / TFMB / 3,3'-DDS) was 100 / 70 / 30. The volume fraction of α-alumina relative to the total volume of this α-alumina-containing polyimide film was determined to be 0.1% by volume.

[0083] Furthermore, the physical properties of the obtained α-alumina-containing polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 32.4 ppm / K, the total light transmittance was 86.3%, the yellowness index (YI) was 4.4, and the haze was 1.0%.

[0084] The target α-alumina-containing polyimide film was obtained in the same manner as in Example 6, except that 12.26 g of biphenyltetracarboxylic dianhydride (BPDA), 10.67 g of 2,2'-bis(trifluoromethyl)benzidine (TFMB), and 2.07 g of 3,3'-diaminodiphenyl sulfone (3,3'-DDS) were reacted in 75 g of N,N-dimethylacetamide (DMAc) to prepare a polyamic acid solution with a solids content of 25% by mass. The molar ratio of the monomers in this polyamic acid (BPDA / TFMB / 3,3'-DDS) was 100 / / 80 / 20. The volume fraction of α-alumina relative to the total volume of this α-alumina-containing polyimide film was determined to be 0.1% by volume.

[0085] Furthermore, the physical properties of the obtained α-alumina-containing polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 30.2 ppm / K, the total light transmittance was 86.0%, the yellowness index (YI) was 4.7, and the haze was 1.0%.

[0086] The target α-alumina-containing polyimide film was obtained in the same manner as in Example 9, except that 10.63 g of biphenyltetracarboxylic dianhydride (BPDA), 2.09 g of 2,2-bis[3,4-(dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), 10.29 g of 2,2'-bis(trifluoromethyl)benzidine (TFMB), and 1.99 g of 3,3'-diaminodiphenylsulfone (3,3'-DDS) were reacted in 75 g of N,N-dimethylacetamide (DMAc) to prepare a polyamic acid solution with a solids content of 25% by mass. The molar ratio of the monomers in this polyamic acid (BPDA / BPADA / TFMB / 3,3'-DDS) was 90 / 10 / 80 / 20. The volume ratio of α-alumina to the total volume of this α-alumina-containing polyimide film was determined to be 1.3% by volume.

[0087] Furthermore, the physical properties of the obtained α-alumina-containing polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 35.7 ppm / K, the total light transmittance was 87.1%, the yellowness index (YI) was 2.7, and the haze was 8.8%.

[0088] The target α-alumina-containing polyimide film was obtained in the same manner as in Example 15, except that an α-alumina dispersion was prepared by dispersing 1.85 g of α-alumina (manufacturer: Kinseimatec Co., Ltd., product name: Seraph, product number: YFA02050, shape: plate-like, particle size: 2 μm, aspect ratio: 50) in 3.69 g of N,N-dimethylacetamide (DMAc). The volume ratio of α-alumina to the total volume of this α-alumina-containing polyimide film was calculated to be 2.6% by volume.

[0089] Furthermore, the physical properties of the obtained α-alumina-containing polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 29.3 ppm / K, the total light transmittance was 86.0%, the yellowness index (YI) was 2.3, and the haze was 16.3%.

[0090] The target α-alumina-containing polyimide film was obtained in the same manner as in Example 6, except that 2000 ppm of an internal mold release agent and 0.5 mass % of an antifoaming agent were added relative to the solid content of the polyamic acid solution. The volume ratio of α-alumina to the total volume of this α-alumina-containing polyimide film was determined to be 0.1 volume %.

[0091] The physical properties of the resulting α-alumina-containing polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 43.2 ppm / K, the total light transmittance was 87.8%, the yellowness index (YI) was 3.1, and the haze was 0.64%. The anti-blocking performance of this α-alumina-containing polyimide film was also examined, but no sufficient anti-blocking performance was observed.

[0092] An α-alumina-containing polyimide film was obtained in the same manner as in Example 1, except that (a) an α-alumina dispersion was prepared by dispersing 0.32 g of α-alumina (manufacturer: Kinseimatec Co., Ltd., product name: Seraph, product number: YFA02050, shape: plate-like, particle size: 2 μm, aspect ratio: 50) in 0.64 g of N,N-dimethylacetamide (DMAc), and (b) 2000 ppm of an internal release agent and 0.5 mass % of an antifoaming agent were added relative to the solids content of the polyamic acid solution. The volume ratio of α-alumina to the total volume of this α-alumina-containing polyimide film was determined to be 0.46 vol %.

[0093] The physical properties of the resulting α-alumina-containing polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 39.2 ppm / K, the total light transmittance was 87.6%, the yellowness index (YI) was 2.9, and the haze was 1.89%. The anti-blocking performance of the α-alumina-containing polyimide film was also confirmed to be sufficient.

[0094] The target α-alumina-containing polyimide film was obtained in the same manner as in Example 9, except that the film was formed to a thickness of 50 μm.

[0095] Furthermore, the physical properties of the obtained α-alumina-containing polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 38.3 ppm / K, the total light transmittance was 86.2%, the yellowness index (YI) was 4.2, and the haze was 10.0%.

[0096] 1. Preparation of Additive-Containing Polyamic Acid Solution An additive-containing polyamic acid solution was prepared in the same manner as in Example 1, except that (a) an α-alumina dispersion was prepared by dispersing 0.32 g of α-alumina (manufacturer: Kinseimatec Co., Ltd., product name: Seraph, product number: YFA02050, shape: plate-like, particle size: 2 μm, aspect ratio: 50) in 0.64 g of N,N-dimethylacetamide (DMAc), and (b) 2000 ppm of an internal mold release agent and 0.5 mass % of an antifoaming agent were added relative to the solids content of the polyamic acid solution.

[0097] 2. Film Formation The additive-containing polyamic acid solution was applied to a glass substrate to form a coating film, which was then placed in an oven at 80°C and dried for 15 minutes to obtain a precursor film. The precursor film was then peeled from the glass substrate, and, with its edges fixed with a frame, placed in an oven at 175°C and maintained there for 5 minutes. The oven temperature was then raised to 300°C. The oven temperature was raised from 175°C to 300°C over 25 minutes, and maintained at 300°C for 5 minutes after reaching that temperature. As a result, an α-alumina-containing polyimide film was formed on the glass substrate. The fixtures that had been fixing the edges of the α-alumina-containing polyimide film were then removed to obtain a 50 μm-thick α-alumina-containing polyimide film.

[0098] It should be noted that α-alumina does not volatilize even at 300°C. Based on this fact, the amount of α-alumina added and the density (3.97 g / cm3) mentioned above were ３ ) and the solids concentration of the polyamic acid and the density of the polyimide (1.35 g / cm ３ The volume ratio of α-alumina to the total volume of the finally obtained α-alumina-containing polyimide film was calculated to be 0.46% by volume.

[0099] 3. Measurement of Physical Properties of α-Alumina-Containing Polyimide Film The physical properties of the obtained α-alumina-containing polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 42.7 ppm / K, the total light transmittance was 87.3%, the yellowness index (YI) was 4.5, and the haze was 3.43%.

[0100] 4. Formation of a Metal Layer on an α-Alumina-Containing Polyimide Film The α-alumina-containing polyimide film obtained above was cut into a 65 mm × 30 mm piece to prepare a measurement film. This measurement film was then set in a magnetron sputtering device (E-200S, manufactured by Canon Anelva Corporation). One side of this measurement film was then subjected to plasma treatment for 90 seconds under the following (treatment condition 1). Note that the "ultimate vacuum" in the following (treatment condition 1) to (treatment condition 3) refers to the ultimate vacuum in the vacuum chamber of the magnetron sputtering device (E-200S, manufactured by Canon Anelva Corporation).

[0101] (Processing Condition 1) Ultimate vacuum: 1.5×10 -3 Pa Plasma generating gas: argon gas Gas flow rate: 12 sccm Type of applied power: RF (high frequency) Output power: 10 W

[0102] The surface of the polyimide film that had been subjected to the plasma treatment was subjected to a sputtering treatment using a magnetron sputtering device (E-200S, manufactured by Canon Anelva Corporation) under the following (treatment condition 2), to form a 20-nm-thick underlayer (metal layer) made of a nickel-20% by mass chromium alloy on the surface, thereby obtaining a underlayer-formed polyimide film.

[0103] (Processing condition 2) Ultimate vacuum: 1.5×10 -3 Pa Sputtering gas: argon gas Gas flow rate: 12 sccm Type of applied power: DC (series) Output power: 50 W Target shape: 2-inch diameter disc Target material: nickel-chromium alloy (manufacturer: Toshima Manufacturing Co., Ltd., nickel-20% by mass chromium, purity 99.9% by mass)

[0104] Subsequently, the underlayer formed above was subjected to sputtering treatment using a magnetron sputtering device (E-200S manufactured by Canon Anelva Corporation) under the following (treatment condition 3) to form a copper layer having a thickness of 0.5 μm, thereby obtaining a polyimide film having a plating underlayer formed thereon. That is, in this polyimide film having a plating underlayer formed thereon, a underlayer (metal layer) made of a nickel-20% by mass chromium alloy is formed on the surface of the polyimide film that has been subjected to the plasma treatment, and a copper layer is laminated on the underlayer to form the plating underlayer.

[0105] (Processing condition 3) Ultimate vacuum: 1.5×10 -3 Pa Sputtering gas: argon gas Gas flow rate: 12 sccm Type of applied power: RF (radio frequency) Output power: 200 W Target shape: 2-inch diameter disc Target material: copper (manufacturer: Toshima Manufacturing Co., Ltd., purity 99.99% by mass)

[0106] The polyimide film with a plating underlayer formed thereon obtained above was placed in an electroplating apparatus and subjected to copper plating under the following (Processing Condition 4) to form a copper coating on the plating underlayer of the polyimide film with a plating underlayer formed thereon, thereby obtaining a copper-plated substrate. This copper plating was continued until the copper coating formed on the plating underlayer reached a thickness of 45 μm.

[0107] (Processing condition 4) DC stabilized power supply: PMX18-5A manufactured by Kikusui Electronics Co., Ltd. Anode: copper Cathode: polyimide film for forming plating underlayer Plating solution composition: sulfuric acid: copper sulfate = 2:1 Processing temperature: 25°C Current value: 2.0 mA / dm ２

[0108] 5. Evaluation of Peel Strength of α-Alumina-Containing Polyimide Films The copper-plated substrate obtained above was cut into a 55 mm × 3 mm measurement substrate. An incision was then made at the interface between the polyimide film and the underlayer (metal layer) made of a nickel-20% by mass chromium alloy in this measurement substrate, and the edge of the underlayer made of a nickel-20% by mass chromium alloy on which the copper coating was formed was peeled off by approximately 1 mm. The underlayer was then further peeled off to a length of 5 mm using tweezers, and cellophane tape was applied to the peeled portion. This cellophane tape was then held in the gripping portion of a precision universal testing machine (AGS-10kNG, manufactured by Shimadzu Corporation). Next, double-sided tape was applied to the non-copper-coated side of the polyimide film in the measurement substrate, and the measurement substrate was fixed to the jig portion of the precision universal testing machine. A peel test was then performed under the following (Measurement Condition 1) (see Figure 7). As a result, the peel strength between the polyimide film and the underlayer (metal layer) made of a nickel-20 mass % chromium alloy on which the copper coating was formed was 479.5 N / m.

[0109] (Measurement condition 1) Peel angle: 90° Peel speed: 50 mm / min Measurement temperature: 25°C under normal pressure Load cell used: 10 N load cell (load capacity: 10 N)

[0110] The target α-alumina-containing polyimide film was obtained in the same manner as in Example 20. Then, the target copper-plated substrate was obtained in the same manner as in Example 20, except that the plasma treatment time for one side of the polyimide film was set to 75 seconds. The obtained copper-plated substrate was cut into a 55 mm × 3 mm piece to obtain a measurement substrate, and the peel strength between the polyimide film and an underlayer (metal layer) made of a nickel-20% by mass chromium alloy on which a copper coating was formed was measured in the same manner as in Example 20, and the peel strength was found to be 302.8 N / m.

[0111] The target α-alumina-containing polyimide film was obtained by the same method as that shown in Example 20. Then, a plating underlayer-forming polyimide film was obtained by the same method as that shown in Example 20, except that the "target material" in (Processing Condition 2) above was changed from a nickel-chromium alloy to aluminum (manufacturer: USTRON Corporation, purity 99.99% by mass), and the "type of applied power" in (Processing Condition 2) above was changed from DC (series) to RF (radio frequency). That is, in this plating underlayer-forming polyimide film, an underlayer (metal layer) made of aluminum was formed on the surface of a plasma-treated polyimide film, and a copper layer was laminated on the underlayer to form a plating underlayer.

[0112] Next, a copper-plated substrate was obtained from the polyimide film with a plating underlayer formed thereon by the same method as in Example 20. The copper-plated substrate was then cut into a size of 55 mm × 3 mm to obtain a measurement substrate, and the peel strength between the polyimide film and the underlayer (metal layer) made of aluminum and having a copper coating formed thereon was measured by the same method as in Example 20, resulting in a peel strength of 107.3 N / m.

[0113] The target α-alumina-containing polyimide film was obtained by the same method as that shown in Example 20. Then, a plating underlayer-forming polyimide film was obtained by the same method as that shown in Example 20, except that the "target material" in (Processing Condition 2) above was changed from a nickel-chromium alloy to silver (manufacturer: USTRON Corporation, purity 99.99% by mass), and the "type of applied power" in (Processing Condition 2) above was changed from DC (series) to RF (radio frequency). That is, in this plating underlayer-forming polyimide film, a silver underlayer (metal layer) was formed on the surface of a plasma-treated polyimide film, and a copper layer was laminated on the underlayer to form a plating underlayer.

[0114] Next, a copper-plated substrate was obtained from the polyimide film with a plating underlayer formed thereon by the same method as in Example 20. The copper-plated substrate was then cut into a size of 55 mm x 3 mm to obtain a measurement substrate, and the peel strength between the polyimide film and the underlayer (metal layer) made of silver and having a copper coating formed thereon was measured by the same method as in Example 20, resulting in a peel strength of 143.8 N / m.

[0115] The target α-alumina-containing polyimide film was obtained in the same manner as in Example 2, except that 7.98 g of biphenyltetracarboxylic dianhydride (BPDA), 5.17 g of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 9.93 g of 2,2'-bis(trifluoromethyl)benzidine (TFMB), and 1.92 g of 3,3'-diaminodiphenylsulfone (3,3'-DDS) were reacted in 75 g of N,N-dimethylacetamide (DMAc) to prepare a polyamic acid solution with a solids content of 25% by weight. The molar ratio of the monomers in this polyamic acid (BPDA / 6FDA / TFMB / 3,3'-DDS) was 70 / 30 / 80 / 20. The volume ratio of α-alumina to the total volume of this α-alumina-containing polyimide film was determined to be 2.6% by volume.

[0116] Furthermore, the physical properties of the obtained α-alumina-containing polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 33.3 ppm / K, the total light transmittance was 86.2%, the yellowness index (YI) was 2.3, and the haze was 15.37%.

[0117] The target α-alumina-containing polyimide film was obtained in the same manner as in Example 2, except that 10.63 g of biphenyltetracarboxylic dianhydride (BPDA), 2.09 g of 2,2-bis[3,4-(dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), 10.29 g of 2,2'-bis(trifluoromethyl)benzidine (TFMB), and 1.99 g of 4,4'-diaminodiphenylsulfone (4,4'-DDS) were reacted in 75 g of N,N-dimethylacetamide (DMAc) to prepare a polyamic acid solution with a solids content of 25% by weight. The molar ratio of the monomers in this polyamic acid (BPDA / BPADA / TFMB / 4,4'-DDS) was 90 / 10 / 80 / 20. The volume ratio of α-alumina to the total volume of this α-alumina-containing polyimide film was determined to be 2.6% by volume.

[0118] Furthermore, the physical properties of the obtained α-alumina-containing polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 30.4 ppm / K, the total light transmittance was 86.0%, the yellowness index (YI) was 1.8, and the haze was 19.62%.

[0119] Comparative Example 1 The target polyimide film was obtained in the same manner as in Example 1, except that no α-alumina dispersion was added to the polyamic acid solution (i.e., no α-alumina was added to the polyamic acid solution prepared in this comparative example).

[0120] The physical properties of the obtained polyimide film were measured in the same manner as in Example 1, and the linear expansion coefficient was 47.7 ppm / K, the total light transmittance was 88.0%, the yellowness index (YI) was 3.0, and the haze was 0.05%. The anti-blocking performance of this polyimide film was also checked, but it was found to be insufficient.

[0121] Comparative Example 2 A boehmite dispersion was prepared by dispersing 1.41 g of boehmite (manufacturer: Kawai Lime Industry Co., Ltd., product name: Cerasure, product number: BMF240, shape: flaky, particle size: 2 μm, aspect ratio: 40) in 2.82 g of N,N-dimethylacetamide (DMAc), and a target boehmite-containing polyimide film was obtained in the same manner as in Example 1, except that the boehmite dispersion was added to the polyamic acid solution instead of the α-alumina dispersion.

[0122] In addition, boehmite does not volatilize even at 280°C, and is not converted into other substances. Based on this fact, the amount of boehmite added and the density (3.03 g / cm3) described above were ３ ) and the solids concentration of the polyamic acid and the density of the polyimide (1.35 g / cm ３ The volume ratio of boehmite to the total volume of the finally obtained boehmite-containing polyimide film was calculated to be 2.6% by volume.

[0123] Furthermore, the physical properties of the obtained boehmite-containing polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 38.1 ppm / K, the total light transmittance was 87.3%, the yellowness index (YI) was 3.8, and the haze was 9.16%.

[0124] Comparative Example 3 A γ-alumina dispersion was prepared by dispersing 1.58 g of γ-alumina (manufacturer: Kawai Lime Industry Co., Ltd., product name: Cerasure, product number: BMF240γ, shape: flaky, particle size: 2 μm, aspect ratio: 40) in 3.16 g of N,N-dimethylacetamide (DMAc), and the target γ-alumina-containing polyimide film was obtained in the same manner as in Example 1, except that the γ-alumina dispersion was added to the polyamic acid solution instead of the α-alumina dispersion. The volume ratio of γ-alumina to the total volume of this γ-alumina-containing polyimide film was determined to be 2.6% by volume.

[0125] Furthermore, the physical properties of the obtained γ-alumina-containing polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 37.5 ppm / K, the total light transmittance was 86.1%, the yellowness index (YI) was 5.1, and the haze was 20.67%.

[0126] Comparative Example 4 The target polyimide film was obtained in the same manner as in Example 11, except that no α-alumina dispersion was added to the polyamic acid solution (i.e., no α-alumina was added to the polyamic acid solution prepared in this comparative example).

[0127] The physical properties of the obtained polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 40.3 ppm / K, the total light transmittance was 87.4%, the yellowness index (YI) was 4.2, and the haze was 0.2%.

[0128] Comparative Example 5 A target polyimide film was obtained in the same manner as in Example 12, except that no α-alumina dispersion was added to the polyamic acid solution (i.e., no α-alumina was added to the polyamic acid solution prepared in this comparative example).

[0129] The physical properties of the obtained polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 37.5 ppm / K, the total light transmittance was 87.0%, the yellowness index (YI) was 4.5, and the haze was 0.2%.

[0130] Comparative Example 6 A target polyimide film was obtained in the same manner as in Example 13, except that no α-alumina dispersion was added to the polyamic acid solution (i.e., no α-alumina was added to the polyamic acid solution prepared in this comparative example).

[0131] The physical properties of the obtained polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 34.1 ppm / K, the total light transmittance was 87.0%, the yellowness index (YI) was 5.0, and the haze was 0.1%.

[0132] Comparative Example 7 A target polyimide film was obtained in the same manner as in Example 14, except that no α-alumina dispersion was added to the polyamic acid solution (i.e., no α-alumina was added to the polyamic acid solution prepared in this comparative example).

[0133] The physical properties of the obtained polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 31.9 ppm / K, the total light transmittance was 86.0%, the yellowness index (YI) was 5.1, and the haze was 0.1%.

[0134] Comparative Example 8 A target polyimide film was obtained in the same manner as in Example 15, except that no α-alumina dispersion was added to the polyamic acid solution (i.e., no α-alumina was added to the polyamic acid solution prepared in this comparative example).

[0135] The physical properties of the obtained polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 40.8 ppm / K, the total light transmittance was 87.5%, the yellowness index (YI) was 4.0, and the haze was 0.9%.

[0136] Comparative Example 9 The target polyimide film was obtained in the same manner as in Example 19, except that no α-alumina dispersion was added to the polyamic acid solution (i.e., no α-alumina was added to the polyamic acid solution prepared in this comparative example).

[0137] The physical properties of the obtained polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 47.5 ppm / K, the total light transmittance was 87.6%, the yellowness index (YI) was 4.9, and the haze was 0.2%.

[0138] Furthermore, a copper-plated substrate was prepared from the polyimide film obtained above by the same method as in Example 20. This copper-plated substrate was then cut into a size of 55 mm × 3 mm to obtain a measurement substrate, and the peel strength between the polyimide film on this measurement substrate and an underlayer (metal layer) made of a nickel-20% by mass chromium alloy on which a copper coating was formed was measured by the same method as in Example 20, and the peel strength was found to be 161.5 N / m.

[0139] Comparative Example 10 A target polyimide film was obtained in the same manner as in Example 19, except that no α-alumina dispersion was added to the polyamic acid solution (i.e., no α-alumina was added to the polyamic acid solution prepared in this comparative example).

[0140] Furthermore, a copper-plated substrate was prepared from the polyimide film obtained above by the same method as in Example 21. This copper-plated substrate was then cut into a size of 55 mm × 3 mm to obtain a measurement substrate, and the peel strength between the polyimide film on this measurement substrate and the underlayer (metal layer) made of a nickel-20% by mass chromium alloy on which a copper coating was formed was measured by the same method as in Example 20, and the peel strength was found to be 125.7 N / m.

[0141] Comparative Example 11 A target polyimide film was obtained in the same manner as in Example 19, except that no α-alumina dispersion was added to the polyamic acid solution (i.e., no α-alumina was added to the polyamic acid solution prepared in this comparative example).

[0142] Furthermore, a copper-plated substrate was prepared from the polyimide film obtained above in the same manner as in Example 22. This copper-plated substrate was then cut into a size of 55 mm × 3 mm to obtain a measurement substrate, and the peel strength between the polyimide film and an aluminum underlayer (metal layer) on which a copper coating was formed was measured in the same manner as in Example 20, resulting in a peel strength of 83.9 N / m.

[0143] Comparative Example 12 A target polyimide film was obtained in the same manner as in Example 19, except that no α-alumina dispersion was added to the polyamic acid solution (i.e., no α-alumina was added to the polyamic acid solution prepared in this comparative example).

[0144] Furthermore, a copper-plated substrate was prepared from the polyimide film obtained above in the same manner as in Example 23. This copper-plated substrate was then cut into a size of 55 mm × 3 mm to obtain a measurement substrate, and the peel strength between the polyimide film and a silver underlayer (metal layer) on which a copper coating was formed was measured in the same manner as in Example 20, resulting in a peel strength of 113.1 N / m.

[0145] The peel strengths in Examples 20-23 and Comparative Examples 9-12 are shown in Table 1.

[0146]

[0147] Comparative Example 13 A target polyimide film was obtained in the same manner as in Example 24, except that no α-alumina dispersion was added to the polyamic acid solution (i.e., no α-alumina was added to the polyamic acid solution prepared in this comparative example).

[0148] The physical properties of the obtained polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 39.9 ppm / K, the total light transmittance was 88.3%, the yellowness index (YI) was 3.3, and the haze was 0.12%.

[0149] Comparative Example 14 A target polyimide film was obtained in the same manner as in Example 25, except that no α-alumina dispersion was added to the polyamic acid solution (i.e., no α-alumina was added to the polyamic acid solution prepared in this comparative example).

[0150] The physical properties of the obtained polyimide film were measured in the same manner as in Example 1. The linear expansion coefficient was 40.1 ppm / K, the total light transmittance was 89.5%, the yellowness index (YI) was 2.6, and the haze was 0.21%.

[0151] Reference Example 1 A target silica-containing polyimide film was obtained in the same manner as in Example 2, except that (a) a silica dispersion was prepared by dispersing 0.019 g of silica (manufacturer: Fuji Silysia Scientific Ltd., product name: Sylysia, product number: 310P, shape: spherical, particle size: 2 μm) in 0.038 g of N,N-dimethylacetamide (DMAc), and the silica dispersion was added to the polyamic acid solution instead of the α-alumina dispersion, and (b) 2000 ppm of an internal release agent and 0.5 mass % of an antifoaming agent were added relative to the solid content of the polyamic acid solution.

[0152] Silica does not volatilize even at 280°C, nor is it converted into other substances. Based on this fact, the above-mentioned amount of silica added and density (2.20 g / cm ３ ) and the solids concentration of the polyamic acid and the density of the polyimide (1.35 g / cm ３ The volume percentage of silica relative to the total volume of the silica-containing polyimide film finally obtained from the above mixture was calculated to be 0.05% by volume.

[0153] The physical properties of the obtained silica-containing polyimide film were measured in the same manner as in Example 1, and the linear expansion coefficient was 44.5 ppm / K, the total light transmittance was 87.7%, the yellowness index (YI) was 3.2, and the haze was 2.00%. The anti-blocking performance of this silica-containing polyimide film was also confirmed to be sufficient.

[0154] <Discussion of Examples, Comparative Examples, and Reference Examples> It was found that the yellowness index (YI) and linear expansion coefficient of each of the α-alumina-containing polyimide films obtained in Examples 1 to 5 were reduced compared to the polyimide film obtained in Comparative Example 1, the boehmite-containing polyimide film obtained in Comparative Example 2, and the γ-alumina-containing polyimide film obtained in Comparative Example 3. It was also found that the yellowness index (YI) and linear expansion coefficient of the α-alumina-containing polyimide film obtained in Example 24 were reduced compared to the polyimide film obtained in Comparative Example 13, and that the yellowness index (YI) and linear expansion coefficient of the α-alumina-containing polyimide film obtained in Example 25 were reduced compared to the polyimide film obtained in Comparative Example 14. In other words, it was found that the yellowness index (YI) and linear expansion coefficient of a polyimide film can be reduced as long as it is α-alumina, regardless of the manufacturer, trade name, or product number. Furthermore, a graph showing the effect of the aspect ratio of α-alumina on the yellowness index (YI) of the α-alumina-containing polyimide films according to Examples 1 to 5 is shown in Figure 1, and a graph showing the effect of the aspect ratio of α-alumina on the linear expansion coefficient of the α-alumina-containing polyimide films according to Examples 1 to 5 is shown in Figure 2. As shown in Figures 1 and 2, it was revealed that the yellowness index (YI) and linear expansion coefficient of the α-alumina-containing polyimide films decreased as the aspect ratio of α-alumina increased.

[0155] Based on the results of Examples 1 and 6-10, a graph showing the effect of the α-alumina content on the yellowness index (YI) of the α-alumina-containing polyimide film is shown in Figure 3, and a graph showing the effect of the α-alumina content on the linear expansion coefficient of the α-alumina-containing polyimide film is shown in Figure 4. As shown in Figures 3 and 4, it was revealed that the yellowness index (YI) and linear expansion coefficient of the α-alumina-containing polyimide film decreased as the α-alumina content increased. In other words, it was suggested that the yellowness index (YI) and linear expansion coefficient of the α-alumina-containing polyimide film could be controlled by controlling the α-alumina content.

[0156] Furthermore, based on the results of Examples 11 to 14 and Comparative Examples 4 to 7, a graph showing the effect of the molar ratio of TFMB on the yellowness index (YI) of an α-alumina-containing polyimide film and a polyimide film is shown in Figure 5, and a graph showing the effect of the molar ratio of TFMB on the linear expansion coefficient of an α-alumina-containing polyimide film and a polyimide film is shown in Figure 6. As shown in Figures 5 and 6, it became clear that the effect of adding α-alumina, i.e., the effect of reducing the yellowness index (YI) and the linear expansion coefficient, can be obtained even for films made of polyimides with different compositions.

[0157] Furthermore, the results of Examples 17 and 18 revealed that even if an internal mold release agent or an antifoaming agent is mixed into an α-alumina-containing polyimide film, the yellowness index (YI) and linear expansion coefficient reducing effect of α-alumina can be fully enjoyed.

[0158] Furthermore, the results of Examples 6 and 18 reveal that when the content of α-alumina in an α-alumina-containing polyimide film exceeds a certain value, α-alumina functions as an antiblocking agent.

[0159] Finally, the results of Examples 20-23 and Comparative Examples 9-12 demonstrated that the peel strength between the α-alumina-containing polyimide film according to the present invention and an underlayer (metal layer) made of a nickel-chromium alloy, aluminum, or silver was higher than that of a polyimide film not containing α-alumina (α-alumina-free polyimide film). This demonstrates that the α-alumina-containing polyimide film has higher adhesion to a metal layer than the α-alumina-free polyimide film.

[0160] The film according to the present invention exhibits a lower yellowness index (YI) and linear expansion coefficient than polyimide films composed solely of the same polyimide resin. Furthermore, the film according to the present invention has high adhesion to metals. Therefore, the film according to the present invention can be used, for example, as components and members of electrical and electronic devices, components and members other than electrical and electronic devices, heat-resistant tape, and substrates, boards, and coverlays constituting solar cells (e.g., silicon solar cells, perovskite solar cells, etc.). Examples of substrates constituting solar cells (e.g., silicon solar cells, perovskite solar cells, etc.) include terrestrial solar panels and space solar panels. Examples of substrates include circuit boards for mounting light-emitting elements and substrates for printing barcodes. Examples of electrical and electronic devices include computers (e.g., personal computers, smartphones, foldable smartphones, automobile control devices, car navigation devices, etc.), television receivers, wearable devices (e.g., AR / VR glasses, smart watches, etc.), lighting equipment, display devices (e.g., computer displays, large display devices, large vision devices, LED display devices, LED vision devices, various monitors such as digital signage), MRI, and automobile headlights. Examples of parts and members of electrical and electronic devices include flexible printed circuit boards (FPC), antennas, OSRs (optical solar reflectors), LiDAR, home and office lighting, designer lighting, transparent antennas, electromagnetic wave shields, and direct LED back panel reflectors. Examples of parts and members that are not electrical or electronic devices include conference room partitions, office window glass, car headlight window glass, glass surfaces of buildings and automobiles, aircraft and automobile windows, and packaging materials.

Claims

1. Polyimide film containing α-alumina.

2. The polyimide film according to claim 1, comprising as its main component a polyimide resin comprising at least one acid-derived moiety selected from the group consisting of biphenyltetracarboxylic acid compound (BPDA)-derived moieties and 2,2-bis[3,4-(dicarboxyphenoxy)phenyl]propane compound (BPADA)-derived moieties, and at least one diamine-derived moiety selected from the group consisting of 2,2'-bis(trifluoromethyl)benzidine (TFMB)-derived moieties and 3,3'-diaminodiphenylsulfone (3,3'-DDS)-derived moieties.

3. The polyimide film according to claim 1, comprising as its main component a polyimide resin comprising at least one acid-derived moiety selected from the group consisting of biphenyltetracarboxylic acid compound (BPDA)-derived moieties and 4,4'-(hexafluoroisopropylidene)diphthalic acid compound (6FDA)-derived moieties, and at least one diamine-derived moiety selected from the group consisting of 2,2'-bis(trifluoromethyl)benzidine (TFMB)-derived moieties and 3,3'-diaminodiphenylsulfone (3,3'-DDS)-derived moieties.

4. The polyimide film according to claim 2 or 3, wherein the diamine-derived moieties include both the 2,2'-bis(trifluoromethyl)benzidine (TFMB)-derived moieties and the 3,3'-diaminodiphenyl sulfone (3,3'-DDS)-derived moieties, and the molar ratio of the 2,2'-bis(trifluoromethyl)benzidine (TFMB)-derived moieties to the 3,3'-diaminodiphenyl sulfone (3,3'-DDS)-derived moieties is within the range of 1 or more and 4 or less.

5. The polyimide film according to claim 1, comprising as a main component a polyimide resin comprising at least one acid-derived moiety selected from the group consisting of biphenyltetracarboxylic acid compound (BPDA)-derived moieties and 2,2-bis[3,4-(dicarboxyphenoxy)phenyl]propane compound (BPADA)-derived moieties, and at least one diamine-derived moiety selected from the group consisting of 2,2'-bis(trifluoromethyl)benzidine (TFMB)-derived moieties and 4,4'-diaminodiphenylsulfone (4,4'-DDS)-derived moieties.

6. The polyimide film according to claim 5, wherein the diamine-derived moieties include both the 2,2'-bis(trifluoromethyl)benzidine (TFMB)-derived moieties and the 4,4'-diaminodiphenyl sulfone (4,4'-DDS)-derived moieties, and the molar ratio of the 2,2'-bis(trifluoromethyl)benzidine (TFMB)-derived moieties to the 4,4'-diaminodiphenyl sulfone (4,4'-DDS)-derived moieties is within the range of 1 or more and 4 or less.

7. The polyimide film according to claim 1, wherein the α-alumina is plate-shaped and has an aspect ratio of 2 or more.

8. The polyimide film according to claim 1, wherein the particle size of the α-alumina is in the range of more than 0.2 μm to 8 μm.

9. The polyimide film according to claim 1, which has a yellowness index of less than 5.

10. The polyimide film of claim 9, which has a haze of less than 15%.

11. The polyimide film according to claim 1, which has a linear expansion coefficient of less than 47 ppm / K.

12. A laminate comprising the polyimide film according to claim 1 and a metal layer of any one of nickel-chromium alloy, aluminum and silver laminated to the polyimide film.

13. The laminate of claim 12, further comprising a layer of copper laminated to said metal layer.

14. A polyimide film yellowing reducing agent containing α-alumina as the active ingredient.

15. A material that reduces the linear expansion coefficient of polyimide film, with α-alumina as the active ingredient.

16. A material that improves the adhesion of polyimide films to metals, with α-alumina as the active ingredient.

17. The metal adhesion improving material according to claim 16, wherein the metal is a nickel-chromium alloy, aluminum, or silver.

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