Sheet material and method for producing sheet material

Abstract

This sheet material includes: a graphene layer including graphene; and a highly heat-resistant transparent polyimide film. The highly heat-resistant transparent polyimide film has a glass transition temperature of 300°C or more and a yellowness index of 10 or less.

Description

Sheet material and method for manufacturing the sheet material

[0001] The present invention relates to a sheet material and a method for manufacturing the sheet material.

[0002] In recent years, flexible transparent conductive films have been attracting attention for applications in solar cells, touch panels, etc. Graphene has excellent physical properties, such as high carrier mobility, high visible light transmittance, and flexibility, making it a promising material for flexible transparent conductive films.

[0003] Patent Document 1 discloses a transparent electrode manufactured using a PET (polyethylene terephthalate)-graphene single-layer laminate in which a graphene single layer is formed on a PET substrate (particularly, paragraphs

[0113] to

[0118] ).

[0004] Japanese Patent Application Laid-Open No. 2017-092031

[0005] In Patent Document 1, a graphene single layer is deposited on one surface of a copper (Cu) foil by chemical vapor deposition (CVD), a polymethyl methacrylate (hereinafter also referred to as PMMA) layer is formed on the deposited graphene single layer, the copper foil is then removed by etching, and the graphene single layer with the PMMA layer formed thereon is transferred onto a PET substrate, and the PMMA layer is then removed, thereby obtaining a PET-graphene single layer laminate in which the graphene single layer is formed on the PET substrate (see, in particular, paragraph

[0114] ).

[0006] However, the present inventors found that the PET substrate has low heat resistance, and it is difficult to remove the PMMA residue left behind during transfer by heat treatment, which poses a problem in improving the electrical properties of the transferred graphene.

[0007] The present inventors have conducted extensive research into this issue and have found that by using a specific highly heat-resistant, transparent polyimide film as a substrate, it is possible to provide a sheet material that can realize a graphene transparent conductive film that has high heat resistance, sufficient transparency, and good electrical properties, and have thereby completed the present invention.

[0008] The present invention provides the following: [1] A sheet material comprising: a graphene layer having graphene; and a highly heat-resistant, transparent polyimide film, wherein the highly heat-resistant, transparent polyimide film has a glass transition temperature of 300°C or higher and a yellowness index of 10 or lower.

[0009] According to the above configuration, a highly heat-resistant, transparent polyimide film having a glass transition temperature of 300°C or higher and a yellowness index of 10 or lower is used as the substrate. That is, a highly heat-resistant, transparent polyimide film having high heat resistance and sufficient transparency is used as the substrate. Furthermore, the graphene layer has high heat resistance and sufficient transparency. Therefore, a sheet material composed of a graphene layer and a highly heat-resistant, transparent polyimide film as a whole has high heat resistance and sufficient transparency. Furthermore, since the highly heat-resistant, transparent polyimide film has a glass transition temperature of 300°C or higher and excellent heat resistance, it is possible to remove foreign matter, etc. on the sheet material by heat treatment, for example. As a result, electrical properties can be improved. As described above, according to the above configuration, it is possible to realize a graphene transparent conductive film having high heat resistance, sufficient transparency, and excellent electrical properties.

[0010] [2] The sheet material according to [1] above, having a sheet resistance of 1200 Ω / sq or less.

[0011] If the sheet resistance is 1200 Ω / sq or less, it can be suitably used as a conductive film.

[0012] [3] Carrier mobility is 900 cm ２ The sheet material according to [1] or [2], wherein the resistivity is / Vs or more.

[0013] The sheet material has high heat resistance, and foreign matter on the sheet material can be removed by heat treatment. Removing foreign matter on the sheet material by heat treatment improves carrier mobility. This is also clear from the examples. When used as a conductive film, low sheet resistance is preferable, but the sheet resistance decreases as the carrier mobility increases. Therefore, when the carrier mobility is 900 cm ２ When the resistivity is / Vs or more, the film can be suitably used as a conductive film.

[0014] [4] The sheet material according to any one of [1] to [3], which has a light transmittance of 80% or more at a wavelength of 550 nm.

[0015] If the light transmittance at a wavelength of 550 nm is 80% or more, it can be said that the film has sufficient transparency.

[0016] [5] The sheet material according to any one of [1] to [4], wherein the graphene layer is a graphene layer having 3 to 7 layers, where 1 layer has a thickness of 1 atom.

[0017] The sheet resistance of the graphene layer decreases as the number of layers increases. On the other hand, the light transmittance decreases as the number of layers increases. Therefore, when the graphene layer has 3 to 7 layers, the sheet resistance is sufficiently low and the light transmittance is high.

[0018] Furthermore, the present invention provides the following: [6] The sheet material according to claim 1 or 2, characterized in that the surface of the highly heat-resistant transparent polyimide film on which the graphene layer is laminated has a surface roughness Ra of 0.2 nm or more and 2.0 nm or less.

[0019] When the surface roughness Ra is 0.2 nm or more and 2.0 nm or less, the stacked graphene layers tend to be homogeneous and have excellent adhesion.

[0020] The present invention further provides the following: [7] A method for producing a sheet material according to any one of [1] to [6] above, comprising: a step A of preparing a highly heat-resistant, transparent polyimide film; and a step B of providing a graphene layer on the highly heat-resistant, transparent polyimide film, wherein the highly heat-resistant, transparent polyimide film has a glass transition temperature of 300°C or higher and a yellowness index of 10 or lower.

[0021] According to the method for producing the sheet material, it is possible to obtain a sheet material that is capable of realizing a graphene transparent conductive film that has high heat resistance, sufficient transparency, and good electrical properties.

[0022] According to the present invention, it is possible to provide a sheet material capable of realizing a graphene transparent conductive film having high heat resistance, sufficient transparency, and good electrical properties, and also to provide a method for manufacturing the sheet material.

[0023] 1 is a graph showing film formation conditions (time, temperature, gas) according to Example 1. FIG. 2 is a diagram showing transmission spectra of 1-layer to 4-layer graphene. FIG. 3 is a diagram showing transmission spectra of the sheet material of Example 3 and a polyimide film alone. FIG. 4 is a diagram showing a Hall bar used in Hall effect measurement. FIG. 5 is a schematic diagram of an apparatus for applying a silane coupling agent to a quartz glass substrate.

[0024] Hereinafter, an embodiment of the present invention will be described.

[0025] <Sheet Material> The sheet material according to this embodiment includes a graphene layer having graphene and a highly heat-resistant transparent polyimide film.

[0026] <Graphene layer> "Graphene" is a single-atom-thick sp ２ It is a sheet-like substance of bonded carbon atoms. In this specification, a "graphene layer" is sufficient as long as it has graphene, and may be a single graphene (a sheet-like graphene with a thickness of one atom) or a stack of two or more graphenes. In this specification, a layer made of a single graphene (a sheet-like graphene with a thickness of one atom) may be referred to as a "single-layer graphene layer," and a layer made of two stacked graphenes (sheet-like graphene with a thickness of two atoms) may be referred to as a "two-layer graphene layer."

[0027] The number of graphene layers (the number of sheet-like graphene sheets) constituting the graphene layer is not particularly limited, and may be 1 or more. Here, the sheet resistance of the graphene layer decreases as the number of graphene layers (the number of sheet-like graphene sheets) increases. On the other hand, the light transmittance decreases as the number of graphene layers increases. Therefore, from the viewpoint of achieving both transparency and electrical properties, the number of graphene layers constituting the graphene layer is preferably 3 or more and 7 or less, and more preferably 3 or more and 5 or less. When the number of graphene layers is 3 or more and 7 or less, the graphene layer has a sufficiently low sheet resistance and a high light transmittance.

[0028] The graphene layer may be doped with a doping material to improve the carrier concentration. Doping the graphene layer with a doping material can improve the carrier concentration of the sheet material. The doping material is not particularly limited as long as it can improve the carrier concentration, and can be selected from, for example, bis(trifluoromethane-sulfonyl)amine (TFSA), nitric acid, gold chloride, palladium chloride, iron chloride, silver chloride, platinum chloride, gold iodide, and the like. Doping can be chemical doping, in which the doping material is applied to the graphene layer by spin coating or the like, and the doping material is chemically adsorbed to the graphene layer. The doping amount can be adjusted by adjusting the solution concentration and the rotation speed of the spin coater during spin coating to achieve the desired carrier concentration. Doping can also be performed by intercalation, in which the doping material is inserted between graphene layers.

[0029] <Highly Heat-Resistant Transparent Polyimide Film> The highly heat-resistant transparent polyimide film (hereinafter also simply referred to as "polyimide film") has a glass transition temperature of 300°C or higher. Since this results in better heat resistance, the glass transition temperature is preferably 350°C or higher, more preferably 375°C or higher, and even more preferably 400°C or higher. The glass transition temperature of the polyimide film is measured by the method described in the Examples. Since the glass transition temperature of the polyimide film is 300°C or higher, it can be said that the heat resistance is high.

[0030] The polyimide film has a yellowness index (hereinafter also referred to as "yellow index" or "YI") of 10 or less. Since transparency is improved, the yellowness index is preferably 8 or less, more preferably 7 or less, even more preferably 6 or less, still more preferably 5 or less, even more preferably 4 or less, and particularly preferably 3 or less. The lower limit of the yellowness index of the polyimide film is not particularly limited, but is, for example, 0.1 or more, 0.2 or more, 0.3 or more, etc. The yellowness index of the polyimide film is measured by the method described in the Examples. Since the yellowness index of the polyimide film is 10 or less, it can be said to have sufficient transparency.

[0031] The polyimide film is not particularly limited as long as it has a glass transition temperature of 300°C or higher, a yellowness index of 10 or less, and a polyimide structure. Examples include aromatic polyimide films, aliphatic polyimide films, alicyclic polyimide films, aromatic polyamideimide films, aliphatic polyamideimide films, alicyclic polyamideimide films, and mixtures thereof. Preferred are aromatic polyimide films, aliphatic polyimide films, and alicyclic polyimide films. Polyimide films are generally obtained by applying a polyamic acid (polyimide precursor) solution obtained by reacting diamines and tetracarboxylic acids in a solvent to a polyimide film preparation support, drying the solution to form a green film (hereinafter also referred to as a "polyamic acid film"), and then subjecting the green film to high-temperature heat treatment on the polyimide film preparation support or after peeling it off the support to cause a dehydration ring-closing reaction.

[0032] The polyamic acid (polyimide precursor) solution can be applied by any of the conventionally known solution application methods, such as spin coating, doctor blade, applicator, comma coater, screen printing, slit coating, reverse coating, dip coating, curtain coating, and slit die coating.

[0033] Examples of aromatic tetracarboxylic acids for obtaining colorless and highly transparent polyimides include 4,4'-(2,2-hexafluoroisopropylidene)diphthalic acid, 4,4'-oxydiphthalic acid, bis(1,3-dioxo-1,3-dihydro-2-benzofuran-5-carboxylic acid)1,4-phenylene, bis(1,3-dioxo-1,3-dihydro-2-benzofuran-5-yl)benzene-1,4-dicarboxylate, 4,4'-[4,4'-(3-oxo-1,3-dihydro-2-benzofuran-1,1-diyl)bis(benzene-1,4-diyloxy)] ]dibenzene-1,2-dicarboxylic acid, 3,3',4,4'-benzophenonetetracarboxylic acid, 4,4'-[(3-oxo-1,3-dihydro-2-benzofuran-1,1-diyl)bis(toluene-2,5-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4'-[(3-oxo-1,3-dihydro-2-benzofuran-1,1-diyl)bis(1,4-xylene-2,5-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4'-[4,4'-(3-oxo-1,3-dihydro-2-benzofuran-1,1-diyl)bis(4 -isopropyl-toluene-2,5-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4'-[4,4'-(3-oxo-1,3-dihydro-2-benzofuran-1,1-diyl)bis(naphthalene-1,4-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4'-[4,4'-(3H-2,1-benzoxathiol-1,1-dioxide-3,3-diyl)bis(benzene-1,4-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4'-benzophenonetetracarboxylic acid, 4,4'-[(3H-2,1-benzo 4,4'-[(3H-2,1-benzoxathiol-1,1-dioxide-3,3-diyl)bis(toluene-2,5-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4'-[(3H-2,1-benzoxathiol-1,1-dioxide-3,3-diyl)bis(1,4-xylene-2,5-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4'-[4,4'-(3H-2,1-benzoxathiol-1,1-dioxide-3,3-diyl)bis(4-isopropyl-toluene-2,5-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4'-[4,4'-(3H-2,1-benzoxathiol-1,1-dioxide-3,3-diyl)bis(naphthalene-1,4-diyloxy)]dibenzene-1,2-dicarboxylic acid, 3,3',4,4'-benzophenonetetracarboxylic acid, 3,3',4,4'-benzophenonetetracarboxylic acid, 3,3',4,4'-diphenylsulfonetetracarboxylic acid, 3,3',4,4'-biphenyltetracarboxylic acid, 2,3,3',4'-biphenyltetracarboxylic acid, pyromellitic acid, 4,4'-[spiro(xanthene-9,9'-fluorene)-2,6-diylbis(oxycarbonyl)]diphthalic acid, 4,4'-[spiro(xanthene-9,9'-fluorene)-3,6-diylbis(oxycarbonyl)]diphthalic acid, and tetracarboxylic acids such as these acid anhydrides. Among these, dianhydrides having two acid anhydride structures are preferred, and 4,4'-(2,2-hexafluoroisopropylidene)diphthalic dianhydride, 4,4'-oxydiphthalic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, and pyromellitic dianhydride are particularly preferred. The aromatic tetracarboxylic acids may be used alone or in combination of two or more. When heat resistance is important, the copolymerization amount of the aromatic tetracarboxylic acids is, for example, preferably 50% by mass or more of the total tetracarboxylic acids, more preferably 60% by mass or more, even more preferably 70% by mass or more, still more preferably 80% by mass or more, and particularly preferably 90% by mass or more, and may even be 100% by mass.

[0034] Examples of alicyclic tetracarboxylic acids include 1,2,3,4-cyclobutanetetracarboxylic acid, 1,2,3,4-cyclopentanetetracarboxylic acid, 1,2,3,4-cyclohexanetetracarboxylic acid, 1,2,4,5-cyclohexanetetracarboxylic acid, 3,3',4,4'-bicyclohexyltetracarboxylic acid, bicyclo[2,2,1]heptane-2,3,5,6-tetracarboxylic acid, bicyclo[2,2,2]octane-2,3,5,6-tetracarboxylic acid, and bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic acid. carboxylic acid, tetrahydroanthracene-2,3,6,7-tetracarboxylic acid, tetradecahydro-1,4:5,8:9,10-trimethanoanthracene-2,3,6,7-tetracarboxylic acid, decahydronaphthalene-2,3,6,7-tetracarboxylic acid, decahydro-1,4:5,8-dimethanonaphthalene-2,3,6,7-tetracarboxylic acid, decahydro-1,4-ethano-5,8-methanonaphthalene-2,3,6,7-tetracarboxylic acid, norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane -5,5'',6,6''-tetracarboxylic acid (also known as "norbornane-2-spiro-2'-cyclopentanone-5'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid"), methylnorbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-(methylnorbornane)-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclohexanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid (also known as "norbornane-2-spiro-α-cyclohexanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid pyro-2'-cyclohexanone-6'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid), methylnorbornane-2-spiro-α-cyclohexanone-α'-spiro-2''-(methylnorbornane)-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclopropanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclobutanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cycloheptanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclooctanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclononanone-α'-spiro-2''-norbornane-5,5'',6 ,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclodecanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cycloundecanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclododecanone-α'-spiro-2''-norbornane-5,5'', ,6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclotridecanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclotetradecanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclopentadecanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-(methylcyclopentanone)-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, and norbornane-2-spiro-α-(methylcyclohexanone)-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, and tetracarboxylic acids such as these acid anhydrides. Among these, dianhydrides having two acid anhydride structures are preferred, and in particular, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclohexanetetracarboxylic dianhydride, and 1,2,4,5-cyclohexanetetracarboxylic dianhydride are preferred, and 1,2,3,4-cyclobutanetetracarboxylic dianhydride and 1,2,4,5-cyclohexanetetracarboxylic dianhydride are more preferred, and 1,2,3,4-Cyclobutanetetracarboxylic dianhydride is more preferred. These may be used alone or in combination of two or more. When transparency is important, the copolymerization amount of the alicyclic tetracarboxylic acids is, for example, preferably 50% by mass or more of the total tetracarboxylic acids, more preferably 60% by mass or more, even more preferably 70% by mass or more, still more preferably 80% by mass or more, and particularly preferably 90% by mass or more, and may even be 100% by mass.

[0035] Examples of tricarboxylic acids include aromatic tricarboxylic acids such as trimellitic acid, 1,2,5-naphthalenetricarboxylic acid, diphenylether-3,3',4'-tricarboxylic acid, and diphenylsulfone-3,3',4'-tricarboxylic acid, as well as hydrogenated products of the above aromatic tricarboxylic acids such as hexahydrotrimellitic acid, alkylene glycol bistrimellitates such as ethylene glycol bistrimellitate, propylene glycol bistrimellitate, 1,4-butanediol bistrimellitate, and polyethylene glycol bistrimellitate, and monoanhydrides and esterified products thereof. Among these, monoanhydrides having one acid anhydride structure are preferred, with trimellitic anhydride and hexahydrotrimellitic anhydride being particularly preferred. These may be used alone or in combination.

[0036] Examples of dicarboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, and 4,4'-oxydibenzenecarboxylic acid, as well as hydrogenated versions of these aromatic dicarboxylic acids such as 1,6-cyclohexanedicarboxylic acid, oxalic acid, succinic acid, glutaric acid, adipic acid, heptanedioic acid, octanedioic acid, azelaic acid, sebacic acid, undecadioic acid, dodecanedioic acid, and 2-methylsuccinic acid, as well as acid chlorides and esters thereof. Among these, aromatic dicarboxylic acids and hydrogenated versions thereof are preferred, with terephthalic acid, 1,6-cyclohexanedicarboxylic acid, and 4,4'-oxydibenzenecarboxylic acid being particularly preferred. The dicarboxylic acids may be used alone or in combination.

[0037] The diamines or isocyanates used to obtain colorless and highly transparent polyimides are not particularly limited, and aromatic diamines, aliphatic diamines, alicyclic diamines, aromatic diisocyanates, aliphatic diisocyanates, alicyclic diisocyanates, and the like, which are commonly used in polyimide synthesis, polyamideimide synthesis, and polyamide synthesis, can be used. From the viewpoint of heat resistance, aromatic diamines are preferred, and from the viewpoint of transparency, alicyclic diamines are preferred. Furthermore, the use of aromatic diamines having a benzoxazole structure makes it possible to achieve high heat resistance, as well as a high elastic modulus, low heat shrinkage, and a low coefficient of linear expansion. Diamines and isocyanates can be used alone or in combination of two or more.

[0038] Examples of aromatic diamines include 2,2'-dimethyl-4,4'-diaminobiphenyl, 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene, 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene, 2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl, 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-bis(3-aminophenoxy)biphenyl, bis[4-(3-aminophenoxy)phenyl]ketone, bis[4-(3-aminophenoxy)phenyl]sulfide, bis[4 -(3-aminophenoxy)phenyl]sulfone, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2-bis[4-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, m-aminobenzylamine, p-aminobenzylamine, 4-amino-N-(4-aminophenyl)benzamide, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 2,2'-trifluoromethyl-4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfoxide, 3,4'-diaminodiphenyl sulfoxide, 4,4'-diaminodiphenyl sulfoxide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminobenzophenone, 3,4'-diaminobenzophenone, 4, 4'-Diaminobenzophenone, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, bis[4-(4-aminophenoxy)phenyl]methane, 1,1-bis[4-(4-aminophenoxy)phenyl]ethane, 1,2-bis[4-(4-aminophenoxy)phenyl]ethane, 1,1-bis[4-(4-aminophenoxy)phenyl]propane, 1,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,3-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,1-bis[4-(4-aminophenoxy)phenyl]butane, 1,3-bis[4-(4-aminophenoxy)phenyl]butane, 1,4-bis[4-(4-aminophenoxy)phenyl]butane, 2,2-bis[4-(4-aminophenoxy)phenyl]butane, 2,3-bis[4-(4-aminophenoxy)phenyl]butane, 2-[4-(4-aminophenoxy)phenyl]-2-[4-(4-aminophenoxy)-3-methylphenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl] 2-[4-(4-aminophenoxy)phenyl]-2-[4-(4-aminophenoxy)-3,5-dimethylphenyl]propane, 2,2-bis[4-(4-aminophenoxy)-3,5-dimethylphenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 1,4-bis(3-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 4,4'-bis( 4-aminophenoxy)biphenyl, bis[4-(4-aminophenoxy)phenyl]ketone, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfoxide, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ether, 1,3-bis[4-(4-aminophenoxy)benzoyl]benzene, 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene, 1,4- Bis[4-(3-aminophenoxy)benzoyl]benzene, 4,4'-bis[(3-aminophenoxy)benzoyl]benzene, 1,1-bis[4-(3-aminophenoxy)phenyl]propane, 1,3-bis[4-(3-aminophenoxy)phenyl]propane, 3,4'-diaminodiphenyl sulfide, 2,2-bis[3-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, bis[4-(3-aminophenoxy)phenyl]methane, 1,1-bis[4-(3-aminophenoxy)phenyl]ethane, 1,2-bis[4-(3-aminophenoxy)phenyl]ethane, bis[4-(3-aminophenoxy)phenyl]sulfoxide, 4,4'-bis[3-(4-aminophenoxy)benzoyl]diphenyl ether, 4,4'-bis[3-(3-aminophenoxy)benzoyl]diphenyl ether, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzophenone, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]diphenyl sulfone, bis[4-{4-(4-aminophenoxy)pheno hydroxy}phenyl] sulfone, 1,4-bis[4-(4-aminophenoxy)phenoxy-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-aminophenoxy)phenoxy-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-amino-6-trifluoromethylphenoxy)-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-amino-6-fluorophenoxy)-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-amino-6-methylphenoxy)-α,α-dimethylbenzyl]benzene , 1,3-bis[4-(4-amino-6-cyanophenoxy)-α,α-dimethylbenzyl]benzene, 3,3'-diamino-4,4'-diphenoxybenzophenone, 4,4'-diamino-5,5'-diphenoxybenzophenone, 3,4'-diamino-4,5'-diphenoxybenzophenone, 3,3'-diamino-4-phenoxybenzophenone, 4,4'-diamino-5-phenoxybenzophenone, 3,4'-diamino-4-phenoxybenzophenone, 3,4'-diamino-5'-phenoxybenzophenone, 3,3'-diamino-4, 4'-diviphenoxybenzophenone, 4,4'-diamino-5,5'-diviphenoxybenzophenone, 3,4'-diamino-4,5'-diviphenoxybenzophenone, 3,3'-diamino-4-biphenoxybenzophenone, 4,4'-diamino-5-biphenoxybenzophenone, 3,4'-diamino-4-biphenoxybenzophenone, 3,4'-diamino-5'-biphenoxybenzophenone, 1,3-bis(3-amino-4-phenoxybenzoyl)benzene, 1,4-bis(3-amino-4-phenoxybenzoyl)benzene, 1,3-bis(4-amino-5-phenoxybenzoyl)benzene, 1,4-bis(4-amino-5-phenoxybenzoyl)benzene, 1,3-bis(3-amino-4-biphenoxybenzoyl)benzene, 1,4-bis(3-amino-4-biphenoxybenzoyl)benzene, 1,3-bis(4-amino-5-biphenoxybenzoyl)benzene, 1,4-bis(4-amino-5-biphenoxybenzoyl)benzene, 2,6-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzoni tolyl, 4,4'-[9H-fluorene-9,9-diyl]bisaniline (also known as "9,9-bis(4-aminophenyl)fluorene"), spiro(xanthene-9,9'-fluorene)-2,6-diylbis(oxycarbonyl)]bisaniline, 4,4'-[spiro(xanthene-9,9'-fluorene)-2,6-diylbis(oxycarbonyl)]bisaniline, 4,4'-[spiro(xanthene-9,9'-fluorene)-3,6-diylbis(oxycarbonyl)]bisaniline, etc. In addition, some or all of the hydrogen atoms on the aromatic ring of the aromatic diamine may be substituted with halogen atoms, alkyl or alkoxy groups having 1 to 3 carbon atoms, or cyano groups, and further some or all of the hydrogen atoms of the alkyl or alkoxy groups having 1 to 3 carbon atoms may be substituted with halogen atoms. The aromatic diamines having a benzoxazole structure are not particularly limited, and examples thereof include 5-amino-2-(p-aminophenyl)benzoxazole, 6-amino-2-(p-aminophenyl)benzoxazole, 5-amino-2-(m-aminophenyl)benzoxazole, 6-amino-2-(m-aminophenyl)benzoxazole, 2,2'-p-phenylenebis(5-aminobenzoxazole), 2,2'-p-phenylene Nylenebis(6-aminobenzoxazole), 1-(5-aminobenzoxazolo)-4-(6-aminobenzoxazolo)benzene, 2,6-(4,4'-diaminodiphenyl)benzo[1,2-d:5,4-d']bisoxazole, 2,6-(4,4'-diaminodiphenyl)benzo[1,2-d:4,5-d']bisoxazole, 2,6-(3,4'-diaminodiphenyl)benzo[1,2-d:5,4-d']bisoxazole, 2,Examples of the aromatic diamines include 6-(3,4'-diaminodiphenyl)benzo[1,2-d:4,5-d']bisoxazole, 2,6-(3,3'-diaminodiphenyl)benzo[1,2-d:5,4-d']bisoxazole, and 2,6-(3,3'-diaminodiphenyl)benzo[1,2-d:4,5-d']bisoxazole. Among these, 2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl, 4-amino-N-(4-aminophenyl)benzamide, 4,4'-diaminodiphenyl sulfone, and 3,3'-diaminobenzophenone are particularly preferred. The aromatic diamines may be used alone or in combination.

[0039] Examples of alicyclic diamines include 1,4-diaminocyclohexane, 1,4-diamino-2-methylcyclohexane, 1,4-diamino-2-ethylcyclohexane, 1,4-diamino-2-n-propylcyclohexane, 1,4-diamino-2-isopropylcyclohexane, 1,4-diamino-2-n-butylcyclohexane, 1,4-diamino-2-isobutylcyclohexane, 1,4-diamino-2-sec-butylcyclohexane, 1,4-diamino-2-tert-butylcyclohexane, and 4,4'-methylenebis(2,6-dimethylcyclohexylamine). Among these, 1,4-diaminocyclohexane and 1,4-diamino-2-methylcyclohexane are particularly preferred, and 1,4-diaminocyclohexane is more preferred. The alicyclic diamines may be used alone or in combination.

[0040] Examples of diisocyanates include diphenylmethane-2,4'-diisocyanate, 3,2'- or 3,3'- or 4,2'- or 4,3'- or 5,2'- or 5,3'- or 6,2'- or 6,3'-dimethyldiphenylmethane-2,4'-diisocyanate, 3,2'- or 3,3'- or 4,2'- or 4,3'- or 5,2'- or 5,3'- or 6,2'- or 6,3'-diethyl Diphenylmethane-2,4'-diisocyanate, 3,2'- or 3,3'- or 4,2'- or 4,3'- or 5,2'- or 5,3'- or 6,2'- or 6,3'-dimethoxydiphenylmethane-2,4'-diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-3,3'-diisocyanate, diphenylmethane-3,4'-diisocyanate, diphenylether-4,4' -diisocyanate, benzophenone-4,4'-diisocyanate, diphenylsulfone-4,4'-diisocyanate, tolylene-2,4-diisocyanate, tolylene-2,6-diisocyanate, m-xylylene diisocyanate, p-xylylene diisocyanate, naphthalene-2,6-diisocyanate, 4,4'-(2,2-bis(4-phenoxyphenyl)propane)diisocyanate, 3,3'- or 2,2'-dimethylbiphenyl-4,4'-diisocyanate, 3,3'- or 2,2'-di Examples of the diisocyanate include aromatic diisocyanates such as ethylbiphenyl-4,4'-diisocyanate, 3,3'-dimethoxybiphenyl-4,4'-diisocyanate, and 3,3'-diethoxybiphenyl-4,4'-diisocyanate, and diisocyanates obtained by hydrogenating any of these (for example, isophorone diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and hexamethylene diisocyanate).Among these, diphenylmethane-4,4'-diisocyanate, tolylene-2,4-diisocyanate, tolylene-2,6-diisocyanate, 3,3'-dimethylbiphenyl-4,4'-diisocyanate, naphthalene-2,6-diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and 1,4-cyclohexane diisocyanate are preferred from the viewpoints of low moisture absorption, dimensional stability, cost, and polymerizability. The diisocyanates may be used alone or in combination.

[0041] The thickness of the polyimide film is preferably 3 μm or more, more preferably 7 μm or more, even more preferably 14 μm or more, and even more preferably 20 μm or more. The upper limit of the thickness of the polyimide film is preferably 40 μm or less, more preferably 30 μm or less, in order to exhibit excellent optical properties. By keeping the thickness within the above range, the transparency and stiffness of the polyimide film are improved. Furthermore, the flexibility is improved.

[0042] The average coefficient of linear expansion (CTE) of the polyimide film between 30°C and 250°C is preferably 65 ppm / K or less. It is more preferably 55 ppm / K or less, even more preferably 45 ppm / K or less, even more preferably 35 ppm / K or less, particularly preferably 25 ppm / K or less, even more preferably 15 ppm / K or less, and particularly preferably 10 ppm / K or less. It is also preferably -5 ppm / K or more, more preferably -3 ppm / K or more, and even more preferably 1 ppm / K or more. When the CTE is within the above range, the difference in the coefficient of linear expansion between the polyimide film and a typical support (e.g., a glass substrate) can be kept small, and peeling between the polyimide film and the support or warping of the support can be avoided even when the polyimide film is subjected to a heat-applied process. Here, CTE is a factor that represents reversible expansion and contraction with temperature. The CTE of the polyimide film refers to the average value of the CTE in the coating direction (MD) of the polyimide solution or polyimide precursor solution and the CTE in the width direction (TD). The CTE of the polyimide film is measured by the method described in the Examples.

[0043] The polyimide film preferably has a total light transmittance of 75% or more. Since this results in good transparency, it is more preferably 80% or more, even more preferably 85% or more, even more preferably 87% or more, and particularly preferably 88% or more. There is no particular upper limit to the total light transmittance of the polyimide film, but for use as a flexible transparent conductive film, it is preferably 98% or less, more preferably 97% or less. By setting the total light transmittance of the polyimide film within the above range, good transparency (transparent polyimide film) is achieved. The total light transmittance of the polyimide film is measured according to the method described in the Examples.

[0044] The haze of the polyimide film is preferably 1.0 or less, more preferably 0.8 or less, even more preferably 0.5 or less, and even more preferably 0.3 or less. There is no particular lower limit, but from an industrial perspective, a haze of 0.01 or more is acceptable, and even 0.05 or more is acceptable. By setting the haze of the polyimide film within the above range, good transparency (transparent polyimide film) is obtained. The haze of the polyimide film is measured by the method described in the Examples.

[0045] The tensile breaking strength of the polyimide film is preferably 60 MPa or more, more preferably 80 MPa or more, and even more preferably 100 MPa or more. The upper limit of the tensile breaking strength is not particularly limited, but is practically less than about 1000 MPa. The tensile breaking strength of the polyimide film refers to the average value of the tensile breaking strength in the machine direction (MD) and the width direction (TD) of the polyimide film.

[0046] The tensile breaking elongation of the polyimide film is preferably 1% or more, more preferably 5% or more, and even more preferably 10% or more. When the tensile breaking elongation is 1% or more, the polyimide film has excellent handleability. The tensile breaking elongation of the polyimide film refers to the average value of the tensile breaking elongation in the machine direction (MD) and the tensile breaking elongation in the width direction (TD) of the polyimide film.

[0047] The tensile modulus of the polyimide film is preferably 3.0 GPa or more, more preferably 4.0 GPa or more, even more preferably 5.0 GPa or more, and even more preferably 6.0 GPa or more. When the tensile modulus is 3.0 GPa or more, the polyimide film has little elongation deformation and excellent handleability. Furthermore, when the tensile modulus of the polyimide film is 3.0 GPa or more, the wobble width during transportation and handling can be kept small. The tensile modulus is preferably 9.0 GPa or less, more preferably 8.8 GPa or less, and even more preferably 8.5 GPa or less. When the tensile modulus is 9.0 GPa or less, the polyimide film can be used as a flexible film. The tensile modulus of the polyimide film refers to the average value of the tensile modulus in the machine direction (MD) and the width direction (TD) of the polyimide film.

[0048] The thickness unevenness of the polyimide film is preferably 20% or less, more preferably 12% or less, even more preferably 7% or less, and particularly preferably 4% or less. If the thickness unevenness exceeds 20%, it tends to be difficult to apply to narrow sections. The thickness unevenness of the film can be calculated, for example, by measuring the film thickness at approximately 10 randomly selected positions on the film to be measured using a contact film thickness meter, and then calculating it based on the following formula: Film thickness unevenness (%) = 100 x (maximum film thickness - minimum film thickness) / average film thickness

[0049] The surface roughness Ra of the polyimide film is preferably 2.0 nm or less, more preferably 1.5 nm or less, and even more preferably 1.0 nm or less. The surface roughness of the polyimide film is, for example, 0.2 nm or more, 0.3 nm or more, 0.4 nm or more, etc. When the surface roughness Ra is within the above range, the laminated graphene layer tends to be uniform and tends to have excellent adhesion.

[0050] The sheet material preferably has a sheet resistance of 1200 Ω / sq or less, more preferably 900 Ω / sq or less, and even more preferably 500 Ω / sq or less. The lower the sheet resistance, the more preferable it is, for example, 1 Ω / sq or more, 10 Ω / sq or more, etc. A sheet resistance of 1200 Ω / sq or less can be suitably used as a conductive film. The sheet resistance can be reduced to 1200 Ω / sq or less by using a graphene layer. The sheet resistance can also be reduced by increasing carrier mobility. The sheet resistance can also be reduced by doping the graphene layer with a doping material. As a result, a sheet resistance of 1200 Ω / sq or less can be achieved. The sheet resistance was measured according to the method described in the Examples.

[0051] The sheet material has a carrier mobility of 900 cm ２ / Vs or more, and more preferably 1500 cm ２ / Vs or more, more preferably 2000 cm ２ The higher the carrier mobility, the more preferable. ２ / Vs or less, 6000cm ２ / Vs or less. By using a graphene layer, the carrier mobility is 900 cm ２ / Vs or more. Furthermore, the carrier mobility can be further improved by removing foreign matter on the sheet material. Foreign matter on the sheet material can be removed by heat treating the sheet material at a high temperature. ２ When the carrier mobility is 1 / Vs or more, the film can be suitably used as a conductive film. The method for measuring the carrier mobility is the method described in the Examples.

[0052] The sheet material has a carrier concentration of 10 １２ cm －２ It is preferable that the ratio is equal to or greater than 5×10 １２ cm －２ More preferably, 10 １３ cm －２ The higher the carrier concentration, the better.１４ cm －２ Below, 7 x 10 １３ cm －２ The carrier concentration is 10 １２ cm －２ Furthermore, the carrier concentration can be increased by doping the graphene layer with a doping material. １２ cm －２ When the carrier concentration is above this level, the film can be suitably used as a conductive film. The carrier concentration was measured by the method described in the Examples.

[0053] The sheet material preferably has a light transmittance of 80% or more at a wavelength of 550 nm, more preferably 85% or more, and even more preferably 90% or more. The higher the light transmittance, the better, for example, 98% or less, 95% or less, etc. When the light transmittance at a wavelength of 550 nm is 80% or more, it can be said to have sufficient transparency. The light transmittance was measured according to the method described in the examples.

[0054] As described above, according to the sheet material of this embodiment, a highly heat-resistant, transparent polyimide film having high heat resistance and sufficient transparency is used as the substrate. Furthermore, the graphene layer has high heat resistance and sufficient transparency. Therefore, a sheet material composed of a graphene layer and a highly heat-resistant, transparent polyimide film has high heat resistance and sufficient transparency as a whole. Furthermore, the highly heat-resistant, transparent polyimide film has a glass transition temperature of 300°C or higher and excellent heat resistance, making it possible to remove foreign matter, etc., on the sheet material by heat treatment, for example. As a result, electrical properties can be improved. Therefore, the sheet material makes it possible to realize a graphene transparent conductive film having high heat resistance, sufficient transparency, and excellent electrical properties.

[0055] <Method for manufacturing sheet material> Hereinafter, a method for manufacturing a sheet material according to this embodiment will be described. The method for manufacturing a sheet material according to this embodiment includes: a step A of preparing a highly heat-resistant, transparent polyimide film; and a step B of providing a graphene layer on the highly heat-resistant, transparent polyimide film, wherein the highly heat-resistant, transparent polyimide film has a glass transition temperature of 300°C or higher and a yellowness index of 10 or lower.

[0056] <Step A> In the method for producing a sheet material according to this embodiment, first, a highly heat-resistant, transparent polyimide film (hereinafter also referred to as "polyimide film") having a glass transition temperature of 300°C or higher and a yellowness index of 10 or lower is prepared. The highly heat-resistant, transparent polyimide film has already been described, so a description thereof will be omitted here.

[0057] <Step B> Next, a graphene layer is provided on the polyimide film. As a method for providing a graphene layer on the polyimide film, a conventionally known method can be used.

[0058] Specifically, for example, a laminate of "polyimide film / quartz glass substrate" and a laminate of "Cu substrate / graphene layer" are bonded together, the Cu substrate is removed by etching, and the quartz glass substrate is peeled off, thereby obtaining a sheet material in which a graphene layer and a polyimide film are laminated.

[0059] The laminate of "polyimide film / quartz glass substrate" and the laminate of "Cu substrate / graphene layer" can be bonded together by pressure bonding.

[0060] <Method for manufacturing a "polyimide film / quartz glass substrate" laminate> The method for manufacturing a "polyimide film / quartz glass substrate" laminate according to this embodiment includes the steps of: forming a silane coupling agent layer containing a silane coupling agent on a quartz glass substrate; and bonding a polyimide film to the silane coupling agent layer.

[0061] In the method for producing a "polyimide film / quartz glass substrate" laminate according to this embodiment, first, a silane coupling agent layer containing a silane coupling agent is formed on the quartz glass substrate.

[0062] The silane coupling agent is physically or chemically interposed between the quartz glass substrate and the polyimide film, and has the effect of increasing the adhesive strength between the quartz glass substrate and the polyimide film. The coupling agent is not particularly limited, but a silane coupling agent having an amino group or an epoxy group is preferred.Specific preferred examples of the silane coupling agent include N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane. , 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, p-styryltrimethoxysilane, 3-methyl Examples of suitable alkylsilanes include methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride, 3-ureidopropyltriethoxysilane, 3-chloropropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, bis(triethoxysilylpropyl)tetrasulfide, 3-isocyanatepropyltriethoxysilane, tris-(3-trimethoxysilylpropyl)isocyanurate, chloromethylphenethyltrimethoxysilane, chloromethyltrimethoxysilane, aminophenyltrimethoxysilane, aminophenethyltrimethoxysilane, and aminophenylaminomethylphenethyltrimethoxysilane.

[0063] In addition to the above, examples of the silane coupling agent include n-propyltrimethoxysilane, butyltrichlorosilane, 2-cyanoethyltriethoxysilane, cyclohexyltrichlorosilane, decyltrichlorosilane, diacetoxydimethylsilane, diethoxydimethylsilane, dimethoxydimethylsilane, dimethoxydiphenylsilane, dimethoxymethylphenylsilane, dodecyltrichlorosilane, dodecyltrimethoxysilane, ethyltrichlorosilane, hexyltrimethoxysilane, octadecyltriethoxysilane, octadecyltrimethoxysilane, n-octyltrichlorosilane, n-octyltriethoxysilane, n-octyltrimethoxysilane, triethoxyethylsilane, triethoxymethylsilane, trimethoxymethylsilane, and trimethoxyphenylsilane. , pentyltriethoxysilane, pentyltrichlorosilane, triacetoxymethylsilane, trichlorohexylsilane, trichloromethylsilane, trichlorooctadecylsilane, trichloropropylsilane, trichlorotetradecylsilane, trimethoxypropylsilane, allyltrichlorosilane, allyltriethoxysilane, allyltrimethoxysilane, diethoxymethylvinylsilane, dimethoxymethylvinylsilane, trichlorovinylsilane, triethoxyvinylsilane, vinyltris(2-methoxyethoxy)silane, trichloro-2-cyanoethylsilane, diethoxy(3-glycidyloxypropyl)methylsilane, 3-glycidyloxypropyl(dimethoxy)methylsilane, 3-glycidyloxypropyltrimethoxysilane, and the like can also be used.

[0064] Among the above-mentioned silane coupling agents, silane coupling agents having one silicon atom in one molecule are particularly preferred, and examples thereof include N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, aminophenyltrimethoxysilane, aminophenethyltrimethoxysilane, and aminophenylaminomethylphenethyltrimethoxysilane. When particularly high heat resistance is required in the process, a compound in which Si and an amino group are linked by an aromatic group is desirable. In addition to the above, examples of the coupling agent include 1-mercapto-2-propanol, methyl 3-mercaptopropionate, 3-mercapto-2-butanol, butyl 3-mercaptopropionate, 3-(dimethoxymethylsilyl)-1-propanethiol, 4-(6-mercaptohexaloyl)benzyl alcohol, 11-amino-1-undecenethiol, 11-mercaptoundecylphosphonic acid, 11-mercaptoundecyltrifluoroacetic acid, 2,2'-(ethylenedioxy)diethanethiol, 11-mercaptoundecyltri(ethylene glycol), (1-mercaptoundic-11-yl)tetra(ethylene glycol), 1-(methylcarboxy)undec-11-yl)hexa(ethylene glycol), hydroxyundecyl disulfide, carboxyundecyl disulfide, hydroxyhexadodecyl disulfide, carboxyhexadecyl disulfide, tetrakis(2-ethylhexyloxy)titanium, titanium Dioctyloxybis(octylene glycolate), zirconium tributoxymonoacetylacetonate, zirconium monobutoxyacetylacetonate bis(ethyl acetoacetate), zirconium tributoxymonostearate, acetoalkoxyaluminum diisopropylate, 3-glycidyloxypropyltrimethoxysilane, 2,3-butanedithiol, 1-butanethiol, 2-butanethiol, cyclohexanethiol, cyclopentanethiol, 1-decanethiol ol, 1-dodecanethiol, 2-ethylhexyl 3-mercaptopropionate, ethyl 3-mercaptopropionate, 1-heptanethiol, 1-hexadecanethiol, hexyl mercaptan, isoamyl mercaptan, isobutyl mercaptan, 3-mercaptopropionic acid, 3-methoxybutyl 3-mercaptopropionate, 2-methyl-1-butanethiol, 1-octadecanethiol, 1-octanethiol, 1-pentadecanethiol, 1-pentanethiol, 1- Propanethiol, 1-tetradecanethiol, 1-undecanethiol, 1-(12-mercaptododecyl)imidazole, 1-(11-mercaptoundecyl)imidazole, 1-(10-mercaptodecyl)imidazole, 1-(16-mercaptohexadecyl)imidazole, 1-(17-mercaptoheptadecyl)imidazole, 1-(15-mercapto)dodecanoic acid, 1-(11-mercapto)undecanoic acid, 1-(10-mercapto)decanoic acid, and the like can also be used.

[0065] <Method of Forming Silane Coupling Agent Layer> The silane coupling agent layer can be formed by applying a silane coupling agent solution to the quartz glass substrate or by vapor deposition.

[0066] As a method for applying the silane coupling agent solution, a solution obtained by diluting the silane coupling agent with a solvent such as alcohol can be appropriately used by a conventionally known solution application method such as spin coating, curtain coating, dip coating, slit die coating, gravure coating, bar coating, comma coating, applicator method, screen printing, or spray coating.

[0067] The silane coupling agent layer can also be formed by vapor deposition. Specifically, the quartz glass substrate is exposed to silane coupling agent vapor, i.e., a silane coupling agent in a substantially gaseous state. Silane coupling agent vapor can be obtained by heating a liquid silane coupling agent to a temperature between 40°C and the boiling point of the silane coupling agent. The boiling point of the silane coupling agent varies depending on its chemical structure, but is generally in the range of 100 to 250°C. The silane coupling agent can be heated under pressure, atmospheric pressure, or reduced pressure; however, atmospheric pressure or reduced pressure is preferred to promote vaporization of the silane coupling agent. Since many silane coupling agents are flammable liquids, the vaporization process is preferably carried out in a sealed container, preferably after replacing the atmosphere with an inert gas. The exposure time of the quartz glass substrate to the silane coupling agent is not particularly limited, but is preferably within 20 hours, more preferably within 60 minutes, even more preferably within 15 minutes, and most preferably within 1 minute. The temperature of the quartz glass substrate while it is exposed to the silane coupling agent is preferably controlled to an appropriate temperature between −50° C. and 200° C. depending on the type of silane coupling agent and the desired thickness of the silane coupling agent layer.

[0068] The film thickness of the silane coupling agent layer is extremely thin compared with that of quartz glass substrate, polyimide film, etc., and is negligible from the viewpoint of mechanical design. In principle, the thickness of the monolayer order is sufficient at the very least. Generally, it is less than 400 nm, preferably 200 nm or less, more preferably 100 nm or less in practical use, more preferably 50 nm or less, and even more preferably 10 nm or less. However, when the calculated thickness is less than 5 nm, the silane coupling agent layer may not be a uniform coating film, but may exist in cluster form. The film thickness of the silane coupling agent layer can be calculated by ellipsometry or by calculating the concentration and coating amount of the silane coupling agent solution during coating.

[0069] Next, a polyimide film is bonded to the silane coupling agent layer. Specifically, the surface of the silane coupling agent layer formed on the quartz glass substrate and the polyimide film are bonded together under pressure and heat.

[0070] The pressure and heat treatment may be carried out, for example, under atmospheric pressure or in a vacuum by pressing, laminating, roll laminating, or the like while heating. A method of pressurizing and heating in a flexible bag can also be applied. From the viewpoint of improving productivity and reducing processing costs brought about by high productivity, pressing or roll laminating under atmospheric pressure is preferred, and a method using a roll (roll laminating, etc.) is particularly preferred.

[0071] The pressure during the pressure and heat treatment is preferably 1 MPa to 20 MPa, more preferably 3 MPa to 10 MPa. A pressure of 20 MPa or less can prevent damage to the quartz glass substrate. Furthermore, a pressure of 1 MPa or more can prevent the occurrence of areas where adhesion is poor or insufficient. The temperature during the pressure and heat treatment is preferably 150°C to 400°C, more preferably 250°C to 350°C. If the temperature is too high, there is a risk of damaging the polyimide film, while if the temperature is too low, the adhesion tends to be weak. Furthermore, while the pressure and heat treatment can be performed in an atmospheric pressure atmosphere as described above, it is preferable to perform it under vacuum in order to obtain stable peel strength over the entire surface. The degree of vacuum required for this process is sufficient, with a vacuum of approximately 10 Torr or less being sufficient. As for equipment that can be used for pressure and heat treatment, for example, the "11FD" manufactured by Imoto Manufacturing Co., Ltd. can be used for pressing in a vacuum, and for vacuum lamination using a roll-type film laminator in a vacuum or a film laminator that applies pressure to the entire surface of the glass at once using a thin rubber film after creating a vacuum, for example, the "MVLP" manufactured by Meiki Manufacturing Co., Ltd. can be used.

[0072] The pressure and heat treatment can be performed separately as a pressure process and a heating process. In this case, the polyimide film and the quartz glass substrate are first pressurized (preferably about 0.2 to 50 MPa) at a relatively low temperature (for example, a temperature below 120°C, more preferably 95°C or less) to ensure close contact between them, and then heated at a relatively high temperature (for example, 120°C or higher, more preferably 120 to 250°C, and even more preferably 150 to 230°C) under low pressure (preferably below 0.2 MPa, more preferably 0.1 MPa or less) or atmospheric pressure, thereby accelerating the chemical reaction at the adhesive interface and laminating the polyimide film and the quartz glass substrate.

[0073] In this way, a laminate of "polyimide film / quartz glass substrate" can be obtained.

[0074] When one graphene layer is provided on a glass substrate, the following PMMA-supported transfer method can be employed. When two or more graphene layers are provided on a glass substrate, the following layer-by-layer transfer method can be employed.

[0075] <PMMA Support Transfer Method> First, one graphene layer is formed on a Cu substrate by CVD (chemical vapor deposition) using methane. The Cu substrate also functions as a catalyst for methane decomposition. Cu has low carbon solid solubility, so carbon does not penetrate into Cu. Therefore, growth automatically stops when one layer of graphene has grown on the Cu substrate. This results in a laminate of "Cu substrate / graphene layer."

[0076] Next, a PMMA (polymethyl methacrylate) layer is formed on the obtained graphene layer. The PMMA layer can be formed by a known method such as spin coating. This results in a laminate of "Cu substrate / graphene layer / PMMA layer."

[0077] Next, the Cu substrate is removed by etching, thereby exposing the graphene layer, thereby obtaining a laminate of "graphene layer / PMMA layer."

[0078] Next, the graphene layer is transferred onto a glass substrate, resulting in a laminate of glass substrate / graphene layer / PMMA layer.

[0079] Finally, the laminate of "glass substrate / graphene layer / PMMA layer" is immersed in acetone to remove the PMMA layer, thereby obtaining a laminate of "glass substrate / graphene layer" (a laminate of "glass substrate / one graphene layer").

[0080] <Layer-by-Layer Method> (When Providing Two Graphene Layers on a Glass Substrate) First, a laminate A of "graphene layer / PMMA layer" is obtained in the same manner as in the PMMA-supported transfer method. Then, a laminate B of "Cu substrate / one graphene layer" is prepared in the same manner as in the PMMA-supported transfer method.

[0081] Next, laminate A of "graphene layer / PMMA layer" and laminate B of "Cu substrate / graphene layer" are bonded together, and the graphene layer of laminate B is transferred onto the graphene layer of laminate A. This yields a laminate of "Cu substrate / graphene layer / graphene layer / PMMA layer."

[0082] Next, the Cu substrate is removed by etching, thereby obtaining a "graphene layer / graphene layer / PMMA layer" structure. Next, the "graphene layer / graphene layer / PMMA layer" structure is transferred to a glass substrate, thereby obtaining a "glass substrate / graphene layer / graphene layer / PMMA layer" stack.

[0083] Finally, the glass substrate / graphene layer / graphene layer / PMMA layer stack is immersed in acetone to remove the PMMA layer, thereby obtaining a glass substrate / graphene layer / graphene layer stack, i.e., a "glass substrate / two graphene layers" stack.

[0084] (When Providing Three or More Graphene Layers on a Glass Substrate) First, a laminate A of "graphene layer / PMMA layer" is obtained in the same manner as in the PMMA support transfer method.

[0085] In addition, a laminate C of "Cu substrate / graphene layer" is prepared in the same manner as in the PMMA support transfer method. The number of laminates C prepared corresponds to the number of graphene layers.

[0086] The graphene layer of laminate C is transferred onto the graphene layer of laminate A, with the graphene layers of laminate A of "graphene layer / PMMA layer" and laminate C of "Cu substrate / graphene layer" bonded together. This results in a laminate of "Cu substrate / graphene layer / graphene layer / PMMA layer."

[0087] Next, the Cu substrate is removed by etching, thereby obtaining a laminate D of "graphene layer / graphene layer / PMMA layer."

[0088] When a graphene layer is further added, the step of bonding the laminate C of "Cu substrate / graphene layer" and the step of removing the Cu substrate by etching are repeated, thereby obtaining a laminate of "multiple graphene layers / PMMA layers."

[0089] Next, the laminate of "multiple graphene layers / PMMA layers" is transferred to a glass substrate to obtain "glass substrate / multiple graphene layers / PMMA layers." The PMMA layer is then removed. This results in a laminate of "glass substrate / multiple graphene layers."

[0090] The method for manufacturing a sheet material according to this embodiment has been described above.

[0091] The present invention will be described in detail below using examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention.

[0092] <Polymerization Example 1: Preparation of Polyamic Acid Solution A1> After the atmosphere inside a reaction vessel equipped with a nitrogen inlet tube, a reflux condenser, and a stirrer was replaced with nitrogen, 9.61 g of 2,2′-bis(trifluoromethyl)benzidine (TFMB), 3.91 g of pyromellitic dianhydride (PMDA), and 3.51 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) were added as solids, and then 96.65 g of N,N-dimethylacetamide (DMAc) was added so that the total polymer solid content in the polyamic acid solution was 0.15 mass %, and the mixture was completely dissolved, followed by stirring at room temperature for 24 hours. 0.03 g of maleic anhydride (MAA) was added 2 hours before stirring was stopped, and then a polyamic acid solution A1 (molar ratio of TFMB / / PMDA / BPDA=1.00 / / 0.60 / 0.40) having a solids content of 15 mass % and a reduced viscosity of 2.7 dl / g was obtained.

[0093] <Production Example 1: Preparation of Polyimide Film F1> Polyamic acid solution A1 was coated onto the lubricated surface of Xenomax (manufactured by Xenomax Japan Co., Ltd.) using an applicator, adjusting conditions so that the final film thickness would be approximately 15 μm. This was dried at 100°C in a nitrogen atmosphere for 10 minutes. The edges of the Xenomax were then fixed in a metal frame, and the film was heated at 360°C in a nitrogen atmosphere for 30 minutes to allow the imidization reaction to proceed. The film was then cooled to room temperature, and the resulting film was peeled off from the Xenomax to obtain a 200 mm square polyimide film F1.

[0094] <Measurement of Polyimide Film Thickness Tpi (μm)> The thickness of the polyimide film was measured using a high-precision Digimatic Micrometer (MDH-25M, manufactured by Mitutoyo Corporation). Measurements were taken at five locations, one at each of the four corners of the film and one at the center, and the arithmetic average value was used. As a result, the thickness of the polyimide film F1 was 15 μm.

[0095] <Glass Transition Temperature> Three polyimide film test pieces were prepared, and for each test piece, temperature dependence curves of storage modulus (E'), loss modulus (E"), and tan δ (=E" / E'), which is the value obtained by dividing the loss modulus by the storage modulus, were obtained under the following conditions to determine the peak temperature. The average value of the three test pieces was calculated as the glass transition temperature. As a result, the glass transition temperature of polyimide film F1 was 400°C. Instrument name: DMA Q800 manufactured by TA Instruments Sample length: 20 mm Sample width: 5 mm Heating start temperature: 25°C Heating end temperature: 500°C Heating rate: 10°C / min Measurement frequency: 10 Hz

[0096] <Method for measuring yellowness index (YI)> Using a color meter (ZE6000, manufactured by Nippon Denshoku Industries Co., Ltd.) and a C2 light source, the tristimulus values ​​X, Y, and Z of the film were measured in accordance with ASTM D1925, and the yellowness index (YI) was calculated using the following formula. The same measurement was performed three times, and the arithmetic mean value was used. As a result, the yellowness index of polyimide film F1 was 9. YI=100×(1.28X−1.06Z) / Y

[0097] <Coefficient of Linear Expansion (CTE)> The expansion / contraction rate of the polyimide film was measured under the following conditions, measuring the expansion / contraction rate / temperature at 15°C intervals, such as from 30°C to 45°C and from 45°C to 60°C. This measurement was continued up to 300°C, and the average value of all measurements was calculated as CTE (ppm / K). As a result, the linear expansion coefficient of polyimide film F1 was 8 ppm / K. Instrument name: TMA4000S manufactured by MAC Sciences, Inc. Sample length: 20 mm Sample width: 2 mm Heat-up start temperature: 25°C Heat-up end temperature: 300°C Heat-up rate: 5°C / min Atmosphere: Argon

[0098] <Total Light Transmittance> The total light transmittance (TT) of the film was measured using a HAZEMETER (NDH5000, manufactured by Nippon Denshoku Industries Co., Ltd.). A D65 lamp was used as the light source. The same measurement was performed three times, and the arithmetic average value was used. As a result, the total light transmittance of the polyimide film F1 was 87%.

[0099] <Haze> The haze of the film was measured using a HAZEMETER (NDH5000, manufactured by Nippon Denshoku Industries Co., Ltd.). A D65 lamp was used as the light source. The same measurement was performed three times, and the arithmetic average value was used. As a result, the haze of the polyimide film F1 was 0.4%.

[0100] <Measurement of tensile modulus, tensile elongation, and tensile strength of polyimide film> Polyimide film was cut into 100 mm x 10 mm strips using a cutter knife to prepare polyimide film test pieces. Using a tensile tester (Shimadzu Corporation, Autograph model AG-5000A), the tensile modulus, tensile elongation, and tensile strength were measured at a tensile speed of 50 mm / min and a chuck distance of 40 mm. As a result, polyimide film F1 had a tensile modulus of 7.5 GPa, a tensile elongation of 20%, and a tensile strength of 310 MPa.

[0101] <Preparation of a "polyimide film / quartz glass substrate" laminate> A silane coupling agent was applied to a quartz glass substrate (manufactured by Taiko Seisakusho Co., Ltd., product name: Labo-USQ) using the device shown in Figure 5. Figure 5 is a schematic diagram of the device for applying a silane coupling agent to a quartz glass substrate. A quartz glass substrate (cut into a size of 20 mm x 20 mm) was used. The quartz glass substrate was washed with pure water, dried, and then irradiated with UV / O ３ The substrate was irradiated with an irradiator (SKR1102N-03 manufactured by LAN Technical) for 3 minutes and then dry-cleaned. 100 g of 3-aminopropyltrimethoxysilane (silane coupling agent, Shin-Etsu Chemical KBM903) was placed in a 1 L capacity chemical tank, and the outer water bath was heated to 43°C. The vapor that emerged was then sent to the chamber. The gas flow rate was 20 L / min, and the substrate temperature was 24°C. The exhaust was connected to a negative pressure exhaust port, and a differential pressure gauge confirmed that the chamber was at a negative pressure of approximately 2 Pa.

[0102] Next, a polyimide film F1 (16 mm × 16 mm size) was bonded onto the silane coupling agent layer to obtain a laminate. For bonding, a laminator manufactured by MCK Corporation was used, and the bonding conditions were laminator pressure: 8 kgf / cm, temperature: 24.9 ° C, humidity: 53% RH, and lamination speed: 37.5 mm / sec. This laminate was heated from room temperature to 110 ° C over 24 minutes, heated for 10 minutes while maintaining the temperature, removed, and allowed to cool. Subsequently, the laminate was heated from room temperature to 200 ° C, and heated for 60 minutes while maintaining the temperature to obtain a "polyimide film / quartz glass substrate" laminate.

[0103] <Surface roughness Ra> The surface roughness (Ra) of a polyimide film on a quartz glass substrate was measured using a scanning probe microscope E Sweep (manufactured by SII Nano Technology Inc.). After fixing the sample on the sample stage, static electricity was removed using a static eliminator blower, and the surface morphology was observed. Secondary tilt correction and flattening were performed using the attached analysis software. The observation mode was DFM mode, and a 20 μm scanner was used. The cantilever was Si DF20, and the observation field was 5 μm × 5 μm, 512 × 256 pixels. The average of four measured values ​​was taken as the Ra value. As a result, the Ra of polyimide film F1 was 0.87 nm.

[0104] <Preparation of Laminate of "Glass Substrate / Graphene Layer"> (Preparation Example 2) A laminate of "glass substrate / one graphene layer" was prepared as follows. First, one graphene layer was formed on a Cu substrate (manufactured by Graphene Platform, product name: copper foil dedicated to graphene deposition, thickness 35 μm) by CVD (chemical vapor deposition). Specifically, the graphene layer was formed under the following deposition conditions and the deposition conditions shown in FIG. 1 . [Graphene Layer Formation Conditions] CVD apparatus: MPCVD-Graphene manufactured by Microphase Co., Ltd. Substrate: Cu foil, thickness 35 μm Pressure: 6 Torr Gas flow: CH ４ 2 sccm H ２ 20sccm Growth temp: 1000℃ Growth time: 30 min Pre-annealing: 1000℃, 60min (under H ２ The Cu substrate also functions as a catalyst for methane decomposition. Furthermore, because Cu has low carbon solubility, carbon does not penetrate into Cu. Therefore, the growth of graphene automatically stops after one layer is grown.

[0105] Next, a PMMA layer (polymethyl methacrylate layer) was formed on the obtained graphene layer. Specifically, the PMMA layer was formed under the following film formation conditions. This resulted in a laminate of "Cu substrate / graphene layer / PMMA layer." [PMMA layer formation conditions] PMMA: Sigma-Aldrich, 182265-25G Concentration: 4 wt % (solvent: ethyl lactate) Spin coating: 2500 rpm, Thickness: approximately 150 nm Solidification temperature and time: 180°C, 1 min

[0106] Next, the Cu substrate was removed by etching. Specifically, the Cu substrate was etched and removed under the following etching conditions. This exposed the graphene layer. In other words, a "graphene layer / PMMA layer" laminate was obtained. Note that when graphene is grown by CVD using a Cu substrate, one layer of graphene is formed on both the front and back surfaces of the Cu substrate. Only the graphene on the front surface is transferred and used, but if the graphene on the back surface remains, etching of the Cu substrate becomes difficult. Therefore, before etching the Cu substrate, the graphene on the back surface of the Cu substrate was removed using oxygen plasma. The oxygen plasma irradiation conditions were 20 W and 30 seconds. [Cu substrate etching conditions] Iron (III) nitrate nonahydrate: 0.52 M, Nacalai Tesque 19514-55 Etching time: 5 hours Washing with ultrapure water: 3 hours (ultrapure water was replaced every hour)

[0107] Next, the graphene layer was transferred onto a glass substrate (manufactured by Taiko Seisakusho Co., Ltd., product name: Labo-USQ). Specifically, the transfer was performed by scooping up the "graphene layer / PMMA layer" floating in pure water with organically cleaned quartz glass and drying it in a dry desiccator for at least one hour. This resulted in a laminate of "glass substrate / graphene layer / PMMA layer."

[0108] Finally, the laminate of "glass substrate / graphene layer / PMMA layer" was immersed in acetone for 24 hours to remove the PMMA layer, thereby obtaining a laminate of "glass substrate / graphene layer" (laminate of "glass substrate / one graphene layer").

[0109] (Production Example 3) A laminate of "glass substrate / two graphene layers" was produced as follows. First, a laminate A of "graphene layer / PMMA layer" was obtained in the same manner as in Production Example 2. The etching conditions were the same as in Production Example 2.

[0110] Furthermore, in the same manner as in Production Example 2, a laminate B of "glass substrate / graphene layer" was prepared.

[0111] The graphene layers of laminate A of "graphene layer / PMMA layer" and laminate B of "Cu substrate / graphene layer" were bonded together, and the graphene layer of laminate B was transferred onto the graphene layer of laminate A. This resulted in a laminate of "Cu substrate / graphene layer / graphene layer / PMMA layer."

[0112] Next, the Cu substrate was removed by etching. This resulted in a "graphene layer / graphene layer / PMMA layer" structure. Next, the "graphene layer / graphene layer / PMMA layer" structure was transferred to a glass substrate. This resulted in a "glass substrate / graphene layer / graphene layer / PMMA layer" stack.

[0113] Finally, the laminate of "glass substrate / graphene layer / graphene layer / PMMA layer" was immersed in acetone for 24 hours to remove the PMMA layer, thereby obtaining a laminate of "glass substrate / graphene layer / graphene layer," i.e., a laminate of "glass substrate / two graphene layers."

[0114] (Production Example 4) A laminate of "glass substrate / three graphene layers" was produced as follows: First, in the same manner as in Production Example 2, a laminate A of "graphene layer / PMMA layer" was obtained.

[0115] Furthermore, a laminate C of "Cu substrate / graphene layer" was prepared in the same manner as in Production Example 2. Two laminates C were prepared.

[0116] The graphene layers of laminate A of "graphene layer / PMMA layer" and laminate C of "Cu substrate / graphene layer" were bonded together, and the graphene layer of laminate C was transferred onto the graphene layer of laminate A. This yielded a laminate of "Cu substrate / graphene layer / graphene layer / PMMA layer."

[0117] Next, the Cu substrate was removed by etching, thereby obtaining a laminate D of "graphene layer / graphene layer / PMMA layer."

[0118] Next, the graphene layer of the laminate C was transferred onto the two graphene layers of the laminate D, with the graphene layers of the laminate D being the bonding surfaces of the "graphene layer / graphene layer / PMMA layer" laminate D and the "Cu substrate / graphene layer" laminate C. This resulted in a "Cu substrate / graphene layer / graphene layer / graphene layer / PMMA layer" laminate. Next, the Cu substrate was removed by etching. This resulted in a "graphene layer / graphene layer / graphene layer / PMMA layer" laminate.

[0119] Next, the stack of "graphene layer / graphene layer / graphene layer / PMMA layer" was transferred onto a glass substrate to obtain "glass substrate / graphene layer / graphene layer / graphene layer / PMMA layer."

[0120] Finally, the laminate of "glass substrate / graphene layer / graphene layer / graphene layer / PMMA layer" was immersed in acetone for 24 hours to remove the PMMA layer, thereby obtaining a laminate of "glass substrate / graphene layer / graphene layer / graphene layer", i.e., a laminate of "glass substrate / three graphene layers".

[0121] (Production Example 5) A laminate of "glass substrate / four graphene layers" was produced as follows. First, a laminate D of "graphene layer / graphene layer / graphene layer / PMMA layer" was obtained in the same manner as in Production Example 4.

[0122] A laminate D of "graphene layer / graphene layer / graphene layer / PMMA layer" and a separately prepared laminate C of "Cu substrate / graphene layer" were bonded together, and the graphene layer of laminate C was transferred onto the graphene layer of laminate D. This resulted in a laminate of "Cu substrate / graphene layer / graphene layer / graphene layer / graphene layer / PMMA layer."

[0123] Next, the Cu substrate was removed by etching, thereby obtaining a laminate E of "graphene layer / graphene layer / graphene layer / graphene layer / PMMA layer".

[0124] Next, the stack of "graphene layer / graphene layer / graphene layer / graphene layer / PMMA layer" was transferred onto a glass substrate to obtain "glass substrate / graphene layer / graphene layer / graphene layer / graphene layer / PMMA layer."

[0125] Finally, the laminate of "glass substrate / graphene layer / graphene layer / graphene layer / graphene layer / PMMA layer" was immersed in acetone for 24 hours to remove the PMMA layer, thereby obtaining a laminate of "glass substrate / graphene layer / graphene layer / graphene layer / graphene layer", i.e., a laminate of "glass substrate / four graphene layers".

[0126] (Production Example 6) A laminate of "glass substrate / five graphene layers" was obtained in the same manner as in Production Example 5. Specifically, laminate A of "graphene layer / PMMA layer" was repeatedly laminated with laminate C of "Cu substrate / graphene layer" and the Cu substrate was etched to form a total of five graphene layers, which was then transferred to a glass substrate to form a laminate of "glass substrate / five graphene layers / PMMA layers," and finally, the PMMA layer was removed to obtain a laminate of "glass substrate / five graphene layers."

[0127] (Production Example 7) A laminate of "glass substrate / six graphene layers" was obtained in the same manner as in Production Example 5. Specifically, laminate A of "graphene layer / PMMA layer" was repeatedly laminated with laminate C of "Cu substrate / graphene layer" and the Cu substrate was etched to form a total of six graphene layers, which was then transferred to a glass substrate to form a laminate of "glass substrate / six graphene layers / PMMA layers," and finally, the PMMA layer was removed to obtain a laminate of "glass substrate / six graphene layers."

[0128] <Preparation of Sheet Material> (Example 1) A single graphene layer was transferred to a polyimide film F1 to obtain a sheet material according to Example 1. Specifically, the "PMMA layer / single graphene layer" laminate of Production Example 2 was transferred to a "polyimide film / quartz glass substrate" laminate to obtain a "PMMA layer / single graphene layer / polyimide film / quartz glass substrate." The PMMA layer was then removed to obtain a quartz glass substrate-attached sheet material of "single graphene layer / polyimide film / quartz glass substrate." The quartz glass substrate was then peeled off to obtain a "single graphene layer / polyimide film" sheet material according to Example 1. The transfer was performed by scooping up the "graphene layer / PMMA layer" floating in pure water with organically cleaned quartz glass and drying it in a desiccator for at least one hour. The quartz glass substrate was also peeled off by grasping the edge of the "single graphene layer / polyimide film" with tweezers and gradually peeling the entire piece off starting from the edge.

[0129] (Example 2) Two graphene layers were transferred onto polyimide film F1 to obtain a sheet material according to Example 2. Specifically, the "PMMA layer / two graphene layers" laminate of Production Example 3 was transferred onto a "polyimide film / quartz glass substrate" laminate to obtain a "PMMA layer / two graphene layers / polyimide film / quartz glass substrate." The PMMA layer was then removed to obtain a sheet material with a quartz glass substrate of "two graphene layers / polyimide film / quartz glass substrate." The quartz glass substrate was then peeled off to obtain a "two graphene layers / polyimide film" sheet material according to Example 2.

[0130] (Example 3) Three graphene layers were transferred onto polyimide film F1 to obtain a sheet material according to Example 3. Specifically, the "PMMA layer / three graphene layers" laminate of Production Example 4 was transferred onto a "polyimide film / quartz glass substrate" laminate to obtain a "PMMA layer / three graphene layers / polyimide film / quartz glass substrate." The PMMA layer was then removed to obtain a quartz glass substrate-attached sheet material of "three graphene layers / polyimide film / quartz glass substrate." The quartz glass substrate was then peeled off to obtain a "three graphene layers / polyimide film" sheet material according to Example 3.

[0131] Example 4 Four graphene layers were transferred onto polyimide film F1 to obtain a sheet material according to Example 4. Specifically, the "PMMA layer / four graphene layers" laminate of Production Example 5 was transferred onto a "polyimide film / quartz glass substrate" laminate to obtain a "PMMA layer / four graphene layers / polyimide film / quartz glass substrate." The PMMA layer was then removed to obtain a quartz glass substrate-attached sheet material of "four graphene layers / polyimide film / quartz glass substrate." The quartz glass substrate was then peeled off to obtain a "four graphene layers / polyimide film" sheet material according to Example 4.

[0132] <Measurement of Light Transmittance> The light transmittance of 1-layer to 4-layer graphene was measured using an ultraviolet-visible spectrophotometer (Shimadzu Corporation, UV-1900). Specifically, for the "glass substrate / (1-layer to 4-layer) graphene layers" of Production Examples 2 to 5, a quartz glass substrate was used as a reference to measure the transmittance. The transmittance of the quartz glass substrate was subtracted to obtain the light transmittance of 1-layer to 4-layer graphene. FIG. 2 shows the transmission spectra of 1-layer to 4-layer graphene. Furthermore, the light transmittance of the sheet material of Example 3 and the polyimide film alone was measured using an ultraviolet-visible spectrophotometer (Shimadzu Corporation, UV-1900). FIG. 3 shows the transmission spectra of the sheet material of Example 3 and the polyimide film alone. As a result of the measurement, the light transmittance of the sheet material of Example 3 at a wavelength of 550 nm was 89.1%. Furthermore, the light transmittance of polyimide film F1 alone at a wavelength of 550 nm was 97.5%. Although the light transmittance at a wavelength of 550 nm of the sheet materials of Examples 1, 2, and 4 was not measured, the light absorption of three graphene layers is (97.5% - 89.1%), and since the light transmittance of graphene decreases proportionally with each additional layer as shown in Figure 2, it is estimated that the light absorption of one layer is (97.5% - 89.1%) divided by 3 (2.8%). Therefore, the light transmittance of the sheet material of Example 1 at a wavelength of 550 nm is 94.7%, the light transmittance of the sheet material of Example 2 at a wavelength of 550 nm is 91.9%, and the light transmittance of the sheet material of Example 4 at a wavelength of 550 nm is 86.3%.

[0133] <Hall Effect Measurement> As shown in Fig. 4, a Hall bar was fabricated by photolithography, in which a rectangular graphene layer measuring 600 µm in length and 500 µm in width was formed on a polyimide film, and gold electrodes were provided at the four corners of the graphene layer. The polyimide film was the same as that prepared in the Production Examples, and the graphene layer was a single graphene layer in Example 1 and a three-layer graphene layer in Example 3.

[0134] The sheet resistance, carrier mobility, and carrier concentration were measured using the prepared Hall bar. Furthermore, the sheet resistance, carrier mobility, and carrier concentration were measured after heating at 250°C for 180 minutes. Furthermore, after heating at 250°C for 180 minutes, the sheet resistance, carrier mobility, and carrier concentration were measured after further doping with TFSA (bis(trifluoromethane-sulfonyl)amine).

[0135] TFSA doping was performed by spin coating using the following procedure. 1. A sample was prepared using 1-butanol as a solvent, with a TFSA concentration of 50 mM. 2. A dropper was used to drop the sample (TFSA / 1-butanol) onto the graphene layer. 3. The rotation speed of the spin coater was first increased to 2500 rpm over 60 seconds, then rotated at 2500 rpm for 60 seconds, and then decreased from 2500 rpm to 0 rpm over 60 seconds. 4. After spin coating, the sample was allowed to dry naturally for 10 minutes.

[0136] The measurement results of the sheet resistance, carrier mobility, and carrier concentration of the sheet material of Example 1 are shown in Table 1. The measurement results of the sheet resistance, carrier mobility, and carrier concentration of the sheet material of Example 3 are shown in Table 2.

[0137]

[0138]

[0139] (Results) In Example 3, the carrier mobility was 2060 cm before heating. ２ / Vs, whereas after heating at 250 °C it is 2710 cm ２ / Vs. This is thought to be because foreign matter (especially PMMA) on the sheet material was removed by exposing it to a high temperature (250°C). In Example 3, the sheet resistance was 390 Ω / sq before heating, but was 610 Ω / sq after heating at 250°C. However, as mentioned above, the carrier mobility is improved, which is an advantage. Because the carrier mobility is improved, it is possible to maintain a sufficiently high mobility even if TFSA is doped to improve the carrier concentration. In Example 3, the carrier mobility was 2710 cm after heating at 250°C. ２ / Vs, even when doped with TFSA, the ２ / Vs. Therefore, the sheet resistance of the sheet material after doping with TFSA is 210 Ω / sq. This value is lower than the 390 Ω / sq before heating, and it can be said that the sheet material has better electrical properties. In other words, in Example 3, a highly heat-resistant transparent polyimide film having high heat resistance is used as the substrate, so that it can be heated at 250°C. Since it can be heated at 250°C, the carrier mobility of the sheet material can be increased, and by doping with TFSA, it has better electrical properties than before heating at 250°C. In particular, in Example 3, a high carrier mobility (2060 cm) was observed even before the heat treatment. ２ / Vs) was obtained. Therefore, it was confirmed that the temperature increased further when heat treatment was performed (2710 cm ２ / Vs). This is presumably due to the relatively low dielectric constant of the polyimide film. As in Example 3, Example 1 also uses a highly heat-resistant, transparent polyimide film as the substrate, so that it can be heated at 250°C. Since it can be heated at 250°C, the carrier mobility of the sheet material can be increased, and by doping with TFSA, it has better electrical properties (sheet resistance 340 Ω / sq) than before heating at 250°C (sheet resistance 660 Ω / sq). In particular, Example 1 has a high carrier mobility (1340 cm) even before heat treatment. ２ / Vs) was obtained. Therefore, it was confirmed that the temperature increased further when heat treatment was performed (1690 cm ２ / Vs), which is presumably due to the relatively low dielectric constant of the polyimide film.

[0140] REFERENCE SIGNS LIST 1 Flow meter 2 Gas inlet 3 Chemical tank (silane coupling agent tank) 4 Hot water tank (water bath) 5 Heater 6 Treatment chamber (chamber) 7 Substrate 8 Exhaust port

Claims

1. A sheet material comprising: a graphene layer having graphene; and a highly heat-resistant, transparent polyimide film, wherein the highly heat-resistant, transparent polyimide film has a glass transition temperature of 300°C or higher and a yellowness index of 10 or lower.

2. The sheet material according to claim 1, characterized in that the sheet resistance is 1200 Ω / sq or less.

3. Carrier mobility is 900 cm ２ 3. The sheet material according to claim 1, wherein the resistivity is greater than or equal to Vs.

4. The sheet material according to claim 1 or 2, characterized in that the light transmittance at a wavelength of 550 nm is 80% or more.

5. The sheet material according to claim 1 or 2, characterized in that the graphene layer is a graphene layer having 3 to 7 layers, where a layer having a thickness of 1 atom is one graphene layer.

6. The sheet material according to claim 1 or 2, characterized in that the surface of the highly heat-resistant transparent polyimide film on which the graphene layer is laminated has a surface roughness Ra of 0.2 nm or more and 2.0 nm or less.

7. A method for producing a sheet material as described in claim 1 or 2, characterized in that it comprises: a step A of preparing a highly heat-resistant, transparent polyimide film; and a step B of providing a graphene layer on the highly heat-resistant, transparent polyimide film, wherein the highly heat-resistant, transparent polyimide film has a glass transition temperature of 300°C or higher and a yellowness index of 10 or lower.

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