JP7107451B2 - Polyimide film and its manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a colorless polyimide film having a low coefficient of linear expansion and good mechanical properties, and a method for producing the same.

Polyimide films have excellent heat resistance, good mechanical properties, and are widely used in the electrical and electronic fields as flexible materials. However, since a general polyimide film is colored yellowish brown, it cannot be applied to parts such as display devices that require light transmission.
On the other hand, display devices are becoming thinner and lighter, and are required to be more flexible. Attempts have therefore been made to replace glass substrates with flexible polymer film substrates, but colored polyimide films are used as substrate materials for liquid crystal displays that display images by turning light transmission on and off. Therefore, it can be applied only to a small part, such as peripheral circuits such as TABs and COFs on which drive circuits of display devices are mounted, and the rear side of reflective display systems or self-luminous display devices.

Against this background, colorless and transparent polyimide films have been developed. Typical examples include attempts to develop colorless and transparent polyimide films using fluorinated polyimide resins, semi-alicyclic or fully alicyclic polyimide resins, and the like (Patent Documents 1 to 3). These films are less colored and have transparency, but their mechanical properties are not as good as colored polyimide films. Colorlessness and transparency cannot always be maintained due to thermal decomposition or oxidation reaction. From this point of view, a method of heat treatment while blowing a gas with a specified oxygen content has been proposed (Patent Document 4), but the production cost is high in an environment where the oxygen concentration is less than 18%, and industrial production is not possible. Extremely difficult.

JP-A-11-106508 Japanese Patent Application Laid-Open No. 2002-146021 JP-A-2002-348374 WO2008/146637

In other words, practical properties such as heat resistance and mechanical properties are in a trade-off relationship with colorless transparency, and it has been very difficult to produce a colorless transparent polyimide film that satisfies all requirements. An object of the present invention is to provide a polyimide film having excellent mechanical properties and colorless transparency.

The present inventors attempted to realize a well-balanced polyimide film by combining a plurality of polyimide resins. In general, when compounding, blending, or copolymerizing multiple component resins, it is not always possible to obtain the result of combining only the good points of each component, rather, the drawbacks are synergistic and appear. There are quite a few cases where However, as a result of continuing intensive research, the present inventors have found that by forming a film by combining polyimide resins so as to form a specific structure, the advantages of each component can be sufficiently brought out, and the present invention has been achieved. did.

That is, the present invention has the following configurations.
[1] A multilayer polyimide layer in which at least two polyimide layers having different compositions are laminated in the thickness direction,
A transition layer that exists between the (a) layer constituting the multilayer polyimide layer and the (b) layer adjacent to the (a) layer and whose chemical composition changes with a gradient,
the thickness of the transition layer has a lower limit of either 3% of the total film thickness or 1 μm and an upper limit of either 10% of the total film thickness or 3 μm;
The thickness 3 of the entire film is μm or more and 120 μm or less,
The yellow index of the entire film is 5 or less,
A multilayer polyimide film having a total light transmittance of 86% or more.
[2] The layer (a) is mainly composed of a polyimide having a yellow index of 10 or less and a total light transmittance of 85% or more when made into a film having a thickness of 25±2 μm by itself,
The layer (b) is mainly composed of polyimide having a yellow index of 5 or less and a total light transmittance of 90% or more when made into a film having a thickness of 25±2 μm by itself. , the multilayer polyimide film according to [1].
[3] The layer (a) is present on both one side and the other side of the layer (b),
The transition layer is provided between the (a) layer and the (b) layer on one side of the (b) layer, and between the (a) layer and the (b) layer on the other side of the (b) layer. b) present between the layers,
[1] or [2], characterized by having a layer structure in which the (a) layer, the transition layer, the (b) layer, the transition layer, and the (a) layer are laminated in this order. The multilayer polyimide film according to .
[4] The polyimide of the layer (a) is
A polyimide having a chemical structure obtained by condensation polymerization of a tetracarboxylic anhydride containing 70% by mass or more of an alicyclic tetracarboxylic acid anhydride and a diamine containing 70% by mass or more of a diamine having an amide bond in the molecule. ,
Or a chemical structure obtained by condensation polymerization of a tetracarboxylic anhydride containing 30% by mass or more of an alicyclic tetracarboxylic anhydride and a diamine containing 70% by mass or more of a diamine having a trifluoromethyl group in the molecule polyimide, consisting of
The multilayer polyimide film according to any one of [1] to [3], characterized in that:
[5] The polyimide of the layer (b) is
A polyimide having a chemical structure obtained from a tetracarboxylic anhydride containing 70% by mass or more of an aromatic tetracarboxylic anhydride and a diamine containing 70% by mass or more of a diamine having a sulfur atom in the molecule;
or condensation polymerization of a tetracarboxylic acid anhydride containing 70% by mass or more of a tetracarboxylic acid containing a trifluoromethyl group in the molecule and a diamine containing 70% by weight or more of a diamine having a trifluoromethyl group in the molecule A polyimide consisting of a chemical structure obtained by
The multilayer polyimide film according to any one of [1] to [4], characterized in that:
[6] 1: (a) a step of applying a layer-forming polyimide solution or polyimide precursor solution to a temporary support to obtain a coating film a1;
2: Within 100 seconds after the coating film a1 is produced, (b) a step of applying a layer-forming polyimide solution or polyimide precursor solution to the coating film a1 to obtain the coating film ab1;
3: A step of heating all layers to obtain a laminate having a residual solvent amount of 0.5% by mass or less based on all layers;
The method for producing a multilayer polyimide film according to [1], [2], [4] or [5].
[7] 1: (a) a step of applying a layer-forming polyimide solution or polyimide precursor solution to a temporary support to obtain a coating film a1;
2: Within 100 seconds after the coating film a1 is produced, (b) a step of applying a layer-forming polyimide solution or polyimide precursor solution to the coating film a1 to obtain the coating film ab1;
3: After heating all layers to obtain a laminate having a residual solvent amount of 5% by mass or more and 40% by mass based on all layers, peeling from the temporary support to obtain a self-supporting film;
5: A step of holding both ends of the self-supporting film and further obtaining a film having a residual solvent amount of 0.5% by mass or less based on all layers;
The method for producing a multilayer polyimide film according to [1], [2], [4] or [5].
[8] 1: (a) a step of applying a layer-forming polyimide solution or polyimide precursor solution onto a temporary support to obtain a coating film a1;
2: Within 100 seconds after the coating film a1 is produced, (b) a step of applying a layer-forming polyimide solution or polyimide precursor solution to the coating film a1 to obtain the coating film ab1;
3: Within 100 seconds after the coating film ab1 is produced, (a) a step of applying a layer-forming polyimide solution or polyimide precursor solution to the coating film ab1 to obtain the coating film aba1;
4: A step of heating all layers to obtain a laminate having a residual solvent amount of 0.5% by mass or less based on all layers;
The method for producing a multilayer polyimide film according to any one of [1] to [5].
[9] 1: (a) a step of applying a layer-forming polyimide solution or polyimide precursor solution to a temporary support to obtain a coating film a1;
2: Within 100 seconds after the coating film a1 is produced, (b) a step of applying a layer-forming polyimide solution or polyimide precursor solution to the coating film a1 to obtain the coating film ab1;
3: Within 100 seconds after the coating film ab1 is produced, (a) a step of applying a layer-forming polyimide solution or polyimide precursor solution to the coating film ab1 to obtain the coating film aba1;
4: After heating all layers to obtain a laminate having a residual solvent amount of 8% by mass or more and 40% by mass based on all layers, peeling from the temporary support to obtain a self-supporting film;
5: A step of holding both ends of the self-supporting film and further obtaining a film having a residual solvent amount of 0.5% by mass or less based on all layers;
The method for producing a multilayer polyimide film according to any one of [1] to [5].

The present invention may further include the following configurations.
[10] A method for producing a multilayer polyimide film, wherein 1 and 2 in the above [6] are repeated to form 5 or more odd-numbered layers.
[11] The multilayer polyimide film of [1] to [5], wherein the thickness of the layer (a) is 34% or less of the total thickness of the film. However, when there are multiple layers (a), the total thickness of the layers (a) is 1% or more, preferably 2% or more, more preferably 4% or more, and preferably 25% or less, of the total thickness of the film. is 13% or less, more preferably 7% or less, the multilayer polyimide film according to [1] to [5].

The present invention realizes a heat-resistant film with excellent optical properties (colorless transparency) and mechanical properties that provide sufficient handling properties as a flexible film by forming the film from multiple layers of different compositions. It is something to do.

The polyimide of the (a) layer in the present invention preferably contains 70% by mass or more of a tetracarboxylic anhydride containing 70% by mass or more of an alicyclic tetracarboxylic anhydride and 70% by mass or more of a diamine having an amide bond in the molecule. A polyimide having a chemical structure obtained by condensation polymerization with a diamine, or a tetracarboxylic anhydride containing 30% by mass or more of an alicyclic tetracarboxylic anhydride and a diamine having a trifluoromethyl group in the molecule at 70 It is a polyimide having a chemical structure obtained by condensation polymerization with a diamine containing more than 1% by mass, and such polyimide has excellent mechanical properties, high elongation at break, and low CTE. easy to color.
The polyimide of one (b) layer is preferably a tetracarboxylic anhydride containing 70% by mass or more of an aromatic tetracarboxylic anhydride and a diamine containing 70% by mass or more of a diamine having a sulfur atom in the molecule. or a tetracarboxylic anhydride containing 70% by mass or more of a tetracarboxylic acid containing a trifluoromethyl group in the molecule, and a diamine having a trifluoromethyl group in the molecule 70 It is a polyimide having a chemical structure obtained by condensation polymerization with a diamine containing more than 10% by mass, and has high colorless transparency. It is not always suitable for flexible applications because it is difficult to process, and it is also difficult to produce as a continuous film.
When the two are blended or copolymerized, it is possible to obtain a film having physical properties intermediate or lower than those of the two, and the colorless transparency tends to be influenced by the properties of the (a) layer, which is easily colored.

However, as in the present invention, these two-component polyimides are formed as independent layers to divide the functions, and by applying a specific manufacturing method, a well-balanced colorless transparency and transparency can be obtained. A film having practically sufficient film strength, high elongation at break, and low coefficient of linear expansion can be obtained.
A polyimide film can be obtained by applying a polyimide solution or a solution of a polyimide precursor to a support, drying it, and optionally chemically reacting it. Most preferably, it is characterized by using a manufacturing method of simultaneous coating. According to such a coating method, mass transfer by diffusion or flow occurs in a limited thickness region on the surface where different components come into contact, forming a transition layer with a graded composition. Since the transition layer buffers mismatches such as stress occurring between layers having different physical properties, a well-balanced film can be obtained without concentrating internal strain on a specific site.

The multilayer polyimide film of the present invention has a thickness of 3 μm or more and 120 μm or less. The thickness is preferably 4 μm or more, more preferably 5 μm or more, and still more preferably 8 μm or more, because good mechanical properties are obtained. Further, the thickness is preferably 100 μm or less, more preferably 80 μm or less, and still more preferably 60 μm or less, because transparency is improved.

The multilayer polyimide film of the present invention has a yellow index of 5 or less. It is preferably 4 or less, more preferably 3.5 or less, and still more preferably 3 or less, because the transparency becomes good. Since the lower the yellow index is, the better, the lower limit is not particularly limited.

The multilayer polyimide film of the present invention has a total light transmittance of 86% or more. It is preferably 87% or more, more preferably 88% or more, and still more preferably 89% or more, because good transparency is achieved. Although the upper limit is not particularly limited, it may be 99% or less industrially, and may be 98% or less.

In the present invention, at least two kinds of polyimides having different compositions are used and laminated in the thickness direction. Polyimide is generally a polymer obtained by condensation polymerization reaction of tetracarboxylic anhydride and diamine. Preferably, the at least two polyimide layers include a layer (a) and a layer (b), and the layers (a) and (b) are each mainly composed of polyimide having the following characteristics. Here, the term "mainly" means that each layer preferably contains 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly Preferably it is 100% by mass. In addition, "having different compositions" means that at least the resin composition of each polyimide is different.

Polyimide mainly used in the (a) layer (hereinafter, "mainly" is omitted, and may be simply described as "polyimide used in the (a) layer" or "polyimide used as the (a) layer", etc.) is preferably a polyimide having a yellow index of 10 or less and a total light transmittance of 85% or more when made into a film having a thickness of 25±2 μm by itself. The yellow index is preferably 9 or less, more preferably 8 or less, and still more preferably 7 or less, because good transparency is obtained. The lower limit of the yellow index is not particularly limited. The total light transmittance is preferably 86% or higher, more preferably 87% or higher, and still more preferably 88% or higher. Although the upper limit is not particularly limited, it may be 99% or less industrially, and may be 98% or less.

The thickness of the (a) layer in the multilayer polyimide film is preferably more than 1 μm, more preferably 1.5 μm or more, still more preferably 2 μm or more, and particularly preferably 3 μm, because the mechanical strength is improved. That's it. Further, the thickness is preferably less than 119 μm, more preferably 100 μm or less, still more preferably 50 μm or less, and particularly preferably 20 μm or less, because transparency is improved.

The polyimide mainly used in the layer (a) is preferably a tetracarboxylic anhydride containing 70% by mass or more of an alicyclic tetracarboxylic anhydride when the total acid component is 100% by mass, and all amine components is 100% by mass, a polyimide having a chemical structure obtained by condensation polymerization with a diamine containing 70% by mass or more of a diamine having an amide bond in the molecule, or 30% by mass of an alicyclic tetracarboxylic acid anhydride It is a polyimide having a chemical structure obtained by condensation polymerization of a tetracarboxylic anhydride containing the above and a diamine containing 70% by mass or more of a diamine having a trifluoromethyl group in the molecule.

Polyimide mainly used in the (b) layer (hereinafter, "mainly" is omitted, and may be simply described as "polyimide used in the (b) layer" or "polyimide used as the (b) layer", etc.) is preferably a polyimide having a yellow index of 5 or less and a total light transmittance of 90% or more when made into a film having a thickness of 25±2 μm by itself. The yellow index is preferably 4 or less, and more preferably 3 or less, because good transparency is achieved. The lower limit of the yellow index is not particularly limited. The total light transmittance is preferably 91% or more, more preferably 92% or more. Although the upper limit is not particularly limited, it may be 99% or less industrially, and may be 98% or less. The yellow index of the polyimide used in the (b) layer is preferably smaller than the yellow index of the polyimide used in the (a) layer. Moreover, the total light transmittance of the polyimide used for the (b) layer is preferably higher than the total light transmittance of the polyimide used for the (a) layer.

The thickness of the (b) layer in the multilayer polyimide film is preferably more than 1 μm, more preferably 2 μm or more, still more preferably 3 μm or more, and particularly preferably 4 μm or more, because the mechanical strength is improved. be. Further, the thickness is preferably less than 119 μm, more preferably 100 μm or less, still more preferably 80 μm or less, and particularly preferably 50 μm or less, because transparency is improved.

The polyimide mainly used in the layer (b) is preferably a tetracarboxylic anhydride containing 70% by mass or more of an aromatic tetracarboxylic anhydride when the total acid component is 100% by mass, and all amine components. A polyimide having a chemical structure obtained from a diamine containing 70% by mass or more of a diamine having at least a sulfur atom in the molecule when 100% by mass, or a tetracarboxylic acid containing at least a trifluoromethyl group in the molecule. It is a polyimide having a chemical structure obtained by condensation polymerization of a tetracarboxylic anhydride containing 70% by mass or more and a diamine containing 70% by mass or more of a diamine having at least a trifluoromethyl group in the molecule.

The alicyclic tetracarboxylic acid anhydrides used in the present invention include 1,2,3,4-cyclobutanetetracarboxylic acid, 1,2,3,4-cyclopentanetetracarboxylic acid, and 1,2,3,4-cyclohexane. Tetracarboxylic 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, bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetra carboxylic acids, 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-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-cyclo Heptanone- 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''-tetra Carboxylic acid, norbornane-2-spiro-α-cyclodecanone-α'-spiro-2″-norbornane-5,5″,6,6″-tetracarboxylic acid, norbornane-2-spiro-α-cyclounde Kanone-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, norbornane-2-spiro-α-(methylcyclohexanone)-α′-spiro-2″ -norbornane-5,5″,6,6″-tetracarboxylic acid, and other tetracarboxylic acids and their acid anhydrides. Among these, dianhydrides having two acid anhydride structures are preferred, particularly 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclohexanetetracarboxylic acid Acid dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride is preferred, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic An acid dianhydride is more preferred, and 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride is even more preferred. In addition, these may be used independently and may use 2 or more types together.

The aromatic tetracarboxylic anhydrides used in the present invention 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-dicarbon 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- Benzoxathiol-1,1-dioxide-3,3-diyl)bis(toluene-2,5-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4′-[(3H-2,1-benz oxathiol-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-benzoxathio diyl-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, tetracarboxylic acids and acid anhydrides thereof. Aromatic tetracarboxylic acids may be used alone, or two or more of them may be used in combination.

In the present invention, tricarboxylic acid and dicarboxylic acid may be used in addition to tetracarboxylic anhydride.
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. acids or hydrogenated products of the above aromatic tricarboxylic acids such as hexahydrotrimellitic acid; Glycol bistrimellitate, and their monoanhydrides and esters. Among these, monoanhydrides having one acid anhydride structure are preferred, and trimellitic anhydride and hexahydrotrimellitic anhydride are particularly preferred. In addition, these may be used individually and may be used in combination.

Dicarboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, 4,4'-oxydibenzenecarboxylic acid, or the above aromatic dicarboxylic acids such as 1,6-cyclohexanedicarboxylic acid. Hydrogenates of oxalic acid, succinic acid, glutaric acid, adipic acid, heptanedioic acid, octanedioic acid, azelaic acid, sebacic acid, undecadeic acid, dodecanedioic acid, 2-methylsuccinic acid, and their acid chlorides Alternatively, an esterified product and the like can be mentioned. Among these, aromatic dicarboxylic acids and hydrogenated products thereof are preferred, and terephthalic acid, 1,6-cyclohexanedicarboxylic acid, and 4,4'-oxydibenzenecarboxylic acid are particularly preferred. In addition, dicarboxylic acids may be used alone or in combination.

Aromatic diamines and alicyclic amines can be mainly used as the diamine having an amide bond in the molecule in the present invention.
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-hexafluoro Propane, 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 '-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 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-amino phenoxy)-3-methylphenyl]propane, 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-hexafluoro Propane, 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 Su[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]diphenylsulfone, bis[4-{4-(4-aminophenoxy)phenoxy}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'-dibiphenoxybenzophenone, 4,4'-diamino-5,5'-dibiphenoxybenzophenone, 3,4'-diamino-4,5'-dibiphenoxybenzophenone, 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-pheno xybenzoyl)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]benzonitrile, 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, 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-phenylenebis(6-aminobenzoxazole), 1-(5-aminobenzoxazolo)-4-(6-aminobenzo oxazolo)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, 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, 2,6-(3,3'-diaminodiphenyl)benzo[1,2-d:4,5-d']bisoxazole and the like. In addition, some or all of the hydrogen atoms on the aromatic ring of the aromatic diamine may be substituted with a halogen atom, an alkyl or alkoxyl group having 1 to 3 carbon atoms, or a cyano group, and Some or all of the hydrogen atoms in the alkyl or alkoxyl groups of 1 to 3 may be substituted with halogen atoms.

Alicyclic diamines include, for example, 1,4-diaminocyclohexane, 1,4-diamino-2-methylcyclohexane, 1,4-diamino-2-ethylcyclohexane, 1,4-diamino-2-n-propyl cyclohexane, 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, 4,4′-methylenebis(2,6-dimethylcyclohexylamine), 9,10-bis(4-aminophenyl)adenine, 2,4-bis(4- aminophenyl)cyclobutane-dimethyl-1,3-dicarboxylate, and the like.

In the present invention, the (a) layer exists on both one surface side and the other surface side of the (b) layer, and the transition layer includes the (a) layer on one surface side of the (b) layer and ( (a) layer, transition layer, (b) layer, transition layer , (a) layers are laminated in this order. Hereinafter, the layer structure in which the (a) layer, the transition layer, the (b) layer, the transition layer, and the (a) layer are laminated in this order is also referred to as "(a)/(b)/(a)". Similarly, a layer structure in which the (a) layer, the transition layer, and the (b) layer are laminated in this order is also referred to as "(a)/(b)", and the (a) layer, the transition layer, the (b) layer, The layer structure in which the transition layer, (a) layer, transition layer, (b) layer, transition layer, and (a) layer are laminated in this order is expressed as "(a)/(b)/(a)/(b)/(a )”.
In the present invention, the (a) layer and the (b) layer have a two-layer structure of (a) / (b), or a three-layer structure of (a) / (b) / (a), and preferably, ( A film having a five-layer structure of a)/(b)/(a)/(b)/(a), or an odd-numbered film having seven layers, nine layers, or more layers may be used. In the case of an odd number of layers, it is preferred that the layer (a) be positioned as the outermost layer. By making the (a) layer, which has excellent mechanical properties and a small linear expansion coefficient compared to the (b) layer, the outermost layer, the linear expansion coefficient of the entire film can be suppressed to a low side, and mechanical strength is improved. By providing an excellent surface layer, the handling of the film is improved and the excellent optical properties of the (b) layer polyimide, which is the inner layer, can be maximized. The (b) layer is preferably thicker than the (a) layer. The ratio of the thickness of the (b) layer to the thickness of the (a) layer is preferably greater than (b) layer/(a) layer = 1, more preferably 1.5 or more, and still more preferably 2 That's it. Also, it is preferably 20 or less, more preferably 15 or less, and even more preferably 12 or less.

In the present invention, the thickness of the (a) layer is preferably 34% or less of the total thickness of the film when the (a) layer has a plurality of layers, and more preferably 26% or less. It is preferable to configure it to be 13% or less, more preferably 7% or less. The thickness of the layer (a) is 1% or more, preferably 2% or more, more preferably 4% or more of the total thickness of the film. By setting the thickness of the (a) layer within this range, it is possible to obtain a film in which the mechanical properties of the (a) layer and the optical properties of the (b) layer are well balanced.
In addition, when indicating the thickness of the (a) layer and the (b) layer, from the center of the thickness direction of the transition layer, the (a) layer side is the (a) layer, and the (b) layer side is the (b) layer. shall be included in the layer.

In the present invention, a transition layer (mixed layer) exists between the (a) layer and the (b) layer, the composition of which continuously changes from the polyimide of the (a) layer to the polyimide of the (b) layer. . Preferably, the lower limit of the transition layer thickness is either 3% of the total film thickness, or 1 μm, and the upper limit of the transition layer thickness is either 10% of the total film thickness, or 3 μm. . The lower limit is preferably more than 3% of the total thickness of the film, or 1.1 μm, more preferably 3.2% of the total thickness of the film, or 1.2 μm. More preferably, it is either 3.5% of the total thickness, or 1.5 μm. The upper limit is preferably 9% of the total thickness of the film or 2.8 μm, more preferably 8% of the total thickness of the film or 2.6 μm. By adjusting the thickness of the transition layer within the above range, both transparency and mechanical strength can be achieved.
The thickness of the transition layer is the thickness of the region where the polyimide of the (a) layer and the polyimide of the (b) layer are mixed and the composition is inclined from one side to the other, and the (a) layer of the mixed layer. The composition ratio (mass ratio) of the polyimide of the layer/the polyimide of the layer (b) is in the range of 5/95 to 95/5. The thickness of the transition layer can be measured by obliquely cutting the film in the thickness direction and observing the composition distribution of the polyimide.

The thickness of the transition layer is obtained from the thickness of the transition layer present at the interface and the total thickness of the film, since there is one place between the layers (interface) when the multilayer polyimide film has a laminated structure of two layers. be able to. When the multilayer polyimide film has a laminated structure of three layers, there are two layers (interfaces) between the layers, so it can be determined from the total thickness of each transition layer and the total thickness of the film. When the multi-layered polyimide film has a laminated structure of four or more layers, it can be similarly determined from the total thickness of all the transition layers and the total thickness of the film.

The polyimide used for the layer (a) in the present invention is preferably a polyimide having a yellow index of 10 or less and a total light transmittance of 85% or more when made into a film having a thickness of 25±2 μm alone. . Furthermore, the polyimide used for the layer (a) preferably has a CTE of 25 ppm/K or less, more preferably 20 ppm/K or less, a tensile strength at break of 100 MPa or more, preferably 120 MPa or more, and a breaking elongation of It is preferably 10% or more, more preferably 12% or more.
Preferred polyimides for the layer (a) include a tetracarboxylic anhydride containing 70% by mass or more of an alicyclic tetracarboxylic anhydride and a diamine containing 70% by mass or more of a diamine having an amide bond in the molecule. A polyimide having a chemical structure obtained by condensation polymerization can be exemplified.
Further, the polyimide used for the layer (a) contains a tetracarboxylic anhydride containing 70% by mass or more of an alicyclic tetracarboxylic anhydride and 70% by mass or more of a diamine having a trifluoromethyl group in the molecule. A polyimide having a chemical structure obtained by condensation polymerization with a diamine can be exemplified.
An alicyclic tetracarboxylic acid anhydride can be used for any polyimide for layer (a). The content of the alicyclic tetracarboxylic anhydride is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and even more preferably 70% by mass or more of the total tetracarboxylic anhydride. is 95% by mass or more. Coloring is suppressed by keeping the content of the alicyclic tetracarboxylic acid within a predetermined range.

As the diamine having an amide bond in the molecule, 4-amino-N-(4-aminophenyl)benzamide is preferred. The diamine having an amide bond is preferably used in an amount of 70% by mass or more, more preferably 80% by mass or more, more preferably 90% by mass or more in the total diamine.
Diamines having a trifluoromethyl group in the molecule include 2,2′-ditrifluoromethyl-4,4′-diaminobiphenyl and 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene. , 2,2′-trifluoromethyl-4,4′-diaminodiphenyl ether are preferred. When using a diamine compound having a fluorine atom in the molecule, particularly a diamine having a trifluoromethyl group in the molecule, the amount used is preferably 70% by mass or more, preferably 80% by mass or more, of the total diamine. is preferably used in an amount of 90% by mass or more.

The polyimide used for the layer (b) in the present invention is preferably a polyimide having a yellow index of 5 or less and a total light transmittance of 90% or more when made into a film having a thickness of 25±2 μm alone. .
The polyimide used in the layer (b) includes a tetracarboxylic anhydride containing 70% by mass or more of an aromatic tetracarboxylic acid anhydride and a diamine containing 70% by mass or more of a diamine having at least a sulfur atom in the molecule. A polyimide having a chemical structure obtained from can be exemplified.
Further, as a polyimide suitable for the (b) layer, a tetracarboxylic anhydride containing 30% by mass or more of a tetracarboxylic acid containing at least a trifluoromethyl group in the molecule and at least a trifluoromethyl group in the molecule A polyimide having a chemical structure obtained by condensation polymerization with a diamine containing 70% by mass or more of diamine can be exemplified.

As the aromatic tetracarboxylic acid anhydride preferably used in the polyimide of layer (b), 4,4'-oxydiphthalic acid, pyromellitic acid, and 3,3',4,4'-biphenyltetracarboxylic acid are preferred. The aromatic tetracarboxylic dianhydride used in the (b) layer polyimide is preferably 70% by mass or more, more preferably 80% by mass or more, more preferably 80% by mass or more of the total tetracarboxylic acid in the (b) layer polyimide It is 90% by mass or more, and still more preferably 95% by mass or more. The heat resistance is improved by setting the content of the aromatic tetracarboxylic acid within a predetermined range.

4,4'-(2,2-hexafluoroisopropylidene)diphthalic dianhydride is preferable as the tetracarboxylic acid containing a trifluoromethyl group in the molecule used in the polyimide of the layer (b). The tetracarboxylic acid containing a trifluoromethyl group in the molecule used in the polyimide layer (b) is preferably 30% by mass or more, more preferably 45% by mass or more, of the total tetracarboxylic acid in the polyimide layer (b). more preferably 60% by mass or more, and even more preferably 80% by mass or more. The colorless transparency is improved by keeping the content of the tetracarboxylic acid containing a trifluoromethyl group in the molecule within a predetermined range.

In the polyimide preferably used as the (b) layer of the present invention, the diamine preferably used is a diamine having at least a sulfur atom in the molecule and/or a diamine having a trifluoromethyl group in the molecule.
3,3'-diaminodiphenylsulfone, 3,4'-diaminodiphenylsulfone, and 4,4'-diaminodiphenylsulfone can be used as the diamine having a sulfur atom in the molecule. In the present invention, a diamine containing 70% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more of a diamine having a sulfur atom in the molecule is used in combination with an aromatic tetracarboxylic acid anhydride. Colorless transparency can be obtained also in the case.
Diamines having a trifluoromethyl group include 2,2′-ditrifluoromethyl-4,4′-diaminobiphenyl, 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene, 2,2′ -trifluoromethyl-4,4'-diaminodiphenyl ether is preferred.
When using a diamine compound having a fluorine atom in the molecule, particularly a diamine having a trifluoromethyl group in the molecule, the amount used is preferably 70% by mass or more, 80% by mass or more, and further 90% by mass of the total diamine. It is preferable to use at least 10% by mass.

The polyimide layer (a) and the polyimide layer (b) in the present invention are characterized by their yellow index, total light transmittance, mechanical properties, etc. when made into a film having a thickness of 25±2 μm. Here, the operation to form a film with a thickness of 25 ± 2 µm alone is an evaluation on a scale possible in a laboratory, and the polyimide solution or polyimide precursor solution is 10 cm square, preferably 20 cm square or more. It is applied to a glass plate, first preheated at a temperature of up to 120°C, preheated and dried until the amount of residual solvent is 40% by mass or less of the coating film, and further at 300°C in an inert gas such as nitrogen. It is a numerical value obtained by evaluating a film obtained by heating for 20 minutes. When inorganic components such as lubricants and fillers are contained for adjustment of physical properties, numerical values of the physical properties of the film obtained using a solution containing them are used.

The polyimide layer (a) and the polyimide layer (b) in the present invention may each contain a lubricant (filler). The lubricant may be an inorganic filler or an organic filler, but an inorganic filler is preferred. The lubricant is not particularly limited, and includes silica, carbon, ceramics, etc. Among them, silica is preferable. These lubricants may be used alone, or two or more of them may be used in combination. The average particle size of the lubricant is preferably 10 nm or more, more preferably 30 nm or more, and still more preferably 50 nm or more. Also, it is preferably 1 μm or less, more preferably 500 nm or less, and still more preferably 100 nm or less. The content of the lubricant in the polyimide of layer (a) and the polyimide of layer (b) is preferably 0.01% by mass or more. It is more preferably 0.02% by mass or more, still more preferably 0.05% by mass or more, and particularly preferably 0.1% by mass or more because the smoothness of the polyimide film is improved. From the viewpoint of transparency, the content is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, and particularly preferably 5% by mass or less.

The manufacturing method for obtaining the multilayer polyimide film of the present invention is described below. Among the multilayer polyimide films of the present invention, the polyimide film having a two-layer structure is
Preferably, the temperature is 10 ° C. or higher and 40 ° C. or lower and the humidity is 10% or higher and 55% or lower in the atmosphere or in an inert gas, 1: (a) Temporarily supporting the polyimide solution or polyimide precursor solution for layer formation Applying to the body to obtain a coating film a1,
2: Within 100 seconds after the coating film a1 is produced, (b) a step of applying a layer-forming polyimide solution or polyimide precursor solution to the coating film a1 to obtain the coating film ab1;
3: A step of heating all layers to obtain a laminate having a residual solvent amount of 0.5% by mass or less based on all layers;
can be made via
The temporary support is preferably long and flexible. Also, the heating time in step 3 is preferably 5 minutes or more and 60 minutes or less. The amount of residual solvent on the basis of all layers in step 3 is obtained from the mass of the coating film ab1 only, and does not include the mass of the temporary support. In addition, the starting point of 100 seconds in the step 2 is after the completion of applying the (a) layer-forming polyimide solution or polyimide precursor solution to the temporary support. The same applies to the following operations.
Furthermore, the process of 3 is divided into two stages,
3′: After heating for 5 minutes or more and 45 minutes or less until the residual solvent amount based on all layers reaches 8% by mass or more and 40% by mass, peel from the temporary support to form a self-supporting film. the step of obtaining
4: A step of holding both ends of the self-supporting film and further heating until the amount of residual solvent on the basis of all layers is 0.5% by mass or less,
It is good as By peeling off the temporary support at the stage of the self-supporting film, it is possible to quickly discharge the by-products generated by drying and chemical reaction from the film, and further reduce the difference in physical properties and structure between the front and back. be able to.

In the case of a film having three or more layers, the (a) layer polyimide solution or polyimide precursor solution may be applied once again after the above 1 and 2, and the (a) layer and the (b) layer are further repeated. A multi-layered film can be obtained by coating.

In the present invention, the polyimide solution or polyimide precursor solution is applied at a temperature of 10° C. or higher and 40° C. or lower, preferably 15° C. or higher and 35° C. or lower, and a humidity of 10% RH or higher and 55% RH or lower, preferably 20% RH or higher. It is preferably carried out on a long flexible temporary support in the atmosphere of 50% RH or in an inert gas. In addition, it is preferable to apply the next layer within 100 seconds, preferably within 50 seconds, more preferably within 25 seconds after applying the layer one step before. Since it is preferable that the time until the next layer is applied is as short as possible, the lower limit is not particularly limited. As for the coating method, the first layer can be coated using a comma coater, bar coater, slit coater, etc., and the second and subsequent layers can be coated using a die coater, curtain coater, spray coater, etc. . It is also possible to apply these multiple layers virtually simultaneously by using a multi-layer die.

The environment in which the solution is applied is preferably in the air or in an inert gas. The inert gas may be interpreted as a gas having a substantially low oxygen concentration, and nitrogen or carbon dioxide may be used from an economical point of view.

The temperature in the coating environment affects the viscosity of the coating fluid and the formation of the transition layer thickness when the two coating fluids mix with each other at the interface to form the transition layer when the two coating fluids are superimposed. affects The viscosity of the polyimide solution or polyimide precursor solution of the present invention is preferably adjusted to an appropriate viscosity range, particularly in the non-contact coating method for the second and subsequent layers, and such a temperature range is in the mixing of the two-layer interface. also contributes to maintaining appropriate fluidity in this viscosity range.

Many of the solvents used for polyimide solutions and polyimide precursor solutions are hygroscopic. When the solvent absorbs moisture and the water content of the solvent increases, the solubility of the resin component decreases, the dissolved component precipitates in the solution, and the solution A rapid increase in viscosity may occur. After application, if such a situation occurs, formation of a transition layer of adequate thickness will be inhibited. By keeping the humidity within a predetermined range, it is possible to sufficiently prevent the precipitation of such dissolved components within a period of about 100 seconds.

Glass, a metal plate, a metal belt, a metal drum, a polymer film, a metal foil, etc. can be used as the temporary support used in the present invention. In the present invention, it is preferable to use a long and flexible temporary support, and a film of polyethylene terephthalate, polyethylene naphthalate, polyimide, or the like can be used as the temporary support. It is one of preferred embodiments to subject the surface of the temporary support to release treatment.

In the present invention, after all the layers have been applied, they are subjected to heat treatment to dry and, if necessary, to undergo chemical reactions. When a polyimide solution is used, it may be simply dried in the sense of solvent removal, but when a polyimide precursor solution is used, both drying and chemical reaction are required. Polyimide precursors are preferably in the form of polyamic acids or polyisoimides. A dehydration condensation reaction is required to convert polyamic acid to polyimide. The dehydration-condensation reaction can be carried out only by heating, but if necessary, an imidization catalyst can be used. In the case of polyisoimide as well, isoimide bonds can be converted to imide bonds by heating. Moreover, it is also possible to use an appropriate catalyst together.
The residual solvent content of the final film is 0.5% by mass or less, preferably 0.2% by mass or less, more preferably 0.08% by mass or less as an average value of all layers of the film. The heating time is preferably 5 minutes or more and 60 minutes or less, preferably 6 minutes or more and 50 minutes or less, more preferably 7 minutes or more and 30 minutes or less. By keeping the heating time within a predetermined range, the removal of the solvent and the necessary chemical reaction can be completed, the transition layer can be controlled to an appropriate thickness, and colorless transparency, mechanical properties, especially breaking elongation can be kept high. If the heating time is short, the formation of the transition layer will be delayed, and if the heating time is longer than necessary, the film may be highly colored and the breaking elongation of the film may be lowered.

In the present invention, if the applied solution dries or undergoes a chemical reaction by heating and is self-supporting and can be peeled off from the temporary support, it may be peeled off from the temporary support during the heating step.
More specifically, it takes 5 minutes or more and 45 minutes or less, preferably 6 minutes or more and 30 minutes or less, more preferably 7 minutes or more, until the average amount of residual solvent in all film layers reaches the range of 8% by mass or more and 40% by mass. After heating for 20 minutes or less, the self-supporting film is peeled off from the temporary support, and both ends of the self-supporting film are clamped with clips or pierced with pins and held, and the heating environment The multilayer polyimide film is conveyed inside and heated until the residual solvent amount based on all layers is 0.5% by mass or less, preferably 0.2% by mass or less, more preferably 0.08% by mass or less. can be adopted.
By peeling the self-supporting film from the temporary support in the middle of the heating process and continuing the heating process, the evaporation of the solvent and the water generated when polyamic acid converts to polyimide through dehydration and ring closure can be quickly removed from both sides of the film. It can be discharged, and a film with a small physical property difference between the front and back can be obtained.

In the present invention, the self-supporting film may be stretched. Stretching may be performed in either the longitudinal direction (MD direction) or the width direction (TD) of the film, or both. Stretching in the longitudinal direction of the film can be carried out using the speed difference between the transport rolls or the speed difference between the transport rolls and the speed after both ends are gripped. Stretching in the width direction of the film can be carried out by widening the gripped clips or pins. Stretching and heating may be performed simultaneously. The draw ratio can be arbitrarily selected between 1.00 times and 2.5 times. In the present invention, by making the film into a multilayer structure, by combining a polyimide that is difficult to stretch alone and a polyimide that can be stretched, it is possible to stretch the polyimide to a composition that is difficult to stretch, that is, is likely to break when stretched. Mechanical properties can be improved.
Since the volume of polyimide decreases during film formation due to drying or dehydration condensation, the stretching effect is exhibited even when both ends are held at equal intervals (stretching ratio is 1.00).

For the layers (a) and (b) in the multilayer polyimide film of the present invention, fine unevenness is imparted to the layer (film) surface by, for example, adding a lubricant to the polyimide to improve the slipperiness of the film. is preferred. A form in which the lubricant is added only to the layer (a), which is the outer layer, is preferred.
As the lubricant, inorganic or organic fine particles having an average particle diameter of about 0.03 μm to 3 μm can be used. Specific examples include titanium oxide, alumina, silica, calcium carbonate, calcium phosphate, calcium hydrogen phosphate, calcium pyrophosphate, Examples include magnesium oxide, calcium oxide, and clay minerals. The lubricant content in the polyimide (polymer) is preferably 0.1% by mass or more, more preferably 0.4% by mass or more. Moreover, it is preferably 50% by mass or less, more preferably 30% by mass or less.

Hereinafter, the present invention will be described in detail using examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. In addition, each physical property value in the production examples and examples was measured by the following methods.

<Thickness measurement of polyimide film>
It was measured using a micrometer (Millitron 1245D manufactured by Finereuf).

<Tensile modulus, tensile strength (breaking strength), and breaking elongation>
A strip of 100 mm×10 mm was cut from the film in the flow direction (MD direction) and the width direction (TD direction) at the time of application to prepare a test piece. Using a tensile tester (manufactured by Shimadzu Corporation, Autograph (R) model name AG-5000A), under the conditions of a tensile speed of 50 mm / min and a distance between chucks of 40 mm, the tensile modulus and tensile strength are measured in each of the MD and TD directions. And the breaking elongation was determined, and the average value of the measured values in the MD direction and the TD direction was determined.

<Coefficient of linear expansion (CTE)>
The film is stretched in the machine direction (MD direction) and width direction (TD direction) at the time of coating, and the expansion ratio is measured under the following conditions, and at intervals of 15 ° C. such as 30 ° C. to 45 ° C. and 45 ° C. to 60 ° C. This measurement was performed up to 300° C., the average value of all measured values was calculated as CTE, and the average value of the measured values in the MD and TD directions was obtained.
Equipment name; TMA4000S manufactured by MAC Science
Sample length; 20mm
Sample width; 2 mm
Heating start temperature; 25°C
Heating end temperature; 300°C
Temperature rise rate; 5°C/min
atmosphere; argon

<Transition layer thickness>
A slanted cut surface of the film was prepared by SAICAS DN-20S (Daipla Wintes), and then this slanted cut surface was subjected to microscopic ATR using a germanium crystal (incidence angle of 30°) using a microscopic IRCary 620 FTIR (Agilent). The spectrum is obtained by the method, and the increase and decrease in the characteristic peaks of each of the (a) layer and the (b) layer, and the inclination of the composition is obtained in terms of mass ratio from the calibration curve obtained in advance, and the (a) layer composition / ( b) The transition layer thickness was obtained when the layer composition ratio was in the range of 5/95 mass ratio to 95/5 mass ratio.

<Haze>
The haze of the film was measured using a Hazemeter (NDH5000, manufactured by Nippon Denshoku Co., Ltd.). A D65 lamp was used as the light source. In addition, the same measurement was performed 3 times and the arithmetic mean value was adopted.

<Total light transmittance>
The total light transmittance (TT) of the film was measured using a Hazemeter (NDH5000, manufactured by Nippon Denshoku Co., Ltd.). A D65 lamp was used as the light source. In addition, the same measurement was performed 3 times and the arithmetic mean value was adopted.
The results are shown in Tables 2-6.

<Yellow index>
Using a color meter (ZE6000, manufactured by Nippon Denshoku Co., Ltd.) and a C2 light source, the tristimulus values XYZ values of the film were measured according to ASTM D1925, and the yellowness index (YI) was calculated according to the following formula. In addition, the same measurement was performed 3 times and the arithmetic mean value was adopted.
YI=100×(1.28X−1.06Z)/Y

<Warp of film>
A film cut into a square with a size of 100 mm × 100 mm is used as a test piece, and the test piece is placed on a flat surface at room temperature so that it becomes concave, and the distance from the flat surface at the four corners (h1rt, h2rt, h3rt, h4rt: unit mm ) was measured, and the average value was taken as the amount of warpage (mm).

[Production Example 1 Production of polyamic acid solution A]
After purging the interior of a reaction vessel equipped with a nitrogen inlet tube, a reflux tube, and a stirring rod with nitrogen, 22.73 parts by mass of 4,4'-diaminobenzanilide (DABAN) was added to 201.1 parts by mass of N,N-dimethyl. It was dissolved in acetamide (DMAc), then 19.32 parts by mass of 1,2,3,4-cyclobutanetetracarboxylic acid anhydride (CBDA) was added as a solid in portions, and then stirred at room temperature for 24 hours. . Thereafter, 173.1 parts by mass of DMAc was added for dilution to obtain a polyamic acid solution A having NV (solid content) of 10 mass % and reduced viscosity of 3.10 dl/g.

[Production Example 2 (a) Production of layer-forming lubricant-containing polyamic acid solution As)]
In the polyamic acid solution A obtained in Production Example 1, a dispersion obtained by dispersing colloidal silica as a lubricant in dimethylacetamide (“Snowtex (registered trademark) DMAC-ST-ZL” manufactured by Nissan Chemical Industries) and silica. (Lubricant) was added so that the total polymer solid content in the polyamic acid solution was 1.4% by mass) to obtain a uniform polyamic acid solution As.

[Production Example 3 Production of polyamic acid solution B]
After purging the inside of a reaction vessel equipped with a nitrogen inlet tube, a reflux tube, and a stirring rod, 32.02 parts by mass of 2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl (TFMB) was added to 279.5 parts by mass. Dissolve in 9 parts by weight of N,N-dimethylacetamide (DMAc), then 9.81 parts by weight of 1,2,3,4-cyclobutanetetracarboxylic anhydride (CBDA) and 15.51 parts by weight 4,4′-oxydiphthalic dianhydride (ODPA) was added in portions as a solid, and then stirred at room temperature for 24 hours. Thereafter, a polyamic acid solution B having a solid content of 17% by mass and a reduced viscosity of 3.60 dl/g was obtained.

[Production Example 4 (a) Production of Polyamic Acid Solution Bs Containing Lubricant for Layer Formation)]
In the polyamic acid solution B obtained in Production Example 3, a dispersion obtained by dispersing colloidal silica as a lubricant in dimethylacetamide (manufactured by Nissan Chemical Industries, Ltd. "Snowtex (registered trademark) DMAC-ST-ZL") and silica ( A uniform polyamic acid solution Bs was obtained by adding a lubricant) so that the total polymer solid content in the polyamic acid solution was 0.45% by mass).

[Production Example 5 (b) Production of layer-forming polyimide solution C]
32.02 parts by mass of 2,2'-ditrifluoromethyl-4,4' was introduced into a reaction vessel equipped with a nitrogen inlet tube, a Dean-Stark apparatus, a reflux tube, a thermometer, and a stirring rod while introducing nitrogen gas. -Diaminobiphenyl (TFMB), 230 parts by weight of N,N-dimethylacetamide (DMAc) are added and completely dissolved, and then 44.42 parts by weight of 4,4'-(2,2-hexafluoroisopropylidene ) Diphthalic dianhydride (6FDA) was added portionwise as a solid, followed by stirring at room temperature for 24 hours. Thereafter, a polyamic acid solution Caa having a solid content of 25% by mass and a reduction end of 1.10 dl/g was obtained.
Next, 204 parts by mass of DMAc was added to the resulting polyamic acid solution Caa to dilute it so that the polyamic acid concentration was 15% by mass, and then 1.3 parts by mass of isoquinoline was added as an imidization accelerator. Then, while stirring the polyamic acid solution, 12.25 parts by mass of acetic anhydride was slowly added dropwise as an imidizing agent. After that, stirring was continued for 24 hours to carry out a chemical imidization reaction to obtain a polyimide solution Cpi.
Next, 100 parts by mass of the obtained polyimide solution Cpi was transferred to a reaction vessel equipped with a stirrer and a stirrer, and 150 parts by mass of methanol was slowly added dropwise while stirring. rice field.
Thereafter, the powder contained in the reaction vessel was dehydrated and filtered, washed with methanol, vacuum dried at 50°C for 24 hours, and then heated at 260°C for 5 hours to obtain polyimide powder Cpd. A polyimide solution C was obtained by dissolving 20 parts by mass of the obtained polyimide powder in 80 parts by mass of DMAc.

[Production Example 6 (b) Production of layer-forming polyimide solution D]
120.5 parts by mass of 4,4′-diaminodiphenylsulfone (4,4′ -DDS), 51.6 parts by weight of 3,3′-diaminodiphenylsulfone (3,3′-DDS), and 500 parts by weight of gamma-butyrolactone (GBL) were added. Subsequently, 217.1 parts by mass of 4,4′-oxydiphthalic anhydride (ODPA), 223 parts by mass of GBL, and 260 parts by mass of toluene were added at room temperature, and then the internal temperature was raised to 160° C., The mixture was heated to reflux at 160° C. for 1 hour to effect imidization. After completion of imidization, the temperature was raised to 180° C., and the reaction was continued while extracting toluene. After reacting for 12 hours, the oil bath was removed and the temperature was returned to room temperature.

[Production Example 7 Production of polyamic acid solution E]
161 parts by mass of 2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl (TFMB) and 1090 parts by mass of N-methyl-2-pyrrolidone were placed in a reaction vessel equipped with a nitrogen inlet tube, a reflux tube, and a stirring rod under a nitrogen atmosphere. After dissolving by mixing and stirring, 112 parts by mass of 1,2,4,5-cyclohexanetetracarboxylic dianhydride (CHDA) was added portionwise as a solid at room temperature and stirred at room temperature for 12 hours. Next, 400 parts by mass of xylene was added as an azeotropic solvent, the temperature was raised to 180° C., and the reaction was carried out for 3 hours to separate the azeotropically produced water. After confirming that the outflow of water had ended, xylene was removed while the temperature was raised to 190° C. over 1 hour to obtain a polyamic acid solution E.

[Production Example 8 (a) Production of layer-forming lubricant-containing polyamic acid solution Es)]
In the polyamic acid solution E obtained in Production Example 7, a dispersion obtained by dispersing colloidal silica as a lubricant in dimethylacetamide (manufactured by Nissan Chemical Industries, Ltd. "Snowtex (registered trademark) DMAC-ST-ZL") and silica ( A uniform polyamic acid solution Es was obtained by adding a lubricant) so that the total polymer solid content in the polyamic acid solution was 1.0% by mass).

[Production Example 9 (b) Production of layer-forming filler-containing polyamic acid solution Ef)]
In the polyamic acid solution E obtained in Production Example 7, a dispersion obtained by dispersing colloidal silica as a lubricant in dimethylacetamide (manufactured by Nissan Chemical Industries, Ltd. "Snowtex (registered trademark) DMAC-ST-ZL") and silica ( Lubricant) was added so that the total polymer solid content in the polyamic acid solution was 25% by mass) to obtain a filler-containing polyamic acid solution Ef.

The polyimide solutions and polyamic acid solutions (polyimide precursor solutions) obtained in Production Examples 1 to 9 were formed into films by the following method, and optical properties and mechanical properties were measured. Table 1 shows the results.

(How to obtain a film for physical property measurement alone)
A polyimide solution or a polyamic acid solution was applied to the central part of a glass plate with a side of 30 cm and an area of about 20 cm square using a bar coater so that the final thickness was 25 ± 2 µm, and dry nitrogen was gently flowed. After heating at 100° C. for 30 minutes in an inert oven and confirming that the amount of residual solvent in the coating film was 40% by mass or less, heating was performed at 300° C. for 20 minutes in a muffle furnace purged with dry nitrogen. Then, it is taken out from the muffle furnace, the edges of the dried coating (film) are raised with a utility knife, and carefully separated from the glass to obtain a film.

(Example 1)
Polyamide acid solution As obtained in Production Example 2 was applied to a polyethylene terephthalate film A4100 (manufactured by Toyobo Co., Ltd., hereinafter abbreviated as PET film) using a comma coater in an air conditioned at 25° C. and 45% RH. After 10 seconds, the polyimide solution C obtained in Production Example 5 was coated on the polyamic acid solution As with a die coater so that the final film thickness was 20 μm. applied. It was dried at 110° C. for 10 minutes. After drying, the film obtained self-supporting property is separated from the A4100 film used as the support, passed through a pin tenter having a pin sheet on which pins are arranged, and gripped by inserting the ends of the film into the pins so as not to break the film. And conveyed by adjusting the pin sheet interval so that unnecessary slack does not occur, and heated under the conditions of 200 ° C. for 3 minutes, 250 ° C. for 3 minutes, and 300 ° C. for 6 minutes to advance the imidization reaction. rice field. After that, the film was cooled to room temperature for 2 minutes, and portions of the film having poor flatness at both ends were cut off with a slitter and rolled up into a roll to obtain a roll of film (Example 1) having a width of 580 mm and a length of 100 m.
Table 2 shows the evaluation results of the obtained film (Example 1).

(Examples 2-4)
Films (Ex. 2) to (Ex. 4) and a comparative example film (Comp. 1) were obtained by setting the conditions shown in Table 2 below. Table 2 shows the results of the same evaluation.

(Comparative Examples 1 to 4)
As Comparative Example 1, a film (Comparison 1) was obtained under the same conditions as in Example 3 with a thickness of 25 μm using only the polyamic acid solution As. Similarly, films (ratio 2) to (ratio 4) were obtained using polyimide solution C, polyamic acid solution Bs alone, and polyimide solution D alone. Each evaluation result is shown in Table 3.
The mechanical property values of the films (Comparison 1) to (Comparison 4) show higher breaking strength and breaking elongation than those of the test pieces obtained in the production examples. This difference is due to the fact that the production example film, which was formed into a film while being coated on the glass, was peeled off from the PET film, which is a temporary support, during the heat treatment, and the film was formed while the solvent and reaction product were discharged from the front and back of the film. It shows the difference if you go.

(Calculation examples 1 and 2)
The numerical values shown in column 1 of calculation example in Table 4 are the arithmetic mean values of the evaluation results of films (comparison 1) and (comparison 2). Calculation Example 2 is an average value weighted by the thickness ratio of the (a) layer and the (b) layer in Examples 1-4.
Comparing the evaluation results of the films obtained in the examples with the calculation examples, the films obtained in the examples both have lower haze and higher total light transmittance than calculation examples 1 and 2. The yellow index also shows a small value, indicating that the optical properties are improved. In addition, both the tensile strength and the elongation at break are higher in the example, and it can be seen that the mechanical properties are also improved.
This is because the warp is asymmetrical in the thickness direction of the film.

(Comparative Examples 5 and 6)
Subsequently, according to the conditions shown in Table 5, the polyamic acid solution As and the polyimide solution C were used to obtain films (ratio 5) (ratio 6). Table 5 shows the evaluation results. A significant increase in haze was observed in Comparative Example 5 in which the time interval from the coating of the (a) layer to the coating of the (b) layer was lengthened. It is presumed that the solution absorbed moisture in the atmosphere due to the longer heating time, causing a phase-separated structure in the coating film, and whitening occurred as drying progressed while the structure remained. . Also, the thickness of the transition layer is increased. The presence of the transition layer is necessary for the (a) layer and the (b) layer to bond firmly and gently with a composition gradient. Therefore, if this layer grows too thick, the advantage of dividing into multiple layers and sharing functions will be lost.
Comparative Example 6 is a case in which the polyimides of the (a) layer and the (b) layer are exchanged, but in this case, the synergistic effect seen in the example is not observed, and the optical properties are the same as those of the polyimides alone. It is inferior to the case where it is made into a film.

(Examples 5 to 9, 12, 13) [(a)/(b)/(a) production of three-layer film]
Polyamide acid solution As obtained in Production Example 2 was applied to a polyethylene terephthalate film A4100 (manufactured by Toyobo Co., Ltd., hereinafter abbreviated as PET film) using a comma coater in an air conditioned at 25° C. and 45% RH. The polyimide solution C obtained in Production Example 5 was coated on the non-slip material surface so that the final film thickness was 3 μm, and after 30 seconds, the polyimide solution C obtained in Production Example 5 was applied onto the polyamic acid solution As by a die coater so that the final film thickness was 31 μm. applied. After another 30 seconds, another die coater was used to apply polyamic acid solution As to a final film thickness of 3 μm.
This is dried at 110° C. for 10 minutes, and the film that has acquired self-supporting properties after drying is peeled off from the A4100 film used as a support, passed through a pin tenter having a pin sheet on which pins are arranged, and the ends of the film are inserted into the pins. Then, the film is conveyed by adjusting the interval between the pin sheets so that the film does not break and unnecessary slack occurs, and the film is heated at 200°C for 4 minutes, 250°C for 4 minutes, and 300°C for 6 minutes. The imidization reaction was allowed to proceed by heating under these conditions. After that, the film was cooled to room temperature for 2 minutes, and portions of the film having poor flatness at both ends were cut off with a slitter and rolled up into a roll to obtain a roll of film (Example 5) having a width of 580 mm and a length of 80 m. Table 6 shows the evaluation results of the obtained film (Example 5).
Similarly, according to Tables 6 and 7, films (Ex. 6) to (Ex. 9) were obtained by changing the polyamic acid solution, the polyimide solution, and the operating conditions. In addition, films (Example 12) and (Example 13) were obtained according to Table 5. Evaluation results are shown in each table.
As in Examples 1-4, it is shown that the properties are better than those of films made of a single layer. Furthermore, the warpage is greatly reduced as compared with Examples 1 to 4, and this is because the contrast in the thickness direction is improved.

(Calculation examples 3 and 4)
The numerical values shown in column 3 of calculation example in Table 4 are the arithmetic mean values of the evaluation results of films (comparison 3) and (comparison 4). Calculation Example 4 is an average value weighted by the thickness ratio of the (a) layer and the (b) layer in Example 8.
Comparing the evaluation results of the film obtained in Example 8 with the calculation example, it is shown that the film obtained in the example has better optical properties than calculation examples 3 and 4. Improvements in mechanical properties are also observed.

(Comparative Example 9)
Using the polyamic acid solution Ef to which the filler was added obtained in Production Example 9, a monolayer film of 50 μm was trial-manufactured. Table 7 shows the set conditions. After temporary drying, the self-supporting film was peeled off from the PET temporary support and introduced into a pin tenter, but the film broke in the longitudinal direction at the initial stage of heating. The test was continued by adjusting the pin width, but the film became very brittle during the drying and conversion reaction to polyimide, and it was not possible to obtain a film sufficient for physical property evaluation.

(Example 10)
Using the polyamic acid solution Es in which only the filler was added as a lubricant for the (a) layer and the filler-containing polyamic acid solution Ef obtained in Production Example 9 for the (b) layer, under the conditions set in Table 7 (a) A film having a /(b)/(a) configuration was produced as an experiment. Although it took time to adjust the pin width, a polyimide film (Example 10) having a width of 480 mm and a length of 50 m was finally obtained. Table 7 shows the evaluation results.

(Example 11)
The polyamic acid solution As and the polyimide solution C obtained in the production example were coated on a mirror-finished stainless steel belt using a three-layer co-extrusion T-shaped die. The lip gap of the die was 150 μm for the skin layer and 500 μm for the core layer. Thereafter, the film was heated according to the conditions shown in Table 7, the ends were slipped, and the film was wound up into a roll to obtain a film (Example 11) having a width of 1100 mm and a length of 300 m. Table 7 shows the evaluation results.

[Production Example 10 (Production of lubricant-containing polyamic acid solution Fs)]
After purging the inside of a reaction vessel equipped with a nitrogen inlet tube, a reflux tube, and a stirring rod, 33.36 parts by mass of 2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl (TFMB), 336.31 Parts by mass of N-methyl-2-pyrrolidone (NMP) and a dispersion obtained by dispersing colloidal silica as a lubricant in dimethylacetamide (manufactured by Nissan Chemical Industries, Ltd. "Snowtex (registered trademark) DMAC-ST-ZL") and silica (lubricant) was added so that the total polymer solid content in the polyamic acid solution was 0.3% by mass) and completely dissolved, and then 9.81 parts by mass of 1,2,3,4-cyclobutanetetracarboxylic Acid anhydride (CBDA), 11.34 parts by weight of 3,3′,4,4′-biphenyltetracarboxylic acid, 4.85 parts by weight of 4,4′-oxydiphthalic anhydride (ODPA) were added in portions as solids, and then stirred at room temperature for 24 hours. After that, a polyamic acid solution Fs with a solid content of 15% by mass and a reduced viscosity of 3.50 dl / g (molar ratio of TFMB // CBDA / BPDA / ODPA = 1.00 // 0.48 / 0.37 / 0.15) got

[Production Example 11 (Production of non-lubricant polyamic acid solution F)]
After purging the inside of the reaction vessel equipped with a nitrogen inlet tube, a reflux tube, and a stirring rod, 33.36 parts by mass of 2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl (TFMB) was added with 336.31 9.81 parts by mass of 1,2,3,4-cyclobutanetetracarboxylic anhydride (CBDA),11. 34 parts by mass of 3,3′,4,4′-biphenyltetracarboxylic acid and 4.85 parts by mass of 4,4′-oxydiphthalic anhydride (ODPA) were separately added as solids, and then cooled to room temperature. for 24 hours. After that, a polyamic acid solution F with a solid content of 15% by mass and a reduced viscosity of 3.50 dl / g (molar ratio of TFMB // CBDA / BPDA / ODPA = 1.00 // 0.48 / 0.37 / 0.15) got

(Example 14)
The polyamic acid solution Fs obtained in Production Example 10 was coated on a temporary support using an apparatus equipped with a roll-to-roll comma coater and a continuous drying furnace in an air conditioned at 25° C. and 45% RH. A certain PET film was coated on the non-lubricating surface so as to have a final film thickness of 5 μm, and then 10 seconds later, the polyamic acid solution F obtained in Production Example 11 was applied on the polyamic acid solution Fs to a final film thickness of 20 μm. It was applied by a die coater so that It was dried at 110° C. for 10 minutes.
After drying, the film that has acquired self-supporting properties is peeled off from the PET film used as the support, passed through a pin tenter having a pin sheet on which pins are arranged, and gripped by inserting the ends of the film into the pins so as not to break the film. And conveyed by adjusting the pin sheet interval so that unnecessary slack does not occur, and the final heating conditions are 200 ° C. for 3 minutes, 250 ° C. for 3 minutes, 300 ° C. for 3 minutes, and 400 ° C. for 3 minutes. to advance the imidization reaction. After that, the film was cooled to room temperature for 2 minutes, and portions of the film with poor flatness at both ends were cut off with a slitter and rolled up into a roll to obtain a roll of film (Example 14) having a width of 530 mm and a length of 80 m. The resulting film (Example 14) had a total film thickness of 25 μm, a haze of 0.41%, a total light transmittance of 88.2%, a yellow index of 4.1, a breaking strength of 230 MPa, a breaking elongation of 13.1%, and an elastic modulus of The results were 4.4 GPa, CTE 29 ppm/K, warpage 0.1 mm or less, and transition layer thickness 0.9 μm.

(Example 15)
The polyamic acid solution Fs obtained in Production Example 10 was coated on a temporary support using an apparatus equipped with a roll-to-roll comma coater and a continuous drying furnace in an air conditioned at 25° C. and 45% RH. A certain PET film was coated on the non-lubricating surface to a final film thickness of 3 μm, and then 10 seconds later, the polyamic acid solution F obtained in Production Example 11 was applied on the polyamic acid solution Fs to a final film thickness of 19 μm. After 30 seconds, another die coater was used to apply polyamic acid solution Fs to a final film thickness of 3 μm, which was dried at 110° C. for 10 minutes.
After drying, the film obtained self-supporting property was peeled off from the PET film used as the support, and a pin tenter was used in the same manner as in Example 12 at 200°C for 3 minutes, 250°C for 3 minutes, 300°C for 3 minutes, and 400°C. The imidization reaction was allowed to proceed by heating under the condition of 3 minutes at . Thereafter, the same operation was performed to obtain a roll of film (Example 15) having a width of 530 mm and a length of 80 m. The resulting film (Example 15) had a three-layer structure of Fs/F/Fs, with a total film thickness of 25 μm, a haze of 0.43%, a total light transmittance of 88.1%, a yellow index of 4.1, and a breaking strength of 180 MPa. , a breaking elongation of 12.5%, an elastic modulus of 4.2 GPa, a CTE of 30 ppm/K, a warp of 0.1 mm or less, and a transition layer thickness (air surface side/base surface side) of 1.2 μm/1.3 μm.

(Comparative Example 10)
In the air conditioned at 25° C. and 45% RH, using an apparatus equipped with a roll-to-roll comma coater and a continuous drying furnace, the polyamic acid solution As obtained in Production Example 2 was coated on a temporary support. It was applied to a final film thickness of 20 μm on the non-lubricated side of a PET film. Next, the film was heated at 110° C. for 5 minutes as primary heating using a continuous dryer to obtain a semi-dry film Agfx having a residual solvent content of 28% by mass, and the film was wound together with the temporary support into a roll.
The dry film Agfx, which has acquired self-supporting properties, is peeled off from the PET film used as the support, passed through a pin tenter having a pin sheet on which pins are arranged, and gripped by inserting the ends of the film into the pins so as not to break the film. And conveyed by adjusting the pin sheet interval so that unnecessary slack does not occur, and the final heating is performed under the conditions of 200 ° C. for 3 minutes, 250 ° C. for 3 minutes, and 300 ° C. for 6 minutes to imidize. The reaction was allowed to proceed. After that, the film was cooled to room temperature for 2 minutes, and portions of the film with poor flatness at both ends were cut off with a slitter and rolled up into a roll to obtain a roll of polyimide film (ratio 10a) with a width of 530 mm and a length of 50 m.

The resulting polyimide film (ratio 10a) roll is again set in the above-described apparatus, the polyimide film (ratio 10a) is unwound, and the polyimide solution C obtained in Production Example 5 is applied thereon to a final film thickness of 5 μm. It was coated with a comma coater. This was dried at 110° C. for 10 minutes as secondary heating.
After drying, the film is passed through a pin tenter having a pin sheet on which pins are arranged, and the edge of the film is gripped by inserting it into the pin. It was transported and heated under the conditions of 200° C. for 3 minutes, 250° C. for 3 minutes, and 300° C. for 6 minutes as the final heating to proceed the imidization reaction. After that, the film was cooled to room temperature for 2 minutes, and portions of the film with poor flatness at both ends were cut off with a slitter and rolled up into a roll to obtain a roll of polyimide film (ratio 10b) with a width of 450 mm and a length of 30 m.
The resulting polyimide film (ratio 10b) had a two-layer structure of As (20 μm)/C (5 μm), with a total film thickness of 25 μm, a haze of 0.63%, a total light transmittance of 86.9%, and a yellow index of 4.0. 3. The breaking strength was 154 MPa, the breaking elongation was 18%, the elasticity was 3.9 GPa, the CTE was 19.6 ppm/K, the warp was 2.8 mm or less, and the transition layer thickness was 0.0 µm. The warping amount of the film is large as compared with the examples.

(Comparative Example 11)
In the air conditioned at 25° C. and 45% RH, the polyamic acid solution As obtained in Production Example 2 was applied onto a glass substrate using an applicator so that the final film thickness was 3 μm, followed by 60 seconds. Later, the polyimide solution C obtained in Production Example 5 was applied onto the polyamic acid solution As by an applicator so that the final film thickness was 31 μm. After 60 seconds, the polyamic acid solution As was applied using an applicator so that the final film thickness was 3 μm. The final film thickness in this comparative example is a value determined from the film thickness obtained by separately applying each solution to a glass substrate.
This was dried in an inert oven at 110°C for 20 minutes, then heated in a vacuum dryer at 200°C for 10 minutes and 250°C for 10 minutes, and further heated in a muffle furnace at 350°C for 5 minutes, The imidization reaction was allowed to proceed, and the film was peeled off from the glass substrate to obtain a polyimide film (comparison 11).
The resulting polyimide film (ratio 11) is positioned as a film produced with the intention of having a three-layer structure of As (3 μm)/C (31 μm)/As (3 μm). The characteristics of polyimide film ratio 11 are total film thickness 37 μm, haze 5.2%, total light transmittance 83.9%, yellow index 1.8, breaking strength 130 MPa, breaking elongation 5.8%, elasticity 3.9 GPa. , CTE 37 ppm/K, warpage 3.5 mm, transition layer thickness (air surface side/base surface side) 3.5 μm/5.6 μm. The warp amount of the film is larger than that of Example 5, and the haze value is also increased. The thickness of the transition layer is thicker than the intended As layer at the time of coating, and rather than a multi-layered structure, it is close to a state in which the composition has been mixed in the middle. is not expressed.

As described above, it was shown that the multilayer polyimide film of the present invention has better optical properties and mechanical properties than polyimides with different compositions that are individually formed into films. Further, according to the production method of the present invention, it is possible to form a transition layer having a specific thickness and a compositional gradient between layers of different compositions divided into multiple layers and sharing functions, so that a well-balanced film can be formed. becomes possible.
The multilayer polyimide film of the present invention has excellent optical properties, colorless transparency, excellent mechanical properties, and a relatively low CTE. It can be used for switch elements such as touch panels, pointing devices, and the like.

Claims (8)

A multilayer polyimide layer in which at least two polyimide layers having different compositions are laminated in the thickness direction;
A transition layer that exists between the (a) layer constituting the multilayer polyimide layer and the (b) layer adjacent to the (a) layer and whose chemical composition changes with a gradient,
The layer (a) has a yellow index of 6.8 or more and 10 or less, a total light transmittance of 85% or more, and a linear expansion coefficient of 25 ppm/K when made into a film having a thickness of 25 ± 2 µm alone. Contains 70% by mass or more of the following polyimide,
The thickness of the layer (a) is more than 1 μm and less than 119 μm,
The (b) layer contains 70% by mass or more of a polyimide having a yellow index of 0.1 or more and 5 or less and a total light transmittance of 90% or more when made into a film having a thickness of 25 ± 2 µm alone,
The thickness of the layer (b) is more than 1 μm and less than 119 μm,
The transition layer is a layer whose composition continuously changes from the polyimide of the (a) layer to the polyimide of the (b) layer,
the thickness of the transition layer has a lower limit of either 3% of the total film thickness or 1 μm and an upper limit of either 10% of the total film thickness or 3 μm;
The thickness of the entire film is 3 μm or more and 120 μm or less,
The yellow index of the entire film is 5 or less,
A multilayer polyimide film having a total light transmittance of 86% or more. The (a) layer is present on both one side and the other side of the (b) layer,
The transition layer is provided between the (a) layer and the (b) layer on one side of the (b) layer, and between the (a) layer and the (b) layer on the other side of the (b) layer. b) present between the layers,
2. The multilayer according to claim 1, having a layer structure in which the (a) layer, the transition layer, the (b) layer, the transition layer, and the (a) layer are laminated in this order. polyimide film. The polyimide of the layer (a) is
A polyimide having a chemical structure obtained by condensation polymerization of a tetracarboxylic anhydride containing 70% by mass or more of an alicyclic tetracarboxylic acid anhydride and a diamine containing 70% by mass or more of a diamine having an amide bond in the molecule. ,
Or a chemical structure obtained by condensation polymerization of a tetracarboxylic anhydride containing 70% by mass or more of an alicyclic tetracarboxylic anhydride and a diamine containing 70% by mass or more of a diamine having a trifluoromethyl group in the molecule polyimide, consisting of
The multilayer polyimide film according to claim 1 or 2, characterized in that: The polyimide of the layer (b) is
A polyimide having a chemical structure obtained from a tetracarboxylic anhydride containing 70% by mass or more of an aromatic tetracarboxylic anhydride and a diamine containing 70% by mass or more of a diamine having a sulfur atom in the molecule;
or condensation polymerization of a tetracarboxylic anhydride containing 30% by mass or more of a tetracarboxylic acid containing a trifluoromethyl group in the molecule and a diamine containing 70% by weight or more of a diamine having a trifluoromethyl group in the molecule A polyimide consisting of a chemical structure obtained by
The multilayer polyimide film according to any one of claims 1 to 3, characterized in that: 1: (a) a step of applying a layer-forming polyimide solution or polyimide precursor solution to a temporary support to obtain a coating film a1;
2: Within 100 seconds after the coating film a1 is produced, (b) a step of applying a layer-forming polyimide solution or polyimide precursor solution to the coating film a1 to obtain the coating film ab1;
3: A step of heating all layers to obtain a laminate having a residual solvent amount of 0.5% by mass or less based on all layers;
The method for producing a multilayer polyimide film according to claim 1, 3 or 4, comprising at least 1: (a) a step of applying a layer-forming polyimide solution or polyimide precursor solution to a temporary support to obtain a coating film a1;
2: Within 100 seconds after the coating film a1 is produced, (b) a step of applying a layer-forming polyimide solution or polyimide precursor solution to the coating film a1 to obtain the coating film ab1;
3: After heating all layers to obtain a laminate having a residual solvent amount of 5% by mass or more and 40% by mass or less based on all layers, peeling from the temporary support to obtain a self-supporting film;
5: A step of holding both ends of the self-supporting film and further obtaining a film having a residual solvent amount of 0.5% by mass or less based on all layers;
The method for producing a multilayer polyimide film according to claim 1, 3 or 4, comprising at least 1: (a) a step of applying a layer-forming polyimide solution or polyimide precursor solution onto a temporary support to obtain a coating film a1;
2: Within 100 seconds after the coating film a1 is produced, (b) a step of applying a layer-forming polyimide solution or polyimide precursor solution to the coating film a1 to obtain the coating film ab1;
3: Within 100 seconds after the coating film ab1 is produced, (a) a step of applying a layer-forming polyimide solution or polyimide precursor solution to the coating film ab1 to obtain the coating film aba1;
4: A step of heating all layers to obtain a laminate having a residual solvent amount of 0.5% by mass or less based on all layers;
The method for producing a multilayer polyimide film according to any one of claims 1 to 4, comprising at least 1: (a) a step of applying a layer-forming polyimide solution or polyimide precursor solution to a temporary support to obtain a coating film a1;
2: Within 100 seconds after the coating film a1 is produced, (b) a step of applying a layer-forming polyimide solution or polyimide precursor solution to the coating film a1 to obtain the coating film ab1;
3: Within 100 seconds after the coating film ab1 is produced, (a) a step of applying a layer-forming polyimide solution or polyimide precursor solution to the coating film ab1 to obtain the coating film aba1;
4: After heating all layers to obtain a laminate having a residual solvent amount of 8% by mass or more and 40% by mass or less based on all layers, peeling from the temporary support to obtain a self-supporting film;
5: A step of holding both ends of the self-supporting film and further obtaining a film having a residual solvent amount of 0.5% by mass or less based on all layers;
The method for producing a multilayer polyimide film according to any one of claims 1 to 4, comprising at least