WO2022102451A1 - Polyimide film and production method therefor - Google Patents

Abstract

The present invention can obtain, without any trouble such as warpage, a film having a well-balanced combination of properties, which are colorlessness and transparency, practically sufficient film strength, high elongation at break, and low coefficient of linear expansion, by forming two polyimide ingredients as respective independent layers to perform allocation of functions and regulating the film-thickness ratio between the two layers to a value within a certain range.　This film is a two-layer film composed of a high-strength polyimide as an inner layer (a) and a polyimide with excellent optical properties as an outer layer (b). Polyimide or polyimide-precursor solutions for constituting the two layers are applied to a temporary support and heat-treated to form said imide film. The two layers are combined so that one of the two layers is far thinner than the other, thereby making it possible to obtain a film which is free from warpage and is colorless and transparent.

Description

Polyimide film and its manufacturing method

The present invention relates to a laminated polyimide film that is colorless, has a low coefficient of linear expansion and good mechanical properties, and has no defects such as warpage, and a method for producing the same.

Polyimide film has excellent heat resistance and good mechanical properties, and is widely used in the electric and electronic fields as a flexible material. However, since a general polyimide film is colored yellowish brown, it cannot be applied to a part such as a display device that requires light transmission.
On the other hand, display devices are becoming thinner and lighter, and further flexibility is required. Therefore, attempts are being made to replace the substrate material from a glass substrate with a flexible polymer film substrate, but the colored polyimide film is a substrate material for a liquid crystal display that displays by turning on / off light transmission. It cannot be used as a peripheral circuit such as a TAB or COF on which a drive circuit of a display device is mounted, or can be applied only to a small part such as the back side of a reflective display system or a self-luminous display device.

Against this background, the development of colorless and transparent polyimide films is underway. As a typical example, there is an attempt to develop a colorless transparent polyimide film using a fluorinated polyimide resin, a semi-lipid ring type or a full alicyclic polyimide resin (Patent Documents 1 to 3). These films are less colored and more transparent, but do not have as mechanical properties as colored polyimide films, and are intended for industrial production and high temperature exposure applications. Since thermal decomposition or oxidation reaction occurs, it is not always possible to maintain colorlessness and transparency. From this point of view, a method of heat treatment while spraying a gas having an oxygen content has been proposed (Patent Document 4), but the manufacturing cost is high in an environment where the oxygen concentration is less than 18%, and industrial production is not possible. It's extremely difficult.

Japanese Unexamined Patent Publication No. 11-106508 Japanese Unexamined Patent Publication No. 2002-146021 Japanese Unexamined Patent Publication No. 2002-348374 WO2008 / 146637A Gazette

Semi-alicyclic or full-alicyclic polyimides can obtain colorless transparency by increasing the number of monomer components having an alicyclic structure, but become hard and brittle and the elongation at break decreases, making it difficult to produce as a film. Become. On the other hand, if an aromatic monomer or a monomer having an amide bond in the molecule is introduced, the toughness is increased, the mechanical properties of the film are improved, but the color is easily colored and the colorless transparency is lowered. By introducing an inorganic component having a refractive index close to that of the resin component, heat resistance and colorless transparency are improved, the coefficient of linear expansion is further lowered, and processing suitability is improved, but the resin physical properties become hard and brittle, and the mechanical properties are descend.
That is, there is a trade-off relationship between practical properties such as heat resistance and mechanical properties and colorless transparency, and it has been extremely difficult to produce a colorless transparent polyimide film that satisfies all of them.

The present inventors tried to realize a well-balanced polyimide film by combining a plurality of polyimide resins. Generally, when a combination of resins of a plurality of components is blended, blended, or copolymerized, it is not always possible to obtain a result in which only the good points of each component are combined, but rather the drawbacks are synergistically expressed. There are many cases of doing so. However, as a result of diligent research, the present inventors have found that the advantages of each component can be fully brought out by forming each of the two component polyimides as an independent layer and forming a film.

When a film was formed by combining polyimide resins, warpage was sometimes seen due to the difference in the coefficient of linear expansion between the films. Therefore, as a result of diligent studies, the present inventors have been able to obtain a colorless transparent film without warpage by combining two types of layers so that one layer becomes significantly thinner than the other layer. We found what we could do and arrived at the present invention.
That is, the present invention has the following configuration.
[1] A multilayer polyimide film containing at least a polyimide layer (a) and a polyimide layer (b).
The composition of the polyimide layer (a) and the polyimide layer (b) are different.
The thickness of the polyimide layer (a) is 0.03 μm or more, and the film thickness is 0.03 μm or more.
The film thickness of the polyimide layer (b) is more than 5 times and 500 times or less the film thickness of the polyimide layer (a).
A multilayer polyimide film having a thickness of 3 μm or more and 120 μm or less, a yellow index of 5 or less, and a total light transmittance of 86% or more.
[2] The multilayer polyimide film according to [1], wherein the layer (a) and the layer (b) are mainly composed of polyimide having the following characteristics.
(A) Layer: Polyimide (b) layer having a yellow index of 10 or less and a total light transmittance of 80% or more when a film having a thickness of 25 ± 2 μm is used alone: A film having a thickness of 25 ± 2 μm alone. Polyimide with a yellow index of 5 or less and a total light transmittance of 85% or more when made into a film.
[3] The polyimide of the layer (a) is a polyimide having a chemical structure obtained by polycondensation of a tetracarboxylic acid anhydride and a diamine.
The tetracarboxylic acid anhydride contains an alicyclic tetracarboxylic acid anhydride, an acid dianhydride having a biphenyl bond in the molecule, an acid dianhydride having a trifluoromethyl group in the molecule, and an ether bond in the molecule. It is a tetracarboxylic acid anhydride containing at least one selected from the group consisting of acid dianhydride having.
The diamine is a diamine containing at least one selected from the group consisting of a diamine having an amide bond in the molecule and a diamine having a trifluoromethyl group in the molecule.
The multilayer polyimide film according to [1] or [2].
[4] The polyimide of the layer (b) is a polyimide having a chemical structure obtained by polycondensation of a tetracarboxylic acid anhydride and a diamine.
The tetracarboxylic acid anhydride contains an alicyclic tetracarboxylic acid anhydride, an acid dianhydride having a biphenyl bond in the molecule, an acid dianhydride having a trifluoromethyl group in the molecule, and an ether bond in the molecule. It is a tetracarboxylic acid anhydride containing at least one selected from the group consisting of acid dianhydride having.
The diamine is a diamine containing at least one selected from the group consisting of a diamine having a sulfone group in the molecule and a diamine having a trifluoromethyl group in the molecule.
The multilayer polyimide film according to any one of [1] to [3].
[5] 1: (a) A step of applying a polyimide solution for forming a layer or a polyimide precursor solution to a temporary support to obtain a coating film a1.
2: A step of drying the coating film a1 to obtain a coating film a2 having a residual solvent amount of 5 to 40% by mass.
3: (b) A step of applying a polyimide solution for forming a layer or a polyimide precursor solution to the coating film a2 to obtain the coating film ab1.
4: A step of heating the coating film ab1 to obtain a coating film ab2 having a residual solvent amount of 0.5% by mass or less based on the total layer of the coating film.
The method for producing a multilayer polyimide film according to any one of [1] to [4], which comprises at least.
[6] 1: (a) A step of applying a polyimide solution for forming a layer or a polyimide precursor solution to a temporary support to obtain a coating film a1.
2: A step of drying the coating film a1 to obtain a coating film a2 having a residual solvent amount of 5 to 40% by mass.
3: (b) A step of applying a polyimide solution for forming a layer or a polyimide precursor solution to the coating film a2 to obtain the coating film ab1.
4: A step of heating the coating film ab1 to obtain a coating film ab2 having a residual solvent amount of 5% by mass or more and 40% by mass based on the total layer of the coating film.
5: Step of peeling the coating film ab3 from the temporary support,
6: A step of heating the coating film ab3 to obtain a coating film ab4 having a residual solvent amount of 0.5% by mass or less based on the total layer of the coating film.
The method for producing a multilayer polyimide film according to any one of [1] to [5], which comprises at least.

By forming the two-component polyimide as independent layers, the functions are shared, and by setting the film thickness ratio of the two layers within a certain range, a well-balanced, that is, colorless transparency and practically sufficient film strength are achieved. A film having a high elongation at break and a low coefficient of linear expansion can be realized without any problems such as warpage.

The polyimide of the layer (a) in the present invention is preferably an alicyclic tetracarboxylic acid anhydride, an acid dianhydride having a biphenyl bond in the molecule, an acid dianhydride having a trifluoromethyl group in the molecule, and an acid dianhydride having a trifluoromethyl group in the molecule. A tetracarboxylic acid anhydride containing at least one selected from the group consisting of acid dianhydrides having an ether bond in the molecule, a diamine having an amide bond in the molecule, and a trifluoromethyl group in the molecule. It is a polyimide having a chemical structure obtained by condensation polymerization with a diamine containing at least one selected from the group consisting of diamines, and such polyimides have excellent properties showing low CTE, but are relatively easy to color.
The polyimide of one layer (b) is preferably an alicyclic tetracarboxylic acid anhydride, an acid dianhydride having a biphenyl bond in the molecule, an acid dianhydride having a trifluoromethyl group in the molecule, and an ether. A tetracarboxylic acid anhydride containing at least one selected from the group consisting of acid dianhydrides having a bond in the molecule, a diamine having a sulfone group in the molecule, and a diamine having a trifluoromethyl group in the molecule. It is a polyimide having a chemical structure obtained by condensation polymerization with a diamine containing at least one selected from the group consisting of, and has high colorless transparency, but is flexible because CTE may be high. It cannot be said that the suitability for various applications is always good, and it is also difficult to produce it as a continuous film.
When both are blended or copolymerized, only a film having a physical characteristic intermediate or lower than that of the film can be obtained, and the colorless transparency tends to be pulled by the characteristics of the layer (a) which is easily colored.

However, as in the present invention, the polyimides of these two components are formed as independent layers to divide the functions, and the film thickness ratio of the two layers is set within a certain range to achieve a good balance. A film having colorless transparency, practically sufficient film strength, high breaking elongation, and low coefficient of linear expansion can be obtained without warpage.
The polyimide film is obtained by applying a polyimide solution or a solution of a polyimide precursor to a support, drying it, and subjecting it to a chemical reaction as necessary. In the present invention, it is two different components (a). By coating the resin constituting the layer and the resin constituting the layer (b) so as to have a limited thickness, the stress generated from one of the layers can be significantly reduced. As a result, the warp caused by the CTE difference between the layer (a) and the layer (b) is reduced, and a well-balanced film can be obtained without concentrating internal strain on a specific portion.

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

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 further preferably 3 or less because the transparency is good. Since the lower the yellow index is, the lower limit is not particularly limited, but industrially, it may be 0.1 or more, and 0.2 or more may be used.

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 further preferably 89% or more because the transparency becomes good. The upper limit is not particularly limited, but industrially, it may be 99% or less, and may be 98% or less.

In the present invention, two types of polyimides having different compositions are used, and these are laminated in the thickness direction. Polyimide is generally a polymer obtained by a polycondensation reaction between a tetracarboxylic acid anhydride and a diamine. It is preferable that the two types of polyimide layers include a layer (a) and a layer (b), and the layer (a) and the layer (b) are mainly composed of polyimides having the following characteristics. Here, mainly, the polyimide having the following characteristics is preferably contained in each layer in an amount of 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly. It is preferably 100% by mass.

Polyimide mainly used for the (a) layer (hereinafter, "mainly" may be omitted and simply referred to as "polyimide used for the (a) layer", "polyimide used as the (a) layer", or the like). Is preferably a polyimide having a yellow index of 10 or less and a total light transmittance of 80% or more when a film having a thickness of 25 ± 2 μm is used alone. The yellow index is preferably 9 or less, more preferably 8 or less, and even more preferably 7 or less because the transparency is good. The lower limit of the yellow index is not particularly limited, but industrially, it may be 0.1 or more, and may be 0.2 or more. The total light transmittance is preferably 82% or more, more preferably 84% or more, still more preferably 86% or more. The upper limit is not particularly limited, but industrially, it may be 99% or less, and may be 98% or less.

The thickness (thickness) of the (a) layer in the multilayer polyimide film needs to be 0.03 μm or more in order to obtain an independent layer without penetrating the (b) layer, and is 0.03 μm. It is preferably super, more preferably 0.04 μm or more, still more preferably 0.05 μm or more. Further, it is preferably 20 μm or less, more preferably 10 μm or less, still more preferably 7.5 μm or less, and particularly preferably 5 μm or less because the transparency is good.

The polyimide mainly used for the layer (a) is preferably a polyimide having a chemical structure obtained by polycondensation of tetracarboxylic acid anhydride and diamine. The tetracarboxylic acid anhydride contains an alicyclic tetracarboxylic acid anhydride, an acid dianhydride having a biphenyl bond in the molecule, an acid dianhydride having a trifluoromethyl group in the molecule, and an ether bond in the molecule. It is preferable that it is a tetracarboxylic acid anhydride containing at least one selected from the group consisting of acid dianhydride having. Further, the diamine is preferably a diamine containing at least one selected from the group consisting of a diamine having an amide bond in the molecule and a diamine having a trifluoromethyl group in the molecule. The total of the alicyclic tracarboxylic acid anhydride, the acid dianhydride having a biphenyl bond in the molecule, the acid dianhydride having a trifluoromethyl group in the molecule, and the acid dianhydride having an ether bond in the molecule. The amount is preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more, and particularly preferably 95 mol% when the total acid component is 100 mol%. As mentioned above, 100 mol% may be used. Further, the total amount of the diamine having an amide bond in the molecule and the diamine having a trifluoromethyl group in the molecule is preferably 70 mol% or more, more preferably 70 mol% or more when the total diamine component is 100 mol%. It is preferably 80 mol% or more, more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may be 100 mol% or more. Within the above range, the mechanical properties of the multilayer polyimide film are improved.

Polyimide mainly used for the layer (b) (hereinafter, "mainly" may be omitted and simply referred to as "polyimide used for the layer (b)" or "polyimide used as the layer (b)"). Is preferably a polyimide having a yellow index of 5 or less and a total light transmittance of 85% or more when a film having a thickness of 25 ± 2 μm is used alone. The yellow index is preferably 4 or less, and more preferably 3 or less because the transparency is good. The lower limit of the yellow index is not particularly limited, but industrially, it may be 0.1 or more, and may be 0.2 or more. The total light transmittance is preferably 90% or more, more preferably 92% or more. The upper limit is not particularly limited, but industrially, it may be 99% or less, and may be 98% or less.

The thickness of the layer (b) in the multilayer polyimide film is preferably 3 μm or more, more preferably 4 μm or more, still more preferably 5 μm or more, and particularly preferably 6 μm or more because the mechanical strength is good. Is. Further, it is preferably less than 120 μm, more preferably 100 μm or less, still more preferably 80 μm or less, and particularly preferably 50 μm or less because the transparency is good.

The polyimide mainly used for the layer (b) is preferably a polyimide having a chemical structure obtained by polycondensation of tetracarboxylic acid anhydride and diamine. The tetracarboxylic acid anhydride contains an alicyclic tetracarboxylic acid anhydride, an acid dianhydride having a biphenyl bond in the molecule, an acid dianhydride having a trifluoromethyl group in the molecule, and an ether bond in the molecule. It is preferable that it is a tetracarboxylic acid anhydride containing at least one selected from the group consisting of acid dianhydride having. Further, the diamine is preferably a diamine containing at least one selected from the group consisting of a diamine having a sulfone group in the molecule and a diamine having a trifluoromethyl group in the molecule. The total of the alicyclic tetracarboxylic acid anhydride, the acid dianhydride having a biphenyl bond in the molecule, the acid dianhydride having a trifluoromethyl group in the molecule, and the acid dianhydride having an ether bond in the molecule. The amount is preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more, and particularly preferably 95 mol% when the total acid component is 100 mol%. As mentioned above, 100 mol% may be used. Further, the total amount of the diamine having a sulfone group in the molecule and the diamine having a trifluoromethyl group in the molecule is preferably 70 mol% or more, more preferably 70 mol% or more when the total diamine component is 100 mol%. It is preferably 80 mol% or more, more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may be 100 mol% or more. Within the above range, the transparency of the multilayer polyimide film becomes good.

Examples of the alicyclic tetracarboxylic acid anhydride 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] octo-7-en-2,3,5,6-tetra Carboxylic acid, tetrahydroanthracene-2,3,6,7-tetracarboxylic acid, tetradecahydro-1,4: 5,8: 9,10-trimethanoanthracene-2,3,6,7-tetracarboxylic acid, Decahydronaphthalene-2,3,6,7-tetracarboxylic acid, decahydro-1,4: 5,8-dimethanonaphthalene-2,3,6,7-tetracarboxylic acid, decahydro-1,4-ethano- 5,8-methanonaphthalene-2,3,6,7-tetracarboxylic acid, norbornan-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornan-5,5'',6 6''-Tetracarboxylic acid (also known as "norbornan-2-spiriro-2'-cyclopentanone-5'-spiro-2''-norbornan-5,5'', 6,6''-tetracarboxylic acid" ), Methylnorbornan-2-spiro-α-cyclopentanone-α'-spiro-2''-(methylnorbornan) -5,5'',6,6''-tetracarboxylic acid, norbornan-2-spiro -Α-Cyclohexanone-α'-Spiro-2''-Norbornane-5,5'', 6,6''-Tetracarboxylic acid (also known as "norbornan-2-spiriro-2'-cyclohexanone-6'-spiro-" 2''-norbornan-5,5'', 6,6''-tetracarboxylic acid "), methylnorbornan-2-spiro-α-cyclohexanone-α'-spiro-2''-(methylnorbornan) -5 , 5'', 6,6''-tetracarboxylic acid, norbornan-2-spiro-α-cyclopropanol-α'-spiro-2''-norbornan-5,5'', 6,6''- Tetracarboxylic acid, norbornan-2-spiro-α-cyclobutanone-α'-spiro-2''-norbornan-5,5'', 6,6''-tetracarboxylic acid, norbornan-2-spiro-α-cyclo Heptanone -Α'-Spiro-2''-norbornan-5,5'', 6,6''-tetracarboxylic acid, norbornan-2-spiro-α-cyclooctanone-α'-spiro-2''-norbornan -5,5'', 6,6''-tetracarboxylic acid, norbornan-2-spiro-α-cyclononanonone-α'-spiro-2''-norbornan-5,5'', 6,6''- Tetracarboxylic acid, norbornan-2-spiro-α-cyclodecanone-α'-spiro-2''-norbornan-5,5'', 6,6''-tetracarboxylic acid, norbornan-2-spiro-α-cyclo Undecanone-α'-Spiro-2''-norbornan-5,5'', 6,6''-tetracarboxylic acid, norbornan-2-spiro-α-cyclododecanone-α'-spiro-2'' -Norbornan-5,5'', 6,6''-tetracarboxylic acid, norbornan-2-spiro-α-cyclotridecanone-α'-spiro-2''-norbornan-5,5'', 6, 6''-tetracarboxylic acid, norbornan-2-spiro-α-cyclotetradecanone-α'-spiro-2''-norbornan-5,5'', 6,6''-tetracarboxylic acid, norbornan- 2-Spiro-α-Cyclopentadecanone-α'-Spiro-2''-norbornan-5,5'', 6,6''-tetracarboxylic acid, norbornan-2-spiro-α- (methylcyclopenta) Non) -α'-spiro-2''-norbornan-5,5'', 6,6''-tetracarboxylic acid, norbornan-2-spiro-α- (methylcyclohexanone) -α'-spiro-2' Examples thereof include tetracarboxylic acids such as'-norbornan-5,5'', 6,6''-tetracarboxylic acid, and acid anhydrides thereof. Among these, dianhydride having two acid anhydride structures is preferable, and in particular, 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride and 1,2,3,4-cyclohexanetetracarboxylic acid are preferable. Acid dianhydride, 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride is preferred, 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, 1,2,4,5-cyclohexanetetracarboxylic Acid dianhydride is more preferred, and 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride is even more preferred. These may be used alone or in combination of two or more.

In the present invention, the acid benzene having a biphenyl bond in the molecule, the acid benzene having a trifluoromethyl group in the molecule, and the acid benzene having an ether bond in the molecule are 4,4'-( 2,2-Hexafluoroisopropylidene) diphthalic acid, 4,4'-oxydiphthalic acid, bis (1,3-dioxo-1,3-dihydro-2-benzofuran-5-carboxylic acid) 1,4-phenylene, bis (1,3-Dioxo-1,3-dihydro-2-benzofuran-5-yl) Benzene-1,4-dicarboxylate, 4,4'-[4,4'-(3-oxo-1,3) -Dihydro-2-benzofuran-1,1-diyl) bis (benzene-1,4-diyloxy)] dibenzene-1,2-dicarboxylic acid, 3,3', 4,4'-benzophenonetetracarboxylic acid, 4, 4'-[(3-oxo-1,3-dihydro-2-benzofuran-1,1-diyl) bis (toluene-2,5-diyloxy)] dibenzene-1,2-dicarboxylic acid, 4,4'- [(3-oxo-1,3-dihydro-2-benzofuran-1,1-diyl) bis (1,4-xylene-2,5-diyloxy)] Dibenzene-1,2-dicarboxylic acid, 4,4' -[4,4'-(3-oxo-1,3-dihydro-2-benzofuran-1,1-diyl) bis (4-isopropyl-toluene-2,5-diyloxy)] dibenzene-1,2-dicarboxylic acid Acid, 4,4'-[4,4'-(3-oxo-1,3-dihydro-2-benzofuran-1,1-diyl) bis (naphthalen-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-benzoxathiol-1,1-dioxide-3,3-diyl) bis (1,3) 4-Xylene-2,5-diyloxy)] dibenzene-1,2-dicarboxylic acid, 4,4'-[4,4'-(3H-2,1-benzoxathiol-1,1-dioxide-3,) 3-Diyl) bis (4-isopropyl-toluene-2,5 -Diyloxy)] Dibenzene-1,2-dicarboxylic acid, 4,4'-[4,4'-(3H-2,1-benzoxathiol-1,1-dioxide-3,3-diyl) bis (naphthalene) -1,4-diyloxy)] dibenzene-1,2-dicarboxylic acid, 3,3', 4,4'-benzophenone tetracarboxylic acid, 3,3', 4,4'-benzophenone tetracarboxylic acid, 3,3 ', 4,4'-diphenylsulfonetetracarboxylic acid, 3,3', 4,4'-biphenyltetracarboxylic acid, 2,3,3', 4'-biphenyltetracarboxylic acid, pyromellitic acid, 4,4 '-[Spiro (xanthen-9,9'-fluorene) -2,6-diylbis (oxycarbonyl)] diphthalic acid, 4,4'-[spiro (xanthen-9,9'-fluorene) -3,6- Diylbis (oxycarbonyl)] Tetracarboxylic acids such as diphthalic acid and acid anhydrides thereof. These aromatic tetracarboxylic acids may be used alone or in combination of two or more. It was

Acid dianhydrides having a trifluoromethyl group in the molecule include 4,4'-(2,2-hexafluoroisopropylidene) diphthalic acid dianhydride and 1,4-di (trifluoromethyl) pyromerit. Acid dianhydride, 1,4-di (pentafluoroethyl) pyromellitic acid dianhydride and the like can be mentioned.

Acid dianhydrides having an ether bond in the molecule include 4,4'-oxydiphthalic acid anhydride, 4,4'-(4,4'-isopropylidene diphenoxy) diphthalic acid anhydride, 4,4-[ 4,4- (Propane-2,2-diyl) diphenoxy] Diphthalic acid dianhydride and the like can be mentioned.

In the present invention, tricarboxylic acid and dicarboxylic acid may be used in addition to tetracarboxylic acid anhydride.
Examples of the tricarboxylic acids include aromatic tricarboxylic acids such as trimellitic acid, 1,2,5-naphthalene tricarboxylic acid, diphenyl ether-3,3', 4'-tricarboxylic acid, and diphenylsulfone-3,3', 4'-tricarboxylic acid. An acid or an alkylene such as a hydrogenated additive of the above aromatic tricarboxylic acid such as hexahydrotrimeric acid, ethylene glycol bistrimericte, propylene glycol bistrimerite, 1,4-butanediol bistrimerite and polyethylene glycol bistrimerite. Glycol bistrimerictes and their monoanhydrides, esterified products and the like. Among these, monoanhydride having one acid anhydride structure is preferable, and in particular, trimellitic acid anhydride and hexahydrotrimellitic acid anhydride are preferable. These may be used alone or in combination of two or more.

Examples of the dicarboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, 4,4'-oxydibenzenecarboxylic acid, and the above aromatic dicarboxylic acid such as 1,6-cyclohexanedicarboxylic acid. Hydrogen additives, oxalic acid, succinic acid, glutaric acid, adipic acid, heptanedioic acid, octanedioic acid, azelaioic acid, sebacic acid, undecadioic acid, dodecanedioic acid, 2-methylsuccinic acid, and acid acidates thereof. Alternatively, an esterified product or the like can be mentioned. Of these, aromatic dicarboxylic acids and hydrogen additives thereof are preferable, and terephthalic acid, 1,6-cyclohexanedicarboxylic acid, and 4,4'-oxydibenzenecarboxylic acid are particularly preferable. The dicarboxylic acids may be used alone or in combination of two or more.

As the diamine having an amide bond in the molecule in the present invention, aromatic diamines and alicyclic amines can be mainly used.
Examples of aromatic diamines include 2,2'-dimethyl-4,4'-diaminobiphenyl, 1,4-bis [2- (4-aminophenyl) -2-propyl] benzene, and 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 Sulfur, 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- (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) Benzene] 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] Methan, 1,1-bis [4- (3-aminophenoxy) phenyl] ethane, 1,2-bi 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] diphenyl sulfone, 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-phenoyl) Xybenzoyl) benzene, 1,4-bis (4-amino-5-phenoxybenzoyl) benzene, 1,3-bis (3-amino-4-biphenoxybenzoyl) benzene, 1,4-bis (3-amino-) 4-Bifenoxybenzoyl) 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-fluoren-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 (xanthen-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) Benzeneoxazole, 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-aminobenzoxol) 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 can be mentioned. Further, a part or all of the hydrogen atoms on the aromatic ring of the aromatic diamine may be substituted with a halogen atom, an alkyl group or an alkoxyl group having 1 to 3 carbon atoms, or a cyano group, and further, the carbon number 1 may be substituted. A part or all of the hydrogen atom of the alkyl group or the alkoxyl group of ~ 3 may be substituted with a halogen atom.

Examples of alicyclic diamines include 1,4-diaminocyclohexane, 1,4-diamino-2-methylcyclohexane, 1,4-diamino-2-ethylcyclohexane, and 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-1,3-dimethyl dicarboxylate, and the like can be mentioned.

Examples of the diamine having a sulfone group in the molecule include 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone and the like.

In the present invention, the (a) layer polyimide and the (b) layer polyimide have a structure of two or more layers (a) / (b), and the (b) layer is on an upper layer, that is, a surface (air surface) in contact with air. It is preferable to arrange it so that it is located. By using the layer (a), which has a smaller coefficient of linear expansion than the layer (b), as the lower layer, that is, the surface in contact with the coating support, the handling of the film is improved and the (b) layer polyimide as the upper layer is excellent. The optical characteristics can be maximized.

The layer (b) is preferably thicker than the layer (a). The ratio of the thickness of the layer (b) to the thickness of the layer (a) is (b) layer / layer (a) = 25 or more, preferably 50 or more, more preferably 75 or more, and further. It is preferably 100 or more. By making one layer significantly thinner than the other, it is possible to suppress the warpage of the film caused by the difference in the coefficient of linear expansion. Further, it is 500 or less, preferably 450 or less, more preferably 400 or less, and further preferably 200 or less. By keeping the (b) layer / (a) layer in this range, the mechanical characteristics of the (a) layer and the optical characteristics of the (b) layer can be obtained without the (b) layer penetrating the (a) layer. It is possible to obtain a well-balanced film without any problems such as warpage. Further, the multilayer polyimide film of the present invention may have a multilayer structure of three or more layers. For example, a three-layer structure of (a) layer / (b) layer / (a) layer, a four-layer structure of (a) layer / (b) layer / (a) layer / (b) layer, (a) layer / It may have a five-layer structure of (b) layer / (a) layer / (b) layer / (a) layer. Further, in the multilayer polyimide film of the present invention, layers other than the layer (a) and the layer (b) may be laminated. Further, the third resin layer (c), the fourth resin layer (d), and the like may be inserted into any layer as long as the effects of the present invention are not impaired. Further, in order to cope with the fact that the roles required for both sides of the film differ depending on the application such as manufacturing a device on one side, the composition and surface roughness of both sides may be changed.

In the present invention, the thickness of the layer (a) is preferably 0.03 μm or more, preferably 0.05 μm or more, more preferably 0.1 μm or more, still more preferably 0.5 μm or more. Is preferable. By keeping the thickness of the layer (a) within this range, the mechanical properties of the layer (a) and the optical properties of the layer (b) are balanced without the layer (b) penetrating the layer (a). , It is possible to obtain a film without defects such as warpage.

In the present invention, the thickness of the laminated layers (a) and (b) can be measured by cutting the film diagonally in the thickness direction and observing the composition distribution of the polyimide.

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 80% or more when a film having a thickness of 25 ± 2 μm is used alone. .. Further, the polyimide used for the layer (a) preferably has a CTE of 30 ppm / K or less, more preferably 20 ppm / K or less, a tensile breaking strength of 120 MPa or more, further preferably 140 MPa or more, and a breaking elongation. It is preferably 8% or more, more preferably 10% or more.
Preferred polyimides for the layer (a) include an alicyclic tetracarboxylic acid anhydride, an acid dianhydride having a biphenyl bond in the molecule, an acid dianhydride having a trifluoromethyl group in the molecule, and an ether bond. A group consisting of a tetracarboxylic acid anhydride containing at least one selected from the group consisting of acid dianhydride contained therein, a diamine having an amide bond in the molecule, and a diamine having a trifluoromethyl group in the molecule. An example thereof is a polyimide having a chemical structure obtained by condensation polymerization with a diamine containing one or more of the selected substances. By adopting these configurations, coloring is suppressed.

As the diamine having an amide bond in the molecule, 4-amino-N- (4-aminophenyl) benzamide is preferable. When a diamine having an amide bond is used, it is preferably 70 mol% or more, more preferably 80 mol% or more, and further preferably 90 mol% or more of the total diamine.
Examples of the diamine 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 is preferred. When a diamine compound having a fluorine atom in these molecules, particularly a diamine having a trifluoromethyl group in the molecule is used, the amount used is preferably 70 mol% or more, more preferably 80 mol% or more, and further, 80 mol% or more of the total diamine. Is preferably used in an amount of 90 mol% 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 85% or more when a film having a thickness of 25 ± 2 μm is used alone. ..
The polyimide used for the layer (b) includes an alicyclic tetracarboxylic acid anhydride, an acid dianhydride having a biphenyl bond in the molecule, an acid dianhydride having a trifluoromethyl group in the molecule, and an ether bond. A tetracarboxylic acid anhydride containing at least one selected from the group consisting of acid dianhydrides having an acid dianhydride in the molecule.
Illustrate a polyimide having a chemical structure obtained by polycondensation with a diamine containing at least one selected from the group consisting of a diamine having a sulfone group in the molecule and a diamine having a trifluoromethyl group in the molecule. Can be done.

As the aromatic tetracarboxylic acid anhydride preferably used for the polyimide of the layer (b), 4,4'-oxydiphthalic acid, pyromellitic acid, and 3,3', 4,4'-biphenyltetracarboxylic acid are preferable. When the aromatic tetracarboxylic acid dianhydride used for the (b) layer polyimide is used, it is preferably 30 mol% or more, more preferably 50 mol% or more of the total tetracarboxylic acid of the (b) layer polyimide. .. Transparency is improved by keeping the content of the aromatic tetracarboxylic acid within a predetermined range.

As the tetracarboxylic acid containing a trifluoromethyl group used in the polyimide of the layer (b) in the molecule, 4,4'-(2,2-hexafluoroisopropylidene) diphthalic acid dianhydride is preferable. When a tetracarboxylic acid containing a trifluoromethyl group used in the (b) layer polyimide is used, 30 mol% or more of the total tetracarboxylic acid in the (b) layer polyimide is preferable, and more preferably 50. More than mol%. 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 layer (b) of the present invention, the diamine preferably used is a diamine having at least a sulfone group in the molecule and / or a diamine having a trifluoromethyl group in the molecule.
As the diamine having a sulfone group in the molecule, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, and 4,4'-diaminodiphenyl sulfone can be used. In the present invention, a diamine containing 70 mol% or more, preferably 80 mol% or more, more preferably 90 mol% or more of a diamine having a sulfone group in the molecule is used in combination with the aromatic tetracarboxylic acid anhydride. Colorless transparency can also be obtained in some cases. Diamines having a trifluoromethyl group include 4,4'-diamino-2,2'-bis (trifluoromethyl) biphenyl, 2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl, 1,4. -Bis (4-amino-2-trifluoromethylphenoxy) benzene, 2,2'-trifluoromethyl-4,4'-diaminodiphenyl ether is preferred.
When a diamine compound having a fluorine atom in the molecule, particularly a diamine having a trifluoromethyl group in the molecule is used, the amount used is preferably 70 mol% or more, 80 mol% or more, and further 90 in the total diamine. It is preferable to use mol% or more.

The polyimide of the layer (a) and the polyimide of the layer (b) in the present invention are characterized by the yellow index, total light transmittance, mechanical properties, etc. when a film having a thickness of 25 ± 2 μm is used alone. The operation of forming a film having a thickness of 25 ± 2 μm alone here is an evaluation of a scale possible in the laboratory, and the polyimide solution or the polyimide precursor solution has a size of 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 then at 300 ° C. in an inert gas such as nitrogen. It is a numerical value obtained by evaluating the film obtained by heating for 20 minutes. When inorganic components such as lubricants and fillers are contained for adjusting the physical characteristics, the physical property values of the film obtained by using the solution containing them are used.

The polyimide of the (a) layer and the polyimide of the (b) layer in the present invention can each contain a lubricant (filler). The lubricant may be an inorganic filler or an organic filler, but an inorganic filler is preferable. The lubricant is not particularly limited, and examples thereof include silica, carbon, and ceramic, and silica is preferable. These lubricants may be used alone or in combination of two or more. The average particle size of the lubricant is preferably 10 nm or more, more preferably 30 nm or more, still more preferably 50 nm or more. Further, it is preferably 1 μm or less, more preferably 500 nm or less, still more preferably 100 nm or less. The content of the lubricant in the polyimide of the layer (a) and the polyimide of the layer (b) is preferably 0.01% by mass or more with respect to the polymer mass. Since the smoothness of the polyimide film is good, it is more preferably 0.02% by mass or more, further preferably 0.05% by mass or more, and particularly preferably 0.1% by mass or more. Further, from the viewpoint of enhancing heat resistance, it is also good to add 20% by mass or more. From the viewpoint of transparency, it is preferably 50% by mass or less, more preferably 30% by mass or less, further preferably 10% by mass or less, and particularly preferably 5% by mass or less.

Hereinafter, a preferable manufacturing method for obtaining the multilayer polyimide film of the present invention will be described. The method for producing a multilayer polyimide film of the present invention is
1: (a) A step of applying a polyimide solution for forming a layer or a polyimide precursor solution to a temporary support to obtain a coating film a1.
2: A step of drying the coating film a1 to obtain a coating film a2 having a residual solvent amount of 5 to 40% by mass.
3: (b) A step of applying a polyimide solution for forming a layer or a polyimide precursor solution to the coating film a2 to obtain the coating film ab1.
4: A step of heating the coating film ab1 to obtain a coating film ab2 having a residual solvent amount of 0.5% by mass or less based on the total layer of the coating film.
It can be manufactured through.
The amount of residual solvent in the step 2 is preferably 8% by mass or more and 35% by mass or less, and more preferably 10% by mass or more and 30% by mass or less. Further, when the polyimide precursor solution is used in the step 1, it is preferable to carry out the imidization reaction in the drying step 4 (operation of reducing the residual solvent amount to 0.5% by mass or less).
The temporary support is preferably long and flexible. In addition, the residual solvent amount based on all layers in the second step shall be obtained from the mass of only the coating film ab1 and shall not include the mass of the temporary support. The same applies to the following operations.

Hereinafter, another preferable manufacturing method for obtaining the multilayer polyimide film of the present invention will be described. The method for producing a multilayer polyimide film of the present invention is
Preferably, in the atmosphere or an inert gas having a temperature of 10 ° C. or higher and 40 ° C. or lower and a humidity of 10% or higher and 55% or lower, 1: (a) a polyimide solution for forming a layer or a polyimide precursor solution is temporarily supported. The process of applying to the body to obtain the coating film a1
2: A step of drying the coating film a1 to obtain a coating film a2 having a residual solvent amount of 5 to 40% by mass.
3: (b) A step of applying a polyimide solution for forming a layer or a polyimide precursor solution to the coating film a2 to obtain a coating film ab1 4: The coating film ab1 is heated, and the residual solvent amount based on the entire layer of the coating film is 5 A step of obtaining a coating film ab3 having a mass% or more of 40% by mass,
5: Step of peeling the coating film ab3 from the temporary support,
6: A step of heating the coating film ab3 to obtain a coating film ab4 having a residual solvent amount of 0.5% by mass or less based on the total layer of the coating film.
It can be manufactured through.
The amount of residual solvent in the steps 2 and 4 is preferably 8% by mass or more and 35% by mass or less, and more preferably 10% by mass or more and 30% by mass or less. Further, when the polyimide precursor solution is used in the step 1, it is preferable to carry out the imidization reaction in the drying step 5 (operation of reducing the residual solvent amount to 0.5% by mass or less). The coating film ab3 peeled off from the temporary support in the step 5 becomes a self-supporting film. Then, when the coating film ab3 is heated in the step 6, it is preferable to grip both ends of the coating film ab3 (self-supporting film).
The temporary support is preferably long and flexible. In addition, the residual solvent amount based on all layers in the second step shall be obtained from the mass of only the coating film ab1 and shall not include the mass of the temporary support. The same applies to the following operations. By peeling from the temporary support at the stage of self-supporting film, by-products generated by drying and chemical reaction can be quickly discharged from the film, and the difference in physical properties and structure on the front and back can be reduced. be able to.

By peeling from the temporary support at the stage of self-supporting film, by-products generated by drying and chemical reaction can be quickly discharged from the film, and the difference in physical properties and structure between the front and back can be reduced. be able to.

In the present invention, the application of the polyimide solution or the polyimide precursor solution is performed 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 and flexible temporary support in the atmosphere of 50% RH or in an inert gas. As an application method, the first layer to be applied can be applied using a comma coater, a bar coater, a slit coater, or the like, and the second and subsequent layers can be applied by a die coater, a curtain coater, a spray coater, or the like. .. It is also possible to apply these plurality of layers substantially at the same time by using a multilayer die.

The environment for applying the solution is preferably in the atmosphere 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.

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

In the present invention, after all the layers have been applied, they are dried by heat treatment and, if necessary, subjected to a chemical reaction. When a polyimide solution is used, it may be simply dried in the sense of removing the solvent, but when a polyimide precursor solution is used, both drying and a chemical reaction are required. Here, the polyimide precursor is preferably in the form of polyamic acid or polyisoimide. A dehydration condensation reaction is required to convert polyamic acid to polyimide. The dehydration condensation reaction can be carried out only by heating, but an imidization catalyst can also be allowed to act if necessary. Even in the case of polyisoimide, conversion from an isoimide bond to an imide bond can be performed by heating. It is also possible to use an appropriate catalyst in combination.
The amount of residual solvent in the final film is 0.5% by mass or less, preferably 0.2% by mass or less, and 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, and more preferably 7 minutes or more and 30 minutes or less. By keeping the heating time within a predetermined range, it is possible to remove the solvent, complete the necessary chemical reaction, reduce the warp of the film, and keep the colorless transparency, mechanical properties, especially the elongation at break. Can be done. If the heating time is short, the warp of the film becomes large, and if the heating time is longer than necessary, the film coloring becomes stronger and the breaking elongation of the film may decrease.

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, and more preferably 7 minutes or more until the average residual solvent amount of all film layers reaches the range of 15% by mass or more and 40% by mass or less. After heating for 20 minutes or less, the self-supporting film is peeled off from the temporary support.

In the present invention, the self-supporting film may be stretched. The stretching may be in either the longitudinal direction of the film (MD direction) or the width direction (TD) of the film, or both. Stretching in the longitudinal direction of the film can be performed by using the speed difference of the transport roll or the difference in speed between the transport roll and the speed after gripping both ends. Stretching in the film width direction can be performed by widening the gripped clip or pin. Stretching and heating may be performed at the same time. The draw ratio can be arbitrarily selected from 1.00 times to 2.5 times. In the present invention, by forming the film into a multilayer structure, a polyimide that is difficult to stretch by itself and a polyimide that can be stretched can be combined to enable the polyimide to be stretched to a composition that is difficult to stretch, that is, easily broken by stretching. Mechanical properties can be improved.
Since the volume of polyimide becomes smaller during film formation due to drying or dehydration condensation, the stretching effect is exhibited even when both ends are gripped at equal intervals (stretching ratio is 1.00 times).

In the layer (a) and the layer (b) of the multilayer polyimide film of the present invention, a lubricant is added and contained in the polyimide to impart fine irregularities on the surface of the layer (film) to improve the slipperiness of the film. Is preferable. The lubricant is preferably added only to the outer layer (a).
As the lubricant, fine particles having an average particle size of about 0.03 μm to 3 μm of inorganic or organic can be used, and specific examples thereof include titanium oxide, alumina, silica, calcium carbonate, calcium phosphate, calcium hydrogen phosphate, calcium pyrophosphate, and the like. Examples include magnesium oxide, calcium oxide and clay minerals. The content of the lubricant is preferably 0.01% by mass or more with respect to the polymer mass. Since the smoothness of the polyimide film is good, it is more preferably 0.02% by mass or more, further preferably 0.05% by mass or more, and particularly preferably 0.1% by mass or more. Further, from the viewpoint of enhancing heat resistance, it is also good to add 20% by mass or more. From the viewpoint of transparency, it is preferably 50% by mass or less, more preferably 30% by mass or less, further preferably 10% by mass or less, and particularly preferably 5% by mass or less.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded. The physical property values in the production examples and the examples were measured by the following methods.

<Measurement of polyimide film thickness>
The measurement was performed using a micrometer (Millitron 1245D manufactured by Fine Wolf Co., Ltd.).

<Tension modulus, tensile strength (breaking strength), and breaking elongation>
The film was cut into strips of 100 mm × 10 mm in the flow direction (MD direction) and the width direction (TD direction) at the time of coating, and used as test pieces. Tensile tester (manufactured by Shimadzu, Autograph (R) model name AG-5000A) is used, and the tensile elastic modulus and tensile strength are obtained in each of the MD and TD directions under the conditions of a tensile speed of 50 mm / min and a chuck distance of 40 mm. And the elongation at break were obtained, and the average value of the measured values in the MD direction and the TD direction was obtained.

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

<Film thickness>
A diagonally cut surface of the film was prepared by SAICAS DN-20S type (Dipla Wintes), and then this diagonally cut surface was microscopically ATR using germanium crystals (incident angle 30 °) by microscopic IR Cary 620 FTIR (Agilent). The spectrum is obtained by the method, and the ratio of (b) layer film thickness / (a) layer film thickness is obtained from the increase / decrease of the characteristic peaks of each of the (a) layer and (b) layer and the calibration curve obtained in advance. rice field.

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

<Total light transmittance>
The total light transmittance (TT) of the film was measured using HAZEMETER (NDH5000, manufactured by Nippon Denshoku Co., Ltd.). A D65 lamp was used as the light source. The same measurement was performed three times, and the arithmetic mean value was adopted.
The results are shown in Tables 1 and 2.

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

<Film warp>
A film cut into a square having a size of 100 mm × 100 mm is used as a test piece, and the test piece is allowed to stand on a flat surface at room temperature so as to be concave, and the distances 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 (a) Production of Polyamic Acid Solution As with Lubricants for Layer Formation]
After nitrogen substitution in the reaction vessel equipped with a nitrogen introduction tube, a reflux tube and a stirring rod, 21.73 parts by mass of 4,4'-diaminobenzanilide (DABAN) was added to 21.1 parts by mass of N, N-dimethyl. It was dissolved in acetamide (DMAc), and then 19.61 parts by mass of 1,2,3,4-cyclobutanetetracarboxylic acid anilides (CBDA) was added separately as a solid, and then stirred at room temperature for 24 hours. .. Then, 173.1 parts by mass of DMAc was added and diluted to obtain a polyamic acid solution A having an NV (solid content) of 10% by mass and a reduction viscosity of 3.10 dl / g. Silica (lubricant) is added to the obtained polyamic acid solution A with a dispersion (“Snowtex (registered trademark) DMAC-ST-ZL” manufactured by Nissan Chemical Industries, Ltd.) in which colloidal silica is further dispersed in dimethylacetamide as a lubricant. The total amount of polymer solids in the polyamic acid solution was 1.4% by mass), and a uniform polyamic acid solution As was obtained.

[Production Example 2 (a) Production of Polyamic Acid Solution Bs Containing Lubricants for Layer Formation]
After nitrogen substitution in the reaction vessel equipped with a nitrogen introduction 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. Dissolve in 9 parts by weight of N, N-dimethylacetamide (DMAc), then 10.30 parts by weight of diphenyl-3,3', 4,4'-tetracarboxylic acid dianhydride (BPDA) and 4.65 parts. After dividing and adding parts of 4,4'-oxydiphthalic acid dianhydride (ODPA) in solid form, the mixture was stirred at room temperature for 24 hours. Then, a polyamic acid solution B having a solid content of 14% by mass and a reduction viscosity of 2.50 dl / g was obtained. In the obtained polyamic acid solution B, a dispersion obtained by dispersing colloidal silica as a lubricant in dimethylacetamide (“Snowtex (registered trademark) DMAC-ST-ZL” manufactured by Nissan Chemical Industries, Ltd.) and silica (slipper) is a polyamide. The total amount of polymer solids in the acid solution was 0.45% by mass), and a uniform polyamic acid solution Bs was obtained.

[Production Example 3 (a) Production of Polyamic Acid Solution Cs Containing Lubricants for Layer Formation]
After nitrogen substitution in the reaction vessel equipped with a nitrogen introduction 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. Dissolve in 9 parts by weight of N, N-dimethylacetamide (DMAc), then leave 29.42 parts by weight of diphenyl-3,3', 4,4'-tetracarboxylic acid dianhydride (BPDA) solid. After the addition in portions, the mixture was stirred at room temperature for 24 hours. Then, 173.1 parts by mass of DMAc was added and diluted to obtain a polyamic acid solution C having a solid content of 13.5% by mass and a reduction viscosity of 2.80 dl / g. The obtained polyamic acid solution C is mixed with a dispersion (“Snowtex (registered trademark) DMAC-ST-ZL” manufactured by Nissan Chemical Industries, Ltd.) in which colloidal silica is dispersed in dimethylacetamide as a lubricant, and silica (slipper) is a polyamide. The total amount of polymer solids in the acid solution was 0.5% by mass), and a uniform polyamic acid solution Cs was obtained.

[Production Example 4 (b) Production of Polyimide Solution D for Layer Formation]
32.02 parts by mass of 2,2'-ditrifluoromethyl-4,4'while introducing nitrogen gas into a reaction vessel equipped with a nitrogen introduction tube, a Dean Stark device and a recirculation tube, a thermometer, and a stirring rod. -Diaminobiphenyl (TFMB), 230 parts by weight N, N-dimethylacetamide (DMAc) was added to completely dissolve, followed by 44.42 parts by weight of 4,4'-(2,2-hexafluoroisopropylidene). ) Diphthalic acid dianhydride (6FDA) was added in portions as a solid, and then stirred at room temperature for 24 hours. Then, a polyamic acid solution D having a solid content of 25% by mass and a reduction viscosity of 1.10 dl / g was obtained.

[Production Example 5 (b) Production of Polyimide Solution E for Layer Formation]
While introducing nitrogen gas into a reaction vessel equipped with a nitrogen introduction tube, a Dean Stark device and a recirculation tube, a thermometer, and a stirring rod, 120.5 parts by mass of 4,4'-diaminodiphenyl sulfone (4,4') was introduced. -DDS), 51.6 parts by mass of 3,3'-diaminodiphenyl sulfone (3,3'-DDS) and 500 parts by mass of gamma butyrolactone (GBL) were added. Subsequently, 217.1 parts by mass of 4,4'-oxydiphthalic acid unihydrate (ODPA), 223 parts by mass of GBL, and 260 parts by mass of toluene were added at room temperature, and then the temperature was raised to 160 ° C. The mixture was heated under reflux at 160 ° C. for 1 hour for imidization. After the imidization was completed, the temperature was raised to 180 ° C., and the reaction was continued while extracting toluene. After the reaction for 12 hours, the oil bath was removed and the temperature was returned to room temperature, GBL was added so that the solid content had a concentration of 20% by mass, and a polyimide solution D was obtained.

[Production Example 6 Production of Polyamic Acid Solution F]
After nitrogen substitution in the reaction vessel equipped with a nitrogen introduction 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. Dissolve in 9 parts by mass of N, N-dimethylacetamide (DMAc), then 9.81 parts by mass of 1,2,3,4-cyclobutanetetracarboxylic acid anhydrate (CBDA), 10.30 parts by mass. Diphenyl-3,3', 4,4'-tetracarboxylic acid dianhydride (BPDA) and 4.65 parts by mass of 4,4'-oxydiphthalic acid dianhydride (ODPA) were added separately in solid form. Then, it was stirred at room temperature for 24 hours. Then, 173.1 parts by mass of DMAc was added and diluted to obtain a polyamic acid solution F having a solid content of 11.1% by mass and a reduction viscosity of 2.80 dl / g.

[Production Example 7 (b) Production of polyamic acid solution Fs containing lubricant for layer formation)]
In the polyamic acid solution F obtained in Production Example 6, a dispersion (“Snowtex (registered trademark) DMAC-ST” manufactured by Nissan Chemical Industries, Ltd.) in which colloidal silica is dispersed in dimethylacetamide is added to the polyamic acid (lubricant). The total amount of polymer solids in the solution was 30.0% by mass), and a uniform polyamic acid solution Es was obtained.

The polyimide solution and the polyamic acid solution (polyimide precursor solution) obtained in Production Examples 1 to 7 were formed into a film by the following method, and the optical properties and mechanical properties were measured. The results are shown in Table 1.
(How to obtain a film for measuring physical properties by itself)
A polyimide solution or a polyamic acid solution was applied to the center of a glass plate having a side of 30 cm, approximately 20 cm square, using a bar coater so that the final thickness was 25 ± 2 μm, and dry nitrogen was gently poured. After heating in an inert oven at 100 ° C. for 30 minutes and confirming that the residual solvent content of the coating film is 5% by mass or more and 40% by mass or less, a muffle furnace replaced with dry nitrogen is used at 300 ° C. for 20 minutes. Heated. Then, it is taken out from the muffle furnace, the end of the dry coating film (film) is raised with a utility knife, and it is carefully peeled from the glass to obtain a film.

(Example 1)
In the air air-conditioned at 25 ° C. and 45% RH, the polyamic acid solution As obtained in Production Example 1 was prepared by using a polyethylene terephthalate film A4100 (manufactured by Toyobo Co., Ltd., hereinafter abbreviated as PET film) using a comma coater. The film was applied onto the non-slip material surface so that the final film thickness was 0.8 μm, and dried at 110 ° C. for 5 minutes. Subsequently, the polyimide solution D obtained in Production Example 4 was applied onto the polyamic acid solution As with a die coater so that the final film thickness was 25 μm, and this was dried at 110 ° C. for 10 minutes. The self-supporting film after drying is peeled off from the A4100 film that has been used as a support, passed through a pin tenter having a pin sheet on which pins are arranged, and the film end is gripped by inserting it into the pins so that the film does not break. And, the pin sheet spacing is adjusted so that unnecessary slack does not occur, and the film is transported, and heated at 200 ° C for 3 minutes, 250 ° C for 3 minutes, and 300 ° C for 6 minutes to proceed with the imidization reaction. rice field. Then, the film was cooled to room temperature in 2 minutes, and the portions of the film having poor flatness were cut off with a slitter and wound into a roll to obtain a roll of the film having a width of 580 mm and a length of 100 m. The evaluation results of the obtained film are shown in Table 2.

(Examples 2 to 7)
Hereinafter, films were obtained by setting the conditions shown in Examples 2 to 7 in Table 2. The results of the same evaluation are shown in Table 2.

(Comparative Example 1)
In the air air-conditioned at 25 ° C. and 45% RH, the polyamic acid solution As obtained in Production Example 1 was prepared by using a polyethylene terephthalate film A4100 (manufactured by Toyobo Co., Ltd., hereinafter abbreviated as PET film) using a comma coater. The film was applied onto the non-slip material surface so that the final film thickness was 5.0 μm, and dried at 110 ° C. for 5 minutes. Subsequently, the polyimide solution D obtained in Production Example 4 was applied onto the polyamic acid solution As with a die coater so that the final film thickness was 25 μm, and this was dried at 110 ° C. for 10 minutes. The self-supporting film after drying is peeled off from the A4100 film that has been used as a support, passed through a pin tenter having a pin sheet on which pins are arranged, and the film end is gripped by inserting it into the pins so that the film does not break. In addition, the pin sheet spacing is adjusted and transported so that unnecessary slack does not occur, and the film is heated at 200 ° C for 3 minutes, 250 ° C for 3 minutes, and 300 ° C for 6 minutes to proceed with the imidization reaction. rice field. Then, the film was cooled to room temperature in 2 minutes, and the portions of the film having poor flatness were cut off with a slitter and wound into a roll to obtain a film roll having a width of 580 mm and a length of 100 m. The evaluation results of the obtained film are shown in Table 2.

(Comparative Example 2)
The polyamic acid solution As of Comparative Example 1 was changed to the polyamic acid solution Bs, and the film was applied so that the final film thickness was 0.05 μm. Then, 10 seconds later, the polyimide solution D obtained in Production Example 4 was used as the polyamic acid solution Bs. A film roll having a width of 580 mm and a length of 100 m was obtained by performing the same operation as in Comparative Example 1 except that the film was applied onto the film with a die coater so that the final film thickness was 30.0 μm. The evaluation results of the obtained film are shown in Table 2.

(Comparative Example 3)
The polyamic acid solution As of Comparative Example 1 was changed to the polyamic acid solution Bs, and the film was applied so that the final film thickness was 0.02 μm. Then, 10 seconds later, the polyimide solution D obtained in Production Example 4 was used as the polyamic acid solution Cs. A film roll having a width of 580 mm and a length of 100 m was obtained by performing the same operation as in Comparative Example 1 except that the film was applied onto the film with a die coater so that the final film thickness was 8.0 μm. The evaluation results of the obtained film are shown in Table 2.

As described above, the multilayer polyimide film of the present invention is balanced by forming the two-component polyimides as independent layers to divide the functions and setting the film thickness ratio of the two layers within a certain range. It is possible to obtain a film having a clear color, that is, colorless transparency, practically sufficient film strength, high breaking elongation, and a low coefficient of linear expansion, without any problems such as warpage.
The multilayer polyimide film of the present invention has excellent optical properties, colorless transparency, excellent mechanical properties, and exhibits a relatively low CTE. Therefore, it is necessary to use it as a member of a flexible and lightweight display device or to have transparency. It can be used for switch elements such as touch panels and pointing devices.

Claims (6)

1. A multilayer polyimide film containing at least a polyimide layer (a) and a polyimide layer (b).
   The composition of the polyimide layer (a) and the polyimide layer (b) are different.
   The thickness of the polyimide layer (a) is 0.03 μm or more, and the film thickness is 0.03 μm or more.
   The film thickness of the polyimide layer (b) is more than 5 times and 500 times or less the film thickness of the polyimide layer (a).
   A multilayer polyimide film having a thickness of 3 μm or more and 120 μm or less, a yellow index of 5 or less, and a total light transmittance of 86% or more.
2. The multilayer polyimide film according to claim 1, wherein the layer (a) and the layer (b) are each mainly composed of polyimide having the following characteristics.
   (A) Layer: Polyimide (b) layer having a yellow index of 10 or less and a total light transmittance of 80% or more when a film having a thickness of 25 ± 2 μm is used alone: A film having a thickness of 25 ± 2 μm alone. Polyimide with a yellow index of 5 or less and a total light transmittance of 85% or more when made into a film.
3. The polyimide of the layer (a) is a polyimide having a chemical structure obtained by polycondensation of a tetracarboxylic acid anhydride and a diamine.
   The tetracarboxylic acid anhydride contains an alicyclic tetracarboxylic acid anhydride, an acid dianhydride having a biphenyl bond in the molecule, an acid dianhydride having a trifluoromethyl group in the molecule, and an ether bond in the molecule. It is a tetracarboxylic acid anhydride containing at least one selected from the group consisting of acid dianhydride having.
   The diamine is a diamine containing at least one selected from the group consisting of a diamine having an amide bond in the molecule and a diamine having a trifluoromethyl group in the molecule.
   The multilayer polyimide film according to claim 1 or 2.
4. The polyimide of the layer (b) is a polyimide having a chemical structure obtained by polycondensation of a tetracarboxylic acid anhydride and a diamine.
   The tetracarboxylic acid anhydride contains an alicyclic tetracarboxylic acid anhydride, an acid dianhydride having a biphenyl bond in the molecule, an acid dianhydride having a trifluoromethyl group in the molecule, and an ether bond in the molecule. It is a tetracarboxylic acid anhydride containing at least one selected from the group consisting of acid dianhydride having.
   The diamine is a diamine containing at least one selected from the group consisting of a diamine having a sulfone group in the molecule and a diamine having a trifluoromethyl group in the molecule.
   The multilayer polyimide film according to any one of claims 1 to 3.
5. 1: (a) A step of applying a polyimide solution for forming a layer or a polyimide precursor solution to a temporary support to obtain a coating film a1.
   2: A step of drying the coating film a1 to obtain a coating film a2 having a residual solvent amount of 5 to 40% by mass.
   3: (b) A step of applying a polyimide solution for forming a layer or a polyimide precursor solution to the coating film a2 to obtain the coating film ab1.
   4: A step of heating the coating film ab1 to obtain a coating film ab2 having a residual solvent amount of 0.5% by mass or less based on the total layer of the coating film.
   The method for producing a multilayer polyimide film according to any one of claims 1 to 4, which comprises at least.
6. 1: (a) A step of applying a polyimide solution for forming a layer or a polyimide precursor solution to a temporary support to obtain a coating film a1.
   2: A step of drying the coating film a1 to obtain a coating film a2 having a residual solvent amount of 5 to 40% by mass.
   3: (b) A step of applying a polyimide solution for forming a layer or a polyimide precursor solution to the coating film a2 to obtain the coating film ab1.
   4: A step of heating the coating film ab1 to obtain a coating film ab3 having a residual solvent amount of 5% by mass or more and 40% by mass based on the total layer of the coating film.
   5: Step of peeling the coating film ab3 from the temporary support,
   6: A step of heating the coating film ab3 to obtain a coating film ab4 having a residual solvent amount of 0.5% by mass or less based on the total layer of the coating film.
   The method for producing a multilayer polyimide film according to any one of claims 1 to 4, which comprises at least.