CN116133854A

CN116133854A - Polyimide film and method for producing same

Info

Publication number: CN116133854A
Application number: CN202180057720.XA
Authority: CN
Inventors: 米虫治美; 中村诚; 奥山哲雄; 前田乡司; 渡边直树; 水口传一朗; 涌井洋行
Original assignee: Toyobo Co Ltd
Current assignee: Toyobo Co Ltd
Priority date: 2020-11-10
Filing date: 2021-11-01
Publication date: 2023-05-16
Also published as: TW202224947A; WO2022102449A1; JPWO2022102449A1; KR20230098779A

Abstract

The present invention provides a colorless polyimide film having high tensile breaking strength and tensile elastic modulus, large elongation at break and a low linear expansion coefficient, and a method for producing the same. A multilayer polyimide film having a thickness of 3 [ mu ] m or more and 120 [ mu ] m or less, a yellow index of 5 or less, and a total light transmittance of 86% or more, and having a layer structure in which at least 2 polyimide layers having different compositions are laminated in the thickness direction, wherein the 2 polyimide layers include a layer (a) and a layer (b), the film thickness of the layer (a) is 0.3 [ mu ] m or more, and the film thickness of the layer (b) is 5 times or more and 25 times or less the film thickness of the layer (a).

Description

Polyimide film and method for producing same

Technical Field

The present invention relates to a polyimide film which is colorless and has a low linear expansion coefficient and good mechanical properties, and a method for producing the same.

Background

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 in a tan, it is not suitable for a portion requiring light transmission such as a display device.

On the other hand, with the progress of thinning and weight reduction of display devices, flexibility is further required. Accordingly, attempts have been made to replace the substrate material with a flexible polymer film substrate from a glass substrate, but a colored polyimide film cannot be used as a substrate material for a liquid crystal display that displays by transmitting ON/OFF light, and is applicable to only a very small portion of peripheral circuits such as TAB and COF of a display device, a reflective display system, a back surface side of a self-luminous display device, and the like, in which a driving circuit is mounted.

Under such a background, development of a colorless transparent polyimide film is underway. As a representative example, attempts have been made to develop colorless transparent polyimide films using fluorinated polyimide resins, semi-alicyclic or full-alicyclic polyimide resins, or the like (patent documents 1 to 3). These films are less colored and have transparency, but have mechanical properties not as high as those of colored polyimide films, and in the case of industrial production and application to high temperature exposure, colorless properties and transparency are not necessarily maintained due to thermal decomposition, oxidation reaction, or the like. From this viewpoint, a method of performing heat treatment while injecting a gas having a predetermined oxygen content has been proposed (patent document 4), but in an environment where the oxygen concentration is less than 18%, the production cost is high, and industrial production is extremely difficult.

Prior art literature

Patent literature

Patent document 1 Japanese patent laid-open No. 11-106508

Patent document 2 Japanese patent laid-open No. 2002-146021

Patent document 3 Japanese patent laid-open No. 2002-348374

Patent document 4, WO2008/146637

Disclosure of Invention

Problems to be solved by the invention

If the monomer component having an alicyclic structure is added to the semi-alicyclic or full-alicyclic polyimide, colorless transparency is obtained, but the polyimide becomes hard and brittle, and the elongation at break is lowered, which makes it difficult to produce the polyimide as a film. On the other hand, if an aromatic monomer or a monomer having an amide bond in the molecule is introduced, the toughness is improved and the mechanical properties of the film are improved, but the film is easily colored and colorless transparency is lowered. By introducing an inorganic component having a refractive index close to that of the resin component, the heat resistance and colorless transparency are improved, the linear expansion coefficient is further reduced, and the processability is improved, but the resin composition becomes hard and brittle, and the mechanical properties are reduced.

That is, practical characteristics such as heat resistance and mechanical characteristics and colorless transparency are in a relationship that is equivalent to each other, and it is very difficult to produce a colorless transparent polyimide film that satisfies all of them.

Means for solving the problems

The present inventors have attempted to achieve a polyimide film that attains balance by combining a plurality of polyimide resins. In general, when a plurality of resin components are combined, mixed, or copolymerized, the result of combining only the advantages of the respective components is not necessarily obtained, but rather there are few cases where disadvantages are synergistically exhibited. However, as a result of intensive studies, the present inventors have found that the advantages of the respective components can be fully exerted by forming a specific structure by combining polyimide resins and forming films, and have completed the present invention.

That is, the present invention has the following configuration.

[1] A multilayer polyimide film comprising at least a polyimide layer (a) and a polyimide layer (b), wherein the polyimide layer (a) and the polyimide layer (b) have different compositions, the thickness of the polyimide layer (a) is 0.3 [ mu ] m or more, the thickness of the polyimide layer (b) is 5-25 times or less the thickness of the polyimide layer (a), the thickness of the multilayer polyimide film is 3 [ mu ] m-120 [ mu ] m, the yellow index is 5-5, and the total light transmittance is 86% or more.

[2] The multilayer polyimide film according to [1], wherein the (a) layer and the (b) layer are each composed mainly of polyimide having the following characteristics.

(a) Layer (c): when a film having a thickness of 25.+ -.2 μm is produced alone, a polyimide having a yellowness index of 10 or less and a total light transmittance of 85% or more,

(b) Layer (c): when a film having a thickness of 25.+ -.2. Mu.m, is produced alone, the polyimide has a yellowness index of 5 or less and a total light transmittance of 90% or more.

[3] The multilayer polyimide film according to [1] or [2], wherein the polyimide of the layer (a) is a polyimide having a chemical structure obtained by polycondensation of tetracarboxylic anhydride and diamine,

the tetracarboxylic anhydride is a tetracarboxylic anhydride containing 1 or more kinds selected from the group consisting of alicyclic tetracarboxylic anhydride, aromatic tetracarboxylic anhydride having an ether group in the molecule, and biphenyl aromatic tetracarboxylic anhydride having a biphenyl aromatic tetracarboxylic anhydride in the molecule,

the diamine contains 1 or more diamines selected from the group consisting of diamines having an amide bond in the molecule and diamines having a trifluoromethyl group in the molecule.

[4] The multilayer polyimide film according to any one of [1] to [3],

the polyimide of the layer (b) is a polyimide having a chemical structure obtained by polycondensation of tetracarboxylic anhydride and diamine,

The tetracarboxylic anhydride is a tetracarboxylic anhydride containing 1 or more kinds selected from the group consisting of alicyclic tetracarboxylic anhydride, aromatic tetracarboxylic anhydride having an ether group in a molecule, aromatic tetracarboxylic anhydride having a biphenyl group in a molecule, and aromatic tetracarboxylic anhydride having a trifluoromethyl group in a molecule,

the diamine contains 1 or more diamines selected from the group consisting of diamines having sulfone groups in the molecule and diamines having trifluoromethyl groups in the molecule.

[5] The method for producing a multilayer polyimide film according to any one of [1] to [4], characterized by comprising at least:

1) A step of applying a polyimide solution or a polyimide precursor solution for forming the layer (a) to the temporary support to obtain a coating film a 1;

2) A step of applying a polyimide solution or a polyimide precursor solution for forming the layer (b) onto the coating film a1 within 100 seconds after the production of the coating film a1 to obtain a coating film ab 1;

3) A step of heating the coating film ab1 to obtain a coating film ab2 having a residual solvent content of 15 to 40 mass% based on the whole coating film;

4) A step of peeling off the coating film ab2 from the temporary support;

5) Heating the coating film ab2 to a temperature of 150 ℃ or more and less than 200 ℃ to obtain a coating film ab3 having a residual solvent content of 5 mass% or more and less than 15 mass% based on the whole coating film;

6) And a step of heating the coating film ab3 to obtain a coating film ab4 having a residual solvent content of 0.5 mass% or less based on the total coating film.

ADVANTAGEOUS EFFECTS OF INVENTION

The present invention can realize a heat-resistant film having mechanical properties excellent in optical properties (colorless transparency) and capable of obtaining sufficient handleability as a flexible film without problems such as warpage by constituting the film with a plurality of layers composed of different compositions.

In the present invention, the polyimide of the layer (a) has a chemical structure obtained by polycondensation of a tetracarboxylic anhydride containing 1 or more selected from the group consisting of alicyclic tetracarboxylic anhydride, aromatic tetracarboxylic anhydride having an ether group in the molecule, and aromatic tetracarboxylic anhydride having a biphenyl group in the molecule, and a diamine containing 1 or more selected from the group consisting of diamine having an amide bond in the molecule and diamine having a trifluoromethyl group in the molecule, and the polyimide is preferable. The total amount of the alicyclic tetracarboxylic anhydride, the aromatic tetracarboxylic acid having an ether group in the molecule, and the aromatic tetracarboxylic anhydride having a biphenyl group in the molecule is preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may be 100 mol% or more, based on the tetracarboxylic anhydride. The total amount of diamine having an amide bond in the molecule and diamine having a trifluoromethyl group in the molecule is preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more, particularly preferably 95 mol% or more, and 100 mol% of the diamines. Within the above range, the mechanical properties of the multilayered polyimide film become good.

The chemical structure of the polyimide of the other layer (b) is not limited, but a polyimide having a chemical structure obtained by polycondensation of a tetracarboxylic anhydride containing 1 kind selected from the group consisting of alicyclic tetracarboxylic anhydride, aromatic tetracarboxylic anhydride having an ether group in the molecule, aromatic tetracarboxylic anhydride having a biphenyl group in the molecule, and aromatic tetracarboxylic anhydride having a trifluoromethyl group in the molecule, and a diamine containing 1 or more kinds selected from the group consisting of diamine having a sulfone group in the molecule and diamine having a trifluoromethyl group in the molecule is preferable. The total amount of the alicyclic tetracarboxylic anhydride, the aromatic tetracarboxylic anhydride having an ether group in the molecule, the aromatic tetracarboxylic anhydride having a biphenyl group in the molecule, and the aromatic tetracarboxylic anhydride having a trifluoromethyl group in the molecule is preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may be 100 mol% or more. The total amount of diamine having a sulfone group in the molecule and diamine having a trifluoromethyl group in the molecule is preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may be 100 mol% or more in the diamine component. Within the above range, the multilayered polyimide film becomes excellent in transparency.

If the two are mixed or copolymerized, only a film having physical properties of the two or less can be obtained, and further, the properties of the layer (a) which is easily colored tend to be close to the properties of the colorless transparent film.

However, as in the present invention, by forming the polyimide of these two components as separate layers to perform functional sharing and further applying a specific manufacturing method, a film having balanced properties, i.e., colorless transparency, practically sufficient film strength, high elongation at break, and low linear expansion coefficient can be obtained.

The polyimide film is obtained by applying a polyimide solution or a polyimide precursor solution to a support, drying the same, and performing a chemical reaction as needed, but the present invention is characterized by using a method for producing a solution in which a plurality of components are applied at the same time, most preferably, in a short time. That is, by applying the resin constituting the layer (a) and the resin constituting the layer (b) of 2 different components to a defined thickness, respectively, and further setting the amount of the residual solvent at the time of drying to a defined range, it is possible to make the dry state of the layer (a) and the dry state of the layer (b) different. Thus, warpage due to the CTE difference between the layer (a) and the layer (b) can be reduced, and a well-balanced film in which internal strain is not concentrated at a specific portion can be obtained.

Detailed Description

The thickness of the multilayered polyimide film of the present invention is 3 μm to 120 μm. The mechanical properties are good, and are preferably 4 μm or more, more preferably 5 μm or more, and still more preferably 8 μm or more. The transparency is preferably 100 μm or less, more preferably 80 μm or less, and still more preferably 60 μm or less.

The multilayer polyimide film of the present invention has a yellowness index of 5 or less. The transparency is preferably 4 or less, more preferably 3.5 or less, and even more preferably 3 or less. The lower limit is not particularly limited, but may be 0.1 or more, or 0.2 or more, industrially.

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

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

When a polyimide used mainly for the layer (a) (hereinafter, abbreviated as "main" in some cases as "polyimide used for the layer (a)", or "polyimide used for the layer (a)", etc.) is formed into a single film having a thickness of 25±2 μm, it is preferable that the polyimide has a yellow index of 10 or less and a total light transmittance of 85% or more. The yellow index is preferably 9 or less, more preferably 8 or less, and further preferably 7 or less, based on good transparency. The lower limit of the yellow index is not particularly limited, but may be 0.1 or more, or 0.2 or more in industry. The total light transmittance is preferably 86% or more, more preferably 87% or more, and still more preferably 88% or more. The upper limit is not particularly limited, but may be 99% or less or 98% or less industrially.

The thickness (film thickness) of the layer (a) in the multilayer polyimide film is 0.3 μm or more. The mechanical strength is preferably more than 0.3. Mu.m, more preferably 0.4. Mu.m, still more preferably 0.5. Mu.m. The transparency is preferably 20 μm or less, more preferably 10 μm or less, further preferably 7.5 μm or less, and particularly preferably 5 μm or less.

The chemical structure of polyimide mainly used as the layer (a) is not limited, but polyimide having a chemical structure obtained by polycondensation of tetracarboxylic anhydride and diamine is preferable. The tetracarboxylic anhydride preferably contains 1 or more tetracarboxylic anhydrides selected from the group consisting of alicyclic tetracarboxylic anhydrides, aromatic tetracarboxylic anhydrides having an ether group in the molecule, and aromatic tetracarboxylic anhydrides having a biphenyl group in the molecule. The diamine preferably contains 1 or more kinds of diamines selected from the group consisting of diamines having an amide bond in the molecule and diamines having a trifluoromethyl group in the molecule. The total amount of the alicyclic tetracarboxylic anhydride, the aromatic tetracarboxylic acid having an ether group in the molecule, and the aromatic tetracarboxylic anhydride having a biphenyl group in the molecule is preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may be 100 mol% or more, based on the tetracarboxylic anhydride. The total amount of diamine having an amide bond in the molecule and diamine having a trifluoromethyl group in the molecule is preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more, particularly preferably 95 mol% or more, and 100 mol% of the diamines. Within the above range, the mechanical properties of the multilayered polyimide film become good.

The polyimide used mainly for the layer (b) (hereinafter, abbreviated as "main" in some cases as "polyimide used for the layer (b)", or "polyimide used for the layer (b)", etc.) is preferably a polyimide having a yellow index of 5 or less and a total light transmittance of 90% or more when a film having a thickness of 25±2 μm alone is formed. The yellow index is preferably 4 or less, more preferably 3 or less, because of good transparency. The lower limit of the yellow index is not particularly limited, but may be 0.1 or more, or 0.2 or more in industry. The total light transmittance is preferably 91% or more, more preferably 92% or more. The upper limit is not particularly limited, but may be 99% or less or 98% or less industrially.

The thickness (film thickness) of the layer (b) in the multilayer polyimide film is 5 to 25 times the film thickness of the layer (a). The transparency is preferably 7.5 times or more, more preferably 10 times or more, based on the transparency. The mechanical strength is preferably 23.5 times or less, more preferably 20 times or less.

The thickness of the layer (b) in the multilayered polyimide film is preferably 1.5 μm or more, more preferably 3 μm or more, further preferably 4 μm or more, more preferably 5 μm or more, and particularly preferably 6 μm or more, because the mechanical strength becomes good. The transparency is preferably 115 μm or less, more preferably 100 μm or less, further preferably 80 μm or less, particularly preferably 50 μm or less.

The polyimide used as the layer (b) is not limited to a chemical structure, but a polyimide having a chemical structure obtained by polycondensation of tetracarboxylic anhydride and diamine is preferable. The tetracarboxylic anhydride preferably contains 1 or more tetracarboxylic anhydrides selected from the group consisting of alicyclic tetracarboxylic anhydrides, aromatic tetracarboxylic anhydrides having an ether group in the molecule, aromatic tetracarboxylic anhydrides having a biphenyl group in the molecule, and aromatic tetracarboxylic anhydrides having a trifluoromethyl group in the molecule. The diamine preferably contains 1 or more kinds of diamines selected from the group consisting of diamines having a sulfone group in the molecule and diamines having a trifluoromethyl group in the molecule. The total amount of the alicyclic tetracarboxylic anhydride, the aromatic tetracarboxylic anhydride having an ether group in the molecule, the aromatic tetracarboxylic anhydride having a biphenyl group in the molecule, and the aromatic tetracarboxylic anhydride having a trifluoromethyl group in the molecule is preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may be 100 mol% or more in the tetracarboxylic anhydride. The total amount of diamine having a sulfone group in the molecule and diamine having a trifluoromethyl group in the molecule is preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may be 100 mol% or more in the diamine component. Within the above range, the multilayered polyimide film becomes excellent in transparency.

Examples of the alicyclic tetracarboxylic acid anhydride in the present invention include 1,2,3, 4-cyclobutanetetracarboxylic acid, 1,2,3, 4-cyclopentanetetracarboxylic acid, 1,2,3, 4-cyclohexanedicarboxylic acid, 1,2,4, 5-cyclohexanedicarboxylic acid, 3', 4' -dicyclohexyltetracarboxylic acid, bicyclo [2, 1] heptane-2, 3,5, 6-tetracarboxylic acid, bicyclo [2, 2] octane-2, 3,5, 6-tetracarboxylic acid, bicyclo [2, 2] -7-octene-2, 3,5, 6-tetracarboxylic acid, tetrahydroanthracene-2, 3,6, 7-tetracarboxylic acid, tetradecahydro-1, 4:5,8:9, 10-Tri-bridge methylene anthracene-2, 3,6, 7-tetracarboxylic acid, decahydronaphthalene-2, 3,6, 7-tetracarboxylic acid, decahydro-1, 4:5, 8-Di-methanonaphthalene-2, 3,6, 7-tetracarboxylic acid, decahydro-1, 4-methanonaphthalene-5, 8-methanonaphthalene-2, 3,6, 7-tetracarboxylic acid, norbornane-2-spiro-alpha-cyclopentanone-alpha '-spiro-2' -norbornane-5, 5', 6, 6' -Tetracarboxylic acid (alias "norbornane-2-spiro-2 '-cyclopentanone-5' -spiro-2 '-norbornane-5, 5', 6,6 '-tetracarboxylic acid"), methyl norbornane-2-spiro-alpha-cyclopentanone-alpha' -spiro-2 '- (methyl norbornane) -5, 5', 6,6 "-Tetracarboxylic acid, norbornane-2-spiro-alpha-cyclohexano-2" -norbornane-5, 5", 6" -Tetracarboxylic acid (alias "norbornane-2-spiro-2 '-cyclohexano-6' -spiro-2" -norbornane-5, 5", 6" -Tetracarboxylic acid "), methyl norbornane-2-spiro-alpha-cyclohexano-2" - (methyl norbornane) -5,5", 6" -Tetracarboxylic acid, norbornane-2-spiro-alpha-cyclo-propanone-alpha '-spiro-2 "-norbornane-5, 5",6 "-tetracarboxylic acid, norbornane-2-spiro-alpha-cyclo-butanone-alpha' -spiro-2" -norbornane-5, 5",6,6 '-tetracarboxylic acid, norbornane-2-spiro-alpha-cycloheptanone-alpha' -spiro-2 '-norbornane-5, 5', 6,6 '-tetracarboxylic acid, norbornane-2-spiro-alpha-cyclooctanone-alpha' -spiro-2 '-norbornane-5, 5', 6,6" -Tetracarboxylic acid, norbornane-2-spiro-alpha-cyclononone-alpha '-spiro-2 "-norbornane-5, 5",6 "-Tetracarboxylic acid, norbornane-2-spiro-alpha-cyclodecone-alpha' -spiro-2" -norbornane-5, 5", 6" -Tetracarboxylic acid, norbornane-2-spiro-alpha-cycloundecone-alpha '-spiro-2 "-norbornane-5, 5",6 "-Tetracarboxylic acid, norbornane-2-spiro-alpha-cyclododecanone-alpha' -spiro-2" -norbornane-5, 5", 6" -Tetracarboxylic acid, norbornane-2-spiro-alpha-cyclotridecanone-alpha ' -spiro-2 "-norbornane-5, 5",6, 6' -tetracarboxylic acid, norbornane-2-spiro-alpha-cyclotetradecane-alpha ' -spiro-2 ' -norbornane-5, 5', 6, 6' -tetracarboxylic acid, norbornane-2-spiro-alpha-cyclopentanone-alpha ' -spiro-2 ' -norbornane-5, 5', tetracarboxylic acids such as 6,6 "-tetracarboxylic acid, norbornane-2-spiro- α - (methylcyclopentanone) - α ' -spiro-2" -norbornane-5, 5", 6" -tetracarboxylic acid, norbornane-2-spiro- α - (methylcyclohexanone) - α ' -spiro-2 "-norbornane-5, 5",6 "-tetracarboxylic acid, and anhydrides thereof. Among them, dianhydride having 2 acid anhydride structures is preferable, and in particular, 1,2,3, 4-cyclobutane tetracarboxylic dianhydride, 1,2,3, 4-cyclohexanedicarboxylic dianhydride, 1,2,4, 5-cyclohexanedicarboxylic dianhydride is preferable, 1,2,3, 4-cyclobutane tetracarboxylic dianhydride is more preferable, and 1,2,4, 5-cyclohexanedicarboxylic dianhydride is more preferable, and 1,2,3, 4-cyclobutane tetracarboxylic dianhydride is still more preferable. In addition, they may be used alone or in combination of two or more.

The aromatic tetracarboxylic acid anhydride having an ether group in the molecule, the aromatic tetracarboxylic acid anhydride having a biphenyl group in the molecule, and the aromatic tetracarboxylic acid anhydride having a trifluoromethyl group in the molecule of the present invention are preferably tetracarboxylic dianhydride, respectively. Specifically, it is possible to cite 4,4'- (2, 2-hexafluoroisopropylidene) diphthalic acid, 4' -oxybisphthalic acid, bis (1, 3-dioxo-1, 3-dihydro-2-benzofuran-5-carboxylic acid) 1, 4-phenylene ester, bis (1, 3-dioxo-1, 3-dihydro-2-benzofuran-5-yl) benzene-1, 4-dicarboxylic acid ester, 4'- [4,4' - (3-oxo-1, 3-dihydro-2-benzofuran-1, 1-diyl) bis (benzene-1, 4-dioxy) ] diphenyl-1, 2-dicarboxylic acid, 3',4,4' -benzophenone tetracarboxylic acid, 4'- [ (3-oxo-1, 3-dihydro-2-benzofuran-1, 1-diyl) bis (toluene-2, 5-dioxy) ] diphenyl-1, 2-dicarboxylic acid, 4' - [ (3-oxo-1, 3-dihydro-2-benzofuran-1, 1-diyl) bis (1, 4-xylene-2, 5-dioxy) ] diphenyl-1, 2-dicarboxylic acid, 4'- [4,4' - (3-oxo-1, 3-dihydro-2-benzofuran-1, 1-diyl) bis (4-isopropyl-toluene-2, 5-dioxy) ] dibenzo-1, 2-dicarboxylic acid, 4' - [4,4' - (3-oxo-1, 3-dihydro-2-benzofuran-1, 1-diyl) bis (naphthalene-1, 4-dioxy) ] dibenzo-1, 2-dicarboxylic acid, 4' - [4,4' - (3H-2, 1-benzoxathiane-1, 1-dioxo-3, 3-diyl) bis (benzene-1, 4-dioxy) ] dibenzo-1, 2-dicarboxylic acid, 4' -benzophenone tetracarboxylic acid, 4' - [ (3H-2, 1-benzoxathiane-1, 1-dioxo-3, 3-diyl) ] dibenzo-1, 2-dicarboxylic acid, 4' - [ 4' - (3H-2, 1-benzoxathiane-1, 1-dioxo-3-diyl) ] bis (toluene-2, 5-dioxy) ] dibenzo-1, 2-dicarboxylic acid, 4' - [4,4' - [ 3H-2, 3-dioxo-diphenyl) ] dibenzo-1, 2-dioxan-1, 2-dicarboxylic acid, 4' - [4,4' -benzophenone-tetracarboxylic acid, 4' - [ (3H-2, 1-dioxo-diyl-3-diyl) ] dibenzo-1, 2-dicarboxylic acid, 1-dioxo-3, 3-diyl) bis (4-isopropyl-toluene-2, 5-diyloxy) ] diphenyl-1, 2-dicarboxylic acid, 4'- [4,4' - (3H-2, 1-benzoxathiane-1, 1-dioxo-3, 3-diyl) bis (naphthalene-1, 4-diyloxy) ] diphenyl-1, 2-dicarboxylic acid, 3',4' -benzophenone tetracarboxylic acid, 3', tetracarboxylic acids such as 4,4' -diphenylsulfone tetracarboxylic acid, 3',4' -biphenyltetracarboxylic acid, 2, 3',4' -biphenyltetracarboxylic acid, pyromellitic acid, 4'- [ spiro (xanthene-9, 9' -fluorene) -2, 6-diylbis (oxycarbonyl) ] diphthalic acid, 4'- [ spiro (xanthene-9, 9' -fluorene) -3, 6-diylbis (oxycarbonyl) ] diphthalic acid, and anhydrides (acid dianhydrides) thereof. These aromatic tetracarboxylic acids may be used alone or in combination of two or more.

In the present invention, in addition to the tetracarboxylic anhydride, tricarboxylic acids and dicarboxylic acids may be used.

Examples of the tricarboxylic acids include trimellitic acid, aromatic tricarboxylic acids such as 1,2, 5-naphthalene tricarboxylic acid, diphenyl ether-3, 3',4' -tricarboxylic acid, diphenyl sulfone-3, 3',4' -tricarboxylic acid, and alkylene glycol trimellitates such as hexahydrotrimellitic acid, hydrogenated aromatic tricarboxylic acids such as ethylene glycol ditolytrimellitate, propylene glycol ditolytrimellitate, 1, 4-butanediol ditolytrimellitate, polyethylene glycol ditolytrimellitate, and monoanhydrides and esters thereof. Among them, monoanhydrides having 1 acid anhydride structure are preferable, and trimellitic anhydride and hexahydrotrimellitic anhydride are particularly preferable. In addition, 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, phthalic acid, naphthalene dicarboxylic acid, and 4,4' -oxybenzoic acid, and the above aromatic dicarboxylic acid hydrides such as 1, 6-cyclohexanedicarboxylic acid, oxalic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedicarboxylic acid, dodecanedioic acid, 2-methylsuccinic acid, and acid chlorides and esters thereof. Among them, aromatic dicarboxylic acids and their hydrides are preferable, and terephthalic acid, 1, 6-cyclohexanedicarboxylic acid, and 4,4' -dibenzoic acid oxide 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 of the present invention, aromatic diamine and alicyclic amine can be mainly used.

As the aromatic diamine compound(s), there are, examples thereof 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' -bistrifluoromethyl-4, 4' -diaminobiphenyl, 4' -bis (4-aminophenoxy) biphenyl, 4' -bis (3-aminophenoxy) biphenyl, bis [4- (3-aminophenoxy) phenyl ] ketone, bis [4- (3-aminophenoxy) phenyl ] sulfide, bis [4- (3-aminophenoxy) phenyl ] sulfone, and 2, 2-bis [4- (3-aminophenoxy) phenyl ] propane, 2-bis [4- (3-aminophenoxy) phenyl ] -1, 3-hexafluoropropane, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, m-aminobenzylamine, p-aminobenzylamine, 4-amino-N- (4-aminophenyl) benzamide 3,3' -diaminodiphenyl ether, 3,4' -diaminodiphenyl ether, 4' -diaminodiphenyl ether, 2' -trifluoromethyl-4, 4' -diaminodiphenyl ether, 3' -diaminodiphenyl sulfide, 3,4' -diaminodiphenyl sulfide, 4,4' -diaminodiphenyl sulfide, 3' -diaminodiphenyl sulfoxide, 3,4' -diaminodiphenyl sulfoxide, 4' -diaminodiphenyl sulfoxide, 3' -diaminodiphenyl sulfone, 3,4' -diaminodiphenyl sulfone, 4' -diaminodiphenyl sulfone, and 3,3' -diaminobenzophenone, 3,4' -diaminobenzophenone, 4' -diaminobenzophenone, 3' -diaminodiphenylmethane, 3,4' -diaminodiphenylmethane, 4' -diaminodiphenylmethane, bis [4- (4-aminophenoxy) phenyl ] methane, and 1, 1-bis [4- (4-aminophenoxy) phenyl ] ethane, 1, 2-bis [4- (4-aminophenoxy) phenyl ] ethane, 1-bis [4- (4-aminophenoxy) phenyl ] propane, 1, 2-bis [4- (4-aminophenoxy) phenyl ] propane, 1, 3-bis [4- (4-aminophenoxy) phenyl ] propane, 2-bis [4- (4-aminophenoxy) phenyl ] propane, 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-bis [4- (4-aminophenoxy) -3-methylphenyl ] propane, 2- [4- (4-aminophenoxy) phenyl ] -2- [4- (4-aminophenoxy) -3, 5-dimethylphenyl ] propane, 2-bis [4- (4-aminophenoxy) -3, 5-dimethylphenyl ] propane 2, 2-bis [4- (4-aminophenoxy) phenyl ] -1, 3-hexafluoropropane, 1, 4-bis (3-aminophenoxy) benzene, 1, 3-bis (3-aminophenoxy) benzene, 1, 4-bis (4-aminophenoxy) benzene, 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 '-bis [ (3-aminophenoxy) benzoyl ] benzene, 1-bis [4- (3-aminophenoxy) phenyl ] propane, 1, 3-bis [4- (3-aminophenoxy) phenyl ] propane 3,4' -diaminodiphenyl sulfide, 2-bis [3- (3-aminophenoxy) phenyl ] -1, 3-hexafluoropropane bis [4- (3-aminophenoxy) phenyl ] methane, 1-bis [4- (3-aminophenoxy) phenyl ] ethane 1, 2-bis [4- (3-aminophenoxy) phenyl ] ethane, bis [4- (3-aminophenoxy) phenyl ] sulfoxide, 4 '-bis [3- (4-aminophenoxy) benzoyl ] diphenyl ether, 4' -bis [3- (3-aminophenoxy) benzoyl ] diphenyl ether, 4,4 '-bis [4- (4-amino- α, α -dimethylbenzyl) phenoxy ] benzophenone, 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-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 '-diamino-4, 4' -diphenoxybenzophenone, 4 '-diamino-5, 5' -diphenoxybenzophenone, 3,4 '-diamino-4, 5' -diphenoxybenzophenone, 3,3 '-diamino-4-phenoxybenzophenone, 4' -diamino-5-phenoxybenzophenone, 3,4 '-diamino-4-phenoxybenzophenone, 3,4' -diamino-5 '-phenoxybenzophenone, 3' -diamino-4, 4 '-biphenoxybenzophenone, 4' -diamino-5, 5 '-biphenoxybenzophenone, 3,4' -diamino-4, 5 '-biphenoxybenzophenone, 3' -diamino-4-biphenoxybenzophenone, 4 '-diamino-5-biphenoxybenzophenone, 3,4' -diamino-4-biphenoxybenzophenone, 3,4 '-diamino-5' -biphenoxybenzophenone, 1, 3-bis (3-amino-4-phenoxybenzoyl) benzene, 1, 4-bis (3-amino-4-phenoxybenzoyl) benzene, 1, 3-bis (4-amino-5-phenoxybenzoyl) benzene, 1, 4-bis (4-amino-5-phenoxybenzoyl) benzene, 1, 3-bis (3-amino-4-biphenylyl) phenoxy) benzene, 1, 4-bis (3-amino-4-phenoxybenzoyl) benzene, 3-bis (4-amino-5-diphenoxybenzoyl) benzene, 1, 4-bis (4-amino-5-diphenoxybenzoyl) benzene, 2, 6-bis [4- (4-amino- α, α -dimethylbenzyl) phenoxy ] benzonitrile, 4'- [ 9H-fluorene-9, 9-diyl ] bis-aniline (alias "9, 9-bis (4-aminophenyl) fluorene"), spiro (xanthene-9, 9' -fluorene) -2, 6-diylbis (oxycarbonyl) bis-aniline, 4'- [ spiro (xanthene-9, 9' -fluorene) -3, 6-diylbis (oxycarbonyl) bis-aniline, 5-amino-2- (p-aminophenyl) benzoxazole, 6-amino-2- (p-aminophenyl) benzoxazole, 5-amino-2- (m-benzoxazole, 6-diaminobenzoxazole, 2- (p-aminophenyl) benzoxazole, 2, 6-diaminobenzoxazole, 2-p-amino-2- (2, 6-aminophenyl) benzoxazole, 2-p-amino-2 '-2-benzoxazole, 2' -2-p-aminophenyl) benzoxazole 1- (5-aminobenzoxazole) -4- (6-aminobenzoxazole) benzene, 2,6- (4, 4' -diaminodiphenyl) benzo [1,2-d:5,4-d '] diazole, 2,6- (4, 4' -diaminodiphenyl) benzo [1,2-d:4,5-d '] diazole, 2,6- (3, 4' -diaminodiphenyl) benzo [1,2-d:5,4-d '] diazole, 2,6- (3, 4' -diaminodiphenyl) benzo [1,2-d:4,5-d '] diazole, 2,6- (3, 3' -diaminodiphenyl) benzo [1,2-d:5,4-d '] diazole, 2,6- (3, 3' -diaminodiphenyl) benzo [1,2-d:4,5-d' ] diazole, and the like. Further, part or all of hydrogen atoms on the aromatic ring of the aromatic diamine may be substituted with halogen atoms, alkyl groups having 1 to 3 carbon atoms, alkoxy groups, or cyano groups, and part or all of hydrogen atoms of the alkyl groups having 1 to 3 carbon atoms may be substituted with halogen atoms.

Examples of the alicyclic diamine include 1, 4-diaminocyclohexane, 1, 4-diamino-2-methylcyclohexane, 1, 4-diamino-2-ethylcyclohexane, 1, 4-diamino-2-n-propylcyclohexane, 1, 4-diamino-2-isopropylcyclohexane, 1, 4-diamino-2-n-butylcyclohexane, 1, 4-diamino-2-isobutylcyclohexane, 1, 4-diamino-2-sec-butylcyclohexane, 1, 4-diamino-2-tert-butylcyclohexane, 4' -methylenebis (2, 6-dimethylcyclohexylamine), 9, 10-bis (4-aminophenyl) adenine, and dimethyl 2, 4-bis (4-aminophenyl) cyclobutane-1, 3-dicarboxylate.

In the present invention, it is preferable that the polyimide (a) and the polyimide (b) have a structure of two or more layers (a)/(b), and the polyimide (b) is located on the upper layer, i.e., the surface (air surface) contacting with air. By setting the layer (a) having excellent mechanical properties and a small linear expansion coefficient as the lower layer, that is, the surface in contact with the coating support, as compared with the layer (b), the linear expansion coefficient of the whole film can be suppressed to a low level, the film handleability can be improved, and the excellent optical properties of the polyimide layer (b) serving as the upper layer can be maximally exerted. The layer (b) is preferably thicker than the layer (a). (b) The ratio of the thickness (film thickness) of the layer (a) to the thickness (film thickness) of the layer (b)/layer (a) =5 or more, preferably 7.5 or more, and more preferably 10 or more. The content is 25 or less, preferably 23 or less, and more preferably 20 or less. The multilayered polyimide film of the present invention may have a multilayered structure of 3 or more layers. For example, it may be (a) layer/(b) layer/(a) layer 3-layer structure, (a) layer/(b) layer/(a) layer/(b) layer 4-layer structure, (a) layer/(b) layer/(a) layer 5-layer structure. The multilayered polyimide film of the present invention may be laminated with layers other than the layer (a) and the layer (b). Further, the 3 rd resin layer (c), the 4 th resin layer (d), and the like may be inserted as arbitrary layers within a range that does not impair the effects of the present invention. Depending on the application of the film to a single-sided device, the composition and surface roughness of both sides may be changed depending on the desired effect of both sides of the film.

In the present invention, the layer (a) has a thickness of 0.3 μm or more, preferably 0.4 μm or more, more preferably 0.5 μm or more. By controlling the thickness of the layer (a) within this range, a film having balanced mechanical properties of the layer (a) and optical properties of the layer (b) and free from defects such as warpage can be obtained.

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

The polyimide used in the layer (a) of 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 a film having a thickness of 25.+ -.2. Mu.m is formed alone. Further, the polyimide used in the layer (a) preferably has a CTE of 25ppm/K or less, more preferably 20ppm/K or less, a tensile breaking strength of 120MPa or more, more preferably 140MPa or more, and an elongation at break of 8% or more, more preferably 10% or more.

As a preferred polyimide for the layer (a), a polyimide having a chemical structure obtained by polycondensation of a tetracarboxylic acid anhydride containing 70 mol% or more of an alicyclic tetracarboxylic acid anhydride and a diamine containing 70 mol% or more of a diamine having an amide bond in the molecule can be exemplified.

Further, as the polyimide used in the layer (a), a polyimide having a chemical structure obtained by polycondensing a tetracarboxylic anhydride containing 70 mol% or more of an aromatic tetracarboxylic anhydride and a diamine containing 70 mol% or more of a diamine having a trifluoromethyl group in the molecule can be exemplified. By adopting these structures, coloring can be suppressed.

As the diamine having an amide bond in the molecule, 4-amino-N- (4-aminophenyl) benzamide is preferable. The diamine having an amide bond is preferably used in an amount of 70 mol% or more and 80 mol% or more, more preferably 90 mol% or more, based on the total diamine.

In addition, as the diamine having a trifluoromethyl group in the molecule, 2 '-bistrifluoromethyl-4, 4' -diaminobiphenyl, 1, 4-bis (4-amino-2-trifluoromethylphenoxy) benzene, 2 '-trifluoromethyl-4, 4' -diaminodiphenyl ether are preferable. When these diamine compounds having a fluorine atom in the molecule, particularly diamine having a trifluoromethyl group in the molecule, are used, the amount thereof is preferably 70 mol% or more, 80 mol% or more, and more preferably 90 mol% or more of the total diamine.

The polyimide used in the layer (b) of 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 formed into a film having a thickness of 25.+ -.2. Mu.m.

Examples of the polyimide used in the layer (b) include polyimides having a chemical structure obtained by polycondensation of a tetracarboxylic anhydride containing 70 mol% or more of an aromatic tetracarboxylic anhydride and a diamine containing at least 70 mol% or more of a diamine having a sulfur atom in the molecule.

Further, as a polyimide suitable for the layer (b), a polyimide having a chemical structure obtained by polycondensation of a tetracarboxylic anhydride containing at least 30 mol% or more of a tetracarboxylic acid having a trifluoromethyl group in a molecule and a diamine containing at least 70 mol% or more of a diamine having a trifluoromethyl group in a molecule can be exemplified.

The aromatic tetracarboxylic anhydride preferably used for the polyimide in the layer (b) is preferably 4,4' -oxydiphthalic acid, pyromellitic acid or 3,3', 4' -biphenyltetracarboxylic acid. (b) The aromatic tetracarboxylic dianhydride used for the polyimide of the layer is preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more, and still more preferably 95 mol% or more of the total tetracarboxylic acids of the polyimide of the layer (b). By controlling the content of the aromatic tetracarboxylic acid within a prescribed range, heat resistance is improved.

As the tetracarboxylic acid having a trifluoromethyl group in the molecule used in the polyimide of the layer (b), 4' - (2, 2-hexafluoroisopropylidene) diphthalic dianhydride is preferable. The tetracarboxylic acid containing trifluoromethyl group in the molecule used in the polyimide of the layer (b) is preferably 30 mol% or more, more preferably 45 mol% or more, still more preferably 60 mol% or more, and still more preferably 80 mol% or more of the total tetracarboxylic acid of the polyimide of the layer (b). By controlling the content of the tetracarboxylic acid containing a trifluoromethyl group in the molecule within a prescribed range, colorless transparency is improved.

Among the polyimides 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' -diaminodiphenyl sulfone, 3,4' -diaminodiphenyl sulfone, 4' -diaminodiphenyl sulfone can be used. In the present invention, colorless transparency can be obtained by using 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, in combination with an aromatic tetracarboxylic anhydride.

As the diamine having a trifluoromethyl group, 2 '-bistrifluoromethyl-4, 4' -diaminobiphenyl, 1, 4-bis (4-amino-2-trifluoromethylphenoxy) benzene, 2 '-trifluoromethyl-4, 4' -diaminodiphenyl ether are preferable.

The amount of diamine having trifluoromethyl groups in the molecule is preferably 70% by mass or more, more preferably 80% by mass or more, and still more preferably 90% by mass or more of the total diamine.

In the present invention, the polyimide of the layer (a) and the polyimide of the layer (b) are characterized by a yellow index, a total light transmittance, mechanical properties, and the like when a film having a thickness of 25.+ -.2. Mu.m is produced alone. The procedure for preparing a film having a thickness of 25.+ -.2. Mu.m, alone, is a possible scale in a laboratory, and is a numerical value obtained by coating the polyimide solution or polyimide precursor solution on a glass plate having a size of 10cm square, preferably 20cm square or more, preheating to a temperature of 120℃and drying to a residual solvent content of 40% by mass or less of the coating film, and further heating at 300℃for 20 minutes in an inert gas such as nitrogen, and evaluating the obtained film. When the physical properties of the film are adjusted by containing inorganic components such as a slipping agent and a filler, the physical property values of the film are obtained by using a solution containing the inorganic components.

The polyimide of the layer (a) and the polyimide of the layer (b) of the present invention may contain a slipping agent (filler), respectively. The slipping agent may be an inorganic filler or an organic filler, but is preferably an inorganic filler. The slip agent is not particularly limited, and examples thereof include silica, carbon, and ceramics, and silica is preferable. These slipping agents may be used alone or in combination of 2 or more. The average particle diameter of the slipping agent is preferably 10nm or more, more preferably 30nm or more, and still more preferably 50nm or more. Further, the particle size is preferably 1 μm or less, more preferably 500nm or less, and still more preferably 100nm or less. (a) The content of the slipping agent in the polyimide of the layer (b) is preferably 0.01 mass% or more. The smoothness based on the polyimide film is good, and is more preferably 0.02 mass% or more, still more preferably 0.05 mass% or more, and particularly preferably 0.1 mass% or more. From the viewpoint of transparency, it is preferably 30% by mass or less, more preferably 20% by mass or less, further preferably 10% by mass or less, and particularly preferably 5% by mass or less.

Hereinafter, a preferred method for producing the multilayered polyimide film of the present invention will be described. The method for producing a multilayered polyimide film of the present invention is preferably carried out in an atmosphere or inert gas having a temperature of 10 to 40 ℃ and a humidity of 10 to 55%, by:

2) A step of applying a polyimide solution or a polyimide precursor solution for forming the layer (b) to the coating film a1 within 100 seconds after the production of the coating film a1 to obtain a coating film ab 1;

3) Drying the coating film ab1, and heating for a period of time of 5 minutes to 45 minutes until the amount of residual solvent in the coating film ab1 on a whole layer basis is 15 mass% to 40 mass%, thereby obtaining a coating film ab 2;

4) A step of peeling off the coating film ab2 from the temporary support to obtain a film having self-supporting properties (coating film ab 2);

5) A step of sandwiching both ends of the film (coating film ab 2) having self-supporting properties, and further heating the film at a temperature range of 150 ℃ or higher and lower than 200 ℃ until the amount of residual solvent in the whole layer of the coating film ab2 becomes 5 mass% or higher and 15 mass% or higher, thereby obtaining a coating film ab 3;

6) And continuing the heating step, and further heating until the residual solvent content of the coating film ab3 is 0.5 mass% or less based on the total layer.

The temporary support is preferably a long flexible temporary support. The total-layer-standard residual solvent amount in step 3 is a value obtained from only the mass of the coating film ab1, and does not include the mass of the temporary support. The starting point of 100 seconds in step 2 is (a) after the completion of the application of the polyimide solution for forming a layer or the polyimide precursor solution to the temporary support. The same applies to the following operations.

By peeling off the temporary support at the stage of the self-supporting film, by-products generated by the drying and chemical reaction can be rapidly discharged from the film.

In the present invention, the polyimide solution or polyimide precursor solution is applied to an atmosphere or inert gas having a temperature of 10 ℃ to 40 ℃, preferably 15 ℃ to 35 ℃, a humidity of 10% to 55% rh, preferably 20% to 50% rh, preferably on a long and flexible temporary support. The next layer is preferably applied within 100 seconds, preferably within 50 seconds, more preferably within 25 seconds after the layer of the previous step is applied. The lower limit is not particularly limited, since the shorter the time until the next layer is applied, but it is industrially 1 second or more, or 2 seconds or more. As a coating method, the layer to be coated first may be coated using a comma coater, a bar coater, a slit coater, or the like, and the second layer may be coated later by a die coater, a curtain coater, a spray coater, or the like. In addition, by using a multilayer die, these multiple layers can be applied practically simultaneously.

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

The solvent used in the polyimide solution or polyimide precursor solution often has hygroscopicity, and when the solvent absorbs moisture and increases its water content, the solubility of the resin component decreases, and the dissolved component is precipitated in the solution, which may cause a rapid increase in solution viscosity. After coating, if this occurs, the formation of a transition layer of appropriate thickness is hindered. By controlling the humidity within a predetermined range, it is possible to sufficiently prevent precipitation of such dissolved components as long as the time is within about 100 seconds.

As the temporary support used in the present invention, glass, a metal plate, a metal belt, a metal roll, a polymer film, a metal foil, or the like can be used. In the present invention, a long and flexible temporary support is preferably used, and a film of polyethylene terephthalate, polyethylene naphthalate, polyimide, or the like can be used as the temporary support. The release treatment is one of the preferred modes for the surface of the temporary support.

In the present invention, after all layers are coated, drying is performed by heat treatment and chemical reaction is performed as needed. In the case of using a polyimide solution, only drying may be performed in order to remove the solvent, but in the case of using a polyimide precursor solution, both drying and chemical reaction are required. Here, the polyimide precursor is preferably in the form of a polyamic acid or a polyisoimide. In order to convert the polyamic acid into polyimide, a dehydration condensation reaction is required. The dehydration condensation reaction may be carried out by heating only, but an imidization catalyst may be used as needed. In the case of polyisoimides, the conversion of the iso-imide bond to an imide bond can also be achieved by heating. In addition, a suitable catalyst may be used in combination.

The amount of the residual solvent in the final film is 0.5 mass% or less, preferably 0.2 mass% or less, and more preferably 0.08 mass% or less, based on the average value of the entire film layer. The heating time is preferably 5 minutes to 60 minutes, more preferably 6 minutes to 50 minutes, and still more preferably 7 minutes to 30 minutes. By controlling the heating time within a predetermined range, the removal of the solvent, the necessary chemical reaction, and the warpage of the film can be reduced, and colorless transparency, mechanical properties, particularly high elongation at break can be maintained. In the case where the heating time is short, the warpage of the film becomes large, and in addition, if the heating time is too long, the film becomes strong in coloration, and the elongation at break of the film sometimes decreases.

In the present invention, if the applied solution can be peeled from the temporary support by self-supporting property by drying or chemical reaction by heating, the applied solution may be peeled from the temporary support in the middle of the heating step.

More specifically, the self-supporting film is peeled from the temporary support after heating for a period of time of 5 minutes to 45 minutes, preferably 6 minutes to 30 minutes, more preferably 7 minutes to 20 minutes, until the average residual solvent content of the entire film layer becomes 15 mass% to 40 mass%. In the peeled film having self-supporting properties, the drying of the layer (a) sandwiched between the temporary support and the layer (b) is relatively not performed with respect to the layer (b) in contact with air or an inert gas. In this state, both ends of the self-supporting film are further held by a clip or by a needle bar, and the film is transported in a heating environment, and further heated in a temperature range of 150 ℃ or higher and less than 200 ℃ until the amount of the residual solvent on the whole layer basis is 5 mass% or higher and 15 mass%, whereby the front and rear surfaces are simultaneously and rapidly dried by the heating step. By performing rapid drying, a film having reduced warpage and thus reduced CTE can be obtained as compared with a case where the drying temperature is 150 ℃ or lower. The mechanism of obtaining such an effect is presumed by the inventors that the residual solvent is present in an amount of 5 mass% or more and 15 mass% or less when heated at 150 ℃ or more and less than 200 ℃, whereby the residual component of the solvent is greater in the (a) layer than in the (b) layer. Therefore, the layer (a) has a slightly larger CTE than the case where the layer is not subjected to this step because the alignment of the polymer chains is disturbed due to the presence of the solvent. On the other hand, it is presumed that the residual part of the solvent in the layer (b) is relatively reduced, and therefore the layer (b) is less likely to cause disorder of alignment of polymer chains, and as a result, CTE is reduced. As a result, the CTE difference between the two layers is smaller than the difference that would otherwise be exhibited, and this is considered to be related to the effect of reducing warpage when the laminated film is formed. In addition, the CTE of the layer (b) is reduced by the present step as compared with the case where the layer (b) is not subjected to the present step. It is considered that by lowering the CTE of the layer (b) of the laminated film in which the thickness ratio is dominant, the effect of lowering the CTE of the laminated film as a whole is obtained.

In the present invention, the self-supporting film may be stretched. Stretching may be either the film longitudinal direction (MD direction) or the film width direction (TD), or both. Stretching in the film longitudinal direction can be performed using a difference in speed between the conveying rollers or a difference in speed between the conveying rollers and the nip ends. Stretching in the film width direction can be performed by enlarging the clip or pin pitch of the clip. Stretching and heating may be performed simultaneously. The stretching 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, by combining a polyimide which is difficult to stretch alone and a polyimide which can be stretched, the polyimide can be stretched even in a composition which is difficult to stretch, that is, which is easily broken by stretching, and thus the mechanical properties can be improved.

Further, since polyimide has a small volume during film formation by drying or dehydration condensation, it exhibits a stretching effect even in a state where both ends are held at equal intervals (stretching ratio of 1.00).

In the multilayer polyimide film of the present invention, it is preferable that the layer (a) and the layer (b) contain a slipping agent or the like, so that fine irregularities are provided on the surface of the layer (film) to improve the slipping property of the film or the like. The slipping agent is preferably added only to the layer (a) serving as the outer layer.

As the slipping agent, inorganic or organic fine particles having an average particle diameter of about 0.03 μm to 3 μm can be used, and specific examples thereof include titanium oxide, aluminum oxide, silicon dioxide, calcium carbonate, calcium phosphate, calcium hydrogen phosphate, calcium pyrophosphate, magnesium oxide, calcium oxide, clay minerals, and the like. The content of the slipping agent in the polyimide (polymer) is preferably 0.1 mass% or more, more preferably 0.4 mass% or more. Further, it is preferably 50% by mass or less, more preferably 30% by mass or less.

Examples

The present invention will be described in detail with reference to examples, but the present invention is not limited to the examples below unless the gist thereof is exceeded. The physical properties and the like in the production examples and examples were measured by the following methods.

< measurement of thickness of polyimide film >

Measurement was performed using a micrometer (dicing tape 1245D manufactured by dicing tape co).

< tensile elastic modulus, tensile Strength (breaking Strength), and elongation at break >

Samples obtained by cutting the film into strips of 100mm×10mm in the flow direction (MD direction) and width direction (TD direction) at the time of coating were used as test pieces. The tensile modulus, tensile strength and elongation at break were obtained in the MD direction and TD direction under conditions of a tensile speed of 50mm/min and a distance between chucks of 40mm using a tensile tester (model name AG-5000A, manufactured by Shimadzu corporation, auto graph (R)), and the average value of the measured values in the MD direction and TD direction was obtained.

< coefficient of linear expansion (CTE) >)

The elongation and contraction of the film was measured in the flow direction (MD direction) and the width direction (TD direction) at the time of coating, and the elongation and contraction were measured at 15 ℃ intervals such as 30 to 45 ℃, 45 to 60 ℃, and the measurement was performed up to 300 ℃, and 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.

A machine name; TMA 4000S manufactured by MAC Science Co., ltd

Sample length; 20mm of

Sample width; 2mm of

Heating to an initial temperature; 25 DEG C

The temperature of the heating end; 300 DEG C

The temperature rising speed; 5 ℃/min

An atmosphere; argon gas

< film thickness >

A chamfer surface of a film was formed by SAICAS DN-20S type (DAIPLAWINTES Co., ltd.), then a spectrum of the chamfer surface was obtained by microscopic IRCary 620FTIR (Agilent Co., ltd.) using a microscopic ATR method of germanium crystal (incidence angle 30 DEG), and a thickness in which a ratio of (b) layer thickness/(a) layer thickness was 5-fold to 25-fold was obtained by increasing or decreasing characteristic peaks of each of (a) layer and (b) layer and a calibration line obtained in advance.

< haze >

Haze of the film was measured using a HAZEMETER (NDH 5000, manufactured by japan electric color corporation). A D65 lamp was used as a light source. The same measurement was performed 3 times, and the arithmetic average value was used.

< total light transmittance >

The total light transmittance (TT) of the film was measured using a HAZEMETER (NDH 5000, manufactured by Nippon Denshoku Co., ltd.). A D65 lamp was used as a light source. The same measurement was performed 3 times, and the arithmetic average value was used. The results are shown in tables 1 and 2.

< yellow index >

The tristimulus values XYZ values of the films were measured by using a colorimeter (ZE 6000, manufactured by japan electric color corporation) and a C2 light source according to ASTM D1925, and the Yellowness Index (YI) was calculated by the following formula. The same measurement was performed 3 times, and the arithmetic average value was used.

YI＝100×(1.28X-1.06Z)/Y

Film warp >, film warp

A film cut into a square of 100mm by 100mm was used as a test piece, the test piece was left standing on a flat surface at room temperature to be concave, and distances (h 1rt, h2rt, h3rt, h4rt: unit mm) between four corners and the flat surface were measured, and the average value was used as a warpage amount (mm).

Production example 1 (a) production of a polyamic acid solution As containing a slipping agent for layer formation

After nitrogen substitution in a reaction vessel equipped with a nitrogen inlet tube, a reflux tube and a stirring rod, 22.73 parts by mass of 4,4' -Diaminobenzanilide (DABAN) was dissolved in 201.1 parts by mass of N, N-dimethylacetamide (DMAc), and then 19.32 parts by mass of 1,2,3, 4-cyclobutanetetracarboxylic dianhydride (CBDA) was added in a solid state in portions, followed by stirring at room temperature for 24 hours. Then, 173.1 parts by mass of DMAc was added to the mixture and diluted to obtain a polyamic acid solution having an NV (solid content) of 10% by mass and a reduced viscosity of 3.10 dl/g. To the polyamic acid solution thus obtained, a dispersion of colloidal silica dispersed in dimethylacetamide (SNOWTEX (registered trademark) DMAC-ST-ZL manufactured by the chemical industry of japanese industrial Co., ltd.) was further added As a slipping agent, and the silica (slipping agent) was made to be 1.4 mass% of the total amount of polymer solid components in the polyamic acid solution, thereby obtaining a uniform polyamic acid solution As.

Production example 2 (a) production of a polyamic acid solution Bs containing a slipping agent for layer formation

After nitrogen substitution in a reaction vessel equipped with a nitrogen inlet tube, a reflux tube and a stirring rod, 32.02 parts by mass of 2,2' -bistrifluoromethyl-4, 4' -diaminobiphenyl (TFMB) was dissolved in 279.9 parts by mass of N, N-dimethylacetamide (DMAc), and then 20.59 parts by weight of 3,3', 4' -biphenyltetracarboxylic anhydride (BPDA) and 9.31 parts by weight of 4,4' -Oxydiphthalic Dianhydride (ODPA) were added in portions as solids, respectively, followed by stirring at room temperature for 24 hours. Then, a polyamic acid solution having a solid content of 17% by mass and a reduced viscosity of 3.60dl/g was obtained. To the polyamic acid solution, a dispersion of colloidal silica dispersed in dimethylacetamide (SNOWTEX (registered trademark) DMAC-ST-ZL manufactured by the japanese chemical industry) was further added as a slipping agent, and the total amount of polymer solid content of silica (slipping agent) in the polyamic acid solution was 0.45 mass%, to obtain a uniform polyamic acid solution Bs.

Production example 3 (a) production of a polyamic acid solution Cs to which a slipping agent is added for layer formation

After nitrogen substitution in a reaction vessel equipped with a nitrogen inlet tube, a reflux tube and a stirring bar, 32.02 parts by mass of 2,2 '-bistrifluoromethyl-4, 4' -diaminobiphenyl (TFMB) was dissolved in 279.9 parts by mass of N, N-dimethylacetamide (DMAc), and 29.42 parts by weight of 3,3', 4' -biphenyltetracarboxylic anhydride (BPDA) was added in a solid state in portions, followed by stirring at room temperature for 24 hours. Then, a polyamic acid solution having a solid content of 17% by mass and a reduced viscosity of 3.80dl/g was obtained. To the polyamic acid solution, a dispersion of colloidal silica dispersed in dimethylacetamide (SNOWTEX (registered trademark) DMAC-ST-ZL manufactured by japanese chemical industry) was added as a slip agent, and the total amount of polymer solid content of silica (slip agent) in the polyamic acid solution was made 0.5 mass%, to obtain a uniform polyamic acid solution Cs.

Production example 4 (b) production of polyimide solution D for layer formation

To a reaction vessel equipped with a nitrogen inlet tube, a dean-stark apparatus, a reflux tube, a thermometer, and a stirrer, 32.02 parts by mass of 2,2' -bistrifluoromethyl-4, 4' -diaminobiphenyl (TFMB) was added to 230 parts by mass of N, N-dimethylacetamide (DMAc) to completely dissolve the biphenyl, and 44.42 parts by mass of 4,4' - (2, 2-hexafluoroisopropylidene) diphthalic dianhydride (6 FDA) was added in solid form in portions, followed by stirring at room temperature for 24 hours. Then, a polyamic acid solution Daa having a reduced viscosity of 1.10dl/g and a solid content of 25% by mass was obtained.

Then, 204 parts by mass of DMAc was added to the obtained polyamic acid solution Daa, and after dilution to a concentration of 15% by mass of polyamic acid, 1.3 parts by mass of isoquinoline as an imidization accelerator was added. Subsequently, 12.25 parts by mass of acetic anhydride was slowly added dropwise as an imidizing agent while stirring the polyamic acid solution. Then, the chemical imidization reaction was performed with stirring for 24 hours, to obtain a polyimide solution Dpi.

Subsequently, 100 parts by mass of the obtained polyimide solution Dpi 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, and as a result, precipitation of a powdery solid was confirmed.

Then, the powder as the content of the reaction vessel was dehydrated and filtered, washed with methanol, dried under vacuum at 50℃for 24 hours, and then heated at 260℃for 5 hours to obtain polyimide powder Dpd. 20 parts by mass of the obtained polyimide powder was dissolved in 80 parts by mass of DMAc to obtain a polyimide solution D.

Production example 5 (b) production of polyimide solution E for layer formation

To a reaction vessel equipped with a nitrogen inlet, a dean-stark apparatus, a reflux tube, a thermometer, and a stirrer, 120.5 parts by mass of 4,4 '-diaminodiphenyl sulfone (4, 4' -DDS), 51.6 parts by mass of 3,3 '-diaminodiphenyl sulfone (3, 3' -DDS), and 500 parts by mass of γ -butyrolactone (GBL) were added. Then, 217.1 parts by mass of 4,4' -Oxydiphthalic Dianhydride (ODPA), 223 parts by mass of GBL, and 260 parts by mass of toluene were added at room temperature, and the mixture was heated to 160 ℃ and refluxed at 160 ℃ for 1 hour to effect imidization. After imidization was completed, the temperature was raised to 180℃and the reaction was continued while toluene was withdrawn. After the reaction for 12 hours, the polyimide solution E was obtained by taking out the oil bath, cooling to room temperature, and adding GBL to a concentration of 20 mass% as a solid component.

Production example 6 (b) production of a layer-forming polyamic acid solution F

After nitrogen substitution in a reaction vessel equipped with a nitrogen inlet tube, a reflux tube and a stirring rod, 33.36 parts by mass of 2,2 '-bistrifluoromethyl-4, 4' -diaminobiphenyl (TFMB) and 336.31 parts by mass of N-methyl-2-pyrrolidone (NMP) were added and dissolved completely, and then 9.81 parts by mass of 1,2,3, 4-cyclobutane tetracarboxylic dianhydride (CBDA), 11.34 parts by mass of 3,3', 4' -biphenyltetracarboxylic acid and 4.85 parts by weight of (ODPA) were added in solid form, and the mixture was stirred at room temperature for 24 hours. Then, a polyamic acid solution F having a solid content of 15% by mass and a reduced viscosity of 3.50dl/g (molar ratio of TFMB// CBDA/BPDA/ODPA=1.00// 0.48/0.37/0.15) was obtained.

Production example 7 (b) production of a polyamic acid solution Fs added with a slipping agent for layer formation

After a reaction vessel equipped with a nitrogen inlet pipe, a return pipe and a stirring rod was replaced with nitrogen, 33.36 parts by mass of 2,2' -bis (trifluoromethyl) biphenyl (TFMB), 270.37 parts by mass of N-methyl-2-pyrrolidone (NMP) and a dispersion of colloidal silica dispersed in dimethylacetamide (SNOWTEX (registered trademark) DMAC-ST manufactured by the daily chemical industry) were added thereto to completely dissolve silica so that the total amount of polymer solid content in a polyamic acid solution became 30.0% by mass, 9.81 parts by mass of 1,2,3, 4-cyclobutanetetracarboxylic dianhydride (CBDA), 11.34 parts by mass of 3,3', 4' -biphenyltetracarboxylic acid and 4.85 parts by weight (ODPA) were added in solid form, and then stirred at room temperature for 24 hours. Then, 165.7 parts by mass of DMAc was added for dilution to obtain a polyamic acid solution Fs (molar ratio of TFMB// CBDA/BPDA/ODPA=1.00// 0.48/0.37/0.15) having a solid content of 18% by mass and a reduced viscosity of 2.7 dl/g.

The polyimide solutions and the polyamic acid solutions (polyimide precursor solutions) obtained in production examples 1 to 7 were subjected to film formation by the following methods, and optical properties and mechanical properties were measured. The results are shown in Table 1.

(method for obtaining a film for measuring physical Properties alone)

The polyimide solution or the polyamic acid solution was applied to a region of approximately 20cm square at the center of a 30cm glass plate on one side by using a bar coater, and the final thickness was set to 25.+ -.2. Mu.m, and the resultant was heated at 100℃for 30 minutes in an inert oven in which dry nitrogen was slowly circulated, and after confirming that the residual solvent content of the coating film was 40% by mass or less, the film was heated at 300℃for 20 minutes in a muffle furnace in which dry nitrogen was substituted. Then, the film was taken out of the muffle furnace, and the end of the dried coating film (film) was peeled off by a cutter, and the film was peeled off from the glass with care.

Example 1

The polyamic acid solution As obtained in production example 1 was applied to the non-slip surface of a polyethylene terephthalate film a4100 (manufactured by eastern corporation, hereinafter referred to As PET film) with a comma coater in an atmosphere adjusted to 45% rh at 25 ℃ so that the final film thickness was 2.3 μm, and then, after 10 seconds, the polyimide solution D obtained in production example 4 was applied to the polyamic acid solution As with a die coater so that the final film thickness was 22.7 μm. It was dried at 100℃for 10 minutes. The film having been dried and obtained as a self-supporting was peeled off from the a4100 film as a support, and the film was fixed by inserting the end of the film into a pin tenter having pins, and the pitch of the pins was adjusted so that the film was conveyed without breaking and without causing unnecessary relaxation, and imidization was performed under conditions of heating at 150 ℃ for 3 minutes, 200 ℃ for 3 minutes, 250 ℃ for 3 minutes, and 300 ℃ for 6 minutes. Then, the film was cooled to room temperature in 2 minutes, and the portions of the film having poor flatness at both ends were cut by a film slitting machine and wound into rolls to obtain film rolls having a width of 580mm and a length of 100 m. The evaluation results of the obtained films are shown in table 2.

Examples 2 to 9

Films were obtained by the setting conditions shown in examples 2 to 8 of table 2. The results of the same evaluation are shown in table 2.

Comparative example 1

The polyamic acid solution As obtained in production example 1 was applied to a non-slip surface of a polyethylene terephthalate film a4100 (manufactured by eastern corporation, hereinafter referred to As PET film) with a comma coater in an atmosphere adjusted to 45% rh at 25 ℃ so that the final film thickness was 5.0 μm, and then, after 10 seconds, the polyimide solution D obtained in production example 4 was applied to the polyamic acid solution As with a die coater so that the final film thickness was 20.0 μm. It was dried at 100℃for 10 minutes. The film having been dried and obtained as a self-supporting was peeled off from the a4100 film as a support, and the film was fixed by inserting the end of the film into a pin tenter having pins, and the pitch of the pins was adjusted so that the film was conveyed without breaking and without causing unnecessary relaxation, and imidization was performed under conditions of heating at 150 ℃ for 3 minutes, 200 ℃ for 3 minutes, 250 ℃ for 3 minutes, and 300 ℃ for 6 minutes. Then, the film was cooled to room temperature for 2 minutes, and the portions of the film having poor flatness at both ends were cut by a film slitting machine and wound into rolls to obtain film rolls having a width of 580mm and a length of 100 m. The evaluation results of the obtained films are shown in table 2.

Comparative example 2

The same procedure As in comparative example 1 was repeated except that the polyamic acid solution As in comparative example 1 was changed to the polyamic acid solution Bs and applied so that the final film thickness was 0.8. Mu.m, and then the polyimide solution D obtained in production example 4 was applied to the polyamic acid solution Bs by a die coater so that the final film thickness was 24.2. Mu.m, after 10 seconds, to obtain a film roll having a width of 580mm and a length of 100 m. The evaluation results of the obtained films are shown in table 2.

Comparative example 3

The same operation As in comparative example 1 was performed except that the polyamic acid solution As in comparative example 1 was changed to the polyamic acid solution Cs so that the final film thickness was 0.2 μm, and then the polyimide solution D obtained in production example 4 was applied to the polyamic acid solution Cs by a die coater for 10 seconds so that the final film thickness was 4.8 μm, to obtain a film roll having a width of 580mm and a length of 100 m. The evaluation results of the obtained films are shown in table 2.

As is clear from Table 2, in examples 1 to 9, the warpage was less than 5mm and the CTE was less than 45ppm/K, and good multilayer polyimide films were obtained. On the other hand, in comparative examples 1 to 3, the warpage was 5mm or more, or the CTE exceeded 45ppm/K.

TABLE 1

TABLE 2

Industrial applicability

As described above, the multilayered polyimide film of the present invention exhibits good optical and mechanical properties as compared with the case where polyimides of different compositions are individually formed into films. Further, according to the production method of the present invention, even a laminate of polyimides having different compositions, which are divided into a plurality of layers and function-shared, can be formed with a balanced film having a low CTE while suppressing warpage.

The multilayer polyimide film of the present invention has excellent optical properties, colorless transparency, and excellent mechanical properties and low CTE, and therefore, can be used as a member of a flexible and lightweight display device, or can be used for a switching element, a pointing device, or the like of a touch panel or the like requiring transparency.

Claims

1. A multilayer polyimide film comprising at least a polyimide layer (a) and a polyimide layer (b),

the polyimide layer (a) and the polyimide layer (b) are different in composition,

the polyimide layer (a) has a film thickness of 0.3 μm or more, the polyimide layer (b) has a film thickness of 5 to 25 times the film thickness of the polyimide layer (a),

the thickness of the multilayer polyimide film is 3-120 [ mu ] m, the yellow index is 5-86% and the total light transmittance is 86%.

2. The multilayer polyimide film according to claim 1, wherein the (a) layer and the (b) layer are each composed mainly of polyimide having the following characteristics,

3. The multilayer polyimide film according to claim 1 or 2, wherein the polyimide of the layer (a) is a polyimide having a chemical structure obtained by polycondensation of tetracarboxylic anhydride and diamine,

the tetracarboxylic anhydride is a tetracarboxylic anhydride containing 1 or more kinds selected from the group consisting of alicyclic tetracarboxylic anhydride, aromatic tetracarboxylic anhydride having an ether group in the molecule, and aromatic tetracarboxylic anhydride having a biphenyl group in the molecule,

4. The multilayer polyimide film according to any one of claim 1 to 3, wherein the polyimide of the layer (b) is a polyimide having a chemical structure obtained by polycondensation of tetracarboxylic anhydride and diamine,

5. The method for producing a multilayer polyimide film according to any one of claims 1 to 4, comprising at least:

4) A step of peeling off the coating film ab2 from the temporary support;