CN115379951A

CN115379951A - Polyimide film and method for producing same

Info

Publication number: CN115379951A
Application number: CN202180022891.9A
Authority: CN
Inventors: 水口传一朗; 奥山哲雄; 涌井洋行; 中村诚; 渡边直树; 米虫治美; 前田乡司
Original assignee: Toyobo Co Ltd
Current assignee: Toyobo Co Ltd
Priority date: 2020-05-29
Filing date: 2021-05-25
Publication date: 2022-11-22
Also published as: JPWO2021241572A1; WO2021241572A1; KR20230016613A; TW202202554A; JP7103534B2; JP7287535B2; JP2022119814A

Abstract

A colorless polyimide film having high tensile breaking strength and tensile elastic modulus, high elongation at break, and a low linear expansion coefficient, and a method for producing the same are provided. The multilayer film is obtained by using a high-strength polyimide as the outer layer (a) and a polyimide having excellent optical characteristics as the inner layer (b). The polyimide solution or polyimide precursor solution for forming the layer (a) is applied to a temporary support, dried until the solvent content is 5 to 40 mass%, then the polyimide solution or polyimide precursor solution for forming the layer (b) is applied, the same application is repeated as necessary, and finally heat treatment is performed to obtain a multilayer polyimide film.

Description

Polyimide film and method for producing same

Technical Field

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

Background

Polyimide films have excellent heat resistance and good mechanical properties, and are widely used in the electrical and electronic fields as flexible materials. However, since the polyimide film is usually colored in a yellowish brown color, it cannot be applied to a portion requiring light transmission such as a display device.

On the other hand, with the trend toward thinner and lighter display devices, further flexibility is required. Therefore, attempts have been made to use a flexible polymer film substrate as a substrate material instead of a glass substrate, but a dyed polyimide film cannot be used as a substrate material for liquid crystal display that performs ON/OFF display by transmitting light, and is applicable only to a small portion of peripheral circuits such as TAB and COF that carry driving circuits of a display device, and the rear surface side in a display system without reflection or a self-emission display device.

Against the background described above, development of a colorless and transparent polyimide film is proceeding. As a representative example, development of a colorless transparent polyimide film using a fluorinated polyimide resin, a semi-alicyclic or full-alicyclic polyimide resin, or the like has been attempted (patent documents 1 to 3). These films have a low degree of dyeing and transparency, but do not have mechanical properties comparable to dyed polyimide films, and are supposed to be incapable of always maintaining colorlessness and transparency due to thermal decomposition, oxidation reaction, and the like during industrial production and use at high temperatures. From this viewpoint, a method of performing a heat treatment while injecting a gas having a specific oxygen content has been proposed (patent document 4), but the production cost is high in an environment where the oxygen concentration is less than 18% or the like, and industrial production is extremely difficult.

Documents of the prior art

Patent literature

Patent document 1, japanese patent laid-open publication No. 11-106508

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

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

Patent document 4

Disclosure of Invention

Problems to be solved by the invention

That is, practical properties such as heat resistance and mechanical properties and colorless transparency are in a trade-off (tradeoff) relationship, and it is very difficult to produce a colorless transparent polyimide film satisfying all the properties. The present invention addresses the problem of providing a polyimide film having excellent mechanical properties and colorless transparency.

Means for solving the problems

The present inventors have tried to realize a polyimide film having a balance by combining a plurality of polyimide resins. When a plurality of resin components are blended, mixed or copolymerized in general, the advantageous results of combining the respective components cannot always be obtained, and the combination showing the disadvantage is not rare. However, the present inventors have made extensive studies and as a result, have found that the strength of each component can be sufficiently exhibited by combining polyimide resins to form a film so as to form a specific structure, and have reached the present invention.

Namely, the present invention has the following composition.

[1] A multilayer polyimide film comprising a multilayer polyimide layer obtained by laminating at least two polyimide layers having different compositions in the thickness direction, and

a transition layer having a gradient in chemical composition, which is present between (a) a layer constituting the multilayer polyimide layer and (b) a layer adjacent to the (a) layer,

the thickness of the whole film is 3 to 120 μm,

the yellow index of the whole film is 5 or less,

the total light transmittance of the entire film was 86% or more.

[2] The multilayer polyimide film according to [1], wherein the thickness of the transition layer has a lower limit of 0.01 μm and an upper limit of either 3% or 1 μm of the total film thickness.

[3] The multilayer polyimide film according to [1] or [2], wherein the layer (a) is mainly composed of a polyimide having a yellow index of 10 or less and a total light transmittance of 85% or more when used alone as a film having a thickness of 25. + -. 2 μm,

the layer (b) is mainly composed of polyimide having a yellow index of 5 or less and a total light transmittance of 90% or more when used alone as a film having a thickness of 25. + -. 2 μm.

[4] The multilayer polyimide film according to any one of [1] to [3], comprising: the (a) layer is present on both sides of one surface side and the other surface side of the (b) layer,

the transition layer is present between the (a) layer and the (b) layer on one surface side of the (b) layer, and between the (a) layer and the (b) layer on the other surface side of the (b) layer,

and (c) sequentially laminating the layer (a), the transition layer, the layer (b), the transition layer and the layer (a).

[5] The multilayer polyimide film according to any one of [1] to [4], wherein the polyimide in the layer (a) is a polyimide having a chemical structure obtained by polycondensation of a tetracarboxylic anhydride containing 70 mass% or more of an alicyclic tetracarboxylic anhydride and a diamine containing 70 mass% or more of a diamine having an amide bond in the molecule,

or a polyimide having a chemical structure obtained by polycondensation of a tetracarboxylic anhydride containing 30 mass% or more of an alicyclic tetracarboxylic anhydride and a diamine containing 70 mass% or more of a diamine having a trifluoromethyl group in the molecule.

[6] The multilayer polyimide film according to any one of [1] to [5], wherein the polyimide in the layer (b) is a polyimide having a chemical structure obtained by polycondensation of a tetracarboxylic anhydride containing 70 mass% or more of an aromatic tetracarboxylic anhydride and a diamine containing 70 mass% or more of a diamine having a sulfur atom in a molecule,

or a polyimide having a chemical structure obtained by polycondensation of a tetracarboxylic anhydride containing 70 mass% or more of a tetracarboxylic acid containing a trifluoromethyl group in the molecule and a diamine containing 70 mass% or more of a diamine having a trifluoromethyl group in the molecule.

[7] The method for producing a multilayer polyimide film according to [1], [2], [3] [5] or [6], which comprises at least,

1: a step of applying a polyimide solution or a polyimide precursor solution for forming the layer (a) 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 content of 5 to 40 mass%,

3: a step of applying a polyimide solution or a polyimide precursor solution for forming the layer (b) to the coating film a2 to obtain a coating film ab1,

4: heating all layers to obtain a laminate having a residual solvent content of 0.5 mass% or less based on all layers.

[8] The method for producing a multilayer polyimide film according to [1], [2], [3] [5] or [6], which comprises at least,

4: heating all the layers to obtain a laminate having a residual solvent content of 5 to 40 mass% based on all the layers, and then peeling the laminate from the temporary support to obtain a self-supporting film,

5: and fixing both ends of the self-supporting film to obtain a film having a residual solvent content of 0.5 mass% or less based on the entire layer.

[9] The method for producing a multilayer polyimide film according to any one of [1] to [6], which comprises at least,

1: a step of applying a polyimide solution or a polyimide precursor solution for forming the layer (a) onto a temporary support to obtain a coating film a1,

4: a step of drying the coating film ab1 to obtain a coating film ab2 having a residual solvent content of 5 to 40 mass% based on the entire layer,

5. a step of applying a polyimide solution or a polyimide precursor solution for forming the layer (a) to a coating film ab2 to obtain a coating film aba1,

6: heating all layers to obtain a laminate having a residual solvent content of 0.5 mass% or less based on all layers.

[10] The method for producing a multilayer polyimide film according to any one of [1] to [6], which comprises

4: a step of drying the coated film ab1 to obtain a coated film ab2 having a residual solvent content of 5 to 40 mass% based on the entire layer,

5: a step of applying a polyimide solution or a polyimide precursor solution for forming the layer (a) to a coating film ab2 to obtain a coating film aba1,

6: heating all layers to obtain a laminate having a residual solvent content of 8 to 40 mass% based on all layers, and then peeling the laminate from the temporary support to obtain a self-supporting film,

7: and fixing both ends of the self-supporting film to obtain a film having a residual solvent content of 0.5 mass% or less based on the entire layer.

The present invention may further include the following composition.

[11] A method for producing a multilayer polyimide film, characterized in that 1 and 2 in [8] are repeated to obtain odd-numbered layers of 5 or more.

[12] The multilayer polyimide film according to any one of [1] to [6], wherein the thickness of the layer (a) is 25% or less of the total thickness of the film. However, when the layer (a) is a multilayer, the total thickness of the layer (a) is 1% or more, preferably 2% or more, and more preferably 4% or more, and 25% or less, preferably 13% or less, and more preferably 7% or less of the total thickness of the film.

Effects of the invention

The multilayer polyimide film of the present invention is excellent in mechanical properties and colorless transparency by laminating at least two polyimide layers having different compositions in the thickness direction, and forming a transition layer having a gradient change in chemical composition between the two polyimide layers.

Detailed Description

The polyimide of the layer (a) in the present invention is preferably a polyimide having a chemical structure obtained by polycondensation of a tetracarboxylic anhydride containing at least 70 mass% of an alicyclic tetracarboxylic anhydride and a diamine containing at least 70 mass% of a diamine having an amide bond in the molecule, or a polyimide having a chemical structure obtained by polycondensation of a tetracarboxylic anhydride containing at least 30 mass% of an alicyclic tetracarboxylic anhydride and a diamine containing at least 70 mass% of a diamine having a trifluoromethyl group in the molecule, which has good mechanical properties, high elongation at break, and excellent properties such as low CTE, but is relatively easy to dye.

On the other hand, the polyimide of the layer (b) is preferably a polyimide having a chemical structure obtained by polycondensation of a tetracarboxylic anhydride containing 70 mass% or more of an aromatic tetracarboxylic anhydride and a diamine containing 70 mass% or more of a diamine having a sulfur atom in the molecule, or a polyimide having a chemical structure obtained by polycondensation of a tetracarboxylic anhydride containing 70 mass% or more of a tetracarboxylic acid containing a trifluoromethyl group in the molecule and a diamine containing 70 mass% or more of a diamine having a trifluoromethyl group in the molecule, and although it has high colorless transparency, it is hard and brittle as a resin, and hardly exhibits sufficient elongation at break at the time of film formation, and is not well suited for flexible use, and further it is difficult to produce it as a continuous film.

When both are mixed or copolymerized, only a film having properties between those of the two or less can be obtained, and further, the properties of the layer (a) which is easily dyed tend to be more prominent in terms of colorless transparency.

However, by molding the two component polyimides as separate layers to share the functions as in the present invention, and further applying a specific production method, a film having a balance of colorless transparency and 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 applied solution, and if necessary, performing a chemical reaction. In the present invention, a solution of a plurality of components is applied one by one repeatedly a plurality of times, dried until it becomes semi-solid due to loss of fluidity to form a multilayer structure, and after a necessary layer is formed, it is finally heated, dried and, if necessary, chemically reacted to obtain a solid film. Since polyimide is chemically stable, for example, even when a solution of a second polyimide or a polyimide precursor solution having a different composition (or, alternatively, the same chemical composition) is coated on a first polyimide film and dried by heating or by catalytic action, a solid polyimide coating film is obtained, but since chemical bonds are not generated between the first polyimide and the second polyimide, the adhesive strength at the interface is weak, and only a film that is easily peeled between layers can be obtained.

However, according to the present invention, if the coating and semi-drying operations are repeated, since the solvent concentration of the first coated portion is low and the solvent concentration of the second coated portion is high, solvent diffusion across the boundary surface occurs due to the concentration gradient, and the dissolved polymer moves with the solvent, micro flow mixing occurs in the vicinity of the boundary surface, and an extremely thin transition layer with a chemical composition gradient changing is formed. The transition layer can buffer stress dislocation generated between layers with different physical properties, and can show strong adhesive strength between the layers, thereby obtaining a multilayer film with stable and balanced properties.

The thickness of the multilayer polyimide film of the present invention is 3 μm to 120 μm. From the viewpoint of good mechanical properties, it is preferably 4 μm or more, more preferably 5 μm or more, and still more preferably 8 μm or more. Further, from the viewpoint of good transparency, it is preferably 100 μm or less, more preferably 80 μm or less, and further preferably 60 μm or less.

The multilayer polyimide film of the present invention has a yellowness index of 5 or less. From the viewpoint of good transparency, it is preferably 4 or less, more preferably 3.5 or less, and still more preferably 3 or less. The lower limit is not particularly limited as the yellowness index is lower, and the lower limit may be 0.1 or more, and 0.2 or more is not particularly limited in industry.

The total light transmittance of the multilayer polyimide film is over 86 percent. From the viewpoint of improving transparency, the content is preferably 87% or more, more preferably 88% or more, and further preferably 89% or more. The upper limit is not particularly limited, and may be 99% or less, or 98% or less, in industry.

In the present invention, at least two types of polyimides different in composition are used and stacked in the thickness direction. The polyimide is generally a polymer obtained by polycondensation of tetracarboxylic anhydride and diamine. The at least two polyimide layers include a layer (a) and a layer (b), and preferably, the layer (a) and the layer (b) are each composed mainly of a polyimide having the following characteristics. Here, the polyimide having the following characteristics is mainly contained in each layer in an amount of preferably 70% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, and particularly preferably 100% by mass. The different composition means that at least the resins of the polyimides need to have different compositions, and is different from the case where, for example, the resin components are the same, and only the presence or absence of a slip agent, the amount of a blending agent, and the like are different.

(a) The polyimide mainly used for the layer (hereinafter, the "main" may be omitted, and may be simply referred to as "polyimide used for the layer (a)", and "polyimide used for the layer (a)") is preferably a polyimide having a yellow index of 10 or less and a total light transmittance of 85% or more when used alone as a film having a thickness of 25 ± 2 μm. The yellowness index is preferably 9 or less, more preferably 8 or less, and further preferably 7 or less, from the viewpoint of improving transparency. The lower limit of the yellowness index is not particularly limited, and 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 further preferably 88% or more. The upper limit is not particularly limited, and may be 99% or less, or 98% or less in the industry.

The thickness of the layer (a) in the multilayer polyimide film is preferably more than 1 μm, more preferably 1.5 μm or more, further preferably 2 μm or more, and particularly preferably 3 μm or more, from the viewpoint of improving mechanical strength. From the viewpoint of improving transparency, the thickness is preferably less than 119 μm, more preferably 100 μm or less, still more preferably 50 μm or less, and particularly preferably 20 μm or less.

(a) The polyimide mainly used in the layer is preferably a polyimide having a chemical structure obtained by polycondensation of a tetracarboxylic anhydride containing an alicyclic tetracarboxylic anhydride in an amount of 70 mass% or more based on 100 mass% of the total acid component and a diamine containing a diamine having an amide bond in a molecule in an amount of 70 mass% or more based on 100 mass% of the total amine component, or a polyimide having a chemical structure obtained by polycondensation of a tetracarboxylic anhydride containing an alicyclic tetracarboxylic anhydride in an amount of 30 mass% or more and a diamine containing a diamine having a trifluoromethyl group in a molecule in an amount of 70 mass% or more.

(b) The polyimide mainly used in the layer (hereinafter, sometimes "mainly" may be omitted, and simply referred to as "polyimide used in the layer (b)", "polyimide used as the layer (b)", and the like) is preferably a polyimide having a yellow index of 5 or less and a total light transmittance of 90% or more when used alone as a film having a thickness of 25 ± 2 μm. The yellowness index is preferably 4 or less, more preferably 3 or less, from the viewpoint of improving transparency. The lower limit of the yellowness index is not particularly limited, and may be 0.1 or more and 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, and may be 99% or less and 98% or less in industry. (b) The yellow index of the polyimide used in the layer (a) is preferably smaller than the yellow index of the polyimide used in the layer (a). The total light transmittance of the polyimide used in the layer (b) is preferably higher than that of the polyimide used in the layer (a).

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

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

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-cyclohexanetetracarboxylic acid, 1,2,4, 5-cyclohexanetetracarboxylic acid, 3',4' -dicyclohexyltetracarboxylic acid, bicyclo [2,2,1] heptane-2,3,5,6-tetracarboxylic acid, bicyclo [2,2,2] octane-2,3,5,6-tetracarboxylic acid, bicyclo [2,2,2] oct-7-enyl-2,3,5,6-tetracarboxylic acid, tetrahydroanthracene-2,3,6,7-tetracarboxylic acid, tetradecahydro-1,4: 6,6 "-tetracarboxylic acid (the name" norbornane-2-spiro-2 ' -cyclopentanone-5 ' -spiro-2 "-norbornane-5, 5",6 "-tetracarboxylic acid"), methylnorbornane-2-spiro- α -cyclopentanone- α ' -spiro-2 "- (methylnorbornane) -5,5",6 "-tetracarboxylic acid, norbornane-2-spiro- α -cyclohexanone- α ' -spiro-2" -norbornane-5, 5", 6" -tetracarboxylic acid (the name "norbornane-2-spiro-2 ' -cyclohexyl-methane <xnotran> -6' - -2"- -5,5",6,6"- "), -2- - α - - α ' - -2"- ( ) -5,5",6,6"- , -2- - α - - α ' - -2" - -5,5",6,6" - , -2- - α - - α ' - -2"- -5,5",6,6"- , -2- - α - - α ' - -2" - -5,5",6,6" - , -2- - α - - α ' - -2"- -5,5",6,6"- , -2- - α - - α ' - -2" - -5,5",6,6" - , -2- - α - - α ' - -2"- -5,5",6,6"- , -2- - α - - α ' - -2" - -5,5",6,6" - , </xnotran> Norbornane-2-spiro- α -cyclododecanone- α ' -spiro-2 "-norbornane-5, 5",6 "-tetracarboxylic acid, norbornane-2-spiro- α -cyclotridecanone- α ' -spiro-2" -norbornane-5, 5", 6" -tetracarboxylic acid, norbornane-2-spiro- α -cyclotetradecanone- α ' -spiro-2 "-norbornane-5, 5",6 "-tetracarboxylic acid, norbornane-2-spiro- α -cyclopentadecanone- α ' -spiro-2" -norbornane-5, 5",6,6 ' -tetracarboxylic acid, norbornane-2-spiro-alpha- (methylcyclopentanone) -alpha ' -spiro-2 ' -norbornane-5,5 ', tetracarboxylic acids such as 6,6 ' -tetracarboxylic acid, norbornane-2-spiro-alpha- (methylcyclohexanone) -alpha ' -spiro-2 ' -norbornane-5, 5', 6' -tetracarboxylic acid and anhydrides thereof. Among these, dianhydrides having 2 anhydride structures are preferable, and in particular, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclohexanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride are preferable, 1,2,3,4-cyclohexanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, and 1,2,3,4-cyclohexanetetracarboxylic dianhydride are more preferable, and 1,2,3,4-cyclobutanetetracarboxylic dianhydride is further preferable. These may be used alone, or two or more of them may be used in combination.

Examples of the aromatic tetracarboxylic anhydride in the present invention include 4,4'- (2, 2-hexafluoroisopropylidene) diphthalic acid, 4' -oxydiphthalic acid, bis (1, 3-dioxy-1, 3-dihydro-2-benzofuran-5-carboxylic acid) 1, 4-phenylene, bis (1, 3-dioxy-1, 3-dihydro-2-benzofuran-5-yl) benzene-1, 4-dicarboxy-late, 4'- [4,4' - (3-dioxy-1, 3-dihydro-2-benzofuran-1, 1-diyl) bis (benzene-1, 4-diyloxy) ] diphenyl-1, 2-dicarboxylic acid, 3',4,4' -Benzophenone tetracarboxylic acid, 4'- [ (3-oxolene-1, 3-dihydro-2-benzofuran-1, 1-diyl) bis (toluene-2, 5-diyloxy) ] diphenyl-1, 2-dicarboxylic acid, 4' - [ (3-oxolene-1, 3-dihydro-2-benzofuran-1, 1-diyl) bis (1, 4-xylene-2, 5-diyloxy) ] diphenyl-1, 2-dicarboxylic acid, 4'- [4,4' - (3-oxolene-1, 3-dihydro-2-benzofuran-1, 1-diyl) bis (4-isopropyl-toluene-2, 5-diyloxy) ] diphenyl-1, 2-dicarboxylic acid, 4,4' - [4,4' - (3-oxoylidene-1, 3-dihydro-2-benzofuran-1, 1-diyl) bis (naphthalene-1, 4-diyloxy) ] biphenyl-1, 2-dicarboxylic acid, 4' - [4,4' - (3H-2, 1-benzoxazothioyl) bis (benzene-1, 4-diyloxy) ] biphenyl-1, 2-dicarboxylic acid, 4' -benzophenonetetracarboxylic acid, 4' - [ (3H-2, 1-benzoxazothioyl) bis (toluene-2, 5-diyloxy) ] biphenyl-1, 2-dicarboxylic acid, 4' - [ (3H-2, 1-benzoxazothioyl) lane-1, 1-dioxide-3, 3-diyl) bis (toluene-2, 5-diyloxy) ] biphenyl-1, 2-dicarboxylic acid 4,4' - [ (3H-2, 1-benzoxazolylo-1, 1-dioxide-3, 3-diyl) bis (1, 4-xylene-2, 5-diyloxy) ] diphenyl-1, 2-dicarboxylic acid, 4' - [4,4' - (3H-2, 1-benzoxazolylo-1, 1-dioxide-3, 3-diyl) bis (4-isopropyl-toluene-2, 5-diyloxy) ] diphenyl-1, 2-dicarboxylic acid, 4' - [4,4' - (3H-2, 1-benzoxazolylo-1, 1-dioxide-3, 3-diyl) bis (naphthalene-1, 4-diyloxy) ] diphenyl-1, 2-dicarboxylic acid, 1, 4' -bis (naphthalene-1, 4-diyloxy) ] diphenyl-1, 2-dicarboxylic acid, 3,3',4' -benzophenonetetracarboxylic acid, 3',4,4' -diphenylsulfone tetracarboxylic acid, 3',4' -biphenyltetracarboxylic acid, 2, 3', tetracarboxylic acids such as 4' -biphenyltetracarboxylic acid, pyromellitic acid, 4'- [ spiro (xanthene-9, 9' -fluorene) -2, 6-diylbis (oxycarbonyl) ] diphthalic acid, and 4,4'- [ spiro (xanthene-9, 9' -fluorene) -3, 6-diylbis (oxycarbonyl) ] diphenyldicarboxylic acid, and acid anhydrides thereof. The aromatic tetracarboxylic acids may be used alone or in combination of two or more.

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

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 diphenyl sulfone-3, 3',4' -tricarboxylic acid, hydrides of the above aromatic tricarboxylic acids such as hexahydrotrimellitic acid, alkylene glycol trimellitate such as ethylene glycol bistrimellitate, propylene glycol bistrimellitate, 1, 4-butanediol bistrimellitate, and polyethylene glycol bistrimellitate, and monoanhydrides and esters thereof. Among these, monoanhydrides having 1 acid anhydride structure are preferable, and trimellitic anhydride and hexahydrotrimellitic anhydride are particularly preferable. These may be used alone or in combination of two or more.

The dicarboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, and 4,4' -oxydibenzoic acid, hydrogenated products of the above aromatic dicarboxylic acids such as 1, 6-cyclohexanedicarboxylic acid, oxalic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, and 2-methylsuccinic acid, and acid chlorides and esters thereof. Of these, aromatic dicarboxylic acids and hydrides thereof are preferable, and particularly, terephthalic acid, 1, 6-cyclohexanedicarboxylic acid, 4' -oxydibenzoic acid are preferable. The dicarboxylic acids may be used alone or in combination.

As the diamine having an amide bond in the molecule in the present invention, an aromatic diamine or an alicyclic amine can be mainly used.

<xnotran> , , 2,2'- -4,4' - ,1,4- [2- (4- ) -2- ] ,1,4- (4- -2- ) ,2,2 '- ( ) -4,4' - ,4,4'- (4- ) ,4,4' - (3- ) , [4- (3- ) ] , [4- (3- ) ] , [4- (3- ) ] ,2,2- [4- (3- ) ] ,2,2- [4- (3- ) ] -1,1,1,3,3,3- , , , , , ,4- -N- (4- ) ,3,3 '- ,3,4' - ,4,4'- ,2,2' - -4,4'- ,3,3' - ,3,3 '- ,3,4' - ,4,4'- ,3,3' - , </xnotran> <xnotran> 3,4'- ,4,4' - ,3,3 '- ,3,4' - ,4,4'- ,3,3' - ,3,4 '- ,4,4' - , [4- (4- ) ] ,1,1- [4- (4- ) ] ,1,2- [4- (4- ) ] ,1,1- [4- (4- ) ] ,1,2- [4- (4- ) ] ,1,3- [4- (4- ) ] ,2,2- [4- (4- ) ] ,1,1- [4- (4- ) ] ,1,3- [4- (4- ) ] ,1,4- [4- (4- ) ] ,2,2- [4- (4- ) ] ,2,3- [4- (4- ) ] ,2- [4- (4- ) ] -2- [4- (4- ) -3- ] , </xnotran> <xnotran> 2,2- [4- (4- ) -3- ] ,2- [4- (4- ) ] -2- [4- (4- ) -3,5- ] ,2,2- [4- (4- ) -3,5- ] ,2,2- [4- (4- ) ] -1,1,1,3,3,3- ,1,4- (3- ) ,1,3- (3- ) ,1,4- (4- ) ,4,4' - (4- ) , [4- (4- ) ] , [4- (4- ) ] , [4- (4- ) ] , [4- (4- ) ] , [4- (3- ) ] , [4- (4- ) ] ,1,3- [4- (4- ) ] ,1,3- [4- (3- ) ] ,1,4- [4- (3- ) ] , </xnotran> <xnotran> 4,4'- [ (3- ) ] ,1,1- [4- (3- ) ] ,1,3- [4- (3- ) ] ,3,4' - ,2,2- [3- (3- ) ] -1,1,1,3,3,3- , [4- (3- ) ] ,1,1- [4- (3- ) ] ,1,2- [4- (3- ) ] , [4- (3- ) ] ,4,4'- [3- (4- ) ] ,4,4' - [3- (3- ) ] ,4,4'- [4- (4- - α, α - ) ] ,4,4' - [4- (4- - α, α - ) ] , [4- {4- (4- ) } ] ,1,4- [4- (4- ) - α, α - ] ,1,3- [4- (4- ) - α, </xnotran> 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, alpha-dimethylbenzyl ] benzene, 3 '-diamino-4, 4' -diphenoxybenzophenone, 4 '-diamino-5, 5' -diphenoxybenzophenone, 3,4 '-diamino-4, 5' -diphenoxybenzophenone, 3 '-diamino-4-phenoxybenzophenone, 4' -diamino-5-phenoxybenzophenone, 3,4 '-diamino-4-phenoxybenzophenone, alpha-dimethylbenzyl 3,4' -diamino-5 '-phenoxy benzophenone, 3' -diamino-4, 4 '-bigeminphenoxy benzophenone, 4' -diamino-5, 5 '-bigeminphenoxy benzophenone, 3,4' -diamino-4, 5 '-bigeminphenoxy benzophenone, 3' -diamino-4-diphenoxybenzophenone, 4 '-diamino-5-diphenoxybenzophenone, 3,4' -diamino-4-diphenoxybenzophenone, 3,4' -diamino-5 ' -biphenyloxybenzophenone, 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-biphenyloxybenzoyl) benzene, 1, 4-bis (3-amino-4-biphenyloxybenzoyl) benzene, 1, 3-bis (4-amino-5-biphenyloxybenzoyl) benzene, 1, 4-bis (4-amino-5-biphenyloxybenzoyl) benzene, 2, 6-bis [4- (4-amino- α, α -dimethylbenzyl) phenoxy ] benzonitrile, 4' - [ 9H-fluorene-9, 9-diyl ] dianiline (another name: 9-aminophenyl) fluorene, 9-bis (4-spirofluorene-9-bis (4-carbonyloxy) ] fluorene, 9-bis (9-spirofluorene-9-6-carbonylspirofluorene-6-bis (4-carbonyloxy) ] fluorene, 5-amino-2- (p-aminophenyl) benzoxazole, 6-amino-2- (p-aminophenyl) benzoxazole, 5-amino-2- (m-aminophenyl) benzoxazole, 6-amino-2- (m-aminophenyl) benzoxazole, 2' -p-phenylenebis (5-aminobenzoxazole), 2' -p-phenylenebis (6-aminobenzoxazole), 1- (5-aminobenzoxazole) -4- (6-aminobenzoxazole) 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, 3' -diaminodiphenyl ] bisoxazole, etc. In addition, a part or all of the hydrogen atoms on the aromatic ring of the aromatic diamine may be substituted by a halogen atom, an alkyl group or an alkoxy group having 1 to 3 carbon atoms, or a cyano group, and a part or all of the hydrogen atoms of the alkyl group or the alkoxy group having 1 to 3 carbon atoms may be substituted by a halogen atom.

Examples of the alicyclic diamines include 1, 4-cyclohexanediamine, 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 to have a layer structure in which the (a) layer is present on both sides of one surface side and the other surface side of the (b) layer, the transition layer is present between the (a) layer and the (b) layer on the one surface side of the (b) layer, and the (a) layer and the (b) layer on the other surface side of the (b) layer, and the (a) layer, the transition layer, the (b) layer, the transition layer, and the (a) layer are stacked in this order. Hereinafter, the layer structure in which the layer (a), the transition layer, the layer (b), the transition layer, and the layer (a) are sequentially stacked is also referred to as "(a)/(b)/(a)". Similarly, a layer structure in which the layer (a), the transition layer, and the layer (b) are sequentially stacked is referred to as "(a)/(b)", and a layer structure in which the layer (a), the transition layer, (b), the transition layer, and the layer (a) are sequentially stacked is referred to as "(a)/(b)/(a)/(b)/(a)".

In the present invention, the (a) layer and the (b) layer have a two-layer structure of (a)/(b), a three-layer structure of (a)/(b)/(a), or preferably a five-layer structure of (a)/(b)/(a)/(b)/(a), and further may be films of seven layers, nine layers, or odd-numbered layers above them. In the case of the odd-numbered layers, the layer (a) is preferably disposed at the outermost layer position. By using the layer (a) having a smaller linear expansion coefficient than the layer (b) and excellent mechanical properties as the outermost layer, the linear expansion coefficient of the entire film can be suppressed to be low, and the surface layer having excellent mechanical strength is provided, whereby the handling properties of the film are improved, and the excellent optical properties of the polyimide as the inner layer (b) can be maximally exhibited. The (b) layer is preferably thicker than the (a) layer. (b) The ratio of the thickness of the layer (b)/the thickness of the layer (a) is preferably greater than 1, more preferably 1.5 or more, and still more preferably 2 or more. Further, it is preferably 20 or less, more preferably 15 or less, and further preferably 12 or less.

In the present invention, the thickness of the layer (a) is preferably 34% or less, more preferably 26% or less, more preferably 13% or less, and even more preferably 7% or less of the total thickness of the film, when the layer (a) has a plurality of layers. (a) The thickness of the layer is 1% or more, preferably 2% or more, and more preferably 4% or more of the total thickness of the film. By controlling the thickness of the layer (a) within this range, a film having the mechanical properties of the layer (a) and the optical properties of the layer (b) in a well-balanced manner can be obtained.

In the case of indicating the thicknesses of the (a) layer and the (b) layer, the (a) layer side and the (b) layer side from the center in the thickness direction of the transition layer are included in the (a) layer and the (b) layer, respectively.

In the present invention, it is preferable that a transition layer (mixed layer) in which the polyimide composition changes continuously from the polyimide in the layer (a) to the polyimide in the layer (b) is present between the layer (a) and the layer (b). The lower limit of the thickness of the transition layer is preferably 0.01 μm or more. More preferably 0.02 μm or more, and still more preferably 0.05 μm or more. The upper limit of the thickness of the transition layer is preferably 3% or less or 1 μm or less of the total thickness of the film. As a preferable range of the upper limit, any one of 2.8% or 0.9 μm of the total film thickness is more preferable, and any one of 2.5% or 0.8 μm of the total film thickness is even more preferable. When the transition layer is in the above range, transparency and mechanical strength can be achieved at the same time.

The thickness of the transition layer is a region where the mixed composition of the polyimide of the layer (a) and the polyimide of the layer (b) changes in a gradient manner from one side to the other side, and the composition ratio (mass ratio) of the polyimide of the layer (a) to the polyimide of the layer (b) in the mixed layer is in the range of 5/95 to 95/5. The thickness of the transition layer can be measured by obliquely cutting the film in the thickness direction and observing the distribution of the polyimide component.

The thickness of the transition layer can be determined based on the thickness of the transition layer existing at the interface and the total thickness of the film, since the number of layers (interface) is 1 when the multilayer polyimide film has a laminated structure of 2 layers. When the multilayer polyimide film has a laminated structure of 3 layers, the number of layers (interfaces) is 2, and thus the thickness can be determined from the total thickness of the transition layer and the total thickness of the film. The multilayer polyimide film has a laminated structure of 4 or more layers, and can be determined from the total thickness of all the transition layers and the total thickness of the film.

The polyimide used in the layer (a) in the present invention is preferably a polyimide having a yellow index of 10 or less and a total light transmittance of 85% or more when used alone as a film having a thickness of 25 ± 2 μm. The polyimide used as the layer (a) preferably has a CTE of 25ppm/K or less, preferably 20ppm/K or less, a tensile breaking strength of 100MPa or more, preferably 120MPa or more, and an elongation at break of 10% or more, preferably 12% or more, when used alone as a film having a thickness of 25 ± 2 μm.

As a preferable polyimide of the layer (a), polyimide having a chemical structure obtained by polycondensation of tetracarboxylic anhydride containing at least 70 mass% of alicyclic tetracarboxylic anhydride and diamine containing at least 70 mass% of diamine having an amide bond in the molecule can be exemplified.

Examples of the polyimide used in the layer (a) include polyimides having a chemical structure obtained by polycondensation of a tetracarboxylic anhydride containing at least 70 mass% of an alicyclic tetracarboxylic anhydride and a diamine containing at least 70 mass% of a diamine having a trifluoromethyl group in the molecule.

An alicyclic tetracarboxylic anhydride may be used as the polyimide for the layer (a). The content of the alicyclic tetracarboxylic anhydride is preferably 70% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, and still further preferably 95% by mass or more of the total tetracarboxylic anhydride. By controlling the content of the alicyclic tetracarboxylic acid within a specific range, dyeing 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 70% by mass or more, 80% by mass or more, and more preferably 90% by mass or more of the total diamines.

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

The polyimide used in the layer (b) in the present invention is preferably a polyimide having a yellow index of 5 or less and a total light transmittance of 90% or more when used alone as 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 from a tetracarboxylic anhydride containing 70 mass% or more of an aromatic tetracarboxylic anhydride and a diamine containing 70 mass% or more of a diamine having at least a sulfur atom in the molecule.

The polyimide used as the layer (b) preferably has a chemical structure obtained by polycondensation of a tetracarboxylic anhydride containing 30 mass% or more of a tetracarboxylic acid having at least a trifluoromethyl group in the molecule and a diamine containing 70 mass% or more of a diamine having at least a trifluoromethyl group in the molecule.

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

The tetracarboxylic acid containing a trifluoromethyl group in the molecule used for the polyimide of the layer (b) is preferably 4,4' - (2, 2-hexafluoroisopropylidene) diphthalic dianhydride. (b) The tetracarboxylic acid containing a trifluoromethyl group in the molecule used for the polyimide of the layer (b) is preferably 30% by mass or more, more preferably 45% by mass or more, further preferably 60% by mass or more, and further preferably 80% by mass 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 to a specific range, the colorless transparency is improved.

In the polyimide preferably used in the layer (b) of the present invention, the diamine preferably used is a diamine having at least a sulfur atom in the molecule and/or a diamine having a trifluoromethyl group in the molecule.

As the diamine having a sulfur atom in the molecule, 3' -diaminodiphenyl sulfone, 3,4' -diaminodiphenyl sulfone, and 4,4' -diaminodiphenyl sulfone can be used. In the present invention, by using a diamine containing 70 mass% or more, preferably 80 mass% or more, and more preferably 90 mass% or more of a diamine having a sulfur atom in the molecule, when combined with an aromatic tetracarboxylic acid anhydride, colorless transparency can be obtained.

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

When these diamine compounds having a fluorine element in the molecule, particularly diamines having a trifluoromethyl group in the molecule are used, the amount of the diamine used is preferably 70% by mass or more, 80% by mass or more, and more preferably 90% by mass or more of the total diamine.

The polyimide of the layer (a) and the polyimide of the layer (b) in the present invention are characterized based on the yellow index and the total light transmittance when used alone as a film having a thickness of 25 ± 2 μm, mechanical characteristics, and the like. Here, for the evaluation on a laboratory scale, the polyimide solution or the polyimide precursor solution is applied to a glass plate having a size of 10cm square, preferably 20cm square or more, as a film having a thickness of 25 ± 2 μm alone, preheated to a temperature of 120 ℃, preheated and dried until the solvent residue is 40 mass% or less of the coating film, and further heated at 300 ℃ for 20 minutes in an inert gas such as nitrogen gas to obtain a film, and the obtained film is evaluated to obtain a value. When inorganic components such as a slipping agent and a filler are contained to adjust physical properties, the physical property values of the film obtained from a solution containing these components are used.

In the present invention, the polyimide of the layer (a) and the polyimide of the layer (b) may contain a slipping agent (filler). The slip agent may be an inorganic filler or an organic filler, but an inorganic filler is preferable. The slipping agent is not particularly limited, and may be silica, carbon, ceramics, etc., and among them, 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, it is preferably 1 μm or less, more preferably 500nm or less, and further preferably 100nm or less. (a) The content of the slipping agent in the polyimide of the layer (a) and the polyimide of the layer (b) is preferably 0.01 mass% or more. From the viewpoint of satisfactory smoothness of the polyimide film, the content is more preferably 0.02% by mass or more, still more preferably 0.05% by mass or more, and particularly preferably 0.1% by mass or more. From the viewpoint of transparency, the content is preferably 30% by mass or less, more preferably 20% by mass or less, still more preferably 10% by mass or less, and particularly preferably 5% by mass or less.

The method for producing the multilayer polyimide film of the present invention will be described below. Among the multilayer polyimide films of the present invention, a polyimide film having a 2-layer structure:

preferably, the film can be produced by the following steps in an atmosphere or an inert gas having a temperature of 10 ℃ to 40 ℃ and a humidity of 10% to 55%:

4: heating all layers to obtain a laminate having a residual solvent content of 0.5 mass% or less based on all layers,

the temporary support is preferably an elongated flexible member. The heating time in step 4 is preferably 5 minutes to 60 minutes. The solvent remaining amount in step 4 based on all layers was determined only from the mass of the coating film ab1, and the mass of the temporary support was not included.

Further, the step 4 may be divided into two stages:

4': a step of heating the resultant to a residual solvent content of 8 to 40 mass% based on the whole layer for 5 to 45 minutes, and then peeling the resultant from the temporary support to obtain a self-supporting film,

5: and fixing both ends of the self-supporting film, and further heating the film until the residual solvent content of the entire film is 0.5 mass% or less.

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

In the case of a film having 3 or more layers, after the above 1 and 2, the polyimide solution or polyimide precursor solution (a) layer may be applied again, and the application of the layers (a) and (b) may be repeated to obtain a further multilayer film.

In the present invention, it is preferable that the polyimide solution or the polyimide precursor solution is applied on a long flexible temporary support in an atmosphere or an inert gas at a temperature of 10 ℃ to 40 ℃, preferably 15 ℃ to 35 ℃, and a humidity of 10% to 55% RH, preferably 20% to 50% RH. As a coating method, the first coating layer may be coated using a comma coater, a bar coater, a slit coater, or the like, and the second coating layer may be coated using a die coater, a curtain coater, a spray coater, or the like. In addition, by using a multilayer die (die), these plural layers can be applied substantially simultaneously.

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

The temperature in the coating environment affects the viscosity of the coating liquid, and the thickness of the transition layer when the two coating liquids are mixed with each other to form the transition layer in the interface when the two coating liquids are overlapped. The viscosity of the polyimide solution or polyimide precursor solution of the present invention, particularly in the non-contact coating method after the second layer, is preferably adjusted within an appropriate viscosity range, and even when the interface between the two layers is mixed, the temperature range contributes to appropriately securing the fluidity in the viscosity range.

The solvent used in the polyimide solution or the polyimide precursor solution is often hygroscopic, and when the water content of the solvent increases after moisture absorption of the solvent, the solubility of the resin component decreases, and the dissolved component precipitates from the solution, resulting in a rapid increase in the solution viscosity. If such a situation occurs after coating, the internal structure of the film becomes heterogeneous, and transparency is impaired. In the present invention, it is preferable that the humidity of the coating environment is controlled to a specific range and the heat drying step is conducted within 100 seconds after the coating.

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. The long flexible temporary support used in the present invention can be preferably used as a temporary support made of a film such as polyethylene terephthalate, polyethylene naphthalate, or polyimide. One preferable mode is to subject the temporary support surface to a mold release treatment.

In the present invention, it is preferable to apply the polyimide solution or the polyimide precursor solution to the temporary support, dry the coating film until the residual solvent content of the coating film is 5 to 40 mass%, and apply the next layer. The reason why the drying is carried out to a residual solvent amount of 40 mass% is to obtain a sufficiently dried state of a semisolid in which the applied coating liquid loses fluidity.

When the amount of the residual solvent in the coating film is 5% by mass or less, the coating film dried before the coating film is swollen again to form a non-homogeneous state, and the boundary between the adjacent two layers may be disturbed. Therefore, the residual solvent amount is in the range of 5 to 40 mass%, the solvent of the coating liquid on the boundary surface is uniformly diffused and moved, and a transition layer having an appropriate thickness can be formed by micro flow mixing. The residual solvent amount is preferably 6% by mass or more, and more preferably 8% by mass or more. Further, it is preferably 35% by mass or less, more preferably 30% by mass or less.

In the present invention, after all layers are coated, drying by heat treatment and, if necessary, promoting chemical reaction. When a polyimide solution is used, only drying in the sense of removing the solvent is sufficient, but when a polyimide precursor solution is used, both drying and chemical reaction are required. Here, the polyimide precursor is preferably polyamic acid or polyisoimide. The conversion of polyamic acid to polyimide requires a dehydration condensation reaction. The dehydration condensation reaction can be carried out by heating alone, and may function as an imidization catalyst if necessary. Polyisoimides can also be converted from imide linkages to imide linkages by heating. In addition, an appropriate catalyst may be used in combination.

The solvent residual amount 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 5 minutes to 60 minutes, preferably 6 minutes to 50 minutes, and more preferably 7 minutes to 30 minutes. By controlling the heating time within a specific range, the solvent is removed, the necessary chemical reaction is completed, and the transition layer can be controlled to have an appropriate thickness, and further, the colorless transparency and the mechanical properties, particularly, the high elongation at break can be ensured. When the heating time is short, the formation of the transition layer is slow, and further, if the heating time is longer than necessary, the film dyeing becomes strong and the elongation at break of the film is lowered in some cases.

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

More specifically, a process can be employed in which the self-supporting film is peeled from the temporary support after heating for a time of 5 minutes to 45 minutes, preferably 6 minutes to 30 minutes, and more preferably 7 minutes to 20 minutes until the solvent remaining amount of the entire film layer reaches 5 mass% to 40 mass%, the self-supporting film is further held between clamps or fixed by needle punching at both ends of the self-supporting film, the self-supporting film is conveyed to a heating environment, and the self-supporting film is further heated until the solvent remaining amount based on the entire layer becomes 0.5 mass% or less, preferably 0.2 mass% or less, and more preferably 0.08 mass% or less, thereby obtaining a multilayer polyimide film.

In the heating step, the self-supporting film is peeled off from the temporary support and further heated, and when the solvent is evaporated and the polyamic acid is dehydrated to be converted into polyimide, water produced can be rapidly discharged from both sides of the film, and the film having a small difference in physical properties between the front and back can be obtained.

In the present invention, the self-supporting film may be stretched. The stretching may be performed in either one of the longitudinal direction (MD direction) of the film and the width direction (TD) of the film, or may be performed in two. The stretching in the longitudinal direction of the film can be performed using the speed difference between the transport rollers or the speed difference between the transport rollers and the fixed ends. The stretching in the film width direction can be performed between clamps or needles that are fixed by stretching. Stretching and heating may also be performed simultaneously. The stretch ratio can be arbitrarily selected from 1.00 to 2.5 times. In the present invention, the film has a multilayer structure, and the polyimide which is difficult to be stretched alone and the polyimide which is stretchable are combined, whereby the polyimide which is difficult to be stretched, that is, the polyimide which is a component which is likely to be broken by stretching is also stretchable, and the mechanical properties can be improved.

Since polyimide has a smaller volume during film production by drying or dehydration condensation, it exhibits a stretching effect even in a state where both ends are fixed at equal intervals (stretching ratio of 1.00 times).

In the layer (a) and the layer (b) in the multilayer polyimide film of the present invention, it is preferable to add a slipping agent or the like to the polyimide to impart fine irregularities on the surface of the layer (film) to improve the sliding property of the film. It is preferable that the slipping agent is added only to the layer (a) as the outer layer.

As the slipping agent, inorganic or organic fine particles having an average particle diameter of about 0.03 to 3 μm can be used, and specific examples thereof include titanium oxide, alumina, silica, calcium carbonate, calcium phosphate, calcium hydrogen phosphate, calcium pyrophosphate, magnesium oxide, calcium oxide, clay minerals and the like.

Examples

The present invention will be described in detail below 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 and the like in the production examples and examples were measured by the following methods.

< measurement of thickness of polyimide film >

The measurement was carried out using a micrometer (FEINPRUF, millitron 1245D).

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

The test pieces were cut out in 100mm × 10mm long strips in the flow direction (MD direction) and width direction (TD direction) during film application. The tensile modulus, tensile strength and tensile elongation at break in the MD and TD directions were obtained at a tensile rate of 50 mm/min and a chuck (chuck) spacing of 40mm using a tensile tester (Autograph (R) manufactured by Shimadzu corporation, equipment name AG-5000A), and the average values of the measured values in the MD and TD directions were obtained.

< coefficient of linear expansion (CTE) >

The stretching ratio under the following conditions was measured in the flow direction (MD direction) and the width direction (TD direction) at the time of coating the film, the stretching ratio/temperature was measured at intervals of 15 ℃ such as 30 to 45 ℃ and 45 to 60 ℃, the measurement was carried out up to 300 ℃, 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 further obtained.

< thickness of transition layer >

A diagonal cut of the film was produced by SAICAS DN-20S type (daipl wines), and then a spectrum was obtained from the diagonal cut by microscopic IR Cary 620FTIR (Agilent) using a microscopic ATR method of a germanium crystal (incident angle 30 °), a gradient mass ratio of the components was obtained by conversion based on increase and decrease of characteristic peaks of each of the (a) layer and the (b) layer and a calibration curve obtained in advance, and a thickness in which the ratio of the (a) layer component/(b) layer component was in a range of 5/95 to 95/5 mass ratio was obtained as a transition layer thickness.

< haze >)

Haze of the film was measured by using a HAZEMETER (NDH 5000, manufactured by Nippon Denshoku Co., ltd.). As the light source, a D65 lamp was used. The same measurement was performed 3 times, and an average value was calculated using the measurements.

< Total light transmittance >

The total light transmittance (TT) of the film was measured using a HAZEMETER (NDH 5000, manufactured by Nippon Denshoku Co., ltd.). As the light source, a D65 lamp was used. The same measurement was performed 3 times, and an average value was calculated using the measurements.

The results are shown in tables 2 to 6.

< yellow index >

The tristimulus XYZ values of the film were measured using a colorimeter (ZE 6000, manufactured by japan electric color corporation) and a C2 light source based on ASTM D1925, and the Yellowness Index (YI) was calculated from the following formula. The same measurement was performed 3 times, and an average value was calculated using the measurements.

YI＝100×(1.28X-1.06Z)/Y

< warpage of film >

A square film cut into a size of 100mm × 100mm was set as a test piece, the test piece was placed on a flat surface so as to be recessed at room temperature, distances (h 1rt, h2rt, h3rt, h4rt: unit mm) from four corners to the flat surface were measured, and the average value thereof was set as a warpage amount (mm).

Production example 1 production of polyamic acid solution A

After a reaction vessel equipped with a nitrogen introduction tube, a reflux tube and a stirring rod was purged with nitrogen, 22.73 parts by mass of 4,4' -diaminobenzamide benzene (DABAN) was dissolved in 201.1 parts by mass of N, N-dimethylacetamide (DMAc), and 19.32 parts by mass of 1,2,3, 4-cyclobutanetetracarboxylic dianhydride (CBDA) was added in portions in solid form and then stirred at room temperature for 24 hours. Then, 173.1 parts by mass of DMAc was added thereto and the mixture was diluted to obtain a polyamic acid solution A having 10% by mass of NV (solid content) and a reduced viscosity of 3.10 dl/g.

Production example 2 production of As polyamic acid solution containing slipping agent for forming layer (a) ]

To the polyamic acid solution a obtained in production example 1, colloidal silica was further added As a slipping agent to a dispersion of dimethylacetamide ("SNOWTEX (registered trademark) DMAC-ST-ZL" manufactured by the chemical industry of japan, and the total amount of polymer solids in the polyimide solution of silica (slipping agent) was 1.4 mass%), to obtain a uniform polyamic acid solution As.

Production example 3 production of polyamic acid solution B

After a reaction vessel having a nitrogen introduction tube, a reflux tube and a stirring rod was purged with nitrogen, 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 9.81 parts by mass of 1,2,3, 4-cyclobutanetetracarboxylic dianhydride (CBDA) and 15.51 parts by mass of 4,4' -Oxydiphthalic Dianhydride (ODPA) were added in portions in solid form, followed by stirring at room temperature for 24 hours. Then, a polyamic acid solution B having a solid content of 17% by mass and a reduced viscosity of 3.60dl/g was obtained.

Production example 4 production of slipping agent-containing polyamic acid solution Bs for forming layer (a)

To the polyamic acid solution B obtained in production example 3, colloidal silica was further added as a slipping agent in the form of a dispersion in which colloidal silica was dispersed in dimethylacetamide ("SNOWTEX (registered trademark) DMAC-ST-ZL" manufactured by japan chemical industry, the total amount of polymer solids in the polyimide solution of silica (slipping agent) being 0.45 mass%), to obtain a uniform polyamic acid solution Bs.

Production example 5 production of polyimide solution C for Forming layer (b)

To a reaction vessel equipped with a nitrogen gas inlet tube, a Dean-Stark apparatus (Dean-Stark apparatus), a reflux tube, a thermometer and a stirring rod, 32.02 parts by mass of 2,2' -bistrifluoromethyl-4, 4' -diaminobiphenyl (TFMB) and 230 parts by mass of N, N-dimethylacetamide (DMAc) were added while introducing nitrogen gas until complete dissolution, and 44.42 parts by mass of 4,4' - (2, 2-hexafluoroisopropylidene) diphthalic dianhydride (6 FDA) was added in portions in solid form, followed by stirring at room temperature for 24 hours. Then, a polyamic acid solution Caa having a solid content of 25% by mass and a reduced viscosity of 1.10dl/g was obtained.

Then, 204 parts by mass of DMAc was added to the obtained polyamic acid solution Caa to dilute the concentration of polyamic acid to 15% by mass, and then 1.3 parts by mass of isoquinoline as an imidization accelerator was added. Then, while stirring the polyamic acid solution, 12.25 parts by mass of acetic anhydride as an imidizing agent was slowly added dropwise. Then, the stirring was continued for 24 hours to perform chemical imidization reaction, thereby obtaining a polyimide solution Cpi.

Subsequently, 100 parts by mass of the resulting polyimide solution Cpi was transferred to a reaction vessel equipped with a stirrer and a stirrer, and 150 parts by mass of methanol was slowly added dropwise while stirring, and it was confirmed that a powdery solid was precipitated.

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

Production example 6 production of polyimide solution D for Forming layer (b)

To a reaction vessel equipped with a nitrogen gas inlet tube, a dean stark apparatus, a reflux tube, a thermometer, and a stirring bar, 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 while introducing nitrogen gas. Subsequently, 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 thereto at room temperature, and then heated to an internal temperature of 160 ℃ and heated under reflux at 160 ℃ for 1 hour to effect imidization. After the imidization was completed, the temperature was raised to 180 ℃ and the reaction was continued while removing toluene. After 12 hours of reaction, the reaction mixture was taken out of the oil bath and returned to room temperature, and GBL was added thereto so that the solid content became 20 mass%, whereby a polyimide solution D was obtained.

[ production of polyamic acid solution E of production example 7]

In a reaction vessel equipped with a nitrogen gas inlet pipe, a reflux pipe and a stirring rod, 161 parts by mass of 2,2 '-bistrifluoromethyl-4, 4' -diaminobiphenyl (TFMB) and 1090 parts by mass of N-methyl-2-pyrrolidone were mixed and stirred under a nitrogen gas atmosphere to dissolve them, 112 parts by mass of 1,2,4, 5-cyclohexanetetracarboxylic dianhydride (CHDA) was added in portions in the form of a solid at room temperature, and then stirred at room temperature for 12 hours. Then, 400 parts by mass of xylene as an azeotropic solvent was added, and the temperature was raised to 180 ℃ to conduct a reaction for 3 hours, thereby separating water produced by azeotropy. After completion of the water flow, xylene was removed while raising the temperature to 190 ℃ for 1 hour to obtain a polyamic acid solution E.

Production example 8 production of slipping agent-containing polyamic acid solution Es for forming layer (a)

To polyamic acid solution E obtained in production example 7, colloidal silica as a slipping agent was added in the form of a dispersion in which colloidal silica was dispersed in dimethylacetamide ("SNOWTEX (registered trademark) DMAC-ST-ZL" manufactured by the chemical industry of japan) and the total amount of polymer solids in the polyamic acid solution was 1.0 mass%, to obtain uniform polyamic acid solution Es.

Production example 9 production of Filler-containing polyamic acid solution Ef for Forming layer (b)

To polyamic acid solution E obtained in production example 7, colloidal silica as a slipping agent was added in the form of a dispersion in which colloidal silica was dispersed in dimethylacetamide ("SNOWTEX (registered trademark) DMAC-ST-ZL" by the chemical industry of japan), and the total amount of polymer solids in the polyamic acid solution was 25 mass%, to obtain polyamic acid solution Ef with a filler.

The polyimide solutions and polyamic acid solutions (polyimide precursor solutions) obtained in production examples 1 to 9 were formed into films by the following methods, and optical properties and mechanical properties were measured. The results are shown in Table 1.

(method of obtaining a film for measuring Properties alone)

A polyimide solution or a polyamic acid solution was applied to a final thickness of 25. + -.2 μm in a region of about 20cm square at the center of a 30 cm-sided glass plate by using a bar coater, and the resultant coating film was heated at 100 ℃ for 30 minutes in an inert oven in which dry nitrogen gas was allowed to flow smoothly, and after confirming that the residual solvent content of the coating film was 40 mass% or less, the coating film was heated at 300 ℃ for 20 minutes in a muffle furnace substituted with dry nitrogen gas. Subsequently, the film was taken out of the muffle furnace, and the edge of the dried coating film (film) was lifted up with a utility knife and carefully peeled off from the glass to obtain a film.

(example 1)

The polyamic acid solution As obtained in production example 2 was applied to a lubricant-free surface of a temporary support polyethylene terephthalate film A4100 (manufactured by Toyo chemical Co., ltd., hereinafter abbreviated As "PET film") in an atmosphere air-conditioned at 25 ℃ 45% RH using an apparatus having a comma coater and a continuous drying furnace, until the final film thickness was 5 μm. Subsequently, the film was heated at 110 ℃ for 5 minutes by a continuous dryer as a primary heating to obtain a semi-dried film Agf having a residual solvent content of 28 mass%, and each temporary support was wound into a coil.

The obtained coil was mounted again on the above-mentioned apparatus, and Agf was unwound together with the temporary support, and the polyimide solution C obtained in production example 5 was applied to Agf with a comma coater to a final film thickness of 20 μm. It was dried at 110 ℃ for 10 minutes as secondary heating.

The film obtained after drying was peeled off from the PET film as a support, passed through a needle tenter having a needle plate on which needles were arranged, and fixed by inserting the needles into the ends of the film so that the film was not broken and unnecessary slack was not generated, and conveyed while adjusting the needle plate interval, and finally heated at 200 ℃ for 3 minutes, 250 ℃ for 3 minutes, and 300 ℃ for 6 minutes to perform imidization. Then, the film was cooled to room temperature over 2 minutes, and the portions of the film having poor planarity at both ends were cut off with a cutter and wound into a roll to obtain a roll of the film (real 1) having a width of 530mm and a length of 80 m.

The evaluation results of the obtained film (example 1) are shown in table 2.

(examples 2 to 4)

The conditions shown in table 2 were set to obtain films (examples 2 to 4) and comparative example film (ratio 1). Similarly, the evaluation results are shown in table 2.

Comparative example 1

As comparative example 1, only the polyamic acid solution As obtained in production example was coated on a temporary support in a coating atmosphere by the same equipment As in example 1 to a final film thickness of 25 μm. Subsequently, the self-supporting film was peeled from the temporary support by heating at 110 ℃ for 10 minutes as a primary heating, and the resultant was transferred with the needle bed interval adjusted so as not to break the film and not to cause unnecessary slack by inserting needles into the ends of the film using a needle tenter used in example 1, and imidized at 200 ℃ for 3 minutes, 250 ℃ for 3 minutes, and 300 ℃ for 6 minutes as a final heating. Then, the film was cooled to room temperature over 2 minutes, and the portions of the film having poor planarity at both ends were cut out with a cutter and wound into a roll to obtain a roll of the film having a width of 560mm and a length of 50m (ratio 1). The evaluation results of the obtained film (ratio 1) are shown in table 3.

Comparative examples 2 to 4

In the same manner as in comparative example 1, films (ratio 2) to (ratio 4) were obtained using the polyamic acid solution Bs, the polyimide solution C, and the polyimide solution D obtained in the production examples, respectively, alone. The evaluation results of each are shown in table 3.

(calculation examples 1 to 4)

The values of comparative examples 1 to 4 in table 4 show the calculated average values obtained by weighting the thicknesses of the layer (a) and the layer (b) in examples 1 to 4.

Example 1 corresponds to calculation example 1, and examples 2 to 4 correspond to calculation examples 2 to 4, respectively, in the same manner as described below. Comparing the examples and the calculated examples, the films obtained in the examples have lower haze and higher total light transmittance than the calculated examples. In addition, the yellowness index also shows a smaller value, indicating that the optical characteristics are improved. Further, the tensile strength and the elongation at break were higher than those of the examples, and the CTE was controlled to a low level, whereby the mechanical properties were improved.

Note that, as for the warpage, the warpage is naturally large because of the asymmetric structure in the film thickness direction.

(examples 5 to 10)

The polyamic acid solution As obtained in production example 2 was applied to the non-lubricant surface of the PET film As a temporary support in an atmosphere air-conditioned at 25 ℃ and 45% RH by using a comma coater to a final film thickness of 3 μm, and the resultant was heated once under the conditions shown in Table 5 to obtain a coil together with the temporary support. The obtained coil was mounted on the same apparatus again, and the polyimide solution C obtained in production example 5 was applied by a die coater to a final film thickness of 31 μm, and after secondary heating under the conditions shown in table 5, the coil was wound up again together with the temporary support. The obtained coil was mounted again on the same apparatus, a polyamic acid solution As was applied by a comma coater to a final film thickness of 3 μm, and the film was heated three times under the conditions shown in table 5, the 3-layer structure coating film having a self-supporting property was peeled off from the temporary support, passed through a pin tenter, and the ends of the film were fixed by inserting a pin into the film, and the film was conveyed with the intervals of the pin plates adjusted so that the film was not broken and unnecessary slack was not generated, and the final heating treatment was performed under the conditions shown in table 5, and then, after cooling to room temperature for 3 minutes, the portions having poor flatness at both ends of the film were cut off by a cutter and wound into a coil to obtain a coil of a film (real 5) having a width of 510mm and a length of 100 m. The evaluation results of the obtained film (example 5) are shown in table 5.

In the same manner, polyimide films (examples 6 to 10) having a three-layer structure of (a)/(b)/(a) were obtained according to the solutions and conditions shown in tables 5 and 6, and the results are shown in tables 5 and 6.

The film exhibited improved characteristics compared to the film produced in the same single layer as in examples 1 to 4. Further, the warpage was greatly reduced as compared with examples 1 to 4, because the contrast in the thickness direction became good.

Comparative example 5

An attempt was made to produce a film having a single layer of 50 μm using polyamic acid solution Ef to which the filler obtained in production example 5 was added. The set conditions are shown in table 6. After the short drying, the film having self-supporting properties was peeled off from the PET of the temporary support, introduced into a pin tenter, and at the initial stage of heating, the film was broken in the longitudinal direction. The test was continued by adjusting the pin width, and the film became very brittle during drying and the progress of the conversion reaction of polyimide, and a film sufficient for evaluation of physical properties could not be obtained.

(example 11)

A film having a structure of (a)/(b)/(a) was prepared by using, as a filler, a polyamic acid solution Es to which only a slipping agent was added as a filler for the layer (a) and a polyamic acid solution Ef containing a filler obtained in production example 9 for the layer (b) under the conditions set forth in table 6. Although it took time to adjust the width of the needle, a polyimide film having a width of 510mm and a length of 80m was finally obtained (real 11). The evaluation results are shown in table 6.

Production example 10 (production of Polyamic acid solution Fs containing slipping agent)

After a reaction vessel having a nitrogen gas introduction tube, a reflux tube and a stirring rod was purged with nitrogen gas, 33.36 parts by mass of 2,2' -bistrifluoromethyl-4, 4' -diaminobiphenyl (TFMB), 336.31 parts by mass of N-methyl-2-pyrrolidone (NMP) and colloidal silica dispersed in dimethylacetamide (hereinafter, "SNOWTEX (registered trademark) DMAC-ST-ZL" manufactured by the chemical industry of japan) as a slipping agent were added to completely dissolve the colloidal silica, and 9.81 parts by mass of 1,2,3, 4-cyclobutanetetracarboxylic dianhydride (CBDA), 11.34 parts by mass of 3,3',4' -biphenyltetracarboxylic dianhydride and 4.85 parts by mass of 4,4' -Oxydiphthalic Dianhydride (ODPA) were added in solid portions and stirred at room temperature for 24 hours. Then, a polyamic acid solution Fs having a solid content of 15 mass% and a reduced viscosity of 3.50dl/g was obtained (molar ratio of TFMB// CBDA/BPDA/ODPA =1.00// 0.48/0.37/0.15).

Production example 11 (production of non-slipping agent Polyamic acid solution F)

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

(example 12)

The polyamic acid solution Fs obtained in production example 10 was coated on the non-lubricant surface of the PET film as a temporary support in an atmosphere air-conditioned at 25 ℃ 45% RH using a device having a comma coater of roll-to-roll type and a continuous drying furnace to a final film thickness of 5 μm. Subsequently, the sheet was heated at 110 ℃ for 5 minutes by a continuous dryer as a single heating to obtain a semi-dry film Fsgf having a residual solvent content of 28 mass%, and each temporary support was wound into a roll shape.

The obtained coil was again mounted on the above-mentioned apparatus, and the Fsgf was unwound together with the temporary support, and the polyamic acid solution F obtained in production example 11 was applied to the Fsgf by means of a comma coater to a final film thickness of 20 μm. This was dried at 110 ℃ for 10 minutes by secondary heating to obtain a dried film Fgf2.

The film obtained as a self-supporting after drying was peeled off from the PET film as a support, passed through a pin tenter having pin plates provided with pins, and fixed by inserting the pins into the ends of the film, the film was conveyed while adjusting the pin plate interval so that the film was not broken and unnecessary slack was not generated, and finally heated under conditions of 200 ℃ for 3 minutes, 250 ℃ for 3 minutes, 300 ℃ for 3 minutes, and 400 ℃ for 3 minutes to perform imidization. Then, the film was cooled to room temperature over 2 minutes, and the portions of the film having poor planarity at both ends were cut off with a cutter and wound into a roll to obtain a film (solid 12) having a width of 530mm and a length of 80 m. The film (real 12) had a total film thickness of 25 μm, a haze of 0.42%, a total light transmittance of 87.5%, a yellow index of 4.1, a breaking strength of 212MPa, an elongation at break of 10.5%, an elastic modulus of 4.3GPa, a CTE of 32ppm/K, a warpage of 0.1mm or less, and a transition layer thickness of 0.1 μm.

(example 13)

The polyamic acid solution Fs obtained in production example 10 was applied to the dried film Fgf2 obtained in the intermediate stage of example 12 with a comma coater to a final film thickness of 5 μm, and dried at 100 ℃ for 10 minutes as three times of heating to obtain a dried film Fgf3.

The self-supporting film obtained after drying was peeled off from the PET film as a support, and heated under conditions of 200 ℃ for 3 minutes, 250 ℃ for 3 minutes, 300 ℃ for 3 minutes, and 400 ℃ for 3 minutes using a pin tenter in the same manner as in example 12 to perform imidization. Thereafter, the same operation was carried out to obtain a roll of a film (real 13) having a width of 530mm and a length of 80 m. The resulting film (example 13) had a three-layer structure of Fs/F/Fs, and had a total film thickness of 30 μm, a haze of 0.45%, a total light transmittance of 87.1%, a yellowness index of 4.0, a breaking strength of 189MPa, an elongation at break of 9.5%, an elastic modulus of 4.2GPa, a CTE of 31ppm/K, a warpage of 0.1mm or less, and a transition layer thickness (air-side/substrate-side) of 0.1 μm/0.1. Mu.m.

Comparative example 6

The polyamic acid solution As obtained in production example 2 was applied to the non-lubricant surface of a PET film As a temporary support in an atmosphere air-conditioned at 25 ℃ 45% RH using a device having a comma coater and a continuous drying furnace, and the final film thickness was 20 μm. Then, the sheet was heated at 110 ℃ for 5 minutes by a continuous dryer as a primary heating to obtain a semi-dry film Agfx having a residual solvent content of 28 mass%, and each temporary support was wound into a roll.

The obtained self-supporting dry film Agfx was peeled off from the PET film as a support, passed through a needle tenter having a needle plate on which needles were arranged, and fixed by inserting the needles into the ends of the film, and conveyed while adjusting the intervals of the needle plates so that the film was not broken and unnecessary slack was not generated, and finally heated under conditions of 3 minutes at 200 ℃,3 minutes at 250 ℃, and 6 minutes at 300 ℃ to perform imidization. Then, the film was cooled to room temperature over 2 minutes, and the portions of the film having poor planarity at both ends were cut off with a cutter and wound into a roll to obtain a roll of a polyimide film (having a width of 530mm and a length of 50 m) (see FIG. 6 a).

The obtained polyimide film (comparative 6 a) roll was mounted on the above-described apparatus again, the polyimide film (comparative 6 a) was unwound, and the polyimide solution C obtained in production example 5 was applied thereon by means of a comma coater to a final film thickness of 5 μm. It was dried at 110 ℃ for 10 minutes as secondary heating.

After drying, the film was passed through a needle tenter having a needle plate on which needles were arranged, and the needles were inserted into the ends of the film and fixed, so that the film was not broken and unnecessary slack was not generated, and the film was conveyed while adjusting the intervals between the needle plates, and heated under conditions of 3 minutes at 200 ℃,3 minutes at 250 ℃ and 6 minutes at 300 ℃ as final heating to perform imidization. Then, the film was cooled to room temperature over 2 minutes, and the portions of the film having poor flatness at both ends were cut off by a cutter and wound into a roll to obtain a roll of a polyimide film (comparative 6 b) having a width of 450mm and a length of 30 m.

The polyimide film (ratio 6 b) thus obtained had a two-layer structure of As (20 μm)/C (5 μm), and had a total film thickness of 25 μm, a haze of 0.63%, a total light transmittance of 86.9%, a yellow index of 4.3, a breaking strength of 154MPa, an elongation at break of 18%, an elastic modulus of 3.9GPa, CTE19.6ppm/K, a warpage of 2.8mm or less, and a transition layer thickness of 0.0 μm. The amount of warpage of the film was greater compared to the examples.

[ Table 1]

[ Table 2]

[ Table 3]

[ Table 4]

[ Table 5]

[ Table 6]

Industrial applicability of the invention

As described above, the multilayer polyimide film of the present invention has better optical properties and mechanical properties than when polyimides having different components are separately formed. In addition, according to the manufacturing method of the present invention, a transition layer having a gradient composition with a specific thickness can be formed between layers having different compositions and having a function of dividing into a plurality of layers, thereby forming a film having a balance.

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

Claims

1. A multilayer polyimide film characterized by having: a multilayer polyimide layer obtained by laminating at least two polyimide layers having different compositions in the thickness direction, and

a transition layer having a gradient in chemical composition, which is present between (a) a layer constituting the multilayer polyimide layer and (b) a layer adjacent to the (a) layer;

the thickness of the whole film is 3 to 120 μm,

the yellow index of the whole film is 5 or less,

the total light transmittance of the entire film was 86% or more.

2. The multilayer polyimide film of claim 1 wherein the transition layer has a thickness with a lower limit of 0.01 μ ι η and an upper limit of either 3% or 1 μ ι η of the total film thickness.

3. The multilayer polyimide film according to claim 1 or 2, wherein the layer (a) is mainly composed of a polyimide having a yellowness index of 10 or less and a total light transmittance of 85% or more as a film having a thickness of 25 ± 2 μm alone,

4. The multilayer polyimide film according to any one of claims 1 to 3, having: the (a) layer is present on both sides of one surface side and the other surface side of the (b) layer,

and (c) a layer structure formed by sequentially stacking the layer (a), the transition layer, the layer (b), the transition layer and the layer (a).

5. The multilayer polyimide film according to any one of claims 1 to 4, wherein the polyimide in the layer (a) is a polyimide having a chemical structure obtained by polycondensation of a tetracarboxylic anhydride containing 70% by mass or more of an alicyclic tetracarboxylic anhydride and a diamine containing 70% by mass or more of a diamine having an amide bond in a molecule,

6. The multilayer polyimide film according to any one of claims 1 to 5,

the polyimide of the layer (b) is a polyimide having a chemical structure obtained from a tetracarboxylic anhydride containing 70 mass% or more of an aromatic tetracarboxylic anhydride and a diamine containing 70 mass% or more of a diamine having a sulfur atom in the molecule,

7. A method for producing a multilayer polyimide film described in claim 1,2,3, 5 or 6, comprising at least,

(1): a step of applying a polyimide solution or a polyimide precursor solution for forming the layer (a) 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 content of 5 to 40 mass%,

(3): a step of applying a polyimide solution or a polyimide precursor solution for forming the layer (b) to the coating film a2 to obtain a coating film ab1,

(4): and heating all the layers to obtain a laminate having a residual solvent content of 0.5 mass% or less based on all the layers.

8. A method for producing a multilayer polyimide film described in claim 1,2,3, 5 or 6, comprising at least,

(4): heating all the layers to obtain a laminate having a residual solvent content of 5 to 40 mass% based on all the layers, and then peeling the laminate from the temporary support to obtain a self-supporting film,

(5): and fixing both ends of the self-supporting film to obtain a film having a residual solvent content of 0.5 mass% or less based on the entire layer.

9. A method for producing a multilayer polyimide film according to any one of claims 1 to 6, comprising at least,

(1): a step of coating the temporary support with a polyimide solution or a polyimide precursor solution for forming the layer (a) to obtain a coating film a1,

(4): a step of drying the coating film ab1 to obtain a coating film ab2 having a residual solvent content of 5 to 40 mass% based on the entire layer,

(5): a step of applying a polyimide solution or a polyimide precursor solution for forming the layer (a) to a coating film ab2 to obtain a coating film aba1,

(6): and heating the entire layer to obtain a laminate having a residual solvent content of 0.5 mass% or less based on the entire layer.

10. A method for producing a multilayer polyimide film according to any one of claims 1 to 6, comprising at least,

(6): heating all the layers to obtain a laminate having a residual solvent content of 8 to 40 mass% based on all the layers, and then peeling the laminate from the temporary support to obtain a self-supporting film,

(7): and fixing both ends of the self-supporting film to obtain a film having a residual solvent content of 0.5 mass% or less based on the entire layer.