JP2018002963A - Polyimide precursor, resin composition, polyimide containing resin film and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyimide precursor that gives a polyimide resin film having transparency sufficient for use in a colorless transparent flexible substrate and a high Young's modulus, and also sufficiently reduces foreign matter in the polyimide resin film and has excellent surface smoothness, a polyimide resin film obtained by curing the precursor and a method for producing the same.SOLUTION: A polyimide resin film is obtained by copolymerization of 1, 4-cyclohexane diamine and two tetracarboxylic acid dianhydrides of specific structures. The polyimide resin film has excellence of both transparency and Young's moduli, has sufficiently reduced foreign matter, and excellent surface smoothness.SELECTED DRAWING: None

Description

  The present invention relates to, for example, a polyimide precursor, a resin composition, a resin film containing polyimide, and a method for manufacturing the same, which are used for manufacturing a substrate for a flexible device.

In recent years, in the field of display devices such as liquid crystal displays, organic electroluminescence displays, and electronic paper, light-weight and flexible plastic substrates have been studied instead of conventionally used transparent substrates such as glass substrates and cover glasses. For such applications, polyimide resins having excellent heat resistance, mechanical characteristics, heat oxidation resistance, and chemical resistance have been developed.
A transparent substrate used in a display device is required to have a high Young's modulus in order to improve transparency, scratch resistance, and display device rigidity. However, since a general polyimide resin is colored brown or yellow due to a high aromatic ring density, it has been difficult to use in a field where transparency is required. Therefore, a method has been proposed in which the introduction of fluorine into the polyimide resin, the flexibility of the main chain, and the introduction of a bulky side chain inhibit the formation of a charge transfer complex and exhibit transparency. .
However, the conventional methods of imparting flexibility to the main chain and introducing bulky side chains have a problem that the Young's modulus of the polyimide resin is lowered, although the transparency is improved.
In response to such a problem, Non-Patent Document 1 includes 1,4-cyclohexanediamine (CHDA), which is an alicyclic diamine, and p-phenylenebis (trimellitic acid anhydride) (TAHQ) having an ester bond. By using, it is disclosed that both transparency and Young's modulus are achieved.

Special table 2007-512568 gazette Special table 2012-511173 gazette JP 2010-67957 A JP 2013-179306 A

: High Performance Polymers, 18, p697-717, 2006

From the viewpoint of visibility, polyimide used for transparent substrates and protective films for flexible displays is required to have not only sufficient transparency, but also reduced foreign matter and good surface smoothness. Furthermore, a high Young's modulus is required.
However, known polyimide resins do not have sufficient characteristics to be applied, for example, as a transparent substrate or a protective film for flexible displays.
The present invention has been made in view of the above-described problems, and provides a polyimide resin film having sufficient transparency and high Young's modulus for use in a colorless transparent flexible substrate, and foreign matter in the polyimide resin film An object of the present invention is to provide a polyimide precursor that is sufficiently reduced and has excellent surface smoothness.
It is another object of the present invention to provide a polyimide resin film and a method for producing the same.

｛式中、複数ある場合のＲ_１はそれぞれ独立に、ハロゲン原子、炭素数１〜６のアルキル基、アルコキシ基、ハロゲン化アルキル基のいずれかを表し、ｎは０以上４以下、Ｘ_１は下記式（３）〜（５）：

で表される部分構造からなる群より選ばれる少なくとも１種である。｝
［２］前記式（１）のＲ_１が水素原子である［１］に記載のポリイミド前駆体。
［３］前記式（２）のＸ_１が前記式（３）又は（４）で表される部分構造である［１］または［２］に記載のポリイミド前駆体。
［４］前記式（２）のＸ_１が前記式（３）で表される部分構造である［１］〜［３］のいずれか１項に記載のポリイミド前駆体。
［５］前記式（１）で示される構造単位と前記式（２）で示される構造単位とのモル比が（１）：（２）＝８０：２０〜４０：６０である、［１］〜［４］のいずれか１項に記載のポリイミド前駆体。
［６］［１］〜［５］のいずれか１項に記載のポリイミド前駆体と、有機溶剤と、を含有する樹脂組成物。
［７］下記一般式（７）及び（８）で示される構造単位を有する共重合体であるポリイミド。

｛式中、複数ある場合のＲ_１はそれぞれ独立に、ハロゲン原子、炭素数１〜６のアルキル基、アルコキシ基、ハロゲン化アルキル基のいずれかを表し、ｎは０以上４以下、Ｘ_１は前記式（３）〜（５）：

で表される部分構造からなる群より選ばれる少なくとも１種である。｝
［８］［７］に記載のポリイミド樹脂膜を含む、樹脂膜。
［９］［６］に記載の樹脂組成物を支持体の表面上に塗布する工程と、
塗布した樹脂組成物を乾燥し、溶媒を除去する工程と、
前記支持体及び前記樹脂組成物を加熱してポリイミド樹脂膜を形成する工程と、
を含む、ポリイミド樹脂膜の製造方法。
［１０］［７］に記載のポリイミド樹脂膜を含む透明基板。
［１１］［７］に記載のポリイミド樹脂膜を含む保護膜。 The inventors of the present invention have made extensive studies to solve the above problems. As a result, by copolymerizing 1,4-cyclohexanediamine and two types of tetracarboxylic dianhydrides having a specific structure, both transparency and Young's modulus are achieved, foreign matters are sufficiently reduced, and surface smoothness is good. The present inventors have found that a polyimide resin film can be provided and have made the present invention.
That is, the present invention is as follows.
[1] A polyimide precursor which is a copolymer having a structural unit represented by the following general formulas (1) and (2).

{In the formula, when there are a plurality of R _{1 s} each independently represents a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group, or a halogenated alkyl group, n is 0 or more and 4 or less, and X ₁ is The following formulas (3) to (5):

It is at least 1 sort (s) chosen from the group which consists of the partial structure represented by these. }
[2] The polyimide precursor according to [1], wherein R _{1 in the} formula (1) is a hydrogen atom.
[3] The polyimide precursor according to [1] or [2], wherein X _{1 in the} formula (2) is a partial structure represented by the formula (3) or (4).
[4] The polyimide precursor according to any one of [1] to [3], wherein X _{1 in the} formula (2) is a partial structure represented by the formula (3).
[5] The molar ratio of the structural unit represented by the formula (1) and the structural unit represented by the formula (2) is (1) :( 2) = 80: 20 to 40:60, [1] -The polyimide precursor of any one of [4].
[6] A resin composition comprising the polyimide precursor according to any one of [1] to [5] and an organic solvent.
[7] A polyimide which is a copolymer having a structural unit represented by the following general formulas (7) and (8).

{In the formula, when there are a plurality of R _{1 s} each independently represents a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group, or a halogenated alkyl group, n is 0 or more and 4 or less, and X ₁ is Formulas (3) to (5):

It is at least 1 sort (s) chosen from the group which consists of the partial structure represented by these. }
[8] A resin film including the polyimide resin film according to [7].
[9] A step of applying the resin composition according to [6] on the surface of the support;
Drying the applied resin composition and removing the solvent;
Heating the support and the resin composition to form a polyimide resin film;
A method for producing a polyimide resin film, comprising:
[10] A transparent substrate comprising the polyimide resin film according to [7].
[11] A protective film comprising the polyimide resin film according to [7].

  Provided is a polyimide precursor that provides a polyimide resin film having sufficient transparency and high Young's modulus for use in a colorless transparent flexible substrate, and that foreign matter in the polyimide resin film is sufficiently reduced and has excellent surface smoothness. be able to.

｛式中、複数ある場合のＲ_１はそれぞれ独立に、ハロゲン原子、炭素数１〜６のアルキル基、アルコキシ基、ハロゲン化アルキル基のいずれかを表し、ｎは０以上４以下、Ｘ_１は下記一般式（３）〜（５）で表される部分構造からなる群より選ばれる少なくとも１種である。｝

本発明のポリイミド前駆体を硬化膜とした時の耐熱性及び透明性の観点から前記式（１）中の複数ある場合のＲ_１は炭素数１〜６のアルキル基、ハロゲン化アルキル基が好ましい。
式（１）中のｎは０以上４以下であれば限定されない。その中で透明性の観点から０以上２以下が好ましく、０がより好ましい。
前記式（２）中のＸ_１は、前記式（３）、（４）、（５）で表される部分構造かならなる群より選択される少なくとも１種であれば限定されない。透明性及び濾過性の観点から、前記式（３）及び前記式（４）で表される部分構造であることがより好ましい。前記式（２）中のＸ_１は、これらのうち、得られるポリイミド樹脂膜の黄色度（ＹＩ）の抑制、ヘイズの低下、の観点から、前記式（３）で表される部分構造であることが特に好ましい。 Hereinafter, exemplary embodiments of the present invention (hereinafter abbreviated as “embodiments”) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary. It should be noted that the structural units in the formulas of the present disclosure are not intended for a specific bonding mode such as a block structure. Further, unless otherwise specified, the characteristic values described in the present disclosure are values measured by a method described in the section of [Example] or a method understood by those skilled in the art to be equivalent thereto. Intended.
[Polyimide precursor]
The polyimide precursor in this embodiment is a copolymer having structural units represented by the following general formulas (1) and (2).

{In the formula, when there are a plurality of R _{1 s} each independently represents a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group, or a halogenated alkyl group, n is 0 or more and 4 or less, and X ₁ is It is at least one selected from the group consisting of partial structures represented by the following general formulas (3) to (5). }

From the viewpoint of heat resistance and transparency when the polyimide precursor of the present invention is used as a cured film, R _{1 in the} case where there are a plurality of formulas (1) is preferably an alkyl group having 1 to 6 carbon atoms or an alkyl halide group. .
If n in Formula (1) is 0 or more and 4 or less, it will not be limited. Among these, from the viewpoint of transparency, 0 or more and 2 or less are preferable, and 0 is more preferable.
X ₁ in the formula (2) is not limited as long as it is at least one selected from the group consisting of partial structures represented by the formulas (3), (4), and (5). From the viewpoint of transparency and filterability, the partial structure represented by the formula (3) and the formula (4) is more preferable. X ₁ in the formula (2) is a partial structure represented by the formula (3) from the viewpoints of suppression of yellowness (YI) and reduction of haze of the obtained polyimide resin film. It is particularly preferred.

The ratio (molar ratio) between the structural units (1) and (2) of the copolymer is (1) :( 2) = 80: from the viewpoints of YI, Young's modulus, and filterability of the resulting polyimide resin film. 20-40: 60 is preferable, 70: 30-40: 60 is more preferable, and 70: 30-50: 50 is especially preferable. By setting the molar ratio of the formula (1) to 80 or less, it can be filtered at a solid content concentration that can improve the surface smoothness when the polyimide precursor of the present invention is used as a cured film, and The YI of the resin film can be lowered. By setting the molar ratio of the formula (1) to 40 or more, the Young's modulus when the polyimide precursor of the present invention is used as a cured film can be kept high. The ratio of said Formula (1) and (2) can be calculated | required from the result of a < ¹ > H-NMR spectrum, for example.
The polyimide precursor in the present embodiment may contain a structural unit other than the structural units represented by the formulas (1) and (2) as necessary, as long as the performance of the present invention is not impaired. .
In the polyimide precursor (copolymer) according to the present embodiment, the mass of the structural units (1) and (2) is 30% by mass from the viewpoint of Young's modulus based on the total mass of the copolymer. From the viewpoint of transparency, it is preferably 70% by mass or less. Most preferably, it is 100 mass%.
The weight average molecular weight (Mw) of the polyimide precursor in this embodiment is preferably 10,000 to 300,000, and particularly preferably 30,000 to 200,000. When the weight average molecular weight is greater than 10,000, mechanical properties such as Young's modulus and elongation are excellent, and YI decreases. When the weight average molecular weight is smaller than 300,000, the polyimide precursor solution can be filtered at a high solid content concentration, and the smoothness when the resin composition is used as a cured film can be maintained. In the present disclosure, the weight average molecular weight is a value obtained as a standard polystyrene equivalent value using gel permeation chromatography (hereinafter also referred to as GPC).

In the polyimide precursor according to the present embodiment, the content of molecules having a molecular weight of less than 1,000 is preferably less than 5% by mass and more preferably less than 1% by mass with respect to the total amount of the polyimide precursor. preferable. A polyimide resin film obtained by thermosetting such a polyimide precursor is preferable because it has excellent mechanical properties such as Young's modulus and elongation.
The content of molecules having a molecular weight of less than 1,000 relative to the total amount of the polyimide precursor can be calculated from the peak area obtained by performing GPC measurement using a solution in which the polyimide precursor is dissolved.
[Production method of polyimide precursor]
The polyimide precursor (polyamic acid) of the present invention includes tetracarboxylic dianhydride (for example, p-phenylenebis (trimellitic acid anhydride) (TAHQ)) used for the structural unit represented by the general formula (1). , Tetracarboxylic dianhydride (for example, 4,4 ′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 4,4′-oxydiphthalic acid) used in the structural unit represented by the general formula (2) It can be synthesized by polycondensation reaction of dianhydride (ODPA), biphenyltetracarboxylic dianhydride (BPDA)) and CHDA. This reaction is preferably carried out in a suitable solvent. Specifically, for example, after a predetermined amount of CHDA is dissolved in a solvent, a predetermined amount of tetracarboxylic dianhydride is added to the obtained diamine solution and stirred.
When the polyimide precursor is synthesized, the ratio (molar ratio) of the tetracarboxylic dianhydride component to the diamine component is the viewpoint that the Young's modulus, elongation, and YI of the resulting resin film are controlled within a desired range. To tetracarboxylic dianhydride: diamine = 100: 90 to 100: 110 (diamine 0.90 to 1.10 mol part relative to 1 mol part of tetracarboxylic dianhydride), More preferably, it is in the range of 100: 95 to 100: 105 (0.95 to 1.05 mole part of diamine with respect to 1 mole part of acid dianhydride).

｛式中、Ｒ_６＝メチル基で表されるエクアミドＭ１００（商品名：出光興産社製）、及び、Ｒ_６＝ｎ−ブチル基で表されるエクアミドＢ１００（商品名：出光興産社製）等のアミド系溶媒；
γ−ブチロラクトン、γ−バレロラクトン等のラクトン系溶媒；
ヘキサメチルホスホリックアミド、ヘキサメチルホスフィントリアミド等の含りん系アミド系溶媒；
ジメチルスルホン、ジメチルスルホキシド、スルホラン等の含硫黄系溶媒；
シクロヘキサノン、メチルシクロヘキサノン等のケトン系溶媒；
ピコリン、ピリジン等の３級アミン系溶媒；
酢酸（２−メトキシ−１−メチルエチル）等のエステル系溶媒
等が：
前記フェノ−ル系溶媒として、例えば、フェノ−ル、ｏ−クレゾ−ル、ｍ−クレゾ−ル、ｐ−クレゾ−ル、２，３−キシレノ−ル、２，４−キシレノ−ル、２，５−キシレノ−ル、２，６−キシレノ−ル、３，４−キシレノ−ル、３，５−キシレノ−ル等が：
前記エ−テル及びグリコ−ル系溶媒として、例えば、１，２−ジメトキシエタン、ビス（２−メトキシエチル）エ−テル、１，２−ビス（２−メトキシエトキシ）エタン、ビス［２− （２−メトキシエトキシ）エチル］エ−テル、テトラヒドロフラン、１，４−ジオキサン等が、
それぞれ挙げられる。｝ In this embodiment, when synthesizing a polyamic acid which is a preferable polyimide precursor, the molecular weight is controlled by adjusting the ratio of the tetracarboxylic dianhydride component and the diamine component and adding a terminal blocking agent. It is possible. The molecular weight of the polyamic acid can be increased as the ratio of the tetracarboxylic dianhydride component to the diamine component is closer to 1: 1 and as the amount of the end-capping agent used is smaller.
It is recommended to use high-purity products as the tetracarboxylic dianhydride component and the diamine component. The purity is preferably 98% by mass or more, more preferably 99% by mass or more, and still more preferably 99.5% by mass or more. When using multiple types of tetracarboxylic dianhydride components or diamine components in combination, it is sufficient if the purity of the tetracarboxylic dianhydride component or diamine component as a whole is sufficient, It is preferable that the tetracarboxylic dianhydride component and the diamine component each have the above-described purity.
The solvent for the reaction is not particularly limited as long as it is a solvent that can dissolve the tetracarboxylic dianhydride component and the diamine component, and the resulting polyamic acid, and obtain a high molecular weight polymer. Specific examples of such solvents include aprotic solvents, phenolic solvents, ethers and glycolic solvents.
Examples of the aprotic solvent include N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), N-methylcaprolactam, and 1,3-dimethyl. Imidazolidinone, tetramethylurea, the following general formula (6):

{In the formula, R ₆ = Mex group represented by methyl group M100 (trade name: manufactured by Idemitsu Kosan Co., Ltd.), R ₆ = Ecamide B100 represented by n-butyl group (trade name: manufactured by Idemitsu Kosan Co., Ltd.), etc. An amide solvent of
Lactone solvents such as γ-butyrolactone and γ-valerolactone;
Phosphorus-containing amide solvents such as hexamethylphosphoric amide and hexamethylphosphine triamide;
Sulfur-containing solvents such as dimethyl sulfone, dimethyl sulfoxide, sulfolane;
Ketone solvents such as cyclohexanone and methylcyclohexanone;
Tertiary amine solvents such as picoline and pyridine;
Ester solvents such as acetic acid (2-methoxy-1-methylethyl) include:
Examples of the phenol solvent include phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2, 5-xylenol, 2,6-xylenol, 3,4-xylenol, 3,5-xylenol and the like:
Examples of the ether and glycol solvents include 1,2-dimethoxyethane, bis (2-methoxyethyl) ether, 1,2-bis (2-methoxyethoxy) ethane, and bis [2- ( 2-methoxyethoxy) ethyl] ether, tetrahydrofuran, 1,4-dioxane, etc.
Each is listed. }

60-300 degreeC is preferable, as for the boiling point in the normal pressure of the solvent used for the synthesis | combination of a polyamic acid, 140-280 degreeC is more preferable, and 170-270 degreeC is especially preferable. When the boiling point of the solvent is higher than 300 ° C., a drying process is required for a long time. On the other hand, if the boiling point of the solvent is lower than 60 ° C., the surface of the resin film may be roughened during the drying process, bubbles may be mixed into the resin film, and a uniform film may not be obtained.
As described above, it is preferable to use a solvent having a boiling point of 170 to 270 ° C., more preferably a vapor pressure of 20 Pa or less at 20 ° C. from the viewpoint of solubility and edge repelling during coating. More specifically, it is preferable to use one or more selected from the group consisting of N-methyl-2-pyrrolidone, γ-butyrolactone, and the compound represented by the general formula (6).
The water content in the solvent is preferably 3000 ppm by mass or less.
These solvents may be used alone or in combination of two or more.
The polyimide precursor in the present embodiment preferably has a content of molecules having a molecular weight of less than 1,000 of less than 5% by mass.

  The reason why the molecules having a molecular weight of less than 1,000 are present in the polyimide precursor is considered to be due to the water content of the solvent used during the synthesis. That is, it is considered that the acid anhydride group of some acid dianhydride monomers is hydrolyzed by moisture to become a carboxyl group and remains in a low molecular weight state without increasing its molecular weight. Therefore, the water content of the solvent used for the above polymerization reaction should be as small as possible. The water content of this solvent is preferably 3,000 mass ppm or less, more preferably 1,000 mass ppm or less.

The water content of the solvent includes the grade of solvent used (dehydration grade, general-purpose grade, etc.), solvent container (bottle, 18L can, canister can, etc.), solvent storage status (whether or not rare gas is sealed, etc.), from opening to use (Such as use immediately after opening or use after lapse of time after opening) and the like. In addition, it is considered that the rare gas replacement in the reactor before the synthesis, the presence or absence of a rare gas flow during the synthesis, etc. are also involved. Therefore, when synthesizing a polyimide precursor, it is recommended to use a high-purity product as a raw material, use a solvent with a small amount of water, and take measures to prevent moisture from the environment from entering the system before and during the reaction. Is done.
When each monomer component is dissolved in the solvent, it may be heated as necessary.

  The reaction temperature during the synthesis of the polyimide precursor is preferably 0 ° C. to 140 ° C., more preferably 40 ° C. to 130 ° C., and still more preferably 60 to 120 ° C. The polyimide precursor of this embodiment is synthesized from 1,4-cyclohexanediamine, which is an alicyclic diamine, for example. The alicyclic diamine has a high basicity and easily forms a salt with the carboxylic acid of the reaction product during synthesis. By performing the polymerization reaction at the above temperature, the formation of a salt can be suppressed, and a polyimide precursor having a high degree of polymerization can be obtained. The polymerization time is preferably 1 to 100 hours, and more preferably 2 to 10 hours. By setting the polymerization time to 1 hour or more, a polyimide precursor having a uniform polymerization degree can be obtained, and by setting the polymerization time to 100 hours or less, a polyimide precursor having a high polymerization degree can be obtained.

The solution viscosity of the polyimide precursor of this embodiment is preferably 500 to 200,000 mPa · s, more preferably 2,000 to 100,000 mPa · s, and particularly preferably 3,000 to 30,000 mPa · s at 25 ° C. preferable. The solution viscosity can be measured using an E-type viscometer (VISCONICEHD manufactured by Toki Sangyo Co., Ltd.). If the solution viscosity is 300 mPa · s or more, it can be easily applied during film formation. On the other hand, if the solution viscosity is 200,000 mPa · s or less, stirring and filtration when the polyimide precursor is synthesized are facilitated.
However, even if the solution becomes highly viscous during the synthesis of the polyamic acid, it is possible to obtain a polyamic acid solution with a good handleability by adding a solvent after the reaction and stirring.
In the present embodiment, a part of the polyimide precursor may be imidized. In this case, the imidization rate is preferably 80% or less, and more preferably 50% or less. This partial imidization can be obtained by heating the above polyimide precursor (a) and dehydrating and closing the ring. This heating is preferably 120 to 200 ° C., more preferably 150 to 180 ° C., and preferably 15 minutes to 20 hours, more preferably 30 minutes to 10 hours.

  In addition, N, N-dimethylformamide dimethyl acetal or N, N-dimethylformamide diethyl acetal is added to the polyamic acid obtained by the above reaction and heated to esterify part or all of the carboxylic acid. By using it as a polyimide precursor in the present embodiment, a resin composition having improved viscosity stability during storage at room temperature can be obtained. In addition to these ester-modified polyamic acids, the above acid dianhydride component is sequentially reacted with one equivalent of a monohydric alcohol with respect to the acid anhydride group and a dehydration condensing agent such as thionyl chloride or dicyclohexylcarbodiimide. Thereafter, it can also be obtained by a condensation reaction with a diamine component.

  The proportion of the polyimide precursor (preferably polyamic acid) in the resin composition of the present embodiment is preferably 3 to 50% by mass, more preferably 6 to 40% by mass, and more preferably 10 to 30% by mass from the viewpoint of coating film formation. Is particularly preferred. When the solid content concentration is 3% by mass or more, sufficient surface smoothness can be obtained when the polyimide precursor is used as a cured film.

[Resin composition]
The resin composition of the present invention includes the polyimide precursor of the present invention and an organic solvent.
The organic solvent in this Embodiment will not be restrict | limited especially if the polyimide precursor mentioned above and the other component used arbitrarily can be melt | dissolved. As such an organic solvent, those described above as solvents that can be used during the synthesis of the polyimide precursor can be used. Preferred organic solvents are also the same as described above. The organic solvent in the resin composition of the present embodiment may be the same as or different from the solvent used for the synthesis of the polyimide precursor of the present invention.
The organic solvent is particularly preferably 3 to 50% by mass in terms of the solid content concentration of the resin composition from the viewpoint of coating film formation. When the solid content concentration is 3% by mass or more, sufficient surface smoothness can be obtained when the resin composition is used as a cured film. Moreover, it is preferable to add after adjusting the structure and quantity of an organic solvent so that the viscosity (25 degreeC) of a resin composition may be set to 500 mPa * s-100,000 mPa * s.

[Other ingredients]
The resin composition of the present embodiment may further contain a surfactant, an alkoxysilane compound, and the like in addition to the polyimide precursor and the organic solvent.
(Surfactant)
By adding a surfactant to the resin composition of the present embodiment, the applicability of the resin composition can be improved. Specifically, the generation of streaks in the coating film can be prevented.
Examples of such surfactants include silicone surfactants, fluorosurfactants, and other nonionic surfactants. Examples of these are:
Examples of silicone surfactants include organosiloxane polymers KF-640, 642, 643, KP341, X-70-092, X-70-093, KBM303, KBM403, KBM803 (above, trade names, manufactured by Shin-Etsu Chemical Co., Ltd.) ), SH-28PA, SH-190, SH-193, SZ-6032, SF-8428, DC-57, DC-190 (above, trade name, manufactured by Toray Dow Corning Silicone), SILWET L-77, L-7001, FZ-2105, FZ-2120, FZ-2154, FZ-2164, FZ-2166, L-7604 (above, trade name, manufactured by Nihon Unicar), DBE-814, DBE-224, DBE-621 , CMS-626, CMS-222, KF-352A, KF-354L, KF-355A, KF-6020, DBE-821, DBE-712 (Gelest), BYK-307, BYK-310, BYK-378, BYK-333 (above, trade name, manufactured by Big Chemie Japan), granol (trade name, Kyoeisha Chemical Co., Ltd.) Manufactured) etc .;
Examples of the fluorine-based surfactant include Megafac F171, F173, R-08 (trade name, manufactured by Dainippon Ink & Chemicals, Inc.), Fluorard FC4430, FC4432 (tradename, Sumitomo 3M Co., Ltd.);
Examples of nonionic surfactants other than these include polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene octylphenol ether, and the like.
Among these surfactants, silicone surfactants and fluorine surfactants are preferable from the viewpoint of coating properties (streaks suppression) of the resin composition. From the viewpoint of influence on the rate, a silicone-based surfactant is preferable.
When using surfactant, the compounding quantity has preferable 0.001-5 mass parts with respect to 100 mass parts of polyimide precursors in a resin composition, and 0.01-3 mass parts is more preferable.

本実施の形態における樹脂組成物の製造方法は、特に限定されるものではない。例えば、以下の方法によることができる。 (Alkoxysilane compound)
In order for the resin film obtained from the resin composition according to the present embodiment to exhibit sufficient adhesion between the resin film and the support in a manufacturing process such as a flexible device, the resin composition is a polyimide precursor. 0.01-100 mass% of alkoxysilane compounds can be contained with respect to 100 mass%. When the content of the alkoxysilane compound with respect to 100% by mass of the polyimide precursor is 0.01% by mass or more, good adhesion to the support can be obtained. Moreover, it is preferable from a viewpoint of the storage stability of a resin composition that content of an alkoxysilane compound is 20 mass% or less. The content of the alkoxysilane compound is more preferably 0.02 to 15% by mass, still more preferably 0.05 to 10% by mass, with respect to 100 parts by mass of the polyimide precursor, It is especially preferable that it is 8 mass%.
By using an alkoxysilane compound as an additive of the resin composition according to the present embodiment, in addition to the above improvement in adhesion, the coating property (smoothness suppression) of the resin composition is further improved and obtained. The curing oxygen concentration dependency of the YI value of the cured film can be reduced.
Examples of the alkoxysilane compound include 3-ureidopropyltriethoxysilane, bis (2-hydroxyethyl) -3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltripropoxysilane, γ-aminopropyltributoxysilane, γ-aminoethyltriethoxysilane, γ-aminoethyltripropoxysilane, γ-aminoethyltributoxysilane, γ-aminobutyltriethoxysilane, γ- Aminobutyltrimethoxysilane, γ-aminobutyltripropoxysilane, γ-aminobutyltributoxysilane, phenylsilanetriol, trimethoxyphenylsilane, trimethoxy (p-tolyl) silane, diphenylsilanediol , Dimethoxydiphenylsilane, diethoxydiphenylsilane, dimethoxydi-p-tolylsilane, triphenylsilanol, and alkoxysilane compounds represented by the following structures, respectively, and one or more selected from these compounds should be used: Is preferred.

The method for producing the resin composition in the present embodiment is not particularly limited. For example, the following method can be used.

When (a) the solvent used when synthesizing the polyimide precursor and (b) the organic solvent are the same, the synthesized polyimide precursor solution can be used as it is as the resin composition. In addition, if necessary, at least one of (b) an organic solvent and other components is added to the polyimide precursor in a temperature range of room temperature (25 ° C.) to 80 ° C., and the mixture is stirred and mixed. You may use as a thing. For this stirring and mixing, an appropriate device such as a three-one motor (manufactured by Shinto Chemical Co., Ltd.) equipped with a stirring blade, a rotation and revolution mixer, or the like can be used. Moreover, you may add a 40-100 degreeC heat | fever as needed.
On the other hand, when (a) the solvent used when synthesizing the polyimide precursor is different from (b) the organic solvent, the solvent in the synthesized polyimide precursor solution may be reprecipitated, e.g. After removing by an appropriate method (a) isolating the polyimide precursor, (b) adding an organic solvent and other components as necessary in a temperature range of room temperature to 80 ° C., and stirring and mixing. Thus, a resin composition may be prepared.
After preparing the resin composition as described above, a part of the polyimide precursor is dehydrated to such an extent that the polymer does not precipitate by heating the composition solution at 130 to 200 ° C., for example, for 5 minutes to 2 hours. It may be imidized. Here, the imidization rate can be controlled by controlling the heating temperature and the heating time. By partially imidizing the polyimide precursor, the viscosity stability of the resin composition when stored at room temperature can be improved. The imidation ratio is preferably 5% to 70% from the viewpoint of balancing the solubility of the polyimide precursor in the resin composition solution and the storage stability of the solution.

The resin composition according to the present embodiment preferably has a water content of 3,000 mass ppm or less.
The water content of the resin composition is more preferably 1,000 ppm by mass or less, and still more preferably 500 ppm by mass or less, from the viewpoint of viscosity stability when the resin composition is stored.

式中、複数あるＲ_１はそれぞれ独立に、ハロゲン原子、炭素数１〜６のアルキル基、アルコキシ基、ハロゲン化アルキル基のいずれかを表し、ｎは０以上４以下、Ｘ_１は下記一般式（３）〜（５）で表される部分構造からなる群より選ばれる少なくとも１種である。
式（７）中のｎは０以上４以下であれば限定されない。その中で透明性の観点から０以上２以下が好ましく、０がより好ましい。 The solution viscosity of the resin composition according to the present embodiment is preferably 500 to 200,000 mPa · s, more preferably 2,000 to 100,000 mPa · s, and 3,000 to 30,000 mPa · s at 25 ° C. Is particularly preferred. This solution viscosity can be measured using an E-type viscometer (manufactured by Toki Sangyo Co., Ltd., VISCONICEHD). When the solution viscosity is lower than 300 mPa · s, it is difficult to apply the film during film formation, and when it is higher than 200,000 mPa · s, there is a possibility that the stirring and filtration during the resin composition preparation become difficult.
(A) When a polyimide precursor is synthesized, even if the solution becomes highly viscous, it is possible to obtain a resin composition having a good handleability by adding a solvent after the reaction and stirring. is there.
The resin composition according to the present embodiment is preferably 300 or less, more preferably 100 or less, and more preferably 50 or less, from the viewpoint of obtaining a polyimide film with sufficiently reduced foreign matter, from 3 μm or less per gram. Is particularly preferred. If the number of foreign substances is 300 or less, the resin composition may be applied to an 8-inch wafer with a film thickness of 1 μm and cured, and the number of foreign substances in the polyimide resin film obtained by curing can be 500 or less.
The polyimide of the present embodiment is a polyimide having a structure represented by the following general formulas (7) and (8).

In the formula, a plurality of R _{1 s} each independently represent a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group, or a halogenated alkyl group, n is 0 or more and 4 or less, and X ₁ is the following general formula. It is at least one selected from the group consisting of the partial structures represented by (3) to (5).
If n in Formula (7) is 0 or more and 4 or less, it will not be limited. Among these, from the viewpoint of transparency, 0 or more and 2 or less are preferable, and 0 is more preferable.

本実施の形態にかかるポリイミドは、２０μｍ膜厚における黄色度ＹＩが１２以下であると好ましい。より好ましくは８以下であり、特に好ましくは６以下である。また、ヤング率が４ＧＰａ以上であることが好ましい。特に、２０μｍ膜厚における黄色度ＹＩが１２以下であり、かつ、ヤング率が４ＧＰａ以上であることがより好ましい。
また、本実施の形態にかかるポリイミドは、膜厚１μｍで、８インチウェハー上に製膜した場合、異物が５００個以下であることを特徴とする。また、膜厚の斑を２μｍ以下にすることもできる。 X ₁ in the formula (2) is not limited as long as it is at least one selected from the group consisting of partial structures represented by the formulas (3), (4), and (5). From the viewpoint of transparency and filterability, a partial structure represented by the formula (3) and the formula (4) is preferable. X ₁ in the formula (2) is a partial structure represented by the formula (3) from the viewpoints of suppression of yellowness (YI) and reduction of haze of the obtained polyimide resin film. It is preferable.

The polyimide according to the present embodiment preferably has a yellowness YI of 12 or less at a film thickness of 20 μm. More preferably, it is 8 or less, Especially preferably, it is 6 or less. Moreover, it is preferable that Young's modulus is 4 GPa or more. In particular, it is more preferable that the yellowness YI at a film thickness of 20 μm is 12 or less and the Young's modulus is 4 GPa or more.
In addition, the polyimide according to the present embodiment has a film thickness of 1 μm and is characterized in that, when formed on an 8-inch wafer, the number of foreign matters is 500 or less. Further, the unevenness of the film thickness can be reduced to 2 μm or less.

[Production method of polyimide resin film]
The polyimide resin film concerning this Embodiment can be obtained by heating or chemically imidating the resin composition containing the above-mentioned polyimide precursor.
As another aspect of the present embodiment, a step of forming a coating film by applying the resin composition described above on the surface of the support (application step);
Heating the support and the coating film to imidize the polyimide precursor contained in the coating film to form a polyimide resin film (heating process);
Can be provided.
Here, a support body will not be specifically limited if it has the heat resistance in the heating temperature of a subsequent process. For example, a glass (eg, alkali-free glass) substrate;
Silicon wafers;
Resin substrates such as PET (polyethylene terephthalate), OPP (stretched polypropylene), polyethylene glycol terephthalate, polyethylene glycol naphthalate, polycarbonate, polyimide, polyamideimide, polyetherimide, polyetheretherketone, polyethersulfone, polyphenylenesulfone, polyphenylenesulfide ;
A metal substrate such as stainless steel, alumina, copper, or nickel is used.
In the case of forming a film-like polyimide molded body, for example, a glass substrate, a silicon wafer or the like is preferable. In the case of forming a film-like or sheet-like polyimide molded body, for example, PET (polyethylene terephthalate), OPP A support made of (stretched polypropylene), polyimide or the like is preferable.
Examples of coating methods include doctor blade knife coaters, air knife coaters, roll coaters, rotary coaters, flow coaters, die coaters, bar coaters, and other coating methods, spin coating, spray coating, dip coating and the like; screen printing and Printing techniques such as gravure printing can be applied.
The coating thickness should be appropriately adjusted according to the desired thickness of the resin film and the content of the polyimide precursor in the resin composition, but is preferably about 1 to 1,000 μm. The application step is sufficient at room temperature, but the resin composition may be heated in the range of 40 to 80 ° C. for the purpose of reducing viscosity and improving workability.
Following the coating process, a drying process may be performed, or the drying process may be omitted and the process may proceed directly to the next heating process. This drying step is performed for the purpose of removing the organic solvent. When performing a drying process, suitable apparatuses, such as a hot plate, a box-type dryer, and a conveyor type dryer, can be utilized, for example. It is preferable to perform a drying process at 80-200 degreeC, and it is more preferable to carry out at 100-150 degreeC. The duration of the drying step is preferably 1 minute to 10 hours, and more preferably 3 minutes to 1 hour.
As described above, a coating film containing a polyimide precursor is formed on the support.
Subsequently, a heating process is performed. The heating step is a step of removing the organic solvent remaining in the coating film in the above-described drying process and advancing the imidization reaction of the polyimide precursor in the coating film to obtain a film made of polyimide.
This heating process can be performed using apparatuses, such as an inert gas oven, a hot plate, a box-type dryer, and a conveyor type dryer, for example. This step may be performed simultaneously with the drying step, or both steps may be performed sequentially.
The heating step may be performed in an air atmosphere, but it is recommended that the heating step be performed in an inert gas atmosphere from the viewpoints of safety, transparency of the obtained polyimide film, and YI value. Examples of the inert gas include nitrogen and argon.
Although heating temperature may be suitably set according to the kind of (b) organic solvent, 180 to 450 degreeC is preferable and 200 to 400 degreeC is more preferable. When it is lower than 180 ° C., imidization becomes insufficient, and when it is higher than 450 ° C., there is a possibility that inconveniences such as a decrease in transparency of the obtained polyimide film and a deterioration in heat resistance may occur. The heating time is preferably about 0.5 to 3 hours.
In the present embodiment, the oxygen concentration in the ambient atmosphere in the heating step is preferably 2,000 ppm by mass or less, more preferably 100 ppm by mass or less, from the viewpoint of the transparency and YI value of the obtained polyimide film. More preferred is mass ppm or less. By heating in an atmosphere with an oxygen concentration of 2,000 mass ppm or less, the YI value of the resulting polyimide film can be made 12 or less.
Depending on the intended use and purpose of the polyimide resin film, a peeling step of peeling the resin film from the support may be included after the heating step. This peeling step is preferably performed after cooling the resin film on the support to room temperature to about 50 ° C.

Examples of the peeling step include the following aspects (1) to (4).
(1) After producing a structure including a polyimide resin film / support by the above method, a laser is irradiated from the support side of the structure to ablate the interface between the support and the polyimide resin film. , A method of peeling polyimide resin. Examples of the laser include a solid (YAG) laser and a gas (UV excimer) laser. It is preferable to use a spectrum such as a wavelength of 308 nm (see Patent Document 1, Patent Document 2, etc.).
(2) A method in which a release layer is formed on a support before applying the resin composition to the support, and then a polyimide resin film / release layer / a structure including the support is obtained to release the polyimide resin film. . Examples of the release layer include a method using parylene (registered trademark, manufactured by Japan Parylene Godo Kaisha), tungsten oxide; a method using a release agent such as vegetable oil, silicone, fluorine, alkyd and the like. (See Patent Document 3, Patent Document 4, etc.).
You may use together this method (2) and the laser irradiation of said (1).
(3) A method of obtaining a polyimide resin film by etching a metal with an etchant after obtaining a structure including a polyimide resin film / support using a metal substrate that can be etched as a support. As the metal, for example, copper (as an example, electrolytic copper foil “DFF” manufactured by Mitsui Mining & Smelting Co., Ltd.), aluminum, or the like can be used. As the etchant, ferric chloride or the like can be used for copper, and dilute hydrochloric acid or the like can be used for aluminum.
(4) After obtaining the structure including the polyimide resin film / support by the above method, an adhesive film is attached to the surface of the polyimide resin film to separate the adhesive film / polyimide resin film from the support, and then the adhesive film Of separating the polyimide resin film from the substrate.
Among these peeling methods, the method (1) or (2) is appropriate from the viewpoint of the refractive index difference between the front and back of the polyimide resin film to be obtained, the YI value, and the elongation. The method (1) is more appropriate from the viewpoint of the refractive index difference.
Although the thickness of the resin film obtained by said method is not specifically limited, It is preferable that it is the range of 1-200 micrometers, More preferably, it is 5-100 micrometers.

[Transparent substrate, protective film]
Another embodiment of the present invention is a transparent substrate and a protective film.
The transparent substrate and protective film of the present invention are composed of the polyimide resin film of the present invention, and conventionally known methods can be used. For example, the above-mentioned resin composition is applied to the surface of the support, dried and heated, and then subjected to a resist process according to the use, and can be used as a transparent substrate.
In addition, the above resin composition can be applied to a support, dried and heated, peeled from the support and used as a protective film.
Since the transparent substrate and protective film of the present invention have sufficient transparency, have a high Young's modulus, and can easily remove foreign substances using a filtration method or the like, a liquid crystal display, an organic electroluminescence display, a field emission display It can be preferably used for forming a transparent substrate or a protective film of a display device such as electronic paper. Specifically, the transparent substrate of the present invention forms a substrate for forming a thin film transistor (TFT), a substrate for forming a color filter, a substrate for forming a transparent conductive film (ITO, Indium Thin Oxide), and the like. Can be used for
This will be described in detail below.
It is considered that the transparent substrate of the present invention can improve the breakage resistance, which is a problem of the conventional glass substrate, and can realize a reduction in weight and thickness of the substrate. In addition, the transparent substrate of the present invention has high transparency and is excellent in visibility because the number of foreign substances contained in the substrate is small. Furthermore, since the transparent substrate of the present invention has a high Young's modulus, it has excellent scratch resistance and can be used as a substrate for a flexible display.
The protective film of the present invention can be used as a flexible display substrate, a color filter protective film, and the like, and can also be used as a surface protective film of a solar cell.

EXAMPLES Hereinafter, although this invention is further explained in full detail based on an Example, these are described for description and the range of this invention is not limited to the following Example.
Various evaluations in Examples and Comparative Examples were performed as follows.
(Measurement of weight average molecular weight and number average molecular weight)
The weight average molecular weight (Mw) and the number average molecular weight (Mn) were each measured by gel permeation chromatography (GPC) under the following conditions.
Solvent: 24.8 mmol / L lithium bromide monohydrate (manufactured by Wako Pure Chemical Industries, Ltd.) before measurement, relative to N, N-dimethylformamide (manufactured by Wako Pure Chemical Industries, Ltd., for high performance liquid chromatograph) Purity 99.5%) and 63.2 mmol / L phosphoric acid (manufactured by Wako Pure Chemical Industries, Ltd., for high performance liquid chromatograph).
Calibration curve for calculating the weight average molecular weight: Prepared using standard polystyrene (manufactured by Tosoh Corporation).
Column: Shodex KD-806M (manufactured by Showa Denko KK)
Flow rate: 1.0 mL / min Column temperature: 40 ° C
Pump: PU-2080 Plus (manufactured by JASCO)
Detector: RI-2031Plus (RI: differential refractometer, manufactured by JASCO)
UV-2075 Plus (UV-VIS: UV-Visible Absorber, manufactured by JASCO)

(Evaluation of yellowness (YI value))
The resin composition prepared in each of the examples and comparative examples was coated on a 6-inch silicon wafer substrate having an aluminum vapor deposition layer on the surface by bar coating so that the film thickness after curing was 20 μm. A coating film was formed. This substrate with a coating film is pre-baked at 80 ° C. for 40 minutes, and then heat-cured at 350 ° C. for 1 hour in a nitrogen atmosphere using a vertical curing furnace (manufactured by Koyo Lindberg, model name VF-2000B). As a result, a wafer having a polyimide film formed thereon was produced. This wafer was immersed in a dilute hydrochloric acid aqueous solution and the polyimide film was peeled off to obtain a polyimide film.
The YI (film thickness 10 μm conversion) of the obtained polyimide film was measured with a D65 light source using Nippon Denshoku Industries Co., Ltd. (Spectrophotometer: SE600).

(Evaluation of Young's modulus)
A wafer on which a polyimide film was formed was produced in the same manner as described above (evaluation of yellowness (YI value)). Using a dicing saw (DAD 3350, manufactured by DISCO Corporation), a 3 mm wide cut was made in the polyimide resin film on the wafer, and the resin film piece was peeled off by dipping overnight in a dilute hydrochloric acid aqueous solution and dried. This was cut into a length of 50 mm to obtain a sample.
With respect to the above samples, Young's modulus was measured at a test speed of 40 mm / min and an initial load of 0.5 fs using TENSILON (UTM-II-20 manufactured by Orientec).
(Evaluation of the number of foreign objects)
A wafer on which a polyimide film was formed was prepared in the same manner as described above (evaluation of yellowness (YI value)) except that an 8-inch silicon wafer was used as the substrate and the film thickness after curing was 1 μm. The number of foreign matters contained in the polyimide resin film on the wafer was measured with a TOPCON WM-75. The evaluation criteria are as follows.
○: Less than 500 foreign matters having a diameter of 3 μm or less ×: 500 foreign matters having a diameter of 3 μm or less (surface smoothness evaluation)
A wafer on which a polyimide film was formed was prepared in the same manner as in (Evaluation of yellowness (YI value)) except that 10 cm × 10 cm non-alkali glass was used as the substrate. The film thickness was measured for any 10 points of the polyimide film on the glass substrate, and the surface smoothness was evaluated based on the following criteria.
A: The difference between the maximum value and the minimum value of the film thickness at 10 points is from 0 μm to less than 1 μm. ○: The difference between the maximum value and the minimum value of the film thickness at 10 points is from 1 μm to less than 2 μm. The difference between the maximum and minimum values is 2μm or more

[Synthesis of polyimide precursor]
[Synthesis Example 1]
The 500 ml separable flask was purged with nitrogen, and N-methyl-2-pyrrolidone (NMP) was added as a solvent to the separable flask, and the solid content after polymerization was 12% by mass. 1.65 g (49.0 mmol) of 1,4-cyclohexanediamine (CHDA) was added and stirred to dissolve CHDA. Thereafter, 18.33 g (40.0 mmol) of p-phenylenebis (trimellitic acid anhydride) and 4.44 g of 4,4 ′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) as tetracarboxylic dianhydrides ( 10.0 mmol) was added. Next, the mixture was stirred at 120 ° C. for 15 minutes under a nitrogen flow, and then stirred at room temperature for 24 hours to obtain an NMP solution P-1 of polyamic acid. The obtained polyamic acid had a weight average molecular weight (Mw) of 82,000.
[Synthesis Examples 2 to 11]
In the said synthesis example 1, except having synthesize | combined by the solid content density | concentration of Table 1 using the diamine and tetracarboxylic dianhydride of the kind and quantity which are described in Table 1, respectively, An NMP solution of polyamic acid was obtained. Table 1 shows the weight average molecular weight (Mw) of the obtained polyamic acid and the evaluation results of the cured film, respectively.
[Filter purification of polyamic acid solution]
The NMP solution of polyamic acid obtained in Synthesis Examples 1 to 11 was filtered under pressure at a pressure of 0.3 kPa using MEMBRANE FILTER (material: polytetrafluoroethylene (PTFE), pore size: 3 μm). The filtration rate of each solution is shown in Table 1.

[Examples 1-7, Comparative Examples 1-4]
Table 1 shows the results of evaluating the polyamic acid solution obtained by the synthesis and filtration by the method described above. Moreover, about the polyamic acid solution which could not be filtered (filtration rate 0g / min), the evaluation result of the unfiltered polyamic acid solution was shown.

Abbreviations of compound names in Table 1 have the following meanings, respectively.
(Diamine)
CHDA: 1,4-cyclohexanediamine (tetracarboxylic dianhydride)
TAHQ: p-phenylenebis (trimellitic acid anhydride)
6FDA: 4,4 '-(hexafluoroisopropylidene) diphthalic anhydride ODPA: 4,4'-oxydiphthalic dianhydride BPDA: biphenyltetracarboxylic dianhydride From the above results, the polyimide precursor according to the present invention The polyimide film obtained from is low YI,
In addition, it was confirmed that the resin film had a high Young's modulus, foreign substances in the polyimide resin film were sufficiently reduced, and excellent surface smoothness.
In addition, this invention is not limited to the said embodiment, It can change and implement variously.

  The polyimide precursor of this invention can be utilized as a transparent substrate of a flexible display, or a protective film, for example.

Claims (11)

The polyimide precursor which is a copolymer which has a structural unit shown by following General formula (1) and (2).

{In the formula, when there are a plurality of R _{1 s} each independently represents a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group, or a halogenated alkyl group, n is 0 or more and 4 or less, and X ₁ is It is at least one selected from the group consisting of partial structures represented by the following formulas (3) to (5). }

  The polyimide precursor according to claim 1, wherein n in the formula (1) is 0. The polyimide precursor according to claim 1 or 2, wherein X _{1 in the} formula (2) is a partial structure represented by the formula (3) or (4). The polyimide precursor according to claim ₁ , wherein X _{1 in the} formula (2) is a partial structure represented by the formula (3).   The molar ratio of the structural unit represented by the formula (1) and the structural unit represented by the formula (2) is (1) :( 2) = 80: 20 to 40:60. The polyimide precursor of any one of Claims.   The resin composition containing the polyimide precursor of any one of Claims 1-5, and an organic solvent. A polyimide which is a copolymer having structural units represented by the following general formulas (7) and (8).

{In the formula, when there are a plurality of R _{1 s} each independently represents a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group, or a halogenated alkyl group, n is 0 or more and 4 or less, and X ₁ is The following formulas (3) to (5):

It is at least 1 sort (s) chosen from the group which consists of the partial structure represented by these. }   A resin film comprising the polyimide according to claim 7. Applying the resin composition according to claim 6 on the surface of the support;
Drying the applied resin composition and removing the solvent;
Heating the support and the resin composition to form a polyimide;
A method for producing polyimide, comprising:   A transparent substrate comprising the polyimide according to claim 7.   A protective film comprising the polyimide according to claim 7.