阅读说明：本技术 聚酰亚胺前体溶液和使用其的聚酰亚胺膜 (Polyimide precursor solution and polyimide film using same ) 是由 李珍昊 朴珍永 朴彩媛 朴灿晓 于 2019-09-26 设计创作，主要内容包括：根据本发明,通过使四羧酸酐与二胺以1:0.93至1:0.99的摩尔比反应生产聚酰亚胺前体溶液。所述聚酰亚胺前体溶液包含数均分子量为至少38000g/mol的聚酰亚胺前体,并因此可以生产具有高耐热性的聚酰亚胺膜。通过对溶液的消泡特性进行量化并控制气泡的含量,可以提供具有改善的储存稳定性的聚酰亚胺前体溶液。此外,由其生产的聚酰亚胺膜在膜中具有减少的气泡量,并因此可以抑制在形成装置时可能在无机层中形成的裂纹的形成。(According to the present invention, a polyimide precursor solution is produced by reacting tetracarboxylic anhydride and diamine in a molar ratio of 1:0.93 to 1: 0.99. The polyimide precursor solution contains a polyimide precursor having a number average molecular weight of at least 38000g/mol, and thus a polyimide film having high heat resistance can be produced. By quantifying the defoaming characteristics of the solution and controlling the content of bubbles, a polyimide precursor solution having improved storage stability can be provided. Further, the polyimide film produced therefrom has a reduced amount of bubbles in the film, and thus can suppress the formation of cracks that may be formed in the inorganic layer when forming a device.)

1. A polyimide precursor solution comprising a polyimide precursor prepared by reacting a tetracarboxylic dianhydride with a diamine in a molar ratio of 1:0.93 to 1:0.99 and having a number average molecular weight (Mn) of 38000g/mol or more,

wherein the value of T is 0.9 or greater according to the following equation 1:

[ equation 1]

Wherein the content of the first and second substances,

a is the transmittance of the solution after 30 minutes of standing after bubble generation, and

b is the transmittance of the solution before bubble generation.

2. The polyimide precursor solution according to claim 1, wherein the polyimide precursor comprises repeating units prepared by reacting PDA (phenylenediamine) with BPDA (biphenyl dianhydride).

3. The polyimide precursor solution according to claim 1, wherein a transmittance of the polyimide precursor solution before bubble generation is 75% or more, and a transmittance of the solution after being left for 30 minutes after bubble generation is 75% or more.

4. The polyimide precursor solution according to claim 1, wherein the transmittance of the polyimide precursor solution is measured using a Turbiscan (formula, Turbisca L AB) at a wavelength of 880 nm.

5. The polyimide precursor solution according to claim 1, wherein the polyimide precursor has a number average molecular weight of less than 60000 g/mol.

6. The polyimide precursor solution according to claim 1, wherein the polyimide precursor solution comprises the polyimide precursor and a pyrrolidone-based solvent.

7. A polyimide film prepared by curing the polyimide precursor solution according to any one of claims 1 to 6.

8. The polyimide film of claim 7, wherein the polyimide film has a thermal decomposition temperature (Td _ 5%) of at least 600 ℃.

9. A flexible device comprising the polyimide film according to claim 7 as a substrate.

Technical Field

This application claims the benefit of priority from korean patent application No. 10-2018-0114781, filed on 27.9.2018, and korean patent application No. 10-2019-0101527, filed on 20.8.2019, which are incorporated herein by reference in their entirety.

The present invention relates to a polyimide precursor solution and a polyimide film prepared therefrom, and more particularly, to a polyimide film prepared from a polyimide precursor solution having an improved defoaming rate.

Background

In recent years, weight reduction and miniaturization of products have been emphasized in the field of displays. However, glass substrates are heavy and brittle and are difficult to apply to a continuous process. Therefore, research is being actively conducted to apply a plastic substrate, which has advantages of being light, flexible, and applicable to a continuous process, and can replace a glass substrate, to a cellular phone, a notebook computer, and a PDA (personal digital Assistant).

In particular, Polyimide (PI) resins have advantages of being easy to synthesize, being formable into thin films, and not requiring a crosslinking agent for curing, recently, polyimides have been widely used as materials for integration in semiconductors such as L CD, PDP, and the like due to weight reduction and precision of electronic products.

A Polyimide (PI) film prepared by forming a polyimide resin into a film is generally prepared by the following process: solution polymerization of aromatic dianhydride and aromatic diamine or aromatic diisocyanate is performed to prepare a solution of polyamic acid derivative, which is coated on a silicon wafer or glass and cured by heat treatment.

Disclosure of Invention

Technical problem

The problem to be solved by the present invention is to provide a polyimide precursor solution having improved storage stability.

The present invention also provides a polyimide film prepared from the polyimide precursor solution.

Another problem to be solved by the present invention is to provide a flexible device using the polyimide film.

Technical scheme

In order to solve the above-mentioned problems,

the present invention provides a polyimide precursor solution comprising a polyimide precursor prepared by reacting a tetracarboxylic dianhydride with a diamine in a molar ratio of 1:0.93 to 1:0.99 and having a number average molecular weight (Mn) of 38000g/mol or more,

wherein the value of T according to the following equation 1 is 0.9 or more.

[ equation 1]

Wherein the content of the first and second substances,

a is the transmittance of the solution after 30 minutes of standing after bubble generation, an

B is the transmittance of the solution before bubble generation.

According to one embodiment, the polyimide precursor may comprise a polymer prepared by reacting PDA (phenylenediamine) with BPDA (biphenyl dianhydride).

According to one embodiment, the transmittance of the polyimide precursor solution before bubble generation may be 75% or more, and the transmittance of the solution after being left for 30 minutes after bubble generation may be 75% or more.

According to one embodiment, the transmittance of the polyimide precursor solution may be measured at a wavelength of 880nm using a Turbiscan (formula, Turbisca L AB).

According to one embodiment, the number average molecular weight of the polyimide precursor may be less than 60000 g/mol.

According to one embodiment, the solvent contained in the polyimide precursor solution may be a pyrrolidone-based solvent.

In order to solve another problem of the present invention, the present invention provides a polyimide film prepared by curing a polyimide precursor solution.

According to one embodiment, the polyimide film may have a thermal decomposition temperature (Td — 5%) of at least 600 ℃.

The present invention also provides a flexible device comprising the polyimide film.

Advantageous effects

The polyimide precursor solution according to the present invention includes a polyimide precursor which is prepared by reacting tetracarboxylic dianhydride with diamine in a molar ratio of 1:0.93 to 1:0.99 and has a number average molecular weight of 38000g/mol or more, thereby preparing a polyimide film having high heat resistance. In addition, the defoaming property of the polyimide precursor solution can be quantified by transmittance to control the content of bubbles, thereby obtaining a polyimide precursor solution having improved storage stability. In addition, the polyimide film prepared from the polyimide precursor solution according to the present invention can suppress crack formation in the inorganic film, which may occur during device fabrication, by reducing bubbles inside the film.

Detailed Description

Since many modifications and changes may be made in the present invention, specific embodiments thereof are shown in the drawings and will be described herein in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described, but to include all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. In the following description of the present invention, a detailed description of known functions will be omitted if it is determined that the detailed description of the known functions may obscure the gist of the present invention.

In the present disclosure, all compounds or organic groups may be substituted or unsubstituted, unless otherwise specified. Herein, the term "substituted" means that at least one hydrogen contained in a compound or organic group is replaced by a substituent selected from the group consisting of: a halogen atom, an alkyl group or a haloalkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, a hydroxyl group, an alkoxy group having 1 to 10 carbon atoms, a carboxyl group, an aldehyde group, an epoxy group, a cyano group, a nitro group, an amino group, a sulfonic acid group, or a derivative thereof.

In particular, display devices in which O L ED elements are bonded to a plastic substrate have the advantage of bending or folding.

When a plastic substrate is used instead of a glass substrate, uniformity of the substrate and process stability are very important.

If foreign substances or bubbles are present inside and on the surface of the plastic substrate, cracking of the inorganic film may occur when forming a Thin Film Transistor (TFT) device. In particular, since the moving charge caused by the micro bubbles in the film may affect the TFT driving, a defoaming process is performed for at least 8 hours before curing the polyimide precursor solution.

In order to solve these conventional problems, the present invention aims to provide a polyimide precursor composition having a low bubble generation rate and a high defoaming rate, and a film prepared therefrom.

The present invention provides a polyimide precursor solution comprising a polyimide precursor prepared by reacting a tetracarboxylic dianhydride with a diamine in a molar ratio of 1:0.93 to 1:0.99 and having a number average molecular weight (Mn) of 38000g/mol or more,

wherein the value of T according to the following equation 1 is 0.9 or more.

[ equation 1]

Wherein the content of the first and second substances,

a is the transmittance of the solution after 30 minutes of standing after bubble generation, an

B is the transmittance of the solution before bubble generation.

Here, the transmittance may be measured by any method of measuring the transmittance of a solution containing particles, and is not particularly limited, for example, measurement may be performed at a wavelength of 880nm using Turbiscan (formula, Turbisca L AB).

The precursor solution of the present invention comprises a polyimide precursor having a high number average molecular weight of at least 38000g/mol or at least 40000 g/mol. According to one embodiment, the number average molecular weight may be less than 60000g/mol or 55000g/mol or less or 50000g/mol or less. When the polyimide precursor satisfies the number average molecular weight within the above range, the solid content of the precursor solution thereof is 9% to 13%, the viscosity is 1000cp to 5000cp, and the polyimide precursor has a high degassing rate and improved heat resistance as compared with a precursor solution having a viscosity exceeding the above range (e.g., 7000cp to 20000 cp). On the other hand, when the number average molecular weight of the polyimide precursor is lower than the above range, heat resistance and physical properties of the film may be deteriorated, and thus a phenomenon such as film lifting may occur during the process.

The number average molecular weight of the polyimide precursor can be measured by various methods known in the art, such as those described in the experimental examples below.

Further, in the present invention, the defoaming property of the polyimide precursor solution can be quantified by the T value defined by equation 1, and the content of bubbles present in the polyimide precursor solution can be more systematically controlled by using the T value than by controlling the defoaming property by visual observation. Accordingly, a polyimide precursor solution having improved storage stability can be provided. That is, the polyimide film prepared from the polyimide precursor solution having a T value of 0.9 or more according to equation 1 can not only maintain high heat resistance (even during high-temperature equipment), but also effectively suppress crack formation due to bubbles remaining in the polyimide film.

According to one embodiment, the transmittance of the polyimide precursor solution before bubble generation is 70% or more, preferably 75% or more, and the transmittance of the solution after being left for 30 minutes after bubble generation is 70% or more, preferably 75% or more. That is, the difference in transmittance between before and after the generation of bubbles is not large. In this case, the bubble generation may be performed by rotating the precursor solution at 200 to 500rpm for 20 to 60 seconds using a stirrer to which an impeller is attached.

The polyimide precursor is prepared by reacting a tetracarboxylic dianhydride with a diamine, and preferably by adding an excess amount of the tetracarboxylic dianhydride relative to the diamine, more preferably it can be prepared by reacting the tetracarboxylic dianhydride with the diamine in a molar ratio of 1:0.93 to 1:0.99, for example 1:0.93 to 1:0.98 or 1:0.94 to 1: 0.98. If the molar ratio of diamine to tetracarboxylic dianhydride is less than 0.93, the heat resistance of the polyimide film produced may decrease, and if the molar ratio of diamine to tetracarboxylic dianhydride exceeds 0.99, for example, if tetracarboxylic dianhydride and diamine are reacted in the same amount, defoaming characteristics may decrease due to an increase in solution viscosity or the like.

The polyimide precursor according to the present invention can be obtained by polymerizing at least one tetracarboxylic dianhydride with at least one diamine.

According to one embodiment, the polyimide precursor may include a repeating structure formed by reacting BPDA (biphenyl dianhydride) as tetracarboxylic dianhydride with PDA (phenylene diamine) as diamine, for example, a repeating structure including formula (1).

[ formula 1]

According to one embodiment, at least one tetracarboxylic dianhydride may be further included together with the BPDA in preparing the polyimide precursor.

For example, as the tetracarboxylic dianhydride, a tetracarboxylic dianhydride containing an aromatic, alicyclic or aliphatic tetravalent organic group, or a combination thereof in the molecule, wherein the aliphatic, alicyclic or aromatic tetravalent organic groups are crosslinked with each other, is used. Preferably, it may include an acid dianhydride having a structure in which a single-ring or multi-ring aromatic, a single-ring or multi-ring alicyclic, or two or more of these are linked by a single bond or a functional group. Alternatively, it may include tetracarboxylic dianhydride comprising tetravalent organic groups having a rigid structure, in which aromatic or aliphatic rings are single ring structures, fused to each other to form a heterocyclic structure, or connected by a single bond.

For example, the tetracarboxylic dianhydride may comprise a tetravalent organic group selected from the structures of formulae 2a to 2 e.

[ formula 2a ]

[ formula 2b ]

[ formula 2c ]

[ formula 2d ]

[ formula 2e ]

In formulae 2a to 2e, R₁₁To R₁₇Each independently selected from: a halogen atom selected from the group consisting of-F, -Cl, -Br and-I; hydroxyl (-OH); a thiol group (-SH); nitro (-NO)₂) (ii) a A cyano group; an alkyl group having 1 to 10 carbon atoms; haloalkoxy having 1 to 4 carbon atoms; haloalkyl having 1 to 10 carbon atoms; and an aryl group having 6 to 20 carbon atoms,

a1 is an integer from 0 to 2, a2 is an integer from 0 to 4, a3 is an integer from 0 to 8, a4 and a5 are each independently an integer from 0 to 3, a6 and a9 are each independently an integer from 0 to 3, and a7 and a8 are each independently an integer from 0 to 7, and

A₁₁and A₁₂Each independently selected from the group consisting of a single bond, -O-, -CR₁₈R₁₉-、-C(＝O)-、-C(＝O)NH-、-S-、-SO₂-, phenylene and combinations thereof, wherein R₁₈And R₁₉Each independently selected from a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, and a fluoroalkyl group having 1 to 10 carbon atoms.

Alternatively, the tetracarboxylic dianhydride may comprise a tetravalent organic group selected from the following formulas 3a to 3 n.

At least one hydrogen atom in the tetravalent organic group of formulae 3a to 3n may be replaced by a substituent selected from: a halogen atom selected from the group consisting of-F, -Cl, -Br and-I; hydroxyl (-OH); a thiol group (-SH); nitro (-NO)₂) (ii) a A cyano group; an alkyl group having 1 to 10 carbon atoms; haloalkoxy having 1 to 4 carbon atoms; haloalkyl having 1 to 10 carbon atoms; and an aryl group having 6 to 20 carbon atoms. For example, the halogen atom may be fluorine (-F); the haloalkyl group may be a fluoroalkyl group having 1 to 10 carbon atoms and containing a fluorine atom, and may be selected from, for example, a fluoromethyl group, a perfluoroethyl group, a trifluoromethyl group, and the like; the alkyl group may be selected from methyl, ethyl, propyl, isopropyl, tert-butyl, pentyl, hexyl, and the like; the aryl group may be selected from phenyl, naphthyl, more preferably a fluorine atom or a substituent comprising a fluorine atom, such as fluoroalkyl.

Alternatively, the tetracarboxylic dianhydride may comprise a tetravalent organic group comprising an aromatic ring or an aliphatic ring, wherein each ring structure is a rigid structure, i.e., a single ring structure, each ring is connected by a single bond, or each ring is directly connected to each other to form a heterocyclic structure, for example may comprise a tetravalent organic group selected from the following formulas 4a to 4 k.

At least one hydrogen atom in the tetravalent functional group represented by formulae 4a to 4k may be replaced with a substituent selected from the group consisting of: an alkyl group having 1 to 10 carbon atoms (e.g., methyl, ethyl, propyl, isopropyl, t-butyl, pentyl, hexyl, etc.), a fluoroalkyl group having 1 to 10 carbon atoms (e.g., fluoromethyl, perfluoroethyl, trifluoromethyl, etc.), an aryl group having 6 to 12 carbon atoms (e.g., phenyl, naphthyl, etc.), a sulfonic acid group, and a carboxylic acid group are preferably replaced with a fluoroalkyl group having 1 to 10 carbon atoms.

According to one embodiment, at least one diamine may be further included together with the PDA in preparing the polyimide precursor.

The diamine may include diamines such as: comprising a divalent organic radical selected from the group consisting of monocyclic or polycyclic aromatic divalent organic radicals having 6 to 24 carbon atoms, monocyclic or polycyclic cycloaliphatic divalent organic radicals having 6 to 18 carbon atoms; or a divalent organic group containing a structure in which two or more of the above are connected by a single bond or a functional group, or the diamine may include a diamine comprising: it comprises a divalent organic group having a rigid structure in which an aromatic ring or an aliphatic ring is a single ring structure, is connected by a single bond, or is fused with each other to form a heterocyclic structure.

For example, the diamine may comprise a divalent organic group selected from formulas 5a to 5 e.

[ formula 5a ]

[ formula 5b ]

[ formula 5c ]

[ formula 5d ]

[ formula 5e ]

In the formulae 5a to 5e,

R₂₁to R₂₇Each independently is selected from: a halogen atom selected from the group consisting of-F, -Cl, -Br and-I; hydroxyl (-OH); a thiol group (-SH); nitro (-NO)₂) (ii) a A cyano group; an alkyl group having 1 to 10 carbon atoms; haloalkoxy having 1 to 4 carbon atoms; haloalkyl having 1 to 10 carbon atoms; and an aryl group having 6 to 20 carbon atoms.

A₂₁And A₂₂Each independently selected from a single bond, -O-, -CR 'R "- (wherein R' and R" are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms (e.g., methyl, ethyl, propyl, isopropyl, n-butyl, t-butyl, pentyl, etc.), and a haloalkyl group having 1 to 10 carbon atoms (e.g., trifluoromethyl, etc.)), -C (═ O) -, -C (═ O) O-, -C (═ O) NH-, -S-, -SO-, -and₂-、-O[CH₂CH₂O]_y- (where y is an integer of 1 to 44), -NH (C ═ O) NH-, -NH (C ═ O) O-, monocyclic or polycyclic cycloalkylene groups having 6 to 18 carbon atoms (e.g., cyclohexylene), monocyclic or polycyclic arylene groups having 6 to 18 carbon atoms (e.g., phenylene, naphthyl, fluorenylene), and combinations thereof, and

b1 is an integer from 0 to 4, b2 is an integer from 0 to 6, b3 is an integer from 0 to 3, b4 and b5 are each independently an integer from 0 to 4, b7 and b8 are each independently an integer from 0 to 9, and b6 and b9 are each independently an integer from 0 to 3.

Alternatively, the diamine may comprise a divalent organic group selected from formulas 6a to 6 p.

At least one hydrogen atom in the divalent organic groups of formulae 6a to 6p may be replaced by a substituent selected from: a halogen atom selected from the group consisting of-F, -Cl, -Br and-I; hydroxyl (-OH); a thiol group (-SH); nitro (-NO)₂) (ii) a A cyano group; an alkyl group having 1 to 10 carbon atoms; haloalkoxy having 1 to 4 carbon atoms; haloalkyl having 1 to 10 carbon atoms; and an aryl group having 6 to 20 carbon atoms. For example, the halogen atom may be fluorine (-F); the haloalkyl group may be a fluoroalkyl group having 1 to 10 carbon atoms and containing a fluorine atom, and may be selected from, for example, a fluoromethyl group, a perfluoroethyl group, a trifluoromethyl group, and the like; the alkyl group may be selected from methyl, ethyl, propyl, isopropyl, tert-butyl, pentyl, hexyl, and the like; the aryl group may be selected from phenyl, naphthyl, more preferably a fluorine atom or a substituent comprising a fluorine atom, such as fluoroalkyl.

Alternatively, the diamine may comprise a divalent organic group having a rigid chain structure in which an aromatic ring or an aliphatic ring is a single ring structure, is connected by a single bond, or is condensed with each other to form a heterocyclic structure. For example, it may comprise a divalent organic group selected from formulas 7a to 7k, but is not limited thereto.

At least one hydrogen atom in the divalent functional groups represented by formulae 7a to 7k may be replaced with a substituent selected from the group consisting of: an alkyl group having 1 to 10 carbon atoms (e.g., methyl, ethyl, propyl, isopropyl, t-butyl, pentyl, hexyl, etc.), a fluoroalkyl group having 1 to 10 carbon atoms (e.g., fluoromethyl, perfluoroethyl, trifluoromethyl, etc.), an aryl group having 6 to 12 carbon atoms (e.g., phenyl, naphthyl, etc.), a sulfonic acid group, and a carboxylic acid group are preferably replaced with a fluoroalkyl group having 1 to 10 carbon atoms.

As the content of the organic group having a rigid structure, such as the monomer of formulae 4a to 4k or formulae 7a to 7k, increases, the heat resistance of the polyimide film at high temperature may increase. When used in combination with an organic group of a flexible structure, a polyimide film having improved transparency as well as heat resistance can be prepared.

The reaction of the acid dianhydride with the diamine can be carried out by a conventional polymerization method of polyimide or a precursor thereof, for example, solution polymerization.

In addition, the organic solvent that may be used for the polymerization reaction of polyamic acid may be selected from: ketones such as gamma-butyrolactone, 1, 3-dimethyl-imidazolidinone, methyl ethyl ketone, cyclohexanone, cyclopentanone, and 4-hydroxy-4-methyl-2-pentanone; aromatic hydrocarbons such as toluene, xylene, and tetramethylbenzene; glycol ethers (cellosolves) such as ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol diethyl ether and triethylene glycol monoethyl ether; ethyl acetate, butyl acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, dipropylene glycol monomethyl ether acetate, ethanol, propanol, ethylene glycol, propylene glycol, carbitol, Dimethylpropionamide (DMPA), Diethylpropionamide (DEPA), dimethylacetamide (DMAc), N-diethylacetamide, Dimethylformamide (DMF), Diethylformamide (DEF), N-methylpyrrolidone (NMP), N-ethylpyrrolidone (NEP), N-dimethylmethoxyacetamide, dimethyl sulfoxide, pyridine, dimethyl sulfone, hexamethylphosphoramide, tetramethylurea, N-methylcaprolactam, tetrahydrofuran, m-di-N-butyl acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, dipropylene glycol monomethyl ether acetate, ethanol, propanol, ethylene glycol, propylene glycolAlkane, para-diAlkane, 1, 2-dimethoxyethane, bis (2-methoxyethyl) ether, 1, 2-bis (2-methoxyethoxy) ethane, bis [2- (2-methoxyethoxy)]Ethers, Equamide M100, Equamide b100, and the like, and these solvents may be used alone or as a mixture of two or more.

Preferably, sulfoxide-based solvents such as dimethyl sulfoxide and diethyl sulfoxide; formamide-based solvents such as N, N-dimethylformamide, N-diethylformamide; acetamide-based solvents such as N, N-dimethylacetamide, N-diethylacetamide; pyrrolidone-based solvents such as N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, and N-vinyl-2-pyrrolidone may be used alone or as a mixture, but the solvent is not limited thereto.

In addition, aromatic hydrocarbons such as xylene and toluene may also be used, and about 50 wt% or less of an alkali metal salt or an alkaline earth metal salt based on the total amount of the solvent may also be added to the solvent to facilitate the dissolution of the polymer.

Further, in the case of synthesizing a polyamic acid or polyimide, in order to inactivate an excess of polyamino groups or acid anhydride groups, a capping agent may also be added in which the ends of the molecules are reacted with a dicarboxylic anhydride or a monoamine to cap the ends of the polyimide.

The reaction of the tetracarboxylic dianhydride with the diamine can be carried out by a conventional polymerization method of a polyimide precursor such as solution polymerization. Specifically, it can be prepared by dissolving a diamine in an organic solvent and then performing polymerization by adding a tetracarboxylic dianhydride to the resulting mixed solution.

The polymerization reaction may be carried out in a flow of inert gas or nitrogen, and may be carried out under anhydrous conditions.

The reaction temperature during the polymerization reaction may be from-20 ℃ to 80 ℃, preferably from 0 ℃ to 80 ℃. If the reaction temperature is too high, reactivity may become high, molecular weight may become large, and viscosity of the precursor composition may increase, which may be disadvantageous in terms of processes.

The polyamic acid solution prepared according to the above-described manufacturing method preferably contains a solid content in an amount such that the composition has an appropriate viscosity, in view of workability such as coating characteristics during film formation.

The polyimide precursor composition including the polyamic acid may be in the form of a solution dissolved in an organic solvent. For example, when the polyimide precursor is synthesized in an organic solvent, the solution may be the obtained reaction solution, or may be obtained by diluting the reaction solution with another solvent. When the polyimide precursor is obtained as a solid powder, it may be dissolved in an organic solvent to prepare a solution.

According to one embodiment, the solid content of the composition may be adjusted by adding the organic solvent in an amount such that the content of the total polyimide precursor is 8 to 25 wt%, preferably 10 to 25 wt%, more preferably 10 to 20 wt% or less.

Alternatively, the polyimide precursor composition may be adjusted to have a viscosity of 3000cP or more, or 4000cP or more. The viscosity of the polyimide precursor composition is 10000cP or less, preferably 9000cP or less, and more preferably 8000cP or less. When the viscosity of the polyimide precursor composition exceeds 10000cP, the efficiency of defoaming during processing of the polyimide film is reduced. This not only results in a decrease in the efficiency of the process, but also results in deterioration of the surface roughness of the prepared film due to bubble generation. This may cause deterioration of electrical, optical, and mechanical characteristics. The viscosity of the polyimide precursor composition can be measured by methods well known in the art, for example, viscosity measurements can be made using Viscotek TDA 302.

Then, the polyimide precursor resulting from the polymerization reaction may be imidized to prepare a transparent polyimide film.

According to one embodiment, the polyimide film may be manufactured by a method including the steps of: applying a polyimide film composition to a substrate; and

the applied polyimide film composition is subjected to a heat treatment.

As the substrate, a glass substrate, a metal substrate, a plastic substrate, or the like can be used without any particular limitation. Among them, a glass substrate may be preferred which has excellent thermal and chemical stability during the imidization and curing process of the polyimide precursor and can be easily separated even without any treatment with an additional release agent while not damaging the polyimide film formed after curing.

The application process may be carried out according to conventional application methods. Specifically, a spin coating method, a bar coating method, a roll coating method, an air knife method, a gravure printing method, a reverse roll method, a kiss roll method, a doctor blade method, a spray coating method, a dipping method, a brush coating method, or the like can be used. Among them, it is more preferable to carry out the process by a casting method which allows a continuous process and can increase the imidization rate of polyimide.

In addition, the polyimide precursor composition may be applied on the substrate in a thickness range such that the finally prepared polyimide film has a thickness suitable for a display substrate.

Specifically, it may be applied in an amount such that the thickness is 10 μm to 30 μm. After the polyimide precursor composition is applied, a drying process for removing the solvent remaining in the polyimide precursor composition may be optionally performed before the curing process.

The drying process may be carried out according to a conventional method. Specifically, the drying process may be performed at a temperature of 140 ℃ or less or 80 ℃ to 140 ℃. If the drying temperature is lower than 80 deg.C, the drying process becomes long. If the drying temperature exceeds 140 ℃, imidization rapidly proceeds, making it difficult to form a polyimide film having a uniform thickness.

The polyimide precursor composition applied to the substrate is then heat treated in an IR oven, in a hot air oven, or on a hot plate. The heat treatment temperature may be in the range of 300 ℃ to 500 ℃, preferably 320 ℃ to 480 ℃. The heat treatment may be performed in a multi-step heating process within the above temperature range. The heat treatment process may be performed for 20 minutes to 70 minutes, preferably 20 minutes to 60 minutes.

Thereafter, a polyimide film can be prepared by peeling the polyimide film from the substrate according to a conventional method.

In addition, the polyimide film prepared from the polyimide precursor solution according to the present invention may have excellent thermal stability against temperature variation, for example, the thermal decomposition temperature (Td 5%) of the polyimide film may be at least 600 ℃.

Further, the glass transition temperature of the polyimide may be about 360 ℃ or higher. Since it has such excellent heat resistance, the film containing the polyimide can maintain excellent heat resistance and mechanical characteristics against high-temperature heat added during the manufacturing process of the device.

Accordingly, in the present invention, the content of bubbles remaining in the polyimide precursor solution may be controlled by quantifying the defoaming characteristics of the polyimide precursor and adjusting it to be lower than a certain value.

The polyimide film according to the present invention may be usefully used for manufacturing flexible devices in electronic devices (e.g., O L ED or L CD, electronic paper, solar cells), particularly as a substrate for flexible devices.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily practice the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

< example 1> BPDA PDA ═ 1:0.967

0.059mol of PDA (phenylenediamine) was dissolved in 100g of N-methylpyrrolidone (NMP) under a nitrogen atmosphere while stirring for 20 minutes. 0.061mol of BPDA (biphenyl dianhydride) was added to the PDA solution together with 80g of NMP, and then reacted at 30 ℃ for 12 hours to prepare a polyimide precursor solution.

< example 2> BPDA PDA ═ 1:0.98

A polyimide precursor solution was prepared in the same manner as in example 1, except that 0.060mol of PDA was used.

< example 3> BPDA PDA ═ 1:0.936

A polyimide precursor solution was prepared in the same manner as in example 1, except that 0.063mol of BPDA was used.

< comparative example 1> BPDA PDA ═ 1:1

A polyimide precursor solution was prepared in the same manner as in example 1, except that 0.061mol of PDA was used.

< comparative example 2> BPDA: PDA: 1:0.922

A polyimide precursor solution was prepared in the same manner as in example 1, except that 0.064mol of BPDA was used.

< Experimental example 1> measurement of number average molecular weight

The number average molecular weights of the polyimide precursors prepared in examples 1 to 3 and comparative examples 1 and 2 were measured under the following conditions.

GPC (gel permeation chromatography): viscotek TDA302, Malvern

A detector: RI (refractive index), laser detector

Column temperature: 40 deg.C

Standard substance: PS (polystyrene, MW: 105,000)

Eluting solvent DMF (dimethylformamide) + THF (tetrahydrofuran) (L iBr, H)₃PO₄)

< experimental example 2> measurement of transmittance of polyimide precursor solution

The polyimide precursor solutions prepared in examples 1 to 3 and comparative examples 1 and 2 were prepared to measure the transmittance before bubble generation, immediately after bubble generation, and after being left for 30 minutes after bubble generation, respectively, at room temperature in this case, bubble generation was performed by rotating the precursor solution at 300rpm for 30 seconds using a stirrer to which an impeller was attached, the transmittance of the solution was measured at a wavelength of 880nm using a Turbiscan (formula, Turbisca L AB), and the measured value was substituted into the following equation 1 to calculate a "T" value.

[ equation 1]

Wherein the content of the first and second substances,

a is the transmittance of the solution after 30 minutes of standing after bubble generation, an

B is the transmittance of the solution before bubble generation.

< experimental example 3> measurement of Heat resistance of polyimide film

Each of the polyimide precursor solutions of examples 1 to 3 and comparative examples 1 and 2 was spin-coated on a glass substrate. The glass substrate coated with the polyimide precursor solution was put into an oven and heated at a rate of 5 deg.c/min, held at 80 deg.c for 30 minutes, and held at 400 deg.c for 30 minutes to form a polyimide film having a thickness of 10 μm.

For each polyimide film prepared, the thermal decomposition temperature (Td 5%) is defined as the temperature at which the weight loss of the polymer as measured using TGA in a nitrogen atmosphere is 5%.

The measurement results are shown in table 1 below.

[ Table 1]

As can be seen from table 1, it can be seen that the transmittance of the polyimide precursor solutions according to examples 1 to 3, which contain a polyimide precursor prepared by reacting a tetracarboxylic dianhydride with a diamine in a molar ratio of 1:0.93 to 1:0.99 and having a number average molecular weight (Mn) of 38,000g/mol or more, was almost recovered to the state before bubble generation after about 30 minutes from bubble generation. This is because defoaming occurs rapidly after bubble generation, and thus the storage stability of the polyimide precursor solution can be improved.

In the case of comparative example 1 in which BPDA and PDA were polymerized at the same molar ratio, the polymerized polyimide precursor had a high number average molecular weight, but the solution had a high viscosity, indicating that the defoaming characteristics were reduced. This can be demonstrated by the T value of 0.9 or less in equation 1.

In the case of comparative example 2 in which BPDA reacted excessively with respect to PDA, it was found that the molecular weight was low, resulting in deterioration of the thermal decomposition characteristics.

Accordingly, the present invention provides a polyimide precursor solution having improved defoaming characteristics by using a polyimide precursor having a high number average molecular weight, thereby improving the heat resistance of a polyimide film and suppressing crack formation caused by bubbles remaining inside the polyimide film during a high temperature process.

While this invention has been particularly shown and described with references to particular embodiments thereof, it will be obvious to those skilled in the art that the particular description is of a preferred embodiment only and that the scope of the invention is not limited thereto. It is therefore intended that the scope of the invention be defined by the following claims and their equivalents.