WO2020067727A1 - Polyimide precursor solution and polyimide film using same - Google Patents

Abstract

According to the present invention, a polyimide precursor solution is produced by reacting tetracarboxylic acid anhydride with diamine at 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 38,000 g/mol and can thus produce a polyimide film having high heat resistance. A polyimide precursor solution having improved storage stability can be provided by quantifying the defoaming properties of the solution and controlling the content of bubbles. Moreover, a polyimide film produced therefrom has a reduced amount of bubbles in the film, and can thus suppress the formation of cracks that can form in an inorganic layer when forming a device.

Description

Polyimide precursor solution and polyimide film using the same

This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0114781 filed on September 27, 2018 and Korean Patent Application No. 10-2019-0101527 filed on August 20, 2019, above All contents disclosed in the patent document are included as part of the present specification.

The present invention relates to a polyimide precursor solution and a polyimide film prepared therefrom, and more particularly, to a polyimide film made of a polyimide precursor solution with improved defoaming rate.

In the display field, weight reduction and miniaturization of products are considered important, and since glass substrates currently being used are heavy, brittle and difficult to process continuously, plastic substrates that have the advantage of being light, flexible, and capable of continuous processing can be replaced by replacing glass substrates. Research is being actively conducted to apply mobile phones, notebooks, and PDAs (Personal Digital Assistants).

In particular, polyimide (PI) resin is easy to synthesize, can make a thin film, and has the advantage of not requiring a crosslinker for curing. Recently, it has been integrated into semiconductor materials such as LCD and PDP due to light weight and precision of electronic products. As a result, many studies have been conducted to use PI for a flexible plastic display board having light and flexible properties.

A polyimide (PI) film is produced by filming the polyimide resin, and in general, a polyimide resin is solution-polymerized with an aromatic dianhydride and an aromatic diamine or an aromatic diisocyanate to prepare a polyamic acid derivative solution, and then the silicone It is manufactured by coating on a wafer or glass and curing by heat treatment.

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

In addition, the present invention 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.

The present invention to solve the above problems,

It is prepared by reacting tetracarboxylic dianhydride and diamine in a molar ratio of 1: 0.93 to 1: 0.99, and includes a polyimide precursor having a number average molecular weight (Mn) of 38,000 g / mol or more,

A polyimide precursor solution having a T value of 0.9 or more according to Equation 1 below is provided.

[Equation 1]

In the above formula,

A is the permeability of the solution after bubbling and then left for 30 minutes,

B is the permeability of the solution before bubble generation.

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

According to an embodiment, the permeability of the polyimide precursor solution before bubble generation may be 75% or more, and the permeability of the solution after standing for 30 minutes after bubble generation may be 75% or more.

According to an embodiment, the transmittance of the polyimide precursor solution may be measured at a wavelength of 880 nm using Turbiscan (Formulaction, Turbisca LAB).

According to an embodiment, the number average molecular weight of the polyimide precursor may be less than 60,000 g / mol.

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

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

According to an embodiment, the thermal decomposition temperature (Td 5%) of the polyimide film may be 600 ° C or higher.

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

The polyimide precursor solution according to the present invention is prepared by reacting tetracarboxylic dianhydride and diamine at a molar ratio of 1: 0.93 to 1: 0.99, and includes a polyimide precursor having a number average molecular weight of 38,000 g / mol or higher, thereby providing heat resistance. A high polyimide film can be prepared, and the defoaming properties of the solution are digitized using permeability to control the content of air bubbles, so that storage stability can be improved. In addition, the polyimide film made of the polyimide precursor solution according to the present invention can suppress crack formation of an inorganic film that may occur during device formation by reducing bubbles inside the film.

The present invention can be applied to various transformations and can have various embodiments, and specific embodiments will be illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all conversions, equivalents, and substitutes included in the spirit and scope of the present invention. In the description of the present invention, when it is determined that a detailed description of known technologies related to the present invention may obscure the subject matter of the present invention, the detailed description will be omitted.

All compounds or organic groups herein may be substituted or unsubstituted unless otherwise specified. Here, 'substituted' means that at least one hydrogen contained in the compound or organic group is a halogen atom, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group, a cycloalkyl group having 3 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, a hydroxyl group , Substituted with a substituent selected from the group consisting of alkoxy groups having 1 to 10 carbon atoms, carboxylic acid groups, aldehyde groups, epoxy groups, cyano groups, nitro groups, amino groups, sulfonic acid groups and derivatives thereof.

Currently, the display industry manufactures a display device using a plastic substrate instead of a glass substrate to reduce the weight and thickness of the substrate. In particular, a display device incorporating an OLED element on a plastic substrate has the advantage of being able to bend or fold.

When replacing a glass substrate with a plastic substrate, the uniformity and process stability of the substrate are very important items.

When foreign materials or bubbles are present inside and on the plastic substrate, cracks in the inorganic film may occur when forming a thin film transistor (TFT) device. In particular, since the mobile charge due to micro bubbles in the film may affect the TFT driving, a defoaming process is applied for 8 hours or more before curing the polyimide precursor solution.

In order to solve this conventional problem, the present invention is to provide a polyimide precursor composition having a small amount of bubbles and a high degassing rate, and a film prepared therefrom.

The present invention is prepared by reacting tetracarboxylic dianhydride and diamine in a molar ratio of 1: 0.93 to 1: 0.99, and includes a polyimide precursor having a number average molecular weight (Mn) of 38,000 or more,

A polyimide precursor solution having a T value of 0.9 or more calculated according to Equation 1 below is provided.

[Equation 1]

In the above formula,

A is the permeability of the solution after 30 minutes of bubbling,

B is the permeability of the solution before bubble generation.

At this time, the permeability can be measured by any method for measuring the permeability of a solution containing particles present in the solution and is not particularly limited. For example, it may be measured at a wavelength of 880 nm using Turbiscan (Formulaction, Turbisca LAB).

The precursor solution of the present invention includes a polyimide precursor having a number average molecular weight of 38,000 g / mol or higher or 40,000 g / mol or higher. According to one embodiment, the number average molecular weight may be less than 60,000 g / mol or 55,000 g / mol or less or 50,000 g / mol or less. When the polyimide precursor satisfies the number average molecular weight in the above range, the solid content of the precursor solution is 9% to 13%, and the viscosity becomes 1,000 to 5,000 cp, so that the precursor solution having a higher viscosity (for example, 7,000 to 20,000 cp) In comparison, when bubbles are generated, the degassing rate is fast and heat resistance can be improved. On the other hand, when the number average molecular weight of the polyimide precursor is lower than the above range, the heat resistance and the physical properties of the film may be poor, such as film lifting during processing.

The number average molecular weight of the polyimide precursor can be measured by various methods well known in the art, such as those described in Experimental Examples described later.

In addition, the present invention, by quantifying the defoaming property of the polyimide precursor solution to a T value defined by Equation 1, the content of air bubbles present in the polyimide precursor solution more systematically than the method of observing and controlling the defoaming property with the naked eye It can be used to control, it is possible to provide a polyimide precursor solution with improved storage stability. That is, a polyimide film prepared from a polyimide precursor solution having a T value of 0.9 or more according to Equation 1 may not only maintain high heat resistance even in a high-temperature device process, but may also occur due to bubbles remaining in the polyimide film. It is possible to effectively suppress crack formation.

According to one embodiment, the polyimide precursor solution has a transmittance of 70% or more, preferably 75% or more before air bubbles are generated, and after the air bubbles are generated for 30 minutes, the permeability of the solution is 70% or more, preferably More than 75%. That is, the difference in the permeability before and after the generation of bubbles is not large. At this time, bubble generation may be performed by rotating the precursor solution at 200 to 500 rpm for 20 to 60 seconds using a stirrer connected to the impeller.

The polyimide precursor is prepared by reacting tetracarboxylic dianhydride with diamine, and is preferably prepared by reacting tetracarboxylic dianhydride with an excess of diamine, more preferably tetracarboxylic acid It may be prepared by reacting dianhydride and diamine in a molar ratio of 1: 0.93 to 1: 0.99, such as 1: 0.93 to 1: 0.98 or 1: 0.94 to 1: 0.98. When the molar ratio of diamine to the tetracarboxylic dianhydride is reacted to less than 0.93 molar ratio, the heat resistance of the prepared polyimide film may be lowered, and when the molar ratio of diamine is reacted in excess of 0.99, for example, tetracar When the carboxylic acid dianhydride and diamine are reacted in the same amount, defoaming properties may be deteriorated due to reasons such as an increase in viscosity of the solution.

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

According to one embodiment, the polyimide precursor may include a repeating structure formed by reacting BPDA (biphenyl dianhydride) as a tetracarboxylic dianhydride and PDA (phenylenediamine) as a diamine, for example , It may be to include a repeating structure of the formula (1).

[Formula 1]

According to one embodiment, in the preparation of the polyimide precursor, it may further include at least one tetracarboxylic dianhydride together with BPDA.

For example, as the tetracarboxylic dianhydride, intramolecular aromatic, cycloaliphatic, or aliphatic tetravalent organic groups, or combinations thereof, aliphatic, cycloaliphatic or aromatic tetravalent organic groups can cross each other through a crosslinked structure. Tetracarboxylic dianhydrides containing linked tetravalent organic groups can be used. Preferably, monocyclic or polycyclic aromatic, monocyclic or polycyclic alicyclic, or two or more of these may include an acid dianhydride having a structure connected by a single bond or a functional group. Or, a tetracarboxylic acid containing a tetravalent organic group having a rigid structure such as a heterocyclic ring structure in which a ring structure such as aromatic or cycloaliphatic is single or fused, or a structure connected by a single bond. It may contain dianhydride.

For example, the tetracarboxylic dianhydride may include a tetravalent organic group having the structure of Formulas 2a to 2e:

[Formula 2a]

[Formula 2b]

[Formula 2c]

[Formula 2d]

[Formula 2e]

In Formulas 2a to 2e, R ₁₁ to R ₁₇ are each independently a halogen atom selected from -F, -Cl, -Br and -I, a hydroxyl group (-OH), a thiol group (-SH), a nitro group (-NO ₂ ), a cyano group, an alkyl group having 1 to 10 carbon atoms, a halogenoalkoxy having 1 to 4 carbon atoms, a halogenoalkyl having 1 to 10 carbon atoms, or 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 may be each independently an integer of 0 to 7,

A11 and A12 are each independently a single bond, -O-, -CR ₁₈ R _19- , -C (= O)-, -C (= O) NH-, -S-, -SO _2- , a phenylene group and It may be selected from the group consisting of a combination of these, wherein R ₁₈ and R ₁₉ may be independently selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 10 carbon atoms and a fluoroalkyl group having 1 to 10 carbon atoms, respectively. have.

Alternatively, the tetracarboxylic dianhydride may include a tetravalent organic group selected from the group consisting of the following Chemical Formulas 3a to 3n.

At least one hydrogen atom in the tetravalent organic group of the formulas 3a to 3n is a halogen atom selected from -F, -Cl, -Br and -I, a hydroxyl group (-OH), a thiol group (-SH), a nitro group (- NO ₂ ), a cyano group, an alkyl group having 1 to 10 carbon atoms, a halogenoalkoxy having 1 to 4 carbon atoms, a halogenoalkyl having 1 to 10 carbon atoms, and an aryl group having 6 to 20 carbon atoms. For example, the halogen atom may be fluoro (-F), the halogenoalkyl group is a fluoroalkyl group having 1 to 10 carbon atoms containing a fluoro atom, fluoromethyl group, perfluoroethyl group, trifluoro It may be selected from methyl groups, and the alkyl group may be selected from methyl groups, ethyl groups, propyl groups, isopropyl groups, t-butyl groups, pentyl groups, and hexyl groups, and the aryl groups are selected from phenyl groups and naphthalenyl groups. It may be, and more preferably, it may be a substituent containing a fluoro atom such as a fluoro atom and a fluoroalkyl group.

Alternatively, in the tetracarboxylic dianhydride, an aromatic ring or an aliphatic structure is a structure in which each ring structure is rigid, that is, a single ring structure, a structure in which each ring is bonded by a single bond, or each ring It may include a tetravalent organic group containing a heterocyclic structure directly connected, for example, may include a tetravalent organic group selected from the following formulas 4a to 4k.

At least one hydrogen atom in the tetravalent functional group of Formulas 4a to 4k is an alkyl group having 1 to 10 carbon atoms (for example, methyl group, ethyl group, propyl group, isopropyl group, t-butyl group, pentyl group, hexyl group, etc.), carbon number 1 to 10 fluoroalkyl groups (eg, fluoromethyl groups, perfluoroethyl groups, trifluoromethyl groups, etc.), aryl groups having 6 to 12 carbon atoms (eg, phenyl groups, naphthalenyl groups, etc.), sulfonic acids It may be substituted with a substituent selected from the group consisting of groups and carboxylic acid groups, and preferably may be substituted with a fluoroalkyl group having 1 to 10 carbon atoms.

According to one embodiment, in the preparation of the polyimide precursor, it may further include one or more diamines with PDA.

As the diamine, a monocyclic or polycyclic aromatic divalent organic group having 6 to 24 carbon atoms, a monocyclic or polycyclic alicyclic divalent organic group having 6 to 18 carbon atoms, or a structure in which two or more of these are connected by a single bond or a functional group The divalent organic group may include a diamine containing a divalent organic group structure, or a heterocyclic ring structure in which a cyclic compound such as aromatic or cycloaliphatic is singly or fused. It may be selected from divalent organic groups having a rigid structure, such as a structure linked by a bond.

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

[Formula 5a]

[Formula 5b]

[Formula 5c]

[Formula 5d]

[Formula 5e]

In formulas 5a to 5e,

R ₂₁ to R ₂₇ are each independently a halogen atom selected from -F, -Cl, -Br and -I, hydroxyl group (-OH), thiol group (-SH), nitro group (-NO ₂ ), cyan It may be selected from the group consisting of a furnace group, an alkyl group having 1 to 10 carbon atoms, a halogenoalkoxy having 1 to 4 carbon atoms, a halogenoalkyl having 1 to 10 carbon atoms, and an aryl group having 6 to 20 carbon atoms,

In addition, A21 and A22 are each independently a single bond, -O-, -CR'R "-(where R 'and R" are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms (for example, a methyl group, Ethyl groups, propyl groups, isopropyl groups, n-butyl groups, tert-butyl groups, pentyl groups, etc.) and haloalkyl groups having 1 to 10 carbon atoms (for example, those selected from trifluoromethyl groups, etc.) , -C (= O)-, -C (= O) O-, -C (= O) NH-, -S-, -SO-, -SO2-, -O [CH2CH2O] y- (y is 1 To 44), -NH (C = O) NH-, -NH (C = O) O-, monocyclic or polycyclic cycloalkylene group having 6 to 18 carbon atoms (for example, cyclohexylene group, etc.) ), A monocyclic or polycyclic arylene group having 6 to 18 carbon atoms (for example, a phenylene group, a naphthalene group, a fluorenylene group, etc.), and combinations thereof, and may be selected from the group consisting of,

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 integers from 0 to 4, and b7 and b8 are each independently 0 to 0 It is an integer of 9, and b6 and b9 are each independently an integer of 0-3.

Alternatively, the diamine may include a divalent organic group selected from the group consisting of the following Chemical Formulas 6a to 6p.

At least one hydrogen atom in the divalent organic group of the formulas 6a to 6p is a halogen atom selected from -F, -Cl, -Br and -I, a hydroxyl group (-OH), a thiol group (-SH), a nitro group (- NO2), a cyano group, an alkyl group having 1 to 10 carbon atoms, a halogenoalkoxy having 1 to 4 carbon atoms, a halogenoalkyl having 1 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms. For example, the halogen atom may be fluoro (-F), the halogenoalkyl group is a fluoroalkyl group having 1 to 10 carbon atoms containing a fluoro-based atom, a fluoromethyl group, perfluoroethyl group, trifluor It may be selected from a romethyl group, etc., the alkyl group may be selected from methyl group, ethyl group, propyl group, isopropyl group, t-butyl group, pentyl group, hexyl group, the aryl group is selected from phenyl group, naphthalenyl group It may be, and more preferably, it may be a substituent including a fluoro atom such as a fluoro atom and a fluoroalkyl group.

Alternatively, the diamine may include a divalent organic group forming a rigid chain structure of an aromatic ring or an aliphatic structure, for example, a single ring structure, a structure in which each ring is bonded by a single bond, or Each ring may include a divalent organic group structure including a heterocyclic ring structure directly fused (fused), for example, to include a divalent organic group structure selected from the following formulas 7a to 7k However, it is not limited thereto.

At least one hydrogen atom in the divalent functional group of the formulas 7a to 7k is an alkyl group having 1 to 10 carbon atoms (for example, methyl group, ethyl group, propyl group, isopropyl group, t-butyl group, pentyl group, hexyl group, etc.), Fluoroalkyl groups having 1 to 10 carbon atoms (for example, fluoromethyl group, perfluoroethyl group, trifluoromethyl group, etc.), aryl groups having 6 to 12 carbon atoms (for example, phenyl group, naphthalenyl group, etc.), It may be substituted with a substituent selected from the group consisting of sulfonic acid groups and carboxylic acid groups, and preferably may be substituted with a fluoroalkyl group having 1 to 10 carbon atoms.

When the content of the monomer having an organic group having a rigid structure as in the formulas 4a to 4k or 7a to 7k increases, heat resistance at a high temperature of the polyimide film may increase, and when used with an organic group having a flexible structure A polyimide film having improved transparency as well as heat resistance can be produced.

The polymerization reaction of the acid dianhydride and the diamine-based compound can be carried out according to a polymerization method of a conventional polyimide or its precursor, such as solution polymerization.

Examples of the organic solvent that can be used in the polyamic acid polymerization reaction include gamma-butyrolactone, 1,3-dimethyl-2-imidazolidinone, methyl ethyl ketone, cyclohexanone, cyclopentanone, and 4-hydroxy-4. Ketones such as -methyl-2-pentanone; Aromatic hydrocarbons such as toluene, xylene, and tetramethylbenzene; 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 , Glycol ethers such as dipropylene glycol diethyl ether and triethylene glycol monoethyl ether (cellosolve); 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, dimethyl Dimethylpropionamide (DMPA), diethylpropionamide (DEPA), dimethylacetamide (DMAc), N, N-diethylacetamide, dimethylformamide (DMF), diethylformamide (DEF), N -Methylpyrrolidone (NMP), N-ethylpyrrolidone (NEP), N, N-dimethylmethoxyacetamide, dimethylsulfoxide, pyridine, dimethylsulfone, hexamethylphosphoramide, tetramethylurea, N- Methylcaprolactam, tetrahydrofuran, m-dioxane, P-dioxane, 1,2-dimethoxyethane, bis (2-methoxyethyl) ether, 1,2-bis (2-methoxyethoxy) ethane , 'S [2- (2-methoxyethoxy)] ether, amide Ek (Equamide) M100, amides Ek (Equamide) and the like B100, there is a singly or as mixtures of two or more thereof may be used of these.

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

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

In addition, in the case of synthesizing polyamic acid or polyimide, in order to inactivate excess polyamino group or acid anhydride group, a terminal blocking agent is added to seal the terminal of the polyimide by reacting the molecular terminal with dicarboxylic acid anhydride or monoamine. can do.

The method for reacting the tetracarboxylic dianhydride with diamine can be carried out according to a conventional polyimide precursor polymerization production method such as solution polymerization. Specifically, after diamine is dissolved in an organic solvent, it can be prepared by adding a tetracarboxylic dianhydride to the resultant mixed solution to polymerize it.

The polymerization reaction may be performed under an inert gas or nitrogen stream, and may be performed under anhydrous conditions.

In addition, the reaction temperature during the polymerization reaction can be carried out at -20 to 80 ℃, preferably 0 to 80 ℃. If the reaction temperature is too high, the reactivity becomes high and the molecular weight may increase, and the viscosity of the precursor composition increases, which may be disadvantageous in the process.

The polyamic acid solution prepared according to the above-described manufacturing method preferably contains solid content in an amount such that the composition has an appropriate viscosity in consideration of processability such as coatability during the film forming process.

The polyimide precursor composition containing the polyamic acid may be in the form of a solution dissolved in an organic solvent, and when it has such a form, for example, when a polyimide precursor is synthesized in an organic solvent, the solution is a reaction solution obtained. It may be itself, or this reaction solution may be diluted with another solvent. Moreover, when a polyimide precursor was obtained as a solid powder, you may melt | dissolve this in the organic solvent and make it a solution.

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

Alternatively, the polyimide precursor composition may be adjusted to have a viscosity of 3,000 cP or more, or 4,000 cP or more, and the viscosity of the polyimide precursor composition is 10,000 cP or less, preferably 9,000 cP or less, more preferably 8,000 cP It is preferable to adjust to have the following viscosity. When the viscosity of the polyimide precursor composition exceeds 10,000 cP, the efficiency of defoaming decreases during processing of the polyimide film, and thus, not only the process efficiency, but also the prepared film has poor surface roughness due to the generation of bubbles, resulting in poor electrical, optical, and mechanical properties. It may degrade. The viscosity of the polyimide precursor composition can be measured by a method well known in the art, and for example, Viscotek TDA302 can be used for viscosity measurement.

Subsequently, a transparent polyimide film can be prepared by imidizing the polyimide precursor obtained as a result of the polymerization reaction.

According to one embodiment, applying the polyimide film composition on a substrate; And

A polyimide film may be manufactured through a step of heat-treating the applied polyimide film composition.

At this time, as the substrate, a glass, metal substrate, or plastic substrate may be used without particular limitation, and among them, excellent thermal and chemical stability during the imidization and curing process for the polyimide precursor, and curing without additional release agent treatment. A glass substrate that can be easily separated without damage to the formed polyimide-based film may be desirable.

In addition, the coating process may be performed according to a conventional coating method, specifically, spin coating method, bar coating method, roll coating method, air-knife method, gravure method, reverse roll method, kiss roll method, doctor blade method, Spray method, immersion method or brushing method may be used. Among them, a continuous process is possible, and it may be more preferable to be carried out by a casting method capable of increasing the imidation rate of polyimide.

In addition, the polyimide precursor composition may be applied on the substrate in a thickness range that allows the final manufactured polyimide film to have a suitable thickness for a display substrate.

Specifically, it may be applied to a thickness of 10 to 30㎛. After application of the polyimide precursor composition, a drying process for removing the solvent present in the polyimide precursor composition may be selectively performed prior to the curing process.

The drying process may be carried out according to a conventional method, specifically 140 ℃ or less, or may be carried out at a temperature of 80 ℃ to 140 ℃. If the temperature of the drying process is less than 80 ° C, the drying process becomes longer, and if it exceeds 140 ° C, imidization proceeds rapidly, making it difficult to form a polyimide film of uniform thickness.

Subsequently, the polyimide precursor composition applied to the substrate is heat-treated on an IR oven, a hot air oven or a hot plate, wherein the heat treatment temperature may be in the range of 300 to 500 ° C, preferably 320 to 480 ° C, and the temperature It may be carried out by a multi-stage heat treatment within the range. The heat treatment process may be performed for 20 minutes to 70 minutes, and preferably 20 minutes to 60 minutes.

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

In addition, the polyimide film prepared with the polyimide precursor solution according to the present invention may have excellent thermal stability according to a temperature change, for example, the thermal decomposition temperature (Td 5%) of the polyimide film may be 600 ° C or higher. have.

Further, the polyimide may have a glass transition temperature of about 360 ° C or higher. Since it has such excellent heat resistance, the film containing the polyimide can maintain excellent heat resistance and mechanical properties even with high temperature heat added during the device manufacturing process.

The pores in the polyimide film may cause cracks on the inorganic film (polysilicon thin film) by a high temperature heat treatment process during LTPS (low temperature polysilicon) TFT process. Therefore, the present invention can control the content of bubbles remaining in the polyimide precursor solution by controlling the defoaming properties in the polyimide precursor to a numerical value or less. Therefore, it is possible to suppress or significantly reduce the occurrence of cracks in the inorganic film layer, which may be caused by residual bubbles in the polyimide film produced therefrom.

The polyimide film according to the present invention can be particularly useful in the manufacture of flexible devices in electronic devices such as OLEDs, LCDs, electronic papers, and solar cells, and in particular, can be usefully used as a substrate for flexible devices.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art to which the present invention pertains can easily practice. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

<Example 1> BPDA: PDA = 1: 0.967

0.059 mol of PDA (phenylenediamine) was dissolved in 100 g of N-methylpyrrolidone (NMP) under nitrogen atmosphere by stirring over 20 minutes. To the PDA solution, 0.061 mol of BPDA (biphenyl dianhydride) was added together with 80 g of NMP, and then reacted at 30 ° C. 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 PDA was used at 0.060 mol.

<Example 3> BPDA: PDA = 1: 0.936

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

<Comparative Example 1> BPDA: PDA = 1: 1

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

<Comparative Example 2> BPDA: PDA = 1: 0.922

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

<Experimental Example 1> Number average molecular weight measurement

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

GPC (Gel permeation chromatography): Viscotek TDA302, Malvern

Detector: RI (Refractive Index), Laser detector

Column temperature: 40 ℃

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

Development solvent: DMF (Dimethylformamide) + THF (tetrahydrofuran) (LiBr, H ₃ PO ₄ )

<Experimental Example 2> Measurement of permeability of the polyimide precursor solution

The permeability of the polyimide precursor solutions prepared in Examples 1 to 3 and Comparative Examples 1 to 2 was measured before bubble formation at room temperature, immediately after bubble generation, and after 30 minutes of standing after bubble generation. At this time, bubble generation was performed by rotating the precursor solution at 300 rpm for 30 seconds using a stirrer connected to the impeller. The transmittance of the solution was measured at a wavelength of 880 nm using Turbiscan (Formulaction, Turbisca LAB), and the measured value was substituted into Equation 1 below to calculate a “T” value.

[Equation 1]

In the above formula,

A is the permeability of the solution after bubbling and then left for 30 minutes,

B is the permeability of the solution before bubble generation

<Experimental Example 3> Measurement of heat resistance of the polyimide film

The polyimide precursor solutions prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were spin coated on a glass substrate. A glass substrate coated with a polyimide precursor solution was placed in an oven and heated at a rate of 5 ° C./min, and cured by maintaining 30 minutes at 80 ° C. and 30 minutes at 400 ° C. to prepare a polyimide film having a thickness of 10 μm.

For each polyimide film prepared, the thermal decomposition temperature (Td_5%) was measured as a temperature at a weight reduction rate of 5% of the polymer in a nitrogen atmosphere using TGA.

The measurement results are shown in Table 1 below.

Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 BPDA: PDA (molar ratio) 1: 0.0967 1: 0.98 1: 0.936 1: 1 1: 0.922 Permeability before bubble generation (%) 78 78 79 76 80 Permeability immediately after bubble generation (%) 33 28 33 28 38 Permeability after 30 minutes of standing (%) 78 72 79 64 80 T One 0.92 One 0.84 One Number average molecular weight 45,000 53,000 38,000 60,000 35,000 Pyrolysis temperature (Td_5%), ℃ > 600 > 600 600 > 600 585

As can be seen from Table 1, prepared by reacting tetracarboxylic dianhydride and diamine at a molar ratio of 1: 0.93 to 1: 0.99, Examples 1 to 1 comprising a polyimide precursor having a number average molecular weight of 38,000 g / mol or more. It can be seen that the permeability of the polyimide precursor solution according to 3 is almost restored to the state before the bubble generation after about 30 minutes after the bubble generation. This is because defoaming occurs rapidly after air bubbles, so that the storage stability of the polyimide precursor solution can be improved.

In Comparative Example 1, BPDA and PDA were polymerized in the same molar ratio, and the number average molecular weight of the polymerized polyimide precursor was high, but the viscosity of the solution was high, indicating that the defoaming property was lowered, and the T value of Equation 1 was 0.9. It can be numerically proved by indicating the following values.

In the case of Comparative Example 2, it can be seen that BPDA is excessively reacted as compared with PDA, so that the molecular weight is not only low, but also the thermal decomposition properties are lowered.

As described above, the present invention uses a polyimide precursor having a high number average molecular weight, and provides a polyimide precursor solution with improved defoaming properties, thereby improving heat resistance of the polyimide film and remaining inside the polyimide film during high temperature processing. The generation of cracks formed by the bubbles can be suppressed.

Since the specific parts of the present invention have been described in detail above, it is obvious to those skilled in the art that this specific technique is only a preferred embodiment, and the scope of the present invention is not limited thereby. something to do. Therefore, the substantial scope of the present invention will be defined by the appended claims and their equivalents.

Claims (9)

It is prepared by reacting tetracarboxylic dianhydride and diamine in a molar ratio of 1: 0.93 to 1: 0.99, and includes a polyimide precursor having a number average molecular weight (Mn) of 38,000 g / mol or more, A polyimide precursor solution having a T value of 0.9 or more according to Equation 1 below: [Equation 1]

In the above formula, A is the permeability of the solution after 30 minutes of bubbling, B is the permeability of the solution before bubble generation. According to claim 1, The polyimide precursor solution is a polyimide precursor solution comprising a repeating structure prepared by reacting PDA (phenylenediamine) and BPDA (biphenyl dianhydride). According to claim 1, The polyimide precursor solution having a transmittance of 75% or more before bubble generation in the polyimide precursor solution, and a permeability of the solution after standing for 30 minutes after bubble generation is 75% or more. According to claim 1, The transmittance of the polyimide precursor solution was measured at a wavelength of 880 nm using Turbiscan (Formulaction, Turbiscan LAB). According to claim 1, The polyimide precursor solution having a number average molecular weight of the polyimide precursor is less than 60,000 g / mol. According to claim 1, The polyimide precursor solution containing the polyimide precursor and a pyrrolidone-based organic solvent. A polyimide film obtained by curing the polyimide precursor solution according to any one of claims 1 to 6. The method of claim 7, A polyimide film having a thermal decomposition temperature (Td_5%) of the polyimide film of 600 ° C or higher. A flexible device comprising the polyimide film of claim 7 as a substrate.