KR101748931B1 - Polyimide-based solution and polyimide-based film prepared by using same - Google Patents

Abstract

The present invention relates to a composition for forming a polyimide-based film capable of producing a transparent polyimide-based film having high heat resistance and mechanical properties together with excellent transparency. The polyimide-based solution is cured The haze of the obtained film is 2% or less.

Description

TECHNICAL FIELD [0001] The present invention relates to a composition for forming a polyimide-based film and a polyimide-

The present invention relates to a composition for forming a polyimide-based film for producing a transparent polyimide-based film having high heat resistance, high transparency and excellent mechanical properties.

Flexible devices are typically manufactured on the basis of high temperature thin film transistor (TFT) processes. The process temperature may vary depending on the type of the semiconductor layer, the insulating film, and the barrier layer included in the device during the manufacture of the flexible device, but usually a temperature of about 300 to 500 ° C is required in the TFT process. However, the polymer material capable of withstanding such a processing temperature is extremely limited, and polyimide known to have excellent heat resistance is mainly used.

A flexible device is usually manufactured by applying a polyimide precursor on a carrier substrate, curing the film to form a film, and then removing the completed device from the carrier substrate through a subsequent process.

The storage stability of the polyimide precursor at room temperature in this manufacturing process is particularly important. If the storage stability of the polyimide precursor is poor, the process viscosity is changed, and as a result, the coating and curing process of the polyimide substrate material becomes unstable. However, the polyimide precursor polyimic acid is known to have poor storage stability because the carboxylic acid that promotes hydrolysis is adjacent to the amide bond.

On the other hand, a flexible device involving a high-temperature process is required to have heat resistance at high temperatures. In particular, in the case of an organic light emitting diode (OLED) device using a low temperature polysilane (LTPS) process, the process temperature may approach 500 ° C. However, at such a temperature, even a polyimide having excellent heat resistance tends to undergo thermal decomposition.

Further, in the case where the light emitted from the display element is emitted through the film substrate (for example, a bottom emission type organic EL or the like), transparency is required for the film substrate. In particular, it is required to have a high light transmittance in a wavelength region of 400 nm or less, which is a visible light region. Further, in the case where light passes through a retardation film or a polarizing plate, for example, a liquid crystal display, a touch panel or the like needs to have high transparency.

On the other hand, since the solubility of the polyimide resin may be lowered after the imidization proceeds, it may be difficult to prepare the polyimide resin in a solution state, thereby limiting its use for coating. However, if the improvement is attempted, there is a disadvantage that the heat resistance decreases, and if it is tried to improve it again, the light transmittance may be lowered.

Therefore, in order to manufacture flexible devices, it is required to develop polyimide which can prevent hydrolysis, exhibit excellent chemical resistance and storage stability, and can simultaneously improve heat resistance and transparency while maintaining mechanical properties.

An object of the present invention is to provide a transparent polyimide-based film and a composition for forming a polyimide-based film which have excellent mechanical properties and high heat resistance and high transparency.

Another object of the present invention is to provide a method for producing a polyimide-based film using the composition for forming a polyimide system.

It is another object of the present invention to provide a device comprising a substrate made using the polyimide-based film.

The composition according to the present invention comprises A composition for forming a polyimide film, comprising a polyimide having a structure represented by the following formula (1) or a precursor thereof and a solvent, and having a haze of 2% or less after being coated on a substrate and cured at a temperature of 300 캜 or higher.

 [Chemical Formula 1]

In Formula 1,

X is a divalent organic group derived from an acid dianhydride, and is an aromatic, alicyclic, or a divalent organic group having a structure in which two or more of them are connected by a single bond,

Y is a divalent organic group selected from the group consisting of aromatic, alicyclic, and aliphatic groups derived from a diamine and having a substituent group containing at least one fluorine atom.

According to one embodiment, the solvent may have a positive distribution coefficient (LogP value) at 25 < 0 > C.

In addition, the distribution coefficient may be 0.1 or less.

The solvent may be a tertiary amine substituted with an alkyl group having 2 or more carbon atoms, or a tertiary amine having 2 or more alkyl groups having 2 to 6 carbon atoms.

According to one embodiment, the solvent may comprise diethyl formamide or diethylacetamide.

Further, the X may include a compound represented by the following formulas (2d) and (2e).

(2d)

[Formula 2e]

Each of R ₁₄ to R ₁₇ is independently an alkyl group having 1 to 10 carbon atoms or a fluoroalkyl group having 1 to 10 carbon atoms, a ₄ and a ₅ are each independently an integer of 0 to 3, a ₆ and a ₉ are And a ₇ and a ₈ each independently may be an integer of 0 to 9, and A ₁₁ and A ₁₂ each independently represents a single bond, -O-, -CR ₁₈ R ₁₉ -, -C (= O) -, -C (= O) NH-, -S-, -SO ₂ -, phenylene and combinations thereof, wherein R ₁₈ and R ₁₉ each independently may be 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.

According to one embodiment, X may comprise a biphenyl tetracarboxylic dianhydride.

The above-mentioned Y is an aromatic group having 6 to 18 carbon atoms, an alicyclic group having 6 to 18 carbon atoms, or a divalent organic group having at least two of these bonded to each other through a single bond, and the amine terminal having at least one fluorine substituent, And may contain an alkyl group having 1 to 10 carbon atoms having a fluorine atom-containing substituent.

According to one embodiment, the Y may comprise bistrifluoromethylbenzidine.

The number of moles of the divalent organic group or the divalent organic group having a fluorine atom-containing substituent may be at least one selected from the group consisting of divalent organic groups And more than 50 moles based on 100 moles of the total moles of the organic solvent.

The polyimide-based solution may have a solids content of 10 wt% or more and 25 wt% or less based on the total weight of the solution.

The polyimide may have a weight average molecular weight of 40,000 or more.

The polyimide may have a glass transition temperature (Tg) of 250 DEG C or higher.

The polyimide-based solution may have a viscosity of not less than 2,000 cP and not more than 10,000 cP measured at 25 ° C in a Brookfield rotational viscometer.

The present invention also provides a method for producing a polyimide-based film comprising applying and curing the above-mentioned polyimide-based solution on one surface of a substrate and then separating the solution from the substrate.

Also provided is a polyimide-based film produced by the above method.

The polyimide-based film may have a transmittance of at least 85%, a yellowness index (YI) of 8 or less and a modulus of 1.5 GPa or more at a wavelength of 380 to 760 nm in a film thickness range of 10 to 30 탆 have.

The polyimide-based film may have a coefficient of thermal expansion (CTE) of 70 ppm / ° C or less at 100 ° C to 300 ° C.

The film may have a maximum stress value of 40 to 400 MPa and a maximum elongation of 10 to 100%.

The present invention can also provide a display substrate comprising the above-mentioned polyimide-based film.

The present invention also provides an element comprising the above-mentioned polyimide-based film.

Other details of the embodiments of the present invention are included in the following detailed description.

According to the composition for forming a polyimide film according to the present invention, a polyimide film having high transparency, high heat resistance and excellent mechanical properties can be provided. Therefore, it may be useful for processing substrates in solar cells, organic light emitting diodes, semiconductor devices, or flexible display devices.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is capable of various modifications and various embodiments, and specific embodiments are illustrated in the drawings and described in detail in the detailed description. It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

In the present specification, all the compounds or functional groups may be substituted or unsubstituted, unless otherwise specified. Herein, the term "substituted" means that at least one hydrogen contained in the compound or the functional 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, Substituted with a substituent selected from the group consisting of an alkoxy group having 1 to 10 carbon atoms, a carboxylic acid group, an aldehyde group, an epoxy group, a cyano group, a nitro group, an amino group, a sulfonic acid group and derivatives thereof.

In the present specification, unless otherwise specified, the term " combination thereof " means that two or more functional groups are single bonds, Triple bond; An alkylene group having 1 to 10 carbon atoms including a methylene group, an ethylene group and the like; A fluoroalkylene group having 1 to 10 carbon atoms including a fluoromethylene group, a perfluoroethylene group and the like; A linking group such as a heteroatom such as N, O, P, S, or Si or a functional group containing it, including a carbonyl group, an ether group, an ester group, -S-, -NH- or -N = Or two or more functional groups are condensed and connected to each other.

In the present invention, the polyimide-based solution means a polyimide precursor solution, a polyamic acid solution, or a mixture thereof. The polyimide precursor includes, but is not limited to, polyamic acid, and includes, without limitation, those that can be converted into polyimide by a subsequent process.

Hereinafter, a polyimide-based solution according to an embodiment of the present invention, a polyimide-based film using the same, a method for producing the same, and a display substrate and an element including the polyimide-based film will be described in detail.

The present invention relates to a polyimide film comprising a polyimide comprising a repeating unit having a structure represented by the following formula (1) or a precursor thereof and a solvent, wherein the film obtained by curing the coating film at a temperature of 300 ° C or higher after coating on a substrate has a haze of 2% Based film forming composition.

 [Chemical Formula 1]

In Formula 1,

X is a divalent organic group derived from an acid dianhydride, and is an aromatic, alicyclic, or a divalent organic group having a structure in which two or more of them are connected by a single bond,

Y is a divalent organic group selected from the group consisting of aromatic, alicyclic and aliphatic groups derived from a diamine, and has a substituent containing at least one fluoro atom.

According to one embodiment, the solvent may have a distribution coefficient (Log P value) at 25 ° C being a positive number and having a boiling point of less than or equal to 180 ° C, more specifically a LogP value of from 0.01 to 3, or 0.01 to 2, or 0.01 To 1, or from 0.01 to 0.1.

The partition coefficient can be calculated using the ACD / LogP module of the ACD / Percepta platform of ACD / Labs. The ACD / LogP module can calculate the quantitative structure-property relationship (QSPR) .

When the distribution coefficient value is a positive number, it means that the polarity of the solvent is hydrophobic. According to the studies of the present inventors, a polyimide precursor solution was prepared using a specific solvent having a positive distribution coefficient, A film having high heat resistance and mechanical properties together with excellent transparency can be obtained.

According to an embodiment of the present invention, the solvent may be a tertiary amine substituted with an alkyl group having 2 or more carbon atoms, and more preferably a tertiary amine having 2 or more alkyl groups having 2 to 6 carbon atoms. When a conventionally used solvent such as N-methylpyrrolidone or N, N-dimethylacetamide is used as a polymerization solvent, haze indicating haziness of the film upon curing at a temperature of 300 ° C or higher And the transmittance may decrease.

In particular, studies by the inventors have shown that by using a particular solvent, more specifically N, N-diethylformamide or N, N-diethylacetamide, as a solvent for the polyimide precursor solution, When the film is cured after being coated on a substrate to produce a film, the haze of the film is 2% or less, which indicates that the whitening phenomenon can be remarkably improved as compared with the case of using a conventionally used solvent.

The acid dianhydride which can be used in the production of the polyimide containing the repeating unit of the formula (1) may be an acid dianhydride containing the functional group X in the above formula (1), for example, an aromatic, alicyclic or aliphatic A tetravalent organic group (X), or a combination thereof, may be a tetracarboxylic dianhydride including a tetravalent organic group in which aliphatic, alicyclic or aromatic tetravalent organic groups are linked to each other through a crosslinking structure. For example, it may be an alicyclic or polycyclic aromatic, a monocyclic or polycyclic alicyclic group, or an acid dianhydride having a structure in which two or more of them are linked by a single bond.

X is specifically an aromatic divalent organic group represented by the following general formulas (2a) to (2d); An alicyclic tetravalent organic group containing a structure of a cycloalkane having 3 to 12 carbon atoms; An alicyclic divalent organic group represented by the following formula (3e); An aliphatic tetravalent organic group having a branched alkane structure having 3 to 10 carbon atoms, and combinations thereof.

(2a)

(2b)

[Chemical Formula 2c]

(2d)

[Formula 2e]

In the above formulas (2a) to (2e), each of R ₁₁ to R ₁₇ may independently be an alkyl group having 1 to 10 carbon atoms or a fluoroalkyl group having 1 to 10 carbon atoms,

Wherein a ₁ is an integer of 0 or 2, a ₂ is an integer of 0 to 4, a ₃ is an integer of 0 to 8, a ₄ and a ₅ are each independently an integer of 0 to 3, a ₆ and a ₉ are Independently, an integer of 0 to 3, and a ₇ and a ₈ each independently may be an integer of 0 to 9, and A ₁₁ and A ₁₂ each independently represent a single bond, -O-, -CR ₁₈ R ₁₉ - , -C (= O) -, -C (= O) NH-, -S-, -SO ₂ -, phenylene and combinations thereof, wherein R ₁₈ and R ₁₉ May each independently be 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.

According to one embodiment, in Formula 1, X is, for example, a 4 represented by Formula 2a to 2c may be an organic group or a ₆ and 2e of a ₉ to 0 in 4 pseudogenes unit of formula 2d, but , But is not limited thereto.

More specifically, as the quaternary organic group (X), quaternary organic groups such as the following chemical formulas (3a) to (3t) can be exemplified, but not limited thereto:

In the above formulas (3a) to (3t), x is an integer of 1 to 3.

Further, the tetravalent organic group of the above-mentioned formulas (3a) to (3t) or (4a) to (4l) may be substituted with a substituent by at least one hydrogen atom present in the tetravalent organic group, with an alkyl group having 1 to 10 carbon atoms or a fluoroalkyl group having 1 to 10 carbon atoms .

More specifically, in Formula 1, X is May be a tetravalent organic group selected from the following formulas (4a) to (4c), but are not limited thereto:

In Formula 4s, x is an integer of 1 to 3.

According to one embodiment, in Formula 1, X may be an aromatic dianhydride, specifically, an aromatic dianhydride having a substituent having a fluoro atom. The tetracarboxylic acid dianhydride containing the tetravalent organic group (X) as described above is specifically exemplified by butanetetracarboxylic acid dianhydride, pentanetetracarboxylic acid dianhydride, hexanetetracarboxylic acid dianhydride, cyclopentanetetra (PMDA-H), pyromellitic dianhydride (PMDA), cyclopentanetetracarboxylic acid dianhydride, cyclohexanetetracarboxylic acid dianhydride, , Methylcyclohexanetetracarboxylic acid dianhydride, 3,3 ', 4,4'-benzophenonetetracarboxylic acid dianhydride, 3,4,9,10-perylenetetracarboxylic acid dianhydride, 4,4 '-Sulfonyldiphthalic dianhydride, 3,3', 4,4'-biphenyltetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic acid dianhydride, 2,3,6 , 7-naphthalenetetracarboxylic acid dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid Dianhydride, 2,3,5,6-pyridine tetracarboxylic acid dianhydride, m-terphenyl-3,3 ', 4,4'-tetracarboxylic acid dianhydride, p-terphenyl-3,3 4,4'-tetracarboxylic acid dianhydride, 4,4'-oxydiphthalic dianhydride, 1,1,1,3,3,3-hexafluoro-2,2-bis [(2 (2,3- or 3,4-dicarboxyphenoxy) phenyl] propane dianhydride, and 1, 2-bis [4- , 1,1,3,3,3-hexafluoro-2,2-bis [4- (2,3- or 4-dicarboxyphenoxy) phenyl] propane dianhydride, and the like.

The aromatic dianhydride ensures high transparency of the resulting polyimide and excellent oxidation resistance at high temperature curing. The substituent having the fluorine atom may be a fluoroalkyl group having 1 to 10 carbon atoms or 1 to 6 carbon atoms.

Thus, according to one embodiment, X in formula (1) may include the above compounds, and the most preferred example is biphenyl tetracarboxylic dianhydride.

Meanwhile, the diamine compound which can be used in the production of the polyimide may be a compound containing two amino groups bonded to the Y together with the functional group Y in the formula (1).

Specifically, in formula (1), Y is an aliphatic, alicyclic or aromatic divalent organic group derived from a diamine compound, or a combination thereof, wherein a divalent aliphatic, alicyclic or aromatic divalent organic group is directly connected, or And may be a divalent organic group linked to each other through a crosslinking structure.

According to an embodiment of the present invention, the diamine compound may be a monocyclic or polycyclic aromatic group having 6 to 18 carbon atoms, a monocyclic or polycyclic alicyclic group having 6 to 18 carbon atoms, Lt; / RTI >

More specifically, the above-mentioned diamine compound may be at least one selected from the group consisting of 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylsulfide, 4,4'-diaminodiphenylsulfone, Phenone, bis [4- (4-aminophenoxy) phenyl] methane, 2,2-bis [4- ) Phenyl] -1,1,1,3,3,3-hexafluoropropane, 1,3-bis (4-aminophenoxy) benzene, 4,4'- , Bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (4-aminophenoxy) (4-aminophenoxy) phenyl] ether, 4,4'-bis (4-aminophenylsulfonyl) diphenyl ether, 4,4'- , 4-bis [4- (4-aminophenoxy) benzoyl] benzene, 3,3'-diaminodiphenyl ether, 3,3-diaminodiphenyl sulfide, , 3,3'-diaminobenzophenone, Bis [4- (3-aminophenoxy) phenyl] methane, 2,2-bis [4- Phenyl-1,1,1,3,3,3-hexafluoropropane, 1,3-bis (3-aminophenoxy) benzene, 4,4'-bis (3-aminophenoxy) Bis [4- (3-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] ether, 4,4'-bis (3-aminophenylsulfonyl) diphenyl ether, 4-bis [4- (3-aminophenoxy) benzoyl] benzene, and the like, alone or in a mixture of two or more.

In order to obtain the physical properties of the polyimide film according to the present invention, among diamines mentioned above, diamines having an aromatic group are preferred. More specifically, it may be desirable to use an aromatic diamine having a fluorine atom-containing substituent, especially when the acid dianhydride does not have a fluoro substituent. Preferable examples may include bistrifluoromethylbenzidine.

The fluoro atom-containing substituent is the same as described above, preferably a fluoroalkyl having 1 to 10 carbon atoms or a fluoroalkyl having 1 to 6 carbon atoms. The diamine having a fluorine atom as a substituent contributes to improvement of the transparency of the resulting polyimide film, and a substituent having no fluorine atom can contribute to improvement of the chemical resistance, heat resistance and mechanical strength of the polyimide film.

It is also possible to use a diamine having a substituent having a fluorine atom and a diamine that does not have a fluorine atom at the same time in a ratio of 1: 9 to 9: 1, or 2: 8 to 8: 2, or 3: 7 to 7: 3, but the present invention is not limited thereto.

According to a preferred embodiment according to the present invention, the polyimide may be used together with an acid anhydride and a diamine having a fluoro substituent. Here, the term "fluoro substituent" is used interchangeably with the term "fluoro atom-containing substituent" as well as "fluoro atom substituent" as well as "substituent group containing fluoro atom".

The fluoro atom-containing substituent to which the aromatic acid may be substituted is a fluoroalkyl group having 1 to 10 carbon atoms or 1 to 6 carbon atoms.

According to a preferred embodiment, the divalent organic group or the divalent organic group, or both of them may have a substituent group containing a fluorine atom, and the divalent organic group or the divalent organic group having a fluorine atom- The number of moles can be more than 50 mol% relative to the total number of moles of the divalent organic group and the quaternary organic group. That is, it may be 50 moles or more based on 100 moles of the total composition.

According to a preferred embodiment of the present invention, the diamine having a fluoro substituent may be 2,2'-bis (trifluoromethyl) -benzidine (TFMB).

 The acid dianhydride and the diamine compound are preferably used in appropriate reaction ratios in consideration of the physical properties of the final polyimide. Specifically, it is preferable that the diamine compound is used in a molar ratio of about 0.9 to 1.1 per mole of the acid dianhydride. If the content ratio is out of the above range, the imidization ratio or the molecular weight of the polyimide to be produced may be lowered, and film formation may be difficult.

The polymerization of the acid dianhydride and the diamine compound may be carried out according to a conventional method for polymerization of a polyimide or a precursor thereof such as solution polymerization.

Specifically, when it is carried out by solution polymerization, it can be carried out by dissolving a diamine compound in the above-mentioned polymerization solvent, and then adding and reacting with an acid dianhydride. In this case, the polymerization solvent can be calculated using ACD / LogP module of ACD / Percepta platform of ACD / Labs and ACD / LogP module can be calculated by using QDF (Quantitative Structure-Property Relationship) . It may be desirable to use a positive distribution coefficient (LogP value) calculated in this manner.

The polymerization reaction may be carried out at a temperature of less than about 10 to 30 DEG C or at a temperature of about 15 to 25 DEG C or at room temperature for about 0.5 to 5 hours or for about 1 to 3 hours, Deg.] C or at a temperature of about 40 to 60 [deg.] C for about 5 to 50 hours, or for about 10 to 40 hours, or for about 20 to 30 hours.

As a result of the polymerization reaction, polyamic acid, which is a precursor of polyimide, is produced. The polyamic acid is an acid or an acid derivative containing an -CO-NH- group and a CO-OR group (wherein R is a hydrogen atom or an alkyl group) according to the reaction of an acid anhydride group with an amino group, According to one embodiment there is provided a polyamic acid having the structure of Formula 2:

(2)

Wherein X and Y are the same as defined above.

The polyamic acid thus obtained as a result of the polymerization reaction is subjected to an imidation process. At this time, the imidization process may be specifically performed by a chemical imidization or thermal imidization process.

Specifically, the chemical imidization may include acid anhydrides such as acetic anhydride, propionic anhydride, benzoic anhydride, or acid chlorides thereof; A carbodiimide compound such as dicyclohexylcarbodiimide, or the like. The dehydrating agent may be used in an amount of 0.1 to 10 mol based on 1 mol of the acid dianhydride.

The chemical imidization may also be carried out at a temperature of 60 to 120 ° C.

In the case of thermal imidization, the thermal imidization may be carried out by heat treatment at a temperature of 80 to 400 ° C. At this time, a step of azeotropically removing water generated as a result of the dehydration reaction using benzene, toluene, May be more preferable.

On the other hand, the chemical or thermal imidization process may be carried out in the presence of a base catalyst such as pyridine, isoquinoline, trimethylamine, triethylamine, N, N-dimethylaminopyridine, imidazole, 1-methylpiperidine, . The base catalyst may be used in an amount of 0.1 to 5 mol based on 1 mol of the acid dianhydride.

By the imidation process, OH of -CO-NH- and OH of -CO-OH in the polyamic acid molecule are dehydrated to obtain a polyimide having the cyclic chemical structure (-CO-N-CO-) .

At this time, the polyimide of Formula 1 is obtained in a solution state dissolved in an organic solvent used in the polymerization reaction, and the solution may contain polyamic acid which is a precursor of a polyimide which is not imidized.

Accordingly, the polyimide or its precursor thus produced may be separated as a solid component and then redissolved in an organic solvent to prepare the polyimide-based solution according to the present invention, or may be used in the form of the solution obtained. The polyimide may be separated by adding a poor solvent for the polyimide such as methanol or isopropyl ether to the resultant solution to precipitate the polyimide, followed by filtration, washing, drying, and the like. , And as the re-dissolving solvent, the same organic solvent as used in the above polymerization reaction may be used.

The polyimide-based solution produced by the above-described method can produce an anisotropic polyimide-based film having high permeability, excellent heat resistance and excellent mechanical properties.

According to one embodiment, it is possible to provide a method for producing a polyimide-based film comprising applying and curing a polyimide-based solution according to the present invention to one surface of a substrate, and separating the solution from the substrate.

Specifically, CN band appearing at 1350 to 1400cm ^-1 or 1550 to 1650cm ^-1 in the IR spectrum, applying the composition containing the polyester precursor, polyamic acid and the polyimide of the polyimide after imidization proceeds at a temperature above 500 ℃ About 60% to about 99%, or about 70% to about 98%, of the relative intensities of the CN bands after imidization at a temperature of 200 ° C or more with respect to the integral intensity of 100% And may have an imidization rate of about 75 to 96%.

The polyimide of Formula 1 may have a weight average molecular weight in terms of polystyrene of 10,000 to 200,000 g / mol, or 20,000 to 100,000 g / mol, or 40,000 to 200,000 g / mol.

The polyimide of the above formula (1) preferably has a molecular weight distribution (Mw / Mn) of 1.1 to 2.5.

If the imidization rate, the weight average molecular weight, or the molecular weight distribution of the polyimide of Formula 1 is out of the above range, film formation may be difficult or the characteristics of the polyimide-based film such as transparency, heat resistance and mechanical properties may deteriorate .

The polyimide of the above formula (1) may have a glass transition temperature of about 250 ° C or more, or 250 to 320 ° C. Since the polyimide film has excellent heat resistance, the polyimide film can exhibit excellent heat resistance against high temperature heat added during the device manufacturing process, and the polyimide film can be used as a display substrate, It is possible to suppress occurrence of warpage and lowering of reliability of other elements during the process of manufacturing the device, and as a result, it is possible to manufacture devices having improved characteristics and reliability.

The composition for forming a polyimide film according to the present invention preferably contains a solid content in such an amount that the suitable film-forming composition has an appropriate viscosity in consideration of processability such as coating properties in the film-forming step. Specifically, it may be preferable that the composition for forming a polyimide-based film is contained in an amount such that it has a viscosity of 400 to 20,000 cP. When the content of the organic solvent is too small and the viscosity of the composition for forming a polyimide film is less than 400 cP or the content of the organic solvent is excessively large and the content of the composition for forming a polyimide film is more than 20,000 cP, There is a fear that the processability in manufacturing the display substrate using the composition is lowered. Most preferably, the solids content is 10 wt% to 25 wt%, and may have a viscosity of 2,000 to 10,000 cP.

On the other hand, when the polyimide-based solution contains a precursor of polyimide, the polyamic acid-containing solution obtained as a result of the polymerization reaction of the acid dianhydride and the diamine compound in a polymerization solvent may be used.

The polyimide-based solution containing the polyimide or a precursor thereof may be in the form of a binder, a solvent, a crosslinking agent, an initiator, a dispersing agent, a plasticizer, a viscosity modifier, an ultraviolet absorber, a photosensitive monomer, And an additive such as a sensitizer.

Next, a polyimide-based film is prepared by applying the above-prepared polyimide-based solution to one surface of a substrate, curing it at a temperature of 80 to 400 ° C, and then separating from the substrate.

In this case, glass, a metal substrate, a plastic substrate, or the like can be used as the substrate without any particular limitations. Among these, the substrate is excellent in thermal and chemical stability during the curing process for the polyimide precursor, A glass substrate that can be easily separated without damaging the system film may be desirable.

Specific examples of the coating method include a spin coating method, a bar coating method, a roll coating method, an air-knife method, a gravure method, a reverse roll method, a kiss roll method, a doctor blade method, A spray method, a dipping method, a brushing method, or the like may be used. It is more preferable to carry out the continuous process by the casting method which can increase the imidization rate of the polyimide resin.

In addition, the polyimide-based solution can be applied onto the substrate in a thickness range such that the polyimide-based film to be finally produced has a thickness suitable for a display substrate. Specifically, it may be applied in an amount such that the thickness is 10 to 30 mu m.

After the application of the polyimide-based solution, a drying process for removing the solvent present in the polyimide-based solution prior to the curing process may be further optionally performed.

The drying process may be carried out according to a conventional method. Specifically, the drying process may be performed at a temperature of 140 ° C or lower, or 80-140 ° C. If the drying temperature is lower than 80 캜, the drying process becomes longer. If the drying temperature is higher than 140 캜, the imidization rapidly proceeds to make it difficult to form a polyimide film having a uniform thickness.

The curing process may then be carried out by heat treatment at a temperature of 80 to 400 < 0 > C. The curing process may be carried out by a multi-stage heat treatment at various temperatures within the above-mentioned temperature range. The curing time in the curing step is not particularly limited, and may be, for example, 30 minutes to 6 hours.

After the curing step, a subsequent heat treatment step may be optionally performed to increase the imidization ratio of the polyimide resin in the polyimide film to form the polyimide film having the above-mentioned physical properties.

The subsequent heat treatment is preferably performed at 200 ° C or higher, or 200 ° C to 450 ° C for 1 minute to 30 minutes. The subsequent heat treatment process may be performed once or may be performed in two or more stages. Specifically, it may be carried out in three stages including a first heat treatment at 200 to 220 占 폚, a second heat treatment at 300 to 380 占 폚, and a third heat treatment at 400 to 450 占 폚.

Thereafter, the polyimide-based film formed on the substrate can be produced from the substrate by a conventional method to produce a polyimide-based film.

The polyimide film produced by the above-described production method exhibits high heat resistance and mechanical strength together with high transparency by including the polyimide of the above formula (1). As a result, the polyimide-based film is useful as a substrate for an OLED, an LCD, an electronic paper, a solar cell, and other devices that require high transparency, excellent heat resistance, and mechanical strength.

The polyimide-based film may have a coefficient of thermal expansion (CTE) of about 70 ppm / ° C or lower, or about 40 ppm / ° C or lower at an elevation of 100 ° C to 300 ° C, Resistant polyimide film having a value of 30 ppm / 占 폚 or less in the range of 300 占 폚 to 100 占 폚.

The polyimide-based film has haze of 2 or less, transmittance to light of 380 to 760 nm in a film thickness range of 10 to 30 탆 is 85% or more, or 87% or more, and yellowness (YI ) Is about 8 or less, or about 6 or less. By having excellent light transmittance and yellowness as described above, it is possible to exhibit significantly improved transparency and optical characteristics.

The polyimide-based film has a modulus of about 1.0 GPa or more, or about 1.5 to 2.5 GPa, a maximum stress value of about 40 to 400 MPa, or about 85 to 300 MPa, and a maximum elongation of about 10 to 100 MPa %, Or about 10 to 45%, based on the total weight of the film.

According to one embodiment, the polyimide-based film may be an anisotropic or isotropic film. Wherein the anisotropic polyimide film has an in-plane retardation value (R _in ) of about 0.05 to 1 nm, a retardation value (R _th ) in a thickness direction of about 100 nm or more, or an in-plane retardation value (R _in ) of about 0.1 to 0.5 nm And the retardation value (R _th ) in the thickness direction is about 150 nm or more. The isotropic polyimide film preferably has an in-plane retardation (Rin) of about 0.05 to 1 nm, a retardation value (Rth) in the thickness direction of about 100 nm or less, or an in-plane retardation value (Rin) of about 0.1 to 0.5 nm, And an isotropic film whose retardation value (Rth) in the thickness direction is about 90 nm or less.

Accordingly, according to another embodiment of the present invention, a display substrate and an element including the polyimide-based film may be provided.

Specifically, the device can be any solar cell having a flexible substrate (e.g., a flexible solar cell), organic light emitting diode (OLED) lighting (e.g., flexible OLED lighting) Device, or an organic electroluminescent device having a flexible substrate, an electrophoretic device, or an LCD device.

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

Examples and Comparative Examples

Distribution coefficient

First, the ACD / LogP module of the ACD / Percepta platform of ACD / Labs (where the ACD / LogP module is computed using the Quantitative Structure-Property Relationship (QSPR) methodology algorithm method using the 2D structure of the molecule) The partition coefficient (LogP value) at 0 ° C is as follows.

menstruum DEF DMF DEAc DMAc NMP NEP LogP (25 캜) 0.05 -1.01 0.32 -0.75 -0.28 0.22 Boiling point (캜) 176-177 152-154 182-186 165 202-204 97

In Table 1 above, the English abbreviations have the following meanings:

DMAc: N, N-Dimethylacetamide (N, N-dimethylacetamide)

DEAc: N, N-diethylacetamide (N, N-diethylacetamide)

DEF: N, N-diethyl formamide (N, N-diethyl formamide)

DMF: N, N-dimethyl foramide.

NMP: N-methylpyrrolidone (N-methylpyrrolidone)

NEP: N-ethylpyrrolidone (N-ethylpyrrolidone)

Example 1

30 g of 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride was added to 150 g of diethylformamide (DEF) in a nitrogen atmosphere to prepare 20 Min. ≪ / RTI > The resulting BPDA / DEF solution was prepared by dissolving 32.6 g of 2,2'-bis (trifluoromethyl) benzidine (TFMB) as a diamine compound in 110 g of DEF as a diamine compound One TFMB / DEF solution was added and reacted at 25 ° C for 2 hours, then the temperature was increased to 40 ° C and allowed to react for 24 hours. DEF was added to the resultant reaction solution to adjust the solid content to 10 wt% so that the viscosity of the reaction solution became 5,000 cP and then uniformly mixed for 24 hours to prepare a polyimide precursor solution.

The prepared polyimide precursor solution was spin-coated on a glass substrate to a thickness of about 15 microns. The glass substrate coated with the polyimide precursor solution was placed in an oven and heated at a rate of 2 ° C / min. The glass substrate was cured at 80 ° C for 15 minutes, at 150 ° C for 30 minutes, at 220 ° C for 30 minutes, The process was carried out. After completion of the curing process, the glass substrate was immersed in water, and the film formed on the glass substrate was peeled off and dried at 100 DEG C in an oven.

Example 2 and Comparative Examples 1 to 3

Except that the solvent was changed as shown in Table 2 below.

Experimental Example

The film properties such as haze, transmittance, yellowness, retardation value, and thermal expansion coefficient of each of the polyimide films prepared in Examples and Comparative Examples were measured by the following methods.

The haze was measured according to ASTM D1003 measurement using a hazemeter (NDH5000SP (Nippon denshoku)).

The transmittance was measured by a transmittance meter (model name HR-100, manufactured by Murakami Color Research Laboratory) according to JIS K 7105.

The Yellowness Index (YI) was measured according to ASTM E313-73 using a color difference meter (Color Eye 7000A).

The thermal expansion coefficient (CTE) and dimensional change of the film were measured using Q400 manufactured by TA. Prepare the film in 5x20mm size and load the sample using accessories. The actual measured film length was equal to 16 mm. The film pulling force was set at 0.02 N, and the measurement starting temperature was heated to 300 캜 at a rate of 5 캜 at 30 캜, and the coefficient of linear thermal expansion of the polyimide film was measured as an average value in the range of 100 to 300 캜 .

Zwick's UTM was also used to measure the mechanical properties (modulus, peak stress, and maximum elongation) of the film. The film was cut to a width of 5 mm or more and a length of 60 mm or more. The gap between the grips was set to 40 mm, and the sample was pulled at a speed of 20 mm / min.

The results of the physical properties measurement are shown in Table 2 below. (- in Table 2 means - not measured)

Test Film No. Example 1 Comparative Example 1 Example 2 Comparative Example 2 Comparative Example 3 menstruum DEF DMAc DEAc NMP DMF Thickness (㎛) 11.7 11.6 12.5 11.8 14.6 Hayes 0.88 2.75 1.62 2.22 3.43 Transmittance
(%) T _{ave. (380 to 760 nm)} 88.88 87.95 88.01 85.93 86.69 YI 4.1 5.5 5.8 8.6 9.7 CTE 100 to 300 ° C
(ppm / DEG C) 17.48 19.93 - - -    CTE 300 ~ 100 ℃
(ppm / DEG C) 25.74 24.51 - - - Tg (占 폚) 359 360 - - - Modulus (GPa)
(GPa) 4.8 5.0 - - - Maximum stress (MPa) 292 291 - - - Maximum elongation (%) 38 43 - - -

As shown in Table 2, it can be seen that the polyimide-based films of Examples 1 and 2 according to the present invention are films having excellent transparency and high heat resistance and mechanical properties.

While the present invention has been particularly shown and described with reference to specific embodiments thereof, those skilled in the art will appreciate that such specific embodiments are merely preferred embodiments and that the scope of the present invention is not limited thereby. something to do. It is therefore intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

Claims (22)

A polyimide comprising a repeating unit having a structure represented by the following formula (1) or a precursor thereof and a solvent having a positive distribution coefficient (Log P value) at 25 캜, Wherein the film has a haze of 2% or less.
[Chemical Formula 1]

In Formula 1,
X is a tetravalent organic group derived from 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride,
Y is a divalent organic group derived from 2,2'-bis (trifluoromethyl) -benzidine. delete The composition for forming a polyimide film according to claim 1, wherein the partition coefficient is 0.1 or less. The method according to claim 1,
Wherein the solvent is a tertiary amine substituted with an alkyl group having 2 or more carbon atoms. The method according to claim 1,
Wherein the solvent is a tertiary amine having two or more alkyl groups having 2 to 6 carbon atoms. The method according to claim 1,
Wherein the solvent comprises N, N-diethylformamide or N, N-diethylacetamide. The method according to claim 1,
Wherein the polyimide-based solution has a solid content of 10 wt% or more and 25 wt% or less based on the total weight of the solution. delete delete delete delete delete The method according to claim 1,
Wherein the polyimide has a weight average molecular weight of 40,000 or more. The method according to claim 1,
Wherein the polyimide has a glass transition temperature (Tg) of 250 DEG C or more. The method according to claim 1,
Wherein the composition for forming a polyimide film has a viscosity of not less than 400 cP and not more than 20,000 cP measured at 25 캜 by a Brookfield rotational viscometer. A process for producing a polyimide-based film, comprising applying the polyimide film-forming composition of claim 1 to one surface of a substrate, curing the film, and then separating the film from the substrate. A polyimide-based film produced by the method of claim 16. 18. The method of claim 17,
Wherein the film has a transparency to light of 380 to 760 nm in a film thickness range of 10 to 30 占 퐉 of 85% or more, a yellowness index (YI) of 8 or less, and a modulus of 1.5 GPa or more film. 18. The method of claim 17,
Wherein a coefficient of thermal expansion (CTE) at 100 占 폚 to 300 占 폚 is 70 ppm / 占 폚 or lower. 18. The method of claim 17,
A maximum stress value of 40 to 400 MPa, and a maximum elongation of 10 to 100%. 18. A display substrate comprising the polyimide-based film of claim 17. An element comprising a polyimide-based film according to claim 17.