KR20160097682A - Polyimide-based solution and polyimide-based film prepared by using same - Google Patents

Abstract

The present invention relates to a polyimide-based solution which can be used to manufacture a transparent isotropic polyimide-based film having high thermal resistance and mechanical properties with excellent transmittance. After being coated on a substrate and being left for 30 minutes at 30C and humidity of 70%, the polyimide-based solution exhibits haze of 1% or less. The polyimide-based solution comprises: polyimide having a structure represented by chemical formula 1, or polyamic acid represented by chemical formula 2; and a solvent.

Description

POLYIMIDE BASED SOLUTION AND POLYIMIDE BASED FILM PREPARED BY USING SAME Technical Field [1] The present invention relates to a polyimide-

The present invention relates to a polyimide-based solution capable of producing an isotropic transparent polyimide-based film having excellent heat resistance 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 accompanied by 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.

Therefore, there is a need for the development of a polyimide which can exhibit excellent chemical resistance and storage stability by preventing hydrolysis for the production of a flexible device, and which can exhibit excellent thermal stability at high temperature with sufficient mechanical properties.

Korea patent registration No. 1175812 (registered on August 14, 2012) Korean Patent Registration No. 1167483 (registered on July 13, 2012)

An object of the present invention is to provide a polyimide-based solution capable of providing an isotropic transparent polyimide-based film having excellent heat resistance and excellent mechanical properties.

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

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

The polyimide-based solution according to one aspect of the present invention comprises A precursor of a polyimide having a structure represented by the following general formula (1) or a polyamic acid represented by the following general formula (2) and a solvent, and has a haze of 1% or less after being left on a substrate for 30 minutes at 30 ° C and 70% humidity.

 [Chemical Formula 1]

(2)

In Formula 1,

X is a tetravalent organic group selected from the group consisting of aromatic, alicyclic, and aliphatic tetravalent organic groups derived from an acid dianhydride,

And Y comprises a divalent organic group selected from the group consisting of aromatic, alicyclic and aliphatic divalent organic groups derived from diamines.

According to one embodiment, the solvent may be that the partition coefficient (LogP value) at 25 DEG C is positive.

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

In addition, the solvent may be a tertiary amine substituted with an alkyl group having 2 or more carbon atoms.

The solvent may be a tertiary amine having two or more alkyl groups having 2 to 6 carbon atoms.

The solvent may be one comprising N, N-diethylformamide.

According to one embodiment, X may be a tetravalent organic group having a fluoro atom containing substituent.

According to one embodiment, Y may be a divalent organic group having a fluoro atom containing substituent.

According to one embodiment, 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.

According to one embodiment, the polyimide-based solution may have a viscosity of from 2,000 cP to 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.

The present invention also provides a polyimide-based film produced by the above-described method.

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

The polyimide may have a glass transition temperature of 250 ° C or higher and a transmittance of 85% or more at a wavelength of 380 to 760 nm in a film thickness range of 10 to 30 μm.

In addition, the polyimide film may have a coefficient of thermal expansion (CTE) at 250 占 폚 of 70 ppm / K or less.

The present invention also provides 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.

By using the polyimide-based solution according to the present invention, it is possible to produce a polyimide film having high transparency, high heat resistance, excellent mechanical properties and isotropic properties. I will. As a result, the polyimide-based film is useful as a substrate in a solar cell, an organic light emitting diode, a semiconductor device, or a flexible display device.

Fig. 1 is a photograph showing the clouding phenomenon of the polyimide film produced in Examples and Comparative Examples. Fig.

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, "a combination thereof" means a compound wherein at least two functional groups are a single bond, a double bond, a triple bond, an alkylene group having 1 to 10 carbon atoms (for example, a methylene group (-CH ₂ -), Ethylene group (-CH ₂ CH ₂ -), etc.), a fluoroalkylene group having 1 to 10 carbon atoms (for example, a fluoromethylene group (-CF ₂ -), a perfluoroethylene group (-CF ₂ CF ₂ -, etc.), a hetero atom such as N, O, P, S, or Si or a functional group containing the same (specifically, a carbonyl group (-C═O-), an ether group (-O-) Or a heteroalkylene group containing a heteroatom (-COO-), -S-, -NH- or -N = N-, etc.), or two or more functional groups are condensed and connected.

In the present invention, 'isotropic' means that the thickness direction retardation value (R _th ) is about 100 nm or less.

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 comprises a precursor of a polyimide having a structure represented by the following formula (1) or a polyamic acid represented by the following formula (2) and a solvent. After coating the substrate on a substrate at 30 ° C and 70% humidity for 30 minutes, the haze is 1% Polyimide-based solution.

 [Chemical Formula 1]

(2)

In Formula 1,

X is a tetravalent organic group selected from the group consisting of aromatic, alicyclic, and aliphatic tetravalent organic groups derived from an acid dianhydride,

And Y comprises a divalent organic group selected from the group consisting of aromatic, alicyclic and aliphatic divalent organic groups derived from diamines.

According to one embodiment, the solvent may be that the partition coefficient (LogP value) at 25 DEG C is positive. More specifically, the partition coefficient LogP value may be 0.01 to 3, or 0.01 to 2, or 0.01 to 1, or 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, , An isotropic film having high heat resistance and mechanical properties together with excellent transparency can be obtained.

According to a preferred embodiment of the present invention, the solvent may be a tertiary amine substituted with an alkyl group having 2 or more carbon atoms, more preferably a tertiary amine having 2 or more alkyl groups having 2 to 6 carbon atoms. More specifically, it may include, for example, N, N-diethylacetamide, N, N-diethylformamide or a mixture thereof. Most preferably N, N-diethylformamide.

In particular, according to the studies of the present inventors, the polyimide-based solution according to the present invention has a haze of 1% or less after being allowed to stand at 30 ° C and 70% humidity for 30 minutes after coating on a glass substrate, The whitening phenomenon can be remarkably improved.

When the polyamic acid meets with water and forms a salt, clouding occurs and the degree of agglomeration may occur. When the film is cured in this state, a rough film is formed on the surface. That is, when the haze of the polyimide-based solution coating is too high, the coating property is poor and surface roughness may occur after curing. Such improvement of the opacity contributes to improvement of the surface characteristics after curing.

The acid dianhydride which can be used in the preparation of the polyimide of the formula 1 or the polyamic acid of the formula 2 may be an acid dianhydride containing the functional group X in the formula 1 or 2, , Or an aliphatic divalent 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 .

The tetravalent organic group (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 (2e); An aliphatic quadrivalent organic group having a branched alkane structure having 1 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 from 0 to 3, and a ₇ and a ₈ each independently may be an integer from 0 to 9, and

Wherein A ₂₁ and A ₂₂ are each independently a single _{bond, -O-, -CR 18 R 19 -} NH C (= O) - -, - C (= O) -,, - S -, - SO 2 -, A phenylene group and a combination thereof, wherein R ₁₈ and R ₁₉ are each 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 .

More specifically, as the quaternary organic group (X), quaternary organic groups represented by the following formulas (3a) to (3t), or (4a) to (4l)

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) 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.

The tetravalent organic group represented by any one of formulas (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.

The tetracarboxylic acid dianhydride containing the above-described tetravalent organic group (X) is specifically exemplified by butanetetracarboxylic acid dianhydride, pentanetetracarboxylic acid dianhydride, hexanetetracarboxylic acid dianhydride, cyclo Cyclopentanetetracarboxylic acid dianhydride, cyclohexanetetracarboxylic acid dianhydride (PMDA-H), pyromellitic dianhydride, cyclopentanetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, PMDA), 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 Acid dianhydride, 2,3,5,6-pyridine tetracarboxylic acid dianhydride, m-terphenyl-3,3 ', 4,4'-tetracarboxylic acid dianhydride, p- 3 ', 4,4'-tetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, 1,1,1,3,3,3-hexafluoro-2,2-bis [ Bis [4- (2,3- or 3,4-dicarboxyphenoxy) phenyl] propane dianhydride, and 1,1,1,3,3,3-hexafluoro-2,2-bis [4- (2,3- or 4-dicarboxyphenoxy) phenyl] propane dianhydride, and the like.

Particularly preferably an aromatic dianhydride, more preferably an aromatic dianhydride having a substituent having a fluoro atom. 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.

Meanwhile, the diamine compound that 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) or (2).

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.

More specifically, the diamine may include 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylsulfide, 4,4'-diaminodiphenylsulfone, 4,4'-diaminobenzophenone 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, Benzoyl] benzene, 3,3'-diaminodiphenyl ether, 3,3-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,3'-diaminobenzophenone, bis [4- (3-aminophenoxy) - Phenyl] propane, 2,2-bis [4- (3-aminophenoxy) phenyl-1,1,1,3,3,3- (3-aminophenoxy) benzene, 4,4'-bis (3-aminophenoxy) biphenyl, bis [4- Ketone, bis [4- (3-aminophenoxy) phenyl] sulfide, bis [4- Bis (4-aminophenylsulfonyl) diphenyl ether, 4,4'-bis (3-aminothiophenoxy) diphenyl sulfone, ) Benzoyl] benzene, and the like, alone or in a mixture of two or more of them may be used.

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, a diamine having a substituent having a fluorine atom may be preferred, particularly when the acid dianhydride does not have a fluoro substituent. The substituent having a fluoro atom 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.

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 0.9 to 1.1 based on 1 mol 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 reaction of the acid dianhydride and the diamine compound may be carried out according to a conventional polymerization method such as solution polymerization or the polymerization of a precursor thereof.

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. The ACD / LogP module of the ACD / Percepta platform of ACD / Labs' ACD / LogP module is used as a quantitative structure-property relationship (QSPR) (LogP value) calculated at 25 캜 is a positive number.

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. That is, the ACD / LogP module of the ACD / Percepta platform of the ACD / Labs company (here, the ACD / LogP module calculates the quantitative structure-property relationship (QSPR) (LogP value) is positive can be used.

The polyimide-based solution produced by the above-described method is capable of producing an isotropic polyimide-based film having high light transmittance, excellent ultrahigh heat resistance and excellent mechanical properties.

That is, the present invention also provides a method for producing a polyimide-based film comprising applying and curing a polyimide-based solution according to the present invention on one side of a substrate, followed by separation 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 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 polyimide-based solution 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 generally used as a binder, a solvent, a crosslinking agent, an initiator, a dispersant plasticizer, a viscosity modifier, an ultraviolet absorber, a photosensitive monomer or a sensitizer used for forming a polyimide- As shown in FIG.

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, 3 to 30 minutes.

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 350 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 as well as high transparency by including the polyimide of formula (1), and exhibits isotropy. As a result, the polyimide-based film is useful as a substrate for an OLED or an LCD, an electronic paper, a solar cell, or the like which requires high transparency, excellent heat resistance, mechanical strength, and isotropy.

More specifically, the polyimide-based film preferably has a coefficient of thermal expansion (CTE) at 280 ° C. of about 70 ppm / K or less, or about 65 ppm / K or less, or about 1 to 63 ppm / Based film.

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 120 MPa, or about 85 to 120 MPa, and a maximum elongation of about 10 to 100 MPa %, Or about 10 to 45%, based on the total weight of the film.

The polyimide-based film may have an in-plane retardation (R _in ) of about 0.05 to 1 nm, a retardation value (R _th ) in the thickness direction of about 100 nm or less, or an in-plane retardation value (R _in ) nm and a retardation value (R _th ) in the thickness direction of 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.

Example 1

18 g of 4,4'-oxydiphthalic anhydride (ODPA) was dissolved in 45 g of diethylformamide (DEF) over 20 minutes under a nitrogen atmosphere. The resulting ODPA / DEF solution was prepared by dissolving 18.5 g of 2,2'-bis (trifluoromethyl) benzidine (TFMB) as a diamine compound in 45 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 18 wt% so that the viscosity of the reaction solution became 5,000 cP and then uniformly mixed for 24 hours to prepare a polyamic acid solution (polyimide precursor solution).

A polyimide precursor solution was prepared in the same manner as the above-mentioned method except that the compounds shown in the following Table 1 were used as acid dianhydrides and diamine compounds for preparing polyamic acid.

Comparative Examples 1 to 4

A polyamic acid solution was prepared by the same method as in Example 1 except that the compounds shown in the following Table 1 were used as the acid dianhydride and the diamine compound for preparing the polyamic acid, and the solvent was changed.

Experimental Example 1

The prepared polyimide precursor solution was spin-coated on a glass substrate to a thickness of 20 microns and then allowed to stand in an atmosphere of 70% humidity at 30 DEG C for 30 minutes. Thereafter, using a hazemeter (Hazemeter: NIPPON DENSHOKU, NDH5000SP) The haze was measured, and the results are shown in Table 1. In the following table, the English abbreviations have the following meanings:

ODPA: 4,4'-oxydiphthalic anhydride

aODPA: 2,3,3 ', 4'-oxydiphthalic anhydride

TFMB: 2,2'-bis (trifluoromethyl) benzidine

HFBAPP: 2,2-Bis [4 - (- aminophenoxy) phenyl] hexafluoropropane

BPDA: 3,3 ', 4,4'-Biphenyltetracarboxylic dianhydride

aBPDA: 2,3,3 ', 4'-Biphenyltetracarboxylic dianhydride

PMDA: Pyromellitic Anhydride

PMDA-H: 1,2,4,5-cyclohexanetetracarboxylic dianhydride

6FDA: 4,4 '- (Hexafluoroisopropylidene) diphthalic anhydride

PDA: para-phenylenediamine

m-PDA: meta-phenylenediamine

DEF: diethylformamide

DMAc: dimethylacetamide

DMF: dimethylformamide

NMP: N-methyl-2-pyrrolidone

EQ-M100: Idemitsu Kosan Co., Ltd. Priests

exam
No. Anhydrous / diamine Haze (%) Example 1
DEF Comparative Example 1
DMAc Comparative Example 2
DMF Comparative Example 3
NMP Comparative Example 4
EQ-M100 One ODPA / TFMB 0.6 75 74 85 47 2 ODPA / HFBAPP 0.4 50 60 70 30 3 BPDA / TFMB 0.5 52 63 84 35 4 aBPDA / TFMB 0.4 67 61 78 41 5 aODPA / TFMB 0.6 86 87 87 46 6 PMDA-H / TFMB 0.4 50 60 70 30 7 PMDA-H / HFBAPP 0.5 63 78 79 35 8 6FDA / TFMB 0.5 72 76 87 43 9 6FDA / PDA 0.4 50 60 70 30 10 6FDA / m-PDA 0.6 52 63 84 35

1 is a photograph of a polyamic acid solution of Test No. 8 (6FDA / TFMB) taken 30 minutes after substrate coating.

As can be seen from Table 1 and FIG. 1, the polyamic acid solution prepared using the solvent according to the present invention shows remarkably improved whitening even after 30 minutes of coating.

Experimental Example 2

The glass substrate coated with the polyimide precursor solution in Experimental Example 1 was placed in an oven and heated at a rate of 2 DEG C / min. After heating at 80 DEG C for 15 minutes, at 150 DEG C for 30 minutes, at 220 DEG C for 30 minutes, And the curing 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.

Film properties such as transmittance, yellowing degree, retardation value, glass transition temperature, and thermal expansion coefficient were measured for each of the polyimide-based films prepared as described below.

Specifically, the transmittance of the polyimide-based film was measured by a transmittance meter (model name: HR-100, manufactured by Murakami Color Research Laboratory) according to JIS K 7105.

Yellowness Index (YI) was measured using a color difference meter (Color Eye 7000A).

The retardation in the plane direction (Rin) and the retardation in the thickness direction (Rth) of the film were measured using Axoscan. The thickness of the film was measured by cutting the film to a certain size. Then, the thickness was measured while correcting the retardation value in the C-plate direction in order to compensate the retardation value by measuring the phase difference with the Axoscan. The refractive index at this time was measured by inputting the refractive index of the polyimide to be measured.

The glass transition temperature (Tg) and the thermal expansion coefficient (CTE) of the film were measured using Q400 manufactured by TA Corporation. 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 to 0.02 N and the measurement starting temperature was heated to 350 캜 at a rate of 5 캜 at 30 캜 to measure a linear thermal expansion coefficient of the polyimide film as an average value in the range of 300 to 350 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.

Test Film No. Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 DEF  DMAc DMF NMP EQ-M100 LogP (25 캜) 0.05 -0.75 -1.01 -0.28 -0.74 thickness
(mm) 10.9 10.6 10.8 10.7 10.6 Transmittance
(%) T ₅₅₅ 89.9 89.6 89.4 88.4 88.3 Tg (占 폚) 300 300 300 300 300 CTE
(ppm / K, ~ 250 < 0 > C) 50 53 51 50 54

As shown in Table 2, the polyimide film prepared using the polyamic acid solution according to the present invention is an isotropic film having excellent transparency and high heat resistance and mechanical properties.

In the case of the comparative example, the physical properties of the resultant film are not different, but as shown in Table 1, the haze of the polyamic acid solution coating is high, which means that the polyamic acid meets the water and the flocculation phenomenon occurs due to the formation of the salt. Therefore, it can be seen that the film made of the solution of the comparative example has a rough surface.

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 (17)

A polyimide-based solution having a haze of 1% or less after being coated on a substrate and left for 30 minutes at 30 ° C and 70% humidity, comprising a polyimide having a structure represented by the following Chemical Formula 1 or a polyamic acid represented by Chemical Formula 2:
[Chemical Formula 1]

(2)

In Formula 1,
X is a tetravalent organic group selected from the group consisting of aromatic, alicyclic, and aliphatic tetravalent organic groups derived from an acid dianhydride,
And Y comprises a divalent organic group selected from the group consisting of aromatic, alicyclic and aliphatic divalent organic groups derived from diamines. The method according to claim 1,
Wherein the solvent has a distribution coefficient (LogP value) at 25 DEG C of a positive number. The polyimide-based solution according to claim 2, 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. The method according to claim 1,
Wherein X is a tetravalent organic group having a fluoro atom-containing substituent. The method according to claim 1,
And Y is a divalent organic group having a fluorine atom-containing substituent. The method according to claim 1,
Wherein the polyimide-based solution has a solids content of 10 wt% or more and 25 wt% or less based on the total weight of the solution. The method according to claim 1,
Based solution is a polyimide-based solution having a viscosity of not less than 2,000 cP and not more than 10,000 cP measured at 25 캜 by a Brookfield rotational viscometer. The method according to claim 1,
Wherein the polyimide has a weight average molecular weight of 40,000 or more. 12. A method for producing a polyimide-based film, comprising applying the polyimide-based solution according to any one of claims 1 to 11 to one surface of a substrate, curing the substrate, and then separating the solution from the substrate. A polyimide-based film produced by the method of claim 12. 14. The method of claim 13,
Wherein the polyimide has a glass transition temperature of 250 캜 or more and a transmittance of 85% or more at a wavelength of 380 to 760 nm in a film thickness range of 10 to 30 탆. 14. The method of claim 13,
And a thermal expansion coefficient (CTE) at 250 占 폚 of 70 ppm / K or less. 14. A display substrate comprising the polyimide-based film of claim 13. 14. An element comprising a polyimide-based film according to claim 13.

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