Patent Description:
Generally, a polyimide (PI) film is obtained by shaping a polyimide resin into a film. The polyimide resin is a highly heat-resistant resin which is prepared by performing solution polymerization of aromatic dianhydride and aromatic diamine or aromatic diisocyanate to prepare a polyamic acid derivative and then performing imidization by ring-closing dehydration at a high temperature. Having excellent mechanical, heat resistance, and electrical insulation properties, the polyimide film is used in a wide range of electronic materials such as semiconductor insulating films, electrode-protective films of TFT-LCDs, and substrates for flexible printed wiring circuits.

Polyimide resins, however, are usually colored brown and yellow due to a high aromatic ring density, so that transmittance in a visible ray region is low and the resins exhibit a yellowish color. Accordingly, light transmittance is reduced and birefringence is high, which makes it difficult to use the polyimide resins as optical members.

In order to solve the above-described limitation, attempts have been made to perform polymerization using purification of monomers and solvents, but the improvement in transmittance was not significant. With respect thereto, in <CIT>, the transparency and hue are improved when the resin is in a solution or in a film form using a method using an aliphatic cyclic dianhydride component instead of aromatic dianhydride. However, this was only an improvement of the purification method, and there remains a limitation in the ultimate increase in transmittance. Accordingly, high transmittance could not be achieved, but the thermal and mechanical deterioration resulted.

Further, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, and <CIT> and <CIT> disclose a novel structure of polyimide having improved transmittance and color transparency while thermal properties are not significantly reduced using aromatic dianhydride and aromatic diamine monomers having a substituent group such as -CF<NUM> or having a bent structure in which connection to a m-position instead of a p-position occurs due to a connection group such as - O-, -SO<NUM>-, or CH<NUM>-. However, this has been found to be insufficient for use as materials for display devices such as OLEDs, TFT-LCDs, and flexible displays due to limitations in terms of mechanical properties, heat resistance, and birefringence.

Polyimide films and methods for manufacturing polyimide films are disclosed in <CIT>, <CIT>, <CIT> and <CIT>.

Accordingly, the present invention is intended to provide a polyamide-imide precursor for forming a colorless and transparent film having low birefringence and excellent mechanical properties and heat resistance. In addition, the present invention is intended to provide a polyamide-imide film, manufactured by imidizing the polyamide-imide precursor, and an image display device including the polyamide-imide film.

Therefore, the present invention provides a polyamide-imide film which is manufactured by imidizing a polyamide-imide precursor in accordance with the appended claims.

Moreover, the present invention further provides an image display device including the polyamide-imide film of the present invention.

When the polyamide-imide precursor disclosed herein is imidized, it is possible to form a colorless and transparent film having low birefringence and excellent mechanical properties and heat resistance. Particularly, the polyamide-imide film manufactured according to the present invention may be useful for various fields such as a semiconductor insulating film, a TFT-LCD insulating film, a passivation film, a liquid crystal alignment film, an optical communication material, a protective film for a solar cell, and a flexible display substrate.

<FIG> is a graph showing a dimension change of an example of a polyimide film of the present invention (based on a film thickness of <NUM>) when repeatedly measured one to three times in a section at <NUM> to <NUM> using a thermomechanical analysis method (TMA-method).

The present invention provides a polyamide-imide precursor which consists of, in the molecular structure thereof, a first block, obtained by copolymerizing monomers including dianhydride and diamine, and a second block, obtained by copolymerizing monomers including an aromatic dicarbonyl compound and aromatic diamine, as specified in the appended claims. The dianhydride is selected from biphenyltetracarboxylic acid dianhydride (BPDA) and <NUM>-bis(<NUM>,<NUM>-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), and the diamine is bistrifluoromethylbenzidine (TFDB).

To be more specific, the present invention provides a polyamide-imide precursor which consists of, in a molecular structure thereof, a first block, obtained by copolymerizing dianhydride which is selected from biphenyltetracarboxylic acid dianhydride (BPDA) and <NUM>-bis(<NUM>,<NUM>-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) with bistrifluoromethylbenzidine (TFDB), and a second block obtained by copolymerizing an aromatic dicarbonyl compound with aromatic diamine.

When the polyamide-imide precursor disclosed herein is formed into a film for use as a substrate or a protective layer of an image display device, the polyamide-imide precursor is obtained by polymerization which is performed so that both the first block including an imide bond and the second block including an amide bond are present in the molecular structure thereof, thus ensuring excellent thermal and mechanical properties as well as excellent optical properties. That is, the mechanical properties, which may be poor when the precursor is composed only of the imide structure, may be improved using the second block including the amide bond, thereby ultimately improving thermal stability, mechanical properties, low birefringence, and optical characteristics in a balanced manner.

In the present invention, bistrifluoromethyl benzidine (TFDB) is used as the diamine for forming the first block, thus improving thermal stability and optical characteristics, and <NUM>-bis(<NUM>,<NUM>-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and biphenyltetracarboxylic acid dianhydride (BPDA) is used as the dianhydride, thus improving birefringence and ensuring heat resistance.

The dianhydride for forming the first block is selected from both kinds of dianhydrides, that is, both 6FDA and BPDA. Accordingly, in the first block, a polymer, in which TFDB and 6FDA are combined, and a polymer, in which TFDB and BPDA are combined, are separately included on the basis of separate repeating units.

In the present invention, among the monomers for forming the first block, BPDA and 6FDA as the dianhydride are included at a molar ratio of <NUM> : <NUM> to <NUM> : <NUM> so as to ensure the optical properties, to prevent the mechanical properties and the heat resistance from being reduced, and to exhibit excellent birefringence. When the ratio of BPDA is less than <NUM>/<NUM> of that of 6FDA, that is, when 6FDA is added in an amount which is more than <NUM> times that of BPDA, the heat resistance and the mechanical properties may not be ensured. On the other hand, when the ratio of BPDA is more than <NUM> times that of 6FDA, that is, when the ratio of 6FDA is less than <NUM>/<NUM> that of BPDA, the mechanical properties may be improved while the birefringence value increases, which is not desirable.

Further, in the present invention, the molar ratio of the first block and the second block is <NUM> : <NUM> to <NUM> : <NUM>. When the content of the second block is remarkably low, since the improvement in thermal stability and mechanical properties is insignificant, twisting and tearing phenomena may occur during a process for manufacturing displays. On the other hand, when the content of the second block is higher than the content of the first block, the thermal stability and the mechanical properties may be improved, but optical properties such as a yellow index or a transmittance may be reduced and birefringence may be increased, which makes the precursor difficult to apply to optical devices. However, the first block and the second block constitute a block copolymer.

In the present invention, the aromatic dicarbonyl compound for forming the second block is one or more selected from the group consisting of terephthaloyl chloride (p-terephthaloyl chloride, TPC), and iso-phthaloyl dichloride.

Further, the diamine for forming the second block is a diamine having one or more flexible groups selected from the group consisting of <NUM>,<NUM>-bis(<NUM>-(<NUM>-aminophenoxy)phenyl)hexafluoropropane (HFBAPP), bis(<NUM>-(<NUM>-minophenoxy)phenyl)sulfone (BAPSM), <NUM>,<NUM>'-diaminodiphenylsulfone (4DDS), and <NUM>,<NUM>'-diaminodiphenylsulfone (3DDS).

When the aromatic dicarbonyl compound is used, it may be easy to realize high thermal stability and mechanical properties, but birefringence may be high due to a benzene ring in the molecular structure. Accordingly, in order to prevent a reduction in birefringence caused by the second block in the present invention, preferably, the diamine has a molecular structure including a flexible group. More preferably, the diamine is one or more selected from among bis(<NUM>-(<NUM>-aminophenoxy)phenyl)sulfone (BAPSM), <NUM>,<NUM>'-diaminodiphenylsulfone (4DDS), and <NUM>,<NUM>-bis(<NUM>-(<NUM>-aminophenoxy)phenyl)hexafluoropropane (HFBAPP). Particularly, the diamine, such as BAPSM, having a long flexible group and a substituent group, which is present at a meta position, may exhibit the excellent birefringence.

In the present invention, the polyamide-imide precursor consists of, in the molecular structure thereof, the first block, obtained by copolymerizing the dianhydride selected from biphenyltetracarboxylic acid dianhydride (BPDA) and <NUM>-bis(<NUM>,<NUM>-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) with bistrifluoromethylbenzidine (TFDB), and the second block, obtained by copolymerizing the aromatic dicarbonyl compound with the aromatic diamine using polymerization of the monomers. The polyamide-imide precursor preferably has a a weight average molecular weight of <NUM>,<NUM> to <NUM>,<NUM>, measured using GPC (gel permeation chromatography), and a viscosity of <NUM>-<NUM> Pa·s (<NUM> to <NUM> poise).

Meanwhile, the present invention provides a polyamide-imide film manufactured by imidizing the polyamide-imide precursor. In the embodiment of the present invention, in order to manufacture the polyamide-imide resin or the polyamide-imide film using the polyamide-imide precursor, the following imidization step as described in the appended claims are carried out.

First, a polyamide-imide precursor solution is manufactured by copolymerizing <aromatic dianhydride> and <aromatic dicarbonyl compound and diamine> satisfying the above-described conditions of the present invention at an equivalent ratio of <NUM> : <NUM>. The polymerization reaction condition is not particularly limited, but the polymerization reaction may be preferably performed in an inert atmosphere such as nitrogen or argon at -<NUM> to <NUM> for <NUM> to <NUM> hours.

A solvent may be used for the solution polymerization reaction of the monomers. The solvent is not particularly limited as long as it is a known reaction solvent, but one or more polar solvents selected from among m-cresol, N-methyl-<NUM>-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), acetone, and ethyl acetate may be preferably used. In addition, a low-boiling-point solution, such as tetrahydrofuran (THF) and chloroform, or a low-absorbency solvent, such as γ-butyrolactone, may be used.

Further, the content of the solvent is not particularly limited. However, in order to obtain the appropriate molecular weight and viscosity of the polyamide-imide precursor solution, the content of the solvent may be preferably <NUM> to <NUM> wt%, and more preferably <NUM> to <NUM> wt%, based on the total content of the polyamide-imide precursor solution.

Subsequently, a known imidization method may be appropriately selected to imidize the obtained polyamide-imide precursor solution. For example, a thermal imidization method or a chemical imidization method may be applied, or a thermal imidization method and a chemical imidization method may be applied in combination.

In the chemical imidization method, a dehydrating agent, which is represented by acid anhydride such as acetic anhydride, and an imidization catalyst, which is represented by tertiary amines such as isoquinoline, β-picoline, and pyridine, are added to the polyimide-imide precursor solution to perform a reaction. In the thermal imidization method, the polyamide-imide precursor solution is slowly heated at a temperature range of <NUM> to <NUM> for <NUM> to <NUM> hours to perform a reaction.

In the embodiment of the present invention, a complex imidization method in which the thermal imidization method and the chemical imidization method are used in combination may be applied as an example of a method of manufacturing the polyamide-imide film. To be more specific, the complex imidization method may be performed through a series of processes. In the processes, the dehydrating agent and the imidization catalyst are added to the polyamide-imide precursor solution to be cast on a support, and are then heated to <NUM> to <NUM>, and preferably <NUM> to <NUM>, to be activated. The resulting substance is partially cured and dried, followed by heating at <NUM> to <NUM> for <NUM> to <NUM> seconds.

Further, in the embodiment of the present invention, the obtained polyamide-imide precursor solution may be imidized, and the imidized solution may be added to a second solvent, followed by precipitation, filtration, and drying to thus obtain a polyamide-imide resin solid. The obtained polyamide-imide resin solid may be dissolved in a first solvent for film formation, thereby manufacturing a polyamide-imide film. As for the drying conditions after the polyamide-imide resin solid is filtered, preferably, the temperature is <NUM> to <NUM> and the time is <NUM> to <NUM> hours in consideration of the boiling point of the second solvent. Casting may be performed and the temperature may be slowly increased at a temperature range of <NUM> to <NUM> for <NUM> minutes to <NUM> hours, thereby achieving the film formation process.

Further, the first solvent may be the same as the solvent used during the polymerization of the polyamide-imide precursor solution. As the second solvent, a solvent having a polarity lower than that of the first solvent, that is, one or more selected from among water, alcohols, ethers, and ketones, may be used in order to obtain the polyamide-imide resin solid. The content of the second solvent is not particularly limited, but is preferably <NUM> to <NUM> times by weight based on the weight of the polyamide-imide precursor solution.

In the present invention, the obtained polyamide-imide film may be additionally heat-treated once more in order to eliminate the thermal history and the residual stress remaining in the film. The temperature of the additional heat treatment process is preferably <NUM> to <NUM> and the heat treatment time is preferably <NUM> minutes to <NUM> hours. The residual volatile content of the heat-treated film may be <NUM>% or less, and preferably <NUM>% or less. As a result, the heat-treated film ultimately exhibits very stable thermal properties.

In the present invention, the thickness of the polyamide-imide film is not particularly limited, but is preferably in the range of <NUM> to <NUM>, and more preferably <NUM> to <NUM>.

The polyamide-imide film according to the present invention exhibits optical properties including a birefringence (n) of <NUM> or less, preferably <NUM> or less, and more preferably <NUM> or less which is defined using TE (transverse electric)-TM (transverse magnetic) based on a film thickness of <NUM> to <NUM>, a transmittance of <NUM>% or more, and preferably <NUM>% or more which is measured at <NUM>, and a yellow index of <NUM> or less, preferably <NUM> or less, and more preferably <NUM> or less thus being useful for an optical device such as a substrate or a protective layer of a display.

Further, the polyamide-imide film according to the present invention may have a coefficient of linear thermal expansion (CTE) of <NUM> ppm/°C or less, preferably <NUM> ppm/°C or less, and more preferably <NUM> ppm/°C or less which is repeatedly measured twice at <NUM> to <NUM> using a thermomechanical analysis method (TMA method) based on a film thickness of <NUM> to <NUM>, and has a dimension change difference (ΔDC) of <NUM> or less, preferably <NUM> or less, more preferably <NUM> or less, and more preferably <NUM> or less which is defined by a difference (|A-B|) between a minimum value on a first heat-increasing curve (a dimension change value measured at <NUM>, A) and a minimum value on a cooling curve (a dimension change value measured at <NUM>, B) when repeatedly measured one to three times in a section at <NUM> to <NUM> using a thermomechanical analysis method (TMA-method) based on <NUM> to <NUM>.

Further, since an elongation at break measured based on ASTM D882 (a film thickness of <NUM> to <NUM>) is <NUM>% or more, and preferably <NUM>% or more bending or deformation does not easily occur even under severe process conditions or sudden temperature change during the manufacture of displays. Accordingly, excellent yield may be exhibited.

Further, since the above-mentioned polyimide film is included in the present invention, it is possible to provide an image display device having excellent optical and physical properties and high manufacturing yield.

A better understanding of the present invention may be obtained through the following Examples which are set forth to illustrate, but are not to be construed to limit the present invention.

In a <NUM> reactor which was equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller, and a condenser, <NUM> of N-methyl-<NUM>-pyrrolidone (NMP) was charged while passing nitrogen therethrough, and <NUM> (<NUM> mol) of bistrifluoromethylbenzidine (TFDB) was dissolved. <NUM> (<NUM> mol) of biphenyltetracarboxylic acid dianhydride (BPDA) was reacted therewith for <NUM> hour. Subsequently, <NUM> (<NUM> mol) of <NUM>-bis(<NUM>,<NUM>-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) was added and reacted for <NUM> hours, and then <NUM> (<NUM> mol) of <NUM>,<NUM>-bis(<NUM>-(<NUM>-aminophenoxy)phenyl)hexafluoropropane (HFBAPP) was added and dissolved for <NUM> hour. After the temperature of the solution was maintained at <NUM> or less, <NUM> (<NUM> mol) of propylene oxide was added, and then <NUM> (<NUM> mol) of terephthaloyl chloride (TPC) was added and reacted for <NUM> hours, thus obtaining a polyamide-imide precursor solution having a solid concentration of <NUM> wt% and a viscosity of <NUM> Pa·s (<NUM> poise).

After the completion of the reaction, the obtained solution was applied on a stainless steel plate, cast to <NUM>, dried in hot air at <NUM> for <NUM> minutes, at <NUM> for <NUM> minutes, and at <NUM> for <NUM> minutes, slowly cooled, and separated from the plate, thus manufacturing a polyamide-imide film having a thickness of <NUM>.

In a <NUM> reactor which was equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller, and a condenser, <NUM> of N-methyl-<NUM>-pyrrolidone (NMP) was charged while passing nitrogen therethrough, and <NUM> (<NUM> mol) of TFDB was dissolved. <NUM> (<NUM> mol) of BPDA was reacted therewith for <NUM> hour. Subsequently, <NUM> (<NUM> mol) of 6FDA was added and reacted for <NUM> hours, and then <NUM> (<NUM> mol) of HFBAPP was added and dissolved for <NUM> hour. After the temperature of the solution was maintained at <NUM> or less, <NUM> (<NUM> mol) of propylene oxide was added, and then <NUM> (<NUM> mol) of TPC was added and reacted for <NUM> hours, thus obtaining a polyamide-imide precursor solution having a solid concentration of <NUM> wt% and a viscosity of <NUM> Pa·s (<NUM> poise).

Subsequently, a polyamide-imide film was manufactured according to the same procedure as in Example <NUM>.

In a <NUM> reactor which was equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller, and a condenser, <NUM> of N-methyl-<NUM>-pyrrolidone (NMP) was charged while passing nitrogen therethrough, and <NUM> (<NUM> mol) of TFDB was dissolved. <NUM> (<NUM> mol) of BPDA was reacted therewith for <NUM> hour. Subsequently, <NUM> (<NUM> mol) of 6FDA was added and reacted for <NUM> hours, and then <NUM> (<NUM> mol) of HFBAPP was added and dissolved for <NUM> hour. After the temperature of the solution was maintained at <NUM> or less, <NUM> (<NUM> mol) of propylene oxide was added, and then <NUM> (<NUM> mol) of TPC was added and reacted for <NUM> hours, thus obtaining a polyamide-imide precursor solution having a solid concentration of <NUM> wt% and a viscosity of <NUM><NUM> Pa·s (<NUM> poise).

In a <NUM> reactor which was equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller, and a condenser, <NUM> of N-methyl-<NUM>-pyrrolidone (NMP) was charged while passing nitrogen therethrough, and <NUM> (<NUM> mol) of TFDB was dissolved. <NUM> (<NUM> mol) of BPDA was reacted therewith for <NUM> hour. Subsequently, <NUM> (<NUM> mol) of 6FDA was added and reacted for <NUM> hours, and then <NUM> (<NUM> mol) of HFBAPP was added and dissolved for <NUM> hour. After the temperature of the solution was maintained at <NUM> or less, <NUM> (<NUM> mol) of propylene oxide was added, and then <NUM> (<NUM> mol) of iso-phthaloyl dichloride (IPC) was added and reacted for <NUM> hours, thus obtaining a polyamide-imide precursor solution having a solid concentration of <NUM> wt% and a viscosity of <NUM> poise.

In a <NUM> reactor which was equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller, and a condenser, <NUM> of N-methyl-<NUM>-pyrrolidone (NMP) was charged while passing nitrogen therethrough, and <NUM> (<NUM> mol) of TFDB was dissolved. <NUM> (<NUM> mol) of BPDA was reacted therewith for <NUM> hour. Subsequently, <NUM> (<NUM> mol) of 6FDA was added and reacted for <NUM> hours, and then <NUM> (<NUM> mol) of HFBAPP was added and dissolved for <NUM> hour. After the temperature of the solution was maintained at <NUM> or less, <NUM> (<NUM> mol) of propylene oxide was added, and then <NUM> (<NUM> mol) of TPC was added and reacted for <NUM> hours, thus obtaining a polyamide-imide precursor solution having a solid concentration of <NUM> wt% and a viscosity of <NUM> Pa·s (<NUM> poise).

In a <NUM> reactor which was equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller, and a condenser, <NUM> of N-methyl-<NUM>-pyrrolidone (NMP) was charged while passing nitrogen therethrough, and <NUM> (<NUM> mol) of TFDB was dissolved. <NUM> (<NUM> mol) of BPDA was reacted therewith for <NUM> hour. Subsequently, <NUM> (<NUM> mol) of 6FDA was added and reacted for <NUM> hours, and then <NUM> (<NUM> mol) of bis(<NUM>-(<NUM>-aminophenoxy)phenyl)sulfone (BAPSM) was added and dissolved for <NUM> hour. After the temperature of the solution was maintained at <NUM> or less, <NUM> (<NUM> mol) of propylene oxide was added, and then <NUM> (<NUM> mol) of TPC was added and reacted for <NUM> hours, thus obtaining a polyamide-imide precursor solution having a solid concentration of <NUM> wt% and a viscosity of <NUM> Pa·s (<NUM> poise).

In a <NUM> reactor which was equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller, and a condenser, <NUM> of N-methyl-<NUM>-pyrrolidone (NMP) was charged while passing nitrogen therethrough, and <NUM> (<NUM> mol) of TFDB was dissolved. <NUM> (<NUM> mol) of BPDA was reacted therewith for <NUM> hour. Subsequently, <NUM> (<NUM> mol) of 6FDA was added and reacted for <NUM> hours, and then <NUM> (<NUM> mol) of <NUM>,<NUM>'-diaminodiphenylsulfone (4DDS) was added and dissolved for <NUM> hour. After the temperature of the solution was maintained at <NUM> or less, <NUM> (<NUM> mol) of propylene oxide was added, and then <NUM> (<NUM> mol) of TPC was added and reacted for <NUM> hours, thus obtaining a polyamide-imide precursor solution having a solid concentration of <NUM> wt% and a viscosity of <NUM> Pa·s (<NUM> poise).

In a <NUM> reactor which was equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller, and a condenser, <NUM> of N-methyl-<NUM>-pyrrolidone (NMP) was charged while passing nitrogen therethrough, and <NUM> (<NUM> mol) of HFBAPP was added and dissolved. After the temperature of the solution was maintained at <NUM> or less, <NUM> (<NUM> mol) of propylene oxide was added, and then <NUM> (<NUM> mol) of TPC was added and reacted for <NUM> hours, thus obtaining a polyamide-imide precursor solution having a solid concentration of <NUM> wt% and a viscosity of <NUM> Pa·s (<NUM> poise).

In a <NUM> reactor which was equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller, and a condenser, <NUM> of N-methyl-<NUM>-pyrrolidone (NMP) was charged while passing nitrogen therethrough, and <NUM> (<NUM> mol) of HFBAPP was added and dissolved. After the temperature of the solution was maintained at <NUM> or less, <NUM> (<NUM> mol) of propylene oxide was added, and then <NUM> (<NUM> mol) of IPC was added and reacted for <NUM> hours, thus obtaining a polyamide-imide precursor solution having a solid concentration of <NUM> wt% and a viscosity of <NUM> Pa·s (<NUM> poise).

In a <NUM> reactor which was equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller, and a condenser, <NUM> of N-methyl-<NUM>-pyrrolidone (NMP) was charged while passing nitrogen therethrough, and <NUM> (<NUM> mol) of BAPSM was added and dissolved. After the temperature of the solution was maintained at <NUM> or less, <NUM> (<NUM> mol) of propylene oxide was added, and then <NUM> (<NUM> mol) of TPC was added and reacted for <NUM> hours, thus obtaining a polyamide-imide precursor solution having a solid concentration of <NUM> wt% and a viscosity of <NUM> Pa·s (<NUM> poise).

In a <NUM> reactor which was equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller, and a condenser, <NUM> of N-methyl-<NUM>-pyrrolidone (NMP) was charged while passing nitrogen therethrough, and <NUM> (<NUM> mol) of 4DDS was added and dissolved. After the temperature of the solution was maintained at <NUM> or less, <NUM> (<NUM> mol) of propylene oxide was added, and then <NUM> (<NUM> mol) of TPC was added and reacted for <NUM> hours, thus obtaining a polyamide-imide precursor solution having a solid concentration of <NUM> wt% and a viscosity of <NUM> Pa·s (<NUM> poise).

In a <NUM> reactor which was equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller, and a condenser, <NUM> of N-methyl-<NUM>-pyrrolidone (NMP) was charged while passing nitrogen therethrough, and <NUM> (<NUM> mol) of TFDB was added and dissolved. Subsequently, <NUM> (<NUM> mol) of BPDA was added and reacted for <NUM> hours, and then <NUM> (<NUM> mol) of 6FDA was added thereto and reacted for <NUM> hours, thus obtaining a polyamide-imide precursor solution having a solid concentration of <NUM> wt% and a viscosity of <NUM> Pa·s (<NUM> poise).

In a <NUM> reactor which was equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller, and a condenser, <NUM> of N-methyl-<NUM>-pyrrolidone (NMP) was charged while passing nitrogen therethrough, and <NUM> (<NUM> mol) of TFDB was added and dissolved. Subsequently, <NUM> (<NUM> mol) of BPDA was added and reacted for <NUM> hours, and then <NUM> (<NUM> mol) of 6FDA was added thereto and reacted for <NUM> hours, thus obtaining a polyamide-imide precursor solution having a solid concentration of <NUM> wt% and a viscosity of <NUM> Pa·s (<NUM> poise).

In a <NUM> reactor which was equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller, and a condenser, <NUM> of N-methyl-<NUM>-pyrrolidone (NMP) was charged while passing nitrogen therethrough, and <NUM> (<NUM> mol) of TFDB was dissolved. <NUM> (<NUM> mol) of 6FDA was added thereto and reacted for <NUM> hours, and then <NUM> (<NUM> mol) of HFBAPP was added and dissolved for <NUM> hour. After the temperature of the solution was maintained at <NUM> or less, <NUM> (<NUM> mol) of propylene oxide was added, and then <NUM> (<NUM> mol) of TPC was added and reacted for <NUM> hours, thus obtaining a polyamide-imide precursor solution having a solid concentration of <NUM> wt% and a viscosity of <NUM> Pa·s (<NUM> poise). Subsequently, a polyamide-imide film was manufactured according to the same procedure as in Example <NUM>.

In a <NUM> reactor which was equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller, and a condenser, <NUM> of N-methyl-<NUM>-pyrrolidone (NMP) was charged while passing nitrogen therethrough, and <NUM> (<NUM> mol) of TFDB was dissolved. <NUM> (<NUM> mol) of BPDA was added and reacted for <NUM> hours, and then <NUM> (<NUM> mol) of HFBAPP was added and dissolved for <NUM> hour. After the temperature of the solution was maintained at <NUM> or less, <NUM> (<NUM> mol) of propylene oxide was added, and then <NUM> (<NUM> mol) of TPC was added and reacted for <NUM> hours, thus obtaining a polyamide-imide precursor solution having a solid concentration of <NUM> wt% and a viscosity of <NUM> Pa·s (<NUM> poise). Subsequently, a polyamide-imide film was manufactured according to the same procedure as in Example <NUM>.

In a <NUM> reactor which was equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller, and a condenser, <NUM> of N-methyl-<NUM>-pyrrolidone (NMP) was charged while passing nitrogen therethrough, and <NUM> (<NUM> mol) of 4DDS was dissolved. <NUM> (<NUM> mol) of BPDA was added and reacted for <NUM> hours, and <NUM> (<NUM> mol) of 6FDA was added and then reacted for <NUM> hours. Subsequently, <NUM> (<NUM> mol) of HFBAPP was added and dissolved for <NUM> hour. After the temperature of the solution was maintained at <NUM> or less, <NUM> (<NUM> mol) of propylene oxide was added, and then <NUM> (<NUM> mol) of TPC was added and reacted for <NUM> hours, thus obtaining a polyamide-imide precursor solution having a solid concentration of <NUM> wt% and a viscosity of <NUM> Pa·s (<NUM> poise). Subsequently, a polyamide-imide film was manufactured according to the same procedure as in Example <NUM>.

In a <NUM> reactor which was equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller, and a condenser, <NUM> of N-methyl-<NUM>-pyrrolidone (NMP) was charged while passing nitrogen therethrough, and <NUM> (<NUM> mol) of TFDB and <NUM> (<NUM> mol) of 4DDS were dissolved. <NUM> (<NUM> mol) of BPDA and <NUM> (<NUM> mol) of 6FDA were added and dissolved. After the temperature of the solution was maintained at <NUM> or less, <NUM> (<NUM> mol) of propylene oxide was added, and then <NUM> (<NUM> mol) of TPC was added and reacted for <NUM> hours, thus obtaining a polyamide-imide precursor solution having a solid concentration of <NUM> wt% and a viscosity of <NUM> Pa·s (<NUM> poise). Subsequently, a polyamide-imide film was manufactured according to the same procedure as in Example <NUM>.

In a <NUM> reactor which was equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller, and a condenser, <NUM> of N-methyl-<NUM>-pyrrolidone (NMP) was charged while passing nitrogen therethrough, and <NUM> (<NUM> mol) of TFDB was dissolved. <NUM> (<NUM> mol) of BPDA and <NUM> (<NUM> mol) of 6FDA were added and dissolved. After the temperature of the solution was maintained at <NUM> or less, <NUM> (<NUM> mol) of propylene oxide was added, and then <NUM> (<NUM> mol) of TPC was added and reacted for <NUM> hours, thus obtaining a polyamide-imide precursor solution having a solid concentration of <NUM> wt% and a viscosity of <NUM> Pa·s (<NUM> poise). Subsequently, a polyamide-imide film was manufactured according to the same procedure as in Example <NUM>.

In a <NUM> reactor which was equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller, and a condenser, <NUM> of N-methyl-<NUM>-pyrrolidone (NMP) was charged while passing nitrogen therethrough, and <NUM> (<NUM> mol) of TFDB was dissolved. <NUM> (<NUM> mol) of BPDA was reacted therewith for <NUM> hours, and <NUM> (<NUM> mol) of 6FDA was added and reacted for <NUM> hours. Subsequently, <NUM> (<NUM> mol) of HFBAPP was added and dissolved for <NUM> hour. After the temperature of the solution was maintained at <NUM> or less, <NUM> (<NUM> mol) of propylene oxide was added, and then <NUM> (<NUM> mol) of TPC was added and reacted for <NUM> hours, thus obtaining a polyamide-imide precursor solution having a solid concentration of <NUM> wt% and a viscosity of <NUM> Pa·s (<NUM> poise). Subsequently, a polyamide-imide film was manufactured according to the same procedure as in Example <NUM>.

The physical properties of the polyamide-imide films manufactured in the Examples and the Comparative Examples were evaluated using the following methods. The results are described in Table <NUM> below.

From Tables <NUM> and <NUM>, it could be found that the transmittance was higher and the yellow index (YI) and the birefringence were lower in Examples <NUM> to <NUM> than in Comparative Examples <NUM> to <NUM> on average, so that Examples <NUM> to <NUM> were suitable for a colorless and transparent film having excellent birefringence. Further, in Examples <NUM> to <NUM>, the coefficient of thermal expansion was low, showing the excellent heat resistance.

Meanwhile, in Comparative Examples <NUM> to <NUM>, the transmittance and the yellow index were excellent but the mechanical properties (elongation at break %) and the dimension change were large. However, in Examples <NUM> to <NUM>, the transmittance was similar to that of Comparative Examples <NUM> to <NUM>, better birefringence was obtained, the dimensional change was small, and the elongation at break was excellent, which showed that Examples <NUM> to <NUM> had better mechanical properties than typical polyimide films. Particularly, it could be confirmed that the birefringence and CTE values were further improved when the diamine (BAPSM) having a long flexible group and a substituent group, which was present at a meta position, was added (Example <NUM>).

Further, in the case of Comparative Example <NUM> where BPDA was not included in the dianhydride, there was a limitation in improving the heat resistance and the elongation, and in the case of Comparative Example <NUM> where 6FDA was not included, the optical properties and the dimension change were reduced. When TFDB was not used as the diamine for forming the first block, the effect of improving the elongation at break was poor, as in Comparative Example <NUM>. In the case of Comparative Example <NUM>, where the first block and the second block were not formed in order and the polymerization was randomly performed, the birefringence and the transmittance were lower than in Example <NUM> where the polymerization was performed so that the blocks were separated.

Claim 1:
A polyamide-imide film which is manufactured by imidizing a polyamide-imide precursor, the method for manufacturing the polyamide-imide precursor consisting of the following steps (<NUM>) to (<NUM>):
(<NUM>) solution polymerizing bistrifluoromethylbenzidine (TFDB) and biphenyltetracarboxylic acid dianhydride (BPDA),
(<NUM>) adding to the solution of step (<NUM>) and solution polymerizing <NUM>-bis(<NUM>,<NUM>-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) to obtain a first block,
(<NUM>) adding to the solution of step (<NUM>) an aromatic diamine,
(<NUM>) adding Propylene oxide to the solution of step (<NUM>) and then adding an aromatic dicarbonyl compound to solution polymerizing to obtain a second block;
wherein the aromatic diamine is one or more selected from the group consisting of <NUM>,<NUM>-bis(<NUM>-(<NUM>-aminophenoxy)phenyl)hexafluoropropane (HFBAPP), bis(<NUM>-(<NUM>-minophenoxy)phenyl)sulfone (BAPSM), <NUM>,<NUM>'-diaminodiphenylsulfone (4DDS), and <NUM>,<NUM>'-diaminodiphenylsulfone (3DDS), and
wherein the aromatic dicarbonyl compound is one or more selected from the group consisting of terephthaloyl chloride (p-terephthaloyl chloride, TPC) and iso-phthaloyl dichloride, and
wherein a molar ratio of the Propylene oxide to the aromatic dicarbonyl compound is <NUM>:<NUM>, and
wherein a molar ratio of the first block to the second block is <NUM> : <NUM> to <NUM> : <NUM>, and
wherein a molar ratio of the TFDB to the aromatic diamine is <NUM> : <NUM> to <NUM> : <NUM>, and
wherein a molar ratio of the "BPDA and 6FDA" to the aromatic dicarbonyl compound is <NUM> : <NUM> to <NUM> : <NUM>, and
wherein a molar ratio of the BPDA to the 6FDA is <NUM> : <NUM> to <NUM> : <NUM>, and
wherein the polyimide film has an elongation at break of <NUM>% or more, which is measured based on ASTM D882 based on a film thickness of <NUM> to <NUM>, and
wherein a polyimide film has the dimension change difference ΔDC of <NUM> or less, which is defined by a difference |A-B| between a minimum value on a first heat increasing curve, a dimension change value measured at <NUM>, A, and a minimum value on a cooling curve, a dimension change value measured at <NUM>, B, when repeatedly measured one to three times in a section at <NUM> to <NUM> using a thermomechanical analysis method based on a film thickness of <NUM> to <NUM>.