KR101642563B1 - Retardation film comprising polyimide copolymer and display device comprising the same - Google Patents

Abstract

The present invention relates to a phase difference film comprising a polyimide copolymer containing a repeating unit represented by the formula (1), wherein the in-plane retardation value R _in calculated by converting the film thickness to 4 탆 is 100 nm or more.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a retardation film including a polyimide copolymer, and a display device including the retardation film.

The present invention relates to a retardation film comprising a polyimide copolymer and a display device including the same, and more particularly, to a retardation film which is excellent in transparency and adhesiveness and can exhibit a high retardation in a thin shape, And a display device.

Liquid crystal displays (LCDs) are widely used in televisions, monitors, and the like because they have lower power consumption, smaller volume, lighter weight and easier portability than cathode ray tubes. On the other hand, in such a liquid crystal display, a retardation film for compensating the optical anisotropy of the liquid crystal cell may be used to improve the viewing angle, contrast ratio, and the like.

As such a retardation film, a film in which a retardation is developed by stretching a polymer film formed by a liquid crystal film, a cycloolefin polymer (COP), a polycarbonate (PC) Has come. However, in the case of a liquid crystal film, liquid crystal, which is a main material, is very expensive, so that the manufacturing cost is high, and it is very difficult to orient the liquid crystal at the same angle with respect to the whole film. In addition, in the case of COP or PC film, since the orientation is low, the thickness of the film must be made as large as several tens of micrometers in order to exhibit a desired retardation, which is a problem in that it is not suitable for the slimming tendency of the device.

In order to solve such a problem, there have been attempts to fabricate a retardation film using a polyimide resin having a high orientation property and realizing a high retardation in a thin film.

However, it is difficult to form the polyimide resin itself into a film because the polyimide resin, which is commonly used, is low in solubility in an organic solvent. Therefore, after a varnish obtained by dissolving the polyimide precursor in a solvent is coated on a substrate, Lt; RTI ID = 0.0 > C < / RTI > to progress the imidization. However, this method has a problem in that resin shrinkage or stress is likely to occur during the high-temperature treatment process, and organic solution remains at the time of film formation, resulting in coloring or peeling. In addition, in this method, since the conversion ratio at which the precursor is converted into the imide is not generally high, unconverted polyamic acid remains in the film, and as a result, the mechanical and optical properties of the film deteriorate.

In order to solve such a problem, techniques for improving solubility in an organic solvent using an acid dianhydride or a specific structure of a dianhydride compound have been proposed. Japanese Patent Application Laid-Open No. 2008-280417 (Patent Document 1) discloses a polyimide resin containing a repeating unit derived from an acid dianhydride containing a cyclic bullet.

However, in the case of the film produced using the polyimide resin disclosed in Patent Document 1, the adhesive force with the polarizer adhesive is insufficient, so that the film is easily peeled off at the time of attaching the polarizer and is difficult to be commercialized. Since the mechanical properties are low, There is a problem that breakage is likely to occur in the process.

Disclosure of Invention Technical Problem [8] The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a retardation film excellent in adhesion to an adhesive for a polarizing plate and having mechanical properties to such an extent that high-

In one aspect, the present invention provides a retardation film comprising a polyimide copolymer containing a repeating unit represented by the following formula (1) and having an in-plane retardation value R _in calculated in terms of a film thickness of 4 탆, do.

[Chemical Formula 1]

In the above formula (1)

X ₁ is a quadrivalent organic group derived from an alicyclic or aromatic acid dianhydride containing an ester group or an ether group, X ₂ is a quadrivalent organic group derived from an acid dianhydride different from X ₁ , Q ₁ and Q ₂ B, c and d represent the molar ratios of the respective repeating units, wherein a + b + c + d = 1 and 0.1? A + b? 1 And 0? C + d? 0.9.

The polyimide copolymer preferably has a solubility of about 1% to about 60%, preferably about 5% to about 40%, more preferably about 10% to about 100% of an organic solvent having a boiling point of 80 ° C to 200 ° C at 25 ° C. To 30%, and the glass transition temperature is preferably about 170 캜 to 280 캜.

On the other hand, the retardation film of the present invention is not limited to this, but may have an average transmittance of 70% to 100% for light having a wavelength band of 380 nm to 760 nm at a thickness of 1 to 10 mu m, , A tensile strength of 50 MPa to 500 MPa, and a elongation at break of 10% to 200%.

In addition, the retardation film of the present invention may have an adhesive strength of 0.4 to 10 N / cm to the adhesive for a polarizing plate. At this time, the polarizing plate was prepared by attaching a retardation film to one side of the polarizing element using a polarizer adhesive, and then a polarizer sample having a width of 2 cm and a length of 8 cm was placed on the lower surface of a texture analyzer (XT-Plus, Stable Micro System) And the film was peeled off while applying a peel force of 90 degrees at a distance of 5 cm.

The retardation film of the present invention makes it possible to produce a retardation film having excellent optical properties and transparency by minimizing the residual organic solvent during film formation by using an organic solvent having a low boiling point.

In addition, the retardation film of the present invention is excellent in mechanical strength and can be stretched at a high temperature and a high magnification, and as a result, a high retardation can be realized as a thin film.

Further, the retardation film of the present invention is excellent in adhesion to an adhesive for a polarizing plate, and can be easily attached to a display panel or a polarizing plate.

First, the terms of the present invention will be described.

In this specification, the aliphatic chain means an aliphatic compound in the form of a straight chain or branched chain, and includes, but is not limited to, a saturated or unsaturated hydrocarbon having 1 to 20 carbon atoms, an alkoxy having 1 to 20 carbon atoms, Alkyl esters of 1 to 20 carbon atoms, alkyl ethers of 1 to 20 carbon atoms, thioalkyl of 1 to 20 carbon atoms, and the like. The aliphatic chain may include at least one substituent on the main chain and / or side chain, and the substituent may include, for example, a halogen, an oxygen, a sulfur, a nitrogen, a hydroxyl group, An alkyl group, a haloalkyl group, a nitro group, a cyano group, an ester group, an ether group, an amide group, an imide group, an alkoxy group or a combination thereof.

In the present specification, the aliphatic ring means an aliphatic compound in the form of a ring, which may be a monocyclic or polycyclic compound formed by condensation of two or more rings. For example, saturated aliphatic compounds having 3 to 20 carbon atoms such as cycloalkyl Or an unsaturated hydrocarbon ring. The substituent may include, but is not limited to, halogen, oxygen, sulfur, nitrogen, a hydroxyl group, a carboxy group, an alkyl group, a haloalkyl group, a nitro group, A cyano group, an ester group, an ether group, an amide group, an imide group, an alkoxy group, or a combination thereof.

In the present specification, the aromatic ring means an aromatic compound in the form of a ring, which may be a monocyclic or a polycyclic compound formed by condensation of two or more rings, and examples thereof include monocyclic aromatic rings having 6 to 20 carbon atoms such as phenyl and naphthalene Lt; / RTI > The aromatic ring may contain at least one or more substituents such as, but not limited to, halogen, oxygen, sulfur, nitrogen, hydroxyl, carboxyl, alkyl, haloalkyl, nitro, A cyano group, an ester group, an ether group, an amide group, an imide group, an alkoxy group, or a combination thereof.

In the present invention, when two or more rings are directly connected, it means that a ring is connected to a ring by a bond, such as biphenyl, bicyclohexyl and the like, It is, _{alkylene, -O-, -SO 2 - -S-,} -SO-, -C (= O) -, -C (= O) O-, -C (= O) NH-, -O [ CH ₂ CH ₂ O] _p - wherein p is an integer of 1 to 20, and the like.

In the present specification, the in-plane retardation value R _in means a value calculated through the following equation (1), and the thickness direction retardation value R _th means a value calculated through the following equation (2).

Equation (1): Rin = (n x -n y) · d

(2): Rth = (n _z -n _x ) · d

Where n _x is the refractive index of the slow axis in the film plane direction measured at a wavelength of 550 nm and n _y is the refractive index in the direction perpendicular to the film plane direction slow axis measured at a wavelength of 550 nm and n _z Is the refractive index in the film thickness direction measured at a wavelength of 550 nm. Further, d means the film thickness, and the retardation value converted to the film thickness of 4 mu m is a value calculated by d = 4000.

Hereinafter, the present invention will be described in more detail.

The inventors of the present invention have found that when a retardation film is produced using a polyimide copolymer prepared by reacting an alicyclic or aromatic acid anhydride containing an ester group or an ether group with a diamine compound, And thus the present invention has been completed.

More specifically, the retardation film of the present invention comprises a polyimide copolymer containing a repeating unit represented by the following formula (1), and has an in-plane retardation value R _in calculated as a film thickness of 4 탆 is 100 nm or more .

[Chemical Formula 1]

In the above formula (1)

X ₁ is a quadrivalent organic group derived from an alicyclic or aromatic acid dianhydride containing an ester group or an ether group, X ₂ is a quadrivalent organic group derived from an acid dianhydride different from X ₁ , Q ₁ and Q ₂ Are each independently a divalent organic group derived from a diamine.

A, b, c and d represent the molar ratios of the respective repeating units, wherein a + b + c + d = 1, 0.1? A + b? 1, and 0? C + d? 0.9. A + b and c + d may have appropriate values in a range that satisfies the numerical range. For example, 0.6? A + b? 0.9, 0.1? C + d? 0.4, or 0.1? a + b? 0.5, and 0.5? c + d? 0.9.

More specifically, a may be 0.1 to 1, b may be 0 to 0.5, c may be 0 to 1, d may be 0 to 1, preferably a is 0.1 to 0.9, b is 0.1 to 0.5, c is 0.1 to 0.8, and d may be 0.1 to 0.3. More preferably, a may be 0.1 to 0.5, b may be 0.1 to 0.3, c may be 0.5 to 0.8, and d may be 0.1 to 0.2.

First, the polyimide copolymer contained in the retardation film of the present invention will be described.

The polyimide copolymer used in the present invention includes a tetravalent organic group X ₁ derived from an aliphatic or aromatic acid dianhydride containing an ester group or an ether group.

As described above, the polyimide copolymer containing a tetravalent organic group derived from an acid dianhydride containing an ester group or an ether group has a high solubility in an organic solvent, especially an organic solvent having a low boiling point, It is not necessary to perform the high temperature treatment to imidize the precursor as in the conventional method. In addition, when the film is directly formed with the polyimide resin, the mechanical properties and the optical characteristics can be prevented from being lowered due to the low imidization ratio.

Preferably, X ₁ is a tetravalent organic group derived from an acid dianhydride represented by the following formula (2) or (3).

(2)

In the above formula (2)

A ₁ is an aliphatic ring or aromatic ring having 1 to 10 carbon atoms, B ₁ is a single bond; A substituted or unsubstituted aliphatic chain group; A substituted or unsubstituted aliphatic cyclic group; A substituted or unsubstituted aromatic ring group; Two or more aliphatic or aromatic ring groups connected either directly or via a bridging structure; Or a combination thereof.

(3)

In the above formula 3,

A ₂ is an aliphatic ring or aromatic ring having 1 to 10 carbon atoms, B ₂ is a single bond; A substituted or unsubstituted aliphatic chain group; A substituted or unsubstituted aliphatic cyclic group; A substituted or unsubstituted aromatic ring group; Two or more aliphatic or aromatic ring groups connected either directly or via a bridging structure; Or a combination thereof.

More specifically, X ₁ may be, but is not limited to, a tetravalent organic group derived from an acid dianhydride selected from the group consisting of compounds represented by Formula 4 below.

[Chemical Formula 4]

In Formula 4, B ₁ and B ₂ each independently represent a single bond; A substituted or unsubstituted aliphatic chain group; A substituted or unsubstituted aliphatic cyclic group; A substituted or unsubstituted aromatic ring group; Two or more aromatic or aliphatic ring groups linked directly or through a bridging structure; Or a combination thereof. Preferably, B ₁ and B ₂ each independently represent an alkylene group having 1 to 10 carbon atoms; A monocyclic or polycyclic cycloalkylene group having 6 to 20 carbon atoms; A monocyclic or polycyclic arylene group having 6 to 20 carbon atoms; Two or more cycloalkyl groups linked by an alkylene structure; Or two or more aryl groups connected by an alkylene structure, and more preferably a phenylene group, a naphthalene group, a fluorene group, a cyclohexylene group, a biphenyl group, a bicyclohexyl group, a tricyclodecanyl group or an alkylene structure Lt; RTI ID = 0.0 > cyclohexyl < / RTI >

Specific examples of the acid dianhydride which can be used in the present invention to derive the X < ₁ > However, the following compounds are only examples of the compounds usable in the present invention, but the present invention is not limited thereto.

(1) 5-isobenzofurancarboxylic acid, 1,3-dihydro-1,3-dioxo-, 1, 5-isobenzofurancarboxylic acid, dioxo-, 1,4-phenylenediyl ester),

(2) 5-isobenzofurancarboxylic acid, 1,3-dihydro-1,3-dioxo-, 1,3-phenylene dicarboxylic acid, dioxo-, 1,3-phenylenediyl ester),

(3) 5-isobenzofurancarboxylic acid, 1,3-dihydro-1,3-dioxo-, 1,4-cyclohexanedicarboxylic acid, 1,3-dihydro- dioxo-, 1,4-cyclohexanediyl ester),

(4) 5-isobenzofurancarboxylic acid, 1,3-dihydro-1,3-dioxo-, 1,3-cyclohexanedicarboxylic acid, dioxo-, 1,3-cyclohexanediyl ester),

(5) 5-isobenzofurancarboxylic acid, 1,3-dihydro-1,3-dioxo-, [1,1'-bicyclohexyl] -4,4'- 1,3-dihydro-1,3-dioxo-, [1,1'-bicyclohexyl] -4,4'-diyl ester),

(6) 5-isobenzofurancarboxylic acid, 1,3-dihydro-1,3-dioxo-, tricyclo [3.3.1.1] decane- 1,3-diyl ester dihydro-1,3-dioxo-, tricycle [3.3.1.1] decane-1,3-diyl ester)

(7) 5-isobenzofurancarboxylic acid, 1,3-dihydro-1,3-dioxo-, methylenedi-4,1-cyclohexyl dicyl ester , 3-dioxo-, methylenedio-4,1-cyclohexyldiyl ester),

(8) 5-isobenzofurancarboxylic acid, 1,3-dihydro-1,3-dioxo-, (1-methylethylidene) 1,3-dihydro-1,3-dioxo-, (1-methylethylidene) di-4,1-cyclohexyldiyl ester)

(9) 5-isobenzofurancarboxylic acid, 1,3-dihydro-1,3-dioxo-, 5-isobenzofurancarboxylic acid, 1,3-dihydro-1,3-dioxo -, 2,7-naphthalenediyl ester),

(10) isobenzofurancarboxylic acid, 1,3-dihydro-1,3-dioxo-, 2,6-naphthalenedicarboxylic acid, 1,3-dihydro-1,3-dioxo -, 2,6-naphthalenediyl ester),

(11) 5-isobenzofurancarboxylic acid, 1,3-dihydro-1,3-dioxo-, 1,5-naphthalenedicarboxylic acid, 1,3-dihydro- -, 1,5-naphthalenediyl ester),

(12) isobenzofurancarboxylic acid, 1,3-dihydro-1,3-dioxo-, 1,4-naphthalenedicarboxylic acid, 1,3-dihydro-1,3-dioxo -, 1,4-naphthalenediyl ester),

(13) 5-isobenzofurancarboxylic acid, 1,3-dihydro-1,3-dioxo-, 9H-fluorene-2,7- , 3-dioxo-, 9H-fluorene-2,7-diyl ester),

(14) ethylene glycol bis (4-trimellitic anhydride) ester,

(15) A liquid crystal composition comprising 1, 2, 4-benzenetricarboxylic acid, cyclic 1,2-anhydride, diester-, 4,4'-

(16) 4,4'-oxydiphthalic dianhydride,

(17) Synthesis of 2,2-bis [4- (2,3-dicarboxyphenoxy) phenyl] propanedialdehyde,

(18) 2,2-bis [4- (3,4-dicarboxyphenoxy) phenyl] propane dianhydride,

(19) Synthesis of 4,4 '- (3,4-dicarboxyphenoxy) diphenyl sulfide dianhydride,

(20) Synthesis of 1,1,1,3,3,3-hexafluoro-2,2-bis [4- (2,3-dicarboxyphenoxy) phenyl] propanedial hydride,

(21) 1,1,1,3,3,3-Hexafluoro-2,2-bis [4- (3,4-dicarboxyphenoxy) phenyl] propanedial hydride.

On the other hand, the polyimide copolymer used in the present invention, polyimide in order to control the thermal properties, a phase difference value, the mechanical properties and / or optical properties of the copolymer, the acid dianhydride that the X ₁ is induced (for convenience the first acid dianhydride 4 which is derived from the term water quot;) different kind of dianhydride (for convenience, the second dianhydride) may further include an organic group X _2.

For example, X ₂ is a substituted or unsubstituted aliphatic chain group; A substituted or unsubstituted aliphatic cyclic group; A substituted or unsubstituted aromatic ring group; A structure wherein two or more aromatic or aliphatic rings are linked directly or in a bridged structure; Or a tetravalent organic group derived from an acid dianhydride containing a combination thereof.

The second acid dianhydride used to derive X ₂ may be different from the first acid dianhydride, and the kind thereof is not particularly limited. That is, as the second acid dianhydride, various kinds of acid dianhydrides known in the art, such as an aliphatic acid dianhydride, an alicyclic dianhydride, an aromatic acid dianhydride, can be used without limitation, But not limited to, for example, 4,4'-oxydiphthalic dianhydride, 1,2,3,4-cyclobutane tetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxyl Cyclohexanetetracarboxylic dianhydride, cyclopropane tetracarboxylic dianhydride, 3,3 ', 4 < RTI ID = 0.0 > , 4'-benzophenone tetracarboxylic dianhydride, 3,4,9,10-perylene tetracarboxylic dianhydride, 4,4'-sulfonyldiphthalic dianhydride, 3,3 '4,4'-biphenyltetracarboxylate Naphthalene tetracarboxylic dianhydride, 1,2,5,6-naphthalene tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride, 2,3,5,6-pyridine tetracarboxylic dianhydride, M-terphenyl-3,3 ', 4,4'-tetracarboxylic dianhydride, p-terphenyl-3,3', 4,4'-tetracarboxylic dianhydride Rides, and mixtures thereof.

Next, in the above polyimide copolymer, Q ₁ and Q ₂ are each independently a divalent organic group derived from a diamine, preferably an aliphatic chain having 1 to 10 carbon atoms; 1 to 5 aromatic rings; 1 to 5 aliphatic rings; Ether group; An ester group; Or a combination thereof. ≪ / RTI > Here, Q ₁ and Q ₂ may be the same or different from each other.

The diamine compounds usable in the present invention are not particularly limited, and aromatic diamines, alicyclic diamines or aliphatic diamines generally used in the art can be used without limitation.

For example, Q ₁ and Q ₂ may each independently be a divalent organic group derived from a diamine selected from the group consisting of compounds represented by the following formula (5).

[Chemical Formula 5]

In the formula (5), each of R ₁ to R ₇ independently represents a substituted or unsubstituted aliphatic chain group; A substituted or unsubstituted aliphatic cyclic group; A substituted or unsubstituted aromatic ring group; Two or more aromatic or aliphatic ring groups linked directly or through a bridging structure; And R ₈ to R ₁₁ are each independently a C 1-10 alkyl group, a C 1-10 haloalkyl group or a hydroxy group, and q is an integer of 1-8.

Given such properties of the economy and the film, at least one of the Q ₁ and Q ₂ are, the from the [Formula 5] of 5 (e), 5 (f ) and 5 (h) the group consisting of the compounds represented by (Hereinafter, referred to as a first diamine for convenience). More preferably, Q ₁ may be a divalent organic group derived from a first diamine compound, more preferably Q ₁ And Q _{2 may} all be a divalent organic group derived from the first diamine compound.

More specifically, the first diamine compound may be at least one selected from the group consisting of 2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane, 4,4'-diaminodiphenyl ether, 4,4'-diaminobenzophenone, 4,4'-bis (4-aminophenylsulfonyl) diphenyl ether, 3,3'-dia Aminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl , 4,4'-methylenebis (cyclohexylamine), 3,3'-diaminobenzophenone, 4,4'-methylenebis (2-methylcyclohexylamine) And mixtures thereof, but are not limited thereto.

More specifically, at least one of Q ₁ and Q _{2 may} be at least one selected from the group consisting of the functional groups represented by the following formula (6), more preferably the above Q ₁ is represented by the following formula ], And still more preferably Q ₁ and Q ₂ may be at least one kind selected from the group consisting of functional groups represented by the following formula (6).

[Chemical Formula 6]

The [Formula 6] in, R ₁₂ is -0-, -CR ₁₃ R ₁₄ - (wherein, R ₁₃ and R ₁₄ each independently represent a hydrogen atom, a haloalkyl group having 1 to 10 carbon atoms and an alkyl group having 1 to 10 carbon atoms in the ( (= O) -, -C (= O) O-, -C (= O) NH-, -S-, -S0 -, -SO ₂ -, -O [CH ₂ CH ₂ O] _P - (wherein p is an integer of 1 to 20), a monocyclic or polycyclic cycloalkylene group having 6 to 19 carbon atoms (for example, cyclohexyl A silylene group), a monocyclic or polycyclic arylene group having 6 to 19 carbon atoms (e.g., a phenylene group, a naphthalene group, etc.), and combinations thereof.

The above Q ₁ and Q ₂ medium At least one of which may be a divalent organic group derived from an aromatic or alicyclic diamine compound (conveniently referred to as a second diamine) containing an ester group, an ether group or a combination thereof. For example, the second diamine may be at least one compound selected from the group consisting of compounds represented by 5 (a) to 5 (d) and 5 (g) in the following formula 5.

More specifically, the second diamine compound may be selected from the group consisting of 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2- , 1,1,3,3,3-hexafluoropropane, 1,3-bis (4-aminophenoxy) phenyl) benzene, 4,4'-bis (4-aminophenoxy) Bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (4-aminophenoxy) benzoyl] benzene, bis [4-aminophenoxy) phenyl] Phenyl] propane, 2,2-bis [4- (3-aminophenoxy) phenyl-1, , 1,1,3,3,3-hexafluoropropane, 1,3-bis (3-aminophenoxy) benzene, 4,4'-bis (3-aminophenoxy) biphenyl, bis [4- (3-aminophenoxy) phenyl] ketone, bis [4- (3-aminophenoxy) phenyl] sulfide, bis [4- Bis [4- (3-aminophenoxy) phenyl] ether, 4,4'-bis [3-aminothiophenoxy) diphenyl sulfone, ) Benzoyl] benzene, O, O'-bis (2-aminopropyl) polypropylene glycol, and mixtures thereof.

More specifically, Q ₁ and Q ₂ medium At least one of them may be at least one selected from the group consisting of functional groups represented by the following formula (7), more preferably Q ₂ is at least one selected from the group consisting of the functional groups represented by the following formula Or more.

(7)

In Formula (7), q is an integer of 1 to 8.

As described above, Q ₁ and Q ₂ Is derived from a second diamine compound containing an ester, an ether or a combination thereof, the solubility in a low-boiling solvent and the adhesive strength with an adhesive can be further improved.

The polyimide copolymer of the present invention having the above structure can be produced by a method of synthesizing a polyimide copolymer that is well known in the art and includes, but is not limited to, for example, a method in which a diamine compound is dissolved in an organic solvent Dissolving the polyimide precursor in an organic solvent, dissolving the polyimide precursor in the solution, adding an acid dianhydride to the resultant solution to cause a polymerization reaction to prepare a polyimide precursor, and polymerizing the polyimide precursor with a solution melt polymerization method, And then polymerized in the presence of a catalyst to directly prepare the polyimide copolymer without passing through the precursor polyamic acid.

The diamine compound and / or acid dianhydride may be used alone or in combination of two or more. When two or more diamine compounds and / or acid dianhydride are used as a reactant, the content ratio of each compound is Can be suitably adjusted in consideration of the ratio of the functional groups derived from the respective acid anhydrides and diamine compounds in the finally produced polyimide copolymer.

On the other hand, when the polyimide copolymer is produced through the polyamide precursor, the polymerization reaction can be carried out under anhydrous conditions. The temperature for the polymerization reaction of the polyimide precursor may be about 25 캜 to 50 캜, preferably about 40 캜 to 45 캜, and the temperature for solution melt polymerization is preferably 130 캜 to 200 캜, To 180 < 0 > C.

On the other hand, when the polyimide copolymer is directly produced from the reaction product, the catalyst is preferably a catalyst having a boiling point of 60 ° C to 100 ° C, for example, N, N-diethylmethylamine, N, Propylamine, N-methylpyrrolidine, pyrrolidine, and triethylamine. Preferably, the catalyst is contained in an amount of about 0.5 to 30 parts by weight based on 100 parts by weight of the sum of the contents of diamines and acid dianhydrides, and the polymerization temperature is preferably about 120 to 200 ° C .

Examples of the organic solvent used for preparing the polyimide copolymer include N, N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), N, N-dimethylformamide , N, N-diethylacetamide (DEAc), N, N-dimethylmethoxyacetamide, dimethylsulfoxide, pyridine, dimethylsulfone, hexamethylphosphoramide, tetra (2-methoxyethyl) ether, 1,2-bis (2-methoxyethyl) ether, 1,2-dimethoxyethane, 1,2-dimethoxyethane, (Ethylene glycol) methacrylate (PMGMA), gamma -butyrolactone (GBL), eqamide (Equamide® M100, Idemitsu Kosan Co., Ltd.) Ltd., Ltd.), water, and mixtures thereof.

The polyimide copolymer of the present invention produced by the above process may have a weight average molecular weight of 10,000 g / mol or more, more preferably 10,000 to 10,000 g / mol, . If the molecular weight of the polyimide copolymer is less than 10,000 g / mol, the mechanical properties may deteriorate.

The polyimide copolymer of the present invention preferably has a solubility of about 1% to about 60%, preferably about 5% to about 40%, more preferably about 5% to about 40%, at 25 ° C in an organic solvent having a boiling point of 80 ° C to 200 ° C And preferably about 10% to 30%. When the solubility in the low-boiling organic solvent is in the above range, excellent workability and coating property can be secured at the time of film-forming.

The polyimide copolymer of the present invention preferably has an imide conversion of 90% or more, and preferably 90% to 100% at the time of polymerization. In the case of the conventional method of producing a polyimide film by high temperature treatment after coating a solution of a polyamic acid precursor on a substrate, not only is there a process restriction due to the high temperature treatment, but also the conversion rate of the precursor into the polyimide is low, And optical characteristics are deteriorated, and reliability of the device is deteriorated. However, when the imide conversion ratio satisfies the above-described numerical value range, solubility in a solvent having a low boiling point is improved, so that not only a film can be formed using the polyimide resin itself, but a coating solvent having a low boiling point As a result, it is possible to produce a film even at a low process temperature, thereby increasing the degree of freedom in the process. Even if a film is produced at a low temperature, problems such as residual solvent are not generated, Deterioration of the characteristics can be prevented.

On the other hand, the polyimide copolymer of the present invention may have a glass transition temperature of about 170 ° C to 280 ° C, preferably 170 ° C to 270 ° C, and more preferably 170 ° C to 250 ° C. When the glass transition temperature of the polyimide copolymer satisfies the above-described numerical range, it is possible to suppress the occurrence of breakage during film stretching, and as a result, a film of a thin film having a high retardation can be realized.

Meanwhile, the retardation film of the present invention can be produced by using the polyimide resin composition prepared by dissolving the polyimide copolymer as described above in an organic solvent.

At this time, as the organic solvent, it is preferable to use a solvent having a boiling point of 80 ° C to 200 ° C, preferably a boiling point of 80 ° C to 180 ° C. When a film is formed using a solvent having a low boiling point as described above, the solvent can be prevented from remaining in the film even if the process is performed at a relatively low temperature. Therefore, process selectivity is improved and the film is advantageous in terms of physical properties.

The organic solvent having a boiling point of 80 ° C to 200 ° C may be, for example, diethylene glycol methyl ethyl ether, diethylene glycol dimethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol diethyl ether, dipropylene glycol dimethyl Ether, methyl 3-methoxypropionate, ethyl-3-ethoxypropionate, propylene glycol methyl ether propionate, dipropylene glycol dimethyl ether, propylene glycol monomethyl ether acetate (PGMEA) Salen, 1,3-dioxane, tetrahydrofuran, cyclohexanone, and cyclopentanone. Among them, alicyclic ether-based solvents such as 1,3-dioxane, 1,3-dioxane, tetrahydrofuran and the like are particularly preferable.

On the other hand, the polyimide resin composition may further contain glycine together with the organic solvent, if necessary. When an organic solvent having a boiling point of 80 ° C to 200 ° C is used together with glycine, the volatility of the solvent can be improved, and the risk of the process can be lowered and the coating property can be improved. The mixing ratio of the organic solvent having a boiling point of 80 ° C to 200 ° C and glycine may be about 90:10 to 60:40 by weight, but is not limited thereto. The glycine may be selected from, for example, polyglyme, higlyme, tetraglyme, butyl diglyme, triglyme, proglyme proglyme, ethyl diglyme, ethyl glyme, diglyme, and monoglyme. In the present invention, it is possible to use at least one selected from the group consisting of proglyme, ethyl diglyme, ethyl glyme, diglyme and monoglyme.

Meanwhile, in the polyimide resin composition, the organic solvent may be contained in an amount such that the composition has a viscosity of 100 cP to 25,000 cP, preferably, an amount such that the composition has a viscosity of 100 cP to 7000 cP Do. When the viscosity of the composition is in the above range, excellent workability and coating property can be obtained at the time of film formation.

In the polyimide resin composition, the polyimide copolymer is contained in an amount of about 5% by weight to 50% by weight, preferably 5% by weight to 30% by weight, more preferably 5 to 20% by weight %. ≪ / RTI >

On the other hand, the retardation film of the present invention can be produced by coating the above-mentioned polyimide resin composition on a substrate, drying it, and then stretching it. At this time, the substrate may be any substrate that can be stretched, and its kind is not particularly limited. For example, a polymer film such as an acrylic film may be used. The drying temperature may be about 80 ° C to 150 ° C, and the drying time may be about 1 minute to 5 minutes. The stretching temperature is preferably about 100 ° C to 150 ° C, and the stretching speed is preferably about 100 mm / min to 200 mm / min.

The thickness of the retardation film of the present invention produced by the above-described method is preferably about 1 to 10 mu m. When the thickness of the film satisfies the above-described numerical range, both the optical characteristic and the mechanical characteristic may be excellent.

In addition, the retardation film of the present invention comprising the polyimide copolymer as described above is excellent in transparency with an average transmittance of 70% to 100% with respect to light having a wavelength band of 380 nm to 760 nm at a thickness of 1 탆 to 10 탆. At this time, the light transmittance can be measured using a UV-Visible spectrum of the film.

In addition, the retardation film of the present invention has an elongation at break of about 10% to 200%, which is excellent in mechanical properties. When the elongation at break is low, the film is cracked in the film stretching process. As a result, the film can not withstand the stretching force and may be broken. In general, the mechanical properties of the polyimide film are greatly affected by the drying temperature at the time of film formation. When the polyimide copolymer used in the present invention is used, a solvent having a relatively low boiling point can be used. As a result, it is possible to obtain a film having superior mechanical properties as compared with conventional polyimide films.

On the other hand, the stretch elongation was obtained by coating a polyimide resin composition on an acrylic film, drying it at 100 DEG C and 1000 rpm for 2 minutes, and then stretching it at a rate of 150 mm / min at 130 DEG C using a stretching machine The elongation can be measured by the elongation immediately before the fracture occurs.

As described above, the retardation film of the present invention is excellent in transparency, has excellent mechanical strength, can be stretched at a high magnification, and as a result, can achieve a high retardation in a thin film. In fact, the retardation film of the present invention may have an in-plane retardation value of about 100 nm or more, preferably about 100 nm to 180 nm when the film thickness is converted into 4 mu m. More preferably, the retardation film of the present invention has an in-plane retardation value as high as 80 nm or more, preferably 80 nm to 180 nm even at a thin thickness of 10 탆 or less.

Further, in the case of the retardation film of the present invention, the adhesive strength to the adhesive for the polarizing plate is excellent and can be easily attached to the display panel or the polarizing plate. More specifically, the retardation film of the present invention has an adhesive strength of about 0.4 N / cm to 10 N / cm on the adhesive for a polarizing plate. Considering that the adhesion between the conventional polyimide-based films and the adhesive for the polarizing plate is 0.3 N / cm or less, it is understood that the adhesion strength of the retardation film of the present invention is superior to the conventional one. On the other hand, the polarizing plate was prepared by attaching a retardation film to one surface of a polarizing element using a polarizer adhesive, and then a polarizing plate sample having a width of 2 cm and a length of 8 cm was placed on the lower surface of a texture analyzer (XT-Plus, Stable Micro System) And the film was peeled off while applying a peel force of 90 degrees at a distance of 5 cm.

On the other hand, the adhesive for a polarizing plate used for measuring the adhesive force may be any of ordinary adhesives used for attaching a polyvinyl alcohol polarizer and a protective film without any limitations. For example, an adhesive for a photo cationic polarizer including an epoxy compound Or a photo-curable adhesive such as an adhesive for a radical-type polarizing plate containing an acrylic compound can be used.

More preferably, the adhesive for a polarizing plate comprises 100 parts by weight of a first epoxy compound having a glass transition temperature of 120 DEG C or higher of the homopolymer; 30 to 100 parts by weight of a second epoxy compound having a glass transition temperature of 60 占 폚 or less of the homopolymer; And 0.5 to 20 parts by weight of a cationic photopolymerization initiator.

The first epoxy compound may be, for example, 3,4-epoxycyclohexylmethyl-3,4'-epoxycyclohexanecarboxylate, vinylcyclohexene dioxide dicyclopentadienedioxide, bis epoxycyclopentyl ether, bisphenol A-based epoxy compound, bisphenol F-based epoxy compound, and the like, and the second epoxy compound may be one containing at least one glycidyl ether group, for example, 1,4-cyclohexanedimethanol diglycidyl ether , 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, neopentyldiglycidyl ether, resorcinol diglycidyl ether, diethylene glycol di diglycidyl ether, ethylene glycol Butyl glycidyl ether, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, and o-cresyl glycidyl ether. The glycidyl ether is preferably selected from the group consisting of glycidyl ether, lauryl diglycidyl ether, trimethylol propane triglycidyl ether, It may be at least one member selected from the group consisting of a hotel. The cationic photopolymerization initiator is a compound which produces a cationic species or Lewis acid by irradiation with an active energy ray. Examples of the cationic photopolymerization initiator include an onium salt such as an aromatic diazonium salt, an aromatic iodo aluminum salt or an aromatic sulfonium salt, Iron-arene complex, and the like. If necessary, the adhesive for a polarizing plate may further include 100 to 400 parts by weight of an oxetane compound having at least one oxetanyl group in the molecule. The oxetane compound may include, but is not limited to, (3-ethyloxetan-3-yl) methoxymethyl] benzene, 1,4-bis [ Bis (3-ethyloxetan-3-yl) methoxy] benzene, 1,2-bis [(3 Methoxy] benzene, 4,4'-bis [(3-ethyloxetan-3-yl) methoxy] biphenyl, 2,2'-bis [ 3-yl) methoxy] biphenyl, 3,3 ', 5,5'-tetramethyl-4,4'-bis [ Methoxy] naphthalene, bis [4- {(3-ethyloxetan-3-yl) methoxy} phenyl] methane, bis [2- { 3-ethyloxetan-3-yl) methoxy} phenyl] methane, 2,2-bis [ Methoxy} phenyl] propane, an etherified product of 3-chloromethyl-3-ethyloxetane of a novolac phenol-formaldehyde resin, 3 (4-ethyloxetane- ), 8 (9) -bis [(3-ethyloxetan-3-yl) methoxymethyl] -tricyclo [5.2.1.0 2,6] decane, 2,3- Methoxymethyl] norbornane, 1,1,1-tris [(3-ethyloxetan-3-yl) methoxymethyl] propane, 1-butoxy-2,2- Ethyloxetane-3-yl) methoxymethyl] butane, 1,2-bis [{2- Ethyloxetane-3-yl) methylthio} phenyl] sulfide, 1,6-bis [ 5,5-octafluorohexane and the like can be used.

The retardation film of the present invention can be used as a viewing angle compensation film of a display device such as a liquid crystal display device.

Hereinafter, the present invention will be described in more detail with reference to specific examples.

Manufacturing example  1: polyimide copolymer A

2.9019 g of 2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane (BisAP / AF) and 10 g of dimethylacetamide (DMAc, boiling point: about 165 ° C) were sequentially added to a 250 ml round bottom flask After the solution was completely dissolved by slow stirring, 20.980 g of ethylene glycol bis (4-trimellitic anhydride) (TMEG-100) and 20 g of dimethylacetamide were added slowly while maintaining the flask at 0 캜 , 13.22 g of 4,4'-methylenebis (2-methylcyclohexylamine) (MBMCHA) and 3.64 g of O, O'-bis (2-aminopropyl) polypropylene glycol were dissolved in 30 g of dimethylacetamide, After dropping for 1 hour at 0 ° C using a dropping funnel and stirring, the mixture was further stirred at 50 ° C for 23 hours, 13.8g of toluene was added thereto, and the mixture was subjected to dean-stark distillation. To remove water. After refluxing at 180 ° C for 6 hours The. After the water in the Dean-Stark distillation apparatus was removed, the solution was cooled to room temperature to obtain a polyimide copolymer solution A. The polyimide copolymer A produced had a weight average molecular weight of 25,000.

Manufacturing example  2: polyimide copolymer B

In a 250 ml round-bottomed flask, 4.93 g of 3,3 ', 4,4'-biphenyltetracarboxylic dihydride (BPDA), 4.93 g of ethylene glycol bis (4-trimellitic anhydride) After 40 g of dimethylacetamide was slowly added, 19 g of 4,4'-methylenebis (2-methylcyclohexylamine) (MBMCHA) was dissolved in 30 g of dimethylacetamide, and dropping funnel The mixture was stirred at 0 ° C. for 1 hour and then stirred at 50 ° C. for 23 hours. 13.8 g of toluene was added thereto, and water was removed through a dean-stark distillation apparatus And then refluxed at 180 ° C for 6 hours. After the water in the Dean-Stark distillation apparatus was removed, the solution was cooled at room temperature to obtain polyimide copolymer solution B. The produced polyimide copolymer B had a weight average molecular weight of 32,000.

Manufacturing example  3: Polyimide Copolymer C

In a 250 ml round-bottomed flask, 15.9 g of 3,3 ', 4,4'-biphenyltetracarboxylic dihydride (BPDA), 9.55 g of ethylene glycol bis (4-trimellitic anhydride) And 30 g of dimethylacetamide were slowly added thereto, and then 16.6 g of 4,4'-methylenebis (2-methylcyclohexylamine) (MBMCHA), 0.15 g of O, O'-bis (2-aminopropyl) polypropylene glycol 17.8 g was dissolved in 30 g of dimethylacetamide and then dropping was carried out at 0 ° C for 1 hour using a dropping funnel, followed by further stirring at 50 ° C for 23 hours. Then, 13.8 g of toluene And the mixture was allowed to remove water through a dean-stark distillation apparatus, and then refluxed at 180 ° C for 6 hours. After the water in the Dean-Stark distillation apparatus was removed, the solution was cooled at room temperature to obtain a polyimide copolymer solution C. The produced polyimide copolymer C had a weight average molecular weight of 29,000.

Manufacturing example  4: polyimide copolymer D

In a 250 ml round-bottomed flask, 15.9 g of 3,3 ', 4,4'-biphenyltetracarboxylic dihydride (BPDA), 9.46 g of ethylene glycol bis (4-trimellitic anhydride) And 30 g of dimethylacetamide were slowly added thereto. Then 9.54 g of bis (3-aminophenol) sulfide (3,3, DDS) and 10 g of dimethylacetamide were slowly added thereto. Then, 9.16 g of 4,4'-methylenebis (2-methylcyclohexylamine) (MBMCHA) was dissolved in 30 g of dimethylacetamide, and the mixture was stirred at 0 ° C. for 1 hour using a dropping funnel After dropping and stirring, the mixture was further stirred at 50 ° C. for 23 hours. 13.8 g of toluene was added thereto, and water was removed through a dean-stark distillation apparatus. Lt; / RTI > After the water in the Dean-Stark distillation apparatus was removed, the solution was cooled to room temperature to obtain a polyimide copolymer solution D. The prepared polyimide copolymer D had a weight average molecular weight of 36,000.

Manufacturing example  5: polyimide copolymer E

In a 250 ml round-bottomed flask, 10.9 g of 3,3 ', 4,4'-biphenyltetracarboxylic dihydride (BPDA) and 15.3 g of ethylene glycol bis (4-trimellitic anhydride) And 30 g of dimethylacetamide were slowly added and then 17.7 g of 4,4'-methylenebis (2-methylcyclohexylamine) (MBMCHA) was dissolved in 30 g of dimethylacetamide, and the mixture was dropping funnel, At 0 ° C for 1 hour, followed by stirring at 50 ° C for another 23 hours. Then, 13.8 g of toluene was added thereto, and water was removed through a dean-stark distillation apparatus And then refluxed at 180 ° C for 6 hours. After the water in the Dean-Stark distillation apparatus was removed, the solution was cooled to room temperature to obtain a polyimide copolymer solution E. The polyimide copolymer E produced had a weight average molecular weight of 37,000.

Manufacturing example  6: Polyimide Copolymer F

To a 250 ml round bottom flask was added 11.2 g of 3,3 ', 4,4'-biphenyltetracarboxylic dihydride (BPDA), 15.6 g of ethylene glycol bis (4-trimellitic anhydride) (TMEG-100) And 30 g of dimethylacetamide were slowly added thereto. Then, 7.27 g of 4,4'-methylenebis (2-methylcyclohexylamine) (MBMCHA), 0.70 g of O, O'-bis g and 4.40 g of 4,4'-methylenebis (cyclohexylamine) (MBCHA) were dissolved in 30 g of dimethylacetamide and then dropping was carried out at 0 ° C. for 1 hour using a dropping funnel, The mixture was stirred for further 23 hours at 50 ° C. Then, 13.8 g of toluene was added thereto, and water was removed through a dean-stark distillation apparatus. The mixture was refluxed at 180 ° C. for 6 hours. After the water in the Dean-Stark distillation apparatus was removed, the solution was cooled to room temperature to obtain a polyimide copolymer solution F. The produced polyimide copolymer F had a weight average molecular weight of 29,000.

Manufacturing example  7: Polyimide Copolymer G

In a 250 ml round-bottomed flask, 4.93 g of 3,3 ', 4,4'-biphenyltetracarboxylic dihydride (BPDA), 4.93 g of ethylene glycol bis (4-trimellitic anhydride) And 30 g of dimethylacetamide were slowly added thereto and then 17.2 g of 4,4'-methylenebis (2-methylcyclohexylamine) (MBMCHA) and 1.84 g of O, O'-bis (2-aminopropyl) Was dissolved in 30 g of dimethylacetamide, and the mixture was dropping at 0 ° C for 1 hour using a dropping funnel, followed by further stirring at 50 ° C for 23 hours. Then, 13.8 g of toluene was added thereto, The reaction mixture was placed in a dean-stark distillation apparatus to remove water, and then refluxed at 180 ° C for 6 hours. After the water in the Dean-Stark distillation apparatus was removed, the solution was cooled to room temperature to obtain a polyimide copolymer solution G. The produced polyimide copolymer G had a weight average molecular weight of 33,000.

Manufacturing example  8: polyimide copolymer H

20 g of ethylene glycol bis (4-trimellitic anhydride) (TMEG-100) and 30 g of dimethylacetamide were slowly added to a 250 ml round-bottom flask and then 4,4'-methylenebis (2-methylcyclohexyl Amine) (MBMCHA) was dissolved in 30 g of dimethylacetamide, and the mixture was dropwise added at 0 ° C for 1 hour using a dropping funnel, stirred and further stirred at 50 ° C for 23 hours Then, 13.8 g of toluene was added thereto, and water was removed through a dean-stark distillation apparatus, and the mixture was refluxed at 180 ° C for 6 hours. After the water in the Dean-Stark distillation apparatus was removed, the solution was cooled to room temperature to obtain a polyimide copolymer solution H. The produced polyimide copolymer H had a weight average molecular weight of 34,000.

compare Manufacturing example  1: polyimide copolymer I

20 g of 3,3 ', 4,4'-biphenyltetracarboxylic dihydride (BPDA) and 50 g of dimethylacetamide (DMAc, boiling point: about 165 ° C) were slowly added to a 250 ml round- And 19.1 g of 4'-methylenebis (2-methylcyclohexylamine) (MBMCHA) were dissolved in 50 g of dimethylacetamide, followed by dropping at 0 ° C for 1 hour using a dropping funnel, The mixture was stirred for further 23 hours at 50 ° C. Then, 13.8 g of toluene was added thereto, and water was removed through a dean-stark distillation apparatus. The mixture was refluxed at 180 ° C. for 6 hours. After the water in the Dean-Stark distillation apparatus was removed, the solution was cooled to room temperature to obtain a polyimide copolymer solution I. The prepared polyimide copolymer I had a weight average molecular weight of 22,000.

compare Manufacturing example  2: polyimide copolymer J

20 g of 3,3 ', 4,4'-biphenyltetracarboxylic dihydride (BPDA) and 50 g of dimethylacetamide were slowly added to a 250 ml round bottom flask, and 4,4'-methylene bis (2 -Methylcyclohexylamine) (MBMCHA) and 3.69 g of O, O'-bis (2-aminopropyl) polypropylene glycol were dissolved in 30 g of dimethylacetamide followed by dropping using a dropping funnel The mixture was stirred at 0 ° C for 1 hour and then stirred at 50 ° C for 23 hours. Then, 13.8 g of toluene was added thereto, and water was removed through a dean-stark distillation apparatus And then refluxed at 180 ° C for 6 hours. After the water in the Dean-Stark distillation apparatus was removed, the solution was cooled to room temperature to obtain a polyimide copolymer solution J. The produced polyimide copolymer J had a weight average molecular weight of 21,000.

Experimental Example  1: Solvent availability evaluation

The polyimide copolymer solutions prepared in Preparation Examples 1 to 8 and Comparative Preparation Examples 1 and 2 were precipitated and then dried to obtain a polyimide copolymer. A sample of 1 g was obtained from the obtained polyimide copolymers, and then tetrahydrofuran (boiling point: 66 캜), 1,3-dioxolane (boiling point: 75 캜), 1,3-dioxane (boiling point: (Boiling point: 170 占 폚), cyclohexanone (boiling point: 155 占 폚), dimethylacetamide (boiling point: 165 占 폚) and diethylformamide Respectively. The measurement results are shown in Table 1 below.

division Tetrahydrofuran 1,3-dioxolane 1,3-dioxane Cyclopentanone Cyclohexanone Dimethylacetamide Diethylformamide Production Example 1 Available Available Available Available Available Available Available Production Example 2 Available Available Available Available Available Available Available Production Example 3 Available Available Available Available Available Available Available Production Example 4 Available Available Available Available Available Available Available Production Example 5 Available Available Available Available Available Available Available Production Example 6 Available Available Available Available Available Available Available Production Example 7 Available Available Available Available Available Available Available Production Example 8 Available Available Available Available Available Available Available Comparative Preparation Example 1 Insolvency Insolvency Insolvency Insolvency Insolvency Insolvency Insolvency Comparative Production Example 2 Insolvency Insolvency Insolvency Insolvency Insolvency Insolvency Insolvency

As shown in Table 1, it can be seen that the copolymers of Production Examples 1 to 8 are excellent in solubility in low-boiling organic solvents, but the copolymers of Comparative Production Examples 1 and 2 are not soluble in low boiling point solvents.

Example  1 to 8

The polyimide copolymers A to H prepared in Production Examples 1 to 8 were dissolved in 1,3-dioxolane so as to have a concentration of 15% by weight to prepare a polyimide resin composition. Then, the polyimide resin composition was slip coated on a zero-retardation acrylic film, dried at 100 ° C for 2 minutes, and stretched twice in the TD direction at a rate of 150 mm / min at 130 ° C using a stretching machine, . At this time, the thickness of the polyimide resin composition was 4 탆.

Comparative Example  One

A retardation film was prepared in the same manner as in Examples 1 to 8 except that commercially available polyimide copolymer Ultem 1000 (manufactured by SABIC) was used.

Experimental Example  2: Evaluation of adhesion

25% by weight of 3,4-epoxycyclohexylmethyl-3,4'-epoxycyclohexanecarboxylate (Celloxide 2021P from Dicel) having a glass transition temperature of the homopolymer of 190 ° C, a glass transition temperature of the homopolymer of 25 ° C 50% by weight of cyclohexanedimethanol diglycidyl ether and 25% by weight of 3-ethyl-3 - [(3-ethyloxetan-3-yl) methoxymethyl] oxetane (Doagoseiaron oxetane DOX221) 5 parts by weight of CPI 100P (Sanapro) as a cationic initiator was added to 100 parts by weight of the resin composition prepared to prepare an adhesive for a polarizing plate.

Then, the polarizing plate adhesive was applied to both surfaces of the polyvinyl alcohol polarizer, and an acrylic film was laminated on one surface and a retardation film prepared in Examples 1 to 8 and Comparative Example 1 on the other surface, The laminator conditions were set to be 1 to 2 mu m, and then passed through a laminator. Then, a polarizing plate was produced by irradiating ultraviolet rays of 500 mJ / cm ² using a UV irradiation device of a metal halide light source.

The thus-prepared polarizing plate was cut to a width of 2 cm and a length of 8 cm. A polarizing plate sample was fixed on the lower surface of a texture analyzer (XT-Plus, Stable Micro System), and a 90 degree feel- And the adhesive strength was measured. The measurement results are shown in Table 2 below.

division Polyimide copolymer Adhesion (N / cm ² ) Example 1 A 1.0 Example 2 B 1.1 Example 3 C 0.9 Example 4 D 1.2 Example 5 E 1.0 Example 6 F 1.1 Example 7 G 1.1 Example 8 H 1.3 Comparative Example 1 Ultem 0.1

Experimental Example  3: Evaluation of optical characteristics

The retardation value in the plane direction, the retardation value in the thickness direction, and the light transmittance of the retardation film produced in Examples 1 to 8 were measured. The light transmittance is measured by Agilent Tech. The transmittance at a wavelength of 550 nm was measured in a transmittance mode using a UV-Visible Spectrum of the company. The measurement results are shown in Table 3 below.

division Polyimide copolymer Plane retardation value (nm) Thickness direction retardation value (nm) Transmittance (%) Example 1 A 140 -28 over 90 Example 2 B 140 -27 over 90 Example 3 C 130 -25 over 90 Example 4 D 145 -30 over 90 Example 5 E 128 -26 over 90 Example 6 F 121 -29 over 90 Example 7 G 120 -22 over 90 Example 8 H 118 -28 over 90

Claims (14)

A polyimide copolymer comprising a polyimide copolymer containing a repeating unit represented by the following formula (1)
Plane retardation value R _in calculated from conversion of the film thickness to 4 탆 is 100 nm to 180 nm, and the in-plane retardation value R _in is calculated by the following formula (1).
[Chemical Formula 1]

In the above formula (1)
X ₁ is a divalent organic group derived from an alicyclic or aromatic acid dianhydride containing an ester group or an ether group,
X ₂ is a _divalent organic group derived from an acid dianhydride different from X ₁ ,
Q ₁ and Q ₂ are each independently a divalent organic group derived from a diamine,
Wherein a, b, c and d represent the molar ratio of the respective repeating units, a + b + c + d = 1, 0.1? A + b? 1 and 0? C + d? 0.9.
Equation (1): R _in = (n _x -n _y ) · d
In the above formula (1), R _in is the in-plane retardation value, n _x is the refractive index of the retardation axis of the retardation film surface direction measured at a wavelength of 550 nm, n _y is the retardation D is the film thickness, and the retardation value converted to the film thickness of 4 mu m is the value calculated by the above d = 4000.
The method according to claim 1,
Wherein the polyimide copolymer has a solubility of 1% to 60% in 100 g of an organic solvent having a boiling point of 80 캜 to 200 캜 at 25 캜.
The method according to claim 1,
Wherein the polyimide copolymer has a glass transition temperature of 170 캜 to 280 캜.
The method according to claim 1,
Wherein X < ₁ > is a tetravalent organic group derived from an acid dianhydride represented by the following formula (2) or (3)
(2)

In the above formula (2)
A ₁ is an aliphatic or aromatic ring having 1 to 10 carbon atoms,
B ₁ is a single bond; A substituted or unsubstituted aliphatic chain; A substituted or unsubstituted aliphatic ring; A substituted or unsubstituted aromatic ring; Two or more aromatic rings linked directly or via a bridging structure; Or a combination thereof.

(3)

In the above formula 3,
A ₂ is an aliphatic or aromatic ring having 1 to 10 carbon atoms,
B ₂ is a single bond; A substituted or unsubstituted aliphatic chain; A substituted or unsubstituted aliphatic ring; A substituted or unsubstituted aromatic ring; Two or more aromatic rings linked directly or via a bridging structure; Or a combination thereof.
The method according to claim 1,
Wherein X < ₁ > is a tetravalent organic group derived from an acid dianhydride selected from the group consisting of compounds represented by Formula 4 below.
[Chemical Formula 4]

In the above formula (4)
B ₁ and B ₂ are each independently a single bond; A substituted or unsubstituted aliphatic chain; A substituted or unsubstituted aliphatic ring; A substituted or unsubstituted aromatic ring; Two or more aromatic rings linked directly or via a bridging structure; Or a combination thereof.
The method according to claim 1,
Wherein each of Q ₁ and Q ₂ is independently a divalent organic group derived from a diamine selected from the group consisting of compounds represented by the following formula (5).
[Chemical Formula 5]

In the above formula 5,
R ₁ to R ₇ are each independently a substituted or unsubstituted aliphatic chain; A substituted or unsubstituted aliphatic ring; A substituted or unsubstituted aromatic ring; Two or more aromatic rings linked directly or via a bridging structure; Or a combination thereof,
R ₈ to R ₁₁ are each independently a C 1-10 alkyl group, a C 1-10 haloalkyl group or a hydroxy group,
q is an integer of 1 to 8;
The method according to claim 1,
Wherein at least one of Q ₁ and Q ₂ is a divalent organic group selected from the group consisting of the functional groups represented by the following formula (6).
[Chemical Formula 6]

In the above formula (6)
R ₁₂ is -O-, -CR ₁₃ R ₁₄ - (wherein R ₁₃ and R ₁₄ are each independently selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 10 carbon atoms and a haloalkyl group having 1 to 10 carbon atoms) , -C (= O) -, -C (= O) O-, -C (= O) NH-, -S-, -S0-, -SO 2 -, -O [CH 2 CH 2 O] P - (wherein p is an integer of 1 to 10), a monocyclic or polycyclic cycloalkylene group having 6 to 19 carbon atoms, a monocyclic or polycyclic arylene group having 6 to 19 carbon atoms, and combinations thereof. .
The method according to claim 1,
Wherein at least one of Q ₁ and Q ₂ is a divalent organic group selected from the group consisting of the functional groups represented by the following formula (7).
(7)

In the above formula (7), q is an integer of 1 to 8.
The method according to claim 1,
Wherein the polyimide copolymer has an imidization ratio of 90% to 100%.
The method according to claim 1,
Wherein the retardation film has a thickness of 1 占 퐉 to 10 占 퐉.
The method according to claim 1,
And an average transmittance of 70% to 100% for light in a wavelength band of 380 nm to 760 nm at a thickness of 1 탆 to 10 탆.
The method according to claim 1,
Wherein the retardation film has an elongation at break of 10% to 200%.
The method according to claim 1,
Wherein the retardation film has an adhesive force of 0.4 N / cm to 10 N / cm with respect to the adhesive for a polarizing plate.
A display device comprising the retardation film according to any one of claims 1 to 13.