KR101497180B1 - Acryl copolymer having excellent strength, resin composition comprising the same, opticla film and ips mode liquid crystal display comprising thereof - Google Patents

Abstract

At least one monomer selected from the group consisting of an alkyl (meth) acrylate monomer, a monomer having a cyclic pendant structure, a (meth) acrylamide monomer and a tert-butyl (meth) An acrylic copolymer for an optical film, a resin composition containing the same, an optical film using the same, and an IPS mode liquid crystal display.

Description

TECHNICAL FIELD [0001] The present invention relates to an acrylic copolymer for an optical film having improved strength, a resin composition containing the same, an optical film containing the same, and a liquid crystal display device for an IPS mode (ACRYL COPOLYMER HAVING EXCELLENT STRENGTH, RESIN COMPOUND COMPRESSING THE SAME, OPTICAL FILM AND IPS MODE LIQUID CRYSTAL DISPLAY COMPRISING THEREOF}

The present invention relates to an acrylic copolymer for an optical film, a resin composition containing the same, and an optical film using the acrylic copolymer. More particularly, the present invention relates to an acrylic copolymer having optical characteristics suitable for an IPS mode liquid crystal display device and excellent in strength and heat resistance, And an optical film produced using the resin composition.

2. Description of the Related Art In recent years, liquid crystal displays (LCDs) have been widely used in the field of displays, replacing conventional CRTs. The liquid crystal display device is becoming thinner, lighter, and larger in size. In order to realize a higher quality image with such a trend, studies have been made to improve the uniformity of the screen, the contrast ratio, and the viewing angle.

In general, a liquid crystal display device includes a color filter array substrate on which a black matrix for preventing light leakage and a color filter layer for color implementation are formed, a thin film transistor, and a liquid crystal cell interposed between the TFT array substrate on which electrodes are formed, Twisted nematic, super twisted nematic, vertical alignment, and inflation switching mode, depending on the liquid crystal arrangement in the liquid crystal cell.

In a liquid crystal display device, a refractive index is changed according to a viewing angle due to an optical anisotropy of a liquid crystal molecule in a liquid crystal cell, and a color and a brightness of a screen are changed accordingly. At this time, since the optical anisotropy of the liquid crystal cell changes depending on the arrangement of the liquid crystal, the optical characteristics of the compensation film also depend on the mode of the liquid crystal cell.

Conventionally, a uniaxially or biaxially stretched TAC film (TriAcetyl Cellulose film) or a COP film (Cyclo-Olefin Polymer film) has been used to solve the viewing angle problem due to birefringence characteristics of liquid crystal molecules. However, since the optical characteristics (in particular, the retardation characteristics) of the compensation film are determined according to the fundamental birefringence and the polymer chain orientation of the raw material, there is a limit in manufacturing a compensation film having desired optical characteristics by using only existing films.

Therefore, there is a need to develop new raw materials in order to produce a compensation film having better optical properties.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an acrylic copolymer having superior optical properties, particularly optical characteristics suitable for an IPS mode liquid crystal display device and excellent in strength and heat resistance, And an IPS mode compensation film.

In one aspect, the present invention provides a composition comprising an alkyl (meth) acrylate-based monomer; Monomers comprising an annular pendant structure; At least one monomer selected from the group consisting of (meth) acrylamide-based monomers and tert-butyl (meth) acrylate-based monomers; And an acrylic copolymer for an optical film comprising a crosslinking agent.

In the acrylic copolymer of the present invention, the content of each component is preferably from 50 to 90 parts by weight of an alkyl (meth) acrylate monomer, from 10 to 40 parts by weight of a monomer containing a cyclic pendant structure, from 0.1 to 100 parts by weight of a (meth) acrylamide monomer 1 to 30 parts by weight of a tert-butyl (meth) acrylate monomer, and 0 to 1 part by weight of a crosslinking agent.

In another aspect, the present invention provides a resin composition for an optical film comprising the acrylic copolymer, and an optical film produced using the resin composition.

It is preferable that the optical film produced using the resin composition of the present invention has a phase retardation value of 100 to 120 nm and a thickness retardation value of 100 to 200 nm and a retardation value of thickness direction / phase retardation value of 1.3 to 1.6 desirable. Further, the above-mentioned optical film preferably has a hole generation height of 700 mm or more, more preferably 700 mm to 1000 mm, which is measured at the time of the volumetric experiment.

The optical film of the present invention having the above characteristics can be particularly useful for a compensation film for an IPS mode.

In another aspect, the present invention provides an IPS mode liquid crystal display device including the optical film of the present invention.

The optical film prepared by using the acrylic copolymer of the present invention has a high glass transition temperature of 120 ° C or more and is excellent in heat resistance and has optical properties suitable for preparing an IPS mode compensation film and has excellent strength, And is excellent in handleability and durability.

Hereinafter, the present invention will be described more specifically.

First, the terminology will be described.

As used herein, the term "copolymer" means that two or more kinds of monomers are contained as repeating units, and the form thereof is not particularly limited, and any type of copolymer such as an alternating copolymer, a block copolymer, Random copolymers, and graft copolymers.

 In the present specification, the term "(meth) acrylate-based monomer" should be understood to mean an acrylate-based monomer or a methacrylate-based monomer.

In the present specification, the term "(meth) acrylamide-based monomer" should be understood to mean an acrylamide-based monomer or a methacrylamide-based monomer.

In the present specification, the term "tert-butyl (meth) acrylate monomer" should be understood to mean a tert-butyl methacrylate monomer or a tert-butyl acrylate monomer.

The acrylic copolymer for an optical film of the present invention is obtained by copolymerizing (a) an alkyl (meth) acrylate monomer, (2) a monomer containing a cyclic pendant structure, (3) a tert- butyl (meth) acrylate monomer and / ) Acrylamide monomer and (4) a crosslinking agent.

The alkyl (meth) acrylate-based monomer improves the strength and heat resistance of the optical film. The alkyl group of the alkyl (meth) acrylate-based monomer preferably has about 1 to 10 carbon atoms, More preferably a methyl group or an ethyl group, and still more preferably a methyl group or an ethyl group. In particular, methyl methacrylate is preferable, but not limited thereto.

On the other hand, in the acrylic copolymer of the present invention, the content of the alkyl (meth) acrylate monomer is preferably about 50 to 90 parts by weight. When the content of the alkyl (meth) acrylate monomer is in the above range, excellent properties such as transparency, heat resistance and strength are exhibited.

On the other hand, the monomer including the annular pendant structure is for imparting a positive retardation property for the IPS mode, and is preferably a styrene-based monomer. Here, the styrene-based monomer refers to a compound having a styrene skeleton in its structure, for example, an aromatic vinyl compound monomer, an isopropenyl aromatic monomer, or the like.

More specifically, the styrenic monomer may be, for example, styrene,? -Methylstyrene, 3-methylstyrene, 4-methylstyrene, 2,4-dimethylstyrene, 2,5- -Chlorostyrene, 2,4,6-trimethylstyrene, cis-? -Methylstyrene, trans-? -Methylstyrene, 4-methyl-? -Methylstyrene, 4-fluoro-? 2-fluorostyrene, 4-fluorostyrene, 4-fluorostyrene, 2,4-difluorostyrene, 2, 3-fluorostyrene, But are not limited to, 4,5,6-pentafluorostyrene, 2-chlorostyrene, 3-fluorostyrene, 4-fluorostyrene, 2,4-dichlorostyrene, 2,6-dichlorostyrene, octachlorostyrene, From the group consisting of styrene, 3-bromostyrene, 4-bromostyrene, 2,4-dibromostyrene,? -Bromostyrene,? -Bromostyrene, 2-hydroxystyrene and 4-hydroxystyrene More than one selected It has, styrene, α- methyl styrene is especially preferred.

On the other hand, in the acrylic copolymer of the present invention, the content of the monomer including the cyclic pendant structure is preferably about 10 to 40 parts by weight. When the optical film is produced using the acrylic copolymer of the present invention, the retardation value varies depending on the content of the monomer including the cyclic pendant structure. When the content of the monomer of the cyclic pendant structure is in the above range, , That is, an optical film having a retardation property suitable for application to a compensation film. The acrylic copolymer of the present invention is particularly suitable for producing an optical film having a positive retardation value in the thickness direction, preferably a thickness direction retardation value of about 100 to 200 nm, and a retardation value in the plane direction of about 100 to 120 nm Do. In the case of an optical film produced using the acrylic copolymer, it is preferable that the ratio of the retardation value in the thickness direction / the retardation value in the plane direction is about 1.3 to 1.6, preferably about 1.3 to 1.5. It is preferable that the content of the monomer including the annular pendant structure is within the above range.

Next, the (meth) acrylamide-based monomer and the tert-butyl (meth) acrylate-based monomer are used for improving the heat resistance, and these monomers serve to increase the glass transition temperature of the copolymer. In the copolymer of the present invention, the tert-butyl (meth) acrylate monomer and the (meth) acrylamide monomer may be used alone or in combination.

As the (meth) acrylamide monomer, for example, methacrylamide, methacrylamide, N-substituted methacrylamide, methacrylamide containing an aliphatic ring and / or an aromatic ring, and the like can be used. On the other hand, the substituent of the N-substituted methacrylamide may include, but is not limited to, ethyl, isopropyl, tert-butyl, cyclohexyl, benzyl, phenyl and the like. Of these, methacrylamide is particularly preferable. The content thereof is preferably about 0.1 to 10 parts by weight. When the content of the (meth) acrylamide monomer is within the above range, sufficient heat resistance can be ensured.

Next, as the tert-butyl (meth) acrylate monomer, for example, tert-butyl methacrylate may be used, and the content thereof is preferably about 1 to 30 parts by weight. This is because sufficient heat resistance can be ensured within this range.

On the other hand, the crosslinking agent is used for enhancing the strength by strengthening the bonding of the monomers. In the present invention, an acrylate crosslinking agent having two or more unsaturated double bonds can be used. In particular, the cross-linking agent used in the composition of the present invention is preferably as long as the carbon chain between the double bonds is long, and preferably has 2 to 30 carbon atoms between the double bonds. When the number of carbon atoms between the double bonds is within the above range, a stable resin composition can be produced.

Specific examples of such crosslinking agents include, but are not limited to, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol diacrylate, 1,4-butanediol dimethacrylate, 1,6-hexane Diol dimethacrylate, 1,10-decanediol dimethacrylate, 1,3-butylene glycol dimethacrylate, diethylene glycol dimethacrylate, tricyclodecane dimethylol dimethacrylate, and the like. have. The content of the crosslinking agent is preferably more than 0 and 1 part by weight. If the crosslinking agent content exceeds 1 part by weight, gelation may occur.

In the present invention including the above-mentioned components, the acrylic copolymer has a glass transition temperature of 120 ° C. or higher, preferably 120 ° C. to 500 ° C., and more preferably about 130 ° C. to 200 ° C. In general, an optical film used in a display device such as a liquid crystal display device is required to have high heat resistance because it is easily deformed or damaged by heat generated in a backlight or the like. The acrylic copolymer of the present invention has a glass transition temperature of 120 ° C or higher So that it is not easily damaged by heat or the like.

On the other hand, the acrylic copolymer for optical film of the present invention can be obtained by polymerizing the above components by a general copolymer production method used in the related art, for example, by solution polymerization, bulk polymerization, suspension polymerization, Among them, solution polymerization or bulk polymerization is particularly preferable.

The acrylic copolymer of the present invention preferably has a weight average molecular weight of about 50,000 to 500,000 for heat resistance, sufficient processability and productivity.

On the other hand, the present invention provides, in another aspect, a resin composition comprising the acrylic copolymer and an optical film produced using the resin composition.

The resin composition of the present invention may contain, in addition to the above acrylic copolymer, additives such as colorants, flame retardants, reinforcing agents, fillers, antioxidants, heat stabilizers and ultraviolet absorbers within the range that does not impair the object of the present invention May be further included. The content of such an additive is preferably about 0.001 to 70 parts by weight.

The glass transition temperature of the resin composition is preferably 120 ° C or higher, preferably 120 ° C to 200 ° C, more preferably 130 ° C to 200 ° C. In consideration of heat resistance, workability, productivity and the like, It is preferably about 50,000 to 500,000.

The resin composition of the present invention can be produced into an optical film using a film production method well known in the art such as solution casting or extrusion, and the produced film is uniaxially or biaxially stretched for phase difference development. At this time, an improving agent or the like may be added as needed.

The stretching may be longitudinal (MD) stretching, or transverse (TD) stretching, or both. In the case where both the longitudinal direction stretching and the transverse stretching are performed, either one of them may be stretched first, then the stretching may be performed in another direction, or both directions may be simultaneously stretched. The stretching may be performed in one step or in multiple steps.

The stretching is preferably performed at a temperature of (Tg-20) ° C to (T + 30) ° C, more preferably at a glass transition temperature, when the glass transition temperature of the resin composition is Tg . The glass transition temperature refers to a range from the temperature at which the storage elastic modulus of the resin composition begins to decrease and the loss elastic modulus becomes larger than the storage elastic modulus to the temperature at which the orientation of the polymer chain is relaxed and disappears, and a differential scanning calorimeter (DSC ). ≪ / RTI >

The stretching speed is preferably in the range of 1 to 100 mm / min in the case of a universal teating machine (Zwick Z010) and in the range of 0.1 to 2 m / min in the case of a pile stretching machine, The elongation is preferably about 5 to 300%.

The optical film prepared by using the resin composition comprising the acrylic copolymer of the present invention has a retardation value in the range of 80 to 120 nm, preferably 90 to 120 nm, more preferably 100 to 120 nm , And the retardation value in the thickness direction is about 100 to 200 nm, more preferably about 130 to 170 nm.

In the optical film of the present invention, the ratio of the retardation in the thickness direction / the retardation in the plane direction is preferably 1.3 to 2.0, more preferably 1.3 to 1.6.

Here, the in-plane retardation value (R _in ) refers to a value defined by the following expression (1), and the thickness direction retardation value (R _th ) refers to a value defined by the following expression (2).

[Formula 1]

R _in = (n _x -n _y ) x d

[Formula 2]

R _th = (n _z -n _y ) x d

In [Formula 1] and [Formula 2] above,

n _x is the refractive index in the direction with the largest refractive index in the plane direction of the film,

n _y is the refractive index in the direction perpendicular to the nx direction in the plane direction of the film,

n _z is the refractive index in the thickness direction,

d is the thickness of the film.

It is also preferable that the hole generation height measured when the optical film of the present invention is subjected to the dropping test is 700 mm or more, and more preferably 700 mm to 1000 mm.

On the other hand, the optical film of the present invention having the above-described optical characteristics can be suitably used as a retardation compensation film. At this time, the optical film may be used alone or may be used after a predetermined post-process for controlling the refractive index such as coating. In particular, the optical film of the present invention can be usefully used as an IPS mode compensation film after a post-process for controlling the refractive index in the thickness direction.

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

Example

In the examples of the present invention, the physical property evaluation method is as follows.

1. Weight average molecular weight (Mw): The prepared resin was dissolved in tetrahydrofuran and measured by gel permeation chromatography (GPC).

2. Tg (Glass Transition Temperature): Measured using DSC (Differential Scanning Calorimeter) manufactured by TA Instrument.

3. Phase difference value (Rth / Rin): After stretching at the glass transition temperature of the film, Axoscan of Axometrics Inc. was used.

4. Accretion test: A steel ball having a particle diameter of 15.5 mm and a weight of 16.3 g was dropped on the film to measure the height at which holes were formed in the film.

Example  One

65 parts by weight of methyl methacrylate, 15 parts by weight of styrene, 20 parts by weight of tert-butyl methacrylate, and 0.05 parts by weight of ethylene glycol dimethacrylate. The prepared resin had a glass transition temperature of 132 占 폚 and a weight average molecular weight of 190,000. This resin was made into a film using a solution casting method and then stretched at a glass transition temperature to prepare an optical film. The retardation value of the produced film was measured, and an fall test was conducted. The measured thickness direction phase difference / plane phase difference value was 107/116, and the result of the fall test was 880 mm.

Example  2

70 parts by weight of methyl methacrylate, 20 parts by weight of styrene, 10 parts by weight of methacrylamide, and 0.01 part by weight of ethylene glycol dimethacrylate. The prepared resin had a glass transition temperature of 131 占 폚 and a weight average molecular weight of 240,000. This resin was made into a film using a solution casting method and then stretched at a glass transition temperature to prepare an optical film. The retardation value of the produced film was measured, and an fall test was conducted. The measured thickness direction phase difference / plane phase difference value was 116/125, and the result of the fall test was 900mm.

Example  3

60 parts by weight of methyl methacrylate, 20 parts by weight of styrene, 15 parts by weight of tert-butyl methacrylate, 5 parts by weight of methacrylamide and 0.01 part by weight of triethylene glycol dimethacrylate. The resin thus prepared had a glass transition temperature of 133 占 폚 and a weight average molecular weight of 228,000. This resin was made into a film using a solution casting method and then stretched at a glass transition temperature to prepare an optical film. The retardation value of the produced film was measured, and an fall test was conducted. The measured thickness direction phase difference / plane phase difference value was 112/121, and the result of the fall test was 910mm.

Example  4

60 parts by weight of methyl methacrylate, 20 parts by weight of styrene, 20 parts by weight of tert-butyl methacrylate, and 0.05 parts by weight of tetraethylene glycol dimethacrylate. The produced resin had a glass transition temperature of 133 占 폚 and a weight average molecular weight of 192,000. This resin was made into a film using a solution casting method and then stretched at a glass transition temperature to prepare an optical film. The retardation value of the produced film was measured, and an fall test was conducted. The measured thickness direction phase difference / plane phase difference value was 137/148, and the result of the fall test was 860 mm.

Example  5

70 parts by weight of methyl methacrylate, 20 parts by weight of styrene, 10 parts by weight of methacrylamide and 0.05 parts by weight of 1,4-butanediol dimethacrylate were mixed to prepare an acrylic copolymer resin. The prepared resin had a glass transition temperature of 131 占 폚 and a weight average molecular weight of 220,000. This resin was made into a film using a solution casting method and then stretched at a glass transition temperature to prepare an optical film. The retardation value of the produced film was measured, and an fall test was conducted. The measured thickness direction phase difference / plane phase difference value was 110/121, and the result of the fall test was 840mm.

Comparative Example  One

An acrylic copolymer resin was prepared in the same manner as in Example 1, except that a crosslinking agent was not used. The produced resin had a glass transition temperature of 130 占 폚 and a weight average molecular weight of 108,000. This resin was made into a film using a solution casting method and then stretched at a glass transition temperature to prepare an optical film. The retardation value of the produced film was measured, and an fall test was conducted. The measured thickness direction retardation value / plane retardation value was 100/107, and the result of the fatigue test was 650 mm.

Comparative Example  2

65 parts by weight of methyl methacrylate, 15 parts by weight of styrene, 20 parts by weight of tert-butyl methacrylate and 1.5 parts by weight of ethylene glycol dimethacrylate. The produced resin was not able to generate a gel and to recover the resin, making it impossible to produce a film.

Through the above Examples 1 to 5, it can be confirmed that when an optical film is produced using the resin composition of the present invention, an optical film having high glass transition temperature and optical characteristics suitable for the IPS mode is produced. It was also confirmed that when the crosslinking agent was added through Example 1 and Comparative Example 1, the strength of the film was remarkably increased.

Claims (18)

50 to 90 parts by weight of an alkyl (meth) acrylate-based monomer;
10 to 40 parts by weight of a monomer comprising a cyclic pendant structure;
At least one monomer selected from the group consisting of 0.1 to 10 parts by weight of a (meth) acrylamide-based monomer and 1 to 30 parts by weight of a tert-butyl (meth) acrylate-based monomer; And
0 to 1 part by weight of a crosslinking agent,
Wherein the crosslinking agent is a (meth) acrylate having at least two unsaturated double bonds.
delete The method according to claim 1,
Wherein the alkyl (meth) acrylate-based monomer is an acrylic copolymer for an optical film having an alkyl group of 1 to 10 carbon atoms.
The method according to claim 1,
Wherein the alkyl (meth) acrylate monomer is methyl (meth) acrylate.
The method according to claim 1,
Wherein the monomer containing the annular pendant structure is a styrene-based monomer.
6. The method of claim 5,
Wherein the styrenic monomer is selected from the group consisting of styrene,? -Methylstyrene, 3-methylstyrene, 4-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, -Methylstyrene, 4-fluoro-a-methylstyrene, 4-chloro-a-methylstyrene, 4-bromo-methylstyrene, styrene, 4-methylstyrene, 4-t-butylstyrene, 2-fluorostyrene, 3-fluorostyrene, 4-fluorostyrene, 2,4-difluorostyrene, 2,3,4,5,6-pentafluoro Styrene, 2-chlorostyrene, 3-fluorostyrene, 4-fluorostyrene, 2,4-dichlorostyrene, 2,6-dichlorostyrene, octachlorostyrene, 2-bromostyrene, 3- Acrylic-based copolymer for an optical film which is at least one selected from the group consisting of -bromostyrene, 2,4-dibromostyrene, -bromostyrene,? -Bromostyrene, 2-hydroxystyrene and 4-hydroxystyrene coalescence.
The method according to claim 1,
Wherein the tert-butyl (meth) acrylate monomer is tert-butyl methacrylate.
The method according to claim 1,
Wherein the (meth) acrylamide-based monomer is at least one selected from the group consisting of methacrylamide, N-substituted methacrylamide, and methacrylamide containing an aliphatic and / or aromatic ring.
delete The method according to claim 1,
The crosslinking agent may be selected from the group consisting of ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol diacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, 1,10- Acrylate copolymer for optical films having at least one selected from the group consisting of decane diol dimethacrylate, 1,3-butylene glycol dimethacrylate, diethylene glycol dimethacrylate and tricyclodecane dimethylol dimethacrylate. coalescence.
The method according to claim 1,
Wherein the acrylic copolymer has a glass transition temperature of 120 ° C to 500 ° C.
A resin composition for an optical film comprising the acrylic copolymer of any one of claims 1, 3 to 8, 10 and 11.
An optical film produced from the resin composition of claim 12.
14. The method of claim 13,
Wherein the optical film has a phase retardation value of 100 to 120 nm and a thickness retardation value of 100 to 200 nm.
14. The method of claim 13,
Wherein the optical film has a retardation value in the thickness direction / a retardation value in the plane direction of 1.3 to 1.6.
14. The method of claim 13,
Wherein the optical film has a hole generation height of 700 mm to 1000 mm as measured in a volumetric experiment.
A compensation film for IPS mode comprising the optical film of claim 13.
An IPS mode liquid crystal display device comprising the optical film of claim 13.