KR101190981B1 - An optical anisotropic film with high heat resistance and a liquid crystal display device comprising the same - Google Patents

Abstract

The present invention is 20 to 95% by weight of a polymethyl (meth) acrylate polymer, 4 to 60% by weight of a styrene-maleic anhydride copolymer comprising a styrene compound repeating unit and a maleic anhydride or imide maleic anhydride compound repeating unit and Disclosed is an uniaxial or biaxially stretched optically anisotropic film prepared from a resin composition comprising 1 to 20% by weight of rubber. According to the present invention, an optically anisotropic film excellent in transparency and heat resistance can be produced at low cost, and in particular, a positive C-plate type optical anisotropic film prepared according to the present invention is clear at a wide viewing angle. Since image quality and high contrast ratio can be obtained, it can be used suitably for the liquid crystal display of IPS mode as an optical compensation film.

Polymethylmethacrylate, polymethylacrylate, styrene, maleic anhydride, rubber, optically anisotropic film, C-plate compensation film, liquid crystal display device

Description

Optical anisotropic film excellent in heat resistance and a liquid crystal display device including the same {AN OPTICAL ANISOTROPIC FILM WITH HIGH HEAT RESISTANCE AND A LIQUID CRYSTAL DISPLAY DEVICE COMPRISING THE SAME}

The present invention relates to an optically anisotropic film excellent in transparency and heat resistance, preferably a positive C-plate type optically anisotropic film, and a liquid crystal display device including the same, and more particularly to polymethyl (meth) A heat resistant optically anisotropic film prepared by stretching a film obtained from a three-component transparent blend containing an acrylate polymer, a styrene-maleic anhydride-based copolymer and a rubber as an impact modifier, and a liquid crystal display device including the same.

BACKGROUND ART Liquid crystal displays have a lower power consumption, smaller volume, and lighter weight than portable cathode ray tube displays. In general, the liquid crystal display has a basic configuration in which polarizers are provided on both sides of the liquid crystal cell, and the orientation of the liquid crystal cell is changed depending on whether an electric field is applied to the driving circuit, thereby changing the characteristics of the transmitted light emitted through the polarizer. Visualization takes place. At this time, the path and birefringence of the light change according to the incident angle of the incident light, because the liquid crystal is an anisotropic material having two different refractive indices. Due to these characteristics, the liquid crystal display has a disadvantage in that the contrast ratio, which is a measure of how sharply the image is seen according to the viewing angle, changes, and gray scale inversion occurs, thereby reducing visibility. Has

In order to overcome the drawbacks described above, an optical compensation film (compensation film) for compensating for the optical phase difference generated in the liquid crystal cell is used in the liquid crystal display device, and a stretched birefringent polymer film is conventionally used as the optical compensation film. .

Examples of the material for the stretched birefringent polymer film include polymethyl methacrylate (PMMA), polystyrene (PS), polycarbonate (PC), maleimide-based copolymers and cyclic polyolefins (cyclic PO). Among them, PC, maleimide-based copolymers and cyclic PO are optically anisotropic polymer materials which have a large refractive index in the orientation direction when the molecular chains are stretched orientated, that is, have positive birefringence. PMMA or PS, on the other hand, is an optically anisotropic polymer material in which the molecular chain is stretched orientated so that the refractive index in a direction different from that of the orientation becomes large, that is, negative birefringence. The polymer materials currently used mainly in optical compensation films for improving the viewing angle of liquid crystal displays include PC, maleimide copolymers and cyclic PO.

Meanwhile, various liquid crystal modes have been developed in order to secure clear image quality and wide viewing angle in liquid crystal displays. Representatively, Double Domain TN (Twisted Nematic), ASM (axially symmetric aligned microcell), OCB (optically compensated blend), Vertical alignment (VA), multidomain VA (MVA), surrounding electrode (SE), patterned VA (PVA), in-plane switching (IPS), and fringe-field switching (FFS) modes. Each of these modes has a unique liquid crystal array and has inherent optical anisotropy. Therefore, in order to compensate for the retardation due to the optical anisotropy of these liquid crystal modes, a compensation film corresponding to each mode is required. Particularly in the case of IPS mode, the liquid crystal having positive dielectric anisotropy is filled between the polarizing plates. Therefore, since the refractive index in the plane direction is more oriented than the refractive index in the thickness direction, the optical compensation film has a positive phase difference in the thickness direction. (+) C-plate type anisotropic film is required.

As a result, studies on (+) C-plate type anisotropic films that can be used as optical compensation films in IPS mode are being conducted. As a result, vertically oriented liquid crystal films and polymers having negative birefringence such as PS or PMMA Biaxially oriented films and the like have been proposed. However, in the case of the vertically oriented liquid crystal film, since the rod-shaped low molecular weight or high molecular weight liquid crystal molecules are precisely coated on the transparent support with a thickness of several μm, the coating process costs are incurred, and the relative difference is caused by the slight difference in the coating thickness. It causes a large retardation non-uniformity, there is a problem such as optical defects due to foreign matter such as dust remaining on the surface of the coating substrate film or liquid crystal solution, and negative birefringence polymer such as PS or PMMA In the case of the biaxially stretched film, there is no problem of the vertically oriented liquid crystal compensation film as described above, but there is a problem that the glass transition temperature is in the vicinity of 100 ^° C. and the heat resistance is insufficient.

Japanese Unexamined Patent Publication No. 2001-194530 proposes a PC having a specific structure having a fluorene skeleton having a methyl group as a polymer material for a compensation film for solving the heat resistance problem of a biaxially oriented film of a polymer having negative birefringence. Japanese Laid-Open Patent Publication No. 2004-269842 discloses an alternating copolymer of an olefin and a specific N-phenyl substituted maleimide. However, when using the polymer materials disclosed in these Japanese Patent Publications, the heat resistance and negative birefringence of the compensation film are secured to some extent, but the cost of controlling the molecular structure such as stereoregularity and orientation of the polymer during polymer polymerization is high. Not only is it significantly higher, the resulting transparency and color of the polymer film does not meet the required properties of the optical compensation film.

The present invention is to solve the problems of the prior art as described above, an object of the present invention is an optically anisotropic film, preferably (+) C-plate (opposite C-plate), which is low in manufacturing cost and excellent in transparency and heat resistance It is to provide a type optically anisotropic film and a liquid crystal display device including the same.

The optically anisotropic film of the present invention is a styrene-maleic anhydride-based copolymer 4 to 20 to 95% by weight of a polymethyl (meth) acrylate polymer, a styrene compound repeating unit and a maleic anhydride or imide maleic anhydride compound repeating unit A film is formed from a resin composition comprising 60% by weight and 1 to 20% by weight of rubber, followed by uniaxial or biaxial stretching. Such an optically anisotropic film of the present invention is preferably one used as a (+) C-plate in a liquid crystal display device.

When the thickness of the optically anisotropic film is 30 to 200 micrometers, the retardation value R _th in the thickness direction represented by the following equation is preferably 30 to 1000 nm.

R _th = (n _z -n _y ) xd

In the above equation,

n _y and n _z respectively represent the refractive index of the in-plane high speed axial direction and the thickness direction measured at wavelength 550 nm, and d represents the thickness of a film.

In addition, the optically anisotropic film of the present invention has excellent heat resistance as the glass transition temperature of the resin composition for producing it is 115 ° C or higher, and has a linear light transmittance of 80% or more and a turbidity of 2% at a light wavelength of 400 to 800 nm. It has excellent light transmittance and transparency to the following.

In addition, the present invention is a liquid crystal panel and an optical compensation film between the first polarizing film and the second polarizing film A-plate compensation film to compensate for the phase in the horizontal direction and (+) C-plate compensation film to compensate for the phase in the vertical direction Provided is a liquid crystal display device which is formed interposed in this arbitrary order. At this time, the optically anisotropic film is used as the (+) C-plate compensation film. In particular, the present invention is suitable for the liquid crystal display device of the in-plane switching (IPS) mode.

According to the present invention, an optically anisotropic film excellent in transparency and heat resistance can be produced at low cost, and in particular, a positive C-plate type optical anisotropic film prepared according to the present invention is clear at a wide viewing angle. Since image quality and high contrast ratio can be obtained, it can be used suitably for the liquid crystal display of IPS mode as an optical compensation film.

The polymethyl (meth) acrylate polymers referred to herein are polymerized with only methyl (meth) acrylate monomers, as well as methyl (meth) acrylate monomers and methyls, unless otherwise noted, as described in detail below. It is to be understood that the copolymer includes a copolymer of a (meth) acrylate monomer and a polymerizable unsaturated monomer.

As used herein, styrene-maleic anhydride copolymer refers to a copolymer formed by copolymerization of a styrene compound monomer and a maleic anhydride compound or an imidized maleic anhydride compound monomer, wherein styrene It is to be understood that the system compound includes not only styrene but also substituted styrene compounds, and the maleic anhydride compound includes not only maleic anhydride but also a substituted maleic anhydride compound, which is further applied to the imidized maleic anhydride compound. The same applies to.

The optically anisotropic film of the present invention is 20 to 95% by weight of polymethyl (meth) acrylate polymer, preferably 55 to 80% by weight, 4 to 60% by weight of styrene-maleic anhydride copolymer, preferably 17 to 35% by weight. %, And 1 to 20% by weight of rubber, preferably 3 to 10% by weight of the resin composition is prepared by uniaxially or biaxially stretching the film.

At this time, when the content of the styrene-maleic anhydride copolymer exceeds 60% by weight and thus the content of the polymethyl (meth) acrylate polymer and the impact modifier is less than 40% by weight, the transparency and flexibility of the heat resistant blend decreases. When the content of the polymethyl (meth) acrylate polymer is more than 95% by weight, and thus the content of the styrene-maleic anhydride-based copolymer and the impact modifier is less than 5% by weight, the heat resistance is lowered and optically. There is a disadvantage that the birefringence is reduced. In particular, rubber, an impact reinforcing material, is an important factor controlling flexibility and transparency of the heat resistant optically anisotropic film. When the rubber content is less than 1% by weight, the optical film may be inferior in flexibility, and when the rubber content is 20% by weight or more, the optical film There is a problem that the transparency and the birefringence of the deterioration.

In the optically anisotropic film of the present invention, the polymethyl (meth) acrylate polymer may be a polymer obtained by polymerizing (meth) acrylic acid methyl ester alone, or a (meth) acrylic acid methyl ester and The copolymer which copolymerized the unsaturated monomer copolymerizable with this may be sufficient. In addition, when the polymethyl (meth) acrylate polymer is a copolymer, it is preferable to include (meth) acrylic acid methyl ester at least 50% by weight, preferably 50 to 90% by weight, in view of transparency and heat resistance of the optically isotropic film. . Moreover, as said polymethyl (meth) acrylate polymer, the polymethyl methacrylate polymer formed by superposing | polymerizing only with the methyl methacrylate monomer is more preferable.

In the above, the unsaturated monomer copolymerizable with the (meth) acrylic acid methyl ester is, for example, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate. (phenyl methacrylate), benzyl methacrylate, 2-ethylhexyl methacrylate or 2-hydroxyethyl methacrylate, or substituted with a hydroxy group; unsubstituted alicyclic or aliphatic C _{1 -12} alkyl methacrylate or C _{6 -12} aryl methacrylate; For example, methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, 2-ethylhexyl acrylate (2-ethylhexyl acrylate) or 2-hydroxyethyl acrylate (2-hydroxyethyl acrylate), such as, hydroxyl group substituted or unsubstituted alicyclic or aliphatic C _{1 -12} alkyl acrylate or C _6-12 aryl acrylates; Such as for example styrene or α- methylstyrene, C _{1 -4} alkyl or halogen-substituted styrene or unsubstituted styrene compounds such as; Acrylonitrile; And for example, such as cyclohexyl maleimide (cyclohexyl maleimide) or phenylmaleimide (phenyl maleimide), consisting of maleimide compounds, such as substituted or unsubstituted alicyclic or aliphatic C _{1 -12} alkyl or C _{6 -12} aryl-maleimide It is preferable that it is at least 1 type selected from the group.

In the optically anisotropic film of the present invention, the styrene-maleic anhydride copolymer is used to compensate for the insufficient heat resistance of the polymethyl (meth) acrylate polymer, and the styrene monomer and the maleic anhydride monomer or imidization ( imidized) can be prepared by copolymerizing maleic anhydride monomer.

The styrene-based monomers include C _{1 -4} alkyl, or substituted with halogen or may be a unsubstituted styrene compounds, and more preferably styrene, α- methylstyrene (α-methyl styrene), bromostyrene p- (p and at least one selected from the group consisting of -bromo styrene, p-methyl styrene, and p-chloro styrene.

The styrene-maleic anhydride copolymer is preferably prepared by copolymerizing 50 to 96 wt% of a styrene monomer and 4 to 50 wt% of a maleic anhydride monomer or an imidized maleic anhydride monomer, and more preferably a styrene monomer. It is prepared by copolymerizing 70 to 90% by weight and 10 to 30% by weight of maleic anhydride monomer or imidized maleic anhydride monomer. When the amount of the maleic anhydride monomer or the imidated maleic anhydride monomer used in the production of the styrene-maleic anhydride-based copolymer is less than 4% by weight, the heat resistance of the optically anisotropic film may be insufficient, and the amount exceeds 50 wt%. In this case, there is a problem that the impact strength of the optically anisotropic film is lowered.

In the optically anisotropic film of the present invention, the impact modifier rubber is used to improve the low impact resistance and flexibility of the two-component transparent blend composed of a polymethyl (meth) acrylate polymer and a styrene-maleic anhydride copolymer. , Methacrylonitrile-butadiene-styrene (MBS) system, acrylonitrile-butadiene-styrene (ABS) system, acrylonitrile-ethylene-propylene-diene terpolymer-styrene (AES) system, acrylonitrile-styrene Butyl acrylate (ASA), ethylene-propylene-diene terpolymer (EPDM) system, styrene-butadiene-styrene (SBS) system, styrene-isoprene-styrene (SIS) system, styrene-butadiene (SB) system, Styrene-isoprene rubber, ethylene-vinylacetate (EVA) -based, ethylene-ethyl acrylate (EEA) -based, ethylene-vinyl alcohol (EVOH) copolymer, ethylene chloride (CPE) -based resin, silicone rubber, acrylic-silicone-based It may be any one selected from the group consisting of rubber, PBT-based elastomer, PET-based elastomer and nylon-based elastomer. In particular, in order to maintain the high transmittance of the optically anisotropic film prepared from the three-component transparent resin composition, the rubber is a two-component transparent blend composed of a polymethyl (meth) acrylate polymer and a styrene-maleic anhydride copolymer and an impact reinforcing material It is important to control the refractive index difference of within 0.01, preferably within 0.005.

In the optically anisotropic film of the present invention, in addition to the above components, at least one additive selected from the group consisting of antioxidants, heat stabilizers, plasticizers, antistatic agents, nucleating agents, flame retardants, weathering stabilizers, lubricants and mold releasing agents may be used for the purpose of the present invention. It may be added further within the range which can be achieved. In particular, in including the ultraviolet absorber in the optically isotropic film, in order to increase the weather resistance of the polarizer protective film, it is preferable to add at least one ultraviolet absorber so as to have ultraviolet absorbing ability over a wide wavelength range. As the ultraviolet absorber, 2- (2H-benzotriazole) -2-

1) -4- (1,1,3,3-tetramethylbutyl) phenol (phenol), 2,4-di-t-butyl (butyl) -6- (5-chlorobenzotriazole ) -2-yl) Benzotriazole-based ultraviolet absorber such as phenol, 2- (4,6-diphenyl-1,3,5-triazin-2-yl Triazin-based ultraviolet absorbers such as) -5- (hexyloxy) phenol, and benzophenones such as 2-hydroxyl-4-octoxybenzophenone Salicylic acid type ultraviolet absorbers, such as a) type | system | group ultraviolet absorber and p-octylphenyl salicylate, etc. are mentioned, 2, 4- di-t- butylphenyl (butyl phenyl) -3, 5- di-t Benzoate-based light stabilizers such as butyl-4-hydroxy benzoate or bis (2,2,6,6-tetramethyl-4-piperi Light stabilizers, such as hindered amine light stabilizers, such as dill (piperidyl) sebacate It can be used.

In the optically anisotropic film of the present invention, a three-component transparent blend including a polymethyl (meth) acrylate polymer, a styrene-maleic anhydride copolymer and a rubber as an impact modifier is an injection molding method, an extrusion molding method, an inflation molding method which is a method for producing a general film. Alternatively, the film is processed into a film by a solution casting method or the like, and the resulting film is produced by uniaxial stretching such as free-width stretching or constant-width stretching, biaxial stretching such as sequential stretching or simultaneous stretching, preferably biaxial stretching. This stretching step is performed to orient the polymer chain to impart optical anisotropy to the film.

In order to increase the orientation of the polymer chain, it is preferable to perform the stretching process in a temperature range of T _g -30 ^o C to T _g +30 ^o C based on the glass transition temperature ( T _g ) of the heat resistant blend. In particular, it is more preferable to carry out in a temperature range of T _g -20 ^o C to T _g +10 ^o C. In addition, the drawing speed and the drawing rate can be appropriately adjusted within the range of achieving the object of the present invention. There is no restriction | limiting in particular in the apparatus used for an extending process, Any apparatus which can extend | stretch a polymer film can be used, including well-known stretching apparatuses, such as a roll stretching machine or a tender type stretching machine.

As mentioned above, the stretching process is an important process for birefringence expression. In particular, the stretching temperature and the elongation are the main factors affecting the birefringence expression, the stretching temperature is based on the glass transition temperature of the resin composition, the lower the glass transition temperature, the greater the degree of birefringence expression. As the elongation increases, the birefringence also increases proportionally. Therefore, in the present invention, it is preferable to perform the stretching process at an elongation of 20% or more.

First, in the optically anisotropic film of the present invention, the degree of optical anisotropy may be determined by the phase difference value R _e in the plane direction and the phase difference value R _{th in the} thickness direction represented by Equations 1 and 2, respectively. have.

R _e = (n _x -n _y ) × d (1)

R _th = (n _z -n _y ) × d (2)

In Equations 1 and 2, n _x represents an index of refraction in an in-plane slow axis (x-axis) measured at a wavelength of 550 nm, and n _y represents an in-plane fast axis measured at a wavelength of 550 nm. axis: the refractive index in the y-axis) direction, and n _z represents the refractive index in the thickness (z-axis) direction, and d represents the thickness of the film.

One of R _e and R _th represented by Equations 1 and 2 is much larger than the other film can be used as a compensation film having uniaxial optical anisotropy, and the absolute value of both phase difference values is greater than 0, and both Films with similar values can be used as compensation films with biaxial optical anisotropy. Compensation films with uniaxial optical anisotropy are largely classified into A-plates and C-plates according to the relative magnitudes of the refractive indices, and A-plates have n _x > n _y = n _z and C-plates in the relative magnitude of the refractive indices. Is defined as an optically anisotropic film that satisfies n _x = n _y ≠ n _z , respectively. Therefore, in the A-plate, the in-plane retardation value R _e has a positive value, and the retardation value R _th in the thickness direction has a value of almost zero. On the other hand, in C-plates, the in-plane retardation value is almost 0, and according to the values of n _z and n _y (or n _x ), they have positive or negative R _th , which is (+) C-plate or (- ) Is defined as C-plate.

In the optically anisotropic film of the present invention, when the film thickness is 30 to 200 micrometers, the retardation value R _th in the thickness direction represented by the following equation is preferably 30 to 1000 nm, more preferably 50 to 500 nm. It is characterized by.

R _th = (n _z -n _y ) × d

In the above equation,

n _y and n _z respectively represent the refractive index in the in-plane fast axis (y-axis) direction and the refractive index in the thickness (z-axis) direction measured at a wavelength of 550 nm, and d represents the thickness of the film.

In the present invention, if the retardation value (R _th ) in the thickness direction is less than 30 nm or more than 1000 nm, the retardation value of the light passing through the liquid crystal cell does not match the retardation value of the optically anisotropic film, and thus an optical compensation effect. It is not preferable because there is a problem that is not expressed.

In the optically anisotropic film of the present invention, the linear transmittance at 400 to 800 nm is preferably 80% or more, more preferably 90% or more. In addition, the haze of the optically anisotropic film is preferably 2% or less, more preferably 1% or less. If the linear transmittance and turbidity of the optically anisotropic film are less than 80% and 2% or more, respectively, the luminance of the liquid crystal display device manufactured therefrom may be reduced.

It is preferable that glass transition temperature is 105 degreeC or more, and, as for the optically anisotropic film of this invention, it is more preferable that it is 115 degreeC or more. If the glass transition temperature of the optically anisotropic film is less than 105 ℃, the heat resistance is insufficient to easily deform the film under high temperature and high humidity conditions, thereby causing a problem that the viewing angle compensation characteristics of the optically anisotropic film is non-uniform.

The optically anisotropic film of the present invention has various wavelength dispersion such as normal wavelength dispersion, flat wavelength dispersion, or reverse wavelength dispersion depending on the composition of the three-component transparent blend. Can have characteristics.

In addition, the optically anisotropic film of the present invention has excellent adhesion to materials such as polyvinyl alcohol and can be attached to a polyvinyl alcohol polarizing plate or the like, and, if necessary, corona discharge treatment, glow discharge treatment, flame treatment, and acid treatment. Transparency and anisotropy do not deteriorate even when used with one or more surface treatments selected from the group consisting of alkali treatments, ultraviolet irradiation treatments and coating treatments.

When used as an optical compensation film, the optically anisotropic film of the present invention can exhibit a clear picture quality at a wide viewing angle of a wide angle, and can improve the brightness contrast ratio when the driving cell is ON / OFF, so that a liquid crystal display device, in particular, an IPS It is suitable for use in a liquid crystal display device in mode. Accordingly, according to another aspect of the present invention, there is provided a liquid crystal display device, preferably an IPS mode liquid crystal display device, comprising the heat resistant optically anisotropic film of the present invention as a compensation film for viewing angle enhancement and color compensation.

Hereinafter, a liquid crystal display device in IPS mode including the optically anisotropic film of the present invention as a (+) C-plate type optical compensation film for viewing angle enhancement and color compensation will be described in detail with reference to the accompanying drawings.

1 is a cross-sectional view of one embodiment of a liquid crystal display device in IPS mode including the optically anisotropic film of the present invention as a (+) C-plate type optical compensation film. The liquid crystal display device of the IPS mode as shown in FIG. 1 includes a color filter array substrate 21 and a TFT array substrate 11 that are disposed to face each other and have a liquid crystal layer 31 therebetween.

The color filter array substrate 21 has a black matrix 22 to prevent light leakage and a color filter layer 23 of red (R), green (G), and blue (B) to implement color. . The TFT array substrate 11 includes a gate wiring (not shown) and a data wiring 15 defining a unit pixel, a thin film transistor formed at an intersection point of the gate wiring and the data wiring, and alternately cross each other. The common electrode 24 and the pixel electrode 17 which generate | occur | produce are formed.

The thin film transistor TFT may include a gate electrode 12a branched from the gate line, a gate insulating layer 13 formed on the entire surface including the gate electrode 12a, and a gate insulating layer 13 on the gate electrode 12a. And a source electrode 15a and a drain electrode 15b branched from the data line 15 and formed at both ends of the semiconductor layer 14, respectively. The pixel electrode 17 penetrates through the passivation layer 16 and is connected to the drain electrode 15b of the thin film transistor TFT to receive a voltage. The common electrode 24 is integrally connected to form a voltage outside the active region. Received.

In this manner, the liquid crystal display device in the IPS mode forms the common electrode 24 and the pixel electrode 17 on the same substrate, and applies a voltage between the two electrodes to form a transverse electric field E in the horizontal direction with respect to the substrate. It is characterized by rotating the liquid crystal molecules in a state where the liquid crystal molecules are kept horizontal with respect to the substrate. At this time, alignment layers 30a and 30b are further formed inside the TFT array substrate 11 and the color filter array substrate 21 having various patterns to initially align the liquid crystal molecules of the liquid crystal layer 31.

As such, the first and second polarizing films 53 and 54 are attached to the outer surface of the liquid crystal panel 50 including the two substrates and the liquid crystal layer to transmit only light having a specific wavelength, and the second polarizing film 54 A plate compensation film 52 and a (+) C plate compensation film 51 which is the optically anisotropic film of the present invention are further provided between the liquid crystal panel 50 and the liquid crystal panel 50 to compensate for the phase change of light according to the visual direction.

Referring to FIG. 2, the compensation film and the polarizing film of the liquid crystal display of the IPS mode will be described in more detail.

One side of the IPS mode liquid crystal panel 50 is further provided with (+) C plate compensation film 51 and A plate compensation film 52 which is the optically anisotropic film of the present invention, the (+) C plate compensation film ( 51) the optically anisotropic film of the present invention serves to compensate for the phase in the vertical direction, the A plate compensation film 52 serves to compensate for the phase in the horizontal direction. In addition, the first and second polarizing films 53 and 54 attached to the outermost sides of the liquid crystal panel 50 are stretched films, including a triacate cellulose (TAC) film, a poly vinyl alcohol (PVA) film, a protective film, It consists of several layers of film such as release film, and transmits the natural light having the vibration surface of 360 ° forward only the light having the vibration surface in a certain direction, and absorbs the remaining light to provide polarized light.

In this case, the liquid crystal panel 50, the (+) C plate compensation film 51, and the A plate compensation film 52 are interposed between the first and second polarizing films 53 and 54. The optically anisotropic film (+) C plate compensation film 51 of the present invention may be attached to the outer surface or the inner surface of the liquid crystal panel 50. The first and second polarizing films 53 and 54 are formed by attaching an adhesive surface from which the release film is removed to the outer surface of the liquid crystal panel 50, respectively. The order of the liquid crystal panel 50, the (+) C plate compensation film 51, and the A plate compensation film 52 interposed between the first and second polarizing films may be arbitrary, and FIG. 2 is one example thereof. Is shown. For example, the (+) C plate compensation film 51, which is the optically anisotropic film of the present invention, is attached to the upper surface of the liquid crystal panel 50, and the A plate compensation film 52 is installed thereon. What is necessary is just to attach the 2nd polarizing film 54 on a film, and to attach the 1st polarizing film 53 to the liquid crystal panel of the opposite side.

Hereinafter, preferred examples are provided to help understanding of the present invention, but the following examples are merely to illustrate the present invention, and the scope of the present invention is not limited to the following examples.

[Example]

Example 1

75% by weight of polymethyl methacrylate polymer (trade name HP202, manufactured by LG MMA) and 20% by weight of styrene-maleic anhydride copolymer (trade name Dylark 332, 15% by weight maleic anhydride monomer content, manufactured by NOVA Chemical), ABS-based impact After dry blending the three-component resin composition consisting of 5% of reinforcing materials (core-shell structure, rubber content 40%, manufactured by LG Chemical), a coaxial twin screw extruder (screw diameter 27mm, L / D = 48, manufactured by Leistritz) was used. To produce a heat resistant blend in pellet state. After drying the prepared pellets, an unstretched extruded film having a thickness of 80 μm was prepared using an extruder including a T-die.

An optically anisotropic film uniaxially stretched 30% at a temperature of 112 ^° C. was prepared using a roll drawing machine for the prepared non-stretched film. The following characteristics of the prepared optically anisotropic film were measured based on the following method, and the results are shown in Table 1.

(1) Glass transition temperature ( T _g )

: Using a differential scanning calorimeter (trade name: DSC 2010, TA instrument, Ltd.) was measured with a 10 ^o C / min temperature rising speed.

(2) light transmittance

: As an item for transparency evaluation, it measured with the transmittance meter (model name HR-100, a Murakami Color Research Laboratory manufacture) based on JISK7105.

(3) optical anisotropy

: Refractive index (n) was measured using an Abbe refractometer, and an in-plane phase difference value (R _e ) was measured using a sample inclination type automatic birefringence meter (model name KOBRA-21 ADH, manufactured by a prince measuring instrument). The retardation value ( _Rθ ) when the angle between the incident light and the film surface was 50 ^° was measured, and the retardation value (R _th ) in the film thickness direction was obtained according to the following equation.

In the above equation, θ _f is an internal angle.

[Example 2]

65% by weight of the same polymethyl methacrylate polymer as in Example 1 and 30% by weight of styrene-maleic anhydride copolymer, 5% by weight of MBS-based impact modifier (core-shell structure, rubber content 65%, manufactured by LG Chemical) An optically anisotropic film was prepared in the same manner as in Example 1 except that stretching was performed at 115 ^° C. using the composition, and the same properties as in Example 1 were measured for the prepared optically anisotropic film in the same manner. The results are shown in Table 1.

[Example 3]

45% by weight of the same polymethyl methacrylate polymer as in Example 1 and 50% by weight of styrene-maleic anhydride copolymer, 5% by weight of ABS-based impact modifier (core-shell structure, rubber content of 65%, manufactured by LG Chemical) An optically anisotropic film was prepared in the same manner as in Example 1, except that stretching was performed at 118 ^° C. using the composition, and the same characteristics as in Example 1 for the prepared optically anisotropic film Were measured in the same manner, and the results are shown in Table 1.

Example 4

A non-stretched film was prepared in the same manner as in Example 1, and the biaxially stretched film was simultaneously subjected to 30% simultaneous biaxial stretching in the x- and y-axis directions using a biaxial stretching apparatus (Lab Stretcher, TOYOSEIKI) at a temperature of 112 ^o. An optically anisotropic film was prepared under C condition, and the same properties as in Example 1 were measured for the prepared optically anisotropic film by the same method, and the results are shown in Table 1.

[Example 5]

An unstretched film was prepared in the same manner as in Example 2 (using a resin composition composed of 65 wt% of polymethyl methacrylate polymer, 30 wt% of styrene-maleic anhydride copolymer, and 5 wt% of MBS-based impact modifier). An optically anisotropic film was prepared by performing the same simultaneous biaxial stretching as Example 4 with respect to the prepared non-oriented film at a temperature of 115 ^° C., and the same properties as those of Example 1 were measured for the prepared optically anisotropic film by the same method. The results are shown in Table 1.

[Example 6]

A non-stretched film was prepared in the same manner as in Example 3 (using a resin composition composed of 45 wt% polymethyl methacrylate polymer, 50 wt% styrene-maleic anhydride copolymer, and 5 wt% ABS-based impact modifier). An optically anisotropic film was prepared by performing the same simultaneous biaxial stretching as in Example 4 with respect to the prepared non-oriented film at a temperature of 118 ^° C., and the same properties as in Example 1 were measured for the prepared optically anisotropic film by the same method. The results are shown in Table 1.

[Example 7]

An optically anisotropic film was prepared in the same manner as in Example 4 except that Dylark 232 (maleic anhydride monomer content 8%, manufactured by NOVA Chemical) was used as a styrene-maleic anhydride copolymer at a temperature of 108 ^° C. The same characteristics as in Example 1 were measured for the optically anisotropic film thus obtained, and the results are shown in Table 1.

[Example 8]

62% by weight of the same polymethyl methacrylate polymer as in Example 1 and 28% by weight of styrene-maleic anhydride copolymer, 10% by weight of ABS-based impact modifier (core-shell structure, rubber content of 40%, manufactured by LG Chemical) A non-stretched film was prepared in the same manner as in Example 1 except that a composition was used, and the optically anisotropic film was prepared by performing the same biaxial stretching as in Example 4 with respect to the prepared non-stretched film. The same properties as in Example 1 were measured for the anisotropic film by the same method, and the results are shown in Table 1 below.

Comparative Example 1

A non-stretched film was prepared in the same manner as in Example 1 using only the same polymethyl methacrylate polymer (HP202, manufactured by LG MMA) as in Example 1, and the same properties as in Example 1 were obtained for the prepared non-stretched film. It was measured by the method, the results are shown in Table 1.

Comparative Example 2

An unstretched film was prepared in the same manner as in Example 1 using only the same polymethyl methacrylate polymer as in Example 1 (HP202, manufactured by LG MMA), and the resulting stretched film was prepared at an stretching temperature of 104 ^° C. Uniaxial stretching was performed similarly to 1, and the optically anisotropic film was manufactured. The same properties as in Example 1 were measured for the prepared optically anisotropic film in the same manner, and the results are shown in Table 1.

[Comparative Example 3]

A non-stretched film was prepared in the same manner as in Example 1, and the same properties as in Example 1 were measured for the prepared non-stretched film in the same manner, and the results are shown in Table 1.

[Comparative Example 4]

A non-stretched film was prepared in the same manner as in Example 1, except that a composition including 68 wt% of the same polymethyl methacrylate polymer and 32 wt% of the styrene-maleic anhydride copolymer was used. The optically anisotropic film was prepared by performing the same simultaneous biaxial stretching as in Example 4 with respect to the prepared non-oriented film, and the same properties as in Example 1 were measured for the prepared optically anisotropic film by the same method, and the results are shown in Table 1 below. Indicated.

[Table 1]

division T _g
( ^o C) Thickness d
(Μm) Light transmittance
(%) Turbidity
(%) Refractive index n R _th
(nm) R _e
(nm) flexibility*
(O, X) Example 1 119 80 94.1 0.6 1.509 95 121 ○ Example 2 123 80 94.0 0.7 1.519 121 150 ○ Example 3 126 80 93.9 0.8 1.537 145 187 ○ Example 4 119 78 93.9 0.8 1.509 112 2 ○ Example 5 123 77 93.8 0.9 1.519 141 One ○ Example 6 126 77 93.8 0.9 1.537 172 2 ○ Example 7 115 75 94.1 1.0 1.510 101 2 ○ Example 8 119 80 93.7 0.9 1.509 67 One     ? Comparative Example 1 110 80 94.7 0.3 1.480 One One X Comparative Example 2 110 80 94.7 0.5 1.480 4 7 X Comparative Example 3 119 78 94.3 0.5 1.509 3 4 △ Comparative Example 4 119 78 94.5 0.4 1.509 128 3 X

* X (bad, brittle), △ (intermediate), ○ (good),? (Excellent, flexible)

As can be seen in Table 1, in the uniaxially stretched optically anisotropic film, the glass transition temperature and retardation values (R _e and R _th ) increased as the styrene-maleic anhydride copolymer content increased (Examples 1 to 3). In particular, as a result of manufacturing an optically anisotropic film by applying a biaxial stretching process (Examples 4 to 6), R _e is close to 0 and a positive C-plate type optical anisotropic film in which R _th represents a positive value is produced. Could. In addition, as a result of preparing a biaxially stretched film using a styrene-maleic anhydride copolymer having a different content of maleic anhydride monomer (Examples 4 and 7), (+) C-plate type optical anisotropic film having different glass transition temperatures. Could be prepared.

On the other hand, the non-stretched films of Comparative Examples 1 and 3 showed little birefringence, and the polymethyl methacrylate polymer films of Comparative Examples 1 and 2 exhibited low birefringence, heat resistance, and flexibility. It was found to be inappropriate to use. On the other hand, the heat-resistant optically anisotropic film without the impact modifier of Comparative Example 4 showed almost similar retardation characteristics compared to Example 4, but it was found that the film flexibility was very weak and not suitable for use as an optical compensation film.

On the other hand, while the glass transition temperature of the composition of Example 1 is 119 ° C, the stretching process is carried out at a temperature sufficiently lower than the glass transition temperature it can be confirmed that the expression of sufficient anisotropy. In some cases, when the stretching temperature is not sufficiently higher than the glass transition temperature or higher than the glass transition temperature, optical anisotropy may be expressed instead of optical anisotropy.

In addition, it was confirmed that the unstretched film of Comparative Example 3 had a lower degree of flexibility than the stretched film. This is because the orientation of the polymer chain occurs in the stretching direction in the film as the stretching is performed, resulting in the improvement of mechanical properties.

1 is a cross-sectional view of one embodiment of a liquid crystal display device in IPS mode including the optically anisotropic film of the present invention as a (+) C-plate type optical compensation film.

2 is a cross-sectional view schematically showing one embodiment of the liquid crystal display device of the IPS mode including the optically anisotropic film of the present invention as a (+) C-plate type optical compensation film.

* Explanation of code for main part of drawing

11 TFT array substrate 12a gate electrode

13 gate insulating film 14 semiconductor layer

15: data wiring 15a: source electrode

15b: drain electrode 16: protective film

17 pixel electrode 21 color filter array substrate

22: black matrix 23: color filter layer

24: common electrode 30a, 30b: alignment film

31 liquid crystal layer 50 liquid crystal panel

51: (+) C plate compensation film 52: A plate compensation film

53: first polarizing film 54: second polarizing film

Claims (23)

20 to 95% by weight of polymethyl (meth) acrylate polymer, 4 to 60% by weight of styrene-maleic anhydride copolymer comprising styrene compound repeating unit and maleic anhydride or imidized maleic anhydride repeating unit, and rubber 1 to Prepared from a resin composition comprising 20% by weight and then uniaxially or biaxially stretched, The rubber is methacrylonitrile-butadiene-styrene (MBS), acrylonitrile-butadiene-styrene (ABS), acrylonitrile-ethylene-propylene-diene copolymer-styrene (AES), acrylonitrile- Styrene-butylacrylate (ASA) system, ethylene-propylene-diene terpolymer (EPDM) system, styrene-butadiene-styrene (SBS) system, styrene-isoprene-styrene (SIS) system, styrene-butadiene (SB) system , Styrene-isoprene rubber, ethylene-vinyl acetate (EVA), ethylene-ethyl acrylate (EEA), ethylene-vinyl alcohol (EVOH) copolymer, ethylene chloride (CPE) resin, silicone rubber, acrylic-silicone Optically anisotropic film, characterized in that at least one selected from the group consisting of rubber, PBT-based elastomer, PET-based elastomer and nylon-based elastomer. The method of claim 1, The content of the polymethyl (meth) acrylate polymer is 55 to 80% by weight, the content of the styrene-maleic anhydride copolymer is 17 to 35% by weight, the content of the rubber is 3 to 10% by weight Optically anisotropic film made. The method of claim 1, The optically anisotropic film is biaxially stretched, which is used as a (+) C-plate in the liquid crystal display device. The method of claim 1, When the film thickness is 30 to 200 micrometers, the optically anisotropic film, characterized in that the phase difference value (R _th ) in the thickness direction represented by the following equation is 30 ~ 1000 nm. R _th = (n _z -n _y ) xd In the above equation, n _y and n _z respectively represent the refractive index of the in-plane high speed axial direction and the thickness direction measured at wavelength 550 nm, and d represents the thickness of a film. The method of claim 1, The polymethyl (meth) acrylate polymer is an optically anisotropic film, characterized in that the polymer formed by the polymerization of only the methyl (meth) acrylate monomer. The method of claim 1, The polymethyl (meth) acrylate polymer is an optical anisotropy characterized in that the copolymer is formed by copolymerizing 50 to 90% by weight of the methyl (meth) acrylate monomer and the unsaturated monomer copolymerizable with the methyl (meth) acrylate monomer. film. The method of claim 6, The unsaturated monomer copolymerizable with the methyl (meth) acrylate monomer may be an alicyclic or aliphatic C _1-12 methacrylic acid, which is unsubstituted or substituted with a hydroxy group, or an alicyclic or aliphatic C _{1-12 which} is not substituted or substituted with a hydroxy group. C _6-12 aryl methacrylic acid, optionally substituted with hydroxy groups, C _6-12 aryl acrylic acid, _optionally substituted with hydroxy groups, styrene compounds optionally substituted with C _1-4 alkyl or halogen, And an acrylonitrile, and alicyclic or aliphatic C _1-12 maleimide or C _6-12 aryl maleimide compound. The method of claim 1, The styrene-maleic anhydride-based copolymer is an optically anisotropic film, characterized in that formed by copolymerization of 50 to 96% by weight of styrene monomer and 4 to 50% by weight of maleic anhydride monomer or imide maleic anhydride monomer. 9. The method of claim 8, The styrene-based monomer is an optically anisotropic film, characterized in that at least one selected from the group consisting of styrene, α-methylstyrene, p-bromostyrene, p-methylstyrene and p-chlorostyrene. delete The method of claim 1, The optically anisotropic film, characterized in that the refractive index difference between the two-component transparent blend consisting of the polymethyl (meth) acrylate polymer and the styrene-maleic anhydride copolymer and the rubber is within 0.01. The method of claim 1, The resin composition has an optical anisotropy film having a glass transition temperature of 115 ℃ or more. The method of claim 1, The optically anisotropic film has a straight light transmittance of 80% or more at a light wavelength of 400 to 800 nm. The method of claim 1, The resin composition further comprises one or more additives from the group consisting of antioxidants, thermal stabilizers, plasticizers, antistatic agents, nucleating agents, flame retardants, weather stabilizers, mold release agents, ultraviolet absorbers, light stabilizers and lubricants. . The method of claim 1, The optically anisotropic film has an turbidity of 2% or less. The method of claim 1, When the optically anisotropic film is based on the glass transition temperature (Tg) of the resin composition, characterized in that formed by the stretching carried out at 20% or more elongation in the temperature range of Tg-30 ℃ to Tg + 30 ℃. Optically anisotropic film. The liquid crystal panel and the optical compensation film between the first polarizing film and the second polarizing film are A-plate compensation films for compensating the phase in the horizontal direction and (+) C-plate compensation films for compensating the phase in the vertical direction. In the liquid crystal display device formed by interposing, the (+) C-plate compensation film is a polymethyl (meth) acrylate polymer 20 to 95% by weight, styrene compound repeating units and maleic anhydride or imide maleic anhydride compound A biaxially stretched optically anisotropic film prepared from a resin composition comprising 4 to 60% by weight of a styrene-maleic anhydride copolymer comprising repeating units and 1 to 20% by weight of rubber, wherein the rubber is methacrylonitrile-butadiene -Styrene (MBS) system, acrylonitrile-butadiene-styrene (ABS) system, acrylonitrile-ethylene-propylene-diene copolymer-styrene (AES) system, acrylonitrile Reel-styrene-butylacrylate (ASA) system, ethylene-propylene-diene terpolymer (EPDM) system, styrene-butadiene-styrene (SBS) system, styrene-isoprene-styrene (SIS) system, styrene-butadiene (SB) ), Styrene-isoprene rubber, ethylene-vinylacetate (EVA), ethylene-ethyl acrylate (EEA), ethylene-vinyl alcohol (EVOH) copolymer, ethylene chloride (CPE) -based resin, silicone rubber, acrylic -At least one member selected from the group consisting of silicone rubber, PBT elastomer, PET elastomer and nylon elastomer. 18. The method of claim 17, And the liquid crystal panel, the A-plate compensation film and the (+) C-plate compensation film are sequentially stacked from the first polarizing film toward the second polarizing film. 18. The method of claim 17, The liquid crystal display device is a liquid crystal display device of the IPS (in-plane switching) mode. 18. The method of claim 17, When the optically anisotropic film thickness is 30 to 200 micrometers, the liquid crystal display device characterized in that the retardation value (R _th ) in the thickness direction represented by the following equation is 30 ~ 1000 nm. R _th = (n _z -n _y ) xd In the above equation, n _y and n _z respectively represent the refractive index of the in-plane high speed axial direction and the thickness direction measured at wavelength 550 nm, and d represents the thickness of a film. 18. The method of claim 17, The styrene-maleic anhydride-based copolymer is formed by copolymerization of 50 to 96% by weight of styrene monomer and 4 to 50% by weight of maleic anhydride monomer or imide maleic anhydride monomer. 18. The method of claim 17, The resin composition has a glass transition temperature of 115 ℃ or more. 18. The method of claim 17, The optically anisotropic film has a straight light transmittance of 80% or more at a light wavelength of 400 to 800 nm.

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