KR20150033623A - Retardation film for in-plane swiching mode liquid crystal display and liquid crystal display comprising the same - Google Patents

Abstract

The present invention relates to a retardation film for in-plane switching (IPS) mode liquid crystal display and liquid crystal display comprising the same. In greater detail, the present invention relates to a retardation film for IPS mode liquid crystal display comprising: an acrylic film with the value of retardation in the direction of the plane indicated with the below mathematical formula 1 of 60-200 nm and the value of retardation in the direction of thickness indicated with the below Mathematical Formula 2 of 100-250 nm at the wavelength of 550 nm; and a negative C plate comprising: a binder resin comprising inorganic matter. [Mathematical Formula 1] R_in = (n_x - n_y) × d [Mathematical Formula 2] R_th = (n_z - n_y) × d In the Mathematical Formulas 1 and 2, n__x is in the direction of plane of the film and is the refractive index in the direction with the greatest refractive index. In the direction of plane of the film, n_y is the refractive index in the vertical direction of the direction of n_x. n_z is the refractive index in the direction of thickness, and d is the thickness of the film. The retardation compensation film, according to the present invention can properly adjust the value of retardation in the direction of the plane and the value of retardation in the direction of thickness; has a superior viewing angle characteristic; can provide a thinner polarizing plate than the conventional ones; and is especially proper as a retardation compensation film used for IPS mode.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a retardation film for an IPS mode liquid crystal display device and a liquid crystal display device including the retardation film for an IPS mode liquid crystal display device,

The present invention relates to a retardation film capable of improving viewing angle characteristics for an IPS mode by laminating a negative C plate layer on an acrylic retardation film, and a liquid crystal display device including the retardation film.

The liquid crystal display is spreading as an optical display device because it has lower power consumption, smaller volume, lighter weight and easier to carry than a cathode ray tube display. In general, a liquid crystal display has a basic structure in which a polarizing plate is provided on both sides of a liquid crystal cell, and the orientation of the liquid crystal cell is changed according to whether an electric field of the driving circuit is applied or not and the characteristics of light transmitted through the polarizing plate are changed, Visualization is done. At this time, the path of light and the birefringence change depending on the incident angle of the incident light because the liquid crystal is an anisotropic material having two different refractive indices.

Due to such characteristics, the liquid crystal display has a disadvantage that the contrast ratio, which is a measure of how clearly the image looks depending on the viewing angle, is changed and a gray scale inversion phenomenon occurs, .

In order to overcome such disadvantages, an optical compensation film for compensating an optical retardation generated in a liquid crystal cell is used for a liquid crystal display device, and a stretched birefringent polymer film is used as such an optical compensation film.

Various liquid crystal modes have been developed to secure a clear image quality and a wide viewing angle in a liquid crystal display. Typical examples include Double Domain Twisted Nematic (TN), axially symmetric aligned microcell (ASM), optically compensated blend (OCB) 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 arrangement and has inherent optical anisotropy.

Therefore, in order to compensate the retardation due to the optical anisotropy of these liquid crystal modes, an optically anisotropic compensation film corresponding to each mode is required. In particular, since the liquid crystal having a positive dielectric anisotropy is horizontally aligned in the IPS mode, the optical anisotropy in the non-driven state is not greater than the other modes, which is advantageous in that an excellent viewing angle can be secured even by using the isotropic protective film alone . In this case, however, compensation for the absorption axis of the polarizer at the high inclination angle is not performed at all, so that the contrast may be deteriorated due to the viewing angle and color modulation may occur. Therefore, in order to secure a perfect viewing angle, the IPS mode liquid crystal display should also use an appropriate retardation film do.

The structure in which the retardation film for IPS mode is composed of two or more layers of multilayer films is actually being presented. Typically, a COP (cyclic olefin polymer) is uniaxially stretched and then a nematic liquid crystal (+ C plate) is coated to compensate for the viewing angle. However, in this case, the birefringence of the liquid crystal is so high that the retardation of the entire compensating film largely changes even if the alignment of the liquid crystal and the thickness of the coating slightly change, and it is difficult to control the retardation in the case of a thin film. In addition, the manufacturing cost is increased due to the expensive liquid crystal unit price, so that it is difficult to be commercialized in general.

Therefore, in order to improve the viewing angle characteristics of an in-plane switching (IPS) mode liquid crystal display device, a retardation film capable of appropriately adjusting a retardation value in a plane direction and a thickness direction retardation value, and an in- A display device is required.

One aspect of the present invention is to provide a retardation film capable of improving the viewing angle characteristics of an IPS mode liquid crystal display device without light leakage by appropriately adjusting the retardation value in the plane direction and the thickness direction retardation value by laminating a negative C plate layer on the acrylic retardation film And to provide a compensation film.

Another aspect of the present invention is to provide an IPS (in-plane switching) mode liquid crystal display including at least one phase difference film for the IPS (in-plane switching) mode liquid crystal display.

According to one aspect of the present invention, there is provided an acrylic film having a surface direction retardation value of 60 to 200 nm and a thickness direction retardation value of 100 to 250 nm represented by the following formula (2) and having an in- There is provided a phase difference film for an in-plane switching (IPS) mode liquid crystal display comprising a negative C plate made of a binder resin containing

[Equation 1] R _in = (n _x - n _y ) x d

&_Quot; (2) " R _th = (n _z - n _y ) x d

In the above equations (1) and (2), 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 vertical direction in the n _x direction in the plane direction of the film, n _z is the refractive index in the thickness direction, and d is the thickness of the film.

The acrylic film may be at least one selected from the group consisting of methyl methacrylate, ethyl methacrylate, propyl methacrylate, n -butyl methacrylate, t -butyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, methoxyethyl methacrylate , Ethoxyethyl methacrylate, and butoxymethyl methacrylate. The term " polymer "

The acrylic film preferably further comprises at least one monomer selected from the group consisting of a styrenic monomer and a maleic anhydride monomer or a maleimide monomer.

The acrylic film is preferably a blending resin obtained by blending a styrene-based copolymer with a polymer containing an acrylic monomer.

The styrene-based copolymer is preferably a styrene-maleic anhydride copolymer (SMA), a styrene-acrylonitrile copolymer (SAN), or an a-methylstyrene-acrylonitrile copolymer (AMSAN).

The acrylic film preferably further comprises a rubber component.

The inorganic material contained in the negative C plate is preferably at least one selected from the group consisting of sodium tetrasilicate mica, montmorillonite, saponite and hectorite.

The binder resin of the negative C plate is preferably at least one selected from the group consisting of polyvinyl alcohol, polyacrylamide, urethane water dispersion, acrylic water dispersion, and urethane-acrylic water dispersion.

The thickness of the acrylic film is preferably 30 to 100 탆.

It is preferable that the thickness of the negative C plate is more than 0 to 20 占 퐉.

The negative C plate preferably has a retardation value in the plane direction of 0 to 10 nm and a thickness retardation value in the formula (2) of -40 to -200 nm at a wavelength of 550 nm.

The weight ratio of the inorganic material constituting the negative C plate to the binder resin is preferably 1: 0.6 to 1: 2, more preferably 1: 0.8 to 1: 1.2.

The negative C plate is preferably coated on the acrylic film.

According to another aspect of the present invention, there is provided an IPS (in-plane switching) mode liquid crystal display including at least one phase difference film for the IPS (in-plane switching) mode liquid crystal display.

The retardation compensation film according to the present invention can appropriately adjust the retardation value in the plane direction and the retardation in the thickness direction, has excellent viewing angle characteristics, can provide a thinner polarizing plate than the conventional one, and is particularly suitable as a retardation compensation film used in the IPS mode Do.

Hereinafter, the present invention will be described in detail.

The retardation film for an in-plane switching (IPS) mode liquid crystal display according to the present invention has a retardation value in a plane direction of 60 to 200 nm represented by the following Equation 1 at a wavelength of 550 nm and a thickness retardation value Plane switching mode liquid crystal display device comprising a negative C plate composed of an acrylic film having a thickness of 100 to 250 nm and a binder resin containing an inorganic substance.

[Equation 1] R _in = (n _x - n _y ) x d

&_Quot; (2) " R _th = (n _z - n _y ) x d

In the above Equation 1 and Equation 2, n _x is the refractive index of the refractive index of the largest direction in the plane of the film, n _y is a refractive index in the direction perpendicular to the n _x direction in the plane of the film, n _z Is the refractive index in the thickness direction, and d is the thickness of the film.

The acryl-based film described in this specification means not only acrylates but also monomers including acrylate derivatives. Specifically, the acrylic monomers include methyl methacrylate, ethyl methacrylate methacrylate), methacrylate (propyl methacrylate), n - butyl methacrylate (n -butyl methacrylate), t - butyl methacrylate (t -butyl methacrylate), cyclohexyl methacrylate (cyclohexyl methacrylate), benzyl meta But are not limited to, benzyl methacrylate, methoxyethyl methacrylate, ethoxyethyl methacrylate, butoxymethyl methacrylate, and oligomers thereof. However, But is not limited thereto.

The acrylic film may be a copolymer further comprising at least one monomer selected from the group consisting of styrene type, maleic anhydride type and maleimide type together with the acrylic copolymer, preferably acrylic and styrene type monomers , More preferably a maleic anhydride-based or maleimide-based monomer.

When the monomer is further contained in addition to the acrylic monomer, the content of the acrylic monomer is preferably 50 to 95 parts by weight, more preferably 60 to 90 parts by weight, per 100 parts by weight of the entire acrylic film. If the content of the acrylic monomer is less than 50 parts by weight, high heat resistance, high durability and high transparency inherent to the acrylic polymer may not be sufficiently exhibited. If the content of the acrylic monomer exceeds 95 parts by weight, mechanical strength may be deteriorated.

Examples of the styrene monomer that can be contained in the acrylic copolymer include styrene,? -Methylstyrene, 4-methylstyrene, and the like, and it is preferably, but not limited to, styrene.

The content of the styrene-based monomer in the acrylic copolymer is preferably 5 to 40 parts by weight, more preferably 10 to 30 parts by weight, per 100 parts by weight of the entire acrylic film. When the amount is less than 5 parts by weight, there is a problem that it is difficult to produce a desired retardation film due to a decrease in retardation development. When the amount is more than 40 parts by weight, high durability and high transparency inherent to the acrylic polymer may not be sufficiently exhibited.

The styrenic monomer is preferably prepared in a copolymerized form with an acrylic monomer, but alternatively, a separate styrenic copolymer may be blended with a polymer comprising the acrylic monomer. For example, the styrenic copolymer may be a styrene-maleic anhydride copolymer (SMA), a styrene-acrylonitrile copolymer (SAN), an a-methylstyrene-acrylonitrile copolymer (AMSAN) But is not limited thereto.

Examples of the maleic anhydride-based or maleimide-based monomer that can be contained in the acrylic copolymer include maleic anhydride, maleimide, N-methylmaleimide, N-ethylmaleimide, N-propylmaleimide, N- But the present invention is not limited thereto.

The content of the maleic anhydride-based or maleimide-based monomer in the acrylic copolymer is preferably 1 to 20 parts by weight, more preferably 3 to 15 parts by weight, per 100 parts by weight of the entire acrylic film. If the content of the maleic anhydride-based or maleimide-based monomer is less than 1 part by weight, the effect of improving the heat resistance is insignificant. If the content is more than 20 parts by weight, the brittleness of the film increases, .

Further, the acrylic film may further include a rubber component for improving the toughness, impact resistance, and the like of the film. Preferably, the rubber component is an acrylic rubber, a rubber-acrylic graft-type core-shell polymer, or a mixture thereof, but is not limited thereto.

The acrylic rubber is not particularly limited as long as it is an acrylic rubber having a refractive index similar to that of the acrylic resin of 1.480 to 1.550 because a thermoplastic resin composition having excellent transparency can be obtained when the refractive index of the acrylic resin is similar to that of the acrylic resin.

For example, alkyl acrylates such as butyl acrylate and 2-ethylhexyl acrylate. The rubber-acrylic graft-type core-shell polymer is not particularly limited as long as it is a rubber-acrylic graft-type core-shell polymer having a refractive index of 1.480 to 1.550. For example, particles having a size of 50 to 400 nm made of butadiene, butyl acrylate or butyl acrylate-styrene copolymer-based rubber as the core and polymethyl methacrylate or polystyrene as a shell may be used.

The content of the rubber component is preferably 1 to 20 parts by weight, more preferably 1 to 15 parts by weight, based on 100 parts by weight of the entire acrylic film. If the content of the rubber component is less than 1 part by weight, it may be impossible to exhibit excellent mechanical strength of the film, and the film tends to be broken, causing problems in the processing step, and the optical performance is not sufficiently manifested. When the content is more than 20 parts by weight, the acrylic copolymer may not exhibit high heat resistance and high transparency, which may lead to processing problems such as haze in the stretching process.

The glass transition temperature (Tg) of the acrylic film is preferably 100 to 160 ° C. A film having a glass transition temperature (Tg) of 100 to 160 ° C may have excellent durability. If the glass transition temperature is less than 100 ° C, the film may be deformed under high temperature and high humidity conditions due to insufficient heat resistance. There is a problem that the compensation characteristic becomes uneven.

The acrylic film is usually manufactured using a melt extruder, and the thickness of the acrylic film is 30 to 100 탆. When the thickness is less than 30 탆, the polarizing element is not supported properly, If the thickness exceeds 100 탆, a large amount of heat is required for uniform drawing, so that high-speed drawing is difficult and economical.

The acrylic film produced by the melt extrusion method can be produced by a method such as uniaxial stretching or biaxial stretching. For example, they can be produced in a tenter equipped with a preheating portion, a stretching portion and a heat treatment portion. The term "preheating" refers to a process of softening an acrylic film by heating in advance so that it can be satisfactorily stretched in a subsequent stretching process. The acrylic film introduced into the preheating device is heated at a temperature lower than Tg, The stretching process is performed at a higher temperature. Thereafter, the stretched film is subjected to heat treatment for the purpose of fixing the orientation of the film in the heat treatment section. At this time, the stretching magnification can be adjusted in the stretching portion according to the phase difference value to be acquired.

In the retardation film for an IPS mode liquid crystal display device according to the present invention, a negative C plate may be introduced into the above acrylic film to adjust the R _in / R _th value of the entire retardation film.

The negative C plate is made of a binder resin containing an inorganic substance and may be prepared by any method known in the art. Preferably, the inorganic C is dispersed in water and then mixed with the binder resin, And dried.

The inorganic substance contained in the negative C plate is preferably sodium tetrasilicate mica or smectite group having a small amount of impurities. The inorganic substance belonging to the smectite family may be at least one selected from the group consisting of montmorillonite, bideite, saponite, hectorite and a compound having a crystal structure similar to them.

The solvent used for expanding or dispersing the inorganic material may be selected from the group consisting of dimethylformamide, dimethylsulfoxide, nitromethane, water, methanol, ethylene glycol and the like, but is not limited thereto.

In the production of the negative C plate of the present invention, it is preferable to mix an optically transparent hydrophilic binder resin or an aqueous dispersion to prevent cracking of the inorganic layer and to form a coating film. At this time, the binder resin may be at least one selected from the group consisting of polyvinyl alcohol, polyacrylamide, urethane water dispersion, acrylic water dispersion, and urethane-acrylic water dispersion. However, in the case of a hydrophilic resin, there may be a problem of being dissolved in water every day, so it is preferable to use an aqueous dispersion, and considering the toughness of the coated film after coating and the adhesion to an acrylic film as a base film, It is more preferable to use a urethane-based water dispersion of about 45% or more.

The weight ratio of the inorganic material to the binder resin is preferably 1: 0.6 to 1: 2, more preferably 1: 0.8 to 1: 1.2. When the ratio of the inorganic material and the binder resin is in the range of 1: 0.6 to 1: 2 by weight, it is preferable to improve mechanical properties such as prevention of cracking of the negative C plate layer made of an inorganic material and a binder resin.

Furthermore, when the negative C plate is made of an inorganic material and a binder resin water dispersion, the total concentration is preferably in the range of 4 to 8 wt%, particularly in the range of 4.5 to 6.5 wt%. When the content is less than 4 wt%, the viscosity of the web becomes low, and the thickness of the web becomes thick. After coating, there is a problem that the coating solution flows due to the low viscosity of the coating layer, In case of high viscosity there is difficulty in coating.

The thickness of the negative C plate is preferably in the range of more than 0 to 20 μm, and when it is more than 20 μm, problems such as drying failure and curling of the film may occur.

The negative C plate preferably has a retardation value in the plane direction of 0 to 10 nm and a thickness retardation value in the formula (2) of -40 to -200 nm at a wavelength of 550 nm.

As described above, the retardation film for an IPS mode liquid crystal display according to the present invention can realize a wider viewing angle characteristic by using an acrylic film and a negative C plate in combination.

In general, an acrylic retardation film having a negative birefringence is a + B-plate having a positive retardation value in a positive direction and a negative retardation value in a biaxial or biaxial stretching state and a ratio (R _th / R _in ) ). However, when the IPS mode liquid crystal display device is used alone, it is not possible to obtain a large viewing angle improvement effect. On the other hand, when using a combination of negative (negative) C plate of the present invention R _th / R _in the ratio of 1 or lower design possible as a phase difference film, and can provide a high viewing angle compensation performance by applying it to the IPS mode liquid crystal display device have.

In particular, in the IPS mode liquid crystal display device according to the present invention, the value of R _in / R _th of the retardation film is preferably 0.2 to 0.8, more preferably 0.3 to 0.7.

In the IPS mode liquid crystal display according to the present invention, the retardation value in the plane direction represented by Equation (1) of the entire retardation film including the acrylic film and the negative C plate is 60 to 200 nm, Is preferably smaller than the retardation in the plane direction within the range of 100 to 250 nm. When the retardation range is out of the above range, a high viewing angle improving effect can not be expected when applied to an IPS mode liquid crystal display device.

The thickness of the entire retardation film including the acrylic film and the negative C plate is preferably 30 to 120 탆, more preferably 40 to 100 탆, but is not limited thereto. When the thickness is less than 30 탆, the polarizing element can not be properly supported, and element shrinkage, device cracking, curling and the like are liable to occur. When the thickness exceeds 120 탆, the thickness of the entire polarizing plate becomes too thick, There is a possibility that a defect may occur due to the above.

Further additives known in the art such as lubricants, antioxidants, UV stabilizers, heat stabilizers, UV absorbers, plasticizers, and retardation enhancers generally used in the production of the retardation film of the present invention may be added to the entire retardation film In an amount of 0 to 10 parts by weight per 100 parts by weight.

In the production of the retardation film according to the present invention, a method of laminating a negative C plate on an acrylic film is not particularly limited. For example, a method of directly laminating a negative C plate on the acrylic film, A method of laminating a negative C plate directly on an acrylic film includes a step of preparing an acrylic film for example and a method of laminating at least one of the acrylic films Coating the material constituting the negative C plate on the surface of the substrate. That is, in the retardation film of the present invention, the negative C plate may be coated on the acrylic film.

In the manufacturing method of the retardation film according to the present invention, the specific details of the acrylic film and the negative C type material are the same as those described above, and therefore, a description thereof will be omitted.

In the method for producing a retardation film according to the present invention, the method for forming the coating layer is not particularly limited and any method known in the art can be used. For example, a flow coating, a roll coating, a bar coating, Can be used.

In addition, the present invention provides an in-plane switching (IPS) mode liquid crystal display device including one or more of the retardation films. An exemplary liquid crystal display device including one or more of the retardation films will be described in more detail as follows.

In a liquid crystal display comprising a liquid crystal cell and first and second polarizing plates provided on both sides of the liquid crystal cell, a retardation film may be provided between the liquid crystal cell and the first polarizing plate and / or the second polarizing plate have. That is, a retardation film may be provided between the first polarizing plate and the liquid crystal cell, and a retardation film may be provided between the second polarizing plate and the liquid crystal cell, or between the first polarizing plate and the liquid crystal cell, 2 or more .

The first polarizing plate and the second polarizing plate may include a protective film on one or both sides. Examples of the inner protective film include a triacetate cellulose (TAC) film, a polynorbornene-based film produced by ring opening metathesis polymerization (ROMP), a HROMP obtained by hydrogenation of a ring-opening polymerized cyclic olefin polymer ring opening metathesis polymerization followed by hydrogenation) polymer film, a polyester film, or a polynorbornene-based film produced by addition polymerization. In addition, a protective film or the like made of a transparent polymer material may be used, but is not limited thereto.

Hereinafter, preferred embodiments of the present invention will be described in order to facilitate understanding of the present invention. However, the following examples are provided only for the purpose of easier understanding of the present invention, and the present invention is not limited thereto.

Example

One. Phase difference  Production of film

≪ Example 1 >

Acrylonitrile copolymer (LG Chem, SAN80HF, acrylonitrile content: 24% by weight) and poly (cyclohexylmaleimide-co-methylmethacrylate) (LGMMA and PMMA830HR) : 20 in a twin extruder at 250 캜 and 200 rpm to prepare a resin composition. An unoriented film having a width of 800 mm was prepared using the resin composition under the conditions of 250 ° C and 250 rpm using a T-die die. The unstretched film was stretched 1.5 times in the MD direction at a temperature of 125 DEG C in a roll-to-roll manner, and then stretched 3.0 times in the TD direction using a tenter stretching machine at the same temperature to obtain an acrylic + B- a plate was prepared. The final stretched film thus obtained had a thickness of about 55 mu m, a retardation value in a plane direction (Rin) and a retardation value in a thickness direction (Rth) of 110 nm and 174 nm, respectively.

The negative C coating solution was prepared by mixing a commercially available synthetic nano-silicate Laponite (Rockwood XLG) with 7: 3 of an anionic water-dispersed polyurethane (Neorez R972 manufactured by DSM) and acrylic emulsion (Neocryl XK-62 manufactured by DSM) And then stirred at a high speed. At this time, purified water was added so that the total solid concentration was 4.5%, and the weight ratio of the laponite to the mixed binder resin was 1: 0.8.

The negative C coating solution was applied onto a corona-treated stretched acrylic film using an applicator, and dried at 90 DEG C for 5 minutes to form a coating retardation layer of 6.2 mu m.

The retardation of the final film thus prepared was measured, and the adhesion between the negative C coating layer and the acrylic film was confirmed. As can be seen from Table 1, the adhesion between the negative C coating layer and the substrate acrylic film was excellent in the present invention, and the retardation values of the entire retardation films were Rin 108 nm and Rth 65 nm, satisfying the condition that the Rin / Rth ratio was 1 or less A retardation film could be obtained.

The contrast ratio of the retardation film at an oblique angle of 60 DEG was measured, and the results are shown in Table 1. The panel to which the polarizing plate including the retardation film of the present invention was applied had a contrast ratio of 180: 1.

≪ Example 2 >

A retardation film was prepared in the same manner as in Example 1, except that the weight ratio of laponite to the mixed binder in the negative C coating liquid was 1: 1 and the thickness of the coating layer was 7.2 μm. As can be seen from the following Table 1, the adhesion between the negative C coating layer and the base acrylic film was excellent, and the contrast ratio of the panel using the retardation film at an inclination angle of 60 ° was excellent at 170: 1.

≪ Example 3 >

100 parts by weight of an acrylic resin (Tg = 129) containing 75% by weight of methyl methacrylate, 11% by weight of maleic anhydride, and 14% by weight of styrene was added to 100 parts by weight of butyl acrylate-methyl methacrylate resin grafted core- Weight part was compounded at 250 DEG C and 200 rpm using a twin extruder to prepare a resin composition. An unoriented film having a width of 800 mm was prepared using the resin composition under the conditions of 250 DEG C and 250 rpm using a T-die die. The undrawn film was stretched twice at 110 DEG C in the TD direction using a tenter stretcher to obtain a retardation film having a thickness of 60 mu m.

As can be seen from the following Table 1, the in-plane retardation of the retardation film was 118 nm and the retardation in the thickness direction was 145 nm.

The negative C coating was carried out in the same manner as in Example 1, except that a coating retardation layer having a thickness of 6.0 mu m was formed.

As shown in Table 1, both the adhesion to the substrate and the contrast ratio were excellent.

≪ Comparative Example 1 &

A 60 탆 -thick acrylic stretched film prepared in the same manner as in Example 3 was bonded to a polyvinyl alcohol polarizer and a triacetate cellulose film adhered to each other without a negative C coating treatment using an adhesive, and then CR ratio.

As shown in Table 1, since the condition that the Rth / Rin ratio of the retardation film is 1 or less was not satisfied, the contrast ratio at an oblique angle of 60 was extremely low at 20: 1, and therefore, It can be confirmed that it is inappropriate.

≪ Comparative Example 2 &

A retardation film was prepared in the same manner as in Example 1 except that the weight ratio of laponite to the mixed binder in the negative C coating liquid was 2: 1 and the thickness of the coating layer was 5.0 μm.

As shown in Table 1, the contrast ratio at an inclination angle of 60 ° was excellent, but the negative C coating layer was easily cracked or broken due to external force due to a low binder content, and the adhesive strength to the base acrylic film was also poor.

≪ Comparative Example 3 &

A retardation film was prepared in the same manner as in Example 1, except that the weight ratio of laponite to the mixed binder in the negative C coating liquid was 1: 3 and the coating layer thickness was 9.5 μm.

The negative C coating layer was excellent in adhesion, but had a low Rth value, and the contrast ratio at a tilt angle of 60 ° was very low at 30: 1.

2. Evaluation of physical properties according to resin composition

(1) Evaluation method

1) Phase difference value (nm): The phase difference of the final film was measured by Axoscan of Axometrics.

2) Adhesion: Adhesion between the negative C coating layer and the acrylic film was evaluated using a cross-cut test (ASTM 3002).

More specifically, the cutter was scratched five times or more on each side of the coated surface in an appropriate manner, and the tape was peeled off in a diagonal direction.

Adhesion was poor when the distance was 5% or more, good adhesion when the distance was 1 ~ 5%, and good adhesion when it was not falling at all.

3) Contrast ratio at an oblique angle of 60: The retardation film was attached to the upper surface of a polyvinyl alcohol polarizer and a triacetate cellulose liquid crystal display panel of a dyed polyvinyl alcohol film, and a contrast ratio at an oblique angle of 60 ° and an oblique angle of 45 ° was measured by Eldim .

At this time, an optically isotropic TAC film (FUJIFILM Corporation, NRT) / PVA polarizer / general TAC was laminated on the bottom surface of the panel as a polarizing plate.

(2) Evaluation results

Acrylic + B plate - C plate Whole phase difference film Adhesiveness Tilt angle 60 °
Contrast ratio R _in
(nm) R _th
(nm) thickness
(탆) R _in
(nm) R _th
(nm) thickness
(탆) R _in
(nm) R _th
(nm) thickness
(탆) Example 1 110 174 55 <2 -109 6.8 108 65 61.8 Great 180: 1 Example 2 110 174 55 <1 -101 7.2 109 73 62.2 Great 170: 1 Example 3 118 145 60 <1 -96 6.0 117 49 66 Great 180: 1 Comparative Example 1 118 145 60 - - - 118 145 60 - 20: 1 Comparative Example 2 110 174 55 <1 -105 5.1 109 69 60.1 Bad 180: 1 Comparative Example 3 110 174 55 <2 -52 9.5 108 122 65 Great 30: 1

It can be seen that the contrast ratio of the panel using the polarizing plate including the retardation film of the present invention is much higher than that of the comparative example. Since the contrast ratio value is an index indicating the sharpness of the screen, the liquid crystal display device according to the present invention can realize a clearer image quality.

Claims (15)

An acrylic film having a retardation value in the plane direction of 60 to 200 nm and a thickness retardation value in the range of 100 to 250 nm represented by the following formula (2) at a wavelength of 550 nm and represented by the following formula
An in-plane switching (IPS) mode liquid crystal display comprising a negative C plate made of a binder resin containing an inorganic material;

[Equation 1] R _in = (n _x - n _y ) x d
&_Quot; (2) &quot; R _th = (n _z - n _y ) x d

In the above equations (1) and (2)
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 n _x 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. The film according to claim 1, wherein the acrylic film is at least one selected from the group consisting of methyl methacrylate, ethyl methacrylate, propyl methacrylate, n -butyl methacrylate, t -butyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, A phase difference film for an IPS (in-plane switching) mode liquid crystal display, which is a polymer comprising at least one acrylic monomer selected from methoxyethyl methacrylate, ethoxyethyl methacrylate, and butoxymethyl methacrylate. The liquid crystal display according to claim 1, wherein the acrylic film is an acrylic polymer which further comprises at least one monomer selected from the group consisting of a styrenic monomer and a maleic anhydride monomer or a maleimide monomer, Phase retardation film. The phase difference film for an IPS (in-plane switching) mode liquid crystal display device according to claim 1, wherein the acrylic film is a blending resin obtained by blending a styrene-based copolymer with a polymer containing an acrylic monomer. The styrene-based copolymer according to claim 4, wherein the styrenic copolymer is at least one selected from the group consisting of styrene-maleic anhydride copolymer (SMA), styrene-acrylonitrile copolymer (SAN) (in-plane switching) mode phase difference film for liquid crystal display. The phase difference film for an in-plane switching (IPS) mode liquid crystal display device according to claim 1, wherein the acrylic film further comprises a rubber component. The method of claim 1, wherein the inorganic material contained in the negative C plate is at least one selected from the group consisting of sodium tetrasilicate mica, montmorillonite, laponite, and hectorite, Mode phase difference film for a liquid crystal display device. The negative binder of claim 1, wherein the binder resin of the negative C plate is at least one selected from the group consisting of polyvinyl alcohol, polyacrylamide, urethane water dispersion, acrylic water dispersion, and urethane- in-plane switching mode phase difference film for liquid crystal display. The phase difference film for an IPS (in-plane switching) mode liquid crystal display device according to claim 1, wherein the acrylic film has a thickness of 30 to 100 탆. The retardation film for an IPS (in-plane switching) mode liquid crystal display device according to claim 1, wherein the thickness of the negative C plate is more than 0 to 20 占 퐉. The negative C plate according to claim 1, wherein the negative C plate has a retardation value in the plane direction of 0 to 10 nm and a thickness retardation value in the range of -40 to -200 nm, (in-plane switching) mode phase difference film for liquid crystal display. The phase difference film for an IPS (in-plane switching) mode liquid crystal display device according to claim 1, wherein the weight ratio of the inorganic material constituting the negative C plate to the binder resin is 1: 0.6 to 1: 2. The phase difference film for an IPS (in-plane switching) mode liquid crystal display device according to claim 12, wherein the weight ratio of the inorganic material constituting the negative C plate to the binder resin is 1: 0.8 to 1: 1.2. The phase difference film for an IPS (in-plane switching) mode liquid crystal display device according to claim 1, wherein the negative C plate is coated on the acrylic film. An in-plane switching (IPS) mode liquid crystal display comprising at least one phase difference film for an IPS (in-plane switching) mode liquid crystal display according to any one of claims 1 to 14.