KR101211605B1 - Phase difference compensation film for in plane switching mode liquid crystal display device and in plane switching mode liquid crystal display device having the same - Google Patents

Abstract

The present invention relates to a retardation compensation film for in-plane switching (IPS) mode liquid crystal display. The retardation compensation film of the present invention has birefringence in the plane direction to prevent light leakage in the horizontal direction, and in-plane switching (IPS) having positive birefringence in the thickness direction to prevent light leakage in the vertical direction. A retardation compensation film for a mode liquid crystal display device, wherein the retardation compensation film comprises a styrene containing a first styrene monomer unit (A) and a maleic anhydride monomer unit (B) in a weight ratio (A: B) of 98 to 60: 2 to 40. Styrene-methylmethacrylate air containing maleic anhydride copolymer, second styrene monomer unit (C) and methyl methacrylate monomer unit (D) in a weight ratio (C: D) of 80 to 20:20 to 80 Characterized in that it is formed of a mixture of coalescing. The retardation compensation film for in-plane switching (IPS) mode liquid crystal display of the present invention not only improves heat resistance and light transmittance, but also functions as a C plate compensation film that compensates for leakage of light in the vertical direction with the A plate compensation film. Can be performed simultaneously.

Description

Retardation compensation film for in-plane switching (IPS) mode liquid crystal display device and in-plane switching (IFS) mode liquid crystal display device having the same {PHASE DIFFERENCE COMPENSATION FILM FOR IN PLANE SWITCHING MODE LIQUID CRYSTAL DISPLAY DEVICE AND IN PLANE SWITCHING MODE LIQUID CRYSTAL DISPLAY DEVICE HAVING THE SAME}

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate the presently preferred embodiments of the invention and, together with the description of the following preferred embodiments, serve to explain the principles of the invention.

1 and 2 are schematic cross-sectional views of a conventional IPS mode liquid crystal display.

The present invention relates to a retardation compensation film used in an in-plane switching (IPS) mode liquid crystal display and an in-plane switching (IPS) mode liquid crystal display having the same.

Liquid crystal display devices are the most important display device used in the multimedia society in recent years, and are widely used in mobile phones, computer monitors, notebook computers, and televisions. As the liquid crystal display, a TN mode in which a liquid crystal layer in which a nematic liquid crystal is twisted between two orthogonal polarizing plates is interposed, and the electric field is oriented perpendicular to the substrate is widely used. . In this manner, since the liquid crystal is oriented in a direction perpendicular to the substrate during black display, birefringence by liquid crystal molecules occurs and light leakage occurs at an inclined viewing angle.

In order to solve the TN type viewing angle problem, an IPS mode (In-Plane Switching Mode) for forming two electrodes on one substrate and controlling the director of the liquid crystal with a transverse electric field generated between the old electrodes has been introduced. As shown in Fig. 1, the IPS mode liquid crystal display element is composed of a color filter array substrate 21 and a TFT array substrate 11 which are disposed to face each other and have a liquid crystal layer 31 therebetween.

That is, the color filter array substrate 21 has a black matrix 22 to prevent light leakage and a color filter layer 23 of R, G, and B to implement color. The TFT array substrate 11 has 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 cross each other alternately. The common electrode 24 and the pixel electrode 17 which generate an electric field are formed. In this case, the TFT may include a gate electrode 12a branched from the gate wiring, a gate insulating layer 13 formed on the entire surface including the gate electrode 12a, and a gate insulating layer 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 is connected to the drain electrode 15b of the thin film transistor TFT through the passivation layer 16 to receive a voltage, and the common electrode 24 is integrally connected to receive a voltage outside the active region. I receive it. Alignment layers 30a and 30b are further formed inside the TFT array substrate 11 and the color filter array substrate 21 on which various patterns are formed to initially align the liquid crystal molecules of the liquid crystal layer 31.

In this manner, the IPS mode liquid crystal display device forms the common electrode 24 and the pixel electrode 17 on the same substrate, and applies a voltage between the two electrodes to generate a transverse electric field E in the horizontal direction with respect to the substrate. The liquid crystal molecules are rotated in a state where the liquid crystal molecules are kept horizontal with respect to the substrate.

Meanwhile, first and second polarizing films 53 and 54 are attached to an outer surface of the liquid crystal panel 50 including two substrates and a liquid crystal layer to transmit only light having a specific wavelength, and the second polarizing film 54 and The A plate compensating film 52 and the C plate compensating film 51 are further provided between the liquid crystal panels 50 to compensate for the phase change of light according to the visual direction.

Referring to FIG. 2, the retardation compensation film and the polarizing film of the IPS mode LCD are described in more detail.

One side of the IPS mode liquid crystal panel 50 is further provided with a C plate compensation film 51 and A plate compensation film 52, the C plate compensation film 51 is made of a liquid crystal material having a positive dielectric constant The phase compensation in the vertical direction, and the A plate compensation film 52 is made of a liquid crystal material having a negative dielectric constant to serve to compensate for the phase in the horizontal direction. As described above, the IPS mode liquid crystal display device compensates for the phase by using a biaxial film or two compensation films, A plate compensation film and C plate compensation film. In addition, the first and second polarizing films 53 and 54 respectively 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, and 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 A plate compensating film 52 and the C plate compensating film 51 may be formed by coating and curing the outer surface or the inner surface of the liquid crystal panel 50 as the coating type. The polarizing films 53 and 54 are formed by attaching the adhesive surface from which the release film is removed to the outer surface of the liquid crystal panel 50, respectively.

That is, after coating and curing the C plate compensation film 51 on the upper surface of the liquid crystal panel 50, coating and curing the A plate compensation film 52 thereon, and finally, a second polarized light on the A plate compensation film. It is prepared by attaching the film 54 and attaching the first polarizing film 53 to the opposite liquid crystal panel.

In the IPS mode liquid crystal display described above, a method of applying a compensation film made of a polymer having a positive birefringence characteristic or a discotic liquid crystal compound as a compensation film has been proposed (Japanese Patent Laid-Open Nos. 10-54982 and 11-202323). , 9-292522 et al.). In addition, a method of combining a film having a positive birefringence and having an optical axis in-plane with a film having a positive birefringence and having an optical axis in the normal direction of the film (see Japanese Patent Laid-Open No. 11-133408), A method of using a biaxial optical compensation sheet having a wavelength of 1/2 (see Japanese Patent Laid-Open No. 11-305217), a film having a negative retardation is applied as a protective film of a polarizing plate, and a positive A method of providing an optical compensation layer having a retardation (see Japanese Patent Laid-Open No. 10-307291) and the like have been proposed.

Such a compensation film is mainly made of polystyrene, and since polystyrene has a positive birefringence in the thickness direction, it is useful to compensate for light leakage in the vertical direction. However, since the phase difference compensation film made of polystyrene has a glass transition temperature (Tg) of about 100 ° C. and a light transmittance of 90% or less, a compensation film material having higher glass transition temperature and higher light transmittance while maintaining the properties of polystyrene is required. It is becoming.

Therefore, the technical problem to be achieved by the present invention was devised to solve the above-mentioned problems, not only excellent heat resistance and light transmittance, but also a C plate compensation film that compensates for leakage of the A plate compensation film and the vertical direction. The present invention provides a retardation compensation film for an in-plane switching (IPS) mode liquid crystal display and an in-plane switching (IPS) mode liquid crystal display having the same.

In order to achieve the above technical problem, the retardation compensation film according to the present invention has a birefringence in the plane direction to prevent light leakage in the horizontal direction, the positive birefringence in the thickness direction to prevent light leakage in the vertical direction A retardation compensation film for an in-plane switching (IPS) mode liquid crystal display having a weight ratio of 98 to 60: 2 to 40 for the first styrene monomer unit (A) and maleic anhydride monomer unit (B). Styrene-maleic anhydride copolymer containing styrene and a second styrene monomer unit (C) and a methyl methacrylate monomer unit (D) in a weight ratio (C: D) of 80 to 20:20 to 80 It is characterized in that it is formed of a mixture of butyl methacrylate copolymer.

The retardation compensation film for in-plane switching (IPS) mode liquid crystal display device of the present invention copolymerizes monomers capable of improving heat resistance and light transmittance with styrene monomers, and then uses a blend of these copolymers. In addition to improving light transmittance, only one film can simultaneously perform the functions of the A plate compensation film and the C plate compensation film to compensate for light leakage in the vertical direction.

In the retardation compensation film for in-plane switching (IPS) mode liquid crystal display device of the present invention, the ratio of the retardation value in the thickness direction to the retardation value in the plane direction of the retardation compensation film is preferably 0.4 to 1.5.

In addition, the retardation value in the plane direction and the retardation value in the thickness direction of the retardation compensation film for in-plane switching (IPS) mode liquid crystal display according to the present invention are preferably 50 to 250 nm in light having a wavelength of 550 nm, respectively.

Hereinafter, the present invention will be described in detail. Prior to this, terms or words used in the specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

Retardation compensation film according to the present invention has a birefringence (nx ≠ ny = nz, nx and ny are in-plane refractive index, nz represents the refractive index in the thickness direction) in the plane direction to prevent light leakage in the horizontal direction , Positive birefringence (nx = ny <nz) in the thickness direction to prevent light leakage in the vertical direction. The retardation compensation film of the present invention is a styrene-maleic anhydride copolymer containing the first styrene monomer unit (A) and the maleic anhydride monomer unit (B) in a weight ratio (A: B) of 98 to 60: 2 to 40, and A second styrene monomer unit (C) and a methyl methacrylate monomer unit (D) are prepared from a mixture of styrene-methyl methacrylate copolymers containing a weight ratio (C: D) of 80 to 20:20 to 80.

The styrene-maleic anhydride copolymer constituting the retardation compensation film of the present invention has a weight ratio (A: B) of 98 to 60: 2 to 40, preferably a first styrene monomer unit (A) and a maleic anhydride monomer unit (B). Is contained in the weight ratio of 95-70: 5-25. When the weight ratio of the maleic anhydride monomer unit to the first styrene monomer unit is less than 2% by weight, the effect of improving the heat resistance of the film is insignificant, and when the weight ratio exceeds 40% by weight, it becomes difficult to express the phase difference value of the film. In addition, the styrene-methyl methacrylate copolymer constituting the retardation compensation film of the present invention is a weight ratio (C) of the second styrene monomer unit (C) and the methyl methacrylate monomer unit (D) of 80 to 20:20 to 80 : D), Preferably it is contained in the weight ratio of 60-40: 40-60. When the weight ratio of the methyl methacrylate monomer unit to the second styrene monomer unit is less than 20% by weight, the light transmittance improvement effect of the film is insignificant, and when the weight ratio exceeds 80% by weight, it becomes difficult to express the phase difference value of the film.

The styrene-maleic anhydride copolymer and the styrene-methyl methacrylate copolymer are preferably mixed in a weight ratio of 30 to 90:70 to 10 in view of heat resistance and light transmittance improvement.

As described above, according to the present invention, a styrene-maleic anhydride copolymer copolymerized with a maleic anhydride monomer unit to a styrene monomer unit and a styrene-methylmethacrylate copolymer copolymerized with a methyl methacrylate monomer unit to a styrene monomer unit according to the present invention. The retardation compensation film prepared by mixing is to improve the heat resistance and light transmittance of the film while maintaining the birefringence characteristics inherent to polystyrene.

In the retardation compensation film for in-plane switching (IPS) mode liquid crystal display device of the present invention, retardation compensation using a copolymer mixture further blended with other homopolymers or copolymers within the scope of not impairing the object of the present invention. Films can be prepared, and other monomer units such as norbornene, norbornene derivatives, butadiene, etc., may be used as styrene-maleic anhydride copolymers or styrene-methylmethacrylate copolymers to the extent that they do not impair the object of the present invention. Of course, a predetermined amount can be further copolymerized.

In the retardation compensation film for in-plane switching (IPS) mode liquid crystal display device of the present invention, the ratio of the retardation value in the thickness direction to the retardation value in the plane direction is preferably 0.4 to 1.5. In the plane direction and the thickness direction, each preferably has a value of 50 to 250 nm. In addition, the optical axis of the retardation compensation film is perpendicular to the stretching direction (90 degrees) or the same as the stretching direction.

As a method for producing a retardation film for in-plane switching (IPS) mode liquid crystal display device, a melt extrusion method in which a molten amorphous thermoplastic resin is extruded from a die of an extruder in a sheet form, and a polymer resin is dissolved in an organic solvent. However, a general manufacturing method such as a solution cast method for casting and drying the film to a support may be used, but a solution cast method is preferable for producing a uniform film.

As a solvent for dissolving the copolymers constituting the retardation film of the present invention when using the solution cast method, aromatic hydrocarbons such as toluene, xylene, ethylbenzene, and cyclic cyclic cyclohexane Aromatic halogenated hydrocarbons such as hydrocarbons, chlorobenzene, dichloro benzene, trichloro benzene, non-aromatic halogenated hydrocarbons such as halogenated methane, heterohydrocarbons such as tetrahydrofurane, and the like Can be mentioned. From the standpoint of safety (fire prevention), halogenated hydrocarbons are relatively safe, and among them, low boiling point non-aromatic halogenated hydrocarbons are more preferable in terms of solvent volatilization. Methylene chloride is the most preferred solvent.

  For example, the specific method of manufacturing the retardation film of this invention is as follows. According to the present invention, an amorphous thermoplastic styrene-maleic anhydride copolymer resin copolymerized with a first styrene monomer and a maleic anhydride monomer in a predetermined content ratio, and an amorphous thermoplastic styrene-methyl copolymerized with a styrene monomer and a methyl methacrylate monomer in a predetermined content ratio The methacrylate copolymer is dissolved in organic solvent methylene chloride (MC). The copolymers are dissolved in the solvent in a total content of 5 to 70% by weight, more preferably 10 to 50% by weight, most preferably 20 to 40% by weight.

The solution in which the copolymers are dissolved is cast on a support having a smooth surface by using a bar coater, a doctor knife, a gold meir bar, a roll, a T die, or the like. Cast) or applied and dried to remove the solvent and then peeled off on the support to obtain a film. When removing the solvent, it is preferable that bubbles are not generated by rapid drying or hot air drying. For example, after evaporating the solvent to some extent through low temperature drying, it is better to raise the temperature to remove the residual solvent. As a support body which has a smooth surface, it is preferable to use a mirror plate-processed metal plate, a glass plate, a carrier film of a polymeric resin material, etc. In general, the polymer film that can be produced by the cast (Cast) method has a thickness of 10 ~ 1000um.

The film produced through the above method may be manufactured with a film having retardation compensation characteristics as the stretching treatment, and may exhibit uniform retardation in the in-plane and thickness directions. As long as the stretching method can compensate for the phase difference of the liquid crystal molecules in the liquid crystal display device, stretching in the uniaxial direction or in the biaxial direction may be possible, and a special stretching method capable of controlling the polymer orientation in the thickness direction may be applied.

When stretching the solution cast unstretched film, the elongation is adjusted according to the desired birefringence. That is, although draw ratio is set according to expression of the thickness of an unstretched film and an appropriate retardation value, 1.1-3 times is preferable normally. When the draw ratio is lower than 1.1, it is difficult to obtain a film having a sufficient retardation due to the low birefringence. When the draw ratio is higher than 3, the deviation of the retardation value of the stretched film is increased, and the neck in is increased. .

The retardation film obtained by the above-described method may be used as it is, and may be applied to an in-plane switching (IPS) mode liquid crystal display by attaching it to an optically isotropic film or a polarizer protective film by performing various processing.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, embodiments according to the present invention can be modified in many different forms, the scope of the present invention should not be construed as limited to the embodiments described below. Embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Table 1 shows the properties of the polystyrene and styrene-maleic anhydride copolymers used in this example.

&Lt; Example 1 >

The styrene-methylmethacrylate copolymer and styrene-maleic anhydride copolymer (7 wt% of styrene-maleic anhydride) specified in Table 1 were mixed in a weight ratio of 1: 4 to methylene chloride (Methylene Chloride, MC) to 28 wt%. It was added and stirred for 24 hours to obtain a resin solution. The obtained resin solution was applied to a surface polished plate glass, and a film having a width of about 250 mm and a length of 300 mm was cast using a bar coater to obtain a film having a thickness of 113 μm. The film cast glass was dried in an air reflux oven at 20 ° C. for 1 hour, then dried in a 60 ° C. vacuum oven for 2 hours, and then peeled off. The surface direction retardation (Rin) value of the unstretched film was 0.32 nm, and the thickness direction retardation (Rth) value was 32.9 nm.

The prepared unstretched cast film was cut to have a width of 10 cm and a length of 15 cm, and 20% of the film length was stretched at a speed of 100 mm / min at Tg. The prepared compensation film had a transmittance of 90.0%, Tg 113 ° C., and the optical axis direction was perpendicular to the stretching direction. The planar retardation (Rin) value of the film was 178 nm and the thickness retardation (Rth) value of 182 nm. The plane direction retardation value Rin and the thickness direction retardation value Rth were measured in the center part of the film, respectively. Rin and Rth values are defined as follows.

Rin = (nx-ny) x d

Rth = (nz-ny) x d

Here, nx is a refractive index of a extending | stretching direction among the planar refractive index of a stretched film, ny is a vertical refractive index of a extending | stretching direction, ny and a refractive index of a thickness direction is called nz, and d represents the thickness of a film.

<Example 2>

A styrene-methyl methacrylate copolymer and a styrene-maleic anhydride copolymer (14 wt% styrene-maleic anhydride 14%) specified in Table 1 were mixed in a weight ratio of 1: 4, and a film having a thickness of 113 um was cast. Except what was obtained, the film was manufactured by the same method as Example 1. The prepared compensation film showed a transmittance of 90.1% and Tg 121 ° C., and the optical axis direction was perpendicular to the stretching direction.

The plane direction retardation (Rin) of the unstretched film was 0.54 nm and the thickness retardation (Rth) was 40.9 nm, and the plane direction retardation (Rin) of the film stretched 20% in the longitudinal direction was 134 nm and the thickness retardation (Rth) value was 82.1 nm.

<Example 3>

Styrene-methylmethacrylate copolymer and styrene-maleic anhydride copolymer (14 wt% of styrene-maleic anhydride) specified in Table 1 were mixed in a weight ratio of 1: 1, and a film having a thickness of 118 um was cast. Except what was obtained, the film was manufactured by the same method as Example 1. The prepared compensation film showed a transmittance of 90.0% and Tg 113 ° C., and the optical axis direction was perpendicular to the stretching direction.

The surface direction retardation (Rin) of the unstretched film was 0.17 nm, and the thickness retardation (Rth) was 22.2 nm, and the film stretched 20% in the longitudinal direction was 143 nm and the thickness direction retardation (Rth) value was 66.5 nm.

&Lt; Comparative Example 1 &

A film was manufactured in the same manner as in Example 1, except that a film having a thickness of 110 μm was obtained using a polystyrene resin (Aldrich, pellet is transparent, and Mw is 350,000). The prepared compensation film showed a transmittance of 89.5% and Tg 100 ° C., and the optical axis direction was perpendicular to the stretching direction.

The surface direction retardation (Rin) of the unstretched film was 0.45 nm, and the thickness retardation (Rth) was 82 nm. The film stretched 20% in the longitudinal direction was 180 nm, and the thickness direction retardation (Rin) was 90 nm. Rth) was 182 nm.

As described above, the retardation compensation film for in-plane switching (IPS) mode liquid crystal display of the present invention is a blend of these copolymers after copolymerizing monomers capable of improving heat resistance and light transmittance with styrene monomers, respectively. By using, not only improved heat resistance and light transmittance, but also one film can perform the function of the A plate compensation film and the C plate compensation film to compensate for the leakage of light in the vertical direction at the same time.

Claims (8)

Phase difference compensation for in-plane switching (IPS) mode liquid crystal display with birefringence in the plane direction to prevent light leakage in the horizontal direction and positive birefringence in the thickness direction to prevent light leakage in the vertical direction In the film, The retardation compensation film is a styrene-maleic anhydride copolymer containing a first styrene monomer unit (A) and a maleic anhydride monomer unit (B) in a weight ratio (A: B) of 98 to 60: 2 to 40, and the second styrene Phase difference characterized in that it is formed from a mixture of styrene-methylmethacrylate copolymers containing monomer unit (C) and methyl methacrylate monomer unit (D) in a weight ratio (C: D) of 80 to 20:20 to 80. Compensation film. The method of claim 1, The mixed weight ratio of the styrene-maleic anhydride copolymer and the styrene-methyl methacrylate copolymer is 30 ~ 90: 70 ~ 10 phase difference compensation film, characterized in that. The method of claim 1, Retardation compensation film, characterized in that the weight ratio of the first styrene monomer unit (A) and the maleic anhydride monomer unit (B) of the styrene-maleic anhydride copolymer is 95 ~ 75: 5 ~ 25. The method of claim 1, Retardation compensation film, characterized in that the weight ratio of the second styrene monomer unit (C) and the methyl methacrylate monomer unit (D) of the styrene-methyl methacrylate copolymer is from 60 to 40:40 to 60. The method of claim 1, Retardation compensation film, characterized in that the ratio of the retardation value in the thickness direction to the retardation value in the plane direction of the retardation compensation film is 0.4 ~ 1.5. The method of claim 1, Retardation compensation film, characterized in that the optical axis of the retardation compensation film perpendicular to the stretching direction. The method of claim 1, Retardation compensation film, characterized in that the retardation value in the surface direction and the retardation value in the thickness direction of the retardation compensation film is 50 ~ 250nm respectively in the light of 550nm wavelength. An in-plane switching (IPS) mode liquid crystal display device comprising the retardation compensation film of claim 1.

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