KR101211603B1 - 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, characterized by being formed of a copolymer containing a styrene monomer unit (A) and an acrylic monomer unit (B) in a weight ratio (A: B) of 80 to 20:20 to 80. The retardation compensation film for in-plane switching (IPS) mode liquid crystal display of the present invention not only has excellent light transmittance, but also simultaneously performs the functions of the A plate compensation film and the C plate compensation film which compensates for light leakage in the vertical direction. Can be done.

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.

3 is a light transmittance spectrum of the retardation compensation film according to the embodiment and the comparative example of the present invention.

4 is a graph showing changes in the retardation value in the plane direction and the retardation value in the thickness direction before and after the stretching of the retardation compensation film according to Examples and Comparative Examples.

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. TN mode is widely used as a liquid crystal display device by interposing a liquid crystal layer in which a nematic liquid crystal is twisted between two orthogonal polarizing plates, and then causing an electric field to be perpendicular to the substrate. . 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 Compensation for the vertical phase, 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 attached to the outermost sides of the liquid crystal panel 50 are stretched films, which include a triacate cellulose (TAC) film, a poly vinyl alcohol (PVA) film, a protective film, It consists of several layers of film such as a 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 the plane of the film and 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 retardation compensation film made of polystyrene has a light transmittance of 90% or less, a compensation film material having higher light transmittance while maintaining the properties of polystyrene is required.

Therefore, the technical problem to be achieved by the present invention was devised to solve the above-mentioned problems, not only excellent light transmittance, but also the function of the C plate compensation film to compensate for the leakage of light in the vertical direction and the A plate compensation film The present invention provides a retardation compensation film for an in-plane switching (IPS) mode liquid crystal display device and an in-plane switching (IPS) mode liquid crystal display device 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 in-plane switching (IPS) mode liquid crystal display having a styrene monomer unit (A) and an acrylic monomer unit (B) in a weight ratio (A: B) of 80 to 20:20 to 80. It is characterized by being formed of one copolymer.

The retardation compensation film for in-plane switching (IPS) mode liquid crystal display of the present invention not only improves light transmittance by the copolymerized acrylic monomer unit, but also prevents light leakage in the vertical direction from the A plate compensation film with only one film. Can perform the function of the compensation C plate compensation film at the same time.

In the retardation compensation film for in-plane switching (IPS) mode liquid crystal display device of the present invention, it is preferable to use methyl methacrylate as the acrylic monomer unit, and the thickness direction with respect to the retardation value in the plane direction of the retardation compensation film. It is preferable that ratio of retardation value of is 1-1.2.

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 configuration shown in the drawings are only the most preferred embodiments 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 made of a copolymer comprising a styrene monomer unit (A) and an acrylic monomer unit, the weight ratio of the styrene monomer unit (A) and the acrylic monomer unit (B) 80 ~ 20: 20 ~ 80 ( A: B), Preferably it is contained in the weight ratio of 60-40: 40-60. When the weight ratio of the acrylic monomer unit to the 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.

As described above, the retardation compensation film prepared by using the polymer copolymerized with the acrylic monomer unit to the styrene monomer unit according to the present invention improves the light transmittance of the film while maintaining the birefringence characteristic of polystyrene.

In the retardation compensation film for in-plane switching (IPS) mode liquid crystal display device of the present invention, the acrylic monomer unit is preferably methyl methacrylate, and a monomer unit made of another acrylate derivative may be used. In addition, other monomer units such as norbornene, norbornene derivatives, butadiene, etc. may be further included in a predetermined amount as long as the object of the present invention is not impaired.

In the retardation compensation film for in-plane switching (IPS) mode liquid crystal display device of the present invention, it is preferable that the ratio of the retardation value in the thickness direction to the retardation value in the plane direction is 1 to 1.2. In the plane direction and the thickness direction, each preferably has a value of 50 to 250 nm, more preferably 100 to 150 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 copolymer constituting the retardation film of the present invention when using the solution cast method, aromatic hydrocarbons such as toluene, xylene, ethylbenzene, and cyclic compounds such as cyclohexane Aromatic halogenated hydrocarbons such as hydrocarbons, chlorobenzene, dichloro benzene, trichloro benzene, non-aromatic halogenated hydrocarbons such as halogenated methane, heterohydrocarbons such as tetrahydrofuran, 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-methylmethacrylate copolymer resin obtained by copolymerizing a styrene monomer and a methyl methacrylate monomer in a predetermined content ratio is dissolved in methylene chloride (MC) which is an organic solvent. The styrene-methylmethacrylate copolymer is dissolved in the solvent in an amount 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 styrene-methyl methacrylate copolymer was dissolved may be smoothed by using a bar coater, a doctor knife, a gold meir bar, a roll, a T die, or the like. Cast or apply onto the excitation support and dry to remove the solvent, then peel off from the support to obtain a styrene-methylmethacrylate film. When removing the solvent, it is preferable that bubbles are not generated by rapid drying or hot air drying. For example, it is better to volatize the solvent to some extent through low temperature drying, and then 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 (PS), polymethyl methacrylate (PMMA) and styrene-methyl methacrylate (St-MMA) copolymers used in this example.

&Lt; Example 1 >

The styrene-methylmethacrylate copolymer resin specified in Table 1 was added with methylene chloride (Methylene Chloride, MC) to 28% by weight and stirred for 24 hours to obtain a resin solution. The obtained resin solution was applied to the surface polished plate glass, and a film of about 250 mm in width and 300 mm in length was cast using a bar coater. 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 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 optical axis direction of the prepared compensation film was perpendicular to the stretching direction.

In Table 2, the film thickness before and after extending | stretching, surface direction retardation value Rin, thickness direction retardation value Rth, and light transmittance in 550 nm were shown.

3 and 4 show graphs showing changes in the light transmittance spectrum of the compensation film according to the present embodiment, the retardation value in the plane direction and the retardation value in the thickness direction before and after stretching. 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.

&Lt; Comparative Example 1 &

A film was prepared in the same manner as in Example 1, except that the film was prepared using the polystyrene resin shown in Table 1. The optical axis direction of the prepared compensation film was perpendicular to the stretching direction.

In Table 2, the film thickness before and after extending | stretching, surface direction retardation value Rin, thickness direction retardation value Rth, and light transmittance in 550 nm were shown. 3 and 4 show graphs showing changes in the light transmittance spectrum of the compensation film according to the present comparative example, the retardation value in the plane direction and the retardation value in the thickness direction before and after stretching.

Comparative Example 2

A film was prepared in the same manner as in Example 1, except that the film was prepared using the polymethylmethacrylate resin shown in Table 1. The optical axis direction of the prepared compensation film was the same as the stretching direction.

In Table 2, the film thickness before and after extending | stretching, surface direction retardation value Rin, thickness direction retardation value Rth, and light transmittance in 550 nm were shown. 3 and 4 show graphs showing changes in the light transmittance spectrum of the compensation film according to the present comparative example, the retardation value in the plane direction and the retardation value in the thickness direction before and after stretching.

Referring to Table 2 and Figures 3 to 4, the retardation compensation film for in-plane switching (IPS) mode liquid crystal display device made of the styrene-methyl methacrylate copolymer of Example 1 according to the present invention is made of polystyrene It can be seen that the light transmittance is improved and the retardation value is well expressed than the compensation film.

On the other hand, the compensation film made of polymethyl methacrylate is excellent in transparency, but it can be seen that the phase difference value was not expressed.

As described above, the retardation compensation film for in-plane switching (IPS) mode liquid crystal display device of the present invention is not only improved light transmittance by the copolymerized acrylic monomer unit, but also perpendicular to the A plate compensation film with only one film. It can simultaneously perform the function of the C plate compensation film to compensate for the leakage of light in the direction.

Claims (7)

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 retardation compensation film, characterized in that formed from a copolymer containing a styrene monomer unit (A) and an acrylic monomer unit (B) in a weight ratio (A: B) of 80 to 20: 20 to 80. The method of claim 1, The acrylic monomer unit is a phase difference compensation film, characterized in that methyl methacrylate. The method of claim 1, Retardation compensation film, characterized in that the weight ratio of the styrene monomer unit (A) and the acrylic monomer unit (B) of the copolymer is 60 ~ 40: 40 ~ 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 1 to 1.2. 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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