KR20130087169A - A laminated polarizer set and in-plane switching mode liquid crystal display comprising the same - Google Patents

Abstract

The present invention relates to a composite polarizer set and an IPS mode liquid crystal display including the same. More specifically, the refractive index ratio NZ is 0 and the front phase difference value R0 is 600 nm or less in the upper and lower polarizing plates, respectively. The present invention relates to a composite polarizer set including a uniaxially stretched negative A plate having a slow axis orthogonal to an absorption axis of an adjacent polarizer, and a liquid crystal display device including the composite polarizer set and the IPS mode liquid crystal.
The IPS mode liquid crystal display device including the composite polarizing plate set according to the present invention exhibits a viewing angle equivalent to that of a conventional isotropic film, and is exposed to a high temperature and high humidity for a long time to change the front phase difference value R0 of the negative A plate. Even the first designed optical characteristics can be maintained.

Description

A composite set polarizer and an IPS mode liquid crystal display including the same {A LAMINATED POLARIZER SET AND IN-PLANE SWITCHING MODE LIQUID CRYSTAL DISPLAY COMPRISING THE SAME}

The present invention relates to a composite polarizing plate set having a small change in color according to a viewing angle and environment (temperature, humidity change) at an equivalent level to an isotropic film, and an IPS mode liquid crystal display including the same.

Liquid crystal display (LCD) is widely used as a popular image display device.

Such liquid crystal displays are classified into modes according to the initial arrangement of the liquid crystal, the electrode structure, and the physical properties of the liquid crystal. Most commonly used liquid crystal display devices include twisted nematic (TN), vertical alignment (VA), and plane switching (IPS). In addition, it is classified into a normal black or normal white mode according to whether light is transmitted when no voltage is applied. In addition, the VA mode is classified into PVA (Patterned VA), SPVA (Super PVA) and MVA (multidomain VA), and the IPS mode is classified into S-IPS or FFS according to domain and liquid crystal initial arrangement.

In the planar switching mode (hereinafter referred to as IPS mode), the liquid crystal molecules have a substantially horizontal and uniform arrangement on the surface of the liquid crystal substrate in a non-driven state. In the IPS mode, when the transmission axis of the lower substrate and the fast axis of the liquid crystal molecules coincide with each other in the front side, the transmission axis of the lower substrate and the fastening axis of the liquid crystal molecules coincide on all four sides. Accordingly, in the IPS mode liquid crystal display, since the light passing through the lower polarizer passes through the liquid crystal without causing a change in the polarization state, the dark state can be realized in the non-driven state by the polarizers arranged above and below.

The IPS mode liquid crystal display can obtain a wide viewing angle without using an optical film that compensates for the change in polarization state of light, thereby ensuring natural transmittance and uniform image quality and viewing angle on the entire screen.

Conventional IPS mode liquid crystal display device includes a liquid crystal cell containing a liquid crystal, a polarizer for polarizing light on both sides of the liquid crystal cell, a polarizer protective film made of a triacetate cellulose (TAC) film on one side or both sides of the polarizer. . In this case, when the liquid crystal expresses a black state, the light polarized by the polarizer provided in the lower plate is elliptically polarized by triacetate cellulose on the inclined plane, and the elliptically polarized light is amplified in the liquid crystal cell and the light leakage is At the same time, they have various colors.

Recently, the IPS mode liquid crystal display has been required to secure a wide viewing angle by improving the phenomenon of light leakage and various colors while increasing the size.

In the IPS mode LCD, an isotropic protective film is provided between one polarizer (PVA) and a liquid crystal cell, and two or more retardation films having different optical characteristics are laminated between the other polarizer (PVA) and the liquid crystal cell. One Z-axis orientation (thickness orientation) film is provided.

However, the retardation film is easy to improve the optical properties, but there is a problem that the retardation and visibility change occurs because the physical properties of the film sensitively reacts to physical changes under high temperature and humid external environment. In order to suppress the occurrence of the above problems, most of the planar switching mode liquid crystal display devices use an isotropic protective film that does not generate a phase difference by the influence of the surrounding environment in addition to the optimum environment instead of the retardation film.

An object of the present invention is to provide a composite polarizer set having less change in color in view angle and environment (temperature, humidity) change equivalent to that of an isotropic film in which a conventional phase difference does not occur.

In addition, the present invention, even if the front phase difference value (R0) of the retardation film is changed due to prolonged exposure to a high temperature and high humidity environment for the first time designed optical properties (the change of color according to the viewing angle and environment equivalent to that of the isotropic film is less). It is intended to provide a sustainable composite polarizer set.

The present invention also provides an IPS mode liquid crystal display device to which the composite polarizer set is applied.

The present inventors have attempted to maintain the originally designed viewing angle even with a change in the front retardation value R0 of the retardation film, out of the general concept that the viewing angle is changed when the retardation film deviates from the originally designed front retardation value R0. As a result, it was found that the negative A plate having the specific refractive index ratio NZ and the front phase retardation value R0 exhibits a viewing angle equivalent to that of the conventional isotropic film within the above range, thereby completing the present invention.

Accordingly, the present invention includes a top plate polarizer laminated in the order of the protective film, the polarizer and the uniaxially-stretched negative A plate, and a bottom plate polarizer laminated in the order of the uniaxially stretched negative A plate, the polarizer and the protective film. The negative A plates of the lower polarizing plate each provide a composite polarizing plate set having a refractive index ratio NZ of 0, a front phase difference value R0 of 600 nm or less, and whose slow axis is orthogonal to the absorption axis of adjacent polarizers.

Preferably, the negative A plate may have a front retardation value R0 of 0 to 250 nm.

The negative A plate may be selected from the group consisting of polycarbonate (PC), polystyrene (PS), and polymethyl methacrylate (PMMA).

Each absorption axis of the upper polarizing plate and the lower polarizing plate may be perpendicular to each other.

In addition, the present invention provides an IPS mode liquid crystal display device including the composite polarizer set.

The IPS mode liquid crystal display including the polarizing plate set of the present invention may exhibit a viewing angle equivalent to that of an isotropic film in which a phase difference is not generated even by the influence of the surrounding environment in addition to the conventional optimum environment.

In addition, the IPS mode liquid crystal display device including the polarizing plate set according to the present invention has the first optical characteristics (equivalent to that of an isotropic film) even when the front phase difference value R0 of the negative A plate is changed due to prolonged exposure to a high temperature and high humidity environment. Less change in color depending on the viewing angle and environment).

In addition, since the physical behavior of the polarizer and the negative A plate is similar, the IPS mode liquid crystal display including the polarizing plate set according to the present invention has a low possibility of staining even when exposed to a high temperature and high humidity environment for a long time.

In addition, the present invention may be useful when the composite polarizer set or the liquid crystal display including the composite polarizer set is transported or used in a high temperature and high humidity region such as a tropical region, an area adjacent to the sea, and an equator. have.

In addition, the present invention can be effectively used even when the distance between the polarizer and the backlight is reduced by using a backlight with a large amount of heat generation for better clarity or thinning the liquid crystal display.

1 is a perspective view showing the structure of an IPS mode liquid crystal display device according to the present invention;
2 is a schematic view for explaining the refractive index of the retardation film according to the present invention,
Figure 3 is a schematic diagram showing the MD direction in the manufacturing process for explaining the stretching direction of the retardation film and the polarizing plate according to the present invention,
FIG. 4 shows the omnidirectional transmittance when the isotropic film is applied instead of the negative A plate in the structure of the IPS mode liquid crystal display of FIG.
FIG. 5 illustrates omnidirectional transmittance and omnidirectional color according to a change in the front phase difference value of the negative A plate in the IPS mode liquid crystal display of Example 1 according to the present invention.
FIG. 6 illustrates omnidirectional transmittance and omnidirectional color according to a change in the front phase difference value of the negative A plate in the IPS mode liquid crystal display of Example 2 according to the present invention.
FIG. 7 shows the omnidirectional transmittance and omnidirectional color according to the change of the front phase difference value of the negative A plate in the IPS mode liquid crystal display of Example 3 according to the present invention.
FIG. 8 illustrates omnidirectional transmittance and omnidirectional color according to a change in the front phase difference value of the negative A plate in the IPS mode liquid crystal display of Comparative Example 1;
FIG. 9 shows the omnidirectional transmittance and omnidirectional color according to the change of the front phase difference value of the negative A plate in the IPS mode liquid crystal display of Comparative Example 2. FIG.

The present invention relates to a composite polarizing plate set having a small change in color according to a viewing angle and environment (temperature, humidity change) at an equivalent level to an isotropic film, and an IPS mode liquid crystal display including the same.

Hereinafter, the composite polarizing plate set of the present invention will be described in detail.

The composite polarizing plate set of the present invention includes a top plate polarizer laminated in the order of the protective film, the polarizer and the uniaxially stretched negative A plate, and a bottom plate polarizer laminated in the order of the uniaxially stretched negative A plate, the polarizer and the protective film.

The negative A plates of the upper and lower polarizing plates each have a refractive index ratio NZ of 0, a front phase difference value R0 of 600 nm or less, and a slow axis thereof is disposed orthogonal to the absorption axis of the adjacent polarizer.

The polarizer is an optical film which serves to convert incident natural light into a desired single polarization state (linear polarization state), and is not particularly limited as long as it can generally perform a polarization function in the art.

The polarizer may be prepared by, for example, dyeing iodine or dichroic dye in a polyvinyl alcohol (PVA) film and stretching it in a predetermined direction. In addition, a thin polarizing plate having a fine pattern of conductive gratings having a polarizing function and having an insulating layer coated on the valleys and floors of the grating may be used on the transparent substrate.

Polyvinyl alcohol-type resin which comprises a polarizer can be manufactured by saponifying polyvinyl acetate type resin. As an example of polyvinyl acetate type resin, the copolymer with polyvinyl acetate which is a homopolymer of vinyl acetate, and the other monomer copolymerizable with vinyl acetate etc. are mentioned. Specific examples of the other monomer copolymerizable with vinyl acetate include unsaturated carboxylic acids, unsaturated sulfonic acids, olefins, vinyl ethers, acrylamides having an ammonium group, and the like.

In addition, the polyvinyl alcohol resin may be modified. For example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used. The degree of saponification of the polyvinyl alcohol resin may be generally 85 to 100 mol%, preferably 98 mol% or more. In addition, the degree of polymerization of the polyvinyl alcohol-based resin is usually 1,000 to 10,000, preferably 1,500 to 5,000.

This polyvinyl alcohol-based resin is formed into a film and used as a polarizer. The film forming method of the polyvinyl alcohol-based resin is not particularly limited, and various known methods can be used. The film thickness of the polyvinyl alcohol-based resin is not particularly limited, and may be, for example, 10 to 150 μm.

A polarizer is normally manufactured through the process of uniaxially stretching a polyvinyl alcohol-type film as described above, a process of dyeing with a dichroic dye, adsorbing, treating with an aqueous solution of boric acid, and washing with water and drying.

The process of uniaxially stretching the polyvinyl alcohol-based film may be performed before dyeing, simultaneously with dyeing, or after dyeing. If uniaxial stretching is carried out after dyeing, it may be carried out before or during boric acid treatment. Of course, it is also possible to perform uniaxial stretching in a plurality of steps. Uniaxial stretching may use rolls or thermal rolls having different circumferential speeds, and may be dry stretching in the air or wet stretching in a state swelled with a solvent. The draw ratio is usually 3 to 8 times.

In the step of dyeing a stretched polyvinyl alcohol film with a dichroic dye, for example, a method of immersing a polyvinyl alcohol film in an aqueous solution containing a dichroic dye may be used. Specific examples of dichroic dyes include iodine or dichroic dyes. It is preferable that the polyvinyl alcohol film is pre-immersed in water before dyeing to swell.

When iodine is used as the dichroic dye, a method in which a polyvinyl alcohol-based film is dipped in an aqueous solution for dyeing usually containing iodine and potassium iodide may be used. Usually, the content of iodine in an aqueous solution for dyeing is 0.01 to 1 part by weight with respect to 100 parts by weight of water (distilled water), and the content of potassium iodide is 0.5 to 20 parts by weight with respect to 100 parts by weight of water. The temperature of the aqueous solution for dyeing is usually 20 to 40 占 폚, and the immersion time, for example, the dyeing time is usually 20 to 1800 seconds.

On the other hand, when a dichroic organic dye is used as the dichroic dye, a method in which a polyvinyl alcohol film is dipped in an aqueous solution for dyeing usually containing a water-soluble dichroic organic dye is used. The content of the dichroic organic dye in the aqueous solution for dyeing is usually 1 × 10 ^-4 to 10 parts by weight, preferably 1 × 10 ^-3 to 1 part by weight based on 100 parts by weight of water. The aqueous solution for dyeing may further contain an inorganic salt such as sodium sulfate as a dyeing aid. The temperature of the aqueous solution for dyeing is usually 20 to 80 캜, and the immersion time, for example, the dyeing time is usually 10 to 1,800 seconds.

The step of treating the dyed polyvinyl alcohol film with boric acid can be carried out by immersing it in an aqueous solution containing boric acid. The content of boric acid in an aqueous solution containing boric acid is usually 2 to 15 parts by weight, preferably 5 to 12 parts by weight based on 100 parts by weight of water. The boric acid-containing aqueous solution in the case of using iodine as a dichroic dye preferably contains potassium iodide, and its content is usually 0.1 to 15 parts by weight, preferably 5 to 12 parts by weight with respect to 100 parts by weight of water. The temperature of the boric acid-containing aqueous solution is 50 ° C or higher, preferably 50 to 85 ° C, more preferably 60 to 80 ° C, and the immersion time is 60 to 1,200 seconds, preferably 150 to 600 seconds, more preferably It is preferable that it is 200 to 400 seconds.

After the boric acid treatment, the polyvinyl alcohol-based film is washed with water and dried. Washing treatment can be performed by immersing the boric acid-treated polyvinyl alcohol-based film in water. The temperature of the water during the washing treatment is 5 to 40 ℃, immersion time is 1 to 120 seconds. After washing with water, it is dried to obtain a polarizer. The drying treatment may be generally performed using a hot air dryer or a far infrared heater, and the drying treatment temperature is usually 30 to 100 ° C., preferably 50 to 80 ° C., and the drying time is usually 60 to 600 seconds, preferably 120 to 80 ° C. 600 seconds is good.

The polarizer may have a thickness of 5 to 40 μm.

In the present invention, the uniaxially stretched negative A plate has a refractive index ratio NZ of 0 and a front phase difference value R0 of 600 nm or less.

The negative A plate of the present invention is produced by stretching a film fabric having a negative refractive index characteristic in which the refractive index becomes smaller in the stretching direction in the direction of unwinding the fabric. Therefore, the slow axis of the film is perpendicular to the direction in which the fabric unwinds relative to the film fabric.

The negative A plate theoretically means a case where the refractive index ratio NZ is zero, but in order to obtain the effect of the film manufacturing process and the viewing angle compensation, in reality, the negative A plate may exhibit substantially the same characteristics as the case where the refractive index ratio NZ is zero. The refractive index ratio (NZ) range is also treated as being a negative A plate.

However, the present invention is limited to a negative A plate having a refractive index ratio NZ of 0, which exhibits a viewing angle and a color equivalent to that of an isotropic film in which a conventional phase difference does not occur.

In addition, when the front retardation value (R0) exceeds 600 nm, since the width of the film fabric becomes narrow due to high stretching, it is preferably 0 to 450 nm, more preferably in consideration of the width and color change of the film fabric. It is preferable that it is 0-250 nm below. That is, in the above range, the smaller the front retardation value, the smaller the color change caused by the environment (temperature, humidity) change.

The optical characteristics of the negative A plate are defined by the following equations (1) to (3) for the electric field in the visible light region.

In general, it is the optical characteristic for 589nm which is most easily obtained when there is no mention of the wavelength of the light source. Where Nx is the refractive index of the axis with the largest refractive index in the in-plane direction, Ny is the vertical direction of Nx in the in-plane direction, and Nz is the refractive index in the thickness direction as shown in FIG. 2.

(Where Nx and Ny are planar refractive indices, Nx ≧ Ny, Nz is the thickness direction refractive index of the film, and d represents the thickness of the film)

(Where Nx and Ny are the plane refractive indices of the retardation film, and d represents the thickness of the film, where Nx ≧ Ny)

Where Nx and Ny are planar refractive indices, and Nx≥Ny, Nz is the thickness direction refractive index of the film, and d is the thickness of the film.

Rth is a thickness retardation, and represents a difference in refractive index in the thickness direction with respect to the in-plane average refractive index. This is a reference value that cannot be referred to as the actual phase difference.

R0 is a front phase difference, which is a substantial phase difference when light passes through the normal direction (vertical direction) of the film. NZ is a refractive index ratio, and can distinguish the kind of plate of retardation film by this.

The type of plate applied to the retardation film may include an A plate when an optical axis in which the retardation does not exist exists in the in-plane direction of the film; A C plate when the optical axis is present in the vertical direction of the plane; And when there are two optical axes are divided into biaxial plates.

The negative A plate of the present invention may be made of a film having negative refractive index characteristics. Specifically, one selected from the group consisting of polycarbonate (PC), polystyrene (PS), and polymethyl methacrylate (PMMA) may be used.

Stretching is divided into fixed end stretching and free end stretching. Fixed-end stretching is a method of fixing lengths other than the extending direction while stretching the film. Free end stretching is a method of giving freedom in directions other than the stretching direction while stretching the film.

The negative A plate of this invention uniaxially stretches to the free end at high temperature.

Further, in addition to stretching, an additional process may be applied to control a direction of a slow axis, a phase difference value, and a value of NZ, and the additional process is not particularly limited to a process generally applied in the art.

Uniaxially stretched negative A plates cause their slow axes to be perpendicular to each other with the polarizer absorption axis of the lower polarizer. The polarizer made of polyvinyl alcohol (PVA) having a polarization function reacts most sensitively in a high temperature and high humidity environment of the polarizer. This is a result of stretching at a high draw ratio in the MD direction in order to impart polarization in the manufacturing process of the polarizer.

In addition, the negative A plate according to the present invention is also stretched in the MD direction. The MD direction is as shown in FIG.

Therefore, the present invention can improve the physical resistance to the external environment by arranging the stretching direction of the polarizer and the stretching direction of the negative A plate to be parallel to induce physical behavior to occur in the same direction.

The protective film is a generic term for a film for protecting the polarizer because the polarizer is mechanically weak.

As the protective film, a film having excellent transparency, mechanical strength, thermal stability, moisture shielding, and isotropy can be used. Since the moisture permeability varies depending on the type of the resin constituting the protective film, it is preferable to select the enemy in consideration of this.

Specific examples of the protective film include polyester-based resins such as polyethylene terephthalate, polyethylene isophthalate, polyethylene naphthalate, and polybutylene terephthalate; Cellulose-based resins such as diacetylcellulose and triacetylcellulose; Polycarbonate resin; Acrylic resins such as polymethyl (meth) acrylate and polyethyl (meth) acrylate; Styrene resins such as polystyrene and acrylonitrile-styrene copolymer; Polyolefin resins such as polyethylene, polypropylene, cyclo-based or norbornene-structured polyolefins, ethylene-propylene copolymers; Vinyl chloride resin; Amide resins such as nylon and aromatic polyamide; Imide resin; Polyether sulfone type resin; Sulfone based resin; Polyether sulfone type resin; Polyether ether ketone resin; A sulfided polyphenylene resin; Vinyl alcohol-based resins; Vinylidene chloride resins; Vinyl butyral resin; Allylate series resin; Polyoxymethylene type resin; Films selected from the group consisting of thermoplastic resins such as epoxy resins can be used, and films composed of blends of the thermoplastic resins can also be used. Further, a film made of a thermosetting resin such as (meth) acrylic, urethane, acrylic urethane, epoxy, or silicone or a film made of an ultraviolet curable resin may also be used.

The content of the thermoplastic resin in the protective film is 50 to 100% by weight, preferably 50 to 99% by weight, more preferably 60 to 98% by weight, most preferably 70 to 97% by weight. If the content is less than 50% by weight, it may not sufficiently express the inherent high transparency of the thermoplastic resin.

Polarizing plates are usually manufactured using a roll to roll process and a sheet to sheet process. Preferably, it is preferable to apply a roll to roll process in consideration of yield and efficiency in the manufacturing process, and in particular, the application thereof is effective because the absorption axis of the PVA polarizer is always fixed in the MD direction.

The composite polarizing plate set according to the present invention has characteristics similar to the omnidirectional transmittance of the black state (Fig. 4) when an isotropic protective film is used instead of the negative A plate of the upper and lower polarizing plates.

In addition, the composite polarizing plate set according to the present invention exhibits the first designed optical characteristics (a viewing angle and color equivalent to that of an isotropic film) even when the front phase difference value R0 of the negative A plate changes due to prolonged exposure to a high temperature and high humidity environment. I can keep it.

In general, the retardation change value of the retardation film provided in the polarizing plate at the time of environmental change is within ± 30nm range. At this time, the environmental change is usually changed at 60 to 105 ℃, Dry to 90 RH%, about 250 to 1000 hours.

In particular, in the present invention, since the stretching direction between the PVA polarizer and the retardation film is the same, stress does not accumulate between the two films, and therefore, the retardation change value is extremely rarely out of the range of ± 30 nm.

However, in the present invention, the simulation was performed by maximizing the amount of change in the phase difference value to ± 50 nm to obtain a result including the case out of the ± 30 nm range.

In addition, the composite polarizing plate set according to the present invention has a similar physical behavior between the polarizer and the negative A plate, so even when exposed to a high temperature and high humidity environment for a long time, a small stress is generated between the two films, which lowers the possibility of unintended staining.

The composite polarizer set of the present invention can be used in an IPS mode liquid crystal display device including the same.

The liquid crystal cell has a 90 ° (S-IPS) direction or a 0 ° liquid crystal alignment direction when the counterclockwise direction is set to the positive (+) direction based on the horizontal direction on the right side of the viewer while no voltage is applied. FFS) can be used.

The S-IPS has a panel retardation value (Δn × d) defined by Equation 4 below in a range of 300 to 330 nm at a wavelength of 589 nm, and an FFS of 330 to 400 nm.

(Where n _e represents the extraordinary refractive index of the liquid crystal, n _o represents the normal ray refractive index, and d represents the cell gap; Note. DELTA n, d is a scalar rather than a vector).

The absorption axis of the upper polarizing plate of the present invention is configured to be perpendicular to the absorption axis of the lower polarizing plate.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention. Such variations and modifications are intended to be within the scope of the appended claims.

Example 1

Measurement data of each optical film, a liquid crystal cell, and a backlight according to the present invention were stacked on a TECH WIZ LCD 1D (man system, KOREA) with the structure of FIG. 1. Referring to the structure of Figure 1 in detail.

IPS mode liquid crystal cell 30 in which the liquid crystal alignment direction is 90 ° when the counterclockwise direction is set to the positive (+) direction based on the right horizontal direction of the viewer side in the state where no voltage is applied, the lower polarizing plate 10 from the backlight side, and It consisted of the upper plate polarizing plate 20. The lower plate polarizer 10 laminated the negative A plate 14, the polarizer 11, and the protective film 13 from the liquid crystal cell side. The upper polarizing plate 20 laminated the negative A plate 24, the polarizer 21, and the protective film 23 from the liquid crystal cell side.

When the counterclockwise direction is set to the positive (+) direction based on the horizontal direction on the right side of the viewer, the polarizer 11 of the lower polarizer 10 has an absorption axis 12 of 90 ° and the polarizer 21 of the upper polarizer 20. ) The absorption shaft 22 was configured to be 0 °.

The liquid crystal cell used was applied to LG Display's 42-inch panel LC420WU5.

On the other hand, each of the optical film and the backlight used in the embodiment of the present invention was used to have the optical properties as follows.

The polarizers 11 and 21 of the lower polarizing plate 10 and the upper polarizing plate 20 were dyed with iodine on the stretched PVA to impart a polarizer function. The polarization performance of the polarizer has a visibility polarization of 99.9% or more and a visible light transmittance of 41% or more in a visible light region of 370 to 780 nm.

The visibility polarization and the visibility single transmittance are TD (λ) of the transmission axis according to wavelength, MD (λ) of the absorption axis according to the wavelength, and the visibility correction value defined in JIS Z 8701: 1999.

Is defined by the following equations (5) to (9). Where S (λ) is the light source spectrum and usually uses a C light source.

At the light source 589.3 nm, the negative A plate 24 of the upper polarizing plate and the negative A plate 14 of the lower polarizing plate each used a front phase difference value R0 of 150 nm and a refractive index ratio NZ of zero.

The absorption axis 22 of the upper polarizer 21 and the slow axis 25 of the negative A plate 24 are perpendicular to each other, and the slow axis of the absorption axis 12 and the negative A plate 14 of the lower polarizer 11 is orthogonal to each other. 15 was configured to be orthogonal.

The negative A plate 24 of the upper plate polarizing plate and the negative A plate 14 of the lower plate polarizing plate had the above optical characteristics in a uniaxial stretching step of free end stretching.

Simulation was performed by setting the initial front phase difference value ± 50 nm as the phase difference value change amount.

Specifically, the upper and lower polarizing plates prepared above were exposed to a high temperature and high humidity environment such that the front retardation value R0 of each of the negative A plates 14 and 24 was 100 nm and the refractive index ratio NZ was zero.

The upper and lower polarizing plates prepared above were exposed to a high temperature and high humidity environment such that the front retardation value R0 of each of the negative A plates 14 and 24 was 200 nm and the refractive index ratio NZ was zero.

FIG. 5 compares the omnidirectional transmittance and color of the black state of the liquid crystal display when the front phase difference values R0 of the negative A plates 14 and 24 are 100 nm, 150 nm and 200 nm, respectively.

The omnidirectional transmittance in the black state of the liquid crystal display device is similar to that of FIG. 4 using an isotropic protective film instead of the negative A plates 14 and 24, and can be confirmed to be similar regardless of the change in the front phase difference value R0. .

Example 2

In the same manner as in Example 1, except that the negative A plate 24 of the upper polarizer and the negative A plate 14 of the lower polarizer are each having a front retardation value R0 of 250 nm and a refractive index ratio NZ of 0, respectively. It was.

FIG. 6 compares the omnidirectional transmittance and color of the black state of the liquid crystal display when the front retardation values R0 of the negative A plates 14 and 24 are 200 nm, 250 nm, and 300 nm, respectively.

The omnidirectional transmittance in the black state of the liquid crystal display device is similar to that of FIG. 4 using an isotropic protective film instead of the negative A plates 14 and 24, and can be confirmed to be similar regardless of the change in the front phase difference value R0. .

Example 3

In the same manner as in Example 1, except that the negative A plate 24 of the upper polarizer and the negative A plate 14 of the lower polarizer are each having a front phase difference value R0 of 600 nm and a refractive index ratio NZ of 0, respectively. It was.

FIG. 7 compares the omnidirectional transmittance and color of the black state of the LCD when the front phase difference values R0 of the negative A plates 14 and 24 are 550 nm, 600 nm, and 650 nm, respectively.

The omnidirectional transmittance in the black state of the liquid crystal display device is similar to that of FIG. 4 using an isotropic protective film instead of the negative A plates 14 and 24, and can be confirmed to be similar regardless of the change in the front phase difference value R0. .

Comparative Example 1

In the same manner as in Example 1, the biaxial (Biaxial) having a refractive index ratio (NZ) of -0.5 made by transverse uniaxial stretching instead of the negative A plate 24 of the upper polarizing plate and the negative A plate 14 of the lower polarizing plate. Plates were used.

FIG. 8 compares the transmittance and color of the black state of the liquid crystal display when the front phase difference values R0 of the biaxial plates 14 and 24 are 100 nm, 150 nm and 200 nm, respectively. It can be seen that the viewing angle is narrow.

Comparative Example 2

In the same manner as in Example 1, instead of the negative A plate 24 of the upper polarizing plate and the negative A plate 14 of the lower polarizing plate, the retardation film having positive (+) refractive index characteristics through transverse uniaxial stretching Biaxial plates with a ratio (NZ) of 1.5 were used.

FIG. 9 compares the transmittance and color of the black state of the liquid crystal display when the front retardation values R0 of the biaxial plates 14 and 24 are 100 nm, 150 nm, and 200 nm, respectively. When compared with the embodiment of the present invention, it can be seen that the color change with time is large.

Claims (5)

A top plate polarizer laminated in the order of the protective film, the polarizer and the uniaxially stretched negative A plate, and a lower plate polarizer laminated in the order of the uniaxially stretched negative A plate, the polarizer and the protective film,
The negative A plate of the upper polarizing plate and the lower polarizing plate, respectively, has a refractive index ratio (NZ) of 0, a front phase difference value (R0) of 600 nm or less, and a slow axis of which is arranged orthogonally to an absorption axis of an adjacent polarizer.
The composite polarizing plate set of claim 1, wherein the negative A plate has a front retardation value (R 0) of 0 to 250 nm.
The composite polarizing plate set of claim 1, wherein the negative A plate is selected from the group consisting of polycarbonate (PC), polystyrene (PS), and polymethyl methacrylate (PMMA).
The composite polarizing plate set according to claim 1, wherein the absorption axes of the upper polarizing plate and the lower polarizing plate are perpendicular to each other.
An IPS mode liquid crystal display comprising the composite polarizer set of any one of claims 1 to 4.

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