KR20070080731A - Polarizer and liquid crystal display - Google Patents

Abstract

A polarizing plate and an LCD(Liquid Crystal Display) having the same are provided to secure the viewing angle, by forming a negative-C-plate at least one side of an LCD panel, thereby realizing excellent display quality. An LCD comprises an LCD panel(110), and a first polarizing plate(130) and a second polarizing plate(140) formed at both sides of the LCD panel. The LCD panel includes a liquid crystal layer aligned in a twisted nematic mode. The first polarizing plate or the second polarizing plate includes a negative-C-plate(120). The negative-C-plate satisfies the following equation; nx≒nynz, wherein, the nx represents refractive index in an x-axis, the ny represents refractive index in a y-axis, and the nz represents refractive index in a z-axis.

Description

Polarizer and Liquid Crystal Display

1 is a cross-sectional view showing a liquid crystal display panel provided in the liquid crystal display device according to the present invention.

2 is a schematic cross-sectional view illustrating a liquid crystal display device according to an exemplary embodiment of the present invention.

3 is a schematic cross-sectional view showing a liquid crystal display device according to another embodiment of the present invention.

4 and 5 are graphs showing viewing angles of the liquid crystal display according to the present invention;

<Explanation of symbols for the main parts of the drawings>

110: liquid crystal display panel 120, 152: C plate

130, 140, 150, 160: polarizer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing plate and a liquid crystal display device, and more particularly, to a liquid crystal display device capable of reducing cost and securing a viewing angle.

A liquid crystal display (LCD) displays a desired image by applying an electric field to a liquid crystal material having an anisotropic dielectric constant injected between two substrates, and controlling the amount of light transmitted through the substrate by adjusting the intensity of the electric field. Device. Such liquid crystal display devices are expanding in application range due to features such as light weight, thinness, low power driving, full color, and high resolution. Currently, liquid crystal displays are used in computers, notebooks, PDAs, telephones, TVs, and audio / video devices.

Twisted Nematic (TN) mode liquid crystal display devices having excellent optical characteristics, clear black and white display, and excellent response characteristics are mainly used among liquid crystal display devices. The liquid crystal display device includes a liquid crystal drive electrode and an alignment layer formed on the opposing upper and lower substrates and the upper and lower substrate opposing surfaces, respectively, or a polarizing plate formed on the back of the opposing surfaces of the upper and lower substrates. In the liquid crystal display of the TN mode, liquid crystal molecules are arranged in a spiral twist between the upper and lower substrates under the influence of the vertical alignment layer, and since the liquid crystal molecules are highly uniformly aligned, the liquid crystal molecules have refractive index anisotropy. There is a disadvantage that the display quality such as contrast ratio or color tone due to it varies with time. In general, an optimal contrast ratio is shown only within a narrow viewing angle centered on a vertical incidence to the liquid crystal display, and rapidly decreases as the viewing angle increases. In particular, there is a problem in the color display device that not only degrades the contrast ratio but also exhibits deterioration of color reproduction related to color or color tone changes.

Conventionally, in order to compensate for the viewing angle, a wide view (WV) compensation film is provided between the opposite back surface of the upper and lower substrates, that is, between the upper and lower substrates and the polarizing plate. The wide viewing angle compensation film is manufactured by forming a rubbing treatment alignment film on a transparent film, and then applying a liquid crystal polymer or the like on the alignment film to perform heat treatment or ultraviolet curing, and the manufacturing process is complicated and expensive. There is a disadvantage in that the cost of the display device is increased.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a polarizing plate and a liquid crystal display device capable of securing a viewing angle to realize good display quality, and at the same time reducing costs and improving productivity.

(여기서, nx는 x축의 광굴절률, ny는 y축의 광굴절률, nz는 z축의 광굴절률)를 만족하는 네가티브 C 플레이트를 포함하는 것을 특징으로 하는 액정 표시 장치를 제공한다. The present invention includes a liquid crystal display panel including a liquid crystal layer oriented in a twisted nematic (TN) mode and first and second polarizing plates formed on both sides of the liquid crystal display panel to achieve the above object, The first or second polarizing plate

(Nx is an optical refractive index on the x-axis, ny is an optical refractive index on the y-axis, and nz is an optical refractive index on the z-axis).

The C plate may include a vertically oriented liquid crystal film, a biaxially stretched polycarbonate film, a triacetyl cellulose (TAC) film, a cyclic olefinic copolymer film or a UV curable short pitch cholesteric liquid crystal film. The C plate preferably has a retardation value (Rth = ((nx + ny) / 2-nz) × d) in the thickness direction in a range of 120 to 160 nm.

The first or second polarizing plate has a polyvinyl alcohol (PVA) polarizing film for polarizing incident light, a triacetyl cellulose (TAC) protective film attached to both sides of the polarizing film, and a side facing the liquid crystal display panel of the protective film. It may include the C plate formed in.

In addition, the first or second polarizing plate is a polyvinyl alcohol (PVA) polarizing film for polarizing the incident light, the C plate attached to one surface facing the liquid crystal display panel of the polarizing film and a tree attached to the other surface of the polarizing film Acetyl cellulose (TAC) protective film.

The liquid crystal display panel includes a first substrate including a black matrix layer, a color filter layer, and a common electrode, a second substrate including a thin film transistor, a gate line, a data line, and a pixel electrode and coupled to the first substrate, and And the liquid crystal layer encapsulated between the first substrate and the second substrate.

The first and second substrates include rubbing treated first and second alignment layers to define an alignment direction of the liquid crystal layer positioned between the substrates, and the first and second alignment layers have an angle of 90 ° to each other. It can be characterized in that.

(여기서, nx는 x축의 광굴절률, ny는 y축의 광굴절률, nz는 z축의 광굴절률)를 만족하는 네가티브 C 플레이트 및 상기 편광 필름의 타면에 부착된 보호 필름을 포함하는 것을 특징으로 하는 편광판을 제공한다. 상기 C 플레이트는 수직 배향된 액정 필름, 이축 연신된 폴리카보네이트 필름, 트리아세틸 셀룰로오스(TAC) 필름, 고리형 올레핀계 공중합 필름 또는 UV 경화형 짧은 피치 콜레스테릭 액정 필름을 포함할 수 있다.The present invention is attached to a polyvinyl alcohol (PVA) polarizing film for polarizing the incident light, one surface of the polarizing film

(Nx is the optical refractive index of the x-axis, ny is the optical refractive index of the y-axis, nz is the optical refractive index of the z-axis) and a polarizing plate comprising a protective film attached to the other surface of the polarizing film to provide. The C plate may include a vertically oriented liquid crystal film, a biaxially stretched polycarbonate film, a triacetyl cellulose (TAC) film, a cyclic olefin copolymer film or a UV curable short pitch cholesteric liquid crystal film.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention in more detail. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various forms, and only the embodiments are intended to complete the disclosure of the present invention, and to those skilled in the art to fully understand the scope of the invention. It is provided to inform you.

In the drawings, the thickness of layers, films, panels, regions, etc., may be exaggerated for clarity, and like reference numerals designate like elements. In addition, when a part such as a layer, a film, an area, or a plate is expressed as being on or above another part, not only when each part is directly above or directly above the other part but also another part between each part and another part This includes cases.

1 is a cross-sectional view showing a liquid crystal display panel included in the liquid crystal display device of the present invention.

Referring to FIG. 1, the liquid crystal display panel 110 includes a first substrate 111 including a plurality of color filters, a second substrate including a plurality of thin film transistors and coupled to the first substrate 111. 112, the liquid crystal 113 encapsulated between the first substrate 111 and the second substrate 112 coupled through the sealant 114.

The first substrate 111 has a black matrix and a red, green, and blue color filter formed on a lower surface of an insulating substrate made of a transparent insulating material such as glass to prevent optical interference between cell regions. An overcoat film made of an organic material is formed thereon, and a common electrode made of a transparent conductive material such as ITO or IZO is formed on the overcoat film.

The second substrate 112 has a plurality of gate lines arranged in one direction at regular intervals, a plurality of source lines arranged at regular intervals in a direction perpendicular to the gate line, and the gate lines and the source lines intersect each other. A plurality of pixel electrodes formed in a matrix form in a defined pixel area and a plurality of thin film transistors that are switched by the gate line signal to transfer a source line signal to each pixel electrode are formed. The thin film transistor includes a gate electrode, a gate insulating film, an active layer and an ohmic contact layer, a source electrode and a drain electrode. And a protective layer for insulating between the thin film transistor and the pixel electrode.

The liquid crystal display panel 110 is formed by combining the first substrate 111 and the second substrate 112 and forming a liquid crystal layer 113 therebetween, and formed on the second substrate 112. By driving the thin film transistor to orient the liquid crystal 113, the transmittance of light is adjusted to display an image.

2 is a schematic cross-sectional view illustrating a liquid crystal display according to an exemplary embodiment of the present invention.

Referring to FIG. 2, the liquid crystal display includes a liquid crystal display panel 110, upper and lower polarizers 140 and 130 formed on upper and lower portions of the liquid crystal display panel 110, and the liquid crystal display panel 110. And a C plate 120 formed between the lower polarizer 130.

The liquid crystal display panel 110 according to the present exemplary embodiment includes a liquid crystal layer between a first substrate including a color filter and a second substrate including a thin film transistor, and the liquid crystal layer is in a twisted nematic (TN) mode. Orientated. That is, the liquid crystal molecules in the liquid crystal layer are twisted and oriented at a predetermined angle between the first substrate and the second substrate.

To this end, an alignment layer is formed on inner surfaces of the first and second substrates, and the alignment layers of the first and second substrates are rubbed to form a predetermined angle. At this time, the predetermined angle is preferably 90 degrees. The first and second substrates having the rubbed alignment layers are bonded to each other so that the liquid crystal molecules are twisted.

The liquid crystal layer comprises a horizontally oriented liquid crystal layer having liquid crystal molecules having positive dielectric anisotropy, that is, having a smaller dielectric constant in the thickness direction than the dielectric constant in the longitudinal direction. The horizontally oriented liquid crystal layer refers to a liquid crystal layer in which liquid crystal molecules align the long axis of the molecules in parallel to the substrate surface when no electric field is applied.

The upper and lower polarizers 140 and 130 are formed on outer surfaces of the first substrate and the second substrate such that the vibration directions of the linearly polarized light are parallel to the directions of the alignment layers in contact with each substrate. That is, the upper and lower polarizers 140 and 130 include a transmission axis that transmits only the light oscillating in the transmission axis, and the upper polarizer 140 formed on the outer surface of the first substrate has the direction of the alignment layer of the first substrate. The lower polarizer 130 including a parallel transmission axis and formed on an outer surface of the second substrate includes a transmission axis parallel to the direction of the alignment layer of the second substrate. Therefore, the transmission axes of the pair of polarizing plates 140 and 130 are configured to be perpendicular to each other.

In general, the polarizing plates 140 and 130 have upper and lower surfaces to protect the polyvinyl alcohol film (PVA) polarizing films 141 and 131 having polarization characteristics and the PVA polarizing films 141 and 131. And tri-acetyl cellulose (TAC) protective films 142, 143, 132, and 133 attached thereto. Of course, the present invention is not limited thereto, and as the protective films 142, 143, 132, and 133 for protecting the polarizing films 141 and 131, films of various materials having excellent transparency, mechanical strength, and thermal stability may be used.

In the liquid crystal display having such a structure, when an electric field is not applied, the light linearly linearized from the lower polarizer 130 rotates in a stepwise twisted structure along the liquid crystal layer, and the upper polarizer 140 is formed on the upper part of the liquid crystal layer. It is polarized parallel to the transmission axis of) and is displayed in white.

In addition, when an electric field is applied, the liquid crystal molecules of the liquid crystal layer are almost perpendicular to the substrate surface, and the twisted structure disappears, and the polarization direction of the light linearly flattened from the lower polarizer 130 does not rotate anymore. The light passing through is absorbed by the upper polarizer 140 and displayed as black.

As described above, a mode in which light is transmitted when no electric field is applied is referred to as a normally white mode.

However, since the liquid crystal molecules present near the surface of the alignment film have a strong anchoring effect (an anchoring effect) from the alignment film, the orientation of these liquid crystal molecules does not change even when an electric field is applied. That is, even when a voltage for performing black display is applied, liquid crystal molecules remain oriented parallel to the substrate surface. Such liquid crystal molecules cause retardation distortion with respect to light incident perpendicularly to the liquid crystal layer and become a cause of light leakage in a black display state, thereby lowering the contrast ratio. In particular, as the viewing angle increases from the vertical of the display surface of the liquid crystal display device, display quality is degraded due to light leakage.

의 관계를 갖는 것을 특징으로 한다. 여기서, nx는 x축의 광굴절율, ny는 y축의 광굴절율, nz는 z축의 광굴절율이다. 상기 C 플레이트(120)는 상기 광굴절율(nx, ny, nz)에 따라 입사된 광을 굴절시키는 기능을 가진다.In order to compensate for the retardation distortion, a negative C plate 120 is formed between the liquid crystal display panel 110 and the polarizing plates 140 and 130 formed at one side thereof. C plate 120 has a predetermined optical refractive index (nx, ny, nz) in the x-axis, y-axis, and the vertical z-axis of the C plate,

It is characterized by having a relationship of. Where nx is the optical refractive index on the x-axis, ny is the optical refractive index on the y-axis, and nz is the optical refractive index on the z-axis. The C plate 120 has a function of refracting incident light according to the light refractive indices nx, ny, and nz.

The optical anisotropy of the C plate 120 may be represented by Re, which is an in-plane retardation value represented by Equation 1 and Equation 2 below, and Rth, which is a retardation value in the thickness direction.

Re = (nx-ny) × d

Rth = ((nx + ny) / 2-nz) × d

C plate 120 has a very small in-plane retardation value Re, and in order to compensate for the distorted residual retardation, Rth, which is a retardation value in the thickness direction, is preferably in a range of 120 to 160 nm.

The C plate 120 may include a vertically aligned liquid crystal film, a biaxially stretched polycarbonate film, a triacetyl cellulose (TAC) film, and a cyclo-olefin. olefin-based copolymer films, UV curable short pitch cholesteric liquid crystal films, and the like.

In addition, the triacetyl cellulose (TAC) protective films 142, 143, 132, and 133 of the polarizers 140 and 130 may compensate for the residual retardation. In general, the triacetyl cellulose (TAC) protective films 142, 143, 132, and 133, which are used for the protective role of the polarizing films 141 and 131, have an in-plane retardation value of Re of 2 to 5 nm. The retardation value Rth includes a range of 40 to 55 nm.

Due to the retardation value of the triacetyl cellulose (TAC) protective film (142, 143, 132, 133) and the retardation value of the C plate 120, to compensate for the residual retardation of the liquid crystal layer and prevent light leakage Can be.

The retardation value of the triacetyl cellulose (TAC) protective film may be adjusted to increase the compensation effect of the residual retardation. For example, the stretching conditions of the triacetyl cellulose (TAC) protective film may be adjusted to adjust the in-plane retardation value Re or the retardation value Rth in the thickness direction.

Therefore, the present invention can compensate for the residual retardation of the liquid crystal layer in the black display state and prevent light leakage in the black display state. In particular, the display quality can be improved by securing a relatively wide viewing angle compared with the case where the C plate is not used. At the same time, the present invention has the advantage of reducing the cost compared to the case of using a wide viewing angle compensation film, which is complicated and expensive in the conventional manufacturing process, by using a single C plate.

The C plate is formed between the liquid crystal display panel and the polarizing plate formed on one side, and is preferably formed inside the polarizing plate formed in the direction from the liquid crystal display panel toward the light source, that is, between the liquid crystal display panel and the lower polarizing plate. Of course, the present invention is not limited thereto, and the C plate may be formed between the liquid crystal display panel and the upper polarizing plate, or may be formed on both sides of the liquid crystal display panel. It may also further comprise a separate optical compensation film for compensating for the residual retardation.

Although the above-described example is configured to include a separate C plate, an integrated polarizing plate having a C plate attached to the polarizing film of the upper or lower polarizing plate may be used. That is, the polarizing plate includes a PVA polarizing film and a TAC protective film formed of protective films on both sides of the polarizing film. However, the polarizing plate is not limited thereto. The integrated polarizing plate is formed by forming a C plate on one side of the upper or lower polarizing plate. You can also use This will be described below, and descriptions overlapping with those of the embodiment will be omitted.

3 is a schematic cross-sectional view illustrating a liquid crystal display according to another exemplary embodiment of the present invention.

를 만족하는 것을 특징으로 한다.Referring to FIG. 3, the liquid crystal display includes a liquid crystal display panel 110, upper and lower polarizers 160 and 150 formed on upper and lower portions of the liquid crystal display panel 110, respectively. ) Is characterized in that the C plate 152 is attached and formed integrally. That is, the lower polarizing plate 150 includes a PVA polarizing film 151 having polarization characteristics, a C plate 152 attached to one surface of the polarizing film 151 facing the liquid crystal display panel 110, and the polarizing film ( And a triacetyl cellulose (TAC) protective film 153 attached to the other side of 151. Here, the C plate 152 has a predetermined optical refractive index (nx, ny, nz) on the x-axis, the y-axis, and the vertical z-axis of the C plate 152, respectively.

Characterized by satisfying.

As described above, the integrated polarizer including the C plate is used as the lower polarizer, but the present invention is not limited thereto. The integrated polarizer may be configured as the upper polarizer or the upper and lower polarizers.

4 and 5 are graphs showing changes in viewing angles according to retardation of a C plate using the liquid crystal display of the present invention. 4 illustrates a viewing angle in the vertical direction, and FIG. 5 illustrates a viewing angle in the horizontal direction.

4 and 5, it can be seen that the viewing angle of the liquid crystal display including the C plate is improved compared to the case without the C plate. In particular, when the Rth which is the retardation value of the thickness direction is 120 nm and 140 nm, it turns out that a wider viewing angle can be ensured.

As described above, the present invention forms a C plate on one side of the liquid crystal display panel, thereby preventing light leakage in a black display state, and securing a relatively wide viewing angle as compared with the case where the C plate is not used, thereby achieving good display quality. have. In addition, the present invention has the advantage of improving the productivity by reducing the cost compared to the case of using a wide viewing angle compensation film, which is complicated and expensive in the conventional manufacturing process, by using a single C plate.

As mentioned above, although this invention was demonstrated in detail using the preferable Example, the scope of the present invention is not limited to a specific Example and should be interpreted by the attached Claim. In addition, those skilled in the art should understand that many modifications and variations are possible without departing from the scope of the present invention.

According to the present invention, by forming a C plate on one side of the liquid crystal display panel, a viewing angle can be ensured and good display quality can be realized. At the same time, there is an advantage to improve productivity by reducing costs.

Claims (9)

A liquid crystal display panel including a liquid crystal layer oriented in a twisted nematic (TN) mode; And First and second polarizing plates formed on both sides of the liquid crystal display panel, The first or second polarizing plate

Wherein nx comprises a negative C plate that satisfies the optical refractive index of the x-axis, ny the optical refractive index of the y-axis, and nz the optical refractive index of the z-axis. The method according to claim 1, The C plate comprises a vertically oriented liquid crystal film, a biaxially stretched polycarbonate film, a triacetyl cellulose (TAC) film, a cyclic olefin copolymer film or a UV curable short pitch cholesteric liquid crystal film. Device. The method according to claim 1 or 2, The C plate has a retardation value (Rth = ((nx + ny) / 2-nz) × d) in a thickness direction in a range of 120 to 160 nm. The method according to claim 1 or 2, The first or second polarizing plate, Polyvinyl alcohol (PVA) polarizing films for polarizing incident light; Triacetyl cellulose (TAC) protective films attached to both sides of the polarizing film; And And the C plate formed on a side facing the liquid crystal display panel of the protective film. The method according to claim 1 or 2, The first or second polarizing plate, Polyvinyl alcohol (PVA) polarizing films for polarizing incident light; The C plate attached to one surface of the polarizing film facing the liquid crystal display panel; And And a triacetyl cellulose (TAC) protective film attached to the other surface of the polarizing film. The method according to claim 1 or 2, The liquid crystal display panel, A first substrate comprising a black matrix layer, a color filter layer and a common electrode; A second substrate including a thin film transistor, a gate line, a data line, and a pixel electrode and coupled to the first substrate; And And the liquid crystal layer encapsulated between the first substrate and the second substrate. The method according to claim 6, The first and second substrates include rubbing treated first and second alignment layers to define an alignment direction of the liquid crystal layer positioned between the substrates, and the first and second alignment layers have an angle of 90 ° to each other. A liquid crystal display device, characterized in that. Polyvinyl alcohol (PVA) polarizing films for polarizing incident light; Attached to one surface of the polarizing film

A negative C plate satisfying (where nx is an optical refractive index on the x-axis, ny is an optical refractive index on the y-axis, and nz is an optical refractive index on the z-axis); And And a protective film attached to the other surface of the polarizing film. The method according to claim 8, Wherein the C plate comprises a vertically oriented liquid crystal film, a biaxially stretched polycarbonate film, a triacetyl cellulose (TAC) film, a cyclic olefin copolymer film or a UV curable short pitch cholesteric liquid crystal film.

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