Patent Description:
In recent years, as there has been a growing interest in information display and a demand for a portable information medium to be used has increased, research and commercialization of a lightweight thin film flat panel display (FPD), which replaces a cathode ray tube (CRT) which is the existing display device have been mainly carried out. In particular, among such flat panel display devices, a liquid crystal display (LCD) as a device for displaying an image using optical anisotropy of a liquid crystal is excellent in resolution, color display, and image quality and is actively applied to a notebook or a desktop monitor.

In such a liquid crystal display, liquid crystal molecules of a liquid crystal layer are driven by a difference in voltage applied to a common electrode and a pixel electrode.

Liquid crystals have features such as dielectric anisotropy and refractive anisotropy. The dielectric anisotropy means that the degree of polarization induced by an electric field varies depending on long axis and short axis directions of the liquid crystal and the refractive anisotropy means that a refractive index varies depending on the long axis and short axis directions of the liquid crystal, which causes a polarization state to be changed because the refractive index felt varies according to a direction when light passes through the liquid crystal molecules.

As a result, the liquid crystal display has a liquid crystal panel constituted by a pair of transparent insulating substrates formed by planes facing each other with the liquid crystal layer interposed therebetween as a required component and arbitrarily controls the polarization of the liquid crystal molecules through a change in electric field between respective electric field generating electrodes and displays various images by using transmittance of light which is changed at this time.

In this case, a polarizer is located at each of upper and lower portions of the liquid crystal panel and the polarizer transmits the light a polarization component, which coincides with a transmission axis determines a transmission degree of light by arrangement of transmission axes of two polarizers and arrangement characteristics of the liquid crystals.

The polarizer used in the liquid crystal display in the related art is mainly a PVA elongated type in which iodine ions are aligned through stretching by using polyvinyl alcohol (PVA) having good adsorption ability with iodine.

<CIT> describes a liquid crystal panel which includes an upper polarizing plate and a lower polarizing plate arranged in parallel to an absorption axis, and a liquid crystal cell arranged between the upper polarizing plate and the lower polarizing plate, and a liquid crystal display device comprising the same. The liquid crystal panel includes a polarizing rotation layer which has a specific optical property between the upper polarizing plate and the lower polarizing plate, a negative B-plate and a negative C-plate.

<CIT> describes a liquid crystal panel including an upper polarizing plate and a lower polarizing plate whose absorption axes are disposed to be parallel to each other, a liquid crystal cell disposed between the upper polarizing plate and the lower polarizing plate, and a polarization rotating layer which is disposed between the upper polarizing plate and the lower polarizing plate to rotate linearly polarized light by <NUM>° to <NUM>°, and has reverse wavelength dispersion characteristics.

<CIT> describes a liquid crystal panel having a liquid crystal cell, a visible-side polarizer disposed on the visible-side surface of the liquid crystal cell, and an anti-visible-side polarizer disposed on a side opposite to the visible surface of the liquid crystal cell. The visible-side polarizer and the anti-visible-side polarizer are disposed so that the absorption axis direction of the visible-side polarizer and the absorption axis direction of the anti-visible-side polarizer will be approximately parallel to each other. A polarization rotating layer that rotates linearly polarized light by <NUM>±<NUM> degrees is disposed between the visible-side polarizer and the anti-visible-side polarizer.

The present application has been made in an effort to provide a liquid crystal display capable of resolving a size limitation of a polarizer and having an enhanced front CR characteristic.

The device according to the present invention comprises the features of claim <NUM>.

According to claimed invention, absorption axes of an upper polarizer and a lower polarizer of a liquid crystal display are provided to be parallel to each other, thereby resolving a size limitation of a polarizer according to a width of a polarizer raw material.

Further, according to the claimed invention, a wave plate is comprised between the upper polarizer and a liquid crystal panel, which rotates linear polarization at <NUM> to <NUM> degrees, and as a result, a front contrast ratio (CR) can be increased by reducing black luminance due to scattering of side light as compared with a case where the wave plate is comprised between the lower polarizer and the liquid crystal panel.

Hereinafter, preferred embodiments of the present application will be described. However, the embodiments of the present application may be modified into various other forms, and the present application is not limited to the embodiments described below. Further, the embodiments of the present application are provided for more completely describing the present application to those having average knowledge in the art.

In this specification, a case where a part "comprises" an element will be understood to imply the inclusion of stated elements but not the exclusion of any other elements unless explicitly described to the contrary.

The structure of the liquid crystal display in the related art is schematically illustrated in <FIG> below. In the liquid crystal display in the related art, an absorption axis of any one polarizer of an upper polarizer and a lower polarizer is set to <NUM> degree and the absorption axis of the other one polarizer is set to <NUM> degrees and the absorption axes of the upper polarizer and the lower polarizer are orthogonal to each other. However, when the absorption axis of the polarizer is <NUM> degrees, a horizontal length of the polarizer is limited by a width of a roll that manufactures the polarizer, and as a result, there is a limiting factor for enlarging a product size. A maximum width of the roll that manufactures a current polarizer is approximately <NUM>, which means that a maximum size of a <NUM>:<NUM> standard TV is approximately a <NUM> inch level.

In order to improve the limitation of the size of such a polarizer, a method for transversely stretching a polyvinyl alcohol (PVA) film to form the absorption axis of a polarizer roll in TD is proposed. However, even in such a case, unevenness due to lowering of the uniformity of the transverse stretching may occur and the degree of polarization due to the lowering of a stretching ratio may be lowered.

Thus, in the present application, the absorption axes of the upper polarizer and the lower polarizer of the liquid crystal display are all set to <NUM> degree, thereby resolving the size limitation of the polarizer according to the width of the polarizer raw material.

According to the claimed invention, there is provided a liquid crystal display comprising the features of claim <NUM>. These features comprise, inter alia, : an upper polarizer; a lower polarizer; and a liquid crystal panel provided between the upper polarizer and the lower polarizer, in which the upper polarizer and the lower polarizer are provided such that the absorption axes thereof are parallel to each other, a wave plate is provided between the upper polarizer and the liquid crystal panel, which rotates linear polarized light at <NUM> to <NUM> degrees, and the liquid crystal panel is a horizontally aligned liquid crystal mode.

In the claimed invention, the wave plate is provided between the upper polarizer and the liquid crystal panel instead of the case where the wave plate is provided between the lower polarizer and the liquid crystal panel.

In an embodiment of the present application, in regard to the upper polarizer and the lower polarizer, the polarizer which is attached to a TFT glass surface, which is a lower portion of the liquid crystal panel, based the liquid crystal panel, is referred to as the lower polarizer and the polarizer attached to an upper portion of the liquid crystal panel which is an opposite side is referred to as the upper polarizer.

Light emitted from a backlight unit (BLU) and incident on the lower polarizer has a black luminance rising element at a front due to scattering inside a cell in a lower panel. In this case, scattered light may be absorbed by the polarizer of an upper plate as long as there is no retardation of the lower plate, so that as compared with the case where the wave plate is provided between the lower polarizer and the liquid crystal panel, in the case where the wave plate is provided between the upper polarizer and the liquid crystal panel, the black luminance is reduced due to side light scattering, and as a result, front CR is raised.

In the claimed invention, the upper polarizer and the lower polarizer are provided such that the absorption axes thereof are parallel to each other. For example, the absorption axes of the upper polarizer and the lower polarizer may all be zero degree.

In the claimed invention, a wave plate for rotating the linearly polarized light at <NUM> to <NUM> degrees is provided between the upper polarizer and the liquid crystal panel. For example, a wave plate for rotating the linearly polarized light at <NUM> degrees is provided between the upper polarizer and the liquid crystal panel.

In an embodiment not according to the claimed invention, the wave plate may comprise one or two half wave plates. In this case, the wave plate comprises one half wave plate and an angle formed by an optical axis of the one half wave plate and the absorption axis of the upper polarizer is preferably <NUM> to <NUM> degrees or <NUM> or <NUM> degrees. When the angle is out of the above range, <NUM>-degree linearly polarized light conversion may not be made (e.g., <NUM> degree → <NUM> degrees), the optical axis is not orthogonal to the absorption axis of the upper polarizer and light leakage occurs in black and C/R drop occurs. Ideal optical axis angles are <NUM> degrees and <NUM> degrees, and the reason for setting such a range is to consider manufacturing tolerances of general optical films.

Further, the wave plate comprises two half wave plates, and an angle formed between the optical axis of one of the two half wave plates and the absorption axis of the upper polarizer is in the range of <NUM> degrees to <NUM> degrees and an angle formed between the optical axis of the other half wave plate and the absorption axis of the upper polarizer is preferably in the range of <NUM> degrees to <NUM> degrees. When the angle is out of the above range, the <NUM>-degree linearly polarized light conversion may not be made (e.g., <NUM> degree → <NUM> degrees), the optical axis is not orthogonal to the absorption axis of the upper polarizer and the light leakage occurs in black and the C/R drop occurs. The ideal optical axis angles are <NUM> degrees and <NUM> degrees, and the reason for setting such a range is to consider the manufacturing tolerances of the general optical films.

The half wave plate may be made of materials known in the art and is not particularly limited. For example, polyolefin (polyethylene, polypropylene, polynorbornene and the like), amorphous polyolefin, polyimide, polyamideimide, polyamide, polyetherimide, polyetheretherketone, polyetherketone, polyketone sulfide, polyether sulfone, polysulfone, polyphenylene sulfide, polyphenylene oxide, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyacetal, polycarbonate, polyarylate, polymethyl methacrylate, polymethacrylate, polyacrylate, polystyrene, cellulose-based polymer (such as triacetyl cellulose), PVA, epoxy resin, phenol resin, norbornene resin, polyester resin, acrylic resin, vinyl chloride resin, vinylidene chloride resin, etc. may be singly used or two or more thereof may be mixedly used, but the present application is not limited thereto.

The half wave plate may be obtained by forming the resin compositions and performing uniaxial or biaxial stretching. Further, as the half wave plate, an alignment film in which a liquid crystalline polymer or a liquid crystalline monomer is aligned may be used.

The half wave plate is a retarder that implements a phase difference as λ/<NUM> so that a relative phase difference between an e-ray and an o-ray becomes π. The phase difference may be represented as Δnd and the half wave plate may be manufactured by adjusting a thickness according to Δn of a material.

Further, according to the invention as claimed, the wave plate <NUM>. comprises two or four quarter wave plates. In this case, the wave plate comprises two quarter wave plate and angles formed by the optical axes of the two quarter wave plates and the absorption axis of the upper polarizer are preferably in the range of <NUM> to <NUM> degrees or <NUM> or <NUM> degrees. When the angle is out of the above range, the <NUM>-degree linearly polarized light conversion may not be made (e.g., <NUM> degree → <NUM> degrees), the optical axis is not orthogonal to the absorption axis of the upper polarizer and the light leakage occurs in black and the C/R drop occurs. The ideal optical axis angles are <NUM> degrees and <NUM> degrees, and the reason for setting such a range is to consider manufacturing tolerances of general optical films.

Further, the wave plate comprises four quarter wave plates, and angles formed between the optical axes of any two quarter wave plates among the four quarter wave plates and the absorption axis of the upper polarizer are in the range of <NUM> degrees to <NUM> degrees and angles formed between the optical axes of the other two quarter wave plates and the absorption axis of the upper polarizer are preferably in the range of <NUM> degrees to <NUM> degrees. When the angle is out of the above range, the <NUM>-degree linearly polarized light conversion may not be made (e.g., <NUM> degree → <NUM> degrees), the optical axis is not orthogonal to the absorption axis of the upper polarizer and the light leakage occurs in black and the C/R drop occurs. The ideal optical axis angles are <NUM> degrees and <NUM> degrees, and the reason for setting such a range is to consider the manufacturing tolerances of the general optical films.

The quarter wave plate may be made of materials known in the art and is not particularly limited. For example, the quarter wave plate may be formed by a uniaxially stretched cycloolefin film, a uniaxially stretched polyethylene terephthalate film, a uniaxially stretched polycarbonate film, or a liquid crystal film.

The quarter wave plate may be obtained by forming the resin compositions and performing uniaxial or biaxial stretching. Further, as the quarter wave plate, an alignment film in which a liquid crystalline polymer or a liquid crystalline monomer is aligned may be used.

The quarter wave plate is a film made so that the relative phase difference between the e-ray and the o-ray becomes π/<NUM>. Linear polarization is made to circular polarization or the circular polarization is made to the linear polarization.

In an embodiment of the present application, the quarter wave plate may additionally comprise a viewing angle compensation film on the upper and lower portions of the wave plate independently. More specifically, the viewing angle compensation film may be additionally provided between the wave plate and the liquid crystal panel and the viewing angle compensation film may be additionally provided between the wave plate and the upper polarizer or the lower polarizer.

The viewing angle compensation film may be made of materials known in the art and is not particularly limited.

The liquid crystal panel and the upper polarizer or the lower polarizer, the wave plate and the upper polarizer or the lower polarizer, the wave plate and the liquid crystal panel, the quarter wave plate, and the like may be bonded by using an aqueous adhesive or a UV curable adhesive or a PSA gluing agent.

In an embodiment of the present application, the upper polarizer and the lower polarizer may be polyvinyl alcohol polarizers in which at least one of iodine and dichroic dyes is individually dyed.

As an example of the method for preparing the polyvinyl alcohol polarizer, a method comprising a step of preparing a polyvinyl alcohol polarizer in which iodine and/or a dichroic dye is dyed and a step of laminating a protective film on one surface of the polarizer may be used. For example, the method is not limited thereto, but the step of preparing the polyvinyl alcohol polarizer may comprise a dying step of dying the polyvinyl alcohol polymer film with the iodine and/or the dichroic dye, a cross-linking step of cross-linking the polyvinyl alcohol film and the dye, and a stretching step of stretching the polyvinyl alcohol film.

A film for protecting the polarizer refers to a transparent film attached on one surface of the polarizer and may adopt a film which is excellent in mechanical strength, thermal stability, moisture shielding property, isotropy, and the like. For example, an acetate based film such as triacetyl cellulose (TAC), polyester based, polyether sulfone based, polycarbonate based, polyamide based, polyimide based, polyolefin based, cycloolefin based, polyurethane based, and acryl based resin films may be used, but the present application is not limited thereto.

In addition, the protective film may be an isotropic film, may be an anisotropic film having an optical compensation function such as the phase difference, or may be composed of one sheet or may be composed of two or more sheets bonded together. Further, the protective film may be an unstretched, uniaxially or biaxially stretched film, and the thickness of the protective film is generally <NUM> to <NUM> and preferably <NUM> to <NUM>.

Meanwhile, in the step of laminating the protective film on one surface of the polyvinyl alcohol polarizer, the protective film is bonded to the polarizer and the protective film may be bonded to the polarizer by using the adhesive. In this case, the bonding may be performed through a joining method of the film well known to the art and for example, the bonding may be performed by using adhesives well known to the art, which comprise the aqueous adhesive such as the polyvinyl alcohol adhesive, a thermosetting adhesive such as the urethane based adhesive, etc., a photo-cation curable adhesive such as the epoxy based adhesive, etc., and optical radical curable adhesives such as the acryl based adhesive, etc..

The liquid crystal display according to an embodiment of the present application may additionally comprise a backlight unit. The backlight unit serves to supply light to the liquid crystal panel and a light source of the backlight unit may adopt any one of a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), a fluorescent lamp of a hot cold fluorescent lamp (HCFL), or a light emitting diode (LED).

In an embodiment of the present application, the liquid crystal panel may be an In Plane Switching (IPS) mode liquid crystal panel or a Plane to Line Switching (PLS) mode liquid crystal panel, but is not limited only thereto.

Further, the types of the other constituent elements constituting the liquid crystal display, for example, upper and lower substrates (e.g., color filter substrate or array substrate) are not also particularly limited, and the configurations known in this field may be adopted without the limitation.

The structure of the liquid crystal display schematically illustrated in <FIG>, <FIG>, <FIG>, and <FIG> below. More specifically according to the claimed invention, <FIG> below illustrates a liquid crystal display comprising two quarter wave plates as the wave plate and <FIG> below illustrates a liquid crystal display comprising four quarter wave plates as the wave plate. In addition and not according to the claimed invention, <FIG> below illustrates a liquid crystal display comprising one half wave plate as the wave plate and <FIG> below illustrates a liquid crystal display comprising two half wave plates as the wave plate.

Hereinafter, the present invention will be described in more detail with reference to examples. The following Examples are provided to aid understanding of the present invention and are not thus intended to limit the present invention.

A mass-produced polarizer (made by LG Chemical Co. ) which is laminated in a structure of TAC/PVA/TAC was cut so that the absorption axis becomes <NUM> degree and used as a base substrate and two quarter wave plates (<NUM>, made by Fuji Film) having an optical axis of <NUM> degrees are joined to the cut polarizer by using the gluing agent. Thereafter, the same quarter wave plate fabric was cut to have an optical axis of <NUM> degrees and then, two additional sheets were attached to the lower portion of a half wave plate which was previously attached to the bonding product by using the gluing agent. Thereafter, a polarization plate was fabricated by applying the gluing agent to the lower portion of the half wave plate having the optical axis of <NUM> degrees.

The polarization plate was attached to the upper portion of the liquid crystal panel and a general polarizer used as the base substrate was attached to the lower portion of the liquid crystal panel with an absorption axis of <NUM> degree.

The structure of Example <NUM>, which is according to the claimed invention, is schematically illustrated in <FIG> below.

A polarization plate comprising the half wave plate was fabricated by the same method as Example <NUM>, the fabricated polarization plate was attached to the lower portion of the liquid crystal panel with the absorption axis of <NUM> degree, and the general polarizer used as the base substrate was attached to the upper portion of the liquid crystal panel with the absorption axis of <NUM> degree.

The structure of Comparative Example <NUM>, which is not according to the claimed invention, is schematically illustrated in <FIG> below.

A general polarizer which is laminated in a structure of TAC/PVA/TAC was cut so that the absorption axis becomes <NUM> degree and used as the base substrate and two quarter wave plates (<NUM>, made by Fuji Film) having the optical axis of <NUM> degrees are joined to the cut polarizer by using the gluing agent. Thereafter, the polarization plate was fabricated by applying the gluing agent to the lower portion of the half wave plate which was previously attached.

The polarization plate comprising the half wave plate was fabricated by the same method as Example <NUM>, the fabricated polarization plate was attached to the lower portion of the liquid crystal panel with the absorption axis of <NUM> degree, and the general polarizer used as the base substrate was attached to the upper portion of the liquid crystal panel with the absorption axis of <NUM> degree.

The structure of Comparative Example <NUM> which is not according to the claimed invention, is schematically illustrated in <FIG> below.

Optical characteristics of the polarization plate attached to the panel according to Examples <NUM> and <NUM> and Comparative Examples <NUM> and <NUM> were measured and shown in Tables <NUM>, <NUM>, and <NUM> below. <FIG> below illustrates results depending on Example <NUM> and Comparative Example <NUM> and <FIG> illustrates results depending on Example <NUM> and Comparative Example <NUM>.

In order to avoid a deviation factor of the optical characteristics according to a position in the panel, the optical characteristics were measured and compared at the same position of the same panel.

A panel used for evaluation is a <NUM>" product of IPS mode and black luminance and white luminance were measured b using EZ contrast 160R made by Eldim as an optical measurer and relatively compared with the comparative example.

Here, C/R represents a contrast ratio representing a white luminance/black luminance value, and the data shows a relative ratio of luminance values in black and white at the front having an azimuth angle of <NUM> degree and a polar angle of <NUM> degree. The C/R value of Example <NUM> having +<NUM>% means that the C/R value increases as compared with Comparative Example <NUM> by <NUM>% and +<NUM>% of Example <NUM> means that the C/R value increases as compared with Comparative Example <NUM> by <NUM>%.

It may be apparently known that in a case where the polarization plate comprising all half wave plates is positioned at the upper portion of the panel, the C/R increases by approximately <NUM>% or more as compared with a case where the polarization plate is positioned at the lower portion of the panel.

Example <NUM> is configured by setting the absorption axis of the upper polarizer to <NUM> degree and sequentially laminating two quarter wave plates on the lower portion, which have the optical axis of <NUM> degrees, and sequentially laminating two quarter wave plates on the lower portion, which have the optical axis of <NUM> degrees. In this case, R(<NUM>)/R(<NUM>) of the applied quarter wave plate is <NUM>, R(<NUM>) means retardation at <NUM>, and R (<NUM>) means retardation at <NUM>. The Example is configured by locating the structure of the polarization plate at the upper portion of the liquid crystal layer and setting the absorption axis of the polarizer to <NUM> degree at the lower portion.

Example <NUM> is configured by setting the absorption axis of the upper polarizer to <NUM> degree and sequentially laminating two quarter wave plates on the lower portion, which have the optical axis of <NUM> degrees, and sequentially laminating two quarter wave plates on the lower portion, which have the optical axis of <NUM> degrees. In this case, R(<NUM>)/R(<NUM>) of the applied quarter wave plate is <NUM>, R(<NUM>) means retardation at <NUM>, and R (<NUM>) means retardation at <NUM>. Example <NUM> is configured by locating the structure of the polarization plate at the upper portion of the liquid crystal layer and setting the absorption axis of the polarizer to <NUM> degree at the lower portion.

The absorption axis of the upper polarizer is set to <NUM>, and one half wave plate having an optical axis of <NUM> degrees, one half wave plate having an optical axis of <NUM> degrees, and one half wave plate having an optical axis of <NUM> degrees are sequentially laminated at the lower portion. In this case, R(<NUM>)/R(<NUM>) of the applied half wave plate is <NUM>, R(<NUM>) means retardation at <NUM>, and R (<NUM>) means retardation at <NUM>. Comparative Example <NUM> is configured by locating the structure of the polarization plate at the upper portion of the liquid crystal layer and setting the absorption axis of the polarizer to <NUM> degree at the lower portion.

The structures configured according to Examples <NUM> and <NUM> and Comparative Example <NUM> are shown in Table <NUM> and <FIG> by simulating the optical characteristic in a black state by using a Techwiz 1D program.

Here, the front black luminance means luminance at the azimuth angle of <NUM> degree and the polar angle of <NUM> degree, and the viewing angle black max means a value of a portion with highest black luminance at a front azimuth angle and a front azimuth angle.

Claim 1:
A liquid crystal display comprising:
an upper polarizer (<NUM>);
a lower polarizer (<NUM>); and
a liquid crystal panel (<NUM>) provided between the upper polarizer (<NUM>) and the lower polarizer (<NUM>),
wherein the upper polarizer (<NUM>) and the lower polarizer (<NUM>) are provided such that absorption axes thereof are parallel to each other,
a wave plate (<NUM>) is provided between the upper polarizer (<NUM>) and the liquid crystal panel (<NUM>), the wave plate (<NUM>) configured to rotate linearly polarized light by <NUM> to <NUM> degrees, and
the liquid crystal panel (<NUM>) is configured to be in a horizontally aligned liquid crystal mode,
wherein the wave plate (<NUM>) comprises two or four quarter wave plates (<NUM>),
wherein the lower polarizer (<NUM>) is attached to a lower portion of the liquid crystal panel (<NUM>) and between the liquid crystal panel (<NUM>) and a backlight unit, and the upper polarizer (<NUM>) is attached to an upper portion of the liquid crystal panel (<NUM>) opposite to the lower portion.