KR101822699B1 - Optical sheet and liquid crystal display comprising the same - Google Patents

Abstract

The present invention includes a base film and a light-converging pattern layer formed on one surface of the base film, wherein the base film is stretched in the TD (transverse direction) direction and has an in-plane retardation value Re ) Is from 5,000 nm to 15,500 nm.
<Formula 1>
Re = (nx - ny) xd
In the above formula (1), nx and ny are refractive indices in the x and y axis directions, respectively, and d is the film thickness.

Description

TECHNICAL FIELD [0001] The present invention relates to an optical sheet and a liquid crystal display including the optical sheet.

The present invention relates to an optical sheet and a liquid crystal display device including the same.

The polarizing plate is used in and out of the liquid crystal cell for the purpose of controlling the direction of light oscillation in order to visualize the display pattern of the liquid crystal display device. Liquid crystal display devices have been used in a wide range from small-sized devices at the beginning of development to notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, navigation systems for vehicles, personal phones, and measurement devices used indoors and outdoors Respectively. Particularly, liquid crystal monitors, liquid crystal televisions, and the like are often used in high luminance backlights among applications of liquid crystal display devices. Therefore, the polarizing film used for the polarizing plate is required to have higher performance than that of the conventional product.

In a liquid crystal display device, an image is formed by arranging a polarizing plate on both sides of a glass substrate that forms the surface of a liquid crystal panel. The polarizing plate is generally formed of a transparent protective film for a polarizer using triacetyl cellulose (TAC) or the like on one side or both sides of a polarizer made of a polyvinyl alcohol (PVA) film and a dichroic material such as iodine or the like as a polyvinyl alcohol- Are used.

However, triacetylcellulose film is higher in price than general polymer film. As a result, a low-cost polymer film has been used as a protective film, and a polarizer using a polyethylene terephthalate film as a protective film has been developed. However, when a polyethylene terephthalate film is stretched at a low magnification rate when it is laminated on a polarizing plate, its mechanical strength is low due to its low mechanical strength when used in a liquid crystal display device, and it is difficult to secure physical properties. When stretched at a high magnification, .

Further, since the liquid crystal display device does not emit light itself, a backlight unit is required. The backlight unit may include an optical sheet such as a light source such as a light emitting diode or a fluorescent lamp, a light guide plate, a prism sheet, a diffusion sheet, and a protective sheet.

In general, a prism sheet is used for collecting light. The pattern of the prism sheet is regularly formed in a triangular pattern in cross section, and serves to enhance the brightness by condensing light. At least one prism sheet may be laminated, a pattern of a specific shape may be formed on the upper portion, and irregular irregularities may be formed on the lower portion. Further, another optical sheet such as a protective sheet may be laminated on the prism sheet by using an adhesive layer.

However, when a plurality of optical sheets used for condensing or diffusing light are provided in the backlight unit, there is a problem that it is difficult to make slimming or thinning of electronic devices such as mobile phones and tablets.

An object of the present invention is to provide an optical sheet which does not cause rainbow stains.

Another object of the present invention is to provide an optical sheet capable of realizing a thin film of a liquid crystal display device.

Another object of the present invention is to provide an optical sheet having excellent brightness.

Another object of the present invention is to provide a liquid crystal display device including the optical sheet.

One aspect of the present invention includes a base film and a light-converging pattern layer formed on one surface of the base film, wherein the base film is stretched in the TD (transverse direction) direction and has an in-plane phase And the retardation value (Re) is 5,000 nm to 15,500 nm.

<Formula 1>

Re = (nx - ny) xd

In the above formula (1), nx and ny are refractive indices in the x and y axis directions, respectively, and d is the film thickness.

The light converging pattern layer includes a condensing pattern having a longitudinal direction, and the stretching direction (TD) of the base film and the length direction of the condensing pattern may be the same.

The base film may have a phase retardation value (Rth) in the thickness direction of the following formula (2) at a wavelength of 550 nm of 15,500 nm or less:

<Formula 2>

Rth = ((nx + ny) / 2 - nz) xd

In the formula (2), nx, ny and nz are refractive indices of the polyester film in the x-, y- and z-axis directions, respectively, and d is the thickness (unit: nm) of the polyester film.

The base film may have an Nz value of not more than 2.0 at 550 nm represented by the following formula 3:

<Formula 3>

Nz = (nx - nz) / (nx - ny)

In the above equation (3), nx, ny, and nz are refractive indices in the x-axis, y-axis, and z-axis (thickness) directions, respectively.

Wherein the light converging pattern layer is a prism pattern layer including a plurality of unit prisms continuously arranged on one surface of a base film, the height H of the unit prism is about 2 to about 65 mu m, the pitch P is about 5 To about 60 [mu] m, and the apex angle alpha may be about 50 [deg.] To about 100 [deg.].

The optical sheet may further include a flat layer formed between the base film and the condensing pattern layer.

Wherein the base film comprises a light incidence surface and a light emergence surface opposed to the light incidence surface, wherein the light converging pattern layer is an inverse prism pattern layer comprising a plurality of unit prisms successively arranged on a light incident surface of the base film .

The apex angle alpha of the unit prism of the inverse prism pattern layer may be about 50 [deg.] To about 80 [deg.].

The thickness of the base film may be about 10 to 300 mu m.

The base film may be a film of one or more resins selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate and polybutylene naphthalate.

The light-converging pattern layer may be formed of at least one of a polyacetal resin, an acrylic resin, a polycarbonate resin, a styrene resin, a polyester resin, a vinyl resin, a polyphenylene resin, a polyolefin resin, a cycloolefin resin, acrylonitrile- -Styrene copolymer resins, polyacrylate resins, polyaryl sulfone resins, polyethersulfone resins, polyphenylene sulfide resins, polyethylene naphthalate resins, polyethylene resins and fluororesins. have.

Another aspect of the present invention relates to a liquid crystal display including a polarizing plate integrally formed with the optical sheet.

The optical sheet of the present invention does not cause rainbow stains and has excellent brightness, and a liquid crystal display device including the optical sheet can be realized as a thin film.

1 is a perspective view of an optical sheet according to one embodiment of the present invention.
2 is a cross-sectional view taken along the line X-X 'in FIG.
Fig. 3 shows an optical sheet (a) having a positive prism pattern layer and an optical sheet (b) having an inverse prism pattern layer formed thereon, respectively, as an optical sheet according to an embodiment of the present invention.
4 is a conceptual view schematically showing a liquid crystal display device according to one embodiment of the present invention.
5 is a conceptual diagram schematically showing a liquid crystal display device according to another embodiment of the present invention.

Embodiments of the present application will now be described in more detail with reference to the accompanying drawings. However, the techniques disclosed in this application are not limited to the embodiments described herein but may be embodied in other forms. It should be understood, however, that the embodiments disclosed herein are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the width, thickness, and the like of the components are enlarged in order to clearly illustrate the components of each device. Like numbers refer to like elements throughout the several views.

The terms "upper" and "lower" in this specification are defined with reference to the drawings, wherein "upper" may be changed to "lower", "lower" What is referred to as "on" may include not only superposition, but also intervening other structures in the middle. On the other hand, what is referred to as " directly on "or " directly " refers to not intervening other structures such as intermediates.

Optical sheet

An optical sheet according to one embodiment of the present invention includes a base film and a light converging pattern layer formed on one surface of the base film.

In the present invention, the light converging pattern layer means an optical pattern layer including optical members having a longitudinal direction such as a prism, a lenticular lens, an n-prism, and the like, but is not limited thereto.

Hereinafter, an optical sheet according to a specific embodiment of the present invention will be described with reference to Figs. 1 to 3. Fig.

FIG. 1 is a perspective view of an optical sheet according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along a line X-X 'in FIG.

Referring to FIG. 1, an optical sheet 100 according to an embodiment of the present invention includes a base film 110 and a prism pattern layer 120 formed as a light-converging pattern layer on one surface of the base film 110.

The base film 110 is a polyester film provided with a light incidence surface and a light emergence surface, and is an ultra high-retardation film.

The polyester film is a film stretched only in the TD direction (transverse direction) without stretching in the MD direction (Machine Direction). The stretching ratio in the TD direction is 5 to 10 times and the stretching ratio in the MD direction is 1 to 1.1. The "MD direction stretching ratio of 1 to 1.1" means that there is no further stretching step except that it is stretched by a machine direction, and a stretching ratio 1 means a non-stretched state without stretching. Within the above-mentioned range, an ultra violet ray film is formed to prevent the occurrence of rainbow stains and to improve the image quality.

The polyester film is not particularly limited as long as it is a transparent film of a polyester resin. In a specific example, the polyester film is a film made of one or more resins selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate and polybutylene naphthalate .

As a specific example, the base film 110 may have an in-plane phase retardation value (Re) expressed by the following formula 1 at a wavelength (?) 550 nm under a range of 5,000 nm to 15,500 nm.

<Formula 1>

Re = (nx - ny) xd

In the above formula (1), nx and ny are the refractive index in the x and y axis directions, respectively, and d is the thickness of the film.

As a specific example, the base film 110 may have a retardation value (Rth) in the thickness direction of the following formula 2 at a wavelength of 550 nm of 15,500 nm or less, specifically 5,000 nm to 15,000 nm.

<Formula 2>

Rth = ((nx + ny) / 2 - nz) xd

In the formula (2), nx, ny and nz are refractive indices of the polyester film in the x-, y- and z-axis directions, respectively, and d is the thickness (unit: nm) of the polyester film.

The occurrence of rainbow stains can be minimized within a range of the in-plane phase retardation value Re and the thickness direction phase retardation value Rth without lowering the brightness.

As a specific example, Nz represented by the following formula 3 indicating the degree of biaxiality of the base film 110 may be 2.0 or less at a wavelength of 550 nm, and specifically may be 1.5 to 1.7.

<Formula 3>

Nz = (nx - nz) / (nx - ny)

In the above equation (3), nx, ny, and nz are refractive indices in the x-axis, y-axis, and z-axis (thickness) directions, respectively.

The thickness (D) of the base film 110 is not limited, but may be about 10 to about 300 mu m, specifically about 50 to about 125 mu m, and may be used for the optical sheet in the above range.

As a specific example, the TD stretching direction of the base film 100 may be the same as the longitudinal direction (Y-Y ') of the prism pattern layer 120. Thus, when the stretching direction of the base film and the longitudinal direction of the prism pattern layer are the same, the occurrence of rainbow stains can be minimized without lowering the luminance.

Referring to FIG. 2, the prism pattern layer 120 includes a plurality of unit prisms successively arranged on one surface of the base film 110. The height H of the unit prisms may be equal to or different from each other, and may range from about 2 to about 65 占 퐉, specifically about 10 to about 30 占 퐉. In this range, there is no moire, . The pitch P of the unit prisms may be the same or different from each other. Specifically, the pitch may be about 5 to about 60 탆, for example, about 10 to about 30 탆. In this range, there is no moire, . The apex angle alpha of the unit prism can be about 50 DEG to about 100 DEG, and the brightness enhancement effect can be obtained in the above range.

In one embodiment of the present invention, the refractive index of the prism pattern layer 120 may be 1.50 to 1.70, specifically 1.58 to 1.67. There is an advantage that light incident at the above-mentioned range can be emitted with high luminance.

Fig. 3 shows an optical sheet (a) having a positive prism pattern layer and an optical sheet (b) having an inverse prism pattern layer formed thereon as an optical sheet according to an embodiment of the present invention.

3, in the optical sheet (a) having the positive prism pattern layer, the light incident on the base film is transmitted to the prism pattern layer, while the optical sheet (b) Is transmitted to the base film. The optical sheet (b) having the inverse prism pattern layer can minimize the occurrence of rainbow stains without lowering the brightness in the liquid crystal display device.

The apex angle alpha of the unit prisms constituting the inverse prism pattern layer can be about 50 to about 80, and the occurrence of rainbow stains can be minimized without lowering the brightness in the above range.

The prism pattern layer 120 may be formed on one side of the base film 110 by a compression molding process. For example, in the optical sheet 100, a transparent resin composition is injected between the pulling roll and the base film to cure the base film while the mold-pulling roll with the prism pattern stamped thereon is cured, Can be formed by separating the coated transparent resin composition coating layer from the pulling roll.

The light-converging pattern layer other than the prism pattern layer 120 and the prism pattern layer may include a thermoplastic resin or a composition containing the thermoplastic resin as a transparent material in the visible light region. Examples of the thermoplastic resin include acrylic resins, polyacetal resins, polycarbonate resins, styrene resins, polyester resins, vinyl resins, polyphenylene ether resins, polyolefin resins, cycloolefin resins, acrylonitrile- Styrene copolymer resins, polyacrylate resins, polyaryl sulfone resins, polyether sulfone resins, polyphenylene sulfide resins, polyethylene naphthalate resins, polyethylene resins, and fluorine resins.

Although not shown in the drawing, the optical sheet according to another embodiment of the present invention may further include a flat layer formed between the base film and the light condensing pattern layer.

The thickness of the flat layer is preferably 2 to 200 占 퐉 in consideration of the transmittance and planarization effect of the light-converging pattern layer. The flat layer can be manufactured using the same material as the light-converging pattern layer.

Liquid crystal display

4 is a conceptual view schematically showing a liquid crystal display device according to one embodiment of the present invention. 4, a liquid crystal display device 700 according to one embodiment of the present invention includes a liquid crystal display panel 200, a backlight unit 500 positioned at the rear of the liquid crystal display panel 200, a liquid crystal display panel 200 And a second polarizing plate 400 positioned between the liquid crystal display panel 200 and the backlight unit 500. The backlight unit 500 includes the first polarizer 300, And may include an optical sheet. Since the optical sheet includes all of the above-mentioned contents, detailed description of the contents will be omitted.

5 is a conceptual diagram schematically showing a liquid crystal display device according to another embodiment of the present invention. 5, the first polarizer 300 includes a first polarizer 160 including a light incident surface and a light exit surface, and a first retardation compensation film 170 formed on the light incident surface of the first polarizer 160 And a protective film 180 formed on the light exit surface of the first polarizer 160. [

The second polarizer 400 includes a second polarizer 130 including a light incident surface and a light exit surface, an optical sheet 100 directly formed on the light incident surface of the second polarizer 130, And a second retardation compensation film 140 formed on a light exit surface of the first retardation film 130. More specifically, the optical sheet 100 is configured such that the base film of the optical sheet is directly formed on the light incident surface of the second polarizer 130, that is, the optical sheet 100 having the inverse prism pattern layer formed thereon Sheet 100 as shown in FIG. When the base film of the optical sheet 100 on which an inverse prism pattern layer is formed as described above is integrated with the second polarizer, the refractive index difference at the interface between the inverse prism pattern layer and the base film is reduced, the flux loss can be reduced. In the present invention, 'integrated' means that the polarizer and the base film are bonded to each other without an adhesive layer or a space therebetween.

The polarizers 130 and 160 can be used without limitation as long as they are polarizers commonly used in the production of polarizers. Polarizers 130 and 160 are prepared by dyeing a polyvinyl alcohol film with iodine or a dichroic dye and stretching it in a predetermined direction. Specifically, it is produced through a swelling process, a dyeing step, a stretching step and a crosslinking step. Methods of performing each step are commonly known to those skilled in the art.

The thickness of the polarizers 130 and 160 is not particularly limited, but may preferably be 20 to 30 占 퐉.

The polarizers 130 and 160 may be monoaxially stretched films drawn in MD or TD directions. However, since the base film of the optical sheet 100 is different from the stretching direction of the second polarizer 130, it is advantageous in securing mechanical properties. Therefore, when the stretching direction of the base film is TD, the stretching direction of the polarizer is MD. It is advantageous to secure.

A method for laminating a protective film, an optical sheet and a retardation compensation film on a polarizer is not particularly limited. For example, a protective film, an optical sheet, and a retardation compensation film can be laminated to a polarizer through an adhesive layer. As the adhesive layer, a common adhesive such as an aqueous adhesive or a pressure-sensitive adhesive can be used.

The retardation compensation films 140 and 170 are typically used in a polarizing plate, and any film having a retardation compensation function can be used without limitation. As the retardation compensation film, an acrylic compound, a cellulose compound, an olefin compound, or a film made of a mixture thereof can be used. Preferably, cellulose-based, more preferably triacetylcellulose (TAC) films can be used.

The retardation compensation film can adjust the phase difference by adjusting the optical characteristics of the light passing through the liquid crystal display panel or have a viewing angle improving function.

The thickness of the retardation compensation film may be 10 탆 to 100 탆. In the above range, it is possible to provide an optical compensation effect when used in a polarizing plate, have a good polarization state with respect to the liquid crystal, and have an effect of preventing color change and stain. Preferably 40 to 80 占 퐉 thick.

The protective film 180 protects the polarizer as a transparent protective layer disposed on one side of the polarizer.

As the protective film, it is preferable to use an acetylcellulose-based resin film containing triacetylcellulose or diacetylcellulose which is used as a protective layer of a polarizer, but it is preferable to use a polyethylene terephthalate or polyethylene naphthalate resin film. When a polyethylene terephthalate film or a polyethylene naphthalate resin film is used as a protective film, it is possible to cope with thinning of the liquid crystal panel to be applied and high durability, so that it can be used as a vehicle mounting application.

Although not shown in the figure, in the polarizing plate of the present invention, the protective film may further include a surface coating layer. Preferably, a surface coating layer may be formed between the polarizer and the protective film.

The protective film is generally hydrophobic on the surface, and hydrophobicity is increased particularly when a polyethylene terephthalate film is used as a protective film. In order to use such a film as a polarizing plate, a surface modification that converts it to a hydrophilic property is required. Such surface modification may not sufficiently modify the surface of the film or may damage the surface of the film by using the sodium hydroxide used in conventional cellulose-based films. To this end, a surface coating layer comprising a primer having hydrophobic and hydrophilic functional groups can be formed on the protective film. The primer having a hydrophobic and hydrophilic functional group may include, but is not limited to, a polyester-based resin, a polyvinyl acetate-based resin, or a combination thereof.

By adding such a surface coating layer, by maximizing the mechanical properties and low moisture permeability of the protective film, a high resistance against external harsh conditions can be added to the polarizing plate. Further, the surface coating layer is formed between the protective film and the polarizing plate, so that the adhesion between the protective film and the polarizing film can be improved.

The protective film is preferably stretched such as uniaxial stretching or biaxial stretching.

The protective film is transparent considering the use of the polarizing plate, and can have a haze of 0.001 to 10%, preferably 0.1 to 5%.

Considering the use of the polarizing plate, the protective film may have a total light transmittance of 50 to 99%, preferably 85 to 99%.

The protective film may have an in-plane retardation value (Re) of more than 10,000 nm, preferably 12,000 nm to 30,000 nm at a wavelength of 550 nm. When the in-plane retardation value is more than 10,000 nm, the polarizing efficiency of the polarizing plate is good, rainbow stains do not occur, the light leakage phenomenon in which light leaks from the side, and the problem that the retardation value varies greatly depending on the incident angle, There may be no.

The protective film may have a thickness of 25 to 500 mu m. Within the above range, the protective film of the polarizer can be easily handled and thinned, and can be used as a polarizing plate when laminated to a polarizer. Preferably 25 占 퐉 to 300 占 퐉, and more preferably 25 占 퐉 to 150 占 퐉.

The protective film may be subjected to surface treatment such as antiglare treatment, hard coating treatment, antistatic treatment, AG (anti glare) treatment and AR (anti reflection) treatment on the opposite side of the surface to which the polarizer is adhered. Further, on the portion formed by the surface treatment, a coating layer composed of a liquid crystalline compound or a polymer compound thereof may be further formed.

Further, on the surface treatment, a surface protective film for protecting the surface treatment may be further laminated

The backlight unit 500 may include a light source, a light guide plate, a reflective sheet, a diffusion sheet, and the like. The liquid crystal display 1000 of the present invention can be manufactured by directly forming the base film of the optical sheet described above on the lower surface of the second polarizing plate 400, that is, by forming the reverse prism pattern layer, It is possible to secure a sufficient luminance without using an optical film such as a liquid crystal display device, and thus it is possible to realize a thin film of a liquid crystal display device.

Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.

The contents not described here are sufficiently technically inferior to those skilled in the art, and a description thereof will be omitted.

Examples 1-2 and Comparative Examples 1-4 - Preparation of optical sheets

The base film used in Examples 1 and 2 was a polyethylene terephthalate film (Toyobo), the base film used in Comparative Examples 1 and 2 was a polyethylene terephthalate film (MITSUBISH PLASTICS, INC, T910E), and Comparative Examples 3 and 4 Was a polyethylene terephthalate film (TORAY, XG7PK2). The retardation value and the thickness of each used base film are shown in Table 1 below.

The phase retardation value of the base film Base film thickness (占 퐉) The unit prism of the light- Re (nm) Rth (nm) Height pitch Vertex angle Example 1 9,114 8,882 80 25 m 50 탆 90 ° Example 2 15 탆 20 탆 68 ° Comparative Example 1 1,715 9,505 50 25 m 50 탆 90 ° Comparative Example 2 15 탆 20 탆 68 ° Comparative Example 3 4,042 23,229 100 25 m 50 탆 90 ° Comparative Example 4 15 탆 20 탆 68 °

The in-plane phase retardation value Re and the phase retardation value Rth in the thickness direction are values calculated in accordance with Equations 1 and 2 at a wavelength?

The photocurable resin composition was applied to a metal mold having a prism layer formed thereon, and the coated composition was photocured by irradiating ultraviolet rays in a state where one side of the substrate film in Table 1 was in contact with the coating side coated with the engraved mold , And the cured coating layer adhered to the base film was separated from the engraved mold to produce an optical sheet having a light converging pattern layer on one side of the base film. At this time, the stretching direction of the base film and the longitudinal direction of the condensing pattern are made equal. The height, pitch, and apex angle of the unit prisms constituting the light converging pattern layer are shown in Table 1, respectively.

A D type bulb (Type-D bulb) was attached to a non-electromotive ultraviolet irradiator (600 W / inch) at a wavelength of 190 nm for the ultraviolet rays, and irradiated at an energy of 500 mJ / cm 2.

Specifically, the photo-curable resin composition was prepared by mixing 70 wt% of an acrylate resin having ethylene oxide repeating units (TBP102, a proprietary company), 5 wt% of phenoxybenzyl acrylate, 7 wt% of bisphenol F acrylate, 1% by weight of a silicone additive (BYK UV-3530), 1% by weight of an ester type acrylate (COGNIS ECX 5031), 2% by weight of an antistatic agent (Nano Chemtech HR-E) , And 4% by weight of an initiator (Ciba Irgacure 184, Irgacure TPO).

Example 3, Comparative Example 5 and Comparative Example 7 - Production of liquid crystal display device

A liquid crystal display device having the structure as shown in FIG. 4 was manufactured. The liquid crystal display device includes a liquid crystal display panel, a backlight unit disposed on a rear surface of the liquid crystal display panel, a first polarizer disposed on the front surface of the liquid crystal display panel, and a second polarizer disposed between the liquid crystal display panel and the backlight unit.

Specifically, a polarizer was prepared by subjecting a polarizer material to a process such as dyeing and drawing. A polyvinyl alcohol film (VF-PS6000, Kuraray) was stretched three times at 60 DEG C, adsorbed iodine, and then 2.5 times stretched in an aqueous boric acid solution at 40 DEG C to prepare a polarizer.

A triacetate cellulose (TAC) protective film (KC4DR-1, manufactured by Konica Corp., thickness: 40 μm) was bonded to both sides of the polarizer using the polarizer adhesive (Z-200, Nippon Goshei) to prepare a first polarizing plate . A second polarizing plate was similarly prepared.

The liquid crystal display panel uses an 8-inch PLS (Samsung Electronics) mode, and a first polarizing plate is disposed on the front surface of the liquid crystal display panel, and a second polarizing plate is disposed between the liquid crystal display panel and the backlight unit.

The backlight unit uses an LED lamp (samsung LED, eight elements) as a side light source, a light guide plate on which a light source is incident, a reflection sheet provided on a lower portion of the light guide plate, a diffusion sheet sequentially stacked on the light guide plate, An optical sheet having a configuration, and a diffusion sheet.

In the case of the optical sheet having the positive prism pattern layer formed as in Example 3, Comparative Examples 5 and 7, the light guide plate and the base sheet of the optical sheet were stacked to face each other.

Table 3 shows the results of evaluating the occurrence of rainbow stains in the liquid crystal display.

Example 4, Comparative Example 6 and Comparative Example 8

The backlight unit used an optical sheet including only a light source, a light guide plate, and a reflective sheet without using a diffusion sheet, and having the configuration shown in Table 2 below, and the optical sheet was laminated on the bottom surface of the second polarizer plate, A liquid crystal display device having the same structure as that of Example 3, Comparative Example 5, and Comparative Example 7 was manufactured, except that the prism pattern layer was positioned so as to face the light guide plate. Then, occurrence of rainbow staining was evaluated.

Liquid crystal display Optical sheet The structure of the condensing pattern layer buying Example 3 Example 1 Crystal prism pattern 2 pieces Example 4 Example 2 Reverse prism pattern 1 piece Comparative Example 5 Comparative Example 1 Crystal prism pattern 2 pieces Comparative Example 6 Comparative Example 2 Reverse prism pattern 1 piece Comparative Example 7 Comparative Example 3 Crystal prism pattern 2 pieces Comparative Example 8 Comparative Example 4 Reverse prism pattern 1 piece

Evaluation of Rainbow Stains:

A spectral radiance luminance meter (SR-3A, Topcon) was used to observe whether rainbow stains occurred. A case where iridescence is not generated, a case where iridescence occurs weakly, a case where iridescence occurs moderately, a case where iridescence occurs strongly, and a case where iridescence occurs strongly.

Rainbow spot occurrence Example 3 X Example 4 X Comparative Example 5 O Comparative Example 6 O Comparative Example 7 O Comparative Example 8 O

 As shown in the results of Table 3, Examples 3 and 4 using an optical sheet having an in-plane phase retardation value (Re) of 5,000 nm to 15,500 nm represented by Formula 1 did not cause rainbow stains, 8 shows that rainbow stains have occurred.

Claims (13)

An optical sheet comprising a base film and a light-converging pattern layer formed on one surface of the base film,
The base film is stretched in TD (transverse direction) direction and has an in-plane phase retardation value (Re) expressed by the following formula 1 at a wavelength of 550 nm of 5,000 nm to 15,500 nm,
Wherein the base film comprises a light incidence surface and a light emergence surface opposed to the light incidence surface, the light converging pattern layer includes a light collecting pattern having a longitudinal direction, and the light collecting pattern having the longitudinal direction is light An inverse prism pattern comprising a plurality of unit prisms continuously arranged on an incident surface,
Wherein the stretching direction (TD) of the base film and the longitudinal direction of the condensing pattern are the same,
<Formula 1>
Re = (nx - ny) xd
In the above formula (1), nx and ny are refractive indices in the x and y axis directions, respectively, and d is the film thickness. delete The method according to claim 1,
Wherein the base film has a retardation value (Rth) in the thickness direction of the following formula (2) at a wavelength of 550 nm of 15,500 nm or less:
<Formula 2>
Rth = ((nx + ny) / 2 - nz) xd
In the formula (2), nx, ny and nz are refractive indices of the polyester film in the x-, y- and z-axis directions, respectively, and d is the thickness (unit: nm) of the polyester film. The method according to claim 1,
Wherein the base film has an Nz value of not more than 2.0 at 550 nm represented by the following formula 3:
<Formula 3>
Nz = (nx - nz) / (nx - ny)
In the above equation (3), nx, ny, and nz are refractive indices in the x-axis, y-axis, and z-axis (thickness) directions, respectively. The method according to claim 1,
Wherein the unit prism has a height H of 2 to 65 占 퐉, a pitch P of 5 to 60 占 퐉, and an apex angle? Of 50 to 100 占. The method according to claim 1,
And a flat layer formed between the base film and the condensing pattern layer. delete The method according to claim 1,
Wherein an apex angle alpha of the unit prism of the inverse prism pattern layer is 50 DEG to 80 DEG. The method according to claim 1,
Wherein the base film has a thickness of 10 to 300 占 퐉. The method according to claim 1,
Wherein the base film is a film made of one or more resins selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polybutylene naphthalate. The method according to claim 1,
The light-converging pattern layer may be formed of at least one of a polyacetal resin, an acrylic resin, a polycarbonate resin, a styrene resin, a polyester resin, a vinyl resin, a polyphenylene resin, a polyolefin resin, a cycloolefin resin, acrylonitrile- - at least one resin selected from the group consisting of a styrene copolymer resin, a polyacrylate resin, a polyaryl sulfone resin, a polyether sulfone resin, a polyphenylene sulfide resin, a polyethylene naphthalate resin, a polyethylene resin and a fluorine resin Characterized by an optical sheet. A liquid crystal display comprising a polarizing plate integrally formed with the optical sheet according to any one of claims 1, 3 to 6, and 8 to 11. 13. The method of claim 12,
Wherein the base film of the optical sheet is formed directly on the light incidence surface of the polarizer.

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