KR100869276B1 - Reflective plarizer, and backlight unit and display device including it - Google Patents

Abstract

A broadband reflection polarizer, and a backlight unit and an LCD device having the same are provided to simplify the element and manufacturing process by omitting a process for controlling light strength of blue wave length. A reflection polarization film(130) selectively reflects the Green of the Blue LED light ray including the Yellow fluorescent substance and light of the Red wavelength band domain, and transmits the light of the Blue wavelength band(130). A phase delay layer(150) converts the circular polarization of the Red wavelength band and the Green penetrating the reflection polarization film into the linear polarization. An absorption type polarizing film(170) transmits the linear polarization of the Red wavelength band and the Green, transmits 50% of the circular polarization of the Blue wavelength band and absorbs the rest.

Description

Broadband reflective polarizer, backlight unit and liquid crystal display device including the same {Reflective plarizer, and backlight unit and display device including it}

The present invention relates to a reflective polarizer used in a liquid crystal display (LCD) and the like and a back light unit including the same. More particularly, a broadband reflective polarizer and a back light including the same can be omitted from the reflective polarization film. Unit, etc.

Generally, a liquid crystal display injects a liquid crystal between the glass plates in which the transparent electrode was formed, and has a structure which arrange | positioned the polarizing film before and behind the said glass plate. The polarizing film used for such a liquid crystal display is manufactured by making an iodine, a dichroic dye, etc. adsorb | suck to a polyvinyl alcohol film, and extending this in a fixed direction. However, the polarizing film prepared in this way absorbs light vibrating in one direction, and passes only light vibrating in the other direction to make linearly polarized light. Therefore, the efficiency of a polarizer cannot theoretically exceed 50%, and is the largest factor which lowers the efficiency of a liquid crystal display.

Therefore, a technique of using a cholesteric liquid crystal having a circularly polarized light separation function as a reflective polarizing film has been proposed. The cholesteric liquid crystal has a selective reflection characteristic in which the rotational direction of the spiral of the liquid crystal coincides with the circular polarization direction, and the wavelength reflects only circularly polarized light such as the spiral pitch of the liquid crystal. Therefore, by using such selective reflection characteristics, it is possible to manufacture a highly efficient polarizing film by transmitting and separating only specific circularly polarized light of natural light of a certain wavelength band and reflecting and reusing the rest.

By the way, the circularly polarized light transmitted at this time is converted into linearly polarized light by passing through the λ / 4 wave plate, and the liquid crystal display device having high transmittance can be obtained by matching the direction of the linearly polarized light with the transmission direction of the absorption type polarizer used in the liquid crystal display. . In other words, when the cholesteric liquid crystal film is used as a linear polarizer in combination with a λ / 4 wave plate, there is no theoretical loss of light. Therefore, a theoretical absorption type polarizer that absorbs 50% of light is theoretically compared with the case of using a single absorption polarizer alone. In the image, the brightness improvement can be doubled.

In the prior art using such cholesteric liquid crystals, the cholesteric liquid crystal film layers each of which are provided with selective reflection characteristics by inducing horizontal alignment are laminated in the order of short wavelength to long wavelength so that the visible light region is selected as the selective reflection wavelength region. Broadband cholesteric liquid crystal film manufacturing technology (application number: 10-1998-0000498, 10-1999-0065640, 10-2004-0078416, 10-2004-0060853) is proposed.

In addition, two or more cholesteric liquid crystal polymer layers are stacked on each other in a state of being in close contact with each other in a long and short order based on the center wavelength of the reflected light, and the circularly polarized light separation layer having the spiral pitch in the thickness direction and the long wavelength side of the center wavelength of the reflected light A polarizer manufacturing technique (application number: 10-1998-0043207, 10-1998-0017719, 10-1999- 0006902, 10-1998-0019146, 10-2005-7015572) including a disposed retardation layer is also proposed.

1 is a schematic diagram of a liquid crystal display device including the above-described reflective polarizer. As shown in FIG. 1, the liquid crystal display device is largely composed of a backlight unit A and a liquid crystal panel B. As shown in FIG. The backlight unit A includes a light guide plate 12 and a diffusion plate 13 for diffusing and radiating the light incident from the LED light source 11, and a prism for condensing and emitting light incident from the diffusion plate 13. A sheet 15, a reflective polarizing film 16 for selectively reflecting light incident from the prism sheet 15, and a phase delay layer 18 for converting circularly polarized light transmitted through the reflective polarizing film 16 into linearly polarized light. It is configured to include. In FIG. 1, reference numeral 12a denotes a reflecting plate, and 19 denotes an absorption type reflective polarizing film.

In the conventional reflective polarizing film 16 constituting such a liquid crystal display device, all of the blue, green, and red wavelength bands are selected to secure the function of the broadband reflective polarizer whose wavelength range is visible. It has reflectivity. By the way, when using a blue LED including a yellow phosphor as a light source of the liquid crystal display device, the light emitted here is different in intensity of the light in the blue, green and red wavelength bands. In detail, since the light emitted from the LED generally has the intensity of light in the blue wavelength band more than twice the light intensity in the green and red wavelength bands, the light in the wavelength band passes through the above-mentioned reflective polarizer to the liquid crystal panel of the liquid crystal display device. This difference in light intensity remains upon incidence. Therefore, this difference in light intensity causes a problem in the color appearance of the liquid crystal display device, and in general, it is inconvenient in that it is necessary to separately operate equipment for controlling the blue light intensity emitted from the liquid crystal cell of the liquid crystal panel small. Follow.

Therefore, the present invention has been made to solve the above-mentioned problems of the prior art, and it is not necessary to adjust the light intensity of a separate blue wavelength band in the liquid crystal cell of the liquid crystal panel of the liquid crystal display device, and at the same time simplify the device and process economy. It is an object of the present invention to provide a broadband reflective polarizer.

Another object of the present invention is to provide a backlight unit or a liquid crystal display device including the reflective polarizer.

The present invention to achieve the above object,
A reflective polarizing film for selectively reflecting light in the green and red wavelength band regions of the blue LED light including the yellow phosphor and transmitting light in the blue wavelength band;
A phase delay layer for converting circularly polarized light in the green and red wavelength bands transmitted through the reflective polarization film into linearly polarized light and transmitting the incident light in the blue wavelength band as it is;

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And an absorption type polarizing film that transmits 50% of the circularly polarized light in the blue wavelength band while transmitting the linearly polarized light incident from the phase delay layer and absorbs the rest.

The present invention also relates to a back light unit including the reflective polarizer.

The present invention also relates to a liquid crystal display device including the reflective polarizer.

The broadband reflective polarizer of the present invention described above can implement a broadband reflective band having a reflection band for the entire visible light even if there is no reflective polarizing film having selective reflectivity for light in the blue wavelength band.

Therefore, it is possible to reduce the lamination of the reflective polarizing film and to reduce the number of processes, thereby manufacturing the reflective polarizer more economically, and at the same time reducing the thickness of the manufactured device.

In addition, the light emitted from the reflective polarizer of the present invention is different from the conventional broadband reflective polarizer, the light intensity of the blue wavelength band is substantially the same as the light intensity of the green and red wavelength band, so in the liquid crystal cell of the liquid crystal panel of the prior art blue wavelength band It is advantageous in that there is no need to adjust the light intensity.

Hereinafter, the present invention will be described.

2 is a schematic cross-sectional view showing a reflective polarizer 100 according to an embodiment of the present invention.

As shown in FIG. 2, the reflective polarizer 100 of the present invention includes a reflective polarizer 130 having selective reflectivity of green and red wavelength bands of incident visible light. That is, the reflective polarizing film 130 of the present application transmits light in the blue wavelength band of visible light incident from a blue LED including a yellow phosphor.

In addition, the reflective polarizer 100 of the present invention includes a phase delay layer 150 formed on the reflective polarization film 130. The phase delay layer 150 converts circularly polarized light in the green and red wavelength bands having transmitted the reflected polarization into linearly polarized light, and transmits the incident light in the blue wavelength band as it is.

As described above, the reflective polarizing film constituting the reflective polarizer of the present invention does not perform a selective reflection function for light in the blue wavelength band, unlike the prior art, and the liquid crystal panel effectively enables the light of the wavelengths in the entire visible ray effectively by such a configuration. Its technical significance is provided in. Detailed description thereof is as follows.

First, the broadband polarizer 100 of the present invention includes a reflective polarizing film 130 for selectively reflecting light incident on the green and red wavelength bands incident from a blue LED including a yellow phosphor. Therefore, some of the light in the green and red wavelength bands of the light incident from the reflective polarizing film 130 is transmitted through circularly polarized light, and the rest of the light is reflected from the lower reflector of the back light unit, and then transmitted into circularly polarized light. . However, in the present invention, light of the blue wavelength band of the incident light is transmitted without being reflected by the reflective polarization film 130.

In the present invention, the reflective polarizing film 130 may be formed by laminating a cholesteric liquid crystal layer for selectively reflecting light in the green wavelength band and a cholesteric liquid crystal layer for selectively reflecting light in the red wavelength band. It is not limited. As an example, as shown in FIG. 3, a cholesteric liquid crystal layer 130a for selectively reflecting light in the green wavelength band and a cholesteric liquid crystal layer 130b for selectively reflecting light in the red wavelength band are formed on the liquid crystal layer. The stacking order may be different. That is, it can be easily implemented by laminating a cholesteric liquid crystal layer for selectively reflecting light of two or more different wavelength bands.

In the present invention, the cholesteric liquid crystal layer is a mixture of a curable nematic liquid crystal material and a curable chiral material, and the selective reflection wavelength range may be adjusted according to the composition of the two materials. The curable nematic liquid crystal material and the curable chiral material may be used as long as the liquid crystal material includes a mesogenic group representing a nematic liquid crystal. In addition, the chiral material may be any material having chiral carbon in a conventional nematic liquid crystal, and is not limited to a specific material. In the present invention, the curable may be any material having a thermosetting or photocurable reactive group in its molecular structure. For example, in the case of thermosetting, a combination of monomers including vinyl groups such as vinyl group, acrylic group and methacryl group, or having various reactive groups capable of condensation polymerization may be used. As the photocurable, a reactive group crosslinkable by ultraviolet rays such as a vinyl group, an acryl group, and an aryl group may be used.

In addition, in the present invention, one cholesteric liquid crystal layer may be used as the reflective polarizing film 130. The one cholesteric liquid crystal layer may be implemented as a cholesteric liquid crystal layer having a long wavelength or a short wavelength pitch while going from the bottom to the top so as to have the wavelengths of the green and red regions of the visible light region as the selective reflection wavelength region. . In general, when the nematic liquid crystal material and the chiral material are mixed to form a cholesteric liquid crystal layer, the higher the content of the chiral liquid crystal material to be mixed, the wavelength range of the selective reflection is shifted to a shorter wavelength.

Furthermore, the broadband reflective polarizer 100 of the present invention includes a phase delay layer 150 formed on the reflective polarizer film 130. The phase delay layer 150 serves to convert circularly polarized light in the green and red wavelength bands transmitted from the reflective polarization film 130 into linearly polarized light, but is transmitted without being selectively reflected in the reflective polarization film 150. The incident light of the blue wavelength band is transmitted as it is.

In the present invention, the phase delay layer 150 may use a variety of materials for λ / 4 phase delay, for example, a stretched polymer film may be used. Although the said stretched polymer film in this invention is not specifically limited, It is preferable that a thermoplastic polymer is included and the said thermoplastic polymer may be used independently or may be used together 2 or more types. As the thermoplastic polymer, for example, polyolefin (polyethylene, polyprop

Styrene), polynorbornene-based polymer, polyester, polyvinyl chloride, polystyrene, polyacrylonitrile, polysulfone, polyallylate, polyvinyl alcohol, polymethacrylic acid ester, polyacrylic acid ester, cellulose ester and their air Coalescence etc. can be used

Furthermore, in the present invention, a nematic liquid crystal layer may be used as the phase delay layer 150.

More preferably, the phase delay layer 150 is a cover band of 500-800nm wavelength band.

In addition, the reflective polarizer of the present invention is preferably formed by adding the optical sheet layer 160 on the phase delay layer 150, as shown in FIG. The optical sheet layer 160 can effectively suppress the scattering phenomenon caused when light passes through the liquid crystal layer, thereby improving the brightness of the liquid crystal display device. The optical sheet layer 160 has a microstructure, that is, a pattern is formed thereon, the cross-sectional shape of the pattern may be a prism shape, an arc shape, and the like.

More preferably, to form another optical sheet layer on the upper or lower portion of the optical sheet layer 160 to cross the pattern. By forming an optical sheet layer in which these patterns intersect, the horizontal and vertical viewing angle enlargement effects can be more effectively realized.

In addition, in the present invention, the optical sheet layer 160 is preferable in terms of light condensing effect that the pitch of each individual pattern (that is, the interval between the individual patterns) satisfies the range of 10 to 100 μm.

In addition, the optical sheet layer 160 has a vertex angle of 70 to 110 ° of each of the individual patterns is desired in terms of ensuring luminance characteristics.

In addition, the optical sheet layer 160 may be linearly arranged in parallel in the longitudinal direction of the pattern, the individual patterns may be further arranged in a non-linear chaos pattern in the longitudinal direction of the pattern.

In addition, as shown in FIG. 5, the reflective polarizer 100 of the present invention preferably further includes an optical sheet layer 110 formed below the reflective polarizer film 130 so that the pattern peak is directed downward.

Furthermore, the reflective polarizer of the present invention may include an absorption type polarizing film 170 formed on the phase delay layer 150. The absorption type polarizing film 170 transmits linearly polarized light of the incident light as it is, but transmits 50% of circularly polarized light but absorbs the rest. Therefore, in order to prevent additional light absorption in the absorption type polarizing film 170, the conventional broadband reflective polarizer converts circularly polarized light into linearly polarized light in the phase delay layer.

More preferably, the absorption type polarizing film 170 is formed such that its optical axis has an angle of approximately 45 ° with the phase delay layer 150.

On the other hand, Figure 6 is a graph showing the light intensity of each wavelength band of a blue LED light beam including a yellow phosphor used as a light source of the backlight unit. As shown in FIG. 6, the blue wavelength of visible light has a wavelength range of approximately 450-490 nm, green 490-560 nm, and red 630-780 nm. In addition, when looking at the light intensity in each wavelength band for each color, it can be seen that the light intensity of the wavelength band of the B region in general is significantly greater than the light intensity of the wavelength of the G and R region. However, in the case of the liquid crystal panel, when the light intensity of the incident three primary color wavelength band (B, G, R) region is constant, it is possible to easily implement a variety of colors in the display device. Therefore, conventionally, in order to preserve the difference in light intensity for each wavelength band, there is a problem that the light intensity in the blue wavelength band must be adjusted on the light incident side of the liquid crystal panel.

When looking at the light intensity before and after passing through the absorption type polarizing film of the light emitted from the broadband reflective polarizer having selective reflectivity in the conventional B, G and R wavelength band, the light intensity before and after the pass appears substantially the same as in FIG. That is, in the case of the conventional broadband reflective polarizer, there is little change in the light intensity of the B, G, and R wavelength bands before and after passing through the absorption type polarizing film, and thus, the light intensity of the B wavelength band is significantly larger than that of the G and R wavelength bands.

FIG. 7 is a graph showing the light intensity before and after passing of an absorption type polarizing film of light emitted from a broadband reflective polarizer having selective reflectivity in the G and R wavelength bands of the present invention. As shown in FIG. 7, in the present invention, since the light of the wavelength B maintains the circularly polarized state before passing through the absorbing polarizing film, about 50% of the light passes through the absorbing polarizing film but absorbs about 50% of the light. It becomes. Therefore, the light of the G and R wavelengths have almost no change in the light intensity after passing through the absorption type polarizing film, but the light of the B wavelength band has decreased by 50% after passing through the absorption type polarizing film.

Therefore, in the case of using the reflective polarizer of the present invention, it can be seen that the difference in the light intensity of the B wavelength band is substantially reduced compared to the case of the conventional reflective polarizer, whereby the liquid crystal cell of the liquid crystal panel It can be seen that there is no need to reduce the light intensity in the B wavelength band at.

As described above, the present invention reduces the light intensity of the blue wavelength band as in the prior art by forming a reflective polarizing film that selectively reflects light of the green and red wavelength bands and transmits the light of the blue wavelength band as it is, unlike the prior art. You don't have to. In addition, since a simpler reflective polarizer can be used, there is an effect that is useful for the manufacturing process and manufacturing cost reduction.

Although the present invention has been described in detail through the above preferred embodiments, the present invention is not limited to the contents of these embodiments. Those skilled in the art to which the present application pertains, although not shown in the examples, can be imitated or improved for various inventions within the scope of the appended claims, all of which fall within the technical scope of the present invention. Would be too self-explanatory.

1 is a schematic cross-sectional view showing a conventional liquid crystal display device.

2 is a schematic cross-sectional view illustrating a reflective polarizer according to an exemplary embodiment of the present invention.

3 is a cross-sectional view showing an example of a reflective polarizing film constituting the reflective polarizer of the present invention.

4 is a schematic cross-sectional view showing a reflective polarizer according to another embodiment of the present invention.

5 is a schematic cross-sectional view showing a reflective polarizer according to still another embodiment of the present invention.

FIG. 6 is a graph showing light intensity for each wavelength band of a blue LED light ray including a yellow phosphor used as a light source of a backlight unit; FIG.

7 is a graph showing the light intensity before and after passing through the absorption type polarizing film of light emitted from the broadband reflective polarizer having selective reflectivity in the green and red wavelength band of the present invention.

Claims (16)

A reflective polarizing film for selectively reflecting light in the green and red wavelength band regions of the blue LED light including the yellow phosphor and transmitting light in the blue wavelength band; A phase delay layer for converting the circularly polarized light in the green and red wavelength bands transmitted through the reflective polarization film into linearly polarized light and transmitting the incident light in the blue wavelength band as it is; An absorption type polarizing film that transmits linearly polarized light incident from the phase delay layer and transmits 50% of circularly polarized light in the blue wavelength band and absorbs the rest; Broadband reflective polarizer comprising a. The method of claim 1, wherein the reflective polarizing film comprises a cholesteric liquid crystal layer for selectively reflecting light of the green wavelength band of visible light and a cholesteric liquid crystal layer for selectively reflecting light of the red wavelength band; Broadband reflective polarizer. The method of claim 1, wherein the reflective polarizing film is one cholesteric liquid crystal layer having a long wavelength or short wavelength pitch while going from the bottom to the top to have the wavelength of the green and red regions of the visible light as the selective reflection wavelength region. Broadband reflective polarizer. The wideband reflective polarizer of claim 1, wherein the phase delay layer is a stretched polymer film. The broadband reflective polarizer of claim 1, wherein the phase delay layer is a nematic liquid crystal layer. The reflective polarizer of claim 1, wherein the phase delay layer covers a wavelength band of 500-800 nm. The broadband reflective polarizer of claim 1, further comprising an optical sheet layer formed on the phase delay layer. The broadband reflective polarizer of claim 7, further comprising an optical sheet layer having a pattern intersecting a pattern of the optical sheet layer on one side of the upper and lower portions of the optical sheet layer. The broadband reflective polarizer according to claim 7 or 8, wherein the pitch of the pattern constituting the optical sheet layer satisfies a range of 10 to 100 µm. The broadband reflective polarizer according to claim 7 or 8, wherein a vertex angle of each pattern constituting the optical sheet layer is 70 to 110 degrees. The broadband reflective polarizer according to claim 7 or 8, wherein the individual patterns constituting the optical sheet layer are arranged non-linearly in the longitudinal direction. delete The broadband reflective polarizer of claim 1, wherein the absorption polarizing film is formed such that its optical axis has an angle of 45 DEG with the phase delay layer. 2. The broadband reflective polarizer of claim 1, further comprising an optical sheet layer below the reflective polarizing film whose pattern peak is directed downward. Backlight unit comprising the reflective polarizer of claim 1 A liquid crystal display device comprising the reflective polarizer of claim 1.

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