KR100925726B1 - Backlight unit and liquid crystal display including the same - Google Patents

Abstract

PURPOSE: A backlight unit and a liquid crystal display including the same are provided to remove the necessity of a cholesteric liquid crystal layer which has the selective reflection characteristic of R,G,B wavelength bands and a phase delay layer. CONSTITUTION: A backlight unit(100) includes an absorption polarizing film, an RGB LED light source, and a reflection polarized film. The absorption polarizing film passes the first polarized light and absorbs the second polarized light. A plurality of R,G,B LED light sources(110) generate R,G,B random polarized lights. The reflection polarized film passes the first polarized light and reflects the second polarized light with respect to at least one of R,G,B random polarized lights. The reflection polarized film transmits the first and second polarized lights to the absorption polarizing film with respect to the rest random polarized lights.

Description

BACKLIGHT UNIT AND LIQUID CRYSTAL DISPLAY INCLUDING THE SAME}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight unit used in a liquid crystal display (LCD), and more particularly, to reduce power consumption of a direct type backlight unit using a light emitting diode (LED) as a light source and to prolong the life of the LED light source. It relates to a backlight unit and a liquid crystal display including the same that can extend.

Recently, liquid crystal displays (LCDs) are widely used in various fields such as computer monitors and TVs of large areas as well as small mobile phones and electronic calculators. Since the liquid crystal display is a light-receiving element that does not generate light in itself, a separate light source device capable of illuminating the entire screen from the back is required. To this end, the liquid crystal display further includes a backlight unit as a light source device in addition to the liquid crystal panel.

In the backlight unit, an edge-lighting method of injecting light generated from a light source installed at the lower side of the liquid crystal panel into the liquid crystal panel by using a light guide plate, a reflection plate, an optical sheet, a reflective polarizer, and the like, and a light guide plate is not used. Instead, there is a direct-lighting method in which a plurality of light sources are disposed on the rear surface of the diffusion plate disposed at the bottom of the liquid crystal panel and the light emitted from the light source is directly incident on the liquid crystal panel.

Conventionally, the backlight unit uses a cold cathode fluorescent lamp (CCFL) or an external electrode fluorescent lamp (EEFL) as a light source for illumination. However, these conventional light sources have a problem in that their lifespan is shortened as the gas pressure of the plasma changes, and an inverter for obtaining a high voltage required for plasma discharge is required. In addition, the conventional light sources have a problem that the power consumption efficiency is not good so that excessive power is consumed.

In order to solve such a conventional problem, a backlight unit using a light emitting diode (LED) is used. LEDs may emit light such as red (R), green (G), blue (B), and the like, depending on the type of semiconductor material and impurities, and may generate white light by combining these R, G, and B LEDs. LEDs have the advantages of small size, long life, high energy efficiency, and low operating voltage compared to conventional light sources.

In the case of a direct type backlight unit using an LED as a light source, the light is emitted to the liquid crystal panel by changing the path of light upward or downward, using a reflector. However, LEDs typically have shorter lifetimes for green (G) and blue (B) LEDs than red (R) LEDs at the same current input (life: R LED> G LED> B LED), so these LEDs can be used for a long time. In this case, the luminous efficiency of green (G) and blue (B) is lower than that of red (R), and thus there is a problem in that the quality of the product is deteriorated. In this case, it is cumbersome to replace the green (G) or blue (B) LED, which has an end of life in the liquid crystal display.

Therefore, the technical field is required to develop a technology that can reduce the power consumption according to the extension of the service life of the LED in the backlight unit using the LED light source.

The present invention has been proposed to solve the problems of the prior art, and an object of the present invention is to provide a backlight unit that can reduce the power consumption while extending the life of the LED light source in the direct type backlight unit using the LED as a light source.

In addition, the present invention has another object to provide a reflective polarizing film used in such a backlight unit.

In addition, another object of the present invention is to provide a liquid crystal display device including the backlight unit or the reflective polarizing film.

The present invention for achieving the above object,

In a direct type backlight unit used in a liquid crystal display device including an absorption polarization film that transmits light of a first polarization and absorbs light of a second polarization, a plurality of R, G, B LED light source; And at least one of the R, G, and B random polarizations generated by the LED light source, transmits the light of the first polarized light and reflects the light of the second polarized light, and the first and the second random polarized light. A reflective polarizing film that transmits light of two polarizations and is emitted to the absorption polarizing film; Including;

The intensity of the current input to the at least one LED light source is smaller than the intensity of the current input to the other LED light sources so that white light is emitted by the combination of R, G, and B light passing through the absorption polarizing film.

In an embodiment of the present invention, the ratio of the R, G, B light intensity transmitted through the absorption polarizing film is preferably equal to the ratio of the R, G, B light intensity generated by the R, G, B LED light source.

In an embodiment of the present invention, the reflective polarizing film transmits light of the first polarized light and reflects light of the second polarized light with respect to G and B light among R, G, and B random polarized light, and the first and second light for R light. It is preferable to transmit the light of the second polarization as it is,

At this time, it is preferable that the intensity of the current input to the G and B LED light source is smaller than the intensity of the current input to the R LED light source, more preferably the input to the B LED light source than the intensity of the current input to the G LED light source. The intensity of the current being small is small.

In an embodiment of the present invention, the first polarized light of R among the R, G, and B light transmitted through the reflective polarizing film is preferably the same light in the same polarization direction as the light of the first polarized light of G and B.

In an embodiment of the present invention, the plurality of R, G, B LED light source is preferably composed of one set of R, G, B LED light source and arranged in a plurality of sets.

In an embodiment of the present disclosure, the backlight unit may include: a diffusion plate configured to diffuse light emitted from the R, G, and B LED light sources; And an optical sheet layer condensing the light diffused by the diffusion plate and outputting the light to the reflective polarizing film. It may further include.

Here, in another embodiment, the backlight unit further includes another optical sheet layer having an optical microstructure intersecting with the optical microstructure of the optical sheet layer, at any one of the upper and lower portions of the optical sheet layer. You may.

In an embodiment of the invention, the reflective polarizing film comprises a stack of at least two layers, at least one of the layers having a birefringent material, and at least two adjacent layers having wavelengths in accordance with at least one refractive index component. It is desirable to have a difference in refractive index for each band.

In addition, the present invention for achieving the above object,

At least one randomly polarized light is transmitted, the first polarized light is transmitted, the second polarized light is reflected, and the remaining random polarized light is transmitted to the first and second polarized light. Provided is a reflective polarizing film.

In addition, the present invention provides a liquid crystal display device including any one of a backlight unit or a reflective polarizing film according to the above embodiments.

According to the present invention, the life of the LED light source used in the backlight unit can be extended, and furthermore, it can be used for a long time without replacing the LED light source.

In addition, according to the present invention, the power consumption can be reduced by reducing the intensity of the current input to the LED light source of the backlight unit while maintaining high brightness in the liquid crystal display device.

In addition, according to the present invention, since the cholesteric liquid crystal layer and the phase delay layer having the selective reflection characteristics of the R, G, and B wavelength bands are not required to implement the backlight unit, the manufacturing process is simplified and more in terms of manufacturing cost. It is advantageous.

Hereinafter, a detailed description of a preferred embodiment of the present invention will be described with reference to the accompanying drawings. In the backlight unit according to the present invention, the spirit of the present invention may be widely applied to any structure commonly used in liquid crystal display devices. Therefore, the backlight unit described below is provided as an example for explaining the present invention as a basic structure of the element used in the liquid crystal display device.

Furthermore, in the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

1 is a cross-sectional view of a backlight unit according to an exemplary embodiment of the present invention.

Referring to FIG. 1, the backlight unit 100 according to the present invention includes a plurality of R, G, and B LED light sources 110 and LEDs generating random polarizations of red (R), green (G), and blue (B). At least one of the R, G, and B random polarizations generated by the light source 110 transmits the light of the first polarization and reflects the light of the second polarization, and the first and second polarizations for the remaining random polarization. Reflective polarizing film 120 that transmits the light as it is. Here, the random polarized light includes light of the first polarization in one polarization direction and light of the second polarization in another polarization direction (for example, in the opposite or orthogonal direction). When the random polarized light is transmitted through the reflective polarizing film 120, the light of the first polarized light is transmitted and the light of the second polarized light is reflected.

According to a preferred embodiment of the present invention, the backlight unit 100 of the present invention is applied to a liquid crystal display (LCD) including an absorption polarizing film 130 that transmits light of a first polarization and absorbs light of a second polarization. Therefore, the light emitted from the backlight unit 100 is incident on the absorbing polarizing film 130. Preferably, the absorption polarizing film 130 is positioned on the reflective polarizing film 120 and includes randomly polarized light (light of first polarization and light of second polarization) among the light transmitted through the reflective polarization film 120. ), The light of the first polarized light is transmitted as it is, and the light of the second polarized light is absorbed. Typically, the absorption polarizing film 130 transmits only 50% and absorbs the rest. This light absorption and transmission ratio can be adjusted.

The LED light source 110 generates random polarized light of the R, G, and B wavelength bands. The LED light source 110 of the present invention is disposed under the backlight unit 100 to emit R, G, B light upward. The wavelength of the light emitted as described above may be set differently according to the type of impurities added to the semiconductor constituting the LED. For example, in the case of gallium phosphide, light emission involving zinc and oxygen atoms is red (R), and light emission involving nitrogen cost is green (G). White light may be realized by the combination of R, G, and B lights. In the embodiment of the present invention, the LED light source 110 is preferably implemented as a set of R, G, B LED light source, a plurality of sets are disposed under the backlight unit 100.

In order to optimally express colors in the liquid crystal display, it is important to optimally express white light by a combination of R, G, and B light incident on the liquid crystal panel (not shown) through the absorption polarizing film 130. For this purpose, theoretically, it is ideal to combine the intensities of R, G, and B light in the same ratio. Therefore, in theory, it is ideal that the intensity of R, G, B light emitted from the backlight unit 100 and passed through the absorption polarizing film 130 is 1: 1: 1. In practice, however, these ratios of R, G and B light intensities are difficult to implement. Therefore, in the exemplary embodiment of the present invention, a combination of R, G, and B light intensities for expressing white light may be sufficient to properly express colors in the liquid crystal display. The degree of the white light may be variously set according to the environment of the liquid crystal display.

To this end, in the embodiment of the present invention, the intensity of the current input to at least one LED light source is input to the other LED light source so that white light is emitted by a combination of R, G, and B light transmitted through the absorption polarizing film 130. It is desirable to be smaller than the strength of the current to be. More preferably, the intensity of the current input to the R LED light source is smaller than the intensity of the current input to the G or B LED light source 110. Furthermore, it is further preferable that the intensity input to the B LED light source is smaller than the intensity of the current input to the G LED light source. This will be described in more detail with reference to FIG. 3.

The reflective polarizing film 120 transmits the first polarized light of at least one random polarized light among the red (R), green (G), and blue (B) random polarizations generated by the R, G, and B LED light sources 110. The second polarized light is transmitted, and the remaining random polarized light transmits both the first polarized light and the second polarized light as it is. More preferably, the first polarization of the random polarization of the green (G) or blue (B) wavelength band is transmitted and the second polarization is reflected, and the first and second polarizations of the random polarization of the red (R) wavelength band are left as they are. Permeate. In more detail, the light generated by the R, G, and B LED light sources 110 is randomly polarized light in the R, G, and B wavelength bands. The random polarized light consists of a first polarized light in one direction and a second polarized light in a different direction. In this case, the reflective polarizing film 120 transmits the first polarized light in one direction of the G or B random polarized light as it is, and reflects the second polarized light in the other direction, and the R random polarized light transmits both the first and second polarized light. The second polarized light of G or B selectively reflected as described above is reflected back by the reflecting plate 111 disposed under the LED light source 110 to be converted into the first polarized light and the second polarized light, wherein the first polarized light is Again, the second polarized light is transmitted through the reflective polarizing film 120, and the above process is repeatedly repeated, so that finally, G or B is transmitted through the reflective polarizing film 120 as the first polarized light. This is explained in detail in FIG.

In another embodiment of the present invention, the light of the R and G wavelength bands may be randomly polarized light (including the first and second polarizations), and the light of the B wavelength band may be the first polarized light, and in another embodiment of the present invention, The light in the R and B wavelength bands may be randomly polarized light (including the first and second polarized light) and the light in the G wavelength band may be the first polarized light.

The reflective polarizing film 120 of the present invention may be implemented as a stretched polymer film. Such stretched polymer films can be produced by, for example, adsorbing iodine or dichroic dyes on polyvinyl alcohol films and stretching them in a predetermined direction. The polymer film thus prepared transmits light of the first polarized light and absorbs light of the second polarized light using the refractive index. Preferably, the reflective polarizing film 120 of the present invention comprises a stack of at least two layers, at least one of the layers having a birefringent material, and at least two adjacent layers are selected according to at least one refractive index component. The refractive indexes are different for each of the G, B wavelength bands. By using the difference in refractive index for each wavelength band, transmission and reflection characteristics can be realized for each of R, G, and B wavelength bands.

In the embodiment of the present invention, the stretched polymer film is not particularly limited, but preferably includes a thermoplastic polymer. At this time, a thermoplastic polymer may be used independently or may be used together 2 or more types. As the thermoplastic polymer, for example, polyolefin (polyethylene, polypropylene, etc.), polynorbornene-based polymer, polyester, polyvinyl chloride, polystyrene, polyacrylonitrile, polysulfone, polyallylate, polyvinyl alcohol, poly Methacrylic acid ester, polyacrylic acid ester, a cellulose ester, those copolymers, etc. can be used.

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

Referring to FIG. 2A, the R, G, and B random polarizations generated by the R, G, and B LED light sources 110 are incident on the reflective polarization film 120. In this case, the R random polarized light includes the first polarized light R ₁ and the second polarized light R ₂ , and the G random polarized light includes the first polarized light G ₁ and the second polarized light G ₂ . In addition, the B random polarized light includes a first polarized light B ₁ and a second polarized light B ₂ . Each first polarized light R ₁ , G ₁ , B ₁ is polarized light in one direction, and the second polarized light R ₂ , G ₂ , B ₂ is polarized light in another direction.

The reflective polarization film 120 according to the present invention transmits both the first polarization R ₁ and the second polarization R ₂ with respect to the random polarization of the R wavelength band. However, only the _first and second polarizations G ₁ and B ₁ transmit light and the second polarizations G ₂ and B ₂ reflect random polarizations in the G and B wavelength bands.

Subsequently, as shown in FIG. 2B, the reflected second polarized light G ₂ and B ₂ are reflected by the reflecting plate 111 disposed below the first polarized light G ₁ ′, B _1. ') And second polarization (G ₂ ', B ₂ '). The reflective polarizing film 120 transmits the converted first polarized light G ₁ ′, B ₁ ′ and reflects the second polarized light G ₂ ′, B ₂ ′. The second polarized light G ₂ ′, B ₂ ′ reflected as described above is re-reflected by the lower reflector 111, and the first polarized light G ₁ ″, B ₁ ″ and the second polarized light G ₂ ″, B ₂ ″), and transmission and reflection again take place.

As these processes are repeated, finally, as shown in FIG. 2 (c), the light of the R wavelength band transmits both the first polarized light R ₁ and the second polarized light R ₂ , and the light of the G and B wavelength bands. Light transmits only the first polarized light G ₁ and B ₁ . In this case, the first polarized light G ₁ and B ₁ transmitted are finally transmitted after the transmission and reflection are repeated as described above. That is, in the case of G light, the first polarized light G ₁ is G ₁ + G ₁ '+ G ₁ "+ ..., and in the case of B light, the first polarized light B ₁ is B ₁ + B ₁ '. + B ₁ "+ ... Therefore, the R, G, B light generated by the R, G, B LED light source 110 is all transmitted through the reflective polarizing film 120, R, G, before, after passing through the reflective polarizing film 120 The intensity of B light remains unchanged.

In the present invention, the present invention is not limited thereto, and as another example, the reflective polarizing film 120 may include the first polarized light R ₁ and G ₁ and the second polarized light R ₂ and G for light in the R and G wavelength bands. ₂ ) can be transmitted, and the first polarized light B ₁ is transmitted and the second polarized light B ₂ is reflected to light in the B wavelength band. In another embodiment, the reflective polarizing film 120 transmits both the first polarized light R ₁ and B ₁ and the second polarized light R ₂ and B ₂ to the light of the R and B wavelength bands, and transmits the G wave. The first polarized light G ₁ is transmitted to the long band light and the second polarized light G ₂ is reflected.

In this way, the R, G, and B light transmitted through the reflective polarizing film 120 is incident to the upper absorption polarizing film 130. At this time, the R, G, B light transmitted through the reflective polarizing film 120 is R ₁ , R ₂ , G ₁ , B _1, respectively. The absorption polarizing film 130 transmits the first polarized light R ₁ , G ₁ , and B ₁ as it is, and absorbs the second polarized light R _{2 in} the other direction. For example, 50% of the light in the R wavelength band is absorbed (second polarization) and the rest is transmitted (first polarization). Therefore, after passing through the absorption polarizing film 130, the light intensity of the G or B wavelength band is maintained as it is, but the light intensity of the R wavelength band is lower than when incident on the absorption polarizing film 130 (50% in the example above). As described above, in the light of the R, G, and B wavelength bands transmitted through the absorption polarizing film 140, when the intensity of the light in the R wavelength band is relatively decreased, the white light may not be optimally expressed in the liquid crystal display device. The present invention is to optimize the combination of R, G, B light by appropriately adjusting the intensity of the R, G, B light for the optimal expression of such white light.

3 is a cross-sectional view of a backlight unit according to another exemplary embodiment of the present invention.

Referring to FIG. 3, the backlight unit 200 according to another embodiment of the present invention is positioned on the LED light source 110 in the backlight unit 100 described with reference to FIG. 1 to generate light generated from the LED light source 110. It further comprises a diffusion plate 140 for diffusing and an optical sheet layer 150 for condensing the light diffused by the diffusion plate 140 to be emitted to the reflective polarizing film 120.

The diffusion plate 140 serves to diffuse the light generated from the plurality of R, G, B LED light source 110. As a result, the light transmitted through the diffusion plate 140 is uniformly diffused and emitted upward. The diffusion plate 140 may be implemented by applying a resin layer containing a plurality of beads (beads) to the lower portion of the base film. In other words, light is emitted in an arbitrary direction by the beads to cause light diffusion.

The optical sheet layer 150 is positioned on the diffuser plate 140 to condense the light diffused by the diffuser plate 140 so as to be emitted upward to increase luminance. Although not shown in the drawing, two optical sheet layers 150 of the present invention are preferably disposed up and down. At this time, it is preferable that the individual patterns constituting the optical sheet layer 150 made up and down cross each other perpendicularly. This ensures a viewing angle vertically and horizontally. In addition, it is preferable that each optical microstructure constituting the optical sheet layer 150 has one cross section of a triangle, an arc shape, and a quadrangle in projecting the cross section.

4 is a view showing a change in light intensity in the backlight unit according to an embodiment of the present invention.

Referring to FIG. 4, in the backlight unit 100 according to the present invention, light of red (R), green (G), and blue (B) wavelength bands is generated by a plurality of R, G, and B LED light sources 110. . These lights are incident to the upper reflective polarizing film 110. In this case, all incident R, G, and B light include randomly polarized light R ₁ , G ₁ , and B ₁ and second polarized light R ₂ , G ₂ , and B ₂ as random polarized light. As such, the R, G, and B light incident on the reflective polarizing film 110 are preferably combined at a ratio suitable to generate white light. In the present invention, as an example, the conditions for generating white light will be described assuming that the ratio of the R, G, and B light intensities is I _R : I _G : I _B. For example, I _R : I _G : I _B may be 1: 1: 1, and of course, white light may be generated at other ratios.

In the present exemplary embodiment, the reflective polarizing film 120 transmits the random polarized light of the R wavelength band as it is and randomly reflects the random polarized light of the G and B wavelength band among the random polarized light of the R, G, and B wavelength bands. More specifically, among the randomly polarized light in the G and B wavelength bands, the first polarized light G ₁ , B ₁ in one direction is transmitted as it is, and the second polarized light G ₂ , B ₂ in the other direction is reflected. . The first polarized light R ₁ and the second polarized light R ₂ are transmitted to the randomly polarized light in the R wavelength band. At this time, the second polarized light (G ₂ , B ₂ ) of the reflected G, B light is reflected by the lower reflector 111, and is then randomly polarized (first polarized light (G ₁ ′, B ₁ ′) and second polarized light ( G ₂ 'B ₂ '), which is incident to the reflective polarizing film 120, and the transmission and reflection are repeated on the same principle as above. Through these processes, the light of the R wavelength band finally transmitted through the reflective polarizing film 120 is randomly polarized light (including the first polarized light R ₁ and the second polarized light R ₂ ), and the light of the G or B wavelength band. The light becomes the light of the first polarized light G ₁ , B ₁ . In the drawing, in the case of G and B light, the first polarized light first transmitted through the reflective polarizing film 120 is denoted by G ₁ , and then all the first polarized light transmitted through the reflective polarizing film 120 is repeated by repeated reflection and transmission processes. Denotes G ₁ ^* . Therefore, the G and B light transmitted through the reflective polarizing film 120 are G ₁ + G ₁ ^* and B ₁ + B ₁ ^*, respectively.

At this time, assuming that the ratio of the R, G, B light intensity generated from the R, G, B LED light source 100 is I _R : I _G : I _B , all of the R, G, B light is reflected polarizing film 120 Since the light is transmitted through the reflective polarizing film 120, the ratio of the R, G, and B light intensities is also I _R : I _G : I _B.

However, light in the R wavelength band transmitted through the reflective polarizing film 120 is random polarizations R ₁ and R ₂ in various directions, and light in the G and B wavelength bands is light of the first polarization light G ₁ + G _1. ^* , B ₁ + B ₁ ^* ). Therefore, the absorption polarizing film 130 transmits the first polarized light (G ₁ + G ₁ ^* , B ₁ + B ₁ ^* ) of the G and B wavelength bands as it is, and randomly polarizes the R wavelength band (R ₁ , R _2). ) Only partially transmits. That is, the first polarized light R ₁ having the same direction as the first polarized light of G and B is transmitted, and the second polarized light R ₂ having a different direction is absorbed. Therefore, in the embodiment of the present invention, the light of the G or B wavelength band is transmitted as it is to maintain the light intensity, but the light of the R wavelength band is absorbed a part of the light intensity is reduced. For example, when the absorbing polarizing film 130 absorbs 50% of light, only 50% of light in the R wavelength band is transmitted. In this case, the light in R, G, and B wavelength bands passing through the absorption polarizing film 130 has a ratio of light intensity of I _R / 2: I _G : I _B. This change in light intensity ratio can cause problems in overall color reproduction.

The inventors of the present invention have repeatedly carried out various experiments in order to make the ratio of light intensity substantially the same by paying attention to the change of light intensity. The inventors of the present invention reduce the light intensity of G and B light relative to the light intensity of R light so as to make the ratio of R, G, B light intensity to I _R : I _G : I _{B which} is a condition for generating white light under the above conditions. Considered. To this end, the present inventors have been able to solve this problem through the relationship between the intensity of light generated from the LED light source and the intensity of the current input to the LED light source. That is, as shown in Figure 5, the intensity of the current input to the LED light source and the light intensity has a proportional relationship. That is, as the current input to the LED light source increases (I1-> I2), the light intensity of the LED light source increases (T1-> T2), and the light intensity saturates at a constant current. In general, the voltage for turning on the LED light source is slightly different depending on the LED color, brightness, and the like. Normally, the driving voltage of LED needs 1.8 ~ 5V. The smaller the light intensity, the longer the lifetime of the LED. For example, when comparing the lifespan in A and B in the drawing, the service life of 50,000 hours is shown for A having a relatively high light intensity, while the service life of 80,000 hours is obtained for B having a relatively low light intensity. Increases. This applies to conventional LEDs.

Therefore, the light intensity is reduced by relatively reducing the intensity of the current input from the R, G, B LED light source 110 to the G, B LED light source, but the light intensity ratio of I _R / 2: I _G : I _B is reduced to I _R. / 2: I _G / 2: I _B / 2, that is, I _R : I _G : I _B.

For this purpose, it is preferable that the intensity of the current input to the LED light source of at least one of G or B is smaller than that of the current input to the R LED light source. In addition, considering that the B LED light source has a shorter lifetime than the G LED light source, the intensity of the current input to the B LED light source may be relatively smaller than the intensity of the current input to the G LED light source. Which of the R, G, and B LED light sources 110 controls the input current intensity of the light source 110 may be determined according to the selective reflection characteristic of the reflective polarizing film 120. For example, when the reflective polarizing film 120 transmits R light and selectively reflects G and B light, it is preferable to lower the input current of the G and B LED light sources, and the reflective polarizing film 120 may use R and When the G light is transmitted and the B light is selectively reflected, it is desirable to lower the input current of the G LED light source.

As described above, in the present invention, the LED light source having different intensities of the current input to the at least one LED light source 110 so that the predetermined white light is emitted by the combination of the R, G, and B light passing through the absorption polarizing film 130. It is preferable to reduce the intensity of the G or B light by reducing the intensity of the current input to at least one of the G or B LED light source than the intensity of the current input to the R LED light source. The light intensity ratio of the R, G, B light is set to I _R : I _G : I _B which is a ratio for optimal white light generation. As a result, the color and luminance problems of the liquid crystal display device can be solved, and thus the service life of the LED can be increased. In addition, it is possible to reduce the power consumption of the LED light source as a whole by reducing the intensity of the current used.

The reflective polarizing film 120 according to the exemplary embodiment of the present invention provides a backlight unit without a cholesteric liquid crystal layer of three R, G, and B layers for selective reflection of R, G, and B wavelength bands as in the related art. In particular, it is possible to increase the life of the LED light source of the direct type backlight unit. Furthermore, in the exemplary embodiment of the present invention, since the phase delay layer for converting the R, G, and B light incident on the absorption polarizing film 130 into linearly polarized light does not need to be provided, there is an advantage in the manufacturing process and production cost. .

In another embodiment of the present invention, as shown in FIG. 6A, the optical sheet layer 160 may be further included on the reflective polarizing film 120. The optical sheet layer 160 has a fine microstructure pattern formed on the upper surface thereof, collects the light transmitted through the reflective polarizing film 120, and emits the light upward. The optical sheet layer 160 may effectively suppress scattering caused when light passes, thereby improving luminance in the liquid crystal display device. Meanwhile, in another embodiment, the optical sheet layer 170 may be included below the reflective polarization film 120 of FIG. 6B. Further, although not shown in the drawings, the optical sheet layers 160 and 170 may be simultaneously included on the upper and lower portions of the reflective polarizing film 120, respectively.

Each of the optical microstructures constituting the optical sheet layers 160 and 170 may have various cross-sectional shapes of triangles, arcs, squares, polygons, and the like. These patterns preferably have a prism shape.

7 is a graph showing the ratio of the R, G, B light intensity generated from the LED light source in the backlight unit according to the present invention and the ratio of the R, G, B light intensity transmitted through the absorption polarizing film.

Referring to FIG. 7A, the light intensities of the R, G, and B random polarizations generated by the R, G, and B LED light sources 110 are represented by I _R : I _G : I _B (1: 1 in the drawing. Shown as 1). Figure 7 (b) shows the ratio of the R, G, B light intensity transmitted through the absorption polarizing film in the prior art, Figure 7 (c) shows the ratio of R, G, B light intensity transmitted through the absorption polarizing film according to the present invention The ratio is shown.

In Figure 7 (b) it can be seen that the light intensity ratio of the R, G, B light transmitted through the absorption polarizing film is I _R / 2: I _G : I _B. In this case, since the intensity of R light is relatively small compared to the intensity of G and B light, the quality is deteriorated in terms of reproduction of white light.

However, in Figure 7 (c) by reducing the current input to the G, B LED light source, although the intensity of the R, G, B light transmitted through the absorption polarizing film is reduced to 1/2 (X-> Y), R, It can be seen that the ratio of G and B light intensity is a ratio of I _R : I _G : I _B. This is equal to the ratio of I _R : I _G : I _{B, which} is the intensity of R, G, B light emitted to generate white light from the first R, G, B LED light source 110, thereby providing excellent white light representation and color reproduction. It can solve the imbalance of R, G, B color in.

7 (a) to 7 (c) illustrate the reproduction of white light by implementing the light intensity ratio of I _R : I _G : I _B by reducing the intensities of the G and B light, but in other embodiments of the present invention. It has been described above that the white light may be reproduced by reducing the light intensity of at least one of G or B to implement the light intensity ratio of I _R : I _G : I _B.

Although the present invention described above has been described in detail through the preferred embodiments, the present invention is not limited to the content of these embodiments. Those skilled in the art to which the present invention pertains, although not shown in the embodiments, 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. Belonging will be too self-evident. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

In the display field, the use of LCD is expanding, and high brightness and high definition LCD products are appearing. Since the LCD is a light receiving element, a separate light source is required. LEDs have recently been spotlighted as LCD light sources because they are smaller and have a longer lifespan than conventional light sources (eg, fluorescent lamps) and have low power and efficiency because electrical energy is directly converted into light energy. However, in general, at least one of the G or B LED light source in the R, G, B LED light source has a short lifespan, there is a need to replace the light source when using a long time.

Therefore, according to the present invention, since the power consumption can be reduced while extending the lifespan of the LED light source, it may be usefully used in future LCD devices. Furthermore, in applying the backlight unit according to the present invention to the LCD, since a reflective polarizing film having a selective reflection characteristic of at least one wavelength band of G or B is implemented, the reflective unit has selective reflection characteristics of conventional R, G, and B wavelength bands. Since it is more advantageous in terms of manufacturing cost than reflective polarizing film, it may be applied to LCD devices in the future.

1 is a cross-sectional view of a backlight unit according to an exemplary embodiment of the present invention.

2 is a schematic cross-sectional view of a reflective polarizing film according to an embodiment of the present invention.

3 is a cross-sectional view of a backlight unit according to another exemplary embodiment of the present invention.

4 is a view showing a change in light intensity in the backlight unit according to an embodiment of the present invention.

5 is a graph showing the relationship between the intensity of the current and the intensity of the LED light in the LED light source according to the present invention.

6 is a cross-sectional view of a backlight unit according to another exemplary embodiment of the present invention.

7 is a graph showing the ratio of the R, G, B light intensity generated from the LED light source and the ratio of the R, G, B light intensity transmitted through the absorption polarizing film in the backlight unit according to the present invention.

Claims (12)

A direct type backlight unit for use in a liquid crystal display device including an absorption polarizing film that transmits light of a first polarization and absorbs light of a second polarization. A plurality of R, G, B LED light sources each generating R, G, B random polarization; And The first polarized light is transmitted and the second polarized light is transmitted to at least one random polarized light among the R, G, and B random polarized light generated by the LED light source, and the first and second light is reflected for the remaining random polarized light. A reflective polarizing film that transmits polarized light and exits the absorbing polarizing film; Including; The intensity of the current input to the at least one LED light source to emit white light by the combination of R, G, B light passing through the absorption polarizing film is less than the intensity of the current input to the other LED light source. The method of claim 1, And a ratio of R, G, B light intensity transmitted through the absorption polarizing film is equal to a ratio of R, G, B light intensity generated from the R, G, B LED light source. The method of claim 1, The reflective polarizing film transmits light of the first polarized light and reflects light of the second polarized light with respect to G and B light among R, G, and B random polarized light, and reflects light of the first and second polarized light with respect to the R light. A backlight unit, characterized in that the transmission. The method of claim 3, A backlight unit, characterized in that the intensity of the current input to the G and B LED light source is less than the intensity of the current input to the R LED light source. The method of claim 4, wherein A backlight unit, characterized in that the intensity of the current input to the B LED light source is less than the intensity of the current input to the G LED light source. The method of claim 3, The first polarized light of R among the R, G, and B light transmitted through the reflective polarizing film is light in the same polarization direction as the light of the first polarized light of G and B. The method of claim 1, The plurality of R, G, B LED light source is a backlight unit, characterized in that each of the R, G, B LED light source is made of one set and arranged in a plurality of sets. The method of claim 1, A diffuser plate configured to diffuse light emitted from the R, G, and B LED light sources; And An optical sheet layer condensing the light diffused by the diffusion plate and outputting the light to the reflective polarizing film; Backlight unit, characterized in that it further comprises. The method of claim 8, And at least one of an upper and a lower portion of the optical sheet layer, further comprising another optical sheet layer having an optical microstructure intersecting with the optical microstructure of the optical sheet layer. The method of claim 1, wherein the reflective polarizing film, A backlight unit comprising a stack of at least two layers, at least one of said layers having a birefringent material, and at least two adjacent layers having a difference in refractive index for each wavelength band according to at least one refractive index component . At least one randomly polarized light is transmitted, the first polarized light is transmitted, the second polarized light is reflected, and the remaining random polarized light is transmitted to the first and second polarized light. Reflective polarizing film. 12. A liquid crystal display device comprising any one of the backlight unit and the reflective polarizing film of claim 1.

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