KR20070036966A - Diffuser plate and back light unit using the same - Google Patents

Abstract

The present invention relates to a diffusion plate and a backlight unit using the same to increase light efficiency and front brightness.

The diffusion plate includes a diffusion layer for diffusing light; An upper microlens for condensing the light; A polarization selective reflection pattern disposed between the light exit surface of the diffusion layer and the upper microlens or on the light entrance surface of the diffusion layer to transmit only a specific polarization in the light while reflecting light having a polarization different from the specific polarization do.

Description

Diffuser Plate and Back Light Unit using the same

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

2 is a cross-sectional view showing the configuration of the optical sheets shown in FIG.

3 is a cross-sectional view showing a backlight unit according to the present invention.

4 is a cross-sectional view showing a first embodiment of the diffusion plate shown in FIG.

FIG. 5 is a sectional view showing a second embodiment of the diffusion plate shown in FIG. 3; FIG.

FIG. 6 is a sectional view showing a third embodiment of the diffuser plate shown in FIG. 3; FIG.

7 is a cross-sectional view showing a structure using a foamed resin layer as the air layer in FIG.

FIG. 8 is a sectional view showing a fourth embodiment of the diffuser plate shown in FIG. 3; FIG.

FIG. 9 is a sectional view showing a fifth embodiment of the diffusion plate shown in FIG. 3; FIG.

FIG. 10 is a sectional view showing a sixth embodiment of the diffusion plate shown in FIG. 3; FIG.

FIG. 11 is a sectional view showing a seventh embodiment of the diffusion plate shown in FIG. 3; FIG.

12A and 12B are cross-sectional views showing the shapes of beads incorporated into the diffusion layer of each embodiment.

13 is a simulation diagram showing the light collecting effect of the microlens.

14 is a simulation diagram showing reflection of incident light by polarization selective reflection patterns.

<Explanation of symbols for main parts of drawing>

11 LCD panel 12, 32 bottom cover

13, 33: diffuser 14: optical sheet

14a: diffusion sheet 14b: prism sheet

31: light source 33a: diffusion layer

33b, 33c, 33g: microlens 33d: transparent sheet

40b: resin bulkhead 40a: air

40: air layer 101, 102: polarization selective reflection pattern

42: foamed resin layer 42a: air hole

The present invention relates to a diffuser plate to increase light efficiency and front brightness. The present invention also relates to a backlight unit using the diffusion plate.

BACKGROUND ART In general, liquid crystal display devices have tended to be gradually widened due to their light weight, thinness, and low power consumption. In accordance with this trend, liquid crystal displays are used in office automation equipment, audio / video equipment, and the like. In such a liquid crystal display device, a transmission amount of a light beam is adjusted according to a signal applied to a plurality of control switches arranged in a matrix to display a desired image on a screen.

Since the liquid crystal display is not a self-luminous display, a separate light source such as a back light is required.

The backlight includes a direct type and an edge type according to the position of the light source. The edge type backlight is provided with a light source at one edge of the liquid crystal display, and irradiates the liquid crystal display panel with light incident from the light source through the light guide plate and the plurality of optical sheets. In the direct type backlight, a plurality of light sources are disposed directly below the liquid crystal display, and light incident from the light sources is irradiated onto the liquid crystal display panel through the diffusion plate and the plurality of optical sheets. Light sources used for backlights include a cold cathode fluorescent lamp (CCFL) and a light emitting diode (LED).

Recently, the direct type backlight having higher luminance, light uniformity and color purity than the edge type has been used more mainly in LCD TVs.

Referring to FIG. 1, a conventional liquid crystal display device includes a liquid crystal display panel 11 for displaying an image and a backlight unit 10 for irradiating light onto the liquid crystal display panel 11.

In the liquid crystal display panel 11, a plurality of data lines and a plurality of scan lines are arranged to cross each other, and liquid crystal cells are arranged in an active matrix form between the upper and lower substrates. Further, pixel electrodes and a common electrode for applying an electric field to each of the liquid crystal cells are formed in the liquid crystal display panel. Thin film transistors (TFTs) for switching data voltages to be applied to the pixel electrodes are formed at intersections of the plurality of data lines and the plurality of scan lines. Gate drive integrated circuits and data drive integrated circuits are electrically connected to the liquid crystal display panel through a tape carrier package (TCP).

The backlight unit 10 includes a plurality of lamps 15, a bottom cover 12, a diffusion plate 13, and a plurality of optical sheets 14.

The lamps 15 emit light by an alternating current high voltage from an inverter (not shown) to generate light toward the diffusion plate 13.

The bottom cover 12 is manufactured in a container structure in which a plurality of lamps 15 are accommodated in an inner space, and reflecting plates are formed on the bottom and side surfaces of the inner space.

The diffusion plate 13 is assembled with the bottom cover 12. The diffuser plate 13 includes a plurality of beads and scatters the light incident through the lamps 15 using the beads to display the lamps 15 on the display surface of the liquid crystal display panel 11. ) And the luminance difference does not occur at the position between the lamps 15 and the position of the lamps 15. Since the diffuser plate 13 is manufactured in a structure in which beads are dispersed in a medium having the same refractive index, light cannot be collected.

The optical sheets 14 include one or more diffusion sheets 14a and one or more prism sheets 14b as shown in FIG. 2 to uniformly light the incident light from the diffusion plate 13 to the entire liquid crystal display panel 11. It serves to condense light and to condense the light traveling path in a direction perpendicular to the display surface to condense the light to the front of the display surface.

However, such a backlight unit 10 requires a large number of optical components such as a diffuser plate 13 and a plurality of optical sheets 14 for light uniformity and a light collecting effect. There are many problems and high production cost. In addition, according to the related art, only a specific polarization (P polarization) of the light incident on the liquid crystal display panel in the backlight unit 10 is used in the liquid crystal display panel, whereas the other polarization (S polarization) is absorbed in the liquid crystal display panel. Since it is converted into heat and consumed, there is a problem of low light efficiency and low brightness of the front surface of the backlight unit.

Accordingly, it is an object of the present invention to provide a diffuser plate for enhancing light efficiency and front surface luminance.

Another object of the present invention relates to a backlight unit using the diffusion plate to reduce the number of optical components and to increase light efficiency and front brightness.

In order to achieve the above object, the diffusion plate according to the present invention comprises a diffusion layer for diffusing light; An upper microlens for condensing the light; A polarization selective reflection pattern disposed between the light exit surface of the diffusion layer and the upper microlens or on the light entrance surface of the diffusion layer to transmit only a specific polarization in the light while reflecting light having a polarization different from the specific polarization Characterized in that.

And an air layer disposed between the upper microlens and the diffusion layer.

And a lower microlens formed on the light incident surface of the diffusion layer.

The polarization selective reflection pattern may include a wire grid through which light is reflected and an opening through which light is transmitted.

The microlenses have a vertical cross section of any one of a semicircle, a semi-ellipse, and a triangle, and a horizontal cross section of the microlens has a shape of any one of a rectangle, a circle, and an oval.

The air layer is characterized in that the foamed resin layer formed with a plurality of air holes.

The backlight unit according to the present invention includes a light source for generating light; A diffusion layer for diffusing the light, an upper microlens for condensing the light, and disposed between the light exit surface of the diffusion layer and the upper microlens or on a light incidence surface of the diffusion layer to transmit only a specific polarization in the light On the other hand, it characterized in that it comprises a diffusion layer including a polarization selective reflection pattern for reflecting light of a different polarization and the specific polarization.

And an air layer disposed between the upper microlenses and the diffusion plate.

And a lower microlens formed on the light incident surface of the diffusion layer.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS. 3 to 14.

Referring to FIG. 3, the backlight unit according to the exemplary embodiment of the present invention may include a bottom cover 32 in which the light sources 31 are accommodated, and an air layer or a fine layer for directing light from the light sources 31. An integrated diffuser plate 33 having a micro air buble is provided to irradiate a liquid crystal display panel with only a specific polarized light, for example, P waves.

The light sources 31 include a plurality of lamps, a plurality of light emitting diodes, or surface light emitters to generate light.

The bottom cover 32 includes a bottom surface and a side surface and a reflecting plate is attached thereto.

4 through 11, a microlens, a lenticular lens or a prism lens is formed on the diffusion layer 33a and a polarization selective reflection pattern is formed between the diffusion layer 33a and the diffusion layer 33a. Or a polarization selective reflection pattern is formed under the diffusion layer 33a. Here, a micro lens, a lenticular lens and a prism lens may be further formed below the diffusion layer 33a.

Referring to FIG. 4, the integrated diffusion plate 33 according to the first embodiment of the present invention includes a diffusion layer 33a, a polarization selective reflection pattern 101, and a microlens 33b. The microlens 33b is formed on the transparent sheet 33d corresponding to the substrate.

The diffusion layer 33a scatters the light from the light source 31 to diffuse the light so that the luminance difference between the position of the light sources 31 and the shadow position therebetween does not occur. As the main material of the diffusion layer 33a, polycarbonate (PC), polymethylmethacrylate (PMMA), cyclic olefin copolymer (Cyclic Olefin Copolymer, COC) and the like can be used. The diffusion layer 33a may include a plurality of spherical beads as shown in FIG. 12A or cylindrical beads as shown in FIG. 12B, or may not include the beads.

The polarization selective reflection pattern 101 is formed of a grill-type thin film metal pattern having a pitch of 100 to 300 nm on the diffusion layer 33a and performs P polarization through openings between the metal patterns among the light diffused by the diffusion layer 33a. While transmitting, it serves to selectively reflect the S polarization of the optical axis orthogonal to the P polarization. That is, since a plurality of wire grids are provided in the polarization selective reflection pattern, light incident on the wire grid is reflected, and light incident on the opening region excluding the wire grid is reflected.

Here, the polarization selective reflection pattern 101 may be formed on the diffusion layer 33a or positioned between the diffusion layer and the plurality of lamps.

Assuming that the amount of light generated by the light source 31 is 100%, only about 50% of P polarized waves of 100% of light incident from the light source 31 are transmitted through the polarization selective reflection pattern 101. On the other hand, about 50% of S polarized waves are reflected. The light of the S-polarized wave reflected by the polarization selection reflecting pattern 101 is reflected by the reflecting plate of the diffusion layer 33a or the bottom cover 32, and approximately 25% of the light is changed to P-polarized wave by phase delay, thereby selecting polarization. Passes through the reflective pattern 101. Therefore, the amount of P-waves incident on the liquid crystal display panel among the light generated from the light source 101 increases from 50% to 75% (including 25% of the first reflection), and is reflected by the polarization selective reflection pattern 101. The repetition of the light increases further. Through this process, in the backlight unit according to the present invention, most of the light generated from the light source 31 is converted into a P polarized wave used as effective light in the liquid crystal display panel and is incident on the liquid crystal display panel.

Therefore, the liquid crystal display device to which the backlight unit according to the present invention is applied increases the light efficiency and luminance.

In the integrated diffusion plate 33 according to the second embodiment of the present invention, polarization selective reflection patterns 102 are formed on the bottom surface of the diffusion layer 33a as shown in FIG. 5. The light from the light source 31 is transmitted through the opening between the polarization selective reflection patterns, and the P polarized light is reflected by the wire grid, and only the transmitted P polarized light is transmitted to the upper diffusion layer 33a.

The integrated diffusion plate 33 according to the third embodiment of the present invention includes a diffusion layer 33a, an air layer 40, a polarization selective reflection pattern 101, and an upper microlens 33b as shown in FIG. 6. The air layer 40 is disposed between the upper microlens 33b and the diffusion layer 33a, and the polarization selective reflection pattern 101 is disposed above the air layer 40. The diffusion layer 33a and the polarization selective reflection pattern 101 are substantially the same as in the above-described embodiment.

The air layer 40 includes the air 40a filled in the space provided by the resin partition 40b and the resin partition 40b. In the air layer 40, the light incident through the diffusion layer 33a due to the difference in refractive index with respect to the diffusion layer 33a is bent in the upper microlens 33b by increasing the diffusivity of the light as the traveling path is bent by the difference in refractive index. The light loss is reduced to improve the brightness of the final straight light passing through the upper microlens 33b.

Meanwhile, as the air layer 40, as shown in FIG. 7, a foamed resin layer 42 having a plurality of air holes 42 a formed therein may be used.

The integrated diffusion plate 33 according to the fourth embodiment of the present invention is formed on the air layer 40 disposed between the microlens 33b and the diffusion layer 33a and the lower surface of the diffusion layer 33a as shown in FIG. 8. Polarization selective reflection patterns 102.

In the integrated diffusion plate 33 according to the fifth embodiment of the present invention, an air layer 40 is disposed between the microlens 33b and the diffusion layer 33a as shown in FIG. 9, and a polarization selective reflection pattern is disposed below the air layer 40. Field 101 is described.

4 to 9, a microlens may be further formed on the lower portion, and some of the embodiments will be described with reference to FIGS. 10 and 11.

In the integrated diffusion plate 33 according to the sixth embodiment of the present invention, polarization selective reflection patterns 101 are disposed between the upper microlens 33b and the diffusion layer 33a, as shown in FIG. The lower microlens 33b is formed on the lower surface. As described in the above-described embodiment, the upper microlens 33b condenses the light of the P polarization wave incident through the polarization selective reflection pattern 101, and the lower microlens 33c is incident from the light source 31. The light is diffused to increase the diffusivity of the light incident on the diffusion layer 33a. The polarization selective reflection patterns 101 transmit only P polarized light among incident light, while reflecting S polarized light.

The integrated diffuser plate 33 according to the seventh embodiment of the present invention has a structure in which a lower microlens 33g having a triangular cross section is added in the embodiment of FIG. 6 as shown in FIG. 11.

The lower microlenses 33c and 33g in the sixth and seventh embodiments of the present invention have a vertical cross section of any one of a semicircle, a semi-ellipse, and a triangle, and a horizontal cross section has a quadrangle and a circular oval shape. For example, a micro lens array (MLA), a lenticular lens, a prism, or the like may be used. 10 and 11 as well as other embodiments may be applied to increase the diffusivity of light incident on the diffusion layer 33a.

Optical effects due to the polarization selective reflection patterns 101 and 102 and the openings disposed therebetween can be seen in FIG. As shown in FIG. 14, the polarization selective reflection patterns 101 and 102 including the polarization selective reflection patterns 101 and 102 and the opening therebetween transmit only the P polarization wave, whereas the reflected S polarization wave is reflected in the lower reflector. The light is re-reflected to be converted into P and S waves, and the above-mentioned transmission / reflection is repeated in the polarization selective reflection patterns 101 and 102 to increase the efficiency of the P polarization wave incident to the liquid crystal display panel.

Therefore, the diffusion plate according to the present invention stacks a diffusion plate, an air layer, a polarization selective reflection pattern, and a microlens array into one integrated diffusion plate to increase light efficiency and front surface luminance. The backlight unit according to the present invention, unlike the conventional backlight structure that requires a diffuser plate and a plurality of optical sheets by using the diffuser plate to condense and diffuse light with only one diffuser plate can reduce the number of optical components compared to the conventional As a result, assembly tolerances and defects can be minimized, thereby reducing manufacturing costs and increasing light efficiency and luminance irradiated to the liquid crystal display panel. In fact, according to the result of measuring the brightness of the backlight unit of the present invention including the conventional backlight unit without the polarization selective reflection pattern and the polarization selective reflection pattern, the amount of front light of the backlight unit according to the present invention increases by about 20%. The result was confirmed.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (9)

A diffusion layer for diffusing light; An upper microlens for condensing the light; A polarization selective reflection pattern disposed between the light exit surface of the diffusion layer and the upper microlens or on the light entrance surface of the diffusion layer to transmit only a specific polarization in the light while reflecting light having a polarization different from the specific polarization Diffusion plate characterized in that. The method of claim 1, And an air layer disposed between the upper microlens and the diffusion layer. The method according to any one of claims 1 to 2, And a lower microlens formed on the light incident surface of the diffusion layer. The method of claim 1, The polarization selective reflection pattern includes a wire grid to which light is reflected and an opening through which light is transmitted. The method according to claim 1 or 3, The microlenses have a vertical cross section in the form of one of a semi-circle, semi-ellipse, triangle, and the horizontal cross-section is a diffuser plate, characterized in that any one of the shape of a rectangle, circle and oval. The method of claim 2, The air layer is a diffusion plate, characterized in that the foamed resin layer formed with a plurality of air holes. A light source for generating light; A diffusion layer for diffusing the light, an upper microlens for condensing the light, and disposed between the light exit surface of the diffusion layer and the upper microlens or on a light incidence surface of the diffusion layer to transmit only a specific polarization in the light And a diffuser plate including a polarization selective reflection pattern for reflecting light of a specific polarization and other polarizations. The method of claim 7, wherein And an air layer disposed between the upper microlens and the diffusion layer. The method according to any one of claims 7 to 8, And a lower microlens formed on the light incident surface of the diffusion layer.

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