KR20100073840A - Optical sheet and back light unit of liquid crystal display device having thereof - Google Patents

Abstract

PURPOSE: An optical sheet and a backlight unit of a liquid crystal display device with the same are provided to form a moire pattern compensating for a mura due to a lamp, thereby supplying light with uniform brightness to a liquid crystal panel all the time. CONSTITUTION: A lamp(121) supplies light to a liquid crystal panel. A diffusing plate(125) diffuses light incident into the lamp. The first optical sheet(140) is arranged on the diffusing plate. The first optical sheet refracts the light diffused on the diffusing plate to form a moire pattern. The second optical sheet supplies refracted light to the liquid crystal panel after refracting the incident light. The first prism(146) and the second prism(147) are respectively formed on upper/lower sides of a base film.

Description

Optical sheet and backlight of liquid crystal display device having the same {OPTICAL SHEET AND BACK LIGHT UNIT OF LIQUID CRYSTAL DISPLAY DEVICE HAVING THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical sheet and a backlight device of a liquid crystal display device having the same. Particularly, prisms are formed on upper and lower portions of the optical sheet to form moiré patterns, and the image quality is improved by offsetting it with mura caused by the lamp of the backlight device. An optical sheet and a backlight device of a liquid crystal display device having the same.

Recently, with the development of various portable electronic devices such as mobile phones, PDAs, and notebook computers, there is a growing demand for flat panel display devices for light and thin applications. Such flat panel displays are being actively researched, such as LCD (Liquid Crystal Display), PDP (Plasma Display Panel), FED (Field Emission Display), VFD (Vacuum Fluorescent Display), but mass production technology, ease of driving means, Liquid crystal display devices (LCDs) are in the spotlight for reasons of implementation.

The liquid crystal display is a transmissive display and displays a desired image on the screen by controlling the amount of light passing through the liquid crystal layer by the refractive index anisotropy of the liquid crystal molecules. Accordingly, in the liquid crystal display device, a back light, which is a light source passing through the liquid crystal layer, is provided for displaying an image. In general, the backlight can be classified into two types.

The first is a side type backlight that is provided on the side of the liquid crystal panel to provide light to the liquid crystal layer, and the second is a direct type backlight that provides light directly under the liquid crystal panel.

The side backlight may be installed on the side of the liquid crystal panel to supply light to the liquid crystal layer through the reflection plate and the light guide plate. Therefore, since the thickness can be made thin, it is mainly used in notebooks and the like which require a thin display device. However, the side backlight is difficult to apply to a large area liquid crystal panel because the lamp for emitting light is located on the side of the liquid crystal panel, it is difficult to obtain high brightness because light is supplied through the light guide plate. Therefore, there has been a problem that it is not suitable for the large-area liquid crystal panel for LCD TVs, which is in the spotlight recently.

The direct type backlight is used to manufacture a liquid crystal panel for an LCD TV since the light emitted from the lamp is directly supplied to the liquid crystal layer and can be applied to a large area liquid crystal panel as well as high brightness.

 1 shows a structure of a conventional liquid crystal display device in which a direct type backlight is applied.

As shown in FIG. 1, the liquid crystal display device 1 is largely comprised of a liquid crystal panel 10 and a backlight device 20 disposed on the rear surface of the liquid crystal panel 10. Although not shown in the drawing, the liquid crystal panel 10 is a place where an actual image is realized, and includes an upper substrate and a lower substrate such as glass and a liquid crystal layer formed therebetween. In particular, the lower substrate is a thin film transistor substrate on which a driving element such as a thin film transistor and a pixel electrode are formed, and the upper substrate is a color filter substrate on which a color filter layer is formed.

The backlight 20 includes a lamp 21 emitting actual light, a reflector 27 reflecting light emitted from the lamp 21 to improve light efficiency, and a light emitted from the lamp 11. The diffuser plate 25 to diffuse and the light emitted from the diffuser plate 25, which is disposed on the diffuser plate 25, are diffused and condensed once again, so that the luminance is improved and uniformized to the liquid crystal panel 10. It consists of the optical sheet 30 to supply.

The liquid crystal panel 10 and the backlight device 20 are fixed to the main support 2, and then assembled by the lower cover 3 and the upper cover 4.

2 conceptually illustrates a backlight device 20 applied to the liquid crystal display device.

As shown in FIG. 2, the optical sheet 30 of the backlight device 20 is disposed on the diffuser plate 25 to diffuse the light diffused from the diffuser plate once again, and the diffuser sheet. A prism sheet 34 for refracting and condensing the light diffused from the 32, and a protective film 38 disposed on the prism sheet 34 to protect the diffusion sheet 32 and the prism sheet 34. Is done.

In the optical sheet 30 configured as described above, the light emitted from the lamp 21 and diffused from the diffusion plate 25 is diffused once again from the diffusion sheet 32 and then enters the first prism sheet 34. After being refracted to the front, the front luminance is improved and then supplied to the liquid crystal panel 10.

However, the following problem occurs in the backlight device 20 having the above structure.

Recently, in order to reduce the thickness of the liquid crystal display device, research for reducing the thickness of the backlight device 20 has been continued. The best way to reduce the thickness of the backlight device 20 is to minimize the gap between the lamp 21 and the diffuser plate 25 which has the greatest effect on the thickness of the backlight device. However, when the distance between the lamp 21 and the diffuser plate 25 is reduced, as shown in FIG. 2, the area a directly irradiated with the light emitted from the plurality of lamps 21 and the light are not directly irradiated. Area b is generated.

Therefore, the light input to the diffuser plate 25 has a luminance greater than that of the region b, and the luminance difference of the light does not completely disappear even after the light passes through the diffuser plate 25 and the optical sheet 30. Due to the difference in luminance of the light supplied to the liquid crystal panel 10, spots such as streaks (called mura) are generated on the screen. This mura is not only generated by an area where light emitted from the lamp 21 is not irradiated, but when the distance between the lamp 21 and the lamp 21 of the backlight device 20 is too large, the plurality of lamps 21 This occurs even when a luminance difference occurs between a region where the light emitted from the light overlaps with the light emitted from the adjacent lamp 21 and a region where the light does not overlap.

The present invention is to solve the above problems, by placing an optical sheet forming a moire pattern to cancel the moire pattern with the mura by the lamp to supply light of uniform brightness to the liquid crystal panel and a liquid crystal having the same It is an object to provide a backlight of a display element.

In order to achieve the above object, the backlight device according to the present invention comprises a lamp for supplying light to the liquid crystal panel; A diffuser plate configured to diffuse light incident on the lamp; A first optical sheet disposed on the diffuser plate and refracting light diffused from the diffuser plate to form a moire pattern; And a second optical sheet disposed on the diffusion plate and refracting incident light to be supplied to the liquid crystal panel.

The first optical sheet is a base film; First and second prisms formed on upper and lower surfaces of the base film, respectively; A diffusion layer formed on upper and lower surfaces of the base film; Comprising a scattering layer formed between the first pattern and the second pattern, the second optical sheet includes a diffusion sheet, a prism sheet and a protective sheet.

In the present invention, by providing the optical sheet formed on the prism on the upper and lower surfaces of the base film on the upper part of the lamp to form a moire pattern offset from the mura by the lamp, it is possible to always supply light of uniform brightness to the liquid crystal panel.

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

In the liquid crystal display device, the best way to remove the mura caused by the backlight device is to add a diffusion sheet and a prism sheet to the backlight device to improve the diffusion efficiency and the light collection efficiency of the light emitted from the lamp. However, in this case, not only the cost of the backlight device increases but also the thickness of the backlight device increases due to the added diffusion sheet and prism sheet.

The present invention provides a backlight device capable of removing mura by the lamp of the backlight device without adding a diffusion sheet and a prism sheet. In particular, the present invention provides a backlight device capable of preventing the mura while simplifying the structure of the backlight device.

3 is a view showing a liquid crystal display device having a backlight device 120 according to the present invention.

As shown in FIG. 3, the liquid crystal display device according to the present invention includes a liquid crystal panel 110 displaying an image and a backlight device 120 supplying light to the liquid crystal panel 110. The liquid crystal panel 110 and the backlight device 120 are fixedly supported by the main support part 102, and the liquid crystal panel 110, the backlight device 120, and the main support part 102 have a lower cover 103 and an upper part. Assembled by the cover 104.

Although not shown in the drawing, the liquid crystal panel 110 includes a first substrate on which a thin film transistor is formed, a second substrate on which a color filter is formed, and a liquid crystal layer formed between the first substrate and the second substrate. A plurality of pixels are formed on the first substrate, a thin film transistor and a pixel electrode are formed on each pixel, and a color filter layer is formed on the second substrate. A printed circuit board 112 having a driving element (not shown) mounted thereon is attached to at least one edge of the liquid crystal panel 110.

When a signal is input from an external driving element in the liquid crystal panel as described above, a thin film transistor disposed in each pixel is turned on to apply an image signal from an external driving element to the pixel electrode through the thin film transistor, and according to the image signal. An electric field is applied to the liquid crystal layer to adjust the light transmittance of the liquid crystal layer to realize an image.

A backlight device 120 including a plurality of lamps 121 is provided on the rear surface of the liquid crystal panel 110 to supply light to the liquid crystal panel 110. The backlight device 120 includes a plurality of lamps 121 disposed under the liquid crystal panel 110, a fixing part 105 formed across the entire ends of the liquid crystal panel, and fixing the plurality of lamps 121. A reflection plate 127 disposed under the lamp 121 and reflecting light emitted from the lamp 121 and incident on the lower cover 103 to the liquid crystal panel 110, and disposed on the lamp 121. A diffusion plate 125 for diffusing the incident light, a first optical sheet 140 disposed on the diffusion plate 125 to refract the light diffused by the diffusion plate 125 to form a moire pattern, and The second optical sheet 130 is disposed on the first optical sheet 140 and diffuses or condenses the light forming the moire pattern.

4 is a view conceptually showing a lamp 121 and an optical element thereon of the backlight device according to the present invention.

As shown in FIG. 4, the diffusion plate 125 is disposed on the plurality of lamps 121, the first optical sheet 140 is disposed on the diffusion plate 125, and the diffusion sheet is disposed on the first optical sheet 140. A second optical sheet such as 132 is disposed.

It is preferable to mainly use a Cold Cathod Fluoroscent Lamp (CCFL) as the lamp 121, but an External Electorde Fluoroscent Lamp (EEFL) or an LED (Light Emitting Device) emitting white light may be used.

As shown in FIG. 5, the first optical sheet 140 includes a base film 141 made of polyethylene terephthalate (PET) and a first prism 146 made of acrylic resin formed on an upper surface of the base film 141. ) And a second prism 147 made of acrylic resin formed on the bottom surface of the base film 141. The first prism 146 and the second prism 147 are triangular in cross section, and extend from one side of the base film 141 to the other side, wherein the first prism (upper and lower surfaces of the base film 141 is formed). 146 and the second prism 147 are aligned at the same position with each other.

Diffusion sheet 132 is to diffuse the light output from the first optical sheet 140 to maintain a constant brightness, mainly a spherical seed made of acrylic resin on a base film made of polyethylene terephthalate (PET) It is produced by distributing. The light output from the first optical sheet 140 is diffused from the spherical seed so that the brightness of the light output is uniform.

In the backlight device 120 having the above-described configuration, the light emitted from the lamp 121 overlaps with the adjacent lamp 121, or the gap between the lamp 121 and the diffusion plate 125 is too narrow. The luminance of the light input to 125 is not uniform, which causes Mura.

As described above, light generated by Mura (that is, light having a partially different luminance) is not output as a light having a uniform luminance even when diffused from the diffusion plate 125, and a luminance is output unevenly. When light having non-uniform brightness is incident on the first optical sheet 140, the light is first refracted by the second prism 147 of the first optical sheet 140, and then refracted by the first prism 146 again. do. The light passing through the second prism 147 and the first prism 146 interferes with the second prism 147 and the first prism 146, and in particular, the light passes through the second prism 147 and the first prism 146. As the light penetrates the prism 146, the interference is reinforced, and the luminance difference is more clearly generated. As a result, a wavy moiré pattern is displayed on the screen.

FIG. 6A is a view showing that mura occurs when the light emitted from the lamp 121 passes through the diffuser plate 125. FIG. 6B shows that light emitted from the lamp 121 does not pass through the diffuser plate 125. FIG. 1 is a view showing that the moire pattern occurs when the optical sheet 140 is transmitted. 6A and 6B, a plurality of mura by the lamp 121 is formed in the horizontal direction on the screen, but the moire pattern by the first optical sheet 140 is formed with a wavy pattern in the horizontal direction. At this time, the spacing of the moire fringes is narrower than that of the stripes due to Mura.

In the backlight device 120 illustrated in FIG. 4, light emitted from the lamp 121 passes through the first optical sheet 140 and is incident to the liquid crystal panel 110. Therefore, since the light generated by Mura as shown in FIG. 6A is transmitted through the first optical sheet 140 which generates the moire pattern as shown in 6b, the pattern by the light output from the first optical sheet 140 is illustrated in FIG. The mura shown in FIG. 6A and the moire pattern shown in FIG. 6B cancel each other out to form a pattern as shown in FIG. 6C. Comparing the pattern shown in FIG. 6C with the moire pattern shown in FIG. 6A and the moire pattern shown in FIG. 6B, it can be seen that the stain is weak and the stain is greatly reduced.

Therefore, when the light generated by the pattern as shown in FIG. 6C, that is, light emitted from the lamp 121 and transmitted through the first optical sheet 140 is diffused while passing through the diffusion sheet 132, the first optical sheet 140 Since the light transmitted through the Mura and the moire patterns are canceled and the stain is reduced, light of uniform brightness in which the stain is completely removed by the diffusion sheet 132 is input to the liquid crystal panel 110.

FIG. 7 is a partially enlarged view of the first optical sheet 140 shown in FIG. 5.

As shown in FIG. 7, diffusion layers 142 are formed on upper and lower surfaces of the base film 141, respectively. The diffusion layer 142 contains a diffusion material such as a bead in the resin, and diffuses the light input from the diffusion plate 125 once again on the upper and lower surfaces of the first optical sheet 140 to provide light. This is to make the luminance even more uniform.

The first prism 146 and the second prism 147 are formed on the diffusion layer 142. The pitch P of the first prism 146 and the second prism 147 is about 50 &lt; P &lt; 100 mu m and the angle θ of the vertex on the cross-sectional triangle of the first prism 146 and the second prism 147 Is about 88 ° <θ <92 °. In this case, the first prism 146 and the second prism 147 have the same shape, that is, the same pitch (P) and the vertex angle (θ). In addition, although the first prism 146 and the second prism 147 are formed at positions corresponding to each other, the positions of the first prism 146 and the second prism 147 are slightly different from each other (about 10 μm). It may be out of order.

In FIG. 4, although the extending direction of the first prism 146 and the second prism 147 and the longitudinal direction of the lamp 121 are arranged in the same manner, the first prism 146 and the second prism 147 The extending direction may be arranged in a direction different from the longitudinal direction of the lamp 121, for example, vertically.

The mura by the lamp 121 determines the direction of the stripes according to the arrangement of the lamp, and the moire pattern by the first optical sheet 140 also extends in the extending direction of the first prism 146 and the second prism 147. Since the direction of the wave pattern is formed differently, the Mura and the moire pattern may be effectively canceled by adjusting the arrangement of the lamp 121 and the extension directions of the first prism 146 and the second prism 147.

In addition, as shown in FIG. 7, a scattering layer 143 filled with air or the like may be formed in the base film 141 of the first optical sheet 140. Since the air of the scattering layer 143 has a different refractive index from that of the base film 141 made of resin, the air may be disposed between the first prism 146 and the second prism 147 of the first optical sheet 140. Input light is scattered on the surface of the scattering layer 143. As such, since light is scattered on the surface of the scattering layer 143, light incident between the prisms 146 and 147 is incident again to the prisms 146 and 147, thereby supplying light of more uniform brightness to the liquid crystal panel 110. That is, the scattering layer 143 scatters the light input between the first prism 146 and the second prism 147 with a prism and refracts the light by the first prism 146 and the second prism 147. By forming the moire pattern by the first optical sheet 140 more reliably, the mura and the moire pattern by the lamp 121 can be more effectively canceled.

The scattering layer 143 is for scattering light incident on the surface. Therefore, the material included in the scattering layer 143 may have any refractive index different from that of the base film 141, and any material including air may be used as long as it can scatter incident light.

In addition, as shown in FIG. 7B, the reflective layer 144 may be formed on the base film 141 between the first prism 146 and the second prism 147 instead of the scattering layer 143. In this structure, light incident between the first prism 146 and the second prism 147 is reflected by the reflective layer 144, and then is incident on the bottom surface of the base film 141 at an angle greater than or equal to a threshold value. The light reflected from the lower surface of the base film 141 is incident to the first prism 146 again, and the light incident to the lower surface of the base film 141 at an angle equal to or less than a threshold value is reflected by the reflector of the backlight device and is then reflected on the first prism 146. It is incident on the optical sheet 140. As such, as the reflective layer 144 is formed between the prisms 146 and 147, light is incident between the prisms 146 and 147 to prevent the light that is not refracted by the first optical sheet 140 from being supplied to the liquid crystal panel 110. You can do it.

The first prism 146 and the second prism 147 of the first optical sheet 140 do not need to have a triangular cross section. As shown in FIGS. 8A and 8B, the cross sections of the first prism 146 and the second prism 147 may be formed into a base film (including all possible polygons, not a specific polygon). It may be formed to extend from one side of the other side 141.

In addition, other patterns may be formed on the first optical sheet 140 instead of the first prism 146 and the second prism 147. Since the role of the first prism 146 and the second prism 147 is to form a moiré pattern by refracting and reinforcing the incident light, the base film 141 of the first optical sheet 140 of a predetermined interval The moiré pattern may be formed by diffractive interference by diffraction of incident light by forming a pattern. In this regard, the first prism 146 and the second prism 147 having a triangular, circular or polygonal cross section may also be regarded as a form of a pattern.

In addition, although only one diffusion sheet 132 is provided as the second optical sheet in addition to the first optical sheet 140 in FIG. 4, the second optical sheet is not composed of only the diffusion sheet. Although not shown in the drawing, a transparent protective film may be provided on the diffusion sheet 132 to protect the first optical sheet 140 and the diffusion sheet 132.

In addition, as shown in FIG. 9A, two diffusion sheets 232 and 233 and a protective film 238 are provided as the second optical sheet, and the first diffusion sheet 232 includes the diffusion plate 225 and the first optical. It is arranged between the sheets 240 and the second diffusion sheet 233 is disposed on the first optical sheet 240, the protective film 238 is disposed on the second diffusion sheet 233 to diffuse the sheets 232, 233 and The first optical sheet 240 may be protected.

In addition, as shown in FIG. 9B, the prism sheet 234 and the diffusion sheet 234 may be disposed on the first optical sheet 240 as the second optical sheet. In this case, a protective film may or may not be provided on the diffusion sheet 234.

As mentioned above, in this invention, the optical sheet of all possible structures can be arrange | positioned. In addition, various various optical sheets such as a diffusion sheet or a prism sheet are not limited to a specific structure, and optical sheets having all known structures may be applied to the present invention. In other words, other examples or modifications of the present invention can be easily created by anyone in the technical field to which the liquid crystal display device using the basic concept of the present invention belongs.

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

2 conceptually illustrates a backlight device of a conventional liquid crystal display device;

3 is a perspective view showing the structure of a liquid crystal display device according to the present invention;

4 is a view conceptually illustrating a backlight device of a liquid crystal display device according to an embodiment of the present invention;

5 is a perspective view showing the structure of a first optical sheet of a backlight device according to the present invention;

Figure 6a is a view showing the mura generated by the light emitted from the lamp of the backlight device according to the present invention.

6B is a view showing a moire fringe generated by light transmitted through a first optical sheet of a backlight device according to the present invention.

Figure 6c is a view showing that the moiré generated by the lamp of the backlight device according to the present invention and the moire pattern generated by the light transmitted through the first optical sheet is canceled.

7A and 7B are partially enlarged views of a first optical sheet of a backlight device according to the present invention;

8A and 8B show another structure of the first optical sheet of the backlight device according to the present invention;

9A and 9B conceptually illustrate a backlight device of a liquid crystal display device according to another exemplary embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

121: lamp 132,134: diffusion sheet

140: first optical sheet 141: base film

142: diffusion layer 143: scattering layer

144: reflective layer 146, 147: prism

Claims (16)

A lamp supplying light to the liquid crystal panel; A diffuser plate configured to diffuse light incident on the lamp; A first optical sheet disposed on the diffuser plate and refracting light diffused from the diffuser plate to form a moire pattern; And And a second optical sheet disposed on the diffusion plate and refracting incident light to be supplied to the liquid crystal panel. The method of claim 1, wherein the first optical sheet, Base film; And And a first prism and a second prism formed on upper and lower surfaces of the base film, respectively. The backlight device of claim 2, wherein the first optical sheet further comprises a diffusion layer formed on upper and lower surfaces of the base film. The backlight device of claim 2, wherein the first optical sheet further comprises a scattering layer formed between the first pattern and the second pattern. The backlight device of claim 4, wherein the scattering layer comprises air. The backlight device of claim 2, wherein the first optical sheet further comprises a reflective layer formed between the first pattern and the second pattern. The backlight device of claim 1, wherein the second optical sheet comprises a diffusion sheet disposed over the first optical sheet. The method of claim 1, wherein the second optical sheet, A diffusion sheet disposed on the first optical sheet; And And a protective sheet disposed on the diffusion sheet. The method of claim 1, wherein the second optical sheet, A first diffusion sheet disposed below the first optical sheet; A second diffusion sheet disposed on the first optical sheet; And And a protective sheet disposed on the diffusion sheet. The method of claim 1, wherein the second optical sheet, A diffusion sheet disposed on the first optical sheet; A prism sheet disposed on the diffusion sheet; And And a protective sheet disposed on the diffusion sheet. The backlight device of claim 1, wherein the moire fringe generated by the first optical sheet is canceled out with the mura generated by the lamp. Base film; And A diffusion layer formed on upper and lower surfaces of the base film; And It is composed of a first pattern and a second pattern on the upper and lower diffusion layers of the base film, The optical sheet, characterized in that to form a moire pattern as the incident light is transmitted. The optical sheet according to claim 12, wherein the first pattern and the second pattern have a triangular, circular or polygonal cross section and a prism extending from one side of the base film to the other side. The optical sheet of claim 12, wherein the first optical sheet further comprises a scattering layer formed between the first pattern and the second pattern. The optical sheet of claim 12, wherein the first optical sheet further comprises a reflective layer formed between the first pattern and the second pattern. The optical sheet according to claim 13, wherein the prism having a triangular cross section has a pitch P of 50 &lt; P &lt; 100 mu m and a vertex angle &amp;thetas; of 88 degrees &lt;

Images