KR20080004802A - Optical plate for surface light source and backlight unit having the same - Google Patents

Abstract

An optical plate for a surface light source and a backlight unit having the same are provided to improve luminance and luminance uniformity of a surface light source unit, and obtain reliability of a product by removing bright lines. An optical plate(210) includes the first patterns(210a) of an oval apex shape separated at the first pitches on an upper surface thereof. The apex angle of the first pattern is within the range of 38 degrees to 43 degrees. An aspect ratio of the first pattern is 0.5 or smaller. The first pitch of the first pattern is 300 micrometer or smaller. The second patterns(210b) are formed on a lower surface of the optical plate and separated at the second pitches larger than the first pitches of the first patterns. The apex angle of the second pattern is greater than that of the first pattern. The apex angle of the second pattern is within the range of 90 degrees to 150 degrees.

Description

Optical plate for surface light source and backlight unit having the same {OPTICAL PLATE FOR SURFACE LIGHT SOURCE AND BACKLIGHT UNIT HAVING THE SAME}

1 is a perspective view showing an example of a flat fluorescent lamp.

2 is a perspective view showing an optical plate according to an embodiment of the present invention.

3 is a perspective view showing an optical plate according to another embodiment of the present invention.

4 is a cross-sectional view taken along line II ′ of FIG. 2.

5 is an enlarged view of a portion A of FIG. 4;

6 is a cross-sectional view showing an optical plate of the present invention.

Figure 7 is a schematic diagram showing the ellipsoid peak of the first pattern of the optical plate of the present invention.

8A to 8D are graphs showing optical characteristics of the optical plate of the present invention.

9 is an exploded perspective view of a backlight unit including the optical plate of the present invention.

*** Explanation of symbols for the main parts of the drawing ***

210: optical plate 210a: first pattern

210b: second pattern 240 ': ellipsoid peak

The present invention relates to an optical plate for a surface light source and a backlight unit having the same, and to a novel optical member for a surface light source capable of improving luminance and eliminating bright lines without additional diffusion plates and diffusion sheets.

Liquid crystal display devices have been developed as display devices to replace CRTs because of low driving voltage and low power consumption. In particular, thin film transistor liquid crystal display devices have been used in various fields in recent years by realizing high quality, large size, and color matching comparable to CRTs. have. Unlike the CRT, the liquid crystal display device is not a display device that emits light by itself, and thus a separate light source is provided on the rear surface of the liquid crystal panel. A lamp or LED is used as a light source of the liquid crystal display, and a back-light unit having such a light source is provided in the liquid crystal panel.

Cold Cathode Fluorescent Lamps (CCFLs) are widely used as light sources using lamps, but the structure is complicated and consumes a lot of power due to a line light source method in which a plurality of fluorescent lamps are arranged. Therefore, development of a flat florescent lamp (FFL) of a surface light source method rather than a linear light source is being actively progressed.

1, a flat fluorescent lamp is shown as an example of a surface light source device. The surface light source device 100 includes a light source body 110 and electrodes 160 provided on outer surfaces of both edges of the light source body 110. The light source body 100 includes an upper substrate and a lower substrate disposed to face each other to form the discharge space 150. The partition walls 140 formed by a portion of the upper substrate abutting the lower substrate divide the space between the upper substrate and the lower substrate into a plurality of light emitting regions 120. Discharge gas is injected into the discharge space 150, and discharge is performed by a voltage applied through the electrode 160.

As the liquid crystal display device becomes larger, the luminance required for the rear light source continues to increase. In order to increase the luminance, the tube current supplied to the surface light source device must be increased. However, when the tube current is increased, the lifespan of the surface light source device is reduced, and the driving inverter of the surface light source device has a limit in the available power.

In the surface light source device including the plurality of discharge regions 120 and the partition wall portion 140 as illustrated in FIG. 1, light is emitted only in the discharge region, and the partition portion acts as a dark portion to reduce the overall brightness. There is a problem that a bright line is generated due to the difference in luminance between the units.

Conventionally, an optical member including a diffusion plate and a diffusion sheet is disposed at a predetermined distance from the surface light source device to remove the bright lines and increase the luminance uniformity. However, the optical member including the diffusion plate and the diffusion sheet has a problem of increasing the manufacturing cost of the backlight unit and complicating the manufacturing process. In addition, the diffuser plate is formed in a structure in which fine glass beads are dispersed therein, and scatters light emitted from the surface light source device to achieve uniformity in luminance, but there is a limitation in that the overall luminance decreases.

Therefore, there is a demand for an optical member having a new structure for improving luminance and removing bright lines of the surface light source device.

SUMMARY OF THE INVENTION The present invention has been made under such a technical background, and an object thereof is to provide a high quality backlight unit by preventing the luminance deterioration of light emitted from the surface light source device as a single optical plate and removing the bright lines.

In addition, another object of the present invention is to provide a new optical member that is easy to manufacture while satisfying both the luminance improvement and the luminance uniformity of the light emitted from the surface light source device.

Other objects and features of the present invention will be presented in more detail in the following detailed description.

In order to achieve the above object, the present invention is a plate having a first pattern of ellipsoidal peak shape spaced apart by a first pitch on the upper surface, the apex angle of the first pattern is 38 ° It provides an optical plate for a surface light source, characterized in that in the range of ~ 43 °.

The first pattern is formed on one surface by molding the optical plate by extrusion.

The aspect ratio of the first pattern is preferably 0.5 or less, preferably in the range of 0.05 to 0.4. In addition, the first pitch of the first pattern is 300 µm or less, preferably 60 to 240 µm.

A second pattern spaced apart from the second pitch larger than the first pitch of the first pattern may be formed on the bottom surface of the optical plate. The second pattern may be in a regular form or may be in an irregular pattern form. In addition, the peak angle of the second pattern is greater than the peak angle of the first pattern, for example, the peak angle of the second pattern may be formed in the range of 90 ° ~ 150 °.

The present invention also provides a surface light source including at least one discharge space and an electrode unit for applying a voltage to the discharge space; A case accommodating the surface light source; An optical plate disposed between the surface light source and the case, the first pattern having an ellipsoidal peak shape spaced apart by a first pitch on an upper surface thereof, and the peak angle of the first pattern being in a range of 38 ° to 432 °; And an inverter configured to apply a discharge voltage to the electrode to drive the surface light source.

The surface light source may be a flat fluorescent lamp in which a plurality of discharge spaces are spaced apart from each other by a partition wall part. However, the optical plate according to the present invention can be applied not only to a flat fluorescent lamp (FFL) but also to a cold cathode fluorescent lamp (CCFL) or a light emitting diode flat lamp.

According to the present invention, it is possible to improve the optical characteristics such as the light condensing property, the light uniformity of the backlight, and the like, without using additional optical sheets including the diffusion plate and the diffusion sheet. The bright line can be removed from the surface light source. The backlight unit according to the present invention does not exclude that a separate light collecting or diffusing optical sheet is included in addition to the optical plate.

2, there is shown an optical plate 210 in accordance with one embodiment of the present invention. The first plate 210a is formed on the upper surface of the optical plate, and the second pattern 210b is formed on the lower surface of the optical plate. The first pattern 210a on the upper surface improves the concentration of light emitted from the surface light source device (not shown) positioned under the optical plate and reduces the bright lines caused by the partition wall of the surface light source device. In addition, the second pattern on the lower surface improves the brightness uniformity characteristic of the optical plate and prevents the decrease in the transmittance of the optical plate.

In the embodiment shown in FIG. 2, the first pattern 210a of the upper surface of the optical plate is formed in a bar shape extending in one direction (X direction). As described in detail below, the cross section of the first pattern has a peak shape of an ellipsoid and is similar to a tunnel shape in which an upper portion of the ellipsoid is cut out.

3 illustrates an optical plate 220 according to another embodiment of the present invention. Unlike the above-described embodiment, the first pattern 220a of the upper surface of the optical plate is arranged in at least two directions (X direction and Y direction). It is. Such a structure is that the ellipsoid apex is two-dimensionally arranged on the upper surface of the optical plate, and the luminance characteristic can be improved in response to a change in the shape of the discharge space of the surface light source device.

The optical plate according to the present invention may use a polymer material of transparent material, for example, polymethyl methacrylate (PMMA), polycarbonate (PC), polystyrene (PS), methyl methacrylate-styrene copolymer (MS ), Cycloolefin (COP) and the like, but is not necessarily limited to these materials. In the present invention, the material used as the optical plate preferably has a refractive index in the range of 1.45 to 1.6 for excellent light condensing properties.

4 is a cross-sectional view taken along line II ′ of the embodiment of FIG. 2, and an enlarged portion A of FIG. 4 is illustrated in FIG. 5. The optical plate 210 according to the present invention has a first feature in that an ellipsoidal peak-shaped first pattern 210a is formed on an opposite surface of the surface opposite to the surface light source device. The first pattern 210a serves to condense the light L1 emitted from the surface light source device through the optical plate to be uniformly emitted to the front surface. As a result, the luminance unevenness caused by the difference in the luminance of the discharge region and the partition wall portion of the surface light source device is reduced, and in particular, the bright lines caused by the partition wall portion can be eliminated.

According to the second aspect of the present invention, an additional second pattern 210b is formed on the lower surface of the optical plate. Light emitted from the surface light source device is scattered through the second pattern 210b to increase luminance uniformity. In addition, the light reflected from the inner surface 210a 'of the first pattern is reflected (total reflection) on the inner surface 210b' of the second pattern, thereby reducing light loss and improving the transmittance of the optical plate.

Referring to FIG. 6, detailed structures of the first pattern 210a and the second pattern 210b are illustrated. In the first pattern 210a, the pitch t1 between the peaks of the adjacent patterns is 300 μm or less. More preferably, the range of 60-240 micrometers is appropriate, and it was confirmed that there is no big difference in the condensing characteristic in this range. On the other hand, the second pattern 210b preferably has a pitch t2 greater than the pitch t1 of the first pattern in order to increase scattering of light emitted from the surface light source device and to improve light condensing efficiency to the first pattern. Do.

As shown in FIG. 7, the first pattern 210a is formed to partially remove a part of the ellipsoid 240 so that only the peak 240 'remains. The first pattern 210a has an apex angle θ. ) Was found to be effective in the condensing characteristics to form in the range of 38 ° ~ 43 °. Since the second pattern is preferably formed with a larger pitch than the first pattern, the peak angle of the second pattern is larger than the peak angle of the first pattern, for example, the peak angle of the second pattern is in a range of 90 ° to 150 °. It can be formed as.

In addition, in the present invention, an aspect ratio of the first pattern is very important for light condensing characteristics. Referring to FIG. 7, the appearance ratio may be defined as a ratio (b / a) of the long diameter (a) and the short diameter (b) of the ellipsoid 240, and the appearance ratio of the first pattern may be 0.5 or less, more preferably. In the range of 0.05 ~ 0.4 it was confirmed that the light collecting characteristics of the optical plate is excellent.

In the case of using the optical plate according to the present invention, the following experiments were performed to confirm the overall luminance and luminance uniformity improvement of the surface light source device including the discharge space and the non-light emitting partition.

The luminance and luminance uniformity of the light passing through the optical plate were examined while changing the apex angle (θ) and the appearance ratio of the ellipsoid peak of the first pattern. In addition, in order to confirm the luminance and luminance uniformity of the light emitted in the vertical direction, that is, the light emitted toward the front of the optical plate and the oblique angle, the luminance and luminance uniformity of the light having a 0 ° inclination and the light having 40 ° Investigate. 8A to 8B are graphs showing changes in condensing characteristics according to the shape of the first pattern of the optical plate according to the present invention.

The overall trend in this study shows that the larger the value of the aspect ratio (the higher the vertical axis), the easier the incident light is in the vertical direction, and the smaller the light is in the rectangular direction. This is more than 70 degrees. Also, in the case of apex angle, the larger the value (to the right of the horizontal axis) tends to be totally reflected in the vertical direction, the smaller the peak angle is 70 degrees to the incident light in the square direction It is bent over. On the other hand, as the peak angle increases, the plane incidence angle becomes closer to vertical.

Referring to FIG. 8A, it is a graph showing luminance in a vertical direction (0 ° inclination of the emitted light) and it can be seen that the luminance is excellent when the peak angle is in the range of about 36 ° to 48 ° and the appearance ratio is 0.4 or less. On the other hand, when looking at the vertical luminance uniformity in Figure 8b it can be seen that the peak angle is in the range of about 40 ° ~ 60 ° and the appearance ratio is very excellent at 0.7 or less. 8C and 8D, the luminance and luminance uniformity of the square direction (the inclination angle of the emitted light 40 °) were slightly different from those of the vertical direction.

Since the flux of the light passing through the optical plate is mainly concentrated in the vertical direction, the peak angle of the first pattern is 38 ° to 43 ° in consideration of the luminance and luminance uniformity in the vertical direction based on the above experimental results. Appearance ratio can set 0.5 or less to a preferable range. In the case of the appearance ratio, it was confirmed that the luminance characteristic is further improved in the range of 0.05 ~ 0.4.

In the optical plate according to the present invention, an ellipsoid apex pattern may be formed at a fine pitch on one surface by an extrusion process. Since the extrusion process is advantageous for mass production and the process is relatively simple, the optical plate of the present invention is very mass-producible, and in particular, the repeatability of the product is excellent and can be manufactured in high yield.

9 is an exploded perspective view showing a backlight unit including an optical plate according to the present invention. As shown, the backlight unit 1000 includes the optical plate 210, the surface light source device 300, the upper and lower cases 1100 and 1200, and the inverter 1300 according to the above-described embodiment.

The lower case 1200 includes a bottom portion 1210 and a plurality of sidewall portions 1220 extending to form an accommodation space from an edge of the bottom portion 1210 to accommodate the surface light source device 300. The surface light source device 300 is accommodated in the storage space of the lower case 1200. The inverter 1300 is disposed on the rear surface of the lower case 1200 and generates a discharge voltage for driving the surface light source device 300. The discharge voltage generated from the inverter 1300 is applied to the electrodes 360 of the surface light source device 300 through the first and second power lines 1352 and 1354, respectively. The upper case 1100 is coupled to the lower case 1200 to support the light source 300 and the optical sheet 900. The upper case 1100 prevents the light source 300 from being separated from the lower case 1200.

The optical plate 210 is spaced apart from the surface light source device 300 at a predetermined interval, and uniformly condenses the light emitted from the surface light source device. Therefore, there is an advantage that the optical characteristics of the backlight unit can be improved and the overall volume can be reduced.

In the above, it has been described with reference to preferred embodiments of the present invention, but those skilled in the art or those skilled in the art from the spirit and scope of the invention described in the claims to be described later Various modifications and variations can be made in the present invention without departing from the scope thereof.

According to the present invention, by using a single optical member it is possible to improve the light collection characteristics and transmittance of light generated in the surface light source device to improve the light efficiency of the backlight unit. In particular, it is possible to secure the product reliability by improving the luminance and luminance uniformity of the surface light source device and removing the bright lines. In addition, it is easy to manufacture the optical plate, it is possible to reduce the volume of the backlight unit can extend the application range of the backlight.

Claims (14)

A plate having a first pattern of ellipsoidal peak shape spaced apart by a first pitch on an upper surface thereof, wherein the apex angle of the first pattern is in a range of 38 ° to 43 °. doing Optical plate for surface light source. The optical plate for a surface light source according to claim 1, wherein an aspect ratio of the first pattern is 0.5 or less. The optical plate for a surface light source according to claim 1, wherein the first pitch of the first pattern is 300 µm or less. The optical plate for a surface light source according to claim 1, wherein a second pattern spaced apart from the second pitch larger than the first pitch of the first pattern is formed on the lower surface of the optical plate. The optical plate for a surface light source according to claim 4, wherein the peak angle of the second pattern is larger than the peak angle of the first pattern. The optical plate for a surface light source according to claim 5, wherein the peak angle of the second pattern is in a range of 90 ° to 150 °. The optical plate of claim 1, wherein the first plate is formed on one surface of the optical plate by an extrusion process. The optical plate for a surface light source according to claim 1, wherein a second pattern having a nonuniform pitch is formed on a lower surface of the optical plate. A surface light source including at least one discharge space and an electrode unit applying a voltage to the discharge space; A case accommodating the surface light source; An optical plate disposed between the surface light source and the case, the first pattern having an ellipsoidal peak shape spaced apart by a first pitch on an upper surface thereof, and the peak angle of the first pattern being in a range of 38 ° to 43 °; And And an inverter for applying a discharge voltage for driving the surface light source to the electrode. The backlight unit of claim 9, wherein an aspect ratio of the first pattern is 0.5 or less. The backlight unit of claim 9, wherein the first pitch of the first pattern is 300 μm or less. The backlight unit of claim 9, wherein a second pattern is formed on a lower surface of the optical plate, the second pattern being spaced apart by a second pitch larger than the first pitch of the first pattern. The surface light source of claim 9, wherein the surface light source is any one selected from a flat fluorescent lamp, a cold cathode fluorescent lamp, and a flat lamp including a plurality of light emitting diodes in which a plurality of discharge spaces are spaced apart from each other by a partition wall part. The backlight unit characterized by the above-mentioned. 10. The backlight unit according to claim 9, further comprising a light converging or diffusing optical sheet.

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