KR100394351B1 - Method for making backlit lightguide for display system and display system thereof - Google Patents

Abstract

The present invention relates to a light guide plate manufacturing method and a backlight device including the light guide plate manufactured by the manufacturing method.

The backlight device according to the present invention has a structure in which a groove is formed in the hole of the light guide plate as a path conversion part for changing the path of the light, and serves as a backlight device while the path of the light is changed by a plurality of grooves arranged on the surface of the light guide plate. Pressurized Surface Forming method of forming a fine groove on the surface of the light guide plate, and when a pressure is applied to the acrylic resin, a groove is formed on the surface and a specific shape is engraved. In particular, hot rolling of the acrylic resin By using the oxidizing property, the pressurized disc having a prefabricated protrusion is heated above a certain temperature to apply pressure to the surface of the light guide plate made of organic material such as acrylic resin, and the protrusion of the disc is pressed while softening or melting the surface of the light guide plate disc. The protrusion of the disc can dig into the groove by digging into the surface of the light guide plate. The. Therefore, the material loss is less than the structure of the conventional manufacturing method, there is an advantage that the light transmission efficiency can be increased and the manufacturing method is simple.

Description

Method for manufacturing light guide plate and backlight device using the same {METHOD FOR MAKING BACKLIT LIGHTGUIDE FOR DISPLAY SYSTEM AND DISPLAY SYSTEM THEREOF}

The present invention relates to a method for manufacturing a light guide plate and a backlight device using the same. Specifically, the method includes a light guide plate manufacturing method and a light guide plate manufactured by the manufacturing method among components of a backlight device used for a display requiring a back light source such as a liquid crystal display. It relates to a backlight device.

The role of the light guide plate is to keep the light propagating direction from the side light source to the end of the light guide plate, and part of it to spread out of the surface of the light guide plate while the light is in progress.

Conventionally, a method of manufacturing a light guide plate which is most commonly used is to print the diffusion ink on the surface of the light guide plate so that the light diffuses when the light reaches the diffusion ink and is dispersed to the outside of the light guide plate.

1 is a schematic diagram of a surface light source device using a conventional side light source 1 and a light guide plate 2.

As shown in FIG. 1, the light source 1 mainly composed of fluorescent lamps is located on the side of the light guide plate, and the light guide plate 2 is made of a transparent organic polymer material, but has a diffusion pattern part 3 arranged therein for dispersing light. . In the case of a light guide plate using a printing method, which is a method commonly used in the related art, the diffusion pattern portion 3 is printed on the transparent light guide plate so that light reaching the portion is diffused to come out.

The light guide plate disc described in the present invention refers to an organic polymer plate in a transparent state before the diffusion structure for light path conversion is generated, and the light guide plate refers to a light diffusion plate formed on the transparent plate.

In the case of manufacturing the light guide plate 2 by the printing method, the diffusion pattern portion 3 is printed and bonded to the light guide plate original plate prepared in advance, so that the light is diffused.

The advantage of manufacturing the light guide plate in advance is that it is possible to manufacture the light guide plate inexpensively because it can be manufactured in large quantities.

The light guide plate original plate is mainly made of acrylic resin, and the light guide plate original plate has good productivity because the original plate is made into a large area and then cut into the required area.

In addition, when the diffusion structure is formed by the screen printing method, since the productivity is good, it is suitable for the case of mass production.

2 is a partial cross-sectional view of FIG. 1.

As can be seen in FIG. 2, the light 4 emitted from the side light source 1 is reflected by the total reflection effect of the light below a certain angle inward from the surface of the light guide plate 2.

Therefore, light below the total reflection angle continues and continues to the end of the light guide plate.

However, when the light reaches the surface on which the diffusion pattern part 3 shown in FIG. 3 is printed, the light is diffused and the light is scattered out of the light guide plate (5).

Therefore, if the diffusion pattern portion is properly arranged, the part of the light propagates to the end of the light guide plate, and the part of the light is scattered at the portion where the diffusion pattern part is printed so that the angle of the light changes, and the light beyond the total reflection angle pops out of the light guide plate. .

The method of manufacturing a light guide plate for a surface light source device according to the above method has an advantage of easily manufacturing a light guide plate by using a screen printing method.

However, the printed diffusion pattern part has a disadvantage in that light utilization efficiency is lowered by absorbing a portion without fully reflecting light.

In general, titanium oxide (TiO 2) is used as a scattering material, but since the refractive index does not exactly match that of the light guide plate material, it is a ceramic powder.

As a method different from screen printing, there is a method of manufacturing a light guide plate in which a desired pattern is formed in advance using a mold.

This method takes advantage of the property that acrylic materials become liquid at elevated temperatures, become fluid, inject into molds, and harden when temperatures are reduced.

At this time, the light guide plate has a pattern formed on the mold in advance.

As an example, the structure of the light guide plate in which the recessed acicular groove | channel was formed in the surface is shown as an example in FIG. As shown in this structure, a part of the light emitted from the side light source 1 is reflected by total reflection on the flat surface of the light guide plate 2 and continues through the light guide plate (4). However, the light striking the needle-shaped groove 6 is projected by the difference in the refractive index between the air and the light guide plate and protrudes out of the light guide plate (7).

FIG. 5 shows the conversion of the path 7 of light when light is incident on an inclined portion that is an inclined surface of the needle-shaped groove 6. The path conversion of the light is changed by the ratio of each A and each B due to the difference in the refractive indices of both sides with the boundary surface interposed with respect to the perpendicular line 8 with respect to the inclined surface.

6 shows a method of manufacturing a light guide plate by injection molding using a mold.

The heater 16 is mounted on the mold 15. When the temperature of the heater is raised by raising the temperature of the heater, when the temperature is raised in advance, pressure is applied to the acrylic resin 17 having fluidity, such as a liquid, in the mold ( 19). In the case of this drawing, there is a case where the needle-like protrusions 20 are present in the mold disc.

After that, when the temperature of the mold is lowered, the acrylic hardens again to give a transparent solid state.

Subsequently, when the mold 15 is separated as shown in FIG. 7, the light guide plate 2 having the needle-shaped groove 6 on the surface thereof is obtained.

In the above structure, when the grooves 6 on the surface of the light guide plate 2 are arranged as a function of the distance from the side light source 1, the light in the light guide plate is uniformly dispersed to serve as a surface light source.

The method of converting the optical path by forming grooves or protrusions on the surface of the light guide plate by using the mold according to the above method has good light efficiency because there is no absorption of light on the surface of the light guide plate.

Therefore, compared with the printing method described above, using the same light source increases the light efficiency of the light guide plate made by the mold method.

However, the method using a mold uses a method of making a light guide plate by making a polymer organic material such as acrylic, which is a raw material of the light guide plate, raising the temperature to a liquid state, injecting it into a mold, and lowering the temperature to solidify it, and then separating the mold to make a light guide plate. It takes a long time to make.

Therefore, there is a disadvantage that the productivity falls.

In the conventional method of making a light guide plate, a screen printing method is used to prepare a light guide plate in advance and to print a diffusion pattern thereon, whereby the manufacturing cost of the light guide plate is low and high in productivity. As light absorption takes place, light efficiency is lowered.

In addition, the method using a mold has good light efficiency, but has a long production time, and thus productivity is low.

In the present invention, to solve the above-mentioned problems, by using a light guide plate made of a pre-prepared light guide plate to lower the manufacturing cost and to improve the light efficiency by making a grooved structure on the surface of the light guide plate.

In addition, to increase the productivity by using a pressure molding method using the surface pressure molding method.

1 is a structural diagram of a light guide plate according to the prior art

2 is a conceptual diagram showing a traveling direction of light by total reflection of a light guide plate;

3 is a conceptual diagram showing a diffusion direction of light reaching the diffusion pattern portion;

4 is a conceptual diagram illustrating an optical path of a light guide plate having grooves formed therein;

Fig. 5 is a detailed view showing the path conversion of light reaching the inclined portion of the groove;

6 is an explanatory diagram showing a method of manufacturing a light guide plate by a conventional injection molding method;

7 is a light guide plate completed by a conventional injection molding method

8 is a configuration diagram for a light guide plate manufacturing method according to the present invention;

9 is a light guide plate manufacturing method by the pressing method according to the invention

10 is a detailed view of the needle pattern formation

11 is a top plate separation after hot pressing

12 is an embodiment with a right angle cross-sectional structure

13 shows an embodiment having a rectangular structure.

14 is an embodiment having a circular structure

15 is an embodiment having a structure of lines

16 is a structure of a fine diffusion pattern on the surface of a projecting portion of the pressing disc;

17 is a structural diagram in which the inclination of the surface of the protrusion of the pressing disc is an angle within 90 degrees;

18 is a structural diagram in which the pressing disc proceeds obliquely

19 is an exploded view of the pressurized disc with the protrusion inclined;

20 is a light progression in the groove inclined plane having an angle within 90 degrees

Fig. 21 is a view of optical path conversion of groove slopes and protruding hill slopes;

22 is a process diagram in which a gentle curved slope is formed

Figure 23 is a structural diagram formed with a gentle curved slope

24 is a view showing the optical path conversion due to the smooth curved slope

25 is a schematic diagram of a backlight device

Fig. 26 is a structural diagram of light guide plate having different groove inclination;

27 is a structural view of a light guide plate having different inclinations of grooves;

Fig. 28 is a structural view of light guide plate having different groove depths;

<Description of the symbols for the main parts of the drawings>

31: pressurized disc with heater and needle projection

35: light guide plate disc made of organic materials

37: projection formed by the needle-shaped projection portion of the light guide plate protruded

41: needle groove formed in the light guide plate

Method of manufacturing a light guide plate of the present invention for achieving the above object comprises the steps of providing a light guide plate made of an organic material having a thermal softening property; Providing a pressurizing disc having a protrusion on a first surface to stamp a groove to be formed in the light guide plate disc; Disposing the first surface of the pressing disc and the light guide plate surface to face each other; Heating the protrusion of the pressurizing disc; Accessing the pressing disc to the surface of the light guide plate to form the groove on the surface of the light guide plate by pressing the protrusion of the pressing plate onto the surface of the light guide plate; And separating the pressurized disc from the light guide plate disc, wherein the two portions of the pressurized plate do not come into contact with the original surface of the light guide plate when the protrusion of the pressurized disc squeezes the surface of the light guide plate to the maximum. The light guide plate material pushed out to the periphery of the groove by the protrusion to generate a protruding hill shape surrounding the periphery of the groove. The pattern using the softness property and the thermoplastic property of the acrylic counter A method of making a light guide plate for a surface light source by applying a pressure to the disc to the light guide plate while raising the temperature of the metal plate formed with a protrusion on the light guide plate without the plate.

In general, the ductility of plastics is lower than that of metals, so it is easy to dig under pressure with a pointed metal. Thermosoftening is softening when the temperature is raised.

In particular, polymer plastic materials such as acrylic have properties such as liquidity when the temperature rises.

In general, the pressure molding method using surface pressure molding is to press a pressure plate made mainly of metal while applying pressure to a plate made of organic material or other material, and the pattern engraved on the pressure plate is made of organic material or other material. It is a method to be molded in.

The present invention relates to a method for making a light guide plate using the above conventional pressing technology and the properties of soft organic materials, in particular thermosoft organic materials.

Among the materials used in the light guide plate, acrylic materials such as PMMA, which are most commonly used, have thermosoftening properties.

The thermosoftening property is a property in which a polymer material, such as an acrylic material, has a low viscosity in a solid phase and fluidity occurs as the temperature increases.

At this time, when the thermal softening point or more, the acrylic material is easily flowed or pushed under pressure.

Typically, the temperature at which the thermal softening point is formed is between 50 and 500 degrees Celsius.

The temperature of the pressurized disc for forming the pattern on the light guide plate is between 50 degrees Celsius and 500 degrees Celsius, depending on the characteristics of the thermosoft organic material, and the temperature is higher than 500 degrees Celsius when the pressurized plate is rapidly bonded and separated by the instant melting method. Production is possible even if it becomes.

In particular, since the plastic softens even at a temperature below the thermal softening point, surface forming is easy.

After FIG. 8, the light guide plate manufacturing method by this process is shown.

8 shows a pressing 31 disc engraved with a needle-like protrusion 33 shape. Pressurized disc refers to a disc that forms a projection pattern on the surface of the light guide plate while applying pressure.

In FIG. 8, as an example, a metal plate having a plurality of needle-like protrusions engraved on the surface of the pressure disc is used, and various patterns are possible in an actual design. The production of the pressurized disc may be performed by a conventionally used method of manufacturing a machine, or may be previously engraved in a wax plate or the like, and then may be made by nickel metal plating or the like, or may be manufactured by stamping by photolithography. The protrusion of the pressurizing disc has a needle-like or semi-oval or quadrangular vertical cross-sectional structure, which can be used by changing various shapes as necessary.

In the present invention, the heater 32 is mounted on the pressure disc 31 so that the temperature can be increased.

FIG. 9 relates to a method of manufacturing a light guide plate by the press molding method according to the present invention, and shows a step of aligning the pressurized disc 31 and the light guide plate 35 which have been heated, and then applying pressure thereto (36).

In order to facilitate the separation of the light guide plate and the pressurized plate during the adhesion process, a release agent may be sprayed onto the pressurized disc and coated. When the needle part 33 of the pressurized disc 31 and the light guide plate disc 35 which have risen in temperature during the adhesion process are brought into contact with the light guide plate high temperature, the part in contact with the light guide plate disc temporarily has liquid flowability or softened state. do.

In FIG. 9, the needle protrusion is pressed into the surface of the light guide plate by a desired depth.

At this time, the depth traveled by the pressure disc 31 should be such that the surface where the protrusion of the pressure disc is not formed, that is, the flat surface of the pressure disc and the original surface of the light guide plate do not contact. That is, when the discs are spaced apart at regular intervals 38 so that the needle-shaped protrusions of the pressurizing disk proceed to the inside of the light guide plate, and when the molten acrylic is pushed out, the protruding portion 37 is not pressed by the pressurizing disk. Do it. The reason for doing this is to maintain the surface smoothness of the part where total reflection of the light guide plate should occur. If the flat surface of the light guide plate is contacted by the pressurizing plate, the part 37 to be protruded is pressed and a non-uniform point is formed on the surface. This is because the surface smoothness of the light guide plate is lowered overall.

10 illustrates the shape of the protrusion structure of the light guide plate on which the needle pattern according to the present invention is formed. When the needle-shaped protrusion 33 of the pressure disc 31 softens or melts while guiding the light guide plate 35, the portion pushed out while the needle-shaped groove is formed on the light guide plate has a hill-shaped protrusion 37 on the light guide plate. Form.

11 shows a process of separating the pressurized disc from the light guide plate after the above process. At this time, after the temperature of the pressurizing disk is lowered in the contact state, the pressurizing disk may be separated. However, since the pressurizing disk is separated from the heat source, the part contacted with the pressurizing disk of the light guide plate is naturally solidified as the temperature decreases. 41) is formed. The portion pushed out of the groove forms the light guide plate protruding hill portion 37 around the groove.

The traveling direction of the optical path is basically the same as the traveling direction of the light shown in Figs. 4 and 5, but more protruding hills 37 are formed in addition to the grooves 41 so that more paths of light can be converted.

In the above process, the portion forming the needle-shaped protrusion in the pressurizing disc may be formed as an example of the needle, but if the same principle can be realized, other structures such as square or curved surface may be used instead of the needle.

12 shows a structure in which a square groove is formed. When the incident light 53 meets the surface of the square groove 51, the traveling angle is bent and the outside of the light guide plate 54 (54). The protruding hill portion 52 pushed out around the square groove also performs a similar function.

Usually, the diameter of the protruding hill portion formed in the light guide plate may be from 1 micrometer to 3 mm in diameter and from 1 micrometer to 3 mm in depth.

Not only the light guide plate depth direction, but also the shape engraved on the surface can be produced in various ways.

FIG. 13 shows an example in which the shape engraved on the surface of the light guide plate 55 is patterned in a square 56 structure when viewed from above.

FIG. 14 shows another example in which the shape engraved on the surface of the light guide plate 55 is patterned in the structure of the circle 57 when viewed from above.

FIG. 15 shows a case where the shape engraved on the surface of the light guide plate 55 is patterned into a long line structure 58 when viewed from above as another example.

Another embodiment for making a light guide plate is directed to a method of making a fine diffusion pattern on a surface. In this case, the refraction and interference effects of light are used to induce light diffusion by engraving a pattern having a size of 0.05 micrometers to several hundred micrometers. Among these diffusion patterns, there are a hologram diffusion pattern, an interference pattern, and the like, an example of which is shown in FIG. 16. The pressurizing disc 61 has a projection 62, and on the surface of the projection there is a fine diffusion pattern 63 made of a holographic diffusion pattern or the like. The cross section of the fine diffusion pattern has a regular or irregular concave-convex structure, and the height of the concave-convex surface is usually within 100 micrometers. When the protrusions of the pressurizing disc are raised as described above and compressed onto the surface of the light guide plate, a fine diffusion pattern engraved on the surface of the protrusion of the pressurized disc is molded on the surface of the light guide plate. At this time, only the fine diffusion pattern of the surface of the protrusion is molded without the protrusion of the pressing disc deeply.

17 shows that the inclined surface 72 of the projection of the pressing disc 71 is perpendicular to the flat surface of the pressing disc. In other words, the angle is smaller than 90 degrees. Further, in order to engrave this pattern on the light guide plate disc 74, the pressure disc is moved 73 in an oblique direction to press the light guide plate disc.

FIG. 18 shows a case where the projection of the pressing disc 81 is inserted 82 at an angle to the light guide plate 83.

19 illustrates a case in which the inclined pattern is formed on the surface of the light guide plate 93 by removing the pressing disc 91 at an angle.

FIG. 20 illustrates a case where an angle formed by the inclined portion 102 of the pattern formed as described above with the surface of the light guide plate 101 is an acute angle. Since the angle formed between the incident light and the inclined portion 102 becomes an angle at which total reflection occurs more easily, the final direction 104 of the light is further upward. With this structure, more light is emitted to the front of the light guide plate as a whole.

Since the structure of the present patent increases the scattering of light compared to the prior art, it is possible to manufacture a system having a more uniform light distribution as a whole.

FIG. 21 is a diagram showing various optical path conversions as a light path conversion diagram between a groove slope and a protrusion slope of the light guide plate of the present invention. Since the protruding slope is generated by the thermal flow of the polymer, it is generally easy to be curved. Therefore, as shown in FIG. 21, the light 114 incident on the protruding hill slope 111 and the light 113 incident on the inclined surface of the groove 112 have different angles 115 by the angle difference between the protruding hill slope and the groove slope. 116), it is possible to increase the light diffusion as a whole.

FIG. 22 is a view illustrating another shape that may be formed in the process of manufacturing a light guide plate according to the present invention. FIG. This is a case in which the protrusions of the pressurizing disk engrave the grooves of the light guide plate, and thus the parts pushed out from the grooves are closely adjacent to each other to eventually swell like a plateau. This case is generated when the gap between the groove and the groove is small or the temperature is gradually raised.

As shown in FIG. 23, the portion pushed out of the groove 123 of the light guide plate causes the height of the light guide plate to be pushed up higher than the original height 124 (125) to form a surface 126 higher than the original height of the light guide plate original. The peripheral portion where the protrusion of the pressing disc is not in contact forms a gentle curved slope 127 having a slope different from that of the groove slope. These smooth curved slopes are produced by the thermal flow phenomenon of the polymer.

As shown in FIG. 24, the light 133 incident on the groove inclined surface 131 and the light 134 incident on the curved inclined surface 132 proceed to different light paths 136 and 137, respectively, to efficiently diffuse light. It is possible.

In conclusion, in the present invention, the light guide plate surface grooves are formed in a state in which the pressure disc and the surface of the light guide plate are not completely contacted and spaced apart by a predetermined interval, thereby maintaining lightness around the groove and simultaneously forming a protruding hill or curved slope 127. It can cause a double positive effect to spread more efficiently.

25 to 28 are embodiments illustrating a backlight device employing a light guide plate manufactured by the light guide plate manufacturing method of the present invention in order to have uniform brightness and high light intensity on the upper surface of the light guide plate.

FIG. 25 illustrates a light source 143 provided on at least one of four sides of the transparent light guide plate 142, a reflector 144 surrounding one side of the light source and reflecting light from the light source to the light guide plate, and formed on an upper surface of the transparent light guide plate. Embodiment showing a backlight device including a diffusion pattern composed of a groove 150 having a periphery projecting 149, a mirror reflective layer 145 disposed on a rear surface of the transparent light guide plate, and a light diffusing layer 146 positioned above the diffusion pattern. to be. The spacing of the grooves has a diffusion pattern having a higher density 148 of the portion farther from the light source than the portion 147 close to the light source for uniform luminance.

Another embodiment proposed by the present invention for uniform brightness is shown in FIG. 26. That is, the closer the inclination of the groove of the light guide plate 151 is to the light source, the larger the method. In this case, the slope of the light source side groove 152 is inclined more rapidly than the groove 153 far away from the light source, so that the farther away the light source is, the longer the diagonal line is, the more the diffusion structure receives more light.

Another embodiment of the groove shape formed in the light guide plate proposed in the present invention is shown in FIG. 27. In one groove formed in the light guide plate 161, the inclination of the inclined surface 163 opposite to the light source is smaller than the inclined surface 162 of the light source so that light scattered from the inclined surface 162 of the light source does not reach the inclined surface 163 opposite to the light source. will be..

Another embodiment is the same as FIG. 28. The depth of the groove constituting the diffusion pattern of the light guide plate 171 increases so as to move away from the light source (172, 173, 174) so that the area receiving light increases as it moves away from the light source.

So far, the shape of the groove of the light guide plate has been exemplified by needles, but arbitrary shapes such as circular columns, elliptical columns, and square columns may be manufactured as necessary.

As described above, the light guide plate manufacturing method by the pressure molding method according to the present invention has the following effects.

First, it is possible to purchase the light guide plate relatively cheaply by using the light guide plate produced in large quantities.

Second, by forming a diffusion structure using a pressing method to shorten the formation time of the diffusion plate to facilitate productivity improvement.

Third, by increasing the temperature of the pressure plate to reduce the wear of the pressure plate to increase the service life of the pressure plate.

Fourth, because the light guide plate is formed by instantaneous melting or softening, a relatively smooth surface can be obtained.

Fifth, the projecting portion of the light guide plate is formed into a portion which is pushed in by the pressure disk and melted and protruded outwardly protruding hill portions, so that light scattering occurs at various angles to increase the diffusion angle of the light of the surface light source.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (14)

In the method of manufacturing a light guide plate of the surface light source device used as a back light source, Providing a light guide plate disc made of an organic material having thermal softening properties; Providing a pressurizing disc having a protrusion on a first surface to stamp a groove to be formed in the light guide plate disc; Disposing the first surface of the pressing disc and the light guide plate surface to face each other; Heating the protrusion of the pressurizing disc; Accessing the pressing disc to the surface of the light guide plate to form the groove on the surface of the light guide plate by pressing the protrusion of the pressing plate onto the surface of the light guide plate; Separating the pressure disc from the light guide plate; As containing, The light guide plate material pushed out around the groove by the protrusion by spacing the two plates so that the periphery of the protrusion of the pressure disc is not in contact with the original surface of the light guide plate when the protrusion of the pressing disc squeezes the surface of the light guide plate to the maximum. The light guide plate manufacturing method, characterized in that for generating a protruding hill shape surrounding the groove. The method of claim 1, wherein the heating of the protrusion of the pressing disc comprises using a heater mounted inside the pressing disc. The method of claim 1, wherein the temperature of the protrusion is maintained between 50 ° C. and 500 ° C. when the protrusion of the pressing disc presses the surface of the light guide plate. The method of claim 1, wherein the vertical cross-sectional structure of the protrusion of the pressing disc is one of needle, semi-ellipse, and quadrangles. The method of claim 1, wherein the surface of the protruding portion of the pressing disc further includes a fine diffusion pattern, so that only the fine diffusion pattern is molded in the molding of the light guide plate. According to claim 1, wherein the projecting portion of the pressing disc is projected obliquely inclined at a predetermined angle to the surface of the pressing disc, and in the step of forming on the light guide plate disc, characterized in that the pressing of the light guide plate obliquely at this predetermined angle. Light guide plate production method. A transparent light guide plate having a diffusion pattern formed with a groove on an upper surface thereof, a light source disposed on at least one side of four sides of the transparent light guide plate, a mirror reflective layer provided on a rear surface of the transparent light guide plate, and a light diffusion layer disposed above the diffusion pattern. The backlight device of claim 1, wherein the groove further includes a protruding hill shape at an edge thereof. A transparent light guide plate having a diffusion pattern formed with a groove on an upper surface thereof, a light source disposed on at least one of four side surfaces of the transparent light guide plate, a mirror reflective layer provided on a rear surface of the transparent light guide plate, and a light diffusion layer provided on the diffusion pattern. 2. The backlight device of claim 1, further comprising a gentle curved slope between the groove and the groove. 9. The backlight device according to any one of claims 7 to 8, wherein the groove increases as its density moves away from the light source. 9. The backlight device according to any one of claims 7 to 8, wherein the groove becomes smoother as the side slope becomes farther from the light source. The backlight device according to any one of claims 7 to 8, wherein both of the inclined surfaces of the grooves are inclined opposite to the light source so that the inclined surfaces are gentler than the inclined surface of the light source side. 9. The backlight device according to any one of claims 7 to 8, wherein the groove increases as its depth moves away from the light source. The backlight device according to any one of claims 7 and 8, wherein the groove is any one of a needle, a cylinder, an elliptic cylinder, and a square cylinder. The backlight device according to any one of claims 7 to 8, wherein the groove further includes a concave-convex fine diffusion pattern at a lowermost end thereof.