Related Art Generally, the light guide plate in backlight system includes transparent plate which accepts light rays emitted from the light source and disperse the light evenly on the surface of the display panel by changing the direction of the light rays.

Fig. 1 shows a light guide plate (2) made of acrylic resin and side- positioned light source (l). In the figure, the light source formed by COLD CATHODE FLUORESCENT LAMPS (hereinafter CCFL) is placed on a sides of light guide plate (2). On the upper surface of the plate, patterns (3) for light diffusion are formed to disperse the rays entered the plate.

In case of the patterned light guide plate, in Fig. l, made by screen printing method, the patterns (3) are printed on transparent light guide plate (2).

Once the rays reach the pattern, it is scattered or refracted (hereinafter refracted) in the patterns and paths of the ray change to normal or similar direction to the surface of the plate. As a result, the ray exits the light guide plate and enter the LCD panel (not shown) positioned above for

working as the back light.

For reference, the raw plate in this invention is referred to as plastic plate before formation of any structure for light diffusion such as the printed patterns and the light guide plate refers to the completed plate with the structure for light diffusion.

Fig. 2 shows some kind of rays with different incident angle into the plate are shown. Same numbers and symbols represent same or similar subjects as per Fig. 1.

In Fig. 2, light rays emitted from the side light source (l) proceed with various angles and some of them are refracted or reflected on the surfaces of the light guide plate (4). The rays proceeding in the light guide plate with angle greater than critical value will be totally reflected on the surface of the plate while light rays with smaller angles may exit the plate and proceed in the air toward display panel positioned above (not shown).

The light ray (6) impinging on the pattern (3) for diffusion in the plate may be refracted and as a result, the angle of the ray changes to exit the plate and exert action on the display panel. Therefore, as the number of patterns increases, the exiting rays from the light guide plate will be more.

The patterns for light diffusion is made by screen printing method in general. The method is simple as patterns are printed and glued to the raw plate. Also, it can be said to be productive and economical because large- area patterns can be easily printed on a large area raw plate which can be divided into smaller pieces. The process is not limited by the area of the light guide plate and is compatible with for mass production.

Problem arises when the patterns do not refract all rays but absorb some of rays. Generally, the patterns are made of TiO2 and its refractive index does not coincide with the refractive index of materials for the raw plate.

Additionally, it has strong characteristics for absorbing light rays as the pattern is made of TiO2 ceramic powder. Therefore, the light efficiency, changing the angle of incident ray and enabling the ray to be effective back light, will adversely decreases when the density of the patterns exceeds critical value. This is a trade-off problem of the screen-printing method.

To overcome the limitation, an alternative method for forming unevenness on the surface of the raw plate is presented.

Fig. 3 shows an embodiment of the light guide plate with the unevenness, for example, groove (7) on its surface. When light ray (8) with greater angle than critical angle, which will be inherently reflected on the surface, incident into the groove (7), it may be refracted and exit the plate due to geometrical optics caused by unevenness of the groove.

Fig. 4 shows change in light paths (9) for the ray incident on the slant side of the groove (7), in detail. The ray will change its light path due to the difference between refractive indexes of the plate and air, from the angle A to the angle B at the boundary surface.

The light guide plate with mechanical unevenness such as the grooves can deflect or change the path of the ray more efficiently than the patterned plate as there is no absorption of the ray because the plate does not have any other material involved other than the plate material itself.

Fig. 5 shows schematic diagram of producing the light guide plate by using the injection molding process. It is a prior method to producing the light guide plate with the grooves. When melted plastic material (17) such as acrylic plastic or resin is injected (18) into the cavity of mold (19) and cooled by the cooling channel (21), the groove (20) will be made on the surface of the plate.

Disadvantageous aspects of the injection molding method is that it takes a long time to produce light guide plate as it requires melting and cooling the raw material of the plate. Additionally, during the cooling process, thermal distortion may occur which harms the flatness of the plate surface and the function of the light guide plate.

To solve such problems, another method using master stamp, having multiple blade molds on the contacting surface of it, to produce the grooves on the surface of the plate is presented. It is a method of stamping grooves by pressing the master stamp on the surface of the raw plate. Fig.

6 shows process of forming the grooves by pressing master stamp. This process will be called as"Direct Surface Forming"or DSF, hereinafter.

Generally, as it is the case that the light source is placed on the side of the plate, the area close to the light source is brighter than the area apart from the source. To overcome such irregularity in brightness, it requires repositioning of light diffusion means such as the groove.

For instance, if less number of grooves or shallower grooves are positioned in close area to the source, the number or effect of the refracted

ray will be smaller as close to the source. Adversely, for the areas away from the light source, increase in density or depth of grooves will cause more rays to be refracted. Therefore, the density of light ray refracted and exit from the plate will be even on the whole area of the plate as the density or depth of the grooves controlled as mentioned above.

Fig. 7 shows an example of a light guide plate (72) with light sources (71) on both sides. As it gets closer to the center, the depth of the groove becomes deepened. Such change of density of refraction patterns or grooves according to the distance from the light source is a critical factor for designing the light guide plate.

For the stamping process, a delicate mechanical process or semiconduct process is required for producing accurate master stamp because depth or width of the groove is in micrometer dimensions. Therefore, the work to produce a master stamp is not easy, and as a result, probability of process error is high.

The master stamp is made into one piece so far. Therefore, if failure occurs when manufacturing at least one blade molds of the master stamp, whole piece of the master stamp should be discarded. This will increases cost of light guide plate production.

Also, a new master stamp production is required every time when the disposition or shape of the grooves is required to change, for various reasons. While considering the probability of failure in manufacturing the master stamp, production cost becomes more high.

So it is demanded to find a new type of master stamp or DSF mold (DSF mold hereinafter) for solve this problem of high manufacturing cost.

Summary of the invention A primary object of this invention is to provide a new structure of DSF mold for backlight system, which will decrease the manufacturing cost.

The DSF mold in this invention is made by assembling multiple blade molds to function as a master stamp. The production cost of it will decrease because the mold will be modified easily when a failure occurs in manufacturing process, due to its assembling characteristics.

Another object of this invention is to provide a new structure of DSF mold which enable to produce various types of backlight unit without changing whole piece of master stamp.

In carrying out the invention and according to aspects thereof, there is provided; A mold system for manufacturing light guide plate comprising: at least one base mold supporting multiple blade molds; a set of multiple blade molds disposed in parallel and supported by said base mold, wherein edge shape of each blade mold is sharp for forming grooves on a surface of light guide plate ; at least one assembly hole formed on sides of each blade mold; at least one assembling means that penetrate said assembly hole in series of all blade molds; and fixture means for compressing both sides of said set of blade molds to secure positions of said blade molds, positioned at each end of said assembling means. The longitudinal width of said assembly hole may be larger than diameter of said assembling means. Further, the mold system comprises at least one heating wire hole penetrating on said side of the blade mold to increase the temperature of the blade. The assembling means are curved for adjusting height of each blade mold. The mold system further comprises at least one height controlling means for controlling height of said set of

blade molds or at least one heating wire that penetrates said heating wire hole for heating the edge of the said blade mold; and an electric supply means to supply electricity to said heating wire.

The mold system further comprises at least one cooling means for cooling the edge of the said blade mold, placed in said base mold or a flat board supporting said light guide plate when said set of multiple blade molds compresses the plate.

The mold system further comprises a height supporting means, positioned in between said base mold and said set of multiple blade molds, for supporting back ends of said blade molds to prevent displacement of said blade molds. Also, said assembling means may be bolt and said fixture means may be female screw on accordance with both ends of said bolt.

Brief Description of the drawings Fig. 1 shows a light guide plate with printed patterns on its surface according to prior art.

Fig. 2 shows schematic diagram showing various paths of ray in the plate with the printed patterns.

Fig. 3 shows schematic diagram showing various paths of ray in the plate with grooves on its surface.

Fig. 4 shows schematic diagram showing path of ray impinging on the groove.

Fig. 5 shows schematic diagram showing injection molding process.

Fig. 6 shows schematic diagram showing DSF process according to prior art.

Fig. 7 shows schematic diagram showing arrangement of grooves when the light sources are positioned on both sides of the plate.

Fig. 8 shows the DSF mold in this invention.

Fig. 9 shows an embodiment of side shape of blade mold in this invention.

Fig. 10 shows schematic diagram showing the process of assembling the blade molds Fig. 11 shows an embodiment of curved assembling means used in this invention.

Fig. 12 shows an embodiment of the height supporting means used in this invention.

Fig. 13 shows front view of DSF mold in this invention.

Fig. 14 shows in-situ process when suppressing the surface of the plate by the DSF mold in this invention.

Fig. 15 shows an embodiment of the light guide plate manufactured by the DSF mold in this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Detailed embodiments are provided below in reference to the firures.

Fig. 8 shows an embodiment of a new structure of the DSF mold in this invention.

The DSF mold of this invention comprises base molds (82, 82') supporting a set of multiple blade molds (83) assembled in parallel. It is different from prior arts for the facts that the mold is not made in one piece, but a set of single blades assembled together to form the DSF mold.

In Fig. 8, base molds (82,82') can clamp a set of blade molds (83) in one.

The set of blade molds can stamp grooves on a surface of a raw plate (85) placed on a flat board (84) by lifted down and suppressing sharp edges of the blade molds on the surface.

Further, base molds (82,82') comprise a pair of'n'-shaped mold for

clamping the set of blade molds (83) and means (87) for assembling the set of blade molds. The means for assembling may be bolt or etc. , passing through holes in the blade molds to fix or secure the blade molds in designed positions.

The shape of the base molds can be other than the'n'shape as long as it can perform same function of the clamping. For examples, it is possible for a base mold to be a wall-shaped structure or one piece of structure, if it could support the assembled set of the blade molds. Further, a cooling channel (88) can be placed inside the base molds.

For the even brightness of the light mentioned above, depth of the suppression should be deeper as the distance from the light source becomes farther. In Fig. 8, the blade molds, for example, positioned in the center part protrude more than others for making light guide plate with light sources on both sides. The depths or heights (height hereinafter) of the blade molds will change gradually or stepwise.

The advantageous aspects of the DSF mold in this invention are as followed.

It is economical as there is no need to waste or discard a whole piece of mold in case when manufacturing failure occurs. Every single blade mold is manufactured separately or individually, and if the failure occurs, only the failed blade mold will be wasted instead of whole piece. Therefore, production cost for the mold is decreased.

Further, the DSF mold is freely adjustable in blade molds'height and width because it is assembly. This is further explained in the following Fig. 9 and Fig. 10 show shape of single blade mold and its assembling

process, respectively. The shape is only for example and it is obvious to a skilled person in the area that various forms or shapes are possible.

In Fig. 9, the blade mold comprises assembly hole (91) for fixing on the base molds and heating wire hole (92) for heating wire. As shown in Fig.

10, bar-type assembling means, e. g. bolt (110) penetrates through each assembly hole (91) in series and connect and fix the whole set of blade molds after fixed by fixture means, e. g. nuts or female screws (120) at one end or both ends of it. Alternatively, the bolt may connect whole blade molds in a set and attach the set of blade molds to the base molds simultaneously with the fixture means.

The assembling bolt does not necessarily attach the whole set of blade molds to the base mold, but only assembles the blade molds in series.

Other means for attaching may be used to secure the set of blade molds on to the base molds. For example, horizontal compression force exerted inwardly by compressing both base molds can be used to secure the set of blade molds. In this case, means for compressing the base molds, for example, clamping bar positioned on external surfaces of both base molds may be used. A skilled person in this area who understands this invention can easily think of various means.

For the assembling bolt, one end of it may be in form of rivet and the other end is male screw, alternatively. Also, more than one assembling bolt may be used for assembling blade molds.

The number, shape and positions of the heating wire holes (92) may be varied when necessary.

The shape of the assembly hole (91) may be an oval wherein its longitudinal width is greater than the diameter of the assembling means for adjusting height of each blade mold.

The DSF mold in this invention can be used in manufacturing various type of light guide plate mentioned above by adjusting the height of each blade mold. When light sources are placed on both sides of a light guide plate, the center part of the blade molds should protrude more than others. In other case, for example, when one side light source is used, the blade molds should protrude gradually as the distance from the light source becomes larger. In these cases, assembling bolt shall penetrate lower part or upper part of assembly hole to control heights of the blade molds.

For comparison, the prior DSF mold can't be used for various type plate because it is only one piece mold and the height of the blades is not adjustable after completing the mold.

The assembly hole does not have to be an oval shape, as long as longitudinal width of the assembly hole is larger than the diameter of the assembling bolt for adjusting the height of the blade mold vertically. For example, its shape can be in a form of rectangle.

Another embodiment to control the height of the blade molds is to use bended assembling bolt. Fig. 11 shows an example case of such structure.

An assembling bolt (119) is curved so that end line shape of the blade molds is concave. For this case, the diameter of the assembly hole corresponds to fit to the diameter of the assembling bolt.

Fig. 12 illustrates an embodiment of another method to adjust and support the height of blade molds. In Fig. 12, a rigid height supporting means (118) is placed in between blade molds and base molds to support back ends of blade molds. This rigid height supporting means is designed to have a gradient or steps. The role of the supporting means is to accurately support and fix delicate height difference of the blade molds. Also, this prevents recessions of the blade molds from intended height when the blade molds suppress the plate. Further, this rigid height supporting means can be used as means of height adjuster at the time of assembling and means for securing blade mold to base mold. For a skilled person in this area may use this height supporter means with the curved assembling bolt.

Lengths and widths of each blade molds depend on optical design of the plate, and its size varies from a few micrometers to a couple of hundred micrometers. The blade mold is produced by various methods such as mechanical forming or arc forming process.

Reasons for inserting (a) heating wire (s) are briefed in the following. The light guide plate is made of acrylic resin or plastics such as PMMA, and this material becomes softened when heated to the temperature of 50°C ~ 500 *C. To stamp the grooves on the raw plate without any distortion or crack, it is required for the raw plate to be heated to this temperature range.

However, when a whole raw plate is heated and cooled, the surface of the plate may deform with irregularity. Therefore, only the blade molds should rather be heated instantaneously at the time of stamping or suppressing onto the plate, instead of heating the plate itself. The heating wire is used for increasing the temperature of the blade. Heating wire may

be electric heating wire and it accompanies modules for electricity.

To prevent thermal deformation of the plate, another means for fixing and holding the plate, e. g. by vacuum force, can be used. In Fig. 13, a view of DSF mold assembled in direct surface forming equipment is shown. The raw plate (85) is on flat board (84) and stamping mold (DSF) is directly fixed to the supporting body (112) by connecting means (111). Stroke control means (113) is used for lifting up or down the DSF mold. Also, heating wire is connected to temperature controller (not shown in the figure) through the blade molds.

The temperature of the blade molds increases to 50 °C~ 500 °C by the heating wire and the raw plate will be pressed by the DSF mold to form the grooves. The cooling channel (88) is built internally to the base molds and cooling water supplier means (not shown) may be connected. As mentioned above, to prevent deformation of the plate in the process, vacuum holes (not shown) may be formed on the flat board (84) which securely fixes the plate and prevents the thermal deformation by pulling down the plate by vacuum force.

Fig. 14 shows the in-situ process of shaping the grooves (86) on the plate at the time of lowering the DSF mold. After grooves are formed, the surface of the plate should be solidified quickly so as not the grooves to be deformed when the mold is lifting up. The cooling channel (88) in the base molds are used to cool the blade molds and the surface of the plate.

When the mold is displaced and lifted up, the light guide plate having grooves on its surface is produced as shown in Fig. 15.

It is possible in this invention to adjust space between each blade mold in the DSF mold structure for controlling the density of the grooves. Simple examples of such embodiment are to modulate the thickness of each blade mold or place dummy spacers in between the blades when assembling.

The edge shape of the blade mold can be any form including plain edge.

For example, triangle shape, isosceles triangle shape or scalene triangle shape can be used. Also, continuous or discontinuous saw tooth shape can be used as the edge shape. The forms or shapes are dependent on the optical design of the light guide plate.

Industrial Applicability As mentioned above, DSF mold of this invention has following advantages; At first, it is an assembly of each blade molds manufactured individually.

Therefore, in case of occurrence of any error or failure in manufacturing processing, waste is limited to that single blade mold only, not the whole body or piece of the DSF mold.

Also, it is possible to adjust or control precise heights of and space in between the blade molds as they are assembled mechanically.

By using this invention, it is rather easy and economical to produce wide area light guide plate with high precision. Hence productiveness of the light guide plate will be increased. Additionally, in case of new designing of the light guide plate due to various factors that many arise in actual processing, only rearrangement of the blade is required. Hence, feedback is quick and easy while manufacturing cost is lessened.

It should be apparent to those skilled in the art that the present invention may be embodied in many other specific : forms without departing from the spirit or scope of the invention. Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.