TECHNICAL FIELD The present invention relates to a press roller apparatus for an equipment of cutting a brittle material, and more particularly to a press roller apparatus for an equipment of cutting a brittle material suitable for improving a cut quality of a brittle material as well as capable of reducing a re-tooling time and costs of manufacturing and maintenance of the roller, by making only a part of the roller directly contacting the brittle material be exchangeable.

BACKGROUND ART Brittleness is a property that an object is broken without a permanent strain or shows an extremely partial permanent strain when applying a force to the object beyond an elastic limit. Atypical material having such brittleness includes, for example, a glass, a ceramic, a LCD glass, a PDP glass and a semiconductor wafer. There is a prior method for cutting the brittle material that a micro crack line is formed on a surface of the brittle material along a line to be cut by a scribing work and a cleaving (cutting) is made by applying a bending or impulsive force in a widening direction of the crack line. Like this, a typical method of cutting the brittle material by applying the bending or impulsive force is shown in Fig. 16. The cutting method shown in Fig. 16 is one using a braking bar 10. According to this method, a micro crack line 22 is firstly formed on a surface of a brittle material 20 such as a LCD glass by a scribing process. The brittle material 20 is turned over so that the crack line 22 faces downward, and then the cutting process is made by bring the braking bar 10 down at a surface opposed to the crack line 22. However, since the brittle material 20 should be turned over with the crack line 22 being formed, it is difficult to cut a large brittle material. For example, a size of 5th LCD glass is very large such as a 1,100 x 1,250 mm (width x length). Moreover, a size of 6th LCD glass is much larger such as a 1,800 x 2,100 mm. In order to turn over of a brittle material having such a large size, it is necessary to provide a turnover apparatus having a size well-fitting to the brittle material and a much wider rotating space should be also secured. Further, when a turnover of the brittle material having the micro crack line 22 formed is made, there is a danger of fracturing the brittle material due to an advance of the micro crack line 22 during the turnover. In addition, as the size of the brittle material becomes larger, a length of the micro crack line 22 as well as a length of the braking bar 10 is also larger. Accordingly, it is difficult to secure a straightness accuracy of an edge of the braking bar 10 and to obtain a high-quality cut surface. There is an exemplary method for improving the drawbacks of the prior apparatus for cutting the brittle material, which uses a press roller developed by the applicant and inventors. This is particularly suited to cut a brittle material having a large size. Such a cutting method is shown in Figs. 11 to 15. Fig. 11 is a schematic view illustrating a structure of an apparatus for cutting a brittle material using a press roller. As shown in Fig. 11 , a brittle material 20 is fixed on upper surfaces of vacuum chucks 31, 32. The vacuum chucks 31, 32 are fixed on upper surfaces of moving plates 41, 42. The moving plates 41, 42 are mounted to driving devices 51, 52 for driving the moving plates. The driving devices 51, 52 move the moving plates 41, 42 in directions of right and left. A press roller 60 is located oppositely to the surfaces on which a micro crack line 22 of the brittle material 20 is formed. With the apparatus having the above structure, it is possible to perform a cutting process in a manner as shown in Figs. 12 to 15, according to a position and the number of the press roller 60. In Fig. 12, the brittle material 20 is located on the vacuum chucks 31, 32 so that the crack line 22 faces downward, and fixed with a vacuum force generated by the vacuum chucks 31, 32. Subsequently, the moving plates 41, 42 and the vacuum chucks 31, 32 are moved outward by the driving devices 51, 52 and the brittle material 20 is maintained with both sides thereof being tensioned outward on the basis of the crack line 22. Then, when the press roller 60 is lowered to press the surface of the brittle material 20 opposed to the crack line 22 and at the same time moved along the crack line 22 at a constant velocity, the brittle material 20 is cut along the crack line 22 due to a notch effect of the crack line 22. Meanwhile, Fig. 13 shows that the crack line 22 is formed on an upper surface of the brittle material 20 and the press roller 60 is forced upward and moved at a constant velocity at the same time for the purpose of cutting the brittle material 20. Fig. 14 shows that the brittle material 20 is cut by a pair of press rollers 61, 62 which are opposed to each other. Fig. 15 illustrates that two pairs of press rollers 63,64 and 65,66 are arranged at an interval above and below a brittle material 21 consisting of two plates and sequentially moved to cut the brittle material 21. The methods of cutting a brittle material using a press roller as described above have advantages over the prior art. That is, it solves the problem of turning over the brittle material so that the micro crack line always faces a predetermined direction. In addition, it is possible to minimize the apparatus and to perform an accurate cutting at a high speed. However, there are disadvantages that it is difficult to manufacture a press roller and a manufacturing cost is high. As the press roller, Teflon®, Duracon®, polyurethane and rigid rubber are shaped and used to a roller form. However, since the press roller should be made in a one body, it is difficult to perform a precise processing (forming) and thus a manufacturing cost is high. In addition, when the press roller is repeatedly used, the roller is worn away and glass powders or various particles occurred during cutting the brittle material are sometimes adhered to the surface of the press roller. In these cases, a cut quality is deteriorated and a certain damage is induced to the surface of the brittle material due to the glass powders or particles adhered to the press roller. Accordingly, the press roller should be periodically re-tooled with a new product. However, since the high price press roller is entirely re-tooled, it takes much cost and time. Additionally, the entire press roller should be re-tooled and at this time there is a large deviation between the products due to a difficulty of an accurate processing, as described above. Accordingly, since a center of a new press roller and the crack line are deviated when re-tooling with the new product, the new press roller and the crack line should be re-arranged and thus it takes much time.

DISCLOSURE OF THE INVENTION TECHNICAL PROBLEM The present invention has been made to solve the above-mentioned problems occurring in the prior art. The object of the present invention is to provide a press roller apparatus for an equipment of cutting a brittle material capable of reducing a re¬ tooling time and costs of manufacturing and maintenance of the press roller and improving a cut quality, by making only a part of the roller directly contacting the brittle material be exchangeable.

TECHNICAL SOLUTION The above objects are achieved by a novel press roller apparatus for an equipment of cutting a brittle material wherein a press roller is divided into a wheel part mounted to a delivery frame and an elastic ring part detachably mounted to the wheel part and the elastic ring is press-contacted with a surface of the brittle material, so that the elastic ring only is re-tooled without a re-tooling of the wheel. According to an embodiment of the invention, there is provided a press roller apparatus for an equipment of cutting a brittle material comprising a delivery frame ascended and descended and linearly moved along a crack line by a roller driving device; a wheel rotatably mounted to the delivery frame; and an elastic ring detachably connected to a periphery of the wheel and closely contacted with a surface of the brittle material. According to a preferred embodiment of the invention, a concave recess may be formed on the periphery of the wheel along the circumference thereof and the elastic ring may be elastically fitted and connected to the concave recess. Preferably, an axis may be provided to the delivery frame and the wheel may be mounted to the axis with being rotatably supported by at least one bearing. In addition, preferably, the concave recess has a depth corresponding to 1/2-1/3 of a line diameter of the elastic ring, and 1 /2-2/3 of the line diameter of the elastic ring may be further protruded beyond an outer diameter of the wheel when the elastic ring is fitted into the concave recess. An outer diameter which is constituted by a bottom surface of the concave recess is preferably larger than an inner diameter of the elastic ring by 5-10%. The elastic ring is preferably made of one of rubber, silicon, polyurethane having an elasticity.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: FIG. 1 is an exploded perspective view showing a preferred embodiment of the invention; FIG. 2 is a front view of a preferred embodiment of the invention; FIG. 3 is a sectional view of a preferred embodiment of the invention; FIG. 4 is a sectional view for illustrating a relation between a depth of a concave recess of a wheel and a diameter of an elastic ring in the press roller apparatus according to an embodiment of the invention; FIG. 5 is a sectional view for illustrating a relation between an outer diameter of a bottom surface of a concave recess of a wheel and an inner diameter of an elastic ring in the press roller apparatus according to an embodiment of the invention; FIG. 6 shows an extremely deformed state of an elastic ring during cutting, when the elastic ring is loosely fitted to a wheel, in the press roller apparatus of an embodiment of the invention; FIGS. 7 to 9 show various cross-sectional shapes of an elastic ring; FIG. 10 is a schematic view showing an aspect of cutting a brittle material using a press roller apparatus according to an embodiment of the invention; FIG. 11 is a schematic view illustrating a structure of an apparatus for cutting a brittle material using a press roller according to the prior art; FIG. 12 shows an example of an aspect of cutting the brittle material using a press roller according to the prior art; FIG. 13 shows another example of an aspect of cutting the brittle material using a press roller according to the prior art; FIG. 14 is a schematic view illustrating another example of an aspect of cutting the brittle material using a press roller according to the prior art; FIG. 15 is a schematic view illustrating another example of an aspect of cutting the brittle material using a press roller of the prior art; and FIG. 16 is a schematic view an aspect of cutting the brittle material using a braking bar according to the prior art.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. Figs. 1 to 3 show an entire structure of a press roller apparatus according to a preferred embodiment of the invention. As shown in Figs. 1 and 2, the press roller apparatus according to an embodiment of the invention has a delivery frame 100, a wheel 200 and an elastic ring 300. The delivery frame 100 are ascended and descended above a brittle material to be cut and can linearly move along a crack line formed on the brittle material at the same time, by a roller driving unit (not shown) of an equipment for cutting a brittle material in a press roller manner. The wheel 200 is rotatably mounted to the delivery frame 100. A concave recess 201 is formed on an outer circumference of the wheel 200. The elastic ring 300 is fitted into the concave recess 201. Since the elastic ring 300 has resilience, i.e., elasticity, when the elastic ring 300 is fitted into the concave recess 201, the elastic ring 300 is closely connected while pressing a bottom and a side of the concave recess 201. The elastic ring 300 is directly press-contacted with a surface of the brittle material and rolls along a crack line of the brittle material, so that it applies a bending moment to the crack line and thus cuts the brittle material. The elastic ring 300 is a part that directly contacts the surface of the brittle material, and is substantially damaged (for example, abrasion) as the cutting is repeated. According to the present invention, a damage of the roller, which inevitably occurs as a cutting process proceeds, is limited to the elastic ring 300 and only the damaged elastic ring 300 is re-tooled. Fig. 3 shows a mounted structure of the wheel 200 and the elastic ring 300. As shown in Fig. 3, the wheel 200 is rotatably mounted to an axis 400 which is provided at an end of the delivery frame 100. The wheel 200 is rotatably supported on the axis 400 by bearings 500. Preferably, the bearings 500 are oppositely mounted on both sides of the wheel 200 for reducing a rotation error of the axis and stably transmitting a pressure of the wheel 200 when the wheel 200 is rotated. Preferably, an accurate bearing, for example, a cross roller bearing is used as the bearing 500 so that the wheel 200 can smoothly rotate without a slip or shake when the wheel 200 moves along the crack line of the brittle material. In Fig. 3, a gap is shown between the elastic ring 300 and the bottom of the concave recess 201. However, this is for the purpose of illustration only, and actually the elastic ring 300 is contracted by its elastic restoring force and thus closely in contacted with the bottom of the concave recess 201 with a pressure. Meanwhile, according to an embodiment of the invention shown in Figs. 1 to 3, the elastic ring 300 is fitted into the concave recess 201 formed on the circumference of the wheel 200. However, the invention is not limited to this embodiment. For example, a plurality of protrusions protruding from an inner surface of the elastic ring is radially formed and a plurality of holes into which the protrusions are inserted is formed on an outer circumference of the wheel without the concave recess. Accordingly, when the elastic ring is fitted in the wheel as the protrusions are inserted into the holes. Fig. 4 shows a relation between a depth (DP) of the concave recess 201 and a line diameter (dl) of the elastic ring 300. According to the present invention, the depth (DP) of the concave recess 201 preferably has a size corresponding to 1/2-1/3 of the diameter (dl) of the elastic ring 300. If the depth (DP) of the concave recess 201 is too shallow, the elastic ring 300 is prone to fall off during the cutting process. On the other hand, if the depth (DP) of the concave recess 201 is too deep, when the elastic ring 300 is pressed during the cutting process, the brittle material is prone to be damaged because the wheel 200 is contacted with the surface of the brittle material. When the elastic ring 300 is fitted to the concave recess 201, it is preferred that 1/2-1/3 of the line diameter (dl) of the elastic ring 300 is outwardly protruded beyond an outer diameter of the wheel 200. Fig. 5 shows a relation between an outer diameter (D) of the bottom surface 202 of the concave recess 201 and an inner diameter (d) of the elastic ring 300. It is preferred that the outer diameter (D) of the bottom surface 202 of the concave recess 201 is larger than the inner diameter (d) of the elastic ring 300 by 5-10%. By doing like this, the elastic ring 300 is closely contacted with the bottom surface 202 and side of the concave recess 201 by its elastic restoring force and thus fixed without a slip. If the outer diameter (D) of the bottom surface 202 of the concave recess 201 is too small, the elastic ring 300 is loosely fitted. In this case, as shown in Fig. 6, when the elastic ring 300 rolls with being closely pressure-contacted to the surface of the brittle, a curled up portion 301 by a friction force with the surface of the brittle material is generated. This may be a cause of deteriorating a product quality. The wheel 200 is preferably made of material that is light and can be accurately cast or processed such as aluminum alloy. The elastic ring 300 is preferably made of one of rubber, silicon and polyurethane having an elasticity. A typical soft rubber or fluoro rubber may be used as the rubber. The elastic ring 300 may have various cross-sectional shapes, as shown in Figs. 7 to 9. Likewise, a sectional cross of the concave recess 201 of the wheel 200 may be variously shaped, such as a circular bottom shape, in addition to the shapes shown in Figs. 4 and 5. Fig. 10 is a schematic view showing an aspect of cutting the brittle material using a press roller apparatus according to an embodiment of the present invention. In Fig. 10, the brittle material 20 has a crack line 22 formed on a lower surface thereof. The press roller apparatus is located above an upper surface of the brittle material 20 opposed to the crack line 22. Meanwhile, to the contrary, the crack line 22 may be formed on the upper surface of the brittle material 20 and the press roller apparatus may be located below the brittle material. The brittle material 20 is suction-fixed to an upper surface of a vacuum chuck by vacuum of the vacuum chuck, as described above when explaining the prior art. The brittle material 20 maintains to be tensioned in left and light directions by a moving plate and a driving device for the moving plate (Fig. 11). Under such a state, the delivery frame 100 is descended to the surface of the brittle material 20 opposed to the crack line 22 and moved along the crack line 22 while pressing the surface with the elastic ring 300. Then, a shear force by a bending moment is applied to the crack line 22 of the brittle material 20 and thus the material is fractured. If the surface of the elastic ring 300 is worn away or glass powders are adhered to the surface of the elastic ring 300 due to repeating uses, it only has to remove the elastic ring 300 from the wheel and to re-tool it with a new elastic ring.

INDUSTRIAL APPLICABILITY As described above, according to the invention, a press roller is divided into a wheel part mounted to a delivery frame and an elastic ring detachably connected to the wheel part and the elastic ring only is contacted with a surface of a brittle material. In other words, a part that is substantially damaged (for example, abrasion) due to a contact with the surface of the brittle material is limited to the elastic ring. Accordingly, it only has to re-tool the elastic ring without replacing the entire roller. According to the prior art, since a press roller is constructed to a one elastic body, it is difficult to accurately process (forming), a manufacturing cost is high, and it takes much time and cost to re-tool the roller. In addition, according to the prior art, since it is difficult to precisely process the roller and thus there is a large deviation between the products, it should be made to re-arrange a crack line and a center of a new press roller whenever replacing with the new press roller. However, according to the invention, the press roller is divided into a wheel and an elastic roller and if the wheel is accurately made, it is possible to use the roller for a long time just by replacing the elastic ring only. Accordingly, it costs less than the prior art that should accurately make or process the entire press roller every time. In addition, according to the present invention, the elastic ring is fitted into a concave recess of the wheel, which is already precisely made, with a predetermined elasticity. At this time, the ring is closely contacted with the recess and pressed by a certain amount. Accordingly, when the wheel is correctly arranged even if the elastic ring is not precisely shaped, it is not required an re-arrangement since there is little deviation from the centers after a re-tooling of the elastic ring, and a cutting quality is not deteriorated. Additionally, since the re-tooling is made just by fitting and removing the elastic ring only, the re-tooling is easy and it does not take much time to perform the re-tooling. Further, according to the present invention, since a price of the elastic ring is much cheaper than the prior roller in a unity, it is a less burden on a re-tooling. Accordingly, since it is allowed to frequently re-tool the elastic ring without excessively using the ring, it is possible to maintain a quality of the brittle material to a level of high quality with a low cost. While the present invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.