Patent Publication Number: US-6221190-B1

Title: Method and apparatus for processing glass panel

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method and apparatus for processing a glass panel. 
     A conventional process for fabricating a glass panel such as a vacuum heat-insulating glass panel or a plasma display panel (hereinafter abbreviated to PDP) comprises the step of sealing a glass panel assembly constructed from two glass plates, one with an exhaust pipe thereto, which are joined together by a jig such as a clip with a sealant applied to the periphery of one or the other of the opposing surfaces of the two glass plates, the step of evacuating the interior of the sealed glass panel through the exhaust pipe and the step of cutting and sealing up the exhaust pipe. 
     In the sealing step, the glass panel assembly is loaded into a batch-type sealing furnace and heated to a predetermined temperature (sealing temperature) to seal the two glass plates which are thus fabricated into a glass panel. In the evacuating step, many such glass panels, each with the exhaust pipe attached thereto, are loaded into a batch-type evacuating furnace and, while heating the glass panels at a predetermined temperature (evacuating temperature), an evacuating apparatus connected to the exhaust pipe is driven to evacuate the interior of the glass plate, and finally the exhaust pipe is sealed up and cut to complete the fabrication of the glass panel. 
     In particular, in the fabrication process of the PDP, the evacuating step is followed by the step of filling a discharge gas into the glass panel to a predetermined pressure (400 to 600 Torr), after which the exhaust pipe is sealed up and cut. 
     However, since the sealing step and the evacuating step are batch processes separately performed in special-purpose furnaces, raising and lowering the furnace temperature is repeated for each process, the resulting problem being that not only thermal efficiency is low but productivity also decreases enormously. 
     SUMMARY OF THE INVENTION 
     The present invention has been developed to substantially eliminate the above-described disadvantages. 
     It is therefore an object of the present invention to provide a method and apparatus for processing a glass panel in which not only thermal efficiency can be enhanced but productivity can also be improved. 
     According to the invention, there is provided a method for processing a glass panel, comprising the steps of: 
     supporting at least one glass panel assembly on an evacuating cart in such a manner as to be positioned inside a furnace, the glass panel assembly being constructed from two glass plates, any one of the glass panels being provided with an exhaust pipe, the glass plates being joined together by a jig with a sealant applied along a periphery of one or the other of the opposing surfaces of the two glass plates, the exhaust pipe being connected to an evacuating system; 
     sealing the two glass plates to form a glass panel by heating the glass panel assembly and melting the sealant while moving the evacuating cart through the furnace; 
     evacuating air and dirty gas between the two glass plates of the glass panel by the evacuating system until the predetermined degree of vacuum is achieved; and 
     sealing and cutting the exhaust pipe. 
     In the above invention, the glass panel assembly with the exhaust pipe attached thereto is loaded onto the evacuating cart mounted with the evacuating system, and is passed through the sealing/evacuating furnace where the glass plates are sealed together with a sealant and then the interior is evacuated by a vacuum. After this evacuating step, the exhaust pipe is fused and sealed up. That is, the glass panel sealing and evacuation and exhaust pipe sealing steps are performed continuously as the evacuating cart moves. In this way, according to the present invention, since the sealing of the glass plates and the evacuation of the panel interior are not performed by batch processes as was the case with the prior art, not only thermal efficiency can be enhanced but productivity can also be improved. 
     Preferably, the exhaust pipe is connected switchably between the evacuating system and a discharge gas supply system, and wherein the method further comprises the step of filling a discharge gas into the glass panel after the step of evacuating and before the step of sealing and cutting. 
     In this case, the evacuating cart is mounted with a discharge gas supply system, and the step of filling a discharge gas is performed after the evacuating step but before the exhaust pipe sealing step. This contributes to increasing thermal efficiency and improving productivity of the PDP. 
     The present invention is also directed to an apparatus for processing a glass panel, comprising: 
     a plurality of evacuating carts for supporting at least one glass panel assembly, the glass panel assembly being constructed from two glass plates, any one of the glass panels being provided with an exhaust pipe, the glass plates being joined together by a jig with a sealant applied along a periphery of one or the other of the opposing surfaces of the two glass plates, each evacuating cart being provided with an evacuating system connected to the exhaust pipe and a sealing heater for fusing and cutting the exhaust pipe; and 
     a furnace for heating the glass panel assembly on the plurality of evacuating carts which are moved on rails and charged into the furnace in a connected condition one behind another; 
     whereby the glass panel assembly is heated so that the sealant melted to seal the two glass plates and form a glass panel; 
     air between the two glass plates of the glass panel is evacuated by the evacuating system until the predetermined degree of vacuum is achieved; and 
     the exhaust pipe is sealed and cut. 
     Preferably, the furnace has an opening in the furnace bed extending along the moving direction of the evacuating cart, 
     the evacuating cart moves on the rails laid beneath the furnace bed, and 
     the evacuating cart is provided with a plurality of mounting members each comprising a supporting pillar extending into the furnace through the opening in the furnace and a holding member for holding the glass panel assembly in the furnace. In this case, the supporting pillar of the mounting members are preferably provided with an insulating member for closing the opening of the furnace. 
     Preferably, the furnace comprises a sealing zone, an evacuating zone and a cooling zone, and wherein in the sealing zone the two glass plates are sealed to form the glass panel, in the evacuating zone air and dirty gas in the glass panel are evacuated, and in the cooling zone the glass panel is cooled. 
     Preferably, the exhaust pipe is connected switchably between the evacuating system and a discharge gas supply system, and wherein a discharge gas is filled into the glass panel from the discharge gas supply system after evacuating the glass panel and before sealing and cutting the exhaust pipe. 
     Preferably, the appratus further comprises a discharge gas filling/sealing zone, whereby in the discharge gas filling/sealing zone a discharge gas is filled into the glass panel from the discharge gas supply system after evacuating the glass panel and before sealing and cutting the exhaust pipe. 
     Preferably, the apparatus further comprises; 
     a second rails laid on one side of the furnace on which the evacuating carts move in a direction opposite to the moving direction of the evacuating carts on the first rails; 
     a charge side transfer car for transferring the evacuating cart to the upstream end of the first rails from the downstream end of the second rails; and 
     a discharge side transfer car for transferring the evacuating cart to the upstream end of the second rails form the downstream end of the first rails; 
     wherein the evacuating carts are circulated for use. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further objects and advantages of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which: 
     FIG. 1 is a diagrammatic plan view of sealing, evacuating and discharge gas filling equipment for fabricating plasma display panels as glass panels according to the present invention; 
     FIG. 2 is an enlarged cross-sectional view of a sealing (or evacuating) zone in FIG. 1; 
     FIG. 3 is an enlarged longitudinal-sectional view of an evacuating cart in FIG. 2; 
     FIG. 4 is an enlarged partial sectional view of a PDP assembly; and 
     FIG. 5 is a heat curve for a sealing and evacuating furnace. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiment hereinafter described employs a PDP as a glass panel. In the drawings, reference numeral  1  indicates a sealing/evacuating furnace which has an opening  3  in the furnace bed  2  extending along the entire length thereof. The sealing/evacuating furnace  1  comprises a sealing zone A, an evacuating zone B, and a cooling zone C, each consisting of a plurality of chambers. 
     In the furnace  1 , the sealing zone A and evacuating zone B are provided with circulating baffles  4 , as shown in FIG. 2 to form a circulating passage  5  between the circulating baffles  4  and the inner surface of the furnace  1 . A heating source  6  such as radiant tube burners or electric heaters is arranged in the circulating passage  5 . Furnace atmosphere is drawn through an inlet  8  by means of a circulating fan  7 , is heated by the heating source  6 , and is delivered through delivery ports  9 . The atmosphere is thus circulated in the furnace  1  to heat the PDP assembly P 1  hereinafter described. 
     The cooling zone C has, in addition to the heating source  6  in the sealing zone A and evacuating zone B, a cooling source (not shown) such as a cooling air supply tube. Otherwise, the construction is the same as that of the sealing zone A (or the evacuating zone B). 
     The PDP assembly P 1  comprises a front glass plate W 1  and a back glass plate W 2  with an exhaust pipe Pa attached thereto, as shown in FIG.  4 . The front glass plate W 1  and the back glass plate W 2  face each other with a sealant S applied along the periphery of one or the other of the opposing surfaces thereof, and are rigidly fastened together by clamping them with a jig  10  such as a clip. The sealant S is prepared by kneading low-melting composite glass (a mixture of PbO·B 2 O 3 -based low-melting glass powder and special ceramic powder) with vehicle added consisting of a synthetic resin binder dissolved in a solvent. In the figure, the jig  10  is of a type that is applied to the exhaust pipe Pa. A slit  11  slightly larger in diameter than the exhaust pipe Pa is formed in one wing part of the jig  10 . With the exhaust pipe Pa passed through the slit  11 , a holding member  13  having a through-hole  12  is fitted to hold the exhaust pipe Pa in place. The method of holding the exhaust pipe Pa is not limited to using the holding member  13 , but other means or construction may be used. 
     The slit  11  need not be provided in clips that clamp the glass plates W 1 , W 2  at other portions than the portion where the exhaust pipe Pa is mounted. 
     Turning back to FIGS. 2 and 3, an evacuating cart  20  is moved by a pusher (not shown) on the rails  21  laid beneath the furnace bed  2 . On the upper surface of the evacuating cart  20  are arranged a plurality of mounting members  22 . Each mounting member  22  consists of a supporting pillar  22   a  extending into the furnace  1  through the opening  3  in the sealing/evacuating furnace  1  and a holding member  22   b  for holding the PDP assembly P 1  in a substantially vertical position and parallel to the widthwise direction of the furnace. The support pillars  22   a  of the mounting members  22  are provided with an insulating member  23  extending along the entire length of the evacuating cart  20 . The insulating member  23  is formed in such a manner as to close the opening  3  with a slight clearance provided therebetween. The insulating member  23  is provided with a hole  24  through which the exhaust pipe Pa is inserted. 
     Further, the evacuating cart  20  is mounted with an evacuating system having a vacuum pump  25  and a discharge gas supply system having a discharge gas cylinder  26 . They are connected to pipe fittings  29  via electromagnetic valves  27   a ,  27   b , and  28 . The evacuating cart  20  is also provided with a sealing heater  30  for fusing the exhaust pipe Pa on the PDP assembly P 1 . 
     In the present embodiment, the rails  21  are provided on one side of the sealing/evacuating furnace  1  as well as beneath the furnace  1 , as shown in FIG.  1 . On the rails  21  on the side of the sealing/evacuating furnace  1  is provided a loading/unloading zone Z. Each pair of rails  21  is connected to a charge transfer car  31  at one end and a discharge transfer car  32  at the other end so that the evacuating cart  20  is circulated for use. A discharge gas filling/sealing zone Zg is provided between the cooling zone C and the discharge transfer car  32 . 
     Next, the method of PDP processing will be described. 
     First, the PDP assembly P 1  is loaded onto the evacuating cart  20  in a loading/unloading zone Z. 
     In loading the PDP assembly P 1 , the exhaust pipe Pa is inserted into a hole  24  opened through the insulating member  23 , and the PDP assembly P 1  is fixed to the mounting member  22  by using suitable means such as a clip not shown so that the PDP assembly P 1  is placed on the evacuating cart  20  and held rigidly in a substantially vertical position and parallel to the furnace width, as shown in FIGS. 2 and 3. Then, the exhaust pipe Pa is connected to the pipe fitting  29 . Further, the sealing heater  30  is attached to the exhaust pipe Pa. 
     The evacuating cart  20 , which is loaded with many such PDP assemblies P 1 , is transported by suitable means to the charge transfer car  31 , where the evacuating cart  20  is redirected to the charge side of the sealing/evacuating furnace  1 . The evacuating cart  20 , actually a train of evacuating carts  20  connected one behind another as shown in FIG. 3, is then moved by a pusher or the like into the sealing/evacuating furnace  1 . Accordingly, the opening  3  is substantially closed with the insulating members  23  on the evacuating carts  20 , thus preventing the outside air from entering the interior of the furnace  1 . 
     When the evacuating cart  20  is charged into the furnace  1 , each assembly P 1  is heated in accordance with the heat curve shown in FIG. 5 while it is being passed through the sealing/evacuating furnace  1 . First, the sealant S melts in the sealing zone A so that the glass plates W 1  and W 2  are sealed together and the PDP assembly P 1  is thus fabricated into a glass panel P 2 . When the evacuating cart  20  enters the evacuating zone B, the electromagnetic valves  27   a  and  28  are opened so that the interior of each glass panel P 2  now communicates with the vacuum pump  25 . Air and dirty gas inside the glass panel P 2  are exhausted together with gasses released from the glass plates W 1  and W 2 , until the interior of the glass panel P 2  is evacuated to 10 −4  to 10 −7  Torr. The glass panel P 2  is then passed through the cooling zone C and discharged outside the furnace  1 . 
     When the glass panel P 2  enters the discharge gas filling/sealing zone Zg, the vacuum pump  25  is stopped and the valve  27   a  is closed and  27   b  opened so that a discharge gas, such as neon (Ne), helium (He), argon (Ar), and/or xenon (Xe), is filled from the discharge cylinder  26  into the glass panel P 2  up to a specified pressure (200 to 760 Torr). 
     When the discharge gas has been filled into the glass panel P 2 , then the sealing heater  30  is energized to seal up and cut the exhaust pipe Pa to complete the fabrication of the desired PDP. 
     Thereafter, the evacuating cart  20  is moved through the transfer car  32  to the loading/unloading zone Z where the processed PDPs are unloaded and new PDP assemblies P 1  are loaded for the processing described above. 
     The above description has dealt with the processing method for a PDP in which a discharge gas is filled into the glass panel, but it will be appreciated that the present invention can also be applied to a processing method for an vacuum heat-insulating glass panel. In that case, the discharge gas filling/sealing zone Zg is not provided, and after evacuating the interior to a predetermined pressure, the vacuum pump  25  is stopped and the sealing heater  30  is energized to seal up and cut the exhaust pipe Pa. 
     Although the present invention has been fully described by way of the examples with reference to the accompanying drawing, it is to be noted that here that various changes and modifications will be apparent to those skilled in the art. Therefore, unless such changes and modifications otherwise depart from the spirit and scope of the present invention, they should be construed as being included therein.