Method of making tubeless gas panel

Abstract

During the course of fabricating a gas panel, a partially completed gas panel is placed in a vacuum oven for a bake-out, back fill and sealing operation. During the bake-out, the oven is evacuated to remove gaseous and vapors contaminants from the gas panel. Thereafter, during the back fill operation, a display gas atmosphere is admitted to the oven which fills the gas panel. Thereafter, the panel is sealed to lock in the desired display gas. The sealing is accomplished by providing a hole in the back panel in which is placed a plug so shaped as to allow the gas panel to be initially evacuated and thereafter back filled with gas. Once the panel is back filled, the plug is selectively melted to fill the hole and then allowed to solidify to complete the seal.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method of making or fabricating a gas panel and, more particularly, to an improved method for sealing a gas panel assembly containing the display gas.

2. Description of the Prior Art

U.S. patent application Ser. No. 214,348, filed Dec. 30, 1971, now abandoned, for "Gas Panel Fabrication" by P. H. Haberland et al., assigned to the assignee of the present application, discloses a method of making a gas panel which method is typical of the type which the present invention is designed to improve. In accordance with the method disclosed in such application, front and back panel subassemblies are first constructed having conductors geometrically arranged according to the pattern desired for the eventual display. The front and back panels are connected together by means of a seal which forms a chamber for receiving the display gas. The panels are spaced apart by a suitable spacer. After the partially completed gas panel has been assembled, it is necessary to bake-out and back fill the assembly. To accomplish this, a hole is provided in the back plate which lies outside of the viewing area of the panel but communicates with the inner chamber. In accordance with the prior art method, a glass tubulation or tube is fitted into this hole and sealed to the assembly, the purpose of the tube being to allow the inner chamber to be first evacuated at elevated temperature to remove any gases and vapors. Thereafter, while the inner chamber is evacuated, the display gas can be admitted through the tube by a back fill operation. Then, the tube is sealed off.

The use of the tube, while it provides a convenient way to both evacuate and back fill the gas panel assembly, is also disadvantageous because of the somewhat brittle nature of the tube. During the course of making the gas panel and later assembling it into the complete display device, the panel is subject to mechanical handling. Thus, should this tube hit something or be hit, it can snap off. If it snaps in the oven, it may contaminate the entire batch of other panels being made or it might contaminate only the particular panel. Hence, it is desirable to eliminate the use of such a tube.

The disadvantages of the tubular process have been recognized by others. For example, U.S. patent application Ser. No. 214,174, filed Dec. 30, 1971, now Pat. No. 3,778,126, for "Gas Display Structure Without Exhaust Tube Structure" by D. M. Wilson, and assigned to the assignee of the present application, recognizes the disadvantages of the tubulation method and proposes an alternate method in which the front and back panels, neither of which contains any holes, are assembled in an oven. Before the front and back panels are permanently connected by the peripheral seal, the oven is evacuated and then the display gas is admitted. Thereafter, the parts are sealed together in this gaseous atmosphere to form the final display.

SUMMARY OF THE INVENTION

One of the objects of the invention is to provide a method of making a gas panel which eliminates the need for any tubulation for evacuating and back filling the gas panel during assembly thereof.

Another object of the invention is to provide a relatively inexpensive and easy to use method of fabricating a gas panel and sealing the inner chamber containing a display gas.

Briefly, the manner in which the above and other objects of the invention are attained is to provide a hole within the back panel which communicates with the inner chamber in an area removed from the viewing portion of the display. When the panel is placed in an oven for back-out and back fill, a glass plug is placed in the hole. The plug is so shaped, such as by having a hole in the center, to allow gases to be first evacuated from the chamber and then allow a display gas to be admitted to the chamber. When the display gas is back filled into the chamber, then the plug is selectively softened or melted so as to completely fill the hole. Upon solidification, the plug then completely seals the display gas within the inner chamber.

BRIEF DESCRIPTION OF THE DRAWING

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawing.

FIG. 1 is a side elevational view, partly in section, showing a portion of a gas panel during the fabrication thereof in accordance with a typical prior art method;

FIG. 2 is a view similar to FIG. 1 showing the gas panel at another stage of completion in accordance with the prior art method;

FIG. 3 is a view similar to FIG. 1 on an enlarged scale illustrating a portion of the method embodying the invention;

FIGS. 4 and 5 are views similar to FIG. 3 but with portions removed, illustrating further steps of the method of the invention.

It is to be understood in connection with the invention that it is a subset or step of the overall fabrication process where the overall process can be in accordance with prior art techniques using the known materials and procedures. The difference between the prior art and the present technique will be pointed out in detail below. Reference may be had to the aforementioned copending applications for details which are not necessary for an understanding of the method of the invention.

Referring now to the drawing, FIG. 1 shows a part of a gas panel display after the completion of one step in the fabrication. As shown, a front panel subassembly 10 and back panel subassembly 11 are held in a predetermined fixed spaced relationship relative to each other by a glass spacer 16. A glass seal 15 joins panels 10 and 11 together in such a manner as to form an inner chamber 17 that will eventually be filled with the display gas. A necked down glass tube 13 has its lower end fitted into a stepped down cylindrical hole 12 and is joined to back panel 11 by a glass seal 14 of the same composition or reflow properties as seal 15. At such a stage of construction, the partially completed back panel is placed in an oven for a bake-out, a back fill and a seal steps during the course of which the upper end of tube 13 is first connected to a manifold for first evacuating chamber 17 and back filling it with the desired display gas. After the display gas is placed in chamber 17, then the necked down portion of tube 13 can be melted to seal off the upper end of tube 13', as shown in FIG. 2 and completely seal the display gas within the inner chamber of the gas panel assembly. It can be readily seen that the tube protrudes from the back panel 11 and is highly subject to breakage during mechanical handling.

The improved process of the invention will now be described. With reference to FIG. 3, the gas panel assembly is first partially constructed so as to form the subassembly of front and back panels 10 and 11 connected by a seal 15 and separated by a spacer 16 to form an inner chamber 17. Back panel 11 is provided with a hole 20 at a section thereof which lies outside of the viewing area of panel 10 but which communicates with chamber 17. The shape of hole 20 is designed to receive a glass plug 21 and support it until the plug is finally melted. As shown, hole 20 has a counter sunk upper portion terminating in a cylindrical lower portion of reduced diameter so that the lower edge of plug 21 can be received in the enlarged upper portion and supported by the walls. The plug 21 is placed in hole 20 either before or after the subassembly is placed in an oven for bake-out and back fill. The shape of plug 21 includes a central passage which allows gases to be withdrawn from chamber 17 during the evacuation and allows the display gas to be admitted to chamber 17 during the back fill. As shown, plug 21 has a cylindrical tubular shape provided with the central passage way for accomplishing this.

With reference to FIG. 4, when the plug 21 is placed on the assembly and it is put into the oven, a selectively energizable annular electrical heater 22 is positioned around plug 21. This heater is normally de-energized until after the back fill operation has occurred. Then, by energizing heater 22, plug 21 is melted or softened to a sufficient viscosity allowing it to flow by gravity into and partially fill hole 20. Upon solidification, as shown in FIG. 5, plug 21' is formed which completely seals the display gas in inner chamber 17.

The amount of material in plug 21 is sufficient to at least partially fill hole 20 when the plug is melted but without having any excess material project outwardly beyond the plane of the back surface of panel 11. While the lower end of plug 21' is shown in FIG. 5 as not touching panel 10, it may sometimes happen that it would because of the relatively small distance (in the order of 4 mils) between 10 and 11. Since plug 21' is outside of the viewing area, this touching has no adverse effect.

The selective melting of plug 20 is due to the composition of plug 21 having a much lower softening point than that of the material of back panel 11. To accomplish this, it is preferable that plug 21 be of the same material as that of seal 15. While the selection of compatible materials is well within the skill of the art and many different materials can be used, the following glasses may be used, it being understood that the following compositions are merely examples and are in no way intended to limit the invention. The glass substrate of panel 11 may be of the following composition:

material % by weight ______________________________________ Sl O.sub.2 72.78 FE.sub.2 O.sub.3 .484 AL.sub.2 O.sub.3 .16 Ti O.sub.2 .013 Ca O 8.63 MG O 3.94 Na.sub.2 O 13.86 SO.sub.3 .26 ______________________________________

The above particular glass has a softening point of 729.degree.C.

Plug 21 may have the following percentage by weight composition:

PbO 64.0 B.sub.2 O.sub.3 15.3 ZnO 14.9 CuO 3.0 Si O.sub.2 1.5 Bi.sub.2 O.sub.3 1.3

This particular glass has a softening point of 419.degree.C.

While the method of the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that varous changes in form, shape and compositions may be made within the materials without departing from the spirit and scope of the invention.

Claims

What is claimed is:

1. In the method of making a gas display panel having a front panel and a back panel joined in a spaced sealed arrangement forming an inner chamber containing display gas, wherein the method comprises baking out a partially completed panel assembly and backfilling such assembly with display gas, said backfilling being done by creating an atmosphere of display gas around said panel assembly, the improvment comprising the steps of:

providing said back panel with a passageway communicating between said inner chamber and the exterior of said back panel;

detachably supporting a preform on said back panel in said passageway, said preform being shaped to allow gas to flow through said passageway;

and, after said backfilling step has been completed and while said panel assembly is in said atmosphere of display gas, melting said preform and allowing it to flow downwardly by gravity so as to fill said passageway, and solidifying said melted preform to seal said display gas in said inner chamber.

2. The method of claim 1 wherein said preform is of a glass material having a softening point lower than that of the substrate of said back panel, whereby said melting step selectively melts said preform without softening said substrate.

3. The method of claim 1 wherein:

the volume of material in said preform is such as to seal said passageway without any preform material projecting outwardly beyond the plane of the back surface of said back panel.

4. The method of claim 1 wherein said providing step includes providing said passageway with a countersunk portion facing upwardly, and said preform is provided with a tubular cylindrical shape.