APPLICATION METHOD OF SEALING AGENT

Abstract: In the process for producing a laminated substrate (1) such as electronic substrates (2; 3), when applying a sealing agent (7) to the end face of substrates (2; 3) combined together to seal it, first the sealing agent (7) is applied to a target area in the form of successive beads (7), and then a stream of compressed gas (10) is blown against the successive beads (7) from a gas ejecting nozzle (9) so as to scan the successive beads (7). The method can effectively fill the indentation or the stepped area formed along the end face with the sealing agent (7).

Description: DESCRIPTION APPLICATION METHOD OF SEALING AGENT TECHNICAL FILED This invention relates to a method of applying a sealing agent (or sealant) for the purposes of insulation and moistureproofing in the process of manufacturing electronic substrates. More particularly, the present invention relates to a method of applying a sealing agent adapted to seal the end face of the glass substrates of a plasma display to be put together. BACKGROUND ART Firstly, a known method of the above identified category will be described by way of the process of manufacturing a plasma display. A plasma display is adapted to generate ultraviolet rays by means of electric discharge in gas between a pair of electrodes, irradiating a fluorescent member thereof with the generated ultraviolet rays to generate visible light. The plasma display typically has a sandwich-like layered structure in which various kinds of functional thin films are formed between a front glass and a rear glass, including electrode films, a fluorescent film and ribs for holding the fluorescent film. After bonding lead wires to the electrodes for electric energization, the end face of the combined glass substrates are sealed by means of a sealing agent mainly for the purposes of insulation and moistureproofing. That structure is outlined in FIG. 2. FIG. 2 is a schematic perspective view showing the portion of a plasma display where a sealing agent is applied and FIG. 3 is a schematic cross sectional view of the portion of a plasma display where the sealing agent is applied. In FIGS. 2 and 3, the plasma display 1 comprises a front glass 2, a rear glass 3 and various kinds of functional thin films 4 arranged between the glass plates, including electrode films, a fluorescent film and ribs for holding the fluorescent film. Thus, the plasma display 1 has a layered structure like that of a sandwich. Reference numeral 5 in FIGS. 2 and 3 denotes a drive substrate for driving the plasma display 1. A large number of thin lead wires 6 are arranged in a film state to connect the drive substrate 5 and the electrodes formed in the functional films 4 of the plasma display 1. It should be noted that the front glass 2 is dimensionally smaller than the rear glass 3 while the functional films 4 are dimensionally smaller than the front glass 2. After bonding the lead wires 6 to the electrodes of the plasma display 1, a sealing agent 7 is applied to the entire end face of the front glass 2 and the functional films 4 laid on the rear glass 3, including the connecting area of the lead wires 6, in order to seal the plasma display for the purposes of insulation and moistureproofing. Accordingly, as clearly seen in FIG. 2, the shape of the portion to which the sealing agent 7 is applied has an indentation formed between the front glass 2 and the rear glass 3. Referring to FIG. 3, the functional films 4 has a total thickness a that is between 100 and 400μm and the front glass 2 projects from the functional films 4 by a distance b that is between 500 and 3,000μm. Thus, the indentation is defined by the thickness a and the distance b. The aforementioned known method has a drawback as described below. When manufacturing plasma displays of the above described type, there often occur occasions where the indentation ends up without being filled with the applied sealing agent 7 to leave a void ( denoted by c in FIG. 3) because the end face of the functional films 4 is located inside that of the front glass 2 on manufacturing considerations. The sealing agent 7 is typically of the silicon type or of the epoxy type that can be set by ultraviolet rays or heat and shows a viscosity between 100 and 1,000 poise/20 'C. When the sealing agent is applied by using an application nozzle directed perpendicularly to the substrate to produce continuous beads of the agent, the indentation may cause a void. While this problem may be avoided by using a low viscosity sealing agent obtained by dissolving the agent into solvent, the gas produced as a result of evaporation of the solvent can contaminate the environment to give rise to a pollution problem. Therefore, there is a demand for the improvement in the sealing. DISCLOSURE OF THE INVENTION In view of the above problems, it is therefore the object of the present invention to provide a method of applying a sealing agent to the end face of a laminated substrate such as electronic substrates, in which the indentation or the stepped area formed along the end face can effectively be filled with the sealing agent, i.e., the sealing agent can be improved in throwing power or entering properties. According to the present invention, the above mentioned object is achieved by a method of applying a sealing agent to a target region, which comprises the steps of: first applying the sealing agent to the target area in the form of successive beads; and then causing a stream of compressed gas from a gas ejecting nozzle to impinge upon said successive beads of the sealing agent as applied, while scanning said successive beads of the sealing agent with said gas ejecting nozzle. Thus according to the invention, a sealing agent is applied to a target region in the form of successive beads, and then a stream of compressed gas is blown out of a gas ejecting nozzle while scanning the beads as applied, thereby crushing the beads of the sealing agent and spreading over the face so as to effectively fill the indentation or the stepped area formed along the end face. BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A and IB are schematic illustrations of the method of applying a sealing agent according to the invention used in an example. FIG. 2 is a schematic perspective view of the portion of a plasma display to which a sealing agent has been applied by the method according to the invention. FIG. 3 is a schematic cross sectional view of the portion of a plasma display to which a sealing agent has been applied by prior art. PREFERRED MODES FOR CARRYING OUT THE INVENTION The method of applying a sealing agent according to the invention will be described in greater detail by way of an example using the accompanying drawings . The present invention is described in terms of a plasma display comprising glass substrates that are put together and sealed at the end face thereof as illustrated in FIG. 2 and described above with a known method. FIGS. 1A and IB schematically illustrate the method of applying a sealing agent according to the invention in the process of manufacturing a plasma display. The same components as in FIGS. 2 and 3 are denoted by the same reference numerals. FIG. 1A is a schematic illustration of the sealing agent applied in the form of beads and FIG. IB is a schematic illustration of the sealing agent to which compressed gas is being blown from a gas ejecting nozzle. Referring to the drawings, the plasma display 1 comprises a front glass 2, a rear glass 3 and various kinds of functional thin films 4 arranged between the glass plates, including electrode films, a fluorescent film and ribs for holding the fluorescent film. Thus, the plasma display 1 has a layered structure like that of a sandwich. Reference numeral 5 denotes a drive substrate for driving the plasma display 1. A large number of thin lead wires 6 are arranged in a film to connect the drive substrate 5 and the electrodes formed in the functional films 4 of the plasma display 1. The front glass 2 is dimensionally smaller than the rear glass 3 while the functional films 4 are dimensionally smaller than the front glass 2. After bonding the lead wires 6 to the electrodes of the plasma display 1, a sealing agent 7 is applied to the entire end face of the front glass 2 and the functional films 4 laid on the rear glass 3, including the connecting area of the lead wires 6, in order to seal the plasma display for the purposes of insulation and moistureproofing. Accordingly, as clearly seen in the drawings, the shape of the portion to which the sealing agent 7 is applied has an indentation formed between the front glass 2 and the rear glass 3. Referring to FIG. 3, the functional films 4 has a total thickness of from 100 to 400μm and the front glass 2 projects from the functional films 4 by a distance b of from 500 to 3,000μm. Thus, the indentation is defined by the thickness a and the distance b. Thus, firstly, the sealing agent 7 is ejected from a sealing agent ejecting nozzle 8 onto the zone to be sealed to form successive beads of the sealing agent as shown in FIG. 1A, and then, as shown in FIG. IB, compressed gas 10 is blown out of a gas ejecting nozzle 9 onto the applied sealing agent 7 so as to scan it. As a result, the beads of the sealing agent are crushed under the pressure of the gas and spread over the face so that the sealing agent is sufficiently charged into the indentation or the stepped area produced along the end facets. The experiments conducted in the example will be discussed below. 1. the indentation of the applied area as defined by the thickness a of the functional films and the gap b thickness a of functional films: 100 - 400μm gap b: 500 - 3,000μm 2. the sealing agent sealing agent: silicon type adapted to be set by ultraviolet rays or epoxy type adapted to be set by heat viscosity: 100 - 1,000 poise/20 'C (solventless type) beads of sealing agent: 0.5 - 3.0mm (width) x 0.5 - 5.0mm (height) 3. the gas blow distance between gas jet nozzle front end and sealing agent-carrying substrate surface: 5 - 25mm gas pressure: 1 - 3kg/cm 2 (air) gas flow rate: 50 - 900 liter/min. moving speed of gas jet nozzle: 100 - l,000mm/sec. Compressed gas (air) was blown against the beads of the applied sealing agents under the above conditions of scanning and spread the beads of the sealing agents. A number of experiments were carried out under the above conditions to find that the indentation was always filled with the sealing agent. There is known a swirl application technique of applying a sealing agent that is designed to produce beads broader than those produced by a popular linear one-pass application technique. Satisfactory results were obtained also in the experiments where the swirl application technique was used to produce broad beads to which compressed gas was blown. INDUSTRIAL APPLICABILITY While the present invention is described above in terms of a method of applying a sealing agent to the end face of the glass substrate of a plasma display that are put together in order to seal the end face, the present invention is by no means limited thereto and it can be used for various objects having an indentation or a stepped area along the edges thereof to which a sealing agent should be applied. As described above, according to the present invention, there is provided a method of applying a sealing agent to the end face of laminated substrates that are laid one on the other such as electronic substrates, by which the indentation or the stepped area produced along the end face can be effectively filled with the sealing agent.

Claims: CLAIMS A method of applying a sealing agent to a target region, which comprises the steps of: first applying the sealing agent to a target region in the form of successive beads; and then causing a stream of compressed gas from a gas ejecting nozzle to impinge upon said successive beads of the sealing agent as applied, while scanning said successive beads of the sealing agent with said gas ejecting nozzle.

Inventors: SHIMADA TAKAJI, SHIMADA, TAKAJI
Applicants: NORDSON CORP, SHIMADA TAKAJI, NORDSON CORPORATION, SHIMADA, TAKAJI
Application year: 2000
Main classification: H01J9
IPC codes: B05C5, B05C11, B05D3, B05D7, F16J15, H01J9, H01J29