Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
2001-04-23
2002-06-04
Walberg, Teresa (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S390000, C219S395000, C219S540000, C034S267000, C034S211000
Reexamination Certificate
active
06399923
ABSTRACT:
This application is based on Japanese Patent Application No. 2000-133634 filed on May 2, 2000, the contents of which are incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multi-stage heating furnace arranged to heat a stack of large-sized substrates in the form of glass plates used for a liquid crystal display (LCD) panel and a plasma display panel (PDP), and a heating type far-infrared-radiation panel heater. The present invention is also concerned with a method of controlling flows of a fluid (air) through the heating furnace.
2. Discussion of Related Art
In the manufacture of large-sized substrates for the liquid crystal display (LCD) panel and plasma display panel (PDP) indicated above, it is indispensable to perform drying and heating steps for drying and heating the substrates after washing and after application of a coating, to remove a washing liquid and a solvent contained in the coatings. To this end, a heating furnace is required. The substrates are thin rectangular sheets each side of which has a length of about 1.0-2.0 m and the thickness of which is about 0.7-3.0 mm. Thus, the substrates to be dried and heated are considerably large.
Heating furnaces generally used to dry and heat such large-sized substrates include, for instance: (1) a heating furnace of hot-air circulating type; (2) a heating furnace of far-infrared-radiation type; and (3) a heating furnace of hot-plate type. The heating furnace of hot-air circulating type can be easily designed to heat the substrates arranged in a stack, and has an advantage in the efficiency of space utilization. However, the heating furnace of hot-air circulating type suffers from difficult control of temperature distribution and contamination of the substrate with a dust blown by the hot air. Therefore, this type of heating furnace is not suitable for drying the large-sized substrates, where the substrates are required to be dried in a clean atmosphere with an even distribution of the heating temperature over the entire area of the substrate surface.
The heating furnace of far-infrared-radiation type has the following advantages: improved heating efficiency for removing the solvent; a comparatively high degree of accuracy of control of the heating temperature for even distribution over the entire range of the substrate surface, by controlling a heater; and a comparatively high degree of cleanliness of the atmosphere within the furnace, owing to radiation heating without circulation of a hot air. However, the heating furnace of far-infrared-radiation type is generally required to position its heating portion (adapted to generate a far infrared radiation) in opposed relationship with the substrates, for effecting the radiation heating of the substrates. Accordingly, the heating furnace of this type is usually required to be a tunnel furnace (continuous furnace) in which the substrates to be dried are fed one after another along a horizontal path by a suitable conveying mechanism. The tunnel type heating furnace must have a relatively large overall length and accordingly requires a relatively large installation space, where the substrates are required to be dried to a comparatively large extent per unit time or where the substrates have a relatively large size, as indicated above.
The heating furnace of hot-plate type is arranged to effect conduction heating on the lower side of the substrates, and therefore has advantages of even or uniform heating (even distribution of the heating temperature) and a relatively high rate of rise of the heating temperature, where the substrates have a relatively small size. Where the substrates are relatively large, however, this type of heating furnace suffers from the following drawbacks: difficulty to achieve even heating: lower heating efficiency for removing the solvent contained in the coating applied to the upper surface of each substrate, than in the heating furnace of far-infrared-radiation heating; and requirement for a relatively large installation space where the hot-plate type heating furnace is designed to be a tunnel or continuous type furnace.
SUMMARY OF THE INVENTION
It is therefore a first object of the present invention to provide a multi-stage heating furnace which is capable of heating large-sized substrates in a clean atmosphere with a high degree of accuracy of temperature control and which requires a reduced installation space.
A second object of the invention is to provide a far-infrared-radiation panel heater suitable for use in the heating furnace of the present invention. A third object of the invention is to provide a method suitable for controlling flows of a fluid through the heating furnace of the invention.
The first object indicated may be achieved according to a first aspect of this invention, which provides a multi-stage heating furnace for drying a plurality of large-sized substrates arranged in a stack, the multi-stage heating furnace comprising:
a furnace body; and
a plurality of shelf heaters arranged within the furnace body such that the shelf heaters are spaced from each other in a vertical direction at a predetermined spacing pitch and such that adjacent ones of the shelf heaters partially define a plurality of drying chambers for accommodating the plurality of large-sized substrates, respectively, each of said plurality of shelf heaters consisting of a far-infrared-radiation panel heater of double-side heating type including a heat radiating plate in which a heat-generating body is embedded, the panel heater having opposite major surfaces covered with respective thin ceramic layers which emit a far infrared radiation when the heat radiating plate is heated by energization of the heat-generating body.
In the multi-phase heating furnace constructed according to the first aspect of this invention, each of the shelf heaters arranged within the furnace body in vertically spaced-apart relation with each other includes a heat radiating plate incorporating a heat-generating body, and has opposite major surfaces covered with respective thin ceramic layers for emitting a far infrared radiation, so that heat is radiated on the opposite sides of each panel heater. The electric wires and terminals for energizing the heat-generating body may be accommodated in the peripheral portion of the panel heater.
The shelf heaters consisting of the respective panel heaters thus constructed are spaced apart from each other within the furnace body, so as to partially define the drying chambers. In operation of the heating furnace, the large-sized substrates are placed on the respective shelf heaters, via suitable support blocks, so that each substrate is heated concurrently on its opposite sides, by radiation heating by the adjacent shelf heaters, whereby the substrates are suitably dried. Owing to the arrangement of the shelf heaters consisting of the double-sided far-infrared-radiation panel heaters in the vertically spaced-apart relation with each other within the furnace body, the space required for installing the present multi-stage heating furnace is significantly reduced with respect to that of a conventional tunnel type heating furnace, for drying a given number of large-sized substrates in one drying cycle. Further, each panel heater of the shelf heaters can be made comparatively thin, so that the shelf heaters can be arranged at a relatively small spacing interval or pitch in the vertical direction. Accordingly, the required height of the present multi-stage heating furnace can be reduced.
The present multi-stage heating furnace is capable of heating the large-sized substrates for liquid crystal display (LCD) panels and plasma display panels (PDP), in an atmosphere having a high degree of cleanliness, with a high degree of accuracy of control of the heating temperature, so that the quality of the dried large-sized substrates can be significantly improved. This advantage in the operating performance of the present heating furnace is enjoyed in addition to the above-indicated advantage of the
Kano Takahiro
Sakai Tamotsu
Tachikawa Hisayasu
Fuqua Shawntina T.
Noritake Co., Limited
Oliff & Berridg,e PLC
Walberg Teresa
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