Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2001-10-30
2003-11-18
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S408000, C428S698000
Reexamination Certificate
active
06649270
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a jig for use in heat treatment onto which a vitreous plate having had films exhibiting respective given functions, such as a glass substrate for a plasma display panel, formed on its surface is to be loaded when the vitreous plate undergoes heat treatment.
In recent years, large screen flat panel displays (hereinafter referred to as “FPDs”) which can be used as displays for wall-mounted televisions and multimedia are being put into practical use steadily. And a plasma display panel (hereinafter referred to as “PDP”), which has not only qualitative merit of good-quality displaying due to its self-emitting characteristic and its wide viewing angle, but also production merit of simple production process and allowing a large size display with ease, is considered to be one of the promising large size FPDs.
PDP is produced by first forming films, which exhibit respective given functions such as electrode, dielectric and fluorescent material, one by one on the respective surfaces of large size glass substrates referred to as front and rear glass substrates by the thick film method, in which the process steps of printing, drying and firing are repeated more than one time, and finally bonding and sealing the front and rear glass substrates together.
Vitreous plates, such as glass substrates for PDP, on the surface of which films exhibiting respective given functions are formed are subjected to heat treatment at 500 to 900° C. so as to, for example, form films, eliminate the distortion of glass substrates and bond and seal the glass substrates, and the heat treatment process requires a jig for use in heat treatment, referred to as setter, which carries the vitreous plates loaded thereon through a heat treating furnace. Generally jigs for use in heat treatment have been those made of an alumina material or a crystallized glass material.
However, jigs for use in heat treatment which are made of an alumina material have problems of causing warps in themselves and losing their flatness with time due to heating/cooling operations repeated during the heat treatment since their coefficient of thermal expansion is as large as about 8×10
−6
/°C., which in turn causes warps in the vitreous plates, as the object of heat treatment, and causes defects in the films having been formed on the vitreous plates. These problems have been becoming serious with the increase in size of the vitreous plates. In the aforementioned PDPs, for example, those as large as about 42 to 60 inches are commercially produced to make a clear distinction between the PDPs and the conventional display media such as cathode ray tubes; as a result, defects are more likely to occur due to the warps caused in the jigs themselves.
For jigs for use in heat treatment which are made of a crystallized glass material, their coefficient of thermal expansion is as small as about −0.4×10
−6
/°C., and they are less likely to warp themselves. They, however, have problems such that since vitreous plates used for FPD, such as the aforementioned glass substrates for PDP, have coefficients of thermal expansion as large as about 8×10
−6
/°C., the difference in thermal expansion between the jig and the vitreous plates causes friction during the heat treatment, and the shape of the vitreous plates is changed into a trapezoid in the direction of advance thereof in a heat treating furnace if soaking is not carried out sufficiently. Further, for jigs for use in heat treatment which are made of a crystallized glass material, since their thermal conductivity is as small as about 1 W/mK, subjecting the vitreous plates loaded onto such jigs to a uniform heat treatment requires a plenty of heating and cooling durations, which makes the heat treatment inefficient.
Further, for jigs for use in heat treatment which are made of a crystallized glass material, since their apparent porosity is very close to zero, when vitreous plates for FPDs, such as the aforementioned glass substrates for a PDP, are loaded onto them, it takes a longer time to position the vitreous plates sliding on the jigs. And when unloading the vitreous plates from the crystallized glass jigs for use in heat treatment, the unloading operation cannot be carried out smoothly due to the jigs' adsorbing action. In order to overcome this problem, it is necessary, for example, to provide such jigs with new fine pores through which the air is allowed to flow in. This problem also has become more serious with the increase in size of the vitreous plates.
SUMMARY OF THE INVENTION
This invention has been made in light of the aforementioned problems which the prior art has. Accordingly, the object of this invention is to provide a jig for use in heat treatment which has a coefficient of thermal expansion appropriate to inhibiting occurrence of warps in the jig itself with time and occurrence of deformations in vitreous plates due to the friction caused when heat treating large sized vitreous plates as large as about 42 to 60 inches, has such an excellent thermal conductivity that heat treatment of vitreous plates can be performed uniformly and effectively in a relatively short period of time, and exhibits improved handleability in loading and unloading the vitreous plates.
This invention provides a SiC jig for use in heat treatment onto which a vitreous plate having had films exhibiting respective given functions formed on its surface is to be loaded when the vitreous plate undergoes heat treatment, the SiC jig being characterized in that it contains 50% by weight or more phase containing SiC, its thermal conductivity is 10 W/mK or more, its apparent porosity 0.2 to 25%, and its coefficient of thermal expansion 3.8×10
−6
/°C. to 5.5×10
−6
/°C. (a first jig for use in heat treatment).
Further, this invention provides a SiC jig for use in heat treatment onto which a vitreous plate having had films exhibiting respective given functions formed on its surface is to be loaded when the vitreous plate undergoes heat treatment, the SiC jig being characterized in that it contains 50% by weight or more SiC particles of particle diameter 3.5 mm or less, its thermal conductivity is 10 W/mK or more, its apparent porosity 0.2 to 25%, and its coefficient of thermal expansion 3.8×10
−6
/°C. to 5.5×10
−6
/°C. (a second jig for use in heat treatment).
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
In either of the first and second jigs for use in heat treatment according to this invention, warps can be inhibited which are caused with time in the jig itself due to the heating/cooling operations repeated during the heat treatment, since its coefficient of thermal expansion is controlled to be 5.5×10
−6
/°C. or less. Further the difference in thermal expansion between the jig and the vitreous plate, which is to be used for FPD, becomes small compared with the case where jigs of the prior art made of crystallized glass material are used, since its coefficient of thermal expansion is controlled to be 3.8×10
−6
/°C. or more, whereby the change can be inhibited of the vitreous plate shape into a trapezoid due to the friction caused during the heat treatment by the difference in thermal expansion between the vitreous plate and the jig. Further, the jig itself becomes more likely to be heated uniformly, since its thermal conductivity is controlled to be 10 W/mK or more, whereby the heating/cooling durations for subjecting the vitreous plate to uniform heat treatment can be reduced, resulting in improvement in production efficiency.
In the first and second jigs for use in heat treatment, their apparent porosities are controlled to be in the range of 0.2 to 25%, preferably in the range of 3 to 25%, whereby any one of the jigs according to this invention offers the advantages, in addition to the aforementioned advantages, of being able to promptly discharge the air introduced thereinto when loaded with a vitreous plate through the
Kinoshita Toshiharu
Ogura Shigeru
Bahta Abraham
Jones Deborah
NGK Insulators Ltd.
Parkhurst & Wendel L.L.P.
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