Glass manufacturing – Processes – With measuring – sensing – inspecting – indicating – or testing
Reexamination Certificate
1999-04-20
2002-02-19
Vincent, Sean (Department: 1731)
Glass manufacturing
Processes
With measuring, sensing, inspecting, indicating, or testing
C065S043000, C219S446100, C219S448110, C219S448170, C219S451100
Reexamination Certificate
active
06347535
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a heating apparatus and method and, more particularly, to a technique for supporting an object to be heated such as a glass plate and subjecting it to a uniform temperature process in order to uniformly heat it.
Conventionally, in a heating apparatus for uniformly heating an object to be heated, as shown in
FIG. 37
, a plurality of cartridge type rod heaters
213
are inserted in a plate
212
made of one material. Outputs from the rod heaters
213
are controlled by a controller
214
by referring to a temperature obtained by at least one temperature sensor (not shown) provided to the plate
212
, thereby heating an object
1
to be heated. To decrease in-plane temperature nonuniformity of a heating surface
212
a
of the plate
212
, a material such as an aluminum alloy having a large thermal conductivity is used. To prevent deformation of the plate
212
, a material such as stainless steel having a small thermal conductivity and a large rigidity is used. Although a materials such as ceramics with a large thermal conductivity is an ideal material for use as the plate
212
, ceramics is very hard to machine and expensive.
When a material having a large thermal conductivity is used to form the plate
212
, if the plate
212
is, e.g., a 400-mm square aluminum alloy plate, a temperature distribution of ±3° C. or less near 200° C. and ±5° C. or less near 400° C. is achieved by controlling the rod heaters
213
.
When a material having a small thermal conductivity but a large rigidity is used to form the plate
212
, if the plate
212
is a 400-mm square plate, warp of the plate
212
is suppressed to 0.2 mm or less even after the plate
212
is subjected to a heat cycle of 400° C. or more.
As an apparatus for heating a flat plate such as a glass plate, one disclosed in Japanese Patent Laid-Open No. 10-55754 filed by the present applicant is available. The invention of this reference relates to a technique for adhering and heat-bonding two flat glass plates through a spacer. According to this technique, the flat glass plates are heated to a predetermined temperature by heating flat plates and are heat-bonded to each other.
Each heating flat plate of the above apparatus incorporates a heating means in itself and is supported on the base of the apparatus with a support member. In the apparatus shown in the above reference, the support member is made of a heat insulating material such as a ceramic member to cope with high temperatures.
In order to suppress thermal deformation of the plate
212
and to reduce its heat capacity and temperature distribution, if the plate of the heating apparatus is a 400-mm square plate, an in-plane temperature distribution of ±3° C. or less near 200° C. and ±5° C. or less near 400° C. is achieved. Even after the plate
212
is subjected to a heat cycle from room temperature to 400° C. or more, warp of the plate
212
must be suppressed to 0.2 mm or less.
A glass plate used in, e.g., a liquid crystal display, often undergoes a heating process in the display fabrication process. To process the display or to form and assemble elements at predetermined positions on a glass plate, deformation of the glass plate caused by heat must be prevented to increase positional precision and to increase processing precision and assembling precision. For this purpose, in the heating apparatus, the glass plate must be heated by using a plate having a least possible temperature distribution.
When forming display pixels and an optical filter on a glass plate, as the positional precision of each pixel and filter largely influences the image quality of the display, the glass plate as a substrate where pixels and filter are to be formed should not largely thermally deform by a positional error factor, i.e., a temperature nonuniformity or temperature gradient.
For example, when a glass plate having a length L=400 mm is heated from 20° C. to 220° C., it expands by &Dgr;T×L×&agr;=(220−20)×400×(10×10
−6
)=800 &mgr;m where the coefficient of expansion of glass is &mgr;=10×10
−6
. At this time, if a temperature distribution (nonuniformity) exists and a temperature gradient of 20° C. exists per 400 mm, &Dgr;T×L×&agr;/2=20×400×10×10
−6
/2=40 &mgr;m occurs, and a positional error of 40 &mgr;m occurs as compared to a case wherein the temperature is uniform. Depending on the precision required by the process, element formation, and assembly, the temperature gradient must be set to 10° C. or less. If the temperature increases uniformly and the glass plate expands uniformly, the actual or desired positions of the respective portions of the glass surface after deformation can be predicted. If irregular temperature nonuniformity or temperature gradient occurs, the glass plate deforms irregularly or nonuniformly. Then, it is difficult to predict the position of a desired portion of the glass plate.
For example, as the size of the display increases, the area of the object to be heated, e.g., a glass plate used in the display, increases, and the area of the plate of the heating apparatus also increases. When the area of the heating apparatus increases, the heat capacity increases naturally, leading to an increase in power consumption of the heating apparatus and an increase in heating and cooling times. For cooling, it is indispensable to increase the cooling capability and to add a cooling means. Hence, in the heating apparatus, particularly in relation to increased area of the object to be heated, temperature distribution of the heating apparatus must be minimized, as described above, and its heat capacity must be designed as small as possible.
SUMMARY OF THE INVENTION
When the area of the plate increases, in the above prior art, since the cartridge heaters are inserted in the tunnel holes formed in the plate, the depth of the holes and the length of the cartridge heaters increase. As for the hole depth, increasing the depth while maintaining the same diameter as that of the prior art is technically difficult, and highly precise hole formation is limited in depth. If the hole diameter is increased, while the processability increases and a deep hole can be formed easily, the plate thickness increases and the weight and heat capacity increase, leading to an increase in power consumption and heating and cooling times. For the heater, a length with which the heater can be fabricated with good precision for a certain diameter is limited. If the heater length increases, the heater diameter must be increased. As a result, the thickness of the plate into which this large-diameter heater is to be inserted increases. In this manner, if the area is increased without taking any special measure, the plate thickness increases due to limitations on the hole and heater, and the heat capacity increases more than the area increase. In other words, an issue of realizing a large plate area without increasing the heat capacity per unit area of the plate arises.
Along with a further increase in area of the plate of the heating apparatus, it has become necessary to enable free selection of the portion (region) to be heated by each heater and to perform temperature control of each heater separately, thereby reducing temperature distribution. For example, the temperature of the periphery of the plate decreases due to heat dissipation from the sidesurface. When outputs from heaters provided to the periphery of the plate are separately controlled to uniform the temperature, temperature distribution can be reduced. In the prior art, however, since the heaters are inserted in one direction of the plate, the thickness of the plate of the heating apparatus must be increased to prevent interference between the heaters in two directions, and the heaters must be set at different heights. As a result, the weight of the plate increases to increase its heat capacity, leading to an increase in power consumptio
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Vincent Sean
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