Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
1999-12-09
2004-11-23
Morris, Terrel (Department: 1771)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S064100, C428S210000, C501S004000, C501S006000, C501S007000, C501S068000, C501S069000, C501S070000, C501S071000, C501S005000, C501S063000, C501S064000, C501S014000, C501S018000, C501S021000, C501S022000, C501S023000
Reexamination Certificate
active
06821628
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The subject matter of the present invention includes a glass-ceramic cooking panel made from an opaque, uniformly colored glass-ceramic material with keatite mixed crystals as the predominant crystalline phase. The cooking panel the invention has an improved less-soiled appearance when deposited material, such as dirt and the like, is present on it.
2. Prior Art
Transparent uniformly colored glass-ceramic cooking panels, which appear dark to black, are known and have already been on the market for a comparatively long time.
When decorative light printed colors are desired on these cooking panels, it is necessary to print the entire surface to provide those decorative bright colors. These printed colors are sensitive in use, because any change of a light color is conspicuous. Also most decorative colors soon have a pale and less intense appearance because of their reduced layer thickness of typically 1 &mgr;m to 10&mgr;m.
Also opaque, white glass-ceramic molded bodies for use as cooking panels are known, e.g. from NEG, Japan, and are marketed under the trade name NEOCERAM® N11. They are currently used exclusively in induction cooking units. A colored glass-ceramic made from a glass starting material based on the Li
2
—Al
2
O—SiO
2
is known from U.S. Pat. No. 5,491,115, with &bgr;-Quartz and &bgr;-spodumene mixed crystals as the principal crystalline phase. The colored substance contained in this glass-ceramic is up to 6 percent by weight TiO
2
. The nuclei formers included in this glass-ceramic are from 700 to 900 ppm Fe
2
O
3
and 500 to 3000 ppm Co
3
O
4
. This glass-ceramic is transparent according to which crystalline phase is dominant. If &bgr;-Quartz is the principal crystalline phase, the glass-ceramic is transparent. If &bgr;-spodumene mixed crystals are the principal crystalline phase, then the glass-ceramic is opaque and has accordingly a certain definite color location.
U.S. Pat. 5,492,869 similarly has an opaque so-called LAS- (Li
2
O—Al
2
O—SiO
2
) glass-ceramic material, with &bgr;-spodumene as the main crystalline phase and 1500 to 4000 ppm CeO
2
, 1500 to 4000 ppm Fe
2
O
3
and 50 to 500 ppm V
2
O
5
as coloring substances and with a color location in the CIE system of x=0.3200−0.3330, y=0.3265-0.3380 and Y=40−70. This patent recommends the use of this type of glass-ceramic material in cooking utensils, baking molds or dishes, cooking vessels and flat cooking surfaces. Its purpose is to provide suitable coloring substances in order to produce glass-ceramic articles containing &bgr;-spodumene mixed crystals and having a pleasing beige color.
U.S. Pat. 4,461,839 discloses a transparent, translucent or opaque glass-ceramic article with colors from black through brown and to red with &bgr;-Quartz mixed crystals as the principal phase whose composition (in percent by weight based on the oxide content) is as follows: SiO
2
, 63.5-69; Al
2
O
3
, 15-25; Li
2
O, 2.5-4; Na
2
O, 0.1-0.6; K
2
O, 0.1-0.6; ZnO, 0-2; BaO, 0-5; TiO
2
, 2.5-6; ZrO
2
, 0-2; As
2
O
3
, 0.4-0.8; Fe
2
O
3
, 0.05-0.2 and free of MgO. The composition also contains 0.3 to 3 percent by weight of at least two of the oxides CaO, CeO
2
, NiO, SnO
2
, V
2
O
5
and WO
3
. When included in the composition, these latter ingredients are present in the following concentration ranges: CaO, 0-2; CeO
2
, 0-3; NiO, 0-1; SnO
2
, 0-1.5; V
2
O
5
, 0-0.3 and WO
3
, 0-1.
This U.S. Patent also discloses opaque glass-ceramic articles having &bgr;-spodumene mixed crystals with gray, brown, almond, beige, yellow to blue colors and compositions whose compositions are identical with the above-mentioned glass-ceramic articles.
Examples for applications of this type of colored glass-ceramic material include chimney or flue viewing glass, and all other articles in flat form, e.g. working panels and cooking panels.
German Patent DE 43 21 373 C2 discloses a glass-ceramic material with high quartz (h-quartz) and/or keatite mixed crystals as the essential crystalline phase. This glass-ceramic material has a water content of less than 0.03 mole/l and an adjustable transmission of more than 10% for a 3 mm thick body in the entire wavelength range between 2700 and 3300 nm.
In all these glass-ceramic molded bodies, especially those which are used as cooking panels, it is disadvantageous that they “show the dirt” or are susceptible to having a conspicuously soiled appearance, because of the phenomenon that cracks necessarily formed during usage in the upper surface of the molded body catch the dirt, overflowing cooking materials and cleaning agent residues.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a cooking panel made from an opaque uniformly colored glass-ceramic material with keatite mixed crystals as the predominant crystalline phase, which makes deposited and/or adhering material, such as dirt and the like, less conspicuous soiling, considering its later service and wear pattern.
Furthermore both ceramicized glass, the so-called green glass, and also already ceramicized glass-ceramic material with a high quartz mixed crystals as the dominant crystalline phase can be used.
This object is attained with a cooking panel made from an opaque uniformly colored glass-ceramic material with keatite mixed crystals as the predominant crystalline phase, which is ceramicized a ceramicizable glass in a color location range in the L*a*b* color system (CIELAB system) with a brightness value L*<85.
This object is also attained with a cooking panel made from an opaque uniformly colored glass-ceramic material with keatite mixed crystals as the predominant crystalline phase, which is made by ceramicizing with a transparent glass-ceramic material having high quartz mixed crystals as the predominant crystalline phase in a color location range in the L*a*b* color system (CIELAB system) with a brightness parameter value L*<85.
This feature provides the advantage that it is possible to color a cooking panel made from glass-ceramic material that has a reduced susceptibility to show the dirt or to have conspicuous soiling according to its later application and wear pattern.
The cooking panel made from opaque glass-ceramic material according to the invention can be colored so that it has a reduced susceptibility to show the dirt or to have conspicuous soiling according to its later application and wear pattern.
Both transparent and also opaque cooking panels, which differ only be additional temperature treatment, can be made form a glass melt. Small imperfections within the transparent glass-ceramic material, e.g. small bubbles or streaks, which would eventually cause interference in the transparent modification, are no longer visible in the opaque state after this additional temperature treatment.
In a preferred embodiment of the invention the color of the cooking panel is between dark gray and light gray. The color shade parameter C* (C*=, {(a*)
2
+(b*)
2
}
1/2
) in the L*C*h color system (CIELAB System) is set or fixed C*≦10. The parameters a* and b* are also color shade parameters.
Cooking panels whose colors are between dark gray and light gray may be made by ceramicizing glasses (green glass) described in European Patent EP 0 220 333 B1 to make a transparent glass-ceramic containing high quartz mixed crystals or by additionally ceramicizing the transparent glass-ceramic material having the following composition (in percent by weight): SiO
2
, 62-68; Al
2
O
3
, 19.5-22.5; Li
2
O, 3.0-4.0; Na
2
O, 0-1.0; K
2
O, 0-1.0; BaO, 1.5-3.5; CaO, 0-1.0; MgO, 0-0.5; ZnO, 0.5-2.5; TiO
2
, 1.5-5.0; ZrO
2
, 0-3.0; MnO
2
, 0-0.4; Fe
2
O
3
, 0-0.2; CoO, 0-0.30; NiO, 0-0.30; V
2
O
5
, 0-0.80; Cr
2
O
3
, 0-0.20; F, 0-0.20; Sb
2
O
3
, 0-2.0 and As
2
O
3
, 0-2.0. Furthermore the total amount Na
2
O+K
2
O in the glass-ceramic material should be between 0.5 and 1.5; the total amount of BaO+CaO, between 1.5 and 4.0; the total amount of TiO
2
and ZrO
2
, between 3.5 and 5.5; and the total amount of Sb
2
O
3
and As
2
O
Cotlear De Witzmann Monica
Dudek Roland
Schoenberger Klaus
Schultheis Bernd
Siebers Friedrich
Morris Terrel
Schott Glas
Striker Michael J.
Vo Hai
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