Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
2001-07-16
2003-01-28
Bell, Mark L. (Department: 1755)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
C501S014000, C501S021000, C501S024000, C501S045000, C501S046000, C501S073000, C501S077000, C501S032000, C428S432000, C428S426000, C428S469000, C428S471000
Reexamination Certificate
active
06511931
ABSTRACT:
FIELD OF INVENTION
The present invention provides an enamel ground coat composition for use on sheet steel. More particularly, the present invention provides a ground coat composition for use in forming an enamel layer on cleaned-only sheet steel that exhibits good spot acid resistance, a satin finish, good bond, and is easy-to-clean.
BACKGROUND OF THE INVENTION
An oven can be one of the most difficult kitchen appliances to clean. Food that splatters onto the interior surfaces of the oven during cooking usually becomes baked-on, making the removal thereof particularly difficult. If the oven is not cleaned often, the amount of baked-on food can build up rapidly, thereby increasing the cleaning difficulty.
There are several known methods for facilitating the removal of baked-on food from the interior surfaces of ovens. The most widely used methods involve pyrolysis or the application of highly alkaline chemical oven cleaners. Although these known methods are relatively effective for removing baked-on food from the interior surfaces of ovens, they present several disadvantages.
Many ovens feature a high-temperature “self-cleaning” cycle during which baked-on foods are pyrolyzed (i.e., decomposed) to carbon ash residue that can be wiped from the interior surfaces of the oven once it cools. To be effective, such pyrolytic heating cycles must maintain the temperature within the oven cavity above about 480° C. (900° F.) for a period of approximately 60 minutes.
One of the disadvantages of using pyrolysis to remove baked-on food from the interior surfaces of ovens is the tendency for the porcelain enamels applied to the interior surfaces of ovens to craze and in some cases flake off when they are repeatedly exposed to such elevated temperatures. Moreover, ovens having pyrolytic heating cycles are more expensive to manufacture than conventional ovens due to the need for extra insulation. Furthermore, such ovens are more expensive to operate than conventional ovens because of the power consumed to generate and maintain the high temperatures during the pyrolytic heating cycle. Such ovens can also present safety concerns because the exterior surfaces of the oven can become quite hot during the pyrolytic heating cycle.
Another method for facilitating the removal of baked-on food from the interior surfaces of ovens involves the use of “catalytic” enamel compositions such as the composition disclosed in Faust, U.S. Pat. No. 4,084,975. Catalytic enamel compositions such as disclosed in Faust that have been fired on the interior surfaces of ovens have a porous texture and contain a substantial quantity of metallic oxides that can catalyze the oxidation of food material that is spilled or spattered on the surface of the enamel. In operation, food material is absorbed into the porous enamel surface where the catalytic metallic oxides catalyze oxidation of the food material at a substantially lower temperature than is required for pyrolytic enamels.
One of the disadvantages of the use of catalytic enamels on the interior surfaces of ovens is that the pores in the enamel can rapidly become saturated and clogged with food material, which significantly diminishes the ease with which the enamel can be cleaned. Furthermore, because the surface of a catalytic enamel coating is porous, it is readily subject to staining.
The other widely used method for removing baked-on food from the interior surfaces of ovens involves the use of highly alkaline chemical oven cleaners. Most oven cleaners of this type include significant quantities of caustics, such as sodium hydroxide and/or potassium hydroxide. While such products are relatively effective in their ability to remove baked-on food from the interior surfaces of ovens, they are highly alkaline (pH typically greater than about 12) and therefore present safety hazards. Fumes from such products, which are best used when the oven is warm, can irritate the eyes and throat and can also cause chemical skin burns. Moreover, the resulting product of the chemical reaction between these cleaners and baked-on food is unpleasant to handle.
There exists a need for a composition that can be applied to the interior surfaces of oven cavities and other articles from which baked-on foods can be removed without the need for pyrolysis or highly alkaline cleaners.
SUMMARY OF INVENTION
The present invention provides a ground coat composition for use in forming an enamel layer on cleaned-only sheet steel that exhibits good spot acid resistance, a matte to satin finish, good bond, and is easy-to-clean (i.e., food residue can be easily removed using water, steam, or humid air). The composition according to the invention comprises a glass component comprising a blend of from about 40% to about 70% by weight of a first glass portion comprising one or more alkali aluminophosphate frits, up to about 30% by weight of a second glass portion comprising one or more zirconia-phosphate frits, and up to about 30% by weight of a third glass portion comprising one or more alkali borosilicate frits. The present invention also provides an article having at least one steel surface coated with an enamel ground coat formed by applying a composition according to the invention to the steel surface and then firing the composition.
The foregoing and other features of the invention are hereinafter more fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the present invention may be employed.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The enamel ground coat composition according to the present invention comprises a glass component comprising a blend of from about 40% to about 70% by weight of a first glass portion comprising one or more alkali aluminophosphate frits, up to about 30% by weight of a second glass portion comprising one or more zirconia-phosphate frits, and up to about 30% by weight of a third glass portion comprising one or more alkali borosilicate frits. Alkali aluminophosphate frits generally comprise by weight from about 15 to about 30% Al
2
O
3
, from about 20% to about 60% P
2
O
5
, and from about 5% to about 30% alkali metal oxides. Zirconium-phosphate frits generally comprise by weight from about 20% to about 40% ZrO
2
, from about 15% to about 40% P
2
O
5
, from about 5% to about 30% alkali metal oxides, and from about 5% to about 40% SiO
2
. Alkali borosilicate frits generally contain from about 5% to about 30% B
2
O
3
, from about 30% to about 70% SiO
2
, and from about 5% to about 35% alkali metal oxides. Some alkali borosilicate frits are known in the art as “no pickle-no nickel” ground coats when the glass also contains Co
2
O
3
, NiO, MnO, Fe
2
O
3
, and the like for adhesion to cleaned-only steel.
The alkali aluminophosphate frits used in the composition according to the invention preferably comprise by weight from about 30% to about 50% P
2
O
5
, from about 20% to about 25% Al
2
O
3
, from about 10% to about 25% Na
2
O, up to about 10% K
2
O, up to about 10% SiO
2
, up to about 5% B
2
O
3
, from about 1% to about 3% NiO, from about 1% to about 2% MnO
2
, from about 1% to about 3% Co
2
O
3
, up to about 3% Li
2
O from about 0.5% to about 1.5% Fe
2
O
3
, from about 1% to about 2% CuO, up to about 1% Sb
2
O
3
, and up to about 0.5% MoO
3
, and up to about 4% ZnO. The CuO, Co
2
O
3
, and NiO are present in the frit to assist in obtaining a good bond to steel. Alkali aluminophosphate frits are generally soft and can be fired at a temperature below about 600° C.
The zirconia-phosphate frits used in the composition according to the invention preferably comprise by weight from about 25% to about 35% ZrO
2
, from about 20% to about 30% P
2
O
5
, from about 10% to about 20% SiO
2
, from about 10% to about 25% Na
2
O, from about 5% to about 10% K
2
O, up to about 8% TiO
2
, up to about 7% BaO, from about 0.05% to about 3% Co
2
O
3
, and up to about 3% NiO. The high ZrO
2
content of t
Bell Mark L.
Bolden Elizabeth A.
Ferro Corporation
Rankin, Hill Porter & Clark LLP
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