Patent Description:
Enamel is a substance where a glass glaze is applied onto a surface of a metallic plate. Ordinary enamel is used for cooking appliances, such as microwave ovens and ovens, for example. Cooking appliances, such as electric ovens and gas ovens, for example, are devices that cook food or other items (hereinafter, collectively "food") using a heat source. Contaminants, for example, produced during cooking, are attached to an inner wall of a cavity of a cooking appliance. Accordingly, the inner wall of the cavity needs to be cleaned. Enamel is coated on a surface of the inner wall of the cavity of the cooking appliance, for example, and helps remove contaminants attached to the cooking appliance easily. Among the technologies for readily cleaning the inner wall of a cavity, a process of pyrolysis (thermal decomposition) by which contaminants are burned to ashes at high temperatures is widely known. Enamel compositions including components, such as phosphorus pentoxide (P<NUM>O<NUM>), silicon dioxide (SiO<NUM>), and boron oxide (B<NUM>O<NUM>), for example, are known as an enamel composition to which the process of pyrolysis can be applied.

Even though an enamel composition includes P<NUM>O<NUM>, SiO<NUM>, B<NUM>O<NUM>, and group I-based oxides, contaminants of poultry fat or monster mash may be removed after being soaked in water for a certain period of time. Additionally, as P<NUM>O<NUM>, and group I-based oxides are included in enamel compositions, durability of a calcined enamel composition may decrease.

The document <CIT> describes enamel compositions for cooking appliances.

The enamel composition is defined in independent claim <NUM>.

P<NUM>O<NUM> is a component that forms an alkali phosphate glass structure. P<NUM>O<NUM> is also a glass former that helps addition of a large amount of transition metal oxides into an enamel composition, and helps water to permeate between an enamel surface and a contaminant, such that the contaminant is easily removed. P<NUM>O<NUM> is contained in a range of <NUM> to <NUM> wt%. When more than <NUM> wt% of P<NUM>O<NUM> is included, the enamel composition is hardly glazed, and thermal properties of the enamel composition may be deteriorated. Additionally, when less than <NUM> wt% of P<NUM>O<NUM> is included, an amount of added transition metal oxides is reduced. Thus, a cleaning performance may be deteriorated.

Li<NUM>O, Na<NUM>O, and K<NUM>O improve a cleaning performance of an enamel composition. One or more of Li2O, Na<NUM>O, or K<NUM>O are contained in the enamel composition in a range of <NUM> to <NUM> wt%. When more than <NUM> wt% of the one or more of Li2O, Na<NUM>O, or K<NUM>O is included, the coefficient of thermal expansion of glass may be extremely increased. Accordingly, a coating performance may be deteriorated. When less than <NUM> wt% of the one or more of Li2O, Na<NUM>O, or K<NUM>O is included, a cleaning performance may be deteriorated.

NaF, CaF<NUM>, and AlF<NUM> are components that control surface tension of an enamel coating layer and improve surface properties of the enamel coating layer. One or more of NaF, CaF<NUM>, or AlF<NUM> are included in the enamel composition in a range of <NUM> to <NUM> wt%. When more than <NUM> wt% of the one or more of NaF, CaF<NUM>, or AlF<NUM> is included, thermal properties may be deteriorated. When less than <NUM> wt% of the one or more of NaF, CaF<NUM>, or AlF<NUM> is included, surface properties of the enamel coating layer may be deteriorated.

MgO, BaO, and CaO are components that improve adhesion between the enamel coating layer and a base metal plate. One or more of the MgO, BaO, or CaO are contained in the enamel composition in a range of <NUM> to <NUM> wt%. When more than <NUM> wt% of the one or more of MgO, BaO, or CaO is included, a cleaning performance may be deteriorated. When less than <NUM> wt% of the one or more of MgO, BaO, or CaO is included, adhesion between the enamel coating layer and the metal plate may be reduced. Thus, glass stability may be reduced.

MnO<NUM>, MoO<NUM>, Bi2O<NUM>, and NiO function as a catalyst on a surface of the enamel coating layer. Accordingly, MnO<NUM>, MoO<NUM>, Bi2O<NUM>, and NiO easily disconnect the surface of the enamel coating layer and the contaminant. One or more of MnO<NUM>, MoO<NUM>, Bi<NUM>O<NUM>, or NiO are included in a range of <NUM> to <NUM> wt%. When more than <NUM> wt% of the one or more of the MnO<NUM>, MoO<NUM>, Bi<NUM>O<NUM>, or NiO is included, the enamel composition is hardly glazed and thermal properties of the enamel composition are deteriorated. When less than <NUM> wt% of one or more of the MnO<NUM>, MoO<NUM>, Bi<NUM>O<NUM>, or NiO is included, a catalytic reaction on the surface of the enamel coating layer occurs less frequently. Accordingly, a cleaning performance of enamel may be deteriorated.

Additionally, the enamel composition may further include SiO<NUM> and/or B<NUM>O<NUM>. Silicon dioxide (SiO<NUM>) is a ingredient that forms a glass structure. SiO<NUM> reinforces a skeleton of the glass structure and enhances chemical resistance of the enamel composition. The enamel composition may further include <NUM> or less wt% of SiO<NUM>. When more than <NUM> wt% of SiO<NUM> is included, the ingredient may interfere with the addition of transition metal oxides, thereby deteriorating cleaning performance.

Boron Oxide (B<NUM>O<NUM>) serves as a glass former and helps each ingredient of the enamel composition to melt uniformly. B<NUM>O<NUM> enhances a coating performance by adjusting a coefficient of thermal expansion and fusion flow of the enamel composition. Twenty or less wt% of B<NUM>O<NUM> may be included. When more than <NUM> wt% of B<NUM>O<NUM> is included, the ingredient may interfere with the addition of transition metal oxides, thereby deteriorating a cleaning performance.

Next, the enamel composition may further include <NUM> to <NUM> wt% of aluminum oxide (Al<NUM>O<NUM>); <NUM> to <NUM> wt% of zirconium dioxide (ZrO<NUM>); and <NUM> to <NUM> wt% of one or more of stannous oxide (SnO) or zinc oxide (ZnO). The above-described ingredients of Al<NUM>O<NUM>, ZrO<NUM>, SnO, and ZnO may enhance durability of a weak alkali phosphate glass structure and may improve a hardness of the enamel surface. When more than <NUM> wt% of Al<NUM>O<NUM> is included, melting temperatures may increase and fusion flow may increase, thereby reducing adhesion of the enamel coating layer. When more than <NUM> wt% of ZrO<NUM> is included, or when more than <NUM> wt% of SnO and/or ZnO are included, a glass structure may not be formed. Additionally, when a content of each ingredient is less than a minimum content thereof, durability of the enamel coating layer may be reduced.

The enamel composition further includes <NUM> or less wt% of titanium dioxide (TiO<NUM>) to give a concealment force to a coating layer. When more than <NUM> wt% of TiO<NUM> is included, the ingredient may interfere with the addition of other ingredients, thereby deteriorating a cleaning performance, for example.

Both molybdenum trioxide (MoO<NUM>) and bismuth trioxide (Bi<NUM>O<NUM>) are included in the enamel composition and the enamel composition includes <NUM> or less wt% of any one of MoO<NUM> or Bi<NUM>O<NUM>. The ingredients of Mo and Bi may collide with each other in the phosphate-based enamel composition. Accordingly, a metallic crystal may be disposed in the enamel coating layer.

The enamel composition may have the above-described composition ratio, thereby making it possible to clean contaminants with no need to soak the contaminants in water.

The method <NUM> for preparing an enamel composition according to embodiments may include providing the materials for the above described enamel composition (<NUM>); melting the materials (<NUM>); and quenching the melted materials (<NUM>) to form the enamel composition.

The materials may be sufficiently mixed and then melted. The materials may be melted in a range of temperatures of <NUM> to <NUM>. Additionally, the materials may be melted for one to two hours. Then, the melted materials may be rapidly cooled by a chiller, for example, such as a quenching roller.

An enamel composition according to embodiments may be coated on a surface of a target object. The target object may be all or a portion of a metallic plate, a glass plate, or a cooking appliance, for example. The enamel composition may be coated on an inner surface of a cavity of a cooking appliance, or on an inner surface of a door of a cooking appliance, for example.

Referring to <FIG>, a cooking appliance <NUM> according to an embodiment may include a cavity <NUM> in which a cooking chamber is formed, a door <NUM> that opens and closes the cooking chamber, at least one of heat sources <NUM>, <NUM>, <NUM> that supplies heat to the cooking chamber, a buffer layer <NUM>, <NUM> coated on an inner surface of the cavity <NUM> or an inner surface of the door <NUM>, and a coating layer <NUM>, <NUM> formed by the enamel composition according to embodiments.

The cavity <NUM> may have a cuboid shape, a front surface of which is open. The heat sources <NUM>, <NUM>, <NUM> may include a convection assembly <NUM> that discharges heated air into the cavity <NUM>, an upper heater <NUM> disposed at an upper portion of the cavity <NUM>, and a lower heater <NUM> disposed at a lower portion of the cavity <NUM>. The upper heater <NUM> and the lower heater <NUM> may be provided inside or outside of the cavity <NUM>. The heat sources <NUM>, <NUM>, <NUM> may not include all of the convection assembly <NUM>, the upper heater <NUM>, and the lower heater <NUM>. That is, the heat sources <NUM>, <NUM>, <NUM> may include any one or more of the convection assembly <NUM>, the upper heater <NUM>, and the lower heater <NUM>.

Referring to <FIG>, the enamel composition may be coated on an inner surface of the cavity <NUM> of the cooking appliance <NUM> or on an inner surface of the door <NUM> of the cooking appliance <NUM> through a dry process or a wet process, for example. The cavity <NUM> and the door <NUM> may include a metallic plate. The buffer layer <NUM>, <NUM> may be formed on surfaces of the cavity <NUM> and the door <NUM>, and the coating layer <NUM>, <NUM> formed using the enamel composition according to embodiments may be coated on the buffer layer <NUM>, <NUM>.

The buffer layer <NUM>, <NUM> may be formed into a coating layer having ingredients similar to those of the enamel composition according to embodiments. The buffer layer <NUM>, <NUM> may include a ingredient having a coefficient of thermal expansion matching a coefficient of thermal expansion of a base metal plate and a ingredient having excellent adhesion to the base metal plate.

During the dry process, materials for the enamel composition may be dispersed in an organic binder, the mixed materials and organic binder may be milled in a ball mill, and a glass frit may be manufactured. During the wet process, materials for the enamel composition may be dispersed in water (H<NUM>O) and pigment, the mixed materials, water (H<NUM>O), and pigment may be milled in a ball mill, and a glass frit may be manufactured.

Then, the glass frit prepared according to the dry process or the wet process may be applied onto the buffer layer through a spray process, for example. The applied glass frit may be calcined for <NUM> to <NUM> seconds in a range of temperatures of <NUM> to <NUM>, and may be coated on the inner surface of the cavity <NUM> or the inner surface of the door <NUM> of the cooking appliance <NUM>.

Hereinafter, embodiments will be described with reference to examples.

Examples (embodiments <NUM>-<NUM> are not according to independent claim <NUM>).

An enamel composition having a composition ratio described in the following Table <NUM> was prepared. Raw materials of each ingredient were sufficiently mixed for three hours in a V-mixer. Ammonium dihydrogen phosphate (NH<NUM>H<NUM>PO<NUM>) was used as a raw material of P<NUM>O<NUM>. Sodium carbonate (Na<NUM>CO<NUM>), potassium carbonate (K<NUM>CO<NUM>), and lithium carbonate (Li<NUM>CO<NUM>) were respectively used as raw materials for Na<NUM>O, K<NUM>O, and Li<NUM>O. The mixed materials were sufficiently melted for one and a half hours at <NUM> and were rapidly cooled in a quenching roller. Then a glass cullet was obtained.

For producing frits (powder), initial granularity of the glass cullet obtained through the above-described processes was controlled with the ball mill, was ground for about five hours using a jet mill, and then passed through a <NUM> mesh sieve (ASTM C285-<NUM>) such that a particle diameter of the glass cullet was limited to <NUM> or less.

A low carbon steel sheet having <NUM>×<NUM> and a thickness of <NUM> or less to be used for a sample was prepared. A buffer layer including ingredients in the following Table <NUM> was formed on the sheet. The buffer layer was manufactured in the same way that the above-described enamel composition was manufactured. A method of forming the buffer layer on the sheet is the same as a below-described method of forming an enamel coating layer.

Next, the frits, which were manufactured using the enamel composition according to Embodiments <NUM> to <NUM>, and Comparative Examples <NUM> to <NUM>, were sprayed onto the buffer layer with a corona discharge gun. A voltage of the corona discharge gun was controlled under the conditions of <NUM> kV to <NUM> kV, and an amount of the frits sprayed on the low carbon steel sheet was <NUM>/m<NUM>. The low carbon steel sheet onto which the frits were sprayed was calcined at temperatures of <NUM> to <NUM> for <NUM> to <NUM> seconds to form a coating layer on one surface of the low carbon steel sheet. In this case, the coating layer was formed to have thicknesses of about <NUM> to <NUM>. By doing so, the sample was prepared according to Embodiments <NUM> to <NUM>, and Comparative Examples <NUM> to <NUM>.

Performance of the sample according to the above-described embodiments and comparative examples was evaluated as follows. Table <NUM> shows the results.

One gram of chicken fat was thinly applied as a contaminant onto the surface of the sample, where a metallic substrate (<NUM>×<NUM> (mm)) was coated with the enamel composition, with a brush evenly. Then, the sample to which the contaminant was applied was put into a thermostat and the contaminant was fixed for an hour in a range of temperatures of <NUM> to <NUM>. After the contaminant was fixed, the sample was cooled naturally and was burned for an hour at a temperature of <NUM>. Then, the hardened contaminant was cleaned with a kitchen scrubber for a frying pan, which was wet with room-temperature water, using a force of 3kgf or less. Cleaned portions of the contaminated surface of the sample were uniformalized using a rod having a flat bottom and a diameter of <NUM>.

Cleaning performance of monster mash was evaluated using the same method as the above-described method. Frequency of back and forth cleaning motions made to the samples was measured and the frequency was defined as a frequency of back and forth cleaning motions. Table <NUM> shows indices of evaluation of cleaning performance.

As shown in <FIG>, the embodiments disclosed herein have excellent cleaning performance. The comparative examples were less excellent in cleaning performance than the embodiments as the comparative examples had a composition less optimal than the composition of the embodiments.

Embodiments disclosed herein provide an enamel composition where contaminants, such as poultry fat, may be easily cleaned without being soaked in water. Further, embodiments disclosed herein provide a new enamel composition having a composition ratio that may cause no decrease in durability even though the enamel composition includes P<NUM>O<NUM>, and group I-based oxides.

The enamel composition according to embodiments may include a new phosphate-based glass composition and may be easily cleaned without being soaked in water. The enamel composition according to embodiments may further include additional ingredients, thereby causing no decrease in durability, and a content of some ingredients may be controlled, thereby maximizing cleaning performance. The enamel composition may also be coated onto a buffer layer formed on a base metal plate with no need to consider adhesion to the base metal plate.

Embodiments are described with reference to embodiments illustrated in the drawings. However, the embodiments are not limited to the embodiments and the drawings set forth herein. Further, various modifications may be made by one having ordinary skill in the art within the scope. Furthermore, though not explicitly described during description of the embodiments, effects and predictable effects according to the configuration should be included in the scope.

Embodiments of the disclosure are described herein with reference to cross-section illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of the disclosure. Thus, embodiments of the disclosure should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing.

Any reference in this specification to "one embodiment," "an embodiment," "example embodiment," etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments.

Claim 1:
An enamel composition, comprising:
<NUM> to <NUM> wt% of phosphorus pentoxide (P<NUM>O<NUM>);
<NUM> to <NUM> wt% of one or more of lithium oxide (Li<NUM>O), sodium oxide (Na<NUM>O), or potassium oxide (K<NUM>O);
<NUM> to <NUM> wt% of one or more of sodium fluoride (NaF), calcium fluoride (CaF<NUM>), or aluminum fluoride (AlF<NUM>);
<NUM> to <NUM> wt% of one or more of magnesium oxide (MgO), barium oxide (BaO), or calcium oxide (CaO); and
<NUM> to <NUM> wt% of one or more of manganese dioxide (MnO<NUM>), molybdenum trioxide (MoOs), bismuth oxide (Bi<NUM>O<NUM>), or nickel oxide (NiO),
wherein the enamel composition includes both molybdenum oxide (MoOs) and bismuth oxide (Bi<NUM>O<NUM>), and <NUM> or less wt% of any one of the molybdenum oxide (MoOs) or the bismuth oxide (Bi<NUM>O<NUM>) is included,
and wherein the enamel composition further comprises titanium dioxide (TiO<NUM>), and <NUM> or less wt% of the titanium dioxide (TiO<NUM>) is included.