Patent Description:
Enamel is a material made by applying a vitreous glaze onto a surface of a metal plate. Common enamel is used in cooking appliances, such as microwaves and ovens. Cooking appliances, such as electric ovens and gas ovens, for example, are appliances that cook food or other items (hereinafter, collectively "food") using a heating source. As contaminants generated during cooking adhere to an inner wall of a cavity of the cooking appliance, the inner wall of the cavity needs to be cleaned. In this case, enamel applied onto the inner wall surface of the cavity of the cooking appliance facilitates removal of contaminants adhered to the cooking appliance. Generally, a pyrolysis method, in which contaminants are burned at high temperature to produce ashes, is known as a technique that easily cleans the inner wall of the cavity, and as a enamel composition to which the pyrolysis method can be applied, an enamel composition containing components, such as phosphorus pentoxide (P<NUM>O<NUM>), silicon dioxide (SiO<NUM>), and boron oxide (B<NUM>O<NUM>), for example, is known.

However, the conventional enamel compositions consume a large amount of energy because the conventional enamel compositions enable cleaning only when heated (pyrolyzed) under a condition of a high temperature of <NUM> to <NUM> for about <NUM> hours. Further, in the case of the conventional enamel compositions, oil contaminants, such as cattle, pig, and poultry oils, cannot be removed easily. Furthermore, enamel compositions should not be denatured and damaged at a high temperature of <NUM> to <NUM>, but the conventional enamel compositions have a problem of degradation of durability at high temperature.

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

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

P<NUM>O<NUM> is a component that functions to form an alkali phosphate glass structure. In addition, P<NUM>O<NUM> is a glass former that facilitates the addition of a large amount of transition metal oxides to the enamel composition and helps water to penetrate between the enamel surface and a contaminant such that the contaminant is able to be easily removed. P<NUM>O<NUM> may be included at <NUM> to <NUM> wt%. When P<NUM>O<NUM> is included at greater than <NUM> wt%, vitrification of the enamel composition may be difficult, and thermal properties of the enamel composition may be degraded. When P<NUM>O<NUM> is included at less than <NUM> wt%, an amount of added transition metal oxides may be decreased, degrading cleanability.

SiO<NUM> is a component that forms a glass structure. SiO<NUM> strengthens a skeleton of the glass structure to enhance chemical resistance of the enamel composition. SiO<NUM> may be included at <NUM> to <NUM> wt%. When SiO<NUM> is included at greater than <NUM> wt%, it may interfere with the addition of transition metal oxides, degrading cleanability. When SiO<NUM> is included at less than <NUM> wt%, the glass composition may break down.

B<NUM>O<NUM> serves as a glass former and is a component that acts to allow each component of the enamel composition to be uniformly melted. In addition, B<NUM>O<NUM> serves to adjust a coefficient of thermal expansion and a fusion flow of the enamel composition to enhance coatability. B<NUM>O<NUM> may be included at <NUM> to <NUM> wt%. When B<NUM>O<NUM> is included at greater than <NUM> wt%, it may interfere with the addition of transition metal oxides to degrade cleanability. When B<NUM>O<NUM> is included at less than <NUM> wt%, the glass composition may break down, or the glass composition may be crystallized.

Li<NUM>O, Na<NUM>O, and K<NUM>O serve to enhance cleanability of the enamel composition. One or more of Li<NUM>O, Na<NUM>O, or K<NUM>O may be included at <NUM> to <NUM> wt% in the enamel composition. When the one or more of the Li<NUM>O, the Na<NUM>O, or the K<NUM>O are included at greater than <NUM> wt%, a coefficient of thermal expansion of the glass may be greatly increased, degrading coatability. When the one or more of the Li<NUM>O, the Na<NUM>O, or the K<NUM>O are included at less than <NUM> wt%, cleanability may be degraded.

NaF, CaF<NUM>, and AlF<NUM> are components that control a surface tension of an enamel coating layer to enhance surface characteristics of the enamel coating layer. One or more of NaF, CaF<NUM>, or AlF<NUM> may be included at <NUM> to <NUM> wt% in the enamel composition. When the one or more of the NaF, the CaF<NUM>, or the AlF<NUM> are included at greater than <NUM> wt%, thermal properties may be degraded. When the one or more of the NaF, the CaF<NUM>, pr AlF<NUM> are included at less than <NUM> wt%, surface characteristics of the enamel coating layer may be degraded.

MgO, BaO, and CaO are components that enhance adhesion between a enamel coating layer and a base steel plate. One or more of MgO, BaO, or CaO may be included at <NUM> to <NUM> wt% in the enamel composition. When the one or more of the MgO, the BaO, or the CaO are included at greater than <NUM> wt%, cleanability may be degraded. When the one or more of the MgO, the BaO, or the CaO are included at less than <NUM> wt%, adhesion between an enamel coating layer and a base steel plate may be decreased, degrading glass stability.

TiO<NUM>, CeO<NUM>, MoO<NUM>, Bi<NUM>O<NUM>, and CuO function as catalysts on a surface of an enamel coating layer. Therefore, TiO<NUM>, CeO<NUM>, MoO<NUM>, Bi<NUM>O<NUM>, and CuO easily cut attachment between the surface of an enamel coating layer and a contaminant. One or more of TiO<NUM>, CeO<NUM>, MoO<NUM>, Bi<NUM>O<NUM>, or CuO may be included at <NUM> to <NUM> wt%. When the one or more of the above-listed components are included at greater than <NUM> wt%, vitrification may be difficult, and thermal properties may be degraded. On the other hand, when one or more of the above-listed components are included at less than <NUM> wt%, a catalytic reaction on the surface of an enamel coating layer may be reduced, degrading cleanability of enamel.

In addition, the enamel composition according to embodiments may further include aluminum oxide (Al<NUM>O<NUM>) at <NUM> to <NUM> wt%; zirconium dioxide (ZrO<NUM>) at <NUM> to <NUM> wt%; and one or more of tin oxide (SnO) or zinc oxide (ZnO) at <NUM> to <NUM> wt%. Al<NUM>O<NUM>, ZrO<NUM>, SnO, and ZnO compensate for low durability of an alkali phosphate glass structure and enhance hardness of the enamel surface. When Al<NUM>O<NUM> is included at greater than <NUM> wt%, a melting temperature and fusion flow may be increased, degrading adhesion of an enamel coating layer. In addition, when ZrO<NUM> is included at greater than <NUM> wt% or SnO and/or ZnO are/is included at greater than <NUM> wt%, a glass structure may not be formed. When each component is included below its lower limit, durability of an enamel coating layer may be degraded.

Additionally, the enamel composition according to embodiments may include the MoO<NUM> at <NUM> to <NUM> wt% and the CuO at <NUM> to <NUM> wt% to maximize cleanability and prevent durability of an enamel coating layer from being degraded. In a case of a phosphate-based enamel composition, especially when both Mo and Cu are included, cleanability is maximized. When MoO<NUM> is included at greater than <NUM> wt% and CuO is included at greater than <NUM> wt%, an addition amount of other components is decreased, and thus, vitrification of enamel may be difficult, and durability may be degraded. On the other hand, when MoO<NUM> is included at less than <NUM> wt% and CuO is included at less than <NUM> wt%, cleanability of enamel may be degraded.

In addition, the enamel composition includes both MoO<NUM> and Bi<NUM>O<NUM>, any one of the MoO<NUM> or the Bi<NUM>O<NUM> may be included at <NUM> wt% or less. Mo and Bi may collide with each other in the phosphate-based enamel composition, and accordingly, metallic crystals may be precipitated on an enamel coating layer. Therefore, both Mo and Bi are included in the enamel composition and any one of the two components may be included at <NUM> wt% or less.

As mentioned above, the conventional enamel compositions consume a large amount of energy because the conventional enamel compositions enable cleaning only when heated (pyrolyzed) under a condition of a high temperature of <NUM> to <NUM> for about <NUM> hours. However, the enamel composition according to embodiments enables removal of sugar contaminants containing sugar even when heated (pyrolyzed) under a condition of a high temperature of <NUM> to <NUM> for less than an hour due to having the above-described novel composition ratio. Accordingly, use of the enamel composition according to embodiments provides an effect of energy saving and a reduction in cleaning time. In addition, the enamel composition according to embodiments exhibits a superior oil contaminant cleaning ability. Accordingly, hygiene of a cooking appliance using the enamel composition according to embodiments may be is easily managed.

A method <NUM> of preparing an enamel composition according to embodiments may include providing the materials for the above-described enamel composition (<NUM>); melting the materials for the enamel composition (<NUM>); and quenching the melted materials for the enamel composition (<NUM>) to form an enamel composition. The materials may be sufficiently blended and then melted. The materials may be melted at <NUM>,<NUM> to <NUM>,<NUM>. In addition, the materials may be melted for <NUM> to <NUM> hours. Afterward, the melted materials may be quenched by a quenching roller using a chiller, for example. As a result, the enamel composition may be formed.

The enamel composition according to embodiments may be applied on one surface of a target object to be coated with the enamel composition. The target object may be a metal plate, a glass plate, or a portion or entirety of a cooking appliance. The enamel composition may be applied onto an inner surface of the cavity of the cooking appliance or an inner surface of the door of the cooking appliance.

Referring to <FIG>, a cooking appliance <NUM> according to embodiments may include a cavity <NUM> that forms a cooking chamber, a door <NUM> that selectively opens and closes the cooking chamber, one or more heating sources <NUM>, <NUM>, and <NUM> that provide heat to the cooking chamber, and a coating layer that is formed of the enamel composition according to embodiments applied onto an inner surface of the cavity <NUM> or an inner surface of the door <NUM>.

The cavity <NUM> may be formed in a hexahedral shape, a front surface of which is open. The heating sources <NUM>, <NUM>, and <NUM> may include a convection assembly <NUM> that discharges heated air into the cavity <NUM>, an upper heater <NUM> disposed at a top of the cavity <NUM>, and a lower heater <NUM> disposed at the bottom of a cavity <NUM>. The upper heater <NUM> and the lower heater <NUM> may be provided inside or outside of the cavity <NUM>. Of course, the heating sources <NUM>, <NUM>, and <NUM> do not necessarily include the convection assembly <NUM>, the upper heater <NUM>, and the lower heater <NUM>. That is, the heating sources <NUM>, <NUM>, and <NUM> may include one or more of the convection assembly <NUM>, the upper heater <NUM>, or the lower heater <NUM>.

Referring to <FIG>, the enamel composition according to embodiments may be applied onto an inner surface of the cavity <NUM> of the cooking appliance <NUM> or an inner surface of the door <NUM> thereof by a dry process or a wet process. The cavity <NUM> and the door <NUM> may be formed of a metal plate, and coating layers <NUM> and <NUM> formed of the enamel composition according to embodiments may be directly formed as a single layer on the metal plate.

According to the dry process, the enamel composition materials may be dispersed in an organic binder, and the enamel composition materials and organic binder, which have been blended, may be subjected to milling in a ball mill to prepare frit. On the other hand, according to the wet process, the enamel composition materials may be dispersed in water (H<NUM>O) and a pigment, and the enamel composition materials, water (H<NUM>O), and pigment, which have been blended, may be subjected to milling in a ball mill to prepare frit.

Afterward, the frit prepared by the dry process or the wet process may be applied onto an inner surface of the cavity <NUM> of the cooking appliance <NUM> or an inner surface of the door <NUM> thereof by a spraying method. The applied frit may be fired at <NUM> to <NUM> for <NUM> to <NUM> seconds and applied on an inner surface of the cavity <NUM> of the cooking appliance <NUM> or an inner surface of the door <NUM> thereof.

Hereinafter, embodiments will be described with respect to examples.

Enamel compositions were prepared in the compositions shown in Table <NUM> below. Example <NUM> is according to independent claim <NUM>, whereas examples <NUM> and <NUM>-<NUM> are not according to independent claim <NUM>. Raw materials of components were sufficiently blended in a V-mixer for <NUM> hours. In this case, ammonium dihydrogen phosphate (NH<NUM>H<NUM>PO<NUM>) was used as a raw material of phosphorus pentoxide (P<NUM>O<NUM>), and sodium carbonate (Na<NUM>CO<NUM>), potassium carbonate (K<NUM>CO<NUM>), and lithium carbonate (Li<NUM>CO<NUM>) were used, respectively, as raw materials of Na<NUM>O, K<NUM>O, and Li<NUM>O. The blended material was sufficiently melted at <NUM>,<NUM> for one and a half hours and then quenched in a quenching roller to obtain cullet.

An initial particle size of the cullet thus obtained by the above process was controlled using a grinder (ball mill), and then, the resulting cullet was ground using a jet mill for about <NUM> hours and passed through a <NUM> mesh sieve (ASTM C285-<NUM>) to control the particle diameter thereof to be <NUM> or less, thereby preparing frit (a powder).

Each of the frits prepared using the enamel compositions according to Examples <NUM> to <NUM> and Comparative Examples <NUM> and <NUM> was sprayed on a low carbon steel sheet having an area of <NUM> (mm)×<NUM> (mm) and a thickness of <NUM> (mm) or less using a corona discharge gun. In this case, a voltage of the discharge gun was controlled under a condition within the range of <NUM> kV to <NUM> kV, and an amount of the frit sprayed on the low carbon steel sheet was <NUM>/m<NUM>. The low carbon steel on which the frit had been sprayed was fired at <NUM> to <NUM> for <NUM> to <NUM> seconds to form a coating layer on one surface of the low carbon steel. In this case, the coating layer was formed to have a thickness of about <NUM> to <NUM>. As a result, specimens according to Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM> were manufactured.

The specimens according to Examples and Comparative Examples were evaluated for abilities as described below, and results thereof are shown in Table <NUM>.

<NUM> of chicken oil as a contaminant was uniformly and thinly spread on a surface of the specimen, in which a metal substrate (<NUM> (mm)×<NUM> (mm)) had been coated with the enamel composition, with a brush, and the specimen to which the contaminant had been applied was placed in a thermostat at <NUM> to <NUM> for an hour to solidify the contaminant. After solidification of the contaminant, the resulting specimen was cooled naturally, and the contaminant was burned at <NUM> for an hour. Afterward, the hardened contaminant was subjected to back and forth (one round trip) wiping at a force of <NUM> kgf or less with a scouring pad for a frying pan which had been soaked with room-temperature water. A portion wiped on the contaminated specimen surface was uniformalized using a stick whose bottom has a diameter of <NUM> and is flat.

In addition, cleanability against monster mash was measured by the same method as described above. In this case, a number of round trips of wiping the specimen was measured and defined as the number of round trips for cleaning, and evaluation standards for cleanability are shown in Table <NUM>.

The specimens which had undergone the cleaning test according to the above item <NUM> were evaluated for durability, such as heat resistance and chemical resistance. The durability of each specimen was evaluated by determining a staining phenomenon. The staining phenomenon was determined by observing the surface of each specimen and quantifying a ratio of the area of the residue or stain to the entire surface area. Evaluation standards for the staining phenomenon are the same as shown in Table <NUM>.

As shown in Table <NUM>, it can be seen that Examples according to embodiments exhibited not only excellent cleanability but also excellent durability. On the other hand, it can be seen that Comparative Examples exhibited not only degraded cleanability due to not having an optimal composition ratio but also highly unsatisfactory durability due to an unstable glass composition, as compared with Examples according to embodiments.

The enamel composition according to according to embodiments may dramatically reduce a heating time in comparison to a conventional enamel composition. Accordingly, the enamel composition according to embodiments may save energy consumed in cleaning due to the shortened heating time.

Further, the enamel composition according to embodiments may allow especially oil contaminants to be completely removed. Accordingly, the enamel composition according to embodiments may enhance hygiene of a cooking appliance.

Furthermore, the enamel composition according to embodiments may exhibit enhanced adhesion to a base steel plate and also ensure excellent cleanability due to a special component ratio. Also, as the enamel composition according to embodiments may include a phosphate-based component in an optimal composition ratio, it can exhibit high heat resistance and high chemical durability as well as excellent cleanability. Additionally, as the enamel composition according to embodiments may be directly applied as a single layer onto a base steel plate in the absence of an intermediate buffer layer, the layer may be simply formed.

Embodiments disclosed herein provide a novel enamel composition which allows a heating time required for cleaning to be shortened. Embodiments disclosed herein provide a novel enamel composition which allows oil contaminants to be completely removed. Further, embodiments disclosed herein provide a novel enamel composition which is excellent in not only cleanability but also durability, such as heat resistance and chemical resistance.

Although embodiments have been described above with reference to the illustrated drawings, it is obvious that embodiments are not limited to the embodiments and drawings disclosed herein, and various modifications may be made by those skilled in the art within the scope. In addition, even when the effect of the configuration is not explicitly described while the above-described embodiments are described, it is obvious that the effect predictable by the corresponding configuration should also be recognized.

Embodiments are described herein with reference to cross-section illustrations that are schematic illustrations of idealized embodiments (and intermediate structures). Thus, embodiments 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:
phosphorus pentoxide (P<NUM>O<NUM>) at <NUM> to <NUM> wt%;
silicon dioxide (SiO<NUM>) at <NUM> to <NUM> wt%;
boron oxide (B<NUM>O<NUM>) at <NUM> to <NUM> wt%;
one or more of lithium oxide (Li<NUM>O), sodium oxide (Na<NUM>O), or potassium oxide (K<NUM>O) at <NUM> to <NUM> wt%;
one or more of sodium fluoride (NaF), calcium fluoride (CaF<NUM>), or aluminum fluoride (AlF<NUM>) at <NUM> to <NUM> wt%;
one or more of magnesium oxide (MgO), barium oxide (BaO), or calcium oxide (CaO) at <NUM> to <NUM> wt%; and
one or more of titanium dioxide (TiO<NUM>), cerium dioxide (CeO<NUM>), molybdenum trioxide (MoOs), bismuth oxide (Bi<NUM>O<NUM>), or copper oxide (CuO) at <NUM> to <NUM> wt%,
wherein the enamel composition includes both MoO<NUM> and Bi<NUM>O<NUM>, and any one of the MoO<NUM> or the Bi<NUM>O<NUM> is included at <NUM> wt% or less.