Patent Publication Number: US-2021163343-A1

Title: Enamel composition, manufacturing method therefor, and cooking utensils

Description:
TECHNICAL FIELD 
     Disclosed herein is an enamel composition, a preparation method therefor, and a cooking appliance using the same which can be cleaned without being soaked in water. 
     BACKGROUND ART 
     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. The inner wall of the cavity can be easily cleaned through a pyrolysis where contaminants are burned to ashes at high temperatures, or with a strong alkaline detergent. Further, the inner wall of the cavity, coated with an enamel composition including phosphorus pentoxide (P 2 O 5 ), silicon dioxide (SiO 2 ), boron trioxide (B 2 O 3 ), and Group I oxides, can be easily cleaned without a high-temperature heating process. 
     Although the enamel composition includes P 2 O 5 , SiO 2 , B 2 O 3 , and Group I oxides, the enamel composition needs to be soaked in water for a certain period of time such that a contaminant such as poultry fat or monster mash is cleaned from the enamel composition. 
     When the enamel composition includes P 2 O 5  and Group I oxides, durability of a calcinated enamel composition can be degraded. 
     Additionally, when the enamel composition includes P 2 O 5 -B 2 O 3 , glass crystallization tendencies can be increased during a calcination process, causing degradation in color quality and luminance. 
     SUMMARY 
     Technical Problems 
     The present disclosure is directed to an enamel composition from which a contaminant such as poultry fat or monster mash may be cleaned without being soaked in water. 
     The present disclosure is also directed to an enamel composition that may have a new composition ratio not to cause degradation in durability although the enamel composition includes P 2 O 5  and Group I oxides. 
     The present disclosure is also directed to an enamel composition that may not cause glass crystallization during a calcination process although the enamel composition includes P 2 O 5 —B 2 O 3 . 
     TECHNICAL SOLUTIONS 
     According to embodiments, an enamel composition, from which a contaminant such as poultry fat or monster mash is cleaned without being soaked in water, may comprise 20 wt % to 60 wt % of phosphorus pentoxide (P 2 O 5 ), 1 wt % to 20 wt % of silicon dioxide (SiO 2 ), 1 wt % to 30 wt % of boron trioxide (B 2 O 3 ), 10 wt % to 30 wt % of at least one of lithium oxide (Li 2 O), sodium oxide (Na 2 O), and potassium oxide (K 2 O), and 10 wt % to 40 wt % of at least one from a group consisting of post-transition metal oxides and transition metal oxides. 
     According to embodiments, an enamel composition, which has a new composition ratio not to cause degradation in durability although the enamel composition comprises P 2 O 5  and Group I oxides, may comprise at least one of Group II oxides including magnesium oxide (MgO), barium oxide (BaO) and calcium oxide (CaO), 10 wt % to 30 wt % of aluminum oxide (Al 2 O 3 ), 1 wt % to 5 wt % of zirconium dioxide (ZrO 2 ) and 1 wt % to 5 wt % of tin oxide (SnO). 
     According to embodiments, for an enamel composition which causes no glass crystallization during a calcination process although the enamel composition comprises P 2 O 5 —B 2 O 3 , an amount of P 2 O 5  and B 2 O 3  may satisfy a formula below. 
       1≤P 2 O 5 (wt %)/B 2 O 3 (wt %)≤10   [Formula]
 
     Advantageous Effects 
     The enamel composition may comprise P 2 O 5 ; SiO 2 ; B 2 O 3 ; at least one of Li 2 O, Na 2 O, K 2 O; and at least one from a group consisting of post-transition metal oxides and transition metal oxides. Accordingly, the enamel composition may have a new component system at a unique ratio, and may be cleaned without being soaked in water. 
     Additionally, for the enamel composition, glass frits may comprise at least one of Group II oxides including magnesium oxide (MgO), barium oxide (BaO) and calcium oxide (CaO), and 10 wt % to 30 wt % of aluminum oxide (Al 2 O 3 ), 1 wt % to 5 wt % of zirconium dioxide (ZrO 2 ) and 1 wt % to 5 wt % of tin oxide (SnO). Accordingly, the enamel composition may not cause degradation in durability. 
     Further, the enamel composition may have an optimal ratio of P 2 O 5  to B 2 O 3 . Accordingly, the enamel composition causes no glass crystallization during a calcination process and may ensure excellent color quality and luminance. 
    
    
     
       BRIEF DESCRIPTION OF DRAWING 
         FIG. 1  is a front view showing an example cooking appliance. 
     
    
    
     BEST MODE 
     The above-described aspects, features and advantages are specifically described with reference to the accompanying drawings hereunder such that one having ordinary skill in the art to which the present disclosure pertains may easily implement the technical spirit of the disclosure. In description of the disclosure, detailed description of known technologies in relation to the disclosure is omitted if it is deemed to make the gist of the disclosure unnecessarily vague. Below, preferred embodiments according to the disclosure are specifically described. 
     The embodiments set forth herein may be implemented in various different forms, and should not be construed as being limited to the present disclosure. Rather, these embodiments are provided as examples so that the disclosure will be thorough and complete and will fully convey the subject matter to one having ordinary skill in the art to which the disclosure pertains. Below, an enamel composition, a preparation method therefor, and a cooking appliance using the same, which may be cleaned without being soaked in water, are described specifically. 
     Enamel Composition 
     An enamel composition according to embodiments may comprise 20 wt % to 60 wt % of phosphorus pentoxide (P 2 O 5 ); 1 wt % to 20 wt % of silicon dioxide (SiO 2 ); 1 wt % to 30 wt % of boron trioxide (B 2 O 3 ); 10 wt % to 30 wt % of at least one of lithium oxide (Li 2 O), sodium oxide (Na 2 O) and potassium oxide (K 2 O); and 10 wt % to 40 wt % of at least one from a group consisting of post-transition metal oxides and transition metal oxides. 
     In the disclosure, the post-transition metal oxides may denote a compound in which metallic elements such as aluminum (Al), gallium (Ga), indium (In), tin (Sn), thallium (Tl), plumbum (Pb), bismuth (Bi) or polonium (Po) in the p-block of the periodic table are combined with oxygen. The post-transition metal oxides and the transition metal oxides usually serve as a catalyst thanks to their structural stability. 
     P 2 O 5  may form an alkali phosphate glass structure. P 2 O 5  may serve as a glass former that helps addition of a large amount of transition metal oxides into the enamel composition and helps water to permeate between an enamel surface and a contaminant, such that the contaminant is easily removed. The component P 2 O 5  may be included in a range of 20 to 60 wt %. When more than 60 wt % of P 2 O 5  is included, the enamel composition is hardly glazed, and thermal properties of the enamel composition may be degraded. When less than 20 wt % of P 2 O 5  is included, an amount of added transition metal oxides may be reduced. Accordingly, P 2 O 5  may not properly serve as a glass former and may not properly remove contaminants. 
     SiO 2 , which is a component for forming a glass structure, may strengthen a skeleton of the glass structure and improve chemical resistance of the enamel composition. The component SiO 2  may be included in a range of 1 wt % to 20 wt %. When more than 20 wt % of SiO 2  is included, the component may interfere with an addition of a transition metal oxide, causing deterioration in a cleaning performance of the enamel composition. When less than 1 wt % of SiO 2  is included, glass composition may be collapsed. 
     B 2 O 3  may serve as a glass former and help each component of the enamel composition to melt uniformly, thereby making it possible to prevent crystallization of a glass composition. B 2 O 3  may also adjust a coefficient of thermal expansion and a fusion flow of the enamel composition to improve a coating performance of the enamel composition. B 2 O 3  may be included in a range of 1 wt % to 30 wt %. When more than 30 wt % of B 2 O 3  is included, the component may interfere with an addition of a transition metal oxide, causing deterioration in the cleaning performance of the enamel composition. When less than 1 wt % of B 2 O 3  is included, glass composition may be collapsed, or crystallization of a glass composition may occur. 
     Li 2 O, Na 2 O, and K 2 O, which are Group I oxides, may be include in the enamel composition to improve the cleaning performance of the enamel composition along with P 2 O 5 . At least one of Li 2 O, Na 2 O, and K 2 O may be included in a range of 10 wt % to 30 wt %. When more than 30 wt % of at least one of Li 2 O, Na 2 O, and K 2 O is included, the thermal properties of the enamel composition may be degraded. When less than 10 wt % of at least one of Li 2 O, Na 2 O, and K 2 O is included, the cleaning performance of the enamel composition may be deteriorated. 
     Post-transition metal oxides and transition metal oxides may facilitate catalysis on an enamel surface and may easily disconnect a contaminant from the enamel surface. At least one from the group consisting of post-transition metal oxides and transition metal oxides may be included in a range of 10 wt % to 40 wt %. When more than 40 wt % of at least one from the group consisting of post-transition metal oxides and transition metal oxides is included, the enamel composition may be hardly glazed and the thermal properties of the enamel composition may be degraded. When less than 10 wt % of at least one from the group consisting of post-transition metal oxides and transition metal oxides is included, a level of catalysis on the enamel surface may be reduced, causing deterioration in the cleaning performance. 
     The post-transition metal oxide may comprise bismuth oxide (Bi 2 O 3 ) Additionally, the transition metal oxide may comprise at least one of titanium oxide (TiO 2 ), vanadium oxide (V 2 O 5 ), manganese oxide (MnO), iron oxide (Fe 2 O 3 ), copper oxide (CuO), zinc oxide (ZnO), tungsten trioxide (WO 3 ), and molybdenum trioxide (MoO 3 ) The transition metal oxide ZnO may be included in a range of 5 wt % to 20 wt %, the transition metal oxide MoO 3  may be included in a range of 1 wt % to 20 wt %, and the post-transition metal oxide Bi 2 O 3  may be included in a range of 10 wt % to 20 wt %. 
     ZnO may improve the cleaning performance and control a surface tension, thereby making it possible to improve surface characteristics of an enamel coating layer. The component ZnO may be included in a range of 5 wt % to 20 wt %. When more than 20 wt % of ZnO is included, a fusion flow may be reduced. When less than 5 wt % of ZnO is included, the surface characteristics of the enamel coating layer may be degraded, causing deterioration in the coating performance. 
     MoO 3  may facilitate catalysis on the enamel surface and provide the effect of cleaning. MoO 3 , which is a transition metal oxide having a valence of 6, may trigger catalysis excellently and improve the cleaning performance. The component MoO 3  may be included in a range of 1 wt % to 20 wt %. When more than 20 wt % of MoO 3  is included, the thermal properties may be degraded. When less than 1 wt % of MoO 3  is included, the cleaning performance may be deteriorated. 
     Bi 2 O 3  may facilitate catalysis on the enamel surface and provide the effect of cleaning. Additionally, Bi 2 O 3  may improve chemical resistance and thermal resistance of enamel. The component Bi 2 O 3  may be included in a range of 10 wt % to 20 wt %. When more than 20 wt % of B 2 O 3  is included, a level of catalysis may be reduced, and the cleaning performance may be deteriorated. When less than 10 wt % of B 2 O 3  is included, chemical resistance and thermal resistance of enamel may be degraded. 
     The enamel composition according to embodiments may comprise at least one of magnesium oxide (MgO), barium oxide (BaO), and calcium oxide (CaO) that are Group Iloxides. MgO, BaO, and CaO, which are Group Iloxides, may improve adhesion between a calcinated enamel composition and a steel sheet. At least one of MgO, BaO, and CaO may be included in a range of 1 wt % to 30 wt %. When more than 30 wt % of at least one of MgO, BaO, and CaO is included, the cleaning performance may be deteriorated. When less than 1 wt % of at least one of MgO, BaO, and CaO is included, adhesion between a calcinated enamel composition and a steel sheet may be reduced, resulting in a lower stability of glass. 
     The enamel composition according to embodiments may comprise at least one of sodium fluoride (NaF), calcium fluoride (CaF 2 ), and aluminum fluoride (AlF 3 ). The components NaF, CaF 2 , and AlF 3  may control a surface tension of enamel and improve surface characteristics of an enamel coating layer. At least one of the components NaF, CaF 2 , and AlF 3  may be included in a range of 1 wt % to 5 wt %. When more than 5 wt % of at least one of the components NaF, CaF 2 , and AlF 3  is included, the thermal properties may be degraded. When less than 1 wt % of at least one of the components NaF, CaF 2 , and AlF 3  is included, the surface characteristics of the enamel coating layer may be degraded, and stability of glass may be reduced. 
     The enamel composition according to embodiments may comprise at least one of aluminum oxide (Al 2 O 3 ), zirconium dioxide (ZrO 2 ), and tin oxide (SnO). The component Al 2 O 3  may be included in a range of 10 wt % to 30 wt %, the component ZrO 2  may be included in a range of 1 wt % to 5 wt %, and the component SnO may be included in a range of 1 wt % to 5 wt %. Al 2 O 3 , ZrO 2 , and SnO may improve durability of an alkali phosphate glass structure and hardness of the enamel surface. When more than 30 wt % of Al 2 O 3  is included, adhesion of the enamel composition may be reduced due to a high melting temperature and fusion flow. When more than 5 wt % of ZrO 2  or SnO is included, a glass structure may hardly be formed. When less than 10 wt % of Al 2 O 3  is included, or when less than 1 wt % of ZrO 2  or SnO is included, durability of enamel may be reduced. 
     When P 2 O 5  and B 2 O 3  included in the enamel composition according to embodiments satisfy the following formula, calcination reliability in relation to glass crystallization tendencies may be ensured. 
       1≤P 2 O 5 (wt %)/B 2 O 3 (wt %)≤10   [Formula]
 
     The components P 2 O 5  and B 2 O 3  may control a surface tension and a coefficient of thermal expansion of a calcinated enamel composition. Accordingly, the components P 2 O 5  and B 2 O 3  may affect calcination reliability related to glass crystallization tendencies. When a greater amount of P 2 O 5  is included, a large amount of transition metal oxides may be easily added. However, glass crystallization tendencies of the enamel composition may increase. Accordingly, an optimal ratio has to be ensured between P 2 O 5  and B 2 O 3 . Thus, in the enamel composition, P 2 O 5  (wt %)/B 2 O 3  (wt %) may be 1 to 10. 
     The enamel composition, for example, may have a coefficient of thermal expansion (CTE) of 70 to 90×10 −7 /° C. within a range of 50° C. to 350° C. and a glass strain temperature of a range of 520° C. to 720° C., after calcination. The coefficient of thermal expansion (CTE) may be within a range of 70 to 90×10 −7 /° C. in the range of 50° C. to 350° C. Accordingly, as adhesion of the enamel composition is increased, a glass structure may become more reliable. As the glass strain temperature is within the range of 520° C. to 720° C., the enamel composition may form a structure that is not deformed even at high temperatures. 
     Preparation Method for Enamel Composition 
     A preparation method for an enamel composition according to embodiments may comprise supplying materials for an enamel composition including 20 wt % to 60 wt % of phosphorus pentoxide (P 2 O 5 ), 1 wt % to 20 wt % of silicon dioxide (SiO 2 ), 1 wt % to 30 wt % of boron trioxide (B 2 O 3 ), and 10 wt % to 30 wt % of at least one of lithium oxide (Li 2 O), sodium oxide (Na 2 O), and potassium oxide (K 2 O), and 10 wt % to 40 wt % of at least one from a group consisting of post-transition metal oxides and transition metal oxides; melting the materials for an enamel composition; and cooling the melted materials in a quenching roller and forming an enamel composition. 
     The enamel composition may comprise at least one of magnesium oxide (MgO), barium oxide (BaO), and calcium oxide (CaO). Additionally, the enamel composition may further comprise at least one of sodium fluoride (NaF), calcium fluoride (CaF 2 ), and aluminum fluoride (AlF 3 ). Further, the enamel composition may further comprise 10 wt % to 30 wt % of aluminum oxide (Al 2 O 3 ), 1 wt % to 5 wt % of zirconium dioxide (ZrO 2 ), and 1 wt % to 5wt % of tin oxide (SnO). 
     Ammonium dihydrogen phosphate (NH 4 H 2 PO 4 ) may be used as a raw material for P 2 O 5 , and sodium carbonate (Na 2 CO 3 ), potassium carbonate (K 2 CO 3 ), lithium carbonate (Li 2 CO 3 ), barium carbonate (BaCO 3 ), and calcium carbonate (CaCO 3 ) may be respectively used as a raw material for Na 2 O, K 2 O, Li 2 O, Ba), and CaO, but not be limited. 
     After sufficiently mixed, the materials for an enamel composition may be melted. For example, the materials for an enamel composition may be melted at 1200° C. to 1400° C. for one to two hours. 
     Then the melted materials for an enamel composition may be rapidly cooled in a quenching roller, using a chiller and the like. Thus, the enamel composition may be prepared. 
     Cooking Appliance 
     The enamel composition according to embodiments may be coated on one surface of an object to be coated with the enamel composition. The object may comprise a metal plate, a glass plate, and all or part of a cooking appliance. For example, an inner surface of a cavity or a door of a cooking appliance may be coated with the enamel composition. 
     Referring to  FIG. 1 , a cooking appliance  1  may comprise a cavity  11  in which a cooking chamber  12  is formed, a door  14  that opens and closes the cooking chamber  12 , and at least one heat source  13 , 15 , 16  that supplies heat for cooking food in the cooking chamber  12 . The cavity  11  may have a cuboid shape, a front surface of which is open. The heat source  13 ,  15 ,  16  may comprise a convection assembly  13  that discharges heated air into the cavity  11 , an upper heater  15  disposed at an upper portion of the cavity  11 , and a lower heater  16  disposed at a lower portion of the cavity  11 . The upper heater  15  and the lower heater  16  may be provided inside or outside of the cavity  11 . The heat source  13 ,  15 ,  16  may not necessarily include all the convection assembly  13 , the upper heater  15 , and the lower heater  16 . That is, the heat source  13 ,  15 ,  16  may include at least one of the convection assembly  13 , the upper heater  15 , and the lower heater  16 . 
     The enamel composition according to embodiments may be coated on an inner surface of the cavity  11  or the door  14  of the cooking appliance  1  in a dry process or a wet process. 
     During the dry process, the materials for an 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, the materials for an enamel composition may be dispersed in water (H 2 O) and pigment, the mixed materials, water (H 2 O) and pigment may be milled in a ball mill, and a glass frit may be manufactured. 
     Then the glass frit prepared in the dry process or the wet process may be applied onto the inner surface of the cavity  11  or the door  14  of the cooking appliance  1  through a spray process, for example. The applied glass frit may be calcinated for 100 to 450 seconds at 600° C. to 900° C., and may be coated on the inner surface of the cavity  11  or the door  14  of the cooking appliance  1 . 
     Hereinafter, embodiments will be described with reference to examples. 
     EXAMPLE 
     Preparation for Enamel Composition 
     An enamel composition having a composition ratio in table 1 below was prepared. A raw material for each component was sufficiently mixed for three hours in a V-mixer. Ammonium dihydrogen phosphate (NH 4 H 2 PO 4 ) was used as a raw material for P 2 O 5 , and sodium carbonate (Na 2 CO 3 ), potassium carbonate (K 2 CO 3 ), lithium carbonate (Li 2 CO 3 ), barium carbonate (BaCO 3 ), and calcium carbonate (CaCO 3 ) were respectively used as a raw material for Na 2 O, K 2 O, Li 2 O, BaO, and CaO. The remaining materials are shown in table 1. The mixed materials were sufficiently melted for one and a half hours at 1300° C. and were rapidly cooled in a quenching roller. Then a glass cullet was obtained. 
     Initial granularity of the glass cullet obtained in the above-described processes was controlled with a grinder (a ball mill), and the glass cullet was ground for about five hours using a jet mill. Then the ground glass cullet was allowed to pass through a 325 mesh sieve (ASTM C285-88) such that a particle diameter of the glass cullet was limited to 45 μm or less. As a result, frits (powder) were prepared. The frits were sprayed onto a low carbon steel sheet with a width of 200 mm, a height of 200 mm, and a thickness of 1 mm or less, using a corona discharge gun. A voltage of the discharge gun was controlled under the conditions of 40 kV to 100 kV, and an amount of the frits sprayed on the low carbon steel sheet was 300 g/m 2 . The low carbon steel sheet, onto which the frits were sprayed, was calcinated at 830° C. to 870° C. for 300 to 450 seconds to form a coating layer on one surface of the low carbon steel sheet. The coating layer was formed to have thicknesses of about 80 μm to 250 μm. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Component 
                 Embodiment 
                 Comparative example 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 (wt %) 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 1 
                 2 
                 3 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 P 2 O 5   
                 24.26 
                 22.34 
                 30.82 
                 22.65 
                 22.69 
                 24.12 
                 23.22 
                 22.34 
                 22.34 
                 36.82 
               
               
                 SiO 2   
                 14.12 
                 14.56 
                 7.92 
                 10.52 
                 10.51 
                 9.23 
                 10.32 
                 26.56 
                 46.56 
                 7.92 
               
               
                 B 2 O 3   
                 8.88 
                 12.29 
                 6.79 
                 10.23 
                 10.22 
                 10.14 
                 6.22 
                 12.29 
                 11.46 
                 0.79 
               
               
                 Li 2 O 
                 0.86 
                 0.88 
                 0.00 
                 0.00 
                 0.00 
                 2.11 
                 2.11 
                 0.88 
                 0.88 
                 0.00 
               
               
                 Na 2 O 
                 4.52 
                 4.21 
                 2.73 
                 4.02 
                 5.78 
                 0.00 
                 1.66 
                 4.21 
                 4.21 
                 2.73 
               
               
                 K 2 O 
                 10.15 
                 10.48 
                 10.77 
                 6.56 
                 6.65 
                 10.22 
                 10.32 
                 10.48 
                 2.48 
                 10.77 
               
               
                 TiO 2   
                 0.87 
                 0.89 
                 0.00 
                 0.26 
                 0.58 
                 0.00 
                 1.32 
                 0.89 
                 3.89 
                 1.87 
               
               
                 V 2 O 5   
                 0.00 
                 0.00 
                 0.00 
                 0.64 
                 0.00 
                 1.33 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
               
               
                 MnO 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 1.32 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
               
               
                 Fe 2 O 3   
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 3.32 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
               
               
                 CuO 
                 0.00 
                 0.00 
                 0.00 
                 0.18 
                 0.00 
                 1.23 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
               
               
                 WO 3   
                 0.00 
                 0.00 
                 0.00 
                 0.89 
                 5.15 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
               
               
                 Bi 2 O 3   
                 0.00 
                 0.00 
                 1.87 
                 11.24 
                 6.25 
                 5.26 
                 15.21 
                 0.00 
                 0.00 
                 0.00 
               
               
                 ZnO 
                 5.76 
                 5.02 
                 5.74 
                 5.69 
                 6.25 
                 5.65 
                 5.02 
                 5.02 
                 5.02 
                 5.74 
               
               
                 MoO 3   
                 9.66 
                 13.40 
                 13.96 
                 11.22 
                 8.25 
                 10.31 
                 8.55 
                 1.40 
                 1.40 
                 13.96 
               
               
                 MgO 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 1.02 
                 0.00 
                 1.23 
                 0.00 
                 0.00 
                 0.00 
               
               
                 BaO 
                 0.00 
                 1.02 
                 1.23 
                 1.03 
                 0.00 
                 0.00 
                 0.00 
                 1.02 
                 0.00 
                 1.23 
               
               
                 CaO 
                 1.72 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 1.14 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
               
               
                 NaF 
                 0.00 
                 1.76 
                 1.12 
                 1.65 
                 0.00 
                 1.25 
                 0.00 
                 1.76 
                 1.76 
                 1.12 
               
               
                 CaF 2   
                 1.7 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 1.14 
                 0.00 
                 0.00 
                 0.00 
               
               
                 AlF 3   
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 1.23 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
               
               
                 Al 2 O 3   
                 11.53 
                 10.79 
                 14.09 
                 10.54 
                 10.56 
                 11.32 
                 10.56 
                 10.79 
                 0.00 
                 14.09 
               
               
                 ZrO 2   
                 4.1 
                 1.24 
                 1.75 
                 1.45 
                 2.32 
                 1.26 
                 1.47 
                 1.24 
                 0.00 
                 1.75 
               
               
                 SnO 
                 1.87 
                 1.12 
                 1.21 
                 1.23 
                 1.22 
                 2.11 
                 1.65 
                 1.12 
                 0.00 
                 1.21 
               
               
                   
               
            
           
         
       
     
     Preparation for Enamel Composition Sample 
     About four grams of 10 enamel compositions according to embodiments 1 to 7 and comparative examples 1 to 3 were put on a low carbon steel sheet with a width of 100 mm, a height of 100 mm, and a thickness of 1 mm, and was coated on the low carbon steel sheet simply by hand. Then the enamel composition samples were calcinated at about 700° C. for 400 seconds. Finally, a total of 10 enamel compositions samples were obtained. 
     EXPERIMENTAL EXAMPLE 
     Performance of the enamel composition samples prepared in the embodiments and comparative examples was evaluated as follows. Table 3 shows results of the evaluation. 
     1. Evaluation of Cleaning Performance 
     To evaluate a cleaning performance of the enamel composition samples, lg of chicken fat as a contaminant was evenly thinly applied using a brush on a surface of the samples, where a metallic substrate (100×100 mm) was coated with the enamel compositions, and then a specimen, to which the contaminant was applied, was put into a thermostat at 250° C. to 290° C. for an hour to fix the contaminant. 
     After the fixation, the specimen was naturally cooled and a hardness of the contaminant was checked. Then the hardened chicken fat was cleaned with a kitchen scrubber for a frying pan wet with room-temperature water, using a force of 3 kgf or less. A portion on the contaminated surface of the samples, cleaned using a rod having a flat bottom and a diameter of 5 cm, was uniformized. Frequency of back and forth cleaning motions was measured and the frequency was defined as frequency of back and forth cleaning motions. Table 2 shows indices of evaluation of the cleaning performance. 
     Additionally, a cleaning performance against monster mash was evaluated according to the same method as the method described above. 
     
       
         
           
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Frequency of back and 
                   
               
               
                 forth cleaning motion 
                 Level 
               
               
                   
               
             
            
               
                  1~10 
                 LV. 5 
               
               
                 10~15 
                 LV. 4 
               
               
                 16~25 
                 LV. 3 
               
               
                 26~50 
                 LV. 2 
               
               
                 51~ 
                 LV. 1 
               
               
                   
               
            
           
         
       
     
     2. Evaluation of Acid Resistance and Alkali Resistance 
     Acid resistance and alkali resistance of the enamel composition samples were evaluated based on ASTM and ISO 2722. The grading scale is described as follows: AA (Very good); A (Good); B (Average); C (Poor); D (Very poor). 
     3. Evaluation of Calcination Reliability 
     The enamel compositions were put into a metallic mold, pressed, molded and then calcinated at a temperature that was raised up to 600° C. at a rate of 10° C./min, and observed to determine whether the enamel compositions were crystallized (⊚: No crystallization, and excellent color quality and luminance; ∘: No crystallization, and good color quality and luminance; ×: Crystallization and no color glow). 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 3 
               
             
            
               
                   
                   
               
               
                   
                 Embodiment 
                 Comparative example 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 1 
                 2 
                 3 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Cleaning performance 
                 LV. 4 
                 LV. 5 
                 LV. 5 
                 LV. 5 
                 LV. 5 
                 LV. 5 
                 LV. 5 
                 LV. 2 
                 LV. 1 
                 LV. 3 
               
               
                 Acid resistance 
                 A 
                 A 
                 A 
                 A 
                 A 
                 A 
                 A 
                 A 
                 A 
                 B 
               
               
                 Alkali resistance 
                 A 
                 A 
                 AA 
                 AA 
                 A 
                 AA 
                 AA 
                 AA 
                 AA 
                 A 
               
               
                 Calcination reliability 
                 ◯ 
                 ⊚ 
                 ◯ 
                 ⊚ 
                 ◯ 
                 ⊚ 
                 ⊚ 
                 ◯ 
                 ◯ 
                 X 
               
               
                   
               
            
           
         
       
     
     As shown in Table 3, the embodiments according to the present disclosure ensured an excellent cleaning performance and had excellent acid resistance, alkali resistance and calcination reliability. 
     Unlike the embodiments, the comparative examples showed deterioration in the cleaning performance due to a small amount of the post-transition metal oxide and transition metal oxides, or caused a degradation in durability and calcination reliability due to instability in glass composition. 
     The embodiments have been described with reference to a number of illustrative embodiments thereof. However, it should be understood that the present disclosure is not intended to limit the embodiments and drawings set forth herein and that numerous other modifications and embodiments can be devised by those skilled in the art. Additionally, though not explicitly described during description of the embodiments, predictable effects based on the configurations of the embodiments should be acknowledged. 
     DESCRIPTION OF SYMBOLS 
       1 : Cooking appliance 
       11 : Cavity 
       12 : Cooking chamber 
       13 : Convection assembly 
       14 : Door 
       15 : Upper heater 
       16 : Lower heater