Oven

Abstract

Provided is an oven having an improved structure for keeping a cooking chamber clean. The oven includes a main body, a cooking chamber provided inside the main body, a main heater disposed inside the cooking chamber, a fan disposed inside the cooking chamber to circulate air heated by the main heater, a coating film formed on at least a part of a cooking chamber inner wall and having a liquid repellency, and a contaminant collecting portion having a liquid repellency smaller than that of the coating film and provided on the cooking chamber inner wall with which air circulated by the fan collides.

Claims

1. An oven comprising: a main body; a cooking chamber provided inside the main body; and a coating film formed on at least a part of a cooking chamber inner wall, and having a liquid repellency and a heat resistance, wherein the coating film comprises: a base comprising silsesquioxane; and a coating material comprising at least one of a silicon-based liquid repellent agent and an alkyl-based liquid repellent agent.

2. The oven according to claim 1, wherein the coating film has a water contact angle of 100 or more, and a thickness of 0.2 m or more and 3 m or less.

3. The oven according to claim 1, wherein the coating film has an oil contact angle of 40 or more, and a thickness of 0.2 m or more and 3 m or less.

4. The oven according to claim 1, further comprising: a contaminant collecting portion having a liquid repellency smaller than that of the coating film.

5. The oven according to claim 4, further comprising: a door rotatably installed at the main body to open or close the cooking chamber, wherein the contaminant collecting portion is provided on an inner surface of the door toward the cooking chamber.

6. An oven comprising: a main body; a cooking chamber provided inside the main body; a main heater disposed inside the cooking chamber; a fan disposed inside the cooking chamber to circulate air heated by the main heater; a coating film formed on at least a part of a cooking chamber inner wall and having a liquid repellency; and a contaminant collecting portion having a liquid repellency smaller than that of the coating film and provided on the cooking chamber inner wall with which air circulated by the fan collides wherein the contaminant collecting portion comprises a plurality of vanes installed along an outer circumferential direction of the fan to gradually deflect an air flow discharged from the fan in a tangential direction of the fan from a centrifugal direction of the fan.

7. The oven according to claim 6, wherein a surface energy of the coating film is 20 mJ/m.sup.2 or less, and a surface energy of the contaminant collecting portion is 25 mJ/m.sup.2 or more.

8. The oven according to claim 6, wherein the contaminant collecting portion comprises: a body detachably installed on the cooking chamber inner wall; and a waste liquid receiver provided to collect a contaminant separated from the body by contaminant's own weight.

9. The oven according to claim 6, wherein a plurality of protrusions are formed between the plurality of vanes.

10. The oven according to claim 6, wherein the contaminant collecting portion comprises a filter disposed at least one of an inlet and an outlet of the fan, and the filter is formed of at least one of a porous material and a fibrous material.

11. The oven according to claim 6, wherein the contaminant collecting portion is detachably provided on the cooking chamber inner wall.

12. The oven according to claim 11, wherein the contaminant collecting portion is detachable by a magnetic force.

13. The oven according to claim 6, wherein: the contaminant collecting portion comprises a catalyst coating layer, and the catalyst coating layer comprises: a catalyst comprising at least one of Ag, Pt, Pd, Au, Cu, Ru, Ti and Ni; and a cocatalyst comprising at least one of MnO.sub.2, CeO.sub.2, Al.sub.2O.sub.3, Bi.sub.2O.sub.3, SnO, TiO.sub.2, Cr.sub.2O.sub.3, Co.sub.2O.sub.3, Fe.sub.2O.sub.3, CuO, ZrO.sub.2, SrO, LaO, V.sub.2O.sub.5, Li.sub.2O, ZnO, MgO, NiO, CuO and BaO.

14. The oven according to claim 13, further comprising: a catalyst coating layer heater installed in the cooking chamber to heat the catalyst coating layer, wherein a distance between the catalyst coating layer and the catalyst coating layer heater is 1 mm or less.

15. The oven according to claim 6, wherein the coating film comprises: a base comprising silsesquioxane; and a coating material comprising at least one of a silicon-based liquid repellent agent and an alkyl-based liquid repellent agent.

16. The oven according to claim 15, wherein the coating film has a water contact angle of 100 or more, and a thickness of 0.2 m or more and 3 m or less.

17. The oven according to claim 15, wherein the coating film has an oil contact angle of 40 or more, and a thickness of 0.2 m or more and 3 m or less.

18. The oven according to claim 15, wherein the coating film comprises at least one layer.

19. The oven according to claim 18, wherein the at least one layer comprises: a first layer applied to at least a part of the cooking chamber inner wall; and a second layer applied on the first layer before the first layer is cured.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) These and/or other aspects of the disclosure will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

(2) FIG. 1 is a schematic view showing a structure of an oven according to a first embodiment of the present disclosure;

(3) FIG. 2 is a schematic cross-sectional view showing a structure of a coating film according to the first embodiment;

(4) FIG. 3 is a schematic graph showing a temperature profile when the coating film is cured according to the first embodiment;

(5) FIG. 4 shows a comparison result showing a contaminant preventing effect of the coating film according to the first embodiment;

(6) FIG. 5 is a graph showing a water contact angle according to thickness of the coating film, and durability against heating time according to the first embodiment;

(7) FIG. 6 is a schematic cross-sectional view showing a coating film according to a first modification of the first embodiment;

(8) FIG. 7 is a schematic graph showing a temperature profile when a coating film is cured according to a fourth modification of the first embodiment;

(9) FIG. 8 is a comparison result showing a contaminant preventing effect in a case in which a coating film is formed on a window according to a fifth modification of the first embodiment;

(10) FIG. 9 is a comparison result showing a contaminant preventing effect in a case in which a coating film is formed on a steel plate according to a sixth modification of the first embodiment;

(11) FIGS. 10A and 10B are experiment's photographs showing a movement of water droplets by vibrating a cooking chamber inner wall according to a second embodiment;

(12) FIGS. 11A and 11B are experiment's photographs showing a movement of oil droplets by vibrating the cooking chamber inner wall in the second embodiment;

(13) FIG. 12 is a schematic view showing a structure of an oven according to a third embodiment of the present disclosure;

(14) FIG. 13 is a schematic timing chart showing an operation of a heater and a fan according to the third embodiment;

(15) FIG. 14 is a graph showing a measurement result of changes in temperature over time at each point of the cooking chamber inner wall according to the third embodiment;

(16) FIG. 15 is a thermography showing a temperature distribution of the cooking chamber inner wall according to the third embodiment;

(17) FIGS. 16A and 16B are comparison results showing an effect of a cleaning according to the third embodiment;

(18) FIG. 17 is a schematic view showing distribution of wind speeds near cooking chamber inner wall according to a modification of the third embodiment;

(19) FIGS. 18A and 18B are comparison results showing an effect of a cleaning in the modification of the third embodiment;

(20) FIG. 19 is an experimental result showing a relationship between air flow and an effect of a cleaning according to the third embodiment;

(21) FIG. 20 is a schematic view showing a structure of an oven according to a fourth embodiment;

(22) FIG. 21 is an experimental result showing an improvement of a contaminant preventing effect on a coating film by providing a contaminant collecting portion according to the fourth embodiment;

(23) FIG. 22 is an experimental result showing a contaminant in a case in which a coating film is not formed in an oven;

(24) FIG. 23 is an experimental result showing a contaminant preventing effect in a case in which a coating film is formed on all surfaces in an oven;

(25) FIG. 24 is a view showing a contaminant collecting portion formed of a metal plate according to a first modification of the fourth embodiment of the oven;

(26) FIG. 25 is a schematic view showing a structure of the contaminant collecting portion according to the first modification of the fourth embodiment;

(27) FIG. 26 is a view showing a groove and a waste liquid receiver of the contaminant collecting portion according to the first modification of the fourth embodiment;

(28) FIG. 27 is an experimental result showing a contaminant preventing effect according to the first modification of the fourth embodiment;

(29) FIG. 28 is an experimental result showing a difference in the contaminant preventing effect according to the presence of the contaminant collecting portion according to the first modification of the fourth embodiment;

(30) FIG. 29 is an experimental result showing a difference in the amount of smoke discharged to the outside according to the presence of the contaminant collecting portion according to the first modification of the fourth embodiment;

(31) FIG. 30 is a view showing a contaminant collecting portion according to a second modification of the fourth embodiment;

(32) FIG. 31 is a schematic view showing a cleaning result according to the second modification of the fourth embodiment;

(33) FIG. 32 is a view showing a contaminant collecting portion according to a third modification of the fourth embodiment;

(34) FIG. 33 is an experimental result showing a contaminant preventing effect by a contaminant collecting portion according to a fourth modification of the fourth embodiment;

(35) FIG. 34 is a view showing a vane as a contaminant collecting portion according to a fifth modification of the fourth embodiment;

(36) FIG. 35 is a schematic view showing a spiral curved shape of the vane according to the fifth modification of the fourth embodiment;

(37) FIG. 36 is an experimental result showing a contaminant preventing effect by the vane according to the fifth modification of the fourth embodiment;

(38) FIG. 37 is a view showing a vane of another example in the fifth modification of the fourth embodiment;

(39) FIG. 38 is an experimental result showing a contaminant preventing effect by the vane of another example in the fifth modification of the fourth embodiment;

(40) FIG. 39 is a view showing a vane of still another example in the fifth modification of the fourth embodiment;

(41) FIG. 40 is a view showing details of a vortex generator in still another example of the fifth modification of the fourth embodiment;

(42) FIG. 41 is an experimental result showing a contaminant preventing effect by the vane of still another example in the fifth modification of the fourth embodiment;

(43) FIG. 42 is an experimental result showing a difference in a contaminant collecting effect according to the presence of the vortex generator according to the fifth modification of the fourth embodiment;

(44) FIG. 43 is a view showing an example in which a catalyst coating layer is formed on the vane according to the fifth modification of the fourth embodiment;

(45) FIG. 44 is an experimental result showing a contaminant preventing effect in the middle of a case in which the catalyst coating layer is formed on the vane according to the fifth modification of the fourth embodiment;

(46) FIG. 45 is an experimental result showing a final contaminant preventing effect in a case in which the catalyst coating layer is formed on the vane according to the fifth modification of the fourth embodiment;

(47) FIG. 46 is a view showing an experimental configuration example for obtaining a relationship between a decomposition effect of a contaminant by a catalyst coating layer and a temperature;

(48) FIG. 47 is a view showing a temperature profile in the experimental configuration example for obtaining the relationship between the decomposition effect of the contaminant by the catalyst coating layer and the temperature;

(49) FIG. 48 is an experimental result showing a decomposition effect of a contaminant by a catalyst coating layer at 380 C.;

(50) FIG. 49 is an experimental result showing a decomposition effect of a contaminant by a catalyst coating layer at 350 C.;

(51) FIG. 50 is a view showing a sixth modification of the fourth embodiment of the present disclosure, and

(52) FIG. 51 is a view showing a seventh modification of the fourth embodiment of the present disclosure.

DETAILED DESCRIPTION

(53) Hereinafter, embodiments of the present disclosure will be described in detail with reference to the appended drawings. In the following description, the terms front end, rear end, upper portion, lower portion, upper end, and lower end are defined based on the drawings, and the shapes and positions of the corresponding components are not limited by the terms.

(54) <An Oven Having a Coating Film>

(55) An oven 100 according to a first embodiment of the present disclosure will be described with reference to a respective drawing.

(56) As shown in FIG. 1, the oven 100 may be configured such that a food to be cooked is received in a cooking chamber 1, and the food to be cooked is heated by a heater 5. Particularly, the oven 100 may include a main body 2 forming an appearance. The main body 2 may have a substantially rectangular parallelepiped shape with its front surface opened. Further, the oven 100 may further include the cooking chamber 1 provided inside the main body 2. The cooking chamber 1 may have a substantially rectangular parallelepiped shape with its front surface opened. The cooking chamber 1 may be defined by a cooking chamber inner wall 4. The cooking chamber inner wall 4 may include an upper face 4a, a lower face 4b, a right face, a left face, and a rear face 4c. Further, the oven 100 may further include a door 3 rotatably installed at the main body 2 to open or close the cooking chamber 1. The door 3 may be provided with a window so that the inside of the cooking chamber 1 can be checked from the outside. Further, the oven 100 may further include a heater 5 installed inside the cooking chamber 1 or near the cooking chamber 1. Further, the oven 100 may further include a fan 61 installed to convect or circulate air heated by the heater 5. Further, the oven 100 may further include a vibrator 7 for slightly vibrating the cooking chamber inner wall 4 and dropping contaminants adhered to the cooking chamber inner wall 4 from the cooking chamber inner wall 4. Further, the oven 100 may further include a control board 8 for controlling the heater 5, a motor 62 for driving the fan 61 and the vibrator 7.

(57) The heater 5 may include an upper heater 51 installed in an upper portion of the inside of the cooking chamber 1, a lower heater 52 installed in a lower portion of the cooking chamber 1, and a rear heater 53 installed at a rear surface of the cooking chamber 1 with the fan 61. The upper heater 51 and the rear heater 53 may be installed to be exposed to the inside of the cooking chamber 1, and the lower heater 52 may be installed between the cooking chamber 1 and the main body 2. That is, the lower heater 52 may be installed on the outer side of the cooking chamber inner wall 4 and the inner side of the main body 2.

(58) The oven 100 may further include a heat insulating material 9 disposed between the cooking chamber 1 and the main body 2. That is, the heat insulating material 9 may be disposed between an outer surface of the cooking chamber inner wall 4 and an inner surface of the main body 2. Further, the heat insulating material 9 may be disposed inside the door 3.

(59) The oven 100 may further include a coating film 43 formed on at least a part of the cooking chamber inner wall 4. A detailed description of the coating film 43 will be described later.

(60) The heater 5, the fan 61 and the control board 8 may control a temperature and a temperature distribution inside the cooking chamber 1 in cooperation with each other. The present embodiment may be configured to perform a cooking mode in which a temperature of the cooking chamber inner wall 4 is about 350 C., and a cleaning mode in which the inside of the cooking chamber 1 is maintained at a temperature higher than that in the cooking mode for a predetermined time, and a convection of the air inside the cooking chamber 1 is controlled by the fan 61 to remove contaminants adhering to the cooking chamber inner wall 4.

(61) Hereinafter, the coating film 43 will be described in detail.

(62) As shown in FIG. 2, the cooking chamber inner wall 4 may include an enamel steel plate 41 corresponding to a base, and an enamel 42 formed on the enamel steel plate 41 to face the inside of the cooking chamber 1. The coating film 43 may be formed on the enamel 42 to be exposed to the inside of the cooking chamber 1. That is, the coating film 43 may be formed on the enamel 42 to face the inside of the cooking chamber 1.

(63) The coating film 43 may have a liquid repellency. In other words, at least the outer surface of the coating film 43 may have the liquid repellency. The outer surface of the coating film 43 refers to a surface facing the inside of the cooking chamber 1. The coating film 43 may have a water contact angle of 100 or more. Further, the coating film 43 may have an oil contact angle of 40 or more when a vegetable oil such as rapeseed oil, canola oil, or safflower oil, and a chicken oil are at 60 C.

(64) More particularly, the coating film 43 may include a base including silsesquioxane, and a coating material including at least one of a silicon-based liquid repellent agent and an alkyl-based liquid repellent agent. In other words, the coating film 43 may be obtained by adding a silicon-based or alkyl-based liquid repellent material to the material having silsesquioxane as a skeleton. adding is a concept that includes mixing the material having silsesquioxane as the skeleton with the silicon-based or alkyl-based liquid repellent material, or coupling the silicon-based or alkyl-based liquid repellent material to the material having silsesquioxane as the skeleton. For example, a derivative obtained by replacing a part of the material having silsesquioxane as the skeleton with the silicon-based or alkyl-based liquid repellent material may be used as the coating film. More particularly, the coating film 43 may hardly have thermal denaturation even when the surface temperature reaches 350 C., and continue to exhibit predetermined liquid repellency. That is, the coating film 43 may have the liquid repellency and a heat resistance.

(65) The coating film 43 may be formed to have a predetermined thickness by a spray coating after the enamel steel plate 41 and the enamel 42 are formed into a substantially rectangular parallelepiped like the cooking chamber inner wall 4. Alternatively, the coating film 43 may be formed by a spin coating in a flat plate state before forming the cooking chamber inner wall 4, and then the cooking chamber inner wall 4 may be formed in a rectangular parallelepiped shape. The coating film 43 can be cured while simultaneously exhibiting its liquid repellency by applying a liquid-type coating material on the enamel 42 and then heating it.

(66) In this embodiment, a plurality of stages of curing may be performed in order to prevent cracks or the like when the thickness of the coating film 43 is made larger than a predetermined thickness. More particularly, as shown in the temperature profile of the graph of FIG. 3, the coating film 43 may be heated to a first temperature for a first predetermined time in a state of being applied to the surface of the cooking chamber inner wall 4, and then heated to a second temperature higher than the first temperature for a second predetermined time and cured.

(67) The thickness of the coating film 43 may be set so that even when the cooking mode is repeated, the above-described surface characteristics are kept almost constant, and cracks or the like do not occur on the surface even if the heat load is repeated a predetermined number of times. More particularly, the thickness of the coating film 43 may be 0.2 m or more and 3 m or less.

(68) A difference in a contamination method in a case in which the coating film 43 is formed on the surface of the cooking chamber inner wall 4 will be described with reference to FIG. 4. In a sample 1 and a sample 2, a coating film 43 having a different thickness is formed on the cooking chamber inner wall 4. In a comparative example, the coating film 43 is not formed on the cooking chamber inner wall 4, and the enamel 42 is exposed. FIG. 4 shows a state of the cooking chamber inner wall 4 for each number of chickens when a chicken, as the food to be cooked, is roasted as a whole in the oven 100. A level of contaminant is the average value of sensory evaluation by several persons.

(69) As shown in FIG. 4, in the comparative example similar to the conventional state in which the coating film 43 is not provided, when 40 chickens are roasted, the contaminant due to oil adheres to the cooking chamber inner wall 4. On the other hand, in the sample 1 and sample 2, even when 40 chickens are roasted, an adhesion amount of contaminant are reduced as compared with the comparative example. In addition, since the contaminant does not strongly adhere to the cooking chamber inner wall 4, it is possible to easily drop the contaminant by simply rubbing the contaminant with a brush or the like. In other words, by allowing the coating film 43 to have a surface characteristic in which the water contact angle of the coating film 43 is 100 or more and 120 or less as an example, an adhesion of the contaminant can be largely reduced, and time and effort required for cleaning can be reduced. In addition, since the contaminant does not adhere to the cooking chamber inner wall 4 like the comparative example, cleaning by means such as the Pyro cleaning can be omitted.

(70) Next, a test result of the thickness of the coating film 43 and durability against the heat load is shown in a graph of FIG. 5. The graph of FIG. 5 shows a change in the water contact angle with respect to a cumulative heating time by applying the heat load to the coating film 43 formed with thickness of 0.5 m, 0.7 m, 1.0 m, 1.5 m and 2.0 m. As described above, a magnitude of the water contact angle positively correlates with a difficulty of adhesion of the contaminant. Further, a fact that the graph is broken indicates that a measurement is stopped because it is judged that the crack or the like occur at that point and thus the coating film 43 is no longer usable.

(71) In the graph of FIG. 5, when the thickness of the coating film 43 is 0.5 m or more and 2 m or less, it is found that a good contaminant preventing performance can be obtained in which the water contact angle is 100 or more until the heating time reaches about 50 hours. Such a range of thickness is preferable for the liquid repellency and durability against the heat load. In addition, when the thickness of the coating film 43 is 0.7 m or more and 1.5 m or less, a time for maintaining the water contact angle from 105 to 110 can be longer, and the durability against the heat load can be increased to 200 hours or more in the cumulative heating time. Further, according to an experiment, which is different from the experiment of FIG. 5 performed by the present inventors or the like, it can be seen that the durability against the heat load is improved even when the thickness of the coating film 43 is 0.7 m or less, and further, 0.2 m or less, as long as the coating film 43 is uniformly formed with a predetermined thickness. Further, the coating film 43 may have a thickness larger than 0 m.

(72) Next, the oven 100 according to a first modification of the first embodiment will be described.

(73) In the oven 100 of the first modification of the first embodiment, the coating film 43 formed on the cooking chamber inner wall 4 may be formed as two layers instead of one layer as shown in FIG. 6. The two layers refer to a state before the coating film 43 is fully cured or after curing.

(74) More particularly, in the first modification of the first embodiment, the coating film 43 may be formed by applying the second layer of the coating film 43 on the first layer before the first layer of the coating film 43 is completely cured on the enamel 42 and the liquid repellency develops in the first layer. Accordingly, even if the thickness of the coating film 43 is 2.0 m or more, cracks or the like hardly occur in a curing process, and it is easy to realize thickening. Further, the heat resistance of the coating film 43 can be improved by thickening. In other respects, the coating film 43 may include at least one layer. The at least one layer may include a first layer applied to at least a portion of the cooking chamber inner wall 4, and a second layer applied on the first layer before the first layer is cured.

(75) Next, the oven 100 according to the second modification of the first embodiment will be described.

(76) The oven 100 of the second modification of the first embodiment is the same as the first modification in that the coating film 43 is formed in two layers. However, the oven 100 of the second modification of the first embodiment differs from the first modification in that the first layer is a resin layer having no liquid repellency and only the second layer contains solid component that exhibit the liquid repellency.

(77) Table 1 shows a result of comparison of a surface state when the coating film 43 having such a structure is cured.

(78) TABLE-US-00001 TABLE 1 composition first layer second layer thickness (m) surface state transparent Solid 1.6 good resin paint content 28% transparent Solid 2.6 There is a little uneven resin paint content 40% surface. transparent Solid 2.9 There is a slight crack. resin paint content 50% There is an uneven surface.

(79) As shown in Table 1, even if a coating film is formed so that the first layer does not contain a liquid repellent component and the second layer contains the solid component that exhibits the liquid repellency up to 40% of the total weight, the coating film can be thickened without cracks. That is, according to the second modification, even in a case of the coating film 43 in which the solid component of the material is combined at a ratio of 28% or more and 40% or less with respect to the total weight including the solvent, high durability against the heat load and further improvement in the liquid repellency can be realized by curing. In addition, the most favorable surface state can be obtained and the coating film 43 can be easily applied to the cooking chamber inner wall 4 when the solid component of the material is combined at a ratio of 5% or more and 28% or less with respect to the total weight including the solvent.

(80) Next, the oven 100 according to the fourth modification of the first embodiment will be described.

(81) In the fourth modification of the first embodiment, the coating film 43 formed on the cooking chamber inner wall 4 may be cured by a temperature change in three stages as shown in a graph of a temperature profile of FIG. 7. That is, by raising a temperature such as a first predetermined temperature, a second predetermined temperature and a third predetermined temperature in order, the temperature is kept constant for each of the temperatures for a first predetermined time, a second predetermined time and a third predetermined time. The first predetermined time and the second predetermined time are set to be shorter than the third predetermined time, and lengths of the first predetermined time and the second predetermined time are equal to each other. Further, a difference between the first predetermined temperature and the second predetermined temperature is set to be smaller than a difference between the second predetermined temperature and the third predetermined temperature.

(82) As described above, by increasing the number of stages of the temperature profile in curing, generation of cracks or the like may be further prevented. In addition, the thickness of the coating film 43 may be easily thicker. Further, the temperature profile is not limited to those shown in FIGS. 3 and 7, and a temperature may be smoothly changed so that a plurality of stages of temperature differences is formed.

(83) Next, the oven 100 according to the fifth modification of the first embodiment will be described.

(84) In the fifth modification of the first embodiment, a transparent coating film 43 may also be formed on an inner surface of the window of the door 3. That is, the coating film 43 may be further formed on the inner surface of the window of the door 3 facing the cooking chamber 1. At this time, the coating film 43 may be transparent.

(85) FIG. 8 shows a result of a comparison of the contaminant adhering inside the cooking chamber 1 when the coating film 43 is formed only on the right side portion of the window and the food to be cooked is cooked. As shown in FIG. 8, by forming the coating film 43 on the inner surface of the window, it can be seen that a phenomenon of blurring and contamination of the window due to oil or the like generated from the food to be cooked is reduced.

(86) Next, the oven 100 according to the sixth modification of the first embodiment will be described.

(87) In the sixth modification of the first embodiment, the coating film 43 may be formed directly on the surface of the steel plate 41 instead of forming the coating film 43 on the surface of the enamel 42. FIG. 9 shows a result of comparison in a case in which an oil causing the contaminant and being extracted from the food to be cooked is dropped on each of a SUS 304 on which the coating film 43 is formed and a glass plate on which the coating film 43 is not formed.

(88) As can be seen in FIG. 9, when a viscosity of the oil is lowered by heating, droplets of the oil are scattered, which causes the contaminant to adhere to the surface, in the glass plate on which the coating film 43 is not formed, but, a state of droplets of the oil is hardly changed in the steel plate 41 on which the coating film 43 is formed. That is, when the coating film 43 is formed, a change in the oil contact angle due to the temperature change is hardly recognized, and the liquid repellency is maintained. Further, as can be seen from a result obtained when the steel plate 41 and the glass plate are tilted up, in the glass plate, a trace of a movement of the oil becomes a mark and becomes a noticeable contaminant. On the other hand, in the steel plate 41 in which the liquid repellency is exhibited by the coating film 43, the mark is not left even after the oil passes, so that it is difficult that the mark is left as the contaminant.

(89) As can be seen from the fifth and sixth modifications, the coating film 43 can exhibit substantially the same contaminant preventing effect even if it is formed on the glass or the steel plate 41 instead of the enamel 42.

(90) Other modifications of the first embodiment will be described.

(91) The coating film according to the present disclosure is not limited to those shown in the embodiments and the modifications of the embodiments, and may have other compositions. More particularly, the coating film may be a material that does not contain fluorine such as Teflon and does not lose its liquid repellency due to thermal deformation even when the temperature reaches about 350 C. at the time of cooking.

(92) Further, when the thickness of coating film is 0.2 m or more and 3 m or less regardless of the composition, the occurrence of cracks or the like can be suppressed and the durability against repeated heat load can be realized with a problem-free level in use. In addition, the coating film according to the present disclosure can be used for both an electric oven and a gas oven.

(93) <A Method of Forming a Coating Film>

(94) Next, a method of forming the coating film 43 according to the first embodiment of the present disclosure will be described with reference to the drawings. Hereinafter, a method of forming the coating film 43 by a spray coating method will be described in detail.

(95) In this embodiment, at least one of hexane, heptane octane, butyl acetate, PEGMEA and ethyl acetate may be used as a solvent, and the coating material is present in an amount of 12.5% by weight, based on the weight of the solution. The solution may be applied to the cooking chamber inner wall 4 using a spray gun having a nozzle diameter of 0.5 mm. When this solution is applied, a spray target may be moved while being sprayed by the spray gun and the spray target may be passed through three times with respect to each point of the cooking chamber inner wall 4. It is also possible that the spray target is passed through twice depending on the thickness of the coating film 43.

(96) In this embodiment, a plurality of stages of curing may be performed in order to prevent cracks or the like from occurring when the thickness of the coating film 43 is made larger than a predetermined value. That is, the coating film 43 may be heated to a first temperature for a first predetermined time in a state of being applied to the surface of the cooking chamber inner wall 4, and then heated to a second temperature higher than the first temperature for a second predetermined time and cured.

(97) In a case of the above-described film forming method, it is possible to prevent the surface of the coating film 43 from being cracked while making the coating film 43 thick.

(98) Next, a modification relating to the method of forming the coating film will be described.

(99) Although a basis material on which the coating film 43 is formed is the enamel 42 in the above embodiment, the coating film 43 may be formed on the surface of the steel plate such as SUS 304 or the like. Further, the coating film 43 may be formed on the inner surface of the window installed on the door 3. When the basis material on which the coating film 43 is formed is other than the enamel 42, a concentration of the coating material, which is a solid component in the solution, may be different from that in a case of coating the enamel 42.

(100) Embodiments of other method of forming the coating film will be described.

(101) The coating film according to the present disclosure is not limited to those shown in the embodiments and the modification of the embodiments, and may have other compositions. More particularly, the coating film may be a material that does not contain fluorine, and may be any material that does not lose its liquid repellency due to thermal deformation even when the temperature reaches about 320 C. at the time of cooking.

(102) Further, when the thickness of coating film is 0.2 m or more and 3 m or less regardless of the composition, the occurrence of cracks or the like can be suppressed and the durability against repeated heat load can be realized with a problem-free level in use. In addition, the coating film according to the present disclosure can be used for both an electric oven and a gas oven.

(103) <Removal of Contaminants by Micro Vibration>

(104) An oven 100 according to a second embodiment of the present disclosure will be described with reference to the drawings. The oven 100 according to the second embodiment is the same as the oven 100 shown in FIG. 1. However, the oven 100 according to the second embodiment differs from the oven 100 according to the first embodiment in an operation of the vibrator 7 and the heater 5.

(105) Hereinafter, a structure of the vibrator 7, and a removal action and a removal effect of droplets, which are adhered to the cooking chamber inner wall 4 and do not fall by their own weight, by using a vibration of the vibrator 7 will be described in detail.

(106) The vibrator 7 may include an eccentric motor 71 (see FIG. 1), and a vibration transmitting plate 72 (see FIG. 1) having one end vibrated by an eccentric weight of the eccentric motor 71 and the other end being a drive shaft connected to the outer surface of the cooking chamber inner wall 4. More particularly, an oscillation frequency of the eccentric motor 71 may be changed according to a magnitude of an input current. The eccentric weight of the eccentric motor 71 may come into contact with the vibration transmitting plate 72 in a direction perpendicular to a surface plate portion of the vibration transmitting plate 72, and vibrate the vibration transmitting plate 72 in a vertical direction. Further, the vibration transmitting plate 72 may be installed to be connected to the cooking chamber inner wall 4 while not being in contact with the main body 2. That is, a vibration generated from the vibrator 7 may not be transmitted to the main body 2. Further, the vibration transmitting plate 72 may be connected to a rear surface extending in the vertical direction of the cooking chamber inner wall 4 so that a bending vibration in the vertical direction of the vibration transmitting plate 72 is transmitted to the rear surface of the cooking chamber inner wall 4.

(107) The control board 8 (a controller) may control the heater 5, the vibrator 7 and the motor 62 so that each of the heater 5, the vibrator 7 and the motor 62 performs different operations in at least the cooking mode and the cleaning mode. The control board 8 may be a so-called computer having a CPU, a memory, an A/D.Math.D/A converter or the like. By executing an oven program stored in the memory, the control board 8 may function as at least a heater controller, a vibrator controller, and a fan controller in cooperation with various devices.

(108) The heater controller may control a current flowing through the upper heater 51, the lower heater 52 and the rear heater 53 constituting the heater 5 to maintain a temperature in the cooking chamber 1 at a set temperature. In the cooking mode, the heater controller may control the heater 5 to maintain the temperature in the cooking chamber 1 at a temperature suitable for the cooking of the food to be cooked. On the other hand, in the cleaning mode, the heater controller may control the heater 5 to keep the inside of the cooking chamber 1 at a predetermined temperature that makes it easier to move the droplets adhered to the cooking chamber inner wall 4 by the vibration of the vibrator 7.

(109) When the heating is performed by the heater 5, the fan controller may control the number of revolutions of the motor 62 to control an air volume in the cooking chamber 1 generated from the fan 61. Convection in the cooking chamber 1 generated by the fan 61 can prevent only a part of the cooking chamber 1 from becoming hot and the liquid repellency of the coating film 41 from being lost.

(110) Next, an operation of the control board 8 in the cleaning mode will be described in detail.

(111) The control board 8 will perform the cleaning mode when the cooking mode is finished.

(112) At this time, the vibrator controller may vibrate the vibrator 7 in a predetermined amplitude range and a predetermined frequency range to vibrate the cooking chamber inner wall 4 in the vertical direction. The predetermined amplitude range may be set to a value at which a vibrating sound of the cooking chamber inner wall 4 from the main body 2 to the outside does not leak over a predetermined level, while applying a force required to move small droplets which are adhered on the coating film 43 and are not dropped by their own weight. The predetermined frequency range may be set to include a resonance frequency of the droplets determined in accordance with a size of the droplets adhered to the cooking chamber inner wall 4 in the present embodiment. In the present embodiment, the predetermined amplitude range may be set to 10 m or more and 100 m or less, and the predetermined frequency range may be set to 20 Hz or more and 220 Hz or less. In addition, the vibration controller may control the vibrator 7 to continuously vibrate the cooking chamber inner wall 4 for 10 seconds or more and 60 seconds or less.

(113) When the vibrator 7 is vibrated in the cleaning mode, the heater controller may also perform a temperature control to keep the inside of the cooking chamber 1 at a predetermined temperature by operating the heater 5. In the present embodiment, the temperature inside the cooking chamber 1 may be maintained at a temperature higher than the room temperature by the heater 5 in the cleaning mode. More particularly, in the cleaning mode, the temperature in the cooking chamber 1 may be kept at 60 C. or higher and 350 C. or lower.

(114) Hereinafter, it will be described based on an experimental data a fact in which the vibrator 7 and the heater 5 can drop the small droplets, which are continuously adhered even if the coating film 43 has the liquid repellency, through cooperation between the vibrator 7 and the heater 5.

(115) As shown in FIG. 10A, a small vibration was generated at the room temperature by the vibrator 7 after water droplets of 1.0 l, 1.5 l, 2.0 l, 2.5 l, 3.0 l and 3.5 l were adhered to a standing face of the cooking chamber inner wall 4. Particularly, a waveform of a sinusoidal wave whose frequency changes from 20 Hz to 120 Hz for 10 seconds was applied three times by the vibrator 7. As a result, the water droplets could be moved as shown in FIG. 10B.

(116) As shown in FIG. 11A, a small vibration was generated at the room temperature and when the temperature was maintained at 60 C. by the heater 5, respectively, by the vibrator 7 after oil droplets of 1.0 l, 1.5 l, 2.0 l, 2.5 l, 3.0 l and 3.5 l were adhered to a standing face of the cooing chamber inner wall 4. Particularly, a waveform of a sinusoidal wave whose frequency changes from 20 Hz to 120 Hz for 10 seconds was applied three times by the vibrator 7. As a result, at the room temperature, it was not possible to move the oil droplets even if the small vibration was applied. However, when the temperature in the cooking chamber 1 was maintained at 60 C., the oil droplets could be moved as shown in FIG. 11B.

(117) These results are summarized in Table 2.

(118) TABLE-US-00002 TABLE 2 waveform temper- droplet modulation movement droplets ature diameter conditions distance droplets room about 0.5 mm change a 1 mm or less temper- about 0.8 mm sinusoidal wave about 2 mm ature about 1.0 mm of 20 Hz to 10 mm or more 120 Hz for 10 seconds oil room about 0.5 mm change a no movement droplets temper- about 0.8 mm sinusoidal wave (oil taken ature about 1.0 mm of 20 Hz to after a 220 Hz for 20 chicken seconds cooking) 60 about 0.5 mm change a 1 mm or less about 0.8 mm sinusoidal wave about 2 mm about 1.0 mm of 20 Hz to about 5 mm 220 Hz for 20 seconds

(119) As described above, in the oven 100 of the second embodiment, the droplets including the small water droplets or the oil droplets can be separated from the cooking chamber inner wall 4 and be dropped by slightly vibrating the cooking chamber inner wall 4 in the vertical direction by the vibrator 7 after the temperature inside the cooking chamber 1 is maintained at 60 C. or higher by the heater 5 in the cleaning mode.

(120) The droplets having a large droplet diameter may be dropped by their own weight due to the liquid repellency of the coating film 43, and the small droplets adhered to the coating film 43 having the liquid repellency may be moved and dropped by an action of the heater 5 and the vibrator 7.

(121) Therefore, the water droplets or the oil droplets remaining on the cooking chamber inner wall 4 can be substantially removed. As a result, the small oil droplets, which are continuously adhered to the cooking chamber inner wall 4 and deteriorated by the heat during cooking, can be prevented from adhering to the cooking chamber inner wall 4 as a small black mass. As a result, a time required for cleaning in the oven 100 may be greatly reduced. Even if a small contaminant remains, the contaminant can be sufficiently dropped without a high-temperature cleaning method such as the Pyro cleaning in which the temperature in the cooking chamber 1 reaches 420 C. Therefore, a load on the heater 5 can be reduced and a failure frequency of the oven 100 can be reduced.

(122) A modification of the second embodiment will be described.

(123) In the second embodiment, the cooking chamber inner wall 4 may be vibrated by the vibrator 7 while the temperature inside the cooking chamber 1 is maintained at 60 C. or higher by the heater 5. However, for example, the vibrator 7 may be vibrated in a stage in which a remaining heat of the cooking mode remains so that the oil droplets move. Further, in the cleaning mode, the temperature inside the cooking chamber 1 may be appropriately set, or may be set at a temperature other than 60 C. For example, the temperature in the cooking chamber 1 may be set within a temperature range in which the coating film 43 does not lose its liquid repellency due to the thermal deformation.

(124) The vibrator 7 is not limited to being operated by the eccentric motor, and various types such as an electromagnetic vibrator, a piezoelectric element or the like can be used. A vibration direction by the vibrator 7 may include at least a vertical direction, and may include other vibration direction components. A predetermined frequency range for vibrating the vibrator 7 may be set according to a size of the droplets to be dropped from the cooking chamber inner wall 4. For example, the predetermined frequency range may be set to include only a part of the resonance frequency, instead of setting the predetermined frequency range to include the resonance frequency with respect to the entire diameter distribution of the droplets. Also, the predetermined frequency range is not limited to that shown in the above embodiment, and may be set appropriately according to parameters such as a size of the oven, a size of the cooking chamber inner wall, a sound insulation performance, and a length of time for vibrating the vibrator. In addition, a vibration by the vibrator 7 is not limited to being continuously applied, but may be intermittently applied. For example, an idle period may be provided every time a frequency of the vibrator is changed.

(125) <Cleaning with the Heater and the Fan Only>

(126) Next, the oven 100 according to the third embodiment will be described with reference to the drawings.

(127) As shown in FIG. 12, the oven 100 of the third embodiment is different from the oven 100 of the first embodiment and the second embodiment in that the vibrator 7 is not provided. In addition, the oven 100 of the third embodiment is different from the oven 100 of the first embodiment and the second embodiment in a configuration of the control board 8 related to the cleaning mode.

(128) More particularly, in the cleaning mode for dropping the contaminant adhering to the cooking chamber inner wall 4, the control board 8 (the controller) may drive the heater 5 so that the temperature of the cooking chamber inner wall 4 is maintained at 350 C. or higher and 400 C. or lower for a predetermined holding time or longer while simultaneously driving the fan 61. That is, this embodiment differs from the conventional Pyro cleaning in that the fan 61 is driven when the inside of the cooking chamber 1 and the cooking chamber inner wall 4 are brought into a high temperature state. In addition, in this embodiment, the temperature of the inside of the cooking chamber 1 and the temperature of the cooking chamber inner wall 4 may be raised only to a temperature lower than 420 C. conventionally required for dropping the contaminant.

(129) More particularly, as shown in a timing chart of FIG. 13, the fan 61, the upper heater 51, the lower heater 52 and the rear heater 53 may be controlled by the control board 8 over a predetermined holding time of one hour or longer. As can be seen from FIG. 13, the fan 61 may be driven at all times, and constantly form an air flow in the cooking chamber 1 to uniformize a temperature. Each of the heaters constituting the heater 5 may be designed to perform periodic ON/OFF control. More particularly, the upper heater 51 and the lower heater 52 may be alternately driven so that their ON periods do not overlap. More particularly, the upper heater 51 may be designed so that the ON/OFF control in which the ON state maintains for 20 seconds in one cycle and the OFF state maintains for 32 seconds in one cycle is periodically performed. On the other hand, the lower heater 52 may be designed so that the ON/OFF control in the ON state maintains for 10 seconds in one cycle and the OFF state maintains for 42 seconds in one cycle is periodically performed. Further, a phase of a control period of the upper heater 51 and the lower heater 52 are different from each other. Therefore, the ON state of the lower heater 52 may be started from the time when the ON state of the upper heater 51 is finished. The rear heater 53 may be designed so that the ON/OFF control in which the ON state maintains for 40 seconds in one cycle and the OFF state maintains for 12 seconds in one cycle is periodically performed. A start time of the ON state of the rear heater 53 may be the same as a start time of the ON state of the upper heater 51. Therefore, while the upper heater 51 and the lower heater 52 are alternately turned to the ON state, the rear heater 53 may be always the ON state. Every 40 seconds, all the heaters may be turned to the OFF state for 12 seconds.

(130) Changes in the temperature of the cooking chamber inner wall 4 caused by the control of the heater 5 and the fan 61 will be described with reference to FIGS. 14 and 15. FIG. 14 is a graph showing a result of measurement of changes in temperature over time by installing a temperature sensor on each surface of the cooking chamber inner wall 4. FIG. 15 shows a result of measurement of temperature of the cooking chamber 1 and the cooking chamber inner wall 4 with a thermography.

(131) As can be seen from FIGS. 14 and 15, in the cooking chamber inner wall 4, a temperature of each standing faces gradually rises from a start of the cleaning mode so that all the faces of the cooking chamber inner wall 4 are maintained substantially at a uniform temperature of 385 C. to 400 C.

(132) FIGS. 16A and 16B show a cleaning effect by maintaining such a temperature state for one hour or longer. FIG. 16A shows a state in which contaminants before cleaning are adhered to the cooking chamber inner wall 4 in a form of spots. By carrying out the above-described cleaning mode from this state, most contaminants can be dropped as shown in FIG. 16B. Further, in this cleaning mode, it is possible to drop the contaminants at temperature lower than 420 C., where the conventional Pyro cleaning is performed. Since the temperature of the cooking chamber inner wall 4 rises only up to 400 C., the liquid repellency of the coating film 43 may not be lost by the thermal deformation.

(133) Next, a modification of the third embodiment will be described.

(134) In this modification, an air flow of at least 1 m/s or more may be formed by the fan 61 at a position 1 cm away from a standing face of the cooking chamber inner wall 4 as shown in FIG. 17.

(135) By maintaining a temperature of the cooking chamber inner wall 4 at 350 C. to 400 C. while forming such an air flow, as shown in FIG. 18A, an oil stain adhered to the rear surface of the cooking chamber inner wall 4 before the cleaning may be removed and become clean as shown in FIG. 18B. More particularly, in FIG. 17, it can be seen that the contaminants are completely removed in a portion where the air flow of 1 m/s or more is formed.

(136) Next, a verification experiment was conducted on an influence of an air volume. Two test specimens having the same configuration as the cooking chamber inner wall 4 were prepared, and the contaminants adhering to the test specimens due to an oil extracted from a chicken were reproduced. One test specimens was wrapped with aluminum foil to block contact with an air flow, and a surface of the other test specimens was brought into contact with the air flow. In this state, when held at 400 C. for 1 hour or more, the test specimen contacted with the air flow may have an area where an enamel portion is largely exposed since the contaminants were removed as shown in the tight side of FIG. 19, compared to the test specimen prevented to contact with the air flow as shown in the left side of FIG. 19. Therefore, it can be seen that in the cleaning mode, formation of the air flow in addition to merely heating is more effective to drop the contaminants well.

(137) A modification of the third embodiment will be described.

(138) The control of the heater 5 and the fan 61 is not limited to that described above, and PWM control or feedback control based on the output of a measurement sensor such as a temperature sensor or the like may be performed. Further, as shown in the third embodiment, when the feedforward control is performed, simplification and cost reduction of the oven are likely to be realized.

(139) In the cleaning mode, a temperature of the cooking chamber 1 or the cooking chamber inner wall 4 may be suitably set within a range of 350 C. to 400 C. The upper limit of this temperature may be set as high as possible within a range in which the liquid repellency of the coating film is not lost. Further, by using the vibrator 7 in the first and second embodiments, the small vibration by the vibrator 7 may be further applied to the cooking chamber inner wall 4 in the cleaning mode.

(140) <Oven Having Coating Film and Contaminant Collecting Portion>

(141) An oven 100 according to a fourth embodiment of the present disclosure will be described with reference to the drawings. It should be noted that configurations corresponding to the configurations described in the above embodiments are denoted by the same reference numerals.

(142) As shown in FIG. 20, the oven 100 may be configured such that the food to be cooked in received in the cooking chamber 1, and the food to be cooked is heated by the heater 5. Specifically, the oven 100 may include the main body 2 forming an appearance. The main body 2 may have a substantially rectangular parallelepiped shape with its front surface opened. Further, the oven 100 may further include the cooking chamber 1 provided inside the main body 2. The cooking chamber 1 may have a substantially rectangular parallelepiped shape with its front surface opened. The cooking chamber 1 may be defined by the cooking chamber inner wall 4. The cooking chamber inner wall 4 may include the upper face 4a, the lower face 4b, the right face, the left face, and the rear face 4c. Further, the oven 100 may further include the door 3 rotatably installed at the main body 2 to open or close the cooking chamber 1. The door 3 may be provided with the window so that the inside of the cooking chamber 1 can be checked from the outside. Further, the oven 100 may further include a heater 5 installed inside the cooking chamber 1 or near the cooking chamber 1. Further, the oven 100 may further include the fan 61 installed to convect or circulate air heated by the heater 5. Further, the oven 100 may further include the control board 8 for controlling the heater 5, the motor 62 for driving the fan 61.

(143) The heater 5 may include the upper heater 51 installed in the upper portion of the inside of the cooking chamber 1, the lower heater 52 installed in the lower portion of the cooking chamber 1, and the rear heater 53 installed at the rear surface of the cooking chamber 1 with the fan 61. The upper heater 51 and the rear heater 53 may be installed to be exposed to the inside of the cooking chamber 1, and the lower heater 52 may be installed between the cooking chamber 1 and the main body 2. That is, the lower heater 52 may be installed on the outer side of the cooking chamber inner wall 4 and the inner side of the main body 2. In the present embodiment, the upper heater 51 corresponds to a main heater.

(144) The oven 100 may further include the heat insulating material 9 disposed between the cooking chamber 1 and the main body 2. That is, the heat insulating material 9 may be disposed between the outer surface of the cooking chamber inner wall 4 and the inner surface of the main body 2. Further, the heat insulating material 9 may be disposed inside the door 3.

(145) The oven 100 may further include the coating film 43 formed on at least a part of the cooking chamber inner wall 4. The oven 100 may further include a contaminant collecting portion 44 formed on at least a part of the cooking chamber inner wall 4. For example, the coating film 43 may be formed on a part of the cooking chamber inner wall 4, and the contaminant collecting portion 44 may be formed on the remaining part of the cooking chamber inner wall 4.

(146) The heater 5, the fan 61 and the control board 8 may control a temperature and a temperature distribution inside the cooking chamber 1 in cooperation with each other. The present embodiment may be configured to perform a cooking mode in which a temperature of the cooking chamber inner wall 4 is about 350 C., and a cleaning mode in which the inside of the cooking chamber 1 is maintained at a temperature higher than that in the cooking mode for a predetermined time, a convection of the air inside the cooking chamber 1 is controlled by the fan 61 to remove contaminants adhering to the cooking chamber inner wall 4.

(147) Hereinafter, a difference between a portion where the coating film 43 is formed and a portion where the coating film 43 is not formed and which functions as the contaminant collecting portion 44 in the fourth embodiment will be described. The coating film 43 may have the liquid repellency and have a surface energy of 0 mJ/m.sup.2 or more and 20 mJ/m.sup.2 or less. Further, the contaminant collecting portion 44 may have a smaller liquid repellency as compared with that of the coating film 43 and a surface energy of 25 mJ/m.sup.2 or more. A difference in a surface energy of each surface may be set to be 5 mJ/m.sup.2 or more. Further, the contaminant collecting portion 44 may be provided at a portion where a circulation of a hot air formed in the cooking chamber 1 by the fan 61 is first moved. In other words, the contaminant collecting portion 44 may be provided at a portion where an air circulating inside the cooking chamber 1 by the fan 61 is first hit. In the fourth embodiment, since the hot air is first applied to the cooking chamber inner wall 4 on the rear side of the cooking chamber 1 by the fan, a part of the cooking chamber inner wall 4 forming this rear face may be provided with the contaminant collecting portion 44 so as to collect a small oil droplet, which is generated and scattered from the food to be cooked. That is, the contaminant collecting portion 44 may be formed on the rear face 4c of the cooking chamber inner wall 4.

(148) The difference in a manner of contamination on the surface of the cooking chamber inner wall 4 in the oven of the fourth embodiment will be described with reference to FIG. 21. In an experimental example of FIG. 21, the coating film 43 was formed on the left side of the rear face of the cooking chamber inner wall 4, and the contaminant collecting portion 44 was formed without forming the coating film 43 on the tight side of the rear face of the cooking chamber inner wall 4. Then, a raw chicken was roasted as the food to be cooked at 230 C. for 1 hour. The cooking was repeated until the total number of the raw chicken reaches 20, and then a contaminant of the cooking chamber inner wall 4 was observed. As a result, as shown in FIG. 21, it can be seen that oil stains are hardly existed on the left side of the rear face where the coating film 43 is formed, but the oil stains are concentrated on the contaminant collecting portion 44. Further, in a case in which the coating film 43 is not formed on the cooking chamber inner wall 4 as shown in FIG. 22, the oil stains are generated on the entire surface when the raw chicken is cooked under the same conditions as in FIG. 21. Further, as shown in FIG. 23, when the coating film 43 is formed on the entire of the cooking chamber inner wall 4, a cleanliness of the entire of the cooking chamber inner wall 4 may become high. However, although the coating film 43 is formed near the fan 61, a small spot-shaped oil stain may be formed on the cooking chamber inner wall 4 forming the rear face. As can be seen from a comparison between contamination states shown in FIG. 21 and FIG. 23, the cleanliness may be improved not only by forming the coating film 43 but also by forming the contaminant collecting portion 44 instead of forming the coating film 43. As described above, the oven 100 of the fourth embodiment may be provided with the contaminant collecting portion 44 in the cooking chamber 1, so that a higher degree of cleanliness can be achieved over a long period than when the coating film 43 is formed on all the surfaces of the cooking chamber inner wall 4.

(149) This is because of the following reasons. In other words, the oil droplets having a small diameter, which are not sufficiently repelled out by the liquid repellency of the coating film 43, may be deposited on the coating film 43 to finally form the small spot-shaped contaminants on the coating film 43 as shown in FIG. 23. On the other hand, when the contaminant collecting portion 44 is formed in parallel with the coating film 43 as in the fourth embodiment, the oil droplets having the small diameter may be collected in the contaminant collecting portion 44, so that the oil droplets having the small diameter may not be deposited on the coating film 43. Thus, an occurrence of spot-shaped contaminants may be prevented. This may make it possible to maintain the cleanliness of the coating film 43 over a longer period of time than when the entire surfaces are covered with the coating film 43.

(150) Next, a first modification of the fourth embodiment will be described. In the first modification, the coating film 43 may be not formed on the cooking chamber inner wall 4. Particularly, in the first modification, a metal plate on which the coating film 43 is not formed may be detachably disposed in the cooking chamber 1 instead of forming the contaminant collecting portion 44. More particularly, the contaminant collecting portion 44 according to the modification 1 may be provided in such a manner that an aluminum plate detachable by a magnet is standing on the cooking chamber inner wall 4 forming the rear face of the cooking chamber 1 and having the fan 61. The contaminant collecting portion 44 may include a body 44a detachably installed on one side of the cooking chamber inner wall 4, a groove 44b through which a liquid oil collected on a surface of the body 44a and gathered downward by gravity flows, and a waste liquid receiver 44e installed below the groove 44b to receive the oil corresponding to a waste liquid. At this time, the body 44a may be formed of a metal plate. Particularly, the body 44a may be formed of an aluminum plate. The groove 44b may be inclined so that the oil collected in the groove 44b can smoothly move toward the waste liquid receiver 44e. Further, as shown in FIG. 25, a guide rib 44d may be formed at the body 44a so as to guide the contaminants adhered to a surface of the body 44a to the lower portion of the cooking chamber 1. Further, the body 44a may be provided with a handle 44c for facilitating attachment or detachment of the contaminant collecting portion 44. The same experiment, as shown in FIGS. 21 to 23, was performed to the oven 100 of the modification 1, and a checking was performed to see if there is a contaminant in the oven 100 or not. As shown in FIG. 27, since the small oil is absorbed in the detachable contaminant collecting portion 44, a contaminant in a form of a small spot was not formed on the coating film 43 which is formed on the side face of the cooking chamber inner wall 4, and the cleanliness of the side face of the cooking chamber inner wall 4 was maintained.

(151) On the other hand, when the coating film 43 is formed on the entire cooking chamber inner wall 4, a contaminant due to a deposition of a small oil is also generated in a portion where the coating film 43 is formed as shown in FIG. 28.

(152) The oven 100 of the modification 1 can prevent a spot-shaped contaminant from being deposited on the coating film 43 even in long-term use due to an effect of collecting a small oil of the contaminant collecting portion 44. In addition, the contaminant collecting portion 44 for collecting the contaminant can be separated from the inside of the cooking chamber 1 and can be easily cleaned. Therefore, an oil collecting effect by the contaminant collecting portion 44 can be simply restored, and an ability to maintain the cleanliness of the cooking chamber inner wall 4 can be continuously exhibited.

(153) Further, with respect to the contaminant collecting portion 44, an experiment was performed to see if there is a collecting effect by materials having different surface energies. The experimental results are shown in Table 3.

(154) TABLE-US-00003 TABLE 3 liquid repellent hydrophilic material coating aluminum SUS 430 enamel coating surface 20 25 28 56 64 energy (mJ/m.sup.2) oil stain no yes yes yes yes collecting effect

(155) According to the above described comparison experiment, when the material's surface energy is 25 mJ/m.sup.2, the material may be the contaminant collecting portion 44 because the material can exhibit the contaminant collecting effect. In other words, if a difference in surface energy between the contaminant collecting portion 44 and the coating film 43 is at least 5 mJ/m.sup.2 or more, a generation of the small contaminant on the coating film 43 can be suppressed due to the contaminant collecting effect.

(156) Further, if the contaminant collecting portion 44 is provided, even when the door is opened during cooking, the amount of smoke discharged to the outside can be reduced since a smoke generated from the food to be cooked is absorbed. FIG. 29 shows a difference in the amount of smoke between an oven 100 in which the contaminant collecting portion 44 is installed and an oven 100 in which the contaminant collecting portion 44 is not installed. At this time, the cooking is carried out under the same conditions in the two ovens, and the doors are opened at the same time in the of the cooking. The oven 100 provided with the contaminant collecting portion 44 on the left side in FIG. 29 has a smaller amount of smoke that is discharged to the outside than the oven 100 not provided with the contaminant collecting portion 44 on the right side in FIG. 29.

(157) Next, a second modification of the fourth embodiment will be described. As shown in FIG. 30, in the second modification, the window of the door 3 of the oven 100 may be coated with a hydrophilic coating so as to exert a function as the contaminant collecting portion 44. Even in such a case, it is possible to prevent small oil droplet from being deposited on the coating film 43 and from being blackened to the spot-shaped contaminant, so that a cleanliness of the inside of the cooking chamber 1 can be maintained over a long period of time. Further, as shown in FIG. 31, the window of the door 3 where the contaminant is collected may be simply cleaned because the contaminant is floated just by flushing the window of the door 3.

(158) Next, a third modification of the fourth embodiment will be described. In the foregoing embodiments, the contaminant collecting portion 44 is stood up in the cooking chamber 1. However, for example, as shown in FIG. 32, a metal tray on which the water repellent coating film 43 is not formed may be disposed at the lowermost end of the cooking chamber 1 of the oven 100. Even in this case, the contaminant can be collected in the metal tray, and the contaminant on the cooking chamber inner wall 4 on which the other coating film 43 is formed can be reduced. Further, in a case in which the metal tray is used, during a roasting in which the upper heater 51 is mainly used, the oil spouted from the food to be cooked can be prevented from contaminating the lower surface of the cooking chamber 1, and the falling oil can be received. During a baking in which the lower heater 52 is used, the metal tray may be removed so as not to interfere with the baking.

(159) Next, a fourth modification of the fourth embodiment will be described. The fourth modification relates to an oven 100 in which a catalyst coating layer is formed as a contaminant collecting portion 44. In other words, the contaminant collecting portion 44 may include the catalyst coating layer. The catalyst coating layer may be formed by applying a thermal catalyst to a detachable component from the oven 100, and the contaminant collecting portion 44 may include such a catalyst coating layer. Particularly, Ag is used as a catalyst material and MnO.sub.2 is used as a cocatalyst. A SiO.sub.2 film having a thickness of nm order may be formed between a surface of a metal component of a basis material and the catalyst material. The SiO.sub.2 may be formed of a low molecular weight based Silane coating agent including Silane coupling agent, Vinyl-Siloxane, Ethoxy-Aluminaphosphate and Alkyl-Aryl Siloxane, and Polysilazane based coating solution including PerHydro-Polysilazane (PHPS) or Organo-Polysilazane (OPSZ) as a main component.

(160) Accordingly, by collecting the small oil droplets in the contaminant collecting portion 44, it is possible to prevent a contaminant in the form of black spot from being generated on the cooking chamber inner wall 4 on which the coating film 43 is formed by a deposition of the small oil. More, as shown in FIG. 33, since an oil stain is concentrated on the rear face of the cooking chamber inner wall 4 of the oven 100 on which the catalyst coating layer is formed, the contaminant may be hardly generated on the side faces of the cooking chamber inner wall 4 on which the coating film 43 having the liquid repellency is formed. Further, a contaminant in the contaminant collecting portion 44, that is, an oil stain of the catalyst surface, can be decomposed and cleaned by heating by the heater 5, for example, raising the temperature in the cooking chamber 1 to 380 C.

(161) Further, a main component of the catalyst may include a noble metal, various catalyst metals (Ag, Pt, Pd, Au, Cu, Ru, Ti, Ni) and a material including at least one of these metal elements. In addition, the cocatalyst may include a metal oxide (MnO.sub.2, CeO.sub.2, Al.sub.2O.sub.3, Bi.sub.2O.sub.3, SnO, TiO.sub.2, Cr.sub.2O.sub.3, Co.sub.2O.sub.3, Fe.sub.2O.sub.3, CuO, ZrO.sub.2, SrO, LaO, V.sub.2O.sub.5, Li.sub.2O, ZnO, MgO, NiO, CuO, BaO) and a compound including at least one kind thereof. In other words, the catalyst coating layer may include a catalyst including at least one of Ag, Pt, Pd, Au, Cu, Ru, Ti and Ni, and a cocatalyst including at least one of MnO.sub.2, CeO.sub.2, Al.sub.2O.sub.3, Bi.sub.2O.sub.3, SnO, TiO.sub.2, Cr.sub.2O.sub.3, Co.sub.2O.sub.3, Fe.sub.2O.sub.3, CuO, ZrO.sub.2, SrO, LaO, V.sub.2O.sub.5, Li.sub.2O, ZnO, MgO, NiO, CuO and BaO.

(162) Next, a fifth modification of the fourth embodiment of the present disclosure will be described. In the fifth modification, a vane may be a contaminant collecting portion 44. As shown in FIG. 34, a plurality of vanes may be provided so as to stand perpendicularly to the cooking chamber inner wall 4 on which the fan 61 is installed and forming the rear face of the cooking chamber 1. The vane may be convexly formed with respect to an outer circumferential direction of the fan and may stand up with respect to the cooking chamber inner wall 4 provided around the fan 61. In addition, the vane may be configured to allow the air flow discharged from the fan 61 to move along the vane and to be gradually deflected tangentially from a centrifugal direction. That is, the contaminant collecting portion 44 may include a plurality of vanes installed along the outer circumferential direction of the fan 61 so that the air flow discharged from the fan 61 is gradually deflected in the tangential direction of the fan 61 from the centrifugal direction of the fan 61. More particularly, as shown in FIG. 35, each vane may be radially arranged by a helical curve centering on the fan 61. Each vane may be arranged at substantially equal intervals in the circumferential direction. In addition, a size and a length of each vane may be designed in consideration of air resistance so that an air volume is 23 to 26 L per a second. At this time, the air volume may be obtained by integrating an air flow rate distribution of an inlet port and a division area. As shown in FIG. 36, at the time of use, each vane may be accommodated in a case and may not be visible to the user.

(163) In a case of the oven 100 constructed as described above, as shown in FIG. 36, even if the cooking is repeated over a long period of time, a small oil droplet contained in the air flow may be collected in the vane corresponding to the contaminant collecting portion 44, so that the oil may not be accumulated on the cooking chamber inner wall 4 on which the coating film 43 is formed. Therefore, it is possible to prevent an occurrence of a spot-shaped contaminant.

(164) Next, another example of a vane will be described. A plurality of vanes may not be all formed in the same shape but a plurality of vanes having different lengths in a flow direction as shown in FIG. 37 may be arranged. More particularly, a long vane and a short vane may be alternately arranged along the circumferential direction of the fan 61. FIG. 38 shows a contamination state when 20 raw chickens were cooked using the vanes. As can be seen from a comparison between FIGS. 36 and 38, an amount of contaminant adhering to the side face and the rear face of the cooking chamber inner wall 4 corresponding to a periphery of a fan case may be smaller when the vanes having different lengths in the air flow direction are provided than when the same vanes are radially arranged. That is, by using the vanes having different lengths, it can be confirmed that a fact in that a collecting area increases, a fact in which a separation effect of the smoke is improved due to an improvement of a rectification effect of the air flow, and a fact in which a collecting effect of the air flow passing between the vanes at an outer peripheral part where a distance from a center becomes larger acts.

(165) Next, still another example of a vane will be described. As shown in FIGS. 39 and 40, a plurality of protrusions 44j having a substantially triangular shape as a vortex generator may be provided between the vanes along the air flow direction. The protrusions 44j may be bent. A vortex may be generated in the air flow by the protrusions 44j, and the air flow passing between the vanes may collide with the vanes. As a result, oil droplets contained in the air flow can be easily collected in the vanes. The left drawing of FIG. 40 shows a position of the vortex generators, that is, a position of the protrusions 44j, in one quarter of the entire area. The central drawing of FIG. 40 shows a bending position. The right drawing of FIG. 40 shows a planar dimension of a bent portion. The detailed dimension may be determined by a relationship with a wind speed, an air flow width, and a spiral curve of the vane, but may be determined as shown in view of workability. But is not limited to the dimension shown.

(166) When the vortex generator, that is, the protrusion 44j, is formed as described above, a collecting effect of a small oil droplet or the like in the vanes may be further enhanced as shown in FIG. 41. Therefore, it is possible to further prevent an oil stain from adhering to the cooking chamber inner wall 4.

(167) FIG. 42 shows a difference in the collecting effect of the contaminant depending on a presence or absence of the vortex generator, that is, the protrusions 44j. The left drawing of FIG. 42 is an experimental example in which the vortex generator, that is, the protrusions 44j, is not provided, and a support plate is planar, and the right drawing of FIG. 42 shows an experimental example in which the vortex generator, that is, the protrusions 44j, is provided. It is considered that a vortex was generated because a lot of contaminants were collected when the vortex generator was installed and contaminants adhered to two sides of a bent triangular plate (a surface which can be visually recognized from the drawing as a downstream side surface of a wind). Therefore, it can be seen that an installation position and the number of installations of the vortex generator can be changed and increased or decreased according to the optimization.

(168) In addition, an example, in hick the catalyst coating layer is formed on the vane or the periphery of the vane in the above embodiment, and it can be cleaned in a cleaning operation mode involving heating when contaminants are accumulated in the inside of the fan case, will be described. FIG. 43 shows a state before the oven 100 is used. At this time, the oven 100 may include the contaminant collecting portion 44 composed of the vortex generator and the vane, and the catalyst coating layer formed on the vane or around the vane. The catalyst may be formed of a metal (Ag, Pt, Pd, Au, Cu, Ru, Ti, Ni) and a material containing at least one of these metal elements. In this example, Pt is used.

(169) FIG. 44 shows a state when 20 raw chickens were cooked, and FIG. 45 shows a state when 40 raw chickens were cooked. From the drawings, it can be seen that a contaminant collecting effect dose not deteriorate for a long period of time because the catalyst coating layer is formed, and as a result, a cleanliness of the cooking chamber inner wall 4 is increased. In particular, in a comparison with FIG. 44, it can be seen that the contaminant was overwhelmingly less than when 20 raw chickens were cooked in a state in which the catalyst coating layer is not provided. Therefore, it can be seen that a capability of collecting contaminant is improved by at least two times by forming the catalyst coating layer. Further, in order to sufficiently exert an action of the catalyst coating layer, a content of Pt caused a remarkable effect at 220 C., which is the normal cooking temperature range.

(170) Next, a cleaning method such as the vane or the like having the catalyst coating layer and a construction therefor will be described. The control board 8 may control the ON/OFF of the fan 61 by operating the heater 5 to heat the catalyst coating layer. As a result, the temperature at a portion where the catalyst coating layer is formed may become a temperature range of 250 C. or more and 400 C. or less. More particularly, the control board 8 may function to lower a duty of the fan in the cleaning than a duty of the fan in the normal cooking. In order to exert a decomposition function in the catalyst coating layer, for example, an ON/OFF control cycle may be 5 to 60 seconds, and an ON duty may be 16% to 20%. As a result of the experiment using Pt as the catalyst, that is, as shown in Table 4, a contaminant decomposition effect was confirmed under the above conditions.

(171) TABLE-US-00004 TABLE 4 fan operation on: 10 sec/ on: 1 sec/ on: 0.5 sec/ off 60 sec 5 sec 5 sec Fan case surface 280 or 280 or 280 or 280 or temperature more more more more Difference 60 or 60 or 60 or 60 or between fan case more more more more surface temperature and inside of cooking chamber set temperature Internal vane about 220 variation about 270 about 220 temperature between about 230 to 260 Difference no 10 to 50 about 50 no between fan case surface temperature and inside of cooking chamber set temperature Variation of no yes no no internal vane temperature Decomposition possible possible possible possible of contaminant on surface of fan case Decomposition impossible possible (low possible impossible of contaminant efficiency) of internal vane

(172) In such a case, it is convenient to use because it does not require a special cleaning operation. If it is possible to set at a locally high temperature and include the catalyst material described above, that is, the noble metal (Ag, Pt, Pd, Au, Cu, Ru, Ti, Ni) and the material containing at least one kinds of the metal elements, particularly, Pt is not contained, a cleaning may be possible in the normal operation mode.

(173) Next, it shows an example in which a decomposition of an oil stain is possible in a temperature range of 400 C. or lower when a SiO.sub.2 film, which has a thickness of nm-order and is made of a Polysilazane based coating solution, is disposed between a catalyst containing Ag and the MnO.sub.2, as the cocatalyst, and a surface of a metal component of a material. As shown in FIG. 46, an oil stain fixedly adhered on a surface of the catalyst and a surface of an enamel as a comparative object was generated randomly. Further, a temperature environment in the cooking chamber 1 was realized with a temperature profile shown in FIG. 47, and a decomposition speed of the oil stain was compared with the conditions. FIG. 47 shows a case in which a set temperature in the cooking chamber 1 is 350 C. It has been confirmed that a temperature fluctuation, when the high temperature is maintained, is minimized by the ON/OFF control of the heater 5. However, if an average temperature is the same even if there is variation, it is expected that no large difference will occur in the result.

(174) FIG. 48 shows an experimental result under a condition that a set temperature is 380 C. A decomposition rate was determined by a decrease rate in weight measurement. Under the condition of 380 C., it is possible for contaminants on the surface of the catalyst to be completely decomposed for 0.5 hour (30 minutes). Observation with an optical microscope revealed no oil stain stuck to black.

(175) FIG. 49 shows an experimental result under a condition that a set temperature is 350 C. As a decomposition rate is lowered, it takes 2 hours for complete decomposition. Therefore, in the cleaning mode, it can be seen that when a cleaning, under a condition that a set temperature in the cooking chamber 1 is 380 C. and an operation time is within 2 hours, is performed, the cleaning can be performed at a cleaning time equivalent to the conventional cleaning mode.

(176) Next, a sixth modification of the fourth embodiment of the present disclosure will be described. In the sixth modification, not only the entire inside of the cooking chamber 1 is heated, but only a portion where the catalyst coating layer is formed is locally heated during cooking to decompose contaminants. That is, a cleanliness of the cooking chamber inner wall 4 can be maintained for a long period of time without executing the cleaning mode which consumes a large amount of electric power and takes a long time. In FIG. 50, as an experiment, only a part is carried out at 380 C. by a nichrome wire. As shown in the left drawing of FIG. 50, it can be seen that a cleanliness is maintained in the heated part because the contaminants are decomposed in the heated part. Therefore, in the sixth modification, a catalyst coating layer heating heater may be brought close to a portion where the catalyst coating layer is formed, so that a decomposition reaction occurs even in the heating cooking. The catalyst coating layer and the catalyst coating layer heating heater may be designed so that a distance therebetween is, for example, 1 mm or less. As described above, the oven 100 may further include the catalyst coating layer heating heater installed in the cooking chamber 1 to heat the catalyst coating layer.

(177) Next, a seventh modification of the fourth embodiment of the present disclosure will be described. In the seventh modification, in the inside of the cooking chamber 1, a member having a large specific surface area and no liquid repellency is disposed in an air flow path formed by the fan 61. For example, as shown in FIG. 51, a filter may be disposed at the inlet of the fan 61 so as to exhibit a function as the contaminant collection portion 44. By forming the catalyst coating layer on the filter described above, it is possible to decompose the contaminants deposited in the contaminant collecting portion 44, thereby preventing a small oil stain from being deposited on the coating film 43 over a long period of time. That is, the contaminant collecting portion 44 may include the filter disposed at least one of the inlet and the outlet of the fan 61. Preferably, the filter may be disposed at the inlet of the fan 61.

(178) Further, the filter may be formed of a porous material, and the catalyst coating layer may be appropriately selected. Particularly, the filter may be formed of at least one of a porous material and a fibrous material.

(179) In addition, combinations and modifications of various embodiments may be carried out without departing from the spirit of the present disclosure.

(180) While the present disclosure has been particularly described with reference to exemplary embodiments, it should be understood by those of skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the present disclosure.