Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B6/00—Heating by electric, magnetic or electromagnetic fields
  • H05B6/64—Heating using microwaves
  • H05B6/647—Aspects related to microwave heating combined with other heating techniques
  • H05B6/6491—Aspects related to microwave heating combined with other heating techniques combined with the use of susceptors
  • H05B6/6494—Aspects related to microwave heating combined with other heating techniques combined with the use of susceptors for cooking
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S99/00—Foods and beverages: apparatus
  • Y10S99/14—Induction heating

Definitions

• the browning containers for microwave ovens currently available on the market include a conductive film of tin oxide as a browning coating. They have a fairly limited lifespan. Depending on the use, the heating time becomes longer and longer. This deterioration in heating characteristics is related to the low resistance to detergents of the electrically conductive tin film.
• This tin oxide film is normally applied by a process comprising heating the support with a solution of a thermally decomposable tin compound. In addition, this tin oxide film is not flame resistant, which limits the use of this dish exclusively in the microwave.
• the subject of the present invention is a culinary container (dish, pan etc.) provided with a browning coating for a microwave oven, as well as a method for producing the coating, eliminating the drawbacks indicated above.
• the browning coating which makes it possible to brown the food in a microwave oven, is applied to the external surface of the container.
• the electrically conductive metallic elements are no longer provided by a thermally decomposable compound, they are incorporated into an enamel which can be applied in different ways to an unheated substrate (which widens the possibility of choice as to the nature of the electro element -conductor and greatly facilitates the implementation of the process).
• a protective enamel layer can be applied by superimposition on the electrically conductive enamel layer.
• the present culinary container is therefore characterized in that its browning coating, which is external, essentially comprises a heating layer, of lead-free enamel in which are incorporated electrically conductive elements in the form of a metal powder composed of at least one substance chosen from electrically conductive metals and their mixtures, the oxides of these metals and their mixtures, and mixtures of these metals and their oxides, said powder being intimately mixed with enamel.
• electrically conductive elements in the form of a metal powder composed of at least one substance chosen from electrically conductive metals and their mixtures, the oxides of these metals and their mixtures, and mixtures of these metals and their oxides, said powder being intimately mixed with enamel.
• metals mention may be made of zinc, aluminum, copper, nickel, chromium, transition elements, in particular iridium, platinum, ruthenium, rhodium, palladium, silver, gold. , mixtures of these metals.
• the oxides which can be used are, in particular, those of the abovementioned metals and their mixtures, and mixtures of metals and oxides can also be used.
• Zinc, transition metals, corresponding oxides and mixtures of these substances are preferred; they provide particularly strong and durable coatings, resistant well to detergents and acids.
• the proportion of metallic powder in said heating layer is generally from 15 to 40% by weight.
• Said heating layer is advantageously covered with a protective layer of lead-free enamel.
• the thickness of the layers is approximately 12 to 30 microns for the first and 10 to 20 microns for the second.
• the lead-free enamel of the heating layer or the protective layer can be based on acrylic resins including various mineral substances such as oxides, anhydrides, salts.
• the process according to the invention for producing a browning coating on a culinary container for a microwave oven is characterized in that a layer of lead-free enamel containing an intimate mixture is deposited on the external surface of the container.
• a metallic powder composed at least one substance chosen from electrically conductive metals and their mixtures, the oxides of these metals and their mixtures, and mixtures of these metals and their oxides, the layer thus formed being subjected to baking at a temperature included between 620 and 800 ° C to provide a heating layer, in which the proportion of metal powder is generally 15 to 40% by weight. More particularly usable substances have been mentioned above.
• a protective lead-free enamel protective layer is advantageously deposited, after which all of the two layers are subjected to said cooking, the thicknesses of which are those indicated above.
• the lead-free enamel used for the two coats can be as defined above.
• This enamel is said to be lead-free, because its lead content (toxic metal) is much lower than the maximum content accepted by the standards existing in the various countries for household or culinary utensils, the analysis being made on acetic acid at 4% by weight, in which the container has been soaked for 24 hours at room temperature.
• each of the two layers can be carried out by screen printing, hot, in which case a lead-free enamel with a hot-melt medium melting at around 40-60 ° C. is used, enamel which is applied through a conductive screen-printed fabric heated to a temperature of around 60-80 * C.
• each of the two layers can also be carried out by decalcomania, at room temperature, in which case a lead-free enamel with an oily medium is used.
• the deposit can also be obtained by a transfer process: the enamel layer is deposited, hot or cold depending on the nature of the enamel, by means of a plate or a screen, on a plate or a membrane, then it is taken up with a silicone-based pad to be transferred to the external surface of the container to be coated.
• the lead-free enamel, initially in the solid state, used for the heating layer comprises, at a rate of 25 to 30% by weight, a hot-melt or thermoplastic medium which is a mixture of acrylic resins and a plasticizer of these resins and, in an amount of 15 to 40% by weight, an electrically conductive metal powder, for example zinc powder or zinc oxides, or at least one transition metal or oxide of such a metal, or a mixture of these substances, the remainder consisting of various mineral substances (comprising the following constituents: SiO 2 , B 2 0 3 , Al 2 O 3 , ZnO, Li 2 O, ZrO 2 , BaO, F 2 , Sn0 2 , TiO 2 ).
• the hot-melt medium melts at a temperature of 40 to 60 * C.
• the heating layer is therefore deposited by screen printing, by heating the conductive screen fabric, on which the enamel is spread, at a temperature of 60 to 80 ° C. , by direct heating (by Joule effect) or indirect (for example by means of infrared rays).
• a heat application time of 30 seconds is sufficient to form the coating on the outer surface of the container, placed under the screen fabric.
• the protective layer is produced in the same way, with a lead-free enamel of the same composition, except that it does not contain any electrically conductive metallic powder; it is therefore richer in various mineral substances.
• the coating comprising the two layers is baked in an annealing oven (of the annealing arch type), at a temperature between 620 and 800 ° C.
• the total duration of the cooking cycle is 50 to 60 minutes.
• the first layer has a thickness of approximately 15 to 25 microns and the second has a thickness of approximately 10 to 15 microns, the optimum thickness of the assembly of the two layers being 25 to 30 microns.
• the lead-free enamels used for each of the two layers are initially oily.
• Their oily medium which represents 15 to 20% of their weight, is a mixture of acrylic resins and terpene oils. Their other constituents are qualitatively identical to those of the two enamels described in Example 1.
• the proportion of electrically conductive powder in the enamel used for the heating layer is, as in Example 1, from 15 to 40% by weight.
• the heating layer is deposited, then the protective layer, by decal, at room temperature.
• the thickness of the layers is approximately 20 microns for the first and approximately 10 microns for the second, the optimum thickness of the assembly of the two layers being 25 to 30 microns.
• Example 1 The whole of the two layers is cooked as in Example 1.
• an empty dish, 6 millimeters thick, coated by the method according to example 1 or 2 reaches a temperature of 300 ° C. after 5 minutes of exposure in a microwave oven, instead of 80 at 100 * C without the coating.
• the electrically conductive metal contained in the coating allows the temperature of the dish to rise enough to brown the food, which will be placed in the dish. It is noted, on the other hand, that there is no electric arc, that there are therefore no excessive hot spots, which could destroy the coating; it is assumed that this stabilization of the temperature rise is due to the presence in the coating of metal oxides, whether they are initially introduced into the heating layer or whether they are formed from the metal or metals initially introduced work, during the final coating firing operation.
• the life of the coating is practically unlimited.
• the enamels which are the basis of its composition, provide resistance to fire and chemicals and the fact that the coating comprises two layers reinforces this resistance.

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• Electromagnetism (AREA)
• Cookers (AREA)

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• 1987
  • 1987-05-07 US US07/047,335 patent/US4751358A/en not_active Expired - Fee Related
  • 1987-05-14 EP EP87401085A patent/EP0247922A1/de not_active Withdrawn

Patent Citations (11)

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