HU210599B - Process for producing special coat-work of dish and/or inset for microwave ovens - Google Patents

Abstract

The object of the invention is a process for producing microwave crockery and/or inserts fitted therein in which an absorbent layer is applied to the ceramic base in such a way that the microwave-absorbing material of the absorbent layer consists of metal oxides or ferrites or a mixture thereof. The ferrite components are produced by powder metallurgy from the mixture of metal oxides and/or metal carbonates in accordance with the general formula: Me<2+>Me<3+>2O4 spinel ferrite, or Me<2+>Me<3+>12O19 and or Me<2+>2Mê<2+>2Me<3+>12O22 hexagonal ferrite, where Me<2> and Mê<2> are different divalent metal ions and Me<3+> is a trivalent metal ion. These metal oxides and/or ferrites are mixed in a proportion of 1 to 50 wt %, and preferably 5 to 20 wt % with a material, the natural Fe2O3 content of which is at least 4.5 wt %. It is then homogenised in a proportion of 50 wt % at most with a semi-porcelain filler compound and finally the engobe thus produced is evenly applied, e.g. by spraying, to the ceramic base and then fired.

Description

The present invention relates to a process for producing a special coating of a microwave oven pan and / or insert placed in a microwave vessel.

The principle of microwave oven heating and cooking is fundamentally different from the traditional external heating method. The energy emitted by the microwave energy stimulates the rotational movement of the water and fat molecules of the food - as a result, the temperature inside the food rises very steeply - as a result of the energy transferred, the food is cooked. Conventional cooking time using microwave cooking techniques is reduced to a fraction. In this case, the container must be made of microwave permeable material; such as glass, paper, plastic or non-metal-ionic ceramics.

Since in this case the food is not heated "externally", it follows from the technique that the food baked in the microwave does not have the traditional slightly brownish color, texture and taste. Manufacturers have long been seeking several solutions to overcome this disadvantage.

It is known in the art to integrate a conventional infrared oven with a microwave oven. The food is cooked with the help of microwave energy and then a pleasant color is achieved with the infrared oven. Such kitchen appliances are also commercially available. These units are complex in design, high in electricity (more kW) and high in commodities.

Alternatively, the food to be cooked is placed in or under the microwave-absorbing heaters in the microwave-transmitting vessel. Such a solution is disclosed in U.S. Patent No. 3,701,872, which allows a special design of bottom and top baking and even rotating barbecue. The container material is microwave permeable material, e.g. glass, ceramic, epoxy - cardboard compositions; insulated with sand, concrete and other materials. gravel, covered with ferrite or carbon absorbents and fitted with good heat conductive bars.

A special microwave heating element is proposed for use in application number 5643/89, published under T / 56 216, wherein the microwave absorbing fuel element is zeolite.

The disadvantage of the above solutions is that the rapid heating of the concentrated fuel elements results in significant dilatation, which leads to material fatigue and cracks during repeated heating and cooling. They are complex in structure, costly to produce and do not meet strict food health standards.

It is also known that the food to be prepared is wrapped in a metal foil, e.g. packed in aluminum foil as a heating element. Such a solution is described in U.S. Patent No. 4,190,757. The disadvantage of this solution is that the metal material in the microwave space can cause harmful overheating.

A microwave cooking apparatus has been proposed where the food to be prepared is placed in a completely enclosed space and the cooking function is accomplished by using a metal coating and an absorbent heater, or a solid ferrite or silicon carbide pottery. The disadvantage of the solution known from the above-mentioned U.S. Patent No. 3,941,967 is the complicated and closed arrangement which completely encloses the material to be cooked. As a result, the microwave energy cooking mechanism does not work because the dish shades the microwave energy, thus significantly increasing the cooking time.

Several methods are known in which a microwave absorbing layer (made of ferrite, metal, and various oxides) is applied to the bottom of the cookware or insert. The absorbent layer thus applied is generally absorbent, and is therefore e.g. in U.S. Patent No. 4,496,815, the ferrite absorber is embedded in a high molecular weight organic material in a silicone resin, U.S. Patent No. 4,542,271 uses TEFLON, and US Patent 4,454,403 discloses epoxy. These technologies are relatively sophisticated and far from the finnamon ceramic industry.

It is an object of the present invention to overcome the drawbacks of known processes by a novel process which is well adapted to ceramic technology.

The present invention is based on the discovery that when a powdered mixture of metal oxides or spinel or hexagonal ferrites as a microwave absorber is blended with a high iron oxide content and then coated with a semi-porcelain casting compound, inserts can be made in any dish that is otherwise suitable for a microwave kitchen operation.

A further basis of the invention is the discovery that the microwave absorbent material can be applied to the raw glaze formed on the ceramic substrate by indirect screen printing (dyeing) also commonly used in the ceramic industry.

The present invention therefore relates to a process for preparing a special coating of a microwave oven pan and / or insert in a microwave vessel, comprising applying an absorbent layer on a ceramic substrate such that the microwave absorbent material of the absorbent layer consists of metal oxides or ferrites. wherein the ferrite component is prepared from a mixture of metal oxides and / or metal carbonates by powder metallurgy according to the following formula

Me ²⁺ Me ^ O ₄ spinel ferrite, respectively

Me ²⁺ Me ³ , ⁺ p19, and / or Me ² ^ Me '^ Me' ^ 2 O ₂₂ hexagonal ferrite, wherein

Me ²⁺ and Me ' ^{2+ are} different divalent metal ions and Me ³⁺ is a 3 divalent metal ion, some of which is necessarily Fe ³⁺ .

These metal oxides and / or ferrites are present in an amount of from 1 to 50% by weight, preferably at 1260 ° C, 0.52.

HU 210 599 B

5% by weight in the case of 3.0% water uptake of semi-porcelain - mixed with a material having its own Fe ₂ O ₃ content min. 4.0% w / w and then max. It is homogenized with 50% by weight of semi-porcelain molding compound and finally the coating thus prepared is uniformly applied to the ceramic substrate, e.g. spray technology, and finally burn at 1260 'Con. Characteristics and role of the ingredients used in the composition:

Casting compound: The composition is the same as the base compound for good bonding, good coverage in spray application and stabilizes the melting point.

Best application is in the range of 10-30% by weight. (The percentages here and below refer to weight percentages.)

Clay: low melting point: 1150 ° C-1200 ° C; high Fe ₂ O ₃ content: 4-6%, SiO ₂ content 45-50%, Al ₂ O ₃ content 14-15% and alkaline content 3.1-3.5%. The addition of clay varies according to the desired melting point within a range of 40-70%. The Fe ₂ O ₃ content of the clay enhances the tanning and toasting effect of ferrite.

Ferrit: Can be applied within the range of 5-20%, the softening effect is greatly reduced below 5%, the tanning effect is increased with 20%, but the price of the finished product is increased by the higher or max. 20% ferrite additive. Ferrite has a melting point enhancer.

Thus, examples suggesting the use of preferably 5 to 20% by weight of ferrite are:

1. When using 5% by weight of ferrite:

casting mass 30% clay 65% ferrite 5%

1OO%

2. 20% by weight of ferrite:

casting mass 10% clay 70% ferrite 20%

100%

According to the invention, it is also possible to apply a crude glaze coating on the ceramic substrate in a first step and then apply a microwave absorbent material to the crude glaze on the base of the microwave baking dish or insert by indirect screen printing.

In one embodiment of the method of the invention, the useful surface of the microwave oven pan or dish is min. 70% is coated with a microwave absorbent material. Useful surface refers to the baking or cooking surface of the container or liner which, when perpendicular to the side walls, is approximately the same as the surface of the base.

It is a further essential feature of the invention that the ceramic substrate and the layer containing the microwave absorbent material applied thereto can be fired in a single technological step in a neutral atmosphere between 1200 and 1300 ° C.

The main advantages of the process according to the invention are as follows:

- simple technology used in the practical ceramics industry,

- productive process, eg. spray technology can be well automated in mass production,

- energy saving because it only requires a single burn.

Advantages of the article made according to the invention.

- as a stand-alone oven-baking dish, without the need for separate grilling, it is capable of performing a toasting operation within the usual cooking time in commonly used microwave appliances,

- as any insert in a microwave-permeable container, it also performs the same function,

- where appropriate, the pan or liner may be used on a conventional stove,

- the coating thus produced has an aesthetic appearance, is solid, water and abrasion resistant, well tolerated by heat and can be cleaned in the dishwasher,

- the price of the dish and the insert are in line with that of other household utensils.

The process of the invention is illustrated by the following examples:

Example 1

A microwave absorbent coating is formed on the microwave-permeable pad. The insert containing the microwave absorbent coating is located in a heat-resistant vessel, such that the height of the insert is max. 60%. The insert was made by the following procedure.

A uniform weight distribution of 1550 g / l is applied over the entire surface of the raw, dry, disked pad with a spray gun of 0.5 to 0.8 mm film thickness.

Composition of the coating:

clay, containing by weight at least 4% Fe 2, at 1260 ° C, with a sieve residue of 63 μm (10 000 holes / cm ² ), 0.01-0.04% by weight, 31% by weight of heat-resistant crude semi-porcelain molded particle scrap with a mesh residue of 0.02-0.07% by weight on a 90 μm sieve (4900 holes / cm ² ), 8% by weight of powdered Fe, obtained as follows:

A mixture of powders by weight of Fe ₂ O ₃ , 18 wt% NiO and 21 wt% ZnO, i.e. a mixture of spinel ferrite Me ²⁺ Me 2 O ₄ , is homogenized in a ball mill and heated at 1050 ° C for 4 hours under an inert atmosphere. It is then milled in a ball mill and subjected to repeated heat treatment for 2 hours in a neutral atmosphere. After sintering, grind in a ball mill to an average particle size of 1-5 μιη. To the dry substance of the above composition was added 20% by weight of water and homogenized. The insert is fired after drying in a neutral oven at 1260 ° C.

Example 2

The microwave absorbent coating has the same design as in Example 1, except that Fe ₂ O ₃ is used instead of ferrite powder.

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Composition of the coating:

% by weight of casting mass% by weight of clay by weight% magnetite

Example 3

The microwave absorber layer is deposited by indirect screen printing on the outer surface of the container, which is in contact with food, with a surface of min. 70% to achieve the right efficiency.

A mixture of 83% by weight of Fe ₂ O ₃ , 17% by weight of BaCO _3, i.e. hexagonal ferrites of the formula Me ²⁺ Me 2 O ₉ , was homogenized in a ball mill, heated at 1050 ° C for 4 hours in a neutral atmosphere and then milled in a ball mill . It is then sintered at 1260 ° C for 2 hours in an inert atmosphere and then milled to a mean particle size of 1-5 gm in a ball mill.

The ferrite powder thus prepared is made into a well-spread, homogeneous paste by means of a water-soluble paste material used in the manufacture of stickers. The paste is composed of 75% by weight ferrite powder and 25% by weight water soluble paste. The thickness of the paper backing layer is determined by the density of the 90 μm (4900 holes / cm ² ) screen and the paste described above. The sticker is applied manually to the base of the finished glazed heat-resistant pan, followed by 2 hours drying. The vessel is then fired in a neutral atmosphere at 1260 ° C. During the firing, the organic paste is sufficient and the base of the vessel is covered with a 100% microwave absorbing layer of microwave, according to the decor used.

Depending on the function, the décor used can be a pattern of dots, hearts, squares, flowers, placed at a distance of 23 mm. Spacing between evenly distributed décor over the entire surface max. They make up 30%.

Functional decoration can also be applied to the raw glaze by using a suitable media or by machine decoration - direct printing. The drying and firing are carried out as described above.

Claims (4)

CLAIMS 1. A process for preparing a coating of a microwave oven pan and / or insert in a microwave vessel, comprising applying an absorbent layer to a ceramic substrate, wherein the microwave absorbent material comprises metal oxides or ferrites or mixtures thereof; the ferrite component is prepared from a mixture of metal oxides and / or metal carbonates by powder metallurgy according to the following formula Me ²⁺ Me ^ O ₄ spinel ferrite, respectively Me ²⁺ Me 2 O ₁₉ , and / or Me 2 Me 4 O 2 hexagonal ferrite, wherein Me ²⁺ and Me ' ²⁺ different 2-valent metal ions, Me ³⁺ is a 3-valent metal ion, some of which is necessarily Fe ³⁺ . and then mixing said metal oxides and / or ferrites in a weight proportion of 150% by weight, preferably 5-20% by weight, with a material having an intrinsic Fe ₂ O ₃ content of min. 4.0% w / w and then max. It is homogenized with 50% by weight of semi-porcelain molding compound and finally the coating thus prepared is uniformly applied to the ceramic substrate, e.g. applied by spray technology and then fired. 2. The method of claim 1, wherein the ceramic substrate is first coated with a raw glaze coating, and then the microwave absorbent material is applied to said crude glaze by indirect screen printing (sticking), in the microwave baking dish, or on the sole of the insert. Method according to claim 2, characterized in that the useful cross-sectional area of the microwave oven or dish is min. 70% is coated with a microwave absorbent material. 4. A process according to any one of claims 1 to 3, characterized in that the layer containing the ceramic substrate and the material absorbed by the microwave is fired in a single technological step in a neutral atmosphere between 1200 and 1300 ° C.