KITCHEN APPLIANCES WITH EASY-TO-CLEAN SURFACES AND METHODS FOR APPLYING THEM

Abstract

Method for applying easily cleanable surfaces to kitchen appliances, wherein at least one surface of the kitchen appliance is coated by a coating process in low-pressure plasma, wherein the kitchen appliance is an oven, characterized in that the low-pressure plasma required for the coating process is generated in the oven interior (1), wherein the low-pressure plasma in the oven interior (1) is ignited using a coupling electrode (4) located therein, which is connected via a feedthrough (7) to a generator (6) located outside the oven interior (1), and wherein the coupling electrode (4) has a geometry which is modeled on the geometry of the oven interior (1).

Description

Technical field

[0001] The present invention relates to a method for applying easily cleanable surfaces to kitchen appliances, characterized in that the application of the surface coating takes place in low-pressure plasma.

[0002] The present invention further relates to kitchen appliances whose surfaces have been coated by the aforementioned method. State of the art

[0003] Various kitchen appliances (e.g., ovens, grills, microwaves) become heavily soiled over their lifespan due to a wide variety of fats and organic materials that come into contact with hot surfaces. If these materials are not removed promptly, stubborn carbon deposits form, which can usually be removed with chemical cleaning agents, abrasive cleaners, or by pyrolysis.

[0004] Various solutions to the described problem are available on the market. Modern ovens are often equipped with a highly porous coating capable of decomposing grease residues without high-temperature pyrolysis at relatively low temperatures (typically 250°C) (e.g., the "ActiveClean" brand from BSH Bosch Siemens Home Appliances). The self-cleaning effect results from the highly porous structure of the ceramic coating. Organic deposits are absorbed by the highly porous layer and thus exposed to a significantly larger substrate surface. The thermal decomposition of these dispersed deposits then occurs even at moderate temperatures of 300°C (see, e.g., DE 10143837 A1).

[0005] Pyrolysis represents another approach. In pyrolysis (EP 0 995 951 B1) or thermocatalytic (DE 10 2008 039 684 A1) self-cleaning, a thermochemical cleavage of organic compounds is achieved, in which high temperatures (> 450°C) force the breaking of bonds within large molecules into smaller ones. Unlike other cleaning methods, this occurs solely through the action of heat and without the use of chemicals. Due to the required high temperatures, this pyrolytic cleaning process is complex in terms of the design and material selection of the furnaces and is uneconomical due to steadily rising energy costs.

[0006] Another class of ovens is equipped with a special steam cleaning program. Here, a specific amount of water (several hundred ml), mixed with a few drops of dish soap, is poured into the oven cavity and evaporated and circulated inside. This allows for a relatively energy-efficient cleaning of the oven, but it is only suitable for removing light and, above all, fresh soiling.

[0007] Furthermore, repellent sol-gel coatings based on alkylsilanes are used to facilitate the cleaning of ovens. One implementation of this approach is the coating of metallic surfaces based on monolayer or sol-gel coating systems (sol-gel non-stick coating) (e.g., DE 19714949 A1), which exhibit good adhesion to the metallic surface as well as good scratch resistance and a low surface energy of < 20 mN / m. Under moderate conditions (temperature up to approximately 180°C), the coating systems exhibit improved cleanability compared to uncoated metallic surfaces. At higher temperatures (i.e., above 200°C) and especially with greasy soiling, such coating systems can no longer be easily cleaned, or only by destroying the coating system. This ultimately results in an unsatisfactory short service life or limited temperature range of the coatings.

[0008] The excellent non-stick and easy-clean properties of Teflon-based non-stick coatings are well-known in the kitchen, particularly in the coating of pans, and are widely used. Nevertheless, Teflon-based coatings are not yet used in ovens. This is partly because their application would require an additional coating and curing step, and partly because the material compositions used would be susceptible to slow degradation and a loss of properties at high oven temperatures, which can significantly exceed the set oven temperature of 250°C. Furthermore, the currently available materials do not offer the necessary mechanical stability to guarantee long-term effectiveness throughout the oven's lifespan.

[0009] The processes and surface coatings described so far only partially solve the aforementioned problems. The reason for the poor cleanability results in the case of repellent coatings is that their development prioritized minimal wettability by aqueous or oily media. Since forced cross-linking occurs in practice anyway, and the wetting material is inevitably fused or burned by the temperature, the design of non-stick coatings should focus on a surface that is as smooth and highly lubricated as possible, and also exhibits a minimum of polar groups. According to current knowledge, this is hardly achievable with wet-chemical coating systems. Brief description of the invention

[0010] According to the invention, the described contamination problem is solved by applying a coating in low-pressure plasma.

[0011] In detail, the present invention provides a method for applying easily cleanable surfaces to kitchen appliances, characterized in that at least one surface of the kitchen appliance is coated by a coating process in low-pressure plasma.

[0012] In a preferred embodiment, the kitchen appliance is an oven. Preferably, in this embodiment, the low-pressure plasma required for the coating process is generated inside the oven. The low-pressure plasma can be ignited inside the oven using a coupling electrode located therein, which is connected via a feedthrough to a generator located outside the oven. Preferably, a plasma generator with an output frequency in the range of 1 kHz to 1 GHz is used as the energy source for the low-pressure plasma. In a further preferred embodiment, the coupling electrode has a geometry that replicates the geometry of the oven interior.

[0013] In a further preferred embodiment, the aforementioned method may also comprise at least one of the following process steps: feeding one or more precursors for coating the furnace interior via the fan opening; and evacuating the furnace interior with a pump to generate the low pressure. Here, one or more precursors preferably comprise a fluorine and carbon-containing compound, particularly preferably fluorocarbons, an organosilicon compound, and / or one or more hydrocarbons.

[0014] In a preferred embodiment, a gradient coating can be produced by continuously changing the ratio of at least two precursors introduced into the low-pressure plasma during the coating process. Alternatively, a multilayer coating can be produced by exchanging at least two precursors during the coating process.

[0015] The present invention also provides a kitchen appliance whose surface has been coated, at least partially, according to the methods described above, characterized in that the coated surface has practically no polar groups. Preferably, the kitchen appliance according to the invention further comprises either a gradient coating produced by continuously changing the ratio of at least two precursors introduced into the low-pressure plasma during the coating process, or a multilayer coating produced by exchanging at least two precursors during the coating process. In a preferred embodiment, the kitchen appliance is an oven. In a further preferred embodiment, the inner walls of the oven constitute the coated surface. Detailed description of the invention

[0016] An exemplary embodiment according to the present invention is described in detail below with reference to Fig. explains which schematically illustrates the principle of plasma coating in the oven.

[0017] During the inlet of the precursor into the furnace interior ( 1 ) via the fan opening ( 2 ) can be carried out, it is possible to control the pumping process via an opening in the base plate ( 3 ) connected pump ( 5 ). to carry out. A generator is used as the plasma energy source ( 6 ) used, which has a procedure ( 7 ) with which in the open interior space ( 1 ) coupling electrode located ( 4 ) is connected and is therefore able to be subjected to an external electrical voltage.

[0018] Igniting the plasma required for coating directly inside the oven offers the advantage of coating the entire interior with an easy-to-clean surface. Furthermore, generating the plasma directly within the oven without the need for the vacuum reactor typically used in such processes allows for optimization of both the process / cycle time (short pumping and homogenization times) and minimizes the equipment required for manufacturing. With the exemplary setup shown, the total coating time is approximately 10 minutes (including setup, pumping, and ventilation), making the inventive method extremely economical, even compared to conventional painting processes.

[0019] In general, a low-pressure plasma is characterized by the fact that the pressure in the plasma is below mean atmospheric pressure, i.e., less than 1013.25 hPa. Preferably, the plasma pressure is 0.1 to 1000 Pa, particularly preferably 10 to 500 Pa.

[0020] In principle, all currently available generators can be used as an energy source for the plasma. For example, radio frequency or high-frequency generators (from the kHz to the GHz range) can be used. If ionization is performed at frequencies in the GHz range, commercially available microwave horn radiators are suitable for exciting the gas. In a particularly preferred embodiment, kHz or MHz sources (i.e., plasma generators with an output frequency in the range of 1 kHz to 1 GHz) are used.

[0021] Various geometric designs are conceivable for the coupling electrodes. However, a shape that replicates the geometry of the oven is preferred, so that largely uniform deposition rates and thus advantageously uniform layer thicknesses are achieved throughout. Perforated sheets, among other materials, can be used as the starting material for the coupling electrodes.

[0022] Fluorine- and carbon-containing compounds are preferably used as precursors. In a particularly preferred embodiment, fluorocarbons such as perfluorocyclobutane (PFCB) are used. Organosilicon compounds or fluorocarbons can also be used as preferably suitable precursors. Depending on the required mechanical stress level of the coating, it may be advantageous to additionally use organosilicon precursors or hydrocarbons. In the process, this is achieved either by creating multilayer structures or by continuously changing the precursor gas content to deposit gradient layers that are very hard and resistant on the substrate side and exhibit increasingly polymeric and therefore poorly adhesive properties towards the baking chamber.

[0023] Examples of organosilicon precursors include organosilanes or siloxanes such as hexamethyldisiloxane (HMDSO).

[0024] Furthermore, in addition to fluorine and carbon-containing compounds and organosilicon precursors or hydrocarbons, the process gas may contain additional residual gases such as noble gases (e.g. argon), oxygen, nitrogen, carbon dioxide, carbon tetrachloride and gas mixtures, provided that this does not adversely affect the process control and the resulting coating.

[0025] The coating thickness can be selected according to requirements and precursor composition. Generally, the single-layer thickness is less than 100 μm, preferably approximately 10 nm to approximately 10 μm.

[0026] Thus, the inventive method, not least due to the easily achievable layer properties, enables an effective and, above all, comparatively cost-effective and long-lasting solution to the problems described above. Compared to wet-chemically applied surfaces, it is possible, by means of suitable precursor and process parameters, to produce completely non-polar surfaces that practically no longer exhibit any polar groups that would promote adhesion.

[0027] According to the present invention, a kitchen appliance is also provided, the surface of which has been coated at least partially according to the methods described above.

[0028] The kitchen appliance according to the present invention comprises both non-electric kitchen appliances (such as cookware, pans, roasters) and electric kitchen appliances such as ovens, grills, or microwaves. In a preferred embodiment, the kitchen appliance is an oven.

[0029] The coated surface of the kitchen appliance according to the invention is generally characterized by the fact that it has practically no polar groups. Preferably, the polar component of the surface energy is less than 5 mN / m, more preferably less than 1 mN / m, particularly preferably less than 0.5 mN / m, and especially preferably 0 mN / m. The surface energy is measured, and its polar and dispersive components are determined, according to common methods known to those skilled in the art (e.g., contact angle measurement and the methods of ZISMAN or OWEN, WENDT, RABEL & KAELBE).

[0030] In a preferred embodiment, the kitchen appliance according to the invention has a multilayer coating, which is achieved by deposition of the plasma-polymer layer using at least two precursors. As described above, the boundary between the layers can be indistinct (gradient layers due to continuous changes in the precursor gas proportions) or clearly defined (in the case that the precursors supplied are exchanged during the low-pressure plasma process). QUOTES INCLUDED IN THE DESCRIPTION

[0031] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0032] DE 10143837 A1

[0004] EP 0995951 B1

[0005] DE 102008039684 A1

[0005] DE 19714949 A1

[0007]

Claims

[1] Method for applying easily cleanable surfaces to kitchen appliances, characterized in that at least one surface of the kitchen appliance is coated by a coating process in low-pressure plasma. [2] Method for applying easily cleanable surfaces to kitchen appliances according to claim 1, wherein the kitchen appliance is an oven. [3] Method for applying easily cleanable surfaces to kitchen appliances according to claim 2, wherein the low-pressure plasma required for the coating process is located inside the oven ( 1 ) is generated. [4] Method for applying easily cleanable surfaces to kitchen appliances according to one of claims 2 or 3, wherein the low-pressure plasma is located inside the oven ( 1 ) using a coupling electrode located therein ( 4 ), which involves an implementation ( 7 ) with one located outside the oven interior ( 1) located generator ( 6 ) is connected, is ignited. [5] Method for applying easily cleanable surfaces to kitchen appliances according to claim 4, wherein the generator ( 6 ) a plasma generator with an output frequency of 1 kHz to 1 GHz. [6] Method for applying easily cleanable surfaces to kitchen appliances according to one of claims 4 or 5, wherein the coupling electrode ( 4 ) has a geometry which corresponds to the geometry of the oven interior ( 1 ) is replicated. [7] Method for applying easily cleanable surfaces to kitchen appliances according to any one of claims 2 to 6, which further comprises at least one of the following method steps: Feeding one or more precursor(s) for coating the furnace interior ( 1 ) via the fan opening ( 2 ); and Evacuating the furnace interior ( 1) with a pump ( 5 ) to generate the low pressure. [8] Method for applying easily cleanable surfaces to kitchen appliances according to claim 7, wherein at least one precursor comprises a compound containing fluorine and carbon. [9] Method for applying easily cleanable surfaces to kitchen appliances according to claim 7, wherein at least one precursor comprises fluorocarbons. [10] Method for applying easily cleanable surfaces to kitchen appliances according to any one of claims 7 to 9, wherein one or more precursor(s) are selected from the group consisting of fluorine and carbon-containing compounds, organosilicon compounds and / or hydrocarbons. [11] Method for applying easily cleanable surfaces to kitchen appliances according to any one of claims 7 to 10, wherein A gradient coating is produced by continuously changing the ratio of at least two precursors fed into the low-pressure plasma during the coating process; or a multilayer coating is created by exchanging at least two precursors during the coating process. [12] Kitchen appliance, the surface of which has been coated at least partially according to the method of claims 1 to 11, further characterized in that the coated surface has practically no polar groups. [13] Kitchen appliance according to claim 12, which further comprises either a gradient coating produced by continuously changing the ratio of at least two precursors fed into the low-pressure plasma during the coating process or a multilayer coating produced by exchanging at least two precursors during the coating process. [14] Kitchen appliance according to one of claims 12 or 13, wherein the kitchen appliance is an oven. [15] Kitchen appliance according to one of claims 12 to 14, wherein the inner walls of an oven constitute the coated surface.

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