ELEMENT WITH A FUNCTIONAL COATING

DESCRIPTION

The invention relates to a household appliance component comprising a base element, wherein at least one surface of the base element is at least partly coated with a functional coating. The invention further relates to a method for coating a household appliance component and a household appliance.

Energy efficiency and cleanability are topics of increasing importance in all household appliances. In particular the drying performance is a key factor and consists of the removal of water present in the household appliance because of condensation of water onto different components of the household appliance during the use of the household appliance. Household appliance components usually comprising a base element, wherein at least one surface of the base element is at least partly coated with a functional coating to reduce or foster the condensation of water and to ameliorate the cleanability of the household appliance.

Condensation related problems, which are described as "sweating" by customers, are for example present in household refrigerators. This problem has various reasons, such as storing goods without a lid. Especially in humid regions of a refrigerator, condensed water droplets may form and drip onto food, thus causing shorter shelf lives. Condensation of water droplets on the surface of components like linings and inner walls may also affect the performance of a refrigerator. In dishwashers complaints focus on water stains which are formed on the dishes after the washing process. In contrast, a low wettability may impair the cleanability of household appliances like cooktops. However, currently known functional coatings still exhibit a rather low performance with regard to avoiding such condensation related problems in household appliances.

It is the task of the present invention to provide a household appliance component with better condensation properties of water. A further task of the invention consists in providing a method for coating a household appliance component with a coating having better condensation properties. Still further, it is an object of the current invention to provide a household appliance comprising at least one household appliance component with better condensation properties.

These tasks are solved by a household appliance component, a method for coating a household appliance component, a household appliance, and a use according to the independent claims. Advantageous developments of the invention are specified in the respective dependent claims, wherein advantageous developments of the household appliance component are to be regarded as advantageous developments of the method and the household appliance and vice versa. A first aspect of the invention relates to a household appliance component comprising a base element, wherein at least one surface of the base element is at least partly coated with a functional coating. According to the invention, ameliorated condensation properties of the household appliance component are achieved in that the coating comprises at least one organically modified silicate (Ormosil). Organically modified silicate coatings show unique properties, standing between organic polymers and silica. They can be resistant against atmospheric conditions like silicas and flexible like polymers. They are not as brittle as silica coatings thanks to their flexibility and are very important for production of durable coatings due to their exceptional mechanical properties. Another feature of Ormosil coatings is their good adherence to many different materials. Thus, they can be coated on various surfaces such as plastic materials (e.g. polystyrene or polypropylene), metals, glasses, silicon, paper, cardboard, stones, and wood without an additional binder. Ormosils may have very high water repellence and thus effectively prevent the condensation of water on the coated areas of the base element, for example on walls of a refrigerator. This enhancement of the condensation properties leads to a reduction of the temperature required for drying of household appliances like dryers, washing machines, and dishwashers as well as to a reduction of the time required for the drying process. Thus, the energy consumption required for carrying out such a drying process as for example in dishwashers and dryers is reduced. Alternatively or additionally Ormosils may have a very high water affinity and thus effectively prevent the condensation of water on uncoated areas, for example on dishes whithin a dishwasher. Thus, the coating effectively repels hydrophobic components like oil and food residue, thereby simplifying the cleaning process of different household appliance components. The wettability or non-wettability of such coated surfaces is generally not affected by the material of the underlying substrate or the pH of the water. Further, Ormosil coatings are durable and stable, both mechanically and chemically. The coating of the base element generally may consist of one or more Ormosils. The coating may also comprise one or more additional components. The surface of the base element may be coated only partly. Further, the entire surface of the base element may be coated. Still further, the base element may comprise different coatings on different surface areas, wherein at least one of the coatings comprises or consist of at least one organically modified silicate (Ormosil).

In an advantageous development of the invention, it is provided that the at least one Ormosil is superhydrophobic. In that at least one Ormosil is superhydrophobic, condensation of water on the coating can be reduced or even completely avoided. According to the present invention, the term "superhydrophobic" relates to Ormosils having water contact angles of at least 120° and preferably of 140 ° or more.. The superhydrophilic behavior is achieved by Polydopamine (PDA) based coatings. PDA may act as a sink or catcher for water, thereby aiding in removing water from other less hydrophilic surfaces of the household appliance component. The term "superhydrophilic" within the scope of the present invention is generally understood to relate to Ormosils having water contact angles of less than 40 ^Q and preferably of 30 ^{Q o} or less.

In a further advantageous development of the invention, it is provided that the coating is arranged in one layer or in multiple layers. This allows for a precise tuning of the coating's mechanical and chemical properties.

In a further advantageous development of the invention, it is provided that the coating comprises cavities, in particular nano and/or micro sized cavities. This nano-/microstructured topography offers the advantage of improved thermal stability and improved mechanical properties. In a further advantageous development of the invention it is provided that the household appliance component is configured as a lining or wall element of a household appliance. This allows for avoidance and/or improvement of water contact to such inner and/or outer walls of household appliance surfaces. Alternatively or additionally it is provided that the household appliance component is configured as a cooktop, in particular as a cooktop of at least one induction hob. In case of cooktops like induction hobs, ceramic glass cooktops and the like, a coating on the glass of induction hob reduces the adherence of oil and food residue, thereby simplifying the cleaning process of such cooktops giving them an easy cleaning property. Alternatively or additionally it is provided that the household appliance component is configured as a rack or basket of a dishwasher. In dishwashers, the customer complaints focus on the water stains which form on the dishes after washing process. Formation of such stains might mainly be related to water hardness. To eliminate this water stains, coating of a rack and/or basket of the dishwasher may assist in binding water droplets on the rack/basket since the water droplets settle more on coated rack or basket and less on common materials of dishes (glass, steel, ceramic, etc.).

A further aspect of the invention relates to a method for coating a household appliance component, in which at least one surface of a base element of the household appliance component is at least partly coated with at least one organically modified silicate (Ormosil). Ormosils may have very high water repellence and thus effectively prevent the condensation of water on the coated areas of the base element, for example on walls of a refrigerator. This enhancement of the condensation properties leads to a reduction of the temperature required for drying of household appliances like dryers, washing machines, and dishwashers as well as to a reduction of the time required for the drying process. Thus, the energy consumption required for carrying out such a drying process as for example in dishwashers and dryers is reduced. Alternatively or additionally, Ormosils may have a very high water affinity and thus effectively prevent the condensation of water on uncoated areas, for example on dishes whithin a dishwasher. Thus, the coating effectively repels hydrophobic components like oil and food residue, thereby simplifying the cleaning process of different household appliance components. Furthermore, Ormosils can be directly coated on any material that is commonly used for the surface of base elements of household appliance components, for example on plastic materials (e.g. polystyrene or polypropylene), metals, glass, silicon, paper, cardboard, and stones. The wettability or non-wettability of such coated surfaces is generally not affected by the material of the underlying substrate or the pH of the water. Further, Ormosil coatings are durable and stable, both mechanically and chemically. The coating of the base element generally may consist of one or more Ormosils. The at least one surface of a base element may be coated with a composition that comprises Ormosil together with one or more additional components. The surface of the base element may be coated only partly. Alternatively, the entire surface of the base element may be coated. Still further, the base element may be coated with different coatings on different surface areas, wherein at least on of the coatings comprises or consist of at least one organically modified silicate (Ormosil). In an advantageous development of the invention, it is provided that the at least one Ormosil is spray-coated onto the base element. In other words, it is provided that at least one section of a surface of the household appliance component is coated with the at least one Ormosil by a spray-coating process. Coatings generated by spray-coating exhibit excellent mechanical and chemical properties and are easy to apply to all commonly used base materials and shapes. Spray-coating further allows for low production costs.

In a further advantageous development of the invention, it is provided that the at least one Ormosil is first mixed with at least one plastic material and/or with at least one solvent, and wherein the mixture is subsequently spray-coated onto the at least one surface. Coatings must be mechanically stable and need to securely adhere to the base element during the lifetime of the household appliance component. Ormosil(s) may thus be mixed with plastic materials like granular polystyrene which functions as a binder. Alternatively or additionally, Ormosil(s) may be mixed with one or more solvents like ethanol and/or tetrahydrofuran to ease the coating of the base element for example by spray-coating.

In a further advantageous development of the invention, it is provided that the at least one employed Ormosil is synthesized via a sol-gel process. The sol-gel process is a method for producing solid materials from small molecules and involves conversion of monomers into a colloidal solution (sol) that acts as the precursor for an integrated network (or gel) of either discrete particles or network polymers. In this chemical procedure, the 'sol' (or solution) gradually evolves towards the formation of a gel-like diphasic system containing both a liquid phase and solid phase whose morphologies range from discrete particles to continuous polymer networks. Gels according to the present invention may for example be produced by using methyltrimethoxysilane (MTMS) and phenyltrimethoxysilane (PhTES) for superhydrophobic coatings and/or by using tetraethylorthosilicate for superhydrophilic coatings. Of course, different monomers and/or monomer mixtures may equally be used. The respective monomers may be dissolved in a solvent like ethanol and hydrolyzed at room temperature with an acidic catalyst (e. g. oxalic acid). The resulting compounds may then be polymerized using an alkaline catalyst (e. g. ammonium hydroxide), thereby forming a gel.

In a further advantageous development of the invention, it is provided that the formed Ormosil gel is aged for a predetermined period at a predetermined temperature before coating the at least one surface of the household appliance component. Aging leads to a change in the physical and chemical properties of the Ormosil gel. The aging process can be speeded up or slowed down by physical and/or chemical influences like lowered or increased temperature and/or pressure, oxygen, inert gas, moisture, light, ultraviolet radiation and the like. Formed Ormosil containing gels may for example be aged at room temperature for 1 to 3 days to improve their mechanical and chemical properties.

In a further advantageous development of the invention, vibrations in the ultrasonic regime are applied to the at least one Ormosil before coating the at least one surface of the household appliance component. Due to cavitational shear forces by the application of ultrasound vibrations, the molecular weight of the Ormosil(s) is/are lowered by particle size reduction, resulting in a polydisperse colloidal solution. Multiphase systems are dispersed and emulsified very efficiently, so that very fine mixtures are prepared. The resulting "Sono-Ormosil(s)" exhibit a higher density as well as an improved thermal stability compared to Ormosils that were produced without the application of vibrations in the ultrasonic regime.

In a further advantageous development of the invention, it is provided that the coating is brought into contact with an organic solvent. This improves the adhesion of the Ormosil containing coating on the surface of the base element. The coating may for example be dipped for a few seconds in an organic solvent like acetone. Alternatively or additionally, the organic solvent may be sprayed onto the coating.

A third aspect of the invention relates to a household appliance comprising at least one household appliance component according to the first aspect of the invention and/or at least one household appliance component, which is at least partly coated by a method according to the second aspect of the invention. The household appliance is provided with tailor-made Ormosil containing coatings and thus with controlled wettability and/or non-wettability. Further features and their advantages can be gathered from the description of the first and second aspect of the invention.

A forth aspect of the invention relates to a use of at least one organically modified silicate (Ormosil) for at least partly coating a surface of a base element of a household appliance component. The resulting features and their advantages can be gathered from the description of the first, second, and third aspect of the invention.

Further features of the invention appear from the claims as well as based on the following embodiments. The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the embodiments are usable not only in the respective specified combination, but also in other combinations without departing from the scope of the invention. There are thus also variations of the invention possible that are not explicitly shown and described in the embodiments but can, however, be formulated through different combinations of separated features from the described embodiments. Also variations and combinations of features are possible that do not contain all the features of an originally formulated independent claim. In the following, embodiments of the invention are shown in more detail by referring to schematic drawings. These show in: Fig. 1 a regular household appliance component without coating after 10 minutes of water treatment; and

Fig. 2 a household appliance component according to the invention after 10 minutes of water treatment.

1 . Synthesis of Ormosil Gels

Ormosil gels with nanosized cavities that may be employed in the context of the present invention are obtained by a sol-gel method. Gels are formed by using methyltrimethoxysilane (MTMS) and phenyltrimethoxysilane (PhTES) for superhydrophobic coatings or by using tetraethylorthosilicate for superhydrophilic coatings. The respective monomer(s) is/are dissolved in ethanol (a safe solvent to use) and hydrolyzed at room temperature with an acidic catalyst (oxalic acid). The resulting compounds are then polymerized at room temperature using an alkaline catalyst (ammonium hydroxide) thereby forming a gel.

2. Preparation of Ormosil Colloids The thus formed gels are aged at room temperature for 1 to 3 days. The aged gels are diluted with ethanol and then broken up by sonification using ultrasonic vibrations which results in a colloidal solution. The ultrasonic vibrations can be produced by an ultrasonic bath or an ultrasonic probe. 3. Preparation and Characterization of the Coatings

Organically modified silicate coatings show unique properties, standing between organic polymers and silica. They are resistant against atmospheric conditions like silicas and flexible like polymers. They are not as brittle as silica coatings thanks to their flexibility and are ideal for the production of durable coatings due to their exceptional mechanical and chemical properties. Another feature of Ormosil coatings is their good adherence to many different surfaces. Thus, they can be coated on various surfaces such as plastics, metals, glasses or wood, without an additional binder.

Coatings must generally be mechanically stable in order to securely adhere to the respective base element. Ormosil gels, that are prepared according to the above-described method, are mixed with granular polystyrene and tetrahydrofuran and then applied onto a household appliance component using spray-coating. The household appliance component may be an inner liner for a refrigerator and comprise a base element made of polystyrene or another suitable plastic material. The coated household appliance component is then dipped into acetone to improve the adhesion of the Ormosil containing coating. After these steps, several tests are conducted to examine the adhesion and mechanical properties of the coating.

3.1 . Examination of Adhesion and Mechanical Properties of the Coatings · Band Test:

Adhesion properties are examined using a band. In this test, the band is applied onto the surface of the household appliance component with a specified pressure. The properties of the coating is examined after the band is removed.

• Scratch Test: The coating's durability against scratches is tested by using a metal stick. The effect of the scratching is examined by measuring the water contact angle in the area where the stick was used to scratch the coating. · Abrasion Test:

This test is used to determine the coating's durability against wiping and pressure. A test apparatus, weighing 120 grams, is wrapped in a damp cloth and moved on the surface of the coating with a predetermined speed and time. After the test, the properties and morphology of the coating is examined.

• Chemical Stability Test:

To test the coating's stability against aggressive chemicals, various solutions with different concentrations are prepared and applied onto the coating. The solutions are designed to mimic the chemical properties of common foods such as vinegar, lemon or milk etc. Also, to test the durability against commonly used cleaners, compounds like dishwashing soap, fat solvent and caustic soda were used for testing. The water contact angles within the areas of the coating that were subjected to these solutions are measured to determine the chemical stability.

4. Testing of Anti-Condensation Properties:

To examine the anti-condensation property of a superhydrophobic coating, the coated household appliance component is treated with water vapour for a predetermined time (e. g. 10 minutes). Afterwards, the amount of water that remains on the coating is measured. Also, the performance of the coating is determined by measuring water contact angles if there are any remaining droplets.

Fig. 1 shows a regular household appliance component 1 without any coating after 10 minutes of water treatment. The household appliance component 1 is made of polystyrene and is completely covered with water drops 2. Fig. 2 shows a household appliance component 3 according to the invention. The household appliance component 3 comprises a base element made of polystyrene which is entirely coated with a superhydrophobic Ormosil (MTMS-PhTES) containing coating. Even after 10 minutes of water treatment, no water drops 2 adhere to the coating. Condensation problems in household refrigerators, which are described as "sweating" by customers, can thus be completely avoided. Especially in humid regions of the refrigerator, no water droplets 2 can form on the surface of the coated household appliance component 3.

In dishwashers, the customer complaints focus on the water stains which form on the dishes after washing process. To eliminate these water stains household appliance components like polypropylene racks and baskets comprising superhydrophilic PDA-coatings can be used. Thereby water droplets are formed on the superhydrophilic PDA-coating rather than on the less hydrophilic material of dishes (glass, steel, ceramic, etc.) In case of induction hobs or other cooktops, a superhydrophilic coating on the covering glass of the cooktop simplifies the cleaning process.

It will be understood by those skilled in the art that while the present invention has been disclosed above with reference to preferred embodiments, various modifications, changes and additions can be made to the foregoing invention, without departing from the spirit and scope thereof. The parameter values used in the claims and the description for defining process and measurement conditions for the characterization of specific properties of the invention are also encompassed within the scope of deviations, for example due to measurement errors, system errors, weighing errors, DIN tolerances and the like.

LIST OF REFERENCES regular household appliance component

water drop

household appliance component according to the invention