EP3003581B1 - Coating of usage surfaces with plasma polymer layers under atmospheric pressure in order to improve the cleanability - Google Patents

Description

Technical area

The present invention relates to a method for depositing a plasma polymer layer on contact surfaces of enamel, glass, glass ceramic or metal, which is characterized in that the application of the surface coating takes place in the atmospheric pressure plasma.

The present invention further relates to household articles whose surface of enamel, glass, glass ceramic or metal has been coated by the aforesaid method.

State of the art

The production of a light cleaning surface of enamel, glass, glass ceramic or metal based on the reduction of their surface energy. For example, glasses, glass-ceramics and enamels have surface energies of more than 40 mN / m with a pronounced polar fraction because of their oxidic composition (inter alia SiO ₂ , Al ₂ O ₃ , Na ₂ O, K ₂ O). A similar behavior is shown by metals, since the boundary layer metal - air always has an oxide layer. This polar portion is responsible for the good adhesion of baked food residues (oils, starch, sugar, ...).

Therefore, attempts have been made to reduce the surface energy by a coating from the liquid phase and to reduce the polar fraction to 0 mN / m. For example, a coating with silicone polymers are known for enamel ( EP 0 937 012 B1 ) or PTFE-based coatings ( DE 19 833 375 A1 ). In EP 1 858 819 A1 In addition, coatings using scavenger-enriched polysiloxanes are disclosed.

The general feature of these coatings is that the coating material is applied liquid to the substrate and then (possibly after drying) at elevated Temperature (about 150 ° C - 400 ° C) must be baked, making this coating process as energy and time consuming.

If, in addition, a coating of selected partial surfaces is desired, the methods mentioned inevitably require further masking or masking steps, which additionally increase the expenditure of time.

In addition, the methods mentioned often rely on the use of solvents and thus disadvantageous with regard to the protection of the environment.

Therefore, there is a need for alternative methods that allow for a fast, clean, environmentally friendly, and inexpensive coating that may optionally be selective without additional masking steps.

US 2007/148407 A1 . DE 10 2008 059909 A1 . US 5 041 304 A . DE 10 2005 034764 A1 and EP 1 997 565 A2 disclose the provision of plasma polymer coatings using silicon- or fluorine-containing precursors.

Brief description of the invention

According to the invention, the described problem of contamination is solved by obtaining the surface energy lowering coating on at least part of the surface (also substrate surface) by a plasma polymerization process under atmospheric pressure conditions.

More particularly, the present invention provides a method of applying easily cleanable surfaces to household articles, which is characterized in that at least a portion of the substrate surface of the household article, e.g. consisting of glass, enamel, glass ceramic or metal, using one or more nozzle (s) and starting from a plurality of precursors with the aid of an atmospheric pressure plasma, a polymeric surface layer is deposited, wherein one of said precursors hexamethyldisiloxane (HMDSO), and wherein in addition to hexamethyldisiloxane ( HMDSO) is another precursor perfluorocyclobutane (PFCB).

The atmospheric pressure plasma is generated in a preferred embodiment by a plasma generator with an output frequency in the range of 1 kHz to 1 MHz.

In one embodiment, the layer thickness of the deposited polymeric surface layer is about 10 nm to about 10 μm.

In one embodiment, an adhesion promoting layer can be deposited prior to deposition of the polymeric surface layer by plasma polymerization. The adhesion-promoting layer is preferably SiO ₂ -containing.

In a preferred embodiment, prior to the deposition of the polymeric surface layer by plasma polymerization, the part of the substrate surface is roughened.

For large-area coating, in a further embodiment, a plurality of nozzles can be arranged in a row to form an array.

Furthermore, the present invention provides a household article comprising at least a partial surface, preferably consisting of glass, enamel, glass ceramic or metal, which has been coated by the methods described above, wherein the polymeric surface layer has a surface energy of 20 mN / m or less having.

In a preferred embodiment, between the partial surface consisting of glass, enamel, glass ceramic or metal and the polymeric surface layer is a preferably SiO ₂ -containing, adhesion-promoting layer.

In preferred embodiments, the aforementioned household article is a kitchen appliance, more preferably an oven muffle.

Detailed description of the invention

According to the present invention, the surface energy lowering coating is performed by a plasma polymerization process under atmospheric pressure conditions.

Generally, the term atmospheric pressure plasma (also known as AD plasma or normal pressure plasma) designates a plasma in which the pressure approximately corresponds to that of the surrounding atmosphere, the so-called normal pressure.

The coating method according to the invention is carried out by exciting suitable precursors in a nozzle, in which an electrically excited plasma is ignited, in such a way that they form a low-energy surface on the surface of the substrate (made of enamel, glass, glass-ceramic or metal). In detail, a pulsed arc is generated in the plasma nozzle by means of high-voltage discharge. A precursor gas, which is usually passed by this discharge path, is excited and converted into the plasma state. This plasma then passes through a nozzle head onto the substrate surface to be coated.

In principle, all currently available generators can be used as the energy source for the plasma. For example, radio-frequency or high-frequency generators can be used (from the kHz range to the GHz range). In a preferred embodiment, kHz sources (i.e., plasma generators having an output frequency in the range of 1 kHz to 1 MHz) are used.

In addition to hexamethyldisiloxane (HMDSO) and perfluorocyclobutane (PFCB), preference is given to using fluorine and carbon-containing compounds and / or organosilicon compounds as the precursor gas.

It is also conceivable to first apply an adhesion-promoting layer (eg a SiO ₂ -containing layer) with this method and subsequently to produce a low-energy surface by varying the process conditions or changing the precursor.

Depending on the mechanical stress level of the coating to be set, it may be advantageous to use compounds containing fluorine and carbon in combination with organosilicon compounds or hydrocarbons as precursor material.

In the process, this is done in such a way that either multilayer structures are realized or deposited by continuous changes of Precursorgasanteile gradient, the substrate side are very hard and resistant and in the direction of the outer surface more and more polymeric and poorly adhering properties.

Furthermore, the process gas may contain, in addition to HMDSO and PFCB, other fluorine and carbon-containing compounds and organosilicon precursors or hydrocarbons as well as additional residual gases such as noble gases (eg argon), oxygen, nitrogen, carbon dioxide, carbon tetrachloride and gas mixtures, if not adversely affects the process control and the resulting coating.
Thus, not least because of the layer properties which can be generated in a simple manner, the method according to the invention makes possible an effective and, above all, comparatively cost-effective and long-term solution to the problems described above.
The coating thickness can be chosen depending on the desired properties and the precursor composition. In general, the single-layer thickness is less than 100 μm, preferably about 10 nm to about 10 μm.
Overall, it is possible with the proposed method particularly temperature-stable, chemical-resistant and - if necessary - to produce transparent non-stick layers.
In a preferred embodiment, the non-stick effect is further enhanced by roughening the surface prior to coating. By the subsequent low-energy coating, the water only wets the tips and can thus easily carry along adhering dirt particles on the surface ("lotus effect").
Since the use of a plasma jet in contrast to the spray application of a liquid coating form no spray and the plasma jet is thus limited in space, and partial partial coatings of the surface without masking or masking are possible without further effort.

For a large-area coating (eg, a baking tube bottom), it is also possible to arrange a plurality of plasma nozzles in a row. With this array can thus also large areas -. B. by a robot - be coated quickly and evenly (see illustration 1 ).

The deposition of the plasma polymer layer under atmospheric conditions also requires no solvents, whereby the inventive method over conventional liquid coatings in terms of environmental friendliness is advantageous.

Compared to wet-chemically applied surfaces, it is possible by means of suitable precursor and process parameters to produce absolutely nonpolar surfaces which have virtually no more polar groups which would promote adhesion. According to the present invention, there is also provided a kitchen utensil whose surface has been at least partially coated by the methods described above.

The present invention also relates to a household article which has an application surface of enamel, glass, glass ceramic or metal, which has been coated at least in part by the methods described above, characterized in that the coated surface has virtually no polar groups.

The household article according to the present invention comprises both non-electrical kitchen appliances (such as cookware, pans, roasters), electrical kitchen appliances (such as blenders, ovens, grills, refrigerators or microwaves) and other household appliances and furniture which at least have a partial surface of enamel, glass, glass ceramic or metal (such as glass doors, control panels). In a preferred embodiment, the household article is an oven, more preferably an oven muffle.

The coated surface of the household article according to the invention is generally characterized by having virtually no polar groups. The surface energy of the coated surface is less than 20 mN / m. The polar fraction of the surface energy is preferably less than 5 mN / m, more preferably less than 1 mN / m, particularly preferably less than 0.5 mN / m, especially preferably 0 mN / m. The measurement of Surface energy and the determination of their polar and disperse fractions are carried out by customary methods known to the person skilled in the art (eg contact angle measurement and methods according to ZISMAN or OWEN, WENDT, RABEL & KAELBE).

Claims (13)

1. Method for applying easily cleanable surfaces to domestic articles, characterised in that a polymer surface layer is deposited with the help of an atmospheric pressure plasma on at least a part of the surface of a domestic article, consisting of glass, enamel, glass ceramic or metal, using one or more nozzles and based on one or more precursors, wherein one of the cited precursors is hexamethyldisiloxane (HMDSO), and wherein in addition to hexamethyldisiloxane (HMDSO) a further precursor is perfluorocyclobutane (PFCB).
2. Method for applying easily cleanable surfaces to domestic articles according to claim 1, wherein the atmospheric pressure plasma is created by a plasma generator with an output frequency in the range between 1 kHz and 1 MHz.
3. Method for applying easily cleanable surfaces to domestic articles according to one of claims 1 or 2, wherein the layer thickness of the deposited polymer surface layer is approximately 10 nm to approximately 10 µm.
4. Method for applying easily cleanable surfaces to domestic articles according to one of claims 1 to 3, wherein an adhesion-enhancing layer is deposited prior to the deposition of the polymer surface layer by means of plasma polymerisation.
5. Method for applying easily cleanable surfaces to domestic articles according to claim 4, wherein the adhesion-enhancing layer contains SiO₂.
6. Method for applying easily cleanable surfaces to domestic articles according to one of claims 1 to 5, wherein the part of the surface to be coated is roughened prior to the deposition of the polymer surface layer by means of plasma polymerisation.
7. Method for applying easily cleanable surfaces to domestic articles according to one of claims 1 to 6, wherein a plurality of nozzles is arranged in series.
8. Method for applying easily cleanable surfaces to domestic articles according to one of claims 1 to 7, wherein the domestic article is a kitchen appliance.
9. Method for applying easily cleanable surfaces to domestic articles according to one of claims 1 to 8, wherein the domestic article is a baking oven muffle.
10. Domestic article which has at least one partial surface, consisting of glass, enamel, glass ceramic or metal, which has been coated with the help of the method according to one of claims 1 to 9, as a result of which a polymer surface layer is obtained, the surface of which has a surface energy of 20 mN/m or less.
11. Domestic article according to claim 10, further characterised in that an adhesion-enhancing layer preferably containing SiO₂ is located between the partial surface, preferably consisting of glass, enamel, glass ceramic or metal, and the polymer surface layer.
12. Domestic article according to one of claims 10 or 11, wherein the domestic article is a kitchen appliance.
13. Domestic article according to one of claims 10 to 12, wherein the domestic article is a baking oven muffle.

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