CA2264944A1 - Temperature and scratch-resistant anti-sticking coating - Google Patents

Abstract

The invention relates to a carrier material having an inorganic molecular structure and a surface coating produced by applying a substance and by heat treatment. The invention also relates to a method for the production and to the appropriate uses of said surface coating. Carrier materials made of glass, metal or ceramic should be provided with a surface coating with anti-sticking properties against water-based and/or oil-based organic materials or water-oil emulsions while exhibiting at the same time essentially better temperature-resistant and anti-scratch characteristics than conventional PTFE or silicone coatings. These requirements are met by an inventive surface coating consisting of a combination of inorganic molecules of the carrier material and organic molecules of an applied substance on the uppermost molecular layer of said coating. In order to produce such a surface, an inorganic substance with silicone-like networks is initially applied. Subsequently, heat treatment is carried out, whereby the temperature and duration of said treatment are chosen in such a way that the purely organic coating applied is fully decomposed and/or removed so that a combination of inorganic molecules of the carrier material and organic molecules of the applied substance is formed. The appropriate carrier materials with the inventive surface coating can be advantageously used above all in household appliances and kitchenware.

Description

1015202530CA 02264944 1999-03-05Temperature and Scratch Resistant Anti Sticking CoatingThe invention relates to a carrier substance of an inorganic molecularstructure and provided with a surface coating produced by application of asubstance and heat treatment. Furthermore, the invention relates to amethod of producing, as well as suitable uses for, the surface coating.For providing a scratch and temperature resistant surface, it isgenerally known to use surfaces of enamel, glass, glass ceramics or similarlystructured systems, i.e. networks particularly of silicon dioxide and/or othermetal oxides. Also, metal surfaces such as, for instance, steel, stainlesssteel, aluminum, and chromium, which while inferior as regards theseproperties, are, nevertheless, acceptable compared to surfaces of organicmaterials. The above mentioned properties are especially needed in surfacesused in the field of household appliances.Also, surfaces coated with polytetrafluoroethylene (Teflon®) or siliconeare known which are distinguished by their non-stick properties. Theexcellent non-stick properties of PTFE and silicone-like surface systemsagainst burnt-in food are particularly noticeable in baking pans, cooking andbaking utensils. However, since those coatings are relatively thick theirmaximum useful temperatures are below 250 °C to 300 °C. Moreover,because of its relatively thick coating such a surface will suffer significantdamage when used frequently and abusively, and will lose its favorablecharateristics in those areas which have been damaged. A furtherdisadvantage of the known surface coating is that bonding agents have to beapplied to a scratch and temperature resistant surface prior to the applicationAttorney Docket 990313 11015202530CA 02264944 1999-03-05of the organic coating. While non-sticking is the resultant new property, thescratch and temperature resistance of the surface of the carrier material willbe lost. While in its new state a non-stick surface requires no scrubbing orscouring to be cleaned, its non-stick properties will deteriorate after severaluses particularly close to their maximum useful temperature, and cleaning ispossible only with greater effort. The surface will thus be damagedmechanically, and the non-stick property of the surface will deteriorate.Bonding with water or oil based materials or with water/oil emulsions isaccomplished by bonding forces between molecular groups of the surfaceand corresponding atoms / molecules of the bonded organic material. Typicalreactive molecular groups of the surface are, for instance, OH groups whichto a great extent define the surfaces of silicone based systems. The OHgroups at the carrier surface are either absorbed by bonding the coating, orthey escape from the system as a result of chemical reaction. The remainingfew reactive molecular groups of the coating material then define the non-stick characteristics. A substantial draw back is that such relatively thicksurface coating behaves very much like organic materials of low scratch andtemperature resistance. The properties of the underlying inorganic layercannot permeate to the outer surface.It is, therefore, an object of the invention to provide a surface onmetallic, ceramic and glass-like carrier materials with non-stick propertiesagainst water and/or oil based organic materials or water/oil emulsions whileat the same time being substantially more temperature and scratch resistantthan conventional coatings of PTFE or silicone.In accordance with the invention the object is accomplished by acarrier material and a surface coating according to patent claim 1. A methodof producing a surface in accordance with the invention has been describedin claim 7. The use of such a surface in suitable applications is defined inAttorney Docket 990313 21015202530CA 02264944 1999-03-05claim 17. Claims 19 and 20 relate to a particularly advantageous operation instoves using the surface in accordance with the invention. Advantageousembodiments and improvements of the invention are set forth in therespective ensuing subclaims.Aside from a scratch and temperature resistant surface the advantagesattainable by the invention are, in particular, that the surface is resistant evenagainst temperatures in excess of 300 °C and that it has non—stick propertieswith respect to water and/or oil based organic materials or water/oilemulsions. On a molecular plane the surface of the substrate has at leastlocal network structures with at least one layer of molecules of reactivebonding molecular groups being bonded to the uppermost network plane. A|ayer—forming organic substance with silicon-like networks is applied to thissurface. in the upper molecular layer of the substrate surface close to thesurface the reactive bonding molecular groups react chemically with themolecules of the organic substance and form a transitional range with respectto the organic surface without leading to the formation of a pure organic layer.Within this transitional range the reacting molecular groups are substituted byhydrophobic and/or oleophobic atoms or molecules or groups of molecules. Ifthe non—stick coating does not reject another surface when in use, the lattersurface will define the surface characteristics of the entire system. Inaccordance with a further embodiment unintended organic protective films onthe non—stick surface can be removed without loss of the non—stick properties.Except in the mentioned transitional range between inorganic and organicsubstances the growth of an organic layer is prevented at the end of or duringa heat treatment process above the decomposition temperature of thesilicone-like substance. As a result, the organically modified uppermostplane of the inorganic substrate remains. An advantageous field ofapplication of surfaces modified in this manner relates to enameled surfacesof substrates. The modified surface is used especially in connection withelectrical household appliances or kitchen furniture. The use of a modifiedAttorney Docket 990313 31015202530CA 02264944 1999-03-05surface imparts especially advantageous properties to a glass-ceramiccooking surface, baking, roasting, broiling and/or microwave oven and/or tocomponents to be placed into a roasting chamber and/or to baking, roasting,cooking containers, for instance, cooked food containers.Embodiments of the invention will be described in greater detail withreference to the drawings and the ensuing specification. In the drawings:Fig. 1 depicts a silicon oxygen network of a conventional glass surface orof a surface of a glass-like material (prior art);Fig. 2 depicts the silicon oxygen network of Fig. 1 with a conventional surfacecoating (prior art); andFig. 3 depicts the silicon oxygen network of Fig. 1 with a surface modified inaccordance with the invention.ln use, the properties of a surface are always defined by its finalexposed coating. A surface made, i.e. modified in accordance with theinvention and a method for producing a surface thus modified will hereafter bedescribed in connection with a substrate surface similar to glass or ceramic.The description is not, however, intended to exclude the modification of othertypes of substrate surfaces.Fig. 1 depicts a silicon oxygen network of a conventional glass orglass-like carrier material without coating. Typically, molecular groups similarto the OH groups shown are formed at the surface of such a carrier material.By a chemical reaction, for instance by condensation, these molecular groupsmay be made to react with aqueous and/or water based coatings on thesurface. They also react strongly with vegetable and/or animal fats. In usethis leads to the formation on the surface of strongly bonded residues whichcan only be removed with difficulties.Attorney Docket 990313 41015202530CA 02264944 1999-03-05Fig. 2 depicts a network which exhibits structures resulting fromapplying to the carrier material an inherently permanent organic coating.Though an improved non-stick effect is obtained by low reactive moleculargroups (CH3) formed at the outer molecular layers, yet the inherentlypermanent relatively thick organic coating is prone to suffer from mechanicalaction.Fig. 3, by contrast, depicts a network produced in accordance with theinvention in which even the uppermost molecular layer is formed bysubstantially non-reactive molecules of the CH3 group immediately adjacentto which there is positioned the molecular structure of the carrier material.Hence, the terminal or final molecular groups shown in Fig. 1 as OHgroups are substituted by substantially non-reactive molecular groups of theapplied substance. The methyl groups depicted here have hydrophobic andoleophobic properties. The OH groups of the prior art may, however, also besubstituted by phenyl groups. It is essential that the organic modification ofthe surfaces, i.e. the incorporation of carbon (C atoms) is restricted to theuppermost layer of the surface, but in any event to the upper several layers.In this manner, the thermal and mechanical characteristics of the inorganicmaterial will be substantially maintained. in connection with the modifiedsurfaces it was experimentally proved that, for instance, methyl groups areretained in the SiO nets even at very high temperatures (> 500 °C).The reactive bonding molecular groups forming the uppermostmolecular layer of the initial substrate surface are substituted by atoms,molekules or molecular groupos which are hydrophobic, oleophobic orsimultaneously hydrophobic and oleophobic. The surface of the modifiedsystem consists of only one, but in no case more than very few net layers inwhich substantially non-reactive molecular groups are bound. Hence, anorganically modified inorganic system is produced only in the uppermost layerAttorney Docket 990313 51015202530CA 02264944 1999-03-05of the surface. Any excess organic substance is substantially dissolvedduring the heat treatment of the coating process, without forming apermanent layer of its own. The surface produced by this process may bemechanically cleaned with impunity by the same means as a glass or ceramicsurface. It is stable at temperatures up to about 500 °C and possesses non-stick characteristics.The organic substance may be applied in various ways. In a mannerknown per se the surface of the carrier material which exhibits a local networkstructure is brought into contact with at least one silicon-like component orthermal decomposition products thereof at a low temperature, in liquid form orin a gaseous phase. This leads to cross-linking within the liquid with thereactive bonding molecular groups of the carrier material. Thereafter, for atime dependent upon the thickness of the layer, the changed surface(including the carrier) is tempered at a temperature above the decompositiontemperature of the silicon—like network. The organic layer of the cross-linkedsilicon-like liquid which may have become too thick during the coatingprocess will evaporate and will thus decompose pyrolytically. Only the onerequired molecular layer of this substance with non-stick properties remains,which connect to the silicon oxide or other metal oxide net or to the exterior,e.g., OH groups. The preferred tempering temperature is a temperature inthe range between 300 °C and 700 °C. The silicon-like liquid containspolydimethylsiloxanes or polydimethylsiloxanes with special ends, suchphenyl, vinyl, hybrid, silanol, amino, epoxy, or carbinol ends. The siliconliquids are substantially non-reactive or they are modified by reactive groups.The silicon-like liquid may contain additional components such as, forinstance, silicon resins and organic solvents and thinners, water, emulsifiers,cleaning compounds, cross-linking accelerators, encapsulation systems andthe like.Another way of modifying the surface of the carrier material isAttorney Docket 990313 61015202530CA 02264944 1999-03-05preferably carried out by heating the substrate surface, as well as the oveninto which the surface has been placed for modification, to an elevated -aboutequal— temperature. Following this, a liquid or solid silicon-based substanceis evaporated, preferably in a separate chamber, and the substanceconverted into a gaseous state is brought into contact with the surface of thesubstrate. To this end, the temperature of the substrate surface is to bechosen to be higher than the evaporation temperature of the si|icon—|ikesubstance. At the same time, the temperature of the substrate surface shouldbe higher than the decomposition temperature of the silicon-like substance.Since the temperature of the source (evaporator) is lower than that of thesurface to be modified (sink) the formation of “thicker” layers on the surface tobe modified is prevented. In the event, but for the concentration gradientbetween source and sink no accumulation would occur. Raising thetemperature of the surface to a temperature above the decompositiontemperature of the organic substance will additionally result in preventingorganic layers from accumulating. Only the desired organic modification ofthe inorganic surface will remain. The temperature of the evaporator liesbetween 150 °C and 600 °C, whereas the temperature of the surface isbetween 300 °C and 700 °C.The carrier material provided with the surface coating in accordancewith the invention is particularly useful either where frequent cleaning isunavoidable or where improved corrosion protection is necessary againstthermal corrosion or chemical attacks (laundry lye, salt water). A modifiedsurface is of special advantage in household appliances, for instance cookingsurfaces of glass ceramics, baking, roasting, broiling and/or microwaveovens, including parts thereof, baking, roasting and cooking vessels withenameled, chromium—p|ated or stainless steel surfaces, washing machinedrums, or dish washing sinks of stainless steel. In addition, many advantagessuch as , for instance, repelling chemicals (e.g. starch from laundry) arederived from a modified surface in clothes mangles having aluminum parts,Attorney Docket 990313 71015202530CA 02264944 1999-03-05aluminum oxide with or without anodized hardened surfaces and/or laundryiron surfaces. Scarcely any lime or calcium sediments are formed on tubularheaters the carrier material surfaces of which have been modified, forinstance in water boilers, washing machines and dish washers. Such amodification may also be applied, however, to glass and glass-like carriermaterials, such as, for instance, bottles for beverages, laboratory glasses,glass, glass ceramic and ceramic surfaces, systems of a similar chemicalstructure, such as glass shop counters, glass door panels in general, shopwindows, large surface three—dimensional glass structures of vapor venthoods, (kitchen) cupboard windows or on plain metal and coated metalsurfaces, such as, for instance, any kind of stainless steel or aluminumsurfaces. In many individual cases a surface of a carrier material of the kinddescribed supra is structured more smoothly which results in reduced slidingfriction and often, because of it, lower noise.At least the interior surface of the coated carrier material of cooking,roasting, baking or frying vessels of enameled steel, glass, glass ceramic,ceramic, porcelain and the like (e.g. pots or cake forms) which comes intocontact with the food to be prepared should be treated by one of theprocesses described above. Of course, it would be best if their other surfacewould be additionally treated in accordance with the process. Also, in doorglass panes with IR reflecting properties of known tin dioxide coatings, the tindioxide reflector may be provided with an organically modified surface coatingmade be the same process as silicon dioxide and other glass or glassceramic-like metal oxide surfaces.Surfaces suitable for modification may be applied to glass, glassceramic, ceramic surfaces and systems of a similar chemical structure onelectric household appliances such as, for instance, glass service panels,door panes in general, display windows, large surface 3D glass structures onventing hoods, doors of (kitchen) cupboards and so forth. Components of aAttorney Docket 990313 81015202530CA 02264944 1999-03-05warming chamber made of glass, glass ceramic, ceramic or related materials,such as baking sheets, drip pans, removable side and surface panels, lampcovers, interior door panes of a stove, such as a baking oven or a microwaveapparatus. At least one side, preferably all sides, however, of their surfaceare organically modified for the above described non-stick properties. Incooking, roasting, baking and frying vessels of glass, glass ceramic, ceramic,porcelain and the like (e.g. pot or cake forms) at least the inner surface whichcomes into contact with the food to be processed should be modified asdescribed above. It is best, however, to modify their exterior surfaces as well.IR reflectors based upon known tin dioxide coatings of door panes may beorganically modified as well by the same process as silicon dioxide and otherglass, and ceramic—|ike metal oxide surfaces.In a pyrolysis oven provided with an oven chamber and componentscoated with pyrolysis enamel and providing for a pyrolytic cleaning cycle atconventional temperatures between 400 °C and 600 °C the enamel ismodified as described above. The modified non-stick layer is also resistantagainst the usual pyrolytic temperatures of 480 °C. The interior door paneshould be modified to be stick resistant. Preferably the pyrolysis oven isprovided with a glass door inclusing a glass ceramic interior pane without astructural frame and, preferably, the glass ceramic interior pane should alsobe modified. lts temperature resistance makes it possible after each cleaningcycle to regenerate its modified surface followed by an exposure to a hightemperature. But even in an oven with chrome-plated accessories orstainless steel parts in or at the roasting chamber, such a broiling grids,broiling skewers, support grids for baking sheets, telescoping arms, vaporvanes and/or air exhaust vanes (outside of the oven chamber !) and the like,the surfaces of those parts should be modified in the manner describedsupra.If, in use, another layer adheres to the non-stick coating the formerAttorney Docket 990313 91015202530CA 02264944 1999-03-05layer defines the surface characteristics of the entire system. Hence, it isapparent that the sedimentation of undesired layers is to be prevented.Some cleaning agents, for instance stainless steel cleaners, are combinationsof cleaning agents and protective agents specifically developed to form suchprotective layers on the surfaces to be treated by them. Such protective filmson non—stick surfaces are contraindicative, for either their non—stick property issuch that the protective films cannot adhere, or a simple method has to bedeveloped for removing such foreign protective film in order to reestablish thenon—stick properties. It is for this reason that the surface should have non-stick as well as scratch and scouring resistant properties. A conventionalenamel coated surfaces may be the basis of such a treated surface. Themodified surface is regenerated by exposing the non—stick surface previouslycleaned, serviced and/or protected for a short time to a temperature abovethe decomposition temperature of the protective film. This eliminates theundesired protective film of the treatment agent by evaporation or pyrolyticdecomposition. Since its non—stick properties suffer no damage as a result ofsuch heat treatment, the surface will be fully reuseable after each cleaning,servicing and/or protective treatment. The organically modified layer withnon—stick properties below an undesired organic cover layer may beregenerated by heat treatment.Baking ovens equipped in their baking chambers with surfaces orcomponents modified in the above described manner are suitable forregeneration of the modified surfaces. They should be equipped with a useractuated switching element for cycling the oven through a regeneration. Inthis manner, a user, after first carefully cleaning the oven and its accessorieswith little effort in the usual manner, may then cause the modified surface toregenerate itself. To this end, the accessories are placed in an empty stateinto the oven chamber. Under its function or setting “Regeneration of thenon—stick property” the oven executes regeneration cycle along a time /temperature curve, and any organic protective films formed by cleaningAttorney Docket 990313 1 01015202530CA 02264944 1999-03-05agents are removed from the modified surface. The surface is cleaned fromany present organic layer and the modified non—stick surface will be exposedagain. By input means, the user may alter duration and temperature of theregeneration process within predetermined limits (from a minimum to amaximum effect). Preferably, the treatment temperature lies between 200 °Cand 400 °C and the holding time 15 to 30 min.A stainless steel surface is not particularly scratch resistant and,therefore, it is recommended to provide it with a surface coating withoutchanging the expensive look of the stainless steel. Since at highertemperatures stainless steel quickly and irreversibly takes on heat-tintingcolors, a way has to be found of modifying the surface coating withoutdiscoloring the stainless steel. Such a way consist of directly applying at lowtemperatures (e.g. < 100 °C) a very thin coating of transparent glass orceramic (e.g. water glass) to the stainless steel surface in order to prevent achange in color of the stainless steel. Thereafter the surface is treated by theabove described process.Attorney Docket 990313 1 1

Claims (20)

Claims

1. Carrier material with an anorganic molecular structure and a surface coating provided by application of a substance and heat treatment, characterized by the fact that the surface coating in its uppermost molecular layers consists of a compound of inorganic molecules of the carrier material and organic molecules of an applied substance.

2. Carrier material with a surface coating according to claim 1, characterized by the fact that the applied substance contains silicon molecules and that the surface coating comprises organo-functional molecular groups connected to silicon at at least one outwardly directed molecule layer.

3. Carrier material with a surface coating according to at least one of claims 1 or 2, characterized by the fact that the organo-functional molecular groups are hydrophobic and/or oleophobic and/or autophobic.

4. Carrier material with a surface coating according to at least one of claims 1 to 3, characterized by the fact that the mounted or incorporated molecular groups are polymers or oligomers from one or more fractions, the fractions containing silicon with organo-functional molecular groups as well as oxygen-bonded silicon-functional molecular groups which react among each other and/or with the carrier material and/or which are bonded to the carrier material.

5. Carrier material with a surface coating according to at least one of claims 1 to 4, characterized by the fact that the carrier material is metal, glass, ceramic and that the applied substance is a silicon-containing material.

6. Carrier material with a surface coating according to at least one of claims 1 to 5, characterized by the fact stainless steel with an additional glass or ceramic coating is the carrier material for the substance to be applied.

7. Method of fabricating a carrier material with surface coating according to one or more of claims 1 to 6, characterized by the fact that an organic substance with silicon-like networks is applied to the inorganiccarrier material, that thereafter the carrier material and the applied substance are subjected to heat treatment, the duration and temperature of the heat treatment being chosen to result in decomposing or evaporation of excess organic substance and that at the same time a reaction is taking place by which the molecules of the organic substance are cross-linked and, likewise, molecules of the carrier material are connected to molecules of the applied substance such that in the uppermost molecular layers a new network is formed of molecules of the carrier material and molecules of the applied substance whereby a new coating stable against temperature and decomposition is formed on the carrier material.

8. Method of producing a carrier material with an surface coating according to claim 7, characterized by the fact that following the application of the organic substance on the carrier material a reaction time is provided as a function of the thickness of the coating and the kind of the applied substance during which cross-linking of molecules of the organic substance is taking place with reactively bonding molecular groups of the carrier material before initiation of the heat treatment.

9. Method of producing a carrier material with a surface coating according to claim 7 or 8, characterized by the fact that when using an inorganic carrier material of stainless steel a transparent glass or ceramic layer is initially applied before applying the organic substance with silicon-like networks.

10. Method according to claim 7, 8 or 9 characterized by the fact that the heat treatment is performed at a temperature which is higher than the permissible operating temperature of the organic substance.

11. Method according to at least one of claims 7 to 10 characterized by the fact that during application of the organic layer the temperature in the surrounding treatment chamber does not drop below the permissible operational temperature of the organic substance.

12. Method according to at least one of claims 7 to 11, characterized by the fact that the organic substance is converted from a solid or liquid aggregate state to a gaseous state, that its temperature is raised to above or below its decomposition temperature and that it is thereafter applied to the carrier material.

13. Method according to at least one of claims 7 to 12, characterized by the fact that the gaseous organic substance is distributed to and evaporated in a hot treatment chamber and that it condensates on the carrier material.

14. Method according to at least one of claims 7 to 13, characterized by the fact that the organic substance is conveyed into the treatment chamber at a temperature higher than or equal to the carrier material and/or the treatment chamber.

15. Method according to at least one of claims 7 to 14, characterized by the fact that the organic substance is brought into contact with the carrier material at temperatures below its decomposition temperature and that both are thereafter subjected to a treatment at a higher temperature.

16. Method according to at least one of claims 7 to 15, characterized by the fact that during heat treatment the temperature lies between 300 °C and 700 °C.

17. Use of the carrier material with a surface coating according to one of the preceding claims 1 to 6 and/or carrier material with a surface coating produced by practicing the method according to one of claims 7 to 16 for electric household appliances, kitchen furniture and their components which are provided with surfaces of glass, ceramic, metal and enamel.

18. Use of the carrier material with a surface coating according to claim 17 for stainless steel surfaces of household appliances of all kinds and/or glass doors and service panels of these household appliances, for cooking surfaces of glass ceramic, for roasting chamber vessels or baking ovens of enameled sheet metal or stainless steel.

19. Method of operating a stove having a baking oven according to claim 18, characterized by the fact that there is provided a selectable and controllable regeneration process by which residues such as cleaning agent residues on the surface coating are removed by a process effective by heat treatment at a temperature between 200 °C and 400 °C.

20. Method of operating a stove with a pyrolysis step according to claim 19, characterized by the fact that the modified surface coating in accordance with the invention is performed during the pyrolysis operation.