MXPA97006160A - Stain release coating for ac transfer surfaces - Google Patents

Abstract

The present invention relates to a barrier coating composition for heat transfer surfaces comprising: a) 0.1 to 99% by weight of an inorganic salt composition having a phosphate source and a carbonate source in a ratio of weight from 10: 1 to 1: 8, and b) 0.01 to 30% by weight of a surfactant composition, wherein the coating composition forms a substantially uniform barrier between the heat transfer surface and the coating.

Description

STAIN RELEASE COATING FOR HEAT TRANSFER SURFACES Field of the Invention Cleaning the internal surface of food preparation units that include large industrial electrically heated furnaces, gas fired ovens, microwave ovens, smokehouses, fryers, etc. , and associated surfaces is a difficult and annoying task. The food stains involved are frequently untreatable and unpleasant and the cleaners used to remove the stains are rough. The invention relates to compositions that can be used to introduce a barrier coating onto heat transfer surfaces that come into contact with food stains. The coatings act to promote the removal of such unpleasant and difficult spots from the food preparation unit. The coatings of the invention form a barrier coating, between the stain derived from the hardened cooking and the surfaces of the food preparation unit, which promotes the removal of the stain. Such stains and debris formed on the coating are then removed more easily with the use of a high pressure hot water hose resulting in less scraping and rubbing than with the use of commercially available cleaning preparations. Therefore, the food preparation surfaces can be easily cleaned using substantially less unpleasant and less harsh cleaning preparations.

Background of the Invention The formation of food stains derived from cooking on the surfaces of food preparation units has been a problem that has been faced by the cleaning staff of institutions and industries for many years. During cooking, food stains commonly come into contact with heated metal or porcelain surfaces in the food preparation units. Food stains, which contain various proportions of inorganic materials and spots of organic proteins, fat or carbohydrate, can be cooked and become hard or can be carbonized. Such stains are very difficult to remove, require a substantial energy consumption during cleaning and often require very high concentrations of unpleasant and rough cleaning materials. There has been a substantial need in this technique for solutions, other than using stronger cleaners, to improve the effective removal of such spots. An attempt to reduce the difficulty in removing these stains is related to the use of self-cleaning ovens that reduce ash stains at high temperatures. Self-cleaning ovens commonly contain a catalytic coating on the internal heated surface. of the food preparation unit. Periodically, the food preparation unit is heated to a temperature of approximately 260 ° C-315.5 ° C. at this temperature the catalytic surface is designed to promote the combustion and removal of stains derived from cooking which results in the reduction to ashes of the stain which can then be removed without difficulty. An example of such catalytic coatings is found in Stiles et al. , U.S. Patent No. 3, 460,523, which is directed to a finely divided thermally stable oxidation catalyst. Another attempt to reduce the difficulty in removing such stains derived from cooking is found in attempts to formulate barrier coatings that can be used on food preparation units. Examples of such materials include White et al. , U.S. Patent No. 3, 196, 027, which teaches a hydrocarbon solvent containing a dimethylpolysiloxane. Hatch et al, United States Patent No. 3, 303, 052, teaches a hydrophilic synthetic tetrasilic fluoride mica which is applied to a food preparation surface in the form of an aqueous aerosol with a fluorocarbon propellant. Arnold, U.S. Patent No. 3,877,972, teaches a metal phosphate polymer composition that is exemplified by an ethyl oleoyl aluminum orthophosphate dissolved in hexane. Di mond, Canadian Patent N o. 1, 047, 903 teaches a furnace cleaning composition. The aqueous cleaner, which is not used as a barrier coating, uses active cleaning ingredients, a substantial proportion of an aqueous base comprising a mixture of sodium hydroxide and monoethanol amine, a bentonite thickener similar to clay with other ingredients to form a spray oven cleaner. Cockrell, Jr., U.S. Patent No. 4,877,691 (PCT International Application No. PCT / US91 / 05092), teaches a pretreatment composition comprising an aqueous dispersion of an inorganic thickening agent such as Veegum® clay, a salt soluble in inorganic water such as sodium or potassium bicarbonate with a small amount of wetting agent. Makiko et al., Japanese Patent Publication No. 03-038,254, teaches a film that provides a hard sliding surface to allow the removal of greasy stains. The film comprises a composite of layered structure and a solid inorganic oxide with a polysiloxane binder. Russian Patent SU 167 1678 discloses a release coating from an aqueous composition containing approximately a ratio of 20: 1 of commercial soda to sodium tripolyphosphate, liquid silicate, alkyl sulfate and laundry soap. U.S. Patent No. 5,370,729 discloses a barrier coating using a combination of a neutral organic fatty component, an inorganic material having some finite water solubility and an organic water soluble thickener composition. The materials used to form the barrier coatings in ovens that promote the release of greasy stains derived from cooking have had some success. However, the highly inorganic nature of certain materials makes the dispersion of partially insoluble coatings difficult. In addition, barrier coatings tend to become hardened and difficult to remove with mild aqueous detergents. For example, lecithin or mixtures of lecithin currently in use, at high furnace temperatures, form a surface deposit similar to varnish that becomes part of the "stain" that is difficult to remove. Finally, many materials in the prior art do not tend to form a sufficient barrier. In many cases, coatings do not produce a sufficient barrier and do not sufficiently promote stain removal to be acceptable in many institutional or domestic environments. There remains a substantial need in the art for forming an aqueous composition that can be applied to act as a barrier between the formation of carbonized, hardened cooking fatty spots and heat transfer surfaces. Barrier coatings and subsequent cooking stains should be easily removed without substantial difficulty with less aggressive and / or reduced amounts of cleaning compositions.

Brief Description of the Invention It has been found that a substantial improvement in the properties of the barrier coatings for the heated food preparation surfaces can be made by using a combination of an inorganic composition having a phosphate and a carbonate source and a surfactant composition. . These materials, when applied to a food preparation unit, can form a coating composition that resists a wide variety of temperatures during the heating cycle in the commonly available institutional and domestic ovens while maintaining substantial barrier properties against accumulation of food stains. After the composition is applied to a cold surface in the unit, the unit can be heated to dry the film in a firm coating barrier, somehow hardened but viable. These materials are also applicable to hoods and ducts in institutional furnaces or processing surfaces (horizontal or vertical) that have indirect contact with food, at ambient or elevated temperatures, in other words anywhere the organic stain adheres to the surfaces in food plants, even if it is not in contact with water.

The compositions of the invention comprise a) from about 0.1 to 99% by weight of an inorganic salt composition having a phosphate source and a carbonate source in a weight ratio of 10: 1 to 1: 8; and b) about 0.1 to 30% by weight of a surfactant composition. Such a composition can be applied to furnace surfaces using the commonly available spray devices to form a uniform, stable coating. The coatings formed by the spraying of those compositions can resist becoming brittle, chipped or de-scaled at the high temperatures found in the food preparation units. These coating compositions are substantially soluble or dispersible in aqueous liquids or cleaners and can be easily removed using water or less aggressive and / or reduced amounts of aqueous cleansing compositions. The inorganic salts and the surfactant, for example a fatty acid salt (soap), cooperate with the aqueous cleaners to promote the removal. The coating compositions of the invention avoid the use of insoluble inorganic compositions, in particular insoluble inorganic thickeners such as clays which can cause difficulty in removing the barrier layers after the heating cycle. Accordingly, the compositions of the invention are substantially free of any proportion of an insoluble inorganic thickener or clay. The compositions are also free of organic thickeners Detailed Description of the Invention The barrier coating compositions of the invention are made in aqueous solution and contain soluble inorganic salts. Such inorganic salts comprise a combination of alkali metal phosphate and carbonate salts. Preferred salts are salts that are harmless to foods, totally inorganic water soluble, including sodium phosphate, potassium phosphate, sodium tripolyphosphate, trisodium phosphate, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, sesquicarbonate sodium, potassium sesquicarbonate and the like. The compositions of the invention combine the aqueous soluble salt composition with a surfactant composition. The surfactant composition is an anionic, amphoteric or non-ionic surfactant and mixtures thereof. Preferred mixtures are amphoteric or anionic surfactants. These surfactants are easily mixed in solid form with the inorganic salt composition or in an aqueous dispersion to form a substantially uniform material. The surfactants assist in wetting the surface of the food preparation unit and participate in the formation of the barrier coating which can withstand substantial amounts of protein or fatty spots.

Surfactant The aqueous cleansing compositions of the invention contain an organic surfactant composition. Nonionic or amphoteric surfactants can be used. The anionic materials that can be used in the compositions of the invention are surfactants containing a large lyophilic portion and a strong anionic group. Such surfactants typically contain anionic groups selected from the group consisting of sulphonic, sulfuric or phosphoric, phosphonic or carboxylic acid groups which when neutralized produce sulfonate, sulfate, phosphonate or carboxylate with a cation thereof being preferably selected from the group consisting of an alkali metal, ammonium, alkanolamine, such as sodium, ammonium or triethanolamine. Examples of functional anionic sulphonate or sulfate surfactants include alkylbenzene sulphonates, sodium xylene sulphonates, sodium dodecylbenzenesulfonates, linear sodium tridecylbenzenesulfonates, potassium octylbenzenesulfonate, sodium lauryl sulfate, potassium lauryl sulfate, amino lauryl sulfate, sodium palmitylsulfate, sodium cocoalkylsulfate, sodium olefinsulfonate. Other anionic surfactants operative for the present invention are fatty carboxylic acid soaps commonly made by saponification of natural fats with inorganic base such as sodium or potassium hydroxide or can be made by neutralization or partial neutralization of free fatty acids with metal bases alkali such as sodium hydroxide or potassium hydroxide or with an organic base such as an alkanolamine, for example, triethanolamine. The saturated and unsaturated fatty acid materials or mixtures thereof used in the invention may comprise a C6-24 fatty acid or mixtures thereof. Examples of such acids include caproic (C6), caprylic (C8), capric (C10), lauric (C12), myristic (C14), palmitic (C? 6), stearic (C? 8), eicosanoic (C20), docosanoic (C22), tetracosanoic (C24) and mixtures thereof. Preferred acids include coconut fatty acid and oleic acid or a mixture thereof. Amphoteric surfactants are also useful in the invention. Amphoteric surfactants contain an acid and a hydrophilic base portion in the structure. These ionic functions can be any of the ionic or cationic groups that have been previously described in the sections related to anionic or cationic surfactants. In summary, the anionic groups include carboxylate, sulfate, sulfonate, phosphonate, etc., while the cationic groups typically comprise compounds having amine nitrogens. Many amphoteric surfactants also contain oxides or hydroxyl groups that strengthen their hydrophilic tendency. The amphoteric surfactants of this invention comprise surfactants having a cationic amino group combined with an anionic carboxylate or a sulfonate group.

Examples of useful amphoteric surfactants include sulfobetaipas, N-coco-3, 3-aminoproponic acid and its sodium salt, n-bait-3-amino-dipropionate disodium salt, sodium lauriminodipropionate, sodium hydroxide disodium salt 1,1-bis (carboxymethyl) -2-undecyl-2-imidazolinium, cocoaminobutyric acid, cocoaminopropionic acid, cocoamidocarboxiglycinate and cocobetaine. Preferred amphoteric surfactants for use in the compositions of the invention include cocoamidoprilbetaine, cocoaminoethylbetaine and sodium lauriminodipropionate. Nonionic surfactants are also useful as surfactants active in the present invention. Nonionic surfactants do not carry discrete charge when dissolved in aqueous media. The non-ionic hydrophilicity is provided by hydrogen bonding with water molecules. Such nonionic surfactants typically comprise molecules containing large segments of a polyoxyethylene group in conjunction with a hydrophobic portion or a compound comprising a polyoxypropylene and a polyoxyethylene segment. Polyoxyethylene surfactants are commonly made by catalyzed base ethoxylation of aliphatic alcoholsAlkylphenols and fatty acids. Polyoxyethylene block copolymers typically comprise molecules having large segments of ethylene oxide coupled with large segments of propylene oxide. Examples of nonionics useful in the present invention are block copolymers of ethylene oxide / propylene oxide, glycerol esters, polyoxyethylene glycerol esters, polyglycerol esters, sorbitan esters, polyoxyethylene sorbitan esters, sucrose esters, and polyethylene ethers. The coating compositions of the invention can be made by mixing the ingredients in commonly available manufacturing equipment to form a homogeneous powder or a stable single-phase aqueous solution or dispersion. The usual method involves adding the surfactant (s) of choice to the organic salt composition. Accordingly, it is preferred that the surfactant be dispersed first within the service. In the case that soap is used as a surfactant, the soap is prepared during or before the manufacture of the material by neutralization or partial neutralization of carboxylic acids or mixtures with a proportion of an alkali metal base such as hydroxide. of sodium or potassium hydroxide. After the preparation of the soap, it can be absorbed on the inorganic salt combination to form a powder or tablet, or be diluted in an aqueous solution, to which the inorganic salt combination is then added, forming a paste, concentrate or solution diluted The illustrative formulations of the materials are shown in Table 1 below.

TABLE 1 Formulations (% by weight) Preferred Useful Most Preferred Composition of Inorganic Salt 0.1-99 0.15-90 0.50-80 Composition of Surfactant 0.01-30 0.015-25 0.05-20 Water 0-99 0-99 0-99 The above formulations include the barrier coating composition in powder form as well as dispersions or aqueous solutions. After processing, the compositions can be applied to a hard surface using a pump sprinkler or an aerosol spray device. In an aerosol spray device, the composition of the invention is combined with a propellant such as butane, propane, freon, nitrous oxide or other commonly available propellants or mixtures thereof. The amount of propellant used commonly ranges from about 5 to about 50% by weight of the contents of the aerosol container. In the event that a pump sprinkler is used, the spray nozzle and material are coupled for viscosity and material supply purposes. After application, the aqueous materials are dried under ambient conditions or at elevated temperatures to ensure that the coatings dry to an organic / inorganic deposit similar to white film. A preferred method to ensure that the coatings of the invention are completely dried involves cycling the food preparation unit through a heating cycle wherein the composition reaches a temperature greater than about 100 ° C to about 300 ° C during 10 to 40 minutes. The coatings of the invention when formed are of inorganic / organic nature; while they are flexible and resistant, they are not hard or brittle. Once the films have been completely formed, the oven can be operated in a normal way. The food can be processed and cooked in the normal cycles at the recommended temperatures. No changes are required in the operation of the oven for the compositions of the invention. The following examples and data provide a basis for understanding the operation of the invention and include a better mode.

EXAMPLES General Procedure for the Preparation of Coating Compositions A) Soap as a Surfactant The oleic fatty acid is neutralized or partially neutralized with a 45% by weight active aqueous potassium hydroxide solution, until a homogeneous, smooth paste is produced. This can be diluted with water to form a flowable concentrated solution, which can be absorbed onto a combination of sodium tripolyphosphate and sodium carbonate having a weight ratio between about 10: 1 to 1: 8, resulting in a powder.

Otherwise, the solid soap can be ground and then mixed with the inorganic salt combination to form a powder.

Alternatively, an aqueous composition can be made by charging an amount of water with a carboxylic acid or mixture of carboxylic acids, followed by an amount of active aqueous potassium hydroxide solution at 45% by weight sufficient to neutralize or partially neutralize the carboxylic acid, producing a soap in situ. After the soap is formed, the inorganic salts can be added to the solution, mixing until it is clear and uniform.

B) Other Surfactants Surfactants other than soaps are mixed with a mixture of alkali metal phosphate and carbonate, whose weight ratio is between about 10: 1 to 1: 8, resulting in a powder. Alternatively, this may be formed as an aqueous composition by first dispersing the surfactant in water, followed by the addition of the inorganic salts, mixing until it is clear and uniform.

C) Preparation of Use Solution The above powder composition of A) and / or B) can be dissolved in warm water to a concentration of about 1-20%, preferably about 5-10% by weight, or more preferably about 6-8% and sprayed on the surfaces to be treated. These powders can be sprayed alternately on a dry to wet surface. The liquid compositions described above do not necessarily require additional dilution and can be used at full strength.

Basic test method: 1) Prototype formulas (ie compositions) are applied to stainless steel test panels by dipping half of the panel into the product solution. 2) The panels are placed inside an oven at 200 ° C for 15 minutes to evaporate the water, leaving a dry film behind. 3) The panels are removed from the oven and a test spot (3 parts of butter to 4 parts of all-purpose pastry mix Golden-Dipt®) is applied to the entire hot surface of the panel to allow even distribution of the stain. 4) The panels are returned to an oven at 200 ° C and placed in a horizontal position for about 2 hours to develop a difficult spot. 5) The panels are placed in laboratory beakers containing 130 g of water at 71.1 ° C in which the stained area of the panel is fully submerged. NOTE: There is no agitation.

The panels remain in the water for 30 minutes and a determination of the stain removal is made. 7. The panels are removed and rinsed with a water rinse from the moderate warm wrench. The stain removal is again determined visually.

FORMULATIONS The following compositions (formulations) were prepared: Example 1 Example 2% by weight% by weight Na2CO3 10.30 Na2CO3 5.30 TSP 6.00 STPP 6.00 LAS, 97% 0.24 Trietanol 0.08 Water fls -amine 100.0% Fatty Acid 0.17 Oléic Water qs 100.0% Example 3 Example 4% by weight% by weight Na2CO3 5.30 Na2CO3 5.30 STPP 6.00 STPP 6.00 KOH, 45% 0.05 SLS 0.83 Acid Water fls Coconut fat 0.20 100.0% Water gs 100.0% Example 5 Example 6% by weight% by weight Na2CO3 10.30 Na2CO3 5. 30 STPP 6.00 STPP 6. 00 SLS, 30% 1.00 LAS 97% 0. 25 Water gs Water gs 100.0% 100.0% Example 7 Example 8% by weight% by weight Na2CO3 5.30 K2CO3 10.30 STPP 6.00 STPP 6.00 LAS, 97% 0.25 KOH: 45 0.05 Water Acid Gi -aso 100.0% of Coconut 0.20 Water gs 100.0% Example 9 Example 10% by weight% by weight Na2CO3 2. 82 K2CO3 5.30 STPP 3. 75 STPP 6.00 Tween 20 0. 73 KOH: 45% 0.05 KOH: 45% 0. 17 Fatty Acid 0.20 Oily Coconut Fatty Acid 0. 56 Water gs Water gs 100.0% Example 11 Example 12% by weight% by weight Na2CO3 10.30 Na2CO3 2.74 STPP 6.00 STPP 3.65 LAS, 97% 0.24 KOH, 45% 0.17 Water gs Fatty acid 100.0% Oleic 0.56 Water gs 100.0% Example 13 Example 14% by weight% by weight Na2CO3 5.48 Na2CO3 3.30 STPP 1.10 STPP 2.00 KOH, 45% 0.17 STPP 10.00 Fatty Acid SLS, 30% 1.50 Oleic 0.56 Water gs Water gs 100.0% 100.0% Example 15 Example 16% by weight% by weight Na2CO3 5.84 Na2CO3 5.30 STPP 0.73 STPP 6.00 KOH, 45% 0.17 SLS, 30% 0.83 Fatty acid Water as Oléic 0.56 100.0% Water gs 100.0% Example 17 Example 18% by weight 7th weight Na2CO3 82 Na2CO3 2. 82 STPP 75 STPP 3 .75 Hodag PGS-101 15 Shercotaine Water _gs. CAB-G, 35% 2 .86 100.0% Water gs 100.0% Example 19 Example 20% by weight% by weight Na2CO3 2.82 Na2CO3 2.82 STPP 3.75 STPP 3.75 Schercotaine KOH, 45% 0.17 CAB-G, 35% 1.00 Fatty acid KOH, 45% 0.06 Oleic 0.56 Acid Fat Water gs Oleic 0.19 100.0% Water gs 100.0% Comparative Example A 1:20 (phosphonate.carbonate) 1 Na2CO3 10.30 Na2SiO3 5.30 LAS, 97% 0.24 STPP 0.48 KOH, 45% 0.03 Coconut Fatty Acid 0.10 Water os 100.0% Comparative Example B Grease Guard ™ A commercially available composition that does not contain a carbonate salt and contains an organic thickener.

Comparative Example C STPP 3.00 LAS, 97% 0.25 Water OS 100.0% Comparative Example D STPP 10.00 KOH, 45% 0.17 Oily Fatty Acid 0.56 Water gs 100.0% Comparative Example E Na2CO3 5.30 SLS, 30% 0.80 Water gs 100.0% Example C omponent F Na2CO3 10.00 KOH, 45% 0.17 Oleate Fatty Acid 0.56 Water gs 100.0% Comparative Example G Na2CO3 5.97 STPP 0.60 KOH, 45% 0.17 Oleate Fatty Acid 0.56 Water gs 100.0% Glossary of terms TSP Trisodium phosphate LAS linear dodecylbenzenesulfonic acid STPP Sodium tripolyphosphate TEA Triethanolamine Tween 20 Polyethylene oxide (20) sorbitan monolaurate SLS Sodium lauryl sulfate Hodag PGS-W1 Polyglycerol stearate Schercotaine Cocoamidopropylbetaine Examples 1-20 were tested as previously described and all exhibited effective spot release. The composition of Example 1 exhibited excellent stain release in hot water only although it is not very soluble in the use solution when applied. The composition of Example 5 which replaces LAS with sodium lauryl sulfate (SLS) provides the same excellent results with improved solubility in the use solution. Better results were obtained using sodium lauryl sulfate or fatty acid soaps as the surfactant, oleaic fatty acid providing the best results for the soaps. Screening of different surfactants, examples 17-19, showed that all were more effective than comparative example A. The combination of surfactants, Example 9, also showed effective spot removal. The composition of Example 20 was tested against the compositions of Comparative Examples A and B and was superior in stain release. After immersion in hot water only, the test stain peeled off the surface of the panel while the material of Comparative Example A did not remove the entire stain and left behind a white film. When the performance was tested, those compositions containing only phosphate or only carbonate (Comparative Examples D, E and F respectively) were lower (including the Russian formula, Comparative Example A). Also, increasing the ratio outside the phosphate: carbonate 1: 8 ratio (as in Comparative Example G) resulted in poor stain removal. In an attempt to discover the mechanism by which some of the aforementioned formulations affected or not the stain release, electronic scanning microscope ("SEM") photos were taken of the test panels coated with various formulas, Examples 3, 7 and 10 and Comparative Example A. The compositions of Examples 3, 7 and 10 appear as an almost continuous, soft film, while Comparative Example A exhibits more cracks and tears, exposing the underlying panel. These photos also demonstrated the synergistic effect of phosphate and carbonate to form a physical barrier on the test panels, when compared to the composition of Comparative Example C, which contains only phosphate salt. The above specification, examples and experimentation provide a basis for understanding the invention. However, the invention can be made in a variety of modalities without departing from the spirit and scope of the invention. Accordingly, the invention appears in the appended claims which follow herein.

Claims (23)

1. A barrier coating composition for heat transfer surfaces comprising: a) 0.1 to 99% by weight of an inorganic salt composition having a phosphate source and a carbonate source in a weight ratio of 10: 1 to 1: 8; and b) 0.01 to 30% by weight of a surfactant composition; wherein the coating composition forms a substantially uniform barrier between the heat transfer surface and the stain.

The composition of claim 1, wherein the inorganic salt composition is an alkali metal salt.

3. The composition of claim 1, wherein the surfactant composition is an anionic, amphoteric or non-ionic surfactant and mixtures thereof.

The composition of claim 3, wherein the surfactant composition is a mixture of an anionic and an amphoteric surfactant.

The composition of claim 3, wherein the anionic surfactant is an alkali metal or alkanolamine salt of a saturated or unsaturated C6-24 carboxylic acid or mixtures thereof, an alkylarylsulfonic acid or an alkylsulfuric acid.

6. The composition of claim 3, wherein the amphoteric surfactant has a cationic amino group and an anionic carboxylate or sulfonate group.

The composition of claim 3, wherein the nonionic surfactant is a fatty acid ester of glycerol, a polyoxyethylene glycerol fatty acid ester, a polyoxyethylene sorbitan fatty acid ester, a polyethylene glycol fatty acid ester or a polyoxyethylene-polyoxypropylene block copolymer with terminal hydroxyl groups.

The composition of claim 1 comprising: a) 0.25-90% by weight of an inorganic salt composition consisting of an alkali metal phosphate and an alkali metal carbonate in a weight ratio of 4: 1 to 1 :1; and b) 0.015 to 25% by weight of an anionic, amphoteric or nonionic surfactant and mixtures thereof wherein the coating composition forms a substantially uniform barrier between the heat transfer surface and the stain.

The composition of claim 8, wherein the anionic surfactant is an alkali metal or alkanolamine salt of a saturated or unsaturated carboxylic acid C6.24 or mixtures thereof, an alkylarylsulfonic acid or an alkylsulfuric acid.

The composition of claim 8, wherein the amphoteric surfactant has a cationic amino group and an anionic carboxylate or sulfonate group.

11. The composition of claim 8, wherein the nonionic surfactant is a glycerol fatty acid ester, a polyoxyethylene glycerol fatty acid ester, a polyoxyethylene sorbitan fatty acid ester, a polyethylene glycol fatty acid ester or a polyethylene glycol copolymer. polyoxyethylene-polyoxypropylene block with terminal hydroxyl groups.

The composition of claim 9, wherein the surfactant is a sodium, potassium or triethanolamine salt of oleic or coconut fatty acid or a mixture thereof.

The composition of claim 9, wherein the anionic surfactant is sodium lauryl sulfate, potassium lauryl sulfate or ammonium lauryl sulfate.

The composition of claim 10, wherein the amphoteric surfactant is cocoamidopropylbetaine or cocoamidoethylbetaine or sodium lauriminodipropionate.

15. A method for forming a barrier coating on a surface in a heated food preparation unit, the coating of which facilitates the removal of stains from hardened foods or foods derived from cooking, the coating formed from an aqueous coating composition, which method comprises: applying an aqueous coating composition comprising: a) 0.1 to 30% by weight of an inorganic salt composition consisting of an alkali metal phosphate and an alkali metal carbonate in a weight ratio of 10: 1 up to 1.8; b) 0.1 to 20% by weight of an anionic, amphoteric or nonionic surfactant and mixtures thereof; and c) water; wherein the coating composition forms a substantially uniform barrier between the surface and the stain upon drying.

16. The method of claim 15, wherein the anionic surfactant contained in the aqueous coating composition is an alkali metal or alkanolamine salt of a saturated or unsaturated C6-24 carboxylic acid or mixtures thereof, an alkylarylsulfonic acid or an alkylsulfuric acid.

The method of claim 15, wherein the amphoteric surfactant contained in the aqueous coating composition has a cationic amino group and an anionic carboxylate or sulfonate group.

The method of claim 15, wherein the nonionic surfactant contained in the aqueous coating composition is a fatty acid ester of glycerol, a polyoxyethylene glycerol fatty acid ester, a polyoxyethylene sorbitan fatty acid ester, an ester of polyethylene glycol fatty acid or a polyoxyethylene-polyoxypropylene block copolymer with terminal hydroxyl groups.

The method of claim 15, wherein the weight ratio of alkali metal phosphate to alkali metal carbonate in the inorganic salt composition is from 4: 1 to 1: 1.

20. The method of claim 16, wherein the anionic surfactant is a sodium, potassium or triethanolamine salt of oleic or coconut fatty acid or a mixture thereof.

The method of claim 16, wherein the anionic surfactant is sodium lauryl sulfate, potassium lauryl sulfate or ammonium lauryl sulfate.

22. The method of claim 17, wherein the amphoteric surfactant is cocoamidopropylbetaine, cocoamidoethylbetaine or sodium lauriminopropionate.

23. The method of claim 16, wherein the surfactant in the aqueous coating composition is a mixture of an anionic and an amphoteric surfactant.