CH350777A - Method for providing metal kitchen utensils with a coating preventing food from sticking to the utensil - Google Patents

Description

Process for providing metal cooking utensils with a coating preventing food from sticking to the utensil It is known that silicone compositions applied to bread pans, waffle tins, etc. release and prevent overheated food from sticking. 0n has tried to use the same compositions with silicones for the coating of saucepans or frying pans, in particular aluminum. But the results observed are less good. Indeed, in this case, the layer of silicones turns out to be too soft, even after polymerization by prolonged cooking with appropriate catalysts. The silicone coating is scratched when hot both by the food that is moved on the stove or in the saucepan and by the forks, knives or cookers with which it is handled.

On the other hand, the coating of silicones applied to the aluminum does not give complete satisfaction from the point of view of sticking certain food materials, and in particular more or less carbonized milk.

Polytetrafluoroethylene, a product sold under the trade name Teflon, is also known to be applied to aluminum utensils to prevent food from sticking. It forms a coating on stoves which is generally harder than that obtained with silicones. It has been recommended to coat kitchen utensils with polytetrafluoroethylene using, for example, an aqueous emulsion called Teflon 30 prepared by <B>E.1.</B> du Pont de Nemours Co.

But, by following this technique, it is difficult to achieve a layer which adheres well to the metal and this because of the very properties of Teflon. Despite the prior treatment of the metal with acids, alkalis, sandblasting, etc., the Teflon layer adheres poorly to the metal and, after cooking the food a few times, it is easily removed in the form of films.

It has been found that the combined use of silicones and Teflon provides a successful solution which allows the particular properties of these two materials to be applied.

According to the process of the present invention, an application to the utensil of at least two successive layers of a composition containing silicones and polytetrafluoroethylene, the silicone content of the composition decreasing as one moves away from it. metal, or in that the utensil is first applied with a silicone composition and then a layer of a polytetrafluoroethylene composition.

The silicones provide very strong adhesion of the film to metal, particularly aluminum, while the polytetrafluoroethylene imparts hardness to it and prevents food from sticking. The hardness of the layers thus produced is greater than that of aluminum and exceeds 7 H to 8 H on the Wilkinson scale (pencil scale). The hardness of aluminum is around 3H to 4H on the same scale. As for the sticking of food, even strongly heated, it is eliminated.

The process of the invention can be applied in several ways. The number of layers is variable and is generally from 2 to 4. It is thus possible to begin with a composition containing 50 parts by weight of silicones and 50 parts by weight of polytetraethylene and end with a composition containing 25 parts by weight of silicones and 75 parts by weight of polytitraethylene, or alternatively 5 parts by weight of silicones and 95 parts by weight of polytitraethylene.

When using Polytetraethylene in Water Emulsion, it makes sense to mix it with a Silicone Emulsion. However, an organic silicone composition can also be applied first and then a polytetraethylene emulsion. The polymerization of the two products can be done separately. However, it is generally preferable to cure silicones and polytetraethylene in one operation.

The silicone compositions which are particularly suitable for carrying out the process according to the invention are obtained from methyl-, phenyl- or methyl-phenyl-silicones for which the R:Si ratio is less than 1.8. Example <I>1</I> An aluminum pan is treated for 3-4 minutes with 50% nitric acid. Wash carefully with distilled water and dry.

A mixture of an aqueous emulsion (a methyl phenyl silicone resin (Me -I-Ph: Si = 1.6) and an emulsion of Uflon 30 is then applied with a brush. The mixture is prepared in such a way as to have (ans l emulsification of equal weights of each active product. The pan is dried by the action of infrared rays. It is then heated very rapidly with a Bunsen burner at around 300-4000 C until the Tiflon droplets melt and agglomerate. 0n then applies a coat of emulsion containing 10% of the same silicone resin and 90% of Uflon 30. 0n heat-polymerized in the same way. 0n obtains a gray layer, smooth and hard, which, examined under a microscope, seems to penetrate (into all the aluminum holes.

Condensed, unsweetened milk is poured over this pan and evaporated to dryness by heating the pan over the medium flame of a gas stove. A partially scorched crust forms. This crust can be removed very easily from the pan, without leaving any traces. After a month of very safe domestic use, the coating still adheres perfectly. It has taken on a darker shade. Example <I>2</I> (comparative) An aluminum pan is treated with nitric acid as (in Example 1. A coat of Uflon 30 emulsion is then sprayed on, a sicher is hoisted to Fair and the Uflon is melted as (in Example 1.

After RTI ID="0002.0276" WI="6" HE="4" LX="469" LY="2406"> one week of home use, the Uflon coating peels off in places and becomes encrusted. rises in very thin layers.

Example <I>3</I> An aluminum pan is sandblasted, washed and dried. A coat of mithyl-phenyl silicone varnish is applied to this stove with a spray gun, characterized by the following data

The pan is heated for 2 hours at 1500° C. A layer of Uflon 30 is applied to the cooled pan. We end the processing as (in example 1.

0n breaks a =f on the pan heated over low heat. Cook it for 2-3 minutes and then remove it easily without sticking to the pan. Such an operation is impossible without the Uflon-silicone coating. Example <I>4</I> A mild steel stove is sandblasted. An emulsion containing 25% Uflon and 75% of a mithyl silicone resin, characterized by the ratio Me:Si=1.5, is applied to the pan.

It is polymerized by heating with a Bunsen burner as in Example 1 and a second emulsion containing 95% Uflon and 5% of the same silicone is then applied. It is copolymerized with the Teflon-silicones as above.

In this pan, you boil water for two days, then you heat margarine to 150o C for another two days.

After this treatment, the Uflon-silicone layer is intact.

A comparative test carried out on a stove treated according to Example 2 shows that, in this case, the Uflon layer flakes off in films.

Claims (1)

CLAIMS I. Process for providing metal kitchen utensils with a coating preventing food from sticking to the utensil, characterized in that Fon applies to the utensil at least two successive layers of a composition containing silicones and polytetrafluorethylene, the silicone content of the composition decreasing as one moves away from the mäa1, or else in that one applies to the utensil first a layer of a silicone composition, then a layer of a polytetrafluoroethylene composition. II. Metal kitchen utensil provided with a coating preventing food from sticking to the utensil obtained according to the process of claim I. TXF FR="8" WI="45" HE="6" LX="1342" LY="2302" SIZE="10" FONT="TimesNew Roman"> SUB-CLAIM </TAB> ProcM6 according to claim I characterized in that more than two coats of the composition containing silicones and polytetrafluoroethylene are applied, the silicone content decreasing with increasing distance from the metal.