CA1080563A

CA1080563A - Kitchen utensils used for the cooking of food

Info

Publication number: CA1080563A
Application number: CA254,795A
Authority: CA
Inventors: Jean-Claude M.A. Gastel; Serge A.M. Renault; Colette M. Genisson
Original assignee: Corning Glass Works
Current assignee: Corning Glass Works
Priority date: 1975-07-28
Filing date: 1976-06-14
Publication date: 1980-07-01
Also published as: DE2631761B2; ES449523A1; GB1556193A; FR2319594A1; DE2631761C3; IT1063128B; DE2631761A1

Abstract

IMPROVEMENT OF KITCHEN UTENSILS USED
FOR THE COOKING OF FOOD

Abstract of the Disclosure A cooking utensil is disclosed that has a vitreous cooking surface and a metal oxide coating applied to that surface, the metal oxide coating being highly adherent, mechanically and chemically inert, and resistant to food sticking. The coating is composed of alumina, zirconia, titania, or a mixture of these oxides.

Description

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~^- ' 10 Back~round of the Invention .; , .~ ! The present invention concerns a kitchen utensil that ~, r -' has a vitreous cooking surface, and that is rendered resist-ant to food sticking by application of a highly adherent, rc.
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_ selected metal oxide coating. The coating is useful on both ~.~ cooking and baking ware, and facilitates the removal of food ,.. . ..
after cooking, especially in subsequent cleaning of the cooking utensil.
Heretofore, the property of non-sticking has been imparted to cooking utensils by coating the inside surface of the utensils with an organic resin, especially a resin containing fluorine, such as polytetrafluoroethylene, or a silicone resin. However, these organic resin coated utensils - tend to lack resistance to scratching and to overheating.
;i ~ Thus, in order to avoid damage of the coating by scratching, ..I,~ff* ~.
it is frequently recommended that metal implements, such as spoons and knives, should not be used in contact with the coating. Likewise, it is necessary to avoid overheating so that the organic resin is not decomposed, since such decom-position will not only destroy the characteristic non ~ cking . -1-:

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- character of the coating, but also may release toxic pro-_ duct.
It is then the object of the present invention to pro-vide a kitchen utensil with an improved non-sticking coating which is not subject to decomposition on overheating, which is not subject to mechanical damage from metal implements, ~ and which otherwise avoids or minimizes the problems encoun-`~';' tered with prior non-sticking coatings.

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~ State of the Art . ..,, ~, "p, "~ 10 United States Patent No. 2,464,242, granted February r 22, 1949 to P. S. Webb et al., discloses and claims a cook-, ing implement having a silicone coated surface to facilitate cleaning. United States Patent No. 3,393,086, granted July 16, 1968 to J. H. Keating, describes prior practice of applying polytetrafluoroethylene to the surfaces of cooking ;^ and baking utensils to prevent food sticking. This patent al`so points out the problem of poor adhesion of the coating, and proposes a solution wherein a heavy metal frit is fired on a rough aluminum surface to provide a base for the resin .~._ coating. I
~- Superficial oxide coatings applied to the external surfaces of bottles and jars in order to décrease the fric-tion between such glass articles and to improve resistance ~h~ to surface scratching are already known. For example, United States Patent No. 2,831,780, granted April 22, 1958 to A. J. Deyrup, discloses that the scratch resistance and ; strength of glass articles are improved by pyrolyzing an alkyl titanate, zirconate, or aluminate, on a hot glass surface to form a corresponding metal oxide coating thereon.
However, it is not disclosed that such metal oxide coatings ~080563 have the necessary mechanical and chemical durability required in cooking utensils, nor is it disclosed that such coatings impart any resistance to the adherence of food in the course of cooking or subsequent standing in contact with food.
Statement of Invention The present invention provides a cooking utensil comprising a vitreous cooking surface containing silica in the compoisition thereof and having covalently chemically bonded thereto a highly adherent, mechanically and chemically inert, coating of a metal oxide that is resistant to food sticking, the metal oxide being selected from the group consisting of alumina, zirconia, titania, and mixtures thereof.
The invention further contemplates a method of rendering the ~-vitreous cooking surface of a cooking utensil resistant to food sticking, I said vitreous cooking surface containing silica in the composition thereof, which comprises applying a metal oxide coating selected from the group consisting of alumina, zirconia, titania and mixtures thereof to the vitreous surface and then thermally treating the metal oxide coated vitreous surface at a temperature of at least 475C., but below the temperature at which the utensil deforms, to covalently chemically bond the metal oxide of the coating to the silica of the vitreous surface.
General ~escription The cooking utensil of the present invention may be of any ;~ construction that embodies an internal vitreous surface, that is, a vitreous cooking surface on the utensil. Thus, it may be a molded utensil of any ~i conventional glass or glass-ceramic material, such utensil being molded from glass and either used as such or thermally converted to a glass-ceramic u~ensil. Alternatively, the utensil may be glazed ceramic ware or enameled metal ware. The single requisite of the utensil, as such, is a vitreous cooking surface.
The problem of food adherence to dishes in general, and cooking dishes in particular, is well recognized. As pointed l ~080563 out earlier, a great deal of effort has been expended in the development of organic resin ~oatings to provide a surface f- ~ resistant to such food sticking or adherence. In at least some instances, these coatings have been eminently successful with respect to the prevention of food sticking, until they were mechanically damaged by metal cutlery or by other mechanical scraping or impact. In spite of intensive study, the problems of mechanical damage and lack of adherence have persisted with the known coatings. In contrast, the coating of the present invention is a highly adherent, mechanically and chemically inert coating that avoids the problems inherent " in prior organic type coatings.
.j The present coating is a very thin oxide coating which may consist of alumina, zirconia, or titania, either singly or in mixture, as desired. These coatings are mechanically resistant to scraping or scratching with metal cutlery or other implements, and are chemically inert with respect to such materials as food acids and detergents. Further, they can be rendered highly adherent to vitreous surfaces. The _ 20 coating must of course be a continuous coating, that is must not leave any open areas or discontinuities on the coated surface. Otherwise, thickness is not particularly important, except as greater thicknesses become economically wasteful of material, or may tend to spall or crack in case of excess-: ~ 3 ively thick coating The oxide coating may be applied by any conventional coating practice. Thus, the selected oxide may be vaporized, ~ .
for example by electron bombardment, and the vapors con- i densed on the vitreous surface~ The technique described in earlier mentioned United States Patent No~ 2,831,780, that ~~~-- is, pyrolysis of an organo-metallic compound, is also a ~- -4-very useful technique. Cathodic sputtering is another frequently used method of oxide application. Other thermal 7''t decomposition and vapor deposition techniques are known and ~~ may be used when particular conditions warrant.
Thus, the formation of an oxide coating on a surface is a well known technique, and the present invention is not based on either this principle, as such, or on a specific method of applying an oxide. As mentioned earlier, oxide coatings have been applied to the external surfaces of ~ Y
~s3 lo bottles and jars as a lubricant to minimize sticking of such glass surfaces to one another, and consequent scratching and .z~ damage thereto. Such external coatings on containers were not exposed to food sticking as occurs in cooking utensils.
Neither are they exposed to the repeated usage that is -customary with cooking utensils. Efforts to substitute such coating for organic resin coatings on cooking surfaces have heretofore proved unsatisfactory.
The excellent adherence obtained between the oxide film and the vitreous surface, in accordance with the present invention, is attributed to a superior bond between the oxide constituents thereof. In our preferred practice, we thermally treat an oxide coated vitreous surface after deposition of the oxide coating.1 Such thermal treatment may -be at a temperature above 450C. but necessarily below the deformation temperature of the ware being treated. It is our belief that a covalent chemical bonding is established . _ _ _ . .
between the metal oxide of the coating and the silica of the vitreous network of the cooking utensil surface.
The kitchen utensils conforming to the present inven-,, ~' ~ 30 tion can be characterized by the following test method, ~ which demonstrates the non-adherence of food and the fact ~.
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that this property is conserved in spite of subsequent chemical and mechanical treatment.
__ Two cooking vessels, one treated according to the pre-~` ~ sent invention and one untreated, both containing a piece of meat, are placed side by side in a domestic oven the meat being cooked in the normal manner. When the meat is cooked _ the two dishes are equally blackened, on almost all their interior surface, either by spattering onto the sides or by -r- ~ burnt juices on the base.
o After taking out the meat and quickly emptying out the remaining contents, the two vessels are placed side by side in an automatic dish washing machine where they are sub-~r-r~ mitted to a normal washing cycle. After removal, the treated vessel is perfectly clean whereas untreated vessel is still black on almost all its surface and must be scoured.
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' . i J The treated vessel is now submitted to a test of 4 '~r~` 'p~l ~ ~ ~ hours duration in a boiling 0.1% solution of a commercial , ~ .....
detergent (trademark Mach I) recommended or use in industrial dishwashing machines. This test simulates about 2000 actual machine cycles and is generally equivalent to approximately I
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10 years service for a cooking vessel.
An alternative detergent test is to place the vessel in a boiling solution of 1% trisodium phosphate Ma3PO4 for 30 minutes. According to the German standard DIN 51 035, this .
test is equivalent to 5000 machine cycles.
After one of these detergent tests, the vessel con-forming to the invention has not changed in appearance. In order to verify that there has been no effect on the property of non-adhesion the vessel is resubmitted to the cooking and .
washing test. The result obtained is identical to that ~ obtained previously.
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The following are some non-limi~ing examples of pro-cedures used to produce non-adherent cooking utensils con-forming to the invention:
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Example 1 A PYREX~ brand cooking vessel molded from a borosili-' cate glass, previously degreased, is placed in an enclosure ~ ~ under vacuum. Titanium monoxide, TiO, is evaporated by '-r~ ~~ means of electronic bombardment and deposited onto the glass - ~ forming a thin film, pale brown in color. ~he vessel is then submitted ~o a thermal treatment of l hour at 500C.
";,~ The titanium monoxide coating, TiO, is converted to a higher . ~ .,, ~, . . I
oxide TinO2n_l or TiO2 and the film becomes transparent, possibly slightly colored because of the phenomenon of light interference.

Example 2 . . ~ i A TAMARA~ brand cooking vessel molded from a borosili-cate opal glass is heated at 500C. for 10 minutes. A
_ solution of titanium isopropylate in isopropyl alcohol is then sprayed onto the hot vessel with the aid of a spray gun as is described in U.S. Patent No. 2,831,780 or Dutch Patent 64 04159 published on October 19, 1964. The film of titanium oxide thus obtained is not sufficiently adherent to the ` ~ substrate. Adequate adhesion of the film is obtained by a ;,`t~ t~ subsequent heat treatment of 1 hour at 600C. This treatment . can be replaced by heating directly in a flame.
The oxide film finally obtained is transparent and possibly irridescent as that of Example 1.

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Example 3 A steel frying-pan with a vitreous coating and an -enamelled cast iron frying-pan are coated with a film of titanium monoxide, TiO, following the method described in Example 1. They are then heat-treated for 1 hour at 475C.

Example 4 ., ~ ,, . f;
~ ; A PYREX~ brand cooking vessel molded from a borosili-. ... _, "~ cate glass is heated to 400C. and then exposed for 30 .,S seconds to the vapor of aluminum isopropylate as described . ,~.. ,-~.
` 10 in U.S. Patent No. 2,831,780 previousIy cited. The film $ thus obtained is not durable.
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The vessel then undergoes a subsequent heat-treatment of 1 hour at 650C.
~ ._ Example 5 J` In vacuum equipment furnished ~ith apparatus for cathodic ~..
sputtering, a glass cooking vessel is placed on the anode and alumina at the cathode.
Under the effect of the high tension existing between the two electrodes, the alumina volatilizes into a plasma which is attracted to the anode and thus onto the glass vessel.
With a film thickness of about 0.1 micron and in any case more than 0.05 micron the vessel possesses the required qualities of non-adherence and durability.

Example 6 A PYREX~ brand vessel molded from a borosilicate glass is placed in a vacuum chamber, under very low pressure.

~080563 Under the effect of electronic bombardment, alumina is evaporated onto the vessel to form a thin film. The film thus obtained is not durable. Adequate durability is obtained by a subsequent heat treatment, in the circumstances by direct flame treatment.

Example 7 A solution of 1% by weight of hydrated zirconyl chloride, --i''' ZrOC128H20, is prepared. This solution is sprayed onto a d'~ PYREX~ brand cooking vessel previously heated to 400C. The s q vessel then undergoes a thermal treatment of 1 hour at ;;i~,.~J 600C. or at 700C. One obtains a thin transparent uncolored film.

~ Example 8 .~
' r~ . A glass cooking vessel is placed in a vacuum chamber under very low pressure. Under the effect of electronic bombardment a mixture of titanium monoxide and alumina, essentially equal in proportion, is evaporated onto the _ vessel.
The film thus obtained is only durable after a subse- I
quent thermal treatment, in the circumstances a treatment of 1 hour at 550C.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A cooking utensil comprising a vitreous cooking surface containing silica in the composition thereof and having covalently chemically bonded thereto a highly adherent, mechanically and chemically inert, metal oxide coating that is resistant to food sticking, said coating being selected from the group consisting of alumina, zirconia, titania and mixtures thereof.

2. A method of rendering the vitreous cooking surface of a cooking utensil resistant to food sticking, said vitreous cooking surface containing silica in the composition thereof, which comprises applying a metal oxide coating selected from the group consisting of alumina, zirconia, titania and mixtures thereof to the vitreous surface and then thermally treating the metal oxide coated vitreous surface at a temperature of at least 475°C., but below the temperature at which the utensil deforms, to covalently chemically bond the metal oxide of the coating to the silica of the vitreous surface.