Coating processes – With post-treatment of coating or coating material – Heating or drying
Patent
1998-03-04
1999-11-30
Marquis, Melvyn I.
Coating processes
With post-treatment of coating or coating material
Heating or drying
428447, 524430, 524431, 524437, 524783, 524786, 524837, B05D 302
Patent
active
059939109
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The field is a material system and a process for coating articles, particularly glass and glass-ceramic articles, to impart durable, non-stick and non-wetting properties.
BACKGROUND OF THE INVENTION
Considerable effort has been directed at producing an effective, non-stick and non-wetting coating on the surface of an inorganic article, in particular a utensil for preparing and/or serving food. The term "non-stick" signifies a surface that resists adherence of foreign substances, such as food. This property permits easy cleaning of dishes in which foods are cooked or baked. The term "non-wetting" indicates a surface that repels liquids such as water. The property is evidenced by a large contact angle between a drop of water and the surface on which the drop rests. An advancing angle of at least 90.degree. is considered as representative of a non-wettable surface.
Non-stick, non-wetting articles are commonly produced by coating article surfaces with a polytetrafluoroethylene (PTFE) layer. For example, U.S. Pat. No. 4,683,168 (Hares et al.) describes a process for coating glass or glass-ceramic articles with such a layer to produce non-stick cooking utensils. However, PTFE coatings exhibit the disadvantage of being opaque. Also, they require a thermal sintering process at 350.degree.-400.degree. C. for their production, are relatively expensive to produce, and do not provide a desired degree of abrasion resistance.
French Patent No. 2,674,862 (Carre) discloses an alternative material system and process for producing durable, non-stick and water repellent coatings on glass and glass-ceramic surfaces. The process involves applying a mixture of a selected silane with a lower alkanol and water which may be acidified. The silane has the formula R.sub.n SiX.sub.4-n, where R is an alkyl radical and X is a hydrolyzable alkoxy or chloro group. The mixture is applied to a surface containing hydroxyl groups, the silane is hydrolyzed and the alkanol-water mixture eliminated to form a polysiloxane coating adhering to the surface.
Numerous other processes and material systems have been proposed for rendering inorganic surfaces, particularly vitreous surfaces, non-sticking and water repellent. The desired properties can be obtained initially. However, there has persisted a problem with respect to wear during use, in particular, scratching by cleaning agents. It is, then, a purpose of the present invention to improve on the Carre process by imparting a greater abrasion resistance to the coating there disclosed.
SUMMARY OF THE INVENTION
The present invention resides in part in a material system for imparting non-stick and non-wetting properties to an inorganic article having hydroxyl groups on its surface, the system comprising a silane having the formula R.sub.n SiX.sub.4-n wherein n is 1-2 and X is a hydrolyzable group, a colloidal metal oxide sol, and an acidified aqueous mixture with a lower alkanol.
The invention further resides in a method of imparting non-stick and non-wetting properties to an inorganic article having hydroxyl groups on its surface which comprises mixing a colloidal metal oxide sol with a silane having a formula R.sub.n SiX.sub.4-n, wherein n is 1-2 and X is a hydrolyzable group, and an acidified aqueous mixture of a lower alkanol, applying a coating of the mixture to a surface on the inorganic article, and thermally processing the coating at a temperature of at least 100.degree. C. to form a solid, transparent film on the article surface.
DESCRIPTION OF THE INVENTION
The present invention arose from studies directed at improving the polysiloxane, non-stick coating disclosed in French Patent No. 2,674,862 (Carre). The non-stick properties of the Carre coating are adequate. However the coating, like other known non-stick coatings, is prone to damage and removal. This is particularly true when the coating is subjected to the abrasion occasioned by normal scrubbing. Accordingly, efforts were directed at improving the abrasion-resistance of the known coating while either re
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patent: 4275118 (1981-06-01), Baney et al.
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patent: 4439239 (1984-03-01), Greigger et al.
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Carre Alain
Prassas Michel
Waku-Nsimba Jean
Corning Incorporated
Gheorghiu Anca C.
Marquis Melvyn I.
Peterson Milton M.
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