Protective coating of silver

Abstract

In the method, silver is protected against tarnishing using an Atomic Layer Deposition method. In the Atomic Layer Deposition method, a thin film coating is formed on the surface of silver by depositing successive molecule layers of the coating material. For example aluminium oxide (Al2O3) or zirconium oxide may be used as the coating material.

Description

[0001]This application is a continuation of application Ser. No. 12 / 162,051, filed Jul. 24, 2008, which in turn is a National Phase of International Application No. PCT / FI2007 / 050056 filed on Jan. 31, 2007, which claims priority to Finnish Patent Application No. 20065082 filed on Feb. 2, 2006. The disclosures of the prior applications are hereby incorporated by reference herein in their entireties.FIELD OF THE INVENTION[0002]The present invention relates to a method for coating silver products, and more particularly to a method according to the preamble of claim 1 coating silver.BACKGROUND OF THE INVENTION[0003]Silver naturally tarnishes in the atmosphere, especially in the presence of sulphur. Industrial atmospheres and natural digestive processes are important sources for the tarnishing of silver. When silver is tarnished, sulphides, oxides or carbonates are formed on the surface of silver. The tarnishing of silver and silverware is a problem for example for the utility article, j...

AI Technical Summary

Benefits of technology

The patent describes a method for depositing a thin coating of Al2O3 on a silver product using atomic layer deposition (ALD) to prevent tarnishing without altering the appearance of the product. The coating is about 70 nm thick and is colorless, smooth, and compatible with foodstuffs. The method is cost-effective and repeatable, and can be controlled in detail. The coating can be applied to three-dimensional objects and is not visible to the naked eye. Overall, the method provides a stable, uniform, and attractive coating that effectively passivates the silver surface.

Problems solved by technology

Silver naturally tarnishes in the atmosphere, especially in the presence of sulphur.

The tarnishing of silver and silverware is a problem for example for the utility article, jewellery and giftware industries as well as to the end users of the silver products.

It can be removed but this is usually a laborious process, and the process may affect the appearance of the product negatively.

Also in technical applications the tarnishing of the silver reduces the optical properties, such as reflectivity, of silver and silver products and parts.

One of the problems associated with the above arrangement using silver alloys is that the method requires all factors to be carefully controlled during manufacture, like using extremely pure new metal and accurate temperature control in melting and annealing.

As a result, the manufacturing process and the equipment to carry out the process are very expensive to set up.

The cost is also prohibitive in the method for coating silver with rhodium.

The problem with these known coating methods is that the coating layer is not uniform over the whole product or part of the product that has been coated.

This further has a negative influence on the appearance of a silver product.

Thus, the known methods for preventing tarnishing of a silver product do not provide a uniform and substantially to human eye invisible coating, but a non-uniform coating and / or a coating producing discoloration of a silver product.

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