Machine dishwashing compositions containing an oxygen bleach and

Cleaning compositions for solid surfaces – auxiliary compositions – Cleaning compositions or processes of preparing – For cleaning a specific substrate or removing a specific...

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Details

510255, 510367, 510375, 510401, C11D 3395, C11D 718, C11D 754, C11D 760

Patent

active

058438777

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to oxygen-bleach containing compositions, adapted for use in machine dishwashing, exhibiting good bleachable stain removal and reduced silver-tarnishing properties.


BACKGROUND TO THE INVENTION

Compositions designed for use in automatic dishwasher machines are well known, and a consistent effort has been made by detergent manufacturers to improve the cleaning and/or rinsing efficiency of said compositions on chinaware, glassware and silverware, as reflected by numerous patent publications.
The satisfactory removal of bleachable soils such as tea, fruit juice and coloured vegetable soils, such as carotenoid soils is a particular challenge to the formulator of a machine dishwashing composition. Traditionally, the removal of such soils has been enabled by the use of bleach components such as oxygen and chlorine bleaches.
A problem encountered with the use of oxygen bleaches, in particular, is the tarnishing of any silverware components of the washload. Chlorine bleaches can under certain circumstances give rise to silver tarnishing, but the problem is significantly less pronounced than that arising from the use of oxygen bleaches. The level of tarnishing observed with oxygen bleaches can range from slight discolouration of the silverware to the formation of a dense black coating on the surface of the silverware.
The formulator thus faces the dual challenge of formulating an oxygen bleach containing product which maximises bleachable soil cleaning but minimises the occurrence of tarnishing of silverware components of the washload.
It has been surprisingly found that reduced silver tarnishing as well as good cleaning performance can be achieved through the inclusion in an oxygen bleach containing formulation of a water-soluble bismuth compound.
It has also been found that the presence of water-soluble sulphate salts surprisingly enhances the silver tarnish inhibition capability of the bismuth compound.
To further reduce the occurence of silver tarnishing, the rate of release of the oxygen bleach is preferably also controlled. The rate of release of oxygen bleach is preferably rapid enough to provide satisfactory cleaning, but not so rapid that tarnishing is enabled.
Compositions having low alkalinity, and in particular those having alkalinity systems including a minor proportion of a metasilicate component are preferred, as are compositions having a pH which is not unduly high.
UK Patent Specification No. 1,586,067 in the name of the Procter and Gamble Company, discloses automatic dishwashing compositions containing bismuth salts to provide protection to china overglaze without any negative glassware irridescence effects. It is taught therein that chlorine bleaching agents are preferable components of these compositions and specific examples of chlorine containing compositions are given. The use of oxygen bleaches in such compositions is not disclosed. The problem of silver tarnishing is not addressed by this document, nor is any teaching provided of the use of bismuth salts as silver tarnish inhibition agents.
In another aspect it has been found that treatment of silverware with a composition containing bismuth prior to washing in a machine dishwashing method using an oxygen bleach-containing detergent can also reduce the tendency of that silverware to tarnish during the wash.
In a further aspect it has been found that the provision of a means of delivering bismuth to a machine silverware washing/bleaching solution separate from the bleaching/detergent composition employed therein can also lead to a reduction in the tendency for tarnishing to occur. Said means may comprise some kind of a bismuth ion delivery system placed inside a dishwasher machine which is designed to allow release of bismuth ions during the course of the washing process.
It is an object of the present invention to provide compositions, suitable for use in machine dishwashing methods, having reduced silver-tarnishing properties, as well as good cleaning performance, particularly bleachable soi

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