Cleaning and liquid contact with solids – Processes – Work handled in bulk or groups
Patent
1996-08-26
1998-12-08
Smith, Lynette F.
Cleaning and liquid contact with solids
Processes
Work handled in bulk or groups
134 47, 134 48, 134 52, 134 72, 25217424, 25217421, B08B 920, B08B 300, B22D 706
Patent
active
058463399
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a machine dishwashing process for cleaning soiled crockery and to the use of a composition as an additive in such a process.
BACKGROUND TO THE INVENTION
In a typical machine dishwashing process, crockery, such as tableware or cookware, soiled with food or other matter is subjected to a number of treatments in a sequence of zones or cycles. In a main wash zone the soiled crockery is usually sprayed with washing liquor at a pressure sufficient to detach much of the soil present on the crockery. The wash zone may be preceded by a prewash zone in which the crockery is also sprayed with water or with overflow from the wash zone. After the wash zone the crockery is usually rinsed in one or more clear washing zones using fresh water.
Although a major factor in the effectiveness of the wash zone is the mechanical action of the washing liquor on the soiled crockery, in most cases the water pressure exerted is insufficient to detach completely adherent soil such as food residues which have dried on, are firmly adherent, or which contain colouring matter, especially when they contain protein and/or starch. It is also found that a deposit can build up on the crockery over the course of time during successive cleaning operations. In order to make the cleaning of the crockery more effective, it is therefore usual to add into the process a cleaning solution, which is usually supplied to the washing liquor as a concentrated liquid cleaner.
The cleaning solution generally contains alkali, such as sodium hydroxide or potassium hydroxide and is intended to remove the adherent soil by swelling or partially dissolving it to facilitate rinsing. The cleaning solution also contains complexing agents which are essential for sequestering metal ions present in hard water. Other additives may include bleach to decolourise food residues which contain colouring matter, surfactants to aid binding of dirt particles, and disinfecting components.
EP-A-0282214 discloses an improvement in machine dishwashing processes in which the crockery is washed in the normal way in the main wash zone and thereafter sprayed in a spraying step with a concentrated spraying solution before further rinsing. In the spraying step the crockery is subjected to a low volume/low intensity mist-like application of concentrated cleaning formulation and the crockery is allowed to remain in contact with the cleaning formulation for, say, at least ten seconds before rinsing. The concentrated cleaning formulation contains as essential ingredients both concentrated alkali and concentrated complexing agents.
A disadvantage of the arrangement of EP-A-0282214 is that the amounts of raw materials such as caustic and complexing agents are not easy to control. Typically, fresh water is applied in the rinse stage but concentrated cleaning solutions are supplied during the spraying step and in the main wash zone. In one typical arrangement, the water and other materials in the process pass in cascade-fashion in the rinse zone to prewash zone direction, counter-current to the direction of the transport of the crockery. Because concentrated raw materials are supplied to various stages of the wash cycle it is very difficult, therefore, to measure and control simply and accurately the amount of raw materials needed to be effective in cleaning the crockery. As a result, to ensure effective cleaning there is a tendency to put in more raw material than would actually be necessary. This adds to the running costs of the process and increases the amount of pollution when the waste water is discharged into the environment. Moreover, because a variety of different water hardness conditions are encountered at the site of use of the dishwashing process, it has hitherto been necessary to offer to users a range of products. The user then has had to select the product with the best combination of water hardness and causticity.
SUMMARY OF THE INVENTION
The present invention provides a machine dishwashing process for cleaning soiled crockery,
REFERENCES:
patent: 3850832 (1974-11-01), Wegemund et al.
patent: 4891148 (1990-01-01), Ouhadi et al.
Masshoff Hans Wilhelm
Praeckel Udo Fritz Walter
Diversey Lever Inc.
Huffman A. Kate
Smith Lynette F.
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