Improvement to dishwashing machine operation

Abstract

 The dishwashing machine operation is improved by the provision of an additional ion-exchange device for removing bicarbonate ions comprising a column (1) containing an anion-exchange resin in the intake water line.
The device can be installed as a separate device connected in series either before or after the existing water-softening device or in parallel or it can form an integral part of the water-softening device.
The invention enables the use of lower alkaline detergent products.

Description

[0001] The invention relates to a method for improving the dishwashinq machine operation.

[0002] Industrial and household dishwashing machines of various types and designs are known in the art. The present invention is not concerned with the basic mechanics of such washing machines, but proposes to improve the dishwashing machine operation in that it allows the use of detergents with a lower content of alkaline ingredients.

[0003] The operation of a dishwashing machine is based on the combination cf three distinct actions, viz,

1) mechanical action exerted by water-spray,

2) thermal action exerted by heating,

3) physico-chemical action exerted by the added detergent.

[0004] Current detergent powders or liquids for use in dishwashing machines are generally highly alkaline products comprising essentially nonionic surfactant, sodium triphosphate, sodium metasilicate and chlorine bleach.

[0005] Lowering the alkaline content of such detergent products for machine- dishwashing without affecting their physico-chemical performance could be an important step towards milder products and environmental consequences.

[0006] All dishwashing machines are provided with a water-softening device, operating on the principle of removing the water-hardnes: cations, viz Ca²⁺ and Mg²⁺ ions, from tap water by ion-exchange, using a cation-exchange resin which is capable of exchanging Ca²⁺ and Mg²⁺ ions. Such a device generally comprises a column containing a cation-exchange resin, through which the intake water is passed before entering the machine. Many natural waters also contain bicarbonate anions (HCO₃-) which form the so-called temporary hardness of the water. These ions are not removed by the water-softening device containing a cation-exchange resin.

[0007] The invention now provides a method for improving the dishwashing machine operation in that it enables the use of detergent products of lower alkaline content, comprising the removal of both the water-hardness cations as well as the bicarbonate anions from the intake water entering the machine during the washing programme.

[0008] According to the invention the dishwashing machine is operated with an additional ion-exchange device in the intake water line comprising a column containing an anion-exchange resin for removing said bicarbonate anions from the water in conjunction with a water-softening device.

[0009] This device can be installed either as a separate device connected in series with the water-softening device either before or after it, or in parallel therewith, or it can form an integral part of combined water-softening and decarbonating system. In the latter case the ion-exchange resin column contains a mixture of cation-exchange resin and anion-exchange resin.

[0010] In this manner the water entering the dishwashing machine will be substantially free from Ca2+, Mg2+ and HC0₃- ions.

[0011] It has been found that with such water washing can be accomplished with equally good results using a detergent product having a significantly lower alkaline content than the conventional products. Good washing results have been observed with a dishwashing machine modified accoring to the invention, using a product containing 30% sodium metasilicate, whereas in a conventional dishwashing machine the same results were only obtainable with products containing 49-50% sodium metasilicate.

[0012] The anion-exchange resins which can be used in the present invention are known in the art and various types are commercially available, ranging from the very basic types to the slightly acid types. "Lewatit" anion-exchange resins, supplied by the Bayer Company, Leverkusen, Germany, are typical examples of readily available commercial products.

[0013] Preferred anion-exchange resins are those which can be regenerated with a solution of NaCl, as such resins will be regeneratable with the same regeneration salt as that used for regenerating the water-softening resin. Regeneration may then take place simultaneously for both water-softening resin and the anion-exchange resin without any special measures. An example of such resin is the commercial product "Lewatit M 600", supplied by the Bayer Company.

[0014] An example of a combined ion-exchange device according to the invention for installing in a dishwashing machine is shown schematically in the attached Figure 1. The figure shows a column (1) containing a mixture cf anion- and cation-exchange resins and a containerr (2) for the regenerating salt. In operation water is taken, in via line (3) and passes through the ion-exchange column, where it is softened ano decarbonated at the same time before entering the machine at point (4). For regeneration, all or part of the water stream can be passed through the regenerating salt versol (2) via line (5) .

[0015] In practice the whole water stream during the wash programme needs softening. but only the water stream for the main wash will need passing through the anion-exchanger for decarbonation. In the above embodiment, decarbonation of the water takes place during the whole wash programme, since the water stream cannot be by-passed from the anion-exchanger during pre-washing and rinsing. This by-passing is possible using an embodiment wherein the anion-exchange device is installed separately from the water-softening device, either in series or in parallel.

Example

[0016] A column containing the anion-exchange resin "Lewatit M 600" was installed in the water intake line of a Flandria dishwashing machine type R 12 before the water-softening device.

[0017] The tap water initially contained (64-78) 10^-4 mole/l of HCO₃-. After the water passed through the anion-exchange resin column, the concentration of bicarbonate ions was markedly reduced (max. 14. 10^-4 mole/l). Fig. 2 is a graph showing the evolution of HC0₃- concentration in a dishwashing machine with and without an anion-exchanger column, containing "Lewatit M 600", which was regenerated after each cycle with NaCl.

[0018] The upper curve shows HC0₃- concentration in the machine without an anion-exchange device.

[0019] The lower curve shows HC0₃- concentration in the machine provided with an anion-exchange device.

[0020] The regeneration efficiency of NaC1₂ is clearly seen from the lower curve, since a low amount of HC0₃- was found after each cycle at point R.

Example II

[0021] Washing experiments were made, using a Flandria type R 12 machine wherein a combined anion/cation-exchange device, as shown in Figure 1, is installed. The column had a capacity of 6 litres and contained 2 litres of cation-exchange resin "Lewatit S 100" ex Bayer Company and 4 litres of anion-exchange resin "Lewatit M 600" ex Bayer Company.

[0022] The machine was operated according to a programme including the regeneration of the resins, using the following detergent products.

(A) A standard machine dishwashing powder of the following nominal composition:

2% nonionic surface-active agent

37% sodium triphosphate

50% sodium metasilicate

5%sodium carbonate

1.5% K-dichloro cyanuric acid.

(B) Experimental product similar to standard but containing 25% sodium metasilicate and 25% sodium sulphate.

(C) Experimental product similar to standard but containing 30% sodium metasilicate and 20% sodium sulphate.

The results were rated as follows:

[0023] 





The general conclusion can be made that using the device of the invention, the effectiveness of detergent products containing 30% sodium metasilicate is comparable with that of a product containing 50% sodium metasilicate.

Claims

1. A method for improving the dishwashing machine operation in that it enables the use of detergent products of lower alkaline content, comprising the removal of both the water-hardness cations as well as the bicarbonate anions from the intake water entering the machine during the washing programme.

2. A method according to claim 1, characterised in that the dishwashing machine is operated with an additional ion-exchange device in the intake water line comprising a column containing an anion-exchange resin for removing said bicarbonate anions, in conjunction with a water-softening device.

3. A method according to claim 2, characterised in that the additional ion-exchange device is an integral part of a combined water-softening and decarbonating system comprising a column containing a mixture of cation-exchange resin and anion-exchange resin.

4. A method according to claim 2 or 3, characterised in that the anion-exchange resin is regenerated with NaCl.

Drawing