Dishwashing compositions

Abstract

 A detergent powder composition for dishwashing machines comprising 25-40% amorphous sodium silicate, l0-40% sodium carbonate, l5-40% phosphate builder, 0.25 to 5% of each of an amylolytic enzyme and a proteolytic enzyme and up to 60% of bulking agents and optionally up to 5% surfactant. The preferred builder is sodium tripolyphosphate and the preferred bulking agent is sodium sulphate (optionally together with sodium chloride) in an amount of at least 30%.

Description

[0001] This invention relates to dishwashing compositions and particularly to compositions in the form of a powder suitable for use in automatic dishwashing machines.

[0002] Detergent compositions for automatic dishwashing machines are known which comprise a bleaching agent, usually a chlorine-containing bleaching agent, and which are highly alkaline compositions having a solution pH above ll.5. These conventional highly alkaline compositions are efficient in cleaning dishes but suffer from a number of disadvantages, notably that they are corrosive towards some metal components, ceramic glazes and pigments. Compositions containing a chlorine bleach have the further disadvantages of odour problems and that due to instability of the bleach they may be difficult to perfume and/or dye and have a limited shelf-life.

[0003] A detergent composition free from a chlorine bleach and purporting to obviate the disadvantages of conventional dishwashing compositions is proposed in European Patent Application No l35227 A2. This composition is based on a peroxy compound bleach used in combination with an amylolytic enzyme, is mildly alkaline with a solution pH of about 9.3 to about l0.8 and can be presented in the form of a particulate product thereby obviating the disadvantages of using a liquid composition. This composition overcomes many of the disadvantages of the conventional highly alkaline compositions containing a chlorine bleach but still has the disadvantage that it contains a bleaching agent.

[0004] The present invention is concerned with a bleach-free dishwashing composition which is only mildly alkaline but is at least as effective in cleaning dishes as compositions proposed hitherto. The composition is presented in powder form and exhibits a solution pH under dishwashing conditions in an automatic dishwashing machine of below ll.0 and preferably no greater than about l0.0.

[0005] According to the present invention there is provided a detergent powder composition for use in automatic dishwashing machines comprising -

(a) 25 to 40% by weight of amorphous sodium silicate powder,

(b) l0 to 40% by weight of sodium carbonate,

(c) l5 to 40% by weight of a phosphate builder,

(d) 0.25 to 5% by weight of each of an amylolytic enzyme and a proteolytic enzyme,

(e) up to 60% by weight of bulking agents, and

(f) 0 to 5% by weight of a low-foaming surfactant.

[0006] The composition is mildly alkaline and in particular has a solution pH of about l0.0, this being the pH of a solution of 3 g/litre of the composition in water. The alkalinity or solution pH of the composition, which should generally be maintained above about 9 in order that the enzymes be effective, is largely established and maintained by components (a), (b) and (c) which exhibit a builder/buffer effect on the solution and are used in sufficient amounts to provide the desired solution pH. The optimum relative proportions of components (a), (b) and (c) are readily determined by simple trial for any particular composition but as a guide the ratio by weight is typically about l:l:0.5 of amorphous sodium silicate (a):sodium tripolyphosphate (c):sodium carbonate (b).

[0007] The combined weight of builder and buffering agents, components (a), (b) and (c) should be at least 50% of the composition and may be up to 90% or even higher of the composition. Usually, however, the composition will contain an appreciable amount of one or more bulking agents so that the combined weight of components (a), (b) and (c) will be no more than about 70% of the composition. As a guide only, we have obtained good cleaning using compositions containing about 65% by weight of components (a), (b) and (c) combined in the ratio of about l:0.5:l.

[0008] The composition will usually contain one or more bulking agents in an amount of from 30% to 60% by weight. Any bulking agent may be used which does not appreciably inhibit the effectiveness of the enzymes or adversely modify the alkalinity of the composition. Sodium sulphate is a typical and preferred bulking agent and sodium chloride may also be used. Our preferred compositions contain both sodium sulphate and sodium chloride in a ratio of about l:0.5 by weight.

[0009] The preferred phosphate, component (c), is sodium tripolyphosphate.

[0010] The composition may contain a low-foaming surfactant and advantageously does contain a small amount, for example up to 5% by weight, of such a component. However we have found that if present, only very small amounts of surfactant are required and in particular amounts below 0.5% by weight. Any low-­foaming surfactant may be employed but will usually be a non-ionic surfactant such as an alkylene oxide condensate in which the alkoxy moity is derived from ethylene oxide or propylene oxide or a mixture thereof. Examples of suitable surfactants are the well-known ethoxylated straight-chain alcohols. Preferably, the surface active agent is biodegradable.

[0011] The composition contains both an amylolytic enzyme and a proteolytic enzyme. Preferably at least one of the enzymes and especially preferably both of the enzymes are in granular form. The enzymes are used in mixtures in which the ratio by weight of amylolytic enzyme: proteolytic enzyme is from l:4 to 4:l and usually from l:2 to 2:l. We prefer to employ approximately equal amounts (by weight) of proteolytic enzyme and amylolytic enzyme, typically from 0.5 to l.5% by weight of each enzyme based on the weight of the composition.

[0012] Any amylolytic enzyme and any proteolytic enzyme may be used which at pHl0 exhibits at least 50% and preferably at least 60% of its maximum activity. The enzyme mixture is present in the composition in an amount such that the composition has an amylolytic activity of at least l50 KNU (Kilo Novo units), preferably at least 300 KNU, per kilogram and a proteolytic activity of at least 6 Anson units per kilogram. Amylolytic activity in KNU is determined as described in United States Patent Specification No 3,93l,034. Proteolytic activity in Anson units is determined as the amount of enzyme which degrades haemaglobin under standard conditions as described in Journal of General Physiology, Vol 22 (l938), page 79.

[0013] The compositions of the invention may if desired contain other ingredients known for use in automatic dishwasher compositions, for example sequestering agents, soil-suspending agents, corrosion inhibitors, drainage-promoting agents, crystal modifiers, dyes and perfumes.

[0014] The compositions of the invention are presented as powders which can be produced by dry-mixing the powdered/granular materials and spraying any liquid components, e.g. a surfactant, on to the mixture during mixing.

[0015] The invention is illustrated by the following Examples in which all parts are weight.

EXAMPLES l-5

[0016] Five powder dishwashing compositions were prepared to the following formulations in which the ingredients are expressed as percentages by weight of the compositions:-

[0017] The sodium tripolyphosphate was stirred in a Kenwood food mixer and the surfactant (liquid) was added, followed by the other liquid ingredients. When all the liquids had been absorbed, the remaining ingredients were added to and mixed in the composition.

[0018] A sample of each composition was used to clean dirty plates in a domestic automatic dishwashing machine (Indesit 2260E). The water softener reservoir in the machine was kept topped-up with sodium chloride and a rinse-aid was employed during the rinse cycle of the cleaning operation. l5 g of the powder dishwashing composition was loaded into the machine in each trial.

[0019] The dirty plates being cleaned were soiled by coating them with both a greasy soil and a protein soil and baking them at l50°C in an oven. Some plates were baked for 5 minutes, some for 7.5 minutes and others for l0 minutes.

[0020] The greasy soil was a mixture of peanut butter (5), butter (2), lard (2.5) and a mineral oil (2), the figures indicating parts by weight.

[0021] The protein soil was a mixture of raw egg (5) peanut butter (l), lard (l), butter (l) and milk (l), the figures being parts by weight.

[0022] After a full wash-cycle (including drying) in the machine, the dry plates were removed and assessed for cleanliness. The plates were coated with a thin film of activated charcoal and their reflectance was then determined at several points on the surface using a Bosch Light Reflectance meter. The amount of activated charcoal adhering to the surface corresponds to the amount of soil remaining on the plate, being greater the greater the amount of soil. Using this technique a numerical assessment was derived of the cleanliness of the plates and hence of the cleaning ability of the dishwashing composition. As a blank against which cleanliness was assessed there was taken a new, unsoiled plate which was washed in the machine and assessed for cleanliness as above.

[0023] Based on the results of a minimum of ten dishwashing trials, the relative cleaning ability of each composition was determined to be as follows on an arbitrary scale of 0 to ll0:-

[0024] For purposes of comparison, plates dirtied as above were washed in the machine using a well-known proprietary dishwashing composition available under the trade name "Finish". The relative cleaning ability of this composition was assessed on the 0 to ll0 scale as 53.

Claims

1. A detergent powder composition for use in automatic dishwashing machines, comprising:-

(a) 25 to 40% by weight of amorphous sodium silicate powder,

(b) l0 to 40% by weight of sodium carbonate,

(c) l5 to 40% by weight of a phosphate builder,

(d) 0.25 to 5% by weight of each of an amylolytic enzyme and a proteolytic enzyme,

(e) up to 60% by weight of bulking agents, and

(f) 0 to 5% by weight of a low-foaming surfactant.

2. A detergent powder composition as claimed in claim l having a solution pH of from 9.0 to ll.0.

3. A composition as claimed in claim l or claim 2 wherein the combined weight of components (a), (b) and (c) is from 50% to 90% by weight of the composition.

4. A composition as claimed in claim l, 2 or 3 wherein the ratio by weight of components (a):(c):(b) is about l:l:0.5.

5. A composition as claimed in any one of claims l to 4 wherein the amount of the bulking agent(s) is at least 30% by weight of the composition.

6. A composition as claimed in any one of the preceding claims wherein the enzymes are in granular form.

7. A composition as claimed in any one of the preceding claims wherein the ratio by weight of amylolytic enzyme:proteolytic enzyme is from l:4 to 4:l.

8. A composition as claimed in claim 7 wherein the amylolytic enzyme and the proteolytic enzyme are present in approximately equal amounts by weight.

9. A composition as claimed in any one of the preceding claims wherein the amount of the surfactant is less than 0.5% by weight of the composition.

l0. A composition as claimed in any one of the preceding claims which contains in addition one or more ingredients selected from sequestering agents, soil-­suspending agents, corrosion inhibitors, drainage-­promoting agents, crystal modifiers, dyes and perfumes.