GB2293829A - Detergent compositions - Google Patents

Abstract

A solidified detergent composition comprising (a) a plurality of hydrated alkaline compounds having a total free alkalinity equivalent to from 15% to 40%, by weight of the composition, calculated as sodium hydroxide of which not more than 15% is contributed by alkali metal hydroxide and (b) at least 30% of a plurality of compounds capable of sequestering calcium or magnesium cations comprising one or more phosphate sequestrants having a higher binding affinity for calcium or magnesium cations than phosphate sequestrants.

Description

Detergent Compositions This invention relates to detergent compositions, to components therefor and to methods for producing and using the same.

Large-scale washing machines such as institutional or catering dishwashing machines may be designed or adapted for the use of detergent compositions in solid form and for dispensing the detergent by dissolving portions of it in wash water as required. The detergent composition may be in the form of a solidified cast, produced by the combination of hydratable chemicals and water, which may be dissolved by contacting a surface of the cast a stream or spray of aqueous liquid. The dosage of detergent may be controlled at a desired level by monitoring the conductivity of the wash liquid and controlling the duration of contact of the aqueous stream or spray with the surface in response to variations in that conductivity. Such washing machines and detergent compositions suitable for use in them are described in European Patent Specification No. 0003769.

The detergent compositions described in that specification contain high levels of from 35% to 40% of sodium hydroxide and usually include a source of available chlorine, which has been used in the art to control food stains such as tea and coffee stains, a phosphate or other hardness-precipitating or sequestering agent, a defoamer and other optional ingredients.

Degradation of the chlorine source may occur when it comes into contact with a defoamer and it is taught that this may be minimised by including the chlorine source and the defoamer in separate preformed plugs incorporated within the solid cast detergent.

The present invention is directed to a solidified detergent composition, or a component thereof, which is relatively effective in removing food stains but which need not contain a source of active chlorine, which is relatively stable in storage and which is usable at low dosages.

According to one aspect thereof the present invention provides a solidified detergent composition comprising (a) a plurality of hydrated alkaline compounds having a total free alkalinity equivalent to from 15% to 40% but preferably not more than 25%, by weight of the composition, calculated as sodium hydroxide of which not more than 15% is contributed by alkali metal hydroxide and (b) at least 30% of a plurality of compounds capable of sequestering calcium or magnesium cations comprising one or more phosphate sequestrants and one or more sequestrants having a higher binding affinity for calcium or magnesium cations than phosphate sequestrants.

The term "phosphate" is used to include both simple monomeric phosphates, such as the orthophosphates or the metaphosphates,and the condensed phosphates such as the pyrophosphates or tripolyphosphates. There may be substituted for the phosphates, in whole or in part, other sequestrants of approximately equivalent binding affinity for calcium or magnesium cations, i.e. other so-called "soft" sequestrants.

There is used in conjunction with the phosphate sequestrant one or more sequestrants having higher binding affinity for calcium and magnesium cations such as, for example, ethylene diamine tetraacetic acid, nitrilotriacetic acid or derivatives thereof or other sequestrants having a similar or greater level of binding affinity, the so-called "hard" sequestrants. Such compounds are preferably present in at least 15%, particularly preferably at least 20% by weight and up to 35%, preferably below 30% by weight. There may be included as appropriate in the sequestrant classes used in the present invention other suitable compounds such as gluconates, glucoheptonates, boro heptonates or heptonates.

It is a preferred feature of the invention that the phosphate sequestrants comprises both sodium tripolyphosphate and trisodium phosphate both compounds being initially included in the anhydrous form to contribute to the solidification mechanism. The latter compound has the better detergent properties and the greater capacity for hydration. Preferably the tripolyphosphate is used in at least 5% and particularly preferably less than 20%, suitably at least 10% and not more than 15% by weight. Preferably the trisodium phosphate is used in at least 1% and up to 10%, suitably at least 2% and not more than 7.5% by weight.

It is found that the medium alkalinity high sequestrant solid detergent compositions of the invention are particularly suitable for use in dishwashing or other washing machines adapted for the use of cast detergents. The selected level of sequestrants contributes to the removal of food stains and is necessary for satisfactory performance particularly where the wash water is hard e.g. 200ppm CaC03 equivalent or more.

Preferably the total free alkalinity of the composition is from 18% to 22% calculated as sodium hydroxide and/or not more than 12.5%, suitably at least 5%, thereof is contributed by alkali metal hydroxide and/or the composition contains at least 37.5% of the plurality of compounds capable of sequestering calcium or magnesium cations. The total alkalinity of the compositions is preferably 26% to 30% and particularly preferably below 30% calculated as sodium hydroxide.

The alkalinity of the compositions of the invention is determined by titration with hydrochloric acid. The free alkalinity is determined using a phenolphthalein indicator and the total alkalinity is obtained using a methyl orange indicator. The figures so obtained are converted to sodium hydroxide equivalence.

The plurality of hydrated alkaline compounds, besides alkali metal, preferably sodium, hydroxide, particularly preferably comprises a quantity of sodium carbonate within the same ranges and particularly preferably an approximately equal quantity. While contributing to the hydration solidification of the composition as a result of initial inclusion in the substantially anhydrous form, this compound also enables a reduced total free alkalinity to be attained. Other hydratable bases of lower alkalinity than sodium hydroxide may be used as substitutes, in whole or in part, for the sodium carbonate.

The presence of an antiredeposition agent may improve the effectiveness of the present detergent compositions. Preferably a polyacrylate or derivative having a molecular weight, preferably of about 3000 to 5000 is used. A particularly suitable material is a phosphino-polyacrylate having a molecular weight of 3800 and available, for instance, under the trade name Belsperse 164. These compounds are known as crystal growth modifiers/dispersants and might have been expected to retard setting but this effect has not been observed in the present formulation. The quantity of antiredeposition agent is preferably from 1% to 5% by weight.

The detergent compositions may contain additives known in the art and which do not detract from the solid state of the detergent such as suitable defoamers, polyelectrolytes, fragrances or the like. Preferably it includes a rinse-aid, such as a suitable non-ionic surfactant known for such purpose, to provide a dual effect product. It is preferred that a source of active chlorine is not included in the compositions.

The above description has been directed to the composition of the final solid detergents according to the invention. The invention also provides a method for producing such compositions and component compositions for use in such a process. The component compositions comprise (a) a solid powdered or granular premix containing a plurality of hydratable alkaline compounds, comprising alkali metal hydroxide, corresponding to the hydrated alkaline compounds present in the final compositions, and the phosphate sequestrant compounds and (b) an aqueous composition comprising the high affinity sequestrant, the antiredeposition agent and optionally the rinse aid. The quantity of water in component (b) is such that it may be bound by the hydratable materials in component (a) to give a solidified composition for example 25% to 50%, preferably 30% to 45% of the total composition.The final detergent compositions may be produced by establishing a stirred and preferably warm body of component (b) and adding to it component (a) in a suitable proportion.

Preferably component (b) is subjected to stirring, for example in a Silverson stirrer, and is held at a temperature of 800C to below boiling temperature, preferably at 800C to 900C, and at high shear sufficient to produce a homogeneous dispersion while component (a) is added. The resulting viscous liquid may be filled into a suitable container, for example a container suitable for use in washing machines adapted for the use of cast detergents, and allowed to stand until it has solidified.

The following composition is one example of components of a detergent according to the present invention stated in parts by weight of the total composition.

Component (a) Sodium tripolyphosphate (anhydrous) 13.3 Sodium hydroxide (pearl) 8.75 Trisodium phosphate (anhydrous) 4.2 Sodium carbonate (low bulk density) 8.75 Component (b) Trisodium nitrilotriacetic acid 25.2 Water (as solvent for the nitrilotriacetic acid product) 37.8 Phosphino polyacrylate (M.Wt.3800) 2.0 Component (b) was subjected to high shear stirring at a temperature of 800C to 900C and component (a) was added progressively until a homogeneous mixture was obtained. The mixture was poured into a container adapted for use in the washing machines referred to below and allowed to stand at room temperature until it had solidified to produce a cast within the container.

The detergent composition was tested in use in industrial conveyor type dishwashing machines utilising dosing by contacting the surface of a solid detergent block cast in an open container with hot water jets.

Machine (1) was an initially heavily scaled Crypto Peerless twin tank using a pre-wash at 380C, a main wash at 68-700C and a separate rinse stage at 800C. The wash water had a hardness of 495 ppm CaCo3. The trial was begun at a dosage of detergent of 0.3% w/w, in comparison with previous dosage of a commercial detergent of 0.3% to 0.38% v/v, and during the trial this was reduced to 0.27% w/w. The trial duration was 1 week under fairly low throughput conditions. Good cleaning of plates and dishes was obtained and tea and coffee cups were cleaned to an acceptable standard without and need for a chlorine bleach. By the end of the first week of trial appreciable descaling of the machine was evident. Erosion of the detergent block was even with no tendency to break away from the sides of the container.

Machine (2) was a conveyor type dishwasher having a first wash at 650C, a second wash at 780C and a rinse at 950C taking in total 1 to 1.5 minutes ot feed an item through. The water had a hardness of 290 ppm CaC03. A dosage of 0.3% w/v gave satisfactory cleaning performance over a period of 1 week. A gradual reduction in dose down to 0.1% to 0.15% w/v was achieved over a three week period without reducing cleaning efficiency.

Claims (15)

Claims.

1. A solidified detergent composition comprising (a) a plurality of hydrated alkaline compounds having a total free alkalinity equivalent to from 15% to 40%, by weight of the composition, calculated as sodium hydroxide of which not more than 15% is contributed by alkali metal hydroxide and (b) at least 30% of a plurality of compounds capable of sequestering calcium or magnesium cations comprising one or more phosphate sequestrants or other sequestrants having a similar binding affinity for calcium or magnesium cations and one or more sequestrants having a higher binding affinity for calcium or magnesium cations than phosphate sequestrants.

2. A detergent composition as claimed in claim 1 having a content of one or more sequestrants having higher binding affinity for calcium and magnesium cations in at least 15% and up to 35% by weight.

3. A detergent composition as claimed in claim 1 or 2 wherein the one or more sequestrants having higher binding affinity for calcium and magnesium cations comprises ethylene do gamine tetraacetic acid, nitrilotriacetic acid or derivatives thereof or other sequestrants having a similar or greater level of binding affinity.

4. A detergent composition as claimed in any preceding claim including as a sequestrant gluconates, glucoheptonates, boro heptonates or heptonates.

5. A detergent composition as claimed in any preceding claim having a content of tripolyphosphate of at least 5% and less than 20% and of trisodium phosphate of at least 1% and up to 10% by weight.

6. A detergent composition as claimed in any preceding claim having a total free alkalinity of from 18% to 22% calculated as sodium hydroxide of which at least 5% and not more than 12.5% thereof is contributed by alkali metal hydroxide and the composition contains at least 37.5% of the plurality of compounds capable of sequestering calcium or magnesium cations.

7. A detergent composition as claimed in any preceding claim having a content of from 5% to 12.5% of sodium carbonate.

8. A detergent composition as claimed in any preceding claim having a content of a polyacrylate or derivative thereof having a molecular weight of 3000 to 5000.

9. A detergent composition as claimed in claim 8 wherein the polyacrylate is a phosphino-polyacrylate.

10. A detergent composition as claimed in any preceding claim additionally containing a rinse aid.

11. A method of producing a composition as claimed in any preceding claim comprising forming component compositions comprising (a) a solid powdered or granular premix containing a plurality of hydratable alkaline compounds, comprising alkali metal hydroxide, corresponding to the hydrated alkaline compounds present in the final compositions, and the phosphate sequestrant compounds and (b) an aqueous composition comprising the high affinity sequestrant, the antiredeposition agent and optionally the rinse aid and a quantity of water such that it may be bound by the hydratable materials in component (a) to give a solidified composition, dispersing component (a) in component (b) and allowing the solution to solidify.

12. A liquid component for a solidified detergent comprising an aqueous composition comprising a sequestrant having a high affinity for calcium and magnesium cations, an antiredeposition agent and water.

13. A detergent component as claimed in claim 12 wherein the sequestrant is ethylene do gamine tetraacetic acid, nitrilotriacetic acid or the sodium salts thereof and is present in the component in 30% to 50% w/w, the antiredeposition agent is a polyacrylate derivative having a molecular weight of 3000 to 5000 present in the component in from 1% to 5% w/w.

14. A detergent composition or component as claimed in claim 1 or claim 12 and substantially as described in the example herein.

15. A method of washing dishes comprising applying thereto an aqueous solution of a detergent as claimed in any one of claims 1 to 10.