GB2172301A - Laundry detergent bars comprising alkali metal sulphite - Google Patents

Abstract

A laundry bar for use in the handwashing of fabrics comprises from 15% to 45% by weight of anionic detergent material, from 5% to 60% by weight of detergency builder material, and from 5% to 25% by weight of an alkali metal sulphite. Preferred builder material is a mixture comprising sodium carbonate. Preferred alkali metal sulphite is sodium sulphite. The laundry bar shows bleach stability on storage and during use.

Description

SPECIFICATION Laundry bars This invention relates to improved laundry bars for use in the handwashing of fabrics.

Laundry bars for use in the handwashing of fabrics, as distinct from laundry or detergent powders used in washing machines or bowl washing, must have a good strength to ensure that they retain their structural integrity during handling after manufacture, transport and use. They are popular because they are economical in use, and as the bar is applied directly to the fabric surface by rubbing, they are particularly suitable for use in handwash areas, where little water is employed in the washing process.

The commonly known laundry bars of the art, such as described in GB-A- 2 083 490, generally contain from about 7% to about 45% by weight of detergent-active materials and from about 5% to about 60% by weight of detergency builder materials together with a number of optional components, such as abrasives, fillers, perfumes, colouring agents and alkaline salts.

They are used under cold water or luke-warm water conditions.

In an attempt to improve the cleaning performance, it has also been proposed to include a bleaching agent in the laundry bars, but so far without much success.

German Patent Application N" 1 086 214 discloses built detergent bars containing sodium perborate. Such perborate bars of the art, however, decompose rapidly both in use and during storage.

Since laundry bars for use in the handwashing of fabrics are intended for repeated use, as distinct from detergent powders for use in a single wash operation, the main problem of bleach incorporation in laundry bars lies not only in keeping the bleach stable in the formulation on storage before use but also during use, i.e. in the bar after first and each subsequent use and contact with water.

It is an object of the present invention to provide an improved and more effective laundry bar comprising a stable and effective bleaching agent.

It has now been found that an alkali metal sulphite, particularly sodium sulphite (Na2SO3) can be incorporated as a stable and effective bleach in laundry detergent bar formulations, having a natural pH in the region of 10.5. The term "natural pH" refers to the pH of the wash liquor.

Though the use of sodium sulphite as a bleach in dry built detergent compositions is known, from e.g. US Patents 3,940,341 and 3,741,901, and GB Patents 1,315,937 and 1,417,840, the pH of such known compositions never exceeds 10. French Patent 1 186 901 discloses detergent compositions comprising a sulphite to reduce the tarnishing of metals.

The improved laundry bar of the invention has a natural pH of above 10 and comprises from 20% to 45% by weight of an anionic detergent-active material, from 5% to about 60% by weight of a detergency builder material and incorporates from about 5% to about 25% by weight of an alkali metal sulphite, preferably from about 7.5% to 15% by weight of sodium sulpite.

As desired and preferably, the laundry bar of the invention may further incorporate a photobleach compound, such as aluminium phthalocyanine sulphonate (AIPCS), which gives an additional dimension to the bar performance when used under sunlight conditions. Such photobleach compounds are usually incorporated in very minor amounts in the order of from 0.001% to 1.0%, particularly from 0.002% to 0.1% by weight.

The detergent-active and builder components usable in the present invention are well characterised in detergent bar technology. These components are characterized in "Surface Active Agents" Volume I, by Schwartz and Perry (Interscience, 1958). Suitable detergent actives are found in the general class of anionic actives, and can be used in admixture with nonionic, amphoteric, betaine and zwitterionic actives.

A preferred detergent-active component comprises linear or branched-chain alkyl benzene sulphonates (having from 8 to 16 carbon atoms in the alkyl chain), either alone or in admixture with other actives, preferably in minor amounts to the alkyl benzene sulphonate. Specific examples of detergent actives usable in admixture with alkyl benzene sulphonates are alkane sulphonates, alcohol sulphates, olefin sulphonates, monocarboxylic acid salts, ethoxylated alcohols and fatty acid ester sulphonates.

Examples of builder components are: water-soluble phosphate salts, e.g. pentasodium triphosphate, tetrasodium pyrophosphate and sodium orthophosphate; water-soluble carbonates, e.g.

sodium carbonate; organic builders, e.g. sodium nitrilotriacetate, sodium tartrate, trisodium carboxymethyl oxysuccinate, sodium oxydisuccinate and sodium sulphonated long-chain monocarboxylic acids.

Preferred detergency builders for use in the laundry bar of the invention are builder mixtures comprising water-soluble carbonates. Examples of such preferred builder mixtures are: sodium triphosphate/sodium carbonate; tetrasodium pyrophosphate/sodium carbonate; and sodium triphosphate/tetrasodium pyrophosphate/sodium carbonate mixtures.

Fillers such as calcite, various types of clays (e.g. kaolin and bentonite) and sodium sulphate are non-essential ingredients, the amounts and choice of which are adaptable to volume and economical considerations.

Other ingredients, such as silicates, e.g. sodium alkaline silicate; starch, sodium carboxymethylcellulose, colouring materials, fluorescers, opacifiers, germicides, perfumes, including deoperfumes, etc., may also be incorporated as desired.

The laundry bar of the invention can be and is preferably prepared by a process, e.g. in a high shear "Z" blade mixer, comprising the steps of neutralising the anionic-active acid, e.g. alkyl benzene sulphonic acid, with alkali, e.g. sodium carbonate, adding all or the major part of the formulation water during or after neutralisation, followed by mixing therewith the appropriate builders and fillers to form a dough and adding the bleach, i.e. sodium sulphite and photobleach if present, and other sensitive and minor ingredients at the final mixing stage.

Heat is normally generated during the neutralisation, hydration and by the high shear rates, but, if not sufficient, heating can be applied to adjust the temperature to about 60-65 C.

Care must be taken of the following conditions: The active(s) must be fully neutralised before the sulphite is added, to prevent bleach decomposition and liberation of sulphur dioxide during manufacture.

As the rate of photobleach decomposition increases with increasing temperature and pH, the photobleach, e.g. AIPCS, if present, should be added as the final ingredient when the dough has cooled to below 60 C, to minimise loss of photobleach during manufacture. After this final mixing operation, the dough is passed through a roller-mill, before plodding.

Satisfactory bars can be obtained with a wide range of moisture contents, e.g. from 3.5-15% by weight, preferably from 6 to 11 % by weight.

Examples 1-111 Laundry bars of the following compositions were prepared: Composition (% by weight) I Il Ill A Sodium branched C,2-alkyl benzene sulphonate 31.0 31.0 31.0 31.0 Tetrasodium pyrophosphate 6.0 6.0 6.0 6.0 Sodium triphosphate 2.0 2.0 2.0 2.0 Sodium carbonate 18.0 18.0 18.0 18.0 Calcite 12.86 13.35 16.85 19.86 Kaolin 6.0 6.0 7.5 9.0 Bentonite 2.0 2.0 2.0 2.0 Sodium sulphate 4.5 4.0 4.0 4.5 Perfume 0.3 0.3 0.3 0.3 Fluorescent agent 0.24 0.24 0.24 0.24 Titanium dioxide 0.15 0.15 0.15 0.15 Water 6.5 6.5 6.5 6.5 Sodium sulphite 10.0 10.0 5.0 Aluminium phthalocyanine sulphonate (AIPCS) - 0.006 - Non-detergent organic matter ------ to 100 ------ I, II and Ill were compositions of laundry bar products of the invention; A was a composition of a control laundry bar without bleach.

Although the filler systems of the laundry bars I, ll and Ill of the invention differ somewhat from that of the control bar A and the bars were extruded at relatively lower temperature, no problems were encountered during processing. Furthermore, penetrometer measurements taken immediately after extrusion show that bleach incorporation had little, if any, effect on initial bar properties.

Bar type: Bar temperature Average penetration ( C) (mm) A 37 7.5 I, II and Ill 37 7.5 The results of storage stability tests of the bleaching components, in bars I, ll and Ill, determined over a period of three months at 28 C/70% RH and 37 C/70% RH, showed that there was no sulphite loss observed in all three bar-types.

Assessments were also carried out to determine the bleach loss during use.

The bars were analysed before washing and stored overnight in a soap tray at 370C/70% RH.

This wash/store cycle was repeated and the bars re-analysed. The results are tabulated in Table 1 below: Table 1 Stability of the bleach systems during use (initial value normalised to 100%) % Na2SO3 % AIPCS Initial 100 100 After first storage 100 91.9 After second storage 100 91.9 Both sulphite and AIPCS were found to be stable during use.

Evaluation of bar performance using natural stains: The action of bar I was compared with bar A on a range of bleachable and proteinaceous stains.

Performance comparison after bowl wash: The effect of direct bar application to the stain site was examined in the absence of sunlight.

Stained fabrics taken from the soaping stage were rinsed and tumble-dried. The bleaching contribution resulting from highly localised concentration of bar components on fabrics could thus be isolated. The results clearly show that sulphite was extremely effective on most of the stain types examined. Despite the short contact times, the laundry bar I of the invention gave a significant improvement in stain removal as shown in the following Table 2.

Table 2 Stain Stain removal (AR) Bar A Bar I Red wine 4.8 6.8 Coffee milk 25.0 33.5 Tea 4.3 8.0 Worcester sauce 32.8 35.5 Blood 3.0 3.0 Blackberry 2.8 2.8 Tea milk 14.0 20.3 Under these conditions the following performance ranking was obtained: Bar l=Bar lI > Bar IlI Bar A.

Bar performance was also evaluated under the following simulated "wash habit" conditions: (a) Irradiate after rinse (line dry) After washing, the fabrics were rinsed and line-dried (irradiated) in the Weatherometer*.

"Weatherometer is a Registered Trademark of Atlas Electric Devices Co., Chicago, Illinois.

(b) Irradiate, then rinse (sun bleaching process) Clothes were taken from the bowl wash and, prior to to the rinse, were exposed in the Weatherometer" for 30, 60, 90 and 120 minutes. The monitors were then rinsed and tumbledried.

From the above experiments the following conclusions can be drawn: During normal use, laundry bars are rubbed directly onto the fabric surface. This results in a high local concentration of bar components on the stain site. High concentrations of bleaching species-which have previously been shown to give only marignal benefits when delivered from powder solutions-on the fabric surface can deliver a signigicant bleaching benefit, despite the low wash temperatures, short contact times and high soil loadings encountered in typical laundry bar wash systems.

These benefits can be obtained on most stains in the absence of light. In addition to this concentration effect, enhanced results were obtained by irradiation or sun-bleaching, as are shown in the following Table 3.

Table 3 Performance comparison of control bar A with bar I and bar Il after sunbleaching: Stain Stain removal (AR) Bar A Bar I Bar II Tea 9.6 12.4 29.4 Blood 3.0 4.6 5.3 Blackberry 1.0 5.8 15.2 Curry 48.0 51.0 59.0 Tea milk 14.3 14.6 22.2 Example IV The laundry bar of Example I was compared with a similar laundry bar composition, except that the sodium sulphite was replaced by sodium perborate tetrahydrate (control composition B).

The bleach concentrations in the bars were determined after storage at 370C and 280C in sealed polythene bags. The results are given in Table 4 below: Table 4 Time Na-perborate (%)-B Na-sulphite (%)- 1 (days) 37"C 28"C 27"C 28"C Initial 10.3 10.3 10.0 10.0 1 5.8 - - 2 4.5 9.4 7 2.7 8.5 14 - 8.0 - 28 - 6.8 9.8 10.0 35 - 6.7 50 - 5.6 10.0 10.0 75 - 4.2 10.0 10.0 The above results show the excellent bleach stability of the laundry bar (I) of the invention during storage.

The bleach concentrations in the bars were determined under in use conditions after first and second washes.

The results are shown in the following Table 5.

Table 5 % Na2 SO3 (I) % Perborate (B) Initial bleach level 9.8 9.5 After first wash and storage overnight at 37"C/70"C RH 9.98 6.0 After second wash and storage overnight at 37"C/70"C RH 10.0 5.0 The clear superiority of the bleach stability of the laundry bar of the invention over the laundry bar B of the art is evident.

Claims (11)

1. Laundry bar for use in the handwashing of fabrics, comprising from 15% to 45% by weight of an anionic detergent-active material, from 5% to about 60% by weight of a detergency builder material, and from about 5% to 25% by weight of an alkali metal sulphite, and having a natural pH of above 10.

2. Laundry bar according to claim 1, characterised in that said alkali metal sulphite is sodium sulphite.

3. Laundry bar according to claim 1 or 2, characterised in that it contains from 7.5% to 15% by weight of sodium sulphite.

4. Laundry bar according to claim 1, 2 or 3, characterised in that the anionic detergent-active material is a linear or branched chain alkyl benzene sulphonate having from 8 to 16 carbon atoms in the alkyl chain.

5. Laundry bar according to any one of the claims 1-4, characterised in that the detergency builder is a mixture comprising a water-soluble carbonate builder.

6. Laundry bar according to any of the above claims, characterised in that it further comprises a photobleach compound in an amount of from about 0.001% to 1.0% by weight, based on the total bar composition.

7. Laundry bar according to claim 6, characterised in that said amount of photobleach compound is from 0.002% to 0.1% by weight.

8. Laundry bar according to claim 6 or 7, characterised in that said photobleach compound is aluminium phthalocyanine sulphonate.

9. A process for preparing a laundry bar according to any of claims 1-8, characterised in that it comprises the steps of neutralising the anionic active acid with an alkali, adding all or the major part of the formulation water during or after neutralisation, followed by mixing therewith the detergency builder material to form a dough, and adding thereto the sodium sulphite (and photobleach compound if present) at the final mixing stage, whereafter the dough is passed through a roller-mill before extrusion to form the bar.

10. A process according to claim 9, characterised in that the photobleach is added when the dough temperature has dropped to below 60 C.

11. A process according to claim 9 or 10, characterised in that the alkali used for the neutralisation reaction is sodium carbonate.