GB2505977A - Use of sorbic acid or water soluble sorbate as a radical scavenger - Google Patents

Abstract

The invention relates to the use of sorbic acid or a water soluble sorbate salt as a radical scavenger in an aqueous liquid which comprises at least one source of free radicals. The concentration of sorbic acid or soluble sorbate salt may be 0.025-0.1 wt %. An aqueous liquid comprising at least one source of free radicals, potassium sorbate, and no other radical scavenger is also provided. Preferably, the liquid is a rinse aid used in a laundry or automatic dishwashing process.

Description

Radical scaventer for rinse aid formulations

DESCRIPTION

Technical field

The present invention relates to a new use of sorbic acid or a water soluble sorbate salt, such as potassium sorbate. In particular, the new use finds utility in improving the storage stability of aqueous liquid solutions. The aqueous liquid solutions may be rinse aid compositions.

Background

Rinse aids are compositions that arc added to automatic dishwashers to improve drying performance and reduce "spotting" on the items washed (caused by the minerals left behind when water droplets evaporate). They contain surfactants which prevent water droplet formation on hard surfaces, helping the wash water to drain away; any remaining thin layer of water on the surfaces will evaporate more easily. Such surfactants can be included in the detergent formulation (so-called "2-in-i" or "3-in-i" formulations, the latter including water-softening salt too). However, performance is significantly improved if a separate rinse aid is used, which is dosed automaticaHy into the wash, specifically during the rinse cycle, usually from a separate dispenser compartment of the machine.

Some aqueous rinse aid compositions deteriorate upon storage and undergo changes that arc unpleasant and noticeable to the consumer, as well as potentially adversely affecting the activity of the composition. For instance, even after a relatively short exposure to sunlight, they may produce a smell of rotten eggs and change of colour.

The present inventors tested these compositions for microbial contamination but found that they were surprisingly clean. They then realised that these compositions contain potential sources of free radicals, like sulphur groups. Such sources include sulphur groups of antibacterial agents, polymers with sulphur groups, and residual epoxides which are present as impurities in the surfactant system. The free radicals are produced at elevated temperature, in the presence of oxygen, and/or upon exposure to light (e.g. visible or IJV).

Whcn the inventors added butylhydroxytoluene (BHT), a known radical scavenger, to the compositions, the stability problem was solved. This confirms that free radicals are the source of the problem. However, there are toxicity concerns about BHT, and so it would be useful to find an alternative radical scavenger for use in aqueous rinse aid formulations.

Potassium sorbate is known as an antimicrobial agent and is commonly used as a preservative for food and drinks, inhibiting the growth of mould, yeast and fungi (E number 202), as is sorbic acid (International.Journal of Food Microbiology, 50(1999) 1- 1 7). Obviously as is necessary for such use, it has no toxicity problems, unlike BHT. It has also been used in personal care products to inhibit the development of microorganisms for shelf stability, as well as several laundry and hand dishwashing detergents. Some manufacturers are using this preservative as a replacement for parabens.

US 6,372,702 discloses a dishwashing composition for coating dishware, which is a detergent wash or a rinse aid, and may be aqueous. The rinse aid composition may include one of a number of preservatives including sorbic acid, potassium sorbate, sodium sorbate and BHT, which may be used in an amount of 0.01 -0.8 wt %, preferably from 0.02 -0.1 wt %. The mechanism of action is not stated there, and it is to be presumed that those in the field thought it was acting conventionally as an anti-microbial agent.

Radical scavengers have also been used in cleaning compositions, e.g. US 6,569,826.

US 5,972,993 discloses the use of sorbie acid as an antioxidant or radical scavenger for treating skin conditions such as rosacea and sensitive skin.

Prior to the present invention, however, the ability of potassium sorbate to act as a radical scavenger in aqueous rinse aid formulations had not been investigated.

The inventors added potassium sorbate to their problematic rinse aid formulations, without using any BHT, and found that the stability problem was solved. In fact the preyention of the evolution of the bad smell etc. was as effective as with using BHT. On the other hand, resistance to microbial challenge was not significantly changed by the addition of the potassium sorbatc.

The invention thcrcfore rcsides in the discovery that potassium sorbatc acts is capable of acting as an anti-radical or radical scavenger in rinse aid formulations, whereas previously it was just thought to be an antimicrobial. Accordingly, BHT or other radical scavengers do not need to be used for storage stability.

By extension, this discovery also applies to sorbic acid and other water soluble sorbate salts, and other aqueous liquids containing a free radical source. For instance, it should be applicable in aqueous liquids in the medicinal, food, cleaning and other industries.

Summary of the invention

In a first aspect of the invention there is provided the use of sorbic acid or a water soluble sorbate salt as a radical scavenger in an aqueous liquid which comprises at least one source of free radicals.

In a secoild aspect of the invention there is provided an aqueous liquid comprising at least onc source of free radicals, potassium sorbate, and no other radical scavenger.

In a third aspect of the invention there is provided a laundry or dishwashing process, which utilizes the aqueous liquid according to the invention in its second aspect.

Detailed description

Potassium sorbate has the structure: Without wishing to be bound by theory, it is proposed that the free radicals may be stabilised as follows:

I A.

I t

J

Suitable water soluble sorbate salts include alkali metal, ammonium or substituted ammonium salts, preferably the sodium, potassium or ammonium salt, preferably potassium sorbate. Mixtures of such salts may also be used. Sorbic acid, although less soluble in water, can still be used if the pH of the aqueous liquid is adjusted appropriately.

In a preferred embodiment, the aqueous liquid is a rinse aid.

The sorbic acid or water soluble sorbate salt may be used in conventional concentrations e.g. 0.025 -0.1 wt %.

The pH may be conventional, e.g. <pH 6.5. The rinse aid formulation of the invention is preferably acidic. Acidity of the formulation may enhance its biocidal properties.

Other conventional ingredients which may be included in the rinse aid are: non-ionic surfaetants (e.g. 5 -20 %); hydrotropes (e.g. 0 -20 %); citric acid (e.g. 1 -S %); preservatives and other excipients, such as dyes and fragrances.

Suitable non-ionic surfactants are known in the art. Some are described in WO 10/067054, the contents of which are incorporated herein by reference.

Preservatives that may be used include methylchloroisothiazolinone ("CIT") and methylisothiazolinone ("MIT"). Preferably, however, the formulation contains no CIT or MTT, preferably no preservative other than the sorbic acid or water soluble sorbate salt.

Suitable hydrotropes are also familiar to the skilled person and include sodium cumcnc suiphonate and similar compounds.

The aqueous liquid may contain a sulphonated polymer. A preferred example is a copolymer of: i) CH2CR'-CR2R3-O-C4H3R4-503X, wherein R1, R2, R3 and R4 are each independently 1 to 6 carbon alkyl or hydrogen, and X is hydrogen or allali; with ii) any suitable other monomer unit, including modified acrylic, flimaric, maleic, itaconic, aconitie, mesaconic, citraconic and methylenemalonic acid or their salts, maleic anhydridc, acrylamidc, alkylene, vinylmethyl ether, styrene, or a mixture thereof. Other suitable sulfonated monomers for incorporation in sulfonated (co)polymers are 2- acrylamido-2-methyl-1-propanesulfonic acid, 2-methacrylamido-2-methyl-l-propanesulfonic acid, 3-methacrylamido-2-hydroxy-propane sulfonic acid, allysulfonic acid, methallysulfonic acid, 2-hydroxy-3-2-propenyloxyropane sulfonic acid, 2- methyl-2-propenen-1 -sulfonic acid, styrenesulfonic acid, vinylsulfonic acid, 3-sulfopropyl acrylatc, 3-sulfopropylmethacrylatc, sulfomethylacrylamide, sulfomethylmethaerylamide and water soluble salts thereof Suitable sulfonated polymers are also described inUS 5308532 and in WO 2005/090541.

It is known to include a source of multivalent ions in cleaning compositions, and dishwashing compositions, in particular in automatic dishwashing compositions, for technical and/or performance reasons. Such optional ingredients are especially preferred according to the present invention. For example, multivalent ions and especially zinc and/or manganese ions have been included for their ability to inhibit corrosion on metal and/or glass. Bismuth ions may also have benefits when included in such compositions.

For example, organic and inorganic redox-aetive substances which are known as suitable for use as silver/copper corrosion inhibitors are mentioned in WO 94/26860 and WO 94/26859. Suitable inorganic redox active substances are, for example, metal salts and/or metal complexes chosen from the group consisting of zinc, manganese, titanium, zirconium, hafiuium, vanadium, cobalt and cerium salts and/or complexes, the metals being in one of the oxidation states II, III, IV, V or VI. Particularly suitable metal salts and/or metal complexes are chosen from the group consisting of MnSO4, Mn (II) citrate, Mn (II) stcaratc, Mn (II) acctylacetonatc, Mn (II) [1-hydroxyethane-1,1-diphosphonate], V205, V204, V02, TiOSO4, K2TiF5, K2ZrF6, CoSO4, Co(N03)2 and Ce(N03)3. Zinc salts arc especially preferred corrosion inhibitors.

The composition according to the invention may comprise one or more foam control agents. Suitable foam control agents for this purpose are all those conventionally used in this field, such as, for example, silicones and paraffin oil.

In an embodiment, the aqueous liquid contains no butyihydroxytoluene. Preferably the composition contains no radical scavenger at all, save for the potassium sorbate or other sorbate / sorbie acid described herein. Known radical scavengers include BUT, hydroquinone, mono-t-butyl hydroquinone, benzoic acid, toluic acid, eateehol, t-butyl catecho I, benzylamine, and N-propyl-gallate.

In an embodiment, when the aqueous liquid is a detergent or rinse aid formulation, this is phosphate free.

If the compositions of the invention are dishwashing detergent compositions, they preferably further comprise a bleaching compound. If the compositions of the invention are rinse aid compositions they are preferably substantially bleach free.

When the formulation is for another use, e.g. a laundry detergent, other ingredients may be included as are well-known and conventional in the art.

The invention is further demonstrated bythe following non limiting examples.

Examyles Three rinse aids were prepared with the following formulations. Formulation Cl is a comparative example, whereas El and E2 are examples of the invention.

After a short exposure to sunlight, Cl produced a smell of rotten eggs and was discoloured, whereas El and E2 did not exhibit this effect.

All three formulations showed a similar resistance to microbial challenge (both bacterial and yeast).

Formulation Cl El E2 % byweight PlurafacLF300 13 13 13 Citric acid, anhydrous 0.75 0.75 0.75 Zinc acetate 0.15 0.15 0.15 Potassium sorbate 0 0.066 0.1 Sodium cumcnc 7.5 7.5 7.5 sulfonate, 40 (y0 Water to /00 Va to /00 Va to /00 Va

Claims (10)

1. CLAIMSI. The use of sorbic acid or a water soluble sorbate salt as a radical scavenger in an aqueous liquid which comprises at least one source of free radicals.
2. 2. The use as claimed in claim 1, wherein said water soluble sorbate salt is sodium sorbate, potassium sorbate or ammonium sorbate.
3. 3. The use as claimed in claim 2, wherein said water soluble sorbate salt is potassium sorbate.
4. 4. The use as claimed in any of the preceding claims, wherein the aqueous liquid is a detergent formulation.
5. 5. The use as in any of claims Ito 3, wherein the aqueous liquid is a rinse aid formulation.
6. 6. The use as in claim 5, wherein the concentration of sorbic acid or the water soluble sorbate salt is 0.025-0.1 wt %.
7. 7. An aqueous liquid comprising at least one source of free radicals, potassium sorbate, and no other radical scavenger.
8. 8. An aqueous liquid as claimed in claim 7, which is a detergent formulation.
9. 9. An aqueous liquid as claimed in claim 7, which is a rinse aid formulation.
10. 10. A laundry or dishwashing process, which utilizes the aqueous liquid as claimed in claim 8 or 9.

    II. A process as claimed in claim 10, which is an automatic dishwashing process using the aqueous liquid as claimed in claim 9.