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(11) | EP 0 021 830 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Low sudsing detergent compositions |
| (57) Low sudsing detergent compositions are manufactured by the use of anionic detergent
active sulphate compounds selected according to their calcium salt solubility product
and their critical micelle concentration, and by the use of a non-soap anti-foam compound.
Preferred anionic sulphates are the primary and secondary alkyl sulphates having particular
carbon chain length distributions, and a preferred non-soap anti-foam is an alkyl
phosphate ester, desirably used in conjunction with a hydrophobic wax or oil. |
[0002] It is now conventional for detergent compositions designed for front-loading washing machines to be formulated as low-sudsing compositions. The commonest types of low-sudsing compositions are the so-called "ternary" products, i.e. those based on mixtures of anionic surfactants, most commonly long chain alkyl benzene sulphonates and nonionic surfactants in which the sudsing capacity is controlled by the use of a calcium soap, formed in situ by the reaction of sodium salts of fatty acids and calcium ions forming part of the water hardness. The nonionit surfactant also exerts an effect in controlling foam in these formulations as well as contributing to the detergency properties of the system. The detergencies obtained from the compositions outlined above, which are embodied in consumer products such as "Persil Automatic" and "Bold Automatic" (registered Trade Marks) are quite acceptable.
[0003] We have now discovered that by careful selection of anionic surfactants, detergent compositions can be produced which do not require the presence of nonionic surfactants but which exhibit equivalent detergency and suds control to those of ternary products. At the same time the use of long chain alkyl benzene sulphonates, which can be environmentally unsatisfactory, is avoided.
[0004] According to the present invention there is provided a detergent composition comprising an anionic sulphate surfactant or mixture of such surfactants having
(a) a calcium salt solubility product greater than 1 x 10-12 moles3 litre-3
(b) a maximum critical micelle concentration of 6 x 10-2 gms/litre
together with a non-soap anti-foam.
[0005] The significance of the parameters (a) and (b) in selecting the anionic surfactant for use in this invention can be summarised as follows:
The calcium salt solubility product is a measure of the tendency of the substance to precipitate from a solution containing calcium ions and anionic surfactant ions. In the absence of nonionic surfactants, which help to solubilise the other surfactants ; in the normal binary or ternary detergent formulations, control of precipitation boundaries is extremely important.
[0006] The critical micelle concentration, of course, determines the point at which a substance attains maximum surface activity.
[0007] For the purposes of this invention, both the solubility product and the critical micelle concentration are measured at 60°C in the presence of 0.05 moles/litre of sodium chloride.
[0008] Reference to Tables 1 and 2 will enable the skilled man to determine which sulphate surfactants are inside and which are outside the invention.
[0009] As implied above, mixtures of different detergent active sulphates can be used, providing that the solubility product and critical micelle concentration of the mixture lies in the required range.
[0010] The anionic surfactant may be present in the mixture in an amount of from 5 to 35%, preferably, for economic reasons, from 5 to 25% by weight of the composition.
[0011] The specified anionic surfactants are sulphates rather than sulphonates, since in general the sulphates are much more biodegradable than the sulphonates. Within the sulphate class, primary and secondary alkyl sulphates are preferred.
[0012] Most preferred are the high crystalline fraction secondary alkyl sulphates (i.e. those in which a high percentage of the material has the sulphate group attached . at the 2 or 3 position), particularly the C16-18 sulphates and the C15-16 primary alcohol sulphates.
[0013] The second essential component of the compositions of this invention is a non-soap anti-foam compound. Typical of non-soap anti-foam compounds are phosphate esters, both used alone and used in conjunction with waxes or hydrophobic oils such as mineral and vegetable oils. Silicone anti-foams and derivatives of nitrogen-containing heterocyclic compounds such as s-triazine may also be used.
[0014] In general, the non-soap anti-foam compounds of this invention may be present in the compositions in amounts from, 0.05%, which would be the minimum amount which could possibly be effective, to 5%, which would be the practical maximum having regard to the extreme efficacy of the majority of non-soap anti-foam compounds, to their expense and to the necessity for keeping as much room in the composition as possible for other compounds.
[0015] In greater detail, the phosphate esters which may be used, optionally in salt form, have the following general formula:
where A is -OH or R2O(EO)m-, R1 and R2 are the same or different C12-C24, preferably C16-C22, straight or branched chain, saturated or unsaturated alkyl groups, especially C16-C18 linear saturated groups and m and n are the same or different and are 0 or an integer of from 1 to 6. Preferably, A is -OH and n is 0, so that the compounds are the monoalkyl phosphoric acids, preferably with linear alkyl groups. If any ethylene oxide (EO) groups are present in the alkyl phosphoric acids, they should not be too long in relation to the alkyl chain length to make the calcium or magnesium salts soluble in water during use.
[0016] In practice, the alkyl phosphate compounds are commonly mixtures of both mono- and di-alkyl phosphoric acids, with a range of alkyl chain lengths. Predominantly monoalkyl phosphates are usually made by phosphorylation of alcohols or ethoxylated alcohols, when n or m is 1 to 6, using a polyphosphoric acid. Phosphorylation may alternatively be accomplished using phosphorus peroxide, in which case the mixed mono- and di-alkyl phosphates are produced. Under optimum reaction conditions only small quantities of unreacted materials or by-products are produced, and the reaction products can advantageously be used directly in the detergent compositions.
[0017] When a mixture of phosphate ester and wax is to be used as the non-soap anti-foam compound the wax may be of synthetic, mineral, vegetable or animal origin.
[0018] The waxes should normally melt at a temperature between about 20°C and about 120°C, preferably not more than about 90°C and especially in the range of about 30°C to about 70°C, i.e. lower than the maximum intended wash temperatures for the detergent compositions. When waxes having melting points above the maximum intended wash temperatures are used they should be adequately dispersed in the wash liquor by suitable incorporation in the original detergent compositions.
[0019] The preferred waxes are of mineral origin, especially those derived from petroleum, including microcrystalline and oxidised microcrystalline petroleum waxes, petroleum jelly ("Vaseline") and paraffin waxes. Petroleum jelly is correctly a semi-solid wax, usually having a melting point about 30-40°C, but is for convenience here grouped with other solid waxes. Synthetic waxes such as Fischer-Tropsch and oxidised Fischer-Tropsch waxes, or Montan waxes, or natural waxes such as beeswax, candelilla and carnauba waxes may be used if desired. Any of the waxes described may be used alone or in admixture with other waxes. The waxes should be readily dispersible in the detergent liquor but not soluble therein and, preferably, they should not have very high saponification values, e.g. not in excess of about 100. It is advantageous to include emulsifying or stabilising agents for the waxes in the detergent compositions.
[0020] Examples of suitable oils which may be used if desired are vegetable oils such as sesame oil, cotton seed oil, corn oil, sweet almond oil, olive oil, wheat germ oil, rice bran oil, or peanut oil, or animal oils such as lanolin, neat's foot oil, bone oil, sperm oil or cod liver oil. Any such oils used should of course not be highly coloured, of strong odour or otherwise unacceptable for use in a detergent composition.
[0021] The remaining components of the composition are conventional and will be present in conventional amounts. Sodium ortho-, pyro- and tripolyphosphates are amongst several suitable detergency builders which are well known and commercially available, whilst many more have been described in the literature, especially in recent patent specifications on replacements for these phosphate based materials. Other detergency builders which may be mentioned by way of example are alkali metal carbonates, especially sodium carbonate, alkali metal polyphosphonates, e.g. sodium ethane-1-hydroxy-1,1-diphosphonate, alkali metal amine carboxylates, such as sodium nitrilotriacetate and sodium ethylenediamine tetraacetate, alkali metal ether carboxylates, such as sodium oxydiacetate, sodium carboxy- methyloxysuccinate, sodium carboxymethyloxymalonate and homologues thereof, alkali metal citrates, alkali metal mellitates and salts of polymeric carboxylic acids, such as sodium polymaleate, copolyethylenemaleate, polyitaconate and polyacrylate. When sodium carbonate is used as a detergency builder, it is advantageous to have present some calcium carbonate having a surface area of at least about 10 m2/g, as described in UK patent 1,437,950.
[0022] Another type of detergency builder which can be used, either alone or in admixture with other builders, is a cation exchange material, especially a sodium aluminosilicate such as described in UK patent 1,429,143 or in Netherlands patent application 7403381. Preferred materials of this type have the formula:
and may be amorphous or crystalline, with some bound water usually in an amount of about 10-30% depending on the drying conditions used. Such sodium aluminosilicate materials should, of course, be very finely divided so as to minimise deposition on the fabrics during washing.
[0023] The amount of the detergency builder which is used is normally from about 5% up to about 80% by weight of the composition, preferably about 10% to about 60%, and the ratio by weight of the detergency builders to the detergent active compounds which are used is generally from about 10:1 to about 1:5 parts by weight.
[0024] The detergent compositions of the invention may take any of the usual physical forms, preferably as solid compositions, for example as powders, granules, flakes, ribbons, noodles or tablets, or they may be in liquid or paste form. The detergent compositions may also be made by any of the conventional processes for making detergent compositions, especially by the technique of slurry making and spray-drying in the case of the preferred powder detergent compositions.
[0025] The detergent compositions of the invention may also include any of the conventional optional additives in the amounts usually employed in detergent compositions. Examples of these additives include powder flow aids such as finely divided silicas and aluminosilicates, other lather controllers, anti-redeposition agents such as sodium carboxymethylcellulose, oxygen-releasing bleaching agents such as sodium perborate and sodium percarbonate, per-acid bleach precursors such as tetraacetylethylenediamine, chlorine-releasing bleaching agents such as trichloroisocyanuric acid and alkali metal salts of dichloroiso- cyanuric acid, fabric softening agents such as clays of the smectite and illite types, anti-ashing aids, starches, slurry stabilisers such as copolyethylenemaleic anhydride and copolyvinylmethylether-maleic anhydride, usually in salt form, inorganic salts such as sodium silicates and sodium sulphate, and usually present in very minor amounts, fluorescent agents, perfumes, enzymes such as proteases and amylases, germicides: and colourants. The detergent compositions usually have an alkaline pH, generally in the region of pH 9-11, which is achieved by the presence of alkaline salts, especially sodium silicates such as the meta-, neutral or alkaline silicates, preferably at levels up to about 15% by weight.
[0026] The invention is illustrated by the following Examples in which parts and percentages are by weight except where otherwise indicated.
Example 1
[0027] A series of fabric washing powders having the following formulation were prepared by spray-drying and post-dosing techniques.
[0028] The powders were used to wash polyester cotton test cloths soiled with a soil consisting of a mixture of inorganic materials and a synthetic sebum. The detergent efficiency was followed by determing the reflectance of the washed cloth and expressing this as a percentage of the reflectance of the unsoiled cloth. The washing procedures were carried out in Tergotometers (registered Trade Mark) using water of 40° French hardness, a temperature of 60°C, a product concentration of 0.15% and a 50 cpm agitation rate.
Example 2
[0030] Two detergent powders according to the following formulation were prepared by spray-drying and post-dosing techniques.
[0031] In one of the powders, the anionic detergent was the sodium salt of C16-C18 high crystalline fraction secondary alkyl sulphate (SALS) and in the other it was the sodium salt of C12.5 alkyl benzene sulphonate (DOBS-055) prepared by sulphonation of dodecylbenzene obtained from Shell Chemicals Limited as DOBS-055.
[0032] Naturally soiled cotton articles were halved and washed in a Hotpoint (registered Trade Mark) washing machine. The washing time was 10 minutes, the cloth to liquor ratio was 2.3 kg to 37 litres and the temperature 55°C.
[0033] One half of each divided article was washed with the powder containing SALS and half with that containing DOBS-055. For each set of conditions a total of 18 articles were halved and used in 6 tests.
[0034] After washing, the test pieces were assessed by a panel of trained assessors. The results are shown in Table 4.
Example 3
[0035] An experiment similar to that described in Example 2 was performed, except that the pair of powders contained the sodium salt of C15-16 primary alkyl sulphate (D56) and DOBS-055. The results are shown in Table 5.
[0036] No non-soap anti-foam is included .in any of the powders tested in Examples 2 and 3, but this omission would not significantly affect the comparison of detergency exhibited by the two products.
Example 4
[0037] Two fabric-washing powders were prepared by spray-drying and dry-dosing techniques according to the following formulation:
[0038] Lather studies under practical conditions were made in a Miele W429 washing machine with a 5 lb (= 2.3 kg) naturally soiled cotton load. The main wash (95°C) programme was selected, 100 grams of powder were dosed, and the machine was supplied with cold 240H (London type) water. In addition to the above powders, Persil Automatic (registered Trade Mark), a well-known conventional low sudsing fabric-washing powder was included in the test.
Results
[0039] Lather heights were measured every 3 minutes using an arbitrary scale on the window of the machine.
[0040] The results are shown in Figure 1 of the accompanying drawing, and demonstrate that Powder B exhibits similar foaming characteristics to Persil Automatic until the washing process has lasted about 35 minutes, whereas Powder A, not containing a non-soap anti-foam exceeded the Persil Automatic foam level after about 12 minutes.
1. A detergent composition comprising an anionic sulphate surfactant or mixture of
such surfactants having
and a non-soap anti-foam.
(a) a calcium salt solubility product greater than 10-12 moles3 litre-3; and
(b) a maximum critical micelle concentration of 6 x 10-2 gms/litre;
and a non-soap anti-foam.
2. A detergent composition according to claim 1 comprising from 5 to 35% by weight
of the anionic sulphate surfactant.
3. A detergent composition according to claim 2 comprising from 5 to 25% by weight
of the anionic sulphate surfactant.
4. A detergent composition according to any one of the preceding claims wherein the
anionic sulphate surfactant comprises a primary or secondary alkyl sulphate.
5. A detergent composition according to claim 4 wherein the anionic sulphate surfactant
comprises a high crystalline fraction secondary alkyl sulphate.
6. A detergent composition according to claim 5 wherein the secondary alkyl sulphate
comprises a mixture of compounds having 16 to 18 carbon atoms in the alkyl group.
7. A detergent composition according to claim 4 wherein the anionic sulphate surfactant
comprises a C15-16 primary alcohol sulphate.
8. A detergent composition according to any one of the preceding claims comprising
from 0.05 to 5% by weight of a non-soap anti-foam.
9. A detergent composition according to any one of the preceding claims wherein the
non-soap anti-foam comprises a phosphate ester.
10. A detergent composition according to any one of the preceding claims wherein the
non-soap anti-foam comprises a mixture of a phosphate ester and a hydrophobic wax
or oil.
11. A detergent composition according to claim 9 wherein the phosphate ester has the
general formula
where A is -OH, or R2O(EO)m-,
where A is -OH, or R2O(EO)m-,
R1 and R2 are the same or different C12-24 straight or branched chain, saturated or unsaturated alkyl groups,
m and n are the same or different and are 0 or an integer from 1 to 6.
12. A detergent composition according to claim 11 wherein A is -OH and n is 0.
13. A detergent composition according to claim 10 wherein the wax has a melting or
softening point in the range 30 to 70°C.
14. A detergent composition according to claim 13 wherein the wax is petroleum jelly
having a melting point of from 30-400C.
15. A detergent composition comprising an anionic sulphate surfactant having a calcium
solubility product and a critical micelle concentration as defined in claim 1, and
a non-soap anti-foam, substantially as hereinbefore described with reference to any
one of the formulations illustrated in Examples 1 to 4.