WO2002031099A1 - Solid shaped detergent composition - Google Patents

Abstract

A melt-cast detergent composition which retains rigidity at least up to 40 °C comprising: (a) 2-50 (Xa) % by wt. saturated fatty acid soap comprising one or more salts of C6-C24 fatty acids; (b) 2-40 % by wt. of detergent active species; (c) 0.5-20 % by wt. of a salting-in electrolyte; and (d) 30-80 % by wt. water; wherein the fatty acid soap present forms an Xa % solution in water with a liquid phase having a viscosity less than 50 Pa.s at a shear rate of 1 sec-1 in the temperature range 50-100 °C, shows phase separation and presence of a solid phase during cooling up to 20 °C and the solid phase is present at least up to 40 °C during heating.

Description

SOLID SHAPED DETERGENT COMPOSITION

The present invention relates to providing a suitable type and combination of fatty acid(s) to form soap for obtaining melt-cast solid shaped detergent compositions comprising very high levels of water or liquid benefit agents.

Detergent tablets or bars are conventionally manufactured by one of the two methods: (i) shear working /homogenisation of the formulation followed by extrusion and stamping, or (ii) casting.

In the manufacture of detergent tablets by shear working and extrusion, the amount of water that can be incorporated into the formulation is typically less than ~15%. These systems are multiphase composites which exhibit "bricks suspended in mortar" type of morphology. The bricks are solid particles, which in the case of toilet soaps are crystalline salts of long chain saturated fatty acids, inorganic fillers, etc. The mortar is a mixture of various lyotropic liquid crystalline or isotropic solution phases comprising water, liquid additives, and relatively water-soluble soaps or surfactants. These compositions would typically comprise 50- 60% solids, 20-30% lyotropic liquid crystalline phases and about 10% isotropic liquid.

In the manufacture of detergent compositions by casting, the formulated system is taken to a fluid state by raising the temperature, filled into moulds, and is then cooled. This technology is commonly employed for manufacturing transparent personal wash tablets that contain among other ingredients (such as soap and synthetic surfactants) typically 15-50% of expensive components such as ethanol, polyhydric alcohols, sugars, etc., at the time of casting.

US 4,165,293 (Amway, 1979) and WO 96/04361 (P&G, 1996) disclose a solid transparent soap bar comprising soap, synthetic surfactants and a water soluble organic solvent for e.g. propylene glycol. The level of water in these compositions is about typically about 10-32%.

The problem in manufacturing non-transparent detergent tablets by casting is that the typical compositions do not form a pourable liquid at elevated temperatures . US 5,340,492 (P&G, 1994) claims a castable composition having a three-dimentional skeleton structure comprising a relatively rigid, interlocking mesh of neutralised crystalline carboxylic acids (soap) , synthetic surfactants and high levels of water and other liquids.

The compositions claimed in US 5,340,492 will be soft, exhibiting an yield stress of less than 75 kPa as measured using a cheese wire cutter apparatus, and hence can not be employed as firm tablets which are rigid enough to be conveniently held in the hand for use. In order to increase the rigidity of the bar, the examples in the patent employ ingredients such as polyols (e.g. propylene glycol) in the composition, under the guise of so called "bar appearance aids" . The patent does not disclose any composition without the incorporation of^""bar appearance aids" when synthetic surfactants are also present in the composition. These bar appearance aids are expensive, and also reduce the amount and speed of lather.

In our co-pending application (717/Bom/99) it has been disclosed that the incorporation of low amounts of salting- in electrolytes in melt-cast detergent compositions comprising fatty acid soap, detergent active, very high levels of water or liquid benefit agents result in rigid solid shaped articles exhibiting an yield stress greater than 75 kPa as measured using a cheese wire cutter apparatus. These compositions can be held in the hand, are economical, high foaming and demonstrate good in-use properties. The fatty acid soap according to the above application is one or more of neutralised C₆-C₂ fatty acids.

All combinations of neutralised fatty acids chosen to form the soap to be incorporated into the detergent bars will not result in a solid product when cooled during casting from elevated temperatures to ambient temperatures in the range 20- 35°C. It is necessary to optimise the combination of fatty acid soap in order to obtain a detergent bar at ambient temperatures with. sufficient rigidity such that it can be conveniently held during use. It is also essential that the bar retains rigidity over the natural environmental temperatures generally encountered during storage and transport.

The object of the present invention is thus to provide the required fatty acid combination to form the soap in melt cast detergent bar compositions comprising very high levels of water or liquid benefit agents, such that the detergent composition forms a rigid tablet at temperatures greater than 20°C and retains rigidity at least up to 40°C.

Accordingly, the invention relates to a melt-cast solid shaped detergent composition that forms a rigid product at temperatures greater than 20°C and retains rigidity at least up to 40°C comprising: a) 2-50 (X_a) % by weight saturated fatty acid soap comprising one or more salts of C6-C2₄ fatty acids, b) 2-40% by weight of detergent active species, c) 0.5-20% by weight of a salting-in electrolyte, and d) 30-80% by weight water and optionally other liquid benefit agents,

wherein the saturated soap comprises one or more salts of

Cg-C24 fatty acids is characterised in that its (X_a)% solution in water forms a liquid phase with a viscosity <50 Pa.s at a shear rate of 1/sec in the temperature range 50- 100°C, shows phase separation and presence of a solid phase during cooling up to 20°C and the said solid phase is present at least up to 40°C during heating.

The cooling or heating to detect the solid phase is preferably at a rate of 0.1°C/minute to 10°C/minute, more preferably l°C/minute. The presence of solid phase is preferably detected using low field NMR technique where the said solid phase exhibits Gaussian decay with relaxation time constant T₂ < 15 μsec. During the use of the low field

NMR technique to detect the solid phase, it is preferred to equilibrate the sample at the temperature of detection for 30 minutes.

It is preferred that the detergent active is predominantly non-soap.

According to another aspect of the invention there is provided a process for manufacturing the solid shaped detergent composition comprising the steps of: a. selecting the fatty acid soap comprising one or more of salts of C₆-C₂₄ fatty acids such that the solution of the soap in water forms a liquid phase with a viscosity < 50 Pa.s at a shear rate of 1/sec in the temperature range 50- 100°C, shows phase separation and presence of a solid phase during cooling up to 20°C and the said solid phase is present at least up to 40°C during heating; b. mixing the said fatty acid soap with 2-40% of a detergent active species, 0.5-20% of a salting-in electrolyte, and 30-80% water and optionally other liquid benefit agents; c. melting the composition of step (b) ; d. pouring the said melt into a mould to obtain the desired shape; and e. cooling the mould under quiescent conditions to bring about solidification.

According to a preferred aspect of the invention there is provided a process for manufacturing cast-in-pack solid shaped detergent composition comprising the steps of: a. selecting the fatty acid soap comprising one or more of salts of C₆-C₂₄ fatty acids such that the solution of the soap in water forms a liquid phase with a viscosity < 50 Pa.s at a shear rate of 1/sec in the temperature range 50- 100°C, shows phase separation and presence of a solid phase during cooling up to 20°C and the said solid phase is present at least up to 40°C during heating; b. mixing the said fatty acid soap with 2-40% of a detergent active species, 0.5-20% of a salting-in electrolyte, and 30-80% water and optionally other liquid benefit agents; c. melting the composition of step (b) and pouring the said melt into a pre-formed polymeric mould to obtain the desired shape; d. sealing the mould; and e. cooling the mould under quiescent conditions to bring about solidification

The present invention relates to melt-cast solid shaped detergent compositions that essentially comprises selecting the fatty acid soap comprising one or more of salts of C₆-C₂₄ fatty acids such that the solution of the soap in water forms a liquid phase with a viscosity < 50 Pa.s at a shear rate of 1/sec in the temperature range 50-100°C, shows phase separation and presence of a solid phase when cooled up to 20°C and the said solid phase is present at least up to 40°C during heating. The cooling or heating to detect the solid phase is preferably at a rate of 0.1°C/minute to 10°C/minute more preferably l°C/minute. The presence of solid phase is preferably detected using low field NMR technique where the said solid phase exhibits Gaussian decay with relaxation time constant T₂ < 15μsec. During the use of the low field NMR technique to detect the solid phase it is preferred to equilibrate the sample at the temperature of detection for 30 minutes.

The solid shaped articles of the composition according to the invention are rigid enough to be conveniently held in the hand, economical, high foaming, and exhibit good in-use properties. The compositions exhibit yield stress values greater than 75 kPa as measured using the automatic penetrometer.

Fatty acid soap

The saturated fatty acid soap is preferably selected from one or more salts of saturated C₆-C₂₄ fatty acids. The soap employed may be a sodium, potassium, magnesium, aluminium, calcium or lithium salt of saturated fatty acids. It is especially preferred to have soap obtained as sodium or potassium salt of saturated fatty acid.

The saturated fatty acid soap in the composition is preferably 5-50% by weight and more preferably 5-40% by wt.

The viscosity of the soap-water system in the temperature range 50-100°C is measured using Carri-Med rheometer (Model CSL 500 from TA instruments) at a shear rate of 1/sec. The viscosity measurements were carried out in the steady state flow mode using cone and plate geometry of 2 cm diameter and 1 deg 58 in dimensions with 55 micron truncation, along with a solvent trap. The melt of the soap-water system at elevated temperature is then cooled to a temperature up to 20°C to determine the temperature at which phase separation occurs and solid phase is formed. The system is then heated to ensure that the said solid phase is present at least up to 40°C during heating. The presence of solid phase is detected using low field NMR with variable temperature accessory where the said solid phase exhibits Gaussian decay with relaxation time constant T₂ < 15 μsec, using the procedure described in the following reference: Suresh M. Nadakatti, "Modified Data Handling for Rapid Low Field NMR Characterisation of Lyotropic Liquid Crystal Composites", J. Surfactants and Detergents, Vol. 2, No. 4, pp. 515-521, 1999.

Detergent Active

The compositions according to the invention comprise detergent actives that may be soap or non-soap based. It is preferable to employ non-soap detergent actives that are selected from anionic, non-ionic, cationic, amphoteric or zwitterionic surfactants or their mixtures.

Suitable anionic detergent active compounds are water soluble salts of organic sulphuric reaction products having in the molecular structure an alkyl radical containing from 8 to 22 carbon atoms, and a radical chosen from sulphonic acid or sulphuric acid ester radicals and mixtures thereof. Some examples of synthetic anionic detergent active compounds are linear alkyl benzene sulphonate, sodium lauryl sulphate, sodium lauryl ether sulphate, alpha olefin sulphonate, alkyl ether sulphate, fatty methyl ester sulphonate, alkyl isothionate, etc.

The cations most suitable in above detergent active species are sodium, potassium, ammonium, and various amines e.g. monoethanol amine, diethanolamine and triethanolamine.

Suitable non-ionic detergent active compounds can be broadly described as compounds produced by the condensation of alkylene oxide groups, which are hydrophilic in nature, with an organic hydrophobic compound which may be aliphatic or alkyl aromatic in nature. The common non-ionic surfactants are the condensation products of aliphatic alcohols having from 8 to 22 carbon atoms in either straight or branched chain configuration with ethylene oxide, such as a coconut oil ethylene oxide condensate having from 2 to 15 moles of ethylene oxide per mole of coconut alcohol. Some examples of non-ionic surfactants are alkyl phenol ethylene oxide (EO) condensate, tallow alcohol 10 EO condensate, alkyl de- methyl amine oxides, lauryl mono-ethanolamide, sugar esters, etc.

Some examples of amphoteric detergent active are coco amidopropyl betaine, cocobetaine, etc.

It is also possible optionally to include cationic or zwitterionic detergent actives in the compositions according to the invention.

Further examples of suitable detergent-active species are given in the following well-known textbooks: (i) "Surface Active Agents", Volume I by Schwartz and Perry, (ii) "Surface Active Agents and Detergents", Volume II by Schwartz, Perry and Berch, (iii) "Handbook of Surfactants", M. R. Porter, Chapman and Hall, New York, 1991.

The detergent active to be employed in the detergent composition of this invention is preferably anionic and will generally be up to 50% and more preferably from 2 to 30%.

Salting-in electrolytes

Salting-in electrolytes for use in the composition are selected from those listed in the^ΛHofmeister' or^λLyotropic' series. The salting-in electrolytes are generally those wherein the lyotropic number for the anion of the electrolyte is > 10. Some examples of anions with lyotropic number > 10 are NO₂ , CIO₃ , Br , NO₃ , CIO₄ , I ,

- - 2-

CNS , C₆H₅SO₃ , C₆H₄CH₃SO₃- and Cr₂θ₇ . The preferred examples of salting-in electrolytes for use in compositions according to the present invention are alkali metal salts of the above mentioned anions. The most preferred examples of the salting-in electrolytes for use in compositions according to the present invention are sodium toluene sulphonate, sodium cumene sulphonate and sodium xylene sulphonate.

Further examples of salting-in electrolytes may be selected form those described in (i) Collins, K.D.; Washabaugh, M.W. Quart. Rev. Biophys . , 1985, 18, 323; (ii) Schuster. P, Zundel. G and Sandorfy. C, 1976, The Hydrogen Bond'^', Recent developments in theory and experiments, Vol. Ill, North- Holland Publishing Co. Amsterdam, New York, Oxford.

Liquid benefit agents

According to a preferred aspect of the invention, liquid skin benefit materials such as moisturisers, emollients, sunscreens, anti-aging compounds are incorporated in the composition. Examples of moisturisers and humectants include polyols, glycerol, cetyl alcohol, Carbopol 934, ethoxylated castor oil, paraffin oils, lanolin and its derivatives. Silicone compounds such as silicone surfactants like DC3225C (Dow Corning) and/or silicone emollients, silicone oil (DC-200 Ex-Dow Corning) may also be included. Sun-screens such as 4-tertiary butyl-4 ' -methoxy dibenzoylmethane (available under the trade name PARSOL 1789 from Givaudan) and/or 2-ethylhexylmethoxy cinnamate (available under the trade name PARSOL MCX from Givaudan) or other UV-A and UV-B sun-screens.

Optional ingredients

Other optional ingredients such as hair conditioning agents, fillers, colour, perfume, opacifier, preservatives, one or more water insoluble particulate materials such as talc, kaolin, polysaccharides and other conventional ingredients may be incorporated in the composition.

Process The process of manufacturing of the solid shaped detergent compositions according to the invention comprises following steps : a. selecting the fatty acid soap comprising one or more of salts of C₆-C₂₄ fatty acids such that the solution of the soap in water forms a liquid phase with a viscosity < 50 Pa.s at a shear rate of 1/sec in the temperature range 50- 100°C, shows phase separation and presence of a solid phase when cooled up to 20°C and the said solid phase is present at least up to 40°C during heating; b. mixing the said fatty acid soap with 2-40% of a detergent active species, 0.5-20% of a salting-in electrolyte, and 30-80% water and optionally other liquid benefit agents; c. melting the composition of step (b) ; d. pouring the said melt into a mould to obtain the desired shape; and e. cooling the mould under quiescent conditions to bring about solidification.

The mould may be suitably selected to produce near net shape tablet or to produce bars/blocks. The bars/blocks may be further shaped into a detergent article.

If the solid detergent article is produced using a near net shape thermoformed polymer, the mould is preferably sealed to obtain a cast-in pack detergent composition. To obtain cast-in pack detergent composition the mould is preferably sealed immediately after filling the mould.

The invention will now be illustrated with respect to the following non-limiting examples. Examples

Example 1

Screening of fatty acid soap blend for preparation of detergent composition: Several soap and water mixtures wherein the soap was obtained from a fatty acid blend of lauric acid (C₁₂)_r myristic acid (C_3.4), palmitic acid (Cie) and stearic acid (Cie) and were taken in two litre capacity round bottomed flasks. The ratio of the fatty acid soaps was varied as mentioned in Table 1.

The batch temperature was raised to and maintained at 80 °C to obtain a pourable liquid which would have a viscosity of about 10 Pa.s at a shear rate of 1/sec.

Low field NMR

Low field NMR technique was used to detect presence of solid phase in soap-water systems. The solid phase exhibits a

Gaussian decay with a relaxation time constant T₂ < 15 μsec.

The low field NMR used for studies was procured from M/s Resonance Instruments, U.K. (Model MARAN 25) . The instrument had the following features: (i) a 600W transmitter that produced 90° pulses of ~ 2 μs and (ii) a 5 MHz digitiser that allowed 2 data points to be collected per μs. The presence of solid phase in soap-water systems was detected using the procedure described in the following reference: Suresh M. Nadakatti, "Modified Data Handling for Rapid Low Field NMR Characterisation of Lyotropic Liquid Crystal Composites", J. Surfactants and Detergents, Vol. 2, No. 4, pp. 515-521, 1999.

The melted soap-water system was taken in a 10 mm diameter NMR tube. The tube was placed in the sample chamber of the low field NMR instrument. The temperature was raised to 80°C using variable temperature accessory of the instrument. The system was then cooled to a temperature up to 20°C at intervals of 5 °C and equilibrated at each temperature for 30 minutes. The temperature at which phase separation occurs and solid phase is formed is noted down. The system is then heated to ensure that the said solid phase is present at least up to 40°C during heating.

Table 1

The data presented in Table 1 show that only in Examples la, 2a, 7a and 8a were the pourability, the temperature at which solid phase is formed during cooling and the temperature up to which solid phase is present during heating, in accordance with the invention.

Example 2

Process for preparing the detergent bar

Based on the screening procedure described in Example 1, fatty acid mixture corresponding to example la to 8a were taken in two litre capacity round bottomed flasks and mixed with non-soap detergent actives such as alpha olefin sulphonate (AOS) or sodium lauryl ether sulphate (SLES), salting-in electrolyte such as sodium toluene sulphonate (STS) and water as given below in Table 2. The batch temperature was raised to 80°C. The aqueous solution of sodium hydroxide was added to the mixture to neutralise the fatty acids. The batch temperature was maintained at 80 °C so that a clear solution was obtained. The melt of the detergent composition at 80°C was poured into a thermoformed polymeric mould and the inlet of the mould was sealed. The mould was allowed to cool to bring about solidification of soap and a cast-in-pack detergent tablet was thus obtained.

The rigidity of the bars processed was determined in terms of yield stress using the procedure described below.

Yield Stress Measurement The detergent tablets were then kept in ovens maintained at 25°C and 40°C, respectively, for 4 hours and allowed to equilibrate. The yield stress of the tablets at 25°C and 40°C was measured using a automatic penetrometer using the procedure described below.

The automatic penetrometer used for yield stress measurements was model PNR 10 from M/s Petrotest Instruments GmbH. Standard Hollow Cone (part # 18-0101, as per ASTM D 217 - IP 50) along with Plunger (part # 18-0042) was used for the measurements. The cone consisted of a conical body of brass with detachable, hardened steel tip. The total mass of the cone was 102.5 g. The total mass of the movable plunger was 47.5 g. Total mass of cone and plunger that fall on the detergent tablet was therefore 150 g.

Additional weights of 50 g and 100 g (making the total weight falling on the sample 200 g and 250 g, respectively) were also used. The yield stress values of the sample at 25°C and 40°C were measured using the standard procedure comprising following steps:

1. The detergent tablet was placed on the table of the penetrometer.

2. The measuring device of the penetrometer was lowered so that the tip of the penetrometer touched the tablet but did not penetrate it.

3. The measurement operation was started by pressing "start" key.

4. The penetration depth was read in mm as indicated on the display. 5. The measured penetration depth value was used to calculate the yield stress of the detergent tablet using the following equation:

Yield stress = Applied force / (Projected area of the cone)

= (m x g ) x 10 3 / [π (p tan θ + tip diameter) 2 ] where

Yield stress is in kPa m : total mass falling on the flat surface of the bar in kg

2 g : acceleration due to gravity in m/s p : penetration achieved in mm θ : Cone angle (30°) tip diameter = 0.359 mm

According to the above equation if the measured penetration depth is <10 mm for 200 g total mass falling on the sample then the yield stress of the detergent tablet is > 75 kPa. Three yield stress values were calculated for 150 g, 200 g, and 250 g total mass falling on the detergent tablet and the average of the three values was used as the yield stress of the detergent tablet.

Table 2

The data presented in Table 2 show that only if the soap- water system is according to the invention it will produce detergent bars that solidify and result in a rigid products when cooled to temperatures greater than 20°C during casting and retain rigidity at least up to 40°C. This is confirmed by the yield stress data for detergent bars (Ex lb, Ex 2b, Ex 7b and Ex 8b) which show values >75 kPa when the screening of the soap water system is according to the invention (Ex la, Ex 2a, Ex 7a and 8a) . If the soap-water system does not satisfy_. the screening requirement, the detergent product produced using such soap will not form rigid bars.

Claims

1. A melt-cast detergent composition which retains rigidity at least up to 40 °C comprising: (a) 2-50 (X_a)% by wt. saturated fatty acid soap comprising one or more salts of C6-C2 fatty acids;

(b) 2-40% by wt. of detergent active species;

(c) 0.5-20% by wt. of a salting-in electrolyte; .and^'(d) 30-80% by wt. water; wherein the fatty acid soap present forms an X_a% solution in water with a liquid phase having a viscosity less than 50

Pa.s at a shear rate of 1 sec in the temperature range 50-

100 °C, shows phase separation and presence of a solid phase during cooling up to 20 °C and the solid phase is present at least up to 40°C during heating.

2. A melt-cast detergent composition according to Claim 1, wherein the detergent active is a non-soap detergent active selected from ionic, non-ionic, cationic, amphoteric or zwitterionic surfactants, or mixtures thereof.

3. A melt-cast detergent composition according to Claim 1 or Claim 2, wherein the fatty acid soap is a sodium, potassium, magnesium, aluminium, calcium or lithium salt of a saturated C5-C24 fatty acid.

4. A melt-cast detergent composition according to any one of Claim 1 to 3, wherein the salting-in electrolyte has lyotropic number for the anion of >10.

5. A melt-cast detergent composition according to Claim 4, wherein the salting-in electrolyte is an alkali metal salt of an anion selected from NO2 , CIO3 , Br -, NO3 , CIO₄ , I ,

CNS^~, C6H₅S03^~, C6H4CH3SO3^" or Cr2θ7^2~.

6. A melt-cast detergent composition according to any of the preceding claims, wherein the composition further comprises a liquid benefit agent.

7. A melt-cast detergent composition according to Claim 6, wherein the liquid benefit agent is selected from moisturisers, emollients, sunscreens or anti-ageing compounds .

8. A process of manufacturing a melt-cast solid-shaped detergent composition comprising the steps of:

(a) selecting the fatty acid soap comprising one or more of salts of C6-C2₄ fatty acids such that the solution of the soap in water forms a liquid phase with a viscosity <50 Pa.s at a shear rate of 1/sec on the temperature range 50-100 °C, shows phase separation and presence of a solid phase when cooled up to 20°C and the said solid phase is present at least up to 40 °C during heating; (b) mixing the said fatty acid soap with 2-40% of a detergent active species, 0.5-20% of a salting-in electrolyte, and 30-80% water;

(c) melting the composition of step (b) ;

(d) pouring the melt into a mould to obtain the desired shape; and (e) cooling the mould under quiescent conditions to bring about solidification.

9. A process according to Claim 8, wherein step (b) further comprises the addition of a liquid benefit agent.

10. A solid-shaped detergent composition prepared according to the process of Claim 8 or 9.