AU2002219186A1

AU2002219186A1 - Detergent composition

Info

Publication number: AU2002219186A1
Application number: AU2002219186A
Authority: AU
Inventors: Suresh Murigeppa Nadakatti; Vijay Mukund Naik; Shiju Thomas
Original assignee: Unilever PLC
Current assignee: Unilever PLC
Priority date: 2000-12-29
Filing date: 2001-12-13
Publication date: 2003-01-23
Anticipated expiration: 2021-12-13

Description

IMPROVED DETERGENT COMPOSITION

The present invention relates to melt-cast solid shaped detergent compositions with a solid content less than 30% and very high levels of water or liquid benefit agents, but exhibiting high rigidity and good in-use properties.

Detergent tablets 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 particles, 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 40- 60% solids, 20-50% lyotropic liquid crystalline phases and upto 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 cooling. 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 alcoholic ingredients such as ethanol, polyhydric alcohols, sugars, etc., at the time of casting.

US 4,165,293 (Amway, 1979); WO 96/04361 (P&G, 1996) disclose a solid transparent soap bar comprising soap, synthetic surfactants and a water soluble organic solvent such as e.g. propylene glycol. The level of water in these compositions is 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 comprising neutralised crystalline carboxylic acids (soap) , synthetic surfactants and high levels of water and other liquids. The compositions prepared as per disclosure in US 5,340,492 are soft, exhibiting an yield stress of less than 75 kPa as measured using a cheese wire cutter apparatus and hence are not suitable as firm tablets which are rigid enough to be conveniently held in 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, reduce the amount and speed of lather, and more over they are well known in prior art (US 4,165,293, WO 96/04361).

In our copending 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, results 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 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-C₂₄ fatty acids.

The prior art generally teaches the use of additives such as polyols or salting-in-electrolytes or other bar appearance aids in melt cast compositions comprising fatty acid soap, detergent active, very high levels of water or liquid benefit agents to enhance the rigidity of the bar.

It has now been possible to obtain a melt cast detergent composition using nil or very low levels of additives, having a solid content less than 30% and high levels of water or other liquid benefit agents, that are rigid and exhibit an yield stress >75 kPa at a temperature range of 20-40°C.

In a first embodiment, the invention comprises a melt cast detergent composition which is preferably a tablet with a solid content less than 30%, exhibiting an yield stress >75 kPa at a temperature range 20-40°C, comprising:

a) 2-50% 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, and c) 30-80% by weight water and optionally other liquid benefit agents

characterised in that the composition does not show pure lyotropic liquid crystalline phase in the temperature range 20-100°C and forms an isotropic liquid phase or a dispersion of lyotropic liquid crystalline phase in the continuum of isotropic liquid in the temperature range 40-100°C.

According to a more preferred aspect of the invention there is provided a melt cast detergent tablet composition with a solid content less than 30% and that is free of additives, exhibiting an yield stress >75 kPa at a temperature range 20-40°C, comprising:

The additives generally employed in the prior art are ethanol, propylene glycol and other polyols, salting-in- electrolytes, etc. The present invention preferably avoids the use of any of these in the composition.

In more detail, the detergent composition of the invention is preferably free of solvent alcohols, and also is preferably free of polyhydric alcohols. By "free" in this context is meant theat the composition contains less than 5wt%, more preferably less than lwt%, even more preferably less than 0.5wt%, and may even be totally free of polyhydric alcohols.

In addition, compositions according to the invention are preferably free of salting in electrolyte; that is they contain less than 1%, more preferably less than 0.5%, and conveniently may be totally free of salting in electrolyte. It is preferred that the detergent active is predominantly non-soap.

The presence of isotropic liquid phase and the liquid crystalline phases in surfactant systems is preferably detected using optical polarising microscopy technique. Liquid crystalline phases are inherently anisotropic, making the index of refraction depend on orientation. In general, such bi-refringent systems change the plane of polarisation of polarized light. An isotropic liquid appears black between crossed polarizers, but a liquid crystalline system is more transparent e.g. lamellar liquid crystalline phases show maltese-cross or oil streak (large loop like) textures, whereas hexagonal phases show fan-like textures. Characteristic textures of various lyotropic liquid crystalline phases and their dispersions have been reported in the literature.

According to another aspect of the invention, there is provided a process for manufacturing the solid shaped detergent composition of the invention comprising the steps of:

a) making a melt of the above composition, b) pouring the said melt into a mould to obtain the desired shape, c) 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) making a melt of the above composition, b) pouring the said melt into a pre-formed polymeric mould to obtain the desired shape, c) sealing the mould, and d) cooling the mould under quiescent conditions to bring about solidification

The present invention relates to detergent compositions that essentially have a specific phase behaviour that results in rigid melt-cast tablet with a solid content less than 30%, and very high levels of water or other liquid benefit agents. The detergent composition is characterised in that the composition does not show pure lyotropic liquid crystalline phase in the temperature range 20-100°C and forms an isotropic liquid phase or a dispersion of lyotropic liquid crystalline phase in the continuum of isotropic liquid in the temperature range 40-100°C.

The presence of isotropic liquid phase and the liquid crystalline phases in surfactant systems is preferably detected using optical polarising microscopy technique. Liquid crystalline phases are inherently anisotropic, making the index of refraction depend on orientation. In general, such bi-refringent systems change the plane of polarisation of polarized light. An isotropic liquid appears black between crossed polarizers, but a liquid crystalline system is more transparent e.g. lamellar liquid crystalline phases show maltese-cross or oil streak (large loop-like) textures whereas hexagonal phases show non geometric, fan-like textures. Several textures may be observed within the same phase structure.

Characteristic textures of various lyotropic liquid crystalline phases (and their dispersions) have been reported in following references: (i) "The Aqueous Phase Behaviour of Surfactants" by Robert G. Laughlin, Academic Press, New York, 1994, Pages 538-542. (ii) "The Colloidal Domain Where Physics, Chemistry, Biology, and Technology Meet" by D. Fennell Evans, Hakan Wennerstrom, VCH Publishers, New York, 1994, Pages 251-252. The solid shaped articles of the composition according to the invention are rigid enough to be conveniently held in 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.

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 compositions according to the invention also 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, patissium, ammonium, and various amines e.g. monoethanol amine, diethanolamine and triethanolamine.

Suitable nonionic 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 nonionic 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 nonionic 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 reference: "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 40% and more preferably from 2 to 30%.

According to a preferred aspect of the invention, liquid skin benefit materials such as moisturisers, emollients, sunscreens, and anti-ageing 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- ethyl hexyl methoxy cinnamate (available under the trade name Parsol MCX from Givaudan) or other UV-A and UV-B sun-screens. Other skin benefit agents such as polyethylene glycol (PEG) can also be incorporated in the composition.

Other optional ingredients such as salting-in-electrolytes, polyols, 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, though the composition is preferably free of polyols and salting-in electrolytes.

A preferred process of the invention may be a method of manufacturing a melt of the detergent composition comprising 2-50% by weight of saturated fatty acid soap, 2-40% by weight of non-soap detergent active and 30-80% water or other liquid benefit agents, characterised in that the composition does not show pure lyotropic liquid crystalline phase in the temperature range 20-100°C and forms an isotropic liquid phase or a dispersion of lyotropic liquid crystalline phase in the continuum of isotropic liquid in the temperature range 40-100°C, is prepared. In the method, this melt is poured into any suitable mould or a pre-formed polymeric mould to obtain the desired shape, the mould is sealed, and cooled 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 in to detergent article.

If the solid detergent article is produced using a near net shape thermoformed polymer, the mould is 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 the Compositions with respect to their Phase Behaviour The composition according to the invention is characterised in that the composition does not show pure lyotropic liquid crystalline phase in the temperature range 20-100°C and forms an isotropic liquid phase or a dispersion of lyotropic liquid crystalline phase in the continuum of isotropic liquid in the temperature range 40-100°C. The comparative examples according to the invention and beyond the invention are presented in Table 1.

a. Phase Characterisation:

Phase characterisation of the composition was carried out using optical polarising microscopy technique. A drop of the melt of the composition at elevated temperature of about 80°C was transferred on to a microscope glass slide and covered with a cover slip. The edges of the cover slip were sealed using UV glue to minimise moisture loss. The glass slide was mounted on the stage of the microscope provided with a controlled heating/cooling facility. The system was heated to 110°C at a rate of 1°C per minute. The temperature at which isotropic liquid phase or its dispersion, or pure liquid crystalline phase was formed, was noted down.

The system was then cooled to bring about solidification at the rate of 1°C per minute to check if pure liquid crystalline phases are formed during cooling. Lyotropic liquid crystalline phases are inherently anisotropic, making the index of refraction depend on orientation. In general, such birefringent systems change the plane of polarisation of polarized light. An isotropic liquid appears black between crossed polarizers, but a liquid crystalline system is more transparent e.g. lamellar liquid crystalline phases show maltese-cross or oil streak (large loop like) textures whereas hexagonal phases show non geometric, fan like textures .

Several textures may be observed within the same phase structure. Characteristic textures of various lyotropic liquid crystalline phases (and their dispersions) have been reported in following references: (i) "The Aqueous Phase Behaviour of Surfactants" by Robert G. Laughlin, Academic

Press, New York, 1994, Pages 538-542. (ii) "The Colloidal Domain Where Physics, Chemistry, Biology, and Technology Meet" by D. Fennell Evans, Hakan Wennerstrom, VCH Publishers, NewYork, 1994, Pages 251-252.

b. Determination of solid content:

Low field NMR technique was used to determine the solid content in the detergent compositions 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.

c. Preparation of Detergent Tablet

A melt of the detergent composition at an elevated temperature of 80°C is poured in to a rectangular mould of dimensions 75mm (L) x 55mm (W) x 40mm (H) . The composition was allowed to cool to bring about solidification and a detergent tablet was obtained.

d. 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 a 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)

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

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.

e. Examples of Detergent Tablet Compositions Data presented in Table 1 show that only the composition as described in Ex 1.1 that satisfied the phase characterisation according to the invention formed rigid detergent tablet exhibiting an yield stress > 75kPa. The compositions of Examples 1.2 and 1.3 are soft because they form a pure lyotropic liquid crystalline phase in the temperature range 35-75°C, and do not form isotropic liquid phase or its dispersion in the temperature range 40-100 °C. In Example 1.4 the temperature at which isotropic phase or its dispersion was formed during heating was within the range specified in the invention but the pure liquid crystalline phase was formed during cooling, and consequently the bar was soft. This demonstrates that it is essential to satisfy both the phase behaviour criteria to obtain bars that are rigid and show a yield stress > 75 kPa.

Table 1

*H1 is pure hexagonal liquid crystalline phase. Further examples of compositions that exhibit phase behaviour according to the invention are shown in Table 2 and those with phase behaviour not according to the invention are shown in Table 3. All examples in Table 2 have less than 20% solids and yet form rigid tablets exhibiting yield stress > 75 kPa at 25°C. The examples described in Table 3 on the contrary are soft.

Table 2

Table 3

*H1 is pure hexagonal liquid crystalline . phase.

Example 2

Process for preparing the detergent tablet

Based on the screening procedure described in Example 1, fatty acid mixture corresponding to examples 1.5 to 1.11 were taken in two litre capacity round bottomed flasks and mixed with non-soap detergent active and water. 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 isotropic 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.

Claims

C1AI S

1. A melt cast detergent composition with a solids content less than 30%, exhibiting a yield stress >75kPa at a temperature range 20-40°C, comprising

(i) 2-50% by weight saturated fatty acid soap comprising one or more salts of Cg-C₂4 fatty acids;

(ii) 2-40% by weight of detergent active species; (iϋ) 30-80% by weight water and optionally one or more liquid benefit agents, wherein the composition does not show pure lyotropic liquid crystalline phase in the temperature range 20- 100 °C and forms an isotropic liquid phase or a dispersion of lyotropic liquid crystalline phase in a continuum of isotropic liquid at a temperature within the range 40-100°C.

2. A melt cast detergent composition according to Claim 1, wherein the water and optional liquid benefit agents are present in an amount of 60-80% by weight of the composition.

3. A melt cast detergent composition according to Claim 1 or Claim 2, wherein the composition is substantially free of additives selected from alcohols, propylene glycol and other polyols, and salting-in electrolytes.

4. A melt cast detergent composition according to any preceding claim, wherein the detergent active species is a non-soap detergent.

A melt cast detergent composition according to any preceding claim, wherein the fatty acid soap is a sodium or potassium salt of the fatty acid.

A melt cast detergent composition according to any preceding claim, wherein the liquid benefit agent is selected from moisturisers, humectants, emollients, sunscreens and anti ageing compounds.

A process for preparing the melt cast detergent composition according to any one of claims 1 to 6, the process including:

(i) making a melt of the detergent composition;

(ii) pouring the melt into a mould suitable to obtain the desired shape; and (iii) causing or allowing the mould to cool whereby a solid detergent composition is produced.

8. A process according to Claim 7, wherein step (ii) includes the substeps

(iia) pouring the melt into a pre-formed polymeric mould to obtain the desired shape; and

(iib) sealing the mould,

thereby to produce a cast-in-pack solid shaped detergent composition.