GB2231882A - Laundry soap bar - Google Patents

Abstract

A laundry soap bar comprises soap (eg. 30 to 70% by weight), tetrasodiumpyrophosphate or trisodiumorthophosphate or mixtures thereof (eg. 0.5 to 20% by weight) and water (eg. 10 to 60% by weight). The addition of the phosphate salts allows the amount of soap in the bar to be reduced while maintaining acceptable bar properties.

Description

SOAP COMPOSITIONS Laundry soap compositions typically contain 60 to 80% by weight of soaps and 20 to 40% by weight of water and optionally small amounts of inorganic salt and filler.

In the past laundry soap bar manufacturers have been limited to such formulations due to processing and/or resulting bar quality constraints.

It is particularly desirable to reduce the soap content of such compositions since this can lead to cost savings.

One possible way of reducing overall soap content would be to increase the water content. However this gives a composition which is soft, sticky and cannot be processed into bars using conventional equipment. It is thought that the increase in water content causes the soap in the composition to exist in a viscous phase at typical processing temperatures (800C). In the past additions of electrolyte eg. NaCl have been made to induce rheology modifying phase changes in the soap by causing it to 'salt out' of solution. However, the solubility of NaCl is relatively independent of temperature in the range of concern so that on cooling the soap remains salted out leading to poor bar properties, for example cracking. In general increasing the water content of laundry bars has the consequence that the bars tend to shrink on storage, leading to stress cracking.

It is also desirable to use unsaturated feedstocks of blend iodine value greater than 60 for soap production since the increase in soluble active tends to increase lather formation valued by the consumer. Use of unsaturated feedstocks however produces a composition which is too soft to process on conventional plant.

Another possible way of reducing soap content is to include fillers.

Use of soluble fillers (eg. polyols) tends to produce deterioration in properties perceived by the user, such as lather formation, bar hardness, rate of wear and development of surface mush.

Use of insoluble fillers (eg. kaolin) tends to increase the viscosity of the composition again leading to processing difficulties.

We have now found that the incorporation of particular electrolytes makes it possible to avoid the constraints referred to above while still maintaining satisfactory bar properties.

According to a first aspect of the present invention we provide a soap bar comprising soap, tetrasodiumpyrophosphate (TSPP), trisodiumorthophosphate (TSOP) or mixtures thereof and water.

Preferably the bar comprises: 30 to 70% by weight of soap reckoned as anhydrous 0.5 to 20% by weight of tetrasodiumpyrophosphate trisodiumorthophosphate or mixtures thereof reckoned as anhydrous, and 10 to 60% by weight of water the yield stress of the bar being less than 3.0 x 105cm 2 at 20 cm.

By including ortho or pyro phosphate or mixtures thereof the amount of soap in the composition may be reduced while maintaining an acceptable hardness and allowing processing on conventional plant.

Whilst not wishing to be bound by any theory it is thought that the ortho and pyro phosphate have this advantageous effect due to the formation of low solubility hydrates in the soap composition as it cools from the processing temperature to below the hydration temperature of the electrolyte. These hydrates bind water in the composition and form a network structure. Since the water bound as a hydrate is immobile, undesirable bar properties associated with excess water are less likely to occur.

The water present in the bar at room temperature therefore consists of "free" water and bound water of crystallisation. Preferably the bars have soap to free water ratios in the range of 1:1 to 5:1, more preferably 3:1. The composition preferably comprises from 18 to 14% tetrasodiumpyrophosphate or trisodiumorthophosphate or a mixture thereof more preferably 1% to 10%.

The composition may also comprise up to 35% by weight of kaolin as a filler. The invention making possible the inclusion of fillers, in compositions which are processable on conventional plant. Other fillers such as soda ash and alkaline silicate may also be included in compositions according to the invention.

The hardness of a soap bar can be quantified by measuring the yield stress of the bar. Measurement of yield stress is described inter alia in Elementary Rheology by G W Scott Blair, Academic Press, London 1969.

Preferably, laundry bars according to the invention have yield stresses of less than 3.0 x 105cm 2 at 200C when measured in the following manner. A horizontal cheesewire of diameter dcm attached to a counter balanced, and freely pivotable arm is brought into contact with a freshly prepared bar of soap which has cooled to room temperature (200C). The soap is positioned under the wire such that when a weight (W gm) is placed directly above the cheesewire the length of cut (Lcm) made by the wire increases to the limit where the stress exerted by the wire equals the resistance of the soap and the wire comes to a stop. The stress at this limit is equal to the yield stress of the soap. The time taken to reach this limit is approximately 30 seconds, in practise a standard 1 minute cut-time was allowed.

For a soap bar of square transverse cross-section the bar is positioned such that the cheesewire first contacts a corner of the bar. The yield stress can then be calculated using the following formula: Yield Stress = 3 W98.1 Nm 2 8 Ld Soaps suitable for use in this invention are the salts of the higher fatty acids. This class of compound includes ordinary alkali metal soaps such as sodium, potassium, ammonium and alkylol ammonium salts of higher fatty acids containing from about 8 to about 24 carbon atoms and preferably from about 12 to about 22 carbon atoms. Soaps can be made by direct saponification of fats and oils or by the neutralization of free fatty acids.

Particularly useful are the sodium and potassium salts of the mixtures of fatty acids derived from coconut oil, tallow, fish oil, soya oil, e.g. sodium and potassium tallow soap.

Compositions according to the invention can be produced by mixing pyro or ortho phosphate with moisture-containing soap. A preferred technique is to add anhydrous phosphate to molten soap comprising approximately 70% soap and 308 water. The phosphate can be added as a dry powder, as a hot concentrated solution or as a slurry with a small amount of hot water. The composition can then be cooled and/or dried to its intended water content, possibly by use of a vacuum flash dryer as is conventionally used for drying soap. However, less drying will be required for compositions of this invention.

An alternative production route is to mix the ortho or pyro phosphate with dried soap eg. soap noodles coming from a vacuum flash dryer. Mixing with such soap noodles can be carried out in a shear mixer.

By adding the phosphate at these relatively early stages in the processing of the bars, a composition is obtained which can be subjected to conventional subsequent processing steps. Normally these are admixing of minor ingredients, eg. with a chip mixer, milling, plodding and stamping into bars. At phosphate addition levels greater than 10% it may be convenient to add a small amount of a hydrotrope to further reduce the viscosity of the composition.

In a second aspect therefore this invention provides a process of preparing a composition as specified above comprising the steps of subjecting a soap with a water content in excess of 10% by weight to a drying step and admixing tetrasodiumpyrophosphate or trisodiumorthophosphate before or after the drying step.

Generally the resulting composition will then be milled, plodded and shaped into bars.

The invention will now be described further and exemplified in the following examples in which percentages are by weight of anhydrous soap and pyro or ortho phosphate and the percentage water is the total for the composition i.e. free and bound.

Examples In the following examples samples were prepared in a Winkworth i-blade mixer at 800C. Soap Chips were added to the mixer together with any additional water required in the final formulation. The phosphate and kaolin if appropriate were added separately as solids to the soap/water mix.

Viscosity measurements were made using a Macklow-Smith Plastometer at 800C. Extensional viscosities are quoted for an extension rate of 104 sex 1.

Extensional Viscositv at % % k % % 104 sex 1 Example Soap Water TSOP TSPP Kaolin at 800C. Nm2 1 68 32 - - - 2.1x105 2 50 50 - - - 3.1x105 5 3 47.5 47.5 0 5 - 1.4x105 4 48 48 4 - - 7.8x104 5 5 45 45 - - 10 3.3x105 6 43.2 43.2 3.6 - 10 9.6x104 4 7 42.3 42.3 - 5.4 10 8.0x104 8 35 35 - - 30 4.85x105 5 9 33.6 33.6 2.8 - 30 1.45x105 10 32.9 32.9 - 4.2 30 8.0x104 11 50 35 - - 15 4.75x105 12 47 32 - 6 15 6.8x104 Example 1 is a control composition typical of a conventional laundry bar processable on conventional equipment.

Comparison of Examples 2 and 3 with 1 shows that the addition of 5% TSPP reduces the viscosity of the composition to below that of conventional laundry bar compositions. Similarly comparison of Examples 2 and 4 with 1 show a similar effect with 4% TSOP addition.

Comparison of Example 5, with Example 1 show the effect on processability of the addition of 10% kaolin and Examples 6 and 7 the effect of adding 3.6% TSOP or 5.4% TSPP to such a composition. Examples 8, 9 and 10 show a similar effect for higher kaolin levels. Examples 11 and 12 show the effect on viscosity of replacing water with kaolin and the subsequent reduction in viscosity on incorporation of TSPP rendering the composition processable.

In the following Examples compositions were prepared in a conventional liquid paddle mixer at 800C. Soap chips were added to the mixing chamber followed by additional water if necessary. TSOP or TSPP ex BDH was then sprinkled in. Lastly kaolin (Speswhite Grade X ex English China Clays) was added.

The resulting compositions were then pumped through a Mazzoni Vacuum Flash Cooler The resulting samples were then extruded through a Hampson and Edwards 6" single screw plodder producing 1 square billets.

The yield stress of the bars was determined by the cheesewire method directly after formation of the bar once it had cooled to room temperature (200C).

The in-use property of mush was determined by the weight of wet mush that could be scraped from a 22mm square bar produced on an Edwards and Jones 2" Pugmill, the bar having been allowed to stand in a-3cm immersion of 140FH water of water for 120 minutes at 300C.

Constituent Example (% by weight) 1 13 14 1 13 14 Soap 68 44 55 TSPP 0 6 6 Kaolin 0 31.2 16.6 Water (free and bound) 32 18.8 22.4 Yield Stress (cm 2) 1.6x105 2.64x105 2.18x105 at 200C Wet Mush (g) 2.9 2.8 1.6 Comparison of Examples 1 and 13 or 1 and 14 show that compositions according to the invention have acceptable hardness and mush characteristics.

In the following examples samples were prepared as in Examples 13 and 14 excepting that higher levels of TSPP were used.

Constituent Example (% by weight) 15 16 Soap 53.6 60.2 TSPP 9.8 9.8 Water (free and bound) 36.6 30 2 5 5 Yield Stress (Nm ) 0.56x10 1.9x10 at 300C In the following examples compositions were prepared in a conventional paddle mixer at 900C by adding carbonated alkaline silicate to neat soap, followed by addition of TSPP and hot water. The resulting compositions were pumped through a Mazzoni Vacuum Flash Cooler and plodded into rectangular billets.

Constituent Example (% by weight) 17 18 19 Soap 59 56 54 Alkaline Silicate 5 5 5 Sodium Carbonate 1 1 1 TSPP - 2 3 Perfume, Colour, etc 1 1 1 Water (free and bound) 34 35 36 -2 5 5 5 Yield Stress (Nm ) l.7x10 1.8xl0 1.8x10 at 200C Wet Mush(g) 5.8 5.9 5.4 Comparison of Examples 17 and 18 or 17 and 19 show that compositions according to the invention have acceptable hardness and mush characteristics.

Claims (8)

Claims

1. A laundry soap bar comprising soap, tetrasodiumpyrophosphate, trisodiumorthophosphate or mixtures thereof and water.

2. A laundry soap bar as claimed in claim 1 comprising 30 to 70% by weight of soap reckoned as anhydrous 0.5 to 20% by weight of tetrasodiumpyrophosphate or trisodiumorthophosphate or mixtures thereof reckoned as anhydrous and 10 to 60% by weight of water.

3. A laundry soap bar as claimed in claim 1 or claim 2 wherein the yield stress of the bar is less than 3.0 x 105 Nm 2 at 200C.

4. A laundry soap bar as claimed in any preceding claim wherein the soap to free water ratio is in the range of 1:1 to 5:1.

5. A laundry soap bar as claimed in any preceding claim wherein the soap to free water ratio is 3:1.

6. A laundry soap bar as claimed in any preceding claim wherein the bar comprises from 1% to 14% of tetrasodiumpyrophosphate or trisodiumorthophosphate or a mixture thereof.

7. A laundry soap bar as claimed in any preceding claim wherein the bar comprises from 1% to 10% of tetrasodiumpyrophosphate or trisodiumorthophosphate or a mixture thereof.

8. A laundry soap bar as claimed in any preceding claim wherein the bar-additionally comprises up to 35% by weight of kaolin.