EP1037949A1

EP1037949A1 - Particle agglomerates

Info

Publication number: EP1037949A1
Application number: EP98958359A
Authority: EP
Inventors: Pamela Elizabeth Baines; Maurice Webb
Original assignee: Joseph Crosfield and Sons Ltd; Crosfield Ltd
Current assignee: Ineos Silicas Ltd
Priority date: 1997-12-12
Filing date: 1998-12-08
Publication date: 2000-09-27
Also published as: AU1442899A; CA2311758A1; PL341049A1; ID26820A; GB9726227D0; BR9813500A; JP2002508430A; CN1282355A; WO1999031184A1; KR20010033013A

Abstract

Liquid-based products such as personal care, personal hygiene and cosmetic formulations incorporate a material which serves to impart a desired characteristic, such as a sensory attribute (e.g. tactile), to the product, the material being in the form of granules of high density inorganic particles co-agglomerated with particles having a density lower than that of water.

Description

PARTICLE AGGLOMERATES

This invention relates to particle agglomerates and is particularly but not necessarily exclusively concerned with particle agglomerates intended for suspension in liquid-based media, especially media in which the liquid base is of relatively low viscosity.

In one application of the invention, the particle agglomerates are employed in liquid-based personal care and hygiene formulations and cosmetic formulations in order to impart a desired characteristic, such as a sensory attribute (e.g. tactile), to the product. Examples of the use of particle agglomerates in such formulations are disclosed in published International Patent Applications Nos. WO-A-94/12151 ,

WO-A-96/09033, WO-A-96/09034 and WO-A-97/30126. Typically such agglomerates are composed of inorganic particles such as for example amorphous silica or silicas. Wide variations in particle density cause suspension problems when formulating into typical exfoliating compositions in that the dense particles tend to sediment and the low density particles tend to float which impairs the visual or functional performance. Until now, adding a suspending agent or increasing the viscosity by adding rheology modifiers to the formulation has been the only way to prevent settlement - thus the entire formulation had to be modified in order to modulate the suspension of a component which might only be present at 1 % or less. In formulations to which the present invention has application, the base liquid is often of low viscosity for aesthetic, functional or cost reasons. Aggregates of dense materials such as silicas will tend to settle in such formulations with consequent impairment of the visual appearance, sensory qualities and/or functional performance of the formulation. For this reason, especially where the formulation has a relatively low viscosity liquid base, suspending or thickening agents have to be incorporated in the formulation in order to maintain the agglomerates in suspension. Examples of the types of suspending or thickening agents used for this purpose are given in for instance International Patent Application No. WO 94/12151 and EP-A-0571 193. The addition of suspending or thickening agents results in changes in the rheology of the formulation which, in turn, can have a radical affect on the sensory or other desirable qualities of the formulation.

There is therefore a need to control the aggregated particle density without adversely affecting the particle functionality (be it tactile sensation or carrying) so that its settlement can be tailored to the medium rather than tailoring the physical characteristics of the medium to the particle properties. This gives considerably more freedom of formulation in the product and/or cost reduction by avoiding the need for suspending agents and/or thickeners or at least reducing the amounts required . According to one aspect of the present invention there is provided a material in the form of granules of high density inorganic particles co-agglomerated with particles having a density lower than that of water.

Preferably the lower density particles have a density in the range from 0.01 to 0.4 g/ml, more preferably 0.015 to 0.25 g/ml and typically 0.02 to 0.15 g/ml. The lower density particles are conveniently in the form of low density, gas-encapsulating particles; however, we do not exclude the possibility of other low density particles being employed, e.g. polyethylene particles such as those solid available from Allied Signal Inc, New Jersey, USA under the trade name A-C Polyethylene.

The combination, by agglomeration, of the high density inorganic particles and said low density particles allows the density of the granules to be tailored according to requirements. For instance, the material as defined in the above aspects of the invention is particularly suitable for incorporation in liquid-based media, especially media having low viscosity liquid bases, since the low density particles impart buoyancy to the granules thereby largely eliminating the need for inclusion of suspending or thickening agents for the purpose of counteracting sedimentation of the high density particle agglomerates. Usually the high density particles will be the primary particle in terms of imparting a particular attribute, e.g. a sensory attribute, to the liquid-based composition in which they are incorporated; however, we do not exclude the possibility that the low density particle may be primary particle in this sense and that the co-agglomeration with high density particles is effected in order to adjust the effective density of such primary particles to counteract, largely without the aid of suspending or thickening agents, any tendency for the low density particles to float with consequent impairment of the visual appearance or functional performance of the liquid-based composition. Thus for example, the previously mentioned polyethylene particles, such as those solid available from Allied Signal Inc, New Jersey, USA under the trade name A-C Polyethylene, are suitable for use as a low density particle having a sensory attribute. According to a second aspect of the invention there is provided a material in the form of granules of high density inorganic particles co-agglomerated with low density, gas-encapsulating particles.

According to a further aspect of the invention there is provided a liquid-based medium containing material according to the above aspects of the invention, the granules being dispersed throughout said medium.

"Liquid-based medium" as used herein is not limited to formulations which are of a pourable nature; also included are other liquid-based formulations such as lotions, creams and gels. However, the invention is particularly expedient in the case of liquid-based media employing low viscosity liquids, particularly liquids having viscosities in the range of 1 ,000 to 10,000 mPas^"1 but is also expedient for lotions, creams and gels having viscosities in the range of 1 ,000 to 100,000 mPas^"1, preferably 2,000 to 40,000 mPas ¹ and more preferably 2,000 to 20,000 mPas^-1.

The amount of low density particles employed in the granules will depend on the extent to which the density of the granules needs to be tailored for a particular application . Typically the low density particles will constitute up to 20% by weight of the granular composition, for instance from 1 to 12% by weight, with 1 to 8% by weight being preferred, more preferably 1 to 5% by weight.

The liquid-based medium may take various forms such as a personal care formulation (e.g. skin cleansing/exfoliating agent, mouthwash, liquid toothpastes, shower gel or hair care agent such as shampoo), a personal hygiene formulation or a cosmetic formulation. The liquid-based medium for such applications will typically contain the granular material according to the invention in an amount up to of 20% by weight, e.g. 1 to 20% by weight, more usually from 1 to 8% by weight. The medium may be aqueous or non-aqueous and may also include other components conventionally employed in personal care, personal hygiene and cosmetic products. For aqueous systems, water may be present in a total amount of from 10 to 90% by weight, preferably from 20 to 80% by weight and most preferably from 40 to 75% by weight. Also surfactants may be present, e.g. selected from anionic, nonionic, amphoteric and zwitterionic surfactants or mixtures thereof, typically in an amount in excess of 0.1 % by weight, e.g. 1 to 80% by weight and more preferably from 2 to 50% by weight. Any surfactants may be used. Also, for products such as liquid toothpastes, one or more humectants may be present in the range of 1 to 70% by weight, preferably 5 to 70% by weight.

Suitable additional ingredients may include components selected from: electrolytes, for instance water soluble alkali metal or ammonium salts (e.g. sodium chloride); pearlescing agents; perfumes; flavours; vitamins; opacifiers; colourings; dentrifice agents such as anti-plaque agents and agents for combating tooth-sensitivity; preservatives; anti-dandruff agents; hair conditioning agents; skin moisturising agents; herb and plant extracts; essential oils; emollients; proteins; pH adjusting agents; or anti-microbials.

In a liquid-based medium in accordance with the invention, sedimentation can be overcome without the aid of suspending agents (e.g. Carbomers) or rheology modifiers (e.g. synthetic hectorite (laponite) clay) or organic builders such as sodium carboxymethyl cellulose, xanthan gum and carrageen. However, while we do not exclude the inclusion of such components from liquid-based media in accordance with' the invention, preferably the liquid-based media is substantially free of components (such as suspending agents and/or rheology modifiers) which are conventionally incorporated primarily or solely for their ability to counteract sedimentation of particulate solids within the medium.

Conventional inorganic particles, e.g. calcite or agglomerated inorganic particles as disclosed in WO-A-97/30126, will typically have a density which, when measured by Vertical Scan Macroscopic analysis, is at least 10%, more usually 25%, greater than that of the liquid base whereas the density of the co-agglomerate granules of the invention when so measured will on average be substantially the same as, preferably no more than 5% greater than that, of the liquid.

In typical liquid-based media in accordance with said further aspect of the invention the co-agglomerate granules have a density which, when measured by Vertical Scan Macroscopic analysis, is less (or no more than 4% greater) than that of the liquid base - for example up to 10% less than the density of the liquid base.

However, we do not exclude the possibility of the co-agglomerates having a density which in excess of 10% less or more than that of the base since, in this event, there is scope for stable suspension with suitable formulation modifications using relatively low levels of suspension enhancing components such as swelling clays (e.g Laponite ex Laporte Industries) and polyacrylic acid (e.g. Carbopol 943 ex BF Goodrich).

The inorganic content may comprise one or more inorganic particulate materials; where more than one inorganic particulate material is employed they may be chemically and/or physically different.

The inorganic particles may be composed of material selected from the group comprising silicas, especially amorphous silicas, aluminas, calcium carbonates, dicalcium phosphate, tribasic calcium phosphates, hectorites, saponites, aragonites, dolomites, talcites, hydroxytalcites, spangolites, zincites, zincosilicates, insoluble metaphosphates, calcium pyrophosphates, hydroxyapatites, perlites, zeolites, clays, magnesium carbonate, pumice and volcanic ash, or mixtures of two or more of these components.

Examples of mixtures of two or more inorganic particulate materials are silicas plus carbonates, silicas plus dicalcium phosphate, silicas plus perlite, abrasive silicas plus thickening silicas, hydroxyapatites plus silicas or metaphosphates, calcium carbonates plus dicalcium phosphates etc. Particularly preferred are mixtures of lower and higher structure silicas.

The granules may, in addition to the co-agglomerated higher and lower density particles, incorporate other components such that the granules act (for instance by virtue of their porosity and/or friability) as vehicles for carrying and, during use of the medium, releasing or delivering benefit ingredients. The benefit ingredients employed may include substances such as colouring dyes or pigments, cosmetic benefit agents (e.g. silicone oils) or pharmaceutical actives such as salicyclic acid or anti-dandruff actives (e.g. zinc pyrithione) in the case of hair treatment products. If coloured co-agglomerates are required, then suitable coloured pigments, for example pigment dispersions under the Cosmenyl tradename or pigment powders under the Hostaperm trade name or Cosmetic Pink RC 01 ( D & C red No. 30 ) supplied by Ciariant (formerly Hoechst) or Ultramarine Grade 54 supplied by Holliday Pigments, can be added to the composition without affecting the strength of the granule.

Other materials that can be delivered in this way are anti-microbial agents, fragrances and flavours. In the case of dental or oral compositions for instance, the granules may incorporate opacifiers such as titanium dioxide and/or material having a therapeutic affect on the gums or teeth or oral cavity, e.g. an anti-plaque agent such as zinc citrate or stannous pyrophospate, anti-microbial agents such as Triclosan, anti-caries agents such as sodium fluoride and sodium monofluorophosphate, anti-tartar agents such as sodium pyrophosphate and potassium pyrophosphate, and agents such as potassium salts or strontium salts for countering tooth sensitivity.

In some applications, the granules may be so constituted as to be friable under conditions of use of liquid-based media incorporating the granules so that the additional component or components incorporated in the granules may be released in use, for example as disclosed in WO-A-94/12151 , WO-A-96/09033 and WO-A-96/09034, the disclosures of which are incorporated herein by this reference. Also the granular strength of the granules may be in accordance with the teaching of WO-A-97/30126, the entire disclosure of which is incorporated herein by this reference.

In a preferred aspect of the invention, granules are in the form of a granular composition comprising 45 to 99% by weight of a water insoluble particulate of which 5 to 90% is made from a first particulate component which is composed of material selected from said group and has a weight mean particle size of less than 20 micron and an oil absorption capacity from 60 to 180g/100g, and of which

5 to 90% is made from a second particulate component which is composed of material selected from the group consisting of amorphous silicas, low density aluminas and expanded perlites and has a weight mean particle size of less than 20 micron and an oil absorption capacity from 150 to 350g/100g, the granular composition preferably having a particle size, as measured by sieve analysis, of 95% below 1500 micron (more preferably below 1000 micron and most preferably below 800 micron) and 95% above 40 micron (more preferably above 45 micron).

The particle size of the granule can be over a broad range. For example, in dental applications 40 to 600 microns is optimum and for skin treatment formulations particles within the range of 40 to 1000 microns are preferred.

The granules may be produced by any agglomeration or compaction technique. Agglomeration for instance can be achieved by pan granulation, dry roller compaction, extrusion, spray granulation or spinning disc granulation.

The liquid-based medium is preferably in the form of a cosmetic, personal care or personal hygiene formulation in which the granules impart a sensory benefit which is perceivable in use of the formulation for instance by virtue of their size, shape and strength.

Where employed as the low density particle, the gas-encapsulating particles typically have a weight average diameter in the range of 1 to 150 micron, more preferably 10 to 100 micron and even more preferably 10 to 30 micron.

Preferably the gas-encapsulating particles are of the type comprising a polymeric shell enclosing a gas, preferably expanded thermoplastic gas-encapsulating particles of the type described for example in EP -A-56219, EP-A-1 12807, EP-A-320473, EP-A-348372, EP-A-486080 and US-A-3615972, the disclosures of which are incorporated herein by this reference. Such particles are typically produced by suspension polymerisation where a liquid monomer or monomer mixture containing condensed propellant is dispersed in an aqueous medium containing suspending agent and polymerisation catalyst. The resulting microbeads or spheres consist of a polymer shell containing the liquid, volatile propellant. The beads expand by heating to a temperature above the boiling point of the propellant and the softening point of the polymer. The thermoplastic shell of the beads may consist of polymers or copolymers of e.g. vinyl chloride, vinylidene chloride, acryionitrile, methyl methacrylate or styrene or mixtures thereof. The particle size of the unexpanded beads and, hence, of the expanded ones may vary within wide limits; the unexpanded beads may, for example, be 1 micron to 1 mm, preferably 2 micron to 0.5 mm and particularly 5 micron to 50 micron. Upon expansion, the diameter of the microbeads increases by a factor 2 to 5. The propellant suitably makes up 5-30% by weighf of the microbead.

One example of a suitable, commercially available microbead product is Expancel (Registered Trade Mark) which has a thermoplastic shell of a vinylidene chloride/acrylonitrile copolymer and contains iso-butane as propellant. Typically the amount of microbead of the Expancel type employed in the production of the granular material of the invention ranges from 1 to 10%, e.g. from 2 to 8%, by weight of the granular composition.

In another aspect of the invention there is provided a material in the form of granules of high density inorganic particles co-agglomerated with expandable particles comprising a volatile medium encapsulated within a shell of polymeric material.

In this embodiment of the invention expansion of the expandable particles may be implemented (for instance by the application of heat) prior to, subsequent to or at the time of incorporation of the granules in a liquid-based medium, with consequent reduction in density of the granules. According to another aspect of the present invention there is provided a liquid-based medium in which are dispersed inorganic particle agglomerates having a density which, when measured by Vertical Scan Macroscopic analysis, is no more than 4% greater than that of the base liquid.

The invention further encompasses a process for the production of a granular material of controlled density, which process comprises combining particles of one or more high density inorganic materials with density-reducing particles to form co-agglomerates of the high density particles with the density-reducing particles, the density-reducing particles being constituted by particles having a density less than that of water or by precursors of such particles. By "precursors" we mean that particles which in the precursor state may or may not have a density less than that of water but are susceptible to treatment resulting in a reduction in their density to below that of water. Such precursor particles may for instance be of the type described in EP -A-56219, EP-A-1 12807, EP-A-320473, EP-A-348372, EP-A-486080 and US-A-3615972 when in their unexpanded form, expansion and density reduction being effected by the application of heat.

According to yet another aspect of the invention there is provided a process of producing a liquid-based formulation in which particles are suspended substantially without the aid of suspending agents and/or rheology modifiers, said process comprising combining particles of one or more high density inorganic materials with density-reducing particles to form co-agglomerates of the high density particles with the density-reducing particles to allow or cause modification of the density of the granular material consistent with securing suspension of the granules in the formulation in the absence of any suspending agent or rheology modifier, and dispersing the granular material in said formulation. Terminology and Procedures Properties of Expancel particles Density: The density of Expancel particles is measured with an Accupyc 1330 Pycnometer according to Analytical Method MS 29b as referenced in the Expancel (RTM) Product Specification (Issue 95.04) for Expanded Microspheres, issued by Nobel Industries, Sweden and supplied in the UK by Boud Marketing Limited of Laddingford, Kent, England.

Particle size: Particle size of Expancel particles is measured according to the method described in Technical Bulletin No.3 "Particle size of Expancel Microspheres" as referenced in the Expancel (RTM) Product Specification (Issue 95.04), issued by Nobel Industries, Sweden and supplied in the U.K. by Boud Marketing, Laddingford, Kent. The manufacturer/supplier defines particle size for Expancel microspheres as the weight average diameter, which is the same as the weight mean particle size.

Properties of Inorganic Particles Oil absorption : The oil absorption is determined by the ASTM spatula rub-out method (American Society of Test Material Standards D, 281 ). The test is based on the principle of mixing linseed oil with a given weight of the particulate matter, e.g. silica, by rubbing with a spatula until a stiff putty-like paste is formed which will not break or separate when it is cut with a spatula. The oil absorption is then calculated from the volume of oil (V cm³) used to achieve this condition and the weight W in grams of particulate matter by means of the equation:

Oil absorption = (V x 100)/W, i.e. expressed in terms of cm³ oil/100 g particulate matter. Particle Size: The particle size of the particulate material before agglomeration is determined using a Malvern Mastersizer model X, made by Malvern Instruments of

Malvern, Worcestershire, England, with MS15 sample presentation unit. This instrument uses the principle of Fraunhofer diffraction, utilising a low power He/Ne laser. The particulate material is dispersed uitrasonically in water for 7 minutes to form an aqueous suspension, the suspension then being mechanically stirred before carrying out the measurement procedure outlined in the instruction manual for the instrument, using a 45 mm lens in the detector system. The Malvern Particle Sizer measures the weight mean particle size of the particulate material. The weight mean particle size (d₅₀) or 50 percentile; the 10 percentile d₁₀ and 90 percentile d₉₀ are readily obtained from the data generated by the instrument. Properties of the Co-agglomerates Particle Size Distribution by Sieve Analysis: The particle size distribution of the granular composition is carried out using sieve analysis. 100 g of the sample is placed on the top sieve of a series of BS sieves, at approximately 50 micron intervals between 45 and 1000 micron. The sieves are arranged in order with the finest at the bottom and the coarsest at the top of the stack. The sieves are placed in a mechanical vibrator, e.g. Inclyno Mechanical Sieve Shaker by Pascall Engineering Company Limited, covered with a lid and shaken for 10 minutes. Each sieve fraction is accurately weighed and the results calculated: % residue = Weight of residue x 100/Weight of sample

A particle size distribution can then be plotted from the data obtained. Dry Compacted Bulk Density (DCBD): The bulk density of the particle aggregates is determined using a measuring cylinder containing a known weight of particles and measuring the settled particle volume after tapping to constant volume. Between 100ml and 200ml of sample is weighed into a clean dry measuring cylinder and the weight of the sample is noted. The particles are gently loosened to remove air pockets. The cylinder is then placed on a mechanical tapper and tapped for 200 taps. The settled volume on the measuring cylinder is recorded. The compacted bulk density is calculated using the following calculation: Compacted bulk density ( g/ml ) = Weight/Volume

Particle Density (Vertical Scan Macroscopic Analyser): The density of the particle aggregates is determined using a Turbiscan MA 1000 automated, near infrared, vertical scan macroscopic analyser manufactured by Formulaction, Ramonville, France and supplied in the U.K. by Fullbrook Systems, Hertfordshire. The Turbiscan MA1000 carries out step-by-step vertical scanning of the sample and converts the macroscopic aspect of the mixture into graphics. It works in kinetic mode and shows the physical evolution of the sample by simple comparison of graphs. The Turbiscan MA1000 is able to detect accurately and reproducibly particle migration (creaming, sedimentation) and particle aggregation (coalescence, flocculation) at a very early stage in opaque and concentrated colloidal dispersions. The core system in the Turbiscan MA 100 is its reading head which moves vertically along a flat bottomed cylindrical cell. The detection head contains a pulsed near-infrared light source and two synchronous detectors. The transmission detector picks up the light through the sample; the light scattering detector receives the light scattered back from the sample. The reading head scans the entire length of the sample, acquiring transmission and light scattering data every 40um. The signal is first treated by the Turbiscan MA1000 current to voltage convertor. The integrated microprocessor's software handles data acquisistion, analog to digital conversion, data storage, motor control and computer dialogue. Two kinds of light scattering/transmission graph modifications are detected by the Turbiscan MA1000:

1 . Decreases or increases of particular areas of the graphs are often the result of particle migration to the top or bottom of the sample (creaming, sedimentation). In this case, Turbiscan's detectors are only sensitive to particle concentration variations.

2. Conversely, decreases or increases of the complete length of the graph indicate particle or aggregate size variations (coalescence, flocculation). In these cases, particle migration to the top or the bottom of the sample leads to phase separation, which appears on the graph as two superimposed peaks.

A paper presented by Mr Gerard Meunier (Formulaction, France) in the World Surfactants Congress journal, 4th 1996 Vol 4 (pages 300-314) entitled "Turbiscan MA 1000: A new concept in stability analysis of concentrated colloidal dispersions (emulsions, suspensions, foams, gels)" provides further detailed information of the principles involved in this experimental technique.

The particle aggregate samples for particle migration velocity measurement and hence particle density determination were prepared by stirring the particle aggregates with a spatula into a simple liquid base surfactant formulation in which no suspending agent or rheology modifier was included, as detailed in Example 5 of the invention, followed by:

1 . Shaking the samples with a Vortex (IKA minishaker) at l OOOrpm

2. Filling 6ml of the sample in the measurement cell without introducing bubbles, with no sample sticking to the wall of the tube under the meniscus so that the meniscus is well formed 3. Screwing up the top stopper

4. Introducing the measurement cell in the Turbiscan MA1000.

5. Starting the analysis by programming the Turbiscan in automatic scan mode (1 scan/ 2minutes)

The analysis was performed at ambient temperature (19°C) By using the particle migration velocity measurement with the peak width at mid-height software the density of the agglomerates can be indirectly calculated using the Stokes Einstein Law: V = delta r * α * d² 18 * h V = particle migration velocity (ms^"1) delta r = density difference between the 2 phases (kg nr³) g = gravity constant (ms^"2) d = particle diameter (micron) h = continuous phase viscosity (Kg nv¹ s^'1)

Properties of the Liquid Density: The density of the liquid base samples is determined using an Anton Paar Calculating Density meter (DMA.46 ), obtainable from Paar Scientific Ltd, London, England. The instrument is based on the principle of the change of the natural frequency of a hollow oscillator when filled with a different liquid or gas. The mass and thus the density of the liquid changes this natural frequency due to a gross mass change. The instrument is calibrated at 20 °C. The calibration procedure is detailed in the operating manual for the instrument. The sample is injected into the lower hole of the U tube using a plastic tipped syringe until there are no air bubbles. The density of the sample is recorded when the instrument records six consecutive readings that are the same.

The instrument is then rinsed with deionised water and filled with deionised water and the density noted . This should be 1 .0000 +/1 0.0001 . The pump is switched on and the nozzle inserted into the top hole to thoroughly dry the tube and to obtain a minimum reading, which should be 0.0012 +/- 0.0001 . If higher than 0.0013 this indicates the tube is not clean and dry and should be recleaned ready for denisty measurement of the next sample. The invention will now be described further by way of example only with reference to the Examples that follow. Example 1 (comparative)

Two silicas, one of medium bordering on low structure (Sorbosil AC39, obtainable from Crosfield Limited, Warrington, England) and the other of medium structure (Neosyl AC, also obtainable from Crosfield Limited), were blended together in a 3: 1 ratio by weight. The resulting silica blend was agglomerated at 200 g batch size, laboratory scale with deionised water (in a wateπsolids ratio of 1 .1 :1 ) using a Sirman SV6 mixer, supplied by Metcalfe Catering Equipment Limited of Blaenau Ffestiniog, Wales. The resulting wet agglomerate was then dried in an oven at 1 50°C for 4 hours, gently forced through a 500 micron sieve screen and sieved at 106 micron to adjust the particle size distribution.

The silicas obtained had the properties shown in Table 1 below. Table 1

Examples 2 to 5

The following agglomerate compositions were prepared according to the method of Example 1 with the exception that the silicas were initially blended together with an amount of an expanded polymeric gas-containing beads or microspheres, Expancel 461 DE20 (available from Nobel Industries, Sweden through Boud Marketing Limited of Laddingford, Kent, England) to obtain the compositions given in the Table 2 below.

Table 2

The percentages given in Table 2 are on a percent by weight basis.

Each blend so obtained was agglomerated at 200g powder batch size, laboratory scale with deionised water (in a wateπsolids ratio of 1 .1 : 1 ) using a Sirman SV6 mixer, supplied by Metcalfe Catering Equipment Limited of Blaenau Ffestiniog, Wales. The resulting wet agglomerate was then dried in an oven at 150°C for 4 hours, gently forced through a 500 micron sieve screen and sieved at 106 micron to adjust the particle size distribution.

To determine the differences in sedimentation characteristics and hence density, several types of density measurement were carried out on the samples of Examples 1 to 5. Dry Compacted Bulk Density

The differences in density of the samples of the granules prepared according to Examples 1 to 5 were measured using a dry compacted bulk density method (DCBD). The DCBD results obtained are given in Table 3.

Table 3

From these results, it can be seen that the inclusion of small amounts of Expancel particles in the granules produced by blending and agglomeration markedly affects the bulk density of the samples thereby allowing the density of the granules to be tailored according to requirements.

Density in liquid systems

The density of the granules produced by agglomeration (Examples 1 to 5) was measured in a simple base surfactant system in which no suspending agent or rheology modifier was included, density being measured by means of a Vertical Scan

Macroscopic analyser (Turbiscan MA1000, obtainable from Formulaction, Ramonville, France).

The base solution had the following composition:

Component % wt

Ammonium lauryl sulphate¹ (30%) 50.00

Cocamidopropyl betaine² (30%) 15.00 Sodium chloride 2.50 Sample (Ex 1 to 5) 1 .00 Preservatives qs Deionised water balance to 100% Manro ALS30 ( ex Hickson-Manro Ltd )

²Emigen BS/P ( ex. Albright and Wilson )

The density of the base solution is 1 .038g/ml, measured using a density meter. The average particle size of the aggregates is 300 microns and the base viscosity is -JOOcps, which is required for calculation of agregate density using Stokes Einstein law.

In the samples containing Examples 1 - 5, two kinds of phenomena appear: For Examples 1 and 2, a back-scattering increase at the bottom of the samples and a back-scattering decrease at the middle and top of the samples. These back-scattering variations are characteristic of a sedimentation phenomenon.

For examples 3, 4 and 5, a back-scattering increase at the top of the samples and a back-scattering decrease at the middle and bottom of the samples. These back-scattering variations correspond to a creaming process.

The destabilisation kinetics were followed using the mid-height peak thickness measurement of the clarification area over or below the sediment or cream layer. This method allows measurement of sedimentation or creaming fronts and so permits determination of the particle migration velocity. By using the particle migration velocity measurement with the peak width at mid-height and applying the Stokes Einstein law the density of the aggregates were calculated as recorded in Table 4.

Table 4

Again it can be seen that the co-agglomeration of Expancel microspheres with the silica particles readily allows the density of the granules to be modified (radically if desired) and hence tailored according to requirements. In particular, the co-agglomeration of the Expancel microspheres with the inorganic particles gives ample scope for the optimisation of the granule density for a given base system and for the elimination of auxiliary suspending agents or rheology modifiers as used in the prior art. This is further illustrated by Example 6 below. Example 6

The following base liquid surfactant system was prepared in which inorganic materials according to Examples 1 to 5 were used. No thickeners and/or suspending agents were included in this base formulation. Component %wt

Ammonium lauryl sulphate¹ ( 30% ) 50.00 Cocamidopropyl betaine² (30%) 2.00 Preservatives, fragrance qs Sample (Ex 1 to 5) 5.00 Deionised water balance to 100%

The density of the liquid base in this case is 1 .0193, measured using a density meter.

The sedimentation characteristics of the inorganic materials prepared according to Examples 1 to 5 in the base formulation were observed visually and are recorded in Table 5 below.

Table 5

From Table 5, it can be seen that for a given liquid base, the density of the granules can be controlled by addition of Expancel microspheres so as to avoid settlement of the granules. It can be concluded that the density of Example 3 aggregates matches that of the liquid base employed in Example 6 as the Example 3 aggregates were stably suspended without the need for auxiliary suspending agents or rheology modifiers.

Claims

1 . A material in the form of granules of high density inorganic particles co-agglomerated with particles having a density lower than that of water.

2. A material as claimed in Claim 1 in which the lower density particles have a density in the range from 0.01 to 0.4 g/ml.

3. A material as claimed in Claim 1 in which the lower density particles have a density in the range from 0.015 to 0.25 g/ml.

4. A material as claimed in Claim 1 in which the lower density particles have a density in the range from 0.02 to 0.15 g/ml.

5. A material as claimed in any one of Claims 1 to 4 in which the lower density particles are in the form of low density, gas-encapsulating particles.

6. A material as claimed in any one of Claims 1 to 4 in which the lower density particles comprise polyethylene particles.

7. A liquid-based medium containing material according to any one of Claims 1 to 6, the granules being dispersed throughout said medium.

8. A medium as claimed in Claim 7 in which the liquid base is substantially free of suspending or thickening agents.

9. A medium as claimed in Claim 7 or 8 in which the high density particles constitute the primary particle in terms of imparting a particular attribute, e.g. a sensory attribute, to the liquid-based composition.

10. A medium as claimed in Claim 7 or 8 in which the low density particles constitute the primary particle in terms of imparting a particular attribute, e.g. a sensory attribute, to the liquid-based composition.

1 1 . A medium as claimed in any one of Claims 7 to 10 in which the low density particles will constitute up to 20% by weight of the granular composition.

12. A medium as claimed in any one of Claims 7 to 10 in which the co-agglomerate granules have a density which, when measured by Vertical Scan Macroscopic analysis, is less than that of the liquid base.

13. A material or medium as claimed in any one of the preceding claims in which the inorganic particles are selected from the group comprising silicas, especially amorphous silicas, aluminas, calcium carbonates, dicalcium phosphate, tribasic calcium phosphates, hectorites, saponites, aragonites, dolomites, talcites, hydroxytalcites, spangolites, zincites, zincosilicates, insoluble metaphosphates, calcium pyrophosphates, hydroxyapatites, perlites, zeolites, clays, magnesium carbonate, pumice and volcanic ash, or mixtures of two or more of these components.

14. A material or medium as claimed in any one of the preceding claims in which the granules have a granular composition comprising 45 to 99% by weight of a water insoluble particulate of which

5 to 90% is made from a first particulate component which is composed of material selected from said group and has a weight mean particle size of less than 20 micron and an oil absorption capacity from 60 to 180g/100g, and of which

5 to 90% is made from a second particulate component which is composed of material selected from the group consisting of amorphous silicas, low density aluminas and expanded perlites and has a weight mean particle size of less than

20 micron and an oil absorption capacity from 150 to 350g/100g.

15. A material or medium as claimed in Claim 14 in which the granular composition having a particle size, as measured by sieve analysis, of 95% below 1500 micron and 95% above 40 micron.

16. A liquid-based medium in which are dispersed inorganic particle agglomerates having a density which, when measured by Vertical Scan Macroscopic analysis, is no more than 4% greater than that of the base liquid.

17. A medium as claimed in any one of Claims 7 to 16 in the form of a lotion, cream, gel, mouthwash or low viscosity dentrifice.

18. A material in the form of granules of high density inorganic particles co-ag╧äjlomerated with expandable particles comprising a volatile medium encapsulated within a shell of polymeric material.

19. A process for the production of a granular material of controlled density, which process comprises combining particles of one or more high density inorganic materials with density-reducing particles to form co-agglomerates of the high density particles with the density-reducing particles, the density-reducing particles being constituted by particles having a density less than that of water or by precursors of such particles.

20. A process of producing a liquid-based formulation in which particles are suspended substantially without the aid of suspending agents and/or rheology modifiers, said process comprising combining particles of one or more high density inorganic materials with density-reducing particles to form co-agglomerates of the high density particles with the density-reducing particles to allow or cause modification of the density of the granular material consistent with securing suspension of the granules in the formulation in the absence of any suspending agent or rheology modifier, and dispersing the granular material in said formulation.