EP2243822A1

EP2243822A1 - Detergent powder with high active detergent particles

Info

Publication number: EP2243822A1
Application number: EP09158719A
Authority: EP
Inventors: designation of the inventor has not yet been filed The
Original assignee: Unilever PLC
Current assignee: Unilever PLC
Priority date: 2009-04-24
Filing date: 2009-04-24
Publication date: 2010-10-27

Abstract

A detergent powder composition comprising a minor part of high active detergent particles comprising surfactant blends with a major amount of linear alkylbenzene sulphonate anionic surfactant wherein the high active detergent particles comprise less than 40 wt% of the detergent composition and have an average volume at least ten times the average volume of the particles comprising the residue of the detergent powder composition, which comprises at least 40 wt% base powder, the balance of the composition comprising post dosed material.

Description

This invention relates to a detergent powder comprising a minor part of high active granules comprising surfactant blends with a major amount of linear alkylbenzene sulphonate anionic surfactant.

BACKGROUND AND PRIOR ART

To reduce the chemicals used in the laundry washing process it has been proposed to decrease the builder salts in laundry detergent formulations. Without other formulation changes, this reduction could adversely affect the performance of the composition in hard water. It has been proposed to ameliorate this problem by using surfactant blends that are tolerant of the presence of hardness ions in the wash water, in particular blends tolerant to calcium ions. These surfactant blends have been termed "calcium tolerant surfactant blends".
For the detergent formulator use of such calcium tolerant surfactant blends poses a new problem. Builder materials have often been included in the formulation not only to provide hard water detergency performance, but also to enable efficient manufacture of free flowing granular detergent formulations. Thus, reduction of builders in a formulation, whilst leaving it in the form of free flowing particles, is not straightforward.
Extrusion of detergent compositions is known. WO9932599 describes a method of manufacturing laundry detergent particles, being an extrusion method in which a builder and surfactant, the latter comprising as a major component a sulphated or sulphonated anionic surfactant, are fed into an extruder, mechanically worked at a temperature of at least 40 °C, preferably at least 60°C, and extruded through an extrusion head having a multiplicity of extrusion apertures. In most examples, the surfactant is fed to the extruder along with builder in a weight ratio of more than 1 part builder to 2 parts surfactant. The extrudate apparently required further drying. In Example 6, PAS paste was dried and extruded. Such PAS noodles are well known in the prior art. The noodles are typically cylindrical in shape and their length exceeds their diameter, as described in example 2.
GB1303479 describes the formation of a water-soluble cleaning composition by extrusion of particles of length 0.5-10 mm. and cross-sectional area 0.04-0.8 mm² each comprising (a) a higher (C_9-18) alkyl aryl sulphonate, (b) a lower (C_1-3) alkyl benzene sulphonate, (c) an inorganic salt and (d) water. In one embodiment (Example 1), the dry ingredients are ground together in a mill, mixed with wet ingredients in a ribbon amalgamator and milled into ribbons, which are carried by conveyer belt to a plodder. The plodder is equipped with a wire mesh of 0.5 mm. openings and a perforated plate having holes, which taper from 12 to 16 mm, with the larger diameter at the exit. The material is extruded through the plate, cooled by an air jet and then carried on a conveyer belt through a further air flow to a granulator fitted with an 8-mesh screen, which breaks the extruded strands into the required lengths. This document proposes the addition of sodium aryl sulphonate as a hydrotrope, to get fast dissolution. Thus, in the examples, there are comparatively low levels of surfactants in order to make space for the high levels of hydrotrope and builders. The drying process appears to happen post-extrusion. The particles have small cross-sectional area and are relatively long at 3 to 4 mm.
Surfactant blends comprising linear alkylbenzene sulphonate (LAS) and at least one co-surfactant have been shown to provide excellent detergency, even in the presence of hardness ions. However, these blends tend to be soft and lead to sticky compositions that cake upon storage. One solution to this caking problem is to enclose the detergent in a rigid capsule as proposed in WO2006/002755 . This solution is excellent for use in washing machines but it has drawbacks when the dose needs to be fine tuned for the amount of laundry or water used, as is often the case for hand washing of laundry. Thus, the present inventors sought a solution to the problem of caking of detergent compositions comprising high active surfactant blends with a major part of LAS, which did not need a special unit dose storage container for the detergent composition.

Summary of the Invention

According to the present invention there is provided a detergent powder composition comprising a minor part of high active detergent particles comprising surfactant blends with a major amount of linear alkylbenzene sulphonate anionic surfactant wherein the high active detergent particles comprise less than 40 wt% of the detergent composition and have an average volume at least ten times the average volume of the particles comprising the residue of the detergent powder composition, which comprises at least 40 wt% base powder, the balance of the composition comprising post dosed granules.
If the high active detergent particles are used up to a maximum level of less than 40 wt%, preferably less than 30 wt% and even more preferably 20 wt% or less, in the powder it is found not to exhibit excessive stickiness and it remains evenly dispersed throughout the composition and does not cause the composition to cake. Thus, the level of surfactant can be increased without the usual need for a similar increase in unwanted builder salts, or other inorganic material. To achieve this it is preferred that the high active particles are uncoated as this lowers the complexity of their processing and eliminates the introduction of unwanted coating materials into the composition. However, coating is potentially advantageous to avoid stickiness at the higher levels of inclusion and to impart a contrasting and pleasing visual appearance to the particles.
The high active detergent particles may advantageously be manufactured by a process comprising the steps of:

a) forming a liquid surfactant blend comprising a major amount of surfactant and a minor amount of water, the surfactant part consisting of at least 51 wt% linear alkylbenzene sulfonate and at least one co-surfactant, the surfactant blend consisting of at most 20 wt% nonionic surfactant;
b) drying the liquid surfactant blend of step (a) in an evaporator or drier to a moisture content of at most 2 wt% and cooling the output from the evaporator or dryer;
c) feeding the cooled material, which output comprises at least 93 wt%, preferably 95 wt%, more preferably 96 wt%, even more preferably 97 wt% and most preferably 98 wt% surfactant blend with a major part of LAS, to an extruder, optionally along with less than 10 wt%, preferably less than 5 wt%, of other materials such as perfume, fluorescer, and extruding the surfactant blend to form an extrudate while periodically cutting the extrudate to form hard detergent particles with a diameter across the extruder of greater than 2 mm and a thickness along the axis of the extruder of greater than 0.2 mm, provided that the diameter is greater than the thickness;
d) optionally, coating the extruded hard detergent particles with up to 30 wt% coating material selected from powdered inorganic material and mixtures of such material and nonionic material with a melting point in the range 40 to 90 °C.

Preferably, the co-surfactant is chosen from the group consisting of: SLES, and nonionic, together with optional soap and mixtures thereof. The only proviso is that when nonionic is used the upper limit for the amount of nonionic surfactant has been found to be 20 wt% of the total surfactant to avoid the dried material being too soft and cohesive to extrude because it has a hardness value less than 0.5 MPa.
The blend fed to the evaporator or drier is a liquid surfactant blend comprising a major amount of surfactant and a minor amount of water, preferably at least about 60 wt%, most preferably at least about 70 wt% surfactant and preferably at most about 40 wt%, most preferably at most 30 wt% water, the surfactant part consisting of at least 51 wt% linear alkyl benzene sulphonate salt (LAS) and at least one co-surfactant;
The liquid surfactant blend is dried to form a dried material with surfactant content of at least 98 wt% and a moisture content of at most 2 wt%, preferably at most 1.5 wt%, more preferably at most 1.2 wt% and most preferably less than 1 wt%.
Drying may suitably be carried out using a wiped film evaporator or a Chemithon turbo tube drier.
Optionally the dried material from step (b) may be milled in a mill to form particles of less than 1.5 mm average diameter, preferably less than 1 mm average diameter, before it is fed to the extruder. Optionally 0.5 to 5 wt% preferably 0.5 to 3 wt% (based on output from the mill), powdered mill aid, preferably with particle size 0.1 to 10 µm, such as Aerosil®, Alusil®, or Microsil®, is also added to the mill; the blended milled output of the mill comprising at least 95 wt% surfactant blend, with a major part of LAS;
The dried, cooled and optionally milled material is fed to the extruder, optionally along with minor amounts (less than 10, preferably less than 5wt% total) of other materials such as perfume and /or fluorescer, and the mixture is extruded to form an extrudate with a diameter of greater than 2 mm, preferably greater than 3 mm, more preferably greater than 4 mm and preferably with a diameter of less than 7 mm, most preferably less than 5 mm, while periodically cutting the extrudate to form hard detergent particles with a maximum thickness of greater than 0.2 mm and less than 3 mm, preferably less than 2 mm, most preferably less than about 1.5 mm and more than about 0.5 mm, even 0.7 mm. Whilst the preferred extrudate is of circular cross section, the invention also encompasses other cross sections such as triangular, rectangular and even complex cross sections, such as one mimicking a flower with rotationally symmetrical "petals". Indeed the invention can be operated on any extrudate that can be forced through a hole in the extruder or extruder plate; the key being that the average thickness of the extrudate should be kept below the level where dissolution will be slow. As discussed above this is a thickness of about 2 mm. Desirably multiple extrusions are made simultaneously and they may all have the same cross section or may have different cross sections. Normally they will all have the same length as they are cut off by the knife. The cutting knife should be as thin as possible to allow high speed extrusion and minimal distortion of the extrudate during cutting. The only major constraint that we have found for the surfactant blend extrusion is that the extrusion should take place at a temperature of less than 45°C, preferably less than 40°C to avoid stickiness and facilitate cutting. The other major point to note is that the extrudates according to the present process are cut so that their major dimension is across the extruder and the minor dimension is along the axis of the extruder. This is the opposite to the normal extrusion of surfactants. Cutting in this way increases the surface area that is a "cut" surface. It also allows the extruded particle to expand considerably along its axis after cutting, whilst maintaining a relatively high surface to volume ratio, which is believed to increase its solubility and also results in an attractive biconvex, or lentil, appearance. Elsewhere we refer to this shape as an oblate spheroid. This is essentially a rotation of an ellipse about its minor axis.
It is surprising that at very low water contents the LAS containing surfactant blends can be extruded to make solid detergent particles that are hard enough to be used without any need to be structured by inorganic materials or other structurants as commonly found in prior art extruded detergent particles. Thus, the amount of surfactant in the detergent particle can be much higher and the amount of builder in the detergent particle can be much lower.
If coating of the high active detergent particles is required it may be accomplished by either:

(i) transferring the extruded particles to a fluid bed and spraying onto them up to 30wt% (based on coated detergent particle) of powdered inorganic material in aqueous solution and drying off the water; or
(ii) dry coating with up to 30wt% of a water soluble or insoluble particulate of mean PSD <100 µm followed by spraying with either aqueous or non-aqueous liquid and optionally drying/cooling.

If the coating material is not contributing to the wash performance of the composition then it is desirable to keep the level of coating as low as possible, preferably less than 20wt%, more preferably less than 15wt% or even 10wt% or as low as 5wt%, especially for larger extruded particles with a surface area to volume ratio of greater than 4 mm^-1.
Surprisingly we have found that at low coating levels the appearance of the coating is very pleasing. Without wishing to be bound by theory, we believe that this high quality coating appearance is due to the smoothness of the underlying extruded and cut particle. By starting with a smooth surface, we unexpectedly found it easy to obtain a high quality coating finish (as measured by light reflectance and smoothness) using simple coating techniques.
When the particle is coated it is preferred if the coating is coloured. Particles of different colours may be used in admixture, or they can be blended with contrasting base powder and or post dosed materials. Of course, particles of the same colour as one another may also be used to form a full composition. As described above the coating quality and appearance is very good due to the excellent surface of the cut extrudates onto which the coating is applied in association with the large particle size and S/V ratios of the preferred particles.
It is particularly preferred that the detergent particles comprise perfume. The perfume may be added into the extruder or premixed with the surfactant blend in the mill, or in a mixer placed after the mill, either as a liquid or as encapsulated perfume particles. In an alternative process, the perfume may be mixed with a nonionic material and blended. Such a blend may alternatively be applied by coating the extruded particles, for example by spraying it mixed with molten nonionic surfactant. Perfume may also be introduced into the composition by means of a separate perfume granule and then the detergent particle does not need to comprise any perfume.

Detailed description of the invention

The Surfactant Blend

Surfactant blends that do not require builders to be present for effective detergency in hard water are preferred. Such blends are called calcium tolerant surfactant blends if they pass the test set out hereinafter. However, the invention may also be of use for washing with soft water, either naturally occurring or made using a water softener. In this case, calcium tolerance is no longer important and blends other than calcium tolerant ones may be used.
Calcium-tolerance of the surfactant blend is tested as follows:

The surfactant blend in question is prepared at a concentration of 0.7 g surfactant solids per litre of water containing sufficient calcium ions to give a French hardness of 40 (4 x 10^-3 Molar Ca²⁺). Other hardness ion free electrolytes such as sodium chloride, sodium sulphate, and sodium hydroxide are added to the solution to adjust the ionic strength to 0.05M and the pH to 10. The adsorption of light of wavelength 540 nm through 4 mm of sample is measured 15 minutes after sample preparation. Ten measurements are made and an average value is calculated. Samples that give an absorption value of less than 0.08 are deemed to be calcium tolerant.

Examples of surfactant blends that satisfy the above test for calcium tolerance include those having a major part of LAS surfactant (which is not of itself calcium tolerant) blended with one or more other surfactants (co-surfactants) that are calcium tolerant to give a blend that is sufficiently calcium tolerant to be usable with little or no builder and to pass the given test. Suitable calcium tolerant co-surfactants include SLES 1-7EO, and alkyl ethoxylate non-ionic surfactants, particularly those with melting points less than 40°C. calcium tolerant blends are already well known in the literature. In a further refinement of the surfactant system it has been found that calcium tolerant LAS systems formed by the addition of SLES or High chain-length nonionic often require use of a third surfactant to more closely match the cleaning performance of fully built detergent systems. Suitable third surfactants include betaines, amine oxides, and cationics, such as the Praepagen® materials from Clariant.
A LAS SLES surfactant blend has a superior foam profile to a LAS Nonionic surfactant blend and is therefore preferred for hand washing formulations requiring high levels of foam. SLES may be used at levels of up to 30%.
Addition of a nonionic surfactant (5-20%) to LAS changes the behaviour of the surfactant blend in the dryer. This gives a surprising increase in throughput. Nonionic 7EO may be used at levels of between 5 and 20 % based on dry surfactant. NI 30EO may be used at levels of up to 20%.

Material Characteristics of the Surfactant Blends

To enable sufficient Calcium tolerance for LAS blends an additional surfactant material such as SLES or Nonionic surfactant is added. The level that needs to be added to achieve calcium tolerance for the LAS rich blend varies according to the exact surfactant system but the effect can easily be tested to arrive at a suitable level for calcium tolerance. The added non-LAS surfactants should also be liquid-like and not exceed 50wt% of the total surfactant, the balance of surfactant being LAS. Preferred added surfactants are selected from Nonionic 7EO and/or Nonionic 30EO and /or SLES and/or PAS.
The structuring of the surfactant blend is done by the LAS. This eliminates the need for the usual inorganic structurant, such as silicate However, such an approach is found to require the surfactant blend to be dried to very low moisture contents of at most 2 wt%, preferably at most 1.5 wt% and most preferably at most 1 wt%. At these moisture levels, a high active mixed surfactant detergent particle with dimensional integrity and free flowing behaviour can be extruded.
Increasing the nonionic content within the LAS rich surfactant blend reduces the hardness of the dried blend. Hardness is also related to moisture content of the dried blend. The maximum nonionic level that can be included is about 20%, above this the dried blend is too soft to mill before the extruder, or cut after the extruder. The minimum inclusion level of nonionic in a LAS /nonionic binary blend is about 5%.
A preferred detergent composition has a LAS/SLES surfactant blend. However, the replacement of 20% of the LAS with PAS results in a product with improved storage stability and a similar cleaning profile.

Processing

Blending

The surfactants are mixed together before being input to the drier. Conventional mixing equipment is used.

Drying

To achieve the very low moisture content of the surfactant blend, scraped film devices may be used. A preferred form of scraped film device is a wiped film evaporator. One such suitable wiped film evaporator is the "Dryex system" based on a wiped film evaporator available from Ballestra S.p.A.. Alternative drying equipment includes tube-type driers, such as a Chemithon drier, and soap driers.

Chilling and milling

The hot material exiting the scraped film drier is subsequently cooled and broken up into suitable sized pieces to feed to the extruder. Simultaneous cooling and breaking into flakes may conveniently be carried out using a chill roll. If the flakes from the chill roll are not suitable for direct feed to the extruder then they can be milled in a milling apparatus and /or they can be blended with other liquid or solid ingredients in a blending and milling apparatus, such as a ribbon mill. Such milled or blended material is desirably of particle size 1 mm or less for feeding to the extruder.
It is particularly advantageous to add a milling aid at this point in the process. Particulate material with a mean particle size of 10 nm to 10 µm is preferred for use as a milling aid. Among such materials, there may be mentioned, by way of example: aerosil®, alusil®, and microsil®.

Extruding and cutting

The extruder provides further opportunities to blend in ingredients other than surfactants, or even to add further surfactants. However, it is generally preferred that all of the anionic surfactant, or other surfactant supplied in admixture with water; i.e. as paste or as solution, is added into the drier to ensure that the water content can then be reduced and the material fed to and through the extruder is sufficiently dry. Additional materials that can be blended into the extruder are thus mainly those that are used at very low levels in a detergent composition: such as fluorescer, shading dye, enzymes, perfume, silicone antifoams, polymeric additives and preservatives. The limit on such additional materials blended in the extruder has been found to be about 5 wt%. Solid additives are generally preferred. Liquids, such as perfume may be added at levels up to 2.5 wt%, preferably up to 1.5 wt%.
The output from the extruder is shaped by the die plate used. The extruded material has a tendency to swell up in the centre relative to the periphery. We have found that if a cylindrical extrudate is regularly sliced as it exits the extruder the resulting shapes are short cylinders with two convex ends. These particles may be described as oblate spheroids. This shape is pleasing visually and its slightly rounded appearance also contributes to improved flow properties of the extruded particles in bulk.
The sliced output from the extruder can be used as is, especially if it is dosed into a powder formulation. If used up to a maximum level of less than 40wt%, preferably less than 30 wt% and even more preferably 20 wt% or less, in the powder it is found not to exhibit excessive stickiness and it remains evenly dispersed throughout the composition and does not cause the composition to cake. Thus, the level of surfactant can be increased without the usual need for a similar increase in unwanted builder salts, or other inorganic material.

Coating

A variant of the process takes the sliced extruded particles and coats them. This allows the particles to be coloured easily. It also further reduces the stickiness to a point where the particles are free flowing which makes them easier to process and transport.
By coating such large extruded particles the thickness of coating obtainable by use of a coating level of say 5 wt% is much greater than would be achieved on typically sized detergent granules (0.5-2mm diameter sphere).
The extruded particles can be considered as oblate spheroids with a major radius "a" and minor radius "b". Hence, the surface area(S) to volume (V) ratio can be calculated as: $\frac{S}{V} = \frac{3}{2 b} + \frac{3 b}{4 \in a^{2}} \ln (\frac{1 + \in}{1 - \in}) {mm}^{- 1}$

When ∈ is the eccentricity of the particle.
For optimum dissolution properties, this surface area to volume ratio must be greater than 3 mm^-1. However, the coating thickness is inversely proportional to this coefficient and hence for the coating the ratio "Surface area of coated particle" divided by "Volume of coated particle" should be less than 15 mm^-1.
By using the process of the invention, a more effective coating can be obtained at a lower level of coating material. It is particularly advantageous to use a coating deposited by crystallisation from an aqueous solution as this appears to give positive dissolution benefits and the coating gives a good colour to the detergent particle, even at low deposition levels. An aqueous spray-on of the coating solution in a fluidised bed has been found to give good results and may also generate a slight rounding of the detergent particles during the fluidisation process.
Suitable coating solutions include sodium carbonate, possibly in admixture with sodium sulphate, and sodium chloride. Food dyes, shading dyes, fluorescer and other optical modifiers can be added to the coating by dissolving them in the spray-on solution or dispersion. Use of a builder salt such as sodium carbonate is particularly advantageous because it allows the detergent particle to have an even better performance by buffering the system in use at an ideal pH for maximum detergency of the anionic surfactant system. It also increases ionic strength, which is known to improve cleaning in hard water, and it is compatible with other detergent ingredients that may be admixed with the coated extruded detergent particles. If a fluid bed is used to apply the coating solution, the skilled worker will know how to adjust the spray conditions in terms of Stokes number and possibly Akkermans number (FNm) so that the particles are coated and not significantly agglomerated. Suitable teaching to assist in this may be found in EP1187903 , EP993505 and Powder technology 65 (1991) 257-272 (Ennis).
Another coating technique that may be used is to first dry-coat the extruded particle surface with a layer of electrolyte with mean diameter less than 100 µm using a simple drum-type mixer and subsequently to use an aqueous spray to harden this layer. Drying and/or cooling may be needed to finish the process. The aqueous spray may be replaced by an organic melt using a high melting point nonionic surfactant or nonionic material. In this case, no drying is necessary but cooling may be needed.
It will be appreciated by those skilled in the art that multiple layered coatings, of the same or different coating materials, could be applied, but a single coating layer is preferred, for simplicity of operation, and to maximise the thickness of the coating. The amount of coating should lay in the range 3 to 50 wt% of the particle, preferably 20 to 40 wt% for the best results in terms of anti-caking properties of the detergent particles.

The extruded high active detergent particles

Whether coated or uncoated the particles dissolve easily in water and leave very low or no residues on dissolution, due to the absence of insoluble structurant materials such as zeolite. When they are coated, the particles have an exceptional visual appearance, due to the smoothness of the coating coupled with the smoothness of the underlying particles, which is also believed to be a result of the lack of particulate structuring material in the extruded particles.

The powder composition

In addition to the high active detergent particles the composition comprises base powder and post dosed material. The base powder will typically be granular and have an average particle size in the range 0.5 to 2 mm. It may be manufacture by a conventional spray drying or non-tower process. Its formulation may be any typical laundry detergent base powder formulation. Similarly, the post dosed materials may be any of those conventionally used in laundry detergents. It may take the form of a granule or a so called visual cue, which may be an elongated or shaped particle or even a film particle. The base powder and the post dosed materials may be white or coloured.
The invention will now be further described by way of example only.

In the examples, the following nomenclature is used:

LAS	-	means neutralised LAS acid (LABSA)
LAB	-	means the "liner" alkylate
LABSA	-	means LAS acid.
PAS	-	means primary alkyl sulphate
SCMC	-	Sodium carboxymethyl cellulose
SLES (XEO)	-	means sodium lauryl ether sulphate (X moles average ethoxylation)

Test parameters used in the examples are defined and determined in accordance with the following:

Unconfined Compression Test (UCT)

In this test, freshly produced detergent composition was compressed into a compact and the force required to break the compact was measured. The detergent composition was loaded into a cylinder and the surface levelled. A 50 g plastic disc was placed on top of the detergent composition and a 10 kg weighted plunger was placed slowly on top of the disc and allowed to remain in position for 2 minutes. The weight and plunger were then removed and the cylinder removed carefully from the detergent composition to leave a free-standing cylinder of detergent composition with the 50g plastic disc on top of it. If the compact were unbroken, a second 50 g plastic disc was placed on top of the first and left for approximately ten seconds. Then if the compact were still unbroken, a 100 g disc was added to the plastic discs and left for ten seconds. Then the weight was increased in 250g increments at 10 second intervals until the compact collapsed. The total weight needed to effect collapse was noted.
For freshly made detergent composition tested under ambient temperature conditions, the cohesiveness of the detergent composition was classified by the weight (w) as follows, (assuming the standard 10.0 kg compaction load is used).

w < 1 kg Good flowing.

1 kg < w < 2 kg Moderate flowing.

2 kg < w < 5 kg Cohesive.

5 kg < w Very cohesive.

Dynamic Flow Rate (DFR)

Dynamic Flow Rate (DFR) in ml/sec. was measured using a cylindrical glass tube having an internal diameter of 35 mm and a length of 600 mm. The tube was securely clamped with its longitudinal axis vertical. Its lower end was terminated by means of a smooth cone of polyvinyl chloride having an internal angle of 15 DEG and a lower outlet orifice of diameter 22.5 mm. A beam sensor was positioned 150 mm above the outlet, and a second beam sensor was positioned 250 mm above the first sensor.
To determine the dynamic flow rate of a detergent composition sample, the outlet orifice was temporarily closed, for example, by covering with a piece of card, and detergent composition was poured into the top of the cylinder until the detergent composition level was about 100 mm above the upper sensor. The outlet was then opened and the time t (seconds) taken for the detergent composition level to fall from the upper sensor to the lower sensor was measured electronically. The DFR is the tube volume between the sensors, divided by the time measured.

Bulk Density (BD)

"Bulk density" means the bulk density of the whole detergent composition in the uncompacted (untapped) aerated form. It was measured by taking the increase in weight due to filling a 1 litre container with the detergent composition.

Equilibrium Relative Humidity (ERH)

Water activity (usually given the parameter Aw) is related to equilibrium relative humidity (%ERH) by the equation: $ERH = 100 x Aw$
Aw = equilibrium partial pressure of moisture/saturation partial pressure of moisture at that temp.
A value for water activity of 1 (ERH=100) indicates pure water, whereas zero indicates total absence of water.

Example 1

Surfactant raw materials were mixed together to give a 67wt% active paste comprising 56.5 parts LAS, 15.2 parts PAS and 28.3 parts SLES.
Raw Materials used were:

LABSA
Caustic (48% Solution)
PAS
SLES (3E0) Stepan BES70

The paste was pre-heated to the feed temperature and fed to the top of a wiped film evaporator to reduce the moisture content and produce a solid intimate surfactant blend, which passed the calcium tolerance test. The conditions used to produce this LAS/PAS/SLES blend are given in Table 1. Table 1

Jacket Vessel Temp. 80 °C

Feed Nominal Throughput 65 kg/hr

Temperature 70 °C

Density 1.2 kg/l

Product Moisture (KF*) 1.0 %

Free NaOH 0.16 %

*analysed by Karl Fischer method
On exit from the base of the wiped film evaporator, the dried surfactant blend dropped onto a chill roll, where it was cooled to less than 30°C.
After leaving the chill roll, the cooled dried surfactant blend particles were milled using a hammer mill, 2% Aerosil® was also added to the hammer mill as a mill aid. The resulting milled material is hygroscopic and so it was stored in sealed containers. Its properties are given in table 2. Table 2

ERH Phys Props Particle size

UCT DFR BD D(50) >180 >1400

kg ml/s g/l µm µm (%) µm (%)

8.7 1.9 70/71 558 342.97 33.0 3.38
The cooled dried milled composition was fed to a twin-screw co-rotating extruder fitted with a shaped orifice plate and cutter blade.
The average particle diameter and thickness of samples of the extruded particles were found to be 4.46 mm and 1.13 mm respectively. The standard deviation was acceptably low.

The particles were then coated using a Strea 1 fluid bed. The coating was added as an aqueous solution and coating completed under conditions given in Table 3. Coating wt% is based on weight of the coated particle.

Table 3

Target	5wt%	10wt%	15wt%
coating
Level
Mass Solid	1.25	1.25	1.25
[kg]
Coating	Sodium	Sodium	Sodium
Solution	Carbonate	Carbonate	Carbonate
	(25%)	(25%)	(25%)
	Dye	Dye	Dye
	(0.1%)	(0.1%)	(0.1%)
Mass Coating	0.263	0.555	0.882
Solution
[kg]
Air Inlet	80	80	80
Temperature
[°C]
Air Outlet	42	40	41
Temperature
[°C]
Coating Feed	14	15	15
Rate [g/min]
Coating Feed	38	41	40
temperature
[°C]

As can be seen from Table 3 the samples have different coating levels. These samples and additional samples made using the same process were then equilibrated at 48 and 65% relative humidity and their hardness measured. The hardness measurements are shown in Table 4. Table 4

Coating Average Average

Level Hardness Hardness

20°C / 21°C /

48%RH 65%RH

(%) (MPa) (MPa)

5 0.07 0.03

10 0.19 0.06

15 0.40 0.22

25 0.85 0.59

Example 2

Conventional detergent base powder containing sodium linear alkyl sulphonate (LAS) as surfactant and sodium tripolyphosphate as builder was dry mixed with uncoated extruded particles made according to the first part of the process of example 1 and using a blend of LAS/PAS/SLES with ratio 58.3/14.6/27. The extruded particles used had a circular cross section with average diameter 5 mm and average maximum thickness 1 mm.
The mixtures of detergent powder and extruded particles were sealed in conventional unlaminated cardboard packs and stored at 28°C and 70% Relative Humidity for 4 weeks. Packs were examined periodically to determine how much caking had occurred by pouring the product from the pack onto a tray and visually estimating the percentage of lumped powder. Examples 5A, 5B and 5C in Table 5 correspond to extruded particle levels of 0, 20 and 40% by weight based on the combined weight of particles and powder.
The results in Table 5 show that powders containing up to and including 20 wt% uncoated extruded particles according to the invention are storage stable, but above that level and at some point below 40 wt% extruded particles, the mixture with base powder becomes unstable on storage. Table 5

Example Weight% of extrudates in pack Caking ex-pack week 2 Caking ex-pack week 4

5A 0 <25% <50%

5B 20 <25% <50%

5C 40 >75% >75%
Similar results are obtained with base powders including zeolite and/or carbonate in place of the sodium tripolyphosphate.

Example 3

This example shows that the superior appearance of the extruded particles is due to the uncoated particle being smoother than conventional detergent particles and the final surface being smoother still. This need for the underlying surface to be smooth before a coating is applied is known generally but it was nevertheless surprising just how improved the coated particles appear compared with other conventional detergent particles. The underlying smoothness of the extruded particles is thought to be assisted by their not containing solid structuring materials, unlike prior art extruded particles. The particles are also superior in appearance when compared to prior art granules made by other processes.
In order to determine the value of Ra (average surface roughness) for each particle sample we used a non contact optical profilometer equipment comprising a low powered near-infrared Laser Stylus mounted on a moveable stage controlled by a computer. A Laser stylus is a displacement transducer based on technology found in a compact disc player. In a compact disc player, a focussed laser is used to record the pits embedded within the disk. Since the disk wobbles slightly as it spins, an auto-focus mechanism is needed to maintain the in-focus condition. This auto-focus mechanism uses the light reflected from the disc to generate an error signal that can be used to lock the laser onto the surface. The error signal is minimised through the real-time adjustment of a lens position, and a feedback loop to achieve an acceptable response time.
To use such a device to measure surface topography requires the laser to be focussed on the surface, and then the surface moved in a raster fashion (line scan Y and step scan X) underneath it. A recording of the lens position gives a measurement of the surface height variation.
The major component of the Laser Profilometer is a laser displacement transducer (Rodenstock Laser Stylus RM 600 LS10) which operates in the near-infrared at 780 nm. This transducer gives a spot size of about 1.3 µm on the measured surface, has a distance resolution of 1 nm and an operational range of ± 400 µm. The 'stand-off' distance between the end of the transducer and the measured surface is about 10 mm, in air, and the full included cone angle of the focused beam is approximately 47°. This transducer is an example of an "optical follower' that utilises auto-focusing optics to 'lock-onto' an interface and to measure its location relative to a reference position internal to the device.
Ra (average surface roughness) is one of the most effective surface roughness measures and is commonly adopted in general engineering practice. It gives a good general description of the height variations in the surface. A mean line is first found that is parallel to the general surface direction and divides the surface in such a way that the sum of the areas formed above the line is equal to the sum of the areas formed below the line. The surface roughness Ra is now given by the sum of the absolute values of all the areas above and below the mean line divided by the sampling length.
The test sample is mounted on the stage to reflect the laser. The sample is held sufficiently firmly to prevent any spurious movement during scanning.
Data is evaluated on a computer where programs flatten the topography, line by line, to leave deviations net of tilt and curvature. Ra is the mean roughness of the measured surface heights of a sample.
Because some of the original sample particles proved to be insufficiently reflective for the profilometer instrument to be able to lock onto the surface, we made surface replicates of all three test particles using a material called Silflo (Ex - Flexico), which is a light-bodies silicone rubber impression material that readily flows into surface features. The material was prepared and then a coated particle was pushed (gently) into the rubber before it hardened. On removing the particle, a surface replicate is left in the Silflo.
We then placed this replicate impression into the laser profilometer and measured a section, up to 1000 µm by 1000 µm, with data taken every µm in both x and y directions.
For each type of particle, we measured multiple replicates in this way. Results are given in Table 12. The details of the original particles are given below.
Extruded particles were made according to the first part of the process of example 1 and using a blend of LAS/PAS/SLES with ratio 58.3/14.6/27. The extruded particles had a circular cross section and dimensions of about 5 mm diameter by 1 mm.
A fraction of these extruded particles was coated using a 25% sodium carbonate coating solution to give a final coating level of 30 wt%.
The conventional High active granule was made using the process described in WO2002/24853 and had the composition:

LAS 65.5%

Soda Ash 11.5%

Zeolite 17.9%

Sodium Sulphate 2.2%

Water and minors balance
To be as good a comparison as possible with the larger extruded particles we used an oversized granule (retained on a 1.18mm sieve). Even so, due to this being smaller than the extruded particles, we could only measure a 500µm by 500µm segment. Table 6

Ra (µm) Ra (µm) Ra (µm)

High Active Granule 18.020 21.732 -

uncoated extruded 7.611 6.439 6.371

particles

coated extruded 5.384 2.610 3.116

particles
It can be seen from table 6 that a conventional high active granule detergent particle is much rougher than the uncoated extruded particle and that when coated the extruded particle is smoother still. Ra (µm) of less than 6, even less than 4, was achieved for the coated extruded particles. The combination of larger radius of curvature, smooth base particle and coating gives the coated extruded particle a stunning appearance when compared to the typical appearance of a detergent particle. When coupled with a low particle size distribution this leads to a dramatically visually different and enticing particle that consumers would really appreciate is different from their normal product.

Claims

A detergent powder composition comprising a minor part of high active detergent particles comprising surfactant blends with a major amount of linear alkylbenzene sulphonate anionic surfactant wherein the high active detergent particles comprise less than 40 wt% of the detergent composition and have an average volume at least ten times the average volume of the particles comprising the residue of the detergent powder composition, which comprises at least 40 wt% base powder, the balance of the composition comprising post dosed material.
A detergent powder composition according to claim 1 in which the high active detergent particles are used up to a maximum level of less than 30 wt% preferably 20 wt% or less.
A detergent powder composition according to any preceding claim in which the high active detergent particles are uncoated.
A detergent powder composition according to claim 1 or claim 2 in which the high active detergent particles are coated.
A detergent powder composition according to claim 4 in which the coating has a contrasting colour to the base powder and / or the post dosed material.
A detergent powder according to any preceding claim in which the high active detergent particles are made using a process comprising the steps of:
a) forming a liquid surfactant blend comprising a major amount of surfactant and a minor amount of water, the surfactant part consisting of at least 51 wt% linear alkylbenzene sulfonate and at least one co-surfactant, the surfactant blend consisting of at most 20 wt% nonionic surfactant;

b) drying the liquid surfactant blend of step (a) in an evaporator or drier to a moisture content of at most 2 wt% and cooling the output from the evaporator or dryer;

c) feeding the cooled material, which output comprises at least 93 wt% surfactant blend with a major part of LAS, to an extruder, optionally along with less than 10 wt% of other materials such as perfume, fluorescer, and extruding the surfactant blend to form an extrudate while periodically cutting the extrudate to form hard detergent particles with a diameter across the extruder of greater than 2 mm and a thickness along the axis of the extruder of greater than 0.2 mm, provided that the diameter is greater than the thickness;

d) optionally, coating the extruded hard detergent particles with up to 30 wt% coating material selected from powdered inorganic material and mixtures of such material and nonionic material with a melting point in the range 40 to 90 °C.
A detergent powder according to claim 6 in which the high active detergent particles are made using a process in which the blend in step (a) comprises at least 60 wt% total surfactant and at most 40 wt% water.
A detergent powder according to claim 6 or claim 7 in which the high active detergent particles are made using a process in which the blend made in step (b) is calcium tolerant according to the test hereinbefore described.
A detergent powder according to any one of claims 6 to 8 in which the high active detergent particles are made using a process in which the cooled output from the evaporator or drier stage (b) comprising at least 95 wt% preferably 96 wt%, more preferably 97 wt%, most preferably 98 wt% surfactant is transferred to a mill and milled to particles of less than 1.5 mm, preferably less than 1 mm before it is fed to the extrusion step (c).
A detergent powder according to any one of claims 6 to 9 in which powdered flow aid, preferably with a particle diameter of from 0.1 to 10 µm, is added to the mill in an amount of 0.5 to 5 wt% (based on output from the mill) and blended into the particles during milling.
A detergent powder according to any one of claims 6 to 10 in which the temperature of the blend does not exceed 45 °C, and preferably does not exceed 40°C, during the extrusion step (c).
A detergent powder according to any one of claims 6 to 11 in which perfume is added to the extruder.
A detergent powder according to any one of claims 6 to 12 in which the surfactant blend is dried in step (b) to a moisture content of less than 1.5 wt%, preferably less than 1.2 wt%, most preferably less than 1 wt%.
A detergent powder according to any one of claims 6 to 13 in which the evaporator or drier is a wiped film evaporator or a Chemithon turbo tube drier.
A detergent powder according to any one of claims 6 to 14 in which the particles made by the extrusion step are oblate spheroids.
A detergent powder according to any one of claims 6 to 15 in which the diameter of the extruded particles is greater than 4 mm.