Note: Descriptions are shown in the official language in which they were submitted.
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SO~P P~DERS ~
This invention relates to soap powders and to a
process for preparing them.
The wetting, dispersion and solubility characteristics
of soap powders are a continuing problem to the industry
and much effort has been expended over the years in
improving them. For example, it is disclosed in British
Patent No 907,~9~ that granular soap compositions need to
be Einely-divided to ensure rapid solution but that fines
lead to clotting. This can be avoided, it is stated, by
the addition of a sodium acetate or sodium benzoate
anti-lumping agent in granular form. A different solution
to this same problem of clotting is proposed in Unitecl
States Patent No 2,940,935 in which an alkali metal xylene
sulphonate and an alkali metal silicate or carbonate are
incorporated into the soap-containing slurry prior to
spray-dryin~.
We have now discovered that clottin~ o~ spray-dried
soap powders can be reduced by coating the powder with a
~inely-divided water-soluble inorganic salt.
71E22V
f~3~
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Accordingly, the present invention provides
spray-dried particles comprising a major proportion of
water-soluble soap and having an average diameter of
300-700 microns coate~ wit~ particles o~ an inorganic
substance, characterised in tha-t the inorganic substance
is water-soluble and that at least 80% by weight of its
particles have an average diame~er of less than 100
microns.
Treatment of spray-dried soap particles with
finely-divided inorganic salts has been suggested before,
in United States Patent No 2,715,110. Ilowever the inventor
found that the treatment led to no improvement in the
agglomeration eharaeteristies of the soap powder and he
conse~u~ntly rejeetcd it in Eavo~lr of a treatment with
gaseous carbon dioxide. It is not clear why the ~reatmen-t
with inorganic salt was found ineffective, but we believe
it to have been a consequenee of the relative particle
sizes o~ the spray-dried soap and the inorganic salt. The
sizes whieh we specify are eritical to obtaining the
effeet~
United States Patent No 2,592,535 also discloses the
eoating of soap with hygroscopic salts, sueh as ~hosphates,
to reduee loss of moisture ~rom spray-drie~ soap particles
and consequenkly to reduce dusting. However the critical
size relationships which we speeify are not referred to in
this speeifieation either.
British Patent Nos 1,401,726 and 1,463,973 relate to
partieles containing major proportions of soaps ancl
lime-so~p dispersants sueh as ether sulphates. ~t was
apparently Eound that the lime-soap dispersants adversely
af~eeted the solubility properties of the soap particles
ancl it was proposed to counteract that by impregnating them
with smeetite elay partieles having a size below 50
microns. However sueh partieles are not water-soluble and
so will rernain in suspension in the wash liquor, which may
not be desirable.
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As stated above the relationship of the particle size
oE the water-soluble soap particle to that of the coatin~
particle of inorganic salt is an important feature o~ this
invention. The average diameter of the soap particles can
vary from 300-700 microns, preferably 500-600 microns, in
~hich case thc average diameter of the inorganic particles
is such that at least 80% by weight of them are less than
1~0 microns, preferably less than 50 microns. The ratio of
the diameter oF the soap particles to that of the coating
particles is preferably from 6:1 to 8:1, most preferably
7:1.
The spray-dried soap-containing particles need not
consist entirely of soap, but may contain up to 49~ by
weight of other soap powder componentsO Examples of these
are detergency builders, foam boosters or foam
suppressants, powder structurants, anti-oxi~ants, softenillg
agents and water. Preferably the particles comprise from
60-80% by weight of soap.
The term 'spray-dried' is used herein as a convenient
shorthand. Soap powders are either produced by
spray-drying in which a relatively cool slurry is sprayed
lnto a hot dryiny gas, or by spray-cooling, in which hotter
slurry is sprayed into relatively cold drying gas, and
there are a number of intermediate processes which combine
~5 bott~ sprAy-drying and spray-cooling. All o~ these
processes are included within the term 'spray-dried' as
used herein.
Similarly, the term 'coatec~' is used herein to denote
a situa~ on where a plurality of particles oE the
watcr-soluble inor~anic substance are adherent to the
spray-dried soap particles. It does not necessarily imply
that so many are adherent that the soap particle is
completely coated~ It is within the scope of the invention
for i-t to be only par~ly so~
The nature oE the water-soluble soap is not critical
to the invention. For economic reasons it will normally be
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a sodium or potassium soap, but any other cation will be
satisfactory provided that it is non toxic and does not
cause unwanted sidc effects in the composition~ The fatty
acid component oE the soap may be derived from mixtures of
S saturated an~ partially unsatura~ed fatty acids in the
C~-C~6 chain length region. Coconut oil and tallow,
which are the traditional soap-making materials are
preferred sources of the mixed fatty acids~ -the former
containing predominantly C12 and C14 saturated fatty
acids and the latter saturated Cl~ and Cl~ acids and
mono-unsa-turated C16 acids. Mowever, the invention is
also particularly applicable to soaps formed from fatty
acid mixtures containing high proportions oE unsaturated
acids such as oleic acid and linoleic acid. These soaps
tend to be soft and creepy when in spray-dried form and the
coating of the invention is especially suitable for
improving their powder properties. Sunflower seed oil is
an example o~ an oil which contains fatty acids of this
type. When the spray-dried particles contain an
unsaturated fatty acid having 16 or more carbon atoms then
it is preferred that the content of this acid should be 25%
or more by weight of the particle.
The soap particles may also contain anionic
surfactants in amounts up to 15% by weight oE the particle.
The nature of the anionic surfactant is not critical, any
of the surEactants conventionally used or proposed for use
in fabric washing powders being suitable. Examples oE
these are sodium alkyl benzene sulphonates, preferably
Clo-Cl~ alkyl, sodium primary and secondary alkyl
sulphate, preEerably ClO~C22 alkyl, olefine sulphonate
salts and sodium alkane sulphonates.
The soap particles may also contain nonionic
surfactants in amounts up to about 306 by weight of the
particles. Ethox~lated and propoxylated primary and
secondary alcohols are the preferred nonionic surfactants,
primary alcohols containin~ 7 to 25 carbon atoms
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ethoxylated with from 5 to 30 moles of ethylene oxide per
mole oE alcohol being most preferred.
As has been sai~, the invention is particularly
applicable to spray-dried particles which are soft, and
exam~les of components which may make ~he par~icl~s soft
are polyethylene glycols, ethoxylated alkanolamides, alkyl
phosphoric acid esters and qua-ternary ammonium salts.
The water-soluble inorganic salt for coating the
spray-dried soap particles is preferably present in an
amount oE Erom 3 to 25% by weight of the total soap powder
~ormulation. The lower amount is the general level which
will normally be used when the salt is only performing a
coating function, whereas the upper amount is the maximum
amount which will normally be used when the sal~ performs a
function in addition to coating, such as deter~ency
building or bleaching.
Examples of suitable salts, within which term are
included oxides as well as oxyacid salts, are the
water-soluble phosphates, carbonates, percarbonates,
borates, perborates, sulphates and metasilicates and
aluminosilicates, particularly the sodium and potassium
salts. In addition to the inorganic compounds referred to
above, but not as an alternative to them, certain organic
compounds can be uscd Eor coating. Examples of such
compounds are the salts of nitrilotriacetic acid,
preferably sodium nitrilotriacetate, and tetraacetyl
ethylene diamine.
The invention provides, in a second aspect, a process
Eor the manufacture of spray-dried particles comprising a
major proportion of a water-soluble soap inorganic
substance, at least 80% o~ which have an average diameter
of less than 100 microns, characterised by forming a
mixture of the two types of particle, imparting relative
motion to them and spraying them with an aqueous solution
of a binder.
The nature of the binder, which ensures adhesion
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between the spray-dried soap particles and the inorganic
salt particles is not critical, conventional binders such
as water, sodium silicate solution and sodium carboxymethyl
cellulose solution being satisfactory. In the case of
sodium silicate solution, 3-10~ by weicJht based on the
~otal soap powder composition, in the form oE a 20-60% w/v
solution, would be a typical amount of binder to be used.
It is possible to perform the process of the invention
in a number of the conventional granulating apparatus. One
such apparatus is the Eirich pan (registered trade mark)
which is an inclined pan rotatable about its major axis.
Another is the Schugi mixer (registered trade mark) whlch
consists of a cylindrical chamber provided with inclined
ribbon-like mixing bLades rotatable about the major axis of
the cylinderO Whichever of these apparatus is used, the
coated particles will require drying in a fluidised bed
through which warm air is pumped, so since it is necessary
to have a ~luidised bed apparatus available and since it is
possible to carry out the coating process ab initio in a
fluidised bed, it is preferred to carry out the process in
that way.
In the following Example, a process of coating in
accordance with the invention is described.
~5 Example
Spray-dried particles con-taining a major proportion of
soap ancl having the composi-tion shown below were prepared
by conventional slurry-making and spray-drying techniques
in two size ranges, 450 and 350 microns. The resultant
particles are subsequently referred to as 'core particles'.
5~3~
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Parts by Weight
Sodium soap (28.5% lauric acid) 42.0
Coconut oil monoethanolamide2.6
Magnesium sulphate 0-5
Ethylene diamine tetra acetic acid 0.13
L~ree ~att~ aci~s 2.17
~ater 6.5
A mixture of finely-divided inorganic salts suitable
for forming a coating on the above spray-dried pa-cticles
was then prepared. The composition is shown below
Parts
Sodium tripolyphosphate 12.0
Sodium carbonate 2.6
Sodium carboxymethyl cellulose 0.5
The core particles and the mixture of inorganic salts,
together with 25 parts of sodium perborate were then placed
in an Anhydro (registered trade mark) fluidised bed and
sprayed with a 30% w/v aqueous solution of sodium silicate
(Na20:SiO2, 2:1)~
In a second experiment the core particles, the mixture
oE inorganic salts and sodium perborate were fed to a
Schugi cylinder mixer and sprayed wi~h the sodiu~ silicate
solution.
The coa-ted particles obtained had good flow
properties, a narrow particle size distribution and a bulk
density of around 0.4 g/cc.
The wetting, dispersion and dissolution properties oE
the coated particles were then assessed as Eollows.
A standard weight of powder was poured onto the
surEace oE hot water (40C) in a hand bowl and swirled
round. The resultant wash liquor was then scored for
wetting (ie whether the powder was floating on the surface
or had sunk), dispersion (ie whether clots had formed) and
dissolution on a score of 0 to 5, 5 beiny the best score.
This scoring procedure was carried out by a panel of
skilled assessors, and the scores given were averaged.
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The results are shown in Table 1.
Table 1
~lettiny (I~), Dispersion ~Dp) and
Dissolution ~Ds) Tes~ Results
Core Particle Size
450 ~icrons 350 microns
W Dp Ds _ _ _ Dp Ds
Core Particles 3 3 3 3 4 4
(uncoated)
15 Coated Particles
ex cy:linder mixer 5 5 4 5 4 4
(Schugi)
ex Eluidised bed 5 5 4 5 4 4
(Anhydro) _ _ ~ _ _
_ _
:[t can be seen Erom the above results that all of the
coated particles are as good as or superior to the uncoated
ones in wetting, dispersing and dissolving propertiesO The
superiority is more marked with the larger core particles,
and we have evidence that this is a general trend. The
increase .in the wetting scores of the coated par~icles in
accordance with the invention is especially significant
because this indicates that less powder floats on the
surEace of the water in a clot.
