Process for preparing low silicate detergent compositions

The structure and hence the powder properties of spray-dried detergent powders are improved by the incorporation of a small amount of a succinate salt. In particular the invention is applicable to powders which are low in inherent structurants, especially to powders low in sodium silicate and in phosphate builder salts. Buccinic acid partially neutralized with sodium hydroxide is especially effective as a structuring aid.

This invention relates to detergent powders and to a process for preparing 
them. In particular, it relates to detergent powders containing only 
relatively small amounts of sodium silicate, or no sodium silicate at all. 
It is now appreciated in the detergents art that sodium silicate has a 
pronounced effect in structuring of spray-dried detergent powders. 
However, inclusion of sodium silicate inevitably leads to a powder having 
a high pH which is preferably avoided if possible. There is also the 
difficulty that sodium silicate interacts adversely with the zeolite 
materials recently suggested as replacements for phosphate salts. As a 
consequence of these factors we believe that the sodium silicate content 
of the spray-dried powders of the future will contain lower amounts of 
sodium silicate than they do at present, and that this will lead to a 
powder which is inadequately structured. 
We have now discovered that succinate salts can structure detergent powders 
and thus can perform the structurant function normally performed by sodium 
silicate. 
Accordingly, the present invention provides a process for the preparation 
of a crisp, non-caking detergent powder which contains less than 4% by 
weight of sodium silicate, which process comprises the steps of 
(a) forming an aqueous slurry comprising nonionic surfactant, 
(b) conducting pressurised slurry to spray nozzles and 
(c) spray-drying the slurry to detergent powder, 
wherein the slurry comprises from 0.5 to 5% by weight, based on the 
spray-dried powder, of a water-soluble succinate salt. 
In a second aspect of the invention there is provided a crisp, non-caking 
detergent powder containing a nonionic surfactant, and less than 4% by 
weight of sodium silicate comprising from 0.5 to 5% by weight of a 
water-soluble succinate salt. 
U.S. Pat. No. 3,998,762 discloses detergent powders in which succinic acid 
or sodium succinate can be present, in combination with polyethylene 
glycol. However, in all of the powders disclosed in this patent 
specification the content of sodium silicate is at least 8% by weight and 
in some instances as high as 13%. This contrasts strongly with the field 
in which the present invention lies, namely that of detergent powders in 
which the content of sodium silicate is less than 4% by weight. We believe 
the contrast is a result of the fact that the behaviour of succinate in 
the two systems is different. In U.S. Pat. No. 3,998,762 the combination 
of polyethylene glycol with succinate (for example) is used to shift the 
phase boundaries in the aqueous slurry and inhibit the formation of a 
liquid crystal detergent active phase which would inevitably spray-dry to 
a sticky powder. In our invention on the other hand sodium succinate is 
believed to act as a film former and as a particle core. 
U.S. Pat. No. 3,962,149 discloses spray-dried absorbent beads for absorbing 
nonionic surfactant. The beads are based essentially on sodium sulphate 
and are made in the conventional manner for spray-dried materials, that is 
to say, the components are made up into an aqueous slurry prior to 
spraying. In this particular specification it is proposed to use dibasic 
acids or salts thereof, such as sodium adipate (although sodium succinate 
is contemplated) in amounts of 2-30% of the bead, and it is believed that 
the function of these materials is to salt out sodium sulphate from 
solution in the slurry. Thus, in principle, any sodium or sulphate salt 
which is more soluble than sodium sulphate could be used. Were the sodium 
sulphate content of the bead not so high, the use of the dibasic acids or 
salts would not be necessary. The high level of sodium sulphate is 
necessary to get the required absorbency in a post-spray-on addition of 
nonionic surfactant, whereas in our invention the nonionic surfactant is 
incorporated into the powder via the slurry. 
There are two ways in which the succinate salt can be incorporated in the 
slurry. First it can be incorporated prior to pressurising, for example by 
direct addition to a crutcher or, secondly, it may be incorporated into 
the pressurised slurry, for example into the pressurising pump itself or 
into the line conducting pressurised slurry to the spray nozzles. 
Whichever way is chosen, the amount of succinate which is incorporated is 
from 0.5% to 5% by weight based on the weight of the spray-dried powder, 
preferably 1 to 3% by weight. 
It is believed that sodium succinate hexahydrate can play an important role 
in the securing of the technical effect of this invention, and 
consequently sodium is strongly preferred as the cation of the succinate 
ion. However, we believe that other water-soluble succinate salts may 
perform a similar role, albeit to a lesser extent. 
If succinic acid partially neutralised with sodium hydroxide is used, we 
have discovered that this results in a spray-dried powder having 
particularly favourable powder properties. Although we do not wish to be 
limited by theory, we believe that this is due to the acid salt acting as 
a slurry hydrotrope as well as a powder structurant. 
It will now be evident to the skilled man that our invention is concerned 
with one of the problems which arise when detergent powders are made which 
do not contain high proportions of sodium silicate. The problem is 
exacerbated when large amounts of sodium tripolyphosphate or other 
phosphate salts are absent and so the invention is particularly applicable 
to detergent powders which are low both in sodium silicate and in sodium 
tripolyphosphate. Of course, if no phosphate builder salt at all or only a 
small amount of such a salt is present, then the detergent performance of 
the powder will be unsatisfactory unless the deficiency of builder salt is 
made up with a non-phosphate builder compound. If no phosphate at all is 
present it is preferred that the builder salts present should be synthetic 
sodium aluminosilicate or sodium nitrilotriacetate or mixtures thereof. 
Where some phosphate salt is present, the builder may consist of binary or 
ternary mixtures of these compounds, or mixtures of the phosphate salt and 
some other builder such as sodium carboxymethyloxysuccinate. 
Generally, the builder compound or compounds will be present in an amount 
of from 15-60% by weight. Non-phosphate builder compounds, when used in 
conjunction with phosphate salts, are preferably present in amounts of 
from 10-25% by weight, and when used by themselves, in amounts of from 
20-40% by weight. 
Detergent active compounds will, of course, be present in the detergent 
powders. Anionic detergent active compounds, including soaps, and nonionic 
surfactants as well as mixtures of these compounds can all be used. 
Typical amounts of detergent active compounds present in the powders are 
from 2 to 20% by weight when a nonionic surfactant is present alone, and 
from 2 to 25% by anionic surfactant and from 0.5 to 10% by weight of 
nonionic surfactant when a binary mixture is used. 
A particularly preferred detergent active system is the so-called ternary 
mixture of anionic surfactant, nonionic surfactant and soap. Preferred 
amounts of the individual components of this mixture are from 2 to 15% by 
weight of anionic surfactant, from 0.5 to 7.5% by weight of nonionic 
surfactant and from 1 to 7.5% by weight of soap. 
Examples of anionic surfactants which can be used are alkyl benzene 
sulphonates, particularly sodium alkyl benzene sulphonates having an 
average alkyl chain length of C.sub.12 ; primary and secondary alcohol 
sulphates, particularly sodium C.sub.12 -C.sub.15 primary alcohol 
sulphates, olefine sulphonates and alkane sulphonates. 
The soaps which can be used are preferably sodium soaps derived from 
naturally-occurring fatty acids, preferably fatty acids from coconut oil, 
tallow or one of the oils high in unsaturated acids such as sunflower oil. 
The nonionic surfactants which can be used are the primary and secondary 
alcohol ethoxylates, especially the C.sub.12-15 primary and secondary 
alcohols ethoxylated with from 5 to 20 moles of ethylene oxide per mole of 
alcohol. 
Other components of detergent powders which may optionally be present 
include lather controllers, antiredeposition agents, oxygen and chlorine 
bleaches, fabric softening agents, anti-ashing aids, slurry stabilisers, 
fluorescent agents, perfumes, germicides and colourants. 
The process of the invention is particularly applicable to detergent 
powders which contain a reactive amide bleach precursor and a peroxy 
compound. The preferred reactive amide bleach precursor is 
tetraacetylethylenediamine (TAED) and preferred peroxy compounds are 
sodium perborate and sodium percarbonate. TAED may be present in an amount 
of 0.5 to 10% by weight and the peroxy compound in an amount of up to 45% 
by weight.

The invention is further illustrated by the following Example: 
EXAMPLE 
Three crutcher slurries of different formulation were made up and 
spray-dried to low phosphate powders of similar water content. The bulk 
densities of the powders were varied by varying the degree of aeration of 
the slurries, and the compressibilities of the resultant powders were 
measured by conventional means. 
The formulations of the slurries is shown below and a plot of the bulk 
density against compressibility of the spray-dried powders is shown in 
FIG. 1. 
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Parts by weight 
A B C 
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Sodium alkylbenzene 
6.5 6.5 6.5 
sulphonate 
Primary alcohol ethoxylate 
3.0 3.0 3.0 
Sodium soap 5.0 5.0 5.0 
Sodium tripolyphosphate 
18.0 18.0 18.0 
Sodium aluminosilicate 
26.0 26.0 26.0 
(Zeolite) 
Sodium silicate Nil 4.0 Nil 
Sodium sulphate 6.0 4.0 6.0 
Sodium succinate Nil Nil 3.0 
Minor components and water 
52.0 52.0 52.0 
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It can be seen from the FIGURE that plot C, which relates to the powder 
containing 3 parts (about 2% by weight of finished powder) of sodium 
succinate shows a powder having a substantially lower compressibility at 
equivalent bulk density than similar powders containing either no 
structurant at all, or containing sodium silicate as structurant.