Bleach composition

A low temperature bleach system comprises a peracid percursor system and bromide ions. The bromide ions may be supplied by sodium bromide. A theoretical peracid to bromide equivalent ratio between 2:1 and 1:2 is preferred, but dye transfer and hygiene benefits are possible with a ratio up to 1:32. The precursor system is typically diphthaloyl peroxide or sodium perborate plus tetraacetyl ethylenediamine (TAED). If the perborate is in excess, a scavenger such as catalase should be included. The system may be used as such or incorporated in a conventional detergent base.

TECHNICAL FIELD 
This invention relates to a bleach system, particularly for fabrics, which 
is effective at low temperatures. The invention also relates to fabric 
washing compositions comprising said bleach system which can be used for 
washing at high temperatures as well as at low temperatures. By the term 
"low temperatures," temperatures .ltoreq.40.degree. C. are meant here. 
With the increasing trend of saving energy, housewives are becoming more 
and more energy-conscious and have gradually changed their washing habit 
towards lower wash temperatures. 
BACKGROUND ART 
Inorganic persalts and other percompounds giving hydrogen peroxide in 
solution, such as sodium perborate and sodium percarbonate, are widely 
used as a bleaching agent in detergent compositions. These persalts 
provide a satisfactory bleach when the detergent composition is used at 
high temperatures, e.g. from 80.degree.-100.degree. C., but their action 
is rather slow to substantially nil at lower wash-temperature. 
It is known that organic peracids, e.g. peracetic acid, are active at lower 
temperatures and the use of peracid in detergent compositions, either as 
such or formed in situ, has been suggested to give the detergent 
composition satisfactory bleaching properties at lower wash-temperatures, 
e.g. in the 60.degree. C. wash-cycle. 
A considerable saving of energy would be obtained if washing habits could 
be further shifted towards cold and cold water washing, e.g. below 
40.degree. C., also for whites. 
Unfortunately, however, organic peracids do not exhibit adequate bleaching 
at these low temperatures. 
It is an object of the present invention to provide an improved bleach 
system which is also effective at temperatures below 40.degree. C. 
Another object of the present invention is to provide a bleach composition 
suitable for use in cold and cool water washing at temperatures below 
40.degree. C. 
DISCLOSURE OF INVENTION 
It has now been found surprisingly that the bleaching action of organic 
peracids can be enhanced to enable the bleaching of fabrics at low 
temperatures by using one or more precursors which form an organic peracid 
in aqueous solution and by the addition of bromide ions. Although the 
exact mode of action of this specific bromide catalysis is not fully 
understood, it is believed that bromides, unlike chlorides, react 
sufficiently rapidly with peracids to form effective amounts of 
hypobromite. The hypobromite formed is a far superior bleach to peracids 
and more effective at low temperatures. 
As the reaction of bromides with peracids probably involves a nucleophilic 
attack of bromide ion on the eletrophilic peroxidic oxygen, the rate of 
reaction will depend on the concentration and reactivities of the bromide 
and peracid. Though theoretically an equimolar amount of bromide would be 
necessary for complete conversion of bromide to hypobromite, it has been 
found that surprisingly a significant improvement of the bleaching effect 
at low temperatures can already be achieved with less than said 
theoretical equimolar amount of bromide. An explanation thereof may be 
that on reaction with certain components of the wash system (including 
soil components), hypobromites are expected to reform the parent bromide 
ion according to the following reaction equation: 
EQU OB1.crclbar.+wash component .fwdarw.oxidised wash component+B1.crclbar. 
According to the present invention there is provided a bleach composition 
comprising a peracid precursor or precursors which form an organic peracid 
in aqueous media and an organic or inorganic material which delivers 
bromide ions in aqueous media, the theoretical molar equivalent ratio of 
said organic peracid to said bromide being not more than about 5:1. 
BEST MODE OF CARRYING OUT THE INVENTION 
For best bleaching results it is preferred that the theoretical molar 
equivalent ratio of the peracid to the bromide-delivering material lies 
between 5:1 and about 1:3, most preferably between about 2:1 and about 
1:2. However, advantageous effects, particularly a hygiene effect, can be 
achieved where the peracid precursor(s) is or are present in a relatively 
minor amount, i.e. where the theoretical molar equivalent ratio of the 
peracid to the bromide-delivering material lies between about 1:3 and 
about 1:32. It may be necessary to use the higher proportions of 
bromide-delivering material in case halogenation of the soil occurs, which 
consumes bromide ions. 
The peracid is formed in situ from its precursor or precursors by 
hydrolysis or perhydrolysis. In the latter case an organic persalt 
activator and a persalt of the peroxyhydrate type, e.g. sodiumperborate, 
can be added separately to the system or composition of the invention. In 
both cases, whether formed by hydrolysis or perhydrolysis peracid 
formation takes place in the bleach or wash solution as an intermediary 
step before the reaction with the bromide. Hence various precursors will 
fall within the scope of the composition of the invention. These include 
benzoylperoxide, and diphthaloyl peroxide both of which are capable of 
generating peracid by hydrolysis. Precursors which generate peracids only 
on perhydrolysis include esters (such as those described in British 
Patents 836 988 and 970 950), acylamides (such as N,N,N',N' tetraacetyl 
ethylene diamine (TAED), Tetraacetyl glycoluril, N,N' diacetyl acetoxy 
methyl malonamide and others described in British Pat. Nos. 907 356, 855 
735, 1 246 339 and US patent 4 128 494), acyl azoles (such as those 
described in Canadian patent 844 481), acyl imides (such as those 
described in South African patent 68/6344) and triacyl cyanurates (such as 
described in US Pat. No. 3 332 882). 
In systems comprising an organic precursor and a persalt the organic 
precursor will advantageously be in at least the stoichiometric ratio to 
the persalt, since excess of persalt will tend to consume the active 
hypobromite bleach, unless a persalt bleach scavenger such as catalase is 
present to remove said excess of persalt. 
The bleach system of the present invention can be used as such or it can be 
used in conjunction with a detergent product for washing and bleaching 
fabrics. It can be used in relatively short washes as well as in 
relatively longer soak-washings under room temperature conditions up to 
40.degree. C., or at higher temperatures, with much less risk of 
discolouring dyed fabrics than common commercial chlorine bleaches, e.g. 
sodium hypochlorite or potassium chloro isocyanurate. It is, moreover, 
less aggressive to fabrics than chlorine bleaches. A further advantage of 
the invention is that staining of white fabrics by dye transfer is 
inhibited. 
The bleach system of the invention can be either employed as part of a 
complete detergent bleach composition comprising any of the usual 
detergent ingredients or as a separate bleach additive for use in bowl 
washing or in fabric washing machines. It may be presented in the form of 
either a powder or granules, a water-soluble or water-permeable unit 
package, or a tablet. 
Hence, the bleach composition of the present invention may comprise a 
mixture of: 
1. from 0.1 to 40 parts, preferably 0.5-35 parts by weight of an organic 
peracid in the form of its equivalent parts by weight of one or more 
precursors; and 
2. from 0.1 to 40 parts, preferably 0.5-35 parts by weight of a water 
soluble bromide salt; optionally mixed together with 
3. from 0 to 40 parts, preferably 5-35 parts by weight, of a water-soluble 
organic detergent selected from the group consisting of organic synthetic 
anionic detergents, nonionic detergents, alkalimetal soaps (e.g. of 
C.sub.8 -C.sub.22 fatty acids), or mixtures thereof; 
4. from 0 to 80 parts, preferably 10-60 parts by weight, of a water-soluble 
builder salt; 
5. from 0 to 30 parts, preferably 0-25 parts by weight of fillers; and 
6. from 0 to 30 parts, preferably 0.2-20 parts by weight of other suitable 
adjuncts and ingredients, such as for example N-H compounds such as urea, 
optical brighteners, soil-suspending agents, dyestuffs, perfumes, enzymes, 
including proteolytic and amylolytic enzymes and catalase, moisture and 
mixtures thereof. 
Typical synthetic anionic detergents are the alkyl benzene sulphonates 
having from 8-16 carbon atoms in the alkyl group, e.g. sodium dodedyl 
benzene sulphonate; the aliphatic sulphonates, e.g. C.sub.8 -C.sub.18 
alkane sulphonates; the olefin sulphonates having from 10-20 carbon atoms, 
obtained by reacting an alpha-olefin with gaseous diluted sulphur trioxide 
and hydrolysing the resulting product; the alkyl sulphates such as tallow 
alcohol sulphate; and further the sulphation products of ethoxylates 
and/or propoxylated fatty alcohols, alkyl phenols with 8-15 carbon atoms 
in the alkyl group, and fatty acid amides, having 1-8 moles of ethoxylene 
or propylene groups. 
Typical nonionic detergents are the condensation products of alkyl phenols 
having 5-15 carbon atoms in the alkyl group with ethylene oxide, e.g. the 
reaction product of nonyl phenol with 6-30 ethylene oxide units; the 
condensation products of higher fatty alcohols, such as tridecyl alcohol 
and secondary C.sub.10 -C.sub.15 alcohols, with ethylene oxide, known 
under the trade name of "Tergitols.RTM." supplied by Union Carbide; the 
condensation products of fatty acid amide with 8-15 ethylene oxide units 
and the condensation products of polypropylene glycol with ethylene oxide. 
Suitable builders are weakly acid, neutral or alkaline reacting, inorganic 
or organic compounds, especially inorganic or organic complex-forming 
substances, e.g. the bicarbonates, carbonates, borates or silicates of the 
alkalimetals; the alkalimetal ortho-, meta-, pyro- and tripolyphosphates. 
Another class of suitable builders are the insoluble sodium 
aluminosilicates as described in Belgian Specification No. 814 874. 
It has been discovered that in some bleach systems of compositions 
comprising an organic peracid precursor and a bromide, the presence of 
aldehydes, ketones or materials which yield aldehydes or ketones in 
aqueous solution has a negative effect on bleaching performances. Thus, in 
preferred embodiments of the present invention such materials are absent 
or present only up to the extent of one weight part of aldehyde, ketone or 
material that yields aldehydes or ketones in aqueous solution per 100 
weight parts of organic peracid precursor. 
Usual fillers are the alkalimetal sulphates, especially sodium sulphate. 
A major advantage of the bleach composition of the invention is that it can 
be used as an energy-saving product in cold and cool water washing of 
white fabrics with good results.