Hypochlorite bleaching compositions

Liquid aqueous bleaching compositions are disclosed which comprise a pH buffering means with low sensitivity to water hardness and an alkali metal hypochlorite. A method of treating fabrics with said compositions is also disclosed.

TECHNICAL FIELD 
The present invention relates to a liquid bleaching composition which is 
suitable for laundry applications including hand washing as well as 
washing with automatic washing machines. 
BACKGROUND OF THE INVENTION 
Liquid bleaching compositions are well-known in the art. Amongst the 
different bleaching compositions available, those relying on bleaching by 
hypochlorite are often preferred, mainly for performance reasons, 
especially at lower temperature. 
However, there are some limitations to the convenience of hypochlorite 
bleaches. In particular, it is well-known from consumers that the 
drawbacks associated with the use of hypochlorite-based compositions are 
that said compositions may damage and/or yellow the fabrics which are 
being bleached. 
It is therefore an object of the present invention to provide a 
hypochlorite-containing composition, suitable for use in laundry 
application, whereby the fabric whiteness is improved. 
It is a further object of the present invention to provide a 
hypochlorite-containing composition, suitable for use in laundry 
application, whereby fabric safety is improved. 
We have now found that the previous objects can be met by formulating an 
alkaline liquid composition comprising an alkali metal hypochlorite or 
mixtures thereof and a pH buffering means with low sensitivity to water 
hardness, i.e. a pH buffering means which, when used in a 1M solution at 
pH 10, requires more than 2.5 mM of calcium ion, in order to cause 
precipitation at 25.degree. C. of the calcium salt of the alkali anion of 
said pH buffering means. Said composition allows to provide improved 
fabric whiteness and/or improved fabric safety on the fabrics treated 
therewith, as compared to the same composition without said pH buffering 
means with low sensitivity to water hardness according to the present 
invention. We have also found that, in the preferred embodiment of the 
present invention wherein the liquid hypochlorite bleach-containing 
compositions comprise said pH buffering means with low sensitivity to 
water hardness together with a precipitation agent like carbonate salt 
and/or silicate salt, outstanding whiteness and/or fabric safety 
performance are provided. Indeed, it has been found that the use of a pH 
buffering means with low sensitivity to water hardness together with a 
precipitation agent like silicate salt and/or carbonate salt in a 
hypochlorite bleaching composition results in a complementary effect on 
fabric whiteness performance and/or fabric safety performance. 
An advantage of the compositions of the present invention is that they 
allow to provide outstanding fabric whitening action and/or fabric safety 
properties without compromising on the stain removal performance on 
different types of stains including bleachable stains (e.g. coffee), 
enzymatic stains (e.g. blood) and greasy stains (e.g. lipstick). 
Another advantage of the compositions of the present invention is that said 
bleaching compositions are suitable for the bleaching of different types 
of fabrics including natural fabrics, (e.g., fabrics made of cotton, 
viscose, linen, silk and wool), synthetic fabrics such as those made of 
polymeric fibers of synthetic origin as well as those made of both natural 
and synthetic fibers. Indeed, the compositions of the present invention 
may be used on synthetic fibers despite a standing prejudice against using 
hypochlorite bleaches on synthetic fibers, as evidenced by warnings on 
labels of commercially available hypochlorite bleaches and clothes. 
A further advantage is that the liquid compositions according to the 
present invention comprising a pH buffering means with low sensitivity to 
water hardness allow a prolonged through-the-bleach buffering action, i.e. 
to maintain the pH of the bleaching solution as high as possible during 
the whole bleaching cycle from the moment the dilution is completed, 
without increasing the pH of the compositions per se as compared to the 
same compositions but without said pH buffering means. 
Compositions comprising hypochlorite and pH buffering means have been 
described in the art. 
WO 88/05462 discloses a composition for removing stains from fabrics 
comprising an aqueous solution of trisodium phosphate, sodium hydroxide, 
sodium hypochlorite and a buffer to maintain a pH of between about 10 and 
12 such a sodium carbonate, sodium bicarbonate, sodium sesquicarbonate or 
mixtures thereof. WO 88/05462 further discloses that it is preferred that 
the buffer system employed holds the pH as close to pH 10 as possible, 
consistent with effective stain removal to provide a product which is more 
gentle to skin and fabrics than a higher pH. WO 88/0562 also discloses a 
process of removing stains from fabrics with said compositions. However, 
pH buffering means having a low sensitivity to water hardness as described 
herein are nowhere disclosed in WO 88/05462. 
EP-A-622 451 discloses compositions suitable for use in diluted form, 
comprising hypochlorite, sodium hydroxide, a bleach stable perfume and as 
a buffering system whereby the pH of the diluted composition is buffered 
to a constant value throughout use, carbonate and/or silicate. EP-A-622 
451 also discloses a method of bleaching wherein such a composition is 
contacted with fabrics. No pH buffering means with low sensitivity to 
water hardness are disclosed. 
EP-A-653 482 and EP-A-668 345 disclose hypochlorite-containing compositions 
comprising a source of strong alkalinity, a pH buffering means and 
optionally other types of ingredients such as respectively radical 
scavengers and polycarboxylate acids of pyridine. The pH buffering means 
disclosed therein are alkali metal silicate and/or carbonate, sodium 
borate and sodium sesquicarbonate. pH buffering means having a low 
sensitivity to water hardness as described herein are nowhere disclosed in 
said patent applications. 
UK 1282 906 discloses stabilised aqueous alkali metal hypochlorite 
solutions comprising as a stabiliser an alkali metal heptonate or 
boroheptonate. "Alkali metal boroheptonate" as used in UK 1282 906 refers 
to a mixture of an alkali metal heptonate with either boric acid or an 
alkali metal metaborate and generally containing two gram moles of alkali 
metal heptonate per gram atom of boron in the boric acid or metaborate. 
However, no strong source of alkalinity nor the pH of the solutions 
therein are disclosed. Also no laundry application is disclosed. 
BE-749728 discloses an aqueous system comprising an N-hydrogenate and a 
hypohalite such as hypobromite, hypochlorite or hypoiodite in equilibrium 
with the corresponding N-halogenated compound, and a buffering system to 
maintain the pH of said system in a range of 4 to 11 to stabilise it 
before use. The buffering system mentioned therein are generically 
acetates, carbonates, phosphates, polyphosphates, organophosphates, 
borates, polyborates, organoborates, silicates, polysilicates, 
organosilicates or mixtures thereof. Strong sources of alkalinity such as 
sodium/potassium hydroxide are also disclosed. These bleaching 
compositions are particularly suitable to bleach textiles. But BE 749728 
fails to make a distinction between pH buffering means being sensitive to 
water hardness like silicates or carbonates and pH buffering means with a 
low sensitivity to water hardness, as the ones described in the present 
invention. 
U.S. Pat. No. 4,000,082 discloses defoaming compositions based on lithium 
salts. More particularly, U.S. Pat. No. 4,000,082 discloses aqueous 
cleaning compositions comprising anionic surfactants, nonionic 
surfactants, from 5% to 50% by weight of the total composition of a highly 
alkaline compound selected from the group of sodium hydroxide, sodium 
carbonate, sodium bicarbonate, sodium metaborate and the like, and from 1% 
to 5% by weight of a lithium salt including lithium hypochlorite. No 
bleaching application is disclosed, let alone laundry bleaching 
application. 
Actually, the benefits derivable from the use of a pH buffering means 
according to the present invention, which, when used in a 1M solution at 
pH 10, requires more than 2.5 mM of calcium ions, in order to cause 
precipitation at 25.degree. C. of the calcium salt of the alkali anion of 
said pH buffering means, in an alkaline liquid bleaching composition 
comprising hypochlorite, for bleaching fabrics, i.e. improved fabric 
whiteness and/or fabric safety on the fabrics treated therewith, have not 
been acknowledged in the prior art. 
SUMMARY OF THE INVENTION 
The present invention encompasses a liquid bleaching composition having a 
pH of from 8 to 14, said composition comprising an alkali metal 
hypochlorite, or mixtures thereof, and a pH buffering means which, when 
used in a 1M solution at pH 10, requires more than 2.5 mM of calcium ions, 
in order to cause precipitation at 25.degree. C. of the calcium salt of 
the alkali anion of said pH buffering means, with the proviso that said 
alkali metal hypochlorite is not lithium hypochlorite when said pH 
buffering means is sodium metaborate. 
A method of bleaching fabrics to improve fabric whiteness and/or fabric 
safety which comprises the step of contacting said fabrics with a liquid 
bleaching composition having a pH of from 8 to 14, said composition 
comprising an alkali metal hypochlorite, or mixtures thereof, and a pH 
buffering means which, when used in a 1M solution at pH 10, requires more 
than 2.5 mM of calcium ions, in order to cause precipitation at 25.degree. 
C. of the calcium salt of the alkali anion of said pH buffering means. 
DETAILED DESCRIPTION OF THE INVENTION 
The compositions of the present invention are liquid bleaching 
compositions. Thus, as a first essential ingredient, the compositions of 
the present invention comprise hypochlorite. Various forms of alkali metal 
hypochlorite are commercially available and, although this is not critical 
for the present invention, it is preferred herein to use sodium 
hypochlorite. Compositions according to the present invention comprise a 
bleaching amount of an alkali metal hypochlorite, or mixtures thereof, 
which typically represent from 0.1% to 20% by weight of the total 
composition, based on active chlorine, of said alkali metal hypochlorite. 
Preferred compositions herein comprise from 0.5% to 8%, based on active 
chlorine, of an alkali metal hypochlorite, or mixtures thereof. 
As a second essential ingredient, the compositions according to the present 
invention comprise a pH buffering means with a low sensitivity to water 
hardness or mixtures thereof, i.e. a pH buffering means which, when used 
in a 1M solution of the buffer at pH 10, requires more than 2.5 millimoles 
(mM) of calcium ions, preferably more than 3.5 mM, and more preferably 
more than 5 mM of said calcium ions, in order to cause precipitation at 
25.degree. C. of the calcium salt of the alkali anion of said pH buffering 
means. 
Accordingly, suitable pH buffering means to be used herein are selected by 
evaluating the amount of Ca ions required, when used in a 1M solution at 
pH 10, in order to cause precipitation at 25.degree. C. of the calcium 
salt of the alkali anion of said buffering means. This amount of Ca ions 
requested can be measured with the test method reported hereinafter in the 
experimental data. 
Suitable pH buffering means with a low sensitivity to water hardness 
preferably have their buffering pH, i.e. pKa of their conjugated acids, 
between 8.5 and 13, and more preferably between 9 and 11. 
Examples of said pH buffering means with a low sensitivity to water 
hardness include alkali metal salts of metaborate and stannate and 
mixtures thereof. Particularly preferred herein are the alkali metal salts 
of metaborate such as sodium metaborate and potassium metaborate, or 
mixtures thereof. 
The compositions according to the present invention comprise from 0.01% to 
20% by weight of the total composition of said pH buffering means which, 
when used in a 1M solution at pH 10, requires more than 2.5 mM of calcium 
ions, in order to cause precipitation at 25.degree. C. of the calcium salt 
of the alkali anion of said pH buffering means, preferably from 0.1% to 
15%, and more preferably from 0.5% to 8%. 
It has now been found that the addition of a pH buffering means which, when 
used in a 1M solution at pH 10, requires more than 2.5 mM of calcium ions, 
in order to cause precipitation at 25.degree. C. of the calcium salt of 
the alkali anion of said pH buffering means, in a liquid composition 
containing hypochlorite allows a prolonged through-the-bleach buffering 
action, i.e. allows to maintain the pH of the bleaching solution as high 
as possible for a longer period of time from the moment the dilution is 
completed, as compared to the buffering action obtained with the same 
composition without said pH buffering means or with the same composition 
but with another ingredient acting as a pH buffering means such as 
carbonate salts and/or silicate salts instead of said pH buffering means. 
It has been found that the buffering action of said pH buffering means 
allows to reduce the conversion of hypochlorite into hypochlorous acid, 
one of the species which are most responsible for the fabric damage and/or 
fabric whiteness, thereby providing improved fabric safety and/or fabric 
whiteness. 
By "improved fabric whiteness" it is meant herein that the whiteness on 
fabric achieved by using the hypochlorite compositions of the present 
invention is improved compared to the whiteness obtained by using the same 
hypochlorite compositions without said pH buffering means or by using the 
same compositions but with another ingredient acting as a pH buffering 
means such as carbonate salts and/or silicate salts instead of said pH 
buffering means according to the present invention. 
By "improved fabric safety" it is meant herein that the damage caused on 
fabric by using the hypochlorite compositions of the present invention is 
reduced compared to the damage caused by using the same hypochlorite 
compositions without said pH buffering means or by using the same 
compositions but with another ingredient acting as a pH buffering means 
such as carbonate salts and/or silicate salts instead of said pH buffering 
means according to the present invention. 
Fabric safety may be evaluated by different test methods including the 
copper number test. Indeed, the copper number on a fabric is proportional 
to the amount of aldehydic groups derived from the oxydation of cellulose 
and therefore is proportional to the fabric damage. Thus, the higher the 
copper number, the more damaged the fabric. The copper number test can 
consist in measuring the number of grams of copper which are reduced from 
cupric to the cuprous state by 100 g of cellulose. To this effect, a 
copper sulphate solution is added in excess so as to obtain the following 
reaction: 
EQU [aldehydic group] from fabrics+Cu++.fwdarw.Cu2O (cuprous oxide) 
Then Fe+++ ions is added so as to form ferrous sulphate in an amount 
exactly equivalent to the cuprous oxide present. 
EQU Fe2(SO4)3+Cu2O+H2SO4.fwdarw.2FeSO4+H2SO4+2CuSO4 
Finally, the ferrous sulphate is measured by titration with 0.1N potassium 
permanganate that oxide Fe++ (ferrous) ions to Fe+++ (ferric) ions. Fabric 
safety may also be evaluated by the tensile strength loss test. This 
method consists in measuring the tensile strength of a given fabric by 
pulling said fabrics until they break. The force, expressed in Kg, 
necessary to break said fabrics is the "ultimate tensile stress" and may 
be measured with "the stress-strain Instron tensilometer". The lower the 
force needed to break said fabrics, the less fabric damage is caused on 
the fabrics. 
An advantage of the present invention is that the buffering of the 
hypochlorite compositions of the present invention reduces harshness to 
hands. 
As a third essential feature, the compositions according to the present 
invention have a pH as is of from 8 to 14, preferably of from 9 to 13.5, 
and more preferably of from 9.5 to 13.5. It is in this alkaline range that 
the optimum stability and performance of the hypochlorite is obtained. 
Accordingly, the compositions of the present invention comprise a strong 
source of alkalinity. Preferred compositions herein comprise up to 10% by 
weight of the total composition of said strong source of alkalinity, or 
mixtures thereof, preferably of from 0.04% to 5% and more preferably of 
from 0.1% to 2%. Examples of strong sources of alkalinity are alkali metal 
hydroxides, such as potassium and/or sodium hydroxide, or alkali metal 
oxides such as sodium and/or potassium oxide. 
The compositions of the present invention are aqueous. Thus, they comprise 
is water preferably in an amount of from 60% to 98% by weight of the total 
aqueous liquid bleaching composition, more preferably of from 80% to 97% 
and most preferably of from 85% to 97%. 
The composition according to the present invention may further comprise as 
an optional but preferred ingredient a precipitation agent. Particularly 
useful to be used herein are alkali metal salts of carbonates, 
polycarbonates, sesquicarbonates, silicates, polysilicates or mixtures 
thereof. The preferred alkali metal salts to be used herein are sodium and 
potassium. Particularly preferred precipitation agents are alkali metal 
salts of silicate and/or carbonate. The preferred alkali metal salts of 
silicate and carbonates are sodium silicate and sodium carbonate, both of 
which are commercially available, or mixtures thereof. 
The compositions of the present invention comprise up to 5% by weight of 
the total composition of a precipitation agent, preferably from 0.01% to 
4% and more preferably from 0.02% to 3% 
We speculate that said precipitation agents such as sodium carbonate and/or 
sodium silicate, when added in an alkaline liquid composition comprising 
hypochlorite and a pH buffering means which, when used in a 1M solution at 
pH 10, requires more than 2.5 mM of calcium ions, in order to cause 
precipitation at 25.degree. C. of the calcium salt of the alkali anion of 
said pH buffering means, have a further action on top of the one of said 
pH buffering means allowing thereby to further improve the fabric 
whiteness and/or the fabric safety of fabrics treated with said 
composition. Indeed, said precipitation agent allows to reduce or even 
eliminate the impurities both in said compositions as is and especially in 
the bleaching environment. Said impurities include calcium, magnesium as 
well as heavy metal ions such as Cu, Fe, Ni, Co and the like, which have 
been found to adversely affect both fabric whiteness and fabric safety. 
Indeed, we believe that in the bleaching/washing environment the metal ions 
catalyse the attack of hypochlorite on fabrics with the generation of 
yellow oxidised species. It is further speculated that said metal ions are 
adsorbed per se on oxidised fabrics as coloured species and catalyse the 
degradation of the brighteners adsorbed on fabrics. Also said metal ions 
stabilise colored pigments of enzymatic stains such as blood and grass. 
Also metal ions catalyse the depolymerisation of cotton fibres which leads 
to reduced tensile strength of the fabrics, thereby reducing fabrics 
resistance. 
The precipitation agents according to the present invention may also act as 
pH buffering means, completing thereby the pH buffering action of the pH 
buffering means according to the present invention. 
The compositions according to the present invention may further comprise 
other optional ingredients such as bleach-stable surfactants, organic or 
inorganic alkalis, pigments, dyes, optical brighteners, solvents, 
chelating agents, radical scavengers and the like. 
The compositions according to the present invention are preferably used in 
diluted form in laundry application. The expression "use in diluted form" 
herein includes dilution by the user, which occurs for instance in hand 
laundry applications, as well as dilution by other means, such as in a 
washing machine. Preferred dilution levels are of from 0.1% to 20% for 
hand laundry application and 0.1% to 10% in a washing machine. 
The present invention further encompasses a method of bleaching fabrics 
which comprises the step of contacting said fabrics with a liquid 
bleaching composition having a pH of from 8 to 14, said composition 
comprising an alkali metal hypochlorite, or mixtures thereof, and a pH 
buffering means which, when used in a 1M solution at pH 10, requires more 
than 2.5 mM of calcium ions, in order to cause precipitation at 25.degree. 
C. of the calcium salt of the alkali anion of said pH buffering means. In 
a preferred embodiment, the compositions used in said method of bleaching 
fabrics may further comprise a precipitation agent as defined herein 
before. Said method according to the present invention improves the fabric 
whiteness and/or the fabric safety. 
More specifically, the method of bleaching fabrics according to the present 
invention comprises the steps of first contacting said fabrics with a 
liquid bleaching composition having a pH of from 8 to 14, said composition 
comprising an alkali metal hypochlorite, or mixtures thereof and a pH 
buffering means which, when used in a 1M solution, at pH 10, requires more 
than 2.5 mM of calcium ions, in order to cause precipitation at 25.degree. 
C. of the calcium salt of the alkali anion of said pH buffering means, 
then allowing said fabrics to remain in contact with said composition, for 
a period of time sufficient to bleach said fabrics, typically 1 to 60 
minutes, preferably 5 to 30 minutes, then rinsing said fabrics in water to 
remove said composition. If said fabrics are to be washed, i.e. with a 
conventional composition comprising at least one surface active agent, 
said washing may be conducted together with the bleaching of said fabrics 
by contacting said fabrics at the same time with a bleaching composition 
according to the present invention and said detergent composition, or said 
washing may be conducted before or after that said fabrics have been 
bleached. Accordingly, said method according to the present invention 
allows to bleach fabrics and optionally to wash fabrics with a detergent 
composition comprising at least one surface active agent before the step 
of contacting said fabrics with said bleaching composition and/or in the 
step where said fabrics are contacted with said bleaching composition 
and/or after the rinsing step when said bleaching composition has been 
removed from said fabrics. 
It is preferred to perform the bleaching method herein before said fabrics 
are washed. Indeed, it has been observed that bleaching said fabrics with 
the compositions according to the present invention prior to washing them 
with a detergent composition provides superior whiteness and stain removal 
with less energy and detergent than if said fabrics are washed first, then 
bleached. 
The alkaline liquid compositions according to the present invention 
comprising an alkali metal hypochlorite, a pH buffering means which, when 
used in a 1M solution at pH 10, requires more than 2.5 mM of calcium ions, 
in order to cause precipitation at 25.degree. C. of the calcium salt of 
the alkali anion of said pH buffering means, a strong source of alkalinity 
to obtain the desired pH, and optionally a precipitation agent may be 
manufactured by a process comprising the steps of: 
mixing said alkali metal hypochlorite, said strong source of alkalinity and 
water, 
adding said pH buffering means and optionally said precipitation agent, 
and thereafter separating the precipitates formed from said composition. 
By "separating the precipitates formed" it is meant herein that any means 
known to remove a solid phase from a liquid phase may be used. Accordingly 
the precipitates formed may be removed from the compositions of the 
present invention by settling and/or filtration and/or centrifugation.

EXPERIMENTAL DATA 
Sensitivity to water hardness was defined by the following test method: 
1M solutions of the buffers to study were prepared, 100 g of each solution 
were weighted, the pH was trimmed down to 10, and said solutions were 
filtered to eliminate any precipitates that may have formed. Then to each 
of said 1M solution of buffering means a stock solution (0.05M) of calcium 
chloride was added by 0.5 ml steps. After 20 minutes of stirring, 
turbidity was measured by optical spectroscopy at 360 nm versus a 
reference made of the neat solution. The experiment was stopped on 
formation of precipitates and the amount of calcium added was recorded. 
The results are the following: 
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Buffer means [Ca] mM ml Ca added 
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Carbonate 0.5 1.0 
Silicate 0.015 0.3 
Stannate 3.7 7.3 
Borate 0.025 0.5 
Metaborate more than 7.5 
more than 15 
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The following compositions which further illustrate the present invention 
were made by mixing the listed ingredients in the listed proportions: 
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Compositions (weight %) 
1 2 3 4 5 6 7 
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Sodium hypochlorite 
5.0 5.0 5.0 2.5 2.5 5.0 5.0 
Sodium hydroxide 
0.7 0.7 1.4 0.7 1.4 0.7 1.4 
Sodium carbonate 
1.0 -- 1.2 1.0 1.2 1.2 1.2 
Sodium silicate 
-- -- -- -- -- 0.2 -- 
Sodium metaborate 
1.0 1.0 1.0 0.75 
1.0 0.75 
0.5 
Water 
100% ------------------ 
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All the compositions above provided improved fabric safety and/or improved 
whiteness to fabrics when used to treat fabrics without compromising on 
stains removal performance on a wide variety of stains like bleachable 
stains, enzymatic stains and greasy stains.