Note: Descriptions are shown in the official language in which they were submitted.
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C3348
BLEACHING COMPOSITION
This invention relates to liquid bleach
compositions which may be thickened liquids suitable for
sale and use as a domestic bleach. The compositions of the
invention may be pourable liquids, albeit more viscous than
water, or may be even more viscous liquids which cannot be
poured easily. Thickening of a pourable domestic bleach
helps the user to control dispensing of the composition and
retards drainage from surfaces to which it is applied.
A domestic bleach needs to be adequately stable so
that a substantial proportion of the bleaching agent
survives during storage between manufacture and use. Prior
to the present invention, commercial liquid bleach products
have frequently utilised hypochlorite as bleaching agent.
It is well known that hydrogen peroxide is
unstable unless stabilising agents are present. These
counteract decomposition catalysed by transition metal
ions. Hydrogen peroxide gives better bleaching action if
used under alkaline conditions. However, stabilisation of
hydrogen peroxide under alkaline conditions is difficult and
in consequence commercial solutions of hydrogen peroxide
have generally been acidic for the sake of stability.
EP-B-9839 discloses that the stabilisation of
hydrogen peroxide under alkaline conditions can be
accomplished using certain specified phosphonate compounds.
It also contains comparative results testing the
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effectiveness of various materials as stabilisers under
alkaline conditions. These comparative results show that
many materials which are known to stabilise acidic hydrogen
peroxide have very little effect under alkaline conditions.
One material which has been disclosed as a
stabiliser for hydrogen peroxide in acidic solution is
colloidal hydrous stannic oxide. US 3781409 and US 3607053
are examples of disclosures of the use of sodium stannate as
a stabilising agent for acidic hydrogen peroxide solution.
In these US patents the sodium stannate is dissolved in an
alkaline but peroxide-free solution which is then added as a
stabiliser to very much larger volumes of acidic hydrogen
peroxide solution. The sodium stannate will undergo
hydrolysis to colloidal hydrous stannic oxide in the
solution. The alkaline solution contains other salts in
addition to sodium stannate but these are diluted to a very
low electrolyte level when added to the acidic hydrogen
peroxide solution.
Pourable domestic liquid bleach is frequently
thickened by including one or more surfactants which, in the
presence of electrolyte, act to thicken the solution so that
it becomes more viscous than water.
The presence of electrolyte tends to cause
decomposition of alkaline hydrogen peroxide solution. For
instance, we have found that a 4% by weight solution of
hydrogen peroxide, made alkaline to pH 10 and containing
0.25% of ethylene diamine tetramethylene phosphonic acid as
stabiliser (which is not as effective as phosphonates in
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accordance with EP-B-9839) was found to retain 95% of its
hydrogen peroxide after two weeks storage at 37C. By
contrast, 85% or less of the hydrogen peroxide was retained
if the solution also contained 1% by weight of sodium
chloride, while only about 50% of the hydrogen peroxide was
retained if the solution contained 10% by weight of sodium
chloride. Similar results were observed using sodium
tripolyphosphate rather than sodium chloride as the added
electrolyte. Doubling the quantity of the phosphonate
stabiliser had little effect on the rate of decomposition.
Thus, any attempt to make a surfactant-thickened,
alkaline domestic liquid bleach product using hydrogen
peroxide as the bleaching agent would encounter the
potential problem that the thickening of the solution would
require the presence of some electrolyte but that this
electrolyte would serve to accelerate decomposition of the
peroxide.
A further potential problem arises because
electrolyte inherently tends to bring about flocculation of
colloidal suspensions. Consequently the presence of
electrolyte also has the potential to bring about a
reduction of the effectiveness of any stabilising agent
which is in the form of a colloidal suspension.
It is surprising that - as we have now found -
colloidal hydrous stannic oxide can act as a very effectivestabilising agent for alkaline hydrogen peroxide solutions.
It is also surprising that colloidal hydrous stannic oxide
will tolerate the inclusion of surfactant and electrolyte in
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sufficient quantities to effect thickening.
In a first aspect, therefore, the present invention provides a liquid
bleaching composition comprising an aqueous alkaline solution, wherein the
total quantity of inorganic salts in the composition does not exceed 5% by weight
5 based on the whole composition, said solution comprising:
a) 0.05-0.30 molar electrolyte,
b) 0.75-3.0%wt of at least one surfactant which thickens in the presence
of the electrolyte (a) so as to increase the viscosity of the
composition,
c) 2-10%wt of hydrogen peroxide, and,
d) an effective amount of colloidal hydrous stannic oxide as a stabilizer
for the hydrogen peroxide.
The colloidal hydrous stannic oxide which is used as a stabilising agent is
preferably formed in-situ in the solution as the product of hydrolysis of a soluble
15 tin compound. Consequently in a second aspect this invention provides a
method of preparing a liquid bleaching composition which comprises including
in the composition, successively or together, hydrogen peroxide, sufficient
alkaline material to give the solution an alkaline pH, and a tin compound
capable of hydrolysis to stannic oxide, so that the tin compound is hydrolysed in
2 0 the solution to colloidal hydrous stannic oxide. The hydrolysis may take place in
a solution which is already thickened by the presence of surfactant therein, even
though the peroxide may not yet have been added to the solution. Various tin
compounds can be added to the solution to undergo hydrolysis to form the
stannic oxide. Those preferred are tin sulphate and sodium
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stannate. Other tin compounds can be used, including tin
dichloride and tin tetrachloride.
The concentrations of tin compound included in the
composition may lie in the range from 10- 4 molar to 10- 2
molar, preferably 3 x 10- 3 to 6 x 10- 3 molar. The quantity
of tin compound should not be substantially greater than
necessary, since excess of it can itself cause peroxide
decomposition. An optimum concentration of the tin compound
can be determined by making test solutions with various
concentrations of the tin compound and analytically
determining the amount of peroxide retained on storage.
The compositions of this invention preferably
have a pH in the range from 8.0 to 10.5, better 8.5 to 9.8
or 10.0, yet more preferably 8.7 to 9.3. A buffer may be
included to set the pH.
As already mentioned above, it is preferred to
include at least one surfactant to increase the viscosity of
the composition. It is desirable that this surfactant or
surfactants has the ability to thicken a solution in the
presence of a fairly low electrolyte concentration. This
may make it possible for the electrolyte to be provided by
salts which are in the composition for another purpose,
without deliberate addition of any salt for the sole purpose
of enhancing ionic strength. Since electrolyte is known to
be detrimental to hydrogen peroxide stability, it is
desirable to keep the electrolyte concentration low. A
further benefit of a low electrolyte concentration is a
reduced tendency for the composition to leave streaks on a
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surface which is cleaned with it.
One surfactant which is suitable to effect
thickening is alkyl ether sulphate having the formula:
R ( OC2 H4 )n OSO3 M
where R is an alkyl group, preferably linear alkyl,
containing 8 to 20 carbon atoms, n has an average value in
the range from 0.5 to 12 better 1 to 6 and M is a
solubilising cation, preferably alkali metal such as sodium.
A pair of surfactants used to effect thickening
may be a combination of a nonionic or amphoteric surfactant
together with an anionic surfactant. Two specific
possibilities are the combinations of:
i) an amine oxide surfactant, preferably a trialkyl
amine oxide with one long chain alkyl of 8 to 20 carbon
atoms and two alkyl groups of 1 to 4 carbon atoms; and
ii) an anionic surfactant which is either primary
alcohol sulphate with 8 to 20 carbon atoms in the alkyl
group thereof or alkane sulphonate derived from alkane of 8
to 20 carbon atoms.
Further surfactants may also be present. The
total amount of surfactant(s) included may be a small
proportion of the composition, for example the thickening
surfactant(s) may constitute 0.75 to 3% of the composition.
Larger amounts, giving greater viscosity, may be used but
are less preferred.
When primary alcohol sulphate is employed, the
weight ratio of amine oxide:alcohol sulphate preferably
ranges from 82:18 or 80:20 to 65:35, better 80:20 to 70:30.
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Alkane sulphonate ls preferred over alcohol
sulphate, because the vlscoslty is less sensitive to changes
in the compositlon, so making it easler to produce an end
product with repeatable viscosity. The weight ratio of
amine oxide to alkane sulphonate ls preferably in the range
from 80:20 to 50:50 or 65:35, better 70:30 to 65:35.
An appropriate viscosity for a pourable
composition having the appearance of a thick liquid is a
dynamic viscosity in the range from 50 to 250 centipoise
(0.05 to 0.25 Pa.sec), preferably about 100 centipoise
(0.1 Pa.sec). More viscous liquids for example with
viscosity in the range from 250 to 1000 cent~poise or more
are also within the scope of the invention.
Since the compositions of this invention are
generally aqueous, they will usually have specific yravity
close to unity. Consequently values of kinematic
viscosities (in stokes) will be numerically approximately
iiB
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the same as values of dynamic viscosity (in poise). Dynamic
viscosities expressed in Pascal.sec will be approximately
1000 times kinetic viscosities expressed in m2.sec~1.
Example 1
Formulations were prepared containing the
constituents set out in Table 1 below. The compositions
were stored in plastic bottles at 37C. At intervals
aliquots were removed and titrated with potassium
permanganate to determine the level of hydrogen peroxide
remaining. Results are included in Table 1.
The viscosity of these formulations was measured
using a Ubbelohde capillary viscometer and found to be
approximately lOOcS.
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TABLE 1
% by weight
Constituent A B C
5 Hydrogen peroxide 5 5 5
(reckoned as anhydrous)
Tallow dimethylamine oxide 1.0 1.0 1.0
Sodium alkane sulphonate 0.5 0.5 0.5
Perfume 1.0 1.0 1.0
Tetrasodium pyrophosphate 1.8 - -
(reckoned as anhydrous)
Phosphonate stabiliser 0.15 - -
according to EP 9839
20 Borax (reckoned as anhydrous) - 1.6 1.6
Sodium stannate trihydrate - 0.5 0.1
Sodium hydroxide to give: pH 9.6 pH 9.6 pH 9.0
Water ----- balance to 100% -----
Hz 2 remaining after 50 days: 85% 79%
H2 2 remaining after 100 days: 96%
The stabiliser in accordance with EP 9839 was
diethylene triamine penta (methylene phosphonic acid).
Example 2
The procedure of Example 1 was repeated, using
formulations with the same amounts of hydrogen peroxide,
surfactant, perfume and dye. Various tin compounds were
used at a concentration of 6 x 10- 3 molar, both with and
without 3.0% borax decahydrate. Glass bottles were used,
which are somewhat detrimental to stability. In every case
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pH was 9.6 initially. Proportions of hydrogen peroxide
remaining after 28 days were:-
SnCl2 with borax 68%
5 Na2SnO3 with borax 47%
SnS04 with borax 45%
Na2SnO3 without borax 96%
SnS04 without borax 95%
Example 3
The procedure of Example 1 was repeated using adifferent surfactant and with stannous chloride as the tin
salt. The surfactant used was a linear alkyl ether
sulphate of general formula:
R(OC2H4) n 0S03 Na
where the alkyl group R was C1 2 and C1 3 linear alkyl
groups, and n had an average value of 3. A comparative
experiment replaced the stannous-chloride with the same
phosphonate stabiliser according to EP 9839 as used in
Example 1. The formulations and results are set out in the
following Table. Viscosities were determined using a Haake
roto-viscometer and were approximately lOOcP at a shear rate
of 21 sec~l.
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TABLE 2
% by weight
Constituent A B
Hydrogen peroxide 5 5
(reckoned as anhydrous)
Alkyl ether sulphate 1.25 1.25
Sodium chloride 6.5 6.5
Perfume 0.08 0.08
Stannous chloride dihydrate 0.14
Phosphonate stabiliser
according to EP 9839 - 0.15
Sodium hydroxide to give: pH 9.6 pH 9.6
20 Water -- balance to 100% --
H2 2 remaining
after 5 weeks at 37C 80% 79%
Example 4
An alkaline solution of hydrogen peroxide was
prepared containing 4% by weight hydrogen peroxide (reckoned
as anhydrous) sodium hydroxide to give a pH of 10 and a
5.7 x 10- 3 molar quantity of stannic chloride which
hydrolysed to colloidal hydrous stannic oxide.
The composition was stored at 40C and the amount
of hydrogen peroxide remaining was determined analytically
at intervals. It was found that 75% of the hydrogen
peroxide remained after 3 weeks.
Although this test was made without surfactant or
much electrolyte present, it confirms the effectiveness of
colloidal stannic oxide as a stabiliser in alkaline
solution.
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Example 5
Alkaline solutions of hydrogen peroxide were
prepared containing surfactant, sodium chloride and stannic
chloride which hydrolysed to colloidal hydrous stannic
oxide. Two surfactant combinations were used.
The quantities of surfactant and sodium chloride
were such as to give viscosities well in excess of that
preferred for a pourable type of bleach product. Smaller
quantities could be used to give a "thick liquid" type of
bleach product.
In each case the initial concentration of
hydrogen peroxide, reckoned as anhydrous, was 4% by weight.
The solutions were made alkaline to pH 10 with sodium
hydroxide.
Stannic chloride was used at a concentration of
2.3 x 10- 3 molar.
One surfactant system consisted of 4.5~ by weight
of C1 2 -Cl 4 alkyl dimethyl amine oxide and 4.5% by weight
sodium lauryl sulphate. This was used with a sodium
chloride concentration of 9% by weight.
The second surfactant system consisted of 5% by
weight of C11-C1 5 secondary alcohol ethoxylated with average
3 ethylene oxide residues, and 5~ by weight of sodium lauryl
sulphate. This combination was used with 3.37% by weight
sodium chloride.
The solutions were stored at 40C and the amount
of hydrogen peroxide remaining was determined at intervals.
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It was found that the amounts of hydrogen peroxide remaining
were between 80 and 85% with either of the surfactant
combinations.
Example 6
A base solution was prepared containing tallow
dimethylamine oxide, sodium alkane sulphonate and borax.
This was used to make up solutions containing hydrogen
peroxide and colloidal stannic oxide, but two procedures
were used.
In one procedure stannous chloride dihydrate was
added to the base solution and stirred until it was
completely dissolved or dispersed, after which hydrogen
peroxide solution was added. The solution pH at this stage
was 6.5. It was adjusted to pH 9.9 by adding 20% w/v sodium
hydroxide solution and some distilled water.
The quantities used were such that the composition
contained:
20 Hydrogen peroxide 4.98g
(reckoned as anhydrous)
Tallow dimethylamine oxide 0.98g
25 Sodium alkane sulphonate 0.48g
Borax (reckoned as anhydrous) 1.6 g
SnCl2.2H20 0.14g
Sodium hydroxide to give: pH 9.9
Water balance to lOOg total
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In the alternative procedure a suspension of
stannic oxide was prepared by dissolving 5g of stannous
chloride dihydrate in approximately 115g distilled water,
and then adding sodium hydroxide solution to give a pH of
5 9.7. The resulting suspension of stannic oxide was stored
overnight.
Hydrogen peroxide was added to the base solution,
followed by sodium hydroxide solution and some distilled
water to give a pH of 9.9. A small quantity of suspension
10 was then added. This was calculated to be the quantity of
suspension produced from 0.14g of SnCl2.2H20. Other
quantities were as for the first procedure.
The solutions were both stored at 37C (to
accelerate aging) and the concentration of hydrogen peroxide
remaining was determined by analysis after 48 and 120 hours.
The results were as follows:
H2O2 concentrations
After After
Initially48 hours120 hours
Stannic oxide
formed in presence
of H2 2 and 4.98 4.95 4.88
surfactant
Stannic oxide
formed separately 4.98 4.81 4.82
and aged
