Stable sodium percarbonate formulation

This invention provides a stable hydrogen peroxide-releasing formulation in liquid or gel form, having a content of sodium percarbonate which is stabilized by a specific proportion of deionized water. The formulation can be incorporated as a constituent of detergent or dentifrice compositions.

BACKGROUND OF THE INVENTION 
Sodium carbonate forms a crystalline addition compound with hydrogen 
peroxide, corresponding to the formula 2 Na.sub.2 CO.sub.3.3 H.sub.2 
O.sub.2 (sodium carbonate sesquiperoxide), and is commonly known as sodium 
percarbonate. The compound has many potential applications as a peroxygen 
source when dissolved in an aqueous medium. 
Sodium percarbonate has a high active oxygen content (15.28% theoretical) 
and high water solubility. It is produced from low cost starting 
materials, and it is an environmentally safe chemical. 
Sodium percarbonate has not achieved the commercial acceptance of sodium 
perborate, mainly because it is less stable than sodium perborate. Solid 
sodium percarbonate decomposes with a loss of active oxygen which is 
substantially greater than the decomposition of sodium perborate under the 
same conditions. This problem is particularly undesirable in detergent 
cartons sold at retail. The problem also is evident during processing and 
storage of detergent compositions. 
Stabilizers such as magnesium sulfate are suitable for stabilizing sodium 
perborate, but provide only limited protection with sodium percarbonate. 
Various methods for stabilization of sodium percarbonate have been 
proposed. 
U.S. Pat No. 2,380,620 discloses that sodium silicate, magnesium sulphate 
or gum arabic are unsatisfactory stabilizers when incorporated in sodium 
percarbonate, but diphenylguanidine lessens the decomposition in the 
presence of the conventional stabilizers. 
U.S. Pat No. 3,951,838 discloses that prior attempts at chemical 
stabilization of sodium percarbonate, primarily by magnesium silicate, are 
generally ineffective in promoting long term stability, particularly in a 
humid atmosphere. The patent proposes coating of the particles with an 
aqueous silica sol and drying to accomplish stabilization. 
U.S. Pat. No. 4,075,116 describes cocrystallizing of sodium percarbonate 
with other salts known to form perhydrates such as sodium sulfate, sodium 
pyrophosphate, sodium glucoheptonate, sodium perborate, and the like. 
U.S. Pat. No. 4,171,280 discloses that a non-caking bleach composition may 
be formed containing up to 6% active oxygen by spraying only sufficient 
hydrogen peroxide onto sodium carbonate particles to convert a part of the 
sodium carbonate to sodium percarbonate. U.S. Pat. No. 4,260,408 teaches 
the addition of sodium phosphate to the composition as a stabilizer. Both 
patents demonstrate that an assay of less than 6% active oxygen (less than 
40% sodium percarbonate) is necessary to obtain satisfactory stability. 
U.S. Pat. No. 5,244,644 describes a process for producing alkali metal 
percarbonate with improved caking resistance which involves admixing 
percarbonate powder with a particulate fatty acid metal salt additive. 
There is continuing research and development effort to produce sodium 
percarbonate in a form which exhibits long term stability under storage 
conditions, and when incorporated as a peroxygen ingredient in commercial 
products. 
Accordingly, it is an object of this invention to provide a sodium 
percarbonate formulation which is stable under ambient temperature and 
moisture conditions. 
It is a further object of this invention to provide a sodium percarbonate 
formulation which is stable when incorporated as an ingredient in a 
detergent or dentifrice type consumer product, and which releases active 
oxygen under product utilization conditions. 
Other objects and advantages of the present invention shall become apparent 
from the accompanying description and examples.

DESCRIPTION OF THE INVENTION 
One or more objects of the present invention are accomplished by the 
provision of a stable hydrogen peroxide-releasing formulation comprising 
(1) between about 55-90 weight percent of polyalkylene glycol; (2) between 
about 5-20 weight percent of sodium percarbonate; (3) between about 0.5-3 
weight percent of colloidal silica; (4) between about 1-5 weight percent 
of alkali metal pyrophosphate; and (5) between about 0.2-1 part by weight 
of water per part of sodium percarbonate. 
In a further embodiment the invention hydrogen peroxide-releasing 
formulation contains between about 0.05-2 weight percent of a stabilizer 
ingredient such as sodium silicate, magnesium silicate or magnesium 
sulfate. 
The polyalkylene glycol ingredient of an invention formulation preferably 
is selected from liquid oxyalkylated diols which have a molecular weight 
in the range between about 200-8000. Polyethylene glycols are commercially 
available under tradenames such as Carbowax 200, 300, 400, 600, 900, 1000, 
2000, 4000, 6000 and 8000 (Union Carbide), in which the number values are 
approximations of average molecular weight. Polyethylene-propylene glycols 
are commercially available under tradenames such as Pluracare/Pluronic 
L-31 and L-35 (BASF). 
The polyalkylene glycol ingredient serves as a hydrophilic vehicle for the 
other formulation ingredients, and it enhances the compatibility of the 
ingredients when the formulation is incorporated as a constituent in a 
detergent or dentifrice composition. 
The sodium percarbonate ingredient of an invention formulation is employed 
in the form of a crystalline powder, which preferably has an average 
particle size between about 20-600 microns. Methods of manufacturing 
sodium percarbonate are described in technical publications such as U.S. 
Pat. No. 4,966,762 and references cited therein. 
The colloidal silica ingredient of an invention formulation can be selected 
from amorphous silica compounds which function as a thickening agent 
relative to the polyalkylene glycol ingredient. Commercial colloidal 
silica compounds are available under tradenames such as Sylodent 15 and 
Sylodent 2 (W. R. Grace), Aerosil 200 (Degussa) and Cabosil fumed silica 
(Cabot). The colloidal silica ingredient is compatible with the 
polyalkylene glycol ingredient. 
Aerosil 200 is a preferred type of hydrophilic fumed silica having a 
surface area of about 200 M.sup.2 /g, and an average particle size between 
about 10-12 nanometers. Aerosil R972 is a hydrophobic fumed silica having 
a surface area of about 100 M.sup.2 /g, and an average particle size of 
about 15 nanometers. 
The alkali metal pyrophosphate ingredient is selected from suitable 
inorganic salts which include dialkali metal pyrophosphate and tetraalkali 
metal pyrophosphate and mixtures thereof in a hydrated or unhydrated form. 
Illustrative of pyrophosphate salts are Na.sub.2 H.sub.2 P.sub.2 O.sub.7, 
Na.sub.4 P.sub.2 O.sub.7 and K.sub.4 P.sub.2 O.sub.7. 
If tetrasodium pyrophosphate is employed as the salt ingredient, preferably 
it is employed in the form of an anhydrous crystalline powder (Na.sub.4 
P.sub.2 O.sub.7) which contributes multiple advantages to an invention 
formulation. A tetrasodium pyrophosphate ingredient provides an alkalinity 
which neutralizes the acidity of the colloidal silica ingredient, and 
prevents a reaction with sodium percarbonate which causes generation of 
carbon dioxide gas. A tetrasodium pyrophosphate ingredient also can 
function as a chelating agent for polyvalent metals such as iron or 
manganese which catalyze the decomposition of sodium percarbonate with a 
resultant loss of active oxygen. 
As a further advantage, when an invention formulation is incorporated as a 
constituent of a dentifrice composition, a pyrophosphate salt such as 
tetrasodium pyrophosphate ingredient functions an anti-tartar agent. 
A present invention hydroxygen peroxide-releasing formulation can be 
blended with other ingredients to form a powder detergent composition, 
which can include builder, surfactant, optical brightener, perfume, and 
other conventional detergent constituents. 
A present invention hydrogen peroxide-releasing formulation also can be 
formed into a toothpaste by blending the formulation with dentifrice 
ingredients, such as sodium bicarbonate, flavorant, sweetener, and the 
like. 
Suitable flavorants include oils of spearmint, peppermint, wintergreen, 
sassafras, clove, sage, eucalyptus, marjoram and cinnamon, and flavorants 
such as methyl salicylate and menthol. 
Suitable sweeteners include sodium saccharin, sodium cyclamate, xylitol, 
perillartine, D-tryptophan, aspartame, and the like. 
A present invention hydrogen peroxide-releasing formulation can be prepared 
conveniently by blending each of the particulate ingredients into the 
polyalkylene glycol ingredient, which normally is a viscous liquid at room 
temperature. Depending on the relative proportions of ingredients, the 
formulation product will be a homogenous two-phase suspension in a liquid 
or gel form at 25.degree. C. As an alternative means of preparation, each 
of the particulate ingredients can be blended into a separate portion of 
the polyalkylene glycol medium, and the separate portions then are 
combined to form the formulation product. 
As an alternative ingredient to sodium percarbonate, the present invention 
also contemplates the use of other inorganic peroxyhydrate compounds which 
yield hydrogen peroxide when dissolved in an aqueous medium, such as 
sodium pyrophosphate peroxyhydrate. 
The following examples are further illustrative of the present invention. 
The components and specific ingredients are presented as being typical, 
and various modifications can be derived in view of the foregoing 
disclosure within the scope of the invention. 
FIGS. 1-3 are bar graphs which are a representation of the comparative 
stability data corresponding to the 14 formulations as prepared and tested 
in Example I. 
For test purposes in Example I, the level of active oxygen content retained 
in each formulation under simulated storage conditions is determined as 
follows: 
A 1-2 gram sample of a formulation is weighted accurately, and transferred 
into 250 ml Erlenmeyer flask. A 75-100 ml aliquot of 3M sulfuric acid is 
added dropwise while the flask contents are swirled gently. The acidified 
aqueous medium then is titrated with 0.1N KMnO.sub.4 solution until a 
permanent pink color is evident. 
##EQU1## 
where V is ml of KMnO.sub.4 solution consumed; and N is normality of 
KMnO.sub.4 solution. 
EXAMPLE I 
This Example illustrates the stability of hydrogen peroxide-releasing 
formulations in accordance with the present invention. 
A series of gel formulations are prepared by blending the ingredients 
listed in the Table. 
The effect of water content on the stability of sodium percarbonate is 
tested for the 14 formulations in the Table. FIG. 1-3 are bar graphs which 
summarize the comparative stability data at temperatures of 25.degree. C. 
and 37.5.degree. C. over extended periods of time. 
The comparative data demonstrate that the highest sodium percarbonate 
stability is exhibited by gel formulations which have a water content 
between about 0.2-1 part by weight per part of sodium percarbonate. 
TABLE 
__________________________________________________________________________ 
Formulation Numbers 
Ingredient Parts By Weight 
1 2 3 4 5 6 7 8 9 10 11 12 13 14 
__________________________________________________________________________ 
Polyethylene glycol (M.W. 400) 
34 33 31 29 34 33 31 29 34 32 30 28 26 26 
Deionized water 0 1 3 5 0 1 3 5 0 2 4 6 8 10 
Sodium percarbonate 
6 6 6 6 6 6 6 6 6 6 6 6 6 6 
Aerosil 200 (Degussa) 
1 1 1 1 1 1 1 1 1 1 1 1 1 1 
Tetrasodium pyrophosphate 
0.5 
0.5 
0.5 
0.5 
0.5 
0.5 
0.5 
0.5 
0.5 
0.5 
0.5 
0.5 
0.5 
0.5 
__________________________________________________________________________ 
EXAMPLE II 
This example illustrates the incorporation of a stable hydrogen 
peroxide-releasing formulation into a heavy duty detergent powder 
composition in accordance with the present invention. 
A pre-blend gel is prepared with the following ingredient: 
______________________________________ 
Parts By Weight 
______________________________________ 
Polyethylene glycol (M.W. 400) 
30.45 
Polyethylene glycol (M.W. 8000) 
0.9 
Sodium percarbonate 6.0 
Aerosil 200 (Degussa) 
1.0 
Tetrasodium pyrophosphate 
2.0 
Water 6.0 
______________________________________ 
The pre-blend is admixed with detergent ingredients to form a heavy duty 
powder detergent composition with a content of about 2 weight percent of 
sodium percarbonate. The sodium percarbonate is blended first with sodium 
carbonate, and then with the other detergent ingredients except for the 
water. The blended powder is sprayed with water to form granules having an 
average diameter of 500 microns, and then dried. 
______________________________________ 
Hydrogen peroxide-releasing Detergent Composition 
Parts By Weight 
______________________________________ 
Sodium carbonate 75.0 
Sodium Neodol 25-3 sulfate.sup.(1) 
4.5 
Neodol 25-3 2.5 
Sodium sulfate 1.5 
Sodium bicarbonate 1.5 
Acusol 912N.sup.(2) 0.5 
Sodium carboxymethylcellulose.sup.(3) 
0.2 
Optical brightener 0.2 
Perfume 0.1 
Water 7.0 
Sodium percarbonate formulation 
16.0 
______________________________________ 
.sup.(1) Ethoxylated C.sub.12 -C.sub.15 alcohol sulfate salt (Shell 
Chemical Company). 
.sup.(2) Sodium polyacrylate; Rohm & Haas 
.sup.(3) Finetex Inc. 
EXAMPLE III 
This Example illustrates the preparation of a stable dentifrice composition 
in accordance with the present invention. 
A pre-blend is prepared with the following ingredients: 
______________________________________ 
Parts By Weight 
______________________________________ 
Polyethylene glycol (M.W. 400) 
30.45 
Polyethylene glycol (M.W. 8000) 
0.9 
Sodium percarbonate 6.0 
Aerosil 200 (Degussa) 
1.0 
Tetrasodium pyrophosphate 
2.0 
Water 6.0 
______________________________________ 
The pre-blend is admixed with additional ingredients to form a composition 
with a toothpaste consistency: 
______________________________________ 
Weight Percent 
______________________________________ 
Polyethylene glycol (M.W. 400) 
30.45 
Polyethylene glycol (M.W. 8000) 
0.9 
Sodium percarbonate 6.0 
Aerosil 200 (Degussa) 
1.0 
Tetrasodium pyrophosphate 
2.0 
Water 6.0 
Sodium bicarbonate 52.0 
Flavor 0.75 
Saccharin 0.9 
______________________________________ 
The invention toothpaste is more stable than control toothpastes which have 
a water content of one weight percent and zero weight percent 
respectively, when tested at 37.5.degree. C. for 21 days. The invention 
toothpaste has an active oxygen loss of about 4%, and the control 
toothpastes have an active oxygen loss in the range of about 10-14 
percent.