Cleaning compositions for solid surfaces – auxiliary compositions – Cleaning compositions or processes of preparing – With oxygen or halogen containing chemical bleach or oxidant...
Reexamination Certificate
2001-04-16
2003-02-18
Gupta, Yogendra N. (Department: 1751)
Cleaning compositions for solid surfaces, auxiliary compositions
Cleaning compositions or processes of preparing
With oxygen or halogen containing chemical bleach or oxidant...
C510S442000
Reexamination Certificate
active
06521583
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to coated sodium percarbonate particles, to a process for the preparation of the coated sodium percarbonate particles, to the use of the coated sodium percarbonate particles in detergent compositions and to detergent compositions comprising the coated sodium percarbonate particles.
BACKGROUND OF THE INVENTION
The use of sodium percarbonate (or sodium carbonate peroxyhydrate) as the active bleach constituent in detergent compositions for household fabric washing or dish washing is well known. Commonly such detergent compositions contain among other components zeolites as builder material, enzymes, bleach activators and/or perfumes. However, the interaction between sodium percarbonate and other formulation components leads to progressive decomposition of the percarbonate and hence to loss of bleaching power during storage and transportation of the composition. A number of proposals have been made to overcome this problem by interposing a layer between the sodium percarbonate and its environment, called a coating layer. For instance in the Belgian patent BE 842014 sodium sulfate is used as one of the constituents of the coating layer. In the international patent application WO 96/14389 a magnesium salt is used as one of the constituents of the coating layer. In the patent application JP 59/204697 a borate is used as one of the constituents of the coating layer. These known coating layers do not result in man optimum combination of properties since they do not confer simultaneously a good stability to the sodium percarbonate when present in the detergent composition, a rapid dissolution rate when the composition is used in washing applications and a low moisture affinity when the composition is stored at high humidity.
SUMMARY OF THE INVENTION
The aim of the present invention is to overcome the aforementioned drawback by proposing new coated sodium percarbonate particles presenting simultaneously a good stability, a rapid dissolution rate and a low moisture affinity.
Consequently, the invention concerns coated sodium percarbonate particles containing:
a) a sodium percarbonate core, and
b) a coating layer substantially free from sulfate, borate and magnesium compounds, comprising at least 30 and at most 75% w/w of an alkali metal carbonate and at least 25 and at most 70% w/w of an alkali metal silicate, the alkali metal carbonate and silicate being uniformly dispersed in the coating layer.
By substantially free from sulfate, borate and magnesium compounds is meant less than 5% w/w of the total coating, preferably less than 2% w/w of the total coating, more preferably less than 1% w/w of the total coating, most preferably less than 0.5% w/w of the total coating, of sulfate, borate and/or magnesium compounds.
In a preferred embodiment, the coating layer contains only the alkali metal carbonate and silicate.
One of the essential characteristics of the invention resides in the combination of an alkali metal carbonate with an alkali metal silicate in the coating layer in the given proportions and the substantial absence of sulfate, borate and magnesium compounds in the coating layer. It has indeed been found that this combination confers advantageous properties to the sodium percarbonate which become clear in the following paragraphs.
Another important element of the invention resides in the uniform distribution of the alkali metal carbonate and silicate in the coating layer. This means that it is not possible to determine within the coating layer the presence of parts which contain solely alkali metal carbonate and/or parts which contain solely alkali metal silicate. In other words, the carbonate and the silicate have been applied together to the sodium percarbonate core as a uniform mixture so that they are equally dispersed on the surface of the core particles and that the coating layer comprises a homogeneous mixture of carbonate and silicate.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The coating layer of the coated sodium percarbonate according to the invention comprises preferably at least 40% w/w of alkali metal carbonate. Advantageously it comprises at most 70% w/w of alkali metal carbonate. Preferably it comprises at least 30% w/w of alkali metal silicate. Advantageously it comprises at most 60% w/w of alkali metal silicate. Coating layers comprising from 40 to 70% w/w of alkali metal carbonate and from 30 to 60% w/w of alkali metal silicate are convenient. It has been observed that low levels of alkali metal carbonate are not desirable because the tackiness of these systems facilitate agglomeration of the coated particles which is undesirable.
Preferably, sodium carbonate and sodium silicate are used as the alkali metal carbonate and silicate.
In the coated sodium percarbonate particles according to the invention the fraction of the coating layer is usually at least 1% w/w. It is in particular at least 2% w/w. The fraction of coating layer is commonly at most 5% w/w. More particularly it is at most 4% w/w. Fractions of coating layer from 1 to 5% w/w of the coated sodium percarbonate, preferably from 2 to 4% w/w are convenient. Fractions of coating layer superior to 5% lead to lowering of Avox and are difficult to achieve in a single coating operation without significant product agglomeration.
The coated sodium percarbonate particles according to the invention present usually an Avox of at least 12% w/w. The Avox is preferably at least 13.9% w/w. The Avox is generally at most 15% w/w. It is in particular at most 14.6% w/w. Avox values from 12 to 15% w/w and preferably from 13.9 to 14.4% w/w are convenient. The highest Avox values are obtained when the coating layer contains at least 50% w/w of alkali metal carbonate. The Avox is the available oxygen found in sodium percarbonate and indicates the amount of oxygen utilizable in a chemical reaction. It is measured by titration with potassium permanganate after dissolution in sulfuric acid (see ISO 1917-1982) according to the following reaction:
6H
+
+2MnO
4
−
+5H
2
O
2
→2Mn
2+
+8H
2
O+5O
2
For Avox calculation:
H
2
O
2
→H
2
O+O
where O represents Avox.
The coated sodium percarbonate particles according to the invention usually have a bulk density of at least 0.9 g/cm
3
. The bulk density is preferably at least 1.0 g/cm
3
. It is generally at most 1.2 g/cm
3
. It is in particular at most 1.1 g/cm
3
. Bulk densities from 0.9 to 1.2 g/cm
3
, preferably from 1.0 to 1.1 g/cm
3
give good results. The bulk density is measured by recording the mass of sample in a stainless steel cylinder of internal height and diameter of 86.1 mm, after running the sample out of a funnel (upper internal diameter 108 mm, lower internal diameter 40 mm, height 130 mm) placed 50 mm directly above the receiver. The higher levels of alkali metal carbonate in the coating layer ensure that a high bulk density is achieved.
The coated sodium percarbonate particles according to the invention present usually a low rate at which it picks up moisture from a humid atmosphere. The capability to pick up moisture is measured by the following test. A 9 cm diameter petri dish with a 1 cm depth rim is weighed accurately on a 4 decimal place balance (W
1
). A sample of dry coated sodium percarbonate (about 20 g) is placed on the petri dish which is gently agitated to generate an even particulate layer across the base of the dish and reweighed on the same balance (W
2
). The sample on the petri dish is stored in a room, about 3 m high, wide and long in an atmosphere maintained for a period of 24 hours at 32° C. by a thermostat controlled heater and at 80% Relative Humidity (RH) by introduction of a fine droplet water spray under the control of a humidity detector and weighed on the same balance (W
3
). The samples are protected by a shield from the spray. The moisture pick-up of the coated sodium percarbonate is calculated as follows:
Moisture
Pick
-
up
(
g
/
kg
)
=
1000
×
(
W3
-
W2
)
(
W2
-
W1
)
The coated
Candy Tom
Horne Graham R.
James Alun P.
Mathes Manfred
Rösler Richard
Gupta Yogendra N.
Larson & Taylor PLC
Petruncio John M
Solvay ( Societe Anonyme)
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