Note: Descriptions are shown in the official language in which they were submitted.
1 216~2~l
Description
The invention relates to coated sodium percarbonate
particles consisting of a core of sodium percarbonate and a
coating which contains sodium carbonate, which constitutes
1 to 25 wt.~ of the sodium percarbonate. The coated sodium
percarbonate particles, which also contain a magnesium
compound as a coating component, are characterised by high
storage stability in the presence of washing powders in a
moist and warm environment. The invention further relates
to a process for preparing the coated sodium percarbonate
particles by applying a mono or multi-layered coating in a
fluidised bed. The invention also relates to the uæe of the
coated sodium percarbonate particles as bleaching
co,.,~ollents in detergent, cleansing agent and bleaching
agent formulations.
Sodium percarbonate (2Na2C03.3H202) is used as an active
oxygen component in detergents, bleaches and cleansing
agents. Due to the unsatisfactory storage stability of
sodium percarbonate in a warm and moist environment and in
the presence of various components in detergents and
cleansing agents, sodium percarbonate has to be stabilised
against the loss of active oxygen (8). An essential
principle for stabilisation consists of surrounding the
sodium percarbonate particles with a coating of stabilising
components.
GB 174 891 has already disclosed spraying active oxygen-
containing compounds with a sodium waterglass solution and
then drying, in order to increase the storage stability.
- Sodium percarbonate is also stabilised by applying an
adequate amount of silicate to sodium percarbonate
2166281
particles, obtained by crystallisation, in the process in
DE-OS 26 52 776. A satisfactory stabilising effect,
especially in the presence of detergents and cleansing
agents, is not produced by the previously mentioned
methods.
Processes for stabilising particulate sodium percarbonate
are known from DE-OS 24 17 572 and DE-PS 26 22 610, wherein
either a mixed compound which is formed by crystallising a
sodium carbonate with other inorganic salts such as sodium
bicarbonate and/or sodium sulphate, or a mixture of sodium
carbonate, sodium sulphate and a sodium silicate is used as
a coating substance. In these processes, an aqueous
solution of the constituents for the coating material is
sprayed onto sodium percarbonate particles in a fluidised
bed while maintaining a fluidised bed temperature of
between 30 and 80C, wherein a solid coating is built up by
evaporation of the water which is introduced. Despite the
greatly improved stability of sodium percarbonate particles
20 coated in this way, the active oxygen content still
decreases too rapidly during long-term storage in the
presence of a washing powder.
Numerous methods for the effective stabilisation of sodium
25 percarbonate by using boron compounds, such as boric acids
(DE-PS 28 00 916), borates (DE-OS 33 21 082) and perborates
(DE-PS 26 51 442 and DE-PS 28 10 379) are known. Despite a
sometimes very good stabilising effect, the market is
increasingly interested in coated sodium percarbonate which
30 does not contain boron compounds.
Another type of coating component is known from US
4,325,933. According to this, stabilisation is achieved by
treating the sodium percarbonate with an aqueous solution
35 of an alkaline earth metal salt, either magnesium sulphate
or magnesium chloride. When treating the sQdium
percarbonate particles, a layer made of an alkaline earth
66~l
_ 3
carbonate is formed on the surface of the particles, which
reduces the hygroscopic character of the sodium
percarbonate and increases the stability. However, it has
been shown that this type of stabilised product does not
possess satisfactory storage stability.
EP-A 0 405 797 discloses sodium percarbonate compositions
which are more reliable. According to one embodiment, the
composition contains a compound from the group of inorganic
magnesium compounds in addition to an alkali metal
carbonate. The composition mentioned does not comprise
sodium percarbonate particles with a uniform coating which
adheres firmly to the sodium percarbonate core, but a
mixture of substances which can also be granulated. During
the finishing operations in the process given in the
document mentioned, it was established that the storage
stability of this type of composition, in the presence of a
washing powder in a warm and moist environment, is not
satisfactory; see comparison examples VB 2 to VB 4.
Accordingly, the object of the invention is to provide new,
coated, sodium percarbonate particles with high storage
stability in the presence of washing powders, wherein the
coating should not contain boron compounds. The storage
stability of the new coated sodium percarbonate particles
is intended preferably to surpass that which has been
obtainable using hitherto known, boron-free, coated sodium
percarbonate particles. A further object of the invention
relates to the provision of a suitable process for
preparing particularly storage-stable, boron-free, coated,
sodium percarbonate particles.
Coated sodium percarbonate particles comprising a core of
sodium percarbonate and a coating which contains sodium
carbonate, which constitutes 0.5 to 25 wt/~ (calculated
hydrate-free) of the sodium percarbonate, which are
characterised in that the coating also contains one or more
216~
_ 4
magnesium compounds from the group of salts of sulphuric
acid, hydrochloric acid and carboxylic acids with 1 to 4
carbon atoms or the reaction products of the salts
mentioned with sodium carbonate and/or other optionally
present coating components, wherein the coating components
may be partially hydrated and sodium carbonate and the one
or more magnesium compounds may be located in a single
layer or in separate layers of the coating, were found.
The coated sodium percarbonate particles according to the
invention thus consist of a sodium percarbonate core and a
mono or multi-layered coating which contains the
stabilising components in a hydrate-free and/or partially
hydrated form. The sodium percarbonate core is completely
surrounded by the coating which adheres firmly thereto,
wherein the thickness of the coating layer is approximately
constant over the whole particle.
The amount of coating, calculated as hydrate-free,
generally constitutes 0.5 to 25 wt.% of the sodium
percarbonate. Although it is possible to prepare particles
with a coating of less then 0.5 wt.~ or more than 25 wt.%,
the products in the first case possess only moderate
storage stability and in the second case have a reduced
active oxygen content, corresponding to the increased
amount of coating material.
In preferred products, the coating constitutes a total of
about 1 to 15 wt.% of the sodium percarbonate, calculated
as hydrate-free.
An essential feature of the invention is that the coating
contains both sodium carbonate and one or more magnesium
compounds, wherein the substances mentioned may be present
in an anhydrous and/or in a partially hydrated form. The
term ~'partially hydrated~ is to be understood as me~n;ng
that the m~; ml]m possible water acceptance capacity of the
2i6~28l
coating components due to hydrate formation has not been
exhausted in the coated sodium percarbonate particles
according to the invention. In the case of, for example, a
coating consisting of MgSO4 and Na2CO3 in the form of their
hydrates the water acceptance capacity is exhausted when
Na2CO3 is present as the monohydrate and MgSO4 is present as
the heptahydrate.
The coating contains one or more magnesium compounds from
the group magnesium sulphate, magnesium chloride and
magnesium salts of a carboxylic acid with 1 to 4 carbon
atoms. Hydrates of the compounds mentioned are also
included. From the magnesium salts of carboxylic acids,
which may contain one or two carboxyl groups and optionally
one or two hydroxyl groups, magneRium acetate is preferred.
When preparing mono-layered coated sodium percarbonate
particles, the coating may also contain reaction products
- of the previously mentioned salts with sodium carbonate
and/or other optionally present coating components such as,
for example, sodium silicates; in this way, for example,
magnesium carbonate, basic magnesium carbonate, mixed salts
of sodium carbonate and magnesium sulphate and, in the case
of the presence of sodium silicates, also magnesium
silicates, may also arise as constituents of the coating.
Coated sodium percarbonate particles according to the
invention may have a mono or multi-layered, preferably two
or three-layered, coating. The coating on preferred coated
sodium percarbonate particles comprises at least one layer
of essentially sodium carbonate and at least one layer of
essentially one or more magnesium compounds, in particular
magnesium sulphate and hydrates of the same. When building
up the at least two-layered structure mentioned for the
coating, reactions between the various components in the
coating can be restricted to the relevant boundary surfaces
of the layers. A two or three-layered coating of the
previously mentioned type has an advantageous effect on the
`` 216~28~
_ 6
storage stability of the coated sodium percarbonate
particles.
With a two-layered structure for the coating, the layer
which contains sodium carbonate may also contain other
stabilisers, but it preferably does not contain magnesium
compounds. The supplementary stabilisers should produce a
clear solution in the presence of sodium carbonate and also
should not display any stability-reducing effect in the
solid coating. Active components which can be found in the
layer which contains sodium carbonate are alkali metal
silicates, especially sodium silicate with a molar ratio of
SiO2 to Na20 in the range 4 to 1 to 1 to 1, preferably in
the range 2.5 to 1 to 3.5 to 1. Although in the case of a
multi-layered structure for the coating, the layer which
contains at least one magnesium compound may also contain
other components, among which is also sodium carbonate, it
is generally expedient to allocate no compounds other than
the magnesium compounds which are being considered to this
layer. Preferably, this layer consists of magnesium
sulphate and/or some of its hydrates or of magnesium
chloride or magnesium acetate and/or some of their
hydrates. Magnesium sulphate with a hydrate content between
2 and less than 7 moles of H20 per mole of MgS04 is
particularly preferred.
In addition to a layer which contains essentially sodium
carbonate and a layer which contains essentially at least
one magnesium compound, preferred coated sodium
percarbonate particles may also possess one or more layers
of essentially alkali metal silicates, especially sodium
silicates of the previously mentioned composition.
With regard to the stabilising effect, the sequence of the
35- layered structure in the coating has only a moderate
effect. The sequence of layers can have an effect, however,
on the flowability of the coated particles. In order to
` 2l~6~l
_ 7
obtain a product which flows particularly well, it may
therefore be advantageouæ to build up the coating so that
the external layer consistæ essentially of sodium
carbonate. Coated particles with a layered structure in the
sequence, from inside to outside, of magnesium sulphate,
sodium carbonate, sodium silicates, wherein these
substances may be partially hydrated, exhibit exceptional
storage-stability. The storage stability of thiæ type of
product exceedæ that of productæ which have only a
magneæium sulphate and a sodiùm carbonate layer with no
alkali metal silicate in either layer.
Preferred coated sodium percarbonate particles contain, in
one or more coating layers, as stabilising components,
essentially sodium carbonate and/or hydrates of the same in
an amount of 0.2 to 10 wt.~, preferably 0.5 to 5 wt.~,
calculated as Na2cO3, one or more magnesium compounds and/or
hydrates of the same, especially magneæium sulphate, in an
amount of 1 to 10 wt.~, preferably 0.5 to 5 wt.~,
calculated as MgSO4, and æodium æilicates and/or hydrateæ of
the æame with a molar ratio of SiO2 to Na2O of 4 to 1 to 1
to 1 in an amount of 0 to 5 wt.~, preferably 0.2 to 3 wt.~,
calculated hydrate-free, wherein the amountæ given are each
with reference to sodium percarbonate.
In addition to the substances mentioned and to the optional
reaction products arising therefrom, other stabilising
components may also be contained in one or more of the
coating layers in generally smaller amounts, i.e. up to
about 2 wt.~, with reference to sodium percarbonate. The
additional stabilising componentæ are in particular typical
active oxygen stabilisers such as aminopolycarboxylic acids
which form chelate complexes, such as ethylenediamine
tetraacetic acid and diethylenetriamine pentaacetic acid;
- 35 phosphonic acid compounds which form chelate complexes,
su-ch as, for instance, 1-hydroxyethane-1,1-diphosphonic
acid and ethylenediamine-tetra(methylphosphonic acid) and
C~16~281
_ 8
diethylenetriamine-penta(methylenephosphonic acid) and
their salts; water-soluble polymeræ with carboxyl and
hydroxyl groups which are capable of forming complexes,
such as, for instance, polymers based on alpha-
hydroxyacrylic acid; stabilisers such as pyridinecarboxylicacids, such as, for instance, dipicolinic acid, may also be
present.
Particularly preferred coated sodium percarbonate particles
with a core of sodium percarbonate produced by
crystallisation from aqueous phase, contain, in the
coating, sodium carbonate and/or some of its hydrates in an
amount of 2 to 6 wt.~, hydrate-free and/or some hydrate-
cont~in;ng magnesium sulphate in an amount of 2 to 6 wt.~,
hydrate-free and/or some hydrate-containing sodium
silicates, with a molar ratio of SiO2 to Na20 between 3.5 to
1 and 2.5 to 1, in an amount of 0.5 to 3 wt.% and if
required one or more of the previously mentioned other
stabilising components in an amount of 0 to 2 wt.%, in
particular 0 to 1 wt.~, each with reference to sodium
percarbonate and calculated as hydrate-free.
If sodium percarbonate produced by spray granulation is
coated, the amount of coating may be reduced as compared
with the previously mentioned amounts because in this case
the surface of the particleæ to be coated is smoother than
in the case of particles produced by crystallisation. To
coat sodium percarbonate particles with smooth surfaces,
0.5 to 5 wt.~ of Na203, 0.5 to 5 wt.% of MgS04 and 0.2 to 2
wt.~ of sodium silicates (SiO2:Na20 = 2.5 to 3.5 to 1), each
with reference to sodium percarbonate, are used.
As can be seen from the examples and comparison examples,
the coated sodium percarbonate particles according to the
invention are distinguished by unexpectedly high storage
stability in the presence of zeolite-containing detergent
tower powders as compared with previously known, also
2~6~
g
boron-free, coated particles. After 8 weeks storage at 30C
and 80~ relative humidity, the relative active oxygen
content (Oa-retention) of the products according to the
invention is approximately 70 to almost 100%, depending on
the structure of the layers, the amount of coating and the
method of preparation of the sodium percarbonate used.
Particularly preferred coated sodium percarbonate particles
have an Oa-retention of between 93~ and about 97~ after 8
weeks a~m;xe~ with a detergent under the storage conditions
mentioned.
Among the methods frequently used in the specialist sector
for applying a coating layer to products being stabilised
are methods using a mixer, wherein the product being
stabilised, optionally after moistening the same, is
treated with powdered stabilisers, and so-called fluidised
bed methods, wherein the coating components, in the form of
an aqueous solution, are sprayed onto the product being
stabilised which is located in the fluidised bed and the
water which is hereby introduced is simultaneously
evaporated. It was found that coating sodium percarbonate
with coating components according to the invention in a
fluidised bed led to a product with an essentially higher
storage stability than the previously known coating
procedure using a mixer.
The process for preparing coated sodium percarbonate
particles according to the invention comprises spraying an
aqueous solution which contains one or more coating
components onto the particles to be coated, which are
located in a fluidised bed, and evaporating the water while
maintaining a fluidised bed temperature of 30 to 100C, and
is characterised in that at least one aqueous solution
which contains sodium carbonate and at least one aqueous
solution which contains a magnesium salt from the group Mg
sulphate, Mg chloride and Mg carboxylate of a carboxylic
acid with 1 to 4 carbon atoms, are sprayed onto the
2~ ~62~1
--- 10
particles being coated, simultaneously or one after the
other in any sequence, wherein the total amount of coating
components applied is 1 to 25 wt.~ (calculated hydrate-
free), with respect to the sodium percarbonate.
The solutions containing sodium carbonate and magnesium
salt are preferably sprayed on one after the other. It is
particularly expedient if a layer which contains soda is
applied as the outermost layer on the particles. According
to another embodiment of the process, an aqueous solution
which contains essentially sodium carbonate is initially
sprayed onto the particles being coated, then an aqueous
solution which contains essentially magnesium sulphate and
lastly a solution which again contains essentially sodium
carbonate.
According to another embodiment of the process, a solution
containing sodium carbonate which also contains alkali
metal silicates, preferably sodium silicates, is used. As
an alternative to this, one or more coating layers
consisting essentially of an alkali metal silicate and/or
some of its hydrates may be built up by spraying an aqueous
solution of one or more alkali metal silicates, such as for
example a sodium waterglass solution, onto the particles
being coated, which may already possess one or more coating
layers. When using a solution which contains sodium
silicates, a molar ratio of SiO2 to Na20 of 4 to 1 to 1 to
1, preferably 2.5 to 1 to 3.5 to 1, and in particular about
3 to 3.5 to 1, is the basic parameter.
If the coating components sodium carbonate and one or more
magnesium compounds are intended to be located in a single
coating layer, the sodium carbonate solution and the
magnesium salt solution, preferably magnesium sulphate
solution, are sprayed onto the particles to be coated from
two separate nozzles which are suitably positioned in the
fluidised bed or from a three-component nozzle with
11 2l662~l
external mixing. In this emboA;ment also, the solution
containing sodium carbonate may also contain alkali metal
silicates. In addition, the solutions may contain other
stabilisers which are compatible with sodium carbonate or
the magnesium compounds.
The relevant solutions are sprayed onto the particles to be
coated in an amount such that the resulting coated
particles possess the previously mentioned amounts of
coating components in one or more layers. The concentration
of coating components in the solutions being sprayed is any
at all per se, but the most highly concentrated solutions
possible are preferred in order to keep the amount of water
to be evaporated as low as possible. Preferably, an
approximately saturated sodium carbonate solution and an
approximately saturated magnesium salt, in particular
magnesium sulphate, solution, are used. Sodium silicates
are preferably used in the form of a waterglass solution
(35 to 40 Baumé), which contains SiO2 and Na20 in a molar
ratio of about 3.5 to 1.
The technique of applying an aqueous solution which
contains one or more coating components to the particles to
be coated, that is sodium percarbonate or already partly
coated sodium percarbonate, in a fluidised bed is known to
a person skilled in the art, reference being made, for
example, to DE-PS 26 22 610. In a conventional continuously
or batchwise operated fluidised bed device, a fluidised bed
is formed from the sodium percarbonate to be coated by
using the drying air. The aqueous solutions containing the
coating components are sprayed from nozzles, simultaneously
or one after the other, wherein the water introduced with
the solutions is simultaneously evaporated. The amount of
drying air and its temperature are governed both by the
amount of water introduced to the fluidised bed with the
- solutions and by the degree of drying which is desired. The
two parameters are matched to each other by the person
~l~628l
12
skilled in the art in such a way that a temperature in the
range 30 to 100C, preferably 50 to 80C, is maintained in
the fluidised bed. Furthermore, it may be expedient that
the solutions being sprayed already have a temperature in
the range 30 to 80C. If required, the coated particles may
subsequently be dried at 60 to 100C, in particular at 70
to 90C, in order to produce satisfactory dehydration of
the hydrate-forming coating components.
For the continuous preparation of multi-layered coated
sodium percarbonate particles, trough-shaped fluidised bed
dryers with two or more spray zones and, if required, an
after-drying zone, are preferably used.
The sodium percarbonate particles to be coated may have
been produced by any method of preparation of sodium
percarbonate at all. Those which may be mentioned ;n
particular are: (i) wet methods, wherein soda and hydrogen
peroxide are reacted in an aqueous phase and the resulting
sodium percarbonate is separated from the mother liquor;
(ii) methods, wherein solid soda is reacted directly with
hydrogen peroxide; (iii) so-called spray granulation
methods, wherein a soda solution and a hydrogen peroxide
solution, or a solution which contains Na2CO3 and H202, are
sprayed onto sodium percarbonate seeds located in a
fluidised bed in a fluidised bed dryer with or without a
grading outlet, with simultaneous evaporation of the water,
until the desired particle size is reached, reference being
made, for example, to the method in accordance with
DE-OS 27 33 935.
The advantage of the process according to the invention is
regarded as being that uniformly coated sodium percarbonate
particles with a mono or multi-layered coating which are
distinguished by extraordinarily good storage stability,
are thereby obtainable. The principle of applying a coating
to sodium percarbonate particles and suitable devices for
21S~8~
_ 13
this procedure are known and proven per se in the
specialist sector. Performing the process is simple and the
amount of coating being applied can be controlled without
any problems.
The coated sodium percarbonate particles according to the
invention can be used as a bleaching comro~ent in
detergents, cleansing agents and bleaching compositions.
This type of detergent, cleansing agent and bleaching
composition is characterised in that the coated sodium
percarbonate cont~;n~d therein has an unexpectedly high
storage stability, even in the presence of zeolites, so
that there is only a very slow loss of active oxygen during
conventional storage times for this type of composition.
Detergent, cleansing agent and bleaching compositions which
are suitable consist of 1 to 99 wt.~ of the coated sodium
percarbonate according to the invention and the rem~;n;ng
amount consists of up to 100 wt.~ of other conventional
components for this type of composition. The following
components in particular may be mentioned:
1. Surface active agents from the group of cationic,
anionic, non-ionic, amphoteric or ampholytic surface
active agents.
2. Inorganic and/or organic builders, whose main action
comprises sequestering or complexing the metal ions
which are responsible for hardness in the water, for
example zeolites, sheet silicates, polyphosphates,
aminopolyacetic acids and aminopolyphosphonic acids as
well as polyoxycarboxylic acids.
3. Alkaline and inorganic electrolytes such as, for
example, alkanolamines and silicates, carbonates and
sulphates.
`` . . 21~6281
14
4. Bleach activators from the group of N-acyl compounds
and O-acyl compounds, for example tetraacetyl
ethylenediamine (TAED).
5. Other constituents in the agents may be stabilisers
for peroxides such as in particular magnesium salts,
anti-deposition agentæ, optical brighteners, foam
inhibitors, enzymes, disinfectants, corrosion
inhibitors, fragrances, dyes and agents for regulating
the pH. With regard to individual compounds included
in the classes of substances 1 to 5, reference is
made, for example, to DE-OS 33 21 082, pages 14-30.
The following examples and comparison examples clearly show
the much higher stabilising effect of the coating according
to the invention as compared to similarly structured and
similarly prepared previously known, boron-free, coatings
on sodium percarbonate.
2i~28l
_ 15
Examples
a) General description of coating in a mixer, not according
to the invention
The sodium percarbonate to be coated, which has a moisture
content of 5 to 10 wt.~ as a result of the method of
preparation, is treated with the coating componentæ(s)
under continuous mixing in a plough-share mixer. If dry
sodium percarbonate is used, this is first brought up to
the previously mentioned moisture content by spraying with
water or an aqueous solution which contains one or more of
the coating components and then mixed with further coating
components. Magnesium sulphate was used as the
lS heptahydrate, sodium carbonate as calcined soda; alkali
metal silicate was used in the form of a sodium waterglass
solution (37Bé) (SiO2 : Na20 = ca. 3.5 to 1) and sprayed
onto dry sodium percarbonate. After completion of the
m; ~; ng procedure, the coated product is dried at 60 to 70C
in a fluidised bed dryer until it has a residual moisture
content (Karl Fischer) of less than 0.5~.
b) General description of coating in a fluidiæed bed
according to the invention
In a laboratory fluidised bed dryer, the aqueous solutions
containing the coating components are sprayed,
simultaneously or one after the other, onto the fluidised
bed constructed by using the drying air (inlet temperature
100 to 110C) and the sodium percarbonate (NaPc) to be
coated, wherein the temperature of the fluidised bed is
maintained within the range 40 to 60C. After-drying is
performed at 80 to 90C. The solutions are sprayed by using
conventional two-component nozzles with air as the
propellant, wherein, to prepare mono-layered coatings
according to the invention, the solutions to be used are
applied by means of two two-component nozzles, but
16 21 562~1
preferably by means of one three-component nozzle with
external mixing.
Aqueous solutions used: MgSO4 solution (30 or 20 wt.%
S MgSO4); Na2CO3 solution (30 or 20 wt.~ Na2cO3); sodium
silicate solution ca. 37 Bé (SiO2: Na2O3 about 3.5 : 1);
combined Na2CO3/sodium silicate solution (20 wt.% Na2CO3,
8 wt.% sodium silicate), prepared from a sodium waterglass
solution with ca. 37 B~ and a SiO2 to Na2O molar ratio af
about 3.5 to 1. The temperature of the solutions being
sprayed is 30 to 40C.
c) Determination of the storage stability when mixed with
a detergent
Commercially available tower washing powder (Persil Supra
SP), which is phosphate-free ~ut contains zeolite, TAED
activator and the sodium percarbonate to be tested were
mixed in amounts such that the mixture contained 5% TAED
and the a content was about 2.35 wt.~.
400 g or 800 g (from example 5 and comparison example 10
onwards) of the mixture are stored at 30C and 80~ relative
humidity in a climatic test cabinet in commercially
available E1 detergent packets which were impregnated to be
water-repellent and glued together. One packet was stored
for each period prior to removal, 2, 4 and 8 weeks
respectively. The a content is determined iodometrically in
the usual way. The respective Oa-retentions are determined
as a ~-age, from the initial a content and the a contents
after 2, 4 and 8 weeks.
- 35
"' 216~28~
17
Examples E 1 to E 4 and comparison examples CE 1 to CE 4
Table 1 shows the storage stability when mixed with
detergent of the non-coated sodium percarbonate (CE 1)
which is used as the starting product for the coated sodium
percarbonate particles listed in Table 1, examples E 1 to
E 4 and comparison examples CE 2 to CE 4 and for comparison
examples CE 5 to CE 9 in Table 3.
Two- and three-layered coating according to the invention
took place using the sequence of coating components given
in the first column of Table 1. In the case of coating not
according to the invention, in a mixer, MgSO4.7H2O and Na2CO3
were used simultaneously. The residual moisture content of
the NaPc used in CE 2 and CE 3 was ca. 7%. In CE 4, NaPc
was initially moistened with a waterglass solution.
The results show that the storage stability of coated
sodium percarbonate according to the invention surpassed
that of the product coated in a mixer, despite identical
amounts of coating.
Table 2 shows the active oxygen content (a content) of
sodium percarbonate coated in a mixer and in a fluidised
bed, immediately after preparation and after 10 weeks
storage (without mixing with a detergent). Coated sodium
percarbonate according to the invention was characterised
in that the a content decreased to an essentially smaller
extent during storage.
18 2lG~281
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Comparison examples CE 5 to CE 9
Sodium percarbonate according to CE 1 was coated in the
fluidiæed bed with the previously known substances and
previously known combinations of substances given in Table
3. The storage stability when mixed with a detergent was
unsatisfactory, which is particularly clear after 8 weeks
storage.
21662~1
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Examples E 5 to E 7 and compari~on example CE 10
Table 4 shows the storage stability when mixed with a
detergent. Commercially available, non-coated sodium
percarbonate from the applicant (CE 10), which had been
prepared by reacting soda and hydrogen peroxide in the
aqueous phase, crystallising the NaPc, separating it from
the aqueous phase and drying, was uæed.
Coating was performed each time with magnesium sulphate
(5 wt.~), sodium carbonate (5 wt.%) and sodium waterglass
(2 wt.~, SiO2 : Na20 = 3.5 to 1~, wt.% with reference to the
NaPc used. Mono-layered coating (E 5) was performed by
simultaneous use of a MgS04 solution and an aqueous solution
cont~;n;ng Na2C03 and sodium waterglass, which were sprayed
onto the NaPc by means of a three-component nozzle. In the
case of two-layered coating (E 6), the solutions mentioned
were used one after the other by means of a two-component
nozzle. In the case of three-layered coating (B 7), the
MgS04 solution, a Na2C03 solution and lastly a sodium
waterglass solution were sprayed on one after the other.
Two and three-layered coating produced an essentially
better stabilising effect than mono-layered coating.
23 ~) B6281
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_ 24
Ex~mples E 8 and E 9, comparison examrle CE 11
A sodium percarbonate (CE 11) was used which had been
prepared by spray granulation in a.fluidised bed, in the
same way as in the process in DE 27 33 935. 10~ of the
particleæ had a particle diameter between 0.2 and 0.5 mm,
70~ had a diameter between 0.5 and 0.7 mm and 20~ had a
diameter between 0.7 and 1.0 mm.
This was coated according to the invention in a fluidised
bed, into which was sprayed first a MgSO4 solution and then
a solution of Na2CO3 and sodium waterglass (SiO2 : Na2O = 3.5
to 1). The temperature of the spray solutions was 40C. The
temperature of the fluidised bed during spraying was 50 to
60C. The temperature of the fluidised bed during after-
drying was 80C.
The examples verify the extraordinary increase in storage
stability of coated sodium percarbonate particles according
to the invention.
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