Note: Descriptions are shown in the official language in which they were submitted.
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WO 99/14296 1 PCT/EP98/05629
Coated ammonium nitrite bleach activator granules
Bleach activators are important constituents in detergents, stain removal
salts and dishwashing detergents. They permit a bleaching action even at
relatively low temperatures by reacting with a source of hydrogen
peroxide - in most cases perborates or percarbonates - to release an
organic peroxycarboxylic acid or when ammonium nitrites are added as
activator, form a peroxyimidic acid as bleaching agent.
Representative examples of bleach activators are, for example, N,N,N'N'-
tetraacetylethylenediamine (TAED), glucose pentaacetate (GPA), xylose
tetraacetate (TAX), sodium 4-benzoyloxybenzenesulfonate (SBOBS),
sodium trimethylhexanoyloxybenzenesulfonate (STHOBS),
tetraacetylglucoluril (TAGU), tetraacetylcyanic acid (TACA), di-N-
acetyldimethylglyoxine (ADMG) and 1-phenyl-3-acet?;~!~~ydantoin (PAH).
Reference may be made, for example, to GB-A-836 988, GB-A-907 356,
EP-A-0 098 129 and EP-A-0 120 591.
Cationic bleach activators which contain a quaternary ammonium group
have gained importance over time since they are highly effective bleach
activators. Such cationic bleach activators are described, for example, in
GB-A-1 382 594, US-A-4 751 015, EP-A-0 284 292 and EP-A-0 331 229.
In this connection, ammonium nitrites of the formula
Rz
~+
R~ N CHZCN X
R3
constitute a particular class of cationic bleach activators. Compounds of
this type and their use as bleach activators in bleaches are described in
EP-A-303 520, EP-A-464 880, EP-A-458 396 and US-4 883 917. In all of
the compounds described therein, the nitrogen atom of the ammonium
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group is substituted by alkyl, alkenyl or aryl groups. A further class of
ammonium nitrites is described in German Patent Application 19605526.
The high reactivity and sensitivity to hydrolysis of the bleach activators,
particularly in the presence of alkaline detergent constituents, does,
however, require said ammonium nitrites to be granulated in order to
ensure an adequate shelf life and in order to release the bleaching effect
only in the wash.
Numerous auxiliaries and processes have been proposed in the past for
granulating these substances. EP-A-0 037 026 describes a process for
producing readily soluble activator granules comprising 90 to 98% activator
with 10 to 2% cellulose ethers, starch or starch ethers. Granules consisting
of bleach activator, film-forming polymers and added organic C3-Cs
carboxylic, hydroxycarboxylic or ether carboxylic acid are specified in
WO 90/01535. EP-A-0 468 824 discloses gr,~nules comprising bleach
activator and a film-forming polymer which is more soluble at a pH of 10
than at a pH of 7. DE-A-44 39 039 describes a process for producing
activator granules by mixing a dry bleach activator with a dry, inorganic
binder material containing water of hydration, compressing this mixture to
form relatively large agglomerates, and comminuting these agglomerates
to the desired grain size. A waterless production process, by compacting
the bleach activator with at least one water-swellable auxiliary, without the
use of water, is known from EP-A-0 075 818.
Disadvantages of these activator granules are that the properties of the
granules are fixed essentially by the binder and by the granulating method
used and that the resulting granules, besides the advantages described in
the literature, often have certain disadvantages as well, for example
suboptimal release of active substance, low abrasion resistance, high dust
content, inadequate shelf life, separation within the powder or damage to
the color of the fabric when used in detergents and cleaning compositions.
In order to give granules defined properties a coating step is often carried
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out subsequent to the granulating step. Common methods are coating in
mixers (mechanically induced fluidized bed) or coating in fluidized-bed
apparatus (pneumatically induced fluidized bed).
For instance, WO 92/13798 describes, for a bleach activator, coating with
a water-soluble organic acid which melts at above 30°C, and
WO 94/03305 describes coating with a water-soluble acidic polymer in
order to reduce color damage to the laundry.
WO 94/26862 discloses the coating of granules consisting of bleach
activator and water- and/or alkali-soluble polymer with an organic
compound melting at between 30°C and 100°C for reducing
separation in
the pulverulent end product. In this case the activator granules are placed
in a Ltidige plowshare mixer, circulated at from 160 to 180 rpm at room
temperature, without using the pelletizer, and then sprayed with the hot
melt. A disadvantage of this process is the very poor coating quality, which,
although it brings about a reduction in. separation in the pulverulent end
product, has no effect on the other granule properties, such as release of
active substance, abrasion resistance, dust content or shelf life, for
example. The positive effect on the separation behavior can probably be
attributed to a droplet-like solidification of the coating substance on the
granule surface allowing the individual grains to hook together in the bulk
product.
The object of the present invention was to develop a coating process for
activator granules containing ammonium nitrite as activator which makes it
possible to tailor the granule properties within a wide range at the same
time as making optimum use of the coating material.
This object was achieved by coating with a water-soluble substance. The
granules coated in this way can be thermally conditioned during or after
coating.
The invention thus provides coated granules of an ammonium nitrite and a
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process for the preparation of coated granules of an ammonium nitrite
which comprises coating base granules of an ammonium nitrite with a
water-soluble coating substance. These coated granules can be thermally
conditioned during coating or subsequently thereto.
The base granules which can be used are all ammonium nitrites which in
granulated form have a melting point above 60°C. Particularly suitable
granules in this connection are the ammonium nitrites described in the
aforementioned literature.
Particular preference is given to ammonium nitrites of the formula
R1
H3C-N-CHZCN X~
R
in which R' and R2 of C,-C4 alkyl, and X is an anion, for example chloride
or methosulfate.
The base granules can comprise one or more of these ammonium nitrites
or in addition also bleach activators of another structure, for example
N,N,N',N'-tetraacetylethylenediamine (TAED), glucose pentaacetate
(GPA), xylose tetraacetate (TAX), sodium 4-benzoyloxybenzenesulfonate
(SBOBS), sodium trimethylhexanoyloxybenzenesulfonate (STHOBS),
tetraacetylglucoluril (TAGU), tetraacetylcyanic acid (TACA), di-N-
acetyldimethylglyoxine (ADMG) and 1-phenyl-3-acetylhydantoin (PAH).
These base granules can include the customary granulating auxiliaries,
which should have a melting point above 60°C, preferably above
100°C.
Suitable such auxiliaries are film-forming polymers, for example cellulose
ethers, starch, starch ethers, homopolymers, copolymers and graft
copolymers of unsaturated carboxylic acids and/or sulfonic acids and also
the salts thereof; organic substances, for example cellulose, crosslinked
polyvinylpyrrolidone, or inorganic substances, for example silicic acid,
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amorphous silicates, zeolites, bentonites, alkali metal phyllosilicates of the
formula MM'SiXO~-, * y H20 (M, M' = Na, K, H; x = 1.9 - 23; y = 0 - 25),
orthophosphates, pyrophosphates and polyphosphates, phosphonic acids
and their salts, sulfates, carbonates and bicarbonates. Depending on what
is required these granulating auxiliaries can be employed as individual
substances or as mixtures.
In addition to the bleach activator and the granulating auxiliary the bleach
activator base granules may also include further additives which enhance
properties such as, for example, shelf life and bleach activation. Such
additives include inorganic acids, organic acids, for instance mono- or
polybasic carboxylic acids, hydroxycarboxylic acids and/or ether carboxylic
acids, and also salts thereof, complexing agents, metal complexes and
ketones. Depending on what is required, the abovementioned additives
can be employed as individual substances or as mixtures.
These base granules are prepared by mixing the dry bleach activator with
the dry granulating auxiliary, compressing this mixture to give relatively
large agglomerates and comminuting these agglomerates to the desired
particle size.
The weight ratio of bleach activators to granulating auxiliary is usually from
50:50 to 98:2, preferably from 70:30 to 96:4. The amount of additive is
particularly dependent on its type. For example acidifying additives and
organic catalysts for increasing the performance of the peracid are added
in amounts of 0-20% by weight, in particular in amounts of 1-10% by
weight, based on the total weight, whereas metal complexes are added in
concentrations in the ppm range.
Suitable coating substances are all compounds or mixtures thereof which
are solid at room temperature and which soften or melt in the range from
30 to 100°C. Examples of such are:
CB C3, fatty acids (e.g. lauric, myristic, stearic acid); C8 C3, fatty
alcohols;
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polyalkenyl glycols (e.g. polyethylene glycols having a molar mass of from
1000 to 50,000 g/mol); nonionics (e.g. Ce C3, fatty alcohol polyalkoxylates
with from 1 to 100 moles of EO); anionics (e.g. alkanesulfonates, alkyl-
benzenesulfonates, a-olefinsulfonates, alkylsulfates, alkyl ether sulfates
having C8 C3, hydrocarbon radicals); polymers (e.g. polyvinyl alcohols);
waxes (e.g. montan waxes, paraffin waxes, ester waxes, polyolefin waxes);
silicones.
Within the coating substance which softens or melts in the range from 30
to 100°C there may additionally be other substances, not softening or
melting in this temperature range, in dissolved or suspended form,
examples being polymers (e.g. homopolymers, copolymers or graft
copolymers of unsaturated carboxylic acids andlor sulfonic acids and alkali
metal salts thereof, cellulose ethers, starch, starch ethers, polyvinyl-
pyrrolidone); organic substances (e.g. mono- or polybasic carboxylic acids,
hydroxycarboxylic acids or ether carboxylic acids having 3 to 8 C atoms,
and the salts thereof); colorants; inorganic substances (e.g. silicates,
carbonates, bicarbonates, sulfates, phosphates, phosphonates).
Depending on the desired properties of the coated activator granules, the
content of coating substance can be from 1 to 30% by weight, preferably
from 5 to 15% by weight, based on coated activator granules.
The coating substances can be applied using mixers (mechanically
induced fluidized bed) and fluidized-bed apparatus (pneumatically induced
fluidized bed). Examples of possible mixers are plowshare mixers
(continuous and batchwise), annular bed mixers or else Schugi mixers. If a
mixer is used, the thermal conditioning can take place in a granule
preheater and/or directly in the mixer and/or in a fluidized bed downstream
of the mixer. The coated granules can be cooled using granule coolers or
fluidized-bed coolers. In the case of fluidized-bed apparatus, the thermal
conditioning takes place by way of the hot gas used for fluidizing. The
granules coated by the fluidized-bed method, as with the mixer method,
can be cooled by way of a granule cooler or a fluidized-bed cooler. In both
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the mixer method and the fluidized-bed method the coating substance can
be sprayed on by way of a single-substance or dual-substance nozzle
apparatus.
The optional thermal conditioning comprises a heat treatment at a
temperature from 30 to 100°C but no higher than the melting or
softening
temperature of the respective coating substance. It is preferred to operate
at a temperature which lies just below the melting or softening
temperature.
The grain size of the coated bleach activator granules is from 0.1 to
2.0 mm, preferably from 0.2 to 1.0 mm and, with particular preference,
from 0.3 to 0.8 mm.
The precise temperature during thermal conditioning or the difference in
temperature from the melting point of the coating substance is dependent
on the coating rate, on the thermal conditioning time and on the properties
desired for the coated bleach activator granules, and must be determined
in preliminary experiments for the particular system.
The period for thermal conditioning is from approximately 1 to 180,
preferably from 3 to 60 and, with particular preference, from 5 to
minutes.
25 The advantage of this thermal conditioning is that the liquid coating
material does not solidify too rapidly and thus has the possibility of running
as a thin film over the surface of the granules. This produces a highly
uniform coating of the grain in a thin layer with the coating substance, and
an optimum coating effect for use of a minimum amount of coating
30 substance. In conventional processes, i.e. those without a thermal
conditioning step, solidification of the individual droplets on the cold
granule surface is too rapid. Consequently, the surface is covered only with
fine individual droplets and still has large coating voids. As a result, the
desired coating effect is not fully obtained or a much higher amount of
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coating substance is required in order to obtain the desired coating effect.
In the latter case, however, the content of activator substance is reduced,
which in many cases is undesirable.
By means of the novel process it is possible to tailor the properties of the
ammonium nitrite granules within broad ranges to the desired
specifications by an appropriate choice of the coating substance, the
coating rate and the process temperature regime. In this context it is
possible in particular to optimize in a targeted manner the following
activator granule properties.
Time-optimized release of active substance
In order to avoid interaction between the bleaching system and the
enzyme system it is advantageous to couple a slightly delayed
reaction and active-substance release of the bleaching system with
rapid enzyme action. In this way the enzymes can develop their
washing power fully within the first few minutes of the washing
process without being damaged by the bleaching system. Only after
the enzymes have done their job is the bleaching process set in
motion by reaction of the bleach activator with the hydrogen
peroxide source. Appropriate coating of the bleach activator makes
it possible to tailor the reactivity, i.e. the rate of dissolution or the
rate of formation of the peracid, specifically to the enzyme system.
The process permits controlled adjustment of the rate of formation
of the peracid at the same time as having a minimal amount of
coating substance and thus the maximum activator content.
2. Increasing the abrasion resistance
By coating granules with softening or melting substances it is
possible to increase the abrasion resistance of activator granules.
The increase in abrasion resistance is greater the better the coating
of the granule surface with the coating substance. The novel coating
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process makes it possible, with a minimum coating rate, to bring
about optimum flow of the coating substance over the granule
surface and thus an optimum enhancement of the abrasion
resistance.
3. Extending the shelf life
When a detergent and cleaning composition is stored there may be
a reaction at the boundary between the activator grain and a directly
adjacent grain of the hydrogen peroxide source, with subsequent
loss of active oxygen and thus uncontrolled breakdown of the
bleaching system. By means of optimum coating, as is possible only
through the novel coating process, a complete protective layer is
constructed at the grain size, which layer then prevents reaction of
the activator grain with the grain of the hydrogen peroxide source in
the course of storage. When water-soluble andlor low-melting
coating substances are used it is nevertheless possible to obtain the
required bleaching performance in the washing process.
The granules obtained in this way are directly suitable for use in detergents
and cleaning compositions. They are ideal for use in heavy-duty
detergents, stain removal salts, dishwashing detergents, all-purpose
cleaning powders and denture cleaners. In such formulations the granules
of the invention are in most cases employed in combination with a
hydrogen peroxide source. Examples thereof are perborate monohydrate,
perborate tetrahydrate, percarbonates, and adducts of hydrogen peroxide
with urea or with amine oxides. The formulation may also feature further,
prior art detergent constituents, such as organic or inorganic builders and
cobuilders, surfactants, enzymes, washing additives, optical brighteners
and fragrance.
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Examples
Example 1: Preparation
10 kg of a mixture of 92% by weight of ammonium nitrite
(trimethylammonium acetonitrile toluenesulfonate) and 8% by weight of
bentonite (Laundrosil DGA) are intensively mixed in a 50 I Lbdige mixer at
a speed of 70 rpm over a period of 10 min. This homogeneous mixture is
then compressed to flakes on a Pharmapaktor roller compactor (Bepex
(DE)) at a pressing force of from 50 to 60 kN; the flakes are then
comminuted in a two-stage grinding process, pregrinding with toothed-disk
rollers (Alexanderwerk (DE)) and comminution in a sieve (Fewitt (DE)) at a
mesh size of 2000 arm.
This gives 5.3 kg of granules, referred to as G1, having a particle size
distribution of from 200 to 1600 Nm. (Yield: 53%), and also 2.8 kg of a fine
material < 200 Nm (28%), which can be recycled by recompacting, and
1.9 kg of coarse material > 1600 Nm (19%), which can be processed by
regrinding.
Example 2: Coating by the fluidized-bed method with downstream
thermal conditioning
500 - 600 g of granules (G1 ) were placed in a fluidized bed (fluidized-bed
apparatus Strea 1 from Aeromatic) and sprayed with a hot (about 80°C)
melt of stearic acid. For comparison purposes, in one case the fluidized
bed was operated at low temperatures and after the end of spraying was
cooled again for about 5 minutes. In the other case, in accordance with the
preferred process, the coated granules were placed back in the fluid.ized
bed and subjected to thermal conditioning. To this end the fluidized bed
was heated gradually to temperatures of about 65 to 70°C and this
product
temperature was held constant for about 5 to 8 minutes. The thermally
conditioned product was then cooled down again in stages.
The coating quality of the products was assessed by determining the rate
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of formation of peracetic acid at a temperature of 20°C. The slower the
formation of peracetic acid the better the degree of coating achieved.
In order to determine the rate of formation of peracetic acid, 1 I of
distilled
water, 8.0 g of test detergent WMP and 1.5 g of sodium perborate
monohydrate were placed in a 2 I glass beaker at 20°C and the mixture
was stirred at from 250 to 280 rpm using a magnetic stirrer. Then, after 1
to 2 minutes, 0.5 g of the coated granules was added. After one minute an
aliquot of 50 ml was removed by pipette and introduced onto 150 g of ice
and 5 ml of 20% strength acetic acid in an Erlenmeyer flask. Immediately
following the addition of 2 to 3 ml of 10% strength potassium iodide
solution, the sample was titrated to the potentiometric endpoint with
0.01 molar sodium thiosulfate solution (Titroprocessor 716 DMS from
Metrohm) and the amount of peracetic acid was calculated from the
amount of sodium thiosulfate consumed. Then further samples were taken
at intervals of 2 to 5 minutes and were titrated as described. The entire
procedure was repeated until equal .or descending amounts of peracetic
acid were found after three successive titrations. The maximum amount of
peracetic acid found was then taken as being 100% and on this basis,
finally, the amount of peracetic acid formed after 5, 10 and 20 minutes was
determined in percent as a measure of the rate of formation of peracetic
acid.
Table 1: Rate of formation of peracid by uncoated granules I and
granules I coated in the fluidized-bed method, with or without
subsequent thermal conditioning:
Peracetic acid formed5 min 10 min 20 min
[%J
G1 (uncoated) 70 92 100
G 1 +10% Stearic acid,11 _ 24 50
thermally conditioned
G1 + 20% stearic acid,14 25 54
thermally conditioned
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G1 + 10% stearic acid,72 87 97
not thermally conditioned
G 1 + 20% stearic 42 63 82
acid,
not thermally conditioned
Coating greatly delays the release of peracid. By means of the thermal
conditioning, it is possible to bring about a marked improvement in the
coating quality, expressed by the delay in the formation of per acid, for the
same coating rate (compare products 2 and 4 and products 3 and 5). To
achieve an optimum coating quality, an amount of 10% coating substance
(product 2) is sufi'icient given appropriate thermal conditioning.
Example 3: Shelf life of ammonium nitrite granules in detergent
formulations
The shelf life was tested in ready made-up folding boxes (height: 6.5 cm;
width 3.2 cm; depth 2.2 cm) at 38°C and 80% relative atmospheric
humidity (rH) over a period of 28 days. Each folding box was filled with a
homogeneous mixture of 8.0 g of test detergent WMP, 1.5 g of sodium
percarbonate and 0.5 g of the ammonium nitrite granules to be tested and
then was sealed at the top with Tesafilm. All samples were mixed and
dispensed into the boxes on the same day. The filled folding boxes were
then placed at a sufficient distance from one another in the climatically
controlled cabinet and stored at 38°C/80% rH. After storage periods of
0,
3, 6, 9, 15, 23 and 28 days the samples were removed from the cabinet,
the entire sample was introduced at 20°C into 1 I of distilled water,
while
stirring with a magnetic stirrer (250 to 280 rpm), and 1 g of sodium
percarbonate was added. Subsequent determination of the amount of
peracid formed was as indicated in Example 2. The ammonium nitrite
content of the sample was then calculated from the maximum value of
peracid found. The ammonium nitrite durability represents the percentage
ammonium nitrite content of the sample after storage relative to the
ammonium nitrite content of the unstored sample.
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Table 2: Shelf life in detergent formulations of ammonium nitrite
granules coated by the fluidized-bed method
Ammonium nitrite granules (G1 ) Ammonium nitrite durability after storage
Od 3d 6d 9d 15d 23d 28d
G1 100 29 15 12 10 7 6
G1 + 10% stearic- 100 88 69 62 57 55 55
acid, thermally conditioned
G1 + 10% stearic 100 69 35 30 28 26 23
acid, not thermally conditioned
Example 4
The shelf life of the coated granules was additionally tested under
conditions simulating those met in pracfice in an CSko-Lavamat 6753 multi-
component washing machine (AEG, Nuremberg) on bleach test fabrics in
the presence of pure test laundry. In accordance with the metering
instructions for water hardness region 3, 70 g of reference detergent
(WMP) are introduced into the detergent compartments of the washing
machine. The bleach component introduced into the detergent
compartment was 8.0 g of percarbonate and also
a) 3.18 g of granules G1 + 10% stearic acid (82%), coated, thermally
conditioned
b) 3.18 g of granules G1 + 10% stearic acid (82%), coated, not
thermally conditioned
c) 2.93 g of granules G1 (92%), uncoated
For comparison purposes, ammonium nitrite trimethylammonium
acetonitrile toluenesulfonate (2.7 g) in powder form was tested (Ex. 4d)
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The ballast material used is 2 kg of terry fabric, and the test soiling
bleachable soilings (tea, red wine, curry, grass from Krefeld Laundry
Research). The laundry was washed in a main wash at 40°C. Evaluation
takes place by determining the degree of whiteness after washing by
5 addition of the reflectance differences.
Table 3: Reflectance differences of the bleach components a) - d)
Ex.4a) Ex.4b) Ex.4c) Ex.4d)
10 352 304 275 50
T = 40°C, tea, red wine, curry, grass
