Coated sodium percarbonate particles

The invention relates to coated sodium percarbonate

particles which have improved storage stability following mechanical stress of the particles.

Sodium percarbonate is used as a bleaching-active component in detergents and cleaners. For this application, sodium percarbonate has to have adequate storage stability in detergent and cleaner preparations since otherwise storage of the detergents and cleaners results in undesired loss of active oxygen and therefore of bleaching effect. Sodium percarbonate is moisture-sensitive and decomposes in detergent and cleaner preparations under the action of moisture with the loss of active oxygen. Consequently, sodium percarbonate is usually used for producing

detergents or cleaners in coated form, with the coating layer preventing the action of moisture on the coated sodium percarbonate particles. Suitable coating layers made of inorganic hydrate-forming salts, such as, for example, sodium carbonate, sodium sulphate or mixtures thereof, are known for example from DE 24 17 572, EP 863 842 and WO 2008/012184.

EP 1 149 800 Al discloses sodium percarbonate particles with an inner coating layer, which comprises an alkali metal silicate and at least one alkali metal sulphate, carbonate or bicarbonate, and also an outer coating layer, which comprises an alkali metal sulphate and at least one alkali metal carbonate or bicarbonate. The fraction of alkali metal sulphate, carbonate or bicarbonate in the inner coating layer is preferably one to three times as high as the fraction of alkali metal silicate. Comparative examples 1 and 2 describe coated sodium percarbonate particles with an inner coating layer made of sodium silicate and an outer coating layer made of sodium sulphate and sodium carbonate where the fraction of sodium sulphate in the outer coating layer is less than 50% by weight.

WO 2004/056954 describes coated sodium percarbonate

particles with a delayed release of active oxygen into an aqueous phase, which have an inner coating layer made of an inorganic salt and an outer coating layer made of an alkali metal silicate with an Si0 ₂ :M ₂ 0 modulus of more than 2.5. The particles can have further coating layers on the outer coating layer, with coating layers made of finely dispersed inorganic oxides, mixed oxides and silicates being

specified. The examples disclose coated sodium percarbonate particles with an inner coating layer made of sodium sulphate and an outer coating layer made of sodium

silicate, which have no additional coating layer. WO

2008/012184 desribes corresponding coated sodium

percarbonate particles in which the inner coating layer comprises sodium sulphate and sodium carbonate in a weight ratio of 95:5 to 75:25 and the fraction of sodium sulphate and sodium carbonate in the coating layer is at least 80% by weight.

WO 2006/063668 describes compressed mouldings which

comprise coated sodium percarbonate particles with an inner and an outer coating layer, where the inner coating layer comprises one or more hydrate-forming salts and the outer coating layer comprises an alkali metal silicate. The examples describe mouldings which comprise sodium

percarbonate particles with an inner coating layer made of sodium sulphate and an outer coating layer made of sodium waterglass . WO 2011/134972 describes bleach particles which have a core made of sodium percarbonate, an inner coating layer

comprising at least 50% by weight of sodium sulphate in the form of thenardite or burkeite and an outer coating layer comprising a water-soluble binder and a bleach activator. The bleach particles can have an additional coating layer over the outer coating layer which comprises at least 50% by weight of sodium sulphate in the form of thenardite or burkeite. The binder can be a water-soluble alkali metal silicate. Example 4 discloses bleach particles with an inner coating layer made of sodium sulphate and sodium carbonate in the weight ratio 87:13, an outer coating layer made of TAED particles and sodium waterglass in the weight ratio 89:11 and an additional coating layer made of sodium sulphate .

The inventors of the present invention have now found that although the multiply coated sodium percarbonate particles known from the prior art have good storage stability in detergents if they are formulated directly after

manufacture with other components to give a pulverulent or granular detergent and the detergent is then stored, the storage stability decreases considerably if the coated sodium percarbonate particles are mechanically stressed before or during formulation to give a detergent, for example by means of pneumatic conveyance or intensive mixing of the components during the manufacture of the detergent. Moreover, the inventors have found that the loss in storage stability due to mechanical stressing of the coated sodium percarbonate particles can be reduced if the particles have an at least three-layered coating in which the inner layer consists predominantly of sodium sulphate, the middle layer consists predominantly of an alkali metal silicate and the outer layer consists predominantly of sodium sulphate and/or sodium carbonate.

The invention therefore provides coated sodium percarbonate particles which comprise a core comprising sodium

percarbonate, an inner coating layer, an outer coating layer and a middle coating layer arranged between the inner and the outer coating layer, where the core comprises at least 50% by weight of sodium percarbonate, the inner coating layer comprises at least 50% by weight of sodium sulphate in the form of thenardite or burkeite, the middle coating layer comprises at least 50% by weight of alkali metal silicate and the outer coating layer comprises sodium sulphate, sodium carbonate or a mixture of sodium sulphate and sodium carbonate, where the fraction of sodium sulphate and sodium carbonate in the outer coating layer is at least 50% by weight.

The coated sodium percarbonate particles according to the invention comprise a core which comprises at least 50% by weight of sodium percarbonate, i.e. sodium carbonate perhydrate with the composition 2 Na ₂ CC>3 · 3 H ₂ O ₂ . Besides sodium percarbonate, the core can also comprise sodium carbonate, sodium hydrogencarbonate and mixed salts

thereof, and also small amounts of known stabilizers for peroxygen compounds, such as, for example, magnesium salts, silicates, phosphates and/or chelate complexing agents. The fraction of sodium percarbonate in the core of the coated sodium percarbonate particles according to the invention is preferably more than 80% by weight and particularly

preferably 80 to 95% by weight, based on the mass of the core. The fraction of organic carbon compounds in the core is preferably less than 1% by weight, particularly

preferably less than 0.1% by weight, based on the mass of the core . In a preferred embodiment, the core comprises small amounts of additives which have a stabilizing effect on the active oxygen content, the fraction of stabilizing additives in the core being preferably less than 2% by weight, based on the mass of the core. The stability-increasing additives used are preferably magnesium salts, waterglass, stannates, pyrophosphates, polyphosphates, and chelate complexing agents from the series of hydroxycarboxylic acids,

aminocarboxylic acids, aminophosphonic acids,

phosphonocarboxylic acids and hydroxyphosphonic acids, and alkali metal, ammonium or magnesium salts thereof. In a particularly preferred embodiment, the core comprises, as stabilizing additive, an alkali metal silicate, preferably waterglass with an SiO ₂ / a ₂ <0 modulus in the range from 1 to 3, in an amount of from 0.1 to 1% by weight, based on the mass of the core. In the most preferred embodiment, in addition to this amount of alkali metal silicate, the core also comprises a magnesium compound in an amount of from 50 to 2000 ppm of Mg ²⁺ , based on the mass of the core. By adding these stabilizing additives it is possible to further reduce the evolution of heat as a result of

decomposition of the sodium percarbonate in the core during storage .

The core of the coated sodium percarbonate particles according to the invention can have been produced by one of the known preparation processes for sodium percarbonate. A suitable preparation process for sodium percarbonate is the crystallization of sodium percarbonate from aqueous

solutions of hydrogen peroxide and sodium carbonate, where the crystallization can either be carried out in the presence or in the absence of a salting-out agent, for which purpose reference is made by way of example to

EP 0 703 190 and DE 2 744 574. Sodium percarbonate

particles prepared by the crystallization process in the presence of a salting-out agent can also comprise small amounts of the salting-out agent used, such as e.g. sodium chloride. Likewise suitable is the fluidized-bed buildup granulation by spraying aqueous hydrogen peroxide solution and aqueous sodium carbonate solution onto sodium

percarbonate seeds in a fluidized bed with simultaneous evaporation of water, reference being made by way of example to WO 95/06615. In a similar way, the fluidized bed buildup granulation known from EP 0 654 440 and

EP 0 873 971 by spraying aqueous hydrogen peroxide solution and aqueous sodium carbonate solution onto sodium

percarbonate prepared by crystallization is suitable.

Furthermore, the reaction of solid sodium carbonate with an aqueous hydrogen peroxide solution and subsequent drying is also a suitable preparation process, reference being made by way of example to DE 196 08 000.

In a preferred embodiment, the coated sodium percarbonate particles according to the invention have a core comprising sodium percarbonate which is obtainable by fluidized-bed buildup granulation. As a result of such a fluidized-bed buildup granulation, a core is obtained which differs from the cores obtained by other preparation processes by virtue of a particularly dense, shell-like structure and a

smoother surface. Coated sodium percarbonate particles according to the invention, the core of which has been produced by fluidized-bed buildup granulation, exhibit a further significantly improved storage stability and a considerably lower evolution of heat during storage

compared with particles whose core has been produced by a different process.

Preferably, the core of the coated sodium percarbonate particles according to the invention has an essentially spherical shape with a smooth interface to the coating layer positioned on top. The average roughness R _a of the interface between core and innermost coating layer is preferably less than 5 pm, determined by SEM images with material contrast on cut surfaces of the particles for interfacial sections of 100 pm in length.

Preferably, the core has a diameter in the range from 0.4 to 2.0 mm, particularly preferably from 0.6 to 1.5 mm. By selecting a core diameter within this range, it is possible to avoid segregation of the coated sodium percarbonate particles in granular cleaners, and to ensure high storage stability of the granular cleaners.

In addition to the core, the coated sodium percarbonate particles according to the invention also comprise an inner coating layer which comprises at least 50% by weight, preferably at least 75% by weight, of sodium sulphate in the form of thenardite or burkeite. Preferably, the inner coating layer lies directly on the core comprising sodium percarbonate . In a preferred embodiment, the inner coating layer

comprises sodium sulphate and sodium carbonate in a weight ratio of from 95:5 to 75:25. Particularly preferably, the weight ratio of sodium sulphate and sodium carbonate is in the range from 95:5 to 80:20, most preferably in the range from 90:10 to 80:20. The total fraction of sodium sulphate and sodium carbonate in the inner coating layer is

preferably at least 80% by weight, particularly preferably at least 90% by weight. The sodium carbonate present in the coating layer is preferably present to an extent of more than 80% in the form of burkeite of the composition

Na ₄ (SO ₄ ) i+n (CO3) i-n, where n is from 0 to 0.5. The fraction of burkeite relative to other phases present in the bleach particles which comprise sodium carbonate can be determined by Rietveld analysis of powder X-ray diagrams of the bleach particles.

In a preferred embodiment, the inner coating layer

additionally comprises 0.1 to 1% by weight of sodium silicate, particularly preferably 0.2 to 0.5% by weight of sodium silicate. The sodium silicate is preferably a water- soluble sodium silicate, in particular a waterglass. By adding small amounts of sodium silicate it is possible to further improve the storage stability of the coated sodium percarbonate particles according to the invention.

The weight fraction of the inner coating layer is

preferably 2 to 25%, particularly preferably 2 to 10% and most preferably 4 to 7%, in each case based on the mass of the coated sodium percarbonate particles. The inner coating layer is preferably formed such that it covers the material underneath to an extent of more than 95%, preferably to an extent of more than 98% and in particular completely. The coated sodium percarbonate particles according to the invention comprise, between the inner and the outer coating layer, a middle coating layer which comprises at least 50% by weight and preferably at least 90% by weight of alkali metal silicate. The middle coating layer preferably

comprises sodium silicate and particularly preferably sodium waterglass, in which case the fraction of sodium silicate is preferably at least 50% by weight and

particularly preferably at least 90% by weight. The middle coating layer is preferably produced by spraying on an aqueous solution comprising alkali metal silicate,

particularly preferably by spraying on an aqueous solution comprising alkali metal silicate in a fluidized bed with simultaneous evaporation of water. The weight fraction of the middle coating layer is preferably 0.2 to 5%,

particularly preferably 0.2 to 3%, based on the mass of the coated sodium percarbonate particles.

In a preferred embodiment, the middle coating layer is produced by spraying on an aqueous sodium silicate solution with an SiO ₂ : a ₂ <0 modulus in the range between 2.0 and 2.4. By using a modulus in this range, coated sodium

percarbonate particles are obtained according to the invention which dissolve within a short time even in cold water . In a further preferred embodiment, the middle coating layer is produced by spraying on an aqueous sodium silicate solution with an SiO ₂ : a ₂ <0 modulus in the range from 2.4 to 4.0, preferably 3.2 to 4.0. By using a modulus in this range, sodium percarbonate particles coated according to the invention are obtained which release the active oxygen in a delayed manner upon incorporating the particles into an aqueous washing liquor, it being possible to influence the delay via the choice of modulus and the amount of coating layer. In both embodiments, the middle coating layer is preferably produced by spraying on an aqueous sodium silicate solution with a concentration of from 2 to 20% by weight of sodium silicate. By using a sodium silicate solution with a concentration in this range, it is possible to attain a high stability and a high dissolution time delay even with small amounts of sodium silicate.

Moreover, the coated sodium percarbonate particles

according to the invention comprise an outer coating layer positioned on top of the middle coating layer and

comprising sodium sulphate, sodium carbonate or a mixture of sodium sulphate and sodium carbonate, where the fraction of sodium sulphate and sodium carbonate in the outer coating layer is at least 50% by weight. Preferably, there is no further coating layer on the outer coating layer.

In a preferred embodiment, the outer coating layer

comprises sodium sulphate and sodium carbonate in a weight ratio of from 95:5 to 75:25. Particularly preferably, the weight ratio of sodium sulphate and sodium carbonate is in the range from 95:5 to 80:20. In this embodiment, the sodium carbonate present in the outer coating layer is preferably present to an extent of more than 80% in the form of burkeite of the composition Na ₄ (S0 ₄ ) i _+n (CO3) i_ _n , where n is from 0 to 0.5. The total fraction of sodium sulphate and sodium carbonate in the outer coating layer is preferably at least 80% by weight, particularly preferably at least 90% by weight.

In a further preferred embodiment, the outer coating layer consists essentially of sodium sulphate. In an alternative preferred embodiment to this, the outer coating layer consists essentially of sodium carbonate.

The weight fraction of the outer coating layer is

preferably 2 to 15%, particularly preferably 3 to 10% and most preferably 4 to 7%, in each case based on the mass of the coated sodium percarbonate particles. The outer coating layer is preferably formed such that it covers the material underneath to an extent of more than 95%, preferably to an extent of more than 98% and in particular completely.

Between the coating layers and also between the innermost coating layer and the core there may be a sharp boundary at which the composition changes suddenly. As a rule, however, between the individual coating layers, as well as between the innermost coating layer and the core, a transition zone will form in each case which comprises the components of the two adjacent layers. Such transition zones arise for example as a result of applying a coating layer in the form of an aqueous solution, with some of the layer underneath partially dissolving as the layer starts to form, thus giving rise to a transition zone which comprises the constituents of both layers. If the inner coating layer is positioned directly on the core, a transition layer can thus form between the core and the inner coating layer which comprises sodium sulphate, sodium carbonate, sodium hydrogencarbonate and sodium percarbonate, and also mixed salts of these components.

The three coating layers of the coated sodium percarbonate particles according to the invention preferably have a homogeneous layer thickness, where the thickness of the coating layer deviates for more than 90% of the layer by less than 50% from the average layer thickness.

The coating layers of the coated sodium percarbonate particles according to the invention are preferably

produced by spraying on aqueous solutions in a fluidized bed. In this process, in a first step, an aqueous solution comprising sodium sulphate and optionally sodium carbonate is preferably sprayed onto a core material comprising sodium percarbonate, with the simultaneous evaporation of water. In a subsequent second step, an aqueous solution comprising alkali metal silicate is sprayed onto the product obtained in the first step, with the simultaneous evaporation of water. In a subsequent third step, an aqueous solution comprising sodium sulphate, sodium

carbonate or a mixture of sodium sulphate and sodium carbonate is sprayed onto the product obtained in the second step, with the simultaneous evaporation of water. Preferably, aqueous solutions of identical composition are sprayed on in the first and third step. Preferably, in order to apply the inner and the outer coating layer, aqueous solutions are sprayed on which comprise in total not more than 30% by weight, preferably 10 to 25% by weight, of dissolved salts. In order to apply the middle coating layer, an aqueous sodium silicate solution with a concentration of from 2 to 30% by weight and particularly preferably 2 to 20% by weight, of sodium silicate is preferably sprayed on.

During the spraying on of the aqueous solutions, the majority of the water present therein, in particular more than 90% of the water present in the aqueous solution, is preferably already evaporated as a result of supply of heat, such that only a small section of the underlying material is partly dissolved during application of the coating layers, and a solid coating layer is already formed during the spraying on. The coating layers are preferably applied in accordance with the process described in

EP 0 970 917, with which it is possible to achieve a dense coating layer even with small amounts of coating layer material. The application of the coating layers in a fluidized bed preferably takes place with the introduction of a drying gas to the fluidized bed, such that a

temperature in the range from 30 to 90°C, preferably 45 to 70°C, is established in the fluidized bed. The drying gas used is preferably heated air or a mixture of air and a combustion gas, the combustion gas used preferably being a combustion gas obtained by combustion of natural gas with air .

The coated sodium percarbonate particles according to the invention are preferably dried after applying the outer coating layer at a temperature in the range from 60 to

95°C, particularly preferably in the range from 70 to 90°C, the drying preferably taking place over at least 2 min and particularly preferably over 4 to 20 min.

The coated sodium percarbonate particles according to the invention preferably have a mass-based median of the particle size in the range from 0.4 to 2 mm. Particularly preferably, less than 10% by weight of the particles are smaller than 0.2 mm, and particularly preferably less than 10% by weight of the particles are smaller than 0.3 mm. Through appropriate choice of particle size it is possible to improve the storage stability of the sodium percarbonate particles according to the invention in detergent and cleaner preparations.

Compared to the sodium percarbonate particles known from the prior art and having coating layers comprising sodium sulphate and alkali metal silicate, the coated sodium percarbonate particles according to the invention have improved storage stability in pulverulent or granular detergents, even following mechanical stress before or during the manufacture of the detergent. At the same time, the sodium percarbonate particles coated according to the invention have particularly good silo storability since, in bulk, they have only a low liberation of heat and neither cake nor lose storage stability under compressive loading. The examples below illustrate the invention without, however, limiting the subject matter of the invention.

Examples For examples 1 to 21, a sodium percarbonate produced by fluidized-bed buildup granulation was used which was coated with 7.2% by weight of a coating layer which comprised sodium sulphate and sodium carbonate in the weight ratio 9:1. The coated sodium percarbonate used had an active oxygen content of 13.3%, a bulk density of 1096 g/1 and a weight-based average particle size of 0.71 mm.

Further coating layers comprising sodium sulphate, sodium carbonate and sodium waterglass were applied by spraying on aqueous solutions in a fluidized bed. The spraying on was carried out in a Microlab fluidized-bed coater from OYSTAR Huttlin, which was equipped with a l l product container and a three-component nozzle installed from the bottom and was operated with subatmospheric pressure in the fluidized bed and 35 m ³ /h (STP) air at 90°C as fluidizing gas. The coated sodium percarbonate used was charged to the

preheated fluidized-bed coater and, after a fluidized-bed temperature of 60°C had been reached, coating solution was sprayed on with air as propellant medium at a spraying pressure of 0.6 bar at a temperature of the fluidizing gas of 95°C. The compositions of the coating solutions used and the spraying rates used are listed in Table 1. After spraying on the coating solution, post-drying was carried out for 30 min at a temperature of the fluidizing gas of 90°C in the fluidized bed. In the event of applying two coating layers, no drying was carried out between the spraying on of the coating solutions of differing

composition . Table 1

Coating solutions used

A further coating layer made of fumed silica was applied in a turbular mixer. For this, 750 g of coated sodium

percarbonate were charged to a 2000 ml polyethylene bottle with the fumed silica, the sealed bottle was clamped on a turbular mixer model T2C from Willy A. Backofen AG and shaken for 10 min. The coating material used was

hydrophilic Aerosil® 200 or hydrophobicized Aerosil® R974.

Table 2 gives the compositions and amounts of the further coating layers (second and third coating layer) applied in examples 2 to 21 to the coated sodium percarbonate from example 1 used, the amounts being given in % by weight, based on the coated sodium percarbonate used. Table 2

Further coating layers applied

Example Second coating layer Third coating layer

1* none none

2* 0.5% Waterglass Modulus 2.0 none

3* 0.5% Waterglass Modulus 3.4 none

4 * 0.2% Aerosil® 200 none

5* 0.2% Aerosil® R974 none

6* 0.5% Waterglass modulus 2.0 0.2% Aerosil® 200

7* 0.5% Waterglass modulus 2.0 0.2% Aerosil® R974

8 0.5% Waterglass modulus 2.0 3% Na ₂ S0 ₄

9 0.5% Waterglass modulus 2.0 6% Na ₂ S0 ₄

10 0.5% Waterglass modulus 2.0 3% Na ₂ C0 ₃

11 0.5% Waterglass modulus 2.0 6% Na ₂ C0 ₃

12 0.5% Waterglass modulus 2.0 3% Na ₂ S0 ₄ /Na ₂ C0 ₃ 9:1

13 0.5% Waterglass modulus 2.0 6% Na ₂ S0 ₄ /Na ₂ C0 ₃ 9:1

14* 0.5% Waterglass modulus 3.4 0.2% Aerosil® 200

15* 0.5% Waterglass modulus 3.4 0.2% Aerosil® R974

16 0.5% Waterglass modulus 3.4 3% Na ₂ S0 ₄

17 0.5% Waterglass modulus 3.4 6% Na ₂ S0 ₄

18 0.5% Waterglass modulus 3.4 3% Na ₂ C0 ₃

19 0.5% Waterglass modulus 3.4 6% Na ₂ C0 ₃ Example Second coating layer Third coating layer

20 0.5% Waterglass modulus 3.4 3% a ₂ S04/ a ₂ C03 9:1

21 0.5% Waterglass modulus 3.4 6% a ₂ S04/ a ₂ C03 9:1

Comparative example not according to the invention

The resistance of the coated sodium percarbonate particles to mechanical stress was determined in an abrasion test in accordance with ISO 5937:1980. For this, 50 g of sample were charged to a vertical glass tube with an internal diameter of 25 mm and a length of 600 mm which has a metal plate with a central bore measuring 0.6 mm in diameter at the lower end and a dust filter at the upper end, and air is introduced for 10 min through the orifice at a volume stream of 13.0 1/min (STP) at a pressure of approx.

3.5 bar, such that the sample was whirled up and fluidized in the glass tube. The sample mechanically stressed in this way and a comparative sample of the non-mechanically- stressed sodium percarbonate were sieved on a sieving machine in each case over sieves with mesh widths of 100, 200, 300, 400, 710, 1000 and 1250 pm for 10 min, the sieve fractions were weighed and the mass of the particles with a particle diameter of more than 300 pm was determined. The abrasion in per cent was calculated therefrom to

100* (m _v -m _f ) /m ₀ , where m _v refers to the mass of the particles with a particle diameter of more than 300 pm in the

comparison sample, m _f refers to the mass of the particles with a particle diameter of more than 300 pm in the

fluidized sample and m ₀ refers to the mass of the sample used in the abrasion experiment.

Table 3 summarizes the results of the abrasion test. Table 3

Abrasion as a result of mechanical stressing of the sodium percarbonate particles

Example Abrasion in %

1* 1.3

2* 4.4

3* 4.0

4 * 4.5

5* 7.2

6* 4.6

7* 4.6

8 3.2

9 2.7

10 3.4

11 2.5

12 3.2

13 3.8

14* 4.8

15* 6.5

16 2.5 Example Abrasion in %

19 2.8

20 3.1

21 3.4

Comparative example not according to the invention

To determine the storage stability in a pulverulent

detergent preparation, 405 g of zeolite-containing standard detergent powder IEC-A* BASE (wfk-Testgewebe GmbH, Krefeld) were mixed with 15 g of TAED and 80 g of sodium

percarbonate in a tumble mixer for at least 10 min, with either the mechanically nonstressed sodium percarbonate or the combined sieve fractions of the particles with a particle diameter of more than 300 pm from the abrasion test being used to produce the mixtures. The mixture was transferred to a water-repellingly impregnated E2 detergent pouch (dimensions 19 x 14 x 4.5 cm), which was sealed with hot-melt adhesive. The detergent pouch was then stored in a climatically controlled cabinet at 35°C and 80% relative humidity. After cooling the detergent pouch to room

temperature outside of the climatically controlled cabinet, the contents of the detergent pouch were divided by means of a sample divider into samples each of 3 g. The active oxygen content before and after storage was determined permanganometrically in the usual manner. The active oxygen content before storage and the active oxygen content following storage for 4 or 8 weeks were used to ascertain the preservation of the active oxygen content (Oa

preservation) in per cent as a measure of the storage stability in the detergent preparation. The results are summarized in Table 4. Table 4

Stability of mechanically unstressed and stressed

percarbonate particles in a pulverulent detergent

preparation

Example Oa preservation Oa preservation Oa preservation in % after 4 in % after 4 in % after 8 weeks, not weeks , weeks , mechanically mechanically mechanically stressed stressed stressed

1* 94 82 64

2* 96 82 71

3* 96 84 64

4* 95 85 72

5* 94 80 61

6* 97 91 71

7* 95 87 66

8 95 89 82

9 96 96 87

10 94 94 81

11 95 93 87

12 96 92 82

13 98 97 84

14* 96 84 72

15* 94 83 66 Example Oa preservation Oa preservation Oa preservation in % after 4 in % after 4 in % after 8 weeks, not weeks , weeks , mechanically mechanically mechanically stressed stressed stressed

16 94 91 80

17 97 96 87

18 94 93 85

19 96 96 85

20 97 91 78

21 98 95 87

Comparative example not according to the invention

To determine the storage stability in a liquid detergent, 2 g of mechanically nonstressed sodium percarbonate and 18 g of Henkel Persil Mega Caps were stored in a 50 ml polyethylene bottle for 7 days at room temperature, during which time the sample was mixed daily for 60 min in a tumble mixer. The active oxygen content of the sample after storage was determined permanganometrically in the

customary manner. The active oxygen content of the sodium percarbonate used and the active oxygen content of the sample following storage for 7 days were used to ascertain the preservation of the active oxygen content (Oa

preservation) in per cent as a measure of the storage stability in the detergent. The results are summarized in Table 5. Table 5

Stability of the sodium percarbonate particles in a liquid detergent

Example Oa preservation in %

1* 93

2* 95

3* 96

4 * 94

5* 94

6* 95

7* 95

8 95

9 98

10 96

11 97

12 97

13 98

14* 95

15* 95

16 95

17 96

18 96 Example Oa preservation in %

19 97

20 96

21 97

Comparative example not according to the invention

Moreover, the dissolution time in water was determined for the coated sodium percarbonate particles. For this, 2.5 g of sodium percarbonate particles were dissolved in a thermostatted measuring cell made of glass (diameter 130 mm, height 150 mm) with stirring using a magnetic stirrer at 20°C in 1 1 of water. The stirring rate was selected such that a vortex funnel 4 cm in depth was formed. During the dissolution operation, the change in electrical conductivity of the solution was measured. The dissolution time is the time in which 90% of the final conductivity is reached. The results are summarized in Table 6.

Table 6

Dissolution time of the coated sodium percarbonate

particles

Example Dissolution

time in s

1* 60

2* 152

3* 312 Example Dissolution time in s

4 * 63

5* 72

6* 166

7* 164

8 156

9 138

10 187

11 195

12 149

13 138

14* 323

15* 328

16 362

17 317

18 383

19 389

20 336

21 317