DE29522415U1 - Encapsulated sodium percarbonate particles - with a sheath of sodium sulphate applied by spraying an aqueous solution onto a heated fluidised bed of the particles - Google Patents

Abstract

Encapsulated Na percarbonate particles with a core essentially of Na percarbonate and an adherent sheath enveloping the particles consisting of one or more layers are claimed. The outermost layer of the sheath is essentially of optionally partially hydrated Na sulphate which has been formed by spraying an aqueous solution of Na sulphate onto a fluidised bed of Na percarbonate particles which may be uncoated or covered with a single or multilayer coating, and evaporating water by maintaining a temperature of 35-100[deg]C in the fluidised bed.

Description

The invention is directed to washing and bleaching agents containing silicate builders, containing coated sodium percarbonate particles consisting essentially of sodium percarbonate and a firmly adhering coating layer surrounding the core. The sodium percarbonate particles coated according to the invention by means of a fluidized bed spraying process are characterized by their very good storage and ensiling properties.

Sodium percarbonate (2 Na ₂ CO ₃ . 3 H ₂ O ₂ ) is used as an active oxygen component in washing, bleaching and cleaning agents. Due to the insufficient storage stability of sodium percarbonate in warm, humid environments and in the presence of various washing and cleaning agent components, sodium percarbonate must be stabilized against the loss of active oxygen (Oa). An essential principle for stabilization is

20 to surround the sodium percarbonate particles with a shell of stabilising components.

GB Patent 174 891 teaches how to stabilize compounds that are decomposed by weathering or catalysts by coating them. Coating is carried out by spraying a coating component in liquid form onto the powdery material to be stabilized, which is kept in motion; in order to avoid liquefaction or caking, it is cooled or dried using an air stream. Using this process, per compounds such as

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Sodium perborate, coated with water glass. In the case of sodium percarbonate, sufficient stabilization cannot be achieved by coating it with a water glass layer alone. With reference to the coating of soda containing water of crystallization, Glauber's salt, i.e. sodium sulfate decahydrate, is also mentioned in this document as a possible coating component. The coating of sodium percarbonate with a layer consisting essentially of sodium sulfate, which is not present or only partially present in the form of its hydrates, is not suggested by this document.

DE-OS 24 17 572 discloses a coated sodium percarbonate, the coating substance being a mixed compound formed by crystallization of sodium carbonate or bicarbonate with sodium sulfate. According to DE Patent 26 22 610, the single-layer coating contains sodium sulfate and sodium carbonate as well as sodium silicate. In the processes described in the two documents mentioned above, an aqueous solution of the components of the coating material is sprayed onto sodium percarbonate particles in a fluidized bed while maintaining a fluidized bed temperature of between 30 and 80 ^° C, whereby a solid coating is formed by evaporation of the water introduced. Despite significantly improved stability of the sodium percarbonate particles coated in this way, the active oxygen content still decreases too much during longer storage in the presence of a detergent powder. In addition, it was found that coated sodium percarbonate particles, the outermost layer of which contains soda exclusively or as the main component of a mixture, show unsatisfactory ensiling behavior, as bulk materials of such products solidify with increasing storage time and thus show poor flow behavior and make handling difficult.

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According to DE-OS 43 15 380, the coating material of a coated sodium percarbonate consists of a mineral salt mixture consisting essentially of alkali metal sulfate and alkali metal chloride. Although products coated in this way have a satisfactory active oxygen stability and, provided no alkali metal silicate is also present, a high dissolving rate, they are considered disadvantageous due to their alkali metal chloride content and the associated risk of corrosion. This document does not suggest using sodium sulfate as the sole coating material.

According to US Patent 4,325,933, the hygroscopic character of sodium percarbonate can be reduced and stability increased by coating sodium percarbonate particles with a coating of magnesium salts, in particular magnesium sulfate. However, a coating containing only magnesium salts no longer meets the current requirements for active oxygen stability. Accordingly, WO 95/02555 and EP-A 0 623 553 are directed at coated sodium percarbonate particles whose coating contains not only magnesium sulfate and a silicate but also soda or an alkali metal salt from the series of carbonates, bicarbonates and sulfates. The single or multi-layer coating does lead to very good active oxygen stability, but the disadvantage is the need to use three different coating components. In addition, products with a multi-layer structure and soda in the outermost coating layer tend to cake.

30 The object of the present invention is to provide coated

To provide sodium percarbonate particles which, in addition to very good active oxygen stability in washing, bleaching and cleaning agents, have a good, compared to previously known products with the same number of coating components

35 show improved silage performance. Another

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The task is to demonstrate measures to achieve the required combination of material properties with a coating that contains, if possible, fewer than three different coating components.

5 The task is solved by coated

Sodium percarbonate particles comprising a core of essentially sodium percarbonate and a firmly adhering, sodium sulfate-containing single- or multi-layer coating surrounding this core, which are characterized in that the outermost coating layer consists essentially of sodium sulfate, which may be partially hydrated, and is obtainable by spraying an aqueous sodium sulfate solution onto non-coated or single- or multi-layer coated particles of essentially sodium percarbonate located in a fluidized bed and evaporating water while maintaining a fluidized bed temperature of 35 to 100 ^° C.

The further claims are directed to preferred embodiments of the coated sodium percarbonate particles as well as a process for their preparation and their use.

The core of the coated sodium percarbonate particles consists essentially of sodium percarbonate. The term "essentially" means that the core to be coated may contain a small amount of auxiliary materials, i.e. materials other than sodium percarbonate, for production reasons. The auxiliary materials are usually contained in an amount of less than 20% by weight and in particular less than 10% by weight, based on the core. The auxiliary materials are in particular active oxygen stabilizers, such as silicates and/or magnesium compounds. Another class of auxiliary materials are inorganic or organic compounds which serve as seeds for a fluidized bed spray granulation process for the production of

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of sodium percarbonate - for example, soda and other substances that are used in conventional washing and cleaning products.

The core of essentially sodium percarbonate to be coated according to the invention can have been produced according to conventional process principles, for example by reacting hydrogen peroxide with sodium carbonate in an aqueous phase and crystallizing the sodium percarbonate or by reacting solid soda with aqueous hydrogen peroxide or by fluidized bed spray granulation, whereby a hydrogen peroxide solution and a soda solution are sprayed onto nuclei of sodium percarbonate or other organic or inorganic substances in a fluidized bed apparatus and water is evaporated at the same time. The sodium percarbonate particles coated according to the invention preferably contain a core of essentially sodium percarbonate which has been produced by a fluidized bed spray granulation process. With regard to the production of the core of essentially sodium percarbonate by fluidized bed spray granulation processes, reference is made to DE-OS 27 33 935 and WO 95/06615 as examples.

According to the invention, the outermost coating layer consists essentially of sodium sulfate, which can be partially hydrated. Underneath this outermost coating layer, one or more further coating layers can be arranged on the core consisting essentially of sodium percarbonate. Coating layers beneath the outermost coating layer can be applied in a manner known per se to a core consisting essentially of sodium percarbonate, preferably by spraying an aqueous solution containing one or more coating components onto cores consisting essentially of sodium percarbonate in a fluidized bed and evaporating water. In the case of the coating components of the

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The coating layers arranged below the outermost coating layer according to the invention are in particular substances from the series of alkali metal silicates, alkali metal carbonates, alkali metal bicarbonates, mixed salts of soda or sodium bicarbonate with other mineral salts, such as sodium sulfate, magnesium salts, in particular magnesium sulfate, magnesium chloride and magnesium salts of mono-, di- and polycarboxylic acids and hydroxycarboxylic acids, in particular citric acids, and aminocarboxylic acids, such as ethylenediaminetetraacetic acid, as well as boron compounds from the series of boric acids, borates and perborates. One or more coating layers arranged below the outermost coating layer can each contain a single coating component or several coating components

15. Preferred coated according to the invention

Sodium percarbonate particles have no more than a single coating layer below the outermost coating layer of essentially sodium sulfate, which may be partially hydrated. The coating layer according to the invention of essentially sodium sulfate, which may be partially hydrated, is particularly preferably located directly on the core of essentially sodium percarbonate, which in turn is preferably produced by means of a fluidized bed spray granulation process.

25 has been turned.

As is well known, sodium sulfate forms various hydrates, in particular the decahydrate. The sodium sulfate that forms the outermost coating layer can be partially hydrated. In order to achieve a good stabilizing effect, attempts are made during production to obtain a product with as low a degree of hydration as possible. For this reason, the fluidized bed temperature is kept above the transformation temperature of the decahydrate (32.4 ⁰ C) when applying the outermost coating layer.

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The weight proportion of the entire coating of the core, which comprises one or more layers and is essentially sodium percarbonate, is usually between 0.5 and 25% by weight, calculated hydrate-free, based on sodium percarbonate. The total coating amount is preferably 1 to 15% by weight, in particular 2 to 10% by weight, each calculated hydrate-free and based on sodium percarbonate. The amounts mentioned also apply to coatings made of sodium sulfate. In the case of two-layer coatings, the outermost layer expediently consists of 1 to 15% by weight, in particular 2 to 10% by weight, of sodium sulfate, calculated hydrate-free and based on sodium carbonate.

A feature of the coated sodium percarbonate particles that is essential to the invention is that the outermost coating layer is obtainable by the process according to the claim, comprising spraying an aqueous sodium sulfate solution onto non-coated or single- or multi-layer coated sodium percarbonate particles in a fluidized bed and evaporating water while maintaining a fluidized bed temperature of 35 to 100 ^° C. The air used for fluidization and drying usually has a temperature between 50 and 200 ^° C, in particular 80 to 120 ^° C. As can be seen from the examples and comparative examples, the selection of the substance(s) in the outermost coating layer has a significant influence on the active oxygen stability and the caking behavior and thus the ensilability.

Sodium sulfate was obviously not previously considered as the sole coating component for sodium percarbonate. In the context of the development of sodium percarbonate with good active oxygen stability, it was considered necessary, as the previously assessed state of the art shows, to use sodium sulfate in the form of mixed salts or as a component of a multi-component composition. It was therefore

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It is surprising that using sodium sulfate as the sole component of the outermost and preferably only coating layer, both very good active oxygen stability and also excellent ensilability are achieved. While coated sodium percarbonate particles with soda in the outermost coating layer tend to cake during storage, this cake can be avoided if the outermost coating layer consists of sodium sulfate, which can be partially hydrated. A further advantage of the preferred sodium percarbonate particles coated according to the invention is that using a single coating component, namely sodium sulfate, which can be partially hydrated, both good active oxygen stability and good ensilability are achieved. Due to the good ensilability of the coated sodium percarbonate particles according to the invention,

Sodium percarbonate particles do not cause clumping and therefore no emptying problems or bridging in silos, nor do they cause handling and dosing problems with large and small containers.

As already mentioned above, the sodium percarbonate particles coated according to the invention can be produced by coating in a fluidized bed. The process for applying a coating to sodium percarbonate by spraying an aqueous solution containing one or more coating components onto coated or non-coated sodium percarbonate particles in a fluidized bed is known per se - reference is made, for example, to EP-A 0 623 553, WO 95/02555, US 4,325,933 and DE-PS 26 22 610, in which the process for coating the fluidized bed is described in detail, but the sole use of sodium sulfate to produce an outermost coating layer is not disclosed or suggested. Using air as a fluidizing and drying gas and

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A fluidized bed is built up using sodium percarbonate, which may already contain a coating layer. The Na2SC>4 solution to be sprayed on is preferably one with a content of between 10 and 30% by weight of sodium sulfate. This solution is sprayed onto the particles in the fluidized bed using one or more spray nozzles. Spraying is preferably carried out at a fluidized bed temperature of 50 to 80 ^° C. The outermost coating layer can be applied in conventional apparatus for fluidized bed spray granulation, for example in essentially round fluidized bed apparatus or in a flow channel. During or after the application of the outermost coating layer, the material in the fluidized bed or taken from it can be subjected to a

15 usual visual inspection process.

The mean grain diameter and the grain spectrum of the single- or multi-layer coated particles to be coated, consisting essentially of sodium percarbonate, are selected in such a way that the coated product according to the invention meets the application requirements - with regard to high Oa stability, a coarse material is often preferred, with regard to a short dissolution time, a finer material.

The sodium percarbonate particles coated according to the invention can be used as a bleaching component in washing, cleaning, bleaching and disinfecting agents. The cleaning agents mentioned include not only conventional cleaning and scouring agents, but also dishwashing detergents and denture cleaners. Such washing, cleaning, bleaching and disinfecting agent compositions are characterized by the fact that the coated sodium percarbonate contained therein has an unexpectedly high storage stability in the presence of conventional components, such as in particular zeolites, so that during the usual storage of such compositions it only

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a very slow loss of active oxygen occurs. The washing, cleaning, bleaching and disinfecting agents under consideration consist of 1 to 99% by weight of the sodium percarbonate particles coated according to the invention or a mixture of these and other active oxygen bleaching agents and the remaining amount up to 100% by weight of other usual components of such agents. These components include in particular:

1. Surfactants from the series of cationic, anionic, non-ionic, amphoteric or ampholytic surfactants.

2. Inorganic and/or organic builders whose main action is to sequester or complex the metal ions responsible for the hardness of the water, for example zeolites, layered silicates, polyphosphates, aminopolyacetic acids and aminopolyphosphonic acids as well as polyoxycarboxylic acids.

3. Alkaline components, such as alkanolamines, and inorganic electrolytes, such as silicates, carbonates and sulfates.

4. Bleach activators from the series of N-acyl compounds and O-acyl compounds, such as tetraacetylethylenediamine (TAED) and nonanoyloxybenzenesulfonate (NOBS).

5. Other components of the agents may be stabilizers for peroxides, such as in particular magnesium salts, antiredeposition agents, optical brighteners, foam inhibitors, enzymes, disinfectants, corrosion inhibitors, fragrances, dyes and agents for regulating

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the pH value. For individual compounds belonging to substance classes 1 to 5, reference is made to DE-OS 33 21 082, pages 14-30.

Examples

(a) General rule for applying a sodium sulphate coating to coated or uncoated sodium percarbonate in the fluidised bed:

In a laboratory fluidized bed dryer,

Using drying air (supply air temperature 100 to 110 ⁰ C) a fluidized bed of the material to be coated, possibly already having one or more coating layers

Sodium percarbonate (NaPc) is formed during the

The fluidized bed is maintained by enveloping it. A 20 wt. % aqueous sodium sulfate solution is sprayed onto the particles in the fluidized bed, whereby the temperature of the fluidized bed

is kept in the range of 50 to 60 ⁰ C; it is then dried at 80 to 90 ⁰ C. The solution is sprayed using conventional two-fluid nozzles with air as the propellant. The coating quantities given in the examples are % by weight and refer in each case to the sodium percarbonate used.

The production of coating layers beneath the coating layer according to the invention as well as products coated in one or two layers not according to the invention was carried out in an analogous manner, but with aqueous solutions containing one or two coating components being sprayed onto the core of sodium percarbonate.

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b) Determination of the storage stability of coated sodium percarbonate particles produced according to the invention and for comparison purposes in detergent mixtures (= Oa retention (%) ): 5

A phosphate-free but zeolite-containing detergent powder, activator TAED and a coated or non-coated sodium percarbonate (NaPc) are mixed in such an amount that the mixture contains 5% TAED and the Oa content is about 2.35% by weight. Components in the detergent powder in % by weight:
Anionic surfactants 12
Non-ionic surfactants 8

15 Zeolite A 36

Soda 10

Na-silicates 3

Rest incl. humidity 31.

20 800 g of the respective mixture are placed in

, commercially available, water-repellent impregnated and glued El detergent packages are stored in a climate cabinet at 30 ⁰ C and 80 % relative humidity. One package is stored per sampling date - after 4 and 8 weeks. The Oa content is determined in the usual way permanganometrically; the respective Oa retention in % is determined from the initial Oa content and the Oa content after 4 and 8 weeks.

c) Determination of silage properties:

The determination was carried out according to Jenike (SiIo-Handbuch, Peter Martens (ed.) Ernst & Söhn Verlag, Berlin (1988) pages 41-56) over a period of 28 days. The storage was largely carried out under exclusion of air at room temperature in

35 encapsulated measuring cells of the time hardening bench.

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The tests were carried out in the Jenike measuring cell (diameter: 92 mm) with a hanger weight of H = 251 g plus 1, 2 and 4 kg as pre-shear normal stress. For time consolidation, product samples were pre-sheared with H + 2 kg and sheared with H + kg. The load during storage in the time consolidation bench was 4.5 kg.

In the Jenike method, the consolidation stress σγ [Pa] and the

Bulk solids strength fc [Pa] is determined as a function of storage time. The ffc value is determined as a measure of the flowability of bulk solids, where

applies: ffc = -3-fc

The following applies to the classification: 15 ffc > 10 free flowing ffc 10-4 slightly flowing ffc 4-2 cohesive

ffc < 2 very cohesive, not flowing

On the one hand, sodium percarbonate was coated which had been produced by fluidized bed spray granulation according to WO 95/06615 - see VB 1 in Table 1, and on the other hand, commercially available sodium percarbonate obtained by crystallization from an aqueous solution containing NaCl - see VB 6 in Table 2.

Examples B 1 to B 3 and comparative examples VB 1 to VB

The products were manufactured according to general instructions. The Oa contents are shown in Table 1. The total moisture content of the coated products, determined by drying loss at 160 ⁰ C minus Oa content, was between 0.8 and 1.2 %. Grain spectrum of the NaPc-

·

·

·

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Fluidized bed granules: on 0.5 mm 27%, on 0.6 mm 40%, on 0.7 mm 14%, on 0.8 mm 16%, on 1 mm 3%.

Table 1 shows that despite different coatings, all products can be classified as "free-flowing" at the beginning of storage. Coated sodium percarbonate with only Na ₂ SO ₄ as coating (B 1 and B 3) and with Na ₂ SO ₄ as the outermost layer of a coating (B 2) show both a high Oa retention in the detergent mixture and good ensiling behavior, namely "slightly flowing" from the first day of storage; the flowability does not change after that. Sodium percarbonate particles whose outermost layer essentially contains soda (VB 2, VB 3, VB 5) sometimes show a high Oa retention (VB and VB 5), but these products solidify during storage.

15 Storage - they are cohesive to very cohesive

From Example B 1 it follows that a single-layer coating with Na ₂ SO ₄ leads to essentially the same Oa retention as a single-layer (VB 4) or two-layer (B 2 and VB 3) coating containing Na ₂ SO ₄ and Na ₂ CO3.

20 Wrapping.

Examples B 4 and B 5 and comparative examples VB 6 to VB 8

Table 2 shows the results of the products examined, in which the core was always a NaPc crystal. The active oxygen stability of a non-coated NaPc crystal (VB 6) is lower than that of a NaPc fluidized bed spray granulate (VB 1). By coating with Na ₂ SO ₄ (B 4 and B 5) a stronger increase in the Oa retention in the detergent mixture can be achieved and there is no tendency to caking. In contrast, previously known products with a two-layer coating (VB 7 and VB 8) have an even higher Oa retention, but at the same time a weak tendency to caking.

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15

Table 1

B-No. or VB-
No. NaPc core NaPc coating
(Substance/wt.%) Oa content
(%) Oa preservation (%) in
Detergent after 4
Weeks 8 Weeks 25 ffc values according to Jenike in
Dependence on storage time
Start 1 day 7 days 2 8 days n.b. n.b n.b. VB1 WS-Spray
granules 14.2 52 34 n.b. VB2 ff Na ₂ CO ₃ / 5 13.5 56 88 7.9 7.9 7.9 B1 Na2SO4 / 5 13.5 95 89 OO 38 1.5 0.6 VB3 U 1.Na2SO4 /2.5
2.Na2SO3 /2.5 13.6: 92 87 OO 6.9 6.9 6.9 B2 &eegr; 1. Na2CO3 /2.5
2. _Na2SO4 /2.5 13.5 93 86 26.1 n.b. n.b. n.b. VB4 a Mixture of
Na2CO3 and Na2SO4
(1:1 wt.
parts)/5 13.6 95 n.b. 7.2 7.2 7.2 B3 &eegr; _Na2SO4 / _2.5 13.9 85 OO 18.3 2.5 1.0 VB5 u 1. _MgSO4 /2.0
2. Mixture of
Na2CO3 / 2 and
Water glass (module
2) /1 13.4 92 OO

NaPc = sodium percarbonate; WS = fluidized bed; n.d. = not determined

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Table 2

16

B-No. or
VB-No. NaPc core NaPc coating
(Substance/wt.%) Oa preservation (%) in
Detergent after
4 weeks Baking
Tilt *) VB6 Crystallizate — 30 B4 _{Na2SO4 /} 5 50 no B5 // _{Na2SO4 /} 10 70 no VB7 The 1. _MgSO4 / 2
2. Mixture of
Na ₂ CO ₃ /2 and
Water glass
(Module 2)/l 62 weak VB8 &eegr; 1. _MgSO4 / 4
2. Mixture of
Na ₂ CO ₃ /4 and
Water glass
(Module 2.0)/2 78 weak

*) qualitative determination: none - weak - medium - strong (lump formation when pouring from sample bottle after 10 days storage in closed bottle

Claims (2)

1. A washing or bleaching agent containing silicate builders, containing coated sodium percarbonate particles as the bleaching component, consisting of a core of essentially sodium percarbonate and a firmly adhering, single coating layer surrounding this core, which consists of sodium sulfate, which may be partially hydrated, wherein the coated sodium percarbonate particles are obtainable by spraying an aqueous sodium sulfate solution in a fluidized bed onto the non-coated core of a sodium percarbonate produced by fluidized bed spray granulation, while maintaining a fluidized bed temperature of 35 to 100°C and evaporating water, and wherein the coating layer makes up 2 to 10% by weight of sodium sulfate, calculated hydrate-free and based on sodium percarbonate. 2. Detergent and bleaching agent according to claim 1, characterized in that the coating layer of the coated sodium percarbonate particles comprises 5 to 10 wt. % sodium sulfate, calculated hydrate-free and based on sodium percarbonate.