EP2144989A1

EP2144989A1 - Process for the preparation of coated sodium percarbonate

Info

Publication number: EP2144989A1
Application number: EP08749854A
Authority: EP
Inventors: Jürgen H. Rabe; Henk L.J. Venbrux; Gerd Hecken; Bernd Hoffmann; Alfred Söntgerath
Original assignee: Solvay SA
Current assignee: Solvay SA
Priority date: 2007-05-02
Filing date: 2008-04-29
Publication date: 2010-01-20
Also published as: WO2008135461A1; CN101688161B; CN101688161A

Abstract

A process for the preparation of coated sodium percarbonate containing particles, comprising (a) a manufacturing step of sodium percarbonate containing core particles, comprising the crystallisation of sodium percarbonate from aqueous solution and the separation from aqueous solution, (b) an at least partial drying step of the sodium percarbonate containing core particles, (c) a coating step comprising the application of a base coating on the so obtained core particles with one or more sodium percarbonate containing or generating solutions and/or suspensions, and optionally one or more additives, and (d) a drying step of the coated sodium percarbonate containing particles, wherein step (c) and/or (d), and optionally (b), are carried out in a fluid bed reactor and the global molar ratio between hydrogen peroxide and sodium carbonate in the sodium percarbonate containing or generating solutions and suspensions is below 1,35 or above 1,65.

Description

Process for the preparation of coated sodium percarbonate

The present application claims the benefit of the European application no. 07107377.9 filed on May 2, 2007, herein incorporated by reference. Introduction

The present invention relates to an enhanced process for the preparation of coated sodium percarbonate (PCS) containing particles, the so obtained particles, as well as their use in detergent compositions.

The use of sodium percarbonate (or sodium carbonate peroxyhydrate, 2 NaCO₃ . 3 H₂O₂) as bleaching agent in detergent compositions for household fabric washing or dish washing is well known. Commonly such detergent compositions contain among other components zeolites as builder material, enzymes, bleach activators and/or perfumes.

Different processes are known to produce sodium percarbonate, among them so-called crystallisation processes comprising the crystallisation of sodium percarbonate from aqueous solution and the separation from this aqueous solution, e.g. with salting-out agents, such as sodium chloride, etc. Other processes make use of fluid bed reactors, wherein small seed particles are grown by spraying solutions of sodium carbonate and hydrogen peroxide in the appropriate stoechiometric ratio.

While crystallisation processes need less energy, they generally suffer from the drawback that the resulting particles often contain salting-out agents and that due to the irregular shaped particles having a large surface to volume ratio, these particles are more likely to be prone to attrition and early percarbonate decomposition.

On the other hand, fluid bed processes yield particles with a smooth surface and good attrition behaviour, however the need to introduce the reactants in solution and the subsequent energy intensive evaporation is economically detrimental.

Hence, in an effort to benefit from both techniques to reduce costs and nevertheless obtain PCS particles with good properties, both processes have been combined, e.g. by coating in the fluid bed reactor seed particles obtained by crystallisation from solution. Furthermore, it is known that the interaction between sodium percarbonate and other formulation components in detergent compositions leads to progressive decomposition of the percarbonate and hence to loss of bleaching power during storage and transportation of the composition. A number of proposals have been made to overcome this problem, e.g. by interposing a layer between the sodium percarbonate and its environment, called a coating layer. However, while these coatings generally enhance the long term stability of the percarbonate, they introduce further extraneous components into the detergent compositions, which should not only be avoided with respect to environmental considerations, but which in turn are likely to negatively affect the washing properties of the resulting formulations.

Furthermore, even before the percarbonate powders or particles for use in detergent compositions are introduced in such formulations by the detergent manufacturer, they are relatively hazardous goods and therefore must comply with strict national and international regulations with respect to packaging, handling, storage and transportation.

Hence as the amount of sodium percarbonate based raw materials for use in the manufacture of detergent, dishwashing and similar household and industrial compositions shipped worldwide represents approximately 500 000 MT per year with increasing tendency, one can easily imagine the economic impact even of a small reduction of costs resulting from an enhanced process or a less stringent classification. Object of the invention

Consequently, the object of the present invention is to provide an optimized and more energy efficient process for producing coated sodium percarbonate particles having an appropriate and easily adjustable sodium percarbonate content, being highly soluble and having good attrition resistance. General description of the invention

In order to overcome at least some of the abovementioned problems, the present invention proposes a process for the preparation of coated sodium percarbonate containing particles, comprising the following steps: (a) a manufacturing step of sodium percarbonate containing core particles, comprising the crystallisation of sodium percarbonate from aqueous solution and the separation from aqueous solution, (b) an at least partial drying step of the sodium percarbonate containing core particles, (c) a coating step comprising the application of a base coating on the so obtained core particles with one or more sodium percarbonate containing or generating solutions and/or suspensions, and optionally one or more additives, and (d) a drying step of the coated sodium percarbonate containing particles, wherein step (c) and/or (d), and optionally (b), are carried out in a fluid bed reactor and the global molar ratio between hydrogen peroxide and sodium carbonate in the sodium percarbonate containing or generating solutions and suspensions in step (c) is below 1,35 or above 1,65. The major advantage of such a process of the invention, when operated with the given global molar ratio, is not only the enhanced cost effectiveness of the process itself due to reduced energy needs and reduced operating costs, but also the versatility of the resulting products allowing to reduce storage, handling and/or transportation costs. These savings, e.g. the energy savings due to the process are to be understood as compared to a similar process using the same starting materials with the same solutions or suspensions (which, in practice, in order not to introduce unnecessary water are already used as concentrated as permitted by the operating conditions) and the same operating conditions, but where the global molar ratio between hydrogen peroxide and sodium carbonate in the sodium percarbonate containing or generating solutions and suspensions in step (c) is not according to the invention, i.e. between 1.35 and 1.65.

Although these energy savings might at first glance look unimportant, it has to be kept in mind that, first, the enthalpy of vaporization of water itself is very high as compared to that of other solvents; second, as the temperature during evaporation cannot be significantly raised in view of the decomposition of the peroxide, the quantities of air and hence the dimensions and power consumption of the equipment will rise with every additional amount of water to be evaporated (or else the throughput and thus the yield of percarbonate particles will decrease); and, third, the multiplicative effect of the huge quantities of percarbonate particles produced worldwide every year. Hence, even a comparatively small percentage in the reduction of the above costs is highly desirable, particularly as the implementation of the process according to the invention does not require particular investments or even equipment.

Further savings considerations resulting from the process, but more particularly associated with the products are due to the greatly adaptable properties of these products. Actually, the process of the invention is of - A -

particular use to finely and adequately adjust the sodium percarbonate content in percarbonate particles depending of the intended use, the applicable legal requirements and the preferences of the customer, e.g. the detergent manufacturer. All of these embodiments will result in cost savings aspects, as will be further illustrated below.

The percarbonate particles obtainable with the above process are furthermore highly soluble and show adequate attrition behaviour, which are important requirements in the art.

These advantages, as well as further benefits of the invention will be explained more in detail below with reference to particular alternatives and embodiments of the different aspects of the invention.

In the first alternative, by using a global molar ratio between hydrogen peroxide and sodium carbonate in the sodium percarbonate containing or generating solutions and suspensions in step (c) of less than 1,35 not all of the sodium carbonate will be converted to sodium percarbonate. However, the resulting excess of sodium carbonate may be desirable, not only because this compound as such acts as a detergent builder, but also because it allows to adjust the content of sodium percarbonate in the PCS particles such that the particles are classified as non-oxidiser according to the standard test method 0.1 of the UN Manual of Tests and Criteria, 4th revised Edition, sub-section 34.4.1.

In fact, the United Nations, UN, have developed a scheme for the classification of certain types of dangerous goods and give descriptions of the tests and procedures to arrive at a classification for transport.

Dangerous goods are chemical substances or articles containing chemical substances, which can pose threat to public safety or to the environment during transport through chemical, physical, or nuclear properties if not properly identified or packaged. If they are accidentally released undesirable outcomes such as fires and explosions can occur. The purpose of the various tests is to provide adequate protection against the risks to life and property inherent in the transportation of hazardous materials in commerce.

For example, percarbonate powders or particles, such as those currently used for the preparation of detergent formulations, are typically classified as oxidisers (Class 5 - Oxidising Substances / Division 5.1) according to the test method O.I of the UN Manual of Tests and Criteria, sub-section 34.4.1 (UN-0.1 test, Transport of dangerous goods, 4th revised edition) and must be labelled and handled accordingly. Hence, another advantage of the invention is that the present process allows to produce PCS particles which are not only inherently safer during packaging, handling, storage and transportation, but which also suffice to less stringent (and hence less costly) safety regulations. In this case, the sodium percarbonate particles of the invention preferably have a content of available oxygen (AvOx) below 12,0 % by weight. The content of available oxygen may be adjusted to any value below this limit, such as from 4,0 to 11,5 % by weight, preferably from 5,0 to 10,5 % by weight, as required or desired for the intended use by controlling the molar ratio between hydrogen peroxide and sodium carbonate in the sodium percarbonate containing or generating solutions and suspensions at values below 1,35, said molar ratio being preferably at least 0,01, more preferably at least 0,05. The content of available oxygen is measured by titration with potassium permanganate after dissolution in sulphuric acid (see ISO standard 1917-1982). Hence, as a further important advantage, it has been found that the upper available oxygen content indicated above is not only sufficient for most needs in the art of detergent and bleaching formulation, but this available oxygen content is furthermore easily adjustable within these limits so as to provide particles which are ready for use by the detergent manufacturer in the formulation of its detergents, without the need for any further treatment, equipment or handling. This is particularly true because the surplus of sodium carbonate is of particular use at a later stage for the detergent manufacturer, as the carbonate acts as a useful detergent builder. Hence, the sodium carbonate advantageously comprised in the above particles need not to be conditioned, handled and introduced separately in the final detergent composition, thereby reducing the number of discrete ingredient forms in the final detergent, without sacrificing any desirable property.

Finally, it has been found that sodium carbonate coatings comprising sodium percarbonate have an enhanced attrition behaviour, as compared to coatings solely composed of sodium carbonate.

With respect to the second alternative, it is generally known to the skilled person that a stoechiometric excess of one reactant as compared to its co- reactants may be used to speed up a given reaction or to compensate for possible losses during reaction, especially where said reactant is susceptible of decomposition as in the case of hydrogen peroxide. It is also known that nearly all the water introduced during the process must be eliminated at some point to obtain sodium percarbonate particles usable e.g. in detergent compositions. However, while the bulk of the water from step (a) may be removed quite easily and without using much energy, e.g. in a centrifuge, the remaining water, as well as the water introduced in the subsequent coating step(s) with the different solutions and suspensions must be evaporated, e.g. in a fluid bed reactor, thereby consuming expensive energy. In this context, an at least partial drying preferably yields particles having from 5 to 20 % by weight, preferably from 10 to 15 % by weight of free water content. One benefit of the invention stems from the fact that if a global molar ratio between hydrogen peroxide and sodium carbonate in the sodium percarbonate containing or generating solutions and suspensions in step (c) of more than 1,65 is used, sodium carbonate already contained in/on the at least partially dried core particles entering coating step (c) is converted to sodium percarbonate, which is not possible with processes of the prior art. This conversion is not only desirable from the point of view of overall AvOx content, it is particularly advantageous with respect to the energy savings due to the fact that no water is or needs to be introduced for the (not yet peroxyhydrated) sodium carbonate already in the particles. In this case, the coated sodium percarbonate particles usually have a content of available oxygen (AvOx) of at least 12,0 % by weight, in particular at least 13,0 % by weight, contents of at least 13,5 % by weight being particularly satisfactory. The content of available oxygen is generally at most 15,0 % by weight, in particular at most 14,0 %, for instance at most 14,2 %, the content of available oxygen being measured by titration with potassium permanganate after dissolution in sulfuric acid (see ISO standard 1917-1982). However, it has to be noted, that, contrary to the known processes, the actually achievable maximum contents of available oxygen (AvOx) in the present PCS particles are very close to the theoretical maximum, if so desired, i.e. close to about 15,2 % by weight, e.g. above 14,5 % by weight.

As mentioned above, PCS core particles obtained from crystallisation almost always contain salting-out agents, which are used to precipitate the sodium percarbonate from solution, usually about 3,5 to 5% by weight, an important part of these salting-out agents being contained in the remaining water (mother liquor) bound to the wet particles. However, these agents are not useful, neither in the PCS particles as such, nor in the detergent end product as they may even impair the detergent properties. Furthermore, as their presence inherently reduces the total AvOx content of the PCS particles, they are disadvantageous for high PCS contents.

Although, one could imagine washing away these salting-out agents at least partially using fresh water, the concomitant and inevitable risk of also washing out valuable sodium percarbonate would probably outweigh the possible benefit of reducing the amount of salting-out agents.

Hence, in a particularly preferred aspect of the invention, the core particles from step (a) are washed before or during step (b) with a sodium carbonate containing solution or suspension. If step (b) is effected in a centrifuge, it is particularly advantageous to wash the core particles with a sodium carbonate containing solution or suspension, because it not only allows to remove at least part of the enclosed salting-out agents, typically at least 20 % by weight, preferably at least 40 % by weight of the initially included salting-out agent(s), but it also introduces sodium carbonate instead, which may be used to further control the initial AvOx content as described in the first alternative above (and which, as already mentioned above, advantageously at a later stage act as a detergent builder) or which, in the second alternative of the invention, may subsequently be beneficially converted into its peroxyhydrate with the excess of hydrogen peroxide. As mentioned above, for economic reasons, the washing step has to be done carefully not to wash out the soluble sodium percarbonate. This is achieved by reducing its solubility in the washing solution or suspension, preferably by using relatively concentrated or even saturated sodium carbonate solutions, and/or by adjusting the temperature and/or time, and/or by any other appropriate method or combination known to the skilled person.

The washed core particles preferably contain at most 3 % by weight, more preferably at most 2,5 % by weight of salting-out agents, with respect to the washed core particle.

What is more, whatever of the above alternatives of the present process, this washing of the core particles not only advantageously replaces at least some of the extraneous salting-out agents with sodium carbonate; but in fact, it does so without introducing further amounts of water into the washed and centrifuged particles compared to particles having only been centrifuged. No additional energy will be necessary to evaporate additional water, which would otherwise be introduced along with the sodium carbonate (i.e. dissolved or suspended in water). Alternatively or preferably additionally to the washing, still further sodium carbonate in the form of solid sodium carbonate (soda ash) can be added to the partially dried sodium percarbonate core particles after a partial drying step (b) e.g. in a centrifuge. This solid carbonate is preferably included in the process before step (c) in the form of a fine powder or dust with a dso < 0,2 mm, which adheres on the still moist core particles. This may be achieved using a mixing system, which can be run batch or continuous, e.g. a ploughshear mixer from Lδdige; a screw conveyor, which will usually run in continuous mode; a Flexomix-System from Hosokawa, etc. The systems mentioned are only examples and the skilled person will be aware of other systems, which are suitable to granulate small particles onto the wet granules.

If desirable, to improve the binding forces of the wet granules, it is possible to add some amount of hydrogen peroxide solution up to a humidity of 20 %. Adding an excess of dry powdered soda ash to this mixture will result in a partial reaction of the added hydrogen peroxide and soda ash to percarbonate. These percarbonate crystals are helping to bind the excess of soda ash onto the percarbonate granules.

Another method to granulate the small particles onto the granules can be used: the dust can be directly introduced into the fluid bed granulator, preferably into the fluid bed during step (c) to avoid a direct loss with the upstreaming air, the inlet of the dust can be done near the bottom or near the spraying nozzles. A further advantage of such an embodiment is that fine powder or dust always occurring in such processes may be efficiently and conveniently recycled. It has to be noted that the sodium carbonate dust may also contain sodium percarbonate.

It is clear from the above that further sodium carbonate (possibly even containing sodium percarbonate) may be introduced as needed within step (c). However, the global molar ratio between hydrogen peroxide and sodium carbonate in the sodium percarbonate containing or generating solutions and suspensions in step (c) must be below 1,35 to allow for a protective yet detergent compatible coating and even for a non oxidizer classification or above 1,65 to allow for the peroxyhydration of the sodium carbonate already present in the particles entering the coating step (c). In the latter case, therefore, it has been observed that the use of an excess of hydrogen peroxide not only advantageously converts at least part of the carbonate already present in/on the particles into percarbonate, but that the energetic benefit outweighs by far possible losses of hydrogen peroxide.

The coated sodium percarbonate particles of the present invention have a mean particle size of at least 300 μm, in particular at least 400 μm, and more particularly at least 500 μm. The mean particle size is at most 1600 μm, especially at most 1400 μm, values of at most 1000 μm being preferred, for instance at most 800 μm.

The mean particle size of particles may be measured using a sieve set (containing at least 6 sieves of known sieve aperture) to obtain several fractions and weighing each fraction. The mean particle size in μm (MPS) is then calculated according to the formula

MPS = 0.005∑[mAk_{ι +} k_ι+1)] ι=0 in which n is the number of sieves (not including the sieve pan), Hi₁ is the weight fraction in % on sieve i and Ic₁ is the sieve aperture in μm of sieve / . The index i increases with increasing sieve aperture. The sieve pan is indicated with the index 0 and has an aperture of ko = 0 μm and mo is the weight retained in the sieve pan after the sieving process. k_n+i equals to 1800 μm and is the maximum size considered for the MPS calculation. A typical sieve set which gives reliable results is defined as follows: n = 6; kβ = 1400 μm; £₅ = 1000 μm; L_t = 850 μm; k₃ = 600 μm; k₂ = 425 μm; ki = 150 μm.

The coating layer(s) present in the coated sodium percarbonate particles of the present invention represent(s) in general at least 0,1 % by weight of the core particles, in particular at least 0,5 % by weight and most preferably at least 1 % by weight. The coating layer(s) represent(s) in many cases at most 50 % by weight of the core particles, especially at most 35 % by weight, and most often at most 25 % by weight. Amounts of from 0,1 to 50 % by weight give good results.

The coated sodium percarbonate particles of the invention have a good storage or in-detergent stability, and especially long-term storage stability, which can be expressed in two different ways. According to the first way, it is expressed as heat output at 40 ⁰C measured after storage of 1 g of the product during 12 weeks at 40 ⁰C in a closed ampoule of 3,5 ml. The measurement of heat output by microcalorimetry consists of using the heat flow or heat leakage principle using a LKB2277 Bio Activity Monitor. The heat flow between an ampoule containing the coated sodium percarbonate particles and a temperature controlled water bath is measured and compared to a reference material with a known heat of reaction. This long-term stability is generally less than 10 μW/g, in particular less than 8 μW/g, preferably less than 6 μW/g, and most preferably less than 4 μW/g.

According to the second way, the long-term stability is expressed as the AvOx (or available oxygen content) recovery after storage of 1 g of the product for 8 weeks at 55 ⁰C in a closed ampoule of 3,5 ml. The AvOx recovery corresponds to the difference between the available oxygen content before and after the storage expressed as percentage of the initial available oxygen content. The available oxygen content is measured as explained below. This AvOx recovery is in many cases at least 60 %, especially at least 70 %, values of at least 75 % being very suitable, those of at least 80 % being preferred.

The coated sodium percarbonate particles of the present invention usually have a 90 % dissolution time of at least 0,1 min, in particular at least 0,5 min. Generally, the 90 % dissolution time is at most 3 min, especially at most 2,5 min. The 90 % dissolution time is the time taken for conductivity to achieve 90 % of its final value after addition of the coated sodium percarbonate particles to water at 15 +/-1 ⁰C and 2 g/1 concentration. The method used is adapted from ISO 3123-1976 for industrial perborates, the only differences being the stirrer height of 10 mm from the beaker bottom and a 2 liter beaker (internal diameter 120 mm).

The coated sodium percarbonate particles of the present invention usually have a bulk density of at least 0,8 g/cm³, in particular at least 0,9 g/cm³. It is generally at most 1,2 g/cm³, especially at most 1,1 g/cm³. The bulk density is measured by recording the mass of a sample in a stainless steel cylinder of internal height and diameter 86,1 mm, after running the sample out of a funnel (upper internal diameter 108 mm, lower internal diameter 40 mm, height 130 mm) placed 50 mm directly above the cylinder. The coated sodium percarbonate particles of the invention usually have an attrition measured according to the ISO standard method 5937-1980 of at most 8 %, in particular at most 5 %, especially at most 3 %. The attrition is in most cases at least 0,05 %.

In the above process, the sodium percarbonate containing or generating solutions and/or suspensions are preferably chosen from (1) a solution or suspension of sodium carbonate optionally comprising sodium percarbonate and a solution of hydrogen peroxide or (2) a solution or suspension of sodium carbonate, a solution or suspension of sodium percarbonate and a solution of hydrogen peroxide, the molar ratio between hydrogen peroxide and sodium carbonate in the sodium percarbonate containing or generating solutions and suspensions being as described above.

In a further embodiment, the above process further comprises one or more additional coating steps (c'), (c"), (c'"), ... between steps (c) and (d), one, more or all of these additional coating step(s) being optionally associated with (e.g. preceded by or concomitant to) an at least partial drying step, wherein each additional coating step comprises the coating of the particles from the previous step with one or more additives, and optionally one or more sodium percarbonate containing or generating solutions and/or suspensions, the composition of each coating being different from that of its adjacent coating(s).

Preferably, one or more, more preferably all of the additional coating step(s) and if applicable one or more, more preferably all of their optionally associated drying step(s) are carried out in fluid bed reactor(s). The additive(s) used in the additional coatings or optionally used for the base coating is/are preferably chosen from organic or inorganic stabilizers, builders, alkaline sources, fillers, flowability enhancers and/or glass corrosion protectors, such as alkali metal or alkaline-earth metal sulphates, bicarbonates, carbonates, citrates, phosphates, borates, silicates and/or chlorides, as well as their hydrates, polycarboxylate, polyphosphonate or polyhydroxyacrylate salts, as such or in acid form, for example polyaminocarboxylates like EDTA or DTPA, or polyaminomethylene-phosphonates like EDTMPA, CDTMPA or DTPMPA, or hydroalkylenephosphonates like hydroxyethylidenediphosphonate), or from mixtures of the above. It is to be understood that the process may also comprise at least one sieving step after step (d) or at any appropriate point in the process, e.g. to collect undesirable size fractions of the particles and possibly to recycle them at any appropriate step.

As a further aspect, the invention pertains to coated sodium percarbonate particles obtained by a process as described above. Hence, such particles comprise a core of sodium percarbonate, obtained by the crystallisation of sodium percarbonate from aqueous solution and the separation from aqueous solution, and on said core a sodium percarbonate containing base coating optionally comprising one or more additive(s), wherein said base coating is obtained by a coating step comprising the application of a base coating on the so obtained core particles with one or more sodium percarbonate containing or generating solutions and/or suspensions, and optionally one or more additives, followed by a drying step of the coated sodium percarbonate containing particles, the global molar ratio between hydrogen peroxide and sodium carbonate in the sodium percarbonate containing or generating solutions and suspensions being below 1,35 or above 1,65.

The sodium percarbonate core particles thereof preferably have a reduced salting-out agent content, typically reduced by at least 20 % by weight, preferably at least 40 % by weight of the initially included salting-out agent(s). In practise, the core particles therefore contain preferably at most 3 % by weight of the core particle, more preferably at most 2,5 % by weight of the washed core particle.

These particles may further comprise on said base coating one or more additional coating(s) containing sodium percarbonate and/or one or more additive(s), the composition of each additional coating being different from that of its adjacent coating(s).

Further characteristics of the coated sodium percarbonate particles are as already described above.

A still further aspect of the invention pertains to the use of the coated sodium percarbonate particles as described above as bleaching agent in detergent compositions.

Hence, a still further aspect of the invention is concerned with detergent compositions containing such coated sodium percarbonate particles.

Claims

C L A I M S

1. A process for the preparation of coated sodium percarbonate containing particles, comprising the following steps:

(a) a manufacturing step of sodium percarbonate containing core particles, comprising the crystallisation of sodium percarbonate from aqueous solution and the separation from aqueous solution,

(b) an at least partial drying step of the sodium percarbonate containing core particles,

(c) a coating step comprising the application of a base coating on the so obtained core particles with one or more sodium percarbonate containing or generating solutions and/or suspensions, and optionally one or more additives, and

(d) a drying step of the coated sodium percarbonate containing particles,

wherein step (c) and/or (d), and optionally (b), are carried out in a fluid bed reactor and the global molar ratio between hydrogen peroxide and sodium carbonate in the sodium percarbonate containing or generating solutions and suspensions is below 1,35 or above 1,65.

2. The process according to claim 1, wherein before or during step (b) the core particles are washed with a sodium carbonate containing solution or suspension.

3. The process according to claim 1 or 2, wherein step (b) is a partial drying step, preferably in a centrifuge, and solid sodium carbonate is added to the partially dried sodium percarbonate core particles.

4. The process according to any of claims 1 to 3, wherein the sodium percarbonate containing or generating solutions and/or suspensions are chosen from (1) a solution or suspension of sodium carbonate optionally comprising sodium percarbonate and a solution of hydrogen peroxide or (2) a solution or suspension of sodium carbonate, a solution or suspension of sodium percarbonate and a solution of hydrogen peroxide.

5. The process according to any of claims 1 to 4, further comprising one or more additional coating steps between steps (c) and (d), one, more or all of these additional coating step(s) being optionally associated with an at least partial drying step, wherein each additional coating step comprises the coating of the particles from the previous step with one or more additives, and optionally one or more sodium percarbonate containing or generating solutions and/or suspensions.

6. The process according to claim 5, wherein one, more or all of the additional coating step(s) and if applicable one, more or all of their optionally associated drying step(s) are carried out in fluid bed reactor(s).

7. The process according to any one of the preceding claims, wherein the additive(s) is/are chosen from organic or inorganic stabilizers, builders, alkaline sources, fillers, flowability enhancers and/or glass corrosion protectors, such as alkali metal or alkaline-earth metal sulphates, bicarbonates, carbonates, citrates, phosphates, borates, silicates and/or chlorides, as well as their hydrates, polycarboxylate, polyphosphonate or polyhydroxyacrylate salts, as such or in acid form, or from mixtures of the above.

8. The process according to any of the preceding claims wherein the coated particles have a mean particle size from 300 to 1600 μm.

9. The process according to any of the preceding claims, further comprising between steps (b) and (c) and/or after (d), at least one sieving step.

10. Coated sodium percarbonate particles obtained by a process according to claims 1 to 9.

11. The particles according to claim 10, comprising a sodium percarbonate containing core, obtained by the crystallisation of sodium percarbonate from aqueous solution and the separation from aqueous solution, and on said core a sodium percarbonate containing base coating optionally comprising one or more additive(s), wherein said base coating is obtained by a coating step comprising the application of a base coating on the so obtained core particles with one or more sodium percarbonate containing or generating solutions and/or suspensions, and optionally one or more additives, followed by a drying step of the coated sodium percarbonate containing particles, the global molar ratio between hydrogen peroxide and sodium carbonate in the sodium percarbonate containing or generating solutions and suspensions being below 1,35 or above 1,65.

12. The particles according to claim 10 or 11, wherein the core of sodium percarbonate comprises at most 3 % by weight, preferably at most 2,5 % by weight of salting-out agent(s).

13. The particles according to any of claims 10 to 12, comprising one or more additional coating(s) containing sodium percarbonate and/or one or more additive(s).

14. The particles according to any of claims 10 to 13, wherein the additive(s) is/are chosen from organic or inorganic stabilizers, builders, alkaline sources, fillers, flowability enhancers and/or glass corrosion protectors, such as alkali metal or alkaline-earth metal sulphates, bicarbonates, carbonates, citrates, phosphates, borates, silicates and/or chlorides, as well as their hydrates, polycarboxylate, polyphosphonate or polyhydroxyacrylate salts, as such or in acid form, or from mixtures of the above.

15. The particles according to any of claims 10 to 14, having a mean particle size from 300 to 1600 μm.

16. Use of the sodium percarbonate particles according to any one of claims 10 to 15 as bleaching agent in detergent compositions.

17. Detergent compositions containing the sodium percarbonate particles of any one of claims 10 to 14.