DE69031824T2 - Bleach particles encapsulated with wax and manufacturing process - Google Patents

Description

Field of the invention

The invention relates to paraffin wax-encapsulated bleach particles which remain stable when used in liquid and granular cleaning products, and to a process for encapsulating the bleach.

BACKGROUND OF THE INVENTION

Numerous materials have been used to coat bleach particles. In US-A-3,908,045 (Alterman et al.) bleach particles were coated with fatty acids, polyvinyl alcohol or polyethylene glycols, US-A-4,078,099, 4,126,717 and 4,136,052 (Mazzola) teach bleach particles coated with a mixture of 35 to 89 weight percent fatty acid and 1 to 16 weight percent microcrystalline wax, the wax having a melting point of 51 to 99°C. Other coating materials include polymer latex, US-A-4,759,956 (Amer et al.); polycarboxylate materials, US-A-4,762,637 (Aronson et al.); Polyethylene waxes with a melting point of 50 to 65ºC, EP-A-132 184 (Scotte); and various waxes, US-A-4 421 669 (Brichard). The wax coating in Brichard makes up 0.01 to 10% by weight of the bleaching agent to be coated.

A disadvantage of conventional coated bleach particles is the instability of the bleach in liquid, aqueous cleaning agents: water or other components of the agent that are incompatible with the bleach interact with the bleach during storage. This results in little bleaching activity remaining as a cleaning agent.

Attempts have been made to increase the stability of encapsulated bleach particles by applying a second coating. Alterman et al. taught optionally applying a second coating of soap to the encapsulated bleach. And US-A-4 657 784 (Olson) taught a double coating of the bleach core in an inner coating of paraffin or microcrystalline waxes having melting points of 40 to 94ºC and a second coating of a material such as sodium carbonate. Encapsulation of bleaches in an inner shell of fatty acid or waxes and an outer coating of water soluble cellulose ether has also been taught, EP-A-307 587 (Olson) Second coatings are said to improve the stability of the capsules of the bleach and other materials since cracks or depressions in the first coating allow materials to contact and react with the bleach.

These second coatings are expensive and, although they increase stability somewhat, they do not guarantee that the bleach will be available as a cleaning agent after storage.

Bleaching agents have been encapsulated by a variety of methods. US-A-3,847,830 (Williams et al.) describes various methods for encapsulating normally unstable peroxygen compounds in water-dispersible coatings, including paraffin waxes. A coating material is "water-dispersible" if it releases at least 75% of the peroxygen within 30 minutes of adding 2 g of encapsulated peroxygen to 1 liter of water at 15°C. Three of the methods described by Williams et al. require that the encapsulating agent be melted in a fluidized bed prior to spraying onto the peroxygen particles. Two other methods involve dissolving the encapsulating agent in an organic solvent and either spraying the resulting solution onto the particles or immersing them in the bulk solution to achieve a coating. The disadvantages of these two processes are the cost of the organic solvents and, more importantly, the associated environmental pollution problems.

US-A-3 856 699 (Miyano et al.) describes a process for dispersing core particles by heating in a waxy material, cooling the resulting dispersion and grinding it to powder. The powdered waxy material is agitated in an aqueous medium at a temperature higher than the melting point of the waxy material. Waxed core material is then passed into a non-agitated aqueous medium at a temperature below the melting point of the waxy material. US-A-4,919,841 (Kamel et al.) teaches the steps of dispersing active material in molten wax to form an active material/wax dispersion, adding the dispersion to water containing at least one surfactant, and emulsifying the dispersion of active material and wax therein for not more than 4 minutes to form capsules; immediately thereafter cooling the capsules and recovering the cooled capsules from the water to form capsules of improved quality.

Bleach particles have also been sprayed directly with coating material in fluidized bed devices as reported in Brichard. Thus, in US-A-3,908,045, fatty acid coating material was sprayed onto particles. In US-A-3,983,254, the spray height of the spray nozzle above the fluidized bed was considered critical. In US-A-4,078,099, an apparatus with a rotating drum was used to apply the coating material. In US-A-4,759,956, polymer latex was also sprayed onto core materials (such as bleach) in a fluidized bed operated in a "Wurster" process.

TASKS OF THE INVENTION

An object of the invention is to provide a single-coated wax-encapsulated bleach particle with improved stability against degradation in ambient humidity or in aqueous liquid media.

Another objective is to provide wax-encapsulated bleach particles that provide a smooth, continuous coating with excellent surface integrity.

A further object is to produce such encapsulated particles by a process that avoids poor coating and the resulting problems of poor bleach stability and particle agglomeration.

A further object is to provide an encapsulated bleach with a coating that melts or softens sufficiently early in most automatic dishwasher wash cycles to release the active bleach.

Another object of the invention is to provide an encapsulation process that does not require organic solvents that cause environmental pollution problems.

A further object of the invention is to provide a method that operates with a minimum of process steps.

A further object of the invention is to provide a liquid or solid cleaning agent that contains the above-mentioned bleach particles encapsulated in wax and provided with a coating, whereby the capsules provide a stable bleaching effect without leaving waxy soiling after washing. A very special object is to provide liquid cleaners for dishwashers or cleaners for other hard surfaces that also contain oxidation-sensitive components such as enzymes, perfumes, fabric softeners, structure-forming agents and surfactants with a stable bleaching effect.

These and other objects of the present invention will become apparent as further details are given in the discussion and examples below.

SUMMARY OF THE INVENTION

In a first aspect, the invention comprises encapsulated bleach particles suitable for use in household cleaning products. Bleaching agents form the core of these particles and comprise 45 to 65%, preferably 50-60% by weight of the finished particles (ie core plus coating). A simple wax coating on the particles comprises 35 to 55% by weight, or preferably 40 to 55% by weight, and more preferably 45 to 55% by weight of the particles and is selected from one or more low Melting point, having melting points of 35 to 50ºC and having penetration values of 10-60 mm at 25ºC. The simple wax coating having a thickness of 10 to 30ºC, preferably 100 to 1,000 µm, is applied to the particles. Preferably, the coating thickness is 200 to 750 µm and most preferably 200 to 600 µm.

In a second aspect, the invention comprises a process for producing encapsulated bleach particles according to claim 1. Thus, this process comprises the steps of spraying molten paraffin wax having a low melting point, i.e. a melting point of 35°C to 50°C, onto the uncoated bleach particles in a fluidized bed. The bed temperature is 20°C to a temperature not higher than the melting point of the wax. The atomization temperature of the molten wax applied to the particles is preferably 5°C to 40°C, preferably 5°C to 10°C above the melting point of the wax. A simple wax coating having a thickness of 10 to 3,000, preferably 100 to 1,000 µm is applied to the bleach particles. The rate of application of the wax layer is 10 to 40 grams per minute per kilogram of bleach particles in the fluidized bed.

The fluid bed can be operated in overspray mode or in Wurster spray mode. If overspray is used, the tempering step can advantageously follow the coating step to give the coating a continuous surface and excellent surface integrity. If the fluid bed is operated in Wurster spray mode, no tempering step is required.

In a third aspect, the invention includes cleaning compositions that include 0.1 to 30% by weight of these encapsulated bleach particles. The compositions may also comprise 0.01 to 15% surfactant, 1 to 75% builder and other ingredients. These compositions leave little or no waxy soil on the surfaces being cleaned.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an illustration of the amount of wax for coating that remains non-emulsified after a dishwasher wash cycle as described in Example III.

Figure 2 is a representation of the staining characteristics for automatic dishwashing liquids containing bleach encapsulated with waxes of different melting points as described in Example IV.

Figure 3 is a graphical representation of the chlorine release by bleaches encapsulated with waxes of different melting points, as described in Example VII.

DETAILED DESCRIPTION OF THE INVENTION The enclosed particles

The encapsulated bleach particles of the present invention comprise 35 to 55% by weight of the particles a simple coating of paraffin wax and 45 to 65% by weight of a core of bleach suitable for use in household cleaning compositions. Preferably the paraffin wax coating comprises 40 to 50% by weight of the particles and the core comprises 50 to 60% by weight of the particles.

The bleaching agent to be encapsulated in the paraffin wax coating may be a chlorine or bromine releasing agent or a peroxygen compound. Among suitable reactive oxidizing chlorine or bromine materials are heterocyclic N-bromo and N-chloroimides such as trichloroisocyanuric, tribromoisocyanuric, dibromoisocyanuric and dichloroisocyanuric acids and salts thereof with water-solubilizing cations such as potassium and sodium. Hydantoin compounds such as 1,3-dichloro-5,5-dimethylhydantoin are also quite suitable.

Dry, particulate, water-soluble, anhydrous, inorganic salts are also suitable for use herein, such as lithium, sodium or calcium hypochlorite and hypobromite. Chlorinated trisodium phosphate is another core material. However, chloroisocyanurates are the preferred bleaching agents. Potassium dichloroisocyanurate is sold by the Monsanto Company as ACL-59R. Sodium dichloroisocyanurates are also sold by Monsanto as ACL-60R and in the Dihydrate form available from Olin Corporation as Olearon CDB-56R and is available in powder (particle diameter of less than 150 µm), medium particle size (about 50 to 400 µm) and coarse particle size (150 to 850 µm). Very large particles (850 to 1,700 µm) are also found to be suitable for encapsulation.

Organic peroxyacids can be used as the bleach core. The peroxyacids useful in the present invention are solid and preferably substantially water-insoluble compounds. "Substantially water-insoluble" as used herein means a water solubility of less than about 1 weight percent at ambient temperature. In general, peroxyacids containing at least about 7 carbon atoms are sufficiently water-insoluble for use herein.

Typical monoperoxyacids useful herein include alkyl peroxyacids and aryl peroxyacids, such as:

(i) Peroxybenzoic acid and ring-substituted peroxybenzoic acids, for example peroxy-α-naphthoic acid,

(ii) aliphatic and substituted aliphatic monoperoxyacids, for example peroxylauric acid and peroxystearic acid.

Typical diperoxyacids useful here include alkyl diperoxyacids and aryl diperoxyacids, such as:

(iii) 1,12-diperoxydodecanedioic acid

(iv) 1,9-diperoxyazelaic acid

(v) Diperoxybrassylic acid; diperoxysebacic acid and diperoxyisophthalic acid

(vi) 2-Decyldiperoxybutane-1,4-diacid Inorganic peroxygen evolving compounds may also be suitable as cores for the particles of the present invention. Examples of these materials are salts of monopersulfate, perborate monohydrate, perborate tetrahydrate and percarbonate.

The coating materials suitable for encapsulating the core parts are paraffin waxes, which have low melting points, ie between 35ºC, preferably 40ºC and 50ºC and a penetration value of 10 to 60 mm at 25ºC.

This melting point range for the coating is desirable for several reasons. First, the minimum of 35°C, preferably 40°C, generally exceeds the storage temperature encountered in detergents. Thus, the wax coating will protect the bleach core during storage of the detergent. The melting point peak at 50°C for the wax coating was selected to provide a wax that will melt quickly or soften early in an automatic dishwasher wash cycle. Sufficient melting or softening to release the bleach core occurs due to the operating temperatures in automatic dishwashers, which are generally between 40 and 70°C. Thus, the paraffin waxes of the invention release the core material when the capsule is exposed to the warm water bath, but not before.

Furthermore, in the case of the capsules according to the invention, molten paraffin waxes remain essentially molten at 40 to 50°C. Such molten wax is easily emulsified by surfactant elements in cleaning compositions. Consequently, such wax will leave less undesirable wax residues on objects to be cleaned than waxes with higher melting points.

As a class, paraffin waxes have a melting point in the range of roughly 30 to 80ºC and are composed largely of normal alkanes with minor amounts of isoalkanes and cycloalkanes. Isoalkanes and cycloalkanes contribute to the lack of order in the solid wax structures and paraffin waxes are largely crystalline when solid. Thus, the wax coating should not include paraffins that have a melting point substantially above 50ºC, lest the higher melting point components remain solid throughout the washing process and form unsightly residues on the surfaces being cleaned.

The amount of solids in a wax at a given temperature can be determined by differential scanning calorimetry. The more solids in a wax at room temperature, the more suitable the wax is for the present invention: this is because solids solidify the wax coating, making the particles less susceptible to ambient moisture or liquid aqueous environments, whereas "oil" or liquid wax softens the wax, opens the pores of the coating and thereby provides poorer protection for the bleach particles. The wax solids content, measured by differential scanning calorimetry, for suitable waxes can be in the range 100 to 40%, optimally 100 to 75% at 40°C and 0 to 15%, and preferably 0 to 5% at 50°C.

In contrast to paraffin waxes, microcrystalline waxes generally have higher molecular weights and melting points. Thus, the melting point range for microcrystalline waxes is about 50 to about 100°C. In addition, microcrystalline waxes are more viscous than paraffin waxes when molten and softer than paraffin waxes when solid. Particles coated with microcrystalline waxes would therefore have a poorer protective coating and the wax coating melting from such particles would be less likely to emulsify in cleaning compositions. Thus, within the scope of this invention, microcrystalline waxes are not considered.

The penetration test (ASTM D-1321) is an industry standard test for the hardness of waxes. This test measures the depth in tenths of a millimeter that a needle of a specified configuration under a specified weight penetrates into the surface of a wax at a specified temperature. Paraffin waxes suitable for use in encapsulating the bleach particles have penetration values of 10 to 60 mm at 25ºC.

Commercial paraffin waxes suitable for encapsulating the solid core materials include Merck 7150 and 7151 from E. Merck, Darmstadt, Germany; Boler 1397 from Boler (penetration value 40 mm at 25 ºC); and Ross's completely Purified Paraffin Wax 115/120 from Frank D. Ross Co., Inc. (penetration value 40-50 mm at 25ºC) and Altafin "Okerin-2033" from Durachem Inc. (penetration value 15-20 mm at 25ºC). Most preferred is Boler 1397.

The process for encapsulating bleach particles

The processes for producing a coherent, continuous coating around the bleach particles suitable for use in cleaning compositions include:

a) keeping bleach particles suspended in a fluidized bed,

b) selecting one or more paraffin waxes to provide the coating, the waxes having a melting point between 35ºC, preferably 40ºC and 50ºC, and a needle penetration value of 10 to 60 mm at 25ºC,

(c) heating the one or more paraffin waxes to a temperature sufficiently above their melting point to melt all of the wax,

d) fluidizing the layer by passing air through the bleach particles so that a layer temperature of at least 20ºC up to a temperature not higher than the melting point of the wax is maintained and

e) spraying the molten paraffin wax onto the fluidized bed, preferably at an atomization temperature of 5ºC to 40ºC above the melting temperature of the wax, at a rate of 10 to 40 g/min per kilogram of bleach particles in the fluidized bed and for a period of time sufficient to form a coating of 10 to 3 000 µm, preferably 100 to 1 000 µm, thickness on the bleach particles.

The amount of coating applied to the bleach core particles is generally from 35 to 55%, preferably from about 45 to 50%, by weight of the total particles (i.e., core plus coating).

The coating or coating is applied in a fluidized bed. There are various methods for operating a fluidized bed. In a typical fluidized bed process Air is introduced into the layer from below, while the coating material is sprayed onto the fluidized material from above. During this spraying process, the particles move randomly in the layer.

Unless care is taken when applying the molten coating materials in fluidized beds, the resulting material may be poorly coated or, alternatively, agglomerate with one another. These equally undesirable results result from temperature settings when operating the fluidized bed. For example, if the temperature of the bed is too far below that of the molten wax, the molten wax begins to solidify once it reaches the cool bed region. The wax thus loses some of its ability to adhere to the surface of the bleach particles and the wax itself solidifies rapidly. When this occurs, the fluidized bed is operated with spray drying of wax, with the result that little or no wax covers the bleach. The poorly coated bleach particles therefore have little stability in ambient humidity or in an aqueous liquid environment. Alternatively, if the bed temperature is too high, the wax in contact with the bleach particles cannot be cooled sufficiently and therefore remains soft and sticky. The bleach particles consequently clump and agglomerate. It becomes difficult to control the size of the resulting clumps. These clumps can become so large that they cannot be melted in the wash cycle and so remain as solid soil on the materials to be cleaned. Inaccurate control of the fluidized bed temperatures can thus produce encapsulated bleach particles which do not meet the objective of the invention.

Applicants have found that, even for coatings up to 1 000 µm thick, appropriate control of the layer temperature and the atomization temperature in a fluidized bed avoids both agglomeration and inadequate coating. Thus, if the layer temperature is from at least 20ºC to not higher than the melting point of the wax, "wax spray drying" and agglomeration of the coated bleach particles is reduced. Preferably, the layer temperature is 20 to 35ºC and most preferably 25 to 32ºC.

Applicants have also found that the atomization temperature, or the temperature at which the wax is sprayed from a nozzle onto the fluidized bed, is advantageously maintained at 5 to 40°C, preferably 5 to 10°C, above the melting temperature of the wax. When the spraying process is used, the maximum atomization temperature is about 35°C higher than the wax melting point; above this temperature too high a percentage of particles agglomerate. When the Wurster process is used to coat the particles, the atomization temperature can be as high as 50°C and more above the wax melting point temperature. This has been found to be a practical atomization temperature, notwithstanding the expectation that partially coated particles with molten coatings would stick to the spray nozzle. However, it has been found that the air flow is strong enough to dislodge these partially coated particles. Alternatively, applicants have found that the temperature of the molten wax can be maintained substantially above the wax melting point, e.g. from 50 to 100°C above the melting point. If this is the case, the atomization temperature is preferably near or just below the melting temperature of the wax in order to lower the wax temperature sufficiently to rapidly solidify onto the bleach particles in the fluidized bed.

The preferred encapsulation process of the invention thus provides coated particles with an average diameter in the range 800 to 4,000 µm.

There are a variety of commercially available fluid bed devices suitable for the process of the invention, among them the models GPCG-50 and GPCG-60 from Glatt Air Techniques. These can coat 10 to 50 kg loads of bleach particles in 0.5 to 3 hours. Benchtop encapsulation in devices in the Laboratory scale can also be implemented, for example in the Granuglatt model, No. WSG-3 from Glatt Air Techniques.

Surprisingly, applicants have found that encapsulated particles prepared by the process of the invention exhibit improved stability in ambient humidity when present in powdered cleaning products and stability against aqueous media when present in liquid products. This increased stability is obtained regardless of whether the bleach is encapsulated by overspray or by the Wurster process in the fluidized bed. The increased stability is demonstrated in Examples V and VII.

A preferred alternative to overspraying molten coating material is the Wurster spray process. This process is described in detail in US-A-3,253,944. In general, fluidized beds are characterized by randomness of particle motion. When coating particles, random motion is undesirable because of the slow coating speeds obtained. To overcome this problem, a cyclic flow pattern is developed in the Wurster spray process by controlled velocity differentials. The Wurster process involves the use of a vertically oriented coating tower wherein the particles are suspended in an upwardly flowing air stream entering through the bottom of the tower. This air stream imparts controlled cyclic motion to the particles, with part of the suspended layer flowing upward in the tower and the other part flowing downward outside the tower. All of the coating material is directed into the high velocity air stream providing a coating to the particles moving upwards in the tower. The liquid coating solidifies on the surface of the particles as the air stream lifts off the nozzle. The particles are carried to the top of the tower from which point they fall to the bottom of the tower along a path outside the tower. At the bottom the particles are drawn off through orifices and are directed upwards into the air stream within of the tower. This cycle is repeated until the desired amount of coating has been deposited on the particles.

It was believed, when considering the steps of the Wurster process, that it would be unsuitable for encapsulating bleach particles in wax. The spray nozzle of the Wurster process is located at the bottom of the fluidized bed and sprays the coating materials upwards. It was believed that this spray nozzle arrangement would result in clogging of the spray nozzle during application and agglomerated particles falling into the nozzle area from the downward spraying air. This risk seemed particularly high since the nozzle temperature is generally above the melting temperature of the wax coating. However, applicants have surprisingly found that the use of the Wurster spray process leads to many advantages.

Thus, agglomeration of coated bleach particles can also be reduced when a fluidized bed is operated using the Wurster process. While about 5-15% of the particles coated by spraying can agglomerate and thus become unusable, the level of agglomerated particles from the Wurster application of the fluidized bed usually does not exceed 5% of the particles.

Furthermore, the coating time in the Wurster arrangement can be half the time of the spraying process or less, even with a much lower air flow rate, as shown in Example 1 below. Although the batch size is often smaller than with the spraying process and the speed of spraying the wax onto the core is not significantly faster with the Wurster process, the production rate of the encapsulated particles can be two to three times faster than with the Wurster process. This higher production rate can be maintained even though the air flow rate through the fluidized bed is lower than with the spraying process. Thus, the Wurster process provides higher production rates at lower Air flow velocities particles with less agglomeration than with the spraying process.

Applicants have also found that by performing an additional annealing step after coating the bleach particles in a fluidized bed, the capsules can be further improved. "Annealing" means further heating the wax-encapsulated bleach particles at a temperature higher than room temperature, but below the wax melting point. This heating step is performed when the layer is fluidized, i.e., with warm air flowing through it, but no molten wax is sprayed onto the particles during annealing. The annealing step renders the wax sufficiently mobile so that it fills the gaps and cracks on its surface, thereby providing a better seal for the bleach therein.

The temperature chosen for tempering is such that the wax softens without becoming sticky. In general, this temperature is 5 to 15ºC higher than the layer temperature during coating and 3 to 15ºC lower than the melting point of the wax coating. If the wax has a melting point of, for example, 46ºC, the tempering temperature may be about 33-34ºC. The layer temperature during spraying is only about 31-32ºC. Above 32ºC, there is a possibility of the particles agglomerating: the high temperature of the molten wax combined with a tempering temperature would soften the wax to such an extent that the particles in the fluidized bed would agglomerate. However, if hot, molten wax is not sprayed onto the particles, the annealing temperature in the layer alone is not warm enough to cause agglomeration.

Most preferably, annealing should be carried out for a period of between 10 minutes and 48 hours, optimally between about 1 hour and about 24 hours, for example between 10 and 45 minutes, after completion of spraying. Mixing the capsules with an inert material, such as amorphous silica, alumina or clay, prevents the capsules from sticking together during the annealing process.

The use of inorganic tempering aids allows the use of higher temperatures during the tempering process, thereby shortening the tempering time. Excipients can be used in an amount based on the weight of the entire capsule in a ratio of 1:200 to 1:20, preferably 1:100.

Another advantage found by the inventors in using the Wurster spray process is that no tempering step is required. More specifically, self-tempering occurs automatically as part of the coating process when the Wurster process is used. The hot melted wax droplets contact the partially coated bleach particles and cause the solid wax to melt already on the particles and fill cracks in the wax surface. Unlike the spray coated particles in the overspray process, which fall into the fluidized bed in a tightly packed mass of other particles, the particles in the Wurster process move out of the spray tower and fall through the less crowded space outside the tower. In this space, the particles thus have time to slowly cool. The smaller amount of bleach particles to be coated in the Wurster process reduces the likelihood of them coming into contact with other particles during cooling. The result is annealing as part of the coating process.

The cleaning agents that contain the encapsulated particles

The encapsulated bleach particles according to the invention can be used in a variety of cleaning agents. These agents include laundry detergents, fabric softeners, dishwasher detergents, mild detergents and hard surface cleaners in powder and liquid form. These agents contain 0.1 to 30%, preferably 0.1 to 15% by weight, of the encapsulated bleach particles, 1 to 75% of a builder component and optionally 0.001 to 5% of a perfume component. Certain of the The above forms also contain from 0.01% (preferably 0.1%) to 15% of a surfactant, preferably from about 0.5% to 10% by weight of the composition. Wax-encapsulated chlorine bleach is particularly suitable for automatic dishwashing liquid or "gei" laundry products, the capsules being present in an amount of from 0.1% to 20%, preferably from 0.1% to 15%, by weight of the composition. Washing powders and liquids for automatic dishwashers have the preferred composition shown in Table I. Table I Detergents for dishwashers

Gels differ from liquids in that they are mainly structured by polymeric substances and contain only small amounts of clay.

Detergent Builder

The detergent compositions of the invention may contain any type of detergent builder commonly taught for use in automatic dishwashing machines or other detergents. The builders may contain any of the usual inorganic or organic water-soluble builder salts or mixtures thereof and may comprise from 1 to 75%, and preferably from about 5 to about 75% by weight of the detergent composition.

Typical examples of known inorganic builders are the sodium and potassium salts of the following: pyrophosphate, tripolyphosphate, orthophosphate, carbonate, bicarbonate, Sesquicarbonate and borate. Other non-phosphorus salts, including crystalline and amorphous aluminosilicates, may also be used.

Particularly preferred builders can be selected from the group consisting of sodium tripolyphosphate, sodium carbonate, sodium bicarbonate and mixtures thereof. When present in these compositions, sodium tripolyphosphate concentrations are in the range of 2 to 40%, preferably 5 to 30%. Sodium carbonate and bicarbonate, when present, can be in the range of 10 to 50%, preferably 20 to 40%, by weight of the detergent. Potassium pyrophosphate is a preferred builder in gel formulations and can be used in an amount of 3 to 30%, preferably 10 to 20%.

Organic detergent builders can also be used in the present invention. They are generally sodium and potassium salts of the following: citrate, nitrilotriacetates, phytates, polyphosphonates, oxydisuccinates, oxydiacetates, carboxymethyloxysuccinates, tetracarboxylates, starch, oxidized heteropolymeric polysaccharides and polymeric polycarboxylates such as polyacrylates having a molecular weight of from about 5,000 to about 200,000. Polyacetal carboxylates such as those described in U.S. Patents 4,144,226 and 4,146,495 can also be used.

Sodium citrate is a particularly preferred builder. If present, it is preferably present in an amount of 1% to 35% of the total weight of the detergent.

The above builders are provided for illustrative purposes only and are not intended to limit the type of builders that can be used in the present invention.

Surfactants

Surfactants may preferably be included in the household cleaning products containing the encapsulated bleach particles. Suitable surfactants are anionic, nonionic, cationic, amphoteric, zwitterionic types and mixtures of these surfactants. Such surfactants are known in the detergent field and are described in detail in "Surface Active Agents and Detergents", Vol. II, by Schwartz, Perry & Berch, Interscience Publishers, Inc. 1958.

Anionic synthetic detergents can generally be described as surfactant compounds having one or more negatively charged functional groups. Soaps are included in this category. A soap is a C8-C22 alkyl fatty acid salt of an alkali metal, alkaline earth metal, ammonium, alkyl substituted ammonium or alkaline ammonium salt. Sodium salts of tallow and coconut fatty acids and mixtures thereof are the most common. Another important class of anionic compounds are the water soluble salts, particularly the alkali metal salts of organic sulfur reaction products having in their molecular structure an alkyl radical of about 8 to 22 carbon atoms and a radical selected from the group consisting of sulfonic and sulfuric acid ester radicals. Organosulphur surfactants are salts of C₁₀-C₁₆ alkylbenzenesulphonates, C₁₀-C₂₂ alkanesulphonates, C₁₀-C₂₂ alkyl ether sulphates, C₁₀-C₂₂ alkyl sulphates, C₄-C₁₆ dialkyl sulphosuccinates, C₁₀-C₂₂ acyl isethionates, alkyldiphenyloxide sulphonates, alkylnaphthalenesulphonates and 2-acetamidohexadecanesulphonates. Two suitable commercial anionic surfactants are mono- and di-C8 -C14 alkyl diphenyl oxide mono- and/or disulfates sold under the trademark Dowfax 2A-1R and Dowfax 38-2R by Dow Chemical Co. Anionic organophosphate surfactants include organic phosphate esters such as complex mono- or diester phosphates of hydroxyl terminated alkoxide condensates, or salts thereof. Included in the organic phosphate esters are phosphate ester derivatives of polyoxyalkylated alkylaryl phosphate esters, of ethoxylated linear alcohols and ethoxylates of phenol. A surfactant that is particularly suitable for combination in cleaning compositions with the wax-encapsulated bleach is Emphos CS-1361R from Witco Chemical Co., Inc., which is believed to be a complex of mono- or diesters of ethoxylated nonylphenols. Also included are nonionic alkoxylates with a sodium alkylene carboxylate residue linked via an ether bond to a terminal hydroxyl group of the nonionic surfactant. Counterions of the salts to all of the above substances can be those of alkali metal, alkaline earth metal, ammonium, alkanolammonium and alkylammonium species.

Nonionic surfactants can be broadly defined as compounds prepared by condensation of alkylene oxide groups with an organic hydrophobic material, which may be aliphatic or alkyl aromatic in nature. The length of the hydrophilic or polyoxyalkylene moiety condensed with a particular hydrophobic group can be readily adjusted to yield a water-soluble compound with the desired degree of balance between hydrophilic and hydrophobic elements. Illustrative, but non-limiting, examples of various suitable nonionic surfactant types are:

(a) Polyoxyethylene or polyoxypropylene condensates of aliphatic carboxylic acids, whether linear or branched chain and unsaturated or saturated having from about 8 to about 18 carbon atoms in the aliphatic chain and from 5 to about 50 ethylene oxide and/or propylene oxide units. Suitable carboxylic acids are "coconut fatty acids" (derived from coconut oil) which have an average of about 12 carbon atoms, "tallow" fatty acids (derived from fats of the tallow class) which have an average of about 18 carbon atoms, palmitic acid, myristic acid, stearic acid and lauric acid.

(b) Polyoxyethylene or polyoxypropylene condensates of aliphatic alcohols, whether linear or branched chain and unsaturated or saturated with about 6 to about 24 carbon atoms and with about 5 to about 50 ethylene oxide and/or propylene oxide units. Suitable alcohols are the "coconut fatty alcohols", "tallow" fatty alcohol, lauryl alcohol, myristyl alcohol and oleyl alcohol. Particularly preferred nonionic surfactant compounds of this category are products of the "Neodol" type, a registered trademark of Shell Chemical Company.

Also included in this category are non-ionic surfactants of the formula:

wherein R is a linear alkyl hydrocarbon radical having an average of 6 to 10 carbon atoms, R' and R" are each linear alkyl hydrocarbon radicals having about 1 to about 4 carbon atoms, x is an integer from 1 to 6, y is an integer from 4 to 15, and z is an integer from 4 to 25. A preferred example of this category is Poly-Tergent SLF-18, a registered trademark of Olin Corporation, New Haven, Conn. Poly-Tergent SLF-18 has a composition of the above formula wherein R is a C6-C10 linear alkyl mixture, R' and R" are methyl, x is 3 on average, y is 12 on average, and z is 16 on average. Also suitable are alkylated nonionic surfactants described in US-A-4 877 544 (Gabriel et al.).

(c) Polyoxyethylene or polyoxypropylene condensates of alkylphenols, whether linear or branched chain and unsaturated or saturated with about 6 to 12 carbon atoms and with about 5 to about 25 moles of ethylene oxide and/or propylene oxide.

(d) Polyoxyethylene derivatives of sorbitan mono-, -di- and tri-fatty acid esters, wherein the fatty acid moiety has between 12 and 24 carbon atoms. The preferred polyoxyethylene derivatives are sorbitan monolaurate, sorbitan trilaurate, sorbitan monopalmitate, sorbitan tripalmitate, sorbitan monostearate, sorbitan monoisostearate, sorbitan tristearate, sorbitan monooleate and sorbitan trioleate. The polyoxyethylene chains can contain between about 4 and 30 ethylene oxide units, preferably about 20. The sorbitan ester derivatives contain 1, 2 or 3 polyoxyethylene chains depending on whether they are mono-, di- or triacid esters.

(e) Polyoxyethylene-polyoxypropylene block copolymers of the formula:

HO(OH₂OH₂O)a(OH(OH₃)CH₂O)b(OH₂OH₂O)cH

where a, b and c are integers representing the corresponding polyethylene oxide and polypropylene oxide blocks of the polymer. The polyoxyethylene portion of the block polymer consists of at least about 40% block polymer. The material preferably has a molecular weight between about 2,000 and 10,000, more preferably about 3,000 to about 6,000. These materials are known in the art. They are available under the trademark "Pluronics", a product of BASF-Wyandotte Corporation.

Amphoteric synthetic detergents can be broadly described as derivatives of aliphatic and tertiary amines, wherein the aliphatic moiety can be straight chain or branched, with one of the aliphatic substituents containing from about 8 to about 18 carbon atoms and the other containing an anionic water-soluble group, namely carboxy, sulfo, sulfato, phosphato or phosphono. Examples of compounds falling under this definition are sodium 3-dodecylaminopropionate and sodium 2-dodecylaminopropanesulfonate.

Zwitterionic synthetic detergents can be broadly described as derivatives of aliphatic quaternary ammonium, phosphonium and sulfonium compounds, where the aliphatic radical can be straight-chain or branched and where one of the aliphatic substituents contains about 8 to about 18 carbon atoms and one contains an anionic water-soluble group, e.g. carboxy, sulfo, sulfate, phosphate or phosphone. These compounds are often referred to as betaines. In addition to alkyl betaines, alkylamino and alkylamidobetaines are included within this invention. Cocoamidopropyldimethylbetaine is a particularly suitable surfactant.

After the wax capsule has been melted, it will remain melted or solidify again depending on the temperature of the washing medium. However, the wax, whether in a melted or solid state, can deposit as a soil on the surface of the items to be washed and give these items a spotty, streaky or filmy appearance. Wax can also deposit on the surface of the Containers in which cleaning is to be carried out, e.g. sinks, bathtubs or dishwashers.

This wax coating contamination can be reduced by using one or more surfactants in the cleaning agent. Applicants have found that certain surfactants are much better at preventing wax residue than others. These surfactants are Polytergent SLF-18R from Olin Corporation and Emphos CS-1361R from Witco Chemical; and Dowfax 2A-1R and Dowfax 38-2R

Thus, in a preferred embodiment, the cleaning composition comprises 0.1 to 30% by weight of wax-encapsulated bleach as described above; 1 to 75% builder and 0.01 to 15% surfactant selected from the group consisting of polyoxyalkylated alkylaryl phosphate esters; mono and di-C₈-C₁₄-alkyldiphenyloxide mono- and/or disulfates and nonionic surfactants of the formula

wherein R is a mixture of linear C₆-C₁₀-alkyl radicals, R' and R" are methyl, x is on average 3, y is on average 12 and z is on average 16.

silicate

The compositions of the invention may contain sodium or potassium silicate in an amount of from 1 to 40%, preferably from 5 to 20% by weight of the cleaning composition. This substance is used as a cleaning ingredient, source of alkalinity, metal corrosion inhibitor and glaze protectant on porcelain tableware. Sodium silicate is particularly effective in a ratio of SiO₂:Na₂O of from about 1.0 to about 3.3, preferably from about 2 to about 3.2. Some of the silicate may be in solid form.

filler

An inert particulate filler material which is water soluble may also be present in the cleaning agents in powder form. This material should not contain calcium or magnesium ions to the extent used by the filler. Suitable for this purpose are organic or inorganic compounds. Organic fillers include sucrose esters and urea. Representative inorganic fillers include sodium sulfate, sodium chloride and potassium chloride. A suitable filler is sodium sulfate. Its concentration may range from 0% to 60%, preferably from about 10 to 20% by weight of the cleaning agent.

Thickeners and stabilizers

Thickeners are often desirable for liquid detergents. Thixotropic thickeners such as smectite clays, including montmorillonite (bentonite), hectorite, saponite, and the like, can be used to impart viscosity to liquid detergents. Silica, silica gel, and aluminosilicate can also be used as thickeners. Salts of polyacrylic acid (molecular weight of about 300,000 to 6 million and higher), including polymers that are cross-linked, can also be used individually or in combination with other thickeners. The use of clay thickeners in automatic dishwasher detergents is disclosed, for example, in U.S. Patent Nos. 4,431,559, 4,511,487, 4,740,327, 4,752,409. The use of salts of polymeric carboxylic acids is disclosed, for example, in GB-A-2 164 350. Commercially available bentonite clays include Korthix H and VWH from Combustion Engineering, Inc.; Polargel T from American Colloid Co. and Gelwhite Clay (particularly Gelwhite GP and H) from English China Clay Co. Polargel T is preferred as it gives the composition a more intense white appearance than other clays.

For liquid formulations with a "gel" appearance and rheology, especially when a clear gel is desired, chlorine-stable polymer thickeners are particularly suitable. US-A-4 260 528 discloses natural gums and resins for use in clear dishwashing detergents which are not chlorine stable. Crosslinked acrylic acid polymers which for example, manufactured by BF Goodrich and sold under the trademark "Carbopol" have been found to be effective in producing a clear gel and CarbopolR 940 having a molecular weight of about 4,000,000 is particularly preferred for maintaining a high viscosity with excellent chlorine stability over extended periods of time. Other suitable chlorine stable polymeric thickeners are described in US-A-4,867,896 (Elliott et al.).

The amount of thickeners used in the products is 0 to 5%, preferably 1 to 3%.

Stabilizers and/or costructuring agents such as long chain calcium and sodium soaps and C12 to C18 sulfates are described in detail in U.S. Patent Nos. 3,956,158 and 4,271,030, and the use of other metal salts of long chain soaps is described in detail in U.S. Patent No. 4,752,409. The amount of stabilizer that can be used in the liquid detergent compositions is from about 0.01% to about 5% by weight of the composition, preferably 0.1% to 2%. Such stabilizers are optionally present in gel formulations. Costructuring agents found particularly suitable for gels include trivalent metal ions at 0.01% to 4% of the compositions and/or water-soluble structuring chelating agents at 1% to 60%. These co-structuring agents are described in more detail in US-A-4,836,948 (Corring et al.).

Defoamers

Liquid and "gel" formulations of detergents containing surfactant may additionally include a defoamer. Suitable defoamers include mono- and distearylic acid phosphates, silicone oil and mineral oil. Even if the detergent contains only defoaming surfactant, the defoamer helps to minimize foam that can be caused by food soils. The detergents may include 0.2 to 2% by weight of defoamer or preferably 0.05 to 1.0%.

Small amounts of various other components may be present in the detergent. These include flow control agents (in granular form), soil suspending agents, anti-redeposition agents, anti-dulling agents, enzymes (such as protease, amylase and/or lipase at 0.05-2% by weight, preferably 0.5-1.5% by weight) and other functional additives and perfumes. The pH of the detergent may be adjusted by adding strong acid or base.

The following examples more fully illustrate embodiments of the invention. All parts, percentages and ratios recited herein and in the appended claims are by weight unless otherwise indicated.

example 1

Two batches of wax encapsulated bleach particles with low melting waxes are produced in the Glatt WSG-5 fluid bed. Batch A is coated with a mixture of Boler 941/Altafin 125 paraffin waxes in a ratio of 79.54/20.46. Batch B was coated with 100% Boler 941. The following conditions were used to coat the Clearon CDB-56 bleach particles.

Batches produced by the spray process typically lose 15 to 20% as agglomerated material. The 5 kg (11 pounds) Clearon CDB-56 Bleach particles are coated in batch A with 6 kg of a mixture of 79.54/20.46 Boler 941 and Altafin 125 paraffin. The resulting encapsulated bleach particles exhibit excellent stability in dishwashing liquids.

Batch B is coated with 100% Boler 1397 wax applied in a fluidized bed according to the following settings:

Oharge B’s encapsulated CDB-56 exhibits excellent stability in liquid dishwashing detergents at 40ºC and pH 12.3.

EXAMPLE II

The solubility of the coatings made from microcrystalline wax and fatty acid in alkaline media can be compared to those coating compositions made from paraffin wax having a melting point between 40 and 50°C. Four different coating compositions are made from a microcrystalline wax with a pair of fatty acids in the ratios listed below. Two different paraffin waxes are selected for comparison. The four fatty acid/wax and the two wax coatings are identified as Coating Compositions 1 to 6 below. Equal amounts (0.27 g) of each Coating Composition 1 to 6 are placed in separate Beakers already containing 2.87 liters of a 0.02% aqueous solution of Emphos CS-1361R. The contents of each beaker are heated to 49ºC, maintained at this temperature with stirring for 45 minutes, then cooled to room temperature and poured through a U.S. standard 48 mesh (300 µm) metal sieve.

Solid wax collected through the sieve is dried and weighed to determine the amount of wax remaining as a solid residue after heating with the surfactant. Table II. Coating compositions

* Melting point of Capric acid = 31,200

Lauric acid = 43.9ºC

Myristic acid = 54.1ºC

Multiwax W-145A = 66-71ºC Table III - Quantities of wax residues

The microcrystalline wax/fatty acid compositions leave high levels of wax residue. Comparison of samples 1 to 2 and 3 to 4 shows that less wax is deposited from the coating compositions with lower levels of Multiwax W145-A. In contrast to coating compositions 1 to 4, paraffin waxes with a melting point of 40-50ºC leave very low residue and are therefore highly preferred as coatings for bleach particles.

EXAMPLE III

Bleach is encapsulated as in Example I, but with coatings consisting of a wax melting at 72ºC (30% Epolene 0-16/70% Boler Paraffin 1426), 52ºC (Altafin 125/130) or 46ºC (Ross 115/120). The capsules coated with high melting waxes are coated in a fluid bed like the capsules of Oharge A in Example I, with the exception of the capsules coated with Epolene, where the bed temperature is 60-65ºC. and for capsules coated with Altafin 125/130, the coating temperature is 40-45ºC. The capsules coated with Ross 115/120 are coated in the same way as Oharge B capsules in Example I. All three batches of capsules are coated with a core:coating ratio of 47:53. Thus, expressed in grams of capsule, there should be 0.53 grams of wax.

1.88 grams of each type of capsule are placed in forty grams of a dishwashing liquid composed as follows:

The procedure for preparing this dishwashing gel formulation is as follows. Water is added to a vessel. KOH is added with stirring over one minute, followed by clay and further stirring for another 10 minutes. The mixture of TKPP, STP and oarbopol 941 is then added over the next 12 minutes, followed by 30 minutes of stirring. The TKPP solution is then added and the mixture is stirred for 30 minutes. Then D-silicate, K₂CO₃ and SLF-18 are added separately, each followed by 5 minutes of stirring.

The dishwashing detergent containing the bleach capsules is then placed in a dispenser of a Kenmore dishwasher. A 40 gram sample of dishwashing detergent is placed in the dispenser of the dishwasher at a specific time and the machine is allowed to run a complete wash cycle until it is drained. At the end of the wash cycle the water is drained from the machine and passed through a US standard metal sieve, 43 mesh (0.38 mm), into a bucket. The collected wax capsules or particles are dried and weighed. The results appear in the table below and in Figure 1.

EXAMPLE IV

The same three types of capsules prepared in Example III are tested here in preventing staining of glassware in an automatic dishwasher. The tests to evaluate the appearance of the glass are carried out in a Bosch S-512 dishwasher at 60ºC (140ºF) and using water with 120 ppm hardness.

In the test, two dishwashers are loaded with clear glass plates and drinking glasses (all clean and stain-free). Forty grams of greasy soil is then smeared on the inside of each dishwasher door. The soil is formed by mixing four pounds (1.8 kg) of Imperial margarine with four 12.8 ounce packages of Carnation low-fat dry milk, mixed until homogeneous. Forty grams of the dishwashing detergent with one form of the coated bleach capsules is then placed in the washer's dispensing tray. The glassware is then put through a short wash cycle. After the wash cycle, each glass is removed from the dishwasher and staining is rated according to the scale below.

Stain scale

0 = free from fleas

1 = few stains

2 = 1/3 of the glass stained

3 = 2/3 of the glass stained

4 = the glass is completely covered with stains

The summary of the stain and fume rating is given in Figure 2. The results show that capsules with lower melting point melt more easily and therefore release more bleach, which in turn improves the stain rating.

EXAMPLE V

To compare the stability of bleaches coated with paraffin wax having a melting point of 40-50°C with those coated with a mixture of microcrystalline wax and fatty acid in alkaline media, bleach particles, Olearon CDB-56 from Olin Corporation, are coated with coating composition 3, 4, 5 or 6 described in Example II.

The capsules are produced in a Granuglatt device, model number WSG-3, with the following settings:

Then 1.8 grams of each capsule is uniformly dispersed by the liquid from Example III in the dishwasher. Thus, six liquid dishwashing detergents containing the capsules are formed and each stored at 40ºC. Samples are kept in triplicate in 113 g (4 oz) glass jars. Chlorine analysis is performed after 1, 2, 7, 14, 28, 42 and 56 days.

5 mL aliquots are taken from each of the six liquid dishwashing detergent samples and filtered through a U.S. standard 48 mesh (0.32 mm) metal sieve to remove the capsules. The wax coating is removed from the capsules by gentle stirring in hexane for 20 minutes.

The amount of active chlorine remaining is then determined by conventional iodometric titration. The results are summarized in the table below. Table IV Storage stability results of capsules stored in a liquid dishwashing detergent, pH = 12.3, 40.0ºC

Capsules 3 and 4 have a melting point of 50ºC or coating amounts of 57 and 54 percent by weight of the total capsule, respectively. Capsule 4' has the same composition as that of capsule 4, except that its coating amount is higher, 66%. Capsules 5 and 6 have coating amounts of 54%. These results show that fatty acid/microcrystalline wax coatings are poor at protecting bleach in alkaline medium. Thus, these coating materials are not suitable for use in alkaline aqueous media. In contrast, the amount of bleach protected in the alkaline medium is excellent when the coating is made of paraffin wax with a melting point of 40 to 50ºC.

EXAMPLE VI

The stability of bleach encapsulated in individual wax coatings of varying thickness is measured as follows: a batch of Clearon CDB 56R is introduced into a fluidized bed and coated with enough Boler Paraffin 1397 so that the coating constitutes 35% of the encapsulated bleach (batch A). A second batch (batch B) of Clearon CDB 56R is coated with enough Boler 1397 so that the coating constitutes 55% of the particles. Approximately one gram of each encapsulated bleach is then dispersed in 40 grams of the dishwashing detergent of Example III and stored therein at 40°C.

Samples are placed in triplicate in 113 g (4 oz) glass jars and stored at 40.2ºC. Chlorine analysis is performed after 1, 2, 4 and 6 weeks.

At the time intervals shown in Table V below, 5 ml aliquots are taken from each sample of dishwashing detergent. These are filtered through U.S. standard 48 mesh metal sieves to remove the capsules. The amount of active chlorine remaining is determined by standard iodometric titration. The results are summarized in the table below. Table V Laser stability in ADL gel

Thus, it is demonstrated that the coatings of greater thickness provide greater protection to the bleach particles in aqueous media.

EXAMPLE VII

The capsules of Example III are used in the liquid dishwashing detergent of Example III. Forty grams of each detergent are placed in the dispensing tray of a Kenmore automatic dishwasher and the machine is operated through a wash cycle at 46ºC. Every two minutes throughout the wash cycle, a 5 ml aliquot is removed from the wash liquor. The amount of available chlorine released from the capsules is measured by standard iodometric titration. As the result shows (Figure 3), capsules with lower melting coatings release bleach more rapidly and completely. Thus, these capsules demonstrate a higher level of efficiency.

The foregoing description and examples illustrate selected embodiments of the present invention. In this sense, various modifications will be apparent to those skilled in the art, all of which are within the scope of the invention as defined in the appended claims.

Claims (14)

1. A process for producing a coherent, continuous coating around bleach particles suitable for use in cleaning compositions, the process comprising: a) keeping bleach particles suspended in a fluidized bed, b) selecting one or more paraffin waxes to provide the coating, the waxes having a melting point of between 35ºC and 50ºC and a needle penetration value of 10 to 60 mm at 25ºC, (c) heating the one or more paraffin waxes to a temperature sufficiently above their melting point to melt all of the wax, d) fluidizing the layer by passing air through the bleach particles so that a layer temperature of at least 20ºC up to a temperature not higher than the melting point of the wax is maintained and (e) spraying the molten paraffin wax onto the fluidised bed at a rate of 10 to 40 g/min per kilogram of bleach particles in the fluidised bed and for a period of time sufficient to form a coating of 10 to 3000 µm thickness on the bleach particles. 2. A process according to claim 1, wherein in step (e) the molten paraffin wax is sprayed onto the fluidized bed at an atomization temperature of 5 to 40°C above the melting point of the wax. 3. A process according to claim 1, wherein the paraffin wax is sprayed into the fluidized bed by the Wurster process comprising holding the particles in an upwardly flowing air stream entering the fluidized bed from below, suspended to give the particles a controlled cyclic motion, with part of the layer flowing upwards. 4. The method of claim 1, further comprising annealing the coated particles at a temperature of 5 to 15°C higher than the coating temperature during coating and 3 to 15°C below the melting point of the wax coating for 10 minutes to 48 hours after completion of spraying. 5. The method of claim 1, wherein the encapsulated particles have an average diameter in the range 800 to 4000 µm. 6. The process of claim 1, wherein the paraffin wax has a solids content of 40 to 100% at 40°C and a solids content of 0 to 15% at 50°C. 7. The process of claim 1, wherein in step (c) the one or more paraffin waxes are heated to a temperature of 50 to 100°C above the wax melting point and the atomization temperature of the wax sprayed onto the fluidized bed is below the melting point of the wax. 8. Wax-encapsulated bleach particles suitable for use in cleaning compositions, the encapsulated particles comprising: a) 45-65% by weight of the finished encapsulated particles, a solid particulate core of bleach, b) 35-55% by weight of the finished encapsulated particles, a waxy coating, the coating comprising one or more paraffin waxes having a melting point of 35°C to 50°C and a needle penetration value of 10 to 60 mm at 25°C, and having a thickness of 10 to 3000 µm. 9. Encapsulated particles according to claim 8, wherein the thickness of the coating is 200-750 µm. 10. Encapsulated particles according to claim 8, wherein the bleaching agent is selected from the group consisting of chlorine releasing agents, bromine releasing agents and organic and inorganic peroxygen generating compounds. 11. Encapsulated particles according to claim 10, wherein the bleaching agent is chloroisocyanurate. 12. Liquid cleaning agent comprising a) 0.1-30% by weight of the encapsulated bleach particles of claim 8; b) 1-75% by weight builder; c) 0.01-15% by weight of a surfactant; d) optionally 1-40% by weight of silicate; and e) 15-95% water by weight. 13. Cleaning agent according to claim 12, wherein the agent is a liquid agent for automatic dishwashers, comprising a) 10-60% by weight builder; b) 0.01-3% by weight non-ionic surfactant; c) 5-20% by weight silicate; d) 0.1-20% by weight of the encapsulated bleach particles of claim 8; e) 0-5% by weight of thickener; and f) the remainder being water. 14. Cleaning agent according to claim 12, wherein the surfactant is selected from the group consisting of mono- and di-C₈-C₁₄-alkyldiphenyl oxide mono- and/or disulfates, polyoxyalkylened alkylaryl phosphate esters, surfactants of the formula wherein R is a mixture of linear C₆-C₁₀-alkyl radicals, R' and R" are methyl, x is on average 3, y is on average 12 and z is on average 16, and mixtures thereof.