Process for producing coated bleach activator granules

Details Process for producing coated bleach activator granules Process for producing coated bleach activator granules

2000-07-21

2003-11-11

Delcotto, Gregory (Department: 1751)

Cleaning compositions for solid surfaces, auxiliary compositions

Cleaning compositions or processes of preparing

For cleaning a specific substrate or removing a specific...

C510S312000, C510S349000, C510S356000, C510S358000, C510S376000, C510S444000, C510S445000, C510S457000, C252S186250, C252S186380, C252S186390

Reexamination Certificate

active

06645927

ABSTRACT:

Bleach activators are important ingredients in detergents, scouring salts and dishwashing agents. They permit a bleaching action even at relatively low temperatures in that they react with hydrogen peroxide—usually perborates or percarbonates—to release an organic peroxycarboxylic acid.
The bleaching result obtainable depends on the nature and reactivity of the peroxycarboxylic acid formed, on the structure of the bond that is to be perhydrolyzed and on the solubility of the bleach activator in water. Since the activator is usually a reactive ester or an amide, it is frequently necessary to use it in granulated form for the intended application in order to prevent hydrolysis in the presence of alkaline detergent ingredients and to ensure an adequate shelf life.
Numerous auxiliaries and processes have been proposed in the past for granulating these substances. EP-A-0 037 026 describes a process for producing readily soluble activator granules comprising 90 to 98% activator with 10 to 2% cellulose ethers, starch or starch ethers. Granules consisting of bleach activator, film-forming polymers and added organic C
3
-C
6
-carboxylic, hydroxycarboxylic or ether carboxylic acid are specified in WO 90/01535. EP-A-0 468 824 discloses granules comprising bleach activator and a film-forming polymer which is more soluble at a pH of 10 than at a pH of 7 DE-A-44 39 039 describes a process for producing activator granules by mixing a dry bleach activator with a dry, inorganic binder material containing water of hydration, compressing this mixture to form relatively large agglomerates, and comminuting these agglomerates to the desired grain size. A waterless production process, by compacting the bleach activator with at least one water-swellable auxiliary, without the use of water, is known from EP-A-0 075 818.
Disadvantages of these activator granules are that the properties of the granules are fixed essentially by the binder and by the granulating method used and that the resulting granules, besides the advantages described in the literature, often have certain disadvantages as well, for example suboptimal release of active substance, low abrasion resistance, high dust content, inadequate shelf life, separation within the powder or damage to the color of the fabric when used in detergents and cleaning materials.
In order to give granules defined properties a coating step is often carried out subsequent to the granulating step. Common methods are coating in mixers (mechanically induced fluidized bed) or coating in fluidized-bed apparatus (pneumatically induced fluidized bed).
For instance, WO 92/13798 describes, for a bleach activator, coating with a water-soluble organic acid which melts at above 30° C. and WO 94/03305 describes coating with a water-soluble acidic polymer in order to reduce color damage to the laundry.
WO 94/26862 discloses the coating of granules consisting of bleach activator and a water- and/or alkali-soluble polymer with an organic compound melting at between 30 and 100° C. for reducing separation in the pulverulent end product. In this case the activator granules are placed in a Lödige plowshare mixer, circulated at from 160 to 180 rpm at room temperature, without using the pelletizer, and then sprayed with the hot melt. A disadvantage of this process is the very poor coating quality, which, although it brings about a reduction in separation in the pulverulent end product, has no effect on the other granule properties, such as release of active substance, abrasion resistance, dust content or shelf life, for example. The positive effect on the separation behavior can probably be attributed to a droplet-like solidification of the coating substance on the granule surface allowing the individual grains to hook together in the bulk product.
The object of the present invention was to develop a coating process for activator granules which makes it possible to tailor the granule properties within a wide range at the same time as making optimum use of the coating material.
This object was achieved by a thermal conditioning during and/or after coating.
The invention accordingly provides a process for producing coated bleach activator granules in which bleach activator base granules are coated with a coating substance and are simultaneously or subsequently thermally conditioned.
Base granules which can be used are all activators which in granulated form have a melting point of above 100° C. Examples of activator substances are tetraacetylethylenediamine (TAED), tetraacetylglycoluril (TAGU), diacetyldioxohexahydrotriazine (DADHT), acyloxybenzenesulfonates (e.g. nonanoyloxybenzenesulfonate [NOBS], benzoyloxybenzenesulfonate [BOBS]), acylated sugars (e.g. pentaacetylglucose [PAG]) or compounds as are described in EP-A-0 325 100, EP-A-0 492 000 and WO 91/10719. Other suitable activators are N-acylated amines, amides, lactams, activated carboxylic esters, carboxylic anhydrides, lactones, acylals, carboxamides, acyllactams, acylated ureas and oxamides, and furthermore, especially nitriles, which in addition to the nitrile group may also contain a quaternized ammonium group. Mixtures of different bleach activators can also be present in the base granules.
These base granules can include the customary granulating auxiliaries, which should have a melting point of more than 100° C. Suitable such auxiliaries are film-forming polymers, for example cellulose ethers, starch, starch ethers, homopolymers, copolymers and graft copolymers of unsaturated carboxylic acids and/or sulfonic acids and also the salts thereof, organic substances, for example cellulose, crosslinked polyvinylpyrrolidone, or inorganic substances, for example silicic acid, amorphous silicates, zeolites, bentonites, alkali metal phyllosilicates of the formula MM′Si
x
O
2x-1
*yH
2
O (M,M′=Na, K, H; x=1.9-23; y=0-25), orthophosphates, pyrophosphates and polyphosphates, phosphonic acids and their salts, sulfates, carbonates and bicarbonates, Depending on what is required these granulating auxiliaries can be employed as individual substances or as mixtures.
In addition to the bleach activator and the granulating auxiliary the bleach activator base granules may also include further additives which enhance properties such as, for example, shelf life and bleach activation. Such additives include inorganic acids, organic acids, for instance mono- or polybasic carboxylic acids, hydroxycarboxylic acids and/or ether carboxylic acids, and also salts thereof, complexing agents, metal complexes and ketones.
Depending on what is required, the abovementioned additives can be employed as individual substances or as mixtures.
The base granules are made by mixing a dry bleaching activator with a dry inorganic binder material, pressing this mixture to give relatively large agglomerates and comminution of these agglomerates to the desired particle size.
The ratio of bleaching activator to inorganic binder material is usually 50:50 to 98:2, preferably 70:30 to 96:4% by weight. The amount of additive depends in particular on its nature. Thus, acidifying additives and organic catalysts are added to increase the performance of the peracid in amounts of 0-20% by weight, in particular in amounts of 1-10% by weight, based on the total weight, while metal complexes are added in concentrations in the ppm range.
Suitable coating substances are all compounds or mixtures thereof which are solid at room temperature and which soften or melt in the range from 30 to 100° C.
Examples of such are:
C
8
-C
31
fatty acids (e.g. lauric, myristic, stearic acid): C
8
-C
31
fatty alcohols; polyalkylene glycols (e.g. polyethylene glycols having a molar mass of from 1000 to 50,000 g/mol); nonionics (e.g., C
8
-C
31
fatty alcohol polyalkoxylates with from 1 to 100 moles of EO); anionics (e.g., alkanesulfonates, alkylbenzenesulfonates, &agr;-olefinsulfonates, alkyl sulfates, alkyl ether sulfates having C
8
-C
31
hydrocarbon radicals); polymers (e.g., polyvinyl alcohols); waves (e.g. montan waxes, paraffin wax

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