EP0070474A1 - Process for the production of enveloped granular bleaching activators - Google Patents

Abstract

In order to produce coated granular bleach activators, a pumpable aqueous slurry is spray-dried, which contains 1 part by weight of a mixture of A), a powdery bleach activator from the class of N- or O-acyl compounds, preferably tetraacetylethylenediamine with a certain particle size distribution and B, in 1 to 1.7 parts by weight of water ) contains at least one compound from the class of water-soluble cellulose ethers, starch and starch ethers, preferably carboxycellulose as Na salt in the weight ratio A: B = 99: 1 to 90:10. The dry gas flow, which is preferably conducted in countercurrent, has an inlet temperature of 100-200 ° C and an outlet temperature of 40-120 ° C. The spray product is dried to a moisture content of <= 3% by weight.

Description

Bleach activators are compounds which react in aqueous solutions containing hydrogen peroxide or perhydrates to form peracids with a bleaching effect. The particularly effective bleach activators include N-acylated amines, amides and glycolurils, as described, for example, in DE-AS 11 62 967, DE-AS 12 91 317, DE-OS 20 38 106 and DE-AS 15 94 865; are known. DE-AS 11 62 967 proposes to provide these bleach activators with a water-soluble coating agent before further use, in particular before use in detergents and bleaches, the coating agent being able to consist, for example, of carboxy methyl cellulose. This coating agent, dissolved in water, can be sprayed onto the activator in finely divided form, after which the coated material is dried. The recommendation is made to granulate the activator before coating, but there are no indications as to how and with which granulation aids this should be carried out. If one works according to the specifications of DE-AS 11 62 967 and sprays such a bleach activator, for example tetraacetylethylene diamine, with an aqueous carboxymethyl cellulose solution in a granulator, considerable problems arise. This is because aqueous solutions containing more than 5% by weight of carboxymethyl cellulose can no longer be handled in industrial granulation processes because of their high viscosity and gel-like nature. In order to produce a sufficiently strong coating layer on the activator particles, very large amounts of the must therefore be used highly diluted cellulose ether solutions can be processed. If, as stated in Example 10 of DE-AS 11 62 967, 18 percent by weight of carboxymethyl cellulose is to be applied to the bleach activator and it is assumed that a 5 percent solution that can still be processed due to its high viscosity would be used, 360 percent by weight would be ( based on the amount of activator) of 5 percent cellulose ether solution required. However, it can be shown that when more than 20 to 30 percent by weight of such a solution is used, lumpy to mushy masses are produced instead of usable granules. For this reason it is also proposed in column 3 of DE-AS 11 62 967 to use alcoholic solutions of carboxymethyl cellulose. However, these require the installation of complex explosion protection devices and cause high costs for the recovery of the solvent. Such a method is unsuitable for technical purposes. The same problems occur if, instead of a cellulose ether solution, the fatty acids, fatty acid alkanolamides, fatty alcohols and carbowaxes dissolved in organic solvents, which are also proposed in DE-AS 11 62 967, are used as the covering material. To make matters worse, such coating materials do not dissolve or only dissolve very slowly in cold bleaching solutions and the desired cold bleaching effect is therefore suppressed.

From DE-OS 20 48 331 a process for the production of coated, granulated bleach activators is known, in which the activator is first mixed dry with a suitable coating or granulation agent and sprayed in a second step with water or in water-soluble granulation aids or film formers and is granulated. To prepare the dry premixes, either water-soluble framework salts customary in detergents, such as water of crystallization, bind Phos phates, polyphosphates, carbonates and silicates of alkali metals or water-insoluble fillers such as silica, magnesium silicate or magnesium oxide are proposed. The same water-soluble, water of crystallization salts can also be used as a granulating aid or the dry premixes can be sprayed with an aqueous solution of film-forming substances such as cellulose derivatives or other water-soluble polymers of natural or synthetic origin and granulated at the same time. However, this process is only useful for the production of granules with a comparatively low content of bleach activators, that is to say those with less than 50% by weight. The granules can therefore only be used in areas where the high proportion of additives does not interfere.

In the described processes for enveloping bleach activators, one has expressly limited itself to granulation processes. With conventional granulation processes, however, products with a very inconsistent grain size are often obtained. After granulation and drying have been completed, these must be freed from coarse particles and dust. If the coarse grain were only ground to the desired grain size and mixed into the finished granulate, the regrind would only have a reduced shelf life since the bleach activator grains are not or are not adequately protected at the breaking points. This means that in addition to the fine material, the ground coarse grain must also be returned to the granulation process and thus considerable amounts of product must be recycled. •

From DE-PS.21 38 584 and DE-OS 22 07 974 processes for the production of coated bleach activators are known, in which molten mixtures of polyglycol and fatty acids with bleach activators dispersed therein are sprayed into a falling space by means of nozzles or rotating disks and the: formed Droplets are solidified using cool air. In the prills obtained in this way, the bleach activator is very effectively protected against decomposition. Problems can arise with the application, however, because the prills only dissolve completely at temperatures above the melting point. Additions of fatty alcohols or their ethoxylates and sulfates, as described in DE-OS 23 38 412 and DE-OS 25 35 731, bring only a gradual improvement. At low temperatures, undissolved prills can stick to the textiles during the washing process and spread to small greasy spots during subsequent hot drying or ironing. Finally, the manufacturing process also poses problems on hot summer days when there is not enough cold air to cool and solidify the prills. However, pre-cooling the air introduced into the spray tower is very complex.

The aforementioned granulation and spraying processes have in common that they were carried out at relatively low temperatures. Because of the high thermal sensitivity of the bleach activators, it was previously assumed that they should not be exposed to the conditions of hot spray drying.

The invention has for its object to develop a process for the production of uniformly coated and therefore very stable bleach activator grains of uniform quality and good solubility in cold water, which have a high content of 90% and more by weight of active substance.

• A) einem pulverförmigen Bleichaktivator aus der Klasse der N- bzw. 0-Acylverbindungen und
• B) mindestens einer Verbindung aus der Klasse der wasserlöslichen Celluloseether, Stärke und Stärkeether, wobei das Gewichtsverhältnis von (A) : (B) 99 : 1 bis 90 : 10 beträgt, in einem Trockenraum versprüht, in dem ein Trockengasstrom mit einer Eingangstemperatur von 100° bis 200 °C und einer Austrittstemperatur von 40° bis 120 °C unterhalten wird und das Sprühprodukt auf einen Feuchtigkeitsgehalt von 3 Gew.-% oder weniger trocknet.

The invention relates to a process for the preparation of coated granular bleach activators, characterized in that a pumpable aqueous slurry containing 1 to 1.7 parts by weight of water per 1 part by weight of a mixture

• A) a powdery bleach activator from the class of N- or 0-acyl compounds and
• B) at least one compound from the class of water-soluble cellulose ethers, starch and starch ethers, the weight ratio of (A): (B) being 99: 1 to 90: 10, sprayed in a drying room in which a dry gas stream having an inlet temperature of 100 ° to 200 ° C and an outlet temperature of 40 ° to 120 ° C is maintained and the spray product dries to a moisture content of 3 wt .-% or less.

The aqueous slurry is advantageously prepared by first preparing a solution or swelling of the cellulose ether or starch or starch ether and then stirring in the powdery bleach activator. Examples of cellulose ethers are methyl cellulose, ethyl cellulose, hydroxyethyl cellulose and methyl hy droxyethyl cellulose, methyl hydroxypropyl cellulose, carboxymethyl cellulose (as sodium salt) and methyl carboxymethyl cellulose (sodium salt). For example, depolymerized starch can be considered as starch. Suitable starch ethers are, for example, carboxymethyl starch, hydroxyethyl starch and methyl starch. Sodium carboxymethyl cellulose has proven to be particularly suitable.

The known N-acylated amines, diamines, amides and glycolurils, as disclosed in the patents mentioned at the outset, are suitable as bleach activators. These are, for example, tetraacetylmethylene diamine, tetraacetylethylene diamine, diacetylaniline, .diacetyl-p-toluidine, 1,3-diacetyl-5; 5-dimethylhydantoin, tetraacetylglycoluril, tetrapropionylglycoluril, 1,4-diacetyl-2,5-diketo-diketo- 4-diaceiyl-3,6-dimethyl-2,5-diketopiperazine. Tetraacetylethylenediamine is preferably used as the bleach activator.

The bleach activator preferably has the following grain size distribution, determined by sieve analysis: 0% by weight over 1.5 mm 10-50, preferably 15-40% by weight with 1.5-0.2 mm 15-60, preferably 20 50% by weight with 0.2-0.09 mm 5-50, preferably 10-40% by weight with 0.09-0.03 mm to 30% by weight under 0.03 mm.

The number of sieves is expediently carried out with an air jet sieve in order to avoid errors which occur due to agglomeration of fine particles due to electrostatic charging.

Bleach activators, whose particle size distribution is within the above scheme, lead to products with particularly favorable powder or storage properties and a higher dissolution rate in cold water.

The weight ratio of bleach activator (component A) to the cellulose or starch ethers or starch (component B) is 99: 1 to 90: 10, preferably 97: 3 to 93: 7 with a ratio of water to the sum of the solids of 1, 7: 1 to 1: 1, preferably from 1.5: 1 to 1.3: 1. In any case, the proportions should be chosen so that the aqueous batch can still be pumped and sprayed when heated. This means that batches with higher proportions of component (B) require a higher water content than those with lower proportions of (B).

Besides the two components (A) and (B) the aqueous mixture can be further substances added, the bleach activators or under ^- are resistant conditions of the spray drying and the subsequent use of the means itself or a mixed therewith detergent advantageous properties to lend. These include polyglycols and non-ionic surfactants, in particular linear, for example, of saturated and unsaturated fatty alcohols or methyl-branched, ie of oxo alcohols derived alkyl polyglycol ethers with an average of 4 to 25 glycol ether groups or equivalent polyglycol _'ether derivatives of alkyl phenols, alkyl amines, thioalcohols, fatty acids and fatty acid amides. The amount of these additives can be up to 10, for example 1 to 5% by weight, based on the dry spray product. Such additives reduce the tendency to dust. Dyes and pigments can also be added, as can powder shaped, in particular microfine silica or finely divided zeolites, phosphates such as sodium tripolyphosphate and neutral salts such as sodium sulfate. However, the proportion of these substances should preferably be small, ie below 10% by weight, based on the dry product, in order not to question one of the essential advantages of the process, namely the provision of a product with a high active substance content. In cases in which the process products are to be mixed directly with a detergent, the proportion of such substances which are valuable in terms of washing technology can also be significantly higher and up to 50% by weight of the dry spray product.

It is also possible to add to the granules intended for use in detergents or in washing processes, prior to spray drying, those substances which are usually mixed separately in very small amounts with the detergents in a special mixing process. These additives are those which are inactivated during the usual hot spray drying of a detergent slurry, in particular foam inhibitors. Suitable foam inhibitors are customary known defoamers, preferably organopolysiloxanes, and mixtures thereof with microfine silica. Examples of these are polydimethylsiloxane with a content of approx. 1-10% by weight of microfine silica. The proportion of such polysiloxane defoamers can be 0.5 to 5% by weight, preferably 1 to 4% by weight, based on the finished spray product. The defoamer is advantageously mixed into the aqueous batch after the component (B) has been dissolved or swelled in order to avoid creaming of the silicone liquid. When organopolysiloxanes are used, there is expediently no Addition of surfactants to the aqueous formulation in order to avoid a loss of effectiveness with regard to the foam-suppressing properties.

Spray drying is carried out in conventional drying chambers coated with hot air or hot combustion gases. As a rule, they consist of cylindrical towers into which the hot gases flow in cocurrent, but preferably in countercurrent, i.e. preferably in the lower part of the tower, introduced tangentially at a temperature of preferably 120 ° C. to 150 ° C. and discharged at the tower head with an outlet temperature of preferably 50 ° to 85 ° C. and passed to the dedusting systems. The aqueous batches to be dried are fed to the top of the drying tower via high-pressure lines and sprayed through spray nozzles, of which several are usually arranged in a circle. Rotating spray plates can also be used instead of the high pressure spray nozzles. It is also possible to conduct the dry gases in cocurrent, i.e. to be initiated at the tower head and discharged in the area of the tower floor. The dried spray material can be discharged at the bottom of the tower, for example via screw conveyors or rotary locks.

In the present case, the drying is conducted in such a way that the material to be sprayed after leaving the tower has a water content of not more than 3% by weight, preferably of 0.5 to 2% by weight. The water or crystal water possibly bound in co-sprayed compounds is not included.

It was highly surprising that the bleach activators, which are normally sensitive to heat, remain largely stable under the spray conditions selected. The particular advantages can be seen in the fact that the formation of dust and oversize particles is comparatively low and the spray products have a largely uniform particle size range of 0.2 to 2 mm, mostly 70 to 90% by weight within a desired particle size of 0 , 4 to 1.6 mm. Products with this grain spectrum are particularly suitable for use in spray-dried detergents, which generally have a similar grain spectrum, which is why the mixtures do not tend to separate during transport. In such granular washing powders, usually containing perborate as an additional powder component, the bleach activators are distinguished by a high storage stability.

Examples

The abbreviations used below mean: TAED = tetraacetylethylenediamine TAGU = tetraacetylglycoluril CMC = carboxymethylcellulose, Na salt EO = ethylene glycol ether groups.

The activator powder used had the following grain spectrum, determined by sieve analysis using an air jet sieve (Alpine) (in% by weight):

example 1

In a solution of 5 parts by weight of CMC in 140 parts by weight of water, 94.03 parts by weight of TAED powder and 0.07 part by weight of a blue dye were mixed in and stirred for 20 minutes. The stable slurry was atomized in an amount of 1.5 t / h in a counterflow with tangential introduction of dry air by means of nozzles. The air inlet temperature was 150 ° C, the outlet temperature 70 ° C. The product left the tower floor at a temperature of 70 ° C. and had a residual moisture content of 1.0% by weight. The fine parts with 0.4 mm and coarse parts with over 1.6 mm were sieved and fed back into the following batch. The proportion of granules with a grain spectrum of 0.4 - 1.6 mm was 79.8% by weight. The product was homogeneous and free-flowing. The TAED had not decomposed.

In a mixture with a spray-dried washing powder containing 4% by weight of TAED and 20% by weight of perborate as an admixture, the product proved to be stable with a storage time of 4 weeks at 20 ° C. and 80% relative atmospheric humidity. The product dissolved in water at 30 ° C with stirring within less than 2 minutes.

Example 2

As described in Example 1, a slurry was prepared containing 96 parts by weight of TAED. 4 parts by weight of CMC 130 parts by weight of water. The batch was sprayed with an hourly throughput of 2 t in the drying tower. The inlet temperature of the air conducted in countercurrent was 160 ° C., the outlet temperature 80 ° C., and the residual water content of the spray product was 0.5% by weight. The fraction of the sieve fraction from 0.4 to 1.6 mm was 75% by weight. With regard to the powder and storage properties, the product largely corresponded to that of Example 1.

Example 3

Example 2 was repeated, 2% by weight of the TAED being replaced by a foam-suppressing polydimethylsiloxane (SiO ₂ content approx. 4%). The fraction of the sieve fraction between 0.4 and 1.6 mm rose to 76% by weight at the expense of the dust fraction. In terms of powder, storage and solubility properties, the product was equivalent to that of Example 1. As a 2.5-weight instructor Part of the mixture of a household detergent conventional, but free of other foam damping agents (silicone content of the mixture 0.05% by weight), it has proven its property as a bleaching booster as an effective foam damping agent to prevent the suds from foaming.

Example 4

By dissolving or mixing 5.0 parts by weight of CMC 89.95 parts by weight of TAED 0.05 parts by weight of bluing agent 5.0 parts by weight of tallow fatty alcohol + 5 E0 in 130 parts by weight of water, a slurry was produced with a mixing time of 15 minutes, which had a throughput of 1 , 5 t / h over nozzles in the spray tower in the countercurrent principle at an air inlet temperature of 135 ° C and an air outlet temperature of 68 ° C to a residual moisture content of 1.5 wt .-%. The yield of sieve fraction between 0.4 and 0.6 mm was 80.8% by weight. The product proved to be free-flowing, stable in storage and easily soluble.

Example 5

Example 4 was repeated, but the TAED was replaced by TAGU. The proportion of the sieve fraction between 0.4 and 1.6 mm was 78.5%. For the rest, the properties of the spray product corresponded to that of Example 4.

Claims (9)

1. A process for the preparation of coated granular bleach activators, characterized in that a pumpable aqueous slurry containing 1 to 1.7 parts by weight of water to 1 part by weight of a mixture A) a powdery bleach activator from the class of N- or 0-acyl compounds and B) at least one compound from the class of water-soluble cellulose ethers, starch and starch ethers,
wherein the weight ratio of (A): (B) 99 is 1 to 90:10, sprayed in a drying room in which a dry gas flow is maintained with an inlet temperature of 100 ° to 200 ° C and an outlet temperature of 40 ° to 120 ° C. and drying the spray product to a moisture content of 3% by weight or less. 2. The method according to claim 1, characterized in that tetraacetylethylenediamine is used as the bleach activator (component A). 3. Process according to claims 1 and 2, characterized in that the bleach activator has the following grain size determined by sieve analysis: 0% by weight over 1.5 mm 10-50, preferably 15-40% by weight with 1.5-0.2 mm 15-60, preferably 20-50% by weight with 0.2-0.09 mm 5 - 50, preferably 10 - 40 wt .-% with 0.09 - 0.03 mm up to 30% by weight below 0.03 mm. 4. Process according to claims 1 to 3, characterized in that carboxymethyl cellulose is used as the sodium salt as component B. 5. Process according to claims 1 to 4, characterized in that the weight ratio of A: B ₌ 97: 3 to 93: 7. 6. The method according to claims 1 to 5, characterized in that the weight ratio of water to solids is 1.5: 1 to 1.3: 1. 7. The method according to claims 1 to 6, characterized in that the drying gas is passed in countercurrent and has an inlet temperature of 120 to 150 ° C and an outlet temperature of 50 to 85 ° C. 8. Process according to Claims 1 to 7, characterized in that 0.5 to 5, preferably 1 to 4% by weight, based on solids, of organopolysiloxanes having an antiperspirant effect are added to the aqueous batch. 9. The method according to claims 1 to 8, characterized in that up to 10 wt .-%, based on solids, of nonionic surfactants is added to the aqueous batch.