EP0253323A2 - Process for the preparation of free-flowing alcaline detergents by compacting granulation - Google Patents

Abstract

The process entails powdered sodium metasilicate being mixed with pentasodium triphosphate or zeolite NaA or a triphosphate/zeolite mixture in powder form and being compacted by rollers, the limiting pressure at which no further compaction occurs not being significantly exceeded. The compacted material is subsequently reduced to the required particle size.

Description

An essential component of commercially available cleaners for use in machine cleaning processes - for example in the known dishwashers used in the household - are to date generally sodium metasilicate mixed with sodium tripolyphosphate (also called pentasodium triphosphate and hereinafter referred to as STP). In particular, soda and water glass as well as further components for strengthening the granulating and / or cleaning effect are used as further components. The mixtures of substances exist as free-flowing agglomerates, whereby a number of requirements are placed on the product properties.

The substance mixtures are generally strongly alkaline and therefore irritating to the respiratory tract. Accordingly, the occurrence of dust in the product, as would be expected when using powdered raw materials, must be avoided. Furthermore, products of this type with high fines in the dishwasher's washing-in box tend to clump when water enters, so that a sufficiently short washing-in time is no longer guaranteed.

In addition to being washable and free of dust, other important evaluation criteria are the bulk density and the storage stability of the cleaners. The bulk density should be above 900 g / l to enable the product quantity required for the cleaning cycle to be filled into the dispenser box without problems. Since the free-flowing agglomerates contain water, it must be ensured when processing the recipe that the water remains largely crystalline to prevent caking of the granules during storage.

Today's commercial cleaners are manufactured according to two process variants, namely either by mixing granulation or by mixing granular dust-free raw materials.

Mixed granulation in the presence of water presents a number of complications that require careful control of the process. In the case of water-moist granulation, various components of the mixture of substances (in particular STP, anhydrous metasilicate and soda) compete for the binding of the free water present. The thermodynamically most stable composition may only be achieved when the raw material properties are not constant or the process conditions are not exactly observed when the products are stored. The migration of the water required for this is generally accompanied by a clumping of the product.

The formulation flexibility of the mixed granulation process is also relatively low, and in particular in a very specific direction: The replacement of larger proportions of the STP with the finely crystalline zeolite NaA, which is desirable for reasons of environmental protection, causes difficulties. In particular, products that are too light with unsatisfactory wash-in properties are often obtained here. When mixing granulation in appropriate devices with high energy input, for example in the known Lödige mixer, sticking to the mixer walls occurs, which necessitates regular cleaning of the mixer. The use of soda and water glass as a granulation aid is necessary without these components making a significant contribution to the effectiveness of the cleaning formulation.

The production of mixed products according to the information in the prior art partially avoids the disadvantages of mixed granulation mentioned above, but it is still necessary to use pre-granulated and thus very expensive raw materials in order to ultimately produce dust-free mixed products.

The invention is based on the object of using granular detergent formulation with good flowability, good washability and good storage stability using inexpensive raw materials while reducing the disadvantages of water-wet mixed granulation. In addition to the processability of previously customary formulations for agents of the type specified here, the invention also intends to use finely crystalline zeolite NaA in addition to or instead of STP and to use other components, for. B. of cleaning boosters - enable.

The solution to the problem according to the invention was found by using a preferably continuous compression of a powdery premix of the desired constituents in the nip of a pair of two oppositely running press rolls with subsequent comminution of the resulting plate-shaped compacted material.

Accordingly, the invention relates in a first embodiment to a process for the production of granular, free-flowing alkaline cleaning agents based on sodium metasilicate in intimate admixture with STP and / or finely crystalline zeolite NaA as reinforcing builders and, if desired, further auxiliaries for improved granulation and / or Cleaning effect by means of a mixing process, the hallmark of the new process being that the starting components of the substance mixture are in powder form mixed with each other, this mixture of substances compacted in the nip under increased pressure and the resulting compactate crushed to the desired grain size.

In a further embodiment, the invention relates to granular, in particular free-flowing, alkaline cleaning agents of the type mentioned, which have been produced by the process described here.

In the process according to the invention, in particular the material to be granulated is passed under pressure under the nip of a pair of two rollers running in opposite directions at approximately the same peripheral speed, and is compressed into a plate-shaped material to be pressed. This plate-like or band-shaped pressed material, which is also referred to as "sling belt", is then subjected to a comminution process and granular material of the desired grain size and grain distribution is obtained in the process. The comminution of the plate or band-shaped material can be done in a mill. The comminuted material is then expediently fed to a screening process. Material which is too coarse is separated off and returned to the comminution device, while material which is too fine is added to the batch of the pulverulent mixture and is fed again to the compacting in the roll gap.

The roller compression can take place without or with a pre-compression of the premixed powdery material. The pair of rollers can be arranged in any spatial direction, in particular thus vertically or horizontally to one another. The powdery material is then either by gravity filling or by means of a suitable device, for. B. fed to the nip by means of a stuffing screw.

The pressure in the nip and the dwell time of the material in the area of the pressure are to be set so high that a well-formed, high-density, hard cuff band is produced. The high degree of compaction is to be striven for in order to set the desired bulk densities of the free-flowing material ultimately obtained, which should be above 900 g / l. The abrasion stability of the granules is also influenced by the degree of compaction; high degrees of compaction lead to abrasion-stable granules, which in turn are desirable. However, it must be noted that excessive pressures impair the process reliability, since when they are used the material is plasticized on the rollers and leads to sticking. This undesirable effect occurs when an increase in the pressing pressure no longer causes further compression of the material and the additional force that is now added predominantly causes the heating and plasticization of the material - for example by partial melting of water-containing constituents, in particular water-containing metasilicate.

The optimum pressing force to be used depends on the recipe. Usually, according to the invention, a specific pressing force in the range from approximately 15 to 30 kN / cm roller length is used in the nip, the range from approximately 20 to 25 kN / cm roller length being particularly preferred.

The solid densities set in the compactate are preferably at least about 1.7 g / cm 3. Corresponding solid densities of at least about 1.8 to over 2 g / cm 3 are particularly suitable. Here, too, the optimal density value to be set depends to a certain extent on the recipe.

Contrary to expectations, the ability of the granules to be flushed in - determined as the flushing time of a predetermined amount of material in a test apparatus - is favored by higher compression pressures and thus by higher solids densities, and not deteriorated. Apparently, fillings made of harder particles are less prone to Clump and form less fines even during the induction process, so that an unimpeded water flow through the bed is promoted here.

In addition to the setting of optimal baling pressures in the roll gap, the setting of the thickness of the plate-like or band-shaped compact is important in order to achieve the desired high bulk densities of the finally granulated free-flowing cleaning agents. If the selected bowl thickness is significantly smaller than the desired upper grain limit of the granulated product to be produced, platelet-shaped particles are obtained during the comminution of the plate-shaped compactate which initially results, which lead to beds with a high void volume and therefore a comparatively low bulk weight. At higher compactate thicknesses, however, particles are obtained in the subsequent comminution, the dimensions of which can approach the desired ratio of 1: 1: 1. Such a grain shape leads to denser fillings, the void volume of which is a maximum of about 50%. Although this value is still relatively high compared to fillings made from spherical particles - the usual corresponding values are around 35 to 45% - however, a slightly higher void volume can also bring advantages in the sense of the inventive action. This obviously favors the flushing process in the sense of an unimpeded flow of water through the fill.

In a special embodiment of the invention, however, the chip granulate obtained in the method according to the invention after the shredded ribbon has been comminuted. Here, the primary granulate is subjected to a surface abrasion of corners and edges and, in particular, the bulk density of the granular material is increased again, or that Empty space volume reduced accordingly. For the purpose of such an aftertreatment, for example, the primary granulate chips can be rolled on rotating disks which have a corrugation on their upper side. If necessary, an undesired fine fraction is then separated off again and again fed to the compacting in the roll gap.

The desired upper grain limit in the free-flowing agglomerate is in the range from about 1.6 to 2 mm, while on the other hand fine fractions below about 0.2 mm are undesirable. The preferred free-flowing agglomerates accordingly show a broad grain size range in the range from about 0.2 to 2 mm. In the preferred embodiment, the void volume should not make up significantly more than about 50%, but can be less than 50%. Because of the above-mentioned dependency, in particular of the empty space volume, on the thickness of the preliminary product produced in the compacting stage, it is preferred to produce plate-like or band-shaped compactates with a layer thickness of at least about 1.5 mm after the roll nip. The layer thickness here is preferably at least about 2 mm. Layer thicknesses of the compactate in the range of approximately 4 to 8 mm and in particular in the range of approximately 5 to 6 mm can be particularly preferred.

The essential components of the cleaner mixtures produced in the process according to the invention contain sodium metasilicate in intimate admixture with the framework-forming STP and / or zeolite NaA. The mixture of substances has a certain water content, which is predominantly or exclusively in the form of hydrate or Water of crystallization can be present. In addition, additives such as soda and / or water glass or cleaning-enhancing additives can be present in a mixture.

The following information can be seen as a basic recipe:

Metasilicate is generally present in amounts from 20 to 75% by weight and preferably from about 35 to 65% by weight of the total mixture. Amounts of metasilicate in the range from about 40 to 60% by weight can be particularly suitable. The metasilicate can be used in the powdered feed material as an anhydrous product and / or in the form of hydrated phases with certain predetermined and / or changing amounts of hydrated water contents. Suitable metasilicate phases containing water of hydration are known to be corresponding products with 5 or 9 water of crystallization, with particular importance being attached to the corresponding metasilicate with 5 water of crystallization. Anhydrous metasilicate (KO) and metasilicate containing water of crystallization, in particular corresponding product with 5 water of crystallization (K5), can be used in preferred embodiments of the invention in the feed material in mixing ratios of 5: 1 to 1: 5 and in particular in mixing ratios of 3: 1 to 1: 3 .

STP and / or zeolite NaA are present as intimate mixes with the metasilicate. The amount of these builder substances (anhydrous) is usually in the range from about 20 to 50% by weight, preferably in the range from about 35 to 40% by weight, based on the total mixture. STP can only - d. H. in the absence of zeolite NaA - find use, but it is also possible to replace the STP portion in any mixing ratio by using finely crystalline zeolite NaA - in particular corresponding detergent grade material - in one embodiment of the invention the complete replacement of STP provided by NaA zeolite.

The water content of the finished granules is generally 8 to 25% by weight and is in particular in the range of approximately 10 to 20% by weight. The total water can be added as bound water from the outset as part of the premixing However, it is also possible to add aqueous phase to the powdery starting mixture or to individual components of this starting mixture in order to adjust the overall desired final water contents in the product.

Soda and / or water glass can be used in particular as agglomeration aids and / or as additional alkalizing agents. The amount of soda is generally not more than 20% by weight and in particular not more than 15% by weight, based on the total mixture. The amount of water glass used is usually not more than 10% by weight. In particular, the use of water glass N with a Na₂O / SiO₂ ratio of 1: 3.35 or water glass A with a corresponding ratio of 1: 2 comes into consideration here.

Other auxiliaries that can be used in particular for the purpose of cleaning enhancement are, for example, solubility-improving substances such as sodium acetate or sodium citrate, foam inhibitors, e.g. B. the paraffin foam brakes known from detergent or cleaning agent chemistry, surfactants with washing or cleaning activity, chlorine carriers such as trichloroisocyanuric acid, cleaning enhancers, e.g. B. n-octanol components with complex binding ability such as phosphonobutane tricarboxylic acid and the like. The sum of all these additional auxiliaries generally makes up no more than about 10% by weight and preferably no more than about 5 to 7% by weight. In a preferred embodiment, however, sensitive substances, for example the chlorine carriers mentioned, can also be added to the finished product only after the compaction and subsequent comminution.

The STP portion of the recipe can be used as an STP prehydrate with different water contents or as a non-hydrated STP. Surprisingly, products show at for which non-hydrated STP was used, compared to granules based on STP prehydrates with comparable total water contents of the recipe, better flushability. Cleaners previously available contain STP as partial hydrate or as hexahydrate.

If STP is partially or completely replaced by zeolite NaA, in one embodiment this finely crystalline material is added as part of an STP prehydrate which has been obtained by hydrating STP with an aqueous suspension containing zeolite NaA. Fine crystalline zeolite NaA can also be used as such or as a spray-dried material.

Comparatively higher levels of zeolite NaA can impair the flushability of the agglomerate according to the invention. Here, however, the induction behavior can be improved again by using water-containing metasilicates. The process according to the invention is thus superior to the previously known water-moist granulation, in which water-containing metasilicates cannot readily be used. In the stated manner, products with satisfactory wash-in properties can be obtained even with high zeolite contents.

In connection with the possibilities described here of influencing the improved flushability, the measure mentioned at the outset should be seen to promote the flushability by using the higher compression pressures within the scope desired according to the invention. Overall, this wide range of work and variation options makes it possible to produce cleaning agents of the type concerned here, which are characterized by an optimal combination of parameters in all desired product properties. At the same time, the simple and safe manufacture of such optimal products by the inventive method Proper procedures guaranteed and easily accessible. All in all, a substantial improvement is achieved in comparison with the technical options available to date.

Examples

• 1. A premix consisting of 47.5% STP hydrate (17% H₂O), 30.1% KO and 22.4% K5 was at a specific pressing force of 16 kN / cm on a roller press of the type WP 50 N / 75 (Manufactured by Alexanderwerk / Remscheid) at a roller speed of 16 rpm (roller diameter 15 cm) pressed into scales of approx. 1 mm thickness. The density of the slugs was found to be 1.81 g / cm³. After crushing to a granulate with an average grain diameter of 1.2 mm (grain spectrum sieved to 0.2 to 1.6 mm), a product with a bulk density of 880 g / l was obtained, which in a induction test apparatus in which the ratios in a household dishwasher (HGSM) could be simulated, could be washed in in approx.7.5 minutes (45 g of product are presented to a HGSM in a washing-up box sealed with a grid and at 10 ° C from 15 ° C to 53 ° C increasing temperature approx. 230 ml / min. H₂O sprayed). Repetition of the test at a specific pressing force of 6.4 kN / cm led to flakes with a density of 1.48 g / cm³. The correspondingly comminuted and screened product had a bulk density of 840 g / l and was washed in in 10.5 minutes.
• 2. A premix consisting of 47.5% of an STP hydrate containing 10% zeolite NaA (calculated H₂O-free) and 13.8% H₂O, 30.1% KO and 22.4% K5 was at a specific pressing force compacted from 16 kN / cm. After crushing the flakes and sieving to a grain size of 0.2 to 1.6 mm, a product with a bulk density of 910 g / l was obtained, which was washable in the test apparatus in 6.9 minutes.
• 3. A premix of 17.5% H₂O-free STP, 46.4% K5, 18.1% KO and 18% spray-dried zeolite NaA 20% H₂O was compacted at 16 kN / cm specific pressing pressure and then crushed. The screened product (0.2 to 1.6 mm) with a bulk density of 920 g / l was mixed with 1% trichloroisocyanuric acid and used with 45 g in the dosage box of a commercially available HGSM (Miele G 503 S). The product was washed in after about 19 minutes. No residues were found in the machine.
• 4. A premix of 33.7% K5, 26.3% KO, 22.2% zeolite NaA (80% dry substance, 20% H₂O) and 17.8% H₂O-free STP was compacted at 16 kN / cm and then crushed. The chip granulate with the grain spectrum 0.2 to 1.6 mm had a bulk density of 950 g / l. After-treatment of the material in a Marumerizer for 5, 10 or 20 S resulted in bulk densities of 988 g / l, 996 g / l or 1004 g / l after screening the 0.2 mm fine particles formed.

Claims (13)

1. Process for the production of granular, free-flowing alkaline cleaning agents based on sodium metasilicate in intimate admixture with pentasodium triphosphate (STP) and / or finely crystalline zeolite NaA as reinforcing builders and, if desired, further auxiliaries for an improved granulating and / or cleaning action by means of a mixing process , characterized in that the starting components of the mixture of substances are mixed together in powder form, this mixture of substances is compacted in the nip under increased pressures and the resulting compact is comminuted to the desired particle size. 2. The method according to claim 1, characterized in that one does not significantly exceed the limit pressures in the nip, of which from a further compression no longer occurs. 3. Process according to claims 1 and 2, characterized in that one works in the nip with a specific pressing force in the range of about 15 to 30 kN / cm roller length - preferably in the range of about 20 to 25 kN / cm roller length. 4. The method according to claims 1 to 3, characterized in that the material to be granulated under pressure in the nip of a pair of rolls two converts running at approximately the same circumferential speed in opposite directions to a plate-shaped material to be pressed, which is then reduced to the desired grain shape. 5. Process according to claims 1 to 4, characterized in that the premixed material is compacted to layer thicknesses of at least about 1.5 mm after the nip, preferably layer thicknesses of the compact of at least 2 mm and in particular those in the range from about 4 to 8 mm can be set. 6. Process according to claims 1 to 5, characterized in that the starting mixture is compacted in the nip to form compactates with solid densities of at least about 1.7 g / cm³, preferably in the range from about 1.8 to over 2 g / cm³. 7. The method according to claims 1 to 6, characterized in that after the granulation - preferably by comminution in a mill - sifting accumulating good, too coarse good in the grain and too fine good in the compacting. 8. Process according to claims 1 to 7, characterized in that a grain spectrum of about 0.2 to 2 mm is set in the finished product. 9. The method according to claims 1 to 8, characterized in that the granulate granules primarily obtained in the grain are subjected to a surface abrasion of corners and edges and thus in particular the bulk weight of the granular material is increased again. 10. The method according to claims 1 to 9, characterized in that mixing ratios are set within the following ranges:
20 to 75% by weight metasilicate
20 to 50 wt .-% STP and / or zeolite NaA
not more than 20% by weight of soda
not more than 10% by weight of water glass
not more than 10% by weight of other additives with 8 to 25% by weight of total water .; 11. The method according to claims 1 to 10, characterized in that mixing ratios are set within the following ranges:
35 to 65 wt .-%, preferably 40 to 60 wt .-% metasilicate, which is used at least partially as a hydrated metasilicate
25 to 40% by weight of STP and / or zeolite NaA (calculated as anhydrous substance)
not more than 10% by weight soda
not more than 7% by weight of water glass
no more than 7% by weight of other ingredients with about 10 to 20% by weight of total water. 12. The method according to claims 1 to 11, characterized in that in order to improve the flushability in the powdery batch non-hydrated STP and in the case of the use of larger amounts of zeolite NaA, this is used together with water-containing metasilicate, also by using higher pressure in the specified range the inductibility can be promoted. 13. Free-flowing alkaline cleaning agents, in particular for use in dishwashers based on water-containing agglomerates of sodium metasilicate in intimate admixture with STP and / or finely crystalline zeolite NaA as reinforcing builders, produced by the process of claims 1 to 12.