EP0224128B1 - Multilayered detergent tablets for mechanical dish-washing - Google Patents

Abstract

A multilayer detergent tablet for dishwashing machines based on alkali metal metasilicates, pentaalkali metal triphosphates, active chlorine compound, and surfactant. The tablet comprises a first cold water-soluble layer of alkali metal metasilicate nonahydrate, pentaalkali metal triphosphate, and a low-foaming nonionic surfactant; and a second layer which dissolves rapidly at increasing water temperatures comprising alkali metal metasilicate, pentaalkali metal triphosphate, and an active chlorine compound.

Description

Machine dishwashing generally consists of a pre-rinse cycle, a cleaning cycle, one or more intermediate rinse cycles, a rinse cycle and a drying cycle. This applies to machine washing in the home as well as in business.

So far, it has been common in household dishwashers, hereinafter referred to as HGSM, to store the detergent in a metering box, which is usually located in the door of the machine and opens automatically at the start of the cleaning cycle. The previous pre-rinse cycle is operated exclusively with the incoming cold tap water.

In the case of a commercial dishwasher, hereinafter referred to as GGSM, the pre-clearing zone corresponds in principle to the pre-rinse cycle of an HGSM. When machine washing in commercial kitchens, the cleaning agent added to the cleaning zone is used in the so-called pre-clearing zone to support, pre-clean the surfaces to be cleaned from the adhering food residues. There are also GGSM in which the pre-clearing zone is only operated with fresh water, but a pre-clearing zone with cleaning agent solution is more effective than pre-clearing with fresh water alone.

It was the aim of the present invention to transfer the broad principle of action of pre-clearing zone cleaning from GGSM to HGSM as well. Dosing was the first option of cleaning agents already viewed during the pre-rinse cycle. In tests using conventional HGSM cleaning agents, however, this had the consequence that, in addition to the usual metering of the cleaning agent, additional portions thereof had to be added to the machine via the metering box in the door. Now there is the problem that there are low-flow areas on the floor and in the base of the machine. As a result, the product has dissolved only insufficiently and has been pumped out virtually unused after the pre-rinse cycle has ended.

It does not make sense to sprinkle cleaning agents into the cutlery basket over the items to be washed, since irreversible damage can occur to silver and stainless steel parts.

Surprisingly, it has now been found that these disadvantages mentioned above do not occur when using detergent tablets. One or more tablets can be dosed, for example, in a free part of the cutlery basket, but also elsewhere in the machine.

The use of tablet-shaped cleaning agents is adequately described in the patent literature. For example, from DE-OS 16 17 088 tablets for automatic dishwashing, which are obtained by pressing a powdery mixture of sodium silicate with a ratio of Na₂O: SiO₂ such as 1: 3.25 to 2: 1 and a water content of 0 to 20% , polymeric alkali metal phosphates, active chlorine compounds, low-foaming non-ionic surfactants compatible with the active chlorine compounds, fillers such as alkali metal carbonates, chlorides or sulfates, white paraffin oil and tablet binders, which are said to be stable in storage and transportation.

Such tablets are also known from DE-OS 28 57 001 which contain essentially the same constituents, however should have a particularly high level of alkalinity, which can be achieved, inter alia, by adding alkali metal hydroxide. However, a high level of alkalinity is unsuitable for the use of the agents in the household because improper handling of the agents can lead to skin irritation and can also damage the decor.

According to the teaching of DE-OS 33 15 950, it is particularly advantageous for the required mechanical strength of detergent tablets and their high dissolution rate if one not only compresses the mere mixtures of the components, but first produces a cogranulate from their alkaline-reacting substances and then this after adding other substances and tabletting aids, pressed under high pressure.

At commercially available HGSM, all of these tablets were filled into the detergent dispenser, which is also intended for the addition of powdered or granular detergents, the automatic opening of which is only intended after the pre-wash cycle with cold tap water has ended. They then develop their full effectiveness after about 5 to 7 minutes when the water temperature rises during the cleaning cycle, which lasts for about 20 to 30 minutes, when their total amount has been washed out of the induction chamber into the cleaning liquor. When introducing the tablets, e.g. B. over the cutlery basket, they already came into the pre-rinse of the machine, but either led to increased decor damage due to too high alkalinity and / or dissolved too quickly and / or disintegrated too quickly and sank undissolved into the suds of the machine. This meant that there were no longer sufficient amounts of detergent available for the cleaning cycle.

The present invention was therefore based on the object of providing multilayer, in particular two-layer detergent tablets, the first layer of which cools due to the inlet Tap water largely dissolves in the pre-rinse cycle of the HGSM and there develops the highest possible alkalinity in combination with a good network effect. A second layer should correspond to the current detergent formulations for automatic dishwashing in the usual way and should therefore be equipped with an active chlorine carrier. At most, it should be slightly dissolved by the cold tap water in the pre-rinse cycle, but should dissolve completely in the HGSM wash cycle.

The invention thus relates to multilayer, in particular two-layer detergent tablets for machine dishwashing, containing alkali metasilicates and pentaalkalitriphosphates, active chlorine compounds, tabletting aids and, if appropriate, low-foaming nonionic surfactants, which are characterized in that they contain alkali metal silicate bisonahydrate and preferably 7 in a first, cold water-soluble layer up to 18% by weight of pentalkaliphosphate containing water of crystallization in a ratio of 0: 1 to 1: 0, preferably 0.35: 1 to 1: 1, based on the anhydrous substances, and optionally low-foaming nonionic surfactants and in a second, at increasing temperatures fast-dissolving layer, alkali metasilicate and pentaalkali metal phosphate, each preferably anhydrous, in a weight ratio of 2: 1 to 1: 2, preferably 1: 1 to 1.7: 1, based on anhydrous substances, and compounds containing active chlorine n included.

As stated, the alkali metal silicate used in the second layer is preferably the anhydrous product. However, a mixture of anhydrous metasilicate and its nonahydrate in a weight ratio of at most 1.2: 1 can also be used.

To determine the optimal composition of the differently soluble layers, the dissolving or disintegrating properties were determined of compressed detergent mixtures, in order to subsequently obtain a multilayer tablet with the desired dissolution profile by combining a composition which is readily soluble in cold water with a composition which is only soluble at increasing temperatures.

The desired dissolution profile of a two-layer tablet is to be understood as an almost complete dissolution of the 1st layer with a slight detachment of the 2nd layer in the pre-rinse cycle and a rapid and complete detachment of the remaining tablet in the cleaning cycle of all commercially available HGSMs with rising water temperatures.

The solubility (disintegration) of the tablets was carried out using a universal test device type E 70 from Engelsmann as follows:

Lying on a sieve with a mesh size of 2 mm, the tablets were moved up and down in water at 20 ° C. in such a way that they were at the highest point with the base just at the level of the water surface. The amount of water was 800 g, the number of strokes was 25 per minute. The time required for the disintegration or dissolution of the individual tablets was measured or, in the case of dissolution times of more than 5 minutes after 5 or 10 minutes, the residues remaining on the sieve were weighed out.

The results of the investigations are recorded in Table 1 a) and b). It can be seen from this that for the layer which rapidly dissolves in cold water, the raw materials sodium metasilicate nonahydrate and pentasodium triphosphate with a crystal water content of preferably 15 to 18% by weight can be used in granular form. A combination of the nonahydrate and the partially hydrated triphosphate was preferably suitable. When using these tablets came it with a precisely coordinated composition and appropriate compaction to disintegrate this layer with simultaneous dissolution of the falling particles (partially hydrated triphosphates and the metasilicate nonahydrate are very water-soluble). No undissolved particles could be found in the pumped-out suds from the pre-rinse cycle.

The wetting of the surfaces to be cleaned by the alkaline detergent components in the pre-rinse cycle can be improved by adding surfactants. Surfactants are usually incompatible with active chlorine-releasing compounds. However, their simultaneous use in a two-layer tablet without impairing the chlorine carrier is possible if the two compounds are separated from each other in a different layer. If used, the proportion of surfactant in the layer provided for the pre-rinse cycle is 0.5 to 10, preferably 1 to 5% by weight, based on the pre-rinse cycle layer. Suitable surfactant components are the known low-foaming nonionic surfactants, such as the ethoxylation products of long-chain alcohols and alkylphenols, where the free hydroxyl groups of the polyethylene glycol ether residue can be substituted by ether or acetal groups or by polypropylene glycol ether residues to reduce the tendency to foam. The block polymers of ethylene oxide with polypropylene oxide are also suitable.

The preferred tabletting aid is 0.5 to 2.5, preferably 1 to 2% by weight of calcium hydrogenphosphate dihydrate (to reduce segregation) and 1 to 5, preferably 2 to 3% by weight of sodium acetate, anhydrous (to prevent sticking) Tool parts) used. .

The proportions of these tabletting aids, which are safe from an application point of view with regard to cleaning performance, can be varied beyond the ranges mentioned in order to obtain a recipe to be able to optimally press door variants. The sodium acetate content also affects the solubility of the tablet. Higher amounts of sodium acetate lead to improved solubility in cold water in the pre-rinse cycle.

A further improvement in solubility can also be achieved by adding other water-soluble salts such as. B. sodium chloride can be achieved, but is usually not necessary with the appropriate choice of starting materials. Other usual tableting aids such as. B. lubricants to improve the compressibility (z. B. stearates, talc, glycerides, etc.), disintegrants (z. B. cellulose derivatives, attapulgite (Mg-Al-silicate) etc.) and other auxiliaries can be used in principle, they are undesirable from an application technology point of view and also burden the formulation (costs and additional inert fillers). These otherwise customary aids can be dispensed with in the production of tablets according to the present invention.

In order to clarify to the user the mode of action of the two-layer tablet, there is the possibility of staining a layer which is preferably provided for the pre-rinse cycle, although it has surprisingly been found that the compressed, colored raw materials can be less soluble than compressed, uncolored raw materials. Staining of sodium metasilicate nonahydrate had the least influence on solubility. You can dissolve or suspend the dye in the surfactant and spray it together with the nonahydrate, e.g. B. in a Lödige mixer. An aqueous dye solution can also be introduced with simultaneous drying using a fluidized bed process. The colored nonahydrate is then optionally mixed with other components and, after compression, leads to a uniformly colored tablet layer. For aesthetic reasons For reasons, the tablets can also be pressed in colored layers.

Tablets consisting of a mixture of anhydrous sodium metasilicate with a grain size of less than 0.8 mm and anhydrous pentasodium triphosphate are suitable for the cleaning cycle in the HGSM, whereby the dissolution profile of the tablets can be influenced by adding sodium metasilicate nonahydrate.

The compressibility of raw material mixtures containing almost anhydrous sodium metasilicate depends on the particle size distribution. With a fine grain fraction (less than 0.8 mm), good tabletting properties of the raw material mixture are obtained, while dust (less than 0.2 mm) and unscreened material (20 to 100% larger than 0.8 mm) lead to mixtures that are difficult to tablet . When using completely anhydrous metasilicates (e.g. manufactured after a sintering or melting process), the tablets are mechanically stable even after storage. When using hydrothermally produced metasilicate with a residual moisture content of approx. 2%, the grain size distribution did not play a decisive role. However, after the tablets had been stored under indoor climate conditions, the surface had weathered. Large tablets then also tend to crack. A residual moisture content of more than 2% in the metasilicate is therefore undesirable.

In addition to the quality of the metasilicates used, that of triphosphate also affects the compressibility. Dusty products lead to poorer compressibility compared to somewhat coarser grades.

Metasilicates in anhydrous form and as nonahydrate and also the anhydrous triphosphate are preferred in the form of their Na trium salts used. Their total amount in the mixture to be pressed for the cleaning cycle was 88 to 98, preferably 95 to 97% by weight.

Active chlorine carriers are also common components of cleaning agents for HGSM. Trichloroisocyanuric acid was preferred as the active chlorine carrier, but also other known solid compounds such as e.g. B. sodium dichloroisocyanurate, its dihydrate and potassium dichloroisocyanurate can be used in the marketable form without impairing the tablettability. Their amounts are generally 0.5 to 5.0, preferably 1.0 to 2.5% by weight, based on the total tableting mixture.

Finally, essentially the same tabletting aids are added to the cleaning aisle tablet layer as described for the pre-rinse layer, the amounts of which can also be varied.

Customary chlorine-stable dyes and fragrances can also be added to the tableting mixtures for the cleaning cycle.

On the basis of the results of the experiments described in Table 1 a) and b), it was possible to produce multilayer, in particular two-layer tablets, in which one tablet layer completely or almost completely in the pre-rinse cycle and the other layer only to a lesser extent in the pre-rinse cycle and then completely in HGSM cleaning cycle dissolved.

Tablets are pressed in two layers on rotary presses that are equipped with two dosing and two pressing stations (e.g. Fette / Perfecta 3002, Fette / P3, Kilian / RU-ZS). The first dosing station contains the mixture of the detergent layer, which is smaller in mass, generally for the pre-rinse cycle. It is used to fill in the rotating Matrices located matrices. This material is pre-compressed at the first press station. Subsequently, at the second dosing station, the pre-pressed 1st layer is overlaid with the second detergent mixture, which is then intended for the cleaning cycle. The two-layer tablet is pressed at the second pressing station and then pushed out of the die with the lower punch.

In the tests carried out and described below, this production method was reproduced manually on an eccentric press from Fette, type Exacta, as described below. The pressing conditions found correspond approximately to those of the rotary press.

The detergent layer for the pre-rinse cycle, which was smaller in mass, was filled into the die of the press and pre-compressed.

The upper punch was pulled out of the die by turning the handwheel backwards. The lower stamp, together with the pre-compacted mass, remained in the lowest position in the die. Now the detergent layer intended for the cleaning cycle was filled into the die and, together with the pre-rinse cycle cleaning layer already present, pressed into the tablet with the flexural strength required for the desired dissolution profile. Examples of the compacts obtained in this way and their properties are listed in Table 2. The layer intended for the pre-rinse cycle was referred to in the table as layer 1 and the layer provided for the cleaning cycle as layer 2.

The compression can be done with die lubrication, with usual lubricants such as. B. paraffin oil, almond oil or water or aqueous solutions can be used. The Depending on the design of the machine, lubrication was carried out directly through holes in the die, by spraying the lower punch or by means of felt rings soaked in lubricant on the lower punch. Lubrication may also be dispensed with in the case of raw material mixtures with particularly favorable pressing properties.

In order to avoid problems caused by sticking to the stamps, it is recommended to coat the stamps with plastics. Plexiglass or Vulkolan coatings have proven to be particularly favorable. Good results have also been achieved with other conventional materials.

The pressing conditions were optimized with regard to the setting of the desired dissolution profile with sufficient tablet hardness. The flexural strength served as a measure of the tablet hardness (method: cf. Ritschel, "Die Tablette", C. Contor, 1966, page 313). Tablets with a flexural strength greater than 117/6798 N (12 kp), preferably greater than 147.09975 N (15 kp), were sufficiently stable under simulated transport conditions.

Corresponding tablet hardnesses were at pressing pressures from 4905 .10⁴ up to 49050. 10⁴ Pa (500 up to 5000 kp / cm²), preferably 9810. 10⁴ to 14715. 10⁴ Pa (1000 to 1500 kp / cm²) reached. Higher pressures reduce the release speed. Differences in solubility in the case of different compositions can be compensated for to a limited extent by the choice of the pressing pressure (compare Table 2 / Examples 3 and 4).

The specific weight of the tablets differs in the layers due to the recipe; it is between 1 and 2 g / cm³, preferably between 1.2 and 1.4 g / cm³ for the pre-wash detergent layer and preferably between 1.4 and 1.7 g / cm³ for the main wash detergent layer. The specific weight of the total compact is preferably between 1.35 and 1.55 g / cm³.

The shape of the tablet can also influence the dissolution rate via the outer surface exposed to the H₂O attack. For reasons of stability, compacts with a diameter to height ratio of 0.6 to 1.5: 1, preferably 1: 1, were produced.

The weight of the single tablet can be varied within technically reasonable limits. Depending on the size of the tablets, 1, 2 or more are used. Tablets of 20 to 30 g in weight are preferred, two of which must be used. Larger tablets are generally more sensitive to breakage and, moreover, can be compressed at a lower speed, which leads to a loss in performance in their manufacture. In the case of smaller tablets, the handling advantage compared to powdered cleaning agents (simple dosing) would be reduced.

The two cleaning agent mixtures were first prepared in a conventional mixer (Lödige, Forberg), with layer 1 (for the pre-rinse cycle) spraying the nonahydrate with the nonionic containing the alizarin brilliant, pure blue, GLW before mixing.

The mixture was pressed on an eccentric press from Fette, type "Exacta 31" with pressing tools which are equipped with Vulkolan were coated. For this purpose, the lower punch of the press was first moved into the lowest point of the die and the mixture of layer 1 was poured into the die. Now the top punch was inserted into the bore of the die by actuating the handwheel so that the filled material was pre-compressed from 8.2 mm fill height to 6 mm. By turning the handwheel backwards, the upper punch was pulled out of the die without the pre-compressed mass being expelled through the lower punch. The mixture of layer 2 was then overlaid in the die. Depending on the density of the mixture of 0.89 g / cm³, the filling height of the second layer was 21.8 mm. After changing the immersion depth (by changing the eccentric setting), the tablet was pressed mechanically to a height of 17.3 mm. The height of layer 2 in the compact was 12.3 mm (density = 1.58 g / cm³), that of the 1st layer 2 mm (density = 1.31 g / cm³). The compression ratio of the total tablet was 1: 1.73.

The pressing pressure required for pressing was 13734. 10⁴ Pa (1400 kp / cm²). The tablets obtained had a flexural strength greater than 147.09975 N (15 kp). About 22% of the entire tablet detached when used in the pre-rinse cycle. Layer 1 was almost completely replaced after the pre-wash program. After the cleaning cycle, the tablet was completely dissolved. No cracks in the tablet or weathering of the surface were found after storage.

Numerous other tablets can be produced by combining the compositions 1 to 6 and 7 to 10 from Table 1 a) and b). Examples of this can be found in Table 2.

Since there are no suitable dosing devices for this type of use of dish detergents in the machines currently on the market, the multi-layer detergent tablets can be opened into one before the start of the pre-rinse cycle Zone which exposes the tablets to the dissolving power of the tap water flow, e.g. B. in the cutlery basket of a household dishwasher, and the automatically controlled cleaning process can be started.

The invention therefore also relates to the use of the multilayer detergent tablets for cleaning dishes in automatic household dishwashers, which is characterized in that the tablets are opened in the machine even before the start of the pre-wash cycle in a zone which exposes the tablets to the dissolving power of the tap water inflow of the pre-wash cycle , for example by placing it in the cutlery basket, and then initiating the automatically controlled cleaning process.

Claims (7)

1. Multilayer, more especially two-layer, detergent tab­lets for dishwashing machines containing alkali metasil­icates and pentaalkali triphosphates, active chlorine com­pounds, tabletting aids and optionally low-foaming nonionic surfactants, characterized in that, in a first cold-water­soluble layer, they contain alkali metasilicate nonahydrate and pentaalkali triphosphate containing from 7 to 22.4% by weight and preferably from 15 to 18% by weight water of crystallization in a ratio of from 0:1 to 1: 0 and preferab­ly from 0.35: 1 to 1: 1, based on the anhydrous compounds, and optionally low-foaming nonionic surfactants and, in a second layer which dissolves rapidly at increasing tempera­tures, alkali metasilicate and pentaalkali triphosphate, both preferably anhydrous, in a ratio by weight of from 2: 1 to 1: 2 and preferably from 1: 1 to 1.7: 1, based on anhydrous compounds, and active chlorine compounds.

2. Detergent tablets as claimed in claim 1, characterized in that the first layer contains 0.5 to 10% by weight and preferably 1 to 5% by weight low-foaming nonionic surfac­tants.

3. Detergent tablets as claimed in claim 1, characterized in that the first layer is coloured.

4. Detergent tablets as claimed in claims 1 and 2, characterized in that the alkali metasilicate nonahydrate is coloured.

5. Detergent tablets as claimed in claims 1 and 3, characterized in that the alkali metasilicate nonahydrate is coloured by a dye-containing, low-foaming nonionic surfactant.

6. Detergent tablets as claimed in claim 1, characterized in that the anhydrous alkali metasilicate of the second layer is mixed with its nonahydrate in a ratio by weight of at most 1.2: 1.

7. The use of the multilayer detergent tablets claimed in claims 1 to 6 for dishwashing in automatic domestic dish­washing machines, characterized in that the tablets are introduced after opening into a zone, which exposes the tablets to the dissolving power of the stream of cold tap­water, before the beginning of the prerinse cycle and the automatically controlled dishwashing process is subsequent­ly started.