EP0224129A2 - Uniformly composed detergent tablets for mechanical dish-washing - Google Patents

Abstract

Tablets having a broad solubility profile containing a mixture of sodium metasilicate nonahydrate and anhydrous sodium metasilicate with a grain size of from 0.2 to 0.8 mm in a ratio by weight of from 1:0.75 to 1:1.2, anhydrous pentasodium triphosphate having a grain diameter of 0.2 to 0.3 mm, and 0.5 to 5% by weight of an active chlorine donor. The ratio by weight of pentasodium triphosphate to metasilicates is about 1:1 to 1:1.7, based on anhydrous substances. The tablets are used in automatic dishwashing machines where they are introduced into a free zone of the machine before the start of the prerinse cycle, at least 10% of the tablets being dissolved by inflowing cold water and at least another 70% being available in the main-wash cycle.

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 canteen kitchens, the cleaning agent added to the cleaning zone is already used in the so-called pre-clearing zone to support the cleaning of 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 principle of pre-clearing zone cleaning from GGSM to HGSM as well. Dosage of detergents in the pre-rinse cycle was seen as an option.

In tests using conventional HGSM cleaning agents, this had the consequence that, in addition to the 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 was only insufficiently dissolved and was pumped out practically unused after the pre-rinse cycle.

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 the detergent tablets according to the invention. 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-0S 16 17 088 tablets for machine dishwashing are known which, by pressing a powdery mixture of sodium silicate with a Na₂0: Si0₂ ratio of 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-0S 28 57 001 which contain essentially the same constituents but one should have particularly high 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 also damage the decor.

According to the teaching of DE-0S 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 its alkaline 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-rinse cycle with cold tap water. 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. on the cutlery basket, they already came into the pre-rinse of the machine, but either led to increased decor damage due to excessive alkalinity and / or dissolved too quickly and sank into the suds of the machine. As a result, they were no longer sufficiently available for the cleaning cycle.

The present invention was therefore based on the object of developing a tablet with a broad dissolving profile that already in the pre-rinse cycle of an HGSM from the incoming cold tap water at least 10% by weight is dissolved, a pH of at least 10.0 developed in the rinsing liquor and at least 65% by weight, preferably at least 70% by weight, is still available for the cleaning cycle if it is well soluble in hot water .

The dissolution profile here means the ratio of portions of the tablet dissolved from the usual HGSM under the conditions of the pre-rinse cycle to the entire tablet.

The object was achieved by uniformly composed detergent tablets with a broad dissolution profile for automatic dishwashing, containing customary alkaline components, in particular from the group of alkali metal silicates and pentaalkali metal phosphates, active chlorine compounds and tabletting aids, which are characterized in that the alkali metal silicates are composed of a mixture of sodium metasilicate and water-free silicate Sodium metasilicate and the pentaalkali phosphate consists of anhydrous pentasodium triphosphate, the weight ratio of anhydrous sodium metasilicate to nonahydrate being between 1: 0.3 to 1: 1.5.

The dissolution profile can be varied within wide limits by varying the ratio of sodium metasilicate, anhydrous to nonahydrate. The weight ratio of anhydrous sodium metasilicate to nonahydrate is preferably between 1: 0.75 to 1: 1.2.

In order to achieve good cleaning performance, a balanced formulation with regard to the alkali metal silicate and the pentaalkali phosphate content must be observed. The amounts of pentasodium triphosphate to sodium metasilicate, in each case anhydrous, should be present in a ratio of 2: 1 to 1: 2, preferably from 1: 1 to 1: 1.7.

Active chlorine carriers are also common components of cleaning agents for HGSM. Finally, tableting aids are added, the amounts of which can be varied.

While the nature of the sodium metasilicate nonahydrate is essentially problem-free, the compressibility of raw material mixtures containing anhydrous sodium metasilicate depends on its particle size distribution, its production process, its weight ratio to the nonahydrate present at the same time and on the average particle size of the pentasodium triphosphate. With a grain fraction of the almost water-free sodium metasilicate (e.g. from a sintering or melting process) of less than 0.8 mm, good tableting properties of the raw material mixture can be obtained without or with only small additions of nonahydrate (to adjust the dissolution profile). When using dust (less than 0.2 mm) or unscreened material with 20 to 100% coarser coarsely 0.8 mm, the nonahydrate should be used at least 1.2 times the amount of the water-free metasilicate in order to achieve comparable tablet properties .

When using dust-like pentasodium triphosphate with an average grain diameter of less than 0.1 mm, the compressibility deteriorates. It is therefore preferable to use a triphosphate with an average grain diameter of 0.2 to 0.3 mm.

The use of hydrothermally produced metasilicate with a residual water content of approx. 2% leads to very well compressible raw material mixtures. In contrast to the tablets made with almost water-free metasilicate, however, these were not stable in storage. The surface of the tablets became rough, even cracking occurred with larger tablets. Therefore the use of this metasilicate containing residual moisture is undesirable.

Alkali metasilicate in anhydrous form and as a nonahydrate and also the preferably anhydrous pentaalkali metal phosphate were used in the form of their sodium salts. Their total amount in the mixture to be pressed was 88 to 98, preferably 95 to 97% by weight.

Trichloroisocyanuric acid was preferred as the active chlorine carrier, but also other known solid compounds, such as. B. sodium dichloroisocyanurate, its dihydrate and potassium dichloroisocyanurate can be used in the marketable form without impairing the tablettability. Their amounts are 0.5 to 5.0, preferably 1.0 to 2.5% by weight, based on the active chlorine content and the total tableting mixture.

A mixture of 0.5 to 2.0, preferably 1.0% by weight, based on the entire tablet mixture, of calcium hydrogenphosphate dihydrate (to reduce segregation) and 1.0 to 5.0, preferably 2, was used as the tabletting aid , 0 to 3.0 wt .-%, based on the entire tableting mixture, of anhydrous sodium acetate (to reduce sticking to tool parts) added. The proportions of these tabletting aids, which are safe from an application point of view in terms of their cleaning performance, can be varied beyond the ranges mentioned in order to be able to optimally compress recipe variants. The sodium acetate content also affects the solubility of the tablet. Higher amounts of sodium acetate lead in particular to improved cold water solubility in the pre-rinse cycle. Other conventional tabletting aids such as lubricants to improve the compressibility (stearates, talc, glycerides etc.) and other aids can in principle also be used, but they are undesirable from an application point of view and, moreover, burden the formulation with costs and are only inert fillers Application of this otherwise usual auxiliary agents are not required in the manufacture of tablets according to the present invention.

Customary chlorine-stable colors and fragrances can also be added to the tableting mixtures. For aesthetic reasons, the tablets can also be pressed in colored layers with otherwise the same composition.

The mixture of the fine-grained, anhydrous metasilicates, the corresponding nonahydrates, the triphosphates, active chlorine carriers and tabletting aids can be pressed under die lubrication, with conventional lubricants being used. Depending on the design of the machine, lubrication is 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. With the raw material mixtures according to the invention with their particularly favorable compressibility properties, however, the lubrication can usually also be dispensed with.

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

The pressing conditions must be optimized with a view to setting the desired dissolution profile while at the same time having sufficient tablet hardness. The flexural strength can serve as a measure of the tablet hardness (method: compare Ritschel. Die Tablette, Ed. Cantor, 1966, p. 313). Tablets with a flexural strength greater than 12 kp, preferably greater than 15 kp, are sufficiently stable under simulated transport conditions.

Corresponding tablet hardnesses have been achieved at compression pressures of 500 to 5,000 kp / cm², preferably 1,000 to 1,500 kp / cm². Higher pressures reduce the release speed. Differences in solubility can be compensated within limits for different compositions by choosing the pressure.

The specific weight of the compacts was between 1.2 and 2 g / cm³, preferably between 1.4 and 1.7 g / cm³. The compression during the pressing process caused changes in the specific volume, that of 0.8 to 1.8 cm³ / g, preferably 1.0 to 1.4 cm³ / g to 0.5 to 0.8 cm³ / g, preferably 0.6 decreased to 0.7 cm³ / g.

The shape of the tablet can also influence the dissolving speed via the outer surface exposed to the H₂0 attack. For stability reasons, cylindrical compacts with a diameter / height ratio of 0.6 to 1.5: 1 were produced.

The amounts of the substance mixture to be compressed for the individual tablets can be varied as desired within technically reasonable limits. Depending on their size, 1, 2 or more tablets per machine filling are used to provide the entire cleaning process with the necessary active substance content of cleaning agent. Tablets of 20 to 30 g in weight are preferred, two of which must be used. Larger tablets are usually more sensitive to breakage and, moreover, are compressed at a lower speed, which leads to a loss of performance in the production process. With smaller tablets, the handling advantage compared to granular or powder detergents would be reduced.

The described compositions can be pressed in a known manner using commercially available eccentric presses or rotary presses.

Since there are no suitable dosing devices for this type of use of dishwashing detergents in the machines currently on the market, the tablets can be placed in a cutlery basket of a household dishwasher before opening the pre-rinse cycle into a zone that exposes the tablets to the dissolving power of the tap water flow the automatically controlled cleaning process can be started.

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

The dishes cleaned in this way have better cleaning results for difficult soiling, such as, for example, burnt-on milk or baked oatmeal, than those treated in the conventional manner.

Examples

For better comparison of the recipe variants, tablets with the same diameter and the same content of active substances sodium triphosphate, trichloroisocyanuric acid and sodium metasilicate, water-free, were produced, which weighed between approx. 20 g and 27 g. The different weights are due to the varying content of water of crystallization and tableting aids. The tablet format was also varied with selected recipes.

example 1

28.8% by weight sodium metasilicate, anhydrous, not sieved
33.6% by weight sodium metasilicate nonahydrate
33.6% by weight sodium triphosphate, anhydrous
1.0% by weight of trichloroisocyanuric acid
3.0% by weight sodium acetate, anhydrous
25 mm tablet diameter
20 g tablet weight

The mixture was pressed on an eccentric press from Fette, type "Exacta 31". The pressing tools were coated with Vulkolan. When pressed to a density of 1.58 g / cm³, tablets with a flexural strength greater than 15 kp were obtained, which dissolved to 25% by weight in the pre-rinse cycle and completely in the cleaning cycle.

Example 2

33.7% by weight sodium metasilicate, anhydrous (less than 0.8 mm)
26.3% by weight sodium metasilicate non-hydrate
35.0% by weight sodium triphosphate, anhydrous
1.0% by weight of trichloroisocyanuric acid
1.0% by weight calcium hydrogen phosphate dihydrate
3.0% by weight sodium acetate, anhydrous
35 mm tablet diameter
25 g tablet weight

The mixture was pressed on an eccentric press from Fette, "Exacta 31". The pressing tools were coated with Vulkolan. In order to be able to produce tablets weighing 25 g, a filling height of 30.8 mm was required with a die diameter of 35 mm. This corresponded to a specific volume of 1.18 cm³ / g. A depth of 14.5 mm was necessary to produce the tablet. This then corresponded to a tablet height of 16.3 mm or a specific volume of 0.62 cm³ / g. The compression ratio was therefore 1: 1.9. However, the actual tablet height after manufacture was 17.7 mm. This can be explained by the fact that the tablets can generally be expected to grow slightly after relaxation.

The specific volume of the tablet obtained was thus 0.68 cm³ / g (density = 1.47 g / cm³). This corresponds to a compression ratio of 1: 1.74. The pressing pressure required for pressing was 1,300 kp / cm². The tablets obtained had a flexural strength of greater than 15 kp and dissolved up to 14% by weight in the pre-rinse cycle and completely in the cleaning cycle.

After 8 months of storage in a sealed container at room temperature, no cracks in the tablet and no weathering of the tablet surface were found.

Example 3

The omission of tableting aids and the corresponding variation of the metasilicate components with anhydrous product to 30.7% by weight and nonahydrate to 33.3% by weight led to a dissolution of 40% by weight of the tablet in the pre-rinse cycle when processed analogously to Example 2 with total resolution in the cleaning cycle. During the manufacture of these tablets, however, there were slight signs of sticking in the matrix.

The examples can be varied as desired within the scope of the invention. The above selected are not meant to be conclusive.

Example 4

33.0% by weight sodium metasilicate with 2% residual moisture
28.0% by weight sodium metasilicate nonahydrate
35.0% by weight sodium triphosphate, anhydrous
1.0% by weight of trichloroisocyanuric acid
2.0% by weight sodium acetate, anhydrous
1.0% by weight calcium hydrogen phosphate dihydrate
25 mm tablet diameter
20.3 g tablet weight

The ingredients were mixed in a Lödige mixer.

The mixture was pressed on an eccentric press from Fette, type "Exacta". The pressing tools were coated with Vulkolan. When pressed to a density of 1.56 g / cm³, tablets with a flexural strength (Ritschel, "Die Tablette, page 313) of 13.5 kp were obtained, which were added to tap water by approx. 20% by weight in the pre-rinse cycle of an HGSM. % and completely dissolve in the 40 ° C cleaning program.

Paraffin oil lubrication of the tools was not necessary. The omission of calcium hydrogenphosphate dihydrate led to a dissolution of 25% by weight of the tablet in the pre-rinse cycle and to a 97% by weight total dissolution. However, the residual moisture content caused the surface to show signs of weathering when the tablets were stored.

Example 5

The mixture composition, the tablet weight and the tablet diameter were chosen as in Example 4, but in contrast to Example 4, the density was 1.63 g / cm 3. The bending ability here was greater than 15 kp. When completely dissolved in the 40 ° C cleaning cycle, 12% of the tablet was dissolved after the pre-rinse cycle. With excellent manufacturing and application properties, weathering of the tablet surface was also evident here during storage.

Example 6

Composition as in Example 4.
40 mm tablet diameter
50 g tablet weight

The weight was pressed on an eccentric press from Fette, type "Exacta 31", in which the pressing tools were coated with Vulkolan. When pressed to a density of 1.53 g / cm³, tablets with a flexural strength greater than 15 kp were obtained, which dissolved in the pre-rinse cycle to 14% by weight and in the cleaning program to 97% by weight.

After 8 months of storage in sealed containers at room temperature, this resulted in undesirable crack formation and weathering of the surface.

Example 7

33.0% by weight sodium metasilicate, anhydrous (less than 0.8 mm)
28.0% by weight sodium metasilicate nonahydrate
35.0% by weight sodium triphosphate, anhydrous
3.0% by weight sodium acetate, anhydrous
1.0% by weight calcium hydrogen phosphate dihydrate
25 mm tablet diameter
6.7 g tablet weight

The mixture was pressed on a rotary press from Fette, type "Perfecta 2" with plexiglass-coated tools. The mixture was produced continuously on belt scales in a rack mixer, type "GAC 350". The die was filled by a "Fil-o-Matic" from Fette. Caking of the material was avoided by paraffin oil lubrication (soaked felt rings on the lower punches). When compressed to a density of 1.52, tablets with a flexural strength greater than 15 kp were obtained.

Claims (7)

1. Uniformly composed detergent tablets with a broad dissolving profile for machine dishwashing, containing customary alkaline components, in particular from the group of alkali metal silicates and pentaalkali metal phosphates, active chlorine compounds and tabletting aids, characterized in that the alkali metal silicates are made from a mixture of sodium metasilicate nonahydrate and anhydrous anhydrous pentasodium triphosphate, the weight ratio of anhydrous sodium metasilicate: sodium metasilicate nonahydrate being between 1: 0.3 and 1: 1.5. 2. Tablets according to claim 1, characterized in that the mixing ratio of anhydrous sodium metasilicate to sodium metasilicate nonahydrate is between 1: 0.75 and 1: 1.2. 3. Tablets according to claims 1 and 2, characterized in that the weight ratio of pentasodium triphosphate to metasilicate, in each case anhydrous, is 2: 1 to 1: 2, preferably 1: 1 to 1: 1.7. 4. Tablets according to claims 1 to 3, characterized in that the particle size distribution of the anhydrous sodium metasilicate is between 0.01 and 2.0, preferably between 0.2 and 0.8 mm. 5. Tablets according to claims 1 to 4, characterized in that the average grain diameter of the anhydrous pentasodium triphosphate is greater than 0.1 mm and is preferably between 0.2 and 0.3 mm. 6. Tablets according to claims 1 to 5, characterized in that they contain 0.5 to 5.0, preferably 1.0 to 2.5 wt .-%, based on the active chlorine content and the entire tableting mixture of active chlorine carriers. 7. Use of the detergent tablets according to claims 1 to 6 for cleaning dishes in automatic household dishwashers, characterized in that the tablets before the start of the pre-wash cycle in the machine open into a zone which exposes the tablets to the dissolving power of the cold tap water inflow and then starts the automatically controlled cleaning process.