Block-form detergent free from alkali hydroxides for use in dishwashing machines and a process for its production

A block-form detergent free of alkali metal hydroxides for use in dishwashing machines which contain from 65 to 85% by weight to a mixture of anhydrous sodium metasilicate and anhydrous pentasodium triphosphate in a ratio of from 1:1 to 1:2 and from 0.2 to 4% by weight of uniformly distributed active chlorine donors which are, for example, trichloroisocyanuric acid. The production process comprises heating sodium metasilicate to 45.degree. to 55.degree. C. to obtain a clear melt and then adding other constituents, the pentasodium triphosphate and the active chlorine donor being added last, and pouring the melt into flexible molds in which it is left to solidify into blocks. The detergents are stable for storage with good dissolving power.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
Powder-form, granular or tableted detergents for dishwashing machines 
consist essentially of pentasodium triphosphate, alkali silicate, mainly 
alkali metasilicate, and optionally a low-foaming, preferably 
chlorine-stable, nonionic surfactant and bleaches, preferably those which 
release active chlorine in aqueous solution. They are used above all to 
facilitate the removal of tea, coffee or fruit juice stains. 
Because of their high content of alkali silicates and pentasodium 
triphosphate, the detergents are strongly alkaline, their in-use solutions 
having a pH value of from about 11 to 12. Sodium hydroxide is not added 
because, in view of the normal contact times in domestic dishwashing 
machines, porcelain, glazed-on decorative patterns and glasses would be 
affected by the high alkalinity. This phenomenon is known as corrosion. By 
contrast, silicate synergistically supports the detergent effect of the 
triphosphate and inhibits corrosion in certain concentrations in the 
triphosphate/silicate mixture. 
Known detergents of the type in question are generally produced by standard 
methods, such as mixing or granulation. In powder form or granulate form, 
they are also used in the usual concentrations, i.e. in quantities of from 
about 30 to 50 g per machine load. 
2. Description of the Prior Art 
Powder-form or granular detergents of the type in question are described, 
for example, in British Pat. No. 1,442,885 and in U.S. Pat. Nos. 
3,816,320, 3,936,386, 3,933,670, and 4,083,795. 
U.S. Pat. No. 3,390,092 discloses disc-like tablets which are produced from 
simple mixtures of known detergent ingredients using a tabletting aid. 
Tablets of the type mentioned above are also described in U.S. Pat. No. 
4,219,436. The content of alkaline components (hereinafter referred to as 
active substance [AS]), including the proportion of alkali silicates and 
pentaalkalitriphosphates, is of the order of 65 to 95% by weight, based on 
the tablets as a whole. Accordingly, detergent tablets such as these based 
on compressed raw materials fully correspond in their composition to 
powder-form or granular detergents. 
The disadvantage of producing a tablet based on compressed individual 
components is that mechanical strength is inverse to the dissolving rate. 
Because of this tabletting aids and so-called disintegrating agents have 
to be added. Their function is, on the one hand, to ensure homogeneity of 
the powder-form or granulated raw materials during the compression molding 
operation and, on the other hand, to facilitate disintegration of the 
tablet on contact with water by swelling of the disintegrating agent, so 
that better solubility is obtained. However, neither additive is of any 
value to the washing process as such, in other words, the additives in 
question reprsent ballast and, in addition, take time to incorporate in 
the detergent. 
U.S. Pat. No. 2,412,819 describes briquetted detergents for dishwashing 
machines which are produced simply by mixing together all the 
alkaline-reacting active substances, such as for example up to 65% by 
weight, based on the detergent as a whole, of sodium silicates and 
pentasodium triphosphate and, if necessary, water if the preferred water 
of hydration of the compounds mentioned is not sufficient, and then gently 
heating the mixture with stirring to 90.degree.-100.degree. C. until a 
uniformly molten mass is obtained, subsequently pouring the melt thus 
formed into molds and leaving it to solidify into a compact crystal 
aggregate. No additions of active chlorine donors are mentioned in U.S. 
Pat. No. 2,412,819. This is understandable because the detergents 
themselves are strongly alkaline and, like many substances which it would 
be desirable to add, but which are sensitive to alkali, the active 
chlorine donors would be inactivated during the actual fusion process. 
Detergents in the form of fused blocks for dishwashing machines are also 
described in European Pat. No. 3,769. In most cases, the detergents 
described contain large amounts of alkali hydroxides. However, Example 8 
discloses a composition which is free from alkali hydroxides and although, 
in that example, the active chlorine donor is stirred directly into the 
subsequently solidifying aqueous solution of the ingredients, the chlorine 
donor is generally added in the form of a separate core. In this example, 
the AS-content is only 60% by weight, based on the detergent as a whole, 
which is too low for use in domestic dishwashing machines. Since the 
patent specification repeatedly mentions, even in comparison tests, the 
well known sensitivity of active chlorine donors to alkalis, it can not be 
assumed that active chlorine donors can be directly incorporated into 
strongly alkaline block-form detergents free from alkali hydroxides. 
BRIEF STATEMENT OF INVENTION 
It has now surprisingly been found that it is possible by the fusion 
process to obtain block-form detergents free of alkali metal hydroxides 
for use in dish washing machines which contain from about 65 to about 85% 
by weight, preferably from about 70 to about 80% by weight, based on the 
weight of the detergent as a whole, of a mixture of alkali metal silicates 
and pentaalkalitriphosphates and also, in uniform distribution, organic 
active chlorine donors. 
DETAILED DESCRIPTION OF THE INVENTION 
Other than in the operating examples, or where otherwise indicated, all 
numbers expressing quantities of ingredients or reaction conditions used 
herein are to be understood as modified in all instances by the term 
"about." 
Accordingly, the present invention relates to detergents in the form of 
fused blocks free from alkali metal hydroxides for use in dishwashing 
machines, containing from about 65 to about 85% by weight, and preferably 
from about 70 to about 80% by weight, based on the weight of the detergent 
as a whole, of a mixture of alkali metal silicates and 
pentaalkalitriphosphates and, in uniform distribution, active chlorine 
donors. 
Preferred alkali metal silicates are alkali metasilicates, advantageously 
in the form of sodium metasilicate.9H.sub.2 O, sodium 
metasilicate.6H.sub.2 O and sodium metasilicates 5H.sub.2 O. The 
quantities of silicates used amount to between about 5 and about 60% by 
weight, and preferably to between about 10 and about 50% by weight, based 
on the detergent as a whole. However, the alkali metal metasilicates 
containing water of hydration may even be partly replaced by the anhydrous 
compound and such replacement is desirable because high active substance 
contents can be adjusted in this way for an optimal ratio of alkali 
silicate to pentaalkalitriphosphate. 
The pentaalkalitriphosphate used is in an amount of from about 5 to about 
50% by weight, and preferably from about 5 to about 45% by weight, based 
on the detergent as a whole. The pentaalkalitriphosphate is used as 
hexahydrate or as a mixture of hexahydrate with small quantities of 
anhydrous pentasodium triphosphate calculated to give a total water 
content of about 5.5 moles. In this case, too, anhydrous compounds may be 
used to obtain optimal active substance combinations and contents. 
The optimal ratio of pentasodium triphosphate to sodium metasilicate (both 
anhydrous) is from about 1:1 to about 1:2, and preferably from about 1:1 
to about 1:1.7. 
Suitable organic active chlorine donors for use in the invention are the 
various chlorinated compounds of isocyanuric acid, such as 
trichloroisocyanuric acid (TICA), Na/K-dichloroisocyanurate, Na-dichloro 
isocyanurate dihydrate (Na-DCC-2H.sub.2 O). Also useful are chlorine 
donors such as Na-monochloroamidosulfonate (=N-chlorosulfamate) and sodium 
N-chloro-p-toluene sulfonic acid amide ("Chloramine T"). Inorganic active 
chlorine donors, such as for example chloride of lime, lithium or calcium 
hypochlorite, may also be used, but the organic chlorine donors are 
preferred. These chlorine donors are used in quantities of from about 0.2 
to about 4% by weight, and preferably in quantities of from about 0.5 to 
about 2% by weight based on the active chlorine content of the detergent 
and may be determined for example by iosometric titration. 
The total water content of the block-form detergent is from about 11 to 
about 34.8% by weight, and preferably from about 18 to about 29.5% by 
weight and is preferably introduced by the water of crystallization 
content of the alkaline-reacting active substances. Accordingly, any 
calculation of the water content must be based on these compounds. 
Although small quantities of free water may be added to balance the 
weight, they do not fall within the scope of the invention. 
It has been found that it is possible to work at lower and, therefore, 
safer temperatures than in the prior art, namely at about 45.degree. to 
about 60.degree. C., and preferably at about 50.degree. to about 
55.degree. C., providing the sodium metasilicate.9H.sub.2 O is first 
heated at between 45.degree.-55.degree. C. to form a melt and the other 
constituents, optionally containing water of hydration, are then added 
with stirring or kneading, the pentasodium triphosphate derivative and the 
active chlorine donors being added last, and the still liquid melt is then 
poured into preferably flexible molds of any shape and allowed to solidify 
into blocks. 
The solidification process can take from a few minutes to approximately 1 
hour, depending on the size of the mold. Depending on their composition, 
the fused blocks are very hard, hard, or not very hard, but in any case 
have a uniform composition throughout and dissolve quickly in use.

EXAMPLES 
Example 1 
Quantities of 150 g of detergents having the following compositions were 
prepared (figures in % by weight): 
______________________________________ 
1a 1b 1c 
______________________________________ 
Na.sub.2 SiO.sub.3.9 H.sub.2 O 
52.3 49.5 46.5 
Na.sub.2 SiO.sub.3 
18.5 20.6 22.8 
Na.sub.5 P.sub.3 O.sub.10 
28.2 28.9 29.6 
Trichloroisocyanuric acid 
1.0 1.0 1.0 
______________________________________ 
The Na.sub.2 SiO.sub.3.9H.sub.2 O was first heated to about 53.degree. C. 
until a clear melt was formed. After addition of the other active 
ingredients, the melt was thoroughly stirred and poured into molds in 
which it solidified in a few minutes. 
The active substance (AS) content as defined above was as follows: 
______________________________________ 
1a 1b 1c 
______________________________________ 
AS (Alkaline components as 
68.7% 70.3% 72.0% 
active substance) 
______________________________________ 
After 24 hours, the active chlorine (A-Cl) content was determined, the 
theoretically calculated value being obtained for all three compositions. 
______________________________________ 
1a 1b 1c 
______________________________________ 
% A--Cl (theoretical) 
0.91 0.91 0.91 
Found 0.90 0.88 0.94 
______________________________________ 
Example 2 
A detergent having the following composition (figures in % by weight) was 
prepared in a quantity of 150 g: 
______________________________________ 
Na.sub.2 SiO.sub.3 18.0% 
Na.sub.2 SiO.sub.3.5 H.sub.2 O 
14.0% 
Na.sub.2 SiO.sub.3.9 H.sub.2 O 
36.0% 
Na.sub.5 P.sub.3 O.sub.10 
31.0% 
Trichloroisocyanuric acid 
1.0% 
______________________________________ 
In this case, as in Example 1, Na.sub.2 SiO.sub.3.9H.sub.2 O was heated 
together with Na.sub.2 SiO.sub.3.5H.sub.2 O to about 53.degree. C. until a 
clear melt was formed. After addition of the other components, the melt 
was thoroughly stirred and poured into molds in which it solidified in a 
few minutes. 
The active substances (AS) content amounted to 72.5%. 
After 24 hours, the active chlorine content was determined and amounted to 
0.93% (theoretical 0.91%). 
Example 3 
In order to demonstrate the superiority of the detergents according to the 
invention to the detergents according to European Pat. No. 3,769, a fused 
block having the following composition (figures in % by weight) was 
prepared: 
______________________________________ 
Na.sub.2 SiO.sub.3.9 H.sub.2 O 
53.0% 
Na.sub.2 SiO.sub.3.5 H.sub.2 O 
18.6% 
Na.sub.5 P.sub.3 O.sub.10 
26.0% 
Na--dichloroisocyanurate dihydrate 
2.4% 
______________________________________ 
The detergent block was prepared as described in Example 2. By using a 
combination of Na.sub.2 SiO.sub.3.9H.sub.2 O and Na.sub.2 
SiO.sub.3.5H.sub.2 O, its composition was adjusted in such a way that, 
overall, the same quantities of water were present as in Example 8 of 
European Pat. No. 3,769. It was found that, to prepare the melt according 
to this Example 8, the suspension had to be stirred for about 30 minutes 
at 55.degree. to 60.degree. C. until it began to turn viscous and could be 
poured into molds. Measures such as these are cost-intensive and therefore 
impracticable for commercial processes. Storage at 25.degree. C./85% 
relative humidity produced the following losses of active chlorine: 
______________________________________ 
European Patent 
No. 3,769 
Example 3 
(Example 8) 
Loss Loss 
______________________________________ 
5 weeks 38% 85% 
12 weeks 49% 100% 
______________________________________ 
The results illustrate a clear advantage for the present invention. In this 
connection, it is important to bear in mind that compositions containing 
less water show even better stability.