MACHINE DISHWASHING COMPOSITION

Abstract: An enzyme-containing machine diswashing detergent composition which, in addition to conventional additives, such as dyes, perfume and the like, contains alkali metal silicate, alkali metal phosphate, surfactant and, optionally, a hydrogen peroxide-based bleaching agent. The composition is characterised in that it contains an enzyme, preferably amylase, and that at least half of the alkali metal silicate and at least a part of the alkali metal phosphate are present in the form of two-layer granules having a core of alkali metal silicate surrounded by an outer shell of alkali metal phosphate. The weight ratio alkali metal silicate: alkali metal phosphate in the two-layer granules preferably is from 80:20 to 40:60, and the composition contains, calculated on its total weight, preferably 40-99% by weight of two-layer granules, 1-4% by weight of surfactant and 0-15% by weight of bleaching agent, the balance being additives.

Description: MACHINE DISHWASHING COMPOSITION The present invention relates to a machine dish¬ washing composition, more particularly to an enzyme- containing machine dishwashing composition which in¬ cludes, besides conventional additives, alkali metal silicate, alkali metal phosphate, surfactant and, prefer¬ ably, bleaching agent. Known machine dishwashing detergents typically contain alkali metal silicate, alkali metal phosphate, surfactant, blea ' ching agent and conventional additives. The alkali metal silicate normally is a sodium silicate having a molar ratio SiO_:Na O of between 3.50 and 0.75. Usually, use is made of so-called sodium eta- silicate, which implies that the said ratio is about 1. The sodium metasilicate may be either practically anhy- drous or be present as a hydrate. There are four known hydrates, the commercially most widely used hydrate being the crystal form called pentahydrate. The silicate has for its object on the one hand to act as an inhibitor against attack on glass, gla^e and metals and, on the other hand, to supply the need for alkali in the dish¬ water. The high pH-value of the dishwashing solution obtained from the silicate contributes efficiently to the decomposition of hydrolysable food residues, such as fat, protein and starch. The alkali metal phosphate usually consists of tri- poJyphosphate whose main function is to act as a complex- ing agent for the hardness generating substance of the ' water, primarily calcium and magnesium ions. The tripoly- phosphate furthermore has a not inconsiderable dirt dissolving and dispersing effect. The alkali metal silicate and the alkali metal phosphate are the two main components of conventional machine dishwashing compositions. and usually each amount to 30-60% by weight of the total formulation. The surfactantusually is a nonionic surfactant, preferably a block polymer of ethylene and propylene oxide. Its task is to contribute to wetting and emulsifi- cation, simultaneously as it shall have an antifoaming effect on, for example, proteins. The bleaching agent normally consists of organic chlorine compounds functioning as an oxidative bleaching agent which has the task of attacking deposits of, inter alia, coffee, tea and fruit juices. When the compound comes into contact with water, it gives off chlorine which acts not only as a bleaching agent but also as a disinfectant. In most cases, chlorinated isocyanuric acid or salts thereof are used as the organic chlorine compound, and chlorinated sodium isocyanurates have, primarily for economical reasons, been most widely uti¬ lised. In addition to the above-mentioned components, machine dishwashing detergents frequently also contain varying amounts of conventional additives, such as alkali metal carbonates and bicarbonates, alkali metal sulphate, aluminium silicate, sodium borate, dyes, perfume etc. When using conventional machine dishwashing deter¬ gents, starch-containing dishwashing residues, for example from spaghetti and potatoes, give rise to speci¬ fic problems. Thus, the acetal bond in the starch is difficult to hydrolyse, and also under the highly alka¬ line conditions prevailing during the machine dish¬ washing process the starch is decomposed slowly. One way to accelerate the hydrolysis of starch is to introduce starch decomposing enzymes, so-called amylases, into the machine dishwashing composition, whereby starch-containing food residues are quickly eliminated already at neutral pH. The amylase here acts in that it hydrolyses α-l,4-glucoside bonds in amylose and a ylopectin, whereby the starch is decom¬ posed into soluble dextrins and oligosaccharides. OMPI 3 A considerable difficulty encountered with amylases in this connection is that they are readily decomposed in alkaline environment. Although more alkali resistant enzymes have been developed in recent years, one has still not succeeded in producing amylases functioning satisfactorily together with products of high alkali content, such as silicates. Because the removal of fat and protein requires a high pH in the dishwashing solution, this means that one must compromise between enzyme activity and alkali content. In actual practice, it has been found that the upper effective limit of the etasilicate content in machine dishwashing detergents is about 20% by weight if a fairly intact enzyme activity is desired. This amount of metasilicate is about half the normal amount in machine dishwashing detergents, and this considerable decrease of the alkali content entails a marked deterioration of the dishwashing effect as regards fat and protein. A number of suggestions have been made to eliminate the above problem. For example, it has been tried to use a kind of two-component system in which amylase is first dissolved out in a fairly neutral dishwashing solution and for a requisite period of time is allowed to decompose the starch. In a second dishwashing step, a basically conventional machine dishwashing detergent of high- alkali content is then added. However, using a two-component system implies a longer dishwashing cycle and entails other practical problems. It is the object of the present invention to eli- minate the above-mentioned problems and to provide a machine dishwashing composition which contains enzyme with retained activity and, at the same time, has a normal alkali metal silicate content. In the present invention, it has surprisingly been found that this object can be achieved if the alkali metal silicate content of the composition is present in the form of two-layer granules whose core consists of alkali metal silicate, preferably sodium metasilicate (anhydrous or hydrate) and whose outer shell consists of alkali metal phosphate, preferable sodium tripolyphosphate. The characteristic features of the invention will be apparent from the appended claims. Thus, it has been found in the present invention that if an enzyme, preferably amylase, is combined with a machine dishwashing detergent based upon the above- mentioned two-layer granule, the starch decomposing effect of the enzyme will remain also at very high alkali contents. This is extremely surprising because the alkali content of .the silicate should inactivate the enzyme. The alkali content of the silicate- is available for normal hydrolysis reactions after the two-layer granule has been dissolved in the dishwashing solution, which occurs immediately when the granule is contacted with the dish¬ washing solution. There is still no satisfactory expla¬ nation of the phenomenon that the enzyme is not inactivated by the highly alkaline dishwashing solution when two-layer granules according to the present invention are used. It seems, however, as if it is a protracted contact with dry silicate in the machine dishwashing detergent, rather than a short-term stay in a high-alkaline dish- washing solution, that is detrimental to the enzyme. It should be mentioned in this connection that it is already known from Swedish patent application 7706216-4 to prepare a two-layer granule of the kind used in the present invention, sa ' id granule comprising a core of sodium silicate and ^ " she1-1 of sodium tripolyphosphate. This prior art technique proceeds from granules of silicate, usually sodium metasilicate (anhydrous or hydrate) , said granules suitably having a particle size of 0.05-1.5 mm, preferably 0.2-1.2 mm, and over these granules a shell of pulverulent and partially hydrated tripolyphosphate is applied. The particle size of the finished two-layer granules generally is 0.25-2.5 mm. OMP preferably 0.4-2.0 mm. Thus, these two-layer granules contain both silicate and phosphate, but the outer surface consists of phosphate only and thus is not markedly alkaline. For further details regarding these known two- layer granules, reference may be made to the above- mentioned Swedish patent application 7706216-4. Since chlorine inactivates enzyme in a very short time, presumably by oxidative splitting of peptide bonds, enzyme, such as a ylase, cannot be used together with sub- stances giving, ff chlorine, such as the oxidative chlorine bleaching agents normally comprised by machine dishwashing compositions. To avoid such inactivation of the enzyme, the present invention therefore prescribes either that the bleaching agent be omitted entirely or, if it is included in the composition, that it consist of a hydrogen peroxide- based bleaching agent. Preferred hydrogen peroxide-based bleaching agents are perborates and percarbonates, such as sodium perborate and sodium percarbonate. No special restrictions apply to the remaining com- ponents of the machine dishwashing composition, which may be selected among conventionally employed substances. The contents of the components in. the composition according to the present invention generally lie within the following ranges: two-layer granules of alkali metal silicate/alkali metal phosphate 40-99% by weight surfactant 1-4% by weight oxidative hydrogen peroxide bleaching agent 0-15% by weight enzyme * 0.5-5% by weight additive up to 100% by weight The weight ratio silicate/phosphate in the two-layer granule may vary within wide limits. A weight ratio pre¬ ferred in actual practice is from 80:20 to 40:60, calcu- lated upon anhydrous components. It is also possible, and sometimes advantageous, not to include the entire phosphate amount of the composition in the two-layer granule, but to,. OMPI add part of it as a separate component, on condition that each silicate particle is covered by a phosphate layer of such a thickness that the surface will no longer be highly alkaline. Furthermore, it is not necessary that the entire silicate content of the composition is present in the form of two-layer granules, and part of the silicate may be present in free form, without the protective phosphate layer obtained in the granules. However, in order to avoid a detrimental effect on the enzyme, the amount of silicate which-thus is present in free form, must not be too large, and more particularly the present invention prescribes that at least half of the silicate be present in the form of two-layer granules. The composition preferably contains 1-3% by weight of enzyme which normally is present in the form of a granulated product. To further illustrate the present invention, the following nonrestrictive -Example is given. EXAMPLE Three different machine dishwashing detergents A, B and C having the following composition were produced (the figures are in percent by weight) : A B C tripolyphosphate 40 40 metasilicate 5 aq 56 20 * two-layer-granule - - 96 ** sodium sulphate - 36 *** enzyme (amylase) 3 3 3 antifoaming surfactant 1 . 1 1 * consisting of 40 parts of tripolyphosphate and 55-60 parts of metasilicate 5 aq ** sodium sulphate is an inert filler *** Termamyl 60S from Novo Industri AS. The dishwashing detergent C was a machine dishwashing detergent in accordance with the present invention, while the dishwashing detergents A and B were reference compo¬ sitions. X PI - After 3 months' storage in normal machine dishwashing detergent packages, dishwashing tests were conducted at the ambient temperature and ambient air humidity. The soil load in these tests was a mixture of potato-flour, oatmeal, spinach, eggs, tomato juice, milk, tea, fat and minced meat. After dishwashing, the dishwashing effect was con¬ sidered on one hand as the total effect and, on the other hand, as the effect on starch. The total effect was judged directly visually, while the remaining starch was judged after the articles had been treated with iodine solution. The result is shown by the following Table. The scale goes from 0 to 10, 0 being completely clean and 10 very soiled. The dosage of the dishwashing deter¬ gent was 3 g/1, and the dish-water had a hardness of 3 dH. A B C Total soil 4 5 1 Starch soil 4 1 1 As will appear, formulation A has a rather poor effect on starch but is satisfactory in other respects. The dishwashing effect of formulation B on starch is satisfactory but rather poor in other respects. Only formulation C has a satisfactory effect on all soil. "BUREAU O PI "

Claims: CLAIMS 1. A machine dishwashing detergent composition which comprises, in addition to conventional additives, " alkali metal silicate, alkali metal phosphate, surfactant and, optionally, a hydrogen peroxide-based bleaching 5 agent, c h a r a c t e r i s e d in_that the composition also contains an enzyme, and that at least half of the alkali metal silicate and at least a part of the alkali metal phosphate are present in the form of two-layer granules having a core of alkali metal silicate surrounded Q by an outer shell of alkali metal phosphate. 2. A composition as claimed in claim 1, c h a r ¬ a c t e r i s e d in that the enzyme is amylase. 3. A composition as claimed in claim 1 or- 2, c h a r a c t e r i s e d in that the weight ratio _5 alkali metal silicate:alkali metal phosphate in the two-layer granules is from 80:20 to 40:60. 4. A composition as claimed in any one of claims 1-3, c h a r a c t e r i s e d in that it contains, calculated on its total weight, 40-99% by weight of 0 granules, 1-4% by weight of surfactant, 0-15% by weight of bleaching agent and 0.5-5% by weight of enzyme, the balance being additives. 5. A composition as claimed in any one of claims 1-4, c h a r a c t e r i s e d in that the alkali metal 5 silicate is sodium silicate. 6. A composition as claimed in any one of claims 1-5, c h a r a c t e r i s e d in that the alkali metal phosphate is sodium tripolyphoshate. 7. A composition as claimed in any one of claims 0 1-6, c h a r a c t e r i s e d in that the surfactant is a nonionic surfactant, preferably a block polymer of ethylene and propylene oxide. OMPI 8. A composition as claimed in any one of claims 1-7, c h a r a c t e r i s e d in that the additives consist of alkali metal carbonate, alkali metal hydrogen carbonate, alkali metal sulphate, corrosion inhibitors, dyes, perfume, or mixtures thereof.

Inventors: HOLMBERG KRISTER, SOERENSSON OLLE, HOLMBERG, KRISTER, SOERENSSON, OLLE
Applicants: EKA AB
Application year: 1984
Main classification: C11D7
IPC codes: C11D3