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Description  |
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BACKGROUND OF THE INVENTION
The present invention concerns a detergent dish-washing composition. This
composition can be used in solid granulated or powder form but this
condition is in no way necessary and the composition can also be used in
any other convenient usual form, including the liquid form in special
cases.
Detergent products for dish-washing are generally formulated so as to
provide, after dissolution into water, a cleaning bath for removing soils
of many different kinds such as vegetable fibers, protein soils,
amylaceous products, dyes, tannins, burnt residues and the like; however,
cleaning solutions should not simultaneously attack and corrode kitchen
and dinner-ware made of glass, ceramic, china and metal. Further, cleaning
solutions should be able to prevent a redeposition of mineral contaminants
on the cleaned articles, such contaminants forming unpleasant films or
spots on the washed surfaces.
In order to reconcile together the aforementioned requirements, the known
dish-washing compositions generally contain inert or near to inert mineral
salt builders whose purpose is to provide a degree of ionic strengh to the
bath and to act as buffering agents. As such fillers, one can mention
alkali metal sulfates, phosphates, polyphosphates, carbonates, silicates
and chlorides; and other alkali salts, alkali metal salts of organic acids
and neutral compounds such as urea. By virtue of their surfactive
properties, polyphosphates enable the removal of certain kinds of soils,
namely fatty deposits by emulsification. They also act as antiredeposition
agents because of their dispersive properties and they promote the
dissolving of casein with formation of sodium caseinate. The added
silicates are effective for controlling the alkaline pH of the bath as a
function of the concentration and of the alkali metal content thereof;
they also act as corrosion inhibitors. Dish-washing compositions further
contain sud-repressing surfactants and other additives such as
soil-suspending ingredients, drainage promoting ingredients, perfumes,
softeners and the like. A fully detailed description of the general
features relative to dish-washing compositions can be found in U.S. Pat.
No. 4,162,987 (MAGUIRE et al).
In addition to the above-mentioned ingredients, dish-washing composition
may also comprise "chlorine donor" bleaches, i.e. products which provide
active chloride after hydrolysis in the bath, said chlorine being active
for oxidative and disinfection purposes. The dish-washing products may
also include enzymes for catalytically hydrolyzing food residues. The most
important enzymes are the proteolytic and amylolytic enzymes.
Enzymes impart a significant cleaning power to the dish-washing
compositions but they are unstable in the presence of chlorine bleaches
and, particularly in the case of amylolytic enzymes, they normally lose
their activity in the bath at the high pH values which are normally
necessary for efficient dish-washing activity.
Hence, the dish-washing detergent taught in the aforementioned U.S. Pat.
No. 4,162,987 comprises enzymes but no chlorine bleach and the pH of the
solution never exceeds 11.5, so as to prevent deactivation of the
amylolytic enzymes (.alpha.-amylases). Such pH value is, however, only a
lower limit regarding washing efficiency in dish-washers. Further, in the
absence of oxidants such as the common chlorine bleaches, certain food
residues, e.g. tea residues, are not sufficiently eliminated which is a
major drawback.
Other prior art of some relevance includes French Pat. Nos. 1561078 &
2035547 and German DOS No. 2109389. French No. 1561078 describes laundry
washing agents containing enzymes, which are stated to be active in the pH
range of approximately 4 to 12. There is no clear showing of whether the
pH of the washing solutions shown is in fact below 11.5. The enzymes are
attached to a hydratable salt to protect the enzyme. As the patent makes
manifestly clear the carbohydrases (e.g. amylase) function primarily in
acid to neutral systems.
French Pat. No. 2035547 also relates to clothes laundering detergent
compositions. In this patent the life of amylase enzyme is prolonged by
intimate contact with starch. The detergent composition are those which in
aqueous solution (0.12%) have a pH of from about 8.5 to about 11.
German (DOS) No. 2109389 also relates to protecting enzymes (during
storage) utilizing certain glucose polymers in admixture with derivatives
of mono-saccharides. The only mention of the pH of a laundry solution is
one with a pH of 9.
SUMMARY OF THE INVENTION
It has now been surprisingly noticed, and this finding constitutes one of
the fundamentals of the present invention, that, although the activity of
the amylolytic enzymes is indeed practically naught at pH values above
11.5, the presence of these enzymes in the detergent composition imparts
to the resulting washing bath a remarkable and surprising washing ability
toward amylaceous residues at pH values exceeding 11.5. In addition, it
has also been noticed that it is possible to incorporate, as replacement
for the chlorine bleaches in such a composition, mineral or organic
peroxides without significantly impairing the cleaning efficiency of the
enzymes.
Briefly summarized, the detergent dish-washing composition according to the
invention which includes alkali metals polyphosphates and silicates, at
least one non-ionic surfactant and an oxidizing agent, enzymes and further
conventional detergency and other additives, is characterized in that the
enzymes comprise at least one amylolytic enzyme whose activity is
considered negligible at a pH above 11.5, at least one mineral or organic
peroxide as the oxidant, and in that the pH of the bath obtained therefrom
for use in a dish-washing machine is not below 11.5.
DETAILED DESCRIPTION OF THE INVENTION
Practically, this pH can be chosen between 11.5 and 12.5, although higher
pH values are also possible if desired. The exact value of the pH within
the above mentioned limits can be adjusted by means of the amount of
alkali in the composition. This alkali can be represented by suitable
amounts of alkali metal hydroxides and/or of alkali metal silicates. The
alkali metal silicates can be potassium, lithium or sodium silicate with a
Na.sub.2 O/SiO.sub.2 mole-ratio of, for instance, 0.3 to 4.0, and its
amount by weight in the composition for providing the desired pH will
depend on the particular selected value of said mole ratio.
More specifically, the quantities by weight of the key ingredients in the
present dish-washing composition are as follows:
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Alkali metals (Na, K or Li) polyphosphates
10-70%
Alkali metals (Na, K or Li) silicates
25-70%
Non-ionic surfactants 0.2-5%
Amylolytic enzymes (specific activity
0.1-5%
60 kNU/g)
Peroxide compounds 1-20%
______________________________________
The remainder to make 100% by weight is constituted by the other detergency
additives mentioned above. As such additives, the following ones can be
mentioned: alkaline materials, chelatants and sequestrants,
anti-redeposition agents, corrosion inhibitors such as some complex
aluminates, zincates or phosphates (see also U.S. Pat. No. 3,410,804),
anti-tarnishing agents, bactericides, anti-foam agents, polyelectrolytes,
oligo- and polysaccharides, mineral softeners, urea and the like. All
these agents are known from those skilled in the art and disclosed in many
publication (see for instance: DETERGENCY by W. G. CUTLER and R. C. DAVIS,
Mr. DEKKER Inc., New York and Basel 1981)). As peroxide compounds, one can
mention for instance alkali metals perborates, persulfates, percarbonates,
peracetates and perbenzoates but these examples are not limitative, other
peroxides known in this field being also possible. For embodying the
invention, one prefers using alkali metal perborates, preferably sodium
perborate, because of easy availability and stability and because they
have anti-tarnish properties (see U.S. Pat. No. 3,549,539).
As amylolytic enzymes, one can use most enzymes of this category unless
they are destroyed during storage by the effect of the other ingredients
of the composition or, when in solution, by the effect of the same
ingredients dissolved in the washing bath. However, as heretofore
mentioned, it is immaterial that the activity of the amylases used in the
composition becomes zero or at the least non-measurable according to usual
means under the operating conditions of the present composition, the
washing power contribution of said amylases being considerable despite the
already cited inhibitory effect of high pH solutions. Such amylolytic
enzymes effective according to the present invention are described in
detail in British Pat. No. 1,296,839 and in aforementioned U.S. Pat. No.
4,162,987. One prefers to use the amylolytic enzymes commercially
available under the name of "TERMAMYL" (NOVO INDUSTRI A/S, Bagsvaerd,
Denmark).
The present composition can also comprise 0.1 to 5% by weight of
proteolytic enzymes (specific activity 4 units KNP/g). Such enzymes are
described in detail in British Pat. No. 1,361,386. One prefers using, as
proteolytic enzymes, the substances available under the name of "ESPERASE"
(NOVO INDUSTRI A/S, Bagsvaerd, Denmark).
It should be remarked that the effect of the proteolytic enzymes is
somewhat decreased by the presence of peroxides; however, this inhibitory
effect is of little significance as it occurs only at a later stage of the
washing operation since peroxides, and more particularly perborates,
dissolve only slowly in the scouring bath and only provide their full
oxidative potency at the end of the washing cycle.
The nature of the surfactants usable within the scope of the present
invention is not critical and most commercial non-ionic surfactants
normally used in dish-washing compositions are suitable. A listing of such
surfactants is found in U.S. Pat. No. 3,666,961 and 4,162,987.
Preferably, the used surfactants are polyoxyalkylated fatty esters derived
from polyoxyalkylated fatty acids or alcohols in which the term
"polyoxyalkyl" preferably designates the polyoxyethylene and
polyoxypropylene chain segments. The fatty acids can be, for instance,
oleic acid, palmitic acid, myristic acid, stearic acid and the like. The
fatty alcohols can be, for instance, lauryl alcohol, oleyl alcohol, tallow
alcohols and the like. Preferably, the surfactants used in the present
composition have antifoam or sud-repressing properties.
As alkali metal silicates, one can use most of the usual water soluble
alkali metal silicates (metasilicates, orthosilicates), the mole-ratio
SiO.sub.2 /ME.sub.2 O of which (ME being Na or K) is comprised between
0.30 and 4.0. This ratio value is however not essential because in case
there is a lack of alkali metal in the silicate, this deficiency can be
corrected by adding a corresponding compensating quantity of alkali metal
hydroxide to the present composition. In any event, the quantity of alkali
metal compound of the composition should be such as to provide, after
dissolution of the composition in water (at the concentration of generally
2-10 g of solids per liter), a pH comprised between 11.5 and 12.5 and
preferably of 12.2 to 12.4.
The polyphosphates to be used in the present composition are the
commercially available alkali metal polyphosphates normally used in
compositions for household applications (cloth and fabric washing
compositions). These polyphosphates essentially comprise tripolyphosphate
together with pyrophosphates and monophosphates; occasionally they may
contain polyphosphates with more than three orthophosphate units in the
chain. The nature of these polyphosphates is not critical in the present
composition but at least some polyphosphates should be present to ensure
an effective washing of the dishes and a sequestering effect of the hard
earth-alkali metal ions in the washing waters.
Thus, in short, the composition according to the invention offers the
following advantageous properties as compared to the corresponding
products known from the art:
(a) The washing efficiency with regard to common dish soils exceeds or at
least equals that of the known products.
(b) The composition is economical because it particularly suits the so
called "mild" or "soft" washing cycles which require less water, less time
and a temperature (40.degree.-50.degree. C.) lower than with a "regular"
washing cycle (55.degree.-65.degree. C.).
(c) The washing solution is less corrosive toward the glass and metals of
table wares and it will spare the dainty dishes since the water pressure
associated with the short cycles is lower than the pressure used in a
normal cycle.
(d) The washing efficiency is markedly better toward some of the soils,
namely amylaceous soils.
(e) Prewashing steps can be deleted which saves a lot of time because the
used dishes of several successive meals can be stored in the dish-washer
without prewashing until it is full, drying of the food residues before
eventual washing being of no importance.
(f) Terminal rinsing is improved particularly in regard to glasses, which
enables to use less rinsing product as compared with conventional rinsing.
(g) Since the composition comprises no chlorine bleach, various sensitive
ingredients can be added thereto for improving the washing conditions,
namely fragrant compounds, (it is normally not possible to add perfumes to
chlorine containing detergents as they would be distroyed completely by
said chlorine).
(h) Due to the aforementioned improvements, the composition of the
invention enables one to save time and energy and by reason of its
increased power, it can be used at lower effective concentration as
compared with conventional dish-washing detergents, which condition
contributes to decrease pollution by the phosphates.
The following Examples illustrate the invention on a practical stand point.
BRIEF DESCRIPTION OF THE DRAWING
The annexed drawing, whose information is used as a reference only,
represent graphically the variation of activity of a typical
.alpha.-amylase at different temperatures and pH values. This information
is reproduced from a data sheet by NOVO INDUSTRI, Bagsvard, Denmark (sheet
B204 c-GB-1500, July 1980) concerning amylolytic enzymes sold under the
trade mane of TERMAMYL.
EXAMPLE 1
A basic mixture (C) for a dish-washing composition was prepared with the
following ingredients (parts by weight)
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Sodium tripolyphosphate
11.8
Sodium metasilicate (5H.sub.2 O)
18.7 (or 10.8 if anhydrous)
Sodium perborate 1.5
Urea 4.5
Non ionic surfactant
0.45
(PLURIOL PE-6100)
Proteolytic enzyme (ESPERASE)
0.6
37.55
______________________________________
A test composition (A) according to the invention was then prepared by
adding 0.3 parts by weight of .alpha.-amylase (TERMAMYL 60-L) to mixture
(C).
A set of test soiled kitchen or table wares was prepared by using common
food residues of the following kinds: amylaceous material, proteins,
vegetable fibers, dyestuffs and tannins (tea), burnt food and mixed soils
(protein/starch). This was made by coating the dinner wares (plate, cup,
glass, beaker, forks and spoons, etc., depending on the needs) with a
known quantity of food residue and, thereafter, drying for a known period
at a given temperature. The conditions under which the test articles were
prepared are summarized in Table I below.
TABLE I
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Drying conditions
Weight of food temper-
Type of food residue per ature
stuff residue
utensil (g) time (h) (.degree.C.)
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(a) cellulosic fibers
spinach (2) 2 95
(b) protein egg yolk (2)
2 115
(c) amylaceous pro-
porridge (3)
2 80
ducts
(d) proteins/amyl-
cheese 16 115
aceous products
noodles (2)
(e) dyes and tannins
tea (50) filled cup 1
100
empty cup 2
100
(f) burnt stuff milk (1) 2 80
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The soiled utensils were introduced into commercial dish-washers so as to
provide normal filling loads, i.e. for instance 6 ordinary plates, 6 soup
bowls, 6 dessert plates, 6 stainless knives, spoons and forks, 6 tea cups,
6 beakers with burnt milk residues and, also, clean glasses to check
rinsing efficiency. The washing operation was carried out under "normal"
washing cycle conditions with a prewashing step. The washing steps are
summarized in Table II below (the given parameters stand for 29.95 g of
powdered detergent composition; the initial water temperature was
15.degree. C.).
TABLE II
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Consecutive Duration water used
final
steps (min) (liter) temperature (.degree.C.)
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Prewash 2 7.2-7.6 15
Main wash 26 7.2-7.6 60
with detergent
1st rinse 3 10.2-10.8 35
2nd rinse 2.5 7.2-7.6 25
3rd rinse (with
27 7.2-7.6 60
3 ml of acid
surfactant solution)
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The composition labelled (A) as described above was used in the above
mentioned washing test (using about 3 g of detergent/liter) at a pH of
11.5 in a first test and at pH 12.2 in a second identical test. The pH was
adjusted in both cases into concentrated HCl or NaOH solutions as
required. The washing and rinsing results are gathered in Table III, the
evaluation marks ("good", "sufficient" and "insufficient") being averaged
over several repeats as objectively as possible. The marks "insufficient"
and "much insufficient" indicate that significant soil residues remain on
the dishes; "sufficient" indicates that the test ware is acceptably clean
while "good" indicates that the ware is absolutely clean.
TABLE III
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Type of soil pH = 11.5 pH = 12.2
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(a) sufficient good
(b) insufficient
good
(c) sufficient sufficient
(d) sufficient good
(e) much insufficient
good
(f) sufficient sufficient
rinse (glass) good good
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A comparison was thereafter made between composition (A) and control
composition (C) without TERMAMYL at pH 12.2 and under the same conditions
as above; it was noted that composition (A) provided much better washing
results than the control, especially with regard to the removal of
amylaceous materials (C) and mixed soils amylaceous/proteins (d).
Then, the amylolytic activity of the solutions obtained from composition
(A) at pH values of, respectively, 12.2 and 8.0 was checked as follows: in
a conventional type dish-washer were introduced 4 liters of 25 g/l starch
solution; the machine was started but, before adding the detergent
composition, an aliquot of the liquid was taken for analysis. Then, the
full washing cycle was carried out with the detergent solution and a
second identical sample of liquid was removed. The amylolytic activity was
determined by adding an excess of iodine to the sample (iodine is normally
consumed in alcaline medium in a ratio of 2 atoms of I per aldehyde
function) and back titrating the excess of iodine with thiosulfate. The
consumption difference between the initial sample and the final sample
taken at the end of the washing cycle provides a measurement of the extent
of hydrolytic cleavage of the amylaceous chains (formation of --CHO
groups) undergone by the starch in the course of the washing cycle. The
activity measured for 200 ml samples (from a total volume of 4+3.5=7.5
liters of washing bath) with 30 ml of O.N I.sub.2 solutions provided for
three successive test at pH 12.2 the following iodine consumption values
(in ml of 0.1N I.sub.2 solution): 0.82; 1.14; and 0.16, these results
corresponding approximately to zero activity within the limits of error of
the measurements. In comparison, at pH 8, values averaging to 8-9 ml (over
5 runs) were recorded which indicates the existence of quite a significant
activity. It is hence particularly surprising that the present composition
is so effective at pH 12.2 to eliminate amylaceous residues when its
hydrolyzing activity is indeed naught or non-detectable by the
abovementioned conventional means.
As a confirmation of the aforementioned results, one may referentially
check up with the FIGURE of the annexed drawing. The graph of this FIGURE
represents in KNU'g units the activity of the enzyme TERMAMYL as the
function of pH at three different temperatures. The curves represented
show that the activity is practically zero at pH values over 11. It is
thus particularly surprinsing to note that the composition according to
the invention is active with regard to amylaceous residues at a pH above
11.5.
EXAMPLE 2
A detergent composition (B) was prepared which was identical with
composition (A) of Example 1 except for the sodium perborate which was
omitted. The composition (A) and (B) were comparatively tested at pH 12.2
exactly as disclosed in Example 1 and the results listed in Table IV were
obtained.
TABLE IV
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Composition
Composition
Type of soil (B) (A)
______________________________________
(a) good good
(b) good sufficient
(c) good good
(d) good good
(e) insufficient
good
(f) good good
rinse (glasses)
good good
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The above results indicate that although the protein removal potency of the
composition is somewhat weakened by the presence of perborates, the
efficacy for removing tea spots which was insufficient in the absence of
perborate becomes good when the latter is present.
EXAMPLE 3
A comparison was made between the composition (A) of Example 1 operating at
pH 12.2 and a commercial dish-washing powder (D) without enzymes but
containing about 3% of chlorine bleach. This control powder had the
following composition (for 30.0 g of washing product):
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Tripolyphosphate 12.75 g
Anhydrous sodium metasilicate
12.00 g
PLURAFAC RA 343 (a non-
0.75 g
ionic surfactant)
Sodium carbonate 3.60 g
Sodium dichloroisocyanurate.4H.sub.2 O
0.90 g
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This detergent composition was to operate at pH 12.0.
The tests were carried out with, each time, 30 g of control composition (D)
or test composition (A) but with different washing programs: "normal"
"economical" and "delicate". The results are provided in Table V. The
detailed steps of the "economical" and "delicate" programs are given in
Tables VI and VII hereinafter. The initial water temperature was
15.degree. C.
TABLE V
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Program
Type of Normal Economy Soft
soil A D A D A D
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(a) good suff. good good suff. suff.
(b) good m.ins. suff. insuf.
suff. m.ins.
(c) good m.ins. good m.ins.
suff. m.ins.
(d) good m.ins. good insuf.
suff. m.ins.
(e) good good good good good good
(f) good good good suff. suff. insuf.
rinse good good good good good good
(glasses)
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Suff = sufficient;
insuf = insufficient;
m.ins. = much insufficient.
The above results indicate that in some occasions, the "economy" program
performed with the composition of the invention provides better results
than that obtained with the commercial reference solution under a "normal"
washing cycle.
TABLE VI
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(economy program)
Duration Water Final temperature
Steps (min) (l) (.degree.C.)
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washing with
26 7.2-7.4 50
detergent
1st rinse 3 10.2-10.8 30
2nd rinse 2.5 7.2-7.6 20
3rd rinse 27 7.2-7.6 60
with rinsing agent
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TABLE VII
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(Delicate program)
Duration Water Final temperature
Steps (min) (l) (.degree.C.)
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washing with
16 7.2-7.6 50
detergent
1st rinse 3 10.2-10.8 30
2nd rinse 2.5 7.2-7.6 20
3rd rinse 27 7.2-7.6 60
with rinsing agent
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