Note: Descriptions are shown in the official language in which they were submitted.
CA 02321326 2000-09-28
MACHINE SILVER-CLEANING COMPOSITIONS
Field of the Invention
The present invention relates to compositions for the
machine cleaning of silver surfaces, and to the use of
these compositions in domestic dishwashers, and to a
cleaning method using these compositions.
Background of the Invention
Cleaning compositions for cleaning soiled dishes in
dishwashers are described widely in the prior art. One
disadvantage which these compositions often have,
however, is the cleaning performance on tarnished silver
surfaces. Since machine dishwashing detergents have to
satisfy a large number of requirements both with regard
to the substrates to be treated and also with regard to
the soilings which arise, certain objectives are not
achieved to the complete satisfaction of the user. In the
case of the cleaning of silver or silver-plated surfaces,
therefore, the addition of corrosion inhibitors, which
prevent further tarnishing, but which are unable to clean
tarnished silver surfaces, has in most cases had to
suffice.
Specific cleaning compositions are supplied for the
cleaning of silver, some of which can also be used in
dishwashers. On the basis of well-known method of placing
the silver articles on aluminum foil and covering them
with an electrolyte solution, US 3,701,736 (Colgate)
proposes machine dishwashing detergents (MDDs) which
comprise builder salts and at least 3.25a by weight of
aluminum in the form of the pure metal or of aluminum
alloys.
A similar product for non-machine cleaning is described
in EP 039 193 (Crown & Andrews).
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CA 02321326 2000-09-28
A more recent preparation for the cleaning of silver in
dishwashers arises from i~T098/51769 (Procter & Gamble).
According to the teaching of this specification, the aim
is to use silver-cleaning compositions which comprise
alkaline electrolyte, metal and in each case at least 10
by weight of builders and nonionic surfactant. The metal
must have a more negative standard potential than silver.
The compositions can also be incorporated as a component
in traditional MDDs. A machine silver-cleaning method is
likewise claimed in this specification.
The solutions proposed in the prior art either cannot be
used in dishwashers, or lead to results which are not
comparably good compared with conventional dipping or
polishing methods. There therefore still existed the
object of providing silver-cleaning compositions which
can be used in dishwashers and which have good cleaning
performance which is comparable with cleaners applied
manually.
Summary of the Invention
We have now found that the solubility of the reducing
agent used has a decisive influence on the performance of
the composition.
The present invention provides, in a first embodiment,
compositions for the cleaning of silver in a dishwasher,
which comprise alkaline electrolytes and reducing agents,
where, as reducing agents, water-soluble substances
having a solubility of more than 20 g per liter of water
at 20°C are present in the compositions.
The compositions according to the invention comprise as
essential ingredients one or more alkaline
electrolyte(s), and one or more reducing agents which
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have a certain solubility in accordance with the
invention. Reducing agents which can be used according to
the invention dissolve to give clear solutions at 20°C in
amounts of more than 20 grams per liter of deionized
water. It is preferred to use more soluble reducing
agents, so that preferred compositions according to the
invention comprise, as reducing agents, water-soluble
substances having a solubility of more than 30 g,
preferably of more than 40 g and in particular of more
than 50 g, per liter of water at 20°C.
Detailed Description of the Invention
Reducing agents which can be used according to the
invention may originate from a number of classes of
substance. Thus, for example, inorganic or organic salts
or covalent compounds can be used. The table below gives
an overview of the solubilities of reducing agents which
can be used according to the invention. The solubilities
given refer to a temperature of 20°C, unless another
temperature is given in the first column.
3,4-Dihydroxybenzaldehyde 50 g/1
Ammonium iron(II) sulfate hexahydrate 269 g/1
Ammonium iron(III) citrate 1200 g/1
Ascorbic acid 333 g/1
Pyrocatechol 434 g/1
Citric acid monohydrate 1630 g/1
Cobalt(II) acetate tetrahydrate 380 g/1
Cobalt(II) chloride hexahydrate 76 g/1
Cobalt(II) nitrate hexahydrate 1330 g/1
Cobalt(II) sulfate heptahydrate 260 g/1
D (-) -fructose 3750 g/1
D (+) -galactose (25C) 680 g/1
D (+) -glucose monohydrate (25C) 820 g/1
D(+)-mannose (17C) 2480 g/1
Disodium tartrate dehydrate 290 g/1
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DL-malic acid (26C) 1440 g/1
Iron(II) chloride tetrahydrate (10C) 1600 g/1
Iron(II) sulfate heptahydrate 400 g/1
Gluconic acid, sodium salt (25C) 590 g/1
Urea
1080 g/1
Hydroquinone 70 g/1
L-(-)-malic acid 363 g/1
L-(-)-sorbose (17C) 550 g/1
Lactose monohydrate (25C) 216 g/1
Manganese(II) acetate tetrahydrate 330 g/1
Manganese(II) chloride 1400 g/1
Manganese(II) chloride dehydrate 1200 g/1
Manganese(II) chloride tetrahydrate 1980 g/1
Manganese(II) nitrate tetrahydrate 3800 g/1
Manganese(II) sulfate monohydrate 762 g/1
Melibiose monohydrate (25C) 2500 g/1
Sodium dithionite 224 g/1
Sodium hypophosphite monohydrate 1000 g/1
Sodium sulfite 495 g/1
Sodium tetraborate decahydrate 50 g/1
Sodium thiosulfate pentahydrate 680 g/1
Sucrose (15C) 1970 g/1
Depending on the desired dosing of the compositions
according to the invention and depending on the reducing
agents used, the latter are used in varying amounts.
Preferred compositions according to the invention
comprise the reducing agents) in amounts of from 1 to
60% by weight, preferably from 5 to 40% by weight and in
particular from 10 to 25% by weight, in each case based
on the total composition.
From the group of the abovementioned reducing agents
certain subgroups are in turn preferred. Thus, preferred
compositions according to the invention comprise one or
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more reducing agents from the group of reducing sugars,
D (-) -fructose, D (+) -galactose, D (+) -glucose monohydrate,
D(+)-mannose, L(-)-sorbose, lactose monohydrate,
melibiose monohydrate and sucrose being particularly
preferred reducing agents.
Particularly preferred compositions according to the
invention comprise, as reducing agents, one or more
substances from the group of non-salt-like compounds,
particularly preferably pyrocatechol, hydroquinone and/or
ascorbic acid.
As second constituents, the compositions according to the
invention comprise one or more alkaline electrolyte(s).
This electrolyte content effects a higher conductivity of
the solution and also provides for an advantageous
alkaline pH of the use solution, which is preferably
above 9, particularly preferably above 9.5 and in
particular above 10 or even 10.5. Preferred alkaline
electrolytes are, for example, carbonates,
hydrogencarbonates, silicates, metasilicates and mixtures
thereof.
Preferred compositions according to the invention
comprise, as alkaline electrolyte(s), one or more
substances from the group of carbonates,
hydrogencarbonates, hydroxides, citrates and/or
phosphates, the alkali metal, and in particular the
potassium and/or sodium salts, being preferred.
In preferred compositions according to the invention, the
content in the compositions of alkaline electrolytes is
to 99% by weight, preferably 45 to 95% by weight and
in particular 50 to 90% by weight, in each case based on
35 the total composition.
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Preferred alkaline electrolytes are the citrates, and of
these the alkali metal citrates are in turn preferred.
Compositions preferred within the scope of the present
invention comprise potassium citrate and/or sodium
citrate in amounts of from 5 to 50% by weight, preferably
from 10 to 45% by weight, particularly preferably from 15
to 40% by weight and in particular from 20 to 35% by
weight, in each case based on the total composition.
The use of carbonates as alkaline electrolyte is also
possible and preferred in accordance with the invention.
In the case of the alkali metal carbonates or
hydrogencarbonates, the sodium or potassium salts are
clearly preferred over the other salts for reasons of
cost. Of course, the pure alkali metal carbonates or
hydrogencarbonates concerned do not have to be used;
instead, mixtures of different carbonates and
hydrogencarbonates may be preferred.
Compositions preferred according to the invention
comprise potassium carbonate and/or sodium carbonate in
amounts of from 10 to 70% by weight, preferably from 15
to 55% by weight, particularly preferably from 20 to 45%
by weight and in particular from 25 to 40% by weight, in
each case based on the total composition.
Other alkaline electrolytes which can be used are
hydroxides, silicates and phosphates. In the case of
these substances too the alkali metal salts are
preferred. Crystalline, sheet sodium silicates suitable
as alkaline electrolyte have the formula NaMSiXO2X+1'y H20,
where M is sodium or hydrogen, x is a number from 1.9 to
4 and y is a number from 0 to 20, and preferred values
for x are 2, 3 or 4. Preferred crystalline
phyllosilicates of the formula given are those in which M
is sodium, and x assumes the values 2 or 3. In
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particular, both (3- and 8-sodium disilicates Na2Si205~y Hz0
are preferred.
It is also possible to use amorphous sodium silicates
having an NazO . Si02 modulus of from 1:2 to 1:3.3,
preferably from 1:2 to 1:2.8 and in particular from 1:2
to 1:2.6, which have delayed dissolution and secondary
detergency properties. The dissolution delay relative to
traditional amorphous sodium silicates can have been
induced by various means, for example by surface
treatment, compounding, compaction/consolidation or by
overdrying. Within the scope of this invention the term
"amorphous" includes "X-ray amorphous". This means that
in X-ray defraction experiments, the silicates do not
produce sharp X-ray reflections typical of crystalline
substances, but instead, at best, one or more maxima of
the scattered X-ray radiation which have a breadth of
several degree units of the angle of defraction. However,
particularly good builder properties may be the result
even if in electron defraction experiments the silicate
particles produce poorly defined or even sharp defraction
maxima. This is to be interpreted to the effect that the
products have microcrystalline regions with a size of
from 10 to a few hundred nm, preference being given to
values up to at most 50 nm and in particular up to at
most 20 nm. Particular preference is given to
consolidated/compacted amorphous silicates, compounded
amorphous silicates and overdried X-ray amorphous
silicates.
It is of course also possible to use the generally known
phosphates as alkaline electrolyte. Of the large number
of commercially available phosphates, the alkali metal
phosphates, particularly preferably pentasodium
triphosphate and pentapotassium triphosphate (sodium or
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potassium tripolyphosphate), are of the greatest
importance in the detergents and cleaners industry.
Alkali metal phosphates is the collective term for the
alkali metal (in particular sodium and potassium) salts
of the various phosphoric acids, for which a distinction
can be made between metaphosphoric acids (HP03) and
orthophosphoric acid H3P04, as well as higher molecular
weight representatives. The phosphates combine a number
of advantages: they act as alkali-metal carriers, prevent
lime deposits on machine parts or lime incrustations in
fabrics and moreover contribute to the cleaning
performance.
Sodium dihydrogenphosphate, NaH2P04, exists as the
dehydrate (density 1.91 gcm-3, melting point 60°C) and as
the monohydrate (density 2.04 gcm-3). Both salts are white
powders which are very readily soluble in water, lose the
water of crystallization upon heating and at 200°C
convert to the weakly acidic disphospate (disodium
hydrogendiphosphate, Na2H2P20~), at a higher temperature
to sodium trimetaphosphate (Na2P309) and Maddrell's salt
(see below). NaH2P04 is acidic; it forms when phosphoric
acid is adjusted to a pH of 4.5 using sodium hydroxide
solution and the mash is sprayed. Potassium
dihydrogenphosphate (primary or monobasic potassium
A
phosphate, potassium biphosphate, KDP), KHZPO4, is a white
salt of density 2.33 gcm-3, has a melting point of 253°C
[decomposition with promotion of potassium polyphosphate
(KP03)x] and is readily soluble in water.
Disodium hydrogenphosphate (secondary sodium phosphate),
NazHP04, is a colorless crystalline salt which is very
readily soluble in water. It exists in anhydrous form and
with 2 mol of water (density 2.066 gcm-3, water loss at
95°C), 7 mol of water (density 1.68 gcm-3, melting point
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48°C with loss of 5 H20) and 12 mol of water (density
1. 52 gcm-3, melting point 35°C with loss of 5 H20) , is
anhydrous at 100°C and converts to the diphosphate Na4P20~
upon more intense heating. Disodium hydrogenphosphate is
prepared by neutralizing phosphoric acid with a soda
solution using phenolphthalein as indicator. Dipotassium
hydrogenphosphate (secondary or dibasic potassium
phosphate), KZHP04, is an amorphous white salt which is
readily soluble in water.
Trisodium phosphate, tertiary sodium phosphate, Na3P04,
are colorless crystals which, in the form of the
dodecahydrate, have a density of 1.62 gcm-3 and a melting
point of 73-76°C (decomposition), in the form of the
decahydrate (corresponding to 19-20% of Pz05) have a
melting point of 100°C and in anhydrous form
(corresponding to 39-40 % of P205) have a density of 2 . 536
gcm-3. Trisodium phosphate is readily soluble in water
with an alkaline reaction and is prepared by evaporating
a solution of exactly 1 mol of disodium phosphate and 1
mol of NaOH. Tripotassium phosphate (tertiary or tribasic
potassium phosphate), K3P04, is a white, deliquescent,
granular powder of density 2.56 gcm-3, has a melting point
of 1340°C and is readily soluble in water with an
alkaline reaction. It is formed, for example, during the
heating of Thomas slag with carbon and potassium sulfate.
Despite the higher price, in the detergents industry, the
more readily soluble, therefore highly effective,
potassium phosphates are often preferred over the
corresponding sodium compounds.
Tetrasodium diphosphate (sodium pyrophosphate), Na4Pz0-,,
exists in anhydrous form (density 2.534 gcm-3, melting
point 988°C, also given as 880°C) and as the decahydrate
(density 1.815-1.836 gcm-3, melting point 94°C with loss
of water). Both substances are colorless crystals which
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are soluble in water with an alkaline reaction. Na4P20~
forms during the heating of disodium phosphate to >200°C
or by reacting phosphoric acid with soda in the
stoichiometric ratio and dewatering the solution by
spraying. The decahydrate complexes heavy metal salts and
hardness constituents and therefore reduces the hardness
of water. Potassium diphosphate (potassium
pyrophosphate) , K4PzO~, exists in the form of the
trihydrate and is a colorless hygroscopic powder having a
density of 2.33 gcm-3, which is soluble in water, the pH
of the 1% strength solution at 25°C being 10.4.
By condensing NaH2P04 or KHZP04, higher molecular weight
sodium and potassium phosphates are formed, amongst which
it is possible to differentiate between cyclic
representatives, the sodium or potassium metaphosphates,
and chain-like types, the sodium or potassium
polyphosphates. For the latter in particular, a large
number of names are in use: melt or thermal phosphates,
Graham's salt, Kurrol's and Maddrell's salt. All higher
sodium and potassium phosphates are commonly referred to
as condensed phosphates.
The industrially important pentasodium triphosphate,
Na5P301o (sodium triphosphate), is a nonhygroscopic,
white, water-soluble salt which is anhydrous or
crystallizes with 6 H20 and is of the general formula Na0-
[P(O)(ONa)-O]n-Na where n=3. In 100 g of water, about 17
g of the salt which is free from water of crystallization
dissolve at room temperature, ca. 20 g at 60°C, and about
32 g at 100°C. If the solution is heated for 2 hours at
100°C, about 8% of orthophosphate and 15% of diphosphate
form as a ,result of hydrolysis. In the preparation of
pentasodium triphosphate, phosphoric acid is reacted with
soda solution or sodium hydroxide solution in the
stoichiometric ratio, and the solution is dewatered by
CA 02321326 2000-09-28
spraying. Similarly to Graham's salt and sodium
diphosphate, pentasodium triphosphate dissolves many
insoluble metal compounds (including lime soaps etc.).
Pentapotassium triphosphate, KSP301o (potassium
triphosphate), is available commercially, for example, in
the form of a 50% strength by weight solution (>23% of
PzOs ~ 25 % of K20) . The potassium polyphosphates are used
widely in the detergents and cleaners industry.
Furthermore, within the scope of the present invention,
it is also possible to use sodium potassium
triphosphates. These form, for example, when sodium
trimetaphosphate is hydrolyzed with KOH:
(NaP03 ) 3 + 2 KOH -~ Na3KzP301o + Hz0
According to the invention, these can be used exactly
like sodium triphosphate, potassium triphosphate or
mixtures of the two; mixtures of sodium triphosphate and
sodium potassium triphosphate or mixtures of potassium
triphosphate and sodium potassium triphosphate or
mixtures of sodium triphosphate and potassium
triphosphate and sodium potassium triphosphate can also
be used according to the invention.
As well as reducing agents and alkaline electrolytes, the
compositions according to the invention can comprise
further ingredients which improve product performance
and/or the appearance of the product. Dispersants and
surfactants are particularly suitable here, although dyes
and fragrances and also corrosion inhibitors are also
suitable ingredients.
Dispersants can be added to the compositions according to
the invention in order to disperse detached deposits and
constituents thereof, soilings or other foreign
substances in a stable manner in the cleaning liquor.
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From the group of dispersants, polycarboxylic acid salts
in particular have proven successful. Also in the case of
these salts, the alkali metal salts, and of these in turn
the potassium and/or sodium salts, are preferred. In the
case of the dispersants, particularly preferred salts are
the alkanolammonium salts of polycarboxylic acids, for
example the (substituted) mono-, di- and
trimethanolammonium salts, the rations of which can be
prepared from the corresponding methanaolamines by
protonation or quaternization with methylating or
ethylating agents. Particular preference is also given to
the (substituted) mono-, di- and triethanolammonium
salts, where the ration is preferably protonated or
methylated or ethylated triethanolamine.
Within the scope of the present invention, polycarboxylic
acids whose salts have a dispersing action mean, in
particular, those carboxylic acids which carry more than
one acid function. These are for example citric acid,
adipir acid, succinic acid, glutaric acid, malic acid,
tartaric acid, malefic acid, fumaric acid, sugar acids,
aminocarboxylic acids, nitrilotriacetic acid (NTA),
provided such a use is not objectionable for ecological
reasons, and mixtures thereof. Preferred salts are the
salts of the polycarboxylic acids, such as citric acid,
adipic acid, succinic acid, glutaric acid, tartaric acid,
sugar acids and mixtures thereof.
Other suitable dispersants are polymeric
polycarboxylates, i.e., for example, the alkali metal
salts of polyacrylic acid or of polymethacrylic acid, for
example those having a relative molecular mass of from
500 to 70,000 g/mol.
For the purposes of this specification, the molar masses
given for polymeric polycarboxylates are weight-average
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molar masses Mw of the respective acid form which have in
principle been determined by means of gel permeation
chromatography (GPC), a UV detector being used.
Measurement was made against an external polyacrylic acid
standard which, because of its structural similarity to
the polymers investigated, gives realistic molecular
weight values. This data differs significantly from the
molecular weight data where polystyrenesulfonic acids are
used as standard. The molar masses measured against
polystyrenesulfonic acids are generally significantly
higher than the molar masses given in this specification.
Suitable polymers are, in particular, polyacrylates which
preferably have a molecular mass of from 2000 to 20,000
g/mol. From this group in turn, because of their superior
solubility, the short-chain polyacrylates, which have
molar masses of from 2000 to 10,000 g/mol, and
particularly preferably from 3000 to 5000 g/mol, may be
preferred.
Also suitable are copolymeric polycarboxylates, in
particular those of acrylic acid with methacrylic acid
and of acrylic acid or methacrylic acid with malefic acid.
Copolymers of acrylic acid with malefic acid which contain
50 to 90% by weight of acrylic acid and 50 to 10% by
weight of malefic acid have proven particularly suitable.
Their relative molecular mass, based on free acids, is
generally 2000 to 70,000 g/mol, preferably 20,000 to
50,000 g/mol and in particular 30,000 to 40,000 g/mol.
To improve the water solubility, the polymers can also
comprise allylsulfonic acids, such as, for example,
allyloxybenzenesulfonic acid and methallylsulfonic acid,
as monomers.
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Also particularly preferred are biodegradable polymers of
more than two different monomer units, for example those
which contain, as monomers, salts of acrylic acid and of
malefic acid, and of vinyl alcohol or vinyl alcohol
derivatives, or which contain, as monomers, salts of
acrylic acid and of 2-alkylallylsulfonic acid and sugar
derivatives.
Further preferred builder substances which may likewise
be mentioned are polymeric aminodicarboxylic acids, salts
thereof or precursor substances thereof. Particular
preference is given to polyaspartic acids and to salts
and derivatives thereof which, in addition to cobuilder
properties, also have a bleach-stabilizing action.
Further suitable dispersants are polyacetals, which can
be obtained by reacting dialdehydes with polyol
carboxylic acids which have 5 to 7 carbon atoms and at
least 3 hydroxyl groups. Preferred polyacetals are
obtained from dialdehydes such as glyoxal,
glutaraldehyde, terephthalaldehyde and mixtures thereof,
and from polyol carboxylic acids such as gluconic acid
and/or glucoheptonic acid.
Further suitable organic dispersants are dextrins, for
example oligomers or polymers of carbohydrates, which may
be obtained by partial hydrolysis of starches. The
hydrolysis can be carried out by customary processes, for
example acid-catalyzed or enzyme-catalyzed processes. The
hydrolysis products preferably have average molar masses
in the range from 400 to 500,000 g/mol. Preference is
given here to a polysaccharide with a dextrose equivalent
(DE) in the range from 0.5 to 40, in particular from 2 to
30, where DE is a customary measure of the reducing
effect of a polysaccharide compared with dextrose, which
has a DE of 100. It is also possible to use maltodextrins
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with a DE between 3 and 20 and dry glucose syrups with a
DE between 20 and 37, and also so-called yellow dextrins
and white dextrins having higher molar masses in the
range from 2000 to 30,000 g/mol.
The oxidized derivatives of such dextrins are the
reaction products thereof with oxidizing agents which are
able to oxidize at least one alcohol function of the
saccharide ring to the carboxylic acid function. A
product oxidized on C6 of the saccharide ring may be
particularly advantageous.
Oxydisuccinates and other derivatives of disuccinates,
preferably ethylene diamine disuccinate, are further
suitable dispersants. Here, ethylene diamine N,N'-
disuccinate (EDDS) is preferably used in the form of its
sodium or magnesium salts. Also preferred in this
connection are glycerol disuccinate and glycerol
trisuccinate.
Examples of further organic dispersants which can be used
are acetylated hydroxycarboxylic acids and salts thereof,
which may also be present in lactone form and which
contain at least 4 carbon atoms and at least one hydroxyl
group and at most two acid groups.
Preferred compositions according to the invention
additionally comprise dispersants, preferably from the
group of polycarboxylic acid salts, particularly
preferably the alkanolamine salts of polycarboxylic
acids, in amounts of from 0.1 to 10% by weight,
preferably from 0.25 to 5% by weight and in particular
from 0.5 to 2.5% by weight, in each case based on the
total composition.
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Further preferred ingredients of the compositions
according to the invention are surfactants, nonionic
surfactants being clearly preferred over anionic and/or
cationic surfactants.
The nonionic surfactants used are preferably alkoxylated,
advantageously ethoxylated, in particular primary
alcohols having, preferably, 8 to 18 carbon atoms and on
average 1 to 12 mol of ethylene oxide (EO) per mole of
alcohol, in which the alcohol radical can be linear or,
preferably, methyl-branched in the 2-position, or can
contain linear and methyl-branched radicals as a mixture,
as is usually present in oxo alcohol radicals. In
particular, however, alcohol ethoxylates having linear
radicals from alcohols of native origin having 12 to 18
carbon atoms, e.g. from coconut, palm, tallow fatty or
oleyl alcohol, and on average 2 to 8 EO per mole of
alcohol are preferred. Preferred ethoxylated alcohols
include, for example, Clz-i4-alcohols having 3 EO or 4 EO,
C9_11-alcohol having 7 EO, Cls-is-alcohols having 3 EO, 5
EO, 7 EO or 8 EO, Clz-ia-alcohols having 3 EO, 5 EO or 7 EO
and mixtures of these, such as mixtures of Clz-i4-alcohol
having 3 EO and Clz-la-alcohol having 5 EO. The degrees of
ethoxylation given are statistical averages which may be
an integer or a fraction for a specific product.
Preferred alcohol ethoxylates have a narrowed homolog
distribution (narrow range ethoxylates, NRE). In addition
to these nonionic surfactants, fatty alcohols having more
than 12 EO can also be used. Examples thereof are tallow
fatty alcohol having 14 EO, 25 EO, 30 EO or 40 EO.
In addition, further nonionic surfactants which may be
used are also alkyl glycosides of the general formula
RO(G)X, in which R is a primary straight-chain or methyl-
branched, in particular methyl-branched in the 2-
position, aliphatic radical having 8 to 22, preferably 12
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to 18, carbon atoms, and G is the symbol which stands for
a glycose unit having 5 or 6 carbon atoms, preferably
glucose. The degree of oligomerization x, which indicates
the distribution of monoglycosides and oligoglycosides,
is any number between 1 and 10; preferably, x is 1.2 to
1.4.
A further class of nonionic surfactants used with
preference, which are used either as the sole nonionic
surfactant or in combination with other nonionic
surfactants, are alkoxylated, preferably ethoxylated or
ethoxylated and propoxylated fatty acid alkyl esters,
preferably having 1 to 4 carbon atoms in the alkyl chain,
in particular fatty acid methyl esters.
Nonionic surfactants of the amine oxide type, for example
N-cocoalkyl-N,N-dimethylamine oxide and N-tallowalkyl-
N,N-dihydroxyethylamine oxide, and of the fatty acid
alkanolamide type, may also be suitable. The amount of
these nonionic surfactants is preferably no more than
that of the ethoxylated fatty alcohols, in particular no
more than half thereof.
Further suitable surfactants are polyhydroxy fatty acid
amides of the formula (I),
R1
R-CO-N- [Z] (I)
in which RCO is an aliphatic acyl radical having 6 to 22
carbon atoms, R1 is hydrogen, an alkyl or hydroxyalkyl
radical having 1 to 4 carbon atoms, and [Z] is a linear
or branched polyhydroxyalkyl radical having 3 to 10
carbon atoms and 3 to 10 hydroxyl groups. The polyhydroxy
fatty acid amides are known substances which are
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_ CA 02321326 2000-09-28
customarily obtainable by reductive amination of a
reducing sugar with ammonia, an alkylamine or an
alkanolamine and subsequent acylation with a fatty acid,
a fatty acid alkyl ester or a fatty acid chloride.
The group of polyhydroxy fatty acid amides also includes
compounds of the formula (II),
Ri-O-Rz
R-CO-N- [Z] (II)
in which R is a linear or branched alkyl or alkenyl
radical having 7 to 12 carbon atoms, R1 is a linear,
branched or cyclic alkyl radical or an aryl radical
having 2 to 8 carbon atoms, and Rz is a linear, branched
or cyclic alkyl radical or an aryl radical or an oxyalkyl
radical having 1 to 8 carbon atoms, where C1_4-alkyl or
phenyl radicals are preferred, and [Z] is a linear
polyhydroxylalkyl radical whose alkyl chain is
substituted by at least two hydroxyl groups, or
alkoxylated, preferably ethoxylated or propoxylated,
derivatives of said radical.
[Z] is preferably obtained by reductive amination of a
reducing sugar, for example glucose, fructose, maltose,
lactose, galactose, mannose or xylose. The N-alkoxy- or
N-aryloxy-substituted compounds can be converted to the
desired polyhydroxy fatty acid amides by reaction with
fatty acid methyl esters in the presence of an alkoxide
as catalyst.
Preferred surfactants are weakly foaming nonionic
surfactants. Particularly preferably, the compositions
according to the invention for the machine cleaning of
silver comprise nonionic surfactants, in particular
18
CA 02321326 2000-09-28
nonionic surfactants from the group of alkoxylated
alcohols. The nonionic surfactants used are preferably
alkoxylated, advantageously ethoxylated, in particular
primary alcohols having, preferably, 8 to 18 carbon atoms
and on average 1 to 12 mol of ethylene oxide (EO) per
mole of alcohol, in which the alcohol radical can be
linear or, preferably, methyl-branched in the 2-position,
or can contain linear and methyl-branched radicals as a
mixture, as is usually present in oxo alcohol radicals.
In particular, however, alcohol ethoxylates having linear
radicals from alcohols of native origin having 12 to 18
carbon atoms, e.g. from coconut, palm, tallow fatty or
oleyl alcohol, and on average 2 to 8 EO per mole of
alcohol are preferred. Preferred ethoxylated alcohols
include, for example, Clz-i4-alcohols having 3 EO or 4 EO,
Cs-11-alcohol having 7 E0, C13-ls-alcohols having 3 EO, 5
EO, 7 EO or 8 EO, Clz-ls-alcohols having 3 EO, 5 EO or 7 EO
and mixtures of these, such as mixtures of Clz-14-alcohol
having 3 EO and Clz-is-alcohol having 5 EO. The degrees of
ethoxylation given are statistical averages which may be
an integer or a fraction for a specific product.
Preferred alcohol ethoxylates have a narrowed homolog
distribution (narrow range ethoxylates, NRE). In addition
to these nonionic surfactants, fatty alcohols having more
than 12 EO can also be used. Examples thereof are tallow
fatty alcohol having 14 EO, 25 EO, 30 EO or 40 EO.
Particular preference is given to compositions according
to the invention which comprise a nonionic surfactant
which has a melting point above room temperature.
Accordingly, preferred compositions comprise nonionic
surfactants) with a melting point above 20°C, preferably
above 25°C, particularly preferably between 25 and 60°C
and in particular between 26.6 and 43.3°C.
19
CA 02321326 2000-09-28
Suitable nonionic surfactants which have melting or
softening points in said temperature range are, for
example, weakly foaming nonionic surfactants, which may
be solid or of high viscosity at room temperature. If
nonionic surfactants are used which are of high viscosity
at room temperature, then it is preferable for these to
have a viscosity above 20 Pas, preferably above 35 Pas
and in particular above 40 Pas. Nonionic surfactants
which have a wax-like consistency at room temperature are
also preferred.
Preferred nonionic surfactants which are solid at room
temperature and are to be used originate from the groups
of alkoxylated nonionic surfactants, in particular
ethoxylated primary alcohols and mixtures of these
surfactants with structurally complex surfactants, such
as polyoxyproplylene/polyoxyethylene/polyoxypropylene
(PO/EO/PO) surfactants. Such (PO/EO/PO) nonionic
surfactants are, moreover, notable for good foam control.
In a preferred embodiment of the present invention, the
nonionic surfactant having a melting point above room
temperature is an ethoxylated nonionic surfactant
resulting from the reaction of a monohydroxyalkanol or
alkylphenol having 6 to 20 carbon atoms with, preferably,
at least 12 mol, particularly preferably at least 15 mol,
in particular at least 20 mol, of ethylene oxide per mole
of alcohol or alkylphenol.
A particularly preferred nonionic surfactant which is
solid at room temperature and is to be used is obtained
from a straight-chain fatty alcohol having 16 to
20 carbon atoms (Cls-ao-alcohol) , preferably a C18-alcohol,
and at least 12 mol, preferably at least 15 mol and in
particular at least 20 mol, of ethylene oxide. Of these,
CA 02321326 2000-09-28
the so-called "narrow range ethoxylates" (see above) are
particularly preferred.
Accordingly, particularly preferred compositions
according to the invention comprise ethoxylated nonionic
surfactant (s) which has/have been obtained from C6-zo
monohydroxyalkanols or C6_zo-alkylphenols or Cls-zo-fatty
alcohols and more than 12 mol, preferably more than 15
mol and in particular more than 20 mol, of ethylene oxide
per mole of alcohol.
The nonionic surfactant which is solid at room
temperature preferably additionally has propylene oxide
units in the molecule. Such PO units preferably
constitute up to 25% by weight, particularly preferably
up to 20% by weight and in particular up to 15% by weight
of the total molar mass of the nonionic surfactant.
Particularly preferred nonionic surfactants are
ethoxylated monohydroxyalkanols or alkylphenols which
additionally have polyoxyethylene/polyoxypropylene block
copolymer units. The alcohol or alkylphenol moiety of
such nonionic surfactant molecules preferably constitutes
more than 30% by weight, particularly preferably more
than 50% by weight and in particular more than 70% by
weight, of the total molar mass of such nonionic
surfactants. Preferred cleaning composition components
comprise, as ingredient a), ethoxylated and propoxylated
nonionic surfactants in which the propylene oxide units
in the molecule constitute up to 25% by weight,
preferably up to 20% by weight and in particular up to
15% by weight of the total molar mass of the nonionic
surfactant.
Further particularly preferred nonionic surfactants to be
used having melting points above room temperature
comprise 40 to 70% of a polyoxypropylene/polyoxy-
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_ CA 02321326 2000-09-28
ethylene/polyoxypropylene block polymer blend which
comprises 75% by weight of an inverted block copolymer of
polyoxyethylene and polyoxypropylene containing 17 mol of
ethylene oxide and 44 mol of propylene oxide, and 25% by
weight of a block copolymer of polyoxyethylene and
polyoxypropylene initiated with trimethylolpropane and
comprising 24 mol of ethylene oxide and 99 mol of
propylene oxide per mole of trimethylolpropane.
Nonionic surfactants which can be used with particular
preference are, for example, those available under the
name Poly Tergent~ SLF-18 from Olin Chemicals.
Further preferred compositions according to the invention
comprise nonionic surfactants of the formula
R10 [CHzCH (CH3) O] X [CHZCH20] y [CH2CH (OH) Rz] ,
in which R1 is a linear or branched aliphatic hydrocarbon
2 0 radical having 4 to 18 carbon atoms or mixtures thereof ,
RZ is a linear or branched hydrocarbon radical having 2
to 26 carbon atoms or mixtures thereof, and x is a value
between 0.5 and 1.5, and y is a value of at least 15.
Further preferred nonionic surfactants which can be used
are the terminally-capped poly(oxyalkylated) nonionic
surfactants of the formula
R10 [CH2CH (R3) O] X [CHZ] kCH (OH) [CH2] ~OR2
in which R1 and Rz are linear or branched, saturated or
unsaturated, aliphatic or aromatic hydrocarbon radicals
having 1 to 3 0 carbon atoms , R3 is H or a methyl , ethyl ,
n-propyl, isopropyl, n-butyl, 2-butyl or 2-methyl-2-butyl
radical, x is a value between 1 and 30, k and j are
values between 1 and 12, preferably between 1 and 5. If x
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CA 02321326 2000-09-28
is >_ 2, each R3 in the above formula may be different. R1
and RZ are preferably linear or branched, saturated or
unsaturated, aliphatic or aromatic hydrocarbon radicals
having 6 to 22 carbon atoms, radicals having 8 to 18
carbon atoms being particularly preferred. For the
radical R3, H, -CH3 or -CHZCH3 are particularly preferred.
Particularly preferred values for x are in the range from
1 to 20, in particular from 6 to 15.
As described above, each R3 in the above formula can be
different if x is >_ 2. As a result, the alkylene oxide
unit in the square brackets can be varied. If, for
example, x is 3, the radical R3 can be chosen to form
ethylene oxide (R3 - H) or propylene oxide (R3 - CH3)
units which can be joined to one another in any order,
for example (EO) (PO) (EO) , (EO) (EO) (PO) , (EO) (EO) (EO) ,
(PO) (EO) (PO) , (PO) (PO) (EO) and (PO) (PO) (PO) . The value 3
is chosen here for x by way of example and can of course
be greater, the scope for variation increasing with
increasing x values and embracing, for example, a large
number of (EO) groups, combined with a small number of
(PO) groups, or vice versa.
Particularly preferred terminally-capped poly(oxy-
alkylated) alcohols of the above formula have values of k
- 1 and j - 1, thereby simplifying the above formula to
R10 [CHzCH (R3) O] XCHZCH (OH) CHzOR2 .
In the last-mentioned formula, R1, R2 and R3 are as
defined above and x is a number from 1 to 30, preferably
from 1 to 20 and in particular from 6 to 18. Particular
preference is given to surfactants in which the radicals
R1 and Rz have 9 to 14 carbon atoms, R3 is H, and x adopts
values from 6 to 15.
23
19
CA 02321326 2000-09-28
A further group of preferred surfactants are so-called
"fluorine surfactants" which carry a perfluoroalkyl
radical as hydrophobic group. Compared with
nonfluorinated surfactants, fluorine surfactants are
notable for lower critical micelle concentration values
and therefore, even in extremely small concentrations,
effect a significant lowering of the surface tension of
water. They have high chemical and thermal stability,
meaning that they can also be used in aggressive media
and at high temperatures.
In summary, preferred compositions according to the
invention additionally comprise nonionic surfactant(s),
preferably alkoxylated, particularly preferably
ethoxylated and/or propoxylated nonionic surfactants
having 8 to 24, preferably 10 to 20 and in particular 12
to 18, carbon atoms, particularly preferably nonionic
surfactants containing fluoroalkyl groups ("fluorine
surfactants"), in amounts of from 0.1 to 10% by weight,
preferably from 0.25 to 5% by weight and in particular
from 0.5 to 2.5% by weight, in each case based on the
total composition.
Dyes and fragrances can be added to the machine silver-
cleaning compositions according to the invention in order
to improve the esthetic impression of the resulting
products and to provide the consumer with not only the
performance but also a visually and sensorially "typical
and unmistakable" product. Perfume oils and fragrances
which can be used are individual scent compounds, e.g.
the synthetic products of the ester, ether, aldehyde,
ketone, alcohol and hydrocarbon type. Scent compounds of
the ester type are, for example, benzyl acetate,
phenoxyethyl isobutyrate, p-tert-butylcyclohexyl acetate,
linalyl acetate, dimethylbenzylcarbinyl acetate,
phenylethyl acetate, linalyl benzoate, benzyl formate,
24
_ CA 02321326 2000-09-28
ethyl methylphenylglycinate, allyl cyclohexylpropionate,
styrallyl propionate and benzyl salicylate. The ethers
include, for example, benzylethyl ether; the aldehydes
include, for example, the linear alkanals having
8-18 carbon atoms, citral, citronellal, citronellyloxy-
acetaldehyde, cyclamen aldehyde, hydroxycitronellal,
filial and bourgeonal; the ketones include, for example,
the ionones, a-isomethylionone and methyl cedryl ketone;
the alcohols include anethole, citronellol, eugenol,
geraniol, linalool, phenylethyl alcohol and terpineol;
and the hydrocarbons include mainly the terpenes, such as
limonene and pinene. Preference is given, however, to
using mixtures of different scents which together produce
an appealing fragrance note. Such perfume oils can also
comprise natural scent mixtures, as are obtainable from
vegetable sources, e.g. pine oil, citrus oil, jasmine
oil, patchouli oil, rose oil or ylang-ylang oil. Also
suitable are clary sage oil, camomile oil, oil of cloves,
melissa oil, mint oil, cinammon leaf oil, lime blossom
oil, juniperberry oil, vetiver oil, olibanum oil,
galbanum oil and labdanum oil, and also orange blossom
oil, neroliol, orange peel oil and sandalwood oil.
The fragrances can be incorporated directly into the
cleaning compositions according to the invention,
although it may also be advantageous to apply the
fragrances to carriers. Such carriers which have proven
successful are, for example, cyclodextrins, it being
possible in addition for the cyclodextrin-perfume
complexes to be additionally coated with further
auxiliaries.
In order to improve the esthetic impression of the
compositions according to the invention, it (or parts
thereof) can be colored using suitable dyes. Preferred
dyes, the choice of which does not present any problems
CA 02321326 2000-09-28
to the person skilled in the art, have high storage
stability and insensitivity toward the other ingredients
of the composition and toward light, and also no marked
substantivity toward the substrates to be treated with
the compositions, such as glass, ceramic or plastic
dishes, in order not to color these.
The cleaning compositions according to the invention can,
to protect the ware or the machine, comprise corrosion
inhibitors, so-called silver protectants in the area of
machine dishwashing, in particular, being of particular
importance . The known substances of the prior art can be
used. Silver protectants which can be used are, in
general, particularly those chosen from the group of
triazoles, benzotriazoles, bisbenzotriazoles,
aminotriazoles, alkylaminotriazoles and transition metal
salts or complexes. Particular preference is given to
using benzotriazole and/or alkylaminotriazole. Moreover,
cleaning formulations frequently comprise agents which
contain active chlorine, which are able to significantly
reduce corrosion of the silver surface. In chlorine-free
cleaners, use is made in particular of oxygen-containing
and nitrogen-containing organic redox-active compounds,
such as divalent and trivalent phenols, e.g.
hydroquinone, pyrocatechol, hydroxyhydroquinone, gallic
acid, phloroglucinol, pyrogallol, and derivatives of
these classes of compound. Inorganic compounds in the
form of salts and complexes, such as salts of the metals
Mn, Ti, Zr, Hf, V, Co and Ce, are also frequently used.
Preference is given here to the transition metal salts
chosen from the group of manganese and/or cobalt salts
and/or complexes, particularly preferably cobalt (ammine)
complexes, cobalt (acetate) complexes, cobalt (carbonyl)
complexes, chlorides of cobalt or manganese, and
manganese sulfate. Zinc compounds can likewise be used
for preventing corrosion on the ware.
26
CA 02321326 2000-09-28
Taking all of the information given hitherto regarding
ingredients and amounts thereof, then particularly
preferred compositions according to the invention for the
cleaning of silver in a dishwasher comprise, in addition
to further optional constituents,
a) 10 to 70% by weight of potassium carbonate and/or
sodium carbonate,
b) 5 to 50% by weight of potassium citrate and/or
sodium citrate,
c) 1 to 60% by weight of one or more reducing agents
having a solubility of more than 20 g per liter of
water at 20°C,
d) 0 to 10% by weight of one or more dispersants, and
e) 0 to 10% by weight of one or more nonionic
surfactants.
In particularly preferred compositions, the sum of
components a) and b) constitutes 40 to 99% by weight,
preferably 45 to 95% by weight and in particular 50 to
90% by weight, of the total composition.
As well as the carbonates and citrates, the other
alkaline electrolytes described above can also be present
in the compositions, preferred compositions additionally
comprising hydrogencarbonates, hydroxides and/or
phosphates in amounts of from 1 to 30% by weight,
preferably from 2 to 25% by weight and in particular from
5 to 15% by weight, in each case based on the total
composition.
The reducing agents which can be used are in turn the
substances described above. Advantageously, the
compositions comprise, as component c), pyrocatechol,
hydroquinone, ascorbic acid or mixtures thereof in
amounts of from 2.5 to 50% by weight, preferably from 5
27
_ CA 02321326 2000-09-28
to 45% by weight and in particular from 10 to 25% by
weight, in each case based on the total composition.
The compositions according to the invention can be
formulated in different ways, meaning that they can be
used, for example, as powder, granulate or tablet. By
dissolving or suspending the solid ingredients, it is
also possible to provide liquid formulations.
The present invention further provides a method of
cleaning silver in which articles made of silver or
silver-plated articles or alloys of silver are treated
with a cleaning composition according to the invention in
a dishwasher.
For this, the discolored or tarnished silver articles are
placed into a dishwasher, the composition according to
the invention is introduced into the dishwasher, and a
wash program is left to run. The compositions according
to the invention can be added via the dosing chamber of
the machine, although it is also possible to introduce
them directly into the machine, in which case a dosing
aid can be used if required. An analogous method for
removing oxide and/or sulfide deposits from tarnished
silver, which comprises treating articles made of
tarnished silver or alloys thereof with a cleaning
composition according to the invention in a dishwasher,
is further provided by the present invention.
To increase the shine, the articles can be afterpolished
with a soft cloth after the cleaning program.
Corresponding methods according to the invention in
which, after the cleaning in the dishwasher, an
aftertreatment step, in particular afterpolishing, is
carried out are preferred embodiments of the present
invention.
28
CA 02321326 2000-09-28
The dosing of the cleaning composition in the method
according to the invention should preferably be chosen
such that the cleaning liquor in the dishwasher comprises
the reducing agents) in amounts of from 1 to 100 mmol/1,
preferably from 2.5 to 75 mmol/1 and in particular from 5
to 50 mmol/1.
Analogous statements can also be made for ingredients a)
and b) of the preferred compositions according to the
invention. In preferred methods, on the one hand, the
cleaning liquor in the dishwasher comprises carbonate(s),
in particular potassium carbonate and/or sodium
carbonate, in amounts of from 1 to 500 mmol/1, preferably
from 10 to 250 mmol/1 and in particular from 50 to 150
mmol/l, and on the other hand the cleaning liquor in the
dishwasher, in a further preferred method, comprises
citrate(s), in particular potassium citrate and/or sodium
citrate, in amounts of from 1 to 150 mmol/l, preferably
from 2.5 to 100 mmol/1 and in particular from 5 to 75
mmol/1.
The present invention further provides for the use of
cleaning compositions which comprise alkaline
electrolytes and reducing agents having a solubility of
more than 20 g per liter of water at 20°C, for the
cleaning of silver.
The above statements regarding preferred embodiments are
entirely valid here by analogy. Particular preference is
given to using cleaning compositions according to the
invention comprising
a) 10 to 70% by weight of potassium carbonate and/or
sodium carbonate,
b) 5 to 50% by weight of potassium citrate and/or
sodium citrate,
29
CA 02321326 2000-09-28
c) 1 to 60% by weight of one or more reducing agents
having a solubility of more than 20 g per liter of
water at 20°C,
d) 0 to 10% by weight of one or more dispersants, and
e) 0 to 10% by weight of one or more nonionic
surfactants,
for the removal of oxide and/or sulfide deposits on
tarnished silver.
In the case of the use according to the invention too it
is preferred that the compositions are used in a
dishwasher and that, after the cleaning in the
dishwasher, an aftertreatment step, in particular
afterpolishing, is carried out.
CA 02321326 2000-09-28
Examples:
Two cleaning compositions according to the invention
having the compositions below were prepared (stated in
by weight, based on total composition):
E1 E2
Sodium citrate 29.0 27.0
Sodium carbonate 58.1 54.0
Hydroquinone 12.9 -
Ascorbic acid - 19.0
To produce tarnished silver surfaces, sheets of silver
measuring 12 x 12 cm were placed into an oxidizing
solution at 20°C and heated to 65°C. When this
temperature was reached, 5 g of sodium percarbonate were
added to the solution, which was maintained at 65°C. The
plates were left in the solution for a total of 20
minutes (including heating-up time).
Composition of the oxidizing solution:
2.5 liters of water [16° German hardness]
23 g of sodium citrate
16 g of sodium hydrogencarbonate
5 g of sodium carbonate
2 g of TAED
0.5 ml of ammonium sulfide solution [20% strength]*
5 g of sodium percarbonate*
* (added only at 65°C)
The tarnished silver sheets were then removed, rinsed
with distilled water and dried in the air. The powdery
deposit then present on the plate was rubbed with a soft
31
CA 02321326 2000-09-28
cloth, so that an anthracite-colored lustrous surface
remained.
Tarnished sheets were then placed into a dishwasher
(Miele Turbothermic G 590) and washed using a 65°C
universal program [water hardness: 16° German hardness].
In each of the cleaning cycles, an amount of formulation
1 according to the invention or of formulation 2
according to the invention was used such that the amount
of sodium carbonate in the wash liquor was 95 mmol/1, the
amount of sodium citrate was 20 mmol/1 and the amount of
reducing agent was 20 mmol/1.
When the wash program had finished, the silver surfaces
had been completely freed from dark deposits. The shine
on the surfaces could be produced or increased by rubbing
with a soft cloth.
32
