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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a phosphate-free machine dishwashing composition.
More particularly, this invention relates to a machine dishwashing
composition which is free from phosphorus and which more efficiently
removes food soils from cooking and eating utensils with less spotting and
at least equivalent clarity to glassware and dishes when compared to
conventional phosphate-built dishwashing compositions.
Mounting legislation outlawing the use of phosphorus in all household
detergents has created considerable demand for phosphorus-free machine
dishwashing compositions. However, despite significant efforts, no fully
satisfactory phosphate-free machine dishwashing composition has, as yet,
been obtained that is now commercially available.
In the detergent industry, distinctions are drawn between cleaning
compositions on the basis of their functional utility; for example, those
in the art are well aware that there are considerable art-recognized
differences between cleaning compositions that are used for laundering
purposes; cleaning compositions that are used for machine dishwashing
purposes; and cleaning compositions that are used for hand dishwashing
purposes. Generally, cleaning compositions for laundering purposes employ
high foaming organic surfactants as the main cleansing agents. Foaming,
unless it is excessive to the extent that it causes overflow from the
washing machines, is generally considered beneficial in laundering
compositions since it helps to loosen the soil from the fabric substrates
by its local mechanical action. This local action is desirable since the
substrate in the laundry machine receives comparatively poor mechanical
agitation. By way of contrast, machine dishwashing methods that are
currently used to wash china, glass, porcelain, ceramics, metal, and hard
synthetic articles result in there being a high mechanical impact of the
wash liquid that is sprayed onto the articles to be cleaned. Recently,
developments in dishwashing apparatus have been directed toward further
increasing the intensity of liquid motion as well as the water volume
cycled per minute, and in this way to further improve the mechanical
cleansing effect of the cleansing solution. Compared to laundering
compositions, however, machine dishwashing compositions are very
low-foaming compositions and preferably so, since foam formation reduces
the mechanical impact of the liquid sprayed onto the articles to be
cleaned. The surface active agents useful for machine dishwashing
compositions should not only be low foaming materials in and of
themselves, but they should also preferably be foam depressants, so that
the foaming caused by protein and food residues in combination with
alkaline cleansing solutions is kept to a minimum. Accordingly, the
surfactant content of machine dishwashing compositions is very low. This
situation, however, is quite different from hand dishwashing compositions,
which, preferably, are high foaming and have more the attributes of
laundering compositions.
2. Description of the Prior Art
Heretofore, the machine dishwashing detergent compositions that have been
commercially employed in the art have been based on the use of phosphorus
compounds that are now strenuously objected to on ecological grounds. For
example, U.S. Pat. Nos. 3,579,455 and 3,627,686 require, respectively, the
presence of tetra(alkali metal) pyrophosphate and an alkali metal
hexametaphosphate, or the presence of tetra(alkali metal) pyrophosphate
and alkali metal nitrilotriacetate.
In order to circumvent the phosphate requirements of the foregoing patents,
later patents such as those of U.S. Pat. Nos. 3,700,599 and of 3,706,672
have found need to resort to the use of polymeric chelating agents per se
(U.S. Pat. No. 3,700,599), or of such chelating agents in combination with
an alkaline detergent salt or salts (U.S. Pat. No. 3,706,672). However,
the amount of the polymer that is used in these patents is directly
controlled by the degree of hardness of the water in which the dishwashing
composition is to be utilized; for such amount has to be sufficient for
purposes of chelating both the calcium and magnesium ions that are
present. Thus, the primary function of the maleic anhydride/vinyl acetate
copolymer of these latter two patents is to soften the water in which the
dishes, glassware, etc. are to be washed by sequestering those metal
cations which cause the hardness of such water. But this requires, for
relatively hard water having 300 ppm or higher of those cations causing
such water to be hard, a high polymeric or polyelectrolytic concentration
to be present in the composition of the ultimate dishwashing product that
is employed.
Use of strong chelating agents, however, such as the hardness sequestering
polyelectrolytes discussed above as well as those now known and available
to the art, pose, from an ecological standpoint, long range and unknown
potential toxicological sources of danger. For example, strong
sequestrants such as nitrilotriacetate, sodium oxydiacetate, etc., have
been shown to be ecologically unacceptable owing to their potential
toxicity; for it is said that these sequestrants can complex with heavy
metals such as Hg.sup.++ and other trace heavy metals and offset the
biological transport mechanism of these trace metals in living tissues.
Thus, nitrilotriacetate has been blamed for causing fetus abnormality by a
similar mechanism. By way of contrast, however, inefficient metal
complexing agents are free from this drawback and this is believed to be
the case with the polyelectrolytes contained in the present machine
dishwashing compositions.
Contemporary ecological considerations, moreover, in another germane
aspect, require that such formulated products as machine dishwashing
compositions be at least 90% biodegradable. However, past and present
machine dishwashing compositions now available to, and known in and by,
the art, in order to be effective, must contain more than 10%
polyelectrolytes and as such would not meet the stringent ecological
requirements. Furthermore, high molecular weight polyelectrolytes such as
those now used in the art are known to be biorefractory.
By way of contrast, and in resolution of the foregoing art-recognized
deficiencies and needs, the present invention now provides a machine
dishwashing composition that is able to function satisfactorily with low
polyelectrolyte concentrations, i.e., polyelectrolyte concentrations so
low as to fall far short of the amounts required to sequester the metal
cations that cause the hardness of the water present in the wash solution.
In fact, the most effective polyelectrolytes of the present invention are
characterized by such low molecular weights and such a low degree of
polymerization that they would be regarded as poor prospective candidates
as sequestering agents consistent with the needs and requirements of U.S.
Pat. Nos. 3,700,599 and 3,706,672. It has been found, by the present
invention, that the select use of certain polyelectrolytes of a specific
character and description in combination with an alkali metal, or
ammonium, carbonate, whereby the weight ratio of polyelectrolyte to
carbonate is kept within controlled limits, enables the resultant
dishwashing composition, which comprises those two materials as essential
ingredients, not only to function at least as efficiently and effectively
as previous dishwashing compositions (such as those discussed above), but
also to be operable (with less cost of manufacture) with polyelectrolyte
levels previously found to be inoperable by the prior art.
In conclusion, it can be stated that there are two major differences
between the present non-phosphate machine dishwashing compositions and
those low- or non-phosphate polyelectrolyte-built machine dishwashing
compositions that have been heretofore known or used in the machine
dishwashing art, and these differences can be briefly summarized as
follows:
(1) the present machine dishwashing compositions employ low concentrations
of polyelectrolytes, whereas those of the prior art utilize high
concentrations of polyelectrolytes.
(2) the present machine dishwashing compositions employ polyelectrolytes of
low molecular weight which have very poor metal ion sequestering capacity,
whereas those of the prior art utilize polyelectrolytes that are strong
sequestrants for metal ions.
As has been seen, these two major differences to at least a substantial
extent are believed tied to the surprising ecological advantages that
accrue to the present machine dishwashing compositions vis-a-vis those of
the prior art. As but a simple illustration of this, it can be noted that
the present compositions comprise mostly inorganic salts such as an alkali
metal, or ammonium, carbonate and contain less than 10% polyelectrolytes
of low molecular weight, and this enables the resultant or ultimate
machine dishwashing composition or product to be at least 90%
biodegradable, even in the event the polyelectrolytes thereof may be
biorefractory.
SUMMARY OF THE INVENTION
The present invention relates generally to phosphate-free, low foaming
machine dishwashing compositions comprising an admixture of an alkali
metal, or ammonium, carbonate and a water soluble salt of a low molecular
weight polymer, and more particularly relates to a phosphate-free, low
foaming machine dishwashing composition comprising an admixture of an
alkali metal, or ammonium, carbonate and a water soluble salt of a low
molecular weight polyelectrolyte such as a polyacrylate or
polymethacrylate having a molecular weight of about 500-4000 and the
formula:
##STR2##
wherein R.sub.1, R.sub.2, R.sub.4, and R.sub.5 can be hydrogen, C.sub.1
-C.sub.4 lower alkyl, or combinations thereof; R.sub.3 and R.sub.6 can be
hydrogen, carboxy, alkylcarboxy or a combination thereof; and the sum of
(a+b) is .gtoreq.5 to .ltoreq.30, preferably .gtoreq.7 to .ltoreq.15,
employed in a weight ratio (polyelectrolyte:carbonate) of 5:95-20:80, and
preferably with a low-foaming surfactant and/or other conventional
additives or ingredients, results in effective and economical dishwashing.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The phosphate-free, low foaming machine dishwashing compositions of the
present invention comprise, as noted previously:
(i) an alkali metal, or ammonium, carbonate. Typical of the alkali metal or
ammonium carbonates which can be employed in the compositions of the
present invention are the alkali metal, ammonium or substituted ammonium,
carbonates; bicarbonates; sesquicarbonates; and mixtures thereof.
Illustrative of such carbonates are lithium carbonate, sodium carbonate,
potassium carbonate, ammonium carbonate, potassium bicarbonate, potassium
bicarbonate, sodium sesquicarbonate, potassium sesquicarbonate, and
mixtures thereof. The preferred alkali metal carbonate is sodium
carbonate.
(ii) a water soluble salt of a low molecular weight polyelectrolyte having
the structure formula:
##STR3##
wherein R.sub.1, R.sub.2, R.sub.4, and R.sub.5 can be hydrogen, C.sub.1
-C.sub.4 lower alkyl, or combinations thereof; R.sub.3 and R.sub.6 can be
hydrogen, carboxy, lower alkoxycarboxyl, or a combination thereof; and the
sum of (a+b) is .gtoreq.5 to .ltoreq.30, preferably .gtoreq.7 to
.ltoreq.15, the weight ratio of polyelectrolyte:carbonate being
5:95-20:80, the molecular weight of said polyelectrolyte being about
500-4000. Typical of the polyelectrolytes encompassed copolymers of
acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid,
etc. Preferably, the polyelectrolyte is a polyacrylic acid,
polymethacrylic acid, or a copolymer of acrylic and methacrylic acids,
said homopolymers and copolymer ranging in molecular weight from about 504
to 1291 when they contain the preferred 7 to 15 monomeric units per
molecule.
The polyelectrolytes that can be employed in the present invention include
polyelectrolytes exhibiting a low molecular weight such as those having
molecular weights of from about 500 to about 4000.
The preferred low molecular weight polymeric polyelectrolytes of the
present invention can be prepared by conventional methods of
polymerization of vinyl monomers in the presence of a chain transfer
agent, the function of the latter being to control the chain length of the
polymer. Although any chain transfer agent can be suitably employed, the
preferred chain transfer agents are the mercapto(-SH) bearing compounds
such as alkyl mercaptans, mercapto acids, thio acids, inorganic thio
compounds, and the like.
The water soluble salts of the polyelectrolytes described above can be the
alkali metal salts or the ammonium or substituted ammonium salts thereof.
The alkali metal carbonate and water soluble salt of the polyelectrolyte
which together form the essential ingredients of the low-foaming machine
dishwashing composition of the present invention can be combined, as
noted, in a weight ratio (polyelectrolyte:carbonate) of from about 5:95 to
about 20:80.
The phosphate-free machine dishwashing compositions of the present
invention can also optionally include the following:
(a) Up to about 5% by weight of a foam-suppressing non-ionic surfactant.
Illustrative of such surfactants are the modified ethyoxylated alcohol or
alkyl phenol type, wherein the ethoxylate is modified by replacing the
terminal OH group with halogen, for example, chlorine, or alkoxy, or with
aryloxy and arylalkyloxy groups; amine polyglycol condensates; pluronic
surfactants obtained by the condensation of ethylene oxide with
hydrophobic bases formed by condensing propylene oxide with propylene
glycol, and the like. Typical of such surfactants are: Antarox BL-225 and
BL-330, Antarox LF-330 and LF-334 available from GAF Corporation; Plurofac
RA43, Plurofac RA435, available from Wyandotte Chemical Corporation;
Tergitol Min-Foam 1X and 2X from Union Carbide Corporation; and Triton
CF10, CF21, CF54, DF12, DF16, available from Rohm & Haas Company.
(b) Up to 50% by weight of an alkali metal silicate. The alkali metal
silicates which can be employed in the composition of the present
invention can range from the metasilicates, which are often designated as
1:1 M.sub.2 O:SiO.sub.2 silicates to low M.sub.2 O:SiO.sub.2 silicates
such as 3.2:1 silicates, where M.sub.2 O represents the alkali metal oxide
portion of the silicate. The preferred alkali metal silicates are sodium
and not essential ingredients of the composition of this invention but
although optional, their presence is, however, beneficial to the
composition, particularly when corrosion inhibition of metal parts is
desired. Thus, an institutional dishwashing composition to be used for
washing glassware and china only, a composition free from the silicates
can be suitably employed. In such cases, however, some free caustic such
as sodium hydroxide or potassium hydroxide can be beneficially employed in
place of the silicates to impart higher alkali reserves to the
composition. In a household machine dishwashing composition, however,
where silverware, aluminum pots and pans and other metal utensils are
washed along with china and glassware, a silicate based composition is
preferred. For optimum corrosion inhibition, the composition of the
present invention preferably contains from about 6 to about 10% by weight
SiO.sub.2 derived from the silicate.
(c) Up to about 80% by weight of an inert diluent such as alkali metal
chlorides, sulfates, nitrites, and the like. Illustrative of such diluents
are sodium or potassium chloride, sodium or potassium sulfate, sodium or
potassium nitrite, and the like.
Additionally, small amounts of other conventional additives such as
perfumes, colorants, chlorinated bleaches, antibacterial agents, or other
similar adjuvants can be suitably employed.
The machine dishwashing composition of the present invention can be stored
and used as either a dry mixture of the above composition or a
concentrated solution of the above composition in admixture with from
about 20 to 80% water. Preferably, liquid concentrates of the machine
dishwashing composition of the present invention contain from about 40 to
about 80% water.
The alkaline, phosphate-free, low-foaming machine dishwashing composition
of the present invention is highly effective in removing food soils and
residues from dishes, glassware and other cooking and eating utensils when
employed in conventional dishwashing machines as an aqueous solution
containing from about 0.05 to about 0.5 weight % and preferably, from
about 0.1 to about 0.3 weight % of the machine dishwashing composition of
the present invention at a temperature of from about 70.degree. to about
200.degree. F. and preferably from about 130.degree. to about 160.degree.
F. and applying said aqueous solution at said temperatures to the surfaces
to be cleaned under conditions which effect a high mechanical impact of
the aqueous solution on said surfaces to be cleaned. Although any
technique can be employed for applying the aqueous solution of the
dishwashing composition to the fouled surfaces, it has been found
especially highly effective when used with spray washing equipment of the
type conventionally used in cleaning cooking and eating utensils.
Additionally, highly effective cleaning with low foaming can be obtained
in institutional dishwashing machines when employing the composition of
the present invention. In the final step of the cleaning process, the
clean surfaces are preferably rinsed with clear water. It has been found,
in accordance with the present invention, that not only are the food
residues more effectively removed with the composition of the present
invention, but the cleaned dishes and glassware exhibit less spotting and
greater clarity than conventional cleaning compositions.
The following examples further illustrate the machine dishwashing
compositions and the dishwashing process of the present invention. Unless
otherwise stated, all percentages and parts are by weight.
EXAMPLES 1-17
One important aspect of a dishwashing detergent's performance is its
ability to retard or prevent formation of spots or films on dishes and
glassware. Spotting generally occurs by deposition of insoluble inorganic
salts. Deposit formation also interferes with the operation of the washing
equipment, requiring frequent maintenance. A deposition tendency test was
thus employed in which the dishwashing composition was dissolved in 300
ppm hard water (Ca:Mg=60:40) to give a 0.15% solution, the solution was
heated to 140.degree. F. and held there with magnetic stirring for 30
minutes. The solution at different intervals of time was then examined for
appearance of haze, cloudiness, or precipitation. Non-appearance of
precipitation within 10 minutes at 140.degree. F. was considered to be
satisfactory. Results of such tests are shown in Table 1. These results
indicate that low molecular weight polyelectrolytes are superior to high
molecular weight polyelectrolytes in the composition of the present
invention and both are superior to the control which did not contain any
polyelectrolytes.
Table 1
__________________________________________________________________________
Composition, % by Weight Ratings.sup.(3)
Example
Polyelectrolyte.sup.(1)
Polyelectrolyte
Na.sub.2 SiO.sub.3 .
10 min.
0 min.
10
30 min.
No. Average MW Sodium Salt
Na.sub.2 CO.sub.3
5H.sub.2 O
Surf..sup.(2)
Na.sub.2 SO.sub.4
80.degree. F.
140.degree. F.
140.degree.
140.degree.
__________________________________________________________________________
F.
1 -- -- 33 33 2 32 D D D D
##STR4## 7 33 33 2 25 A B C D
3
##STR5## 5 33 33 2 27 A A A B
4 Same 7 33 33 2 25 A A A A
5 Same 10 88 -- 2 -- A A A C
6
##STR6## 5 33 33 2 27 A A A B
7 Same 7 33 33 2 25 A A A B
8
##STR7## 5 33 33 2 27 A A C D
9
##STR8## 7 33 33 2 25 A A C C
10 Poly AA 4000 7 33 33 2 25 A A/B C D
11
##STR9## 7 33 33 2 25 A A B B
12
##STR10## 5 33 33 2 27 A A A B
13
##STR11## 5 33 33 2 27 A A A B
14
##STR12## 5 33 33 2 27 A A B C
15
##STR13## 5 33 33 2 27 A A B B
16 Poly AA 25,000
7 33 33 2 25 A D D D
17 Same 10 33 33 2 22 A C C/D D
__________________________________________________________________________
.sup.(1) AA = Acrylic Acid; MeA = Methyl Acrylate; MAA = Methacrylic
.sup.(2) Surface active agent used was Antarox BL225 (available from GAF
Corporation)
.sup.(3) A = Clear or very slight haze; B = Hazy or very slightly Cloudy;
C = Cloudy; D = Precipitation.
##STR14##
EXAMPLES 18-21
These examples compare the results obtained with machine dishwashing
compositions of the present invention with those obtained with a
phosphate-built dishwashing composition.
Evaluations were conducted following Procedure No. 198 described in the
Chemical Specialties Manufacturers Assoc., Inc. Bulletin dated July 31,
1957 (A Tentative Spotting and Filming Test in Home Dishwashing Machines).
Results of such evaluations are shown in Table 2.
As may be noted from the results, the compositions of the present invention
are far superior to the controls with or without phosphate.
Table 2
__________________________________________________________________________
Evaluation of Automatic Dishwasher Detergents for Filming and Spotting
Characteristics
Test Conditions
Water Temperature: Initial 120.degree. F. - Final 140.degree. F.; Water
Hardness 300 ppm (Ca:Mg = 60:40) as CaCO.sub.3.
Soil = 20% dried milk/80% margarine (total 40 g.)
Load = 6 glass tumblers
Dishwasher: Kitchen Aid KD15
Detergent Conc.: 0.35% (Total 28.0 g.)
Composition, % by Weight Number of Wash
Cycles.sup.(4)
Example
No. Na.sub.2 CO.sub.3
STPP.sup.(5)
NaPAA-850.sup.(1)
Na.sub.2 SiO.sub.3 . 5H.sub.2 O
Surf..sup.(2)
CDB-63.sup.(3)
Na.sub.2 SO.sub.4
1 2 3 4 5 6
__________________________________________________________________________
18 30 -- -- 33.5 2 2 32.5 2a
2b 2c 2d 5e 5e
19 30 -- 7.5 33.5 2 2 25 1a
1a 1.3a
2.2a
2.7a
3.2a
20 84.7 -- 10 -- 2.7 2.6 -- 1a
1.5a
1.7a
2.2a
-- --
21 30 32.5 -- 33.5 2 2 -- 1a
2a 2.6a
3.2a
3.2a
3.5a
__________________________________________________________________________
##STR15##
.sup.(2) The surfactant used was Antarox BL 225.
.sup.(3) Chlorinated Cyanuric Acid Bleach (sodium dichloroisocyanurate)
from FMC Corp.
.sup.(4) Rating Codes:
1 No spots
2 15 spots or less
3 15 to 30 spots
4 30 to 60 spots
5 More than 60 spots
a No film
b Very slight film
c Slight film
d Moderate film
e Exteme film
.sup.(5) Sodium tripolyphosphate
EXAMPLES 22-27
The following examples show that when properly built with an alkali metal
silicate, the compositions of the present invention do not corrode
aluminum.
Corrosion tests were run according to the procedure set forth in Interim
Federal Specification No. P-D-00425 d (GSA-FSS) of June 17, 1968 for
Machine Dishwashing Compounds.
First, a stock solution of the detergent composition was prepared as
follows: the composition (50 g.) was dissolved in CO.sub.2 -free distilled
water at 55.degree.-65.degree. C. The solution was cooled to
20.degree..+-.1.degree. C., and diluted exactly to 1 liter with water.
Corrosion tests were run on aluminum strips with the above solutions at two
dilution levels--I and II. Dilution level I was obtained by diluting 18.75
ml. of the stock solution to 250 ml. with distilled water. Dilution level
II, was obtained by diluting 13.13 ml. of the stock solution to 250 ml.
with distilled water. Specimens (approximately 3 inches by 0.75 by 0.064
inch) of bright-finished uncoated aluminum alloy sheet (Aluminum Alloy
3003), conforming to temper H14 of QQ-A-250/2 were totally immersed in 250
ml. each of the diluted stock solutions at 82.degree. C. (180.degree. F.)
for 5 hours. The solution levels were maintained with distilled water
during the experiment. After 5 hours' exposure, the specimens were
removed, rinsed with distilled water and dried. They were then examined
for corrosion or etching by weight loss, for discoloration and for
formation of a white film on the surface. Results are shown in Table 3. As
can be seen from these results, alkali metal silicates are necessary in
the composition of the present invention if corrosion inhibition of metals
is desired.
Table 3
__________________________________________________________________________
Composition, & Weight
Ex- Type of Silicate Ratings
ample
Sodium Silicate
as as NaPAA.sup.(2) Dilution
% Wt.
Discolor-
White
No. SiO.sub.2 :Na.sub.2 O
is SiO.sub.2
Na.sub.2 CO.sub.3
##STR16##
Surf..sup.(3)
CDB-63.sup.(4)
Na.sub.2 SO.sub.4
Level
Loss
ation
film
__________________________________________________________________________
22 -- -- -- 35 7.5 2 2 53.5
I 1.3 Yes No
23 -- -- -- 35 7.5 2 2 53.5
II 1.1 Yes No
24 1:1(Na.sub.2 SiO.sub.3 . 5H.sub.2 O)
35 9.8
35 7.5 2 2 18.5
I 0 No No
25 Same 35.sup.(1)
9.8
35 7.5 2 2 18.5
II 0.1 No No
26 2.5:1 18.sup.(1)
9.4
35 7.5 2 2 35.5
I 0 No No
27 Same 18 9.4
35 7.5 2 2 35.5
II 0 No No
__________________________________________________________________________
.sup.(1) Expressed as solid 2.5:1 SiO.sub. 2 :Na.sub.2 O silicate
##STR17##
.sup.(3) Surfactant used was Antarox BL 225 from GAF Corporation
.sup.(4) Chlorinated Cyanuric Acid Bleach from FMC
* * * * *
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Description |
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