Title:
DETERGENT COMPOSITION AND PROCESS
United States Patent 3673098
Abstract:
The invention disclosed is directed to a highly alkaline detergent composition having unexpectedly high tolerance with respect to hard water. The composition includes from about 10 to about 50 parts of an alkaline inorganic detergent component, from about 5 to about 30 parts of a tetra-alkali metal pyrophosphate component, from about 5 to about 30 parts of an alkali metal nitrilo triacetate component, from 0 to about 5 parts of a water-soluble nitrite component, and from 0 to about 5 parts of a low-foaming surfactant. The composition is low-foaming in use dilutions and highly effective for machine dishwashing with less spotting and greater clarity of articles cleaned therewith. Also disclosed is a process for washing articles for cooking and eating using dilute aqueous solutions of the composition. This application is a continuation-in-part of U.S. Pat. Ser. No. 680,966, filed Nov. 6, 1967 and now abandoned.
US Patent References:
Chemical brightening of aluminum
Ferguson - March 1954 - 2671717
Liquid detergent composition
Drew et al. - September 1961 - 3001945
Defoaming detergent composition
Martin et al. - August 1962 - 3048548
Built detergent compositions containing a synergistic mixture of stp, nta, and sodium silicate
Gedge - December 1967 - 3356613
DISHWASHING POWDERS
Mallows - December 1970 - 3549539
Chemical brightening of aluminum
Ferguson - March 1954 - 2671717
Liquid detergent composition
Drew et al. - September 1961 - 3001945
Defoaming detergent composition
Martin et al. - August 1962 - 3048548
Built detergent compositions containing a synergistic mixture of stp, nta, and sodium silicate
Gedge - December 1967 - 3356613
DISHWASHING POWDERS
Mallows - December 1970 - 3549539
Inventors:
Sabatelli, Philip M. (Cincinnati, OH)
Brungs, Charles A. (Ft. Wright, KY)
Brungs, Charles A. (Ft. Wright, KY)
Application Number:
05/057345
Publication Date:
06/27/1972
Filing Date:
07/22/1970
View Patent Images:
Export Citation:
Assignee:
Chemed Corporation (Cincinnati, OH)
Primary Class:
Other Classes:
252/180, 134/29, 510/223, 510/480, 510/229, 510/401, 510/108
International Classes:
C11D7/60; C11D7/06
Field of Search:
252/135,152,156,173,180 134/29
Other References:
Pfizer "Aminocarboxylic Chelating Agents," Data Sheet No. 606, p. 8 (1963) .
"Amino Acid Chelating Agents in Detergent"- Soap & Chemical Specialties, (Sept., 1966) pp. 60, 130, 133 .
"Mechanical Dishwashing Compounds" Lintner, A. E. Soap & Chemical Specialties, (July, 1967) pp. 42 & 89-90.
Primary Examiner:
Weinblatt, Mayer
Claims:
What is claimed is
1. A process for cleaning an article fouled with food or cooking soil which comprises, applying to the article an aqueous solution having a temperature of from about 140°F to about 200°F, said aqueous solution containing from about 0.05 to about 1 weight percent dry basis of a low-foaming dishwashing composition consisting essentially of
2. The process of claim 1 wherein said composition consists essentially of:
3. The process of claim 1 wherein said composition consists essentially of:
1. A process for cleaning an article fouled with food or cooking soil which comprises, applying to the article an aqueous solution having a temperature of from about 140°F to about 200°F, said aqueous solution containing from about 0.05 to about 1 weight percent dry basis of a low-foaming dishwashing composition consisting essentially of
2. The process of claim 1 wherein said composition consists essentially of:
3. The process of claim 1 wherein said composition consists essentially of:
Description:
The present invention relates to a highly alkaline low-foaming detergent composition which more effectively removes food soils from glassware, dishes and the like with less spotting and greater clarity, and to a washing process using the composition. Unexpectedly, the composition exhibits greater tolerance with respect to hard water than is to be expected from the hardness tolerance exhibited by the several components of the composition taken alone.
Institutional and household dishwashing machines have used strongly alkaline solutions for washing dishware, glasses and other cooking and eating utensils. In cleaning processes for using these solutions ordinary tap water having varying degrees of hardness is customarily used to dilute the cleaning solution to use dilution and to rinse the articles after a cleaning step. It is well known to those using these cleaning solutions and processes that spotting by inorganic salt residues and precipitates on the dishware and glassware is a major problem for appearance and other reasons. These precipitates additionally form lime scale and like deposits which interfere with the operation of the washing equipment and necessitate frequent equipment maintenance. Although for softening hard water and other reasons sodium tripolyphosphates and other condensed phosphates have been included in these alkaline cleaning compositions, when used at elevated temperatures the otherwise desirable condensed phosphates rapidly hydrolyze to orthophosphates. These hydrolysis products often precipitate from the cleaning solutions resulting in increased article spotting and interfering scale. Due to the highly alkaline conditions existing in these cleaning solutions, organic compounds generally have not been found suitable to eliminate spotting for reasons such as lack of adequate activity and interference with cleaning. Organic compounds which tend to inhibit spotting by inorganic salt residues have generally been found to function as foaming agents in conjunction with the cleaning agents and food residues under the highly alkaline conditions in the wash solution. As a practical matter, these organic compounds are inoperable in practice for machine dishwashing.
Detergent compositions containing nitrilo triacetates have been disclosed in U.S. Pat. No. 3,324,038 to Chaffee et al. and Canadian Pat. No. 755,588 to Gedge. However, the compositions in both of these patents include nitrilo triacetates as cleaning promoters for soaps and organic detergents in substantially neutral systems where foaming is desirable. Prior to this invention, the utility of nitrilo triacetates in highly alkaline, low foaming dishwashing compositions was not known.
It has now been found by practice of the present invention that there is provided a superior machine dishwashing composition which more effectively removes food soils and residues from eating and cooking utensils such as dishes, glassware and the like while decreasing spotting and increasing clarity of the glassware and dishes relative to most related compositions and methods of the prior art. Unexpectedly, the present composition exhibits greater tolerance with respect to water hardness without formation of hard water scale than is to be expected from the tolerance exhibited by the several components of the composition taken alone. This invention also provides a process for more effectively cleaning dishes, glassware, and other eating and cooking utensils with decreased spotting by salt residues.
Generally stated, practice of the present invention provides a detergent composition having improved use efficiency in hard water. In highly alkaline use dilution, this detergent is characterized with substantially low foam-producing tendency and is highly suitable for use in machine dishwashing. The composition includes from about 10 to about 50 parts by weight of an alkaline inorganic detergent component, from about 5 to about 30 parts by weight of a tetra-alkali metal pyrophosphate component, from about 5 to about 30 parts by a weight of an alkali metal nitrilo triacetate component, from 0 to about 5 parts by weight of a water-soluble nitrite component and from 0 to about about 5 parts by weight of a low-foaming surfactant. This composition may be prepared in liquid form by including water in an amount of up to about 99 parts by weight.
At from 0.05 to about 1 weight percent aqueous use dilution in water having hardness up to about 25 grains per gallon, the present composition exhibits substantial freedom from hard water precipiatates. This substantial freedom may be observed even though a weighted average sequestering value of the composition based on the sequestering value of the components is substantially less than the hardness level of the diluting water used.
Broadly stated, the present process for washing dishes, glassware and other articles for eating and cooking includes applying to the article surfaces an aqueous solution of from about 0.05 to about 1 weight percent, dry basis, of the present composition, and thereafter rinsing the articles.
The alkaline detergent component of the present composition may be selected from alkali metal hydroxides and alkali metal silicates. Suitable alkali metal hydroxides include sodium hydroxide, potassium hydroxide and mixtures thereof. Suitable alkali metal silicates include sodium silicate, potassium silicate and mixtures thereof. A preferred silicate is sodium meta-silicate. The alkaline detergent component may be included in an operable amount of from about 10 to about 50 parts by weight, and preferably from about 10 to about 20 parts by weight. Milder alkaline materials such as sodium and potassium carbonates and sodium and potassium orthophosphates may be substituted to a limited extent for some of the alkaline detergent. For example, 0 to about 20 weight percent of the alkaline detergent may be replaced with sodium and potassium orthophosphates, sodium and potassium carbonates and mixtures of these materials. Preferably, sodium hydroxide is used as the alkaline detergent component.
The tetra-alkali metal pyrophosphate component of this composition may be any alkali metal pyrophosphate such as tetra-sodium and tetra-potassium pyrophosphate. A preferred pyrophosphate is tetrapotassium pyrophosphate. Significantly, other condensed phosphates, such as sodium tripolyphosphate and the like are not required in the composition. The pyrophosphate component may be included in an operable amount of from about 5 to about 30 parts by weight and preferably from about 10 to about 30 parts by weight.
The alkali metal nitrilo triacetate component of this composition may be selected from the sodium and potassium salts. The tri-alkali salts are generally preferred. A preferred triacetate is trisodium nitrilo triacetate. The triacetate may be included in an operable amount from about 5 to about 30 parts by weight, and preferably from about 5 to about 20 parts by weight.
The optional nitrite component of this composition may be any water-soluble nitrite salt such as alkali metal nitrites including sodium, potassium, and lithium nitrite; alkaline earth metal nitrites including calcium and magnesium nitrite; ammonium nitrite and the like. A preferred nitrite is sodium nitrite. Where used, the optional nitrite component is principally included for increased suitability of steel and the like for containerization and extended storage of the present composition. The nitrite component may optionally be included in an amount from 0 to about 5 parts by weight, although an amount from about 0.1 to about 0.5 part by weight is generally suitable for extended storage in steel drums.
The optional surfactant component may be almost any water-soluble surfactant having low foam-producing tendency in highly alkaline aqueous solutions. The surfactant component may be included in an amount from 0 to about 5 parts by weight.
The present composition may be stored and used as either a substantially dry mixture of the various components or a concentrated solution of these components with from about 20 to about 80 weight percent water. Preferably, liquid concentrates of this dishwashing composition include from about 40 to about 80 weight percent water.
A preferred low foaming detergent composition of this invention for machine dishwashing includes from about 5 to about 20 parts by weight of potassium hydroxide, from about 10 to about 20 parts by weight of tetrapotassium pyrophosphate, from about 5 to about 25 parts by weight of trisodium nitrilo triacetate, and from about 20 to about 80 parts by weight of water. This preferred composition may further include from about 0.1 to about 0.5 part by weight of sodium nitrite, if desired.
The present process includes applying to surfaces of articles to be cleaned an aqueous solution including from about 0.05 to about 1 weight percent and preferably from about 0.05 to about 0.5 weight percent of the machine dishwashing composition. The composition may be applied at a temperature of from about 140°F to about 200°F and preferably from about 140°F to about 160°F. Although application of the aqueous detergent solution to the surfaces may be effected by any suitable means, the process is more highly effective when used with spray washing equipment of the type used typically for cleaning utensils for cooking and eating. Highly effective cleaning with low foaming is obtained in institutional and household dishwashing machines with this composition. In the final step of the cleaning process, the cleaned surfaces are preferably rinsed with water.
The improved alkaline dishwashing composition of this invention is highly effective in use for removing food soils and residues from dishes, glassware, and other cooking and eating utensils in dishwashing machines. Not only are the food residues more effectively removed with this composition, but the cleaned dishes and glassware exhibit less spotting and greater clarity than are typically observed for prior art cleaning compositions.
This invention is further illustrated by the following non-limiting examples. In this description, including the examples which follow, all parts and percentages given are by weight unless otherwise specified.
EXAMPLE 1
A mixed condensed phosphate type machine dishwashing composition was prepared by admixing about 15 parts of potassium hydroxide, about 15 parts of tetrapotassium pyrophosphate, about 15 parts of sodium tripolyphosphate, and about 0.3 part of sodium nitrite with about 54.7 parts of water. The concentrated liquid composition thus prepared was then diluted with a quantity of Cincinnati tap water having a hardness of 192.5 ppm. to form a control wash solution including a 0.3 percent of the concentrate.
EXAMPLE 2
A 0.3 wash solution was prepared by the procedure of example 1 except the 15 parts of sodium tripolyphosphate were substituted by 15 parts of sodium nitrilo triacetate.
EXAMPLE 3
The control solution of example 1 and the wash solution of example 2 were tested using a Hobart A.M. dishwashing machine having a 48 second wash cycle and a 12 second rinse cycle. The test articles were 22 squares of plate glass 4 inches on each edge which were soiled with one gram of a soil containing 50 parts peanut butter, 25 parts hydrogenated vegetable oil, and 25 parts butter. No rinse additive was used. The wash solutions had a temperature of 150°F in the wash section. The rinse water was 192.5 ppm. hardness Cincinnati tap water used at 180°F.
In a first test 10 soiled glass plates were run through 8 cycles in the machine with a drying period of 15 minutes allowed between cycles. The test plates washed using the nitrilo triacetate including wash solution of example 2 were substantially clearer and less streaked relative to the glass plates washed using the tripolyphosphate including control solution of example 1. Relative to the control-washed plates, the plates washed using the solution including nitrilo triacetate were notably brighter, and substantially fewer spots appeared thereon. The results of counting the number of spots appearing on both sides of 1 square inch of the center of each plate are shown below:
Wash Solution Control Solution Test Including Sodium Including Plate Nos. Nitrilo Triacetate Tripolyphosphate ____________________________________________________________ ______________ 1 and 11 32 51 2 and 12 41 65 3 and 13 30 63 4 and 14 50 67 5 and 15 36 60 6 and 16 41 57 7 and 17 46 70 8 and 18 29 68 9 and 19 48 80 10 and 20 36 60 TOTAL 389 642 Average 38.9 64.2 ____________________________________________________________ ______________
Inspection of the dishwashing machine before and after using these solutions showed that considerably less hard water scale was deposited thereon using the nitrilo triacetate including solution than was noted when the control solution was used.
A second washing test was performed using test plates nos. 21 and 22 and the washing procedure of the first test, except the number of cycles was reduced from 8 cycles to 1 cycle. The plate used to test the nitrilo triacetate including wash solution exhibited 14 spots whereas 78 spots appeared on the control-washed plate. This test shows that when using less washing time, such as is highly desirable in practice, even greater superiority of the nitrilo triacetate including solution is exhibited than was noted in the first test.
EXAMPLE 4
Samples of the concentrated liquid compositions of examples 1 and 2 are diluted to 0.3 percent aqueous solutions having 5, 15, and 25 grains of hardness per gallon. The hardening agents are calcium acetate and magnesium sulfate. These dilute solutions are heated to 150°F and poured into 27 × 275 glass cylinders and allowed to stand for 24 hours. At the end of this period the tripolyphosphate including solution having 5 grains hardness has a clear appearance and substantially no precipitate. However, the cylinders filled with the 15 grain and 25 grain hardness tripolyphosphate including solutions are found to have substantial depths of precipitates. These results are as expected in view of the weighted average chelating value of the tripolyphosphate containing solution which is calculated to be about 7 grains per gallon. The 7 grain chelating value follows from individual chelating values observed for the tripolyphosphate and pyrophosphate at the dilution, pH and temperature used for precipitate tests.
After 24 hours standing all the 5, 15 and 25 grain hardness samples prepared using the nitrilo triacetate including solutions are observed to be substantially clear and free from precipitates. Although no precipitate is expected for the 5 grain hardness sample, the freedom from precipitate formation is unexpected for the 15 and 25 grain samples in view of the approximate 11 grain weighted average chelating value of the nitrilo triacetate including solutions. The 11 grain chelating value follows from a calculation procedure and observations similar to those used for the tripolyphosphate including solutions.
EXAMPLES 5 and 6
The procedures of Example 3 and 4 are repeated except no nitrite is used. The results are substantially the same as the results noted in Examples 3 and 4.
EXAMPLE 7
A mixed condensed phosphate type machine dishwashing composition was prepared by admixing about 31 parts of liquid caustic potash, about 20 parts of 60 percent liquid tetrapotassium pyrophosphate, and about 13 parts sodium tripolyphosphate with about 36 parts of water. Samples of the concentrated liquid composition thus prepared were then diluted to 0.3 percent solutions using 5 samples of water having hardness of 0, 5, 10, 15 and 20 grains per gallon expressed in equivalent amounts of calcium carbonate. The hard water samples were prepared using calcium acetate and magnesium sulfate hardening agents.
The dilute solutions of this mixed condensed phosphate including composition had a weighted average sequestering ability of 6.8 grains per gallon (i.e., 116.1 milligrams of calcium carbonate per liter) at the pH of the 0.3 percent solutions (i.e., about 12 pH). The sequestering value was calculated from Mehltretter Test sequestering value observations at 12 pH of 246 milligrams of calcium carbonate per gram of the tripolyphosphate component and 33.6 milligrams of calcium carbonate per gram of the liquid pyrophosphate component.
EXAMPLE 8
A Mehltretter Test observation of 370 milligrams per gram sequestering value was made for trisodium nitrilo triacetate monohydrate at 12 pH. Using this value a concentrated composition having a calculated weighted average sequestering ability of 6.8 grains per gallon at 0.3 percent aqueous solution was formulated. This concentrate was prepared by admixing about 31 parts of liquid caustic potash and about 10.5 parts of trisodium nitrilo triacetate monohydrate with about 58.5 parts of water. It is to be noted that at the same use dilution this concentrate had the same calculated sequestering value as the concentrate of example 7, and likewise had a pH of about 12. This concentrate was then diluted to 0.3 percent solutions using the procedure of example 7 to form 5 dilute samples having 0, 5, 10, 15 and 20 grains per gallon hardness.
EXAMPLE 9
The dilute solutions of examples 7 and 8 were heated to 150°F and poured into 27 × 275 mm glass cylinders and allowed to stand for 24 hours. No precipitate was observed in the dilute solutions containing mixed phosphates at 0, 5, and 10 grains of hardness. The 15 and 20 grain hardness solutions were observed to have deep accumulations of lime scale precipitate measuring 22 mm and 38 mm in depth, respectively.
In contrast to the phosphate-containing solutions, no precipitate was observed at any of the hardness levels from 0 to 20 grains for the triacetate containing solutions. No floc was observed for any of these triacetate solutions, not even at the 15 and 20 grain hardness levels. These results are unexpected in view of the mere 6.8 grain sequestering value of the triacetate containing solution.
This example shows that even at the same sequestering value, the nitrilo triacetate is superior to mixed phosphates in water softening ability in highly alkaline, low-foaming detergent compositions at a typical use temperature for machine dishwashing. It is also noted that the nitrilo triacetate prevents formation of lime scale in solutions of hardness considerably in excess of the hardness at which scale formation is to be expected.
It is to be understood that the foregoing detailed description is given merely by way of illustration and that various modifications may be made therein without departing from the spirit or scope of the present invention.
Institutional and household dishwashing machines have used strongly alkaline solutions for washing dishware, glasses and other cooking and eating utensils. In cleaning processes for using these solutions ordinary tap water having varying degrees of hardness is customarily used to dilute the cleaning solution to use dilution and to rinse the articles after a cleaning step. It is well known to those using these cleaning solutions and processes that spotting by inorganic salt residues and precipitates on the dishware and glassware is a major problem for appearance and other reasons. These precipitates additionally form lime scale and like deposits which interfere with the operation of the washing equipment and necessitate frequent equipment maintenance. Although for softening hard water and other reasons sodium tripolyphosphates and other condensed phosphates have been included in these alkaline cleaning compositions, when used at elevated temperatures the otherwise desirable condensed phosphates rapidly hydrolyze to orthophosphates. These hydrolysis products often precipitate from the cleaning solutions resulting in increased article spotting and interfering scale. Due to the highly alkaline conditions existing in these cleaning solutions, organic compounds generally have not been found suitable to eliminate spotting for reasons such as lack of adequate activity and interference with cleaning. Organic compounds which tend to inhibit spotting by inorganic salt residues have generally been found to function as foaming agents in conjunction with the cleaning agents and food residues under the highly alkaline conditions in the wash solution. As a practical matter, these organic compounds are inoperable in practice for machine dishwashing.
Detergent compositions containing nitrilo triacetates have been disclosed in U.S. Pat. No. 3,324,038 to Chaffee et al. and Canadian Pat. No. 755,588 to Gedge. However, the compositions in both of these patents include nitrilo triacetates as cleaning promoters for soaps and organic detergents in substantially neutral systems where foaming is desirable. Prior to this invention, the utility of nitrilo triacetates in highly alkaline, low foaming dishwashing compositions was not known.
It has now been found by practice of the present invention that there is provided a superior machine dishwashing composition which more effectively removes food soils and residues from eating and cooking utensils such as dishes, glassware and the like while decreasing spotting and increasing clarity of the glassware and dishes relative to most related compositions and methods of the prior art. Unexpectedly, the present composition exhibits greater tolerance with respect to water hardness without formation of hard water scale than is to be expected from the tolerance exhibited by the several components of the composition taken alone. This invention also provides a process for more effectively cleaning dishes, glassware, and other eating and cooking utensils with decreased spotting by salt residues.
Generally stated, practice of the present invention provides a detergent composition having improved use efficiency in hard water. In highly alkaline use dilution, this detergent is characterized with substantially low foam-producing tendency and is highly suitable for use in machine dishwashing. The composition includes from about 10 to about 50 parts by weight of an alkaline inorganic detergent component, from about 5 to about 30 parts by weight of a tetra-alkali metal pyrophosphate component, from about 5 to about 30 parts by a weight of an alkali metal nitrilo triacetate component, from 0 to about 5 parts by weight of a water-soluble nitrite component and from 0 to about about 5 parts by weight of a low-foaming surfactant. This composition may be prepared in liquid form by including water in an amount of up to about 99 parts by weight.
At from 0.05 to about 1 weight percent aqueous use dilution in water having hardness up to about 25 grains per gallon, the present composition exhibits substantial freedom from hard water precipiatates. This substantial freedom may be observed even though a weighted average sequestering value of the composition based on the sequestering value of the components is substantially less than the hardness level of the diluting water used.
Broadly stated, the present process for washing dishes, glassware and other articles for eating and cooking includes applying to the article surfaces an aqueous solution of from about 0.05 to about 1 weight percent, dry basis, of the present composition, and thereafter rinsing the articles.
The alkaline detergent component of the present composition may be selected from alkali metal hydroxides and alkali metal silicates. Suitable alkali metal hydroxides include sodium hydroxide, potassium hydroxide and mixtures thereof. Suitable alkali metal silicates include sodium silicate, potassium silicate and mixtures thereof. A preferred silicate is sodium meta-silicate. The alkaline detergent component may be included in an operable amount of from about 10 to about 50 parts by weight, and preferably from about 10 to about 20 parts by weight. Milder alkaline materials such as sodium and potassium carbonates and sodium and potassium orthophosphates may be substituted to a limited extent for some of the alkaline detergent. For example, 0 to about 20 weight percent of the alkaline detergent may be replaced with sodium and potassium orthophosphates, sodium and potassium carbonates and mixtures of these materials. Preferably, sodium hydroxide is used as the alkaline detergent component.
The tetra-alkali metal pyrophosphate component of this composition may be any alkali metal pyrophosphate such as tetra-sodium and tetra-potassium pyrophosphate. A preferred pyrophosphate is tetrapotassium pyrophosphate. Significantly, other condensed phosphates, such as sodium tripolyphosphate and the like are not required in the composition. The pyrophosphate component may be included in an operable amount of from about 5 to about 30 parts by weight and preferably from about 10 to about 30 parts by weight.
The alkali metal nitrilo triacetate component of this composition may be selected from the sodium and potassium salts. The tri-alkali salts are generally preferred. A preferred triacetate is trisodium nitrilo triacetate. The triacetate may be included in an operable amount from about 5 to about 30 parts by weight, and preferably from about 5 to about 20 parts by weight.
The optional nitrite component of this composition may be any water-soluble nitrite salt such as alkali metal nitrites including sodium, potassium, and lithium nitrite; alkaline earth metal nitrites including calcium and magnesium nitrite; ammonium nitrite and the like. A preferred nitrite is sodium nitrite. Where used, the optional nitrite component is principally included for increased suitability of steel and the like for containerization and extended storage of the present composition. The nitrite component may optionally be included in an amount from 0 to about 5 parts by weight, although an amount from about 0.1 to about 0.5 part by weight is generally suitable for extended storage in steel drums.
The optional surfactant component may be almost any water-soluble surfactant having low foam-producing tendency in highly alkaline aqueous solutions. The surfactant component may be included in an amount from 0 to about 5 parts by weight.
The present composition may be stored and used as either a substantially dry mixture of the various components or a concentrated solution of these components with from about 20 to about 80 weight percent water. Preferably, liquid concentrates of this dishwashing composition include from about 40 to about 80 weight percent water.
A preferred low foaming detergent composition of this invention for machine dishwashing includes from about 5 to about 20 parts by weight of potassium hydroxide, from about 10 to about 20 parts by weight of tetrapotassium pyrophosphate, from about 5 to about 25 parts by weight of trisodium nitrilo triacetate, and from about 20 to about 80 parts by weight of water. This preferred composition may further include from about 0.1 to about 0.5 part by weight of sodium nitrite, if desired.
The present process includes applying to surfaces of articles to be cleaned an aqueous solution including from about 0.05 to about 1 weight percent and preferably from about 0.05 to about 0.5 weight percent of the machine dishwashing composition. The composition may be applied at a temperature of from about 140°F to about 200°F and preferably from about 140°F to about 160°F. Although application of the aqueous detergent solution to the surfaces may be effected by any suitable means, the process is more highly effective when used with spray washing equipment of the type used typically for cleaning utensils for cooking and eating. Highly effective cleaning with low foaming is obtained in institutional and household dishwashing machines with this composition. In the final step of the cleaning process, the cleaned surfaces are preferably rinsed with water.
The improved alkaline dishwashing composition of this invention is highly effective in use for removing food soils and residues from dishes, glassware, and other cooking and eating utensils in dishwashing machines. Not only are the food residues more effectively removed with this composition, but the cleaned dishes and glassware exhibit less spotting and greater clarity than are typically observed for prior art cleaning compositions.
This invention is further illustrated by the following non-limiting examples. In this description, including the examples which follow, all parts and percentages given are by weight unless otherwise specified.
EXAMPLE 1
A mixed condensed phosphate type machine dishwashing composition was prepared by admixing about 15 parts of potassium hydroxide, about 15 parts of tetrapotassium pyrophosphate, about 15 parts of sodium tripolyphosphate, and about 0.3 part of sodium nitrite with about 54.7 parts of water. The concentrated liquid composition thus prepared was then diluted with a quantity of Cincinnati tap water having a hardness of 192.5 ppm. to form a control wash solution including a 0.3 percent of the concentrate.
EXAMPLE 2
A 0.3 wash solution was prepared by the procedure of example 1 except the 15 parts of sodium tripolyphosphate were substituted by 15 parts of sodium nitrilo triacetate.
EXAMPLE 3
The control solution of example 1 and the wash solution of example 2 were tested using a Hobart A.M. dishwashing machine having a 48 second wash cycle and a 12 second rinse cycle. The test articles were 22 squares of plate glass 4 inches on each edge which were soiled with one gram of a soil containing 50 parts peanut butter, 25 parts hydrogenated vegetable oil, and 25 parts butter. No rinse additive was used. The wash solutions had a temperature of 150°F in the wash section. The rinse water was 192.5 ppm. hardness Cincinnati tap water used at 180°F.
In a first test 10 soiled glass plates were run through 8 cycles in the machine with a drying period of 15 minutes allowed between cycles. The test plates washed using the nitrilo triacetate including wash solution of example 2 were substantially clearer and less streaked relative to the glass plates washed using the tripolyphosphate including control solution of example 1. Relative to the control-washed plates, the plates washed using the solution including nitrilo triacetate were notably brighter, and substantially fewer spots appeared thereon. The results of counting the number of spots appearing on both sides of 1 square inch of the center of each plate are shown below:
Wash Solution Control Solution Test Including Sodium Including Plate Nos. Nitrilo Triacetate Tripolyphosphate ____________________________________________________________ ______________ 1 and 11 32 51 2 and 12 41 65 3 and 13 30 63 4 and 14 50 67 5 and 15 36 60 6 and 16 41 57 7 and 17 46 70 8 and 18 29 68 9 and 19 48 80 10 and 20 36 60 TOTAL 389 642 Average 38.9 64.2 ____________________________________________________________ ______________
Inspection of the dishwashing machine before and after using these solutions showed that considerably less hard water scale was deposited thereon using the nitrilo triacetate including solution than was noted when the control solution was used.
A second washing test was performed using test plates nos. 21 and 22 and the washing procedure of the first test, except the number of cycles was reduced from 8 cycles to 1 cycle. The plate used to test the nitrilo triacetate including wash solution exhibited 14 spots whereas 78 spots appeared on the control-washed plate. This test shows that when using less washing time, such as is highly desirable in practice, even greater superiority of the nitrilo triacetate including solution is exhibited than was noted in the first test.
EXAMPLE 4
Samples of the concentrated liquid compositions of examples 1 and 2 are diluted to 0.3 percent aqueous solutions having 5, 15, and 25 grains of hardness per gallon. The hardening agents are calcium acetate and magnesium sulfate. These dilute solutions are heated to 150°F and poured into 27 × 275 glass cylinders and allowed to stand for 24 hours. At the end of this period the tripolyphosphate including solution having 5 grains hardness has a clear appearance and substantially no precipitate. However, the cylinders filled with the 15 grain and 25 grain hardness tripolyphosphate including solutions are found to have substantial depths of precipitates. These results are as expected in view of the weighted average chelating value of the tripolyphosphate containing solution which is calculated to be about 7 grains per gallon. The 7 grain chelating value follows from individual chelating values observed for the tripolyphosphate and pyrophosphate at the dilution, pH and temperature used for precipitate tests.
After 24 hours standing all the 5, 15 and 25 grain hardness samples prepared using the nitrilo triacetate including solutions are observed to be substantially clear and free from precipitates. Although no precipitate is expected for the 5 grain hardness sample, the freedom from precipitate formation is unexpected for the 15 and 25 grain samples in view of the approximate 11 grain weighted average chelating value of the nitrilo triacetate including solutions. The 11 grain chelating value follows from a calculation procedure and observations similar to those used for the tripolyphosphate including solutions.
EXAMPLES 5 and 6
The procedures of Example 3 and 4 are repeated except no nitrite is used. The results are substantially the same as the results noted in Examples 3 and 4.
EXAMPLE 7
A mixed condensed phosphate type machine dishwashing composition was prepared by admixing about 31 parts of liquid caustic potash, about 20 parts of 60 percent liquid tetrapotassium pyrophosphate, and about 13 parts sodium tripolyphosphate with about 36 parts of water. Samples of the concentrated liquid composition thus prepared were then diluted to 0.3 percent solutions using 5 samples of water having hardness of 0, 5, 10, 15 and 20 grains per gallon expressed in equivalent amounts of calcium carbonate. The hard water samples were prepared using calcium acetate and magnesium sulfate hardening agents.
The dilute solutions of this mixed condensed phosphate including composition had a weighted average sequestering ability of 6.8 grains per gallon (i.e., 116.1 milligrams of calcium carbonate per liter) at the pH of the 0.3 percent solutions (i.e., about 12 pH). The sequestering value was calculated from Mehltretter Test sequestering value observations at 12 pH of 246 milligrams of calcium carbonate per gram of the tripolyphosphate component and 33.6 milligrams of calcium carbonate per gram of the liquid pyrophosphate component.
EXAMPLE 8
A Mehltretter Test observation of 370 milligrams per gram sequestering value was made for trisodium nitrilo triacetate monohydrate at 12 pH. Using this value a concentrated composition having a calculated weighted average sequestering ability of 6.8 grains per gallon at 0.3 percent aqueous solution was formulated. This concentrate was prepared by admixing about 31 parts of liquid caustic potash and about 10.5 parts of trisodium nitrilo triacetate monohydrate with about 58.5 parts of water. It is to be noted that at the same use dilution this concentrate had the same calculated sequestering value as the concentrate of example 7, and likewise had a pH of about 12. This concentrate was then diluted to 0.3 percent solutions using the procedure of example 7 to form 5 dilute samples having 0, 5, 10, 15 and 20 grains per gallon hardness.
EXAMPLE 9
The dilute solutions of examples 7 and 8 were heated to 150°F and poured into 27 × 275 mm glass cylinders and allowed to stand for 24 hours. No precipitate was observed in the dilute solutions containing mixed phosphates at 0, 5, and 10 grains of hardness. The 15 and 20 grain hardness solutions were observed to have deep accumulations of lime scale precipitate measuring 22 mm and 38 mm in depth, respectively.
In contrast to the phosphate-containing solutions, no precipitate was observed at any of the hardness levels from 0 to 20 grains for the triacetate containing solutions. No floc was observed for any of these triacetate solutions, not even at the 15 and 20 grain hardness levels. These results are unexpected in view of the mere 6.8 grain sequestering value of the triacetate containing solution.
This example shows that even at the same sequestering value, the nitrilo triacetate is superior to mixed phosphates in water softening ability in highly alkaline, low-foaming detergent compositions at a typical use temperature for machine dishwashing. It is also noted that the nitrilo triacetate prevents formation of lime scale in solutions of hardness considerably in excess of the hardness at which scale formation is to be expected.
It is to be understood that the foregoing detailed description is given merely by way of illustration and that various modifications may be made therein without departing from the spirit or scope of the present invention.