US 3700599 A
Description (OCR text may contain errors)
United States Patent 3,700,599- Patented Oct. 24, 1972 3,700,599 COMPOSITION FOR MECHANICALLY CLEANING HARD SURFACES Wililam G. Mizuno and James L. Copeland, St. Paul, and Arlene E. Scholze, Burnsville, Minn., assignors to Economics Laboratory, Inc., St. Paul, Minn. No Drawing. Filed Sept. 25, 1970, Ser. No. 75,676
Int. Cl. Clld 7/56 US. Cl. 252-99 9 Claims ABSTRACT OF THE DISCLOSURE Detergent compositions for mechanically cleaning hard surfaces (e.g. dishes) are characterized by the presence therein of a mixture of metallic salt of citric acid (e.g. sodium citrate) and water soluble polymeric, organic polyelectrolyte (e.g. hydrolyzed maleic anhydride polymers). This mixture permits the reduction of or elimination of condensed phosphate salts commonly used in deter-gent compositions of this type (e.g. machine dishwashing detergents).
CROSS-REFERENCE TO RELATED APPLICATIONS Ser. No. 836,597 filed June 25, 1969, now abandoned describes certain maleic anhydride polymers which are useful as polyelectrolytes in the practice of the present invention.
BACKGROUND OF THE INVENTION Detergents for mechanically cleaning hard surfaces constitute a generally recognized class of detergent compositions. Machine dishwashing detergents constitute a subclass within this broad class that is of particular importance to the present invention. Machine dishwashing detergents must possess these characteristics without subcombination, is to emulsify and remove food soils, to inhibit the foam caused by certain food soils, to promote the wetting of dinnerware to thereby minimize or eliminate visually observable spotting, to remove stains such as those caused by coffee and tea, to prevent a buildup of soil and hard water films on dinner and glassware surfaces, to reduce or eliminate tarnishing of (flatware, and
to destroy bacteria. Additionally, machine dishwashing detergents must possess these characteirstics without substantially etching or corroding or otherwise damaging the surfaces of dinnerware and flatware.
Machine dishwashing detergents are often highly alkaline (a pH above 10.0 and frequently above 12.0 at concentrations of 1 weight percent in water). Frequently, machine dishwashing detergents are formulated by mixing or otherwise combining alkaline condensed phosphate salts with other inorganic alkaline detergent salts or builders. Frequently, chlorine releasing agents and low foaming or defoaming organic surface active agents (e.g. non-ionic surfactants) are optionally and preferably included in such compositions.
In recent years, increasing attention has been focused upon environmental pollution problems (eg water pollution). Phosphates have been identified as a contributing factor to water pollution and considerable eifort has been devoted to attempts at replacing all or at least some significant part of the condensed phosphate salts used in detergents intended for cleaning hard surfaces (e.g. machine dishwashing detergents) with chemicals that are more ecologically acceptable. Of the numerous compounds that have been tested as substitutes for condensed phosphate salts (particularly as substitutes for sodium tripolyphosphate), very few chemicals have given promising results. Many chemicals lack the desired cleaning ability. Other chemicals lack the ability to sequester hard water metal ions beyond their stoichiometric presence (contrary to sodium tripolyphosphate-which has such an ability). Still others create foam problems and still others are as much or more ecologically undesirable as the condensed phosphate salts.
Among the many chemicals tested for use as a substitute for sodium tripolyphosphate, nitrilo tiacetic acid (or its salt) appears to be one of the most promising candidates. However, one disadvantageous effect of nitrilo t-riacetic acid (often called NTA) is its tendency to de-stabilize chlorine in use solutions of such detergent compositions. Other disadvantages of NTA at the present time include cost, lack of general availability, and lack of threshold effect (i.e. inability to sequester hard water metal ions beyond its stoichiometric presence).
SUMMARY OF THE INVENTION The present invention is based upon the discovery that mixtures of metallic salts of citric acid (e.g. sodium citrate) and water soluble polymeric organic polyelectrolytes are elfective substitutes for condensed phosphate salts (e.g. for sodium tripolyphosphate) in detergent compositions intended for use in cleaning hard surfaces. The use of such mixtures in, for example, machine dishwashing detergents, produces dishwashing results that are commercially acceptable by todays industrial standards. The mixture is also effective at sequestering hard water metal ions beyond their stoichiometric presence (i.e. the combination exhibits the same threshold effect of alkaline condensed polyphosphates). Additionally, the mixture is stable toward chlorine releasing agents (e.g. potassium dichloroisocyanurate) DETAILED DISCUSSION Detergent compositions of the present invention can be formulated as either a solid detergent or as single or multiple package liquid detergent. These detergent compositions will be used, after appropriate dilution with water, for the mechanical or machine washing of hard surfaces (e.g. mechanical spray washing). They will find particular application as machine dishwashing detergents.
Solid or dry detergents can be formed by blending together the various detergent-forming ingredients to form a powder or granular product, or they can be agglomerated, pelletized or the like.
Multiple package liquid detergents are those machine ware-washing detergents which are formulated into two or more separate liquid components, each component being packaged separately. In the washing operation, the separate components are dispensed from their separate containers into the washing zone by suitable dispensing apparatus.
Although the present invention can be applied to or embodied in any of these various types of machine washing detergents, its greatest advantage is associated with the production of solid detergent compositions and single package liquid detergent compositions. Of these, the
formulation and use of solid machine dishwashing detergents is of particular significance.
The machine washing detergent compositions of the present invention will contain typical detergent forming ingredients plus the mixture of metallic salt of citric acid and water soluble polyelectrolyte.
The pH of these machine dishwashing detergents will normally be at least 10.0 at a concentration of 1 weight percent in water. pHs of from 12.012.5 are particularly desirable for many machine dishwashing uses. pHs in the 10-11 range are common for home use, while pHs above 12 are desired for industrial use.
The detergent compositions of the present invention are typically free of alkyl benzene sulfonates and, in use, produce little or no foam as contrasted to, for example, laundry detergents containing alkyl benzene sulfonates.
The Qitrates Any of the water soluble metal salts of citric acid can be used in the practice of the present invention. However, all salts do not serve with equal effectiveness and the alkali metal salts are preferred. Sodium and potassium citrate are particularly preferred.
Commercial sodium citrate (more accurately described as trisodium citrate dihydrate) exists as white crystals or a granular powder. :It is odorless, stable in air and has a slightly saline taste. Each molecule of trisodium citrate loses two molecules of water when heated to 150 C. Potassium citrate also exists as white crystals or powder. It is commercially available as the monohydrate (as contrasted to sodium citrate which exists as the dihydrate).
As used in the present invention, the amount of citrate employed will generally fall within the range of -6C weight percent on a dry formula basis. Water of hydration can be considered to be a part of the salt. More usually, the amount of citrate (whether hydrated or not) will be from -40 weight percent, e.g. 15-25 percent on the same basis.
If desired, mixtures of citrates can be used. Although it is not generally preferred, a citrate can be formed in situ from, for example, the combination of citric acid with sodium or potassium hydroxide. Citric acid is desirable when making liquid detergent compositions, but it quickly forms the corresponding salt since such liquid compositions are quite basic (i.e. pH above 10). The use of a pre-formed alkali metal citrate or a mixture thereof is generally preferred, particularly when making solid detergent compositions.
The weight ratio of citrate: polyelectrolyte will generally be above 1:1, frequently within the range of 2-10:1.
The polyelectrolytes The polyelectrolytes useful in this invention are the water soluble organic polymeric polyelectrolytes. A wide variety of such polyelectrolytes are known as illustrated by the following US. patents:
3,308,067; Diehl; Mar. 7, 1967; 252/161 3,346,873; Herrmann; Oct. 10, 1967; 252/137 3,346,504; Herrmann; Oct. 10, 1967; 252/ 137 See also these U.S. patents:
3,463,730; Booth et al.; Aug. 26, 1967; 210/58 2,783,200; Crum et al.; Feb. 26, 1957; 210/23 All water soluble polyelectrolytes do not serve with equal effectiveness in any given dishwashing detergent formulation and it is desirable that the choice of type of polymer, molecular weight, and concentration be optimized for any given detergent formulation.
Suitable polyelectrolytes are the water soluble organic polymers of polycarboxylic acids (e.g. maleic acid) or of esters of ethylenically unsaturated carboxylic acids (e.g. butyl acrylate).
Water soluble carboxyl containing polyelectrolytes having an equivalent weight (calculated on an acid basis) of about 58 to 150, more usually from about 58 to are preferred. One particularly useful class of polyelectrolytes consists of: (a) homopolymers of maleic anhydride; and (b) low molecular weight linear copolymers of maleic anhydride and copolymerizable ethylenically unsaturated organic compounds such as ethylene, propylene, butylene, vinyl acetate, acrylonitrile, acrylic acid, methyl acrylate, ethyl acrylate, methyl vinyl ether, sodium vinyl sulfonate, styrene and the like. Structurally, these copolymers can be represented as follows.
wherein R and R; can each be hydrogen or an organic radical containing from 1 to 8 carbon atoms (R and R can be the same or different), Z is an organic radical containing 1 to 8 carbon atoms (note that Z is absent in the homopolymers), M is hydrogen, ammonium or an alkali metal (e.g. sodium), n is an integer, and
x and y are terminal groups and are hydrogen or short chain organic groups.
In general, the copolymers are preferred.
It is somewhat difiicult to establish an absolute value for an upper limit of the degree of polymerization (i.e. n) above which the polyelectrolyte no longer functions as an efiicient detergent builder. The fact is that practical considerations appear to be the primary determining factor as the degree of polymerization increases. For instance, as the molecular weight of a polymeric material increases, it is generally acknowledged that its water solubility decreases. It is essential to the present invention that the polyelectrolyte be adequately soluble in water under regular usage conditions. Recommended concentrations of polyelectrolytes generally range from about 0.005% to about 0.25% by weight (e.g. 0.01 to 0.12% by weight) of the washing solution. The upper operable limit, therefore, so far as the degree of polymerization is concerned is reached when it is no longer possible to get enough of the polyelectrolyte into solution or, in the case of liquid detergents, no longer possible to get enough polyelectrolyte into the liquid detergent concentrate.
For the purposes of this invention, the specific viscosity of the polyelectrolyte is preferably relatively low. Since there are viscosity differences inherently associated with different polymers, the preferred specific viscosities will vary. The polymer that is selected should be susceptible to handling and blending with the other components of the new detergent, as well as affording satisfactory performance. For example, when using a copolymer of ethylene and maleic anhydride it is preferred that the specific viscosity be not substantially in excess of a value of 2 as determined on a one weight percent solution of the copolymer in dimethyl formamide at 25 C. Similarly, with a vinyl acetatemaleic anhydride copolymer, it is preferred that the specific viscosity range be from 1.0 to 10.0 when determined on a four percent aqueous solution at 25 C.
Copolymerization of the maleic anhydride with unsaturated organic materials is known in the art. For example, US. Pat. No. 2,938,016 describes the production of low molecular weight olefin/maleic anhydride polymers useful in the practice of this invention.
Since all polyelectrolytes do not serve with equal effectiveness, it is useful to screen or select a polyelectrolyte on the basis of its apparent chelation value (ACV) as measured in milligrams of CaCO sequestered per gram of polyelectrolyte. Below 200, the polyelectrolytes are generally ineifect-ive for purposes of this invention. Desirably, the ACV will be above 350, preferably above 500.
Apparent chelation values (ACV) for polyelectrolytes can be determined as follows. Dissolve a 0.5 to 1.0 gram sample in about 85 ml. of water, adjusting the pH to desired use value with NaOH or NH OH, add 10 ml. of 2% Na CO then readjust the pH and make up the volume to 100 ml. with water. The solution is then titrated with a standard calcium acetate solution (0.25 M) using a magnetic stirrer. The titration is carried out in a semidarkened room using a microscope spotlight until the first faint but permanent turbidity is obtained. The endpoint is not always completely sharply defined. Variations of il5% from the average are not uncommon. Consequently, average values are more meaningful than single values (e.g. the average of three or more tests). The use of a spotlight and observation of Tyndall effect facilitates the determination of the end point. The final pH after the titration should be rechecked as the addition of a large amount of titrating solution may cause a drift in pH. It is possible to get two different endpoints for the ACV depending on which side of the equilibrium one approaches the endpoint, i.e. according to the equation:
1 Ca++ CaCO;
In obtaining the data reported herein, the equilibrium was approached from direction 1 titration. It is possible to approach the equilibrium from direction 2 by agitating fine, solid CaCO with chelate solutions.
Some typical results are shown in Table I which follows.
TABLE I.-APPARENT CHELATION VALUES FOR 1 A sulionated polyaerylic acid commercially available in the U.S.A. under the trademark Calnox 214.
1 A hydrolyzed polyaerylamide sold by American Cyanamid Co. under the trademark Cyanamer P-35".
Detergent salts In addition to the mixture of olyelectrolyte and citrate, the machine washing detergents of this invention will contain detergent salts, usually alkaline detergent salts.
Although most alkali metal condensed phosphate salts are alkaline and are often used in detergent compositions in large amounts, such condensed phosphate salts (e.g. sodium tripolyphosphate) can be employed in the compositions of this invention in reduced amounts (e.g., less than 10% by weight on a dry basis, preferably less than 5 weight percent on the same basis) or they can be eliminated entirely, in which case the desired level of alkalinity will be provided by the use of bases and/ or nonphosphate alkaline salts such as carbonates, bicarbonates, silicates, borates, perborates and the like. Representative detergent salts are sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium metasilicate, sodium borate, sodium per-borate, diand tri-sodium orthophosphates, sodium sesquicarbonate, potassium carbonate, sodium sesquisilicate, sodium orthosilicate, potassium bicarbonate, potassium silicates, potassium hydroxide, alkaline con- Some polyelectrolytes having an ACV below 200 are ef fective (e.g. certain styrene/maleic anhydride copolymers and carboxy methyl cellulose).
6 densed phosphate salts (i.e. polyphosphates) such as tetrasodium pyrophosphate, tetrapotassium pyrophosphate and sodium tripolyphosphate, and glassy water soluble polyphosphates as known in the art.
Chlorine releasing agents Chlorine releasing agents are usually and preferably included in the detergent compositions of the present invention.
Among the various chlorine releasing agents are chlorinated trisodium phosphate, polychloroisocyanuric acids and their salts or double salts, tri-chloromelamine, chloramine T, alkali metal and alkaline earth metal hypochlorites (e.g. sodium hypochlorite), mono, di, and trichloroisocyanuric acid, dichlorodimethyl hydantoin, solid chlorinated caustic soda, succinchlorimide, and the like.
Other ingredients or additives which can be included in the machine washing detergent compositions of the present invention include low foaming or non-foaming nonionic surfactants such as various polyoxyalkylene polymers, bases such as sodium and potassium hydroxide, fillers, corrosion inhibitors, coloring agents, and the like.
The present invention is further illustrated by the following specific examples. Unless otherwise indicated, all parts and percentages are by weight.
EXAMPLE 1 A machine dishwashing detergent was prepared from the following ingredients in the amounts indicated:
TABLE II Ingredient: Amount (percent) Polyelectrolyte (see note 2, Table I) 3.0 Commercial sodium citrate 15.0 Soda ash, spray dried 59.0 Liquid sodium silicate (RU) 20.0
Chlorine bleach (sodium dichloroisocyanaurate) 1.0 Defoaming non-ionic surfactant 1 2.0
A polyoxyalkylene product available in the U.S.A. under the trademark DO-97, a product of Economics Laboratory,
EXAMPLE 2 A liquid machine washing concentrate having a pH above 12 was prepared from the following ingredients in the amounts indicated:
TABLE III Ingredient: Amount (percent) Citric acid, anhydrous 10.0 KOH (45%) 50.0 Polyelectrolyte 1 5.0 Sodium hypochlorite (12.5%) 15.0 Water, soft 20.0
1 A 50% active aqueous slurry of a vinyl acetate/maleic anhydride copolymer (sodium salt) made according to the procedure of Serial No. 836,597, previously cited (mole ratio of vinyl acetate to maleic anhydrlde of 1: 1; see Table I, polyelectrolyte number 5 (BO-46, a polymer made by Economics Laboratory, Inc.)
The concentrate was formed by dissolving the citric acid in water, then adding the KOH, and finally adding the olyelectrolyte (all with agitation). The resulting mixture (which had become hot) was cooled below 90 F. and then the sodium hypochlorite was added.
EXAMPLE 3 A liquid machine dishwashing concentrate (less expensive than Example 2) was prepared from the following ingredients by the procedure of Example 2.
TABLE IV Ingredient: Amount (percent) Citric acid, anhydrous 8.0 Sodium hydroxide (50%) 35.0 Polyelectrolyte 1 8.0 Sodium hypochlorite (100%) 2 1.5 Water, soft 47.5
1 Kghe vinyl acetate maleic anhydride copolymer of Examp e =Thls can be provided in several ways, eg, by using dilute aqueous solutions.
1 See footnote 1 to Table IV.
2 Sodium dichloroisocyanurate.
A polyoxyalkyleue known as DO-97, a product of Economlcs Laboratory, Inc.. USA.
The product is made by pouring the polyelectrolyte (a 50% active aqueous slurry) and the organic defoamer onto the ash with mixing until a dry product is obtained. The remaining ingredients can be admixed with the powder in any order.
What is claimed is:
1. Detergent compositions suitable for machine dish- Washing and consisting essentially of:
(a) alkaline detergent salt which may include not more than 10% alkali metal polyphosphates;
(b) from 5 to 60% alkali metal salt of citric acid; and
,(c) water soluble polymeric organic polyelectrolyte in a weight ratio of citrate to polyelectrolyte of at least about 1:1, said polyelectrolyte being selected from the group consisting of maleic anhydride/vinyl acetate copolymer, polyacrylamide, ethylene/maleic copolymer and sulfonated polyacrylic acid.
2. Improved detergents of claim 1 in which the polyelectrolyte is a melic/vinyl acetate copolymer.
3. Detergents of claim 1 which are solid machine dishwashing detergents, wherein said salt of citric acid is sodium citrate and wherein said detergent contains, in addition to the listed ingredients, a chlorine releasing agent selected from the group consisting of polychloroisocyanuric acids and their salts.
4. Detergents of claim 1 wherein said detergent is a liquid concentrate for machine dishwashing, is free of alkali metal polyphosphate and, in addition to the listed ingredients, contains a chlorine releasing agent.
5. Improved detergents of claim 1 which are solid detergents, wherein the polyelectrolyte has an apparent chelation value of at least 350, and wherein the weight ratio of citrate to polyelectrolyte is between about 2:1 and 10:1.
6. Detergents of claim 2 which are solid machine dishwashing detergents, which have a pH at a 1% concentration in water of at least 10.0, and which contain less than 5% by weight of alkali metal polyphosphate.
7. Solid detergent compositions suitable for the machine cleaning of dishes and consisting esesntially of:
(a) water soluble polymeric organic polyelectrolyte having an equivalent weight of about 58-110 and an apparent chelation value above 500; said polyelectrolyte being selected from the group consisting of maleic anhydride/vinyl acetate copolymer, polyacrylamide, ethylene/maleic copolymer and sulfonated polyacrylic acid;
(b) from 10-40% by weight of sodium or potassiumsalt of citric acid, the weight ratio of said salt to said polyelectrolyte being at least 1:1 and not more than about 5: 1;
(c) alkaline detergent salt which may include not more than 10% by weight of alkali metal polyphosphate; and
(d) chlorine releasing agent selected from the group consisting of polychlorisocyanuric acids and their salts;
said compositions being free of alkyl benzene sulfonates.
8. Detergents of claim 7 wherein:
(a) said citric acid salt is sodium citrate;
-,(b) said detergent salt includes soda ash;
(c) said chlorine releasing agent is sodium dichloroisocyanuate;
(d) said detergent includes a defoaming polyoxyalkylene polymer; and
(e) said composition is free of alkali metal polyphosphates.
9. Liquid detergent compositions which consist essentially of:
(a) about 8% by weight of anhydrous citric acid;
(b) about 8% by weight of a 50% aqueous slurry of a vinyl acetate/maleic anhydride copolymer (mole ratio of 1:1) having an apparent chelation value above 500;
\(c) about 35% of a 50% aqueous solution of sodium hydroxide;
(d) about 1.5% of sodium hypochlorite; and
(e) the balance to of water.
References Cited UNITED STATES PATENTS 3,308,067 3/ 1967 Diehl 252-161 3,352,785 11/1967 Corliss et a1. 252-99 3,360,469 12/1967 Fuchs 252-99 2,264,103 11/1941 Tucker 252-437 X 2,311,008 2/1943 Tucker 252137 X 2,400,863 5/ 1946 Gelfand 71-67 MAYER WEINBLA'IT, Primary Examiner U.S. Cl. X.R.
v UNITED STATES PATENT OFFICE v CERTIFICATE OF ECHQN Patent No. 3,700,599 Dated October 24, 1972 WILLIAM G, MIZUNO, JAMES L. COPELAND, ARLENE E ISCHOLZE Inventor(s It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Column 1, Line '38, Delete the entire line which begins "detergents must possess" and insert -detergents are mixtures of ingredients whose purpose, in;
Column 1, Line 47. "characteirstics" should read characteristics--;
Column 5, Line 25. "CO should read CO Column 5, between Line 50 and 5l.- Add paragraph -For the vinyl acetate/maleic copolymer, the theoretical calcium binding value is about 500 mgs CaCO /gram on a basis that one calcium is tied up by two p carboxyl groups.
Column 6, Line 42. At the end of footnote 1, add --The Product is of the type described in U.S. Patent 3,048,548.-
I Column 7, Line 15. Add between "acetate" and F'maleic" Column 7, Line 53. "melic" should read maleic Signed and sealed this 8th day of May 1973.,
(SEAL) l rttestz i-JD'E'JAPLD lLFLETCHERJl-L ROBERT GOTTSCHALK attesting Officer Commissioner of Patents FORM Po-mso (10-69) r USCOMM-DC 60376-P69 y 0 a v1 U.S. GOVERNMENT PRINTING OFFICE: 199 0-366-334-