EP0264975A1

EP0264975A1 - Thickened aqueous dishwashing compositions

Info

Publication number: EP0264975A1
Application number: EP87201496A
Authority: EP
Inventors: Albert James Fuchs; Brian Joseph Roselle
Original assignee: Procter and Gamble Co
Current assignee: Procter and Gamble Co
Priority date: 1986-08-18
Filing date: 1987-08-06
Publication date: 1988-04-27
Also published as: DK429887D0; FI873551A; DK429887A; FI873551A0; AU7710987A

Abstract

Thickened aqueous dishwashing compositions comprising hypochlorite bleach also contain high levels of SiO₂ and, preferably, polycarboxylate polymers to inhibit corrosion.

Description

Technical Field and Background Art

This invention relates to thickened aqueous compositions comprising hydrochlorite bleach for use in automatic dishwashing machines. Compositions of this type are well known. Examples of such compositions are disclosed in U.S. Patent 4,116,851 -Rupe et al, issued September 26, 1978; U.S. Patent 4,431,559 -Ulrich, issued Feb. 14, 1984; U.S. Patent 4,511,487 - Pruhs et al, issued April 16, 1985; U.S. Patent 4,512,908 - Heile, issued April 23, 1985; Canadian Patent 1,031,229 - Bush et al; European Patent Application 0130678 - Heile, published Jan. 9, 1985; European Patent Application 0176163 - Robinson, published April 2, 1986; UK Patent Application GB 2,116,199A - Julemont et al, published Sept. 21, 1983, UK Patent Application GB 2,140,450A -Julemont et al, published Nov. 29, 1984; UK Patent Application GB 2,163,447A - Colarusso, published Feb. 26, 1986; and UK Patent Application GB 2,164,350A - Lai et al, published March 19, 1986. All of said patents and said published applications are incorporated herein by reference.

Summary of The Invention

The compositions of this invention are thickened aqueous automatic dishwasher compositions comprising:

(1) from 0% to about 5%, preferably from about 0.1% to about 2.5% of a bleach-stable, preferably low foaming, detergent surfactant,
(2) from about 5% to about 40%, preferably from about 15% to about 30% of a detergency builder, especially a builder selected from the group consisting of sodium tripolyphosphate, sodium carbonate, potassium pyrophosphate and mixtures thereof;
(3) a hypochlorite bleach to yield available chlorine in an amount from about 0.3% to about 2.5%, preferably from about 0.5% to about 1.5%;
(4) from about 0.1% to about 10%, preferably from about 0.5% to about 5% of a thickening agent, preferably a clay thickening agent;
(5) alkali metal silicate to provide from about 7% to about 15, preferably from about 9% to about 12.5% of SiO₂; and
(6) the balance an aqueous liquid.

Detailed Description of The Invention

The Bleach-Stable Detergent Surfactant

Bleach-stable surfactants which are especially resistant to hypochlorite oxidation fall into two main groups. One such class of bleach-stable surfactants are the water-soluble alkyl sulfates and/or sulfonates, containing from about 8 to 18 carbon atoms in the alkyl group. Alkyl sulfates are the water-soluble salts of sulfated fatty alcohols. They are produced from natural or synthetic fatty alcohols containing from about 8 to 18 carbon atoms. Natural fatty alcohols include those produced by reducing the glycerides of naturally occurring fats and oils. Fatty alcohols can be produced synthetically, for example, by the Oxo process. Examples of suitable alcohols which can be employed in alkyl sulfate manufacture include decyl, lauryl, myristyl, palmityl and stearyl alcohols and the mixtures of fatty alcohols derived by reducing the glycerides of tallow and coconut oil.
Specific examples of alkyl sulfate salts which can be employed in the instant detergent compositions include sodium lauryl alkyl sulfate, sodium stearyl alkyl sulfate, sodium palmityl alkyl sulfate, sodium decyl sulfate, sodium myristly alkyl sulfate, potassium lauryl alkyl sulfate, potassium stearyl alkyl sulfate, potassium decyl sulfate, potassium palmity alkyl sulfate, potassium myristyl alkyl sulfate, sodium dodecyl suflate, potassium dodecyl sulfate, potassium tallow alkyl sulfate, sodium tallow alkyl sulfate, sodium coconut alkyl sulfate, magnesium coconut alkyl sulfate, calcium coconut alkyl sulfate, potassium coconut alkyl sulfate and mixtures of these surfactants. Highly preferred alkyl sulfates are sodium coconut alkyl sulfate, potassium coconut alkyl sulfate, potassium lauryl alkyl sulfate and sodium lauryl alkyl sulfate.
A second class of bleach-stable surfactant materials operable in the instant invention are the water-soluble betaine surfactants. These materials have the general formula:
wherein R₁ is an alkyl group containing from about 8 to 18 carbon atoms; R₂ and R₃ are each lower alkyl groups containing from about 1 to 4 carbon atoms, and R₄ is an alkylene group selected from the group consisting of methylene, propylene, butylene and pentylene. (Propionate betaines decompose in aqueous solution and hence are not included in the instant compositions).
Examples of suitable betaine compounds of this type include dodecyldimethylammonium acetate, tetradecyldimethylammonium acetate, hexadecyldimethylammonium acetate, alkyldimethylammonium acetate wherein the alkyl group averages about 14.8 carbon atoms in length, dodecyldimethylammonium butanoate, tetradecyldimethylammonium butanoate, hexadecyldimethylammonium butanoate, dodecyldimethylammonium hexanoate, hexadecyldimethylammonium hexanoate, tetradecyldimethylammonium pentanotate and tetradecyldipropyl ammonium pentanoate. Especially preferred betaine surfactants include dodecyldimethylammonium acetate, dodecyldimethylammonium hexanoate, hexadecyldimethylammonium acetate, and hexadecyldimethylammonium hexanoate.
Other desirable bleach stable surfactants are the alkyl phosphates, taught in U.S. Patent 4,105,573, of Ronald L. Jacobsen, issued August 8, 1978, incorporated herein by reference.
Still other preferred bleach stable surfactants include Dowfax 3B2 and similar surfactants disclosed in published U.K. Patent Applications 2,163,447A; 2,163,448A; and 2,164,350A, said applications being incorporated herein by reference. Dowfax 3B2 is sodium mono- and didecyl disulfonated diphenyl oxide. It is very bleach resistant.

Detergency Builder

Detergency builders are desirably materials which reduce the free calcium and/or magnesium ion concentration in a surfactant containing aqueous solution. They are used herein at a level of from about 5% to about 40%, preferred from about 15% to about 30%. The preferred detergency builder for use herein is sodium tripolyphosphate in an amount from about 10% to about 40%, preferably from about 20% to about 30%. It is desirable that a certain percentage of the sodium tripolyphosphate be in an undissolved particulate form suspended in the rest of the detergent composition.
Other detergency builders include potassium pyrophosphate and alkali metal carbonates. For various reasons neither of these other builders is preferred. Potassium pyrophosphate, sodium pyrophosphate, and alkali metal carbonates form insoluble calcium pyrophosphate and/or carbonate precipitates which must either be suspended or removed. Also, the carbonates tend to increase the tendency of the composition to adversely affect metal surfaces. Preferably, the carbonate level is kept below about 7%, more preferably below about 2%, and most preferably below about 1%.

The Hypochlorite Bleach

Any suitable bleach agent that yields active chlorine in aqueous solution can be employed. Such bleaching agents yield a hypochlorite species in aqueous solution. The hypochlorite ion is chemically represented by the formula OCl⁻. The hypochlorite ion is a strong oxidizing agent and for this reason materials which yield this species are considered to be powerful bleaching agents.
The strength of an aqueous solution containing hypochlorite ion is measured in terms of available chlorine. This is the oxidizing power of the solution measured by the ability of the solution to liberate iodine from an acidified iodide solution. One hypochlorite ion has the oxidizing power of 2 atoms of chlorine, i.e. one molecule of chlorine gas.
At lower pH levels, aqueous solutions formed by dissolving hypochlorite-yielding compounds contain active chlorine partially in the form of hypochlorous acid moieties and partially in the form of hypochlorite ions. At pH levels above about 10, i.e., at the preferred pH levels of the instant compositions, essentially all of the active chlorine is in the form of hypochlorite ion.
Those bleaching agents which yield a hypochlorite species in aqueous solution include alkali metal and alkaline earth metal hypochlorites, hypochlorite addition products, chloramines, chlorimines, chloramides, and chlorimides. Specific examples of compounds of this type include sodium hypochlorite, potassium hypochlorite, monobasic calcium hypochlorite, dibasic magnesium hypochlorite, chlorinated trisodium phosphate dodecahydrate, potassium dichloroisocyanurate, sodium dichlorosiocyanurate, sodium dichloroisocyanurate dihydrate, trichlorocyanuric acid, 1,3-dichloro-5,5-dimethylhydantoin, N-chlorosulfamide, Chloramine T, Dichloramine T, Chloramine B and Dichloramine B. A preferred bleaching agent for use in the compositions of the instant invention is sodium hypochlorite.
The bleaching agent generally comprises from about 0.5% to about 50% by weight, preferably from about 0.8% to about 30% by weight of the total composition to given available chlorine at a level of from about 0.3% to about 2.5%, preferably from about 0.5% to about 1.5%, most preferably from about 0.7% to about 1.1% by weight of the composition. Higher levels of hypochlorite ion increase the attack on metals. Consequently, it is desirable to keep the hypochlorite ion level low, either by keeping the absolute available chlorine level below about 1.5%, preferably below about 1.1%, or adding a material that will minimize the level of free hypochlorite ion present, e.g. dichlorocyanuric acid.

The Thickening Agent

Any thickening material or materials which can be admixed with the aqueous liquid, preferably to provide shear thinning compositions having sufficient yield values, can be used in the compositions of this invention. The most common thickening agents are clays, but materials such as colloidal silica, particulate polymers, such as polystyrene and oxidized polystyrene, combinations of certain surfactants, and water soluble polymers such as polyacrylate are also known to provide yield values.
The most preferred thickening agents for naturally occurring and synthetic clays.
A preferred synthetic clay is the one disclosed in U.S. Patent 3,843,548, incorporated herein by reference. Naturally occurring clays include smectites and attapulgites. These collodial materials can be described as expandable layered clays, i.e., aluminosilicates and magnesium silicates. The term "expandable" as used to describe the instant clays relates to the ability of the layered clay structure to be swollen, or expanded, on contact with water. The expandable clays used herein are those materials classified geologically as smectities (or montmorillonoids) and attapulgites (or palygorskites).
Smectites are three-layered clays. There are two distinct classes of smectite-clays. In the first, aluminium oxide is present in the silicate crystal lattice; in the second class of smectites, magnesium oxide is present in the silicate crystal lattice. The general formulas of these smectities are Al₂(Si₂O₅)₂(OH)₂ and Mg₃(Si₂O₅)(OH)₂, for the aluminum and magnesium oxide type clays, respectively. It is to be recognized that the range of the water of hydration in the above formulas can vary with the processing to which the clay has been subjected. This is immaterial to the use of the smectite clays in the present compositions in that the expandable characteristics of the hydrated clays are dictated by the silicate lattice structures. Furthermore, atom substitution by iron and magnesium can occur within the crystal lattice of the smectities, while metal cation s such as Na⁺, and Ca⁺⁺, as well as H⁺, can be copresent in the water of hydration to provide electrical neutrality. Although the presence of iron in such clay material is preferably avoided to minimize adverse reactions, e.g., a chemical interaction between clay and bleach, such cation substitutions in general are immaterial to the use of the clays herein since the desirable physical properties of the clay are not substantially altered thereby.
The layered expandable aluminosilicate smectite clays useful herein are further characterized by a dioctahedral crystal lattice, whereas the expandable magnesium silicate clays have a trioctahedral crystal lattice.
The smectite clays used in the compositions herein are all commercially available. such clays include for example, montmorillonite (bentonite), volchonskoite, nontronite, beidellite, hectorite, saponite, sauconite and vermiculite. The clays herein are available under commercial names such as "Fooler Clay" (clay found in a relatively thin vein above the main bentonite or montmorillonite veins in the Black Hills) and various trade names such as Thixogel No. 1 and Gelwhite GP from ECC America, Inc. (both montmorillonites); Volclay BC, Volclay No. 324, and especially Volclay HPM-20 from American Colloid Company, Skokie, Illinois; Black Hills Bentonite BH 450, from International Minerals and Chemicals; Veegum Pro and Veegum F, from R. T. Vanderbilt (both hectorites); Barasym NAS-100, Barasym NAH-100, Barasym SMM 200, and Barasym LIH-200, all synthetic hectorites and saponites marketed by Baroid Division, NL, Industries, Inc.
Smectite clays are preferred for use in the instant invention. Montmorillonite, hectorite and saponite are the preferred smectites. Gelwhite GP, Barasym NAS-100, Barasym NAH-100, and HPM-20 are the preferred montmorillonites, hectorites and saponites.
A second type of expandable clay material useful in the instant invention is classified geologically as attapulgite (palygorskite). Attapulgites are magnesium-rich clays having principles of superposition of tetrahedral and octahedral unit cell elements different from the smectites. An idealized composition of the attapulgite unit cell is given as:
(OH₂)₄(OH)₂Mg₅Si₈O₂₀.4H₂.
A typical attapulgite analysis yields 55.02% SiO₂; 10.24% Al₂O₃; 3.53% Fe₂O₃; 10.45% MgO; 0.47% K₂O; 9.73% H₂O removed at 150°C; 10.13% H₂O removed at higher temperatures.
Like the smectites, attapulgites clays are commercially available. For example, such clays are marketed under the tradename Attagel, i.e. Attagel 40, Attagel 50 and Attagel 150 from Engelhard Minerals & Chemicals Corporation.
Particularly preferred for the colloid-forming clay component in certain embodiments of the instant composition are mixtures of smectite and attapulgite clays. In general, such mixed clay compositions exhibit increased and prolonged fluidity upon application of shear stress but are still adequately thickened solutions at times when flow is not desired. Clay mixtures in a smectite/attapulgite weight ratio of from 5:1 to 1:5 are preferred. Rations of from 2:1 to 1:2 are more preferred. A ratio of about 1:1 is most preferred.
As noted above, the clays employed in the compositions of the present invention contain cationic counter ions such as protons, sodium ions, potassium ions, calcium ions, magnesium ions and the like. It is customary to distinguish between clays on the basis of one cation which is predominantly or exclusively absorbed. For example a sodium clay is one in which the absorbed cation is predominately sodium. Such absorbed cations can become involved in exchange reactions with cations present in aqueous solutions. It is preferred that the present compositions contain up to about 12% or preferably up to about 8% potassium ions since they improve the viscosity increasing characteristics of the clay. Preferably at least ½ ore preferably at least 2% of the potassium ions are present.
Hectorites can also be used, particularly those of the types described in U.S. Patents 4,511,487 and 4,512,908 previously incorporated herein by reference.
Specific preferred clays are disclosed in U.S. Patents Nos. 3,993,573 and 4,005,027, incorporated herein by reference. These materails are preferred for thickening. The amount of clay will normally be from about ¼% to about 20%, preferably from about 0.5% to about 12%, more preferably from about 0.5% to about 2%.
Other less desirable thickening agents which are useful in the process aspect of this invention include those disclosed in U.S. Patent No. 3,393,153, incorporated herein by reference, including colloidal silica having a mean particle diameter ranging from about 0.01 micron to about 0.05 micron and particulate polymers such as polystyrene, oxidized polystyrene having an acid number of from 20 to about 40, sulfonates polystyrene having an acid number of from about 10 to about 30, polyethylene, oxidized polyethylene having an acid number of from about 10 to about 30; sulfonated polyethylene having an acid number of from about 50 to about 25; polypropylene, oxidized polypropylene having an acid number of from about 10 to about 30 and sulfonated polypropylene having an acid number of from about 5 to about 25, all of said particulate polymers having mean particle diameters ranging from said 0.01 micron to about 30 microns. Other examples include copolymers of styrene with monomers such as maleic anhydride, nitrilonitrile, methaacrylic acid and lower alkyl esters of methacrylic acid. Other materials include copolymers of styrene with methyl or ethyl acrylate, methyl or ethyl maleate, vinyl acetate, acrylic maleic or fumaric acids and mixtures thereof. The mole ratio of ester and/or acid to styrene being in the range from about 4 to about 40 styrene units per ester and/or acid unit. The latter materials having a mean particle diameter range of from about 0.05 micron to about 1 micron and molecular weights ranging from about 500,000 to about 2,000,000.
Other thickening agents include polycarboxylate polymers, e.g., polyacrylates, polymethacrylates, etc. and copolymers of such monomers with other monomers such as ethylene, etc.
Still other thickening agents useful herein are described in U.S. Patent 4,226,736-Bush et al, issued Oct. 7, 1980 and incorporated herein by reference.
The compositions contain from about 0.1% to about 20%, preferably from about 0.3% to about 15%, most preferably from about 0.5% to about 5% of thickening agent.
The thickening agents are used to provide a yield value of from about 20 to about 500, preferably from about 50 to about 350, and most preferably from about 100 to about 250.
The yield value is an indicative of the shear stress at which the gel strength is exceeded and flow is initiated. It is measured herein with a Contravis Rheomat 115 viscometer utilizing a Rheoscan 100 controller and a DIN145 spindle at 25°C. The shear rate rises linearly from 0 to 0.4 sec⁻¹ over a period of 10 minutes after an initial 5 minute rest period.

The Alkali-Metal Silicate

The compositions of the type described herein deliver their bleach and alkalinity to the wash water very quickly. Accordingly, they are very aggressive to metals and other materials. This results in either discoloration by etching, chemical reaction, etc. or weight loss. It has been found that levels of silica that are normally used in automatic dishwashing compositions are not sufficient to protect materials, especially those that are most susceptible to attack like aluminum and silver. Levels of SiO₂ of 6% or less provide very little protection. The SiO₂ level should be from about 7% to about 15%, preferably from about 9% to about 12.5%, more preferably from about 10% to about 12%. The ratio of SiO₂ to the alkali metal oxide is typ ically from about 1 to about 3.2, preferably from about 1.6 to about 3, more preferably from about 2 to about 2.6.
Sodium and potassium, and especially sodium silicates are preferred. The high level of silicates improves the stability of the product, especially with respect to suspension of solids.
In addition to the silicates, other materials can be added to protect materials. For example, certain high molecular weight polycarboxylate polymers can be used at levels of from about 0.1% to about 3%, preferably from about 0.5% to about 1.5%, more preferably from about 0.8% to about 1.2%. These polymers have molecular weight of from about 1,000 to about 1,000,000, preferably from about 4,000 to about 100,000, more preferably from about 5,000 to about 80,000. A preferred polymer is a 70:30 polyacrylate/polymaleate copolymer.
Like the high levels of silicates, these polymers also improve the stability of the suspensions.

Optional Materials

Buffering Agent

It is generally desirable to also include one or more buffering agents capable of maintaining the pH of the instant compositions within the alkaline range. It is in this pH range that optimum performance of the bleach and surfactant are realized, and it is also within this pH range that optimum composition chemical stability is achieved.
When the essential thickening agent is a clay material, maintenance of the composition pH within the 10.5 to 12.5 range minimizes undesirable chemical decomposition of the active chlorine, hypochlorite-yielding bleaching agents, said decomposition generally being encountered when such bleaching agents are admixed with clay in unbuffered aqueous solution. Maintenance of this particular pH range also minimizes the chemical interaction between the strong hypochlorite bleach and the surfactant compounds present in the instant compositions. Finally, as noted, high pH values such as those maintained by an optional buffering agent serve to enhance the soil and stain removal properties of the surfactant during utilization of the present composition.
The instant compositions can contain other non-essential materials to enhance their performance, stability, or aesthetic appeal. Such materials include optional nonbuffering builder compounds, coloring agents and perfumes.
Conventional coloring agents and perfumes can also be added to the instant compositions to enhance their aesthetic appeal and/or consumer acceptability. These materials should, of course, be those dye and perfume varieties which are especially stable against degradation by the strong active chlorine bleaching agents which are present.
If present, the above-described other optional materials generally comprise no more than about 35% by weight of the total composition and are dissolved, suspended or emulsified in the aqueous liquid component used to form the preferred false body fluid phase of the instant compositions.
All parts, percentages and ratios herein are by weight unless otherwise specified.

EXAMPLES 1-16

In this example wash and prewash solutions were prepared with equivalent parts per million (ppm) as follows:
Dowfax 3B2 surfactant (23 and 43 ppm); sodium tripolyphosphate (1473 and 2761 ppm); bentonite clay thickener (52 and 97 ppm); monostearyl acid phosphate (1.9 and 4.0 ppm); and minors. The levels of SiO₁, provided by 2.4 ratio sodium silicate; the available chlorine levels, provided by either a sodium hypochlorite solution containing 11.4% available chlorine or sodium dichlorocyanurate; the levels of sodium chloride, from the sodium hypochlorite solution; and the levels of sodium polyacrylate (M.W. - 60,000) were adjusted as indicated and aluminum ware and silverware were washed for 10 cycles and then checked for corrosion. The "low silicate" prewash and wash solutions also contained 42 and 79 ppm of NaOH and 387 and 729 ppm of Na₂CO₃ respectively to balance the solutions for alkalinity. The wash water volume was 2.5 gal. and the prewash water volume was 1.5 gal.
The above compositions were tested for corrosion by weight loss (or gain) and by apparatus in which 10 is perfect and 0 is the worst. The following results were obtained.

Claims

1. An aqueous automatic dishwasher composition comprising:

(1) from 0% to about 5% of bleach-stable detergent surfactant;

(2) from about 5% to about 40% of detergency builder;

(3) hypochlorite bleach to yield available chlorine in an amount of from about 0.3% to about 2.5%;

(4) from about 0.1% to about 10% of thickening agent;

(5) alkali metal silicate to provide from at least about 7% SiO₂; and

(6) the balance an aqueous liquid.

2. The composition of Claim 1 wherein the alkali metal silicate provides from about 9% to about 12.5% SiO₂.

3. The composition of Claim 2 wherein the hypochlorite bleach yields available chlorine in an amount from about 0.5% to about 1.5%.

4. The composition of Claim 3 additionally comprising high molecular weight polycarboxylate polymer in an amount of from about 0.1% to about 3%, said polymer having a molecular weight of from about 1,000 to about 1,000,000.

5. The composition of Claim 3 wherein the hypochlorite bleach yields available chlorine in an amount from about 0.7% to about 1.1%.

6. The composition of Claim 1 wherein the thickening agent is a clay, the builder is sodium tripolyphosphate and there is from about 0.1% to about 2.5% detergent surfactant.

7. The composition of Claim 6 additionally comprising a high molecular weight polycarboxylate polymer in an amount of from about 0.5% to about 1.5%, said polymer having a molecule weight of from about 5,000 to about 100,000.

8. The composition of Claim 1 containing from about 0.5% to about 5% of clay thickening agent, sodium tripolyphosphate builder, and from about 0.1% to about 2.5% detergent surfactant.