Technical Field and Background Art
[0001] 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
[0002] 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
[0003] 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.
[0004] 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.
[0005] 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).
[0006] 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.
[0007] 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.
[0008] 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
[0009] 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.
[0010] 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
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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
[0016] 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.
[0017] The most preferred thickening agents for naturally occurring and synthetic clays.
[0018] 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).
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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%.
[0030] 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.
[0031] Other thickening agents include polycarboxylate polymers, e.g., polyacrylates, polymethacrylates,
etc. and copolymers of such monomers with other monomers such as ethylene, etc.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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
[0036] 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.
[0037] 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.
[0038] 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.
[0039] Like the high levels of silicates, these polymers also improve the stability of the
suspensions.
Optional Materials
Buffering Agent
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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.
[0045] All parts, percentages and ratios herein are by weight unless otherwise specified.
EXAMPLES 1-16
[0046] 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.