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FIELD OF THE INVENTION
This invention relates to a stable microemulsion cleaning composition and to processes for manufacture and use thereof. More particularly, it relates to a stable aqueous microemulsion cleaning composition in concentrated or diluted form which is
especially effective to clean oily and greasy soils from substrates such as bathroom fixtures and walls, leaving such surfaces clean and shiny without the need for extensive rinsing thereof. The described compositions comprise a mixture of anionic
surfactants, a water insoluble organic compound has less than 1.0 wt. % soluble in water at 25 degrees C and having a .delta..sub.H of about 0 to about 12 (MPa) 1/2, a .delta..sub.d of about 19 to about 14, (MPa) 1/2, and .delta..sub.p of about 0 to
about 6 (MPa) 1/2, water and a suitable co-surfactant system, which co-surfactant system adjusts the interface conformation to reduce interfacial tension at interfaces between dispersed and continuous phases of the emulsion to produce a stable normally
clear microemulsion at room temperature. When the pH of the microemulsion is on the acid side, preferably in the range of 1 to 4, the invented compositions are useful for removing lime scale and soap scum from hard substrates.
BACKGROUND OF THE INVENTION
Liquid detergent compositions, usually in solution or emulsion form, have been employed as all-purpose detergents and have been suggested for cleaning hard surfaces such as painted woodwork, bathtubs, sinks, tile floors, tiled walls, linoleum,
paneling and washable wallpaper. Many such preparations, such as those described in U.S. Pat. Nos. 2,560,839, 3,234,138, and 3,350,319 and British Patent Specification No. 1223739, include substantial proportions of inorganic phosphate builder salts,
the presence of which can sometimes be found objectionable for environmental reasons and also because they necessitate thorough rinsing of the liquid detergent from the cleaned surface to avoid the presence of noticeable depositings of phosphate thereon. In U.S. Pat. Nos. 4,017,409 and 4,244,840 liquid detergents of reduced phosphate builder salt contents have been described but such may still require rinsing or can include enough phosphate to be environmentally objectionable. Some liquid detergents
have been made which are phosphate-free, such as those described in U.S. Pat. No. 3,935,130, but these normally include higher percentages of synthetic organic detergent which increased detergent content may be objectionable due to excessive foaming
during use that can result from its presence. The previously described liquid detergent compositions are emulsions but are not disclosed to be microemulsions like those of the present invention.
Microemulsions have been disclosed in various patents and patent applications for liquid detergent compositions which may be useful as hard surface cleaners or all-purpose cleaners, and such compositions have sometimes included detergent,
solvent, water and a co-surfactant. Among such disclosures are European Patent Specification Nos. 0137615, 0137616, and 0160762, and U.S. Pat. No. 4,561,448, all of which describe employing at least 5% by weight of the solvent in the compositions.
The use of magnesium salts to improve grease removing performance of solvents in microemulsion liquid detergent compositions is mentioned in British Patent Specification No. 2144763. Other patents on liquid detergent cleaning compositions in
microemulsion form are U.S. Pat. Nos. 3,723,330, 4,472,291, and 4,540,448. Additional formulas of liquid detergent compositions in emulsion form which include hydrocarbons, such as terpenes, are disclosed in British Patent Specifications Nos.
1603047 and 2033421, European Specification No. 0080749, and U.S. Pat. Nos. 4,017,409, 4,414,128, and 4,540,505. However, the presence of builder salt in such compositions, especially in the presence of magnesium compounds, tends to destabilize the
microemulsions and therefore such builders are considered to be undesirable.
Although the cited prior art relates to liquid all-purpose detergent compositions in emulsion form and although various components of the present compositions are mentioned in the art, it is considered that the art does not anticipate or make
obvious subject matter disclosed and claimed herein. In accordance with the present invention a stable aqueous microemulsion cleaning composition, which may be in concentrated or dilute form, comprises at least two different anionic synthetic organic
detergent, a water insoluble organic compound, water and a co-surfactant system, which co-surfactant system adjusts interfacial conformation to reduce interfacial tension at interfaces between dispersed and continuous phases of an emulsion to produce a
stable concentrated microemulsion which is stable at temperatures in the range of 5.degree. to 50.degree. C. and which has a pH in the range of 1 to 11. Such concentrated microemulsions are dilutable with water to at least five times their weight, to
produce diluted liquid detergent compositions which are often also stable aqueous microemulsions which are useful as all-purpose cleaning compositions. Both the concentrated and diluted compositions are effective for cleaning oily and greasy soils from
substrates, and when the compositions are acidic they are also useful to remove lime scale and soap scum from hard surfaces, such as bathroom fixtures, floors and walls.
Furthermore, the present inventors have observed that in formulations containing grease-removal assisting magnesium compounds, the addition of minor amounts of builder salts, such as alkali metal polyphosphates, alkali metal carbonates,
nitrilotriacetic acid salts, and so on, tends to make it more difficult to form stable microemulsion systems.
In addition to microemulsion concentrates, the present invention also relates to dilute microemulsions to processes for manufacturing such microemulsions and to processes for cleaning surfaces with them.
SUMMARY OF THE INVENTION
The present invention provides an improved liquid cleaning composition in the form of a microemulsion which is suitable for cleaning hard surfaces having greasy build-up deposited thereon, such as plastic, vitreous and metal surfaces, all of
which may have shiny finishes. While the all-purpose cleaning composition may also be used in other cleaning applications, such as removing oily soils and stains from fabrics, it is primarily intended for cleaning hard, shiny surfaces, and desirably
requires little or no rinsing. The improved cleaning compositions of the invention exhibit superior grease removal actions, especially when used in concentrated form, and leave the cleaned surfaces shiny, sometimes without any need for rinsing them.
Little or no residue will be seen on the cleaned surfaces, which overcomes one of the significant disadvantages of various prior art products, and the surfaces will shine, even after little or no wiping thereof. Surprisingly, this desirable cleaning is
accomplished even in the absence of polyphosphates or other inorganic or organic detergent builder salts.
GENERAL DESCRIPTION OF THE INVENTION
In one aspect of the invention, a stable, clear, all-purposed hard surface cleaning composition which is especially effective in the removal of oily and greasy soils from hard surfaces, is in the form of a substantially concentrated or somewhat
diluted microemulsion.
The compositions of the instant invention which are preferably microemulsions especially designed for superior removal of grease deposits on hard surfaces comprise approximately by weight:
a) 6 to 50% of a mixture of two different anionic surfactants, one of said anionic surfactants being a sulphonate and the other said anionic surfactant being a sulphate, a ratio of the sulphonate to the sulphate being about 10:1 to about 1:10,
more preferably about 4:1 to about 2:1 and most preferably about 3.3:1 to about 2:7;
b) 0 to 6% of a nonionic surfactant;
c) 1 to 20% of at least water insoluble organic compound having a .delta..sub.H of about 0 to about 12 (MPa).sup.1/2, a .delta..sub.d of about 14 to about 19 (MPa).sup.1/2, and a .delta..sub.p of about 0 to about 6 (MPa).sup.1/2 ;
d) 0 to 8% of a solubilizing agent;
e) 0 to 14% of at least one cosurfactant; and
f) the balance being water, wherein the composition has a pH of about 1 to about 11, more preferably about 5 to about 9 and is optically clear having at least 90% light transmission, more preferably at least 95% and the interfacial tension
between the lipophile droplets and the aqueous phase is less than about 10.sup.-2 mN/m, more preferably less than about 10.sup.-3 mN/m.
The present invention also provides a light duty liquid microemulsion compositions of the instant invention which can be generally described as comprising approximately by weight:
(a) 15% to 36%, preferably 18% to 34%, of a mixture of a magnesium metal salt of a C.sub.13 -C.sub.17 alkyl sulfonate surfactant;
(b) 1% to 20%, more preferably 2% to 18% of an alkali metal salt or ammonium salt of a C.sub.8 -C.sub.18 alkyl polyethenoxy sulfate surfactant, wherein the ratio of sulfonate surfactant to the sulfate surfactant is about 8:1 to about 1:8, more
preferably about 7:1 to about 1:2;
(c) 0% to about 10%; more preferably 1% to 5% of an alkyl polyglucoside surfactant;
(d) 0.4% to 10.0%, more preferably 2.0% to 7.0% of a perfume, an essential oil or a water insoluble hydrocarbon;
(e) 1% to 25%, more preferably 2 to 8% of a cosurfactant;
(f) 0 to 5%, more preferably 0.1 to 3% of at least one hydrotrope;
(g) 0 to 4%; more preferably 0.1 to 2% of magnesium sulfate;
(h) 0 to 5%, more preferably 0.5 to 3% of an alkyl monoalkanol amide or an alkyl dialkanol amide and mixtures thereof; and
(i) the balance being water, wherein the composition has a Brookfield viscosity at 25.degree. C. at 3 rpms using a #18 spindle of about 20 to 500 cps, more preferably about 100 to 450 cps, a pH of about 5 to about 7, and a light transmission of
at least about 95%, more preferably at least about 98%.
Preferred concentrations of the mentioned components of the concentrated microemulsion are 6 to 50 wt % of synthetic organic detergent, 1 to 20 wt % the water insoluble inorganic compound, 1 to 14 wt % of co-surfactant system, and the balance
being water. At such preferred concentrations, upon dilution of one part of concentrate with four parts of water the resulting microemulsion will be low in detergent and solvent contents, which may be desirable to avoid excessive foaming and to prevent
destabilization of the emulsion due to too great a content of lipophilic phase therein after dissolving in the suitable hydrocarbon or other solvent of the oily or greasy soil to be removed from a substrate to be cleaned. Because of the absence of
builders when the cleaning composition consists of or consists essentially of the described components (with minor proportions of compatible adjuvants being permissible), a chalky appearance of the clean surface is avoided and rinsing may be obviated.
Among the desirable adjuvants that may be present in the microemulsions are divalent or polyvalent metal salts, as sources of magnesium and aluminum, for example, which improve cleaning performances of the dilute compositions, and higher fatty acids
and/or higher fatty acid soaps, such as sodium stearate at a concentration of about 1.0 to 5.0 wt. percent which act as foam suppressants as well as preserving the clarity of the product. Of course, if it is considered aesthetically desirable for the
normally clear microemulsions to be cloudy or pearlescent in appearance, an opacifying or pearlescing agent may be present and in some instances, when it is not considered disadvantageous to have to rinse the builder off the substrate, builder salts,
such as polyphosphates, may be present in the microemulsions, but it should be stressed that normally builders will be absent from them.
Some preferred "dilute" microemulsion cleaning compositions of this invention are those which are of formulas such as are producible by mixing four parts by weight of water with one part by weight of the concentrated microemulsion previously
described. When other dilutions are employed, from 1:1 to 1:19 of concentrated microemulsion:water, the percentages of such ranges and preferred ranges should be adjusted accordingly. In some instances dilutions to 1:99 are feasible and such diluted
compositions may be used as is or may be further diluted in some applications, as when employed for hand dishwashing (with rinsing).
Although most of the microemulsions of thisinvention are of the oil-in-water (o/w) type, some may be water-in-oil (w/o), especially the concentrates. Such may change to o/w on dilution with water, but both the o/w and w/o microemulsions are
stable. However, the preferred detergent compositions are oil-in-water microemulsions, whether as concentrates of after dilution with water, with the essential components thereof being detergent, water insoluble organic compound, co-surfactant and
water.
An useful sulfonated anionic surfactant is a linear sodium alkyl benzene sulfonate (LAS) which is characterized by the formula: ##STR1## wherein n is from about 9 to about 15
The concentration of the paraffin or linear alkyl benzene sulphonate in the instant composition is about 6 to about 60 wt. %, more preferably 5 to about 30 wt %, most preferably about 15 to about 30 wt % and the concentration of the alkyl ether
sulphate is about 1 to about 20 wt %, more preferably about 2 to about 12 wt %.
Among the advantages of the present invention over previously known liquid detergent compositions are the following:
1. Liquid detergent compositions embodying the invention can be produced having comparably efficacy and properties with lower percentages of active ingredients and comparable clarity with significantly lower percentages of solubilizers than are
disclosed in previously known compositions for the removal of grease deposits.
2. Compositions embodying the present invention can produce foam as good or better than that produced by prior art compositions, both in quantity and durability.
3. Compositions embodying the present invention, when diluted to the same concentration for use as the prior art compositions, can give substantially better performance as to grease removal, particularly in dishwashing.
4. Washing solutions made with compositions embodying the present invention have significantly lower surface tension than solutions of the same concentration using prior art compositions.
Additional advantages of the present invention are improved and controlled performance such as foaming and dishwashing ability, viscosity and clarity, which are important features in consumer acceptability.
The paraffin sulphonates (A) used in the compositions of the present invention are usually mixed secondary alkyl sulphonates having from 10 to 20 carbon atoms per molecule; preferably at least 80%, usually at least 90%, of the alkyl groups will
have 13-17 carbon atoms per molecule. Where the major proportion has 14-15 carbon atoms per molecule, optimum foaming performance appears to be obtained at varying concentrations and water hardnesses. Another useful sulfonated anionic surfactant is a
linear sodium alkyl benzene sulfonate (LAS) which is characterized by the formula: wherein n is from about 9 to 15. The sulphonates are generally present in amounts from 15% to 60%, preferably 20% to 35%, by weight of the composition.
A preferred sulfonate is a magnesium salt of a linear alkyl benzene sulfonate having a high content of 3-(or higher) phenyl isomers and a correspondingly low content (well below 50%) of -2 (or lower) phenyl isomers, that is, wherein the benzene
ring is preferably attached in large part at the 3 or higher (for example 4, 5, 6 or 7) position of the alkyl group and the content of the isomers in which the benzene ring is attached in the 2 or 1 position is correspondingly low. Particularly
preferred materials are set forth in U.S. Pat. No. 3,320,174.
The higher alkyl ether sulphates (C) used in the compositions of the present invention are represented by the formula:
in which R represents a primary or secondary alkyl group that may be straight or branched having from 10 to 18 carbon atoms, preferably from 12 to 15, X is a suitable water soluble cation, as hereinafter defined, and n is from 1 to 10, preferably
from 1 to 6. These sulphates are produced by sulphating the corresponding ether alcohol and then neutralizing the resulting sulphuric acid ester.
Examples of satisfactory anionic sulfate detergents are the C.sub.8 -C.sub.18 alkyl ether polyethenoxy sulfate salts having the formula R(OC2H4)n OSO3M wherein n is 1 to 12, preferably 1 to 5, and M is a solubilizing cation selected from the
group consisting of alkali metal cations such as sodium or potassium, alkaline earth metal cations such as magnesium, ammonium, and mono-, di- and triethanol ammonium ions, wherein sodium, potassium and ammonium are preferred. The alkyl ether
polyethenoxy sulfates are obtained by sulfating the condensation product of ethylene oxide with a C.sub.8 -C.sub.18 alkanol and neutralizing the resultant product. The alkyl ether polyethenoxy sulfates differ from one another in the number of moles of
ethylene oxide reacted with one mole of alkanol. Preferred alkyl ether polyethenoxy sulfates contain 10 to 16 carbon atoms in the alkyl group.
The C.sub.8 -C.sub.12 alkylphenyl ether polyethenoxy sulfates containing from 2 to 6 moles of ethylene oxide in the molecule also are suitable for use in the inventive compositions. These detergents can be prepared by reacting an alkyl phenol
with 2 to 6 moles of ethylene oxide and sulfating and neutralizing the resultant ethoxylated alkylphenol.
The cation of the paraffin sulphonate (A) and the alkyl ether sulphate (C) may be an alkali metal (e.g. sodium or potassium), an alkaline earth metal (e.g. magnesium), ammonium or lower amine (including alkylolamines). It is preferred to use the
sodium salt of the paraffin sulphonic acid and a sodium salt of the alkyl ether sulphuric acid ester oxide, dodecyl phenol condensed with 15 moles of ethylene oxide, and dinonyl phenol condensed with 15 moles of ethylene oxide. These aromatic compounds
are not as desirable as the aliphatic alcohol ethoxylates in the invented compositions because they are not as biodegradable.
The water soluble or water dispersible nonionic synthetic organic detergents that are optionally employed in the composition at a concentration of 0 to 6 wt %, preferably 0.1 to 6 wt % in the invented cleaning compositions are usually
condensation products of an organic aliphatic or alkylaromatic hydrophobic compound and ethylene oxide, which is hydrophilic. Almost any hydrophobic compound having a carboxy, hydroxy, amido or amino group with a free hydrogen present can be condensed
with ethylene oxide or with polyethylene glycol to form a nonionic detergent. The length of the polyethenoxy chain of the condensation product can be adjusted to achieve the desired balance between the hydrophobic and hydrophilic elements
(hydrophilic-lipophilic balance, or HLB) and such balances may be estimated as HLB numbers.
Particularly suitable nonionic detergents are the condensation products of a higher aliphatic alcohol, containing about 8 to 18 carbon atoms in a straight or branched chain configuration, condensed with about 2 to 30, preferably 2 to 10 moles of
ethylene oxide. A particularly preferred compound is C.sub.9-11 alkanol ethoxylate of five ethylene oxides per mole (5 EO), which also may be designated as C.sub.9-11 alcohol EO 5:1, C.sub.12-15 alkanol ethoxylate (7 EO), or C.sub.12-15 alcohol EO 7:1
is also preferred, such nonionic detergents are commercially available from Shell Chemical Co. under the trade names Dobanol 91-5 and Neodol 25-7.
Other suitable nonionic detergents are the polyethylene oxide condensates of one mole of alkyl phenol containing from about 6 to 12 carbon atoms in a straight or branched chain configuration, with about 2 to 30, preferably 2 to 15 moles of
ethylene oxide, such as nonyl phenol condensed with 9 moles of ethylene oxide, dodecyl phenol condensed with 15 moles of ethylene oxide, and dinonyl phenol condensed with 15 moles of ethylene oxide. These aromatic compounds are not as desirable as the
aliphatic alcohol ethoxylates in the invented compositions because they are not as biodegradable.
Another well-known group of usable nonionic detergents is marketed under the trade name "Pluronics." These compounds are block copolymers formed by condensing ethylene oxide with a hydrophobic base formed by the condensation of propylene oxide
with propylene glycol. The molecular weight of the hydrophobic portion of the molecule is of the order of 950 to 4000, preferably 1200 to 2500. The condensation of ethylene oxide with the hydrophobic moiety increases the water solubility of the
molecule. The molecular weight of these polymers is in the range of 1000 to 15,000, and the polyethylene oxide content may comprise 20 to 80% thereof.
Still other satisfactory nonionic detergents are a condensation of a C.sub.10-16 alkanol with a heteric mixture of ethylene oxide and propylene oxide. The mole ratio of ethylene oxide to propylene oxide is from 1:1 to 4:1, preferably from 1.5:1
to 3.0:1, with the total weight of the ethylene oxide and propylene oxide contents (including the terminal ethanol group or propanol group) being from 60% to 85%, preferably 70% to 80%, of the molecular weight of the nonionic detergent. Preferably the
higher alkanol contains 12 to 15 carbon atoms and a preferred compound is the condensation product of C.sub.13-15 alkanol with 4 moles of propylene oxide and 7 moles of ethylene oxide. Such preferred compounds are commercially available from BASF
Company under the trade name Lutensol LF.
Also suitable for incorporation in the invented cleaning compositions are the nonionic detergents that are derived from the condensation of ethylene oxide with the product resulting from the reaction of propylene oxide and ethylene diamine. For
example, satisfactory such compounds contain from about 40 to about; 80% of polyoxyethylene by weight, have a molecular weight of from about 5000 to 11,000, and result from the reaction of ethylene oxide with a hydrophobic base which is a reaction
product of ethylene diamine and excess propylene oxide, and which is of a molecular weight in the range of 2500 to 3000.
Additionally, polar nonionic detergents may be substituted for the generally non-polar nonionic detergents described above. Among such polar detergents are those in which a hydrophilic group contains a semi-polar bond directly between two atoms,
for example N-O and P-O. There is charge separation between such directly bonded atoms, but the detergent molecule bears to net charge and does not dissociate into ions. Suitable such polar nonionic detergents include open chain aliphatic amine oxides
of the general formula R.sup.7 --R.sup.8 --R.sup.9 N--O, wherein R.sup.7 is an alkyl, alkenyl or monohydroxyalkyl radical having about 10 to 16 carbon atoms and R.sup.8 and R.sup.9 are each selected from the group consisting of methyl, ethyl, propyl,
ethanol and propanol radicals. Preferred amine oxides are the C.sub.10-16 alkyl dimethyl and dihydroxyethyl amine oxides, e.g. lauryl dimethyl amine oxide and lauryl myristyl dihydroxyethyl amine oxide. Other operable polar nonionic detergents are the
related open chain aliphatic phosphine oxides having the general formula R.sup.10 --R.sup.11 --R.sup.12 P--O wherein R.sup.10 is an alkyl, alkenyl or monohydroxyalkyl radical of a chain length in the range of 10 to 18 carbon atoms, and R.sup.11 and
R.sup.12 are each alkyl or monohydroxyalkyl radicals containing from 1 to 3 carbon atoms. As with the amine oxides, the preferred phosphine oxides are the C.sub.10-16 alkyl dimethyl and dihydroxyethyl phosphone oxides.
In dilute o/w microemulsion compositions of this invention, the nonionic detergent can be present in admixture with the anionic detergent. The proportion of nonionic detergent in such mixed detergent compositions, based on the final dilute o/w
microemulsion composition, may be in the range of 0 to 6 wt %, preferably 0.1 to 6 wt. %.
Many other suitable anionic and nonionic detergents that may be derisive components of the present microemulsion cleaning compositions are described in texts denoted to detergency, detergent compositions and components, including Surface Active
Agents (Their Chemistry and Technology), by Schwartz and Perry, and the various annual editions of John W. McCutcheon's Detergents and Emulsifiers.
The viscosity and clarity control system for the composition comprises a solublizing agent such as urea and a lower aliphatic alcohol which is a co-surfactant, and optionally a water soluble hydrotrope which is effective in promoting the
compatibility of the ingredients in the microemulsion composition and can be substituted for part of the urea or alcohol. Generally, the viscosity and clarity control system is required in concentrated liquid detergent compositions containing at least
30 wt % by weight of active ingredients, namely the sum of paraffin sulphonate and alkyl ether sulphate.
Suitable hydrotropic substances are the alkali metal organic sulphonated (including sulphated) salts having an alkyl group up to 6 carbon atoms. The preferred sulphonated hydrotropes are alkyl aryl sulphonates having up to 3 carbon atoms in the
alkyl group, e.g. the sodium and potassium xylene, toluene, ethylbenzene and isopropyl benzene (cumene) sulphonates. Sulphonates made from xylene include orthoxylene sulphonate, metaxylene sulphonate, paraxylene sulphonate and ethylbenzene sulphonate.
Commercial xylene sulphonates usually contain metaxylene sulphonate as the main ingredient. Analysis of typical commercial xylene sulphonate products shows about 40 to 50% metaxylene sulphonate, 10 to 35% orthoxylene sulphonate and 15 to 30% paraxylene
sulphonate with 0 to 20% ethylbenzene sulphonate. Any suitable isomeric mixture, however, may be employed. Sodium cumene sulphonate and sodium xylene sulphonate are preferred alkyl aryl sulphone hydrotropes for use in the compositions of the present
invention. It is also permissible to use suitably alkyl sulphate salts having 5 or 6 carbon atoms in the alkyl group such as alkali metal n-amyl and n-hexylsulphates.
The use of the viscosity and clarity control system imparts superior low temperature clarity of the liquid detergent composition and provides control of the viscosity of the product over a wider range for any particular concentration of active
ingredients, as will be set forth in greater detail hereinafter. The alcohols preferably have 2 or 3 carbon atoms. Thus, ethyl alcohol, propyl alcohol, isopropyl alcohol or propylene glycol can be used; preferably ethyl alcohol will be used.
The proportions of urea, alcohol and hydrotropic substance best suited for any particular composition depend on the active ingredient components and proportions and can be determined by the formulator by conventional tests. The weight content of
this viscosity and control system based upon the total composition will vary from 0 to 22% and preferably is from 0.5 to 10%. Within that range solublizing will vary within the ranges of from 0 to 8.0%, preferably from 0.5 to 6%, and the co-surfactant
will be from 0 to 14%, preferably 0.15 to 10%. The ratio of alcohol to urea is maintained below 1.3:1, preferably below 1:1 and most preferably is in the range from 0.37:1 to 0.85:1 when using an active ingredient content above 30% by weight, preferably
35 to 45%. Varying amounts of hydrotrope such a xylene sulphonate may be added or substituted in part for the alcohol or urea so as to form a ternary system with special properties such as markedly to increase the viscosity. The amount should be
selected so as to maintain a satisfactory viscosity and cloud point and maintain other desirable properties. Generally, the hydrotrope may constitute up to 15% by weight of the total viscosity and control system.
The co-surfactant component plays an essential role in the concentrated and diluted microemulsions of this invention. In the absence of the co-surfactant the water, detergent(s) and water insoluble organic compound, when mixed in appropriate
proportions, will form either a micellar solution, at lower concentrations, a microemulsion, or a conventional oil-in-water emulsion. With the presence of the co-surfactant in such systems in interfacial tension or surface tension at the interfaces
between the lipophile droplets and the continuous aqueous phase is greatly reduced, to a value close to (10.sup.-3 mN/m). This reduction of the interfacial tension results in spontaneous disintegration of the dispersed phase globules or droplets until
they become so small that they cannot be perceived by the unaided human eye, and a clear microemulsion is formed, which appears to be transparent. In such microemulsion state thermodynamic factors come into balance, with varying degrees of stability
being related to the total free energy of the microemulsion. Some of the thermodynamic factors involved in determining the total free energy of the system are (1) particle-particle potential; (2) interfacial tension or free energy (stretching and
bending); (3) droplet dispersion entropy; and (4) chemical potential changes upon formation of the microemulsion. A thermodynamically stable system is achieved when interfacial tension or free energy is minimized and when droplet dispersion entropy is
maximized. Thus, it appears that the role of the co-surfactant in formation of a stable o/w microemulsion is to decrease interfacial tension and to modify the microemulsion structure and increase the number of possible configurations. Also it seems
likely that the co-surfactant helps to decrease rigidity of the dispersed phase with respect to the continuous phase and with respect to the oily and greasy soils to be removed from surfaces to be contacted by the microemulsions.
The amount of co-surfactant employed to stabilize the microemulsion compositions will depend on such factors as the surface tension characteristics of the co-surfactant, the types and proportions of the detergents and perfumes, and the types and
proportions of any additional components which are present in the composition and which have an influence on the thermodynamic factors previously enumerated. Generally, amounts of co-surfactant in a preferred range of 0 to 25%, more preferably 1 to 25%,
and especially preferred 1 to 15%, provide stable dilute o/w microemulsions for the above-described levels of primary surfactants, water insoluble organic compound, and any other additives as described below, in the diluted microemulsions. Related
ranges for concentrated microemulsions are obtained by multiplying the extremes of the given ranges by five.
The highly suitable cosurfactants of the instant composition over temperature ranges extending from 4.degree. C. to 43.degree. C. are water-soluble C.sub.2 -C.sub.4 alkanols, polypropylene glycol of the formula HO(CH.sub.3)CHCH.sub.2 O).sub.n H
wherein n is a number from 1 to 18 and mono C.sub.1 -C.sub.6 alkyl ethers and esters of ethylene glycol and propylene glycol having the structural formulas R(X).sub.n OH and R.sub.1 (X).sub.n OH wherein R is C.sub.1 -C.sub.6 alkyl, R.sub.1 is C.sub.2
-C.sub.4 acyl group, X is (OCH.sub.2 CH.sub.2) or (OCH.sub.2 CH(CH.sub.3) and n is a number from 1 to 4.
Representative members of the polypropylene glycol include dipropylene glycol and polypropylene glycol having a molecular weight of 200 to 1000, e.g., polypropylene glycol 400. Satisfactory glycol ethers are dipropylene glycol monomethyl ether,
ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monobutyl ether (butyl carbitol), triethylene glycol monobutyl ether, mono, di, tri propylene glycol monobutyl ether, propylene glycol monomethyl ether, tetraethylene glycol monobutyl
ether, propylene glycol tertiary butyl ether, ethylene glycol monoacetate and dipropylene glycol propionate. Also useful cosurfactants are polyethylene glycols having a molecular weight of 300 to 600 and mixtures of polyethylene glycol and polypropylene
glycol sold by Synalox.
The water insoluble organic compound of the instant composition can be one or more water insoluble organic compounds which have a molecular weight of less than 250, more preferably less than 175 and is less than 1.0 wt. % soluble in water at room
temperature which have an average .delta..sub.H (hydrogen bonding solubility parameter) of about 0 to about 12 (MPa).sup.1/2, an average .delta..sub.p (polar solubility parameter) of about 0 to about 6 (MPa).sup.1/2, and an average .delta..sub.d
(dispersion solubility parameter) of about 14 to about 19 (MPa.sup.1/2). When the water insoluble compound has these average solubility parameters, the microemulsion composition of the instant invention will exhibit maximum grease cleaning capacity for
the removal of grease deposits of hard surface. The water insoluble organic compounds are selected from the group consisting essentially of D-limonene, alpha-terpineol, Isopars sold by Exxon Chemical Co which are isoparaffenic hydrocarbons having 6 to
16 carbon atoms. Exxates such as Exxate 1000 and Exxate 1300 sold by Exxon Chemical Co., mixture of water insoluble aliphatic alcohols having about 6 to about 18 carbon atoms and an aliphatic or isoaliphatic hydrocarbons having about 8 to about 30
carbon atoms in a ratio of aliphatic or alcohols to aliphatic or isoaliphatic hydrocarbons of about 10:1 to about 1:10 mixtures of water insoluble aliphatic alcohols having about 6 to about 18 carbon atoms and water insoluble alkyl esters having about 10
to about 20 carbon atoms in a ratio of aliphatic alcohols to alkyl esters of about 10:1 to about 1:10. The concentration of the water insoluble organic compound is about 1 to about 20 wt %, more preferably about 2 to about 15 wt %.
The pHs of the final microemulsion, concentrated or diluted, will be dependent in large part on the identity of the co-surfactant compound, with the choice of the co-surfactant also being affected by cost and cosmetic properties, often
particularly odor or fragrance. For example, microemulsion compositions which are to have a pH in the range of 1 to 10 may employ either an alkanol, propylene glycol, or ethylene glycol or propylene glycol ether or ester, or an alkyl phosphate as the
sole co-surfactant but such pH range may be reduced to 1 to 8.5 when polyvalent metal salt is present.
In addition to their excellent capacity for cleaning greasy and oily soils, the low pH o/w microemulsion formulations of this invention also exhibit excellent other cleaning properties. They satisfactorily remove soap scum and lime scale from
hard surfaces when applied in neat (undiluted) form, as well as when they are diluted. For such applications onto originally hard shiny surfaces having surface deposits of lime scale and/or soap scum, which may also be soiled with oily and greasy
deposits, the microemulsions may be of a pH in the 0.5 to 6 range, preferably 1 to 4 and more preferably 1.5 to 3.5. For general cleaning of oily and greasy surfaces, without lime scale or soap scum deposits, the pH may be in the range of 1 to 11 and
sometimes 6-11 or 6-8 will be preferred and more preferred, respectively (for mildness and effectiveness).
The final essential component of the invented microemulsions is water. Such water may be tap water, usually of less than 150 ppm hardness, as CaCO.sub.3, but preferably will be deionized water or water of hardness less than 50 ppm, as
CaCO.sub.3. The proportion of water in the o/w microemulsion compositions generally is in the range of 15 to 85%.
The essential ingredients discussed above can be solubilized in one preferred embodiment of the invention in water and either an alkyl monoethanol amide such as C.sub.12 -C.sub.14 alkyl monoethanol amide (LMMEA) at a concentration of 0 to 5 wt.
%, or an alkyl diethanol amides such as coco diethanol amide (CDEA) or lauryl diethanol amide (LDEA) at a concentration of 0 to 5 wt. %, preferably 0.5 wt. % to 3 wt. % and mixtures thereof. The instant formulas can contain both alkyl monoethanol amide
and alkyl diethanol amide. The solubilizing ingredient can also include 0 to 5 wt. %, preferably 0.1 wt. % to 3 wt. % of at least one water soluble salt of a C.sub.1 -C.sub.3 substituted benzene sulfonate hydrotrope such as sodium xylene sulfonate or
sodium cumene sulfonate or a mixture of said sulfonates. Inorganic alkali metal or alkaline earth metal salts such as sodium sulfate, magnesium sulfate, sodium chloride and sodium citrate can be added to the microemulsion at concentrations of 0.5 to 4.0
wt. %. Other ingredients which have been added to the compositions at concentrations of about 0.1 to 4.0 wt. percent are perfumes, preservatives, color stabilizers, sodium bisulfite, ETDA, HETDA and proteins such as lexine protein.
In addition to the previously mentioned essential and optional constituents of the light duty liquid microemulsion detergent, one may also employ normal and conventional adjuvants, provided they do not adversely affect the properties of the
detergent. Thus, there may be used various coloring agents and perfumes; sequestering agents such as ethylene diamine tetraacetates; magnesium sulfate heptahydrate; pearlescing agents and opacifiers; pH modifiers; etc. The proportion of such adjuvant
materials, in total will normally not exceed 15% of weight of the detergent composition, and the percentages of most of such individual components will be about 0.1 to 5% by weight and preferably less than about 2% by weight. Sodium bisulfite can be
used as a color stabilizer at a concentration of about 0.01 to 0.2 wt. %. Typical perservatives are dibromodicyano-butane, citric acid, benzylic alcohol and poly (hexamethylene-biguamide) hydrochloride and mixtures thereof.
The instant compositions can contain about 0 to about 10 wt. %, more preferably 1 wt. % to 6 wt. % of an alkyl polysaccharide surfactant. The alkyl polysaccharides surfactants, which are used in conjunction with the aforementioned surfactant
have a hydrophobic group containing from about 8 to about 20 carbon atoms, preferably from about 10 to about 16 carbon atoms, most preferably from about 12 to about 14 carbon atoms, and polysaccharide hydrophilic group containing from about 1.5 to about
10, preferably from about 1.5 to about 4, most preferably from about 1.6 to about 2.7 saccharide units (e.g., galactoside, glucoside, fructoside, glucosyl, fructosyl; and/or galactosyl units). Mixtures of saccharide moieties may be used in the alkyl
polysaccharide surfactants. The number x indicates the number of saccharide units in a particular alkyl polysaccharide surfactant. For a particular alkyl polysaccharide molecule x can only assume integral values. In any physical sample of alkyl
polysaccharide surfactants there will be in general molecules having different x values. The physical sample can be characterized by the average value of x and this average value can assume non-integral values. In this specification the values of x are
to be understood to be average values. The hydrophobic group (R) can be attached at the 2-, 3-, or 4- positions rather than at the 1-position, (thus giving e.g. a glucosyl or galactosyl as opposed to a glucoside or galactoside). However, attachment
through the 1- position, i.e., glucosides, galactoside, fructosides, etc., is preferred. In the preferred product the additional saccharide units are predominately attached to the previous saccharide unit's 2-position. Attachment through the 3-, 4-,
and 6- positions can also occur. Optionally and less desirably there can be a polyalkoxide chain joining the hydrophobic moiety (R) and the polysaccharide chain. The preferred alkoxide moiety is ethoxide.
Typical hydrophobic groups include alkyl groups, either saturated or unsaturated, branched or unbranched containing from about 8 to about 20, preferably from about 10 to about 18 carbon atoms. Preferably, the alkyl group is a straight chain
saturated alkyl group. The alkyl group can contain up to 3 hydroxy groups and/or the polyalkoxide chain can contain up to about 30, preferably less than about 10, alkoxide moieties.
Suitable alkyl polysaccharides are decyl, dodecyl, tetradecyl, pentadecyl, hexadecyl, and octadecyl, di-, tri-, tetra-, penta-, and hexaglucosides, galactosides, lactosides, fructosides, fructosyls, lactosyis, glucosyls and/or galactosyls and
mixtures thereof.
The alkyl monosaccharides are relatively less soluble in water than the higher alkyl polysaccharides. When used in admixture with alkyl polysaccharides, the alkyl monosaccharides are solubilized to some extent. The use of alkyl monosaccharides
in admixture with alkyl polysaccharides is a preferred mode of carrying out the invention. Suitable mixtures include coconut alkyl, di-, tri-, tetra-, and pentaglucosides and tallow alkyl tetra-, penta-, and hexaglucosides.
The preferred alkyl polysaccharides are alkyl polyglucosides having the formula
wherein Z is derived from glucose, R is a hydrophobic group selected from the group consisting of alkyl, alkylphenyl, hydroxyalkylphenyl, and mixtures thereof in which said alkyl groups contain from about 10 to about 18, preferably from about 12
to about 14 carbon atoms; n is 2 or 3 preferably 2, r is from 0 to 10, preferable 0; and x is from 1.5 to 8, preferably from 1.5 to 4, most preferably from 1.6 to 2.7. To prepare these compounds a long chain alcohol (ROH) can be reacted with glucose, in
the presence of an acid catalyst to form the desired glucoside. Alternatively, the alkyl polyglucosides can be prepared by a two step procedure in which a short chain alcohol (C.sub.1-6) is reacted with glucose or a polyglucoside (x=2 to 4) to yield a
short chain alkyl glucoside (x=2 to 4) which can in turn be reacted with a longer chain alcohol (ROH) to displace the short chain alcohol and obtain the desired alkyl polyglucoside. If this two step procedure is used, the short chain alkylglucosde
content of the final alkyl polyglucoside material should be less than 50%, preferably less than 10%, more preferably less than about 5%, most preferably 0% of the alkyl polyglucoside.
The amount of unreacted alcohol (the free fatty alcohol content) in the desired alkyl polysaccharide surfactant is preferably less than about 2%, more preferably less than about 0.5% by weight of the total of the alkyl polysaccharide. For some
uses it is desirable to have the alkyl monosaccharide content less than about 10%.
The used herein, "alkyl polysaccharide surfactant" is intended to represent both the preferred glucose and galactose derived surfactants and the less preferred alkyl polysaccharide surfactants. Throughout this specification, "alkyl
polyglucoside" is used to include alkyl polyglycosides because the stereochemistry of the saccharide moiety is changed during the preparation reaction.
An especially preferred APG glycoside surfactant is APG 625 glycoside manufactured by the Henkel Corporation of Ambler, Pa. APG25 is a nonionic alkyl polyglycoside characterized by the formula:
wherein n=10 (2%); n=12 (65%); n=14 (21-28%); n=16 (4-8%) and n=18 (0.5%) and x (degree of polymerization)=1.6. APG 625 has: a pH of 6 to 10 (10% of APG 625 in distilled water); a specific gravity at 25.degree. C. of 1.1 g/ml; a density at
25.degree. C. of 9.1 lbs/gallon; a calculated HLB of 12.1 and a Brookfield viscosity at 35.degree. C., 21 spindle, 5-10 RPM of 3,000 to 7,000 cps.
The final essential ingredient in the inventive light duty liquid microemulsion compositions having improved interfacial tension properties is water. The proportion of water in the microemulsion compositions generally is in the range of 20% to
97%, preferably 70% to 97% by weight of the usual diluted o/w microemulsion composition.
As believed to have been made clear from the foregoing description, the light duty liquid microemulsion compositions of this invention are especially effective when used as is, that is, without further dilution in water, since the properties of
the composition as a microemulsion are best manifested in the neat (undiluted) form. However, at the same time it should be understood that depending on the levels of surfactants, cosurfactants, perfume and other ingredients, some degree of dilution
without disrupting the microemulsion, per se, is possible. For example, at the preferred low levels of active surfactant compounds dilutions up to about 50% will generally be well tolerated without causing phase separation, that is, the microemulsion
state will be maintained.
However, even when diluted to a great extent, such as a 2- to 10-fold or more dilution, for example, the resulting compositions are still effective in cleaning greasy, oily and other types of soil. Furthermore, the presence of magnesium ions or
other polyvalent ions, e.g., aluminum, as will be described in greater detail below further serves to boost cleaning performance of the primary detergents in dilute usage.
In addition to the above-described essential ingredients required for the formation of the microemulsion composition, the compositions of this invention may possibly contain one or more additional ingredients which serve to improve overall
product performance.
One such ingredient is an inorganic or organic salt or oxide of a multivalent metal cation, particularly Mg.sup.++. The metal salt or oxide provides several benefits including improved cleaning performance in dilute usage, particularly in soft
water areas, and minimized amounts of perfume required to obtain the microemulsion state. Magnesium sulfate, either anhydrous or hydrated (e.g., heptahydrate), is especially preferred as the magnesium salt. Good results also have been obtained with
magnesium oxide, magnesium chloride, magnesium acetate, magnesium propionate and magnesium hydroxide. These magnesium salts can be used with formulations at neutral or acidic pH since magnesium hydroxide will not precipitate at these pH levels.
Although magnesium is the preferred multivalent metal from which the salts (inclusive of the oxide and hydroxide) are formed, other polyvalent metal ions also can be used provided that their salts are nontoxic and are soluble in the aqueous phase
of the system at the desired pH level. Thus, depending on such factors as the the nature of the primary surfactants and cosurfactant, and so on, as well as the availability and cost factors, other suitable polyvalent metal ions include aluminum, copper,
nickel, iron, calcium, etc. can be employed. It should be noted, for example, that with the preferred sulfonate anionic detergent calcium salts will precipitate and should not be used. It has also been found that the aluminum salts work best at pH
below 5 or when a low level, for example about 1 weight percent, of citric acid is added to the composition which is designed to have a neutral pH. Alternatively, the aluminum salt can be directly added as the citrate in such case. As the salt, the
same general classes of anions as mentioned for the magnesium salts can be used, such as halide (e.g., bromide, chloride), sulfate, nitrate, hydroxide, oxide, acetate, propionate, etc.
Preferably, in the dilute compositions the metal compound is added to the composition in an amount sufficient to provide at least a stoichiometric equivalent between the anionic surfactant and the multivalent metal cation. For example, for each
gram-ion of Mg++ there will be 2 gram moles of paraffin sulfonate, alkylbenzene sulfonate, etc., while for each gram-ion of Al.sup.3+ there will be 3 gram moles of anionic surfactant. Thus, the proportion of the multivalent salt generally will be
selected so that one equivalent of compound will neutralize from 0.1 to 1.5 equivalents, preferably 0.9 to 1.4 equivalents, of the acid form of the an | | |
