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Description  |
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TECHNICAL FIELD
The present invention relates to detergent compositions, useful in machine dishwashing, containing in combination, a carboxylate or polycarboxylate builder, an organo diphosphonic acid crystal growth inhibitor and a low molecular weight polymer
containing acrylic acid.
BACKGROUND OF THE INVENTION
Detergent compositions designed for use in automatic dishwasher machines are well known, and a consistent effort has been made by detergent manufacturers to improve the cleaning and/or rinsing efficiency of said compositions on dishes and
glassware, as reflected by numerous patent publications.
The general problem of the formation of deposits as spots and films on the articles in the wash, and on the dishwasher machine parts is well known in the art.
Whilst the general problem of deposit formation is known, a full understanding of the many facets of the problem is however still an active area of research.
A range of deposit types can be encountered. The redeposition of soils or the breakdown products thereof, which have previously been removed from the soiled tableware in the washload, provides one deposit type. Insoluble salts such as calcium
carbonate, calcium fatty acid salts (lime soaps), or certain silicate salts are other common deposit types. Composite deposit types are also common. Indeed, once an initial minor deposit forms it can act as a "seeding centre" for the build up of a
larger, possibly composite, deposit structure.
Deposit formation can occur on a range of commonly encountered substrate surfaces including plastic, glass, metal and china surfaces. Certain deposit types however, show a greater propensity to deposit on certain substrates. For example, lime
soap deposit formation tends to be a particular problem on plastic substrates, and silicate deposit formation tends to occur on glassware.
The formation of insoluble carbonate, especially calcium carbonate, deposits is a particular problem in the machine dishwashing art. There is a general appreciation in the art, as represented for example by EP-A-364,067 in the name of Clorox,
CH-A-673,033 in the name of Cosmina, and EP-A-551,670 in the name of Unilever, that calcium carbonate deposit formation is a particular problem when non-phosphate containing detergent formulations are employed. In general, this can be explained by the
slightly inferior builder capacity of the typically employed non-phosphate builder systems in comparison to phosphate builder formulations. The problem of calcium carbonate deposit formation is understood to be especially apparent when these
formulations contain a carbonate builder component, as for example is essential to the compositions taught by EP-A-364,067.
The Applicants have now found that the problem of CaCO.sub.3 deposit formation can exist even in the absence of a carbonate builder component in the machine dishwashing detergent formulation, and especially when that formulation contains no
phosphate builder component. The naturally sourced, inlet water to the dishwasher machine can be a sufficient source of Ca.sup.2+ and Mg.sup.2+ ions and HCO.sub.3 --/CO.sub.3.sup.2- ions to make deposit formation a problem. Whilst the salt softening
system, through which the inlet water will pass prior to entry into the main cavity of the dishwasher machine, can be efficient at removing the naturally present Ca.sup.2+ and Mg.sup.2+ ions it is inefficient at removing the HCO.sub.3 --/CO.sub.3.sup.2-
ions which therefore enter into the wash/rinse solution.
The Applicants have now established that both the levels of Ca.sup.2+ /Mg.sup.2+ hardness ions and the levels of HCO.sub.3 --/CO.sub.3.sup.2- ions in the wash/rinse water of the dishwasher machine are factors controlling calcium carbonate deposit
formation. Critical levels of both components must be exceeded for deposit formation to occur. These critical levels are to an extent interdependent. Thus, even in wash solutions containing high levels of one component deposit formation will not occur
in the absence of the critical level of the other component.
A relatively high level of Ca.sup.2+ ions in the wash solution can be desirable for the effective performance of certain enzyme components of the detergent formulation, particularly lipolytic and proteolytic enzymes. Such higher levels of
Ca.sup.2+ tend to be present when non-phosphate built formulations are employed. Whilst these relatively high levels of Ca.sup.2+ are desirable for enzyme performance, calcium carbonate deposition will tend to occur if the solution contains a level of
carbonate ion above the critical limit for deposit formation.
The Applicants have also established that the formation of deposit "seeding centres", which in turn enable the build up of more substantial deposits, occurs most commonly in the rinse cycle of the dishwasher machine. Deposit build up is most
apparent on the heater element of the dishwasher machine. It has also been established that the problem is most apparent when more alkaline formulations, such as those of pH of 9.8 and above, are employed. An upper limit to the pH of about 11.5 has
been found to be preferred for the effective working of other preferred components of the composition such as peroxyacid bleaches and enzymes.
The Applicants have found that the problem of calcium carbonate deposit formation may be effectively ameliorated by the inclusion of an organo diphosphonic acid component in combination with an acrylic acid containing polymer having a molecular
weight of less than 15,000 into the detergent formulation.
Acrylic acid containing organic polymers of higher molecular weight, such as the commonly used maleic/acrylic acid copolymers of molecular weight from typically 40,000 to 80,000, did not provide equivalent deposit formation prevention capability. Indeed, the formation of the insoluble calcium salts of such higher molecular weight polymers was noted potentially to lead to a worsening of the deposition profile of the compositions in use.
When the combination of said diphosphonic acid and polymer components is employed in a non-phosphate built formulation the occurrence of calcium carbonate deposits is essentially comparable to that obtained for a more highly built, phosphate
containing formulation which does not contain these components.
The Applicants have also found that carboxylates and polycarboxylates, particularly citrates, are especially useful components of the compositions of the invention because of their magnesium binding capacity which tends to prevent the formation
of insoluble magnesium salts, such as magnesium silicate on the articles in the wash. Such polycarboxylates also provide calcium binding capacity to the compositions, thus contributing further to the prevention of the formation of calcium salt deposits.
The Applicants have also found that the more effective control of calcium carbonate deposition can also lead to benefits in the prevention of the formation of other deposit types, particularly lime soap deposits and silicate deposits.
Lime soap deposits are most commonly encountered when the washload contains fatty soils, which naturally contain levels of free fatty acids, and when lipolytic enzymes are components of the formulation. Lipolytic enzymes catalyse the degradation
of fatty soils into free fatty acids and glycerol. Silicate is a common component of machine dishwashing formulations, where it is added for its china and glass care capability. It is the Applicant's finding that by preventing the formation of calcium
carbonate deposit "seeding centres", most particularly in the rinse cycle, the build up of other deposit types from these "seeding centres" is also prevented.
GB-A-2,203,163 discloses aqueous liquid detergent compositions for use in mechanical dishwashers containing a polyacrylic acid and/or a polyhydroxy acrylic acid and a chlroine resistant phosphonate or organic phosphate, sodium hydroxide and
sources of alkalinity to provide a composition pH of 13. No disclosure is provided of the essential carboxylate or polycarboxylate component of the present inventions.
U.S. Pat. No. 4,846,993 discloses zero phosphate warewashing detergent compositions containing a source of alkalinity, a water-conditioning vinyl polymer with pendant--CO.sub.2 H groups, a soil-dispersing phosphinopolycarboxylic acid, and a
water-conditioning organic phosphonate. The requirement for a polycarboxylate builder component is not taught by this document. Furthermore, the compositions of the present invention preferably do not contain the phosphinopolycarboxylic acid component
taught therein.
U.S. Pat. No. 4,919,845 discloses compositions which may contain HEDP and a copolymer of (meth)acrylic acid and maleic acid. Said copolymer may have a molecular weight of from 2000 to 200,000 but is preferably from 50,000 to 120,000. Such
preferred higher molecular weight copolymers lie outside of the ambit of the present invention. Indeed, as has been previously noted, their presence may lead to a worsening of the calcium salt deposit profile in direct contrast to the object of the
present invention.
WO 92/13061 discloses solid cast silicate-based cleaning compositions which may contain a polyacrylate and a phosphonate, which components are stated to cooperate to form a threshold system which is effective for controlling precipitation of
calcium and magnesium in a use solution. The necessity of a carboxylate or polycarboxylate builder is not taught by this reference.
SUMMARY OF THE INVENTION
There is provided a detergent composition containing builder in combination
(a) a detergent builder system containing a carboxylate or polycarboxylate builder containing from one to four carboxy groups, wherein said detergent builder system has a major proportion by weight of non-carbonate builder compound;
(b) an organo diphosphonic acid or its salts or complexes or any mixture thereof; and
(c) an organic polymer containing acrylic acid or its salts, having an average molecular weight of less than 15,000.
DETAILED DESCRIPTION OF THE INVENTION
Organo Diphosphonic Acid Crystal Growth Inhibitor
An essential component of the detergent compositions in accordance with the invention is an organo diphosphonic acid or one of its salts/complexes. The organo diphosphonic acid component is preferably present at a level of from 0.005% to 20%,
more preferably from 0.1% to 10%, most preferably from 0.2% to 5% by weight of the compositions.
By organo diphosphonic acid it is meant herein an organo diphosphonic acid which does not contain nitrogen as part of its chemical structure. This definition therefore excludes the organo aminophosphonates, which however may be included in
compositions of the invention as heavy metal ion sequestrants.
The organo diphosphonic acid component may be present in its acid form or in the form of one of its salts or complexes with a suitable counter cation and reference hereinafter to the acid implicitly includes reference to said salts or complexes.
Preferably any salts/complexes are water soluble, with the alkali metal and alkaline earth metal salts/complexes being especially preferred.
The organo diphosphonic acid is preferably a C.sub.1 -C.sub.4 diphosphonic acid, more preferably a C.sub.2 diphosphonic acid, such as ethylene diphosphonic acid, or most preferably ethane 1-hydroxy-1, 1-diphosphonic acid (HEDP).
Low Molecular Weight Acrylic Acid Containing Organic Polymer
A second essential component of the detergent compositions in accord with the invention is an organic polymer containing acrylic acid or its salts having an average molecular weight of less than 15,000, hereinafter referred to as low molecular
weight acrylic acid containing polymer.
The low molecular weight acrylic acid containing polymer has an average molecular weight of less than 15,000, preferably from 500 to 12,000, more preferably from 1,500 to 10,000, most preferably from 2,500 to 9,000.
The low molecular weight acrylic acid containing organic polymer is preferably present at a level of from 0.0050% to 20%, more preferably from 0.1% to 10%, most preferably from 0.2% to 8% by weight of the compositions.
The weight ratio of low molecular weight acrylic acid containing polymer to organo diphosphonic acid component is preferably from 50:1 to 1:5, more preferably from 20:1 to 1:1, most preferably from 15:1 to 2:1.
In a preferred aspect, the low molecular weight acrylic acid containing polymer and organo diphosphic acid components are present in the compositions in intimate admixture, most especially in the form of a particle comprising said two components
which itself forms part of a granular composition.
The low molecular weight acrylic acid containing polymer may be either a homopolymer or a copolymer including the essential acrylic acid or acrylic acid salt monomer units. Copolymers may include essentially any suitable other monomer units
including modified acrylic, fumaric, maleic, itaconic, aconitic, mesaconic, citraconic and methylenemalonic acid or their salts, maleic anhydride, acrylamide, alkylene, vinylmethyl ether, styrene and any mixtures thereof.
Preferred commercially available low molecular weight acrylic acid containing homopolymers include those sold under the tradename Sokalan PA30, PA20, PA15 and PA10 by BASF GmbH, and those sold under the tradename Acusol 45N by Rohm and Haas.
Preferred low molecular weight acrylic acid containing copolymers include those which contain as monomer units: a) from 90% to 10%, preferably from 80% to 20% by weight acrylic acid or its salts and b) from 10% to 90%, preferably from 20% to 80%
by weight of a substituted acrylic monomer or its salts having the general formula --CHR.sub.2 .dbd.CR.sub.1 (CO--O--R.sub.3) wherein at least one of the substituents R.sub.1, R.sub.2 or R.sub.3, preferably R.sub.1, or R.sub.2 is a 1 to 4 carbon alkyl or
hydroxyalkyl group, R.sub.1, or R.sub.2 can be a hydrogen and R.sub.3 can be a hydrogen or alkali metal salt. Most preferred is a substituted acrylic monomer wherein R.sub.1 is methyl, R.sub.2 is hydrogen (i.e. a methyl acrylic acid monomer). The most
preferred copolymer of this type has a molecular weight of 3500 and contains 60% to 80% by weight of acrylic acid and 40% to 20% by weight of methyl acrylic acid.
Preferred commercially available low molecular weight acrylic acid containing copolymers include those sold under the tradename Sokalan CP10 by BASF GmbH.
Other suitable polyacrylate/modified polyacrylate copolymers include those copolymers of unsaturated aliphatic carboxylic acids disclosed in U.S. Pat. Nos. 4,530,766, and 5,084,535 which have a molecular weight of less than 15,000 in
accordance with the invention.
Additional Organic Polymeric Compound
Certain additional organic polymeric compounds may be added to the detergent compositions of the invention, however, in certain cases their presence is desirably minimized. By additional organic polymeric compounds it is meant essentially any
polymeric organic compounds commonly used as dispersants, anti-redeposition and soil suspension agents in detergent compositions, which do not fall within the definition of low molecular weight acrylic acid containing polymers given hereinbefore.
Additional organic polymeric compound may be incorporated into the detergent compositions of the invention at a level of from 0.05% to 30%, preferably from 0.5% to 15%, most preferably from 1% to 10% by weight of the compositions.
Examples of additional organic polymeric compounds whose presence is desirably minimized, and which are preferably not present, include the water soluble organic homo- or co-polymeric polycarboxylic acids or their salts in which the
polycarboxylic acid comprises at least two carboxyl radicals separated from each other by not more than two carbon atoms. Polymers of the latter type are disclosed in GB-A-1,596,756. Examples of such salts are the copolymers of polyacrylate with maleic
anhydride having a molecular weight of from 20,000 to 150,000, especially about 40,000 to 80,000.
The polyamino compounds are useful herein including those derived from aspartic acid such as those disclosed in EP-A-305282, EP-A-305283 and EP-A-351629.
Other additional organic polymeric compounds suitable for incorporation in the detergent compositions herein include cellulose derivatives such as methylcellulose, carboxymethylcellulose and hydroxyethylcellulose.
Further useful additional organic polymeric compounds are the polyethylene glycols, particularly those of molecular weight 1000-10000, more particularly 2000 to 8000 and most preferably about 4000.
Detergent Builder System
An essential component of the detergent compositions of the present invention is a detergent builder system containing a major proportion of non-carbonate builder compound, wherein said detergent builder system is preferably present at a level of
from 0.5% to 80% by weight, more preferably from 1% to 60% by weight, most preferably from 2% to 40% weight of the compositions.
The builder system contains at most a minor proportion by weight of carbonate builder compound, more preferably less than 30% by weight of the builder system is carbonate builder compound. Most preferably none of the builder system is carbonate
builder compound.
The detergent builder system is preferably water-soluble, and contains a carboxylate or polycarboxylate builder containing from one to four carboxy groups, particularly selected from monomeric polycarboxylates or their acid forms, homo or
copolymeric polycarboxylic acids or their salts in which the polycarboxylic acid comprises at least two carboxylic radicals separated from each other by not more that two carbon atoms.
The detergent builder system can additionally contain alkali metal, ammonium or alkanonammonium salts of bicarbonates, borates, phosphates, and mixtures of any of the foregoing.
Preferably, the detergent builder system contains no phosphate builder compound.
Carboxylate or Polycarboxylate Builder
Suitable water-soluble monomeric or oligomeric carboxylate builders can be selected from a wide range of compounds but such compounds preferably have a first carboxyl logarithmic acidity/constant (pK.sub.1) of less than 9, preferably of between 2
and 8.5, more preferably of between 4 and 7.5.
The carboxylate or polycarboxylate builder can be momomeric or oligomeric in type although monomeric polycarboxylates are generally preferred for reasons of cost and performance. Monomeric and oligomeric builders can be selected from acyclic,
alicyclic, heterocyclic and aromatic carboxylates.
Suitable carboxylates containing one carboxy group include the water soluble salts of lactic acid, glycolic acid and ether derivatives thereof as disclosed in Belgian Patent Nos. 831,368, 821,369 and 821,370. Polycarboxylates containing two
carboxy groups include the water-soluble salts of succinic acid, malonic acid, (ethylenedioxy) diacetic acid, maleic acid, diglycolic acid, tartaric acid, tartronic acid and fumaric acid, as well as the ether carboxylates described in German
Offenlegenschrift 2,446,686, and 2,446,687 and U.S. Pat. No. 3,935,257 and the sulfinyl carboxylates described in Belgian Patent No. 840,623. Polycarboxylates containing three carboxy groups include, in particular, water-soluble citrates, aconitrates
and citraconates as well as succinate derivatives such as the carboxymethyloxysuccinates described in British Patent No. 1,379,241, lactoxysuccinates described in British Patent No. 1,389,732, and aminosuccinates described in Netherlands Application
7205873, and the oxypolycarboxylate materials such as 2-oxa-1,1,3-propane tricarboxylates described in British Patent No. 1,387,447.
Polycarboxylates containing four carboxy groups include oxydisuccinates disclosed in British Patent No. 1,261,829, 1,1,2,2-ethane tetracarboxylates, 1,1,3,3-propane tetracarboxylates and 1,1,2,3-propane tetracarboxylates. Polycarboxylates
containing sulfo substituents include the sulfosuccinate derivatives disclosed in British Patent Nos. 1,398,421 and 1,398,422 and in U.S. Pat. No. 3,936,448, and the sulfonated pyrolysed citrates described in British Patent No. 1,439,000.
Alicyclic and heterocyclic polycarboxylates include cyclopentane-cis,cis,cis-tetracarboxylates, cyclopentadienide pentacarboxylates, 2,3,4,5-tetrahydrofuran-cis, cis, cis-tetracarboxylates, 2,5-tetrahydrofuran-cis-dicarboxylates,
2,2,5,5-tetrahydrofuran-tetracarboxylates, 1,2,3,4,5,6-hexane-hexacarboxylates and carboxymethyl derivatives of polyhydric alcohols such as sorbitol, mannitol and xylitol. Aromatic polycarboxylates include mellitic acid, pyromellitic acid and the
phthalic acid derivatives disclosed in British Patent No. 1,425,343.
Of the above, the preferred polycarboxylates are hydroxycarboxylates containing up to three carboxy groups per molecule, more particularly citrates, especially sodium citrate.
The parent acids of the monomeric or oligomeric polycarboxylate chelating agents or mixtures thereof with their salts, e.g. citric acid or citrate/citric acid mixtures are also contemplated as components of builder systems of the detergent
compositions in accordance with the present invention.
Carbonate Builder Compound
Specific examples of carbonate builder compound include the alkali metal carbonates, bicarbonates and sesquicarbonates. Carbonate builder compound may be present only as a minor component of the builder system.
Additional Builder Compound
Specific examples of phosphate builders are the alkali metal tripolyphosphates, sodium, potassium and ammonium pyrophosphate, sodium and potassium and ammonium pyrophosphate, sodium and potassium orthophosphate, sodium polymeta/phosphate in which
the degree of polymerization ranges from about 6 to 21, and salts of phytic acid. Preferably, no phosphate builder compound is present.
The detergent compositions of the invention may also include less water soluble builders although preferably their levels of incorporation are minimized. Examples of such less water soluble builders include the crystalline layered silicates, and
the largely water insoluble sodium aluminosilicates.
Alkalinity
An alkalinity source is a preferred component of the compositions of the invention. A useful alkalinity source is provided by silicates which also provide china care properties to the detergent formulation. Suitable silicates include the water
soluble sodium silicates with an SiO.sub.2 :Na.sub.2 O ratio of from 1.0 to 2.8, with ratios of from 1.6 to 2.4 being preferred, and 2.0 ratio being most preferred. The silicates may be in the form of either the anhydrous salt or a hydrated salt.
Sodium silicate with an SiO.sub.2 :Na.sub.2 O ratio of 2.0 is the most preferred silicate.
Silicates are preferably incorporated in the compositions of the invention at a level of from 1% to 50%, preferably from 5% to 40%, most preferably from 5% to 30% by weight.
Surfactant System
A highly preferred component of the detergent compositions of the invention is a surfactant system comprising surfactant selected from anionic, cationic, nonionic ampholytic and zwitterionic surfactants and mixtures thereof. The surfactant
system is typically present at a level of from 0.50to 40% by weight, more preferably 1% to 306 by weight, most preferably from 1.5% to 20% by weight of the compositions.
In one preferred execution of the invention the surfactant system consists of low foaming nonionic surfactant, preferably selected from ethoxylated and/or propoxylated nonionic surfactants, more preferably selected from nonionic
ethoxylated/propoxylated fatty alcohol surfactants.
In an alternative preferred execution of the invention the surfactant system comprises high foaming anionic surfactant, particularly alkyl ethoxysulfate surfactant, in combination with a suds suppressing system.
Anionic Surfactant
Essentially any anionic surfactants useful for detersive purposes can be included in the compositions. These can include salts (including, for example, sodium, potassium, ammonium, and substituted ammonium salts such as mono-, di-and
triethanolamine salts) of the anionic sulfate, sulfonate, carboxylate and sarcosinate surfactants.
Other anionic surfactants include the isethionates such as the acyl isethionates, N-acyl taurates, fatty acid amides of methyl tauride, alkyl succinates and sulfosuccinates, monoesters of sulfosuccinate (especially saturated and unsaturated
C.sub.12 -C.sub.18 monoesters) diesters of sulfosuccinate (especially saturated and unsaturated C.sub.6 -C.sub.14 diesters), N-acyl sarcosinates. Resin acids and hydrogenated resin acids are also suitable, such as rosin, hydrogenated rosin, and resin
acids and hydrogenated resin acids present in or derived from tallow oil.
Anionic Sulfate Surfactant
Anionic sulfate surfactants suitable for use herein include the linear and branched primary alkyl sulfates, alkyl ethoxysulfates, fatty oleyl glycerol sulfates, alkyl phenol ethylene oxide ether sulfates, the C.sub.5 -C.sub.17 acyl-N-(C.sub.1
-C.sub.4 alkyl) and --N-(C.sub.1 -C.sub.2 hydroxyalkyl) glucamine sulfates, and sulfates of alkylpolysaccharides such as the sulfates of alkylpolyglucoside (the nonionic nonsulfated compounds being described herein).
Alkyl ethoxysulfate surfactants are preferably selected from the group consisting of the C.sub.6 -C.sub.18 alkyl sulfates which have been ethoxylated with from about 0.5 to about 20 moles of ethylene oxide per molecule, more preferably, the alkyl
ethoxysulfate surfactant is a C.sub.6 -C.sub.18 alkyl sulfate which has been ethoxylated with from about 0.5 to about 20, preferably from about 0.5 to about 5, moles of ethylene oxide per molecule.
Anionic Sulfonate Surfactant
Anionic sulfonate surfactants suitable for use herein include the salts of C.sub.5 -C.sub.20 linear alkylbenzene sulfonates, alkyl ester sulfonates, C.sub.6 -C.sub.22 primary or secondary alkane sulfonates, C.sub.6 -C.sub.24 olefin sulfonates,
sulfonated polycarboxylic acids, alkyl glycerol sulfonates, fatty acyl glycerol sulfonates, fatty oleyl glycerol sulfonates, and any mixtures thereof.
Anionic Carboxylate Surfactant
Anionic carboxylate surfactants suitable for use herein include the alkyl ethoxy carboxylates, the alkyl polyethoxy polycarboxylate surfactants and the soaps (`alkyl carboxyls`), especially certain secondary soaps as described herein.
Preferred alkyl ethoxy carboxylates for use herein include those with the formula RO(CH.sub.2 CH.sub.2 O).sub.x CH.sub.2 COO.sup.- M.sup.+ wherein R is a C.sub.6 to C.sub.18 alkyl group, x ranges from 0 to 10, and the ethoxylate distribution is
such that, on a weight basis, the amount of material where x is 0 is less than about 20%, and the amount of material where x is greater than 7, is less than about 25%, the average x is from about 2 to 4 when the average R is C.sub.13 or less, and the
average x is from about 3 to 10 when the average R is greater than C.sub.13, and M is a cation, preferably chosen from alkali metal, alkaline earth metal, ammonium, mono-, di-, and tri-ethanol-ammonium, most preferably from sodium, potassium, ammonium
and mixtures thereof with magnesium ions. The preferred alkyl ethoxy carboxylates are those where R is a C.sub.12 to C.sub.18 alkyl group.
Alkyl polyethoxy polycarboxylate surfactants suitable for use herein include those having the formula RO--(CHR.sub.1 --CHR.sub.2 --O)--R.sub.3
wherein R is a C.sub.6 to C.sub.18 alkyl group, x is from 1 to 25, R.sub.1 and R.sub.2 are selected from the group consisting of hydrogen, methyl acid radical, succinic acid radical, hydroxysuccinic acid radical, and mixtures thereof, wherein at
least one R.sub.1 or R.sub.2 is a succinic acid radical or hydroxysuccinic acid radical, and R.sub.3 is selected from the group consisting of hydrogen, substituted or unsubstituted hydrocarbon having between 1 and 8 carbon atoms, and mixtures thereof.
Preferred soap surfactants are secondary soap surfactants which contain a carboxyl unit connected to a secondary carbon. The secondary carbon can be in a ring structure, e.g. as in p-octyl benzoic acid, or as in alkyl-substituted cyclohexyl
carboxylates. The secondary soap surfactants should preferably contain no ether linkages, no ester linkages and no hydroxyl groups. There should preferably be no nitrogen atoms in the head-group (amphiphilic portion). The secondary soap surfactants
usually contain 11-13 total carbon atoms, although slightly more (e.g., up to 16) can be tolerated, e.g. p-octyl benzoic acid.
The following general structures further illustrate some of the preferred secondary soap surfactants:
A. A highly preferred class of secondary soaps comprises the secondary carboxyl materials of the formula R.sup.3 CH(R.sup.4)COOM, wherein R.sup.3 is CH.sub.3 (CH.sub.2)x and R.sup.4 is CH.sub.3 (CH.sub.2)y, wherein y can be O or an integer from 1
to 4, x is an integer from 4 to 10 and the sum of (x+y) is 6-10, preferably 7-9, most preferably 8.
B. Another preferred class of secondary soaps comprises those carboxyl compounds wherein the carboxyl substituent is on a ring hydrocarbyl unit, i.e., | | |
