US2093927A - Soap builder of reduced alkalinity - Google Patents

Description

or sodium silicate, used Patented Sept. 21, 1937 PATENT OFFICE SOAP BUILDER or nan'ucrn ALKALINITY Walter C. Preston, The Procter &

Gam

Cincinnati, Ohio, assixnor to ble Company, Cincinnati,

Ohio, a corporation of Ohio No Drawing. Application May 8, 1935,

Serial No. 20,423

9 Claims.

This invention relates to an eillclent soap builder having alkalinitynot substantiallygreater than that of soap, solutions, consisting of a salt or salts of pyrophosphoric acid.

The word builder" is used herein with the meaning given in Webster's "New International Dictionary of the English Language, second edition, 1935: A substance, as soda ash, caustic soda, with or insoap, to aid in cleansing. Most soap builders improve not only the cleansing power but also the sudsing power of soap, both in soft water and in hard water, and in addition they are capable of softening hard water.

The builders commonly used in laundry soaps, such as sodium carbonate, sodium silicate, and trisodium phosphate, are stronger in alkalinity thansoap itself when measured at the usual concentrations and temperatures of soap usage. They owe their effectiveness as builders partly to their ability to combine with. the constituents present in natural hard water and form precipitates with.them, thus avoiding the loss of a certain amount of soap which would otherwise be used up in precipitating these same constituents. It should be borne in mind that, in general, ordinary soap will "not produce a noticeable lather or exert useful detergent effects in hard water until the hardness (or soap-precipitating) constituents of same have first been precipitated or neutralized in some way.

The alkalinity of soap itself when dissolved in water has been reported by various observers to be about 9 to 10 on the pH scale. Ordinary soap builders, however, when added to soap. in suflicient quantities to be effective as soap builders, unavoidably raise the alkalinity to a point which causes such undesirable effects as irritation of the skin, injury to woolens and other delicate fibers, deterioration of colors, etc.

I have found that a very effective soap builder, which can be readily adjusted in alkalinity so that it is mild in its action on the skin, on fabrics, dyes, etc., without losing its great efficlency as an aid in cleansing, can be prepared from tetrasodium pyrophosphate.

Tetrasodium pyrophosphate by itself has already been suggested as a soap builder, but it has an alkalinity in dilute solution nearly as great as that of sodium carbonate. However, by treating the tetrasodium pyrophosphate with suitable small quantities of an acid such as sulfuric acid, hydrochloric acid, phosphoric acid, pyrophosphoric acid, acetic acid, higher fatty acids such as lauric and oleic, etc., or with acid salts such cated, is peculiar to this as sodium hydrogen sulfate, sodium dihydrogen phosphate, disodlum dihydrogen' pyrophosphate (NazHzPzOv), and similar acid reacting materials, the normal tetrasodiuin pyrophosphate may be transformed in part into an alkali metalhydrogen salt, and the alkalinity of the tetrasodium pyrophosphate can thus be reduced and adjusted within a widerange. For use as a soap builder, however, the alkalinity should not be reduced substantially below that of soap itself under similar conditions such as concentrations of 0.5 per cent and at room temperature. My discovery is that when the alkalinity of the tetrasodium pyrophosphate is thus reduced to any point between that of the original salt and that of a soap as measured in the usual concentrations of use, such as 0.5 per cent, the efliciency of the practically unimpaired,

soap builder remains while its alkalinity and effect on the skin, etc., can be adjusted to any desired degree. Hence, my builder can be used in any desired proportions so as to make soaps suitable for use in any kind of service, while the alkalinity can be regulated so that the soap will be mild in its action on the hands, fabrics and colors. This, therefore, enables adjustment by the soap maker of his formulas to meet the requirements of various cleansing processes and for varying degrees of water hardness such as occur in difierent sections of the country. I

This property of my pyrophosphate builder, of retaining its efliciency as a soap builder practically undiminished when its alkalinity is reduced even as low as that of soap by the means indisubstance alone, as far as I am aware. If one attempts to reduce the alkalinity of other common soap builders such as sodium carbonate, sodium silicate, or trisodium phosphate, for example, in a similar way,'their efiiciency as soap builders is markedly decreased.

.My builder softens water in a manner quite different from sodium carbonate, orthophosphate, silicate and similar water SOftBl'lElSpWhiCh form precipitates with the lime and magnesium, etc., in the water. The reaction of pyrophosphate salts with the calcium, magnesium, iron and other mineral salts present in hard water, in the presence of a suitable excess of the pyrophosphate, is thought to proceed as represented by the following chemical equations:

whether the solution The calcium (also magnesium, iron, etc.) behaves as though it were sequestered in a complex ion, '(CaPzOq), and the concentration of free calcium (magnesium, etc.) ions in the solution is thus negligible when a sufllciently large excess of pyrophosphate is present. Thus, the calcium, magnesium, iron, etc., remain in solution, but in a form not precipitable by soap when suiiicient pyrophosphate is present, and water softening is nevertheless complete, the process not being accompanied by any precipitation.

Other alkali metal pyrophosphate salts such as the potassium salt can be used in place of the sodium salts, but throughout this specification the sodium salt will be spoken of as representative of all.

While any of the means previously mentioned may be used to reduce the alkalinity of tetrasodium pyrophosphate in the practice of my invention, I find that one of the most convenient is.

to add to the normal NarPzOv some NazHzPzO'z, or any alkali metal-hydrogen salt of pyrophosphoric acid of the general formula MrH4-:P20'l, where M is an alkali metal and a: is any positive numerical value less than 4.

Solutions of NazHzPzOw are sufficiently acid to turn methyl orange indicator pink, while solutions of NarPzO'z are alkaline to phenolphthalein as well as methyl orange and have a pH value slightly less than that of NazCOa. these two salts of pyrophosphoric acid in the proper proportions, any degree of alkalinity or pH value lying between these two extremes can be obtained. 7

In preparing suitable mixtures of these salts, or in reducing the alkalinity of Na4PzO'1 by any other means, it is undesirable to reduce the alkalinity appreciablyv below the alkalinity of soap itself, and for the purpose of controlling such mixtures various means may be used. The determination of the pH of soap solutions is rather difficult and subject to considerable error; hence, this is not an easily carried out procedure. For practical purposes, however, indicators may be used to test solutions which have been prepared with the desired concentration and these will indicate with sufiicient accuracy by the color of builder is more or less alkaline than the solution of soap. Another method consists in adding the mixture of pyrophosphate salts to-a soap solution and observing whether an increased cloudiness results, or not. Any increased cloudiness in solutions having the concentrations of soap and builder as ordinarily used in laundering would indicate too low a degree of alkalinity of the pyrophosphate salt mixture. I

My invention, as previously explained, is not limited to pyrophosphatebuilders of an alkalinity equal to that of soap. It includes also any pyrophosphate builders of an alkalinity less than that of tetrasodium pyrophosphate, but not substantially less than that of soap. The exact degree of alkalinity that can be tolerated in the builder is dependent upon the use to which the built product is to be put. In general, mixtures containing more than one part by weight of Na2H2P2O7 to four, parts by weight of Na4PzO1 in solution have too low a pH value to come within the scope of my invention, while mixtures containing less than one part of NazHzPzO'l to four parts of NalPzO-l come within its scope. It will be noted, therefore, that mixtures containing Na2H2P2O'1 and NarPzOw in the proportion of 1 to 4 by weight will have the. following apparts of Na4P2O7 By mixing salt being reduced to proximate apparent formula: Na3.54Ho.4sP201. Thus, in general, the mixtures coming within the scope of my invention have an average general formula of Main-E201 where M represents an alkali metal and a: is any value less than 4 but not less than about 3.54.

In the majority of cases, I prefer to use from per cent to per cent NaaPzOv and from 5 per cent to 10 percent NazHzPzO'z, such mixtures being most widely applicable. The approximate apparent formulas for the 9040 and 95-5 mixtures are Naan'zHoaaPzO'i and Na3.saHo.izP20'z, respectively.

As an example of my invention, I mix nine with one part of NazHzPzOi. I then add two parts of this mixture to eight parts of powdered soda soap made from beef tallow. The resulting built soap is of a mildness similar to that of unbuilt tallow soap and affects indicators in a similar manner. When, under practical washing conditions, thebuilt soap was compared with the unbuilt soap at F. in equal concentrations in water of seven grains hardness per U. S. gallon, it was found that the built soap equaled the unbuilt taliow soap in sudsing power and excelled it in the removal of an oily type of soil from cloth. It will thus be seen that the builder replaced its own weight of soap as measured by sudsing power and more than its own weight of soap as measured by detergent power. When the comparison was made between built and unbuilt soap solutions having equal real soap concentrations, then an improvement in both sudsing and detergency was noted.

Other soaps than tallow soap, for example, coconut oil soap, palm kernel oil soap, palm oil soap and various mixtures of same may be improved in both sudsing and detergent power by the addition of my builder. Likewise, other alkali metal soaps such as the potassium soaps may be similarly improved, in which case, it may be advantageous to use the corresponding alkali metal pyrophosphate salts as builder.

My invention is not limited, however, to any particular method of mixing the pyrophosphate salts with the soap. Pyrophosphate salts of reduced alkalinity may be incorporated into soap in any of the forms in which soap in manufactured, as milled or unmilled bars, as flakes, powder, gel, or solution. It'may be mechanically mixed in, as in the above example; it may be crutched into the molten soap; it may be dissolved in a soap gel or solution. In certain methods involving saponification in the crutcher, it is feasible to conduct the saponification with a mixture of tetrasodium pyrophosphate and caustic alkali, the alkalinity of the pyrophosphate the desired point by the addition of fatty acid toward the end of the reaction,

While such a ready-for-use mixture may be manufactured and is for many purposes preferable, it also lies within the scope of my invention to add my builder to water prior to adding soap, or vice versa, or to add both builder and soap simultaneously but separately to the water. My invention resides in the presence in the detergent solution at thetime of use, of soap and ously with solution in the wash water. My 75 water softening, sudsing, and detergent propera value less than 4 but not less than about 3.54.

builder may, however, be used in conjunction with other known soap builders if'so desired.

Throughout the specification I have referred to the anhydrous pyrophosphate salts in the description of my invention. However, it is understood that I do not exclude from its scope those builders prepared from corresponding hydrated salts.

The word soap as used in this specification and claims means a water-soluble soap suitable for detergent purposes.

Having now described my invention, what I claim and desire to secure by Letters Patent is: 1. A soap builder having substantially the same alkalinity as soap alone under similar conditions of use, and adapted to improve the water softening, sudsing and detergent properties of watersoluble soap, comprising essentially an alkali metal pyrophosphate of reduced alkalinity hav-' ing the general average formula MeH4-zP2O7 wherein M represents an alkali metal and a: has a value less than 4 but not less than 3.54.

2. A soapbuilder suitable for improving the water softening, sudsing and detergent properties of soap, and suitable for use with soap'in any proportion needed for varying cleansing requirements and for water of various degrees of hardness without increasing the alkalinity of the soap product beyond-a predetermined low point, consisting of a tetra-alkali-metal pyrophosphate with an alkali-metal-hydrogen pyrophosphate, said mixture having the general averase formula M:H4-:P207

wherein M represents an alkali metal and a: has any value less than 4' but not less than about 3.54, the proportions of the .two pyrophosphates being selected within this range so as to give the desired low alkalinity to the product.

' 3. A soap builder, efliciert in water softening and in improving the sudsing and cleansing power of soap without substantially increasing the alkalinity of the soap, consisting essentially of a mix-.- ture of about 90 parts by weight of tetra-sodium pyrophosphate and about 10 parts by weight of disodium-dihydrogen pyrophosphate.

4. A soap builder, suitable for improving the ties ofwater-soluble soap without increasing the alkalinity of the soap. which comprises a mixture of a tetra-alkali-metal pyrophosphate and 55 an alkali-metal-hydrogen pyrophosphate, said mixture having substantially the same alkalinity as the soap and having the following general average formula M:;H4-:P2 01 wherein M represents an alkali metal and a: has

5. As-a new washing composition, water-soluble soap anda builder for same consisting essentially of tetra-alkali-metal pyrophosphate and alkali-metal-hydrogen pyrophosphate in suitable proportion so that said builder has the general average formula MzH4-a-P207 wherein M represents an alkali metal and :vhas any value less than 4 but not less than about 3.54.

6. As a new washing composition, water-soluble soap and a builder for same consisting of a mixture of about 90 parts by weight of tetra sodium pyrophosphate and about 10 parts by weight of disodium-dihydrogen pyrophosphate. '7. As a new washing composition, water-'solu ble soap and a builder for same consisting essentially of tetra-alkali-metal pyrophosphate and a sufllcient proportion of a compound selected from the group consisting of acids and acid reacting salts such that said age formula builder has the general averl MJIr-ePiOi wherein M represents an alkali metal and a: has a value less than 4 but not less than 3.54.

9. A-soap builder suitable for improving the water softening, sudsing and detergent properties of water-soluble soap and suitable 'for use with water-soluble soap in any proportion needed for varying cleansing requirements and for water of various degrees of hardness without increasing the alkalinity of the soap product beyond a predetermined low point, comprising a mixture of tetra-alkali-metal pyrophosphate with'a sumcient proportion of a compound selected from the group consisting of acids and acid reacting salts, to reduce the alkalinity of the said pyrophosphateso that it will have the general average formula .wherein M represents an alkali metal and has this range so as to give the