Domestic laundry fabric softener

Abstract

A self-emulsifying domestic laundry fabric active softener base comprised of N-methyl, N,N-di-(.beta.-C.sub.14 - C.sub.18 -acyloxy ethyl), N-.beta.-hydroxy ethyl ammonium metho sulfate characterized by good softening, outstanding whiteness-retention and excellent rewetting properties and has a light color having an index on the Gardner scale in the range of about 1 to 2. The active softener base is dispersed in an inert vehicle such as isopropanol and/or water and may be intermixed with other additives, such as perfumes, nonionic wetting agents, optical brighteners, etc.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to fabric softeners and more particularly to light colored self-emulsifying domestic laundry fabric softeners which exhibit excellent rewetting and whiteness-retention characteristics.

2. Prior Art

A large number of domestic laundry fabric softeners which generally include cationic quaternary compounds are known, and reference is made to W. P. Evans, "Cationic Fabric Softeners", Vol. 5, Chemistry and Industry, July 1969, pages 893-903 for a general discussion thereof. Repeated use of such quaternary softeners tends to discolor or yellow fabrics, causing user dissatisfaction. This yellowing characteristic is particularly noticeable when the fabrics are laundered with nonionic detergents at high pH levels. A nonionic containing detergent composition built with sodium carbonate is an example of a detergent material which tends to produce severe yellowing. Further, repeated use of at least certain known softeners tend to waterproof fabrics causing laundering difficulties.

Laundry-related products, especially those which are intended for domestic use, are judged by consumers for effectiveness on the basis of various factors, including the color of the product. A consumer generally assumes that if a product has a light color, it will be less likely to yellow clothes. A light colored product is generally equated with white colored fabrics after washing. Softeners having a white color, as opposed to a creamy or yellowish color are not readily available. Some manufacturers have either attempted to convince consumers that blue or green colored products are desirable as white products but in fact have incorporated coloring agents, bleaches, dyes, optical brighteners to mask less appealing creamy or yellowish colors. The consumers have generally resisted accepting offwhite products and the addition of various coloring agents have, at best, only achieved an approximation of the desired whiteness and merely increased the cost of the ultimate product.

Prior art workers have suggested that various surfactants of the general class comprising condensation products of alkylol amines and higher fatty acids quaternized with various quaternization reagents, such as dimethyl sulfate, diethyl sulfate, methyl chloride, etc., have some softening properties and that such surfactants may be capable of functioning either as commercial textile lubricants or as domestic softening agents. However, such surfactants either do not perform as expected, discolor fabrics, lessen rewetting of the fabrics, require various additives for successful domestic applications or are themselves of a color unappealing to domestic users.

SUMMARY OF THE INVENTION

The invention provides an economical self-emulsifying domestic laundry fabric softener which does not discolor fabrics or prevent rewetting thereof with repeated use and which is characterized by a clean light color.

It is a novel feature of the invention to provide a selfemulsifying domestic laundry fabric softener agent comprised of a mixture of N-alkyl-N,N-di(.beta.-C.sub.14 - C.sub.18 -acyloxy ethyl), N-.beta.-hydroxy ethyl quaternary ammonium compounds and an inert vehicle thereof; which agent is characterized by a light color having an index on the Gardner scale in the range of about 1 to 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The domestic laundry fabric softeners of the invention are characterized by excellent fabric softening properties, excellent whiteness-retention (non-yellowing) properties, outstanding rewetting characteristics and are of a consumer-appealing light color. The light color of the instant softeners should be differentiated from the whiteness and non-yellowing property imparted to the laundered fabrics with which such softeners are used.

The rewetting characteristics of the fabric softeners of the invention allow fabrics treated thereby to be easily rewetted with aqueous solutions, such as encountered in domestic laundering operation. Conventional softeners are generally combined with various rewetting agents to prevent "waterproofing" softener treated fabrics. The softeners of the invention do not require any rewetting agents and exhibit improved rewetting characteristics over conventional fabric softening formulations which include rewetting agents. Further, the fabric softeners of the invention are self-emulsifying and require no auxiliary emulsifying agents, such as conventional nonionic surface-active agents. Studies have shown that while active softeners of the invention are compatible with nonionics, generally insufficient benefits result for economical justification to include nonionics in softeners formulations utilizing the active softener of the invention.

The light color characteristic of the softeners of the invention render formulations based thereon appealing to consumers. While a dark color of a softener does not necessarily indicate that it is inefficient or will discolor fabrics, nevertheless, consumers prefer light color softeners for domestic laundry usage.

The fabric softeners of the invention are prepared from a C.sub.14 - C.sub.18 fatty acid alkyl ester mixture, preferably methyl esters. These fatty methyl ester mixtures are staple articles of commerce and their synthesis is well known so that no further explanation thereof is required. In the preferred embodiments, the softeners of the invention is formed from 2 molecules of the above fatty acid alkyl ester mixture, which for practical purposes is a mixture of oleic, palmitic, stearic acid alkyl esters, along with minor amounts of other fatty material constituents. Generally, these materials are hydrophobic, especially the saturated entities and require the addition of hydrophilic groups thereto for effective use in aqueous systems. Quite unexpectedly it was found that two molecules of a C.sub.14 - C.sub.18 fatty ester mixture, (which is primarily comprised of oleic, palmitic, and stearic acid methyl esters) when combined with triethanolamine and quaternized yield a product which is very light colored, is a good softener, and exhibits excellent whiteness-retention and rewetting properties.

The self-emulsifying fabric softeners of the invention form stable suspensions over a wide temperature range and can be diluted as desired without phase separation or the like. The active softener of the invention is, in undiluted form, a somewhat viscous gel or solidlike mass which is not readily handleable and must be combined with minor amounts of an inert vehicle for either fabric base formulation or for domestic formulation. For a fabric base formulation (after synthesis and prior to packaging for consumer usage), an C.sub.1 - C.sub.4 aliphatic alcohol, C.sub.1 - C.sub.4 aliphatic glycol, C.sub.1 - C.sub.10 aliphatic alcohol alkali sulfate, urea, alkyl benzene alkali sulfonates, water, other similar hydrotropic agents and mixtures thereof provide a suitable vehicle. Although from a point of economic availabillity, lack of disagreeable odors, compatibility with laundering environments, etc., water, isopropanol and mixtures thereof are preferred. For consumer or domestic formulations, water is a preferred vehicle for obvious reasons and any amount of water can be intermixed with the fabric base formulation. For a fabric base formulationo one of the enumerated organic vehicles, such as isopropanol is preferred since a relatively concentrated formulation is preferred.

In preparing softener base formulations which include the active softener of the invention, it has been noted that a ratio of active softener to vehicle of about 3:1 provides a practical solution. Larger amounts of vehicle and/or softener may be utilized, but as a practical matter a mixture of about 75% by weight of softener and about 25% of vehicle, such as isopropanol, is preferred.

In preparing softener formulations for domestic use, a ratio of active softener to vehicle of about 1:10 or 20 provides a practical solution in the retail sales field. Again, larger amounts of vehicle and/or softener may be utilized, but as a practical matter about 0.1% by weight active fabric softener based on weight of fabrics is sufficient in actual wash machine use. Generally, a mixture of about 6% to 8% by weight of softener and about 92% to 94% by weight of vehicle is often sold in the market place. As indicated earlier, preferred vehicles include isopropanol, water and mixtures thereof.

The active softener of the invention is, in its solidified form, an attractive clean, light color, which on the Gardner scale has a color index of about 1 to 2. As will be understood by workers in the art, the Gardner scale here referred to is based on a Gardner-Hellige colorimeter. The Gardner color scale is a designated scale to aid one in subjectively determining the color of a given substance. It ranges in value from 1 to 18 in designating light to dark colors. The softeners of the invention have a milky-white color in 6% to 8% formulations, which comprise the typical domestic consumer formulations. The Gardner color scale is not directly usable on such consumer formulations since they are emulsions as contrasted to clear solutions. However, the softeners of the invention are readily placed in clear solution by intermixing a fairly small amount (i.e. about 25% by weight) of an organic vehicle, such as isopropanol or ethanol with a fairly large amount (i.e. about 75% by weight) of the active softener and heating the resultant mixture to about 55.degree.C. whereupon the solution becomes clear and is suitable for color comparison on the Gardner scale. Accordingly, the term "color index on the Gardner scale" as utilized herein and in the claims will be understood to refer to the value attained when a clear solution containing about 75% solids in about 25% isopropanol or the like is read at about 55.degree.C. It should also be pointed out that a clear solution of a material may have a Gardner scale index of 8 or 9 and be of a brown color. The active softener of the invention has a Gardner color index of about 1 to 2 and, in a clear solution, has the appearance of a water-white solution but in an emulsified formulation has the appearance of a milky-white solution. If desired, the Gardner scale color index can be fairly accurately translated to other color scale systems.

The fabric softeners of the invention generally comprise the reaction products of a purified C.sub.14 - C.sub.18 fatty acid alkyl ester mixture, triethanolamine and a quaternizing reagent, preferably dimethyl sulfate. The select fatty acid alkyl esters are preferably a mixture of substantial amounts of methyl esters of stearic, palmitic, myristic and oleic and may include minor amounts of other fatty substances.

Through extensive studies, it has been found that care must be utilized in selecting a particular fatty acid alkyl ester mixture if one is to attain a clean light colored product, a functional fabric softener and a product which exhibits excellent rewetting and whiteness-retention (non-yellowing) properties. Crude or insufficiently purified fatty acid alkyl esters, when reacted with triethanolamine and a quaternizing agent, yield dark colored products which are not appealing to consumers. A convenient test for determining whether a select fatty acid alkyl ester mixture is of suitable purity for use in synthesizing the softener of the invention, is to briefly shake a sample of the select fatty esters with a small amount of sodium methoxide methanol solution and observe the resulting color. If the resulting solution turns reddish-brown or brown within about 10 minutes at room temperature, it indicates that the fatty esters contain minute amounts of matter which will discolor the ultimately formed softener. On the other hand, if the resultant solution remains water-white or pale yellow, it indicates that the ester mixture is of sufficient purity and that the ultimately formed softener will have a white color index on the Gardner scale of about 1 to 2.

Attention is also directed to the fact that a select pure fatty acid alkyl ester generally does not yield commercially acceptable softener products. Studies were conducted on the reaction products of substantially pure oleic methyl ester, triethanolamine and dimethyl sulfate and such oleic-based products failed to exhibit good fabric softening characteristics. Similar studies were conducted on the reaction products of substantially pure stearic methyl ester, triethanolamine and dimethyl sulfate and such stearic-based products failed to exhibit good emulsification characteristics. In contrast, the reaction product of a mixture of C.sub.14 - C.sub.18 fatty acid methyl esters, triethanolamine and dimethyl sulfate has good softening, outstanding whiteness-retention, self-emulsification and excellent rewetting properties, along with a light color, having an index on the Gardner scale in the range of 1 to 2.

Once a fatty acid ester mixture of sufficient purity is obtained, the softener is readily synthesized in the following manner. About two moles of a select fatty acid ester mixture are mixed with about 1 mole of triethanolamine, along with a small amount of a transesterification catalyst, such as sodium methoxide. The mixture is reacted at about 75.degree. to 115.degree.C. for a period of time to attain the amine ester. The amine ester is then mixed with a mole equivalent of dimethyl sulfate (or other quaternizing reagent) and reheated to about 70.degree. to 100.degree.C. for a period of time to obtain a viscous quaternary ammonium methol sulfate product, identified as N-methyl-N,N-di-(.beta.-C.sub.14 - C.sub.18 -acyloxy ethyl), N-.beta.-hydroxy ethyl ammonium metho sulfate. This active softener is then mixed with an inert vehicle, such as isopropanol to form a softener base which may be later combined with other additives and increased amounts of vehicle to provide a domestic softener formulation. Such formulations are milky-white and have extended shelf-life over a wide range of temperatures.

A specific exemplary embodiment of a synthesis route for producing a preferred embodiment of the active softener is set forth below.

DEMONSTRATION A

A commercially available fatty acid methyl ester mixture, Stepan C 65-P (a purified C.sub.14 - C.sub.18 fatty acid methyl ester mixture comprised of about 40% to 55% palmitic, about 30% to 40% oleic, about 7% to 12% stearic, about 4% to 8% linoleic and about 1% to 4% myristic along with minor (less than 1%) amounts of other fatty acid substances, available from the Stepan Chemical Company, assignee of the instant application, was tested for purity by placing a small sample thereof in a conventional test tube along with a small amount of 25% methanolic solution of sodium methoxide and vigorously shaken. The color of this solution remained light for more than 10 minutes and was judged to have a color index on the Gardner scale of about 1. From previous experience, this demonstrated that Stepan C 65-P was of sufficient purity to produce a clean light colored softener.

A 4-neck, 1-liter reaction flask fitted with a stirrer, thermometer, nitrogen inlet and a vacuum distillation assembly was charged with 500 grams (1.78 moles) of Stepan C 65-P, 133.2 grams (0.893 moles) of triethanolamine and 8 grams (25% solution in methanol) of a sodium methoxide solution. The mixture was stirred and heated to 91.degree.-105.degree.C. under vacuum (28 inches of Hg) and nitrogen flow (about 50 cc/min.) for about 1 hour and 45 minutes. Approximately 80 ml. of methyl alcohol was collected in a trap under a dry-ice-acetone bath and about 579 grams of the amine ester were obtained. The amine ester was light in color, with a color index of the Gardner scale of about 1.

369 grams (0.56 moles) of this amine ester was then slowly reacted with 71 grams (0.56 moles) of dimethyl sulfate for about 2 hours at a temperature of about 97.degree.C. A viscous quaternary ammonium metho sulfate product was obtained. This product was mixed with 145 grams of isopropanol at a temperature of about 79.degree.C. to form a 75% by weight fabric softener base solution.

This base solution was of a light color characterized by a color index on the Gardner scale of about 1 (read at 55.degree.C., 75% solids in 25% isopropanol). The base solution was then diluted and mixed with large amounts of water. The resultant emulsion was milky-white and did not separate upon standing.

This aqueous softener formulation (i.e. containing about 8% by weight active softener) was then compared for softening and non-coloring characteristics against commercially available softeners by treating identical fabrics laundered with identical detergents in a select cycle laundering operation. White terry cloth towel swatches were placed in a typical domestic washing machine, along with a select amount of detergent, washed in a conventional manner and then, during the rinse cycle, treated with a softener. Each towel was subjected to this cycle a select number of times, adding a fabric softener to the rinse cycle after each washing. The towels were then removed, dried and evaluated for softness and whiteness by a select panel. Each panel member was individually required to list his preference in descending order of whiteness and softness on each towel. Thereafter, the numerical value assigned to each towel was compiled and tabulated so that a towel which had the lowest number under a given characteristic indicated that a majority of the panel members placed this towel most often in first place. In other words, a low numerical value indicates that a large percentage of the panel judged that towel to be whiter or softer than other towels in the test. The average and compiled results are tabulated below.

TABLE I __________________________________________________________________________ A batch of towels was laundered with a typical Na.sub.2 CO.sub.3 built detergent (Sears Roebuck Laundry Detergent) for a select number of cycles, adding softener to the rinse after each wash, and were then judged for the characteristics noted. Whiteness Softness Softener 1 cycle 5 cycles 10 cycles 1 cycle 5 cycles 10 cycles __________________________________________________________________________ None 12 12 21 48 48 46 Nu-Soft.sup.1 27 45 37 35 32 35 Downy.sup.2 44 39 45 23 12 12 T-di-C65Q.sup.3 38 24 15 14 28 27 __________________________________________________________________________

TABLE II __________________________________________________________________________ A batch of towels was laundered with a typical phosphate built detergent (Tide) for a select number of cycles, adding softener to the rinse after each wash. The towels were then evaluated by the panel. Whiteness Softness Softener 1 cycle 5 cycles 10 cycles 1 cycle 5 cycles 10 cycles __________________________________________________________________________ None 14 11 12 48 48 48 Nu-Soft.sup.1 45 48 48 19 25 34 T-di-C65Q 24 32 29 34 26 21 __________________________________________________________________________ .sup.1 "Nu-Soft" is a registered trademark of CPC International Inc. for fabric softener containing about 8% to 9% solids in an inert vehicle. The active softener is a quaternized ditallow imidazoline. .sup.2 "Downy" is a registered trademark of Proctor & Gamble Co. for a fabric softener comprised of about 6% to 7% solids in an inert vehicle. The active softener base is dimethyl ditallow ammonium chloride. .sup.3 "T-di-C65Q" is an 8% by weight of N-methyl-N,N-di-(.beta.-C.sub.14 - C.sub.18 -acyloxy ethyl), N-.beta.-hydroxy ethyl ammonium metho sulfate of the invention in an aqueous-alcohol solution.

It will be noted that the preferred softener of the invention does not yellow fabrics over prolonged usage and provides softening action to treated fabrics at least as good as obtainable from presently available softeners. Further, the softeners of the invention are not adversely affected by carbonate built detergents or by phosphate built detergents, where either anionics or nonionics are utilized as the primary surface active agents.

To demonstrate the outstanding rewetting characteristics of the softeners here disclosed, a swatch-sink test was utilized. Generally this test comprises placing 2 .times. 2 inch swatches of softener-treated toweling on the surface of distilled water and timing, as with a stop watch, the amount of time required for each swatch to absorb water and sink below the surface of the water. Each swatch was subjected to a single wash cycle, adding a softener at the rinse cycle, dried and then carefully placed in the distilled water. The average of four determinations for each softener was recorded and is tabulated below.

TABLE III ______________________________________ *Softness Time ______________________________________ T-di-C65Q.sup.3 1-2 minutes Downy.sup.2 Over 48 hours Nu-Soft.sup.1 Over 48 hours ______________________________________ .sup.1,2,3 ibid *All of the softeners used contained approximately equal amounts of a nonionic wetting agent.

As indicated earlier, the softener of the invention, i.e. T-di-C65Q does not require additions of nonionic wetting agents and in the above tests nonionic wetting agents were included to facilitate a direct comparison with known softener formulations containing nonionic wetting agents.

The softeners of the invention may be formulated with various additives which include perfumes, optical brighteners, nonionics, viscosity control agents, and other like additives conventionally included in domestic softener formulations.

Various changes and modifications to the above described embodiments of the invention may be made without departing from the spirit and scope thereof and it is intended that all matters contained in the above description shall be interpreted as illustrative and not as limiting.

Claims

We claim as our invention:

1. A self-emulsifying domestic laundry fabric softener agent consisting essentially of a mixture comprised of N-alkyl-N,N-di-(.beta.-C.sub.14 - C.sub.18 -acyloxy ethyl), N-.beta.-hydroxy ethyl ammonium compounds and a substantially inert vehicle, said agent being characterized by good fabric softening, whiteness-retention and rewetting properties and by a light color index on the Gardner scale in the range of about 1 to 2, said C.sub.14 - C.sub.18 acyloxy group comprised of a mixture of substantial amounts of palmitic, stearic and oleic radicals.

2. A softening agent as defined in claim 1 wherein said agent is N-methyl, N,N-di-(.beta.-C.sub.14 - C.sub.18 -acyloxy ethyl), N-.beta.-hydroxy ethyl ammonium metho sulfate.

3. A softening agent as defined in claim 1 wherein said inert vehicle includes water.

4. A softening agent as defined in claim 1 wherein said inert vehicle includes isopropanol.

5. A softening agent as defined in claim 1 wherein said inert vehicle comprises a mixture of isopropanol and water.

6. A softening agent as defined in claim 1 wherein said inert vehicle is selected from the group consisting of a C.sub.1 - C.sub.4 aliphatic alcohol, a C.sub.1 - C.sub.4 aliphatic glycol, a C.sub.1 - C.sub.10 aliphatic alcohol alkali sulfate, an alkyl benzene alkali sulfonate, water and mixtures thereof.

7. A softening agent as defined in claim 1 wherein said mixture includes about 75% by weight of said agent and about 25% by weight of said inert vehicle.

8. A softening agent as defined in claim 1 wherein said mixture includes about 8% by weight of said agent and about 92% by weight of said inert vehicle.

9. A method of softening domestic laundry fabrics comprising treating said fabrics in an aqueous media containing an amount of cationic quaternary ammonium softener agent comprising N-methyl-N,N-di-(.beta.-C.sub.14 - C.sub.18 -acyloxy ethyl), N-.beta.-hydroxy ethyl ammonium metho sulfate.