WO1999007636A1

WO1999007636A1 - Crystalline fluorescent whitening agents in aqueous hypochlorite

Info

Publication number: WO1999007636A1
Application number: PCT/US1998/016637
Authority: WO
Inventors: Jeffrey Fisher; William L. Smith
Original assignee: The Clorox Company
Priority date: 1997-08-11
Filing date: 1998-08-11
Publication date: 1999-02-18

Abstract

Marginally soluble fluorescent whitener agents (optical brigtheners) can be made hypochlorite bleach resistant, stable and formulated into concentrated aqueous hypochlorite solutions and into detergent compositions where the aqueous fluorescent whitener agent-bleach solution contains from 0.001 weight percent to about 5.0 weight percent fluorescent whitener agent and from 1.5 weight percent to about 20 weight percent sodium hypochlorite. The fluorescent whitener agent is one that is marginally soluble in water at or near room temperature and, according to the method of the invention, is present in crystalline form.

Description

IN THE UNITED STATES PATENT AND TRADEMARK OFFICE

Title: CRYSTALLINE FLUORESCENT WHITENING AGENTS N

AQUEOUS HYPOCHLORITE

Inventors: JEFFREY J. FISHER and WILLIAM L. SMITH

BACKGROUND OF THE INVENTION

1. Field of the Invention This invention relates to products that contain aqueous hypochlorite bleach and fluorescent whitening agents or optical brighteners, and to a process for making such products.

2. Brief Statement of the Related Art Optical brighteners are dyes which are deposited onto fabrics and impart an added increment of whiteness and/or brightness to the fabric by means of their ability to absorb electromagnetic radiation in the ultraviolet region of the spectrum and re-emit it as visible radiation. Optical brighteners, also known as fluorescent whitener agents, have found widespread use as components of household detergent compositions, which also include laundry boosters and fabric softeners.

Sodium hypochlorite is a highly effective bleaching agent and has long been used in conjunction with soaps and detergents to remove stains and other types of soils encountered in the laundering of fabrics. It is generally formulated at a concentration of about 3.0-8.0% in water for sale for household use, where it is typically diluted to a concentration of about 200 parts per million (ppm) sodium hypochlorite for laundry bleaching. In order to achieve the degree of whiteness desired in the wash by most customers, bleaching alone is not always sufficient. More typically, a dual combination of bleaching and optical brightening are required. Accordingly, an active fluorescent whitener or fluorescent whitener agent- containing detergent composition can be used as the primary washing agent. Hypochlorite bleach can then be added separately to the wash water via one of two methods. Either the fluorescent whitener agent-containing detergent can be used followed by subsequent addition of hypochlorite bleach, or hypochlorite bleach can be added in a separate initial step prior to introduction of the detergent-fluorescent whitener mixture to the wash water.

Because of the disadvantages associated with having to add fluorescent whitener separately from bleaching solutions, it has long been deemed desirable to consolidate and formulate bleaching solutions that contain an optical brightener or fluorescent whitener agent (FWA) into a single-step process. However, optical brighteners are known in some instances to be quickly and irreversibly decomposed in the presence of hypochlorite bleach, even when the latter is present in concentrations well below 200 ppm. Furthermore, FWAs are generally unstable in concentrated hypochlorite, and tend to lose the ability to "whiten" fabrics. In other instances, the simple addition of optical brighteners to concentrated aqueous hypochlorite results in a product which must be vigorously shaken prior to use in order to disperse and evenly mix the ingredients. Because of the tendency for rapid settling, even vigorous shaking before each use does not always result in obtaining a uniform proportion of FWA and hypochlorite in each use thereof.

There have been several attempts to stabilize optical brighteners towards reaction with hypochlorite and/or to achieve successful dispersion of optical brighteners in aqueous hypochlorite solutions. A number of attempts require the presence of surfactants. For example, U.S. Pat. No. 5,057,236 to Petrin & van Buskirk recites the stabilization of anionic FWAs through the use of a stoichiometric quantity of cationic surface-active agents to produce neutral ion-paired salts. U.S. Pat. No. 4,526,700 to Hensley & Kitko incorporates anionic surfactants in a two phase system where the fine dispersion of fluorescent whitener agent must be resuspended by shaking before each use. However, only 4,4'-bis-(4-phenyl-2-H-l,2,3-triazol-2-yl)-2,2'-stilbenedisulfonate or its alkali metal salts have been shown to have sufficient stability to be dissolved in bleach solutions. Both Hensley & Kitko ('700), and Nayar, et al, U.S. 4,623,476, teach dispersions of this FWA using anionic surfactants.

In another approach, U.S. Pat. No. 4,790,953 to Mansy and U.S. 4,946,619 to Fisher teach liquid hypochlorite bleach solutions and the above optical brightener solubilized with amine oxide surfactants to make clear solutions. Eckhardt, DE 3900651 teaches that solutions of hypochlorite and sulfonated dibenzofuranyl biphenyl FWAs are stable for several months. Unfortunately, neither of these FWAs are readily commercially available.

Other prior art teaches that more readily available FWAs can be stabilized in bleach by encapsulation with flocculated polymers (Cramer, U.S. 5,104,571; or Haendler, U.S. 5,075,029 and U.S. 4,929,383); coating particulate FWA with polymers (Chang &

Wiersema, U.S. 4,708,816); or by incorporating FWAs in emulsion polymers (Briggs, U.S. 3,666,680 or Robinson & Briggs, U.S. 3,655,566). Finally, Zimmerer, U.S. Pat. No. 3,393,153, attempts to solve the problem by including a colloidal silica or particulate colloidal polymeric resin in the composition. The silica or resin keeps the optical brightener in suspension in aqueous hypochlorite.

In summary, none of the foregoing references teaches, discloses or suggests a whitening and bleaching composition or a technique for providing a readily available optical brightener or fluorescent whitener agent that is stable in the presence of hypochlorite bleach without the addition of further ingredients. That is, none of the prior references teach a stable fluorescent whitener agent in the presence of hypochlorite without the use of added surfactant or other stabilizing agents to prevent the brightener from being decomposed by the bleach and/or the oxidizing power of the bleach from being reduced by the optical brightener.

SUMMARY OF THE INVENTION AND OBJECTS The present invention is directed towards a stable formulation and a method for the preparation of a stable formulation in which aqueous alkali metal hypochlorite compositions contain extended networks of fluorescent whitener agent or optical brightener crystals. The fluorescent whitener agent or optical brightener is one that is marginally soluble in water at or near room temperature. That is, the inventive hypochlorite solutions incorporate an FWA that is not only soluble in water in the absence of other salts, but also one that is essentially insoluble in water at or near room temperature that contains other dissolved salts. The compositions comprise from about 0.001 to about 5.0 weight percent (wt. %) fluorescent whitener agent, from about 1.5 to about 20 wt. % sodium hypochlorite and the balance, water.

Accordingly, it is an object of the present invention to provide hypochlorite bleach- containing formulations with optical brighteners that retain activity after storage.

It is another object of the present invention to provide uniform delivery of hypochlorite bleach and fluorescent whitener agent from a solution which contains both bleach and FWA without the need for added components to maintain efficacy of the optical brightener and oxidizing power of the bleach.

DETAILED DESCRIPTION OF THE INVENTION Unless specifically indicated otherwise, all amounts given in the text and the examples which follow are understood to be modified by the term "about", and those figures expressed in terms of percent (%) are understood to refer to weight-percent.

The invention provides optical brighteners or fluorescent whitener agents (FWAs) that are stably contained in alkali metal hypochlorite bleach solutions, and a method for producing the same. The invention further concerns the suspension of precipitated crystalline networks of brighteners in hypochlorite bleach solutions that use the colloidal structure of the bleach and the extensive crystal network of the brightener to inhibit settling out of particulate brightener crystals. Accordingly, sparingly water-soluble anionic optical brighteners can be made hypochlorite bleach stable and formulated into hypochlorite laundry additives or into solutions of detergent formulations upon crystallization of the optical brightener into networks of needle- or filament-shaped crystal strands. Crystallization can be made to occur where an optical brightener with marginal solubility in water is dissolved in water that does not contain any other salts. Preferably, water above about 40° C is used to minimize the amount of water required to dissolve the optical brightener. The subsequent addition of hypochlorite to a saturated aqueous solution of optical brightener causes crystalline strands of optical brightener to form that are on the order of several hundreds of microns in length. According to one embodiment of the invention, the hypochlorite is added to a saturated solution of optical brightener. Upon cooling of the mixture, the crystal strands form extensive crystalline networks. It is the distribution of the brightener and the bleach into discrete environments of the aqueous phase that overcomes the problem of brightener oxidation by hypochlorite, and provides greatly enhanced brightener stability, even in the presence of bleach.

A first embodiment of the present invention, therefore, is an aqueous product formulation comprising:

(a) from about 0.001 to about 5.0 weight percent of a distyryl biphenyl fluorescent whitener agent; and

(b) from about 1.5 to about 20.0 weight percent alkali metal hypochlorite; wherein the whitener agent is characterized by crystalline filaments having an average length of at least about 150 microns.

The invention also concerns a technique for stabilizing a sparingly water soluble fluorescent whitener agent in the presence of a hypochlorite bleach solution. Thus, a second embodiment of the invention is a method for imparting aqueous hypochlorite bleach stability to a fluorescent whitener agent, comprising the steps of:

(a) dissolving a distyryl biphenyl fluorescent whitener agent in water; and

(b) combining an alkali metal hypochlorite bleach solution with the mixture produced in step (a) to obtain crystals of the fluorescent whitener agent in aqueous hypochlorite bleach; wherein crystals of the whitener agent are marginally soluble in water at or near room temperature.

The essential ingredients of the invention, as well as optional components that can desirably be incorporated in the compositions of this invention, are described below in greater detail.

FLUORESCENT WHITENER AGENT

The fluorescent whitener agents suitable for use herein are brighteners of mono- or polysulfonated 4,4'-distyryl-biphenyl (DSBP) complexes, substituted derivatives thereof, as well as salts of any of the foregoing, which may be represented by the following:

where: Rj, R₂, R₃ and R₄ may be located at any position on the phenyl (C6 ring) moiety;

R, is — SO₃M; and

R₂, R₃ and R₄ are independently selected from among: — H, — R₅, — SO₃M

— CN, — Cl, — OR₅, — C— OR₅, — SO₂N(R₅)₂ and — C— N(R₅)₂; II II O O wherein R₅ contains from 1 to 8 carbon atoms inclusive; and M is H, Na, K or Li, and combinations thereof.

Examples of particularly preferred DSBP complexes include 2,2'-disulfo-DSBP (also written as 2,2'-(4,4'-DSBP)-dibenzene sulfonic acid), represented by I.

The above is available from Ciba-Geigy, Toms River, New Jersey, under the name Tinopal™ CBS-X. Also available from Ciba-Geigy is another preferred DSBP complex, namely the Tinopal™ ATS-X derivative 4,4'-dichloro-3,3'-disulfo DSBP shown in LI.

The 2,2'-dichloro-5,5'-disulfo DSBP isomer shown in III may also be used and, while not known to be commercially available at present, it is described by Weber, et al, in published European application. No. EP 0 427,670.

Although there are other fluorescent whitener agents that contain the Tinopal™ name, the present invention is concerned only with those species that contain a distyryl biphenyl

(DSBP) backbone as a common structural element. Aside from the Tinopal™ CBS-X and ATS-X species indicated above, other Tinopal™ series compounds lack this characteristic structure.

Tinopal™ CBS-X (often simply referred to as "CBS-X"), which is used herein as an exemplary fluorescent whitener agent, was disclosed in previously cited U.S. Pat. No. 5,057,236 to Petrin, et al., which is owned by the assignee of the present invention. Unlike Petrin, et al., however, the present invention does not require the addition of an at least relative stoichiometric ratio of surface active agent to optical brightener to produce an ion-paired salt, nor must the fluorescent whitener agent be transformed into a neutral ion- pair compound.

An essential feature of the present invention is that the fluorescent whitening agents used herein — i.e., those DSBP-FWA derivatives which are marginally soluble in water at or near room temperature and which are unstable in the presence of hypochlorite bleach in amorphous form — are recrystallized from aqueous solution. It is believed that the formation of an extended network of DSBP-FWA fibrous crystals leads to the observed stability in the inventive FWA-hypochlorite solutions. Although non-crystallized DSBP- FWAs are unstable in aqueous solution in the presence of hypochlorite bleach and are thereby degraded, it is precisely the integrity provided by the physical form of the crystallized DSBP crystals in the inventive FWA-hypochlorite solutions that leads to their chemical stability in the presence of aqueous hypochlorite. Unlike many prior art references, therefore, the stability observed in the inventive FWA-bleach solutions may be attributed to a. physical, and not a chemical, phenomenon.

Non-crystalline particles of amorphous, as-received CBS-X fluorescent whitener agent were studied by electron microscopy. Close examination of the amorphous particles revealed a series of essentially round, spherically shaped particles of powder, whose median size was on the order of approximately 50-75 microns in diameter. By contrast, electron micrographs of brightener that had been crystallized according to the method of the present invention showed a predominance of highly ordered, crystalline segments of CBS- X that give rise to a few short sections (50-75 microns). Most of the material was visible in the form of long chains of fibers on the order of 400 to 500 microns in length, and longer. An enlarged portion of the intra-crystal region of a sample of CBS-X showed the extensive alignment and ordered nature of the crystalline network.

In general, the size of the crystals of the optical brightener or fluorescent whitener agent that are produced in aqueous hypochlorite solution is not crucial. However, there is a direct correlation between crystal size and stability of the optical brightener. The larger the size crystal that is obtained, the greater the improvement in the suspension of the optical brightener in aqueous hypochlorite solution, and the greater the FWA suspension stability and compatibility with hypochlorite. Thus, crystal filaments having an average length of at least about 100 microns show improved stability in the presence of aqueous hypochlorite. Crystals filaments having an average length greater than about 200 microns are preferred, more preferred is an average filament length greater than 300 microns, and an average crystal filament length greater than about 400 microns is most preferred.

Although it is not known for certain, Applicants speculate, without being bound by theory, that the observed increase in stability of DSBP-FWA crystals in hypochlorite as opposed to the amorphous form may also be due to decreased porosity, decreased hydrophilicity, or perhaps a combination of both. A relatively higher level of porosity and/or hydrophilicity for the non-crystalline form could give rise to greater contact between amorphous FWA and water. By contrast, crystallized FWAs would therefore be exposed to — and consequently interact with — comparatively decreased amounts of hypochlorite in aqueous solution. The result is an enhancement in the observed stability for DSBP optical brighteners without the need for added surfactants or superfluous stabilizers.

The fluorescent whitener agent is present in the compositions of the invention at levels of from about 0.001% to about 5.0% by weight, preferably from about 0.01% to about 1.0% by weight, and most preferably from about 0.01% to about 0.5% by weight of the total FWA-hypochlorite formulation.

ALKALI METAL HYPOCHLORΠΈ The second essential ingredient of the stable optical brightener-bleach compositions of the present invention is an oxidant source such as an alkali metal hypochlorite. Alkali metals that are suitable for use with the present invention include sodium, potassium and lithium, as well as combinations or mixtures of any of the foregoing. Sodium is the alkali metal most commonly encountered in commercial hypochlorite solutions, and is therefore preferred for use herein. Sodium hypochlorite may be formulated in aqueous solutions at concentrations of from about 1.5% to about 20.0%. Concentrations of about 3.0% to about 8.0% are more common for commercial purposes, while slightly higher ranges of about 5.0% to about 15.0% hypochlorite are common for industrial use. These solutions typically contain an equimolar amount of sodium chloride. Other salts of additional mono- or divalent cations may also be present.

In one embodiment of this invention for making the inventive compositions described herein, the amounts of aqueous alkali metal hypochlorite that are used for household purposes, e.g. 3.0-8.0%, typically also contain equimolar amounts of the alkali metal chloride in solution. Accordingly, the aqueous sodium hypochlorite source chosen for preparing a composition of the invention should be one which has a sodium hypochlorite concentration such that it can be mixed with an aqueous brightener solution within these volume proportions to produce the desired amounts of sodium hypochlorite and brightener in the finished product. Sodium hypochlorite is present in the compositions of the invention at levels of from about 2% to about 20%, preferably from about 3% to about 15%, and most preferably from about 4% to about 8%.

Mixing sodium hypochlorite with an aqueous solution of a DSBP-FWA or optical brightener in the absence of a surfactant or any other co-precipitation aid results in the formation of a floe of dispersed, fibrous FWA crystals that are suspended throughout the combined hypochlorite-FWA mixture. The FWA remains in crystalline form over time, thus suggesting that the fluorescent whitener has achieved a physically more stable form, perhaps one that is less prone to chemical attack by the hypochlorite species in solution. It is noteworthy that even in the absence of surfactants or other stabilizing agents — as are frequently used in the prior art — the optical brighteners of the present invention can demonstrate remarkable stability in crystal form. By way of illustration, the data in Table LTI below reveal that better than 85% of the fluorescent whitener agent originally present in crystalline form retained its integrity in a surfactant-free, aqueous FWA-bleach solution after a period of 10 days at elevated temperatures. It should therefore be possible to achieve stabilities for even longer durations with inventive FWA-bleach solutions in compositions that are held at or near room temperature. By contrast, note that only 75% of the optical brightener remained after 10 days at elevated temperature where as little as 0.5 wt. % thickener had been added. With 1.0 and 2.0 wt. % thickener, the amount of brightener remaining had fallen to 0 wt. % after only 5 days at elevated temperature.

OPTIONAL ADJUNCTS

Additional ingredients may optionally be used in the aqueous optical brightener and bleach compositions of the present invention in order to promote stability of the formulations, or to impart a variety of esthetic characteristics thereto. Such ingredients may include alkali metal hydroxide, surfactants and thickeners, perfumes and fragrances, dyes and pigments, etc., as described below. The additives may be present in amounts ranging from about 0-30 weight %, and are typically found at amounts of 20 weight % or less, unless specified to the contrary.

PH CONTROL

The pH of the inventive hypochlorite-FWA formulations is typically maintained above about 11.0 for purposes of hypochlorite stability, as is known and understood by those knowledgeable in the field. Accordingly, it is common to add amounts of about 0.1 to 2.0 wt. %, more preferably 0.5 to 1.5 wt. % alkali metal hydroxide or an equivalent amount of another alkaline salt selected from among carbonates, phosphates and silicates, as well as mixtures of any of the foregoing. Sodium or potassium are preferred alkali metal ions. Without being bound by theory, Applicants speculate that the addition of a minor quantity of hydroxide (or other alkaline salt) shifts the equilibrium of hypochlorite- hypochlorous acid in solution to suppress the formation of hypochlorous acid. The hydroxide and/or alkaline salt thus acts as a pH adjusting agent to extend the life of the alkali metal hypochlorite and the organic optical brightener in the FWA-hypochlorite solution, as hypochlorite ions are less likely to attack and degrade the FWA in solution.

SURFACTANTS AND THICKENERS

The essential components of the aqueous optical brightener-bleach compositions of the present invention are a fluorescent whitener agent and sodium hypochlorite, as described above. The FWA filament networks of the present invention are stable, and can remain largely non-degraded in aqueous solution in the presence of hypochlorite for up to several months at room temperature. With time, however, uniformly dispersed FWA crystals may settle out of the FWA-bleach mixtures, whereupon they can be detected in relatively increasing proportions towards lower regions of the containers into which they have been introduced. Gentle mixing or inversion of the container in order to redisperse the crystals throughout the mixture may then be carried out in order to restore overall homogeneity to the crystalline FWA-bleach solution. However, this may be objectionable from a consumer standpoint and impractical during long-term storage.

In order to provide longer shelf-life homogeneity of the brightener-bleach compositions, it may be desirable to include a small amount — i.e. less than 5 wt. %, and typically 0.5 to 2.0 wt. % — of an optional supplemental constituent. In this context, "optional supplemental constituent" is understood to include solid or liquid materials which comprise an effective amount of surfactants, polymers, clays, silicates, aluminates, thickeners and dispersing agents, as well as mixtures of any of the foregoing. If a surfactant is used, it may be selected from among anionic, nonionic, cationic, amphoteric or zwitterionic surfactants, as well as mixtures of any of the foregoing. Counterions that interact with surfactants, cosurfactants, oils and similar materials to produce or enhance thickening may also be added. Typically, supplemental constituents may enhance the stability of the hypochlorite-FWA solutions in one of two ways. They may increase the viscosity and more preferably the yield value of the hypochlorite-FWA solution, and/or increase the physical stability of the dispersion by adsorption onto the surfaces of the FWA crystals. Note, however, that it is to be understood that none of these supplemental constituents are an essential component of the invention. It is therefore understood that any supplemental constituents used with the present invention should be compatible with hypochlorite, and should be chosen such that they do not solubilize the FWA crystals to any appreciable extent. Many such techniques for improving the stability of dispersions are well known in the prior art and may be used in combination with the present invention. For example, Choy, in U.S. Pat. No. 5,705,467, which is commonly owned and assigned to The Clorox Company, discusses clays and several polymeric type thickening agents with and without permanent cross-linking at column 2, lines 36-44, and is incorporated herein by reference. Garabedian, Jr., et al, in U.S. Patent No. 5,688,756, also commonly owned and assigned to The Clorox Company, discloses a variety of ingredients for thickening or viscosity increase and stabilization of hypochlorite-containing compositions at column 2, lines 24-59, and is also incorporated herein by reference. Unlike the Petrin, et al, '236 patent discussed above, however, it is not a requirement of the present invention that any surface active agents which are optionally added form a neutral ion-pair with the fluorescent whitener agent.

The use of supplemental constituents, such as surfactants, for improvements in thickening and/or dispersion stability should be approached with caution, however. While such agents can provide certain beneficial effects, the addition of such constituents can also increase the solubility of DSBP-FWA crystals in aqueous hypochlorite, thus leading to breakdown of FWA crystals and ultimate loss of FWA for reasons already discussed. Indeed, the addition of a thickener to one FWA-bleach solution has suggested that the integrity of the FWA crystals may have been compromised. In one study, 75% of a fluorescent whitener agent originally present in crystalline form remained in an FWA- bleach-surfactant solution after 10 days. This represented a decrease of approximately 10% of the available FWA, down from 85% FWA that remained when no thickener or surface active agent had been used. Such data suggests that the use of surface active agents with crystalline FWA in aqueous hypochlorite should be approached as a compromise between the effective suspension of FWA crystals in solution, and ultimate chemical stability of the FWA in presence of the hypochlorite. An alternate embodiment of the present invention that employs supplemental constituents is therefore an aqueous detergent composition comprising:

(a) from about 0.001 weight percent to about 5.0 weight percent of a distyryl biphenyl fluorescent whitener agent;

(b) from about 1.5 weight percent to about 20 weight percent sodium hypochlorite; and

(c) a solid or liquid material which comprises an effective amount of at least one supplemental constituent chosen from among surfactants, including anionic, nonionic, cationic, amphoteric and zwitterionic surfactants as well as mixtures of the foregoing, as well as polymers, clays, silicates, aluminates, thickeners, dispersing agents, and any combination thereof; wherein crystals of the whitener agent are marginally soluble in water at or near room temperature and the whitener agent is present in crystalline form.

DYES AND PIGMENTS

Dyes and pigments which may be included in the FWA-hypochlorite compositions of the present invention include Monastral blue and anthraquinone dyes (such as those described in Zielske, U.S. Pat. Nos. 4,661,293 and 4,746,461). Pigments, which are also suitable colorants, can be selected, without limitation, from titanium dioxide, Ultramarine Blue (see Chang, et al, U.S. Pat. No. 4,708,816) and colored aluminosilicates.

PERFUMES AND FRAGRANCES

Optional adjuncts include fragrances, such as those commercially available from Firmenich. International Flavors and Fragrance, Inc. (IFF), Quest and other suppliers. Of course, the perfume or fragrance materials used should have a high degree of chemical stability to alkali metal hypochlorite. If used, perfumes may be present in the compositions of the present invention at levels of from 0.001 % to about 5.0%, and preferably from about 0.05% to about 0.3%.

COMPOSITION PREPARATION

The shape of the optical brightener particles are important to the current invention. Because the particles must be supported and suspended by the aqueous structure of the bleach, they must form a space-filling floe. Suitable structures for this purpose are therefore configurations such as needles, filaments or extended networks of similarly- shaped smaller particles. Unfortunately, most commercially available optical brighteners are provided in the form of powders or aggregates of large, roughly spherical structures which do not form space-filling floes. These structures lack the crystalline structure and concomitant attributes described above, and are therefore unsuitable candidates for the stabilized optical brightener systems of the present invention. By way of illustration, Tinopal™ CBS-X, described above, is available from the manufacturer in the form of roughly spherical particles approximately 20 to 120 microns in diameter. When incorporated into thickened bleach solutions such as commercially available Liquid-Plumr® professional strength drain opener, the amorphous CBS-X particles were found to settle out almost immediately.

In order to prepare the stable optical brightener-bleach formulations of the present invention, the optical brightener is first dissolved in water. Preferably, the amount of water used is minimized by heating above about 40° C. The brightener is then precipitated by mixing with hypochlorite to give rise to FWA crystals. Electron micrographs that were obtained for Tinopal™ CBS-X, for example, that had been dissolved and crystallized according to the method of the present invention revealed a comprehensive network of filaments or needle-like fingers. These extensive arrays of space-filling filament networks extended over hundreds of microns. The addition of CBS-X crystals in filament form to aqueous bleach solutions resulted in only the very slow settling out of brightener particles from the brightener-bleach mixture. Indeed, the crystalline form of optical brighteners used herein were found to be stable in the presence of hypochlorite for times on the order of several weeks to months without the addition of stabilizers, surfactants, etc. The following examples serve to further illustrate some of the surprising performance benefits of the various aspects of the inventive optical brightener-bleach solutions of the invention.

EXPERIMENTAL PREPARATION OF STOCK SOLUTIONS

One stock bleach solution and three different stock brightener solutions were used for Experiments 1-4 below. The various stock solutions were prepared as follows.

STOCK BLEACH SOLUTION A stock bleach solution was prepared by mixing 60 g of a 50% solution of sodium hydroxide with 2,940 g of a solution of Clorox® liquid bleach that contained about 5.5% sodium hypochlorite and 4.3% sodium chloride in an approximately equal molar ratio. The resulting stock bleach solution contained about 5.4% sodium hypochlorite and 1% sodium hydroxide.

STOCK BRIGHTENER SOLUTION- 1

Stock brightener solution- 1 was made by dissolving 10.5 g of Tinopal CBS-X in

190 g of water. To aid dissolution, the mixture was placed in a sonicator for about 15 minutes. In addition to helping to reduce particle size, the sonication warmed the solution to about 32.2° C (90° F). STOCK BRIGHTENER SOLUTION-2

Stock brightener solution-2 was prepared by dissolving 10 g of Tinopal CBS-X in 1990 g of water. Sonication for approximately 15 minutes reduced particle size and warmed the solution to about 32.2° C (90° F).

STOCK BRIGHTENER SOLUTION-3

Stock brightener solution-3 was prepared by dissolving 10 g of Tinopal CBS-X in 190 g of water. To aid dissolution, the mixture was placed on a sonicator and sonicated for about 15 minutes. Again, sonication not only helped to reduce particle size, but also warmed the solution to about 32.2° C (90° F).

STOCK BRIGHTENER SOLUTION-4

Stock brightener solution-4 was prepared by dissolving 6 grams of Tinopal CBS-X in 494 g of water. To aid dissolution, the solution was stirred using a magnetic stirrer and warmed to about 40° C (104° F) on a hot plate.

MIXING METHODS

In Experiments 1-5, different mixing techniques were used to combine the various bleach and brightener solutions as indicated below. The various mixing methods are described briefly here.

1. In Method 1, the brightener solution was added to the bleach solution with stirring.

2. In Method 2, the bleach solution was added to the brightener solution with stirring. 3. In Method 3, the bleach solution and brightener solutions were simultaneously poured into a third container to simulate conditions found in a static mixer.

EXPERIMENT 1 For Experiment 1, the stock bleach solution and stock brightener solution- 1 were mixed together using each of Mixing Methods 1, 2 and 3. In each instance, 10.5 g of the brightener solution was used together with 189.5 g of the bleach solution. The final composition contained about 5.1% sodium hypochorite, 0.26% Tinopal CBS-X, 4.0% sodium chloride, and 0.95% sodium hydroxide. Although all three methods produced acceptable crystalline floes, Method 1 produced the most homogeneous mixture, and Method 3 produced the largest crystals.

EXPERIMENT 2 In Experiment 2, the stock bleach solution was mixed with stock brightener solution-2 according to each of the three different Mixing Methods described above. In each instance, 100.5 g of stock brightener solution-2 was mixed with 99.5 g of stock bleach solution- 1. The resulting compositions contained about 2.7% sodium hypochlorite, 0.25% Tinopal CBS-X, 2.1% sodium chloride and 0.5% sodium hydroxide. As in Experiment 1, all three Mixing Methods produced acceptable floes. In Experiment 2, however, Method 3 produced the smallest crystals.

EXPERIMENT 3 In Experiment 3, the stock bleach solution and stock brightener solution-2 were combined together according to Mixing Method 3 described above. In each of four different trials, 100.5 g of stock brightener solution-2 was mixed with 50.5g, 200g, 400g or 800g of the stock bleach solution, respectively. In all cases, the brightener precipitated to form acceptable floes that were similar in appearance. The approximate compositions of the resulting mixtures are indicated in Table I below.

TABLE I

EXPERIMENT 4 In Experiment 4, the stock bleach solution and stock brightener solution-3 were combined together in accordance with Mixing Method 3 described above. Four trials were conducted, for which the amounts of stock brightener solution and stock bleach solution-3 that were used are given in Table LI. In each case, the brightener precipitated to form acceptable floes that were similar in appearance. The floes appeared to have larger crystals than those formed using more dilute stock brightener solution-2 as was used in Experiment 3 above. The approximate compositions of the resulting mixtures are provided in Table II below. // // // // // // TABLE II

As the above experiments show, there is a rather wide variation not only in the amounts and relative ratios, but also in the mixing techniques that can be used to combine brightener and hypochlorite according to the present invention. In each instance, crystal floes of brightener can be made to form. These crystal floes of brightener exhibit enhanced stability in the presence of hypochlorite as opposed to amorphous, powder forms of brightener. Consequently, greater chemical stability is imparted to the brightener crystal floes that are in solution with the aqueous hypochlorite. Without being bound by theory, one explanation for the enhanced stability observed for the brightener crystal floes is that it is attributable to a partitioning effect. That is, once the brightener is present in the form of crystalline floes, it is no longer physically available to the hypochlorite for degradation in aqueous solution. The result is that the brightener retains its activity for durations that are on the order of several weeks to months without the need for additional stabilizers, surfactants, etc. As stated above, the stability observed in the inventive FWA-bleach solutions may therefore be attributed to a. physical, and not a chemical, phenomenon.

EXPERIMENT 5 In Experiment 5, a commercially available bleach that is sold for swimming pool disinfection was used as the hypochlorite source. The swimming pool bleach contained about 13% sodium active hypochlorite and 0.5-1% sodium hydroxide. To several aliquots of the pool bleach a 50% sodium hydroxide solution was added, resulting in the preparation of four solutions, each of which contained about 10.5% sodium hypochlorite and about 2% sodium hydroxide. A thickening system was also prepared, which consisted of cetyltrimethylammonium chloride, sodium nitrate and sodium xylene sulfonate in a 1 : 1 : 1.25 weight ratio.

Four samples designated V-a, V-b, V-c and V-d in Table m below were then prepared from the hypochlorite solution described immediately above. The first solutuion, which was used to prepare Example V-a, was used neat with no added thickening system. The remaining solutions, which were used to prepare Examples V-b through V-d, contained 1.0%, 2.0% and 4.0% total actives, respectively, of the thickening system. All four solutions were then warmed to 40° C (104° F). A five hundred gram (500 g) aliquot of each sample solution was then poured into 500 g of stock brightener solution-4, accompanied by vigorous stirring. Floes of brightener precipitated out from each of the mixtures immediately. Stirring was continued until the product cooled to 20° C (68° F). The resulting aqueous solutions each contained 0.3% Tinopal CBS-X, about 5.25% sodium hypochlorite, about 1.0% sodium hydroxide, and 0.0%, 0.5%, 1.0% and 2.0%, respectively, of the thickening actives. The four samples were then stored at elevated temperature in order to evaluate their relative stabilities. The results are provided in Table IE below.

TABLE III

Stability of FWA in Hypochlorite Bleach at 48.9^C ¹ (C 120°F)

Thickener Relative % Bri ghtener Remaining

Example No.^a Amount (wt. %) Days: 0 J 2. _5_ JO.

V-a 0.0 100 95 90 85 85

V-b 0.5 100 90 85 80 75

V-c 1.0 100 15 5 0 0

V-d 2.0 100 10 0 0 0 ^a The fluorescent whitener agent used in Examples V-a, V-b, V-c and V-d was CBS-X that had been crystallized according to the procedure described for Experiment 5 above.

It will be understood that various other changes of the details, materials, steps and uses which have been described herein and illustrated in order to explain the nature of the invention will occur to and may be made by those skilled in the art upon a reading of this disclosure, and such changes are intended to be included within the principle and scope of this invention. Although specific components, amounts and proportions may have been used in the preceding description of preferred embodiments of the novel crystalline fluorescent whitening agent-hypochlorite solutions, variations and modifications thereof which are within the spirit and scope of this application and the systems listed herein will become evident to those skilled in the art to which this invention pertains. Other materials and steps may be added to those used herein, and variations may be made in the FWA- bleach solutions to improve upon, enhance or otherwise modify the properties of or increase the uses for the invention.

Claims

What is claimed is:

1. An aqueous composition comprising:

(a) from about 0.001 weight percent to about 5.0 weight percent of a distyryl biphenyl fluorescent whitener agent; and (b) from about 1.5 weight percent to about 20 weight percent sodium hypochlorite; wherein crystals of the whitener agent are marginally soluble in water and the whitener agent may be characterized by crystalline filaments.

2. The aqueous composition of Claim 1 , further wherein the fluorescent whitener agent is a mono- or polysulfonated distyryl biphenyl complex or the salts thereof having the formula:

where: R₍, R₂, R₃ and R₄ may be located at any position on the phenyl moiety;

R, is ΓÇö SO₃M; and

R₂, R₃ and R₄ are independently selected from among ΓÇö H, ΓÇö R₅, ΓÇö SO₃M , ΓÇö CN,

ΓÇö CΓÇö OR₅ , ΓÇö SO₂N(R₅)₂ , and ΓÇö CΓÇö N(R₃)₂, ΓÇö Cl, ΓÇö OR₅, II II

O O wherein R₅ contains from 1 to 8 carbon atoms inclusive; and wherein M is H, Na, K or Li, and combinations thereof.

3. The aqueous composition of Claim 2, wherein the fluorescent whitener agent has the formula:

4. The aqueous composition of Claim 2, wherein the fluorescent whitener agent has the formula:

CH=

╬¬O_jNa

5. The aqueous composition of Claim 2, wherein the fluorescent whitener agent has the formula:

6. The aqueous composition of Claim 1, further comprising surface active agents, perfumes, dyes or any combination of the foregoing, except that a stoichiometric amount of surface active agent to fluorescent whitener agent to produce ion-paired salts is not required, nor must the fluorescent whitener agent be transformed into a neutral ion-pair compound.

7. A method for imparting aqueous hypochlorite bleach stability to a fluorescent whitener agent comprising the steps of:

(a) dissolving distyryl-biphenyl fluorescent whitener agent in water; and

(b) obtaining crystals of the fluorescent whitener agent in aqueous hypochlorite bleach upon the addition of a sodium hypochlorite bleach solution to the mixture produced in step (a); wherein crystals of the whitener agent are marginally soluble in water and the whitener agent is characterized by crystalline filaments.

8. The method of Claim 7 further wherein the fluorescent whitener agent or salt thereof is present in an amount of about 0.001 weight percent to about 5.0 weight percent; and the sodium hypochlorite bleach is present in an amount of from about 1.5 weight percent to about 20 weight percent.

9. The method of Claim 7 further comprising the step of:

(c) including at least one surface active agent, thickener, supplemental constituent, pH adjusting agent, perfume, dye or any combination of the foregoing to the mixture produced in step (b), except that a stoichiometric ratio of surface active agent to fluorescent whitener agent to produce an ion-paired salt is not contemplated, and the fluorescent whitener agent is optionally a neutral ion-pair compound.

10. An aqueous detergent composition comprising:

(a) from about 0.001 weight percent to about 5.0 weight percent of a distyryl biphenyl fluorescent whitener agent; (b) from about 1.5 weight percent to about 20 weight percent sodium hypochlorite; and

(c) a solid or liquid material which comprises an effective amount of at least one supplemental constituent chosen from among surfactants, including anionic, nonionic, cationic, amphoteric and zwitterionic surfactants as well as mixtures of the foregoing, as well as polymers, clays, silicates, aluminates, thickeners, dispersing agents, and any combination thereof; wherein crystals of the whitener agent are marginally soluble in water and the whitener agent may be characterized by crystalline filaments.