EP1141229A1

EP1141229A1 - Process for making a low bulk density detergent composition by agglomeration

Info

Publication number: EP1141229A1
Application number: EP98964850A
Authority: EP
Inventors: Manivannan Kandasamy; Yuji Nakamura
Original assignee: Procter and Gamble Co
Current assignee: Procter and Gamble Co
Priority date: 1998-12-22
Filing date: 1998-12-22
Publication date: 2001-10-10
Also published as: CA2353534A1; WO2000037605A1; CN1327477A; AU2008299A; JP2002533532A; AR021975A1; CN1183243C

Abstract

A process is provided which produces a low bulk density (below about 600 g/l) detergent composition directly from starting detergent ingredients. The process includes the steps of agglomerating a detergent binder, an organic acid source, and a carbonate source in a mixer to obtain detergent agglomerates, wherein the reaction of the organic acid source and the carbonate source generates gas, such as carbon dioxide gas, within the particle, and drying the detergent agglomerate so as to form a detergent composition. The process does not require the use of conventional spray drying towers, and therefore, is more efficient, economical and flexible with regard to the variety of detergent compositions that can be produced in the process.

Description

PROCESS FOR MAKING A LOW BULK DENSITY DETERGENT COMPOSITION BY AGGLOMERATION

FIELD The present invention generally relates to a process for producing a low bulk density detergent composition. More particularly, the invention is directed to a process in which low bulk density detergent agglomerates are produced by feeding a binder, such as a surfactant paste, into a mixer. The process produces a free flowing, low bulk density detergent composition which can be commercially sold as a conventional non-compact detergent composition or used as an admix in a low dosage, "compact" detergent product.

BACKGROUND Recently, there has been considerable interest within the detergent industry for laundry detergents which are "compact" and therefore, have low dosage volumes. To facilitate production of these so-called low dosage detergents, many attempts have been made to produce high bulk density detergents, for example with a density of 600 g/l or higher. The low dosage detergents are currently in high demand as they conserve resources and can be sold in small packages which are more convenient for consumers. However, the extent to which modern detergent products need to be "compact" in nature remains unsettled. In fact, many consumers, especially in developing countries, continue to prefer a higher dosage levels in their respective laundering operations. Consequently, there is a need in the art of producing modern detergent compositions for flexibility in the ultimate bulk density of the final composition.

Generally, there are two primary types of processes by which detergent granules or powders can be prepared. The first type of process involves spray- drying an aqueous detergent slurry in a spray-drying tower to produce highly porous detergent granules. In the second type of process, the various detergent components are dry mixed after which they are agglomerated with a binder such as a nonionic or anionic surfactant. In both processes, the most important factors which govern the bulk density of the resulting detergent granules are the bulk density, porosity and surface area, shape of the various starting materials and their respective chemical composition. These parameters, however, can only be varied within a limited range. Thus, flexibility in the substantial bulk density can only be achieved by additional processing steps which lead to lower density of the detergent granules.

There have been many attempts in the art for providing processes which increase the bulk density of detergent granules or powders. Particular attention has been given to densification of spray-dried granules by post tower treatment. For example, one attempt involves a batch process in which spray-dried or granulated detergent powders containing sodium thpolyphosphate and sodium sulfate are densified and spheronized in a Marumerizer®. This apparatus comprises a substantially horizontal, roughened, rotatable table positioned within and at the base of a substantially vertical, smooth walled cylinder. This process, however, is essentially a batch process and is therefore less suitable for the large scale production of detergent powders. More recently, other attempts have been made to provide continuous processes for increasing the bulk density of "post- tower" or spray dried detergent granules. Typically, such processes require a first apparatus which pulverizes or grinds the granules and a second apparatus which increases the bulk density of the pulverized granules by agglomeration. While these processes achieve the desired increase in bulk density by treating or densifying "post tower" or spray dried granules, they do not provide a process which has the flexibility of providing lower bulk density granules. Moreover, all of the aforementioned processes are directed primarily for densifying or otherwise processing spray dried granules. Currently, the relative amounts and types of materials subjected to spray drying processes in the production of detergent granules has been limited. For example, it has been difficult to attain high levels of surfactant in the resulting detergent composition, a feature which facilitates production of detergents in a more efficient manner. Thus, it would be desirable to have a process by which detergent compositions can be produced without having the limitations imposed by conventional spray drying techniques.

To that end, the art is also replete with disclosures of processes which entail agglomerating detergent compositions. For example, attempts have been made to agglomerate detergent builders by mixing zeolite and/or layered silicates in a mixer to form free flowing agglomerates. While such attempts suggest that their process can be used to produce detergent agglomerates, they do not provide a mechanism by which a starting detergent materials in the form of surfactant pastes or acid precursors thereof, liquids and dry materials can be effectively agglomerated into crisp, free flowing detergent agglomerates having low densities rather than high densities (i.e. above 600 g/l).

Accordingly, there remains a need in the art to have a process for producing a low bulk density detergent composition in the form of agglomerates directly from starting detergent ingredients. Also, there remains a need for such a process which is more efficient, flexible and economical to facilitate large-scale production of detergents of low as well as high dosage levels. None of the existing art provides all of the advantages and benefits of the present invention.

BACKGROUND ART The following references are directed to densifying spray-dried granules:

Dugan et al, U.S. Patent No. 4,118,333 (Colgate); Appel et al, U.S. Patent No. 5,133,924 (Lever); Bortolotti et al, U.S. Patent No. 5,160,657 (Lever); Johnson et al, British patent No. 1,517,713 (Unilever); and Curtis, European Patent Application 451 ,894. The following references are directed to producing detergents by agglomeration: Beerse et al, U.S. Patent No. 5,108,646 (Procter & Gamble); Capeci et al, U.S. Patent No. 5,366,652 (Procter & Gamble); Capeci et al, U.S. Patent No. 5,486,303 (Procter & Gamble); Capeci et al, U.S. Patent No. 5,489,392 (Procter & Gamble); Hollingsworth et al, European Patent Application 351 ,937 (Unilever); and Swatling et al, U.S. Patent No. 5,205,958. The following references are directed to surfactant pastes: Aouad et al, WO 93/18123 (Procter & Gamble); Aouad et al, WO 92/18602 (Procter & Gamble); Aouad et al, EP 508,543 (Procter & Gamble); Mueller et al, U.S. Patent no. 5,152,932; Strauss et al, U.S. Patent No. 5,080,848 (Procter & Gamble); Ofosu-Asante et al, U.S. Patent No. 5,066,425 (Procter & Gamble); Jolicoeur et al, U.S. Patent No. 5,045,238 (Procter & Gamble); France et al., U.S. Patent No. 5,665,691 (Procter & Gamble); and Van Zorn et al, EP 504,986 (Shell).

SUMMARY The present invention provides a process which produces an agglomerated low bulk density (below about 600 g/l) detergent composition directly from starting ingredients. The process includes the steps of agglomerating a detergent binder, an organic acid source, and a carbonate source in a mixer to obtain detergent agglomerates, wherein the reaction of the organic acid source and the carbonate source generates gas, such as carbon dioxide gas, within the agglomerate, and drying the detergent agglomerate so as to form a detergent composition. The process does not require the use of conventional spray drying towers, and therefore, is more efficient, economical and flexible with regard to the variety of detergent compositions that can be produced in the process.

These and other features, aspects, and advantages of the present invention will become evident to those skilled in the art from a reading of the present disclosure and the appended claims.

DETAILED DESCRIPTION The present invention provides a process which produces an agglomerated low bulk density (below about 600 g/l) detergent composition directly from starting ingredients. The process does not use the conventional spray drying towers and is therefore more efficient, economical and flexible with regard to the variety of detergent compositions which can be produced in the process. Moreover, the process is more amenable to environmental concerns in that it does not require spray drying towers which require more energy to operate and may emit particulates and volatile organic compounds into the atmosphere if not operated properly.

As used herein, the term "agglomerates" refers to particles formed by agglomerating detergent granules or particles which typically have a smaller mean particle size than the formed agglomerates. All percentages used herein are expressed as "percent-by-weight" unless indicated otherwise and all documents cited herein are incorporated herein by reference. All viscosities described herein are measured at 70°C and at shear rates between about 10 to 50 sec^_1 , preferably at 25 sec^"1. In accordance with one aspect of the invention, a process for producing a low bulk density detergent composition is provided. The process includes the steps of agglomerating a detergent binder, an organic acid source, and a carbonate source in a mixer to obtain detergent agglomerates, wherein the reaction of the organic acid source and the carbonate source generates gas, such as carbon dioxide gas, within the agglomerate, and drying the detergent agglomerate so as to form a detergent composition. Also provided are the low bulk density detergent products produced by any one of the process embodiments described herein. Generally speaking, the present process is used in the production of normal as opposed to low dosage detergents, whereby the resulting detergent agglomerates can be used as a detergent or as a detergent additive. It should be understood that the process described herein can be continuous or batch depending upon the desired application.

Process In the first step of the process, starting detergent materials are fed into a mixer for agglomeration. To achieve the desired bulk density of less than about 600 g/l, the agglomeration step is carried forth in a mixer wherein the starting detergent materials are agglomerated in a mixer. The mixer preferably is a high speed or a low speed mixer. Optionally, a second mixer, which can be a low, moderate, or high speed mixer, may be used for further agglomeration if necessary. The nature and composition of the entering or starting detergent materials can vary as described in detail hereinafter. Preferably, the mean residence time of the starting detergent materials in a high speed mixer (e.g. Lόdige Recycler CB, Schugi, or other similar equipment) is from about 0.1 to 45 seconds while the residence time in a low or moderate speed mixer (e.g. Lodige Recycler KM "Ploughshare" or other similar equipment) is from about 0.5 to 15 minutes.

The starting detergent materials preferably include (1) a detergent binder, such as a highly viscous surfactant paste, non-ionic surfactant, and other viscous binders such as polyethylene glycol, (2) an organic acid source, and (3) a carbonate source, the components of which are described more fully hereinafter. The organic acid source and the carbonate source react and generate gas, such as carbon dioxide gas, within the particle, thereby creating a void volume within the particle. This, of course, results in more porous agglomerates having a relatively low bulk density. Preferably, the mean residence time in the mixer is from about 5 to about 30 seconds and tip speed for the mixer is in range from about 5 m/s to about 10 m/s, the energy per unit mass in the mixer is from about 0.15 kj/kg to about 4.20 kj/kg, more preferably, the mean residence time in the mixer is from about 10 to about 15 seconds and tip speed for the mixer is in range from about 6 m/s to about 8 m/s, the energy per unit mass for the mixer is from about 0.15 kj/kg to about 2.5 kj/kg, and most preferably, the mean residence time in the mixer is from about 10 to about 15 seconds and tip speed for the mixer is in range from about 6.5 m/s to about 7.5 m/s, the energy per unit mass for the mixer is from about 0.15 kj/kg to about 1.30 kj/kg. The agglomerates produced preferably have a bulk density of from about 350 g/l to about 500 g/l.

Preferably, the detergent binder and the carbonate source is first premixed, and the premixture is added to the organic acid source in the mixer. Preferably, the molar ratio of organic acid to carbonate source is preferably from about 1 :1 to about 1 :8, more preferably from about 1 :1 to about 1 :4. Drying may be an optional step in order to further lower the bulk density of the agglomerates. In that regard, the drying temperature used in any of the drying apparatus known, will preferably be from about 50°C to about 300°C, more preferably from about 80°C to about 250°C, and even more preferably, from about 100°C to about 250°C. This heating or drying step enhances the free flowability of the agglomerates and initiates the "fluffed" or "puffed" physical characteristics of the resulting agglomerates, and in effect, lowers the bulk density of the agglomerates. To this end, it is preferable that the detergent agglomerates exiting the mixer (or the optional moderate speed mixer) contain at least about 3%, more preferably at least about 5%, and most preferably from about 5% to about 15%, by weight of water. Optionally, the process may include the step of spraying water in the mixer to insure that the aforementioned water levels are included in the detergent agglomerates. While not intending to be bound by theory, it is believed that during the agglomeration step of the instant process, the water embodied in the agglomerates instantaneously or very quickly evaporates upon being subjected to dielectric heating causing the agglomerates to "puff¹ into a fluffy, light, low bulk density agglomerate particle in the dryer.

The detergent agglomerates produced by the process preferably have a surfactant level of from about 12% to about 55%, more preferably from about 35% to about 55% and, most preferably from about 45% to about 55%. The interparticle and intraparticle porosity of the resulting detergent agglomerates produced according to the process of the invention is preferably in a range from about 5% to about 60%, more preferably at about 35 to about 50%.

In addition, an attribute of dense or densified agglomerates is the relative particle size. The present process typically provides detergent agglomerates having a median particle size of from about 250 microns to about 2000 microns, and more preferably from about 600 microns to about 850 microns. The optional moderate speed mixer can be used to insure build-up to the aforementioned median particle sizes. As used herein, the phrase "median particle size" refers to individual agglomerates and not individual particles or detergent granules. The combination of the above-referenced porosity and particle size results in agglomerates having bulk density values of less than 600 g/l. Such a feature is especially useful in the production of laundry detergents having varying dosage levels as well as other granular compositions such as dishwashing compositions. Optional Process Steps

In an optional step of the present process, the detergent agglomerates exiting the mixer or the moderate speed mixer, if used, are further conditioned by additional cooling or drying in a fluid bed cooler and/or drier or similar apparatus as are well known in the art. Another optional process step involves adding a coating agent to improve flowability and/or minimize over agglomeration of the detergent composition in one or more of the following locations of the instant process: (1 ) the coating agent can be added directly after the fluid bed cooler; (2) the coating agent may be added between the fluid bed dryer and the fluid bed cooler; (3) the coating agent may be added between the fluid bed dryer and the optional moderate speed mixer; and/or (4) the coating agent may be added directly to the optional moderate speed mixer and the fluid bed dryer. The coating agent is preferably selected from the group consisting of aluminosilicates, silicates, carbonates and mixtures thereof. The coating agent not only enhances the free flowability of the resulting detergent composition which is desirable by consumers in that it permits easy scooping of detergent during use, but also serves to control agglomeration by preventing or minimizing over agglomeration, especially when added directly to the moderate speed mixer. As those skilled in the art are well aware, over agglomeration can lead to very undesirable flow properties and aesthetics of the final detergent product. Optionally, the process can comprise the step of spraying an additional binder in one or both of the mixers or dryer. A binder is added for purposes of enhancing agglomeration by providing a "binding" or "sticking" agent for the detergent components. The binder is preferably selected from the group consisting of water, silicates, anionic surfactants, nonionic surfactants, polyethylene glycol, polyvinyi pyrrolidone polyacrylates, citric acid and mixtures thereof. Other suitable binder materials including those listed herein are described in Beerse et al, U.S. Patent No. 5,108,646 (Procter & Gamble Co.), the disclosure of which is incorporated herein by reference.

Other optional steps contemplated by the present process include screening the undersized ("fines") and/or oversized ("overs") detergent agglomerates in a screening apparatus which can take a variety of forms including but not limited to conventional screens chosen for the desired particle size of the finished detergent product. The undersized agglomerates can be recycled back to the mixer and/or the oversized agglomerates can be sized as desired via grinding or similar process. Other optional steps include conditioning of the detergent agglomerates by subjecting the agglomerates to additional drying by way of apparatus discussed previously.

Another optional step of the instant process entails finishing the resulting detergent agglomerates by a variety of processes including spraying and/or admixing other conventional detergent ingredients. For example, the finishing step encompasses spraying perfumes, brighteners and enzymes onto the finished agglomerates to provide a more complete detergent composition. Such techniques and ingredients are well known in the art.

Detergent Binder The detergent binder used in the process is preferably in the form of an aqueous viscous paste, although other forms are also contemplated by the invention. This so-called viscous binder has a viscosity of from about 200 cps to about 100,000 cps, more preferably from about 10,000 cps to about 80,000 cps, and contains at least about 10% water, more typically at least about 30% by weight of water. The viscosity is measured at 70°C and at shear rates of about 10 to 100 sec.^"'' . Furthermore, the detergent binder, if used, preferably comprises a detersive surfactant as described hereinafter in the amounts specified previously and the balance water and other conventional detergent ingredients. A detergent surfactant paste can be used as a detergent binder.

Generally speaking, the surfactant is selected from anionic, nonionic, zwitterionic, ampholytic and cationic classes and compatible mixtures thereof. Detergent surfactants useful herein are described in U.S. Patent 3,664,961 , Norris, issued May 23, 1972, and in U.S. Patent 3,919,678, Laughlin et al., issued December 30, 1975, both of which are incorporated herein by reference. Useful cationic surfactants also include those described in U.S. Patent 4,222,905, Cockrell, issued September 16, 1980, and in U.S. Patent 4,239,659, Murphy, issued December 16, 1980, both of which are also incorporated herein by reference. Of the surfactants, anionics, cationics, zwitterionics and nonionics are preferred and anionics are most preferred.

Nonlimiting examples of the preferred anionic surfactants useful include the conventional C-| i-Ci8 alkyl benzene sulfonates ("LAS"), primary, branched-chain and random C10-C20 ^a'kyl sulfates ("AS"), the C-10-C18 secondary (2,3) alkyl sulfates of the formula CH3(CH2)_x(CHOS03^~M⁺) CH3 and CH3 (CH2)y(CHOSθ3^_M⁺) CH2CH3 where x and (y + 1) are integers of at least about 7, preferably at least about 9, and M is a water-solubilizing cation, especially sodium, unsaturated sulfates such as oleyl sulfate, and the C-|n-Ci 8 alkyl alkoxy sulfates ("AE_XS"; especially EO 1-5 ethoxy sulfates).

Other exemplary surfactants useful in the invention include and C^<ιrj-Ci8 alkyl alkoxy carboxylates (especially the EO 1-5 ethoxycarboxylates), the C-ιo-18 glycerol ethers, the C-10-C18 alkyl polyglycosides and their corresponding sulfated polyglycosides, and C12-C18 alpha-sulfonated fatty acid esters. If desired, the conventional nonionic and amphoteric surfactants such as the C12-C18 alkyl ethoxylates ("AE") including the so-called narrow peaked alkyl ethoxylates and C6-C12 alkyl phenol alkoxylates (especially ethoxylates and mixed ethoxy/propoxy), C12-C18 betaines and sulfobetaines ("sultaines"), C10-C18 arnine oxides, and the like, can also be included in the overall compositions.

The C10-C18 N-alkyl polyhydroxy fatty acid amides can also be used. Typical examples include the C12-C 8 N-methylglucamides. See WO 9,206,154. Other sugar-derived surfactants include the N-alkoxy polyhydroxy fatty acid amides, such as C10-C18 N-(3-methoxypropyl) glucamide. The N- propyl through N-hexyl C-12-C18 glucamides can be used for low sudsing. C-I Q- C20 conventional soaps may also be used. If high sudsing is desired, the branched-chain C^<| rj-Ci6 soaps may be used. Mixtures of anionic and nonionic surfactants are especially useful. Other conventional useful surfactants are listed in standard texts.

In addition to detergent surfactant pastes, other viscous binders such as polyethylene glycol, sodium silicate may be used. Organic acid source The acid source is preferably substantially anhydrous or non-hygroscopic and the acid is preferably water-soluble. It may be preferred that the acid source is overdried. Suitable acids source components include an acid or salt form of a mono or polycarboxylic acid. Such preferred acids include those selected from the group consisting of citric, malic, maleic, fumaric, aspartic, glutaric, tartaric, malonic, succinic or adipic acid, 3 chetoglutaric acid, citramalic acid, and mixtures thereof. Citric acid, maleic or malic acid are especially preferred.

Also preferably, the acid source provides acidic compounds which have an average particle size in the range of from about 10 microns to about 1180 microns, more preferably from about 70 microns to about 710 microns, calculated by sieving a sample of the source of acidity on a series of Tyler sieves.

Carbonate source

Preferably, the carbonate source is a carbonate and/or bicarbonate, and in particular, a carbonate/bicarbonate salt. Examples of preferred carbonates are the alkaline earth and alkali metal carbonates, including sodium or potassium carbonate, bicarbonate and sesqui-carbonate and any mixtures thereof with ultra-fine calcium carbonate such as are disclosed in German Patent Application

No. 2,321 ,001 published on November 15, 1973. Alkali metal percarbonate salts are also suitable sources of carbonate species, which may be present combined with one or more other carbonate sources.

The carbonate and bicarbonate preferably have an amorphous structure.

The carbonate and/ or bicarbonates may be coated. The particles of carbonate and bicarbonate preferably have a mean particle size of about 4 μm or greater, preferably about 10μm or greater, more preferably of about 15μm to about 100μ m.

Adjunct Detergent Ingredients Adjunct detergent ingredients can be included in the process as well and include bleaches, bleach activators, suds boosters or suds suppressors, anti-tarnish and anticorrosion agents, soil suspending agents, soil release agents, germicides, pH adjusting agents, chelating agents, smectite clays, enzymes, enzyme-stabilizing agents and perfumes. See U.S. Patent 3,936,537, issued February 3, 1976 to Baskerville, Jr. et al., incorporated herein by reference.

An alkaline inorganic salt may be used when a liquid acid precursor of a surfactant is used so as to provide a neutralizing agent in the agglomeration step. Other adjunct ingredients preferably includes a detergent aluminosilicate builder referenced as aluminosilicate ion exchange materials and sodium carbonate. The aluminosilicate ion exchange materials used herein as a detergent builder preferably have both a high calcium ion exchange capacity and a high exchange rate. Without intending to be limited by theory, it is believed that such high calcium ion exchange rate and capacity are a function of several interrelated factors which derive from the method by which the aluminosilicate ion exchange material is produced. In that regard, the aluminosilicate ion exchange materials used herein are preferably produced in accordance with Corkill et al, U.S. Patent No. 4,605,509 (Procter & Gamble), the disclosure of which is incorporated herein by reference.

Preferably, the aluminosilicate ion exchange material is in "sodium" form since the potassium and hydrogen forms of the instant aluminosilicate do not exhibit as high of an exchange rate and capacity as provided by the sodium form. Additionally, the aluminosilicate ion exchange material preferably is in over dried form so as to facilitate production of crisp detergent agglomerates as described herein. The aluminosilicate ion exchange materials used herein preferably have particle size diameters which optimize their effectiveness as detergent builders. The term "particle size diameter" as used herein represents the average particle size diameter of a given aluminosilicate ion exchange material as determined by conventional analytical techniques, such as microscopic determination and scanning electron microscope (SEM). The preferred particle size diameter of the aluminosilicate is from about 0.1 micron to about 10 microns, more preferably from about 0.5 microns to about 9 microns. Most preferably, the particle size diameter is from about 1 microns to about 8 microns.

Preferably, the aluminosilicate ion exchange material has the formula Na_z[(AI0₂)z-(Siθ2)y]xH₂0 wherein z and y are integers of at least 6, the molar ratio of z to y is from about 1 to about 5 and x is from about 10 to about 264. More preferably, the aluminosilicate has the formula

Na<|2[(Alθ2)i2*(Siθ2)<|2]xH2θ wherein x is from about 20 to about 30, preferably about 27. These preferred aluminosilicates are available commercially, for example under designations Zeolite A, Zeolite B, Zeolite P, Zeolite MAP and Zeolite X. Alternatively, naturally-occurring or synthetically derived aluminosilicate ion exchange materials suitable for use herein can be made as described in Krummel et al, U.S. Patent No. 3,985,669, the disclosure of which is incorporated herein by reference. The aluminosilicates used herein are further characterized by their ion exchange capacity which is at least about 200 mg equivalent of CaCθ3 hardness/gram, calculated on an anhydrous basis, and which is preferably in a range from about 300 to 352 mg equivalent of CaCθ3 hardness/gram. Additionally, the instant aluminosilicate ion exchange materials are still further characterized by their calcium ion exchange rate which is at least about 2 grains Ca⁺⁺/gallon/minute/-gram/gallon, and more preferably in a range from about 2 grains Ca⁺⁺/gallon/minute/-gram/gallon to about 6 grains Ca⁺⁺/gallon/minute/- gram/gallon .

Other builders can be generally selected from the various water-soluble, alkali metal, ammonium or substituted ammonium phosphates, polyphosphates, phosphonates, polyphosphonates, carbonates, borates, polyhydroxy sulfonates, polyacetates, carboxylates, and polycarboxylates. Preferred are the alkali metal, especially sodium, salts of the above. Preferred for use herein are the phosphates, carbonates, C-|rj-18 f^attv acids, polycarboxylates, and mixtures thereof. More preferred are sodium tripolyphosphate, tetrasodium pyrophosphate, citrate, tartrate mono- and di-succinates, and mixtures thereof (see below).

In comparison with amorphous sodium silicates, crystalline layered sodium silicates exhibit a clearly increased calcium and magnesium ion exchange capacity. In addition, the layered sodium silicates prefer magnesium ions over calcium ions, a feature necessary to insure that substantially all of the "hardness" is removed from the wash water. These crystalline layered sodium silicates, however, are generally more expensive than amorphous silicates as well as other builders. Accordingly, in order to provide an economically feasible laundry detergent, the proportion of crystalline layered sodium silicates used must be determined judiciously.

The crystalline layered sodium silicates suitable for use herein preferably have the formula

NaMSi_xθ2χ+l ^#yH2θ wherein M is sodium or hydrogen, x is from about 1.9 to about 4 and y is from about 0 to about 20. More preferably, the crystalline layered sodium silicate has the formula

NaMSi2θ5^«yH2θ wherein M is sodium or hydrogen, and y is from about 0 to about 20. These and other crystalline layered sodium silicates are discussed in Corkill et al, U.S. Patent No. 4,605,509, previously incorporated herein by reference.

Specific examples of inorganic phosphate builders are sodium and potassium tripolyphosphate, pyrophosphate, polymeric metaphosphate having a degree of polymerization of from about 6 to 21 , and orthophosphates. Examples of polyphosphonate builders are the sodium and potassium salts of ethylene diphosphonic acid, the sodium and potassium salts of ethane 1-hydroxy-1 , 1-diphosphonic acid and the sodium and potassium salts of ethane, 1 ,1 ,2-triphosphonic acid. Other phosphorus builder compounds are disclosed in U.S. Patents 3,159,581 ; 3,213,030; 3,422,021 ; 3,422,137; 3,400,176 and 3,400,148, all of which are incorporated herein by reference.

Examples of nonphosphorus, inorganic builders are tetraborate decahydrate and silicates having a weight ratio of Si0₂ to alkali metal oxide of from about 0.5 to about 4.0, preferably from about 1.0 to about 2.4. Water-soluble, nonphosphorus organic builders useful herein include the various alkali metal, ammonium and substituted ammonium polyacetates, carboxylates, polycarboxylates and polyhydroxy sulfonates. Examples of polyacetate and polycarboxylate builders are the sodium, potassium, lithium, ammonium and substituted ammonium salts of ethylene diamine tetraacetic acid, nitrilotriacetic acid, oxydisuccinic acid, mellitic acid, benzene polycarboxylic acids, and citric acid.

Polymeric polycarboxylate builders are set forth in U.S. Patent 3,308,067, Diehl, issued March 7, 1967, the disclosure of which is incorporated herein by reference. Such materials include the water-soluble salts of homo- and copolymers of aliphatic carboxylic acids such as maleic acid, itaconic acid, mesaconic acid, fumaric acid, aconitic acid, citraconic acid and methylene malonic acid. Some of these materials are useful as the water-soluble anionic polymer as hereinafter described, but only if in intimate admixture with the non-soap anionic surfactant. Other suitable polycarboxylates for use, herein are the polyacetal carboxylates described in U.S. Patent 4,144,226, issued March 13, 1979 to Crutchfield et al, and U.S. Patent 4,246,495, issued March 27, 1979 to Crutchfield et al, both of which are incorporated herein by reference. These polyacetal carboxylates can be prepared by bringing together under polymerization conditions an ester of glyoxylic acid and a polymerization initiator. The resulting polyacetal carboxylate ester is then attached to chemically stable end groups to stabilize the polyacetal carboxylate against rapid depolymerization in alkaline solution, converted to the corresponding salt, and added to a detergent composition. Particularly preferred polycarboxylate builders are the ether carboxylate builder compositions comprising a combination of tartrate monosuccinate and tartrate disuccinate described in U.S. Patent 4,663,071 , Bush et al., issued May 5, 1987, the disclosure of which is incorporated herein by reference. Bleaching agents and activators are described in U.S. Patent 4,412,934,

Chung et al., issued November 1 , 1983, and in U.S. Patent 4,483,781 , Hartman, issued November 20, 1984, both of which are incorporated herein by reference. Chelating agents are also described in U.S. Patent 4,663,071 , Bush et al., from Column 17, line 54 through Column 18, line 68, incorporated herein by reference. Suds modifiers are also optional ingredients and are described in U.S. Patents 3,933,672, issued January 20, 1976 to Bartoletta et al., and 4,136,045, issued January 23, 1979 to Gault et al., both incorporated herein by reference.

Suitable smectite clays for use herein are described in U.S. Patent 4,762,645, Tucker et al, issued August 9, 1988, Column 6, line 3 through Column 7, line 24, incorporated herein by reference. Suitable additional detergency builders for use herein are enumerated in the Baskerville patent, Column 13, line 54 through Column 16, line 16, and in U.S. Patent 4,663,071 , Bush et al, issued May 5, 1987, both incorporated herein by reference. In order to make the present invention more readily understood, reference is made to the following examples, which are intended to be illustrative only and not intended to be limiting in scope.

EXAMPLES l-ll These Examples illustrate one embodiment of the process invention. Specifically, a low bulk density detergent composition is prepared in a batch mode using a lab tilt-a-pin mixer (commercially available from Processall, Inc.). The mixer is first charged with a mixture of dry powders, namely sodium carbonate (median particle size 5-40 microns made via Air Classifier Mill), light bulk density sodium tripolyphosphate (referenced herein as "STPP" and supplied by FMC Corp.), sodium sulfate (median particle size of 5 - 40 microns made via Air Classifier Mill), sodium bicarbonate (median particle size of 5-40 microns made via Air Classifier Mill), granular citric acid monohydrate (median particle size of approximately 400 - 600 microns supplied by Wako Chemicals, Japan) and undersized finished agglomerates having a median particle size of less than 150 microns to mimic the recycling of such undersized particles during continuous large-scale modes of the current process. Neutralized surfactant paste of coconut fatty alcohol sulfate is premixed with Sodium Bicarbonate ground in a Air Classifier mill to 5-40 microns and added on top of the powder mixture in the mixer. Table I

Agglomerate Component in grams i j]

CFAS paste (70% active) 228 228 fiine Sodium Bicarbonate premixed with paste 28 fine sodium Carbonate 178 178

STPP 185 185 fiine Sodium Bicarbonate 50 fine Sodium Sulfate 106

Recycled fines (<150 microns) 250 250 Citric Acid monohydrate 28

Mixer Conditions :

Premix Time (seconds) 2 2

Paste addition Time (seconds) 8-10 8-10

Post mix Time (seconds) 6-8 1-2

Mixer RPM 400 1200

Mixer Jacket Temperature (deg C) 21 21

Mixer Pin Gap (mm) 5.5 5.5

Median Particle Size (microns) 425 325 - 400 Bulk Density (g/l) 470 650 -700

As can be seen from Table I, the densities of the agglomerates produced in

Example I is unexpectedly low after addition of citric acid and sodium bicarbonate in the instant process invention.

In addition void spaces can be observed on micrograph of example I.

They are prominent in the oversized agglomerates (greater than 1180 microns).

This is due to the larger starting particle size of citric acid monohhydrate. This can be achieved in the undersize of 1180 microns by suitably lowering the particle size of citric acid monohydrate. Further analysis shows 27.7% sodium citrate in the oversize (greater than 1180 microns) and 2.3% sodium citrate in the undersize (through 1180 microns) supporting the microscopic observation of the agglomerates.

Having thus described the invention in detail, it will be clear to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is described in the specification.

Claims

WHAT IS CLAIMED IS:

1. A process for preparing a low bulk density detergent composition comprising the steps of:

(a) agglomerating a binder, an organic acid source, and a carbonate source in a mixer to obtain detergent agglomerates, wherein the organic acid source and the carbonate source react and generate gas within the agglomerate;

(b) drying the detergent agglomerate so as to form the detergent composition having a bulk density of below about 600 g/l.

2. The process according to claim 1 , wherein the bulk density of the detergent composition is from about 350 g/l to about 500 g/l.

3. The process according to claim 1 , wherein the acid source is selected from acids and hydrated or anhydrous salts of acids and is a mono or polycarboxylic acid selected from the group consisting of citric, malic, maleic, fumaric aspartic, glutaric, tartaric, malonic, succinic or adipic acid, 3 chetoglutaric acid, citramalic acid, and mixtures thereof.

4. The process according to claim 1 , wherein the carbonate source is a carbonate and/or bicarbonate having a mean particle size of about 4 microns or greater.

5. The process according to claim 1 wherein the mixer has a mean residence time of from about 5 to about 30 seconds and a tip speed in the range from about 5 m/s to about 10 m/s, and wherein the energy per unit mass in the mixer is from about 0.15 kj/kg to about 4.20 kj/kg.

6. The process according to claim 1 wherein the binder is a detergent surfactant paste having a viscosity of from about 5,000 to about 100,000 cps.

7. The process according to claim 1 , wherein the mixer is a high speed mixer and wherein the process further comprises a step mixing the detergent agglomerates in a moderate speed mixer after the agglomerating step and before the drying step to further agglomerate the detergent agglomerates.

8. The process according to claim 1 wherein the detergent binder and the carbonate source are first premixed before the addition of the organic acid source in the mixer.

9. A process for preparing a low bulk density detergent composition comprising the steps of:

(a) agglomerating a detergent binder, an organic acid source, and a carbonate source in a high speed mixer to obtain detergent agglomerates, wherein the organic acid source and the carbonate source react and generate gas within the agglomerate;

(b) mixing said detergent agglomerates in a moderate speed mixer to further agglomerate the detergent agglomerate; and

(c) drying the detergent agglomerate so as to form the detergent composition having a bulk density of below about 600 g/l.

10. A low bulk density detergent composition made according to the process of claims 1 or 9.