US3367880A - Rapidly disintegrating detergent tablets and method of producing same - Google Patents

Description

United States Patent 3,367,880 RAPHDLY DISINTEGRATING DETERGENT TABLET AND METHQD 0F PRODUCING SAME Russell R. Keast, Yardley, Pan, and Allan R. Wirth, Hopewell, and John S. Thompson, Princeton Junction, N.J., assignors to FMC Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed July 8, 1964, Ser. No. 381,216 Claims. (Cl. 252-438) ABSTRACT OF THE DISCLOSURE Process for producing strong but fast dissolving detergent tablets containing about 35 to 65% by weight of sodium tripolyphosphate, 3 to about by weight of sodium silicate and 5 to about 15% by weight of a water soluble, non-soap organic synthetic detergent, wherein compacted sodium tripolyphosphate having a density of from about 1.0 to about 1.25 g./ cc. and having a hydration time of less than about 3 minutes is utilized as the sodium tripolyphosphate in said tablets.

This invention relates to the process for making heavyduty detergent tablets, and more specifically, to the production of detergent tablets which have an unusually high disintegration rate when placed in heated wash water, but which are sufiiciently strong in the dry state towithstand breakage.

Heavy-duty, built, synthetic detergent tablets have become increasingly popular compared with liquid or powdered detergent compositions because of the more desirable handling characteristics which these tablets have. These tablets obviate the need for measuring cups used to dispense the powdered or liquid detergents required in domestic washing machines. They also eliminate spillage and the problem of storing bulky detergent containers. In normal manufacture, the heavy-duty detergent formulations are blended and pressed into tablets so that they have sufficient strength to resist breakage in handling and use, but are capable of disintegration in an acceptable time in wash water under conditions normally found in domestic Washing machines.

In the makeup of detergent tablets, the principal ingredients employed are a phosphate builder such as sodium tripolyphosphate, an anti-redeposition agent such as sodium carboxymethylcellulose, an anionic or nonionic surfactant and an anti-corrosion agent such as sodium silicate. In general these ingredients are mixed together to form a homogeneous dry mixture and are compressed in a mold to form a tablet. Of these ingredients, the surfactant and the phosphate builder are used as the principal cleaning components. The anti-redeposition agent is employed to prevent dirt from being redeposited on the washed clothes in the wash water, and the anti-corrosion agent is added to prevent the alkaline detergent solution from attacking the metallic parts of the washing machine. In addition, some formulas also contain inert ingredients such as sodium sulfate which is added as an extender to obtain the desired bulk density in the pelletizing mix and to yield a smoother and more solid appearing tablet.

In the makeup of detergent tablets it has been customary to use low bulk density sodium tripolyphosphate, i.e. having a density of from about 0.35 to about 0.6 g./cc. This is desirable because the extremely light, fluffy sodium tripolyphosphate can be compressed in the detergent tablet leaving a sufi'icient number of voids in the tablet to accelerate disintegration of the resultant tablet in the wash Water.

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A problem that has arisen in the manufacture of detergent tablets is the inability to produce faster dissolving tablets without also diminishing the strength of the dry tablets to withstand the shocks of packaging, handling, dispensing, and the like.

One approach to obtaining faster dissolution of the highly compressed tablets is the addition of additives such as CO generators, starch, or other inert materials which increase disintegration. However, many of these materials are expensive and are undesirable as ingredients in the detergent tablet and therefore have not met with wide success. Other techniques such as using low ram pressures during the pressing of the tablets have been proposed but have not been successful because the resultant tablet is not sufiiciently strong to withstand normal dry handling.

As a result there is a need for a process for producing a detergent tablet whose strength in the dry state is comparable with other tablets presently used in the art, but whose disintegration rate in the wash water used in conventional washing machines is substantially increased over conventional tablets.

It is an object of the present invention to produce a detergent tablet having acceptable dry strength but whose dissolving rate is extremely high compared with conventional detergent tablets.

These and other objects will be apparent from .the following description.

We have made a surprising discovery that detergent tablets which are made up with a compacted sodium tripolyphosphate having a density of from about 1.0 to about 1.25 g./ cc. and a hydration time of less than about three minutes, have an extremely fast dissolving rate and also have good dry strentghs sufficient to withstand normal handling and packaging.

It is most surprising that a highly dense sodium tripolyphosphate yields a tablet having fast dissolving rates since only low bulk density sodium tripolyphosphate (which is used to make up conventional detergent tablets) produces the large amounts of air voids within the tablet which are considered mandatory to fast dissolving rates. The general belief prevalent in the detergent industry has been that the more dense sodium tripolyphosphate is not suitable for incorporation in detergent tablets because its denseness would preclude a fast dissolving tablet.

A method for producing a compacted sodium tripolyphosphate product having a bulk density of from about 1.0 to about 1.2 and having a hydration rate of less than about three minutes is reported in our co-pending application, Ser. No. 289,315, filed on June 20, 1963 in the names Henry L. Marschall, et al. The term hydration rate refers to the period of time .required for the hydration of a given sample of sodium tripolyphosphate and is carried out as follows:

One hundred mls. of water at 80 to 84 F. is placed in a clean, dry, l-pint, Wide-mouthed vacuum jar. A rotarydriven stirrer is inserted with a blade near the bottom of the jar and set at 400 r.p.m. Twenty-five grams of anhydrous sodium sulfate is then added to the vacuum jar. When the anhydrous sodium sulfate is dissolved, the stirrer speed is decreased to 200 r.p.m. and the solution temperature is adjusted to 80 to 84 F. A -gram sample of the sodium tripolyphosphate to be tested is then added evenly to the liquid over a period of 15 to 20 seconds. When all of the sodium tripolyphosphate has been added, a timer is begun. The surface of the mixture is observed and when all circular motion of the surface stops, excepting the area directly adjacent to the stirrer shaft, the end point has been reached and the timer is stopped. The approach of the end point is easily detectable because the sodium tripolyphosphate-water mixture thickens a minute or so before the end point occurs and the mixture is so thick that the slurrying action becomes very sluggish. When the circulatory motion of the surface stops, this indicates that the end point has been reached. This does not include the small area directly adjacent to the stirrer shaft.

Conventional sodium tripolyphosphate normally has a hydration time of from about 6 to 12 minutes while compacted sodium tripolyphosphate normally has a hydration time of less than 3 minutes.

In the practice of this invention, the detergent formulation is made up as follows: The principal ingredient, the compacted sodium tripolyphosphate, is measured into the detergent formulation in amounts suflicient to constitute from about 35 to about 65% by weight of the detergent formulation. The preferred range of sodium tripolyphosphate is from about 50 to about 65% by weight with about 58% being the optimum amount.

The next added ingredient is the surface active agent (surfactant). The surfactant, which can be used in the makeup of the formulation, may be either nonionic or anionic; certain cationic surfactants cannot be employed because they are incompatible with the compacted sodium tripolyphosphate. The surfactant is added to the mixture in amounts of from about to about 15% by weight of the formulation. Ten percent by weight is generally considered optimum.

To the above mixture is added a sodium silicate having a Na O/SiO mole ratio of from about 1:2 to about 1 :3.2 in amounts of from about 3% to about 15% by weight of the formulation. Generally, about 7% of 81.5% active sodium silicate having a Na O/SiO mole ratio of 1:2 has been found to give good results. In general the optimum amounts of sodium silicate normally supply from about 3 to about 3.5 weight percent of SiO to the formulation.

The next added ingredient is sodium sulfate which constitutes the remaining major portion of the formulation. The sodium sulfate is an inert filler which is added to control the bulk density of the tableting mixture and to improve the surface appearance of the tablets by giving them a smoother and more compact appearance. In addition, there is also added small amounts of auxiliary compounds such as sodium carboxymethyl-cellulose, generally in amounts of from about 0.2 to about 1.5%, foam stabilizers such as lauroyl diethanolamide, tarnish inhibitors, fluorescent brighteners, perfumes, bacteriosta-ts, coloring matter, etc. The resultant mixture thus formulated is uniformly mixed and pressed into tablets. The pressing is normally accomplished using pressures of from about 175 to about 200 p.s.i. and the finished tablet has a bulk density of from about 0.8 to about 1.3 with about 1.02 being preferred. The newly formed tablets normally have strengths (when pressed on edge) of from about 10 to about pounds. If the tablets are suitably aged for at least 24 hours, they have a strength (when pressed on edge) of up to about 25 pounds. Desirably, these tablets have dissolving times of less than 120 seconds when placed in a conventional washing machine containing water at 120 F.

In the makeup of these detergent tablets, the compacted sodium tripolyphosphate preferably has a bulk density of from about 1.0 to about 1.25 g./cc. Further, the sodium tripolyphosphate should be made up of substantially all -16+100 mesh fraction and should contain no more than about 20% 70 mesh.

The anionic surface active agents are useful in the present formulations in amounts of from about 5% to about 15 by weight of the formulation. These anionic surface active agents are non-soap synthetic detergents made up of water-soluble salts or organic sulfuric reaction products having from about 8 to about 18 carbon atoms in the form of an alkyl or acyl radical with the molecular structure and containing sulfuric or sulfonic acid ester radicals. Typical examples of these anionic surface active agents are sodium or potassium alkyl benzene sulfonates in which the alkyl group contains from about 8 to about 18 carbon atoms, e.g. sodium dodecyl benzene sulfonate, sodium tridecyl benzene sulfonate; the sodium and potassium alkyl glycerol ether sulfonates, including ethers of higher fatty alcohols derived from the reduction of coconut oils; the reaction products of higher fatty acids, e.g. coconut oil with sodium or potassium isethionate; sodium or potassium alkyl sulfonates and sulfates obtained by sulfonation or coconut or tallow fatty alcohols and mixtures of such alkyl sulfates; dialkyl esters of sodium or potassium salts of sulfosuccinic acid; sodium and potassium salts of sulfated or sulfonated monoglycerides, e.g. those derived from coconut oil; sodium or potassium salts of higher fatty alcohol esters of sulfocarboxylic acids,- e.g. sodium salt of lauryl alcohol ester of sulfoacetic acid; and other anionic agents set forth in US. Patent 2,486,921 issued to Byerly on Nov. 1, 1949. If desired, the anionic surfactant can be added in the form of a dense, dry bead or as a flake admixed with sodium sulfate. In this latter case, the sodium sulfate constitutes a portion of the total sodium sulfate used in making up the entire mixture.

The sodium silicate that is added to the mixture normally constitutes from about 3 to about 15% by weight of the detergent formulation. The mole ratio of Na O/ in the sodium silicate determines the degree of alkalinity of this compound; as the ratio approaches 1:2 the sodium silicate becomes more alkaline. Ratios above 1:2, e.g. 1:1 are generally too alkaline and cause the wash water to reach pH levels which are unsafe for certain fibers. Ratios below 1:2.2, e.g. 1:4, dissolve too slowly and are not effective.

The nonionic surface active agents useful in the present invention are non-soap synthetic detergents made up of a water solubilizing polyoxyethylene group in chemical combination with an organic hydrophobic compound. Among the hydrophobic compounds which can be used are polyoxypropylene, the reaction product of propylene oxide and ethylene diamine, aliphatic alcohols, etc. Examples of nonionic synthetic detergents useful in the present invention are, condensation products of 6 to 30 moles of ethylene oxide, and preferably 7 to 11 moles, with 1 mole of an alkyl phenol containing 6 to 12 carbon atoms in the alkyl group; condensation products of 6 to 30 moles of ethylene oxide with 1 mole of an aliphatic straight or branch chained alcohol containing 8 to 18 carbon atoms; condensation products of ethylene oxide and the reaction product of propylene oxide and ethylene diamine; nonyl phenol polyethoxy ethanol (commercially known as Triton N series); isooctyl phenol polyethoxy ethanol (commercially known as Triton X series). Another well known group of nonionic detergents is known under the trade name of the Pluronic series. These compounds are the reaction products obtained by condensing ethylene oxide with a hydrophobic base produced by the condensation of propylene oxide with propylene glycol, and have molecular weights on the order of about 1800. The addition of polyoxyethylene radicals to the hydrophobic base increases the water solubility of the nonionic detergent and concurrently increases the foam ing properties of the detergent in aqueous solution in proportion to the mole ratio of polyoxyethylene radicals to the hydrophobic base. In general, a surfactant which has a mole ratio of 7.5 moles of ethylene oxide per mole of an alkyl phenol, e.g. nonylphenol, is low-foaming while one with a mole ratio of 10:1 foams moderately. The molecular weight of these nonionic synthetic detergents will range from as low as 800 up to about 11,000.

Nonionic surfactants should be added to the present formulation in amounts of about 6% by weight of the total formulation or above in order for the surfactant to be completely effective. Amounts below about 6% reduce the cleaning action of the detergent and should be avoided. Amounts over 14% similarly should be avoided because the nonionic surfactant tends to exude or oil out of the detergent formulation when it is pressed into tablets. Within the range of 6% to 14%, the nonionic surfactant gives effective washing action, and has been found to be effective as a binder for the remainder of the detergent formulation without oiling out of the pressed tablet.

After the ingredients have been uniformly mixed together the resulting dry mixture should have a bulk density in the range of from about 0.4 to about 0.85 g./cc. with the preferred bulk density being about 0.7 g./cc. Predetermined quantities of this mixture are then fed to a die and pressed at from 100 to about 350 psi. to yield a tablet havinga bulk density of about 1.02 g./cc. The resulting tablet has the following formulation:

Percent by weight Sodium tripolyphosphate 35 to 65 Sodium silicate 3 to 15 Sodium carboxyrnethylcellulose 0.2 to 1.5 Anionic or nonionic surface active agent to 15 Sodium sulfate Balance In the procedure of tableting this detergent formulation, it has been found that small portions of the pressed mixture do not adhere to the dies, nor is there any capping during the pressing of this formulation. The term capping refers to the internal horizontal separation of the tablet into two or more pieces because of the adherence of these pieces to each of the dies. In general, the use of standard dies is eminently. satisfactory without special provisions for rotation of the dies during the pressing operation.

The resulting pressed tablets may be subjected, it de sired, to steaming in order to hydrate a surface layer of hydratable components, e.g. sodium tripolyphosphate and sodium sulfate. The steaming helps form a film or layer of increased strength to help prevent fracturing of the product during normal handling. This steaming is helpful because the hydratable ingredients crystallize with such action that they create a binding force between adjacent particles. In addition, the application of moisture makes the surface more homogeneous, thereby increasing the surface density and the cohesive force between the particles.

The following examples are given to illustrate the invention and are not deemed to be limiting thereof:

EXAMPLE I Run A.--The following anionic detergent formulations were mixed in a Kitchen-Aid planetary mixer (Model 4-C, Hobart Manufacturing 00., Troy, Ohio) for about 3 /2 minutes.

INGREDIENTS Sodium Tripolyphosphate Spray- Formula Bulk Hydration Dried Density Time Weight, g. Bead, g.

(minutes) A spraydriod powdered product containing the following products Percent by weight Sodium Tripolyphosphate 25 Anionic surfactant (sodium dodocylbenzone sulionate 100%) 26 Sodium Silicate (Na OISiOQ mole ratio 1:2.4) 5 Moisture 8-11 Sodium carboxyrnethylcellulose 0.67 Optical brightauers 0.2 Sodium sulfate a level of 1.4% by weight of the sodium tripolyphosphate. In Formula C, the fines level was 15% by weight of the sodium tripolyphosphate added. The tablets were then conditioned for approximately 16 hours in sealed jars at ambient room temperature before testing.

The tablets were tested for disintegration time by observing the time (in seconds) required for the tablets to be sufficiently reduced in size to allow escape from a /2 inch wire mesh cage suspended in a fixed position in a transparent-sided Kenmore washer containing F. agitating tap water. In addition, the crush strengths of the tablets were obtained by measuring the force in pounds needed to crush the tablets when placed on edge. The tablets were not steamed after manufacture to increase their crush strength in order to obtain the best possible reproducibility in test results. The results of the test are set forth in Tablet I.

Run B.By way of comparison, a detergent mixture (Formula D) was made up using the same proportion of ingredients as set forth in Run A with sodium tripolyphosphate having about the same density as the compacted sodium tripolyphosphate except that it was not produced by the compacted procedure and therefore retained a high hydration time of 7.4. When such tablets were pressed into identical tablets by the same procedure as set forth in Run A, the crush strengths and disintegration times set forth in Table I were obtained.

1 Qompacted. 2 Reg. rotary kiln.

Pursuant to the requirements of the patent statutes, the principle of this invention has been explained and exemplified in a manner so that it can be readily practiced by those skilled in the art, such exemplification including what is considered to represent the best embodiment of the invention. However, it should be clearly understood that, Within the scope of the appended claims, the invention may be practiced by those skilled in the art, and having the benefit of this disclosure otherwise than as specifically described and exemplified herein.

What is claimed is:

1. In a process for producing strong, heavy-duty detergent tablets having a fast dissolving rate, wherein a formulation comprising from about 35% to about 65% by weight of sodium tripolyphosphate, from about 3% to about 15% by weight of sodium silicate, and from about 5% to about 15% by weight of a water-soluble non-soap organic synthetic detergent selected from the group consisting of anionic detergents selected from the group consisting of the sodium and potassium salts of alkyl sulfates, alkyl sulfonates and alkyl aryl sulfonates having from about 8 to about 18 carbon atoms in the alkyl group, and nonionic detergents selected from the group consisting of the condensation products of about 6 to about 30 moles of ethylene oxide with one mole of an alkyl alcohol wherein the alkyl group contains from about 8 to about 18 carbon atoms, and the condensation products of about 7 to about 11 moles of ethylene oxide with one mole of an alkyl phenol wherein the alkyl group contains from about 6 to about 12 carbon atoms, is pressed into tablets having a bulk density of about 1.0 g./cc., the improvement consisting essentially of making up said formulation with sodium tripolyphosphate having a density of from about 1.0 g./ cc.

to about 1.25 g./cc. and a hydration time of less than about 3 minutes, said sodium tripolyphosphate being produced by passing an aqueous sodium orthophosphate mixture through a heated zone to obtain an initial, particulate sodium tripolyphosphate having a bulk density of about 0.4 to about 1.2 g./cc., compacting particles of said initial sodium tripolyphosphate at temperatures below about 350 C. to form non-friable, compacted particles and grinding said compacted particles into granular, sodium tripolyphosphate, whereby the dissolving rate of said tablets is increased without diminishing the dry strength of said tablets.

2. The process of claim 1 in which the formulation contains from about 50% to about 65% by weight of sodium tripolyphosphate.

3. The process of claim 1 in which the watersoluble non-soap organic synthetic detergent is sodium dodecylbenzene sulfonate.

4. In a process for producing strong, heavy-duty detergent tablets having a fast dissolving rate, wherein a formulation comprising about 58% by weight of sodium tripolyphosphate, about 5% by weight of sodium silicate. from about 5% to about by weight of a watersoluble non-soap organic synthetic detergent selected from the group consisting of anionic detergents selected from the group consisting of the sodium and potassium salts of alkyl sulfates, alkyl sulfonates and alkyl aryl sulfonates having from about 8 to about 18 carbon atoms in the alkyl group, and nonionic detergents selected from the group consisting of the condensation products of about 6 to about 30 moles of ethylene oxide with one mole of an alkyl alcohol wherein the alkyl group contains from about 8 to about 18 carbon atoms, and the condensation products of about 7 to about 11 moles of ethylene oxide with one mole of an alkyl phenol wherein the alkyl group contains from about 6 to about 12 carbon atoms, from about 0.2% to about 1.5% by weight of sodium carboxymethylcellulose and sodium sulfate, is pressed into tablets having a bulk density of about 1.0 g./cc., the improvement consisting essentially of making up said formulation with sodium tripolyphosphate having a density of from about 1.0 g./cc. to about 1.25 g./cc. and a hydration time of less than about 3 minutes, said sodium tripolyphosphate being produced by passing an aqueous sodium orthophosphate mixture through a heated zone to obtain an initial, particulate sodium tripolyphosphate having a bulk density of about 0.4 to about 1.2 g./cc., compacting particles of said initial sodium tripolyphosphate at temperatures below about 350 C. to

form non-friable, compacted particles and grinding said compacted particles into granular, sodium tripolyphosphate, whereby the dissolving rate of said tablets is increased without diminishing the dry strength of said tablets.

5. A novel heavy-duty detergent tablet having a fast dissolving rate consisting essentially of from about 35% to about by weight of sodium tripolyphosphate having a density of from about 1.0 g./cc. to about 1.25 g./cc. and a hydration time of less than about 3 minutes, said sodium tripolyphosphate being produced by passing an aqueous sodium orthophosphate mixture through a heated zone to obtain an initial, particulate sodium tripolyphosphate having a bulk density of about 0.4 to about 1.2 g./cc., compacting particles of said initial sodium tripolyphosphate at temperatures below about 350 C. to form non-friable, compacted particles and grinding said compacted particles into granular, sodium tripolyphosphate, from about 3% to about 15% by weight of sodium silicate, from about 5% to about 15% by weight of a water-soluble non-soap organic synthetic detergent selected from the group consisting of anionic detergents selected from the group consisting of the sodium and potassium salts of alkyl sulfates, alkyl sulfonates and alkyl aryl sulfonates having from about 8 to about 18 carbon atoms in the alkyl group, and nonionic detergents selected from the group consisting of the condensation products of about 6 to about 30 moles of ethylene oxide with one mole of an alkyl alcohol wherein the alkyl group contains from about 8 to about 18 carbon atoms, and the condensation products of about 7 to about 11 moles of ethylene oxide with one mole of an alkyl phenol wherein the alkyl group contains from about 6 to about 12 carbon atoms, from about 0.2% to about 1.5% b weight of sodium carboxymethylcellulose, the balance of the formulation being made up of sodium sulfate, said detergent tablets having a bulk density of about 1.0 g./cc.

References Cited UNITED STATES PATENTS 3,081,267 3/1963 Laskey 252 FOREIGN PATENTS 652,764 11/1962 Canada.

LEON D. ROSDOL, Primary Examiner.

B. BETTIS, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,367,880 February 6, 1968 Russell R. Keast et a1.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as showm below:

Column line 34, "strentghs" should read strengths Column 3, l1ne 71, "with" should read within Column 4, l1ne 31, "1:2.2" should read H 1:3.2 Column 6, line 17 "Tablet" should read Table Signed and sealed this 23rd day of September 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, JR.