US3870649A - Process for comminuting fluorescent whitening agents and compositions obtained thereby - Google Patents

Abstract

A process for comminuting relatively large crystals of a solid fluorescent whitening agent to a particle size of approximately 5 microns in the largest dimension which comprises grinding either a dry presscake or a water-containing presscake of said agent in admixture with anhydrous sodium sulfate.

Description

United States Patent Langstroth ]*Mar. 11, 1975 PROCESS FOR COMMINUTING [51] Int. Cl D06l 3/12 FLUORESCENT WHITENING AGENTS AND [58] Field Of Search 252/3013 W COMPOSITIONS OBTAINED THEREBY [75] Inventor: Theodore A. Langstroth, Cincinnati, [56] References C'ted Ohio UNITED STATES PATENTS 73 Assignee; Sterling Drug Inc New York 3,472,842 l0/l969 Hausermann et al. 260/240 B 3,511,833 5/1970 Tscharner 260/240 B Notice: The portion of the term of this Patent q fl to 25/ 1990 Primary Examiner-Arthur P. Demers has been dlsclalmed- Attorney, Agent, or FirmLynn T. Fletcher; B. 22 Filed: June 1, 1973 Woodrow Wyatt 211 App]. NO.2 366,069 [57] ABSTRACT Related Application Data A process for comrninuting relatively large crystals of ClmIinuflIiW-in-Pa" 0f 201,193, Y- a solid fluorescent whitening agent to a particle size of 1971, No. 3,781,215, h c 15 3 approximately" 5 microns in the largest dimension f gf' of 839303 July which comprises grinding either a dry presscake or a 1969 water-containing presscake of said agent in admixture 52 US. CL... 252/3013 w, 241/30, 252/3012 w, anhydrous Sulfate 8 Claims, N0 Drawings 1 PROCESS FOR *COMMINUTING FLUORESCENT WHITENING AGENTS AND COMPOSITIONS QBTA INED THEREBY This application is a continuation-in-part of my prior copending US. patent application Ser. No. 201,198, filed Nov. 22, 1971, now U.S. 'Pat. No. 3,781,2l5 which is in turn a continuation-in part ofmy applica' tion Ser. No. 839,703, filed July 7, i969, copending with said application Ser. No. l,l98 and now abancloned.

This invention relatesto a proccssifor grinding solid particulate materials and to compositions of matter so obtained. More particularly, theiinvention relates to a process for comminuting solid fluorescent whitening agents and toarticles of manufacture comprising solid fluorescent whitening agent compositions useful for :in-

corporation into detergents.

Solid detergent compositions today universally contain fluorescent whitening agents, also called optical bleaches or optical brighteners. In general, the fluorescent whitening agents are amorphous or preferably crystalline solid organic compounds which are reasonably water-soluble by virtue of the presence in the molecule of one or more water-solubilizing substituents, for example the sulfonate anion and/or amine substituents. The compounds are ideally white, but in practice they are generally cream-colored to yellowish'powders, depending upon the nature of the compound itself, the form in which it exists (amorphous or crystalline, and the nature of the crystalline form) and the manner in which it is isolated and dried. Furthermore, a number of fluorescent whitening agents are rather sensitive to heat. and tend to turn yellow during the drying of the presscakes unless a low temperature is maintained. Moreover, certain fluorescent whitening agents, for reasons which are not fully understood, tend to turn yellow in color when ground to very fine particle size. The yellow color imparted to the whitening agents by the above-mentioned processes makes them less desirable for incorporation into white detergents because of the yellowish tint which may result in the detergent composition.

It is an object of the present invention to provide an effective method for comminuting relatively large crystals of a substantially white fluorescent whitening agent to an average particle size in the range of l to 15 microns, but preferably to approximately 5 microns in the largest dimension without undue yellowing of its color. It is another object of this invention to provide an efficient method for removing the excess water from presscakes of fluorescent whitening agents without subjecting the fluorescent whitening agent to high drying temperatures. It is yet another object of this invention to provide an effective method for simultaneously drying and grinding a relatively white fluorescent whitening agent without substantially yellowing the color of the product. And it is a further object of this invention to provide a novel fluorescent whitening agent composition consisting of finely-comminuted fluorescent whitening agent and a compatible, inert diluent in the form ofa free-flowing powder. As used herein, the term relatively large crystals means crystals substantially larger than five microns and generally in the range of to 100 microns or larger in the largest dimension.

It has now been found that all the aforementioned objects of the present invention can be accomplished 2 by'comminuting the crystalline'fluorescent whitening agent, eitherin the form ofa water-containing presscake or in theform ofa dry presscake, with anhydrous sodium sulfate. When a watencontaining presscake of the fluorescent whitening agent is to be comminuted,

there is employed as a minimal amount. a sufficient quantity of anhydrous sodium sulfateto completely interact with the water held by thepresscake. The compositions of this invention prepared from watercontaining presscakes thus contain hydrated sodium sulfate. The compositions may be utilized as such or may optionally be dried to remove the water ofhydration without undue yellowing of the color o'fthe composition.

In the first of its process aspects, this invention resides-in aprocessfor'treatingapresscake consisting essentially of water and relatively large crystals of a fluorescent whitening agent, which comprises grinding said presscake at a'temperatureof 20 to 60C in the presence of at least one and up to eight molecular equivalents of anhydrous sodium sulfate foreach ten molecular equivalents of water in said presscake until the crystals are reduced to an average particle size ofapproximately 5 microns with substantially none of the crystals greater than 15 microns in the largest dimension.

In a second process aspect, this invention resides in a process which comprises drying the product of the first process aspect above-described r0 remove some or all of the moisture content.

In a third process aspect, this invention resides in a process for treating a dried presscake consisting essentially of relatively large crystals ofa fluorescent whitening agent which comprises grinding said presscake in the presence of anhydrous sodium sulfate until the crystals are reduced to an average particle size of ap proximately 5 microns with substantially none of the crystals greater than 15 microns in the largest dimension.

in one of its composition aspects, the invention resides in an article of manufacture which comprises a relatively white fluorescent whitening agent in crystalline solid form having an average particle size of approximately 5 microns with substantially none of the crystals greater than 15 microns in the largest dimension and, in admixture therewith, crystalline sodium sulfate decahydrate.

In a second of its composition aspects, the invention resides in an article of manufacture which comprises a fluorescent whitening composition obtained in accordance with either the second or the third process aspect of this invention and having a moisture content of less than two precent consisting essentially of a crystalline fluorescent whitening agent having an average particle size of approximately 5 microns with substantially none of the crystals greater than 15 microns in the largest dimension and, in admixture therewith, anhydrous sodium sulfate.

In a third composition aspect, the invention resides in an article of manufacture prepared in accordancev with the first process aspect of this invention, which comprises a solid, particulate fluorescent whitening agent having an average particle size of approximately 5 microns with substantially none of the crystals greater than 15 microns in the largest dimension and, in admixture therewith, crystalline sodium sulfate decahydrate.

The manner and process of making and using the invention and the best mode comtemplated by the inventor of carrying out this invention will now be described so as to enable any person skilled in the art to which it pertains to make and use the same.

In accordance with the first process aspect of this invention a solid, crystalline fluorescent whitening agent in the form of a presscake, containing essentially only water and the fluorescent whitening agent, is admixed with anhydrous sodium sulfate and the mixture is ground by one or more of a number of grinding processes known to the art. The quantity of anhydrous sodium sulfate used depends chiefly on the amount of water present in the presscake and the particular active concentration of fluorescent whitening agent desired in the final composition. However, there must be used as a minimal quantity at least a sufficient amount of anhydrous sodium sulfate to interact completely with the water contained in the presscake for the formation of sodium sulfate decahydrate (Glaubers Salt). Thus, as a minimal amount, at least approximately one molecular equivalent of anhydrous sodium sulfate is used for each ten molecular equivalents of water in the presscake, as determined by routine analytical procedures.

Larger amounts of anhydrous sodium sulfate are used in preparing the compositions of this invention in accord with the first and third process aspects when it is desired to obtain a particular concentration or cut of active whitening agent in the composition. With regard .to the content of whitening agent, I have found that when compositions in which the concentration of fluorescent whitening agent ranges from about twenty to about eighty percent are employed in the proper amount to produce equal concentrations of whitening agent, substantially equivalent qualities of whitening effect. solubility and color effect in detergents are obtained. However, for practical use, I prefer to obtain compositions which have an active fluorescent brightening concentration in the range of approximately 35 to 70 percent and conversely a concentration of 65 to 30 percent of the inert non-whitening ingredient.

In accordance with the third process aspect of this invention a solid, crystalline fluorescent whitening agent in the form of a presscake, containing essentially only the fluorescent whitening agent, is admixed with anhydrous sodium sulfate and the mixture is ground by one or more of a number of grinding processes known to the art. However, it is desirable to select a grinding process in which there is provision for controlling the temperature of the material being ground in order to prevent excessive heating and thereby causing undue yellowing of the whitening compositions. I have found in this respect that the grinding operation carried out on the mixture of dry presscake and anhydrous sodium sulfate can be advantageously carried out at temperatures up to 100C without undue yellowing. However, I prefer to effect the grinding operation at a temperature in the range of to 80C. The quantity of anhydrous sodium sulfate used in accordance with the third process aspect ofthis invention depends on the particular active concentration of fluorescent whitening agent desired in the final composition. Generally, I prefer to carry out the grinding of the dry presscake in the presence of approximately to approximately 65 percent of anhydrous sodium sulfate by weight of the resultant mixture.

When a water-wet presscake of fluorescent whitening agent is employed in the processes of this invention, the presscake can have a wide range in the ratio of solids to water, for example, from about 40 to 80 percent of solids. However, I prefer to use thosewater-wet presscakes in which the solid content is in the range of approximately 40 to approximately 60 percent ofthe total weight of the wet presscake. When presscake containing the preferred proportion of solids (40 to 60 percent) is used, one to eight molecular equivalents of anhydrous sodium sulfate for each ten molecular equivalents of anhydrous sodium sulfate for each ten molecular equivalents of water in the presscake is sufficient to obtain compositions of the invention having the preferred concentrations (35 to percent) ofactive whitening agent specified above.

A more specific embodiment of the first process aspect of this invention comprises treating a presscake consisting essentially of water and relatively large crystals of a fluorescent whitening agent by grinding said presscake at a temperature of 20 to 60C in the presence of one molecular equivalent of anhydrous sodium sulfate for each ten molecular equivalents of water in said presscake until substantially all of said crystals are reduced to a diameter of less than approximately 5 microns. Thus, a mixture of approximately one molecular equivalent ofanhydrous sodium sulfate per each ten molecular equivalents of water in the presscake, as determined by routine analytical procedures, is during the initial stages either heated, or allowed to heat spontaneously, by virtue of friction and the heat of hydration ofsodium sulfate, to a temperature within the range 35 to 60C (that is, above the melting point of sodium sulfate dec'ahydrate, 324C), preferably about 50-60C. At this stage, the mixture becomes a paste or doughlike mass consisting of fluorescent whitening agent dispersed in molten sodium sulfate decahydrate. The mixture is then allowed to cool to approximately 33C (i.e., below the melting point of sodium sulfate decahydrate) and the mixture is ground at this temperature for from one-half to 2 hours, depending upon the size of the batch, the original size of the crystals of fluorescent whitening agent, and the nature of the particular fluorescent whitening agent being processed. The-temperature of the mixture is then allowed to fall to room temperature and the resulting dry, free-flowing powder consisting of finely comminuted fluorescent whitening agent dispersed in crystalline sodium sulfate decahydrate is collected.

The nature of the grinding apparatus is not critical in carrying out the processes of my invention, but for those grinding operations carried out on mixtures prepared from water-wet presscakes, I ordinarily prefer apparatus which is capable of exerting a shearing action on the relatively stiff pasty material and thus grinds the fluorescent whitening agent efficiently in the presence of the sodium sulfate as a grinding aid. An example of an efflcient apparatus for this purpose is a dough mixing machine commonly called a flusher fitted either with a sigma-type blade or a dispersion blade. The dough mixing machines are commonly jacketed and can be heated or cooled as desired.

I have also found that a two-roll mill in which the rolls rotate at different rates affords an excellent means of grinding the mixtures prepared from water-wet presscake. Such mills provide the highly desirable shearing action. Particularly advantageous for grinding these mixtures are two-roll mills which have rotation ratios in the range of 111.1 to 111.25 and which can be made to exert separation forces in the range 1,000 to 2,000 pounds per linear inch.

When a two-roll mill is employed as the grinding apparatus in the processes of this invention, the water-wet presscake and the anhydrous sodium sulfate are first intimately mixed or blended. The mixing is carried out in any conventional mixing or blending apparatus such as, for example, a flusher as described above or a ribbon-blender. The mixing is continued only long enough to insure complete blending and the mixture is then passed directly on to the two-roll mill. After passing through the mill, the composition is either pulverized directly or if desired in first dried and then pulverized.

I have found that grinding the mixtures prepared in accordance with the third process aspect of this invention, that is, those mixtures prepared from dry presscake and anhydrous sodium sulfate, it is not necessary to employ grinding apparatus which exerts a shearing action, but rather apparatus which effects the gringing by self-impact gives excellent results. Particularly useful for grinding these compositions are mills generally classified in the art of grinding as fluid energy mills. There are a number of advantages associated with the use of this type of mill, namely: the mixture being ground is readily held at a relatively low temperature during the grinding operation; dusting problems are held to a minimum; and the fluid energy mill permits a continuous grinding operation.

A more specific embodiment of the third process aspect of this invention comprises treating a dry presscake consisting essentially of relatively large unground crystals of a fluorescent whitening agent by blending said presscake with a quantity of anhydrous sodium sulfate sufficient to produce in the resultant mixture a concentration of the fluorecent whitening agent in the range of approximately 35 to approximately 70 percent by weight and a corresponding concentration of anhydrous sodium sulfate in the range of approximately 65 to 30 percent by weight. Any of a number of conventional blending techniques and types of apparatus can be utilized to prepare the mixture prior to the grinding operation. I have found that a ribbon-blender is particularly advantageous for preparing the subject blend. After blending, the dry, free-flowing mixture is passed through a fluid energy mill using for grinding energy pre-dried compressed air at approximately. 50C and approximately 90 pounds per square inch feed pressure and at approximately 120 pounds per square inch grinding pressure. The resulting dry, free-flowing powder consisting of fluorescent whitening agent comminuted to an average particle size ofapproximately 5 microns dispersed in sodium sulfate is collected.

It will be apparent that the compositions of this invention obtained as described above, by converting a watcrwet presscake to a free-flowing granular powder, retains substantially all the water from the presscake. Thus. when one molecular equivalent of anhydrous sodium sulfate is employed for each ten molecular equivalents of water in the presscake, the water is present in the final composition in the form of sodium sulfate decahydrate. For economic considerations and for some applications it is sometimes desirable to utilize substantially dry fluorescent whitening compositions and in these instances the compositions of this invention obtained as described above can be subjected to conventional drying techniques known to the art, for example, oven-drying or flash-drying to remove either some or all of the moisture content with substantially no deleterious effects on the color or effectiveness of the compositions. l have found that compositions in a state of complete dryness tend to absorb small quanti tits of moisture from the atmosphere and equilibrate in a range of approximately /2 to 1 /2 percent moisture content. The compositions dried to less than 2 percent are particularly preferred because in addition to possessing the excellent qualities previously noted, they also have excellent storage properties ordinarily encountered in commercial use.

The new processes of this invention are particularly adapted to treatment of fluorescent whitening agents employed in commerical detergents and fabric softeners thereby to produce compositions with the improved characteristics as herein indicated. The following compounds, useful as fluorescent whitening agcnts, are effectively dried and comminuted by my new process:

Disodium 4,4'-bis(4,6-dianilino-s-triazin-2-ylamino)- 2,2-stilbenedisulfonate Disodium 4,4'-bis(4-anilino-6-morpholino-s-triazin- Z-ylamino)'2,2-stilbcnedisulfonate Disodium 4,4-bis(4-anilino-6-[2,2-

dihydroxyethylamino]-s-triazin-2-ylamino)-2,2-

stilbenedisulfonate Disodium 4,4-bis(4-anilino-6-[2- hydroxyethylamino]-s-triazin-2-ylamino)-2,2-stilbenedisulfonate Sodium 2-(4-stilbyl)-naphtho[1',2:4,5]-l,2,3-

triazole-Z-sulfonate In contrast to the compositions of this invention, flu orescent whitening agents heretofore have been used in commerce either unground or ground in any of a number of common impact-type mills, for example, a hammer mill. Commercial fluorescent whitening agents produced by these known processes commonly average 15 microns or more in their largest dimension. It has also been known to subject fluorescent whitening agents of the type described herein to comminution in fluid energy mills. But such attempts have also been found to have a particle size limitation of approximately 10 microns inthe largest dimension. Efforts to reduce the size of these crystals further have heretofore yielded a product which is much too yellow in color to have value for use in modern detergents.

The composition according to the second composition aspect of the invention is characterized as a white to yellowish-white free-flowing powder which is readily soluble or dispersible in water or aqueous soap or synthetic detergent solutions and which has a moisture content of less than 2 percent. The composition consists essentially of approximately 35 to approximately percent by weight of the crystalline fluorescent whitening agent in finely divided form and approximately 65 to 30 percent by weight of anhydrous sodium sulfate.

The composition according to the third composition aspect of the invention contains from approximately 35 to approximately 70 percent by weight of sodium sulfate decahydrate and from approximatley 65 to approximately 30 percent by weight of dry fluorescent whitening agent is finely divided form. This composition is characterized as a white to yellowish-white free-flowing powder which is readily soluble or dispersible in water or aqueous soap or synthetic detergent solutions.

The compositions provided by this invention are useful as optical whitening and brightening agents, particularly when incorporated into solid detergent or soap compositions, liquid detergent formulations and textile softeners. They are also useful for whitening and brightening textiles and paper in the absence of detergents in accordance with procedures well known to the art. A decided advantage of the compositions of this invention over those of the prior art is the high degree of water solubility of the fluorescent whitening agent, even in cold water. Moreover, more efficient whitening is accomplished by the use of these compositions because of their improved solubility characteristics over the same compounds obtained in accordance with known methods.

The following example serves to further illustrate the invention without limiting the latter thereto.

EXAMPLE 1 A l-gallon laboratory flusher (dough mixer), fitted with a sigma-type blade and a heating and cooling jacket. was charged with a 1035 g presscake of disodium 4,4'-bis(4-anilino-6-morpholino-s-triazin-2- ylamino)-2,2 '-stilbenedisulfonate containing 73 percent solids [766 g of fluorescent whitening agent and 260 g (14.9 moles) of water]. Anhydrous sodium sulfate (206 g; 1.45 moles) was added, while mixing was continuously maintained, and then the mixture was heated to 55C. When the mass became paste-like, the temperature was lowered to 33C, and the mixing was continued for 1 hour. The mixture was then cooled to 28C, whereupon the paste-like mass solidified and was broken up by the blades into a fine granular powder. There was thus obtained 1,172 g ofproduct which contained approximately 65 percent of disodium 4,4- bis(4-anilino-6-morpholino-s-triazin-Z-ylamino)-2,2'- stilbenedisulfonate and approximately 35 percent sodium sulfate decahydrate. Examination of this product under the microscope showed that the fluorescent whitening agent existed as broken crystals averaging 3 microns with substantially no crystals greater than microns in the largest dimension.

The rate ofsolution of the above-described composition in water was determined by continuously measuring the fluorescence of a solution of the composition in contact with a weighed sample of the product. The fluorescence was measured on a Turner Fluorometer (G. K. Turner Associates, Palo Alto, California). Following are the data obtained, comparing the rate of solution of the above described composition of this invention with a standard sample of disodium 4,4'-bis(4-anilino-6'- morpholino-s-triazin-Z-ylamino-2,2'-stilbenedisulfonate dried and ground in the conventional manner. The crystals of the standard sample were needles or rods which had been ground in an impact-type grinding apparatus to an average size of 10-15 microns in length, according to the usual commercial procedure.

These data show that the composition of Example 1 dissolved approximately twice as rapidly as did the standard sample of fluorescent Whitening agent. The sample also showed approximately 25 percent stronger dyeing of cotton cloths after 5 and 10 minute washing cycles than did the standard sample of fluorescent whitening agent.

Detergent compositions incorporating the composition of Example 1 were prepared and were measured for color grade on a Hunterlab Model D25 Color and Color-Difference Meter (Hunter Associates Laboratory, lnc., Fairfax, Virginia), in accordance with the general method described in the Journal of the Optical Society of America, 48, 985 (1958). The abovedescribed composition was found to be within the range of color specifications required for use in detergent powders and desirably much whiter, pinker and bluer than the standard sample of fluorescent whitening agent which had been ground to equivalent particle size in the absence of sodium sulfate.

EXAMPLE 2 A laboratory blender (Kitchenaid Model KS-A manufactured by the Hobart Mfg. Co., Troy, Ohio) was charged with a 700 g presscake of disodium 4,4'-bis(4- anilino-o-morpholino-s-triazin-Z-ylamino)-2,2'-stilbenedisulfonate containing 68.8 percent solids [481g of fluorescent whitening agent and 219 g (12.2 moles) of water]. Anhydrous sodium sulfate (481 g; 3.39 moles) was added, while mixing was continuously maintained at room temperature. After approximately ten minutes, mixing was stopped and the powder-like mixture was passed through a two-roll mill at room temperature. The two-roll mill (manufactured by Reliable Rubber and Plastic Equipt. Mfg. Co., North Bergen, New Jersey) having two rolls six inches in diameter and thirteen inches in length, which rotate in a ratio of approximately 1:1.25, was set to exert separating forces in the range of 1,000 to 2,000 pounds per linear inch. The milled mixture was then dried in an oven at l05l 10C to a constant weight and was finally passed through a pulverizing machine (Mikro Pulverizer Type CF, manufactured by Pulverizing Machinery Div., Metals Disintegrating Inc., Summit, N.J.). The fine granular powder thus obtained contained approximately 51 percent of disodium 4,4'-bis-(4-anilino-6-morpholinos-triazin-2-ylamino)-2,2'-stilbenedisulfonate and approximately 49 percent of anhydrous sodium sulfate. Examination of this product under the microscope showed that the fluorescent whitening agent existed as broken crystals averaging 3 microns with substantially no crystals greater than 15 microns in their largest dimension.

The rate of solution of the above-described composition in water-was determined by following the same procedure described in Example 1 above.

Sample Temp. F 7( Dissolved Time (min) Example 2 5 do. do. 97 7 do. do. 100 l 1 Standard 80 90 23 do. do. 97 28 do. do. 100 3-1.5

These data show that the composition of Example 2 dissolved in approximately one-third the amount of time as did the standard sample of fluorescent whiten ing agent. This sample also exhibited approximately 25 percent stronger dyeing of cotton cloths after five and ten minute washing cycles than did the standard sample of fluorescent whitening agent.

Detergent compositions incorporating the composition of Example 2 were prepared and measured for color grade in accordance with the test procedure described in Example 1. The composition of Example 2 was found to be within the range of color specifications required for use in detergent powders and was found desirably to be much whiter, pinker and bluer than the standard sample of fluorescent whitening agent which had been ground to equivalent particle size in the absence of sodium sulfate.

EXAMPLE 3 Four thousand pounds of dried presscake consisting of crystalline disodium 4,4'-bis(4-anilino-6- morpholino-s-triazin-2-ylamino)-2,2'-stilbenedisulfonate having an average particle size of approximately X l5 microns was charged into a ribbon-blender together with 4,000 pounds of anhydrous sodium sulfate. The mixture was blended for 30 minutes and was then subjected to grinding in a Model No. 0304 Jet-O-Mizer Mill (a fluid energy attrition apparatus manufactured and supplied by the Fluid Energy Processing and Equipment Co., Lausdale, Pa.) using predried compressed air at a temperature of approximately 50C at the mill. The mill was operated at a mill nozzle pressure of 100 pounds per square inch and a feed nozzle pressure of 90 pounds per square inch. The blended composition was passed through the mill at a rate of approximately 1000 pounds per hour. The fine granular powder thus obtained contained approximately 50 per cent of disodium 4,4'-bis(4-anilino-o-morpholino-striazin-2-ylamino)-2,2-stilbenedisulf0nate and approximately 50 percent anhydrous sodium sulfate. Microscopic examination showed that the fluorescent whitening agent existed as broken crystals averaging 5 microns with substantially none of the crystals greater than microns in their largest dimension.

The above-described composition was found to have essentially the same rates of solution as those found for the composition of Example 2 above and was also found to exhibit approximately percent stronger dyeing of cottom cloths after 5 and 10 minute washing cycles than did the standard sample of fluorescent whitening agent.

Detergent compositions incorporating the composition of Example 3 were prepared and measured for color grade in accordance with the test procedure described in Example I. The composition of Example 3 was found to be within the range of color specifications required for use in detergent powders and was found desirably to be much whiter, pinker and bluer than the standard sample of fluorescent whitening agent which had been ground to equivalent particle size in the absence of sodium sulfate.

I claim:

1. A process for treating a presscake consisting essentially of water and relatively large crystals of a fluorescent whitening agent selected from the group consisting of disodium 4,4-bis-(4,6-dianilino-s-triazin-2- ylamino)-2,2-stilbenedisulfonate, disodium 4,4-'bis(4- anilino-6-morpholino-s-triazin-2-ylamino)-2.2-stilbenedisulfonate, disodium 4,4-bis(4-anilino-6-[2,2'- dihydroxyethylamino]-s-triazin-2-ylamino)-2,2-stilbenedisulfonate, disodium 4,4-bis(4-anilino-6-[2 hydroxyethylamino]-s-triazin-2-ylamino)-2,2-stilbenedisulfonate and sodium 2-(4-stilbyl)-naphtho-[l, 2':4,5]-l,2,3-triazole-2-sulfonate, which comprises grinding said presscake at a temperature of 20 to 60C in the presence of at least one and up to eight molecular equivalents of anhydrous sodium sulfate for each ten molecular equivalents of water in said prcsseake until the crystals are reduced to an average particle size of approximately 5 microns with substantially none of the crystals greater than 15 microns in the largest dimension.

2. A process according to claim 1 wherein the fluorescent whitening agent is disodium 4,4-bis(4-anilino- 6 m0rpholino-s-triazin-Z-ylamino)-2,2-stilbenedisulfonate.

3. A process according to claim 1 wherein the grinding is accomplished in the presence of approximately one molecular equivalent of anhydrous sodium sulfate for each 10 molecular equivalents ofwater in the presscake.

4. A process according to claim 3 wherein the fluorescent whitening agent is disodium 4,4'-bis(4-anilino- 6-morpholino-s-triazin-2-ylamino)2,2-stilbenedisulfonate.

5. A process according to claim 1 with the additional step which comprises drying the product obtained in accordance with claim 1 to remove some or all of the moisture content.

6. A process according to claim 5 wherein the fluorescent whitening agent is disodium 4,4'-bis(4-anilino- -morpholino-s-triazin-2-ylamino)-2,2'-stilbenedusulfonate.

7. A process for treating a presscake consisting essen' tially of relatively large crystals of a fluorescent whitening agent selected from the group consisting of disodium 4,4'-bis(4,6-dianilino-s-triazin-2-ylamino)-2,2'- stilbenedisulfonate, disodium 4,4'-bis(4-anilino-6- morpholino-s-triazin-2-ylamino)-2,2'-stilbenedisulfonate, disodium 4,4-bis(4-anilino-6-[2,2'- dihydroxyethylamino]-s-triazin-2-ylamino)-2,2'-stilbenedisulfonate, disodium 4,4-bis(4-anilino-6-[2- hydroxyethylamino]-s-triazin-2-ylamino)-2,2'-stilbenedisulfonate and sodium 2-(4- stilbyl)naphtho[ l ,2:4,5]-1,2,3-triazole-2-sulfonate, which comprises grinding said presscake in the presence of approximately 30 to approximately 65 percent of anhydrous sodium sulfate by weight of the resultant mixture until the crystals are reduced to an average particle size of approximately 5 microns with substantially none of the crystals greater than 15 microns in the largest dimension.

8. A process according to claim 7 wherein the fluorescent whitening agent is disodium 4,4'-bis(4-anilino- 6-morpholino-s-triazin-Z-ylamino)-2,2'-stilbenedisulfonate.

Claims (8)

1. A PROCESS FOR TREATING A PRESSCAKE CONSISTING ESSENTIALLY OF WATER AND RELATIVELY LARGE CRYSTALS OF A FLUOROSCENT WITHENTING AGENT SELECTED FROM THE GROUP CONSISTING OF DISODIUM 4,4''-BIS(4,6-DIANILINO-S-TRAZIN-2-YLAMINO)-2,2''-STIBENEDISULFONATE, DISODIUM 4,4''-BIS(4-ANILINO-6-MORPHOLINO-S-TRIAZIN-2YLAMINO)-2,2''-STILBENEDISULFONATE, DISODIUM4,4''-BIS(4-ANILINO6-(2.2''-DIHYDROXYETHYLAMINO)-S-TRIAZIN-2-YLAMINO) -2,2''STILBENEDISULFONATE, DISODIUM 4,''-BIS(4-ANILINO-6-(2HYDROXYETHYLAMINO)-S-TRIAZIN-2-YLAMINO) -2,2''STILBENEDISULFONATE AND SODIUM 2-(4-STILBYL)-NAPHTHO-(1'', 2''-:4,5)-1,2,3-TRIAZOLE-2-SULFONATE, WHICH COMPRISES GRINDING SAID PRESSCAKE AT A TEMPERATURE OF 20* TO 60*C IN THE PRESENCE OF AT LEAST ONE AND UP TO EIGHT MOLECULAR EQUIVALENTS OF ANHYDROUS SODIUM SULFATE FOR EACH TEN MOLECULAR EQUIVALENTS OF WATER IN SAID PRESSCAKE UNTIL THE CRYSTALS ARE REDUCED TO AN AVERAGE PARTICLE SIZE OF APPROXIMATELY 5 MICRONS WITH SUBSTANTIALLY NONE OF THE CRYSTALS GREATER THAN 15 MICRONS IN THE LARGEST DIMENSION.

1. A process for treating a presscake consisting essentially of water and relatively large crystals of a fluorescent whitening agent selected from the group consisting of disodium 4,4''-bis-(4, 6-dianilino-s-triazin-2-ylamino)-2,2''-stilbenedisulfonate, disodium 4,4''-bis(4-anilino-6-morpholino-s-triazin-2-ylamino)-2, 2''-stilbenedisulfonate, disodium 4,4''-bis(4-anilino-6-(2,2''-dihydroxyethylamino)-s-triazin-2-ylamino)-2,2'' -stilbenedisulfonate, disodium 4,4''-bis(4-anilino-6-(2-hydroxyethylamino)-s-triazin-2-ylamino)-2,2'' -stilbenedisulfonate and sodium 2-(4-stilbyl)-naphtho-(1'', 2'':4,5)-1,2,3-triazole-2-sulfonate, which comprises grinding said presscake at a temperature of 20* to 60*C in the presence of at least one and up to eight molecular equivalents of anhydrous sodium sulfate for each ten molecular equivalents of water in said presscake until the crystals are reduced to an average particle size of approximately 5 microns with substantially none of the crystals greater than 15 microns in the largest dimension.

2. A process according to claim 1 wherein the fluorescent whitening agent is disodium 4,4''-bis(4-anilino-6-morpholino-s-triazin-2-ylamino)-2,2'' -stilbenedisulfonate.

3. A process according to claim 1 wherein the grinding is accomplished in the presence of approximately one molecular equivalent of anhydrous sodium sulfate for each 10 molecular equivalents of water in the presscake.

4. A process according to claim 3 wherein the fluorescent whitening agent is disodium 4,4''-bis(4-anilino-6-morpholino-s-triazin-2-ylamino)-2,2'' -stilbenedisulfonate.

5. A process according to claim 1 with the additional step which comprises drying the product obtained in accordance with claim 1 to remove some or all of the moisture content.

6. A process according to claim 5 wherein the fluorescent whitening agent is disodium 4,4''-bis(4-anilino-6-morpholino-s-triazin-2-ylamino)-2,2'' -stilbenedusulfonate.

7. A process for treating a presscake consisting essentially of relatively large crystals of a fluorescent whitening agent selected from the group consisting of disodium 4,4''-bis(4,6-dianilino-s-triazin-2-ylamino)-2,2''-stilbenedisulfonate, disodium 4,4''-bis(4-anilino-6-morpholino-s-triazin-2-ylamino)-2,2'' -stilbenedisulfonate, disodium 4,4''-bis(4-anilino-6-(2,2''-dihydroxyethylamino)-s-triazin-2-ylamino)-2,2'' -stilbenedisulfonate, disodium 4,4''-bis(4-anilino-6-(2-hydroxyethylamino)-s-triazin-2-ylamino)-2,2'' -stilbenedisulfonate and sodium 2-(4-stilbyl)naphtho(1'',2'':4,5)-1,2,3-triazole-2-sulfonate, which comprises grinding said presscake in the presence of approximately 30 to approximately 65 percent of anhydrous sodium sulfate by weight of the resultant mixture until the crystals are reduced to an average particle size of approximately 5 microns with substantially none of the crystals greater than 15 microns in the largest dimension.