IL22152A - Production of aqueous dispersions of solids insoluble in water - Google Patents

Description

depends on the initial particle size of the grinding stock. .

Solids , for lfia anue dyestuffs , have already been finely. subdivided according to the process of U.S . Patent Specification No. 1 837 772 by stirring the solid s in an aqueous or non-aqueous medium, in the presence of a dispersing agent, with solid grinding elements in an open vessel. Anion active dispersing agents such as the sod ium salt of dinaph hylraethane- 2, 2' -disulphonio acid, the sodium salt of sulphite cellulose and its oxidation product, as we ll as amid a ted sulphite cellulose and sodium benzyl-sulphonate have already bee employed as the dispersing agents . Compact insoluble powders which are harder thai* the material to ho finely subdivided or dispersed and which are recommended as the grinding elements, are for example, iron powder, zinc powder, copper powder or sand with a maximum particle size of 0.125 mm.

Hone of the known processes referred to above has been adopted in practice. The same applies to the process described in U.S. Patent Specification No. 2 581 414. This latter process consists in dispersing a commercial pigment in a film-forming material, agitating the pigment and film-forming material with a sand which is of 20*40 mesh size, and remains within about this else range, the agitating being continued until the commercial size pigment is reduced to a fineness of not more than 0.0005 inch when measured on a scrape*type fineness of grind tester that is graduated from 0.002 to 0.0000 inch, and separating the sand from the dispersed pigment and film-forming material* This known process, though it has been used in practice, offers no appreciable advantages in respect of the fine subdivision of the grinding stocks in comparison with the customary methods of subdivision (for example without solfi insoluble auxiliary grinding elements) in the usual ball mills with grinding elements of a comparable size. The application of the process of t?.S« Patent Specification Ho* 2 581414 Is limited to the preparation of dispersed pigments in non-aqueous film forming media which aqueous pigment pastes, such as are, for example, obtained during the manufacture of pigment dyestuffs, cannot be processed by this process so as to form finely dispersed dyestuffs* In aH known grinding devices with small grinding elements, the agitation of the grinding mixture leads to the formation of turbulent currents at the interface between the - air (or gs) and the dispersion of the grinding stock or the grinding mixture, so that air (or gas) is aspired into the grinding mixture. This has a particularly unfavourable effect on the grinding action or on the dispersion of solids insoluble in water when dispersing agents exhibiting a strong tendency towards the formation of foam are used. Strong formation of foam takes place in particular during grinding with small grinding elements under these conditions, and owing to the resultant air cushion effect, the mobility of the small grinding elements is reduced and the grinding action is decreased to a technically useless value} frequently difficulties appear during the separation of the grinding stock from the grinding elementsi or flotation of the grinding elements occurs during this operation.

TJnfortuately a large number of dispersing agents which exhibit a particularly good dispersing action have a tendency to form the kind of foam described above* Such dise sing agents may already have originated from the process for the production of the solids or their presence may be desirable in order to achieve a fine dispersing action by means of suitable devices. Technologists do in general not like to dispense with the use of such agents, and as a consequence a large number of devices for the fine subdivision of pigments could not be successfully adopted because of the above men* tioned air cushion effect* The known dispersing devices described in U.S. Patent Specification Ιο· 2581414 and German Published Specification lo* 1109988, intended for non-aqueous dispersion, are also unsuitable for processing dispersions containing substances The invention provides a prooess and a device for the dispersion in an aqueous medium of organic or inorganic solids insoluble in water, which are free of the disadvantages known to ooour in the processing in an aqueous medium by means of the devices known as "sand mills" and comparable appliances, and which give optimum results even when strongly foam-forming dispersing agents are used* According to the prooess of the invention an organic or inorganic solid insoluble in water is agitated in an aqueous medium with a dispersing agent and with a grinding material containing silicon dioxide groups, which material has a specific gravity greater than 1.5■ is harder than the product to be dispersed and is in the form of smooth-surfaced rounded elements whose radii do not differ by more than 40$ from the mean radius, and whose diameters are from 0.3 to 1.5 mm, and is used in a proportion of 10 to 300$ of the solid volume, calculated on the volume of the dispersion of the grinding stock} the aqueous medium contains non-ionic, anionic, catlonlo or betaine-type dispersing agents in a proportion of 0*1 to 200$ by weight of the solid to be dispersed, optionally in conjunction with defoaming agents} the agitation of the grinding mixture is continued until the particle size of the grinding stock is 6 u or preferably less} and where dispersing agents are used which increase the volume of the grinding stock during the grinding operation by more than 20$ by the formation of foam, the formation of air (or gas) aspiring currents at the interfaoe between the air (or gas) and the dispersion of the rindin stock or mixture is substantiall revented grindin stook", "grinding eleme ts" and "grinding mixture" are here employed in accordance with the following definitions: the "grinding stock" is the solid to be dispersed the "dispersion of the grinding stock" is the aqueous dispersion of the grinding stock which may optionall contain dispersing agents; the "grinding elements" are the rounded elements co Saining silicon dioxide groups; and the "grinding mixture" is the mixture of the dispersion of the grinding stock with the grinding elements.

The agitation of the grinding mixture during the process according o the invention is effected so- hat he highest possible velocity gradient exists between the grinding elements without causing the .grinding elements to become squashed at any. point in the grinding mixture.. It should not be possible for the grinding stock to escape from: the action of the grinding elements wit in the grinding device* By way of grinding appliances which cause an air aspiring turbulence at the surface of the grinding stock. or grinding mixture, falling, tumbling and turbine mixers may be f employed, such as have for instance been listed in Ullmann: "Bnoyclopadie der technischen Chemie" (Urban und Schwarzehber Veriag, Munich-Berlin), 3rd Edition, Volume I (to be referred to as Ullmann I hereafter) on pages 714 - 715* ' In addition, stirrer mixers have been em loyed, where suitable mixing elements at a low number of revolutions (at circum erential speeds of 1 - 4 m sec) are for ins ance those specified in Ullmann I o page 707. Owing to the risk of abrasion and the possibility that the grindin elements may be destroyed , only st irrers with plane crossed blades, stirrers with a stream line c ross section, stirrer screws and also stirrers wi th one or several flat or conical compa ct or pe rforated c ircular discs or rings connected to the shaft by spokes are suitable at circumferential speeds greater than 4 m/sec; the circular discs or rings should T>e attached vertically to the stirrer shaft and the shaf should pass through their centre . In the case where several mixing eleme nts are employed, they should be spaced at a distance of roughly betwee n their half and the ir full radii in their attachment to the stirrer shaft . The circumferential speed s should be between 4 and 20 m sec , preferably between 7 and IS m/seo . ' In addition, oscillatory mixers operating at moderate frequenoiea (Ullmann I, p . 722 ) and vibrating mills operating at high frequencies such as have for instance been specified in Ullmann I on page 725 are also suitable .

Moreover, the agitation o the grindi ng mixture can be effected by means of a vibro mixe r with the use of one stirrer plate or of several stirrer plates arranged on top of eaoh other as the mixing elements (Ullmann I, p . 02 ) at frequencies of 50 - 100 oyo le s/sec and an amplitude of preferably 2 - 3 mm.

The diameter of the conical apertures at the narrowest point in the stirrer plates should amount t o between 4 and 16 times the mean diameter of the grinding elements . In the case where several stirrer plates are employed , these should be spaced at a distance of roughly betwee n their quarter and their full radii in their attachment to the shaft .

When grind ing devices of this type are operated is continuously, the aspiration of gas or air at the inter faoe be ween the grinding mixture or g indi g stock and the gas or air can sometimes be prevented by carrying out the grinding operation at a reduced pressure of preferably leas than 200 mm Hg The formation of foam may also be eliminated during a discontinuous operation by carrying out the process in sealed vessels whioh are completely filled with the grinding mixture, although this form of execution oan only be applied when there is no appreciable resultant deterioration of the grinding action.

The arrangement of apparatus in machines with a continuous operation is suoh that no appreciable turbulent current of air (or gas) aspiration can occur at the interface between the air (or gas) and the dispersion of the grindin stock or the grinding mixture.

The machines with a continuous operation do not differ from theappliances with a discontinuous operation whioh have already been mentioned above in respect of their grinding devices However, since their operation is continuous, they have an inlet and outlet for the grinding stock. The risk of a formation of foam mainly exists at the side where the grinding stock is discharged from the machine.

A sieve adapted to the required rate of throughput of the grinding stook and to the dimensions of the^grinding elements has to be fitted in front of the disoharge outlet in order to retain the grinding elements. The prevention of a turbulent ourrent of aspired air or gas can be effected in front of or beyond the sieve, hen the constructions represented diagrammati-oally in Figures 1 - 5 are preferably employed.

In Figures 1 - 5, (1) represents a cylindrical grinding vessel surrounded by a cooling or heating jacket (2)j a abaft (3) carrying the mixing elements (4), which have in the given case been drawn in the form of discs, extends oonoentri-cally into the grinding vessel. The grinding vessel is provided with an inlet (5) for the coarse dispersion which has to be ground, this being connected to a liquid pump and optionally provided with a device for preventing the baokflow of the grinding mixture. The discharge outlet (6), which is an overflow in the case of Fig. 1 and Fig. 2, is provided beyond a sieve (7), in relation to the position of the grinding mixture, and this ia preferably adjoining the free side of the grinding vessel. The design of the sieve (7) in Figures 2 - 5 may also be modified in that the part of the sieve which is either vertical (7a) to the shaft (3) or parallel (7b) with it is replaced by a compact surface when in the second case the cooling jacket (2) is raised up to the level of the sieve (7a). The mesh width of the sieve has to be selected so that the smallest employed grinding elements are just prevented from passing through it» The inner surfaces of the grinding vessel (1) and of the sieve (7) enclose the grinding space (8), although the construction according to Fig. 1 constitutes an exception in that the horizontal plane extending from the upper edge of the overflow represents the upper limit of the grinding spaoe in this non-enclosed system. The grinding space is completely filled with the grinding mixture when the dispersion of the solid which has to be ground is pumped through it. The grinding space and where required the external surfaces are sealed by means of seal3 (10) at the locations where the shaft (3) penetrates through them, and these may also act as bearings. The seal (10) may for instance be of rubber, metal, graphite, plastics or sealing liquid, and in the last case the dispersion of the grinding stock rising above the upper surface of the sieve (7a) may also act as the seal, as may the grinding mixture itself in a suitable construction, for instanoe if a sieve or pipe is passed round the shaft.

The grinding mixture is agitated by stirring (rotation) or by vibration. When the agitation is effeoted by stirring, the grinding space contains 30 to 70, and preferably 40 to 60, percent of the solid volume of the grinding elements in relation to the free volume; in that case, the stirrer mixers mentioned on page 6 and 7 are employed as the mixing elements, when the distance between the mixing element and the grinding vessel in eaoh case depends on the diameter of the grinding elements and should amount to between 3 and 30 times the diameter of the grinding elements.

The aspiration of air or gas into the grinding mixture at the interface between the grinding mixture or the dispersion of the grinding stock and the air or gas (9) which occurs to an extremely marked extent in thenormal construc ions of high speed stirred ball mills with circular discs or rings on spokes is prevented in the oaseof the form of execution according to Pig. 1 by replacing the uppermost stirrer element (4a) by a compact cylinder (11) whose radius is of about the same magnitude and by placing the overflow (6) for the dispersion of the grinding stock at an appreciably higher level than the lower side of the sieve (7). The lower surface of the cylinder (11) should be at the level of the lower edge of the sieve (7) or below i j the upper surface of t e cylinder (11) should extend above the upper edge of the overflow (6).

In the case of the form of execution acoording to Fig. 2, only the dispersion of the grinding stock passing through the sieve (7) or (7a) or (7b) sealed on the shaft or closely adjoining the shaft comes into contact with the surrounding gas. The rate of discharge of the dispersion of the grinding stock is selected so that the turbulence transmitted to it by the stirring operation has been damped to the extent that an aspiration of gas will have been eliminated. The upper edge of the overflow (6) is preferably at least 3 cm above the upper extremity of the sieve. This type of exeoution is especially suitable for viscous dispersions of the grinding stook* In the case of the forms of execution according to Figures 3 to 5, the air or gas aspiring turbulenoe of the grinding mixture is eliminated by limiting the extent of the interface between the dispersion of the grinding stock (9) and the air or gas to the interfacial area at the disoharge outlet; moreover, the flow of the dispersion of the grinding stock counteracts the aspiration of gas or air.

When the agitation is effected by vibration, the grinding space contains 10 to 50, and preferably 15 to 40$ of the solid volume of the grinding elements, and use is made of the stirrer plates normally encountered in vibro mixers, where the discs (4) should be fitted so that the narrow ends of the conical apertures point towards the charge inlet, i.e. their effect opposes the direction of the throughput. The distance between the mixing elements and the grinding vessel onoe again depends on the diameter of the grinding elements in eaoh case and generally amounts to between 3 and 10 times the diameter of the grinding elements* The following may inter alia be mentioned as materials containing silicon dioxide suitable a3 the grinding elements* quartz, for instance any type of sand which satisfies the above criteria in respect of dimensions and shape such as Ottawa sand, and also glass and ceramic masses provided that their surface is not porous, such as porcelain and steatite, and other sintered metal silicates insoluble in water such as aluminium silioate.

Tne diameter of the coarse fraction of the solids to be dispersed should not in general exceed 30$ of the mean diameter of the grinding agents and it should preferably be less than 10ϋ of the mean diameter. The following may be mentioned, inter lia, as solids insoluble or barely soluble in water whioh can be dispersed t inorganic solids such as flowers of sulphur, red phosphorus, kaolins and other soft silicates, inorganic oatalysts such as vanadium pentoxide and manganese dioxide, inorganic pigments such as iron oxides, titanium dioxide and cadmium sulphides, organic compounds such as intermediate products insoluble in water before or during a reaction, in particular coupling components for the pre aration of azo dye-stuffs insoluble in water, organic pest control agents and plant protection agents, organic pnarmaceuticals such as analgesics, sulpnonamides, antibiotios and contrast agents. The process is of particular interest for grinding organic dyo stuffs, such as pigments, dispersion dyestuffs and vat dyestuffs, as well as organic whiteners insoluble in water.

In order to supplement the stability of the dispersion or to promote the grinding action, the following surface active agents are added in a proportion of 0.1 to 200$, referred to the weight of the solid, to the 1 to 80%, and preferably 10 to b0% aqueous suspensions or extruded pastes of the solids. In the case where grinding is carried out in machines in which a strong air or gas aspiring turbulence is caused at the interface between the dispersion of the grinding stock or the grinding mixture and the air or gas, it is convenient to employ the alkali metal or alkaline eartn metal salts of dinaphthylmethane-2,2'-disulphonic acid, of p-toluene-sulphonic acid and of polystyrene-sulphonio acid (moleoular weight 10 000 - 15 000) and polyvinylpyrrolidone (molecular weight 10000 - 30 000) as the surfaoe aotive agents* Provided that this will not interfere with the further application of the dispersion of the solids, these may also be processed with up to 10/b, calculated on the amount of solid to "be dispersed, of the alkali metal sa ts of 3pent sulphite cellulose liquor and its amine condensation products or with the condensation product from cresol-formaldehyde resin and the t -sulphoacid obtained from 2,6-naphthol-sulphonio acid in combination with 1 to 2% of a defoaming agent, referred to the amount of solid.

In the types of apparatus in which an interference by gas aspiration into the grinding mixture has been eliminated, the following may be added as the surface active produotsj All types of non-ionic emulsifying agents, such as poly lkoxylated oarboxy-lic acids, alcohols, phenols, amines and mercaptans with a higher molecular weight, as well as anionic dispersing agents such as the alkali metal, ammonium and in some cases also the alkaline earth metal salts of carboxylic acids, sulphonic acids and sulphuric acid esters with a higher molecular weight, and also oationic emulsifying agents such as the salts of primary, secondary and tertiary amines of higher molecular weight with hydro-halide aoids and sulphuric acid and in particular their quaternary ammonium compounds; it is also possible to employ surface active agents of the betaine type such as aminosulphonic acids with a higher molecular weight, where the carbon skeleton in their hydrophobic portion with a higher molecular weight may be interrupted by heteroatoms.

The following Examples are given for the purpose of Example 1: A homogeneous paste is prepared from 250 g of coarsely ground flowers of sulphur, having a particle distribution with a main fraction of diameters at about 50 ^u, larger fractions at about 15 and smaller fractions at about 6 and 80 respectively, by stirring them with 100 cc of water and 50 g of the sodium salt of dinaphthylmethane-2,2,-disulphonlc acid as the dispersing agent. This paste is mixed with 970 g of glass balls (speoific gravity 2.-97) of diameter 0.45 to 0.75 mm each of which does not differ in its radius by more than + 1% from the mean radius of the balls, as the grinding elements in the following device. The latter consists of a vertical cylindrical vessel closed at the bottom, open at the top and externally cooled, with a diameter of 10 cm and a height of about 20 om (internal dimensions) into which a stirrer shaft extends vertically and centrally, three plane circular disos of thickness 0.5 cm and with a diameter of 7.6 cm being fitted horizontally to the shaft on top of each other at a spacing of 2.7 cm as the mixing elements. The free clearance between the lowest disc and the bottom is 1 cm and the rate of rotation is 3000 revolutions per minute. After it has been in operation for 1 hour, the particle distribution of the flowers of sulphur in the paste, which is separated from the grinding elements by means of a sieve, comprises a main fraction at 1 to 2 ^a, a larger fraotlon at 0.3 to 1 and a smaller fraction at 2 to 3 ^i. The increase in volume of the dispersion of the grinding stock owing to foam amounts to about 40%· When flowers of sulphur are subdivided with glass balls in the range of 1.8 to 2.2 mm as the grinding elements under conditions whioh are otherwise the same, the resultant particle distribution of the flowers of sulphur has a main fraction at 2 to and moderate fractions at 1 to 2 j and at 3 to 5 ^i.

When the glass balls have a diameter of 2.7 to 3,1 mm, the main fraction is at 5 to 6^> moderate fractions are at 6 to lO^i and only small fractions at less than 2 u. rfhen a mlxtureof equal parts of glass balls with diameters of about 1,2,3,4,5,6,7 and 8 mm is employed as the grinding element, the particle distribution of the flowers of sulphur achieved under conditions which are otherwise the same has a main fraction at 2 to 5 a, moderate fractions at 5 to 10 u, small fractions at about l^i and individual particles at up Example 2; When flowers of sulphur are subdivided by the use of Ottawa sand as the grinding element under conditions which are otherwise the same as in Example 1, the sand having rounded edges and individual grains whose radii differ by + 2 to + 25 from the mean radius of the separate particles but its size being the same as that of the glass balls, the resultant particle distribution of the flowers of sulphur has a main fraction at 1 to 2 jxt large fractions at 0.5 to 1 jx and at 2 to 3^1, and a small fraction at 3 to 4 u.

When quarry sand with sharp edges and with Individual grains whose radii differ by + 8 to + 40$ from the mean radius of the separate particles is employed as the grinding element, grinding beoomes impossible since the grinding mixture sets solid. Grinding only becomes possible again when about 100 co of water are added.

Example 5: When flowers of sulphur are subdivided under the same conditions as those described in Example 1 except for the use of 50 g of the sodium salt of polystyrone-sulphonic acid (molecular weight about 13 000) as the dispersing agent, the increase in the volume of the dispersion of the grinding stock due to foam amounts to about 10 to 15% and the particle distribution of the flowers of sulphur is almost entirely at less than 1 a, with very small fractions at 1 to 4 ^u.

On the other hand, when the operation is carried out by employing as the dispersing agent the reaction product of hydroxydiphenyl and benzyl chloride to which 12 to 14 moles of ethylene oxide had been added per mole, on average, the increase in volume of the dispersion of the grinding stock due to foam amounts to about 100$, and the particle distribution of the flowers of sulphur has a main fraction at 4 to 5^u and moderate fractions at 2 to 4 and at 5 to 10jx.

Example 4: When grinding of the flowers of sulphur is carried out with the ethylene oxide aadition product of hyd roxydiphenyl by the method described in Example¾ except that the operation is conducted in an appliance which corresponds to that in Example 1, though in this case a light-weight plate sealed on the shaft and on the grinding vessel is placed over the grinding mixture so as to prevent the entry of air, the resultant particle distribution of the flowers of sulphur has a main fraction at less than 1 x. and only small fractions at 1 to 5^ι· Example 5: 400 g of a 36 aqueous suspension of the vat dye stuff Indanthrene Brown R (Schulz, Parbstofftabellen, 7th Edition, No.1227) present in a state of subdivision with a main fraction at 3 to 8 t with a large fraction at 8 to 0^u and a small fraction at 1 to 3 and which contains 10%, referred to the dyestuff, of the sodium salt of polystyrene-sulphonio acid with a molecular weight of about 13 000, are mixed during 15 minutes with 970 g of glass balls having diameters of 0.6 to 0.9 mm in a device like that described in Example 1. The state of fine subdivision of the dyestuff in the resultant dispersion of the grinding stock consists of a main fraction at 2 to 3^i, a large fraction at 1 to 2 u and a small fraction at 3 to 4 u.

Bxamp le 6 : 370 g of a 35;;i aqueous dispersion of copper phthalo-cyanine in the a-nodif icabion, prepared in accordance with German Patent Specification iio. 1 136 303 at a state of subdivision with a main fraction of particles at 7 to 25 ^i, and which contains 10>0, referred to the weight of the pigment, of the sodium salt of dlnaphthylmet ane-2, 2'-disulphonic acid, are mixed with 970 of glass bails with the dimensions of 0.7 to 1 mm as the grinding elements in the following device. The latter consists of a vertical cylindrical vessel, closed at the bottom, open at the top and externally cooled, with a diameter of 10 cm and a height of about 20 cm (internal dimensions), into which a stirrer shaft extends vertically and centrally which carries a vertical flat paddle stirrer of height 10 cm and width 7 cm as the mixing element. The free clearance from the bottom is 1 cm and the rate of rotation is 1000 revolutions per minute. After it has been in operation for 30 minutes, the particle distribution of the pigment comprises a main fraction at 0.5 to 1 u, large fractions it less t an C.5 and at 1 to 2 ^i, and a small fraction at 2 to 5 ^i.

When the pigment is ground in the device described Example 1 under conditions which are otherwise the same, i.e. with 3 horizontal stirrer discs as the mixing elements and at a rate of rotation of 3000 revolutions per minute, the final resultant particle distribution is almost entirely the same as that during the above experiment.

B-sample 7: 200 cc of an aqueous suspension of 30 g of copper pht halocyanine in the α-modif ication, prepared in accordance with Example 1 of German Patent Specification No. 1 136 303, whose main fraction consists of particles at 7 to 25 ^u, are mixed for 1 hour at a frequency of 100 cycles per second and an amplitude of 3 mm together with 9 g of the sodium salt of dinapht yl-methane-2,2l-disulphonic acid and with 300 g of glass balls with a diameter of 0.5 to 0.75 mm in a cylindrical vessel, open at the top, with a diameter of 7 cm and a height of 15 cm (internal dimensions) with the aid of a vibro mixer having a perforated circular disc of thickness 2.4 mm and of diameter 5.4 cm provided with 20 conical drillings uniformly distributed throughout the disc, their largest diameter being 9.0 mm and their least diameter being 5.2 mm. The main fraction of the particles in tnis pigment is at less than 3 ^i, and a few individual particles at up to 6 u are also present.

Example 8: 250 g of a 30 aqueous suspe sion of the organic substance obtained in accordance with Example 1 of German Patent Specification No. 1 080 963, which is hardly soluble in water and hae a particle distribution with a main fraction at 10 to 15 t a large fraction at 1 to 6 and a small fraction at 15 to 40 †.t and containing 20%, referred to the weight of the dye-stuff, of the sodium salt of dinaphthylmethane-2, 2' -disulphonio aoid are ground for 1 hour with 500 g of glass bails with diameters of 0·65 to 0.9 mm as the grinding elements in a vessel of 1 litre oapacity which is placed on a vibrating mill (UHmann1 s Encyclopadio der technischen Chemie, 3rd Edition, Volume I, page 725)· The resultant state of fine subdivision comprises a main fraction at 1 to 2 and a large fraction at 3 to ^x, when use is made of balls at 4.8 to 5.3 mm, the resultant state of subdivision only comprises a main fraction at 4 to 10 ^ , larger fractions at 2 to 4 and at 10 to 14 and merely small fractions at less than 2 \x* exam le 240 g of the compressed filter cake which contains 50 g of the azo pigment dyestuff from 2,4,5-trichloroaniline and naphthol AS-D are stirred intensively in a cylindrical mixing vessel having a ueeful volume of 1 litre with 75 g of the sodium salt of dinapht yljnethane-2,2'-disulphonic acid and treated with 300 g of glass balls with a diameter of 0·6 to 0.8 mm. The mixing vessel is now placed into a vibrating mixer "Turbula" System ^chatz (described in Pharmaoeut ika Acta Helvetial 37 1962? , p. 529 - 543) and shaken for 2 hours. The dyestuff had a particle distribution at 2 to lO u prior to the treatment, with small fractions at 20 u« ^fter the treatment, the particle distribution of the dyestuff was between 0.3 and 3^ .

Example 10; kg of a 10 aqueous paste of the dispersion dye-stuff obtained by the mixed bro ination of 1,5-d iamino-4,8-d i hydroxy- a nthra qui none in accordance with German Patent Specification No. 1 029 506 at an initial particle distribution with a main fraction at 8 to 15 ^i, large fractions at 2 to 8 jx and at 5 to 50 jx, and a very small fraction at 1 to 2 and which contains 150 , referred to the weight of the dyestuff, of the sodium salt of dinaphthylmethane-2,2'-disulphonic acid as the dispersing agent are stirred with 50 kg of glass balls with a diameter of 0.9 to 1.2 mm for 6 hours in a mixer of the following construction. The latter consists of a closed cylindrical vessel inclined to the horizontal at an angle of 15° and having a diameter of 60 cm and a height of 70 cm (internal dimensions) which has been provided on its internal wall with two mixing fins of height 10 cm and length 70 cm positioned opposite each other, parallel with the axis and pointing towards the'axis; its rate of rotation is 20 revolutions per minute. The subsequent fine subdivision of the dyestuff is at less than 4^Ue Example 11: The organic substance obtained in accordance with Example 1 of German Patent Specification No. 1080 963 which is hardly soluble in water and has a particle distribution with a main fraction at 10 to 15^1, a large fraction at 1 to 6^1 and a small fraction at 15 to 40. is pumped in the form of its 0 aqueous suspension, with a content of 0$, referred to the weight of solid to be subdivided, of the sodium salt of dinaphthyl-methane-2,2'-disulpho ic acid and 1$, referred to t e weight of solid to be subdivided, of a silicone defoaming agent, at a uniform speed of 100 litres per hour through the following device. The latter is constructed in accordance with Figure 1, where the mixing elements (4) and (4a) are plane circular discs, the cylinder (11) being missing, and the discharge level is at the level of the lower edge of the sieve. The dimensions of the grinding vessel are height 100 cm and diameter 26 cm (internal dimensions), and those of the discs are diameter 21 cm and thickness 1 cm. The lowest disc is spaced 2 cm clear of the bottom and the uppermost diec (4a) is at the level of the lower edge of the sieve, with 9 other discs spaced at equal distances between them in their attachment to the shaft. The shaft rotates at a rate of 1000 revolutions per minute, and the grinding vessel contains 67 kg of glass balls with a diameter of 0*5 to 0*75 mm* After it has been passed through twice, the resultant partiole distribution comprises a main fraction with particles at 1 to 1.5 ^i, larger fractions at 0.5 to 1 i and at 1.5 to 2 u, as well as traces at 2 to 2.5 u. / r Example 12: A 55 aqueous suspension of C.I. Pigment Yellow 5 (Colour Index, 2nd Edition, 11 710) which conveniently contains 0.04$ of polyglycol-modi led oleic aoid (12 - 16 moles of ethylene oxide per mole of aoid) and 0.56$ of the sodium salts of sulphoohlorination produots of higher hydrooar ons originating from the preparation of the pigment, which has a partiole distribution with a main fraction at 1 to 3^i, large frao ions at 3 to 7^i, small fractions at 0.5 to Xj and at 7 to 40 u, and which has been treated with 10$, referred to the weight of the pigment, of the sodium salt of dinaphthylmethane-2,2'-di3ulpho-nic acid, is pumped through the following device at a uniform rate of throughput amounting to 27 litres per hour. The latter is constructed in accordance with Figures 2 to 5, where the grinding vessel has a diameter of 15 cm and a height of 28 cm (internal dimensions) and the sieve (7b) has a height of 3 om; in the case of a construction according to Pig. 2, the lowest point of the overflow (6) is 3 om above the sieve (7a)· 7 circular discs with a diameter of 12 cm and a thickness of0.6 om are fitted as the mixing elements at equal distances to the shaft (3) of thickness 2.6 cm so that the disc next to the charge inlet (5) is spaced 1 cm clear from the bottom and so that the disc next to the sieve (7a) has a clearance of 3 eat from the latter. The seals (10) are slip rings. The shaft rotates at 1650 revolutions per minute. The grinding vessel (1) contains 7 kg of glass balls with diameters of 0.55 to 0,85 mm* The sieves (7a) and (7b) have a free mesh width of 4 mm. The paste free from foam whioh is thereby obtained and can therefore be readily further processed oontains the pigment in a state of fine subdivision with a main fraction at 1 to 2 ^i, large fractions at 0.5 to 1 ^ and at 2 to 4 u, and small fractions at 4 to 5 i.

When a subdivision of the yellow pigment is attempted in a device of the same dimensions but where the construction is in accordance with Figure 1, when the mixing element (4a) also represents a circular disc of diameter IS cm whilst the cylinder (11) is missing, the discharge level is at the level of the lower edge of the sieve and the sieve has a height of 12 cm, the operation proves to be impossible since the grinding mixture (dispersion of the grinding stock and the grinding balls) spills over the upper edge of the sieve after a short while owing to the resultant stable foam.

When silicone defoaming agents were added, it was still impossible to achieve a satisfactory result of the experiment.

Example 15: A 62.5$ aqueous suspension of flowers of sulphur at a particle distribution with a main fraction at about 50^., larger fractions at about 15 and smaller fractions at 6^ and at 80^1, which contains 0$, referred to the weight of the sulphur, of the sodium salt of dinaphthy3jnethane-2,2'-disulphonlo aoid is pumped at a uniform rate of throughput of.15 litres per hour through devices like those described in Example 12 and constructed in accordance with Figures 2 - 5· The resultant state of fine subdivision of the sulphur comprises a main fraction at 2 to 4 i, large fractions at 0.5 to 2 and at 4 to 5 x, and small fractions at 5 to 6 u» When the same experiment is carried out in a devioe with the same dimensions but where the construction is in accordance with Figure 1, when the mixing element (4a) also represents a circular diso of diameter 12cm whilst the cylinder (11) is missing, the discharge level is at the level of the lower edge of the sieve and the sieve has a height of 12 cm, the resultant increase in the volume of the discharged dispersion of the grinding stock is 35$, oompared with that of the charged dispersion of the grinding stock, even when 1% of a silicone defoaming agent has been added ( calculated'on the sulphur oon-tent). The resultant particle distribution of the sulphur has a main fraction at 7 to 10 x, large fractions at 5 to 7 and at 10 to 15^1, and small fractions at 1 to 5 . and at 15 to 25 i, Example 14: When a subdivision of the flowers of sulphur is carried out under the same conditions as described in Example 13 in a device with the same dimensions but where the construction is in accordance with Figure 1 when the cylinder (11) has a diameter of 12 cm and a height of 10 cm, its lower surfaoe being at the level of the lower edge of the sieve (7), the sieve (7) has a height of 12cm and the highest point of the overflow (6) is 5 cm above the lower edge of the sieve (7), the increase in volume of the discharged dispersion of the grinding stock due to the foam amounts'to 15 to 20% of the volume of the charged dispersion of the grinding stock. The resultant state of fine subdivision of the sulphur comprises a main fraction at 5 to 6 ^α, larger fractions at 2 to 5 JL and at 6 to 8 jxt and small fractions at 1 to 2 and at 8 to 10 ^i.

Example 15 t A 30jS aqueous suspension of copper phthalocyanlne in the a-mod ification, prepared in accordance with German Patent Specification No. 1 136 303 at a particle distribution with a main fraction at 7 to 25 and which contains 20%, referred to the pigment content, of the sodium salt of dina hthylme thane-2, '-di3ulphonic acid and 50 , referred to the pigment content, of the sodium salt of the aniline condensation product of lignin-sulphonic acid is pumped through devices like those described in Example 12 and constructed in accordance with Figures 2 - 5, at a uniform speed of 15 litres per hour. The resultant state of fine subdivision of the pigment oomprises a main fraction at 0.5 to 2 ^u, large fractions at 0.3 to 0.5 and at 2 to 5 ^u, and small fractions at 5 to 6 jx, When the same experiment is carried out in a device with the same dimensions but where the construction is in accordance with Figure 1, when the mixing element (4a) also represents a oircular disc of diameter 12 cm whilst the cylinder (11) is missing, the discharge level is at the level of the lowest edge of the eieve and the sieve has a height of 12 cm, the resultant increase in the volume of the discharged dispersion of the grinding stock is 110 , compared with the volume of the charged dispersion of the grinding stock. Tho resultant particle distribution of the pigment comprises a main fraction at 4 to 10^1, large fractions at 2 to 4 and at 10 to 13 ^u, and small fractions at 1 to 2 7 u aannda aatt 13 t too 15o^u.

Claims (8)

HAVING NOW particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim isi

1. » A process for the production of aqueoi β dispersions of so|i<§ by dispersing an organic or inorganic solid insoluble or barely soluble in water wherein the organic or inorganic solid insoluble in water is agitated in an aqueous medium with a dispersing agent and with a grinding material containing silicon dioxide groups, which material has a specific gravity greater than 1·5» is harder than the product to be dispersed and is in the form of smooth-surfaced rounded elements whose radii do not differ by more than 40 from the mean radius, and whose diameters are from 0*3 to 1·5 mm, and is used in a proportion of 10 to 300$ of the solid volume, calculated on the volume of the dispersion of the grinding stockf the aqueous medium contains non-ionic, anionic, cationic or betaine-type dispersing agents in a proportion of 0.1 to 200 by weight of the solid to be dispersed, optionally in conjunction with defoaming agents; the agitation of the grinding mixture is continued until the particle size of the grinding stock is 6 or preferably less} and where dispersing agents are used which increase the volume of the grinding stock during the grinding operation by more than 20 by the formation of fi>am, the formation of air (or gas) aspiring currents at the interface between the air (or gas) and the dispersion of the grinding stock or mixture is substantially prevented during the grinding operation.

2. « A process according to Claim 1, wherein the solid to be dispersed is an organic or inorganic dyestuff*

3. · A proeess according to Claim 1 or 2, wherein the grinding material consists of glass balls having radii not differing by more than 1G?£ from the mean radius and having a diameter from about 0.4 to 0.9 mm.

4. · A process according to Claim 1, 2 or 3» wherein the dispersing agent is an alkali metal salt of dinaphthyl-methane-2, 2'-disul honic acid or of a polystyrene-sulphonic acid with a molecular weight of 10,000 - 15.000; polyvinylpyrrolidone; an alkali metal salt of spent sulphite cellulose liquor or of an amine condensation product thereof; a condensation product of a cresol-formaldehyde resin and the tJ-sulpho acid obtained from 2,6-naphthol-sulphonic acid; a polyalkoxylated carboxylic acid; an alcohol; a phenol; an amine or a mercaptan of a high molecular weight; an alkali metal, ammonium or alkaline earth metal salt of a carboxylic acid; a sulphonic acid or a sulphuric acid ester of high molecular weight; a salt of a primary, secondary or tertiary amine of high molecular weight with a hydrohalic acid or sulphuric acid; a quaternary ammonium compound or an aminosulphonic acid of high molecular weigh β

5. · An apparatus for the continuous dispersion of solids by the process according to any of Claims 1 to 4, comprising a cylindrical grinding vessel arranged in a horizontal or vertical position and having an inlet and outlet for the dispersion and an axially disposed shaft with mixing elements attached thereto; a sieve on or in the allowing the dispersion to pass and retaining the grinding elements; the discharge outlet being positioned downstream of the plane in which the sieve joins the grinding vessel.

6. * An apparatus according to Claim 5» wherein the last mixing element in the direction of flow of the dispersion is designed as a compact cylinder having about the same radius as the remaining mixing elements.

7. An apparatus according to Claim 5 or 6, v/herein the outlet is so shaped or positioned that a layer of the dispersion is interposed between the sieve and outlet.

8. An apparatus according to Claim 5 or 7» wherein the sieve is a cup-shaped body comprising a part normal to the shaft and a part parallel with the shaft, and one of these may be formed by a compact surface. 9« A process according to any of Claims 1 to 4» operated by means of an apparatus according to Claim 7» wherein the layer of the dispersion which is kept interposed between the sieve and the outlet of the apparatus, is made to have a consistency such that it prevents the aspiration of air or gas into the grinding mixture. 24th Dated this/day of September 1964 For the Applicants DR. PARTNERS Byi