Patent GB-804317-A (GB)
Title: Improvements in or relating to a method of and apparatus for preparing or improving the stability of suspensions or emulsions
Inventor: PAUTARD FREDERICK GEORGE EDWAR
IPC: B01F3/08
Filed: 1953-12-04
Abstract: Emulsions and suspensions or a mixture of the components thereof are passed between one or more pairs of opposed electrodes in contact or separated by not more than 0.01 inch between which passes an alternating or pulsating current of not more than 200 volts, to stabilize or produce the dispersion.  A suitable apparatus comprises a chamber or passage for the material to be treated and at least one pair of electrodes situated, or so adjustable as to be, in contact or to form a gap of not more than 0.01 inch and means for passing said material through said gap, the apparatus being adapted to operate under the above conditions without dispersing the material of the electrodes.  In Fig. 1, an earthed vessel 1 constitutes one electrode and the other consists of the blades 3 which may be rotated at 300 r.p.m. and the outer edges of which are 0.002-0.01 inch from the wall of the vessel. The blades are connected via the shaft 2, e.g. to the line phase of the mains 170 v. 50 cycles alternating current supply. In Fig. 3, one electrode consists of a vessel 4 connected to the neutral phase of a 100 v., 50 cycles supply and has a ring of studs 5 round the inside which corresponds with a similar ring of studs 9 on a disc 8 which can be <PICT:0804317/III/1> <PICT:0804317/III/2> <PICT:0804317/III/3> <PICT:0804317/III/4> <PICT:0804317/III/5> rotated at 1500 r.p.m. on a shaft 7 by which the disc is connected to the line phase of the supply.  A stirrer 10 is also present. In the apparatus shown in Fig. 5, the earthed vessel supports a radially corrugated disc 14 parallel to which is a similar disc 12a which can be rotated at 2000 r.p.m. and to which, by means of the shaft, is applied a potential of 200 volts.  The closest approach of the corrugations may, e.g., be 0.001 inch and the widest separation of the corrugations may be 0.002 inch.  Fig. 7 illustrates a stationary apparatus in which the dispersion to be treated is passed through one electrode 15 connected to the neutral phase of 50 cycles A.C. supply, through the gap 24 between said electrode and an adjustably positioned second electrode 17 connected to the line phase of the supply through a 120 ohm resistance.  The dispersion then enters a chamber 20 surrounding the electrodes which is in turn surrounded by a cooling jacket 19 provided with an inlet and outlet for a medium such as water.  The gap may be about 0.005 inch.  Alternatively, the current may be supplied through the oscillating circuit shown in Fig. 8, wherein an inductance 30 in series with a capacitance 31 is connected across the electrodes which are connected in series with a resistance 34 across the supply.  Such an arrangement might produce a frequency of 500 megacycles per sec.  An apparatus (Fig. 9, not shown), is described which embodies a series of electrodes of a generally similar character to those of Fig. 7, through which the dispersion passes consecutively.  Apparatus of this type or of that illustrated in Fig. 7 may be connected to a stirring or mixing machine or an emulsifying or dispersing apparatus.  In Fig. 10 (not shown), an embodiment similar in operation is illustrated, in which one electrode is tapered and enters the tubular second electrode so as to make contact or near contact with the inner periphery thereof. The tubular electrode can be replaced by a disc having an orifice through which a needle-shaped first electrode enters (see Fig. 11, not shown). Preferred electrodes are made of carbon or semiconductors, and advantageously they are in contact.  If desired, pressure may be applied to the electrodes and the material forced through at a suitable pressure, e.g. 100 lbs./sq. inch or more if the construction of the apparatus permits.  Aqueous media are particularly suitable, but the presence of up to 10 per cent of a liquid of boiling-point up to 80 DEG  C. such as alcohol or acetone is sometimes an advantage; substances (e.g. acetic or citric acid, dextrin or gelatine, or (in other solvents) alcohols, esters, carboxylic acids, phenols, resins, waxes or hydrocarbons), may be added to reduce or increase the resistance of the dispersion treated; an inert gas under pressure, such as nitrogen, may be applied above the liquid in apparatus of the type shown in Figs. 1, 3 and 5, if these are closed, to prevent chemical reaction taking place.  If desired, a unidirectional field may be applied together with the alternating current.  Current densities of at least 60 amps./sq. cm. may be produced at the electrodes.  The dispersion may be repeatedly treated by recirculation to the electrodes, and mechanical agitation may be employed.  For treating inflammable dispersions, an enclosed apparatus should be employed.  Examples refer to the production of the following emulsions or dispersions in the illustrated apparatus: (1) polyvinyl acetate/water/titanium dioxide pigment (for emulsion paint); (2) linseed oil/water/titanium dioxide; (3) linseed oil/white spirit/titanium dioxide pigment, the product being an adequately dispersed paint; (4) an aqueous suspension of titanium dioxide; and (5) carbon black in water.  The first Provisional Specification also refers to the use of a triple-roll mill in which the centre roll is attached to the A.C. source and insulated from all other parts which are earthed, to produce a water suspension of carbon black.