US3228608A - Electrophotographic developer electrode - Google Patents

Description

Jan. 11, 1966 w. SIMM ETAL 3,228,608

ELECTROPHOTOGRAPHIC DEVELOPER ELECTRODE Filed June 11, 1963 2 Sheets-Sheet 1 F/GJ INVENTORS W4LTER S/MM BY OTTO KOC Jan. 11, 1966 w. SIMM ETAL ELECTROPHOTOGRAPHIC DEVELOPER ELECTRODE 2 Sheets-Sheet 2 Filed June 11, 1963 mmm ww m xmw Du Dn E0 m 0 m United States Patent 3,228,608 ELECTROPHOTOGRAPHIC DEVELOPER ELECTRODE Walter Simm, Opladen, and Otto Koch, Cologne-Stammhelm, Germany, assignors to Agfa Aktiengesellschaft,

Leverkusen, Germany, a corporation of Germany Filed June 11, 1963, Ser. No. 287,041 Claims priority, application Germany, June 29, 1962, F 37,187; Dec. 20, 1962, F 38,613 1 Claim. (Cl. 23915) This invention relates to an electrophotographic developer electrode for electrostatically atomizing the electrophotographic developer liquid which is characterized by a hollow cylinder, which widens out at the bottom in the form of a funnel with a sharp edge and a reflux tube being arranged inside the hollow cylinder for transporting back the excess of developer liquid, whereby the opening of the reflux tube lies near the funnel shaped outlet of the hollow cylinder.

In the Belgian Patent 616,914 is described an electrophotographic developer apparatus which is characterised by the combination of an electrostatic atomiser electrode consisting of hollow cylinder which wides out at the bottom in the form of a funnel and has a sharp edge, with a grid electrode.

This atomiser electrode has various disadvantages. Thus, for example, the mechanism for adapting the velocity of the pump which controls the rate of supply of developer fluid, to the desired atomising conditions is very susceptible to trouble and requires additional expenditure due to the use of adjustable gearings for the supply pump. If the apparatus is out of action for any length of time, the electrode very easily dries up so that it first has to to be cleaned, filled and wetted before it can be used again. Even slight leakages in the punmp of faults in the outlet aperture of the electrode disturb the equilibrium between the quantity of fluid supplied and the quantity of fluid used up by atomisation in the atomiser funnel so that uniform atomisation of fluid is then no longer possible. In such cases, large drops are frequently fonrned and corona discharges occur. When using concentrated colour developer solutions, a sludge is easily formed in the electrode funnel due to evaporation of solvent, and this may cause the tubes of the apparatus to get blocked.

We now have found that these disadvantages may be overcome by means of a return flow tube arranged inside the hollow cylindrical atomiser electrode described above. In such an arrangement, the liquid is carried in a cycle from the tank to the opening of the electrode and from this opening back into the tank. The edge of the electrode is continuously wetted, but the liquid does not drip out even when no voltage is applied.

The atomiser electrode according to the invention is shown diagrammatically in the accompanying drawings: FIGURE 1 shows one embodiment, in which the developer liquid is transported by means of pumps.

The hollow cylinder 1 with the tunnel shaped end 2 is provided with a return flow tube 3 which is inserted in the cylindrical part thereof and can be moved longitudinally. Between this tube and the wall of the cylinder there remains a space 4 through which the liquid which is to be atomised and which enters through a lateral filling tube 5, can descend unimpeded into the funnel-shaped portion 2 of the electrode. The bottom open end of the inner tube 3 lies in the bottom end respectively in the funnel shaped part of the cylinder but does not project beyond it. At the top end, the gap between the tube 3 and the wall of the cylinder is tightly sealed with the exception of the inlet through which the liquid enters. The filling tube 5 and the tube 3 communicate with pumps 6 and 7 respectively or with two separate chambers 6, 7

3,228,608 Patented Jan. 11, 1966 of a pump, such as a geared pump. The connections are so arranged that the pump or pumps are in operation, the liquid is sucked from a tank 8 and delivered to the inlet 5 while the liquid, sometimes with a small portion of air, is sucked at the same or slightly greater pump output from the tube 3 and returned to the tank 8.

At the beginning, when the pumps are already in operation but the electrode is not yet filled with liquid, the liquid first flows down in the gap between the tube 3 and the cylinder 1 to the edge of the funnel. However, the space inside the funnel fills only down to the level at which the liquid surface below the bottom opening of the inner tube closes. At that moment, suflicient liquid is immediately sucked olf through this opening so that there is no further change in the level of the liquid, so that no drops will be formed at the bottom end of the electrode. The amount of liquid contained in the electrode when a steady stage has been reached may be varied by varying the immersion depth of the inner tube so that the lower portion of the electrode may be filled with liquid more or less to the edge.

The tunnel shaped extension 2 is not absolutely necessary for regulating the liquid as described above. The lower end of the electrode could be cylindrical but has been designed to expand merely because this improves the atomising conditions.

The atomiser electrode according to the invention has the following advantages:

The pump output may be fixed once and for all to a certain value independently of the physical properties of the liquid, the voltage and the distance between the electrodes. The pump output need not be maintained exactly at this value but may be allowed to fluctuate within relatively wide limits so that it is possible to use very simple pumps. The rate of liquid supply may be considerably greater than the rate at which the liquid is atomised, so that the reserve liquid can be mixed thoroughly. In this connection, a further advantage of the invention is that the pump assembly can be kept in oper ation continuously even when no aerosol is produced. Atomisation is then regulated merely by switching the voltages on and off. One great advantage of the electrode consists in that the apparatus is ready for use almost immediately after it is switched on even if the pumps have been out of operation for some time and the nozzle is dry, because the return flow system ensures wetting of the apparatus and maintains the liquid in the electrode at the normal level.

FIGURES 2 and 3 show another embodiment of the developer apparatus according to the invention. When the embodiment according to FIGURE 1 is used for developing pictures on a continuous paper strip, it has been found inconvenient for the electrode to be connected to a pump and to the liquid tank through an inlet tube and a reflux tube. This is particularly inconvenient when the electrode has to be moved or several electrodes have to be used simultaneously. Another disad vantage of the atomiser electrode is that the liquid sprayed from the electrode is not deposited evenly on the opposite electrode but at greater density at certain areas owing to the liquid cones forming at the edge of the spray. The said disadvantages are overcome by using a developer electrode with a conveyor worm in the space between the reflux tube and the wall of the hollow cylinder. The electrode then consists of the known hollow cylinder 1 which widens at one end in the form of a sharp-edged funnel 2 and which contains a reflux tube 3, the important improvement being effected by arranging a conveyor worm 9 between the reflux tube and the cylinder wall, this worm taking up a portion of the whole length, e.g. /s of the length of the electrode. The electrode may be arranged vertically or obliquely and FIGURE 3).

the sprayedge 2 is positioned at the top end of the cylinder. The conveyor worm is advantageously rigidly connected to the reflux tube and is situated in the lower part of the cylinder so that the liquid cycle, to be described in more detail below, provides a tight liquid seal in the-upper part and as little air as possible is mixed with the liquid. The hollow cylinder with the reflux tube and the conveyor Worm extend directly into the tank and the lower part of the cylinder is immersed in liquid. The hollow cylinder is mounted to be rotatable about itslongitudinal axis at the point where it enters the tank. The reflux tube is rigidly fixed to the bottom of the tank and outlets 11 for-the returning liquid are provided at the lower end of the reflux tube. The edge of the hollow cylinder, which is immersed in liquid, is situated just above these apertures and must not cover them, because, when the apparatus is in operation, air is carried with the returning liquid and this air must be allowed to escape and not be carried into the liquid cycle as otherwise froth is formed which interfered with the operation of the apparatus.

In this arrangement, it is easy to rotate the cylinder -by-means of an external drive, eg, a worm wheel 12 and a worm 13, whereby the liquid is raised from the tank owing to the relative movement between the cylinder wall and the conveyor worm 9, so thatthe liquid can be conveyed to the upper edge of the electrode. When the liquid reaches the --t-op end of the electrode, it we-ts the spray edge 2 and returns to the tank through the reflux tube 3. The liquid-is kept constantly stirred in this cycle so that no deposits will be formed from highly concentrated dyestuff solutions. This rotation of the cylinder not only ensures that the spray edges -will be kept wetted but also ensures uniform distribution and deposition of'the' aerosol because there are no preferred spray directions as is the case witha stationary spray edge. When the electrode is not in operation, the liquid returns to the tank so that allparts of the electrode are emptied.

Owing to the space saving arrangement of the electrode, the conveyor worm'and the tank, the atomisation may=easily be intensified by connecting several electrodes to a common tank and driving them simultaneously (see In this arrangement, it is advantageous to impart .periodic reciprocal movement to the tank and the electrodes, asthis improves the distribution of aerosol. 'For this purpose, the drive shaft 14 must be connected to the drive motor lfi'through a sliding clutch 15 so that the motor will 'not take'part in this movement. The atomiser apparatus may be increased'to any degree of complexity by the provision of any number of electrodes in the manner described above.

The following dimensions are given by way of example for the atomiser electrode according to the invention:

length of cylindrical part, a, to 100 mm. Diameter of the cylindrical part, b, 3 to 6 mm., preferably 4 mm. Internal diameter of the cylindrical part, c, 2.5 to 5-mm.,

preferably 3 mm.

Diameter of the tube 3, d, 0.5 to 4 mm., preferably 2 mm.

Internal diameter of the tube 3, e, 0.3 to 3 mm., preferably 1 mm.

Diameter of the edge of the funnel, f, 1 to 10 mm., preferably 6 mm.

Cone angle of the funnel, g, 20 to 100, preferably The pump output must be sufficient to ensure that atomisation of liquid will not be interrupted due to shortage of liquid. However, the output may be a multiple of the minimum output, e.g., 1 cc. per min. when the rate of atomisation is 0.2 cc./min. The best position for the electrode when in operation is with its longitudinal axis in the vertical position although it may also be inclined.

Atomisation may also be carried out with the electrode rotated through 180 so that the outlet is directed upwards. In that case, the aerosol is preferably sprayed upwardly.

The processing of .the electrophotographic materials up to the stage of development may be carried out in known manner, for example, as described in Belgian Patent 616,914.

Many different types of electrophotographic materials may be processed in this apparatus, for example, those described in German patent specifications 1,090,093; 1,046,493; 1,031,127 and 1,052,811. Particularly suitable are the usual electrophotographic materials which contain 'Zll'lC oxide, dispersed in an insulating binding 3 agent, as the photoconductive substance. 'Suitable developer solutions aredescribed in Belgian Patent 616,914.

We claim:

An electrophot-ographic developer electrode for electrostatically atomizing the electrophotographic developer liquid comprising a hollow cylinder which is widened at its bottom end in the form of a funnel with a sharp edge, a reflux tube disposed within said hollow cylinder for transporting back the excess of developer liquid, said reflux tube being open at its lower end near the funnel shaped outlet of said hollow cylinder, an inlet aperture in the upper end of said hollow cylinder for the admission of the liquid, an outlet aperture in the upper end of said reflux tube, and pump assembly means being connected to said inlet aperture of said hollow cylinder and 'to said outlet aperture of said reflux tube whereby the liquid sucked .from atank may be introduced into said electrode through said inlet aperture of said hollow cylinder and returned to the tank through said outlet aperture of said reflux tube.

M. HENSON WOOD, JR., Primary Examiner.

EVERETT W. KIRBY, Examiner.

Images