US3392707A - Apparatus for developing latent electrostatic images - Google Patents

Description

July 16, 1968 G. MARX 3,392,707

APPARATUS FOR DEVELOPING LATENT ELECTROSTATIC IMAGES Filed Oct. 5, 1966 fi\ J 4 M G/, Ian/ "|4b 3o -3b E; fi/QQ n 5! 5 i V 1 6 "I: H02 FIG?) H64 FIGS 6b 7 INVENTOR GERHARD MARX BY W M ATTORN United States PatCQ --3,392,707- APPARATUS FOR DEVELOPING LATENT ELECTROSTATIC *IMAGES Gerhard Marx, Wiesbaden-Kastel, Germany, assignor, by mesne assignments, to Azoplate Corporation, Murray Hill, NJ.

Filed Oct. 3, 1966, Ser. No. 583,918 Claims priority, application ikrmany, Oct. 6, 1965, K 57 3 8 Claims. (Ci. 118-637) ABSTRACT OF THE DISCLOSURE This invention relates to an apparatus for developing latent electrostatic images using a dispersion developer which comprises at least one elongated nozzle means for producing developer spray, the nozzle means being mounted within a slot in one of two opposed hollow bar means having a space between them, each bar means having at least one longitudinal slot and the slots facing each other, and means for establishing a negative pressure within the bar means.

This invention relates to an apparatus for rendering latent electrostatic images visible by contacting an electrophotographic material carrying such an image with a so-called dispersion developer.

Dispersion developers as used in electrophotography the liquid developers and constitute a dispersion of solid toner particles in a liquid medium which has a high specific resistance and a low dielectric constant. By contacting a developer of this kind with a surface electrostatically charged image-wise, the toner particles are attracted by the surface in accordance with the charge image, while the highly resistant liquid flows off.

A visible image is formed and, depending upon the nature of the charge on the surface of the latent electrostatic image to be developed and the nature of the charge on the dispersed particles, either positive or negative prints of the original are obtained.

Various construction forms of apparatus for developing latent electrostatic images by means of dispersion developers are known. In older arrangements it was customary to contact the electrophotographic material with the developer by immersing it in, or drawing it through, a vessel containing the developer liquid and, in so doing, to develop it. It also is known to develop the electrophotographic material by means of a thin film of developer liquid on the surface of a rotating roller.

It also has been proposed to spray the developer liquid onto the coated side of the image carrier from a wide slotted nozzle or a nozzle with a series of holes. When certain conditions are obeserved, this method has proved to be particularly suitable, especially when reversal developers are employed.

The common feature of all the arrangements heretofore known is that the laminar image carrier is moved through the developing section of the apparatus either lying flat or in a downward direction, or occasionally upwards. So far, no apparatus is known by means of which it is possible to develop an image-carrier sheet which is on edge without altering its vertical position. An apparatus in which an upright image carrier could be developed by moving it to the right or left, however, would be of very great advantage in some cases for reasons of economy of space. Any arrangement in which the image carrier was drawn through the liquid or in which the developer liquid was applied with rollers would be fundamentally unsuitable for solving this problem. Spraying devices could be made suitable, but an undesirdraining of the liquid from the higher to the 3,392,707 Patented July 16, 1968 "Ice able effect occurswhenan "attempt is made to develop a vertical image-carrier sheet with perpendicular or slightly inclined slotted nozzle or nozzles having a series of holes. The lower areas of the image are more strongly developed thanthe upper ones and, in addition, lettering shows blurring in the direction of movement. This is due to the lower part of the image.

The present invention provides an apparatus for developing latent electrostatic images by means of a dispersion developer, in which apparatus means are provided for continuously supplying developer in spray form and for continuously removing unapplied developer and any excess of applied developer, and means including at least one elongated nozzle for producing developer spray, the nozzle or nozzles being spaced within a slot of one of two opposed hollow section bars each having at least one longitudinal slot with the slots facing one another. The bars are spaced for passage of the material to be developed between them and the arrangement is such that, by establishing a negative pressure within both hollow bars, unapplied developer can be removed through the slot or slots in the bar not containing the nozzle and any excess of applied developer can be removed through the slot or slots in the bar containing the nozzle.

By spray form is meant any suitable curtain of liquid, as referred to more particularly below. By una-pplied developer is meant developer which, during continuous delivery, does not strike material to be developed. By excess of applied developer is meant developer which strikes material to be developed and is deflected back therefrom. Elongated nozzles may contain, as nozzle apertures, :a slot or slots or a series of holes.

In a construction of particular interest, the apparatus may be adapted for passage of the material to be developed in a vertical position. Thus, in particular, the nozble aperture may be reduced in cross-section in the direction from the top downwardly. Also, means may be provided for collecting any residual liquid from the lower edge of the material being developed. Such an apparatus is free from the above mentioned disadvantages.

The apparatus of the invention is illustrated by way of example in the accompanying drawings, in which:

FIGURE 1 is a general perspective view,

FIGURE 2 is a cross-section through a simple constructional form of developing device, and

FIGURES 3, 4, and 5 are cross-sections through additional constructional forms of this device.

Referrng to the drawings, in FIGURE 1, the hollow section bars 1 and 2 are shown without any top covering in order to reveal the internal arrangement. These hollow section bars, instead of being of square section as shown in FIGURE 1, may have other desired crosssection and may, for example, be polygonal, circular or oval. The choice of section will be made according to the particular requirements.

Materials from which the hollow section bars are made must be solvent-proof in order to resist the dispersing agents and so as not to become distorted. Accordingly, practically all metals and also a large number of plastics may be employed for producing the hollow section bars.

The longitudinal slots 3 and 4 in the hollow section bars preferably are made by machining. Their width depends on various factors, primarily on whether there are one or more slots in each bar and also on what quantities of liquid are to be delivered per unit of width. Furthermore, the flow behavior of the developer liquid must be considered. With more viscous liquids, wider slots must be provided than in the case of those having a lower viscosity. In addition, when the slots are made, consideration must be given to the suction power with which the pump operates. If it produces only a weak negative pressure, the slots must be narrower than in the case of a stronger negative pressure. Moreover, in the case of the hollow section bar in which the spray nozzle is housed (see below), the width of the nozzle at the outer edge must be taken into account. Generally, it will be found that, with slot widths of 1 mm. to 10 mm., and when the other conditions are suitably selected, successful operation of the apparatus according to the invention always can be achieved.

It is not necessary for both hollow section bars to have the same number of slots or for these always to be exactly opposite one another. In particular, in the case of a low throughput of liquid, it frequently is advantageous to provide the hollow section bar 2 receiving unapplied liquid with two slots which are disposed opposite the spray nozzle and to the right and left of the line of outlet of the liquid, as shown in the case of the slots 3a and 3b in FIGURE 4.

The hollow section bars 1 and 2 are disposed opposite one another at a small distance apart, so that a gap 5 (FIGURE 2) is formed between them. This gap must be at least of such a width that the thickest image-carrier sheet employed can pass through it without difficulty. With a width of about 0.2 mm., this normally will be the case. When only image-carrier sheets of smaller thicknesses are to be processed, smaller separating distances are possible. In order to obtain the most favorable separating distance by adjustment, it is advantageous to install one of the two hollow section bars so that it is horizontally movable with respect to the other. About 5 mm. has been found to be a reasonable upper limit for the separating distance. Greater distances also are possible, but then the other dimensions of the apparatus may have to be adapted accordingly.

When thin image carriers are employed, they may become crumpled in the gap 5. It also may happen that bent corners of the image carrier become jammed in one of the slots. This undesirable effect can be eliminated by means of stripping rods or by arranging one or more rollers in the hollow section bar that does not contain a spray nozzle, as in the case of the roller 14 in FIG- URE 5 and the rollers 14a and 14b in FIGURE 3. The rol ers must be mounted so they can rotate easily. With high feed rates of the printing material, it is occasionally even advantageous to drive these rollers. When only positive prints are to be developed with the apparatus according to the invention, a roller 14, as shown in FIGURE 5, may be so arranged that it is wetted by the developer liquid. When, however, reversal developing also is to be performed, an arrangement of the rollers as shown in FIGURE 3 is advisable. The rollers 14a and 14b are not wetted by the developer liquid, since the spray jet passes through between them.

The nozzles from which the developer liquid is forced may have various forms. As already stated, they may be constructed as broad slotted nozzles or as nozzles with a series of holes. Broad slotted nozzles 6 may consist, for example, of two separate metal jaws pressing one on the other and whose upper inner surfaces, which form the side boundaries of the passage 7 from which the liquid issues, are provided with as high a degree of surface finish as possible. In this constructional form, the passa-ge within the nozzle should be of such length and width that a substantially laminar flow develops therein. The spray jet issuing from the broad slotted nozzle then forms a completely even curtain of liquid with which particularly good prints are obtained. The gap widths in slotted nozzles of this kind should be between 0.1 and 2.0 mm., preferably between 0.2 and 1 mm.

Simpler to produce are constructional forms of broad slotted nozzles as shown in FIGURES 4 and 5. Here, by means of baffle plates inserted in the nozzle space, two ducts or passages 8 are formed leading into the outlet gap in each case. This form preferably is used with low throughputs of liquid. -Low throughputs of liquid are those in which about 0.1-0.3 liter/min. of liquid is delivered per centimeter of nozzle width. Liquids delivered in this way would not normally be described as being sprayed, but in the present case this term conveniently may be used to include this kind of delivery.

Nozzles with a series of holes also may be used. These may consist, for example, of a tube with one or more straight rows of holes. A separate small spray jet issues from each hole. When only one row of spray holes is used, there may be a noticeable effect as regards longitudinal streaking of the print. In order to prevent this undesirable effect when nozzles with a series of holes are employed, it is convenient to arrange at least two rows of holes parallel to one another. The holes in one row are then staggered with respect to those in the adjacent row. Prints of high quality then can be also produced with nozzles having a series of holes. The diameters of the holes in the tubes may be about 0.2-2 mm.

With high rates of feed of the image carrier, it may be necessary to employ more than one spray nozzle in order to ensure adequate development. An example of an arrangement with two spray nozzles 6a and 6b is shown in FIGURE 5.

When the apparatus of the invention is arranged vertically, it has proved to be advantageous to cause the throughput of developer liquid per unit of length to decrease in the downward direction. By this means the result is achieved that the prints are completely free from blurring, which might otherwise be caused by developer liquid flowing downwardly. This latter effect already is very much reduced by the arrangement according to the invention, as previously described, but it can be suppressed practically completely by the means referred to. The decrease in the throughput may be effected in various ways. For example, it is possible to reduce the crosssection of the nozzle space 9 towards the lower portion. Furthermore, the gap widths 7 or 8 can be made narrower towards the lower portion. In the case of nozzles with a series of holes, the diameters of the holes can be continously reduced in the downward direction.

The supply reservoir and the delivery units for circulating the developer liquid are not shown in the drawings. These may be arranged in a conventional manner. It has proved to be advantageous to select an arrangement in which, on the one hand, developer liquid is forced out of the supply reservoir, through a feed hose 12 into the interior of the spray nozzle 9 and in which, on the other hand, the liquid admixed with air is drawn from outlets 13 and conveyed back to the supply reservoir. The result of the second part of this operation is that a small negative pressure prevails in the spaces 10 and 11, so that even developer liquid which might otherwise escape laterally is drawn into these spaces. This arrangement is very simple to achieve with two separate pumps. For this purpose it is possible to use all types of pumps in which only slight variations of the pressure occur. Piston pumps therefore can be employed only with the interposition of air reservoirs. All types of rotary pumps can be used directly. Gear pumps have proved to be particularly suitable as pressure pumps. It is necessary only to take care when selecting the pumps that any packings contained therein consist of a material resistant against the dispersing agent of the developer, which is as a rule a hydrocarbon or a chlorinated hydrocarbon. The delivery rate to be selected for the pump depends upon the rate of advance of the image carrier, the width of the apparatus and also upon the pressure head of the system. When an additional pump is used to draw the liquid out of the hollow section bars, care must be taken that a suction pump is selected in which the developer liquid is not homogenized too greatly with the air drawn off therewith. Otherwise, separation in the supply reservoir takes too long, so that an air-developer liquid mixture may be forced into the nozzles.

The conveyance of an image carrier with a latent electrostatic image through the space between the two hollow section bars in which there is a liquid curtain formed from the dispersion developer may, if desired, be effected manually. It is more appropriate, however, to effect the conveyance by means of suitable elements of the apparatus. Conveying rollers arranged in firont of and behind the hollow section bars and parallel thereto have proved to be suitable for this .purpose, such rollers bearing the reference numerals and 16 in FIGURE 1. The rollers may be moved up closer to the hollow section bars than is shown in FIGURE 1. In order to prevent a sheet which is supported on its lower edge, and rests thereon during the conveying process, from being introduced into the gaps 5 askew or in a bent condition, it is advantageous to mount additional horizontally running conveying elements at the lower edge of the apparatus, on which the sheet can ride. A conveyor belt 17 and two conveyor rollers 21 are shown in FIGURE 1 as a suitable device of this kind.

Both image carriers in individual sheet and in web from unwound from rolls can be developed with the apparatus which has been described. Furthermore, it is an advantage of the apparatus according to the invention that both direct prints and reversal .prints can be produced in it. Reversal prints can not be produced in every developing apparatus, since in reversal developing care must be taken that the developer does not reach the back of the image carrier. In the present apparatus, however, this is generally a normal feature.

The application of a voltage during the developing process is also possible, particularly when roller arrangements as shown in FIGURES 3 and 5 are used. One pole of a suitable source of direct-current voltage may be connected to the nozzle, which in this case must be made of metal, and the other pole to the roller or rollers, which is or are then also made of metal.

As described, the apparatus according to the invention fully meets the requirement initially stated, namely that it should be possible to operate it in a vertical or a slightly inclined position. In order to give an example of how the apparatus can be used, in FIGURE 1 there is shown the projection plane 18 of a re-enlarging apparatus, this plane advantageously taking the form of a suction surface. In order to prevent the printing material from sliding down during the conveying process, an inclined supporting strip 19 is mounted below the projection surface. A sheet dispenser, indicated generally at 20, is advantageously combined with a charging device and pushes the charged, and hence light-sensitive, electrophotographic printing material onto the projection plane 18. After exposure, the conveyor means 17, 15, 16, and 21 are set in motion and move the image carrier through the developing apparatus. Very short developing times can be obtained, since the construction of the apparatus may be very compact. The components can be even more closely associated than is shown in FIGURE 1.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

1. An apparatus for developing latent electrostatic images using a dispersion developer which comprises at least one elongated nozzle means for producing developer spray, the nozzle means being mounted within a slot in one of two opposed hollow bar means having a space between them, each bar means having at least one longitudinal slot and the slots facing each other, and means for establishing a negative pressure Within the bar means.

2. An apparatus according to claim 1 in which the bar means are vertically positioned.

3. An apparatus according to claim 2 in which the nozzle aperture is progressively reduced in cross-section from top to bottom.

4. An apparatus according to claim 2 in which at least one roller is mounted in the bar not containing the nozzle, whereby conveyance between the bars of material to be developed is facilitated.

'5. An apparatus according to claim 2 including conveying means for at least one edge of material to be developed.

References Cited UNITED STATES PATENTS 2,289,753 7/ 1942 Capstaff.

2,956,494 10/1960 Tyler et al. -89 XR 3,027,821 4/1962 Wright 9589 3,038,442 6/1962 Jones et al. 1l8-637 3,168,021 2/1965 Levene 118--637 XR 3,196,832 7/1965 Zin 118-637 3,238,921 3/1966 Engelstad et al 118-637 3,270,711 9/1966 Leach l18--627 CHARLES A. WILLMUTH, Primary Examiner.

PETER FELDMAN, Examiner.

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