Latent Image Recording Method And Electric Recording Apparatus

Abstract

An improvement in the method and apparatus for generating imagery in which information from either an original document or an electronic input is placed on paper or other suitable record medium by the use of control element(s) which establish an electric field adjacent to the record medium; the recording element(s) being immersed in liquid, described in U.S. Pat. 3,623,122 which improvement consists in separating the image forming step from the development step and the apparatus for accomplishing the same.

Description

This invention relates in general to electrophotography and, in particular, to a method and apparatus for producing copies.

Methods and techniques for producing visible images from an electrical input have been known and practiced for many years. Facsimile recorders employing special papers are in wide use. Such images may be formed either through the electrolytic development of a color or through the use of an electrical discharge to vaporize (blast-off) an overlayer.

Another widely practiced technique involves a corona discharge from a fine stylus spaced a very short distance above an insulating surface--generally a paper whose surface is coated with an insulating thermoplastic film. This method of recording is well described in the patent literature, including the following U.S. Pat. Nos. 2,894,799; 3,064,259; 3,068,481; 3,131,256; 3,208,176; 3,217,330; 3,289,209; 3,383,697; 3,384,898; 3,409,899; 3,417,404; 3,434,157; 3,471,861.

Still other methods of generating an image are described in U.S. Pat. No. 3,121,373 and U.S. Pat. No. 3,623,122 and in a recent article appearing in "Photographic Science and Engineering" Volume 15, Number 5 September-October 1971.

The disclosures in this prior art are incorporated herein, by this reference.

The present invention is an improvement upon the invention described in U.S. Pat. No. 3,623,122 which describes a method and apparatus for generating imagery in which information from either an original document or an electronic input is placed on paper or other suitable record medium by the use of control element(s) which establish an electric field adjacent to the record medium, the recording element(s) being immersed in a liquid, such liquid being an electrostatic liquid toner, as is commercially available or can be made.

In the present invention, the recording and development steps are separate and distinct with a highly insulating liquid surrounding the junction between the recording element(s) and the recording medium and covering the recording medium for the recording step and the resulting latent image being exposed to a liquid developer at a later time. By carrying out the process in this manner, several significant advantages are obtained, including the following:

1. The recording and development steps can be separated for up to several minutes under ideal conditions, allowing any background noise or triboelectric charging produced by the recording element(s) rubbing on the recording medium to decay to a low or nonexistent level for the development step;

2. The latent image can be given a short development time to minimize background toner pickup, heretofore experienced with simultaneous recording and development;

3. There is no toner deposit buildup on the recording element(s) since there is no contact between the recording element(s) and the electrostatic liquid toner;

4. An array of closely spaced recording elements may be used since the absence of electrostatic toner eliminates element to element shorting.

The present invention will be more fully understood from the description which follows taken in conjunction with the drawings in which:

FIG. 1 is a schematic view of one kind of recorder which may be used in the practice of the invention and

FIGS. 2-5 show modifications of the invention and of the apparatus of FIG. 1.

EXAMPLE 1

Example 1 is best understood with reference to FIG. 1. The recorder shown in FIG. 1 includes a medium 10 upon which the record is made. This recording sheet 10 may consist of a web of a clear plastic film base or any type of paper. A means 8, comprising a warm air supply or heat lamps, is provided for drying the sheet so that, if the recording medium is paper, it may be thoroughly dried. The recording medium 10 is guided through a compartmented trough 12, the compartment 2 at the entry end containing a highly insulating liquid 3 and the compartment at the exit end containing a liquid developer 14, rollers 16 guide the recording medium through the liquid baths. Any conventional means (not shown) may be utilized for advancing the recording medium through the highly insulating liquid 3 and liquid developer 14 contained in the trough 12. The recording medium may be continuously drawn through the recording system or the drive may be intermittent; for example, if a single frame at a time is to be recorded. Excess developer solvent remaining on the web is removed by squeegee rollers 18 and residual developer solvent remaining on the web is removed by a warm air plenum 20.

The recording stylus 22 includes a stylus tip 25 which may consist of a coarse wire sharpened to a tip width of 2 to 3 mils or the tip 25 may be spherical with a radius of about 5 to 20 mils. The recording stylus is moved over the surface of the recording sheet, the stylus tip contacting the recording surface, by an electromechanical drive 26. A modulated source of electrical potential 30 establishes an electric field between the stylus 22 and a conducting counterelectrode 28, thereby producing a latent image on the recording medium, which image is made visible when the recording medium 10 passes into the developer bath 14.

The electromechanical drive which positions the stylus on the recording medium may be any one of a variety of drives well known to the art, for example, an X-Y recorder or servo drive to position the stylus in two directions or a high-speed recording pen motor or any other suitable known mechanism.

Alternately, the electrode structure 22 may consist of a linear array of stylii extending across the recording medium in a direction perpendicular to the direction of web travel. This array may be formed of printed circuit stripes upon a circuit board, the strips spaced 100 to the inch, for example. The recording potential at each stylii may be controlled by individual high voltage transistors or, for an optical input, by the use of photoconductor or photoemissive elements as described in U.S. Pat. Nos. 3,121,373 or 3,623,122.

Instead of a single trough with a divider as shown in FIG. 1 other means could be used to separate the recording and developing liquids. For instance two separate troughs 12 could be used with rollers 16 as shown in FIG. 2 or other means for guiding the recording medium from one trough to the second trough. Or, as shown in FIG. 3, a single trough 12 with two compartments connected by a narrow slit 17 through which the recording medium passes could be used to achieve separation. Rollers 16 might also be used instead of the slit, as shown in FIG. 4. Developer could be kept out of the insulating liquid compartment in FIGS. 3 and 4 by means of a positive pressure on the insulating liquid side, due to a difference in hydrostatic head, for example.

FIG. 5 shows a transfer method of copying as described in U.S. Pat. No. 3,623,122 with the modification of the copying and development steps. Trough 2 contains the highly insulating liquid 3 and trough 12 contains the liquid electrostatic toner 14. Rather than develop the image directly on a paper 10 or film 10 (as shown in previous examples), the image is formed on the insulating surface of a transfer roller 74. This roller is uniformly coated with an insulating film 76 having a thickness in the range of 1 to 10 mils. A preferred coating material is a vitreous enamel because of its high strength, high abrasion resistance, and ease of cleaning.

The latent image placed on this insulating surface 76 by the control recording head 72, which may consist of any of the previously shown types of recording head is developed in toner 14 and then transferred to the copy paper 10 by a transfer roller 78. In order to effect efficient transfer, a high electrical potential may be connected between rollers 78 and 74 to aid in electrostatically transferring the image from the drum to the paper. Residual image is removed from insulating surface 76 by a cleaning brush 80.

In this example, the highly insulating liquid was a petroleum solvent, (Isopar G manufactured by Humble Oil and Refining Company), but any high flash point, high resistance liquid could be used such as other members of the Isopar series, or Stoddard solvent. The high resistance, highly insulating liquid should preferably be one which is compatible with the developer.

The developer used comprised a black pigment dispersed in a hydrocarbon mixture (Hunt 25-49) diluted to 1/8 percent by volume developer in Isopar G.

For best results, the development step should be timed so that background noise will decay and its developed density be very low or nonexistent. If too long a time factor is involved, the paper recording medium (not being a very good insulator) will allow the image also to decay to a point where adequate density is not obtainable upon development.

Claims

Having now described the invention in accordance with the Patent Statutes, I claim:

1. A recording apparatus including:

at least one recording stylus,

means to move a recording medium relative to said stylus,

means to maintain one end of said stylus in physical contact with said recording medium, said end of said stylus and said recording medium being immersed in an insulating liquid,

a counterelectrode disposed at the face of said recording medium opposite to the face which is maintained in contact with the stylus,

means to feed a signal to said stylus indicative of information to be recorded on said record medium, whereby a latent image is formed on said recording medium,

and means to move said recording medium into physical contact with a liquid developer whereby said latent image is rendered visible, and recording of a visible image is achieved, said liquid developer being in a separate pool from said insulating liquid.

2. The apparatus of claim 1 wherein a source of potential is connected between said stylus and said counterelectrode.

3. The apparatus of claim 1 including at least one electro-optical transducer provided for controlling the potential between said stylus and said counter-electrode and including optics for imaging an optical signal on said electro-optical transducer.

4. The apparatus of claim 1 wherein the stylus comprises an array of recording elements which extend across the width of the recording medium, the signal fed to each of said elements being generated individually by electronic or photoconductor means.