US3444055A - Electrolytic recording medium - Google Patents

Description

May 13, 1969 LIEBLICH ELECTROLYTIC RECORDING MEDIUM Filed on. 27. 1966 IN VEN TOR. /////V4 [/a'z/M United States Patent Int. Cl. 341m /20 US. Cl. 204-2 11 Claims This invention relates to the art of electrolytic recording, and in particular to an improved electrolytic recording medium or paper.

Recording paper of the electrolytic type is generally marked by passing the paper between a positive eroding metal anode electrode and a negative non-eroding cathode electrode. The paper is impregnated with an electrolytically-conducting solution containing certain ingredients. When a voltage is applied between the electrodes and current is passed through the recording paper, metal ions are introduced into the paper from the anode and reacted with one or more of the ingredients of the paper impregnant to form a colored mark on the recording paper.

To be acceptable for facsimile recording purposes, the recording paper preferably should be white initially and should have the ability to produce marks having a density which is at least close in linear relationship to the current passed through the paper. The density of the marked area should be variable uniformly in a range from white for zero current flow through grays for currents of intermediate magnitude to black for currents of maximum value. The mark preferably should be black so as to provide a good contrast with the white background.

There should also be a minimum of bleeding or fringing of the mark so as to provide good resolution. The unmarked paper while stored in moist condition in sealed containers for extended periods of time prior to use should remain stable without chemical decomposition of its ingredients which would cause discoloration of the paper or affect the reproducibility of results without recorder adjustment. Further, the marked recording paper should not become discolored, give off unpleasant or other odors, or be subject to the transfer of the mark to adjacent materials. The marked recording paper should be insensitive to light even after being repeatedly run through any of the conventional duplicating machines involving exposure to ultraviolet or other strong light sources.

Heretofore successful recording papers have been provided employing pyrocatechin, also called catechol, as the marking compound. While generally satisfactory, some difiiculty has been had with the catechol papers because of the tendency of catechol to diffuse or transfer to and to discolor adjacent sheets of paper in contact with or in close proximity thereto. Catechol vapors also may cause discoloration of the walls and other surfaces near the recorder during the recording operation.

This invention provides an improved electrolytic recording medium which is free from objectionable odors. Moreover, the mark produced on the recording medium of this invention is of high resolution and definition with minimal bleed or drag. The medium also shows markedly improved vapor pressure and transfer and stability characteristics over catechol-containing recording media.

The electrolytic recording medium of this invention, is

a porous sheet impregnated with an electrolytically-conducting solution containing catechol oxalate (o-phenylene oxalate). This material gives an excellent blue to bluegreen mark when used as a marking compound in an electrolytic recording medium marked by the passage of current through the sheet and contacting an anode which contains iron. The mark is best obtained on a sheet in the acid pH range preferably between about two to about four.

Although the aqueous solubility of catechol oxalate is only about 0.4 g./ ml. of water, the solubility is significantly improved by the addition of certain glycols, polyethylene glycols, and ether derivatives of polyethylene glycols. These additives act as solubilizers or dispersing agents, or both.

These and other aspects of the invention will be more fully understood from the following detailed description and the accompanying schematic perspective drawing showing the recording system of this invention.

Referring to the drawing, a sheet of paper 10 impregnated with a conductive electrolyte containing catechol oxalate is passed between a stationary eroding anode 11 which contains iron, and a rotatable non-eroding cylindrical cathode 12 which has a prismatic platinum- Compound: Amount, g. Catechol oxalate 1.5 Trimethylene glycol 10.5 Sodium nitrate 10.0

Water 85.0

The above solution had a pH of three and was sufiicient to impregnate ten square feet of paper having high wet strength and a thickness of about three mils.

Ordinarily, the aqueous solubility of catechol oxalate at room temperature is only about 0.4 g./100 ml. of water, but its solubility was significantly increased by the addition of the trimethylene glycol. Other polyethylene glycols and ether derivatives of polyethylene glycols can be used as solubilizers or dispersing agents, or both. For example, Tergitol NPX (a trade name for an ether of polyethylene glycol) is an effective dispersant for catechol oxalate in aqueous solution, and the trimethylene glycol (1,3 propanediol) is a particularly effective solubilizer.

The paper impregnated with the formulation of the above example produced a good blue to blue-green mark when subjected to a marking current as shown in FIG. 1. The contact area of the electrodes against the recording paper was about .0001 inch. The paper was about three mils thick when dry before impregnation, and about 3.5 mils thick after impregnation. The paper was impregnated by passing it through the solution and permitting the impregnant to distribute itself evenly throughout the paper. 'Excess impregnant was removed by passing the paper between pressure rollers (not shown), so that when ready for use in the recorder, the impregnated paper had about twenty-five percent to about fifty percent moisture by weight. To retard evaporation, the impregnated paper was stored in suitable sealed containers until ready for use.

The paper prepared and used in the recorder as just described produced a good mark of satisfactory optical density at a spot speed in the range of between about twenty-three to about 135 inches per second at a voltage between about forty to about one hundred volts with the current flow in the range of milliamperes to about 260 milliamperes.

In the example given, the concentration of the catechol oxalate is shown as about 1.5%. However, the amount can be varied from a minimal quantity up to the maximum which can be dispersed or carried in solution by the use of solubilizers.

It is desirable to keep the pH in the acid range for producing a mark of highest resolution and definition. Preferably, the pH should be between about two and about four. The mark produced on the paper under these conditions has minimal bleed or drag, and improved stability characteristics over catechol-containing recording media.

I claim:

1. An electrolytic recording medium comprising a sheet impregnated with an electrolytically-conducting solution containing at least 0.4 percent of catechol oxalate.

2. A recording medium according to claim 1 in which the pH of the solution of catechol oxalate is between about two and about four.

3. A recording medium according to claim 1 in which the solution includes a solubilizer for the catechol oxalate.

4. A recording medium according to claim 3 in which the solubilizer is a glycol.

5. A recording according to claim 4 in which the solubilizer is trimethylene glycol.

6. A recording medium according to claim 1 in which the solution includes a dispersant for the catechol oxalate.

7. A recording medium according to claim 6 in which the dispersant is a polyethylene glycol ether.

8. An electrolytic recording system comprising a sheet 2 impregnated with an electrolytically-conductive solution containing at least 0.4 percent of catechol oxalate, an

iron-containing anode in contact with one part of the sheet, and a cathode in contact with another part of the sheet so that an electric current can be passed through the electrolyte to change its color where it is contacted by the anode.

9. A system according to claim 8 in which the ironcontaining anode is made of stainless steel.

10. A system according to claim 8 in which the electrolytic solution has a pH between about two and about four.

11. A system according to claim 8 in which the solution includes a solubilizer for enhancing the water solubility of the catechol oxalate.

References Cited UNITED STATES PATENTS 2,358,839 9/1944 Wagner 204-2 2,692,228 10/1954 Clancy 2042 2,953,505 9/1960 Mones 2042 2,995,501 8/1961 Tucker et a1. 2042 JOHN H. MACK, Primary Examiner.

T. TUFARIELLO, Assistant Examiner.

Claims (1)

1. AN ELECTROLYTIC RECORDING MEDIUM COMPRISING A SHEET IMPREGNATED WITH AN ELECTROLYTICALLY-CONDUCTING SOLUTION CONTAINING AT LEAST 0.4 PERCENT OF CATECHOL OXALATE.

Images