US3622468A

US3622468A - High-speed electrolytic printing including image intensification

Info

Publication number: US3622468A
Application number: US878815A
Authority: US
Inventors: Dennis R Turner; Catherine Wolowodiuk
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1969-11-21
Filing date: 1969-11-21
Publication date: 1971-11-23
Anticipated expiration: 1988-11-23
Also published as: GB1309279A; DE2057271A1; JPS4934160B1; BE759043A; NL7016753A; FR2069542A5

Abstract

In order to derive prints from electrical signals at speeds which are required by modern information transmission, a latent image is produced on a moving recording sheet by the electrolytic dissolution of a metal such as silver from an array of anodes onto the sheet. The latent image is subsequently intensified and made visible by the deposition of additional metal on the metal image particles from a solution. Because of the small amount of catalyst such as silver needed on the sheet to develop the image, the erosion of the anodes is relatively slow. The production of one 8 1/2 X 11 inch sheet of printed matter every 2 seconds is well within the capabilities of the process.

Description

United States Patent Appl. No. Filed Patented Assignee HIGH-SPEED ELECTROLYTIC PRINTING INCLUDING IMAGE INTENSIFICATION 11 Claims, 2 Drawing Figs.

U.S. Cl 204/2, 117/130 E, 117/212, 346/74 E Int. Cl B2lh l/20, GOld 15/06, B32b 15/00 Field 01 Search 204/2, 18 PC; 117/130 E, 212; 346/74 E References Cited UNITED STATES PATENTS Friese-Greene Primary Examiner-John H. Mack Assistant Examiner-T. Tufariello AttorneysR. .l. Guenther and Edwin B. Cave ABSTRACT: In order to derive prints from electrical signals at speeds which are required by modern information transmission, a latent image is produced on a moving recording sheet by the electrolytic dissolution of a metal such as silver from an array of anodes onto the sheet. The latent image is subsequently intensified and made visible by the deposition of additional metal on the metal image particles from a solution. Because of the small amount of catalyst such as silver needed on the sheet to develop the image, the erosion of the anodes is relatively slow. The production of one SlXl 1 inch sheet of printed matter every 2 seconds is well within the capabilities of the process,

PATENTEDuuy 23 ISTI 3, 622 ,468

0. R. TURNER WVE/Vmpi c. WOLOWOD/UK ATT RNEV HIGH-SPEED ELECTROLYTIC PRINTING INCLUDING IMAGE INTENSIFICATION BACKGROUND OF THE INVENTION 1 Field of the Invention The disclosed invention concerns the high-speed production of prints derived from electrical signals.

2. Description of the Prior Art A number of printing processes depend upon the fact that finely divided particles of any metallic substance appear black. In one common process silver ions are transferred electrolytically from a silver anode electrode into an electrolyte moistened paper and reduced by reducing agents in the paper to form finely divided silver particles which produce the visual image. In one form of this process the anode electrode is a silver bar which is in contact with the paper over its entire width. As the paper is transported perpendicular to the bar, the cathode electrode which is in the form of a spiral wrapped around a rotating drum is pressed against it from the other side. A conducting path is thus formed which repeatedly moves across the paper as the drum rotates generating a series of lines. By modulating the current which passes through the paper between the electrodes, the darkness of the lines will be modulated. These modulated lines form the resulting print much as the modulated lines on a television picture tube form a video image. Since all of the material forming the image must come from the anode this process is relatively slow, typi' cally producing one 8 1i X 11 inch sheet every minutes. Large amounts of electric charge must be passed and the erosion of the anode bar is rapid.

Another aspect of the prior art which bears on the instant invention is the electroless" plating technique. This is one way of producing a conductive coating on an insulating body, for instance to serve as a conductive base for subsequent electrode plating. It consists of the immersion of a suitable treated body in a solution which contains, among other things, ions of the required metal and a reducing agent. The reduction of metal is catalyzed at the treated surface of the body and a metal film is deposited thereon without the application of an external current. The process then becomes autocatalytic and the plating is allowed to continue until the desired thickness is reached. Bright copper platings, for instance, whose conductivity is as high as the conductivity of electroplated films are regularly produced in this manner.

SUMMARY OF THE INVENTION It has been found possible to increase the speed at which electrolytically produced prints may be generated far beyond the speeds previously realized in the practice of electrolytic print production. This is accomplished by the application of the electroless plating process for the intensification of an electrolytically produced latent" image. If it is not necessary to derive all of the metal, forming the image, from the anode electrode, much less electric charge must be passed during the writing process. This permits an increase in the speed of the process and reduces the erosion of the anode electrode. The metal ions introduced into the recording sheet are reduced and precipitate as fine metal particles which form the latent" image. These particles subsequently serve to catalyze the further plating of metal from the electroless plating solution producing a visual print. The electroless plating must be caused to take place rapidly so that the image develops rapidly and fine black particles of metal are produced instead of the shiny metal deposits desired in the normal use of the electroless process.

The production of one 8 /2 X 1 1 inch sheet of printed material every 2 seconds is well within the capabilities of such a system and in an exemplary system the production of 1000 sheets requires only 0.0013 inches of anode material. In addition to the production of a black image on a white background, the process is capable of producing a grey scale so that the physical transmission of both literal and pictorial records is possible.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic representation of an exemplary printing apparatus; and

FIG. 2 is a schematic representation of a second exemplary printing apparatus.

DETAILED DESCRIPTION Chemical Systems The success of a printed system such as this rests in part on the choice of a suitable anode material, one which will be easily dissolved from the anode, be easily reduced in the recording sheet and be effective in the subsequent catalytic process. Of the several materials tried Ag, Cu, Au, Pd, and Ni were all successful. However, of these, Ag was by far the best material to serve as a catalyst for the subsequent intensification process. The deposition of silver with a density of as little as 10"8 grams per square centimeter of record area results in a visible intensified image. A satisfactorily dark image is produced by the deposition of between five and 10 times this amount depending on the subsequent intensification conditions. Before intensification a silver density of lO' S grams per square centimeter of record area is just visible so that any density less than this would be considered a latent image. These densities refer to the record area, which is the area that actually appears black. In order to minimize the physical abrasion of the anode material other constituents may be alloyed with the catalytic metal to harden it (e.g., Cu to harden Ag). The selected hardening agent must be corrodable so as not to poison the electrode surface during the writing process.

An electrolyte must be chosen which is chemically appropriate to the choice of anode material. The electrochemical reaction at the anode must produce solution of metal ions at a low electrode potential. In addition there should be a cathode reaction not involving the metal ion with a potential lower than the potential of the plating reaction so that the dissolved metal ions are not replated on to the cathode. However, replating can also be minimized by suitable electrode arrangement. In addition, it is advisable that the cathode reaction take place without the evolution of gaseous products. In the case of a silver anode material any of the soluble nitrates, such as potassium or sodium nitrate, are suitable.

Provision must be made for the reduction of the dissolved metallic ions and their deposition as fine metal particles, which will catalyze the subsequent electroless plating reaction. This can be done by the incorporation in the electrolyte of a reducing agent such as formaldehyde or paraformaldehyde (a polymeric form of formaldehyde with no objectional odor). Silver ions may also be reduced to metallic silver with light. A sufficient quantity of the selected reducing agent can be incorporated in the electrolyte to serve as a reducing agent for the subsequent electroless process.

The electroless plating solution contains a source of metal ions, a complexing agent to control the reaction rate and an acid or base, if needed to adjust the pH of the solution. An exemplary plating solution employs copper sulfate as a source of metal ions, Rochelle salt (potassium sodium tartrate) as a complexing agent and some potassium hydroxide. Another complexing agent which has been used extensively in this solution is a soluble salt of ethylene diamine tetra-acetic acid. This plating solution should be kept separate from the reducing agent until the plating is desired to prevent its deterioration.

Mechanical Systems FIG. 1 shows an exemplary printer. The recording sheet 11 is unrolled from its source 12 and passes around roller 13 through solution A,14. The moisten sheet is then held against the writing head 15 which contains an array of electrode pairs. The sheet then passes around roller 16 through solution 8,17, between a heated roller 18 and a drive roller 19 and into a mechanism 111 in which the sheet is dried and processed to final form 112 and collected in a receptacle 113.

The composition of solution A,l4 and 8,17 may be any one of several combinations of the three basic solutions; that is the electrolyte, the reducing agent and the plating solution. For

instance, the electrolyte and reducing agent may be introduced as solution A while the plating solution is introduced as solution B. Alternatively, the electrolyte and plating solution can be introduced as solution A and the reducing agent as solution B as long as the plating solution does not interfere chemically with the electrolytic writing process. As another of the several possibilities, some of the constituents of solution A as described above can be incorporated in the recording sheet in either wet or dry form. If all of the constituents of solution A are incorporated in the recording sheet solution A,l4 and the corresponding roller 13 can be eliminated.

After the metal ions produced by the writing process are injected into the electrolyte moisten recording sheet, as it passes over the printed head 15, these ions must be reduced to metallic form so that they can precipitate as metal particles and serve as the catalyst for the subsequent electroless intensification. These ions can be reduced by a reducing agent present in solution A or by some process such as the exposure to light from a light source 114. If silver ions are used in the writing process and copper ions are used in the intensification process, the reduction of the silver ions by exposure to radiation can take place even in the presence of the copper ions. Since silver is more noble than copper, conditions can be chosen which will allow this selective reduction.

In order to produce a visible image rapidly and form the fine metallic grains which are required for a black image instead of the shiny metal plating usually derived from the electroless plating process, the plating reaction must be caused to take place rapidly. This can be accomplished by heating the recording sheet after it emerges from solution B,l7. One way this can be accomplished is by passing the sheet over the heated roller 18.

FIG. 2 shows another exemplary printer. Here the recording sheet 21, is not passed through the

solutions

24 and 27, but metered portions of these solutions are carried on to the recording sheet 21 by the rough or porous surface of the

rollers

23 and 26. The degree of roughness or porosity can be used to meter the solutions. The constitution of the solutions I EXAMPLE One chemical system which has proven successful is presented below:

KNO, in l molar aqueous solution Paraformaldehyde (HCHO), 130

grams per liter of aqueous solution KOH- [20 grams per liter of aqueous solution Copper sulfate (CuSO,.5H,O)-

grams per liter of aqueous solution Electrolyte Reducing agent plus Plating solution plus Rochelle salt (KNaC,l-l O,.4H,O)- lOO grams per liter of aqueous solution plus KOH-40 grams per liter of aqueous solution Using these solutions, the best results were obtained when intensification took place at 60 C. Below C., the image developed too slowly. Above 80 C. the bath begins to spontaneously decompose over all parts of the sheet. On an experimental scale, printing which is equivalent to the production of one 8% X l 1 inch sheet every 2 seconds has been readily accomplished.

We claim:

1. A process for the production of a record on a porous recording sheet at least partially impre nated with an electrolytic solution, comprising the electro ytic introduction of metallic ions into the said recording sheet from an anode electrode as the said recording sheet is moved relative to the said anode electrode, the reduction of the said ions, and the precipitation of the resulting metal as metallic particles, characterized in that the recording sheet is brought into contact with at least one additional solution and that additional metal is subsequently deposited at the sites of the said metallic particles from the said at least one additional solution by a chemical reaction catalyzed by the said metallic particles whereby the said record is intensified.

2. Process of claim 1 in which the said metallic particles are composed of a metal selected from the group Ag, Cu, Au, Pd, and Ni.

3. Process of claim 2 in which the said additional metal is selected from the group Cu, Ag, Ni, Pd, Au, and Co.

4. Process of claim 3 in which the said metallic particles are silver and the said additional metal is copper.

5. Process of claim 4 in which the said metallic particles are deposited in a concentration of from 1 X 10"8 grams to l X 105 grams per square centimeter of record area.

6. Process of claim 5 in which said electrolytic solution and said at least one additional solution comprise paraforrnaldehyde as a first portion and copper sulfate and a member of the group consisting of potassium sodium tartrate and a soluble salt of ethylene diamine tetra-acetic acid as a second portion and in which said first portion and said second portion are kept separate from one another until said deposition is desired.

7. Process of claim 6 in "which said paraformaldehyde is present in a concentration of 10 to 150 grams per liter of aqueous solution, said copper sulfate is present in a concentration of 20 to 50 grams per liter of aqueous solution and said potassium sodium tartrate is present in a concentration of 50 to 125 grams of its tetrahydrate per liter of aqueous solution.

8. Process of claim 7 in which the said deposition takes place at a temperature between 50 and C.

9. Apparatus for the production of a record on a porous recording sheet at least partially impregnated with an electrolytic solution comprising, feeding means for the storage and dispensing of the said recording sheet, writing means for the electrolytic introduction of first metal ions into said recording sheet, transportation means for the introduction of relative motion between the said recording sheet and said printing means, said first metal ions being reduced and deposited as first metal particles characterized in the subsequent inclusion of wetting means for the introduction into said recording sheet of at least one additional solution said solution containing additional metal ions, a portion of said additional metal ions being subsequently catalytically reduced at the sites of said first metal particles and precipitated, thereby intensifying said record.

10. Apparatus of claim 9 in which the said electrolytic solution and the said at least one additional solution comprise paraformaldehyde as a first portion and copper sulfate and potassium sodium tartrate as a second portion and in which the said first portion and the said second portion are kept separate from one another until the said deposition is desired.

11. Apparatus of claim 10 including, subsequent to said wetting means, thermal means for maintaining the temperature of said recording sheet in the range 50 to 80 C.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,622 -l68 Dated November 23, 1971 Inventofls) Dennis R. Turner, Catherine wolowodiuk It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

II 'YE' "8 Col. 2, line 17, change 10 8 to --l0 line 22, change "10 TE 5'' to --10 7E 8 Col. 4, line 26, change "10 8" to --l0 line 27, change "10 5" to --10' Signed and sealed this 13th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents RM PC4050 (m'sg) USCOMM-DC 6037B-F'69 lLS. GOVERNMENT PRINTING OFFICE 1 ISI! 0-866-384

Claims

1. A process for the production of a record on a porous recording sheet at least partially impregnated with an electrolytic solution, comprising the electrolytic introduction of metallic ions into the said recording sheet from an anode electrode as the said recording sheet is moved relative to the said anode electrode, the reduction of the said ions, and the precipitation of the resulting metal as metallic particles, characterized in that the recording sheet is brought into contact with at least one additional solution and that additional metal is subsequently deposited at the sites of the said metallic particles from the said at least one additional solution by a chemical reaction catalyzed by the said metallic particles whereby the said record is intensified.

5. Process of claim 4 in which the said metallic particles are deposited in a concentration of from 1 X 10 8 grams to 1 X 10 5 grams per square centimeter of record area.

6. Process of claim 5 in which said electrolytic solution and said at least one additional solution comprise paraformaldehyde as a first portion and copper sulfate and a member of the group consisting of potassium sodium tartrate and a soluble salt of ethylene diamine tetra-acetic acid as a second portion and in which said first portion and said second portion are kept separate from one another until said deposition is desired.

7. Process of claim 6 in which said paraformaldehyde is present in a concentration of 10 to 150 grams per liter of aqueous solution, said copper sulfate is present in a concentration of 20 to 50 grams per liter of aqueous solution and said potassium sodium tartrate is present in a concentration of 50 to 125 grams of its tetrahydrate per liter of aqueous solution.

8. Process of claim 7 iN which the said deposition takes place at a temperature between 50* and 80* C.

11. Apparatus of claim 10 including, subsequent to said wetting means, thermal means for maintaining the temperature of said recording sheet in the range 50* to 80* C.