US 2536912 A
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Jan. 2, 1951 l.. B. coRBETT ELECTROLYSIS ETCHING DEVICE Filed July 12, 1944 ATTO R N EY Patented Jan. 2, 1951 UNITED STATES TENT OFFICE ELECTROLYSIS ETCHING DEVICE York Application July 12, 1944i, Serial No. 544,548
This invention relates generally to means for producing gravure printing rollers and more particularly to devices for etching the surface oi such rollers by electrolysis.
Heretofore, printing electro rollers were made by chemical etching, but it is found that the method used in electrolysis is much faster and produces a better formation of the printing surface. Chemical etching, since it is of longer duration, tends not only to eat directly down into the metal but also causes undercutting by removing some portions of metal underneath the design which is supposed to stand proud. A fault encountered in the use of chemically etched rollersis that, when they are reground or resurfaced, the design to be printed is distorted.
An object of the invention is the provision of means for mounting an electro roller to be etched in an electrolytic bath as an anode. A copper cylindrical sleeve is mounted to surround said roller in the bath and act as a cathode.
Another object of the invention is the provision of means for agitating the electroiytic bath by rotating the cathode and anode in opposite directions. As a further aid to agitation, the circular cathode screen is formed with vanes to set up circulation currents in the bath.
Another object of the invention is to provide means for aeratingthe bath solution in the vicinity of the anode. brought into the bottom of the bath solution and allowed to bubble up and is swirled around throughthe electrolytic liquid and prevents small pockets from forming underneath the etched lines. This air also liberates thev hydrogen from the bath.
Another object of the invention is the provision of means for cooling and filtering the electrolytic solution. rlhe liquid is drawn out of an electrolysis chamber and passed through another vessel containing cooling coils, and then directed through a ter before its return again to the chamber for use in the electrolysis operation.
Another object of the invention is the provision of means for maintaining the acidity of the bath. An acid dropper bottle is regulated to direct a small constant stream of hydrochloric acid into the solution to maintain its pH value.
Another feature of the invention is the method of etching printing rollers comprising the steps of mounting the roller as an anode, agitating the electrolytic bath, cooling and liltering the bath, and maintaining the acidity of the bath.
Other objects of the invention will be pointed out in the following description and claim and Air under pressure is (Cl. 20de-212) illustrated in the accompanying drawing, which discloses, by way of example, the principle of the invention and the best mode, which has been contemplated, of applying that principle.
The drawing is a perspective view partly in section showing the containers for the electrolytic solution and the elevated vessel for cooling and ltering the electrolyte.
An electro or gravure printing roller R is prepared by machining to a smooth accurate outside diameter. It is then coated with a light sensitive emulsion, which becomes insoluble when exposed to light. A film with a photographic, geometric or any desired design is then wrapped around the coated roller R and exposed to light. The
roller` is washed in cold water to remove the part of the coating solution not affected by exposure. rihat part of the emulsion which adheres to the roller is burned in over a gas flame to stabilize it and set it firmly on the surface of the roller. This remaining selective coating then serves as a resist during the etching operation and does not allow the metal underneath to etch away. In the electrolyte, the roller is electrically etched to a depth of from .0015 to .002.
After etching, the roller is cleaned and a plating of chromium is applied before the roller is used for printing.
The drawing shows a vertical arbor 2D on the lower end of which is the printing roller R submerged in the electrolyte E which is a solution of sodium chloride (NaCl) and ammonium chloride (NHlCl). 51/2 lbs. of ammonium chloride and 131/2 lbs. of sodium chloride are added to 9 gallons of Water. The arbor is formed with a depressed shoulder 2l which is used to hold it on an insulation board (not shown) extending across the top of the outer cylindrical support 23 which serves as a frame for the moving parts. Attached to the arbor 20 is a bevel gear 2d in mesh with another gear 25 iixed to a horizontal shaft 25 having a worm wheel 2l at the opposite end. The usual bearings are omitted for clearer illustration. Cooperating with wheel 2l is a Worm 28 on a shaft operated by the motor M. The foregoing connections are used to rotate the vertical anode with the printing roller R in a counterclockwise direction While etching takes place.
Within the outer supporting frame 23 is mounted a chamber or tank 30 for holding the electrolytic bath solution E. Inside this tank, and arranged concentric with its outer walls and the centralized arbor 2i), is placed a cylindrical cathode 3l formed of a perforated sheet of copa per. Fixed to this cathode cylinder is a series of vertical Vanes 82 and horizontal vanes 33. These Varies keep the solution in constant motion and help to maintain a uniform pH Value throughout the bath. Driving connections are established to the cathode cylinder 3! by means of a series of extensions Sil connecting it to a movable friction ring 35. This ring has an L-shaped cross section and is supported at intervals on a series of rollers 36 pivotally mounted on the inside of the supporting cylinder 23.
Cooperating with the ring 35 is a friction driving roller t8 mounted on a shaft connected to a pulley 2. A belt i3 carries the drive from a motor Ml and through a small pulley fill. This last mentioned train of driving connections is arranged to turn the ring 35 and the connected cathode 3i in a ciockwise direction so that it rotates in a direction opposite to the rotation of the anode.
Situated on the bottom of the tank 30 is a perforated air cox i5 connected by tubing 5 to an air pump or compressor Il? and a motor M2. The box l5 is placed directly under the anode so that the bubbles arising therefrom move along and against the roller R and prevent small pockets from forming underneath the lines or letters being etched. The air escapes from t1 e top of the bath carrying the emitted hydrogen gas along with it.
The pH value of the solution E is maintained at approximately 6.2. This is accomplished by means of the addition of between 400 to 500 drops per hour of CP hydrochloric acid, generally referred to as concentrated hydrochloric acid. In the drawing, the bottle 56 contains the acid and tube 5i extending therefrom is directed into the bath solution. The flow is regulated by a clamp 52 constricting the opening through the tube.
Electrical connections are established between the cathode and anode. In the drawing it is seen that the top of arbor 28 is provided with a circular contact member 55 having a cooperating brush 56 to which is attached one line running to a switch S and a battery or other source ci current identified as the power source PS. The electrical power used is 35 amperes with 6 volts of current. Also connected to the power source is a second brush 5l maintaining constant contact with the rotating ring 35 which in turn has conductive connections with the cathode 3i.
Means is provided to withdraw a portion of the electrolyte solution E and direct it through a cooling and ltering device before returning it to the electrolysis tank. There is a constant circulation of the electrolyte to keep it clean and cool, otherwise there is a temperature rise of about 6 F. to 8 F. per hour of etching. At the left side of the drawing it is seen that a series of tanks is mounted in an elevated position.
An outer tank 69 is used to contain running water W used to cool the bath solution. An inner tank 6I is used to hold a portion of the bath solution E after it passes through the lter chamber 62 suspended therein.
The solution is drawn out of tank 39 and care ried through tube 63 to a liquid pump 65 driven by motor M3. Another tube then carries the solution into a cooling coil 85 submerged in the cold water W constantly circulating between the walls of tanks and 5i. The top of the coil is curved at 6'! to pour the cooled solution E into the ltel` chamber 62, wherein it passes through the filtering material 68 of cotton packed between layers of cheese cloth before passing out through openings in the lter chamber and dripping to the bottom of the tank 6l. From the bottom of tank SI, the rejuvenated solution now cool and free from sediment is carried out through tube le and back into the electrolysis tank 38.
The stream of cold water W is brought into the cooling tank 69 through pipe i! and allowed to ow out of the upper part of the same tank through the discharge opening '52.
While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a single modification, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention therefore to be limited only as indicated by the scope of the following claim.
What is claimed is:
In a device for etching a printing roller by electrolysis, a tank for holding a liquid solution of electrolyte, a Vertical arbor for holding said printing roller in said tank, an electrical contact to said arbor for connecting said roller to the positive terminal of the electrolysis current source, a cylindrical cathode mounted in said tank concentric with and outside said roller, means for rotating said cathode, means for rotating said arbor, a series of Vanes on said cathode for agitating the solution, a perforated air box piaced in said tank under said roller, and an air pump therefor.
LAWRENCE B. CORBETT.
REFERENCES CITED The following references are of record in the ile of this patent:
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