US3136671A - Method of etching a printing plate - Google Patents

Description

June 9, 1964 c. s. MARTZ ETAL 3,136,671

METHOD OF ETCHING A PRINTING PLATE Filed May 2, 1960 3 Sheets-Sheet 1 INVENTORS 2 CHARLES S. MARTZ MONROE R. HILLHOUSE ATTORNEYS June 9, 1964 c. s. MARTZ ETAL METHOD OF ETCHING A PRINTING PLATE 3 Sheets-Sheet 2 Filed May 2. 1960 :FIkME FIG.

ill ih. 47 4 EHI:

INVENTORS- CHARLES S. MARTZ MONROE R- HILL HOUSE BY FIG.

ATTORNEYS June 9, 1964 s. MARTZ ETAL 3,136,671

METHOD OF ETCHING A PRINTING PLATE Filed May 2. 1960 3 Sheets-Sheet 3 l 29 FIG. 6

3| I r muflkflimu 24 INVENTORS 2o .1l. CHARLES s. MARTZ i n" MONROE R. HILLHOUSE ATTORNEYS United States Patent Filed May 2, 1960, Ser. No. 25,921 Claims. 01. 156l4) This invention relates generally to improvements in an etching machine and method of etching, and more particularly to improvements in an apparatus and method involving an etching bath in which a protective bath additive is utilized. V

The process of etching per se presents no problem. For example, a mixture of water, nitric acid and air will etch zinc. One of the first commercial zinc etching methods used a rocking tray or tub in which a water-acid solution flowed back and forth across the plate, the plate being exposed to air each time the solution passed over the plate. In this method, etching was relatively slow and because the bathcontained no shoulder protecting chemicals, the lateral etch was almost as great as the vertical etch. Consequently powdering between bites was necessary in order to prevent the lateraletch.

Subsequently, paddle machines were introduced and plates were etched in every possible position, from'vertical to horizontal. In such machines, powdering between bites was, of course, necessary. Air etching machines were developed, but none were popular because they presented no advantages over paddle systems.

Every photoengraver engaged in etching looked for ward to the day when dry powdering could be eliminated. A machine and process was visualized which would allow powder to be put right in with the acid and water bath and yet provide side wall protection. When a bath additive was discovered in the early 1950s that would protect side walls, a paddle type etching machine very similar to those in daily use at that time was developed and used. While these paddle machines were ideal for conventional powder etching, they were far short of perfect insofar as automatic side wall protection was concerned.

In the above mentioned paddle type etching machines, the protective chemicals in the bath are known in the trade as liquid powder or bath additive. In powderless paddle or spray type etching machines in which the bath includes a bath additive, the bath is thrown onto the work plate. The zinc plate has an affinity for the oil constituting the bath additive and it forms a film over the surface. This film is porous and it is removed by theaction of the acid through the pores'to'a minor degree. The major removal action however, is mechanical. The force of the paddle action beats the oil oil. Because the sides of the etched images are largely parallel to the force, the sides of the images receive less paddle action and the film adheres to these sides 'while it is being beaten oif the open plate bottom areas.

The present machine and method constituting the invention has definite advantages over the prior known machines that splash the etching and protecting solution over a suspended plate with paddle or spray IIOZi zles. It is an important object of the present invention to eliminate all paddles in the etching machine, and to etch'the plate and protect the side walls of the images while the plate is completely submerged in the bath.

Another important objective is achieved by suspending the plate to be etched completely submerged in the etching bath at an angle to the plane of the bath surface and by rotating the plate while bombarding the plate face with a profusion of bubbles passed upwardly through Limited, Aurora, Mo., a corporation of.

' 3,136,671 Patented June 9, 1964 the bath so as to impinge and roll upwardly on the plate. The protective film formed by the bath additive is in contact with the plate at all times because the plate is submerged in the bath. The air bubbles remove the bath additive in the open areas to be etched. In addition, the flow of the solutioh across the plate caused by the path ofthe bubbles and by the rotation of the plate also causes removal of the protective bath additive in the open areas to be etched, yetcompletely protects the side walls. i

With the above described superionmethod and machine, a much smoother side wall protection is provided than can be had by any other known method or machine. These results are obtained because there is a controlled flow over the plate produced by choosing the particular plate angle and rotation which provides greatest side wall uniformity. of the air bubbles in rolling upthe plate to ,be etched reduces the porosity of the protective bath additive on the side walls. I V 7 Another important object is to provide an etching machine in which there is complete freedom in bath replenishing because the precise depth of the bath is no longer a critical factor as it is in paddle type or spray nozzle type machines. Still another important objective is achieved by the placement of tubes in the bottom of the tank, such tubes having air holes formed and arranged so that bubbles emitting from the air holes will rise upwardly through the bath in a pattern relative to the rotative axis of the work plate in order to eliminate or minimize distortion in the protection of side walls.

The present etching machine and method .has many advantages over the paddle. or spray nozzle type machines in that the paddle dip variable is eliminated. In etching machines using paddles, results are partially governed by the paddle dip, and hence thebath depth becomes critical since it regulates the amount of solution carried by the paddles. In thepresent invention, the

work piece is completely submerged in the bath and the bath depth is not critical. in the least.

There is also a complete elimination of paddle'speed errors and an'elimin'ation of the necessity of synchronizing the speed of paddle shafts where two or more are utilized, and there is a complete elimination of paddle shaft leaks that might cause a change in the bath level and hence in the paddle di'p.

, In the splash type machine, gravity and centrifugal force represent difiicult to control variables. The present invention provides a machine which eliminates these factors and provides side wall protection largely regulated by the gentle flow of bubbles toward the high side of'a revolving work plate, thus, providing fine grained sidewalls having less shoulder porosity.

Another important object is to provide an etching machine that is simple and durable in construction, economical to manufacture, eificient in operation, cost less to maintain, reduces bath cost because of the longer bath life obtained, and which can be easily operated by an etcher with only a minimum "of instruction.

The foregoing and numerous other objects and advantages of the invention will more clearly appear from the following detailed description of a preferred embodiment, particularly when considered in connection with the accompanying drawings, in which: a FIG. 1 is a fragmentary, perspective view of the etching machine with the lid raised;

FIG. 2 is a perspective 'view of the etching tank and its appurtenant parts with the lid closed;

FIG, 3 is a top plan view of the machine illustrated in FIG.- 2, but with the motor removed;

Secondly, the gentle action FIG. 4 is a cross-sectional view of the machine as seen along staggered line 44 of FIG. 3;

FIG. 5 is a cross-sectional view of the tank as seen along line 5-5 of FIG. 4, and

FIG. 6 is an enlarged, fragmentary front elevational view of the adjustment means.

Referring now by characters of reference to the drawings, and first to FIG. 1, it is seen that the etching tank generally indicated at 11) is mounted in and supported by a body or shell referred to at 11. The body 11 serves to enclose certain operating mechanism below the tank in a manner subsequently described, and serves to mount the control panel and instruments 12 at the front of the machine for ready access by the etcher during operation.

The etching tank 10 is substantially square in configuration having opposed side walls 13 and right angularly interconnected front wall 14 and rear wall 15. The tank 10 includes a fiat horizontal bottom wall 16. The tank It) is adapted to hold a supply of etchant or bath 17 (FIG. 4), the composition and nature of which will be later described.

A lid 20 is connected to the top of rear wall by a hinge 21, the lid being adapted selectively to close or cover the open top of tank 10. Attached to opposite sides of lid 20 are a pair of handles 22 to facilitate raising and lowering of such lid. Because the lid 20 and the parts carried thereby are relatively heavy, a pair of counterbalance weights 23 are attached to the lid 20 and extend beyond the other side of the hinge axis 21. Ohviously, the counterbalance weights 23 enable the lid to be lifted and lowered easily with only a minimum of effort.

Mounted on the top of lid 20 by a hinge 24 is a platform 25. Adjustment means is provided for selectively raising and lowering the platform 25 about the axis formed by hinge 24, and hence selectively determine the angular relation of platform 25 relative to lid 20. This adjustment means includes an angle bracket 26 fixed by screws 2'7 to the top of lid 20. Formed in the upstanding bracket portion 28 is an elongate vertical slot 29. Extending through slot 29 is a threaded bolt 30 that is fixed to the forward edge of platform 25. A wing nut 31 is threadedly attached to the end of bolt 30 and engages the vertical bracket portion 28.

In order to adjust the angular position of platform 25, the wing nut 31 is loosened and the platform is selectively raised or lowered within the range determined by the movement of bolt 30 in slot 29. To facilitate accurate and quick placement of platform 25, an angle scale 32 is provided on the bracket portion 28 alongside the slot 29. The platform 25 extends laterally beyond the sides of bracket portion 28, thereby enabling a direct reading on scale 32 of its angular position.

After the platform has been adjusted to the desired angular position, the wing nut 31 is tightened on bolt 30 against the bracket portion 28, thereby clamping the platform 25 and maintaining it in such position.

A drive mechanism generally indicated at 33 and including an electric motor, speed reducer and interconnecting belt assembly is attached to andsupported on the top of platform 25. The drive means 33 includes a driven shaft 34 that extends downwardly through platform 25 and through lid 20 into the interior of tank 10 when the lid 20 is closed. It is seen that because the shaft 34 is rotatively mounted on the platform 25, the angular position of such shaft 34 is changed upon adjustment of the angular position of platform 25. The openings in lid 20 through which the shaft 34 extends, are of sulficient size to permit such angular adjustment.

Attached to the lower end of driven shaft 34 is a work plate holder 35 that is preferably circular in configuration as is best seen in FIG. 1. A zinc work plate 36, shown in FIG. 4 in full lines and illustrated by broken lines in FIG. 1, is clamped to the underside of holder 35 by a pair of adjustable clamps 37 mounted on holder '35. Obviously, the clamps 37 are adjustable toward and away from each other in order to accommodate work plates 35 of different sizes. In the preferred embodiment, and for reasons later discussed, the diameter of holder 35 is at least 4 to 8 inches larger than the greatest dimension of the work plate 36 held by clamps 37.

When the lid 20 is closed over tank 10, the holder 35 maintains the Work plate 36 in an inclined position completely submerged in the etching bath 17. The work plate 36 is held in substantially parallel relation with the platform 25 and is angularly adjusted relative to the bath level 40 upon angular adjustment of platform 25. The preferred angular position of work plate 36 during etching operation in order to obtain optimum results is from two (2) degrees to twelve (12) degrees with respect to the substantially horizontal bath level 40.

While submerged completely under the etching bath 17 in an angular relation to the bath level 40, the drive means 33 operates through driven shaft 34 to rotate the work plate 36. It has been found that optimum etching results are obtained when the work plate 36 is rotated from one-third /3) revolution per minute to ten (10) revolutions per minute.

A ventilating tube 41 is carried by an opening through the forward wall 14 above the top of bath level 40, the ventilating tube 41 being adapted to carry off the fumes from the etching bath 17. A door 42 is provided in the ventilating tube 41 for an opening 43 through which etchant can be introduced into tank 10 to replenish the bath 17 and raise the level 40, if desired or necessary.

Located at the bottom of tank 10 and supported on the bottom wall 16 is an aeration assembly including a header 44 that operatively connects and communicates with a plurality of elongate, parallel air tubes 45 extending transversely of tank 10. Each of the air tubes 45 is provided with a plurality of small air holes 46 on its underside. A feed line 47 is connected to the header 44 and also connects to a centrifugal pump (not shown). The pump, motor and refrigeration unit utilized by this etching machine are located under the tank 10 and within the body 11.

Air is forced through the air tubes 45 and is emitted through air holes 46 in the form of fine bubbles that rise upwardly through the etching bath 17 and impinge and roll upwardly on the work plate 36. In addition to this etching action of the bubbles as explained later, the air emitted through air holes 46 keeps the bath agitated and thoroughly mixed.

Uniform air distribution is most important in protecting side walls of the image evenly on the work plate 36. Accordingly, the air holes 46 are formed in air tubes 45 at particular locations in order that the bubbles rise through the bath 17 and impinge on the work plate 36 in a definite pattern. More particularly, it has been found that for best results and for minimum of distortion in etching the image, the air holes must be staggered in a manner such that a circular pattern relative to the rotative axis of the work plate 36 is not formed. In other words, the air holes 46 are formed in tubes 45 so that no two air holes are formed the same distance from the rotative axis of the work plate 36. In FIG. 5, it is seen that the arrangement of air holes 46 form a definite spiral pattern.

As is usual in etching machines and methods of etching, the temperature of the bath 17 must be maintained within certain specified limits in order to obtain best results. Formed as a part of the bottom tank wall 16 are refrigeration coils 50 as is best seen in FIG. 4. Suitable insulation 51 is provided about such coils 50. Also provided immediately below the bottom tank wall 16 are a plurality of heating elements 52. Upon selective operation of the refrigeration coils 5d and the heating elements 52, either manually or automatically by control means, the bath temperature can be maintained at a desired operating point.

It is thought that the operation and functional advantages of the machine and method has become fully apparent from the foregoing detailed description of parts, but for completeness of disclosure such operation will be briefly described; Y

The protective bath additive is merely combined with water and nitric acid to provide aetching bath 17. The chemicals used in the bath additive are a thick organic oil, a petroleum" solvent and a wetting agent. The heavy oil most widely used is Turkey red oil (sulfonated castor oil), while the thin oils or solvent is kerosene or Solvesso 150 consisting of by percent volume 1.3% C aromatics, 44.4% C aromatics, 25.3% C aromatics, 2.1% C aromatics, 17.7% indans and 6.5% naphthalenes, a product made by Standard Oil Company. Solvesso 150 is a high purity mixture of substituted benzene compounds having the molecular weights indicated. For example, the designation of 44.4% of C aromatics is the representative percentage of substituted benzene compounds of all types and all isomers which are present having a C molecular Weight. This would of course, involve the benzene ring which has six carbon atoms and additional side chains to total the additional four carbon atoms with the necessary hydrogen present for this type,

akyl-aryl sodium sulphonate and 60% sodium sulphate.

The oils plus the wetting agent constitute that which is termed in the art liquid powder or bath additive.

Bath formulation is based on the size of the desired bath. The bath 17 that has been used successfully in the present machine and in the present method of an etching is a twelve gallon bath consisting of 83% Water, 13% 42 degree Beaum technical grade nitric acid and 4% bath additive.

In making the particular powderless etching bath, the tank 10 is filled with water to a preset water gauge and then the nitric acid is added. The Water and acid go into solution. Because the acid heats the Water 10 degrees to 20 degrees, the mixture is cooled to about 75 degrees Fahrenheit, and then the bath additive is introduced. The air pump is turned on and the air emitted through air holes 46 rise upwardly through the bath 17 to provide thorough agitation that mixes the oils, water and acid. Because the mixture is not a true emulsion, the oils will rise to the surface of bath 17 if theair is turned off. Therefore, it is extremely important that the bath must be agitated before the work plate is placed into the bath or else the oil will cover the plate and attach itself so completely that the acid cannot etch the plate at all.

Assuming that the print on the work plate is properly exposed, developed and burnt-in, the first step is to paint out the large bare zinc areas with any lacquer preparation that will stand up under the acid and the oils in' the powderless etching bath 17. This space painting is not absolutely essential to etching and will have little effect upon the actual etching process. Then, the dry plate is brushed thoroughly with a prepared mixture of nitric acid, water and a metal cleaning solution in order to remove scum. This de-scum solution is flushed otf of the work plate and then the print is brushed or sponged with a pre-etch solution consisting of nitric acid and water. After pre-etching the work plate, the plate is flushed with water prior to gumming. Then, a few drops of a regular gum arabic solution is dropped on the wet plate and brushed over the entire surface, thus eliminating oxidation and keeping the plate from drying out while being attached to the plate holder 35.

The air pump is started in order to cause agitation of the bath 17 before the lid 20 is closed. It is assumed 5 that the platform 25 has been adjusted as described previously in order to maintain the work plate 36 at the desired angle in the etching bath 17 when the lid 20 is closed.

The lid 20 is then closed, and the work plate 36 is com rotate the work plate. 36 at the desired revolutions per.

minute.

The zinc work plate has an afiinity for the oil constituting the bath additive and such oil forms a film over the surface. This film is porous and it is removed by the action of the acid through the pores to a minor degree. However, the major etching action is accomplished by the air bubbles that move upwardly. through the bath 17 into impingement with the work plate 36. As the air bubbles engage the work plate 36 and roll. upwardly thereon from the low side to the high side because of the plate inclination, the air bubbles remove the oil in the open areas to be etched, allowing the acid to act. As any bubble moves along the .work plate, the bath following the bubble again covers the plate and the protective oil or bath additive again provides side wall protection.

Furthermore, as a result of the bubbles moving upwardly on the work plate and because of the rotation of such Work plate, the bubbles flow from the low side to the high side of the plate in a curved path across the plate. The curve of the flow is counter to the direction of the plate rotation because the flow is in one direction and the plate is turning away from the flow. The curve is determined by the speed of rotation and the size of the work plate. With the work plate tilted there is less action on the side opposite to the direction of the flow. The great er side wall protection is formed on the high side of the image, and because rotation of the .Work plate puts all sides of all images on the high side, the side Walls are evenly protected. This produces better protection and again aids in producing shoulders or side walls with less porosity. When porosity is eliminated or greatly reduced, halftone etching, especially fine line halftones, take on added quality.

It has been found that the plate holder 35 must have a four to eight inch larger diameter than the diagonal of the largest Work plate 36 to be etched. Without the larger holder, air bubbles striking the work plate at the plates low position tend to be forced off of the plate in a direction opposite to the plate flow and it is also found that the bubbles leaving the work plate on the high side tend to pick up speed and distort the protection. With the larger holder 35 as defined above, bubbles on the low side are fed to the work plate 36 evenly and the accelerated speed at the top is on the holder 35 rather than on the work plate.

It is seen that the air trapped under the revolving work plate 36 is trying to escape at all times. Even though the bubbles flow to the top of the plate, there can be more air trapped than can flow off at the high side. If the bubbles merge, and they certainly do if the plate is perfectly flat rather than being inclined, air'pockets tend to insulate the plate from the bubble action. If this happens, the protective chemicals in the bath attach themselves to the plate, thereby forming cone {shaped bumps on the plate bottom. The ideal plate angle then is partially governed by the air volume, i.e., the bubbles must impinge and roll up the work plate 36.

Although the invention has been described by making detailed reference to a single preferred embodiment, such detail is to be understood in an instructive, rather than in any restrictive sense, many variants being pos sible Within the scope of the claims hereunto appended.

We claim as our invention:

1. The method of etching the exposed metal areas of a metallic printing plate coated with a protective resist comprising the steps of subjecting the plate to submersion face down in a powderless etching bath containing a protective bath additive, inclining the plate relative to the bath level, rotating the plate, and passing air in the form of bubbles upwardly'through the bath so as to impinge and roll upwardly on the face of the inclined and submerged plate.

2. The method of etching the exposed metal areas of a zinc printing plate coated with a protective resist comprising the steps of subjecting the plate to submersion in a powderless etching bath containing an aqueous solution of nitric acid and an additive which includes sulfonated castor oil, a kerosene solvent and a wetting agent, inclining the plate relative to the bath level, rotating the plate, and passing air in the form of bubbles upwardly through the bath so as to impinge and roll upwardly on the face of the inclined and submerged plate.

3. The method of claim 2 in which the bubbles are formed so that they rise in laterally staggered spaced relation to the rotative axis of the plate. A

4-. The method of claim 2 in which the bubbles are passed upwardly through the powderless etching bath before the plate is submerged.

5. The method of claim 4 in which the bubbles rise in a spiral pattern from the rotative axis of the plate.

References Cited in the file of this patent UNITED STATES PATENTS 764,082 Thorpe July 5, 1904 1,016,487 Freer Feb. 6, 1912 1,081,289 Albert Dec. 16, 1913 1,267,754 Flick May 28, 1918 1,313,233 Grass Aug. 12, 1919 1,340,975 Page May 25, 1920 1,776,535 Bekk Sept. 23, 1930 2,640,765 Easley et al June 2, 1953 2,776,512 Guenst Jan. 8, 1957 2,846,295 Patterson et a1. Aug. 5, 1958 FOREIGN PATENTS 372,593 France Feb. 22, 1907 936,984 1948 France Feb. 23,

Claims (1)

1. THE METHOD OF ETCHING THE EXPOSED METAL AREAS OF A METALLIC PRINTING PATE COATED WITH A PROTECTIVE RESIST COMPRISING THE STEPS OF SUBJECTING THE PLATE TO SUBMERSION FACE DOWN IN A POWDERLESS ETCHING BATH CONTAINING A PROTECTIVE BATH ADDITIVE, INCLINING THE PLATE RELATIVE TO THE BATH LEVEL, ROTATING THE PLATE, AND PASSING AIR IN THE FORM OF BUBBLES UPWARDLY THROUGH THE BATH SO AS TO IMJPINGE AND ROLL UPWARDLY THROUGH THE BATH SO AS TO IMPINGE AND ROLL UPWARDLY ON THE SURFACE OF THE INCLINED AND SUBMERGED PLATE.

Images