US3524457A

US3524457A - Etching apparatus

Info

Publication number: US3524457A
Application number: US683409A
Authority: US
Inventors: Jahannes F Laimbock
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1967-11-15
Filing date: 1967-11-15
Publication date: 1970-08-18
Anticipated expiration: 1987-08-18
Also published as: DE6807202U; NL6815473A; DK126177B

Description

United States Patent [72] Inventor Johannes F. Laimbiick Rotterdam, Netherlands [21] Appl. No. 683,409 [22] Filed Nov. 15, 1967 [45] Patented Aug. 18,1970 [73] Assignee The Dow Chemical Company Midland, Michigan at Corp. of Delaware [54] ETCHING APPARATUS 2 Claims, 3 Drawing Figs.

[52] US. Cl. 137/2, 137/386,137/577, 251/229, 134/108, 134/155 [51] lnt.Cl. Fl6k 1/16, B41n 3/02 [50] Field ofSearch 137/386,

[56] References Cited UNITED STATES PATENTS 1,178,973 4/1916 Trimbey 137/577 2,092,926 9/1937 Lithgow 251/229X 2,287,396 6/1942 Roth l37/563X 3,276,421 10/1966 Nichol 137/386X Primary Examiner- William F. O'Dea Assistant Examiner- David R. Matthews Attorney Griswold and Burdick; C. Kenneth Bjork and V. Dean Clausen Patented Aug. 18,1970

Sheet QNN A NNN mm mm INVENTQR. d oh cmh e s E Lmhvboc HG'ENT H ETCHING APPARATUS The present invention is primarily directed to an improvement in etching machines suitable for powderless etching of zinc or magnesium and, in particular, to etching machines of the type generally known to the art as small bath volume etching machines (hereinafter referred to as small volume machines). Generally speaking, the small volume machines have a maximum operating volume of about 80 liters of etching fluid. By comparison, the numerous larger capacity etching machines in use today have a maximum operating etch bath volume of about 200 liters.

An etching machine which is limited to a small volume of etch bath is at a particular disadvantage when it is desired to etch a substantial number of plates or when plates having large open areas are to be etched. In such instances the effectiveness of the etch bath is depleted in a relatively short time and it must be frequently replaced with a fresh etching bath. This procedure, of course, requires an undue amount of the machine operators time, which results in an inefficient operation.

Another problem inherent in the use of a small volume etching machine is that the level of fluid in the tank will rise considerably during the life of a given etch bath, since the bath must be periodically replenished with acid and/or other materials. This results in a substantial increase in the splash paddle dip, which can adversely affect the quality of the etch obtained.

Still another problem is that the size of the cooling apparatus which can be fitted into a small volume etching machine is such that it will not cool the etch fluid sufficiently to obtain a satisfactory etch, when for example, large, open area plates are being processed.

in addition to overcoming these problems, there is a need for improving the present etching machines so that various materials (each requiring a different etch composition) may be etched, in sequence, in the same machine. For example, it would be particularly desirable to etch both zinc and magnesium in the same machine, without having to shut the machine down between operations to make up the appropriate etch formulation.

Although the present invention is primarily directed to control of the etch bath level in a small volume etching machine, those skilled in the art will appreciate that the principle involved is equally applicable to larger capacity machines, such as mentioned hereinabove. In addition to zinc and magnesium etching it is also contemplated that the present invention would be useful in the etching of other metals such as copper, aluminum, iron, or alloys of such metals, as well as plastic materials and silica-containing materials such as glass.

Accordingly, a primary object of the present invention is to provide a means for controlling the level of an etchant bath in order to improve the quality of the etched product obtained.

Another object of the invention is to provide a means for increasing the etch bath capacity of a small volume etching machine to substantially reduce the amount of down time" required for frequent replacement of the etch bath.

Still another object is to provide a means for increasing the cooling capacity of a small volume etching machine in order to improve the quality of the etched product obtained.

Yet another object is to provide a means whereby more than one kind of material may be etched sequentially in the same machine.

Other objects and advantages of the present invention will ,be apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a side elevational view, partly broken away, of a conventional powderless etching machine with one embodiment of a fluid level control assembly, i.e. an adjustable weir apparatus, of this invention installed herein and an auxiliary tank connected thereto.

FIG. 2 is a detailed view of the adjustable weir taken along line 2-2 of FIG. 1.

FIG. 3 is a detailed plan view of the adjustable weir taken along line 33 of FIG. 2.

Broadly, the present invention comprises an auxiliary tank mounted adjacent to and essentially on the same level as the etching tank of a conventional powderless etching machine. The auxiliary tank communicates with the etching machine by means of a transport duct which provides for circulation of an etching bath between the auxiliary tank and the etching machine tank during the etch operation. Additionally, this invention includes a fluid level control assembly usually in the form of an adjustable weir, mounted on an inner wall of the etching tank adjacent the transport duct.

The invention can be best understood from the following description taken in conjunction with the accompanying drawing. The drawings illustrate only one of the numerous embodiments within the scope of this invention and the forms shown were selected from the standpoint of convenience in illustration, satisfactory operation and clear demonstration of the principles involved. Corresponding parts of the illustrated embodiments have been designated by the same numerals in the several views, with letter suffixes being applied where appropriate.

Referring to the drawings, there is illustrated a preferred embodiment of the invention which includes an etching tank 10 having a bottom wall 12,

sidewalls

14, 16, and a cover 18. An etching fluid 20 is contained in tank 10 during the etching operation. In the upper portion of tank 10 is a plate to be etched 22 held in place by plate holder 24 secured to one end of a shaft 26 which extends through cover 18 and is held thereby. The opposite end of shaft 26 is connected to motor 28 mounted on the top side of cover 18. Plate 22 is rotatably driven by motor 28 to assure uniform etching of the plate. In the lower portion of tank 10 is a plurality of spaced rotatable splash paddles 30 which splash or impinge the etchant solution against plate 22 during the etching operation.

Positioned in the lower central portion of wall 16 of tank 10 is a generally rectangular opening 36. Opening 36 is enclosed by a generally rectangular-shaped transport duct or conduit 38, one end of which abuts against and is secured to the outside of wall 16; the opposite end of duct 38, which is normally open, extends into auxiliary tank 11. Since it is desired in the practice of this invention (as explained in more detail hereinafter) to control the level of etching fluid 20 in tank 10, a fluid level control means in the form of an adjustable weir 40 is positioned adjacent to opening 36 and parallel with the inside surface of wall 16. Weir 40, which regulates the flow of the etching fluid through opening 36 and transport duct 38 into tank 11, comprises a generally flat rectangular member having a centrally disposed rectangular opening 42 therein and an upper edge defining a bight portion 44. During the etching operation the level of the etchant in tank 10 is directly controlled by the height of lower edge 46 in opening 42 above lower edge 37 of opening 36. in other words, when theetchant level in tank 10 rises above edge 46, the fluid will flow over edge 46, in the manner of water flowing over a dam, and through opening 36. The volume of etchant in tank 10 can thus be controlled to any desired level by raising or lowering weir 40. An exemplary means for raising or lowering weir 40 is provided by a threaded rod or bar 48 secured at one end to bight portion 44 and extending upwardly from the bight portion through a hole in angle bracket 50 mounted on the inside surface of wall 16. The threaded portion of rod 48 which extends above upper surface 52 of bracket 50 is engaged by an internally threaded round nut 54 which rests against surface 52. For purposes of this invention, rod 48 is equipped with a right hand thread so that by revolving nut 54 in a clockwise direction weir 40 may be raised. Conversely, weir 40 may be lowered by revolving nut 54in a counterclockwise direction. As a guide for maintaining vertical alignment with wall 16, weir 40 is raised or lowered in an opening defined between spaced-apart

yoke members

56, 58. As best shown in FIGS. 1 and 2, yoke member 56 is secured against theinside surface of wall 16 so that it surrounds opening 36, while yoke member 58, which is spaced apart from and in alignment with member 56, is secured to bottom wall l2of tank 10 through flange 60.

As a container for an additional supply of etching fluid, as indicated by reference numeral 20a, there is provided an auxiliary tank 11 generally defining a bottom wall 62, sidewalls 64, 66, and a cover 68. Tank 11 is mounted adjacent to and is positioned at essentially the same level as tank of the etching machine. Extending into tank 11 through an opening in the lower central portion of wall 64 is a generally rectangular-shaped transport duct 38, which links etching tank 10 with auxiliary tank 11 to provide a conduit for the etching fluid to circulate between auxiliary tank 11 and etching tank 10. During the etching operation, end 70 of duct 38, which extends into tank 11, is normally open as indicated in the drawing. When it is so desired end 70 may be closed, as provided by a generally rectangular-shaped solid plate 72 having a peripheral flange 73 adapted to abut against and sealingly enclose end 70 of duct 38. Opening and closing of end 70 with plate 72 is effected by a scissors jack assembly 74 in which the apex or terminus 76 of jack legs 78 is hingedly secured to plate 72 and the base of each jack leg threadedly engages screw rod 84. The lower end of screw rod 84 is threaded into bracket 86 secured to bottom wall 62 of tank 11, while the upper end of the rod extends through and above cover 68 of the tank. Actuation of jack legs 78 is effected by turning handwheel 88 secured to the upper end of rod 84.

To ensure uniformity of the etch bath composition during the etching operation, the fluid mixture is agitated by a propeller stirrer 89 which is driven by motor 90 through shaft 92. The portion of shaft 92 which extends from motor 90 into tank 11 is engaged by hanger bracket 94 anchored to the underside of cover 68, which acts as a stabilizer for the shaft. A circulating pump 96 having a motor 97 mounted on cover 68, with the body of the pump extending into tank 11, provides a fluid input means for delivering etching fluid a from auxiliary tank 11 into etching tank 10. Etching fluid 20a is taken into pump 96 through inlet port 98 and is delivered therefrom through outlet port 100 into feeder pipe line 34 and thence into etching tank 10 through circulation pipes 32. Circulation pipes 32 comprise a plurality of interconnected pipes having small openings 35 therein through which the etching fluid squirts into tank 10.

When it is desired to save etching fluid 20 for a subsequent etching operation, open end 70 to transport duct 38 is sealingly closed with plate 72 according to the procedure described hereinabove and valve 39 is opened to admit the fluid into pump 41. Valve 45 is also opened and the fluid is pumped through return line 43 and back into tank 11. After all of the etch fluid is pumped back into tank 11, valve 45 is closed to prevent the etch fluid from seeping back into return line 43 during the etching operation.

The etching fluid in auxiliary tank 11 may be cooled to a desired temperature by means of cooling coil 102 connected to a source of cold tapwater (or any other suitable coolant) (not shown) through input line 104 and return line 106. When the etching fluid in the present system is depleted to the extent that it requires replenishment, the required acid and/or other materials may be added to the fluid in auxiliary tank 11 through an opening provided by removing hatch 108 from cover 68. It is important to note that the etching fluid in tank 11 may be replenished without creating an undesirable rise in the level of the etching bath in tank 10, since the level of the fluid in tank 10 may be conveniently controlled by means of adjustable weir 40. When it is desired to clean tank 11 or to replace the etching fluid therein, the tank may be drained through draincock 110 by opening valve 112 therein. Bottom wall 62 of tank 11 is canted toward the draincock to facilitate such drainage.

In the practice of this invention certain operating conditions and structural dimensions of the apparatus involved have been found to provide optimum results, it being understood that this invention is not limited to the details set out here. To facilitate uniform mixing of the etch composition auxiliary tank 11 is preferably of a circular shape. The tank is made of 0.04 inch No. 304 stainless steel and is of a welded construction. Circulation pipes 32 comprise a set of three interconnected pipes which are positioned below the splash paddles and may lie parallel with the shafts carrying the paddles or at a right angle thereto, depending upon the type and size of etching machine used. For best results in pumping etching fluid from the auxiliary tank to the etching tank, particularly in a small volume etching machine, circulating pump 96 should have a delivery capacity of not less than about 50 liters per minute. Cooling coil 102 is about 2500 mm. in length, with an inside diameter of about 40 mm. and is constructed of No. 304 stainless steel. The preferred distance between tank 10 of the etching machine and auxiliary tank 11 is about 200 mm. Transport duct 38, which provides a conduit for the etching fluid to flow from tank 10 into tank 11, is preferably of a rectangular shape with an internal width of about 400 mm. and an overall height of about 1 10 mm.

Any of the known conventional mechanisms may be used for rotating the plate to be etched 22 and for driving splash paddles 30. Examples of such mechanisms are disclosed in Easley et. al. U.S. Pat. No. 2,669,048 and Guenst U.S. Pat. No. 2,776,512. Suitable conventional etching fluids which may be employed include a zinc etching composition, as disclosed in Hopkins et al U.S. Pat. No. 2,828,194, and a magnesium etching composition, as disclosed in Easley et al U.S. Pat. No. 3,023,138 and Croisant et. al. U.S. Pat. No. 3,l52,0 83. The amount of etch fluid charged to auxiliary tank 111 will depend upon the desired initial operating volume of etch fluid in tank 10. According to the practice of this invention it is contemplated that the volume of etch fluid in auxiliary tank 11, as compared to the initial etch bath volume in etching tank 10, could be in the range of about 10 to 1, with the preferred operating volume being about 1.5 to l.

The capacity of the auxiliary tank will depend of course on the size of the etching machine with which it is used. For use with a small volume etching machine it is contemplated that an auxiliary tank having a capacity of anywhere from about to about 800 liters would be suitable in the practice of this invention.

in the illustrated embodiment of this invention only one auxiliary tank is employed in conjunction with and in communication with a single etching machine. It is contemplated to be within the scope of this invention, however, that two or more auxiliary tanks may be used in conjunction with one etching machine to accomplish, among other things, etching of several different materials in the same machine, each material requiring a more or less different etchant composition.

In the operation of this invention, a sufficient amount of an appropriate etching fluid is charged to tank 10 of the etching machine and the level of the fluid is brought up to a point such that splash paddles 30 are immersed in the solution of a depth of, for example, about 12.5 mm. Weir 40 is correspondingly adjusted, that is, raised vertically, to a point where lower edge 46 of opening 42 in the weir is a sufficient distance above the level of the etch fluid to prevent the fluid from flowing through opening 36 prior to commencement of the etching operation. With plate 72 abutted against open end 70 of duct 38, so that the plate acts as a cap to close off end 70, an ap propriate amount of etching fluid 20a is charged to auxiliary tank 11.

The plate to be etched 22 is clamped into place on plate holder 24 and weir 40 is lowered by rotating nut 54 manually in a clockwise direction until edge 46 of opening 42 in the weir is just below the surface of etching fluid 20, so that the etching fluid will spill over edge 46 and into duct 38 (as best shown in FIGS. 1 and 2). Plate 72 is drawn back away from end 70 of duct 38 by actuating a scissors jack assembly 74 with handwheel 88 so that the etching fluid may flow out of transport duct 38 and into tank 11. Splash paddles 30 are actuated by a suitable drive mechanism to effect an upward splashing of etching fluid 20 against the image-bearing side of plate 22. During the etch operation, plate 22 rotates in plate holder 24 through power supplied from motor 28, as transmitted through shaft 26.

Pump 96 is actuated by motor 97 and etching fluid 20a in auxiliary tank 11 is drawn into the pump through inlet port 98 and discharged from the pump through outlet port 100 into feeder line 34 where it squirts into tank through circular openings 35 in circulation pipes 32. As explained hereinabove, the uniformity of the etch bath composition during the etching operation is maintained by a propeller stirrer 89, mounted on shaft 92 and driven by motor 90. Cooling coil 102 in auxiliary tank 11 acts as an adjunct to a similar coil in etching tank 10 (not shown for the sake of simplicity in the drawing) to cool the etch bath composition to a desirable operating temperature, in those instances where the cooling apparatus in etching tank 10 is unable to cool the etching fluid to the desired temperature.

Those skilled in the art will appreciate that the operating volume of the etch bath composition (etching fluid may be controlled to any desired height in tank 10 by vertically adjusting, that is, raising or lowering, adjustable weir 40. This feature, in conjunction with the continuous circulation of the etch bath between the auxiliary tank and the etching tank, provides optimum splash paddle dip conditions, as well as insuring uniformity of the etch bath. The net result is an etch bath of consistently high quality, uniform temperature, and a significant improvement in the quality of the etched product obtained.

Another significant feature of the present apparatus is its adaptability to the alternate etching of more than one kind of material in the same machine, without the necessity of having to prepare a new etching solution each time it is desired to etch a different material. For example, a zinc plate may be etched first and when the operation is finished, the open end 70 of transport duct 38 positioned in auxiliary tank 11 is closed off with plate 72 according to the procedure described hereinbefore. The zinc etch composition can then be pumped out of tank 10 and back into auxiliary tank 11 through pump 41, as previously described, where it can be stored and saved for the next zinc etching operation. Etching tank 10 is then readied for the next etching operation by rinsing it out and then opening valve 49 in drain 47 to drain the rinse solution. In the meantime, a magnesium etch composition, for example, which had been prepared and stored in a second auxiliary tank connected to the same etching machine (similar to the tank illustrated herein, but not shown) could be pumped into the etching machine to etch a magnesium plate. When the magnesium etch operation is finished, the composition is pumped back into its appropriate auxiliary tank where it is saved for a subsequent magnesium etching operation. The zinc etching composition which has been previously stored can then be pumped back into the etching tank to again etch a zinc plate. By using several auxiliary tanks each connected to the same etching machine, therefore, it is possible to alternately etch a variety of materials in the same machine without having to shut down the machine between each operation to make up a different etch formulation. This feature, therefore, results in a more economical etching operation by substantially reducing the amount of down time of the etching machine and by reducing the cost of the etch bath solutions.

While the inventive concept is specifically described in the foregoing specification and the accompanying drawing, it will be understood that numerous modifications and variations with respect to form, size, arrangement of parts, operation and mechanical details may be made without departing from the spirit and scope of this invention.

1 claim:

1. In an etching machine for etching printing plates comprising, in combination:

an etching tank adapted to contain an etching fluid;

at least one auxiliary tank adapted to contain an etching fluid, the auxiliary tank being positioned adjacent to and at about the same level as the etching tank;

fluid input means defining a set of circulation pipes positioned in the fluid body of the etching tank and connected to a feeder line communicating with a pump means positioned in the auxiliary tank, for continuously circulating etching fluid from theauxiliary tank to the etching tank; conduit means as provlded by a conduit having one end mounted on the etching tank in communication with an opening in the etching tank and a normally open opposite end positioned in the auxiliary tank, for transporting etching fluid from the etching tank to the auxiliary tank;

closure means defining a solid plate mounted on a scissors jack assembly and having a peripheral flange adapted to abut against and sealingly enclose the open end of the conduit upon actuation of the scissors jack assembly; and

fluid level control means defining a vertically adjustable weir assembly mounted inside the etching tank adjacent the opening in said etching tank, for controlling the level of etching fluid in said tank.

2. In a method for etching printing plates in an etching machine, the improvement comprising the steps of:

providing an etching tank adapted to contain an etching fluid;

positioning at least one auxiliary tank adapted to contain an etching fluid adjacent to the etching tank;

continuously circulating etching fluid from the auxiliary tank into the etching tank through a set of circulation pipes positioned in the fluid body of the etching tank and connected to a feeder line communicating with a pump means positioned in the auxiliary tank;

transporting the circulating etching fluid from the etching tank to the auxiliary tank through a conduit having one end mounted on the etching tank in communication with an opening in the etching tank and a normally open opposite end positioned in the auxiliary tank;

controlling the level of etching fluid in the etching tank by means of a vertically adjustable weir assembly mounted inside the etching tank adjacent the opening in said etching tank.