US3473984A - Method and apparatus for etching curved printing plates - Google Patents

Description

06%. 21, 1969 M, FHSHABER ETAL 3,473,984

METHOD AND APPARATUS FOR ETCHING CURVED PRINTING PLATES Filed June 21, 1985 INVENTOR-S. Marv/h h. Fish (76 er John 0. Hicks/"50H l4 TTORA/E Y 3,473,984 hlETHOl) AND APPARATUS FOR ETCHING UURVED PRINTING PLATES Marvin H. Fishaher, Saginaw, and John D. Hickerson,

Midland, Mich, assignors to The Dow Chemical Company, Midland, Mich, a corporation of Delaware Filed June 21, 1965, Ser. No. 465,584 The portion of the term of the patent subsequent to Nov. 7, 1984, has been disclaimed Int. Cl. C23f 1/02; Bale 1/18 US. Cl. 156-14 9 Claims ABSTRACT THE DISCLOSURE Apparatus for powderless etching curved plates in which the rotatable mandrel holding the curved plate in a substantially horizontal position is disposed in a chamber above a supply of etching liquid and a plurality of horizontally disposed paddles are positioned so that they dip slightly into the etching liquid. The improvement lies in providing at least one rotatable paddle on either side of the curved plate, substantially parallel to the axis of the plate and at a height above the etching liquid at least as great as the height of the mandrel. The paddles are rotated so as to catch splashed etchant passing beside the curved plate and to deflect the same onto the upper part of the curved plate so that substantially the entire surface thereof is receiving etching liquid during the etching process.

This invention relates to etching and more particularly relates to an improvement in etching curved plates, especially to the etching of curved photoengraving plates having large diameters or radii of curvature.

Most, if not all, of the presently available machines for the powderless etching of curved cylindrical etchable plates or curved segments, all referred to herein as curved plates, comprise generally a tank with a top closure to hold a supply of etching liquid, a plurality of horizontally disposed paddles positioned in the lower portion of the tank so that they dip slightly intothe etching bath, and a rotatable mandrel, horizontally suspended within the tank and above the paddles and etchant bath, on which the curved plate to be etched is held. Drive means, of course, are provided to rotate the paddles and mandrel, thereby splashing etchant by means of said paddles on the plate as it rotates. In etching particularly large diameter plates, therefore, such as, for example, plates having a diameter or radius greater than about 12 inches, the plate shields its own upper surface from the splash, especially in those machines where paddles are centered under the mandrel. Moreover, in many of the conventional curved plate etching machines the access of the splash to the top of the plate is further restricted by a low, rounded cover. Thus, at any given instant during the etching operation nearly half of each revolution of the curved plate, is denied impingement with fresh etchant. As a result pimple-like projections sometimes result in the open areas of the final etched plates. This is undesirable in that they must be removed by a hand operation before the photoengraving plate may be used for printing.

One object of the present invention, therefore, is to provide an improved method and apparatus for etching curved plates by directly impinging liquid etchant onto the heretofore shielded upper portions or quadrants of said plate during its rotation in an etching operation.

A further object of the invention is to provide a new and novel etching apparatus and method whereby pimples in open etched areas of a curved plate are minimized, if not substantially eliminated.

'nitc States tent The invention will be fully understood from the following detailed description thereof, particularly when read in conjunction with the accompanying drawing wherein:

FIG. 1 is a cutaway isometric view of one embodiment of an etching apparatus of the present invention depicting a curved plate powderless etching machine comprising a tank containing a level of etchant liquid, a horizontally disposed mandrel holding a curved plate, a horizontally disposed array of paddles positioned in contact with said etchant, and a secondary set of horizontally disposed secondary or helper paddles mounted in a spatial relationship parallel and adjacent to said mandrel above the etchant and said array of paddles. For clarity the apparatus shown is greatly simplified and abbreviated.

FIG. 2 is a cross-sectional view of FIG. 1 from left to right.

It has been established that impingement of the etchant during the powderless etching of a curved plate must be maintained over substantially the entire work cylinder at any given time if a quality etch is to be obtained free from the aforesaid pimples and other disadvantageous results in the final relief image.

Accordingly, an improved method of obtaining impingement of etchant over substantially the entire curved plate during the etching operation has been found and is shown by Way of illustration as to operation and affect in FIGS. 1 and 2. This improvement comprises, as shown in FIG. 1, the spaced positioning of a secondary set of paddles 10 and 12 consisting of at least one such secondary or helper paddle longitudinal with respect to and on each side of a mandrel 14, the mandrel having a fixed, substantially horizontal axis of rotation, and a preferably disposed substantially parallel and horizontally adjacent from said mandrel. Preferably the axis of each of the secondary paddles 10 and 12 is located in the etching machine at a height at least equal to that of the longitudinal axis of the mandrel 14, and more preferably just slightly above the mandrel 14, in order to obtain a lateral deflection of said etchant 16 onto the rotating plate 18. The secondary paddles are disposed to the side of the mandrel 14 such that no part thereof is shielded or obstructed from the upwardly directed etching liquid 16 during etching, said upward splashing etchant being caused by rotation of the array of paddles 20 and 22 in contact with the etchant bath 16 in the bottom of the tank 24.

By this method the heretofore unexposed or shielded portions of the rotating curved plate 18 may now be impinged with etchant by deflection of same from the secondary paddles. This novel process therefore provides an improved etched curved plate having substantially no pimples by impinging etchant on the lower portion of the plate by means of the array of paddles in contact with the etching liquid and simultaneously impinging deflected etching liquid against the upper portion of the plate above the longitudinal axis of the mandrel by means of the secondary paddles not in direct contact with the etchant bath.

The design or construction of the secondary paddles may be varied and is only limited in that they must each comprise 2 or more fins 26, preferably diametrically opposed, and during operation must deflect etchant onto the normally shielded portions of the plate. It is preferable that the edge or lip 28 of the paddle fins 26 be slightly angled in the direction of rotation (as indicated by arrows).

The rotational speed of the secondary paddles as well as that of the plate to be etched, and the array of paddles in contact with the etchant, must be suflicient to fling off the etchant with which it comes into contact. Particularly, the rotational speed of the secondary or helper paddles must be sufl'icient to fling off or deflect the etchant received from the lower paddles and impinge it onto the rotating plate. The direction of rotation of the secondary paddles is preferably toward the mandrel, i.e. each fin on an ascending portion of a revolution catches etching liquid and directs and otherwise propels it toward the plate on the mandrel. The direction of rotation of the lower paddles preferably is as shown in FIG. 2. The mandrel may be rotated in either direction continually or alternately.

Disposition of the secondary paddles need not be limited to being precisely parallel to the mandrel and/ or precisely horizontal to the bath. Thus their disposition may be varied to suit the mechanical limitation of the etching machine in which they are employed and the disposition of the mandrel.

In practicing the improved method of the present invention, a typical curved plate etching machine is first provided with a set of one or more of the secondary helper paddles disposed as described. The machine is then charged with etchant, and a plate of, e.g., magnesium, bearing, e.g., an acid etch resist coating of chromated polyvinyl alcohol over the areas to be protected, is clamped on the mandrel. The paddles, including the secondary paddles, and mandrel are rotated by suitable drive means not shown in the drawings. Rotation speeds of the various paddles and of the mandrel may be the same or different. As the array of paddles in contact with the etching bath rotates they effect a splashing of this liquid against the lower portion of the plate. Simultaneously, the rotating secondary paddles impinges the etching liquid against the upper portion of the rotating plate thereby providing a uniform, substantially pimple-free etched surface. When the proper depth of etch is obtained, etching is terminated and the plate is rinsed and dried.

Among the advantages of the present novel improved method is that etchant may be impinged substantially over the entire rotating plate at any given time. In addition, the problem heretofore encountered as to pimples on the etched plates is minimized, if not substantially eliminated. In addition, conventional curved plate etching machines adapted with secondary paddles have been shown to give consistently clean etches on plates up to, e.g., about 15 to 20 inches in diameter. The improved method of the present invention, however, is not limited in application to use in particular sized machines or for particular sized curved plates.

The invention may be modified and changed without departing from the spirit or scope of the invention and it is understood that the invention is only limited as defined in the appended claims.

We claim:

1. In an etching apparatus for etching curved plates, said apparatus having an array of paddles in contact with an etching liquid and above said array of paddles a rotatable mandrel holding a curved plate to be etched with the axis thereof substantially horizontal, the improvement comprising positioning in a spaced relationship to said mandrel and above said array of paddles at least one secondary rotatable paddle longitudinal with respect to the side of said mandrel and at a height at least equal to that of the longitudinal axis of the mandrel from the level of etching liquid.

2. The improvement in the etching apparatus of claim 1, wherein each of said secondary paddles is positioned substantially horizontal to the etching liquid and parallel to the plate.

3. The improvement in the etching apparatus of claim 1, wherein the longitudinal axis of each of the secondary paddles in the machine is located at a height above that of the longitudinal axis of the mandrel.

4. The improvement in the etching apparatus of claim 1, wherein each of the secondary paddles is equipped wlth at least two fins, each of said fins having its outer edge angled in the direction of rotation of the paddle.

5. The improvement in the etching apparatus of claim 1, wherein during operation each of said secondary paudles is rotated in a direction toward the mandrel.

6. In a method of etching curved plates wherein a supply of etching liquid is contained in a chamber with the curved plate to be etched being rotatably supported therein above said liquid on a fixed substantially horizontal axis by a rotatable mandrel; there also being an array or rotatable paddles in contact with the etching liquid, and drive means to rotate said plate and paddles; the improvement comprising, positioning in a spaced relationship at least one rotatable secondary paddle adjacent each longitudinal side of said plate and at least as elevated vertically as said mandrel, and rotating said secondary paddles simultaneously with the rotation of said plate and the array of rotating paddles in contact with the liquid, thereby deflecting impinging etching liquid onto substantially the entire surface of the rotating plate.

7. The improvement of claim 6, wherein the secondary paddles are rotated in the direction of the curved plate being etched thereby deflecting etching liquid onto the said curved plate.

8. In a process for etching curved plates in an etching apparatus having a first array of paddles in contact with an etching liquid, a mandrel rotatably holding a curved plate to be etched above said array of paddles in a substantially horizontal position and at least one secondary paddle longitudinal with respect to each side of said mandrel and positioned above said first array of paddles, the improvement which comprises during rotation of said mandrel impinging said etching liquid against the lower portion of said plate by means of said first array of paddles and simultaneously impinging said etching liquid against the upper portion of said rotating plate by means of the secondary paddles thereby deflecting etching liquid over substantially the entire curved plate.

9. In a process for etching curved plates in a chamber in which the curved plate is rotatably supported with its axis substantially horizontal, above a supply of etching liquid, and rotated on said axis while etching liquid is directed thereon as well as therebeside by an array of dipping paddles in contact with the said supply, the improvement which comprises: dynamically deflecting, onto the upper part of the curved plate, a substantial part of the etching liquid that is directed beside the curved plate by the dipping paddles, thereby impinging etching liquid upon substantially the entire curved plate at any one time.

References Cited UNITED STATES PATENTS 2,926,076 2/1960 Guenst l34l47 3,351,077 11/1967 Hoonstra 134l47 I STEINBERG, Primary Examiner U.S. Cl. X.R.

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