US3549438A - Method and apparatus for etching curved surfaces - Google Patents

Description

Dea 22, 1970 Q WE HQORNSTRA ET AL 3,549,438

METHOD AND APPARATUS FOR ETCHING CURVED SURFACES Filed May 25, 1967 4 Sheets-Sheet 1 NWN iNvENTORs.

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Dec. 22, 1970 Filed May 23, 1967 c. w. HooRNsTRA ETAL 3,549,438

'METHOD AND APPARATUS FOR ETCHING CURVED SURFACES l 4 Sheets-Sheet B .Jo/vn D. Hieke/*son Dec. 2z, 1970 CQ W HORNSTRA HAL` 3,549,438

METHOD AND APPARATUS FOR ETCHING CURVED SURFACES Filed May 23, 1967 4 Sheets-Sheet 5 5 INVENTORS.

C/Oyfon W//oorns fm BY Richard/E Moore John D. H/'c/(er5-on H7 TOR/VE Y DBC. 22, 1970 C. W HOQ-RNSTRA ET AL 3,549,438

METHOD AND APPARATUS FOR ETCHING CURVED SURFACES Filed May 23, 1967 5 4 Sheets-Sheet 4 N :fm

INVENTORS.

HTOR/VE Y United States Patent O 3,549,438 METHOD AND APPARATUS FOR ETCHING CURVED SURFACES Clayton W. Hoornstra, Richard E. Moore, and John D.

Hickerson, Midland, Mich., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Filed May 23, 1967, Ser. No. 640,562 Int. Cl. B41c 1/18; C23f 1/02 U.S. Cl. 156-14 12 Claims ABSTRACT OF THE DISCLOSURE Improved etching machine and method for the powderless etching of curved surfaces in which liquid etching composition is directed toward respective rotating vaned paddles at predetermined angles and for predetermined periods in an overall continuous manner by at least two series of jets operated alternately, cyclically and mutually exclusively. The liquid is substantially continuously flung as a splash and at a predetermined angle from the rotating paddles to an adjacent, spaced apart, substantially parallel curved plate to be etched, the curved plate being disposed with its axis substantially horizontal and the curved plate being rotated about its axis while etching proceeds. The apparatus includes a housing with a sump, a pump, agitators, a plate holder, means for rotating the plate holder, means for impinging an etching composition upon a curved plate held by the plate holder, an etching bath composition within the sump and means for controlling the temperature of the composition within the sump. The improvement in the apparatus lies mainly in the selection, disposition and utilization of jet injectors and vaned paddles so as to provide for impinging of increments of etching composition on a curved plate in the alternating, preferably angular, manner of the present improved method of etching.

BACKGROUND OF THE INVENTION (1) Field of the invention The invention relates to method and apparatus for etching curved surfaces including, particularly, but not exclusively, curved metal surfaces. Specifically the present invention is directed to method and apparatus for etching curved plates in the photoengraving art.

In etching acid-soluble metal by the widely used and well-understood powderless etching process, the entire surface of a workpiece to be etched is first coated with a material, such as, for example, chromated polyvinyl alcohol (PVA), which when exposed to a light image is insolubilized and where not so-exposed is readily removed by a suitable solvent. The insolubilized coating is cured by heat, and the uncoated or non-image areas are chemically or mechanically cleaned of residue. The workpiece surface so prepared is contacted with an etching bath, for example, by splashing or spraying the bath upon the work. The bath generally contains (1) an acid etchant suitable for dissolving the workpiece metal, and (2) a ilm forming agent or agents and (3) may also contain certain organic liquid solvents and other additive agents for modifying the behavior of the bath. Contacting with the etching bath is continued until the desired extent of relief is obtained. The workpiece is removed from contact with the etching bath, rinsed and dried and is then useful as a photoengraved plate (1) employed to make mats which in turn are used to ultimately produce molded rotary plates or (2) employed directly as a printing plate.

In general, the quality of printed matter is directly related to the quality of the photoengraved plate. For a high quality plate acceptable to the printing trade, the original ice matter must be reproduced with maximum fidelity in the relief plate. A high quality plate is characterized by a uniform outward sloping sidewall or shoulder around the periphery of each image element. The slope of the shoulder can be expressed in terms of the angle formed between the shoulder and a line normal, i.e., perpendicular, to the image surface. Such angle is herein called the shoulder angle. The shoulder angle is conveniently found by first measuring the horizontal width W of the shoulder between the image margin and the shoulder base and then measuring the vertical depth D of relief adjacent to the shoulder by means of suitable instruments. The ratio of W to D, i.e., the tangent of the shoulder angle provides a quantitative index of the degree of shoulder distortion present on an engraved cylindrical surface as the difference between the shoulder angle measured in the direction of curvature and the angle measured in the axial direction (at right angles to the direction of curvature). An ideal shoulder angle difference is about 0, while an acceptable shoulder angle difference is from about 0 to about 17. An unacceptable shoulder angle difference on the other hand is one which exceeds about 17.

The art of etching on flat surfaces is developed to the point where very high quality results may consistently be obtained. In etching on curved surfaces or plates, however, by processes heretofore known to the art, serious distortion of the relief image has been encountered, and the plates so produced have little or very limited use in commercial operations. First, the image shoulders produced on curved surfaces by processes heretofore known and used are inordinately broad or elongated in circumferential directions, that is, in the direction of curvature of the plate and are inordinately narrow in the axial direction or even slope inward so that two sides of the image element may be actually undercut or undermined and etched away. When inordinately elongated shoulders extend into the nonimage areas in the direction of plate curvature from the boundaries of light halftone image areas, the effect or defect is known variously in the vernacular of the trade as tailing, runaround, rundown or bleedoff Secondly in the known art processes for etching of curved plates another phenomenon called channeling is also encountered which involves formation of circumferentially directed channels or grooves in the plate between image areas.

(2) Description of the prior art A number of processes have been developed which purport to produce on curved surfaces a relief image of comparable quality to that commonly obtained on flat surfaces, and machines are commercially available for carrying out these processes. However, none of these processes or machines have actually accomplished this result, but rather, all produce curved engravings having a distorted asymmetric relief to a greater or lesser extent as described.

In the most commonly used prior art processes the curved workpiece, for example a substantially cylindrical piece, is held with its axis of curvature horizontal and is rotated about said axis while being impinged by portions of an etching bath. The etching bath is generally stored in a -sump spaced below the workpiece and is propelled up to the plate by suitable means such as by rotating dipping paddles. One variation of the above process differs only in that the workpiece is simultaneously and further rotated in a horizontal plane about a vertical axis. In both the above processes the axis of curvature of the workpiece remains horizontal throughout the etching step, and incidence of etching bath on the workpiece is in a substantially upward and vertical direction. However, this does not completely eliminate the aforementioned difficulties,

nor produce a photoengraving plate of a quality near that of a iiat plate.

In copending application Ser. No. 477,130, tiled Aug. 4, 1965, there is described a method for etched curved surfaces in which increments of etching bath composition are impinged upon a curved workpiece while it is being rotated about a substantially horizontal axis, and further, while the axis of the workpiece is oscillated or tipped cyclically in substantially a vertical plane. In another embodiment of the method described in the said copending application, the iiight path of etching composition relative to the axis of the rotating workpiece is cyclically and substantially continuously varied between x degrees and (180-x) degrees, wherein x is a number between about l and 80. The methods of the copendng application provide for improved uniformity of etching curved plates but the equipment required to carry out such methods on large curved plates is not easily built or cannot reliably be operated as is desired for commercial operations.

OBJECTS OF THE INVENTION It is a principal object of the present invention to provide a practical commercial process for selectively etching curved surfaces whereby the aforementioned difficulties and defects associated with selective etching of curved surfaces are avoided and wherein the results attained are of a quality more comparable to that of etched at surfaces.

Another object of the present invention is to provide a practical method of etching curved plates wherein the problems of non-uniformity of image shoulder width and slope, of tailing and of channeling are substantially eliminated or reduced and commercially usable photoengraved curved plates are produced.

Yet another object of the invention is to provide practical, reliable apparatus for the carrying out of the method of the invention on large as well as small curved plates.

SUMMARY OF THE INVENTION The objects of the invention are attained upon applying a resist image to the convex surface of a curved acidsoluble metal plate; repeatedly impinging a series of increments of a liquid etching composition against the metal surface while rotating the curved plate about its axis of curvature, the said axis being substantially horizontal; said series of increments being directed towards the curved plate interruptedly, repeatedly, and cyclically, at an angle of about x degrees relative to said axis, and then alternately repeatedly and cyclically being directed at an angle of about (ISO-x) degrees relative to said axis, x being a number in the range of about 30 to 90, but more preferably 30 to 60 and the period in each half cycle being a pre-selected time interval in the range of about to 60 seconds; continuing said rotating and impinging until a predetermined depth of etching is attained; and rinsing the so-etched plate.

The improved etching apparatus for carrying out etching according to the present method includes a housing with a sump, a pump, agitators, a plate holder, means for rotating the plate holder, means for impinging an etching composition upon a curved plate held by the plate holder, an etching bath composition within the sump, and means for controlling the temperature of the etching bath cornposition within the sump. The improvement in means for impinging the etching composition upon the curved plate comprises alternating liquid jetting means and vaned rotating paddle means for interruptedly, repeatedly, alternately and cyclically impinging, i.e. splashing, successive increments of the bath composition upon the curved plate at said preselected angles of about x degrees, and (l80-x) degrees, respectively. f

For the purposes of the specification and claims, the phrase alternating liquid jetting means refers to a subcombination of parts comprising essentially (l) one or more manifolds, (2) a plurality of jet injectors communicating with each manifold, (3) means for supplying liquid etching composition to each manifold, and (4) means for causing rst and second groups of jet injectors alternately to jet forth streams of the etching composition. Further, the phrase jet injectors is intended to embrace any structure having fluid communication with a manifold and adapted to provide a stream of liquid etching composition. Thus the term jet injector embraces both a pipe nipple with a nozzle on the end thereof, and a bar of metal or substantially rigid polymeric material having a bore therethrough that communicates with a port in a manifold. In the case of such bar, an array of jet injectors is understood to be a series of bores extending through the bar and communicating with the manifold.

BRIEF DESCRIPTION OF THE DRAWING The apparatus of the invention will be more clearly understood with reference to the drawings in which like parts are identified by like reference numerals and in which:

FIG. 1 is a view in front elevation, partly broken away and in section, showing substantially the complete apparatus of the invention;

FIG. 2 is a side elevation in section of the apparatus of FIG. l taken along the line 2 2 of FIG. l;

FIG. 3 is a fragmentary portion of a section, somewhat enlarged, showing apparatus similar to that in FIG. 2 but employing different liquid jetting means for jetting etching composition onto the paddles according to another embodiment of the invention;

FIG. 4 is a schematic representation of an array of jet injectors and paddles surrounding a curved plate to be etched, the array being viewed from an end of the apparatus as in FIG. 2, except that only the plate and the injectors and paddles are shown;

FIG. 5 is a schematic representation of an array of jet injectors and paddles surrounding a workpiece in the same manner as in FIG. 4, except that the number of jet injector and paddle combinations is greater;

FIG. 6 is a fragmentary isometric view of a jet injector and paddle combination similar to the combinations employed in FIG. 1 and FIG. 2, showing the spatial relationship between the injector and the paddle;

FIG. 7 is an enlarged sectional view of the novel jet injector apparatus of FIG. l, FIG. 2 and FIG. 6, the section being taken through the jet injector at a point where a passage or bore in the orice bar and a port in the common wall of the cylindrical tube and channel member are aligned;

FIG. 8 is an exploded, foreshortened, enlarged view of the novel jet injector apparatus of the invention showing the shutter valve strip at a first position with certain holes therethrough aligned with a first set of inclined bores in the orifice bar;

FIG. 9 is a view similar to FIG. 8 showing the shutter valve strip in the second or alternate position with some of the same and other holes thereof aligned with a second set of oppositely inclined bores in the oriice bar and the first set of bores being blocked; and

FIG. 10 is a schematic representation, in plan, of the combination of liquid injector means, rotating vaned paddle and curved plate to be etched, with graphic representation of the iiight paths of increments of etching bath composition directed in turn from the jet injectors to the paddle and thence to the curved plate. For ease of illustration, the curved plate, the jetting means and the vaned paddle are depicted as if positioned in a single plane, but it is to be understood that the jetting means is normally positioned substantially below or above the axis of the vaned paddle.

Referring now more specifically to FIG. l and FIG. 2, the present apparatus, which must be made substantially entirely of etchant-resistant materials of construction, is seen to be largely enclosed by an enveloping housing 10 containing a sump 11 in the bottom portion thereof, and a liquid etching composition 12 within the sump 11. The

liquid etching composition in the case of the etching of metal surfaces is generally a plural phase formulation including an aqueous acidic phase, and, an organic solvent phase that is water immiscible. In using such plural phase etching compositions, it is highly desirable to provide means for keeping the composition dispersed, as by agitation, during the times that the liquid jetting means and paddles are stopped, e.g., during placing or removing of a curved plate or workpiece from the housing. It is, therefore, generally necessary to provide agitator means (not shown) such as any suitable propeller or mixer blade driven by an agitator drive motor, but in the apparatus shown takes the form of a pump (not shown) which takes in liquid etching composition from the sump and forces it out through one or more perforated pipes (not shown) submerged in the composition in the sump, the pump being driven by drive motor 13. It is also highly desirable to provide cooling means including, for example, cooling coils 14 immersed in the liquid etching composition 12 and connected to cooling or refrigeration means (not shown). It may also be desirable, depending upon specific environmental conditions, to provide heating means such as heating coils 15, which are connected to piping leading to and from a heater (not shown).

Attached at an end of the housing and aligned with the =body thereof is a run-out table or sink indicated generally by the numeral 16 and on which the curved plate 17 to be etched is conveniently prepared for etching as by descumming, degreasing and/or brushing, and on which the etched piece is washed and rinsed following the etching process. AIn lthe specific apparatus shown, the curved plate is mounted in a conventional manner upon an adjustable, expandable frame that is supported by a central axial shaft 18. Such expandable frame devices that enlarge or decrease in cylindrical diameter as the occasion demands, generally with a scissors-like linkage, are well understood in the art of holding cylindrical plates. If desired, a cylindrical, etchant-resistant sleeve 19, of appropriate size, is mounted iirst on the expandable frame and the curved plate is attached to the sleeve. This is done to provide for a better flow of etchant around the edges of curved plates that have little margin, or that are incomplete cylinders. The axial shaft 18 is rotatably supported at each end thereof by an inverted T-shaped member 20 having rollers 21 at each end of the member 20. The rollers 2'1 ride upon angle irons 22' that extend the length of the housing 10` and serve as guide rails for the rollers.

If desired, any other suitable support means that provides for moving the curved plate into and out of the housing and over the run-out table or sink, may be used if desired. Such support means must provide for rotational drive of the curved plate Within the housing 10. An example of other suitable apparatus that may be used is shown in US. Patent No. 3,078,857.

The axial shaft 18 of the present apparatus is provided with means for coupling with and engaging a short shaft 23 that extends through and is journalled in the end wall 24 of the housing 10 and is driven by a reversible drive motor 25 mounted on said end wall. Any suitable coupling means that is readily engaged and disengaged and that is resistant to the action of the aqueous icidic etching bath composition can be employed. A preferred form of coupling apparatus (not shown) employs two side-byside parallel bullet-nosed shaped projections that mate with and self-centeringly enter and engage complementary cavities in the end face of axial shaft 18 when the curved plate and the supporting mechanisms are shoved into the housing 10.

The housing 10 is found provided with a door or closure means (not shown) for closing a large opening in the end wall 26 of the housing 10 adjacent the run-out table 16. Any suitable closure that substantially retains the splashing, spraying, etching bath composition 12 within the housing 10' can be used. Preferably, a door which is arranged for easy removal of the curved plate and its supportive assembly is incorporated into the assembly.

When a .door is used as in the present embodiment it is preferred to provide a counter-Weighted door that slides vertically upward to open, the lateral edges of the door sliding in channels that provide for better retention of etching composition. `In the present case it is further provided that hinged sections 27 of angle irons that are normally disposed substantially vertically during etching are lowerable to a substantially horizontal position in the run-out table after opening the door. Such hinged sections 27 are aligned with and serve as continuations of channel members 22, for purposes of bringing the curved plate and its supportive assembly out onto the run-out table. It has also been found simple and quite adequate to use fnred angle iron -sections 27 aligned end to end with respective angle irons 2'2 and spaced apart about @ig to 3%; inch, the spacing being aligned with the sliding door.

While the curved plate 17 and its supportive assembly are disposed in the housing 10 as indicated schematically in FIG. 2, it is very desirable before etching commences that none of the etching bath composition drips from the cover section 28 of the housing 10; otherwise, etching of the curved plate will proceed in an uncontrolled and undesired manner. It is therefore necessary that the roof of the housing 10` be sloped and made with no downward projecting ridges or points from which etching composition will drip upon the curved plate 17.

When the curved plate 17 on its supportive assembly is disposed within the housing 10, it is surrounded by an array of vaned rotatable paddles 29, 30. Preferably the array is symmetrical with respect to a vertical line passing through the axis of the curved plate 17. iln the specific apparatus shown, the upper four` paddles 29 in the array are provided with etching bath composition from liquid jetting means 31 while the lower paddles 30 in the array are dipping paddles that extend slightly into the liquid etching composition 12 in the sump 11, usually about 1A; to 2%; of an inch. The liquid jetting means 31 direct small streams or jets of liquid etching composition 12 towards the paddles 2.9 and into the zones swept out by the vanes thereof during rotation. Etching composition is provided to the cylindrical tube portions or manifold portions 32 of liquid jetting means 31 `by pumps (not shown) usually disposed in the liquid etching composition and driven by a pump drive motor such as motor 33. If necessary, the number of pumps may be two or more to provide sufficient volume of composition for each of the liquid jetting means 31.

The liquid etching composition .-12 directed, in each case, from liquid jetting means 31 to vaned paddles 29 during the time the paddles are rotating, is ung off of the vanes of the paddles as splash by centrifugal force due to the rotational movement of the paddles. In general it may be understood that the rotating paddle blade or vane begins throwing oif the liquid etching composition tangentially as a splash immediately at the point where it intercepts each liquid jet and continues to throw off splash for about one quarter revolution of the paddle, thus forming a quadrant or sector shaped splash pattern, taken in a plane normal to the axis of the paddle. In order to expose a substantial portion of the surface of the curved plate 17 to increments of etching composition it is necessary to place the rotating paddles a sufficient distance from the curved plate so that the horizons of the sector or quadrant in each case are large enough to be substantially contiguous to or overlapping with the quadrants covered by the next adjacent paddle and liquid jetting means combination. The liquid jetting means may be disposed above or below the vaned paddle and the paddle may be rotated clockwise or counterclockwise, but the sector or -quadrant in which splash is delivered onto the curved plate is readily pre-selected with a knowledge of the splash pattern behavior described above.

During the etching process, the curved plate 17 is rotated about its substantially horizontal axial shaft 218 at about to 100 revolutions per minute, preferably with a reversal of the direction of rotation, such as, from about one to about nine times per minute. Simultaneously, the paddles 29, 30 are rotated, for example by means of a drive motor 34 connected to pulleys 35 by drive linkage means such as belt 36, the pulleys being mounted on axial shafts 37 of the paddles that extend through the end wall 24 of the housing 10. Splashing of liquid etching composition 12 proceeds as the curved plate 17 turns and the vaned paddles 29, 30 rotate. As indicated in FIG. 2, the vaned paddles disposed on opposite sides of the curved plate 17 rotate in opposite and complementary directions.

For rather small diameter curved plates generally adequate splash coverage is obtained on providing only four combinations of liquid jetting means and paddle, as indicated in FIG. 4, while with very large diameter curved plates it may be necessary to use eight injector means and paddle combinations, as indicated in FIG. 5, or any other larger suitable number selected in accordance with the invention described herein. In general it is much to be preferred to use a symmetrical array in order to have a balance extent of etching or attack on the shoulders of the image obtained on etching.

While it is preferred to use liquid jetting means and paddle combinations it is also possible to use, in addition, dipping paddles such as the dipping paddles 30 shown in FIG. 2,. Such paddles are preferably provided with curved blade or vane extensions 38 in order to more effectively scoop up the liquid etching composition .12 and fling it upwardly toward the curved plate 17. This combination is less to be desired than the liquid jetting means-paddle combinations since it provides, to the extent that dipping paddles are used, only for the direction of increments along lines substantially normal to the curved surfaces of the curved plate v17.

While good etching is obtained with most any combination of liquid jetting means and paddle combinations which directs splash upon a curved plate, it is much to be preferred, for the purpose of the present invention, that the etching composition used be directed toward the curved plate at an angle of about 30 to 60 degrees with respect to the axis of curvature of the curved plate and more preferably at an angle of about 40 to 50 degrees, about 45 degrees being most preferred. This is believed to be necessary in order to avoid channeling The intent is to cause etching composition, at successively short intervals of time, to flow in all directions with respect to any given point on the surface of the curved plate to be etched. It is therefore considered necessary to direct the etching composition from the liquid injector means towards each vaned paddle at a relatively shallow angle y of about to 30 degrees with respect to the axis of the paddle, and therefore inherently with respect to a line parallel to the axis of the curved plate 17, such injection to continue for only a short period after which further injection is directed toward each paddle at an angle of about (lSO-y) degrees, wherein y again has a value of about 20 to 30, and to repeat the foregoing injections alternatingly, successively and cyclically.

Referring now more specifically to FIG. 10, there is shown schematically and by way of illustration, typical flight patterns of increments of liquid etching composition i12 directed in turn from a liquid jetting means 31 at a relatively shallow angle of y degrees and alternatingly and cyclically at (l80\-y) degrees towards the vaned rotating paddle 29 and thence to the curved plate 17 at angles of x degrees and (ISO-x) degrees. The angles x degrees and (ISO-x) degrees are resultant vectors brought about mainly by (l) the selection of the angles y degrees and (ISO-y) degrees in constructing the liquid jetting means 31, (2) by the pressure employed in directing the etching composition out of the apertures or bores in the liquid jetting means 31, (3) by the radial width of the vanes of the paddles 29, and (4) by the rotational speed of paddles 29. Normally, for liquid etching composition injected at a pressure of 2 to 5 pounds per square inch through a jet injector bore or orifice having a diameter in the range of 1A; to 1/2 inch and on employing a paddle with three-.inch vanes turned at a rotational speed of 300 to 400 r.p.m., liquid etching cornposition injected onto the vanes at an angle of about 25 degrees with respect to the axis of the paddle will be flung towards the curved plate at an angle of about 45 degrees relative to the axis of the curved plate, where the curved plate and the paddle are substantially parallel.

Another factor controlling the manner in which splash from the rotating paddles strikes the curved plate is the location of points on the vanes of a given paddle where a given jet of liquid etching composition strikes the vanes. Referring now to FIG. 6 of the drawing, in which is shown a fragmentary portion of an isometric View of an injector and paddle combination, it may be seen that the injector may be rotated on its longitudinal axis so that the impact of the jet varies from the `axis or hub of the paddle throughout the width of the vanes, i.e., in the radial direction. Regardless of the point of impact, the splash flung off the vanes liies off the paddle in a direction tangential to the surface of the cylindrical volume swept out by the vanes. In general, most of the splash is thrown off throughout an angular sector not exceeding about from the tangential line along which the rst droplets are thrown. A stream of liquid impinged upon a vane at a point close to the edge of the vane is thrown oif promptly and the sector through which the vane moves until nearly all the liquid is thrown off is relatively small, e.g., 30 to 60. On the other hand if the stream is impinged closer and closer to the hub or axis of the vane, then the liquid must drain lacross the radial width of the vane, throughout a greater and greater time interval and consequently wider sectors of splash are produced. Such sectors, in practice, when produced by an array of injector jets extend longitudinally of the paddle. In order to reduce the number of injector jets needed for substantially continuous splash to be produced from end to end of the curved plate, it is desirable that the jet of etching composition is directed sufficiently away from the edges of the vanes and at an angle other than 90 with respect to the axis of the paddle in order that the liquid composition will spread out in the longitudinal direction of the vanes before the composition is ung off the edges of the vanes. It will be manifest that the volume 'and momentum of the etching composition applied Will further affect the size of longitudinal zone socreated. In any event it is highly desirable, if not essential, to provide substantially contiguous or overlapping zones of splash on the curved plate to be etched.

'It is also necessary to bring the jets to the vanes at an angle greater than about l0 to 15 degrees simply to get the jets into the sweep of the vanes without positioning the jetting means within said sweep, as by slotting the vanes.

The liquid jetting means and manifold therefore and the operation thereof will be better understood with reference to FIG. 8 and FIG. 9 wherein the injector means 31 is shown in exploded view and in side elevation. Looking rst -at FIG. 8 in conjunction with FIG. 7 there is seen a liquid jetting means 31 having a cylindrical tube or manifold portion 32 integrally formed back to back with a U-shaped channel portion 39 and having a common wall 40 therebetween. Overlying the bottom or recessed floor of the channel is a jet orilice bar 41 that substantially fills the cavity of the channel 39 from wall to wall and throughout the length thereof. The orice bar 41 is provided with an array of bores or passages 42 formed therethrough each at an angle in the range of about 10 to 90 degrees with respect to the longitudinal axis of the injector but preferably at an 'angle in the range of to 30 degrees and even more preferably at an angle of about degrees. The jet orifice bar is further penetrated by a second set of bores or passages 43 that are each directed at an angle of 180 degrees minus the angular 'value for the disposition of the rst set of bores. The openings of the rst set of bores 42 at the inner face of the jet orice bar 41 are aligned with a first set of ports 44 that extend through the common wall 40 between the cylindrical tube 32 and the channel 39, while the openings of a second set of bores 43 are aligned with a corresponding second set of ports 45 in the common wall. Slidably interposed between the common wall 40 and the jet orifice bar 41 is a shutter valve strip 46. The shutter valve strip 46 is movable longitudinally of the jetting means from a rst position to a second position by mechanical means (not shown), coupled to an end thereof. The shutter valve strip 46 is provided with an array of openings 47, formed therethrough so spaced as to provide communication between the iirst set of bores 42 and the corresponding first set of ports 44 in the wall of the channel 39 when the shutter valve strip 46 is in said rst position and to block communication between the second set of bores 43 and the corresponding ports 45 with imperforate portions of the shutter valve strip, as illustrated in FIG. 8. Conversely, when the shutter valve strip 46 is shifted to the said second position, communication is provided between the second set of bores 43 and the second set of ports 45, while bores 42 and ports 44 are blocked. It may be seen that the liquid jetting means in the condition shown in FIG. 8 provides for spraying etching composition upwardly and to the right while the injector in the configuration shown in FIG. 9 provides for jetting liquid etching composition upward and to the left. An important attribute of the injector means of the invention is the provision for jetting substantially without interruption of the overall jetting process, and further, another important attribute is the supplying of oppositely facing bores with but a single manifold.

If desired, however, in lieu of the injector means shown, there may be employed a double manifold system with separate arrays of oppositely facing nozzles 48 as illustrated in the fragmentary View in FIG. 3. In using the nozzles 48 as in FIG. 3, the nozzle openings are positioned adjacent vaned rotating paddles in the same manner as the liquid jetting means previously described. It is necessary, however, to provide flow control means so that jets of liquid etching composition emerge from each set of nozzles facing in a common direction during separate and discrete and mutually exclusive time intervals from the oppositely facing set.

In carrying out etching according to the improved method of the invention, a curved plate to be etched, for example, a metal photoengraving plate etched with an aqueous acidic etching composition, is provided with a resist coating on which is formed an image of variable resistance to the etching composition. The plate is prepared for etching according to methods understood in the art and is then mounted upon a plate holder such as the holder indicated schematically in FIG. 2. The plate holder and plate are placed inside the housing of an etching machine and coupled to a plate holder drive. A liquid etching composition is provided in the sump of the etching machine. In the event that the etching composition comprises two or more immiscible phases, provision is made for keeping the phases dispersed, for example, as by pumping the bath through a perforated pipe that extends longitudinally of the pump thereby to provide a sparginglike effect. This is done without exposing the curved plate to the etching composition until the etching operation is ready to be commenced. When the plate holder has been coupled and the door of the housing has been closed, pumps are started that provide liquid etching composition to the manifolds of the injectors and rotation of the curved plate commences. The drive means for the rotating paddles is also turned on substantially at the same time and jets of etching composition start to strike the rotating paddles and are llung off as a splash upon the curved plate. The direction of rotation of the holder for the curved plate is reversed from l to about 9 times per minute, the rate of rotation being from about 10` to 100 revolutions per minute. The rotating paddles usually are driven at a rotational speed of about 200 to 800 revolutions per minute. letting of the etching composition in a given angular direction is generally continued for a preselected time interval in the range of about 5 to 60 seconds before stopping jetting in that direction and immediately jetting in the opposing, i.e. (ISO-x) degrees for a like pre-selected time interval in the range of about 5 to 60 seconds. Rotation of the curved plate and impinging of the etching composition from alternating directions of x degrees and (1:80-x) degrees continues until a predetermined depth of etch is obtained, ordinarily a depth in the range of about 0.010 to 0.050 inch. In etching acid soluble metal plates, the time for etching is generally in the range of about 4 to 20 minutes, although other times may be used with appropriate etchant and plate combinations. After etching for a predetermined time, the etching machine is shut olf and the etched plate is removed, washed and rinsed.

.The following examples are provided to illustrate the invention and not to limit the scope thereof.

Example 1.-An image pattern including linework, type matter, and halftone images was applied, by methods hereinbefore described, to a curved plate of photoengraving grade magnesium alloy 9 inches in width by 24 inches in length and bowed longitudinally into an arc with a radius of 8 inches. This curved plate was mounted on a cylindrical plate holder and placed in an etching machine similar to the machine of FIGS. l and 2. The paddles were started up at a rotational speed of 375 r.p.m., the plate holder was set in rotation at a speed of 40 rpm., the direction of rotation being reversed every 20 seconds, the injectors employed supplied jets of etching composition to the paddles at angles of about 25 degrees and 155 degrees, respectively, with respect to the axis of each paddle, the jets were applied at sufricient pressure that splash flung from the paddles reached the curved plates at angles of about 45 degrees and 135 degrees, respectively, relative to the axis of the plate holder, the angle of splash application being changed every 7.5 seconds, i.e., through 4 cycles per minute. The acid etching composition was a conventional powderless etching bath comprising nitric acid, water, `filming agent and immiscible organic solvent. The etching composition, while at a temperature of about 75 F., was applied in the manner described for a predetermined period of 10 minutes. The plate was removed, rinsed and dried. The plate was free from the aforedescribed defects such as channeling and bleedolf, and the original image was faithfully retained. The depth of relief was found to be I0.032 inch. Shoulder angles were measured on a round image element about 1%@ inch in diameter. The angles of the shoulders extending in the direction of curvature from the round image element measured 45 degrees While the angle of the shoulders extending axially from the same image element measured` about 38 degrees. Thus, the latter angle was as great as the former, and the engraving was of a high quality suitable for use in critical commercial operations.

Example 2.-An image pattern including linework, type matter, and halftone images was applied, by methods hereinbefore described, to a curved plate of photoengraving grade magnesium alloy 9 inches in width by 24 inches in length and bowed longitudinally into an arc with a radius of 9 inches. This curved plate was mounted on a cylindrical plate holder and placed in an etching machine similar to the machine of FIGS. 1 and 2, except that no dipping paddles were used, the two paddles fbelow the plate holder being positioned substantially above the liquid in the sump and the paddles being provided with injector means. The paddles were started up at a rotational speed of 570 r.p.m., the plate holder was set in rotation at a speed of 60 r.p.m., the direction of rotation being reversed every 6 seconds, the injectors employed supplied jets of etching composition to the paddles at angles of 25 degrees and 155 degrees, respectively, with respect to the axis of each paddle, the jets were applied at sufficient pressure that splash flung from the paddles reached the curved plate at angles of about 45 degrees and 135 degrees, respectively, relative to the axis of the plate holder, the angle of splash application being changed every 10 seconds, i.e., through 3 cycles per minute. The aqueous acid etching composition was a conventional powderless etching bath comprising nitric acid, water, filming agent and immiscible organic solvent. The etching composition, while at a temperature of about 75 F., was applied in the manner described for a predetermined period of 10 minutes. The plate was removed, rinsed and dried. The plate was free from aforedescribed defects such as channeling and bleedoff, and the original image was faithfully retained. The depth of relief was yfound to be 0.031 inch. Shoulder angles were measured on a square image element about one-half inch on a side. The angles of the shoulders extending in the direction of curvature from the square image element measured 44 degrees while the angle of the shoulders extending axially from the circumferential margin of the square image element measured about 36 degrees. Thus the latter angle was 82% as great as the former, and the engraving was of a high quality suitable for use in critical commercial operations.

The method and apparatus of the invention having been thus fully described, various modifications thereof will at once be apparent to those skilled in the art and the scope of the invention is to be yconsidered limited only by the breadth of the claims hereafter appended.

We claim:

1. In an improved etching machine for the powderlesn etching of curved plates, the machine comprising a housing with a sump and including a pump, agitators, a plate holder, means for rotating the plate holder, means for impinging an etching composition upon a curved plate hedl by the plate holder and having an etching bath composition within the sump, the improved means for impinging the etching composition upon the curved plate which comprises, in combination:

(a) a plurality of spaced apart, rotating, vaned paddles with rotating drive means therefor, each said paddle extending longitudinally of the curved plate, substantially parallel therewith and spaced apart therefrom and extending longitudinally beyond each end of the curved plate, and;

(b) liquid jetting means, said jetting means including jet injectors, manifolds and etching composition supply means connected to said manifolds, said jet injectors being operatively connected to said manifolds and disposed in first and second sets linearly arrayed, respectively, adjacent each said paddle, said first sets, in each case, being adapted to bring etching composition increments to the adjacent paddle at a requisite pressure and angle whereby the increments are fiung as a splash from each paddle to the curved plate at a pre-selected angle of x degrees relative to a line parallel to the axis of the rotating workpiece, while the paddles are being rotated, and said second sets, in each case, being adapted to bring etching composition increments to the adjacent paddle at a requisite pressure and angle whereby the increments are iiung as a splash from each paddle to the curved plate at a preselected angle of (l80-x) degrees relative to said line parallel to said axis, while the paddles are being rotated, x being a number in the range of about 30 to 90;

(c) and flow control means adapted to control flow of etching composition to said first and second sets of jet injectors whereby successive increments of the composition emerging from said jet injectors are alternately and cyclically impinged upon the curved plate at said angles of x degrees and (lSG-x) degrecs,

2. The apparatus as in claim 1 in which x is a number in the range of about 30 to 60.

3. The apparatus as in claim 1 which includes means for periodically and cyclically reversing the direction of rotation of the plate holder.

4. Apparatus as in claim 1 wherein the jet injectors in each of the first and second sets are disposed in a sufficiently long linear array to direct increments of etching composition from end to end of the curved plate, the first set extending beyond a first end of the curved plate and having at least one of the outermost jet injectors thereof sufficiently beyond the first end of the curved plate that increments provided by such injector and brought to the curved plate by the associated paddle at an angle of about x degrees are impinged upon the endmost portions of said first end of the curved plate, and the second set extending beyond the second end of the curved plate and having at least one of the outermost jet injectors thereof offset sufficiently beyond the second end of the curved plate that increments provided by such injector and brought to the curved plate by the associated paddle at an angle of about (l-x) degrees are impinged upon the endmost portions of said second end of the curved plate.

5. Apparatus as in claim 1 wherein each of said first sets of jet injectors communicates with a first manifold, each of said first manifolds supplying etching composition to the corresponding set of jet injectors communicating therewith; each of said second sets of jet injectors communicates with a second manifold, each of said second manifolds supplying etching composition to the corresponding set of jet injectors communicating therewith; and means for directing how of etching composition cyclically, alternately, and mutually exclusively to said first manifolds and to said second manifolds.

6. Apparatus as in claim 1 wherein the jet injectors and etching composition supply means therefor comprise: a cylindrical tube integrally formed with a channel member that is U-shaped in section, said tube having a common wall with the closed side of the channel member, said common wall having first and second sets of spaced apart ports formed therethrough, the inside face of said closed side of said channel member being overlain with a substantially rectangular shaped orifice bar sealingly fitted into the channel and substantially filling the channel from side to side, said orifice bar being provided with first and second sets of bores formed transversely therethrough, said first and second sets of bores in the orifice bar being aligned, respectively, at the closed side of the channel member with said first and second sets of ports in the common wall, said first set of bores being formed through the orifice bar at an angle of y degrees from the plane of the closed side of the channel and the second set of bores being formed at an angle of about (lSO-y) degrees from the plane of the closed side of the channel, wherein y is a number in the range of from about 20 to about 30, each set of bores in the orifice bar being spaced apart in a long enough array so as to direct increments of etching composition to the curved plate via the adjacent paddle along at least the entire length of the curved plate, each set of bores having an end group thereof extending beyond an end of the curved plate in a direction wherein the bores of the end group are inclined towards the curved plate and at least one of the outermost end bores of each set being offset, respectively, at least x degrees relative to a line drawn normal to the axis of the curved plate at the end beyond which the set of bores extends each set having the bores thereof spaced apart and each set partly overlapping the other set; a longitudinally slideable shutter Valve strip interposed between the orifice bar and the closed side of the channel, said shutter valve strip having a series of spaced apart holes formed therethrough, said shutter valve strip being slideable from (1) a first position, wherein part of said series of holes is aligned with said first set of bores in the orifice bar and with a corresponding first set of ports in the common wall and all the bores in the second set are obstructed by imperforate portions of the shutter valve strip; to (2) a second position wherein the remainder of the holes and some of said part of said series of holes in the shutter valve strip are aligned with said second set of bores in the orifice bar and with corresponding ports in the common wall and all the bores in the first set are obstructed by imperforate portions of the shutter valve strip;

and means for periodically and cyclically reciprocating the shutter valve strip from the first position to the second position and back to the first position again.

7. The apparatus as in claim 1 wherein the jet injectors are disposed substantially beneath and adjacent to respective paddles.

8. The apparatus as in claim 1 wherein an array of paddle and jet injector combinations is disposed around the curved plate adjacent to and spaced apart therefrom, each combination extending longitudinally of the curved plate and beyond each end thereof, and the array being symmetrical about a vertical axis.

9. The apparatus as in claim 8 wherein the number of paddle and jet injector combinations is six.

10. The improved method of etching a curved metal plate which comprises:

applying a resist image to the convex surface of said curved plate;

repeatedly impinging a series of increments of a liq uid etching composition against said surface while rotating the curved plate about its axis of curvature at a rate of from about l() to 100 revolutions per minute, the said axis being substantially horizontal,

and the direction of rotation being reversed about 1 to 9 times per minute;

the increments being impinged upon the curved plate by directing a plurality of series of jets of such composition towards rotating vaned paddles positioned substantially parallel to, adjacent to and spaced apart from the curved plate, and flinging the splash ofi the vaned paddles to the curved plate by continuously rotating the vaned paddles;

said series of increments being directed towards the curved plate cyclically, periodically and interruptedly at an angle of x degrees relative to a line parallel to said axis and then alternately at an angle of (ISO-x) degrees relative to said line, x being a number in the range of about 30 to 60 and each period being a pre-selected time interval in the range of about 5 to 60 seconds;

continuing said rotating and impinging until a predetermined depth of etch is attained; and rinsing the so-etched plate.

11. The method as in claim 10 in which the value of x is about 45.

12. The method as in claim 10 in which additional etching composition distribution means are employed to impinge etching composition upon the curved plate in a direction substantially normal to the surface thereof and substantially from beneath the curved plate.

References Cited UNITED STATES PATENTS 3,078,857 2/1963 Guenst 134-46 2,926,076 2/1960 Guenst 156-14 3,348,557 10/1967 Adamson 134-113 JACOB H. STEINBERG, Primary Examiner U.S. Cl. X.R.

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