US3271226A

US3271226A - Etching apparatus for making a cellulosic printing plate

Info

Publication number: US3271226A
Application number: US300977A
Authority: US
Inventors: Henry C Staehle; Lincoln A Cundall; Cyril A Horton; Harold J Frelier
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1963-08-09
Filing date: 1963-08-09
Publication date: 1966-09-06
Anticipated expiration: 1983-09-06
Also published as: GB1062282A; DE1479144B2; BE651583A; DE1479144A1

Description

Se t. 6, 1966 H. c. STAEHLE ETAL 3,

ETCHING APPARATUS FOR MAKING A CELLULOSIC PRINTING PLATE Filed Aug. 9, 1963 5 Sheets-Sheet 1 Fl LTER Fig.1 /63 Henry C. S faehle Cyril A.Horfon Linc0lnA.Gandall Harold J Frelier INVENTORS ATTORNEYS Sept. 6, 1966 H. c. STAEHLE ETAL 3,271,226

ETCHING APPARATUS FOR MAKING A GELLULOSIC PRINTING PLATE Filed Aug. 9, 1963 5 Sheets-Sheet 2 FigzZ Henry C. Staehle Cyril A-Hort on Lincoln A.G'undall Harold J Fre lier INVENTORY Sept. 6, 1966 H. c. STAEHLE ETAL 3,

ETCHING APPARATUS FOR MAKING A CELLULOSIC PRINTING PLATE Filed Aug. 9, 1963 I3 Sheets-Sheet 5 Henry C. Siaehle Cyril A.H0rl'0n Linc0lnA.Cundall Harold JFrelier INVENIORS JQTTORNEY'S United States Patent 3,271,226 ETCHHNG APPARATUS FOR MAKING A CELLU- LOSiC PRHNTENG PLATE Henry C. Staehle, Lincoln A. Cundall, Cyril A. Horton, and Harold .l'. Frelier, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed Aug. 9, 1963, Ser. No. 300,977 12 Claims. (Cl. 156345) This invention relates to halftone printing and particularly to an arrangement for solvent etching a relief halftone in a cellulosic sheet protected by a suitable resist stencil such as a photographically produced washoif gelatin image.

Relief plates of cellulose nitrate or of cellulose esters such as cellulose acetate are known, and solvent etching of the latter type is described in US. Patent 2,891,849, Whitbourne. The present invention is directly useful with the process described in the Whitbourne patent.

While the removal of material between the dots of a relief printing plate is normally referred to as etching, the actual operation is a softening of the cellulosic sheet by the solvent accompanied by a brushing to remove the softened areas. With hundred-line halftones or finer, the hairs of the brush must be quite small to operate between the dots, even in the highlight regions where the dots are small, and particularly in the shadow regions where the dots merge and the material to be removed leaves only a small hole. In the Whitbourne patent mentioned above, a nylon velvet pad is suggested as the brush, and such a pad is ideally useful with the present invention.

The primary object of the present invention is to provide an improved and reliable etching arrangement producing a printing plate with excellent dot quality. The etching including brushing according to the present invention is so efficient that good gradation is produced in the shadows, and the light tones or highlights are reliably produced with a minimum of loss of fine highlight dots.

It is a particular object of the invention to permit several successive etching steps or bites of the plate without adversely affecting the highlight dots.

A further object of the invention is to provide an automatic or semi-automatic apparatus into which a plate ready for one or more etching steps can be fed and which will provide just the right degree of etching. Specifically, the invention employs a rotatable drum supporting a plate to be etched and carrying the plate past a plush belt which applied etchant and simultaneously wipes softened material from the plate.

One form of such plate consists of a relatively thick acetate sheet coated with a light-sensitive or sensitized gelatin layer. Alternatively, it is now common to use a laminate in which the cellulose acetate sheet or other plastic sheet is supported by a thin metal plate, but as far as the present invention is concerned, as long as the cellulose acetate sheet or layer is fairly rigid, it does not matter which form is used. On the other hand, a preferred embodiment grips the supporting plate magnetically, and hence the embodiment requires the ferrous metal base. Several specific examples of printing plates etchable by the present invention are set forth in the copending application for Letters Patent Serial No. 269,345, filed April 1, 1963, in the names of C. D. Baxter and H. C. Staehle. The invention will be described with respect to a cellulose acetate sheet, but it is equally applicable to any material which employs solvent etching accompanied by velvet brushing. Cellulosic layer as used hereinafter is intended to include all such suitable plastic or lacquer materials. A cellulosic plate consists essentially of such a layer self-supported or laminated to another support such as a metal sheet.

The light-sensitive gelatin layer may be of any of the forms used for the production of stencils. It is not necessary for the residual gelatin image or stencil to be clear. Accordingly, it is preferable to use one of the more efficient types of recording system, namely that in which a silver salt is incorporated in the gelatin and in which a developer hardens the gelatin adjacent to the silver at the time the silver salt is reduced to silver. Such a cellulosic plate is exposed, for example, to a halftone negative. The exposed areas are developed with any of the standard hardening or tanning developers which reduce the silver salt to metallic silver and which harden the adjacent gelatin. The remaining gelatin is washed off, but the silver is not bleached out, although it could be bleached out. One advantage of leaving the silver in the hardened gelatin is that the image (laterally inverted but positive) is immediately apparent on the plate and the quality can be easily judged. The unexposed areas of the plate are then removed by washing in warm water, just warm enough to remove the unhardened gelatin but not warm enough to remove the hardened areas. This is all well known.

Due to such removal of the unh-ardened gelatin (plus any residual silver salt therein), the cellulose acetate surface is now exposed (directly or through a thin subbing layer which is also soluble in the solvent etchant to be used) in the areas to be etched, but it is still covered with the hardened gel-atin and-silver stencil in the areas which are not to be etched. In practice, at least some of the gelatin-silver layer remains on the finished plate and is inked for printing, but even if the gelatin layer is worn away, the top surface of the cellulose acetate dots may be inked and prints pulled therefrom.

The present invention starts with an exposed, developed and washed-off plate consisting essentially of a cellulosic layer with a stencil thereon which is not soluble in the solvents to be used for softening the cellulosic layer. For example, the Whitbourne patent and the Baxter et al. application mentioned above describe some suitable solvents hereinafter referred to as etchant for cellulose acetate which do not attack the gelatin stencil. For simplicity, the developed and washed-off, but not etched, plate is hereinafter referred to as a cellulosic plate with a developed stencil thereon. The present invention starts with such a cellulosic plate and stencil and finishes with a completed etched plate ready for inking and printing therefrom.

In accordance with the invention, a cellulosic plate with developed stencil thereon is secured to the surface of a drivable drum, which engages, throughout its lowest segment, a plush belt continuously moistened with an etchant. Since the particular etchants used are ineffective without scrubbing, the belt is driven at a speed different from and in a plurality of directions relative to that of the plate so that the pile of the belt continuously rubs against a major surface of the plate to apply etchant thereto and to remove softened portions of the plate between resistant nodules or dots of the developed and tanned stencil. As the drum continues to rotate, moving the plate past the plush belt, the plate is wiped to remove excess etchant, dried by auxiliary heaters, and allowed to cool prior to a next engagement of the etchant applied by the plush belt.

The subject matter which is regarded .as our inventi-on is particularly pointed out and distinctly claimed in the concluding portion of this specification. The invention, however, as to its organization and operation together with further objects and advantages thereof, will best be understood by reference to the following description taken in connection with the accompanying drawings in which:

FIG. 1 is an elevation view partially in section of the etching arrangement of the present invention;

' FIG. 2 is a cross-sectional view taken along the line 2-2 of FIG. 1;

FIG. 3 is a detail view of the surface construction of the roller shown in FIGS. 1 and 2; and

FIG. 4 is a magnified perspective view of a small segment of a partially etched ha-lftone plate being engaged by the plush bristles.

Referring now to the drawings wherein like numbers refer to similar parts, we have shown in FIGS. 1 and 2 a main drum 10 having an outer surface comprising a layer of magnetic materials 11 and a layer of insulation means such as cork 12 covered by a gummed kraft paper tape 13. This construction is such that a cellulosic plate 14 having a magnetizable base will adhere thereto. In the overall construction illustrated, one side of the drum 10 is exposed to facilitate placing the plate 14 thereon and observation of the plate during etching.

As shown more clearly in FIG. 3, the magnetic material 11 may take the form of wide, A" thick Koroseal flexible strips marketed by B. F. Goodrich as Pole #3. These strips are helica'lly applied with the north poles adjacent to the north poles as indicated. In one embodiment, the layer of cork 12 is 4; thick, and with the kraft tape 13, provides sutficient insulation to allow the heating and cooling cycle discussed below without damage to the composite drum 10.

The drum 10 with the plate 14 supported thereon is driven in a clockwise direction (FIG. 2) as indicated by an arrow 16 .by a driving means such as a mot-or 17. Throughout the surface region of the lower segment of the plate 14 is positioned a plush belt 18 supported by a pair of

rollers

20 and 21 with the roller 21 being driven by a reversible motor 22 so that the surface of the plush belt 18 wipes in both directions across the lower surface of the cellulosic plate 14. The

rollers

20 and 21 and the plush belt 18 lie partially within a pan 24 having therein an etchant 26 such as is used for thinning lacquer and specifically set forth in the abovementioned patent application Serial No. 269,345. The level of the etchant 26 is sufficient to engage the lower surface of the plush belt 18 whereby the plush 18 applies the etchant to the plate 14. The generally horizontal placement of the plush belt 1 8, as distinguished from a vertical placement, reduces to a minimum the vertical lift of the etchant. Such construction reduces solvent evaporation and drying out of the belt, as well as allowing lateral access and observation. The etchant is replenished periodically, being applied directly to the belt 1 8 from a distributor pipe 27. In order to prevent build-up of slag on the belt 18, we have provided a plurality of vanes 28 which agitate the pile while it is within the etchant bath 26.

One plush fabric which works satisfactorily in this invention is a mohair plush, having a pile. As the etchant softens portions of the plate 1 4 between the resistant developed nodules 30 (FIG. 4), later bristles 32 of the plush belt 18 wipe away the softened plastic between the nodules 30. However, the hard nodules 30 apparently deflect the bristles as at 32' and prevent them from wiping away plastic material under the nodules 30. As a result, when the etching under the complete, the nodules 30 become supported by a conical configuration, of a height of the order of .01 inch as indicated by the dashed lines 34. Etching a printing plate as much as .01 inch is usually considered necessary to obtain excellent halftone reproductions when using certain printing techniques.

As is shown in FIG. 4, the plate 14 includes a base layer 36. This base layer is preferably of a magnetizable metal such as iron alloys and of sufficient strength to allow handling, etc. The iron base layer 36 enhances 4 securing the plate 1 4 to the magnetic surface of the drum 10.

Because of the softening effect of the etchant on the plastic below each nodule, it is not practicable to complete the etching step in one bite, whereby the etchant would soften all of the plastic so that the nodules 30 as well as the plastic therearound would be wiped away by the bristles 32. Usually, when providing fine relief printing plates, only about .001 may be removed per bite without damage or loss of some of the finest nodules 30. The magnified view of FIG. 4 represents the appearance of the plate after several bites have been taken, with the nodules 30 being about .001 in diameter and the maximum depth (34) of etching about .01". When operating at room temperature, the drum 10 is driven at a speed such as r.p.m., which is substantially greater than that necessary to remove the full depth of the etching required for printing purposes during a single pass over the plush belt 18. The acceptable duration of application of etchant, and therefore the speed of rotation of the drum 10, is primarily a function of the fineness of detail of the developed plate 14. When etching a halftone of lines per inch, 4 rpm. is suitable, while halftones of 40 lines per inch may be etched at rpm.

During the etching process, the surface of the belt 18 travels at about 120 feet per minute and is reversed about 30 times per minute. As the successive portions of the plate 14 leave the region of the plush belt 18, they are wiped by a plush roller 42 to remove substantially all of the etchant remaining. As it is rotated in a clockwise direction by a driving motor 43, the plush roller 42 is wiped clean by a rigid wiper 44. During certain types of operations, a wiper 45 may replace the plush roller 42 or be used in conjunction with it. Used etchant removed from the plate 14 by the roller 42 and collected on the wiper 44 flows into a trough 46. Such waste is directed by an outlet pipe 47 from the trough 46 to a waste material collection receptacle.

As the plate 14 continues to revolve, the etching action may be halted by application of certain non-solvents such as alcohols applied thereto by a nozzle 49 with excess alcohol falling against a shield 50 and draining from the shield to another waste receptacle (not shown). When using volatile etchants such as ethyl acetate or n-butyl acetate and an eflicient drying arrangement, as discussed below, application of the alcohol may be omitted.

During further rotation, in order to assure drying of the partially etched plate 14, the plate surface is heated by suitable means so that a next bite may be taken by the plush belt 18 without loss of detail. The particular drying apparatus shown in FIG. 2 is a combination hot air and radiant heater system. The hot air portion utilizes a plurality of parallel pipes 54 having inwardly opening apertures 55 which direct air, heated to temperatures of the order of 200 F., against the surfaces of the plate 14. The radiant heaters 56 must be operated at temperatures below the ignition temperatures, such as 700 F., of the chemicals being used. The heating operation must be further controlled to prevent blistering of the developed plate 14 by limiting the maximum temperature thereof. Temperatures above about 200 F. tend to blister the plate, and we have provided a temperature sensing means such as a thermocouple or a thermistor 60 on the cork 12 to sense the temperature of the plate 14 and limit the effectiveness of the heating means when temperatures of about F. are reached.

Because of the fact that the etchant (and the alcohol when used) tends to create noxious and inflammable fumes, we have provided exhaust means substantially surrounding the pipes 54 and the heaters 56 in the form of an exhaust hood 57 with a fan 58 (FIG. 1) for removing the heated air containing the volatile solvents. Usually, this contaminated air is removed both from the region of the etching arrangement and from the building housing the equipment.

As shown more clearly in FIG. I, the inlet to the hot air pipes 54 comprises a filter 62, a fan 63, a heater 64 and duct means 65 which conveys the heated air to both ends of the hood 57 wherein plenum chamber distributors 66 convey air to both of the ends of each of the pipes 54. In order to assure removal of noxious fumes, the capacity of the fan 58 is made larger than that of the fan 63.

As a final stage, during each bite, the plate 14 is cooled to near room temperature prior to the next bite. Auxiliary cooling means such as cool air impingement is obtained from a distributor pipe 68 to assure suitable cooling. Depending on the time duration between the heater system and the plush belt 18, additional or no cooling means may be employed.

We have found that during etching simply scrubbing the surface of the developed plate 14 with a continuous straight wiping action prevents obtaining of useful etched plates. Such wiping results in deep ridges which branch and combine in the manner of mountain ranges without regard to the size or location of the developed nodules 30 or other printed matter. This action invariably results in high ridges in large white spaces which provides a wrinkled appearance in margins, etc., of prints pulled from a finished plate. However, by driving the plush belt 18 laterally (generally perpendicular to the motion of the nearest portion of the drum surface) by means of the type illustrated in FIG. 1, while it travels over the

rollers

20 and 21, a sinusoidal scrubbing action is attainable whereby the bristles 32 engage all surfaces of each cone in the region of the nodules 30 to obtain the conical etching as indicated in FIG. 4 and substantially smooth etching of undeveloped spaces in the plate 14.

The lateral drive of the plush belt 18 is preferably accomplished by an eccentric drive 70 connected by a lever 72 to a drive arm 73 of a support 74 for the bearings 75 of the

rollers

20 and 21. We have found a speed of 60 r.p.m. suitable for the eccentric drive 70 when the length of its stroke is of the order of 1.00". The motion of the frame 74 is facilitated by the use of rollers 76 and 77 (FIG. 2). Obviously, with such motion of the support 74, the motor 22 will be most effective if it is mounted on the support 74 or provided wit-h a universal drive linkage 78, as shown in FIG. 1.

An additional control feature enhances the attaining of quality plates, and that is regulation of the pressure between the plush belt 18 and the drum 10. Both the total pressure and the distributed pressure are important. .The total pressure is regulated by upward force developed by the support plates 80 of the rollers 76. We prefer to use pneumatic means such as air cylinders 82 to regulate this force. The distributed pressure is a function of the sag of the plush belt 18 between the

rollers

20 and 21. This sag is most easily regulated by a turnbuckle drive arrangement 84 shown in phantom in FIG. 2. The location of the

rollers

20 and 21 is critical in the sense that the rollers should not directly drive the plush belt 18 against the plate 14 with any greater force than that applied by the belt in regions between the rollers. With the belt 18 being of considerable strength, this spacing requires slight adjustment only once every few days and the spacing between the

rollers

20 and 21 and the plate 14 may be observed during operation to detect excessive sag.

Another feature which simplifies maintenance is the use of removable bearing blocks in the bearings 75 so that the belt 18 may be removed easily.

While we have shown and described particular embodiments of the present invention, other modifications may occur to those skilled in this art. For instance, it is preferable to arrange the air cylinders 82, or other level control means, so that the pan 24 and belt 18 maybe lowered sufiiciently to allow placing a cover thereover when the machine is not in use. Such a cover reduces solvent loss and concurrent explosion risks. Similarly, the main drum could be replaced by a combination of several smaller rollers and an endless belt drivable thereby. Such a construction would somewhat simplify the drive of the plush belt 18 in that it could be conveyed over a flat bed instead of having distributed sag as discussed above. However, the overall construction and maintenance costs of such a system tend to be more expensive and are not preferred. We intend, therefore, to have the appended claims cover all modifications which fall Within the true spirit and scope of our invention.

We claim:

1. An etching apparatus for etching in a plurality of bites a relief printing plate including a cellulosic layer having a resist stencil layer thereon, comprising;

a rotatable drum for supporting the plate with the stencil layer facing outward;

a plush belt drivable to scrub the surface of the plate during rotation of said drum and having bristles fine enough to engage each of the exposed areas of the cellulosic layer;

means for wetting said belt with etchant during its scrubbing of the plate for softening the exposed cellulosic areas; and

means for driving said belt at surface velocities difierent from that of the plate on said drum and in a plurality of directions relative to the surface of the plate so that the softened portions are scrubbed away by the bristles on all sides of each stencil nodule of the stencil layer.

2. An etching apparatus for forming a relief printing plate by etching the exposed portions of a cellulosic layer having a stencil on its surface, comprising:

a rotatable drum for supporting the plate on the drum periphery with the stencil layer facing outward;

a plush belt mounted to engage the periphery of a segment of said drum and drivable at a speed difierent from that of the drum periphery to apply etchant and to scrub the surface of the cellulosic layer, said belt having plush bristles fine enough to engage each of the exposed portions of the cellulosic layer;

means for wetting said plush belt with an etchant which softens only the exposed cellulosic layer;

means for driving said plush belt at surface velocities different from that of the plate on said drum and in a plurality of directions relative thereto so that softened portions of the cellulosic layer are scrubbed away by the bristles;

cleaning means for removing etchant after said drum has conveyed the plate beyond the region of engagement by said belt;

heater means for drying the cleaned plate; and

means rotating said drum to repeatedly move the plate within the region of engagement of said belt, said cleaning means and said heater means in sequence to thus obtain a plurality of etching bites without loss of stencill regions as small as .001" in diameter.

3. An etching apparatus according to claim 2 wherein the plate includes a base layer of magnetizable material and said drum comprises:

a magnetic layer for supporting the plate.

4. An etching apparatus according to claim 3 wherein said drum includes a layer of thermal insulation covering said magnetic layer.

5. An etching apparatus according to claim 2 wherein said cleaning means includes a plush roller which scrubs the surface of the cellulosic layer and a rigid wiper bar which removes waste material from said plush roller.

6. An etching apparatus according to claim 2 wherein said Wetting means includes a pan containing etchant, the pan being positioned to have etchant therein engage a portion of said plush belt during the scrubbing of the plate by another portion of said belt.

7. An etching apparatus according to claim 2 wherein said heater means includes hot air flow control means for removing heated air containing etchant vapors.

8. An etching apparatus according to claim 2 wherein said heater means includes hot air impingement means for directing heated air against the exposed surface of the plate. 9. An etching apparatus according to claim 2 wherein said belt is supported on a pair of spaced apart rollers which are in turn supported on bearing means which cooperate therewith to regulate the overall pressure and the distributed pressure between said belt and said drum.

10. An etching apparatus according to claim 9 wherein means are provided to drive said bearing means laterally in a motion generally perpendicular to the motion of said drum surface whereby the scrubbing action is a reversing sinusoidal action.

11. An etc-hing apparatus according to claim 6 including means for wetting said plush belt with fresh etchant during the scrubbing of the plate and wherein said pan will store sufficient etchant to continually wet said belt.

12. An etching apparatus accordng to claim 11 including a vane within said pan to engage said belt and flex the bristles thereof to remove cellulosic matter scrubbed from said plate.

References Cited by the Examiner UNITED STATES PATENTS 2,604,024 7/1952 Luboshez. 2,891,849 6/1959 Whitbourne l5613 ALEXANDER WY'MAN, Primary Examiner. JACOB STEINBERG, Examiner.

Claims

1. AN ETCHING APPARATUS FOR ETCHING IN A PLURALITY OF BITES A RELIEF PRINTING PLATE INCLUDING A CELLULOSIC LAYER HAVING A RESIST STENCIL LAYER THEREON, COMPRISING; A ROTATABLE DRUM FOR SUPPORTING THE PLATE WITH THE STENCIL LAYER FACING OUTWARD; A PLUSH BELT DRIVABLE TO SCRUB THE SURFACE OF THE PLATE DURING ROTATION OF SAID DRUM AND HAVING BRISTLES FINE ENOUGH TO ENGAGE EACH OF THE EXPOSED AREAS OF THE CELLULOSIC LAYER; MEANS FOR WETTING SAID BELT WITH ETCHANT DURING ITS SCRUBBING OF THE PLATE FOR SOFTENING THE EXPOSED CELLULOSIC AREAS; AND MEANS FOR DRIVING SAID BELT AT SURFACES VELOCITIES DIFFERENT FROM THAT OF THE PLATE ON SAID DRUM AND IN A PLURALITY OF DIRECTIONS RELATIVE TO THE SURFACE OF THE PLATE SO THAT THE SOFTENED PORTIONS ARE SCRUBBED AWAY BY THE BRISTLES ON ALL SIDES OF EACH STENCIL NODULE OF THE STENCIL LAYER.