US1834759A - Rubber printing plate - Google Patents

Description

v s vif J. c. BAKER LSSQJQ RUBBER PRINTING PLATE Fied March 24, 1928 2 swam-smet 2 x n i? 7 gli# 5 provide a method of makin Patented Dec. l, 1931 PATENT OFFICE JOHN C. BAKER, F NUTLEY, NEW JERSEY, .ASSIGNOR TO WALLACE & TIERNAN Y ERGDUCTS, INC., 0F BELLEVILLE, NEW JERSEY, A CORPORATION 0F NEW JERSEY RUBBER PRINTING PLATE Application led March 24, 1928. Serial No. 264,329.

rl"his invention relates enerally to printing and has particular re erence to the making of rubber printing lates.

One of the objects o this invention is to metal-backed rubber printing plates whic are accurate reproduction in all essential particulars of an engraved or etched die or master late.

Another object of the invention 1s to provide improvements in known apparatus for producing rubber printing plates which, in addition to other characteristics, will be of the same thickness as the master plate or die used inmaking the plates.

@ther objects and advanta es will be apparent from the disclosures ereinafter set forth, in connection with the drawings which accompany and form a part of thls specication. Y

w In said drawings:

Fig. 1 shows a suitable press and associated elements for performing one of the early steps involved in the making of metal-backed rubber printing plates.

Fig. 2 is a cross section illustrating a resuit of the operation of the apparatus of `Fi l.

gigs. 3 and 4 illustrate the apparatus and method of producing a lead lined, rigid mold e upon the master plate.

Fig. 5 shows how the master plate is referably removed from the lead lined mol and Fig. 6 is a cross section through the lead lined mold from which the master plate has Fig. 7 shows the essential features of the new apparatus which comprises a vulcanizing press which is more or less conventionally represented. Y v

t1 Fig. 8 shows how the mold may, if desired,

be stripped from the finished rubber print-` i these limiting factors is that it has been im-V possible to get accurate alignnient or registration when printing from such plates, due to unavoidable variations between them and what are, for convenience, usually referred to herein as the dies or master plates. Such dies or plates are produced' in various ways, such as by casting, etching or engraving and are true to the dimensions of the picture or: design which is to be produced.

The variations between the rubber plates of the rior art and the master plates arise partly rom the fact that the molds in which the rubber is formed to 've the printing design, do not expand at t e same ratev as the rubber in vulcanizing, and when the finished plates are removed from the vulcanizing mold and cooled, it is found that the rubber has shrunk so that the plates are smaller than the original, and that the various elements of the design or picture are out of their correct relative positions.

In prior manufactures the rubber plates have, after vulcanization, been mounted on metal or wooden lates so that the can be carried in a printlng press. It has een apreciated that this attaching operation might e made a part of the vulcanizing operation, and thati the rubber plates could be vulcanized on metal backing plates shrinking and other harmful variations from the master plates might largely be revented. However, in prior manufactures 1t has been found dificult to effect such vulcanization on the backing because of the nature of the molds employed and the methods of usin them in manufacturing. While attempts ave been made along the line indicated, they have, so far as known, been" unsatisfacto because of the high percentage of damag or defective plates.

It has now been discovered how these difl ficulties can be overcome and an accurate un damaged plate produced which is vulcanized to a-metal backing of sufficient stiffness to prevent any subsequent shrinking of the rubber or displacement of the rubber.

Stated in general terms the new way of manufacturing such plates comprises the use of lead lined, special molds for the rubber forming and vulcanizing operations. Such a mold is produced by first copying in a sheet of lead the outline and surface configuration of a die or master late. In making the copy the sheet of leadp is forced into and over the master plate b pressure.

In order that t e lead may faithfully receive all of the details of vthe master plate, the pressure is applied by any suitable press through a pad o yielding material which is fibrous enough to revent breaking the pad down too readily, ut which kwill yield suficiently to cause a satisfactory distribution of the pressure. A pad of dry paper pulp or one composed of sheets of newspaper gives very satisfactory results. Applying the press ure throu h such a pad forces the lead into all of the details of the die or master plate, thereby effecting a very accurate embossing in the lead of all features of the picture or design.r The pressure is then released and the pad removed, leaving the lead pressed into and Varound the master plate.

A backing is then a plied which is rigid and which will hold t e design -in the lead after .the lead is removed from the master plate. For thisA purpose a material is used which can be poured over the lead sheet and master plate and whichwill set to a rigid form. A satisfactory material is a mixture of lycerine and litharge or a dent-al cement. Beore starting the pouring operatlon the master plate, and the adhering lead sheet, is laid on a`truly flat surface, and after pouring, and/'before the material hasvhad ytime to set, asimilar truly fiat plate is used to force the material down until this second plate vis arrested by stops rovided for that purpose. These stopsare o such height that suic1ent backing material remains behind thevlead t0 give ample rigidity at all points.

After the backing has set, the master plate, with the attached rigid backing, is removed from the supporting and pressure plates..

The master plate is then removed, leaving a lead lined mold which is ready for use in molding and vulcanizing rubber plates. In the preferred practice this lead lined mold is not quite as deep as the thickness of the master plate, the reasons for this difference and the way in which it is obtained being hereinafter explained in detail. l

The lead lined mold is then placed between relatively movable plates of a. vulcanizing press havin their faces truly `fiat and parallel. Eitherefore or after placing the mold in the press, it is supplied with a suitable plastic rubber compound containing the usual or any desired vulcanizing and similar agents, the quantity of the compound being in excess of that required for the finished plate. v A backing plate previously treated to cause adhesion of the rubber is then applied to the compound and the vulcanizing press operatated to force that plate toward the mold. This compacts the compound in all of the details of the lead lined mold, and extrudes the excess rubber between the top of the mold and the backing plate. Stops between the relatively movable portions of the vulcanizing press arrest that movement at the point where the thickness through the rubber and backing plate is substantially the same as the thickness of the die or master plate used in making the mold. As a result, after the vulcanization is completed the finished rubber plate will be a metal backed rubber reproduction of the master plate in dimensions and all yother essential characteristics. The metal backing plate em loyed is preferably composed of an allo o lead and antimon Such a material as the necessary rigi ity to hold the rubber in position, but is nevertheless capable of being formed to offset irregularities or regulate the impression of the printing face. Such a metal or. alloy presents diiculties in the way of gettinor a good adhesion of the rubber and the bac ing plate, but it has been discovered that if the face of the late which engages the rubberis washed with a dilute solution containing copper sulphate and copper nitrate a perfect adhesion will result from the molding and vulcanizing operation.

Describing the apparatus and the manufacture more in detall and with reference to the drawings, a book press 10, such as is shown in Fig. 1, may be employed when the sizes of the printing plates required do not necessitate a greater press capacity. In making larger plates a hydraulic or other more i powerful press may be em loyed.

The top surface of the be 11, and the lower face 12 of the laten 13 of the press should both be Hat and) substantially parallel.

At the start of the iperation the master I plate 14 which is to befreproduced is placed face up on the bedof the press. Strips of paper or metal 15 are then placed on-tlie bed and around the master plate and a sheet 16 of lead laid over the face of the master l plate. Superimposed on the sheet of lead is a yielding ad 17 which is preferably of a somewhat fi rous nature, a suitable material being dry paper pulp or a number of plies of newsprint paperf l rl.`he press 10 is then operated to apply pressure through the pad 17 to force the lead 16 into and over the master plate and into contact with the strips 15 around the master plate 14. Sto s 18 serve to prevent movement Yl of the platen ar enough to have a destructive eii'ect upon the lead. As a result of the press operation the llead sheet is embossed and shaped to the master plate as illustrated in Fig. 2. Examination of Fig. 2 will show 4-1 that the side portions or extensions 16 of the lead are, owing to the eii'ect of the strips 15, parallel to and slightly above the back ofthe jmaster plate.

The'master plate, with the adhering lead, 1

is then laid on a truly flat surface 18, Fig. 3, of a block or plate 19, with the lead covered face up, after which a bac-king for the lead is applied. This backing is .preferably of a material which can be applied in iiuid condition and which will set readily, but which will also be lsufticientl rigid and strong to stand pressing and vu canizing operations. This material may be varied, but a mixture of glycerine and litharge or dental cement has been found very satisfactory. Before starting the pouring opera/tion it may be necessary to support the portions 16 of the lead sheet by strips similar to the strips 15 used in the matrix forming press 10, as it is desirable that the portions 16 be maintained in substantially the positions given them in the press.

As soon as the pouring is completed and before the backing material has begun to set, a plate 2l (Fig.,4) accurately machined to give a truly iat'surface is laid on the material and forced down by gravity, assisted by a hand pressureor by a weight 22, if desired,

' l until arrestedby stops 23. These stops might be permanently attached to the block 19 when a number of molds of the same depth are to be prepared or they may be interchangeable to suit varying conditions. They mustalways be of suilicient height to'provide for a backing of sufficient thickness to properly support the lead.

After the backing has set, the mast-er plate 14 and the backed lead sheet are removed from the press and the master plate/then removed. This is accomplished or assisted by directing a jet of air 24 around the edge of the master plate as illustrated in Fig. 5. Thisleaves a lead lined mold 25, illustrated in Fig. (i,v

which is slightly less in depth than the thickness or height of the master plate, and which contains a true copy of the master plate.

The mold is then supplied with rubber compound in plastic condition as shown at 27 s in Fig. 7, the quantity of compound, being y preferably considerably in excess of the quantity of rubber which will be found in the finished article. -A backing plate 28 is then laid on the compound and the assembly introduced between the relatively movable ele: ments 31 and 32 of a vulcanizing press of a known type but which have their opposing faces truly fiat and parallel when closed. The press is next operated to mold the'rubber and vulcanize it.

The relative movement of the elements 31 and 32 compresses the rubber plastic in the moldv and extrudes the excess between the edges 34 (Figs. 6 and 7) of the mold and the backing plate 28. The strips 15 (Fig. 1) were used so as to provide a clearance between the plate and mold which. while preventing to'o free an extrusion, will permit the excess rubber to escape. The extruded portions 35 of the rubber are later trimmed olf.

In 'order to limit the relative movements of the press members 31 and 32 to produce a mounted rubber plate of the desired thick ness, stops 36 are employed. These stops should preferably be of the same height as the stops 23 (Fig. 4) in the mold forming press, if the finished plate desired is to have the same thickness as the master p'late. If a finished plate of a thickness different from that of the master plate is desired the stops 36 should be adjusted accordingly.

The molds are not re-used and may be stripped from the finished plates in the manner illustrated in Fig. 8 by means of the sheet of lead 16. I

The composition of the metal backin g plate andthe manner in which it is prepared to secure firm adhesion of the rubber to the metal were, explained above, and repetition is unnecessary.

Vhile the lead is, on the whole, the most satisfactory for the ,matrix making, it is not the desire to be limited to that metal. Any' soft metal or alloy may be used and are yconsidered as. being equivalents coming within this invention.

From all of the foregoing it is apparent that accurate rubber printing plates can be produced with a minimum amount of equipment and at a very low cost. Plates pro- Y duced inthe manner described give very accurate registration of impressions, and the work produced by them, particularly in color printing, presents a` much better appearance than has heretofore'been obtained from rubber plates.

While the method and apparatus set forth are highly satisfactory in all respects, it is obvious that changes in the apparatus and variations in the separate steps or sequence of steps may be made, all of which come within the scope of the claims which follow.

`What is claimed is 1. A method of making metal-backed rubber printing plates which comprises first making a lead-lined mold for the printing face of the plate, supplyin to the mold a quantity of unvulcanized ru ber compound, in plastic condition, compressing the com-` pound between the mold and a rigid backing plate treated to cause adhesion of the rubber duringr vulcanization, said compression effecting the molding and causing extrusion of the excess compound, and vulcanizing the rubber while it is compressed between the mold and the backing plate.

2. The method of making printing plates which comprises applying a sheet of lead to the engraved or etched face of a master plate and applying pressure to force the -lead against and in all parts of said face, casting a backing on the lead sheet while in engagement with said face in such away as tol produce a lead-lined mold having its front and back parallel, separating the mold and plate, applying vulcanizable rubber plastic to the lead-lined mold in excess of the amount required to form a printing plate of the desired thickness, applying a previously prepared metal backing plate to said plastic, forcing said backing late and the mold together to mold the rub r and applying vulcanizing heat to vulcanize the rubber and cause it to adhere to the backing plate, and then removing the mold.

3. The method of making (printin plates which comprises copying 'a esign rom an engraved or etched plate by forcing a lead plate into all parts o the engraved or etched surface of sald plate, pouring on said lead plate while it is in such contact with the engraved or etched plate a cement in fiuid condition, applying suiicient pressure to the cement While in fluid condition to force the cement into close contact with all portions of the lead sheet and then allowing the cement to set, removing the engraved or etched plate from contact with the lead plate, applying unvulcanized rubber in plastic condltionto the exposed face of the lead plate, and applying molding pressure and vulcanizing heat to said rubber.

4. A method of making printing plates which comprises embossing in a lead sheet, from a master plate, a reversed copy of the matter on the etched or engraved face of the plate, attaching a rigid backing to said sheet in such a way asto produce a lead-lined mold of a depth which is from fifteen to thirty thousandths of an inch less than the total thickness of the master plate, supplyin said mold with a quantity of unvulcanize rubber compound in plastic condition in excess of the amount required to fill the mold, ap-

plying a backing plate to the supply of compound, said plate having previously been prepared toeffect adhesion of the rubber in the engraved or etched face of a master plate, applying suiiicient pressure to the sheet of lead through a yielding pad of dry aper pulp to force the lead into and over al portions of said face whereby to emboss in the lead sheet a copy of the matter on said face, casting a backing on said sheet in such a way as to produce a lead-lined mold having the back of the mold parallel with the said face of the master plate and the depth of the mold less than the thickness of the master plate, removing the master plate from the lead-lined mold, supplying the interior of said mold with a quantity of unvulcanized rubber compound, in plastic condition, in excess of the quantity required to fill the mold, placing a backing plate of electroty e metal on the supply of rubber compound, t e face of saiddplate which is in contact with the compoun having previously been Washed with a solution containin copper sulphate, and applying pressure an heat suiiicient to force the backlngand mold together to yproduce a metal-backed rubber printing plate having the same thickness at all points as the master late.

7. A metliod of making molds for rubber printing plates and the like which com rises forming a lead matrix on'the engrave face of a master platein such a way as to copy in the matrix the essential rfeatures represented on said face, castin on the back and sides of the matrix a rein orcing back while the matrix is still on the master plate, and

applying an air jet around the edges of the' master plate to free the plate from the mold. In testimony whereof I hereto aiiix my signature.

JGHN C. BAKER. A

vulcanizing, and applying pressure and heat suliicient to force the backing plate and mold together to produce a metal-backed rubber printing plate having the same thickness at all points as the master plate.

5. A method of making printing plates which comprises making a lead mold for producing the design on said plates, supplying said mold Iwith a quantity of unvulcanized rubber compound in'plastic condition, placing on said supply of compound a backing plate composed of lead and antimony alloy and having the -face in contact with the compound previously washed with a solution containing copper sulphate and copper nitrate, and then forcing the backing plate and the mold together to form the printing plate and extrude the excess rubber, and applying heat to vulcanize the formed plate and attach it to the backing plate.

6. A method of making printing plates which comprises placing a sheet of lead on

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