US3309290A - Method of forming electrotypes - Google Patents

Description

March 1967 R. c. BLACKMORE METHOD OF FORMING ELECTROTYPES Filed March 20, 1963 Y INvENTcR For 'CL/Fm/m ELM/(Mme ATTORNEYS United States Patent 3,309,290 METHOD OF FORMING ELECTROTYPES Roy Clifford Blackmore, Esher, England, assignor to Purnell & Sons Limited, Paulton, near Bristol, Somerset, England, a British company Filed Mar. 20, 1963, Ser. No. 266,748 Claims priority, application Great Britain, Mar. 22, 1962, 11,084/ 62 4 Claims. (Cl. 204-17) The invention relates to a method of producing electrotypes.

In known methods of producing flat electrotypes a mould is first taken from the original which is to be duplicated. The mould may be made of a number of materials, including lead, wax, Tenaplate or plastic sheet.

After suitable treatment the mould is placed in an elec trolytic. deposition tank for the electrolytic deposition of a shell of copper on to the surface of the mould. The thickness of this copper shell is determined by the rate of deposition of copper on to .the mould and the time the mould is kept in the tank. The shell thickness generally lies between 0.010" and 0.020".

The copper shell with its edges turned upwards in the form of a tray is then backed-up with lead in the molten state, an operation which can be carried out by the open pan method in which the molten lead is poured into the copper shell in the form of a pan or tray or with the assistance of a pressure caster. At this stage the flatness of the printing surface of the electrotype will vary from plate to plate but almost without exception will require further mechanical or hand slabbing, or both, in order to provide the electrotype with as nearly as possible a perfectly level printing surface.

This known method has disadvantages. Due to the difference in the coefficient of. expansion of lead and copper, distortion of the copper shell takes place when the molten lead is poured into the copper pan or tray and the need for the many subsequent levelling operations is largely due to this distortion. During these levelling operations, including hand slabbing which is an operation calling for considerable skill and experience, the printing surface of the electrotype can easily be damaged, and hard edges and bruised dots can result. Furthermore, particularly where fine colour work is involved excessive levelling can lead to stretching of the electrotype and the creation of register problems.

When. a pressure caster is used, the Whites or nonprinting areas of the electrotype tend to be forced upwardly towards the printing surface and then subsequently have to be routed out of the electrotype.

It will thus be understood that the production of fiat electrotypes in accordance with known methods is a costly and time-consuming operation due largely to the adjustments which are necessary by reason of the distortion which takes place in backing-up the copper shell.

Curved electrotypes are of three well-known kinds:

(a) Cold curve electrotypes in which the electrotype is produced in a similar manner to the flat electrotype except that on the original before the mould is taken, all the non-printing or white areas have to be packed out solid to within approximately 4;" of"live work. This step is necessary in order to ensure that the electrotype will curve perfectly without flats or other distortions, when passed through the three-roll bender. After the curving operation, all the dead metal has then to be routed away from the electrotype.

(b) Centrifugally cast electrotypes. In these electrotypes also the original has to be packed out in all nonprinting or white areas before the mould is taken. Copper shells grown usually in the fiat state are trimmed to certain dimensions, joined together and then placed, face outwards, in a steel drum or barrel. Whilst the drum is revolving at high speed, molten lead is poured in and centrifugal force acts in the same capacity as the pressure caster in flat electrotyping. The resulting plate, which is heavy and cumbersome, is then cut and bored, handslabbed if necessary and finally routed and bevelled. The electrotype can be left as it is if required for compression lock-up on a rotary printing machine, or if tension lockup is required, the electrotype can be bored to a thinner gauge and the lead which has been removed can be replaced by a sheet of pre-curved aluminium bonded to the electrotype.

(c) Plastic-backed electrotypes. The =Bista and Colorline electrotypes recently introduced into the United States of America also require that all non-printing or white areas be packed out. In the same way a copper shell is grown but instead of backing-up With lead a sandwich of plastic and aluminium is bonded to the shell under heat and pressure in a machine designed to give the required curvature. The plate is then bored to precise size and routed where necessary.

These three methods of producing curved electrotypes all suffer from a number of disadvantages. Thus all three methods require that the original be packed out before the mould is taken, and the subsequent routing away of dead metal from the electrotype.

In addition, cold curved electrotypes suffer from the same disadvantages as the flat electrotype. Furthermore the curved electrotype stretches when curved and is subjected to heavy stress and pressure, which is most undesirable, particularly when close-register colour Work is involved.

The process of centrifugally casting electrotypes results in a heavy plate awkward to handle during production. Furthermore the use of heat and pressure creates some distortion in the electrotype which has to be rectified in subsequent stages.

In plastic-backed electrotypes, if the electrotype is required to be chrome-faced, it either has to be routed after chroming which, due to the hardness of the chrome, is troublesome, or links have to be left to carry the current all over the surface of the electrotype and these links finally removed.

This invention has among its objects to mitigate the disadvantages of known processes as hereinbefore described and to provide a simple method of producing electrotypes which will obviate the necessity for the adjustments essential in such known processes.

According to the method of the invention, sufficient metal or alloy of relatively low melting point is caused to flow into the depressions in the back or non-printing side of the electro-deposited shell, of copper or nickel for example, to eliminate sharp depressions or crevices, after which the shell is backed-up by the electrolytic deposition of a metal or alloy, preferably lead or an alloy of lead and tin.

The electrolytic deposition of the backing layer takes place at ambient temperature or at a slightly elevated temperature so that the distortion produced by application of the backing in molten form is avoided. The use of pressure is also avoided; no Whites are forced up and as packing is unnecessary, the step of routing away of packing metal does not arise.

In the absence of the metal or alloy of relatively low melting point, it would be found that less backing metal would be electro-deposited in depressions on the nonprinting side of the shell, particularly in narrow or shar depressions, than on other parts of the back of the shell. With very narrow depressions, bridging of the depressions might even occur during the electro-deposition of the backing metal with the consequence that the printing surfaces disposed on the other side of such depressions would not be directly supported or backed-pp. Only a relatively small amount of the low melting metal or alloy need be used. The amount need only be sufficient to eliminate sharp depressions or crevices and need not be sufficient, and is preferably not sufiicient, to provide the back with a substantially level surface.

The metal of relatively low melting point employed may, for example, be tin or a tin-lead alloy and a 50-50 alloy of tin and lead has been found to be suitable. The melting point of this metal or alloy employed advantageously lies within the range 69-235" C. and preferably not above 200 C.

The relatively low melting point of the metal or alloy and the relatively small amount of the metal or alloy needed are such that substantially no distortion of the copper shell occurs in the process of so removing the sharp depressions.

In the production of a curved electrotype according to the invention, the shell may itself be electrolytically deposited on to a curved mould after which the metal or alloy of relatively low melting point is applied to eliminate sharp or relatively deep depressions in the back of the shell before the backing-up layer is formed by electrolytic deposition. Thus the mould may be formed to the required curve, fixed to a suitable carrier, and then be suspended in a copper or nickel vat and a copper or nickel shell be deposited on the curved surface of the mould. The curved shell is removed from the mould and a small amount of a relatively low melting point metal or alloy is caused to flow into the depressions on the non-printing side of the shell to eliminate sharp depressions and crevices. The modified back or non-printing side of the shell is then backed up by the electrolytic deposition of a metal or alloy.

A curved electrotype may, in another method according to the invention, be made from a flat shell, the flat shell being formed to the required curvature either before or after the relatively low melting point metal or alloy is caused to flow into the depressions in the back of the shell, after which the backing-up layer of metal is applied electrolytically.

The invention also comprises an electrotype which is a product of the method, that is to say, an electrotype having a copper face, an electrolytically deposited backing layer and an intervening layer of a metal or alloy of relatively low melting point, the intervening layer being only of such thickness that sharp depressions present in the back of the copper shell are much less sharp in that surface of the intervening layer which lies adjacent to the electrolytically deposited backing layer.

One method of carrying out the invention is illustrated by way of example with reference to the accompanying diagrammatic drawings in which FIGURE 1 is a cross section of part of an electrodeposited electrotype shell of copper;

FIGURE 2 is a section corresponding to FIGURE 1 showing strips of a low melting alloy placed on the back of the shell;

FIGURE 3 is a corresponding section after the low melting alloy strips shown in FIGURE 2 have been rendered molten and have flowed into the depressions;

FIGURE 4 is a section according to FIGURE 3 showing the electrotype after it has been backed electrolytically with a lead/ tin layer; and

FIGURE 5 is a section corresponding to FIGURE 4 showing the backed electrotype after the backing has been planed flat.

For the sake of clarity the depressions or lows and highs in the electrotype have been exaggerated,

FIGURE 1 shows, in cross section, part of an electrotype shell of copper after removal from the mould on which the copper was electro-deposited, the thickness of the copper shell being approximately 0.015 inch. The

4 shell 10 has a printing face 11 and a non-printing side or rear face 12.

The rear face 12 is fiuxed and strips 13 of a 40/60 lead tin foil of about 0.05 inch in thickness are laid over the depressions in the rear face 12 of the shell 10. The shell, whilst perfectly fiat, is then heated to approximately 200 C. to melt the strips of lead-tin foil. The molten lead-tin alloy flows in the depressions 14 in the rear face 12 of the shell 10. Upon cooling, the lead-tin alloy forms solid masses 15 in the depressions 14. The lead-tin alloy forming the masses 15 do not completely fill the depressions 14 but they greatly reduce the depth of the depressions, the residual depressions being then very much shallower than the original sharp and relatively deep depressions 14.

The front or printing face 11 of the shell 10 is brushed with a shellac solution to form a protective coating on that face, and the shell is then suspended in a carrier in a lead-tin depositing tank or bath. A lead-tin backing 16 is then electro-deposited on the back of the shell, part of the lead-tin backing 16 being directly in contact with the rear face 12 of the copper shell 10 and the remainder of the lead-tin backing 16 being in contact with the intervening layer 15. When a lead-tin backing 16 of sufficient thickness has been deposited, the electrotype is removed from the bath and the rear surface of the backing 16 is planed to a fiat surface 17. The electro was then bonded through the surface 17 to aluminium of inch thickness in known manner.

The invention is illustrated in the following examples:

Example 1 A laminated plastic mould was secured by adhesive to a sheet of plate glass in order to keep the mould perfectly fiat during the copper-depositing process. The edges of the mould were sealed to the plate glass with wax in order to prevent the plating solution making contact with the adhesive and possibly rendering it less effective. After the mould has been silvered, it was suspended in a copperdepositing tank and a copper shell of 0.020 thickness was grown. The copper shell was carefully removed from the mould and fiuxed on the back, and a 40/60 lead/tin foil of 0.005" thickness was laid on the back of the shell wherever the depressions (caused by the relief printing image on the face of the shell) occurred.

The shell with foil in position and lying perfectly flat was then heated to 200 C. (which is the preferred highest temperature) in an oven, which caused the tin/lead foil to flow into the depressions, making the back of the shell very much smoother and free from any deep or sharp crevices or depressions. The printing face of the shell was then brushed with a shellac solution for protection and, after being placed in a suitable carrier, the shell was suspended in a lead/tin depositing tank containing, per gallon, 1% ozs. stannous tin, 14 /2 ozs. lead, 6 /2 ozs. free fluoboric acid, plus additives. At a current density of 50 amps per sq. ft. a deposit approximately 0.060" thick was obtained in eleven hours. The lead-tin back was planed with standard electrotype equipment down to a thickness of 0.065". The printing surface of the electro was substantially perfect, requiring no further treatment whatever. The electro was then bonded to aluminium of 0.100" thickness and, in total, measured 0.166" thick (Pica plate thickness).

Example 2 A thermoplastic mould having a smooth back was placed in hot water at 70 C. and pressed into a former having the required curvature.

The former with the mould was then placed in cool water and the mould was found to have the required curve and to be quite rigid. After the mould had been silvered it was placed in a suitable carrier and suspended in a copper-depositing tank and a copper shell 0.020" thick was grown. The shell was carefully removed from the mould and fluxed on the non-printing side. A 40/60 lead/tin foil of 0.005" thickness was laid on the back of the shell wherever deep depressions (caused by the relief printing image on the face of the shell) occured.

The shell with foil in position was heated by radiation in 2" strips to approximately 200 C. which caused the lead/ tin foil to flow into the depressions, making the back of the shell very much smoother and free from any deep or sharp crevices or depressions. It Was found necessary to limit the heating to strips, otherwise the tin/ lead would flow to the lowest part of the curved shell rather than just into the depressions.

The printing face of the shell was then brushed with a shellac solution for protection, and, after being placed in a suitable carrier, the shell was suspended in a lead/ tin depositing tank containing, per gallon, 1 ozs. stannous tin, 14 /2 ozs. lead, 6 /2 ozs. free fiuoboric acid and additives.

At a current density of 50 amps per sq. ft. a deposit of approximately 0.060" thickness was obtained in eleven hours. The plate, with its lead/tin back, was then placed in a boring machine and bored to a thickness of 0.065". The printing surface was substantially perfect; no waste or packing metal had to be routed away. The curved electro was then bonded to curved aluminium of 0.100" thickness, the finished plate being 0.166" thick (Pica plate thickness).

Example 3 A laminated plastic mould was attached to a sheet of plate glass by strong rubber bands in order to keep the mould perfectly flat during the copper-depositing process. After the mould has been silvered it was hung in a copper-depositing tank and a copper shell of 0.030" deposited on the silvered surface of the mould. The mould with the copper shell deposited thereon was then removed from the tank and the visible or non-printing side of the copper shell was fiuxed. Pieces of foil of an alloy of lead, tin, bismuth and cadmium having a melting point of 70 C. were laid on the non-printing side of the shell wherever the depressions occurred, the thickness of the foil being 0.005". The pieces of foil were heated by radiation, the heating being only that required to permit the alloy to flow into the depressions. The sharp corners of the depressions were thus eliminated and the depressions were made shallower and relatively broader. The mould with the modified copper shell was placed in a lead-tin depositing tank and left in the 6 tank until a deposit of 0.045" of lead-tin had deposited electrolytically on the surface of the copper.

This copper shell with its backing was then removed from the mould, and the lead-tin back planed flat with standard electrotype equipment down to a thickness of 0.065". The printing surface of the electrotype was found to be substantially perfect and required no further treatment whatever.

The electrotype was then bonded in known manner to a sheet of aluminium of a thickness of 0.100" to provide an electrotype of an overall thickness of 0.166" (Pica plate thickness).

I claim:

1. A method for the production of an electrotype from an electrotype shell which comprises placing a pre-selected amount of alloy in the form of strips and having a melting point in the range of 200 C. over the sharp depressions in the non-printing side of said electrotype shell, heating said shell and alloy strips to melt the strips and cause the molten alloy to flow into said sharp depressions said pre-selected amount of alloy being insuflicient to completely fill the depressions and crevices, and then electroplating a layer of a mixture of metals containing lead onto the non-printing partially-filled side of the shell to form an electrotype.

2. A method according to claim 1, in which the shell is a fiat shell and the shell is curved after the said alloy has been flowed into said sharp depressions and before a mixture comprising lead and tin is electrodeposited on the back of the shell.

3. A method according to claim 1, in which the shell into the depressions on the non-printing side of which the alloy is caused to How, is a curved shell.

4. A method according to claim 1, in which the shell is of copper.

References Cited by the Examiner UNITED STATES PATENTS 287,617 10/1883 Brainerd 2046 X 385,519 7/1888 McIndoe et al. 2046 X 994,705 6/1911 Elliot et al. 2046 X 1,720,430 7/ 1929 OBrian et a1. 2046 2,172,564 9/ 1939 Libberton.

JOHN H. MACK, Primary Examiner.

W. VAN SISE, Assistant Examiner.

Claims (1)

1. A METHOD FOR THE PRODUCTION OF AN ELECTROTYPE FROM AN ELECTROTYPE SHELL WHICH COMPRISES PLACING A PRE-SELECTED AMOUNT OF ALLOY IN THE FORM OF STRIPS AND HAVING A MELTING POINT IN THE RANGE OF 65-200%C. OVER THE SHARP DEPRESSIONS IN THE NON-PRINTING SIDE OF SAID ELECTROTYPE SHELL, HEATING SAID SHELL AND ALLOY STRIPS TO MELT THE STRIPS AND CAUSE THE MOLTEN ALLOY TO FLOW INTO SAID SHARP DEPRESSIONS SAID PRE-SELECTED AMOUNT OF ALLOY BEING INSUFFICIENT TO COMPLETELY FILL THE DEPRESSIONS AND CREVICES, AND THEN ELECTROPLATING A LAYER OF A MIXTURE OF METALS CONTAINING LEAD ONTO THE NON-PRINTING PARTIALLY-FILLED SIDE OF THE SHELL TO FORM AN ELECTROTYPE.

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