US3403082A - Method of backing electrotypes - Google Patents

Description

p 1968 R. c. BLACKMORE 3,403,082

METHOD OF BACKING ELECTROTYPES Filed June 21, 1965 2 Sheets-Sheet 1 Z FIG.| W

5 a INVENTOR Roy CMHOYA Blackmovcz R. c. BLACKMOR$ 3,403,082

I METHOD OF BACKING ELECTROTYPES Sept. 24, 1968 Filed June 21, 1965 v2 Qeets-Sheet 2 ATTORNEY.

United States Patent METHOD OF BACKING ELECTROTYPES Roy Clifford Blackmore, Esher, England, assignor to Nickeloid Limited, London, England, a British company Filed June 21, 1965, Ser. No. 465,562 Claims priority, application Great Britain, June 22, 1964, 25,762/ 64 9 Claims. (Cl. 2046) The invention relates to a method of producing electrotypes and particularly to a method of cold-backing allmetal 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 electrolytic 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 mold is kept in the tank. The shell thickness generally lies between 0.010" and 0.020.

The copper shell with its edge turned upwards in the form of a tray after separation from the mould, 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 the electrotype will require 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 coefiicient 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 curved 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 Ma" of live work; This step is necessary in order to ensure that the electrotype will curve without the formation of 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. 00p per shells grown usually in the flat 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 much the same manner as the pressure caster in fiat electrotyping. The resulting plate, which is heavy and cumbersome, is then cut and bored, hand-slabbed 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 lock-up 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 Col orline 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 a 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 the original to be packed out before the mould is taken, with the consequential step of routing away dead metal from the electrotype.

In addition the cold-curved electrotypes suffer from the same disadvantages as the first 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 which is 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 surface of the electrotype and these links finally removed.

British patent specification No. 931,309 describes a method of mitigating such disadvantages by flowing sufficient of a metal or alloy of relatively low melting point on to the back of the electrotype shell to eliminate sharp depressions or crevices therein, and thereafter electrolytically depositing a backing of metal or alloy on the shell. The electrodeposition of the backing metal or alloy takes place at ambient temperature or at a very slightly elevated temperature so that distortion produced by application of the backing metal or alloy in molten form is avoided.

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 sharp 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 up.

There are however certain disadvantages in this method. Firstly it is necessary either to remove the shell from the mould before fusing the low melting point alloy on the back of the shell, with consequent risk of damage to the shell during removal from the mould and to the unprotected face during subsequent processing, or to sacrifice the mould during this fusion process. Secondly, the loW melting point alloys are relatively expensive. Further there is also the risk of distortions, however slight, occuring when the levelled shell is cooled after fusion, since the coefficients of expansion of copper and of the various alloys are different.

One of the main advantages of the method described in specification No. 931,309 is due to the elimination of deep depressions which are impossible to fill by electrodeposition at the same speed as the backing is grown on to the remaining areas of the electrotype. Without this technique it would be necessary to grow a gross excess of backing on to the majority of the electrotypes to ensure a sufiicient thickness of deposit in the depressions, a method wasteful of time and material.

,According to the invention, the shell is left on the mould throughout the backing process and the filling of depressions by low melting point alloy is eliminated. Instead, the lead, lead alloy or other metal is plated directly on to the unmodified shell. After a suitable period of deposition the partially backed shell, still on its mould, is back-shaved to remove the bulk of the electrodeposited backing alloy from the non-printing areas of the electrotype, the deposit in the depressed areas of the back being left substantially unaffected. The depth of these depressions is thus effectively reduced so that they will then more readily receive an electrodeposited backing alloy or metal. After this first shave the partially backed electrotype is returned to the plating bath and another suitable thickness of deposit is grown on the back.

Depending on the depth of relief in the individual electrotype the second deposit may be sufficient. In the case of deep-relief plates however, the second deposit may be treated as an intermediate deposit as was the first deposit and be subjected to a shaving operation further to reduce the relief of the depressions in the back. A further layer of backing metal or alloy is then electrodeposited. The cycle of deposition and shaving may if necessary, be repeated until all areas of the electrotype are backed to the required thickness. When this stage has been reached, that is to say, when enough backing has been deposited over the whole plate, the mould is removed from the face and this can now be done without distortion of the shell since it is solidly supported.

While one intermediate shaving stage is normal in the method according to the invention, two intermediate shaving stages are somewhat exceptional. However, in extreme circumstances any number of such intermediate shaves can be employed to eliminate relief.

The method according to the invention has a number of advantages which may be summarised as follows:

No heat whatever need be employed.

Until the final shave is made, the face of the electrotype is protected by the mould.

When the mould is eventually removed the shell is amply supported by backing metal and distortion is prevented.

Electrodeposited lead-tin alloy is much cheaper than low melting point alloys.

Less backing alloy is consumed than when the shell is backed entirely by electroplating but without the intermediate shaving; plating times are therefore also reduced.

One example of carrying out the method according to the invention is illustrated in the accompanying diagrammatic drawings in which each of FIGURES l to 9 shows a section of member during the stages of forming an electrotype.

From an original pattern plate 1 which contained typematter, line and tone subjects on its printing face 2 (FIGURE 1), a rigid vinyl mould 3 having about 0.030 of relief was taken (FIGURES 2 and 3). The mould 3 was removed from the pattern plate and after making the face 4 of the mould conducting by spraying with silver, a nickel/copper shell 5 (FIGURE 4) was deposited, the total thickness being 0.012", comprising 0.002" nickel and 0.010 copper. While the shell 5 was still on its mould 3, 0.035" of lead/tin alloy, containing a little copper for hardness control, was deposited in the first backing stage to form the first backing layer 6 (FIGURE 5). The partially backed electro or shell 5 and mould 3 were rinsed, dried and backed-shaved to remove about 0.030" of alloy from the white or non-printing areas 5a of the electro (FIGURE 6), such areas being the highest before the back of the plate was machined or shaved. Inspection at this stage showed that approximately 0.025" of deposit had grown in the depressions 5b and that after the above shaving operation these areas were now no more than 0.010 deep and deposition would no longer be a problem.

The plate and mould were returned to the plating bath and a further 0.0300.035" of backing allow deposited to give a second backing layer 7 (FIGURE 7). Again, after rinsing and drying the plate was back-shaved, this time after removal of the mould 3, to a finished thickness of 0.064" (FIGURE 8). Finally this plate was laminated with an adhesive 9 to an aluminum sheet 8 which was 0.100 thick to make a 0.166 thick (pica) electrotype (FIGURE 9). This laminating step is not essential, since it is common practice to print from 0.0064" (16 gauge) plates also.

By means of the method according to the invention, shells of sharp and deep relief may be backed by electrodeposition of a lead alloy with reasonable speed and economy.

I claim:

1. A method of backing an electrotype shell, which comprises electrodepositing lead or a lead alloy directly on to the back of the shell, shaving the plated back to remove the bulk of the electrodeposited backing metal from the non-printing areas of the shell and electrodepositing a second backing layer of lead or lead alloy on the partially backed shell, such operations being carried out whilst the shell is still on its mould.

2. A method according to claim 1, in which, with the shell still on its mould, the cycle of electrodeposition and shaving is repeated until the desired thickness of backing metal is attained.

3. A method according to claim 1, in which the mould is removed from the backed shell and the said second backing layer is shaved.

4. A method according to claim 1, in which the mould is removed from the backed shell when the electrodeposited metal is of the desired thickness and, after shaving the back, the backed shell is laminated to a metal backing sheet.

5. A method according to claim 2, in which the final shaving of the electrodeposited backing is effected after removal of the mould.

6. A method according to claim 1, in which the backed shell is, after removal from the mould, laminated to a metal backing sheet.

7. A method of backing an electrotype shell, which comprises electrodepositing lead or a lead alloy directly on to the back of the shell whilst the shell is still on its mould, shaving the plated back to remove part of the electrodeposited backing metal from the zones disposed opposite to the non-printing areas on the face of the shell, repeating the cycle of electrodeposition and shaving until the desired thickness of backing metal is obtained on the shell, removing the shell from the mould, and adhesively laminating a metal backing sheet to the backed shell.

5 6 8. A method according to claim 7, in which the final References Cited shaving of the electrodeposited backing metal is eflfected FOREIGN PATENTS after removal of the hacked shell frcm its mould. 27,911 1912 Great Britain.

9. A method accordmg to claim 7, 1n WhlCh sa1d metal backing sheet is a sheet of aluminum or of an aluminum 5 JOHN MACK, Primary Examineralloy. T. M. TUFARIELLO, Assistant Examiner.

Claims (1)

1. A METHOD OF BACKING AN ELECTROTYPE SHELL, WHICH COMPRISES ELECTRODEPOSITING LEAD OR A LEAD ALLOY DIRECTLY ON TO THE BACK OF THE SHELL, SHAVING THE PLATED BACK TO REMOVE THE BULK OF THE ELECTRODEPOSITED BACKING METAL FROM THE NON-PRINTING AREAS OF THE SHELL AND ELECTRODEPOSITING A SECOND BACKING LAYER OF LEAD OR LEAD ALLOY ON THE PARTIALLY BACKED SHELL, SUCH OPERATIONS BEING CARRIED OUT WHILST THE SHELL IS STILL ON ITS MOULD.

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