US2400518A - Electrotyping - Google Patents

Description

y 1946. F. w. KREBER ETAL 2,400,518

ELECTRO'I'YPING Filed June 9, 1942 5 Sheets-Sheet 1 5 U 6 n wmmuwm 8 9 7 6 MIMMHM i m' 5 z '0 i Fro n k w fi i f Bruce WGonser BY Roland M. Schoffzrt TTOPNEYS 59 W Wwm y 1946- F. w. KREBER ETAL 2,400,518

ELECTROTYPING Filed June 9. 1942 5 Sheets-Sheet 2 INVENTORS Frank W. Krebzr. Bruce W Sense Qoiond M. Schoff Q BY M, km

A TTOPNE Y5 y 1946- F. w. KREBER ETAL 2,400,518

ELECTROTYPING Filed June 9, 1942 5 Sheets-Sheet 3 INVENTORS Frank W Krzber? Bruce W Gonszr' Roland MSchaffert BY W. M7 M ATTORNEYS y 1946- F. w. KREBER ETAL 2,400,518

ELECTROTYPING Filed June 9, 1942 5 Sheets-Sheet 4 F iNg/EQ/TOgS re an B2322 W Gonsczr. BY Qokmd M. Sch'affart M Q1 47 v- 4 May 21, 1946. F. w. KREBER r-:rA|..

ELECTROTYPING Filed June 9, 1942 5 heets-Sheet 5 INVENTORS Frank W Kreber Bruce W Gonszzn Roland M. Schofferr.

MI I'- A TTOPNEYS Patented May 21, 1946 UNITED STATES PATENT OFFICE 2,400,518 ELECTROTYPING Application June 9, 1942, Serial No. 446,358

6 Claims.

Our invention relates to electrotyping. It has to do, more particularly, with the making of duplicate printing plates by a process wherein a matrix of the original pattern, printing plate or type form is formed by impression, rendered electro-conductive, and then electroplated to form a shell-like replica of the original, the shell subsequently being backed or filled out with a softer metal to the desired thickness.

In the manufacture of electrotype duplicates from original patterns, such as type forms, photoengravings, and other printing surfaces or combinations thereof, the usual practice is as follows: A wax plate or case is prepared by flowing a special melted wax such as, for instance, ozokerite wax upon a metal backing plate and shaving the wax to produce a smooth surface. The wax case and the pattern, such as type form or printing plate, are then brushed with graphite powder to prevent sticking, after which the pattern is brought into contact with the wax case and pressed down into the wax, by means of a hydraulic press, such that a matrix of the original pattern is formed. After separating the pattern from the wax matrix, graphite is again applied to the matrix to render the impressed surface electro-conductive so that a metal replica of the original pattern can be formed subsequently on the matrix by electro-deposition.

For certain classes of work, requiring more accuracy and greater fidelity of reproduction, an alternative method is used. In this alternative method, sheet lead is used as a molding medium instead of wax, the matrix being formed from a. lead sheet under relatively high pressure in a hydraulic press. Due to the high pressure required, only original patterns which will not be distorted or damaged by this high pressure can be used with this method.

Both the wax molding and lead molding processes have certain defects and disadvantages, the elimination of which would result in an improved electrotype and in the saving of considerable time and expense. These defects are as follows:

1. After the wax case has been molded and the original pattern removed therefrom. it is necessary to trim or cut from the matrix, protruding or excess wax which has been displaced in the molding operation and forced into deep grooves or between lines and characters of the pattern design impressed in the case. Subsequently, it is necessary to build up or add wax to various low portions of the matrix, so that these portions will be at the desired level below the printing surface to properly form corresponding portions on the finished electrotype. After this operation, a gas flame is passed several times over the matrix in order to smooth over sharp edges by partially melting the wax on the surface of the matrix. These three operations are known respectively in the art as cutting down, building up" and flashing," and their execution quite often requires tedious manipulation and considerable skill on the part of the operator, resulting in added expense due to the amount of time consumed and sometimes, unless extreme care is exerted, in a defective electrotype.

2. In molding the original pattern in wax, the matrix is formed almost entirely by displacement of wax, this substance being relatively incompressible. This displacement often results in sidewise shifts of the wax, known to the art as slides." These slides" cause the impressions made by lines, characters, et cetera, of the original to become widened or elongated on the wax matrix so that a true impression of the original pattern is not obtained. The occurrence of these slides often necessitates remolding the matrix, making a new matrix, or, if not corrected on the matrix, these faults must be rectified by delicate cutting and trimming operations on the finished electrotype.

3. Another fault, encountered in wax molding, is that known to the art as concaves. These concaves" are caused by a slight lifting or bulging of the wax over various portions of the matrix surface when the matrix is separated from the pattern after molding. These raised areas on the matrix result in low or concave spots on the replica or electrotype, necessitating added time in straightening and hammering out these spots on the electrotype, and often times causing stretch or distortion of the electrotype and damage to the printing surface thereof.

4. Still another objectionable feature of the wax molding process, lies in the use of graphite in molding the matrix and in rendering the matrix electro-conductive. In carrying out this process, graphite is applied in three operations. It is applied first in powder form to the cooperating surfaces of the wax case and type form or printing plate, prior to molding, to prevent adhesion of the wax to the pattern when the pattern is separated from the wax matrix. It is later applied, in powder form, to the matrix by brushing, and still later, in the form of a suspension of graphite in water. The two latter operations are known to the art as "dry leading and "wet leading." Graphite is considered a nuisance in electrotype plants, because in the dry powder form it floats in the air filling the room with graphite dust and settling upon machinery, often causing electrical shorts in motors and generators. In general, in both forms, it gives a dirty appearance to the entire shop, soiling clothes and producing discomfort. Besides the nuisance factor, graphite often fills or partially fills some of the half-tone dots on the matrix, and in general, hinrers the attainmenhof exact reproduction in the electrotype replica. A graphite coating is not a good conductor, and as a result, the wax matrices cover slowly and irregularly in the plating tank, giving a plated shell which is sometimes porous and is non-uniform in thickness.

5. In connection with lead molding, lead is relatively hard compared to wax, requiring molding pressures of from 10,000 to 20,000 pounds per square inch, as compared to 1000 to 2000 pounds per square inch for wax. For use in this method, the original patterns are thus limited to printing plates of sufllcient strength to withstand these pressures, such as properly prepared copper and zinc photo-engravings and specially prepared electrotype patterns. Type forms and wood-mounted cuts cannot be molded in lead because the high pressures would severely damage the printing surface or base material of these patterns.

6. In removing the lead matrix from the original printing plate or pattern after molding, a certain amount of mechanical sticking is encountered. This often results in bending or distorting the lead matrix so that flatness of the printing surface on the electrotype is adversely affected and reproduction is impaired. This is especially true of co-called undercut photoengravings where considerable difliculty is often encountered in releasing the matrix from the original.

7. Only one electrotype can be made from a wax or lead matrix, the detail of the matrix being destroyed in removing the electroplated replica.

It is an object of our invention to overcome all of the above-mentioned defects and disadvantages. Furthermore, it is an object of our invention to obtain certain additional advantages in the practice of our invention, resulting in an improved electrotype product, as will become apparent from the following description.

The main steps involved in carrying out our invention are as follows:

I. Rectification of the type form.

II. Molding an original type form or printing plate in a thermoplastic sheet material to form a matrix of the original.

III. Rendering the molded surface of matrix electro-conductive.

IV. Depositing a layer or shell of metal over the matrix by electro-plating.

V. Applying a silver coating to the back or nonprinting side of the metal layer or shell, removing the metal layer or shell from the matrix and subsequently pouring or casting a suitable metal onto the back of the shell.

It will be apparent from the following more detailed description that any one or combination of the above steps can be employed, exclusive of the others, in the art of electrotyping, with resultant improvements and advantages, all within the scope and intent of our invention.

In the accompanying drawings, we have illustrated the preferred embodiment of our invention. In these drawings:

the

Figure 1 is a perspective view of a plastic sheet used in rectifying a type form prior to molding the matrix for the electrotype.

Figure 2 illustrates the type form in position on the plastic sheet, the sheet being positioned on heating means.

Figure 2a illustrates the type form in position on the plastic sheet in a hydraulic press.

Figure 3 is a similar view illustrating the press in operation to rectify the type form.

Figure 4 is a view illustrating a master plate in association with a plastic sheet and resilient blanket to be used in forming the matrix for the electrotype.

Figure 4a is a similar view but illustrating the rectified type form in place of the master plate.

Figure 5 is a side elevational view of a hydraulic press which may be used in forming the matrix.

Figures 6 to 10, inclusive, illustrate the different steps in forming the matrix.

Figure 11 is a sectional view of a nozzle used in silvering the matrix to make it conductive.

Figure 12 is a rear. end view of the nozzle shown in Figure 11.

Figure 13 is a diagrammatic view of the com plete apparatus for performing the silvering operation.

Figure 14 is a perspective view of a unit provided for supporting the silver coated matrix in an electroplating bath.

Figure 15 is a view illustrating the unit of Figure 14 supported in the bath.

Figure 16 is a sectional view of the coated matrix after it has been removed from the bath of Figure 15.

Figure 17 is a view illustrating the unit of Figure 16 in a bath adapted to be used to apply a silver coating to the exposed back surface of the electrotype shell.

Figure 18 is a view similar to Figure 16 but showing a. silver coating on the exposed surface of the electrotype.

Figure 19 is a diagrammatic view illustrating the electrotype shell being stripped from the matrix.

Figure 20 is a view illustrating how backing metal is applied to the electrotype shell shown in Figure 19.

Figure 21 is a, sectional view through a portion of a completed electrotype.

Figure 22 is a perspective view of a completed electrotype.

The steps involved in the forming of an electrotype according to our invention will be clear from the following detailed description which refers to the accompanying drawings.

1. Rectification of the time form As previously indicated, the first step in producing an electrotype according to our invention is to rectify the type form. This operation, of course, is only necessary when the pattern to be reproduced is formed of type, wood-mounted cuts, or combination of these or similar members,

One troublesome factor in making electrotypes from type forms, or similar forms, is due to the unsatisfactory condition of the original type form prior to molding. It is known that best results are obtained in printing with a type form when all parts of the printing surface of the type form are at the same level. This condition is not usually obtained on the printing surface of type forms as they are received by the electrotyper. Instead, there are usually considerable variations in height between various portions of the surface and even between the individual unit characters comprising the composition of the type form. These variations, if not corrected on the type form, are carried through the molding and plating operations and are reproduced on th electrotype. In some few eiectrotype plants, various paper underlays are inserted on the back of the type form to bring up the low portions of the type. In most plants, no effort is made to correct the type form, but instead, the low portions and characters are corrected in finishing the electrotype by hammering and punching on the back of the plate, which requires considerable time and skill and often results in more or less damage to the printing surface of the electrotype.

The process which we employ in rectifying the type form is illustrated in Figures 1 to 3 of the drawings. By means of this process we bring all parts of the printing surface of the type form to the same level.

In performing this process, we use a plastic sheet unit of the type illustrated in Figure i. This plastic sheet unit is of such a nature that it can be softened by the application of heat but it has a suillciently high softening point that it will become hard when cooled and remain hard at the temperatures encountered in subsequent operations in forming the electrotype.

The plastic sheet shown in Figure l is indicated generally by the reference character I. It comprises a laminated structure consisting of a relatively thick layer 2 of thermoplastic material sandwiched between two sheets 3 and 4 of paper in such a manner as to adhere to the paper, forming a single compact sheet.

The thermoplastic layer 2 is preferably formed of a thermoplastic resinous material. We may employ various thermoplastic resins or mixtures thereof. For example, we may use petroleum resins; such resins are discussed on page 23 of Synthetic Resins and Allied Plastics" by R. S. Morrell, published by the Oxford University Press (2d edition). On the other hand, if desired, we may employ other well known thermoplastic materials, such as the copolymer of vinyl acetate and vinyl chloride, cellulose acetate, methacrylate resins, et cetera. It is necessary that the thermoplastic resin be economical to use, and be of such a nature that it has a sharp softening point so that it will soften rapidly upon being heated and will set firmly upon cooling. It must have a sufficiently high softening point, for example 180 to 310 F., so that it will not be distorted at the molding temperatures subsequently encountered, in forming the eiectrotype matrix. It must also set sufllciently hard, as will later appear, to hold the type in position and to resist the pressure encountered, for example 250 to 700 pounds per square inch, in subsequent molding operations. We prefer to use a thermoplastic material having the following formula:

Per cent by weight Petroleum res 60 Colophony l0 Filler (such as Portland cement, fly ash, etc.)

The plastic sheet can be used in various thicknesses, as long as it is sufllciently thick to be compressible to the desired extent necessary to rectify the type form, for example, 0.020" to 0.125".

As illustrated in Figure 2a, the type form, indicatcd generally by the numeral 5, as received by the electrotyper comprises type characters or units 0 which are held in position within a chase I by means of adjustable quoins I. The units 0 are clamped within the chase I by means of the quoins. As received by the electrotyper, the upper surface 0 of the type form is usually uneven. To obtain best results in forming the electrotype, it is desirable to bring the upper end of all of the units 8 to the same level in order to produce a level printing surface 9.

This is accomplished by placing the plastic sheet I on a heated table or plate to (Figure 2) which may be heated by a burner lb or in any other suitable manner. The type form I is then placed on the upper surface of sheet I, as shown in Figure 2, so that sheet I will contact the feet or base of the type form. When the plastic sheet becomes sufficiently soft, the sheet and type form are transferred to a hydraulic press such that the plastic sheet rests on the lower platen l0, as shown in Figure 2a. The press is then operated to bring the face of the type form up against the smooth surface of the upper platen H of the press as shown in Figure 3. When sufficient pressure is applied, the plastic sheet, while still soft, will push all low characters, slugs or cuts up against the upper platen and permit the high parts to sink down into the plastic, thus bringing all parts of the printing surface 0 to a common level or plane. The plastic sheet is then allowed to cool and harden under pressure until the plastic material sets. During this rectification step, the quoins 8 are preferably loosened slightly to permit relative movement of the unit 6 when pressure is applied to the type form.

The paper sheets 3 and I are not an essential part of rectifying material but they are useful to facilitate handling of the resin material 2. Furthermore, these sheets prevent sticking of the material 2 to the type. The paper sheets also protect the thermoplastic resin material 2 from contamination by dirt, et cetera.

Thus, as illustrated in Figures 3 and 4a, a type form is produced which has a flat printing surface or face 9. In order to maintain the effectiveness of the surface rectification obtained in this manner, the plastic sheet I is kept in place on the bottom of the type form during subsequent molding operations. The rectification process is applicable only to type forms, or forms containing type matter or separable printing elements such as blocks, cuts, et cetera. When the original pattern is a photo-engraving, electrotype, stereot p or other form of printing plate, the rectification step will be omitted.

The plastic sheet I, as previously indicated, when it cools, becomes sufficiently hard to resist the pressures and temperatures encountered in the subsequent molding operation which will be described hereinafter. During the molding operation, the type form will not be forced further into the plastic sheet because the sheet will still be hard at the molding temperature.

1!. Molding a type form or matrix in thermoplastic sheet The next phase of our process is the molding of a type form of matrix in a sheet of thermoplastic material. We use a thermoplastic resin material instead of using wax, as in the prior art, and obtain a number of important advantages.

This phase of our process employs a therrno plastic sheet different from the thermoplastic sheet i. This sheet is indicated by the numeral II in Figures 4 and 4a. This sheet is made of a thermoplastic resin and is capable of being softened by application of heat and of being substantially hardened again by, cooling. We prefer the vinyl acetate-vlnyl chloride sheet material capable of being molded to matrix or pattern form at temperatures from about 200 F. to about 230 F., because it has dimensional stability and will not shrink after the impression of the pattern is made therein. Furthermore, this material will not warp. Also, it will not absorb moisture in the subsequent operation of making it conductive. Various thicknesses of the thermoplastic sheet material can be used. However, with our process, it is possible to use thin sheets and, therefore, the cost is minimized.

As previously indicated, in Figure 4a. we have illustrated the rectified type form which may be used in forming the electrotype. If this type form 5 is employed, an impression of the surface 9 thereof is made in the sheet [2. In Figure 4, we have illustrated a sol d printing plate 50 having a printing surface So. If this plate 511. is to be used in producing the electrotype, the surface 5a thereof is impressed in the sheet I. In the description of the subsequent phases of our process, we shall refer only to the printing plate id but it is to be understood that the type form 5 can be used in exactly the same manner with the exception that the type form will be supported by sheet I while the plate 5a will not require the sheet I.

The molding procedure for obtaining a matrix of an original pattern, such as a type form or printing plate, on the thermoplastic sheet consists mainly in (l) preheating the thermoplastic sheet while in contact with the original type form or printing plate, (2) applying a resilient blanket to one side of the thermoplastic sheet such that this sheet lies between the original and the resilient blanket, (3) placing the origlnal type form or printing plate, thermoplastic sheet and resilient blanket between the platens of a press, 4) applying pressure sufficient to form the matrix while the thermoplastic sheet is still soft. maintaining this pressure until the thermoplastic material has cooled and set, and (5) finally removing the assembled members from the press and separating the original type form or printing plate from the matrix.

In Figure 5 we have illustrated a hydraulic press which may be used in the molding procedure. This press is mainly of a form commonly used in electrotyping plants. It comprises a base IS. a lower movable platen l4 and an upper stationary platen IS. A form table I6 is supported on the base [3 at one side of the movable platen l4 and being substantially flush with the platen M when it is in its lowermost position. For use in our process, the press is provided with an attachment comprising a supporting arm 11 attached to the upper platen l5 and extending over the form table Hi. This arm I1 carries an elevating device II which, in the present instance, is shown as a cylinder and piston unit. This unit may be air-operated and may be controlled by a valve IS. The lower end of the piston rod of this unit carries a hot plate which is normally spaced above the form table I8. This hot plate 20 is adapted to be heated by any suitable means.

The specific step employed, according to our invention, in obtaining a matrix from the printing plate are illustrated diagrammatically in Figures 6 to 10, inclusive. The printing plate in is first supported in the manner indicated in Figure 4 on the press apron Illa with its printing race 0a uppermost. Then, the sheet II of thermoplastic material is placed over the face of the printing plate 50. A resilient blanket 2| is then placed over the upper surface of the sheet [2.

The use of the resilient blanket It eliminates the need for a thick sheet ii of thermoplastic material and, therefore, cuts down the cost of the sheet l2. As will be apparent hereinafter, the resilient blanket 2| permits portions of the sheet I! to be displaced bodily thereinto. Consequently, it is not necessary to have the sheet I! sufflciently thick to permit this displacement within the material of the sheet. The resilient blanket must be capable of withstanding the temperatures encountered in the molding operation and may consist of various materials. It is preferably of a heat-resisting synthetic rubber material. For example, we may use that type of synthetic rubber material known as Fairprene." Other resilient materials may be used. In fact, it is not necessary that the material be resilient provided it is sufficiently compressible. However, if it is merely compressible and not resilient, it will be necessary to use a difierent blanket for each molding operation.

After the complete unit shown in Figure 4 is assembled on the apron lBa of the press as shown in Figure ,6, the heated plate 20 is lowered until it comes in contact with and rests upon the resilient blanket M, as shown in Figure 7. When the heat has penetrated through the blanket sufllciently to soften the thermoplastic sheet II, the heated plate 20 is raised clear of the blanket as shown in Figure 8. The press apron lid is then moved to a position on the lower platen I4 and beneath the upper platen l5 of the press, carrying with it the printing plate 5a, the plastic sheet I2 and the resilient blanket 2|, as shown in Figure 9. The platens M and Ill are then moved together to apply pressure to the complete unit and this pressure is maintained until the thermoplastic sheet I! cools and sets. When the pressure is applied, the printing face 9a of the plate 5a will be impressed into the sheet I2. Upward displacement of the impressed portions of the sheet into the blanket 2| will be permitted. It will be understood that if the blanket 2| were not employed, it would be necessary to use a thick thermoplastic sheet since portions thereof could not be displaced into the upper platen I 5 and the thermoplastic material itself would have to absorb all of the displacement. The use of this blanket also insures that all details of the pattern will be impressed in the sheet l2. Thus, instead of displacing the thermoplastic material within itself, we mold the matrix by extrusion and bending. After the material of the sheet l2 cools and sets, the composite unit may be removed from the press.

The sheet I! is then removed from between the blanket 21 and the plate 5a and will now be in the form of a matrix Ha, as shown in Figure 13, which has the matching impression of the printing face on one surface thereof. As will be noted, both surfaces of the matrix are irregular due to the bending of the matrix sheet and the matrix is of uniform thickness throughout. Where it is stated in the specification and claims that the matrix has the matching impression of a printing face, it is to be understood that the term printing face is used in its broadest sense to cover either a type, line, or half tone reproduction, or any or all of them.

The temperatures required for molding the thermoplastic sheet I! will depend upon the particular material used. For the vinyl acetate-vinyl chloride material once moldable to matrix or pattern form at temperatures ranging from 200 F. to 230 F. were found satisfactory. The temperature of the hot plate 20 must be higher than the molding temperature of the plastic sheet I! in order that heating of the plastic sheet can be accomplished rapidly. We prefer a temperature for the heated platen in the range of 500 F. to 650 F. Preferably the heating means for plate 20 is provided with thermostatic controls. The pressures required in molding the thermoplastic sheet I: also depend upon the particular material used and upon the type of original subject being molded. The pressure needed, however, is comparatively low, usually falling within the range of 250 to 700 pounds per square inch.

We do not intend that the temperatures and premures to be limited to the values stated above, since under certain conditions it may be necessary with our process to go beyond the range of values given.

It should be pointed out that our process of molding or forming a matrix is simple in manipulation and the time consumed in carrying out the operations is comparatively short, usually requiring about two minutes or less.

It should also be pointed out that the results obtained by our process are unique, inasmuch as the moldability of the thermoplastic sheet material, and especially that of the vinyl acetatevinyl chloride material, is such that impressions of small type and fine-screen half-tones are accurately reproduced to the finest detail in the matrix. The quality of the impression obtained with the thermoplastic matrix was found to be superior to that of the best lead molds. Another unique feature of this new process lies in the dimensional accuracy obtainable. This is important in making duplicates for a set of color plates where exact register is required. In wax molding, the dimensional changes are variable and it is diflicult to duplicate color plates with any degree of accuracy. In lead molding, the dimensional changes, while usually uniform, are such that the lead molds or matrices are invariably larger than the original pattern. This is undoubtedly due to the fact that at the higher pressures used in lead molding the original pattern expands slightly. If this expansion is within the elastic limit of the pattern metal, the pattern returns to its original length when the pressure is released, while the lead, which has a very low elastic limit, retains the larger dimension. In molding by our process, it is possible to obtain a matrix in which the dimensions are exactly the same as those of the pattern. This is due to the fact that the matrix in cooling sets to the dimensions of the pattern, and since low pressures are used, no appreciable expansion of the pattern takes place as a result of pressure. Another advantage in using the thermosplastic sheet material is that the pressure required for molding is so low that there is no danger of damaging the original pattern, whereas when sheet lead is used in molding, permanent distortion of the pattern may occur. Thus, our new molding process is a marked improvement over both wax and lead molding,

This process oi molding an electrotype matrix from a thermoplastic sheet has many other advantages over the customary practice of molding in wax or lead. Some of these advantages are asfollows:

1. No graphite or other releasing agent is required during the process, since there is no sticking between the original type form or printing plate and the matrix, the two being capable of separation with considerable ease after molding.

2. The operations known a cutting down, building up and flashing, which are necessary in wax molding, are eliminated in this new molding process. The thermoplastic sheet, in combination with the resilient blanket, permits the matrix to be molded by extrusion and bending, rather than by displacement as in the case oi wax. Under these conditions suflicient depth can be obtained without displacement of material into the low parts of the original, the action of the resilient blanket giving a smooth rounded contour to the raised portions of the matrix, so that no further alterations on the shape of the matrix are required. Elimination of the wax casting operation or preparation of the wax mold for use is effected. This results in a substantial Saving and better Working conditions.

3. Because of the extrusion-bending action in molding according to our process, the troublesome "slides often encountered in wax moldin are entirely eliminated. Furthermore, since the thermoplastic material is elastic when set, there is no tendency for any portion of the matrix to lift when releasing the original after molding. thus eliminating the distortion sometimes encountered in wax molding. Also, because of this elastic nature of the matrix material. any bending which may occur in releasing the original from the matrix will not .be permanent, but the matrix will regain its normal shape after release from the pattern. Therefore, the bending and distortion often encountered in lead molding, due to the difficulty of releasing the matrix from the original pattern, is entirely eliminated so that the impressions in the matrix of all printing characters retain accuracy of depth corresponding to the accuracy of height of these characters on the original pattern.

4. The pressures required in our molding process are not only extremely low compared to those used in lead molding, as previously indicated, but also are considerably lower than those used in wax molding. This eliminates any danger 01' damage to type matter or printing plates.

5. A significant advantage of the thermoplastic matrix made by our molding process is due to the fact that the matrix can be used to make any number of replicas of the original pattern. That is, when rendered electro-conductive and subsequently electroplated to give a replica of the pattern, the replica can be easily separated from the matrix without damage to the matrix, so that the matrix can be rendered electro-conductive a second time and another replica deposited thereon. This procedure can be repeated an indefinite number of times until the desired number of replicas are obtained. Only one replica can be made from a lead or wax matrix.

6. The thermoplastic sheet can be used over and over again in forming different matrices. The thermoplastic matrix may be softened by heat and may be rendered flat by pressing it between two metal sheets which will remove all the impressed characters therefrom.

7. The thermoplastic sheet material also has an ultimate scrap value. After its re-use possibilities have been exhausted, it may be sold as scrap to the producer of the thermoplastic material, who

can grind it and make new molding powder with it.

HI. Rendering the matrix or mold electro-conductive The next phase of our process relates to rendering the face of the thermoplastic matrix electro-conductive so that a replica thereof can be produced by electro-deposition thereon.

The thermoplastic matrix I2a (Figure 13), as produced by our molding process, can be rendered electro-conductive by one of several meth- Dds of rendering non-metallic surfaces electroconductive. These include graphitin production of metallic coatings on the matrix by evaporation of metal thereon or by cathode sputtering of metals on the surface, and deposition of metal on the surface by chemical reduction, for example, by a spraying process. While any of these methods can be used, it is desirable to avoid the use of graphite because of the disadvantages and nuisances connected with its use. We prefer the method of chemical reduction, and more partlcularly, the process whereby an ammonium silver nitrate solution and a suitable reducing agent are mixed by a spray mechanism and made to impinge upon the surface of the matrix In, depositing a layer of silver thereon.

In Figures 11 to 13, inclusive, we have illustrated apparatus which may be used in this spraying process. This apparatus comprises a spray gun 22 having a pair of passageways 23 formed therein which are connected to a pair or containers 24, one of which is for the silver nitrate and the other of which is for the reducing solution. Flexible tubes 25 connect the passages 23 with rigid tubes 26 leading to points adjacent the bottoms of containers 24. An air passageway 21 is formed in the nozzle 22 and is connected to an air pressure line 28 controlled by a valve 29. An air by-pass 30 is also formed in the nozzle and communicates with passage 21. This by-pass 30 is connected by a divided line 3| to short rigid tubes 32 disposed in each of the containers 24 and terminating above the level of the liquid therein. All of the passageways to the nozzle 22 converge into a single outlet passage 33. Thus. the spray nozzle is such that silver solution reducing solution and compressed air, come together at one focal outlet so that mixing and spraying will occur just as the liquids leave the nozzle. Air from passage 30 will enter the upper end of containers 24 and will force the liquids through the lines 25 into the nozzle.

In applying the silver coating to the matrix A by this spraying process, the face of the thermoplastic matrix or mold l2a is first washed with a. cleaning agent such as denatured alcohol, ethyl alcohol, sodium metasilicate solution, tri-sodium phosphate solution or liquid soap solution. The cleaning agent is applied to the surface of the matrix while the surface is given a somewhat vigorous brushing in order to clean out all crevices of the matrix. The matrix is then rinsed with water. A solution of stannous chloride is then applied to the surface by pouring it on the surface and brushing to insure coverage of all portions of the impression. The strength of the stannous chloride solution is not critical. However, we prefer a solution consisting of about 3 ounces of stannous chloride to 1 gallon of water. The matrix is then given a light rinse in water, after which it is ready for the silvering operation. The stannous chloride helps to initiate the dfipgsit of silver on the surface to which it is app e After treatment with the stannous chloride, the matrix is sprayed with the apparatus illustrated in Figures 11. 12 and 13, Since the silver coating liquid mixture is sprayed on the matrix under pressure, all crevices thereof will be coated.

Although not illustrated in the figures, silver coating apparatus consisting of a series of spray nozzles, or of one unit having multiple sets of the sprays illustrated, may be used for speed and for improved coverage.

The silver solution is preferably repared by adding 1 ounce of silver nitrate to 1 gallon of water. When the silver nitrate is completely dissolved, ammonium hydroxide is added in small quantities until the solution becomes clear. However, other formulas may be used for preparing the silver solution.

The reducing agent is preferably prepared by adding 5 ounces of formaldehyde to 1 gallon of water. However, other formulas may be used for preparing the reducing agent.

As the mixed silver solution and reducing solution are sprayed on the matrix He, the silver is reduced and a continuous film of silver is forme on the face of the matrix.

The advantages of silver-coating the matrix to make it electro-conductive as compared to graphiting are as follows:

1. The silver does not fill the small dots or wells left by the impressions of half-tones in the matrix but merely coats the inner walls of these wells, so that no missing dots occur on the finished electrotype.

2. The silver coat, being highly conductive, permits rapid coverage of the electro-deposited metal in the plating tank, thus cutting down the plating time. This rapid coverage also results in a uniform thickness of the deposited metals.

3. The silver coat being continuous results in the production of a non-porous solid electro-deposited shell as compared to the porous electrodeposited shell often produced when the matrix is coated with the discontinuous graphite particles.

4. The silver coating, being very thin. covers and conforms to the minutest detail of the matrix, so that better reproduction of fine detail is accomplished in the finished electrotype.

5. The use of graphite with its attendant disadvantages and nuisances is eliminated.

IV. Electra-plating the silver-coated matrix After the matrix has been provided with the silver coating, indicated by the numeral 33a in Figure 16, it is placed in an electro-plating bath and plated with copper or other suitable metal to the desired thickness. The copper layer is indicated by the numeral 34 in Figure 16.

In electroplating the silver-coated matrix, the matrix I20. is first mounted on a board 35 (Figure 14) of suitable non-conductive material, for example, plastic material. The member In is disposed flat against one surface of the member 35 and strips 36 are disposed along each side edge of the member I 2a to hold it against board 35. Clamps 31 of suitable non-conductive material hold the strips 35, member I20: and the board 35 in tight contact. Beneath the non-conductive strips 38, metal strips 38 are provided which are in contact with the silver-coated surface of the matrix I20. Terminal clamps 39 are connected to the upper ends of strips 38. A suitable clamp 40 is provided for suspending the unit in the plating bath.

The unit of Figure 14 is suspended in a suitable plating bath 4i (Figure 15) by means of the member 40.' Any desired electro-deposit can then be made on the unit; for example, to make a copper electrotype, a copper plate 42 is suspended in the bath. The plate 42 forms the anode and the silver-coated matrix l2a forms the cathode and the matrix will, therefore, be coated with the layer 34 of copper or other suitable metal of the desired thickness depending upon the time the matrix remains in the bath.

Thus, a replica of the matrix is produced and is in the form of a metal shell.

V. Applying backing metal to shell or replica After an eelctro-plated shell or replica has been produced by electro-typing methods, the usual practice is to apply a suitable liquid flux to the back of the shell, after which a layer of solder or tin foil is placed on the back of the shell and the shell is placed face down in a heated cast iron pan, until the foil has melted. Electrotype backing metal is then pouredover the back of the shell to the desired thickness and allowed to cool and solidify. The purpose of the tin foil is to cause the backing metal to become soldered to the shell.

We have developed an improved method of obtaining a bond between the backing metal and the shell in which the use of metal foil is eliminated.

According to our method, the shell-carrying matrix i2a (Figure 16) after being removed from the copper-plating bath 4i is subjected to an operation to silver coat the back of the shell, that is, the exposed back of the layer 34. The silver coating may be applied to the exposed surface of copper layer 34 by one of several methods, such as silver spraying, electro-plating in the silverplating bath, chemical reduction of silver on the surface, metal spray gun, or by immersion. of the shell in a suitable silver solution to give an adherent silver coating.

We prefer to silver-coat the shell by an electro-plating method. Thus, as shown in Figure 1'7, the shell while still attached to the matrix Ila is placed in a silver-coating bath 43. It will be apparent that only the back of the shell will be exposed. The shell will function as the cathode in the bath and a silver sheet 44 as the anode. The electrolyte preferably comprises a solution having the following formula:

Sodium cyanide "ounces" 4 Silver cyanide -do- 5 A: Sodium carbonate -do- 6 Water gallon 1 Usually a few seconds in the plating solution is suflicient to apply the necessary silver coating to the shell. Thus, as shown in Figure 18, the back of the shell will have a coating of silver, indicated by the numeral 45. applied thereto.

Instead of applying the silver coating by an electroplating method, we may use an immersion process. In using an immersion process, the following solution may be employed:

Sodium cyanide ounces 3% Silver cyanide do Water gallon 1 The shell may be immersed in this solution while still attached to the matrix so that only the back surface becomes coated with silver. Usually one minute immersion in this solution is sufllcient.

portant advantages.

After removal from the silver-plating bath, the shell is rinsed in water. It is then separated from the matrix 12a as shown in Figure 19. A suitable flux is then applied to the silver-coated back of the shell. A number of different fluxes can be used in this operation but we prefer one with the following formula:

Zinc chloride "gallons" Ammonium chloride do 15 Water -liter 1 After the flux is applied to the back of the shell, the shell is placed face down in a cast iron casting pan 44 as shown in Figure 20. Backing metal is then poured over the shell, as indicated by the numeral 41, and is allowed to cool. A flrm adherent bond is obtained between the backing metal and the copper layer 34 by means of the silver coating 45 and the necessity for using a tin-base solder is eliminated. Any suitable backing metal may be employed, for example, an alloy containing 3 to 4 per cent tin, 3 to 4 per cent antimony and the balance lead.

Thus, as shown in Figure 21, we produce an electrotype embodying an electroplated shell backed up by suitable backing metal. This shell may be secured to a wood block 48 as shown in Figure 22.

It will be apparent from the above description that our invention results in a number of im- A number of these advantages have been discussed in detail and others will be apparent from the description, the drawings and the following claims.

Having thus described our invention, what we claim is:

i. A molded electrotype matrix molded from a sheet of vinyl acetate-vinyl chloride co-polymer which is moldable to matrix form within a temperature range of about 200 F. to about 230 F., said matrix sheet being of substantially uniform thickness throughout and being deformed throughout its thickness whereby both surfaces are irregular and one surface has the matching impression of a desired printing face.

2. An elastically flexible molded electrotype matrix molded from a sheet of vinyl acetatevinyl chloride co-polymer which is moldable to matrix form within a temperature range of about 200 F. to about 230 F., said matrix sheet being of substantially uniform thickness throughout and being deformed throughout its thickness whereby both surfaces are irregular and one surface has the matching impression of a desired printing face.

3. The method of making an electrotype matrix which comprises disposing the face of a printing pattern in contact with the face of a sheet formed of a vinyl acetate-vinyl chloride co-polymer which is moldable to pattern form within a temperature range of about 200 F. to about 230 F., applying a compressible blanket to the back of the sheet and heating the sheet sufficiently to render it soft and moldable, pressing the pattern, sheet and blanket firmly together and deforming the sheet throughout its thickness in conformance with the pattern and providing irregularity on both sheet-surfaces, holding the sheet, blanket and pattern under pressure until the sheet has cooled and set in the form of the pattern and thereby preventing objectionable change in the over-all linear dimensions of the matrix.

4. The method of making an electrotype matrix which comprises disposing the face of a printing pattern in contact with the face of a sheet formed of a vinyl acetate-vinyl chloride copolymer which is moldable to pattern form within a temperature range of about 200 F. to about 230 F'., applying a resilient blanket to the back oi the sheet and heating the sheet suillciently to render it soft and moldable, pressing the pattern, sheet and blanket firmly together and deforming the sheet throughout its thickness in conformance with the pattern and providing irregularity on both sheet-surfaces, holding the sheet, blanket and pattern under pressure until the sheet has cooled and set in the form of the pattern and thereby preventing objectionable change in the overall linear dimensions of the matrix.

5. The method of making an electrotype matrix and an electroty'pe shell therefrom which comprises disposing the face of a printing pattern in contact with the face of a sheet formed of a vinyl acetate-vinyl chloride co-polymer which is moldable to pattern form within a temperature range of about 200 F., to about 230 F., applying a compressible blanket to the back of the sheet and heating the sheet sufficiently to render it soft and moidable, pressing the pattern, sheet and blanket firmly together and deforming the sheet throughout its thickness in conformance with the pattern and providing irregularity on both sheet-surfaces, holding the sheet, blanket and pattern under pressure until the sheet has cooled and set in the form of the pattern and thereby preventing objectionable change in the overall linear dimensions of the matrix, electroplating a shell on the matrix, and then stripping the shell from the matrix without damaging the matrix whereby the latter is available for plating additional electrotype shells.

6. The method of making an electrotype matrlx and an electrotype shell therefrom which comprises disposing the face or a printing pattern in contact with the face of a sheet formed of a vinyl acetate-vinyl chloride co-polymer which is moldable to pattern form within a temperature range of about 200 F. to about 230 F., applying a compressible blanket of heat-resisting synthetic rubber to the back of the sheet and heating the sheet suillciently to render it soft and moldable, pressing the pattern, sheet and blanket firmly together and deforming the sheet throughout its thickness in conformance with the pattern and providing irregularity on both sheet-surfaces, holding the sheet, blanket and pattern under pressure until the sheet has cooled and set in the form of the pattern and thereby preventing objectionable change in the overall linear dimensions oi the matrix, electroplating a shell on the matrix, and then stripping the shell from the matrix without damaging the matrix whereby the latter is available for plating additional electrotype shells.

FRANK W. KREBER. BRUCE W. GONSER. ROLAND M. SCHAF'FERT.

Certificate of Correction Patent No. 2,400,518. May 21, 1946.

FRANK W. KREBER ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Page 3, second column, line 37, before the word rectifying insert the; page 7, first column, line 18, for "eelctroplated read electro-plated; and second column, lines 8 and 9, for gallons read grams; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

' Signed and sealed this 30th day of July, A. D. 1946.

[amp] LESLIE FRAZER,

First Assistant Commissioner of Patents.

printing pattern in contact with the face of a sheet formed of a vinyl acetate-vinyl chloride copolymer which is moldable to pattern form within a temperature range of about 200 F. to about 230 F'., applying a resilient blanket to the back oi the sheet and heating the sheet suillciently to render it soft and moldable, pressing the pattern, sheet and blanket firmly together and deforming the sheet throughout its thickness in conformance with the pattern and providing irregularity on both sheet-surfaces, holding the sheet, blanket and pattern under pressure until the sheet has cooled and set in the form of the pattern and thereby preventing objectionable change in the overall linear dimensions of the matrix.

5. The method of making an electrotype matrix and an electroty'pe shell therefrom which comprises disposing the face of a printing pattern in contact with the face of a sheet formed of a vinyl acetate-vinyl chloride co-polymer which is moldable to pattern form within a temperature range of about 200 F., to about 230 F., applying a compressible blanket to the back of the sheet and heating the sheet sufficiently to render it soft and moidable, pressing the pattern, sheet and blanket firmly together and deforming the sheet throughout its thickness in conformance with the pattern and providing irregularity on both sheet-surfaces, holding the sheet, blanket and pattern under pressure until the sheet has cooled and set in the form of the pattern and thereby preventing objectionable change in the overall linear dimensions of the matrix, electroplating a shell on the matrix, and then stripping the shell from the matrix without damaging the matrix whereby the latter is available for plating additional electrotype shells.

6. The method of making an electrotype matrlx and an electrotype shell therefrom which comprises disposing the face or a printing pattern in contact with the face of a sheet formed of a vinyl acetate-vinyl chloride co-polymer which is moldable to pattern form within a temperature range of about 200 F. to about 230 F., applying a compressible blanket of heat-resisting synthetic rubber to the back of the sheet and heating the sheet suillciently to render it soft and moldable, pressing the pattern, sheet and blanket firmly together and deforming the sheet throughout its thickness in conformance with the pattern and providing irregularity on both sheet-surfaces, holding the sheet, blanket and pattern under pressure until the sheet has cooled and set in the form of the pattern and thereby preventing objectionable change in the overall linear dimensions oi the matrix, electroplating a shell on the matrix, and then stripping the shell from the matrix without damaging the matrix whereby the latter is available for plating additional electrotype shells.

FRANK W. KREBER. BRUCE W. GONSER. ROLAND M. SCHAF'FERT.

Certificate of Correction Patent No. 2,400,518. May 21, 1946.

FRANK W. KREBER ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Page 3, second column, line 37, before the word rectifying insert the; page 7, first column, line 18, for "eelctroplated read electro-plated; and second column, lines 8 and 9, for gallons read grams; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

' Signed and sealed this 30th day of July, A. D. 1946.

[amp] LESLIE FRAZER,

First Assistant Commissioner of Patents.

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